Metal Doped Hydrogel Media for Arsenic Removal in Drinking Water and Arsenic Brine Minimization

Arsenic Water Technology Partnership

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More information about the Foundation and how to become a subscriber is available on the Web at www.WaterResearchFoundation.org. Metal Doped Hydrogel Media for Arsenic Removal in Drinking Water and Arsenic Brine Minimization

Prepared by: Joon H. Min, Jiangzhao Zhang, Christian Tasser, and Gil Crozes Carollo Engineers 10540 Talbert Avenue, Suite 200 East Fountain Valley, California 92708

Janet Hering California Institute of Technology 1200 E. California Boulevard (138-78) Pasadena, California 91125

Jointly Sponsored by: Water Research Foundation 6666 West Quincy Avenue, Denver CO 80235-3098

and

U.S. Department of Energy Washington, D.C. 20585-1290

Published by:

WERC, a Consortium for Water Research Foundation Environmental Education and Technology Development at New Mexico State University

DIN NM É U N M

U I S M

M T N

S S A N O D M I A A CONSORTIUM FOR ENVIRONMENTAL EDUCATION A AL AND TECHNOLOGY DEVELOPMENT LOS

DISCLAIMER

This study was jointly funded by the Water Research Foundation and Sandia National Laboratories (SNL) under Agreement No. FI061030711 through the Arsenic Water Technology Partnership. The comments and views detailed herein may not necessarily reflect the views of the Water Research Foundation, its officers, directors, affiliates or agents, or the views of SNL and the Arsenic Water Technology Partnership. The mention of trade names for commercial products does not represent or imply the approval or endorsement of Water Research Foundation or SNL. This report is presented solely for informational purposes.

Printed in the U.S.A. CONTENTS

LIST OF TABLES ...... ix

LIST OF FIGURES ...... xi

FOREWORD ...... xv

ACKNOWLEDGMENTS ...... xvii

EXECUTIVE SUMMARY ...... xix

CHAPTER 1 INTRODUCTION ...... 1 Background ...... 1 Arsenic Regulatory Overview ...... 1 Arsenic Drinking Water Regulation ...... 1 Arsenic Waste Discharge and Disposal Regulations ...... 2 Project Objectives ...... 3

CHAPTER 2 OVERVIEW OF HYDROGEL MEDIA FOR ARSENIC REMOVAL ...... 5 Background on Hydrogel Media ...... 5 Development of Hydrogel Media ...... 5 Chemistry and Composition of Hydrogel Adsorbent Media ...... 5 Application of Hydrogel Media for Arsenic Removal ...... 6 Removal of Other Contaminants (Selenium and Chromium) ...... 6 Effects of Other Anions and Cations on Arsenic Removal ...... 6 Potential Applications ...... 7

CHAPTER 3 OPTIMIZATION OF HYDROGEL MEDIA FOR ARSENIC REMOVAL ...... 9 Introduction ...... 9 Materials and Methods ...... 9 Hydrogel Media Synthesis ...... 10 Dehydration of Spent Hydrogel Media in Column Mode ...... 10 Results and Discussion ...... 11 Hydrogel Media Characteristics ...... 11 Photos of Commercial and Hydrogel Media ...... 12 Dehydration Characteristics ...... 12 Dehydration Kinetics ...... 15 Dehydration of the Spent Hydrogel Media ...... 15 Dehydration of the Spent Hydrogel Media in a Column ...... 15 Summary ...... 18

CHAPTER 4 HYDROGEL AS SINGLE-USE MEDIA FOR ARSENIC TREATMENT ...... 21 Introduction ...... 21 Materials and Methods ...... 21 Source Waters ...... 21 Description of the Media ...... 24

v General Batch-Testing Approach for Arsenic Removal ...... 24 Batch Test Procedure and Reagents Used ...... 25 Analytical Methods ...... 25 Results and Discussion ...... 26 Comparison of the Efficiency of Selected Hydrogel Media and Other Media on Arsenic Removal ...... 26 Effect of Other Types of Hydrogel Media on Arsenic Removal ...... 27 Arsenic Adsorption Kinetics ...... 29 Effect of Arsenic Speciation on Arsenic Removal ...... 30 Effect of Elevated Arsenic Concentration Levels on Arsenic Removal ...... 32 Effect of Hydrogel Media Preparation and Dehydration on Arsenic Removal .....32 Iron Leaching from the Test Media ...... 33 Interference of Silica and Sulfate ...... 34 Effect of Phosphate on Arsenic Removal ...... 36 Removal of Competing Ions (Nitrate, Perchlorate, and Chromium) ...... 37 Effect of Hydrogel Media Size on Removal of Arsenic and Chromium ...... 40 Summary ...... 42

CHAPTER 5 MICRO-HYDROGEL AS A COAGULANT AID FOR ARSENIC TREATMENT ...... 44 Introduction ...... 44 Materials and Methods ...... 44 Source Water ...... 44 Description of the Micro-hydrogel ...... 44 Batch-Jar Testing Setup and Hydrogel Dose ...... 45 Analytical Methods ...... 46 Results and Discussion ...... 46 Removal Efficiency with Ferric Chloride ...... 46 Effect of Micro-hydrogel Dose and Type on Arsenic Removal ...... 48 Combination of Micro-hydrogel with Ferric Chloride ...... 48 Effect of Hydrogel on TOC and Bromide removal ...... 52 Summary ...... 54

CHAPTER 6 HYDROGEL MEDIA FOR ARSENIC-LADEN BRINE AND CONCENTRATE TREATMENT ...... 57 Introduction ...... 57 Materials and Methods ...... 57 Brine and Concentrate Treatment Test Set-up ...... 57 Characteristics of the IX Brine and the RO Concentrate ...... 58 Hydrogel Media and Commercial Media Tested ...... 59 Analytical Methods ...... 59 Results and Discussion ...... 60 Treatment of IX Brine ...... 60 Treatment of RO Concentrate ...... 66 Effect of Alkalinity on Swelling of Hydrogel Media in the IX Brine ...... 72 Summary ...... 73

vi CHAPTER 7 SUMMARY ...... 75

REFERENCES ...... 79

ABBREVIATIONS ...... 81

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LIST OF TABLES

1.1 Arsenic drinking water regulations ...... 2

1.2 Management of solid and liquid waste from arsenic treatment processes ...... 2

3.1 Characteristics of commercial media, resins, and hydrogel media selected for bench-scale testing ...... 11

4.1 Water quality characteristics of groundwater from LA County Public Works, Well No. 50 ...... 22

4.2 Water quality characteristics of groundwater from Signal Hill, Well No. 8 ...... 22

4.3 Water quality characteristics of groundwater from Chino Desalter ...... 23

4.4 Water quality characteristics of groundwater from Glendale ...... 23

4.5 Water quality characteristics of groundwater from the City of Pomona ...... 23

4.6 Analytical methods used in batch tests ...... 26

5.1 Water quality characteristics of surface water ...... 45

5.2 Experimental settings for jar testing ...... 45

5.3 Analytical methods used in jar testing ...... 46

6.1 Experimental conditions for brine and concentrate residual test ...... 58

6.2 Water quality characteristics of IX brine from the City of Pomona ...... 58

6.3 Water quality characteristics of RO concentrate from the City of Corona ...... 59

6.4 Analytical methods used for brine and concentrate testing ...... 59

LIST OF FIGURES

2.1 Proposed workplan flow chart for testing hydrogel media for arsenic treatment ...... 7

3.1 Commercially available arsenic removal media used for comparison testing ...... 13

3.2 Selected hydrogel media (HG-1 through HG-4) used for arsenic removal ...... 14

3.3 Hydrated and dehydrated hydrogel media (shown under 60 × magnification) ...... 14

3.4 Time-lapsed photos of dehydration for the hydrogel media (shown under 60 × magnification) ...... 16

3.5 Weight reductions of hydrogel media and commercial media following dehydration ...... 17

3.6 Reduction of height of the hydrogel media in a bench column as a function of drying time ...... 17 3.7 Before (left, 50 ml volume) and after (right, 3 ml volume) dehydration of the media in a bench column showing 17-fold reduction in volume...... 18

4.1 Final arsenic concentrations with varying media dosages of 5, 10, and 20 g/L, at a contact time of 30 minutes with LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 27

4.2 Effect of media dosages at 5, 10, and 20 g/L on final pH at a contact time of 30 minutes with LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 27

4.3 Final arsenic concentrations with media dosage of 10 g/L and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 28

4.4 Final pH with media dosage of 10 g/L and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 28

4.5 Arsenic adsorption kinetics for up to 60 minutes contact time and a media dosage of 10 g/L with LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 29

4.6 pH variation over time with 10 g/L media using LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 30

4.7 Final arsenic concentrations for low and high level chlorinated groundwater from Signal Hill Well No. 8 containing 12 μg/L of As(III) and 15 μg/L of total arsenic (media dose of 10 g/L and 30 minutes contact time) ...... 31

4.8 Final pH for low and high level chlorinated groundwater from Signal Hill Well No. 8 containing 12 μg/L of As(III) (media dose of 10 g/L and 30 minutes contact time) ...... 31

4.9 Final arsenic concentrations and pH for spiked Chino Desalter Authority found water with nitrate concentration of 160 mg/L as NO3 (media dose of 30 g/L and 30 minutes contact time) ...... 33

4.10 Final arsenic concentrations with media conditions: acid washed, DI washed, and dehydrated using 10 g/L initial media dose (~0.5 g/L or 5 % of hydrogel media weight for dehydrated media weight) and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 33

4.11 Total iron leaching for various media using LA County Well No. 50 water (As0 = 38 μg/L) with 10 g/L media dose and 30 minutes contact time ...... 34

4.12 Final silica concentrations with 10 g/L media dose and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 35

4.13 Final sulfate concentrations with 10 g/L media dose and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 35

4.14 Final arsenic concentrations with varying phosphate concentrations with 10 g/L media dose and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 36

4.15 Final phosphate concentrations with 10 g/L media dose and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L) ...... 37

4.16 Final nitrate concentrations with 10 g/L media dose and 30 minutes contact time using Pomona water (NO3,0 = 54 mg/L) ...... 38

4.17 Final perchlorate concentrations with 10 g/L media dose and 30 minutes contact time using Pomona water (ClO4,0 = 6.7 μg/L) ...... 38

4.18 Final Cr(VI) concentrations with 10 g/L media dose and 30 minutes contact time using Pomona water (Cr0 = 10 μg/L) ...... 39

4.19 Chromium removal kinetics (final chromium concentration) for up to 30 minutes contact time with 10 g/L media dose using Glendale water (As0 = 73 μg/L, Cr0 = 38 μg/L) ...... 40

4.20 Arsenic removal kinetics (final arsenic concentration) for up to 30 minutes contact time with 10 g/L media dose using Glendale water (As0 = 73 μg/L, Cr0 = 38 μg/L) ...... 40

4.21 Effects of hydrogel media size (HG-2: ~400 μm; HG-2M: ~200 μm) on final pH, arsenic and chromium concentrations with 30 minutes contact time and 10 g/L media dose using Glendale water (As0 = 91 μg/L, Cr0 = 38 μg/L) ...... 41

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4.22 Final chromium concentrations with 30 minutes contact time and 10 g/L or 30 g/L micro-hydrogel dose using Glendale water (As0 = 91 μg/L, Cr0 = 38 μg/L) ...... 42

4.23 Final pH with 30 minutes contact time and 10 g/L or 30 g/L micro-hydrogel dose using Glendale water (As0 = 91 μg/L, Cr0 = 38 μg/L)...... 42

5.1 Schematic of jar testing using micro-hydrogel and/or ferric chloride as coagulant ...... 46

5.2 Final total and dissolved arsenic in jar testing using ferric chloride only (settling time of 30 minutes; As0 = 53 μg/L) ...... 47

5.3 Final turbidity, iron, and pH in jar testing using ferric chloride only (settling time of 30 minutes; initial turbidity = 3.1 NTU; initial pH = 8.1 – 8.3) ...... 47

5.4 Final arsenic in supernatant using micro-hydrogel only (settling time 10 minutes; As0 = 53 μg/L) ...... 48

5.5 Final arsenic concentration in supernatant at different settling times using two hydrogel doses (As0 = 53 μg/L) ...... 49

5.6 Final total and dissolved arsenic in supernatant using 2 g/L micro-hydrogel dose (settling time 10 minutes; As0 = 53 μg/L) ...... 49

5.7 Final arsenic in supernatant using a combination of micro-hydrogel and ferric chloride (settling time 30 minutes; As0 = 53 μg/L) ...... 50

5.8 Final pH values in supernatant using micro-hydrogel and a combination of micro-hydrogel and ferric chloride (settling time 10 minutes) ...... 51

5.9 Final iron concentration in supernatant using micro-hydrogel and a combination of micro-hydrogel and ferric chloride (settling time 10 minutes) ...... 51

5.10 Turbidity in settled waters using micro-hydrogel, ferric chloride, and a combination of both for 2 minutes, 10 minutes, and 30 minutes settling time ...... 52

5.11 Effects of various iron and hydrogel dose on final TOC concentration ...... 53

5.12 Effects of micro-hydrogel type and dose on final TOC concentration ...... 53

5.13 Effects of various iron and hydrogel dose on final bromide concentration ...... 54

5.14 Effects of hydrogel type and dose on final bromide concentration ...... 54

6.1 Arsenic removal kinetics (final concentrations) for a hydrogel and commercial media dosage of 200 g/L in the spent IX brine ...... 61

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6.2 pH change over time with a media dosage of 200 g/L in the spent IX brine ...... 61

6.3 Final arsenic concentrations with a media dosage of 200 g/L and 60 minutes of contact time in the IX brine matrix ...... 63

6.4 Final pH with a media dosage of 200 g/L and 60 minutes of contact time in the IX brine matrix ...... 63

6.5 Final nitrate concentrations in the IX brine with a media dosage of 200 g/L and 60 minutes of contact time ...... 64

6.6 Final perchlorate concentrations in the IX brine with a media dosage of 200 g/L and 60 minutes of contact time ...... 65

6.7 Final sulfate concentrations in the IX brine with a media dosage of 200 g/L and 60 minutes of contact time ...... 65

6.8 Final chromium concentrations in the IX brine with a media dosage of 200 g/L and 60 minutes of contact time (113 g/L media dosage for HG-1P) ...... 66

6.9 Arsenic removal kinetics from the RO concentrate with a media dosage of 40 g/L ...... 67

6.10 pH reduction over time during arsenic removal from the RO concentrate with a media dosage of 40 g/L ...... 68 6.11 Final silica concentrations in the RO concentrate with a media dosage of 40 g/L and 30 minutes of contact time ...... 69

6.12 Final phosphate concentrations in the RO concentrate with a media dosage of 40 g/L and 30 minutes of contact time ...... 69

6.13 Final nitrate concentrations in the RO concentrate with media dosage of 40 g/L and 30 minutes of contact time ...... 70

6.14 Final sulfate concentrations in the RO concentrate with a media dosage of 40 g/L and 30 minutes of contact time ...... 70

6.15 Final calcium concentrations in the RO concentrate with a media dosage of 40 g/L and 30 minutes of contact time ...... 71

6.16 Final magnesium concentrations in the RO brine with a media dosage of 40 g/L and 30 minutes of contact time ...... 71

6.17 Iron leaching from media at a media dosage of 40 g/L and 30 minutes of contact time in the RO concentrate with non-detectable iron ...... 72

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FOREWORD

The Water Research Foundation is a nonprofit corporation that is dedicated to the implementation of a research effort to help utilities respond to regulatory requirements and traditional high-priority concerns of the drinking water community.

The Arsenic Water Technology Partnership (AWTP) program is a partnership between Water Research Foundation, Sandia National Laboratories (SNL) and WERC, a Consortium for Environmental Education and Technology Development at New Mexico State University that is funded by DOE and the Water Research Foundation. The goal of the program is to provide drinking water utilities, particularly those serving small and rural communities, with cost- effective solutions for complying with the new 10 ppb arsenic MCL. This goal is being met by accomplishing three tasks: 1) bench-scale research to minimize operating, energy and waste disposal costs; 2) demonstration of technologies in a range of water chemistries, geographic locales, and system sizes; and 3) cost effectiveness evaluations of these technologies and education, training, and technology transfer.

The AWTP program is designed to bring new and innovative technologies developed at the laboratory and bench-scale to full-scale implementation and to provide performance and economic information under actual operating conditions. Technology transfer of research and demonstration results will provide stakeholders with the information necessary to make sound decisions on cost-effective arsenic treatment.

The Foundation participates in the overall management of the program, helps to facilitate the program’s oversight committees, and administer the laboratory/bench-scale studies. SNL conducts the pilot-scale demonstrations and WERC oversees the education, training, economic analysis, and outreach activities associated with this program.

David E. Rager Robert C. Renner, P.E. Chair, Board of Trustees Executive Director Water Research Foundation Water Research Foundation

ACKNOWLEDGMENTS

This report is the product of a collaborative effort between the members of the Arsenic Water Technology Partnership and was made possible by funds from congress and the drinking water community. A special thanks to U.S. Senator Pete Domenici for his support and assistance in helping to bring low-cost, energy efficient solutions for the removal of arsenic from drinking water.

The authors of this report would like to thank the Water Research Foundation project manager, Hsiao-wen Chen for all her support and encouragement during the project. The authors also wish to thank the Project Advisory Committee members, Thomas J. Sorg (USEPA), Bruce Thomson (University of New Mexico), Patrick V. Brady (Sandia National Laboratories), and Peter Nathanson of Doña Ana Community College, who graciously stepped in after Patrick Brady resigned his duty as a PAC member towards the end of the project. Their valuable comments and suggestions throughout the project are greatly appreciated.

A number of utilities and staff participated in the study by providing operational information and water samples: Bob Field (Victor Valley Water District, Calif.); James Conley (Sarasota County/Carlton Water Treatment Plant, Fla.); Jim Taylor, Adam Ly (City of Pomona, Calif.); David Pedersen, Craig David, Toby Taube (Los Angeles County Public Works, Calif.); T.J. Kim (formerly with County of Los Angeles Department of Public Works, Water Works Division, Calif., and currently with Brown & Caldwell); Julius Ma, George Cambero (Elsinore Valley County Water District, Calif.); Gary Stolarik, Roberto Ruiz (Los Angeles Department of Water and Power, Calif.); Bob Bostic, Casey Quinn, Mariano Baltazar, David Winn (City of Signal Hill, Calif.); West Curry (City of Corona, Calif.); Scott Burton, Rick Cunningham (Chino Desalter Authority, Calif.); Norris Brandt, Randy Sundberg, James Hyde, Melinda Bergen (Irvine Ranch Water District, Calif.). Special thanks go to staff at the City of Signal Hill, Calif., for providing their site and other in-kind services during IX and RO brine testing.

The authors would also like to thank a number of staff at Carollo Engineers for assistance with the project: Travis Powell and James Russell for delivering water samples; Stacey Lara, Stacy Fuller, Jason Berroteran, Jesse Thurston, Beth Morgan, Phat Nguyen, and Barbara Schmidt with preparing the document; Matthew Parrott, Tony Ventura, and Lana Yao with graphics; and Laura Corrington for reviewing and editing the document.

