Formation of cyanogen bromide and other volatile DBPs in the disinfection of bromide-rich lake water

Production of cyanogen bromide (CNBr) and other volatile DBPs was studied in bromide-rich lake water during disinfection with chlorine, chloramine, and chlorine dioxide. The different disinfectants were dosed to the lake water in laboratory experiments, and the resulting concentrations of CNBr, trihalomethanes (THMs), and haloacetonitriles (HACNs) were measured. CNBr concentration is a resultant of formation and decomposition by hydrolysis. Maximum concentration (36 mu g/L) was obtained at low chlorine dose (1.5 mg/L) at pH 7.5 and 10 h contact time. Under these conditions, the molar distribution of the volatile DBPs was 50% CNBr, 40% THMs, and 10% HACNs. It is suggested that CNBr is formed by the reaction of hypobromous acid with organic N precursors present in lake water. Fulvic acid was found to be a good precursor for THMs but a poor precursor for CNBr. With chloramination, yields of CNBr, THMs, and HACNs were much lower, only 6, 11, and 2 mu g/L, respectively. CNBr concentration was stable for 10 days. Chlorine dioxide produced insignificant quantities of CNBr, THMs, and HACNs, less than 1 mu g/L. A combination of chlorine dioxide and chloramine enhanced production of CNBr and THMs to maximum yields of 7.8 and 19 mu g/L, respectively.