EXTRACELLULAR POLYANIONS IN DIGESTED-SLUDGE - MEASUREMENT AND RELATIONSHIP TO SLUDGE DEWATERABILITY

The polyanionic fraction of digested sludge extracellular material was quantified using an in situ dye adsorption method, and the relationsh ips between measured extracellular polyanion (ECPA) concentrations and sludge dewaterability were investigated. Measured ECPA concentrations were 18-30% of the sludge total solids (32-46% of the volatile solids ), when expressed as equivalents of sodium alginate. These values may be an overestimate of the true value, but are likely a more accurate e stimate than those derived from extraction-based methodologies. The re lationship between total ECPA concentration and digested sludge dewate rability was dependent on digester feed composition, suggesting that s pecific ECPA biochemical characteristics are more significant than tot al concentration as an influence on dewaterability. The influence of t he soluble/colloidal fraction of the total ECPA on digested sludge dew aterability was consistently adverse, but from a full-scale dewatering perspective was insignificant. (C) 1997 Elsevier Science Ltd.