Comparative evaluation of UV-driven processes for quaternary treatment of urban wastewaters: Trade-offs between micropollutants removal, toxicity reduction, and cost-effectiveness

Abstract

Micropollutants (MP) in urban wastewater pose challenges, requiring advanced treatment solutions to ensure regulatory compliance and environmental safety. This study investigated UV-driven processes (UV-alone, UV/H2O2, and UV/PDS) in a FluHelik photoreactor operating in continuous mode (residence times: 1.0–6.5 min) to remove 19 MPs (spiked at 10 μg L−1 each) from urban wastewater after tertiary treatment. Preliminary trials included bench-scale testing and spiked demineralized water. Pilot-scale trials using real wastewater evaluated treatment performance across different UV lamp types: low-pressure (LP), medium-pressure mercury (MP_Hg), and medium-pressure iron-doped (MP_Fe). Treatment performance was assessed regarding MP removal, ecotoxicity (Chlorella vulgaris growth inhibition), and an integrated cost-effectiveness metric (expressed as € m−3 order−1). UV-alone treatments, particularly using medium-pressure lamps, effectively reduced urban wastewater toxicity but showed limited MP removal, especially for EU-prioritized compounds like carbamazepine and irbesartan. UV/H2O2 under MP_Hg lamp provided moderate removal (up to 56 % for 15 MPs) with acceptable operational costs (~0.09 € m−3), but increased post-treatment toxicity. UV/PDS consistently achieved the highest MP removal, namely for carbamazepine (82 %) and irbesartan (81 %), while also reducing effluent toxicity to C. vulgaris. Despite the higher cost of persulfate, UV/PDS proved more cost-effective when both pollutant removal and ecotoxicity were considered. Persistent MPs such as short-chain PFAS and melamine remained largely unaffected by all treatments. This study underscores the need to optimize UV-driven processes by tailoring UV spectra, oxidant choice, and operational conditions to balance contaminant removal, operational costs, and ecotoxicity.