Visible light plays a significant role during bacterial inactivation by the photo-fenton process, even at sub-critical light intensities

Abstract

The aim of this research is to clarify the contribution of sunlight wavelengths, irradiance and Fe²⁺/H₂O₂ during bacterial disinfection by the photo-Fenton process in clear surface waters. We considered different solar spectrum distributions (visible, UVA-Visible), sub-critical irradiances (0-400 W/m²), focusing on the action modes of E. coli inactivation by the constituents involved in the composite process, at low μM reactants concentration (Fe²⁺/H₂O₂) in in ultrapure (MQ) water. We report that solar disinfection improved with Fenton reagents (photo-Fenton process) is a reality from very low light irradiance values (200 W/m²), and made possible even without the presence of UVA radiation, even when using low quantities of the Fenton reagents (0.5 mg/L Fe²⁺, 5 mg/L H₂O₂). Under light exposure, H₂O₂ was found to augment the intracellular Fenton process and Fe²⁺ to initiate further, distinct oxidative actions. Finally, validation was performed in Lake Geneva water over a wider irradiance range, where the photo-Fenton process was found to be reagent-dependent in low irradiance, shifting to light-driven in the higher values.

Keywords: E. coli; Kinetics; Light intensity; Photo-fenton; Solar disinfection; Water treatment.