Finally, Megan Ferguson and Arthur Fitzmaurice with CalTech, Pasadena, Calif. assisted with providing lab equipment during hydrogel production, and Peter Min in Vista Verde School, Irvine, Calif. provided a digital microscope used in dehydration tests.

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EXECUTIVE SUMMARY

BACKGROUND

There is a need for new cost-effective arsenic treatment technologies for small systems in the U.S. and other parts of the world where minimal operational and maintenance resources are available. Among the arsenic treatment alternatives, single-use media adsorption provides the simplest approach for treatment of arsenic at the wellhead. Unlike other conventional treatment processes, such as membrane filtration, ion exchange (IX), or coagulation/filtration, for which operations may be complex and liquid waste generated requires on-site disposal, the single-use approach is simple, often requiring no additional chemicals, and minimizes the generation of arsenic-laden liquid waste that is difficult to manage. Thus, recent developments in arsenic treatment have focused on innovative media that can reduce operating costs, staffing requirements, and quantities of residual waste. Commercially available single-use adsorbents include granular iron media, resin-based media, titanium-, zirconium-, or lanthanum-based media. In addition, there are other innovative adsorbents that have been developed by various researchers around the world. One of these media is a biopolymer and iron-based hydrogel adsorbent media developed by Min and Hering (Min 1997) for the removal of arsenic and other anionic contaminants, including selenium (Se) and chromium (Cr), from water and process wastewater. The adsorption of arsenic by iron-doped biopolymer-based adsorbent was demonstrated to be effective in removing arsenic over a wide range of conditions tested (Min and Hering 1998a, 1998b). The hydrogel adsorbent media were tested extensively in 2003, as part of Water Research Foundation’s project entitled “Innovative Alternatives to Minimize Arsenic, Perchlorate, and Nitrate Residuals” (Min et al. 2005a), for the removal of arsenic in IX brine.

PROJECT OBJECTIVES AND APPROACHES

The goals of this project were to investigate the feasibility of the hydrogel media technology for cost-effective treatment of drinking water and also minimization of brine or concentrate by utilizing dehydration of the media. Specifically, the objectives of this project include the following:

• Optimize the hydrogel media for arsenic treatment. • Demonstrate the feasibility of hydrogel media for removal of arsenic in various drinking water sources. • Evaluate the feasibility of using micron-sized hydrogel as a coagulant aid. • Evaluate the performance of hydrogel media in minimizing the IX brine or reverse osmosis (RO) concentrate collected from full-scale treatment plants.

In order to meet these objectives, the following tasks were performed by the project team:

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• Literature review. • Synthesis of 11 variations of hydrogel adsorbent as single-use media for arsenic removal. • Bench-scale batch testing of the hydrogel media using five groundwaters of varying water quality. • Jar testing of surface water using micro-hydrogel. • Bench-scale batch testing of IX brine and RO concentrate with high levels of arsenic and other constituents. • Use of commercial media to compare hydrogel media performance.

SUMMARY AND CONCLUSIONS

Hydrogel Media Optimization

• Various synthesis processes were used to produce 11 types of hydrogel media during the optimization phase. The variations included media size, iron loading, stability, and other enhancements. • Typical hydrogel media were uniform in size and had similar physical characteristics as commercially available resin-based media. • The size of the media produced ranged from 500 to 700 µm for the standard hydrogel media and 200 µm for the micro-hydrogel. • In addition, the media were dehydrated using air to reduce the spent media volume to as low as 4 to 7 percent of the original media, which is about 17 to 20 fold reduction from the original volume. • With a column setup for a dehydration test, 50 ml of hydrogel media was reduced with airflow to 3 ml in four hours, resulting in only 6 percent of the original volume. Such reduction in spent media will significantly minimize the residual management effort.

Single Use Hydrogel Media in Drinking Water Treatment

• Most of the hydrogel media produced exhibited arsenic removal capacity for different sources of groundwater with various arsenic speciation, silica, sulfate, phosphate, nitrate, perchlorate, chromium, and pH levels. Under the conditions used, arsenic removal efficiency of hydrogel media was comparable to that of commercial media. A number of hydrogel media showed promise for arsenic removal in groundwater with arsenic ranging from 15 μg/L to 540 μg/L. • Two of the hydrogel types tested (HG-7 and HG-8) with groundwater containing an arsenic concentration of 38 μg/L reduced the final arsenic concentrations to less than 2 μg/L in batch tests, which is comparable to the results of two commercial resin- based media (Resin-1 and Resin-2). In addition, three other hydrogel media types (HG-3, HG-5, and HG-6) showed final arsenic concentrations of less than 4 μg/L, similar to iron-based media (Iron-1) from the initial arsenic concentration of 38 μg/L. • At least one type of hydrogel media also showed a comparable arsenic removal capacity, with resin-based media for groundwater spiked with 540 μg/L of arsenic. For this water that also contains 160 mg/L of nitrate, final arsenic concentrations were

approximately 5 μg/L for HG-1, 10 μg/L for Resin-1, and non-detect for Resin-2, all showing more than 98 percent arsenic removal. • The kinetics data indicate that four of the hydrogel media tested (HG-1 through HG- 4) showed slower kinetics than resin or iron-based media tested as comparison. Further testing of other hydrogel media (HG-7 and HG-8), which exhibited better arsenic removal than other hydrogel media, is recommended. • Total iron leaching from the hydrogel media was minimum, comparable to that of resins, as expected, since iron is incorporated within the hydrogel media (unlike iron- based media that released about eight times more iron than either hydrogel or resin- based media). • Hydrogel media did not remove any significant amount of silica, sulfate, nitrate, or perchlorate. Such low removal of competing ions is desired as arsenic adsorption capacity is not compromised. Resin-based media removed significant amount of these anions while iron-based media only showed removal of silica. All media showed more than 50 percent removal of phosphate, a strong competing anion for arsenic, with a spiked initial phosphate concentration of 1.5 mg/L. Approximately 30 to 40 percent of chromium (Cr(VI)) removal was observed for hydrogel and iron media in groundwater, while more than 50 percent removal was obtained for resin-based media. The removal of these competing ions may decrease the potential arsenic removal capacity of the media, since these competing ions occupy adsorption sites that could otherwise be used for arsenic removal.

Micro-Hydrogel as a Coagulant Aid

• Based on the preliminary test results, micro-hydrogel in the size range of 200 microns with a wet media dose in the range of 0.2 to 2 g/L, did not produce greater arsenic removal when compared to a 30-mg/L ferric chloride dose. • One advantage of applying micro-hydrogel media over dispersed ferric chloride was rapid settling of the hydrogel (1 to 2 minutes), compared to 30 minutes for dispersed- phase iron. • In addition, it is expected that the settled micro-hydrogel media can be managed better than ferric sludge during dewatering. • In addition, the hydrogel media did not show any TOC or bromide removal under the conditions tested, as expected, whereas a marginal TOC removal was achieved with a high level of ferric chloride only. • The combination of iron and micro-hydrogel media did not seem to provide any added benefit, as settling time for the iron flocs was still 30 minutes, negating the benefit of the rapid settling of the micro-hydrogel.

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Arsenic-Laden Brine and Concentrate Treatment

• Hydrogel media were effective at treating high levels of arsenic, up to 300 µg/L, from both the IX brine and the RO concentrate streams to concentrations lower than the detection levels. • The impact of competing anions (e.g., silica, phosphate, nitrate, and sulfate) on hydrogel media performance was less than that observed on commercial media. • Specifically, silica and sulfate are commonly present in groundwater and thus, are concentrated in spent liquid residual streams. Inhibition of arsenic removal by silica is a major concern for commercially available media as it reduces the total capacity of the media by coating the surface of the media. Hydrogel media may be used as an alternative where high silica, sulfate, and other competing ions may be an issue, especially when dealing with liquid-phase residuals. • With an initial chromium concentration of 1.6 mg/L in the IX brine, the hydrogel media showed 50 to 94 percent reduction of Cr(VI) under the conditions tested, with a significant amount of other anions such as nitrate, sulfate, alkalinity, etc. For one hydrogel (HG-2), Cr(VI) was reduced to less than the detection limit of 100 μg/L from the initial chromium concentration. The reduction of Cr(VI) using the commercial media was less effective, showing only 20 to 30 percent removal. As such, reduction of chromium in the IX brine by hydrogel can be a promising application. • The presence of cations in the RO concentrate (e.g., calcium (Ca) and magnesium (Mg) ions) will likely enhance the arsenic removal efficiency, as reported in a previous study (Min 1997). All media tested with RO concentrate showed effective arsenic removal, in the range of 97 percent removal, within 15 minutes of contact time for some media (HG-2 and HG-3). The same percent removal was observed within 30 minutes for all commercial media tested. • Overall, arsenic removal was observed in spent IX brine and RO concentration, where the concentration of competing anions was 3 to 4 orders of magnitude higher than the concentration of arsenic. • In the presence of high carbonate concentrations, exceeding several thousand mg/L, the hydrogel media swell. However, this effect can be mitigated by lowering the pH and aerating the brine prior to contact with the hydrogel to purge out the dissolved CO2. A number of IX plants implement pH reduction in the brine to minimize scaling in the spent brine, and only the aeration of a small brine stream, of typically 0.5 to 2 percent of the influent flow, will be needed for the implementation of hydrogel media where the alkalinity is high. No swelling of the hydrogel media was observed in the RO concentrate or drinking water, where alkalinity is much less that that observed for the IX brine.

RECOMMENDATIONS AND FUTURE RESEARCH

A number of small utilities are considering installing adsorptive arsenic removal systems because of its simplicity compared to other treatment options. However, the cost of implementing the adsorption media technologies is still expensive in comparison to other

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alternatives, (e.g., coagulation filtration), because of the costs associated with replacing the media. There are, however, a few approaches to reduce the cost of implementing the adsorption technology.

Develop media with a high capacity for arsenic uptake. In this case, the media can be used for a prolonged time prior to replacement, thus reducing the life-cycle cost of arsenic treatment. However, the disadvantage of such media may be the significant accumulation of arsenic in the spent media over time, beyond the hazardous waste limit. Develop less-expensive media than the media in the market today. One of the ways to achieve this it to develop media with simplified manufacturing steps to minimize the cost. The proposed hydrogel has the potential to reduce the cost of the media because it requires only a few detailed steps to synthesize the media. There are different methods to produce the hydrogel media, and manufacturing information would be critical to project an accurate media cost, depending on the size of the batch and the procedures used. The production of hydrogel media requires three common chemicals and typical equipment such as containers, pumps, and mixers. Reduce media disposal cost. The overall cost of implementing the media technology can be decreased by reducing the final disposal cost of the spent media. One way to achieve this is by reducing the media volume and weight. As noted, the hydrogel media can be reduced by twenty- fold in volume, which may help further reduce the implementation cost.

Based on the findings from the current project, further evaluation of the proposed technology would be beneficial in order to implement the adsorption technology for arsenic compliance. This project demonstrated effective removal of arsenic by the hydrogel media for a number of treatment applications, including groundwater, IX brine, and RO concentrate using eight different source waters. Thus, further research is recommended in the following areas:

• Evaluate the removal of As(III) with a modified hydrogel enhanced for As(III) removal without pre-oxidation. A few modifications to the media synthesis were conceptualized to enhance the removal of As(III) with hydrogel during this project. Depending on the efficiency of As(III) removal, the hydrogel media may be used without an oxidation step in cases where arsenic is present as As(III). Typically, commercial media for arsenic treatment exhibit some As(III) removal, but the extent of As(III) removal is typically much less than that for As(V). Thus, when arsenic is present as As(III), a pre-oxidation step is generally recommended by media suppliers to utilize the media capacity for arsenic removal, and the research in this area may minimize the use of chemicals. • Develop methods to mass produce the hydrogel to better assess the cost of the media. Since more media will need to be produced to conduct column tests, the evaluation of production techniques can be done prior to the testing. There are a number of methods to control the size of the media and the production rates, depending on the media manufacturing setups used. Various hydrogel synthesis methods were evaluated at the bench scale to produce up to 5 gallons of hydrogel media, but an additional effort is needed for manufacturing larger batches. There are at least several methods to create hydrogel media, and in particular the following aspects can be further developed: 1) reduce the size of the media using optimized dispensing techniques; 2) develop alternative methods to increase media production

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rates using multiple channels; 3) minimize the time for media cross linking for hydrogel formation and doping. In addition to these three core areas to reduce manufacturing costs, other developments can be implemented as necessary (such as alternative chemical supply) to deal with recycling of chemicals and continuous production methods. • Perform column tests to assess and confirm the performance of the media. A flow-thorough column test is necessary to obtain scale-up information for the media application and provide information on empty bed contact time, hydraulic loading rate, etc. Since an RSSCT type test is not recommended for the hydrogel media, as the media cannot be subjected to grinding, typical column tests, using 15 mm diameter columns, can be used to compare the arsenic breakthrough curves for hydrogel and other commercial media. This test can be done either with groundwater or arsenic-laden brine samples. In addition to the bench scale testing, a pilot-scale column test is also recommended to evaluate a more operational oriented performance such as backwashing and pressure drop in the vessels. • Confirm the removal efficiency of hydrogel for other co-occurring contaminants such as Cr(VI) and Se. Although this was not the focus of this project, the hydrogel media have shown effective removal of chromium in the IX brine during this study. Also, previous tests showed an effective removal of selenium. Thus, the application of hydrogel media for other groundwater treatment would benefit utilities, which may have these co-occurring contaminants. A series of quick screening batch tests can be performed to further evaluate the efficacy of hydrogel media for other contaminants.

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CHAPTER 1 INTRODUCTION

BACKGROUND

The recent regulatory decrease in the arsenic maximum contaminant level (MCL) from 50 μg/L to 10 μg/L affects both large and small utilities, and has promoted the development of alternative arsenic treatment technologies. Specifically, since many small utilities are affected by this change, there is an inherent need for innovative, cost-effective and low-maintenance arsenic treatment systems. The hydrogel adsorbent, which was developed in the early 1990s as part of previous research efforts, has a potential to cost-effectively treat arsenic under variable water quality conditions (Min 1997, Min and Hering 1998a, b). The main objectives of this demonstration project are to a) Evaluate arsenic removal from drinking water and spent brine; and b) Demonstrate the reduction of spent media volume using dehydration. Among the various arsenic treatment processes, single-use media and sorption technology is more attractive to small utilities than other technologies, as it provides a simple approach for wellhead treatment that also minimizes generation of arsenic-laden liquid waste. The research described here will further optimize and demonstrate the hydrogel adsorbent media using the research approach described in the subsequent sections.

ARSENIC REGULATORY OVERVIEW

Arsenic Drinking Water Regulation

On January 22, 2001, the United States Environmental Protection Agency (USEPA) adopted a new arsenic standard of 10-μg/L. After publishing the final arsenic rule, USEPA postponed the effective date of the rule until February 22, 2002. The following year (March 2003), the California Office of Environmental Health Hazard Assessment (OEHHA) released a draft Public Health Goal (PHG) of 0.004 μg/L (4 ng/L) for arsenic in drinking water based on the mortality of arsenic-induced lung and urinary bladder cancers observed in epidemiological studies of populations in Taiwan, Chile, and Argentina (OEHHA 2003). On April 23, 2004, OEHHA announced the publication of the final PHG for arsenic in drinking water. The PHG of 4 ng/L was confirmed as a level of arsenic in drinking water that would not be expected to pose a significant human health risk. This PHG and other factors, such as residual treatment cost, will be considered by the California Department of Health Services (CDHS) for developing a California arsenic standard. In the meantime, the new federal arsenic MCL of 10 μg/L became effective on January 23, 2006. In New Jersey, costs are not considered in setting the MCL for carcinogens, and a final arsenic MCL of 5 μg/L was adopted based on the analytical limitation, treatability, and risk factor (New Jersey Register 2004). Most other states, adopted the 10-μg/L MCL. A summary of pending and proposed arsenic regulations and health goals is shown in Table 1.1.

Table 1.1 Arsenic drinking water regulations State MCL Note USEPA and most states 10 μg/L USEPA MCLG* is zero California Pending Final Public Health Goal is set at 0.004 μg/L New Jersey 5 μg/L Final Public Health Goal is set at 0.003 μg/L (New Jersey Register 2004) * Maximum Contaminant Level Goal

Arsenic Waste Discharge and Disposal Regulations

Arsenic residuals from treatment plants that remove arsenic can be classified into two categories: solid and liquid. Examples of solid arsenic-laden wastes include spent media or resin, and examples of liquid wastes include brine from ion-exchange processes or backwash water from conventional filters. A summary of arsenic residual management methods categorized by solid or liquid residuals is provided in Table 1.2.

Table 1.2 Management of solid and liquid waste from arsenic treatment processes* Treatment Form of Arsenic in the Potential disposal technology residual Type of residual waste stream? methods IX (regenerable) Liquid Spent brine Yes Treat and discharge to brine line or discharge to holding tank and haul. Rinse/backwash No Discharge to sewer or waste same options as spent brine if mixed with brine. Solid Spent resin No Disposal to landfill. Media adsorption Liquid Backwash Yes Discharge to sewer if (single-use) arsenic level is low. Solid Spent media Yes Disposal to landfill. Media adsorption Liquid Backwash Yes Treat (if necessary) and (regenerable) discharge to sewer. Spent Yes pH adjustment and regeneration discharge to sewer solution Solid Spent media No Disposal to landfill

(continued)

Table 1.2 (continued) Treatment Form of Arsenic in the Potential disposal technology residual Type of residual waste stream? methods Conventional Liquid Backwash No Discharge to sewer treatment Solid Settled sludge Yes Disposal to landfill Membrane Liquid Concentrate Yes Discharge to sewer, (RO, NF, and evaporation pond, or EDR) limited groundwater injection Membrane No pH adjustment and cleaning waste discharge to sewer * Modified from EPA 2000

PROJECT OBJECTIVES

The previous Water Research Foundation Project 2859 (Min et al. 2005a), led by the current project team, specifically evaluated the hydrogel media for the treatment of arsenic- containing synthetic brines as part of that project. The current project focused on testing the hydrogel media for several drinking water sources and brine and concentrate from full-scale treatment plants. As mentioned previously, one of the main objectives of this demonstration project is to evaluate and demonstrate selective arsenic removal capacity and volume minimization characteristics upon dehydration for full-scale treatment of arsenic. Some of the characteristics of this media allow several potential applications of hydrogel media for water and brine treatment. These include:

• Direct application of the hydrogel media as single-use media for drinking water treatment. • Use of the hydrogel media to treat full-scale IX brine or RO concentrate. • Application of a micron-sized version of the hydrogel media as coagulant aid for drinking water treatment.

The specific objectives of this project are as follows:

• Optimize the sorbent to enhance the physico-chemical stability of the hydrogel media under a wide range of water quality conditions (Chapter 3) • Develop arsenic adsorption characteristics data (capacity and kinetics) for direct application of the media for drinking water (Chapter 4) • Evaluate the application of this sorbent as a coagulant aid in batch jar tests (Chapter 5) • Validate performance of the sorbent for full-scale IX brine and membrane concentrate under varying matrix conditions (Chapter 6)

CHAPTER 2 OVERVIEW OF HYDROGEL MEDIA FOR ARSENIC REMOVAL

BACKGROUND ON HYDROGEL MEDIA

Development of Hydrogel Media

The hydrogel adsorbent media were developed in early 1990s at the University of California at Los Angeles (UCLA) and the California Institute of Technology (CalTech) for removal of arsenic and other anionic contaminants (selenium, chromium, etc.) (Min 1997). Due to the high arsenic sorption capacity exhibited by the hydrogel media, the initial focus of the media was placed on treating liquid wastes containing high concentrations of arsenic, in the range of few hundred µg/L to few mg/L, from industrial processes such as process water from gallium arsenide (GaAs) wafer manufacturing (Min and Hering 1998a, 1998b). This initial work with laboratory-synthesized water was conducted between 1994 and 1997. From 2002 to 2004, the hydrogel media were tested for arsenic removal from a few different types of laboratory- synthesized IX spent brines as part of the Water Research Foundation study entitled “Innovative Alternatives to Minimize Arsenic, Perchlorate, and Nitrate Residuals” (Min et al. 2005a).

