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Electricity-assisted production of caproic acid from grass

Way Cern Khor (UGent) , Stephen Andersen (UGent) , Han Vervaeren (UGent) and Korneel Rabaey (UGent)
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Abstract
Background: Medium chain carboxylic acids, such as caproic acid, are conventionally produced from food materials. Caproic acid can be produced through fermentation by the reverse beta-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. Results: Grass 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-1 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-1 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(-1) h(-1). 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-1 at pH 5.5, at the border of maximum solubility of protonated caproic acid. Conclusions: Grass 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.
Keywords
Grass, Lactic acid, Caproic acid, Decane, Fermentation, Chain elongation, Electrolysis, CHAIN ELONGATION, EXTRACTIVE FERMENTATION, MICROBIAL COMMUNITY, REACTOR MICROBIOMES, KOLBE ELECTROLYSIS, HEXANOIC ACID, LACTIC-ACID, N-CAPROATE, BIOMASS, SEPARATION

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Chicago
Khor, Way Cern, Stephen Andersen, Han Vervaeren, and Korneel Rabaey. 2017. “Electricity-assisted Production of Caproic Acid from Grass.” Biotechnology for Biofuels 10.
APA
Khor, W. C., Andersen, S., Vervaeren, H., & Rabaey, K. (2017). Electricity-assisted production of caproic acid from grass. BIOTECHNOLOGY FOR BIOFUELS, 10.
Vancouver
1.
Khor WC, Andersen S, Vervaeren H, Rabaey K. Electricity-assisted production of caproic acid from grass. BIOTECHNOLOGY FOR BIOFUELS. 2017;10.
MLA
Khor, Way Cern, Stephen Andersen, Han Vervaeren, et al. “Electricity-assisted Production of Caproic Acid from Grass.” BIOTECHNOLOGY FOR BIOFUELS 10 (2017): n. pag. Print.
@article{8541941,
  abstract     = {Background: Medium chain carboxylic acids, such as caproic acid, are conventionally produced from food materials. Caproic acid can be produced through fermentation by the reverse beta-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. 
Results: Grass 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-1 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-1 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(-1) h(-1). 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-1 at pH 5.5, at the border of maximum solubility of protonated caproic acid. 
Conclusions: Grass 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.},
  articleno    = {180},
  author       = {Khor, Way Cern and Andersen, Stephen and Vervaeren, Han and Rabaey, Korneel},
  issn         = {1754-6834},
  journal      = {BIOTECHNOLOGY FOR BIOFUELS},
  keywords     = {Grass,Lactic acid,Caproic acid,Decane,Fermentation,Chain elongation,Electrolysis,CHAIN ELONGATION,EXTRACTIVE FERMENTATION,MICROBIAL COMMUNITY,REACTOR MICROBIOMES,KOLBE ELECTROLYSIS,HEXANOIC ACID,LACTIC-ACID,N-CAPROATE,BIOMASS,SEPARATION},
  language     = {eng},
  pages        = {11},
  title        = {Electricity-assisted production of caproic acid from grass},
  url          = {http://dx.doi.org/10.1186/s13068-017-0863-4},
  volume       = {10},
  year         = {2017},
}

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