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Two bacterial stains were isolated from the activated sludge and identified as Leucobacter sp. and Alcaligenes faecalis by 16S rDNA
sequencing. Pure cultures of these two strains, representing well or poorly settled bacteria, were used to investigate the mechanism of
bioflocculation in activated sludge. Based on the analyses of the characteristics of cells hydrophobicity, -potential, flocculation ability
and extracellular polymeric substance (EPS) composition under di erent growth stages, it was found that the ratio of cell EPS protein
had the highly influence on -potential and hydrophobicity, which were important factors to bioflocculation. Cellulase and Proteinase
K could destroy the extracellular biopolymer and resulted in a decrease in the hydrophobicity and -potential. However, in our study,
the flocculation characteristics exhibited di erently in relation to cellulase and Proteinase K. Flocculation of cells treated with cellulase
and Proteinase K decreased sharply, and then recovered quickly in cellulase treatment, while cells treated with Proteinase K showed no
sign of recovery. This reveals that the presence of protein in extracellular biopolymer plays an important role to the bioflocculation of
cells.
