Impact of Novel Quorum Quenching Strains in Controlling Membrane Biofouling in Membrane Bioreactor

Abstract

Membrane bioreactor is a relatively modern treatment technology that not only treats wastewater but is also able to reclaim water that is of high quality. Furthermore, the technology has lower footprint than other conventional technologies and less sludge production. One of the most challenging aspects of this technology is biofouling where membrane filtration ability is compromised with continuously growing slime layer on membrane surface, known as biofouling. One way to tackle biofouling is by studying quorum sensing, that is basically the way microorganisms communicate and talk to each other using signal molecules such AHLs. These exist in various molecular sizes and contribute to a complex chain of bacteria communication. Counter to quorum sensing is quorum quenching where certain strains show ability to destroy these signal molecules and destroy the process of communication known as quorum sensing. These strains are encapsulated in beads into the activated sludge of MBR. These strains work on the signal molecules also known as auto inducers of quorum sensing bacteria. One of the widely studied quorum quenching strain is Rhodococcus BH-4 which has been marked as the potential candidate to destroy the mechanism of quorum sensing so far. However new strains have been identified of which the noteworthy have been Pseudomonas Aeruginosa and Bacillus Cereus who have shown the ability of quorum quenching as well as quorum sensing. These novel strains were encapsulated in PVDF alginate beads and their effect was studied individually in membrane bioreactor along with comparison with Rhodococcus BH-4 and vacant beads in conventional membrane bioreactor. Flux of 15 LMH, SRT of 20 days and HRT of about 4.16 hrs was maintained while keeping a mixed liquor concentration of 5-6 grams per litre in membrane bioreactor. It was found out that MBR containing Pseudomonas Aeruginosa beads was able to last 13 days in compare to 8 days of Bacillus Cereus. Both were able to do significantly well in comparison to conventional MBR and vacant beads run which lasted 5 to 6 days respectively. However, the best strains were still found to be Rhodococcus BH-4 where membrane lasted 15 days. Product water quality in quorum quenching beads run when compared side by side with conventional MBR, BOD removal dropped from 96 to 90%, total phosphorous dropped from 80 to 67%. SMP and bound EPS concentration were also found to be lower in Pseudomonas and Rhodococcus BH-4 in comparison to conventional and vacant MBR. However SVI was high for both of these strains, reported to be 130 and 140 mL/g respectively in comparison to 60 and 80 mL/g of conventional and vacant MBR respectively.