2 marksShort AnswerSection A

What is the main constituent of biogas ? How is biogas obtained from biomass ? Write any two advantages of using this gas.

Q: What is the main constituent of biogas ? How is biogas obtained from biomass ? Write any two advantages of using this gas.

1. **Main Constituent:** The main constituent of biogas is methane ($CH_4$), making up about 75% of its composition. 2. **Obtaining Biogas from Biomass:** Biogas is produced by the anaerobic decomposition of biomass (such as cow dung, agricultural waste, and sewage) by anaerobic bacteria in the presence of water but in the complete absence of oxygen. 3. **Two Advantages of Biogas:** - **Environment-Friendly Fuel:** It burns cleanly without producing smoke, leaving no ash or residue, which reduces air pollution. - **Nutrient-Rich Manure:** The spent slurry left behind in the biogas plant is highly rich in nitrogen and phosphorus, serving as excellent organic manure.

Our Environment

Biogas and Biomass

Official Answer

Main Constituent: The main constituent of biogas is methane ( $CH_4$ ), making up about 75% of its composition.

Obtaining Biogas from Biomass: Biogas is produced by the anaerobic decomposition of biomass (such as cow dung, agricultural waste, and sewage) by anaerobic bacteria in the presence of water but in the complete absence of oxygen.

Two Advantages of Biogas:

Environment-Friendly Fuel: It burns cleanly without producing smoke, leaving no ash or residue, which reduces air pollution.
Nutrient-Rich Manure: The spent slurry left behind in the biogas plant is highly rich in nitrogen and phosphorus, serving as excellent organic manure.

Methane

CH_4

Anaerobic decompositionBiomassAbsence of oxygenClean fuelNo residueSlurryManureNitrogen and phosphorus

Marking Scheme

1Identification of methane ( $CH_4$ ) as the main constituent. (0.5 marks)
2Explanation of anaerobic decomposition of biomass in the absence of oxygen. (0.5 marks)
3First advantage (e.g., clean burning, no smoke/ash). (0.5 marks)
4Second advantage (e.g., nutrient-rich slurry as manure). (0.5 marks)

Hint

Think about the gas that makes up 75% of biogas, the role of anaerobic bacteria in the absence of oxygen, and how it reduces smoke and provides manure.

Quick Oral Answer

The main constituent of biogas is methane ( $CH_4$ ). It is obtained by the anaerobic digestion of biomass by bacteria in the absence of oxygen. Two advantages are that it burns without smoke and the leftover slurry is an excellent manure rich in nitrogen and phosphorus.

Analysis & Explanation

Biogas is an excellent clean fuel derived from organic waste (biomass). The process occurs in a sealed chamber called a digester where anaerobic microorganisms break down complex organic compounds into simpler gases. Since methane ( $CH_4$ ) is the primary component, it has a high heating value. Utilizing biomass for biogas production solves two environmental problems: waste management (by treating biodegradable waste) and clean energy generation. The leftover slurry acts as a soil conditioner, replenishing soil nutrients naturally, which is a key concept in maintaining ecosystem balance.

Common Mistakes

1Writing carbon dioxide or hydrogen as the main constituent instead of methane.
2Forgetting to mention that the decomposition process must occur in the 'absence of oxygen' (anaerobic conditions).
3Confusing biomass with biogas.

Interesting Facts

Biogas plants not only provide clean energy but also prevent the release of methane directly into the atmosphere. Since methane is a greenhouse gas 25 times more potent than carbon dioxide, burning it as fuel actually helps mitigate global warming!

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2010?

This question carries 2 marks in the CBSE Class 10 Science 2010 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Our Environment" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Biogas and Biomass" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2010 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2010 paper.