Energy production by biomass decomposition at biogas plants is very important for the renewable energy sector, but the specific degradation processes and methanogenic pathways taking place during anaerobic digestion are still largely unknown because the analysis is time consuming and complex. Therefore, reliable, easily measurable, and online control parameters for methane production are needed. Methane is produced by two different pathways, which can be distinguished by their isotopic signature. Acetotrophic methanogenesis shows a carbon isotopic fractionation between 15 and 30 ‰, whereas methane produced by hydrogenotropic methanogenesis is slightly more depleted.

Frank Keppler, Max-Planck Institute for Chemistry, Mainz, Germany, and colleagues used continuous isotope laser spectroscopy to measure δ¹³C(CH₄) in real-time for a 3500 L biogas plant. They established the first continuous real-time measurement of stable carbon isotopes of methane in a pilot project by using an optical isotope spectrograph. By measuring the δ¹³C(CH₄) values they were able to detect changes in the processes taking place inside the biogas plant. This method also makes it possible to detect process failures at an early stage.

• Stable carbon isotopes of methane for real-time process monitoring in anaerobic digesters,
  Daniela Polag, Lutz Christian Krapf , Hauke Heuwinkel, Stephan Laukenmann, Jos Lelieveld, Frank Keppler,
  Eng. Life Sci. 2013.
  DOI: 10.1002/elsc.201200201