Synergistic effect between UV and chlorine (UV/chlorine) on the degradation of carbamazepine: Influence factors and radical species

摘要

For successful wastewater reclamation, advanced oxidation processes have attracted attention for elimination of emerging contaminants. In this study, the synergistic treatment with UV irradiation and chlorine (UV/chlorine) was used to degrade carbamazepine (CBZ). Neither UV irradiation alone nor chlorination alone could efficiently degraded CBZ. UV/chlorine oxidation showed a significant synergistic effect on CBZ degradation through generation of radical species ((OH)-O-center dot and (CI)-C-center dot), and this process could be well depicted by pseudo first order kinetic. The degradation rate constants (k(obs.CBZ)) of CBZ increased linearly with increasing UV irradiance and chlorine dosage. The degradation of CBZ by UV/chlorine in acidic solutions was more efficient than that in basic solutions mainly due to the effect of pH on the dissociation of HOCl and OCl- and then on the quantum yields and radical species quenching of UV/chlorine. When pH was increased from 5.5 to 9.5, the rate constants of degradation of CBZ by (OH)-O-center dot decreased from 0.65 to 0.14 min(-1) and that by Cl-center dot decreased from 0.40 to 0.11 min(-1). The rate constant for the reaction between Cl-center dot and CBZ was 5.6 +/- 1.6 x 10(10) M-1 s(-1). Anions of HCO3- (1-50 mM) showed moderate inhibition of CBZ degradation by UV/chlorine, while Cl- did not. UV/chlorine could efficiently degrade CBZ in wastewater treatment plant effluent, although the degradation was inhibited by about 30% compared with that in ultrapure water with chlorine dosage of 0.14-0.56 mM. Nine main oxidation products of the CBZ degradation by UV/chlorine were identified using the HPLC-QToF MS/MS. Initial oxidation products arose from hydroxylation, carboxylation and hydrogen atom abstraction of CBZ by (OH)-O-center dot and Cl-center dot, and were then further oxidized to generate acylamino cleavage and decarboxylation products of acridine and acridione. (C) 2016 Elsevier Ltd. All rights reserved.