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. 2022 Nov 3:13:100211.
doi: 10.1016/j.ese.2022.100211. eCollection 2023 Jan.

Microbial electrosynthesis of acetate from CO2 under hypersaline conditions

Affiliations

Microbial electrosynthesis of acetate from CO2 under hypersaline conditions

Xiaoting Zhang et al. Environ Sci Ecotechnol. .

Abstract

Microbial electrosynthesis (MES) enables the bioproduction of multicarbon compounds from CO2 using electricity as the driver. Although high salinity can improve the energetic performance of bioelectrochemical systems, acetogenic processes under elevated salinity are poorly known. Here MES under 35-60 g L-1 salinity was evaluated. Acetate production in two-chamber MES systems at 35 g L-1 salinity (seawater composition) gradually decreased within 60 days, both under -1.2 V cathode potential (vs. Ag/AgCl) and -1.56 A m-2 reductive current. Carbonate precipitation on cathodes (mostly CaCO3) likely declined the production through inhibiting CO2 supply, the direct electrode contact for acetogens and H2 production. Upon decreasing Ca2+ and Mg2+ levels in three-chamber reactors, acetate was stably produced over 137 days along with a low cathode apparent resistance at 1.9 ± 0.6 mΩ m2 and an average production rate at 3.80 ± 0.21 g m-2 d-1. Increasing the salinity step-wise from 35 to 60 g L-1 gave the most efficient acetate production at 40 g L-1 salinity with average rates of acetate production and CO2 consumption at 4.56 ± 3.09 and 7.02 ± 4.75 g m-2 d-1, respectively. The instantaneous coulombic efficiency for VFA averaged 55.1 ± 31.4%. Acetate production dropped at higher salinity likely due to the inhibited CO2 dissolution and acetogenic metabolism. Acetobacterium up to 78% was enriched on cathodes as the main acetogen at 35 g L-1. Under high-salinity selection, 96.5% Acetobacterium dominated on the cathode along with 34.0% Sphaerochaeta in catholyte. This research provides a first proof of concept that MES starting from CO2 reduction can be achieved at elevated salinity.

Keywords: Acetogenesis; Carbon capture and utilization; Carbonate precipitates; High salinity; Marine bacteria.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Image 1
Graphical abstract
Fig. 1
Fig. 1
Acetate production performance of S-MES with cathode poised at −1.2 V vs Ag/AgCl using simulated seawater as catholyte. a, VFA production; b, The chronoamperogram of the cathode; c, Coulombic efficiency for cumulative VFA production; d, Cathode CV scan results.
Fig. 2
Fig. 2
ab, SEM-EDX micrographs of the S-MES cathode after the experiment with precipitation on the electrode surface (a) and a new cathode before the experiment (b). c, The XRD patterns of the white precipitate and pure CaCO3 and NaCl.
Fig. 3
Fig. 3
Acetate production performance of B-MES with a reductive current density of −1.56 A m−2 using simulated seawater as catholyte during the first three cycles but lower Ca2+ and Mg2+ concentrations in cycle 4. a, VFA production; b, Cathode CV scan results.
Fig. 4
Fig. 4
Stable acetate production performance of 3C-Bc-MES at seawater salinity (35 g L−1) with low Ca2+ and Mg2+ concentrations. a, VFA production; b, System voltage; c, Coulombic efficiency based on cumulative VFA production; d, Cathode CV scan results.
Fig. 5
Fig. 5
Acetate production performance of 3C–Bi-MES as the salinity gradually increased from 35 to 60 g L−1 in conjunction with low Ca2+ and Mg2+ concentrations. a, VFA production; b, System voltage; c, Coulombic efficiency for cumulative VFA production; d, Cathode CV scan results.
Fig. 6
Fig. 6
SEM images of biofilms on cathodes from different systems and of the blank cathode. a, S-MES; b, B-MES; c, 3C-Bc-MES; d, 3C–Bi-MES systems; e, The blank cathode.
Fig. 7
Fig. 7
Microbial community composition of the cathode and catholyte consortia from B-MES, 3C-Bc-MES, and 3C–Bi-MES systems in genus level over 1% based on 16S rRNA gene analysis.

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