HYDROPHOBICITY OF ACTIVATED-SLUDGE FLOCS AND LABORATORY-GROWN BACTERIA

The cohesion of activated sludge biological flocs is controlled by the ratio between hydrophilic exopolymers in which bacteria are embedded and hydrophobic interactions. As shown in this study highly hydrophobi c bacteria coexist in the flocs with highly hydrophilic bacteria which seem to release large quantities of exopolymers (polysaccharides, DNA , proteins...). Addition to the activated sludge of easily assimilable nutrients such as glucose does not change the hydrophobicity of bacte ria but increases both exopolymer production and the sludge volume ind ex. The environmental conditions and the bioavailability of nutrients may considerably shift the hydrophilic/hydrophobic balance. Moreover e xperiments carried out with four different strains to fourteen isolate d from activated sludges have shown that a few strains (variable types ) have quite considerable possibilities of hydrophobic property variat ions in the course of growth.