Effect of soluble extracellular polymeric substances (soluble eps) on activated sludge dewaterability

Microbial extracellular polymeric substances (EPS) are the major components of the sludge floc matrix and would have large influence on the dewaterability of activated sludge (AS). In this study, laboratory experiments were conducted to investigate the effects of EPS on AS dewaterablity with an emphasis on the importance of soluble extracellular polymeric substances (soluble EPS). Sequencing batch reactors (SBRs) fed on a synthetic wastewater were operated at different sludge retention times (SRT) of 5, 10 and 20 days. The results demonstrated that the amount of soluble EPS of the sludge generally increased with the decrease of SRT from 20 to 5 days. A longer modified capillary suction time (CSTmod), as a reflection of poorer dewaterability, was associated with a larger amount of soluble EPS. The components content of soluble EPS also had a significant positive correlation with CSTmod. However, no significant correlation could be established between the CSTmod and the amount of total EPS. EPS in excess could lead to more bound water contained in floc, weaken cell attachment and deteriorate the floc structure, resulting in poor particle size distribution and dewaterability.