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GASIR2023

27-29 September 2023, University of Bayreuth (UBT)

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Increasing methane productivity in anaerobic digesters by addition of CO2 – the use of stable isotope techniques to identify the mechanisms

Daniela Polag1, Felix Müller2, Konrad Koch2, Mathias Weigoldt3, Michael Lebuhn3, Frank Keppler1
1 Institute of Earth Sciences, Universität Heidelberg
2 Technische Universität München
3 Bayerische Landesanstalt für Landwirtschaft

P 4.9 in Environment and Pollution

In recent years, the demand for renewable energy and the reduction of greenhouse gases such as CO2 has become increasingly important within the framework of energy transition. Sato and Ochi showed in 1994 that CO2 is converted into energetically usable methane (CH4) without the addition of hydrogen (H2). They observed increased CH4 gas production in anaerobic sewage sludge digesters when maintaining high CO2 gas concentration in the headspace. Although follow-up studies confirmed those findings, none of the few recently published studies were able to elucidate the basic effects leading to the bioconversion of CO2 to CH4. Our project (supported by the Fachagentur für Nachwachsende Rohstoffe) investigates bioconversion of CO2 to CH4 with the overall aim of reducing industrial CO2 emissions and transformation of CO2 into energetically usable CH4. This is studied in a long-term anaerobic digestion experiment using different substrates (sewage sludge, maize silage, homogenized organic residuals) and applying stable isotope techniques to identify the underlying mechanisms leading to increased CH4 formation observed within previous studies. For this purpose, two continuous 28 L anaerobic digestion systems were established (reactor with CO2 injection and control) and δ13C-CH4, δ13C-CO2 and δ2H-CH4 values in the headspace gas were measured to investigate the underlying CO2 to CH4 bioconversion pathways, targeting the mechanisms hypothesized so far.

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