Organic micropollutant removal from wastewaters using O3-based and UV-assisted quaternary treatments to comply with the revised urban wastewater treatment directive.

The revised EU Urban Wastewater Treatment Directive (UWWTD) requires wastewater treatment plants (WWTPs) to implement quaternary treatment to achieve 80% average percentage removal of selected organic micropollutants (OMPs), while moving toward energy neutrality. In this context, this study investigated and compared the performance of various pilot-scale ozone (O3)-based and UV-assisted advanced oxidation processes (AOPs) for the removal of OMPs from real secondary- and tertiary-treated effluents, and their energy demands to comply with the UWWTD. O3-based AOPs robustly achieved UWWTD compliance across different wastewater matrices and contaminant combinations. This supports the implementation of O3-based processes within multi-barrier treatment systems coupled with BAC (biological activated carbon) post-treatment. In contrast, H2O2 overdosing in O3-based processes reduced the likelihood of meeting UWWTD targets, suggesting an optimal H2O2/O3 ratio of 1-1.5. The multi-matrix, multi-process energy assessment reveals that O3-based processes are more efficient and cost-effective processes for OMPs removal, and UV-assisted treatments are more sensitive to wastewater quality. Energy self-sufficiency of WWTPs is unrealistic. For instance, photovoltaic (PV)-based supply scenarios face spatial constraints, typically requiring PV areas 2-10 times larger than a conventional WWTP footprint. Sensitivity analysis of biogas energy recovery shows that AOPs self-sufficiency is governed by oxidant dose. Results suggest that achieving energy neutrality may require off-site renewable supply, highlighting the limits of full on-site energy self-sufficiency. Overall, the results identify ozonation as the most robust, energy-efficient, and UWWTD-aligned option for quaternary wastewater treatment.