EPA

United States Office of Water EPA 815-R-99-014

Environmental Protection (4607) April 1999

Agency

Alternative Disinfectants

and Oxidants

Guidance Manual

DISCLAIMER

This manual provides accurate technical data and engineering information on disinfectants and

oxidants that are not as widely used as chlorine. The U.S. Environmental Protection Agency

encourages drinking water treatment utilities and drinking water primacy agencies to examine all

aspects of their current disinfection practices to improve the quality of their finished water

without reducing microbial protection.

This document is EPA guidance only. It does not establish or affect legal rights or obligation.

EPA decisions in any particular case will be made applying the laws and regulation on the basis

of specific facts when permits are issued or regulations promulgated.

Mention of trade names or commercial products does not constitute an EPA endorsement or

recommendation for use.

ACKNOWLEDGMENTS

The Environmental Protection Agency gratefully acknowledges the assistance of the members of

the Microbial and Disinfection Byproducts Federal Advisory Committee and Technical Work

Group for their comments and suggestions to improve this document. EPA also wishes to thank

the representatives of drinking water utilities, researchers, and the American Water Works

Association for their review and comment.

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CONTENTS

1. INTRODUCTION..................................................................................................................1-1

1.1 OBJECTIVE OF THIS MANUAL .......................................................................................1-1

1.2 BACKGROUND .............................................................................................................1-2

1.3 REGULATORY CONTEXT ..............................................................................................1-3

1.3.1 Disinfection Profiling and Benchmarking ........................................................1-7

1.4 USE OF DISINFECTANTS AS CHEMICAL OXIDANTS........................................................1-8

1.5 HOW CHLORINE IS ADDRESSED IN THIS GUIDANCE MANUAL .......................................1-8

1.6 A SUMMARY OF ALTERNATIVE DISINFECTANT PROPERTIES.........................................1-9

1.7 SELECTING A DISINFECTION STRATEGY .....................................................................1-11

1.7.1 Disinfection Strategy Evaluation ...................................................................1-12

1.7.2 Summary.......................................................................................................1-17

1.8 REFERENCES..............................................................................................................1-18

2. DISINFECTANT USE IN WATER TREATMENT.............................................................2-1

2.1 NEED FOR DISINFECTION IN WATER TREATMENT ........................................................2-1

2.1.1 Pathogens of Primary Concern ........................................................................2-2

2.1.2 Recent Waterborne Outbreaks.........................................................................2-8

2.1.3 Mechanism of Pathogen Inactivation ...............................................................2-9

2.2 OTHER USES OF DISINFECTANTS IN WATER TREATMENT...........................................2-10

2.2.1 Minimization of DBP Formation ...................................................................2-10

2.2.2 Control of Nuisance Asiatic Clams and Zebra Mussels..................................2-11

2.2.3 Oxidation of Iron and Manganese..................................................................2-13

2.2.4 Prevention of Regrowth in the Distribution System and Maintenance of

Biological Stability........................................................................................2-14

2.2.5 Removal of Taste and Odors Through Chemical Oxidation............................2-15

2.2.6 Improvement of Coagulation and Filtration Efficiency...................................2-15

2.2.7 Prevention of Algal Growth in Sedimentation Basins and Filters...................2-16

2.2.8 Removal of Color..........................................................................................2-16

2.3 DISINFECTION BYPRODUCTS AND DISINFECTION RESIDUALS .....................................2-16

2.3.1 Types of DBPs and Disinfection Residuals....................................................2-16

2.3.2 Disinfection Byproduct Formation.................................................................2-19

2.3.3 DBP Control Strategies.................................................................................2-23

2.3.4 CT Factor......................................................................................................2-25

2.4 PATHOGEN INACTIVATION VERSUS DBP FORMATION................................................2-26

2.5 DISINFECTANT RESIDUAL REGULATORY REQUIREMENTS ..........................................2-27

2.6 SUMMARY OF CURRENT NATIONAL DISINFECTION PRACTICES ..................................2-28

2.7 CHLORINE..................................................................................................................2-30

2.7.1 Chlorine Chemistry .......................................................................................2-31

2.7.2 Chlorine Generation ......................................................................................2-32

2.7.3 Primary Uses and Points of Application of Chlorine ......................................2-33

2.7.4 Pathogen Inactivation and Disinfection Efficacy............................................2-35

2.7.5 DBP Formation and Control..........................................................................2-39

2.7.6 Operational Considerations ...........................................................................2-41

2.8 SUMMARY ...... .........................................................................................................2-42

2.8.1 Advantages and Disadvantages of Chlorine Use ............................................2-42

2.8.2 Summary Table.............................................................................................2-44

2.8.3 Reference for Additional Information on Chlorine.........................................2-44
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2.9 REFERENCES..............................................................................................................2-45

3. OZONE ..................................................................................................................................3-1

3.1 OZONE CHEMISTRY .....................................................................................................3-1

3.2 OZONE GENERATION ...................................................................................................3-4

3.2.1 Ozone Production............................................................................................3-4

3.2.2 System Components........................................................................................3-5

3.2.3 Operation and Maintenance...........................................................................3-15

3.3 PRIMARY USES AND POINTS OF APPLICATION OF OZONE ...........................................3-16

3.3.1 Primary Uses of Ozone..................................................................................3-16

3.3.2 Points of Application.....................................................................................3-18

3.3.3 Impact on Other Treatment Processes............................................................3-19

3.3.4 Biologically Active Filtration ........................................................................3-19

3.3.5 Pathogen Inactivation and Disinfection Efficacy............................................3-21

3.3.6 Inactivation Mechanisms...............................................................................3-22

3.3.7 Disinfection Parameters.................................................................................3-22

3.3.8 Inactivation of Microorganisms.....................................................................3-24

3.4 OZONATION DISINFECTION BYPRODUCTS ..................................................................3-27

3.4.1 Ozone Byproduct Control..............................................................................3-30

3.5 STATUS OF ANALYTICAL METHODS...........................................................................3-31

3.5.1 Monitoring of Gas Phase Ozone ....................................................................3-31

3.5.2 Monitoring of Liquid Phase Residual Ozone..................................................3-35

3.5.3 Bromate Monitoring for Systems Using Ozone..............................................3-37

3.6 OPERATIONAL CONSIDERATIONS ...............................................................................3-38

3.6.1 Process Considerations..................................................................................3-38

3.6.2 Space Requirements......................................................................................3-38

3.6.3 Material Selection .........................................................................................3-39

3.6.4 Ozone System Maintenance...........................................................................3-39

3.6.5 Ozone Safety.................................................................................................3-39

3.7 SUMMARY .................................................................................................................3-41

3.7.1 Advantages and Disadvantages of Ozone Use................................................3-41

3.7.2 Summary Table.............................................................................................3-42

3.8 REFERENCES..............................................................................................................3-43

4. CHLORINE DIOXIDE..........................................................................................................4-1

4.1 CHLORINE DIOXIDE CHEMISTRY..................................................................................4-1

4.1.1 Oxidation Potential..........................................................................................4-1

4.2 GENERATION ...............................................................................................................4-2

4.2.1 Introduction ....................................................................................................4-2

4.2.2 Chlorine Dioxide Purity ..................................................................................4-3

4.2.3 Methods of Generating Chlorine Dioxide ........................................................4-4

4.2.4 Generator Design ............................................................................................4-9

4.2.5 Chemical Feed Systems.................................................................................4-11

4.2.6 Generator Power Requirements.....................................................................4-13

4.3 PRIMARY USES AND POINTS OF APPLICATION FOR CHLORINE DIOXIDE......................4-13

4.3.1 Disinfection ..................................................................................................4-13

4.3.2 Taste and Odor Control .................................................................................4-14

4.3.3 Oxidation of Iron and Manganese..................................................................4-14

4.4 PATHOGEN INACTIVATION AND DISINFECTION EFFICACY ..........................................4-15

4.4.1 Inactivation Mechanisms...............................................................................4-15

4.4.2 Environmental Effects...................................................................................4-15
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4.4.3 Disinfection Efficacy.....................................................................................4-17

4.5 CHLORINE DIOXIDE DISINFECTION BYPRODUCTS.......................................................4-22

4.5.1 Production of Chlorite and Chlorate ..............................................................4-22

4.5.2 Organic DBPs Produced by Chlorine Dioxide................................................4-25

4.5.3 Chlorine Dioxide DBP Control Strategies......................................................4-25

4.6 STATUS OF ANALYTICAL METHODS...........................................................................4-26

4.6.1 Chlorine Dioxide and Chlorite Analytical Methods........................................4-27

4.6.2 Chlorine Dioxide Monitoring for Systems Using Chlorine Dioxide................4-27

4.6.3 Chlorite Monitoring for Systems Using Chlorine Dioxide..............................4-28

4.7 OPERATIONAL CONSIDERATIONS ...............................................................................4-28

4.7.1 Process Considerations..................................................................................4-30

4.7.2 Generator Operation......................................................................................4-31

4.7.3 Feed Chemicals.............................................................................................4-31

4.8 SUMMARY .................................................................................................................4-33

4.8.1 Advantages and Disadvantages of Chlorine Dioxide Use ...............................4-33

4.8.2 Summary Table.............................................................................................4-34

4.9 REFERENCES..............................................................................................................4-35

5. POTASSIUM PERMANGANATE .......................................................................................5-1

5.1 POTASSIUM PERMANGANATE CHEMISTRY ...................................................................5-1

5.1.1 Oxidation Potential..........................................................................................5-1

5.1.2 Ability to Form a Residual ..............................................................................5-1

5.2 GENERATION ...............................................................................................................5-1

5.3 PRIMARY USES AND POINTS OF APPLICATION ..............................................................5-2

5.3.1 Primary Uses...................................................................................................5-2

5.3.2 Points of Application.......................................................................................5-4

5.4 PATHOGEN INACTIVATION AND DISINFECTION EFFICACY ............................................5-4

5.4.1 Inactivation Mechanisms.................................................................................5-4

5.4.2 Environmental Effects.....................................................................................5-5

5.4.3 Use as a Disinfectant.......................................................................................5-5

5.5 DISINFECTION BYPRODUCT FORMATION......................................................................5-7

5.5.1 Chapel-Hill and Durham, North Carolina Water Treatment Plants...................5-7

5.5.2 American Water Works Association Research Foundation TTHM Study.........5-9

5.6 STATUS OF ANALYTICAL METHODS.............................................................................5-9

5.7 OPERATIONAL CONSIDERATIONS .................................................................................5-9

5.8 SUMMARY .................................................................................................................5-10

5.8.1 Advantages and Disadvantages of Potassium Permanganate Use ...................5-10

5.8.2 Summary Table.............................................................................................5-11

5.9 REFERENCES..............................................................................................................5-12

6. CHLORAMINES...................................................................................................................6-1

6.1 CHLORAMINES CHEMISTRY .........................................................................................6-1

6.1.1 Equilibrium, Kinetic, and Physiochemical Properties.......................................6-1

6.2 GENERATION ...............................................................................................................6-3

6.2.1 Chlorine Feed Facilities...................................................................................6-4

6.2.2 Ammonia Feed Facilities.................................................................................6-5

6.3 PRIMARY USES AND POINTS OF APPLICATION ............................................................6-10

6.3.1 Primary Uses.................................................................................................6-10

6.3.2 Points of Application.....................................................................................6-11

6.4 PATHOGEN INACTIVATION AND DISINFECTION EFFICACY ..........................................6-12

6.4.1 Inactivation Mechanisms...............................................................................6-12
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6.4.2 Environmental Effects...................................................................................6-12

6.4.3 Disinfection Efficacy.....................................................................................6-13

6.5 DBP FORMATION.......................................................................................................6-15

6.6 STATUS OF ANALYTICAL METHODS...........................................................................6-16

6.6.1 Monitoring of Chloramines ...........................................................................6-16

6.6.2 Disinfectant Interferences..............................................................................6-17

6.6.3 Chloramine Monitoring for Systems Using Chloramines ...............................6-19

6.7 OPERATIONAL CONSIDERATIONS ...............................................................................6-20

6.7.1 Conversion to Chloramination from Chlorination ..........................................6-20

6.7.2 Potential Operational Impacts from Chloramination Disinfection...................6-22

6.7.3 Special Considerations for Chloramination Facilities.....................................6-25

6.8 SUMMARY .................................................................................................................6-27

6.8.1 Advantages and Disadvantages of Chloramine Use........................................6-27

6.8.2 Summary Table.............................................................................................6-28

6.9 REFERENCES..............................................................................................................6-29

7. PEROXONE (OZONE/HYDROGEN PEROXIDE).............................................................7-1

7.1 PEROXONE CHEMISTRY ...............................................................................................7-1

7.1.1 Oxidation Reactions........................................................................................7-2

7.1.2 Reactions with Other Water Quality Parameters..............................................7-3

7.1.3 Comparison between Ozone and Peroxone ......................................................7-3

7.2 GENERATION ...............................................................................................................7-4

7.3 PRIMARY USES AND POINTS OF APPLICATION ..............................................................7-5

7.3.1 Primary Uses...................................................................................................7-5

7.3.2 Points of Application.......................................................................................7-6

7.4 PATHOGEN INACTIVATION ...........................................................................................7-6

7.4.1 Inactivation Mechanism ..................................................................................7-6

7.4.2 Environmental Effects.....................................................................................7-7

7.4.3 Disinfection Efficacy and Pathogen Inactivation..............................................7-8

7.5 DISINFECTION BYPRODUCTS........................................................................................7-9

7.6 STATUS OF ANALYTICAL METHODS...........................................................................7-10

7.6.1 Monitoring of Hydrogen Peroxide .................................................................7-10

7.7 OPERATIONAL CONSIDERATIONS ...............................................................................7-13

7.7.1 Process Considerations..................................................................................7-13

7.7.2 Space Requirements......................................................................................7-13

7.7.3 Materials.......................................................................................................7-13

7.8 SUMMARY .................................................................................................................7-14

7.8.1 Advantages and Disadvantages of Peroxone Use (Ozone/Hydrogen Peroxide)7-14

7.8.2 Summary Table.............................................................................................7-15

7.9 REFERENCES..............................................................................................................7-16

8. ULTRAVIOLET RADIATION.............................................................................................8-1

8.1 UV CHEMISTRY (PHOTOCHEMICAL) ............................................................................8-1

8.1.1 UV Radiation ..................................................................................................8-1

8.1.2 UV Disinfection Reactions..............................................................................8-2

8.1.3 Process Variables............................................................................................8-2

8.2 GENERATION ...............................................................................................................8-3

8.2.1 UV Lamps ......................................................................................................8-4

8.2.2 Ballasts...........................................................................................................8-4

8.2.3 UV Reactor Design .........................................................................................8-5

8.3 PRIMARY USES AND POINTS OF APPLICATION ..............................................................8-8
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8.4 PATHOGEN INACTIVATION AND DISINFECTION EFFICIENCY .........................................8-8

8.4.1 Inactivation Mechanism ..................................................................................8-8

8.4.2 Environmental Effects...................................................................................8-10

8.4.3 Disinfection Efficacy.....................................................................................8-12

8.5 DISINFECTION BYPRODUCTS OF UV RADIATION ........................................................8-15

8.5.1 Ground Water ...............................................................................................8-15

8.5.2 Surface Water ...............................................................................................8-16

8.5.3 DBP Formation with Chlorination and Chloramination following UV Radiation8-16

8.6 STATUS OF ANALYTICAL METHODS...........................................................................8-17

8.6.1 Monitoring of Generated Ultraviolet Radiation..............................................8-17

8.6.2 Disinfectant Interferences..............................................................................8-18

8.7 OPERATIONAL CONSIDERATIONS ...............................................................................8-18

8.7.1 Equipment Operation ....................................................................................8-19

8.7.2 Equipment Maintenance................................................................................8-19

8.7.3 Standby Power..............................................................................................8-20

8.8 SUMMARY TABLE......................................................................................................8-21

8.9 REFERENCES..............................................................................................................8-21

9. COMBINED DISINFECTANTS...........................................................................................9-1

9.1 PRIMARY AND SECONDARY DISINFECTANTS ................................................................9-1

9.1.1 DBP Formation with Various Primary and Secondary Disinfectant

Combinations..................................................................................................9-3

9.1.2 Impact of Modifying Disinfection Practices.....................................................9-6

9.1.3 Chlorine/Chlorine to Chlorine/Chloramine ......................................................9-8

9.1.4 Chlorine/Chlorine to Ozone/Chlorine ..............................................................9-8

9.1.5 Chlorine/Chlorine to Ozone/Chloramine..........................................................9-9

9.1.6 Chlorine/Chlorine to Chlorine Dioxide/Chlorine..............................................9-9

9.1.7 Chlorine/Chlorine to Chlorine Dioxide/Chlorine Dioxide...............................9-10

9.1.8 Chlorine/Chloramine to Ozone/Chloramine ...................................................9-10

9.1.9 Chlorine/Chloramine to Chlorine Dioxide/Chloramine ..................................9-10

9.1.10 Ozone/Chlorine to Ozone/Chloramine ...........................................................9-11

9.1.11 Summary.......................................................................................................9-11

9.2 PATHOGEN INACTIVATION WITH INTERACTIVE DISINFECTANTS .................................9-11

9.2.1 Inactivation Mechanism ................................................................................9-12

9.2.2 Environmental Effects...................................................................................9-13

9.2.3 Pathogen Inactivation Efficiency Using Interactive Disinfectants...................9-16

9.2.4 Summary: Pathogen Inactivation with Interactive Disinfectants....................9-23

9.3 ANALYTICAL METHODS.............................................................................................9-23

9.3.1 Ozone ...........................................................................................................9-23

9.3.2 Chlorine Dioxide...........................................................................................9-24

9.3.3 Potassium Permanganate ...............................................................................9-24

9.3.4 Chloramine ...................................................................................................9-24

9.3.5 Hydrogen Peroxide........................................................................................9-24

9.3.6 UV Radiation ................................................................................................9-24

9.3.7 Summary of Analytical Methods...................................................................9-24

9.4 SUMMARY .................................................................................................................9-25

9.5 REFERENCES..............................................................................................................9-26

APPENDIX A. SUMMARY OF DISINFECTANT USAGE IN THE UNITED STATES .............A-1

APPENDIX B. SELECTED COSTS OF ALTERNATIVE DISINFECTION SYSTEMS.............B-1
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FIGURES

Figure 1-1. Flow Diagram to Evaluate Current Disinfection Practices ................................................1-14

Figure 1-2. Flow Diagram to Narrow Selection of a New Primary Disinfectant ..................................1-16

Figure 1-3. Flow Diagram to Narrow Selection of a New Secondary Disinfectant ..............................1-17

Figure 2-1. Free Chlorine Giardia and Virus CT Requirements..........................................................2-38

Figure 2-2. CT Values for Inactivation of Giardia Cysts by Free Chlorine at 10°C

(at Cl2 dose of 3.0 mg/L)............................................................................................2-38

Figure 2-3. CT Values for Inactivation of Giardia Cysts by Free Chlorine at pH 7.0

(at Cl2 dose of 3.0 mg/L)............................................................................................2-39

Figure 3-1. Oxidation Reactions of Compounds (Substrate) During Ozonation of Water ......................3-2

Figure 3-2. Reaction of Ozone and Bromide Ion Can Produce Bromate Ion and Brominated

Organics......................................................................................................................3-3

Figure 3-3. Basic Ozone Generator ......................................................................................................3-4

Figure 3-5. Schematic of an Air Preparation System.............................................................................3-7

Figure 3-6. Cylindrical Electrode Schematic ........................................................................................3-9

Figure 3-7. Ozone Bubble Contactor..................................................................................................3-11

Figure 3-8. Sidestream Ozone Injection System .................................................................................3-12

Figure 3-9. Turbine Mixer Ozone Contactor.......................................................................................3-14

Figure 3-10. CT Values for Inactivation of Viruses by Ozone (pH 6 to 9)...........................................3-26

Figure 3-11. Principal Reactions Producing Ozone Byproducts..........................................................3-28

Figure 3-12. Main Pathways of Bromate Ion Formation when Ozone Reacts with Bromide

Ion.............................................................................................................................3-30

Figure 4-1. Conventional Chlorine Dioxide Generator When Using Chlorine-Chlorite

Method .......................................................................................................................4-7

Figure 4-2. Chlorine Dioxide Generation Using Recycled Aqueous Chlorine Method ...........................4-8

Figure 4-3. Effect of Temperature on N. Gruberi Cyst Inactivation at pH 7 ........................................4-17

Figure 4-4. Comparison of Germicidal Efficiency of Chlorine Dioxide and Chlorine..........................4-19

Figure 4-5. CT Values for Inactivation of Giardia Cysts by Chlorine Dioxide ....................................4-21

Figure 4-6. CT Values for Inactivation of Viruses by Chlorine Dioxide..............................................4-22

Figure 4-7. C. parvum Inactivation by Chlorine Dioxide at 20°C........................................................4-23

Figure 4-8. C. parvum Inactivation by Chlorine Dioxide at 10°C........................................................4-23

Figure 6-1. Theoretical Breakpoint Curve ............................................................................................6-2

Figure 6-2. Distribution Diagram for Chloramine Species with pH.......................................................6-3

Figure 6-3. Gaseous Chlorine Feed System ..........................................................................................6-5

Figure 6-4. Hypochlorite Feed System .................................................................................................6-6

Figure 6-5. Anhydrous Ammonia Direct Feed System..........................................................................6-7

Figure 6-6. Anhydrous Ammonia Solution Feed System ......................................................................6-8

Figure 6-7. Aqua Ammonia Feed System.............................................................................................6-9

Figure 8-1. Closed Vessel Ultraviolet Reactor......................................................................................8-6

Figure 8-2. Germicidal Inactivation by UV Radiation...........................................................................8-9

Figure 8-3. UV Dose Required for Inactivation of MS-2 Coliphage....................................................8-11

Figure 8-4. Particle Interactions that Impact UV Effectiveness...........................................................8-12

Figure 8-5. UV Doses Required to Achieve Inactivation of Giardia lamblia Cysts Obtained

from Two Different Sources ......................................................................................8-14

Figure 8-6. Impact of Growth Stage of A. rhysodes on the Required UV Dosage to Achieve

Inactivation................................................................................................................8-14

Figure 9-1. Inactivation of C. parvum Attributed to Synergistic Effects. Application of

Ozone Followed by Chlorine Dioxide ........................................................................9-14

Figure 9-2. Inactivation of C. parvum Attributed to Synergistic Effects. Application of
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Chlorine Dioxide Followed by Free Chlorine .............................................................9-14

Figure 9-3. Inactivation of C. parvum Attributed to Synergistic Effects. Application of

Chlorine Dioxide Followed by Monochloramine........................................................9-15

Figure 9-4. Inactivation of E. coli Using Free Chlorine and Monochloramine.....................................9-18

TABLES

Table 1-1. Key Dates for Regulatory Activities....................................................................................1-4

Table 1-2. Primary Drinking Water Regulations Related to Microbiological

 Contaminants..............................................................................................................1-6

Table 1-3. Primary Drinking Water Regulations Related to Disinfection Byproducts............................1-6

Table 1-4. Primary Drinking Water Regulations Related to Residual Disinfectants...............................1-7

Table 1-5. Log Removal/Inactivation through Filtration and Disinfection Required

Under the SWTR.........................................................................................................1-7

Table 1-6. Summary of Disinfectant Properties (Based on Typical Disinfectant

Application)...............................................................................................................1-11

Table 2-1. Waterborne Diseases from Bacteria.....................................................................................2-3

Table 2-2. Waterborne Diseases from Human Enteric Viruses..............................................................2-4

Table 2-3. Waterborne Diseases from Parasites....................................................................................2-6

Table 2-4. Attributes of the Three Waterborne Pathogens of Concern in Water

Treatment ....................................................................................................................2-7

Table 2-5. Human Parasitic Protozoans................................................................................................2-7

Table 2-6. The Effects of Various Oxidants on Mortality of the Asiatic Clam

(Corbicula fluminea) .................................................................................................2-12

Table 2-7. Oxidant Doses Required for Oxidation of Iron and Manganese..........................................2-14

Table 2-8. List of Disinfection Byproducts and Disinfection Residuals...............................................2-17

Table 2-9. Status of Health Information for Disinfectants and DBPs...................................................2-18

Table 2-10. Conditions of Formation of DBPs....................................................................................2-22

Table 2-11. Inorganic DBPs Produced During Disinfection................................................................2-23

Table 2-12. Required Removal of TOC by Enhanced Coagulation for Surface Water

Systems Using Conventional Treatment (percent reduction).......................................2-25

Table 2-13. CT Values for Inactivation of Viruses..............................................................................2-26

Table 2-14. CT Values for Inactivation of Giardia Cysts....................................................................2-26

Table 2-15. Summary of Disinfection Impacts ...................................................................................2-27

Table 2-16. Disinfection Practices of Water Systems that Include Some Form of

Treatment ..................................................................................................................2-29

Table 2-17. Ozone Application in Water Treatment Plants in the United States..................................2-30

Table 2-18. Chlorine Uses and Doses.................................................................................................2-34

Table 2-19. Typical Chlorine Points of Application and Uses.............................................................2-34

Table 2-20. Typical Chlorine Dosages at Water Treatment Plants.......................................................2-35

Table 2-21. Percent Reduction in DBP Formation by Moving Chlorination Point Later

In Treatment Train.....................................................................................................2-40

Table 2-22. Summary of Chlorine Disinfection ..................................................................................2-44

Table 3-1. Types of Compressors Used in Air Preparation Systems......................................................3-7

Table 3-2. Comparison of Air and High Purity Oxygen Feed Systems..................................................3-8

Table 3-3. Comparison of Primary Characteristics of Low, Medium, and High Frequency

Ozone Generators.....................................................................................................3-10

Table 3-4. Bubble Diffuser Contactor Advantages and Disadvantages................................................3-12

Table 3-5. Injection Contacting Advantages and Disadvantages.........................................................3-13

Table 3-6. Turbine Mixer Contactor Advantages and Disadvantages..................................................3-14
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Table 3-7. Criteria for Selecting Ozone Feed Points for Small Systems..............................................3-18

Table 3-8. Summary of Reported Ozonation Requirements for 99 Percent Inactivation

of Cryptosporidium Oocycts......................................................................................3-27

Table 3-9. Principal Known Byproducts of Ozonation........................................................................3-28

Table 3-10. Characteristics and Comparisons of Gas-Phase Ozone Analytical Methods......................3-33

Table 3-11. Characteristics and Comparisons of Residual Ozone Analytical Methods.........................3-36

Table 3-12. Summary of Ozone Disinfection Considerations..............................................................3-42

Table 4-1. Commercial Chlorine Dioxide Generators...........................................................................4-5

Table 4-2. Surface Water Chlorine Dioxide Demand Study Results....................................................4-14

Table 4-3. Analytical Methods for Chlorine Dioxide and Related Compounds....................................4-30

Table 4-4. Properties of Sodium Chlorite as Commercially Available.................................................4-32

Table 4-5. Summary for Chlorine Dioxide .........................................................................................4-34

Table 5-1. Potassium Permanganate CT Values for 2-log Inactivation of MS-2

Bacteriophage..............................................................................................................5-7

Table 5-2. Summary of Potassium Permanganate Use ........................................................................5-12

Table 6-1. Chlorine Dose Required for NH3 - Cl2 Reaction .................................................................6-3

Table 6-2. Time to 99 Percent Conversion of Chlorine to Monochloramine..........................................6-4

Table 6-3. Methods of Chlorine Addition.............................................................................................6-4

Table 6-4. CT Values for Giardia Cyst Inactivation Using Chloramines.............................................6-15

Table 6-5. CT Values for Virus Inactivation Using Chloramines........................................................6-15

Table 6-6. Characteristics and Comparisons of Monochloraminea Analytical

Methods ....................................................................................................................6-18

Table 6-7. Survey of Chloramine Users in the United States...............................................................6-25

Table 6-8. Summary of Chloramine Disinfection ...............................................................................6-29

Table 7-1. Comparison Between Ozone and Peroxone Oxidation .........................................................7-4

Table 7-2. Calculated CT Values (Mg•Min/L) for the Inactivation of Giardia Muris............................7-8

Table 7-3. Characteristics and Comparisons of Hydrogen Peroxide Analytical

Methods ....................................................................................................................7-12

Table 7-4. Summary of Peroxone Disinfection Consideration.............................................................7-15

Table 8-1. Water Quality and Associated UV Measurements................................................................8-3

Table 8-2. Doses Required for MS-2 Inactivation...............................................................................8-13

Table 8-3. Summary of UV Disinfection............................................................................................8-21

Table 9-1. Potential Primary Disinfectants...........................................................................................9-2

Table 9-2. Primary/Secondary Disinfectant Combinations and Typical Applications in

Water Treatment..........................................................................................................9-3

Table 9-3. DBPs Associated with Various Combined Oxidation/Disinfection Processes.......................9-4

Table 9-4. Strategies for Primary and Secondary Disinfectants..............................................................9-6

Table 9-5. Impacts of Disinfection Practice on DBP Formation............................................................9-7

Table 9-6. Virus Inactivation By Individual Disinfectants and Simultaneous

Chloramination..........................................................................................................9-17

Table 9-7. C. parvum Inactivation Using Ozone Followed by Chlorine Dioxide .................................9-19

Table 9-8. C. parvum Inactivation Using Chlorine Dioxide Followed by Free Chlorine ......................9-19

Table 9-9. G. muris Inactivation Using Chlorine Dioxide Followed by Free Chlorine.........................9-19

Table 9-10. B. cereus Inactivation Using Chlorine Dioxide Followed by Free Chlorine ......................9-19

Table 9-11. C. parvum Inactivation Using Chlorine Dioxide Followed by Chloramine .......................9-20

Table 9-12. G. muris Inactivation Using Chlorine Dioxide Followed by Chloramine ..........................9-20

Table 9-13. G. muris Inactivation Using Ozone Followed by Free Chlorine........................................9-21

Table 9-14. B. cereus Inactivation Using Chlorine Dioxide Followed by Free Chlorine ......................9-21

Table 9-15. G. muris Inactivation Using Ozone Followed by Chloramine...........................................9-21

Table 9-16. G. muris Inactivation by Free Chlorine Followed by Monochloramine.............................9-22

Table 9-17. C. parvum Inactivation by Sequential Application of Ozone and Chloramine...................9-22
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April 1999 ix EPA Guidance Manual

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Table 9-18. Summary of Combined Disinfectants ..............................................................................9-25

ACRONYMS

AECL Alternate enhanced coagulant level

ACUK Acid chrome violet K

AOC Assimilable organic carbon

ASDWA Association of State Drinking Water Administrators

AWWA American Water Works Association

AWWARF AWWA Research Foundation

BAC Biologically active carbon

BAF Biologically active filtration

BAT Best Available Technology

BCAA Bromochloroacetic acid

BDOC Biodegradable organic carbon

BMP Best management practice

BOM Biodegradable Organic Matter (=BDOC + AOC)

Br- Bromide ion

BrO2- Bromite ion

BrO3- Bromate ion

CI Confidence interval

Cl2 Chlorine

ClO2 Chlorine Dioxide

CT Concentration-Time

CWS Community Water System

D/DBP Disinfectants/disinfection byproducts

DBPR Disinfectants/disinfection byproducts rule

DBP Disinfection byproduct

DBPFP Disinfection byproduct formation potential

DBPP Disinfection byproduct precursors

DBPRAM DBP Regulatory Assessment Model

DBPs Disinfection byproducts

DOC Dissolved organic carbon

DPD N,N-diethyl-p-phenylenediamine

DWEL Drinking Water Equivalent Level

EBCT Empty bed contact time

EMSL EPA Environmental Monitoring and Support Laboratory (Cincinnati)

EPA United States Environmental Protection Agency

ESWTR Enhanced Surface Water Treatment Rule

FBR Filter Backwash Rule

FY Fiscal year

GAC Granular activated carbon

GWR Ground Water Rule

GWSS Ground Water Supply Survey

H2O2 Hydrogen Peroxide

HAA5 Haloacetic acids (five)

HOBr Hypobromous acid

HOCl Hypochlorous acid

IC Ion chromotography
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ICR Information Collection Rule

IESWTR Interim Enhanced Surface Water Treatment Rule

IOA International Ozone Association

IOC Inorganic chemical

KMnO4 Potassium permanganate

LOAEL Lowest observed adverse effect level

LOQ Limit of quantitation

LT1ESWTR Long Term Stage 1 Enhanced Surface Water Treatment Rule

M-DBP Microbial and disinfection byproducts

MCL Maximum Contaminant Level

MCLG Maximum Contaminant Level Goal

MDL Method Detection Limit

mg/L Milligrams per liter

mgd Million gallons per day

MIB Methylisoborneol

MRDL Maximum Residual Disinfectant Level (as mg/l)

MRDLG Maximum Residual Disinfectant Level Goal

MRL Minimum Reporting Level

MX 3-chloro-4-(dichloromethyl)-5-hydroxyl-2(5H)-furanone

NaCl Sodium chloride

NCI National Cancer Institute

ND Not detected

NH2Cl Monochloramine

NIPDWR National Interim Primary Drinking Water Regulation

NIOSH National Institute for Occupational Safety and Health

NOAEL No Observed Adverse Effect Level

NOM Natural Organic Matter

NOMS National Organic Monitoring Survey

NORS National Organics Reconnaissance Survey for Halogenated Organics

NPDWR National Primary Drinking Water Regulation

NTNCWS Nontransient noncommunity water system

NTP Normal Temperature and Pressure

O2 Oxygen

O3 Ozone

OBr- Hypobromite ion

OCl- Hypochlorite ion

PCE Perchloroethylene

PE Performance evaluation

POE Point-of-Entry Technologies

POU Point-of-Use Technologies

ppb Parts per billion

ppm Parts per million

PQL Practical Quantitation Level

PTA Packed Tower Aeration

PWS Public water system

RIA Regulatory Impact Analysis

RMCL Recommended Maximum Contaminant Level

RNDB Regulations Negotiation Data Base

RSC Relative Source Contribution

SDWA Safe Drinking Water Act, or the “Act,” as amended in 1996

SM Standard Method
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SMCL Secondary Maximum Contaminant Level

SMR Standardized mortality ratios

SOC Synthetic Organic Chemical

SWTR Surface Water Treatment Rule

TCE Trichloroethylene

THM Trihalomethane

THMFP Trihalomethane formation potential

TMV Tobacco mosaic virus

TOC Total organic carbon

TTHM Total trihalomethanes

TWG Technologies Working Group

UV Ultraviolet

VOC Volatile Organic Chemical

WIDB Water Industry Data Base

WS Water supply

XDBPs Halogenated DBPs
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1. INTRODUCTION

1.1 Objective of this Manual

Chlorine is, by far, the most commonly used disinfectant in the drinking water treatment industry

(Sawyer et al., 1994). Today, chlorine is used as a primary disinfectant in the vast majority of all

surface water treatment plants, being used as a pre-disinfectant in more than 63 percent and as a postdisinfectant in more than 67 percent of all surface water treatment plants (USEPA, 1997). This

manual is organized to provide technical data and engineering information on disinfectants that are

not as widely used as chlorine. Also, where applicable, this document describes the use of these

disinfectants as oxidants and any associated implications.

The U.S. Environmental Protection Agency (EPA) encourages utilities to examine all aspects of their

current disinfection practices to identify opportunities to improve the quality of the finished water

without reducing microbial protection. The objective of this guidance manual is to describe

alternative disinfectants and disinfection techniques that may be used to comply with both the Stage

1 Disinfectants and Disinfection Byproducts Rule (DBPR) and Interim Enhanced Surface Water

Treatment Rule (IESWTR) and highlight advantages and disadvantages of their use.

EPA is not recommending that utilities employ the disinfectants and oxidants discussed in this

manual, nor is it advocating that utilities switch from one disinfectant or oxidant to another. EPA

acknowledges that selection of the most appropriate disinfection technique is a site-specific decision

best left to utility personnel and state agencies. Utilities should use this guidance as an information

resource to assist in the selection of appropriate disinfectants and disinfectant schemes to meet their

specific goals. Extensive bench and/or pilot scale testing and a thorough review of regulatory

requirements should precede changes to disinfection practice. Systems should refer to the Guidance

Manual for Compliance with the Filtration and Disinfection Requirements for Public Works Systems

Using Surface Water Sources (AWWA, 1991) to ensure disinfectant schemes meet regulatory log

inactivation requirements. Utilities should also refer to EPA's Disinfection Profiling and

Benchmarking Guidance Manual (currently in production) to ensure compliance with the new

regulatory requirements of the IESWTR.

This chapter presents a brief discussion of the background and regulatory context of alternative

disinfectants, including an overview of the disinfection profiling and benchmarking approach to

evaluate disinfection efficiency. In addition, a decision-making framework is provided that utilities

can employ to assess the applicability of various disinfectants and disinfection strategies for

individual systems. Chapter 2 presents an overview of disinfection, including the use of chlorine,

with the next six chapters of this manual devoted to each of the following alternative disinfectants

and oxidants:
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• Chapter 3 - Ozone (O3);

• Chapter 4 - Chlorine dioxide (ClO2);

• Chapter 5 - Potassium permanganate (KMnO4);

• Chapter 6 - Chloramine (NH2Cl);

• Chapter 7 - Ozone/hydrogen peroxide combinations (O3/H2O2); and

• Chapter 8 - Ultraviolet radiation (UV).

For each disinfectant, this guidance manual describes the chemistry specific to the disinfection or

oxidation process, generation, primary uses and points of application, disinfection byproduct (DBP)

formation, pathogen inactivation and disinfection efficacy, the status of analytical methods for

residual monitoring, and operational considerations. Chapter 9 provides similar information

regarding the use of combined disinfectants. A summary of existing disinfectant usage in the United

States is provided in Appendix A. Cost estimates for the use of alternative disinfectants are provided

in Appendix B.

1.2 Background

The most important use of disinfectants in water treatment is to limit waterborne disease and

inactivate pathogenic organisms in water supplies. The first use of chlorine as a continuous process

in water treatment was in a small town in Belgium in the early 1900s (White, 1992). Since

introduction of filtration and disinfection at water treatment plants in the United States, waterborne

diseases such as typhoid and cholera have been virtually eliminated. For example, in Niagara Falls,

NY between 1911 and 1915, the number of typhoid cases dropped from 185 deaths per 100,000

population to nearly zero following introduction of filtration and chlorination (White, 1986).

In 1974, researchers in the Netherlands and the United States demonstrated that trihalomethanes

(THMs) are formed as a result of drinking water chlorination (Rook, 1974; Bellar et al., 1974).

THMs are formed when chlorine or bromide reacts with organic compounds in the water. EPA

subsequently conducted surveys confirming widespread occurrence of THMs in chlorinated water

supplies in the United States (Symons et al., 1975; USEPA, 1978). THMs and other DBPs have been

shown to be carcinogenic, mutagenic, etc. These health risks may be small, but with the large

population exposed, need to be taken seriously.

As a result of DBP concerns from chlorine, EPA, as well as the water treatment industry, placed

more emphasis on the use of disinfectants other than chlorine. Some of these alternative

disinfectants, however, have also been found to produce DBPs as a result of either reactions between

disinfectants and compounds in the water or as a natural decay product of the disinfectant itself

(McGuire et al., 1990; Legube et al; 1989). These DBPs include:

• Halogenated organics, such as THMs, haloacetic acids, haloketones, and others, that are

produced primarily as a result of chlorination.
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• Organic oxidation byproducts such as aldehydes, ketones, assimilable organic carbon (AOC), and

biodegradable organic carbon (BDOC), that are associated primarily with strong oxidants such as

ozone, chlorine, and advanced oxidation; and

• Inorganics such as chlorate and chlorite, associated with chlorine dioxide, and bromate, that is

associated with ozone, and has also has been found when chlorine dioxide is exposed to sunlight.

As documented in this manual, the type and amount of DBPs produced during treatment depends

largely on disinfectant type, water quality, treatment sequences, contact time, and environmental

factors such as temperature and pH.

When considering the use of alternative disinfectants, systems should ensure that the inactivation of

pathogenic organisms is not compromised. Pathogens pose an immediate critical public health threat

due to the risk of an acute disease outbreak. Although most identified public health risks associated

with DBPs are chronic, long-term risks, many systems will be able to lower DBP levels without

compromising microbial protection.

1.3 Regulatory Context

Pursuant to requirements of the Safe Drinking Water Act (SDWA) Amendments of 1996, EPA is

developing interrelated regulations to control microbial pathogens and disinfectant residuals and

disinfection byproducts in drinking water. These rules are collectively known as the

microbial/disinfection byproducts (M-DBP) rules and are intended to address complex risk trade-offs

between the desire to inactivate pathogens found in water and the need to reduce chemical

compounds formed as byproducts during disinfection. The rules are being promulgated in two

phases.

As part of the first phase, the Stage 1 DBPR and the IESWTR were promulgated on December 16,

1998 (63 FR 69390 and 63 FR 69478, respectively). The Stage 1 DBPR applies to all community

water systems (CWS) and non-transient, non-community water systems (NTNCWS) that treat their

water with a disinfectant for either primary or residual treatment. The IESWTR amends the Surface

Water Treatment Rule (SWTR) and includes new and more stringent requirements to control

waterborne pathogens including specifically the protozoan Cryptosporidium. The IESWTR applies

to all public water systems that use surface water, or ground water under the direct influence of

surface water as defined at 40 CFR, Part 141, Subpart H1, and that serve at least 10,000 people.

Three future rules, also included in phase one include the Long-Term 1 Enhanced Surface Water

Treatment Rule (LT1ESWTR), the Ground Water Rule (GWR), and the Filter Backwash Rule

(FBR). Each of these rules are planned for promulgation in November 2000. The LT1ESWTR will

address pathogen inactivation and removal requirements for Subpart H systems serving fewer than

10,000 people. The GWR will specify appropriate disinfection techniques, including the use of best

 

1

 Subpart H systems are defined as public water systems supplied by a surface water source or by a ground water source under the

direct influence of surface water.
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management practices (BMPs) and source control measures. The FBR will set a standard for filter

backwash recycling for all public water systems regardless of size.

The second phase, consisting of the Stage 2 DBPR and the Long-Term 2 ESWTR, will be

promulgated in the year 2002 and will revisit the regulations for the formation of DBPs for all

systems and the inactivation and removal of pathogens for surface water systems, respectively.

The projected dates for future M-DBP regulatory activities are summarized in Table 1-1.

Table 1-1. Key Dates for Regulatory Activities

Date Regulatory Action

November 2000 Promulgate Long-Term 1 Enhanced Surface Water Treatment Rule

November 2000 Promulgate Ground Water Rule

November 2000 Promulgate Filter Backwash Rule

May 2002 Promulgate Stage 2 Disinfectants and Disinfection Byproduct Rule

May 2002 Promulgate Long-Term 2 Enhanced Surface Water Treatment Rule

Concurrent with the M-DBP rules, in May 1996, EPA promulgated the Information Collection Rule

(ICR) to obtain data on source water quality, byproduct formation, and drinking water treatment

plant design and operations. The ICR applies to Subpart H systems serving more than 100,000

people and ground water systems serving more than 50,000 people. EPA intended to use data from

the ICR to address completely the complex trade-offs between chronic DBP health risks and acute

pathogenic health risks, but delays in promulgation of the ICR eliminated this potential data source

for use in the IESWTR. Until the ICR data are analyzed in detail, EPA cannot fully address the issue

of DBP and pathogenic risk trade-offs.

National Primary and Secondary Drinking Water Regulations, published in 40 CFR Parts 141 and

143, respectively, limit the amount of specific contaminants and residual disinfectants and classes of

these compounds that are delivered to users of public water systems. These limits are expressed as

follows:

• Maximum Contaminant Level Goals (MCLGs). MCLGs are non-enforceable health goals for

public water systems. MCLGs are set at levels that, in the EPA Administrator’s judgment, allow

no known or anticipated adverse effect on the health of persons to occur and that allow an

adequate margin of safety.

• Maximum Residual Disinfectant Level Goals (MRDLGs). As with MCLGs, EPA has

established MRDLGs for disinfectants at levels at which no known or anticipated adverse effects

on the health of persons occur and that allow an adequate margin of safety. MRDLGs are nonenforceable health goals based only on health effects and exposure information and do not reflect

the benefit of the addition of the chemicals for control of waterborne microbial contaminants.
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• Maximum Contaminant Levels (MCLs). MCLs are enforceable standards set as close to the

MCLGs as technically and economically feasible.

• Maximum Residual Disinfectant Levels (MRDLs). MRDLs are similar to MCLs. MRDLs

are enforceable standards, analogous to MCLs, that recognize the benefits of adding a

disinfectant to water on a continuous basis and of addressing emergency situations such as

distribution system pipe ruptures. As with MCLs, EPA has set the MRDLs as close to the

MRDLGs as feasible.

In November 1979, the EPA set an interim MCL for Total THMs (TTHMs) of 0.10 mg/L as an

annual average for systems serving at least 10,000 people. This standard was based on the need to

reduce THM levels due to suspected carcinogenicity. Since then, EPA has developed and

promulgated standards for numerous contaminants. As of the December 16, 1998 DBPR

promulgation, MCLGs, MCLs, MRDLGs, and MRDLs are as presented in Tables 1-2 through 1-4.

As included in these tables, the December 16, 1998 Stage 1 DBPR:

• Lowered the existing MCL for TTHMs from 0.10 mg/L to 0.080 mg/L;

• Extended the MCL for TTHMs to all size systems;

• Requires enhanced coagulation or enhanced precipitative softening for certain systems;

• Established MRDLs and MRDLGs for chlorine, chloramine, and chlorine dioxide;

• Established MCLs for haloacetic acid (five) (HAA5), bromate, and chlorite, and

• Established MCLGs for eight disinfection byproducts.

Further, the SWTR of 1989 requires 3.0-log inactivation for Giardia cysts and 4.0-log inactivation

for viruses in surface water supplies. To meet these goals, the SWTR established treatment

requirements for filtration and disinfection. As shown in Table 1-5, these goals can be met using

various treatment schemes that include filtration and disinfection. The IESWTR requires a 2.0 log

removal of Cryptosporidium for Subpart H systems serving at least 10,000 people.
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Table 1-2. Primary Drinking Water Regulations Related to Microbiological Contaminants

Compound MCLG

(mg/L)

MCL

(mg/L) Potential Health Effects Sources of Drinking WaterContamination

Giardia lamblia Zero TT1 Gastroenteric disease Human and animal fecal waste

Legionella Zero TT Legionnaire’s disease Common bacteria in natural

waters; can proliferate in water

heating systems

Heterotrophic

Plate Count

N/A TT Indicates water quality,

effectiveness of treatment

Total Coliform Zero < 5.0%2Indicates potential presence of

gastroenteric pathogens

Human and animal fecal waste

Turbidity N/A TT Indicates water treatment failure

and pathogens in drinking water

Particles from storm runoff,

discharges into source water, and

erosion

Viruses Zero TT Gastroenteric disease Human and animal fecal waste

Source: AWWA Internet, 1997.

1

TT = Treatment technique requirement in lieu of MCL as established in 40 CFR §141.70.

2 No more than 5.0 percent positive if >40 samples/month. No more than 1 positive if <40 samples/month [40 CFR §141.63(a) ].

Table 1-3. Primary Drinking Water Regulations Related to Disinfection Byproducts

Compound MCLG

(mg/L)

MCL

(mg/L) Potential Health Effects Sources of Drinking WaterContamination

Bromate Zero30.0104 Cancer Ozonation byproduct

Bromodichloromethane Zero3see TTHMs Cancer, liver, kidney, and

reproductive effects

Drinking water chlorination and

chloramination byproduct

Bromoform Zero3see TTHMs Cancer, nervous system,

liver and kidney effects

Drinking water ozonation,

chloramination, and chlorination

byproduct

Chlorite 0.831.04 Hemolytic anemia Chlorine dioxide disinfection

byproduct

Chloroform Zero3see TTHMs Cancer, liver, kidney,

reproductive effects

Drinking water chlorination and

chloramination byproduct

Dibromochloromethane 0.063see TTHMs Nervous system, liver,

kidney, reproductive effects

Drinking water chlorination and

chloramination byproduct

Dichloroacetic Acid Zero3See HAA5 Cancer and other effects Drinking water chlorination and

chloramination byproduct

Haloacetic Acids1 (HAA5) N/A 0.0604 Cancer and other effects Drinking water chlorination and

chloramination byproduct

Trichloroacetic Acid 0.33See HAA5 Possibly cancer and

reproductive effects

Drinking water chlorination and

chloramination byproduct

Total Trihalomethanes2

(TTHMs)

N/A 0.084 Cancer and other effects Drinking water chlorination and

chloramination byproduct

Source: 63 FR 69390 (12/16/98)

1

 HAA5 is the sum of the concentrations of mono-, di-, and trichloroacetic acids and mono-and dibromoacetic acids.

2 Total Trihalomethanes are the sum of the concentrations of bromodichloromethane, dibromochloromethane, bromoform, and chloroform.

3

 Finalized on December 16, 1998 (63 FR 69390) as established in 40 CFR §141.53.

4

 Finalized on December 16, 1998 (63 FR 69390) as established in 40 CFR §141.64
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Table 1-4. Primary Drinking Water Regulations Related to Residual Disinfectants

Disinfectant MRDLG3

(mg/L)

MRDL4

(mg/L)

Chlorine14 (as Cl2) 4.0 (as Cl2)

Chloramine24 (as Cl2) 4.0 (as Cl2)

Chlorine Dioxide 0.8 (as ClO2) 0.8 (as ClO2)

1

 Measured as free chlorine

2

 Measured as total chlorine

3

 Finalized on December 16, 1998 (63 FR 69390) as established in 40 CFR §141.54.

4

 Finalized on December 16, 1998 (63 FR 69390) as established in 40 CFR §141.65

Table 1-5. Log Removal/Inactivation through Filtration and

Disinfection Required Under the SWTR

Process Giardia cysts Virus

Total log removal/inactivation Required 3.0 4.0

Conventional sedimentation/filtration credit

Disinfection inactivation required

2.5

0.5

2.0

2.0

Direct filtration credit

Disinfection inactivation required

2.0

1.0

1.0

3.0

Slow sand filtration credit

Disinfection inactivation required

2.0

1.0

2.0

2.0

Diatomaceous earth credit

Disinfection inactivation required

2.0

1.0

1.0

3.0

No Filtration

Disinfection inactivation required

0.0

3.0

0.0

4.0

Source: AWWA, 1991.

Note: Some instances may require higher than 3 and 4 log removal. Also, some states may reduce removal filtration process.

1.3.1 Disinfection Profiling and Benchmarking

The IESWTR establishes disinfection benchmarking as a procedure requiring certain PWSs to

evaluate the impact on microbial risk of proposed changes in disinfection practice. It is designed to

facilitate utilities and States working together to assure that pathogen control is maintained while the

provisions of the Stage 1 DBPR are implemented. This procedure involves a PWS charting daily

levels of pathogen inactivation for a period of at least one year to create a profile of inactivation

performance. The PWS then uses this profile to determine a baseline or benchmark of inactivation

against which proposed changes in disinfection practices can be measured.

Systems are required to prepare a disinfection profile if either TTHM or HAA5 levels are at least

0.064 or 0.048 mg/L, respectively, as an annual average. These levels, equal to 80 percent of the

MCLs established for these compounds by the Stage 1 DBPR, are intended to include most systems

that will modify their disinfection practices to comply with the Stage 1 DBPR. To determine

applicability, systems that collected TTHM and HAA5 data under the ICR must use the results of the
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last 12 months of ICR monitoring unless the State determines there is a more representative data set.

Non-ICR systems may use existing TTHM and HAA5 data, if approved by the State, or must

conduct TTHM and HAA5 monitoring for four quarters. This monitoring must be completed no later

than 15 months after promulgation of the IESWTR (i.e., by March, 2000). Alternatively, systems

can elect to forgo this monitoring if they construct a disinfection profile.

A disinfection profile consists of a compilation of daily Giardia lamblia log inactivations (plus virus

inactivations for systems using either chloramines or ozone for primary disinfection) computed over

a period of at least one year. It is based on daily measurements of disinfectant residual

concentration(s), contact time(s), temperature, and pH. The profile may be developed using up to 3

years of existing (i.e. grandfathered) data, if the State finds the data acceptable. Systems having less

than 3 years of acceptable grandfathered data are required to conduct one year of monitoring to

create the profile. This monitoring must be complete within 27 months of IESWTR promulgation

(i.e., by March, 2001). The disinfection benchmark is equal to the lowest monthly average

inactivation level in the disinfection profile (or average of low months for multi-year profiles).

Any system required to develop a disinfection profile under the IESWTR that decides to make a

significant change to its disinfection practice must consult with the State prior to making the change.

Significant changes in disinfection practice are defined as: 1) moving the point of disinfection, not

including routine seasonal changes, 2) changing the type of disinfectant, 3) changing the disinfection

process, and 4) other modifications designated as significant by the State. As part of the consultation

process, the system must submit to the State the following information: a description of the proposed

change; the disinfection profile for Giardia lamblia (and, if necessary, viruses) and benchmark; and

an analysis of how the proposed change will affect the current levels of disinfection. In addition, the

State is required to review the disinfection profile a part of its periodic sanitary survey.

For more information on disinfection profiling and benchmarking, refer to EPA’s Disinfection

Profiling and Benchmarking Guidance Manual (expected to be available in 1999).

1.4 Use of Disinfectants as Chemical Oxidants

Most disinfectants are strong oxidants and/or generate oxidants as byproducts (such as hydroxyl free

radicals) that react with organic and inorganic compounds in water. While the primary focus of this

manual is disinfection, many of the disinfectants described in this manual are also used for other

purposes in drinking water treatment, such as taste and odor control, improved flocculation, and

nuisance control. Because DBPs are produced irrespective of the intended purpose of the oxidant, it

is important to also address uses of disinfectants as oxidants in water treatment. These additional

uses are described in more detail in Chapter 2.

1.5 How Chlorine is Addressed in this Guidance Manual

This guidance manual does not provide as broad a discussion of chlorine and chlorination practices

as it does for the capabilities and uses of alternative disinfectants. There are two reasons EPA has
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taken this approach: 1) the goal of this manual is to provide technical and engineering information to

utilities and the states on alternative disinfectants and oxidants, about which there is less

comprehensive information than for chlorine; and 2) a great majority of utilities already use chlorine,

in a wide variety of applications, for which there exists a wealth of literature on chlorine’s uses and

performance capabilities. Summarizing this large body of knowledge in this guidance is neither

practical nor necessary.

This manual is not an EPA endorsement of alternative disinfectants nor is it a recommendation for

utilities to switch from chlorine to an alternative disinfectant. Rather, this manual provides technical

and engineering information to assist local professionals in making treatment decisions. EPA

believes that utility and state program personnel are best able to select disinfectants and design a

disinfection scheme, based upon site-specific conditions, that meets operational and regulatory

constraints. EPA does not require the use of chlorine or any other specific disinfectant for sitespecific uses. Again, local professionals are best suited to select disinfectants to address the unique

water treatment challenges posed by their source water and plant infrastructure.

EPA recognizes that, at the present time, chlorination is an important and central component of most

water treatment regimes in this country. As such, a summary of the uses and capabilities of chlorine

is provided in Section 2.7 of this manual. Section 2.7 also contains an extensive reference list for

additional information on chlorination.

1.6 A Summary of Alternative Disinfectant Properties

Subsequent chapters in this manual discuss several disinfectant alternatives available to a water

supplier. Table 1-6 summarizes the key technical and regulatory considerations associated with the

use of the various disinfectants for selecting the most appropriate disinfectant. The table provides

some broad guidelines to provide a framework for decision making. The ratings in Table 1-6 are

based on a typical disinfectant application. Thus, even though chlorine is considered to be prone to

THM formation, the table does not address the degree or amount of THMs produced. Similarly,

more than 2-log inactivation can be achieved for some disinfectants, but the high dose required may

not make it a reasonable application, and in that case, would be identified in the table as not able to

achieve 2-log inactivation.

The following key issues are addressed in Table 1-6:

• THMs, oxidized organics, and halogenated organics are produced. Halogenated organics are

formed when chlorine or ozone (in the presence bromide ion) is used, while oxidized organics

occur in the greatest concentration when a strong oxidant is used. The production of DBPs

depends on the amounts and types of precursors in the water.

• Inorganic byproducts are produced. Inorganic byproducts include chlorate ion, chlorite ion,

and bromate ion associated with chlorine dioxide and ozone.
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• MRDLs are required for some disinfectants. Note that this requirement must be balanced with

the requirement to maintain a residual in the distribution system. For most disinfectants, such as

chlorine, the MRDL is relatively high and will generally not create a problem.

• Lime softening impacts are noted. The high pH treatment during lime softening has an impact

on chlorine, chloramines, and UV.

• Turbidity impacts UV disinfection and ozonation. Ozone may interfere with coagulation and

settling. As such, it is recommended that ozonation be placed after settling but before filters to

minimize turbidity impacts.

• Inactivation requirements are divided into those achieving more or less than 2-log

inactivation. This differentiation is to identify the feasibility of achieving high inactivation at

modest doses. For example, while chlorine can achieve 3-log Giardia cyst inactivation, the CT

requirement for 3-log inactivation of 100 to more than 300 mg-min/L will require high chlorine

doses and/or long contact times. However, 4-log virus inactivation is achievable with a CT of 15

to 60 mg·min/L for most temperatures.

Recently there has been some reports of 2-log and higher Cryptosporidium oocyst inactivation

with UV, using a system that concentrates the oocysts on a filter and then allows extended

exposure to UV to doses as high as 8,000 mW·s/cm2. This type application is considered

experimental at this time.

• Applicability as a secondary disinfectant represents the ability of the disinfectant to

maintain a residual in the distribution system. Only chlorine, chlorine dioxide, and

monochloramine provide residual disinfection in the distribution system. Chlorine dioxide is

limited to systems with smaller distribution systems because the total chlorine dioxide dose that

can be applied is limited by the production of chlorate ion and chlorite ion.

• Operator skill provides general guidance to the amount of operator attention and

maintenance required. All of the disinfectants can be placed on automatic control to limit the

amount of operator attention. The operational attention is rated based on the complexity of the

disinfectant application. Therefore, permanganate, which is a simple chemical feed system with

few mechanical elements, is rated 1 (low attention), while peroxone which include both ozone

systems and hydrogen peroxide feed systems, is rated 5 (high attention).

• All chemical disinfectants are judged to be applicable to small and large utilities. Modular

units of the technologies can cover a large range of flows. Ozone and chlorine dioxide generators

are available with small and large capacities. Chlorine and chemical feed systems have been

used successfully in all applications. Most UV water treatment facilities are less than 200 gpm in

capacity.

Key elements in the decision making process relate to the water source (i.e., ground or surface water)

and existing treatment configuration (including filtration) because these factors have a significant

impact on the degree of log removal required during disinfection. Water quality has a large impact on

the potential for DBP BOM formation.
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Table 1-6. Summary of Disinfectant Properties

(Based on Typical Disinfectant Application)

Condition

Chlorine

Ozone

Chlorine Dioxide

Permanganate

Chloramine

Ozone/Peroxide

Ultraviolet

Produce THM with TOC y s n n y s n

Produce oxidized organics s y s s n y s

Produce halogenated organics y s n n y s n

Produce inorganic byproducts n s y n n s n

Produce BOM s y s n n y n

MRDL applies y n y n y n n

Lime softening impacts y n n n y n y

Turbidity impacts n s n n n s y

Meet Giardia - <2.0 log y y y n n n n

Meet Giardia - >2.0 log n y y n n n n

Meet Crypto - <2.0 log n y y n n n n

Meet Crypto - >2.0 log n y n n n n n

Meet Virus - <2.0 log y y y n n n y

Meet Virus - >2.0 log y y y n n n y

Secondary disinfectant y n s n y n n

Operator skill (1=low; 5=high) 1 5 5 1 2 5 3

Applicable to large utilities y y y y y y n

Applicable to small utilities y y y y y y y

y = yes, n = no, s = sometimes

The following sections describe each of these phases.

1.7 Selecting a Disinfection Strategy

This section presents general guidance that can be used to assess the applicability of various

disinfectants or combination of disinfectants to select an appropriate disinfection strategy. Because

the selection of an appropriate strategy depends on site-specific conditions unique to each water

supply system, final selection of a strategy should be made with appropriate technical guidance (e.g.,

engineering study/evaluation or bench or pilot scale testing of alternatives). Selecting the most

appropriate disinfectant strategy for water treatment requires a balance among three key driving

forces:

• Providing water free of pathogens. Since the SWTR, the regulatory focus for pathogen

removal focused on coliform bacteria, heterotrophic plate counts, Giardia cysts, Legionella, and

viruses. Recently, the focus has been expanded to include Cryptosporidium oocyst removal and

inactivation, especially due to its resistance to chlorine.
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• Avoiding the production of disinfection byproducts (DBPs). Trihalomethanes (THMs), other

halogenated organics, ozone DBPs, oxidation byproducts, and some disinfectant residuals present

a health risk and must be limited in drinking waters. DBP precursor removal through process

optimization or enhanced coagulation is the first step in DBP control.

• Requiring residual disinfectant to maintain the bacteriological quality in the water as it is

distributed to customers to control regrowth. The potential for DBP formation increases with

extended contact between DBP precursors and residual disinfectants.

When changing disinfectants or oxidants water providers should consult with their primacy agencies.

The impact of the change should consider the impact on disinfection credit using disinfection

profiling and benchmarking techniques as summarized in Section 1.3.

1.7.1 Disinfection Strategy Evaluation

The selection of a disinfection strategy, as presented below, is affected by the following:

• Effectiveness of the current disinfection system;

• Need to change disinfectants;

• Selection of an alternative disinfectant; and

• Primary and secondary disinfection requirements.

As used in this guidance, primary and secondary disinfection are defined as follows:

Primary disinfection: The first (i.e., primary) disinfectant used in a treatment system, with the

primary objective of the disinfectant being to achieve the necessary CT (i.e., microbial

inactivation).

Secondary disinfection: The second disinfectant used in a treatment system, with the primary

objective of the disinfectant being to maintain the disinfection residual through the distribution

system.

For discussion, the approach to select a disinfection strategy is divided into three phases:

• Evaluate the current primary disinfection practice

• Select a primary disinfectant

• Select a secondary disinfectant.

1.7.1.1 Evaluate the Current Primary Disinfection Practice

Figure 1-1 presents the decision making process used to determine whether the present primary

disinfectant can meet disinfection and byproduct requirements. The key decision points in Figure 1-1

include:

• Meet current microbial inactivation limits. Microbial limits are defined by the primary

drinking water standards shown in Table 1-2. The regulated indicators of pathogens include
1. I N T R O D U C T I O N

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Giardia lamblia, Legionella, HPC, total coliform turbidity, and viruses. The disinfectant must be

capable of meeting the inactivation requirements for disinfection. If not, the plant must

determine if the current disinfectant can meet the microbial inactivation requirements solely

through process modifications. A process modification may be to move the application point,

increase dose, increase contact time, or adjust pH. If not, a new disinfectant may be needed. In

some instances, a PWS may opt to improve its current microbial inactivation even though the

PWS is meeting current microbial limitations. In these instances, an evaluation is necessary to

ensure that any process modifications to improve inactivation will still provide compliance with

the microbial limits.

• Meet current DBP limits. A second set of limits imposed on disinfectant usage are DBP

requirements. The DBP limits are established in the Stage 1 DBP rule (See Table 1-3 and Table

1-5). To meet these limits on a consistent basis under normal varying water quality conditions,

80 percent of the MCL serves as an action level that requires a change in treatment practice.

Similar to microbial inactivation, some PWSs may desire to improve current DBP protection,

thus requiring evaluation of these modifications. By optimizing existing treatment processes, the

production of DBPs can be reduced. Optimization may include pretreatment optimization (i.e.,

coagulation, filtration, etc.) or process modifications such as moving the point of disinfection.

Enhanced coagulation is required by the Stage 1 DBP rule. Where process modifications are

contemplated, the PWS must ensure that both microbial inactivation and DBP formation comply

with applicable regulatory requirements. If optimized treatment cannot meet DBP and microbial

requirements, a new disinfectant may be needed.

1.7.1.2 Select a Primary Disinfectant

If it is determined that a new disinfectant is required or desired for better public health protection, the

second phase in the decision process (Figure 1-2) addresses the factors concerning selection of a

primary disinfectant. This decision requires knowledge of the following three key components:

• TOC concentration. A high TOC concentration indicates a high potential for DBP formation.

In these cases, the decision tree will favor those disinfectants that will not produce DBPs or will

produce the least amount of DBPs. Note that precursor removal and enhanced coagulation are

used to reduce TOC during treatment optimization as indicated in Figure 1-1. “High TOC”

quantifies the potential to produce DBPs and is defined as a condition meeting one of the

following criteria:

− TOC exceeds 2 mg/L;

− TTHM exceeds MCL (0.08 mg/L under Stage 1 DBPR); or

− HAA5 exceeds MCL (0.06 mg/L under Stage 1 DBPR).
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START

Consult with Primacy

Agency when Changing

Treatment Process

1

Process Modification includes treatment optimization, moving the point of

disinfectant application, increasing disinfectant dosage, increasing contact time,

adjusting the pH, or other changes to existing treatment operations.

Meet

Current

Microbial

Inactivation

Limits?

Desire to

Improve

Current

Microbial

Inactivation?

Meet Microbial

Goals with Process

Modification1?

Change

Disinfectant

(See Figure 1-2)

Meet

Current DBP

Limits?

Desire to

Improve

Current DBP

Protection?

Meet1

DBP Goals

with Process

Modifications?

Yes

No Yes

No

No

Yes

Yes No

No Yes

No

Yes

OK

Figure 1-1. Flow Diagram to Evaluate Current Disinfection Practices
1. I N T R O D U C T I O N

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• Bromide ion concentration. The reactions of strong oxidants (ozone and peroxone) with

bromide ion to produce hypobromous acid and bromate ion, precludes their usage with waters

containing high concentrations of bromide ion. High bromide ion is defined as concentrations

exceeding 0.10 mg/L.

• Filtered versus non-filtered systems. The use of ozone or ozone/peroxide for unfiltered

systems without the benefit of biofiltration to reduce ozonation byproducts and BOM is

strongly discouraged.

1.7.1.3 Select a Secondary Disinfectant

The selection of a secondary disinfectant depends on the selected primary disinfectant. Figure 1-3

identifies three decision points for secondary disinfectants:

• Assimilable organic carbon (AOC) concentration. AOC is produced when a strong oxidant

(e.g., ozone) is used as primary disinfectant in the presence of high TOC water. High AOC is

defined as concentrations exceeding 0.10 mg/L after filtration. In these cases, additional

biological or GAC treatment should be considered to stabilize the finished water and prevent

regrowth in the distribution system.

• DBP formation potential (DBPFP). The DBPFP serves as an indication of the amount of

organic byproducts that could be expected to form in the distribution system if chlorine is used.

Because DBP formation continues in the distribution system, the DBP content at the plant

effluent should be limited. A high DBPFP is defined as a water meeting one of the following

criteria:

− TTHM seven-day formation exceeds the MCL (0.08 mg/L under Stage 1 DBPR); or

− HAA5 seven-day formation exceeds the MCL (0.06 mg/L under the Stage 1 DBPR).

• Distribution system retention time. In a large distribution system, booster stations may be

required to maintain the disinfection residual. Since chlorine dioxide has an upper limit for

application, its usage may not be feasible if relatively high doses are required to maintain a

residual in the distribution system. A distribution system retention time is considered high if it

exceeds 48 hours.
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EPA Guidance Manual 1-16 April 1999

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Start

Chlorine Dioxide

Chlorine

Interactive Disinfectants

Need Bench/Pilot Study

Chlorine Dioxide

Chlorine

Ozone

Interactive Disinfectants

High

Bromide

High

TOC

High

Bromide

Yes

No

High DBPFP

Ozone/BAC

Chlorine Dioxide

Chlorine Dioxide

A. Subpart H Systems

that Filter

Start

High Inactivation Reqmts.

High Disinfection Doses

Chlorine Dioxide

Chlorine

Interactive Disinfectants

Bench/Pilot Studies

Ozone

Chlorine Dioxide

Interactive Disinfectants

High

Bromide

High

TOC

High

Bromide

Yes

No

Excessive DBP Formation likely.

High disinfectant doses

required. May need TOC and

pathogen removal facilities.

Bench and pilot studies needed.

B. Subpart H Systems

that do not Filter

Yes

No

No

Yes

Yes

No

Yes

No

Consult Primacy Agency When

Changing Treatment Process

Excessive DBP Formation likely.

High disinfectant doses

required. May need TOC and

pathogen removal facilities.

Bench and pilot studies needed.

Figure 1-2. Flow Diagram to Narrow Selection of a New Primary Disinfectant
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April 1999 1-17 EPA Guidance Manual

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Consult Primacy Agency When

Changing Treatment Process

Start

High

AOC?

Biological

Treatment

BAF or GAC

High

DBPFP?

Extended

Distribution

Time?

Extended

Distribution

Time?

Chlorine

Chloramine

Chlorine

Chlorine Dioxide

Chloramine

Chlorine Dioxide

Chloramine Chloramine

Yes No

No Yes

Yes No No Yes

Figure 1-3. Flow Diagram to Narrow Selection of a New Secondary Disinfectant

1.7.2 Summary

The approach outlined above serves as a basis to evaluate the need for and to select the most

appropriate alternative disinfectants for drinking water systems. The approach is general enough to

cover the likely outcomes of the inactivation requirements and DBP formation. However, in some

cases, site-specific conditions may dictate a different approach. It is important to consult with the

primacy agency whenever a change in treatment is considered. Remember that the IESWTR requires

certain PWSs to use disinfection profiling and benchmarking procedures when proposing changes to

disinfection practices. In addition, some of the decisions may lead to a situation where additional

treatment will be required. For example, filtration may be needed to reduce the disinfectant dose and
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limit DBP formation in cases of high TOC and high bromide ion levels. In those instances, bench

scale or pilot studies may be required to select the most appropriate disinfectant.

1.8 References

1. AWWA (American Water Works Association). 1991. Guidance Manual for Compliance with

the Filtration and Disinfection Requirements for Public Works Systems Using Surface Water

Sources.

2. AWWA Safe Drinking Water Advisor - Library on Internet (1997).

3. Bellar, T.A, J.J. Lichtenberg, and R.C. Kroner. 1974. “The Occurrence of Organohalides in

Chlorinated Drinking Water.” J. AWWA. 66(12): 703-706.

4. Legube, B., J.P. Croue′, J. De Latt, and M. Dore′. 1989. “Ozonation of an Extracted Aquatic

Fulvic Acid: Theoretical and Practical Aspects.” Ozone Sci. Eng. 11(1): 69-91.

5. McGuire, M.J., D.W. Ferguson, and J.T. Gramith. 1990. Overview of Ozone Technology for

Organics Control and Disinfection. Conference proceedings, AWWA Seminar on Practical

Experiences with Ozone for Organics Control and Disinfection, Cincinnati, OH.

6. Rook, J.J. 1974. “Formation of Haloforms during Chlorination of Natural Water.” Water

Treatment and Examination. 23(2): 234-243.

7. Sawyer, C.N., P.L. McCarty, L. Parkin, and G.F. Parkin. 1994. Chemistry for Environmental

Engineering, fourth edition. McGraw Hill, Inc., New York, NY.

8. Symons, J.M., T.A. Bellar, J.K. Carswell, J. DeMarco, K.L. Kropp, G.G. Robeck, D.R. Seeger,

C.J. Slocum, B.L. Smith and A.A. Stevens. 1975. “National Organics Reconnaissance Survey

for Halogenated Organics.” J. AWWA. 67(11): 634-647.

9. USEPA (U.S. Environmental Protection Agency). 1997. Community Water System Survey -

Volume II. Detailed Survey Result Tables and Methodology Report. EPA 815-R-97-001b.

10. USEPA. 1978. National Organics Monitoring Survey (NOMS). Technical Support Division,

U.S. Environmental Protection Agency, Office of Drinking Water. Cincinnati, OH.

11. White, G.C. 1992. Handbook of Chlorination and Alternative Disinfectants. Vol. 3. Van

Nostrand Reinhold Co. New York, NY.

12. White, G.C. 1986. Handbook of Chlorination. Van Nostrand Reinhold Company, New York,

NY.
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Introduction ........................................................................................................................................................ 1-1

1.1 Objective of this Manual...................................................................................................................... 1-1

1.2 Background ......................................................................................................................................... 1-2

1.3 Regulatory Context .............................................................................................................................. 1-3

1.3.1 Disinfection Profiling and Benchmarking ..................................................................................... 1-7

1.4 Use of Disinfectants as Chemical Oxidants........................................................................................... 1-8

1.5 How Chlorine is Addressed in this Guidance Manual............................................................................ 1-8

1.6 A Summary of Alternative Disinfectant Properties................................................................................ 1-9

1.7 Selecting a Disinfection Strategy........................................................................................................ 1-11

1.7.1 Disinfection Strategy Evaluation................................................................................................. 1-12

1.7.1.1 Evaluate the Current Primary Disinfection Practice ................................................................. 1-12

1.7.1.2 Select a Primary Disinfectant.................................................................................................. 1-13

1.7.1.3 Select a Secondary Disinfectant .............................................................................................. 1-15

1.7.2 Summary.................................................................................................................................... 1-17

1.8 References......................................................................................................................................... 1-18

Table 1-1. Key Dates for Regulatory Activities................................................................................................... 1-4

Table 1-2. Primary Drinking Water Regulations Related to Microbiological Contaminants.................................. 1-6

Table 1-3. Primary Drinking Water Regulations Related to Disinfection Byproducts........................................... 1-6

Table 1-4. Primary Drinking Water Regulations Related to Residual Disinfectants.............................................. 1-7

Table 1-5. Log Removal/Inactivation through Filtration and Disinfection Required Under the SWTR.................. 1-7

Table 1-6. Summary of Disinfectant Properties................................................................................................. 1-11

(Based on Typical Disinfectant Application)...................................................................................................... 1-11

Figure 1-1. Flow Diagram to Evaluate Current Disinfection Practices................................................................ 1-14

Figure 1-2. Flow Diagram to Narrow Selection of a New Primary Disinfectant ................................................. 1-16

Figure 1-3. Flow Diagram to Narrow Selection of a New Secondary Disinfectant.............................................. 1-17
April 1999 2-1 EPA Guidance Manual

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2. DISINFECTANT USE IN WATER

TREATMENT

To comply with the SDWA regulations, the majority of PWSs use some form of water treatment.

The 1995 Community Water Systems Survey (USEPA, 1997a) reports that in the United States, 99

percent of surface water systems provide some treatment to their water, with 99 percent of these

treatment systems using disinfection/oxidation as part of the treatment process. Although 45 percent

of ground water systems provide no treatment, 92 percent of those ground water plants that do

provide some form of treatment include disinfection/oxidation as part of the treatment process. The

most commonly used disinfectants/oxidants (in no particular order) are chlorine, chlorine dioxide,

chloramines, ozone, and potassium permanganate.

Disinfectants are also used to achieve other specific objectives in drinking water treatment. These

other objectives include nuisance control (e.g., for zebra mussels and Asiatic clams), oxidation of

specific compounds (i.e., taste and odor causing compounds, iron, and manganese), and use as a

coagulant and filtration aid.

The purpose of this chapter is to:

• Provide a brief overview of the need for disinfection in water treatment.

• Provide basic information that is common to all disinfectants;

• Discuss other uses for disinfectant chemicals (i.e., as oxidants);

• Describe trends in DBP formation and the health effects of DBPs found in water treatment;

• Discuss microorganisms of concern in water systems, their associated health impact, and the

inactivation mechanisms and efficiencies of various disinfectants; and

• Summarize current disinfection practices in the United States, including the use of chlorine as a

disinfectant and an oxidant.

2.1 Need for Disinfection in Water Treatment

Although the epidemiological relation between water and disease had been suggested as early as the

1850s, it was not until the establishment of the germ theory of disease by Pasteur in the mid-1880s

that water as a carrier of disease-producing organisms was understood. In the 1880s, while London

experienced the “Broad Street Well” cholera epidemic, Dr. John Snow conducted his now famous

epidemiological study. Dr. Snow concluded that the well had become contaminated by a visitor,

with the disease, who had arrived in the vicinity. Cholera was one of the first diseases to be
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recognized as capable of being waterborne. Also, this incident was probably the first reported

disease epidemic attributed to direct recycling of non-disinfected water. Now, over 100 years later,

the list of potential waterborne diseases due to pathogens is considerably larger, and includes

bacterial, viral, and parasitic microorganisms, as shown in Table 2-1, Table 2-2 and Table 2-3,

respectively.

A major cause for the number of disease outbreaks in potable water is contamination of the

distribution system from cross connections and back siphonage with non-potable water. However,

outbreaks resulting from distribution system contamination are usually quickly contained and result

in relatively few illnesses compared to contamination of the source water or a breakdown in the

treatment system, which typically produce many cases of illnesses per incident. When considering

the number of cases, the major causes of disease outbreaks are source water contamination and

treatment deficiencies (White, 1992). For example, in 1993 a Cryptosporidiosis outbreak affected

over 400,000 people in Milwaukee, Wisconsin. The outbreak was associated with deterioration in

the raw water quality and a simultaneous decrease in the effectiveness of the coagulation-filtration

process (Kramer et al., 1996; MacKenzie et al., 1994). Historically, about 46 percent of the

outbreaks in the public water systems are found to be related to deficiencies in source water and

treatment systems with 92 percent of the causes of illness due to these two particular problems.

All natural waters support biological communities. Because some microorganisms can be

responsible for public health problems, biological characteristics of the source water are one of the

most important parameters in water treatment. In addition to public health problems, microbiology

can also affect the physical and chemical water quality and treatment plant operation.

2.1.1 Pathogens of Primary Concern

Table 2-4 shows the attributes of three groups of pathogens of concern in water treatment, namely

bacteria, viruses, and protozoa.

2.1.1.1 Bacteria

Bacteria are single-celled organisms typically ranging in size from 0.1 to 10 μm. Shape,

components, size, and the manner in which they grow can characterize the physical structure of the

bacterial cell. Most bacteria can be grouped by shape into four general categories: spheroid, rod,

curved rod or spiral, and filamentous. Cocci, or spherical bacteria, are approximately 1 to 3 μm in

diameter. Bacilli (rod-shaped bacteria) are variable in size and range from 0.3 to 1.5 μm in width (or

diameter) and from 1.0 to 10.0 μm in length. Vibrios, or curved rod-shaped bacteria, typically vary

in size from 0.6 to 1.0 μm in width (or diameter) and from 2 to 6 μm in length. Spirilla (spiral

bacteria) can be found in lengths up to 50 μm whereas filamentous bacteria can occur in length in

excess of 100 μm.
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2-3

Table 2-1. Waterborne Diseases from Bacteria

Causative Agent Disease Symptoms Reservoir

Salmonella typhosa Typhoid Fever Headache, nausea, loss of appetite, constipation or diarrhea, insomnia, sore throat,

bronchitis, abdominal pain, nose bleeding, shivering and increasing fever. Rose spots on

trunk. Incubation period: 7-14 days.

Feces and urine of typhoid carrier or

patient.

 S. paratyphi

 S. schottinulleri

 S. hirschfeldi C.

Paratyphoid fever General infection characterized by continued fever, diarrhea disturbances, sometimes rose

spots on trunk. Incubation period: 1-10 days.

Feces and urine of carrier or patient.

Shigella flexneri

 Sh. dysenteriae

 Sh. sonnei

 Sh. paradysinteriae

Bacillary dysentery Acute onset with diarrhea, fever, tenesmus and stool frequently containing mucus and

blood. Incubation period: 1-7 days.

Bowel discharges of carriers and infected

persons.

Vibrio comma

 V. cholerae

Cholera Diarrhea, vomiting, rice water stools, thirst, pain, coma. Incubation period: a few hours to 5

days.

Bowel discharges, vomitus, carriers.

Pasteurella tularensis Tularemia Sudden onset with pains and fever; prostration. Incubation period: 1-10 days. Rodent, rabbit, horsefly, woodtick, dog, fox,

hog.

Brucella melitensis Brucellosis (undulant

fever)

Irregular fever, sweating, chills, pain in muscles. Tissues, blood, mold, urine, infected animal.

Pseudomonas pseudomallei Melioidosis Acute diarrhea, vomiting, high fever, delirium, mania. Rats, guinea pigs, cats, rabbits, dogs,

horses.

Leptospira

icterohaemorrhagiae

(spirochaetales)

Leptospirosis (Well’s

disease)

Fevers, rigors, headaches, nausea, muscular pains, vomiting, thirst, prostration and

jaundice may occur.

Urine and feces of rats, swine, dogs, cats,

mice, foxes, sheep.

Enteropathogenic E. coli Gastroenteritis Water diarrhea, nausea, prostration and dehydration. Feces of carrier.

Sources: Salvato, 1972; Geldreich, 1972.
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2-4

Table 2-2. Waterborne Diseases from Human Enteric Viruses

Group Subgroup No. of Types or

Subtypes

Disease Entities Associated with

These Viruses Pathological Changes in Patients Organs Where Virus Multiplies

Enterovirus Poliovirus 3 Muscular paralysis

Aseptic meningitis

Febrile episode

Destruction of motor neurons

Inflammation of meninges from virus

Viremia and viral multiplication

Intestinal mucosa, spinal cord, brain stem

Meninges

Intestinal mucosa and lymph

Echovirus 34 Aseptic meningitis

Muscular paralysis

Guillain-Barre’s Syndrome1

Exanthem

Respiratory diseases

Diarrhea

Epidemic myalgia

Pericarditis and myocarditis

Hepatitis

Inflammation of meninges from virus

Destruction of motor neurons

Destruction of motor neurons

Dilation and rupture of blood vessels

Viral invasion of parenchymiatous of respiratory tracts

and secondary inflammatory responses

intestinal infections

Not well known

Viral invasion of cells with secondary inflammatory

responses

Invasion of parenchyma cells

Stem

Intestinal mucosa, spinal cord, brain

Spinal cord

Skin

Respiratory tracts and lungs

Gastrointestinal tract

Respiratory tract and gastrointestinal tract

Pericardial and myocardial tissue

Liver

Coxsackievirus

>24 Herpangina2 Viral invasion of mucosa with secondary inflammation Mouth

A Acute lymphatic pharyngitis

Aseptic meningitis

Muscular paralysis

Hand-foot-mouth disease3

Respiratory disease

Infantile diarrhea

Hepatitis

Pericarditis and myocarditis

Sore throat, pharyngeal lesions

Inflammation of meninges from virus

Destruction of motor neurons

Viral invasion of skin cells of hands-feet-mouth

Viral invasion of parenchymiatous of respiratory tracts

and secondary inflammatory responses

Viral invasion of cells of mucosa

Invasion of parenchyma cells

Viral invasion of cells with secondary inflammatory

responses

Lymph nodes and pharynx

Meninges

Intestinal mucosa, spinal cord, brain stem

Skin of hands-feet, and much of mouth

Respiratory tracts and lungs

Intestinal mucosa

Liver

Pericardial and myocardial tissue

1

 Ascending type of muscular paralysis

2 Febrile episode with sores in mouth

3

 Rash and blister on hand-foot-mouth with fever
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Table 2-2. Waterborne Diseases from Human Enteric Viruses (Continued)

Group Subgroup No. of Types or

Subtypes

Disease Entities Associated with

These Viruses Pathological Changes in Patients Organs Where Virus Multiplies

Enterovirus

(continued)

B 6 Pleurodynia4

Aseptic meningitis

Muscular paralysis

Meningoencephalitis

Pericarditis, endocarditis,

myocarditis

Respiratory disease

Hepatitis or Rash

Spontaneous abortion

Insulin-dependent diabetes

Congenital heart anomalies

Viral invasion of muscle cells

Inflammation of meninges from virus

Destruction of motor neurons

Viral invasion of cells

Viral invasion of cells with secondary inflammatory

responses

Viral invasion of parenchymiatous of respiratory tracts

and secondary inflammatory responses

Invasion of parenchyma cells

Viral invasion of vascular cells

Viral invasion of insulin-producing cells

Viral invasion of muscle cells

Intercostal muscles

Meninges

Intestinal mucosa, spinal cord, brain stem

Meninges and brains

Pericardial and myocardial tissue

Respiratory tracts and lungs

Liver

Placenta

Langerhan’s cells of pancreases

Developing heart

Reovirus 6 Not well known Not well known

Adenovirus 31 Respiratory diseases

Acute conjunctivitis

Acute appendicitis

Intussusception

Subacute thyroiditis

Sarcoma in hamsters

Viral invasion of parenchymiatous of respiratory tracts

and secondary inflammatory responses

Viral invasion of cells and secondary inflammatory

responses

Viral invasion of mucosa cells

Viral invasion of lymph nodes

Viral invasion of parenchyma cells

Sarcoma in hamsters

Respiratory tracts and lungs

Conjunctival cells and blood vessels

Appendia and lymph nodes

Intestinal lymph nodes

Thyroid

Muscle cells

Hepatitis >2 Infectious hepatitis

Serum hepatitis

Down’s Syndrome

Invasion of parenchyma cells

Invasion of parenchyma cells

Invasion of cells

Liver

Liver

Frontal lobe of brain, muscle, bones

4 Pleuritis type of pain with fever

Source: Taylor, 1974; Beneson, 1981.
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Table 2-3. Waterborne Diseases from Parasites

Causative Agent Disease Symptoms

Ascario

lumbricoides

(round worm)

Ascariasis Vomiting, live worms in feces

Cryptosporidium

muris and parvum

Cryptosporidiosis Acute diarrhea, abdominal pain, vomiting, and low-grade fever.

Can be life-threatening in immunodeficient patients

Entamoeba

histolytica

Amebiasis Diarrhea alternating with constipation, chronic dysentery with

mucus and blood

Giardia lamblia Giardiasis Intermittent diarrhea

Naegleria gruberi Amoebic

meningoecephalitis

Death

Schistosoma

mansoni

Schistosomiasis Liver and bladder infection

Taenia saginata

(beef tapeworm)

Taeniasis Abdominal pain, digestive disturbances, loss of weight

Source: Geldreich, 1972; Beneson, 1981.

2.1.1.2 Viruses

Viruses are microorganisms composed of the genetic material deoxyribonucleic acid (DNA) or

ribonucleic acid (RNA) and a protective protein coat (either single, double, or partially double

stranded). All viruses are obligate parasites, unable to carry out any form of metabolism and are

completely dependent upon host cells for replication. Viruses are typically 0.01 to 0.1 μm in size and

are very species specific with respect to infection, typically attacking only one type of host.

Although the principal modes of transmission for the hepatitis B virus and poliovirus are through

food, personal contact, or exchange of body fluids, these viruses can be transmitted through potable

water. Some viruses, such as the retroviruses (including the HIV group), appear to be too fragile for

water transmission to be a significant danger to public health (Riggs, 1989).

2.1.1.3 Protozoa

Protozoa are single-cell eucaryotic microorganisms without cell walls that utilize bacteria and other

organisms for food. Most protozoa are free-living in nature and can be encountered in water;

however, several species are parasitic and live on or in host organisms. Host organisms can vary

from primitive organisms such as algae to highly complex organisms such as human beings. Several

species of protozoa known to utilize human beings as hosts are shown in Table 2-5.
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Table 2-4. Attributes of the Three Waterborne Pathogens of Concern in Water

Treatment

Organism Size

(μm) Mobility Point(s) of Origin Resistance toDisinfection

Removal by

Sedimentation,

Coagulation, and

Filtration

Bacteria 0.1–10 Motile,

Nonmotile

Humans and

animals, water, and

contaminated food

Type specific -

bacterial spores

typically have the

highest resistance

whereas vegetative

bacteria have the

lowest resistance

Good, 2 to 3-log

removal

Viruses 0.01–0.1 Nonmotile Humans and

animals, polluted

water, and

contaminated food

Generally more

resistant than

vegetative bacteria

Poor, 1 to 3-log

removal

Protozoa 1–20 Motile,

Nonmotile

Humans and

animals, sewage,

decaying vegetation,

and water

More resistant than

viruses or vegetative

bacteria

Good, 2 to 3-log

removal

Table 2-5. Human Parasitic Protozoans

Protozoan Host(s) Disease Transmission Occurrence

Acanathamoeba

castellannii

Fresh water,

sewage, humans,

and soil

Amoebic

meningoencephalitis

Gains entry through

abrasions, ulcers, and as

secondary invader during

other infections

North America

Balantidium coli Pigs, humans Balantidiasis

(dysentery)

Contaminated water Micronesia has

been the only known

site of an outbreak

Cryptosporidium

parvum

Animals, humans Cryptosporidiosis Person-to-person or

animal-to-person contact,

ingestion of fecally

contaminated water or

food, or contact with

fecally contaminated

environmental surfaces.

