Basics About Biogas Plants
	At present there is a boom in biogas plants in Germany. With this technology one obtains so-called biogas from organics. Biogas is renewable energy. It can be used in gas engines to produce heat and electricity. The following report provides an overview of the development and present status of biogas plants in Germany.
		1. A short retrospective survey 2. What is Biogas ? 3. The situation in Germany 4. Comparison: Digestion and Composting
	1. A short retrospective survey
	Directly after World War II a few biogas plants had been constructed and were in operation on some German farms. The reason at that time was a shortage of energy: fuel oil and natural gas were (nearly) unavailable, biogas could be obtained easily and comparatively cheaply through digestion of cattle- and pig-manure by the farmers on themselves.
	Those first German biogas plants vanished in the fifties. Fuel oil was cheap and available anywhere at any time. Again, after the two oil crises in the seventies there were investigations of the feasability of biogas utilisation - this time conducted by some home-mechanics. This second wave soon disappeared, too. Only in the mid-eighties did some people start to work on biogas plants seriously again. This third boom has continued vigorously to the present.
	In Germany a milestone in the development of biogas plants was so-called Electricity Input Law ("Stromeinspeisegesetz") of 1992. This law garanteed fixed rates to all the producers of renewable energy for each electrical kWh delivered into the public electrical grid. This law not only included biogas plants but also all the other renewable energies, such as wind energy, too. But some of the main effects at the beginning of the nineties was the breakthrough of biogas plants. Later on, in February 2000, the Electricity Input Law ("Stromeinspeisegesetz") was replaced by the Renewable Energy Law ("Erneuerbare Energien Gesetz"), which garanteed even higher rates for each electrical kWh delivered into the public electrical grid.
	2. What is Biogas ?
	Biogas is a gas consisting of about 60% methane (CH4) and 40% carbon dioxide (CO2). Other words for biogas are sewage gas, mine gas and marsh gas. Biogas is produced if manure, kitchen waste, garden waste, malt residuum, marc residue, market waste, slaughterhouse waste, fats and other native-organic substrates are treated anaerobically, i. e. without any free oxygen.
	Different kinds of microorganisms metabolize the carbon of organic substrate under anaerobic conditions. This process - called digestion or anaerobic fermentation - follows a food chain.
	For example, if manure is treated in this manner, digested manure is obtained as a final product with much less odour than the fresh manure had previously. In addition, this digested manure has got a neutral pH-value and no further caustic action when applied to plants. After digestion nitrogen is mainly not organically bound any more but is in form of ammonia (NH4). Therefore, it can be assimilated directly by the plant. The farmer gets a good, simple and cheap method for fertilizing. He can dispense with expensive mineral fertilizer.
	3. The situation in Germany
	In the meantime there are about 600 biogas plants in operation in Germany. Those are mainly agricultural, farm-scale biogas plants, the remainder are large-scale central Cofermentation plants and industrial plants for digestion of biowaste and/or kitchen waste. Most of these plants were constructed with help of experienced advisers in self-construction by the owners themselves. As a result, costs could be reduced greatly.
	In the following chapter some of our references are described. All of these biogas plants have been realised within the past few years. The biogas plants described have different characteristics with regard to input substrate, technical construction and intention for the operator.
	4. Comparison: Digestion and Composting
	Digestion has several advantages compared to composting.
	Composting requires electricity, whereas digestion delivers surplus electricity. Liquid wastes like manure and fats are not appropriate for composting. They are ideally used for digestion. Comparatively wet organic wastes, for example kitchen waste or slaughterhouse waste can be digested relatively well. But especially these wastes are only compostable with the addition of large quantities of air = energy - if at all. Very important are odour reductions through digestion.
	Description of a typical farm-scale biogas plant Description of a typical cofermentation biogas plant Description of a typical biowaste/kitchen waste digestion plant

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