Prediction of full-scale dewatering results of sewage sludges by the physical water distribution.

The dewaterability of sewage sludge can be described by the total solids concentration of the sludge cake and the polymer-demand for conditioning. The total solids concentration of the sludge cake depends on the physical water distribution. The various types of water in sewage sludge are mainly distinguished by the type and the intensity of their physical bonding to the solids. In a sewage sludge suspension four different types of water can be distinguished. These are the free water, which is not bound to the particles, the interstitial water, which is bound by capillary forces between the sludge flocs, the surface water, which is bound by adhesive forces and intracellular water. Only the share of free water can be separated during mechanical dewatering. It can be shown, that by thermo-gravimeteric measurement of the free water content, an exact prediction of full-scale dewatering results is possible. By separation of all free water during centrifugation the maximum dewatering result is reached. Polymer conditioning increases the velocity of the sludge water release, but the free water content is not influenced by this process. Furthermore it is not possible, to replace the measuring of the water distribution by other individual parameters such as ignition loss.