Canada, England,

and the United

States

Entamoeba

histolytica

Humans Amoebic dysentery Contaminated water Last United States

outbreak, 1953

Giardia lamblia Animals, humans Giardiasis

(gastroenteritis)

Contaminated water Mexico, United

States, USSR

Naegleria fowleri Soil, water,

humans and

decaying

vegetation

Primary amoebic

meningoencephalitis

Nasal inhalation with

subsequent penetration

of nasopharynx;

exposure from swimming

in freshwater lakes

North America

Source: Montgomery, 1985; AWWA, 1995.
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2.1.2 Recent Waterborne Outbreaks

Within the past 40 years, several pathogenic agents never before associated with documented

waterborne outbreaks have appeared in the United States. Enteropathogenic E. coli and Giardia

lamblia were first identified to be the etiological agent responsible for waterborne outbreaks in the

1960s. The first recorded Cryptosporidium infection in humans occurred in the mid-1970s. Also

during that time was the first recorded outbreak of pneumonia caused by Legionella pneumophila

(Centers for Disease Control, 1989; Witherell et al., 1988). Recently, there have been numerous

documented waterborne disease outbreaks that have been caused by E. coli, Giardia lamblia,

Cryptosporidium, and Legionella pneumophila.

2.1.2.1 E. coli

The first documented case of waterborne disease outbreaks in the United States associated with

enteropathogenic E. coli occurred in the 1960s. Various serotypes of E. coli have been implicated as

the etiological agent responsible for disease in newborn infants, usually the result of cross

contamination in nurseries. Now, there have been several well-documented outbreaks of E. coli

(serotypes 0111:B4 and 0124:B27) associated with adult waterborne disease (AWWA, 1990, and

Craun, 1981). In 1975, the etiologic agent of a large outbreak at Crater Lake National Park was E.

coli serotype 06:H16 (Craun, 1981).

2.1.2.2 Giardia lamblia

Similar to E. coli, Giardia lamblia was first identified in the 1960s to be associated with waterborne

outbreaks in the United States. Giardia lamblia is a flagellated protozoan that is responsible for

Giardiasis, a disease that can range from being mildly to extremely debilitating. Giardia is currently

one of the most commonly identified pathogens responsible for waterborne disease outbreaks. The

life cycle of Giardia includes a cyst stage when the organism remains dormant and is extremely

resilient (i.e., the cyst can survive some extreme environmental conditions). Once ingested by a

warm-blooded animal, the life cycle of Giardia continues with excystation. The cysts are relatively

large (8-14 μm) and can be removed effectively by filtration using diatomaceous earth, granular

media, or membranes.

Giardiasis can be acquired by ingesting viable cysts from food or water or by direct contact with

fecal material. In addition to humans, wild and domestic animals have been implicated as hosts.

Between 1972 and 1981, 50 waterborne outbreaks of Giardiasis occurred with about 20,000 reported

cases (Craun and Jakubowski, 1986). Currently, no simple and reliable method exists to assay

Giardia cysts in water samples. Microscopic methods for detection and enumeration are tedious and

require examiner skill and patience. Giardia cysts are relatively resistant to chlorine, especially at

higher pH and low temperatures.
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2.1.2.3 Cryptosporidium

Cryptosporidium is a protozoan similar to Giardia. It forms resilient oocysts as part of its life cycle.

The oocysts are smaller than Giardia cysts, typically about 4-6 μm in diameter. These oocysts can

survive under adverse conditions until ingested by a warm-blooded animal and then continue with

excystation.

Due to the increase in the number of outbreaks of Cryptosporidiosis, a tremendous amount of

research has focused on Cryptosporidium within the last 10 years. Medical interest has increased

because of its occurrence as a life-threatening infection to individuals with depressed immune

systems. As previously mentioned, in 1993, the largest documented waterborne disease outbreak in

United States history occurred in Milwaukee and was determined to be caused by Cryptosporidium.

An estimated 403,000 people became ill, 4,400 people were hospitalized, and 100 people died. The

outbreak was associated with a deterioration in raw water quality and a simultaneous decrease in

effectiveness of the coagulation-filtration process, which led to an increase in the turbidity of treated

water and inadequate removal of Cryptosporidium oocysts.

2.1.2.4 Legionella pneumophila

An outbreak of pneumonia occurred in 1976 at the annual convention of the Pennsylvania American

Legion. A total of 221 people were affected by the outbreak, and 35 of those afflicted died. The

cause of the pneumonia was not determined immediately despite an intense investigation by the

Centers for Disease Control. Six months after the incident, microbiologists were able to isolate a

bacterium from the autopsy lung tissue of one of the Legionnaires. The bacterium responsible to the

outbreak was found to be distinct from other known bacterium and was named Legionella

pneumophila (Witherell et al., 1988). Following the discovery of this organism, other Legionellalike organisms were discovered. Altogether, 26 species of Legionella have been identified, and

seven are etiologic agents for Legionnaires’ disease (AWWA, 1990).

Legionnaires’ disease does not appear to be transferred person-to-person. Epidemiological studies

have shown that the disease enters the body through the respiratory system. Legionella can be

inhaled in water particles less than 5μm in size from facilities such as cooling towers, hospital hot

water systems, and recreational whirlpools (Witherell et al., 1988).

2.1.3 Mechanism of Pathogen Inactivation

The three primary mechanisms of pathogen inactivation are to:

• Destroy or impair cellular structural organization by attacking major cell constituents, such as

destroying the cell wall or impairing the functions of semi-permeable membranes;

• Interfere with energy-yielding metabolism through enzyme substrates in combination with

prosthetic groups of enzymes, thus rendering the enzymes non-functional; and
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• Interfere with biosynthesis and growth by preventing synthesis of normal proteins, nucleic acids,

coenzymes, or the cell wall.

Depending on the disinfectant and microorganism type, combinations of these mechanisms can also

be responsible for pathogen inactivation. In water treatment, it is believed that the primary factors

controlling disinfection efficiency are: (1) the ability of the disinfectant to oxidize or rupture the cell

wall; and (2) the ability of the disinfectant to diffuse into the cell and interfere with cellular activity

(Montgomery, 1985).

2.2 Other Uses of Disinfectants in Water Treatment

Disinfectants are used for more than just disinfection in drinking water treatment. While inactivation

of pathogenic organisms is a primary function, disinfectants are also used oxidants in drinking water

treatment for several other functions:

• Minimization of DBP formation;

• Control of nuisance Asiatic clams and zebra mussels;

• Oxidation of iron and manganese;

• Prevention of regrowth in the distribution system and maintenance of biological stability;

• Removal of taste and odors through chemical oxidation;

• Improvement of coagulation and filtration efficiency;

• Prevention of algal growth in sedimentation basins and filters;

• Removal of color.

A brief discussion of these additional oxidant uses follows.

2.2.1 Minimization of DBP Formation

Strong oxidants may play a role in disinfection and DBP control strategies in water treatment.

Several strong oxidants, including potassium permanganate and ozone, may be used to control DBP

precursors.

Potassium permanganate can be used to oxidize organic precursors at the head of the treatment plant,

thus minimizing the formation of byproducts at the downstream disinfection stage of the plant. The

use of potassium permanganate as an oxidant and disinfectant is discussed in Chapter 5 of this

guidance manual.
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The use of ozone for oxidation of DBP precursors is currently being studied. Early work has

shown that the effects of ozonation, prior to chlorination, were highly site-specific and

unpredictable. The key variables that seem to determine the effect of ozone are dose, pH,

alkalinity, and the nature of the organic material. Ozone has been shown to be effective for DBP

precursor reduction at low pHs. However, at higher pHs (i.e., above 7.5), ozone may actually

increase the amount of chlorination byproduct precursors. The use of ozone as an oxidant and

disinfectant is addressed in detail in Chapter 3 of this document.

2.2.2 Control of Nuisance Asiatic Clams and Zebra Mussels

The Asiatic clam (Corbicula fluminea) was introduced to the United States from Southeast Asia in

1938 and now inhabits almost every major river system south of 40° latitude (Britton and Morton,

1982; Counts, 1986). Asiatic clams have been found in the Trinity River, TX; the Ohio River at

Evansville, IN; New River at Narrows and Glen Lyn, VA; and the Catawba River in Rock Hill, SC

(Belanger et al., 1991; Cameron et al., 1989a; Matisoff et al., 1996). This animal has invaded many

water utilities, clogging source water transmission systems and valves, screens, and meters;

damaging centrifugal pumps; and causing taste and odor problems (Sinclair, 1964; Evans et al., 1979;

Smith, 1979).

Cameron et al. (1989a) investigated the effectiveness of several oxidants to control the Asiatic clam

in both the juvenile and adult phases. As expected, the adult clam was found to be much more

resistant to oxidants than the juvenile form. In many cases, the traditional method of control, free

chlorination, cannot be used because of the formation of excessive amounts of THMs. As shown in

Table 2-6, Cameron et al. (1989a) compared the effectiveness of four oxidants for controlling the

juvenile Asiatic clam in terms of the LT50 (time required for 50 percent mortality).

Monochloramine was found to be the best for controlling the juvenile clams without forming THMs.

Further research showed that the effectiveness of monochloramine increased greatly as the

temperature increased (Cameron et al., 1989b). Note that the temperatures in this study reflect

conditions in the Lynchburg Reservoir, Houston, Texas. Clams can tolerate temperatures between 2

and 35°C (Cameron et al. 1989a).
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Table 2-6. The Effects of Various Oxidants on Mortality of the

Asiatic Clam (Corbicula fluminea)

Chemical Residual

(mg/L)

Temperature

(°C) pH Life Stage LT50

(days)

Free chlorine 0.5

4.8

4.7

23

21

16

8.0

7.9

7.8

A

A

J

8.7

5.9

4.8

Potassium

Permanganate

1.1

4.8

17

17

7.6

7.6

J

J

7.9

8.6

Monochloramine 2.6

10.7

28

17

7.9

7.9

J

J

0.6

0.5

Chlorine dioxide 1.2

4.7

24

22

6.9

6.6

J

J

0.7

0.6

A=Adult; J=Juvenile

Source: Cameron et al., 1989a.

In a similar study, Belanger et al. (1991) studied the biocidal potential of total residual chlorine,

monochloramine, monochloramine plus excess ammonia, bromine, and copper for controlling the

Asiatic clam. Belanger et al. (1991) showed that monochloramine with excess ammonia was the

most effective for controlling the clams at 30°C. Chlorination at 0.25 to 0.40 mg/L total residual

chlorine at 20 to 25°C controlled clams of all sizes (LT50 below 28 days) but had minimal effect at

12 to 15°C (as low as zero mortality). As in other studies, the toxicity of all the biocides was highly

dependent on temperature and clam size.

The zebra mussel (Dreissena polymorpha) is a recent addition to the fauna of the Great Lakes. It was

first found in Lake St. Clair in 1988, though it is believed that this native of the Black and Caspian

seas, was brought over from Europe in ballast water around 1985 (Herbert et al., 1989). The zebra

mussel population in the Great Lakes has expanded very rapidly, both in size and geographical

distribution (Roberts, 1990). Lang (1994) reported that zebra mussels have been found in the Ohio

River, Cumberland River, Arkansas River, Tennessee River, and the Mississippi River south to New

Orleans.

Klerks and Fraleigh (1991) evaluated the effectiveness of hypochlorite, permanganate, and hydrogen

peroxide with iron for their effectiveness controlling adult zebra mussels. Both continuous and

intermittent 28-day static renewal tests were conducted to determine the impact of intermittent

dosing. Intermittent treatment proved to be much less effective than continuous dosing.

The hydrogen peroxide-iron combination (1–5 mg/L with 25 percent iron) was less effective in

controlling the zebra mussel than either permanganate or hypochlorite. Permanganate (0.5–2.5 mg

KMnO4/L) was usually less effective than hypochlorite (0.5–10 mg Cl2/L).

Van Benschoten et al. (1995) developed a kinetic model to predict the rate of mortality of the zebra

mussel in response to chlorine. The model shows the relationship between chlorine residual and

temperature on the exposure time required to achieve 50 and 95 percent mortality. Data were
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collected for chlorine residuals between 0.5 and 3.0 mg Cl2/L and temperatures from 0.3 to 24°C.

The results show a strong dependence on temperature and required contact times ranging from two

days to more than a month, depending on environmental factors and mortality required.

Brady et al. (1996) compared the efficiency of chlorine to control growth of zebra mussel and quagga

mussel (Dreissena bugensis). The quagga mussel is a newly identified mollusk within the Great

Lakes that is similar in appearance to the zebra mussel. Full-scale chlorination treatment found a

significantly higher mortality for the quagga mussel. The required contact time for 100 percent

mortality for quagga and zebra mussels was 23 days and 37 days, respectively, suggesting that

chlorination programs designed to control zebra mussels should also be effective for controlling

populations of quagga mussels.

Matisoff et al. (1996) evaluated chlorine dioxide (ClO2) to control adult zebra mussels using single,

intermittent, and continuous exposures. A single 30-minute exposure to 20 mg/L chlorine dioxide or

higher concentration induced at least 50 percent mortality, while sodium hypochlorite produced only

26 percent mortality, and permanganate and hydrogen peroxide were totally ineffective when dosed

at 30 mg/L for 30 minutes under the same conditions. These high dosages, even though only used

for a short period, may not allow application directly in water for certain applications due to

byproducts that remain in the water. Continuous exposure to chlorine dioxide for four days was

effective at concentrations above 0.5 mg/L (LC50 = 0.35 mg/L), and 100 percent mortality was

achieved at chlorine dioxide concentrations above 1 mg/L.

These experiences all show that the dose required to induce mortality to these nuisance organisms is

extremely high, both in terms of chemical dose and contact time. The potential impact on DBPs is

significant, especially when the water is high in organic content with a high propensity to form

THMs and other DBPs.

2.2.3 Oxidation of Iron and Manganese

Iron and manganese occur frequently in ground waters but are less problematic in surface waters.

Although not harmful to human health at the low concentrations typically found in water, these

compounds can cause staining and taste problems. These compounds are readily treated by oxidation

to produce a precipitant that is removed in subsequent sedimentation and filtration processes.

Almost all the common oxidants except chloramines will convert ferrous (2+) iron to the ferric (3+)

state and manganese (2+) to the (4+) state, which will precipitate as ferric hydroxide and manganese

dioxide, respectively (AWWA, 1990). The precise chemical composition of the precipitate will

depend on the nature of the water, temperature, and pH.

Table 2-7 shows that oxidant doses for iron and manganese control are relatively low. In addition,

the reactions are relatively rapid, on the order of seconds while DBP formation occurs over hours.

Therefore, with proper dosing, residual chlorine during iron and manganese oxidation is therefore

relatively low and short lived. These factors reduce the potential for DBP formation as a result of

oxidation for iron and manganese removal.
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Table 2-7. Oxidant Doses Required for Oxidation of Iron and Manganese

Oxidant Iron (II)

(mg/mg Fe)

Manganese (II)

(mg/mg Mn)

Chlorine, Cl2 0.62 0.77

Chlorine dioxide, ClO2 1.21 2.45

Ozone, O3 0.43 0.88*

Oxygen, O2 0.14 0.29

Potassium permanganate, KMnO4 0.94 1.92

Source: Culp/Wesner/Culp, 1986; Langlais et al., 1991.

* Optimum pH for manganese oxidation using ozone is 8-8.5 Source: Reckhow et al., 1991.

2.2.4 Prevention of Regrowth in the Distribution System and

Maintenance of Biological Stability

Biodegradable organic compounds and ammonia in treated water can cause microbial growth in the

distribution system. “Biological stability” refers to a condition wherein the treated water quality does

not enhance biological growth in the distribution system. Biological stability can be accomplished in

several ways:

• Removing nutrients from the water prior to distribution;

• Maintaining a disinfectant residual in the treated water; and

• Combining nutrient removal and disinfectant residual maintenance.

To maintain biological stability in the distribution system, the Total Coliform Rule (TCR) requires

that treated water have a residual disinfectant of 0.2 mg/L when entering the distribution system. A

measurable disinfectant residual must be maintained in the distribution system, or the utility must

show through monitoring that the heterotrophic plate count (HPC) remains less than 500/100 mL. A

system remains in compliance as long as 95 percent of samples meet these criteria. Chlorine,

monochloramine, and chlorine dioxide are typically used to maintain a disinfectant residual in the

distribution system. Filtration can also be used to enhance biological stability by reducing the

nutrients in the treated water.

The level of secondary disinfectant residual maintained is low, typically in the range of 0.1-0.3 mg/L,

depending on the distribution system and water quality. However, because the contact times in the

system are quite long, it is possible to generate significant amounts of DBPs in the distribution

system, even at low disinfectant doses.

Distribution system problems associated with the use of combined chlorine residual (chloramines), or

no residual, have been documented in several instances. The use of combined chlorine is

characterized by an initial satisfactory phase in which chloramine residuals are easily maintained

throughout the system and bacterial counts are very low. However, problems may develop over a
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period of years including increased bacterial counts, reduced combined chlorine residual, increased

taste and odor complaints, and reduced transmission main carrying capacity. Conversion of the

system to free-chlorine residual produces an initial increase in consumer complaints of taste and

odors resulting from oxidation of accumulated organic material. Also, it is difficult to maintain a

free-chlorine concentration at the ends of the distribution system (AWWA, 1990).

2.2.5 Removal of Taste and Odors Through Chemical Oxidation

Tastes and odors in drinking water are caused by several sources, including microorganisms,

decaying vegetation, hydrogen sulfide, and specific compounds of municipal, industrial, or

agricultural origin. Disinfectants themselves can also create taste and odor problems. In addition to

a specific taste-and odor-causing compound, the sensory impact is often accentuated by a

combination of compounds. More recently, significant attention has been given to tastes and odors

from specific compounds such as geosmin, 2-methylisoborneol (MIB), and chlorinated inorganic and

organic compounds (AWWARF, 1987).

Oxidation is commonly used to remove taste and odor causing compounds. Because many of these

compounds are very resistant to oxidation, advanced oxidation processes (ozone/hydrogen peroxide,

ozone/UV, etc.) and ozone by itself are often used to address taste and odor problems. The

effectiveness of various chemicals to control taste and odors can be site-specific. Suffet et al. (1986)

found that ozone is generally the most effective oxidant for use in taste and odor treatment. They

found ozone doses of 2.5 to 2.7 mg/L and 10 minutes of contact time (residual 0.2 mg/L)

significantly reduce levels of taste and odors. Lalezary et al. (1986) used chlorine, chlorine dioxide,

ozone, and permanganate to treat earthy-musty smelling compounds. In that study, chlorine dioxide

was found most effective, although none of the oxidants were able to remove geosmin and MIB by

more than 40 to 60 percent. Potassium permanganate has been used in doses of 0.25 to 20 mg/L.

Studies at the Metropolitan Water District of Southern California demonstrated the effectiveness of

peroxone (ozone plus hydrogen peroxide) to remove geosmin and MIB in water treatment (Ferguson

et al., 1990; Ferguson et al., 1991; Huck et al., 1995).

Prior experiences with taste and odor treatment indicate that oxidant doses are dependent on the

source of the water and causative compounds. In general, small doses can be effective for many taste

and odor compounds, but some of the difficult-to-treat compounds require strong oxidants such as

ozone and/or advanced oxidation processes or alternative technologies such as granular activated

carbon (GAC) adsorption.

2.2.6 Improvement of Coagulation and Filtration Efficiency

Oxidants, specifically ozone, have been reported to improve coagulation and filtration efficiency (Gurol

and Pidatella, 1983; Farvardin and Collins, 1990; Reckhow et al., 1993; Masschelein, 1992). Others,

however, have found no improvement in effluent turbidity from oxidation (Tobiason et al., 1992;

Hiltebrand et al., 1986). Prendiville (1986) collected data from a large treatment plant showing that

preozonation was more effective than prechlorination to reduce filter effluent turbidities. The cause of
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the improved coagulation is not clear, but several possibilities have been offered (Reckhow et al.,

1986), including:

• Oxidation of organics into more polar forms;

• Oxidation of metal ions to yield insoluble complexes such as ferric iron complexes; and

• Change in the structure and size of suspended particles.

2.2.7 Prevention of Algal Growth in Sedimentation Basins and

Filters

Prechlorination is often used to minimize operational problems associated with biological growth in

water treatment plants (AWWA, 1990; Culp/Wesner/Culp, 1986). Prechlorination will prevent

slime formation on filters, pipes, and tanks, and reduce potential taste and odor problems associated

with such slimes. Many sedimentation and filtration facilities operate with a small chlorine residual

to prevent growth of algae and bacteria in the launders and on the filter surfaces. This practice has

increased in recent years as utilities take advantage of additional contact time in the treatment units to

meet disinfection requirements under the SWTR.

2.2.8 Removal of Color

Free chlorine is used for color removal. A low pH is favored. Color is caused by humic compounds,

which have a high potential for DBP formation. The chlorine dosage and kinetics for color removal

are best determined through bench studies.

2.3 Disinfection Byproducts and Disinfection Residuals

2.3.1 Types of DBPs and Disinfection Residuals

Table 2-8 is a list, compiled by EPA, of DBPs and disinfection residuals that may be of health

concern. The table includes both the disinfectant residuals and the specific byproducts produced by

the disinfectants of interest in drinking water treatment. These contaminants of concern are grouped

into four distinct categories and include disinfectant residuals, inorganic byproducts, organic

oxidation byproducts, and halogenated organic byproducts. Tables 1-3 and 1-4 list the disinfection

byproducts and disinfectant residuals that are currently regulated.
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Table 2-8. List of Disinfection Byproducts and Disinfection Residuals

DISINFECTANT RESIDUALS HALOGENATED ORGANIC BYPRODUCTS

Free Chlorine Trihalomethanes

Hypochlorous Acid Chloroform

Hypochlorite Ion Bromodichloromethane

Chloramines Dibromochloromethane

Monochloramine Bromoform

Chlorine Dioxide Haloacetic Acids

INORGANIC BYPRODUCTS Monochloroacetic Acid

Chlorate Ion Dichloroacetic Acid

Chlorite Ion Trichloroacetic Acid

Bromate Ion Monobromoacetic Acid

Iodate Ion Dibromoacetic Acid

Hydrogen Peroxide Haloacetonitriles

Ammonia Dichloroacetronitrile

ORGANIC OXIDATION BYPRODUCTS Bromochloroacetonitrile

Aldehydes Dibromoacetonitrile

Formaldehyde Trichloroacetonitrile

Acetaldehyde Haloketones

Glyoxal 1,1-Dichloropropanone

Hexanal 1,1,1-Trichloropropanone

Heptanal Chlorophenols

Carboxylic Acids 2-Chlorophenol

Hexanoic Acid 2,4-Dichlorophenol

Heptanoic Acid 2,4,6-Trichlorophenol

 Oxalic Acid Chloropicrin

Assimilable Organic Carbon Chloral Hydrate

Cyanogen Chloride

N-Organochloramines

MX*

* 3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone

The production of DBPs depend on the type of disinfectant, the presence of organic material (e.g.,

TOC), bromide ion, and other environmental factors as discussed in this manual. By removing DBP

precursors, the formation of DBPs can be reduced.

The health effects of DBPs and disinfectants are generally evaluated with epidemiological studies

and/or toxicological studies using laboratory animals. Table 2-9 indicates the cancer classifications

of both disinfectants and DBPs as of January 1999. The classification scheme used by EPA is

shown at the bottom of Table 2-9. The EPA classification scheme for carcinogenicity weighs both

animal studies and epidemiologic studies, but places greater weight on evidence of carcinogenicity in

humans.
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Table 2-9. Status of Health Information for Disinfectants and DBPs

Contaminant Cancer

Classification(1)

Chloroform B2

Bromodichloromethane B2

Dibromochloromethane C

Bromoform B2

Monochloroacetic Acid --

Dichloroacetic Acid B2

Trichloroacetic Acid C

Dichloroacetonitrile C

Bromochloroacetonitrile --

Dibromoacetonitrile C

Trichloroacetonitrile --

1,1-Dichloropropanone --

1,1,1-Trichloropropanone --

2-Chlorophenol D

2,4-Dichlorophenol D

2,4,6-Trichlorophenol B2

Chloropicrin --

Chloral Hydrate C

Cyanogen Chloride --

Formaldehyde B1(2)

Chlorate --

Chlorite D

Bromate B2

Ammonia D

Hypochlorous Acid --

Hypochlorite --

Monochloramine --

Chlorine Dioxide D

(1) The scheme for categorizing chemicals according to their carcinogenic potential is as follows:*

Group A:

Human Carcinogen

Sufficient evidence in epidemiologic studies to support casual association

between exposure and cancer.

Group B:

Probable Human Carcinogen

Limited evidence in epidemiologic studies (Group B1) and/or sufficient

evidence from animal studies (Group B2)

Group C:

Possible Human Carcinogen

Limited evidence from animal studies and inadequate or no data in humans

Group D:

Not Classifiable

Inadequate or no human and animal evidence of carcinogenicity

Group E:

No Evidence of Carcinogenicity 

for Humans

No evidence of carcinogenicity in at least two adequate animal tests in

different species or in adequate epidemiologic and animal studies.

* EPA is in the process of revising the Cancer Guidelines

Source: USEPA, 1996

(2) Based on inhalation exposure.
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2.3.2 Disinfection Byproduct Formation

Halogenated organic byproducts are formed when natural organic matter (NOM) reacts with free

chlorine or free bromine. Free chlorine can be introduced to water directly as a primary or secondary

disinfectant, with chlorine dioxide, or with chloramines. Free bromine results from the oxidation of

the bromide ion in source water. Factors affecting formation of halogenated DBPs include type and

concentration of natural organic matter, oxidant type and dose, time, bromide ion concentration, pH,

organic nitrogen concentration, and temperature. Organic nitrogen significantly influences the

formation of nitrogen containing DBPs such as the haloacetonitriles, halopicrins, and cyanogen

halides (Reckhow et al., 1990; Hoigné and Bader, 1988). The parameter TOX represents the

concentration of total organic halides in a water sample (calculated as chloride). In general, less than

50 percent of the TOX content has been identified, despite evidence that several of these unknown

halogenated byproducts of water chlorination may be harmful to humans (Singer and Chang, 1989).

Non-halogenated DBPs are also formed when strong oxidants react with organic compounds found in

water. Ozone and peroxone oxidation of organics leads to the production of aldehydes, aldo- and

keto-acids, organic acids, and, when bromide ion is present, brominated organics (Singer, 1992).

Many of the oxidation byproducts are biodegradable and appear as biodegradable dissolved organic

carbon (BDOC) and assimilable organic carbon (AOC) in treated water.

Bromide ion plays a key role in DBP formation. Ozone or free chlorine oxidizes bromide ion to

hypobromate ion/hypobromous acid, which subsequently forms brominated DBPs. Brominated

organic byproducts include compounds such as bromoform, brominated acetic acids and

acetonitriles, bromopicrin, and cyanogen bromide. Only about one third of the bromide ions

incorporated into byproducts has been identified.

2.3.2.1 Disinfection Byproduct Precursors

Numerous researchers have documented that NOM is the principal precursor of organic DBP

formation (Stevens et al., 1976; Babcock and Singer 1979; Christman et al., 1983). Chlorine reacts

with NOM to produce a variety of DBPs, including THMs, haloacetic acids (HAAs), and others.

Ozone reacts with NOM to produce aldehydes, organic acids, and aldo- and keto-acids; many of

these are produced by chlorine as well (Singer and Harrington, 1993).

Natural waters contain mixtures of both humic and nonhumic organic substances. NOM can be

subdivided into a hydrophobic fraction composed of primarily humic material, and a hydrophilic

fraction composed of primarily fulvic material.

The type and concentration of NOM are often assessed using surrogate measures. Although

surrogate parameters have limitations, they are used because they may be measured more easily,

rapidly, and inexpensively than the parameter of interest, often allowing on-line monitoring of the

operation and performance of water treatment plants. Surrogates used to assess NOM include:

• Total and dissolved organic carbon (TOC and DOC);
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• Specific ultraviolet light absorbance (SUVA), which is the absorbance at 254 nm wavelength

(UV-254) divided by DOC (SUVA = (UV-254/DOC)*100, in L/mg-m);

• THM formation potential (THMFP) -- a test measuring the quantity of THMs formed with a high

dosage of free chlorine and a long reaction time; and

• TTHM Simulated Distribution System (SDS) -- a test to predict the TTHM concentration at some

selected point in a given distribution system, where the conditions of the chlorination test

simulate the distribution system at the point desired.

On average, about 90 percent of the TOC is dissolved. DOC is defined as the TOC able to pass

through a 0.45 μm filter. UV absorbance is a good technique for assessing the presence of DOC

because DOC primarily consists of humic substances, which contain aromatic structures that absorb

light in the UV spectrum. Oxidation of DOC reduces the UV absorbance of the water due to

oxidation of some of the organic bonds that absorb UV absorbance. Complete mineralization of

organic compounds to carbon dioxide usually does not occur under water treatment conditions;

therefore, the overall TOC concentration usually is constant.

DBP concentrations vary seasonally and are typically greatest in the summer and early fall for

several reasons:

• The rate of DBP formation increases with increasing temperature (Singer et al., 1992);

• The nature of organic DBP precursors varies with season (Singer et al., 1992); and

• Due to warmer temperatures, chlorine demand may be greater during summer months requiring

higher dosages to maintain disinfection.

If the bromide ion is present in source waters, it can be oxidized to hypobromous acid that can react

with NOM to form brominated DBPs, such as bromoform. Furthermore, under certain conditions,

ozone may react with the hypobromite ion (OBr-) to form bromate ion (BrO3).

The ratio of bromide ion to the chlorine dose affects THM formation and bromine substitution of

chlorine. Increasing the bromide ion to chlorine dose ratio shifts the speciation of THMs to produce

more brominated forms (Krasner et al., 1989; Black et al., 1996). In the Krasner et al. study, the

chlorine dose was roughly proportional to TOC concentration. As TOC was removed through the

treatment train, the chlorine dose decreased and TTHM formation declined. However, at the same

time, the bromide ion to chlorine dose increased, thereby shifting TTHM concentrations to the more

brominated THMs. Therefore, improving the removal of NOM prior to chlorination can shift the

speciation of halogenated byproducts toward more brominated forms.

Chloropicrin is produced by the chlorination of humic materials in the presence of nitrate ion

(Duguet et al., 1985; Thibaud et al., 1987). Thibaud et al. (1988) chlorinated humic compounds in

the presence of bromide ion to demonstrate the formation of brominated analogs to chloropicrin.
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2.3.2.2 Impacts of pH on DBP Formation

The pH of water being chlorinated has an impact on the formation of halogenated byproducts as

shown in Table 2-10 (Reckhow and Singer, 1985; Stevens et al., 1989). THM formation increases

with increasing pH. Trichloroacetic acid, dichloroacetonitrile, and trichloropropanone formation

decrease with increased pH. Overall TOX formation decreases with increasing pH.

Based on chlorination studies of humic material in model systems, high pH tends to favor chloroform

formation over the formation of trichloroacetic acid and other organic halides. Accordingly, water

treatment plants practicing precipitative softening at pH values greater than 9.5 to 10 are likely to

have a higher fraction of TOX attributable to THMs than plants treating surface waters by

conventional treatment in pH ranges of 6 to 8 (Singer and Chang, 1989).

Since the application of chlorine dioxide and chloramines may introduce free chlorine into water,

chlorination byproducts that may be formed would be influenced by pH as discussed above. Ozone

application to bromide ion containing waters at high pH favors the formation of bromate ion, while

application at low pH favors the formation of brominated organic byproducts. See discussion under

individual disinfectants for a more detailed discussion on pH impacts on DBP formation.

The pH also impacts enhanced coagulation (i.e., for ESWTR compliance) and Lead and Copper Rule

Compliance. These issues are addressed in EPA’s Microbial and Disinfection Byproduct

Simultaneous Compliance Guidance Manual (expected to be available in 1999).

2.3.2.3 Organic Oxidation Byproducts

Organic oxidation byproducts are formed by reactions between NOM and all oxidizing agents added

during drinking water treatment. Some of these byproducts are halogenated, as discussed in the

previous section, while others are not. The types and concentrations of organic oxidation byproducts

produced depend on the type and dosage of the oxidant being used, chemical characteristics and

concentration of the NOM being oxidized, and other factors such as the pH and temperature.

Specific chemical byproducts belonging to the classification of halogenated organic oxidation

products are listed in Table 2-10. As presented in Table 2-10, the formation of DBPs is pH

dependent. Comparisons in the table are made to the formation of TTHMs at a pH of 7.0. AOC is

not a specific organic contaminant, but a generally used surrogate measure of bacterial regrowth

potential in distribution systems. AOC is comprised of many chemical species, including the

aldehydes and carboxylic acids listed in Table 2-8. AOC formation studies, primarily performed in

the Netherlands, have shown that both ozonation and chlorination can increase concentrations of

AOC. This increase in AOC concentration is believed to be the result of oxidizing high molecular

weight organics to smaller and more readily bioassimilable molecules. Because AOC is not a

specific chemical contaminant, no specific health effects are attributable to AOC.
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Table 2-10. Conditions of Formation of DBPs

Conditions of Formation

By-product Chlorination at pH 5.0 Chlorination at pH 7.0 Chlorination at pH 9.4

Total Trihalomethanes Lower formation Higher formation

Trichloroacetic Acid Similar formation to that at

pH 7.0

Similar formation to that at

pH 5.0

Lower formation

Dichloroacetic Acid Similar formation to that at

pH 5.0 and 9.4 - perhaps

slightly higher at pH 7.0

Similar formation to that

at pH 5.0 and 9.4-

perhaps slightly higher at

pH 7.0

Similar formation to that at

pH 5.0 and 7.0 - perhaps

slightly higher at pH 7.0

Monochloroacetic Acid At concentrations <5 μg/L,

trends not discernible

At concentrations <5 μg/L,

trends not discernible

At concentrations <5 μg/L,

trends not discernible

Dibromoacetic Acid At concentrations <1 μg/L,

trends not discernible

At concentrations <1 μg/L,

trends not discernible

At concentrations <1 μg/L,

trends not discernible

Chloral Hydrate Similar formation to that at

pH 7.0

Similar formation to that at

pH 5.0

Forms within 4 hours;

decays over time to <5

μg/L

Chloropicrin At concentrations <1 μg/L,

trends not discernible

At concentrations <1 μg/L,

trends not discernible

At concentrations <1 μg/L,

trends not discernible

Dichloroacetonitrile Higher formation Forms within 4 hours;

decays over time to <5

μg/L

Concentrations <2 μg/L,

trends not discernible

Bromochloroacetonitrile At concentrations <2 μg/L,

trends not discernible

At concentrations <2 μg/L,

trends not discernible

At concentrations <2 μg/L,

trends not discernible

Dibromoacetonitrile At concentrations

<.5 μg/L, trends not

discernible

At concentrations

<.5 μg/L, trends not

discernible

At concentrations

<.5 μg/L, trends not

discernible

Trichloroacetonitrile Not detected Not detected Not detected

1,1,1-Trichloropropanone Higher formation At concentrations <2 μg/L,

trends not discernible

Not detected

Source: Stevens et al., 1989.

2.3.2.4 Inorganic Byproducts and Disinfectants

Table 2-11 shows some of the inorganic DBPs that are produced or remain as residual during

disinfection. As discussed earlier, bromide ion reacts with strong oxidants to form bromate ion and

other organic DBPs. Chlorine dioxide and chloramines leave residuals that are of concern for health

considerations, as well as for taste and odor. The significance of these compounds is discussed

further in subsequent chapters.
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Table 2-11. Inorganic DBPs Produced During Disinfection

Disinfectant Inorganic Byproduct or Disinfectant Residual Discussed

Chlorine Dioxide Chlorine Dioxide, Chlorite ion, Chlorate ion, Bromate ion (in presence of light)

Ozone Bromate ion, Hydrogen Peroxide

Chloramination Monochloramine, Dichloramine, Trichloramine, Ammonia, Cyanogen Chloride

2.3.3 DBP Control Strategies

In 1983, the EPA identified technologies, treatment techniques, and plant modifications that

community water systems could use to comply with the maximum contaminant level for TTHMs.

The principal treatment modifications involved moving the point of chlorination downstream in the

water treatment plant, improving the coagulation process to enhance the removal of DBP precursors,

and using chloramines to supplement or replace the use of free chlorine (Singer, 1993). Moving the

point of chlorination downstream in the treatment train often is very effective in reducing DBP

formation, because it allows the NOM precursor concentration to be reduced during treatment prior

to chlorine addition. Replacing prechlorination by preoxidation with an alternate disinfectant that

produces less DBPs is another option for reducing formation of chlorinated byproducts.

Other options to control the formation of DBPs include; source water quality control, DBP precursor

removal, and disinfection strategy selection. An overview of each is provided below.

2.3.3.1 Source Water Quality Control

Source water control strategies involve managing the source water to lower the concentrations of

NOM and bromide ion in the source water. Research has shown that algal growth leads to the

production of DBP precursors (Oliver and Shindler, 1980; Wachter and Andelman, 1984; Karimi and

Singer, 1991). Therefore, nutrient and algal management is one method of controlling DBP

formation potential of source waters. Control of bromide ion in source waters may be accomplished

by preventing brine or salt water intrusion into the water source.

2.3.3.2 DBP Precursor Removal

Raw water can include DBP precursors in both dissolved and particulate forms. For the dissolved

precursors to be removed in conventional treatment, they must be converted to particulate form for

subsequent removal during settling and filtering. The THM formation potential generally decreases

by about 50 percent through conventional coagulation and settling, indicating the importance of

moving the point of chlorine application after coagulation and settling (and even filtration) to control

TOX as well as TTHM formation (Singer and Chang, 1989). Conventional systems can lower the

DBP formation potential of water prior to disinfection by further removing precursors with enhanced

coagulation, GAC adsorption, or membrane filtration prior to disinfection. Precursor removal

efficiencies are site-specific and vary with different source waters and treatment techniques.
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Aluminum (alum) and iron (ferric) salts can remove variable amounts of NOM. For alum, the

optimal pH for NOM removal is in the range of 5.5 to 6.0. The addition of alum decreases pH and

may allow the optimal pH range to be reached without acid addition. However, waters with very low

or very high alkalinities may require the addition of base or acid to reach the optimal NOM

coagulation pH (Singer, 1992).

GAC adsorption can be used following filtration to remove additional NOM. For most applications,

empty bed contact times in excess of 20 minutes are required, with regeneration frequencies on the

order of 2 to 3 months (Singer, 1992). These long contact times and frequent regeneration

requirements make GAC an expensive treatment option. In cases where prechlorination is practiced,

the chlorine rapidly degrades GAC. Addition of a disinfectant to the GAC bed can result in specific

reactions in which previously absorbed compounds leach into the treated water.

Membrane filtration has been shown effective in removing DBP precursors in some instances. In

pilot studies, ultrafiltration (UF) with a molecular weight cutoff (MWCO) of 100,000 daltons was

ineffective for controlling DBP formation. However, when little or no bromide ion was present in

source water, nanofiltration (NF) membranes with MWCOs of 400 to 800 daltons effectively

controlled DBP formation (Lâiné et al., 1993). In waters containing bromide ion, higher bromoform

concentrations were observed after chlorination of membrane permeate (compared with raw water).

This occurs as a result of filtration removing NOM while concentrating bromide ions in the permeate

thus providing a higher ratio of bromide ions to NOM than in raw water. This reduction in chlorine

demand increases the ratio of bromide to chlorine, resulting in higher bromoform concentrations after

chlorination of NF membrane permeate (compared with the raw water). TTHMs were lower in

chlorinated permeate than chlorinated raw water. However, due to the shift in speciation of THMs

toward more brominated forms, bromoform concentrations were actually greater in chlorinated

treated water than in chlorinated raw water. Use of spiral-wound NF membranes (200–300 daltons)

more effectively controlled the formation of brominated THMs, but pretreatment of the water was

necessary (Lâiné et al., 1993). Significant limitations in the use of membranes are disposal of the

waste brine generated, fouling of membranes, cost of membrane replacement, and increasing energy

cost.

The promulgated DBPR requires enhanced coagulation as an initial step for removal of DBP

precursors. In addition to meeting MCLs and MRDLs, some water suppliers also must meet

treatment requirements to control the organic material (DBP precursors) in the raw water that

combines with disinfectant residuals to form DBPs. Systems using conventional treatment are

required to control precursors (measured as TOC) by using enhanced coagulation or enhanced

softening. A system must remove a specified percentage of TOC (based on raw water quality) prior

to the point of continuous disinfection (Table 2-12).

Systems using ozone followed by biologically active filtration or chlorine dioxide that meet specific

criteria would be required to meet the TOC removal requirements prior to addition of a residual

disinfectant. Systems able to reduce TOC by a specified percentage level have met the DBPR

treatment technique requirement.
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Table 2-12. Required Removal of TOC by Enhanced Coagulation for Surface

Water Systems+ Using Conventional Treatment++ (percent reduction)

Source Water Alkalinity (mg/L as CaCO3)

Source Water

TOC (mg/L) 0-60 >60-120 >120+++

>2.0-4.0 35.0 25.0 15.0

>4.0-8.0 45.0 35.0 25.0

>8.0 50.0 40.0 30.0

+ Also applies to utilities that treat ground water under the influence of surface water.

++ Systems meeting at least one of the conditions in 40 CFR §§ 141.135(a)(1)(I)-(iv) are not required to operate with enhanced

coagulation.

+++ Systems practicing precipitative softening must meet the TOC removal requirements in this column.

If the system does not meet the percent reduction, it must determine its alternative minimum TOC

removal level. The primacy agency approves the alternative minimum TOC removal possible for the

system on the basis of the relationship between coagulant dose and TOC in the system based on

results of bench or pilot-scale testing. Enhanced coagulation is determined in part as the coagulant

dose where an incremental addition of 10 mg/L of alum (or an equivalent amount of ferric salt)

results in a TOC removal below 0.3 mg/L.

2.3.3.3 Disinfection Strategy Selection

In addition to improving the raw or predisinfectant water quality, alternative disinfection strategies

can be used to control DBPs. These strategies include the following:

• Use an alternative or supplemental disinfectant or oxidant such as chloramines or chlorine

dioxide that will produce fewer DBPs;

• Move the point of chlorination to reduce TTHM formation and, where necessary, substitute

chloramines, chlorine dioxide, or potassium permanganate for chlorine as a preoxidant;

• Use two different disinfectants or oxidants at various points in the treatment plant to avoid DBP

formation at locations where precursors are still present in high quantities;

• Use of powdered activated carbon for THM precursor or TTHM reduction seasonally or

intermittently; and

• Maximize precursor removal.

2.3.4 CT Factor

One of the most important factors for determining or predicting the germicidal efficiency of any

disinfectant is the CT factor, a version of the Chick-Watson law (Chick, 1908; Watson, 1908). The

CT factor is defined as the product of the residual disinfectant concentration, C, in mg/L, and the

contact time, T, in minutes, that residual disinfectant is in contact with the water.
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EPA developed CT values for the inactivation of Giardia and viruses under the SWTR. Table 2-13

compares the CT values for virus inactivation using chlorine, chlorine dioxide, ozone, chloramine,

and ultraviolet light disinfection under specified conditions. Table 2-14 shows the CT values for

inactivation of Giardia cyst using chlorine, chloramine, chlorine dioxide, and ozone under specified

conditions. The CT values shown in Table 2-13 and Table 2-14 are based on water temperatures of

10°C and pH values in the range of 6 to 9. CT values for chlorine disinfection are based on a free

chlorine residual. Note that chlorine is less effective as pH increases from 6 to 9. In addition, for a

given CT value, a low C and a high T is more effective than the reverse (i.e., a high C and a low T).

For all disinfectants, as temperature increases, effectiveness increases.

Table 2-13. CT Values for Inactivation of Viruses

Disinfectant Units Inactivation

2-log 3-log 4-log

Chlorine1 mg · min/L 3 4 6

Chloramine2 mg · min/L 643 1,067 1,491

Chlorine Dioxide3 mg · min/L 4.2 12.8 25.1

Ozone mg · min/L 0.5 0.8 1.0

UV mW · s/cm221 36 not available

CT values were obtained from AWWA, 1991.

1

 Values are based on a temperature of 10°C, pH range of 6 to 9, and a free chlorine residual of 0.2 to 0.5 mg/L.

2

 Values are based on a temperature of 10°C and a pH of 8.

3

 Values are based on a temperature of 10°C and a pH range of 6 to 9.

Table 2-14. CT Values for Inactivation of Giardia Cysts

Disinfectant Inactivation (mg · min/L)

0.5-log 1-log 1.5-log 2-log 2.5-log 3-log

Chlorine117 35 52 69 87 104

Chloramine2310 615 930 1,230 1,540 1,850

Chlorine Dioxide34 7.7 12 15 19 23

Ozone30.23 0.48 0.72 0.95 1.2 1.43

CT values were obtained from AWWA, 1991.

1

 Values are based on a free chlorine residual less than or equal to 0.4 mg/L, temperature of 10°C, and a pH of 7.

2

 Values are based on a temperature of 10°C and a pH in the range of 6 to 9.

3

 Values are based on a temperature of 10°C and a pH of 6 to 9.

2.4 Pathogen Inactivation Versus DBP Formation

Table 2-15 presents a summary of disinfection parameter impacts on pathogen inactivation and DBP

formation.
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Table 2-15. Summary of Disinfection Impacts

Disinfection Parameter Typical Impact on Pathogen

Inactivation Typical Impact on DBP Formation

Disinfectant Type Depends on inactivation efficacy Depends on disinfectant reactivity

Disinfectant Strength The stronger the disinfectant, the

quicker the disinfection process.

The stronger the disinfectant, the

greater the amount of DBPs.

Disinfectant Dose Increasing the disinfectant dose

increases the disinfection rate.

Increasing the disinfectant dose typically

increases the rate of DBP formation.

Type of Organism Susceptibility to disinfection varies

according to pathogen group. In general,

protozoa are more resistant to

disinfectants than bacteria and viruses.

None.

Contact Time Increasing the contact time decreases

the disinfectant dose required for a

given level of inactivation.

Increasing contact time with an

equivalent disinfectant dose increases

the formation of DBPs.

pH pH may affect the disinfectant form and,

in-turn, the efficiency of the disinfectant.

The impact of pH varies with DBP. See

Section 2.3.2.3 for a brief summary of

relationships between pH and DBP

formation.

Temperature Increasing the temperature increases

the rate of disinfection.

Increasing temperature is typically

associated with faster oxidation kinetics,

hence, increased DBP formation.

Turbidity Particles responsible for turbidity can

surround and shield pathogenic

microorganisms from disinfectants.

Increased turbidity may be associated

with increased NOM, which represents

an increased amount of DBP precursors

for the formation of DBPs when

disinfectant is applied.

Dissolved Organics Dissolved organics can interfere with

disinfection by creating a demand and

reducing the amount of disinfectant

available for pathogen inactivation.

Increased dissolved organics will

represent a larger amount of DBP

precursor for the formation of DBPs

when disinfectant is applied.

2.5 Disinfectant Residual Regulatory Requirements

One of the most important factors for evaluating the merits of alternative disinfectants is their ability

to maintain the microbial quality in the water distribution system. Disinfectant residuals may serve

to protect the distribution system against regrowth (Snead et al., 1980). The SWTR requires that

filtration and disinfection must be provided to ensure that the total treatment of the system achieves

at least a 3-log removal/inactivation of Giardia cysts and a 4-log removal/inactivation of viruses. In

addition, the disinfection process must demonstrate by continuous monitoring and recording that the

disinfectant residual in the water entering the distribution system is never less than 0.2 mg/L for more

than 4 hours.

Several of the alternative disinfectants examined in this manual cannot be used to meet the residual

requirements stated in the SWTR. For example, if either ozone or ultraviolet light disinfection are

used as the primary disinfectant, a secondary disinfectant such as chlorine or chloramines should be

utilized to obtain a residual in the distribution system.
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DBP formation continues in the distribution system due to reactions between the residual disinfectant

and organics in the water. Koch et al. (1991) found that with a chlorine dose of 3-4 mg/L, THM and

HAA concentrations increase rapidly during the first 24 hours in the distribution system. After the

initial 48 hours, the subsequent increase in THMs is very small. Chloral hydrate concentrations

continued to increase after the initial 24 hours, but at a reduced rate. Haloketones actually decreased

in the distribution system.

Nieminski et al. (1993) evaluated DBP formation in the simulated distribution systems of treatment

plants in Utah. Finished water chlorine residuals ranged from 0.4 to 2.8 mg/L. Generally, THM

values in the distribution system studies increased by 50 to 100 percent (range of 30 to 200 percent)

of the plant effluent value after 24-hour contact time. The 24-hour THM concentration was

essentially the same as the 7-day THM formation potential. HAA concentrations in the simulated

distribution system was about 100 percent (range of 30 to 200 percent) of the HAA in the plant

effluent. The 7-day HAA formation potential was sometimes higher, or below the distribution

system values. If chlorine is used as a secondary disinfectant, one should therefore anticipate a 100-

percent increase in the plant effluent THMs, or plan to reach the 7-day THM formation level in the

distribution system.

2.6 Summary of Current National Disinfection Practices

Most water treatment plants disinfect water prior to distribution. The 1995 Community Water

Systems Survey (USEPA, 1997a) reports that 81 percent of all community water systems provide

some form of treatment on all or a portion of their water sources. The survey also found that

virtually all surface water systems provide some treatment of their water. Of those systems reporting

no treatment, 80 percent rely on ground water as their only water source.

The most commonly used disinfectants/oxidants are chlorine, chlorine dioxide, chloramines, ozone,

and potassium permanganate. Table 2-16 shows a breakdown on the chemical usage from the

survey. Note that the table shows the percentages of systems using the particular chemical as either

disinfectant or some other role. The table shows the predominance of chlorine in surface and ground

water disinfection treatment systems with more than 60 percent of the treatment systems using

chlorine as disinfectant/oxidant. Potassium permanganate on the other hand, is used by many

systems, but its application is primarily for oxidation, rather than for disinfection.

Permanganate will have some beneficial impact on disinfection since it is a strong oxidant that will

reduce the chemical demand for the ultimate disinfection chemical. Chloramine is used by some

systems and is more frequently used as a post-treatment disinfectant.

The International Ozone Association conducted a survey of ozone facilities in the United States

(IOA, 1997). The survey documented the types of ozone facilities, size, objective of ozone

application, and year of operation. Table 2-17 summarizes the findings from the survey. The most

common use for ozone is for oxidation of iron and manganese, and for taste and odor control.

Twenty-four of the 158 ozone facilities used GAC following ozonation. In addition to the 158
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operating ozone facilities, the survey identified 19 facilities under construction and another 30 under

design. The capacity of the systems range from less than 25 gpm to exceeding 500 mgd. Nearly half

of the operating facilities have a capacity exceeding 1 mgd. Rice et al. (1998) found that as of May

1998, 264 drinking water plants in the United States are using ozone.

Table 2-16. Disinfection Practices of Water Systems that Include

Some Form of Treatment

Service Population

Treatment

<100 101-500 501-

1,000

1,001-

3,300

3,301-

10,000

10,001-

50,000

50,001-

100,000

Over

100,001 Total

Surface Water Systems

Total Number of

Systems

218 432 330 845 679 626 103 104 3,337

Pre-Disinfection, Oxidation/Softening

Chlorine 59.0% 73.9% 67.3% 66.3% 68.8% 58.6% 47.5% 57.1% 63.8%

Chlorine dioxide 0 0 0 5.0 4.7 13.2 14.2 7.8 6.3

Chloramines 4.6 0 1.1 2.1 0 2.2 15.5 10.8 3.1

Ozone 0 0 0 0 0.3 0 5.4 5.8 0.9

KMnO4 0 4.9 9.6 9.9 15.2 28.3 25.9 28.5 16.0

Predisinfection/oxidation 0 0 2.0 2.9 0.6 9.2 5.1 4.3 3.5

Lime/Soda ash softening 6.8 9.8 20.9 16.2 14.3 11.7 3.5 5.9 12.5

Recarbonation 0 0 0 0 2.1 4.7 0.6 6.3 1.9

Post-Disinfection

Chlorine 49.7 % 51.6% 80.6% 62.8% 77.9% 71.1% 73.8 % 63.6 % 67.5 %

Chlorine dioxide 0 0 0 0 0.3 4.9 5.9 11.2 1.6

Chloramines 0 0 0 2.9 2.1 15.6 29.4 24.2 8.1

Postdisinfection

combinations

0 0 0 2.1 4.0 3.9 1.9 1.6 3.0

Ground Water Systems

Total Number of

Systems

9,042 10,367 4,443 4,422 2,035 1,094 120 56 31,579

Pre-Disinfection, Oxidation/Softening

Chlorine 64.2 % 69.9 % 56.7 % 73.2 % 60.6 % 57.4 % 36.2 % 38.1 % 63.9 %

Chlorine dioxide 1.3 0 0 0 0 0 3.1 0 0.3

Chloramines 0 0 0 0 0 0.6 1.4 0.7 0.1

Ozone 0 0 0 0 0 0 0 0.6 0

KMnO4 0 0.9 2.2 0.6 5.8 3.2 7.0 0 1.8

Predisinfection/oxidation 0.3 0.5 0 0.7 1.0 2.6 0 0 0.7

Lime/Soda ash softening 2.9 2.9 2.2 3.6 3.5 3.8 5.0 9.1 3.2

Recarbonation 0 0.5 0 0.6 1.4 1.5 2.8 1.1 0.6

Post-Disinfection

Chlorine 23.0 % 23.4% 32.5% 28.3 % 42.5% 41.9 % 54.5 % 65.8 % 31.0 %

Chlorine dioxide 0 1.0 0 0 0 0.6 0 0 0.4

Chloramines 0 0 0 0 0.1 1.1 3.9 4.3 0.3

Postdisinfection

combinations

0 0 0 0 0.1 0.1 0 0 0

Source: USEPA, 1997a.
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Table 2-17. Ozone Application in Water Treatment Plants in the United States

Ozone Objective Number of Plants % Plants

THM Control 50 32

Disinfection 63 40

Iron/Manganese, Taste and Odor Control 92 58

Total 158 --

Source: IOA, 1997.

2.7 Chlorine

Although chlorine is not a focus of this guidance manual, the following section provides a brief

overview of chlorine use in the water treatment industry to compare with the alternative disinfectants

discussed in this manual. Since there is a wealth of excellent literature on chlorine’s uses and

performance capabilities, summarizing this large body of knowledge here is neither practical nor

necessary (see, for example: White, 1992; Chlorine Institute, 1996; and Connell, 1996).

One of the recent developments in chlorine disinfection is the use of multiple and interactive

disinfectants. In these applications, chlorine is combined with a second disinfectant to achieve

improved disinfection efficiency and/or effective DBP control. A detailed discussion on multiple

disinfectants, including chlorine combinations, is provided in Chapter 9.

As described earlier, the 1995 Community Water System Survey (USEPA, 1997a), indicated that the

majority of all surface water and ground water systems in the United States use chlorine for

disinfection.

Chlorine has many attractive features that contribute to its wide use in the industry. Four of the key

attributes of chlorine are that it:

• Effectively inactivates a wide range of pathogens commonly found in water;

• Leaves a residual in the water that is easily measured and controlled;

• Is economical; and

• Has an extensive track record of successful use in improving water treatment operations (despite

the dangers associated with chlorine application and handling, specifically chlorine gas, it still

maintains an excellent safety record).

There are, however, some concerns regarding chlorine usage that may impact its uses such as:

• Chlorine reacts with many naturally occurring organic and inorganic compounds in water to

produce undesirable DBPs;

• Hazards associated with using chlorine, specifically chlorine gas, require special treatment and

response programs; and

• High chlorine doses can cause taste and odor problems.
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Chlorination is used in water treatment facilities primarily for disinfection. Because of chlorine’s

oxidizing powers, it has been found to serve other useful purposes in water treatment, such as (White,

1992):

• Taste and odor control;

• Prevention of algal growths;

• Maintenance of clear filter media;

• Removal of iron and manganese;

• Destruction of hydrogen sulfide;

• Bleaching of certain organic colors;

• Maintenance of distribution system water quality by controlling slime growth;

• Restoration and preservation of pipeline capacity;

• Restoration of well capacity, water main sterilization; and

• Improved coagulation by activated silica.

2.7.1 Chlorine Chemistry

Chlorine for disinfection typically is used in one of three forms: chlorine gas, sodium hypochlorite,

or calcium hypochlorite. A brief description of the chemistry of these three chemicals is provided

below.

2.7.1.1 Chlorine Gas

Chlorine gas hydrolyzes rapidly in water to form hypochlorous acid (HOCl). The following equation

presents the hydrolysis reaction:

Cl2(g) + H2O ⇒ HOCl + H+ Cl- Equation 1

Note that the addition of chlorine gas to water reduces the pH of the water due to the production of

hydrogen ion.

Hypochlorous acid is a weak acid (pKa of about 7.5), meaning it dissociates slightly into hydrogen

and hypochlorite ions as noted in Equation 2:

HOCl Û H

+

 + O Cl- Equation 2

Between a pH of 6.5 and 8.5 this dissociation is incomplete and both HOCl and OCl- species are

present to some extent (White, 1992). Below a pH of 6.5, no dissociation of HOCl occurs, while

above a pH of 8.5, complete dissociation to OCl- occurs. As the germicidal effects of HOCl is much

higher than that of OCl-, chlorination at a lower pH is preferred.
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2.7.1.2 Hypochlorite

In addition to chlorine gas, chlorine is also available in hypochlorite form as both aqueous solutions

and dry solids. The most common aqueous hypochlorite solution is sodium hypochlorite. The most

common form of dry solid hypochlorite is calcium hypochlorite (White, 1992).

Sodium Hypochlorite. Sodium hypochlorite is produced when chlorine gas is dissolved in a sodium

hydroxide solution. Sodium hypochlorite solution typically contains 12.5 percent available chlorine

(White, 1992). One gallon of 12.5 percent sodium hypochlorite solution typically contains the

equivalent of one pound of chlorine.

The reaction between sodium hypochlorite and water is shown in the following reaction:

NaOCl + H2O ⇒ HOCl + Na+ + OH- Equation 3

Equation 3 shows that the application of sodium hypochlorite to water produces hypochlorous acid,

similar to chlorine gas hydrolysis (Equation 1). However, unlike chlorine hydrolysis, the addition of

sodium hypochlorite to water yields a hydroxyl ion that will increase the pH of the water. In

addition, excess sodium hydroxide is used to manufacture sodium hypochlorite, which will further

increase the pH of the water.

Calcium Hypochlorite. Calcium hypochlorite is formed from the precipitate that results from

dissolving chlorine gas in a solution of calcium oxide (lime) and sodium hydroxide. Granular

calcium hypochlorite commercially available typically contains 65 percent available chlorine. This

means that 1.5 pounds of calcium hypochlorite contains the equivalent of one pound of chlorine. The

reaction between calcium hypochlorite and water is shown in the following reaction:

Ca(OCl)2 + 2H2O ⇒ 2HOCl + Ca++ + 2OH- Equation 4

Equation 4 shows that the application of calcium hypochlorite to water also produces hypochlorous

acid, similar to chlorine gas hydrolysis (Equation 1). Similar to sodium hypochlorite solution, the

addition of calcium hypochlorite to water yields hydroxyl ions that will increase the pH of the water.

2.7.2 Chlorine Generation

Onsite generation of chlorine has recently become practical. These generation systems, using only

salt and electric power, can be designed to meet disinfection and residual standards and to operate

unattended at remote sites. Considerations for chlorine generation include cost, concentration of the

brine produced, availability of raw materials, and the reliability of the process (AWWA and ASCE,

1997).

2.7.2.1 Chlorine

Chlorine gas can be generated by a number of processes including the electrolysis of alkaline brine or

hydrochloric acid, the reaction between sodium chloride and nitric acid, or the oxidation of
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hydrochloric acid. About 70 percent of the chlorine produced in the United States is manufactured

from the electrolysis of salt brine and caustic solutions in a diaphragm cell (White, 1992). Since

chlorine is a stable compound, it is typically produced off-site by a chemical manufacturer. Once

produced, chlorine is packaged as a liquefied gas under pressure for delivery to the site in railcars,

tanker trucks, or cylinders.

2.7.2.2 Sodium Hypochlorite

Dilute sodium hypochlorite solutions (less than 1 percent) can be generated electrochemically on-site

from salt brine solution. Typically, sodium hypochlorite solutions are referred to as liquid bleach or

Javelle water. Generally, the commercial or industrial grade solutions produced have hypochlorite

strengths of 10 to 16 percent. The stability of sodium hypochlorite solution depends on the

hypochlorite concentration, the storage temperature, the length of storage (time), the impurities of the

solution, and exposure to light. Decomposition of hypochlorite over time can affect the feed rate and

dosage, as well as produce undesirable byproducts such as chlorite ions or chlorate (Gordon et al.,

1995). Because of the storage problems, many systems are investigating onsite generation of

hypochlorite in lieu of its purchase from a manufacturer or vendor (USEPA, 1998b).

2.7.2.3 Calcium Hypochlorite

To produce calcium hypochlorite, hypochlorous acid is made by adding chlorine monoxide to water

and then neutralizing it with a lime slurry to create a solution of calcium hypochlorite. The water is

removed from the solution, leaving granulated calcium hypochlorite. Generally, the final product

contains up to 70 percent available chlorine and 4 to 6 percent lime. Storage of calcium hypochlorite

is a major safety consideration. It should never be stored where it is subject to heat or allowed to

contact any organic material of an easily oxidized nature (USEPA, 1998b).

2.7.3 Primary Uses and Points of Application of Chlorine

2.7.3.1 Uses

The main usage of chlorine in drinking water treatment is for disinfection. However, chlorine has

also found application for a variety of other water treatment objectives such as, the control of

nuisance organisms, oxidation of taste and odor compounds, oxidation of iron and manganese, color

removal, and as a general treatment aid to filtration and sedimentation processes (White, 1992;

Connell, 1996; Culp/Wesner/Culp, 1986). Table 2-18 presents a summary of chlorine uses and

doses.
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Table 2-18. Chlorine Uses and Doses

Application Typical Dose Optimal pH Reaction Time Effectiveness

Other

Considerations

Iron 0.62 mg/mg Fe 7.0 less than 1 hour Good

Manganese 0.77 mg/mg Mn 7–8

9.5

1–3 hour

minutes

Slow kinetics Reaction time

increases at

lower pH

Biological

growth

1–2 mg/L 6–8 NA Good DBP formation

Taste/odor Varies 6–8 Varies Varies Effectiveness

depends on

compound

Color removal Varies 4.0–6.8 Minutes Good DBP formation

Zebra mussels 2–5 mg/L

0.2–0.5 mg/L(a)

Shock level

Maintenance level

Good DBP formation

Asiatic clams 0.3–0.5 mg/L(a) Continuous Good DBP formation

Notes:

(a)

 Residual, not dose

Sources: Adapted in part from White, 1992; Connell, 1996; Culp/Wesner/Culp, 1986.

2.7.3.2 Points of Application

At conventional surface water treatment plants, chlorine is typically added for prechlorination at

either the raw water intake or flash mixer, for intermediate chlorination ahead of the filters, for

postchlorination at the filter clearwell, or for rechlorination of the distribution system (Connell,

1996). Table 2-19 summarizes the typical uses for each point of application.

Table 2-19. Typical Chlorine Points of Application and Uses

Point of Application Typical Uses

Raw Water Intake Zebra mussel and Asiatic clam control, control biological growth

Flash Mixer (prior to sedimentation) Disinfection, iron and manganese oxidation, taste and odor control,

oxidation of hydrogen sulfide

Filter Influent Disinfection, control biological growth in filter, iron and manganese

oxidation, taste and odor control, algae control, color removal

Filter Clearwell Disinfection

Distribution System Maintain disinfectant residual

Sources: Connell, 1996; White, 1992; AWWA, 1990.

2.7.3.3 Typical Doses

Table 2-20 shows the typical dosages for the various forms of chlorine. The wide range of chlorine

gas dosages most likely represents its use as both an oxidant and a disinfectant. While sodium

hypochlorite and calcium hypochlorite can also serve as both an oxidant and a disinfectant, their

higher cost may limit their use.
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Table 2-20. Typical Chlorine Dosages at Water Treatment Plants

Chlorine Compound Range of Doses

Calcium hypochlorite 0.5–5 mg/L

Sodium hypochlorite 0.2–2 mg/L

Chlorine gas 1–16 mg/L

Source: SAIC, 1998, as adapted from EPA's review of public water systems' Initial Sampling Plans which were

required by EPA’s Information Collection Rule (ICR)

2.7.4 Pathogen Inactivation and Disinfection Efficacy

2.7.4.1 Inactivation Mechanisms

Research has shown that chlorine is capable of producing lethal events at or near the cell membrane

as well as affecting DNA. In bacteria, chlorine was found to adversely affect cell respiration,

transport, and possibly DNA activity (Haas and Engelbrecht, 1980). Chlorination was found to cause

an immediate decrease in oxygen utilization in both Escherichia coli and Candida parapsilosis

studies. The results also found that chlorine damages the cell wall membrane, promotes leakage

through the cell membrane, and produces lower levels of DNA synthesis for Escherichia coli,

Candida parapsilosis, and Mycobacterium fortuitum bacteria. This study also showed that chlorine

inactivation is rapid and does not require bacteria reproduction (Haas and Engelbrecht, 1980). These

observations rule out mutation or lesions as the principal inactivation mechanisms since these

mechanisms require at least one generation of replication for inactivation to occur.

2.7.4.2 Environmental Effects

Several environmental factors influence the inactivation efficiency of chlorine, including water

temperature, pH, contact time, mixing, turbidity, interfering substances, and the concentration of

available chlorine. In general, the highest levels of pathogen inactivation are achieved with high

chlorine residuals, long contact times, high water temperature, and good mixing, combined with a

low pH, low turbidity, and the absence of interfering substances. Of the environmental factors, pH

and temperature have the most impact on pathogen inactivation by chlorine. The effect of pH and

temperature on pathogen inactivation are discussed below.

pH. The germicidal efficiency of hypochlorous acid (HOCl) is much higher than that of the

hypochlorite ion (OCl-). The distribution of chlorine species between HOCl and OCl- is determined

by pH, as discussed above. Because HOCl dominates at low pH, chlorination provides more

effective disinfection at low pH. At high pH, OCl- dominates, which causes a decrease in

disinfection efficiency.

The inactivation efficiency of gaseous chlorine and hypochlorite is the same at the same pH after

chlorine addition. Note, however, that addition of gaseous chlorine will decrease the pH (see

Equation 1) while the addition of hypochlorite will increase the pH of the water (see Equation 3 and
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Equation 4). Therefore, without pH adjustment to maintain the same treated water pH, gaseous

chlorine will have greater disinfection efficiency than hypochlorite.

The impact of pH on chlorine disinfection has been demonstrated in the field. For example, virus

inactivation studies have shown that 50 percent more contact time is required at pH 7.0 than at pH

6.0 to achieve comparable levels of inactivation. These studies also demonstrated that a rise in pH

from 7.0 to 8.8 or 9.0 requires six times the contact time to achieve the same level of virus

inactivation (Culp and Culp, 1974). Although these studies found a decrease in inactivation with

increasing pH, some studies have shown the opposite effect. A 1972 study reported that viruses were

more sensitive to free chlorine at high pH than at low pH (Scarpino et al., 1972).

Temperature. For typical drinking water treatment temperatures, pathogen inactivation increases

with temperature. Virus studies indicate that the contact time should be increased by two to three

times to achieve comparable inactivation levels when the water temperature is lowered by 10°C

(Clarke et al., 1962).

2.7.4.3 Disinfection Efficacy

Since its introduction, numerous investigations have been made to determine the germicidal

efficiency of chlorine. Although there are widespread differences in the susceptibility of various

pathogens, the general order of increasing chlorine disinfection difficulty are bacteria, viruses, and

then protozoa.

Bacteria Inactivation. Chlorine is an extremely effective disinfectant for inactivating bacteria. A

study conducted during the 1940s investigated the inactivation levels as a function of time for E. coli,

Pseudomonas aeruginosa, Salmonella typhi, and Shigella dysenteriae (Butterfield et al., 1943).

Study results indicated that HOCl is more effective than OCl- for inactivation of these bacteria.

These results have been confirmed by several researchers that concluded that HOCl is 70 to 80 times

more effective than OCl- for inactivating bacteria. (Culp/Wesner/Culp, 1986).

Virus Inactivation. Chlorine has been shown to be a highly effective viricide. One of the most

comprehensive virus studies was conducted in 1971 using treated Potomac estuary water (Liu et al.,

1971). The tests were performed to determine the resistance of 20 different enteric viruses to free

chlorine under constant conditions of 0.5 mg/L free chlorine and a pH and temperature of 7.8 and

2°C, respectively. In this study, the least resistant virus was found to be reovirus and required 2.7

minutes to achieve 99.99 percent inactivation (4 log removal). The most resistant virus was found to

be a poliovirus, which required more than 60 minutes for 99.99 inactivation. The corresponding CT

range required to achieve 99.99 percent inactivation for all 20 viruses was between 1.4 to over 30

mg·min/L.

Virus survival studies have also been conducted on a variety of both laboratory and field strains

(AWWA, 1979). All of the virus inactivation tests in this study were performed at a free chlorine

residual of 0.4 mg/L, a pH of 7.0, a temperature of 5oC, and contact times of either 10, 100, or 1,000

minutes. Test results showed that of the twenty cultures tested only two poliovirus strains reached
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99.99 percent inactivation after 10 minutes (CT = 4 mg·min/L), six poliovirus strains reached 99.99

percent inactivation after 100 minutes (CT = 40 mg·min/L), and 11 of the 12 polioviruses plus one

Coxsackievirus strain (12 out of a total of 20 viruses) reached 99.99 percent inactivation after 1,000

minutes (CT = 400 mg·min/L).

Protozoa Inactivation. Chlorine has been shown to have limited success inactivating protozoa.

Data obtained during a 1984 study indicated that the resistance of Giardia cysts are two orders of

magnitude higher than that of enteroviruses and more than three orders of magnitude higher than the

enteric bacteria (Hoff et al., 1984). CT requirements for Giardia cysts inactivation when using

chlorine as a disinfectant has been determined for various pH and temperature conditions (AWWA,

1991). These CT values increase at low temperatures and high pH (See also Table 2-13).

Chlorine has little impact on the viability of Cryptosporidium oocysts when used at the relatively low

doses encountered in water treatment (e.g., 5 mg/L). Approximately 40 percent removals (0.2 log) of

Cryptosporidium were achieved at CT values of both 30 and 3,600 mg·min/L (Finch et al., 1994).

Another study determined that “no practical inactivation was observed” when oocysts were exposed

to free chlorine concentrations ranging from 5 to 80 mg/L at pH 8, a temperature of 22°C, and

contact times of 48 to 245 minutes (Gyürék et al., 1996). CT values ranging from 3,000 to 4,000

mg·min/L were required to achieve 1-log of Cryptosporidium inactivation at pH 6.0 and temperature

of 22oC. During this study, one trial in which oocysts were exposed to 80 mg/L of free chlorine for

120 minutes was found to produce greater than 3-logs of inactivation.

2.7.4.4 CT Curves

Chlorine is regarded as a strong disinfectant that is effective at inactivating bacteria and viruses, and

under certain circumstances, Giardia. Because of chlorine’s extremely high virus inactivation

efficiency, CT values are almost always governed by protozoa inactivation. For example, Figure 2-1

shows the CT values required to achieve between 0.5 and 3-logs of virus and Giardia inactivation

(AWWA, 1991). As shown, the CT values required to achieve the recommended disinfection

efficiency for conventional filtration systems (i.e., 0.5-log Giardia cyst and 2-log virus inactivation

level) are 23 and 3 mg min/L, respectively.
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0

20

40

60

80

100

120

140

160

0 0.5 1 1.5 2 2.5 3 3.5

Log Pathogen Inactivation Level

CT Values for Giardia Cyst Inactivation (mg min/L)

0

1

2

3

4

5

6

7

8

9

10

CT Values for Virus Inactivation (mg min/L)

Giardia cysts

Viruses

Figure 2-1. Free Chlorine Giardia and Virus CT Requirements

CT values for Giardia inactivation for various pH values and temperatures at a chlorine dose of

3.0 mg/L are shown in Figures 2-2 and 2-3. As shown, the inactivation efficacy of free chlorine

decreases with increasing pH and/or decreasing temperature. CT values shown in Figures 2-2 and 2-

3 are based on animal infectivity and excystation studies. CT values ranging from 0.5 to 3-log

inactivation at temperatures of 0.5 and 5oC were based on a multiplicative model, and applying first

order kinetics to the 99 percent upper confidence interval of the 99.99-percentile CT values. CT

values for temperatures above 5oC were estimated by assuming a twofold decrease for every 10oC

decrease in temperature.

0

50

100

150

200

250

300

350

6 7 8 9

pH (su)

CT Value (mg min/L)

0.5 -log inactivation

1.0-log inactivation

1.5-log inactivation

2.0-log inactivation

2.5-log inactivation

3.0-log inactivation

Figure 2-2. CT Values for Inactivation of Giardia Cysts by Free Chlorine at 10oC

(at Cl2 dose of 3.0 mg/L)
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0

20

40

60

80

100

120

140

160

180

200

5 10 15 20 25

Temperature (oC)

CT Value (mg min/L)

0.5 -log inactivation

1.0-log inactivation

1.5-log inactivation

2.0-log inactivation

2.5-log inactivation

3.0-log inactivation

Figure 2-3. CT Values for Inactivation of Giardia Cysts by Free Chlorine at pH 7.0

(at Cl2 dose of 3.0 mg/L)

2.7.5 DBP Formation and Control

2.7.5.1 DBP Formation

Halogenated organics are formed when natural organic matter (NOM) reacts with free chlorine or

free bromine. Free chlorine is normally introduced into water directly as a primary or secondary

disinfectant. Free bromine results from the oxidation by chlorine of the bromide ion in the source

water. Factors affecting the formation of these halogenated DBPs include type and concentration of

NOM, chlorine form and dose, time, bromide ion concentration, pH, organic nitrogen concentration,

and temperature. Organic nitrogen significantly influenced the formation of nitrogen containing

DBPs, including haloacetonitriles, halopicrines, and cyanogen halides (Reckhow et al., 1990; Hoigné

and Bader, 1988).

The formation of DBPs is strongly related to TOC at the point of disinfection. DBP formation also

correlates with the amount of chlorine consumed (Singer et al., 1995). Stevens et al. (1989) found

that higher TTHM formation occurs at high pH (9.4) than at low pH (5.0) while HAA showed no

clear trend as a function of pH. A survey of 35 water utilities conducted by MWDSC (Krasner et al.,

1989) showed the median TTHM and HAA concentrations measured as 39 and 19 μg/L (i.e. more

THMs than HAAs are formed). However, a subsequent study by Singer et al. (1995) found a

reversal in dominance, with more HAAs than THMs produced in waters from North Carolina

utilities. They postulated that the reason for this change is due to the lower pH levels and differences

in TOC and bromide concentrations in the North Carolina waters. Pourmoghaddas et al. (1993)

showed that brominated and mixed brominated/chlorinated THMs and HAAs are formed when using

chlorine in the presence of bromide.
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The occurrence of THMs and HAAs is important because regulatory limits are placed on both groups

of compounds. One water utility may therefore find that its chlorination practice is limited by the

production of THMs, while another will find that HAAs limit the use of chlorine. This distribution

of THMs and HAA is a function of the TOC and bromide concentration in the water, as well as the

pH during chlorination.

Of note, Chlorate is produced as a byproduct when hypochlorite degrades during storage.

2.7.5.2 DBP Control

DBPs can be controlled by several means, including removing the DBP precursors, modifying the

chlorination strategy, changing disinfectants, or removing the DBP itself. Because DBPs are

difficult to remove once they are formed, control strategies typically focus on the first three

methods.

Studies have shown that removal of TTHM precursors tends to remove the formation potential for

the other DBPs. Generally, aggregate DBP formation will decrease as the removal of TOC increases.

Recent research indicates that moving the point of chlorination back into the treatment process can

reduce the formation of DBPs.

Summers et al. (1997) recently summarized the results from four studies evaluating the impact of

pretreatment on DBP formation. Jar tests were conducted to simulate the water treatment through

rapid mix, coagulation, flocculation, and sedimentation. Chlorine was added at various points in the

jar testing to simulate the impact of various dose points on production of DBPs. The results clearly

demonstrate the benefits of delaying the point of chlorination downstream in the treatment train to

take advantage of precursor removal during initial flocculation and sedimentation processes. Table

2-21 summarizes the results from this study.

Table 2-21. Percent Reduction in DBP Formation by Moving

Chlorination Point Later In Treatment Train

Chlorination point TTHM

Baseline (%)

TTHM

Enhanced (%)

HAA5

Baseline (%)

HAA5

Enhanced (%)

Pre rapid mix Basis 17 Basis 4.7

Post rapid mix 1.6 21 5.3 21

Mid flocculation 8.7 36 14 36

Post sedimentation 21 48 35 61

Notes: Source: USEPA, 1997b based on Summers et al., 1997.

Baseline = Baseline coagulant (alum) dose for optimal turbidity removal (~30 mg/L)

Enhanced = Enhanced coagulant (alum) dose for optimal TOC removal (~52 mg/L)

Table 2-21 also shows the benefit of enhanced coagulation to reduce DBP production. The THM

reduction of 21 percent by moving the chlorination point to post sedimentation is more than doubled

to 48 percent by enhanced coagulation. The HAA removal increases from 45 to 61 percent under
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enhanced coagulation with post sedimentation chlorination. Therefore, DBP control by selecting the

optimal dose location and conditions along with enhanced precursor removal can significantly reduce

DBP formation at low added cost.

White (1992) suggested that pretreatment goals should include: 1) maximizing THM precursor

removal; 2) reducing ammonia-N concentration to 0.10 mg/L; 3) reducing organic-N concentration to

0.05 mg/L; and 4) limiting 15-minute chlorine demand to 0.5 mg/L. These guidelines should

improve raw water quality sufficiently to allow the use of the free chlorine residual process without

exceeding the EPA MCLs for TTHMs.

2.7.6 Operational Considerations

2.7.6.1 Application Methods

Different application methods are used, depending upon the form of chlorine used. The following

paragraphs describe the typical application methods for chlorine, sodium hypochlorite, and calcium

hypochlorite.

Chlorine. Liquefied chlorine gas is typically evaporated to gaseous chlorine prior to metering. The

heat required for evaporation can be provided through either a liquid chlorine evaporator or the

ambient heat input to the storage container. Once the compressed liquid chlorine is evaporated,

chlorine gas is typically fed under vacuum conditions. Either an injector or a vacuum induction

mixer usually creates the required vacuum. The injector uses water flowing through a venturi to

draw the chlorine gas into a side stream of carrier water to form a concentrated chlorine solution.

This solution is then introduced into the process water through a diffuser or mixed with a mechanical

mixer. A vacuum induction mixer uses the motive forces of the mixer to create a vacuum and draws

the chlorine gas directly into the process water at the mixer.

Sodium Hypochlorite. Sodium hypochlorite solutions degrade over time. For example, a 12.5

percent hypochlorite solution will degrade to 10 percent in 30 days under “best case” conditions

(White, 1992). Increased temperature, exposure to light, and contact with metals increase the rate of

sodium hypochlorite degradation (Connell, 1996).

Sodium hypochlorite solution is typically fed directly into the process water using a type of metering

pump. Similar to chlorine solution, sodium hypochlorite is mixed with the process water with either

a mechanical mixer or induction mixer. Sodium hypochlorite solution is typically not diluted prior to

mixing to reduce scaling problems.

Calcium Hypochlorite. Commercial high-level calcium hypochlorite contains at least 70%

available chlorine (USEPA, 1991). Under normal storage conditions, calcium hypochlorite loses 3 to

5% of its available chlorine in a year (AWWA and ASCE, 1997). Calcium hypochlorite comes in

powder, granular, and compressed tablet forms (USEPA, 1991). Typically, calcium hypochlorite

solution is prepared by mixing powdered or granular calcium hypochlorite with a small flow. The

highly chlorinated solution is then flow paced into drinking water flow.
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2.7.6.2 Safety and Handling Considerations

Chlorine. Chlorine gas is a strong oxidizer. The U.S. Department of Transportation classifies

chlorine as a poisonous gas (Connell, 1996). Fire codes typically regulate the storage and use of

chlorine. In addition, facilities storing more than 2,500 pounds of chlorine are subject to the

following two safety programs:

• Process Safety Management standards regulated by the Occupational Safety and Health

Administration under 29 CFR 1910.

• The Risk Management Program Rule administered by EPA under Section 112(r) of the Clean Air

Act.

All of these regulations (as well as local and state codes and regulations) must be considered during

the design and operation of chlorination facilities at a water treatment plant.

Sodium Hypochlorite. Sodium hypochlorite solution is a corrosive liquid with an approximate pH

of 12 (AWWA, 1990). Therefore, typical precautions for handling corrosive materials such as

avoiding contact with metals, including stainless steel, should be used.

Sodium hypochlorite solutions may contain chlorate. Chlorate is formed during the both the

manufacturing and storage of sodium hypochlorite (due to degradation of the product). Chlorate

formation can be minimized by reducing the degradation of sodium hypochlorite (Gilbert et al.,

1995) by limiting storage time, avoid high temperatures and reduce light exposure.

Spill containment must be provided for the sodium hypochlorite storage tanks. Typical spill

containment structures include containment for the entire contents of the largest tank (plus freeboard

for rainfall or fire sprinklers), no uncontrolled floor drains, and separate containment areas for each

incompatible chemical.

Calcium Hypochlorite. Calcium hypochlorite is an oxidant and as such should be stored separately

from organic materials that can be readily oxidized. It should also be stored away from sources of

heat. Improperly stored calcium hypochlorite has caused spontaneous combustion fires (White,

1992).

2.8 Summary

2.8.1 Advantages and Disadvantages of Chlorine Use

The following list presents selected advantages and disadvantages of using chlorine as a disinfection

method for drinking water (Masschelein, 1992; Process Applications, Inc., 1992). Because of the

wide variation of system size, water quality, and dosages applied, some of these advantages and

disadvantages may not apply to a particular system.
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Advantages

• Oxidizes soluble iron, manganese, and sulfides

• Enhances color removal

• Enhances taste and odor

• May enhance coagulation and filtration of particulate contaminants

• Is an effective biocide

• Is the easiest and least expensive disinfection method, regardless of system size

• Is the most widely used disinfection method, and therefore, the best known

• Is available as calcium and sodium hypochlorite. Use of these solutions is more advantageous

for smaller systems than chlorine gas because they are easier to use, are safer, and need less

equipment compared to chlorine gas

• Provides a residual.

Disadvantages

• May cause a deterioration in coagulation/filtration of dissolved organic substances

• Forms halogen-substituted byproducts

• Finished water could have taste and odor problems, depending on the water quality and dosage

• Chlorine gas is a hazardous corrosive gas

• Special leak containment and scrubber facilities could be required for chlorine gas

• Typically, sodium and calcium hypochlorite are more expensive than chlorine gas

• Sodium hypochlorite degrades over time and with exposure to light

• Sodium hypochlorite is a corrosive chemical

• Calcium hypochlorite must be stored in a cool, dry place because of its reaction with moisture

and heat

• A precipitate may form in a calcium hypochlorite solution because of impurities, therefore, an

antiscalant chemical may be needed

• Higher concentrations of hypochlorite solutions are unstable and will produce chlorate as a

byproduct

• Is less effective at high pH

• Forms oxygenated byproducts that are biodegradable and which can enhance subsequent

biological growth if a chlorine residual is not maintained.
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• Release of constituents bound in the distribution system (e.g., arsenic) by changing the redox

state.

2.8.2 Summary Table

Table 2-22 presents a summary of the considerations for the use of chlorine as a disinfectant.

Table 2-22. Summary of Chlorine Disinfection

Consideration Description

Generation Chlorination may be performed using chlorine gas or other chlorinated

compounds that may be in liquid or solid form. Chlorine gas can be

generated by a number of processes including the electrolysis of alkaline

brine or hydrochloric acid, the reaction between sodium chloride and nitric

acid, or the oxidation of hydrochloric acid. Since chlorine is a stable

compound, chlorine gas, sodium hypochlorite, and calcium hypochlorite are

typically produced off-site by a chemical manufacturer.

Primary uses The primary use of chlorination is disinfection. Chlorine also serves as an

oxidizing agent for taste and odor control, prevention of algal growths,

maintaining clear filter media, removal of iron and manganese, destruction

of hydrogen sulfide, color removal, maintaining the water quality at the

distribution systems, and improving coagulation.

Inactivation efficiency The general order of increasing chlorine disinfection difficulty is bacteria,

viruses, and then protozoa. Chlorine is an extremely effective disinfectant

for inactivating bacteria and highly effective viricide. However, chlorine is

less effective against Giardia cysts. Cryptosporidium oocysts are highly

resistant to chlorine.

Byproduct formation When added to the water, free chlorine reacts with NOM and bromide to

form DBPs, primarily THMs, some haloacetic acids (HAAs), and others.

Point of application Raw water storage, precoagulation/post-raw water storage,

presedimentation/ postcoagulation, postsedimentation/prefiltration, post

filtration (disinfection), or in the distribution system.

Special considerations Because chlorine is such a strong oxidant and extremely corrosive, special

storage and handling considerations should be considered in the planning

of a water treatment plant. Additionally, health concerns associated with

handling and use of chlorine is an important consideration.

2.8.3 Reference for Additional Information on Chlorine

With the focus of this manual on disinfectants other than chlorine, all of chlorine’s uses and

capabilities are not described here. For more detailed information regarding the use of chlorine in

water treatment, refer to the list of references provided below. For complete references, see the

References section at the end of this chapter.
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• AWWA (1990)

• Connell (1996)

• DeMers and Renner (1992)

• Hazen and Sawyer (1992)

• Hoigné and Bader (1988)

• Sawyer et al. (1994)

• Singer (1988)

• White (1992)

2.9 References

1. AWWA (American Water Works Association). 1979. “Committee, Viruses in Drinking Water.”

J. AWWA. 71(8):441.

2. AWWA (American Water Works Association). 1990. Water Quality and Treatment. F.W.

Pontius (editor). McGraw-Hill, New York, NY.

3. AWWA (American Water Works Association). 1991. Guidance Manual for Compliance with

the Filtration and Disinfection Requirements for Public Works Systems using Surface Water

Sources.

4. AWWA (American Water Works Association). 1995. Problem Organisms in Water:

Identification and Treatment. AWWA, Denver, CO.

5. AWWA and ASCE (American Water Works Association and American Society of Civil

Engineers). 1997. Water Treatment Plant Design. McGraw-Hill, New York, NY.

6. AWWARF (American Water Works Association Research Foundation) and Lyonnaise des

Eaux. 1987. Identification and Treatment of Tastes and Odors in Drinking Water. American

Water Works Association, Denver, CO.

7. Babcock, D.S. and P.C. Singer. 1979. “Chlorination and Coagulation of Humic and Fulvic

Acids.” J. AWWA. 71(3):149.

8. Beneson, A.S. 1981. “Control of Communicable Diseases in Man.” APHA.

9. Belanger, S.E., D.S. Cherry, J.L. Farris, K.G. Sappington, and J. Cairns, Jr. 1991. “Sensitivity of

the Asiatic Clam to Various Biocidal Control Agents.” J. AWWA. 83(10):79-87.

10. Black, B.D., , G.W. Harrington, and P.C. Singer. 1996. “Reducing Cancer Risks by Improving

Organic Carbon Removal.” J. AWWA. 88(6):40.
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11. Brady, Thomas J., J.E. Van Benschoten, and J.N. Jensen. 1996. “Chlorination Effectiveness for

Zebra and Quagga Mussels.” J. AWWA. 88(1):107-110.

12. Britton, J.C. and B.A. Morton. 1982. “Dissection Guide, Field and Laboratory Manual for the

Introduced Bivalve Corbicula fluminea.” Malacol. Rev. 3(1).

13. Butterfield, C.T. et al. 1943, Public Health Rep. 58:1837.

14. Cameron, G.N., J.M. Symons, S.R. Spencer, and J.Y. Ma. 1989a. “Minimizing THM Formation

During Control of the Asiatic Clam: A Comparison of Biocides.” J. AWWA. 81(10):53-62.

15. Cameron, G.N., J.M. Symons, D. Bushek and R. Kulkarni. 1989b. “Effect of Temperature and

pH on the Toxicity of Monochloramine to the Asiatic Clam.” J. AWWA. 81(10):63-71.

16. CDC (Centers for Disease Control). 1989. “Assessing the Public Threat Associated with

Waterborne Cryptosporidiosis: Report of a Workshop.” J. AWWA. 80(2):88.

17. Chick, H. 1908. “Investigation of the Laws of Disinfection.” J. Hygiene. 8:92.

18. Christman, R.F., et al. 1983. “Identity and Yields of Major Halogenated Products of Aquatic and

Fulvic Acid Chlorination.” Environ. Sci. Technol. 17(10):625.

19. Chlorine Institute. 1996. Chlorine Institute Manual. 6th Edition, The Chlorine Institute,

Washington, D.C.

20. Clarke, N.A., et al. 1962. Human Enteric Viruses in Water, Source, Survival, and Removability,

International Conference on Water Pollution Research. Landar.

21. Connell, G.F. 1996. The Chlorination/Chloramination Handbook. American Water Works

Association. Denver, CO.

22. Counts, C.L. III. 1986. “The Zoogeography and History of the Invasion of the United States by

Corbicula fluminea (Bivalvia: Corbiculidae).” Amer. Malac. Bull. 2(7), special edition.

23. Craun, G.F. and W. Jakubowski. 1996. “Status of Waterborne Giardiasis Outbreaks and

Monitoring Methods.” American Water Resources Association, Water Related Health Issue

Symp., Atlanta, GA. November.

