Effect of Bromide Ion on Haloacetic Acid Speciation Resulting from Chlorination, Ozonation and Chloramination of Aquatic Humic Substances

The objective of this study was to investigate the effect of bromide ion concentration on the distribution of haloacetic acid (HAA) species resulting from chlorination, ozonation and chloramination of waters containing humic substances. HAAs are by-products of drinking water disinfection, and laboratory animal studies have suggested that these compounds are associated with carcinogenicity, developmental toxicity and reproductive toxicity. The potential risk to human health posed by HAAs and the varying toxicological significance of HAA species necessitate an understanding of the factors that affect HAA formation and speciation. In this study, waters were analyzed for all nine of the HAA species containing bromine and chlorine. Standards for bromodichloroacetic acid and dibromochloroacetic acid were not commercially available but were synthesized at the University of North Carolina and the University of Massachusetts. Aquatic humic substances were obtained by XAD-8 extraction from raw waters at Myrtle Beach, SC and Palm Beach County, FL. Model waters were prepared containing 4 mg/L total organic carbon, 2 mM inorganic carbon, and ten bromide concentrations ranging from 0-25 μM (0-2 mg/L). Samples were chlorinated at pH8 and pH6 with and without pre-ozonation. Additional samples were chloraminated at pH8 with and without pre-ozonation. Chlorinated and chloraminated samples were incubated at 20°C for 24 hours in the dark, after which time oxidant residuals were measured and quenched. The samples were extracted into ether, derivatized with diazomethane, then analyzed for the nine HAAs on a gas chromatograph with electron capture detector. Bromide ion concentration was an important factor in HAA speciation in chlorinated waters. Bromo-chloro species (bromochloroacetic acid, bromodichloroacetic acid and dibromochloroacetic acid) were readily formed from chlorination of bromide-containing waters, and they constituted at least 10% of the total HAAs in waters containing as little as 1.2 μM Br (0.1 mg/L). Distribution of the HAAs among mono-, di-, and trihalogenated species appeared to be independent of bromide ion concentration. In addition, bromide ion appeared to have similar effects on HAA speciation in both waters studied. Lowering the pH of chlorination from pH8 to pH6 enhanced the formation of several species; however, HAA speciation was little affected. Pre-ozonation appeared to enhance bromine incorporation into the HAAs produced from subsequent chlorination. Total HAA formation in chloraminated waters was decreased approximately 90% compared to total HAA formation in chlorinated waters. Dichloroacetic acid was the principal species formed in chloraminated waters. Chloramination of bromide-containing waters resulted in some formation of brominated species, principally bromoacetic acid, dibromoacetic acid and bromochloroacetic acid; little formation of trihalogenated species was observed from chloramination, both in the presence and absence of bromide ion. Pre-ozonation followed by chloramination enhanced total HAA formation compared to chloramination alone; however, total HAA formation was still decreased by approximately 90% compared to chlorination. The results suggest that the bromo-chloro HAAs, whose occurrence in finished drinking waters is presently not known, are readily formed during chlorination of bromide-containing waters. Chloramination and pre-ozonation followed by chloramination appear to be effective means of controlling HAA formation. In addition, the effect of bromide ion on HAA speciation may be independent of the source of humic substances.Master of Science in Public Healt