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Norwegian Small Scale Biogas Plant: Estimations on Energy Use, CO2 Emissions-Reduction and Added Value

Lorenzo Rubino

An anaerobic digestion (AD) process is studied. The AD reactor belongs to UASB (up-flow anaerobic sludge blanket) typology and it was constructed in a typical Norwegian farm (Foss farm) localized in Skien, Norway. The reactor is fed with cattle manure. The process is divided into two different parts: pre-treatment and AD, nitrification and post-treatment. Biogas and compost are outputs of the first section, liquid fertilizer output of the second one. This paper has two core parts: energy/mass flows determination and CO2 emissions-reduction assessment. The study has indicated that energetic consumption is bigger than production. Radiation losses represent the most important terms of consumed energy, but is possible to diminish them by changing insulation and/or reactor shape. The pilot plant has an average energy consumption and thermal production of 1592 kWh/year and 482 kWh/ year, respectively. The equivalent CO2 emissions of open-air-standing cow’s manure are noteworthy. Two different probable situations are analyzed: processed manure and not processed manure. The reduction of carbon dioxide releases in the first case, compared to the second, is significant and goes from 32% to 83%. It could be possible to reduce energetic consumption up to 18% halving radiation losses and raise energetic production up to 250% by increasing the methane yield from 20% to 50% of the maximum value.