As equipment starts running, sludge is pushed into the filter cartridge from sludge inlet and then moved to sludge cake outlet under the screw thrust of the helical blades. The center part is filter cartridge, which is composed of fixes ring, moving ring and screw shaft. The front part is thickening zone, the following part is dewatering zone. Because space among helical blades gradually gets smaller, increasing the pressure on sludge. The waster gradually is squeezed out from those small gaps between fixed ring and moving ring because of pressure difference. With automatic cleaning function, filter cartridge well protected from blocking. Last step, the sludge cake is pushed by helical axis to outlet after being fully dewatered.