Chemistry and Composition of Hydrogel Adsorbent Media

The proposed adsorbent’s composition is based on a low-cost biopolymer called alginic acid, which is a polyuronic acid extracted from various species of brown seaweeds. Alginates are commercially available as water-soluble sodium alginates and have been used for more than 65 years in the food and pharmaceutical industries as thickening, emulsifying, film forming, and gelling agents. A typical extraction process involves first washing and treating seaweed with dilute sulfuric acid (quantitatively transforming calcium alginate into alginic acid), extraction by dissolution with alkali, separation of insolubles, then precipitation as the calcium salt, followed by acid washing to recover alginic acid. The salts of alginic acid are obtained by neutralization. Alginate production facilities are located around the world, including the U.S. (Calif.), the British Isles, Norway, France, Chile, Japan, and China. This biopolymer exhibits polymerization characteristics, and the cross-linking of alginate is obtained through the binding of divalent cations, such as calcium types. Various sizes and formulations of hydrogel media allow for the simple customization for specific applications, such as removal of arsenic from drinking water or spent brine. The hydrogel media proposed for this project incorporates iron in the matrix where arsenic adsorption takes place. The hydrogel adsorbent media are similar to synthetic IX resin in appearance and characteristics. Under normal drinking water conditions, the hydrogel media are physically and chemically stable. However, under extreme conditions, such as IX brine with total dissolved solids (TDS) of 7 percent and alkalinity in the range of 5,500 mg/L, some hydrogel media types swell. One of the proposed tasks for this project is thus to optimize the hydrogel media to be more stable under these extreme conditions and also pre-treat the brine to prevent such swelling.

APPLICATION OF HYDROGEL MEDIA FOR ARSENIC REMOVAL

An important characteristic of the hydrogel adsorbent media is the capacity and selectivity for arsenic adsorption. In the adsorbent media, iron is immobilized throughout the volume of the media within the alginate polymer. Thus, arsenic (As(V)) removal occurs throughout the volume of the adsorbent rather than only at the surface, allowing arsenic sorption densities to reach nearly 1:1 on a molar basis with Fe, unlike dissolved Fe used as coagulant. High maximum arsenic adsorption densities observed in previous studies suggest that the hydrogel media can be used as single-use media (Hering et al. 2004a). The application of the proposed hydrogel media for both low-cost drinking water treatment and residual minimization poses an opportunity for this media to be further tested and optimized with regards to kinetics, sorption capacity, and interference from other anions. In addition to the high sorption capacity, the hydrogel media have a unique characteristic where the spent media can be dehydrated in air to reduce the volume and weight to as low as 5 percent of the original state (or 20 fold reduction), depending on the hydrogel media types used. Such reduction in spent hydrogel media will decrease the cost of the final disposal of the media in a landfill. The hydrogel media may be operated in variable modes, such as hydrated adsorbent or dehydrated adsorbent in typical contactors, including small household containers, or larger vessels. The water can be pumped or allowed to gravity flow to provide enough contact time with the media. A micron-sized hydrogel media (200 µm) were also used as coagulant aid, but a larger size (~500 µm to a few mm range) would be more appropriate as single-use media to minimize headloss and simplify operations and media handling. The hydrogel media does not leach iron under normal operating conditions and thus initial backwash to remove iron fines is not necessary, unlike commercially available granular iron media.

REMOVAL OF OTHER CONTAMINANTS (SELENIUM AND CHROMIUM)

In previous studies (Min 1997, Min and Hering 1998b, Min and Hering 1999) other contaminants, specifically Se(IV) and Cr(VI), were removed from a solution by sorption onto the hydrogel media used for arsenic removal. Both Se and Cr(VI) exist as oxygen containing anionic contaminants (oxyanions) and have shown to be removed by the hydrogel media. The hydrogel media were found to be effective in removing Se(IV) from the solution, while Cr(VI) removal was much less effective, and the rate of sorption was much slower than that of Se(IV). At an initial Se(IV) concentration of 400 µg/L, up to 94 percent removal of selenium from the solution was achieved at equilibrium, with 2.5 mg/L total iron incorporated in the media. Decreasing the pH increased removal and stability of the hydrogel media for Se(IV). Se(IV) sorption and kinetics data were comparable with that of As(V) (Min 1997, Min and Hering 1998a). It was reported that as the hydrogel media became saturated, the extent of sorption of Se(IV) or As(V) was decreased by the presence of competing anions such as phosphate.

EFFECTS OF OTHER ANIONS AND CATIONS ON ARSENIC REMOVAL

The removal of As(V) using the hydrogel media was tested under experimental conditions similar to process wastewater where other anions and cations were present (Min 1997). The parameters investigated were ionic strength and the presence of cations. At - - - background NO3 concentrations of 310 mg/L-NO3 and 3,100 mg/L-NO3 , the amount of As(V)

sorbed was comparable to an initial As(V) concentration of 400 µg/L, even in the presence of - extremely high nitrate concentration. As the NO3 concentration increased to 31 g/L-NO3 , the amount of As(V) sorbed decreased by 20 percent for tests with an initial As(V) concentration of 400 µg/L. At an initial As(V) concentration of 4 mg/L, the amount of arsenic adsorbed increased - with increasing nitrate concentrations of up to 3,100 mg/L-NO3 . The presence of lead (Pb), copper (Cu), and calcium (Ca) at concentrations of 1.7 mg/L, 1.5 mg/L, and 1.57 g/L, respectively, all increased the amount of As(V) sorption by approximately 50 to 125 percent with an initial As(V) concentration of 400 µg/L, and to a lesser degree (20 to 30 percent ) with an initial As(V) concentration of 4 mg/L.

POTENTIAL APPLICATIONS

For a previous Water Research Foundation project — Innovative Alternatives to Minimize Arsenic, Perchlorate, and Nitrate Residuals (Min et al. 2005a) — the hydrogel media were primarily evaluated based on its capacity to treat arsenic-containing IX brines. This project was designed to evaluate selective arsenic adsorption capacity and spent media volume minimization characteristics Figure 2.1 illustrates the flow chart depicting the proposed tasks under this project.

Literature review (Ch2)

Optimization of Hydrogel (Ch3)

Application of Application of micron Use of hydrogel to hydrogel as single sized hydrogel as a treat IX brine and use media for coagulant-aid for membrane concentrate drinking water drinking water (Ch6) treatment (Ch4) treatment (Ch5)

Adsorption capacity and Effectiveness as Residual treatment and kinetics evaluation coagulant-aid minimization

Data Analysis

Summary (Ch7)

Figure 2.1 Proposed workplan flow chart for testing hydrogel media for arsenic treatment

Each major task is described in further detail in the following chapters: Optimization of the Hydrogel Media (Chapter 3); Single-use Media Application for Arsenic Treatment in Drinking Water (Chapter 4); Application of Hydrogel Media as a Coagulant-aid (Chapter 5); IX Brine and RO Concentrate Treatment and Residual Minimization (Chapter 6); and Summary (Chapter 7).

CHAPTER 3 OPTIMIZATION OF HYDROGEL MEDIA FOR ARSENIC REMOVAL

INTRODUCTION

The hydrogel media were developed to remove anionic contaminants such as arsenic, selenium, chromium, etc. Various prototypes with different physical and chemical characteristics have been produced and tested (Min 1997), and some formulations have shown greater contaminant removal capacity and greater stability than others. The objective of this portion of the project is to further optimize and test the hydrogel media for arsenic removal using various types of waters and residual streams, including: groundwater (from a number of Southern California groundwater sources containing As(V), As(III), iron, manganese, etc.); surface water (from California State Project Water and Los Angeles Aqueduct containing arsenic, bromide, and TOC); IX brine (from a Southern California utility with high nitrate, sulfate, perchlorate, chromium(VI), and spiked arsenic), and RO membrane concentrate (from a Southern California utility with high nitrate, sulfate, phosphate, calcium, magnesium, and spiked arsenic). In addition, the removal of other water quality parameters such as silica, sulfate, alkalinity, nitrate, perchlorate, phosphate, etc., were evaluated to find out whether the arsenic removal capacity is compromised by the interference of other anions. For this project, hydrogel media were prepared as described in previously published works (Min 1997, Min and Hering 1998a, 1998b). Some processes were modified as needed to optimize the hydrogel adsorbent performance and simplify production. The hydrogel media exhibit physical characteristics similar to acrylic gel IX resins. Alternative methods for synthesizing the hydrogel media were also evaluated and tested. The goal of this task was to further enhance the formulation of the media such that the adsorbent could be used under varying operating and water quality conditions (e.g., water treatment and residual treatment). During the initial prototype development of the hydrogel media (Min 1997), several synthesis processes were evaluated and tested, some of which included different techniques to enhance the kinetics and capacity of the adsorbent. These process modifications were revisited in this project to evaluate whether other cost-effective modifications could be made to the formulation. The details of these formulations are not included in this report due to the proprietary nature of the information. The results from various types of hydrogel media tested for performance of arsenic sorption capacity are presented in Chapters 4 through 6 of this report.

MATERIALS AND METHODS

Sodium alginates with different gulurionic (G) and mannuronic (M) content from various sources were used in preparing different types of hydrogel media. An appropriate amount of sodium alginate powder was transferred to a container with distilled water. The polymer solution was mixed until no gel mass was observed. Depending on the concentration and viscosity grade of the polymer, the time required for the polymer powder to dissolve ranged from a few hours to a few days. The yellowish viscous solution was then stored in a refrigerator until used.

Hydrogel Media Synthesis

The purpose of employing various media synthesis techniques was to optimize the performance of hydrogel media. Hydrogel media synthesis has been described in previous studies (Min 1997, Min and Hering 1998a, 1998b), and an overview of the process is summarized here. Alginate media were prepared by cross-linking the sodium alginate with a calcium chloride solution. This technique allows the formation of base media. A peristaltic pump was used to dispense the polymer solution using a small tip setup from the surface of the calcium solution. The solution was stirred gently to allow mixing of the media in a calcium solution. The calcium media were then rinsed with distilled water and transferred to a ferric solution to incorporate iron into the hydrogel media and thus provide the binding sites for arsenic. Five different alginate polymers with various compositions were used in synthesizing the hydrogel media. After the iron incorporation, the hydrogel media were either washed with dilute hydrochloric acid (1 mM) or DI water (HG-1 through HG-6) to remove excess iron. For polymer 1b, a higher polymer concentration was used to make hydrogel media HG-2, and for polymer 2, different iron loading and washing techniques were used to produce hydrogel media HG-7 and HG-8. In addition, a secondary agent was used to change the sorption properties in one hydrogel (HG-1P) and smaller size hydrogel media were prepared to improve adsorption kinetics in two others (HG-2M and HG-9M). Detailed characterization of the media, such as iron content, surface area, etc., was not performed as it was beyond the scope of this project where the focus was to compare the performance of hydrogel media to commercial media.

Dehydration of Spent Hydrogel Media in Column Mode

Limited tests were performed to dehydrate the hydrogel media in ambient air by placing the media in various plastic containers without active circulation of air. Approximately 4 to 5 grams of wet media were allowed to air-dry at room temperature for up to 2 days. The initial weights of the media were measured after the surface moisture was removed with absorbent tissues (Kimwipes). Each type of media was spread on a weight boat and the weight of each weight boat with the media was measured with an analytical scale (OHAUS N12120, Switzerland). A controlled test was also performed with the media in a column, where an external air source was introduced to facilitate the dehydration and thus reduce drying time. The drying of the hydrogel media was accomplished with an air pump (Coleman, Wichita, Kan.), attached to a 30-cm height, 1.5-cm diameter glass column (ACE glass, Richmond, Va.) fully packed with HG-6 hydrogel media (Table 3.1). The airflow rate was measured with an airflow meter of approximately 0 to 1 standard cubic feet per minute (scfm) (McMaster-Carr, Calif.). The flow rate was adjusted to 0.7 scfm using a flow meter. The media were dried with air for up to 240 minutes, during which the media height was measured every 10 to 20 minutes. After this drying period, the media remained in the column overnight without any air flow (i.e., no drying). Forced air was reintroduced the following day for another 40 minutes to confirm that no additional drying of the media took place.

RESULTS AND DISCUSSION

Hydrogel Media Characteristics

In order to evaluate the performance of the various hydrogel media types, three commercially available media were also tested side-by-side with the hydrogel media for selected tests performed. These include two resin-based media (Resin-1 and Resin-2) with similar physical characteristics as hydrogel media, and one granular media (Iron-1), which is more widely used. A summary of these media, including shape, color, size range, and other production conditions is presented in Table 3.1.

Table 3.1 Characteristics of commercial media, resins, and hydrogel media selected for bench-scale testing Physical characteristics Size Single-use media Name Description (shape, color, etc.) (µm) type Dark brown and dark red Iron incorporated IX 300- Resin-1 spherical resins (wide size IX resin-based media resin 1,000 distribution range) Black and dark brown Iron incorporated IX 400- Resin-2 spherical resins (wide size IX resin-based media resin 900 distribution range) Iron based granular 100- Iron-1 Dark brown granular media Dry granular media media 2,000 Acid/DI washed or Hydrated or dehydrated Light brown spherical HG-1 ~500 dehydrated hydrogel media w/polymer 1-L2 media (uniform size) media Hydrated media Light brown spherical Hydrogel media doped HG-1P ~500 w/polymer 1-L2P media (uniform size) with a secondary agent Acid/DI washed or Hydrated or dehydrated Light brown spherical HG-2 ~400 dehydrated hydrogel media w/polymer 1b-L4 media (uniform size) media Micro hydrated media Light brown spherical HG-2M ~200 Micro hydrogel media w/polymer 1b-L4 media (uniform size) Acid/DI washed or Hydrated or dehydrated Light brown spherical HG-3 ~500 dehydrated hydrogel media w/polymer 2-M2 media (uniform size) media Acid/DI washed or Hydrated or dehydrated Light brown spherical HG-4 ~700 dehydrated hydrogel media w/polymer 3-W2 media (uniform size) media Cont…

Table 3.1 Characteristics of commercial media, resins, and hydrogel media selected for bench-scale testing Physical characteristics Size Single-use media Name Description (shape, color, etc.) (µm) type Acid/DI washed or Hydrated or dehydrated Light brown spherical HG-5 ~600 dehydrated hydrogel media w/polymer 4-I2 media (uniform size) media Acid/DI washed or Hydrated or dehydrated Light brown spherical HG-6 ~500 dehydrated hydrogel media w/polymer 5-F2 media (uniform size) media Hydrated media Light brown spherical Hydrogel media with HG-7 ~500 w/polymer 2-M2-F media (uniform size) higher iron loading Hydrogel media with Hydrated media Light brown spherical HG-8 ~500 higher iron loading w/polymer 2-M2-FO media (uniform size) and washing Micro hydrated media Light brown spherical HG-9M ~200 Micro hydrogel media w/polymer 3-W4 media (uniform size)

Photos of Commercial and Hydrogel Media

Among the commercially available arsenic removal media, the resin-based media are the most similar to hydrogel media in their physical characteristics and potential application in terms of backwashing and packing in the contactors. Resin-based media, shown in Figures 3.1(a) and (b), and granular media, shown in Figure 3.1 (c), were used as baseline media to compare the performance against hydrogel media. As shown in Figure 3.1, the resin-based media have wide size distribution range and appear to be dark in color. The granular media contains iron fines that must be washed out prior to use. On the other hand, the resin-based media and the hydrogel media do not require an extensive pre-rinsing step since iron leaching is minimum. The hydrogel media appears to have lighter color (dark orange/light brown) compared to the commercial resin-based or granular media, but has uniform media size. Photos of four selected hydrogel media are shown in Figure 3.2.

Dehydration Characteristics

One of the unique characteristics of the hydrogel media is the dehydration property. As mentioned previously, the hydrogel media typically contain over 90 percent of water. Once the hydrogel media are removed from the water for extended period of time, they are dehydrated in ambient air similar to wet media, such as granular ferric hydroxide (GFH). Typically, after several hours of dehydration at room temperature, a steady-state dehydration state is reached. An example of the hydrogel media before and after dehydration is shown in Figure 3.3. Depending on the formulation, dehydrated media exhibit about twenty times less weight and volume than hydrated media. If the hydrogel media are allowed to completely dehydrate, the media will not swell back to the original condition.

(a) Resin-1 (300 – 1,000 µm size) (b) Resin-2 (400 – 900 µm size)

Figure 3.1 Commercially available arsenic removal media used for comparison testing

If the hydrogel media are allowed to partially dehydrate and placed in water, it swells back to the original state (Min 1997). Thus, hydrogel media should be kept hydrated similar to IX resin or GFH. The dehydrated media will also exhibit arsenic removal, and may be better suited under certain circumstances, since more iron can be packed in a same size vessel, although the cost of such media would be higher than the hydrated media. The performance of the dehydrated hydrogel media (xerogel) is presented in Chapter 4 of this report.

(a) HG-1 (~500 µm size) (b) HG-2 (~400 µm size)

(c) HG-3 (~500 µm size) (d) HG-4 (~700 µm size) Figure 3.2 Selected hydrogel media (HG-1 through HG-4) used for arsenic removal

~500 μg/L ~500 μg/L

(a) Completely hydrated hydrogel media (b) Completely dehydrated hydrogel media

Figure 3.3 Hydrated and dehydrated hydrogel media (shown under 60 × magnification)

Dehydration Kinetics

Figures 3.4 (a) through (f) show time-lapsed photos of HG-2 hydrogel media dehydration over a 1-hour period (10-minute increments). Although the media were allowed to dry for more than 4 hours, there was no difference in size between the samples at 50 minutes and all subsequent samples, indicating that most of the dehydration occurred within the first hour. The dehydration was conducted at room temperature, but it is likely that the light from the microscope increased the temperature on the drying surface accelerating the drying process. Depending on the ambient temperature, humidity, and amount of media exposed, the dehydration process can take anywhere from a few hours to a few days.

Dehydration of the Spent Hydrogel Media

Approximately 10 hours after the media were allowed to dehydrate in ambient air in plastic containers without any forced airflow, most of the media reached a final equilibrium weight. After approximately 22 hours, no measurable weight reductions were observed, as shown in Figure 3.5. The final percent weight of the dehydrated commercial media were 40 percent, 49 percent, and 35 percent for Resin-1, Resin-2, and Iron-1, respectively. In comparison, the final percent weight of the dehydrated hydrogel media were as low as 5 percent, 7 percent, 4 percent, and 5 percent for HG-1, HG-2, HG-3, and HG-4, respectively. These significant reductions in weight and size of the hydrogel media may result in decreased final disposal and handling costs.

