Case Study:

In a village near Pune, many families stopped using firewood for cooking after a community biogas plant was installed. Every morning, villagers collect nearly 500 kg of kitchen waste, vegetable peels, leftover food, and animal dung and put it into a large underground tank called a digester. Inside the tank, oxygen is absent, and microorganisms slowly break down the waste. After a few days, a gas mixture rich in methane starts forming.

While this process happens in a digester, it’s fascinating to see how it compares to other systems. You can explore how do biogas and hydroelectric power plants work to see the mechanical side of energy generation.

The plant produces around 25 cubic metres of biogas daily, which is supplied through pipes to nearby houses for cooking. Earlier, families spent about ₹700–₹900 every month on LPG cylinders or firewood. After using biogas, their fuel expenses reduced greatly, and the smoke inside the kitchens also decreased. The leftover slurry from the plant is used as natural manure in farms.

During the rainy season, however, villagers noticed that gas production became slower. On investigation, they found that lower temperatures reduced the activity of microorganisms inside the digester. To solve this problem, the digester was covered properly to maintain warmth.

This sensitivity to the environment is why we are shifting away from traditional fuels. If you're curious about the bigger picture, check out this breakdown of fossil fuels vs renewable sources to see which one truly holds the key to our future.

This system shows how biomass, such as vegetable waste and animal dung, can become a useful renewable source of energy. Instead of throwing waste into open areas where it causes foul smell and pollution, the waste is converted into clean Biogas that can be used every day for cooking and farming purposes.

Biogas is just one piece of the puzzle. To understand the full spectrum of green tech, take a look at solar, wind, and hydropower, and why they are vital for the planet. For a contrast in scale, you might also want to learn how a thermal power plant works or the complex science behind nuclear energy.

 Ready to test your knowledge?   Before diving into these questions, you can sharpen your skills with our Class 10 Physics worksheets. If you're prepping for exams, try timing yourself with an unsolved practice paper or reviewing the ideal answering style with a solved practice paper.

CASE-BASED QUESTIONS

 MCQ 

Q1. Which gas present in biogas burns easily and provides most of the heat energy?
A. Oxygen
B. Nitrogen
C. Methane
D. Carbon dioxide

Q2. Why is the slurry left after biogas production useful for farmers?
A. It increases plastic formation in soil
B. It acts as a natural manure
C. It removes oxygen from soil
D. It reduces crop growth

 Assertion - Reason 

Q3. Assertion (A): Biogas plants help in reducing environmental pollution.
Reason (R): Kitchen waste and animal dung are converted into useful fuel instead of being dumped openly.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.

 Application-Based 

Q4. The villagers observed that gas production reduced during winter and rainy days. What is the most suitable scientific reason for this change?

Q5. A family uses biogas instead of firewood for cooking. Mention one environmental benefit and one health benefit of this change.

Q6. Why is biogas considered a renewable source of energy even though it is produced from waste materials?

 Data/Logic-Based 

Q7. A biogas plant produces 25 cubic metres of biogas daily. If one family requires 5 cubic metres of biogas per day for cooking, how many families can receive gas from the plant daily?

ANSWER KEY WITH EXPLANATION

A1. C. Methane
Explanation: Methane is the main combustible gas in biogas. According to NCERT, methane burns with a clean flame and releases heat energy useful for cooking.

A2. B. It acts as a natural manure
Explanation: The leftover slurry contains nutrients useful for plants. NCERT mentions that the residue from biomass plants can be used as organic manure.

A3. A. Both A and R are true, and R is the correct explanation of A.
Explanation: Biogas plants reduce pollution because waste materials are scientifically managed and converted into fuel instead of rotting in open spaces.

A4. Lower temperatures slow down the activity of microorganisms responsible for decomposition inside the digester, reducing biogas production.

A5. i) Environmental benefit: Reduced cutting of trees and less air pollution.
ii) Health benefit: Reduced smoke inside kitchens, leading to fewer breathing problems.

A6. Biogas is renewable because biomass such as plant waste and animal dung can be produced again and again naturally.

A7. 5 families
Calculation: 25 ÷ 5 = 5
Explanation: The total gas produced is divided by the daily gas requirement of one family.

HOTS EXTENSION QUESTIONS

Q1. If plastic waste is accidentally mixed regularly with kitchen waste in a biogas plant, predict how it may affect gas production and the environment.

Q2. A city wants to reduce LPG consumption by setting up large biogas plants near vegetable markets. Suggest two factors the city should consider before installing the plants.