Control of Biofouling in Membrane Bioreactor for Wastewater Treatment by Quorum-Quenching Bacteria Immobilized in Moving Beads

Abstract

Membrane bioreactor (MBR) is a widely used as an advanced wastewater treatment process, but membrane biofouling is a chronic problem. Recently quorum quenching (QQ) technology has attracted attention as a new solution to suppress biofouling. The purpose of this study is to develop a moving carrier capable of simultaneously anticipating both the physical cleaning and the quorum sensing inhibition to prevent more effective biofouling. <br/> Rhodococcus sp. BH4, known as QQ bacteria, was immobilized on a calcium-alginate matrix and developed a new membrane fouling inhibitor, freely moving bead, called a cell entrapping beads (CEBs). Because CEB has a specific gravity similar to water, it moves freely by aeration, generates physical cleaning effect by colliding with the membrane as well as effectively suppresses QS mechanism by using QQ. Especially, when the QS of membrane fouling microorganisms is disturbed, extracellular polymeric substances (EPS) production is slowed, and loosely bound biofilm is formed. Therefore, the physical cleaning effect of CEB synergistically increased with the QQ effect. Through this combined effect, CEB delayed membrane biofouling by 8 times slower than conventional MBR in a continuous process.<br/> As the following study, improvement of the physical and chemical stability of the CEB have conducted to the application for actual MBR processes. The first is a fluid coating carrier (Macrocapsule), which surrounds CEB with porous membrane using a non-solvent induced phase separation technique. The porous membrane was formed on the surface by a spontaneous phase inversion between the amphipathic polymer solution and the contained water in CEB. Macrocapsule showed excellent biofilm control effect for 80 days on laboratory scale continuous MBR process and retained its QQ activity. The second is W-bead, which is prepared by double cross-linking with polyvinyl alcohol and alginate. The W-bead showed excellent stability and biofouling mitigation effect in the MBR fed with real wastewater. This study suggests the free-moving beads as an efficient QQ bacteria carrier and showed potential for actual MBR application.<br/>