Increased biogas production in the municipality of Borås - A STUDY OF ORGANIC MATERIALS THAT CAN BE UTILIZED FOR ANAEROBIC DIGESTION IN THE SURROUNDINGS OF BORÅS

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Examensarbete för masterexamen
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2021
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Axelsson, Jakob
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South of Borås, at Sobacken, biogas is produced from out-sorted food waste. Organic material is degraded in an anaerobic digestion process which results in biogas. The plant is owned by “Borås Energi & Miljö”, a company owned by the municipality of Borås. During 2021 a reconstruction is finished, and some new technologies are launched in the process. There are especially two important changes that are the provocation for this report. Firstly, there is a new technology for handling solid waste materials that ease the handling of large quantities. Secondly, the old digester tank is now used as a post-digester, which leads to a duplication of the digestion volume. To fill the extra digestion volume, that the reconstruction results in, a study of organic waste materials in the surroundings is made. The study begins with theory about the most common organic wastes in the region. These are cattle manure, pig manure, horse manure, chicken manure and food waste from industries. From the theory, biogas potentials for the different types of materials are collected. The biogas potentials are then used for calculations of the sustainable transport distances considering energy balance and economical balance. In the beginning of the analysis, all the farms holding cattle, pigs, horses, or chickens, in the surroundings of Sobacken, are mapped out. Together with the calculations of sustainable transport distances, the map stands as ground for the advocation of using manure for biogas production at the facility. Horse manure and food waste from industries can be collected in large quantities due to the good possibilities of handling solid wastes, with the new technology. Manure slurry from cattle and pigs can replace some need for water in the process but mainly fill the remaining need of extra organic material in the digestion process. Digestion of several different materials together do often result in extra biogas yield compared with digestion of partial materials. Together, the analyzed organic materials have the possibility to fill the extra digestion volume and increase the biogas production at the facility.
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