Dry Digestion of Organic Residues

Sustainable development closely links to the context of energy. Replacing fossil fuels with sustainably produced biomass or organic residues will not only be a way to cope with the depletion of fossil fuel resources but also to reduce the CO2 emissions into the atmosphere and therefore minimise the risk of global warming. A large variety of methods of biomass energy conversion are available today. Some technologies produce secondary fuel such as methanol or biomass oil which then can be utilized for various purposes. Especially for electricity generation efficient processes might be direct combustion, thermal gasification or the production of biogas. Anaerobic digestion (AD) with biogas production, including utilisation of the organic fraction of waste materials and of residues, is a particularly promising choice and experiences increasing interest worldwide. AD does not only supply a clean and versatile energy carrier, thus displacing other energy sources such as fossil energy, but is well suited to contribute towards appropriate waste management schemes in urban areas and in agriculture. Biogas production has high potential worldwide, and it is in particular digestion of solid materials which is of increasing interest. As a result, it is to be expected that so-called dry digestion systems, operated with an elevated content of total solids (TS) in the reactor, will experience more widespread implementation. Agricultural residues in general are left on field or are brought back to field in order to supply fertilizers and to improve soil quality. Anaerobic digestion offers the possibility to produce renewable energy, and at the same time generates a digestate with an improved fertilizer value. Currently the most common strategy for management of municipal solid waste (MSW) worldwide is still landfill. As a result of higher environmental awareness, and often based on favourable legislative backgrounds, more and more emphasis is given to recycling and recovery, and in particular to efficient use of organic materials. Composting and anaerobic digestion are state-of-the-art for treating organic substrates. Germany today is leading in the area of biogas production. Around 6,000 AD plants are in operation, and the number is further increasing. Most plants are in the agricultural sector, but currently at least 100 plants are run solely on the organic fraction of MSW, a direct result