Addition of charcoal to the filter bed of sand during water treatment for township supply is to?

Analysis

This question tests your knowledge of the water treatment process, specifically the function of different layers in a filtration bed. You are asked to identify the specific purpose of adding charcoal (activated carbon) to a sand filter.

Concept: Water Treatment Processes

In a municipal water treatment plant, water passes through several stages to make it safe for consumption:

1. Sedimentation: Large particles settle at the bottom.
2. Coagulation/Flocculation: Chemicals like alum are added to clump smaller particles together.
3. Filtration: Water passes through layers of sand and gravel to remove remaining suspended solids.
4. Activated Charcoal (Carbon) Treatment: This is often added to the filter bed or used as a separate stage. Activated charcoal has a highly porous structure with a very large surface area. It acts as an adsorbent, meaning it traps molecules on its surface.

Step-by-Step Solution

• Step 1: Analyze the options provided. • A (Prevent goiter): This is achieved by adding iodine to water or salt, not by charcoal. • B (Prevent tooth decay): This is achieved by adding fluoride to the water supply. • C (Remove odour): Charcoal is well-known for its ability to adsorb gases and organic compounds that cause unpleasant tastes and smells in water. • D (Kill germs): This is the role of disinfectants like chlorine or ozone.

• Step 2: Evaluate the role of charcoal. Because charcoal is porous, it effectively adsorbs dissolved organic impurities, which are the primary sources of bad taste and foul odors in water.

• Step 3: Conclusion. Since charcoal is an adsorbent, its primary function in the filter bed is to remove unpleasant odors and tastes.

Correct Answer

The correct option is C.

Exam Tip

Think of charcoal as a "sponge for smells." Whenever you see "charcoal" or "activated carbon" in a Chemistry question regarding water treatment, immediately associate it with adsorption and the removal of taste/odour. Don't confuse it with chlorine, which is for sterilization (killing germs).