Extraction and characterisation of extracellular polymers in digested sewage sludge

Abstract

Abstract Five different bacterial extracellular polymer extraction methods were compared on digested sewage sludge. A washing step was necessary to remove and eliminate the slime from the sludge sample, in order to distinguish it from the material more tightly bound to the sludge solids. An ion‐exchange resin method was the most effective and least disruptive of all treatments tested, based on the relatively high extracellular polymer yield and the small amount of cell disruption demonstrated by the fractionation and characterisation of the extracted material. The extracellular polymer extracted contained protein and polysaccharide in a ratio of approximately 3:1, and contributed a relatively small proportion of the total solids in digested sludge. This was comparatively less than is extracted in activated sludge. The ion‐exchange resin method yielded 1% by weight of polysaccharide and 3% of protein, whereas ethanol‐insoluble material accounted for 3.5% of the solids in digested sludge.