Removal of sulfachloropyridazine, resistant bacteria and resistance genes by UV-LED/PDS and UV-LED/PMS processes

The persistent occurrence of antibiotics in aquatic environments, along with the induced antibiotic-resistant bacteria (ARB) and resistance genes (ARGs), constitute a complex environmental issue encompassing both chemical contamination and biological risks. This study investigates the performance and mechanism of UV-LED/PDS and UV-LED/PMS systems for treating sulfachloropyridazine (SCP), a typical sulfonamide antibiotic, as well as ARB and ARGs. Results showed that both systems significantly enhanced SCP degradation, with UV-LED/PDS showing higher degradation efficiency under the tested conditions. The degradation rate increased with oxidant concentration over the range of 0.5–1.5 mM. Alkaline conditions favored SCP degradation in both systems. Quenching and probe experiments demonstrated that SO 4 ∙ - was the dominant reactive species for SCP removal, with HO· playing an auxiliary role, and the contribution of HO· increased slightly with increasing pH. The proposed degradation pathway was elucidated based on eleven intermediates identified by HPLC-MS, and acute toxicity changes were evaluated using ECOSAR. Furthermore, both systems effectively controlled ARB and ARGs, with UV-LED/PMS outperforming UV-LED/PDS, through the dominant contribution of SO 4 ∙ - , alongside a secondary role of HO·. Flow cytometry, SEM, and enzymatic assays confirmed that both systems compromised membrane integrity, induced morphological damage (roughening, shrinkage, collapse), and overwhelmed antioxidant defenses via oxidative stress, ultimately leading to cell damage. Weakly alkaline conditions resulted in slightly better inactivation performance than acidic conditions.