The screening involves a filtration on a thin support in steps of 2 to 6 millimeters. In accordance to the step’s established size, the head loss will vary from 0,5 to 2 meters and the following performances can be reached:

• BOD5 reduction: 10-15 %
• SS reduction: 15-25 %
• Sands reduction: 10-80 %

Stainless steel is normally used in production processes:

The most common screens are:

Self -cleaning static screens

Self -cleaning static screens formed by a grid of horizontal bars made of stainless steel, that are straight or curved, with a triangular section. Water is distributed in the upper part of the grid, whose inclination to the horizontal decreases steadily at angles of approximately 65° to 45°. In that way, the effects of separation, draining and removal of solid matter are reached.

Rotary screens

Rotary screens have a cylindrical grid, formed by stainless steel bars and with a trapezoidal section, with a horizontal shaft that slowly rotates. The retained matter is recovered through a fixed scraper and then it is evacuated.

Wedge-shaped profile screens

Wedge-shaped profile screens are formed by a cylindrical drum installed in a container or in a channel, with an inclination of 35°. Water enters the drum in a frontal way and the solids are retained in the mesh. The cleaning system starts the process when the water reaches a difference in height above and below the screen. The drum starts to rotate, it takes the waste to the upper part and makes it fall in a hopper placed in the center of the drum through pressurized water and a brush. Eventually, a worm screw transports the solids from this place to the extraction tube. Generally, a hydraulic press system for wastes is integrated into this screen.

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