A number of recent studies have demonstrated that quorum sensing (QS) using signal molecules, N-acyl homoserine lactone (AHL), plays a role in the formation of biofilm on the surface of membranes in a membrane bioreactor (MBR). In this study, the membrane biofouling in an external submerged MBR was inhibited by interrupting AHL-mediated QS with quorum quenching bacteria encapsulated inside the porous vessel (microbial-vessel). The quorum quenching effect of the microbial-vessel was more pronounced when the microbial-vessel was positioned nearer to the filtration membrane in MBR, i.e., in the membrane tank rather than in the bioreactor. Its quorum quenching effect was also largely dependent on the recirculation rate of the mixed liquor between the bioreactor and the membrane tank. The microbial-vessel maintained its quorum quenching activity steadily over 100 days of the MBR operation due to continuous regeneration of living quorum quenching bacteria inside the microbial-vessel. This strategy effectively interrupted cell-to-cell communications (quorum sensing), and thereby exhibited energy saving potential by reducing the aeration rate in MBR. (c) 2012 Elsevier B.V. All rights reserved.