Bacterial lectins are carbohydrate-binding proteins that are involved in bacterial adhesion and aggregation. In order to investigate if lectins are involved in floc formation of activated sludge, Hemaagultination (HA) and HA inhibition assays were conducted on extracellular polymeric
substances (EPS) extracted from activated sludges. Seven sludges from both full-scale and synthetic chemical-fed laboratory activated sludge systems were subjected to extracting EPS and lectin assay. Activated sludge EPS resulted in strong agglutination with trypsin-treated human red blood
cells. While simple monosaccharides failed to exhibit the inhibition on agglutination, several glycoproteins clearly reversed agglutination, indicating that glycoprotein (oligosaccharide)-specific lectins are present in activated sludge. This inhibitory pattern was the same for both the field
and laboratory-grown activated sludges, indicating that these lectins are indigenously generated by activated sludge microorganisms. The major lectin activities were found to be present in a hydrophobic region of EPS. The activities remained unaffected after heat and urea treatment of EPS
but were significantly reduced by the EDTA treatment. These results share similar properties with previously studied pure culture bacterial lectins and support the conclusion that the lectin-mediated bacterial aggregation is one of the mechanisms responsible for activated sludge bioflocculation.
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