EPA/600/R-01/021

March 2001

Laboratory Study on the Oxidation

of Arsenic III to Arsenic V

by

Ganesh Ghurye

Dennis Clifford

University of Houston

Houston, TX 77204-4791

EPA Contract 8C-R311-NAEX

Project Officer

Thomas Sorg

Water Supply and Water Resources Division

National Risk Management Research Laboratory

Cincinnati, OH 46268

National Risk Management Research Laboratory

Office of Research and Development

U.S. Environmental Protection Agency

Cincinnati, OH 45268
ii

Disclaimer

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

Protection Agency (EPA) under Contract No. 8C-R311-NAEX to the Department of Civil and 

Environmental Engineering at the University of Houston. 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. 
iii

Foreword

The United States Environmental Protection Agency (EPA) 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 action 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 (NRMRL) 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 groundwater; and 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. 

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

plan. It is published and made available by the 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
iv

Abstract

A one-year laboratory study was performed to determine the ability of seven oxidants to oxidize 

As(III) to As(V). These included chlorine, permanganate, ozone, chlorine dioxide,

monochloramine, a solid-phase oxidizing media, and 254 nm ultraviolet light. 

Chlorine and permanganate rapidly oxidized As(III) to As(V) in the pH range of 6.3 to 8.3. 

Dissolved manganese, dissolved iron, sulfide and TOC slowed the rate of oxidation slightly, but 

essentially complete oxidation was obtained in less than one minute with chlorine and

permanganate under all conditions studied.

In the absence of interfering reductants, ozone rapidly oxidized As(III). Although, dissolved 

manganese and dissolved iron had no significant effect on As(III) oxidation, the presence of 

sulfide considerably slowed the oxidation reaction. The presence of TOC had a quenching 

effect on As(III) oxidation by ozone, producing incomplete oxidation at the higher TOC

concentration studied.

Only limited As(III) oxidation was obtained using chlorine dioxide, which was probably due to 

the presence of chlorine (as a by-product) in the chlorine dioxide stock solutions. The reason 

for the ineffectiveness of chlorine dioxide was not studied. 

Preformed monochloramine was ineffective for As(III) oxidation, whereas limited oxidation was 

obtained when monochloramine was formed in-situ. This showed that the injected chlorine 

probably reacted with As(III) before being quenched by ammonia to form monochloramine. 

Filox, a manganese dioxide-based media, was effective for As(III) oxidation. When dissolved 

oxygen (DO) was not limiting, complete oxidation was observed under all conditions studied. 

However, when DO was reduced, incomplete oxidation was obtained in the presence of

interfering reductants. The adverse effect of interfering reductants was completely eliminated by 

either (a) supplying enough DO or (b) increasing the contact time. In addition to oxidizing 

As(III), the Filox media also removed some arsenic by adsorption, which diminished greatly as 

the media came into equilibrium with the As(III)-spiked synthetic water.

UV light alone (254 nm) was not very effective for As(III) oxidation. Significant oxidation was 

observed only at very low flow rates representing 0.6 - 2.5% of the rated capacities of the two 

UV sterilizer units tested. However, as reported in a patented process, complete oxidation by 

UV light was observed when the challenge water was spiked with 1.0 mg/L sulfite. 
v

Contents

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

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

Figures .................................................................................................... viii

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

Abbreviations and Acronyms.................................................................................................... x 

Acknowledgments .................................................................................................... xi

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

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

 1.1.1 Previous Studies....................................................................................... 1 

 1.2 Oxidants Evaluated................................................................................................ 2 

1.3 Oxidant Stoichiometry................................................................................................ 2 

 1.3.1 Chlorine.................................................................................................... 2 

 1.3.2 Permanganate........................................................................................... 3 

 1.3.3 Ozone .................................................................................................... 4 

 1.3.4 Chlorine Dioxide....................................................................................... 4 

 1.3.5 Monochloramine....................................................................................... 5 

 1.4 Research Objectives.............................................................................................. 5 

2. Materials and Methods .................................................................................................... 6 

