Chemical description of extracellular polymers: Implication on activated sludge floc structure

Activated sludge extracellular polymers (ECP) were extracted either by soni cation or a combination of sonication and cation exchange resin treatment ( CER). The chemical composition of the aqueous extract was investigated by c hromatographic analysis of amino acids and sugars after hydrolysis. Up to 7 0 to 80% of the total organic carbon (TOC) of ECP was characterized. Protei ns were found to be the major constituent of ECP, which was confirmed by py rolysis/GC/MS analysis. Sugar and protein analysis led to complementary inf ormation both on the origin of extracellular material and on sludge flee st ructure. The monosaccharide composition in ECP and sludge allowed the propo sal of different origins for extracellular polysaccharides. The predominanc e of proteins in ECP underlined their key role in the flee structure, and l ed to hypotheses on their origin. Proteins were better extracted than sugar s when the CER extraction was combined with sonication. This supposed that proteins are more involved than sugars in electrostatic bonds with multival ent cations. Electrostatic bonds were found to be uniformly distributed in the flee and closely combined with hydrophobic bonds. About 25% of ECP amin o acids were negatively charged and 24% exhibited hydrophobic properties, h ighlighting the specific role of proteins in the flee structure. (C) 1998 P ublished by Elsevier Science Ltd. All rights reserved.