Bacteria regulate specific group behaviors such as biofilm formation in response to population density using small signal molecules called autoinducers (quorum sensing, QS). In this study, the concept of bacterial QS was applied to membrane bioreactors (MBRs) for advanced wastewater treatment as a new biofouling control paradigm. The research was conducted in three phases: (1) demonstrate the presence of the autoinducer signal in MBRs, (2) correlate QS activity and membrane biofouling, (3) apply QS-based membrane biofouling control. A bioassay with Agrobacterium tumefaciens reporter strain proved that N-acyl homoserine lactone (AHL) autoinducers were produced in the MBR. Furthermore, thin-layer chromatographic analysis identified at least three different AHLs in the biocake, of which N-octanoyl-homoserine lactone was the most abundant During continuous MBR operation, the biocake showed strong AHL activity simultaneously with abrupt increase in the transmembrane pressure, which implies that QS is in close association with membrane biofouling. Porcine kidney acylase I, which can inactivate the AHL molecule by amide bond cleavage, was confirmed to prevent membrane biofouling by quenching AHL autoinducers. From these results, it was concluded that QS could be a novel target for biofouling control in MBRs.

Recently, enzymatic quorum quenching has proven its potential as an innovative approach for biofouling control in the membrane bioreactor (MBR) for advanced wastewater treatment. However, practical issues on the cost and stability of enzymes are yet to be solved, which requires more effective quorum quenching methods. In this study, a novel quorum quenching strategy, interspecies quorum quenching by bacterial cell, was elaborated and proved to be efficient and economically feasible biofouling control in MBR. A recombinant Escherichia coli which producing N-acyl homoserine lactonase or quorum quenching Rhodococcus sp. isolated from a real MBR plant was encapsulated inside the lumen of microporous hollow fiber membrane, respectively. The porous membrane containing these functional bacteria (i.e., "microbial-vessel") was put into the submerged MBR to alleviate biofouling on the surface of filtration membrane. The effect of biofouling inhibition by the microbial-vessel was evaluated over 80 days of MBR operation. Successful control of biofouling in a laboratory scale MBR suggests that the biofouling control through the interspecies quorum quenching could be expanded to the plant scale of MBR and various environmental engineering systems with economic feasibility.

Recently, interspecies quorum quenching by bacterial cells encapsulated in a vessel was described and shown to be efficient and economically feasible for biofouling control in membrane bioreactors (MBRs). In this study, free-moving beads entrapped with quorum quenching bacteria were applied to the inhibition of biofouling in a MBR. Cell entrapping beads (CEBs) with a porous microstructure were prepared by entrapping quorum quenching bacteria ( Rhodococcus sp. BH4) into alginate beads. In MBRs provided with CEBs, the time to reach a transmembrane pressure (TMP) of 70 kPa was 10 times longer than without CEBs. The mitigation of biofouling was attributed to both physical (friction) and biological (quorum quenching) effects of CEBs, the latter being much more important. Because of the quorum quenching effect of CEBs, microbial cells in the biofilm generated fewer extracellular polymeric substances and thus formed a loosely bound biofilm, which enabled it to slough off from the membrane surface more easily. Furthermore, collisions between the moving CEBs and membranes gave rise to frictional forces that facilitated detachment of the biofilm from the membrane surface. CEBs bring bacterial quorum quenching closer to being a practical solution to the problem of biofouling in MBRs.