Formation of disinfection byproducts upon chlorine dioxide preoxidation followed by chlorination or chloramination of natural organic matter

摘要

Chlorine dioxide (ClO_2) is often used as an oxidant to remove taste, odor and color during water treat-ment. Due to the concerns of the chlorite formation, chlorination or chloramination is often applied after ClO_2 preoxidation. We investigated the formation of regulated and emerging disinfection byproducts (DBPs) in sequential ClO_2-chlorination and ClO_2-chloramination processes. To clarify the relationship between the formation of DBPs and the characteristics of natural organic matter (NOM), changes in the properties of NOM before and after ClO_2 oxidation were characterized by fluorescence, Fourier trans-form infrared spectroscopy (FTIR), and size and resin fractionation techniques. ClO_2 preoxidation destroyed the aromatic and conjugated structures of NOM and transformed large aromatic and long ali-phatic chain organics to small and hydrophilic organics. Treatment with ClO_2 alone did not produce sig-nificant amount of trihalomethanes (THMs) and haloacetic acids (HAAs), but produced chlorite. ClO_2 preoxidation reduced THMs, HAAs, haloacetonitriles (HANs) and chloral hydrate (CH) during subsequent chlorination, but no reduction of THMs was observed during chloramination. Increasing ClO_2 doses enhanced the reduction of most DBPs except halonitromethanes (HNMs) and haloketones (HKs). The presence of bromide increased the formation of total amount of DBPs and also shifted DBPs to more bro-minated ones. Bromine incorporation was higher in ClO_2 treated samples. The results indicated that ClO_2 preoxidation prior to chlorination is applicable for control of THM, HAA and HAN in both pristine and pol-luted waters, but chlorite formation is a concern and HNMs and HKs are not effectively controlled by ClO_2 preoxidation.