Mitigating mammalian cell cytotoxicity of drinking water upon chlorination by conventional and advanced treatment processes.

Ozone (O3)-biological activated carbon (BAC) advanced treatment is increasingly applied after conventional coagulation-sedimentation for controlling the toxic regulated disinfection byproducts (DBPs). The potential reduction of Chinese hamster ovary cell cytotoxicity of chlorinated waters using such measures at full-scale drinking water treatment plants was investigated. Results showed that conventional coagulation-sedimentation processes could achieve ∼13 % to 28 % reduction in chlorinated water cytotoxicity. Ozonation did not provide significant reduction. Yet, BAC treatment could additionally mitigate the cytotoxicity by ∼14 % to 27 %. The reduction of cytotoxicity was correlated well with decreased dissolved organic carbon concentrations of chlorinated waters. The reduction of unknown nonvolatile fractions featured by high molecular-weight (MW) DBPs, accounting for ∼58 % to > 90 % of total cytotoxicity, is a major cause. Using high-resolution mass spectrometry, O3-BAC treatment could substantially promote the reduction in number of halogenated features (from <30 % to up to 80 %), especially for brominated features. 231 features were tentatively identified as 20 groups of halogenated DBPs via suspect screening, machine learning prioritization, and homologous or isomeric series identification. The LC50 values for seven high MW DBPs identified ranged from 4.5 × 10-5 to 3.9 × 10-3 M. While the precursors for trichloroacetyl-containing aliphatics, halobenzenediols, halo(di)nitrophenols, halohydroxy benzoquinones, halohydroxy pyridines, and halothiophen-derivatives persisted in coagulation-sedimentation, they were abated in O3-BAC treatment. This work provides insights into the cytotoxicity mitigation of chlorinated drinking water using conventional and advanced water treatment processes.