Transformation of emerging disinfection byproducts Halobenzoquinones to haloacetic acids during chlorination of drinking water

Halobenzoquinones (HBQs) are emerging disinfection byproducts of high toxicity and frequent occurrence in drinking water. HBQs are unstable and can be transformed to hydroxylated HBQs (OH-HBQs) and haloacetic acids (HAAs) in the presence of multiple reactive species, which are generated during photolysis of chlorine. In this study, we investigated the occurrence of HBQs in the effluent of 10 water treatment systems and household tap water across China, and demonstrated the kinetic and mechanism of 2,6-dichloro-1,4-benzoquinone (2,6DCBQ) degradation to HAAs by the solar/chlorine processes. HBQs were detected in all samples at concentrations from 1.2 to 42.7 ng/L. The degradation of 2,6-DCBQ during solar/chlorine treatment followed the pseudofirst order kinetics. HOCl/OCl- and ClO. contributed to 47.9% and 50.2% of 2,6-DCBQ degradation, whereas the contributions of Cl. and .OH were <1.5%. The degradation rates of 2,6-DCBQ were stable in the presence of chloride, but decreased by 4.3% in the presence of 0.1 mgC/L natural organic matter (NOM). ClO. and Cl. directly attacked the aromatic ring of 2,6-DCBQ to generate HAAs, whereas .OH reacted with OH-HBQs, the intermediate products of 2,6-DCBQ to generate HAAs. Unraveling the mechanism of free radical mediated 2,6-DCBQ transformation would greatly benefit the development of effective HBQ elimination technologies at water treatment plants in the future.