Kinetics and mechanism of reactive radical mediated fluconazole degradation by the UV/chlorine process: Experimental and theoretical studies

The emerging organic contaminants can be effectively removed in the UV/chlorine process by produced hydroxyl radical (HO) and chlorine-derived radicals (Cl, ClO, etc.). However, the degradation mechanism and pathways of reactive radical reaction with contaminants are still unclear. Here we investigated the reactive radical mediated reaction kinetics and mechanism of fluconazole in UV/chlorine process using theoretical calculations and experimental studies. The results showed that fluconazole could be degraded effectively by UV/chlorine treatment than by UV photolysis and chlorination alone. The Cl and HO were found to play a major role in degradation of fluconazole by hydrogen atom transfer and radical adduct formation mechanisms, respectively. The single-electron transfer pathway of Cl, HO and ClO seems to be impossible due to the high free energy barriers of 21.87 kcal mol−1, 35.12 kcal mol−1 and 46.05 kcal mol−1, respectively. Six transformation products were identified by high resolution mass spectrometry and they were formed via fluconazole de-fluorination, hydroxylation, cleavage and cyclization with the triazole ring. The water quality parameters such as pH and coexisting components (DOM, HCO3−/CO32−) could influence the removal of fluconazole in UV/chlorine process by impacting the generation of reactive radicals. The toxicity of fluconazole to aquatic organisms can be decreased by UV/chlorine process, and only trace amounts of chloroform were detected.