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 efficiency of the whole system
• Contaminate waterways

Screens are generally classified into three based on the size of their openings in the screening element and mechanism of removal.

• Coarse screens
• Fine screens
• Micro screens

Coarse screens have a clear opening ranging from 6 to 150 mm (0.25 t0 6 in). Coarse screen consists of parallel bars, rods or wires, wire mesh or a perforated plate with openings generally of circular or rectangular shapes. So, it is also call as “bar rack” and used to remove coarse solids such as rags and large objects that may clog or cause damage to other appurtenances. Based on the Wastewater Screening method used to clean them, coarse screens are classified into two:

• Hand cleaned screens
• Mechanically cleaned screens