Oxalic acid-enhanced sulfamethoxazole degradation by V2O3/percarbonate process: Insights into the reactive oxygen species generation and conversion

Sewage disposal technology in advanced oxidation processes (AOPs) should be enriched for providing more options for practical application. Herein, degradative and mechanistic investigation of heterogeneous V2O3-activated sodium percarbonate (SPC) process was implemented in the presence of oxalic acid (OA). The experimental results indicated a strong dependency of sulfamethoxazole (SMX) degradation on SPC dosage and a wide adaptability to the ambient pH in V2O3/SPC/OA system. Efficient removal of SMX in water reached 93.4 % within 10 min at the initial presence of 0.1 g/L V2O3 and 2 mM SPC. Mechanistic experiments revealed that •OH played an indispensable role in SMX degradation, which partially dominated the degradation process and partially was the main precursor of CO3•- and O2•-. Moreover, except for the single electron transfer from low-valence state of vanadium (V) species to SPC, the intramolecular electron transfer process from –OOH ligand of V complex to hydrogen peroxide (H2O2) also participated in the generation of •OH. Additionally, the introduction of OA could provide a complex, transient acidic and reductive condition for facilitating the SMX removal process. On the other hand, the addition of OA restricted the conversion of •OH to CO3•- and O2•-. Zeolite was employed to absorb the V species in the aqueous solution after the reaction and the residual vanadium concentrations were <2 mg/L. The existence of HPO42-, CO32– and humic acid exerted severe inhibition on the decontamination of SMX, and F- and NO3– exerted slight suppression, whereas the existence of Cl- and SO42- did not show conspicuous impairment. This work filled the gap of decontamination performance of SMX in vanadium based heterogenous SPC system and deepened the understanding of the application of reductant.