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Biotechnology for Biofuels

, 10:180

First Online: 11 July 2017Received: 26 April 2017Accepted: 28 June 2017


BackgroundMedium chain carboxylic acids, such as caproic acid, are conventionally produced from food materials. Caproic acid can be produced through fermentation by the reverse β-oxidation of lactic acid, generated from low value lignocellulosic biomass. In situ extraction of caproic acid can be achieved by membrane electrolysis coupled to the fermentation process, allowing recovery by phase separation.

ResultsGrass was fermented to lactic acid in a leach-bed-type reactor, which was then further converted to caproic acid in a secondary fermenter. The lactic acid concentration was 9.36 ± 0.95 g L over a 33-day semi-continuous operation, and converted to caproic acid at pH 5.5–6.2, with a concentration of 4.09 ± 0.54 g L during stable production. The caproic acid product stream was extracted in its anionic form, concentrated and converted to caproic acid by membrane electrolysis, resulting in a >70 wt% purity solution. In a parallel test exploring the upper limits of production rate through cell retention, we achieved the highest reported caproic acid production rate to date from a lignocellulosic biomass grass, via a coupled process, at 0.99 ± 0.02 g L h. The fermenting microbiome mainly consisting of Clostridium IV and Lactobacillus was capable of producing a maximum caproic acid concentration of 10.92 ± 0.62 g L at pH 5.5, at the border of maximum solubility of protonated caproic acid.

ConclusionsGrass can be utilized as a substrate to produce caproic acid. The biological intermediary steps were enhanced by separating the steps to focus on the lactic acid intermediary. Notably, the pipeline was almost completely powered through electrical inputs, and thus could potentially be driven from sustainable energy without need for chemical input.Open image in new windowGraphical abstractMicrobial and electrochemical production of lactic acid, caproic acid and decane from grass.

KeywordsGrass Lactic acid Caproic acid Decane Fermentation Chain elongation Electrolysis Electronic supplementary materialThe online version of this article doi:10.1186-s13068-017-0863-4 contains supplementary material, which is available to authorized users.

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Autor: Way Cern Khor - Stephen Andersen - Han Vervaeren - Korneel Rabaey

Fuente: https://link.springer.com/

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