Enhanced formation of bromate and brominated disinfection byproducts during chlorination of bromide-containing waters under catalysis of copper corrosion products

Abstract

Copper corrosion products (CCPs) in water distribution pipes may catalyze the reactions among disinfectant, natural organic matter (NOM), and bromide (Br−). This study investigated the simultaneous formation of bromate (BrO3−) and brominated disinfection byproducts (Br-DBPs) during chlorination of Br−-containing waters in the presence of three CCPs (i.e., CuO, Cu2O, and Cu2+). In a synthetic water, both oxidant decay and BrO3− formation were enhanced by CCPs, whereas the presence of humic acid (HA) significantly inhibited BrO3− formation due to its competition for HOBr to form Br-DBPs. In the HOClBr−CuO system, the BrO3− yield increased obviously with increasing CuO dose and initial Br− concentration, while the catalytic formation of Br-DBPs was rather limited. A molar conversion (Br− to BrO3−) of 22.1% was observed under CuO catalysis, compared with little conversion in the absence of CuO. In the HOClBr−Cu2O/Cu2+ systems, Cu2O or Cu2+ mainly enhanced the formation of Br-DBPs, with enhancement ratios of 69.9% and 50.1%, respectively. The degree of enhancement on Br-DBPs formation became more apparent with increasing pH, while that on BrO3− formation reached maximal at pH 7.6. The catalytic formation of Br-DBPs and BrO3− by CCPs was also verified in three filtered real waters, although to a lesser extent because of the water matrix effect. In mechanism, the CCPs promoted the formation of BrO3− and Br-DBPs through catalyzing the HOBr disproportionation pathway and the reaction of HOBr toward HA, respectively.