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

• N-doped TiO2 (NDT) photocatalyst was prepared by sol–gel method.
• Doping process shifted TiO2 band-gap energy from 3.3–3.4 eV to 2.5 eV.
• The lowest band-gap energy was obtained for a calcination time of 30 min at 450 °C.
• Solar NDT photocatalysis did not significantly affect resistance of survived E. coli to TET and VAN.
• A total photocatalytic inactivation of antibiotic resistant E. coli strain was achieved in 60 min.

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 500 nm). The NDT photocatalyst was compared with commercially available TiO2 powders (namely Millennium PC50 and PC100), under solar simulated radiation (250 W lamp) and different photocatalysts loadings (0.025–0.5 g L−1). The higher inactivation rate (8.5 × 105 CFU 100 mL−1 min−1, after 10 min of irradiation) of antibiotic resistant E. coli strain was observed for NDT photocatalyst at 0.2 g L−1 dose. Kinetic test at the optimum photocatalyst loading showed that total inactivation can be achieved after 60 min 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.

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