Dehydration of the Spent Hydrogel Media in a Column

The hydrogel media can be dehydrated with an airflow directly to the column/container such that the spent media volume and weight can be reduced prior to final disposal. This section describes the results from the column dehydration test performed with HG-6 media. This test was done in a glass column (1.5 cm in diameter and 30 cm in height) filled to the top with new hydrogel media (about 50 mL). With an airflow rate of approximately 0.7 scfm in down-flow mode, it took approximately 4 hours to dry the media at ambient temperature to a point where no apparent volume reduction was observed. Figure 3.6 shows a reduction in height of the remaining media over time. During the media dehydration, the top layer of the media in the column dried first, as expected, since the air was in direct contact with the hydrogel media, and subsequently, the bottom layer dried to a point where all hydrogel media were dried. The height of the media was reduced from 30 cm to 1.5 cm (i.e., 28.5 cm reduction) at the end of drying. Despite the disadvantage of the limited contact between the media and the air in the column, dehydration of the media in this setting allows for a better control of high airflow to minimize the spent waste in the column before they are removed for disposal. However, ambient air drying may be more cost effective, especially if some drying can be achieved during transportation of the spent media.

~500 μg/L ~500 μg/L

(a) Dehydration at 0 min (b) Dehydration at 10 min

~500 μg/L ~500 μg/L

(d) Dehydration at 40 min (e) Dehydration at 50 min

Figure 3.4 Time-lapsed photos of dehydration for the hydrogel media (shown under 60 × magnification)

100 HG-1 80 HG-2 HG-3 60 HG-4 Resin-1 40 Resin-2 Iron-1 20

Percent of Initial Wet Weight (%) 0 0.0 0.5 1.0 1.5 2.0 Time (d)

Figure 3.5 Weight reductions of hydrogel media and commercial media following dehydration

28.5 cm (Equilibrium reduction in a column) 28.5 30 25 20 15 10 5 0

Hydrogel Height Reduction (cm) 0 50 100 150 200 250 300 Time (minutes)

Figure 3.6 Reduction of height of the hydrogel media in a bench column as a function of drying time

Figure 3.7 shows photos of the bench-scale column at the start and completion of column dehydration testing. The photo on the left hand side shows a column initially filled with hydrogel media. After a drying time of 240 minutes, the remaining media height was reduced from 30 cm to 1.5 cm. The final media volume remaining in the column was thus 3 mL, approximately 6 percent of the initial volume of 50 mL. The weight and volume of the hydrated media can thus be significantly reduced for final disposal and handling.

SUMMARY

The objective of this task was to simplify the synthesis process and optimize the hydrogel media to increase the stability and capacity so that they can be cost-effectively applied to treat both drinking water as well as IX brine and membrane concentrate. Approximately, a dozen hydrogel media types in the size range of 200 to 700 µm were produced for this task. The flexible formulation of hydrogel media allowed the synthesis of a number of hydrogel media types with varying size, iron content, biopolymer type, secondary functional group, and media rinsing. Customization of media for specific applications can thus be incorporated without significant changes in the formulation. Typical hydrogel media were uniform in size and had similar physical appearance as commercially available resin-based media.

Figure 3.7 Before (left, 50 ml volume) and after (right, 3 ml volume) dehydration of the media in a bench column showing 17-fold reduction in volume.

One of the characteristics of hydrogel media is the dehydration property. Dehydration of the media was performed with ambient air for hydrogel media in an open container and also with forced air in a column. Four types of hydrogel media were dried in an open container without any air circulation, and the final weight of hydrogel media were in the range of 4 to 7 percent of initial wet weight of the media. This is a reduction of the media by almost twenty-fold. Three commercial media were also dried under the same condition, and the final weight of the commercial media was in the range of 35 to 49 percent. A similar result was observed for drying the hydrogel media in a column setup using forced air through a media column. For this test, approximately 50 mL of media in a small column was reduced to 3 mL, resulting in a final volume of only 6 percent of the initial weight. Such reduction in volume (and weight) of the media will help reduce the amount of waste for final disposal.

CHAPTER 4 HYDROGEL AS SINGLE-USE MEDIA FOR ARSENIC TREATMENT

INTRODUCTION

The single-use media, which is simple to implement, has been demonstrated as a wellhead treatment process for arsenic removal at small utilities (US EPA 2005). A number of groundwater samples collected from local utilities in Southern California were used in this study to evaluate the feasibility of applying hydrogel sorbent as single-use media at the bench-scale. One of the main benefits of hydrogel sorbent compared to other single-use sorbents is that the spent media can be dehydrated by 20-fold to minimize waste volume for transportation and disposal purposes, as demonstrated in Chapter 3.

MATERIALS AND METHODS

Source Waters

Several water sources in Southern California were screened for total arsenic, arsenic speciation, pH, and other anions (chromium, selenium, perchlorate, vanadium, phosphate, silica, sulfate, alkalinity, nitrate, and others). The most critical water quality characteristics evaluated were arsenic concentration, speciation, and pH. Based on these, the following water sources have been selected for testing:

• Groundwater from the Los Angeles County Department of Public Works Well No. 50 (containing As(V)) • Groundwater from the City of Signal Hill’s Well No. 8 (containing As(III)) • Groundwater from the Chino Desalter Authority Plant Feed (containing nitrate) • Groundwater from the City of Pomona Well No. 10 (containing perchlorate, chromium, and nitrate) • Groundwater from the City of Glendale Well GS-3 (containing Cr(VI))

Selected water quality parameters from these sources are summarized in Tables 4.1 through 4.5, and additional arsenic spike levels are also noted. The total arsenic concentration in the groundwater sample from LA County’s Well No. 50 used for bench testing was approximately 38 μg/L, unless otherwise noted. The pH and phosphate were also adjusted for selected tests with this water. The total arsenic concentration in the groundwater sample from the City of Signal Hill’s Well No. 8 was 12 μg/L, where a majority of the arsenic was As(III). For selected tests, chlorine was added as described to oxidize arsenic to As(V). In addition to LA County’s Well No. 50 waters, the groundwater samples from the Chino Desalter Authority, the City of Pomona, and the City of Glendale, were used for competing ion testing. These had non-detect to low-level (<10 µg/L) arsenic, and thus for competing ion tests, arsenic was spiked using sodium hydrogen arsenate (ACS 500CT, Fisher Scientific) in the range of 73 to 540 μg/L.

Table 4.1 Water quality characteristics of groundwater from LA County Public Works, Well No. 50 Parameter Units Raw water Arsenic total (As(V) only) μg/L 38 Vanadium μg/L 30

Silica mg/L as SiO2 25 pH - 8.1–8.3 (adjusted to 7.2–7.8 for selected tests) Temperature oC 21 2- Sulfate mg/L as SO4 27 3- Phosphate mg/L as PO4 0.3 (adjusted to 1.5 for selected tests) - Nitrate mg/L as NO3 ND Iron mg/L ND–0.07

Table 4.2 Water quality characteristics of groundwater from Signal Hill, Well No. 8 Parameter Units Raw water Arsenic total μg/L 15 As(III) μg/L 12 As(V) μg/L 3 Vanadium μg/L ND

Silica mg/L as SiO2 22 pH - 8.1

Alkalinity mg/L as CaCO3 165 2- Sulfate mg/L as SO4 40 - Nitrate mg/L as NO3 ND Fluoride mg/L 0.39 Iron mg/L 0.1 Manganese μg/L 47 Chlorine mg/L 0.15 (adjusted to 4.5 for selected tests)

Table 4.3 Water quality characteristics of groundwater from Chino Desalter Parameter Units Raw water Arsenic total μg/L ND (adjusted to 540 for selected tests) pH - 8 (adjusted to 6 for selected tests)

Alkalinity mg/L as CaCO3 119 - Nitrate mg/L as NO3 160

Table 4.4 Water quality characteristics of groundwater from Glendale Parameter Units Raw water Arsenic total μg/L ND (adjusted to 73–91 for selected tests) Chromium μg/L 38 Vanadium μg/L 7 pH - 7.8 - Nitrate mg/L as NO3 38 Iron mg/L ND Manganese μg/L ND

Table 4.5 Water quality characteristics of groundwater from the City of Pomona Parameter Units Raw water Arsenic total μg/L 4.7

Silica mg/L as SiO2 24.3 pH - 7.35–8 2- Sulfate mg/L as SO4 67 - Nitrate mg/L as NO3 54 - Perchlorate μg/L as ClO4 6.7 Iron mg/L 0.01

Description of the Media

As indicated previously, parallel tests were performed using commercial media to compare the performance of the hydrogel with known media. A detailed description of a summary of the hydrogel and commercial media used for testing is presented in Chapter 3 (Table 3.1).

General Batch-Testing Approach for Arsenic Removal

The following tasks were performed for the evaluation and comparison of hydrogel and commercially available media:

• Evaluation of media dose. • Arsenic adsorption kinetics. • Effect of competing anions.

Preliminary batch tests were conducted to evaluate the effect of the media dose on arsenic removal. The results were used to find an experimental condition to be used in subsequent tests. For these tests, the commercial media (IX resin and granular iron media) and hydrogel media were dosed at concentrations of 5, 10, and 20 g/L (wet media). A water sample from LA County Well No. 50 was used to find the optimum conditions for testing. Batch contact times of 5, 15, 30, and 60 minutes were also evaluated to determine the time required for subsequent testing. Based on the optimum media dose and contact time, the performance of hydrogel and commercial media with various source waters (e.g., groundwater, surface water, IX brine, RO concentrate, etc.) and water quality (arsenic concentration, arsenic species, chromium, perchlorate, other competing ions, etc.) were tested in a batch mode. The batch tests are used to provide a quick comparison and screening of performance of various media for arsenic removal with different source waters. However, it should be noted that such an approach does not allow a quantitative prediction of the performance in a continuous column mode. Since there were a number of parameters and source waters to test, a column approach would limit the number of tests to be carried out. In fact, a breakthrough from column tests can occur only after several weeks to several months of testing one condition. In addition, the rapid small-scale column testing (RSSCT), which is often used to minimize the time for breakthrough by grinding the granular media, is not suitable for hydrogel media since the media cannot be subject to grinding. Thus, batch tests were used to evaluate the performance of various types of hydrogel media for this project, and three commercial media were included for all batch tests to provide baseline conditions. The intent of this batch-testing comparison was to evaluate the adsorptive characteristics of various types of hydrogel media compared to commercial media. The contact time used for testing is in the range of 30 minutes in batch mode, as opposed to the 2 to 5 minutes of the empty bed contact time (EBCT) typically recommended by the media manufacturers for a flow through condition. Unlike the column setup where the amount of media is much greater than the amount of water in contact, for the batch setup, the amount of media is smaller than the amount of water being tested. Thus, the batch setup requires more contact time, in the range of 30 minutes, to allow adequate adsorption of arsenic, which is the condition used for these tests.

For most batch experiments, where the effect of water quality on arsenic adsorption were evaluated, the hydrogel media were tested with a media dosage of 10 g/L and a contact time of 30 minutes. A contact time of 30 minutes was used for most of the tests since this contact time in batch mode showed good arsenic adsorption for the amount of media used during the batch testing. Other raw water conditions, with the optimum dose and a contact time of 30 minutes, were performed for comparison as follows:

• Ambient pH at 7.3-7.8 and lowered pH as noted in Tables 4.1 through 4.5. • Ambient phosphate concentration of 0.3 mg/L and spiked phosphate concentration of 1.5 mg/L for selected test (Table 4.1). • As(III) and As(V) using chlorine as an oxidizer for selected tasks (Table 4.2). • Spiked arsenic concentration of up to 540 μg/L (Tables 4.3 and 4.4). • Competing ions such as chromium, nitrate, perchlorate, etc. using various source waters.

The standard parameters analyzed during the testing included arsenic and pH. For selected tests, iron, sulfate, silica, phosphate, nitrate, chromium, perchlorate, and alkalinity were also analyzed, as appropriate. Micro-hydrogel media were also tested to evaluate the effects of media size on selected tests.

Batch Test Procedure and Reagents Used

The wet media were prepared by equilibrating commercial media and hydrogel media in water and removing surface moisture using absorbent tissues (Kimwipes). The wet media were then weighed using an analytical scale (OHAUS N12120, Switzerland), and transferred to 50-ml disposable vials (VWR, 21008-169, West Chester, Pa.) used as batch reactors. The test water was transferred to each 50-ml vial using a bottle-top dispenser (BrandTech-seripettor 4721150, Essex, Conn.), and the vial caps were tightly closed. The vials were placed in rotary shakers (ATR Rotamix RKCS with TT-50, Laurel, Md.) and mixed at 60 rpm for predetermined times. After the reaction time, the media were allowed to settle for a few seconds in the test reactors and supernatant was collected for analyses. Control tests without any media were also performed to determine if there was any adsorption of the parameters by the test setup during the experiments. For selected tests, the pH of the feed waters was decreased with 1 N HCl (reagent grade, Fisher Scientific). Phosphate spike was added using sodium phosphate monohydrate (ACS grade, Polarchem, Garden Grove, Calif.). Arsenic was added to raw water samples collected from the City of Glendale and Chino Desalter Authority using sodium hydrogen arsenate (ACS 500CT, Fisher Scientific). For Signal Hill water, liquid sodium hypochlorite available at the plant was used for chlorine addition.

Analytical Methods

Table 4.6 lists the analytical methods used by the lab and field measurements for the key parameters. The certified labs used were Montgomery Watson Harza Laboratories (MWH Labs) and Associated Laboratories (Assoc. Labs). Field measurements were performed using HACH test kits, and the results were confirmed with lab testing, as applicable.

Table 4.6 Analytical methods used in batch tests Parameter Lab Method Reporting detection limit Arsenic MWH Labs ICP-MS (EPA 200.8) 1 μg/L Chromium MWH Labs ICP-MS (EPA 200.8) 1 μg/L Iron MWH Labs ICP-MS (EPA 200.8) 10 μg/L Field HACH Method 8008 0.01 mg/L - Nitrate MWH Labs IC (EPA 300.0) 2 mg/L as NO3 - Perchlorate Assoc. Labs IC (EPA 314) 4 μg /L as ClO4 pH Field Orion portable pH Meter, Model 250 A+ - Chlorine Field HACH Pocket Colorimeter II 0.01 mg/L 3- Phosphate Field HACH Method 8048 0.01 mg/L as PO4 2- Sulfate Field HACH Method 8051 1 mg/L as SO4

Silica Field HACH Method 8186 0.1 mg/L as SiO2

RESULTS AND DISCUSSION

Comparison of the Efficiency of Selected Hydrogel Media and Other Media on Arsenic Removal

The arsenic removal efficiency for various hydrogel media types and other commercial media at varying doses was tested using LA County Well No. 50 groundwater, as previously mentioned. The effect of media dose is shown in Figure 4.1. A 10 g/L media dose with 30 minutes yielded the final arsenic concentrations in the range of 1 to 10 μg/L where a good arsenic reduction was observed for comparison of the removal efficiency among different types of media. A 20 g/L media dose, on the other hand, removed arsenic to below the detection limit for some media, making the comparison difficult. Thus 10 g/L media dose was used as a standard experimental condition. For all media doses tested, Resin-1 and Resin-2 showed the best arsenic removal efficiency. Among four types of hydrogel media tested, hydrogel HG-3 showed the highest arsenic removal efficiency and the removal efficiency was comparable to granular iron media (Iron-1) at all media doses tested. The effect of varying media doses on pH changes is illustrated in Figure 4.2. The pH was adjusted to 7.8, and the final pH range of the treated water for all media was between 7.1 and 7.8. Treatment with hydrogel media resulted in a final pH of 7.5 at a dosage of 5 g/L and 20 g/L and approximately 7.1 with 10 g/L hydrogel media dose. It is not clear why the pH was consistently lower at a dosage of 10 g/L for hydrogel media. The resin media also decreased the pH, similar to the hydrogel media. The iron media had the least effect on the final pH, where 10 g/L showed the least effect on the pH. The pH results show no clear trend as a function of media dose except for Resin-1 as shown in Figure 4.2.

5 g/L 10 g/L 20 g/L 15

10 As (ug/L) 5

<1 <1 0 HG-1 HG-2 HG-3 HG-4 Resin-1 Resin-2 Iron-1

Figure 4.1 Final arsenic concentrations with varying media dosages of 5, 10, and 20 g/L, at a contact time of 30 minutes with LA County Well No. 50 groundwater (As0 = 38 μg/L)

9 5 g/L 10 g/L 20 g/L

8 Initial pH 7.8 pH

6 HG-1 HG-2 HG-3 HG-4 Resin-1 Resin-2 Iron-1

Figure 4.2 Effect of media dosages at 5, 10, and 20 g/L on final pH at a contact time of 30 minutes with LA County Well No. 50 groundwater (As0 = 38 μg/L)

Effect of Other Types of Hydrogel Media on Arsenic Removal

The arsenic removal achieved by all available types of hydrogel media and commercial media at a dosage of 10 g/L and 30 minutes contact time is shown in Figure 4.3. The arsenic removal data for hydrogel media HG-1 through HG-4 and the commercial media were taken

from Figure 4.1 for comparison purposes. The performance of hydrogel media HG-5 through HG-8 was comparable to commercially available media. Three of the hydrogel media tested, HG-3, HG-5, and HG-6, are at least as efficient in arsenic removal as the granular iron media (Iron-1). In addition to the comparable arsenic removal efficiency, the competition or interference from other anions for hydrogels was significantly less than that of commercial media, as described in the “Interference of Silica and Sulfate” section shown later in this chapter (Figure 4.11). With regards to the pH, the hydrogel lowered the pH more than commercial media in the final effluent water, as shown in Figure 4.4. Granular iron media did not decrease the pH from the initial level.

10 g/L) μ As ( 5

<2 <2

0 HG-1 HG-2 HG-3 HG-4 HG-5 HG-6 HG-7 HG-8 Iron-1

Resin-1 Resin-2 Figure 4.3 Final arsenic concentrations with media dosage of 10 g/L and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L)

8 Initial pH 7.8

7.5

pH 7

6.5

6 HG-1 HG-2 HG-3 HG-4 HG-5 HG-6 HG-7 HG-8 Iron-1

Resin-1 Resin-2

Figure 4.4 Final pH with media dosage of 10 g/L and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L)

HG-7 and HG-8 were experimental versions of hydrogel media, which required some changes in the production technique. Thus, only a limited amount of media was produced with these formulations. For this reason, HG-7 and HG-8 were not used in the IX brine and RO concentrate tests, which required significantly higher media dose.

Arsenic Adsorption Kinetics

Figure 4.5 illustrates the kinetics of arsenic removal over a contact time of 5 to 60 minutes with a media dosage of 10 g/L. At 5-minutes contact time, the arsenic concentrations were in the range of 16 to 26 μg/L, which correspond to 32 to 58 percent removal from the initial concentration of 38 μg/L. For the commercial media, the arsenic concentrations were in the range of 15 to 21 μg/L. For the full-scale application of these media, where the EBCT of a few minutes is used, commercial media, especially the resin-based media, may require less EBCT due to faster kinetics, and thus the size of media contact vessel may be smaller. . HG-3 and HG-4 were able to reduce arsenic to below 10 μg/L within 15-minutes contact time in batch mode. After 30 minutes of contact time, all media tested resulted in arsenic concentrations lower than 10 μg/L except for HG-4. The arsenic level for HG-4 at 30-minutes contact time was higher than the level observed for 15 minutes, and this may be attributed to a test setup where individual reactors were used for each timed series sample. Similar to batch test results, hydrogel media reduced the final pH during the kinetics study as shown in Figure 4.6. Resin media also lowered the pH by approximately half pH unit, but no significant change was observed for granular iron media at up to 60 minutes of contact time.

