IFAS Intermittent Aeration Membrane Bioreactor System: The Influence of Sludge Retention Time

This study presents a comparative evaluation of a Membrane BioReactor – Integrated Fixed Film Activated Sludge – Intermittent Aeration (MBR-IFAS-IA) pilot plant operated under two different (Period I and Period II) sludge retention time (SRT) conditions. Specifically, the SRT was set to 7 and 3.5 days during Period I and II, respectively. The study has the main scope of investigating how lowering the SRT of the biofilm contributes to pollutant removal. During both experimental periods, total chemical oxygen demand (TCOD) removal was very high (97.8% on average). An improvement in orthophosphate (PO4-P) removal efficiency occurred during Period II (43.8%) compared to Period I (27.7%). However, a slight worsening in the removal efficiency performances was obtained during Period II, mainly for ammonia oxidation, total nitrogen (TN) and soluble (sCOD) removal. The reduction of SRT from Period I to Period II showed a substantial reduction of nitrous oxide emission (N2O) from 0.42% to 0.23% of the influent total nitrogen