Long-term operation of microbial electrosynthesis cell reducing CO2 to multi-carbon chemicals with a mixed culture avoiding methanogenesis

In microbial electrosynthesis (IVIES), CO2 can be reduced preferablyto multi-carbon chemicals by a biocathodebased process which uses electrochemically active bacteria as catalysts. A mixed anaerobic consortium from biological origin typically produces methane from CO2 reduction which circumvents production of multi-carbon compounds. This study aimed to develop a stable and robust CO2 reducing biocathode from a mixed culture inoculum avoiding the methane generation. An effective approach was demonstrated based on (i) an enrichment procedure involving inoculum pre-treatment and several culture transfers in H-2:CO2 media, (ii) a transfer from heterotrophic to autotrophic growth and (iii) a sequentialbatch operation. Biomass growth and gradual acclimation to CO2 electro-reduction accomplished a maximum acetate production rate of 400 mg Urlatibolyte (L-catholyte(-1) d(-1) at -1V (vs. Ag/AgCl). Methane was never detected in more than 300 days of operation. Accumulation of acetate up to 7-10 g L-1 was repeatedly attained by supplying (80:20) CO2:N-2 mixture at 0.9 to 1 V (vs. Ag/AgCl). In addition, ethanol and butyrate were also produced from CO2 reduction. Thus, a robust CO2 reducing biocathode can be developed from a mixed culture avoiding methane generation by adopting the specific culture enrichment and operation procedures without the direct addition of chemical inhibitor. (C) 2016 Elsevier B.V. All rights reserved.