Both. Usually solids are specified as dry solids for the solids content (concentration), and the throughput (mass flow) in wet solids. If designing a dewatering unit capacity is set by the wet solids; the likely degree of thickening is set by the capacity and the initial dry solids. If the initial dry solids content is too high then the dewatering method may provide little improvement. Usually a site trial is done, rather than attempt to assess the details of filterability. a Capillary Suction Time test may be used as a surrogate for a filterability test.

The design of sludge dewatering process is the differ from solid dry weight because the density variation. The dewatering unit how to decide how much water in the fluid. For design of plants where sludge characteristics vary like density sludge blending facilities may be recommended. Sludge dewatering also can be done with centrifuge but in solid designing it is differ.