Application of Cobalt/Peracetic Acid to Degrade Sulfamethoxazole at Neutral Condition: Efficiency and Mechanisms

TLDR

An advanced oxidation process combining cobalt and peracetic acid (Co/PAA) was developed to degrade sulfamethoxazole (SMX). The process relies on Co(II)-activated peracetic acid generating acetylperoxy radicals (CH₃CO₃•) as the main oxidant, with acetoxyl radicals (CH₃CO₂•) also contributing. Co/PAA achieves efficient SMX removal even at sub‑micromolar Co, with optimal near‑neutral pH; H₂O₂, humic acid, and bicarbonate hinder degradation, while Cl⁻ has little effect, and although transformation products are more acutely toxic, low Co and SMX concentrations mitigate this risk and the process generates biodegradable carbon sources for subsequent biotreatment.

Abstract

An advanced oxidation process of combining cobalt and peracetic acid (Co/PAA) was developed to degrade sulfamethoxazole (SMX) in this study. The formed acetylperoxy radical (CH3CO3•) through the activation of PAA by Co (Co2+) was the dominant radical responsible for SMX degradation, and acetoxyl radical (CH3CO2•) might also have played a role. The efficient redox cycle of Co3+/Co2+ allows good removal efficiency of SMX even at quite low dosage of Co (<1 μM). The presence of H2O2 in the Co/PAA process has a negative effect on the degradation of SMX due to the competition for reactive radicals. The SMX degradation in the Co/PAA process is pH dependent, and the optimum reaction pH is near-neutral. Humic acid and HCO3- can inhibit SMX degradation in the Co/PAA process, while the presence of Cl- plays a little role in the degradation of SMX in this system. Although transformation products of SMX in the Co/PAA system show higher acute toxicity, the low Co dose and SMX concentration in aquatic solution can efficiently weaken the acute toxicity. After reaction in the Co/PAA process, numerous carbon sources that could be provided for bacteria and algae growth can be produced, suggesting that the proposed Co/PAA process has good potential when combined with the biotreatment processes.