Variation of extracellular polymeric substances (EPS) and specific resistance to filtration in sludge granulation process to the change of influent organic loading rate

Four sequencing batch reactors (SBRs) were operated to evaluate the effects of changing the influent chemical oxygen demand (COD) loading rate (F/M ratio) on various components of EPS and their relationship with other physicochemical characteristics of granular sludges in the SBR system. F/M ratio in R-1, R-2, R-3, and R-4 was 0.11, 0.21, 0.32, and 0.43 kg COD/kg mixed liquor suspended solids (MLSS)·d, respectively. The sludge fed with higher F/M ratio enhanced the granulation process and produced more polysaccharides (PS) and proteins (PN) than the sludge run with lower COD loading rate while humic substances and uronic acids did not show any profound difference in their contents. The total EPS contents in the granular sludges were higher at the beginning of experiment as compared to their values noted at the end of studies. The granular sludge settleability was positively correlated with the F/M ratio and EPS contents. Specific resistance values at the end of studies were 2.37 × 108, 1.38 × 108, 1.86 × 108, and 9.32 × 108 s2/g in R-1, R-2, R-3, and R-4, respectively, to that of seed sludge (6.80 × 109 s2/g). The higher values of specific resistance in R-4 were due to raised contents of PS compared to other reactors. EPS particularly PS were found to be positively correlated with settleability and negatively with dewatering characteristics of sludges.