Unraveling the role of CH₃C(=O)OO^• in the degradation of emerging organic contaminants via boosting activation of peracetic acid by iron oxychloride catalyst

Activated peracetic acid (PAA) processes have received increasing focus on the removal of various micropollutants. In this study, iron oxychloride (FeOCl) was used to activate PAA for emerging organic contaminants (EOCs) degradation and sulfamethoxazole (SMX) was utilized as the target pollutant. The removal rate of SMX can achieve 90.37% at a neutral condition, and the k_obs was 0.0836 min⁻¹. According to the free radical quenching experiment, ESR spectrum, and LC/MS analysis, CH₃C(=O)OO^• was confirmed to be the main contributor to SMX degradation. The redox cycle of Fe(III)/Fe(II) pairs was the core mechanism of the FeOCl catalysis. A total of six possible transformation products in the FeOCl/PAA system were identified, as well as four possible degradation pathways were proposed. After the FeOCl/PAA treatment, most of the TPs exhibited lower toxicity than SMX itself. The repeatability of FeOCl was still > 80% after four uses, inorganic anions (HCO₃^– and Cl^-) had negligible influences, while humic acid could compete for reactive species and lead to a decrease in the degradation of SMX. Besides, the SMX degradation was almost not affected in the actual water bodies, demonstrating that the FeOCl/PAA process possesses high application potential. The degradation efficiency of FeOCl/PAA systems for other pollutants was also measured, and the removal efficiencies were different due to the selectivity of the CH₃C(=O)OO^•. Overall, this study comprehensively revealed the oxidation mechanism of the FeOCl/PAA system and provides theoretical support for practical application.