Enhanced Bromate Formation during Chlorination of Bromide- Containing Waters in the Presence of CuO: Catalytic Disproportionate of Hypobromous Acid

摘要

Bromate (BrO_3~- ) in drinking water is traditionally seen as an ozonation byproduct from the oxidation of bromide (Br~), and its formation during chlorination is usually not significant This study shows enhanced bromate formation during chlorination of bromide-containing waters in the presence of cupric oxide (CuO). CuO was effective to catalyze hypochlorous acid (HOC1) or hypobromous acid (HOBr) decay (e.g., at least 104 times enhancement for HOBr at pH 8.6 by 0.2 g L~(-1) CuO). Significant halate concentrations were formed from a CuO-catalyzed hypohalite disproportjonation pathway. For example, the chlorate concentration was 2.7 ± 0.2 μM (225.5 ± 16.7 n% L~(-1)) after 90 min for HOC1 (C_o = 37 μM, 2.6 mg L~(-1) Cl_2) in the presence of 0.2 g L~(-1) CuO at pH 7.6, and the bromate concentration was 6.6 ± 0.5 μM (844.8 ± 64 μg L~(-1)) after 180 min for HOBr (C_o = 35 μM) in the presence of 0.2 g L~(-1) CuO at pH 8.6. The maximum halate formation was at pHs 7.6 and 8.6 for HOC1 or HOBr, respectively, which are dose to their corresponding pK_a values. In a HOCl-Br~-CuO system, BrO_3~- formation increases with increasing CuO doses and initial HOC1 and Br~- concentrations. A molar conversion (Br~ -to BrO_3~-) of up to (90 ±1)% could be achieved in the HOC1-Br~-CuO system because of recycling of Br" to HOBr by HOC1, whereas the maximum BrO_3~- yield in HOBr-CuO is only 26%. Bromate formation is initiated by the formation of a complex between CuO and HOBr/ OBr~-, which then reacts with HOBr to generate bromite. Bromite is further oxidized to BrO_3~- by a second CuO-catalyzed process. These novel findings may have implications for bromate formation during chlorination of bromide-containing drinking waters in copper pipes.