24. Craun, G.F. 1981. “Outbreaks of Waterborne Disease in the United States.” J. AWWA.

73(7):360.

25. Culp, G.L., and R.L. Culp. 1974. New Concepts in Water Purification. Van Nostrand Reinhold

Company, New York, NY.
2. DISINFECTANT USE IN WATER TREATMENT

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26. Culp/Wesner/Culp. 1986. Handbook of Public Water Systems. Van Nostrand Reinhold, New

York, NY.

27. DeMers, L.D. and R.C. Renner, R.C. 1992. “Alternative Disinfection Technologies for Small

Drinking Water Systems.” AWWA and AWWARF, Denver, CO.

28. Duguet, J.P., Y. Tsutsumi, A. Bruchet, and Mallevialle. 1985. “Chloropicrin in Potable Water:

Conditions of Formation and Production during Treatment Processes.” Water Chlorination:

Chemistry, Environmental Impact and Health Effects, Volume 5. Lewis Publishers.

29. Evans, L.P., Jr., et al. 1979. Salinity Relationships in Corbicula fluminea; Miller (1774).

Conference proceedings, first International Corbicula Symposium. J.C. Britton (editor). Texas

Christian Univ., Ft. Worth, TX.

30. Farvardin, M.R. and A.G. Collins. 1990. Mechanism(s) of Ozone-Induced Coagulation of

Organic Colloids. Conference Proceedings, AWWA Annual Conference, Cincinnati, OH. June

17-21.

31. Ferguson, D.W., J.T. Gramith, and M.J. McGuire. 1991. “Applying Ozone for Organics Control

and Disinfection: A Utility Perspective.” J. AWWA. 83(5):32-39.

32. Ferguson, D.W., M.J. McGuire, B. Koch, R.L. Wolfe, and E.M. Aieta. 1990. “Comparing

PEROXONE and Ozone for Controlling Taste and Odor Compounds, Disinfection Byproducts,

and Microorganisms.” J. AWWA. 82(4):181-191.

33. Finch, G.R., E.K. Black, and L.L. Gyürék. 1994. Ozone and Chlorine Inactivation of

Cryptosporidium. Conference proceedings, Water Quality Technology Conference, Part II. San

Francisco, CA.

34. Geldreich, E.E. 1972. Water Pollution Microbiology. R. Mitchell (editor). John Wiley & Sons,

New York, NY.

35. Gordon, G., L. Adam, and B. Bubnis. 1995. Minimizing Chlorate Ion Formation in Drinking

Water when Hypochlorite Ion is the Chlorinating Agent. AWWA-AWWARF, Denver, CO.

36. Gurol, M.D. and M. Pidatella. 1983. A Study of Ozone-Induced Coagulation. Conference

proceedings, ASCE Environmental Engineering Division Specialty Conference. Allen Medine

and Michael Anderson (editors). Boulder, CO.

37. Gyürék, L.L., L.R.J. Liyanage, M. Belosevic, and G.R. Finch. 1996. “Disinfection of

Cryptosporidium Parvum Using Single and Sequential Application of Ozone and Chlorine

Species.” Conference proceedings, AWWA Water Quality Technology Conference, Boston,

MA.
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38. Haas C.N. and R.S. Engelbrecht. 1980. “Physiological Alterations of Vegetative

Microorganisms Resulting from Aqueous Chlorination.” J. Water Pollution Control Fed.

52(7):1976.

39. Hazen and Sawyer. 1992. Disinfection Alternatives for Safe Drinking Water. Van Nostrand

Reinhold, New York, NY.

40. Herbert, P.D.N., B.W. Muncaster II, and G.L. Mackie. 1989. “Ecological and Genetic Studies on

Dreissena polymorpha (Pallas): A New Mollusc in the Great Lakes.” Can. Jour. Fisheries and

Aquatic Sci. 46:1587.

41. Hiltebrand, D.J., A.F. Hess, P.B. Galant, and C.R. O’Melia. 1986. “Impact of Chlorine Dioxide

and Ozone Preoxidation on Conventional Treatment and Direct Filtration Treatment Processes.”

Conference proceedings, AWWA Annual Conference, Denver, CO.

42. Hoff, J.C., E.W. Rice, and F.W. Schaefer. 1984. “Disinfection and the Control of Waterborne

Giardiasis.” Conference proceedings, ASCE Specialty Conference.

43. Hoigné J., and H. Bader. 1988. “The Formation of Trichloronitromethane (chloropicrin) and

Chloroform in a Combined Ozonation/Chlorination Treatment of Drinking Water.” Water

Resources. 22 (3):313.

44. Huck, P.M., W.B. Anderson, C.L. Lang, W.A. Anderson, J.C. Fraser, S.Y. Jasim, S.A. Andrews,

and G. Pereira. 1995. “Ozone vs. PEROXONE for Geosmin and 2-Methylisoborneol Control:

Laboratory, Pilot and Modeling Studies.” Conference proceedings, AWWA Annual

Conference, Anaheim, CA.

45. IOA. 1997. IOA Survey of Water Treatment Plants. International Ozone Association, Stanford,

CT.

46. Karimi, A.A. and P.C. Singer. 1991. Trihalomethane Formation in Open Reservoirs. J. AWWA.

83 (3):84.

47. Klerks, P.L. and P.C. Fraleigh, P.C. 1991. “Controlling Adult Zebra Mussels with Oxidants.”

J. AWWA. 83 (12):92-100.

48. Koch, B., S.W. Krasner, M.J. Sclimenti, and W.K. Schimpff. 1991. “Predicting the Formation of

DBPs by the Simulated Distribution System.” J. AWWA. 83(10):62-70.

49. Kramer, M.H., B.L. Herwaldt, G.F. Craun, R.L. Calderon, and D.D. Juranek. 1996. “Waterborne

Disease: 1993 and 1994.” J. AWWA. 88(3):66-80.

50. Krasner, S.W., M.J. McGuire, J.G. Jacangelo. 1989. “The Occurrence of Disinfection

Byproducts in US Drinking Water.” J. AWWA.81(8):41-53.
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51. Lâiné, J.M., J.G. Jacangelo, E.W. Cummings, K.E. Carns, J. Mallevialle. 1993. “Influence of

Bromide on Low-Pressure Membrane Filtration for Controlling DBPs in Surface Waters.” J.

AWWA. 85(6):87-99.

52. Lalezary, S., M. Pirbazari, and M.J. McGuire. 1986. “Oxidation of Five Earthy-Musty Taste and

Odor Compounds.” J. AWWA. 78(3):62.

53. Lang, C.L. 1994. “The Impact of the Freshwater Macrofouling Zebra Mussel (Dretssena

Polymorpha) on Drinking Water Suppliers.” Conference proceedings, AWWA Water Quality

Technology Conference Part II, San Francisco, CA.

54. Langlais, B., D.A. Reckhow, and D.R. Brink. (editors). 1991. Ozone in Drinking Water

Treatment: Application and Engineering. AWWARF and Lewis Publishing, Chelsea, MI.

55. Liu, O.C., et al. 1971. “Relative Resistance of Twenty Human Enteric Viruses to Free Chlorine.

Virus and Water Quality: Occurrence and Control.” Conference Proceedings, thirteenth Water

Quality Conference, University of Illinois, Urbana-Champaign.

56. MacKenzie, W.R., et al. 1994. “A Massive Outbreak in Milwaukee of Cryptosporidium

Infection Transmitted Through the Public Water Supply.” New England J. of Medicine.

331(3):161.

57. Masschelein, W.J. 1992. “Unit Processes in Drinking Water Treatment.” Marcel Decker D.C.,

New York, Brussels, Hong Kong.

58. Matisoff, G., G. Brooks, and B.I. Bourland. 1996. “Toxicity of Chlorine Dioxide to Adult Zebra

Mussels.” J. AWWA. 88 (8):93-106.

59. McGuire, M.J., and R.G. Meadow. 1989. “AWWARF Trihalomethane Survey.” J. AWWA.

80(1):61.

60. Montgomery J. M. 1985. Water Treatment Principles and Design. John Wiley & Sons, New

York, NY.

61. Nieminski, E.C., S. Chaudhuri, and T. Lamoreaux. 1993. “The Occurrence of DBPs in Utah

Drinking Waters.” J. AWWA. 85(9):98-105.

62. Oliver, B.G., and D.B. Shindler. 1980. “Trihalomethanes From Chlorination of Aquatic Algae.”

Env. Sci. Tech. 14(12):1502.

63. Olson, K.E. 1982. An Evaluation of Low Chlorine Concentrations on Giardia Cyst Viability,

USDA Forest Service, Equipment Development Center, San Dimas, CA. January.
2. DISINFECTANT USE IN WATER TREATMENT

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64. Pourmoghaddas, H., A.A. Stevens, R.N. Kinman, R.C. Dressman, L.A. Moore, J.C. Ireland.

1993. “Effect of Bromide Ion on Formation of HAAs During Chlorination.” J. AWWA. 85(1):82-

87.

65. Prendiville, P.W. 1986. “Ozonation at the 900 cfs Los Angeles Water Purification Plant.”

Ozone: Sci. Engrg. 8:77.

66. Reckhow D.A., W.R, Knocke, M.J. Kearney, C.A. Parks. 1991. “Oxidation of Iron and

Manganese by Ozonation.” Environ. Sci. and Engrg. 13(6):675-695.

67. Reckhow D.A., P.C. Singer, and R.L. Malcolm. 1990. “Chlorination of Humic Materials:

Byproduct Formation and Chemical Interpretations.” Environ. Sci. Technol. 24(11):1655.

68. Reckhow, D.A., and P.C. Singer. 1985. “Mechanisms of Organic Halide Formation During

Fulvic Acid Chlorination and Implications with Respect to Preozonation.” Water Chlorination:

Chemistry, Environmental Impact and Health Effects, Volume 5. Jolley, R.L. et al. (editors).

Lewis Publishers, Chelsea, MI.

69. Reckhow, D.A., J.K. Edzwald, and J.E. Tobiason. 1993. Ozone as an Aid to Coagulation and

Filtration. AWWARF, AWWA, Denver, CO.

70. Reckhow, D.A., P.C.Singer, and R.R. Trussell. 1986. Ozone as a coagulant aid. Seminar

proceedings, Ozonation, Recent Advances and Research Needs, AWWA Annual Conference,

Denver, CO.

71. Rice, R.G., Overbeck, P.K., Larson, K. 1998. Ozone Treatment for Small Water Systems.

Presented at First International Symposium on Safe Drinking Water in Small Systems, NSF

International/PAHP/WHO, Arlington, VA. (In press)

72. Riggs, J.L. 1989. “Aids Transmission in Drinking Water: No Threat.” J. AWWA. 81(9):69.

73. Roberts, R. 1990. “Zebra Mussel Invasion Threatens US Waters.” Science. 249:1370.

74. Salvato, J.A., Jr. 1972. Environmental Engineering and Sanitation. second edition, John Wiley

& Sons, New York, NY.

75. Sawyer, C.N., P.L. McCarty, L. Parkin, and G.F. Parkin. 1994. Chemistry for Environmental

Engineering. McGraw Hill, Inc., New York, NY.

76. Scarpino P.V., et al. 1972. “A Comparative Study of the Inactivation of Viruses in Water by

Chlorine.” Water Research. 6:959.

77. Sinclair, R.M. 1964. “Clam Pests in Tennessee Water Supplies.” J. AWWA. 56 (5):592.
2. DISINFECTANT USE IN WATER TREATMENT

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78. Singer, P.C. 1988. Alternative Oxidant and Disinfectant Treatment Strategies for Controlling

THM Formation. EPA 600/S2-88/044. October.

79. Singer P.C. 1992. “Formation and Characterization of Disinfection Byproducts.” Presented at

the First International Conference on the Safety of Water Disinfection: Balancing Chemical and

Microbial Risks.

80. Singer P.C. 1993. “Trihalomethanes and Other Byproducts Formed From the Chlorination of

Drinking Water.” National Academy of Engineering Symposium on Environmental Regulation:

Accommodating Changes in Scientific, Technical, or Economic Information. Washington, D.C.

81. Singer P.C., and S.D. Chang. 1989. “Correlations Between Trihalomethanes and Total Organic

Halides Formed During Water Treatment.” J. AWWA. 81(8):61-65.

82. Singer P.C., and G.W. Harrington. 1993. “Coagulation of DBP Precursors: Theoretical and

Practical Considerations.” Conference proceedings, AWWA Water Quality Technology

Conference, Miami, FL.

83. Smith, A.L. et al. 1979. “Clams--A growing Threat to Implant Water Systems.” Plant Engrg.

33:165.

84. Snead, M.C., et al. 1980. Benefits of Maintaining a Chlorine Residual in Water Supply Systems.

EPA 600/2-80-010.

85. Stevens, A.A., et al. 1976. “Chlorination of Organics in Drinking Water.” J. AWWA. 8(11):615.

86. Stevens, A.A., L.A. Moore, R.J. Miltner. 1989. “Formation and Control of Non-Trihalomethane

Disinfection By-products.” J. AWWA. 81(8):54-60.

87. Suffet, I. H., C. Anselme, and J. Mallevialle. 1986. “Removal of Tastes and Odors by

Ozonation.” Conference proceedings, AWWA Seminar on Ozonation: Recent Advances and

Research Needs, Denver, CO.

88. Summers, R.S., G. Solarik, V.A. Hatcher, R.S. Isabel, J.F. Stile. 1997. “Analyzing the Impacts

of Predisinfection Through Jar Testing.” Conference proceedings, AWWA Water Quality

Technology Conference, Denver, CO.

89. Taylor, F.B. 1974. “Viruses - What is Their Significance in Water Supplies.” J. AWWA. 66:306.

90. Thibaud, H., H. DeLaat, N. Merlet, and M. Doré. 1987. “Chloropicrin Formation in Aqueous

Solution: Effect of Nitrites on Precursors Formation During the Oxidation of Organic

Compounds.” Water Res. 21(7):813.
2. DISINFECTANT USE IN WATER TREATMENT

EPA Guidance Manual 2-52 April 1999

Alternative Disinfectants and Oxidants

91. Thibaud, H., J. DeLaat, and M. Doré. 1988. “Effects of Bromide Concentration on the

Production of Chloropicrin During Chlorination of Surface Waters: Formation of Brominated

Trihalonitromethanes.” Water Res. 22(3):381.

92. Tobiason, J.E., J.K. Edzwald, O.D. Schneider, M.B. Fox, and H.J. Dunn. 1992. “Pilot Study of

the Effects of Ozone and PEROXONE on In-Line Direct Filtration.” J. AWWA. 84(12):72-84.

93. USEPA. 1998a. Occurrence Assessment for Disinfectants and Disinfection Byproducts in Public

Drinking Water Supplies. Science Applications International Corporation under contract for

Office of Ground Water and Drinking Water. Washington, DC.

94. USEPA. 1998b. Technologies and Costs for Control of Disinfection Byproducts. Prepared by

Malcolm Pirnie, Inc for U.S. Environmental Protection Agency, Office of Ground Water and

Drinking Water, PB93-162998.

95. USEPA. 1997a. Community Water System Survey - Volumes I and II; Overview. EPA 815-R-97-

001a, -001b. January.

96. USEPA. 1997b. “National Primary Drinking Water Regulations: Disinfectants and Disinfection

Byproducts; Notice of Data Availability; Proposed Rule.” Federal Register. 62(212):59387-

59484. November 3.

97. USEPA. 1996. Drinking Water Regulations and Health Advisories. EPA 822-B-96-002,

October.

98. USEPA. 1991. Manual of Individual and Non-Public Works Supply Systems. Office of Water,

EPA 570/9-91-004.

99. Van Benschoten, J.E., J.N. Jensen, D. Harrington, and D.J. DeGirolamo. 1995. “Zebra Mussel

Mortality With Chlorine.” J. AWWA. 87(5):101-108.

100. Wachter, J.K., and J.B. Andelman. 1984. “Organohalide Formation on Chlorination of Algal

Extracellular Products.” Env. Sci. Technol. 18(111):811.

101. Watson, H.E. 1908. “A Note on the Variation of the Rate of Disinfection With Change in the

Concentration of the Disinfectant.” J. Hygiene. 8:538.

102. White, G.C. 1992. Handbook of Chlorination and Alternative Disinfectants. Van Nostrand

Reinhold, New York, NY.

103. Witherell, L.E, R.W. Duncan, K.M. Stone, L.J. Stratton, L. Orciari, S. Kappel, D.A. Jillson.

1988. “Investigation of Legionella Pneumophila in Drinking Water.” J. AWWA. 80 (2):88-93.
2. DISINFECTANT USE IN WATER TREATMENT

April 1999 EPA Guidance Manual

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2-53

DISINFECTANT USE IN WATER TREATMENT ........................................................................................ 2-1

2.1 NEED FOR DISINFECTION IN WATER TREATMENT................................................................................... 2-1

2.1.1 Pathogens of Primary Concern...................................................................................................... 2-2

2.1.2 Recent Waterborne Outbreaks ...................................................................................................... 2-8

2.1.3 Mechanism of Pathogen Inactivation ............................................................................................ 2-9

2.2 OTHER USES OF DISINFECTANTS IN WATER TREATMENT ..................................................................... 2-10

2.2.1 Minimization of DBP Formation................................................................................................. 2-10

2.2.2 Control of Nuisance Asiatic Clams and Zebra Mussels................................................................ 2-11

2.2.3 Oxidation of Iron and Manganese ............................................................................................... 2-13

2.2.4 Prevention of Regrowth in the Distribution System and Maintenance of Biological Stability........ 2-14

2.2.5 Removal of Taste and Odors Through Chemical Oxidation ......................................................... 2-15

2.2.6 Improvement of Coagulation and Filtration Efficiency ................................................................ 2-15

2.2.7 Prevention of Algal Growth in Sedimentation Basins and Filters................................................. 2-16

2.2.8 Removal of Color....................................................................................................................... 2-16

2.3 DISINFECTION BYPRODUCTS AND DISINFECTION RESIDUALS................................................................ 2-16

2.3.1 Types of DBPs and Disinfection Residuals ................................................................................. 2-16

2.3.2 Disinfection Byproduct Formation.............................................................................................. 2-19

2.3.3 DBP Control Strategies............................................................................................................... 2-23

2.3.4 CT Factor................................................................................................................................... 2-25

2.4 PATHOGEN INACTIVATION VERSUS DBP FORMATION.......................................................................... 2-26

2.5 DISINFECTANT RESIDUAL REGULATORY REQUIREMENTS ..................................................................... 2-27

2.6 SUMMARY OF CURRENT NATIONAL DISINFECTION PRACTICES ............................................................. 2-28

2.7 CHLORINE .......................................................................................................................................... 2-30

2.7.1 Chlorine Chemistry .................................................................................................................... 2-31

2.7.2 Chlorine Generation ................................................................................................................... 2-32

2.7.3 Primary Uses and Points of Application of Chlorine.................................................................... 2-33

2.7.4 Pathogen Inactivation and Disinfection Efficacy.......................................................................... 2-35

2.7.5 DBP Formation and Control ....................................................................................................... 2-39

2.7.6 Operational Considerations......................................................................................................... 2-41

2.8 SUMMARY.......................................................................................................................................... 2-42

2.8.1 Advantages and Disadvantages of Chlorine Use .......................................................................... 2-42

2.8.2 Summary Table .......................................................................................................................... 2-44

2.8.3 Reference for Additional Information on Chlorine ...................................................................... 2-44

2.9 REFERENCES ...................................................................................................................................... 2-45

Table 2-1. Waterborne Diseases from Bacteria.................................................................................................... 2-3

Table 2-2. Waterborne Diseases from Human Enteric Viruses............................................................................. 2-4

Table 2-3. Waterborne Diseases from Parasites................................................................................................... 2-6

Table 2-4. Attributes of the Three Waterborne Pathogens of Concern in Water Treatment................................... 2-7

Table 2-5. Human Parasitic Protozoans............................................................................................................... 2-7

Table 2-6. The Effects of Various Oxidants on Mortality of the Asiatic Clam (Corbicula fluminea)................... 2-12

Table 2-7. Oxidant Doses Required for Oxidation of Iron and Manganese ......................................................... 2-14

Table 2-8. List of Disinfection Byproducts and Disinfection Residuals.............................................................. 2-17

Table 2-9. Status of Health Information for Disinfectants and DBPs.................................................................. 2-18

Table 2-10. Conditions of Formation of DBPs .................................................................................................. 2-22

Table 2-11. Inorganic DBPs Produced During Disinfection............................................................................... 2-23

Table 2-12. Required Removal of TOC by Enhanced Coagulation for Surface Water Systems+ Using Conventional

Treatment++ (percent reduction).................................................................................................................. 2-25

Table 2-13. CT Values for Inactivation of Viruses ............................................................................................ 2-26

Table 2-14. CT Values for Inactivation of Giardia Cysts................................................................................... 2-26

Table 2-15. Summary of Disinfection Impacts.................................................................................................. 2-27
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Table 2-16. Disinfection Practices of Water Systems that Include Some Form of Treatment. 2-29

Table 2-17. Ozone Application in Water Treatment Plants in the United States ................................................. 2-30

Table 2-18. Chlorine Uses and Doses................................................................................................................ 2-34

Table 2-19. Typical Chlorine Points of Application and Uses............................................................................ 2-34

Table 2-20. Typical Chlorine Dosages at Water Treatment Plants...................................................................... 2-35

Table 2-21. Percent Reduction in DBP Formation by Moving Chlorination Point Later In Treatment Train ....... 2-40

Table 2-22. Summary of Chlorine Disinfection................................................................................................. 2-44

Figure 2-1. Free Chlorine Giardia and Virus CT Requirements......................................................................... 2-38

Figure 2-2. CT Values for Inactivation of Giardia Cysts by Free Chlorine at 10oC (at Cl2 dose of 3.0 mg/L)...... 2-38

Figure 2-3. CT Values for Inactivation of Giardia Cysts by Free Chlorine at pH 7.0 (at Cl2 dose of 3.0 mg/L)... 2-39
April 1999 3-1 EPA Guidance Manual

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3. OZONE

Ozone was first used for drinking water treatment in 1893 in the Netherlands. While being used

frequently in Europe for drinking water disinfection and oxidation, it was slow to transfer to the

United States. In 1987, the Los Angeles Aqueduct Filtration Plant was placed in service and now

treats up to 600 mgd of drinking water. In 1991, approximately 40 water treatment plants each

serving more than 10,000 people in the United States utilized ozone (Langlais et al., 1991). This

number has grown significantly, with Rice (in press) reporting that as of April 1998, 264 operating

plants in the United States use ozone. Most of these facilities are small: 149 plants are below 1 mgd.

Ozone is used in water treatment for disinfection and oxidation. Early application of ozone in the

United States was primarily for non-disinfection purposes such as color removal or taste and odor

control. However, since the implementation of the SWTR and proposal of the DBP rule, ozone

usage for primary disinfection has increased in the United States.

3.1 Ozone Chemistry

Ozone exists as a gas at room temperature. The gas is colorless with a pungent odor readily

detectable at concentrations as low as 0.02 to 0.05 ppm (by volume), which is below concentrations

of health concern. Ozone gas is highly corrosive and toxic.

Ozone is a powerful oxidant, second only to the hydroxyl free radical, among chemicals typically

used in water treatment. Therefore, it is capable of oxidizing many organic and inorganic

compounds in water. These reactions with organic and inorganic compounds cause an ozone demand

in the water treated, which should be satisfied during water ozonation prior to developing a

measurable residual.

Ozone is sparingly soluble in water. At 20oC, the solubility of 100 percent ozone is only 570 mg/L

(Kinman, 1975). While ozone is more soluble than oxygen, chlorine is 12 times more soluble than

ozone. Ozone concentrations used in water treatment are typically below 14 percent, which limits

the mass transfer driving force of gaseous ozone into the water. Consequently, typical concentrations

of ozone found during water treatment range from <0.1 to 1mg/L, although higher concentrations can

be attained under optimum conditions.

Basic chemistry research (Hoigné and Bader, 1983a and 1983b; Glaze et al., 1987) has shown that

ozone decomposes spontaneously during water treatment by a complex mechanism that involves the

generation of hydroxyl free radicals. The hydroxyl free radicals are among the most reactive

oxidizing agents in water, with reaction rates on the order of 1010 - 1013 M-1 s-1, approaching the

diffusion control rates for solutes such as aromatic hydrocarbons, unsaturated compounds, aliphatic

alcohols, and formic acid (Hoigné and Bader, 1976). On the other hand, the half-life of hydroxyl free

radicals is on the order of microseconds, therefore concentrations of hydroxyl free radicals can never

reach levels above 10 –12 M (Glaze and Kang, 1988).
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As shown in Figure 3-1 ozone can react by either or both modes in aqueous solution (Hoigné and

Bader, 1977):

• Direct oxidation of compounds by molecular ozone (O3(aq)).

• Oxidation of compounds by hydroxyl free radicals produced during the decomposition of

ozone.

O3

Direct Oxidation of Substrate

Ozone Decomposition

via *OH

Indirect Oxidation of Substrate

by Hydroxyl Radical

Radical Consumption by

HCO3

-

, CO3

-2, etc.

Byproducts

Byproducts

Figure 3-1. Oxidation Reactions of Compounds (Substrate)

During Ozonation of Water

The two oxidation pathways compete for substrate (i.e., compounds to oxidize). The direct oxidation

with aqueous ozone is relatively slow (compared to hydroxyl free radical oxidation) but the

concentration of aqueous ozone is relatively high. On the other hand, the hydroxyl radical reaction is

fast, but the concentration of hydroxyl radicals under normal ozonation conditions is relatively small.

Hoigné and Bader (1977) found that:

• Under acidic conditions, the direct oxidation with molecular ozone is of primary importance;

and

• Under conditions favoring hydroxyl free radical production, such as high pH, exposure to

UV, or addition of hydrogen peroxide, the hydroxyl oxidation starts to dominate.

This latter mechanism is used in advanced oxidation processes such as discussed in Chapter 7,

Peroxone, to increase the oxidation rates of substrates.

The spontaneous decomposition of ozone occurs through a series of steps. The exact mechanism and

reactions associated have not been established, but mechanistic models have been proposed (Hoigné

and Bader, 1983a and 1983b; Glaze, 1987). It is believed that hydroxyl radicals forms as one of the

intermediate products, and can react directly with compounds in the water. The decomposition of

ozone in pure water proceeds with hydroxyl free radicals produced as an intermediate product of

ozone decomposition, resulting in the net production of 1.5 mole hydroxyl free radicals per mole

ozone.
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April 1999 3-3 EPA Guidance Manual

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In the presence of many compounds commonly encountered in water treatment, ozone decomposition

forms hydroxyl free radicals. Ozone demands are associated with the following:

• Reactions with natural organic matter (NOM) in the water. The oxidation of NOM leads to

the formation of aldehydes, organic acids, and aldo- and ketoacids (Singer, 1992).

• Organic oxidation byproducts. Organic oxidation byproducts are generally more amenable to

biological degradation and can be measured as assimilable organic carbon (AOC) or

biodegradable dissolved organic carbon (BDOC).

• Synthetic organic compounds (SOCs). Some SOCs can be oxidized and mineralized under

favorable conditions. To achieve total mineralization, hydroxyl radical oxidation should

usually be the dominant pathway, such as achieved in advanced oxidation processes.

• Oxidation of bromide ion. Oxidation of bromide ion leads to the formation of hypobromous

acid, hypobromite ion, bromate ion, brominated organics, and bromamines (see Figure 3-2).

• Bicarbonate or carbonate ions, commonly measured as alkalinity, will scavenge the hydroxyl

radicals and form carbonate radicals (Staehelin et al., 1984; Glaze and Kang, 1988). These

reactions are of importance for advanced oxidation processes where the radical oxidation

pathway is predominant.

Source: Gunten and Hoigné, 1996.

Figure 3-2. Reaction of Ozone and Bromide Ion Can Produce Bromate Ion and

Brominated Organics
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3.2 Ozone Generation

3.2.1 Ozone Production

Because ozone is an unstable molecule, it should be generated at the point of application for use in

water treatment. It is generally formed by, combining an oxygen atom with an oxygen molecule

(O2):

3O2⇔ 2O3

This reaction is endothermic and requires a considerable input of energy.

Schönbein (Langlais et < biblio >) first discovered synthetic ozone through the electrolysis of

sulfuric acid. Ozone can be produced several ways, although one method, corona discharge,

predominates in the ozone generation industry. Ozone can also be produced by irradiating an

oxygen-containing gas with ultraviolet light, electrolytic reaction and other emerging technologies as

described by Rice (1996).

Corona discharge, also known as silent electrical discharge, consists of passing an oxygen-containing

gas through two electrodes separated by a dielectric and a discharge gap. Voltage is applied to the

electrodes, causing an electron flowthrough across the discharge gap. These electrons provide the

energy to disassociate the oxygen molecules, leading to the formation of ozone. Figure 3-3 shows a

basic ozone generator.

Figure 3-3. Basic Ozone Generator
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3.2.2 System Components

As shown in Figure 3-4, ozone water treatment systems have four basic components: a gas feed

system, an ozone generator, an ozone contactor, and an off-gas destruction system. The gas feed

system provides a clean, dry source of oxygen to the generator. The ozone contactor transfers the

ozone-rich gas into the water to be treated, and provides contact time for disinfection (or other

reactions). The final process step, off-gas destruction, is required as ozone is toxic in the

concentrations present in the off-gas. Some plants include an off-gas recycle system that returns the

ozone-rich off-gas to the first contact chamber to reduce the ozone demand in the subsequent

chambers. Some systems also include a quench chamber to remove ozone residual in solution.

Ozone Destruction

Gas Feed

System

Ozone

Generator

Influent

Effluent

Atmosphere

Ozone Gas

Ozone

Quench

(Option)

Off-Gas

Figure 3-4. Simplified Ozone System Schematic

3.2.2.1 Gas Feed Systems

Ozone feed systems are classified as using air, high purity oxygen or mixture of the two. High purity

oxygen can be purchased and stored as a liquid (LOX), or it can be generated on-site through either a

cryogenic process, with vacuum swing adsorption (VSA), or with pressure swing adsorption (PSA).

Cryogenic generation of oxygen is a complicated process and is feasible only in large systems.

Pressure swing adsorption is a process whereby a special molecular sieve is used under pressure to
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selectively remove nitrogen, carbon dioxide, water vapor, and hydrocarbons from air, producing an

oxygen rich (80–95 percent O2) feed gas. The components used in pressure swing adsorption

systems are similar to high pressure air feed systems in that both use pressure swing molecular

absorption equipment. Low pressure air feed systems use a heat reactivated desiccant dryer.

Oxygen Feed Systems - Liquid oxygen feed systems are relatively simple, consisting of a storage

tank or tanks, evaporators to convert the liquid to a gas, filters to remove impurities, and pressure

regulators to limit the gas pressure to the ozone generators.

Air Feed Systems - Air feed systems for ozone generators are fairly complicated as the air should be

properly conditioned to prevent damage to the generator. Air should be clean and dry, with a

maximum dew point of -60o C (-80o F) and free of contaminants. Air preparation systems typically

consist of air compressors, filters, dryers, and pressure regulators. Figure 3-5 is a schematic of large

scale air preparation system.

Particles greater than 1 μm and oil droplets greater than 0.05 μm should be removed by filtration

(Langlais et al., 1991). If hydrocarbons are present in the feed gas, granular activated carbon filters

should follow the particulate and oil filters. Moisture removal can be achieved by either compression

or cooling (for large-scale system), which lowers the holding capacity of the air, and by desiccant

drying, which strips the moisture from the air with a special medium. Desiccant dryers are required

for all air preparation systems. Large or small particles and moisture cause arcing which damages

generator dielectrics.

Typically, desiccant dryers are supplied with dual towers to allow regeneration of the saturated tower

while the other is in service. Moisture is removed from the dryer by either an external heat source or

by passing a fraction (10 to 30 percent) of the dried air through the saturated tower at reduced

pressure. Formerly, small systems that require only intermittent use of ozone , a single desiccant

tower is sufficient, provided that it is sized for regeneration during ozone decomposition time.

Air preparation systems can be classified by the operating pressure: ambient, low (less than 30 psig),

medium, and high (greater than 60 psig) pressure. The distinguishing feature between low and high

pressure systems is that high pressure systems can use a heatless dryer. A heatless dryer operates

normally in the 100 psig range, rather than the 60 psig range. Rotary lobe, centrifugal, rotary screw,

liquid ring, vane, and reciprocating compressors can be used in air preparation systems. Table 3-1

lists the characteristics of many of these types of compressors.

Reciprocating and liquid ring compressors are the most common type used in the United States,

particularly in small systems, the former because the technology is so prevalent and the latter because

liquid ring compressors do not need aftercoolers. Air receivers are commonly used to provide

variable air flow from constant volume compressors. Oil-less compressors are used in modern

systems to avoid hydrocarbons in the feed gas (Dimitriou, 1990).
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April 1999 3-7 EPA Guidance Manual

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Air

Filter Compressor Aftercooler Separator

Desiccant

Dryer

Air

Receiver

Moist Air

Dry, Clean Air

to Generator

Secondary

Filter

Figure 3-5. Schematic of an Air Preparation System

Table 3-1. Types of Compressors Used in Air Preparation Systems

Compressor Type Pressure Volume Comments

Rotary lobe Low – 15 psi Constant or variable with

unloading

Common in Europe

Centrifugal 30 – 100 psi depending

on no. of stages

Variable, high volume Medium efficiency, cost effective in high

volumes

Rotary Screw 50 psi (single stage) to

100 psi (2 stage)

Variable with unloading Slightly more efficient than rotary lobe, draws

approximately 40% of full load power in

unloaded state, available in non-lubricated

design for larger capacities.

Liquid Ring 10–80 psi Constant volume Does not require lubrication or aftercooler,

relatively inefficient, common in United

States.

Vane High - to 100 psi Constant or variable Relatively inefficient, not common in U.S.
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Table 3-2 presents a comparison of the advantages and disadvantages of each gas feed system.

Table 3-2. Comparison of Air and High Purity Oxygen Feed Systems

Source Advantages Disadvantages

Air • Commonly used equipment

• Proven technology

• Suitable for small and large systems

• More energy consumed per ozone volume

produced

• Extensive gas handling equipment required

• Maximum ozone concentration of 3-5%

Oxygen (general) • Higher ozone concentration (8-14%)

• Approximately doubles ozone concentration

for same generator

• Suitable for small and large systems

• Safety concerns

• Oxygen resistant materials required

LOX • Less equipment required

• Simple to operate and maintain

• Suitable for small and intermediate systems

• Can store excess oxygen to meet peak

demands

• Variable LOX costs

• Storage of oxygen onsite (Fire Codes, i.e.

safety concerns)

• Loss of LOX in storage when not in use

Cryogenic Oxygen

Generation

• Equipment similar to air preparation systems

• Feasible for large systems

• Can store excess oxygen to meet peak

demands

• More complex than LOX

• Extensive gas handling equipment required

• Capital intensive

• Complex systems to operate and maintain

3.2.2.2 Ozone Generators

The voltage required to produce ozone by corona discharge is proportional to the pressure of the

source gas in the generator and the width of the discharge gap. Theoretically, the highest yield

(ozone produced per unit area of dielectric) would result from a high voltage, a high frequency, a

large dielectric constant, and a thin dielectric. However, there are practical limitations to these

parameters. As the voltage increases, the electrodes and dielectric materials are more subject to

failure. Operating at higher frequencies produces higher concentrations of ozone and more heat

requiring increased cooling to prevent ozone decomposition. Thin dielectrics are more susceptible to

puncturing during maintenance. The design of any commercial generator requires a balance of ozone

yield with operational reliability and reduced maintenance.

Two different geometric configurations for the electrodes are used in commercial ozone generators:

concentric cylinders and parallel plates. The parallel plate configuration is commonly used in small

generators and can be air cooled. Figure 3-6 shows the basic arrangement for the cylindrical

configuration. The glass dielectric/high voltage electrode in commercial generators resembles a

fluorescent light bulb and is commonly referred to as a “generator tube.”

Most of the electrical energy input to an ozone generator (about 85 percent) is lost as heat (Rice,

1996). Because of the adverse impact of temperature on the production of ozone, adequate cooling

should be provided to maintain generator efficiency. Excess heat is removed usually by water
3. OZONE

April 1999 3-9 EPA Guidance Manual

Alternative Disinfectants and Oxidants

flowing around the stainless steel ground electrodes. The tubes are arranged in either a horizontal or

vertical configuration in a stainless steel shell, with cooling water circulating through the shell.

Figure 3-6. Cylindrical Electrode Schematic

Ozone generators are classified by the frequency of the power applied to the electrodes. Low

frequency (50 or 60 Hz) and medium frequency (60 to 1,000 Hz) generators are the most common

found in the water industry, however some high frequency generators are available. Table 3-3

presents a comparison of the three types of generators. Medium frequency generators are efficient

and can produce ozone economically at high concentrations, but they generate more heat than low

frequency generators and require a more complicated power supply to step up the frequency supplied

by utility power. New installations tend to use medium or high frequency generators.

3.2.2.3 Ozone Contactors

Once ozone gas is transferred into water, the dissolved ozone reacts with the organic and inorganic

constituents, including any pathogens. Ozone not transferred into the process water during contacting

is released from the contactor as off-gas. Transfer efficiencies of greater than 80 percent typically are

required for efficient ozone disinfection (DeMers and Renner, 1992).

Common ozone dissolution methods include:

• Bubble diffuser contactors;

• Injectors; and

• Turbine mixers.
3. OZONE

EPA Guidance Manual 3-10 April 1999

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Table 3-3. Comparison of Primary Characteristics of Low, Medium, and High

Frequency Ozone Generators

Characteristic Low Frequency

(50 - 60 Hz)

Medium Frequency

(up to 1,000 Hz)

High Frequency

(> 1,000 Hz)

Degree of Electronics Sophistication low high high

Peak Voltages 19.5 11.5 10

Turndown Ratio 5:1 10:1 10:1

Cooling Water Required (gal/lb of

ozone produced)

0.5 to 1.0 0.5 to 1.5 0.25 to 1

Typical Application Range < 500 lb/day to 2,000 lb/day to 2,000 lb/day

Operating Concentrations

wt - % in air

wt - % in oxygen

0.5 to 1.5%

2.0 to 5.0%

1.0 to 2.5%+

2 to 12%

1.0 to 2.5%+

2 to 12%

Optimum Ozone Production (as a

proportion of total generator capacity)

60 to 75% 90 to 95% 90 to 95%

Optimum Cooling Water Differential 8° to 10°F 5° to 8°F 5° to 8°F

Power Required (kW-h/lb O3) air feed: 8 to 12

O2 feed: 4 to 6

air feed: 8 to 12

O2 feed: 4 to 6

air feed: 8 to 12

O2 feed: 4 to 6

Air Feed System Power Requirements

(kW-h/lb O3)

5 to 7 5 to 7 5 to 7

Source: Adapted from Rice, 1996, with modifications.

Bubble Diffuser Contactors

The bubble diffuser contactor is commonly used for ozone contacting in the United States and

throughout the world (Langlais et al., 1991). This method offers the advantages of no additional

energy requirements, high ozone transfer rates, process flexibility, operational simplicity, and no

moving parts. Figure 3-7 illustrates a typical three stage ozone bubble diffuser contactor. This

illustration shows a countercurrent flow configuration (ozone and water flowing in opposite

directions), an alternating cocurrent/countercurrent arrangement, and a cocurrent flow configuration

(ozone and water flowing in the same direction). Also, the number of stages can vary from two to six

for ozone disinfection, with the majority of plants using two or three chambers for contacting and

reaction (Langlais et al., 1991).

Bubble diffuser contactors are typically constructed with 18 to 22 ft water depths to achieve 85 to 95

percent ozone transfer efficiency. Since all the ozone is not transferred into the water, the contactor

chambers are covered to contain the off-gas. Off-gas is routed to an ozone destruct unit, usually

catalysts, thermal, or thermal/catalysts.
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April 1999 3-11 EPA Guidance Manual

Alternative Disinfectants and Oxidants

Influent

Ozone Gas

B. Counter and Cocurrent Contactor

Influent

Ozone Gas

A. Counter Current Contactor

Influent

Ozone Gas

C. Cocurrent Contactor

Figure 3-7. Ozone Bubble Contactor

Bubble diffuser contactors use ceramic or stainless steel diffusers that are either rod-type or disc-type

to generate bubbles. Design considerations for these diffusers (Renner et al., 1988) include:

• Gas flow range of 0.5 to 4.0 scfm;

• Maximum headloss of 0.5 psig;

• Permeability of 2 to 15 cfm/ft2/in of diffuser thickness; and porosity of 35 to 45 percent.

The configuration of the bubble diffuser contactor structure should best be designed to provide plug

flow hydraulics. This configuration will minimize the overall volume of the contactor while still
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EPA Guidance Manual 3-12 April 1999

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meeting the CT requirements for the system. Contactor volume is determined in conjunction with the

applied ozone dosage and estimated residual ozone concentration to satisfy the disinfection CT

requirement.

Table 3-4 summarizes the advantages and disadvantages of the bubble diffuser contactor (Langlais et

al., 1991). Also, diffuser pore clogging can be a problem when ozone dosages are intermittent and/ or

when iron and manganese oxidation is required. Channeling of bubbles is dependent on the type of

diffusers used and the spacing between diffusers.

Table 3-4. Bubble Diffuser Contactor Advantages and Disadvantages

Advantages Disadvantages

No moving parts Deep contact basins

Effective ozone transfer Vertical channeling of bubbles

Low hydraulic headloss Maintenance of gaskets and piping.

Operational simplicity

Injector Dissolution

The injector contacting method is commonly used in Europe, Canada, and the United States

(Langlais et al., 1991). Ozone is injected into a water stream under negative pressure, which is

generated in a venturi section, pulling the ozone into the water stream. In many cases, a sidestream of

the total flow is pumped to a higher pressure to increase the available vacuum for ozone injection.

After the ozone is injected into this sidestream, the sidestream containing all the added ozone is

combined with the remainder of the plant flow under high turbulence to enhance dispersion of ozone

into the water. Figure 3-8 illustrates typical in-line and sidestream ozone injection systems.

Ozone Gas

Injector

Influent

Contactor

Off Gas

A. In-line Injector System

Ozone Gas

Injector

Influent

Contactor

Off Gas

B. Sidestream Injector System

Static

Mixer

Figure 3-8. Sidestream Ozone Injection System
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The gas to liquid ratio is a key parameter used in the design of injector contacting systems. This ratio

should be less than 0.067 cfm/gpm to optimize ozone transfer efficiency (Langlais et al., 1991).

Meeting this criterion typically requires relatively low ozone dosages and ozone gas concentrations

greater than 6 percent by weight (DeMers and Renner, 1992). High concentration ozone gas can be

generated using a medium-frequency generator and/or liquid oxygen as the feed gas.

To meet the CT disinfection requirements, additional contact time is required after the injector,

typically in a plug flow reactor. The additional contact volume is determined in conjunction with the

applied ozone dosage and estimated residual ozone concentration to satisfy the disinfection CT

requirement.

Table 3-5 summarizes the advantages and disadvantages of injection contacting (Langlais et al.,

1991).

Table 3-5. Injection Contacting Advantages and Disadvantages

Advantages Disadvantages

Injection and static mixing have no moving parts Additional headloss (energy usage) due to static mixers

which may require pumping

Very effective ozone transfer Turndown capability limited by injection system

Contactor depth less than bubble diffusion More complex operation and high cost.

Turbine Mixer Contactors

Turbine mixers are used to feed ozone gas into a contactor and mix the ozone with the water in the

contactor. Figure 3-9 illustrates a typical turbine contactor. The illustrated turbine mixer design

shows the motor located outside the basin, allowing for maintenance access. Other designs use a

submerged turbine.

Ozone transfer efficiency for turbine mixers can be in excess of 90 percent. However, the power

required to achieve this efficiency is 2.2 to 2.7 kW-hr of energy per lb of ozone transferred

(Dimitriou, 1990).

Turbine mixing basins vary in water depth from 6 to 15 ft, and dispersion areas vary from 5 to 15 ft

(Dimitriou, 1990). Again, as with injector contacting, sufficient contact time may not be available in

the turbine basin to meet disinfection CT requirements; consequently additional contact volume may

be required.
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Figure 3-9. Turbine Mixer Ozone Contactor

Table 3-6 summarizes advantages and disadvantages for the turbine mixer contactor (Langlais et al.,

1991).

Table 3-6. Turbine Mixer Contactor Advantages and Disadvantages

Advantages Disadvantages

Ozone transfer is enhanced by high turbulence resulting in

small bubble size

Require energy input

Contactor depth less than bubble diffusion Constant gas flow rate should be maintained, reducing ozone

transfer efficiency

Aspirating turbines can draw off-gas from other chambers for

reuse

Maintenance requirements for turbine and motor

Eliminates diffuser clogging concerns

3.2.2.4 Off-gas Destruction Systems

The concentration of ozone in the off-gas from a contactor is usually well above the fatal

concentration. For example, at 90 percent transfer efficiency, a 3 percent ozone feed stream will still

contain 3,000 ppm of ozone in the off-gas. Off-gas is collected and the ozone converted back to

oxygen prior to release to the atmosphere. Ozone is readily destroyed at high temperature (> 350° C

or by a catalyst operating above 100° C) to prevent moisture buildup. The off-gas destruct unit is

designed to reduce the concentration to 0.1 ppm of ozone by volume, the current limit set by OSHA
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for worker exposure in an eight hour shift. A blower is used on the discharge side of the destruct unit

to pull the air from the contactor, placing the contactor under a slight vacuum to ensure that no ozone

escapes.

3.2.2.5 Instrumentation

Instrumentation should be provided for ozone systems to protect both personnel and the equipment.

Gas phase ozone detectors should be provided in spaces such as generator rooms where ozone gas

may be and personnel are routinely present. An ozone detector is also needed on the outlet from the

off-gas destruct unit to ensure the unit is working properly. These units should be interlocked with

the ozone generator controls to shut down the ozone generation system should excess ozone be

detected. A dew point detector on the feed gas supply just upstream of an ozone generator is

required to protect the generator from moisture in the feed gas (when air is the feed gas). Flow

switches on the cooling water supply are needed to protect the generator from overheating and a

pressure switch to prevent over pressurization.

Other instrumentation can be used to monitor and control the ozone process, although manual control

is adequate for small systems, but most small systems are designed to operate automatically,

particularly in remote areas. Ozone monitors can be used in conjunction with process flow meters to

match ozone dose to process demands and control ozone generation. Sophisticated control schemes

can be implemented to minimize the cost of dosing with ozone and reduce operator attention

requirements. Many systems include residual monitoring at various points in the contactor to

maintain a desired ozone residual and prevent energy-wasting overdosing.

3.2.3 Operation and Maintenance

Even though ozone systems are complex, using highly technical instruments, the process is highly

automated and very reliable, requiring only a modest degree of operator skill and time to operate an

ozone system. Maintenance on generators requires skilled technicians. If trained maintenance staff

are not available at the plant, this work can be done by the equipment manufacturer. Some facilities,

such as the 600 mgd Los Angeles Aqueduct Filtration Plant, use plant mechanics to perform

generator and facilities maintenance. Therefore, backup units are usually installed. Generators

should be checked daily when in operation. After a shutdown, dry air or oxygen should be allowed

to flow through the generator to ensure that any moisture has been purged prior to energizing the

electrodes. At initial start up and after long down times, this process may take up to 12 hours and

usually longer when air is the feed gas. As an alternative, a small flow of dry air can be passed

through the generator continuously when it is in standby mode to maintain the dry condition.

Filters and desiccant in air preparation systems should be changed periodically, with the frequency

depending on the quality of the inlet air and the number of hours in operation. Compressors require

periodic service, depending on the type and operating time. LOX tanks should be periodically

pressure tested. Piping and contact chambers should be inspected periodically to check for leaks and

corrosion.
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Dielectric tubes should be periodically cleaned. This operation should be performed when the

generator efficiency drops 10-15 percent. Cleaning the tubes is a delicate operation as the tubes are

fragile and expensive. Adequate space should be provided for the cleaning operation and for storage

of spare tubes.

3.3 Primary Uses and Points of Application of Ozone

3.3.1 Primary Uses of Ozone

Ozone is used in drinking water treatment for a variety of purposes including:

• Disinfection;

• Inorganic pollutant oxidation, including iron, manganese, and sulfide;

• Organic micropollutant oxidation, including taste and odor compounds, phenolic pollutants, and

some pesticides; and

• Organic macropollutant oxidation, including color removal, increasing the biodegradability of

organic compounds, DBP precursor control, and reduction of chlorine demand.

3.3.1.1 Disinfection

Ozone is a powerful oxidant able to achieve disinfection with less contact time and concentration

than all weaker disinfectants, such as chlorine, chlorine dioxide, and monochloramine (Demers and

Renner, 1992). However, ozone can only be used as a primary disinfectant since it cannot maintain a

residual in the distribution system. Thus, ozone disinfection should be coupled with a secondary

disinfectant, such as chlorine, chloramine, or chlorine dioxide for a complete disinfection system.

3.3.1.2 Iron and Manganese Oxidation

Ozone will oxidize iron and manganese, converting ferrous (2+) iron into the ferric (3+) state and 2+

manganese to the 4+ state. The oxidized forms will precipitate as ferric hydroxide and manganese

hydroxide (AWWA, 1990). The precise chemical composition of the precipitate will depend on the

nature of the water, temperature, and pH. The ozone dose required for oxidation is 0.43 mg/mg iron

and 0.88 mg/mg manganese (Langlais et al., 1991). Iron oxidizes at a pH of 6-9 but manganese is

more effective at a pH of around 8. Also, over-ozonation has no effect on iron, but will resolubilize

manganese, which then should be reduced to manganese dioxide downstream.

3.3.1.3 Oxidation of Taste and Odor Compounds

Ozone is used to oxidize/destroy taste and odor-causing compounds because many of these

compounds are very resistant to oxidation. Suffet et al. (1986) confirmed that ozone is an effective

oxidant for use in taste and odor treatment. They found ozone doses of 2.5 to 2.7 mg/L and 10

minutes of contact time (ozone residual of 0.2 mg/L) significantly reduced taste and odors in the
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specific waters they tested. Most early U.S. water plants (i.e., 1940-1986) installed ozonation

specifically for taste and odor removal.

3.3.1.4 DBP Precursor Control

Early work on oxidation of DBP precursors seemed to indicate that the effects of ozonation, prior to

chlorination, were quite site-specific and unpredictable (Umphries et al., 1979). The key variables

that seem to determine ozone’s effect are dose, pH, alkalinity, and, above all, the nature of the

organic material. At low pH levels, precursor destruction by ozone is quite effective; however, above

some critical pH, ozone actually is less effective and in fact sometimes increases the amount of

chlorination byproduct precursors. For most humic substances this critical pH is 7.5, which is the

approximate level at which decomposition of ozone to hydroxyl free radicals increases rapidly, thus

increasing organic oxidation rates. Therefore, the implications that at lower pH (approximately 6-7),

at which molecular ozone predominates over the hydroxyl free radical, the initial THM precursor byproducts are different in nature than those formed by the hydroxyl free radicals oxidized at higher pH

levels. This is logical in light of the greater oxidation potential of the hydroxyl free radical over that

of ozone.

As alkalinity increases, it has a beneficial effect on THM formation potential (THMFP) (Langlais et

al., 1991). This is because alkalinity scavenges any hydroxyl free radicals formed during ozonation,

leaving molecular ozone as the sole oxidant, which is only capable of oxidizing organic precursors to

a lower oxidation sequence than does the hydroxyl free radical. Given neutral pH and moderate

levels of bicarbonate alkalinity, THMFP level reductions of 3 to 20 percent have been shown at

ozone doses ranging from 0.2 to 1.6 mg ozone per mg carbon (Singer et al., 1989; Georgeson and

Karimi, 1988).

3.3.1.5 Increase Organic Biodegradation

Ozone can be effective in partially oxidizing organics in the water to biodegradable compounds that

can be removed by biological filtration (Demers and Renner, 1992). This partial oxidation gives rise

to lower molecular weight organics that are more easily biodegradable. This increase in the

biodegradable fraction of organic carbon occurs as a result of moderate to high levels of ozonation.

These ozone levels are typical of the doses commonly applied for disinfection.

3.3.1.6 Coagulation and Filtration Improvement

Ozone has been reported by some to improve coagulation and filtration efficiency (Gurol and

Pidatella, 1993; Farvardin and Collins, 1990; Reckhow et al., 1993; Stolarik and Christie, 1997).

However, others have found no improvement in filter effluent turbidity due to ozonation (Tobiason et

al., 1992; Hiltebrand et al., 1986). Prendiville (1986) collected data from a large water treatment

plant showing that pre-ozonation was more effective than pre-chlorination to reduce filter effluent

turbidities. The cause of the improved coagulation is not clear, but several possibilities have been

offered (Reckhow et al., 1986), including:
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• Oxidation of organic compounds into more polar forms; and

• Oxidation of metals ions to yield insoluble complexes, such as ferric iron complexes.

3.3.2 Points of Application

The typical locations for feeding ozone in a water treatment plant are at the head of the treatment

plant (raw water) pre-ozonation and after sedimentation.

Raw water quality and turbidity and ozone demand (the amount of ozone required for all oxidation

requirements of the water) can be used to assess how to use ozone in the treatment process. Table 3-7

lists the criteria for selecting ozone feed points based on these two parameters. By moving the

ozonation process further downstream after sedimentation, the ozone demand and production of

byproducts are reduced. The advantage of placing ozone ahead of filtration is that biodegradable

organics produced during ozonation can be removed by subsequent biological activity in the filters.

Table 3-7. Criteria for Selecting Ozone Feed Points for Small Systems

Raw Water Quality Ozone Feed Point(s) Special Considerations

Category I

 Turbidity < 10 NTU

 Ozone Demand < 1mg/L

Raw Water or After Sedimentation

Low ozone demand.

Low disinfection byproducts.

Low biodegradable organics.

Category II

 Turbidity > 10 NTU

 Ozone Demand < 1mg/L

After Sedimentation

Low ozone demand.

High inorganic particulate.

Low biodegradable organics.

Category III

 Turbidity < 10 NTU

 Ozone Demand > 1mg/L

Raw Water and/or After Sedimentation

High ozone demand

Disinfection byproducts

Biodegradable organics formation

Category IV

 Turbidity > 10 NTU

 Ozone Demand > 1mg/L

After Sedimentation and After First

Stage Filtration, if necessary

High ozone demand

Disinfection byproducts

Biodegradable organics formation

Source: DeMers and Renner, 1992.

For high quality water with direct filtration, the only practical ozone feed point is the raw water.

Category II (Table 3-7) water is characterized by low ozone demand and high turbidity. This water

quality indicates the presence of inorganic material, such as clay or silt particles. For ozone to be

most effective for Category II water disinfection, it should be added after either pre-sedimentation or

conventional sedimentation.

Raw water with low turbidity and high ozone demand (Category III, Table 3-7) contains dissolved

constituents, not suspended, that contribute to a high ozone demand. An example of this type of

water is a ground water containing bromide ion, iron, manganese, color, or organics. For this water

quality, ozone can be added to either the raw water or after sedimentation. If the water contains

organic constituents that become more biodegradable by ozonation, a biological treatment step (see
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Section 3.3.4) may be required. The presence of oxidizable organic constituents or bromide ion will

generate disinfection byproducts upon ozonation.

Category IV (Table 3-7) water would be considered the most difficult water to treat with ozone due

to its high turbidity and high ozone demand. An example of this water quality is surface water

containing high concentrations of organic material and inorganic particles. The most effective use of

ozone for this water quality is after sedimentation and possibly after filtration. If the water has an

extremely high ozone demand, dual ozone feed points may be required to achieve disinfection goals,

because the presence of large amounts of organic material may require a biological treatment step

and may generate disinfection byproducts.

3.3.3 Impact on Other Treatment Processes

Ozonation does have an impact on other processes at the water treatment facility. The impacts of

ozone addition include the following:

• The use of ozone generates biodegradable organic matter (BOM) that can result in biological

growth which may also increase corrosion rates in distribution systems if not removed by

biologically active filtration. When ozonation is placed before biological filters, it can impact the

filters by increasing biological growth and increasing backwash frequency.

• Ozone is a strong oxidant that reacts with other oxidants, such as chlorine, chlorine dioxide, and

monochloramine.

• Ozone oxidation of iron and manganese generates insoluble oxides that should be removed by

sedimentation or filtration. These insoluble oxides also impact the filters by increasing load on

the filters and increasing backwash frequency.

• Using pre- and/or internal ozone on most raw waters reduces the subsequent chlorine, chlorine

dioxide, or monochloramine demand of the finished water so as to allow a stable chlorinecompound residual to be maintained at a much lower level.

The reader is referred to EPA’s Simultaneous Compliance Guidance Document (expected to be

available in 1999) for additional information regarding the interaction between oxidants and other

treatment processes.

3.3.4 Biologically Active Filtration

Ozonation typically increases the biodegradability of NOM in water because many large organic

molecules are converted into smaller organic molecules that are readily biodegradable. This increase

in biodegradable dissolved organic carbon (BDOC) can lead to accelerated bacterial growth and

regrowth in the distribution system if not removed in the treatment plant. LeChevallier et al. (1992)

found that AOC levels less than 100 ppb may be necessary to control excessive bacterial regrowth in

the distribution system if not removed in the treatment plant.

When ozonation is placed upstream of filtration, and environmental conditions such as dissolved

oxygen, pH, and temperature are favorable, microbiological activity is increased in the filter and

BDOC/AOC removal is enhanced. Ozone addition not only increases the biodegradability of the
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dissolved organics, but also introduces large amounts of oxygen to the water, thus, creating an

excellent environment for biological growth on the filter media. The advantages of biologically

active filtration (Price, 1994) include the following which are all being met in most U.S. plants using

ozone:

• Production of a biologically stable water that does not promote excessive bacterial growth and

regrowth in the distribution system.

• Removal of NOM that can serve as precursors to byproduct formation as a result of residual

disinfection with free or combined chlorine.

• Ozone oxidation as a primary disinfectant prior to biologically active filtration reduces the

BDOC concentration in finished water, thus reducing chances of regrowth.

• Reduction of the residual disinfectant demand of the product water so that proposed regulations

limiting the maximum disinfectant residual can be met.

• Removal or control of ozonation byproducts.

Biological activity can be supported on slow sand, rapid rate, and GAC media because these media

provide a surface for bacteria to attach. Factors such as available surface area, hydraulic loading rate,

contact time, availability of nutrients, temperature, and others will determine the performance and

BDOC removal efficiency. Biomass develops to higher levels on GAC because of the rougher

surface characteristics than on anthracite and sand.

3.3.4.1 Slow Sand Filters

Ozone addition prior to slow sand filtration can increase the efficiency of TOC removal by about 35

percent (Rachwal et al., 1988; Zabel, 1985). Ozone addition can also increase the efficiency of

BDOC removal with slow sand filters (Eighmy et al., 1991; Malley et al., 1993).

3.3.4.2 Rapid Rate Filters

Research in the area of biologically active rapid rate filters has focused on the reduction of

assimilable organic carbon (AOC) instead of BDOC. While studies have shown rapid rate filtration,

employing either sand or dual media lowers AOC levels following ozonation, AOC does not measure

all the BDOC. AOC measures only that portion of the BDOC that is more easily assimilable or more

easily biodegradable under specific laboratory conditions by two specific microorganisms. Research

data shows that biodegradation of AOC can occur in rapid rate filters. The data should be viewed

with caution, since the more slowly biodegradable DOC, not measured by AOC, may be passing

through rapid rate filters.
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3.3.4.3 Granular Activated Carbon

GAC is made biologically active by the deliberate introduction of sufficient dissolved oxygen to

water just before passing through GAC columns (Katz, 1980). The high surface area and long

retention time in GAC provide an ideal environment to enhance biological growth.

Although ozone actually increases the amount of BDOC, the efficiency of subsequent biodegradation

on GAC can be such that the BDOC in GAC effluent is lower than the BDOC in the ozone influent

(Langlais et al., 1991). The degree to which biodegradable DOC is removed by ozone/GAC depends

upon the process conditions of temperature, amount of BDOC, and the GAC column loading rate,

measured by empty bed contact time (EBCT). For example, with an influent BDOC of 0.65 mg C/L

and a 10 minute EBCT, one would expect an effluent BDOC of 0.25 mg C/L. The effluent BDOC

then could be lowered by either:

• Adding ozone, which would increase the GAC influent BDOC and, therefore, lower the

effluent BDOC; or

• Adding more GAC or decreasing the loading rate, which would extend the EBCT and lower

the effluent BDOC (Billen et al., 1985, as cited in Langlais et al., 1991).

Huck et al. (1991) reported results from AOC profiles measured in a pilot treatment plant. The plant

treated Saskatchewan River water and included coagulation, flocculation, and sedimentation prior to

ozonation. Following ozonation, the water was filtered through a dual media (anthracite-sand) filter

followed by GAC adsorption. The results demonstrate:

• Variable AOC removal through coagulation, flocculation, and sedimentation (80 percent to

zero);

• Increased AOC after ozonation;

• AOC removal through dual media filtration improving at lower hydraulic loading rates and

filtered effluent AOC often less than raw water AOC, but highly variable; and

• AOC levels after GAC were low, almost always below raw water AOC concentrations and

adsorption appears to contribute to some immediate AOC removal.

3.3.5 Pathogen Inactivation and Disinfection Efficacy

Ozone has a high germicidal effectiveness against a wide range of pathogenic organisms including

bacteria, protozoa, and viruses. Because of its high germicidal efficiency, ozone can be used to meet

high inactivation required by water treatment systems with or without filters. However, ozone

cannot be used as a secondary disinfectant because the ozone residual decays too rapidly. The ozone

disinfection efficiency is not affected by pH (Morris, 1975), although because of hydroxyl free

radicals and rapid decay, efficiency is the same but more ozone should be applied at high pH to

maintain “C”.
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3.3.6 Inactivation Mechanisms

Inactivation of bacteria by ozone is attributed to an oxidation reaction (Bringmann, 1954; Chang,

1971). The first site to be attacked appears to be the bacterial membrane (Giese and Christensen,

1954) either through the glycoproteins or glycolipids (Scott and Lesher, 1963) or through certain

amino acids such as typtophan (Goldstein and McDonagh, 1975). In addition, ozone disrupts

enzymatic activity of bacteria by acting on the sulfhydryl groups of certain enzymes. Beyond the cell

membrane and cell wall, ozone may act on the nuclear material within the cell. Ozone has been

found to affect both purines and pyrimidines in nucleic acids (Giese and Christensen, 1954; Scott and

Lesher, 1963).

The first site of action for virus inactivation is the virion capsid, particularly its proteins (Cronholm et

al., 1976 and Riesser et al., 1976). Ozone appears to modify the viral capsid sites that the virion uses

to fix on the cell surfaces. High concentrations of ozone dissociate the capsid completely. One

researcher found that the mechanism of ozone inactivation of bacteriophage f2 ribonucleic acid

(RNA) included releasing RNA from the phage particles after the phage coat was broken into many

pieces (Kim et al., 1980). This finding suggests that ozone breaks the protein capsid, thereby

liberating RNA and disrupting adsorption to the host pili. Further, the naked RNA may be

secondarily inactivated by ozone at a rate less than that for RNA within the intact phage. The

mechanism for inactivation of deoxyribonucleic acid (DNA) bacteriophage T4 has been found to be

quite similar to RNA inactivation: ozone attacks the protein capsid, liberates the nucleic acid, and

inactivates the DNA (Sproul et al., 1982). In contrast, more recent work on the tobacco mosaic virus

(TMV) shows that ozone has a specific effect on RNA. Ozone was found to attack both the protein

coat and RNA. The damaged RNA cross-links with amino acids of the coat protein subunits. The

authors concluded that TMV loses its infectivity because of its loss of protein coating.

Microscopic observation of inactivation of trophozoites of Naegleria and Acanthamoeba showed that

they were rapidly destroyed and the cell membrane was ruptured (Perrine et al., 1984). Perrine and

Langlais showed that ozone affect the plugs in Naegleria gruberi cysts (Langlais and Perrine, 1984).

Depending on the ozonation conditions, these plugs were completely removed or were partially

destroyed. It has been speculated that ozone initially affects the Giardia muris cysts wall and makes

it more permeable (Wickramanayake, 1984c). Subsequently, aqueous ozone penetrates into the cyst

and damages the plasma membranes, additional penetration of ozone eventually affects the nucleus,

ribosomes, and other ultrastructural components.

3.3.7 Disinfection Parameters

Hoigné and Bader demonstrated that the rate of decomposition of ozone is a complex function of

temperature, pH, and concentration of organic solutes and inorganic constituents (Hoigné and Bader,

1975, and 1976). The following sections describe the effects that pH, temperature, and suspended

matter have on the reaction rate of ozone and pathogen inactivation.
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The ability to maintain a high aqueous ozone concentration is critical from a regulatory disinfection

compliance standpoint. This means that factors that accelerate ozone decomposition are undesirable

for inactivation because the ozone residual dissipates faster and therefore reduces the CT credit,

requiring a corresponding increase in the ozone applied, thus increasing cost.

3.3.7.1 pH

Studies have indicated that pH has little effect on the ability of dissolved ozone residuals to inactivate

acid-fast bacteria, such as Mycobacteria and Actinomycetes (Farooq, 1976). A slight decrease has

been found in the virucidal efficacy of ozone residuals as pH decreased (Roy, 1979). However, the

opposite effect was observed by Vaughn et al. (1987) (cited in Hoff, 1986). Changes in disinfection

efficacy with variations in pH appear to be caused by the ozone decomposition rate. Ozone

decomposition occurs faster in higher-pH aqueous solutions and forms various types of oxidants with

differing reactivities (Langlais et al., 1991). Tests carried out at constant ozone residual

concentration and different pH values showed that the degree of microorganism inactivation

remained virtually unchanged (Farooq et al., 1977). More recent studies have indicated decreased

virus inactivation by ozone at alkaline pH (pH 8 to 9) for poliovirus 1 (Harakeh and Butler, 1984)

and rotaviruses SA-11 and Wa (Vaughn et al., 1987).

Inactivation of Giardia muris cysts was found to improve when the pH increased from 7 to 9

(Wickramanayake, 1984a). This phenomenon was attributed to the possible changes in cyst

chemistry making it easier for ozone to react with the cyst constituents at the higher pH levels.

However, the same study found that inactivation of Naegleria gruberi cysts was slower at a pH 9

than at lower pH levels, thereby indicating that pH effects are organism-specific.

3.3.7.2 Temperature

As temperature increases, ozone becomes less soluble and less stable in water (Katzenelson et al.,

1974); however, the disinfection and chemical oxidation rates remain relatively stable. Studies have

shown that although increasing the temperature from 0 to 30oC can significantly reduce the solubility

of ozone and increases its decomposition rate, temperature has virtually no effect on the disinfection

rate of bacteria (Kinman, 1975). In other words, the disinfection rate was found to be relatively

independent of temperature at typical water treatment plant operating temperatures despite the

reduction in solubility and stability at higher temperatures.

3.3.7.3 Suspended Matter

Ozone inactivation of viruses and bacteria contained in aluminum floc (in the size range comparable

to those that could typically escape filtration) was not reduced at floc turbidity levels of 1 and 5 NTU

(Walsh et al., 1980). This study demonstrated that the microorganisms received no protection from

the aluminum floc. Similar results have been obtained for poliovirus 1, coxsackie virus A9, and E.

coli associated with bentonite clay (Boyce et al., 1981). However, adsorption of the f2 bacteriophage

at 1 and 5 NTU of bentonite clay was found to retard the rate of inactivation of ozone (Boyce et al.,

1981).
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In some instances, river waters heavily polluted with organic matter were ozonated, and the results

indicated a degradation of large organic molecules into fragments more easily metabolized by

microorganisms. This fragmentation coupled with the inability of ozone to maintain an active

concentration in the distribution system, has led to increased slime growth and, consequently, water

quality deterioration during distribution (Troyan and Hanson, 1989).

3.3.8 Inactivation of Microorganisms

The following sections contain a description of the disinfection efficiency of ozone in terms of

bacteria, virus, and protozoa inactivation.

3.3.8.1 Bacterial Inactivation

Ozone is very effective against bacteria. Studies have shown the effect of small concentrations of

dissolved ozone (i.e., 0.6 μg/L) on E. coli. (Wuhrmann and Meyrath, 1955) and Legionella

pneumophila (Domingue, et al., 1988). E. coli. levels were reduced by 4 logs (99.99 percent

removal) in less than 1 minute with a ozone residual of 9 μg/L at a temperature of 12oC. Legionella

pneumophila levels were reduced by greater than 2 logs (99 percent removal) within a minimum

contact time of 5 minutes at a ozone concentration of 0.21 mg/L. Results similar to those obtained

for E. coli. have been found for Staphyloccus sp. and Pseudomonas fluorescens inactivation.

Streptococcus faecalis required a contact time twice as long with the same dissolved ozone

concentration, and Mycobacterium tuberculosis required a contact time six times as long for the same

reduction level as E. coli.

In regard to vegetative bacteria, E. coli is one of the most sensitive types of bacteria. Furthermore,

significant difference has been found among all the Gram-negative bacillae, including E. coli and

other pathogens such as Salmonella, which are all sensitive to ozone inactivation. whereas the Grampositive cocci (Staphyloccus and Streptococcus), the Gram-positive bacillae (Bacillus), and the

Mycobacteria are the most resistant forms of bacteria. Sporular bacteria forms are always far more

resistant to ozone disinfection than vegetative forms (Bablon, et al., 1991), but all are easily

destroyed by relatively low levels of ozone.

3.3.8.2 Protozoa Inactivation

Protozoan cysts are much more resistant to ozone and other disinfectants than vegetative forms of

bacteria and viruses. Giardia lamblia has a sensitivity to ozone that is similar to the sporular forms

of Mycobacteria. Both Naegleria and Acanthamoeba cysts are much more resistant to ozone (and all

other disinfectants) than Giardia cysts. (Bablon et al., 1991). CT products for 99 percent inactivation

of Giardia lamblia and N. gruberi at 5oC were 0.53 and 4.23 mg • min/L, respectively

(Wickramanayake et al., 1984a and 1984b). Data available for inactivation of Cryptosporidium

oocysts, suggest that among protozoans, this microorganism is more resistant to ozone (Peeters et al.,

1989; Langlais et al., 1990). One study found that Cryptosporidium oocysts are approximately 10

times more resistant to ozone than Giardia (Owens et al., 1994).
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3.3.8.3 Virus Inactivation

Typically, viruses are more resistant to ozone than vegetative bacteria but less resistant than sporular

forms of Mycobacteria (Bablon, et al., 1991). The most sensitive forms of viruses are phages, and

there seems to be little difference between the polio- and coxsackie viruses. The sensitivity of human

rotavirus to ozone was determined to be comparable to that of Mycobacteria and polio- and

coxsackie viruses (Vaughn et al., 1987).

Keller et al. (1974) studied ozone inactivation of viruses by using both batch tests and pilot plant

data. Inactivation of poliovirus 2 and coxsackie virus B3 was more than 3 logs (99.9 percent) in the

batch tests with an ozone residual of 0.8 mg/L and 1.7 mg/L and a contact time of 5 minutes. Greater

than 5 log (99.999 percent) removal of coxsackie virus was achieved in the pilot plant with an ozone

dosage of 1.45 mg/L, which provided an ozone residual of 0.28 mg/L in lake water.

3.3.8.4 CT Curves for Giardia Lamblia

CT values shown in Figure 3-9 are based on disinfection studies using in vitro excystation of Giardia

lamblia. CT values obtained at 5oC and pH 7 were used as the basis for deriving the CT values at

other temperatures. A safety factor of 2 has been applied to the values shown in Figure 3-9.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

5 10 15 20 25

Temperature (°C)

CT Product (mg min/L)

0.5-log Inactivation

1-log Inactivation

1.5-log Inactivation

2-log Inactivation

2.5-log Inactivation

3-log Inactivation

Figure 3-9. CT Values for Inactivation of Giardia Cysts by Ozone (pH 6 to 9)
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CT values shown in Figure 3-10 for achieving 2-log inactivation of viruses were determined by

applying a safety factor of 3 to data obtained from a previous study on poliovirus 1 (Roy et al.,

1982). CT values for 3 and 4-log removal were derived by applying first order kinetics and assuming

the same safety factor of 3. Data obtained at a pH of 7.2 was assumed to apply for the pH range of 6

to 9.

Several research groups have investigated the efficiency of ozone for Cryptosporidium oocyst

inactivation. Table 3-8 summarizes CT values obtained for 99 percent inactivation of

Cryptosporidium oocysts. Results indicate that ozone is one of the most effective disinfectants for

controlling Cryptosporidium (Finch, et al., 1994) and that Cryptosporidium muris may be slightly

more resistant to ozonation than Cryptosporidium parvum (Owens et al., 1994). A wide range of CT

values has been reported for the same inactivation level, primarily because of the different methods

of Cryptosporidium measurements employed and pH, temperature, and above all, ozonation

conditions.

0

0.2

0.4

0.6

0.8

1

1.2

5 10 15 20 25

Temperature (°C)

CT Product (mg min/L)

2-log Inactivation

3-log Inactiviation

4-log Inactivation

Figure 3-10. CT Values for Inactivation of Viruses by Ozone (pH 6 to 9)
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Table 3-8. Summary of Reported Ozonation Requirements for 99 Percent

Inactivation of Cryptosporidium Oocycts

Species

Ozone

protocol

Ozone

residual

(mg/L)

Contact time

(min)

Temperature

(

oC)

CT

(mg.min/L) Reference

C. baileyi Batch liquid,

modified batch

ozone

0.6 & 0.8 4 25 2.4 - 3.2 Langlais et al.,

1990

C. muris Flow through

contactor,

continuous gas

22 - 25 7.8 Owens et al.,

1994

C. parvum Batch liquid,

batch ozone

0.50

0.50

18

7.8

7

22

9.0

3.9

Finch et al.,

1993

C. parvum Batch liquid,

batch ozone

0.77

0.51

6

8

Room 4.6

4

Peeters et al.,

1989

C. parvum Batch liquid,

continuous gas

1.0 5 & 10 25 5 - 10 Korich et al.,

1990

C. parvum Flow through

contactor,

continuous gas

22 - 25 5.5 Owens et al.,

1994

Ozone dose and contact time (CT) requirements for the inactivation of Cryptosporidium oocysts in

drinking water when using ozone has not been established similar to the CT values for viruses and

Giardia cyst inactivation. Inactivation requirements (log removals) for Cryptosporidium oocysts

have not been established. In addition, as shown in Table 3-8, the CT requirements reported in the

literature vary from study to study which adds uncertainty to design CT requirements for specific

applications or regulatory needs.

3.4 Ozonation Disinfection Byproducts

Ozone does not form halogenated DBPs (TTHMs and HAA5s) when participating in

oxidation/reduction reactions with NOM but it does form a variety of organic and inorganic

byproducts. Table 3-9 and Figure 3-11 show the principal known byproducts associated with

ozonation. However, if bromide ion is present in the raw water halogenated DBPs may be formed.

These brominated DBPs appear to pose a greater health risk than non-brominated DBPs.
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Table 3-9. Principal Known Byproducts of Ozonation

Disinfectant Byproducts

Aldehydes Aldo- and Ketoacids

Formaldehyde Pyruvic acid

Acetaldehyde Brominated Byproducts*

Glyoxal Bromate ion

Methyl Glyoxal Bromoform

Acids Brominated acetic acids

Oxalic acid Bromopicrin

Succinic acid Brominated acetonitriles

Formic acid Others

Acetic acid Hydrogen peroxide

*Brominated byproducts are produced only in waters containing bromide ion

Source: Singer, 1992.

Although ozone is an effective oxidant and disinfectant, it should not be relied upon as a secondary

disinfectant to maintain a residual in the distribution system. Monochloramine is attractive for this

purpose because it produces little to no halogenated DBPs. Chlorine is a candidate for secondary

disinfectant but the ozonated water may actually produce either more or less DBPs following the

addition of free chlorine depending on the nature of the organic material following ozonation unless

biologically active filtration precedes the addition of chlorine. The principal benefit of using ozone

for controlling DBP formation is that it allows free chlorine to be applied later in the treatment

process after precursors have been removed and at lower doses, thereby reducing DBPFP.

Aldehydes and

Oxidized Organics

O3

HOBr H+ + OBr Br -

-

pKa = 8.7 @ 25oC

Organic Precursors

NH3

Organic

Precursors

O3 + OBrNH2Br, NHBr2

Brominated

Organic DBPs

BrO3

-

Figure 3-11. Principal Reactions Producing Ozone Byproducts

Application of a secondary disinfectant following ozonation requires special consideration for

potential interaction between disinfectants. For example, chloral hydrate formation has been
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observed when using chlorine as a secondary disinfectant with ozone (McKnight and Reckhow,

1992; Logsdon et al., 1992). The ozonation byproduct of acetaldehyde is a known precursor for

chloral hydrate, a byproduct of chlorination. Enhancement of chloral hydrate has not been observed

when monochloramine is applied as the secondary disinfectant, or if biologically active filtration is

used following ozonation and prior to chlorination (Singer, 1992). Chloropicrin formation from free

chlorine appears to be enhanced by pre-ozonation (Hoigné and Bader, 1988) in the absence of

biologically active filtration prior to addition of chlorine.

Byproducts such as aldehydes, ketones, acids, and others will be formed upon ozonation of water.

The primary aldehydes that have been measured are: formaldehyde, acetaldehyde, glyoxal, and

methyl glyoxal (Glaze et al., 1991). Total aldehyde concentration in drinking water disinfected with

ozone range from less than 5 μg/L to 300 μg/L, depending on the TOC concentration and the applied

ozone to organic carbon ratio (Van Hoof et al., 1985; Yamada and Somiya, 1989; Glaze et al., 1989a;

Krasner et al., 1989; Glaze et al., 1991; LeLacheur et al., 1991). Aldehydes with higher molecular

weights have also been reported (Glaze et al., 1989b). Other organic byproducts of ozonation are

indicated in Table 3-9

Ozonation of a source water containing bromide ion can produce brominated byproducts, the

brominated analogues of the chlorinated DBPs. Song et al. (1997) found that bromate ion formation

is an important consideration for waters containing more than 0.10 mg/L bromide ion. These

brominated byproducts include bromate ion, bromoform, the brominated acetic acids and

acetonitriles, bromopicrin, and cyanogen bromide (if ammonia is present). An ozone dose of 2 mg/L

produced 53 μg/L of bromoform and 17 μg/L of dibromoacetic acid in a water containing 2 mg/L of

bromide ion (McGuire et al., 1990). Ozonation of the same water spiked with 2 mg/L bromide ion

showed cyanogen bromide formation of 10 μg/L (McGuire et al., 1990). Furthermore, ozone may

react with the hypobromite ion to form bromate ion (Amy and Siddiqui, 1991; Krasner et al., 1993), a

probable human carcinogen (Regli et al., 1992). Bromate ion concentrations in ozonated water up to

60 μg/L have been reported (Amy and Siddiqui, 1991; Krasner et al., 1993). Note that the amount of

bromide ion incorporated into the measured DBPs accounts for only one-third of the total raw water

bromide ion concentration. This indicates that other brominated DBPs exist that are not yet

identified (Krasner et al., 1989; MWDSC and JMM, 1992). Figure 3-12 shows the major pathways

for bromate ion formation.
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B r O 2

−

Direct-Indirect Indirect- Direct Direct

HOBr / BrO -

O3

O3

O3

O3

O3

O3

BrO -

O3

Br -

HO• HO •

Disproportionation

Disproportionation

BrO • Br

− BrO 3

B r O 2

−

B r O 2

− BrO •

B r O 3

−

B r O 3

−

Source: Song et al., 1997.

Figure 3-12. Main Pathways of Bromate Ion Formation when Ozone Reacts

with Bromide Ion

3.4.1 Ozone Byproduct Control

The primary factors affecting the speciation and concentrations of brominated byproducts are pH and

the ozone-to-bromide ion and TOC-to-bromide ion ratios (Singer, 1992). Bromate ion formation can

be controlled by ozonation at acidic pH values of which hypobromous acid dominates over the now

absent hypobromite ion (Haag and Hoigné, 1984; Amy and Siddiqui, 1991; Krasner et al., 1993).

Conversely, under alkaline pH conditions, ozone can oxidize the hypobromous acid further to

produce bromate ion. At low pH values, the brominated organic byproducts are favored, while at

greater pH values, bromate ion formation is favored. Therefore, the application of ozone may be

limited for source waters containing bromide ion. Bromate ion formation can be controlled by

lowering the ambient bromide ion concentration, lowering the ozone residual, and lowering the

ozonation pH. The addition of ammonia with ozonation to form bromamines reduces the formation

of both bromate ion and organic byproducts (Amy and Siddiqui, 1991; MWDSC and JMM, 1992).

However, ammonia can act as a nutrient for nitrifying bacteria.
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The organic acid and aldehyde byproducts of ozonation discussed above appear to be readily

biodegradable and are a component of the assimilable organic carbon (AOC) or biodegradable

organic carbon (BDOC). Ozonation increases the BOM by oxidation. Therefore, if water disinfected

with ozone is coupled with a biologically active process (i.e., biological active carbon), removal of

these biodegradable byproducts can be reduced. The use of biologically active filters, maintained by

discontinuing the application of a disinfectant to the filters, has been shown to successfully remove

aldehydes and other compounds representing a portion of the BDOC in a water (Bablon et al., 1988;

Rittman, 1990; Reckhow et al., 1992). See Section 3.3.4 for a detailed discussion on biological

active filters.

A recent study has shown that bromate ion and brominated organics can be controlled during

ozonation by the following techniques (Song et al., 1997):

• Low pH decreases bromate ion formation while increasing brominated organic formation;

• Ammonia addition with short ozone contact time decreases both bromate ion and brominated

organic formation;

• Hydrogen peroxide decreases brominated organic formation and may increase or decrease

bromate ion formation, depending on other water quality parameters; and

• Low ozone DOC ratio leads to low bromate ion and brominated organic formation.

3.5 Status of Analytical Methods

During operation of an ozonation system it is necessary to analyze for ozone in both the liquid and

gas phase to determine the applied ozone dose, ozone transfer efficiency and (for primary

disinfection) residual ozone level. The gas stream exiting the ozone generator is monitored for ozone

content to determine the applied ozone dose. The off-gas exiting the ozone contactor is monitored to

determine the amount of ozone transferred to the liquid phase in the contactor and to calculate the

ozone transfer efficiency. The disinfected water exiting the ozone contactor is monitored for residual

ozone to ensure that CT values are met.

In addition, the ambient air in any ozone generating or handling room and ozone destruct off-gas are

monitored for ozone concentration to protect workers in the event of leakages or destruct system

failure.

3.5.1 Monitoring of Gas Phase Ozone

Points in an ozone treatment system where gas-phase ozone is monitored include:

• Ozone generator output;

• Contactor off-gas;

• Ozone destruct off-gas; and
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• Ambient air in ozone process areas.

The range of ozone concentrations to be measured in the gas phase varies from less than 0.1 ppm by

volume (0.2 mg/m3 NTP) in ambient air and ozone destruct off-gas, to 1 to 2 percent (10 g/m3 NTP)

in contactor off-gas, to as high as 15 percent by weight (200 g/m3 NTP) in the ozone generator

output.

Analytical methods for monitoring gas-phase ozone include:

• UV absorption;

• Iodometric methods;

• Chemiluminescence; and

• Gas-Phase titration.

Table 3-10 presents the working range, expected accuracy and precision, operator skill level

required, interferences, and current status for gas phase ozone analysis.

3.5.1.1 UV Absorption

Gaseous ozone absorbs light in the short UV wavelength region with a maximum absorbance at

253.7 nm (Gordon et al., 1992). Instruments for measuring ozone by the absorption of UV radiation

are supplied by several manufacturers for gas concentrations below 0.5 ppm by volume (1 g/m3

NTP). In general, these instruments measure the amount of light absorptions when no ozone is

present and the amount of light absorptions when ozone is present. The meter output is the difference

of the two readings, which is directly related to the actual amount of ozone present. The International

Ozone Association (IOA) has accepted this procedure (IOA, 1989).
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Table 3-10. Characteristics and Comparisons of Gas-Phase Ozone Analytical Methods

Type of Test

Working

Range

(mg/L)

Expected

Accuracy

(± %)

Expected

Precision

(± %) Skill LevelaInterferences pH Range Field Test

Automated

Test Current Status

UV Absorption 0.5 - 50,000 2 2.5 1/2 None NA Yes Yes Recommended

Stripping Absorption

Iodometry

0.5 - 100 1 - 35 1 - 2 2 SO2, NO2 NA Yes No Not Recommended

Chemiluminescence 0.005 - 1 7 5 1/2 None NA Yes Yes Recommended

Gas-Phase Titration 0.005 - 30 8 8.5 2 None NA Yes No Not Recommended

Source: Gordon et al., 1992.

Notes: a Operator Skill Levels: 1 = minimal, 2 = good technician, 3 = experienced chemist. NA = Not Applicable
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3-34

3.5.1.2 Iodometric Methods

Iodometric procedures have been used for all of the ozone concentration ranges encountered in water

treatment plants (Gordon et al., 1992). This includes measurement of ozone directly from the

generator and of ozone as stripped from aqueous solution. For the iodometric method, the ozonecontaining gas is passed into an aqueous solution containing excess potassium iodide.

All other oxidizing materials act as interferences with iodometry (Gordon et al., 1992). Nitrogen

oxides (that may be present when ozone is generated in air) also act as interferences to iodometric

methods. The effects of nitrogen oxides may be eliminated by passing the ozone-containing gas

through absorbents such as potassium permanganate that are specific for nitrogen oxide gases.

However, no iodometric method is recommended for the determination of ozone in solution because

of the unreliability of the method (Gordon et al., 1989).

3.5.1.3 Chemiluminescence

Chemiluminescence methods can be used for the determination of low concentrations of ozone in the

gas phase (Gordon et al., 1992). One of the most commonly used methods is ethylene

chemiluminescence. Gas-phase ozone can be measured using the chemiluminescent reaction between

ethylene and ozone. This method is specific to ozone and is suitable for measurement of ozone in the

ambient air. The ethylene chemiluminescence procedure was adopted in 1985 by the EPA as its

reference method for determining ozone in the ambient atmosphere (McKee et al., 1975).

Chemiluminescent instruments are approved by the EPA for monitoring ambient ozone

concentrations of 0 to 0.5 or 0 to 1.0 ppm by volume. With regular calibration, this type of

instrument is capable of providing reliable analysis of any ozone in the ambient air from an

ozonation plant.

An alternative to ethylene chemiluminescence is rhodamine B/gallic acid chemiluminescence, which

avoids the handling of ethylene (Gordon et al., 1992). This alternative method is considerably more

complex than the more common ethylene chemiluminescence instruments. The sensitivity of this

method tends to drift and a procedure has been developed by which corrections are made for the

sensitivity on a frequent basis (Van Dijk and Falkenberg, 1977). Given the wide availability of

ethylene chemiluminescence monitors and their approval by EPA, ethylene monitors should be

considered before rhodamine B/gallic acid monitors.

3.5.1.4 Gas-Phase Titration

Two gas-phase titration methods have been studied as possible calibration methods for ambient

ozone analyzers and monitors (Gordon et al., 1992). These procedures are based on titration with

nitric oxide and back titration of excess nitric oxide (Rehme et al., 1980). These gas phase titration

procedures, evaluated by EPA, were compared with UV absorption and iodometry as calibration

methods for ethylene chemiluminescent ambient air ozone analyzers. As a result of these

comparisons, UV absorption has been specified as the method of calibration for ambient ozone
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analyzers. Therefore, gas-phase titration methods are not recommended for use at ozonation facilities

(Gordon et al., 1992).

3.5.2 Monitoring of Liquid Phase Residual Ozone

There are numerous methods for monitoring ozone in aqueous solutions. Gordon et al. (1992)

recommended the following methods for analyzing residual ozone:

• Indigo colorimetric method;

• Acid chrome violet K (ACVK) method;

• Bis-(Terpyridine) iron(II) method; and

• Stripping into the gas-phase.

Table 3-11 shows the working range, expected accuracy and precision, operator skill level required,

interferences and current status for liquid phase residual ozone analytical methods.

3.5.2.1 Indigo Colorimetric Method

The indigo colorimetric method is the only method for monitoring residual ozone in Standard

Methods, 1995. The indigo colorimetric method is sensitive, precise, fast, and more selective for

ozone than other methods. There are two indigo colorimetric methods: spectrophotometric and

visual. For the spectrophotometric procedure the lower limit of detection is 2 μg/L, while for the

visual procedure the detection limit is 10 μg/L.

