When organic materials decompose in the absence of oxygen they release large quantities of methane. This is known as ‘anaerobic digestion’ and it’s a different process from regular composting. Anaerobic digestion takes place in large tanks, which contains the odours and allows for the easy capture of the resulting gases which can then be fed into the local power grid.
The solid residue left over from anaerobic digestion becomes compost and the liquid is transformed into a fertiliser which is able to improve the quality of soil for farmers and gardeners.