A screw press can be used in place of a belt press, centrifuge, or filter presses. It is a simple, slow moving device that accomplishes dewatering by continuous gravitational drainage. Screw presses are often used for materials that are difficult to press, for example those that tend to pack together. The screw press squeezes the material against a screen or filter and the liquid is collected through the screen for collection and use. Chemical conditioning is required prior to the slurry reaching the press.