Specific enrichment of different Geobacter sp. in anode biofilm by varying interspatial distance of electrodes in air-cathode microbial fuel cell (MFC)

Air-cathode microbial fuel cells (MFCs) were operated with variation of interspatial distance (0, 3, 6, and 9 mm), and the electrochemical performance and microbial community were comparatively evaluated. In polarization analysis the highest power densities (325 mW/m²) was obtained with an electrode spacing of 6 mm showing high capacitance and low charge transfer resistance. The MFC with 0 mm spacing resulted in much lower power density (53 mW/m²) than the other distances possibly due to high oxygen diffusion from the cathode. To compare the anode bacterial community compositions between biomass attached on the anodic electrodes, high throughput sequencing was performed. The community analyses results revealed that the three different clusters of Geobacter belonging to the Deltaproteobacteria were specifically enriched. The cluster I and II of Geobacter were most abundantly distributed in the 0 mm distanced sample which was exposed to relatively higher dissolved oxygen conditions while that of the cluster III was enriched in the 3, 6, and 9 mm samples. These results suggested that the cluster I and II of Geobacter species might survive better under relatively higher oxygen conditions than the cluster III Geobacter. On the other hand, relatively higher voltage and max power density were generated in the 3, 6, and 9 mm distanced MFC systems, where the cluster III Geobacter was highly enriched conditions. These results also suggested that the cluster III Geobacter might efficiently generate higher voltage and maximum power density than the other Geobacter clusters under oxygen limited conditions in air-cathode MFC system.