EPA/600/R-01/033 

June 2001 

Treatment of Arsenic Residuals from 

Drinking Water Removal Processes 

by

Michael J. MacPhee

Gail E. Charles

David A. Cornwell

Environmental Engineering & Technology, Inc.

Newport News, VA 23606

Contract No. 8C-R613-NTSA

Project Officer

Thomas J. Sorg

Water Supply and Water Resources Division

National Risk Management Research Laboratory

Cincinnati, OH 45268

National Risk Management Research Laboratory

Office of Research and Development

U.S. Environmental Protection Agency

Cincinnati, OH 45268
Disclaimer 

The information in this document has been funded by the United States Environmental 

Protection Agency (EPA) under Contract No. 8C-R613-NTSA to Environmental Engineering 

& Technology, Inc. It has been subjected to the Agency’s peer and administrative reviews 

and has been approved for publication as an EPA document. Mention of trade names or 

commercial products does not constitute an endorsement or recommendation for use. 

ii 
Foreword 

The U.S. Environmental Protection Agency is charged by Congress with protecting 

the Nation’s land, air, and water resources. Under a mandate of national environmental 

laws, the Agency strives to formulate and implement actions leading to a compatible balance 

between human activities and the ability of natural systems to support and nurture life. To 

meet this mandate, EPA’s research program is providing data and technical support for 

solving environmental problems today and building a science knowledge base necessary 

to manage our ecological resources wisely, understand how pollutants affect our health, and 

prevent or reduce environmental risks in the future. 

The National Risk Management Research Laboratory is the Agency’s center for 

investigation of technological and management approaches for preventing and reducing 

risks from pollution that threatens human health and the environment. The focus of the 

Laboratory’s research program is on methods and their cost-effectiveness for prevention 

and control of pollution to air, land, water, and subsurface resources; protection of water 

quality in public water systems; remediation of contaminated sites, sediments and ground 

water; prevention and control of indoor air pollution; and restoration of ecosystems. NRMRL 

collaborates with both public and private sector partners to foster technologies that reduce 

the cost of compliance and to anticipate emerging problems. NRMRL’s research provides 

solutions to environmental problems by: developing and promoting technologies that protect 

and improve the environment; advancing scientific and engineering information to support 

regulatory and policy decisions; and providing the technical support and information transfer 

to ensure implementation of environmental regulations and strategies at the national, state, 

and community levels. The goal of this research effort is to evaluate the effectiveness of 

various treatment processes for removing arsenic from residuals produced by arsenic 

removal drinking water treatment technologies. 

This publication has been produced as part of the Laboratory’s strategic long-term 

research plan. It is published and made available by EPA’s Office of Research and 

Development to assist the user community and to link researchers with their clients. 

E. Timothy Oppelt, Director 

National Risk Management Research Laboratory 

iii 
Abstract 

The drinking water MCL was recently lowered from 0.05 mg/L to 0.01 mg/L. One concern was 

that a reduction in the TCLP arsenic limit in response to the drinking water MCL could be 

problematic with regard to disposal of solid residuals generated at arsenic removal facilities. 

This project focused on developing a short-list of arsenic removal options for residuals 

produced by ion exchange (Ion Ex), reverse osmosis (RO), nanofiltration (NF), activated 

alumina (AA), and iron removal processes. Both precipitation and adsorption processes were 

evaluated to assess their arsenic removal effectiveness. 

In precipitation tests, ferric chloride outperformed alum for removal of arsenic from residuals 

by sedimentation, generally resulting in arsenic removals of 88 to 99 percent. Arsenic removal 

from the high alkalinity ion exchange samples was poorer. The required iron-to-arsenic molar 

ratio for best removal of arsenic in these screening tests varied widely from 4:1 to 191:1, 

depending on residuals type, and best arsenic removal using ferric chloride typically occurred 

between pH 5.0 and 6.2. Polymer addition typically did not significantly improve arsenic 

removal using either coagulant. Supernatant total arsenic levels of 0.08 mg/L or lower were 

attained with ferric chloride precipitation for membrane concentrates and residuals from iron 

removal facilities compared to an in-stream arsenic limit of 0.05 mg/L in place in some states. 

Settling alone with no coagulant also effectively removed arsenic from iron removal facility 

residuals. Even with ferric chloride dosages of 50 to 200 mg/L applied to ion exchange 

regenerants, supernatant arsenic levels after treatment were 1 to 18 mg/L. Required iron-toarsenic molar ratios developed in precipitation work could be used by utilities as guidelines 

for establishing coagulant dose needs to meet in-stream standards, and to develop preliminary 

treatment costs. 

