Microbial electrosynthesis of acetate from CO2 under hypersaline conditions

Abstract

Microbial electrosynthesis (MES) enables the bioproduction of multicarbon compounds from CO 2 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 CaCO 3 ) likely declined the production through inhibiting CO 2 supply, the direct electrode contact for acetogens and H 2 production. Upon decreasing Ca 2+ and Mg 2+ 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 m 2 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 CO 2 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 CO 2 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 CO 2 reduction can be achieved at elevated salinity.

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Identifiers

DOI

10.1016/j.ese.2022.100211

PubMed

36419905

Journal

Environmental Science and Ecotechnology

Year

2022