Characterization of biogas plants in Germany: methane emission rate quantification and isotopic source signatures

The development of biogas as a renewable energy source in Europe and especially in Germany, the largest biogas producer in Europe, requires an appropriate strategy to quantify potential methane (CH4) losses to ensure the sustainability of renewable energy production in the biogas sector. In addition to high uncertainties in emission factors, there is little information on the temporal variation of CH4 emissions from biogas plants. To evaluate this issue, CH4 emissions were assessed across 65 biogas production sites in Germany using mobile measurements combined with a Gaussian dispersion model. The quantified CH4 emission rates ranged from 0.3 to 255 kg h−1. A significant environmental problem is the uncontrolled release of methane into the atmosphere, which is approximately 5 % (median of all analyzed biogas plants) of the methane produced. To ensure the reliability and consistency of the results, the measurement and quantification method used has been thoroughly tested and refined through controlled CH4 release experiments. These experiments helped to identify and mitigate potential sources of uncertainty. As a result, the method demonstrated n overall accuracy of 30 % in quantifying emission rates. Additionally, the isotopic source signature (δ13CH4) was determined for 18 biogas plants, revealing a wide range of values between -62.7 ‰ to -39.6 ‰, strongly influenced by the feedstock used.