Ozonation is one of the most promising advanced oxidation processes to be implemented as quaternary treatment for the removal of micropollutants in wastewater treatment plants. However, there are some knowledge gaps that limit its implementation. First, the removal efficiency is not known for all pollutants, and second, knowledge about degradation byproducts is limited, as well as the toxicity of the treated waters. In this work, the removal efficiency of azathioprine and flutamide is studied, as well as the transformation products formed during ozonation. A lab-scale reactor was used for ozonation of the drugs in pure water, with ambient air as the source for ozone generation and liquid chromatography–ion mobility-high-resolution mass spectrometry for time-resolved process monitoring. Notably, azathioprine and flutamide were not completely removed by ozonation, with 49–54% remaining after the treatment. Furthermore, two transformation products of azathioprine and three of flutamide were identified, including previously unreported nitroaromatic transformation products of flutamide. While both parent compounds showed relatively low predicted toxicity, transformation products of flutamide exhibited higher predicted chronic toxicity. These results highlight the importance of considering transformation products during ozonation and suggest possible nitration reactions when ozone is generated from ambient air. Further experiments are needed to confirm this.
García-Martínez et al. (Tue,) studied this question.