Abstract
Abstract
Different extracellular polymeric substances (EPS) fractions, including supernatant, slime, loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), have different binding characteristics to sludge flocs and thus different influences on sludge dewaterability and effluent quality. In this study, EPS removal and readdition tests as well as a flocculating test of kaolin clay solution were conducted to explore their binding characteristics. Results showed that removal of different EPS fractions from sludge flocs resulted in a decrease of particle size and an increase in zeta potential; readdition of supernatant and slime fractions to sludge flocs restored the particle size and zeta potential to their initial status, however, readdition of LB-EPS and TB-EPS fractions to sludge flocs did not allow particle size and zeta potential to return to the initial level. Similarly, variations of sludge dewaterability also followed similar trends. Extracellular polymers in the supernatant and slime fractions were likely bound to sludge flocs by physical adsorption, whereas their distributions in the TB-EPS fraction were probably bound to sludge flocs by chemical bonds. Based on the binding characteristics, good effluent quality can be achieved by the control of operating conditions.
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