Transverse vibration as novel membrane fouling mitigation strategy in anaerobic membrane bioreactor applications

• Low frequency transverse membrane vibration for fouling limitation in AnMBR system.
• A two-stage fouling phenomena observed during long term constant flux filtration with transverse vibration.
• Fouling layer with high reversibility formed during filtration with transverse vibration.
• Fouling limitation mechanisms explored with advanced foulant characterization.
• System performance improved by coupling periodical backwash or relaxation with vibration.

While vibratory shear is effective for increasing the shear near the membrane surface, transverse hollow fiber membrane vibration offers additional mass transfer enhancement in terms of generating vortices in the wake of the vibrating surface. In this work, transverse vibration of submerged hollow fibers is explored for enhancing the filtration of anaerobic bioreactor effluents where gas sparging is often undesirable. The critical flux value was increased significantly with the aid of membrane vibration. Even at high mixed liquid suspended solid concentrations, the vibratory system was still able to significantly reduce fouling. In addition to a reduced rate of fouling, fractionation of the fouling layer also showed that a more reversible fouling occurs with vibrational filtration in comparison to traditional fouling limitation method such as gas sparging and crossflow. During the long term constant flux filtration with vibration, a two-stage fouling phenomena was observed, similar with those observed in traditional MBR fouling but with a more extended initial low fouling stage. After the local permeate flux increased above the critical flux, the second rapid fouling stage occurred mainly due to cake formation. By appropriately coupling periodical backwash/relaxation with vibrational filtration, the membrane performance was further improved. At low vibration frequency, filtration with periodical relaxation displayed the best performance, whereas at high frequencies, coupling with periodic backwash was more beneficial.