LAUSR

Abstract 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.