Biosynthesis pathway of extracellular polymeric substance and regulatory mechanism underlying floc formation of activated sludge bacteria

Abstract:

The activated sludge (AS) process has been widely applied for municipal sewage and industrial wastewater treatment for over a century. The microbial floc formation plays a central role in gravitational sludge-effluent separation and sludge recycling. However, very little was known about the mechanism underlying the floc formation of activated sludge bacteria. By summarizing the literature about AS microbiome, molecular biology of AS floc formation and comparative genomics analyses to reveal the molecular mechanism underlying bacterial floc formation. The extracellular polysaccharide biosynthesis gene cluster is widespread among floc-forming bacteria and is required for bacterial floc formation, which was experimentally confirmed in Zoogloea, Thauera, Mitsuaria and Aquincola strains. Furthermore, the prsK-prsR-prsT gene cluster and PEP-CTERM genes are also widely encoded in those floc-forming bacteria. and other genes. It is demonstrated that bacterial floc formation mediated by both exopolysaccharides and PEP-CTERM proteins might be well-conserved among AS bacteria and other floc-formers. These results could provide important implications for the control of sludge bulking, reduction of sludge, and resource and energy recovery from excess sludge.