Biogas

Apple peels, fish bones, leftover pasta and a handful of corn, no this is not some kind of strange secret recipe, but some of the elements that are necessary for the production of a very particular combustible, biogas. Biogas is a gas, but unlike methane that is extracted from the ground, it is produced from the decomposition of organic material (the organic waste of our waste), civil and zootechnical sewage, agricultural biomasses, etc. in anaerobic conditions, i.e. in absence of molecular oxygen (O2) or bound to other elements (as in the case of nitrates NO3).
Remember the production of compost? The concept is similar, as there is a decomposition of organic material, however the products and methods for its realization differ. The principal products of the reaction are methane and carbon dioxide and the presence of the former makes biogas suited for utilization as a fuel. However, unlike traditional methane gas, biogas is a renewable energy resource, it can potentially be produced starting from the raw materials that are available locally and waste, if the plants for the production are designed and managed correctly, with a recovery of the material which would otherwise only be waste material to be disposed of.
The treatment that is carried out is anaerobic, to stabilize the organic material, to produce biogas and recover waste material in special closed reactors called digesters. In this treatment a natural phenomenon is accelerated by adding heat and continuously mixing the materials, besides controlling important parameters of the process such as pH, temperature, solid content, volatile fatty acids and alkaline content. There is a wide interval of biological activity, which ranges from -5° to +70°C, coming from three different classes of anaerobic microorganisms, each activity in a certain temperature range. Initially the anaerobic digestion process only had the scope of stabilizing the organic material, however at present industrial systems for the production of biogas are created, starting, as mentioned above, from water from the food and agricultural industries, muds from sewage water treatment plants, animal faeces, biomasses from agriculture, industrial organic residues and the organic fraction of urban waste.
But, how much and what can we obtain from anaerobic digestion? Average process values indicate a production of biogas of about 100-150 m3/t, where CH4 is equal to 60-65% of the volume, CO2 is equal to 35-40%, and the heating power is equal to 23-25 MJ/m3. The production of biogas can also take place in the waste dumps in a non-controlled manner, therefore it is very important to foresee its capture, for its recovery and also to avoid dispersion in the atmosphere or accidents. The production of biogas has several benefits: 1) biogas is a renewable source of energy produced from waste, and therefore it offers a possible solution from the point of view of energy and of the environment; 2) the production and release of methane in the atmosphere is avoided; 3) the production cycle of biogas is defined carbon neutral, because the carbon dioxide contained in it is the same carbon dioxide that was previously fixed by the plants, and it is not newly created as in the case of petroleum or coal combustion. On the other hand it is necessary to pay attention to some technical aspects, so as not to jeopardize the sustainability of the plant . In fact it is very important that it is built in areas that are suited, possibly near the animal farms, to avoid transporting large quantities of organic material, and to avoid, as far as possible, using dedicated cultures as raw material so as not to subtract an excessive amount of areas from agricultural production.

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