 2.1 Synthetic Test Water Composition......................................................................... 6 

 2.2 Interfering Reductants............................................................................................ 6 

 2.3 Speciation Method................................................................................................ 6 

 2.4 Chemical Oxidation Experiments............................................................................ 7 

 2.4.1 Reactor Design......................................................................................... 7 

 2.4.2 Testing Reactor Set-up .............................................................................11 

 2.4.2.1 Arsenic(V) Retention................................................................11 

 2.4.2.2 Arsenic(III) Passage .................................................................11 

 2.4.2.3 System Dead Volume ............................................................... 11 

 2.4.2.4 Oxidant Mixing Efficiency.......................................................... 11 

 2.4.3 Oxidation Conditions ................................................................................ 12 

 2.4.3.1 pH of Operation....................................................................... 12 

 2.4.3.2 High- and Low-DO Experiments...............................................12 

 2.4.3.3 Oxidation Experiments with TOC.............................................. 13 

 2.4.3.4 Low Temperature (5 °C) Oxidation Experiments.......................13 

 2.5 Solid-Phase Media (Filox) Experiments................................................................. 13 

 2.5.1 Pretreatment of Filox Media...................................................................... 13 

 2.5.2 Preparation of Low- and High-DO Synthetic Water.................................. 14 

 2.5.3 Procedure for Variable-EBCT and Variable pH Experiments.....................14 

 2.5.4 Procedure to Stabilize Arsenic Removal by Filox Media ............................14 

 2.5.5 Procedure for Low-DO Filox Experiments................................................15 
vi

 

 2.6 UV Oxidation Experiments......................................................................................15 

 2.6.1 Unit 1: 0.5 gpm UV Sterilizer Unit .............................................................15 

 2.6.2 Unit 2: 1.0 gpm UV Sterilizer Unit .............................................................16 

 2.7 QA/QC.................................................................................................... 16 

 2.7.1 Arsenic Standards..................................................................................... 16 

 2.7.2 Routine Arsenic Analysis...........................................................................17 

 2.7.3 Arsenic Calibration Curve .........................................................................17 

 2.8 Analytical Methods..................................................................................................18 

3. Results and Discussion ....................................................................................................19 

