Biological CO₂ fixation in up-flow reactors via exogenous H₂ addition

Gas fermentation for the production of building block molecules and biofuels is lately gaining attention as a means to eliminate the greenhouse gases emissions. Especially CO₂ capture and recycling are in focus. Thus, the biological coupling of CO₂ and H₂ is of high interest. Therefore, the focus of the present work was to evaluate the performances of two up-flow reactors for CO₂ and H₂ assimilation. Process monitoring showed that the gas-liquid H₂ transfer was highly affected by reactor design. A reactor filled with Raschig rings could lift up gases utilization leading to a CH₄ content of 81% at 6 h gas retention time and 8.8 L/L_R.h gas recirculation rate. In contrast, limited biomethanation was achieved in the absence of Raschig rings highlighting the positive role of packing material to the performance of up-flow-reactors. Additionally, high-throughput 16S rRNA sequencing revealed that the microbial community was ultimately resided by Methanothermobacter methanogens.