ABSTRACT
Anaerobic digestion is the breaking-down of biological material by micro-organisms in the absence of oxygen i.e., under anaerobic conditions. A number of families of bacteria, working together, transform biological material into biogas. Biogas consists of around two-thirds combustible methane and about one-third carbon dioxide and other gases. The anaerobic bacteria are some of the oldest ‘inhabitants’ of our planet. With a power output of 40GWh of heat and 20GWh of electricity biogas plants are a major source of renewable energy. Anaerobic digestion of organic waste is especially suited to the treatment and stabilization of liquid or solid biological material. The process takes place in a sealed vessel (the so-called fermenter or digester) under controlled conditions and has major advantages: up to 90 per cent of the carbon content will be converted into biogas, and biogas supplies valuable energy in the form of electricity, heat and transportation fuels.
