Question

Choose the correct order of sequence for modern sewage treatment:
• [A.] Primary sedimentation
• [B.] Screening
• [C.] Grit removal
• [D.] Sludge Disposal Choose the correct answer from the options given below:

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

Hint:

The preliminary sewage treatment sequence is: Screening $\rightarrow$ Grit removal $\rightarrow$ Sedimentation $\rightarrow$ Sludge disposal.

Answer 1

The Correct Option is D

Concept: Modern sewage treatment involves a sequence of processes used to remove solid waste, suspended particles, and harmful substances from wastewater before disposal. The important preliminary and primary treatment steps are:
• Screening
• Grit removal
• Primary sedimentation
• Sludge disposal These steps ensure proper purification and safe disposal of sewage.

Step 1: Understand Screening.
Screening is the first step where large floating materials such as plastics, cloth, sticks, and debris are removed from sewage. Hence, the process begins with: \[ B \]

Step 2: Understand Grit removal.
After screening, grit chambers remove sand, gravel, and other heavy inorganic particles. Thus, the next step is: \[ C \]

Step 3: Understand Primary sedimentation.
In primary sedimentation tanks, suspended organic solids settle down to form sludge. Thus, the next step is: \[ A \]

Step 4: Understand Sludge disposal.
Finally, the collected sludge is treated and disposed of safely. Thus, the final step is: \[ D \]

Step 5: Determine the correct sequence.
The correct order is: \[ B \rightarrow C \rightarrow A \rightarrow D \] Therefore, the correct answer is: \[ \boxed{(D)\ B, C, A, D} \]