The paper presents the advantages of using biogas as an alternative source of energy, especially in rural areas and insists on its specific advantages, compared to other alternative fuels, such as bio-ethanol and bio-diesel, which are very significant fuels which can be used in the future, but are contested from the social point of view, because they use as raw materials plants, some of them being used as food sources for mankind. The main advantage of biogas is that it is obtained from residues and wastes, so it has the ability to transform waste material into a valuable resource in the conditions in which many countries are facing enormous problems associated with overproduction of organic wastes from industry, agriculture and households. Biogas production is an excellent way to comply with increasingly restrictive national and European regulations in this domain and to use organic wastes for energy production, which is followed by recycling of the digested substrate as fertilizer. In the paper is emphasized the fact that a biogas plant is not only a supplier of energy. The digested substrate is a valuable soil fertiliser, rich in nitrogen, potassium, phosphorus and micronutrients, which can be applied on soils with the usual equipments for application of liquid manure. A wide range of biomass types can be used as substrates for the production of biogas. The most common biomass categories used in European biogas production are : animal manure and slurry, agricultural residues and by-products,Â ï€ digestible organic wastes from food and agro- industries, organic fraction of municipal waste and from catering, sewage sludge, dedicated energy crops (maize, miscanthus, sorghum, clover). One main advantage of biogas production is the ability to use “wet biomass†types as feedstock, all characterised by moisture content higher than 60- 70% (such as sewage sludge, animal slurries, flotation sludge from food processing etc.). In the late years, a number of energy crops (grains, maize, rapeseed), have been largely used as feedstock for biogas production in countries like Austria or Germany. Besides energy crops, all kinds of agricultural residues, damaged crops, unsuitable for food or resulting from unfavourable growing and weather conditions, can be used to produce biogas and fertiliser. A number of animal by-products, not suitable for human consumption, can also be processed in biogas plants.
Ash transformation during single-pellet gasification of sewage sludge and mixtures with agricultural residues with a focus on phosphorus