40 HG-1 HG-2 30 HG-3 HG-4 20 Resin-1

As (ug/L) Resin-2 Iron-1 10

0 0 102030405060 Time (min)

Figure 4.5 Arsenic adsorption kinetics for up to 60 minutes contact time and a media dosage of 10 g/L with LA County Well No. 50 groundwater (As0 = 38 μg/L)

9 HG-1 HG-2 HG-3 HG-4 8 Resin-1 Resin-2

pH Iron-1

6 0 102030405060 Time (min)

Figure 4.6 pH variation over time with 10 g/L media using LA County Well No. 50 groundwater (As0 = 38 μg/L)

Effect of Arsenic Speciation on Arsenic Removal

The removal of As(III) and As(V) was investigated using groundwater from the City of Signal Hill, Calif., which typically contains 12 μg/L of As(III) and 3 μg/L of As(V). During the sample collection of unchlorinated water from a raw water sampling point, it is believed that the line may have been cross contaminated with chlorinated water, resulting in a low level of chlorine of approximately 0.15 mg/L. Although the oxidant level was low, it may have been enough to oxidize (at least partially) As(III) to As(V). The total arsenic with low levels of chlorination in the groundwater (high As(III) proportion) could not be removed as efficiently as arsenic from chlorinated groundwater, where most arsenic is expected to be in the form of As(V). This was anticipated since most media exhibit enhanced removals for As(V) compared to As(III) (Figure 4.7). Resin-2 showed the highest arsenic removal efficiency after chlorination. All hydrogel media tested showed preference for As(V) removal confirming As(III) removal with hydrogel and other media is less effective. A higher oxidant dose increased arsenic removal when As(III) was a predominant species. The Iron-1 media and Resin-1 showed only slight improvement in total arsenic removal with increased oxidant level. Figure 4.8 shows that the treated water pH was reduced during treatment with hydrogel media, especially for unchlorinated water.

Initial Total As = 15 μg/L; Initial As(III) = 12 μg/L 15 Low chlorine conc. (0.15 mg/L) High chlorine conc. (4.5 mg/L) 10 g/L) μ As ( 5

0 HG-1 HG-2 HG-3 HG-4 Resin-1 Resin-2 Iron-1

Figure 4.7 Final arsenic concentrations for low and high level chlorinated groundwater from Signal Hill Well No. 8 containing 12 μg/L of As(III) and 15 μg/L of total arsenic (media dose of 10 g/L and 30 minutes contact time)

9 Low chlorine conc. (0.15 mg/L) High chlorine conc. (4.5 mg/L) Initial pH 7.8 8 pH

6 HG-1 HG-2 HG-3 HG-4 Resin-1 Resin-2 Iron-1

Figure 4.8 Final pH for low and high level chlorinated groundwater from Signal Hill Well No. 8 containing 12 μg/L of As(III) (media dose of 10 g/L and 30 minutes contact time)

Effect of Elevated Arsenic Concentration Levels on Arsenic Removal

Typical arsenic concentrations in the raw water collected were less than 50 μg/L. For certain contaminated sites, however, arsenic levels above 100 µg/L are possible. Thus, a test was conducted by spiking water samples with elevated levels of arsenic to investigate the effects of high arsenic concentration on removal efficiencies. In order to increase the arsenic removal efficiency with the same amount of hydrogel dose for this high influent arsenic concentration, the pH of the raw water was adjusted to 6. As shown in Figure 4.9, with an initial arsenic concentration of 540 µg/L (as As(V)), all media tested, except one hydrogel media (HG-2), showed over 98 percent of arsenic removal efficiency with an equilibration time of 30 minutes in the presence of high nitrate (160 mg/L as NO3). Even for HG-2, the removal was over 85 percent under the conditions tested. HG-1 showed comparable media performance (and slightly better compared to Resin-1) for arsenic removal. Iron media was not tested due to iron leaching from the media as discussed in the next section.

Effect of Hydrogel Media Preparation and Dehydration on Arsenic Removal

Hydrogel media are rinsed with dilute acid to remove excess iron from the surface of the media after an iron incorporation step. Hydrogel media HG-1 through HG-6 were rinsed with DI water to test if this modified rinsing step could be used to simplify the media synthesis. Also, the same amount of wet hydrogel media used were completely dehydrated over a few days to compare the adsorption of pre-dehydrated media. As discussed in Chapter 3, once the hydrogel media are fully dehydrated, the media does not swell back to its original condition. Thus, the dehydrated media applied for this testing has approximately 20 fold less weight than that of other media. Among six hydrogel media, two types (HG-2 and HG-6) showed less arsenic removal with DI rinsed hydrogel media compared to the dilute acid washed media. Three types (HG-1, HG-3, and HG-4) showed slight improvement, and one (HG-5) did not show any difference in arsenic removal. It is difficult to discern whether one preparation results in better performance over the other, but DI rinse would certainly simplify and reduce the cost of the media synthesis. The dehydrated hydrogel media had the same iron content as the wet media, but the media weight was only about 5 percent of the wet media. The dehydrated HG-1, HG-3, and HG-5 hydrogel media showed about 30 percent arsenic removal (Figure 4.10) because the total weight of the media dose was only 5% (~0.5 g/L) of the amount used for the hydrogel media tests (10 g/L). However, dehydrated media may be preferred for certain cases as more iron can be packed in a unit volume; although, the media cost would be higher than hydrated media per unit volume basis.

80 Initial As 540 ug/L 8 As Initial pH 6.0

60 pH 7

40 pH As (ug/L) 6 20

ND 0 5 HG-1 HG-2 Resin-1 Resin-2

Figure 4.9 Final arsenic concentrations and pH for spiked Chino Desalter Authority found water with nitrate concentration of 160 mg/L as NO3 (media dose of 30 g/L and 30 minutes contact time)

Acid washed (regular) DI washed Dehydrated 40 Initial As 38 µg/L

20 As (ug/L)

0 HG-1 HG-2 HG-3 HG-4 HG-5 HG-6

Figure 4.10 Final arsenic concentrations with media conditions: acid washed, DI washed, and dehydrated using 10 g/L initial media dose (~0.5 g/L or 5 % of hydrogel media weight for dehydrated media weight) and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L)

Iron Leaching from the Test Media

Washing of granular iron media produces backwash water with a high concentration of particulate iron fines in the 100 mg/L range (Min et al. 2005b). Resin and hydrogel media are not

expected to leach any significant amount of iron, as iron is incorporated in either resin or hydrogel media. The hydrogel media showed a comparable amount of iron leaching when compared to Resin-1, (Figure 4.11). The finished water from granular iron media, which was pre-washed, measured a maximum iron concentration of 1.6 mg/L after 30 minutes of mixing time (non- filtered). The dehydrated hydrogel media HG-1 and HG-3 measured iron concentration up to 0.2 mg/L in the finished water as compared to hydrated hydrogel media. As previously mentioned, Iron-1 leached significant iron fines (i.e., particulate iron) during the test, where less than 5 percent of the total iron was found to be in its dissolved form.

Interference of Silica and Sulfate

Silica and sulfate are common constituents in water that affect arsenic removal. Thus the removal of these with hydrogel media and commercial media were evaluated to ascertain whether the arsenic adsorption capacities are compromised in the presence of these constituents. These are typically present in three orders of magnitude higher than arsenic. As demonstrated in Figure 4.12, the resin and granular iron media adsorbed silica strongly reducing the concentration from 25 to 8 mg/L for Resin-1, which is close to 70 percent removal of silica. The final silica concentration was 15 and 13 mg/L for Resin-2 and Iron-1, respectively. On the other hand, no significant removal was observed with hydrogel media. Therefore, it is expected that the long-term arsenic removal efficiency of hydrogel media and media life are minimally affected by the presence of silica.

Wet media Dehydrated (Hydrogel only) 1.8 1.6 1.4 1.2 1 0.8 Fe (mg/L) 0.6 0.4 0.2 0 HG-1 HG-2 HG-3 HG-4 HG-5 HG-6 Iron-1

Resin-1 Resin-2

Figure 4.11 Total iron leaching for various media using LA County Well No. 50 water (As0 = 38 μg/L) with 10 g/L media dose and 30 minutes contact time

The hydrogel media and Iron-1 did not result in any sulfate removal, and the media life, therefore, would not be affected by the presence of sulfate (Figure 4.13). As expected, the resins removed sulfate significantly due to the IX property and such removal of other anions, and this may impede arsenic removal capacity due to a possible loss of adsorption capacity.

30 Initial silica 25 mg/L 25

Silica (mg/L) 10

0 HG-1 HG-2 HG-3 HG-4 HG-5 HG-6 HG-7 HG-8 Iron-1 HG-1P Resin-1 Resin-2 Figure 4.12 Final silica concentrations with 10 g/L media dose and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L)

Initial sulfate 27 mg/L 30

20 Sulfate (mg/L) 10

0 HG-1 HG-2 HG-3 HG-4 HG-5 HG-6 Iron-1

Resin-1 Resin-2 Figure 4.13 Final sulfate concentrations with 10 g/L media dose and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L)

Effect of Phosphate on Arsenic Removal

Phosphate is an analog of arsenic and thus strongly competes with arsenic for adsorption onto iron sites. Arsenic removal efficiency was decreased slightly in the presence of high phosphate as shown in Figure 4.14, but it is not clear why a lower arsenic was observed with a higher phosphate level for HG-4, as shown in the figure. The presence of phosphate did not significantly impact the arsenic removal for the commercial media. With 1.5 mg/L of spiked phosphate, the phosphate remaining in water was in the range of 0.35 to 0.7 mg/L (Figure 4.15). This is a significant amount of anions that will likely be taking up the adsorption sites for arsenic, and such interference will decrease the arsenic removal capacity. All media tested reduced at least 50 percent of the initial 1.5 mg/L phosphate level.

Raw water (0.3 mg/L phosphate) 15 High PO4 (1.5 mg/L phosphate)

10 As (ug/L) 5

<1 <1 0 HG-1 HG-2 HG-3 HG-4 Resin-1 Resin-2 Iron-1

Figure 4.14 Final arsenic concentrations with varying phosphate concentrations with 10 g/L media dose and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L)

Initial phosphate 1.5 mg/L (Spiked) 1.5

1.0

0.5 Phosphate (mg/L)

0.0 HG-1 HG-2 HG-3 HG-4 Resin-1 Resin-2 Iron-1

Figure 4.15 Final phosphate concentrations with 10 g/L media dose and 30 minutes contact time using LA County Well No. 50 groundwater (As0 = 38 μg/L)

Removal of Competing Ions (Nitrate, Perchlorate, and Chromium)

The previous tests done with hydrogel media demonstrated removal of other oxyanions (selenium and chromium) using laboratory synthesized water (Min 1997, Min and Hering 1998b). The objective of this task was to evaluate the removal of other oxyanion contaminants in actual groundwater. For this test, groundwater containing perchlorate, nitrate, and chromium from the City of Pomona (Table 4.5) and groundwater containing chromium from the City of Glendale (Table 4.4) were used. As before, three commercial media were also tested as a basis for comparison. Iron media is similar to hydrogel media in adsorption characteristics; whereas, the resin-based media behave differently in a sense as they exhibit both adsorptive characteristics with iron component in the resin and IX characteristics inherent from the resin material. For certain ions, such as nitrate and perchlorate, these IX properties for the resin-based media result in the removal of these contaminants, unlike hydrogel media or iron-based media which rely on iron adsorption for arsenic removal. Figure 4.16 shows the removal of nitrate from the City of Pomona groundwater by both resins exhibiting IX property. Iron-based media and hydrogel media do not show any removal of nitrate. Similar effects are shown in Figure 4.17 for perchlorate, which also behaves similar to nitrate. None of the media tested removed perchlorate with the exception of two resin-based media, similar to the results shown for nitrate. Unlike nitrate or perchlorate, Cr(VI) may be removed either by IX or adsorption. However, for media that exhibit both properties, removal efficiency would be higher. In fact, resin-based media showed the highest removal for chromium as shown in Figure 4.18.

Initial Nitrate 54 mg/L 60

20 Nitrate (mg/L)

0 HG-1 HG-3 HG-5 HG-6 HG-7 HG-8 Iron-1 HG-1P Resin-1 Resin-2 Figure 4.16 Final nitrate concentrations with 10 g/L media dose and 30 minutes contact time using Pomona water (NO3,0 = 54 mg/L)

8 Initial Perchlorate 6.7 μg/L

6 g/L) μ

4 <4 <4

Perchlorate ( 2

0 HG-1 HG-3 HG-5 HG-6 HG-7 HG-8 Iron-1 HG-1P Resin-1 Resin-2

Figure 4.17 Final perchlorate concentrations with 10 g/L media dose and 30 minutes contact time using Pomona water (ClO4,0 = 6.7 μg/L)

Initial Cr 10 µg/L 10

g/L) <5 <5 μ

Cr ( Cr 4

0 HG-1 HG-3 HG-5 HG-6 HG-7 HG-8 Iron-1 HG-1P Resin-1 Resin-2

Figure 4.18 Final Cr(VI) concentrations with 10 g/L media dose and 30 minutes contact time using Pomona water (Cr0 = 10 μg/L)

Additional tests were done with groundwater from the City of Glendale, which contains higher levels of chromium than the groundwater from the City of Pomona. The adsorption kinetics for chromium is shown in Figure 4.19. For the resin-based media, chromium removal continued until the end of the test run (30 minutes). On the other hand, with hydrogel media no significant removal of chromium was observed after 5 minutes of reaction time. Previous studies (Min and Hering 1998b and 1999) reported that chromium removal exhibited two-stage kinetics where the fast adsorption with hydrogel media of up to 30 minutes was followed by a slower adsorption of up to 120 hours of reaction time. Figure 4.19 shows approximately 25% reduction in initial Cr(VI) in the first 5 minutes, and no uptake of chromium was observed after 15 minutes. It is not clear whether any further chromium uptake would have been observed if the reaction was allowed to continue beyond 30 minutes. If Cr(VI) is reduced to Cr(III) on the surface of the media and precipitate, the surface pores can be blocked to inhibit additional removal of chromium with hydrogel media, similar to the case for silica coating on the surface of the arsenic removal media. Figure 4.20 shows arsenic removal kinetics taken from the same samples, suggesting the possibility of surface precipitation with hydrogel media in the presence of chromium. Comparing Figure 4.20 (with chromium) and Figure 4.5 (without chromium) is also indicative of this effect of chromium. However, additional tests or estimates on the reduction of surface area will be needed in the future to confirm such observation and whether Cr(VI) conversion to Cr(III) indeed takes place as these tasks were beyond the scope of the current study. It is interesting to note though that significantly better performance was observed by hydrogel media compared with commercial media for the chromium-laden IX brine, as presented in Chapter 6.

40 HG-1 35 HG-2 HG-3 30 Resin-1 25 Resin-2 20 Cr (ug/L) 15 10 5 0 0 5 10 15 20 25 30 Time (min)

Figure 4.19 Chromium removal kinetics (final chromium concentration) for up to 30 minutes contact time with 10 g/L media dose using Glendale water (As0 = 73 μg/L, Cr0 = 38 μg/L)

80 HG-1 70 HG-2 HG-3 60 Resin-1 50 Resin-2 40 As (ug/L) 30 20 10 0 0 5 10 15 20 25 30 Time (min)

Figure 4.20 Arsenic removal kinetics (final arsenic concentration) for up to 30 minutes contact time with 10 g/L media dose using Glendale water (As0 = 73 μg/L, Cr0 = 38 μg/L)

Effect of Hydrogel Media Size on Removal of Arsenic and Chromium

The effects of the hydrogel media size on anion removal were evaluated using micro- hydrogel developed and used for Chapter 5 of this report. For this test, HG-2 and HG-2M (Table 4.6) were each made with the same composition but different size range (400 µm and 200 µm diameter, respectively). Smaller size media provide better kinetics because of a shorter diffusion distance to interior adsorption sites, and thus the anion removal efficiency may be higher. The same amount of wet micro-hydrogel media used (30 g/L) were completely dehydrated over a day to further compare the adsorption on dehydrated media. As discussed, dehydrated media does not

swell back to its original condition. Thus, the dehydrated media applied for this testing has approximately 20 fold less weight than that of other media. For arsenic, marked improvement was shown, as indicated in Figure 4.21, using the same dose of smaller size hydrogel media. The increase in the removal efficiency of chromium using the micro-hydrogel media was significantly less than that of arsenic. Use of smaller size media, however, increases the headloss, so the performance benefit must be evaluated with regards to potential operational challenges such as the possibility of plugging of the media filters on a more frequent basis and higher pumping cost. Because normal-sized hydrogel media only provided limited chromium removal (Figure 4.18 and 4.19), micro-hydrogel media HG-2M and HG9-M (Table 4.6) were used for additional testing of chromium removal. For this test, dehydrated media had the same total weight as wet media unlike the previous tests. With groundwater samples containing 38 µg/L of chromium, the two micro-hydrogel media tested showed the opposite trends with respect to media dose and dehydration levels. For HG-2M, when higher media dose was added, less chromium removal was observed. This contradicts previous tests done using various types of media and conditions. With HG-9M, as higher dose of media (30 g/L) was used, more chromium was removed from the system as shown in Figure 4.22. The best performance was obtained with 30 g/L of dehydrated media, resulting in a final chromium concentration of approximately 10 µg/L. Although this level was higher than the levels achieved by commercial resins (in the range of 5 µg/L), it may be possible that certain types of hydrogel media perform better for chromium removal. As such, additional testing will be necessary to confirm the findings to validate these trends and to develop the approach and formulations to remove chromium with hydrogel media. The corresponding pH data for this test is shown in Figure 4.23. The dehydrated hydrogel media had much less effect on the pH than the hydrogel media.

