Biogasproduktion från vall - Analys av metanpotential samt energi-­och miljösystemanalys

In these times, when global warming is escalating and the finite resources of the world are consumed in a fast pace, it is very important to find sustainable solutions for the near future. Transport is one of the sectors that need to find alternative solutions to the utilisation of fossil fuels. This master thesis investigates biogas production from ley crops, which is a mixture of different species of clover and grass. At first the methane potential was determined through laboratory experiments to an average of 270 Nm3 CH4/ton TS or 50 Nm3 CH4/ton wet weight. It was concluded that there was no significant difference in methane potential between ley crops fertilized with bio fertilizer and mineral fertilizer. The methane potential from the first harvest was however significantly higher than from the second harvest of the year. The average methane potential was then used in an energy and environmental systems analysis, where energy consumption and greenhouse gas emissions were analysed in a cradle-to-grave perspective, covering all aspects from cultivation of ley crops to bioconversion to biogas and use as a fuel for transport. Comparing direct land use changes, the emissions where lower if the ley crops were grown on land that had previously been used for cultivation of grain, due to an increased soil carbon content, than if it had been used for cultivation of ley crops. The study also showed that if system expansion was used, which means that the digestion residue produced was used as bio fertilizer replacing mineral fertilizer, both energy consumption and emissions were lowered. The energy input ranged from 28 to 38 percent of the produced biogas, and the emissions ranged from 3 to 32 g CO2e per MJ of biogas