Biomethanation as a building block of the energy transition at wastewater treatment plants

As part of the energy transition, renewable energies are set to play a central role in the German energy system in the long term. One promising solution for flexible and needs-based energy storage is the conversion of hydrogen (H₂) and carbon dioxide (CO₂) into methane (CH₄) using the so-called power-to-methane process. In this process, H₂ is produced from unused renewable electricity using electrolysis and CO₂ from wastewater treatment plants, biogas plants or industry can be utilised directly where it is produced.
The microbiological conversion of H₂ and CO₂ to CH₄ under anaerobic conditions by methanogenic microorganisms is known as a sub-process from biogas plants or digesters. A particularly efficient reactor concept is the gas-filled trickle bed reactor, in which the microorganisms are immobilised on growth bodies.

In the completed DemoMeth project, a pilot reactor with an active reaction volume of 0.8 m³ was installed at the Garching wastewater treatment plant. Raw biogas from the digester’s gas storage tank was used as the CO₂ source, enabling the biogas to be upgraded to feed-in quality (> 96 % CH₄) at the point of origin. A stable methane production rate of 6 m³/(m³ reactor volume*d) was achieved in the pilot reactor. After a 1.5-year shutdown period, the pilot reactor was fully repaired and put back into operation as part of the new KomMeth project. The first start- up tests in a cold start prove that the reactor can achieve stable methane production again within a short time, even after a longer shutdown.

With the aim of testing the conversion technology as a holistic concept and under real conditions, the H₂ supply from gas bundles has now been replaced by the integration of an electrolyser. This coupling of electrolysis and methanation is intended to demonstrate the functionality of the overall process and identify and address any challenges that arise, for example with regard to the necessary intermediate storage of H₂. In addition, various investigations are being carried out in parallel to further optimise methane productivity, process stability and the dynamic operation of the plant.