One-electron oxidant-induced transformation of dissolved organic matter: Optical and antioxidation properties and...

Dissolved organic matter (DOM) is a major sink of radicals in advanced oxidation processes (AOPs) and the radical-induced DOM transformation influences the subsequent water treatment processes or receiving waters. In this study, we quantified and compared DOM transformation by tracking the changes of dissolved organic carbon (DOC), UVA₂₅₄, and electron donating capacity (EDC) as functions of four one-electron oxidants (SO₄^•-, Cl₂^•-, Br₂^•-, and CO₃^•-) exposures as well as the changes of functional groups and molecule distribution. SO₄^•- had the highest DOC reduction while Cl₂^•- had the highest EDC reduction, which could be due to their preferential reaction pathways of decarboxylation and converting phenols to quinones, respectively. Br₂^•- and CO₃^•- induced less changes in DOC, UVA₂₅₄, and EDC than SO₄^•- and Cl₂^•-. Additionally, DOM enriched with high aromatic contents tended to have higher DOC, UVA₂₅₄, and EDC reductions. Decreases in hydroxyl and carboxyl groups and increases in carbonyl groups were observed in these four types of radicals treated DOM using Fourier transform infrared spectroscopy. High resolution mass spectrometry using FTICR-MS showed that one-electron oxidants preferred to attack unsaturated carbon skeletons and transformed into molecules featuring high saturation and low aromaticity. Moreover, SO₄^•- was inclined to decrease oxidation state of carbon and O/C of DOM due to its strong decarboxylation capacity. This study highlights the distinct DOM transformation by four one-electron oxidants and provides comprehensive insights into the reactions of one-electron oxidants with DOM.