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

Marco Isipato; Paolo Dessì; Carlos Sánchez; Simon Mills; Umer Z Ijaz; Fabiano Asunis; Daniela Spiga; Giorgia De Gioannis; Michele Mascia; Gavin Collins; Aldo Muntoni; Piet N L Lens

doi:10.3389/fmicb.2020.599438

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

Front Microbiol. 2020 Dec 15:11:599438. doi: 10.3389/fmicb.2020.599438. eCollection 2020.

Authors

Marco Isipato^{1

2}, Paolo Dessì², Carlos Sánchez², Simon Mills², Umer Z Ijaz³, Fabiano Asunis¹, Daniela Spiga¹, Giorgia De Gioannis^{1

4}, Michele Mascia⁵, Gavin Collins², Aldo Muntoni^{1

4}, Piet N L Lens²

Affiliations

¹ Department of Civil and Environmental Engineering and Architecture, University of Cagliari, Cagliari, Italy.
² Microbiology, School of Natural Sciences and Ryan Institute, National University of Ireland Galway, Galway, Ireland.
³ Infrastructure and Environment Research Division, School of Engineering, University of Glasgow, Glasgow, United Kingdom.
⁴ IGAG-CNR, Environmental Geology and Geoengineering Institute of the National Research Council-Piazza D'Armi 1, Cagliari, Italy.
⁵ Dipartimento di Ingegneria Meccanica, Chimica, e dei Materiali, Università degli Studi di Cagliari, Cagliari, Italy.

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.

Keywords: bioelectrochemical systems; cyclic voltammetry; electrofermentation; lactate fermentation; microbial electrosynthesis; miseq sequencing; propionate production.