Hydrogen peroxide, chlorine, manganese ions, ozone decomposition products, and the products of

organic ozonation exhibit less interference with the indigo colorimetric method than any of the other

methods (Langlais et al., 1991). However, the masking of chlorine in the presence of ozone can make

the indigo method problematic. In the presence of hypobromous acid, which forms during ozonation

of bromide-ion containing methods, an accurate measurement cannot be made with this method

(Standard Methods, 1995).
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3-36

Table 3-11. Characteristics and Comparisons of Residual Ozone Analytical Methods

Type of Test

Working

Range

(mg/L)

Expected

Accuracy

(± %)

Expected

Precision

(± %)

Skill

LevelaInterferences pH Range

Field

Test

Automated

Test Current Status

Indigo Colorimetric,

Spectrophotometric

0.01 -

> 0.3

1 0.5 1 Chlorine, Manganese ions,

Bromine, Iodine

2 No Yes Recommended

Indigo Colorimetric,

Visual

0.01 -

> 0.1

1 0.5 1 Chlorine, Manganese ions,

Bromine, Iodine

2 No Yes Recommended

ACVK 0.05 - 1 NR NR 1 Manganese ions > 1 mg/L,

Chlorine > 10 mg/L

2 No No Recommended

Bis-(Terpyridine) Iron(II) 0.05 - 20 2.7 2.1 3 Chlorine < 7 No Yes Recommended

Lab Test

Source: Gordon et al., 1992.

Notes: a Operator Skill Levels: 1 = minimal, 2 = good technician, 3 = experienced chemist. NR = Not reported in literature cited by referenced source.
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3.5.2.2 ACVK Method

ACVK is readily bleached by ozone, which serves as the basis for this spectrophotometric procedure

first reported by Masschelein (1977). The procedure has been developed further for the measurement

of ozone in the presence of chlorine (Ward and Larder, 1973).

The advantages of this method (Langlais et al., 1991) are:

• Its ease of execution and stability of the dye reagent solution;

• A linear calibration curve over the range of 0.05 to 1.0 mg/L of ozone; and

• The apparent lack of interferences from low levels of manganese, chlorine or combined

chlorine (up to 10 mg/L), organic peroxides, and other organic oxidation products.

3.5.2.3 Bis-(Terpyridine)Iron(II) Method

Bis-(Terpyridine)Iron(II) in dilute hydrochloric acid solution reacts with ozone to change the

absorbance spectra measured at 552 nm (Tomiyasu and Gordon, 1984). The only known interferent

is chlorine. However, chlorine interferences can be masked by the addition of malonic acid.

Alternatively, since the reaction between chlorine and the reagent is slower than the reaction with

ozone, the spectrophotometric measurements can be carried out immediately after reagent mixing to

reduce the chlorine interference. Chlorine dioxide does not interfere (Gordon et al, 1992).

The primary advantages of the Bis-(Terpyridine)Iron(II) Method are its lack of interferences, low

limits of detection (4 μg/L), broad working range (up to 20 mg/L), excellent reproducibility, and

agreement with the indigo colorimetric method.

3.5.2.4 Stripping into the Gas-Phase

In this indirect procedure, residual ozone is stripped from the solution using an inert gas. The amount

of ozone present in the gas phase is then analyzed by gas-phase analytical methods such as UV

absorption or chemiluminescence described previously. This stripping technique was developed to

minimize the complications caused by the presence of other oxidants in solution.

The success of this procedure initially depends upon the ability to strip ozone from the treated water

without any decomposition. Since stripping conditions such as temperature, pH, and salinity can

vary, the reliability of this method is suspect (Langlais et al., 1991).

3.5.3 Bromate Monitoring for Systems Using Ozone

The DBPR requires that community water systems and non-transient non-community water systems that

use ozone for disinfection or oxidation must monitor their system for bromate. These systems are

required to take one sample per month for each treatment plant with samples collected at the entrance to

the distribution system while the ozonation system is operating under normal conditions.
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The DBPR provides reduced monitoring opportunities (i.e., quarterly rather than monthly samples) if the

system demonstrates that the average source water bromide concentration is less than 0.05 mg/L based

upon representative monthly bromide measurements for one year. Systems can remain on the reduced

monitoring schedule until the running annual average source water bromide concentration, computed

quarterly, is equal to or greater than 0.05 mg/L based upon representative monthly measurements.

For compliance monitoring for bromate, systems must use the ion chromatography analytical method as

specified in USEPA Method 300.1, Determination of Inorganic Anions in Drinking Water by Ion

Chromatography, Revision 1.0 (USEPA, 1997).

If the average of samples covering any consecutive four-quarter period exceeds the MCL, the system is in

violation of the MCL and must notify the public pursuant to 40 CFR §141.32. The system must also

report to the State pursuant to 40 CFR §141.134. If the system fails to complete 12 consecutive months'

monitoring, compliance with the MCL for the last four-quarter compliance period must be based on an

average of the available data.

3.6 Operational Considerations

3.6.1 Process Considerations

Because ozone is such a strong oxidant, it will react with many organic and inorganic compounds

present in the water. Ozone is used to remove tastes and odors by breaking down organic

compounds, and to aid in the removal of iron and manganese by oxidizing these compounds to less

soluble forms. These demands should be satisfied before any ozone is available to satisfy primary

disinfection requirements. The presence and concentration of these compounds can dictate the

location of ozone addition, depending on the process goals.

Stolarik and Christie (1997) present the results of 10 years of operation at the 600 mgd Los Angeles

Aqueduct Filtration and Ozone Facility. Operational experiences at this facility showed lower

particle counts (greater than one micron) with ozone use. The optimum ozone concentration in the

gas phase applied was found to be 6 percent when using the cryogenic oxygen production facilities,

and 4 to 5 percent when using liquid oxygen (LOX).

3.6.2 Space Requirements

Storage of LOX is subject to regulations in building and fire codes. These regulations will impact the

space requirements and may dictate the construction materials of adjacent structures if the certain

setback requirements cannot be met. In general, the footprint for ozone generated from air is smaller

than that required for chloramination and chloride dioxide applications. However, the footprint area

for ozone generated from pure oxygen is comparable to that of chlorine dioxide because of the

additional area needed for storage.
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3.6.3 Material Selection

Ozone-resistant materials should be used from the ozone generators through the off-gas destruct unit.

If oxygen is used for the feed gas, oxygen resistant materials should be used up to the generators.

Pure oxygen piping should be specially cleaned after installation for oxygen service, which increases

construction cost. Materials for air preparation systems can be those normally used for compressed

air systems. Langlais et al. (1991) recommended that piping beyond the desiccant dryers be ozoneresistant, as some backflow and ozone diffusion can occur. If a receiver is provided following the

desiccant dryer, the piping should be ozone-resistant, downstream of the pressure regulator. Ozoneresistant (oxygen resistant as well if high purity oxygen is the feed gas) check valves should be

placed in the piping ahead of the generator.

Ozone-resistant materials include the austenitic (300 series) stainless steels, glass and other ceramics,

Teflon and Hypalon, and concrete. The 304 series stainless steels can be used for “dry” ozone gas

(also for oxygen), 316 series should be used for “wet” service. Wet service includes piping in the

contactors and all off-gas piping and the off-gas destruct unit. Teflon or Hypalon should be used for

gasket materials. Concrete should be manufactured from Type II or Type IV cement. Typical

practice in the United States is to provide 3 inches of cover for reinforcing to prevent corrosion by

either ozone gas or ozone in solution, although Fonlupt (1979) reports that 4 cm (1.13 inches) is

adequate for protection. Hatches for access into contactors should be fabricated from 316 series

stainless steels and provided with ozone-resistant seals.

3.6.4 Ozone System Maintenance

Stolarik and Christie (1997) provide a good overview of the operational and maintenance

requirements during the 10 years of operating the 600 mgd Los Angeles Aqueduct Filtration and

Ozone Plant. The ozone system has been available 97.1 percent of the time over the 10 year period.

Fuse failure and generator cleaning comprised the major maintenance chores on the ozone generators

during the first years. Fuse failure was caused by a malfunction when its glass dielectric tube failed.

Vessels are cleaned every three years or when exit gas temperatures rise due to Fe3O4 deposits on the

ground electrode/heat exchanger surfaces.

Rod shaped ceramic diffusers worked well as ozone diffusers for the initial two years. These were

replaced by sintered stainless steel and ultimately a modified ceramic diffuser.

3.6.5 Ozone Safety

Concern for safety even at the risk of being overcautious, would be to follow practices that have been

successfully applied to other oxidants over the years. This would be to generally isolate the

ozonation system from the remainder of the plant. This should not be interpreted to mean a separate

building, but rather separate rooms, separate exterior entrances, separate heating and ventilation

systems, noise control, etc. This method already is manifested in some of the European ozonation

plants, but on a lesser scale.
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Ozone generators should be housed indoors for protection from the environment and to protect

personnel from leaking ozone in the case of a malfunction. Ventilation should be provided to prevent

excess temperature rise in the generator room, and to exhaust the room in the case of a leak.

Adequate space should be provided to remove the tubes from the generator shell and to service the

generator power supplies. Air prep systems tend to be noisy; therefore, it is desirable to separate

them from the ozone generators. Off-gas destruct units can be located outside if the climate is not

too extreme. If placed inside, an ambient ozone detector should be provided in the enclosure. All

rooms should be properly ventilated, heated, and cooled to match the equipment-operating

environment.

Continuous monitoring instruments should be maintained to monitor levels of ozone in the rooms.

Self-contained breathing apparatuses should be located in hallways outside the rooms liable to ozone

hazards. Ambient ozone exposure levels, which have been proposed by appropriate U.S.

organizations, are summarized below. The maximum recommended ozone levels are as follows:

• Occupational Safety and Health Administration. The maximum permissible exposure to

airborne concentrations of ozone not in excess of 0.1 mg/L (by volume) averaged over an eighthour work shift.

• American National Standards Institute/American Society for testing Materials

(ANSI/ASTM). Control occupational exposure such that the worker will not be exposed to

ozone concentrations in excess of a time weighted average of 0.1 mg/L (by volume) for eight

hours or more per workday, and that no worker be exposed to a ceiling concentration of ozone in

excess of 0.3 mg/L 9by volume) for more than ten minutes.

• American Conference of Government Industrial Hygienists (ACGIH). Maximum ozone

level of 0.1 mg/L (by volume) for a normal eight hour work day or 40 hour work week, and a

maximum concentration of 0.3 mg/L (by volume) for exposure of up to 15 minutes.

• American Industrial Hygiene Association. Maximum, concentration for eight hour exposure

of 0.1 mg/L (by volume).

There is a question of whether prolonged exposure to ozone may impair a worker’s ability to smell or

be aware of ozone levels at less than critical levels. Awareness of an odor of ozone should not be

relied upon. Instrumentation and equipment should be provided to measure ambient ozone levels and

perform the following safety functions:

• Initiate an alarm signal at an ambient ozone level of 0.1 mg/L (by volume). Alarms should

include warning lights in the main control panel and at entrances to the ozonation facilities as

well as audible alarms.

• Initiate a second alarm signal at ambient ozone levels of 0.3 mg/L (by volume). This signal

would immediately shut down ozone generation equipment and would initiate a second set of

visual and audible alarms at the control panel and at the ozone generation facility entrances. An
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emergency ventilation system capable of exhausting the room within a period of 2 to 3 minutes

also would be interconnected to the 0.3 mg/L ozone level alarm.

Ozone gas is a hazardous gas and should be handled accordingly. Ambient ozone levels should be

monitored and equipment shut- down and alarmed when levels exceed 0.1 ppm. Emergency

ventilation is typically provided for enclosed areas. Building and fire codes will provide additional

guidance. The OSHA exposure limit for an 8-hour shift is 0.1 ppm by volume. The pungent odor of

ozone will provide warning to operators of any possible ozone leak.

3.7 Summary

3.7.1 Advantages and Disadvantages of Ozone Use

The following list highlights selected advantages and disadvantages of using ozone as a

disinfection method for drinking water (Masschelein, 1992). Because of the wide variation of

system size, water quality, and dosages applied, some of these advantages and disadvantages

may not apply to a particular system.

Advantages

• Ozone is more effective than chlorine, chloramines, and chlorine dioxide for inactivation of viruses,

Cryptosporidium, and Giardia.

• Ozone oxidizes iron, manganese, and sulfides.

• Ozone can sometimes enhance the clarification process and turbidity removal.

• Ozone controls color, taste, and odors.

• One of the most efficient chemical disinfectants, ozone requires a very short contact time.

• In the absence of bromide, halogen-substitutes DBPs are not formed.

• Upon decomposition, the only residual is dissolved oxygen.

• Biocidal activity is not influenced by pH.

Disadvantages

• DBPs are formed, particularly by bromate and bromine-substituted DBPs, in the presence of bromide,

aldehydes, ketones, etc.

• The initial cost of ozonation equipment is high.

• The generation of ozone requires high energy and should be generated on-site.

• Ozone is highly corrosive and toxic.

• Biologically activated filters are needed for removing assimilable organic carbon and biodegradable

DBPs.

• Ozone decays rapidly at high pH and warm temperatures.

• Ozone provides no residual.
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• Ozone requires higher level of maintenance and operator skill.

3.7.2 Summary Table

Table 3-12 presents a summary of the considerations for the use of ozone as a disinfectant.

Table 3-12. Summary of Ozone Disinfection Considerations

Consideration Description

Generation Because of its instability, ozone should be generated at the point of

use. Ozone can be generated from oxygen present in air or high purity

oxygen. The feed gas source should be clean and dry, with a maximum

dewpoint of -60oC. Ozone generation consumes power at a rate of 8 to

17 kWhr/kg O3. Onsite generation saves a lot of storage space.

Primary uses Primary uses include primary disinfection and chemical oxidation. As an

oxidizing agent, ozone can be used to increase the biodegradability of

organic compounds destroys taste and odor control, and reduce levels

of chlorination DBP precursors. Ozone should not be used for

secondary disinfection because it is highly reactive and does not

maintain an appreciable residual level for the length of time desired in

the distribution system.

Inactivation efficiency Ozone is one of the most potent and effective germicide used in water

treatment. It is effective against bacteria, viruses, and protozoan cysts.

Inactivation efficiency for bacteria and viruses is not affected by pH; at

pH levels between 6 and 9. As water temperature increases, ozone

disinfection efficiency increases.

Byproduct formation Ozone itself does not form halogenated DBPs; however, if bromide ion

is present in the raw water or if chlorine is added as a secondary

disinfectant, halogenated DBPs, including bromate ion may be formed.

Other ozonation byproducts include organic acids and aldehydes.

Limitations Ozone generation is a relatively complex process. Storage of LOX (if

oxygen is to be the feed gas) is subject to building and fire codes.

Points of application For primary disinfection, ozone addition should be prior to

biofiltration/filtration and after sedimentation. For oxidation, ozone

addition can be prior to coagulation/sedimentation or filtration

depending on the constituents to be oxidized.

Safety considerations Ozone is a toxic gas and the ozone production and application facilities

should be designed to generate, apply, and control this gas, so as to

protect plant personnel. Ambient ozone levels in plant facilities should

be monitored continuously.
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3.8 References

1. Alceon Corp. 1993. Overview of Available Information on the Toxicity of Drinking Water

Disinfectants and Their By-products. Cambridge, MA.

2. Amy, G.L., M.S. Siddiqui. 1991. “Ozone-Bromide Interactions in Water Treatment.”

Conference proceedings, AWWA Annual Conference, Philadelphia, PA.

3. AWWA (American Water Works Association). 1990. Water Quality and Treatment. F.W.

Pontius (editor), McGraw-Hill, New York, NY.

4. Bablon, G.P., C. Ventresque, R.B. Aim. 1988. “Developing a Sand-GAC Filter to Achieve High

Rate Biological Filtration.” J. AWWA.80(12):47.

5. Bablon, G., et al. 1991. “Practical Application of Ozone: Principles and Case Studies.” Ozone in

Water Treatment Application and Engineering. AWWARF.

6. Billen, G., et al. 1985. Action des Populations Bactériennes Vis-á-Vis des Matiéres Organiques

dans les Filtres Biologiques. Report to Compagnie Genérale des Eaux, Paris.

7. Boyce, D.S., et al. 1981. “The Effect of Bentonite Clay on Ozone Disinfection of Bacteria and

Viruses in Water.” Water Res. 15:759-767.

8. Bringmann, G. 1954. “Determination of the Lethal Activity of Chlorine and Ozone on E. coli.”

Z. f., Hygiene. 139:130-139.

9. Chang, S.L. 1971. “Modern Concept of Disinfection.” J. Sanit. Engin. Division. 97:689-707.

10. Cronholm, L.S., et al.1976. “Enteric Virus Survival in Package Plants and the Upgrading of the

Small Treatment Plants Using Ozone.” Research Report No. 98, Water Resources Research

Institute, University of Kentucky, Lexington, KY.

11. DeMers, L.D. and R.C. Renner. 1992. Alternative Disinfection Technologies for Small Drinking

Water Systems. AWWARF and AWWA, Denver, CO.

12. Dimitriou, M.A. (editor). 1990. Design Guidance Manual for Ozone Systems. International

Ozone Association, Norwalk, CN.

13. Domingue, E. L., et al. 1988. “Effects of Three Oxidizing Biocides on Legionella pneumophila,

Serogroup 1.” Appl. Environ. Microbiol. 40:11-30.

14. Eighmy, T.T., S.K. Spanos, J. Royce, M.R. Collins, J.P. Malley. 1991. “Microbial Activity in

Slow Sand Filters.” Conference proceedings, Slow Sand Filtration Workshop, Timeless

Technology for Modern Applications, Durham, NH.
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15. Farooq, S. et al.1977. “The Effect of Ozone Bubbles on Disinfection.” Progr. Water Ozone Sci.

Eng. 9(2):233.

16. Farooq, S. 1976. Kinetics of Inactivation of Yeasts and Acid-Fast Organisms with Ozone. Ph.D.

Thesis, University of Illinois at Urbana-Champaign, IL.

17. Farvardin, M.R. and A.G. Collins. 1990. “Mechanism(s) of Ozone Induced Coagulation of

Organic Colloids.” Conference proceedings, AWWA Annual Conference, Cincinnati, OH.

18. Finch, G. R., E.K. Black, and L.L. Gyürék. 1994. “Ozone and Chlorine Inactivation of

Cryptosporidium.” Conference proceedings, Water Quality Technology Conference, Part II, San

Francisco, CA.

19. Franson, M.H., Eaton, A.D., Clesceri, L.S., and Greenberg, A.E., (editors). 1995. Standard

Methods for the Examination of Water and Wastewater, Nineteenth Edition. American Public

Health Association, AWWA, and Water Environment Federation, Washington D.C.

20. Georgeson, D.L. and A.A. Karimi. 1988. “Water Quality Improvements with the Use of Ozone

at the Los Angeles Water Treatment Plant.” Ozone Sci. Engrg. 10(3):255-276.

21. Giese, A.C. and E. Christensen. 1954. “Effects of Ozone on Organisms.” Physiol. Zool. 27:101.

22. Glaze W.H., M. Koga, D. Cancilla. 1989a. “Ozonation Byproducts. 2. Improvement of an AqueousPhase Derivatizition Method for the Detection of Formaldehyde and Other Carbonyl Compounds

Formed by the Ozonation of Drinking Water.” Environ. Sci. Technol. 23(7):838.

23. Glaze, W.H., M. Koga M., D. Cancilla, et al. 1989b. “Evaluation of Ozonation Byproducts from

Two California Surface Waters.” J. AWWA. 1(8):66.

24. Glaze, W.H., et al.1987. “The Chemistry of Water Treatment Processes Involving Ozone, Hydrogen

Peroxide, and Ultraviolet Radiation.” Ozone Sci. Engrg. 9(4):335.

25. Glaze, W.H., and J.W. Kang. 1988. “Advanced Oxidation Processes for Treating Groundwater

Contaminated with TCE and PCE: Laboratory Studies.” J. AWWA. 88(5):57- 63.

26. Glaze, W.H., H.S. Weinberg, S.W. Krasner, M.J. Sclimenti. 1991. “Trends in Aldehyde Formation

and Removal Through Plants Using Ozonation and Biological Active Filters.” Conference

proceedings, AWWA, Philadelphia, PA.

27. Goldstein, B.D., and E.M. McDonagh. 1975. “Effect of Ozone on Cell Membrane Protein

Fluorescence I. in vitro Studies Utilizing the Red Cell Membrane.” Environ. Res. 9:179-186.

28. Gordon, G. K. Rankness, D. Vornehm, and D. Wood. 1989. “Limitations of the Iodometric

Determination of Ozone.” J. AWWA. 81(6):72-76.

29. Gordon, G., W.J. Cooper, R.G. Rice, and G.E. Pacey. 1992. Disinfectant Residual Measurement

Methods, second edition. AWWARF and AWWA, Denver, CO.
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30. Gurol, M.D. and M. Pidatella. 1983. “A Study of Ozone-Induced Coagulation.” Conference

proceedings, ASCE Environmental Engineering Division Specialty Conference. Allen Medine

and Michael Anderson (editors), Boulder, CO.

31. Haag, W.R. and J. Hoigné. 1984. “Kinetics and Products of the Reactions of Ozone with

Various Forms of Chlorine and Bromine in Water.” Ozone Sci. Engrg. 6(2):103-14.

32. Hann, V.A. 1956. “Disinfection of Drinking Water with Ozone.” J. AWWA. 48(10):1316.

33. Harakeh, M.S. and M. Butler. 1984. “Factors Influencing the Ozone Inactivation of Enteric

Viruses in Effluent.” Ozone Sci. Engrg. 6:235-243.

34. Hiltebrand, D.J., A.F. Hess, P.B. Galant, and C.R. O’Melia. 1986. “Impact of Chlorine Dioxide

and Ozone Preoxidation on Conventional Treatment and Direct Filtration Treatment Processes.”

Conference proceedings, AWWA Seminar on Ozonation: Recent Advances and Research

Needs, Denver, CO.

35. Hoff, J.C. 1986. Inactivation of Microbial Agents by Chemical Disinfectants, U. S.

Environmental Protection Agency, EPA/600/2-86/067.

36. Hoigné J. and H. Bader. 1976. Role of Hydroxyl Radical Reactions in Ozonation Processes in

Aqueous Solutions, Water Res. 10: 377.

37. Hoigné J., and H. Bader. 1988. “The Formation of Trichloronitromethane (chloropicrin) and

Chloroform in a Combined Ozonation/Chlorination Treatment of Drinking Water.” Water Res.

22(3):313.

38. Hoigné J., and H. Bader. 1983b. “Rate Constants of Reaction of Ozone with Organic and

Inorganic Compounds in Water - II. Dissociating Organic Compounds.” Water Res. 17:185-194.

39. Hoigné J., and H. Bader. 1977. “The Role of Hydroxyl Radical Reactions in Ozonation

Processes in Aqueous Solutions.” Water Res. 10:377-386.

40. Hoigné J., and H. Bader. 1983a. “Rate Constants of Reaction of Ozone with Organic and

Inorganic Compounds in Water - I. Non-dissociating Organic Compounds.” Water Res. 17:173-

183.

41. Hoigné, J. and Bader, H. 1975. Ozonation of Water: Role of Hydroxyl Radicals as Oxidizing

Intermediates. Science, Vol. 190, pp. 782.

42. Huck, P.M., P.M. Fedorak, and W.B. Anderson. 1991. “Formation and Removal of Assimilable

Organic Carbon During Biological Treatment.” J. AWWA. 83(12):69-80.

43. IOA (International Ozone Association). 1989. Photometric Measurement of Low Ozone

Concentrations in the Gas Phase. Standardisation Committee--Europe.
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44. Katz, J. 1980. Ozone and Chlorine Dioxide Technology for Disinfection of Drinking Water.

Noyes Data Corporation, Park Ridge, New Jersey.

45. Katzenelson, E., et al. 1974. “Inactivation Kinetics of Viruses and Bacteria in Water by Use of

Ozone.” J. AWWA. 66:725-729.

46. Keller, J.W., R.A. Morin, and T.J. Schaffernoth. 1974. “Ozone Disinfection Pilot Plants Studies

at Laconia, New Hampshire.” J. AWWA. 66:730.

47. Kim, C.K., et al. 1980. “Mechanism of Ozone Inactivation of Bacteriophage f2.” Appl. Environ.

Microbiol. 39:210-218.

48. Kinman, R.N. 1975. “Water and Wastewater Disinfection with Ozone: A Critical Review.” Crit.

Rev. Environ. Contr. 5:141-152.

49. Krasner, S.W., W.H. Glaze, H.S. Weinberg, et al. 1993. “Formation of Control of Bromate

During Ozonation of Water Containing Bromide.” J. AWWA. 85(5):62..

50. Krasner, S.W., et al. 1989. “The Occurrence of Disinfection By-products in US Drinking

Water.” J. AWWA.81(8):41.

51. Langlais, B., et al. 1990. “New Developments: Ozone in Water and Wastewater Treatment. The

CT Value Concept for Evaluation of Disinfection Process Efficiency; Particular Case of

Ozonation for Inactivation of Some Protozoa, Free-Living Amoeba and Cryptosporidium.”

Presented at the Int. Ozone Assn. Pan-American Conference, Shreveport, Louisiana, March 27-

29.

52. Langlais, B., D.A. Reckhow, and D.R. Brink (editors). 1991. Ozone in Drinking Water

Treatment: Application and Engineering. AWWARF and Lewis Publishers, Boca Raton, FL.

53. Langlais B. and D. Perrine. 1986. “Action of Ozone on Trophozoites and Free Amoeba Cysts,

Whether Pathogenic of Not.” Ozone Sci. Engrg. 8(3):187-198.

54. LeChevallier, M.W., W.C. Becker, P. Schorr, and R.G. Lee. 1992. “Evaluating the Performance of

Biologically Active Rapid Filters.” J. AWWA. 84(4):136-146.

55. LeLacheur, R.M., P.C. Singer, and M.J. Charles. 1991. “Disinfection By-products in New Jersey

Drinking Waters.” Conference proceedings, AWWA Annual Conference, Philadelphia, PA.

56. Logsdon, G.S., S. Foellmi, and B. Long. 1992. “Filtration Pilot Plant Studies for Greater

Vancouver’s Water Supply.” Conference proceedings, AWWA Annual Conference, Vancouver,

British Columbia.

57. Malley, J.P., T.T. Eighmy, M.R. Collins, J.A. Royce, and D.F. Morgan. 1993. “The True

Performance and Microbiology of Ozone - Enhanced Biological Filtration.” J. AWWA.

85(12):47-57.
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58. Masschelein, W.J. 1992. "Unit Processes in Drinking Water Treatment." Marcel Decker D.C.,

New York , Brussels, Hong Kong.

59. Masschelein, W.J. 1977. “Spectrophotometric Determination of Residual Ozone in Water with

ACVK.” J. AWWA. 69:461-462.

60. McGuire, M.J., S.W. Krasner, and J. Gramith. 1990. Comments on Bromide Levels in State

Project Water and Impacts on Control of Disinfection Byproducts Metropolitan Water District

of Southern California.

61. McKee, H.C., R.E. Childers, and V.B. Parr 1975. Collaborative Study of Reference Method for

Measurement of Photochemical Oxidants in the Atmosphere, EPA EPA-650/4-75-016,

Washington, D.C. February.

62. McKnight A., and D.A. Reckhow. 1992. “Reactions of Ozonation Byproducts with Chlorine and

Chloramines.” Conference proceedings, AWWA Annual Conference, Vancouver, British

Columbia.

63. MWDSC and JMM (Metropolitan Water District of Southern California and James M.

Montgomery Consulting Engineers). 1992. “Pilot Scale Evaluation of Ozone and peroxone.”

AWWARF and AWWA, Denver, CO.

64. Morris, J.C. 1975. “Aspects of the Quantitative Assessment of Germicidal Efficiency.”

Disinfection: Water and Wastewater. J.D. Johnson (editor). Ann Arbor Science Publishers, Inc.,

Ann Arbor, MI.

65. Owens, J. H., et al. 1994. “Pilot-Scale Ozone Inactivation of Cryptosporidium and Giardia.”

Conference proceedings, Water Quality Technology Conference, Part II, San Francisco, CA.

66. Peeters, J. E. et al. 1989. “Effect of Disinfection of Drinking Water with Ozone or Chlorine

Dioxide on Survival of Cryptosporidium parvum Oocysts.” Appl. Environ. Microbiol.

55(6):1519-1522.

67. Perrine, D., et al. 1984. “Action d l’Ozone sur les Trophozoites d’Amibes Libres Pathogens ou

Non.” Bull Soc.Frnac. Parasitol. 3:81.

68. Prendiville, D.A. 1986. “Ozonation at the 900 cfs Los Angeles Water Purification Plant.” Ozone

Sci. Engrg. 8:77.

69. Price, M.L. 1994. Ozone and Biological Treatment for DBP Control and Biological Stability.

AWWARF and AWWA, Denver, CO, pp. 252.

70. Rachwal, A.J., et al. 1988. “Advanced Techniques for Upgrading Large Scale Slow Sand

Filters.” Slow Sand Filtration- Recent Developments in Water Treatment Technology, Ellis

Horwood Ltd, Chichester, U.K.
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71. Reckhow, D.A., J.K. Edzwald, and J.E. Tobiason. 1993. “Ozone as an Aid to Coagulation and

Filtration.” AWWARF and AWWA, Denver, CO.

72. Reckhow, D.A., P.C.Singer, and R.R. Trussell. 1986. Ozone as a coagulant aid. Seminar

proceedings, Ozonation, Recent Advances and Research Needs, AWWA Annual Conference,

Denver, CO.

73. Reckhow, D.A., J.E. Tobiason, M.S. Switzenbaum, R. McEnroe, Y. Xie, X. Zhou, P.

McLaughlin, and H.J. Dunn. 1992. “Control of Disinfection Byproducts and AOC by PreOzonation and Biologically Active In-Line Direct Filtration.” Conference proceedings, AWWA

Annual Conference, Vancouver, British Columbia.

74. Regli, S., J.E. Comwell, X. Zhang., et al. 1992. Framework for Decision Making: An EPA

Perspective. EPA 811-R-92-005, EPA, Washington, D.C.

75. Rehme, K.A., J.C. Puzak, M.E. Beard, C.F. Smith, and R.J. Paur. 1980. Evaluation of Ozone

Calibration Procedures, EPA-600/S4-80-050, EPA, Washington, D.C, February.

76. Renner, R.C., M.C. Robson, G.W. Miller, and A.G. Hill. 1988. “Ozone in Water Treatment -

The Designer’s Role.” Ozone Sci. Engrg. 10(1):55-87.

77. Rice, R.G. 1996. Ozone Reference Guide. Electric Power Research Institute, St. Louis, MO.

78. Rice, R.G., P.K. Overbeck, K. Larson. 1998. Ozone Treatment for Small Water Systems.

Presented at the First International Symposium on Safe Drinking water in Small Systems. NSF

International/PAHP/WHO, Arlington, VA, May 10-13, 1998.

79. Riesser, V.W., et al. 1976. “Possible Mechanisms of Poliovirus Inactivation by Ozone.” Forum

on Ozone Disinfection, E. G. Fochtman, R.G. Rice, and M.E. Browning (editors), pp. 186-192,

International Ozone Institute, Syracuse, NY.

80. Rittman, B.E. 1990. “Analyzing Biofilm Processes Used in Biological Filtration.” J. AWWA.

82(12):62.

81. Roy, D. 1979. Inactivation of Enteroviruses by Ozone. Ph.D. Thesis, University of Illinois at

Urbana-Champaign.

82. Roy, D., R.S. Engelbrecht, and E.S.K. Chian. 1982. “Comparative Inactivation of Six

Enteroviruses by Ozone.” J. AWWA. 74(12):660.

83. Scott, D.B.M. and E.C. Lesher. 1963. “Effect of Ozone on Survival and Permeability of

Escherichia coli.” J. Bacteriol. 85:567-576.

84. Singer P.C. 1992. “Formation and Characterization of Disinfection Byproducts.” Presented at

the First International Conference on the Safety of Water Disinfection: Balancing Chemical and

Microbial Risks.
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85. Singer, P.C., et al. 1989. “Ozonation at Belle Glade, Florida: A Case History.” Conference

proceeding, IOA Ninth Ozone World Conference.

86. Song, R., et al. 1997. “Bromate Minimization During Ozonation.” J. AWWA. 89(6):69.

87. Sproul, O. J., et al. 1982. “The Mechanism of Ozone Inactivation of Waterborne Viruses.”

Water Sci. Technol. 14:303-314.

88. Staehelin, J., R.E. Bühler, and J. Hoigné. 1984. “Ozone Decomposition in Water Studies by

Pulse Radiolysis. 2 OH and HO4 as Chain Intermediates.” J. Phys. Chem. 88:5999-6004.

89. Stolarik, G. F., and J.D. Christie. 1997. “A Decade of Ozonation in Los Angeles.” Conference

proceedings, IOA Pan American Group Conference, Lake Tahoe, NV.

90. Suffet, I.H., C. Anselme, and J. Mallevialle. 1986. “Removal of Tastes and Odors by

Ozonation.” Conference proceedings, AWWA Seminar on Ozonation: Recent Advances and

Research Needs, Denver, CO.

91. Tobiason, J.E., J.K. Edzwald, O.D. Schneider, M.B. Fox, and H.J. Dunn. 1992. “Pilot Study of

the Effects of Ozone and Peroxone on In-Line Direct Filtration.” J. AWWA. 84(12):72-84.

92. Tomiyasu, H., and G. Gordon. 1984. “Colorimetric Determination of Ozone in Water Based on

Reaction with Bis-(terpyridine)iron(II).” Analytical Chem. 56:752-754.

93. Troyan, J.J. and S.P. Hansen. 1989. Treatment of Microbial Contaminants in Potable Water

Supplies Technologies and Costs. Noyes Data Corporation, Park Ridge, New Jersey.

94. Umphries, M.D., et al. 1979. “The Effects of Pre-ozonation on the Formation of

Trihalomethanes.” Ozonews. 6(3).

95. USEPA. 1997. USEPA Method 300.1, Determination of Inorganic Anions in Drinking Water

by Ion Chromatography, Revision 1.0. EPA A/600/r-98/118.

96. Van Dijk, J.F.M., and R.A. Falkenberg. 1977. “The Determination of Ozone Using the Reaction

with Rhodamine B/Gallic Acid.” Presented at Third Ozone World Congress sponsored by the

IOA, Paris, France, May.

97. Van Gunten, U. and J. Hoigné. 1996. “Ozonation of Bromide-Containing Waters: Bromate

Formation through Ozone and Hydroxyl Radicals.” Disinfection By-Products in Water

Treatment , Minear, R.A. and G.L. Amy (editors). CRC Press, Inc., Boca Raton, FL.

98. Van Hoof, F., J.G. Janssens, H. van Dijck. 1985. “Formation of Mutagenic Activity During

Surface Water Pre-ozonation and Its Removal in Drinking Water Treatment.” Chemosphere,

14(5):501.
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99. Vaughn, J.M., et al. 1987. “Inactivation of Human and Simian Rotaviruses by Ozone.” Appl.

Env. Microbiol. 53:2218-2221.

100. Walsh, D.S., et al. 1980. “Ozone Inactivation of Floc Associated Viruses and Bacteria.” J.

Environ. Eng. Div. ASCE. 106:711-726.

101. Ward, S.B. and D.W. Larder. 1973. “The Determination of Ozone in the Presence of Chlorine.”

Water Treatment Examination. 22:222-229.

102. Wickramanayake, G.B., et al. 1984b. “Inactivation of Giardia lamblia Cysts with Ozone.” Appl.

Env. Microbiol. 48(3):671-672.

103. Wickramanayake, G.B., et al. 1984a. “Inactivation of Naegleria and Giardia cysts in Water by

Ozonation.” J. Water Pollution Control Fed. 56(8):983-988.

104. Wickramanayake, G.B. 1984c. Kinetics and Mechanism of Ozone Inactivation of Protozoan

Cysts. Ph.D. dissertation, Ohio State University, Columbus, OH.

105. Wuhrmann, K., and J. Meyrath. 1955. “The Bactericidal Action of Ozone Solution. Schweitz.”

J. Allgen. Pathol. Bakteriol., 18:1060.

106. Yamada, H. and I. Somiya. 1989. “The Determination of Carbonyl Compounds in Ozonated

Water By the PFBOA Method.” Ozone Sci. Engrg. 11(2):127.

107. Zabel, T.F. 1985. “The Application of Ozone for Water Treatment in the United Kingdom -

Current Practice and Recent Research.” Ozone Sci. Engrg. 7(1):11.
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OZONE ............................................................................................................................................................. 3-1

3.1 OZONE CHEMISTRY .............................................................................................................................. 3-1

3.2 OZONE GENERATION ............................................................................................................................ 3-4

3.2.1 Ozone Production......................................................................................................................... 3-4

3.2.2 System Components..................................................................................................................... 3-5

3.2.3 Operation and Maintenance ........................................................................................................ 3-15

3.3 PRIMARY USES AND POINTS OF APPLICATION OF OZONE...................................................................... 3-16

3.3.1 Primary Uses of Ozone............................................................................................................... 3-16

3.3.2 Points of Application.................................................................................................................. 3-18

3.3.3 Impact on Other Treatment Processes ......................................................................................... 3-19

3.3.4 Biologically Active Filtration ..................................................................................................... 3-19

3.3.5 Pathogen Inactivation and Disinfection Efficacy.......................................................................... 3-21

3.3.6 Inactivation Mechanisms............................................................................................................ 3-22

3.3.7 Disinfection Parameters.............................................................................................................. 3-22

3.3.8 Inactivation of Microorganisms .................................................................................................. 3-24

3.4 OZONATION DISINFECTION BYPRODUCTS ............................................................................................ 3-27

3.4.1 Ozone Byproduct Control........................................................................................................... 3-30

3.5 STATUS OF ANALYTICAL METHODS..................................................................................................... 3-31

3.5.1 Monitoring of Gas Phase Ozone.................................................................................................. 3-31

3.5.2 Monitoring of Liquid Phase Residual Ozone ............................................................................... 3-35

3.5.3 Bromate Monitoring for Systems Using Ozone ........................................................................... 3-37

3.6 OPERATIONAL CONSIDERATIONS......................................................................................................... 3-38

3.6.1 Process Considerations............................................................................................................... 3-38

3.6.2 Space Requirements................................................................................................................... 3-38

3.6.3 Material Selection ...................................................................................................................... 3-39

3.6.4 Ozone System Maintenance........................................................................................................ 3-39

3.6.5 Ozone Safety.............................................................................................................................. 3-39

3.7 SUMMARY.......................................................................................................................................... 3-41

3.7.1 Advantages and Disadvantages of Ozone Use ............................................................................. 3-41

3.7.2 Summary Table .......................................................................................................................... 3-42

3.8 REFERENCES ...................................................................................................................................... 3-43

Table 3-1. Types of Compressors Used in Air Preparation Systems..................................................................... 3-7

Table 3-2. Comparison of Air and High Purity Oxygen Feed Systems................................................................. 3-8

Table 3-3. Comparison of Primary Characteristics of Low, Medium, and High Frequency Ozone Generators .... 3-10

Table 3-4. Bubble Diffuser Contactor Advantages and Disadvantages............................................................... 3-12

Table 3-5. Injection Contacting Advantages and Disadvantages........................................................................ 3-13

Table 3-6. Turbine Mixer Contactor Advantages and Disadvantages................................................................. 3-14

Table 3-7. Criteria for Selecting Ozone Feed Points for Small Systems ............................................................. 3-18

Table 3-8. Summary of Reported Ozonation Requirements for 99 Percent Inactivation of Cryptosporidium Oocycts

.................................................................................................................................................................. 3-27

Table 3-9. Principal Known Byproducts of Ozonation....................................................................................... 3-28

Table 3-10. Characteristics and Comparisons of Gas-Phase Ozone Analytical Methods..................................... 3-33

Table 3-11. Characteristics and Comparisons of Residual Ozone Analytical Methods........................................ 3-36

Table 3-12. Summary of Ozone Disinfection Considerations............................................................................. 3-42

Figure 3-1. Oxidation Reactions of Compounds (Substrate) During Ozonation of Water...................................... 3-2

Figure 3-2. Reaction of Ozone and Bromide Ion Can Produce Bromate Ion and Brominated Organics................. 3-3

Figure 3-3. Basic Ozone Generator..................................................................................................................... 3-4

Figure 3-5. Schematic of an Air Preparation System............................................................................................ 3-7
3. OZONE

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Figure 3-6. Cylindrical Electrode Schematic ....................................................................................................... 3-9

Figure 3-7. Ozone Bubble Contactor................................................................................................................. 3-11

Figure 3-8. Sidestream Ozone Injection System ................................................................................................ 3-12

Figure 3-9. Turbine Mixer Ozone Contactor ..................................................................................................... 3-14

Figure 3-10. CT Values for Inactivation of Viruses by Ozone (pH 6 to 9).......................................................... 3-26

Figure 3-11. Principal Reactions Producing Ozone Byproducts......................................................................... 3-28

Figure 3-12. Main Pathways of Bromate Ion Formation when Ozone Reacts with Bromide Ion ......................... 3-30
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4. CHLORINE DIOXIDE

Since the beginning of the twentieth century, when it was first used at a spa in Ostend, Belgium,

chlorine dioxide has been known as a powerful disinfectant of water. During the 1950s, it was

introduced more generally as a drinking water disinfectant since it provided less organoleptic

hindering than chlorine. Approximately 700 to 900 public water systems use chlorine dioxide to

treat potable water (Hoehn, 1992). Today, the major uses of chlorine dioxide are:

• CT disinfection credit;

• Preoxidant to control tastes and odor;

• Control of iron and manganese; and

• Control of hydrogen sulfide and phenolic compounds.

4.1 Chlorine Dioxide Chemistry

4.1.1 Oxidation Potential

The metabolism of microorganisms and consequently their ability to survive and propagate are

influenced by the oxidation reduction potential (ORP) of the medium in which it lives (USEPA,

1996).

Chlorine dioxide (ClO2) is a neutral compound of chlorine in the +IV oxidation state. It disinfects by

oxidation; however, it does not chlorinate. It is a relatively small, volatile, and highly energetic

molecule, and a free radical even while in dilute aqueous solutions. At high concentrations, it reacts

violently with reducing agents. However, it is stable in dilute solution in a closed container in the

absence of light (AWWA, 1990). Chlorine dioxide functions as a highly selective oxidant due to its

unique, one-electron transfer mechanism where it is reduced to chlorite (ClO2

-

) (Hoehn et al., 1996).

The pKa for the chlorite ion, chlorous acid equilibrium, is extremely low at pH 1.8. This is

remarkably different from the hypochlorous acid/hypochlorite base ion pair equilibrium found near

neutrality, and indicates the chlorite ion will exist as the dominant species in drinking water. The

oxidation reduction of some key reactions are (CRC, 1990):

ClO2(aq) + e

-

 = ClO2

- E° = 0.954V

Other important half reactions are:

ClO2

-

 + 2H2O +4e

-

 = Cl- + 4OH - E° = 0.76V

ClO3

-

 + H2O + 2e

-

 = ClO2

-

 + 2OH - E° = 0.33V

ClO3

-

 + 2H

+

 + e

-

 = ClO2 + H2O E° = 1.152V
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In drinking water, chlorite (ClO2

-

) is the predominant reaction endproduct, with approximately 50 to

70 percent of the chlorine dioxide converted to chlorite and 30 percent to chlorate (ClO3

-

) and

chloride (Cl-) (Werdehoff and Singer, 1987).

4.2 Generation

4.2.1 Introduction

One of the most important physical properties of chlorine dioxide is its high solubility in water,

particularly in chilled water. In contrast to the hydrolysis of chlorine gas in water, chlorine dioxide

in water does not hydrolyze to any appreciable extent but remains in solution as a dissolved gas

(Aieta and Berg, 1986). It is approximately 10 times more soluble than chlorine (above 11°C), while

it is extremely volatile and can be easily removed from dilute aqueous solutions with minimal

aeration or recarbonation with carbon dioxide (e.g. softening plants). Above 11 to 12°C, the free

radical is found in gaseous form. This characteristic may affect chlorine dioxide's effectiveness when

batching solutions and plumbing appropriate injection points. Other concerns are the increased

difficulty in analyzing for specific compounds in the presence of many interfering

compounds/residual longevity and volatility of gaseous compounds. In the gaseous form, the free

radicals also react slowly with water. The reaction rate is 7 to 10 million times slower than that of

the hydrolysis rate for chlorine gas (Gates, 1989).

Chlorine dioxide cannot be compressed or stored commercially as a gas because it is explosive under

pressure. Therefore, it is never shipped. Chlorine dioxide is considered explosive at higher

concentrations which exceed 10 percent by volume in air, and its ignition temperature is about 130°C

(266°F) at partial pressures (National Safety Council Data Sheet 525 – ClO2, 1967). Strong aqueous

solutions of chlorine dioxide will release gaseous chlorine dioxide into a closed atmosphere above

the solution at levels that may exceed critical concentrations. Some newer generators produce a

continuous supply of dilute gaseous chlorine dioxide in the range of 100 to 300 mm-Hg (abs) rather

than in an aqueous solution (National Safety Council, 1997). For potable water treatment processes,

aqueous solutions between 0.1 and 0.5 percent are common from a number of current generation

technologies.

Most commercial generators use sodium chlorite (NaClO2) as the common precursor feedstock

chemical to generate chlorine dioxide for drinking water application. Recently, production of

chlorine dioxide from sodium chlorate (NaClO3) has been introduced as a generation method where

in NaClO3 is reduced by a mixture of concentrated hydrogen peroxide (H2O2) and concentrated

sulfuric acid (H2SO4). Chlorate-based systems have traditionally been used in pulp and paper

applications, but have recently been tested full-scale at two U.S. municipal water treatment plants.

This is an emerging technology in the drinking water field and is not discussed in this guidance

manual.
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4.2.2 Chlorine Dioxide Purity

Chlorine dioxide generators are operated to obtain the maximum production (yield) of chlorine

dioxide, while minimizing free chlorine or other residual oxidant formation. The specified yield for

chlorine dioxide generators is typically greater than 95 percent. In addition, the measurable excess

chlorine should be less than 2 percent by weight in the generator effluent. Generator yield is defined

as (Gordon et al., 1990):

[ ]

[ ] [ ] ( )[ ]

100

83.45 3

67.45

2 2

2 ×

+ +

= − − ClO ClO ClO

ClO Yield

Where: [ClO2] = Chlorine dioxide concentration, mg/L.

[

− ClO2

] = Chlorite concentration, mg/L.

[

− ClO3

] = Chlorate concentration, mg/L.













83.45

67.45 = Molecular weight ratio of ClO2

-

 to ClO3

-

.

Since any chlorite ion fed to the generator may result in the formation of ClO2, ClO2

-

, or ClO3

-

, the

purity of the resultant mixture can be calculated using the concentrations of each of the species from

appropriate analytical measurements. The determination of purity requires neither flow

measurement, mass recoveries, nor manufacturer-based methods to determine production “yield,”

“theoretical yield,” “efficiency,” or conversion for any precursor feedstock. This approach does not

require flow measurements that can introduce up to 5 percent error in the calculations.

Utilities that use chlorine dioxide should measure excess chlorine (as FAC) in the generator effluent

in addition to the ClO2

- related species. FAC may appear as false ClO2 residuals for CT purposes, or

result in the formation of chlorinated DBPs if high, relative to the ClO2 level in the generated

mixture. Excess chlorine is defined as:

( )

100

]

3

[ClO 83.45

67.45 ]

2

] [ClO 2[ClO

]

2

[Cl

Excess Cl

2 67.45

70.91 2 ×

×

−

+

−

+

=

×

Where:

(2 67.45)

70.91

×

= stoichiometric and molecular weight ratio of Cl2 to ClO2

-

.

The following represents a summarily simpler equation that substantially resolves the problems of

different equipment-specific calibration methods, chlorine-contaminated ClO2, or low efficiency

conversion of either chlorite- or chlorate-based precursor material.
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100

]

3

] [ClO 2] [FAC] [ClO 2[ClO

]

2

[ClO

Purity × −

+

−

+ +

=

This practical (weight-based) calculation permits a variety of approved analytical methods (discussed

in section 4.6) to be used to assess generator performance on unbiased scientific principles, rather

than non-standardized manufacturer specifications.

4.2.3 Methods of Generating Chlorine Dioxide

For potable water application, chlorine dioxide is generated from sodium chlorite solutions. The

principal generation reactions that occur in the majority of generators have been known for a long

time. Chlorine dioxide can be formed by sodium chlorite reacting with gaseous chlorine (Cl2(g)),

hypochlorous acid (HOCl), or hydrochloric acid (HCl). The reactions are:

2NaClO2 + Cl2(g) = 2ClO2(g) + 2NaCl [1a]

2NaClO2 + HOCl = 2ClO2(g) + NaCl + NaOH [1b]

5NaClO2 + 4HCl = 4ClO2(g) + 5NaCl + 2H2O [1c]

Reactions [1a], [1b], and [1c] explain how generators can differ even though the same feedstock

chemicals are used, and why some should be pH controlled and others are not so dependent on low

pH. In most commercial generators, there may be more than one reaction taking place. For example,

the formation and action of hypochlorous acid as an intermediate (formed in aqueous solutions of

chlorine) often obscures the “overall” reaction for chlorine dioxide production.

Table 4-1 provides information on some types of available commercial generators. Conventional

systems react sodium chlorite with either acid, aqueous chlorine, or gaseous chlorine. Emergent

technologies identified in Table 4-1 include electrochemical systems, a solid chlorite inert matrix

(flow-through gaseous chlorine) and a chlorate-based emerging technology that uses concentrated

hydrogen peroxide and sulfuric acid.
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Table 4-1. Commercial Chlorine Dioxide Generators

GENERATOR TYPE

MAIN REACTIONS

Reactants, byproducts, key

reactions, and chemistry notes SPECIAL ATTRIBUTES

ACID-CHLORITE:

(Direct Acid System)

4HCl + 5NaClO2 Ë 4ClO2(aq) + ClO3

-

• Low pH

• ClO3

-

 possible

• Slow reaction rates

Chemical feed pump interlocks required.

Production limit ~ 25-30 lb/day.

Maximum yield at ~80% efficiency.

AQUEOUS CHLORINECHLORITE:

(Cl2 gas ejectors with chemical

pumps for liquids or booster

pump for ejector water).

Cl2 + H2O Ë [HOCl / HCl]

[HOCl/HCl] + NaClO2 Ë

ClO2(g) + H/OCl- + NaOH + ClO3

-

• Low pH

• ClO3

-

 possible

• Relatively slow reaction rates

Excess Cl2 or acid to neutralize NaOH.

Production rates limited to ~ 1000 lb/day.

High conversion but yield only 80-92%

More corrosive effluent due to low pH (~2.8-3.5).

Three chemical systems pump HCl,

hypochlorite, chlorite, and dilution water to

reaction chamber.

RECYCLED AQUEOUS

CHLORINE OR "FRENCH

LOOP"TM

(Saturated Cl2 solution via a

recycling loop prior to mixing

with chlorite solution.)

2HOCl + 2NaClO2 Ë 2ClO2 + Cl2 +

2NaOH

• Excess Cl2 or HCl needed due to

NaOH formed.

Concentration of ~3 g/L required for maximum

efficiency.

Production rate limited to ~ 1000 lb/day.

Yield of 92-98% with ~10% excess Cl2 reported.

Highly corrosive to pumps; draw-down

calibration needed. Maturation tank required

after mixing.

GASEOUS CHLORINECHLORITE

(Gaseous Cl2 and 25% solution

of sodium chlorite; pulled by

ejector into the reaction column.)

Cl2(g) + NaClO2(aq) Ë ClO2(aq)

• Neutral pH

• Rapid reaction

• Potential scaling in reactor under

vacuum due to hardness of

feedstock.

Production rates 5-120,000 lb/day.

Ejector-based, with no pumps. Motive water is

dilution water. Near neutral pH effluent. No

excess Cl2. Turndown rated at 5-10X with yield

of 95-99%. Less than 2% excess Cl2. Highly

calibrated flow meters with min. line pressure ~

40 psig needed.

GASEOUS CHLORINESOLIDS CHLORITE MATRIX

(Humidified Cl2 gas is pulled or

pumped through a stable matrix

containing solid sodium chlorite.)

Cl2(g) + NaClO2(s) Ë ClO2(g) + NaCl

• Rapid reaction rate

• New technology

Cl2 gas diluted with N2 or filtered air to produce

~8% gaseous ClO2 stream. Infinite turndown is

possible with >99% yield. Maximum rate to

~1200 lb/day per column; ganged to >10,000

lb/day.

ELECTROCHEMICAL

(Continuous generation of ClO2

from 25% chlorite solution

recycled through electrolyte cell)

NaClO2(aq) Ë ClO2(aq) + e-

• New technology

Counter-current chilled water stream accepts

gaseous ClO2 from production cell after it

diffuses across the gas permeable membrane.

Small one-pass system requires precise flow for

power requirements (Coulombs law).

ACID/PEROXIDE/CHLORIDE 2NaClO3 + H2O2 + H2SO4 Ë 2ClO2 +

O2 + NaSO4 + H20

Uses concentrated H2O2 and H2SO4.

Downscaled version; Foam binding; Low pH.

Source: Adapted from Gates, 1998.

4.1.1.1 Commercial Generators

The conventional chlorine-chlorite solution method generates chlorine dioxide in a two-step process.

First, chlorine gas is reacted with water to form hypochlorous acid and hydrochloric acid. These
4. CHLORINE DIOXIDE

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acids then react with sodium chlorite to form chlorine dioxide. The ratio of sodium chlorite to

hypochlorous acid should be carefully controlled. Insufficient chlorine feed will result in a large

amount of unreacted chlorite. Excess chlorine feed may result in the formation of chlorate ion,

which is an oxidation product of chlorine dioxide and not currently regulated.

Acid-Chlorite Solution - Chlorine dioxide can be generated in direct-acidification generators by

acidification of sodium chlorite solution. Several stoichiometric reactions have been reported for

such processes (Gordon et al., 1972). When chlorine dioxide is generated in this way, hydrochloric

acid is generally preferred (Reaction [1c]).

Aqueous Chlorine-Chlorite Solution - Chlorite ion (from dissolved sodium chlorite) will react with

hydrochloric acid and hypochlorous acid to form chlorine dioxide in these systems, commonly

referred to as conventional systems (Reaction [1b]):

Figure 4-1 shows a typical chlorine dioxide generator using aqueous chlorine-chlorite solution

(Demers and Renner, 1992).

If chlorine gas and chlorite ion are allowed to react under ideal conditions (not usually formed in

aqueous chlorine type systems), the resulting pH of the effluent may be close to 7. To fully utilize

sodium chlorite solution, the more expensive of the two ingredients, excess chlorine is often used.

This approach lowers the pH and drives the reaction further toward completion. The reaction is

faster than the acid-chlorite solution method, but much slower than the other commercial methods

described in the following discussion.

Recycled Aqueous Chlorine or “French Loop”TM - In this aqueous chlorine design, shown in

Figure 4-2, chlorine gas is injected into a continuously circulating water loop. This eliminates the

need for a great excess of Cl2 gas to be fed to the generator since the molecular chlorine will dissolve

in the feed water, and thus maintain a low pH level of the feed water. Loop-based generators keep

chlorine at or above saturation levels. The low pH condition results in high yields of chlorine

dioxide (greater than 95 percent at design production rate) (Thompson, 1989). Chlorine in the

generator effluent may react with chlorine dioxide to form chlorate if allowed to stand in batch

storage too long. The “French Loop” type of generator is more difficult to operate due to system

start-up and control of sodium chlorite feed rate (meter pump), chlorine feed rate (rotameter), and the

recirculating loop (pump). Newer designs incorporate a second batching tank for continuous

aqueous chlorine storage, thus removing many of these startup or recycling difficulties.

Gaseous Chlorine-Chlorite Solution - Sodium chlorite solution can be “vaporized” and reacted

under vacuum with molecular gaseous chlorine. This process uses undiluted reactants and is much

more rapid than chlorine solution:chlorite solution methods (Pitochelli, 1995). Production rates are

more easily scaled up, and some installed systems have reported producing more than 60,000 pounds

per day.
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Control Box

Level

Switch

Ejector

Rate

Control

Valve

Pressure

Regulator

Bypass

Line

Restrictor

Solenoid Valve

Chlorine

Flowmeter

Water

Flowmeter

Low Vacuum

Switch

pH Sensor

Sight Glass

Chlorine Dioxide

Solution

Check

Valve

Vacuum

Regulator

with Loss of

Chlorine Switch

Vent

Chlorine

Gas Water Inlet

25% Active

Sodium Chlorite

Solution Tank

Source: Demers and Renner, 1992.

Figure 4-1. Conventional Chlorine Dioxide Generator When Using

Chlorine-Chlorite Method

The acid-sodium hypochlorite-sodium chlorite method of generating chlorine dioxide is used when

chlorine gas is not available. First, sodium hypochlorite is combined with hydrochloric or another

acid to form hypochlorous acid. Sodium chlorite is then added to this reaction mixture to produce

chlorine dioxide.

4.1.1.2 pH Effects on Chlorine Dioxide Generation

If hypochlorous acid is formed, one of the byproducts of its reaction with sodium chlorite in solution

is sodium hydroxide. Since sodium hydroxide is also a common stabilizer of sodium chlorite

feedstock, the resulting pH of the mixture can be too high. A high pH slows the formation of

chlorine dioxide and impels less efficient chlorate-forming reactions. This is the same process in

which chlorite and hypochlorite ions react in drinking water to form chlorate ion. This neutralizing

effect of caustic may be influenced by different stabilities used in each of the types and sources of
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sodium chlorite which are approved for use in drinking water under AWWA Standard B303-95

(AWWA, 1995).

Control Box

pH Sensor

Sight Glass

Chlorine Dioxide

Solution

Check

Valve

Solenoid Valve

Pressure

Regulator

Bypass

Line

Restrictor

Water

Flowmeter

Water Inlet

25% Active

Sodium Chlorite

Solution Tank

Level

Switch

Level

Switch

Level

Switch

10% Active

Sodium Chlorite

Solution Tank

Acid Tank

Flow

Switch

Chlorine Dioxide Wall Cabinet

Source: Demers and Renner, 1992.

Figure 4-2. Chlorine Dioxide Generation Using Recycled Aqueous Chlorine

Method

In very low pH aqueous chlorine solutions, chlorous acid (and not the chlorite ion) may be directly

oxidized to chlorine dioxide as shown in reaction [1d]. At this low pH, gaseous chlorine remains

"dissolved" in the water at concentrations higher than the normal occurrence, and allows reaction

[1a] to proceed.

2HClO2 + HOCl = HCl + H2O + 2ClO2 [1d]

4.1.1.3 Chlorate Byproduct Formation

One of the most undesirable byproducts in generators is the chlorate ion (ClO3

-

). Chlorate

production is possible through reactions with the intermediate dimer, {Cl2O2}. Rather than the

chlorite ion being simply "converted" to chlorine dioxide, reactions [1a] through [1d] can result in the

supposed formation of the unstable, unsymmetrical intermediate dimer, {Cl2O2} or {Cl--ClO2} as

shown in reaction [2] (Emmenegger and Gordon, 1967).

Cl2 + ClO2

-

 = {Cl-ClO2} + Cl-[2]
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In some generators that operate with relatively low initial reactant concentrations, a significant

amount of chlorate is formed by reactions with {Cl2O2}, as shown in reactions [3a], [3b], and [3c].

{Cl2O2} + H2O = ClO3

-

 + Cl- + 2H

+

[3a]

{Cl2O2} + HOCl = ClO3

-

 + Cl- + H

+

[3b]

{Cl2O2} + 3HOCl + H2O = 2ClO3

-

 + 5H

+

 + 3Cl-[3c]

Highly acidic (pH <3) reaction mixtures force the degradation of {Cl2O2} to chlorate rather than

chlorine dioxide, as well as the direct oxidation of chlorite to chlorate.

The overall reactions that describe chlorate ion formation are:

ClO2

-

 + HOCl = ClO3

-

 + Cl- + H

+

[4a]

and

ClO2

-

 + Cl2 + H2O = ClO3

-

 + 2Cl- + H

+

[4b]

The following conditions may also produce the chlorate ion:

• Excessively high ratios of Cl2 gas:ClO2

-

.

• Presence of high concentrations of free chlorine at low pH in aqueous solutions.

• Dilute chlorite solutions held at low pH.

• Base-catalyzed disproportionation of chlorine dioxide at high pH values (pH >11).

• Reaction mixtures that are highly acidic (pH <3).

• An excess of hypochlorous acid will directly oxidize chlorite ions to chlorate ions rather than

to chlorine dioxide (independent of the rapid formation of the {Cl2O2} intermediate).

4.1.4 Generator Design

As hypochlorous acid is formed under acidic conditions, the lowering of optimal concentrations of

precursor reactants will also increase chlorate levels in the generator by promoting reaction [3b].

Therefore, if weak precursor feed stocks or high amounts of dilution water are added to the

generator, chlorate will be more prevalent (according to reaction [3a]). These limitations explain

why generators most often use ~25 percent chlorite solutions and gaseous (or near-saturated aqueous)

chlorine. Higher strength solutions of sodium chlorite (e.g., 37 percent) also are more susceptible to

crystallization or stratification at ambient temperatures as high as 25°C(78°F).

Due to these dilution effects, some systems function best as "intermittent batch" generators, (that

produce high concentrations of chlorine dioxide) rather than as "continuous" generators (that produce

lower concentrations (< 1g/L) of chlorine dioxide). The stored solutions are pumped or injected from
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the storage tank. Cycling frequently avoids long-term (over 24 hour periods) storage of the

generated solution.

Chlorine loop-type systems can obtain high conversion rates if excess chlorine is always present.

Excess chlorine permits the molecular chlorine reaction mechanism (described above) to proceed.

The low pH of the mixture also minimizes the contribution of OH- formed via equation [1b] by

neutralizing it. These solutions may still be contaminated with excess chlorine needed to drive the

conversion of chlorite ion, but not to the same degree as found in simple aqueous chlorine systems

when operated under dilute conditions. Chlorine-loop generators run best at high capacity since the

chlorite ion is most available in this production mode.

Conventional or acid-enhanced generators produce chlorine dioxide through the intermediate

{Cl2O2} as long as relatively high concentrations of reactants (~above 20–30 g/L) are maintained in

the reaction chamber prior to dilution. Vapor-phase, recycled loop, and solid chlorite-type generators

that minimize dilute aqueous reaction conditions can obtain high efficiencies by preventing any

chlorite ion from reacting in the "slower" steps described above. This is accomplished by

establishing conditions that force the immediate reaction between chlorite ions and gas-phase or

molecular chlorine at a rate hundreds of times faster than the Cl2 hydrolysis in water. This

essentially minimizes the impact of competitive chlorine hydrolysis or acidification on the dominant

[ClO2

-

:Cl2 gas] mechanism, and prevents the chlorite ion reacting with hypochlorous acid directly.

In all generators, large excess amounts of Cl2 may result in the over-oxidization of chlorite and

directly form chlorate in aqueous solution (reaction [4b]). Precursor chemical feed rates for the

generators should always be adjusted to chart settings supplied with generators, notably with the

continuous flow, direct gas injection systems. Re-calibration of these systems is sometimes needed

on-site if feed stock sodium chlorite is not of the correct strength, or if pre-calibrated flow devices

have been replaced.

If aqueous chlorine solutions are mixed with sodium chlorite feed stock solutions, the following

mechanisms are dominant, which may affect the formation rates of chlorine dioxide:

• Chlorine gas reacts with water to form hypochlorous and hydrochloric acids, rather than

directly with chlorite to form chlorine dioxide. (Water and chlorite both compete for the Cl2

molecule simultaneously) (see equations [4.1a-c] and Section 6.1.1).

• Chlorate ion is formed (reactions [3a], [3b], and [3c]).

• Only 4 moles of chlorine dioxide are obtained from 5 moles of sodium chlorite via direct

acidification (reaction [1c]). This may become important at low pH and high chloride ion

levels.

The practical side of all of this is that different generators operate under different optimal conditions.

For example, reactor columns should not be continuously flooded with excess water in vapor-phase

systems. It is the main reason why dry chlorite-based generator reactor columns should not get wet.

Over-dilution of the precursor reactants themselves will lower conversion efficiencies due to the
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favored formation of chlorate over chlorine dioxide. Batch-type generation should always be carried

out at maximal ClO2 concentration with appropriate adjustments at the pump (located downstream of

the reactor at the batch tank) for dosage or flow. Changes in chlorine dioxide concentrations in the

batch tanks would then be minimized, and pump calibration does not need to include a broad range

of chlorine dioxide levels. For the newer gas chlorine generators using dry sodium chlorite in an

inert matrix, small amounts of humidifying water in the mixture do not interfere significantly with

the simple gaseous Cl2:ClO2

-

 reaction. These small traces of water allow for continuous exposure of

ClO2

-

 on the inert surfaces within the reactor column.

Chlorine dioxide generators are relatively simple mixing chambers. The reactors are frequently filled

with media (Teflon chips, ceramic or raschig rings) to generate hydraulic turbulence for mixing. A

sample petcock valve on the discharge side of the generator is desirable to allow for monitoring of

the generation process.

The Recommended Standards for Water Works (GLUMRB, 1992) and drinking water design

textbooks such as Unit Processes in Drinking Water Treatment by Masschelein (1992) are excellent

sources for chlorine dioxide generation design criteria and application.

4.1.5 Chemical Feed Systems

Fiberglass Reinforced vinyl ester Plastic (FRP) or High Density Linear Polyethylene (HDLPE) tanks

with no internal insulation or heat probes are recommended for bulk storage of 25 to 38 percent

solution sodium chlorite. Nozzles should include truck unloading vents and local level and

temperature indication. Transfer pumps should be centrifugal with 316 stainless steel, fiberglass,

Hypalon, wetted Teflon parts, or epoxy resins. The pump should be sealless or equipped with

double mechanical seals. The recommended piping material is CPVC, although vinyl ester or Teflon

 piping systems are acceptable. Carbon steel and stainless steel piping systems are not

recommended.

Depending upon system size, sodium chlorite can be purchased in 55-gallon drums, 275-gallon nonreturnable totes, or in bulk quantities. A 30-day storage supply of sodium chlorite can easily be met

for most small systems by using 55-gallon drums. A 55-gallon drum weighs approximately 600 lbs.

Equipment should be provided such that one person can easily handle a drum. All gaseous chlorine

or hypochlorite solution-related plumbing should follow Chlorine Institute directives.

Storage and chlorine dioxide systems typically include the following:

• Storage and feeding in a designated space.

• Use of non-combustible materials such as concrete for construction.

• Storage in clean, closed, non-translucent containers. Exposure to sunlight, UV light, or

excessive heat will reduce product strength.
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• Avoid storage and handling of combustible or reactive materials, such as acids or organic

materials, in the sodium chlorite area.

• Secondary containment for storage and handling areas to handle the worse case spill with

sumps provided to facilitate recovery.

• A water supply near storage and handling areas for cleanup.

• Inert material should be used in contact with the strong oxidizing and/or acid solutions

involved in chlorine dioxide systems.

• Storage tanks with vents to outside.

• Adequate ventilation and air monitoring.

• Gas masks and first aid kits outside of the chemical areas.

• Reactor with glass view ports if it is not made of transparent material.

• Flow monitoring on all chemical feed lines, dilution water lines, and chlorine dioxide

solution lines.

• Dilution water should not be excessively hard in order to avoid calcium deposits and should

be near neutral pH.

• On-site and frequent testing of chemical solution strengths should be practiced to achieve

efficient process control.

• Air contact with chlorine dioxide solutions should be controlled to limit the potential for

explosive concentrations possibly building up within the generator. Chlorine dioxide

concentrations in air higher than 8 to 10 percent volume should be avoided. Two methods

can be applied: operation under vacuum or storage under higher positive pressure (45 to 75

psig) to prevent buildup of gas-phase ClO2 in the head space. Bulk storage (batch) tanks

containing ClO2 should be suitably vented to atmosphere.

Sodium chlorite solution feed pumps are commonly diaphragm-metering pumps for liquid feed rate

control. If centrifugal pumps are used, the only acceptable packing material is Teflon. If lubrication

is needed, minimum quantities of fire-resistant lubricants should be used. Pump motors should be

totally enclosed, fan-cooled (TEFC) with sealed-for-life bearings. Couplings should be of the

greaseless type. Water lines for mechanical seals should have a pressure gauge and throttling valve

on the outlet side. Visual means should be provided to verify adequate water flow. Each pump

should include a calibration chamber.

Pipes carrying sodium chlorite should be provided sufficient support to minimize risk of

overstressing joints. Flexible connections to pumps should also be provided to minimize risk of

vibration damage. Pipe should be sloped to drainage points and valved hose connections provided at

strategic points for efficient flushing and draining. Service water for flushing feed lines should be

introduced only through temporarily connected hoses protected by a backflow preventer. Service

water lines should include check valves. Hose connections from service water lines should have a

vent valve to release pressure before the hose is disconnected after use.
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Flows are frequently measured with magnetic flow meters, mass flow meters, or rotameters for

precise control. Provisions should always be made for back-flow prevention. Sodium chlorite is

extremely reactive, especially in the dry form, and care should be taken to protect against potentially

explosive conditions.

Chlorine dioxide solution concentrations below about 10 g/L will not produce sufficiently high vapor

pressures to present an explosion hazard under most ambient conditions of temperature and pressure.

In water treatment, chlorine dioxide solution concentrations rarely exceed 4 g/L for temperatures less

than 40°C, and treatment levels generally range from 0.1 to 5.0 mg/L. If temperatures exceed 50°C,

storage tanks should be suitably vented due to the higher levels of ClO2 possible. As cold

service/potable water is typically used as generator dilution water, these conditions are rarely

encountered.

4.1.6 Generator Power Requirements

Generator power requirements are similar to those for chlorination systems. For all generators (20 to

12,000 lb/day) power can be supplied from 120 VAC single phase, to 480 VAC three phase. Power

demand will vary based upon make-up water pressure available to operate the venturi. Fractional

horsepower metering pumps are required, based upon system configuration.

4.3 Primary Uses and Points of Application for Chlorine

Dioxide

The calculation of CT for chlorine dioxide is similar to other disinfectants, with accurate

determinations of residual concentrations being a prerequisite for effective disinfection. Primary

disinfectant credit is achieved by the residual concentration and the effective contact time. It has

been found in practice that because of the volatile nature of the gas, chlorine dioxide works

extremely well in plug flow reactors such as pipe lines. It can be easily removed from dilute aqueous

solution by turbulent aeration in rapid mix tanks or purging in recarbonation basins. CT credits

should not be expected through a filter because the likelihood that no residual remains in the filtered

water (DeMers and Renner, 1992). For post CT disinfection credit, chlorine dioxide can be added

before clearwells or transfer pipelines. Ample sampling points should be included to allow close

monitoring of residual concentrations. It is well known that chlorine dioxide is commonly destroyed

by UV in basins exposed to sunlight or bright fluorescent lights. Therefore, protective design

elements should be incorporated if such exposure is anticipated.

4.3.1 Disinfection

Before chlorine dioxide is selected for use as a primary disinfectant an oxidant demand study should

be completed. Ideally, this study should consider the seasonal variations in water quality,

temperature, and application points. Table 4-2 shows typical results for a single sample of a demand

study completed on a surface water source.
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The MRDL for chlorine dioxide is 0.8 mg/L and the MCL for chlorite is 1.0 mg/L per the D/DBP

rule. This means that if the oxidant demand is greater than about 1.4 mg/L, chlorine dioxide may not

be used as a disinfectant because the chlorite/chlorate ions byproduct, might exceed the maximum

level allowed, unless inorganic byproducts (e.g., chlorite) are subsequently removed. There are

numerous means to reduce excessive chlorite levels prior to chlorination in conventional water

plants.

Table 4-2. Surface Water Chlorine Dioxide Demand Study Results

Dose (mg/L) Time (min) ClO2 (mg/L) ClO2

- (mg/L) ClO3- (mg/L)

1.4 3 0.47 0.76 0.05

10 0.30 0.98 0.06

20 0.23 1.08 0.07

40 0.16 1.11 0.07

60 0.11 1.11 0.07

Source: DeMers and Renner, 1992.

Note: *Raw water sample, 23°C, 8.5 pH.

Typical dosages of chlorine dioxide used as a disinfectant in drinking water treatment range from

0.07 to 2.0 mg/L. For plants using chlorine dioxide, median concentrations of chlorite and chlorate

were found to be 0.24 and 0.20 mg/L, respectively in an EPA survey (USEPA, 1998), the standard is

1.0 mg/L.

4.3.2 Taste and Odor Control

A common application of chlorine dioxide in drinking water in the United States has been for control

of tastes and odors associated with algae and decaying vegetation. Chlorine dioxide is also effective

in destroying taste and odor producing phenolic compounds. The recommended location for

application of chlorine dioxide for this purpose will depend on raw water quality, the type of

treatment plant and any other purposes for chlorine dioxide addition. In conventional treatment

plants, it is recommended that chlorine dioxide be added near the end of or following, the

sedimentation basin. If the raw water turbidity is low (for example, less than 10 NTU), chlorine

dioxide can be added at the beginning of the plant. Some utilities follow this practice because

chlorine dioxide is effective in controlling algae growth in flocculation and sedimentation basins that

are exposed to sunlight (DeMers and Renner, 1992). Such application during periods of darkness

may be more successful for nuisance algae control.

4.3.3 Oxidation of Iron and Manganese

Chlorine dioxide can be used to oxidize both iron and manganese. Chlorine dioxide reacts with the

soluble forms of iron and manganese to form precipitates that can be removed through sedimentation

and filtration. Chlorine dioxide reduces to chlorite ion in this reaction (Knocke et al., 1993). About

1.2 mg/L of chlorine dioxide is required to remove 1.0 mg/L of iron, and 2.5 mg/L of chlorine

dioxide are required to remove 1.0 mg/L of manganese. For high concentrations of iron and

manganese, the use of chlorine dioxide is limited to the 1.0 mg/L chlorite/chlorate ion byproduct, as
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described before. Ferrous iron may be added prior to conventional coagulation to chemically reduce

chlorite ion (to chloride ion) and improve the overall flocculation process.

4.4 Pathogen Inactivation and Disinfection Efficacy

For water treatment, chlorine dioxide has several advantages over chlorine and other disinfectants.

In contrast to chlorine, chlorine dioxide remains in its molecular form in the pH range typically found

in natural waters (Roberts et al., 1980). Chlorine dioxide is a strong oxidant and disinfectant. Its

disinfection mechanisms are not well understood, but appear to vary by type of microorganism

4.4.1 Inactivation Mechanisms

Gross physical damage to bacterial cells or viral capsids has not been observed at the low

concentrations of chlorine dioxide typically used to disinfect drinking water. Therefore, studies have

focused primarily on two more subtle mechanisms that lead to the inactivation of microorganisms:

determining specific chemical reactions between chlorine dioxide and biomolecules; and observing

the effect chlorine dioxide has on physiological functions.

In the first disinfection mechanism, chlorine dioxide reacts readily with amino acids cysteine,

tryptophan, and tyrosine, but not with viral ribonucleic acid (RNA) (Noss et al., 1983; Olivier et al.,

1985). From this research, it was concluded that chlorine dioxide inactivated viruses by altering the

viral capsid proteins. However, chlorine dioxide reacts with poliovirus RNA and impairs RNA

synthesis (Alvarez and O’Brien, 1982). It has also been shown that chlorine dioxide reacts with free

fatty acids (Ghandbari et al., 1983). At this time, it is unclear whether the primary mode of

inactivation for chlorine dioxide lies in the peripheral structures or nucleic acids. Perhaps reactions in

both regions contribute to pathogen inactivation.

The second type of disinfection mechanism focuses on the effect of chlorine dioxide on physiological

functions. It has been suggested that the primary mechanism for inactivation was the disruption of

protein synthesis (Bernarde et al., 1967a). However, later studies reported the inhibition of protein

synthesis may not be the primary inactivation mechanism (Roller et al., 1980). A more recent study

reported that chlorine dioxide disrupted the permeability of the outer membrane (Aieta and Berg,

1986). The results of this study were supported by the findings of Olivieri et al. (1985) and

Ghandbari et al. (1983), which found that the outer membrane proteins and lipids were sufficiently

altered by chlorine dioxide to increase permeability.

4.4.2 Environmental Effects

Studies have been performed to determine the effect of pH, temperature, and suspended matter on the

disinfection efficiency of chlorine dioxide. Following is a summary of the effects these parameters

have on pathogen inactivation.
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4.4.2.1 pH

In comparison to chlorine, studies have shown that pH has much less effect on pathogen inactivation

for viruses and cysts with chlorine dioxide than with chlorine in the pH range of 6 to 8.5. Unlike

chlorine, studies on chlorine dioxide have shown the degree of inactivation of poliovirus 1 (Scarpino

et al., 1979) and Naegleria gruberi cysts (Chen et al., 1984) increase as the pH increases.

The results of studies on E. coli inactivation are inconclusive. It has been found that the degree of

inactivation by chlorine dioxide increases as pH increases (Bernarde et al., 1967a). However, an

earlier study found that the bactericidal activity of chlorine dioxide was not affected by pH values in

the range of 6.0 to 10.0 (Ridenour and Ingols, 1947). A recent study on Cryptosporidium found that

inactivation of oocysts using chlorine dioxide occurred more rapidly at a pH of 8.0 than 6.0. At a

similar CT value, the level of inactivation at pH of 8.0 was approximately twice that at a pH of 6.0

(Le Chevallier et al., 1997). Another study found that chlorine dioxide efficacy increases for Giardia

inactivation at higher pH levels and that this may be the result of chemical or physical changes in

Giardia cyst structure rather than pH effects on chlorine dioxide disproportionation (Liyanage et al.,

1997). More research is needed to further clarify how pH impacts the effectiveness of chlorine

dioxide.

4.4.2.2 Temperature

Similar to chlorine, the disinfection efficiency of chlorine dioxide decreases as temperature decreases

(Ridenour and Ingols, 1947). This finding is supported by the data from Chen et al. (1984) shown in

Figure 4-3 for the inactivation of Naegleria gruberi cysts. The curve shows the CT required to

achieve 99 percent inactivation for temperatures between 5 and 30°C.

In a more recent study, LeChevallier et al. (1997) found that reducing the temperature from 20°C to

10°C reduced the disinfection effectiveness of chlorine dioxide on Cryptosporidium by 40 percent,

which is similar to previous results for Giardia and viruses. Gregory et al. (1998) found that even

under the most favorable conditions (i.e., at a pH of 8.5), required doses to achieve 2-log

Cryptosporidium inactivation do not appear to be a feasible alternative, requiring doses of more than

3.0 mg/L with a 60 minute detention time. At neutral pH levels, the required doses may be more

than 20 mg/L.
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0

2

4

6

8

10

12

14

16

5 10 15 20 25 30

Temperature (°C)

CT Product (mg min/L)

Figure 4-3. Effect of Temperature on N. Gruberi Cyst Inactivation at pH 7

4.4.2.3 Suspended Matter

Suspended matter and pathogen aggregation affect the disinfection efficiency of chlorine dioxide.

Protection from chlorine dioxide inactivation due to bentonite was determined to be approximately

11 percent for turbidities equal to or less than 5 NTUs and 25 percent for turbidities between 5 and

17 NTUs (Chen et al., 1984).

Laboratory studies of poliovirus 1 preparations containing mostly viral aggregates took 2.7 times

longer to inactivate with chlorine dioxide than single state viruses (Brigano et al., 1978). Chen et al.

(1984) also found that clumps of Naegleria gruberi cysts were more resistant to chlorine dioxide than

unclumped cysts or clumps of smaller size.

4.4.3 Disinfection Efficacy

Several investigations have been made to determine the germicidal efficiency of chlorine dioxide

since its introduction in 1944, as a drinking water disinfectant. Most of the investigations were

carried out as a comparison to chlorine; some studies have compared chlorine dioxide and ozone.

Chloride dioxide is a more effective disinfectant than chlorine but is less effective than ozone.

4.4.3.1 Bacteria Inactivation

Quantitative data were published as early as the 1940s demonstrating the efficacy of chlorine dioxide

as a bactericide. In general, chlorine dioxide has been determined to be equal to or superior to

chlorine on a mass-dose basis. It was demonstrated that even in the presence of suspended matter,
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chlorine dioxide was effective against E. coli and Bacillus anthracoides at dosages in the range of 1

to 5 mg/L (Trakhtman, 1949). Ridenour and Armbruster (1949) reported that an orthotolidine

arsenite (OTA) chlorine dioxide residual of less than 1 mg/L was effective against Eberthella

typhosa, Shigella dysenteriae, and Salmonella paratyphi B. Under similar pH and temperature

slightly greater OTA residuals were required for the inactivation of Pseudomonas aeruginosa and

Staphylococcus aureus.

Chlorine dioxide was shown to be more effective than chlorine at inactivating B. subtilis, B.

mesentericus, and B. megatherium spores (Ridenour et al., 1949). Moreover, chlorine dioxide was

shown to be just as effective or more effective than chlorine at inactivating Salmonella typhosa and

S. paratyphi (Bedulivich et al., 1954).

In the early 1960s several important contributions were made by Bernarde et al. (1967a and 1967b).

Chlorine dioxide was found to be more effective than chlorine at disinfecting sewage effluent and the

rate of inactivation was found to be rapid.

A comprehensive investigation of chlorine dioxide as disinfectant was performed by Roberts et al.

(1980). The investigation was performed using secondary effluents from three different wastewater

treatment plants. One of the objectives was to determine the relationships between dosages and

contact times and bactericidal efficiency. Dosages were compared for 2, 5, and 10 mg/L of chlorine

dioxide and chlorine. The contact times selected were 5, 15 and 30 minutes. Results of the

investigation are shown in Figure 4-4. As shown, chlorine dioxide demonstrated a more rapid

coliform inactivation than chlorine at the shortest contact time of 5 minutes and higher

concentrations. However, after 30 minutes of contact time, chlorine dioxide was equal or slightly

less efficient than chlorine as a bactericide.

Oliveri et al. (1984) studied the effectiveness of chlorine dioxide (and chlorine) residuals in

inactivating total coliform and f2 coliphage virus in sewage introduced to a water distribution system.

Initial chlorine dioxide residuals between 0.85 and 0.95 mg/L resulted in an average 2.8–log

inactivation of the total coliform and an average 4.4-log inactivation of the f2 coliphage virus, over a

contact time of 240 minutes.
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Source: Roberts et al., 1980.

Figure 4-4. Comparison of Germicidal Efficiency of Chlorine Dioxide and Chlorine

4.4.3.2 Protozoa Inactivation

The disinfection efficiency of chlorine dioxide has been shown to be equal to or greater than chlorine

for Giardia inactivation. Based on a 60 minute contact time, chlorine dioxide doses in the range of

1.5 to 2 mg/L are capable of providing a 3-log Giardia inactivation at 1°C to 25°C and pHs of 6 and

9 (Hofmann et al., 1997). Depending on the temperature and pH, Cryptosporidium has been found to

be 8 to 16 times more resistant to chlorine dioxide than Giardia (Hofmann et al., 1997). Although

some Cryptosporidium oocysts remained viable, one group of researchers found that a 30-minute

contact time with 0.22 mg/L chlorine dioxide could significantly reduce oocyst infectivity (Peeters et

al., 1989). In contrast, other researchers have found that CT values in the range of 60 to

80 mg·min/L were necessary to provide 1- to 1.5-log inactivation (Korich et al., 1990; Ransome et

al., 1993). Finch et al. (1995) reported that the CT values for 1-log inactivation was in the range of

27 to 30 mg·min/L. For 2-log inactivation, the CT value was approximately 40 mg·min/L, and 70

mg·min/L for 3-log inactivation. Finch et al. (1997) found 3-log inactivation of Cryptosporidium

oocysts with initial chlorine dioxide residual concentrations of 2.7 and 3.3 mg/L for contact times of

120 minutes, at pH of 8.0 and a temperature of 22oC.
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Both Chen et al. (1985) and Sproul et al. (1983) have investigated the inactivation of Naegleria

gruberi cysts by chlorine dioxide. Both studies concluded that chlorine dioxide is an excellent

disinfectant against cysts and that chlorine dioxide is better than or equal to chlorine in terms of

inactivation. Chlorine dioxide was found to be superior to chlorine at higher pHs. However, the

authors cautioned that the CT required for 2-log inactivation was much higher than normally

employed for water treatment at that time.

4.4.3.3 Virus Inactivation

Chlorine dioxide has been shown to be an effective viricide. Laboratory studies have shown that

inactivation efficiency improves when viruses are in a single state rather than clumped. It was

reported in 1946 that chlorine dioxide inactivated Poliomyelitis (Ridenour and Ingols, 1946). This

investigation also showed that chlorine dioxide and free chlorine yielded similar results. Other

studies have verified these findings for poliovirus 1 (Cronier et al., 1978) and Coxsackie virus A9

(Scarpino, 1979). At greater than neutral pHs (where hypochlorite ion is the predominant species)

chlorine dioxide has been found to be superior to chlorine in the inactivation of numerous viruses

such as echovirus 7, coxsackie virus B3, and sendaivirus (Smith and McVey, 1973). Sobsey (1998)

determined CT values based on a study of Hepatitis A virus, strain HM 175. The study found 4-log

inactivation levels are obtainable at CT values of less than 35 at 5°C and less than 10 at a temperature

of 25°C.

4.4.3.4 CT Values

Chlorine dioxide is regarded as a strong disinfectant that is effective at inactivating bacterial, viral,

and protozoan pathogens. CT values for Giardia and virus inactivation are shown in Figure 4-5 and

Figure 4-6, respectively (AWWA, 1991).

CT values shown in Figure 4-5 are based on disinfection studies using in vitro excystation of Giardia

muris. Average CT values for 2 log removal were extrapolated using first order kinetics and

multiplied by a safety factor of 1.5 to obtain the CT values for other log removal CT values. Due to

the limited amount of data available at pH values other than 7, the same CT values are used for all

pHs. Because chlorine dioxide is more effective at a pH 9 than at a pH of 7, the CT values shown in

Figure 4-5 are more conservative for higher pHs than for lower pHs. A lower safety factor was used

to derive the CT values for chlorine dioxide than for ozone due to the fact that the chlorine dioxide

values were derived from Giardia muris studies, which are more resistant than Giardia lamblia.
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0.0

5.0

10.0

15.0

20.0

25.0

30.0

5 10 15 20 25

Temperature (°C)

CT Product (mg min/L)

0.5-log Inactivation

1-log Inactivation

1.5-log Inactivation

2-log Inactivation

2.5-log Inactivation

3-log Inactivation

Source: AWWA, 1991.

Figure 4-5. CT Values for Inactivation of Giardia Cysts by Chlorine Dioxide

CT values shown in Figure 4-6 were obtained by applying a safety factor 2 to the average CT values

derived from the studies on hepatitis A virus, strain HM 175 (Sobsey, 1988). CT values at

temperatures other than 5°C were derived by applying a twofold decrease for every 10°C increase in

temperature.

Figure 4-7 and Figure 4-8 show the relationship between CT products and log inactivation of

Cryptosporidium at 20 and 10°C, respectively, and pHs of 6 and 8. CT values shown in Figure 4-7

and Figure 4-8 indicate that oocysts were more rapidly inactivated at pH 8 than 6 and that

temperature does impact the disinfection efficiency of chlorine dioxide. Reducing the temperature

from 20 to 10°C reduced the disinfection effectiveness by 40 percent. Finch (1997) is studying

Cryptosporidium inactivation under laboratory conditions using a variety of different disinfectants,

one of which is chloride dioxide.
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0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

5 10 15 20 25

Temperature (°C)

CT

Va

lu

es

(m

g

mi

n/

L)

2-log Inactivation

3-log Inactivation

4-log Inactivation

Source: AWWA, 1991.

Figure 4-6. CT Values for Inactivation of Viruses by Chlorine Dioxide

4.5 Chlorine Dioxide Disinfection Byproducts

Byproducts from the use of chlorine dioxide include chlorite, chlorate, and organic DBPs. This

section discusses the formation of these byproducts and methods to reduce or remove these DBPs.

The use of chlorine dioxide aids in reducing the formation of TTHMs and HAAs by oxidizing

precursors, and by allowing the point of chlorination to be moved farther downstream in the plant

after coagulation, sedimentation, and filtration have reduced the quantity of NOM.

4.5.1 Production of Chlorite and Chlorate

Chlorite and chlorate are produced in varying ratios as endproducts during chlorine dioxide treatment

and subsequent degradation. The primary factors affecting the concentrations of chlorine dioxide,

chlorite, and chlorate in finished drinking water involve:

• Dosage applied/oxidant demand ratio.

• Blending ratios of sodium chlorite and chlorine during the chlorine dioxide generation

process.

• Exposure of water containing chlorine dioxide to sunlight.
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0

0.25

0.5

0.75

1

1.25

1.5

0 10 20 30 40 50 60 70 80 90

CT Product (mg min/L)

Log Inactivation

pH 6.0; 1.52 mg/L dose, 1.23 mg/L residual pH 8.0; 1.52 mg/L dose, 1.23 mg/L residual

pH 6.0; 0.51 mg/L dose, 0.38 mg/L residual pH 8.0; 0.51 mg/L dose, 0.39 mg/L residual

Source: LeChevallier et al., 1996.

Figure 4-7. C. parvum Inactivation by Chlorine Dioxide at 20°C

0

0.25

0.5

0.75

1

0 10 20 30 40 50 60 70 80 90

CT Product (mg min/L)

Log Inactivation

pH 6.0; 1.52 mg/L dose, 1.23 mg/L residual pH 8.0; 1.52 mg/L dose, 1.23 mg/L residual

pH 6.0; 0.51 mg/L dose, 0.39 mg/L residual pH 8.0; 0.51 mg/L dose, 0.39 mg/L residual

Source: LeChevallier et al., 1996.

