ROLE OF HYDROXYL RADICALS AND HYPOBROMOUS ACID REACTIONS ON BROMATE FORMATION DURING OZONATION by Peng-Fei Chao A Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy ARIZONA STATE UNIVERSITY December 2002 ROLE OF HYDROXYL RADICALS AND HYPOBROMOUS ACID REACTIONS ON BROMATE FORMATION DURING OZONATION by Peng-Fei Chao has been approved October 2002 APPROVED: , Chair . Supervisory Committee ACCEPTED: . Department Chair . Dean, Graduate College ABSTRACT Ozonation of waters containing bromide ions (Br-) results in Br- oxidation by ozone and its decomposition by-product (e.g., hydroxyl radical (HO·)) to form different intermediate brominated species (e.g., hypobromous acid (HOBr), hypobromite ions - - · · (OBr ), bromite (BrO2 ), bromide radicals (Br ), and hypobromite radicals (BrO )) and - eventually to form bromate (BrO3 ), a suspected carcinogen. In this study, bench- and pilot-scale experiments were conducted with Colorado River Water (CRW) to investigate the kinetics and control of bromate formation. Bromate formation is strongly influenced by water quality and treatment variables. Some water quality parameters (e.g., bromide level, pH, temperature and (bi)carbonate alkalinity) have positive effects on bromate formation, while the presence of natural organic matter (NOM) and ammonia reduce the amount of bromate formed. Increasing ozone dose and/or contact time increases bromate formation. Quantification · of bromate formation is expressed by the RCT value, the ratio of HO exposure (or concentration) to ozone exposure (or concentration). Two phases of RCT are performed and the values of RCT remain unchanged throughout the ozonation process with a set of -7 -9 water quality. The RCT values for ozonation of CRW water range between 10 and 10 , resulting in HO· concentrations of on the order of 10-12 to 10-14 M. Bromate formation can be controlled by adding acid or ammonia to decrease intermediate OBr-. Acid addition to lower water pH from ambient (8.2) to 7.5 and 6.5 reduces bromate formation by 30% and 80%, respectively. In comparison, adding ammonia reduces bromate formation up to 60% and 85% at pH 7.5 and 8.5, respectively. Ammonia’s efficiency to mitigate bromate formation is lessened with lowered water pH. Bromate formation by HO· radical pathways cannot be controlled unless radicals are being scavenged. Inorganic carbonate species can scavenge HO· and form carbonate radicals that react with OBr- to form bromate. The reaction rate of chlorine or bromine with NOM is rapid and dependent upon NOM characteristics. Bromination is approximately one order of magnitude faster than chlorination. The slower NOM reaction sites have a rate constant of approximately 50 M-1s-1, which is 3 to 4 orders of magnitude less than the fast NOM reaction sites. Pre- ozonation reduces the NOM reactivity by approximately 50%. Kinetically, the impact of bromate reduction by the reaction of intermediate HOBr and NOM is only important during the fast ozonation stage (t < 2 minutes). A negligible impact on bromate reduction by HOBr and NOM reactions at slow ozonation stage (t > 2 minutes) can be implied based upon the rate constants and reactivity of NOM. ACKNOWLEDGEMENTS Many thanks I would like to express to a number of people who have been always supporting me throughout this work. First of all, I would like to thank my advisor, Paul Westerhoff, for his encouragement, guidance and advice throughout my Master and Ph.D. years. Other committee members: Paul Johnson, Peter Fox and James Anderson are also appreciated for their valuable feedbacks. Second, I would like to express my gratitude to Peter Goguen for always providing valuable assistances with laboratory equipment. Special thanks to Heath Mash for suggestions and fruitful discussions. I also would like to extend acknowledge to my colleagues Mario Espara-Soto, My-Linh Nguyen and Yeomin Yoon for assistance and discussion and thanks to Mari Rodriguez and Chaoran Hou for laboratorial assistance. Financial support for this project was provided by the EPA. Lastly, but most importantly, I would like to give special thanks to my family for being always supportive. Further, to my lovely wife, LiWen Chen, for always offering the greatest support with love. TABLE OF CONTENTS Page LIST OF TABLES .......................................................................................................... 11 LIST OF FIGURES ........................................................................................................ 14 CHAPTER 1.............................................................................................................. INTRODUCTION ............................................................................................................................................. 