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Ewalt's Primary Screening Systems

Wastewater Screening

Wastewater Screening is the first unit operation in all wastewater treatment plants. Screen is the device used to retain solids found in the influent wastewater to the treatment plant. The main purpose of screening is to remove solid materials that could:

  • Cause damage to other process equipment.
  • Cause reduction in the efficiency of the whole system
  • Contaminate waterways

The materials that are removed using screens are called screenings.

  1. Coarse screen: Coarse screens remove large solids, rags, and debris from wastewater, and typically have openings of 6 mm (0.25 in) or larger. The coarse screen consists of parallel bars, rods or wires, wire mesh or perforated plates with openings generally of circular or rectangular shapes. So it is also called as “barrack” and used to remove coarse solids such as rags and large objects that may clog or cause damage.
  1. Fine screen: Finescreens are used to remove particles that may cause maintenance issues for process equipment and/or operational problems to the treatment process. Typically in smaller treatment facilities, fine screens can be used in place of primary clarification. Fine screen openings typically range from 0.06 to 0.25 inches.
  1. Drum Screen: In this type, the screening or straining medium is mounted on a cylinder that rotates in the flow channel. The wastewater flows into either end of the drum and flows out through the screen outlet with the solids are being collected on this interior or into the top of the unit. Drum screens with a triangle profile are intended for extraction of fine and medium waste solids from domestic and industrial wastewater with their subsequent mechanized unloading into a transporter or a waste bin. The drum screens with triangle profiles are installed directly onto the wastewater supply pipeline
  1. Mechanical screen: It is designed mainly to reduce the operating and maintenance problems and to increase the efficiency of screening. Mechanically cleaned bar Wastewater Screens are classified into four principal types:

A.) Chain driven screens

B.) Continuous belt screen

5. Curved Screen with Mechanical Cleaning: The curved screen with radial mechanical cleaning is installed on civil and industrial wastewater treatment plants and complies with medium and coarse screening requirements. The most frequent application is for the first screening of sewage in channels with considerable water flow. The screen consists of a filtering screen composed of curved bars, through which the sewage passes, joined to a cleaning comb secured at the revolving arm end. The particular alternate motion of the arm allows the equipment installation also in a limited room. The motion is ensured by a gear motor fit on the main shaft.

  1. Basket Screen: A screen basket is a device with openings (6 – 150 mm), generally of uniform size, used to retain or remove suspended or floating solids in the flow stream. The screen basket prevents the solids from passing a given point in a conduit to protect pumps, valves etc. from damage or clogging. The basket screen is raised and lowered in the shaft by manual hoist or automatic gearbox. The basket is guided by two guide rails built into the shaft and four rollers fitted to the basket. After raising, the basket is turned in the horizontal position. Emptying is carried out by hand with a rake.

This solution is perfect solution, simple and effective to remove big solids in pumping station, the main entrance of WWTP,


  • Easy operation and maintenance.
  • Robust and reliable.
  • Easy damping at the top level.
  • Operable at the outdoor conditions.
  • Low maintenance cost.
  • Ease of adaptation in different working conditions.
  • Simple installation
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