Figure 4-8. C. parvum Inactivation by Chlorine Dioxide at 10°C
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• Reactions between chlorine and chlorite if free chlorine is used for distribution system

residual maintenance.

• Levels of chlorate in sodium chlorite feedstock.

Incomplete reaction or non-stoichiometric addition of the sodium chlorite and chlorine reactants can

result in unreacted chlorite in the chlorine dioxide feed stream. Dilute chlorine dioxide solutions are

stable under low or zero oxidant-demand conditions. The quantity of chlorate produced during the

chlorine dioxide generation process is greater with excess chlorine addition. Likewise, a low or high

pH can increase the quantity of chlorate during the chlorine dioxide generation process. See Section

4.2, “Generation,” for a detailed discussion of the chemistry of chlorine dioxide generation.

Numerous inorganic and biological materials found in raw water will react with chlorine dioxide

(Noack and Doerr, 1977). Chloride (Cl-) and chlorite (ClO2

-

) ions are the dominant degradation

species arising from these reactions, although chlorate (ClO3

-

) can appear for a variety of reasons

when chlorine dioxide is used (Gordon et al., 1990; Werdehoff and Singer, 1987). The immediate

redox reactions with natural organic matter play the dominant role in decay of chlorine dioxide into

chlorite in drinking water (Werdehoff and Singer, 1987). Chlorite ion is generally the primary

product of chlorine dioxide reduction. The distribution of chlorite and chlorate is influenced by pH

and sunlight. Approximately 50 to 70 percent of the chlorine dioxide consumed by oxidation

reactions is converted to chlorite under conditions typical in water treatment (Rav-Acha et al., 1984;

Werdehoff and Singer, 1987). The application of 2 mg/L chlorine dioxide is expected to produce 1

to 1.4 mg/L of chlorite (Singer, 1992).

Chlorite is relatively stable in the presence of organic material but can be oxidized to chlorate by free

chlorine if added as a secondary disinfectant (Singer and O’Neil, 1987).

ClO2

-

 + OCl- = ClO3

-

 + ClChlorate is therefore produced through the reaction of residual chlorite and free chlorine during

secondary disinfection.

In addition, chlorine dioxide also disproportionates under highly alkaline conditions (pH>9) to

chlorite and chlorate according to the following reaction:

2ClO2 + 2OH- = ClO2

-

 + ClO3

-

 + H2O

In water treatment processes that require high pH, such as softening, chlorine dioxide should be

added after the pH has been lowered (Aieta et al., 1984).

The occurrence of photochemical decomposition of chlorine dioxide can affect the ultimate

concentrations of chlorine dioxide, chlorite, and chlorate in water treated with chlorine dioxide.

Moreover, generally, sunlight may increase chlorate concentrations in uncovered storage basins

containing water with chlorine dioxide residuals. Exposure to ultraviolet light will also change the

potential reactions between chlorine dioxide and the bromide ion.
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4.5.2 Organic DBPs Produced by Chlorine Dioxide

Chlorine dioxide generally produces few organic DBPs. However, Singer (1992) noted that the

formation of non-halogenated organic byproducts of chlorine dioxide has not been adequately

researched, and expected that chlorine dioxide will produce the same types of oxidation byproducts

that are produced through ozonation. The application of chlorine dioxide does not produce THMs

and produces only a small amount of total organic halide (TOX) (Werdehoff and Singer, 1987).

A study was conducted in 1994 by Richardson et al., to identify semivolatile, organic DBPs produced

by chlorine dioxide treatment in drinking water. Samples were taken from a pilot plant in Evansville,

Indiana that included the following treatment variations:

• Aqueous chlorine dioxide;

• Aqueous chlorine dioxide, ferrous chloride, (FeCl2), chlorine (Cl2), and dual media filtration

(sand and anthracite);

• Gaseous chlorine dioxide; and

• Gaseous chlorine dioxide, ferrous chloride (FeCl2), chlorine (Cl2), and dual media filtration

(sand and anthracite).

Using multispectral identification techniques, more than 40 different DBPs (many at sub-nanogram/L

[ng/L] levels) were identified including carboxylic acids and maleic anhydrides isolated from

XADTM concentrates, some of which may be regulated in the Stage 2 DBPR. THMs were not found

after chlorine dioxide was added to the water; however, THMs did show up during subsequent

chlorination.

4.5.3 Chlorine Dioxide DBP Control Strategies

EPA recommends that the total concentration of chlorine dioxide, chlorite, and chlorate be less than

1.0 mg/L as Cl2 (USEPA, 1983). In addition, chlorine dioxide concentrations exceeding 0.4 to 0.5

mg/L contribute to taste and odor problems (AWWA, 1990). Due to these issues, the use of chlorine

dioxide to provide a disinfectant residual is somewhat limited in moderate to high TOC water. In

low oxidant-demand water, however, ClO2 residuals may last several days.

Once formed, chlorate is stable in finished drinking water. No known treatment exists for removing

chlorate once it is formed. However, three strategies (Gallagher et al., 1994) that have been proven

effective for chlorite removal are:

• Adding reduced-sulfur compounds such as sulfur dioxide and sodium sulfite (not

recommended).

• Applying either granular activated carbon (GAC) or powdered activated carbon (PAC).

• Adding reduced iron salts, such as ferrous chloride and ferrous sulfate.
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Chlorite removal from drinking water through sulfur dioxide and other sulfur-based reducing agents

has been reported effective, but not desirable. A study of chlorite removal by sulfur dioxide indicates

that a lower pH level yields higher chlorite removal, and chlorite removal efficiencies increase as the

sulfur dioxide dose increases. Unfortunately, this removal process forms significant levels of

chlorate when sulfur dioxide and metasulfite are utilized. Therefore, it is concluded that treatment

with sulfur dioxide and metasulfite is not desirable for chlorite removal (Dixon and Lee, 1991). In

addition, sodium thiosulfate results in effective chlorite reduction, but the degree of removal is highly

dependent upon pH and contact time and relatively high dosages are required. Again, this

application of sodium thiosulfate is not desirable because the required dosages are too high (Griese et

al., 1991).

The addition of ferrous iron in drinking water is effective for chlorite removal, with chloride the

expected byproduct. Chlorite reduction occurs quickly in the pH range of 5 to 7, and complete

reduction occurs within 3 to 5 seconds. Excess reduced iron remaining in solution reacts with

dissolved oxygen at neutral pH, but under acidic conditions (pH < 6.5) the stability of the soluble

iron can create aesthetic (staining) problems if excess iron is used. Special consideration should be

given to ferrous iron dosage requirements so that the secondary MCL for iron is not exceeded

(Knocke and Iatrou, 1993).

Chlorite can be controlled by PAC at relatively high dosages (10 to 20 mg/L) and low pHs (5.5 to

6.5). Unless PAC is used for other purposes, such as odor control, it requires large doses and is not

cost effective. PAC brands can differ in their capacity to reduce chlorite.

GAC can remove chlorite but breakthrough may occur relatively early. The removal of chlorite by

GAC appears to be a result of adsorption and chemical reduction (Dixon and Lee, 1991). There is an

initial high removal efficiency due to chlorite adsorption. As the adsorptive sites are occupied,

chemical reduction on the GAC surface becomes the primary removal mechanism. This results in an

initial high removal efficiency. Although chlorite levels exiting the GAC filters are low, the chlorate

levels are high, most likely a result of reactions in the GAC filters between chlorite and free chlorine.

According to studies, the capacity of GAC beds is low, and if free chlorine and chlorite ion are

present in the GAC influent, chlorate ion will form. The most effective way to operate GAC for

chlorite reduction and avoid chlorate is to minimize production run times and have no chlorine

present in the filter.

4.6 Status of Analytical Methods

In addition to the monitoring requirements that apply regardless of the disinfectant used, the DBPR

requires that water systems that use chlorine dioxide for disinfection or oxidation must also monitor their

system for chlorine dioxide and chlorite.
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4.6.1 Chlorine Dioxide and Chlorite Analytical Methods

For compliance monitoring for chlorine dioxide, systems must use one of the two methods specified in 40

CFR §141.131(c), including (1) DPD, Standard Method 4500-CLO2 D, or (2) Amperometric Method II,

Standard Method 4500-CLO2 E. Where approved by the state, systems may also measure residual

disinfectant concentrations for chlorine dioxide by using DPD colorimetric test kits.

For compliance monitoring for chlorite, systems must use one of the three methods specified in 40 CFR

§141.131(b), including (1) Amperometric Titration, Standard Method 4500-CLO2 E, (2) Ion

Chromatography, EPA Method 300.0, or (3) Ion Chromatography, EPA Method 300.1. The regulations

specify that Amperometric Titration may be used for routine daily monitoring of chlorite at the entrance

to the distribution system, but that Ion Chromatography must be used for routine, monitoring of chlorate

and monthly additional monitoring of chlorate in the distribution system.

Details of these analytical procedures can be found in:

- Standard Methods for the Examination of Water and Wastewater, 19th Edition, American Public

Health Association, 1995.

- Methods for the Determination of Inorganic Substances in Environmental Samples. USEPA.

1993. EPA/600/R-93/100.

- USEPA Method 300.1, Determination of Inorganic Anions in Drinking Water by Ion

Chromatography, Revision 1.0. USEPA. 1997. EPA/600/R-98/118.

Table 4-3 summarizes the analytical methods approved for use for chlorine dioxide and chlorite and

provides some background information for each method.

4.6.2 Chlorine Dioxide Monitoring for Systems Using Chlorine

Dioxide

For chlorine dioxide monitoring, community, non-transient non-community, and transient noncommunity water systems that use chlorine dioxide for disinfection or oxidation, are required to take daily

samples at the entrance to the distribution system. For any daily sample that exceeds the chlorine dioxide

MRDL of 0.8 mg/L, the system must take additional samples in the distribution system the following day

at the locations specified in the DBPR, in addition to the daily sample required at the entrance to the

distribution system.

Additional sampling is to be performed in one of two ways, depending on the disinfectant that is used to

maintain a disinfectant residual in the distribution system. If chlorine dioxide or chloramines are used to

maintain a disinfectant residual, or if chlorine is used to maintain the residual and there are no disinfection

addition points after the entrance to the distribution system (i.e., no booster chlorination), the system must

take three samples as close to the first customer as possible, at intervals of at least six hours. If chlorine is

used to maintain a disinfectant residual and there are one or more disinfection addition points after the

entrance to the distribution system, the system must take one sample at each of the following locations:

(1) as close to the first customer as possible, (2) in a location representative of average residence time,
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and (3) as close to the end of the distribution system as possible (reflecting maximum residence time in

the distribution system). Chlorine dioxide monitoring may not be reduced.

If any daily sample taken at the entrance to the distribution system exceeds the MRDL, and on the

following day one (or more) of the three samples taken in the distribution system exceed the MRDL, the

system is in violation of the MRDL. The system must take immediate corrective action to lower the level

of chlorine dioxide below the MRDL, and must notify the public of the acute violation pursuant to 40

CFR §141.32. The system must also report to the State pursuant to 40 CFR §141.134.

If any two consecutive daily samples taken at the entrance to the distribution system exceed the MRDL,

the system is also in violation of the MRDL and must notify the public of the non-acute violation

pursuant to 40 CFR §141.32. The system must also report to the State pursuant to 40 CFR §141.134.

4.6.3 Chlorite Monitoring for Systems Using Chlorine Dioxide

For chlorite monitoring, community and non-transient non-community water systems that use chlorine

dioxide for disinfection or oxidation are required to take daily samples at the entrance to the distribution

system. For any daily sample that exceeds the chlorite MCL of 1.0 mg/L, the system must take additional

samples in the distribution system the following day at the locations specified in the DBPR. These

additional samples are to be collected at: (1) a location as close to the first customer as possible, (2) a

location representative of average residence time, and (3) a location as close to the end of the distribution

system as possible (reflecting maximum residence time in the distribution system).

In addition, systems using chlorine dioxide must take a three-sample set each month in the distribution

system similar to the three locations required if the chlorite MCL is exceeded in the sample collected at

the entrance to the distribution system. Specifically, these three-sample sets are to be collected: (1) in a

location near the first customer, (2) in a location representative of average residence time, and (3) at a

location reflecting maximum residence time in the distribution system. Any additional routine sampling

must be conducted in the same three-sample sets at the specified locations. This monthly sampling

requirement may be reduced to quarterly after one year of monitoring where: (1) no individual chlorite

sample taken in the distribution system has exceeded the MCL and (2) the system has not been required to

conduct follow-up monitoring as a result of a daily sample collected at the entrance to the distribution

system. These systems can remain on an annual schedule until either the daily sample or any of the three

individual quarterly samples exceed the MCL, at which time, the system must revert to monthly

monitoring.

If the arithmetic average of any three-sample set exceeds the chlorite MCL of 1.0 mg/L, the system is in

violation of the MCL and must notify the public pursuant to 40 CFR §141.32, in addition to reporting to

the State pursuant to 40 CFR §141.134.

4.7 Operational Considerations

As with all disinfectant selections, the primacy agency should be consulted when selecting

disinfectants. Certain states have their own operational, maintenance, and monitoring requirements
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for the application of chlorine dioxide. California prohibits the use of chlorine dioxide in ground

water systems, according to Merkle et al., 1997. Also, in Texas, the Texas Natural Resources

Conservation Commission (TNRCC) requires the public water supply to sign a bilateral agreement

which outlines a detailed operator qualifications requirement, testing methods, and procedures,

monitoring locations, testing frequency and reporting procedures. The chlorine dioxide

concentration leaving the water treatment plant must be less than 0.8 mg/L and the chlorite

concentration in the distribution system must be less than 1.0 mg/L.

State requirements must be reviewed to determine the cost-effectiveness of utilizing chlorine dioxide

as part of the overall water treatment scheme. Analytical testing and reporting requirements may

have significant labor and cost impacts.
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Table 4-3. Analytical Methods for Chlorine Dioxide and Related Compounds

Method Basis Interferences Limits

DPD as Test Kits

Colorimetric

(SM-4500-ClO2·G)

Colored oxidation product.

Use of color comparator is not

recommended. Use instrument

detection.

Mn2

+

, other Cl2, related

oxidants.

> 0.1 mg/L

DPD-glycine Method

Colorimetric

(SM 4500- ClO2·D)

Colored product, free Cl2 is

masked with glycine as

chloraminacetic acid.

ClO2

-

 slowly; other oxidants. > 0.1 mg/L

DPD-FAS

Titrimetric method

(SM 4500- ClO2.D)

DPD color titration with standard

FAS until red color is

discharged.

Iron, other oxidants. > 0.1 mg/L

5-Step Amperometric

Method 4500-ClO2.E

I

-

 oxidation; pH control and gas

purging steps. Skilled analyst

needed.

Suitable for ClO2 generated

solution.

Low levels not okay.

~ PQL ClO2

-

:

 0.1-0.0.5 mg/L;

ClO3

-

 at 0.5 mg/L

Ion Chromatography

(EPA Method 300.0 or 300.1)

Conductivity

Must use AS9 column, ext.

standards & suppression.

No other oxidants.

Chloramines, ClO2; OCl- &

HOCL undetectable.

~ 0.05 mg/L

Two-step Amperometric

Method 4500-ClO2.E

I

-

 Oxidation; pH control.

Amendable to operator-based

dosage control.

Practical method.

Cu2+, Mn2+, NO2

-

Accounts for free Cl2, NH2Cl,

ClO2

-

 species.

> 0.1 mg/L,

not ClO3

-

Source: Gates, 1998.

Notes: SM = Standard Methods

4.7.1 Process Considerations

The basic components of chlorine dioxide generation systems include:

• Aqueous hypochlorite solution storage and feed system;

• Sodium chlorite storage and feed system;

• Acid storage and feed system (for Direct-Acidification generators);

• Chlorine storage and feed system;

• Chlorine dioxide generator; and

• Chlorine dioxide feed piping and dispersion equipment.

Sodium chlorite storage and feed systems are basically liquid systems that consist of a storage tank(s)

and solution feed pumps. Outside storage of 25 percent solutions (or greater) of sodium chlorite is

not recommended in cold climates since stratification may occur below 4°C (40°F). Any ice

formation may also damage the storage tanks. In some cases, storage might be separated into bulk

tanks and smaller operational or day tanks that are filled periodically. Storage of dark drums for long

periods in hot climates should be avoided since sodium chlorite decomposition will occur. In the

storage area, light fixtures, switches, wiring, and conduit runs should be located to avoid the risk of

sodium chlorite spilling on them.
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4.7.2 Generator Operation

A manual chlorine dioxide feed system may be used where the chlorine dioxide dose remains fairly

constant. The reagent chemicals are manually set for the desired chlorine dioxide capacity at a ratio

of chemicals optimized for maximum chlorine dioxide yield. Some generating systems can produce

95 percent pure chlorine dioxide solutions at full design capacity, but purity can vary when the feed

rate is changed. Turndown capacity may be limited by precision of the flow metering devices,

typically 20 percent of rate capacity. Purity can vary when the feed rate is changed significantly.

Feed water alkalinity, operating conditions, and pH also can affect yield. The ratio of reagent

chemicals should be routinely adjusted for optimum operation. Chlorine dioxide generators can be

provided with automated control to provide modulation of chlorine dioxide feed rates based upon

changes in flow (flow paced) and chlorine dioxide demand (residual control). The automatic

modulation of the generators to meet a demand setpoint varies with manufacturer. Generally,

vacuum and combination systems are limited by the hydraulic requirements of the venturi and the

optimum reaction conditions for chlorine dioxide generation. A chemical metering pump or injector

system is then used with a batch production system to control the applied dose of chlorine dioxide.

4.7.3 Feed Chemicals

Chlorine dioxide is generated when sodium chlorite is either oxidized or acidified, or both, under

controlled pH and temperature conditions. Commonly, solutions of 25 percent active sodium chlorite

or less are used in chlorine dioxide generators. The major safety concern for solutions of sodium

chlorite is the unintentional and uncontrollable release of high levels of chlorine dioxide. Such levels

may approach detonation or conflagration concentrations by accidental acidification.

The feedstock acid used by some of the generators is only one source of accidental chemical

acidification. Accidental mixing with large amounts of any reducing agent or oxidizable material

(such as powdered activated carbon or flammable solvents) also represents a significant hazard. The

AWWA Standard B303-95 (a) includes an outline of some of these materials (AWWA, 1995).

Another concern when handling and storing sodium chlorite solutions is crystallization, which occurs

as a result of lower temperatures and/or higher concentrations. Crystallization will plug pipelines,

valves, and other equipment. Sodium chlorite solution should not be allowed to evaporate to a

powder. If dried, this product becomes a fire hazard and can ignite in contact with combustible

materials. A sodium chlorite fire may result in a steam explosion if too much water and

inappropriate fire-fighting techniques are used to quench such a fire. As the temperature of burning

sodium chlorite is around 2200°C, water quickly turns to steam. Because thermal breakdown

products of sodium chlorite at high temperatures include molecular oxygen, appropriate techniques

are required to correctly extinguish closed containers or large amounts of dry material that has been

ignited.

Stratification of sodium chlorite in holding tanks may also occur and would influence the chlorine

dioxide yield. If stratification occurs in the bulk tank, sodium chlorite changes from high density to
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low density as it is fed. The density will continue to change until the material is re-mixed. In

stratified tanks, excess chlorite would be fed to the generator since the bottom of the tank will have

denser material, and this material would have more chlorite than required. Similarly, the bulk tank

would later discharge too little chlorite.

Although infrequent, such stratification is not readily apparent and may likely remain unnoticed by

operations unless the generator performance is evaluated frequently. If stratification or

crystallization occurs in bulk delivery trucks, the entire content should be warmed prior to delivery

so that the sodium chlorite is re-mixed. Operators should be aware of the possibility of stratification

and crystallization during delivery conditions.

Sodium chlorite is commercially available as a 38 percent or 25 percent solution. Chemical and

physical properties are given in Table 4-4.

Table 4-4. Properties of Sodium Chlorite as Commercially Available

38% Solution* 25% Solution*

Sodium Chlorite, (%) NaClO2 38 25

Sodium Chloride, (%) NaCl 1.5-7.5 1-4.5

Inert Ingredients, mixture of other sodium salts (%) 3-4 3-4

Water (%) 55-61 68-74

Appearance Slightly cloudy, pale

yellow

Clear, pale yellow

Density @ 35°C (lb/gal), typical 11.4 10.1

Crystallization Point (°C) 25 -7

* Source: Vulcan Chemicals

For systems handling the 38 percent solution, storage tanks, piping and pumps will require a heated

enclosure, or heat tracing and insulation. The 25 percent solution may not require any special

protection except in cold climates.

The ideal production of 1.0 pound of chlorine dioxide requires 0.5 pounds of chlorine and 1.34

pounds of pure sodium chlorite. Chlorine gas is available as a nearly 100 percent pure chemical on a

weight basis. Gas flow metering devices are typically limited to +/- 5 percent accuracy at full rated

capacity. For example, a 100 pound per day flow tube would allow between 20 and 30 pounds of

chlorine to flow if set at 25 pounds per day (i.e., 25 +/- 5 percent of maximum flow capacity).

Sodium chlorite is supplied commercially as a pre-mixed aqueous solution of various strengths. The

25 percent solution is the most commonly used grade for potable water treatment.

Pure chlorine dioxide solutions (very dark amber and oily in appearance) are very dangerous and are

likely to detonate if exposed to oxidizable materials or vapors, or even to bright lights. They are

extremely uncommon except perhaps in very specific laboratory setup systems using concentrated

sodium chlorite and concentrated acid mixtures. Such laboratory generation methods are not
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recommended for the uninitiated laboratory analyst or operator. Inexperienced personnel should not

mix strong acid and strong sodium chlorite solutions together unless they are familiar with the

purgeable extraction methods for sodium chlorite and have a safely designed setup under a fume

hood.

4.8 Summary

4.8.1 Advantages and Disadvantages of Chlorine Dioxide Use

The following list highlights selected advantages and disadvantages of using chlorine dioxide as a

disinfection method for drinking water (Masschelein, 1992; DeMers and Renner, 1992, Gallagher et

al., 1994). Because of the wide variation of system size, water quality, and dosages applied, some of

these advantages and disadvantages may not apply to a particular system.

Advantages

• Chlorine dioxide is more effective than chlorine and chloramines for inactivation of viruses,

Cryptosporidium, and Giardia.

• Chlorine dioxide oxidizes iron, manganese, and sulfides.

• Chlorine dioxide may enhance the clarification process.

• Taste and odors resulting from algae and decaying vegetation, as well as phenolic compounds, are

controlled by chlorine dioxide.

• Under proper generation conditions (i.e., no excess chlorine), halogen-substituted DBPs are not

formed.

• Chlorine dioxide is easy to generate.

• Biocidal properties are not influenced by pH.

• Chlorine dioxide provides residuals.

Disadvantages

• The chlorine dioxide process forms the specific byproducts chlorite and chlorate.

• Generator efficiency and optimization difficulty can cause excess chlorine to be fed at the application

point, which can potentially form halogen-substitute DBPs.

• Costs associated with training, sampling, and laboratory testing for chlorite and chlorate are high.

• Equipment is typically rented, and the cost of the sodium chlorite is high.

• Measuring chlorine dioxide gas is explosive, so it must be generated on-site.

• Chlorine dioxide decomposes in sunlight.

• Chlorine dioxide must be made on-site.

• Can lead to production noxious odors in some systems.
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4.8.2 Summary Table

Table 4-5 summarizes considerations and descriptions for chlorine dioxide use.

Table 4-5. Summary for Chlorine Dioxide

Consideration Description

Generation Chlorine dioxide must be generated on-site. In most potable water applications, chlorine

dioxide is generated as needed and directly educed or injected into a diluting stream.

Generators are available that utilize sodium chlorite and a variety of feedstocks such as

Cl2 gas, sodium hypochlorite, and sulfuric or hydrochloric acid. Small samples of

generated solutions, up to 1 percent (10 g/L) chlorine dioxide can be safely stored if the

solution is protected from light, chilled (<5°C), and has no unventilated headspace.

Primary Uses Chlorine dioxide is utilized as a primary or secondary disinfectant, for taste and odor

control, TTHM/HAA reduction, Fe and Mn control, color removal, sulfide and phenol

destruction, and Zebra mussel control.

Inactivation Efficiency Chlorine dioxide rapidly inactivates most microorganisms over a wide pH range. It is

more effective than chlorine (for pathogens other than viruses) and is not pH dependent

between pH 5-10, but is less effective than ozone.

Byproducts Formation When added to water, chlorine dioxide reacts with many organic and inorganic

compounds. The reactions produce chlorite and chlorate as endproducts (compounds

that are suspected of causing hemolytic anemia and other health effects). Chlorate ion

is formed predominantly in downstream reactions between residual chlorite and free

chlorine when used as the distribution system disinfectant. Chlorine dioxide does not

produce THMs. The use of chlorine dioxide aids in reducing the formation of TTHMs

and HAAs by oxidizing precursors, and by allowing the point of chlorination to be moved

farther downstream in the plant after coagulation, sedimentation, and filtration have

reduced the quantity of NOM.

Point of Application In conventional treatment plants, chlorine dioxide used for oxidation is fed either in the

raw water, in the sedimentation basins, or following sedimentation. To limit the oxidant

demand, and therefore chlorine dioxide dose and the formation of chlorite, it is common

to add chlorine dioxide following sedimentation. Concerns about possible taste and odor

complaints have limited the use of chlorine dioxide to provide a disinfectant residual in

the distribution system. Consequently, public water suppliers that are considering the

use of chlorine dioxide for oxidation and primary disinfectant applications may want to

consider chloramines for secondary disinfection.

Special Considerations An oxidant demand study should be completed to determine an approximate chlorine

dioxide dosage to obtain the required CT value as a disinfectant. In addition to the toxic

effects of chlorine, chlorine dioxide gas is explosive at levels > 10% in air. The chlorine

dioxide dosage cannot exceed 1.4 mg/L to limit the total combined concentration of

ClO2, ClO2-, ClO3-, to a maximum of 1.0 mg/L. Under the proposed DBP regulations,

the MRDL for chlorine dioxide is 0.8 mg/L and the MCL for chlorite is 1.0 mg/L.

Regulations concerning the use of chlorine dioxide vary from state-to-state.
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4.9 References

1. Aieta, E., and J.D.Berg. 1986. “A Review of Chlorine Dioxide in Drinking Water Treatment.”

J. AWWA. 78(6):62-72.

2. Aieta, E.M., P.V. Roberts, and M. Hernandez. 1984. “Determination of Chlorine Dioxide,

Chlorine and Chlorate in Water.” J. AWWA. 76(1):64-70.

3. Alvarez, M.E. and R.T. O’Brien. 1982. “Mechanism of Inactivation of Poliovirus by Chlorine

Dioxide and Iodine.” Appl. Envir. Microbiol. 44:1064.

4. AWWA (American Water Works Association). 1995. AWWA Standard B303-95: Sodium

Chlorite.

5. AWWA. 1991. Guidance Manual for Compliance with the Filtration and Disinfection

Requirements for Public Water Systems Using Surface Water Sources.

6. AWWA. 1990. Water Quality and Treatment, fourth edition. McGraw-Hill, Inc., New York, NY.

7. Bedulivich, T.S., M.N. Svetlakova, and N.N. Trakhtman. 1954. “Use of Chlorine Dioxide in

Purification of Water.” Chemical Abstracts. 48:2953.

8. Bernarde, M.A., et al.1967a. “Kinetics and Mechanism of Bacterial Disinfection by Chlorine

Dioxide.” J. Appl. Microbiol. 15(2):257.

9. Bernarde, M.A., W.B. Snow, and V.P. Olivieri. 1967b. “Chlorine Dioxide Disinfection

Temperature Effects.” J. Appl. Bacteriol. 30(1):159.

10. Chen, Y.S.R., O.J. Sproul, and A.J. Rubin. 1985. “Inactivation of Naegleria gruberi Cysts by

Chlorine Dioxide.” Water Res. 19(6):783.

11. Chen, Y.S.R., O.J. Sproul, and A.J. Rubin. 1984. “Inactivation of Naegleria Gruberi cysts by

Chlorine Dioxide.” EPA Grant R808150-02-0, Department of Civil Engineering, Ohio State

University.

12. CRC Handbook of Chemistry and Physics. 1990. D.L. Lide (editor), Seventy-first edition, CRC

Press, Boca Raton, FL.

13. Cronier, S., et al. 1978. Water Chlorination Environmental Impact and Health Effects, Vol. 2. R.

L. Jolley, et al. (editors) Ann Arbor Science Publishers, Inc. Ann Arbor, MI.

14. Demers, L.D., and R. Renner. 1992. Alternative Disinfectant Technologies for Small Drinking

Water Systems. AWWARF, Denver, CO.
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15. Dixon, K.L. and R.G. Lee. 1991. “Disinfection By-Products Control: A Survey of American

System Treatment Plants.” Presented at AWWA Conference, Philadelphia, PA.

16. Emmenegger, F. and G. Gordon. 1967. “The Rapid Interaction Between Sodium Chlorite and

Dissolved Chlorine.” Inorg. Chem. 6(3):633.

17. Finch, G.R., L.R. Liyanage, M. Belosevic, and L.L. Gyürek. 1997. “Effects of Chlorine Dioxide

Preconditioning on Inactivation of Cryptosporidium by Free Chlorine and Monochloramine:

Process Design Requirements.” Proceedings 1996 Water Quality Technology Conference; Part

II. Boston, MA.

18. Finch, G.R., L.R. Liyanage, and M. Belosevic. 1995. “Effect of Disinfectants and

Cryptosporidium and Giardia.” Third International Symposium on Chlorine Dioxide: Drinking

Water, Process Water, and Wastewater Issues.

19. Gallagher, D.L., R.C. Hoehn, A.M. Dietrich. 1994. Sources, Occurrence, and Control of

Chlorine Dioxide By-Product Residuals in Drinking Water. AWWARF, Denver, CO.

20. Gates, D.J. 1998. The Chlorine Dioxide Handbook; Water Disinfection Series. AWWA

Publishing, Denver, CO.

21. Gates, D.J. 1989. “Chlorine Dioxide Generation Technology and Mythology.” Conference

proceedings, Advances in Water Analysis and Treatment, AWWA, Philadelphia, PA.

22. Ghandbari, E. H., et al. 1983. “Reactions of Chlorine and Chlorine Dioxide with Free Fatty

Acids, Fatty Acid Esters, and Triglycerides.” Water Chlorination: Environmental Impact and

Health Effects, R. L. Jolley, et al. (editors), Lewis, Chelsea, MI.

23. Gordon, G., G.L. Emmert, and B. Bubnis. 1995. “Bromate Ion Formation in Water When

Chlorine Dioxide is Photolyzed in the Presence of Bromide Ion.” Conference proceedings,

AWWA Water Quality Technology Conference, New Orleans, LA.

24. Gordon, G., et al. 1990. “Minimizing Chlorite Ion and Chlorate Ion in Water Treated with

Chlorine Dioxide.” J. AWWA. 82(4): 160-165.

25. Gordon, G., W.J. Cooper, R.G. Rice, and G.E. Pacey. 1987. Disinfectant Residual Measurement

Methods, AWWARF, Denver, CO.

26. Gordon, G., R.G. Kieffer, and D.H. Rosenblatt. 1972. “The Chemistry of Chlorine Dioxide.”

Progress in Organic Chemistry, vol. 15. S.J. Lippaer (editor). Wiley Interscience, New York,

NY.

27. Great Lakes Upper Mississippi River Board of State Public Health (GLUMRB) and

Environmental Managers. 1992. Recommended Standards for Water Works, Health Research

Inc., Albany, NY.
4. CHLORINE DIOXIDE

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4-37

28. Gregory, D. and K. Carlson. 1998. “Applicability of Chlorine Dioxide for Cryptosporidium

Inactivation.” Proceedings 1998 Water Quality Technology Conference, San Diego, CA.

29. Griese, M.H., K. Hauser, M. Berkemeier, and G. Gordon. 1991. “Using Reducing Agents to

Eliminate Chlorine Dioxide and Chlorite Ion Residuals in Drinking Water.” J. AWWA. 83(5):56.

30. Hoehn, R.C. 1992. “Chlorine Dioxide Use in Water Treatment: Key Issues.” Conference

proceedings, Chlorine Dioxide: Drinking Water Issues: Second International Symposium.

Houston, TX.

31. Hoehn, R.C., A.A. Rosenblatt, and D.J. Gates. 1996. “Considerations for Chlorine Dioxide

Treatment of Drinking Water.” Conference proceedings, AWWA Water Quality Technology

Conference, Boston, MA.

32. Hofman, R., R.C. Andrews, and Q. Ye. 1997. “Chlorite Formation When Disinfecting Drinking

Water to Giardia Inactivation Requirements Using Chlorine Dioxide.” Conference proceedings,

ASCE/CSCE Conference, Edmonton, Alberta, July.

33. Knocke, W.R. and A. Iatrou. 1993. Chlorite Ion Reduction by Ferrous Ion Addition. AWWARF,

Denver, CO.

34. Korich, D.G., et al. 1990. “Effects of Ozone, Chlorine Dioxide, Chlorine, and Monochloramine

on Cryptosporidium parvum oocyst Viability.” Appl. Environ. Microbiol. 56:1423-1428.

35. LeChevallier, M.W., et al. 1997. “Chlorine Dioxide for Control of Cryptosporidium and

Disinfection Byproducts.” Conference proceedings, 1996 AWWA Water Quality Technology

Conference Part II, Boston, Massachusetts.

36. LeChevallier, M.W., et al. 1996. “Chlorine Dioxide for Control of Cryptosporidium and

Disinfection Byproducts.” Conference proceedings, AWWA Water Quality Technology

Conference, Boston, Massachusetts.

37. Liyanage, L.R.J, et al. 1997. “Effects of Aqueous Chlorine and Oxychlorine Compounds on

Cryptosporidium Parvum Oocysts.” Environ. Sci. & Tech. 31(7): 1992-1994

38. Masschelein, W.J. 1992. “Unit Processes in Drinking Water Treatment.” Marcel Decker D.C.,

New York, Brussels, Hong Kong.

39. Merkle, J.C. and C.B. Reeverts. 1997. “Ground Water Treatment: What Are the States Doing

Now?” AWWARF, Denver, CO.

40. Noack, M.G. and R.L. Doerr. 1977. “Reactions of Chlorine, Chlorine Dioxide and Mixtures of

Humic Acid: An Interim Report.” Conference proceedings, Second Conference on the

Environmental Impact of Water Chlorination. R.L. Jolley, H. Gorchev, and D. Heyward (editors),

Gatlinburg, TN.
4. CHLORINE DIOXIDE

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4-38

41. Noss, C.I., W.H. Dennis, V.P. Olivieri. 1983. “Reactivity of Chlorine Dioxide with Nucleic

Acids and Proteins.” Water Chlorination: Environmental Impact and Health Effects. R. L. Jolley,

et al. (editors), Lewis Publishers, Chelsea, MI.

42. Olivieri, V.P., et al. 1985. “Mode of Action of Chlorine Dioxide on Selected Viruses.” Water

Chlorination: Environmental Impact and Health Effects. R. L. Jolley, et al. (editors), Lewis,

Chelsea, MI.

43. Olivieri, V.P., et al. 1984. Stability and Effectiveness of Chlorine Disinfectants in Water

Distribution Systems. USEPA, Cincinnati, OH.

44. Peeters, J. E. et al. 1989. “Effect of Disinfection of Drinking Water with Ozone or Chlorine

Dioxide on Survival of Cryptosporidium parvum oocysts.” Appl. Environ. Microbiol. r5:1519-

1522.

45. Pitochelli, A. 1995. “Chlorine Dioxide Generation Chemistry.” Conference proceedings, Third

International Symposium, Chlorine Dioxide: Drinking Water, Process Water, and Wastewater

Issues. New Orleans, LA.

46. Ransome, M.E., T.N. Whitmore, and E.G. Carrington. 1993. “Effect of Disinfectants on the

Viability of Cryptosporidium parvum Oocysts.” Water Supply. 11(1):103-117.

47. Rav-Acha, C., A. Serri, E. Choshen, B. Limoni. 1984. “Disinfection of Drinking Water Rich in

Bromide with Chlorine and Chlorine Dioxide, While Minimizing the Formation of Undesirable

Byproducts.” Wat. Sci. Technol. 17:611.

48. Richardson, S.D. et al. 1994. “Multispectral Identification of ClO2 Disinfection Byproducts in

Drinking Water.” Environ. Sci. & Technol. 28(4):592-599.

49. Ridenour, G.M. and E.H. Armbruster. 1949. “Bactericidal Effects of Chlorine Dioxide.”

J. AWWA. 41:537.

50. Ridenour, G. M. and R.S. Ingols. 1947. “Bactericidal Properties of Chlorine Dioxide.”

J. AWWA. 39.

51. Ridenour, G.M., and R.S. Ingols. 1946. “Inactivation of Poliomyelitis Virus by Free Chlorine.”

Amer. Public Health. 36:639.

52. Ridenour, G.M., and R.S. Ingols, and E.H. Armbruster. 1949. “Sporicidal Properties of Chlorine

Dioxide.” Water & Sewage Works. 96(8):279.

53. Roberts, P.V., E.M. Aieta, J.D. Berg, and B.M. Chow. 1980. “Chlorine Dioxide for Wastewater

Disinfection: A Feasibility Evaluation.” Stanford University Technical Report 251. October.
4. CHLORINE DIOXIDE

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4-39

54. Roller, S. D. et al. 1980. “Mode of Bacterial Inactivation by Chlorine Dioxide.” Water Res.

14:635.

55. Singer, P.C. 1992. “Formation and Characterization of Disinfection Byproducts.” Presented at

the First International Conference on the Safety of Water Disinfection: Balancing Chemical and

Microbial Risks.

56. Singer, P.C., and W.K. O’Neil. 1987. “Technical Note: The Formation of Chlorate from the

Reaction of Chlorine and Chlorite in Dilute Aqueous Solution.” J. AWWA. 79(11):75.

57. Smith, J. E., and J.L. McVey. 1973. “Virus Inactivation by Chlorine Dioxide and Its Application

to Storm Water Overflow.” Proceeding, ACS annual meeting. 13(2):177.

58. Sobsey, M. 1988. “Detection and Chlorine Disinfection of Hepatitis A in Water.” CR-813-024,

EPA Quarterly Report, December.

59. Sproul, O. J. et al. 1983. “Comparison of Chlorine and Chlorine Dioxide for Inactivation of

Amoebic Cyst.” Envir. Technol. Letters. 4:335.

60. Thompson, A.L. 1989. “Practical Considerations for Application of Chlorine Dioxide in

Municipal Water Systems.” Conference proceedings,, Chlorine Dioxide Workshop. AWWARF,

CMA, EPA. Denver, CO.

61. Trakhtman, N.N. 1949. “Chlorine Dioxide in Water Disinfection.” Chemical Abstracts. 43:1508.

62. USEPA (U.S. Environmental Protection Agency). 1983. “Trihalomethanes in Drinking Water:

Sampling, Analysis, Monitoring, and Compliance.” EPA 570/9-83-002, August.

63. USEPA. 1979. “Effect of Particulates on Disinfection of Enteroviruses and Coliform Bacteria in

Water by Chlorine Dioxide.” EPA-600/2-79-054.

64. USEPA 1978. “Effect of Particulates on Inactivation of Enteroviruses in Water by Chlorine

Dioxide.” EPA-600/9-79-018, Cincinnati, OH.

65. Werdehoff, K.S, and P.C. Singer. 1987. “Chlorine Dioxide Effects on THMFP, TOXFP and the

Formation of Inorganic By-Products.” J. AWWA. 79(9):107.
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4. CHLORINE DIOXIDE ............................................................................................................................. 4-1

4.1 CHLORINE DIOXIDE CHEMISTRY ........................................................................................................... 4-1

4.1.1 Oxidation Potential....................................................................................................................... 4-1

4.2 GENERATION........................................................................................................................................ 4-2

4.2.1 Introduction.................................................................................................................................. 4-2

4.2.2 Chlorine Dioxide Purity................................................................................................................ 4-3

4.2.3 Methods of Generating Chlorine Dioxide...................................................................................... 4-4

4.1.4 Generator Design ......................................................................................................................... 4-9

4.1.5 Chemical Feed Systems.............................................................................................................. 4-11

4.1.6 Generator Power Requirements................................................................................................... 4-13

4.3 PRIMARY USES AND POINTS OF APPLICATION FOR CHLORINE DIOXIDE ................................................. 4-13

4.3.1 Disinfection................................................................................................................................ 4-13

4.3.2 Taste and Odor Control .............................................................................................................. 4-14

4.3.3 Oxidation of Iron and Manganese ............................................................................................... 4-14

4.4 PATHOGEN INACTIVATION AND DISINFECTION EFFICACY ..................................................................... 4-15

4.4.1 Inactivation Mechanisms............................................................................................................ 4-15

4.4.2 Environmental Effects................................................................................................................ 4-15

4.4.3 Disinfection Efficacy.................................................................................................................. 4-17

4.5 CHLORINE DIOXIDE DISINFECTION BYPRODUCTS................................................................................. 4-22

4.5.1 Production of Chlorite and Chlorate............................................................................................ 4-22

4.5.2 Organic DBPs Produced by Chlorine Dioxide ............................................................................. 4-25

4.5.3 Chlorine Dioxide DBP Control Strategies................................................................................... 4-25

4.6 STATUS OF ANALYTICAL METHODS..................................................................................................... 4-26

4.6.1 Chlorine Dioxide and Chlorite Analytical Methods..................................................................... 4-27

4.6.2 Chlorine Dioxide Monitoring for Systems Using Chlorine Dioxide ............................................. 4-27

4.6.3 Chlorite Monitoring for Systems Using Chlorine Dioxide ........................................................... 4-28

4.7 OPERATIONAL CONSIDERATIONS......................................................................................................... 4-28

4.7.1 Process Considerations............................................................................................................... 4-30

4.7.2 Generator Operation................................................................................................................... 4-31

4.7.3 Feed Chemicals.......................................................................................................................... 4-31

4.8 SUMMARY.......................................................................................................................................... 4-33

4.8.1 Advantages and Disadvantages of Chlorine Dioxide Use............................................................. 4-33

4.8.2 Summary Table .......................................................................................................................... 4-34

4.9 REFERENCES ...................................................................................................................................... 4-35

Table 4-1. Commercial Chlorine Dioxide Generators.......................................................................................... 4-5

Table 4-2. Surface Water Chlorine Dioxide Demand Study Results................................................................... 4-14

Table 4-3. Analytical Methods for Chlorine Dioxide and Related Compounds................................................... 4-30

Table 4-4. Properties of Sodium Chlorite as Commercially Available................................................................ 4-32

Table 4-5. Summary for Chlorine Dioxide ........................................................................................................ 4-34

Figure 4-1. Conventional Chlorine Dioxide Generator When Using Chlorine-Chlorite Method............................ 4-7

Figure 4-2. Chlorine Dioxide Generation Using Recycled Aqueous Chlorine Method........................................... 4-8

Figure 4-3. Effect of Temperature on N. Gruberi Cyst Inactivation at pH 7 ....................................................... 4-17

Figure 4-4. Comparison of Germicidal Efficiency of Chlorine Dioxide and Chlorine......................................... 4-19

Figure 4-5. CT Values for Inactivation of Giardia Cysts by Chlorine Dioxide ................................................... 4-21

Figure 4-6. CT Values for Inactivation of Viruses by Chlorine Dioxide............................................................. 4-22

Figure 4-7. C. parvum Inactivation by Chlorine Dioxide at 20°C....................................................................... 4-23

Figure 4-8. C. parvum Inactivation by Chlorine Dioxide at 10°C....................................................................... 4-23
April 1999 5-1 EPA Guidance Manual

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5. POTASSIUM PERMANGANATE

Potassium permanganate (KMnO4) is used primarily to control taste and odors, remove color, control

biological growth in treatment plants, and remove iron and manganese. In a secondary role,

potassium permanganate may be useful in controlling the formation of THMs and other DBPs by

oxidizing precursors and reducing the demand for other disinfectants (Hazen and Sawyer, 1992).

The mechanism of reduced DBPs may be as simple as moving the point of chlorine application

further downstream in the treatment train using potassium permanganate to control taste and odors,

color, algae, etc. instead of chlorine. Although potassium permanganate has many potential uses as

an oxidant, it is a poor disinfectant.

5.1 Potassium Permanganate Chemistry

5.1.1 Oxidation Potential

Potassium permanganate is highly reactive under conditions found in the water industry. It will

oxidize a wide variety of inorganic and organic substances. Potassium permanganate (Mn 7+) is

reduced to manganese dioxide (MnO2) (Mn 4+) which precipitates out of solution (Hazen and

Sawyer, 1992). All reactions are exothermic. Under acidic conditions the oxidation half-reactions

are (CRC, 1990):

MnO4

-

 + 4H

+

 + 3e

- ‡ MnO2 + 2H2O Eo

 = 1.68V

MnO4

-

 + 8H

+

+ 5e

-‡ Mn2+ + 4H2O Eo

 = 1.51V

Under alkaline conditions, the half-reaction is (CRC, 1990):

MnO4

-

+ 2H2O + 3e

- ‡ MnO2 + 4OH- Eo

 = 0.60V

Reaction rates for the oxidation of constituents found in natural waters are relatively fast and depend

on temperature, pH, and dosage.

5.1.2 Ability To Form a Residual

It is not desirable to maintain a residual of KMnO4 because of its tendency to give water a pink color.

5.2 Generation

Potassium permanganate is only supplied in dry form. A concentrated KMnO4 solution (typically 1

to 4 percent) is generated on-site for water treatment applications; the solution is pink or purple in

color. KMnO4 has a bulk density of approximately 100 lb/ft3 and its solubility in water is 6.4 g/mL

at 20oC.
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Depending on the amount of permanganate required, these solutions can be made up in batch modes,

using dissolver/storage tanks with mixers and a metering pump for small feed systems. Larger

systems will include a dry chemical feeder, storage hopper and dust collector configured to

automatically supply permanganate to the solution dissolver/storage tank.

KMnO4 solution is made up of dry crystalline permanganate solids added to make-up water and then

stirred to obtain the desired permanganate concentration. The cost of KMnO4 ranges from $1.50 to

$2.00 per pound (1997 costs), depending on the quantity ordered. Shipment containers are typically

buckets or drums. Potassium permanganate is supplied in various grades. Pure KMnO4 is nonhygroscopic but technical grades will absorb some moisture and will have a tendency to cake

together. For systems using dry chemical feeders, a free-flowing grade is available that contains anticaking additives (Hazen and Sawyer, 1992).

Potassium permanganate is a strong oxidizer and should be carefully handled when preparing the

feed solution. No byproducts are generated from making the solution. However, this dark

purple/black crystalline solid can cause serious eye injury, is a skin and inhalation irritant, and can be

fatal if swallowed. As such, special handling procedures include the use of safety goggles and a face

shield, an MSA/NIOSH approved dust mask, and wearing impervious gloves, coveralls, and boots

to minimize skin contact.

5.3 Primary Uses and Points of Application

Although potassium permanganate can inactivate various bacteria and viruses, it is not used as a

primary or secondary disinfectant when applied at commonly used treatment levels. Potassium

permanganate levels that may be required to obtain primary or secondary disinfection could be cost

prohibitive. However, potassium permanganate is used in drinking water treatment to achieve a

variety of other purposes including:

• Oxidation of iron and manganese;

• Oxidation of taste and odor compound;

• Control of nuisance organisms; and

• Control of DBP formation.

5.3.1 Primary Uses

5.3.1.1 Iron and Manganese Oxidation

A primary use of permanganate is iron and manganese removal. Permanganate will oxidize iron and

manganese to convert ferrous (2+) iron into the ferric (3+) state and 2+ manganese to the 4+ state.

The oxidized forms will precipitate as ferric hydroxide and manganese hydroxide (AWWA, 1991).

The precise chemical composition of the precipitate will depend on the nature of the water,

temperature, and pH.
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The classic reactions for the oxidation of iron and manganese are:

3Fe2+ + KMnO4 + 7H2O Ë 3Fe(OH)3(s) + MnO2(s) + K

+

 + 5H

+

3Mn2+ + 2KMnO4 + 2H2O Ë 5MnO2(s) + 2K

+

 + 4H

+

These reactions show that alkalinity is consumed through acid production at the rate of 1.49 mg/L as

CaCO3 per mg/L of Fe+2 and 1.21 mg/L as CaCO3 per mg/L of Mn+2 oxidized. This consumption of

alkalinity should be considered when permanganate treatment is used along with alum coagulation,

which also requires alkalinity to form precipitates.

The potassium permanganate dose required for oxidation is 0.94 mg/mg iron and 1.92 mg/mg

manganese (Culp/Wesner/Culp, 1986). In practice, the actual amount of potassium permanganate

used has been found to be less than that indicated by stoichiometry. It is thought that this is because

of the catalytic influence of MnO2 on the reactions (O’Connell, 1978). The oxidation time ranges

from 5 to 10 minutes, provided that the pH is over 7.0 (Kawamura, 1991).

5.3.1.2 Oxidation of Taste and Odor Compounds

Potassium permanganate is used to remove taste and odor causing compounds. Lalezary et al. (1986)

used permanganate to treat earthy-musty smelling compounds in drinking water. Doses of potassium

permanganate used to treat taste and odor causing compounds range from 0.25 to 20 mg/L.

5.3.1.3 Control of Nuisance Organisms

Asiatic Clams

Cameron et al. (1989) investigated the effectiveness of potassium permanganate to control the

Asiatic clam in both the juvenile and adult phases. The adult Asiatic clam was found to be much

more resistant to permanganate than the juvenile form. Potassium permanganate doses used to

control the juvenile Asiatic clam range from 1.1 to 4.8 mg/L.

Zebra Mussels

Klerks and Fraleigh (1991) evaluated the effectiveness of permanganate against adult zebra mussels.

Continuous potassium permanganate dosing of 0.5 to 2.5 mg/L proved to be the most effective.

5.3.1.4 DBP Control

It is anticipated that potassium permanganate may play a role in disinfection and DBP control

strategies in water treatment. Potassium permanganate could be used to oxidize organic precursors at

the head of the treatment plant minimizing the formation of byproducts at the downstream

disinfection stage of the plant (Hazen and Sawyer, 1992). Test results from a study conducted at two

water treatment plants in North Carolina (Section 5.5.1) showed that pretreatment with permanganate

reduced chloroform formation; however, the reduction was small at doses typically used at water
5. POTASSIUM PERMANGANATE

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treatment plants. The study also indicated that pre-oxidation with permanganate had no net effect on

the chlorine demand of the water (Singer et al., 1980).

5.3.2 Points of Application

In conventional treatment plants, potassium permanganate solution is added to the raw water intake,

at the rapid mix tank in conjunction with coagulants, or at clarifiers upstream of filters. In direct

filtration plants, this oxidant is typically added at the raw water intake to increase the contact time

upstream of the filter units (Montgomery, 1985). In all cases, potassium permanganate is added prior

to filtration.

Potassium permanganate solution is typically pumped from the concentrated solution tank to the

injection point. If the injection point is a pipeline, a standard injection nozzle protruding midway

into the pipe section is used. Injection nozzles can also be used to supply the solution to mixing

chambers and clarifiers. Permanganate is a reactive, fast-acting oxidizer and does not require special

mixing equipment at the point of injection to be effective.

5.3.2.1 Impact on Other Treatment Processes

The use of potassium permanganate has little impact on other treatment processes at the water

treatment facility. See Section 5.7 for permanganate operational considerations.

5.4 Pathogen Inactivation and Disinfection Efficacy

Potassium permanganate is an oxidizing agent widely used throughout the water industry. While it is

not considered a primary disinfectant, potassium permanganate has an effect on the development of a

disinfection strategy by serving as an alternative to pre-chlorination or other oxidants at locations in a

treatment plant where chemical oxidation is desired for control of color, taste and odor, and algae.

5.4.1 Inactivation Mechanisms

The primary mode of pathogen inactivation by potassium permanganate is direct oxidation of cell

material or specific enzyme destruction (Webber and Posselt, 1972). In the same fashion, the

permanganate ion (MnO4

-

) attacks a wide range of microorganisms such as bacteria, fungi, viruses,

and algae.

Application of potassium permanganate results in the precipitation of manganese dioxide. This

mechanism represents an additional method for the removal of microorganisms from potable water

(Cleasby et al., 1964). In colloidal form, the manganese dioxide precipitant has an outer layer of

exposed OH groups. These groups are capable of adsorbing charged species and particles in addition

to neutral molecules (Posselt et al., 1967). As the precipitant is formed, microorganisms can be

adsorbed into the colloids and settled.
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5.4.2 Environmental Effects

Inactivation efficiency depends upon the permanganate concentration, contact time, temperature, pH,

and presence of other oxidizable material. Several of the key parameters are discussed below.

5.4.2.1 pH

Alkaline conditions enhance the capability of potassium permanganate to oxidize organic matter;

however, the opposite is true for its disinfecting power. Typically, potassium permanganate is a

better biocide under acidic conditions than under alkaline conditions (Cleasby et al., 1964 and

Wagner, 1951). Results from a study conducted in 1964 indicated that permanganate generally was a

more effective biocide for E. coli at lower pHs, exhibiting more than a 2-log removal at a pH of 5.9

and a water temperature of both 0 and 20°C (Cleasby et al., 1964). In fact, Cleasby found that pH is

the major factor affecting disinfection effectiveness with potassium permanganate. As such, natural

waters with pH values of 5.9 or less would be conducive to potassium permanganate disinfection,

particularly as a substitute for prechlorination. Moreover a study conducted at the University of

Arizona found that potassium permanganate will inactivate Legionella pneumophila more rapidly at

pH 6.0 than at pH 8.0 (Yahya et al., 1990a).

These results are consistent with earlier results concerning the effects of pH on commercial antiseptic

performance (Hazen and Sawyer, 1992). In general, based on the limited results from these studies,

disinfection effectiveness of potassium permanganate increases with decreasing pH.

5.4.2.2 Temperature

Higher temperatures slightly enhance bactericidal action of potassium permanganate. The results

from a study conducted on polio virus showed that oxidation deactivation is enhanced by higher

temperatures (Lund, 1963). These results are consistent with results obtained for E. coli. inactivation

(Cleasby et al., 1964).

5.4.2.3 Dissolved Organics and Inorganics

The presence of oxidizable organics or inorganics in the water reduces the disinfection effectiveness

of this disinfectant because some of the applied potassium permanganate will be consumed in the

oxidation of organics and inorganics. Permanganate oxidizes a wide variety of inorganic and organic

substances in the pH range of 4 to 9. Under typical water conditions, iron and manganese are

oxidized and precipitated and most contaminants that cause odors and tastes, such as phenols and

algae, are readily degraded by permanganate (Hazen and Sawyer, 1992).

5.4.3 Use as a Disinfectant

A number of investigations have been performed to determine the relative capability of potassium

permanganate as a disinfectant. The following sections contain a description of the disinfection

efficiency of potassium permanganate in regards to bacteria, virus, and protozoa inactivation.
5. POTASSIUM PERMANGANATE

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5.4.3.1 Bacteria Inactivation

High dosage rates were required to accomplish complete inactivation of bacteria in three studies.

Early research showed that a dose of 2.5 mg/L was required for complete inactivation of coliform

bacteria (Le Strat, 1944). In this study, water from the Marne River was dosed with potassium

permanganate at concentrations of 0 to 2.5 mg/L. Following mixing, the samples were placed in a

darkened room for 2 hours at a constant temperature of 19.8oC.

Banerjea (1950) investigated the disinfectant ability of potassium permanganate on several

waterborne pathogenic microorganisms. The investigation studied Vibrio cholerae, Salm. typhi, and

Bact. flexner. The results indicated that doses of 20 mg/L and contact times of 24 hours were

necessary to deactivate these pathogens; however, even under these conditions the complete absence

of Salm. typhi or Bact. flexner was not assured, even at a potassium permanganate concentration that

turned the water an objectionable pink color.

Results from a study conducted in 1976 at the Las Vegas Valley Water District/Southern Nevada

System of Lake Mead water showed that complete removal of coliform bacteria were accomplished

at doses of 1, 2, 3, 4, 5, and 6 mg/L (Hazen and Sawyer, 1992). Contact times of 30 minutes were

provided with doses of 1 and 2 mg/L, and 10 minutes contact times were provided for higher dosages

in this study.

5.4.3.2 Virus Inactivation

Potassium permanganate has been proven effective against certain viruses. A dose of 50 mg/L of

potassium permanganate and a contact time of 2 hours was required for inactivation of poliovirus

(strain MVA) (Hazen and Sawyer, 1992). A “potassium” permanganate dose of 5.0 mg/L and a

contact time of 33 minutes was needed for 1-log inactivation of type 1 poliovirus (Yahya et al.,

1990b). Tests showed a significantly higher inactivation rate at 23oC than at 7oC; however, there was

no significant difference in activation rates at pH 6.0 and pH 8.0.

Potassium permanganate doses from 0.5 to 5 mg/L were capable of obtaining at least a 2 log

inactivation of the surrogate virus, MS-2 bacteriophage with E. coli as the host bacterium (Yahya et

al., 1989). Results showed that at pH 6.0 and 8.0, a 2-log inactivation occurred after a contact time

of at least 52 minutes and a residual of 0.5 mg/L. At a residual of 5.0 mg/L, approximately 7 and 13

minutes were required for 2-log inactivation at pHs of 8.0 and 6.0, respectively. These results

contradict the previously cited studies that potassium permanganate becomes more effective as the

pH decreases.

5.4.3.3 Protozoa Inactivation

No information pertaining to protozoa inactivation by potassium permanganate is available in the

literature. However, based on the other disinfectants discussed in this report, protozoa are

significantly more resistant than viruses; therefore, it is likely that the dosages and contact times

required for protozoa inactivation would be impractical.
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5.4.3.4 CT Curves

Table 5-1 shows CT values for the inactivation of bacteriophage MS-2. These data have been

provided as an indication of the potential of potassium permanganate. These values are somewhat

inconsistent and do not include a safety factor and should not be used to establish CT requirements.

Table 5-1. Potassium Permanganate CT Values for 2-log Inactivation of

MS-2 Bacteriophage

Residual

(mg/L)

pH 6.01

(mg min / L)

pH 8.01

(mg min / L)

0.5 27.4 (a) 26.1 (a)

1.5 32.0 (a) 50.9 (b)

2 - 53.5 (c)

5 63.8 (a) 35.5 (c)

Source: USEPA, 1990.

Note: 1 Letters indicate different experimental conditions.

A 1990 study investigated CT values for Legionella pneumophila inactivation. CT values for 99

percent (2-log) inactivation of Legionella pneumophila at pH 6.0 were determined to be 42.7 mg

min/L at a dose of 1.0 mg/L (contact time 42.7 minutes) and 41.0 mg min/L at a dose of 5.0 mg/L

(contact time 8.2 minutes) (Yahya et al., 1990a).

5.5 Disinfection Byproduct Formation

No literature is available that specifically addressed DBPs when using potassium permanganate.

However, several studies have been conducted with water treatment plants that have replaced the prechlorination process with potassium permanganate and relocated the point of chlorine addition for

post-treatment disinfection. Pretreatment with permanganate in combination with post-treatment

chlorination will typically result in lower DBP concentrations than would otherwise occur from

traditional pre-chlorination (Ficek and Boll, 1980; and Singer et al., 1980). Under this approach,

potassium permanganate serves as a substitute for chlorine to achieve oxidation and may also reduce

the concentration of natural organic matter (NOM). However, systems should evaluate the impact on

CT values before moving the point of chlorination. The following subsections summarize the

outcomes of two studies.

5.5.1 Chapel-Hill and Durham, North Carolina Water Treatment

Plants

An investigation was conducted at the Chapel-Hill and Durham Water Treatment Plants to evaluate

the effects of potassium permanganate pretreatment on trihalomethane formation (Singer et al.,

1980). The Chapel-Hill Water Treatment Plant uses pre-chlorination prior to the rapid mix tank. At

the Durham Water Treatment Plant, chlorine is not added until after the sedimentation basin prior to

the filtration. Both are surface water treatment plants, treating water with low concentrations of
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alkalinity. Both sources of water are known to have high trihalomethane formation potentials

(Young and Singer, 1979).

Raw water samples taken from Chapel-Hill were found to contain relatively high turbidities, ranging

from 46 to 110 NTU and total organic carbon (TOC) concentrations ranging from 5.6 to 8.9 mg/L.

The Durham samples were coagulated then allowed to settle, which resulted in better water quality

than the Chapel-Hill samples. Following settling, this sample had a turbidity of 6.4 NTU and a TOC

of 2.9 mg/L. Sulfuric acid and sodium hydroxide were used to adjust the sample pH to either 6.5 or

10.3. These pH values were selected because they encompass the pH range typically found in

surface water coagulation-filtration and lime-softening treatment plants.

Potassium permanganate doses of 2 and 5 mg/L were found to be totally consumed within 1 and 4

hours, respectively, by the Chapel-Hill samples. At doses of 2 and 5 mg/L, the potassium

permanganate demand of the Durham samples after 4 hours were approximately 1.3 and 1.8 mg/L,

respectively.

This difference in permanganate demands between the Chapel-Hill and Durham samples may be

attributed to the water quality of the samples, in particular the TOC concentrations. TOC

measurements before and after the application of permanganate were approximately equal; however,

it is likely that the TOC after disinfection was at a higher oxidation state. Results of this study also

showed that permanganate is more reactive as an oxidant at higher pH values.

Despite the high degree of permanganate consumption, the reaction of permanganate appears to have

relatively little effect on chlorine demands. For example, consumption of 6 mg/L of permanganate

resulted in a chlorine demand reduction of approximately 1 mg/L. This observation suggests that

permanganate reacts with water impurities in a different manner, or at different sites, than chlorine.

One other possible explanation is that permanganate oxidizes certain organic substances, thereby

eliminating their chlorine demand and only partially oxidizing other organic substances making them

more reactive to chlorine.

Both the Chapel-Hill and Durham samples were tested for their chloroform formation potential. This

measurement is based on the amount of chloroform produced after seven days. The potential of the

Durham sample was reduced by 30 and 40 percent at pH 6.5 and 10.3, respectively, as a result of the

application of 10 mg/L of potassium permanganate for a period of 2 hours. Similar results were

obtained for the Chapel-Hill samples; however, the results at pH 6.5 did not show a reduction in

chloroform formation potential at low doses.

Two experiments were conducted on Chapel-Hill raw water to further explore the effects of low

doses of permanganate. The results indicated that permanganate has no effect on chloroform

production at doses up to 1 mg/L. At higher doses, chloroform formation potentials were reduced.

In summary, the key results obtained from the studies conducted at the Chapel-Hill and Durham

Water treatment plants were:
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• The reactivity of permanganate is a function of pH, permanganate dose, and raw water

quality.

• Permanganate reduces chloroform formation potentials. The reduction in the chloroform

formation potential is proportional to the amount of permanganate available after the initial

demand is overcome. Doses up to 1 mg/L were found to have no effect on chloroform

formation potentials.

• At pretreatment doses typically employed at water treatment plants, the effect of

permanganate on the overall chloroform production is relatively small. If permanganate is to

be used specifically to reduce trihalomethane formation, larger doses will be required.

However, one advantage for using permanganate for pretreatment is that the point of

application of chlorine can be shifted downstream of the sedimentation basins. This is likely

to result in fewer trihalomethane compounds.

5.5.2 American Water Works Association Research Foundation

TTHM Study

Another investigation examined the impacts of potassium permanganate addition on byproduct

formation at four water treatment plants (Ficek and Boll, 1980). All were conventional plants using

pre-chlorination in the treatment process. Plant design capacities ranged from 4.5 to 15 mgd.

Process modifications were made at each plant to replace the pre-chlorination facilities with

oxidation facilities for potassium permanganate addition. After the modifications were complete, an

AWWARF research team conducted a study to determine the impact of potassium permanganate

addition on total trihalomethane (TTHM) concentrations (George et al., 1990).

Prior to switching from pre-chlorination to pre-oxidation with potassium permanganate, average

daily TTHM concentrations at all four plants were between 79 and 99 μg/L. The average TTHM

concentration for all four plants was 92 μg/L. Following the conversion to potassium permanganate,

three of the four plants experienced greater than 30 percent reduction in TTHM concentrations. In

addition to TTHM reduction, potassium permanganate was found to oxidize taste and odor causing

compounds, iron and manganese, organic and inorganic matter, and reduce algal growth. Results

from the study also showed that the simultaneous application of potassium permanganate and

chlorine can increase THM formation.

5.6 Status of Analytical Methods

The atomic adsorption spectrophotometry method for the measurement of manganese is the preferred

method for measuring permanganate concentrations. Two colorimetric methods, persulfate and

periodate are also available (Standard Methods, 1995).

5.7 Operational Considerations

In utilizing potassium permanganate in water treatment, caution should be taken to prevent

overdosing, in which case, excess manganese will pass through the treatment plant. Proper dosing
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should be maintained to ensure that all of the permanganate is reduced (i.e., forming MnO2 solids)

and removed from the plant upstream of, or within, the filters. If residual manganese is reduced

downstream of the filters, the resulting solids can turn the finished water a brown/black color and

precipitate in the homes of consumers on heat exchange surfaces such as hot water heaters and

dishwashers.

Use of potassium permanganate can also be a source of manganese in the finished water, which is

regulated in drinking water with a secondary maximum contaminant level of 0.05 mg/L. Under

reducing conditions, the MnO2 solids accumulated in filter backwash water and settling basins can be

reduced to soluble Mn2+ and pass through the filters thereby remaining in the finished water.

Also, under these conditions, soluble Mn2+ in return water from settling basin dewatering facilities

and filter backwash water recycled to the head of the plant are potential sources of manganese that

will have to be treated and/or controlled to minimize finished water manganese levels (Singer, 1991).

Overdosing of permanganate in conventional plants is generally corrected by settling the excess

MnO2 solids in the settling basin. Removal of the excess permanganate can be monitored

qualitatively by observing the disappearance of the pink color characteristic of permanganate. In

plants that do not utilize flocculation and sedimentation processes permanganate dosing should be

closely monitored (Montgomery, 1985).

In general, potassium permanganate does not interfere with other treatment processes or plant

conditions. Permanganate can be added downstream of, or concurrently with, coagulant and filter

polymer aids. Powdered activated carbon (PAC) and permanganate should not be added

concurrently. PAC should be added downstream of permanganate because it may consume

permanganate, rendering it unavailable for the oxidation of target organics. (Montgomery, 1985).

The space requirements for permanganate feed equipment vary depending on the type and size of

feed system. Dry feed systems require about half the floor area of batch systems because batch

systems typically have two dissolving tanks for redundancy. However, the head space requirements

are greater for dry feed systems where the storage hopper and dust collector are stacked on top of the

dry feeder (Kawamura, 1991). On-site storage of potassium permanganate also warrants some

consideration. Per OSHA requirements, oxidants such as permanganate should be stored separate

from organic chemicals such as polymers and activated carbon.

5.8 Summary

5.8.1 Advantages and Disadvantages of Potassium

Permanganate Use

The following list highlights selected advantages and disadvantages of using potassium

permanganate as a disinfection method for drinking water. Because of the wide variation of system
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size, water quality, and dosages applied, some of these advantages and disadvantages may not apply

to a particular system.

Advantages

• Potassium permanganate oxidizes iron and manganese.

• Potassium permanganate oxidizes odor and taste-causing compounds.

• Potassium permanganate is easy to transport, store, and apply.

• Potassium permanganate is useful in controlling the formation of THMs and other DBPs.

• Potassium permanganate controls nuisance organisms.

• The use of potassium permanganate has little impact on other treatment processes at the water

treatment facility.

• Potassium permanganate has been proven effective against certain viruses.

Disadvantages

• Long contact time is required.

• Potassium permanganate has a tendency to give water a pink color.

• Potassium permanganate is toxic and irritating to skin and mucous membranes.

• No byproducts are generated when preparing the feed solution, however this dark purple/black

crystalline solid can cause serious eye injury, is a skin and inhalation irritant, and can be fatal if

swallowed. Over-dosing is dangerous and may cause health problems such as chemical jaundice

and drop in blood pressure.

5.8.2 Summary Table

More research is needed regarding the disinfection properties and oxidation byproducts of

permanganate in water treatment. Also, a CT credit needs to be assigned to permanganate if it is to

be utilized as a disinfectant. However, given that alternative oxidants, such as ozone and chlorine

dioxide, demonstrate much greater efficacy in microbial control, permanganate is not likely to be

utilized as a primary oxidant for precursor control. Table 5-2 summarizes the information presented

in this chapter regarding the use of potassium permanganate in the drinking water treatment process.
5. POTASSIUM PERMANGANATE

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Table 5-2. Summary of Potassium Permanganate Use

Consideration Description

Generation Product supplied in dry form in buckets, drums, and bulk. On-site generation of solution is

required using chemical mixing and feed equipment.

Primary uses Control of odor and taste, remove color, control biological growth, and remove iron and

manganese.

Inactivation efficiency Not a good disinfectant. Can serve better as an alternative to chlorine or other disinfectants

where chemical oxidation is desired.

Byproduct formation No literature was found that specifically addressed DBP formation from potassium

permanganate oxidation. Pretreatment with permanganate in combination with post-treatment

chlorination will typically result in lower DBP concentrations than would otherwise occur from

traditional pre-chlorination.

Limitations Not a good disinfectant; primarily used for pretreatment to minimize chlorine usage and

byproduct formation.

Points of application Conventional Treatment: raw water addition, rapid mix tank in conjunction with coagulants,

clarifiers upstream of filters. Direct Filtration: raw water intake. In all cases permanganate

should be added upstream of filters.

Special considerations Caution should be taken to prevent overdosing. More research is needed to determine

disinfection properties and oxidation byproducts.

5.9 References

1. AWWA (American Water Works Association). 1991. Guidance Manual for Compliance with the

Filtration and Disinfection Requirements for Public Water Systems Using Surface Water

Sources.

2. Banerjea, R. 1950. “The Use of Potassium Permanganate in the Disinfection of Water.” Ind.

Med. Gaz. 85:214-219.

3. Cameron, G.N., J.M. Symons, S.R. Spencer, and J.Y. Ma. 1989. “Minimizing THM Formation

During Control of the Asiatic Clam: A Comparison of Biocides.” J. AWWA. 81(10):53-62.

4. Cleasby, J.L., E.R. Baumann, and C.D. Black. 1964. “Effectiveness of Potassium Permanganate

for Disinfection.” J. AWWA. 56:466-474.

5. CRC. 1990. Handbook of Chemistry and Physics, seventy-first edition. D.L. Lide (editor). CRC

Press, Boca Raton, FL.

6. Culp/Wesner/Culp. 1986. Handbook of Public Water Systems. Van Nostrand Reinhold, New

York, NY.
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7. Ficek, K.J., and J.E. Boll. 1980. “Potassium Permanganate: An Alternative to Prechlorination.”

Aque. 7:153-156.

8. George, D.B., V.D. Adams, S.A. Huddleston, K.L. Roberts, and M.B. Borup. 1990. Case Studies

of Modified Disinfection Practices for Trihalomethane Control, Potassium Permanganate.

AWWAR and AWWA, Denver, CO.

9. Hazen and Sawyer. 1992. Disinfection Alternatives for Safe Drinking Water. Van Nostrand

Reinhold, New York, NY.

10. Kawamura, S. 1991. Integrated Design of Water Treatment Facilities. John Wiley & Sons, Inc.,

New York, NY.

11. Klerks, P.L. and P.C. Fraleigh. 1991. “Controlling Adult Zebra Mussels with Oxidants.”

J.AWWA. 83(12):92-100.

12. Lalezary, S., M. Pirbazari, and M.J. McGuire. 1986. “Oxidation of Five Earthy-Musty Taste and

Odor Compounds.” J. AWWA. 78(3):62.

13. Le Strat. 1944. “Comparison des pouvoirs sterilisants du permanganate de potasses et de l’eau de

javel a l’egard d’eaux contaminees.” Ann. Hygiene.

14. Lund, E. 1963. “Significance of Oxidation in Chemical Interaction of Polioviruses.” Arch. Ges.

Virusdorsch. 12(5):648-660.

15. Montgomery, J.M. 1985. Water Treatment Principles and Design. John Wiley & Sons, Inc.,

New York, NY.

16. O’Connell, R.T. 1978. “Suspended Solids Removal.” Water Treatment Plant Design. R.L. Sanks

(editor). Ann Arbor Science Publishers, Inc, Ann Arbor, MI.

17. Posselt, H.S., F. J. Anderson, and W.J. Webber. 1967. “The Surface Chemistry of Hydrous

Manganese Dioxide.” Presented at meeting of Water, Air, and Waste Chemistry Division,

American Chemical Society, Bar Harbor, FL, April.

18. Singer, P.C. 1991. “Research Needs for Alternative Oxidants and Disinfectants.” Presented at the

Annual AWWA Conference, Philadelphia, June 23-27.

19. Singer, P.C., J.H. Borchardt, and J.M. Colthurst. 1980. “The Effects of Permanganate

Pretreatment on Trihalomethane Formation in Drinking Water.” J. AWWA. 72(10):573-578.

20. Standard Methods. 1995. Standard Methods for the Examination of Water and Wastewater,

nineteenth edition. American Public Health Association, AWWA, and Water Pollution Control

Fed., Washington, D.C.
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21. USEPA. 1990. Guidance Manual for Compliance with the Filtration and Disinfection

Requirements for Public Works Systems Using Surface Water Sources. Prepared by Malcolm

Pirnie, Inc. and HDR Engineering for USEPA. Contract No. 68-01-6989.

22. Wagner, R.R. 1951. “Studies on the Inactivation of Influenza Virus.” Yale J. Biol. Med. pp. 288-

298.

23. Webber, W.J., Jr., and H.S. Posselt. 1972. “Disinfection.” Physicochemical Processes in Water

Quality Control. W. J. Webber (editor). John Wiley & Sons, New York, NY.

24. Yahya, M.T., T.M. Straub, and C.P. Gerba. 1990a. Inactivation of poliovirus type 1 by Potassium

Permanganate. University of Arizona Preliminary Research Report, Tucson, AZ.

25. Yahya, M.T., Landeen, L.K., and Gerba, C.P. 1990b. Inactivation of Legionella pneumophila by

Potassium Permanganate. Environ. Technol. 11:657-662.

26. Yahya, M.T., et al. 1989. “Evaluation of Potassium Permanganate for the Inactivation of MS-2 in

Water Systems.” J. Environ. Sci. Health. A34(8):979-989.

27. Young, J.S. and P.C. Singer. 1979. “Chloroform Formation in Public Water Supplies: A Case

Study.” J. AWWA. 71(2):87.
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5. POTASSIUM PERMANGANATE........................................................................................................... 5-1

5.1 POTASSIUM PERMANGANATE CHEMISTRY ............................................................................................. 5-1

5.1.1 Oxidation Potential....................................................................................................................... 5-1

5.1.2 Ability To Form a Residual .......................................................................................................... 5-1

5.2 GENERATION........................................................................................................................................ 5-1

5.3 PRIMARY USES AND POINTS OF APPLICATION ........................................................................................ 5-2

5.3.1 Primary Uses................................................................................................................................ 5-2

5.3.2 Points of Application.................................................................................................................... 5-4

5.4 PATHOGEN INACTIVATION AND DISINFECTION EFFICACY ....................................................................... 5-4

5.4.1 Inactivation Mechanisms.............................................................................................................. 5-4

5.4.2 Environmental Effects.................................................................................................................. 5-5

5.4.3 Use as a Disinfectant .................................................................................................................... 5-5

5.5 DISINFECTION BYPRODUCT FORMATION................................................................................................ 5-7

5.5.1 Chapel-Hill and Durham, North Carolina Water Treatment Plants................................................. 5-7

5.5.2 American Water Works Association Research Foundation TTHM Study....................................... 5-9

5.6 STATUS OF ANALYTICAL METHODS....................................................................................................... 5-9

5.7 OPERATIONAL CONSIDERATIONS........................................................................................................... 5-9

5.8 SUMMARY.......................................................................................................................................... 5-10

5.8.1 Advantages and Disadvantages of Potassium Permanganate Use ................................................. 5-10

5.8.2 Summary Table .......................................................................................................................... 5-11

5.9 REFERENCES ...................................................................................................................................... 5-12

Table 5-1. Potassium Permanganate CT Values for 2-log Inactivation of MS-2 Bacteriophage ............................ 5-7

Table 5-2. Summary of Potassium Permanganate Use ....................................................................................... 5-12
April 1999 6-1 EPA Guidance Manual

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6. CHLORAMINES

The disinfectant potential of chlorine-ammonia compounds or chloramines was identified in the early

1900s. The potential use of chloramines was considered after observing that disinfection by chlorine

occurred in two distinct phases. During the initial phase, chlorine reducing compounds (i.e.,

demand) cause the rapid disappearance of free available chlorine. However, when ammonia was

present bactericidal action was observed to continue [even though free chlorine residual was

dissipated]. The subsequent disinfection phase occurs by the action of the inorganic chloramines.

6.1 Chloramines Chemistry

Chloramines are formed by the reaction of ammonia with aqueous chlorine (i.e., HOCl). Initially,

chloramines were used for taste and odor control. However, it was soon recognized that chloramines

were more stable than free chlorine in the distribution system and consequently were found to be

effective for controlling bacterial regrowth. As a result, chloramines were used regularly during the

1930s and 1940s for disinfection. Due to an ammonia shortage during World War II, however, the

popularity of chloramination declined. Concern during the past two decades over chlorinated

organics (e.g., THM and HAA formation) in water treatment and distribution systems, increased

interest in chloramines because they form very few disinfection byproducts (DBPs).

6.1.1 Equilibrium, Kinetic, and Physiochemical Properties

Chloramines are formed from the reaction of chlorine and ammonia. The mixture that results may

contain monochloramine (NH2Cl), dichloramine (NHCl2), or nitrogen trichloride (NCl3). When

chlorine is dispersed in water, a rapid hydrolysis occurs according to the following reaction:

Cl H O HOCl H Cl 2 + 2 → + +

+ −

The equilibrium constant (Keq) at 25oC is 3.94 x 104 M-1 for this reaction. In dilute solutions at pH

greater than 3, the forward reaction is essentially complete. Hypochlorous acid (HOCl) is a weak

acid that dissociates as follows:

HOCl ⇔ OCl + H pKa =

− +

7.6

Relative proportions of HOCl and OCl- are dependent upon pH. Both of the chlorine species in the

above reaction are powerful oxidants, capable of reacting with many substances present in water. In

aqueous solutions with pH 7.0 to 8.5, HOCl reacts rapidly with ammonia to form inorganic

chloramines in a series of competing reactions (White, 1992). The simplified stoichiometry of

chlorine-ammonia reactions are as follows:

NH3 + HOCl → NH2Cl + H2O (monochloramine)
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6-2

NH2Cl + HOCl → NHCl2 + H2O (dichloramine)

NHCl2 + HOCl → NCl3 + H2O (nitrogen trichloride)

These competing reactions, and several others, are primarily dependent on pH and controlled to a

large extent by the chlorine:ammonia nitrogen (Cl2:N) ratio. Temperature and contact time also play

a role. Figure 6-1shows the typical relationships between the chloramine species at various Cl2:N

ratios for pHs ranging from 6.5 to 8.5. This figure shows that monochloramine is predominately

formed when the applied Cl2:N ratio is less than 5:1 by weight. As the applied Cl2:N ratio increases

from 5:1 to 7.6:1, breakpoint reaction occurs, reducing the residual chlorine level to a minimum.

Breakpoint chlorination results in the formation of nitrogen gas, nitrate, and nitrogen chloride. At

Cl2:N ratios above 7.6:1, free chlorine and nitrogen trichloride are present. Figure 6-2 shows the

relationship between chloramine species as the pH changes (Palin, 1950). The Figure shows that

dichloramine becomes a dominant species at low pH.

HOCl + OClNCl3

0

2

4

6

8

0 2 4 6 8 10 12 14 16

Chlorine Dose, mg Cl2/mg NH4-N

Chlorine Residual

mg Cl

2/mg NH

4-N

NHCl2

NH2Cl

Figure 6-1. Theoretical Breakpoint Curve

To avoid breakpoint reactions, utilities should maintain a Cl2:N ratio between 3 and 5 by weight. A

ratio of 6 is actually optimum for disinfection, but it is difficult to maintain a stable operation at that

point in the breakthrough curve. Therefore, a Cl2:N ratio of 4 is typically accepted as optimal for

chloramination.

Furthermore, over a period of a day or so, without any modification of pH or Cl2:N ratio,

monochloramine will degrade slowly to dichloramine to a ratio of 43 percent NH2Cl to 57 percent

NHCl2. Dichloramine is relatively unstable in the presence of HOCl; therefore, pure solutions of this

form of monochloramine are difficult to generate and maintain.
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6-3

Monochloramine

Dichloramine

Nitrogen

Trichloride

Total Combined Chlorine (%)

20

40

60

80

100

3 5 6 7 8

pH

Source: Palin, 1950.

Figure 6-2. Distribution Diagram for Chloramine Species with pH

6.2 Generation

Chloramines are formed by the reaction of hypochlorous acid and ammonia according to the

equations described in Section 6.1. Table 6-1 summarizes the theoretical doses of chlorine and

ammonia based on these formulas. Monochloramine is the preferred chloramine species for use in

disinfecting drinking water because of taste and odor problems associated with dichloramine and

nitrogen trichloride. To ensure that these compounds are not formed, common practice was to limit

the chlorine to ammonia ratio to 3:1. However, because of problems such as nitrification and biofilm

growth, which can be caused by excess ammonia, current practice is to use a Cl2:N ratio in the range

of 3:1 to 5:1, with a typical value of 4:1.

Table 6-1. Chlorine Dose Required for NH3 - Cl2 Reaction

Reaction mg Cl2/mg NH3

Monochloramine (NH2Cl) 4.2

Dichloramine (NHCl2) 8.4

Nitrogen Trichloride (NCl3) 12.5

Nitrogen (N2) 6.3

Nitrate (NO3) 16.7

Free residual reaction 9

Source: AWWA and ASCE, 1990.
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6-4

The rate of reaction of monochloramine formation is sensitive to pH. Table 6-2 shows the calculated

reaction times for monochloromine formation at 25°C, and at a chlorine:amonia ratio of 3:1 (White,

1992).

Table 6-2. Time to 99 Percent Conversion of Chlorine to Monochloramine

pH Time (seconds)

2 421

4 147

7 0.2

8.3 0.069

12 33.2

6.2.1 Chlorine Feed Facilities

Table 6-3 summarizes commonly used methods of chlorine addition, including their safety

precautions and costs.

Table 6-3. Methods of Chlorine Addition

Method Description Safety precautions Costs

Gaseous

chlorine

Gas delivered in containers

ranging in size from 150 lb

cylinders to 90 ton rail cars. One

ton cylinders are commonly used.

Feed equipment consists of

solution water pump/ejector to

create vacuum and automatic

orifice control to meter the gas.

Gas can be drawn directly from

storage container or be generated

by an evaporator from liquid

withdrawn from the container. A

schematic of gaseous chlorine

feed system is shown in

Figure 6-3.

Gaseous chlorine is classified

by the Uniform Fire Code as

an oxidizing, highly toxic,

compressed gas. New

gaseous chlorine facilities

should be designed with

enclosures and air scrubbers

to capture and neutralize any

gas that leaks. Risk

management prevention plans

should be prepared. Personnel

safety equipment and training

should be provided for

operators.

The cost per

pound of

liquid chlorine

is in the range

of $0.08 to

$0.20 per

pound

depending on

the quantity

purchased.

Sodium

hypochlorite

Sodium hypochlorite can be

purchased bulk in quantities

ranging from 55 gal drums to

4,500 gal truck loads. Bulk loads

can be stored in fiberglass or

plastic tanks. Solution is fed

directly into the process stream. A

schematic of typical hypochlorite

feed system is shown in Figure 6-

4.

Hypochlorite solution is toxic

and classified as hazardous.

Storage facilities should be

designed with secondary

containment.

Typical

chemical cost

is $0.60 to

$1.00 per

pound Cl2.
6. CHLORAMINES

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6-5

6.2.2 Ammonia Feed Facilities

Ammonia feed facilities can be located on-site at the water treatment plant or at remote locations in

the distribution system (Dennis et al., 1991). Most ammonia feed facilities use either gaseous

(anhydrous ammonia) or liquid (aqueous) ammonia. Though anhydrous ammonia is a gas at ambient

temperature and pressure, it is commonly stored and transported as a liquid in pressure vessels. In

this phase, ammonia is highly soluble in water. Storage facilities and handling equipment should be

kept dry (Dennis et al., 1991).

Vacuum Pipe

Gas Feeder

Eductor

Water Supply Chlorine Solution

Flexible Connector

Horizontal Manifold

Assembly

Chlorine Cylinder

(150 lb, Ton, Tanker)

Vacuum Regulator

Controller

Figure 6-3. Gaseous Chlorine Feed System
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Chemical

Storage Tank

Back

Pressure

Valve

Shutoff

Valve

Flow to

Discharge

Point

Calibration

Column

Strainer

Tank

Shut-off

Valve

Metering

Pump

Pulsation

Dampner

Relief

Valve

Figure 6-4. Hypochlorite Feed System

6.2.2.1 Anhydrous Ammonia

Anhydrous ammonia is stored in portable cylinders or stationary tanks. Portable cylinders are similar

to chlorine cylinders and are available in 100, 150, and 800 lb sizes (Dennis et al., 1991). The

cylinders are rated for a minimum service pressure of 480 psi. Stationary tanks are typically 1,000

gallon vessels that can be used on-site. These tanks are refilled by tanker trailers. The storage tanks

can be located indoors or outdoors. Since each tank has a minimum working pressure of 250 psi

(valves and fittings on the tanks are rated for 300 psi), a tank stored outdoors should have protection

from extreme temperatures (greater than 125°F and less than 28°F) (Dennis et al., 1991). In warmer

climates, an outdoor tank should be painted white and protected from sunlight. In colder climates,

the tank should be wrapped with heat tape to prevent impairment of the ammonia vaporization.

Anhydrous ammonia is applied using an ammoniator. An ammoniator is a self-contained modular

unit with a pressure reducing valve, gas flow meter, feed rate control valve, and miscellaneous piping

for controlling the flow of ammonia. Automatic paced ammoniators are available. An evaporator is

used when large quantities of ammonia gas are needed. An anti-siphon valve or check valve should

be used to prevent water from entering the ammoniator.

Anhydrous ammonia is usually applied by direct feed or solution feed. The direct feed method is

typically used when the process stream has a low pressure and the ammonia feed rate is less than

1,000 lb per day (i.e., maximum rated feed capacity). Ammonia is drawn from the storage tank

under high pressure (e.g., 200 psi), and injected directly into the process stream at a low pressure of

15 psi. The tank pressure is first reduced by a pressure reducing valve to approximately 40 psi, and
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then by another pressure reducing valve in the ammoniator. Typical application points are at open

channels and basin facilities. Figure 6-5 is a schematic of a direct anhydrous ammonia feed system.

The solution feed method is typically used where direct feed systems are not adequate (e.g., ammonia

feed rate is greater than 1000 lb/day or where the process stream pressure is high) (Dennis et al.,

1991). This type of application is similar to the chlorine vacuum feed system. The supply tank

pressure is reduced by a pressure reducing valve to create a vacuum. An eductor is used to withdraw

ammonia from the ammoniator where the ammonia is dissolved into a side water stream and pumped

into the process stream. Solution feed ammoniators are available up to 4,000 lb/day capacities and

can operate at discharge pressures up to 100 psi (Dennis et al., 1991). Softened water (i.e., hardness

less than 29 mg/L as CaCO3) is required for the carrier stream. Otherwise, the ammonia addition will

precipitate scale that may plug the eductor and application point. Figure 6-6 shows a schematic of a

solution feed system.

6.2.2.2 Aqueous Ammonia

Aqueous ammonia is produced by dissolving anhydrous ammonia into deionized or softened water.

This form of ammonia is shipped in cargo trucks or polyethylene lined steel drums. Plastic drums

are not recommended since they tend to lose their shape under the slight pressure exerted by the

aqueous ammonia. Aqueous ammonia is stored in low pressure tanks, typically steel or fiberglass.

Since excessive temperatures will cause ammonia gas to vaporize, each storage tank should be

equipped with a water trap or ammonia scrubber to keep vapors from escaping to the atmosphere.

Evaporator

(if necessary)

Direct feed

ammoniators

in parallel

Control System

Flow Signal

Custom gas diffuser

(maximum discharge pressure

= 15 psi for direct-feed

ammoniators)

Ammoniation building

Anhydrous NH3 tank trailer

PRV

Source: Montgomery, 1985.

Figure 6-5. Anhydrous Ammonia Direct Feed System
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Anhydrous NH3 tank trailer

Eductor

Evaporator

(if necessary)

V-Notch

ammoniator

Ammoniation Building Solution diffuser

(~ 150 psi maximum

discharge pressure)

Water

Softener

Utility Water

Brine waste

during regeneration

Pump

Control System

Flow Signal

PRV

Source: Montgomery, 1985.

