Anaerobic Digestion in Germany – Perspectives of Innovations for the Coming Decade

The digestion of organic waste and residues has increased in importance during the last ten years in Germany. New plants have been built mainly for the treatment of agriculture residues (e.g. liquid manure) and municipal solid waste (primarily separately collected organic waste). The potential of biogas generation with 8,7 bill. m/a, which is provided by the accumulating amount of organic waste, is presently hardly utilised at all. Looking ahead, the more efficient use of this great bio-mass resource is an important aim. Many digestion plants do not operate at full capacity, others are overloaded. That fact is due to an improper and uncertain data base during the planning phase. If the conditions have changed in a few years, the plants will not be in the position to operate in an optimal way any longer. Additionally a lot of organic waste accrues only in certain regions during a certain season. The integration of this kind of waste in central, stationary plant concepts seems to be impossible. Therefore a further development of digestion plants should enable an adapted, dynamical processing of biological waste. A combination of using existing capacities and the application of mobile, controllable reactor-units would effect variable capacities of the digestion plants, that would provide the opportunity to respond to alternating loads. The paper gives an overview to the state of the art in Europe and Germany and introduces an innovative concept for a future plant, which is able to readjust the capacity of the process to varying conditions. Introduction During the last decade the capacities of biogas plants have increased significantly. On the one hand government aid for the generation of renewable energy results in increasing plant construction in the field of treatment of agricultural residues, on the other the digestion of separately collected organic waste has become more and more important due to the problems of composting plants with odour, high energy demand and handling materials with a high moisture content. Most of the plants treating agricultural residues are based on the mode of the single stage wet digestion and are run in the mesophilic temperature range. The throughput of those plants varies greatly, depending on the size of the farm. For a cost-efficient operation a minimum size of 100 livestock units (approx. 2000 Mg/a) is recommended (biomasse-info.net 2002), the largest plants have a throughput exceeding 100000 Mg/a. An advantage of agricultural digestion plants is the assured utilisation of the end product of the fermentation process, the digested farm manure on the farm ́s own land. Fig. 1 shows the increasing number of those agricultural plants in Germany. J. Liebetrau, E. Kraft, W. Bidlingmaier 2 Digestion plants in Germ any treating agricultural residues (m ostly liquid m anure) 139 159 186 274 370 450 617 85