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

This work aims to assess the effectiveness of a mild solar photo-Fenton system (low reagent concentrationsand near neutral pH) for the removal of fecal bacteria in urban wastewater effluents. Escherichiacoli and Enterococcus faecalis were simultaneously evaluated in real and simulated effluents at initialconcentrations of 103 and 106 CFU/mL. Several concentrations of ferrous sulfate (2.5–10 mg-Fe2+/L) andhydrogen peroxide (5–50 mg/L) were tested in solar CPC reactors (total volume: 20 L) under natural sunlight.Photo-Fenton results were compared with the bactericidal effects of solar exposure and H2O2 underthe same experimental conditions. Solar photo-Fenton processes at pH 5 and pH 3 were compared. Theresults showed complete bacterial inactivation in almost all conditions, but the solar UVA energy doserequired to achieve similar results at pH 5 (24–30 kJ/L) was higher than at pH 3 (2–20 kJ/L). This work alsoshows experimentally that the presence of precipitated iron at near-neutral pH has no benefits for disinfectionefficacy; 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 verypromising 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 wasobserved in simulated wastewater when the solar photo-Fenton process at pH 5 was used. This resulthas important implications for the treatment of reclaimed wastewater.