Conventional activated sludge with ultrafiltration vs dynamic membrane bioreactor: A comprehensive comparison

This study presents a comprehensive comparison of two Lines treating domestic wastewater with Integrated Fixed-Film Activated Sludge (IFAS). Line 1 consisted of an IFAS with a secondary settler and ultrafiltration (UF). In contrast, Line 2 featured an IFAS coupled with an innovative membrane bioreactor: Encapsulated Biofilm Self-Forming Dynamic Membrane Bioreactor (EBSF-DMBR). Such a membrane comprises a cake and biofilm layers to overcome the fouling issues typical of conventional membranes. The comparison was based on multiple parameters: carbon, nitrogen and phosphorus removal efficiencies, nitrous oxide (N2O) emissions, membrane fouling behaviour, carbon footprint and water reuse. Furthermore, respirometry was performed to assess the kinetics of the two Lines. Line 2 with EBSF-DMBR achieved significantly higher total nitrogen removal (90 ± 6%) compared to Line 1 (66 ± 18%), supported by enhanced nitrification (95 ± 7%) and denitrification (82 ± 10%). These improvements were attributed to the encapsulated biofilm layer formed within the EBSF-DMBR, which promoted simultaneous nitrification and denitrification under stable micro-anoxic conditions. In addition, Line 2 exhibited lower N2O emissions (0.25 ± 0.10%) and a lower fouling rate (0.004 ± 0.002 bar day−1), despite operating at higher membrane resistance due to the encapsulated biofilm layer. EBSF-DMBR exhibited a lower carbon footprint (1.7 kg CO2eq m−3) than Line 1 (2.6 kg CO2eq m−3), with indirect emissions being the dominant source. This study is the first to report N₂O emission data from a dynamic membrane bioreactor, and the first pilot-scale application of an IFAS EBSF-DMBR configuration treating real wastewater, highlighting its potential as a low-energy, low-emission, and fouling-resistant alternative to conventional membrane bioreactors.