Screening is the first unit operation used in wastewater treatment plants (WWTPs). Screening removes objects such as rags, paper, plastics and metals to prevent damage and clogging of downstream equipment, piping, and appurtenances. 

TYPES OF SCREENING:

1. Coarse screen - Typical opening sizes (space between bars) for a coarse screen are between 20 and 25
2. Fine screen - Typical opening size (space between bars) for fine screen is 10 mm.