Comparative Modeling of Integrated Fixed‐Film Activated Sludge Membrane Bioreactor and Aerobic Membrane Bioreactor Systems: Nitrogen Dynamics and Energy Demand

This study presents a process‐oriented modeling assessment of a membrane bioreactor (MBR) and a hybrid integrated fixed‐film activated sludge membrane bioreactor (IFAS‐MBR) system using experimental data collected from parallel pilot‐scale systems, with emphasis on performance‐energy trade‐offs relevant to engineering design and operation. Both configurations were calibrated and validated under dynamic conditions to evaluate carbon removal, nitrogen transformation, and operational energy demand. Model results showed high predictive accuracy for mixed liquor suspended solids (MLSS) (mean relative absolute error, MRAE < 5%) and moderate accuracy for soluble chemical oxygen demand (sCOD) (MRAE: 11%–17%), while particulate COD (xCOD) predictions were governed primarily by membrane separation rather than biological kinetics. Nitrogen modeling revealed moderate agreement for ammonium nitrogen (NH 4 ‐N) (MRAE: 24%–36%), whereas nitrate nitrogen (NO 3 ‐N) predictions showed high accuracy, particularly in the IFAS‐MBR system (MRAE: 7%–14%). This improvement was achieved by calibrating oxygen diffusion within the biofilm, demonstrating that oxygen transport processes can dominate nitrogen transformation under non‐limiting bulk oxygen conditions. The IFAS‐MBR configuration increased total energy demand by approximately 27%, mainly due to intensified aeration requirements. These findings highlight the critical role of aeration in simultaneously governing process performance and energy demand.