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. 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 biogas 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.
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.
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.
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.