The project set out to provide a reliable, site‑specific quantification of greenhouse‑gas emissions from biogas plants, with a particular focus on the open storage of digestate and the operation of under‑ and over‑pressure systems that control biogas release. By combining direct on‑site measurements with remote sensing techniques, the study aimed to generate emission factors that could be used for national inventories and for assessing the environmental performance of biogas production from agricultural waste.
On‑site measurements were carried out at ten biogas plants, each equipped with a different combination of digestate storage and pressure‑control devices. The reference plant (Plant 1) was used to validate the measurement chain, while Plants 2–10 provided data for a range of operating conditions. The measurement suite included open‑path laser spectrometers (GF2 and GF3), tunable diode laser absorption spectroscopy (TDLAS), and a differential absorption lidar (DIAL) system. These instruments were positioned to capture methane and other volatile organic compounds directly from the digestate surface and from the pressure‑control outlets. In addition, meteorological data (wind speed, temperature, humidity) were recorded to support dispersion modelling.
Remote sensing complemented the on‑site approach. Inverse dispersion modelling was applied to the concentration data collected by the open‑path spectrometers, allowing the reconstruction of emission rates over the entire digestate surface. The tracer‑gas method involved injecting a known quantity of a non‑reactive tracer into the digestate and measuring its downstream concentration; the resulting plume dispersion provided an independent estimate of the emission flux. The DIAL system offered vertical profiling of methane concentrations above the digestate, enabling the detection of plume development and the assessment of atmospheric mixing conditions.
The combined methodology yielded emission rates expressed in milligrams per hour, grams per square metre per hour, and cubic metres per hour, depending on the measurement configuration. From these rates, methane emission factors (percentage of methane in the biogas) were calculated for each plant. While the report does not list specific numerical values, it demonstrates that the integrated approach can capture both spatially and temporally variable emissions, and that the derived emission factors are consistent with those reported in the literature for similar systems.
The project was carried out in close collaboration with a network of partners. The German Biomass Research Center (DBFZ) provided expertise in biogas plant operation and data management. TechSim Ltd. supplied the open‑path laser spectrometers and assisted with instrument calibration. TÜV Thuringia performed independent verification of the measurement protocols. Heeren Hepolan Ltd. and Nesemeier Ltd. supplied the pressure‑control devices and contributed to the design of the experimental layout. The German Meteorological Service supplied high‑resolution weather data essential for the dispersion models. The project was funded by the Federal Ministry of Food, Agriculture and Consumer Protection and the Federal Ministry of Environment, Nature Conservation and Nuclear Safety, with project management coordinated by the Renewable Resources Agency. The overall timeframe spanned from 2008 to 2012, with the final report compiled in 2013. This collaborative effort produced a robust dataset and a validated methodology that can be applied to future biogas plant assessments across Germany and beyond.