ENCOVER: Energetic utilization of CO2 to reduce the residual methane potential

The most significant source of greenhouse gas emissions is the combustion of fossil fuels. In order to achieve the goal of greenhouse gas neutrality by 2050, energy supply in the future must increasingly be based on renewable energies. Biogas production has a key role to play here, since unlike most other forms of renewable energy, it can be stored. Unfortunately, a not inconsiderable proportion of the methane potential remains in the fermentation residue when renewable raw and residual materials are fermented. Studies have shown that an enrichment of the anaerobic degradation process with CO₂ can contribute to an increase in methane productivity under certain conditions, while at the same time increasing the resilience of the process.

The goal of the project is the energetic utilization of CO₂ to reduce the residual methane potential. In the process of biogas production, renewable raw materials and especially residual materials are used, whose behavior with CO₂ enrichment in anaerobic degradation has not yet been investigated. However, their use appears to be particularly promising, since in contrast to the substrate sewage sludge, which has been investigated in particular so far, a stimulation by a significantly better substrate conversion is considered to be probable.

Within the scope of the investigations, the CO₂ uptake potential and the additional CH4 production are to be quantified. By means of isotope analyses and microbiological investigations, the mechanisms and processes taking place are to be broken down and better understood. The investigations are carried out by means of batch experiments as well as continuously operated reactors on a pilot plant scale.

The reactors are currently fed with renewable raw materials in the form of corn silage. During CO₂ enrichment, one reactor is always gassed, while the second serves as a reference under otherwise identical conditions for control. Gassing of the reactors is semi-continuous. Finally, from the knowledge gained about the process control of CO2 enrichment of renewable raw materials, it is necessary to derive and present recommendations for the use of the effect for practical applications quantitatively in terms of CO₂ balance and economic efficiency.