Transformation of Bromine Species During Decomposition of Bromate under UV Light from Low Pressure Mercury Vapor Lamps

Abstract

Bromate decomposition with low pressure mercury vapor lamps (LPMVL) was studied in buffer-free and buffered Milli-Q water by following the fate of bromine species BrO3 −, Br−, and free bromine. BrO3 − was converted over time to Br− with total free bromine (TFBr) as secondary reaction product. BrO3 − decay followed pseudo-first-order kinetics and was independent of [BrO3 −]o (0.06–0.6 mM), pHo (6.9–9.5) and HCO3 − (0.05–1.0 mM), slightly dependent on acetate (0.06–0.27 mM), highly dependent on and adversely affected by humic acids (HA) and an increasing function of photon flux I as measured by potassium ferrioxalate actinometry. Reaction pH dropped by as much as 2.2 units at pHo ≤ 8.5 in the buffer-free experiments, while it remained within 0.5 unit at pHo > 9. TFBr decay due to exposure to LPMVL resulted in formation of Br− (major) and BrO3 − (minor). Decay of HA in the presence of BrO3 − was highly augmented by photon emission of LPMVL at 185 nm and was found to substantially contribute to BrO3 − decay in the presence of HA. Correlations on the dependency of bromine species decay or formation rates as a function of photon flux are presented.