Screwpress
Screw Press in Wastewater Treatment Plants
A Screw Press, also known as a Screw Press Dewatering System, is a mechanical dewatering device used in wastewater treatment plants (WWTPs) to reduce the water content in sludge. It utilizes a slow-rotating screw inside a cylindrical screen to compress and dewater sludge effectively. This system is widely used in municipal and industrial WWTPs for primary, secondary, and digested sludge dewatering.
Working Principle
- Sludge Feeding : Sludge is pumped into the inlet hopper of the screw press.
- Flocculation : A polymer may be added to enhance solid-liquid separation by forming flocs.
- Thickening Zone : Sludge enters the first part of the screw where gravity drainage removes free water.
- Pressing Zone : As the screw rotates, it gradually narrows (due to decreasing pitch and increasing shaft diameter), applying pressure to the sludge.
- Filtration : Water is forced through the surrounding screen while solids are pushed forward.
- Discharge : The dewatered sludge (cake) exits from the end of the screw, while the filtrate (liquid) is collected and typically returned to the headworks.
Benefits of Screw Press Dewatering
Low Energy Consumption
Operates at low speeds (~0.1–1 rpm), significantly reducing power usage compared to centrifuges.
Low Maintenance
Fewer moving parts and low wear result in reduced maintenance costs.
Suitable for Wide Sludge Types
Handles both primary and secondary sludge, including oily or fibrous materials.
Automated Control
Often integrated with PLC systems for automatic start/stop, polymer dosing, and cake discharge.
