Biogas production from crop residues on a farm-scale level: is it economically feasible under conditions in Sweden?

Anaerobic digestion would enable the energy potential of agricultural crop residues such as sugar beet tops and straw to be harnessed. Sweden is so spread out that full utilisation of this potential by centralised slurry-based technology is difficult. It appears that simple but effective high-solids reactor systems have a better chance of being economically viable on a farm-scale level (50–500 kW). In the present study, the financial prospects of high-solids digestion, using either single-stage fed-batch or two-stage batch reactor systems, are compared on a farm-scale level (50 kW) with those of conventional slurry digestion, on the basis of experimental results and observations on a laboratory- and pilot-scale. The gas produced can be used for heat, combined heat and power or as vehicle fuel. The results indicate high-solids single-stage fed-batch operations to stand the best chances of being competitive, particularly in connection with organic farming. The methane yield, degree of gas utilisation, and operational costs were found to have the strongest impact on the financial success of the process.