Effect of Organic Characteristics on Sludge Settleability in an AAO System

: The effects of different mixed organic matter ratios on sludge settleability were examined from the succession patterns of microbial community structure, and changes of microbial intracellular and extracellular polymers in the activated sludge. The experimental results showed that when organic matter was dissolved in the influent, the sludge settleability was optimal (SVI=70 mL·g-1), which was better than that for influent water with partially dissolved organic matter (SVI=120 mL·g-1) and particulate organic matter (SVI=280 mL·g-1). According to the analysis of microbial community structure, Thiothrix, Chryseolinea, and Trichococcus were important in influencing the sludge settleability. Of these, particulate organic matter promoted the growth of Trichococcus, and dissolved organic matter promoted the growth of Thiothrix and Chryseolinea. In addition, changes in the bacterial community also had an important influence on the changes of intracellular and extracellular polymers, which either enhanced or impeded settleability. The higher the content of dissolved organic matter in the influent, the higher the storage of intracellular polymeric substances and, therefore, the better the sludge settleability. The sludge settleability was significantly negatively correlated with polysaccharides, proteins, and the Zeta potential in the LB-EPS.