[Effect of Microbial Community Structure and Metabolites on Sludge Settling Ability Under Three Different Switching...

Using sodium acetate as the carbon source, sludge settling ability (settleability) was investigated under three processes:AAO nitrogen and phosphorus removal(process Ⅰ), AO nitrification-denitrification (process Ⅱ), and aerobic carbon removal (process Ⅲ). The succession of microbial community structures in sludge was traced, the content and composition of microbial metabolites were monitored, and the effects of operational mode on sludge settleability were analyzed. The results showed that the settleability of process Ⅰ was the best, followed by process Ⅲ and Ⅱ. Under the different operating conditions, the dominant bacteria and microbial community structure of the system changed significantly. The relative amount of Thiothrix was the dominant bacteria affecting the sludge settleability. The abundances of Thiothrix were only 0.08% and 1.51% with fresh sludge and in process Ⅰ; this abundance increased to 9.41% in process Ⅱ and decreased to 4.29% in process Ⅲ. The anaerobic zone of process I had an inhibitory effect on the growth of the bacterium, while the anoxic zone of process Ⅱ stimulated its dominant growth. At the same time, comparison showed that the microbial population diversity was highest in process Ⅰ. followed by processes Ⅱ and Ⅲ. The introduction of anoxic and anaerobic zones led to the increase of system function and environmental complexity, and increased microbial community diversity. Analyses of extracellular polymeric substances (EPS) and fluorescence characteristics showed that the changes in microbial community structure had a significant effect on the composition and content of EPS, which aggravated the process of improving or deteriorating settleability. The sludge settleability was found to be positively correlated with the ratio of protein and polysaccharide in loosely bound EPS.