Biogas is a renewable energy source produced from the breakdown of organic matter like agricultural waste, manure, sewage, municipal waste, green waste, and energy crops in the absence of oxygen. This process is known as anaerobic digestion.

Major Biogas Component: Methane Explained

The question asks about the major component of biogas. Biogas is primarily a mixture of gases, and its composition can vary depending on the source of the organic material and the conditions of the digestion process. However, the main flammable component that makes biogas useful as a fuel is Methane.

Methane (CH\(_4\)) is the dominant gas in biogas, typically making up about 50% to 75% of the total volume. The next most abundant gas is Carbon Dioxide (CO\(_2\)), usually ranging from 25% to 50%. Other gases are present in much smaller amounts.

Composition of Biogas

While Methane is the major component, other gases contribute to the overall composition of biogas. A typical breakdown might look like this:

• Methane (CH\(_4\)): 50-75%
• Carbon Dioxide (CO\(_2\)): 25-50%
• Nitrogen (N\(_2\)): 0-10%
• Hydrogen Sulphide (H\(_2\)S): 0-3%
• Hydrogen (H\(_2\)): 0-1%
• Oxygen (O\(_2\)): 0-2%
• Water Vapor (H\(_2\)O): Saturated

This composition clearly shows that Methane is present in the largest proportion, making it the major component.

Analysis of Options

Let's look at the provided options:

1. CNG (Compressed Natural Gas): CNG is primarily Methane, but it is natural gas extracted from geological formations, not produced from organic waste breakdown like biogas. While biogas can be upgraded to bio-CNG (or biomethane) by removing CO\(_2\) and other impurities, CNG itself is not biogas.
2. Methane: As discussed, Methane is the main component of biogas, responsible for its energy content.
3. Hydrogen: Hydrogen can be present in biogas in small amounts (typically less than 1%), but it is not the major component.
4. LPG (Liquefied Petroleum Gas): LPG is a mixture of hydrocarbon gases, primarily Propane and Butane. It is derived from petroleum refining or natural gas processing and is completely different from biogas.

Based on the typical composition of biogas, Methane is definitively the major component.

Revision Table: Biogas Key Facts

Additional Information: Anaerobic Digestion Process

Anaerobic digestion is the biological process that produces biogas. It involves several stages carried out by different types of microorganisms in the absence of oxygen:

1. Hydrolysis: Complex organic polymers (carbohydrates, proteins, fats) are broken down into simpler monomers (sugars, amino acids, fatty acids).
2. Acidogenesis: Monomers are converted into volatile fatty acids (VFAs), alcohols, hydrogen, and carbon dioxide.
3. Acetogenesis: VFAs and alcohols are converted into acetic acid, hydrogen, and carbon dioxide.
4. Methanogenesis: Methanogenic archaea convert acetic acid, hydrogen, and carbon dioxide into Methane and carbon dioxide. This final stage is where the majority of Methane is produced.

The efficiency of the methanogenesis stage directly impacts the percentage of Methane in the resulting biogas. Higher Methane content means better fuel quality.