Question

During primary treatment in sewage treatment plants, which of the operation initially takes place?

• A. Removal of organic matter
• B. Removal of fine suspended particles
• C. Removal of floating materials
• D. Removal of harmful bacteria

Hint:

Sewage Treatment Logic:
- Primary = Physical (Screens and Settling).
- Secondary = Biological (Microbes eating organic matter).
- Tertiary = Chemical (Chlorine/UV to kill bacteria).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks about the very first step or operation performed during the "primary treatment" phase of a sewage treatment plant (STP).

Step 2: Detailed Explanation:

• Primary Treatment: This is a physical process designed to remove large solid materials from the sewage.

• Sequential Operations:
- Screening: The very first step involves passing sewage through bar screens. This is intended for the removal of floating materials like plastic bottles, rags, sticks, and paper. If not removed, these could damage pumps and clog pipes later in the system.
- Grit Removal: Next, the sewage flows into grit chambers where heavier inorganic solids (sand, gravel) settle down.
- Primary Sedimentation: The water then goes to a primary settling tank where fine suspended organic particles settle as sludge.

• Other Options: Removal of organic matter (A) and harmful bacteria (D) are primarily biological and chemical processes that occur during secondary (biological) and tertiary (disinfection) treatment phases, respectively.

Step 3: Final Answer:
The initial operation in primary treatment is the removal of floating materials via screening.