Adsorption tests demonstrated the potential for different types of media and resins to remove 

arsenic from liquid residuals, but did not assess ultimate capacity. Overall, the iron-based 

granular ferric hydroxide media evaluated in testing outperformed the aluminum-based media 

and ion exchange resin for removal of arsenic. However, activated alumina and the iron-based 

media provided comparable arsenic removals of close to 100 percent with an empty bed 

contact time (EBCT) of 3-min for most of the membrane concentrates and the settled iron 

removal facility residuals. Removal of suspended solids was key to the success of adsorption 

for spent filter backwash water and clarifier flush residuals. Arsenic breakthrough occurred 

very rapidly for the ion exchange samples and for one RO concentrate, all of which had an 

alkalinity of more than 1,000 mg/L (as CaCO3). This again suggests that alkalinity 

significantly interferes with adsorption of arsenic. Based on this work, use of adsorption media 

for treatment of arsenic-laden water plant residuals merits further exploration. 

Of all of the residuals streams tested, Ion Ex regenerants were the most difficult to treat using 

precipitation or adsorption. Disposal of supernatant streams resulting from treatment of 

arsenic-laden residuals from ion exchange plants could pose a major challenge. TCLP arsenic 

levels in all residuals generated in this work and in full-scale solid media samples were far 

below the regulatory limit of 5 mg/L, and in fact were below 0.5 mg/L. 

