Control of aromatic halogenated disinfection byproducts in chlorinated and chloraminated drinking water through pre-oxidation: Effects and mechanisms.

Aromatic halogenated disinfection byproducts (DBPs) are of great concern in disinfected drinking water due to their high toxicity. Pre-oxidation is commonly employed in drinking water treatment to remove emerging contaminants and also to control DBPs formation. However, the control of aromatic halogenated DBPs in drinking water through pre-oxidation has not been clarified. In this study, the effects of four common pre-oxidants, including ozone (O₃), chlorine dioxide (ClO₂), permanganate (Mn(VII)), and ferrate (Fe(VI)), on the formation of aromatic halogenated DBPs in chlorinated and chloraminated drinking water were systematically examined, the influencing mechanisms of different pre-oxidants on the formation of aromatic halogenated DBPs were explored based on the transformation of organic and inorganic precursors during pre-oxidation, and the key factors affecting the formation of aromatic halogenated DBPs were evaluated in chlorinated and chloraminated drinking water after O3 pre-oxidation. The results demonstrate that O₃, ClO₂, and Fe(VI) effectively controlled the formation and total cytotoxicity of aromatic halogenated DBPs in both chlorinated and chloraminated drinking water following the efficiency order of O₃ > ClO₂ > Fe(VI), while Mn(VII) generally enhanced the formation and total cytotoxicity of aromatic halogenated DBPs. The DBP-control performance of the pre-oxidants was governed by their reactivity toward both organic precursors and halide ions. O₃ demonstrated the highest control efficiencies owing to its effective oxidation of aromatic structures and rapid conversion of halide ions. ClO₂, though weaker toward aromatic rings, efficiently oxidized phenolic sites and halide ions. Fe(VI) removed organic precursors effectively but showed enhanced HOBr generation. Mn(VII) demonstrated the weakest oxidation toward both organic and inorganic precursors, possibly converting organics into aromatic intermediates more susceptible to subsequent halogenation and thus enhancing the formation of certain aromatic halogenated DBPs. The performance of O₃ pre-oxidation for the control of aromatic halogenated DBPs in chlorinated and chloraminated drinking water was significantly affected by the precursor aromaticity, halide levels, and disinfectant dose.