All water treatment plants and wastewater treatment plants have some type of preliminary screening machines and devices, used for the removal of debris and large particles. Some plants use separate pieces of equipment for the removal of debris and grit from the influent while some combines them into one unit, offering a saving of equipment, space, and cost.
The selection of the type of screening equipment should be based on the variety and amount of material that is expected to enter the plant through the influent water. The purpose of the screen is to accept influent water containing a mixture of particles of different sizes. The screens separate the water into two parts, one is underflow that is passed the screen and other is overflow that is rejected by the screen. A perfect screen would separate the influent water into two parts such that the smallest particle in the overflow would be just larger then the largest particle in the underflow.
What is Screening?
In water treatment plants, screening is the process of retention of particles by a grid or longitudinal bars having smaller openings than the particles to be removed. It is the method of separating particles according to the size. The smaller particles are removed by screens with small openings while bigger particles need equipment with larger openings.
Types of Screening Equipment
Screening equipment have a wide range of forms and ranges from microscreens to trash racks. The designing of screens involve selection of materials, mechanical appurtenances, structural calculations, hydraulics, conveyance of screening wastes, disposal of screenings and other processes.