Electricity-driven carbon capture: microbial electrosynthesis of multi-carbon organic acids and chain elongation from...

The rapid rise in CO₂ concentrations poses long-term environmental issues, necessitating the development of effective mitigation techniques. Microbial electrosynthesis (MES) shows promise technology for converting CO₂ into value-added compounds. In MES, chemolithoautotrophic bacteria operate as biocatalysts, converting CO₂ to organic acids in microbial electrochemical reactors. The study aimed to enrich acetogenic chemolithotrophs for CO₂-to-acetic acid conversion, and chain-elongating bacteria for extending short-chain fatty acids into higher-value multi-carbon compounds. Electricity-powered batch tests and MES reactors produced acetic acid (570 mg/L) and other multi-carbon compounds (C2-C7), such as propionic acid (250 ± 14 mg/L), butyric acid (190 ± 20 mg/L), and heptanoic acid (230 ± 25 mg/L). Sporomusa, Pseudomonas, Desulfosporosinus, and Proteiniphilum were the main acetogens (up to 54 %), contributing to chain elongation and C3-C7 acid production. Metabolic activity was associated with the Wood-Ljungdahl pathway for acetogenesis and reverse β-oxidation for fatty acid elongation. The low presence of Clostridium may explain the low yields of elongated products. This work identifies MES-assisted biocatalysis as a promising method for producing multi-carbon compounds from CO₂.