Gram-positive bacteria covered bioanode in a membrane-electrode assembly for use in bioelectrochemical systems

A novel strain of Gram-positive bacteria Paenibacillus profundus YoMME was recognized by sequencing of 16S rRNA gene and after that tested for exoelectrogenicity for the first time. It was found that at an applied potential of -0.195 V (vs. SHE) the bacteria are capable of generating electricity and forming electroactive biofilms for 3-4 days. A tendency for the decrease in double-layer capacitance and the increase in the charge transfer resistance during the maturation of the biofilm was established. The formed bioanodes were used as a part of a membrane-electrode assembly (MEA) together with a selected cathode (E-Tek) and a separator (Zirfon). The applicability of MEA with the bioanode was tested by operating a newly designed bioelectrochemical system in a microbial fuel cell (MFC) or microbial electrolysis cell (MEC) mode. A current density of 200 mA m^-2 was generated by the MFC after the improvement of the cathodic reaction through facilitated air access. The Coulombic efficiency in different MFC runs ranged from 5.2 to 7.4%. It was also determined that 0.65 V applied cell voltage is appropriate for the operation of the cell in the electrolysis mode, during which a current density of 2-3 Am^-2 was reached. This, along with the evolved gas on the cathode, shows that as an anodic biocatalyst P. profundus YoMME assists the electrolysis processes at a significantly lower voltage than the theoretical one (1.23 V) for water decomposition. The hydrogen production rate varied between 0.5 and 0.7 m³/m³d and the cathodic hydrogen recovery ranged from 49.5 to 61.5 %. The estimated energy efficiency based on the electricity input exceeds 100 %, which indicates that additional energy is being gained from the biotic oxidation of the available organics.