Oxic microbial electrosynthesis can be more energy efficient for biomass production than knallgas or photosynthesis based processes
Data on the efficiency and development of continuous processes are scarce in the emerging field of oxic microbial electrosynthesis (OMES). Therefore, the recently isolated knallgas bacterium Kyrpidia spormannii was observed in a bioelectrochemical flow cell setup to study biomass formation and energy efficiency of cathode dependent growth. The study revealed that a potential of -500 mV vs. the standard hydrogen electrode (SHE) caused differences in the structure of the biofilm developing on the cathode, but had almost no impact on biomass growth behavior compared to -375 mV vs. SHE. No growth was observed at 0 mV vs SHE. Coulombic efficiency (CE) was calculated for the cultivation at -500 mV vs. SHE. The process can be conducted with the same electron efficiency as traditional gas fermentation. The solar energy demand with 67.89 kWh kg-1 dry biomass is highly competitive to alternative and already established processes for converting (solar) energy to biomass. Additionally, with suggestions for a biomass harvesting method and subsequent recultivation, proof of principle for a continuously operable process was provided. The results pave the way for a new concept in carbon dioxide-based biotechnology. Significance statementTo mitigate global climate change, it is imperative to transition the human economy to a different resource foundation, moving away from fossil fuels and reducing atmospheric carbon dioxide levels. Biotechnological production based on CO2 necessitates a supply of energy and electrons. This study reveals that an oxic process, wherein bacteria are directly cultivated as a biofilm on the cathode surface of a bioelectrochemical system, can exhibit higher energy efficiency than plant-based systems or systems reliant on hydrogen generated through water electrolysis. This technology could be instrumental in establishing carbon dioxide and renewable energy as the foundation for feed, food, and platform chemical production.