Activated sludge (AS) process has been widely applied to municipal sewage and industrial wastewater treatment around the globe and it has played a central role in water pollution control for a century. The annual yield of excess sludge from around 4,000 municipal sewage treatment plants has reached 30 million cubic meters (wet sludge) in China. Thus, proper disposal and utilization of sludge are urgently needed to avoid secondary contamination.

A research team led by Dr. QIU Dongru at Institute of Hydrobiology of Chinese Academy of Sciences and Dr. ZHANG Tong at University of Hong Kong, has worked on the isolated Zoogloea strains, the predominant floc-forming bacteria in the activated sludge treating municipal sewage. They reported the comparative genomics analyses on two floc forming Z. resiniphila strains, MMB and TS9, isolated from the AS flocs of municipal sewage treatment plants of Wuhan and Hong Kong, respectively.

By using molecular genetics and chemical approaches, the graduate students AN Weixin, GAO Na and co-workers identified a large extracellular polysaccharide biosynthesis gene cluster required for floc formation and characterized the glycosyl composition of Z. resiniphila MMB strain. Interestingly, two asparagine synthase genes have also been found to be involved in floc formation. Interspecific and intraspecific variations among this gene cluster are revealed.

The analyses on the extracellular polysaccharides (EPS) biosynthesis genes across the bacterial genomes indicate that many AS bacteria, including the yet-uncultured polyphosphate-accumulating Candidatus Accumulibacter phosphatis (CAP) strains, harbor similar EPS biosynthesis genes. These findings account for some previous observations on As and indicate that many of key AS bacteria are also capable of floc formation.

This study has been published in Water Research of International Water Association with the title “Comparative genomics analyses on EPS biosynthesis genes required for floc formation of Zoogloea resiniphila and other activated sludge bacteria.”

This work was supported by Chinese Academy of Sciences, One-Hundred Scholar Award, and Hong Kong General Research Funds.