Emerging research worldwide is demonstrating that a variety of liquid fuels and chemicals can be produced from CO2 in microbial electrochemical systems using electrodes as source of reducing equivalents, including organic acids e.g., acetate (C2), butyrate (C4), hexanoate (C6) or alcohols such as ethanol, butanol, hexanol, in a process called microbial electrosynthesis. This process has many proven benefits, including the offset of carbon emissions of many industrial processes producing CO2 as off-gas. However, the translation of these research advances into full-scale application is constrained by:
1) Low production rates and product concentrations, primarily due to poor microbial understanding of electrosynthesis and the chain elongation process;
2) Low energy-transfer efficiency between electrodes and microbes, possibly due to poor biocompatibility of electrodes, leading to interfacial electron transfer limitations;
3) Significant costs of the systems, mainly attributed to electrodes and membranes;
4) Poor selectivity of electrosynthesis towards products of with high commercial value. Carboxylate acetic acid is often reported as the main product of electrosynthesis, although its lower value compared to longer chain carboxylate makes it less interesting from a commercialization perspective;
5) Purity of the final product(s), which is very important for commercialization purposes. For example, carboxylates with C4 and higher are relatively insoluble in water, hence targeting these products would make downstream processing more viable.
Recent work at AWMC showed significant improvements in performance of such systems, achieving a full order of magnitude increase in acetate productivity from CO2. However, acetate remains a chemical with low value ($800/ton) compared to longer chain carboxylates e.g., butyrate $2,000/ton, hexanoate $5,500/ton, etc., and corresponding alcohols e.g., butanol $2,500/ton, hexanol $7,000/ton, etc. Hence, this ARC Laureate sub-project aims to make significant contributions towards finding solutions for 1) product diversification, 2) extraction, 3) microbial understanding, and 4) design, materials and configurations.
