Anaerobic digestion of energy crops, residues, and wastes is of increasing interest in order to reduce the greenhouse gas emissions and to facilitate a sustainable development of energy supply. Production of biogas provides a versatile carrier of renewable energy, as methane can be used for replacement of fossil fuels in both heat and power generation and as a vehicle fuel. For biogas production, various process types are applied which can be classified in wet and dry fermentation systems. Most often applied are wet digester systems using vertical stirred tank digester with different stirrer types dependent on the origin of the feedstock. Biogas is mainly utilized in engine-based combined heat and power plants, whereas microgas turbines and fuel cells are expensive alternatives which need further development work for reducing the costs and increasing their reliability. Gas upgrading and utilization as renewable vehicle fuel or injection into the natural gas grid is of increasing interest because the gas can be used in a more efficient way. The digestate from anaerobic fermentation is a valuable fertilizer due to the increased availability of nitrogen and the better short-term fertilization effect. Anaerobic treatment minimizes the survival of pathogens which is important for using the digested residue as fertilizer. This paper reviews the current state and perspectives of biogas production, including the biochemical parameters and feedstocks which influence the efficiency and reliability of the microbial conversion and gas yield.
Microbial conversion of energy crops and organic wastes to biogas has become one of the most attractive technologies for energy production, resource recovery, and waste treatment. It creates a wide breadth of positive environmental impacts because it reduces emissions of greenhouse gases, improves the management of manure and organic wastes, and replaces mineral fertilizer. Biogas is used today mainly for electricity and heat production, but it can also be applied as a vehicle fuel or for the production of hydrogen which is necessary for fuel cells. Biogas production in the agricultural sector is a very fast growing market in many European countries. This paper presents the current situation in Germany which has the highest number of agricultural biogas plants in Europe.
The production of biogas for reducing fossil CO2 emissions is one of the key strategic issues of the German government and has resulted in the development of new process techniques and new technologies for the energetic use of biogas. Progress has been made in cultivating energy crops for biogas production, in using new reactor systems for anaerobic digestion, and in applying more efficient technologies for combined heat and power production. Recently, integration of fuel cells within the anaerobic digestion process was started, and new technologies for biogas upgrading and conversion to hydrogen were tested. This article describes the trends in Germany for achieving more efficient energy production.
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