Novel insights into the role of Pseudomonas quinolone signal in the control of reverse osmosis membrane biofouling

The role of the Pseudomonas quinolone signal (PQS) pathway in the control of biofouling in reverse osmosis membrane filtration was examined by inoculating Pseudomonas aeruginosa into feed water to simulate biofouling. Various concentrations of PQS (2-heptyl-3-hydroxy-4-quinolone) and an anthranilate analog (methyl anthranilate) were used as the activator and inhibitor of the PQS pathway, respectively. Membrane performance results showed that addition of exogenous PQS caused severe decreases in permeate flux and salt rejection and increase in irreversible membrane fouling. In contrast, the presence of methyl anthranilate mitigated the declines in permeate flux and salt rejection by biofouling and significantly reduced the total fouling resistance and hence shorten the membrane cleaning periods. Biofilm characterization demonstrated that PQS aggravated membrane biofouling by promoting initial bacterial attachment, increasing levels of the extracellular polymeric substances (EPS), total organic carbon (TOC) and extracellular DNA, and changing the mature biofilm structure from a mushroom shape to a denser flat shape. In contrast, addition of methyl anthranilate increased protein adsorption during the initial biofouling stage through electrostatic interactions, but significantly inhibited biofilm growth via reducing levels of EPS and TOC, as well as total cell number in the biofilm. These results provide evidence that PQS pathway plays an important role in biofilm formation and an anthranilate analog, methyl anthranilate, could be a novel agent to control RO membrane biofouling. Therefore, PQS synthetic pathway and precursors of quorum sensing signals may provide viable targets for biofouling control in practical RO membranes applications.