Quorum Quenching Cell Entrapping Bead by Polyvinyl Alcohol Method for Biofouling Mitigation in Lab-scale MBR

Abstract

Quorum Quenching (QQ) bacteria such as Rhodococcus sp. BH4 and Pseudomonas putida have excellent anti-biofouling potential as they disrupt Quorum Sensing (QS) system and inhibit biofilm formation on membranes. Cell Entrapping Beads (CEBs) in which the QQ bacteria are immobilized is one of the most effective methods to mitigate membrane biofouling in MBR. The CEBs are crucial as they mainly protect QQ bacteria from the sludge's harsh environment for a better QQ effect and help in the physical cleaning of membranes in a submerged MBR. Previously simple sodium alginate (SA) beads were used, but it was found that their durability was very low in real wastewater. Polyvinyl Alcohol (PVA) is a better alternative due to its higher durability, chemical stability and low cost. Several brands of PVAs with different polymerization degrees were used here and small amount of SA was added to avoid agglomeration of PVA beads. Concentrations of SA/PVA were varied and different temperatures of cross-linking solution also was examined. Then the quality of the beads was evaluated on the physical and biological aspects. It was found that a PVA of 2,270 polymerization degree with 8% mixed in 1% SA makes the most stable CEBs. A specific brand of SA didn't prevent agglomeration of CEBs, while a particular brand of SA did even at lower concentrations. The temperature of cross-linking solution was also found to have a significant effect on beads' internal structure. The quality of CEBs made by the best method found in this research was confirmed through series of tests, i.e., freeze-drying, scanning electron microscopy, activity test after immobilization of QQ bacteria in the beads.