Identify the incorrect statement w.r.t. biogas plant

Options

A. It consists of a concrete tank, 10-15 feet dep in which bio-wastes are collected and a slurry of dung is fed
B. A floating cover is placed over the slurry, which keeps on rising as the gas is consumed in the tank
C. It has an outlet, which is connected to pipe to supply biogas to nearby houses
D. The spent slurry is removed and may be used as fertiliser

Answer

To identify the incorrect statement regarding biogas plants, we will analyze each statement provided.

### Step-by-Step Solution:

1. **Understanding Biogas Plants**:
- Biogas plants are biological setups designed to produce biogas through the anaerobic digestion of organic materials such as bio-waste and dung.

2. **Evaluating the First Statement**:
- "It consists of a concrete tank 10 to 15 feet deep in which bio-waste are collected and slurry of the dung is fed."
- This statement is correct. Biogas plants typically have a concrete tank of this depth to facilitate the collection of bio-waste and dung slurry.

3. **Evaluating the Second Statement**:
- "A floating cover is placed over the slurry which keeps on rising as the gas is consumed in the tank."
- This statement is incorrect. The floating cover does rise as gas is produced, not consumed. The gas production increases as the anaerobic digestion process occurs, leading to the rising of the cover.

4. **Evaluating the Third Statement**:
- "It has an outlet which is connected to the pipe to supply biogas to nearby houses."
- This statement is correct. Biogas plants are designed with an outlet for biogas to be piped to nearby locations for use.

5. **Evaluating the Fourth Statement**:
- "The spent slurry is removed and may be used as fertilizer."
- This statement is also correct. The remaining slurry after gas production can be used as a nutrient-rich fertilizer in agriculture.

6. **Conclusion**:
- After evaluating all statements, the incorrect statement is the second one about the floating cover. It should state that the cover rises as gas is produced, not consumed.

### Final Answer:
The incorrect statement regarding biogas plants is: "A floating cover is placed over the slurry which keeps on rising as the gas is consumed in the tank."

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