Toward sustainable production of liquid fuels and chemicals: Improving and expanding chain elongation of waste carbon into n-caproate and n-caprylate with reactor microbiomes

Production of n-caproate and n-caprylate has been described previously in pure cultures of anaerobic bacteria (e.g., Megasphaera elsdenii, Clostridium kluyveri) and in reactor microbiomes. In two studies, reactor microbiomes were continuously fed either lactate or ethanol, and the volumetric production rates (productivities) of n-caproate and n-caprylate were systematically improved. In one study, lactate to n-caproate conversion was demonstrated in a continuously fed bioreactor for the first time. The maximum n-caproate productivity achieved was 6.9 g COD/L-d. In a separate study, an n-caprylate productivity of 19.4 g COD/L-d was achieved, with a corresponding n-caprylate to n-caproate product ratio of 11 g COD/ g COD. Each of these values surpassed the maximum reported in the literature. Several operating parameters were varied, and in-line product recovery was achieved via pertraction (membrane-based liquid-liquid extraction). These studies promote the development of resource recovery processes to convert diverse waste carbon into sustainable liquid fuels and chemicals