Question

Arrange the following steps, used in a typical water treatment plant, starting from first to last:
A. Rapid Mixing and Coagulation
B. Flocculation
C. Primary Sedimentation
D. Filtration
E. Disinfection

• A. D, A, B, C, E
• B. A, B, C, D, E
• C. C, A, B, E, D
• D. C, A, B, D, E

Hint:

Think of water treatment as a "size-exclusion" funnel: Start with the biggest dirt (Sedimentation), glue the small dirt together (Coagulation/Flocculation), strain the leftovers (Filtration), and finally kill the germs (Disinfection).

Answer 1

The Correct Option is D

Concept: Water treatment involves a sequence of physical and chemical processes designed to remove impurities and pathogens. The goal is to move from the removal of large, heavy particles to the removal of microscopic contaminants and biological threats.

Step 1: Initial Physical Removal.
The process typically begins with Primary Sedimentation (C). In this stage, water is held in a quiet basin, allowing heavy solid particles to settle to the bottom by gravity before any chemicals are added.

Step 2: Chemical Destabilization and Aggregation.
Next is Rapid Mixing and Coagulation (A), where chemicals (coagulants) are quickly stirred into the water to neutralize the charges of small suspended particles. This is followed by Flocculation (B), a gentle mixing process that encourages these neutralized particles to collide and form larger, heavier clumps called "floc."

Step 3: Final Polishing and Safety.
The water then passes through Filtration (D), often using layers of sand or activated carbon, to catch any remaining fine particles or floc. The final essential step is Disinfection (E), where chlorine or UV light is used to kill any remaining bacteria, viruses, or parasites, making the water safe for consumption.