For Bromate Reduction

TECH UPDATE By Kimberly D. Thompson and Neal E. Megonnell, Calgon Carbon Corp. Activated Carbon ctivated carbon is well-known readily is oxidized to aqueous bromine. for its ability to remove for Bromate Reduction In addition to bromate, aqueous A organic compounds from bromine can cause various types of water through a process known as not all carbons are alike, especially hypochlorite solutions may contain brominated disinfection byproducts adsorption, remove chlorine and when chemical reactions control bromate as a contaminant.1 Bromate such as bromoform and brominated chloramine through various chemical the process. is a highly toxic substance that causes haloacetic acids. reactions, and serve as a general irreversible renal failure, deafness filter medium. However, its use for Regulations and Reactions and death and has been linked to In order to understand the formation – reduction of bromate is unclear. Bromate (BrO3 ) is a disinfection renal tumors in rats. As such, the of aqueous bromate, a corollary Various authors have studied the byproduct formed by the reaction American, Canadian and European understanding of ozone decomposition use of activated carbon and for the of ozone and naturally occurring environmental protection agencies is needed. Ozone can play a direct most part have concluded activated bromine in drinking water. Although have designated 10 µg/L as the (molecular ozone pathway) or indirect carbon is not a cost-effective solution. bromate is unlikely to be formed using maximum acceptable concentration (hydroxyl radical pathway) oxidative However, these authors have failed standard chlorination disinfection, or maximum contaminant level role in forming byproducts. Ozone to realize the limitations of carbon there is some evidence that (MCL) in drinking water. reacts directly with the bromide ion validation methods or the fact that commercially available sodium to form hypobromite and oxygen. The important precursor to bromate – ◊ – formation in drinking water is O3 + Br O2 + OBr Table 1. Carbon Properties bromide. In the United States, the average bromide concentration in Two ozone molecules then react Catalytically Standard drinking water is approximately 100 directly with the hypobromite to form Enhanced GAC Bituminous GAC µg/L. Since bromate is 63 percent bromate and oxygen. Alternatively, the Test Procedure (8×30 mesh) (8×30 mesh) bromide, only 6.3 µg/L of bromide hypobromite can react with multiple needs to be converted to bromate upon hydroxyl radicals created by the Mean Particle Diameter (mm) 1.44 1.44 ozonation to exceed the MCL. Natural destruction of ozone. (Used for Testing) sources of bromine in groundwater are * – ◊ Peroxide Number saltwater intrusion and bromide 2O3 (or OH ) + OBr 2O2 + BrO3 6.6 53.0 (Used for Testing) dissolution from sedimentary rocks. Bromine usually is present in drinking These reactions are generalized and Iodine Number water as either hypobromous acid not necessarily balanced, but they give 825 minimum 900 minimum (Specification) (HOBr–) or hypobromite (OBr–). When a good overview of the mechanisms at exposed to ozonation, the bromide ion work in bromate formation.

While the 10 µg/L MCL is anticipated to impact a limited number of utilities currently using ozone as the primary disinfectant to inactivate Giardia and viruses, a greater number of utilities will be impacted by this MCL when compliance with the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) is required. Compliance will mean continuance of meeting filtration avoidance criteria of two-log Cryptosporidium inactivation and overall inactivation requirements (three-log Giardia, four-log viruses and two-log Cryptosporidium) using a minimum of two disinfectants.

Activated Carbon Research for Bromate Reduction The use of activated carbon has been investigated by various authors for the removal or reduction of bromate.2,3,4 The data to date have been inconsistent and, in some cases, misleading due to the techniques used to determine the applicability of activated carbon.5,6 It also is apparent

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12 Water Quality Products www.wqpmag.com November 2003 About the Authors Kimberly Thompson is an inside technical sales representative at Calgon Carbon Corp. She holds a bachelor of science in biochemistry from Steon Hill College, Greensburg, Pa., and has five years of experience as a chemist at Calgon Carbon. She may be reached at 412-787-6315; [email protected]. Neal Megonnell is a corporate technical sales specialist at Calgon Carbon. He holds a bachelor of science in chemistry from the University of Pittsburgh and a masters of science in chemical engineering/colloids, polymers and surfaces from Carnegie Mellon University. He may be reached at 412-787-6638; [email protected].

