Biogas is obtained from anaerobic digestion process, a fermentation process, which takes place in a closed airtight digester where organic raw materials such as manure, food waste, sewage sludge and organic industrial waste are converted into biogas and digestate as products. The produced biogas is a mixture of 50-70% methane and 30-50% carbon dioxide and smaller amounts of water vapor, hydrogen sulphide and other minor components and trace elements. The wet digestate results from anaerobic digestion of the substrates, which are pumped out of the digester tank, after the extraction of biogas.
Very simple biogas digesters have been in use in China, India and many other Asian countries for many years. Industrial applications of biogas production started well over 50 years ago as a means of stabilizing sewage sludge at waste water treatment plants. The biogas industry expanded in the 1970’s and 1980’s as increased production of different organic materials (such as manure and industrial wastewater from sugar refinery and pulp mills) became more widely used. Starting in the mid 1990’s extraction of landfill gas (low quality biogas) came to the fore, along with the construction of farm-based biogas plants and anaerobic digestion of solid wastes from food industry and food waste. After 2000’s, there was an increased interest in biogas and so, construction of farm-based biogas plants took place and an industrial sector was established.
Biogas, made from organic waste streams, does not add to the carbon dioxide load in the atmosphere. Carbon dioxide produced during combustion of biogas is offset by either the carbon dioxide consumed by the biomass, which is digested. Biogas is thus a “green” sustainable energy vector and has a significant role in shifting to a sustainable decarbonized society. Biogas has many uses in the sustainable society that can be utilized in a broader perspective than today. Industries, as well as households, can use biogas for heating and hot water supply. Biogas can be used to supply warm air for drying, for example, in laundries, carpentries, industrial coating facilities and other places where there is a need for fast and efficient drying. The exhausts from upgraded biogas combustion are clean and do not generate odours or particles.