Propionate Production by Bioelectrochemically-Assisted Lactate Fermentation and Simultaneous CO2 Recycling

Abstract

Production of volatile fatty acids (VFAs), fundamental building blocks for the chemical industry, depends on fossil fuels but organic waste is an emerging alternative substrate. Lactate produced from sugar-containing waste streams can be further processed to VFAs. In this study, electrofermentation (EF) in a two-chamber cell is proposed to enhance propionate production via lactate fermentation. At an initial pH of 5, an applied potential of −1 V vs. Ag/AgCl favored propionate production over butyrate from 20 mM lactate (with respect to non-electrochemical control incubations), due to the pH buffering effect of the cathode electrode, with production rates up to 5.9 mM d–1 (0.44 g L–1 d–1). Microbial community analysis confirmed the enrichment of propionate-producing microorganisms, such as Tyzzerella sp. and Propionibacterium sp. Organisms commonly found in microbial electrosynthesis reactors, such as Desulfovibrio sp. and Acetobacterium sp., were also abundant at the cathode, indicating their involvement in recycling CO2 produced by lactate fermentation into acetate, as confirmed by stoichiometric calculations. Propionate was the main product of lactate fermentation at substrate concentrations up to 150 mM, with a highest production rate of 12.9 mM d–1 (0.96 g L–1 d–1) and a yield of 0.48 mol mol–1 lactate consumed. Furthermore, as high as 81% of the lactate consumed (in terms of carbon) was recovered as soluble product, highlighting the potential for EF application with high-carbon waste streams, such as cheese whey or other food wastes. In summary, EF can be applied to control lactate fermentation toward propionate production and to recycle the resulting CO2 into acetate, increasing the VFA yield and avoiding carbon emissions and addition of chemicals for pH control.

Microbial electrosynthesis of acetate from CO2 in three-chamber cells with gas diffusion biocathode under moderate saline conditions

“…The H-type cells were previously described by Isipato et al [22]. Briefly, they consisted of two glass chambers of 150 mL working volume, each separated by a Nafion 117 proton exchange membrane (8.5 cm 2 , Fuel Cell Store, USA).…”

“…Scanning electrode microscope (SEM) analysis was performed as in Isipato et al [22]. Briefly, cathodic samples were fixed using a glutaraldehyde and paraformaldehyde (2% each) solution in 0.1 M sodium cacodylate buffer, dried in increasing (30e100%) ethanol concentration, gold coated and imaged (SEM Hitachi S4700) at 15 kV and 50 mA.…”

Cascading Integration of Electrofermentation and Photosynthesis—Low‐Carbon Biorefinery in Closed Loop Approach

“…[15][16][17] EF strategy has the potential to impact the overall bioprocess/acidogenic efficiency by in situ utilization of unstable/intermediary metabolic products and maintenance of specific growth rate of acidogenic bacteria for achieving product specificity. [18][19][20] But the substrate conversion efficiency and maximized carbon flux are limited in terms of microbe-electrode synergy. [21][22][23] Energy efficiency with perpetual electron and carbon flux in EF systems needs to be widened to improve the scope of bioeconomy in terms of targeted product outcomes.…”

An Improved Validated Method for the Determination of Short-Chain Fatty Acids in Human Fecal Samples by Gas Chromatography with Flame Ionization Detection (GC-FID)

“…Once succinate is formed, it is then converted into propionic acid via decarboxylation. Propionic acid may also be produced through the acrylate pathway, where acryloyl-CoA mediates the reduction of lactate to propionic acid [7]. Similar to acetic acid, butyric acid is produced by the conversion of acetyl-CoA to butyryl-CoA via microbial butyrate kinase and butyryl-CoA: acetyl-CoA transferase [3,8].…”