Biogas
Biogas is a type of renewable energy produced by the natural breakdown of organic waste matter. When organic materials—such as agricultural waste, cow dung, plant residue, food waste, and sewage—decompose in an environment without oxygen, they release a mixture of gases. This mixture is called biogas.
In rural India, biogas is popularly known as “Gobar Gas” because cow dung (gobar) is the most commonly used raw material.
Composition of Biogas:
Biogas is not a single gas but a mixture. Its primary components are:
- Methane (): Makes up 50% to 75% of the gas. This is the main combustible component that provides energy.
- Carbon Dioxide (): Makes up 25% to 50%.
- Trace Gases: Small amounts of Hydrogen Sulfide (), moisture, and nitrogen
The Science: Anaerobic Digestion
The process of producing biogas is called Anaerobic Digestion.
- “Anaerobic” means “without oxygen.” * Inside a sealed underground tank, special types of bacteria consume the wet organic waste. Because there is no air (oxygen) inside the tank, these bacteria break down the complex organic matter and release methane gas as a byproduct.
Biogas Plant
A biogas plant is a simple brick and cement structure used to carry out this process. It consists of the following key parts:
- Mixing Tank: A tank above the ground where cow dung and water are mixed in equal proportions to form a thick paste called slurry.
- Inlet Pipe: A sloping pipe that carries the slurry from the mixing tank deep into the digester.
- Digester: A large, sealed, underground well made of bricks. This is the main chamber where the anaerobic bacteria break down the slurry in the absence of oxygen.
- Gas Dome / Gas Holder: The curved roof of the digester where the generated biogas collects. It has an outlet pipe with a valve to supply the gas to homes.
- Outlet Pipe and Overflow Tank: As new slurry is poured into the digester, the spent, digested slurry is pushed out through an outlet pipe into an overflow tank. This leftover paste is an excellent organic fertilizer.
Types of Biogas Plants
In India, there are two primary designs used for biogas plants:
- Fixed-Dome Type: The gas dome is rigidly built using bricks and cement. It is cheap to build, has no moving parts, and is very durable.
- Floating Gas-Holder Type: The gas is collected in a large steel drum that floats on top of the slurry. As gas is produced, the drum rises, and as gas is used, the drum sinks.
Advantages and Limitations of Biogas
Advantages (Pros):
- Clean Fuel: It burns without producing smoke, which prevents indoor air pollution and protects the health of rural women and children.
- High Heating Value: Because of its high methane content, it produces a lot of heat when burned, making it excellent for cooking and running small engines.
- Waste Management: It provides a safe, sanitary way to dispose of animal waste, human waste, and garbage, keeping villages clean.
- Rich Fertilizer: The leftover slurry that comes out of the plant is rich in nitrogen and phosphorus, making it a high-quality, free manure for farmers.
Limitations (Cons):
- Temperature Dependent: The bacteria need a warm environment to work efficiently. Biogas production slows down significantly during cold winter months.
- Not Efficient for Large Scale: It is difficult to scale up ordinary biogas plants to power entire cities. It is mostly suitable for rural, decentralized use.
- Impurity: Raw biogas contains Hydrogen Sulfide, which can be corrosive to metal pipes and engines if the gas is not cleaned properly.
Policy Support
- The Galvanizing Organic Bio-Agro Resources Dhan (GOBAR-DHAN) scheme was launched by Government of India to convert cattle dung and solid waste in farms to Bio-CNG (CBG) and compost
- Sustainable Alternative Towards Affordable Transportation (SATAT)
