Low additive peracetic acid enhanced sulfamethazine degradation by permanganate: A mechanistic study

In this study, a novel water treatment process combining permanganate (Mn(VII)) and peracetic acid (PAA, CH₃C(O)OOH) was employed to degrade sulfamethazine (SMT), a typical model contaminant. Simultaneous application of Mn(VII) and a small amount of PAA resulted in much faster oxidation of organics than a single oxidant. Interestingly, coexistent acetic acid played a crucial role in SMT degradation, while background hydrogen peroxide (H₂O₂) had a negligible effect. However, compared with acetic acid, PAA could better improve the oxidation performance of Mn(VII) and accelerate the removal of SMT more significantly. The mechanism of SMT degradation by Mn(VII)-PAA process was systematically evaluated. Firstly, based on the quenching experiments, electron spin resonance (EPR) results and UV-visible spectrum, singlet oxygen (¹O₂), Mn(III)_aq and MnO₂ colloids were the predominant active substances, while organic radicals (R-O^•) showed negligible contribution. Then, the decay of Mn(VII) in the presence of PAA and H₂O₂ was investigated. It was found that the coexisting H₂O₂ accounted for almost all the decay of Mn(VII), PAA and acetic acid both had low reactivity toward Mn(VII). During the degradation process, acetic acid was able to acidify Mn(VII) and simultaneously acted as a ligand to form reactive complexes, while PAA mainly played a role of spontaneously decomposing to produce ¹O₂, they jointly promoted the mineralization of SMT. Finally, the degradation intermediates of SMT and their toxicities were analyzed. This paper reported the Mn(VII)-PAA water treatment process for the first time, which provided a promising approach for rapid decontamination of refractory organics-polluted water.