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 CO₂ into valuable organic chemicals and fuels. This study demonstrates that CO₂ reduction in MES systems can be enhanced by enriching the inoculum and improving CO₂ availability to the biofilm. The proposed system is proven to be a repetitive, efficient, and selective way of consuming CO₂ for the production of acetic acid, showing cathodic efficiencies of over 55% and CO₂ conversions of over 80%. Continuous recirculation of the gas headspace through the catholyte allowed for a 44% improvement in performance, achieving CO₂ fixation rates of 171 mL CO₂ 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 CO₂ 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.

BACKGROUND: The utilization of different kinds of ion exchange membrane is a common practice in bioelectrochemical systems such as two‐chambered microbial fuel cells (MFCs). However, little is known about the effect of membrane materials on the anodic microbial community diversity.RESULTS: The effect of two cationic and one anionic exchange membranes (Nafion N‐117, Ultrex CMI‐7000, and Ultrex AMI‐7000) on the microbial community dynamics of Eubacteria and Archaea has been assessed in two‐chambered MFCs. The experimental results indicated that the eubacterial community in the anodic chamber was not affected by the membrane materials, being predominantly populations of Bacteroidetes (Porphyromonadaceae) and β‐proteobacteria (Alcaligenaceae and Comamonadaceae). On the other hand, the archaeal counterpart appears to be highly dependent on the type of membrane used, as was evidenced by the selective enrichment of Methanosarcina sp. in the MFC equipped with the membrane Nafion N‐117 which was the MFC that showed the highest current production.CONCLUSIONS: The results obtained in the present study suggest that membrane materials affect archaeal diversity whereas both anodofilic eubacteria and methanogenic archaea populations could play an important role in the overall MFC process performance. © 2014 Society of Chemical Industry