Insights into quorum quenching mechanisms to control membrane biofouling under changing organic loading rates

•Impact of OLR on QQ based biofouling control was investigated.•An increase in OLR resulted in higher EPS levels in the biocake and bulk sludge.•S-EPS and LB-EPS were the major contributors to membrane fouling.•Within EPS, polysaccharides contributed more to membrane fouling than proteins.•Transient conditions reduced the efficacy of immobilized QQ bacteria.

A quorum quenching (QQ) consortium comprised of both acyl homoserine lactones (AHLs)- and autoinducer-2 (AI-2)-degrading bacteria, either immobilized in polymer-coated alginate beads or in liquid suspension, was examined for fouling control in lab-scale MBRs under both steady and changing organic loading rates (OLRs). Under steady conditions the QQ consortium retarded biofouling by a factor of 3. However, a continuous increase in OLR vastly reduced the effectiveness of QQ bacteria; the biofouling was retarded only by factors of 1.4-1.8. A significant increase in extracellular polymeric substance (EPS), especially loosely-bound EPS in mixed liquor together with an increase in polysaccharide content up to 4 times in EPS resulted from the increase in OLR, was attributed to the impaired QQ efficacy. In control MBRs, cake layer resistance was the major factor (>60%) contributing to the increased trans-membrane pressure, as compared with pore blockage resistance and intrinsic membrane resistance. In contrast, the pore blockage resistance became dominant in QQ MBRs (>40%).

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