Enhanced degradation of sulfamethoxazole by microwave-activated peracetic acid under alkaline condition: Influencing factors and mechanism

[Display omitted] •Microwave enhances SMX degradation by PAA under alkaline condition.•Alkaline conditions are more favorable for SMX degradation in the MW/PAA system.•1O2, R–C• and •OH formed in the MW/PAA system and 1O2 is dominated under alkaline.•SMX degradation pathways were speculated based on byproducts identified by LC–MS. In this study, microwave (MW)-activated peracetic acid (PAA) system was used for the removal of sulfamethoxazole (SMX, a typical aquatic sulfonamide antibiotic). The rate constant of SMX degradation in the MW/PAA system was about 1.39 times of conventional heating activated PAA system. In MW/PAA system, alkaline condition was more favorable to the SMX degradation than neutral and acidic conditions. Different influencing factors, including the MW output power, reaction temperature, initial PAA concentration and common coexisting substances (Cl–, HCO3– and humic acid), on SMX degradation in MW/PAA system were systematically studied. The results showed that increasing the MW power, the reaction temperature or the concentration of PAA can promote the degradation of SMX. In addition, Cl– slightly promoted SMX degradation, while HCO3– and humic acid significantly inhibited the SMX degradation. The results of quenching and electron paramagnetic resonance experiments indicated that the reaction is dominated by a non-radical process, i.e., singlet oxygen (1O2), followed by radical processes of carbon-centric radicals (R–C•). Based on the results of liquid chromatography-tandem mass spectrometry and theoretical calculations, four pathways of SMX degradation, including benzene ring hydroxylation, amino-oxidation, self-coupling and S-N bond breakage, were proposed. Toxicity of SMX and its intermediate products was predicted by the ECOSAR program, which indicated that SMX was converted to less toxic substances. This work provides theoretical implications for further development of the PAA-based advanced oxidation process for organic contaminants removal in water/wastewater.