Inactivation of natural enteric bacteria in real municipal wastewater by solar photo-Fenton at neutral pH

• Disinfection by solar photo-Fenton at neutral pH as tertiary treatment was studied.
• Photo-Fenton reduces 50% the inactivation time respect to UVA-H2O2.
• Total inactivation by photo-Fenton was achieved in 60 min (H2O2/Fe2+: 50/20 mg L−1).
• Wastewater treated by photo-Fenton was adequate for irrigation reuse.
• In spite to the seasonal variability 99% of disinfection was achieved in 40 min.

This study analyses the use of the solar photo-Fenton treatment in compound parabolic collector photo-reactors at neutral pH for the inactivation of wild enteric Escherichia coli and total coliform present in secondary effluents of a municipal wastewater treatment plant (SEWWTP). Control experiments were carried out to find out the individual effects of mechanical stress, pH, reactants concentration, and UVA radiation as well as the combined effects of UVA-Fe and UVA-H2O2. The synergistic germicidal effect of solar-UVA with 50 mg L−1 of H2O2 led to complete disinfection (up to the detection limit) of total coliforms within 120 min. The disinfection process was accelerated by photo-Fenton, achieving total inactivation in 60 min reducing natural bicarbonate concentration found in the SEWWTP from 250 to 100 mg L−1 did not give rise to a significant enhancement in bacterial inactivation. Additionally, the effect of hydrogen peroxide and iron dosage was evaluated. The best conditions were 50 mg L−1 of H2O2 and 20 mg L−1 of Fe2+. Due to the variability of the SEWWTP during autumn and winter seasons, the inactivation kinetic constant varied between 0.07 ± 0.04 and 0.17 ± 0.04 min−1. Moreover, the water treated by solar photo-Fenton fulfilled the microbiological quality requirement for wastewater reuse in irrigation as per the WHO guidelines and in particular for Spanish legislation.

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