Comparative studies of hydroxyl radical and sulfate radical-mediated degradation of aromatic compounds: Changes in electron-donating moieties and disinfection byproduct formation potential.

Aromatic compounds contribute the majority of UV254, electron-donating moieties (EDM), and disinfection byproduct formation potential (DBP-FP) for natural organic matter (NOM). This study selected 4-ethylphenol (4-EP), 1-(4-hydroxyphenyl)ethanol (4-HPE), 1-(4-hydroxyphenyl)ethenone (4-HPA), and 4-hydroxyphenylacetic acid (4-HPAA) as model compounds representing aromatic hydrocarbons, alcohols, ketones, and carboxylic acids, respectively. 4-HPA behaves differently from the other three: its electron-withdrawing carbonyl group substantially increases UV254 while decreasing EDM. During oxidation, 4-HPA uniquely shifts from a negative to a positive EDM-UV254 correlation, whereas the other three maintain negative correlations. SO4•- oxidation removed more EDM but generated higher UV254 products than •OH. Both radical oxidations enhanced representative DBP-FP (6-108-fold), with •OH showing 1.5-4.4-fold higher DBP-FP than SO4•-. 4-HPA exhibited the highest trichloromethane and 1,1,1-trichloropropanone formation potential before and after oxidation. For •OH, 4-HPE was the primary chloral hydrate precursor, while for SO4•-, multiple compounds contributed comparably. EDM removal serves as a better surrogate for DBP-FP when applied to aromatic hydrocarbons, alcohols, and carboxylic acids, while UV254 change is more suitable for aromatic ketones. These correlations were extended to Suwannee River NOM, providing a potential mechanistic basis for understanding DBP formation from complex NOM during radical-based water treatment.