UPSC Prelims 2011 Q7: Science & Technology – Energy & Environment
Microbial fuel cells are considered a source of sustainable energy. Why?
1. They use living organisms as catalysts to generate electricity from certain substrates.
2. They use a variety of inorganic materials as substrates.
3. They can be installed in waste water treatment plants to cleanse water and produce electricity.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (c) 1 and 3 only
Explanation
Microbial fuel cells as sustainable energy
A microbial fuel cell (MFC) uses living microbes to break down organic matter and generate electricity directly from that chemical reaction.
| Statement | Verdict | Reason |
|---|---|---|
| 1. They use living organisms as catalysts to generate electricity from certain substrates | Correct | Bacteria act as biocatalysts, oxidising organic matter and releasing electrons |
| 2. They use a variety of inorganic materials as substrates | Incorrect | They run on organic matter (wastewater, sugars, organic waste), not inorganic material |
| 3. They can be installed in waste water treatment plants to cleanse water and produce electricity | Correct | Bacteria digest organic pollutants in sewage while the device generates power |
Why it is 'sustainable':
| Point | Detail |
|---|---|
| Fuel source | Waste organic matter, not fossil fuel |
| Dual benefit | Cleans water and produces electricity at the same time |
| Scale today | Mostly pilot/research stage, low power output |
Answer: (c) 1 and 3 only.
Why each option is right or wrong
- (a) Incorrect. Statement 3 is also true; MFCs are used in waste water treatment.
- (b) Incorrect. Statement 2 is false, and statement 1 (living organisms as catalysts) is a correct, core feature.
- (c) CORRECT. Microbes as catalysts and use in waste-water treatment are both correct.
- (d) Incorrect. Statement 2 is false; MFCs run on organic, not inorganic, substrates.
Key point
Microbial fuel cells: bacteria act as catalysts on organic substrates (not inorganic), generating electricity; usable in waste-water treatment plants.
Remember
Microbial fuel cells: organic substrate, bacteria as catalyst, used in sewage treatment.
Common mistakes
- Confusing organic substrates (sugars, sewage) with 'inorganic materials'.
- Not knowing microbes act as biocatalysts, not just fuel.
- Missing the waste-water treatment application, a frequently tested fact.
Exam tip
Anything 'microbial' or 'bio-' runs on organic matter, never inorganic material.
Sources
- Bruce E. Logan et al. — "Microbial Fuel Cells: Methodology and Technology", Environmental Science & Technology, vol. 40 (2006)
- Bruce E. Logan — Microbial Fuel Cells (Wiley, 2008)