Question

Nalgonda technique for defluoridation of water involves the following steps. Arrange them sequentially from first to last step.
A. Addition of two chemicals (lime and alum)
B. Sedimentation
C. Flocculation
D. Filtration
Choose the correct answer from the options given below:

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

Hint:

Remember the standard sequence for water purification by coagulation: 1. Add Chemicals, 2. Mix to form Flocs (Flocculation), 3. Let them Settle (Sedimentation), 4. Separate the clear water (Filtration/Decantation).

Answer 1

The Correct Option is B

Step 1: Understand the Nalgonda Technique. Step 1: The Nalgonda technique is a water treatment method developed in India to remove excess fluoride. It's a process of chemical precipitation.
Step 2: Arrange the steps of the chemical treatment process.
Step 2:

(A) Addition of two chemicals (lime and alum): First, alum (coagulant) and lime (for alkalinity) are added to the water and mixed rapidly.
(C) Flocculation: The water is then stirred gently. The alum reacts with fluoride and alkalinity to form insoluble aluminum hydroxide flocs that trap the fluoride ions.
(B) Sedimentation: The water is allowed to stand without disturbance. The heavy flocs settle at the bottom of the container.
(D) Filtration: Finally, the clear supernatant water is separated from the sludge, often by filtration, to remove any remaining suspended particles.
Step 3: Conclude the correct sequence.
Step 3: The correct sequence of operations is A \(\rightarrow\) C \(\rightarrow\) B \(\rightarrow\) D.