One-Electron Oxidant-Induced Transformations of Aromatic Alcohol to Ketone Moieties in Dissolved Organic Matter Increase Trichloromethane Formation

Radicals in advanced oxidation processes (AOPs) degrade micropollutants during water and wastewater treatment, but the transformation of dissolved organic matter (DOM) may be equally important. Ketone moieties in DOM are known disinfection byproduct precursors, but ketones themselves are intermediates produced during AOPs. We found that aromatic alcohols in DOM underwent transformation to ketones by one-electron oxidants (using SO₄^•- as a representative), and the formed ketones significantly increased trichloromethane (CHCl₃) formation potential (FP) upon subsequent chlorination. CHCl₃-FPs from aromatic ketones (Ar-CO-CH₃, average of 22 mol/mol) were 6-24 times of CHCl₃-FPs from aromatic alcohols (Ar-CH(OH)-CH₃, average of 0.85 mol/mol). At a typical SO₄^•- exposure of 7.0 × 10^-12 M·s, CHCl₃-FPs from aromatic alcohol transformation increased by 24.8%-112% with an average increase of 53.4%. Notably, SO₄^•- oxidation of aliphatic alcohols resulted in minute changes in CHCl₃-FPs due to their low reactivities with SO₄^•- (∼10⁷ M^-1 s^-1). Other one-electron oxidants (Cl₂^•-, Br₂^•-,and CO₃^•-) are present in AOPs and also lead to aromatic alcohol-ketone transformations similar to SO₄^•-. This study highlights that subtle changes in DOM physicochemical properties due to one-electron oxidants can greatly affect the reactivity with free chlorine and the formation of chlorinated byproducts.