Ozonation and UV-C photolysis for the removal of antipsychotics in real hospital wastewater: kinetics, removal efficiency, and insights into transformation products

Hospital wastewater is a significant source of pharmaceutical contaminants, including antipsychotic drugs, which are often inefficiently removed by conventional treatment systems. In this study, the degradation of four antipsychotics was investigated using ozonation and UV-C photolysis under different pH conditions. Kinetic analyses indicated pseudo-first-order behavior, with ozonation achieving faster and more efficient removal compared to photolysis. To complement the evaluation of removal performance, the formation of transformation products (TPs) was assessed. For haloperidol, TPs generated during ozonation were experimentally investigated, while for the other compounds, previously reported TPs from the literature were considered to provide a broader perspective. These compounds were further evaluated using in silico QSAR models to estimate biodegradability and ecotoxicity toward aquatic organisms. The results indicate that although several TPs exhibit increased biodegradability relative to their parent compounds, this trend is not universal and does not consistently translate into reduced ecotoxicity. In the case of haloperidol ozonation, intermediate TPs exhibited a marked increase in predicted toxicity, suggesting that partial oxidation may enhance biological reactivity before subsequent degradation yields less harmful species. Overall, this study highlights that while ozonation is highly effective at removing antipsychotics, assessing TPs is essential for a more comprehensive evaluation of environmental implications.