Screening equipment are one of the important
equipment used in the water and wastewater treatment plants. They are
used for the purpose of removal of bulk of the non biodegradable matter,
such as plastics, woven materials, pieces of wood, metallic items and
other solids from the water stream. The screening equipment helps in
improving the plant operational efficiency as well as it prevents damage
to other components. Screening equipment require a higher level of
maintenance in comparison to other plant equipment components. It occurs
due to the harsh conditions under which they operate.
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.
