Degradation of clofibric acid in UV/chlorine disinfection process: kinetics, reactive species contribution and pathways

As a potential endocrine disruptor, clofibric acid (CA) was investigated in this study for its degradation kinetics and pathways in UV/chlorine process. The results showed that CA in both UV photolysis and UV/chlorine processes could be degraded via pseudo-first-order kinetics, while it almost could not be degraded in the dark chlorination process. The observed rate constant (kobs) in UV photolysis was 0.0078 min(-1), and increased to 0.0107 min(-1) combining with 0.1mM chlorine. The kobs increased to 0.0447 min(-1) with further increasing the chlorine dosage from 0.1 to 1.0mM, and reached a plateau at higher dosage (greater than 1.0 mM). The higher kobs was obtained at acid solution rather than basic solution. Moreover, the calculated contributions of radical species to kobs indicated that the HO center dot contributed significantly to CA degradation in acidic conditions, while the reactive chlorine species and UV direct photolysis dominated in neutral and basic solution. The degradation of CA was slightly inhibited in the presence of HCO3-(1 similar to 50 mM), barely affected by the presence of Cl-(1 similar to 200mM) and greatly suppressed by humic acid (0 similar to 5mg l(-1)). Thirteen main degradation intermediates and three degradation pathways of CA were identified during UV/chlorine process.