Disinfection of real and simulated urban wastewater effluents using a mild solar photo-Fenton

Abstract

This work aims to assess the effectiveness of a mild solar photo-Fenton system (low reagent concentrations and near neutral pH) for the removal of fecal bacteria in urban wastewater effluents. Escherichia coli and Enterococcus faecalis were simultaneously evaluated in real and simulated effluents at initial concentrations of 103 and 106CFU/mL. Several concentrations of ferrous sulfate (2.5–10mg-Fe2+/L) and hydrogen peroxide (5–50mg/L) were tested in solar CPC reactors (total volume: 20L) under natural sunlight. Photo-Fenton results were compared with the bactericidal effects of solar exposure and H2O2 under the same experimental conditions. Solar photo-Fenton processes at pH 5 and pH 3 were compared. The results showed complete bacterial inactivation in almost all conditions, but the solar UVA energy dose required to achieve similar results at pH 5 (24–30kJ/L) was higher than at pH 3 (2–20kJ/L). This work also shows experimentally that the presence of precipitated iron at near-neutral pH has no benefits for disinfection efficacy; it actually causes a slight decrease in effectiveness under these experimental conditions. E. faecalis clearly showed higher resistance than E. coli to all treatments (photo-Fenton and H2O2/solar) using both naturally occurring and seeded bacteria. The disinfection tests in real effluents showed very promising results despite the complexity and variability of the organic and inorganic matter in the effluents. A 3-log decrease in E. coli and E. faecalis was attained in real effluents, and a 6-log abatement was observed in simulated wastewater when the solar photo-Fenton process at pH 5 was used. This result has important implications for the treatment of reclaimed wastewater.