Abstract: Effect of extracelluler polymer substances (EPS) on the flocculation ability, settleability and surface properties of activated sludge were investigated using a sequencing batch bioreactor (SBR) to treat simulated wastewater when glucose was used as carbon source by adjusting influent concentration of carbon sources in order to change the EPS concentration. The results show that the sludge floc weight capacity (FA) and the flocculation are better when the effluent suspended solids (ESS) is more lower. ESS and sludge volume index (SVI) are increased, and FA and regional subsidence rate (ZSV) are decreased gradually with the increasing EPS, which could result in the lower activated sludge flocculation ability and settleability. EPS is positively correlated with the ESS and the SVI (R2 is 0.9916 and 0.9451, respectively) and EPS is negatively correlated with FA and the ZSV (R2 is -0.9941 and -0.9805, respectively). And furthermore, increasing EPS has an important impact on the surface properties of sludge. The sludge Zeta potential and the relative hydrophobicity (RH) of sludge are decreased when the EPS is improved, which can result in the increase of SVI and ESS and decrease of sludge flocculation ability and Settleability. EPS is negatively correlated with the Zeta potential and the RH (R2 is -0.99 and -0.9979, respectively).

Key words: extracellular polymeric substances, sequencing batch bioreactor, flocculation and settlement, surface properties