Effect of solar simulated N-doped TiO2 photocatalysis on the inactivation and antibiotic resistance of an E. coli strain in biologically treated urban wastewater

Abstract

The effect of N-doped TiO2 (NDT) photocatalysis on the inactivation of an antibiotic resistant Escherichia coli strain selected from a biologically treated urban wastewater effluent was investigated. NDT was prepared by sol–gel method and characterized by thermogravimetric analysis, X-ray diffraction, FTIR and Laser Raman spectra and UV–visible reflectance spectra. XRD analysis revealed that anatase is the only crystalline phase in NDT photocatalyst and UV–visible reflectance spectra showed that the absorption onset shifted toward visible region (about 500nm). The NDT photocatalyst was compared with commercially available TiO2 powders (namely Millennium PC50 and PC100), under solar simulated radiation (250W lamp) and different photocatalysts loadings (0.025–0.5gL−1). The higher inactivation rate (8.5×105CFU 100mL−1min−1, after 10min of irradiation) of antibiotic resistant E. coli strain was observed for NDT photocatalyst at 0.2gL−1 dose. Kinetic test at the optimum photocatalyst loading showed that total inactivation can be achieved after 60min of irradiation. Antibiotic resistant test (Kirby–Bauer) on survived colonies showed that solar photocatalytic process with NDT did not significantly affect resistance of E. coli strain to tetracycline and vancomycin as irradiation time increased, but a decreasing trend (p<α=0.05) in resistance to ciprofloxacin (p=0.0311) and sensitivity to cefuroxime (p=0.0018) was observed.