During fermentation, the processed biomasses are broken down by microorganisms in a controlled process, under the absence of oxygen and at a suitable process temperature. The organic matter contained produces biogas, a mixture of mainly methane and carbon dioxide. For this purpose, two separate reactor lines are available for agricultural (cereal straw and cattle manure) and urban (green waste and biowaste) bioresources, which differ in their mode of operation and the possible dry substance contents of the resources. Thus, this constellation allows a direct comparison of the reactor systems, the biogas qualities and quantities of each digester, the influence of hydrothermal pretreatment of the substrates and thus the methane yield over each process stage. Considering economic and ecological aspects, the results serve as a planning basis for process scaling and ideal operating points. A compromise between substrate utilization and costs has to be found.

The biogas mixture of the two digester lines is taken from a gas buffer, cleaned and upgraded to methane (CH₄), the so-called methanation. In the first step, the biogas is cleaned without pressure and at ambient temperature by using adsorbents, such as activated carbons or metal oxides, to separate catalyst- and plant-damaging components, especially hydrogen sulfide (H₂S) and other sulfur-containing molecules, from the gas. The gas is then compressed to 20 bar, heated to 150 °C and passed through a police filter so that the last traces of H₂S are separated. In the second step, biogas upgrading in the methanation reactor, hydrogen (H₂) is added to the biogas, which reacts with the carbon dioxide (CO₂) to form methane. The amount of H₂ is adjusted to the CO₂ content in the gas. Downstream of the reactor, the gas is depressurized and cooled to ambient temperature to condense and separate the water formed during the reaction. Subsequently, excess CO₂ is removed from the dry gas in a two-stage NaOH scrubber. The target for the purified product gas is to meet DIN EN 16723-2 for use as a transport fuel.

As part of the pilot plant for renewable methane, the introduction of hydrothermal processes is used for pre- and post-treatment of the bioresources. In this process, the aqueous biomasses are treated at up to 240 °C and 40 bars. In the course of the reaction, the polymeric biomass components are first broken down into their monomeric building blocks by hydrolysis, and then a broad spectrum of products ranging from fine chemicals to so-called hydrochar are generated by decomposition and recombination. In the context of pretreatment, a stainless-steel reactor with heating jacket, agitator and steam generator is used primarily for pre-digestion, i.e. hydrolysis of the biomasses, in order to achieve a higher methane yield with a low retention time in fermentation process. The post-treatment of the digestate aims for further material value creation. Various digestate from pilot plant campaigns will be hydrothermally carbonized and the suitability of the hydrochar produced for 1) gasification and 2) carbon capture and storage (CCS) via soil application will be investigated. The goal of gasification is to provide a syngas for the chemical industry, thereby providing renewable carbon with the goal of sequestration for material use.

In the digestate treatment module, the portion of biomass that has not been fermented into biogas is treated to produce dischargeable water, a solid organic farm fertilizer rich in nitrogen and phosphorus, and a liquid inorganic farm fertilizer rich in nitrogen and potassium. In addition, a recirculate can be provided from the liquid phase of the digestate for mixing in the biogas process. The first step of digestate treatment consists of separating the solid phase from the liquid phase by means of a press screw separator and decanter centrifuge or chamber filter press with the addition of flocculants. For further treatment or concentration of the liquid phase, the membrane technologies ultrafiltration and reverse osmosis are available. With the separation cascade, an average of 0.1 - 0.5 m³ of digestate can be processed per day with the aim of achieving a volume reduction of at least 50%. The quantity and quality of the recovered nutrients or farm manure depends on the biomass used and the process conditions in the anaerobic fermentation. During processing, all relevant process parameters are recorded for monitoring the separation processes and for determining mass and energy balances.