The correct option is (c) 2 and 3 only.
Explanation
In a wastewater treatment plant (WWTP), water undergoes physical, chemical, and biological processes to remove contaminants. "Clarified water" refers specifically to the effluent obtained after the sedimentation process, where physical separation of solids occurs.
Statement-wise Analysis
- Statement 1 is Incorrect. Water obtained immediately after passing through bar screens is not called clarified water. Bar screens are part of the preliminary treatment used to remove large objects like rags, sticks, cans, and plastic packets. The water at this stage still contains grit, sand, and settleable organic solids.
- Statement 2 is Correct. Clarified water is the output of the primary sedimentation tank (clarifier). In this tank, heavy solids (sludge) settle to the bottom, and floatable impurities like oil and grease are skimmed off the top. The relatively clear water between these layers is termed clarified water.
- Statement 3 is Correct. While clarified water is clearer than raw sewage, it is not yet safe for discharge or consumption. It still contains dissolved organic matter, some suspended impurities, and pathogens. Consequently, it requires further processing, such as biological treatment (aeration) and disinfection (chlorination), before release.
Key Takeaway
Clarified water is the product of the sedimentation process in a treatment plant, characterized by the removal of settleable solids and floatable scum, but it still requires secondary and tertiary treatment to remove dissolved pollutants and pathogens.