Advanced treatment of urban wastewater by UV radiation: Effect on antibiotics and antibiotic-resistant E. coli strains

Urban wastewater treatment plant (UWWTP) effluents are among the possible sources of antibiotics and antibiotic-resistant bacteria (ARB) spread into the environment. In this work, the effect of UV radiation on antibiotic-resistant Escherichia coli (E. coli) strains was compared with that of chlorination process. Under the investigated conditions, UV disinfection process resulted in a total inactivation after 60 min of irradiation (1.25 x 10(4) mu W s cm(-2)) compared to 120 min chlorine contact time (initial chlorine dose of 2 mg L-1). Moreover, no change in E. coli strains' resistance to amoxicillin (AMX) (minimum inhibiting concentration (MIC) > 256 mg L-1) and sulfamethoxazole (SMZ) (MIC > 1024 mg L-1) could be observed after UV treatment, while the treatment affected resistance of the lower resistance strain to ciprofloxacin (CPX) (MIC decreased by 33% and 50% after 60 and 120 min, respectively). Contrarily, chlorination process did not affect antibiotic resistance of the investigated E. coli strains. Finally, the effect of UV radiation on the mixture of three antibiotics was also investigated and photodegradation data fit quite well pseudo first order kinetic models with rip values of 14, 20 and 25 min for CPX, AMX and SMZ, respectively. According to these results, conventional disinfection processes may not be effective in the inactivation of ARB, and the simultaneous release of ARB and antibiotics at sub-lethal concentrations into UWWTP effluent may promote the development of resistance among bacteria in receiving water. (C) 2013 Elsevier Ltd. All rights reserved.