Long-Term n-Caproic Acid Production from Yeast-Fermentation Beer in an Anaerobic Bioreactor with Continuous Product Extraction.
Multifunctional reactor microbiomes can elongate short-chain carboxylic acids (SCCAs) to medium-chain carboxylic acids (MCCAs), such as n-caproic acid. However, it is unclear whether this microbiome biotechnology platform is stable enough during long operating periods to consistently produce MCCAs. During a period of 550 days, we improved the operating conditions of an anaerobic bioreactor for the conversion of complex yeast-fermentation beer from the corn kernel-to-ethanol industry into primarily n-caproic acid. We incorporated and improved in-line, membrane liquid-liquid extraction to prevent inhibition due to undissociated MCCAs at a pH of 5.5 and circumvented the addition of methanogenic inhibitors. The microbiome accomplished several functions, including hydrolysis and acidogenesis of complex organic compounds and sugars into SCCAs, subsequent chain elongation with undistilled ethanol in beer, and hydrogenotrophic methanogenesis. The methane yield was 2.40 ± 0.52% based on COD and was limited by the availability of carbon dioxide. We achieved an average n-caproate production rate of 3.38 ± 0.42 g L(-1) d(-1) (7.52 ± 0.94 g COD L(-1) d(-1)) with an n-caproate yield of 70.3 ± 8.81% and an n-caproate/ethanol ratio of 1.19 ± 0.15 based on COD for a period of ∼55 days. The maximum production rate was achieved by increasing the organic loading rates in tandem with elevating the capacity of the extraction system and a change in the complex feedstock batch.
Department of Biological and Environmental Engineering, Cornell University, 226 Riley-Robb Hall, Ithaca, New York 14853, United States.
Shijian
S
Ge
Department of Biological and Environmental Engineering, Cornell University, 226 Riley-Robb Hall, Ithaca, New York 14853, United States.
Joseph G
JG
Usack
Department of Biological and Environmental Engineering, Cornell University, 226 Riley-Robb Hall, Ithaca, New York 14853, United States.
Catherine M
CM
Spirito
Department of Biological and Environmental Engineering, Cornell University, 226 Riley-Robb Hall, Ithaca, New York 14853, United States.
Largus T
LT
Angenent
D001515:Beer / Q000382:microbiology; D057919:Biological Oxygen Demand Analysis; D019149:Bioreactors / Q000382:microbiology; D001709:Biotechnology / Q000295:instrumentation / Q000379:methods*; D002208:Caproates / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D006868:Hydrolysis; D059625:Liquid-Liquid Extraction; D008697:Methane / Q000032:analysis / Q000378:metabolism; D015003:Yeasts / Q000378:metabolism
D002208:Caproates; C037652:hexanoic acid; D000431:Ethanol; D008697:Methane