Figure 6-6. Anhydrous Ammonia Solution Feed System

Aqueous ammonia feed systems are similar to other liquid chemical feed systems. They require a

storage tank, chemical metering pump, relief valve, pulsation dampener, flow meter, and

backpressure valve. Typically, the feed pumps are positive displacement or progressive cavity type

metering pumps. The feed pumps should be placed fairly close to the storage tank to minimize

chances of ammonia vaporization in the piping (Dennis et al., 1991). The pump should be designed

to compensate for changes in ambient temperatures, different aqueous ammonia solutions, and

changes in the chlorine-to-ammonia ratio (Skadsen, 1993). When aqueous ammonia is applied to

water, complete mixing is required for the ammonia to react with chlorine in the water to reduce the

formation of dichloramine and nitrogen trichlorine. Figure 6-7 shows a schematic of an aqua

ammonia feed system.

Metropolitan Water District of Southern California (MWDSC) uses aqueous ammonia at its

chloramination facility. Ammonia is stored in unlined tanks and pumped to the ammoniator with

progressive cavity pumps. During startup of its aqueous ammonia feed system, MWDSC

experienced complete pump failures. Based on MWDSC’s experience, EPDM rotors with adequate

quality chromed finish stators are recommended for progressive cavity pumps. A mechanical seal is

also recommended instead of a packing box to reduce the possibility of ammonia leaks (Skadsen,

1993). MWDSC also later installed special blow-offs and strainers in the feed pump suction line to

reduce plugging at the magnetic flow meters. The pump problems prior to startup led MWDSC to

install an alternative, redundant ammonia feed system. A pressurized system was designed to feed

aqueous ammonia by pressurizing the ammonia tanks and by-passing the pump.
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Aqua NH3

on-site

storage tank

Control

System

Flow Signal

Relief Valve

Metering

Pump

Pulsation

Dampener

Flow

Meter

Solution diffuser

(~ 150 psi maximum

discharge pressure)

Backpressure

valve

Source: Montgomery, 1985.

Figure 6-7. Aqua Ammonia Feed System

A 5.5 gpm flexible impeller centrifugal pump with a recirculation loop back to the storage tank

regulates the back pressure on the by-passed feed pump. This alternative, redundant method proved

to be reliable and economical. In addition, it provided a stable feed rate and required little

maintenance (Skadsen, 1993).

6.2.2.3 Piping and Valving

For anhydrous ammonia, the typical piping materials for both direct and solution feed systems are

stainless steel, PVC, and black iron (Dennis et al., 1991). Stainless steel or black iron pipe is used in

the high pressure (i.e., greater than 15 psi) portions of the feed system. PVC pipe is used only in the

low pressure portion of the feed system, after the ammoniators.

For aqueous ammonia, PVC piping should be used due to the corrosive nature of aqueous ammonia

(Dennis et al., 1991).

6.2.2.4 Safety Provisions for Chloramine Generation Facilities

A chloramination facility should include some safety provisions to prevent the formation of nitrogen

trichloride and the vaporization of ammonia at ambient temperatures. The possible formation of

nitrogen trichloride at a chloramination facility should be considered when selecting sites for the

ammonia and chlorine storage facilities.

Dennis et al. (1991) provides detailed information about safety provisions for chloramine facilities.

Chlorine gas and ammonia gas should never be stored in the same room. The ammonia gas

application points should be located at least 5 feet away from chlorine feed solution lines. Anhydrous

ammonia is lighter than air, so any leaking vapor will rise quickly. Under pressure, anhydrous

ammonia is a liquid. Great amounts of heat are absorbed when the pressurized liquid reverts to a gas.
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If the storage tanks and/or chemical feed equipment are installed indoors, ventilation and vapor

detection devices should be located at high points in the room. The ventilation rates will vary

depending on the appropriate regulatory agency’s requirements. Typically, a minimum of 6 room

volume changes per minute is recommended.

Ammonia gas storage tanks should be protected from direct sunlight or direct sources of heat (i.e.,

greater than 125oF) to avoid pressure increases in the tank (Dennis et al., 1991). Otherwise,

ammonia gas may be released into the atmosphere through the pressure relief valves. In warm

regions, outdoor tanks should be covered with a shelter or outfitted with a temperature control

sprinkler system. Where fugitive emissions of ammonia are a concern, fume control may be

required. If the accidental release from a storage container is a concern, an emergency scrubber

system similar to a chlorine gas scrubber system should be considered.

6.3 Primary Uses and Points of Application

Monochloramine is used in drinking water treatment for disinfection and nuisance organism control.

Points of application are based on treatment objectives and contact time disinfection requirements.

6.3.1 Primary Uses

6.3.1.1 Disinfection

The primary use of monochloramine in water systems is as a secondary disinfectant for maintaining a

residual in the distribution system. Chloramines are a good choice for secondary disinfectant because

of the following potential benefits:

• Chloramines are not as reactive with organics as free chlorine in forming THMs.

• The monochloramine residual is more stable and longer lasting than free chlorine or chlorine

dioxide, providing better protection against bacterial regrowth in systems with large storage tanks

and dead-end water mains.

• The monochloramine residual has been shown to be more effective in controlling biofilms

because of its superior ability to penetrate the biofilm. Controlling biofilms also tends to reduce

coliform concentrations and biofilm induced corrosion.

• Because chloramines do not tend to react with organic compounds, many systems will experience

less incidence of taste and odor complaints when using chloramines.

Water systems in Indiana and Virginia found that conversion from free chlorine to monochloramine

as the secondary disinfectant significantly reduced coliform concentrations in the distribution system

(Norton and LeChevallier, 1997).

The normal dosage range for monochloramine is in the range of 1.0 to 4.0 mg/L. The minimum

residual of monochloramine in the distribution system is typically regulated at 0.5 mg/L (Texas
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Natural Resource Conservation Commission). For prevention of nitrification in a distribution system,

a minimum monochloramine dosage of 2.0 mg/L is recommended (Norton and LeChevallier, 1997).

6.3.1.2 Nuisance Organism Control

Cameron et al. (1989a) investigated the effectiveness of monochloramine to control the Asiatic clam

in both the juvenile and adult phases. The adult Asiatic clam was found to be much more resistant to

monochloramine than the juvenile form. Monochloramine was found to be the most effective for

controlling the juvenile Asiatic clam in terms of LT50 (time required for 50 percent mortality).

Monochloramine doses used to control the juvenile Asiatic clam range from 1.2 to 4.7 mg/L. Further

research showed that the effectiveness of monochloramine increased greatly as the temperature

increased (Cameron et al., 1989b).

6.3.2 Points of Application

The formation of monochloramine can be accomplished by first adding ammonia and then chlorine,

or vice versa. Ammonia is added first where formation of objectionable taste and odor compounds

caused by the reaction of chlorine and organic matter are a concern. However, most drinking water

systems add chlorine first in the treatment plant in order to achieve the required concentration and

contact time (CT) to meet EPA’s SWTR disinfection requirements. Typically, the point of ammonia

addition is selected to “quench” the free chlorine residual after a target period of time based on

optimizing disinfection versus minimizing DBP formation.

Because the germicidal effectiveness of monochloramine is a factor of 200 less than for free chlorine,

extremely long contact times are required for monochloramine to meet EPA disinfection CT

requirements. Therefore, if ammonia is added first, a means of ensuring that CT requirements are met

must be developed.

6.3.2.1 Impact on Other Treatment Processes

Monochloramine addition impacts other processes at the water treatment facility. These impacts

include:

• Ammonia used in the chloramination process can provide nutrient ammonia for nitrifying

bacteria growth in the distribution system, which can cause increased nitrate levels in the

finished water where systems do not normally test for nitrate.

• Imbalances in chlorine and ammonia concentrations (in greater than an 8 to 1 ratio) can cause

breakpoint chlorination reactions to occur when encountered in distribution system

• Monochloramine addition upstream of filters will reduce biological growth on filters. This

has a favorable impact on the filters by keeping them clean and reducing the backwash

frequency. It also has the undesirable impact of reducing BDOC removal in the filters when

the filters are run in a biological mode.
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The reader is referred to EPA’s Microbial and Disinfection Byproduct Simultaneous Compliance

Guidance Document (expected to be available in 1999) for additional information regarding the

interaction between oxidants and other treatment processes.

6.4 Pathogen Inactivation and Disinfection Efficacy

Chloramination of drinking water has been practiced in the United States for nearly 80 years. In

addition to achieving disinfection, chloramines have been used by the Denver Water Department for

controlling tastes and odors since 1918 (Hazen and Sawyer, 1992). Chloramination has also been

found to provide a more stable residual in water distribution system. However, because of its

relatively weak disinfecting properties for inactivation of viruses and protozoa pathogens, it is rarely

used as a primary disinfectant, and then only with long contact times.

6.4.1 Inactivation Mechanisms

The mechanisms by which chloramines inactivate microorganisms have been studied to a lesser

degree than chlorine. A study of inactivation of E. coli by chloramines concluded that

monochloramine readily reacts with four amino acids; cysteine, cystine, methionine and

tryptophan ( Jacangelo et. al, 1987) . The mechanism of inactivation for chloramine is therefore

thought to involve inhibition of proteins or protein mediated processes such as respiration.

Jacangelo further concluded that because of the inconsistency in rate of inactivation

monochloramine should have “multiple hits” upon bacterial cells before cell death.

Few studies have been performed to determine the mechanism for viral inactivation. The initial site

for destruction of bacteriophage f2 involved the RNA fragment (Olivieri et al., 1980). However, the

primary mechanism for poliovirus inactivation by chloramines involved the protein coat (Fujioka et

al., 1983). Similar to free chlorine, the mechanism of viral inactivation by chloramine may be

dependent on factors such as virus type and disinfectant concentration.

6.4.2 Environmental Effects

Several studies have been performed to determine the effect of pH, temperature, and organic and

inorganic compounds on the disinfection effectiveness of chloramines. Following is a summary of

the affect these parameters have on pathogen inactivation.

6.4.2.1 pH

The effect of pH on disinfection has more to do with the organism than with the disinfectant;

however, pH also impacts disinfection efficiency by controlling the chloramine species distribution.

Studies have indicated that the disinfection efficacy of monochloramine and dichloramine are not

equal. One study showed that the bactericidal properties of dichloramine were superior to that of

monochloramine (Esposito, 1974). However, pH may be a compounding factor because changes in

pH may alter the physiological response of the organism (Hoff and Geldreich, 1981). Other studies
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have shown that monochloramine is superior to dichloramine with regard to virucidal ability (Dorn,

1974; Esposito, 1974; Olivieri et al., 1980). Some evidence suggests that solutions containing

approximately equal concentrations of monochloramine and dichloramine may be more

microbiocidal than those containing only monochloramine or dichloramine (Weber and Levine,

1944).

6.4.2.2 Temperature

Similar to most of the disinfectants discussed in this report, the bactericidal and viral inactivation

efficiency of chloramine increases with increasing temperature. Moreover, the efficiency

dramatically decreases under conditions of high pH and low temperature. For example, the

inactivation of E. coli. is approximately 60 times slower at pH 9.5 and temperatures of 2 and 6o C

than at pH 7 and temperatures between 20 and 25oC (Wolfe et al., 1984). Similar results were

obtained for poliovirus 1 inactivation (Kelley and Sanderson, 1958).

6.4.2.3 Organic Nitrogen and Other Compounds

In addition to ammonia, free chlorine reacts with organic nitrogen compounds to form a variety of

organic chloramines. These organic chloramines are undesirable byproducts because they exhibit

little or no microbiocidal activity (Feng, 1966). Studies have indicated that chlorine binds to aminecontaining compounds more rapidly than to ammonia (Weil and Morris, 1949; Morris, 1967;

Margerum et al., 1978) and that chlorine can be transferred from inorganic chloramines to aminecontaining compounds (Margerum et al., 1978; Isaac and Morris, 1980)

Several other reactions may occur which divert chlorine from the formation of chloramines. These

reactions can include oxidation of iron, manganese, and other inorganics such as hydrogen sulfide

(Hazen and Sawyer, 1992).

6.4.3 Disinfection Efficacy

Chloramines are relatively weak disinfectants for virus and protozoa inactivation. As a consequence,

it is extremely difficult to meet the SWTR CT criteria for primary disinfection of Giardia and viruses

using chloramines because very long detention times are needed. However, given the ability of

chloramines to provide a stable residual, this form of disinfection appears to be feasible for

secondary disinfection protection against microbial growth in distribution systems. The following

paragraphs describe the disinfection efficiency of chloramines in terms of bacteria, virus, and

protozoa inactivation.

6.4.3.1 Bacteria Inactivation

A series of comprehensive experiments was initiated in the mid 1940s to determine the relative

bactericidal effectiveness of free chlorine and inorganic chloramines. Results from these

experiments showed conclusively that under relatively demand-free, laboratory-controlled

conditions, free chlorine inactivated enteric bacteria much faster that chloramines (Wattie and
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Butterfield, 1944). In this experiment, a monochloramine concentration of 0.3 mg/L required 240

minutes of contact time for 3-log inactivation of E. coli whereas exposure to 0.14 mg/L free Cl2

required only 5 minutes to achieve the same level of inactivation at the same temperature and pH.

6.4.3.2 Virus Inactivation

According to reports written by Kabler et al. (1960) and the National Research Council (1980), all

studies conducted prior to 1944 that compared virucidal potency of free and combined chlorine were

inaccurate because the experiments failed to clearly differentiate between free and combined forms

of chlorine and because high-chlorine-demand water was used in the experiments.

The majority of the experiments conducted after the mid-1940s has shown that inorganic chloramines

require much higher concentrations and considerably longer contact times than free chlorine to

achieve comparable levels of virus inactivation. Experiments showed that contact times between 2

and 8 hours were required at concentrations between 0.67 to 1.0 mg chloramines to achieve greater

than 2-log inactivation of poliovirus 1 (Mahoney and MK500), poliovirus 2 (MEF), poliovirus 3

(Sackett), coxsackievirus B1, and coxsackievirus B5 (EA 80) (Kelley and Sanderson, 1958 and

1960). In contrast, 0.2 to 0.35 mg/L free Cl2 required 4 to 16 minutes of contact time to achieve

comparable levels of inactivation under the same conditions.

6.4.3.3 Protozoa Inactivation

Of the three predominant forms of pathogens (i.e., bacteria, viruses, and protozoan [oo]cysts), studies

have shown that protozoan [oo]cysts are usually the most resistant to all forms of disinfection.

Studies have indicated that free chlorine is a more effective disinfectant than chloramines for

[oo]cyst inactivation (Chang and Fair, 1941; Chang, 1944; Stringer and Kruse, 1970). Chloramine

concentrations of 8 mg/L were required for 2-log inactivation of Entamoeba histolytica cysts whereas

only 3 mg/L of free chlorine was required to obtain the same degree of inactivation (Stringer and

Kruse, 1970). Contact times for both disinfectants were 10 minutes.

6.4.3.4 CT Values

CT values for achieving Giardia cyst and virus inactivation using chloramines are shown in

Table 6-4 and Table 6-5, respectively. Values contained in these tables were obtained from the

Guidance Manual for Compliance with Filtration and Disinfection Requirements for Public Water

Systems Using Surface Water Sources (AWWA, 1991).

CT values shown in Table 6-4 are based on disinfection studies using in vitro excystation of Giardia

lamblia. CT values shown in Table 6-5 were based on data using preformed chloramines at pH 8. No

safety factor was applied to laboratory data used to derive the CT values shown in Table 6-4 and

Table 6-5 since chloramination conducted in the field is more effective than using preformed

chloramines, since monochloramine tends to degrade with time and some free chlorine is present

when forming chloramines which enhances the inactivation process.
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Table 6-4. CT Values for Giardia Cyst Inactivation Using Chloramines

Temperature (°C) (mg•min/L)

Inactivation 5 10 15 20 25

0.5-log 365 310 250 185 125

1-log 735 615 500 370 250

1.5-log 1,100 930 750 550 375

2-log 1,470 1,230 1,000 735 500

2.5-log 1,830 1,540 1,250 915 625

3-log 2,200 1,850 1,500 1,100 750

Source: AWWA, 1991.

Values shown in this table are based on a pH range between 6 and 9.

Table 6-5. CT Values for Virus Inactivation Using Chloramines

Temperature (°C) (mg•min/L)

Inactivation 5 10 15 20 25

2-log 857 643 428 321 214

3-log 1,423 1,067 712 534 356

4-log 1,988 1,491 994 746 497

Source: AWWA, 1991.

6.5 DBP Formation

The effectiveness of chloramines to control DBP production depends upon a variety of factors,

notably the chlorine-to-ammonia ratio, the point of addition of ammonia relative to that of chlorine,

the extent of mixing, and pH.

Monochloramine (NH2Cl) does not produce DBPs to any significant degree, although some

dichloroacetic acid can be formed from monochloramine and cyanogen chloride formation is greater

than with free chlorine (Jacangelo et al., 1989; Smith et al., 1993; Cowman and Singer, 1994). The

inability to mix chlorine and ammonia instantaneously allows the free chlorine to react before the

complete formation of chloramines. In addition, monochloramine slowly hydrolyzes to free chlorine

in aqueous solution. Therefore, halogenation reactions occur even when monochloramine is formed

prior to addition in the treatment process (Rice and Gomez-Taylor, 1986). The closer the

chlorine:ammonia ratio is to the breakpoint, the greater the formation of DBPs (Speed et al., 1987).

In addition to controlling the formation of DBPs, chloramination results in lower concentrations of a

number of the other specific organic halides generated from free chlorine, except for cyanogen

chloride (Krasner et al., 1989; Jacangelo et al., 1989). Increased production of cyanogen chloride is

observed when monochloramine is used as a secondary disinfectant instead of free chlorine.

The application of chloramines results in the formation of chlorinated organic material, although it

occurs to a much lesser degree than from an equivalent dose of free chlorine. Little is known about

the nature of these byproducts, except that they are more hydrophilic and larger in molecular size

than the organic halides produced from free chlorine (Jensen et al., 1985; Singer 1993).
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6.6 Status of Analytical Methods

6.6.1 Monitoring of Chloramines

There has been little development of analytical procedures for selective determination of

monochloramines (Gordon, et al., 1992). Typically, the methods used for chlorine residual

measurement are adapted for chloramine measurement. The DBPR promulgated on December 16,

1998 (63 FR 69390) establishes three analytical methods that are acceptable for measuring residual

chloramines (combined chlorine). These methods are presented in 40 CFR § 141.131(c) and include:

• Amperometric Titration (Standard Method 4500-Cl D and ASTM Method D 1253-86);

• DPD Ferrous Titrimetric (Standard Method 4500-Cl F); and

• DPD Colorimetric (Standard Method 4500-Cl G).

If approved by the State, systems may also measure chloramines by using DPD colorimetric test

kits.

6.6.1.1 Amperometric Titrations

The amperometric titration method is utilized extensively in water treatment laboratories (Gordon, et

al., 1992). This method capable of differentiating the three most common forms of chlorine, namely

chlorine/hypochlorous acid/hypochlorite ion, monochloramine, and dichloramine, as long as the

combined forms are not present in concentrations greater than about 2 mg/L (as Cl2). For higher

concentrations, dilution of the samples is required, but differentiation is still possible (Aoki, 1989).

The amperometric titration method is a standard of comparison for the determination of free or

combined chlorine. This method is not greatly affected by common oxidizing agents, temperature

variations, turbidity, and color (Standard Methods, 1995). Amperometric titration requires a greater

degree of skill than colorimetric methods. The differentiation of free chlorine, monochloramine, and

dichloramine is possible by control of potassium iodide (KI) concentration and pH during the

analysis.

Several methods are commonly used to measure chlorine species utilizing the amperometric titration

including forward and back titration (Gordon, et al., 1992). The lower limit of detection of these

methods varies depending on the instrumentation used and type of water sample analyzed. The lower

limit of detection for commercial amperometric titrating equipment is about 30 μg/L as Cl2 (Sugam,

1983).

Table 6-6 shows the working range, expected accuracy and precision, operator skill level required,

interferences, and current status for amperometric method monochloramine analysis comparison.
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6.6.1.2 Colorimetric Methods

Over the years, numerous colorimetric methods have been developed to measure free and combined

chlorine in aqueous solutions (Gordon, et al., 1992). Not many of these methods would be

recommended as the method of choice. Two of the colorimetric methods listed in Standard Methods

(1995), are DPD methods. In addition, the colorimetric LCV method modified by Whittle and

Lapteff (1974) can be used to measure free and combined chlorine species.

The DPD methods (ferrous titration and colorimetric) are operationally simpler for determining free

chlorine than the amperometric titration (Standard Methods, 1995). Procedures are given for

estimating separate monochloramine and dichloramine fractions, as well as combined chlorine

fractions.

The LCV method modified by Whittle and Lapteff modifies the discontinued Standard Method for

LCV. The maximum chlorine concentration that can be determined by this modified procedure,

without dilution of the sample, is 10 mg/L as Cl2 (Whittle and Lapteff, 1974).

See Table 6-6 for the working range, expected accuracy and precision, operator skill level required,

interferences and current status for colorimetric method monochloramine analysis comparison.

6.6.2 Disinfectant Interferences

Interferences to free chlorine may impact the measurement of monochloramine since the methods use

the free chlorine level in the determination of monochloramine. Many strong oxidizing agents

interfere in the measurement of free chlorine in all monochloramine methods, including bromine,

chlorine dioxide, iodine, permanganate, hydrogen peroxide, and ozone. However, the reduced form

of these compounds (i.e. bromide ion, chloride ion, iodide ion, manganous ion, and oxygen) do not

interfere. Reducing agents such as ferrous compounds, hydrogen sulfide, and oxidizable organic

matter generally do not interfere (Standard Methods, 1995).
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Table 6-6. Characteristics and Comparisons of Monochloraminea Analytical Methods

Type of Test

Working

Range

(mg/L)

Expected

Accuracy (± %)

Expected

Precision (± %)

Skill

Levelb Interferences pH Range

Field

Test

Automated

Test Current Status

Amperometric

Titration, Forward

0.1 - 10 NR 0 - 10 2 dichloramine,

nitrogen

trichloride,

pH

dependent

Yes Yes Recommended

Amperometric

Titration, Back

0.1 - 10 NR NF 2 dichloramine,

nitrogen

trichloride,

pH

dependent

Yes Yes Recommended

Colorimetric DPD

Ferrous Titration

0.01 - 10 NR 2 - 7 1 dichloramine,

nitrogen

trichloride,

oxidizing

species

Requires

buffer

No No Recommended

Lab Test

Colorimetric DPD 0.01 - 10 NR 5 - 75 1 dichloramine,

nitrogen

trichloride,

oxidizing

species

Requires

buffer

Yes No Recommended

Field Test

Source: Gordon et al., 1992.

Notes: a Little actual work has been carried out on selective determination of chloramines. The values reported are from extrapolated studies that

had objectives other than the selective determination of chloramines.

b

 Operator skill levels: 1 = minimal, 2 = good technician, 3 = experienced chemist. NR = Not reported in literature cited by referenced

source.
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6.6.2.1 Amperometric Titrations

The amperometric titration methods are unaffected by dichloramine concentrations in the range of 0

to 9 mg/L as Cl2 in the determination of free chlorine. Nitrogen trichloride, if present, may react

partially as free chlorine. The amperometric method will measure organic chloramines as free

chlorine, monochloramine, or dichloramine, depending upon the activity of chlorine in the organic

sample (Standard Methods, 1995). Dichloramine may also interfere with the measurement of both

monochloramine and free chlorine (Marks, et al., 1951). The presence of iodide ion can be a severe

problem if the titrator glassware is not washed carefully between determinations (Johnson, 1978).

Manganese dioxide, a common interference in most chlorine analytical procedures, does not interfere

in the amperometric measurement of free chlorine (Bongers et al., 1977). However, because of its

reaction with iodide ion, added during analysis, manganese dioxide does interfere with the

amperometric measurement of combined forms of chlorine such as monochloramine (Johnson,

1978).

6.6.2.2 Colorimetric Methods

Sample color and turbidity may interfere in all colorimetric procedures. In the DPD colorimetric

methods, high concentrations of monochloramine interfere with free chlorine determination unless

arsenite or thioacetimide are added. In addition, the DPD methods are subject to interference by

oxidized forms of manganese unless compensated for by a blank (Standard Methods, 1995). The

DPD methods are unaffected by dichloramine concentrations in the range of 0 to 9 mg/L as Cl2 in the

determination of free chlorine. Nitrogen trichloride, if present, may react partially as free chlorine.

The extent of this interference in the DPD methods does not appear to be significant (Standard

Methods, 1995).

In the LCV colorimetric method, Whittle and Lapteff (1974) reported that dichloramine did not

interfere with the monochloramine measurement.

6.6.3 Chloramine Monitoring for Systems Using Chloramines

Pursuant to 40 CFR §141.132(c)(1), community water systems and non-transient non-community

water systems that use chloramines, must measure the residual disinfectant level at the same points in

the distribution system, at the same time, and at the same frequency (based on population served) as

total coliforms are sampled, as specified in 40 CFR §141.21. These systems may use the results of

residual disinfectant concentration sampling conducted under §141.74(b)(6)(i) for unfiltered systems

or §141.74(c)(3)(i) for systems which filter, in lieu of taking separate samples. No reduced

monitoring allowances exist for these systems.

Compliance with the MRDL of 4.0 mg/L (as chlorine) is based on a running annual arithmetic

average, computed quarterly, of monthly averages of all samples collected by the system under

§141.132(c)(1). If the average quarterly averages covering any consecutive four-quarter period

exceeds the MRDL, the system is in violation of the MRDL and must notify both the public, pursuant
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to §141.32, and the State, pursuant to §141.134. Where systems switch between the use of chlorine

and chloramines for residual disinfection during the year, compliance is determined by including

together all monitoring results of both chlorine and chloramines in calculating compliance.

6.7 Operational Considerations

The purpose of this section is to address operational considerations in the use of chloramines in

drinking water treatment. Specifically, the following topics are addressed below: the conversion of

chloramination from chlorination; the potential operational impacts from chloramination disinfection;

and special considerations for chloramination facilities. For a more detailed discussion of

chloramine disinfection, refer to “Optimizing Chloramine Treatment” by Kirmeyer et, al. 1993.

6.7.1 Conversion to Chloramination from Chlorination

6.7.1.1 Planning

Project planning and preparation are essential to ensure an efficient changeover, maintain a

dependable and safe system, and preserve the public confidence in the water purveyor (Skadsen,

1993). Planning and preparation should consider the following aspects:

• Raw water composition and suitability to chloramination;

• Treatment plant and distribution system attributes and monitoring program;

• Employee training;

• Public notification and education; and

• Environmental affects from chloraminated water.

6.7.1.2 Preliminary Analysis

A bench scale study is necessary to identify the water characteristics and to determine if

chloramination is suitable. White (1992) describes some of the study objectives and variables to

consider. The reaction time to form free chloramine residuals varies for each water source since the

reaction rate between chlorine and ammonia nitrogen depends on the water’s temperature and pH of

the water. The reaction rate is also affected by the chlorine and ammonia nitrogen concentrations.

To properly control the reaction time between chlorine and ammonia, the study should use different

chlorine:ammonia nitrogen ratios, ammonia feed doses, and contact times.

The amount of ammonia required for chloramine residual disinfection depends on the following

factors (Dennis et al., 1991):

• Organic nitrogen in the water;

• Ammonia residual desired in the distribution system; and
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• Chloramine residual type and concentration required in the distribution system.

If there is organic nitrogen in the untreated water, the amount of supplemental ammonia required

should be carefully determined by subtracting the background ammonia from the desired dose. The

dose should also consider the amount of ammonia residual desired in the distribution system. For

residual disinfection, approximately 1 to 2 mg/L of ammonia is required (Dennis et al., 1991).

For each specific water, a breakpoint curve should be developed to determine the chloramine residual

type required. Monochloramine residuals are preferred for most water distribution systems.

Dichloramine and nitrogen trichloride residuals may cause taste and odor problems when

concentrations exceed 0.8 mg/L or 0.02 mg/L, respectively. Monochloramines are primarily formed

when the theoretical chlorine to ammonia dose ratio is less than 5 to 1 (by weight ratio) and the pH is

greater than 7.0 (Dennis et al., 1991). The chloramine residual concentration leaving the treatment

plant will vary depending on the size of the distribution system and the chloramine demand exerted

by the system. Typical chloramine residuals range from 1 to 4 mg/L (Dennis et al., 1991).

6.7.1.3 The Metropolitan Water District (MWDSC)

MWDSC of Southern California converted from free chlorine to chloramine disinfection in 1985 to

assist its 27 member agencies in complying with the EPA’s total trihalomethane regulation.

MWDSC serves approximately 15 million people and operates five treatment plants, with a

combined capacity of 1,670 MGD. Raw water is taken from two sources: the Colorado River and

California state project water.

Prior to the changeover, MWDSC performed extensive investigations into the chemical,

microbiological, and engineering aspects of chloramine disinfection. To prepare for the changeover,

MWDSC coordinated the efforts among its treatment plants, distribution system reservoirs,

laboratory personnel, and management. A formal request for approval to use chloramines as a

disinfectant was submitted to the California State Department of Health Services. Next, a series of

workshops was held on the engineering, chemical, and microbiological aspects of chloramine

disinfection. MWDSC also prepared a manual for the type of chloramination application method and

ammonia form selected. Information in the manual included the feed equipment information, project

specifications, piping layouts, preliminary analysis, and safety and maintenance issues.

It was essential to notify specific sectors of the public that could be affected by the use of

chloramines. MWDSC made its customers aware of the changeover and kept them apprised of the

options for preventing adverse reactions through an extensive notification program that involved

state and county health departments, appropriate interest groups, and the media.
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6.7.2 Potential Operational Impacts from Chloramination

Disinfection

6.7.2.1 Pretreatment

Ammonia in excess of the required chlorine can promote the growth of nitrifying bacteria in filter

beds (i.e., rapid sand filters) (White, 1992). The excess ammonia acts as a nutrient and causes the

growth of nitrifying bacteria, which convert the excess ammonia to nitrates and nitrites. Excessive

levels of nitrate in drinking water have caused serious illness and sometimes death in infants under

six months of age. The symptoms include shortness of breath and blueness of skin [40 CFR

§141.32(e)(20)]. Prior to designing a chloramination facility, the amount of ammonia naturally

occurring in the raw water should be determined. The required ammonia dosage would then be

based on the anticipated naturally occurring ammonia levels.

A chloramine residual concentration should also be maintained in the discharge stream from the

filters. An adequate residual concentration would be between 0.5 to 1 mg/L chloramine (White,

1992).

6.7.2.2 Nitrification

Nitrification in chloraminated drinking waters is usually partial. Partial nitrification occurs when the

chloraminated water has excess ammonia present in the distribution system (Skadsen, 1993). Partial

nitrification can have various adverse effects on water quality, including a loss of total chlorine and

ammonia residuals and an increase in heterotrophic plate count (HPC) bacteria concentration. The

excess ammonia encourages the growth of nitrifying bacteria that convert ammonia to nitrates. An

intermediate step in this conversion results in a small amount of nitrite being formed. Research has

shown that a chlorine demand of 5 mg/L is exerted by 1 mg/L of nitrite (Cowman and Singer, 1994).

The nitrites rapidly reduce free chlorine, accelerate decomposition of chloramines, and can interfere

with the measurement of free chlorine (Skadsen, 1993). Valentine (1998) found that the decay of

monochloramine was increased (from a second order rate constant of 0.07 to 0.106) by the presence

of 0.5 mg/L of nitrite. If nitrification episodes are allowed to continue, very low (or zero) total

chlorine residual concentration levels may occur. Loss of chlorine residual allows an increase in

HPC bacteria and potentially increases in total coliforms and may result in a positive sample

(Cowman and Singer, 1994). Additional information on nitrification can be found in (Kirmeyer et,

al. 1995), “Nitrification Occurrence and Control in Chloraminated Water Systems.”

Factors. Several possible factors have been implicated as contributing to nitrification. These factors

include low chlorine-to-ammonia ratio, long detention times, and temperatures (Cowman and Singer,

1994). Though some articles noted that low monochloramine dosages may lead to nitrification, other

research has reported nitrification occurring at monochloramine concentrations greater than 5.0 mg/L

(Cowman and Singer, 1994). Nitrifying bacteria are relatively more resistant to disinfection by

monochloramine than free chlorine (Cowman and Singer, 1994). The optimum conditions for

nitrification would be a water system with free-ammonia, a pH of 7.5 to 8.5, a water temperature of
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25 to 30oC, and a dark environment. Nitrifying bacteria exhibit slow growth and have been found in

higher numbers in the sediment of distribution systems than in the biofilm (Cowman and Singer,

1994).

If the water reservoirs in the distribution system are covered, partial nitrification may occur (White,

1992). Nitrification occurred in two of MWDSC’s covered reservoirs (Garvey and Orange County

reservoirs) after the changeover. Approximately 10 weeks after the changeover from chlorine to

chloramine, water quality degradation was occurring in the Garvey Reservoir. MWDSC increased

the amounts of free chlorine added to the plant effluent to maintain a 1.5 mg/L monochloramine

residual at the reservoir effluent and the chlorine to ammonia ratio was increased from 3:1 to 4:1 to

decrease the amount of excess ammonia in the water. These changes were more effective than the

flushing programs for the distribution system, which only helped temporarily.

Control Measures. Nitrification may pose a potential problem for any utility using monochloramine

as a disinfectant (Cowman and Singer, 1994). Thus, nitrification should be carefully assessed and

controlled. Nitrification may be controlled by monitoring at strategic locations throughout the

distribution system for monochloramine and dichloramine residuals (White, 1992).

The chloramine free residual stability is increased throughout the distribution system when there is

increased control of microbial contaminants and decreased bacterial concentrations in the raw water

to acceptable levels. Recommended approaches to prevent and control nitrification in the

distribution system include (Cowman and Singer, 1994):

• Decreasing the detention time;

• Increasing the pH;

• Decreasing the temperature;

• Decreasing TOC concentrations;

• Increasing chloramines residual;

• Increasing the chlorine-to-ammonia ratio; and

• Decreasing the excess ammonia concentration.

For the distribution system, the system should be evaluated to identify the low-flow or dead-end

sections. The detention times in the system should be operationally minimized (Skadsen, 1993). For

reservoirs, those with single inlet-outlet configurations should especially be carefully monitored and

operated (Skadsen, 1993).

MWDSC stresses the importance of developing nitrification strategy control measures. In particular,

a comprehensive monitoring program should be established to alert personnel to implement control

measures when required. To control nitrification, MWDSC developed a control strategy where the

reservoirs and distribution system were first sampled for nitrite levels (Skadsen, 1993). MWDSC
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also decreased the detention times in reservoirs and distribution systems, especially during warmer

weather, which helped to keep nitrite levels down.

The chloramination operation was modified to add more chlorine to the reservoir inlet and increase

the chlorine-to-ammonia ratio from 3:1 to 5:1 at the plant effluent. The initial 3:1 ratio corresponded

with a 1.5 mg/L monochloramine residual and 0.2 mg/L excess ammonia. At these concentrations,

the agencies receiving the water had the flexibility of blending the chloraminated water with

chlorinated water or adding more chlorine to those sections of the system with long detention times.

Increasing the ratio further to 5:1 controlled the nitrification problem by decreasing the amount of

free ammonia in the distribution system. Operating at a 5:1 ratio requires more monitoring since an

overdose of chlorine can reduce the chloramine residual.

A survey of chloramine users in the United States was conducted in June 1991. This survey showed

that the chlorine to ammonia ratio varied from 3:1 to 7:1 (Dennis, et al, 1991). The chloramine

residual varied from 0.8 mg/L to 3 mg/L (Dennis, et al, 1991). Table 6-7 shows the results from this

survey. The agencies surveyed reported excellent results with secondary chloramine disinfection

(Dennis et al, 1991). EPA is in the process of collecting and evaluating chloramine use in the United

States as part of the Information Collection Rule (ICR), but until those data are available, the 1991

survey appears to be the most recent national survey of chloramine use.

Each year, MWDSC also added chlorine past the breakpoint to allow a free residual for 30 days. The

ideal locations for breakpoint chlorination are at the distribution reservoirs and interconnections. The

increased chlorine oxidizes any nitrite and nitrifying bacteria and eliminates the excess ammonia in

the distribution system. For larger water systems, MWDSC recommends maintaining chlorination

stations throughout the distribution system. Both fixed and mobile chlorinators may be used. Mobile

chlorinator units are self-contained and trailer-mounted with evaporators, chlorinators, generator, a

booster pump for transport water, and chlorine injectors. They are designed to draw liquid chlorine

directly from a 17-ton chlorine trailer and to inject a chlorine solution into the distribution system or

reservoir.

Since nitrifying bacteria were found in higher numbers in the sediments of the distribution system

than in the biofilm, flushing sediment from the system will help to control nitrification. The addition

of a disinfectant (i.e., free or combined chlorine) is required to remove nitrification.

At the Indiana American Water Company, the distribution system is temporarily converted back to

free chlorine for scheduled flushing (Lyn et al., 1995). Utilities should evaluate their flushing

program to avoid consumer complaints with inappropriate flushing techniques.

6.7.2.3 Taste and Odor

If the chlorine to ammonia-nitrogen ratios are between 3:1 and 5.5:1, disagreeable tastes and odors

should be evaluated at the consumer tap (White, 1992).
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Fishy tastes and odors (e.g., from source waters and return washwater from the washwater treatment

system) can be controlled by a 1-hour contact time with free-chlorine residual of 2 mg/L prior to the

addition of ammonia (Dennis et al., 1991). This prechlorination eliminates the fishy taste and odor

but may increase the THM concentrations at the plant effluent.

Table 6-7. Survey of Chloramine Users in the United States

Agency

Treatment

Capacity

Type of

Ammonia

Chlorine:

Ammonia

Nitrogen

ratio

Chloramine

Residual

(mg/L)

NH3 Injection

Point

Nitrification

Control

Strategies

City of

Dallas, TX

730 mgd;

3 plants

Anhydrous 5:1 2.1 - 2.3 Presedimenta

-tion, Postfiltration

None

City of

Denver, CO

600 mgd;

3 plants

Aqueous

(30%)

3:1 0.8 - 1.0 Post-filtration,

prior to

chlorine

addition

None

Indianapolis,

Water Co.,

IN

176 mgd;

4 plants

Anhydrous 3:1

varies

1.5 - 2.0 Post-filtration Increase ratio in

summer

Miami-Dade

Water

Authority, FL

300 mgd;

3 plants

Anhydrous 5:1 2.7 - 3.0 10 ft after

chlorine flash

mix

2 weeks free

chlorine every

November

City of

Milwaukee,

WI

305 mgd;

2 plants

Anhydrous 5:1 0.8 - 0.9 Post-filtration None

City of

Philadelphia

, PA

530 mgd;

3 plants

Aqueous

(30%)

3:1 2.0 Post-filtration None

City of

Portland,

OR

225 mgd Anhydrous 7:1 1.8 70 ft

downstream

of chlorine in

conduit

None

Orleans

Parish, LA

300 mgd;

2 plants

Anhydrous 3:1 2.0 - 2.5 Pre-filtration None

St. Louis

Co. Water

Authority,

MO

360 mgd;

4 plants

Aqueous

(30%)

4:1 2.5 Concurrent

with chlorine

at flash mix,

post-filtration

None

Source: Dennis et al.,1991.

6.7.3 Special Considerations for Chloramination Facilities

6.7.3.1 GAC Filters with Ammonia Addition

The Ann Arbor Water Treatment Plant in Michigan is a 50 mgd lime softening plant that draws its

water from the Huron River (80 to 90 percent) and ground water (10 to 20 percent). When

chloramination is applied to the river water, the chlorine is injected into the raw water line
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immediately before ammonia is applied. The total chlorine feed averages 3.3 mg/L with an average

demand of 2.0 mg/L for the river water.

Evidence of nitrification occurred immediately after a change in treatment from sand to GAC

filtration. Prior to the change to GAC, the treatment plant had successfully used monochloramine as

both a primary and a final disinfectant. Nitrification was not evident. The GAC received an

application of approximately 1.3 mg/L ammonia. This input of ammonia to the filters constituted a

nutrient source that allowed nitrifying bacteria to become established and proliferate. The GAC

particles have been observed to harbor nitrifying bacteria and nitrification has been observed in GAC

beds. Higher nitrifying bacteria levels have been observed in other filter beds as compared with

source water. The GAC effluent also showed pronounced seasonal peaks in HPC bacteria from May

to July, and percent total coliforms positive from July to August. These seasonal peaks are most

probably temperature related. During periods of nitrification, GAC effluent HPC bacteria

concentration was steadily decreasing while in the distribution system, HPC bacteria were increasing.

6.7.3.2 Organic Nitrogen

Concentrations of organic nitrogen and ammonia nitrogen as low as 0.3 mg/L may interfere with the

chloramination process. The monochloramine residuals will hydrolyze with the organic nitrogen to

form organochloramines, which are nongermicidal. This reaction would take about 30 to 40 minutes.

After the monochloramine residuals disappear, free ammonia nitrogen reappears. Free ammonia

nitrogen is a powerful biological nutrient. Its presence promotes biological instability in that portion

of the distribution system. Biological instability usually results in foul tastes and odors plus dirty

and/or colored water at the consumers tap (White, 1992).

The free chlorine residual or chloramine residual method may be used to clean an area with

biological instability. Of the two methods, the free chlorine residuals method is superior (White,

1992). Free chlorine residuals restore distribution system stability quicker (i.e., a few days for free

chlorine versus weeks for chloramines), the clean-up process can be monitored, and the clean-up is

complete when the free chlorine residual concentration reaches 85 percent of the free chlorine

concentration.

Based on their conversion to chloramination experience, MWDSC recommends that utilities

employing chloramines for disinfection monitor for total organic nitrogen levels. When levels are

high, the amino acid fraction is also likely to rise. This rise may impair the chloramination

disinfection efficiency if high levels of organic nitrogen are not detected.

6.7.3.3 Mixing

Mixing at the point of application greatly affected the bactericidal efficiency of the chloramine

process. When the pH of the water is between 7 and 8.5, the reaction time between ammonia and

chlorine is practically instantaneous. If chlorine is mixed slowly into the ammoniated water, organic

matter, especially organic matter prone to bleaching with chlorine solution, may react with the

chlorine and interfere with chloramine formation (White, 1992).
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6.7.3.4 Blending Waters

When chlorinated water is blended with chloraminated water, the chloramine residual will decrease

after the excess ammonia has been combined and monochloramine is converted to dichloramine and

nitrogen trichloride. The entire residual can be depleted. Therefore, it is important to know how

much chlorinated water can be blended with a particular chloraminated water stream without

significantly affecting the monochloramine residual. Blended residual curves should be developed

for each specific blend.

6.7.3.5 Corrosion

Chloramination and corrosion control can limit bacterial biofilm development in the distribution

system. If optimum corrosion of iron pipes is not controlled, the chloramination efficiency may be

impacted. Corrosion inhibitors with higher phosphate concentrations may reduce corrosion rates

(Lyn et al., 1995).

6.7.3.6 Formation of Nitrogen Trichloride

If water in the distribution system tends to form nitrogen trichloride, the finished water should be

subjected to post-aeration, which readily removes nitrogen trichloride (White, 1992). Nitrogen

trichloride is also readily destroyed by sunlight (White, 1992).

6.7.3.7 Human Health and the Environment

Users of kidney dialysis equipment are the most critical group that can be impacted by chloramine

use. Chloramines can cause methemoglobinemia and adversely affect the health of kidney dialysis

patients if chloramines are not removed from the dialysate water. Chloramines can also be deadly to

fish. The residuals can damage the gill tissues, enter the red blood cells, and cause an acute blood

disorder. Chloramine residuals should be removed from the water prior to the water contacting any

fish. As such, fish hobbyists should be notified, along with pet stores and aquarium supply

establishments.

6.8 Summary

6.8.1 Advantages and Disadvantages of Chloramine Use

The following list highlights selected advantages and disadvantages of using chloramines as a

disinfection method for drinking water (Masschelein, 1992). Because of the wide variation of

system size, water quality, and dosages applied, some of these advantages and disadvantages

may not apply to a particular system.

Advantages

• Chloramines are not as reactive with organics as free chlorine in forming DBPs.
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• The monochloramine residual is more stable and longer lasting than free chlorine or

chlorine dioxide, thereby providing better protection against bacterial regrowth in

systems with large storage tanks and dead end water mains. However excess ammonia in

the network may cause biofilming.

• Because chloramines do not tend to react with organic compounds, many systems will

experience less incidence of taste and odor complaints when using chloramines.

• Chloramines are inexpensive.

• Chloramines are easy to make.

Disadvantages

• The disinfecting properties of chloramines are not as strong as other disinfectants, such as

chlorine, ozone, and chlorine dioxide.

• Chloramines cannot oxidize iron, manganese, and sulfides.

• When using chloramine as the secondary disinfectant, it may be necessary to periodically

convert to free chlorine for biofilm control in the water distribution system.

• Excess ammonia in the distribution system may lead to nitrification problems, especially

in dead ends and other locations with low disinfectant residual.

• Monochloramines are less effective as disinfectants at high pH than at low pH.

• Dichloramines have treatment and operation problems.

• Chloramines must be made on-site.

6.8.2 Summary Table

Table 6-8 summarizes the considerations for the use of chloramine.
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Table 6-8. Summary of Chloramine Disinfection

Consideration Description

Generation Chloramines are generated by the sequential addition of chlorine (hypochlorous acid) and

ammonia at a Cl2 to NH3 ratio ranging from of 3:1 to 5:1. Either chlorine or ammonia may be added

first. Chlorine is normally added first to act as the primary disinfectant and after 10 to 30 minutes,

ammonia is added to prevent further formation of DPBs.

The most common methods of chlorine addition include gas feed using a dilution water eduction

system or direct feed of bulk hypochlorite solution (12 percent typical commercial strength).

The most common ammonia feed facilities include anhydrous ammonia fed either directly or via a

dilution water eduction system or direct feed of bulk aqua ammonia solution (20 percent typical

commercial strength).

Primary uses Monochloramine is used primarily as a secondary disinfectant to provide a residual in the

distribution system. It is used where elevated DBPFP levels in the treated water can cause high

levels of DBP formation in the distribution system if free chlorine is used as the secondary

disinfectant. Monochloramine has been found to be more effective than free chlorine in controlling

biofilms and coliform bacteria in systems with long detention times due the lower decay rate of

chloramine. Monochloramine will have much less tendency to react with organics present and

hence will form less taste and odor causing compounds.

Inactivation efficiency At pH 7 and below, free chlorine is 200, 200, 50, and 2.5 times more effective in inactivating

bacteria, viruses, spores, and cysts respectively than monochloramine.

Byproduct formation Monochloramine substantially reduces the DBP formation but still forms some DBPs.

Limitations Monochloramine is increasingly being used as a secondary disinfectant to provide a residual in

distribution systems because of its lower decay rate then free chlorine and lesser tendency to form

DBPs.

Caution should be used in using monochloramine in distribution systems where water sources

using free chlorine residual are also used. High Cl2 to N ratios can occur where waters using

different residuals combine leading to the possible formation of taste and odor causing

dichloramine and nitrogen trichloride. In some cases the residual maybe completely removed by

the breakpoint reaction.

Point of application Monochloramine is normally generated at the treatment facility with the addition of ammonia to

chlorinated water. Ammonia is normally added prior to the pumping into the distribution system. In

some cases, ammonia is added prior to the clearwell to minimize formation of DBPs by free

chlorine residual.

Special considerations Nitrification and generation of bacterial growths can occur if the Cl2 to N ratio is too low and

conditions exist for the growth of nitrifying bacteria. A minimum residual of 2.0 mg/L of

monochloramine has been found effective in controlling nitrification in most systems.

6.9 References

1. Aoki, T. 1989. “Continuous Flow Method For Simultaneous Determination Of Monochloramine,

Dichloramine, and Free Chlorine: Application To A Water Purification Plant.” Environ. Sci.

Technol. 23:46-50.
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2. AWWA (American Water Works Association). 1991. Guidance Manual for Compliance with the

Filtration and Disinfection Requirements for Public Works Systems Using Surface Water

Sources.

3. AWWA and ASCE (American Society of Civil Engineers). 1990. Water Treatment Plant Design,

second edition. McGraw-Hill, Inc. New York, NY.

4. Bongers, L.H., T.P O’Connor, and D.T. Burton. 1977. “Bromine Chloride-An Alternative To

Chlorine For Fouling Control in Condenser Cooling Systems.” EPA 600/7-77-053, Washington,

D.C.

5. Cameron, G.N., J.M. Symons, S.R. Spencer, and J.Y. Ma. 1989a. “Minimizing THM Formation

During Control of the Asiatic Clam: A Comparison of Biocides.” J. AWWA. 81(10):53-62.

6. Cameron, G.N., J.M. Symons, D. Bushek, and R. Kulkarni. 1989b. “Effect of Temperature and

pH on the Toxicity of Monochloramine to the Asiatic Clam.” J. AWWA. 81(10):63-71.

7. Chang, S.L. 1944. “Studies on Entamoeba histolytica 3. Destruction of Cysts of Entamoeba

histolytica by Hypochlorite Solution, Chloramines in Tap Water and Gaseous Chlorine in Tap

Water of Varying Degrees of Pollution.” War Med. 5:46.

8. Chang, S.L. and G.M. Fair. 1941. “Viability and Destruction of the Cysts of Entamoeba

histolytica.” J. AWWA. 33(10):1705.

9. Cowman, G.A., and P.C. Singer. 1994. “Effect of Bromide Ion on Haloacetic Acid Speciation

Resulting from Chlorination and Chloramination of Humic Extracts.” Conference proceedings,

AWWA Annual Conference, New York, NY.

10. Dennis, J.P., D.C. Rauscher, and D.A. Foust. 1991. “Practical Aspects of Implementing

Chloramines.” Conference proceedings, AWWA Annual Conference, Philadelphia, PA.

11. Dorn, J. M. 1974. A Comparative Study of Disinfection on Viruses and Bacteria by

Monochloramine. Master’s thesis, Univ. Cincinnati, Ohio.

12. Esposito, M.P. 1974. The Inactivation of Viruses in Water by Dichloramine. Master’s thesis,

Univ. Cincinnati, Ohio.

13. Feng, T.H. 1966. “Behavior of Organic Chloramines.” J. Water Pollution Control Fed.

38(4):614.

14. Fujioka, R.S., K.M. Tenno, and P.C. Loh. 1983. “Mechanism of Chloramine Inactivation of

Poliovirus: A Concern for Regulators.” Water Chlorination: Environmental Impacts and Health

Affects, Vol. 4, R.L. Jolley, et al. (editor). Ann Arbor Science Publishers, Inc., Ann Arbor, MI.
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6-31

15. Gordon, G., W.J. Cooper, R.G. Rice, and G.E. Pacey. 1992. Disinfectant Residual Measurement

Methods. Second Edition, AWWARF and AWWA.

16. Haas, C. N. and R.S. Engelbrecht. 1980. “Chlorine Dynamics During Inactivation of Coliforms,

Acid-Fast Bacteria and Yeasts.” Water Res. 14:1744.

17. Hazen and Sawyer. 1992. Disinfection Alternatives For Safe Drinking Water. Van Nostrand

Reinhold, New York, NY.

18. Hoff, J.C. and E.E. Geldreich. 1981. “Comparison of the Biocidal Efficiency of Alternative

Disinfectants.” J. AWWA. 73(1):40.

19. Isaac, R.A. and J.C. Morris. 1980. “Rates of Transfer of Active Chlorine Between Nitrogenous

Substances.” Water Chlorination: Environmental Impact and Health Affects, Vol. 3. R.L. Jolley

(editor). Ann Arbor Science Publishers, Inc., Ann Arbor, MI.

20. Jacangelo, J.G., Olivieri , V.P., and Kawata, K., 1987. “Mechanism of Inactivation of

Microorganisms by Combined Chlorine.” AWWA Research Foundation, Denver, CO.

21. Jacangelo, J.G., N.L. Patania, K.M. Reagan, E.M. Aieta, S.W. Krasner, and M.J. McGuire. 1989.

“Impact of Ozonation on the Formation and Control of Disinfection Byproducts in Drinking

Water.” J. AWWA.81(8):74.

22. Jensen, J., J. Johnson, J. St. Aubin, R. Christman. 1985. “Effect of Monochloramine on Isolated

Fulvic Acid.” Org. Geochem. 8(1):71.

23. Johnson, J.D. 1978. “Measurement and Persistence of Chlorine Residuals.” Natural Waters. In

Water Chlorination: Environmental Impact and Health Effects. R.L. Jolley (editor). Ann Arbor

Science Publishers, Inc., Ann Arbor, MI. 1:37-63.

24. Kabler, P.W., et al. 1960. “Viricidal Efficiency of Disinfectants in Water.” Public Health Repts.

76(7):565.

25. Kelley, S.M. and W.W. Sanderson. 1958. “The Affect of Chlorine in Water on Enteric Viruses.”

Amer. Jour. Publ. Health. 48:1323.

26. Kelley, S.M. and W.W. Sanderson. 1960. “The Effect of Chlorine in Water on Enteric Viruses 2,

The Effect of Combined Chlorine on Poliomyelitis and Coxsackie Viruses.” Amer. Jour. Publ.

Health. 50(1):14.

27. Kirmeyer, G., et al. 1993. Optimizing Chloramine Treatment. AWWARF.

28. Kirmeyer, G., et al. 1995. Nitrification Occurrence and Control in Chloraminated Water Systems.

AWWARF.
6. C H L O R A M I N E S

EPA Guidance Manual 6-32 April 1999

Alternative Disinfectants and Oxidants

29. Krasner, S.W., M.J. McGuire, and J.J. Jacangelo. 1989. “The Occurrence of Disinfection

Byproducts in U.S. Drinking Water.” J. AWWA. 81(8):41.

30. Lyn, T.L., S.R. Lavinder, and R. Hungate. 1995. “Design Considerations for Ammoniation

Facilities.” Conference proceedings, AWWA Annual Conference, Anaheim, CA.

31. Margerum, D.W., et al. 1978. “Chlorination and the Formation of N-Chloro Compounds in

Water Treatment.” Organometals and Organometal-loids: Occurrence and Fate in the

Environment. R. F. Brinckman and J. M. Bellama (editors). ACS (American Cancer Society),

Washington, D.C.

32. Marks, H.C., D.B. Williams, and G.U. Glasgow. 1951. “Determination of Residual Chlorine

Compounds.” J. AWWA. 43:201-207.

33. Masschelein, W.J. 1992. “Unit Processes in Drinking Water Treatment.” Marcel Decker D.C.,

New York, Brussels, Hong Kong.

34. Montgomery, J.M. 1985. Water Treatment Principles and Design. John Wiley & Sons, Inc.,

New York, NY.

35. Morris, J.C. 1967. “Kinetics of Reactions Between Aqueous Chlorine and Nitrogen

Compounds.” Principles and Applications of Water Chemistry. S.D. Faust and J.V. Hunter

(editor). John Wiley & Sons, New York, NY.

36. NRC (National Research Council). 1980. Drinking Water and Health, Vol. 2. National Academy

Press, Washington, D.C.

37. Norton, C.D. and M.W. LeChevallier. 1997. “Chloramination: Its Effect on Distribution System

Water Quality.” J. AWWA. 89(7):66.

38. Olivieri, V.P., et al. 1980. “Reaction of Chlorine and Chloramines with Nucleic Acids Under

Disinfection Conditions.” Water Chlorination: Environmental Impact and Health Affects, Vol. 3.

R.J. Jolley (editor), Ann Arbor Science Publishers, Inc., Ann Arbor, MI.

39. Palin, A. 1950. 1950. “A Study of the Chloro Derivatives of Ammonia.” Water and Water

Engineering. 54:248-258.

40. Rice, R. and M. Gomez-Taylor. 1986. “Occurrence of By-Products of Strong Oxidants Reating

with Drinking Water Contaminants - Scope of the Problem.” Environ. Health Perspectives.

69:31.

41. Singer, P.C. 1993. “Trihalomethanes and Other Byproducts Formed From the Chlorination of

Drinking Water.” National Academy of Engineering Symposium on Environmental Regulation:

Accommodating Changes in Scientific, Technical, or Economic Information, Washington, D.C.
6. C H L O R A M I N E S

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6-33

42. Skadsen, J. 1993. “Nitrification in a Distribution System.” J. AWWA. 95-103.

43. Smith, M.E., Cowman, G.A., Singer, P.C. 1993. “The Impact of Ozonation and Coagulation on

DBP Formation in Raw Waters.” Conference proceedings, AWWA Annual Conference, San

Antonio, TX.

44. Speed, M.A., et al. 1987. Treatment Alternatives for Controlling Chlorinated Organic

Contaminants in Drinking Water. EPA/60012-87/011, Washington, D.C.

45. Standard Methods. 1995. Standard Methods for the Examination of Water and Wastewater,

ninteenth edition, Franson, M.H., Eaton, A.D., Clesceri, L.S., and Greenberg, A.E., (editors).

APHA (American Public Health Association), AWWA, and Water Environment Federation,

Washington D.C.

46. Stringer, R. and C.W. Kruse. 1970. “Amoebic Cysticidal Properties of Halogens.” Conference

proceedings, National Specialty Conference on Disinfection, ASCE, New York.

47. Sugam, R. 1983. “Chlorine Analysis: Perspectives For Compliance Monitoring.” Water

Chlorination, Environmental Impact and Health Effects. R.L. Jolley, et al. (editor). Ann Arbor

Science Publishers, Ann Arbor, MI.

48. Valentine, R.L. et al. 1998. “Chloramine Decomposition in Distribution System and Model

Waters.” AWWA, Denver, CO.

49. Wattie, E. and C.T. Butterfield. 1944. “Relative Resistance of Escherichia coli and Eberthella

typhosa to Chlorine and Chloramines.” Public Health Repts. 59:1661.

50. Weber, G.R. and M. Levine. 1944. “Factors Affecting the Germicidal Efficiency of Chlorine and

Chloramine.” Amer. J. Public Health: 32:719.

51. Weil, I. and J.C. Morris. 1949. “Kinetic Studies on the Chloramines. The Rates of Formation of

Monochloramine, N-Chlormethylamine and N-Chlordimethylamine.” J. Amer. Chem. Soc.

71:1664.

52. White, G.C. 1992. Handbook Of Chlorination and Alternative Disinfectants. Volume 3. Van

Nostrand Reinhold Co., New York, NY.

53. Whittle, G.P. and Lapteff, A., Jr. 1974. “New Analytical Techniques For The Study Of Water

Disinfection.” Chemistry of Water Supply, Treatment, and Distribution. A.J. Rubin (editor) Ann

Arbor Science Publishers, Inc., Ann Arbor, MI.

54. Wolfe, R.L., N.R. Ward, and B.H. Olson. 1984. “Inorganic Chloramines as Drinking Water

Disinfectant: A Review.” J. AWWA. 76(5):74-88.
6. C H L O R A M I N E S

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6. C H L O R A M I N E S

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6-35

CHLORAMINES.............................................................................................................................................. 6-1

6.1 CHLORAMINES CHEMISTRY................................................................................................................... 6-1

6.1.1 Equilibrium, Kinetic, and Physiochemical Properties .................................................................... 6-1

6.2 GENERATION........................................................................................................................................ 6-3

6.2.1 Chlorine Feed Facilities................................................................................................................ 6-4

6.2.2 Ammonia Feed Facilities.............................................................................................................. 6-5

6.3 PRIMARY USES AND POINTS OF APPLICATION ...................................................................................... 6-10

6.3.1 Primary Uses.............................................................................................................................. 6-10

6.3.2 Points of Application.................................................................................................................. 6-11

6.4 PATHOGEN INACTIVATION AND DISINFECTION EFFICACY ..................................................................... 6-12

6.4.1 Inactivation Mechanisms............................................................................................................ 6-12

6.4.2 Environmental Effects................................................................................................................ 6-12

6.4.3 Disinfection Efficacy.................................................................................................................. 6-13

6.5 DBP FORMATION ............................................................................................................................... 6-15

6.6 STATUS OF ANALYTICAL METHODS..................................................................................................... 6-16

6.6.1 Monitoring of Chloramines......................................................................................................... 6-16

6.6.2 Disinfectant Interferences........................................................................................................... 6-17

6.6.3 Chloramine Monitoring for Systems Using Chloramines............................................................. 6-19

6.7 OPERATIONAL CONSIDERATIONS......................................................................................................... 6-20

6.7.1 Conversion to Chloramination from Chlorination........................................................................ 6-20

6.7.2 Potential Operational Impacts from Chloramination Disinfection ................................................ 6-22

6.7.3 Special Considerations for Chloramination Facilities................................................................... 6-25

6.8 SUMMARY.......................................................................................................................................... 6-27

6.8.1 Advantages and Disadvantages of Chloramine Use ..................................................................... 6-27

6.8.2 Summary Table .......................................................................................................................... 6-28

6.9 REFERENCES ...................................................................................................................................... 6-29

Table 6-1. Chlorine Dose Required for NH3 - Cl2 Reaction ................................................................................. 6-3

Table 6-2. Time to 99 Percent Conversion of Chlorine to Monochloramine ......................................................... 6-4

Table 6-3. Methods of Chlorine Addition............................................................................................................ 6-4

Table 6-4. CT Values for Giardia Cyst Inactivation Using Chloramines............................................................ 6-15

Table 6-5. CT Values for Virus Inactivation Using Chloramines....................................................................... 6-15

Table 6-6. Characteristics and Comparisons of Monochloraminea Analytical Methods....................................... 6-18

Table 6-7. Survey of Chloramine Users in the United States.............................................................................. 6-25

Table 6-8. Summary of Chloramine Disinfection .............................................................................................. 6-29

Figure 6-1. Theoretical Breakpoint Curve ........................................................................................................... 6-2

Figure 6-2. Distribution Diagram for Chloramine Species with pH...................................................................... 6-3

Figure 6-3. Gaseous Chlorine Feed System......................................................................................................... 6-5

Figure 6-4. Hypochlorite Feed System................................................................................................................ 6-6

Figure 6-5. Anhydrous Ammonia Direct Feed System......................................................................................... 6-7

Figure 6-6. Anhydrous Ammonia Solution Feed System ..................................................................................... 6-8

Figure 6-7. Aqua Ammonia Feed System............................................................................................................ 6-9
April 1999 7-1 EPA Guidance Manual

Alternative Disinfectants and Oxidants

7. PEROXONE (OZONE/HYDROGEN

PEROXIDE)

Advanced oxidation processes generate highly reactive hydroxyl free radicals to oxidize various

compounds in the water. As discussed in Chapter 3, hydroxyl radicals are produced during the

spontaneous decomposition of ozone. By accelerating the ozone decomposition rate, the hydroxyl

radical concentration is elevated, which increases the oxidation rate. This procedure increases the

contribution of indirect oxidation over direct ozone oxidation as discussed in Chapter 3.

Several methods have been used to increase ozone decomposition and produce high concentrations of

hydroxyl radicals. One of the most common of these processes involves adding hydrogen peroxide to

ozonated water, a process commonly referred to as peroxone.

The Metropolitan Water District of Southern California (MWDSC) conducted extensive research into

the use of peroxone to control organics and oxidize taste and odor compounds (e.g., geosmin and 2-

methylisoborneol [MIB]) while providing sufficient levels of molecular ozone to guarantee CT values

and primary disinfection. While this chapter focuses on peroxone as a disinfectant, similar results are

expected from other advanced oxidation processes such as ozone plus UV, ozone at high pH, hydrogen

peroxide plus UV, and other combinations.

A key issue with the use of peroxone as a disinfection process is that the process does not provide a

measurable disinfectant residual. It is therefore not possible to calculate CT similar to the use of other

disinfectants. While no credit can be given for hydroxyl free radicals because it cannot be measured

directly, some credit may be considered for any detected ozone in peroxone systems. Peroxone does

provide pathogen inactivation, as discussed in this chapter, but equivalent CT values or methods of

calculating equipment CT credits have not been established at the date of publication of this guidance

document.

7.1 Peroxone Chemistry

The ozone decomposition cycle is similar to that discussed in Chapter 3. However, the added

hydrogen peroxide or ultraviolet radiation accelerates the decomposition of ozone and increases the

hydroxyl radical concentration. By adding hydrogen peroxide, the net production of hydroxyl free

radicals is 1.0 mole hydroxyl radical per mole ozone.

Similar to the discussion of ozone in Chapter 3, oxidation in the peroxone occurs due to two reactions

(Hoigné and Bader, 1978):
7. PEROXONE (OZONE / HYDROGEN PEROXIDE)

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• Direct oxidation of compounds by aqueous ozone (O3(aq)); and

• Oxidation of compounds by hydroxyl radicals produced by the decomposition of ozone.

The two oxidation reactions compete for substrate (i.e., compounds to oxidize). The ratio of direct

oxidation with molecular ozone is relatively slow (10-5-107M

-1

sec

-1) compared to hydroxyl radical

oxidation (1012-1014M

-1

sec

-1), but the concentration of ozone is relatively high. On the other hand, the

hydroxyl radical reactions are very fast, but the concentration of hydroxyl radicals under normal

ozonation conditions is relatively small.

A key difference between the ozone and peroxone processes is that the ozone process relies heavily on

the direct oxidation of aqueous ozone while peroxone relies primarily on oxidation with hydroxyl

radical. In the peroxone process, the ozone residual is short lived because the added peroxide greatly

accelerates the ozone decomposition. However, the increased oxidation achieved by the hydroxyl

radical greatly outweighs the reduction in direct ozone oxidation because the hydroxyl radical is much

more reactive. The net result is that oxidation is more reactive and much faster in the peroxone process

compared to the ozone molecular process. However, because an ozone residual is required for

determining disinfection CT credit, peroxone may not be appropriate as a pre-disinfectant.

The peroxone process utilizes oxidation by hydroxyl radicals. The oxidation potential of the hydroxyl

radical and ozone are as follows:

OH + e → OH − −E

0

= +2.8V

O3 + 2H + 2e → O2 + H2O

+ −

E

0

= +2.07V

O3 + H2O + 2e → O2 + 2OH − −E

0

= +1.24V

In addition to having an oxidation potential of hydroxyl radical higher than ozone, the hydroxyl radical

is also much more reactive approaching the diffusion control rates for solutes such as aromatic

hydrocarbons, unsaturated compounds, aliphatic alcohols, and formic acid (Hoigné and Bader, 1976).

7.1.1 Oxidation Reactions

Because the radical oxidation is much more effective than direct oxidation with ozone, it has been used

extensively to treat difficult to oxidize organics such as taste and odor compounds and chlorinated

organics (e.g., geosmin, MIB, phenolic compounds, trichloroethylene [TCE], and perchloroethylene

[PCE]).

Neither ozone nor peroxone significantly destroys TOC. Peroxone will oxidize the saturated organics

and produce byproducts similar to those found in ozonation; namely, aldehydes, ketones, peroxides,

bromate ion, and biodegradable organics (MWDSC and JMM, 1992). However, with peroxone, the
7. PEROXONE (OZONE / HYDROGEN PEROXIDE)

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biodegradibility of the water (not the organic compounds) increases, rendering “a portion of the TOC”

amenable to removal in biologically active filters.

Peroxone has found a niche in oxidizing difficult-to-treat organics, such as taste and odor compounds

including geosmin and MIB (Pereira et al., 1996; Ferguson et al., 1990). In addition, peroxone and

other advanced oxidation processes have been shown to be effective in oxidizing halogenated

compounds such as 1,1-dichloropropene, trichloroethylene, 1-chloropentane, and 1,2-dichloroethane

(Masten and Hoigné, 1992; Aieta et al., 1988; Glaze and Kang, 1988). Hydroxyl radicals will react

with all these compounds plus refractory aliphatics such as alcohols and short-chain acids (Chutny and

Kucera, 1974).

The optimum peroxide:ozone dose ratio to maximize hydroxyl radicals’ reaction rate can be

determined for a specific oxidation application. For instance, the optimum peroxide:ozone dose ratio

for TCE and PCE oxidation in a ground water was determined to be 0.5 by weight (Glaze and Kang,

1988). Tests showed that TCE required lower ozone dosages for the same percentage removal

compared to PCE.

LADWP conducted pilot studies and operated a 2,000 gpm full scale AOP demonstration plant in

1995. The peroxide:ozone dose ratio used was 0.5 to 0.6. Ground water containing up to 447 mg/L

TCE and 163 mg/L PCE was treated to below the respective MCLs. However, bromate ion was

formed in excess of the 0.010 mg/L MCL (Karimi et al., 1997).

7.1.2 Reactions with Other Water Quality Parameters

As with ozone alone, pH and bicarbonate alkalinity play a major role in peroxone effectiveness (Glaze

and Kang, 1988). This role is primarily related to bicarbonate and carbonate competition for hydroxyl

radical at high alkalinity and carbonate competition for hydroxyl radical at high pH levels. Also,

excessive peroxide can also limit the formation of the hydroxyl radical and reduce the effectiveness of

peroxone.

Turbidity alone does not appear to play a role in peroxone effectiveness nor does peroxone appear to

remove turbidity. Tobiason et al. (1992) studied the impact of pre-oxidation on filtration and

concluded that the pre-oxidation did not improve effluent turbidities, but did appear to increase filter

run times because of lower head loss or delayed turbidity breakthrough. Filter effluent turbidities were

similar for no-oxidant and pre-oxidant trains.

7.1.3 Comparison between Ozone and Peroxone

The key difference between ozone and peroxone is in the primary oxidation mode; that is, direct

oxidation or hydroxyl radical oxidation. The reactivities of these compounds create a different effect in

the reactions with water constituents and, thus, disinfection effectiveness. Table 7-1 summarizes the
7. PEROXONE (OZONE / HYDROGEN PEROXIDE)

EPA Guidance Manual 7-4 April 1999

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key differences between ozone and peroxone as they relate to their application in drinking water

treatment.

Table 7-1. Comparison between Ozone and Peroxone Oxidation

Process Ozone Peroxone

Ozone decomposition

rate

“Normal” decomposition producing

hydroxyl radical as an intermediate

product

Accelerated ozone decomposition

increases the hydroxyl radical

concentration above that of ozone

alone.

Ozone residual 5-10 minutes Very short lived due to rapid reaction.

Oxidation path Usually direct aqueous molecular

ozone oxidation

Primarily hydroxyl radical oxidation.

Ability to oxidize iron

and manganese

Excellent Less effective.

Ability to oxidize taste

and odor compounds

Variable Good, hydroxyl radical more reactive

than ozone.

Ability to oxidize

chlorinated organics

Poor Good, hydroxyl radical more reactive

than ozone.

Disinfection ability Excellent Good, but systems can only receive

CT credit if they have a measurable

ozone residual.

Ability to detect

residual for

disinfection monitoring

Good Poor. Cannot calculate CT value for

disinfection credit.

7.2 Generation

The peroxone process requires an ozone generation system as described in Chapter 3 and a hydrogen

peroxide feed system. The process involves two essential steps: ozone dissolution and hydrogen

peroxide addition. Hydrogen peroxide can be added after ozone (thus allowing ozone oxidation and

disinfection to occur first) or before ozone (i.e., using peroxide as a pre-oxidant, followed by hydroxyl

radical reactions) or simultaneously. Addition of hydrogen peroxide following ozone is the best way to

operate, however a system cannot obtain a CT credit unless the ozone residual is sufficiently high.

There are two major effects from the coupling of ozone with hydrogen peroxide (Duguet et al., 1985):

• Oxidation efficiency is increased by conversion of ozone molecules to hydroxyl radicals; and

• Ozone transfer from the gas phase to the liquid is improved due to an increase in ozone

reaction rates.
7. PEROXONE (OZONE / HYDROGEN PEROXIDE)

April 1999 7-5 EPA Guidance Manual

Alternative Disinfectants and Oxidants

The most efficient operation is to add ozone first to obtain CT disinfection credit, followed by peroxide

for hydroxyl radical oxidation.

Ozonation can be described as occurring in two stages. In the first stage, ozone rapidly destroys the

initial oxidant demand present, thereby enhancing the ozone transfer rate into solution from the gas

phase. Addition of hydroxyl free radicals to the first stage should be minimized since the hydrogen

peroxide competes with ozone-reactive molecules (i.e., initial demand) for the ozone present. In the

second stage, organic matter is oxidized, taking place much slower than in the first stage. Adding

hydrogen peroxide during the second stage makes it possible to raise the overall oxidation efficiency,

since the reaction of hydrogen peroxide with ozone produces hydroxyl radicals enhancing chemical

reaction rates. In practice, the addition of hydrogen peroxide to the second stage of ozonation can be

achieved by injecting the hydrogen peroxide into the second chamber of an ozone contactor (Duguet et

al., 1985). The most efficient operation is to use ozone first to obtain CT credit and peroxone second

for micropollutant destruction.

Energy consumption of the peroxone process includes that for ozone generation and application, plus

for metering pumps to feed peroxide. The peroxide addition step does not require any more training

from an operator than any other liquid chemical feed system. Systems should be checked daily for

proper operation and for leaks. Storage volumes should also be checked daily to ensure sufficient

peroxide is on hand, and to monitor usage.

7.3 Primary Uses and Points of Application

Peroxone is used for oxidation of taste and odor compounds, and oxidation of synthetic organic

compounds. Peroxone is also used for the destruction of herbicides (e.g., atrazine), pesticides, and

VOCs. Peroxone is applied at points similar to ozone for oxidation. Addition of ozone first and

hydrogen peroxide second is the better way to operate. Alternatively, hydrogen peroxide can be added

upstream of ozone.

7.3.1 Primary Uses

7.3.1.1 Taste and Odor Compound Oxidation

Peroxone is used to remove taste and odor causing compounds because many of these compounds are

very resistant to oxidation, even ozone-oxidation. More recently, significant attention has been given to

tastes and odors from specific compounds such as geosmin, 2-methyliosborneol (MIB), and chlorinated

compounds. Studies at MWDSC demonstrated the effectiveness of peroxone to remove geosmin and

MIB during water treatment (Ferguson et al., 1990; Ferguson et al., 1991; Huck et al., 1995).

7.3.1.2 Synthetic Organic Compound Oxidation

Peroxone and other advanced oxidation processes have been shown to be effective in oxidizing

halogenated compounds such as 1,1-dichloropropene (DCPE), TCE, 1-chloropentane (CPA), and 1,2-
7. PEROXONE (OZONE / HYDROGEN PEROXIDE)

EPA Guidance Manual 7-6 April 1999

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dichloroethane (DCA) (Masten and Hoigné, 1992; Aieta et al., 1988; Glaze and Kang, 1988). The

hydroxyl radicals formed react with all these compounds plus refractory aliphatics, such as alcohols

and short-chain acids (Chutny and Kucera, 1974).

7.3.2 Points of Application

The peroxone process is applied at points similar to ozone for oxidation as discussed in Chapter 3.

Importantly, peroxone addition should be after settling and prior to biological filtration. It is important

to add hydrogen peroxide after the initial ozone demand is consumed to avoid hydroxyl free radical

competition with the initial ozone demanding constituents.

7.3.2.1 Impact on Other Treatment Processes

Peroxide addition impacts other processes at the water treatment facility. These impacts include:

• The use of hydroxyl free radicals generates BDOC, which can cause biological growth in

distribution systems if not reduced during biologically active filtration. When peroxide

addition is placed before filters, it impacts the filters by increasing biological growths and

increasing backwash frequency (depending on the level on BDOC produced).

• Hydroxyl free radicals are strong oxidants that interfere with addition of other oxidants, such

as chlorine, until the ozone residual is quenched.

• The oxidation of iron and manganese by hydroxyl free radicals generates insoluble oxides that

should be removed by sedimentation or filtration. This also may impact the filters by

increasing the load on the filters and increasing backwash frequency.

The reader is referred to the Microbial and Disinfection Byproduct Simultaneous Compliance

Guidance Document (currently in production) for additional information regarding the interaction

between oxidants and other treatment processes.

7.4 Pathogen Inactivation

Both peroxone and other advanced oxidation processes have been proven to be equal or more effective

than ozone for pathogen inactivation. Disinfection credits are typically described in terms of CT

requirements. Because peroxone leaves no measurable, sustainable residual, calculation of an

equivalent CT for disinfection credit is not possible unless there is measurable ozone residual.

7.4.1 Inactivation Mechanism

Experiments have indicated that long contact times and high concentrations of hydrogen peroxide are

required for bacteria and virus inactivation (Lund, 1963; Yoshe-Purer and Eylan, 1968; Mentel and

Schmidt, 1973). Achieving a 99 percent inactivation of poliovirus required either a hydrogen peroxide

dose of 3,000 mg/L for 360 minutes or 15,000 mg/L for 24 minutes. Based on these results, when the

combination of ozone and hydrogen peroxide is used, the primary cause for pathogen inactivation is
7. PEROXONE (OZONE / HYDROGEN PEROXIDE)

April 1999 7-7 EPA Guidance Manual

Alternative Disinfectants and Oxidants

attributed to ozone, specifically the mechanisms associated with the oxidation of pathogens by direct

ozone reaction and hydroxyl radicals.

As described in Chapter 3, the mode of action of ozone on microorganisms is poorly understood.

Some studies on bacteria suggest that ozone alters proteins and unsaturated bonds of fatty acids in the

cell membrane, leading to cell lysis (Scott and Lesher, 1963; Pryor et al., 1983), while other studies

suggest that ozone may affect deoxyribonucleic acid (DNA) in the cell (Hamelin and Chung, 1974;

Ohlrogge and Kernan, 1983; Ishizaki et al., 1987). Virus inactivation was reported to be related to the

attack of the protein capsid by ozone (Riesser et al., 1977). Little information was found discussing the

mode of action of ozone on protozoan oocysts. However, a few researchers have suggested that ozone

causes the oocyst density to decrease and alters the oocyst structure (Wickramanayake, 1984; Wallis et

al., 1990).

The debate continues regarding the primary mode of action for hydroxyl free radicals. Some

researchers believe that ozone disinfection is a result of direct ozone reaction (Hoigné and Bader, 1975;

Hoigné and Bader, 1978), while others believe that the hydroxyl radical mechanism for disinfection is

the most important mechanism (Dahi, 1976; Bancroft et al., 1984). Studies using ozone-hydrogen

peroxide have shown that disinfection of E. coli is less effective as the peroxide to ozone ratio increases

to above approximately 0.2 mg/mg (Wolfe et al., 1989a; Wolfe et al., 1989b). The decrease in

disinfection was believed to be cause by lower ozone residuals associated with higher peroxide to

ozone ratios, which indicates that direct ozone reaction is an important mechanism for pathogen

inactivation.

7.4.2 Environmental Effects

Although the chemistry of the peroxone process is still not completely understood, optimal production

of the hydroxyl radical appears to depend on the pH, ozone concentration, ratio of hydrogen peroxide to

ozone, contact time, and water composition (Glaze et al., 1987).

7.4.2.1 Competing Chemical Reactions

One disadvantage of the peroxone process is that it involves radical intermediates that are subject to

interference from substances that react with hydroxyl radical, decreasing the effectiveness of the

process. Alkalinity, bicarbonate, and pH play a major role in the effectiveness of hydroxyl free radicals.

This effect is primarily related to bicarbonate competition for hydroxyl radical at high alkalinity and

carbonate competition for hydroxyl radical at pH levels higher than 10.3 (see Chapter 3). Lowering the

alkalinity prior to the application of the peroxone process may be necessary for water that has a high

bicarbonate level. In addition to carbonate and bicarbonate, organic constituents of humic substances

have also been found to react with the hydroxide radical (Glaze, 1986).
7. PEROXONE (OZONE / HYDROGEN PEROXIDE)

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7.4.2.2 Ratio of Hydrogen Peroxide and Ozone

A study conducted at MWDSC indicated that the performance of peroxone is greatly dependent upon

the peroxide:ozone ratio (Wolfe et al., 1989b). Results from previous studies at MWDSC suggested

that the optimal ratio for disinfection was less than or equal to 0.3. One of the primary objectives of the

1989 study was to optimize further the process for disinfection by altering peroxide:ozone ratios and

contact times. Results from the study indicated that peroxone at a 0.2 ratio of peroxide:ozone was

comparable to ozone for disinfection of indicator organisms and Giardia muris cysts, and that at higher

ratios, disinfection decreased because ozone decreased.

7.4.3 Disinfection Efficacy and Pathogen Inactivation

Recent studies have indicated that the disinfection effectiveness of peroxone and ozone are comparable

(Wolfe et al., 1989b; Ferguson et al., 1990; Scott et al., 1992). A study conducted by Ferguson et al.

(1990) compared the pathogen inactivation capability of peroxone and ozone using MS-2 and f2

coliphages as well as E. coli. and heterotrophic plate count (HPC) bacteria. The f2 and MS-2

coliphages were comparable in their resistance to ozone and peroxone. No differences in the amounts

of MS-2 or f2 inactivation were apparent when the peroxide:ozone ratio was varied from 0 to 0.3.

Results of the E. coli. and HPC studies showed that peroxone and ozone also had comparable results in

regards to bacteria inactivation.

Table 7-2 lists CT values derived for inactivation of Giardia muris cysts by ozone and peroxone from

another study conducted by MWDSC. The contact times used for calculating the CT values were

based on 10% and 50% breakthrough of tracer compounds in the contactor. Ozone concentrations

used for CT were based on the ozone residual and half of the residual and dose. The results of this

study suggest that peroxone is slightly more potent than ozone based on the fact that CT values for

ozone were greater than for peroxone. However, because ozone decomposes more rapidly in the

presence of hydrogen peroxide, higher ozone dosages may be necessary with peroxone to achieve

comparable residuals. Moreover, the use of ozone residuals to calculate CT products for peroxone

may not take into account other oxidizing species that may have disinfectant capabilities.

Table 7-2. Calculated CT Values (mg•min/L) for the Inactivation of Giardia muris

Inactivation Ozone

C1T1

a

Ozone

C2T2

a

Peroxoneb

C1T1

a

Peroxone

C2T2

a

90% 1.6 2.8 1.2 2.6

99% 3.4 5.4 2.6 5.2

 Data obtained from Wolfe et al., 1989b. Results at 14oC.

a

 C1, ozone residual; C2 (ozone dose + ozone residual)/2; T1 and T2 time (in minutes) to reach 10 percent and 50 percent breakthrough,

respectively

b

 The H2O2/O3 ratio for all results was 0.2.
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7.5 Disinfection Byproducts

The principal byproducts associated with peroxone are expected to be similar to those for ozonation

and are listed in Table 3-9. Additional DBPs could form from reactions with hydroxyl radicals.

Peroxone does not form halogenated DBPs when participating in oxidation/reduction reactions with

NOM. However, if bromide ion is present in raw water halogenated DBPs may be formed. Similar to

ozone, the principal benefit of using peroxone for controlling THM formation appears to be that it

eliminates the need for pre-chlorination and allows lower doses of free chlorine or chloramines to be

applied later in the process train after precursors have been removed by coagulation, sedimentation,

and/or filtration and at lower doses. But peroxone does not reduce the DBPFP.

Based upon studies and findings involving peroxone, there is no beneficial lowering of THMs as long

as free chlorine is utilized as a secondary disinfectant, unless the application of peroxone allows

chlorine to be applied later in the process train to water containing reduced precursor concentrations.

The MWDSC study found that the use of peroxone/chlorine resulted in THM concentrations 10 to 38

percent greater than the use of ozone/chorine. However, the THM concentrations of waters disinfected

with peroxone/chloramines and ozone/chloramines were similar (Ferguson et al., 1990).

The use of peroxone as a primary disinfectant and chloramines as a secondary disinfectant can

successfully control halogenated DBP formation if bromide ion is not present and adequate CT credit

can be established. As with ozone, bromate ion formation is a potential concern with source waters

containing bromide ions. The oxidation reaction of bromide ion (Br-) to hypobromite ion (BrO-) and

bromite ion (BrO2

-

) and subsequently to bromate ion (BrO3

-

) occurs due to direct reaction with ozone,

intermediate reactions can also occur through hydroxide radical mediated mechanisms if bromide is not

present and adequate CT credit can be established (Pereira et al., 1996).

In general, peroxone produces more bromate ion than ozone when similar ozone residuals (CT credits)

are achieved (Krasner et al., 1993). On the other hand, when the ozone dosage is kept constant,

peroxone has tended to produce comparable amounts of bromate ion as ozone. Although peroxone

produces hydroxyl radicals that can increase bromate ion formation, hydrogen peroxide may also

reduce the hypobromite ion (produced initially during the ozonation of bromide) back to bromide ion.

A study by MWDSC evaluated the effectiveness of peroxone to control taste and odor, DBPs, and

microorganisms (Ferguson et al., 1990). In attempting to optimize the hydrogen peroxide to ozone

ratio (H2O2:O3) and the contact time for the source water, the study found pre-oxidation of source

waters followed by secondary disinfection with chloramines was an effective strategy for controlling

concentrations of THMs and other DBPs. The study found that the two source waters disinfected with

peroxone, with free chlorine as the secondary disinfectant, resulted in THM concentrations ranging

from 67 to 160 μg/L. Conversely, using chloramines as a secondary disinfectant resulted in THM

concentrations consistently below 3.5 μg/L (Ferguson et al., 1990).
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However, if a short free chlorine contact time is applied after biological filtration and before ammonia

addition to inactivate heterotrophic plate count bacteria in the effluent of the biologically active filter—

THMs and other DBPs will be formed at higher concentrations than from post chloramination alone.

Depending on the TOC and bromide ion concentration of the water, as well as the pH of chlorination,

temperature, and reaction time, between 2 and 28 μg/L of TTHMs have been formed in experiments

conducted at MWDSC (personal communication, 1998).

Bromate formation in conventional ozonation, and advanced oxidation processes combining ozone and

hydrogen peroxide, were recently investigated at five water treatment plants in France. The source

water bromide ion concentrations ranged from 35 to 130 μg/L. Bromate ion formation during the

ozonation step varied from less than 2 to 42 μg/L. In general, advanced oxidation results in greater

bromate ion concentrations when compared with conventional ozonation, provided the same ozone

residual is maintained for both processes. However, lower concentrations of bromate ion result if the

ozone dosage is kept constant between the two processes and the hydrogen peroxide dosage is

increased (von Gunten et al., 1996). To reduce bromate ion formation potential, the proposed ozone

contactor at Stone Canyon Filtration Plant includes three ozone application points instead of two

(Stolarik and Christie, 1997). Thus, when peroxone is used for obtaining CT credit, more bromate ion

may form than during ozonation. However, if peroxone is only used for micropollutant destruction,

less bromate ion may form than when ozone is used.

7.6 Status of Analytical Methods

Hydrogen peroxide in solution reacts with ozone to ultimately form water and oxygen. Consequently,

the simultaneous presence of both oxidants is accepted as being only transient (Masschelein et al.,

1977). Chapter 3 summarizes ozone analytical methods that can be used for ozone/hydrogen peroxide

disinfectant residual monitoring. This section will present the status of analytical methods for hydrogen

peroxide only.

7.6.1 Monitoring of Hydrogen Peroxide

Standard Methods (1995) does not list procedures for measuring hydrogen peroxide. Gordon et al.

(1992) list several methods for hydrogen peroxide analysis including:

• Titration methods;

• Colorimetric methods; and

• Horseradish peroxidase methods.

Table 7-3 shows the working range, expected accuracy and precision, operator skill level required,

interferences and current status for hydrogen peroxide analysis.
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7.6.1.1 Titration Methods

Two titration methods are available for the analysis of hydrogen peroxide; namely, iodometric and

permanganate. Precautions for the iodometric titration include the volatility of iodine, interferences by

metals such as iron, copper, nickel, and chromium, and fading titration end points (Gordon et al.,

1992). Organic and inorganic substances that react with permanganate will interfere with the

permanganate titration.

Titration of hydrogen peroxide with permanganate or iodide ion is not sufficiently sensitive for

determining residual concentrations (Masschelein et al., 1977).

7.6.1.2 Colorimetric Methods

The most widespread method for the colorimetric determination of hydrogen peroxide is that based on

the oxidation of a Titanium (IV) salt (Masschelein et al., 1977). A yellow complex is formed and

measured by absorption at 410 nm. On a qualitative basis, ozone and persulfates do not produce the

same colored complex.

The oxidation of the leuco base of phenolphthalein is used as a qualitative test for hydrogen peroxide

(Dukes and Hydier, 1964). Sensitivity and precision of the method is sufficient in the range between 5

and 100 μg/L. This low working analytical range makes this method impractical for measuring

hydrogen peroxide residual levels. Also, the instability of the color obtained makes the method less

suitable for manual use. No interference data are available, but it is expected that other oxidants would

interfere (Gordon et al., 1992).

The oxidation of cobalt (II) and bicarbonate in the presence of hydrogen peroxide produces a

carbonato-cobaltate (III) complex (Masschelein et al., 1977). This complex has absorption bands at

260, 440, and 635 nm. The 260 nm band has been used for the measurement of hydrogen peroxide. A

detection limit of 0.01 mg/L has been reported (Masschelein et al., 1977). Optical interferences are

caused by 100 mg/L nitrate and 1 mg/L chlorite ions. Other oxidizing agents do interfere with this

method as will any compound with an absorption at 260 nm (Gordon et al., 1992).
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7-12

Table 7-3. Characteristics and Comparisons of Hydrogen Peroxide Analytical Methods

Type of Test

Working

Range

(mg/L)

Expected

Accuracy

(± percent)

Expected

Precision

(± percent

)

Skill

LevelaInterferences

pH

Range

Field

Test

Automated

Test Current Status

Iodometric Titration > 10 5 5 2 Oxidizing Species Acidic Yes No Currently Used

Permanganate

Titration

0.1 - 100 5 5 2 Oxidizing Species Acidic Yes No Currently Used

Colorimetry,

Titanium IV

0.1 - 5 NR NR 2 Ozone Acidic Yes No Not

Recommended

Colorimetry, Leuco

Base of

Phenolphthalein

0.005 - 0.1 NR NR 2 Ozone Neutral Yes Yes Not

Recommended

Colorimetry, Cobalt

III/HCO3

-

0.01 - 1 NR NR 2 Ozone Neutral Yes Yes Not

Recommended

HRPb10-8 - 10-5 NR NR 2 Other Peroxides,

Ozone

4.5 - 5.5 No Yes Currently Used

Notes:

a

 Operator Skill Levels: 1 = minimal, 2 = good technician, 3 = experienced chemist

NR = Not reported in literature cited by referenced source.

