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Electrolytic extraction drives volatile fatty acid chain elongation through lactic acid and replaces chemical pH control in thin stillage fermentation

Stephen Andersen (UGent) , Pieter Candry (UGent) , Thais Basadre Castro (UGent) , Way Cern Khor (UGent) , Hugo Roume (UGent) , Emma Hernandez Sanabria (UGent) , Marta Coma (UGent) and Korneel Rabaey (UGent)
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Abstract
Background: Volatile fatty acids (VFA) are building blocks for the chemical industry. Sustainable, biological production is constrained by production and recovery costs, including the need for intensive pH correction. Membrane electrolysis has been developed as an in situ extraction technology tailored to the direct recovery of VFA from fermentation while stabilizing acidogenesis without caustic addition. A current applied across an anion exchange membrane reduces the fermentation broth (catholyte, water reduction: H2O + e(-) -> H-1/2(2) + OH-) and drives carboxylate ions into a clean, concentrated VFA stream (anolyte, water oxidation: H2O -> 2e + 2 H-1 + O-2). Results: In this study, we fermented thin stillage to generate a mixed VFA extract without chemical pH control. Membrane electrolysis (0.1 A, 3.22 +/- 0.60 V) extracted 28 +/- 6 % of carboxylates generated per day (on a carbon basis) and completely replaced caustic control of pH, with no impact on the total carboxylate production amount or rate. Hydrogen generated from the applied current shifted the fermentation outcome from predominantly C2 and C3 VFA (64 +/- 3 % of the total VFA present in the control) to majority of C4 to C6 (70 +/- 12 % in the experiment), with identical proportions in the VFA acid extract. A strain related to Megasphaera elsdenii (maximum abundance of 57 %), a bacteria capable of producing mid-chain VFA at a high rate, was enriched by the applied current, alongside a stable community of Lactobacillus spp. (10 %), enabling chain elongation of VFA through lactic acid. A conversion of 30 +/- 5 % VFA produced per sCOD fed (60 +/- 10 % of the reactive fraction) was achieved, with a 50 +/- 6 % reduction in suspended solids likely by electro-coagulation. Conclusions: VFA can be extracted directly from a fermentation broth by membrane electrolysis. The electrolytic water reduction products are utilized in the fermentation: OH- is used for pH control without added chemicals, and H-2 is metabolized by species such as Megasphaera elsdenii to produce greater value, more reduced VFA. Electro-fermentation displays promise for generating added value chemical co-products from biorefinery sidestreams and wastes.
Keywords
Chain elongation, Carboxylate platform, Biorefinery, Extraction, Electro-fermentation, Membrane electrolysis, MEGASPHAERA-ELSDENII, REACTOR MICROBIOMES, RUMINAL BACTERIUM, SP-NOV., BIOREFINERY, ETHANOL, PROPIONATE, PECTINATUS, RESOURCES, HYDROGEN

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Chicago
Andersen, Stephen, Pieter Candry, Thais Basadre Castro, Way Cern Khor, Hugo Roume, Emma Hernandez Sanabria, Marta Coma, and Korneel Rabaey. 2015. “Electrolytic Extraction Drives Volatile Fatty Acid Chain Elongation Through Lactic Acid and Replaces Chemical pH Control in Thin Stillage Fermentation.” Biotechnology for Biofuels 8.
APA
Andersen, S., Candry, P., Basadre Castro, T., Khor, W. C., Roume, H., Hernandez Sanabria, E., Coma, M., et al. (2015). Electrolytic extraction drives volatile fatty acid chain elongation through lactic acid and replaces chemical pH control in thin stillage fermentation. BIOTECHNOLOGY FOR BIOFUELS, 8.
Vancouver
1.
Andersen S, Candry P, Basadre Castro T, Khor WC, Roume H, Hernandez Sanabria E, et al. Electrolytic extraction drives volatile fatty acid chain elongation through lactic acid and replaces chemical pH control in thin stillage fermentation. BIOTECHNOLOGY FOR BIOFUELS. 2015;8.
MLA
Andersen, Stephen et al. “Electrolytic Extraction Drives Volatile Fatty Acid Chain Elongation Through Lactic Acid and Replaces Chemical pH Control in Thin Stillage Fermentation.” BIOTECHNOLOGY FOR BIOFUELS 8 (2015): n. pag. Print.
@article{7039819,
  abstract     = {Background: Volatile fatty acids (VFA) are building blocks for the chemical industry. Sustainable, biological production is constrained by production and recovery costs, including the need for intensive pH correction. Membrane electrolysis has been developed as an in situ extraction technology tailored to the direct recovery of VFA from fermentation while stabilizing acidogenesis without caustic addition. A current applied across an anion exchange membrane reduces the fermentation broth (catholyte, water reduction: H2O + e(-) -> H-1/2(2) + OH-) and drives carboxylate ions into a clean, concentrated VFA stream (anolyte, water oxidation: H2O -> 2e + 2 H-1 + O-2). 
Results: In this study, we fermented thin stillage to generate a mixed VFA extract without chemical pH control. Membrane electrolysis (0.1 A, 3.22 +/- 0.60 V) extracted 28 +/- 6 % of carboxylates generated per day (on a carbon basis) and completely replaced caustic control of pH, with no impact on the total carboxylate production amount or rate. Hydrogen generated from the applied current shifted the fermentation outcome from predominantly C2 and C3 VFA (64 +/- 3 % of the total VFA present in the control) to majority of C4 to C6 (70 +/- 12 % in the experiment), with identical proportions in the VFA acid extract. A strain related to Megasphaera elsdenii (maximum abundance of 57 %), a bacteria capable of producing mid-chain VFA at a high rate, was enriched by the applied current, alongside a stable community of Lactobacillus spp. (10 %), enabling chain elongation of VFA through lactic acid. A conversion of 30 +/- 5 % VFA produced per sCOD fed (60 +/- 10 % of the reactive fraction) was achieved, with a 50 +/- 6 % reduction in suspended solids likely by electro-coagulation. 
Conclusions: VFA can be extracted directly from a fermentation broth by membrane electrolysis. The electrolytic water reduction products are utilized in the fermentation: OH- is used for pH control without added chemicals, and H-2 is metabolized by species such as Megasphaera elsdenii to produce greater value, more reduced VFA. Electro-fermentation displays promise for generating added value chemical co-products from biorefinery sidestreams and wastes.},
  articleno    = {221},
  author       = {Andersen, Stephen and Candry, Pieter and Basadre Castro, Thais and Khor, Way Cern and Roume, Hugo and Hernandez Sanabria, Emma and Coma, Marta and Rabaey, Korneel},
  issn         = {1754-6834},
  journal      = {BIOTECHNOLOGY FOR BIOFUELS},
  keywords     = {Chain elongation,Carboxylate platform,Biorefinery,Extraction,Electro-fermentation,Membrane electrolysis,MEGASPHAERA-ELSDENII,REACTOR MICROBIOMES,RUMINAL BACTERIUM,SP-NOV.,BIOREFINERY,ETHANOL,PROPIONATE,PECTINATUS,RESOURCES,HYDROGEN},
  language     = {eng},
  pages        = {14},
  title        = {Electrolytic extraction drives volatile fatty acid chain elongation through lactic acid and replaces chemical pH control in thin stillage fermentation},
  url          = {http://dx.doi.org/10.1186/s13068-015-0396-7},
  volume       = {8},
  year         = {2015},
}

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