Ärtrev som substrat för biogasproduktion
En litteraturstudie och rötning i labbskala
Until 2020, 49% of Sweden's use of energy must derive from renewable sources. Greenhouse gases must as well decline with 40% compared to 1990 as a part of Sweden's 16 environmental objectives. Biogas is part of the effort to achieve these objectives, but as the demand for biogas increases, more substrates are needed to meet the demand. The purpose is to investigate the conditions for pea residue as substrate by performing lab-scale mesophilic digestion with different fractions and notch lengths and then to summarize pea residue as a substrate for biogas production. During anaerobic digestion, 1000 ml bottles were used as reactors for digestion. Analyses of gas production, gas composition, content of dry matter and organic matter, carbon / nitrogen-ratio and pH have been performed.The results from lab scale digestion show that the pea residue has a methane potential of 300-400 liters of methane per kg VS during 25 days of anaerobic mesophilic digestion. Chopped pea residue had a slightly higher methane production than untreated pea residue.. The substrate was very difficult to mix up in a regular household blender because of long and tough fibers. This suggests that the substrate requires to be chopped in order to avoid difficulties with management in pumps. Profitability may be a problem if you chop pea residue as the machine being used is expensive and the increase in methane yield as a result of chopping is too small for the pretreatment to be worthwhile. The cost for collecting and chopping the pea residue has been estimated to 473 SEK per hectare or 0,1 SEK per kWh.Practical experience of digesting chopped ensiled pea residue in large-scale facility shows that the substrate works well in pumps and does not affect the process negatively in any way, which suggests that chopping and ensiling pea residue is preferable. Theoretically, there is an energy potential of pea residue amounting to 40 GWh in Skåne and Halland, which roughly corresponds to the fuel consumption of 130 biogas buses annually. The biogas needs to be upgraded before this is possible.Environmental benefits of digesting pea residue include reducing nitrous oxide emissions of 500-1200g per hectare. Other environmental benefits include the reduction of ammonia emissions and nitrate leaching. Biogas as a fuel is neutral as regards carbon dioxide emissions and can replace fossil fuels. Crop residues as a substrate for biogas production do not compete with land for food production.