National-Scale Quantification of Methane Emissions from Biogas Facilities and Wastewater Treatment Plants in Germany

Mitigation of CH₄ emissions represents an effective short-term strategy for reducing climate change impacts. However, anthropogenic CH₄ emission estimates remain highly uncertain due to the complex and heterogeneous distribution of sources and the strong temporal variability of emission processes. Emission factors for biogas plants and for the waste and wastewater treatment sector are still subject to large uncertainties.
This study focuses on the quantification of CH₄ emission rates from biogas plants and wastewater treatment facilities in Germany using mobile methane measurements conducted at street level with cars and bicycles. Localized CH₄ concentration enhancements are detected and converted into emission rates using a Gaussian plume model. Based on more than seven years of controlled CH₄ release experiments, we developed a best-practice methode for mobile measurements, including optimized driving strategies and data processing procedures, reducing the overall uncertainty of derived emission rates to below 30%.
Mobile measurements were performed at more than 60 biogas plants, with one facility monitored continuously since 2016 to assess long-term emission behavior. Derived methane emission rates ranged from 0.1 to 46 kg CH₄ h^-1, corresponding to relative CH₄ losses of approximately 0.2- 42.7% of the produced CH₄. Methane emissions from wastewater treatment plants (WWTPs) in Germany have been investigated only in a limited number of studies, and current national inventories rely largely on emission factors derived from measurements in other European countries. To address this gap, a systematic survey was conducted at 13 WWTPs in Germany. Measurements were used to identify dominant CH₄ emission sources, investigate diurnal emission patterns, and quantify facility-level CH₄ emission rates and emission factors. At the surveyed sites, sludge treatment units and screening facilities were identified as the main emission sources. Determined CH₄ emission rates ranged from 0.42 to 12.96 kg CH₄ h^-1.
The derived emission rates and emission factors are statistically analyzed, and compared with values currently used in regional and national emission inventories. These findings help to improve inventory accuracy and to target methane mitigation strategies.