### Theory:

2. Biogas:
Biogas is a mixture of methane (about $$75\%$$), hydrogen sulphide, carbon dioxide, and hydrogen. It is produced from the decomposition of raw materials like animal wastes (cow dung), plant wastes, agricultural wastes, municipal wastes, sewage and food wastes. Biogas is produced through anaerobic decomposition (in the absence of oxygen) of raw materials with methanogen or anaerobic organisms

Biogas raw materials
Biogas is commonly known as "Gobar gas" as the starting material is cow dung which means "gobar" in Hindi.
How is biogas produced?
Biogas is produced in a closed dome-like structure where fermentation of raw materials occurs in the absence of oxygen. The dome-like structure is called a biogas plant, an anaerobic digester, or a biodigester.

The raw materials are first mixed with water and fed to the digester through the inlet. The digester is a sealed chamber where decomposition of the raw material takes place in the absence of oxygen. After a couple of days, the raw materials are completely decomposed to produce methane, carbon dioxide, hydrogen sulphide and hydrogen. The gases are collected through pipes from the storage tank present above the digester.

Biogas digester

Uses of biogas:

1. Biogas is utilised as a fuel for cooking.

2. It is utilised to run motors and pump sets.

3. Biogas is also used to generate electricity.

1. It burns without producing smoke, resulting in less pollution.

2. It serves as a great technique to dispose off organic wastes such as bio-waste and sewage.

3. Leftover slurry is a good manure rich in nitrogen and phosphorus.

4. Biogas is safe and convenient to use.

5. Biogas can minimize the amount of greenhouse gases emitted.

6. Biogas plant facilities have a low initial investment and becomes self-sufficient in $$3$$ to $$4$$ months.