Degradation of sulfamethoxazole by medium pressure UV and oxidants: Peroxymonosulfate, persulfate, and hydrogen peroxide

- Degradation of SMX was investigated in MPUV alone, MPUV/PMS, MPUV/PS and MPUV/H2O2 AOPs.
- All the SMX degradation followed the pseudo-first-order kinetics model.
- MPUV/PMS was found to be the most efficient in degrading SMX.
- The best SMX degradation can be achieved at different pH in the three oxidation system.
- Coexisting anions produced different effects on the three oxidation systems.

Ultraviolet (UV)-assisted peroxymonosulfate (PMS), persulfate (PS), and hydrogen peroxide (H2O2) advanced oxidation processes (AOPs) were investigated by comparing the degradation efficiency for sulfamethoxazole (SMX) on a bench scale. A medium pressure (MP) mercury UV lamp housed in a collimated beam apparatus was used. The effect of operational parameters (initial SMX concentrations, oxidant dosage, solution pH, and common coexisting inorganic anions) on UV/PMS, UV/PS, and UV/H2O2 treatment efficiency on SMX degradation was also examined. It was observed that the direct MPUV photolysis could efficiently remove SMX with the calculated quantum yield 0.176 of SMX photodegradation, moreover, the combination of oxidants especially PMS with UV radiation obviously accelerated the degradation process. The rate of SMX degradation during the three UV-based systems was observed in the following order: UV/PMS > UV/PS > UV/H2O2. The SMX degradation efficiency decreased with the initially elevated SMX concentrations and increased proportionally to the oxidant dosage. The maximum SMX degradation occurred at pH 11, 5, 3 in UV/PMS, UV/H2O2 and UV/PS system, respectively. It was found that only PMS could be activated by some inorganic anions as compared to PS and H2O2. Adding Cl− and CO32− into UV/PMS process can differentially raise the degradation rate. SO42− showed no significant effect on UV/PMS and UV/H2O2 system, while the degradation efficiency was improved at a low SO42− concentration in the UV/H2O2 system. The presence of NO3− could improve the SMX degradation in the three UV-based AOPs.