As Cr pH 70 8

50 7 40 pH 30 As, Cr (ug/L) Cr As, 6 20

0 5 HG-2 HG-2M

Figure 4.21 Effects of hydrogel media size (HG-2: ~400 μm; HG-2M: ~200 μm) on final pH, arsenic and chromium concentrations with 30 minutes contact time and 10 g/L media dose using Glendale water (As0 = 91 μg/L, Cr0 = 38 μg/L)

10g/L wet media

Initial Cr 38 ug/L 30g/L wet media 40 30g/L dehydrated

30 g/L)

μ 20 Cr ( Cr 10

0 HG2M HG9M

Figure 4.22 Final chromium concentrations with 30 minutes contact time and 10 g/L or 30 g/L micro-hydrogel dose using Glendale water (As0 = 91 μg/L, Cr0 = 38 μg/L)

8 Initial pH 7.8 10g/L wet media 30g/L wet media 30g/L dehydrated 7 pH

5 HG2M HG9M

Figure 4.23 Final pH with 30 minutes contact time and 10 g/L or 30 g/L micro-hydrogel dose using Glendale water (As0 = 91 μg/L, Cr0 = 38 μg/L)

SUMMARY

The hydrogel media exhibited arsenic removal for different sources of groundwater tested. The test waters varied in terms of arsenic speciation, silica, sulfate, phosphate, nitrate, perchlorate, and other anions. A number of hydrogel media showed promise for arsenic removal in groundwater with arsenic ranging from 15 μg/L to 540 μg/L. Two hydrogel media types (HG-7 and HG-8) tested with groundwater containing 38 μg/L of arsenic reduced the final arsenic concentrations to less than 2 μg/L in batch tests. This arsenic removal was comparable to the results for two commercial resin-based media (Resin-1 and Resin-2). In addition, three other hydrogel media types (HG-3, HG-5, and HG-6) showed final arsenic concentrations of less than 4 μg/L similar to iron-based media (Iron-1). At least one hydrogel media also showed a comparable arsenic removal with resin-based media for groundwater spiked with 540 μg/L of

arsenic. For the water containing 160 mg/L of nitrate, final arsenic concentrations were approximately 5 μg/L for HG-1, 10 μg/L for Resin-1, and non-detect for Resin-2, all showing more than 98 percent arsenic removal. The kinetics data indicate that four hydrogel media tested (HG-1 through HG-4) showed slower kinetics than resin or iron-based media tested as comparison. Further testing of other hydrogel media (HG-7 and HG-8), which exhibited better arsenic removal, is recommended. These hydrogel media were more difficult to produce than HG-1 through HG-4, so not enough media volume was produced to allow testing of kinetics and other conditions with these hydrogel media. Total iron leaching from hydrogel media was minimum, comparable to that of resin-based media as expected, since iron is incorporated within the hydrogel media unlike iron-based media that released about eight times more iron than either hydrogel or resin-based media. The removal of competing ions such as sulfate, phosphate, nitrate, silica, perchlorate, and chromium were also tested. Hydrogel media did not remove any significant amount of silica, sulfate, nitrate, or perchlorate. Such low removal of competing ions is desired as arsenic adsorption capacity is not compromised. Resin-based media removed significant amount of these anions while iron-based media only showed removal of silica. All media showed more than fifty percent removal of phosphate, a strong competing anion for arsenic, with spiked initial phosphate concentration of 1.5 mg/L. Approximately 30 to 40 percent of chromium (Cr(VI)) removal was observed for hydrogel and iron media while more than fifty percent removal was obtained for resin media. Although these tests do not provide the effect of competing anions on arsenic removal, the removal of the competing ions may decrease the potential arsenic removal capacity of the media since the competing ions occupy adsorption sites that could otherwise be used for arsenic removal. Additional testing is recommended to further evaluate the efficiencies of hydrogel media for the removal of other anions or competition of these on arsenic removal as these tasks were beyond the scope of the current project.

CHAPTER 5 MICRO-HYDROGEL AS A COAGULANT AID FOR ARSENIC TREATMENT

INTRODUCTION

There have been studies evaluating the application of micron-size resins as direct additives, in addition to coagulant in conventional treatment (Meyers 2004). The objective of this task is to investigate the feasibility of applying micro-hydrogel as a coagulant aid. Micron-sized hydrogel media have an advantage in improved kinetics for arsenic adsorption over larger hydrogel media. A modified hydrogel adsorbent, in the micron-size range, was synthesized using techniques developed earlier (Min 1997). Smaller size hydrogel media (micro-hydrogel), with a high specific surface area, may be applied in dispersed form in a similar fashion as powdered activated carbon (PAC). In full-scale treatment plants, the micro-hydrogel can be dosed into a basin equipped with a mixer and a barrier to keep the micro-hydrogel in the contact reactor similar to an application approach for MIEX. A small percentage of the micro-hydrogel can be continuously removed and replaced with fresh micro-hydrogel. Alternatively, direct filtration of spent micro-hydrogel may be feasible. The filtrate can be returned to the contactor, and the filter cake can be separated and dried, leaving a small percentage of the micro-hydrogel for disposal. Other configurations may also be implemented, depending on how micro-hydrogel is applied. In order to test the efficiency of micro-hydrogel as a coagulant aid, a number of jar tests were performed using surface water containing arsenic. Control tests were performed with ferric chloride only, and additional jars were used to evaluate the arsenic removal efficiency with several doses of micro-hydrogel and varying combinations of ferric chloride.

MATERIALS AND METHODS

Source Water

Surface water, composed of a blend of Los Angeles Aqueduct Water (LAAW) and State Project Water (SPW), was used in jar testing. Table 5.1 presents the critical water quality parameters for this blend. The source water was further spiked with arsenic to reach a total concentration of 53 μg/L.

Description of the Micro-hydrogel

Two types of micro-hydrogel, HG-2M and HG-9M, were synthesized for use as coagulant aids. The size range of the micro-hydrogel is approximately 200 microns. Other characteristics of the media were same as larger counterparts, HG-2 and HG-9, as described in Table 4.6.

Table 5.1 Water quality characteristics of surface water* Parameter Concentration pH 8.1 to 8.3 TOC (mg/L) 3.1 Temperature (°C) 21 Turbidity (NTU) 3.1 Arsenic (μg/L) 38 (adjusted to 53 μg/L) Bromide (μg/L) 67

Silica (mg/L as SiO2) 25 Vanadium (μg/L) 30 2- Sulfate (mg/L as SO4 ) 14 3- Phosphate (mg/L as PO4 ) ND - Nitrate (mg/L as NO3 ) ND Iron (mg/L) 0.07 *(LAAW/SPW blend – 66 percent LAAW/34 percent SPW sampled on 9/19/2005)

Batch-Jar Testing Setup and Hydrogel Dose

The batch experiments were conducted with micro-hydrogel only, with ferric chloride only, and with both micro-hydrogel and ferric chloride, to evaluate the effects of combining these two. A jar tester (Phipps and Bird 7790-400, Richmond, Va.) was used for all testing to provide flash mix and slow mix using 1 L beakers. Table 5.2 and Figure 5.1 show the experimental settings used in jar testing.

Table 5.2 Experimental settings for jar testing Criteria Mixing speed Duration Rapid mix 110 rpm 1 min Slow mix 65 rpm 30 min Settling — micro-hydrogel only None 2–10 min Settling — ferric chloride and hydrogel None 10–30 min with ferric chloride

Figure 5.1 Schematic of jar testing using micro-hydrogel and/or ferric chloride as coagulant

Analytical Methods

Table 5.3 summarizes the analytical methods used and their corresponding detection limits for key water quality parameters used in this task.

RESULTS AND DISCUSSION

Removal Efficiency with Ferric Chloride

As expected, with increasing dosages of dispersed ferric chloride of 3 mg/L, 15 mg/L, and 30 mg/L, total arsenic concentration was decreased from 53 μg/L in the raw water to 30 μg/L, 4.9 μg/L, and 2.5 μg/L, respectively (Figure 5.2).

Table 5.3 Analytical methods used in jar testing Parameter Method Reporting detection limit Arsenic EPA 200.8 1 μg/L Bromide EPA 300 5 μg/L TOC ML/SM 5310C 0.3 mg/L Turbidity HACH Method 8195 0.01 NTU Iron HACH Method 8008 0.01 mg/L pH Orion Portable pH Meter, Model 250 A+ -

Total As Dissolved As 50

30 g/L) μ

As ( 20

10 <1 0 3 mg/L 15 mg/L 30 mg/L

FeCl3 dose

Figure 5.2 Final total and dissolved arsenic in jar testing using ferric chloride only (settling time of 30 minutes; As0 = 53 μg/L)

After coagulation, flocculation, and settling, about half of the total remaining arsenic in the supernatant was in the dissolved form (Figure 5.2), and the other half was small flocs. The non-dissolved form did not settle in 30 minutes, but it could be retained by filtration using a 0.45 micron pore size filter. The removal of turbidity and the residual iron concentration had the same trend as the removal of arsenic, as expected (Figure 5.3). At the end of the 30-minute settling period, the initial pH of 8.4 was decreased to 7.9, 7.7, and 7.2 with respect to ferric chloride dosages of 3 mg/L, 15 mg/L, and 30 mg/L (Figure 5.3). As the dosage was increased from 15 to 30 mg/L, the pH was depressed from 8 to 7, as shown in Figure 5.3.

Turbidity Fe pH 1.5 9 )

1 8 pH

0.5 7 Turbidity (NTU), Fe (mg/L Fe (NTU), Turbidity

0 6 3 mg/L 15 mg/L 30 mg/L

FeCl3 dose

Figure 5.3 Final turbidity, iron, and pH in jar testing using ferric chloride only (settling time of 30 minutes; initial turbidity = 3.1 NTU; initial pH = 8.1 – 8.3)

Effect of Micro-hydrogel Dose and Type on Arsenic Removal

With increasing doses of micro-hydrogel only, total arsenic concentration was decreased in the supernatant (Figure 5.4). HG-9M performed slightly better than HG-2M for the removal of arsenic. The micro-hydrogel dose is much greater than ferric chloride dose as the media content is mostly water. The removal mechanism of arsenic is expected to be mainly adsorption to micro-hydrogel because the arsenic concentration in the supernatant remained constant between the settling time of 2 minutes and 10 minutes (Figure 5.5). In addition, over 90 percent of total arsenic in the supernatant was in the dissolved form (Figure 5.6). This also suggests that arsenic was removed by adsorption to micro-hydrogel, because the iron that leached to bulk phase was negligible (less than 0.1 mg/L). The removal of arsenic was much higher using ferric chloride (Figure 5.2) than using micro-hydrogel (Figure 5.4) under the conditions used. The intended size range of the micro-hydrogel was much less than 200 μm, and it is expected that smaller media would improve the performance. In addition, the polymer used in synthesizing the micro- hydrogel is not as effective as other polymers used to produce HG-3, which showed better arsenic removal characteristics as shown in Chapter 4. Thus, it is expected that the arsenic removal efficiency can be improved using micro-hydrogel. However, it does not justify the continued evaluation of this approach based on the preliminary test results.

Combination of Micro-hydrogel with Ferric Chloride

Under a constant 3-mg/L ferric chloride dose with increasing micro-hydrogel doses, arsenic removal was nearly the same for all doses tested (Figure 5.7). Although addition of micro-hydrogel slightly improved arsenic removal, it did not follow the expected arsenic decrease trend as the micro-hydrogel dose was increased.

50 HG-2M

HG-9M 40

30 g/L) μ

As ( 20

0 00.511.52 Hydrogel dose (g/L)

Figure 5.4 Final arsenic in supernatant using micro-hydrogel only (settling time 10 minutes; As0 = 53 μg/L)

2 min As 10 min As 30

20 g/L) μ

As ( 10

0 1 g/L 2 g/L HG-9M dose

Figure 5.5 Final arsenic concentration in supernatant at different settling times using two hydrogel doses (As0 = 53 μg/L)

Total As Dissolved As 30

20 g/L) μ

As ( 10

0 HG-2M HG-9M

Figure 5.6 Final total and dissolved arsenic in supernatant using 2 g/L micro-hydrogel dose (settling time 10 minutes; As0 = 53 μg/L)

50 FeCl3 3 mg/L + HG-2M 40

30 g/L) μ

As ( 20

0 0 0.2 0.4 0.6 0.8 1 Hydrogel dose (g/L)

Figure 5.7 Final arsenic in supernatant using a combination of micro-hydrogel and ferric chloride (settling time 30 minutes; As0 = 53 μg/L)

In general, arsenic removal was higher with the combination of ferric chloride and micro- hydrogel compared to micro-hydrogel alone, but the removal was lower than from samples with higher doses of ferric chloride alone, as shown in Figure 5.2. This, again, demonstrates that ferric chloride was more effective than micro-hydrogel. Figure 5.8 shows pH values in the supernatant following the addition of micro-hydrogel only and a combination of micro-hydrogel and 3 mg/L of ferric chloride. As expected, pH generally decreased with increasing micro-hydrogel doses. With the settling time of 10 minutes, addition of micro-hydrogel to ferric chloride reduced the residual iron concentration in supernatant from 0.4 mg/L to approximately 0.2 mg/L. The tests performed with the 3 mg/L ferric chloride and micro-hydrogel decreased the concentration of residual iron to lower concentrations than those with 3 mg/L ferric chloride alone (Figure 5.9). It is possible that micro-hydrogel reduced the residual iron concentration by uptaking the iron into the media. The concentration of residual iron in the tests using micro- hydrogel alone was much lower, suggesting there was no significant iron leaching under the tested conditions. As expected, turbidity measured in the settled water decreased with increasing doses of ferric chloride either with ferric chloride only or with combination of ferric chloride and micro- hydrogel (Figure 5.10). When only micro-hydrogel was used, no significant effect was observed on turbidity. The turbidity in the settled water remained constant regardless of the settling time because micro-hydrogel does not remove turbidity via flocculation.

9 HG-2M only

HG-9M only

FeCl3 3 mg/L 8 +HG-2M pH

6 0 0.5 1 1.5 2 Hydrogel dose (g/L)

Figure 5.8 Final pH values in supernatant using micro-hydrogel and a combination of micro-hydrogel and ferric chloride (settling time 10 minutes)

0.5 HG-2M only

HG-9M only 0.4 FeCl3 3 mg/L +HG-2M 0.3

Fe (mg/L) 0.2

0.1

0 0 0.5 1 1.5 2 Hydrogel dose (g/L)

Figure 5.9 Final iron concentration in supernatant using micro-hydrogel and a combination of micro-hydrogel and ferric chloride (settling time 10 minutes)

2 min 10 min 30 min

Raw 3.1 NTU

) 3

Turbidity (NTU 1

0 FeCl3 3 mg/L FeCl3 15 mg/L FeCl3 30 mg/L HG-2M 0.2 g/L HG-2M 1.0 g/L HG-2M 2.0 g/L HG-9M 0.2 g/L HG-9M 1.0 g/L HG-9M 2.0 g/L HG-2M 0.2 g/L+FeCl3 3 mg/L HG-2M 0.5 g/L+FeCl3 3 mg/L HG-2M 1.0 g/L+FeCl3 3 mg/L

Figure 5.10 Turbidity in settled waters using micro-hydrogel, ferric chloride, and a combination of both for 2 minutes, 10 minutes, and 30 minutes settling time

Effect of Hydrogel on TOC and Bromide removal

The source water tested for this task also has high total organic carbon (TOC) and bromide levels (Table 5.1). In order to assess the effects of micro-hydrogel addition on these water quality constituents, the samples collected during the jar testing were also analyzed for TOC and bromide. With micro-hydrogel only, no reduction of TOC was observed. TOC level was reduced only when ferric chloride was used at 15 and 30 mg/L as shown in Figure 5.11. Also, two types of micro-hydrogel tested (HG-2M and HG-9M) did not show any differences in terms of TOC removal (Figure 5.12).

4 Initial TOC 3.12 mg/L 3

TOC (mg/L) 1

0 FeCl3 FeCl3 FeCl3 HG-2M HG-2M FeCl3 FeCl3 3 mg/L+ 3 mg/L+ 3 mg/L+ 1.0 g/L 2.0 g/L 15 mg/L 30 mg/L HG-2M HG-2M HG-2M 0.2 g/L 0.5 g/L 1.0 g/L

Figure 5.11 Effects of various iron and hydrogel dose on final TOC concentration

4 Initial TOC 3.12 mg/L 1.0 g/L

3 2.0 g/L

2 TOC (mg/L) 1

0 HG-2M HG-9M

Figure 5.12 Effects of micro-hydrogel type and dose on final TOC concentration

Another constituent of concern for this water is bromide, since the plant that treats this water has an ozonation step. Because bromate is formed when elevated levels of bromide contact ozone, removal of bromide during arsenic removal is of interest for this source water. Figure 5.13 shows, however, that bromide is not removed during the coagulation process as expected. As was the case for TOC, two types of micro-hydrogel tested (HG-2M and HG-9M) did not show any differences (Figure 5.14) in terms of bromide removal.

80 Initial Br 67 μg/L

60 g/L)

μ 40 Br (

0 FeCl3 FeCl3 HG-2M HG-2M FeCl3 FeCl3 3 mg/L+ 3 mg/L+ 1.0 g/L 2.0 g/L 15 mg/L 30 mg/L HG-2M HG-2M 0.5 g/L 1.0 g/L

Figure 5.13 Effects of various iron and hydrogel dose on final bromide concentration

Initial Br 67 g/L 80 μ 1.0 g/L

60 2.0 g/L g/L) μ 40 Br ( 20

0 HG-2M HG-9M

Figure 5.14 Effects of hydrogel type and dose on final bromide concentration

SUMMARY

Based on the preliminary test results, micro-hydrogel settled much faster in the range of 1 to 2 minutes, compared with 30 minutes required for settling of dissolved-phase iron. In addition, it is expected that the settled micro-hydrogel can be managed better than ferric sludge produced with the use of ferric chloride only. However, micro-hydrogel (in the size range of 200 microns) with a dose in the range of 0.2 to 2 g/L of wet media did not result in any enhanced arsenic removal compared to dosing 30 mg/L of ferric chloride. Although smaller size micro-hydrogel, less than 200 microns, are expected to perform better with respect to arsenic removal, they will likely require additional settling time. Thus, the combination of ferric chloride and micro-

hydrogel did not seem to provide any added benefit, as the settling time of 30 minutes was still required for the iron flocs to settle. In addition, micro-hydrogel did not show any removal of TOC nor bromide, as expected, under the conditions tested. On the other hand, a marginal removal of TOC was achieved with a high level of ferric chloride only.

CHAPTER 6 HYDROGEL MEDIA FOR ARSENIC-LADEN BRINE AND CONCENTRATE TREATMENT

INTRODUCTION

Arsenic treatment processes such as IX or RO generate brine or concentrate with a high concentration of arsenic in the waste stream. The objective of this task is to investigate single-use hydrogel adsorbent to selectively remove arsenic from the IX brine or the RO concentrate and solidify the adsorbent by dehydrating the spent hydrogel media. Bench-scale tests for arsenic brine treatment were conducted as part of this project and focused on the use of the two hydrogel media (HG-2 and HG-3) and three commercial media tested in Chapter 4. In the previous Water Research Foundation study (Min et al. 2005a), a simulated IX brine with an arsenic concentration as high as 150 mg/L was tested to evaluate the residual minimization using the hydrogel adsorbent. In this study, the IX brine and the RO concentrate collected from full-scale treatment plants at the participating utilities were spiked with arsenic in the range of 60 to 300 µg/L. Both the IX brine and RO concentrate samples contained elevated - levels of nitrate since these two plants remove nitrate in the range of 50 mg/L NO3 . Detailed information on brine or concentrate quality was reviewed for suitability prior to spiking with arsenic. The IX brine contains a significant amount of other anions, such as sulfate, nitrate, carbonate, chromate, and perchlorate, some of which compete with arsenic for the adsorption sites. On the other hand, the RO concentrate contains both anions mentioned above and cations, such as calcium, magnesium, and others, which were shown to facilitate arsenic removal with hydrogel media (Min 1997) as discussed in Chapter 2. Tests were conducted with samples spiked with As(V), since As(III) is not effectively retained by ion-exchange resins or rejected by RO, and would, therefore, not be concentrated in these waste streams. The specific objectives of this task were to: (1) determine the ability of the hydrogel media to selectively remove arsenic from the IX brine and the RO concentrate; (2) determine the removal of competing ions (i.e., phosphate, perchlorate, nitrate, and sulfate) or cations (i.e., calcium and magnesium) by the hydrogel media in batch tests; and (3) evaluate the residual minimization by solidifying and minimizing the liquid waste by removing arsenic and dehydrating the spent media.

