Solar photo-Fenton for water disinfection: An investigation of the competitive role of model organic matter for oxidative species

Abstract

The competitive effect for the oxidative species produced during solar photo-Fenton process at neutral pH between an organic compound (resorcinol) and a model microorganism (Enterococcus faecalis) was investigated. With this purpose, the inactivation of E. faecalis was evaluated under several solar processes, i.e. SODIS, solar-UVA with H2O2 (10, 20 and 50mgL−1) and solar-UVA-Fe2+ (2.5, 5 and 20mgL−1) in the absence and presence of resorcinol (10mgL−1). The effect of resorcinol on the Fenton reaction (H2O2/Fe2+ in the dark: 5/2.5 and 50/20mgL−1) efficacy at neutral pH was also evaluated. In spite of resorcinol maintained a high amount of iron (around 10mgL−1) in solution during the experiments, with the highest concentrations of H2O2/Fe2+ (50/20mgL−1), only a 2-log decrease of bacteria was observed with 10mgL−1 of resorcinol, while a 3.5-log abatement was detected without resorcinol. These results highlight the competitive role of organic matter for the oxidant species against bacteria when photo-oxidation and photo-disinfection processes are occurring at the same time. This competition for the oxidant species, mainly hydroxyl radicals generated during photo-Fenton, was confirmed by (i) the solar photo-Fenton assays at three different concentrations (H2O2/Fe2+): 5/2.5, 10/5 and 20/10mgL−1, although at elevated concentrations of H2O2 and Fe2+ (50/20mgL−1) the disinfection efficiency was independent of the addition of resorcinol because an excess of radicals were generated, and (ii) by the photo-Fenton results obtained when the concentration of resorcinol was increased from 20, 30 till 40mgL−1.