How Does the Anaerobic Digestion Process Work?
The process takes place in an oxygen-free digester, where micro-organisms (bacteria and archaea) breakdown the organic matter. There are four main stages to this process: hydrolysis, acidogenesis, acetogenesis and methanogenesis. Each stage breaks the matter into smaller and smaller parts, until the only remaining substances are methane, carbon dioxide and water, three very simple molecules. At the end of the process we have a mixture of methane and carbon dioxide gases (biogas), water and some organic material (digestate).
Biogas can be used to produce heat and electricity. It can be used in combined heat and power (CHP) gas engines or it can be burned to produce heat only. Alternatively, biomethane can be produced by removing the carbon dioxide from the biogas. The biomethane has many valuable uses. It can be injected into the gas grid as a renewable replacement for natural gas or it can be used as vehicle fuel.
Digestate is a nutrient-rich substance which contains high amounts of nitrogen and phosphate that has value as an agricultural fertiliser or soil conditioner.