[Improvement of the Dewaterability of Excess Activated Sludge with Mixed Yeasts by Degrading Extracellular Polymeric Substances]

The dewaterability of excess sludge directly affects the efficiency and cost of sludge disposal, and improving sludge dewaterability is a crucial way to reduce sludge volume. This study proposes a method to improve the dewaterability of residual sludge by using mixed yeast strains to degrade extracellular polymeric substances (EPS) in activated sludge. Firstly, the mixed cells of three yeast strains were injected into the sterilized EPS solution to investigate the degradation efficiency of EPS components. Secondly, the mixed yeast cells were supplied into the residual sludge, which was aerated for several hours while the sludge dewaterability was evaluated. The results showed that the degradation efficiencies of yeast to proteins, polysaccharides, and nucleic acids in EPS were evident, and reductions of (60.43±2.73)%, (18.94±2.39)%, and (48.30±3.37)% were achieved, respectively, within 72 hours' oscillating cultivation. The capillary suction time (CST) of the sludge decreased by (17.19±1.16)% after aeration, with 1.5 g mixed yeast wet cells added into 2 L excess sludge, (7.03±1.35)% more than that of the control test after 24 hours. Meanwhile, the total amount of EPS in sludge decreased by (17.46±3.91)% more than that in the control sludge, indicating that the yeast can improve the sludge dewaterability in-situ by degrading EPS in sludge.