MATERIALS AND METHODS

Brine and Concentrate Treatment Test Set-up

The batch testing experiments were performed with a rotary shaker (ATR Rotamix RKCS with TT-50, Laurel, Md.) with rotational mixing set at 60 rpm, as described in Chapter 4. Hydrogel media and samples of IX brine or RO concentrate were added into 50-ml centrifuge vials (VWR 21008-169, West Chester, Pa.) used as reactors and mixed to allow arsenic adsorption. At the predetermined contact time presented in Table 6.1, the supernatant was analyzed for arsenic and other relevant parameters similar to the conditions used in Chapter 4. Table 6.1 lists other experimental conditions used during batch testing.

Table 6.1 Experimental conditions for brine and concentrate residual test Item Value Media dosage (g/L) 200 Mixing level (rpm) 60 Mixing time (minutes) 15, 30, and 60

Characteristics of the IX Brine and the RO Concentrate

The IX brine from the City of Pomona, Calif., contained high concentrations of nitrate, sulfate, phosphate, perchlorate, and chromate, as listed in Table 6.2. Since the collected IX brine sample did not contain any arsenic, the IX brine was spiked with arsenic to simulate an IX plant treating groundwater with arsenic in the raw water and concentrating 300 μg/L of arsenic in the brine. The RO concentrate was received from a brackish RO system from the City of Corona, Calif. The RO concentrate did not contain arsenic either; thus, arsenic was spiked to a concentration of 63 μg/L (Table 6.3). This arsenic spike was based on the assumption that the RO is again treating low-level arsenic in the feed, and the RO is operated at a recovery rate of 80 percent, with the membranes achieving 90-percent arsenic rejection.

Table 6.2 Water quality characteristics of IX brine from the City of Pomona Parameter Unit Raw IX brine As total μg/L ND (adjusted to 300) Vanadium μg/L ND

Silica mg/L as SiO2 26.3 pH - 8.5 Iron mg/L 0.15

Alkalinity mg/L as CaCO3 5,500 - Nitrate mg/L as NO3 6,000 2- Sulfate mg/L as SO4 7,900 3- Phosphate mg/L as PO4 15.8 Perchlorate μg/L 840 Chromium μg/L 1,600 (continued)

Table 6.3 Water quality characteristics of RO concentrate from the City of Corona Parameter Unit Raw RO concentrate As total μg/L ND (adjusted to 63)

Silica mg/L as SiO2 190 pH - 8.14 Iron mg/L ND Calcium mg/L 510 Manganese mg/L 230 - Nitrate mg/L as NO3 310 2- Sulfate mg/L as SO4 2,200 3- Phosphate mg/L as PO4 3.5 EC µS/cm 3,980

Hydrogel Media and Commercial Media Tested

In addition to hydrogel media HG-1 through HG-6 used in previous tests, a variation of HG-1 (HG-1P), prepared with a secondary agent for an IX application, was also tested. Only a small amount of this media was produced; thus, the test was limited to IX brine treatment application. A detailed summary of each media used can be found in Chapter 3 (Table 3.1).

Analytical Methods

Table 6.4 lists the analytical methods used for lab and field measurements. MWH Labs and Associates Labs, both certified chemical analytical laboratories, analyzed samples for this task. Field measurements were performed using HACH test kits (DR 890) and were confirmed with lab testing, as needed.

Table 6.4 Analytical methods used for brine and concentrate testing Parameter Lab Method Reporting detection limit Arsenic MWH Labs ICP-MS (EPA 200.8) 2 μg/L Chromium MWH Labs ICP-MS (EPA 200.8) 0.1 mg/L (IX brine only) 2- Sulfate Field HACH Method 8051 1–100 mg/L as SO4 Assoc. Labs IC (EPA 300.0) 1–100 mg/L (continued)

Table 6.4 Analytical methods used for brine and concentrate testing Parameter Lab Method Reporting detection limit

Silica Field HACH Method 8186 0.1–0.02 mg/L as SiO2 Iron Field HACH Method 8008 0.01 mg/L pH Field Orion portable pH Meter, Model 0.01 250 A+ 3- Phosphate Field HACH Method 8048 0.01–0.02 mg/L as PO4

Alkalinity Field HACH Method 8203 10 mg/L as CaCO3 Perchlorate Assoc. Labs IC (EPA 314) 4–400 μg/L - Nitrate Assoc. Labs IC (EPA 300.0) 0.44–440 mg/L as NO3 Bicarbonate Assoc. Labs EPA 2320B 5 mg/L Calcium Assoc. Labs ICP (EPA 200.7) 0.1 mg/L Magnesium Assoc. Labs ICP (EPA 200.7) 0.1 mg/L

RESULTS AND DISCUSSION

Treatment of IX Brine

Removal of Arsenic from IX Brine with Selected Hydrogel Media and Commercial Media

The adsorption kinetics for HG-2, HG-3, Resin-1, Resin-2, and Iron-1 media are presented in Figure 6.1. The dosage of media was 200 g/L of spent IX brine, with an ambient pH of 8.5 and an initial arsenic concentration of 300 μg/L. The hydrogel media HG-2 and HG-3, and the media Resin-1 and Iron-1 had similar arsenic removal efficiencies. Most of the arsenic was removed within the first 15 minutes of contact time. After 30 minutes of contact time, the arsenic concentration in the brine was less than 10 μg/L. However, the actual discharge limits for arsenic depend on local limits, and this needs to be confirmed for each project site. Resin-2, on the other hand, was only capable of decreasing the arsenic concentration to less than 83 μg/L after 60 minutes of contact time. Excess dose of media was used for testing with brine since a significant amount of competing anions, such as sulfate, nitrate, chromate, perchlorate, phosphate, and carbonate were present, as summarized in Table 6.2. The data shows, however, that the competition may not have been significant, since more than 90 percent of the 300 μg/L arsenic concentration was removed in 15 minutes in the presence of competing anions in the g/L range. With hydrogel media HG-2 and HG-3, the pH in the brine was significantly lowered, as compared to the other media. The pH decreased to a range of 7.0 to 7.5 after 15 minutes of contact time and to a range of 7.0 and 7.3 after 60 minutes of contact time for hydrogel media,

similar to the pH reduction observed in Chapter 4. Other commercial media showed a stable pH up to 60 minutes in the IX brine (Figure 6.2).

300 HG-2 HG-3 250 Resin-1 Resin-2 200 Iron-1

150 As (ug/L) 100

0 0 102030405060 Time (min)

Figure 6.1 Arsenic removal kinetics (final concentrations) for a hydrogel and commercial media dosage of 200 g/L in the spent IX brine

9 HG-2 HG-3 Resin-1 Resin-2 8 Iron-1 pH

6 0 102030405060 Time (min)

Figure 6.2 pH change over time with a media dosage of 200 g/L in the spent IX brine

Removal of Arsenic with Other Types of Hydrogel Media

The arsenic adsorption from IX brine with other hydrogel media tested is shown in Figure 6.3. The results for hydrogel media and other commercial media are presented for comparison purposes. The variations in performance of the seven hydrogel media, two resin types, and the iron media were significant. The selected media dosage of 200 g/L seemed to be adequate for the removal of arsenic from the IX brine for a concentration of 300 μg/L with a contact time of up to 60 minutes. The additional time (up to 60 minutes) allowed for this test facilitated arsenic adsorption by all media, especially in the IX brine which had a significant amount of other interfering ions. Again, the excess media dose was used to account for competing anions at levels greater than 3 or 4 orders of magnitude higher. The majority of the hydrogel media and commercial media removed more than 95 percent of the arsenic from the brine solution within 60 minutes of contact time. However, hydrogel media HG-4 removed only 40 percent of the arsenic, resulting in an arsenic concentration of 180 μg/L in the treated brine. This contradicts previous testing done for drinking water where similar arsenic removal efficiencies were observed for different types of hydrogel media. Thus it is not clear whether this was due to sample contamination. Resin-2 also showed lower removal rates, with 125 μg/L of arsenic concentration after 60 minutes of reaction time, which represents only a 57 percent reduction. The decrease of the arsenic to below 10 μg/L or 97 percent removal efficiency was achieved with HG-1, HG-2, HG-3, and HG-6 hydrogel media, and Resin-1 and Iron-1 media. Thus, the application of hydrogel media for selectively removing arsenic from the IX brine followed by dehydration could significantly reduce the amount of hazardous residuals from IX plants. During the brine testing, the initial pH of 8.5 was decreased by the pH unit for most of the hydrogel media, with the exception of HG-2 and HG-3, which resulted in a pH range of 7.0 to 7.2. In comparison, resins and iron media did not significantly change the final pH values from the initial pH (Figure 6.4).

180 Initial As 300 μg/L

160

140

120

100

80 As (ug/L) 60

0 HG-1 HG-2 HG-3 HG-4 HG-5 HG-6 Iron-1 HG-1P Resin-1 Resin-2 Figure 6.3 Final arsenic concentrations with a media dosage of 200 g/L and 60 minutes of contact time in the IX brine matrix

9 Initial pH 8.5

8 pH

6 HG-1 HG-2 HG-3 HG-4 HG-5 HG-6 Iron-1 HG-1P Resin-1 Resin-2 Figure 6.4 Final pH with a media dosage of 200 g/L and 60 minutes of contact time in the IX brine matrix

Removal of Competing Ions in the IX Brine

As previously mentioned, the IX process removes other co-occurring anions, which are concentrated in the spent IX brine at elevated levels. Thus, high concentrations of nitrate, sulfate, phosphate, perchlorate, chromate, and alkalinity can be found and interfere with arsenic removal in the IX brine.

The competition from nitrate and perchlorate anions during arsenic removal with two selected hydrogel media, two resins, and one iron media was investigated. The batch experiments showed that the nitrate removal was highest with Resin-2 and Resin-1, with a total of 30 to 50 percent nitrate removal from 6,000 mg/L of nitrate. The nitrate removal with hydrogel media HG-2 and HG-3 and the iron media was in the range of 15 to 25 percent (Figure 6.5), indicating that interference by nitrate will be less for hydrogel and iron media compared to resins. Another potential competition for arsenic in the brine is perchlorate, which is also effectively removed by the IX process. The hydrogel and iron media removed about 30 percent of the perchlorate from the IX brine. On the other hand, the resins had a very high affinity for perchlorate and reduced the perchlorate concentration to less than the detection limit of 100 μg/L, as expected, similar to commercially used single-use resin for perchlorate removal (Figure 6.6). Because of the dilution required for the brine samples, the detection level was 100 μg/L instead of 4 μg/L used for drinking water application. During this testing, the sulfate uptake by the media tested was less than the uptake of other anions in the IX brine (Figure 6.7). For Resin-1, the sulfate concentration was greater than 10,000 mg/L, and it is not clear what caused the increase or whether this is a contamination issue.

Initial nitrate 6,000 mg/L 6,000

5,000

4,000

3,000 Nitrate (mg/L) 2,000

1,000

0 HG-2 HG-3 Resin-1 Resin-2 Iron-1

Figure 6.5 Final nitrate concentrations in the IX brine with a media dosage of 200 g/L and 60 minutes of contact time

900 Initial perchlorate 840 μg/L 800 700 600 500 400 300 Perchlorate (ug/L) 200 <100 <100 100 0 HG-2 HG-3 Resin-1 Resin-2 Iron-1

Figure 6.6 Final perchlorate concentrations in the IX brine with a media dosage of 200 g/L and 60 minutes of contact time

12,000 Initial sulfate 7,900 mg/L

10,000

8,000

6,000 Sulfate (mg/L) 4,000

2,000

0 HG-2 HG-3 Resin-1 Resin-2 Iron-1

Figure 6.7 Final sulfate concentrations in the IX brine with a media dosage of 200 g/L and 60 minutes of contact time

Removal of Chromium from IX Brine

Another contaminant that is removed during the IX treatment process is Cr(VI). The raw water being treated for the IX plant where the brine sample was obtained, contains a low levels of chromium. The contaminant is concentrated in the IX brine and the level of Cr(VI) measured in the brine was approximately 1.6 mg/L. In previous studies (Min and Hering 1998b and 1999), chromium removal showed two-stage kinetics, where the fast reaction (adsorption) with hydrogel media was followed by a slower adsorption, similar to the data presented for chromium removal in Chapter 4 of this report. As mentioned previously, such observation may have been attributed to the precipitation of chromium as Cr(III) on the surface of the media, similar to the surface

blockage caused by silica. Thus, it is possible that the media is prematurely exhausted in the presence of chromium, as discussed in Chapter 4. The removal of Cr(VI) from the brine using various media types, including three commercial media, is shown in Figure 6.8. With the initial chromium concentration of 1.6 mg/L, the hydrogel media showed 50 to 94 percent reduction of chromium under the conditions tested. The reduction of chromium using the commercial media was less effective, showing only 20 to 30 percent removal. As discussed previously, the IX brine is a challenging water to treat with elevated levels of anions in the spent brine solution. One of the hydrogel media tested (HG-2) showed the best performance, with less than 0.1 mg/L of chromium after 60 minutes of contact time, which corresponds to approximately a 94 percent removal of Cr(VI). Another fact worth mentioning in this experiment was the dose of the media used for one of the batch tests. The standard media dose used for this batch test was 200 grams of wet media per liter of brine sample. For the HG-1P media, however, there was a limited amount of media, so only 113 g/L of wet media was used. Despite the lower media dose, the chromium removal was comparable to the other hydrogel media, indicative of the fact that a better performance (i.e., lower final chromium concentration) could be expected with the same media dose.

Initial Cr 1.6 mg/L 1.6

1.4

1.2

0.8

Cr (mg/L) 0.6

0.4

0.2 <0.1

0 HG-1 HG-2 HG-3 HG-4 Iron-1 HG-1P Resin-1 Resin-2 Figure 6.8 Final chromium concentrations in the IX brine with a media dosage of 200 g/L and 60 minutes of contact time (113 g/L media dosage for HG-1P)

Treatment of RO Concentrate

Removal of Arsenic from the RO Concentrate

The purpose of arsenic media testing using RO concentrate was to evaluate the arsenic removal rates in the RO concentrate, where the water quality is different from the IX brine in terms of composition and concentration. The concentrations of anions in the RO concentrate are

significantly lower than those in the IX brine. In addition, both anions and cations are present in the RO concentrate, unlike the IX brine where only anions are present. The arsenic removal by the hydrogel media in the RO concentrate provides additional information on the performance of the hydrogel media under different brine quality conditions. The arsenic adsorption kinetics presented in Figure 6.9 show that with a media dosage of 40 g/L and an initial arsenic concentration of 63 μg/L, the arsenic concentration decreased to less than 5 μg/L within the first 15 minutes of contact time. The arsenic concentration was less than or equal to 4 μg/L thereafter for all media tested. Even Resin-2, which was the least effective for arsenic removal in the IX brine, showed efficient arsenic removal in the RO concentrate. As shown in Figure 6.10, the initial pH of 8.1 was decreased by the HG-2 and HG-3 hydrogel media, similar to the observation previously made for the IX brine. In the RO concentrate, Resin-1 and Iron-1 also exhibited a decrease in pH and the final pH after 60 minutes of contact time was comparable to that of the hydrogel media, while the pH of Resin-2 did not change during the experiment.

80 HG-2

HG-3 60 Resin-1

40 Resin-2 As (ug/L) Iron-1 20

0 0 102030405060 Time (min)

Figure 6.9 Arsenic removal kinetics from the RO concentrate with a media dosage of 40 g/L

9 HG-2

HG-3

8 Resin-1

pH Resin-2

7 Iron-1

6 0 102030405060 Time (min)

Figure 6.10 pH reduction over time during arsenic removal from the RO concentrate with a media dosage of 40 g/L

Removal of Other Ions in the RO Concentrate

The presence of silica greatly inhibits the arsenic adsorption by coating the surface of the media, which blocks the arsenic from adsorbing to the media (Amy et al. 2005). The batch tests showed that hydrogel media HG-2 and HG-3 exhibited a lower affinity for silica (~35 percent removal) as compared to the resin and iron media, which removed 60 to 70 percent of the silica (Figure 6.11). As such, the interference from silica is expected to be less for the hydrogel media. However, a longer term test in a column mode will be needed to confirm this. Similar to previous tests conducted on drinking water, phosphate was strongly removed by all media tested. In fact, more than 60 percent of the initial phosphate (3.5 mg/L as PO4) was removed by the HG-3 hydrogel media, and more than 75 percent of the phosphate was removed by HG-2, resins, and iron media (Figure 6.12). The nitrate removal in RO concentrate was in the range of 70 percent for both hydrogel media unlike the nitrate removal of less than 20 percent in the IX brine. The nitrate removal by the hydrogel media was comparable to the nitrate removal of 60 to 85 percent observed for the resin-based media. The iron media, however, did not show any significant amount of nitrate removal in the RO concentrate matrix, as shown in Figure 6.13. For a drinking water application with an initial sulfate level of approximately 30 mg/L, only Resin-1 and Resin-2 showed significant sulfate removal. The RO concentrate has significantly different water quality characteristics with a sulfate level in the range of 2,200 mg/L and elevated levels of other constituents. For the RO concentrate, only Resin-2 exhibited sulfate removal, as shown in Figure 6.14. The initial sulfate concentration shown on the figure, which is lower than some final concentrations, may be attributed to a dilution error associated with the field measurement and is not likely due to sulfate release from the media. Although conclusive

results cannot be attained with this data set due to a lack of duplicate samples, the sulfate adsorption was less than the adsorption of other anions monitored in the RO concentrate during this testing.

200 Initial silica 190 mg/L

150

100 Silica (mg/L) Silica 50

0 HG-2 HG-3 Resin-1 Resin-2 Iron-1

Figure 6.11 Final silica concentrations in the RO concentrate with a media dosage of 40 g/L and 30 minutes of contact time

Initial phosphate 3.5 mg/L 3.5 3 2.5 2 1.5 1 Phosphate (mg/L) Phosphate 0.5 0 HG-2 HG-3 Resin-1 Resin-2 Iron-1

Figure 6.12 Final phosphate concentrations in the RO concentrate with a media dosage of 40 g/L and 30 minutes of contact time

350 Initial nitrate 310 mg/L 300 250 200 150

Nitrate (mg/L) Nitrate 100 50 0 HG-2 HG-3 Resin-1 Resin-2 Iron-1

Figure 6.13 Final nitrate concentrations in the RO concentrate with media dosage of 40 g/L and 30 minutes of contact time

3,000 Initial sulfate 2,200 mg/L

2,500

2,000

1,500

1,000

Sulfate (mg/L) Sulfate 500

0 HG-2 HG-3 Resin-1 Resin-2 Iron-1

Figure 6.14 Final sulfate concentrations in the RO concentrate with a media dosage of 40 g/L and 30 minutes of contact time

The RO process rejects both anionic and cationic species, unlike the IX process where only anionic constituents are selectively removed. Among these cations, the most common species are calcium and magnesium, as well as sodium and potassium. As mentioned previously, the presence of the cations was shown to facilitate arsenic removal in a previous study (Min 1997). Figures 6.15 and 6.16 show the removal of calcium and magnesium from the RO concentrate possibly due to direct interaction of cations with alginate functional groups. The amount of cations removed is comparable among various media tested, and no significant variations were observed. The presence of high levels of calcium and magnesium may have assisted all media in achieving greater than 90 percent arsenic removal efficiency with only 15 minutes of contact time, as previously shown in Figure 6.9. It should be noted, however, that

a systematic comparison on the effects of cation on arsenic removal efficiency was not performed during this project.

