A biogas digester (also known as a biogas plant) is a large tank where inside Biogas is produced through the decomposition/breakdown of organic matter through a process called anaerobic digestion. It’s called a digester because organic material is eaten and digested by bacteria to produce biogas.
A biogas digester forms the most critical part of biogas production because without it, no biogas would be produced without the breakdown of organic waste or material.
How A Biogas Digester Works
What Is Biogas?
Biogas is produced by the breaking down of organic, biodegradable waste or material (also known as biomass) such as vegetables, leaves, grass, weeds, leftover food scraps and such. When this organic breakdown happens it produces a gas, called biogas.
Biogas is a mixture of carbon dioxide and methane, and resembles liquid petroleum gas. And like natural gas, biogas is used as a fuel to produce electricity to power farm equipment, for lighting applications, in gas cookers for cooking, and even for transportation.
Biogas is widely used in many homes around the world, especially in countries where this technology has been widely available and used.
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Composition of a Biogas Digester
To understand how biogas is produced, it’s important to understand the components of a biogas digester, which itself is part of a biogas electric generator plant. A typical biogas digester has a container that holds organic matter and water. This mixture of water and organic matter is called slurry.
A digester has another container that holds the gas that has been produced after the organic matter is broken down. The digester has connecting systems in the form of pipes that feed the digester with slurry and connect the container holding slurry to the container that is holding the gas. There is also a transport system to take the biogas to where it will be used. The digester also has a mechanism for ejecting the residue.
Fixed Dome Biogas Digester
This type of biogas digester is very common. In this design, the container collecting the slurry and the container collecting the gas are combined. The gas collects on top of the slurry. As the gas accumulates, the slurry is forced into another container. After the gas is removed the slurry will flow back into the container it was in initially.
In addition to plant matter and vegetation, other types of organic matter that can be broken down is human sewage and cow dung.
- Cow dung as an organic material can also be used as a raw material to produce biogas because of its biodegradable and low cellulose content attributes.
- That’s why biogas digesters are also common in farms, but they can also be built in a home compound in urban areas, like towns and cities. Provided you have an efficient biogas building plan that’s extremely efficient, is low cost, and only requires minimal space or square footage to actually put up.
How Biogas Is Produced
For a biogas digester to produce gas, it needs methane-producing bacteria. After the methane-producing bacteria is introduced, the bacteria will reproduce and the process continues infinitely, and there is no risk that the bacteria will die. Once the bacteria are introduced, the process of biogas production will never stop.
Quick Fact: Cow dung contains methane-producing bacteria.
For this reason, cow dung is commonly used to start the process of biogas production. You can change the organic material to be used to produce biogas after the production has been kicked off by cow dung.
Materials that can produce biogas
Most biogas digesters use cow dung to produce biogas. There are many other organic materials as mentioned above that can be used to produce biogas. Like left over food scraps, vegetation etc.
Some digesters can be fed with grey water (grey water is a term used to refer to used water). Other common organic materials used in biogas digesters include sewage, glycerin, algae and grasses.
In short, anything organic can be fed to the digester provided it’s biodegradable and has very small amounts of cellulose.
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