Probing efficient microbial CO2 utilizationthrough metabolic and process modeling

Abstract

Microbial gas fermentation is proving to be a promising technology to upcycle carbon-rich waste gasses into value-added biochemicals, though production yields of varied products are currently limited. Through the holistic pairing of process modeling with host agnostic black box metabolic modeling, here we investigate an efficient thermophilic CO2 upcycling process, based on acetogenic carbon utilization. From a process engineering perspective, higher temperatures were found to favor overall gas transfer rates, even with lower gas solubility, particularly for the more expensive and often limiting H2 gas. Metabolically, for growth coupled products, thermophilic production favors higher product yields as a result of a higher maintenance energy input. A process simulation for acetate production in a large-scale bubble column reactor predicts an optimal feed gas composition of approximately 9:1 mol H2 to mol CO2 and a process with higher production yields and rates at higher temperatures. To assess the expansion of the product portfolio beyond acetate, both a product volatility analysis and a metabolic pathway model were implemented. In-situ recovery of volatile products is shown to be within range for acetone but challenging due to the extensive evaporation of water, while the production of more valuable compounds is energetically unfavorable compared to acetate. We discuss alternative approaches to overcome these challenges to utilize acetogenic CO2 fixation for the production of a wider range of carbon negative chemicals.