Bromide Ion Incorporation Into Brominated Disinfection By-Products

Abstract

During chlorination and ozonation, a key concern is the conversion of bromide ions (Br−) to disinfection by-products (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs), and bromate (BrO3−). The objective of this study was to investigate the effects of water quality parameters (dissolved organic carbon (DOC), Br−, pH, and temperature) on the percent conversion of Br− to the known DBPs. Ten to twelve surface and ground waters having different DOC (1.2–10.6 mg/L) and Br− (7–312 μg/L) were subjected to bench scale chlorination and ozonation experiments at various pH (6.5–8.5) and temperature (15,∘C–25,∘C) conditions. The results show that the average percent of bromide incorporation was 24.5% for THMs and 9.5% for HAAs, and 12% for BrO3− for the waters, respectively. In addition, the percent of bromide incorporation depends on source water pH. The percent of bromide incorporation increased with increasing pH (6.5 to 8.5) for THMs (18% to 28%) and BrO3− (6.9% to 19%) and was insignificantly influenced by pH for HAAs. Coagulation using alum was effective in removing DBP reactive precursors such as DOC, which resulted in the smaller percentage of bromide incorporation for coagulated waters. The calculated average health risk factor for bromate was 4.3× 10−4 for the ten source waters, which is approximately 10 times higher than that for the average THMs (4.4× 10−5), respectively.