Stratification Structure of Extracellular Polymeric Substances with Implications to Anaerobic Digest Sludge Dewaterability

Laboratory anaerobic digestion studies were conducted to determine the effect of extracellular polymeric substances (EPS) on dewaterability of sludge (TS) with humus soil powder (HS) or not. In this study, an available stratification approach aimed at better understanding the factors influencing the sludge dewaterability was developed, which EPS were divided into soluble EPS and bound EPS by centrifuge and heating extraction, respectively. During digestion, soluble polysaccharides(S-PS), soluble proteins (S-PN), bound polysaccharides (B-PS), bound proteins (B-PN) and capillary suction time (CST) were detected. Results showed that CST of sludge increased corresponding to deterioration of sludge dewaterability, however CST was affected by addition of HS to sludge. Components of EPS had an obvious variation, S-PS had been increasing while others had not changed until the seventh day. Statistical analysis suggested that normalized CST and S-PS had a positive correlation(R²=0.9192). After 21 days, normalized CST value of sludge with HS was less than other about 25%, and S-PS in sludge with HS were about 7% less than without HS, however, S-PN, B-PN and B-PS did not have obvious differences in sludge. It indicated that S-PS markedly impacted sludge dewaterability.