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

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.