Fermentative methanation of hydrogen in biogas plants

The research field of 'power to gas' is growing in importance and can contribute significantly to the energy transition in the future. Surplus electricity from renewable fluctuating sources is converted into hydrogen by electrolysis. After biological methanation in an adapted biogas process, this chemical energy carrier can be stored in the gas grid.

This project focuses on microbiological methanation of hydrogen and carbon dioxide. Hydrogen is added to the biogas process and then converted by hydrogenotrophic archaea to produce methane. If necessary, the methane content of the biogas can be raised by a subsequent, fine purification to the required level to be fed back into the gas grid.

The goal is to base on the single-stage biogas system, which is normally used in the 8000 biogas plants operating in Germany. Under which conditions existing fermentation systems can be used for methanation of hydrogen will be analyzed in this research project. In preliminary experiments in a 400 liter biogas fermenter, the methane content of the biogas could be increased from 52 % to more than 75 % by direct addition of hydrogen (half stoichiometric ratio). The carbon dioxide content of the biogas process decreased accordingly. In the further stage of the project, four laboratory fermenters will be constructed and equipped with measurement technology and automatic data acquisition. Various hydrogen application techniques will be tested and adjusted. To optimize the conversion conditions we will vary fermentation temperature, the organic loading rate and hydraulic retention time. Finally a pilot experiment will be carried out at the research biogas plant Unterer Lindenhof.

In intensive collaborations with partners of the research consortium, data for fermenter dimensioning and process parameters are being exchanged. Moreover, modeling methods are used to optimize the process conditions.