1 1.1. Introduction 1 1.2. Description Chapters 5 1.3. References 7 2.LITERATURE REVIEW ............................................................................................................................................. 9 2.1. Ozonation 9 2.1.1. Ozonation Concerns 9 2.1.2. Source of Bromide 10 2.1.3. Mechanism and Pathways of Bromate Formation 11 2.1.4. Parameters Affecting Bromate Formation 14 2.1.5. Development of Ozonation Kinetic Models 15 2.1.6. Ozone Decomposition 16 2.1.7. Modeling for Bromate Formation Prediction18 2.1.8. Bromate Control 20 2.2. Halogenation (Chlorination/Bromination) 21 2.2.1. Hydrolysis of aqueous Chlorine or Bromine23 2.2.2. Kinetics and Mechanisms of Chlorine/Bromine with NOM 24 CHAPTER... Page 2.3. References 26 3.OBJECTIVES AND RESEARCH HYPOTHESES ........................................................................................................................................... 38 3.1. Objectives 38 3.2. Research Hypotheses 40 · 3.2.1. Hypothesis I: Bromate formation increases proportionally to the ratio of [HO ]/[O3] during ozonation, affected by different water qualities (pH, DOC, temperature, ammonia and (bi)carbonate alkalinity) and water treatment conditions (ozone dose, contact time and flow rate)…………….41 3.2.2. Hypothesis II: HO· concentrations decrease proportionally with increasing DOC and (bi)carbonate alkalinity and decreasing pH in natural waters 42 3.2.3. Hypothesis III: Ammonia addition for controlling bromate formation does not alter · · the [HO ]/[O3] ratio, but shifts bromate formation towards the HO oxidation pathway by scavenging HOBr/OBr-. 44 3.2.4. Hypothesis IV: Aqueous bromine has a higher rate constant with NOM than aqueous chlorine. The rate of reaction between bromine and chlorine with NOM is affected by the characteristics of NOM and pH. 45 3.3. References 48 4.................................................KINETICS OF HYDROXYL RADICAL FORMATION DURING OZONATION PROCESSES ........................................................................................................................................... 51 4.1. Introduction 51 4.2. Methodology 55 CHAPTER... Page 4.3. Results 60 4.3.1. Aqueous Ozone Measurement: 60 4.3.2. Bench-Scale Batch Ozonation 60 4.3.3. Comparison of RCT on CRW water with Pure Water 62 4.3.4. Bench-Scale continuous flow ozonation: 66 4.3.5. Pilot-scale continuous flow ozonation: 67 4.4. Discussion 68 4.4.1. Effect of Water Quality Parameters on RCT 70 4.4.1.1 Effect of Br- ………………………………………………………………70 4.4.1.2 Effect of pH………………………………………………………………70 4.4.1.3 Effect of temperature…………………………………………….……....71 4.4.1.4 Effect of (bi)carbonate Alkalinity…………….….………………………71 4.4.1.5 Effect of DOC…...……………………………………………………….72 4.4.1.6 Effect of treatment variables on RCT …………………………………….72 4.4.1.7 Effect of ozone doses and contact time ………………………………….72 4.4.1.8 Effect of ammonia addition………..…………………………………….73 4.4.2. Comparison of RCT between bench and pilot scale ozonation 74 4.5. Conclusions 74 4.6. References 77 5.EFFECT OF OZONE AND HYDROXYL RADICALS ON BROMATE FORMATION DURING OZONATION .................................................................... 108 CHAPTER... Page 5.1. Introduction 108 5.2. Meterials and Method 111 5.2.1. Materials: 111 5.2.2. Experimental Procedures 113 5.2.3. Analytical Methods 115 5.3. Results 116 5.3.1. Ozone Demand and Decay 117 5.3.2. Bromate Formation and Control 118 5.4. Discussion 122 5.4.1. Parameters Affecting Bromate Formation122 5.4.2. Relationship between Bromate Formation and Ozone Exposure 130 5.4.3. Relationship between Bromate Formation and RCT 132 5.5. Conclusions 134 5.6 References 135 6.KINETIC ASPECTS OF BROMATE MINIMIZATON BY AMMONIA DURING OZONATION OF BROMIDE CONTAINING WATERS....................................... 164 6.1. Introduction 164 6.2. Background 166 6.3. Methodology 170 6.4. Results 173 6.4.1. Ozone Decomposition 173 CHAPTER ... Page · 6.4.2. Determination of [HO ]/[O3] 174 6.4.3. Bromate Formation 175 6.4.4. Intermediate Aqueous Bromine Formation 177 6.5. Discussion 178 6.5.1. Effect of Ammonia on Ozone Decomposition 178 6.5.2. Competition of Reactions 179 6.5.3 Change of Bromate Formation Pathways………………………………...180 6.5.4 Limitations of Ammonia on bromate formation 181 6.6. Conclusions 182 6.7. References 184 7.REACTIVITY AND DISINFECTION BY-PRODUCT FORMATION OF AQUEOUS CHLORINE AND BROMINE WITH NATURAL ORGANIC MATTER....................................................................................................................... 204 7.1. Introduction 204 7.2. Materials and Methods 207 7.3. Results 212 7.3.1. Halogen Consumption and Halofrom Production 212 7.3.2. Aqueous Bromine and Chlorine Reaction Rates with