Enhanced CO 2 Conversion to Acetate through Microbial Electrosynthesis (MES) by Continuous Headspace Gas Recirculation

Bioelectrochemical systems (BESs) is a term that encompasses a group of novel technologies able to interconvert electrical energy and chemical energy by means of a bioelectroactive biofilm. Microbial electrosynthesis (MES) systems, which branch off from BESs, are able to convert CO 2 into valuable organic chemicals and fuels. This study demonstrates that CO 2 reduction in MES systems can be enhanced by enriching the inoculum and improving CO 2 availability to the biofilm. The proposed system is proven to be a repetitive, efficient, and selective way of consuming CO 2 for the production of acetic acid, showing cathodic efficiencies of over 55% and CO 2 conversions of over 80%. Continuous recirculation of the gas headspace through the catholyte allowed for a 44% improvement in performance, achieving CO 2 fixation rates of 171 mL CO 2 L −1 ·d −1 , a maximum daily acetate production rate of 261 mg HAc·L −1 ·d −1 , and a maximum acetate titer of 1957 mg·L −1 . High-throughput sequencing revealed that CO 2 reduction was mainly driven by a mixed-culture biocathode, in which Sporomusa and Clostridium , both bioelectrochemical acetogenic bacteria, were identified together with other species such as Desulfovibrio , Pseudomonas , Arcobacter , Acinetobacter or Sulfurospirillum , which are usually found in cathodic biofilms. Moreover, results suggest that these communities are responsible of maintaining a stable reactor performance.