The bacterial anode in microbial fuel cells was modified by increasing the biofilm's adhesion to the anode material using kaolin and graphite nanoparticles. The MFCs were inoculated with G. sulfurreducens, kaolin (12.5 g·L-1), and three different concentrations of graphite (0.25, 1.25, and 2.5 g·L-1). The modified anode with the graphite nanoparticles (1.25 g·L-1) showed the highest electroactivity and biofilm viability. A potential of 0.59, 0.45, and 0.23 V and a power density of 0.54 W·m-2, 0.3 W·m-2, and 0.2 W·m-2 were obtained by the MFCs based on kaolin-graphite nanoparticles, kaolin, and bare anodes, respectively. The kaolin-graphite anode exhibited the highest Coulombic efficiency (21%) compared with the kaolin (17%) and the bare (14%) anodes. Scanning electron microscopy and confocal laser scanning microscopy revealed a large amount of biofilm on the kaolin-graphite anode. We assume that the graphite nanoparticles increased the charge transfer between the bacteria that are in the biofilm and are far from the anode material. The addition of kaolin and graphite nanoparticles increased the attachment of several bacteria. Thus, for MFCs that are fed with wastewater, the modified anode should be prepared with a pure culture of G. sulfurreducens before adding wastewater that includes non-exoelectrogenic bacteria.
Keywords: Geobacter sulfurreducens; graphite nanoparticles; immobilized anodes; kaolin; microbial fuel cell.