Quorum Sensing: A New Biofouling Control Paradigm in a Membrane Bioreactor for Advanced Wastewater Treatment

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.