iv 
Contents 

Foreword ........................................................... iii

Abstract ............................................................ iv

Figures ............................................................ vii

Tables ............................................................. ix

Acronyms, Abbreviations, and Symbols .................................... xi

1. Introduction ...................................................... 1

1.1 Background ................................................... 1

1.2 Literature Review .............................................. 1

1.3 Project Objectives .............................................. 4

2. Experimental Procedures ........................................... 5

2.1 Introduction ................................................... 5

2.2 Treatment Plant Residuals ....................................... 5

2.2.1 Ion Exchange ........................................... 5

2.2.2 Activated Alumina ........................................ 5

2.2.3 Membrane Filtration ...................................... 7

2.2.4 Iron-Manganese Removal System ........................... 8

2.3 Experimental Design ............................................ 8

2.4 Test Methods and Materials ..................................... 11

2.4.1 Precipitation Tests ...................................... 11

2.4.2 Adsorption Tests ....................................... 12

2.4.3 Analytical Tests ........................................ 12

2.4.4 Quality Assurance/Quality Control .......................... 13

3. Test Results .................................................... 15

3.1 Introduction .................................................. 15

3.2 Residuals Characterization ...................................... 15

3.2.1 Arsenic Concentrations .................................. 15

3.2.2 Alkalinity, pH, and Total Hardness ........................... 15

3.2.3 TDS ................................................. 18

3.2.4 Total Fe and Total Mn .................................... 18

3.2.5 Sulfate ............................................... 18

3.3 Precipitation Test Results ....................................... 20

3.3.1 Overview ............................................. 20

3.3.2 Activated Alumina ....................................... 20

3.3.3 Ion Exchange Regenerants ............................... 20

v 
3.3.4 Reverse Osmosis Concentrates ............................ 22

3.3.5 Nanofiltration Concentrates ............................... 22

3.3.6 Iron Removal Plant Residuals .............................. 22

3.3.7 Summary of Precipitation Testing ........................... 26

3.3.8 Residual Iron and Aluminum Concentrations ................... 31

3.3.9 TCLP Test Results ...................................... 32

3.4 Adsorption Test Results ........................................ 32

3.4.1 Ion Exchange Regenerants ............................... 32

3.4.2 RO Concentrates ....................................... 33

3.4.3 Nanofiltration Concentrates ............................... 33

3.4.4 Iron Removal Plant Residuals .............................. 36

3.4.5. Adsorption Test Summary ................................. 36

3.5 Comparison of Treatment Processes .............................. 38

3.5.1 SFBW (A) and SFBW/ACF (B) ............................. 38

3.5.2 RO (A) and (B) Concentrates .............................. 39

3.5.3 Nanofiltration (A) and (B) Concentrates ...................... 39

3.5.4 Ion Exchange Regenerant (A) and (B) Composite Streams ........ 39

3.5.5 Activated Alumina Regenerant ............................. 41

3.5.6 Summary ............................................. 41

3.6 Solid Fraction Residuals ........................................ 41

4. Sludge Disposal Options ........................................... 43

4.1 Sludge Production ............................................. 43

4.1.1 Normalizing Sludge Quantities According to Treatment Process

Type .......................................... 45

4.2 Federal Disposal Regulations .................................... 46

4.2.1 40 CFR 257: Criteria for Classification of Solid Waste Disposal

Facilities and Practices ............................ 46

4.2.2 40 CFR 258: Criteria for Municipal Solid Waste Landfills (MSWLF) 47

4.2.3 40 CFR 261: Identification and Listing of Hazardous Wastes ..... 47

4.2.4 40 CFR 403: General Pretreatment Regulations for Existing and

New Sources of Pollution ........................... 47

4.2.5 40 CFR 503: Standards for the Use or Disposal of Sewage Sludge . 48

4.2.6 Comprehensive Environmental Response Compensation Liability

Act (CERCLA) ................................... 48

4.2.7 Hazardous Materials Transportation Act (HMTA) ................ 48

4.3 Residuals Disposal Options ..................................... 49

4.3.1 Liquid or Semi-Liquid Waste Disposal ....................... 49

4.3.2 Solid Media Disposal .................................... 50

5. Summary and Conclusions ......................................... 51

5.1 Summary .................................................... 51

5.1.1 Project Description ...................................... 51

5.1.2 Untreated Residuals Sample Characterization ................. 51

5.1.3 Precipitation and Adsorption Test Results .................... 51

5.2 Conclusions ................................................. 54

5.2.1 Precipitation ........................................... 54

5.2.2 Adsorption ............................................ 54

5.2.3 Solids ................................................ 57

5.3 Recommendations for Future Work ................................ 57

6. References ..................................................... 59

vi 
Figures 

Page 

1-1 Natural occurrence factors for arsenic in groundwater systems ........... 2

2-1 Location of full-scale treatment facilities providing residuals samples ....... 6

2-2 Schematic of ion exchange and activated alumina adsorption processes

with regeneration ........................................ 7

2-3 Schematic of membrane and iron-manganese removal filtration process ..... 9

2-4 Summary of arsenic residuals treatment plan ......................... 9

2-5 Coagulant dosage ranges used in precipitation tests .................. 11

3-1 Total arsenic concentrations in the untreated liquid residuals ............ 16

3-2 Alkalinity, total hardness, and pH of the untreated liquid residuals ......... 17

3-3 Total dissolved solids concentrations of untreated liquid residuals ........ 18

3-4 Iron and manganese concentration of untreated liquid residuals .......... 19

3-5 Total arsenic concentration in the untreated residuals and in the

supernatant after ferric chloride precipitation .................. 26

3-6 Total arsenic concentration in the untreated residuals and in the

supernatant after alum precipitation ......................... 27

3-7 Comparison of percent total arsenic reduction after alum and ferric chloride

precipitation ........................................... 27

3-8 Total arsenic removal achieved per milligram of iron in solution using ferric

chloride precipitation .................................... 30

3-9 Comparison of iron concentrations in untreated residuals versus

supernatant iron concentrations after precipitation using ferric

chloride .............................................. 31

3-10 Treatment of ion exchange (A) regenerant with iron-based media and

activated alumina ....................................... 34

3-11 Treatment of ion exchange (B) regenerant with iron-based media and

activated alumina ....................................... 34

vii 
3-12 Treatment of reverse osmosis (A) concentrate with iron-based media and

activated alumina ....................................... 35

3-13 Treatment of reverse osmosis (B) concentrate with iron-based media and

activated alumina ....................................... 35

3-14 Treatment of nanofiltration (A) concentrate with iron-based media, an ion

exchange resin, and activated alumina ....................... 36

3-15 Treatment of nanofiltration (B) concentrate with iron-based media, an ion

exchange resin, and activated alumina ....................... 37

3-16 Treatment of iron removal plant spent filter backwash water A (unsettled)

