The reactivity of organic radicals in the performic, peracetic, perpropionic acids-based advanced oxidation process: A case study of sulfamethoxazole

Advanced oxidation processes (AOPs) based on peracetic acid (PAA) displayed great potential in removing emerging contaminants by generating HO^• and organic radicals. Performic and perpropionic acids (PFA and PPA) also act as disinfectants, but their application potential has not been investigated yet. Here, we investigated the degradation mechanism and kinetics of sulfamethoxazole (SMX) by HO^•, RC(O)O^• species (including HC(O)O^•, CH₃C(O)O^• and CH₃CH₂C(O)O^•) and RC(O)OO^• species (including HC(O)OO^•, CH₃C(O)OO^• and CH₃CH₂C(O)OO^•). The results show that the calculated reaction rate constants of SMX follow the order of HC(O)O^• > CH₃C(O)O^• > CH₃CH₂C(O)O^• > HO^• > HC(O)OO^• > CH₃C(O)OO^• > CH₃CH₂C(O)OO^•. The reactivity towards SMX is strongly correlated with the redox potentials of reactive radicals. Hence, the RCOO^• species play dominant roles in the purification of SMX in PFA/PAA/PPA-based AOPs. The degradation of SMX mainly proceeds via addition at the benzene ring, the hydrogen abstraction from the -NH₂ group as well as the single electron transfer reaction. This study highlights the fundamental aspects of PFA, PAA, and PPA in the purification of sulfamethoxazole and enhances the role of organic radicals in the AOPs based on organic peracetic acids.