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Figure 1 Figure 2 Figure 3

Reaction Rate Data Comparing Catalytically Enhanced GAC to Standard Bituminous GAC Bromate Reduction and Bromide Formation Data Column Study Data

that the carbon selection process was Activated Carbon for Bromate studies show typical properties such • Data show standard carbon overlooked, which has lead to Reduction—Reaction Kinetics as iodine number cannot be used properties such as iodine number generalizations concerning the use of Testing was conducted using a to predict bromate reduction cannot be used to indicate bromate activated carbon for this application. differential reactor to determine performance, however, catalytic reduction performance. the reaction rate for a standard activity as measured by the peroxide • Catalytic activity as measured by One paper however has focused on bituminous coal-based granular number is useful in determining the the peroxide number does give the effect of surface properties on carbon and a catalytically enhanced more applicable carbon. some indication of bromate bromate removal.7 The data shows carbon. Typical carbon properties reduction performance. surface properties can and do affect are shown in Table 1. Reaction rate Activated Carbon— • Column study data show activated bromate removal performance. Other data (Figure 1) show the reaction Real World Application carbon can be utilized to reduce applications such as chloramine follows a first order reaction and, Differential reactor studies are useful bromate to acceptable levels. WQP removal in the liquid phase and more importantly, data show the for the determination of reaction rates. hydrogen sulfide and sulfur dioxide reaction rate for the catalytically However, full scale testing is required References oxidation in the vapor phase also enhanced carbon is 3.4 times faster to verify the data. Studies published 1 American Water Works Association have been shown to be affected by than the standard carbon. concerning the reduction of bromate Research Foundation. “Formation and surface properties. Commercially have utilized the Rapid Small Scale Control of Brominated Ozone available activated carbons produced Analysis of the water confirms the Column Test (RSSCT) procedure, byproducts,” report #90714. for catalytic properties as well as reaction product from bromate which was designed for adsorption 2 Meijers, R.T., and Kruithof, J.C. adsorptive properties do exist destruction is bromide (Figure 2). The applications and may not translate “Potential Treatment Options for and have been investigated for faster reaction rate for the catalytically well to applications where a different Restriction of Bromate Formation and bromate reduction. However, enhanced carbon would allow shorter removal mechanism such as Bromate Removal,” Water Supply, Vol. 13, No.1, Paris, pp.183–189, 1995. the data is misleading due to contact time systems to be designed for oxidation/reduction or ion exchange testing conditions. full-scale use. Experimental design exists. Data from the literature as 3 Asami, M, et. al. “Bromate Removal well as the differential reactor work During Transition from New Granular Activated Carbon (GAC) to Biological conducted for this paper show the Activated Carbon (BAC),” Water reaction to be a reduction of bromate; Research, Vol. 33, No. 12, pp. therefore, the RSSCT column study 2,797–2,804, 1999. procedure may not be accurate. 4 Kirisits, M.J., and Snoeyink, V.L., “Reduction of Bromate in a BAC Column studies were conducted Filter,” Journal AWWA, Vol. 91, No. 8, using actual particle size carbons pp. 74–84, 1999. and full-scale contact times to verify 5 Siddiqui, M., et. al. “Bromate Ion performance. A column study using Removal by Activated Carbon,” a 30-minute contact time and Water Research, Vol. 30, No. 7, pp. catalytically enhanced 8×30 mesh 1651–1660, 1996. carbon showed bromate could be 6 Siddiqui, M., et. al. “Alternative successfully reduced from an average Strategies from Removing Bromate,” of 110 ppb bromate to an average of Journal AWWA, pp. 81–96, less than 5 ppb (see Figure 3). October 1994. 7 Miller, J., et. al. “The Effect of Granular Conclusions Activated Carbon Surface Chemistry • Differential reactor studies indicate on Bromate Reduction,” Disinfection the bromate reduction reaction to Byproducts Water Treatment, pp. bromide to be first order. 293–309, (1996) CA 124-241548U.

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