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

Abstract

Microbial electrosynthesis is the biocathode-driven production of chemicals from CO₂ and has the promise to be a sustainable, carbon-consuming technology. To date, microbial electrosynthesis of acetate, the first step in order to generate liquid fuels from CO₂, has been characterized by low rates and yields. To improve performance, a previously established acetogenic biocathode was operated in semi-batch mode at a poised potential of −590 mV vs SHE for over 150 days beyond its initial development. Rates of acetate production reached a maximum of 17.25 mM day^–1 (1.04 g L^–1 d^–1) with accumulation to 175 mM (10.5 g L^–1) over 20 days. Hydrogen was also produced at high rates by the biocathode, reaching 100 mM d^–1 (0.2 g L^–1 d^–1) and a total accumulation of 1164 mM (2.4 g L^–1) over 20 days. Phylogenetic analysis of the active electrosynthetic microbiome revealed a similar community structure to what was observed during an earlier stage of development of the electroacetogenic microbiome. <i>Acetobacterium</i> spp. dominated the active microbial population on the cathodes. Also prevalent were <i>Sulfurospirillum</i> spp. and an unclassified Rhodobacteraceae. Taken together, these results demonstrate the stability, resilience, and improved performance of electrosynthetic biocathodes following long-term operation. Furthermore, sustained product formation at faster rates by a carbon-capturing microbiome is a key milestone addressed in this study that advances microbial electrosynthesis systems toward commercialization