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

The dewaterabilty of sewage sludge can be described by the total solids con centration 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 disti nguished by the type and the intensity of their physical bonding to the sol ids. In a sewage sludge suspension four different types of water can be dis tinguished. These are the free water, which is not bound to the particles, the interstitial water, which is bound by capillary forces between the slud ge flocs, the surface water, which is bound by adhesive forces and intracel lular water. Only the share of free water can be separated during mechanica l dewatering. It can be shown, that by thermo-gravimeteric measurement of t he free water content, an exact prediction of full-scale dewatering results is possible. By separation of all free water during centrifugation the max imum dewatering result is reached. Polymer conditioning increases the veloc ity of the sludge water release, but the free water content is not influenc ed by this process. Furthermore it is not possible, to replace the measurin g of the water distribution by other individual parameters such as ignition loss.