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 (k_obs) in UV photolysis was 0.0078 min^-1, and increased to 0.0107 min^-1 combining with 0.1 mM chlorine. The k_obs increased to 0.0447 min^-1 with further increasing the chlorine dosage from 0.1 to 1.0 mM, and reached a plateau at higher dosage (greater than 1.0 mM). The higher k_obs was obtained at acid solution rather than basic solution. Moreover, the calculated contributions of radical species to k_obs indicated that the HO• 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 [Formula: see text] (1 ∼ 50 mM), barely affected by the presence of Cl^- (1 ∼ 200 mM) and greatly suppressed by humic acid (0 ∼ 5 mg l^-1). Thirteen main degradation intermediates and three degradation pathways of CA were identified during UV/chlorine process.