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 relationships 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 estimate than those derived from extraction-based methodologies. The relationship between total ECPA concentration and digested sludge dewaterability was dependent on digester feed composition, suggesting that specific ECPA biochemical characteristics are more significant than total concentration as an influence on dewaterability. The influence of the soluble/colloidal fraction of the total ECPA on digested sludge dewaterability was consistently adverse, but from a full-scale dewatering perspective was insignificant.