Abstract
Extracellular polymer (ECP) formation and the effect on the surface charge of anaerobic sludge was investigated using each sludge which degraded glucose, propionate, butyrate, or acetate as a single organic substrate. The effect of ECP accumulation on surface charge of the sludges was also discussed in relation to sludge flocculation.
ECP contents in sludge were measured with time during each substrate degradation test using glass vials. The accumulation ratio of ECP-protein exceeded that of ECP-carbohydrate for all cases. The highest accumulation ratio was observed for the glucose degradation test. The calculation from COD balance on substrate revealed that several percents of the substrate utilized for growth was taken to form ECP. As more ECP was accumulated, the sludge surface was more negative in charge except the case of acetate. The increasing negative charge could be neutralized by added divalent cations such as calcium to promote floculation of anaerobic sludges.
