Inactivation and regrowth of multidrug resistant bacteria in urban wastewater after disinfection by solar-driven and chlorination processes

Solar disinfection and solar-driven advanced oxidation processes (AOPs) (namely H2O2/sunlight,TiO2/sunlight, H2O2/TiO2/sunlight, solar photo-Fenton) were evaluated in the inactivation of indigenousantibiotic-resistant bacteria (ARB) in real urban wastewater. A multidrug resistant (MDR) Escherichia colistrain isolated from the effluent of the biological process of an urban wastewater treatment plant was thetarget ARB. The higher inactivation rates (residual density under detection limit, 2 CFU mL�1) wereachieved with H2O2/TiO2/sunlight (cumulative energy per unit of volume (QUV) in the range 3–5 kJ L�1,depending on H2O2/TiO2 ratio) and H2O2/sunlight (QUV of 8 kJ L�1) processes. All investigated processesdid not affect antibiotic resistance of survived colonies. Moreover, H2O2/sunlight was compared with conventional chlorination process to evaluate bacterial regrowth potential and particularly the proportion ofindigenous MDR E. coli with respect to total indigenous E. coli population. Chlorination (1.0 mg Cl2 L�1)was more effective than H2O2/sunlight (50 mg H2O2 L�1) to achieve total inactivation of MDR E. coli(15 min Vs 90 min) but less effective in controlling their regrowth (24 h Vs 48 h). Interestingly, the percentageof MDR E. coli in H2O2/sunlight treated samples decreased as incubation time increased; theopposite was observed for chlorinated samples.