The correct option is (c) 1 and 3 only
Explanation
Bar screens are mechanical filtration devices used in the preliminary stage of wastewater treatment plants (WWTPs). They serve as the first unit operation to intercept large solid debris contained in raw sewage.
Statement-wise Analysis:
- Statement 1 is Correct: A bar screen is a physical barrier, typically consisting of parallel bars or perforated plates, placed at the inlet (headworks) of the treatment plant. It filters the influent wastewater before it undergoes grit removal or primary sedimentation.
- Statement 2 is Incorrect: The specific purpose of a bar screen is to trap and remove large objects such as cans, plastic packets, rags, sticks, and stones. It does not allow these objects to pass through; instead, it separates them from the water flow to be collected and disposed of separately.
- Statement 3 is Correct: By removing large and abrasive solids, bar screens prevent the clogging of pipes, channels, and valves. Crucially, they prevent physical damage to downstream mechanical equipment, particularly pumps and aerators, which can be easily jammed or broken by coarse debris.
Key Takeaway:
Bar screens constitute the preliminary treatment phase in wastewater management, essential for protecting downstream infrastructure and mechanical assets from clogging and damage caused by coarse solids.