Biogas from Residual Grass: A Territorial Approach for Sustainable Bioenergy Production

Large amounts of residual grass originating from the management of landscape and natural areas are produced in Europe. This material, which is not competing for land use like energy crops, and is only partially recovered for animal feeding, can be profitably used for sustainable bioenergy production. In this study we demonstrated through a GIS based approach that this feedstock can be of some interest for the production of biogas in the Veneto Region, north east Italy, where more than 150 anaerobic digesters are in operation and feedstock availability can be sometime problematic. Specific field trials showed that costs for grass management are around 30 euros/ton while corresponding CO2 emission for grass handling (cutting, wrapping and harvesting) are 25 kg CO2/ton of grass processed. On the other hand, average biogas productions of some 500–600 m3 of biogas/ton of volatile solids (52–56% methane) should be expected from this residual material. Both treatment costs and biogas yields of residual grass are in line with similar data for some energy crops. The technical, environmental, and economic sustainability for the production of bioenergy through the proposed approach was demonstrated.