Bioelectrochemical engineering analysis of formate-mediated microbial electrosynthesis

Mediated microbial electrosynthesis (MES) represents a promising strategy for the capture and conversion of CO2 into carbon-based products. We describe the development and application of a comprehensive multiphysics model to analyze a formate-mediated MES reactor. The model shows that this system can achieve a biomass productivity of [~]1.7 g L-1 hr-1 but is limited by a competitive trade-off between O2 gas/liquid mass transfer and CO2 transport to the cathode. Synthetic metabolic strategies are evaluated for formatotrophic growth, which can enable an energy efficiency of [~]21%, a 30% improvement over the Calvin cycle. However, carbon utilization efficiency is only [~]10% in the best cases due to a futile CO2 cycle, so gas recycle will be necessary for greater efficiency. Finally, separating electrochemical and microbial processes into separate reactors enables a higher biomass productivity of [~]2.4 g L-1 hr-1. The mediated MES model and analysis presented here can guide process design for conversion of CO2 into renewable chemical feedstocks.