Degradation and ecotoxicity of favipiravir and oseltamivir in the presence of microplastics during ozonation and catalytic ozonation of synthetic municipal wastewater effluents

Background: Favipiravir (FAV) and oseltamivir (OSE) are antiviral agents developed against influenza and they were repurposed against SARS-CoV-2 during the COVID-19 pandemic. This study evaluated the potential of ozonation and catalytic ozonation as tertiary treatment approaches for removing FAV and OSE from municipal wastewaters, both in the presence and absence of microplastics (MPs), while comparing the ecotoxicity of untreated and treated secondary effluents to predict the ecotoxicological effects of these technologies during municipal wastewater treatment. Results: At an initial antiviral concentration of 50 μg L⁻¹, ozonation at pH 7 with a specific ozone dose of 0.6 mg O₃ (mg DOC)⁻¹ yielded FAV and OSE removals of 84 and 64%, respectively, while the presence of catalyst or MPs decreased the degradation rate by 30–40%. Raising the pH to 10 had minimal impact on FAV abatement, but improved OSE reduction by 21%. Acute toxicity tests using Vibrio fischeri demonstrated that simultaneous ozonation of the analytes led to the accumulation of transformation products (TPs) of FAV and OSE, with their combined effect almost equal to that of the original compounds. Reproduction toxicity tests indicated that TPs of antiviral drugs generated during ozonation were less toxic to Enchytraeus crypticus than the parent chemicals. Conclusion: Ozonation proved to be a viable option for upgrading existing wastewater treatment facilities, serving as a complementary treatment to minimize the release of antivirals from municipal secondary effluents and reduce their inhibitory effect on earthworm reproduction, thereby enhancing the reuse potential of treated wastewater for irrigation.