Abstract: A screw press apparatus has frames, a screw shaft, an outside tube, a cylindrical screen, a screw blade, a supply pipe, and a cleaning pipe. The screen is fixed between the frames to the outside tube, and has a plurality of fine holes and covers the screw shaft. The screw shaft and the screen define a cylindrical space continuously extending from an upstream region to a downstream region. Raw liquid is fed from the supply pipe via an opening of the screw shaft to the upstream region of the cylindrical space. The cleaning pipe ejects cleaning water onto the screen. Sizes of the fine holes of the screen decrease gradually from the upstream region towards the downstream region.

Abstract: A screw press for dehydrating slurry and comprising an outer screen casing, a screw shaft, a slurry supplying portion, and a driving unit which rotates the outer screen casing and the screw shaft. The driving unit rotates the screw shaft in one rotational direction and the outer screen casing in the opposite rotational direction. The driving unit comprises a transmission for changing the rotational frequency of at least one of the outer screen casings or the screw shaft. It is possible to have a high dehydrating effect by rotating the outer screen casing in the opposite rotational direction of the screw shaft at a predetermined rotational frequency.