Degradation performance and conversion mechanisms of MNZ by advanced oxidation systems with O3: Comparison of O3, O3/UV, O3/H2O2 and UV-H2O2/O3 systems
Yuehua Ren, Yonglei Wang, Jie Xue, Baozhen Liu, Baozhen Liu, Guilin He, Weijian Jia, Baosen Liu, Baosen Liu, Ruibao Jia
Abstract
This study evaluated the degradation performance of ozone (O 3 ), ozone/ultraviolet (O 3 /UV), ozone/hydrogen peroxide (O 3 /H 2 O 2 ), and ultraviolet/hydrogen peroxide/ozone (UV-H 2 O 2 /O 3 ) systems of removing antibiotic metronidazole (MNZ) in aqueous environments. The UV-H 2 O 2 /O 3 system achieved complete degradation of 100 μg·L −1 MNZ within 2 min. Ozone utilization in the UV-H 2 O 2 /O 3 system was enhanced by 30.05 % compared with O 3 alone. Hydroxyl radicals (·OH) and superoxide radicals (·O 2 − ) played crucial roles in process, with ·OH exposure and yields being 4.7 and 28.5 times greater, respectively, than those in the O 3 system. The initial stage rate constant of O 3 conversion increased tenfold in the presence of ·O 2 − . LC–MS analysis and density functional theory (DFT) calculations identified fifteen major intermediates and proposed three primary transformation pathways: alcohol oxidation, hydroxyethyl dissociation, methyl elimination, nitro-group cleavage, and imidazole ring-opening reactions. Cytotoxicity assessments indicated the UV-H 2 O 2 /O 3 system exhibited low biotoxicity during the degradation process. Pilot-scale experiments verified the effectiveness of the UV-H 2 O 2 /O 3 process in removing 500 ng·L −1 MNZ in real water bodies, achieving a 93.8 % removal rate for MNZ, with corresponding removal rates of 66.53 % for UV 254 and 39.52 % for total organic carbon (TOC). This study provides significant insights for removing antibiotics in practical water treatment applications, underscoring their potential engineering implications.