Mechanistic modeling of UV and mild-heat synergistic effect on solar water disinfection

Abstract

A mechanistic model of inactivation of Escherichia coli by the action of solar UV radiation and simultaneous solar mild-heat occurring during solar water disinfection (SODIS) is proposed. Bacterial killing during solar exposure of transparent bottles full of contaminated water for at least 6h in full sunshine is attributed to the combined effect of, i) the UV photons absorbed by bacteria and producing intracellular reactive oxygen species (ROS) that induce oxidative damages, and ii) a mild increase of water temperature (commonly between 25°C and 50°C) that accelerates the bacterial inactivation process. This work proposes a model based on a simplified approach of the kinetic reactions that explain the synergy between UV radiation and temperature to successfully reproduce SODIS experimental results. The main factors considered in this model are (i) the photo-induced formation of intracellular ROS from oxygen and photo-sensitizers that takes into account the internal thermal and photo-Fenton reactions; (ii) the thermal and photo-inactivation of catalase and superoxide dismutase and (iii) the internal damages due to the action of these oxidative and thermal effects. The new model has been demonstrated to reproduce the time-profile of E. coli concentration in clear water at different temperatures (10–55°C) and under different solar irradiances (30–50Wm−2 UV). The excellent fitting between model and experimental results suggests that the mechanistic model considering the synergistic effect between UV radiation and temperature is a realistic approach for the simulation of solar water disinfection process.