Denitrification, activity of bacterial floes, and growth of a filamentous bacterium in relation with the bulking of activated sludge

Floe formation by cells of Zoogloea ramigera, strain I-16-M, was observed after resuspending pre-cultivated cells in fresh medium. It was considerably stimulated by the additional supply of NaCl or Na2HP04/NaH2P04. Stimulated floe formation occurred also at an increased C/N ratio of the medium in which the pre-cultivated cells were resuspended. The growth phase of the cells had no effect on floe formation when measuring the process in suspensions of equal cell density. Metabolites, inhibiting floe formation, were found to be excreted during the pre-cultivation of strain I-16-M in a complex medium. Enzymatic treatment with cellulase completely dispersed "young floes"; addition of toluol caused a partial dispersion. "Aged" floes were more resistant towards the dispersing agents.