 3.1 Reactor Set-up Test-Results..................................................................................19 

 3.1.1 Arsenic(V) Retention................................................................................19 

 3.1.2 Arsenic(III) Recovery...............................................................................20 

 3.1.3 Dead Volume in Oxidation Reactor Set-up................................................21 

 3.1.4 Mixing Efficiency in Oxidation Reactor......................................................22 

 3.2 Chlorine Test Results.............................................................................................23 

 3.2.1 Effect of pH on Chlorine ...........................................................................23 

 3.2.2 Effect of Dissolved Manganese and Iron on Chlorine .................................25 

 3.2.3 Effect of Sulfide on Chlorine......................................................................25 

 3.2.4 Effect of TOC and Temperature on Chlorine .............................................25 

 3.3 Permanganate Test Results....................................................................................25 

 3.3.1 Effect of pH on Permanganate...................................................................26 

 3.3.2 Effect of Dissolved Manganese and Iron on Permanganate.........................27 

 3.3.3 Effect of Sulfide on Permanganate .............................................................27 

 3.3.4 Effect of TOC and Temperature on Permanganate.....................................28 

 3.4 Ozone Test Results................................................................................................28 

 3.4.1 Effect of pH on Ozone .............................................................................29 

 3.4.2 Effect of Dissolved Manganese and Iron on Ozone ...................................30 

 3.4.3 Effect of Sulfide on Ozone.........................................................................30 

 3.4.4 Effect of TOC and Temperature on Ozone ................................................30 

 3.5 Chlorine Dioxide Test Results................................................................................31 

 3.5.1 Effect of pH on Chlorine Dioxide ..............................................................31 

 3.5.2 Verifying Chlorine Dioxide Stock Concentration........................................33 

 3.5.3 Fe(II) Oxidation with Chlorine Dioxide......................................................34 

 3.5.4 Increasing Stoichiometric Dose of Chlorine Dioxide...................................34 

 3.5.5 Effect of Dissolved Manganese and Iron on Chlorine Dioxide.....................34 

 3.5.6 Effect of Sulfide, TOC and Temperature on Chlorine Dioxide ....................34 

 3.6 Monochloramine Test Results................................................................................35 

 3.6.1 Effect of pH on Monochloramine ..............................................................35 

 3.7 Solid-Phase Oxidizing Media (Filox)......................................................................36 

 3.7.1 Filox: Effect of EBCT with High-DO .........................................................36 

 3.7.2 Filox: Effect of pH with High-DO ..............................................................39 

 3.7.3 Filox: Effect of DO in Absence of Interfering Reductants............................40 
vii

 3.7.4 Filox: Effect of Interfering Reductants........................................................40 

 3.7.4.1 Low-DO Synthetic Water at 1.5 min EBCT..............................40 

 3.7.4.2 Low-DO Synthetic Water at 6.0 min EBCT...............................40 

 3.7.4.3 High-DO Synthetic Water at 1.5 min EBCT...............................40 

 3.7.5 Filox: Effect of Low Temperature in low-DO Synthetic Water....................41 

 3.8 UV Oxidation Results............................................................................................41 

 3.8.1 Unit 1—R-Can Ultraviolet, 0.5 gpm.......................................................... 41 

 3.8.2 Unit 2—Atlantic Ultraviolet, 1.0 gpm.........................................................42 

4. Summary and Conclusions..................................................................................................43 

5. References ....................................................................................................45 

6. Appendix A. Preconditioning and Regeneration of IX Filter............................................48 

 A.1 Manufacturer Recommended Preconditioning............................................48 

 A.2 IX Filter Regeneration—UH Method ........................................................48 

Appendix B. Testing Oxidation Reactor Set-up.............................................................. 49 

Appendix C. Variable-DO Experiments.........................................................................50 

 C.1 High-DO Chemical Oxidation Experiments................................................50 

 C.2 Low-DO Chemical Oxidation Experiments................................................51 

Appendix D. Solid-Phase (Filox) Experiments................................................................52 

 D.1 Variable-EBCT and Variable-pH experiments...........................................52 

 D.2 Low-DO Filox Experiments......................................................................52 

Appendix E. Chlorine Oxidation Data............................................................................54 

Appendix F. Permanganate Oxidation Data...................................................................57 

Appendix G. Chlorine Dioxide Oxidation Data...............................................................60 

Appendix H. Monochloramine Oxidation Data...............................................................63 

Appendix I. Ozone Oxidation Data ..............................................................................65 

Appendix J. Filox Oxidation Data.................................................................................68 

Appendix K. UV Oxidation Data...................................................................................70 

Appendix L. Preparation of As(III) Stock Solution........................................................72 

Appendix M. QC Data ..................................................................................................73 
viii

Figures

Page

2-1 Schematic for Oxidation Reactor................................................................ 8

2-2 Elevation View of Oxidation Reactor.......................................................... 9

2-3 Simplified Plan View of Oxidation Reactor.................................................. 10

2-4 Schematic for Solid-Phase (Filox) Oxidizing Experiments............................ 14

2-5 Schematic for UV-Oxidation Experiments................................................... 15

2-6 Typical Arsenic Calibration Curve .............................................................. 18

3-1 50 μg/L-As(V) Retention by IX Filter......................................................... 19

3-2 1000 μg/L-As(V) Retention by IX Filter..................................................... 20

3-3 50 μg/L-As(III) Recovery from IX Filter.................................................... 21

3-4 1000 μg/L-As(III) Recovery from IX Filter................................................ 21

3-5 Estimation of Dead Volume in the Reactor-Set-up ...................................... 22

3-6 Mixing Efficiency in Oxidation Reactor........................................................ 23

3-7 Effect of pH on As(III) Oxidation with Free Chlorine .................................. 24

