Degradation of sulfamethazine by vacuum ultraviolet-activated sulfate radical-advanced oxidation: efficacy, mechanism and influences of water constituents

In-situ collection, purification and reuse of indoor greywater of public buildings or household is an effective way to save water resources. Refractory organic micropollutants in greywater, such as antibiotic sulfamethazine (SMT), can be potentially removed by sulfate radical-advanced oxidation process (SR-AOP) in the presence of peroxymonosulfate (PMS) or peroxydisulfate. Herein, vacuum ultraviolet (VUV) with irradiation at 185 nm and 254 nm activating PMS was systematically investigated in terms of degradation efficacy and influences of water constituents, and the contribution of photolysis and radical oxidative species was determined. We show that SMT removal efficiency and PMS photolysis efficiency of VUV/PMS were 2.2-fold and 1.45-fold compared to UV/PMS, respectively, and VUV/PMS reached a higher mineralization. The main active radicals of VUV/PMS were HO•, SO4•−, and •O2−. Compared to UV/PMS, VUV/PMS resulted in a higher proportion of oxidative degradation and a lower proportion of photolysis. Higher SMT concentrations competed for absorption of VUV or UV-generated photons with H2O and PMS molecules, resulting in a less efficient reaction. VUV/PMS was more efficient at lower initial SMT concentrations and had an optimal pH of 5. The presence of SO42− slightly accelerated degradation performance while HCO3− and NO3− inhibited both processes; the inhibitory effect of HCO3− and NO3− on VUV/PMS are more significant than on UV/PMS. In contrast, the presence of Cl− had no significant effect on each process. In total, 13 intermediates of SMT were identified and four degradation pathways were proposed. VUV/PMS had an advantage over UV/PMS in removing the produced harmful and toxic intermediates. Furthermore, VUV/PMS could remove SMT from real water matrix more effectively than UV/PMS. Generally, the results demonstrate the potential of VUV to displace UV for more effective in-situ treatment of indoor greywater.