Effect of N2 on Biological Methanation in a Continuous Stirred-Tank Reactor with Methanothermobacter marburgensis

In this contribution, the effect of the presence of a presumed inert gas like N2 in the feed gas on the biological methanation of hydrogen and carbon dioxide with Methanothermobacter marburgensis was investigated. N2 can be found as a component besides CO2 in possible feed gases like mine gas, weak gas, or steel mill gas. To determine whether there is an effect on the biological methanation of CO2 and H2 from renewable sources or not, the process was investigated using feed gases containing CO2, H2, and N2 in different ratios, depending on the CO2 content. A possible effect can be a lowered conversion rate of CO2 and H2 to CH4. Feed gases containing up to 47% N2 were investigated. The conversion of hydrogen and carbon dioxide was possible with a conversion rate of up to 91% but was limited by the amount of H2 when feeding a stoichiometric ratio of 4:1 and not by adding N2 to the feed gas.