Dissolved organic matter (DOM) scavenges sulfate radicals (SO4 •–), and SO4 •–-induced DOM transformations influence disinfection byproduct (DBP) formation when chlorination follows advanced oxidation processes (AOPs) used for pollutant destruction during water and wastewater treatment. Competition kinetics experiments and transient kinetics experiments were conducted in the presence of 19 DOM fractions. Second-order reaction rate constants for DOM reactions with SO4 •– (k DOM,SO4 •– ) ranged from (6.38 ± 0.53) × 106 M–1 s–1 to (3.68 ± 0.34) × 107 MC –1 s–1. k DOM,SO4 •– correlated with specific absorbance at 254 nm (SUVA254) (R 2 = 0.78) or total antioxidant capacity (R 2 = 0.78), suggesting that DOM with more aromatics and antioxidative moieties reacted faster with SO4 •–. SO4 •– exposure activated DBP precursors and increased carbonaceous DBP (C-DBP) yields (e.g., trichloromethane, chloral hydrate, and 1,1,1-trichloropropanone) in humic acid and fulvic acid DOM fractions despite the great reduction in their organic carbon, chromophores, and fluorophores. Conversely, SO4 •–-induced reactions reduced nitrogenous DBP yields (e.g., dichloroacetonitrile and trichloronitromethane) in wastewater effluent organic matter and algal organic matter without forming more C-DBP precursors. DBP formation as a function of SO4 •– exposure (concentration × time) provides guidance on optimization strategies for SO4 •–-based AOPs in realistic water matrices.

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 SO 4•− as a representative), and the formed ketones significantly increased trichloromethane (CHCl 3 ) formation potential (FP) upon subsequent chlorination. CHCl 3 -FPs from aromatic ketones (Ar−CO−CH 3 , average of 22 mol/mol) were 6−24 times of CHCl 3 -FPs from aromatic alcohols (Ar−CH(OH)−CH 3 , average of 0.85 mol/mol). At a typical SO 4•− exposure of 7.0 × 10 −12 M•s, CHCl 3 -FPs from aromatic alcohol transformation increased by 24.8%−112% with an average increase of 53.4%. Notably, SO 4•− oxidation of aliphatic alcohols resulted in minute changes in CHCl 3 -FPs due to their low reactivities with SO 4•− (∼10 7 M −1 s −1 ). Other one-electron oxidants (Cl 2 •−, Br 2•− ,and CO 3 •− ) are present in AOPs and also lead to aromatic alcohol−ketone transformations similar to SO 4•− . 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.