Efficiency of fluvial biofilms on urban wastewater treatment in small facilities

This thesis addresses the challenges faced by small urban wastewater treatment plants (UWWTPs; <10,000 population equivalents) under the revised Urban Wastewater Treatment Directive (2024/3019/EU), particularly those discharging into low-order, potentially intermittent streams increasingly affected by climate change. By assessing the self-depuration capacity of these freshwater receiving ecosystems and evaluating the performance of biofilms and planktonic microbial communities from laboratory experiments to a real-scale approach in a small UWWTP, this thesis proposes a nature-based solution (NBS) as an alternative tertiary treatment: the biofilm-plankton reactor (BPR). The BPR achieved high removal efficiencies for nitrogen (particularly ammonium), phosphorus under laboratory conditions, Escherichia coli (considered as a faecal indicator), antimicrobial resistance determinants, and specific contaminants of emerging concern, while requiring less surface area and shorter hydraulic retention times than constructed wetlands. Overall, the BPR emerges as a cost-effective and sustainable NBS to enhance wastewater treatment performance and protect vulnerable aquatic ecosystems.