Biogas Digester 

Biogas is a by-product of organic materials such as plant and animal products being broken down by bacteria in an oxygen-free environment. This process is called  anaerobic digestion.

A biogas digestor uses natural anaerobic decomposition of organic matter under controlled conditions.

The digestor is usually a large, sealed container for the organic matter eg manure from livestock or poultry, green waste from agriculture, sewage or food waste. This is digested by bacteria in the absence of oxygen to produce a gas containing methane and carbon dioxide. The gas is piped away from the digestor and burnt to produce heat energy.