Performance and bacterial enrichment of bioelectrochemical systems during methane and acetate production

A number of studies suggested that anaerobic digestion processes can be enhanced by inserting electrodes in anaerobic digesters, however a thorough work with relation to the bacterial shifts, especially with regards to acetogenesis, is lacking. In our work we investigated the performance and the respective shifts in the bacterial composition of bioelectrochemical systems producing methane and acetate from synthetic wastewater. A membraneless microbial electrolysis cell (MEC) could produce net energy with methane as the main end-product, however a membrane system was promoting acetogenesis and failed to operate as an energy producer. Bacteria present in the effluent of the membraneless system could also produce acetate with cathodic efficiencies over 60% when the cathode potentials dropped below −1000 mV vs. SHE. Different bacterial species were enriched on the two electrodes of each MEC, despite the fact that the electrodes were hydraulically connected and within a close distance from each other. Acetobacterium spp. and Acetoanaerobium spp., which could be found on the cathode of the membrane system, can be considered responsible for acetate production and decreased energy efficiency.