Question

The filters which produce water of higher bacteriological quality is

• A. Slow sand filter
• B. Rapid sand filter
• C. Pressure filter
• D. Dual media filter

Hint:

Remember:
• Slow sand filter $\rightarrow$ Best bacteriological quality.
• Rapid sand filter $\rightarrow$ Higher filtration rate but requires disinfection.
• Schmutzdecke is the biological layer responsible for purification.

Answer 1

The Correct Option is A

Concept: Slow sand filters remove suspended impurities as well as pathogenic microorganisms through mechanical straining, adsorption, and biological action. A biological layer called the Schmutzdecke develops on the top of the filter bed, which is mainly responsible for the excellent bacteriological purification.

Step 1: Understand the filtration mechanism. The Schmutzdecke layer removes bacteria by biological action and adsorption. Hence, slow sand filters produce water of very high bacteriological quality.

Step 2: Compare with rapid sand filters. Rapid sand filters mainly remove suspended solids and require chlorination for effective disinfection. Therefore, \[ \boxed{\text{Slow sand filters produce water of the highest bacteriological quality}.} \] Hence, the correct option is \[ \boxed{(A)\;\text{Slow sand filter}.} \]