The supernatant left after sedimentation of sewage water during primary treatment is known as

Options

A. affluent
B. flocs
C. sludge
D. effluent

Answer

To solve the question regarding the supernatant left after sedimentation of sewage water during primary treatment, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Process of Sewage Treatment**:
- Sewage treatment consists of multiple stages, primarily divided into primary and secondary treatments. The primary treatment involves physical processes to remove solid waste from sewage.

2. **Identify the Components of Primary Treatment**:
- During primary treatment, sewage water undergoes sedimentation. This process allows heavier solid particles to settle at the bottom, forming a layer of sludge.

3. **Define the Terms**:
- **Sludge**: This is the solid waste that settles at the bottom during sedimentation. It consists of organic and inorganic materials.
- **Supernatant**: This is the clear liquid that remains above the settled sludge after sedimentation.

4. **Determine the Correct Term for the Supernatant**:
- The supernatant left after sedimentation in the primary treatment of sewage is referred to as **effluent**. This is the liquid that is discharged from the treatment process.

5. **Review the Options**:
- A) Effluent - This is the correct answer as it refers to the liquid remaining after sedimentation.
- B) Phlox - This is incorrect; it does not relate to sewage treatment.
- C) Sludge - This is incorrect as it refers to the settled solids, not the supernatant.
- D) Effluent - This is the same as option A, reinforcing that effluent is the correct term.

6. **Conclusion**:
- Based on the definitions and the process of primary sewage treatment, the supernatant left after sedimentation of sewage water is known as **effluent**.

### Final Answer:
The supernatant left after sedimentation of sewage water during primary treatment is known as **effluent**.