Removal of favipiravir and oseltamivir in domestic wastewater effluents using ozonation and catalytic ozonation

The surge in pharmaceutical use during global pandemics, like SARS-CoV-2, has led to increased antiviral concentrations in wastewater treatment plant influents. The low biodegradability of certain antivirals poses a challenge for wastewater treatment, threatening aquatic and soil ecosystems. This study aimed to optimize ozonation and catalytic ozonation processes for removing two anti-COVID-19 drugs (namely, favipiravir and oseltamivir) and assess their ecotoxicological effects in the context of potential wastewater reuse.

In this study, samples with 50 µg/L of favipiravir and oseltamivir were added to synthetic wastewater with approximately 50 mg COD/L, mirroring a typical domestic effluent. Experiments involved three ozone doses (0.2, 0.6, and 1 mg O₃/mg DOC) at pH levels of 7 and 10. Adding 0.1 g/L of ZnFe layered double hydroxide as a catalyst aimed to improve the ozonation efficiency. Samples with 0.1 mg/L polyethylene microplastics were prepared to explore the efficiency of the applied processes in the presence of microplastics. The target drugs were quantified by LC-MS/MS. E. crypticus was used to understand the ecotoxicological impact of the treatment techniques on the potential reuse of treated wastewater for irrigation.

Regardless of the ozone dose used, ozonation at pH=7 resulted in removal efficiencies of 84% and 64% for favipiravir and oseltamivir, respectively. Increasing the pH value to 10 did not improve favipiravir elimination, yet an additional removal of 21% was recorded for oseltamivir at all three ozone doses. During catalytic ozonation, an approximately 30% decline in the abatement of drugs was observed when compared with ozonation alone, which could be attributed to either adsorption of ozone on the catalyst’s active-sites (blockage of active-sites and reduction in the availability of ozone radicals) or production of refractory by-products (enhancement in the competition between radicals and active-sites). In the presence of microplastics, ozonation experiments at pH=7 provided an average decrease of about 30% in the removal efficiency for both drugs whereas ozonation at pH of 10 resulted in an approximately 15% fall in the elimination level. Catalytic ozonation in the absence of microplastics, however, showed positive effects on the reduction rates of the examined drugs since the applied process yielded an improvement in the abatement of 14 and 7% for favipiravir and oseltamivir, respectively. Both in the presence and absence of microplastics, ozonation and catalytic ozonation of antivirals at pH=7 did not lead to any toxic effects for the reproduction of E. crypticus; instead, an increase in the reproduction performance was found, possibly due to the formation of more biodegradable organic intermediates. The experimental data obtained revealed that ozonation or catalytic ozonation could be viable alternatives for upgrading the existing wastewater treatment plants as they functioned well as a complementary treatment process not only to reduce the release of antivirals from domestic effluents, but also to substantially increase the reuse potential of treated wastewater for irrigation purposes.

This study was financially supported by the Scientific and Technological Research Council of Turkey (TUBITAK, Project #121Y383) and Scientific Research Projects Coordination Unit of Istanbul Technical University (ITU-BAP, Project # MYL-2023-44496).