Leveraging insights into advanced oxidation processes for quaternary treatments

This study assesses the efficiency of ozonation, photocatalysis, and electrooxidation to treat the effluent from an urban WWTP spiked with a mixture of 17 cytostatic compounds at 25 μg/L. This concentration allowed us to assess the efficiency of the different treatments, reaching good sensitivity for mass spectrometry detection avoiding sample treatments and study the kinetics when necessary. The presence of cytostatic drugs in urban wastewater poses significant environmental and health concerns due to their toxicity and persistence. Conventional wastewater treatment plants (WWTPs) only remove part of these contaminants, being necessary to add additional processes. Ozonation with 200 mg O₃/L achieved over 90 % removal for ten compounds, while the removal of seven compounds was below 60 %. Photocatalysis with TiO₂ (500 mg/L) degraded four compounds by over 90 %, but the removal of the other 13 compounds was below 75 %. Electroxidation was effective for removing 14 out of the 17 compounds with an average global removal of 75 % and 94 % for eight compounds. Results showed: i) single techniques do not achieve a high removal of all contaminants, ii) all compounds were removed by at least one of the treatments, and iii) there is a fragmentation of knowledge, and most lab studies do not predict the kinetic behavior of treatments of complex wastewater. The integration of multiple technologies (e.g. electrooxidation and ozonation would be needed to enhance the overall removal efficiency of WWTPs and accomplish stricter legislation. Further studies on potential challenges as by-product toxicity and energy consumption are necessary.