Resource efficiency and life cycle environmental impacts of biogas production at Greve Biogass - Ressurseffektivitet og livsløps miljøpåvirkning av biogassproduksjon ved Greve Biogass
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In Norway, the municipalities are obligated to contribute to the reduction of greenhouse gas emissions as well as to a transition towards green energy. Biogas production based on manure, sewage sludge and different types of waste holds a large potential for decreasing emissions of climate gases. Greve Biogass AS, on behalf of its owner municipalities in Vestfold and Telemark will build a biogas plant, The Magic Factory , with the purpose of ensuring local recycling. The biogas plant will utilize large amounts of manure as substitution for clean drinking water as process water. The objective of this Thesis is to study the specific choices made regarding the operation of The Magic Factory , considering potential outputs, resource efficiency and environmental impacts. Three main choices have been studied: benefits of establishing The Magic Factory benefits of the water choices benefits of The Magic Factory compared to other biogas plants that do not treat such large amount of manure This has been carried out by use of material flow analysis and life cycle assessment, investigating six different scenarios, each of them representing different substrate mixtures and handlings. The environmental impacts have been concentrated on four impact categories: climate change human toxicity water depletion fossil depletion The results from the material flow analysis show that the outputs and resource efficiency are dependent on substrate mixture and transportation distance. When a co-digestion benefit has not been accounted for, a higher output of biofuel is seen by processing solid manure over liquid manure, and food waste over manure. This Thesis supports the choices made by Greve Biogass AS for the operation of The Magic Factory , considering environmental benefits. The results show that there is an environmental benefit of establishing The Magic Factory , considering all four impact categories. Environmentally, it is slightly beneficial to substitute clean water with liquid manure and The Magic Factory asserts itself good environmentally when compared to other plants by including manure in the biogas production. The sensitivity analysis performed shows that out of the uncertain parameters, degradability is the one with the highest impact on the outputs, resource efficiency as well as on the environment. This means that the parameter should be evaluated and adjusted after the results of a case specific digestion test are known. The driving distance related to collection and transportation of the food waste does have an influence that should be taken into account when considering what waste fractions to be processed at the plant.