Pages last updated:

5 December 2016

Running Small-scale

A biogas plant is a container of a slurry of bacteria and wet organic matter that produces methane and carbon dioxide. The methane-producing bacteria are anaerobic, i.e. they do not work when oxygen is present. A cow’s gut contains a population of bacteria that include anaerobic methanogens, so cattle dung is often used as feedstock or as a starter for the digestion of other types of organic material. Since these bacteria are adapted to a cow’s gut, they run best at 35°C (mesophylic), although some also work at 55°C (thermophyllic). In colder climates the container must be insulated and/or heated to maintain this temperature. The container must be gas tight to retain the gas as it is given off and also to exclude air.

Biogas technology has a long history, especially in countries such as China, India and Nepal. In UK, the rest of Europe and USA, it had a brief burst of interest in the early 1980s, but was seen as uneconomic, when the oil price dropped. Since the 1990s, there has been a strong revival of interest in Germany, followed by Sweden, Denmark and Austria. The UK has been slow in following their lead. However they have followed Germany and other European countries by providing subsidised feed-in tariffs for operators who generate electricity from renewable energy, such as biogas.

Biogas is a fuel gas that can be used in gas burners, for cooking and heating, or in internal (and external) combustion engines to give shaft power or to drive an electric generator.

The main feed material for biogas plants is animal dung, especially cattle dung. Animals process biomass materials, by chewing with the teeth and in the digestive system. Much of the available energy in the biomass materials is used by the animal. Cattle dung also contains the right microbes that convert biomass into biogas.

Raw biomass materials will generate more biogas per kg than animal dung, but needs to be pre-processed. Pre-processing can improve the process of digestion and allow a much wider range of materials to be digested.

The books provide a detailed description of the technology and how it can be used to help people in many countries.

Biogas Technology