Mechanical sludge dewatering serves for further reduction of sludge volume and mass by removal of sludge water from interstices between sludge particles. A more or less firm sludge cake is produced.

Prior to its dewatering, fed sludge is first flocculated by addition of polymers. The choice of polymer and its dosage as well as rapid and intensive mixing are decisive for optimal floc formation and dewatering results.

Filtering presses require a sludge that can take pressure and that does not blind the filter medium. Filtering presses are unsusceptible to sand and other mineral solids.

Decanting centrifuges are used if the sludge solids have a considerably higher specific weight than water. However, centrifuges are susceptible to abrasion by sand and other mineral solids.