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.