Which pre-oxidation methods to choose? From perspective of DBPs formation and toxicities reduction

Pre-oxidation have been widely applied in drinking water treatment plants with micro-polluted water as water sources. In this study, the effects of three commonly used oxidants (ozone, chlorine, and potassium permanganate) on disinfection by-products (DBPs) formation from micro-polluted water during subsequent chlorination and chloramination were investigated. Moreover, the toxicities of treated water were also compared. In addition, principal component analysis was applied to clarify the main components that contributed to DBPs generation. The results demonstrated that all the selected oxidants could reduce DBPs to some extent, but the species and amounts were quite different. Pre-KMnO4 greatly reduced haloacetic acid (HAAs) formation in subsequent chloramination; the removal rate reached up to 45.2%. Pre-HClO could produce trihalomethane (THMs) and HAAs directly, and its effect on DBPs reduction during subsequent disinfection processes was limited. Pre-O3 performed best on N, N-dimethyl nitrosamine (NDMA) reduction during subsequent chloramination; the corresponding removal rates were 49.7%. In addition, pre-O3 significantly reduced UV254 and SUVA. Pre-KMnO4 transferred more organic matter to cationic components (24%), while the highest polar component augmentation was observed during pre-HClO (15%). Based on the analysis of total toxicity of formed DBPs, pre-O3 performed best on toxicity reduction no matter subsequent chlorination or chloramination, which decreased by 25.8% and 46.4%, respectively. The principal component analysis showed that DBPs has a weak correlation with regular water quality parameters, but related with specific organic fractions. The results of this paper had significant guidance for the selection of pre-oxidation methods in drinking water treatment plants for this kind of water sources.