with iron-based media and activated alumina .................. 37

3-17 Comparison of treatment processes for removing arsenic from iron

removal plant residuals—filter backwash and spent filter

backwash/adsorption clarifier flush blend ..................... 39

3-18 Comparison of treatment processes for removing arsenic from reverse

osmosis concentrate .................................... 40

3-19 Comparison of treatment processes for removing arsenic from

nanofiltration A and B concentrate .......................... 40

3-20 Comparison of treatment processes for removing arsenic from ion

exchange A and B regenerant .............................. 41

4-1 Residuals production estimates from alum precipitation of wastewaters

containing arsenic ...................................... 44

4-2 Residuals production estimates from ferric chloride precipitation of

wastewater containing arsenic ............................. 44

5-1 Total arsenic concentrations remaining in the supernatant and percent

reduction after ferric chloride precipitation .................... 53

5-2 Total arsenic concentrations remaining in the supernatant and percent

reduction after alum precipitation ........................... 53

5-3 Total arsenic concentrations in the column effluent and percent reduction

after iron-based media adsorption using a 3 min EBCT ........... 55

5-4 Total arsenic concentration in the column effluent and percent reduction

after activated alumina adsorption using a 3 min EBCT .......... 55

5-5 Total arsenic concentration in the column effluent and percent reduction

after ion exchange using a 3 min EBCT ...................... 56

5-6 Total arsenic concentration in the column effluent and percent reduction

after modified alumina media adsorption using a 3 min EBCT ...... 56

viii 
Tables 

Page 

1-1 Results of TCLP tests from six utilities .............................. 3

1-2 Summary of example residuals characteristics ........................ 4

2-1 Liquid-residuals sample description ................................. 6

2-2 Concentration factors for different membrane system recoveries .......... 8

2-3 Liquid and semi-liquid residuals stream test matrix .................... 10

2-4 Arsenic removal media tested .................................... 12

2-5 Data quality objectives for key measurements ....................... 13

2-6 Analysis methods summary for arsenic-containing residuals ............. 14

3-1 Residuals sample characterization ................................ 16

3-2 Concentration of arsenic in residuals .............................. 17

3-3 Ion exchange run length as a function of influent sulfate concentration ..... 19

3-4 Activated alumina regenerant precipitation results ..................... 20

3-5 Ion exchange regenerant precipitation results ........................ 21

3-6 RO concentrate precipitation results ............................... 23

3-7 NF concentrate precipitation results ............................... 24

3-8 Iron removal plant precipitation results ............................. 25

3-9 Summary of precipitation testing .................................. 28

3-10 Parameters used for calculating arsenic removal versus iron applied (best

ferric chloride precipitation test data) ........................ 29

3-11 Alternative evaluation of arsenic removal by precipitation (best ferric

chloride precipitation test data) ............................. 30

ix 
3-12 Aluminum concentrations in the supernatant following alum precipitation .... 32

3-13 TCLP results from precipitation and settling tests ..................... 32

3-14 Summary of adsorption test results ................................ 38

3-15 Summary of treatment processes for removing arsenic ................. 42

3-16 TCLP arsenic from solid fraction residuals .......................... 42

4-1 Parameters used for calculating residuals production estimates .......... 43

4-2 Estimated sludge production per 1,000 gal of residuals treated by

precipitation ........................................... 45

4-3 Estimated volume of residuals generated per 1 MG treated ............. 45

4-4 Estimated sludge production for a 1-mgd treatment facility .............. 46

4-5 EPA 40 CFR Part 261 TCLP limits ................................ 47

4-6 Part 503 pollutant limits for sewage sludge land application .............. 48

5-1 Comparison of treatment processes for arsenic removal ............... 52

5-2 TCLP arsenic from solid fraction residuals .......................... 54

x 
Acronyms, Abbreviations, and Symbols

AA Activated alumina

As Arsenic

AWWA American Water Works Association

AWWARF American Water Works Association Research Foundation

AWWSC American Water Works Association Service Company

BV Bed volumes

CA California

CERCLA Comprehensive Environmental Response Compensation Liability Act

CFR Code of Federal Register

CWA Clean Water Act

EBCT Empty bed contact time

EE&T Environmental Engineering & Technology, Inc.

EP Extraction procedure

EPA United States Environmental Protection Agency

Fe Iron

FeCl3 Ferric chloride

GFH Granular ferric hydroxide

HMTA Hazardous Materials Transportation Act

ID Identification

Ion Ex Ion exchange

MCL Maximum contaminant level

Mn Manganese

MSWLF Municipal solid waste landfill

NF Nanofiltration

NM New Mexico

NOF Natural occurrence factor

NPDES National Pollutant Discharge Elimination System

NSF National Science Foundation

QA/QC Quality assurance/quality control

QA Quality assurance

QAPP Quality assurance project plan

RCRA Resource Conservation and Recovery Act

RO Reverse osmosis

SDWA Safe Drinking Water Act

SFBW Spent filter backwash water

SFBW/ACF Spent filter backwash water/adsorption clarifier flush

TBLL Technically based local limits

TCLP Toxicity characteristic leaching procedure

TDS Total dissolved solids

USDOT United States Department of Transportation

WTP Water treatment plant

WWTP Wastewater treatment plant

xi