Abstract: Water is recovered from sludge, such as from sewage treatment plants, or wood processing or food processing industries, by either electrically ionizing the sludge or treating the sludge with ultrasound, and then adding coagulant to the sludge to effect coagulation. Prior to or substantially simultaneously with coagulation, the sludge is vigorously mixed, and then the sludge is flocculated and water is mechanically removed from the flocculated sludge. Water removal can be optimized by adding news print pulp, or a tenside, to the sludge just prior to mechanical removal. Free water may also be removed by filtering just prior to mechanical removal, and mechanical removal can take place in two consecutive stages, first a low pressure (1-5 bar) stage to produce a cake, and then the cake is broken up and subjected to a high pressure (5-60 bar) stage.