Work

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

Year: 2025

Type: article

Abstract: 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 (N 2 O) 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 PO 4 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 ). N 2 O 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 CO 2 eq d −1 for Configuration I and 2.27 kg CO 2 eq 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. • Two IFAS-based membrane configurations were systematically compared. • MBR showed higher TN removal (85 %) than UF (75 %) due to higher internal C/N ratio. • UF showed higher heterotrophic activity (Yₕ, fₓ) than MBR, yet lower COD removal. • MBR line achieved low N 2 O emissions (< 0.1 % of influent nitrogen). • Both configurations complied with EU 2024/3019 discharge limits except for phosphate.

Source: The Science of The Total Environment

DOI: 10.1016/j.scitotenv.2025.180884

Authors: Antonio Mineo, Dilsad Soylu, Jie Jiang, Marika Carnesi, Giorgio Mannina

Institutions: University of Palermo, Istanbul Technical University, Hohai University

Language: English

Topic: Wastewater Treatment and Nitrogen Removal

Subfield: Pollution

Field: Environmental Science

Domain: Physical Sciences

SDGs: Clean water and sanitation, Responsible consumption and production, Climate action, Sustainable cities and communities

Open Access status: hybrid

Estimated APC paid: $4,250