The study investigated the degradation kinetic and transformation mechanism of ibuprofen (IBP) in UV/H 2 O 2 process from both experimental and theoretical aspects. Impacts of H 2 O 2 dosage, solution pH, quenching agent, and concentration of nitrite (NO 2 − ) on IBP degradation in UV/H 2 O 2 process were evaluated. Both experimental results and theoretical calculations indicated that • OH played an important role in the degradation of IBP and its transformation products . The second-order rate constants of • OH and • NO 2 with IBP were calculated as 3.93 × 10 9 M −1 s −1 and 5.59 × 10 −3 M −1 s −1 , based on the transition state theory, which explained the phenomenon that addition of NO 2 − inhibited IBP degradation. Further, according to the results of ultra-high-resolution mass and density functional theory calculations, mechanisms of a detailed degradation pathway for IBP were clarified. Namely, the detailed mechanistic formation pathways for hydroxylated and keto-based products were proposed. Then, possible active sites of the keto-based products, as well as the corresponding subsequent products were predicted by Condensed Fukui Function. Our study can broaden the knowledge of the reactions of emerging contaminants with • OH, and provide theoretical foundation for the optimization of UV/H 2 O 2 process.
Kai Yin,Lin Deng,Jinming Luo,John Crittenden,Chengbin Liu,Yuanfeng Wei,Longlu Wang
Phenicol antibiotics (PABs) degradation by UV/H 2 O 2 is important because we need to determine the reduction in toxicity and disinfection byproducts for post-chlorine. In this study, the degradation of PABs, including florfenicol (FLO), chloramphenicol (CAP) and thiamphenicol (THA), was examined. The pseudo-first order degradation rate constants of PABs were 3 times higher in ultrapure water (UW) than that in synthetic wastewater (SW) for these conditions: [PABs] 0 = 1 μM, [H 2 O 2 ] = 0.1 mM, and I 0 = 1.985 × 10 −6 E L −1 s −1 . Fulvic acid (FA) and HCO 3 – inhibited PABs degradation, Cl − and NO 3 – concentrations of up to 5 mM and 10 mM had a negligible impact. The impact of water matrix on PABs degradation was successfully predicted using pseudo-steady-state kinetic model. The degradation of PABs was triggered via hydroxylation and/or hydrogen abstraction. The treatment of PABs via UV/H 2 O 2 could decrease their antimicrobial properties, while the byproducts of FLO and THA showed higher acute toxicity in Vibrio fischeri . In addition, two identification products (TP-276 and TP-354) of FLO had higher ecotoxicity toxicity (using ECOSAR) in fish, daphnid and green algae. The trichloromethane formation potential (TCMFP) for PABs with post-chlorination in UW and SW can be reduced after UV/H 2 O 2 compared to UV, and is related to the corresponding decrease of dissolved organic carbon (DOC).
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