Oxidative treatment of NOM by selective oxidants in drinking water treatment and its impact on DBP formation in postchlorination

Natural organic matter (NOM), as a ubiquitous component in aqueous environments, has raised continuous scientific concerns due to its role as an organic precursor to disinfection by-products (DBPs) in the subsequent chlorination pro-cess. Selective oxidants, including ozone (O3), chlorine dioxide (ClO2), permanganate (Mn(VII)), and ferrate (Fe(VI)) are widely used in the preoxidation stage in drinking water treatment. The selective reactivity of those oxidants toward NOM is expected to alternate NOM properties and consequently DBP formation in postchlorination. Despite extensive studies on the interactions of NOM with selective oxidants, there is currently a lack of an overview of this area. To fill this gap, this study presents the current knowledge of the modification of NOM properties by selective oxidants and its impact on DBP formation in postchlorination. The NOM property changes in three aspects, including bulk property (e.g., total organic carbon, ultraviolet absorbance), fractional constituent (e.g., molecular size, hydrophilicity/hydro-phobicity), and elemental composition (e.g., functional group) by the four selective oxidants (i.e., O3, ClO2, Mn(VII), and Fe(VI)) were discussed. Thereafter, the impacts of alteration of NOM properties by those selective oxidants on DBP formation in the subsequent chlorination were summarized, wherein the key influencing factors were discussed. Finally, the future perspectives in this area were forwarded, which highlighted the significance of process optimization, the attention to the less studied but more toxic DBPs, and the need for the identification of unknown DBPs. This review presented a state-of-the-art knowledge pool of the fate of NOM in oxidation and chlorination pro-cesses, promoted our understanding of the relationship between NOM properties and DBP formation, and identified further research needs in this area.

Automated summary

This study summarizes the effects of selective oxidants, such as ozone, chlorine dioxide, permanganate, and ferrate, on the properties of natural organic matter (NOM) and their impact on disinfection by-product (DBP) formation in drinking water treatment. The changes in NOM properties, including bulk property, fractional constituent, and elemental composition, by these oxidants were discussed, and the resulting effects on DBP formation during postchlorination were summarized. The future perspectives in this area were also presented, highlighting the importance of process optimization, studying more toxic DBPs, and identifying unknown DBPs.