Screen is the first unit operation in wastewater treatment plant. This is used to remove larger particles of floating and suspended matter .
Mechanical Screen is designed for removal of screenings within wastewater prior to being received by the main treatment process. Removal of such screenings minimizes blockages of downstream treatment processes.
The inlet screen works by a driven mechanism which rotates shaft to lift the screenings out of the inlet channel and discharge them into a separate container via a chute. ‘Screened,’ water then flows forward for further downstream treatment.
Mechanical Screens are designed for small and medium sized wastewater treatment.
Types of Mechanical Screen:
- SCREW SCREEN
- DRUM SCREEN
- BASKET TYPE SCREEN
These screens are intended for medium and small waste solids from effluent channel and recommend to be used at waste water treatment plants. Suitable for effluent channel width from 200 mm to 600 mm. And depth up to 4 meters. The perforated sheets provides high efficiency of filtration and screw is equipped with a brush on its edge to ensure cleaning of screen media in filtration zone. The trash retaining screen is made of stainless steel in the form of perforated sheet / wedge wire screen and have larger area for filtration due to inclination in effluent channel. Waste retained on filtering screen are removed by axially rotating screw conveyor up to waste bin.
These screens are being used for screening of very small size solid waste like food waste, feather / meat trimmings, fibres, hair etc. The complete screens are made from stainless steel and non corrosive material for long service life. The filtering screen is made off wedge wire screen that ensures very fine filtration (up to 0.2 mm) High quality of mesh cleaning is ensured by mounting of non metallic scrapper on drum surface.
BASKET TYPE SCREEN
The screen can be installed in a manhole prior to pumps, the size depending on the in flow rate and depth. The sturdy, stable basket screen retains the floating debris at the sewer outlet. The screen bottom plate is perforated to allow static dewatering of the retained material. When a certain amount of material has accumulated, the screen basket is lifted upwards by an electric chain hoist. The vertical basket movement is supported by a stable carrier and guide rails. These rails are curved in the upper section to ensure partly automatic discharge into a suitable container. While the screenings are transported upwards in the basket, material which could impair the function of downstream pumps is removed by a fall screen supported on guide rollers. Control of the screen can be either manual or electrical.