Botswana's offer still stands: Germany can have 20,000 elephants.
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Bioenergy as a Future Option for Biogas Plants
The fermentation of residues such as manure or straw is considered an important future option for biogas plants. Critics fear disadvantages for agriculture. We clarify whether this is true.
Focus of the New Federal Government
According to the new federal government, bioenergy should play an important role in heat, transportation, and controllable electricity generation. "We want to better utilize residues, especially," states the coalition agreement.
Utilization of Residues in Biogas Plants
Residues such as grain or corn straw, as well as manure, have long been an important part of the substrate mix in biogas plants. The Renewable Energies Act, low substrate costs, and relatively high gas yields are the drivers. The Renewable Energy Directive of the EU attributes a high greenhouse gas reduction to biomethane from manure, making it a high-quality fuel when produced from manure or slurry.
Potential in Bavaria
Straw, manure, and slurry in Bavaria have considerable technical potential. According to a recent study by the Bavarian State Research Center for Agriculture, it amounts to about 1.4 billion m³ of methane, or 14.2 TWh. However, only about 14% of this potential is energetically used in biogas plants.
Concerns about Humus Loss
Despite the societal desirability of residue utilization, there are also critical voices. The concern is that the humus content of the soil decreases when straw is broken down in the fermenter and then reapplied as a digestate. According to a statement by the Nature and Biodiversity Conservation Union (NABU), straw, manure, and slurry for the production of biomethane and biofuels are not residues to be used without restrictions but rather valuable by-products from agriculture essential for soil fertility.
Evidence of Humus Buildup
Various studies show that the fermentation of straw, manure, and slurry, when the digestates are returned, does not have a negative impact on soil humus maintenance or buildup. Dr. Maendy Fritz explains that during fermentation, only easily degradable C compounds are converted into biogas, while more complex C compounds remain, supporting humus maintenance and buildup.