Usually sludge pretreatment, improved dewatering and dehydration. The most common method is the addition of inorganic salts or polymer coagulant. In addition, elutriation method and heat treatment method. Mechanical dewatering by filtration and centrifugation. Filter is to filter for wet sludge layer (porous material, such as cloth, metal screen) filter, which allows moisture (filtrate) permeability filter layer, dewatered sludge (filter cake) is trapped on the filter. In centrifugation through sludge solid and liquid produced by the specific gravity of different centrifugal tendency to mud-water separation. Filtration equipment, vacuum filter, plate and frame filter presses and belt filter. Continuous vacuum filter into the mud, mud in a row, smooth operation, but larger facilities. Plate and frame filter presses for the chemical commonly used equipment, filter drivers, lower water content of cake, mud, a mud is intermittent, low production rates. Manual operation of plate and frame filter press, labor intensity greatly, mostly switched to automatic operation. Filter is a new type of belt filter, a variety of designs, there are also different according to the principle of (gravity, pressure filtration, capillary water absorption, granulation), but they have a rotating belt, mud, dehydration, or mud. Their complexity and power consumption are similar. Centrifuge horizontal high speed centrifugal dewatering machine, formed by the inner and outer drum, one end of the drum is cylindrical, tapering at the other end. Speed at around 3000 rpm or higher, inner and outer drum has a certain speed difference. Centrifugal dewatering machine continuous production and automation, better sanitary conditions, covers an area of small, but high requirements of sludge pretreatment. Mechanical dewatering method is mainly used for sludge and digested sludge sedimentation tank for the first time. Moisture content of sludge and sludge and dehydration methods. Under normal circumstances, vacuum filter cake moisture content ranging from 60% to 80%, plate and frame filter for 45% to 80%, centrifuge for 80% to 85%.