Pilot-scale regeneration of wastewater through intensified sulfate radical-based advanced oxidation processes (PMS/UV-A, PMS/H2O2/UV-A, and PMS/O3): Inactivation of bacteria and mechanistic considerations

This research addresses the application of advanced oxidation processes (AOPs) for wastewater reclamation at pilot scale, one of the main limitations usually observed in this type of technology. Although interest in sulfate radical-based AOPs (SR-AOPs) has increased considerably in recent years, pilot-scale application studies are very scarce. The generation of free radicals by activation of peroxymonosulfate (PMS) can be enhanced by the introduction of UV-A radiation, or other oxidants such as hydrogen peroxide (H2O2) or ozone (O3), increasing the efficiency of the processes with lower reagent consumption. The combination of 0.5 mM PMS and 0.25 g·h−1 O3 was the fastest process in inactivation of Enterococcus faecalis, achieving inactivation in less than 45 min. Significant synergies were also observed for the combination of PMS, H2O2 and UV-A radiation, achieving total inactivation in less than 120 min, a performance significantly lower than that of the PMS/O3 system. Mechanistic studies showed that the sulfate radical (SO4•-) was responsible for bacterial inactivation in the PMS/O3 system, while in the PMS/H2O2/UV-A system the predominant species varies according to the molar ratio of the oxidants. Thus, the hydroxyl radical (•OH) is predominant in a 1:1 ratio, and SO4•- is predominant in a 1:3 ratio. This phenomenon occurs because an excess of PMS acts as a sink for radicals, preventing their interaction with bacteria. The treatments studied have been shown to be effective in the simultaneous elimination of several pathogenic microorganisms such as Enterococcus faecalis, Escherichia coli, and Staphylococcus aureus, making this technology an alternative to conventional disinfection treatments.