Degradation of chlortoluron during UV irradiation and UV/chlorine processes and formation of disinfection by-products in sequential chlorination

Abstract

The degradation kinetics and pathways of chlortoluron during UV irradiation and UV/chlorine process as well as the formation of disinfection by-products (DBPs) after post-chlorination were investigated in this study. The quantum yield of chlortoluron was calculated as 0.0258moleinstein−1 and the effect of solution pH was negligible during UV irradiation. On the other hand, the degradation rate of chlortoluron during UV/chlorine process was significantly promoted at acidic conditions as well as high chlorine doses and UV intensity. UV irradiation and UV/chlorination of chlortoluron both followed the pseudo-first order reaction kinetics, but UV/chlorine process is more efficient than UV irradiation with the reaction rate constant between chlortoluron and OH radicals determined as (2.18±0.83)×109M−1s−1. The mineralization of chlortoluron was considerably increased with increasing chlorine dose and decreasing pH during UV/chlorine process. The degradation pathways of chlortoluron during UV irradiation and UV/chlorine processes were proposed according to the identified intermediates. The formation of carbonaceous DBPs (C-DBPs) and nitrogenous DBPs (N-DBPs) during direct chlorination and post chlorination of UV irradiation and UV/chlorine processes were investigated as well. More DBP precursors were formed during UV/chlorine process compared to direct chlorination and UV irradiation, which deserves extensive concerns in drinking water treatment processes.