Decomposition and mineralization of cefaclor by ionizing radiation: Kinetics and effects of the radical scavengers

There has been recent growing interest in the presence of antibiotics in different environmental sectors. One considerable concern is the potential development of antibiotic-resistant bacteria in the environment, even at low concentrations. Cefaclor, one of the beta-lactam antibiotics, is widely used as an antibiotic. Kinetic studies were conducted to evaluate the decomposition and mineralization of cefaclor using gamma radiation. Cefaclor, 30 mg/l, was completely degraded with 1000 Gy of gamma radiation. At a concentration of 30 mg/l, the removal efficiency, represented by the G-value, decreased with increasing accumulated radiation dose. Batch kinetic experiments with initial aqueous concentrations of 8.9, 13.3, 20.0 and 30.0 mg/l showed the decomposition of cefaclor using gamma radiation followed a pseudo first-order reaction, and the dose constant increased with lower initial concentrations. At a given radiation dose, the G-values increased with higher initial cefaclor concentrations. The experimental results using methanol and thiourea as radical scavengers indicated that (OH)-O-center dot radicals were more closely associated with the radiolytic decomposition of cefaclor than other radicals, such as e(aq)(-) or H-center dot. The radical scavenger effects were tested under O-2 and N2O saturations for the enhancement of the TOC percentage removal efficiencies in the radiolytic decomposition of cefaclor. Under O-2 saturation, 90% TOC removal was observed with 100 000 Gy. Oxygen is well known to play a considerable role in the degradation of organic substances with effective chain reaction pathways. According to the effective radical reactions, the enhanced TOC percentage removal efficiencies might be based on the fast conversion reactions of e(aq)(-) and H-center dot with O-2 into oxidizing radicals, such as O-2(center dot-) and HO2 center dot, respectively. 100% TOC removal was obtained with N2O gas at 20 000 Gy, as reducing radicals, such as e(aq)(-) and H-center dot, are scavenged by N2O and converted into (OH)-O-center dot radicals, which have strong oxidative properties. The results of this study showed that gamma irradiation was very effective for the removal of cefaclor in aqueous solution. The use of O-2 or N2O, with radiation, shows promise as effective radical scavengers for enhancing the TOC or COD removal efficiencies in pharmaceutical wastewaters containing antibiotics. However, the biological toxicity and interactions between various chemicals during the radiolytic treatment, as well as treatments under conditions more representative of real wastewater will require further studies. (C) 2008 Elsevier Ltd. All rights reserved.