Disinfection by-product formation and toxicity evaluation for chlorination with powered activated carbon

With the deterioration of source water quality, pre-chlorination and pre-addition of powdered activated carbon (PAC) have been widely applied to improve water treatment efficiency, which would lead to PAC exposure to chlorine. Although previous studies reported that some emerging carbon materials (e.g., graphene) could potentially act as disinfection by-product (DBP) precursors, there were few studies paying attention to the interaction between chlorine and the most commonly used carbon material-PAC on the DBP formation. In this study, the DBPs formed by chlorination with and without PAC were investigated, and the DBP toxicities in different systems were evaluated. The results showed that the PAC could react with chlorine and form trihalomethanes (THMs) and haloacetic acids (HAAs). The amount of surface oxygen groups of the PAC increased during the chlorination, with these oxygen groups, especially the meta-positioned -OH groups, facilitating the formation of THMs and HAAs. In the presence of NOM, lower concentrations of THMs and HAAs were observed in the systems with PAC than in those without PAC, demonstrating the critical role of PAC adsorption towards DBP control. The cytotoxicity evaluation indicated that more toxic reaction products between PAC and chlorine were formed besides conventional DBPs. Moreover, the PAC with higher BET surface area and more lactonic function groups formed less toxic DBPs during chlorination, which might reduce health risk for treatment processes with pre-chlorination.