Habib Etemadi

BACKGROUND: Membrane bioreactor (MBR) is commonly considered as a promising technology for wastewater treatment due to outstanding effluent quality, low sludge production and smaller footprint. However, membrane biofouling is regarded as the bottleneck of MBR processes preventing their universal application. Optimizing operating conditions and improving antifouling properties of membranes have a substantial impact on the rate and characteristics of membrane fouling in MBR systems. RESULTS: In this study, 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 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 mgCOD/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 OLR and SRT of 40 mgCOD/L.d and 7.5 days, respectively. In second stage, 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 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 improving the membrane characteristics in MBR. Finally, the protein of LB-EPS is vitally important factor affecting the irreversible membrane fouling.