Enhanced degradation mechanism of sulfamethazine by vacuum ultraviolet/persulfate

Abstract Vacuum ultraviolet/ persulfate (VUV/PS) has been a prospective method for antibiotics removal, however, the enhanced degradation mechanism is still unclear. This study compared the sulfamethazine (SMT) degradation by VUV/PS and ultraviolet/persulfate (UV/PS) processes using a photoreaction system. Results showed that the SMT degradation rate and PS activation rate by VUV/PS was 1.36 times and 1.39 times those of the conventional UV/PS process under the same dosage of PS, respectively. VUV/PS also achieved a high SMT mineralization. SO4•− and HO• played important roles in the degradation of SMT by both processes, while the role of •O2− was little. SMT concentration changed the distributions of 185 nm and 254 nm photons absorbed by solution components and altered the initiated photolysis reaction. Both processes had faster degradation rates at low initial SMT concentrations and the optimum reaction condition was at solution pH of 5. The inhibited level of the SMT degradation in both processes by four anions was in the following order: NO3−> Cl−> HCO3−>SO42 . VUV/PS process was also more efficient than UV/PS for degrading environmental (200 μg/L) and high (5 mg/L) concentration of SMT from three kinds of typical water matrices (tap, river and lake water). Finally, ten photoproducts of SMT degradation by VUV (or UV) were identified, which were mainly the oxidized products of C-N, -NH2 and S-C on SMT molecules, and four degradation pathways were proposed. Overall, these findings could provide useful insights into the application of VUV/PS in efficient antibiotics removal from water.