Removal of organics and control of bromate for a southern china water supply

Abstract

A pilot plant with successive preozonation, coagulation‐sedimentation, sand filtration, postozonation, and biological activated carbon was operated for more than six months to treat reservoir water containing 15–38 μg/L of bromide in southern China. Preozonation enhanced the removal of chemical oxygen demand using potassium permanganate as the oxidant (CODMn) and ultraviolet light absorbance at 254 nm (UV254) using coagulation‐sedimentation but did not improve total organic carbon (TOC)‐removal effectively. However, preozonation markedly enhanced the removal of trihalomethane formation potential (THMFP) by the conventional process, and THMFP removal by the combination of preozonation and conventional treatment was 57% using an ozone dose of 0.8 mg/L. Almost no bromate formed during preozonation. An ozone dose of 2.0 mg/L (0.5 mg/L and 1.5 mg/L for pre‐ and postozonation, respectively) was found to be the optimal dosage for the maximum removal of organics (65% of THMFP, 52% of TOC, 63% of CODMn, and 84% of UV254) while keeping bromate under 5 μg/L. A combination of conventional treatment with preozonation should be a suitable alternative if the primary goal is to remove THMFP.