Activated sludge is
A. formed after sequential filtration and sedimentation in primary setting tank.
B. bacterial flocs settings after secondary treatment.
C. Passed into anaerobic sludge digester.

Options

A. Only (A) is incorrect
B. Only (A) and (C) are incorrect
C. Only (B) and (C) are incorrect
D. (A) , (B) and (C) are incorrect

Answer

To solve the question regarding activated sludge, we need to analyze each statement provided:

1. **Statement A**: "Activated sludge is formed after sequential filtration and sedimentation in primary settling tank."
- This statement is **incorrect**. In the primary settling tank, the sludge that is formed is known as primary sludge, not activated sludge. Activated sludge is produced during the secondary treatment process, where biological treatment occurs.

2. **Statement B**: "Activated sludge is bacterial flocs settings after secondary treatment."
- This statement is **correct**. Activated sludge consists of a mixture of bacteria and organic matter that is formed during the secondary treatment of wastewater. In this process, bacteria flocculate (clump together) and help in the breakdown of organic material in the wastewater.

3. **Statement C**: "Passed into anaerobic sludge digester."
- This statement is also **correct**. After the secondary treatment, the activated sludge can be sent to an anaerobic digester where anaerobic bacteria decompose the organic matter, reducing the volume of sludge and producing biogas.

Based on the analysis of the statements:
- **Correct Answer**: The correct statements are B and C, while statement A is incorrect.

### Final Answer:
**B and C are correct; A is incorrect.**