Microbial electrosynthesis of liquid chemicals from carbon dioxide

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 a source of reducing equivalents, including organic acids (e.g., acetate (C2), butyrate (C4), hexanoate (C6)) or alcohols (e.g., ethanol, butanol, hexanol) in a process called microbial electrosynthesis, which 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 cost of electrochemical systems, mainly due to electrodes and membranes.
4. Poor selectivity of electrosynthesis towards products with high commercial value (C2 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 commercialisation perspective).
5. Purity of the final product(s), which is very important for commercialisation purposes. E.g., carboxylates with C4 and higher are relatively insoluble in water, hence targeting these products would make downstream processing more viable.

Recent work at the ACWEB showed significant improvements in the performance of such systems, achieving a full order of magnitude increase in acetate productivity from CO2. However, production of chemicals with a longer carbon chain is feasible. Hence, this project aims to make significant contributions towards finding solutions towards:

• product diversification
• extraction of targeted products
• microbial understanding, and
• design, materials and process configurations.

Funding

• FL170100086

Project Outcomes

The key purpose of this project is to:

1. Improve current understanding of microbial electrosynthesis from CO2 and generate know-how that will help shift from oil-based industries for the production of commodity chemicals and fuels.
2. Discover currently unknown species and metabolic pathways responsible for production of longer chain carboxylates and alcohols from CO2 and electricity.
3. Deliver technological solutions for practical implementation of the microbial electrosynthesis technology, including reactor design, electrode materials and surface modifications, optimal reactor operations, and product extraction.

Publications

• Wood, J. C., Marcellin, E., Plan, M. R. & Virdis, B. High methanol-to-formate ratios induce butanol production in Eubacterium limosum. Microb Biotechnol (2021) http://doi.org/10.1111/1751-7915.13963.
• Wood, J. C. et al. Strategies to improve viability of a circular carbon bioeconomy – A techno-economic review of microbial electrosynthesis and gas fermentation. Water Res 117306 (2021) http://doi.org/10.1016/j.watres.2021.117306.
• Hernandez, P. A. et al. Selective Extraction of Medium-Chain Carboxylic Acids by Electrodialysis and Phase Separation. Acs Omega (2021) http://doi.org/10.1021/acsomega.1c00397.  
• Izadi, P., Fontmorin, J.-M., Virdis, B., Head, I. M. & Yu, E. H. The effect of the polarised cathode, formate and ethanol on chain elongation of acetate in microbial electrosynthesis. Applied Energy 116310 (2020) http://doi.org/10.1016/j.apenergy.2020.116310.