Matter such as agricultural waste and sewage sludge is “digested” inside what we call a digester tank, where it is deprived of oxygen and mixed with bacteria. After 20 days or so, the fermentation process results in the production of biogas with 40% to 70% methane content. It is identical to natural gas from hydrocarbon deposits. The biogas can be used to generate electricity and heat on site, or purified and fed into the gas network. Anaerobic digestion is a way of driving the energy transition, in combination with other renewable energies.