3-8 Effect of Sulfide on As(III) Oxidation with Free Chlorine............................. 25

3-9 Effect of pH on As(III) Oxidation with Permanganate.................................. 27

3-10 Effect of Sulfide on As(III) Oxidation with Permanganate............................ 28

3-11 Effect of pH on As(III) Oxidation with Ozone............................................. 29

3-12 Effect of Sulfide on As(III) Oxidation with Ozone ....................................... 30

3-13 Effect of TOC on As(III) Oxidation with Ozone.......................................... 31

3-14 Arsenic(III) Oxidation with Chlorine Dioxide .............................................. 33

3-15 Arsenic(III) Oxidation with Monochloramine .............................................. 35

3-16 Effect of EBCT on Filox Media .................................................................. 38

3-17 Filox Media Equilibration ........................................................................... 39

3-18 Effect of pH on As(III) Oxidation with Filox Media..................................... 40
ix

Tables

 

Page

2-1 Composition of Synthetic Test Water................................................................. 6

2-2 Interfering Reductants........................................................................................ 6

2-3 Previous EPA Standards................................................................................... 16

2-4 Analytical Methods........................................................................................... 18

3-1 Free Chlorine Experiments................................................................................ 24

3-2 Permanganate Experiments................................................................................ 26

3-3 Ozone Experiments........................................................................................... 29

3-4 Chlorine Dioxide Experiments............................................................................ 32

3-5 Chlorine Dioxide Assays ................................................................................... 34

3-6 Monochloramine Experiments............................................................................ 35

3-7 Filox Experiments.............................................................................................. 37

3-8 UV Oxidation Experiments................................................................................ 41

E-1

Residual As(III) Conc. vs Time for Chlorine Experiments................................... 55

F-1

Residual As(III) Conc. vs Time for Permanganate Experiments.......................... 58

G-1 Residual As(III) Conc. vs Time for Chlorine Dioxide Experiments...................... 61

H-1 Residual As(III) Conc. vs Time for Monochloramine Experiments...................... 64

I-1 Residual As(III) Conc. vs Time for Ozone Experiments...................................... 66

J-1 Residual As(III) vs Effluent As Concentration for Filox Experiments...................69

K-1 Residual As(III) Conc. for UV Experiments....................................................... 71

M-1 Results of QC Analysis...................................................................................... 74

M-2 Results of WS Standards Analysis..................................................................... 80

M-3 Recoveries of Spiked WS Standards................................................................. 85
x

Abbreviations and Acronyms

AWWA American Water Works Association

DO Dissolved Oxygen, mg/L

DPD N,N-diethyl-p-phenylenediamine

EBCT Empty Bed Contact Time (media volume/flow rate), min

EPA US Environmental Protection Agency

FIAS Flow Injection Analysis Hydride Generation System

GFAAS Graphite Furnace Atomic Absorption Spectrophotometer

GPM Gallons/min

HDPE High Density Polyethylene

IR Interfering Reductant

MCL Maximum Contaminant Level

MDL Method Detection Limit

NPT Nominal Pipe Thread

NRMRL National Risk Management Research Laboratory

PAO Phenyl Arsenic Oxide

PRV Pressure Relief Valve

QA Quality Assurance

QAPP Quality Assurance Project Plan

QA/QC Quality Assurance/Quality Control

SDWA Safe Drinking Water Act

SM Standard Methods

SR Stoichiometric Ratio, μg oxidant/μg reductant

TOC Total Organic Carbon

UH University of Houston

UV Ultraviolet

WAL Work Assignment Leader

WAM Work Assignment Manager
xi

Acknowledgments

This research was funded by the US EPA under EPA Order Number 8C-R311-NAEX. The 

authors are grateful for the technical and administrative support of Tom Sorg, US EPA

Research Engineer. Anthony Tripp, a doctoral candidate at the University of Houston is 

gratefully acknowledged for serving as the QA/QC Officer and for his considerable technical 

assistance throughout this study.