Acetogenic Conversion of H<sub>2</sub> and CO<sub>2</sub> into Formic Acid and <i>Vice Versa</i> in a Fed-Batch-Operated Stirred-Tank Bioreactor
Fabian Schwarz, Florian Oswald, Volker Müller
Abstract
Currently one of the biggest challenges for society is to combat global warming which requires the implementation of CO2 mitigation strategies as well as strategies to replace fossil-fuel-based energy carriers. Since formic acid is considered as a liquid organic hydrogen carrier which directly addresses major challenges in the field of energy storage and (bio)chemical production, the formate bioeconomy and its popularity are rapidly growing. In this study, we describe a biological route for the storage of H2 and the capturing of CO2 in the compound formic acid using acetogenic bacteria as catalysts. The biocatalysis was proven in batch-operated stirred-tank bioreactors, demonstrating the technical feasibility of upscaling of the established whole-cell system. The process showed an efficiency of 100% for CO2 conversion, and formic acid production proceeded with a specific rate of 48.3 mmol g–1 h–1. Notably, no other products were coproduced in the process. The reverse reaction, H2 production from formic acid, was also possible with a qH2 of 27.6 mmol g–1 h–1. The determined turnover frequency and turnover number underline the potential of acetogenic bacteria as biocatalysts for the two challenging reactions of CO2 hydrogenation and H2 evolution from formic acid.