Long-term Operation of Microbial Electrosynthesis\nSystems Improves Acetate Production by Autotrophic Microbiomes

Abstract

Microbial electrosynthesis\nis the biocathode-driven production\nof chemicals from CO₂ and has the promise to be a sustainable,\ncarbon-consuming technology. To date, microbial electrosynthesis of\nacetate, the first step in order to generate liquid fuels from CO₂, has been characterized by low rates and yields. To improve\nperformance, a previously established acetogenic biocathode was operated\nin semi-batch mode at a poised potential of −590 mV vs SHE\nfor over 150 days beyond its initial development. Rates of acetate\nproduction reached a maximum of 17.25 mM day^–1 (1.04\ng L^–1 d^–1) with accumulation to\n175 mM (10.5 g L^–1) over 20 days. Hydrogen was also\nproduced at high rates by the biocathode, reaching 100 mM d^–1 (0.2 g L^–1 d^–1) and a total\naccumulation of 1164 mM (2.4 g L^–1) over 20 days.\nPhylogenetic analysis of the active electrosynthetic microbiome revealed\na similar community structure to what was observed during an earlier\nstage of development of the electroacetogenic microbiome. <i>Acetobacterium</i> spp. dominated the active microbial population\non the cathodes. Also prevalent were <i>Sulfurospirillum</i> spp. and an unclassified Rhodobacteraceae. Taken together, these\nresults demonstrate the stability, resilience, and improved performance\nof electrosynthetic biocathodes following long-term operation. Furthermore,\nsustained product formation at faster rates by a carbon-capturing\nmicrobiome is a key milestone addressed in this study that advances\nmicrobial electrosynthesis systems toward commercialization.