Sunlight advanced oxidation processes vs ozonation for wastewater disinfection and safe reclamation

Solar processes (sunlight/H₂O_2, solar photo-Fenton with EDDS at neutral pH) were compared to a consolidated technology (ozonation) in the inactivation of target bacteria (E. coli, Salmonella spp. and Enterococcus spp.) under realistic conditions (real secondary treated urban wastewater (WW), pilot scale reactors, natural sunlight) to evaluate their possible industrial application. The highest bacteria inactivation rate (all the target pathogens were inactivated below the detection limit (DL) (100 CFU/100 mL) within 45 min treatment) was observed for ozonation (83 mgO₃/L h). Similar inactivation behavior for all bacteria was observed for sunlight/H₂O₂ (50 mg/L) and solar photo-Fenton (SPF) with EDDS (1:1 molar ratio, 0.1 mM of Fe and 50 mg/L of H₂O₂). Although the DL was not reached, faster inactivation kinetics (0.007, 0.013 and 0.002 1/min for E. coli, Salmonella spp. and Enterococcus spp., respectively) and lower bacterial concentration after a 180 min treatment were observed for sunlight/H₂O₂ process compared to SPF (0.005, 0.01 1/min and no inactivation, respectively), Enterococcus spp. being the higher resistance microorganism. The negative effect of carbonates on disinfection performance was also evaluated. Quantitative microbial risk assessment for the ingestion of lettuce irrigated with untreated and treated WW was estimated. Disinfection by ozonation and sunlight/H₂O₂ processes were found to drastically decrease the associated microbiological risk (the mean risk of illness decreased from 0.10 (untreated) to 1.35 × 10^-4 (treated) for E. coli and from 0.03 to 2.21 × 10^-6 for Salmonella).