Micropollutants removal, residual risk, and costs for quaternary treatments in the framework of the Urban Wastewater Treatment Directive

The revised Urban Wastewater Treatment Directive (UWWTD) imposes stringent regulations for the removal of micropollutants from urban wastewater treatment plants. The analyses conducted in this study are based on current knowledge extrapolated from literature WWTPs, to investigate the occurrence, removal and environmental risk related to the 12 target micropollutants: Amisulpride, Benzotriazole, 4,5-Methylbenzotriazole, Carbamazepine, Clarithromycin, Citalopram, Candesartan, Diclofenac, Hydrochlorothiazide, Irbesartan, Metoprolol, and Venlafaxine. The goal is to provide valuable insights into the challenges and opportunities associated with implementing quaternary treatment processes to comply with the UWWTD. Results indicate that the conventional biological treatment is insufficient, with median removal rates below 50 % for most target micropollutants (except for Benzotriazole and Irbesartan). The implementation of quaternary treatment processes, namely ozonation and activated carbon adsorption, significantly enhances WWTP micropollutants removal, with median removal efficiencies exceeding 80 % for all the target micropollutants, with Candesartan being the most recalcitrant. Environmental risk assessment reveals that some micropollutants pose a significant threat to aquatic ecosystems even with 80 % removal efficiency (Irbesartan, Candesartan, Diclofenac, and Venlafaxine), while others do not pose a risk even at WWTP influent concentrations (4,5-Methylbenzotriazole, Hydrochlorothiazide, Amisulpride, Citalopram, and Metoprolol). Economic analysis shows that the selection of specific operating parameter values significantly impacts the cost of each treatment process, changing the economic feasibility ranking of the different treatment options.