The correct definition of biogas is a natural fuel obtained from “anaerobic digestion”, i.e. the process of biochemical conversion which takes place in biological substances without oxygen, at a suitable temperature and with the continual mixing of the substances used.
In practice, the production of biogas consists in micro-organisms breaking down complex organic substances (lipids, protides, glucides), contained in plants, sludge and by-products of animal origin.
The biogas produced usually consists of approximately 50/70% natural gas and the remaining part carbon dioxide and other minor components. The biogas produced by aerobic digestion is then suitably treated to power the internal combustion engine of the cogeneration plant and produce, at the end of the process, entirely renewable electrical and thermal energy.
As noted in particular by the CONSORZIO ITALIANO BIOGAS (ITALIAN BIOGAS CONSORTIUM) in a specific presentation: “Agricultural biogas is therefore the result of a spontaneous and natural process, which forms the basis of a process that is an opportunity to produce renewable energy in a sustainable way and with full area integration. In the process, the by-products from livestock and agroindustrial activities become resources, and agricultural innovation focussed on growing integrated products for energy production purposes is encouraged. In fact, the considerable development of anaerobic digestion in Italy is linked to the ability of this technology to integrate with the existing agricultural fabric as a “recycling” process which is extremely efficient at using and maintaining the fertility of agricultural soil. Being good at making biogas means adding biogas to the production cycle of the agricultural or livestock company, without this reducing usual capacity to produce food or animal feed. In fact, this integration must stem from a greater capacity of agricultural companies to produce their own specific crops, in a way which is environmentally sustainable and economically viable.
Biogas offers unique opportunities to reduce the environmental impact of agricultural and livestock activities. The use of livestock waste in anaerobic digestion, for example the use of dual crops (e.g. winter harvesting for the digester) makes it possible to reduce the leaching of nitrogen and nutrients of surface and underground water bodies. The possibility for greater rotations with methane-producing crops reduces the spread of parasites such as the corn rootworm in corn single-crop areas. The heat from the cogeneration plants can be used to dry the feed without the need for diesel fuel or methane”.