The effect of sludge retention time and organic loading rate on performance and membrane fouling in membrane bioreactor

Abstract BACKGROUND Membrane bioreactor (MBR) is commonly considered a promising technology for wastewater treatment due to its outstanding effluent quality, low sludge production, and smaller environmental footprint. However, membrane biofouling is regarded as the bottleneck of MBR processes preventing their universal application. Optimizing operating conditions and improving the antifouling properties of membranes have a substantial impact on the rate and characteristics of membrane fouling in MBR systems. RESULTS In this study, a two‐step process was performed to mitigate membrane fouling by optimizing sludge retention time (SRT) and organic loading rate (OLR) and improving membrane characteristics in an MBR system developed for the treatment of pharmaceutical wastewater. At first, pure membrane fouling and sludge characteristics were examined in three identical MBRs at different OLRs (40, 100, and 160 mg chemical oxygen demand(COD)/L.d) under various SRTs (7.5, 22.5, and 37.5 days). The investigation indicated that high protein concentration in loosely bound extracellular polymeric substances (LB‐EPS) caused more irreversible fouling at the OLR and SRT of 40 mgCOD/L.d and 7.5 days, respectively. In the second stage, a modified anti‐biofouling membrane was installed into the optimized submerged MBR at OLR = 100 mgCOD/L.d and SRT of 22.5 days for further mitigation of membrane fouling. Membrane fouling significantly reduced as the protein and gram negative bacteria on the surface of the modified membrane decreased. CONCLUSION The results showed that the reversible and irreversible membrane fouling were controlled successfully through the proposed optimization of operational conditions and by improving the membrane characteristics in MBR. Finally, the protein of LB‐EPS is a vitally important factor affecting the irreversible membrane fouling. © 2020 Society of Chemical Industry (SCI)