DUEME

The X-Energy sub-project DUEME (direct conversion of electricity into methane) explored possible methods for sustainable electricity storage. The focus lay on a new and promising power-to-gas (PtG) technology known as electromethanogenesis. In this process, surplus electricity is used to convert carbon dioxide into methane with the help of microorganisms. The energy can then be stored in a chemical compound and can replace fossil natural gas, which consists primarily of methane. The methane is then fed into the existing natural gas grid without any problems and utilised as a green energy source.

Electromethanogenesis is an alternative PtG process in which the previously separate process steps of ‘electrolysis’ and ‘methanisation’ are combined. The CO₂ is converted directly into methane using electrons without any intermediate electrolysis. For this, renewably generated electricity is used. In contrast to conventional biological methanisation, in which hydrogen is fed into a bioreactor, a significantly better efficiency was to be expected, as the process is not limited by the poor solubility of hydrogen in water.

The DUEME project comprises five areas of work:

• 1. planning and procurement of the instruments for the investigation of electromethanogenesis
• 2. isolating and cultivating various archaea and carrying out a molecular biological and biochemical investigation of these cultures as well as various reference cultures in the so-called H-cells
• 3. and 4. investigation of unknown metabolic pathways
• 5. demonstration of electromethanogenesis

Results

In the course of the research into electromethanogenesis, a total of 4 cultures of archaea were isolated and their temperature and pH optima characterised. Genetic analyses showed that the cultures belong to the species Methanobacterium formicicum.

Two different test systems were developed to analyse the electroactive properties of the isolated cultures. These results were published in the journal Bioresource Technology Reports
(https://doi.org/10.1016/j.biteb.2024.101875). The larger of the developed test systems was further developed in the EmSpe project to investigate the stability of electromethanogenesis under intermittent electricity supply.

The results from the DUEME sub-project were utilised and continued in the sub-project EmSpe.