Solar light and the photo-Fenton process against antibiotic resistant bacteria in wastewater: A kinetic study with a Streptomycin-resistant strain

In this work, we assess the potential of solar light and the solar-assisted photo-Fenton process to inactivate antibiotic resistant bacteria (ARB) in wastewater (WW). A systematic investigation on ARB inactivation and regrowth kinetics after solar-based processes is intended, as well as the modification of their antibiotic resistance (AR). As such, a Streptomycin-resistant (SR) E. coli as a model ARB was subjected to solar exposure (with or without UVB light) at various irradiance levels, as well as the solar/H2O2 and the photo-Fenton process at neutral pH. We report the good fit of the SR E. coli to known kinetic models (> 96% R-2), and analytically present the necessary treatment timed for total inactivation and halting their post-treatment regrowth capability. For all treatment methods, the AR was found to decrease during treatment, prior to loss of cultivability (5-15% lower time for 4-log inactivation). UVB irradiation was determined as the key factor of loss of cultivability, AR and regrowth. Solar/H2O2 and photo-Fenton presented fast inactivation rates, ensured no regrowth of ARB, and indicated moderate effect on modifying the SR of E. coli, with similar inactivation times for both strains. The presence of Streptomycin in WW was found to act synergistically on the faster inactivation by all processes tested. Finally, similar to 1 h of solar-based AOPs was found to ensure 4-log ARB inactivation and no regrowth, even in absence of the residual H2O2, indicating their suitability as proper WW disinfection processes.