Adapted from Gordon et al., 1992

b This method can not be used in real peroxone-treated waters where the hydrogen peroxide concentration is significantly higher.
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7.6.1.3 Horseradish Peroxidase Methods

Several methods incorporate the chemical reactions between peroxidase and hydrogen peroxide.

Horseradish derived peroxidase (HRP) is used most often. The scopoletin procedure is one of the more

widely accepted fluorescent methods of low levels of hydrogen peroxide utilizing HRP (Gordon et al.,

1992). Again, no information is available on potential interference.

7.6.1.4 Summary

In general, the analytical procedures for hydrogen peroxide in drinking water are impacted by other

oxidizing species such as ozone. Three of the methods are currently used, but not recommended for

disinfectant residual measurement (Table 7-3). The scopoletin HRP method is the most promising,

although additional study of potential interferences is required (Gordon et al., 1992).

7.7 Operational Considerations

Peroxide is a strong oxidant and contact with personnel should be avoided. Secondary containment

should be provided for storage tanks to contain any spills. Dual containment piping should be

considered to minimize the risk of exposure to plant personnel. Storage containers may explode in the

presence of extreme heat or fire.

7.7.1 Process Considerations

The impacts of the peroxone process are similar to those described for ozone in Chapter 3. Because an

additional oxidant is added to the water, the tendency to transform organic carbon compounds to a

more biodegradable form may be increased with the addition of peroxide.

7.7.2 Space Requirements

The metering pumps used to add peroxide should be housed with adequate space around each pump

for maintenance access. These pumps are generally not very large, so space requirements are not

significant.

The storage area can range from small where peroxide is obtained in drums, to large tank farms if plant

flow is great. As mentioned previously, secondary containment should be provided. Peroxide has a

lower freezing point than water. Housing or heat tracing should be provided for storage tanks and

exterior piping if extended periods with temperatures below freezing are anticipated.

7.7.3 Materials

Peroxide can be stored in polyethylene drums or tanks. The specific gravity is 1.39 for 50 percent

peroxide, which should be considered in the design of the tank walls. Acceptable pipe materials for

peroxide include 316 stainless steel, polyethylene, CPVC, and Teflon. Gaskets should be Teflon
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because natural rubber, Hypalon and EPDM are not resistant to hydrogen peroxide. Metering pumps

heads should be constructed of peroxide resistant materials.

Hydrogen peroxide is purchased from chemical suppliers and is commercially available in 35, 50, and

75 percent strengths. Peroxide is supplied in drums or in bulk by tankcar. Price depends on strength

and quantity.

Peroxide can be stored onsite, but deteriorates gradually over time even when stored correctly.

Peroxide deteriorates rapidly if contaminated and with heat or exposure to certain materials. Peroxide

is added to the water with metering pumps to accurately control dose. Pumps should be designed to

prevent potential air binding of peroxide off-gas. Multiple pumps should be provided for redundancy.

As with any chemical added to water, adequate mixing should be provided.

7.8 Summary

7.8.1 Advantages and Disadvantages of Peroxone Use

(Ozone/Hydrogen Peroxide)

The following list highlights selected advantages and disadvantages of using peroxone as a disinfection

method for drinking water. Because of the wide variation of system size, water quality, and dosages

applied, some of these advantages and disadvantages may not apply to a particular system.

Advantages

• Oxidation is more reactive and much faster in the peroxone process compared to the ozone

molecular process.

• Peroxone is effective in oxidizing difficult-to-treat organics, such as taste and odor compounds.

• Peroxone processes have been shown to be effective in oxidizing halogenated compounds.

• The tendency to transform organic carbon compounds to a more biodegradable form may be

increased with the addition of peroxide.

• Pumps used to house peroxide are not very large; so space requirements are not significant.

Disadvantages

• Peroxide is a strong oxidant and contact with personnel is extremely dangerous.

• Peroxide can be stored onsite, but deteriorates gradually even when stored correctly.
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• Peroxone as a disinfection process does not provide a measurable disinfectant residual. It is

therefore not possible to calculate CT similar to the use of other disinfectants.

• Peroxone’s ability to oxidize iron and manganese is less effective than that of ozone.

7.8.2 Summary Table

Table 7-4 summarizes the considerations relative to peroxone disinfection considerations.

Table 7-4. Summary of Peroxone Disinfection Consideration

Consideration Description

Generation Because of its instability, ozone must be generated at the point-ofuse. Hydrogen peroxide is purchased from chemical suppliers.

Hydrogen peroxide can be stored onsite, but is subject to

deterioration.

Primary uses Primary use includes chemical oxidation. As an oxidizing agent,

peroxone can be used to remove SOC pollutants and increase the

biodegradability of organic compounds. Peroxone is an effective

disinfectant but its CT credit has not been established. It is highly

reactive and does not maintain an appreciable residual for CT credit

calculations. Peroxone may be difficult to use for disinfection because

it is highly reactive and does not maintain an appreciable ozone

residual level.

Inactivation efficiency Peroxone is one of the most potent and effective germicides used in

water treatment. It is slightly more effective than ozone against

bacteria, viruses, and protozoan cysts.

Byproduct formation Peroxone itself does not form halogenated DBPs; however, if bromide

is present in the raw water or if chlorine is added as a secondary

disinfectant, halogenated DBPs including bromate may be formed.

Other byproducts include organic acids and aldehydes.

Limitations Ideally, ozone should be used as a primary disinfectant prior to

peroxone treatment.

Point of application For disinfection, peroxone addition should be after ozonation. Ozone

contact should precede addition of hydrogen peroxide. For oxidation,

peroxone can be added prior to coagulation/sedimentation or filtration

depending on the constituents to be oxidized.

Special considerations Ozone generation is a relatively complex process. Storage of LOX for

ozone generation is subject to building and fire codes. Ozone is a

highly toxic gas and the ozone production and application facilities

must be monitored for ambient ozone. Hydrogen peroxide is a

hazardous material requiring secondary containment for storage

facilities.
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7.9 References

1. Aieta, E.M., K.M. Reagan, J.S. Lang, L. McReynolds, J-W Kang, and W.H. Glaze. 1988.

“Advanced Oxidation Processes for Treating Groundwater Contaminated with TCE and PCE:

Pilot-Scale Evaluations.” J. AWWA. 88(5): 64-72.

2. Bancroft, K.P., et al. 1984. “Ozonation and Oxidation Competition Values.” Water Res. 18:473.

3. Chutny, B. and J. Kucera. 1974. “High Energy Radiation-induced Synthesis of Organic

Compounds. I. Introduction Isomerization and Carbon-Skeleton Changes, Radiation Synthesis in

Aqueous Solutions.” Rad. Res. Rev. 5:1-54.

4. Dahi, E. 1976. “Physicochemical Aspects of Disinfection of Water by Means of Ultrasound and

Ozone.” Water Res. 10:677.

5. Duguet, J., E. Brodard, B. Dussert, and J. Malevialle. 1985. “Improvement in the Effectiveness of

Ozonation of Drinking Water Through the Use of Hydrogen Peroxide.”Ozone Sci. Engrg.

7(3):241-258.

6. Dukes, E.K., and M.L. Hydier. 1964. “Determination Of Peroxide By Automated Chemistry.”

Anal. Chem. 36:1689-1690.

7. Ferguson, D.W., J.T. Gramith, and M.J. McGuire. 1991. “Applying Ozone for Organics Control

and Disinfection: A Utility Perspective.” J. AWWA. 83(5):32-39.

8. Ferguson, D.W., M.J. McGuire, B. Koch, R.L. Wolfe, and E.M. Aieta. 1990. “Comparing

Peroxone an Ozone for Controlling Taste and Odor Compounds, Disinfection Byproducts, and

Microorganisms.” J. AWWA. 82(4):181.

9. Glaze, W. H., et al. 1987. “The Chemistry of Water Treatment Processes Involving Ozone,

Hydrogen Peroxide, and Ultraviolet Radiation.” Ozone: Sci. Engrg. 9(4):335.

10. Glaze, W.H. 1986. “Reaction Products of Ozone: A Review.” Environ. Health Perspectives,

69:151-157.

11. Glaze, W.H., and J-W Kang. 1988. “Advanced Oxidation Processes for Treating Groundwater

Contaminated With TCE and PCE: Laboratory Studies.” J. AWWA. 88(5): 57-63.

12. Gordon, G., Cooper, W.J., Rice, R.G., and Pacey, G.E. 1992. Disinfectant Residual Measurement

Methods. Second Edition. AWWARF and AWWA, Denver, CO.

13. Hamelin, C. and Y.S. Chung. 1974. “Optimal Conditions for Mutagenesis by Ozone in

Escherichia coli K12.” Mutation Res. 24:271.
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14. Hoigné, J. and H. Bader. 1975. “Ozonation of Water: Role of Hydroxyl Radicals as Oxidizing

Intermediates.” Science. 190(4216):782.

15. Hoigné J. and H. Bader. 1978. “Ozone Initiated Oxidations of Solutes in Wastewater: A Reaction

Kinetic Approach.” Progress Water Technol. 10(516):657.

16. Hoigné J. and Bader. 1976. “The Role of Hydroxyl Radical Reacting in Ozonation Processes in

Aqueous Solutions.” Water Resources. 10:377.

17. Huck, P..M., Anderson, W.B. Lang, C.L. Anderson, W.A. Fraser, J.C. Jasim, S.Y. Andrews, S.A.

and Pereira, G. 1995. Ozone vs. Peroxone for Geosmin and 2-Methylisoborneol Control:

Laboratory, Pilot and Modeling Studies. Conference proceedings, AWWA Annual Conference,

Anaheim, CA.

18. Ishizaki, K. et al. 1987. “Effect of Ozone on Plasmid DNA of Esherichia coli In Situ.” Water Res.

21(7):823.

19. Karimi, A.A., J.A. Redman, W.H. Glaze, and G.F. Stolarik. 1997. “Evaluation an AOP for TCE

and PCE Removal.” J. AWWA. 89(8):41-53.

20. Krasner, S.W., W.H. Glaze, H.S. Weinberg, P.A. Daniel, and I.N. Najm. 1993. “Formation and

Control of Bromate During Ozonation of Waters Containing Bromide.” J. AWWA. 85(1):73-81.

21. Lund, E. 1963. “Significance of Oxidation in Chemical Inactivation of Poliovirus.” Arch. Gesamite

Virusforsch. 12:648.

22. Masschelein, W., M. Denis, and R. Ledent. 1977. “Spectrophotometric Determination Of Residual

Hydrogen Peroxide.” Water Sewage Works. 69-72.

23. Masten, S.J. and J. Hoigné. 1992. “Comparison of Ozone and Hydroxyl Radical-Induced

Oxidation of Chlorinated Hydrocarbons in Water.” Ozone Sci. Engrg. 14(3):197-214.

24. Mentel, R. and J. Schmidt. 1973. “Investigations of Rhinoviruse Inactivation by Hydrogen

Peroxide.” Acta Virol.17:351.

25. MWDSC and JMM (Metropolitan Water District of Southern California and James M.

Montgomery Consulting Engineers). 1992. “Pilot Scale Evaluation of Ozone and Peroxone.”

AWWARF and AWWA, Denver, CO.

26. Ohlrogge, J.B. and T.P. Kernan. 1983. “Toxicity of Activated Oxygen: Lack of Dependence on

Membrane Fatty Acid Composition.” Biochemical and Biophysical Research Communications.

113(1):301.
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27. Pereira, G., P.M. Huck, and W.A. Anderson. 1996. “A Simplified Kinetic Model for Predicting

Peroxone Performance for Geosmin Removal in Full-Scale Processes.” Conference proceedings,

AWWA Water Quality Technology Conference; Part I. New Orleans, LA.

28. Pryor, W.A. M.M. Dooley, and D.F. Church. 1983. “Mechanisms for the Reaction of Ozone with

Biological Molecules: The Source of the Toxic Effects of Ozone.” Advances in Modern

Environmental Toxicology. M.G. Mustafa and M.A. Mehlman (editors). Ann Arbor Science

Publishers, Ann Arbor, MI.

29. Riesser, V. N., et al. 1977. “Possible Mechanisms for Poliovirus Inactivation by Ozone.” Forum

on Ozone Disinfection. E.G. Fochtman, et al. (editors). International Ozone Institute Cleveland,

OH.

30. Scott, D.B.N. and E.C. Lesher. 1963. “Effect of Ozone on Survival and Permeability of

Escherichia coli.” J. Bacteriology. 85:567.

31. Scott, K.N., et al. 1992. “Pilot-Plant-Scale Ozone and Peroxone Disinfection of Giardia muris

Seeded Into Surface Water Supplies.” Ozone Sci. Engrg. 14(1):71.

32. Standard Methods. 1995. Standard Methods for the Examination of Water and Wastewater,

nineteenth edition, Franson, M.H., Eaton, A.D., Clesceri, L.S., and Greenberg, A.E., (editors).

American Public Health Association, AWWA, and Water Environment Federation, Washington

D.C.

33. Stolarik, G., and J.D. Christie. 1997. “A Decade of Ozonation in Los Angeles.” Conference

proceedings, IOA Pan American Group Annual Conference, Lake Tahoe, NV.

34. Tobiason, J.E., J.K. Edzwald, O.D. Schneider, M.B. Fox, and H.J. Dunn. 1992. “Pilot Study of the

Effects of Ozone and Peroxone on In-Line Direct Filtration.” J. AWWA. 84(12):72-84.

35. Von Gunten, U., A. Bruchet, and E. Costentin. 1996. “Bromate Formation in Advanced Oxidation

Processes.” J. AWWA. 88(6):53.

36. Wallis, P.M. et al. 1990. “Inactivation of Giardia Cysts in Pilot Plant Using Chlorine Dioxide and

Ozone.” Conference proceedings, AWWA Water Quality Technology Conference, Philadelphia,

PA.

37. Wickramanayake, G.B. 1984. Kinetics and Mechanism of Ozone Inactivation of Protozoan Cysts.

Ph.D dissertation, Ohio State University.

38. Wolfe, R.L. et al. 1989a. “Disinfection of Model Indicator Organisms in a Drinking Water Pilot

Plant by Using Peroxone.” Appl. Environ. Microbiol. 55:2230.
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39. Wolfe, R.L., et al. 1989b. “Inactivation of Giardia muris and Indicator Organisms Seeded in

Surface Water Supplies by Peroxone and Ozone.” Environ. Sci. Technol. 23(6):774.

40. Yoshe-Purer, Y. and E. Eylan. 1968. “Disinfection of Water by Hydrogen Peroxide.” Health Lab

Sci. 5.
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7. PEROXONE (OZONE/HYDROGEN PEROXIDE) .............................................................................. 7-1

7.1 PEROXONE CHEMISTRY .......................................................................................................................... 7-1

7.1.1 Oxidation Reactions..................................................................................................................... 7-2

7.1.2 Reactions with Other Water Quality Parameters........................................................................... 7-3

7.1.3 Comparison between Ozone and Peroxone ................................................................................... 7-3

7.2 GENERATION.......................................................................................................................................... 7-4

7.3 PRIMARY USES AND POINTS OF APPLICATION........................................................................................... 7-5

7.3.1 Primary Uses................................................................................................................................ 7-5

7.3.2 Points of Application.................................................................................................................... 7-6

7.4 PATHOGEN INACTIVATION ...................................................................................................................... 7-6

7.4.1 Inactivation Mechanism............................................................................................................... 7-6

7.4.2 Environmental Effects.................................................................................................................. 7-7

7.4.3 Disinfection Efficacy and Pathogen Inactivation........................................................................... 7-8

7.5 DISINFECTION BYPRODUCTS ................................................................................................................... 7-9

7.6 STATUS OF ANALYTICAL METHODS....................................................................................................... 7-10

7.6.1 Monitoring of Hydrogen Peroxide .............................................................................................. 7-10

7.7 OPERATIONAL CONSIDERATIONS........................................................................................................... 7-13

7.7.1 Process Considerations............................................................................................................... 7-13

7.7.2 Space Requirements................................................................................................................... 7-13

7.7.3 Materials.................................................................................................................................... 7-13

7.8 SUMMARY............................................................................................................................................ 7-14

7.8.1 Advantages and Disadvantages of Peroxone Use (Ozone/Hydrogen Peroxide) ............................ 7-14

7.8.2 Summary Table.......................................................................................................................... 7-15

7.9 REFERENCES ........................................................................................................................................ 7-16

Table 7-1. Comparison between Ozone and Peroxone Oxidation........................................................................ 7-4

Table 7-2. Calculated CT Values (mg•min/L) for the Inactivation of Giardia muris........................................... 7-8

Table 7-3. Characteristics and Comparisons of Hydrogen Peroxide Analytical Methods................................... 7-12

Table 7-4. Summary of Peroxone Disinfection Consideration........................................................................... 7-15
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8-1

8. ULTRAVIOLET RADIATION

Unlike most disinfectants, ultraviolet (UV) radiation does not inactivate microorganisms by chemical

interaction. UV radiation inactivates organisms by absorption of the light which causes a

photochemical reaction that alters molecular components essential to cell function. As UV rays

penetrate the cell wall of the microorganism, the energy reacts with nucleic acids and other vital cell

components, resulting in injury or death of the exposed cells. There is ample evidence to conclude

that if sufficient dosages of UV energy reach the organisms, UV can disinfect water to whatever

degree is required. However, there has been some public health concerns with respect to the overall

efficiency of UV to disinfect potable water.

Based on the available research literature, it appears that although exceptional for disinfection of

small microorganisms such as bacteria and viruses, UV doses required to inactivate larger protozoa

such as Giardia and Cryptosporidium are several times higher than for bacteria and virus inactivation

(White, 1992; DeMers and Renner, 1992). As a result, UV is often considered in concert with ozone

and/or hydrogen peroxide to enhance the disinfection effectiveness of UV or for ground water where

Giardia and Cryptosporidium are not expected to occur.

8.1 UV Chemistry (Photochemical)

8.1.1 UV Radiation

UV radiation quickly dissipates into water to be absorbed or reflected off material within the water.

As a result, no residual is produced. This process is attractive from a DBP formation standpoint;

however, a secondary chemical disinfectant is required to maintain a residual throughout the

distribution system, which may be subject to recontamination.

UV radiation energy waves are the range of electromagnetic waves 100 to 400 nm long (between the

X-ray and visible light spectrums). The division of UV radiation may be classified as Vacuum UV

(100-200 nm), UV-C (200-280 nm), UV-B (280-315 nm) and UV-A (315-400 nm). In terms of

germicidal effects, the optimum UV range is between 245 and 285 nm. UV disinfection utilizes

either: low-pressure lamps that emit maximum energy output at a wavelength of 253.7 nm; mediumpressure lamps that emit energy at wavelengths from 180 to 1370 nm; or lamps that emit at other

wavelengths in a high intensity “pulsed” manner.
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8.1.2 UV Disinfection Reactions

The degree to which the destruction or inactivation of microorganisms occurs by UV radiation is

directly related to the UV dose. The UV dosage is calculated as:

D = I • t

Where: D = UV Dose, mW⋅s/cm2

I = Intensity, mW/cm2

t = Exposure time, s

Research indicates that when microorganisms are exposed to UV radiation, a constant fraction of the

living population is inactivated during each progressive increment in time. This dose-response

relationship for germicidal effect indicates that high intensity UV energy over a short period of time

would provide the same kill as a lower intensity UV energy at a proportionally longer period of time.

The UV dose required for effective inactivation is determined by site-specific data relating to the

water quality and log removal required. Based on first order kinetics, the survival of microorganisms

can be calculated as a function of dose and contact time (White, 1992; USEPA, 1996). For high

removals, the remaining concentration of organisms appears to be solely related to the dose and

water quality, and not dependent on the initial microorganism density. Tchobanoglous (1997)

suggested the following relationship between coliform survival and UV dose:

N = f · Dn

Where: N = Effluent coliform density, /100mL

D = UV dose, mW⋅s/cm2

n = Empirical coefficient related to dose

f = Empirical water quality factor

The empirical water quality factor reflects the presence of particles, color, etc. in the water. For

water treatment, the water quality factor is expected to be a function of turbidity and transmittance

(or absorbance).

8.1.3 Process Variables

Since UV radiation is energy in the form of electromagnetic waves, its effectiveness is not limited by

chemical water quality parameters. For instance, it appears that pH, temperature, alkalinity, and total
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inorganic carbon do not impact the overall effectiveness of UV disinfection (AWWA and ASCE,

1990). However, hardness may cause problems with keeping the lamp sleeves clean and functional.

The presence, or addition, of oxidants (e.g., ozone and/or hydrogen peroxide) enhances UV radiation

effectiveness. The presence of some dissolved or suspended matter may shield microorganisms from

the UV radiation. For instance, iron, sulfites, nitrites and phenols all absorb UV light (DeMers and

Renner, 1992). Accordingly, the absorbance coefficient is an indication of this demand and is unique

for all waters. As a result, specific “design” parameters vary for individual waters and should be

determined empirically for each application.

UV demand of water is measured by a spectrophotometer set at a wavelength of 254 nm using a 1 cm

thick layer of water. The resulting measurement represents the absorption of energy per unit depth, or

absorbance. Percent transmittance is a parameter commonly used to determine the suitability of UV

radiation for disinfection. The percent transmittance is determined from the absorbance (A) by the

equation:

Percent Transmittance = 100 × 10-A

Table 8-1 shows corresponding absorbance measurements and percent transmittance measurements

for various water qualities.

Table 8-1. Water Quality and Associated UV Measurements

Source Water Quality

Absorbance

(absorbance units/cm)

Percent

Transmittance

Excellent 0.022 95%

Good 0.071 85

Fair 0.125 75

Source: DeMers and Renner, 1992.

Continuous wave UV radiation at doses and wavelengths typically employed in drinking water

applications, does not significantly change the chemistry of water nor does it significantly interact

with any of the chemicals within the water (USEPA, 1996). Therefore, no natural physiochemical

features of the water are changed and no chemical agents are introduced into the water. In addition,

UV radiation does not produce a residual. As a result, formation of THM or other DBPs with UV

disinfection is minimal (See Section 8.5, Disinfection Byproducts of UV Radiation).

8.2 Generation

Producing UV radiation requires electricity to power UV lamps. The lamps typically used in UV

disinfection consist of a quartz tube filled with an inert gas, such as argon, and small quantities of

mercury. Ballasts control the power to the UV lamps.
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8.2.1 UV Lamps

UV lamps operate in much the same way as fluorescent lamps. UV radiation is emitted from electron

flow through ionized mercury vapor to produce UV energy in most units. The difference between the

two lamps is that the fluorescent lamp bulb is coated with phosphorous, which converts the UV

radiation to visible light. The UV lamp is not coated, so it transmits the UV radiation generated by

the arc (White, 1992).

Both low-pressure and medium-pressure lamps are available for disinfection applications. Lowpressure lamps emit their maximum energy output at a wavelength of 253.7 nm, while medium

pressure lamps emit energy with wavelengths ranging from 180 to 1370 nm. The intensity of

medium-pressure lamps is much greater than low-pressure lamps. Thus, fewer medium pressure

lamps are required for an equivalent dosage. For small systems, the medium pressure system may

consist of a single lamp. Although both types of lamps work equally well for inactivation of

organisms, low-pressure UV lamps are recommended for small systems because of the reliability

associated with multiple low-pressure lamps (DeMers and Renner, 1992) as opposed to a single

medium pressure lamp, and for adequate operation during cleaning cycles.

Recommended specifications for low-pressure lamps (DeMers and Renner, 1992) include:

• L-type ozone-free quartz;

• Instant start (minimal delay on startup);

• Designed to withstand vibration and shock; and

• Standard nonproprietary lamp design.

Typically, low-pressure lamps are enclosed in a quartz sleeve to separate the water from the lamp

surface. This arrangement is required to maintain the lamp surface operating temperature near its

optimum of 40oC. Although Teflon sleeves are an alternative to quartz sleeves, quartz sleeves absorb

only 5 percent of the UV radiation, while Teflon sleeves absorb 35 percent (Combs and McGuire,

1989). Therefore, Teflon sleeves are not recommended.

8.2.2 Ballasts

Ballasts are transformers that control the power to the UV lamps. Ballasts should operate at

temperatures below 60oC to prevent premature failure. Typically, the ballasts generate enough heat to

warrant cooling fans or air conditioning (White, 1992).

Two types of transformers are commonly used with UV lamps; namely, electronic and

electromagnetic. Electronic ballasts operate at a much higher frequency than electromagnetic

ballasts, resulting in lower lamp operating temperatures, less energy use, less heat production, and

longer ballast life (DeMers and Renner, 1992).
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Typical ballast selection criteria include (DeMers and Renner, 1992):

• Underwriter’s Laboratories (UL) approval;

• Compatibility with UV lamps; and

• Waterproof enclosure in remote location.

8.2.3 UV Reactor Design

Most conventional UV reactors are available in two types; namely, closed vessel and open channel.

For drinking water applications, the closed vessel is generally the preferred UV reactor for the

following reasons (USEPA, 1996):

• Smaller footprint;

• Minimized pollution from airborne material;

• Minimal personnel exposure to UV; and

• Modular design for installation simplicity.

Figure 8-1 shows a conventional closed vessel UV reactor. This reactor is capable of providing UV

dosages adequate to inactivate bacteria and viruses for flows up to 600 gallons per minute. However,

it is incapable of the higher dosages required for protozoan cysts. To increase the dosage, either the

number of UV lamps and/or the exposure time should be increased.

Additional design features for conventional UV disinfection systems include:

• UV sensors to detect any drop in UV lamp output intensity;

• Alarms and shut-down systems;

• Automatic or manual cleaning cycles; and

• Telemetry systems for remote installations.
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Illumination Lamp

Monitoring Panel Ultrasonic Cleaning

Transducer

Quartz Jackets

Enclosing UV Lamps

UV Intensity

Measuring Cell

Source: USEPA, 1996.

Figure 8-1. Closed Vessel Ultraviolet Reactor

In addition to conventional UV systems, two other UV processes are currently being evaluated for

drinking water disinfection:

• Micro-screening/UV; and

• Pulsed UV

Both of these systems profess to provide sufficient UV dose to inactivate Giardia cysts and

Cryptosporidium oocysts. See Section 8.2.3.2, Emerging UV Reactor Designs, for further discussion

on these emerging technologies.

8.2.3.1 Hydraulic Design Considerations

The major elements that should be considered in the hydraulic design of a UV closed vessel reactor

are: dispersion, turbulence, effective volume, residence time distribution, and flow rate (USEPA,

1996).
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Dispersion

Dispersion is the characteristic of water elements to scatter spatially. The ideal UV reactor is plug

flow, where water particles are assumed to discharge from the reactor in the same sequence they

entered and each element of water passing through the reactor resides in the reactor for the same

period of time. An ideal plug flow reactor has no dispersion and is approximated by a long tank with

high length-to-width ratio in which dispersion is minimal (USEPA, 1996).

Turbulence

In addition to plug flow characteristics, the ideal UV reactor has a flow that is turbulent radially from

the direction of flow, to eliminate dead zones. This radially turbulent flow pattern promotes uniform

application of UV radiation. A negative of having a radially turbulent flow pattern is that some axial

dispersion results, thus disrupting the plug flow characteristics. Techniques such as misaligning the

inlet and outlet, and using perforated stilling plates, have been used to accommodate the

contradicting characteristics of plug flow and turbulence (USEPA, 1996).

8.2.3.2 Emerging UV Reactor Designs

Two emerging technologies in UV reactor design are discussed below. All testing of these two

systems to date has been under controlled laboratory or field conditions. Both of these technologies

require demonstration of efficacy and applicability in real-world treatment operations.

Micro-Screening/UV

This unit consists of two treatment chambers, each containing a 2 μm nominal porosity metal screen.

Each side of the screen has three 85 watt low pressure mercury lamps, with a total of six lamps per

filter. The theoretical minimum dose is 14.6 mW⋅sec/cm2 at the wavelength of 254 nm. The system is

designed to capture Cryptosporidium oocysts from the water onto the first screen. The first cycle is

set to establish the UV dose. The flow within the first screen chamber is then reversed to backflush to

oocysts onto the second screen where the oocysts are trapped until the preset UV dose is reached.

Using valves, the pattern of flow is designed to ensure that oocysts are temporarily captured on both

filters so that they are exposed to a total preset UV dose, which is totally independent of treated water

flowrate (Clancy et al., 1997). Johnson (1997) stated that such a system is capable of achieving total

UV doses of 8,000 mW⋅sec/cm2, sufficient to inactivate Giardia cysts and Cryptosporidium oocysts.

One drawback of this type of reactor is the headloss created (up to 65 feet) by the 2 μm openings in

the screen.

Pulsed UV

In the pulsed UV reactor, capacitors build up and deliver electricity in pulses to xenon flash tubes in

the center of a 2 inch diameter flash chamber through which water flows. The unit is designed to

provide microsecond pulses at 1 to 30 hertz (or per second). With each pulse, the flash tubes give off

high intensity, broad band radiation, including germicidal UV radiation, which irradiates the flowing
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water with irradiences of 75 mW⋅sec/cm2 at 2 cm from the flash tube surface (Clancy et al., 1997).

The UV dose can be adjusted by increasing or decreasing the frequency of the pulsing.

8.3 Primary Uses and Points of Application

The primary use of UV radiation is to inactivate pathogens to regulated levels. UV radiation is a

physical disinfectant that leaves no residual. Therefore, it should be used only as a primary

disinfectant followed by a chemical secondary disinfectant to protect the distribution system against

coliform proliferation and biofilm formation. See Section 8.4, Pathogen Inactivation and

Disinfection Efficiency,” for a detailed discussion of disinfection efficiency and limitations.

The most common point of application for UV radiation is the last step in the treatment process train

just prior to the distribution system and after filtration. The use of UV disinfection has no impact on

other processes at the water treatment facility.

8.4 Pathogen Inactivation and Disinfection Efficiency

As opposed to most alternative disinfectants, UV is a physical process that requires a contact time on

the order of seconds to accomplish pathogen inactivation (Sobotka, 1993). As with any disinfectant,

UV has its limitations. For example, because it is a physical rather than a chemical disinfectant, it

does not provide a residual to control pathogen proliferation and biofilm formation in the distribution

system. When using UV for primary disinfection, some form of secondary chemical disinfectant is

required to maintain water quality within the distribution system.

8.4.1 Inactivation Mechanism

UV radiation is efficient at inactivating vegetative and sporous forms of bacteria, viruses, and other

pathogenic microorganisms. Electromagnetic radiation in the wavelengths ranging from 240 to 280

nanometers (nm) effectively inactivates microorganisms by irreparably damaging their nucleic acid.

The most potent wavelength for damaging deoxyribonucleic acid (DNA) is approximately 254 nm

(Wolfe, 1990). Other UV wavelengths, such as 200 nm, have been shown to exhibit peak absorbance

in aqueous solutions of DNA (von Sonntag and Schuchmann, 1992); however, there is no practical

application for UV inactivation of microorganisms in the wavelength range from 190 to 210 nm

(USEPA, 1996).

The germicidal effects of UV light involve photochemical damage to RNA and DNA within the

microorganisms. Microorganism nucleic acids are the most important absorbers of light energy in

the wavelength of 240 to 280 nm (Jagger, 1967). DNA and RNA carry genetic information

necessary for reproduction; therefore, damage to either of these substances can effectively sterilize

the organism. Damage often results from the dimerization of pyrimidine molecules. Cystosine

(found in both DNA and RNA), thymine (found only in DNA), and uracil (found only in RNA) are

the three primary types of pyrimidine molecules. Replication of the nucleic acid becomes very

difficult once the pyrimidine molecules are bonded together due to the distortion of the DNA helical
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structure by UV radiation (Snider et al., 1991). Moreover, if replication does occur, mutant cells that

are unable to replicate will be produced (USEPA, 1996). Figure 8-2 is a schematic of the germicidal

inactivation observed with UV radiation.

Two phenomena of key importance when using UV disinfection in water treatment are the dark

repair mechanisms and the capability of certain organisms to photoreactivate following exposure to

certain light wavelengths. Under certain conditions, some organisms are capable of repairing

damaged DNA and reverting back to an active state in which reproduction is again possible.

Typically, photoreactivation occurs as a consequence of the catalyzing effects of sunlight at visible

wavelengths outside of the effective disinfecting range. The extent of reactivation varies among

organisms. Coliform indicator organisms and some bacterial pathogens such as Shigella have

exhibited the photoreactivation mechanism; however, viruses (except when they have infected a host

cell that is itself photoreactive) and other types of bacteria cannot photoreactivate (USEPA, 1980;

USEPA, 1986; Hazen and Sawyer, 1992). Because DNA damage tends to become irreversible over

time, there is a critical period during which photoreactivation can occur. To minimize the effect of

photoreactivation, UV contactors should be designed to either shield the process stream or limit the

exposure of the disinfected water to sunlight immediately following disinfection.

Source: Tchobanoglous, 1997.

Figure 8-2. Germicidal Inactivation by UV Radiation
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8.4.2 Environmental Effects

To achieve inactivation, UV should be absorbed into the microorganism. Therefore, anything that

prevents UV from reacting with the microorganism will decrease the disinfection efficiency.

Scheible and Bassell (1981) and Yip and Konasewich (1972) reported that pH had no effect on UV

disinfection. Several factors that are known to affect disinfection efficiency of UV are:

• Chemical and biological films that develop on the surface of UV lamps;

• Dissolved organics and inorganics;

• Clumping or aggregation of microorganisms;

• Turbidity;

• Color; and

• Short-circuiting in water flowing through the UV contactor.

8.4.2.1 Chemical Films and Dissolved Organics and Inorganics

Accumulation of solids onto the surface of the UV sleeves can reduce the applied UV intensity and,

consequently, disinfection efficiency. In addition to biofilms caused by organic material, buildup of

calcium, magnesium, and iron scales have been reported (DeMers and Renner, 1992). Waters

containing high concentrations of iron, hardness, hydrogen sulfide, and organics are more susceptible

to scaling or plating (i.e., the formation of a thin coat on unit surfaces), which gradually decreases the

applied UV intensity. Scaling is likely to occur if dissolved organics are present and inorganic

concentrations exceed the following limits (DeMers and Renner, 1992):

• Iron greater than 0.1 mg/L;

• Hardness greater than 140 mg/L; and

• Hydrogen sulfide greater than 0.2 mg/L.

Figure 8-3 shows the UV dose required for inactivation of MS-2 coliphage at two pilot plants. Snicer

et al. (1996) concluded that one possible explanation for higher UV dose for the same degree of

inactivation required at pilot plant 2 could be the amount of scaling caused by higher iron

concentrations experienced at this plant. Iron concentrations at pilot plant 2 were in the range of 0.45

to 0.65 mg/L, which exceed the limit shown above.

A variety of chemical substances can decrease UV transmission (Yip and Konasewich, 1972),

including humic acids, phenolic compounds, and lignin sulfonates (Snider et al., 1991), as well as

chromium, cobalt, copper, and nickel. It has been reported that coloring agents, such as Orzan S, tea,

and extract of leaves reduce intensity within a UV contactor (Huff, 1965). In addition, iron, sulfites,

nitrites, and phenols can absorb UV (DeMers and Renner, 1992).
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0

1

2

3

4

5

6

0 10 20 30 40 50 60 70 80 90 100

UV Dose (mW sec / cm2)

Log MS-2 Inactivation

Pilot 1 Water Pilot 2 Water

Source: Snicer et al., 1996.

Figure 8-3. UV Dose Required for Inactivation of MS-2 Coliphage

8.4.2.2 Microorganism Clumping and Turbidity

Particles can affect the disinfection efficiency of UV by harboring bacteria and other pathogens,

partially protecting them from UV radiation, and scattering UV light (see Figure 8-4). Typically, the

low turbidity of ground water results in minimal impact on disinfection efficiency. However, the

higher turbidities of surface water can impact disinfection efficiency.

Similar to particles that cause turbidity, microorganism aggregation can impact disinfection

efficiency by harboring pathogens within the aggregates and shade pathogens that would otherwise

be inactivated.

8.4.2.3 Reactor Geometry and Short Circuiting

Poor geometry within the UV contactor (which creates spacing between lamps) can leave dead areas

where inadequate disinfection occurs (Hazen and Sawyer, 1992). A key consideration to improving

disinfection is to minimize the amount of dead spaces where limited UV exposure can occur. Plug

flow conditions should be maintained in the contactor; however, some turbulence should be created

between the lamps to provide radial mixing of flow. In this manner, flow can be uniformly

distributed through the varying regions of UV intensity, allowing exposure to the full range of

available UV radiation (Hazen and Sawyer, 1992).
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As mentioned earlier, UV systems typically provide contact times on the order of seconds.

Therefore, it is extremely important that the system configuration limit the extent of short circuiting.

Source: Tchobanoglous, 1997.

Figure 8-4. Particle Interactions that Impact UV Effectiveness

8.4.3 Disinfection Efficacy

UV disinfection has been determined to be adequate for inactivating bacteria and viruses. Most

bacteria and viruses require relatively low UV dosages for inactivation, typically in the range of 2 to

6 mW⋅s/cm2 for 1-log inactivation. Protozoan [oo]cysts, in particular Giardia and Cryptosporidium,

are considerably more resistant to UV inactivation than other microorganisms. Results of several

studies investigating the ability of UV to inactivate bacteria, viruses, and protozoa, are described in

the following sections.

8.4.3.1 Bacteria and Virus Inactivation

UV doses required for bacteria and virus inactivation are relatively low. One study determined that

UV was comparable to chlorination for inactivation of heterotrophic plate count bacteria following

treatment using granular activated carbon (Kruithof et al., 1989).
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A study of the ability of UV and free chlorine to disinfect a virus-containing ground water showed

that UV is a more potent virucide than free chlorine, even after the chlorine residual was increased to

1.25 mg/L at a contact time of 18 minutes (Slade et al., 1986). The UV dose used in this study was

25 mW⋅s/cm2.

Table 8-2 shows results from a more recent pilot plant study (Snicer et al., 1996). As indicated by

the different UV doses to obtain the same level of inactivation, water characteristics dramatically

impact disinfection efficiency. They believed that the higher concentration of iron in pilot plant 2

water (Figure 8-3) interfered with UV or influenced the aggregation of MS-2 viral particles.

Snicer et al. (1996) also compared the susceptibility of MS-2 coliphage to hepatitis A virus, poliovirus,

and rotavirus for 10 ground water sources. Results indicated that MS-2 was found to be approximately

2 to 3 times more resistant to UV disinfection than the three human pathogenic viruses.

Table 8-2. Doses Required for MS-2 Inactivation

Log MS-2 Inactivation

Pilot Plant 1

(mW•s/cm2)

Pilot Plant 2

(mW•s/cm2)

1 3.9 15.3

2 25.3 39.3

3 46.7 63.3

4 68 87.4

5 89.5 111.4

6 111.0 135.5

Source: Snicer et al., 1996.

8.4.3.2 Protozoa Inactivation

Even though protozoa were once considered resistant to UV radiation, recent studies have shown that

ultraviolet light is capable of inactivating protozoan parasites. However, results indicate that these

organisms require a much higher dose than that needed to inactivate other pathogens. Less than 80

percent of Giardia lamblia cysts were inactivated at UV dosages of 63 mW·s/cm2 (Rice and Hoff,

1981). A 1-log inactivation of Giardia muris cysts was obtained when the UV dose was increased to

82 mW·s/cm2 (Carlson et al., 1982).

To achieve 2-log inactivation of Giardia muris cysts, a minimum ultraviolet light dose of above 121

mW·s/cm2 is needed. Karanis et al. (1992) examined the disinfection capabilities of ultraviolet light

against Giardia lamblia cysts extracted from both animals and humans (Karanis et al., 1992). Both

groups suffered a 2-log reduction at UV doses of 180 mW·s/cm2. Two important factors to consider

when determining dose requirements for Giardia inactivation are the parasite source and the growth

stage of the microorganism (Karanis et al., 1992). Figure 8-5 shows that the source of the parasites is

important in determining dose requirements. Figure 8-6 is from a study conducted in 1992 on

Acanthamoeba rhysodes inactivation (Karanis et al., 1992). These data show that the age of the

protozoa can dramatically affect the dose required to achieve a desired level of inactivation.
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-3

-2.5

-2

-1.5

-1

-0.5

0

0 20 40 60 80 100 120 140 160 180

UV Dose (mWs/cm2)

Survival Ratio (N/No)

Cysts obtained from gerbils Cysts obtained from humans

Source: Karanis et al., 1992.

Figure 8-5. UV Doses Required to Achieve Inactivation of Giardia lamblia Cysts

Obtained from Two Different Sources

-2

-1.75

-1.5

-1.25

-1

-0.75

-0.5

-0.25

0

0 10 20 30 40 50 60 70 80

UV Dose (mWs/cm2)

Survival Ratio (N/No)

7-day-old cysts 28-day-old cysts

Source: Karanis et al., 1992.

Figure 8-6. Impact of Growth Stage of A. rhysodes on the Required UV Dosage to

Achieve Inactivation
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Results from recent studies show a potential for inactivating Cryptosporidium parvum oocysts using

ultraviolet light disinfection. A 2 to 3-log reduction in the viability of Cryptosporidium parvum

oocysts was achieved using a low-pressure ultraviolet light system with a theoretical minimum

intensity of 14.58 mW/cm2 and a contact time of 10 minutes (ultraviolet dose of 8,748 mW·s/cm2)

(Campbell et al., 1995). The combination filter-UV system described by Johnson (1997) is capable

of delivering doses as high as 8,000 mW·s/cm2, sufficient to achieve 2-log Cryptosporidium oocyst

inactivation.

A pulsed UV process that delivered a minimum dose of 1,900 mW⋅s/cm2 to any particle within the

reactor was found to achieve Cryptosporidium oocyst inactivation levels in the range of 2-log.

(Clancy et al., 1997). In this study, the reactor residence time was 4.7 seconds and the unit was

operated to deliver 46.5 pulses per volume (10 Hz). Each pulse transfers power at the intensity rate

of about 41 mW⋅s/cm2 .

8.4.3.3 UV Dose Summary

UV radiation is considered effective for inactivating bacterial and viral pathogens. UV doses for 2

and 3-log inactivation of viruses are 21 and 36 mW⋅s/cm2, respectively (AWWA, 1991). These

doses are based on studies of hepatitis A virus inactivation and were derived by applying a safety

factor of 3 to the inactivation data. Results from a more recent study on several ground water sources

of hepatitis A virus, indicate that a 6 to 15 mW⋅s/cm2 dose is required for a 4-log inactivation (Snicer

et al., 1996). A safety factor was not applied to the doses. A 4-log inactivation of bacteriophage

MS-2 is achieved at a dose of 93 mW⋅s/cm2 (Snicer et al., 1996). In ground water containing high

iron levels (0.65 ppm), applying a safety factor of 1.5 to the highest reported dose against viruses will

yield a UV dose of 140 mWs/cm2 for a minimum 4-log inactivation of viruses

In summary, ultraviolet radiation is effective against bacteria and viruses at low dosages. However,

much higher dosages are required for Cryptosporidium and Giardia inactivation.

8.5 Disinfection Byproducts of UV Radiation

Unlike other disinfectants, UV does not inactivate microorganisms by chemical reaction. However,

UV radiation causes a photochemical reaction in the organism RNA and DNA. The literature

suggests that UV radiation of water can result in the formation of ozone or radical oxidants (Ellis and

Wells, 1941; Murov, 1973). Because of this reaction, there is interest in determining whether UV

forms similar byproducts to those formed by ozonation or advanced oxidation processes.

8.5.1 Ground Water

Malley et al. (1995) analyzed 20 ground water samples for aldehydes and ketones before and after

UV radiation. Only one ground water sample, which contained 24 mg/L non-purgeable DOC and

was highly colored, contained DBPs after exposure to UV. Low levels of formaldehyde were

measure in duplicated experiments for this UV treated ground water sample mentioned above. GC-
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ECD chromatographs before and after UV radiation for the other 19 ground waters studied showed

significant shifts or unknown peaks after exposure to UV.

Malley et al. (1995) also determined the influence of UV on DBP formation during subsequent

chlorination. To examine these effects, the 20 ground water samples were subjected to simulated

distribution system (SDS) DBP tests with chlorine, before and after UV radiation. The data indicate

that UV radiation did not significantly alter the SDS/DBP formation by chlorine in the ground waters

studied.

To examine the effects of varying UV dosages on DBP formation, six new ground water samples

(Malley et al., 1995) were subjected to UV dosages of 60, 130, and 200 mW⋅s/cm2. In this case,

DBPs were not formed by UV radiation for any of the ground waters tested at any of the UV

dosages. A comparison of chromatographs for samples before and after UV radiation, and for each

UV dosage, showed no significant differences or appearances of unknown peaks.

8.5.2 Surface Water

UV radiation was found to produce low levels of formaldehyde in the majority of surface waters

studied (Malley et al., 1995). The highest formaldehyde concentrations, ranging up to 14 μg/L, were

observed in UV treatment of raw water, whereas trace levels (1 to 2 μg/L) were found in UV

treatment of conventionally treated water. Since formaldehyde formation was also observed for one

of the ground water samples, it appears that UV radiation of waters containing humic matter (i.e.,

color producing, UV absorbing organic macromolecules) will result in low levels of formaldehyde

formation. Chromatographic examination of the surface water samples before and after UV radiation

showed no other significant changes in the GC-ECD chromatograms.

Because of the chlorine demands of surface waters, higher chlorine dosages were required for post

disinfection following UV radiation. This resulted in larger DBP concentrations than in the ground

waters studied (Malley et al., 1995). However, the overall effect of UV radiation on SDS/DBPs was

insignificant. As in the ground water studies, UV radiation did not significantly alter the total

concentration or the speciation of the disinfection byproducts (e.g., THMs, HAA5, HANs, or HKs).

8.5.3 DBP Formation with Chlorination and Chloramination

following UV Radiation

Research results suggest that UV radiation does not directly form DBPs or alter the concentration or

species of DBPs formed by post-disinfection (Malley et al., 1995). However, the question of whether

UV radiation influences the rate of DBP formation by post-disinfection is important. Several studies

have addressed this question. Two surface waters that produced significant concentrations of a wide

variety of DBPs in previous tests were chosen as samples. With the chlorine residuals carefully

monitored to ensure they were consistent for pre-UV and post-UV samples, the results of the

experiments suggested that UV radiation did not significantly affect the rate of DBP formation.
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Studies were only performed to determine the pentane extractable DBP formation rate of a surface

water sample for varying pH conditions. The results showed that UV radiation did not affect the rate

of chloroform formation at pH 8.0 (Malley et al., 1995). Similarly, UV did not affect the DBP

formation rate at pH 5.0. At pH 8.0, chloroform was the only pentane extractable detected, whereas

at pH 5.0, chloroform, bromodichloromethane, chlorodibromomethane, and 1,1,1-trichloroacetone

were formed.

The effects of UV radiation on the DBP formation rate following chloramination were also tested in

this study using a surface water sample (Malley et al., 1995). Chloroform, trichloroacetic acid,

dichloroacetonitrile (at low levels), and cyanogen chloride (at low levels) were the only detectable

DBPs. Chloroform was the only compound formed at pH 8.0, and its rate of formation was not

affected by UV radiation. At pH 5.0, chloroform and dichloroacetonitrile were formed, but their rate

of formation was unaffected by UV radiation. Data showed that the effects of UV radiation on

cyanogen chloride formation at pH 8.0 and pH 5.0 had no significant trends.

In summary, the DBP formation rate studies indicated that UV radiation did not significantly affect

DBP formation rates when chlorine or chloramines were used as the post-disinfectant.

8.6 Status of Analytical Methods

Ultraviolet radiation intensity meter readings are taken to monitor the output of the UV disinfection

system. These readings, coupled with the flow through the UV reactor, are used to determine the UV

dosage applied. UV radiation leaves no residual disinfectant behind to monitor. Therefore, some

form of secondary chemical disinfectant should be added to protect the distribution system against

coliform proliferation and biofilm formation. Analytical methods for these chemical disinfectants are

discussed elsewhere in this report.

8.6.1 Monitoring of Generated Ultraviolet Radiation

Ultraviolet intensity at 253.7 nm (the predominant wavelength emitted by low pressure mercury

vapor lamps) is the water quality parameter used to monitor UV disinfection system output (Snider et

al., 1991). The rate of disinfection is directly related to the average intensity of the UV light. Since

UV intensity probes can only indicate UV intensity at a single point, there is no practical way to

measure the average intensity of a UV system in the field by the operator.

The average intensity is dependent upon the three dimensional lamp geometry. Scheible (1983)

developed a mathematical model that calculates the intensity at any point within the UV reactor. This

Point Source Summation (PSS) method is used to estimate the average intensity emitted by any

specific unit. UV disinfection system manufacturers use this method to design the system. The

single point UV intensity probe reading is typically used for routine monitoring of the UV system

only.

UV intensity sensors are typically photodiode sensors properly filtered to monitor the lamp intensity

in the germicidal range only (DeMers and Renner, 1992). A minimum of two sensors (mounted near
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separate lamps) located at the center of each lamp for each reactor is recommended as part of the

system controls and instrumentation. White (1992) recommends installing the sensors in the wall of

the disinfection chamber at the point of greatest distance from the tube or tubes.

The UV sensors should continuously sense the UV intensity produced in the bank of lamps. The

sensor should be field calibrated to account for lamp geometry. Each UV sensor installed should

provide a “low UV output” warning and a “low-low UV output” alarm indication that is field

adjustable.

8.6.1.1 Ultraviolet Sensor Performance

To test electronic sensor performance, Snicer et al. (1996) placed a single electronic UV sensor at the

center of a UV reactor. The UV sensor converted the UV energy into an electronic signal, which was

used to indicate system performance. Initial results indicated that the sensor originally installed with

the two UV reactors tended to wear or degrade in performance over time. The original sensor

readings in the pilot facility were erratic and had a general downward trend over 6 months of

operation. This loss in performance could not be attributed to UV lamp aging. In addition, these

readings did not correlate well to actual system performance. After operation of these original

sensors for 6 months, the manufacturer was consulted and a new type of sensor was installed into

both pilot facilities. The new sensor design specifically addressed the problems encountered during

the initial 6 months of the study. These new proprietary sensors performed consistently and sensor

readings were shown to correlate well with actual MS-2 coliphage inactivation.

8.6.2 Disinfectant Interferences

Suspended solids may be the most important water quality parameter impacting UV intensity

measurements. Particles can harbor bacteria and at least partially protect them from UV light.

Particles can be completely penetrated, partially penetrated, or scatter UV light (Figure 8-4). All

particles in water may not absorb UV light. Qualls et al. (1983) suggested that clays merely scatter

UV light and, therefore, do little to inhibit performance.

Yip and Konasewich (1972) listed many chemical substances that interfere with UV transmission at

253.7 nm including phenolic compounds, humic acids, and ferric iron.

8.7 Operational Considerations

Onsite pilot plant testing is recommended to determine the efficiency and adequacy of UV

disinfection for a specific quality of water. The efficiency test involves injecting select

microorganisms into influent water and sampling effluent water to determine survival rates. The

National Science Foundation’s Standard 55 for ultraviolet water treatment systems recommends that

UV disinfection systems not be used if the UV transmittance is less than 75 percent (NSF, 1991). If

the raw water UV transmittance is less that 75 percent, the UV system should be proceeded by other

treatment processes (to increase UV transmittance) or a different disinfectant should be used.
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As previously discussed, some constituents that adversely interfere with UV disinfection

performance by either scattering and/or absorbing radiation are iron, chromium, copper, cobalt,

sulfites, and nitrites. Care should be taken with chemical processes upstream of UV disinfection

process to minimize increasing concentrations of these constituents since disinfection efficiency may

be adversely affected.

8.7.1 Equipment Operation

UV disinfection facilities should be designed to provide flexibility in handling varying flow rates.

For lower flow rates, a single reactor vessel should be capable of handling the entire flow rate. A

second reactor vessel with equal capacity of the first reactor vessel should be provided for

redundancy should the first reactor vessel be taken out of service. For higher flow rates, multiple

reactor vessels should be provided with lead/lag operation and flow split capacity to balance run time

for each reactor vessel, if desired, and to avoid hydraulic overloading. Valves should be provided

within the interconnecting piping to isolate one reactor vessel from another. There should also be a

positive drainage system to remove water from within a reactor vessel when it is taken out of service.

8.7.1.1 UV Lamp Aging

The output of UV lamps diminishes with time. Two factors that affect their performance are:

solarization which is the effect UV radiation has on the UV lamp that causes it to become opaque;

and, electrode failure which occurs when electrodes deteriorate progressively each time the UV lamp

is cycled on and off. Frequent lamp cycling will lead to premature lamp aging. When determining

the requirement for UV disinfection, a 30 percent reduction of UV output should be used to estimate

end of lamp. Average life expectancy for low pressure UV lamps is approximately 8,800 hours.

8.7.1.2 Quartz Sleeve Fouling

Fouling of the quartz sleeve reduces the amount of UV radiation reaching the water. The quartz

sleeve has a transmissibility of over 90 percent when new and clean. Over time, the surface of the

quartz sleeve that is in contact with the water starts collecting organic and inorganic debris (e.g., iron,

calcium, silt) causing a reduction in transmissibility (USEPA, 1996). When determining the

requirements for UV disinfection, a 30 percent reduction of UV transmission should be used to

reflect the effect of quartz sleeve fouling.

8.7.2 Equipment Maintenance

8.7.2.1 UV Lamp Replacement

Adequate space should be provided around the perimeter of the reactor vessels to allow access for

maintenance and replacement of UV lamps. With modular electrical fittings, lamp replacement

consists of unplugging the pronged connection of the old lamp and plugging in the new.
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8.7.2.2 Quartz Sleeve Cleaning

Quartz sleeve cleaning may be accomplished by physical or chemical means. Physical alternatives

include:

• Automatic mechanical wiper;

• Ultrasonic devices;

• High water pressure wash; and

• Air scour.

Chemical cleaning agents include sulfuric or hydrochloric acid. A UV reactor vessel may contain

one or more physical cleaning system with provision for an occasional chemical cleaning.

8.7.2.3 Miscellaneous

Effective maintenance of a UV system will involve:

• Periodic checks for proper operation;

• Calibration of intensity meter for proper sensitivity; and

• Inspect and/or clean reactor vessel interior.

8.7.3 Standby Power

Producing UV radiation requires electricity to power the electronic ballasts, which in turn power the

UV lamps. Since disinfection is of utmost importance in producing potable water, the UV system

should remain in service during periods of primary power failure. A dual power feed system or

essential circuitry powered by a standby generator are typical ways to achieve the desired reliability.

Each low pressure UV lamp requires approximately 100 Watts of standby power. A second

precaution that should be considered is not powering the UV system from the same motor control

center (MCC) that powers variable frequency drives (VFDs). The electronic ballasts produce

harmonics that may require mitigation (active harmonic filters) for the VFDs.
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8.8 Summary Table

Table 8-3. Summary of UV Disinfection

Consideration Description

Generation Low pressure and medium pressure UV lamps available.

Primary uses Primary physical disinfectant; requires secondary chemical

disinfectant for residual in distribution system.

Inactivation efficiency Very effective against bacteria and viruses at low dosages

(5-25 mW•s/cm2 for 2-log removal and 90-140 mW•s/cm2 for 4-log

removal). Much higher dosage required for Cryptosporidium and

Giardia (100-8,000 mW•s/cm2 for 2-log removal).

Byproduct formation Minimal disinfection byproducts produced.

Limitations Limited experience and data with flows greater than 200 GPM.

Water with high concentrations of iron, calcium, turbidity, and

phenols may not be applicable to UV disinfection.

Point of application Prior to distribution system.

Special considerations Extremely high UV dosages for Cryptosporidium and Giardia may

make surface water treatment impractical.

8.9 References

1. AWWA (American Water Works Association). 1991. Guidance Manual for Compliance with

the Filtration and Disinfection Requirements for Public Water Systems Using Surface Water

Sources.

2. AWWA and ASCE (American Society of Civil Engineers). 1990. Water Treatment Plant Design.

Second edition, McGraw-Hill, Inc., New York, NY.

3. Campbell, A.T., et al. 1995. “Inactivation of Oocysts of Cryptosporidium parvum by Ultraviolet

Radiation.” Water Res. 29(11):2583.

4. Carlson, D. A., et al. 1982. Project Summary: Ultraviolet Disinfection of Water for Small Water

Supplies. Office of Research and Development, U.S. Environmental Protection Agency;

Cincinnati, OH, EPA/600/S2-85/092.

5. Clancy, J.L., T.M. Hargy, M.M. Marshall, and J.E. Dyksen. 1997. “Inactivation of

Cryptosporidium parvum Oocysts in Water Using Ultraviolet Light.” Conference proceedings,

AWWA International Symposium on Cryptosporidium and Cryptosporidiosis, Newport Beach,

CA.
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6. Combs, R., and P. McGuire. 1989. “Back to Basics - The Use of Ultraviolet Light for Microbial

Control.” Ultrapure Water Journal. 6(4):62-68.

7. DeMers, L.D. and R.C. Renner. 1992. Alternative Disinfection Technologies For Small Drinking

Water Systems. AWWARF.

8. Ellis, C., and A.A. Wells. 1941. The Chemical Action of Ultraviolet Rays. Reinhold Publishing

Co., New York, NY.

9. Hazen and Sawyer. 1992. Disinfection Alternatives for Safe Drinking Water. Van Nostrand

Reinhold, New York, NY.

10. Huff, C. B. 1965. “Study of Ultraviolet Disinfection of Water and Factors in Treatment

Efficiency.” Public Health Reports. 80(8):695-705.

11. Jagger, J. 1967. Introduction to Research in Ultraviolet Photobiology. Prentice-Hall Inc.,

Englewood Cliffs, NJ.

12. Johnson, R.C. 1997. “Getting the Jump on Cryptosporidium with UV.” Opflow. 23(10):1.

13. Karanis, P., et al. 1992. “UV Sensitivity of Protozoan Parasites.” J. Water Supply Res. Technol.

Aqua. 41(2):95.

14. Kruithof, J.C., et al. 1989. Summaries, WASSER BERLIN ‘89; International Ozone Association,

European Committee, Paris.

15. Malley Jr., J.P, J.P. Shaw, and J.R. Ropp. 1995. “ Evaluations of Byproducts by Treatment of

Groundwaters With Ultraviolet Irradiation.” AWWARF and AWWA, Denver, CO.

16. Murov, S.L. 1973. Handbook of Photochemistry. Marcel Dekker, New York, NY.

17. NSF (National Science Foundation). 1991. NSF Standard 55: Ultraviolet Water Treatment

Systems. National Sanitation Foundation, Ann Arbor, MI.

18. Qualls, R., Flynn, M., and Johnson, J. 1983. “The Role of Suspended Particles in Ultraviolet

Disinfection.” J. Water Pollution Control Fed. 55(10):1280-1285.

19. Rice, E.W. and J.C. Hoff. 1981. “Inactivation of Giardia lamblia Cysts by Ultraviolet

Irradiation.” Appl. Environ. Microbiol. 42:546-547.

20. Scheible, O.K. and C.D. Bassell. 1981. Ultraviolet Disinfection Of A Secondary Wastewater

Treatment Plant Effluent. EPA-600/2-81-152, PB81-242125, U.S. Environmental Protection

Agency; Cincinnati, OH.
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21. Scheible, O.K. 1983. “Design and Operation of UV Systems.” Presented at Water Pollution

Control Federation Annual Conference, Cincinnati, OH.

22. Slade, J. S., N.R. Harris, and R.G. Chisholm. 1986. “Disinfection of Chlorine Resistant

Enteroviruses in Ground Water by Ultraviolet Radiation.” Water Sci. Technol. 189(10):115-123.

23. Snicer, G.A., J.P. Malley, A.B. Margolin, and S.P. Hogan. 1996. “Evaluation of Ultraviolet

Technology in Drinking Water Treatment.” Presented at AWWA Water Quality Technology

Conference, Boston, MA.

24. Snider, K.E., J.L. Darby, and G. Tchobanoglous. 1991. Evaluation of Ultraviolet Disinfection

For Wastewater Reuse Applications In California. Department of Civil Engineering, University

of California, Davis.

25. Sobotka, J. 1993. “The Efficiency of Water Treatment and Disinfection by Means of Ultraviolet

Radiation.” Water Sci. Technol. 27(3-4):343-346.

26. Tchobanoglous, G.T. 1997. “UV Disinfection: An Update.” Presented at Sacramento Municipal

Utilities District Electrotechnology Seminar Series. Sacramento, CA.

27. USEPA (U.S. Environmental Protection Agency). 1996. Ultraviolet Light Disinfection

Technology in Drinking Water Application - An Overview. EPA 811-R-96-002, Office of Ground

Water and Drinking Water.

28. USEPA. 1986. Design Manual: Municipal Wastewater Disinfection. EPA/625/1-86/021, Office

of Research and Development, Water Engineering Research Laboratory, Center for

Environmental Research Information, Cincinnati, OH

29. USEPA. 1980. Technologies for Upgrading Existing and Designing New Drinking Water

Treatment Facilities. EPA/625/4-89/023, Office Drinking Water.

30. Von Sonntag, C. and H. Schuchmann. 1992. “UV Disinfection of Drinking Water and ByProduct Formation - Some Basic Considerations.” J. Water SRT-Aqua. 41(2):67-74.

31. White, G.C. 1992. Handbook of Chlorination and Alternative Disinfectants. Van Nostrand

Reinhold, New York, NY.

32. Wolfe, R.L. 1990. “Ultraviolet Disinfection of Potable Water.” Environ. Sci. Tech. 24(6):768-

773.

33. Yip, R.W. and D.E. Konasewich. 1972. “Ultraviolet Sterilization Of Water - Its Potential And

Limitations.” Water Pollut. Control (Canada). 14:14-18.
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8. ULTRAVIOLET RADIATION ................................................................................................................ 8-1

8.1 UV CHEMISTRY (PHOTOCHEMICAL)...................................................................................................... 8-1

8.1.1 UV Radiation ............................................................................................................................... 8-1

8.1.2 UV Disinfection Reactions........................................................................................................... 8-2

8.1.3 Process Variables ......................................................................................................................... 8-2

8.2 GENERATION........................................................................................................................................ 8-3

8.2.1 UV Lamps.................................................................................................................................... 8-4

8.2.2 Ballasts........................................................................................................................................ 8-4

8.2.3 UV Reactor Design ...................................................................................................................... 8-5

8.3 PRIMARY USES AND POINTS OF APPLICATION ........................................................................................ 8-8

8.4 PATHOGEN INACTIVATION AND DISINFECTION EFFICIENCY .................................................................... 8-8

8.4.1 Inactivation Mechanism................................................................................................................ 8-8

8.4.2 Environmental Effects................................................................................................................ 8-10

8.4.3 Disinfection Efficacy.................................................................................................................. 8-12

8.5 DISINFECTION BYPRODUCTS OF UV RADIATION .................................................................................. 8-15

8.5.1 Ground Water............................................................................................................................. 8-15

8.5.2 Surface Water............................................................................................................................. 8-16

8.5.3 DBP Formation with Chlorination and Chloramination following UV Radiation.......................... 8-16

8.6 STATUS OF ANALYTICAL METHODS..................................................................................................... 8-17

8.6.1 Monitoring of Generated Ultraviolet Radiation ........................................................................... 8-17

8.6.2 Disinfectant Interferences........................................................................................................... 8-18

8.7 OPERATIONAL CONSIDERATIONS......................................................................................................... 8-18

8.7.1 Equipment Operation.................................................................................................................. 8-19

8.7.2 Equipment Maintenance ............................................................................................................. 8-19

8.7.3 Standby Power ........................................................................................................................... 8-20

8.8 SUMMARY TABLE............................................................................................................................... 8-21

8.9 REFERENCES ...................................................................................................................................... 8-21

Table 8-1. Water Quality and Associated UV Measurements............................................................................... 8-3

Table 8-2. Doses Required for MS-2 Inactivation ............................................................................................. 8-13

Table 8-3. Summary of UV Disinfection........................................................................................................... 8-21

Figure 8-1. Closed Vessel Ultraviolet Reactor..................................................................................................... 8-6

Figure 8-2. Germicidal Inactivation by UV Radiation ......................................................................................... 8-9

Figure 8-3. UV Dose Required for Inactivation of MS-2 Coliphage................................................................... 8-11

Figure 8-4. Particle Interactions that Impact UV Effectiveness.......................................................................... 8-12

Figure 8-5. UV Doses Required to Achieve Inactivation of Giardia lamblia Cysts Obtained from Two Different

Sources...................................................................................................................................................... 8-14

Figure 8-6. Impact of Growth Stage of A. rhysodes on the Required UV Dosage to Achieve Inactivation........... 8-14
April 1999 9-1 EPA Guidance Manual

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9. COMBINED DISINFECTANTS

Multiple disinfectants, the sequential or simultaneous use of two or more disinfectants, have been

used with increasing frequency in recent years. This trend is attributed to the fact that:

• Less reactive disinfectants, such as chloramines, have proven to be quite effective in reducing

DBPs formed during disinfection and are more effective for controlling biofilms in the

distribution system.

• Regulatory and consumer pressure to produce water that has been disinfected to achieve high

inactivation for various pathogens, has pushed the industry towards more effective disinfectants.

Sometimes more effective disinfection meant using higher disinfectant doses which also

produces more DBPs.

• Recent research has shown that the application of sequential disinfectants is more effective than

the added effect of the individual disinfectants. This process where two (or more) disinfectants

produce a synergistic effect by either simultaneous or sequential application to achieve more

effective pathogen inactivation, is referred to as interactive disinfection in this manual.

This chapter discusses recent industry applications of multiple disinfectants to meet the varied

requirements for inactivation and reduction in DBPs. The initial discussion focuses on traditional

disinfectants used in primary and secondary application. This is followed by a discussion of

interactive disinfectants where two disinfectants are applied together specifically to achieve primary

disinfection. Note that the IESWTR does not have any provision for additional credits for interactive

disinfection or taking additional credit for the synergistic effects from interactive disinfection. Until

such credit is established, interactive disinfection is considered an emerging technology. This

chapter does not discuss mixed oxidant systems, which are designed to generate mixed oxidants onsite for drinking water disinfection, and are also considered an emerging technology.

9.1 Primary and Secondary Disinfectants

By separating the inactivation function and residual disinfection function in water treatment, each

can be optimized independently. Thus, the combination of disinfectants currently used in

disinfection is typically identified as a primary or secondary disinfectant, as follows:

• Primary disinfection refers to the inactivation of microorganisms to meet the regulatory

bacteriological requirements. This requirement typically is met by achieving certain CT

requirements to assure a target log inactivation of target organisms as set forth in the Surface

Water Treatment Rule (SWTR) (AWWA, 1991).

• Secondary disinfection refers to application of a disinfectant to meet regulatory requirements for

distribution system bacteriological quality as set forth in the Total Coliform Rule (TCR). The

SWTR requires that a residual disinfectant be measured in the distribution system, or that the

bacteriological quality meet certain standards (heterotrophic plate count (HPC) less than

500/100mL).
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To be an effective primary disinfectant, the disinfectant should effectively inactivate the target

organism. Table 9-1 lists potential primary disinfectants as discussed in Chapters 2 through 8.

Table 9-1. Potential Primary Disinfectants

Potential Primary Disinfectants

Target Organism With Filtration1 Without Filtration

Coliform Bacteria Chlorine

Chloramines

Chlorine dioxide

Ozone

UV

Interactive disinfection

Chlorine

Chlorine dioxide

Interactive disinfection3

Giardia cysts Chlorine2

Chlorine dioxide2

Ozone2

Interactive disinfection

Chlorine2

Chlorine dioxide2

Interactive disinfection3

Viruses Chlorine2

Chlorine dioxide2

Ozone2

UV2

Interactive disinfection

Chlorine2

Chlorine dioxide2

UV2

Interactive disinfection3

Cryptosporidium oocysts Chlorine dioxide

Ozone

Interactive disinfection

Chlorine dioxide

Interactive disinfection3

1

 Natural or treatment filtration reduces disinfection inactivation requirements.

2

 Inactivation credit established in SWTR.

3 Any interactive disinfection that uses ozone or peroxone without filtration is strongly discouraged.

As discussed in earlier chapters, certain disinfectants (e.g., ozone, UV, peroxone, and in some cases

chlorine dioxide), while being effective disinfectants, do not leave a long-lasting residual

disinfectant. Therefore, secondary disinfection is limited to those disinfectants that remain stable in

the distribution system. In order of decreasing stability, these secondary disinfectants are

chloramines, chlorine, and chlorine dioxide.

Based on the above, the combinations of disinfectants that are viable options to meet the disinfection

requirements can be determined for various treatment trains. These combinations are shown for

various treatment objectives. Note that the treatment objectives are dependent on the treatment

currently in place.

To meet DBP, and specifically, THM limits, several studies have evaluated the application of various

primary/secondary disinfectants. Table 9-2 presents the typical application of these combined

disinfectants.
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Table 9-2. Primary/Secondary Disinfectant Combinations and Typical

Applications in Water Treatment

Primary / Secondary Typical application* Comment

Chlorine/Chlorine Low THMFP raw water, low TOC,

conventional treatment with

optimal coagulation.

Most commonly used disinfection

scheme. Effective system.

Chlorine/Chloramine Moderate THM production

situation, typically with

conventional treatment.

Chlorine to provide disinfection

and monochloramine to limit DBP

formation.

Chlorine dioxide/Chlorine

dioxide

High DBP production, require filter

process to remove

Cryptosporidium, low chlorine

dioxide demand in treated water.

Primary and secondary usage

requires a limit on chlorine dioxide

dose to reduce residual

chlorate/chlorite.

Chlorine dioxide/Chloramine High DBP production, require

filtration to remove

Cryptosporidium.

Primary chlorine dioxide dose

limited to residual

chlorate/chlorite. Stable, low

reactive secondary disinfectant.

Ozone/Chlorine Moderate DBP formation, direct or

no filtration, low THMFP.

Highly effective disinfection to

achieve high log inactivation; low

THMFP to accept free chlorine.

Ozone/Chloramine Moderate DBP formation, direct or

no filtration, higher THMFP.

Highly effective disinfection to

achieve high log inactivation, low

THMFP to require combined

chlorine residual.

UV/Chlorine Requires membrane treatment to

provide effective Giardia and

Cryptosporidium removal. UV

only for virus inactivation; ground

water disinfection; low THMFP.

Rare application but feasible in

special circumstances. Little

Giardia and no Cryptosporidium

inactivation.

UV/Chloramine Requires membrane treatment to

provide effective Giardia and

Cryptosporidium removal. UV

only for virus inactivation; ground

water disinfection, moderate

THMFP.

Rare application but feasible in

special circumstances. No

Giardia or Cryptosporidium

inactivation.

Notes:

* Low DBP formation is defined as producing less than the Stage 2 D/DBP Proposed Standard (less than 0.040 mg/L TTHM; less

than 0.030 mg/L HAA5). Moderate DBP formation is defined as producing less than the Stage 1 D/DBP Standard and more

than the Stage 2 D/DBP Proposed Standard. High DBP formation is defined as producing more than the Stage 1 D/DBP

Standard (greater than 0.080 mg/L TTHM; greater than 0.060 mg/L HAA5).

9.1.1 DBP Formation with Various Primary and Secondary

Disinfectant Combinations

The concentrations and types of DBPs formed depend on, among other things, the combination of

disinfectants used to achieve primary and secondary disinfection and the water quality. For example,

under certain water quality conditions, ozone/chloramine disinfection is known to produce lower

THM concentrations than chlorine/chloramine disinfection. However, the ozone/chloramine

alternative can increase the formation of other DBPs such as aldehydes and BOM. No single
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combination of disinfectants is applicable to all situations. Table 9-3 summarizes the potential DBPs

formed by various combinations of disinfectants. The disinfection byproducts referenced here are

discussed in greater detail in earlier chapters of this manual.

Table 9-3. DBPs Associated with Various Combined Oxidation/Disinfection

Processes

Alternative

Preoxidation

Primary

Disinfection

Secondary

Disinfection Potential DBPs Remarks

Chlorine Chlorine Chlorine XDBPs* Maximum XDBP formation compared

to all other strategies. Principal

components are TTHMs and HAAs.

Aldehydes Formed at relatively low levels.

Chlorine Chlorine Chloramine XDBPs

Cyanogen chloride

Cyanogen bromide

Formation of XDBPs (specifically

TTHMs and HAA5s) significantly

reduced compared to chlorine/

chlorine/ chlorine.

Aldehydes Formed at relatively low levels.

Chlorine dioxide Chlorine

dioxide

Chlorine XDBPs Formation of XDBPs may be

decreased by delaying the point of

chlorine addition.

Aldehydes, carboxylic acids, maleic

acids

Formed at relatively low levels.

Chlorate

Chlorite

Chlorite is a major breakdown

product of chlorine dioxide.

Chlorine dioxide Chlorine

dioxide

Chloramine XDBPs Formation of XDBPs (especially

TTHMs and HAA5s) minimized by

avoiding use of free chlorine.

Aldehydes, carboxylic acids, maleic

acid

Formed at relatively low levels.

Chlorate

Chlorite

Chlorite is a major breakdown

product of chlorine dioxide.

Potassium

permanganate

Chlorine Chlorine XDBPs Formation of XDBPs may be

decreased by delaying the point of

chlorine addition.

Aldehydes Formed at relatively low levels.

Potassium

permanganate

Chlorine Chloramine XDBPs

Cyanogen chloride

Cyanogen bromide

Formation of XDBPs may further be

decreased compared to potassium

permanganate/ chlorine/ chlorine.

Aldehydes Formed at relatively low levels.

Ozone Ozone Chlorine XDBPs Formation of certain XDBPs may

increase or decrease compared to

chlorine/ chlorine/ chlorine.

Brominated byproducts may be of

concern when bromides are present

in the raw water.

Bromate, Aldehydes, carboxylic

acids

Although formed at relatively high

levels significant amounts of this

BOM can be removed through

biological filtration.

Ozone Ozone Chloramine XDBPs

Cyanogen chloride

Cyanogen bromide

Formation of XDBPs (especially

TTHMs) minimized by avoiding use

of free chlorine.

Bromate, Aldehydes, carboxylic

acids

Although formed at relatively high

levels significant amounts of this

BOM can be removed through

biological filtration.
9. COMBINED DISINFECTANTS

April 1999 9-5 EPA Guidance Manual

Alternative Disinfectants and Oxidants

Alternative

Preoxidation

Primary

Disinfection

Secondary

Disinfection Potential DBPs Remarks

Peroxone Chlorine or

Ozone

Chlorine XDBPs Formation of certain XDBPs may

increase or decrease compared to

chlorine/ chlorine/ chlorine.

Bromate, Aldehydes, carboxylic

acids

Although formed at relatively high

levels significant amounts of this

BOM can be removed through

biological filtration. Also, the

formation of bromate will increase if

peroxone is used.

Peroxone Chlorine or

Ozone

Chloramine XDBPs

Cyanogen chloride

Cyanogen bromide

Formation of XDBPs may decrease

compared to peroxone/ chlorine/

chlorine.

Bromate, Aldehydes, carboxylic

acids

Although formed at relatively high

levels significant amounts of this

BOM can be removed through

biological filtration. Also, the

formation of bromate will increase if

peroxone is used.

Chlorine UV** Chloramine XDBPs

Cyanogen chloride

Cyanogen bromide

May form XDBP from pre-oxidation.

Aldehydes Low levels.

Potassium

Permanganate

UV** Chloramine XDBPs Very low due to less reactive

oxidants.

Aldehydes, carboxylic acids Very low, if any, due to less reactive

oxidants.

* XDBPs - Halogenated Disinfection Byproducts.

* * Although “conventional” UV use as primary disinfectant is limited to virus inactivation (may require membrane filtration), pulsed

UV may be able to inactivate Giardia and Cryptosporidium.

Source: Adopted in part from USEPA, 1992; Richardson et al., 1994.

Raw water chlorination, applied prior to natural organic matter (NOM) removal processes, combined

with chlorination for residual disinfection produces the greatest concentrations of halogenated DBPs.

Studies indicate that pre-oxidation of raw water with ozone or chlorine dioxide can reduce the

formation of halogenated DBPs because it shifts the point of chlorine application from raw water to

settled or filtered water which has lower DBP precursor concentrations (MWDSC and JMM, 1989).

The use of ozone can reduce the formation of halogenated byproducts in waters containing low

concentrations of bromide. However, ozone increases BOM and may encourage bacterial growth in

the distribution system. Removal of AOC with biological filtration (e.g., biological activated carbon)

reduces the potential for bacterial growth in the distribution system. The use of chloramines as a

secondary disinfectant instead of chlorine shortens the chlorine contact time and thus reduces the

formation of chlorinated byproducts. However, chloramine produces by-products of its own

(cyanogen chloride and cyanogen bromide). In addition, a short chlorine contact time prior to

ammonia addition will help inactivate heterotrophic plate count bacteria that are found in the effluent

of a biologically active filter. Bench or pilot studies will be required to evaluate the trade-offs in

DBP formation for various disinfectant combinations for a specific application.

The application of ozone should be carefully considered because it produces aldehydes,

aldoketoacids, and carboxylic acids. However, these can be removed in a biologically active filter.
9. COMBINED DISINFECTANTS

EPA Guidance Manual 9-6 April 1999

Alternative Disinfectants and Oxidants

In bromide-containing waters, ozonation can increase the formation of brominated organic DBPs and

form bromate.

In pilot plant studies for water containing low concentrations of bromide, Lykins et al. (1991)

determined that ozonation followed by chloramination produced the lowest levels of halogenated

disinfection byproducts. However, this is not applicable to source waters containing significant

bromide concentrations due to the potential for bromate formation and brominated THMs and HAAs.

The addition of chlorine dioxide will produce chlorite and chlorate and may form some oxygenated

DBPs (e.g., maleic acids).

9.1.2 Impact of Modifying Disinfection Practices

EPA and the Association of Metropolitan Water Agencies funded a 2-year study of 35 water

treatment facilities to evaluate DBP production. Among four of the facilities, eleven alternative

disinfection strategies were instigated to evaluate the difference in DBP production from the plants’

previously existing disinfection strategies. Three reports (MWDSC and JMM, 1989; Jacangelo,

1989; USEPA, 1992) analyzed and documented different aspects of the study. Table 9-4 shows the

eleven potential strategies used for primary and secondary disinfection. Table 9-5 shows the changes

in DBP production observed in the four plants after eight of these new strategies were implemented.

Following are overviews of the potential implications of these strategies, as detailed by the three

reports.

Table 9-4. Strategies for Primary and Secondary Disinfectants

Base Disinfection Condition Modified Disinfection Practice

Chlorine/Chlorine Chlorine/Chloramine

Chlorine/Chlorine Chloramine/Chloramine

Chlorine/Chlorine Chlorine Dioxide/Chloramine

Chlorine/Chlorine Ozone/Chlorine

Chlorine/Chlorine Ozone/Chloramine

Chlorine/Chlorine Chlorine Dioxide/Chlorine

Chlorine/Chlorine Chlorine Dioxide/Chlorine Dioxide

Chlorine/Chloramine Ozone/Chloramine

Chlorine/Chloramine Chlorine Dioxide/Chloramine

Ozone/Chlorine Ozone/Chloramine

Chloramine/Chloramine Ozone/Chloramine

Note: Disinfectants are listed as primary disinfectant/secondary disinfectant
9. COMBINED DISINFECTANTS

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9-7

Table 9-5. Impacts of Disinfection Practice on DBP Formation

Disinfection Byproduct Change in Disinfection Practice (Primary Disinfectant/Secondary Disinfectant)

Chlorine/Chlorine

to

Chlorine/Chloramine

Chlorine/Chlorine

to

Ozone/Chlorine

Chlorine/Chloramine

to

Ozone/Chloramine

Chlorine/Chlorine

to

Chloramines/Chloramines

Utility #7 Utility #19 Utility #36 Utility#7 Utility #36

Total Trihalomethanes decrease decrease no change decrease decrease

Total Haloacetic Acids decrease decrease no change decrease decrease

Total Haloacetonitriles decrease decrease no change decrease decrease

Total Haloketones decrease no change increase increase decrease

Total Aldehydes not analyzed not analyzed increase not analyzed decrease

Chloropicrin no change increase increase decrease no change

Chloral Hydrate decrease increase increase decrease decrease

Cyanogen Chloride no change not analyzed no change no change increase

Disinfection By-Product Change in Disinfection Practice (Primary Disinfectant/Secondary Disinfectant)

Ozone/Chlorine

to

Ozone/Chloramine

Chloramines/Chloramines

to

Ozone/Chloramines

Chlorine/Chlorine

to

Ozone/Chloramine

Utility #36 Utility #25 Utility #36 Utility #7 Utility #36

Total Trihalomethanes decrease decrease no change decrease decrease

Total Haloacetic Acids decrease decrease no change decrease decrease

Total Haloacetonitriles decrease no change no change decrease decrease

Total Haloketones decrease no change increase decrease decrease

Total Aldehydes decrease increase increase not analyzed increase

Chloropicrin increase increase increase decrease increase

Chloral Hydrate decrease decrease increase decrease decrease

Cyanogen Chloride increase increase increase no change increase

Notes: Results based on full scale evaluation at Utilities #19 and #25 and on pilot scale evaluations at Utilities #7 and #36.

Free chlorine contact time was 4 hours for Utility #7 during use of chlorine/chloramine strategy.

Systems must demonstrate efficacy of chloramines as a primary disinfectant if they are to be used as such.

Source: USEPA, 1992; Jacangelo, et al., 1989.
9. COMBINED DISINFECTANTS

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Alternative Disinfectants and Oxidants

9.1.3 Chlorine/Chlorine to Chlorine/Chloramine

Chloramines as a secondary disinfectant shortens the free chlorine contact time and, therefore, reduce

the formation of most halogenated DBPs, including TTHM. However, the consumer is exposed to a

chloramine residual that has a different health concern (i.e., can cause methemoglobinemia and

adversely affect the health of kidney dialysis patients) than chlorine residual. For maximum benefit

in reducing halogenated byproducts, the ammonia/chlorine mixing conditions should be optimized to

quickly remove free chlorine from the system, with the optimal pH for the chlorine/ammonia reaction

considered to be pH 8.3. In one case, changing the secondary disinfectant from chlorine to

chloramines resulted in a reduction in average TTHM concentrations from 105 μg/L to 45 μg/L with

most (80 percent) of the TTHM formation in the chloraminated system occurring prior to the addition

of ammonia (Singer, 1988).

9.1.4 Chlorine/Chlorine to Ozone/Chlorine

A change from chlorine to ozone for primary disinfection is attractive because ozone generally

produces fewer regulated DBPs than chlorine. However, as mentioned in previous chapters, ozone

will react with organic compounds to produce BOM, aldehydes, organic acids, and ketones, many of

which are biodegradable. In addition, for water sources containing significant bromide ion

concentrations, site-specific engineering evaluations should be completed prior to using ozone as a

primary disinfectant due to the potential formation of bromate ion or brominated organic byproducts.

At low pH values, the brominated organic byproducts are favored, while at higher pH values,

bromate ion formation is favored. Therefore, changing from chlorine to ozone may be limited in

cases where the source water contains bromide ion. In the ozone/chlorine strategy, bromine has the

opportunity to react with NOM prior to chlorine application, potentially increasing the extent of

bromine incorporation into DBPs. Also, in this situation, switching to biological filtration can

increase regrowth and corrosion rates in the distribution system.

In systems containing negligible concentrations of bromide ion, replacement of pre-chlorination with

ozonation may allow for the point of chlorine addition to be moved beyond clarification or filtration.

The principal benefit derived from using ozone for controlling THM formation is that it allows free

chlorine to be applied later in the treatment process after precursors have been removed. This would

be expected to result in reduced formation of chlorinated DBPs due to the reduced chlorine dose

requirement and the reduced NOM concentrations following treatment. Replacement of chlorine

with ozone appears to be most effective in decreasing chlorinated DBPs when it eliminates the need

for pre-chlorination. However, replacing chlorine with ozone while maintaining free chlorine as a

secondary disinfectant has produced mixed results, with some byproduct concentrations being

reduced at the expense of increasing the concentrations of others. The human health implications of

this trade-off are largely unknown. It has been shown that substituting ozone for chlorine as a

primary disinfectant, while maintaining free chlorine as a secondary disinfectant when not practicing

pre-chlorination, resulted in an increased THM formation in raw waters for the Cities of Phoenix and

San Diego (Malcolm Pirnie, 1989; Malcolm Pirnie, 1990).
9. COMBINED DISINFECTANTS

April 1999 9-9 EPA Guidance Manual

Alternative Disinfectants and Oxidants

An operational consideration of the ozone/chlorine system is the application point for chlorine. The

ozone should be completely decomposed or chemically quenched prior to chlorine addition. If ozone

is present when chlorine is added, the ozone will react with the chlorine and NOM present to form

chlorinated DBPs.

Ozonation converts NOM into low molecular weight humic NOM and may increase the

concentrations of precursors to some DBPs. For instance, ozonation followed by chlorination as a

secondary disinfectant may yield high concentrations of chloral hydrate (Logsdon et al., 1992;

McKnight and Reckhow, 1992). This may occur because the byproduct of ozonation, acetaldehyde,

is a known precursor for chloral hydrate, a byproduct of chlorination. Enhancement of chloral

hydrate has not been observed when biologically active filtration is used following ozonation and

prior to chlorination (Singer, 1992). In addition to chloral hydrate, ozonation followed by

chlorination can produce greater THM and haloketones levels than chlorination alone, particularly

when chlorine is applied at high pH levels (Jacangelo et al., 1989; Reckhow et al., 1986). Ozonation

followed by chlorination or chloramination can increase chloropicrin and cyanogen chloride

concentrations above those observed with chlorination or chloramination alone (Jacangelo et al.,

1989). The most promising treatment strategy for preventing the enhancement of these

biodegradable ozonation byproducts and BOM is to locate ozonation after sedimentation and follow

it by biologically active GAC.

9.1.5 Chlorine/Chlorine to Ozone/Chloramine

In addition to the concerns addressed in Sections 9.1.3 and 9.1.4, switching from chlorine to

chloramine residual exposes the consumer to a residual that may be a more significant health concern

(particularly for kidney dialysis patients). The impact of switching from chlorine/chlorine to

ozone/chloramines on the production of byproducts was investigated in a 5 gpm pilot study

(MWDSC and JMM, 1989; Jacangelo et al., 1989). That switch produced greater concentrations of

chloropicrin, cyanogen chloride, formaldehyde and total aldehydes than in the original

chlorine/chlorine strategy. Concentrations of TTHMs, total haloacetic acids, total haloacetonitriles,

total haloketones and chloral hydrate were lower with ozone/chloramine. Brominated DBPs were

not reported. Ozonation followed by chloramination has been observed to increase cyanogen

chloride concentrations beyond those observed with chlorination only (Jacangelo et al., 1989).

Increased chloral hydrate has not been observed when monochloramine is applied as the secondary

disinfectant (Singer, 1992).

9.1.6 Chlorine/Chlorine to Chlorine Dioxide/Chlorine

Use of chlorine dioxide as a pre-oxidant to replace chlorine may allow moving the point of

chlorination downstream in the process train for application to water with lower NOM

concentrations. The reduced precursor concentration and the reduced chlorine dose should result in a

reduction of chlorinated DBPs. However, if excess chlorine is present in the chlorine dioxide feed

stream, it would react with NOM prior to removal in sedimentation and filtration if pre-oxidation is

practiced. Switching from chlorine/chlorine to chlorine dioxide/chlorine produces mixed results.
9. COMBINED DISINFECTANTS

EPA Guidance Manual 9-10 April 1999

Alternative Disinfectants and Oxidants

Like ozone, chlorine dioxide alters the nature of NOM molecules, potentially forming greater

precursor concentrations for some DBPs while reducing the precursor concentrations for other DBPs.

The human health implications of these trade-offs are largely unknown. Chlorine dioxide/chlorine

appears to be most effective in decreasing chlorinated DBPs when it can replace the need for prechlorination. However, for facilities that use pre-chlorination but do not require it, continuing to use

chlorine/chlorine while eliminating pre-chlorination may be as effective in decreasing chlorinated

DBPs.

9.1.7 Chlorine/Chlorine to Chlorine Dioxide/Chlorine Dioxide

The potential to apply chlorine dioxide as both a primary and secondary disinfectant is limited

because:

• Chlorine dioxide is a strong oxidant and dissipates rapidly in both raw and treated waters;

and

• Approximately 50 to 70 percent of chlorine dioxide is converted to the inorganic byproducts

chlorite and chlorate.

