The Farming community will supply all of the raw materials, agricultural waste, energy crops and slurry. The tanks are sealed to contain the biomethane gas and the whole process is clean within the context of an agricultural process.
The most important piece of plant in the process is the digester itself, and it operates as follows: A mixture of all organic material is pumped into the bottom of the digester which can be a large concrete or stainless steel tank. The mixture is stirred or agitated in the mixing zone at the bottom of the tank and it starts to break down. In the process of breaking down it produces methane gas. Instead of releasing this gas to atmosphere though, we capture it and it is siphoned off to be used to fuel a generator. The generator produces electricity which can then be fed into the national electricity grid.
Capturing this methane, which otherwise would be released into the atmosphere, has obvious benefits in reducing greenhouse gas emissions. Carbon Dioxide is of course produced in the generation process but as it produces both electricity and heat, (heat which can also be used to provide heating to local facilities), the benefits far outweigh the carbon release.