Biogas Production Potential from Economically Usable Green Waste

Biomass production for energy purposes on agricultural land competes with food production. This is a serious problem, considering the limited availability of farmland, rising demand for varied food products, demand for more organic crop production resulting in considerably reduced yields per area and the need for more environmentally sound agricultural practices meeting long-term sustainability criteria. Residual land currently not used for agricultural production has been considered a promising resource, but in terms of potentials, difficult to estimate for biomass for use in the energy sector. Biomass potentials associated with “green waste” from residual grasslands were assessed for Schwäbisch Hall County in the Federal State of Baden-Württemberg, Germany. Roadside edges, conservation grasslands subject to low intensity use (landscape maintenance sites), riparian stretches along ditches and streams, and municipal green spaces (public lawns, parks and sports fields) were the area types considered. Data for biomass and biogas yields were either determined through a sampling program or obtained from the literature and through interviews with experts. In an iterative process and distinguishing between theoretical, technical and realized (economic) potentials, unsuitable areas and fractions were subtracted from the theoretical potentials. Theoretical potentials for Schwäbisch Hall County were originally estimated at 21 million m3 of biogas. The results of the investigation suggest that a very high percentage of the theoretical residual biomass potential cannot be accessed due to various technical, legal, ecological or management (economic) constraints. In fact, in the end, only municipal lawns and green spaces were found to provide suitable substrates. Current use of residual biomass in the model communities did not exceed 0.4% of the theoretical potentials. Provided all residual biomass available under current management practices could be accessed, this would amount to 6.1% of the theoretical maximum potentials.