Co-digestion of energy crops and the source-sorted organic fraction of municipal solid waste

The biological and technical performance during co-digestion of energy crops and the source-sorted organic fraction of municipal solid waste has been investigated at laboratory and pilot scale. A 50:50 (TS-based) mixture of energy crops and organic waste reached a loading rate of 6.0 gVS L⁻¹d⁻¹ with a methane yield of 0.33–0.38 L gVS⁻¹, while a 80:20 mixture showed elevated levels of volatile fatty acids at 5.5 gVS L⁻¹d⁻¹ The better performance of the 50:50 mixture can partly be explained by a better nutritional composition. Mincing the ley crop reduced viscosity and reduced problems with fibre floating and scum-blanket formation. The electricity consumed for mincing and stirring at a full-scale plant corresponds to ca 3% of the energy produced. Calculations of the costs for full-scale plants indicate that the price of the up-graded biogas has to be at least 0.078 Euro/kWh in order to balance the costs.