Anaerobic digestion is the naturel process of the degradation of organic matter in the absence of oxygen. This treatment of organic waste leads to the production of biogas, which is a renewable energy, and digestate, which is the residue of the degradation. This process can be reproduced in specific units which are regulated. These units can exist at both an industrial and on a farm scale. With the anaerobic digestion on farms, the sources involved are livestock waste and sometimes crop residues.
The anaerobic digestion on farms has a low production of energy and uses around 1000 and 5000 t of livestock wats per year (for example, a 120 dairy cows farm produces 4000t of effluents per year). The scale of these units is compatible with the size of farms, it permits the reuse of all the organic waste present on farms.
Biogas, made up of 50 to 70% methane and 20 to 30% carbon dioxide, can produce electricity and heat after combustion. The unit is linked to the electrical system, so the electricity can be sold or used on farms.
The digestate is an organic fertilizer whose mineral elements are easily assimilable by the units. This characteristic permits the reduction of the mineral inputs thus making the farm more autonomous. With this process, the organic matter produced on farms returns to the soil thereby closing nutrient cycles.
The anaerobic digestion is a way to modernize farms: it permits farmers to diversify production and earn an additional income. It is a way to reuse the farm’s organic waste and reduce gas emissions in the atmosphere on a farm scale. Furthermore, the anaerobic digestion does not need much matter movement, thus contributing to reduce the carbon footprint. The anaerobic digestion participates in the agroecological and energetical transition producing a renewable energy and reducing the use of fossil fuel.
Published on 18 April 2019
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To quote this definition or part of it :
Sandrine Hersemeule, Mirentxu Oillarburu, Bernard Reilhac. 2019. Anaerobic digestion on farms : Definition. Dictionnaire d'Agroecologie, https://dicoagroecologie.fr/en/encyclopedia/anaerobic-digestion-on-farms/