Converting peracetic acid activation by FeO from nonradical to radical pathway via the incorporation of L-cysteine.

Recently, peracetic acid (PAA) based Fenton (-like) processes have received much attention in water treatment. However, these processes are limited by the sluggish Fe(III)/Fe(II) redox circulation efficiency. In this study, L-cysteine (L-Cys), an environmentally friendly electron donor, was applied to enhance the FeO/PAA process for the sulfamethoxazole (SMX) abatement. Surprisingly, the L-Cys incorporation was found not only to enhance the SMX degradation rate constant by 3.2 times but also to switch the Fe(IV) dominated nonradical pathway into the OH dominated radical pathway. Experiment and theoretical calculation result elucidated -NH, -SH, and -COOH of L-Cys can increase Fe solubilization by binding to the Fe sites of FeO, while -SH of L-Cys can promote the reduction of bounded/dissolved Fe(III). Similar SMX conversion pathways driven by the FeO/PAA process with or without L-Cys were revealed. Excessive L-Cys or PAA, high pH and the coexisting HCO/HPO exhibit inhibitory effects on SMX degradation, while Cl and humic acid barely affect the SMX removal. This work advances the knowledge of the enhanced mechanism insights of L-Cys toward heterogeneous Fenton (-like) processes and provides experimental data for the efficient treatment of sulfonamide antibiotics in the water treatment.