Organic acid production from CO2/H2 and CO/H2 by mixed‐culture anaerobes

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Abstract
The gases CO, CO2, and H2 were used as substrates in anaerobic fermentations producing organic acids. Various mixed bacterial sources were used, including sewage sludge digester effluent, rabbit feces, and soil. Nonsterile microorganism selection was carried out using CO2/H2 and CO/H2 as the primary carbon and energy sources. Cultures were grown in specially designed, high‐pressure (to 70 psig) flasks. Methanogenic bacteria were eliminated from the cultures. Liquid products of the fermentations were acetic through caproic acids, with the even‐numbered acids predominating. Carbon balances showed conclusively that acetic acid was formed from carbon contained in the CO or CO2 feed gas. Measurements made included rates of acid product formation, cell density, and degree of gas utilization. Limited characterization of the microorganisms was also performed. Production of organic acids by mixed culture inocula from CO2/H2 or CO/H2 had not been reported previously. Application of this work is to the production of organic chemicals from synthesis gas (SNG), produced by the gasification of fossil fuels (peat, lignite, and various ranks of coals), biomass (agricultural and forest residues, and various biomass crops grown expressly for energy recovery), and municipal solid waste.