The correct option is (c).
Explanation
Wastewater treatment involves a series of physical, chemical, and biological processes designed to remove contaminants from water. The treatment process is generally divided into preliminary, primary, secondary, and tertiary stages. Bar screens are an essential component of the preliminary treatment phase.
Statement-wise Analysis:
- Statement 1 is Incorrect. A bar screen is a mechanical/physical filter, not a chemical one. It consists of vertical bars spaced at specific intervals to physically block debris. It does not involve chemical reactions to neutralize acidity or alter the pH of the wastewater. Chemical neutralization, if required, occurs in separate unit operations.
- Statement 2 is Correct. The primary function of a bar screen is to intercept and remove large floating solids and gross debris such as rags, plastic packets, napkins, cans, and sticks. Removing these items is crucial to prevent them from clogging pipes or damaging pumps and other downstream mechanical equipment.
- Statement 3 is Correct. Screening is typically the first major unit operation in a wastewater treatment plant (WWTP). It precedes other preliminary steps like grit removal and primary sedimentation. By removing large objects at the very beginning, the efficiency and safety of the subsequent treatment processes are ensured.
Key Takeaway:
Bar screens are physical filtration devices used in the preliminary stage of wastewater treatment to remove large solid debris, thereby protecting downstream machinery from damage and clogging.