Question

Major composition of biogas is:

• A. Methane and oxygen
• B. Carbon-dioxide and oxygen
• C. Methane and carbon-dioxide
• D. Methane and carbon monoxide

Hint:

The fuel value of biogas is due to methane (\(\text{CH}_4\)).
Carbon dioxide (\(\text{CO}_2\)) is an inert byproduct that must be removed (biogas scrubbing) to upgrade the biogas to biomethane for vehicle fuel use.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Biogas is a renewable gaseous fuel produced by the anaerobic digestion of organic matter, such as animal dung, agricultural waste, and municipal sewage.
The decomposition process is carried out by methanogenic bacteria in an oxygen-free environment.

Step 2: Detailed Explanation:
Anaerobic digestion occurs in several stages (hydrolysis, acidogenesis, acetogenesis, and methanogenesis) to break down organic matter into a mixture of gases:
- Methane (\(\text{CH}_4\)): This is the primary combustible component of biogas, typically making up \(50\%\) to \(75\%\) of the total volume.
The energy content of biogas is directly determined by its methane concentration.
- Carbon dioxide (\(\text{CO}_2\)): This is the second largest component, typically making up \(25\%\) to \(50\%\) of the volume.
It is a non-combustible gas that acts as a diluent, reducing the heating value of the biogas.
- Other trace gases: Biogas also contains very small amounts of nitrogen, hydrogen, water vapor, and hydrogen sulfide (\(\text{H}_2\text{S}\)).
Oxygen and carbon monoxide are not present in significant quantities in standard anaerobic digester gas.
Therefore, the major components of biogas are methane and carbon dioxide.

Step 3: Final Answer:
The major composition of biogas is methane and carbon-dioxide.