Nominal Diameter of Floc Related to Oxygen Transfer

Nominal diameters of activated sludge floc have been determined on samples obtained from eight activated sludge plants. These plants ranged in size from a large conventional plant to a small contact stabilization package plant. To obtain dry densities of the floc, pycnometer analyses were made on activated sludge samples. The wet densities, dry weights, and number of floc per unit volume were also measured to yield average wet floc volumes. By assuming the floc particles were spherical, the nominal diameters were calculated to range from 21 to 115 microns. These nominal diameters were then used to estimate the range of limiting oxygen concentrations to be expected in activated sludge plants.