Specific allocation of encapsulated quorum quenching bacteria in an external submerged MBR for biofouling control

Abstract

Recent studies have demonstrated that quorum quenching (QQ) in which disruption of signal molecules, N-acyl homoserine lactones (AHL) takes place, is effective to mitigate biofouling in membrane bioreactors (MBRs) for wastewater treatment. In the previous study, Rhodococcus sp. BH4 which can degrade signal molecules were isolated from a real MBR plant. These functional microorganisms were encapsulated inside the porous membrane, which was called as Microbialvessel to be used in MBR. The aim of this work was to determine the optimum position of the Microbial-vessel in an external submerged MBR system to mitigate membrane biofouling by continuously destroying the signal molecules(AHL). Two external submerged MBR systems were run for a comparative study where one MBR contained a Microbial-vessel inside the bioreactor, whereas the other MBR contained a Microbial-vessel inside the membrane tank. Microbial-vessel showed quorum quenching effect and inhibited membrane biofouling regardless of its position either inside bioreactor or inside membrane tank. However, the Microbial-vessel showed more efficient control on membrane biofouling, when it was contained inside the membrane tank than that inside the bioreactor. The recirculation rate of sludge affected substantially the rate of biofouling regardless of the position of the Microbial-vessel, which suggested that QQ is governed by a diffusion controlled mechanism. Quorum quenching by the Microbial-vessel has demonstrated the potential of energy saving by providing an opportunity to reduce the aeration rate in the membrane tank.