On the positive side, chlorine dioxide/chlorine dioxide application will significantly lower the

formation of organic DBPs.

9.1.8 Chlorine/Chloramine to Ozone/Chloramine

In addition to the concerns raised in Sections 9.1.4 and 9.1.5, switching from chlorine/chloramine to

ozone/chloramine resulted in reduced formation of most of the halogenated DBPs (MWDSC and

JMM, 1989). Other studies also indicate reduction in the formation of most halogenated DBPs but

increased formation of 1,1-dichloropropanone (MWDSC and JMM, 1989). The primary difference

in chlorinated DBP formation when switching from chlorine/chloramine to ozone/chloramine could

be attributed to the shorter contact time with free chlorine.

9.1.9 Chlorine/Chloramine to Chlorine Dioxide/Chloramine

The Louisville Water Company evaluated the feasibility of switching from a chlorine/chloramine to

chlorine dioxide followed by chloramine to control THM formation (Hubbs et al., 1981). The

treatment plant includes lime soda-ash for softening. Disinfection occurs prior to the lime treatment

step. Ammonia is added to form chloramine before the water enters the softening phase. There is a

10 minute lag period between the first disinfectant (chlorine or chlorine dioxide) and second

disinfectant (chloramine) addition. The study showed a significant decrease in THM formation from

25 μg/L with chlorine to 5 μg/L using chlorine dioxide as the initial disinfectant. At the same time,

treated water coliform densities were essentially unchanged; however, results showed slightly more

scattered data during the chlorine dioxide test period. Based on these results, the Water Company

decided to use chlorine/chloramine to meet disinfection and THM targets. No other DBPs were

measured during the test period.
9. COMBINED DISINFECTANTS

April 1999 9-11 EPA Guidance Manual

Alternative Disinfectants and Oxidants

9.1.10Ozone/Chlorine to Ozone/Chloramine

In addition to concerns raised in Sections 9.1.4 and 9.1.5, when compared with ozone/chlorine,

ozone/chloramine produced greater concentrations of cyanogen chloride. Concentrations of TTHM,

total haloacetic acids, total haloacetonitriles, total haloketones, chloral hydrate, total aldehydes and

formaldehyde were lower with ozone/chloramine than with ozone/chlorine. Ozone/chloramine

produces some chlorinated DBPs at greater concentrations than ozone/chlorine; however,

ozone/chloramine significantly reduces TTHMs compared to ozone/chlorine (LeLacheur et al.,

1991).

9.1.11Summary

EPA is not encouraging systems to switch to different disinfectants due to unknown risks to public

health. When needed for compliance with regulations or increasing Cryptosporidium inactivation,

careful selection of alternative disinfectants as primary and secondary disinfectants, can produce less

DBPs and increase inactivation. In general, the results followed the characteristic DBPs associated

with the primary disinfectant (halogenated DBPs with chlorine compounds or ozone in the presence

of bromide oxidized organics, AOC with ozone or peroxone). However, by carefully selecting the

primary and secondary disinfectant and avoiding long contact times and high dosages of halogens

(chlorine, bromine), the total DBP formation declined. The quantity and types of DBPs that form are

site-specific, depending on the water quality, disinfectant dose and type, and are best determined by

bench testing. Note that any system changing disinfectants is subject to the profiling and

benchmarking requirements as described in Section 1.3.1 and specified in 40 CFR § 141.172.

9.2 Pathogen Inactivation with Interactive Disinfectants

In 1988, several reports appeared on the combined efficiency of some disinfectants on pathogen

inactivation. Worley and Williams (1988) reported that a mixture of free chlorine and organic

N-halamine produced higher levels of inactivation of a variety of bacteria. The combination of free

chlorine and sodium bromide was also investigated and found to be more effective than using free

chlorine alone (Alleman et al., 1988). In a study at the University of Arizona, the synergistic

inactivation of E. coli and MS-2 coliphage was demonstrated by the combined application of

chloramine and cupric chloride (Straub et al., 1994).

Recently there has been a great deal of interest in the potential of interactive disinfectants because

reports showed that some of these combinations are more effective for inactivating Cryptosporidium

(Finch et al., 1994). Research on interactive disinfectants for primary pathogen inactivation is under

way for several combinations of disinfectants:

• Chlorine followed by chloramine;

• Chlorine dioxide followed by chlorine;

• Chlorine dioxide followed by chlorine dioxide;
9. COMBINED DISINFECTANTS

EPA Guidance Manual 9-12 April 1999

Alternative Disinfectants and Oxidants

• Chlorine dioxide followed by chloramine;

• Ozone followed by chlorine;

• Ozone followed by chlorine dioxide; and

• Ozone followed by chloramine.

9.2.1 Inactivation Mechanism

Bernbaum (1981 and 1985) developed a testing method for determining the kind of interaction that

can be expected when agents are combined to produce a given observation. Synergism can be tested

using the mathematical model developed by Bernbaum and modified for disinfection kinetics by

Kouame and Haas (1991). The principle is that, if the agents in a given combination do not interact

in producing the effect observed, then regardless of the effect relations, the following equation is

satisfied:

x

y

i

i i

n

=

∑ =

1

1

where:

xi = Concentration of the individual agent in the combination

yi = Concentration of the agents that individually would produce the same magnitude

of effect as that of the combination

i = Individual agent

n = Total number of agents

The sum calculated from this equation for a set of data is interpreted as follows:

• The sum is less than 1 in the case of synergistic interaction;

• The sum is greater than 1 in the case of antagonistic interaction; and

• The sum is equal to 1 in the case of additivity (zero interaction).

Using this approach, Kouame and Haas (1991) showed that a synergistic interaction exists in the

inactivation of E. coli when exposed simultaneously to free chlorine and monochloramine.

The authors described a possible mechanism in which both of the disinfectants work together to

inactivate bacteria. The researchers hypothesized that bacterial inactivation is caused by

monochloramine penetrating the cell and oxidizing thiol groups, which in turn causes structural

changes in the cell membrane. Once these changes have been made, copper is allowed to pass into

the cell and binds either to sulfhydryl groups of respiratory enzymes or nucleic acids. More recently,

the researchers investigating E. coli inactivation hypothesized that a potential synergistic mechanism

consisting of sub-lethal injury caused by free chlorine resulted in enhanced sensitivity to

monochloramine (Kouame and Haas, 1991).
9. COMBINED DISINFECTANTS

April 1999 9-13 EPA Guidance Manual

Alternative Disinfectants and Oxidants

Another hypothesis for the increased effectiveness of interactive disinfectants is that the first oxidant

(i.e., chlorine, chlorine dioxide, or ozone) conditions the outer membrane of Cryptosporidium

oocysts so that the secondary oxidant (i.e., chlorine, chlorine dioxide, and monochloramine) can

penetrate the oocyst more easily (Liyanage et al., 1996). For example, preliminary work on the

disinfection of Cryptosporidium parvum using free chlorine followed by monochloramine suggested

that there may be a synergism involving two chlorine species. Sequential treatment of these chlorine

species was found to provide greater inactivation than expected from the additive effects of the two

disinfectants used alone (Gyurek et al., 1996).

Recent studies have utilized a straight forward method to determine if synergism has occurred based

on measured inactivation (Finch, 1997; Gyurek et al., 1996; and Liyanage et al., 1996). According to

this approach, synergism is demonstrated if the sequential application of disinfectants provides more

inactivation than is expected from the additive effects of the individual, separate disinfectants. In

addition, the magnitude of the synergistic effects is equal to the difference in the level of inactivation

achieved from multiple disinfectants and the additive inactivations achieved from the single

disinfectants.

9.2.2 Environmental Effects

Similar to most chemical disinfectants, the preliminary results from an AWWARF ongoing study

suggest that pH and temperature affect the amount of synergistic inactivation achieved by sequential

applications of disinfectants (Finch, 1997). The following sections briefly describe the effects these

parameters have on pathogen inactivation.

9.2.2.1 pH

The level of inactivation due to the sequential application of chemical disinfectants is believed to be

pH dependent (Finch, 1997). Figure 9-1, Figure 9-2, and Figure 9-3 illustrate the impact of pH on

the log inactivation of Cryptosporidium parvum attributed to synergistic effects for three sequential

combinations of ozone-chlorine dioxide, chlorine dioxide-free chlorine, and chlorine dioxidechloramine, respectively. As shown in these figures, the amount of log inactivation due to

synergistic effects is lower at high pH (e.g., pH = 11). These results show that neutral pH is more

effective than low pH except for ozone-chlorine dioxide.

9.2.2.2 Combination of Low Temperature and pH

The combined effect of low temperature and high pH is believed to significantly reduce the amount

of Cryptosporidium inactivation attributed to synergism (Finch, 1997). One possible explanation for

this reduction is that the oocysts contract under these conditions and become harder to penetrate.

However, significant reduction in Cryptosporidium oocysts inactivation is true under reduced water

temperature and high pH whether interactive disinfection is practiced or not. Therefore, reduced

inactivation may not be necessarily due to synergism between combined disinfectants.
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EPA Guidance Manual 9-14 April 1999

Alternative Disinfectants and Oxidants

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

6 8 11

pH

Inactivation ratio (log-units)

Ozone 0.9 mg/L for 4 minutes, Chlorine 

dioxide 1.3 mg/L for 120 minutes

Source: Finch, 1997.

Figure 9-1. Inactivation of C. parvum Attributed to Synergistic Effects.

Application of Ozone Followed by Chlorine Dioxide

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

6 8 11

pH

Inactivation ratio (log-units)

Chlorine dioxide 1.3 mg/L for 120 

minutes, Free chlorine 2.0 mg/L for 120 

minutes

Source: Finch, 1997.

Figure 9-2. Inactivation of C. parvum Attributed to Synergistic Effects.

Application of Chlorine Dioxide Followed by Free Chlorine
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Alternative Disinfectants and Oxidants

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

6 8 11

pH

Inactivation ratio (log-units)

Chlorine dioxide 1.3 mg/L for 120 

minutes, Monochloramine: pH 6 and 

11; 2.0 mg/L for 120 minutes; pH 8; 2.8 

mg/L for 180 minutes.

Source: Finch, 1997.

Figure 9-3. Inactivation of C. parvum Attributed to Synergistic Effects.

Application of Chlorine Dioxide Followed by Monochloramine

9.2.2.3 Pathogen Susceptibility

Cryptosporidium oocysts are more susceptible to inactivation by combinations of disinfectants than

by individual disinfectants. Giardia cysts were also found to have a similar response to:

• Ozone followed by free chlorine;

• Ozone followed by monochloramine;

• Chlorine dioxide followed by free chlorine;

• Chlorine dioxide followed by monochloramine; and

• Free chlorine followed by monochloramine.

However, no synergism was observed with bacterial spores, specifically Bacillus cereus spores

(Finch, 1997). These results suggest that encysted parasites might show more susceptibility to

synergistic effects than bacterial spores. Masking effects caused by turbidity for interactive

disinfectants are expected to be similar to those of the individual disinfectants.
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9.2.3 Pathogen Inactivation Efficiency Using Interactive

Disinfectants

Within the last few years there have been several studies to investigate interactive disinfectants.

These studies were conducted under various conditions of pH, bench or laboratory scale, and using

various organisms:

• Battigelli and Sobsey (1993) studied viral inactivation under lime softening conditions using

sequential addition of chlorine and monochloramine;

• Kouame and Haas (1991) determined E. coli inactivation during simultaneous addition of

free chlorine and monochloramine;

• Finch (1997) is studying various combinations of chlorine, chlorine dioxide, ozone, and

monochloramine on inactivation of Cryptosporidium parvum oocysts, Giardia muris cysts,

and Bacillus cereus spores under laboratory conditions; and

• Oppenheimer (1997) is developing CT requirements for Cryptosporidium parvum

inactivation in a variety of natural waters using ozone followed by chlorine.

The following is a summary of the findings of these studies to date.

9.2.3.1 Virus Inactivation Using Chlorine and Monochloramine Under High pH

One of the primary objectives of the Battigelli and Sobsey study (1993) was to evaluate the

disinfection efficiency under high pH conditions encountered in conventional lime softening

treatment with and without the addition of chlorine and monochloramine. The three microorganisms

selected for evaluation were hepatitis A virus, poliovirus 1, and MS-2 coliphage.

During the study, the inactivation kinetics of the three test viruses were determined when 2.0 mg/L

monochloramine were formed dynamically after the viruses had been exposed to lime solution and

free chlorine for 60 seconds. The authors believed that this approach simulates the conditions

typically encountered in a water softening facility where ammonia is applied post-chlorination.

Results indicated that a high degree of inactivation occurs during the first 60 seconds of chlorine

addition at approximately 2.4 mg/L free chlorine.

Table 9-6 shows the amount of inactivation attributed to the lime solution, free chlorine, and

monochloramine for the three viruses. The table also contains the amount of inactivation attributed

to the sequential application of lime solution, free chlorine and monochloramine previously described

(simultaneous chloramination). Results shown in Table 9-6 are based on a pH of 11.0 and a total

contact time of 360 minutes.

Except for poliovirus 1, the summation of the individual disinfectants was greater than the level of

inactivation achieved from the simultaneous chloramination. These results imply that the sequential

addition of free chlorine and monochloramine after lime addition to raise the pH to 11, form an
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April 1999 9-17 EPA Guidance Manual

Alternative Disinfectants and Oxidants

antagonistic (negative) interaction for inactivation of hepatitis A virus and MS-2 coliphage. For

poliovirus 1, under similar conditions, an enhancement of 1.4 log inactivation was achieved

suggesting positive synergism for poliovirus 1 inactivation.

Table 9-6. Virus Inactivation By Individual Disinfectants and Simultaneous

Chloramination

Disinfectant(s) Log Survival1 Condition

Hepatitis

A Virus

Poliovirus MS-2

Coliphage

Lime solution only -3.0 -0.5 -4.0 360 min contact time

Free chlorine -1.8 -1.2 -1.6 60 second contact time,

2.5 mg/L chlorine

Monochloramine -3.7 -1.9 -3.8 2.0 mg/L monochloramine

Summation free+monochloramine -5.5 -3.1 -5.4 Additive

Simultaneous chloramination -4.5 -4.5 -4.5 2.4 mg/L chlorine 60

second contact time, 2.0

mg/L monochloramine,

359 minutes.

1 All data at pH 11 after lime addition

 Source: Battigelli and Sobsey, 1993.

9.2.3.2 Inactivation of E. coli Under Simultaneous Free and Combined

Chlorination

The inactivation of E. coli bacteria by the simultaneous application of free chlorine and

monochloramine was investigated at the Illinois Institute of Technology (Kouame and Haas, 1991).

Figure 9-4 shows the level of E. coli inactivation by free chlorine and monochloramine, separately

and combined. The level of inactivation by monochloramine alone after a contact time of 300

seconds was found to be significantly less than that of free chlorine. Therefore, the sum of the

individual inactivation by free chlorine and monochloramine was assumed to be equal to that of free

chlorine alone. Note that in this case, the residual disinfectant rapidly disappeared due to the

breakpoint reactions that occur when monochloramine and free chlorine are combined.

The surviving fraction of bacteria following the simultaneous application of free chlorine and

monochloramine is substantially less than what would be expected by adding the individual levels of

inactivation. In other words, at similar doses and contact times, the amount of inactivation from the

combined disinfectants was greater than the sum of the inactivation due to free chlorine alone and

monochloramine alone.

In summary the Kouame and Haas (1991) study showed that high levels of bacteria inactivation can

be achieved when free chlorine and monochloramine exist simultaneously in a continuous flow

system and that the combined action of both chemicals on the bacteria is synergistic.
9. COMBINED DISINFECTANTS

EPA Guidance Manual 9-18 April 1999

Alternative Disinfectants and Oxidants

9.2.3.3 Cryptosporidium, Giardia, and Bacillus Inactivation in Laboratory Grade

Water

The preliminary results of an AWWARF study that investigated the application of multiple

disinfectants was presented at a American Water Works Association Technology Transfer

Conference in Portland, OR, in August 1997. The objectives of this study were to screen interactive

chemical disinfectants (ozone, chlorine, chlorine dioxide, and monochloramine) for inactivation of

Cryptosporidium parvum, Giardia muris, and Bacillus cereus and develop design criteria for

Cryptosporidium parvum inactivation using the best combinations.

Ozone Followed By Chlorine Dioxide

Table 9-7 shows the results obtained from ozone and chlorine dioxide application for the inactivation

of Cryptosporidium parvum.

Based on the data shown in Table 9-7, ozone followed by chlorine dioxide was the most effective

disinfectant combination for Cryptosporidium inactivation. A total contact time of 124 minutes was

required to achieve 3 to 4-log inactivation with ozone and chlorine dioxide residuals of 0.9 and 1.3

mg/L, respectively.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

55 68 79 91

Contact Time (seconds)

Inactivation Ratio (log-units)

Summation of expected levels of inactivation by free chlorine and monochloramine

Levels of inactivation obtained from simultaneous application of free chlorine and monochloramine

Amount 

attributed to 

synergistic 

effects.

Source: Kouame and Haas, 1991.

Figure 9-4. Inactivation of E. coli Using Free Chlorine and Monochloramine
9. COMBINED DISINFECTANTS

April 1999 9-19 EPA Guidance Manual

Alternative Disinfectants and Oxidants

Table 9-7. C. parvum Inactivation Using Ozone Followed by Chlorine Dioxide

Disinfectant Level of Inactivation (log-units)

pH 6.0 pH 8.0 pH 11.0

Ozone 1.6 0.8 0

Chlorine dioxide 0.9 1.4 2.4

Ozone followed by chlorine dioxide 4.0 3.6 2.9

Inactivation attributed to synergism 1.5 1.4 0.5

Source: Finch, 1997.

Ozone: 0.9 mg/L for 4 minutes, chlorine dioxide 1.3 mg/L for 120 minutes.

Chlorine Dioxide Followed by Free Chlorine

Table 9-8 through Table 9-10 summarize of the results obtained for chlorine dioxide followed by free

chlorine for Cryptosporidium parvum, Giardia muris, and Bacillus cereus, respectively.

Table 9-8. C. parvum Inactivation Using Chlorine Dioxide Followed by Free

Chlorine

Disinfectant Level of Inactivation (log-units)

pH 6.0 pH 8.0 pH 11.0

Chlorine dioxide 1.0 1.4 1.6

Free chlorine 0 0 0

Chlorine dioxide followed by free chlorine 2.2 3.0 2.3

Inactivation attributed to synergism 1.2 1.6 0.7

Source: Finch, 1997.

Chlorine dioxide 1.3 mg/L for 120 minutes, free chlorine 2.0 mg/L for 120 minutes.

Table 9-9. G. muris Inactivation Using Chlorine Dioxide Followed by Free

Chlorine

Disinfectant Level of Inactivation (log-units)

pH 6.0 pH 8.0

Chlorine dioxide 0.8 0.8

Free chlorine 0.8 0.6

Chlorine dioxide followed by free chlorine 2.2 2.0

Inactivation attributed to synergism 0.6 0.6

Source: Finch, 1997.

Chlorine dioxide: 1.0 mg/L for 10 minutes, free chlorine 2.0 mg/L for 30 minutes.

Table 9-10. B. cereus Inactivation Using Chlorine Dioxide Followed by Free

Chlorine

Disinfectant Level of Inactivation (log-units)

Chlorine dioxide 1.8

Free chlorine 1.2

Chlorine dioxide followed by free chlorine 2.9

Inactivation attributed to synergism 0

Source: Finch, 1997.

Chlorine dioxide: 2.3 mg/L for 20 minutes, free chlorine for 30 minutes.
9. COMBINED DISINFECTANTS

EPA Guidance Manual 9-20 April 1999

Alternative Disinfectants and Oxidants

Chlorine dioxide followed by free chlorine was capable of achieving between 2 and 3 logs of

Cryptosporidium inactivation following a total contact time of 240 minutes and approximately 2 logs

of inactivation of Giardia following only 40 minutes of contact time. No synergism was observed

with Bacillus cereus. However, approximately 3 logs of inactivation after a contact time of 50

minutes were achieved by the additive effects of chlorine dioxide and free chlorine.

Chlorine Dioxide Followed by Chloramine

Table 9-11 and Table 9-12 show the results of the inactivation of Cryptosporidium parvum and

Giardia muris when using chlorine dioxide followed by monochloramine.

Table 9-11. C. parvum Inactivation Using Chlorine Dioxide Followed by

Chloramine

Disinfectant Level of Inactivation (log-units)

pH 6.0 pH 8.0 pH 11.0

Chlorine dioxide 1.0 1.5 1.6

Monochloramine 0 0 0

Chlorine dioxide followed by monochloramine 2.2 2.8 2.1

Inactivation attributed to synergism 1.2 1.3 0.5

Source: Finch, 1997.

Chlorine dioxide: pH 6, 8, and 11: 1.3 mg/L for 120 minutes. Monochloramine: pH 6 and 11: 2.0 mg/L for 120 minutes, pH 8: 2.8

mg/L for 180 minutes.

Table 9-12. G. muris Inactivation Using Chlorine Dioxide Followed by Chloramine

Disinfectant Level of Inactivation (log-units)

pH 8.0 pH 11.0

Chlorine dioxide 0.8 0.8

Monochloramine 0.5 0.7

Chlorine dioxide followed by monochloramine 1.7 1.5

Inactivation attributed to synergism 0.4 0

Source: Finch, 1997.

pH 8.0: Chlorine dioxide 1.0 mg/L for 5 minutes, monochloramine 2.0 mg/L for 150 minutes.

pH 11.0: Chlorine dioxide 1.0 mg/L for 5 minutes, monochloramine 2.0 mg/L for 5 minutes.

At similar disinfect residuals and contact times, chlorine dioxide followed by monochloramine was

found to achieve the same levels of Cryptosporidium inactivation as chlorine dioxide followed by

free chlorine at pH values of 6 and 11. However, at pH 8, a higher monochloramine residual and

contact time were required to achieve inactivation levels comparable to chlorine dioxide and free

chlorine. No synergism was found for Giardia inactivation at pH 11.0 with only a minimal increase

in effectiveness at pH 8.0.

Ozone Followed by Free Chlorine

Table 9-13 and Table 9-14 show the levels of inactivation of Giardia muris and Bacillus cereus

obtained by using ozone followed by free chlorine.
9. COMBINED DISINFECTANTS

April 1999 9-21 EPA Guidance Manual

Alternative Disinfectants and Oxidants

Table 9-13. G. muris Inactivation Using Ozone Followed by Free Chlorine

Disinfectant Level of Inactivation (log-units)

pH 6.0 pH 8.0 pH 11.0

Ozone 0.5 0.8 0.4

Free chlorine 0.8 0.6 0

Ozone followed by free chlorine 2.3 2.2 0.4

Inactivation attributed to synergism 1.0 0.8 0

Source: Finch, 1997.

pH 6.0: ozone 0.1 mg/L for 60 seconds; free chlorine 2.0 mg/L for 30 minutes.

pH 8.0: ozone 0.1 mg/L for 17 seconds; free chlorine 2.0 mg/L for 60 minutes.

pH 11.0: ozone 0.1 mg/L for 5 seconds; free chlorine 2.0 mg/L for 60 minutes.

Table 9-14. B. cereus Inactivation Using Chlorine Dioxide Followed by Free

Chlorine

Disinfectant Level of Inactivation (log-units)

Chlorine dioxide 1.4

Free chlorine 2.0

Chlorine dioxide followed by free chlorine 3.4

Inactivation attributed to synergism 0

Source: Finch, 1997.

Ozone followed by free chlorine was capable of achieving approximately 2 logs of Cryptosporidium

inactivation at pH 6.0 and 8.0; however, only a 0.4 log inactivation was achieved at pH 11.0. The

difference in inactivations was primarily caused by the inability of free chlorine to inactivate

Cryptosporidium at pH 11.0. Similar to the disinfectant combination of chlorine dioxide and free

chlorine, no synergism was observed for Bacillus cereus inactivation; however, the additive effects

of ozone and free chlorine achieved greater than 3 logs of inactivation.

Ozone Followed by Monochloramine

Table 9-15 shows the results obtained for Giardia muris inactivation by ozone followed by

monochloramine.

Table 9-15. G. muris Inactivation Using Ozone Followed by Chloramine

Disinfectant Level of Inactivation (log-units)

pH 8.0 pH 11.0

Ozone 0.8 0.4

Monochloramine 0.5 0.7

Ozone followed by monochloramine 2.1 1.8

Inactivation attributed to synergism 0.8 0.7

Source: Finch, 1997.

pH 8.0: ozone 0.1 mg/L for 17 seconds; monochloramine 2.0 mg/L for 150 minutes.

pH 11.0: ozone 0.1 mg/L for 5 seconds; monochloramine 2.0 mg/L for 5 minutes.

Because of the different residuals and contact times, inactivation efficiencies of ozone followed by

chloramine and ozone followed by free chlorine could not be compared. However, for similar
9. COMBINED DISINFECTANTS

EPA Guidance Manual 9-22 April 1999

Alternative Disinfectants and Oxidants

monochloramine residuals, a very short monochloramine contact time of 5 minutes at pH 11 was

found to achieve a greater inactivation than a contact time of 150 minutes at pH 8.

Free Chlorine Followed by Monochloramine

Table 9-16 shows the results obtained for Giardia muris inactivation by free chlorine followed by

monochloramine.

Similar to the results obtained for ozone followed by monochloramine, a very short monochloramine

contact time of 5 minutes at pH 11 was found to achieve a greater inactivation than a contact time of

150 minutes at pH 8. However, free chlorine did not achieve any inactivation at pH 11.

Table 9-16. G. muris Inactivation by Free Chlorine Followed by Monochloramine

Disinfectant Level of Inactivation (log-units)

pH 8.0 pH 11.0

Free chlorine 0.6 0

Monochloramine 0.5 0.7

Free chlorine followed by monochloramine 2.4 0.7

Inactivation attributed to synergism 1.3 0

Source : Finch, 1997.

pH 8.0: free chlorine 2.0 mg/L for 60 minutes; monochloramine 2.0 mg/L for 150 minutes.

pH 11.0: free chlorine 2.0 mg/L for 60 minutes, monochloramine 2.0 mg/L for 5 minutes.

9.2.3.4 Bench-Scale Tests Using Natural Waters

In another AWWARF study, Oppenheimer (1997) is developing CT requirements for

Cryptosporidium parvum inactivation in a variety of natural waters, developing design criteria for

full-scale contacting systems from bench scale CT values, and investigating the impact of selected

variables on CT requirements. To date, samples have been collected and analyzed from 13

geographically disperse locations. Although a significant amount of data were not available, results

from the California State Water Project and Ohio River appear to show that the sequential application

of ozone and chloramines resulted in an enhanced inactivation of C. parvum as shown in Table 9-17.

The sequential application of free chlorine and monochloramine appears to enhance C. parvum

inactivation by providing some synergistic effects. To obtain the log reduction, however, very high

ozone residuals were required which appear to be impractical. In addition, bromate formation was

also a problem.

Table 9-17. C. parvum Inactivation by Sequential Application of Ozone and

Chloramine

Ozone Chlorine Chloramine

Water Source Residual

mg/L

Contact

min

Residual

mg/L

Contact

min

Residual

mg/L

Contact

min

Log Inactivation

Enhancement

California State Water Project 0.8 12 1.5 ~0 2.5 30 0.3 to > 1.4

Ohio River 4 15 1.5 120 0.5 120 0.9 to 1.4

Source: Oppenheimer, 1997.
9. COMBINED DISINFECTANTS

April 1999 9-23 EPA Guidance Manual

Alternative Disinfectants and Oxidants

9.2.4 Summary: Pathogen Inactivation with Interactive

Disinfectants

Various studies have shown the synergistic effects of interactive disinfectants: either simultaneous

application or sequential application. The improved disinfection efficiency due to interactive

disinfection is variable, ranging from negative (antagonistic) effects (in two studies) to positive

enhancement of disinfection efficiency. Many of the studies show definite improvement in

inactivation for interactive disinfectants.

Several research projects on the effects of combined disinfectants are underway at the time this

manual is being prepared. These projects should provide insight on the mechanisms and applicability

of multiple disinfectants. Based on current information, EPA believes that under appropriate

situations a positive improvement in disinfection efficiency exists. This enhanced inactivation varies

from organism to organism, and with different disinfectant combinations. For the key organisms of

interest under normal pH conditions:

• Coliform bacteria inactivation appears to increase with combined disinfectants;

• Giardia cyst inactivation appears to increase with combined disinfectants;

• Hepatitis A virus and MS-2 coliphage inactivation using combined disinfectants appears to be

less efficient than the individual disinfectants;

• Poliovirus 1 inactivation appears to increase with combined disinfectants;

• Cryptosporidium oocyst inactivation appears to increase with combined disinfectants; and

• Inactivation of spores appears neutral.

Interactive disinfection is still however considered an emerging technology. As such, CT credits for

interactive disinfectants have not yet been established.

9.3 Analytical Methods

In general, most of the analytical methods for residual disinfectants are impacted negatively by the

presence of other disinfectants. Fortunately, for most of the disinfectants and oxidants listed below, at

least one method exists that can be used successfully in the presence of other oxidizing agents. For

analytical method details, see the individual disinfectant chapters.

9.3.1 Ozone

Residual ozone analysis cannot be performed in the presence of other oxidizing agents including

chlorine, chloramine, and potassium permanganate. Typically, the ozone analytical methods exhibit

interferences from chlorine, bromine, iodine, and manganese ions. The ACVK is the least susceptible

to interference and can be used when manganese concentrations are less than 1 mg/L and free or

combined chlorine concentrations are less than 10 mg/L (Gordon et al., 1992).
9. COMBINED DISINFECTANTS

EPA Guidance Manual 9-24 April 1999

Alternative Disinfectants and Oxidants

9.3.2 Chlorine Dioxide

Some of the analytical methods for chlorine dioxide, chlorate, and chlorite cannot be performed in

the presence of oxidizing agents. Amperometric and iodometric methods cannot be used in the

presence of metal ions such as manganese. Analytical methods that can be used in the presence of

other disinfectants and oxidants include UV spectrophotometric methods and ion chromatography

(Gordon et al., 1992).

9.3.3 Potassium Permanganate

The atomic adsorption method for permanganate analysis can be performed in the presence of any of

the other disinfectants (Standard Methods, 1995).

9.3.4 Chloramine

None of the colorimetric analytical methods for chloramine can be performed in the presence of

oxidizing agents such as ozone or hydrogen peroxide. Analytical methods that can be used in the

presence of other disinfectants and oxidants include the UV spectrophotometric method and the

amperometric titration methods (Gordon et al., 1992).

9.3.5 Hydrogen Peroxide

The analytical procedures for hydrogen peroxide in drinking water are all impacted by other

oxidizing species such as ozone and chlorine (Gordon et al., 1992).

9.3.6 UV Radiation

There are no known interferences from other disinfectants with the measurement of UV radiation

(DeMers and Renner, 1992).

9.3.7 Summary of Analytical Methods

Ozone analysis in the presence of chlorine is limited. However, these disinfectants are not commonly

present simultaneously, especially with the rapid decomposition of ozone.

Hydrogen peroxide analysis is difficult in the presence of ozone and other oxidizing agents.

However, when using peroxone, the ozone residual is the analyte used to meet disinfection

requirements.

All of the other disinfectants and oxidizing agents can be selectively monitored in the presence of

other disinfectants.
9. COMBINED DISINFECTANTS

April 1999 9-25 EPA Guidance Manual

Alternative Disinfectants and Oxidants

9.4 Summary

Table 9-18 summarizes, in general, the factors and uses of combined disinfectants. Specific

considerations depend on the actual combination of disinfectants used.

Table 9-18. Summary of Combined Disinfectants

Consideration Description

Generation Generation depends on the type of chemicals used. Ozone,

chlorine dioxide, and chloramines require on-site generation.

Primary uses Two separate disinfectants can be used to provide primary

and secondary disinfection. By separating the primary and

secondary disinfection functions, the processes can be

optimized for maximum inactivation and minimum DBP

formation.

Interactive disinfection (using synergism between two

disinfectants to enhance inactivation) can serve as a primary

disinfectant.

Inactivation efficiency The use of interactive disinfection as primary disinfectant for

inactivation of Giardia, Cryptosporidium, and viruses are

feasible. Interactive disinfection is typically more effective

than the individual disinfectants.

Byproduct formation DBP formation is in general reduced by using combined

disinfectants. Specifically, continued use of chlorine in

combination with other disinfectants can reduce DBP

formation.

Limitations Data on the inactivation efficiency of combined disinfectants

are still being generated with much information coming from

controlled laboratory studies. Additional information is still

needed, specifically on full-scale implementation. Dual

(primary/secondary) disinfection for DBP control is well

established as a preferred treatment option.

Point of application Applied for primary and secondary disinfection. Ozonation

should occur after settling and prior to biofiltration.

Special considerations The efficiency and application of combined disinfectants

follow to a large extent the limitations and features of the

individual disinfectant. The combined disinfectant is often a

more effective disinfectant.
9. COMBINED DISINFECTANTS

EPA Guidance Manual 9-26 April 1999

Alternative Disinfectants and Oxidants

9.5 References

1. Alleman, J. E., et al. 1988. “Comparative evaluation of alternative halogen-based disinfection

strategies.” Conference proceedings, Industrial Waste Conference, forty-second edition.

2. Battigelli, D.A. and M.D. Sobsey. 1993. “The Inactivation of Hepatitis A Virus, Poliovirus and

Coliphage MS2 By Lime Softening and Chlorine/Monochloramine Disinfection.” Conference

proceedings, AWWA Water Quality Technology Conference.

3. Bernbaum, C.M. 1981. “Criteria for Analyzing Interactions Between Biologically Active

Agents.” Adv. Cancer Res. 35:269.

4. Bernbaum, C.M. 1985. “The expected effect of a combination of agents: the general solution.”

J. Theor. Biol. 114:413.

5. DeMers, L.D. and R.C. Renner. 1992. Alternative Disinfection Technologies for Small Drinking

Water Systems. AWWA and AWWARF, Denver, CO.

6. Finch, G.R. 1997. “Control of Cryptosporidium Through Chemical Disinfection: Current Stateof-the-Art.” AWWARF Technology Transfer Conference, Portland, Oregon.

7. Finch, G.R., E.K. Black, and L.L. Gyurek. 1994. “Ozone and Chlorine Inactivation of

Cryptosporidium.” Conference proceedings, Water Quality Technology Conference; San

Francisco, CA.

8. Gordon, G., W.J. Cooper, R.G. Rice, and G.E. Pacey. 1992. Disinfectant Residual Measurement

Methods. Second Edition, AWWARF and AWWA, Denver, CO.

9. Gyurek, L., L. Liyanage, M. Belosevic, and G. Finch. 1996. “Disinfection of Cryptosporidium

Parvum Using Single and Sequential Application of Ozone and Chlorine Species.” Conference

proceedings, AWWA Water Quality Technology Conference, Boston, MA.

10. Hubbs, S., D. Amundsen, and P. Olthius. 1981. “Use of Chlorine Dioxide, Chloramines, and

Short-Term Free Chlorination as Alternative Disinfectants.” J. AWWA. 73(2):97-101.

11. Jacangelo, J.G., N.L. Patania, K.M. Reagan, E.M. Aieta, S.W. Krasner, and M.J. McGuire. 1989.

“Impact of Ozonation on the Formation and Control of Disinfection Byproducts in Drinking

Water.” J. AWWA. 81(8):74.

12. Kouame, Y. and C.N. Haas. 1991. “Inactivation of E coli. by Combined Action of Free Chlorine

and Monochloramine.” Water Res. 25(9):1027.

13. LeLacheur, R.M., P.C. Singer, and M.J. Charles. 1991. “Disinfection Byproducts in New Jersey

Drinking Waters.” Conference proceedings, AWWA Annual Conference, Philadelphia, PA.
9. COMBINED DISINFECTANTS

April 1999 9-27 EPA Guidance Manual

Alternative Disinfectants and Oxidants

14. Liyanage, L., L. Gyurek, M. Belosevic, and G. Finch. 1996. “Effect of Chlorine Dioxide

Preconditioning on Inactivation of Cryptosporidium by Free Chlorine and Monochloramine.”

Conference proceedings, AWWA Water Quality Technology Conference, Boston, MA.

15. Logsdon, G.S., S. Foellmi, and B. Long. 1992. Filtration Pilot Plant Studies for Greater

Vancouver’s Water Supply. Conference proceedings, AWWA Annual Conference, Toronto,

Ontario.

16. Lykins, B.W., J.A. Goodrich, W.E. Koffskey, and M.H. Griese. 1991. “Controlling Disinfection

Byproducts with Alternative Disinfectants.” Conference proceedings, AWWA Annual

Conference, Philadelphia, PA.

17. Malcolm Pirnie, Inc. 1990. “Task 1.3 - Water Quality Report.” Prepared for the Public Utilities

Department, City of San Diego.

18. Malcolm Pirnie, Inc. 1989. “Water Quality Master Plan.” City of Phoenix Water and Wastewater

Department.

19. McKnight, A. and D. Reckhow. 1992. “Reactions of Ozonation Byproducts with Chlorine and

Chloramines.” Conference proceedings, AWWA Annual Conference, Vancouver, British

Columbia.

20. MWDSC AND JMM (Metropolitan Water District of Southern California and James M

Montgomery Consulting Engineers). 1989. Disinfection Byproducts in United States Drinking

Waters. Volume I. EPA and Association of Metropolitan Water Agencies. Cincinnati, OH and

Washington, D.C.

21. Oppenheimer, J.A. 1997. “Cryptosporidium Inactivation in Natural Waters.” AWWARF

Technology Transfer Conference, Portland, OR.

22. Reckhow, D., B. Legube, and P. Singer. 1986. “The Ozonation of Organic Halide Precursors:

Effect of Bicarbonate.” Water Res. 20(8):987-998.

23. Richardson, Susan D., Alfred D. Thurston, Timothy W.Collette, Kathleen Schenck Patterson,

Benjamin w. Lykins, George Majetich, and Yung Zhang. 1994. Multispecial Identification of

Chlorine Dioxide Disinfection Byproducts in Drinking Water. Environ. Sci. Technol. 28:4:592.

24. Singer, P.C. 1988. Alternative Oxidant and Disinfectant Treatment Strategies for Controlling

Trihalomethane Formation. EPA Risk Reduction Engineering Laboratory, Cincinnati OH Rept.

No. EPA/600/2-88/044.

25. Singer, P.C. 1992. Formation and Characterization of Disinfection Byproducts. Presented at the

First International Conference on the Safety of Water Disinfection: Balancing Chemical and

Microbial Risks.
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Alternative Disinfectants and Oxidants

26. Standard Methods. 1995. Standard Methods for the Examination of Water and Wastewater,

nineteenth edition. Franson, M.H., Eaton, A.D., Clesceri, L.S., and Greenberg, A.E., (editors),

American Public Health Association, AWWA, and Water Environment Federation, Washington

D.C..

27. Straub, T. M., et al. 1994. “Synergistic Inactivation of Escherichia coli and MS-2 Coliphage by

Chloramine and Cupric Chloride.” Conference proceedings, AWWA Water Quality Technology

Conference, San Francisco, CA.

28. USEPA (U.S. Environmental Protection Agency). 1992. Technologies and Costs for Control of

Disinfection Byproducts. Prepared by Malcolm Pirnie, Inc. for the Office of Ground Water and

Drinking Water, Report No. PB93-162998.

29. Worley, S.D. and D.E. Williams. 1988. “Disinfecting Water with a Mixture of Free Chlorine and

Organic B-halamine.” J. AWWA. 80(1):6
9. COMBINED DISINFECTANTS

April 1999 9-29 EPA Guidance Manual

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9. COMBINED DISINFECTANTS............................................................................................................... 9-1

9.1 PRIMARY AND SECONDARY DISINFECTANTS .......................................................................................... 9-1

9.1.1 DBP Formation with Various Primary and Secondary Disinfectant Combinations ......................... 9-3

9.1.2 Impact of Modifying Disinfection Practices .................................................................................. 9-6

9.1.3 Chlorine/Chlorine to Chlorine/Chloramine.................................................................................... 9-8

9.1.4 Chlorine/Chlorine to Ozone/Chlorine............................................................................................ 9-8

9.1.5 Chlorine/Chlorine to Ozone/Chloramine ....................................................................................... 9-9

9.1.6 Chlorine/Chlorine to Chlorine Dioxide/Chlorine ........................................................................... 9-9

9.1.7 Chlorine/Chlorine to Chlorine Dioxide/Chlorine Dioxide ............................................................ 9-10

9.1.8 Chlorine/Chloramine to Ozone/Chloramine ................................................................................ 9-10

9.1.9 Chlorine/Chloramine to Chlorine Dioxide/Chloramine................................................................ 9-10

9.1.10 Ozone/Chlorine to Ozone/Chloramine ........................................................................................ 9-11

9.1.11 Summary.................................................................................................................................... 9-11

9.2 PATHOGEN INACTIVATION WITH INTERACTIVE DISINFECTANTS............................................................ 9-11

9.2.1 Inactivation Mechanism.............................................................................................................. 9-12

9.2.2 Environmental Effects................................................................................................................ 9-13

9.2.3 Pathogen Inactivation Efficiency Using Interactive Disinfectants ................................................ 9-16

9.2.4 Summary: Pathogen Inactivation with Interactive Disinfectants.................................................. 9-23

9.3 ANALYTICAL METHODS...................................................................................................................... 9-23

9.3.1 Ozone ........................................................................................................................................ 9-23

9.3.2 Chlorine Dioxide........................................................................................................................ 9-24

9.3.3 Potassium Permanganate ............................................................................................................ 9-24

9.3.4 Chloramine ................................................................................................................................ 9-24

9.3.5 Hydrogen Peroxide..................................................................................................................... 9-24

9.3.6 UV Radiation ............................................................................................................................. 9-24

9.3.7 Summary of Analytical Methods................................................................................................. 9-24

9.4 SUMMARY.......................................................................................................................................... 9-25

9.5 REFERENCES ...................................................................................................................................... 9-26

Table 9-1. Potential Primary Disinfectants.......................................................................................................... 9-2

Table 9-2. Primary/Secondary Disinfectant Combinations and Typical Applications in Water Treatment............. 9-3

Table 9-3. DBPs Associated with Various Combined Oxidation/Disinfection Processes ...................................... 9-4

Table 9-4. Strategies for Primary and Secondary Disinfectants............................................................................. 9-6

Table 9-5. Impacts of Disinfection Practice on DBP Formation........................................................................... 9-7

Table 9-6. Virus Inactivation By Individual Disinfectants and Simultaneous Chloramination............................. 9-17

Table 9-7. C. parvum Inactivation Using Ozone Followed by Chlorine Dioxide ................................................ 9-19

Table 9-8. C. parvum Inactivation Using Chlorine Dioxide Followed by Free Chlorine ..................................... 9-19

Table 9-9. G. muris Inactivation Using Chlorine Dioxide Followed by Free Chlorine ........................................ 9-19

Table 9-10. B. cereus Inactivation Using Chlorine Dioxide Followed by Free Chlorine ..................................... 9-19

Table 9-11. C. parvum Inactivation Using Chlorine Dioxide Followed by Chloramine ...................................... 9-20

Table 9-12. G. muris Inactivation Using Chlorine Dioxide Followed by Chloramine ......................................... 9-20

Table 9-13. G. muris Inactivation Using Ozone Followed by Free Chlorine....................................................... 9-21

Table 9-14. B. cereus Inactivation Using Chlorine Dioxide Followed by Free Chlorine ..................................... 9-21

Table 9-15. G. muris Inactivation Using Ozone Followed by Chloramine.......................................................... 9-21

Table 9-16. G. muris Inactivation by Free Chlorine Followed by Monochloramine............................................ 9-22

Table 9-17. C. parvum Inactivation by Sequential Application of Ozone and Chloramine .................................. 9-22

Table 9-18. Summary of Combined Disinfectants............................................................................................. 9-25

Figure 9-1. Inactivation of C. parvum Attributed to Synergistic Effects. Application of Ozone Followed by

Chlorine Dioxide ....................................................................................................................................... 9-14
9. COMBINED DISINFECTANTS

EPA Guidance Manual 9-30 April 1999

Alternative Disinfectants and Oxidants

Figure 9-2. Inactivation of C. parvum Attributed to Synergistic Effects. Application of Chlorine Dioxide Followed

by Free Chlorine........................................................................................................................................ 9-14

Figure 9-3. Inactivation of C. parvum Attributed to Synergistic Effects. Application of Chlorine Dioxide Followed

by Monochloramine................................................................................................................................... 9-15

Figure 9-4. Inactivation of E. coli Using Free Chlorine and Monochloramine .................................................... 9-18
April 1999 A-1 EPA Guidance Manual

Alternative Disinfectants and Oxidants

APPENDIX A - SUMMARY OF DISINFECTANT

USAGE IN THE UNITED STATES

Two sources of information were consulted regarding disinfectant usage in the United States:

• The Community Water Systems Survey (USEPA, 1997); and

• The Information Collection Rule (ICR) database on water utilities (presently under

development).

A.1 Community Water Systems Survey

Most water treatment plants disinfect water prior to distribution. The 1995 Community Water

Systems Survey (USEPA 1997a) reports that 81 percent of all community water systems provide

some form of treatment on all or a portion of their water sources (Table A-1). The survey found

that 99 percent of the surface water systems provide some treatment of their water. Of those

systems reporting no treatment, 80 percent rely on ground water as their only water source.

Table A-1. Disinfection Practices of Water Systems with Treatment

Treatment Service Population

<100 101-500 501-1,000 1,001-

3,300

3,301-

10,000

10,001-

50,000

50,001-

100,000

Over

100,001

Total

Surface Water Systems

Pre-Disinfection, Oxidation/Softening

Chlorine 59.0% 73.9% 67.3% 66.3% 68.8% 58.6% 47.5% 57.1% 63.8%

Chlorine Dioxide 0.0% 0.0% 0.0% 5.0% 4.7% 13.2% 14.2% 7.8% 6.3%

Chloramines 4.6% 0.0% 1.1% 2.1% 0.0% 2.2% 15.5% 10.8% 3.1%

Ozone 0.0% 0.0% 0.0% 0.0% 0.3% 0.0% 5.4% 5.8% 0.9%

KMnO4 0.0% 4.9% 9.6% 9.9% 15.2% 28.3% 25.9% 28.5% 16.0%

Predisinfection/oxidation 0.0% 0.0% 2.0% 2.9% 0.6% 9.2% 5.1% 4.3% 3.5%

Lime/Soda ash softening 6.8% 9.8% 20.9% 16.2% 14.3% 11.7% 3.5% 5.9% 12.5%

Recarbonation 0.0% 0.0% 0.0% 0.0% 2.1% 4.7% 0.6 % 6.3% 1.9%

Post-Disinfection

Chlorine 49.7% 51.6% 80.6% 62.8% 77.9% 71.1% 73.8% 63.6% 67.5%

Chlorine Dioxide 0.0% 0.0% 0.0% 0.0% 0.3% 4.9% 5.9% 11.2% 1.6%

Chloramines 0.0% 0.0% 0.0% 2.9% 2.1% 15.6% 29.4% 24.2% 8.1%

Postdisinfection combine 0.0% 0.0% 0.0% 2.1% 4.0% 3.9% 1.9% 1.6% 3.0%

Fluoridation 0.0% 4.9% 13.9% 32.4% 42.6% 48.8% 49.9% 63.6% 35.5%

Ground Water Systems

Pre-Disinfection, Oxidation/Softening

Chlorine 64.2% 69.9% 56.7% 73.2% 60.6% 57.4% 36.2% 38.1% 63.9%

Chlorine Dioxide 1.3% 0.0% 0.0% 0.0% 0.0% 0.0% 3.1% 0.0% 0.3%

Chloramines 0.0% 0.0% 0.0% 0.0% 0.0% 0.6% 1.4% 0.7% 0.1%

Ozone 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.6% 0.0%

KMnO4 0.0% 0.9% 2.2% 0.6% 5.8% 3.2% 7.0% 0.0% 1.8%

Predisinfection/oxidation 0.3% 0.5% 0.0% 0.7% 1.0% 2.6% 0.0% 0.0% 0.7%

Lime/Soda ash softening 2.9% 2.9% 2.2% 3.6% 3.5% 3.8% 5.0% 9.1% 3.2%

Recarbonation 0.0% 0.5% 0.0% 0.6% 1.4% 1.5% 2.8% 1.1% 0.6%

Post-Disinfection

Chlorine 23.0% 23.4% 32.5% 28.3% 42.5% 41.9% 54.5% 65.8% 31.0%

Chlorine Dioxide 0.0% 1.0% 0.0% 0.0% 0.0% 0.6% 0.0% 0.0% 0.4%

Chloramines 0.0% 0.0% 0.0% 0.0% 0.1% 1.1% 3.9% 4.3% 0.3%

Postdisinfection combine 0.0% 0.0% 0.0% 0.0% 0.1% 0.1% 0.0% 0.0% 0.0%

Fluoridation 2.4% 6.3% 13.2% 12.4% 45.3% 31.2% 34.3% 52.5% 16.0%

Source: 1995 Community Water Systems survey (USEPA, 1997a)
APPENDIX A – SUMMARY OF DISINFECTANT USAGE IN THE U.S.

EPA Guidance Manual A-2 April 1999

Alternative Disinfectants and Oxidants

A.2 Information Collection Rule Database

The ICR database contains information from 527 community water systems. Some of these

systems are owned by the same utility, representing different treatment plants within the same

organization. The following tables summarize the ICR data regarding disinfectant database entries.

Note that the information about disinfectant includes usage of the disinfectant at the given utility.

In some cases, the utility may use more than one disinfectant. Therefore, the 527 systems reported

use of 740 different disinfectants. Three systems reported using 3 different chemical disinfectants -

for different purposes or during different times of the year. The tables show a breakdown of the

disinfectant usage at these facilities. Capacities are shown in terms of flow. Population served

data are not recorded.

The tables are as follows:

• Table A-2 shows the breakdown of systems based on water source (i.e., surface or ground

water).

• Table A-3 to Table A-5 shows the disinfectant usage at water plants by flow categories for all

water sources, surface water sources, and ground water sources, respectively. The tables show

the percentage of facilities that are using the particular disinfectant. Because some facilities

use more than one disinfectant, the total usage exceeds 100 percent. For example, for facilities

in the range 51-100 mgd, the total disinfectant usage is 155 percent. This means that 155 types

of disinfection systems are used at 100 plants.

• Table A-6 through Table A-8 shows the disinfectant usage in number of applications in water

plants by flow categories for all water sources, surface water sources, and ground water

sources, respectively. These tables show the actual numbers used in calculating the

percentages in Table A-3 to Table A-5.

• Table A-9 through Table A-11 show the number of systems using two or more disinfectants for

all water sources, surface water sources, and ground water sources, respectively. The database

does not separate usage as primary or secondary disinfectant.

Table A-2. Breakdown of systems in Survey based on Water Source

Systems GW SW GW/SW Unknown Total

Number 135 390 2 2 529

Percentage 26% 74% 0% 0% 100%

GW = Ground Water; SW = Surface Water; GW/SW = Choice of Ground or Surface Water Source.
APPENDIX A – SUMMARY OF DISINFECTANT USAGE IN THE U.S.

April 1999 A-3 EPA Guidance Manual

Alternative Disinfectants and Oxidants

Table A-3. Disinfectant usage as a function of flow for all Water Sources.

Numbers show the percentage of systems using a particular disinfectant

Flow, mgd Cl2 NaOCl NH2Cl2 O3 ClO2 Total use

0-5 69% 19% 19% 0% 0% 106%

6-10 90% 10% 10% 0% 0% 110%

11-50 93% 6% 30% 5% 9% 143%

51-100 95% 5% 41% 5% 9% 155%

>100 98% 5% 43% 5% 3% 154%

Unknown 77% 13% 8% 0% 0% 98%

Percentage* 92% 7% 31% 4% 6% 140%

Percentage calculated as a fraction of 527 - the total number of systems. 740 different disinfectants

are used by the 527 systems.

Table A-4. Disinfectant usage as a function of flow for Surface Water Sources.

Numbers show the percentage of systems using a particular disinfectant

Flow, mgd Cl2 NaOCl NH2Cl O3 ClO2 Total use

0-5 89% 11% 0% 0% 0% 100%

6-10 85% 8% 8% 0% 0% 100%

11-50 93% 5% 32% 5% 12% 148%

51-100 96% 4% 42% 6% 11% 158%

>100 96% 6% 46% 6% 4% 158%

Unknown 88% 13% 50% 0% 0% 150%

Percentage* 94% 5% 37% 5% 9% 150%

Percentage calculated as a fraction of 527 - the total number of systems. 576 different disinfectants

are used by the 383 systems.

Table A-5. Disinfectant usage as a function of flow for Ground Water Sources.

Numbers show the percentage of systems using a particular disinfectant

Flow, mgd Cl2 NaOCl NH2Cl O3 ClO2 Total use

0-5 43% 29% 43% 0% 0% 114%

6-10 94% 13% 13% 0% 0% 119%

11-50 92% 6% 24% 2% 2% 125%

51-100 88% 13% 38% 0% 0% 138%

>100 108% 0% 25% 0% 0% 133%

Unknown 79% 14% 0% 0% 0% 93%

Percentage* 87% 10% 18% 1% 1% 117%

Percentage calculated as a fraction of 527 - the total number of systems. 168 different disinfectants

are used by the 144 systems.
APPENDIX A – SUMMARY OF DISINFECTANT USAGE IN THE U.S.

EPA Guidance Manual A-4 April 1999

Alternative Disinfectants and Oxidants

Table A-6. Disinfectant usage as a function of flow for all Water Sources

Flow, mgd Cl2 NaOCl NH2Cl O3 ClO2 Total use Total

plants

0-5 11 3 3 0 0 17 16

6-10 26 3 3 0 0 32 29

11-50 200 12 65 10 20 307 215

51-100 113 6 49 6 11 185 119

>100 94 5 41 5 3 148 96

Unknown 40 7 4 0 0 51 52

Total 484 36 165 21 34 740 527

Percentage* 92% 7% 31% 4% 6% 140%

* Percentage calculated as a fraction of 527 - the total number of systems. 740 different

disinfectants are used by the 527 systems.

Table A-7. Disinfectant usage as a function of flow for Surface Water Sources

Flow, mgd Cl2 NaOCl NH2Cl O3 ClO2 Total use Total

plants

0-5 8 1 0 0 0 9 9

6-10 11 1 1 0 0 13 13

11-50 154 9 53 9 20 245 165

51-100 99 4 43 6 11 163 103

>100 82 5 39 5 3 134 85

Unknown 7 1 4 0 0 12 8

Total 361 21 140 20 34 576 383

Percentage* 94% 5% 37% 5% 9% 150

* Percentage calculated as a fraction of 383 - the total number of plants. 576 different disinfectants

are used by the 383 systems.

Table A-8. Disinfectant usage as a function of flow for Ground Water Sources

Flow, mgd Cl2 NaOCl NH2Cl O3 ClO2 Total use Total

plants

0-5 3 2 3 0 0 8 7

6-10 15 2 2 0 0 19 16

11-50 47 3 12 1 1 64 51

51-100 14 2 6 0 0 22 16

>100 13 0 3 0 0 16 12

Unknown 33 6 0 0 0 39 42

Total 125 15 26 1 1 168 144

Percentage* 87% 10% 18% 1% 1% 117%

* Percentage calculated as a fraction of 144 - the total number of systems. 168 different

disinfectants are used by the 144 systems.
APPENDIX A – SUMMARY OF DISINFECTANT USAGE IN THE U.S.

April 1999 A-5 EPA Guidance Manual

Alternative Disinfectants and Oxidants

Table A-9. Number Water Systems (Ground and Surface Water Sources)

using Two Different Disinfectants

Cl2 NaOCl NH2Cl O3 ClO2

Cl2 --- 8 150 17 32

NaOCl --- --- 8 3 0

NH2Cl --- --- --- 12 18

O3 --- --- --- --- 1

ClO2 --- --- --- --- ---

Table A-10. Number Surface Water Systems using Two Different Disinfectants

Cl2 NaOCl NH2Cl O3 ClO2

Cl2 --- 7 129 16 31

NaOCl --- --- 7 7 3

NH2Cl --- --- --- 11 18

O3 --- --- --- --- 1

ClO2 --- --- --- --- ---

Table A-11. Number Ground Water Systems using Two Different Disinfectants

Cl2 NaOCl NH2Cl O3 ClO2

Cl2 --- 1 21 1 0

NaOCl --- --- 1 0 0

NH2Cl --- --- --- 1 0

O3 --- --- --- --- 0

ClO2 --- --- --- --- ---
APPENDIX A – SUMMARY OF DISINFECTANT USAGE IN THE U.S.

EPA Guidance Manual A-6 April 1999

Alternative Disinfectants and Oxidants

THIS PAGE INTENTIONALLY LEFT BLANK
April 1999 B-1 EPA Guidance Manual

Alternative Disinfectants and Oxidants

Appendix B – Selected Costs of

Alternative Disinfection Systems

B.1 Technologies and Costs for Control of

Disinfection By-Products

Costs were developed for modifying a “base” or “typical” treatment plant to add disinfection and other

technologies. The base plant is described as a conventional treatment plant using chlorine/chlorine

disinfection consisting of rapid mixing, flocculation, sedimentation, chlorination, filtration, contact

basin, chemical feed systems and finished water storage. This appendix contains figures and tables

from Technologies and Costs for Control of Disinfection By-Products (USEPA, 1998), retaining the

report’s original figure and table numbers. Incremental costs are shown, determined by calculating the

cost for the modified treatment plant and subtracting the base treatment plant cost.

The base treatment plant shown in Figure 7-1, is a basic alum coagulation and filtration plant, with

chlorine disinfection. This plant was modified to meet disinfection requirements. The bases for the

cost estimates are shown in Tables 7-3, 7-4, 7-5, and 7-6. The 12 flow categories for which the costs

were determined are shown in Table 7-2.

Schematics and costs to add the following schemes are shown in the attached figures and tables.

• Base treatment plant - Figure 7-1 and Table 7-7.

• Move point of chlorination. This modification assumes no cost for moving the chlorine addition

point, but costs for an added contact basin are shown in Table 7-8.

• Change to Chlorine/Chloramine - Figure 7-2 and Table 7-9.

• Change to Ozone/Chloramine - Figure 7-3 and Table 7-12.

• Change to Chlorine Dioxide – Table 7-13.

See USEPA, 1998 for more details and information upon the costs of other technologies.
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-2 April 1999

Alternative Disinfectants and Oxidants

FIGURE 7-1. ALUM COAGULATION / FILTRATION BASE PLANT

TABLE 7-2. EPA FLOW CATEGORIES

EPA FLOW

CATEGORIES POPULATION

AVERAGE FLOW

mgd) CAPACITY

mgd)

1 0.0056

2 0.024

3 0.086

4 0.23

LARGE SYSTEMS - DESIGN FLOW > 1 MGD

 5,500 1.8

 15,000 4.8

 35,000 11

 60,000 18

 88,000 26

 175,000 51

 73 120

12 270

12a 350
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-3 EPA Guidance Manual

Alternative Disinfectants and

TABLE 7-3. SMALL SYSTEMS BASIS FOR COST ESTIMATES FOR DBP CONTROL

Process

WATER Model

Assumptions

Engineering

Assumption

Package Raw Water

Pumping

Premanufactured packaged pumping station using submersible pump contained in a

20 ft deep steel pump sump.

Manifold piping, sump intake valve, pump check valves, and electrical controls.

Total dynamic head is 50 ft.

Pump and motor efficiencies are 80 and 90%, respectively.

Package Complete

Treatment Plant

Coagulation, flocculation, sedimentation, and filtration equipment provided including

tube settlers rated at 1,500 gpd/sf, mixed media filters with application rates of 2 to 5

gpm/sf and media depth of 30 in.

Chemical feed facilities include storage tanks and feed pumps.

Filter backwash pumps and, where applicable, surface wash water pumps.

Flow measurement and control devices, pneumatic air supply (for 200 gpm or larger

plants), effluent pumps, and building.

Hypochlorite Solution Solution tanks, mixers, and metering pumps Sodium hypochlorite dose of 2.4

mg/L determined by WTP model.

Chlorination System Metering pumps, PVC pipes, valves and controls are included.

Sodium Hydroxide Feed

System

Storage tanks, heater, manual transfer pump, mixers, feed tanks and metering pumps

are included.

PVC pipes, valves and control are also included.

Alum Feed System Solution tanks, mixers, and calibrated metering pumps are included.

PVC pipes, valves and controls are also included.

Alum dose is determined by DBP

control alternatives.
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-4 April 1999

Alternative Disinfectants and Oxidants

TABLE 7-3. SMALL SYSTEMS BASIS FOR COST ESTIMATES FOR DBP CONTROL

Process

WATER Model

Assumptions

Engineering

Assumption

Package High Service

Pump Station

Includes 2 or 3 centrifugal pumps, pressure sensing, flow control valves,

instrumentation and equipment.

Pumps provide a maximum output of 70 psi.

Clearwell Storage Above

Ground

Above ground, steel tanks including instrumentation and control of clearwell water

level and instrumentation for turbidity and residual monitoring is provided.

Clearwell size is based on storage of

25% of the daily operating flow.

Sludge Dewatering

Lagoons

Unlined lagoon and inlet, outlet structures are provided.

2 ft freeboard, 3:1 side slopes, 5 ft depth are also provided.

Sizing of lagoons is based on solids

content of 5%.

Sludge is thickened to a solids

concentration of 30%.

Dewatered Sludge

Hauling

Loading facilities including sludge conveyer, hopper, and hopper enclosure are

provided.

Length of haul is 20 miles one-way.

Contact Basin Below ground tanks without

repumping are assumed.

Size of basin is 60 minutes, as

determined by the WTP model.

The well baffled tanks are assumed

to provide actual contact time of 0.7

times the theoretical according to the

SWTR Guidance Manual.

O&M costs were unpredictable and

were assumed to be negligible.
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-5 EPA Guidance Manual

Alternative Disinfectants and

TABLE 7-4. LARGE SYSTEMS BASIS FOR COST ESTIMATES FOR DBP CONTROL

Process

WATER Model

Assumptions

Engineering

Assumption

Raw Water

Pumping

Total dynamic head 100 ft

Manifold piping velocity

Standby pump, manifold piping, and instrumentation are provided

Alum Feed

System

Diaphragm metering pumps, steel storage hoppers with dust collector, and mechanical weight

belt feeders

Commercial alum density 60 lb/cu ft

Dissolving tank detention time 5 min with 2 gal of water per lb of dry alum added

Maximum hopper volume 6,000 cu ft with fifteen days of storage

Alum dose is determined by

DBP control alternatives

Rapid Mix Vertical shaft, variable speed turbine mixers with stainless steel shafts and paddles and TEFC

motors

Maximum basin capacity 2,500 cu ft

Water temperature 15" C

Overall mechanism efficiency 70%

G = 900/sec

Detention time is 1 min at

design flow

Flocculation

(Horizontal

Paddle)

Rectangular-shaped, reinforced concrete basins with 12 ft depth, 4:1 length to width ratio, and

12,500 cu ft individual maximum basin size

Variable speed drive units requiring 15 min/day routine O&M and an oil change every 6 months

requiring 4 hrs of labor

Overall mechanism efficiency 60%

G = 50/sec

Detention time is 30 min at

design flow

Rectangular

Clarifiers

Chain and flight collector with drive mechanism, sludge pumps, reinforced concrete structure,

and withdraw pumps are included

Overflow rate = 1,000 gpd/sq ft
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-6 April 1999

Alternative Disinfectants and Oxidants

TABLE 7-4. LARGE SYSTEMS BASIS FOR COST ESTIMATES FOR DBP CONTROL

Process

WATER Model

Assumptions

Engineering

Assumption

Side wall depth = 12 ft Maximum number of units is 2

Maximum basin area = 20,000

sq ft

Gravity Filtration

Systems

Filter structure, underdrains, wash water troughs, pipe gallery piping and valves,

instrumentation, control panel, and filter housing are provided

Filter box depth = 16 ft

Maximum filter size = 1,275 sq ft

Minimum 4 filters per plant

Filter loading rate = 4 gpm/sq ft

Filtration Dual

Media

20 in of 1.0 to 1.2 mm effective size anthracite coal (UC = 1.7)

10 in of 0.42 to 0.52 mm effective size silica sand (UC = 1.6)

12 in underdrains. Media consisting of 4 sizes of silica gravel

Backwash

Pumping

Facilities

All required pumps and motors, flow control, sequencing control, valves and backwash headers

are included

Pumping head = 50 ft

Overall mechanism efficiency 70%

Backwash rate = 18 gpm/sq ft

One filter is backwashed at a

time with each filter backwashed

approximately every two days

Wash Water

Surge Basins

Below ground, reinforced concrete basins and level control instrumentation provided Sized to store a 20 min volume

of backwash water at design

flow

Unthickened

Sludge Pumping

Variable speed, centrifugal pumps, piping and valves, electrical equipment housing, dry well,

and a wet well are included

Pipe velocity = 5 ft/sec

Total dynamic head = 30 ft

Unthickened sludge solids

concentration = 1%

12 hr/day of sludge pumping
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-7 EPA Guidance Manual

Alternative Disinfectants and

TABLE 7-4. LARGE SYSTEMS BASIS FOR COST ESTIMATES FOR DBP CONTROL

Process

WATER Model

Assumptions

Engineering

Assumption

Overall pump-motor efficiency = 65%

Sludge

Dewatering

Lagoons

Unlined lagoon and inlet and outlet structures are provided

2 ft freeboard, 3:1 side slopes, and 10 ft depth are also provided

Solids production is determined

by WTP model

Sludge is thickened to a solids

concentration of 30%

Sizing of lagoons is based on a

solids content of 5%

Dewatered Sludge

Hauling

Loading facilities including sludge conveyor, hopper, and hopper enclosure are provided

Length of haul is 20 miles one-way

Dewatered sludge has a solids

content of 30%

In-plant Pumping Constant speed, vertical turbine pumps, pump motor, wet well, and piping and valves are

included

Pipe velocity = 5 ft/sec

Total dynamic head = 50 ft

Chlorine Feed

Facilities

Chlorinator, standby chlorinator, cylinder scales, evaporators, residual analyzers with flow

proportioning device injector pumps, and housing to include 30 days of cylinder storage are

provided

Injector pumps deliver water at 25 psi to allow production of 3,500 mg/L solution

Chlorine dose is 2.4 mg/L as

determined by WTP model

Sodium

Hydroxide Feed

System

Storage tanks, heater, manual transfer pump mixers, feed tanks and metering pumps are

included

PVC pipes, valves and controls are also included

Sodium hydroxide dose is 16

mg/L as determined by WTP

model

Finished Water

Pumping

Vertical turbine pumps powered by constant speed motors, electrical equipment instrumentation,

valves, and manifolds are provided

Total dynamic head is 300 ft
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-8 April 1999

Alternative Disinfectants and Oxidants

TABLE 7-4. LARGE SYSTEMS BASIS FOR COST ESTIMATES FOR DBP CONTROL

Process

WATER Model

Assumptions

Engineering

Assumption

Standby pump is also included
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-9 EPA Guidance Manual

Alternative Disinfectants and

TABLE 7-5. COST ALLOWANCE FACTORS

Item

Small Systems

Water Model (%)

Large Systems

WATERCO$T Model(%)

Site work and Interface

Piping

Subsurface Considerations

Standby Power

General Contractors

Overhead and Profit

10

10

5

12

15

10

5

12

Engineering

Legal, Fiscal and

Administration fees

15(1)

5 to 6(1)

15(2)

9 to 11(2)

Notes:

(1)Percentages added to estimated construction cost plus estimated cost for other

allowances factors.

(2)Percentages added to estimated construction cost only.

TABLE 7-6. INDICES USED IN THE ESCALATION OF COSTS

DESCRIPTION INDEX

REFERENCE

NUMERICAL

VALUE

ESCALATION

VALUE

Building Cost Index ENR 1

3391.86 1.23

Chemical & Allied Products BLS 2

147.2 1.19

Skilled Labor ENR 1

5231.35 1.178

Materials ENR 1

2268.57 1.328

Utility Natural Gas BLS 055 2

111.3 1.679

1

 Engineering News Record (July, 1997)

2

 Bureau of Labor Statistics (March, 1997)
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-10 April 1999

Alternative Disinfectants and Oxidants

TABLE 7-7. ESTIMATED BASE PLANT COSTS

SMALL SYSTEMS

Design

Flow

(mgd)

Capital

Cost1

($M)

O & M

Cost2

(4/1000 gal)

Total

Cost @ 3%

(4/1000 gal)

Total

Cost @ 7%

(4/1000 gal)

Total

Cost @ 10%

(4/1000 gal)

0.024 0.63 600 2672 3509 4233

0.087 0.86 188 848 1115 1343

0.27 1.4 90 390 496 605

0.65 2.0 56 216 277 330

LARGE SYSTEMS

Design

Flow

(mgd)

Capital

Cost1

($M)

O & M

Cost2

(4/1000 gal)

Total

Cost @ 3%

(4/1000 gal)

Total

Cost @ 7%

(4/1000 gal)

Total

Cost @ 10%

(4/1000 gal)

1.8 4.3 74 187 233 272

4.8 7.3 47 111 137 159

11 12 39 83 102 118

18 17 36 72 86 98

26 22 35 66 78 89

51 36 33 58 68 76

210 120 32 50 58 65

430 230 31 47 53 59

520 380 26 46 54 61

1 1991 Cost escalated based upon a factor of 1.23 derived from the ENR BCI

2

 1991 Cost escalated based upon a factor of 1.19 derived from the BLS Chemical and

 Allied Products Index
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-11 EPA Guidance Manual

Alternative Disinfectants and

TABLE 7-8. ESTIMATED UPGRADE COSTS FOR ADDITIONAL CONTACT

BASIN SIZE (x $1000) 1

Chlorine Contact Basin Time

DESIGN

FLOW 30 min 60 min 120 min 180 min 240 min 300 min 360 min

0.024 14 21 26 28 38 46 55

0.087 25 34 66 76 82 84 100

0.27 52 80 103 140 180 220 234

0.65 77 112 218 251 284 317 351

1.8 197 244 335 427 519 611 702

4.8 274 396 642 887 1,132 1,376 1622

11 432 713 1,274 1,836 2,399 2,961 3521

18 611 1,070 1,990 2,909 3,828 4,748 5667

26 815 1,478 2,807 4,135 5,462 6,791 8118

51 1,454 2,755 5,360 7,965 10,569 13,175 15,778

210 5514 10,876 21,600 32,324 43,050 53,774 64,499

430 11,132 22,112 44,071 66,031 87,991 109,951 131,910

520 13,374 26,639 53,224 79,785 106,352 132,193 159,456

1 1991 Cost escalated based upon a factor of 1.23 derived from the ENR BCI
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-12 April 1999

Alternative Disinfectants and Oxidants

FIGURE 7-2. ALUM COAGULATION / FILTRATION SYSTEM UPGRADED WITH

CHLORINE / CHLORAMINE DISINFECTION

TABLE 7-9. ESTIMATED UPGRADE COSTS FOR CHLORAMINES AS SECONDARY

DISINFECTANT

SMALL SYSTEMS

Design

Flow

(mgd)

Capital

Cost1

($M)

O & M

Cost2

(4/1000 gal)

Total

Cost @ 3%

(4/1000 gal)

Total

Cost @ 7%

(4/1000 gal)

Total

Cost @ 10%

(4/1000 gal)

0.024 0.011 21 57 71 83

0.087 0.012 5.5 15 19 22

0.27 0.015 1.9 5.1 6.3 7.4

0.65 0.016 0.98 2.3 2.8 3.2

LARGE SYSTEMS

Design

Flow

(mgd)

Capital

Cost1

($M)

O & M

Cost2

(4/1000 gal)

Total

Cost @ 3%

(4/1000 gal)

Total

Cost @ 7%

(4/1000 gal)

Total

Cost @ 10%

(4/1000 gal)

1.8 0.04 1.4 2.5 3.0 3.4

4.8 0.07 0.70 1.3 1.5 1.8

11 0.11 0.49 0.9 1.1 1.2

18 0.16 0.40 0.73 0.87 0.99

26 0.21 0.37 0.67 0.79 0.89

51 0.28 0.33 0.52 0.60 0.67

210 0.47 0.29 0.36 0.39 0.41

430 0.85 0.26 0.32 0.34 0.36

520 0.91 0.20 0.25 0.27 0.28

1 1991 Cost escalated based upon a factor of 1.23 derived from the ENR BCI

2

 1991 Cost escalated based upon a factor of 1.19 derived from the BLS Chemical and

 Allied Products Index
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-13 EPA Guidance Manual

Alternative Disinfectants and

FIGURE 7-3. ALUM COAGULATION / FILTRATION SYSTEMS UPGRADED WITH

OZONE / CHLORAMINE DISINFECTION
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-14 March 1999

Alternative Disinfectants and Oxidants

TABLE 7- 12. ESTIMATED INSTALLATION AND UPGRADE COSTS FOR OZONE AS PRIMARY DISINFECTANT -

SMALL SYSTEMS

Design Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Flow

(mgd) Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000 gal)

Total

Upgrade

Cost @ 3%

(4/1000 gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000 gal)

Total

Upgrade

Cost @ 3%

(4/1000 gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000 gal)

Total

Upgrade

Cost @ 3%

(4/1000 gal)

0.024 0.22 161 885 0.23 322 1078 0.24 644 1433

0.086 0.24 38 222 0.28 75 290 0.30 150 380

0.27 0.29 10 72 0.40 21 107 0.47 42 143

0.65 0.39 3.9 35 0.64 7.8 59 0.80 16 80

Design Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Flow

(mgd) Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000 gal)

Total

Upgrade

Cost @

7%

(4/1000

gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000

gal)

Total

Upgrade

Cost @

7%

(4/1000

gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000

gal)

Total

Upgrade

Cost @

7%

(4/1000

gal)

0.024 0.22 161 1177 0.23 322 1384 0.24 644 1752

0.086 0.24 38 297 0.28 75 377 0.30 150 473

0.27 0.29 10 97 0.40 21 145 0.47 42 183

0.65 0.39 3.9 48 0.64 7.8 81 0.80 16 106
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-15 EPA Guidance Manual

Alternative Disinfectants and Oxidants

TABLE 7- 12 (cont)

ESTIMATED INSTALLATION AND UPGRADE COSTS FOR OZONE AS PRIMARY DISINFECTANT - SMALL

SYSTEMS

Design Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Flow

(mgd) Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000 gal)

Total

Upgrade

Cost @

10%

(4/1000

gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000

gal)

Total

Upgrade

Cost @

10%

(4/1000

gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000

gal)

Total

Upgrade

Cost @

10%

(4/1000

gal)

0.024 0.22 161 1442 0.23 322 1661 0.24 644 2023

0.086 0.24 38 361 0.28 75 445 0.30 150 551

0.27 0.29 10 119 0.40 21 170 0.47 42 217

0.65 0.39 3.9 59 0.64 7.8 98 0.80 16 128
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-16 April 1999

Alternative Disinfectants and Oxidants

TABLE 7- 12 (cont.)

ESTIMATED INSTALLATION AND UPGRADE COSTS FOR OZONE AS PRIMARY DISINFECTANT -

LARGE SYSTEMS

Design Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Flow

(mgd) Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000 gal)

Total

Upgrade

Cost @3%

(4/1000

gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000

gal)

Total

Upgrade

Cost @

3%

(4/1000

gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000

gal)

Total

Upgrade

Cost @

3%

(4/1000

gal)

1.8 0.89 1.8 25 1.5 4.4 44 1.4 6.3 43

4.8 1.5 1.8 15 1.9 4.4 21 2.0 6.3 24

11 1.9 1.8 9.0 2.6 4.4 14 2.8 6.3 17

18 2.4 1.8 7.0 3.0 4.4 11 3.7 6.3 14

26 2.6 1.8 5.5 3.9 4.4 9.9 4.8 6.3 13

51 3.8 1.8 4.4 6.2 4.4 8.6 7.4 6.3 11

210 9.2 1.8 3.2 18 4.4 7.2 24 6.3 10

430 16.5 1.8 2.9 35 4.4 6.8 47 6.3 9.5

520 20 1.8 2.9 42 4.4 6.6 57 6.3 9.3
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-17 EPA Guidance Manual

Alternative Disinfectants and Oxidants

TABLE 7- 12 (cont.)

ESTIMATED INSTALLATION AND UPGRADE COSTS FOR OZONE AS PRIMARY DISINFECTANT -

LARGE SYSTEMS

Design Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Flow

(mgd) Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000 gal)

Total

Upgrade

Cost @

7%

(4/1000

gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000

gal)

Total

Upgrade

Cost @

7%

(4/1000

gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000

gal)

Total

Upgrade

Cost @

7%

(4/1000

gal)

1.8 0.89 1.8 35 1.5 4.4 58 1.4 6.3 56

4.8 1.5 1.8 21 1.9 4.4 28 2.0 6.3 31

11 1.9 1.8 12 2.6 4.4 17 2.8 6.3 21

18 2.4 1.8 8.9 3.0 4.4 13 3.7 6.3 17

26 2.6 1.8 7.2 3.9 4.4 12 4.8 6.3 15

51 3.8 1.8 5.6 6.2 4.4 10 7.4 6.3 13

210 9.2 1.8 4.0 18 4.4 7.8 24 6.3 11

430 16.5 1.8 3.6 35 4.4 7.4 47 6.3 11

520 20 1.8 3.4 42 4.4 6.1 57 6.3 10
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-18 April 1999

Alternative Disinfectants and Oxidants

TABLE 7- 12 (cont.)

ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR OZONE AS PRIMARY DISINFECTANT

LARGE SYSTEMS

Design Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Flow

(mgd) Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000 gal)

Total

Upgrade

Cost @

10%

(4/1000

gal)

Upgrad

e

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000

gal)

Total

Upgrade

Cost @

10%

(4/1000

gal)

Upgrade

Capital

Cost

($M)

Upgrade

O&M

Cost

(4/1000

gal)

Total

Upgrade

Cost @

10%

(4/1000

gal)

1.8 0.89 1.8 43 1.5 4.4 72 1.4 6.3 69

4.8 1.5 1.8 26 1.9 4.4 34 2.0 6.3 37

11 1.9 1.8 14 2.6 4.4 21 2.8 6.3 24

18 2.4 1.8 11 3.0 4.4 15 3.7 6.3 20

26 2.6 1.8 8.4 3.9 4.4 14 4.8 6.3 18

51 3.8 1.8 6.5 6.2 4.4 11 7.4 6.3 15

210 9.2 1.8 4.5 18 4.4 8.7 24 6.3 12

430 16 1.8 4.0 35 4.4 8.2 47 6.3 12

520 20 1.8 3.6 42 4.4 8.2 57 6.3 10
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-19 EPA Guidance Manual

Alternative Disinfectants and Oxidants

TABLE 7-13 ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR CHLORINE DIOXIDE AS PRIMARY DISINFECTANT

(MANUAL GENERATOR)

SMALL SYSTEMS

Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 3%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 3%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 3%

(¢/1000gal)

0.024 0.10 1929 2258 0.10 1934 2263 0.13 1934 2362

0.087 0.10 452 529 0.10 456 533 0.15 456 571

0.27 0.10 128 149 0.10 132 153 0.22 132 179

0.65 0.10 49 57 0.10 52 60 0.28 52 74

Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 7%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 7%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 7%

(¢/1000gal)

0.024 0.10 1929 2391 0.10 1934 2396 0.13 1934 2534

0.087 0.10 452 560 0.10 456 564 0.15 456 618

0.27 0.10 128 158 0.10 132 162 0.22 132 198

0.65 0.10 49 60 0.10 52 63 0.28 52 63
April 1999 B-20 Final

EPA Guidance Manual

Alternative Disinfectants and Oxidants

TABLE 7-13 (cont)

ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR CHLORINE DIOXIDE AS PRIMARY DISINFECTANT

(MANUAL GENERATOR)

SMALL SYSTEMS

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 10

%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

0.024 0.10 1929 2455 0.10 1934 2460 0.13 1934 2659

0.087 0.10 452 575 0.10 456 579 0.15 456 654

0.27 0.10 128 162 0.10 132 166 0.22 132 215

0.65 0.10 49 62 0.10 52 65 0.28 52 91
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-21 EPA Guidance Manual

Alternative Disinfectants and Oxidants

TABLE 7-13 (cont.)

ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR CHLORINE DIOXIDE AS PRIMARY DISINFECTANT

(AUTOMATIC GENERATOR)

SMALL SYSTEMS

Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 3%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 3%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 3%

(¢/1000gal)

0.024 0.33 1548 2633 0.33 1552 2637 0.37 1552 2769

0.087 0.33 364 617 0.33 367 620 0.39 367 666

0.27 0.33 104 175 0.33 107 178 0.47 107 208

0.65 0.33 40 66 0.33 43 69 0.52 43 85

Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 7%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 7%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 7%

(¢/1000gal)

0.024 0.33 1548 3072 0.33 1552 3076 0.37 1552 3261

0.087 0.33 364 720 0.33 367 723 0.39 367 787

0.27 0.33 104 203 0.33 107 206 0.47 107 248

0.65 0.33 40 77 0.33 43 80 0.52 43 101
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-22 April 1999

Alternative Disinfectants and Oxidants

TABLE 7-13 (cont.)

ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR CHLORINE DIOXIDE AS PRIMARY DISINFECTANT

(AUTOMATIC GENERATOR)

SMALL SYSTEMS

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

0.024 0.33 1548 3459 0.33 1552 3462 0.37 1552 3662

0.087 0.33 364 810 0.33 367 813 0.39 367 888

0.27 0.33 104 228 0.33 107 231 0.47 107 280

0.65 0.33 40 87 0.33 43 90 0.52 43 115

(1) Cost were adjusted to account for an increase in basin contact time from the information reported in Table 7-10
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-23 EPA Guidance Manual

Alternative Disinfectants and Oxidants

TABLE 7-13 (cont.) ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR CHLORINE DIOXIDE AS PRIMARY DISINFECTANT

(MANUAL GENERATOR)

LARGE SYSTEMS

Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

3%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

3%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

3%

(¢/1000gal)

1.8 0.10 18 20.6 0.10 20 22.6 0.50 20 33

4.8 0.10 7.4 8.3 0.10 9.6 10.5 0.75 9.6 16

11 0.10 4.3 4.7 0.10 6.5 6.9 1.3 6.5 11.3

18 0.20 3.8 4.2 0.20 5.8 6.2 3.7 5.8 13.5

26 0.20 3.2 3.5 0.20 5.1 5.4 5.1 5.1 12.3

51 0.28 2.4 2.6 0.28 4.6 4.8 9.4 4.6 11

210 0.29 1.8 1.8 0.29 3.6 3.6 36 3.6 9.1

430 0.35 1.6 1.6 0.35 3.2 3.2 73 3.2 8.2

520 0.35 1.4 1.4 0.35 2.4 2.4 89 2. 7.1
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-24 April 1999

Alternative Disinfectants and Oxidants

TABLE 7-13 (cont.)

ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR CHLORINE DIOXIDE AS PRIMARY DISINFECTANT

(MANUAL GENERATOR)

LARGE SYSTEMS

Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

7%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

7%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @ 7%

(¢/1000gal)

1.8 0.10 18 22 0.10 20 24 0.50 20 38

4.8 0.10 7.4 8.2 0.10 9.6 11 0.75 9.6 19

11 0.10 4.3 4.5 0.10 6.5 6.5 1.3 6.5 13

18 0.20 3.8 4.6 0.20 5.8 6.6 3.7 5.8 17

26 0.20 3.2 3.4 0.20 5.1 5.4 5.1 5.1 15

51 0.28 2.4 2.3 0.28 4.6 4.3 9.4 4.6 13

210 0.29 1.8 2.1 0.29 3.6 4.1 36 3.6 12

430 0.35 1.6 2.0 0.35 3.2 3.0 73 3.2 10

520 0.35 1.4 1.4 0.35 2.4 2.5 89 2.4 9.0
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-25 EPA Guidance Manual

Alternative Disinfectants and Oxidants

TABLE 7-13 (cont.)

 ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR CHLORINE DIOXIDE AS PRIMARY DISINFECTANT

(MANUAL GENERATOR)

LARGE SYSTEMS

Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

1.8 0.10 18 22 0.10 20 25 0.50 20 43

4.8 0.10 7.4 8.8 0.10 10 11 0.75 10 21

11 0.10 4.3 4.9 0.10 6.5 7.1 1.3 6.5 15

18 0.20 3.8 4.5 0.20 5.8 6.5 3.7 5.8 19

26 0.20 3.2 3.7 0.20 5.1 5.6 5.1 5.1 18

51 0.28 2.4 2.8 0.28 4.3 4.6 9.4 4.3 15

210 0.29 1.8 1.9 0.29 3.5 3.6 36 3.5 13

430 0.35 1.6 1.7 0.35 3.2 3.2 73 3.2 12

520 0.35 1.4 1.4 0.35 2.4 2.5 89 2.4 11

(1) Cost were adjusted to account for an increase in basin contact time from the information reported in Table 7-10
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-26 April 1999

Alternative Disinfectants and Oxidants

TABLE 7-13 (cont.)

ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR CHLORINE DIOXIDE AS PRIMARY DISINFECTANT

(AUTOMATIC GENERATOR)

LARGE SYSTEMS

Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

3%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

3%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

3%

(¢/1000gal)

1.8 0.33 15 24 0.33 17 26 0.74 17 37

4.8 0.33 6.3 9.2 0.33 8.6 12 0.99 8.6 17

11 0.33 3.9 5.1 0.33 6.0 7.2 1.5 6.0 12

18 0.68 3.3 4.7 0.68 5.3 6.7 4.2 5.3 14

26 0.68 2.9 3.9 0.68 4.8 5.8 5.6 4.8 13

51 0.76 2.3 2.8 0.76 4.1 4.6 10 4.1 11

210 0.77 1.8 1.9 0.77 3.5 3.6 37 3.5 9.2

430 0.83 1.6 1.7 0.83 3.1 3.2 74 3.1 8.2

520 0.91 1.3 1.4 0.91 2.5 2.6 90 2.5 7.2
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

April 1999 B-27 EPA Guidance Manual

Alternative Disinfectants and Oxidants

TABLE 7-13 (cont.)

ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR CHLORINE DIOXIDE AS PRIMARY DISINFECTANT

(AUTOMATIC GENERATOR)

LARGE SYSTEMS

Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

7%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

7%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

7%

(¢/1000gal)

1.8 0.33 15 27 0.33 17 29 0.74 17 44

4.8 0.33 6.3 10 0.33 8.6 13 0.99 8.6 21

11 0.33 3.9 5.7 0.33 6.0 7.7 1.5 6.0 14

18 0.68 3.3 5.0 0.68 5.3 7.0 4.2 5.3 17

26 0.68 2.9 4.4 0.68 4.8 6.4 5.6 4.8 16

51 0.76 2.3 2.7 0.76 4.1 4.7 10 4.1 13

210 0.77 1.8 2.2 0.77 3.5 4.2 37 3.5 12

430 0.83 1.6 2.1 0.83 3.1 3.1 74 3.1 10

520 0.91 1.3 1.4 0.91 2.5 2.6 90 2.5 9.1

(1) Cost were adjusted to account for an increase in basin contact time from the information reported in Table 7-10
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-28 April 1999

Alternative Disinfectants and Oxidants

TABLE 7-13 (cont.)

 ESTIMATED INSTALLATION AND UPGRADE COSTS

FOR CHLORINE DIOXIDE AS PRIMARY DISINFECTANT

(AUTOMATIC GENERATOR)

LARGE SYSTEMS

Log Inactivation = 1 Log Inactivation = 3 Log Inactivation = 5

Design

Flow

(mgd)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

Upgrade

Capital

Cost(1)

($M)

Upgrade

O&M

Cost

(¢/1000gal)

Total

Upgrade

Cost @

10%

(¢/1000gal)

1.8 0.33 15 30 0.33 17 32 0.74 17 51

4.8 0.33 6.3 11 0.33 8.6 14 0.99 8.6 24

11 0.33 3.9 6.1 0.33 6.0 8.1 1.5 6.0 16

18 0.68 3.3 5.5 0.68 5.3 7.5 4.2 5.3 21

26 0.68 2.9 4.7 0.68 4.8 6.7 5.6 4.8 19

51 0.76 2.3 2.9 0.76 4.1 4.9 10 4.1 16

210 0.77 1.8 2.2 0.77 3.5 4.2 37 3.5 13

430 0.83 1.6 2.1 0.83 3.1 3.1 74 3.1 12

520 0.91 1.3 1.4 0.91 2.5 2.7 90 2.5 11

(1) Cost were adjusted to account for an increase in basin contact time from the information reported in Table 7-10
April 1999 B-29 EPA Guidance Manual

Alternative Disinfectants and Oxidants

B.2 References

1. USEPA. 1998a. Technologies and Costs for Control of Disinfection By-Products. Washington,

DC.

2. USEPA. 1998b. Regulatory Impact Analysis for the Stage 1 Disinfectant/Disinfection Byproduct

Rule. Prepared by Science Applications International Corporation for the USEPA, Office of

Ground Water and Drinking Water, Washington, DC.
APPENDIX B - COST OF ALTERNATIVE DISINFECTION SYSTEMS

EPA Guidance Manual B-30

Alternative Disinfectants and Oxidants

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