600 Initial Ca 510 mg/L

500

400

300

Ca (mg/L) Ca 200

100

0 HG-2 HG-3 Resin-1 Resin-2 Iron-1

Figure 6.15 Final calcium concentrations in the RO concentrate with a media dosage of 40 g/L and 30 minutes of contact time

250 Initial Mg 230 mg/L 120 Initial Mg 230 mg/L 200 100

15080

10060 Mg (mg/L) Mg

Mg (mg/L) Mg 40 50 20 0 0 HG-2HG-2 HG-3 HG-3 Resin-1 Resin-1 Resin-2 Resin-2 Iron-1 Iron-1

Figure 6.16 Final magnesium concentrations in the RO brine with a media dosage of 40 g/L and 30 minutes of contact time

Iron Leaching from the Media in the RO Concentrate

There was a non-detectable level of iron in the RO concentrate (Table 6.3). Among the media tested, iron leaching was highest for Resin-1 and Resin-2 as shown in Figure 6.17. The concentration of iron in the RO concentrate after the test was completed is in the range of 0.14 to

0.21 mg/L for the resins, while the iron was in the range of 0.06 to 0.11 mg/L for hydrogel and iron media.

0.25

0.2

0.15

0.1 Fe (mg/L)

0.05

0 HG-2 HG-3 Resin-1 Resin-2 Iron-1

Figure 6.17 Iron leaching from media at a media dosage of 40 g/L and 30 minutes of contact time in the RO concentrate with non-detectable iron

Effect of Alkalinity on Swelling of Hydrogel Media in the IX Brine

In addition to contaminants such as nitrate, arsenic, and chromium in the spent-IX brine, other water quality constituents, such as alkalinity, had an elevated concentration in the brine solution. This is particularly true for the IX process where bicarbonate is removed. In a previous Water Research Foundation study (Min et al. 2005a), high alkalinity concentrations in the IX brine, in the range of several thousand mg/L, caused swelling of the hydrogel media. Such high level of alkalinity is only seen in some IX brines. This is much higher than the alkalinity level of a few hundred mg/L in drinking water. One of the mitigation processes suggested in that study was to reduce the alkalinity from the IX brine prior to the application of hydrogel media if the alkalinity in the brine is extremely high, as some hydrogel media swells in the presence of very high alkalinity. The swelling of the hydrogel media under high alkalinity conditions, above several thousand mg/L in IX brine, was therefore compared to low-alkalinity conditions (few hundred mg/L). This was done visually by lowering the pH and aerating the brine using compressed air to purge out carbonate alkalinity (i.e., dissolved CO2). Some full-scale IX plants lower the pH of the spent brine to reduce the scaling in the waste brine line; thus, the addition of an aeration step may be sufficient to control the alkalinity prior to brine treatment with hydrogel media only if alkalinity level is high. Typical IX brine rate is in the range of 0.5 to 2 percent of feed flow. Thus, for a 1,000 gpm IX plant, only 5 to 20 gpm of brine need to be subjected to aeration. The brine samples used were from the IX plant at the Chino Desalter Authority in Calif., with an alkalinity level of 5,500 mg/L (Table 6.2). The brine was pretreated with acid to reduce the pH to 6, followed by aeration using an air pump with a stone diffuser to reduce the amount of dissolved CO2. The sample was aerated until the alkalinity was below 100 mg/L (as CaCO3).

The treated IX brine with initial high alkalinity level was compared to a low-alkalinity water sample by mixing the hydrogel media in a rotary shaker (ATR Rotamix RKCS with TT- 50, Laurel, Md.) with water samples in 50-ml vials. After mixing the vials at 60 rpm for 12 hours, the hydrogel media were allowed to settle and the hydrogel media volume was compared. With this new pre-conditioning step, the hydrogel media did not swell for the brine sample. The requirements for this pre-condition depend on the actual alkalinity of the brine to be treated and may not be necessary depending on the raw water alkalinity.

SUMMARY

The removal of arsenic from water treatment processes such as IX or RO generates arsenic-laden liquid residuals. Depending on the local and state disposal regulations and the levels of arsenic in these waste streams, arsenic may need to be removed from these residuals prior to disposal to evaporation ponds or other receiving waters. The testing results indicated that hydrogel media were effective in decreasing arsenic from both the IX brine and the RO concentrate streams to concentrations less than the detection levels. The removal of competing anions (e.g., silica, phosphate, nitrate, and sulfate), which were present in both residual samples, was less for the hydrogel media than that observed for commercial media (Resin-1, Resin-2, and Iron-1). Although these tests do not show the effect of competing anions on arsenic removal by various media types, the interference of these parameters on arsenic removal may be less for the hydrogel media than that for the commercial media, since the removal capacity is not compromised by other competing anions. Specifically, silica and sulfate are commonly present in groundwater and thus concentrate in spent liquid residual streams. Inhibition of arsenic removal by silica is a major concern as it reduces the total capacity of the media due to surface coating by silica, which prevents any ions to be adsorbed. Also, high sulfate may interfere with resin-based media. Thus, under these conditions, the hydrogel media may be used as an alternative as the effect of these interferences are less for the hydrogel media. Another contaminant that is removed during the IX treatment process is Cr(VI), and the level of Cr(VI) measured in the brine tested was approximately 1.6 mg/L. With an initial chromium concentration of 1.6 mg/L, the hydrogel media showed 50 to 94 percent reduction of chromium under the conditions tested, with significantly higher concentrations of other anions such as nitrate, sulfate, alkalinity, etc. For one hydrogel media (HG-2), Cr(VI) was reduced to less than the detection limit of 100 μg/L in the IX brine. The reduction of chromium using the commercial media was less effective showing only 20 to 30 percent removal. As such, the reduction of chromium in IX brine by the hydrogel media can be a promising application. The presence of cations in the RO concentrate (e.g., Ca and Mg ions) enhanced the arsenic removal efficiency as reported in a previous study (Min 1997), and all media tested showed effective arsenic removal in the RO concentrate. Overall, the arsenic removal was observed even when the concentration of competing anions was in large excess of arsenic, typically 3 or 4 orders of magnitude higher. In the presence of high carbonate concentrations, exceeding several thousand mg/L, the hydrogel media swell. However, lowering the pH and aerating the brine prior to contact with the hydrogel media to purge out the dissolved CO2 can mitigate such effect. A number of IX plants implement pH reduction in the spent brine to minimize scaling in the brine discharge pipe. Thus, only the aeration of a small brine stream, of typically 0.5 to 2 percent of the influent flow, will be needed to implement the hydrogel media

where the alkalinity is high. That is, for a typical 1,000 gpm IX treatment system, only 5 to 20 gpm of brine needs to be aerated for the application of hydrogel media where the alkalinity concentration is in the order of several thousands mg/L.

CHAPTER 7 SUMMARY

For a previous Water Research Foundation project, “Innovative Alternatives to Minimize Arsenic, Perchlorate, and Nitrate Residuals” (Min et al. 2005a), the hydrogel media were primarily evaluated as part of that project to treat arsenic-laden IX brines. That project was designed to evaluate selective arsenic adsorption capacity and spent media volume minimization characteristics. The current project expanded on a number of previous projects by developing and evaluating the hydrogel media for arsenic and other contaminants removal in drinking water as well as liquid residual streams, such as IX brine and RO concentrate. The hydrogel media evaluated under this project for arsenic treatment and residual minimization is not commercially available. Thus, this section provides a summary, test results, and residual management aspect of the proposed technology. The commercially available biopolymer alginate derived from seaweed has been used for several decades in a number of applications ranging from food and pharmaceutical industries (thickening, emulsifying, film forming, and gelling agents) to metals removal in water treatment. The biopolymer is currently used in commercial products such as ketchup, beer, milkshakes, ice cream, and other consumer products. This low-cost biopolymer thus may enable cost- effective synthesis of hydrogel adsorbent media for use as an arsenic treatment technology. The uniform hydrogel adsorbent media, in the range of 500 to 700 µm, is similar to synthetic ion-exchange resin in appearance and physical characteristics. The hydrogel media were designed for use as single-use media, so no special maintenance is required. However, since the hydrogel media will be dehydrated when exposed to air for a prolonged period, it is necessary to keep the hydrogel media hydrated similar to ion exchange and wet granular media, such as GFH used for arsenic treatment. If the hydrogel media is dehydrated prior to disposal, the dried hydrogel media will still adsorb arsenic, but the kinetics and arsenic adsorption capacity will be less compared to the hydrated form. Under certain circumstances, pre-dehydrated media may be better suited especially if additional arsenic removal capacity is desired. The pre- dehydrated media, however, will be more expensive per unit volume of the media, and the benefit of residual reduction no longer exists when the hydrogel media is pre-dehydrated. The hydrogel media exhibited arsenic removal for different sources of groundwater tested, with varying levels of arsenic speciation, silica, sulfate, phosphate, and other anions. A number of hydrogel media showed promise for arsenic removal in groundwater with arsenic concentration ranging from 15 μg/L to 540 μg/L. A few hydrogel media types (HG-3, HG-5, HG-6, HG-7, and HG-8) tested with groundwater containing 38 μg/L of arsenic reduced the final arsenic concentrations to less than 4 μg/L in batch tests. This arsenic removal capacity was comparable to the results for commercial resin- and iron-based media. Even for water containing 160 mg/L of nitrate, final arsenic concentrations were approximately 5 μg/L for HG-1, 10 μg/L for Resin-1, and non-detect for Resin-2, all showing more than 98 percent arsenic removal from the initial arsenic concentration of 540 μg/L. Hydrogel media did not remove any significant amount of silica, sulfate, nitrate, or perchlorate, while resin-based media removed these anions effectively, and iron-based media removed only silica. The low removal of competing ions is desired, as arsenic adsorption capacity is not compromised by the adsorption of other ions. Approximately 30 to 40 percent of chromium (Cr(VI)) removal was observed for hydrogel and iron media while more than 50 percent removal was obtained for resin media.

The micro-hydrogel, (in the range of 200 μm) with the same properties as the larger hydrogel media, settled much faster (in approximately 1 to 2 minutes), compared to 30 minutes required for settling of dissolved-phase iron during jar tests. However, micro-hydrogel with a dose in the range of 0.2 to 2 g/L of wet media did not result in any enhanced arsenic removal compared to dosing 30 mg/L of ferric chloride. The combination of ferric chloride and micro- hydrogel did not seem to provide any added benefit, as the settling time of 30 minutes was still required for the iron flocs to settle. In addition, hydrogel media did not show any TOC nor bromide removal, as expected, in the test water under the conditions tested, whereas a marginal removal of TOC was achieved with a high level of ferric chloride only. Hydrogel media were effective in decreasing arsenic in the range of 60 to 300 μg/L from both IX brine and RO concentrate streams to concentrations less than the detection levels in the presence of other anions 3 or 4 orders of magnitude higher. Silica and sulfate are commonly present in groundwater and thus concentrate in spent liquid residual streams. Inhibition of arsenic removal by silica is a major concern, as it reduces the total capacity of the media due to surface coating by silica, which prevents any ions to be adsorbed on to the media. Also, high sulfate may interfere with resin-based media. Thus, under these conditions, hydrogel media may be used as an alternative since these interferences have a lower impact on the hydrogel media. With an initial chromium concentration of 1.6 mg/L in the spent IX brine, the hydrogel media showed 50 to 94 percent reduction of chromium under the conditions tested, with a significantly higher concentration of other anions, such as nitrate, sulfate, alkalinity, etc. For one hydrogel media (HG-2), Cr(VI) was reduced to less than the detection limit of 100 μg/L from the initial concentration. The reduction of chromium using the commercial media was less effective, showing only 20 to 30 percent removal. As such, the reduction of chromium in the IX brine by the hydrogel media can be a promising application. The presence of cations, such as calcium, magnesium, etc. in the RO concentrate enhanced the arsenic removal efficiency, as reported in a previous study (Min 1997), and all media tested showed effective arsenic removal in RO concentrate. Overall, arsenic removal was observed, even in the presence of competing anions with a concentration that largely exceeded that of arsenic, typically 3 or 4 orders of magnitude higher. In the presence of high carbonate concentrations exceeding several thousand mg/L, the hydrogel media swell. However, this effect can be mitigated by lowering the pH and aerating the brine prior to contact with the hydrogel media to purge out the dissolved CO2. A number of IX plants implement pH reduction in the spent brine to minimize scaling in the brine discharge pipe. Thus, only the aeration of a small brine stream, of typically 0.5 to 2 percent of the influent flow, will be needed for implementation of hydrogel media where alkalinity is high. For a 1,000 gpm IX treatment system, only 5 to 20 gpm of brine needs to be aerated for the application of hydrogel media where alkalinity concentration is in the order of several thousand mg/L. Conventional arsenic treatment technologies currently used generate arsenic-laden liquid waste and require special steps to manage it. For single-use adsorbent, where spent media are the only residuals produced during water treatment, minimizing the volume and weight of the spent media will decrease the transportation and disposal costs. For the proposed hydrogel media, the residual can be reduced significantly by dehydrating the spent media with airflow. The spent hydrogel media can be dehydrated to less than 5 percent of the original volume and weight (a 20-fold reduction), and this may be an attractive attribute of this media. In fact, for both batch and column dehydration tests, a volume reduction of 17 to 20 fold was observed for the hydrogel media. In the column mode, 50 ml of hydrogel media was reduced to 3 ml (6 percent of the

original volume) after dehydration using airflow for four hours. Such minimization of the spent media volume and weight after dehydration of the media will likely result in decreased residual transportation and disposal costs. Also, in a recent study where arsenic-laden ion-exchange brine was treated with hydrogel media, dehydrated sorbents were stable under leaching test conditions (TCLP - toxicity characteristics leaching procedure) and released only between 0.3 and 7 percent of their arsenic content, depending on the dehydration conditions, which passed the U.S. federal leaching criteria (Hering et al. 2004, Min et al. 2004). For the California Waste Extraction Test; however, additional modification of the media will likely be needed. Another requirement in California is TTLC (total threshold limit concentration), so some utilities are evaluating media with less capacity for arsenic, such that the spent media do not become hazardous waste. For such application, the hydrogel media production can be easily modified to control the total iron content and subsequent arsenic loading.

REFERENCES

Amy, G., H-W. Chen, A. Drizo, U. von Guten, P. Brandhuber, R. Hund, Z. Chowdhury, S. Kommineni, S. Sinha, M. Jekel, and K. Banerjee. 2005. Adsorbent Treatment Technologies for Arsenic Removal. , Denver, Colo.: AwwaRF. Hering, J.G., N. Vural, Z. Yang, and J.H. Min. 2004a. A Novel Sorbent for Treatment of Arsenic (V) – Contaminated Brines. Poster presentation at the GRA Arsenic Symposium, Fresno, CA, October 18-19, 2004. Hering, J.G., N. Vural, Z. Yang, and J.H. Min. 2004b. A Novel Sorbent for Treatment of Arsenic (V) – Contaminated Ion-Exchange Brine. In Proceedings from the AWWA Water Quality Technology Conference. Denver, Colo.: AWWA. Meyers, P. 2004. The Performance of ASM-10 HP Arsenic Selective Media. Presented at the New Mexico Environmental Health Conference, Albuquerque, NM, October 18-20, 2004. Min, J.H. 1997. Removal of Arsenic, Selenium, and Chromium(VI) from Wastewater Using Fe(III)-Doped Alginate Gel Sorbent. Ph.D. diss., University of California at Los Angeles. Min, J.H., L. Boulos, J. Brown, Y. Le Gouellec, E. Coppola, J. Hering, D. Cornwell, and R. Cushing. 2004. Integration of Residuals Minimization in Managing Arsenic, Perchlorate, and Nitrate Treatment. In Proceedings of Water Quality Technology Conference. Denver, Colo.: AWWA. Min, J.H., L. Boulos, J. Brown, Y. Le Gouellec, D. Cornwell, E. Coppola, S. Baxley, J. Rine, J. Hering, and N. Vural. 2005a. Innovative Alternatives to Minimize Arsenic, Perchlorate, and Nitrate Residuals. Denver, Colo.: AwwaRF and AWWA. Min, J.H., and J.G. Hering. 1998a. Arsenate Sorption by Fe(III)-doped Alginate Gels. Water Research, 32(5):1544-1552. Min, J.H. and J.G. Hering. 1998b. Arsenate, Selenite, and Chromate Sorption by Fe(III)-Doped Alginate Gels. Advances in Environmental Research, 2(2):207-217. Min, J.H. and J.G. Hering. 1999. Removal of Selenite and Chromate Using Iron(III)-Doped Alginate Gels. Water Environmental Research, 71(2):169-175. Min, J.H., C. Tasser, J. Zhang, H. Haileselassie, L. Boulos, G. Crozes, R. Cushing, and J.G. Hering. 2005b. Impact of Unintentional pH Variations during Arsenic Removal. Presented at Awwa CA-NV, Reno, NV, October 11-14, 2005. New Jersey Register December. 2004. New Jersey. Office of Environmental Health Hazard Assessment (OEHHA). 2003. DRAFT Public Health Goal for Arsenic in Drinking Water, California Environmental Protection Agency Pesticide and Environmental Toxicology Section. US Environmental Protection Agency, 2000, Regulations on the Disposal of Arsenic Residuals from Drinking Water Treatment Plants (EPA/600/R-00/25). US Environmental Protection Agency, National Risk Management Research Laboratory. 2005. Treatment Technologies for Arsenic Removal (EPA/600/S-05/006).

ABBREVIATIONS

As Arsenic Assoc. Labs Associated Laboratories

Ca calcium CalTech California Institute of Technology CDHS California Department of Health Services cm centimeter Cr chromium CTR California Toxics Rule Cu copper °C degrees celsius

DI Deionized DWTP drinking water treatment plant

EBCT empty bed contact time EDR electrodialysis reversal

Fe iron g gram G gulurionic GaAs gallium arsenide GFH granular ferric hydroxide g/L grams per liter

IX ion-exchange

L liter LAAW Los Angeles Aqueduct Water

M Mannuronic MCL maximum contaminant level Mg magnesium µg/L micrograms per liter mg/L milligrams per liter µL microliter mL milliliter mL/min milliliter per minute µm micrometer MWH Labs Montgomery Watson Harza Laboratories

NF Nanofiltration NPDES National Pollutant Discharge Elimination System

OEHHA Office of Environmental Health Hazard Assessment

PAC powdered activated carbon Pb lead PHG Public Health Goal POTW Publicity Owned Treatment Works

RCRA Resource Conservancy and Recovery Act RO reverse osmosis rpm revolutions per minute scfm standard cubic feet per minute Se selenium SPW State Project Water STLC soluble threshold limit concentration

TCLP Toxic Characteristics Leaching Procedures TDS total dissolved solids TOC total organic carbon TTLC total threshold limit concentration

U.S. United States UCLA University of California at Los Angeles USEPA United States Environmental Protection Agency

WET waste extraction test