Question

The role of slow sand filters in water treatment facilities is:

• A. To remove water borne microbes upto a set standard.
• B. To remove excess ammonia present in the polluted water
• C. To evaluate the microbiological characteristics of water.
• D. To neutralize the increased pH of the water.

Hint:

The key to understanding slow sand filters is the "schmutzdecke" – the "dirty layer" on top. This biological layer is what "eats" the bad microbes. So, the main job of the filter is biological purification, i.e., removing microbes.

Answer 1

The Correct Option is A

Step 1: Concept Overview:
Slow sand filtration, a centralized water purification method, primarily functions in water treatment to achieve a specific goal.
Step 2: Detailed Explanation:


Slow sand filters purify water by slowly passing it through a fine sand bed.

Purification relies heavily on a biological layer called the schmutzdecke, not just physical straining.

The schmutzdecke, a gelatinous matrix of bacteria, fungi, protozoa, rotifera, and algae, drives most of the purification.

Microorganisms within the schmutzdecke trap, consume, and outcompete pathogenic microbes (bacteria, viruses, and protozoan cysts) in the water.

Consequently, slow sand filters excel at removing waterborne microbes, often reducing turbidity and microbial counts by over 99\%. This ensures the water meets safe drinking standards.

While some ammonia removal via nitrification may occur, it is secondary (B). Filters are for treatment, not evaluation (C), and do not significantly alter pH (D).

Step 3: Conclusion:
The main function of slow sand filters is to eliminate waterborne microbes, making water safe to drink.