Question

A river is the source of water for water supply to a town. Its water is very turbid and polluted. The correct sequence of steps for treating the river water would be

• A. Pre-sedimentation $\rightarrow$ Pre-chlorination $\rightarrow$ Coagulation $\rightarrow$ Sedimentation $\rightarrow$ Filtration $\rightarrow$ Post chlorination
• B. Coagulation $\rightarrow$ Sedimentation $\rightarrow$ Post-chlorination
• C. Coagulation $\rightarrow$ Filtration $\rightarrow$ Sedimentation $\rightarrow$ Post-chlorination
• D. Sedimentation $\rightarrow$ Post-chlorination

Hint:

For highly turbid river water: \[ \boxed{ \text{Pre-sedimentation} \rightarrow \text{Coagulation} \rightarrow \text{Sedimentation} \rightarrow \text{Filtration} \rightarrow \text{Disinfection} } \] Pre-chlorination is often provided before coagulation for polluted surface water.

Answer 1

The Correct Option is A

Concept: Highly turbid and polluted river water requires several treatment stages before it becomes fit for drinking. The treatment sequence removes suspended solids, destroys microorganisms, and improves water quality. The usual sequence is: \[ \boxed{ \text{Pre-sedimentation} \rightarrow \text{Pre-chlorination} \rightarrow \text{Coagulation} \rightarrow \text{Sedimentation} \rightarrow \text{Filtration} \rightarrow \text{Post-chlorination} } \]

Step 1: Purpose of each treatment stage.
• Pre-sedimentation removes coarse suspended matter.
• Pre-chlorination controls algae and bacteria.
• Coagulation destabilizes fine suspended particles.
• Sedimentation removes flocs.
• Filtration removes remaining fine particles.
• Post-chlorination provides final disinfection.

Step 2: Identify the correct sequence. The complete treatment train is \[ \boxed{ \text{Pre-sedimentation} \rightarrow \text{Pre-chlorination} \rightarrow \text{Coagulation} \rightarrow \text{Sedimentation} \rightarrow \text{Filtration} \rightarrow \text{Post chlorination}. } \] Therefore, the correct option is \[ \boxed{(A).} \]