Degradation mechanisms of antibiotics in UV222/H2O2 and UV222/persulfate systems: Dual roles of inorganic anions

Advanced oxidation processes based on KrCl* excimer lamps (UV222-AOPs) have recently received widespread attention in water treatment due to their high radical yields. In this investigation, the degradation of two typical antibiotics, florfenicol (FLO) and ciprofloxacin (CIP), by UV222 and its combination with hydrogen peroxide (H2O2) or persulfate (PDS) were studied, respectively. The dual effects of inorganic anions on the degradation performance of UV222/UV222-AOPs were determined. It was found that NO3– significantly enhanced the photolysis of CIP, and the degradation rate constants increased from 1.03 × 10-4 mJ−1 cm2 (without NO3–) to 2.56 × 10-4 mJ−1 cm2 (with 1 mM NO3–). However, NO3– markedly inhibited the photolysis of FLO, leading to a decrease in the degradation rate constants from 1.18 × 10-3 mJ−1 cm2 (without NO3–) to 5.27 × 10-4 mJ−1 cm2 (with 1 mM NO3–). HCO3– was found to have a certain promoting effect on the photolysis of FLO and CIP, and SO42- has a negligible effect on the photolysis of both antibiotics. The above three inorganic ions decelerated the degradation of CIP and FLO in UV222-AOP, where NO3– exerted the most inhibition. Through LC-MS analysis and ECOSAR model, the main transformation products were individually determined and evaluated for toxicity. In addition, the performance of UV222-AOPs and UV254-AOPs in reclaimed wastewater (RWW) treatment were compared, and the steady-state concentration of radicals was measured. This study provided novel insight into the application of UV222-AOPs in RWW treatment.