Comparing two Integrated Fixed-film Activated Sludge (IFAS) systems in view of the updated European Urban Wastewater Treatment Directive

This study evaluates the pollutant removal performances and environmental impacts of two pilot-scale configurations: (I) an integrated fixed-film activated sludge (IFAS) system combined with a membrane bioreactor (MBR), and (II) IFAS coupled with secondary settling followed by ultrafiltration (UF). Treatment performance, membrane fouling, microbial activity (as measured by respirometry), nitrous oxide (N₂O) emissions, and carbon footprint (CF) were evaluated. Both systems achieved over 97 % total chemical oxygen demand removal, with slightly higher ammonium nitrogen removal in Configuration I (96 ± 3 % vs. 93 ± 6 %). Under the revised UWTD (2024/3019), effluent PO₄^3--P averaged about 5 mg L^-1 for both configurations, exceeding the 1 mg L^-1 discharge limit. For reuse (Regulation (EU) 2020/741), both configurations consistently met the Class B BOD₅ standard but failed to consistently achieve the more stringent Class A standard. All other monitored parameters complied with regulations. Respirometry tests indicated higher heterotrophic activity in the suspended biomass of Configuration II. Configuration I achieved superior total nitrogen removal (85 ± 11 % vs. 75 ± 15 %) due to its higher internal carbon-to‑nitrogen ratio (4.2 vs. 2.1 gCOD/gN). Membrane fouling was more pronounced in the MBR system, with an average fouling rate of 0.21 ± 0.2 bar day^-1 (0.16 ± 0.2 bar day^-1). N₂O emissions remained low, with emission factors slightly lower in the MBR (0.13 %) compared to the Settler-UF (0.09 %). The carbon footprint was estimated at 1.47 kg CO₂eq d^-1 for Configuration I and 2.27 kg CO₂eq d^-1 for Configuration II, mainly reflecting differences in energy consumption and nitrogen removal performance. Overall, combining IFAS with membrane technologies provides clear advantages for producing high-quality effluent, meeting regulatory requirements, and reducing greenhouse gas emissions.