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

• Multidrug resistant (MDR) E. coli has been effectively inactivated by solar AOPs.
• H2O2/sunlight resulted in a lower but comparable efficiency than H2O2/TiO2/sunlight.
• H2O2/sunlight is a more attractive solution for small communities.
• H2O2/sunlight is more effective than chlorination in controlling bacterial regrowth.
• Opposite to chlorination, MDR E. coli percentage decreased after H2O2/sunlight.

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 indigenous antibiotic-resistant bacteria (ARB) in real urban wastewater. A multidrug resistant (MDR) Escherichia coli strain isolated from the effluent of the biological process of an urban wastewater treatment plant was the target ARB. The higher inactivation rates (residual density under detection limit, 2 CFU mL−1) were achieved 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 processes did 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 of indigenous 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 percentage of MDR E. coli in H2O2/sunlight treated samples decreased as incubation time increased; the opposite was observed for chlorinated samples.

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