Mineral transformation of poorly crystalline ferrihydrite to hematite and goethite facilitated by an acclimated microbial consortium in electrodes of soil microbial fuel cells.

In this study, we investigated the biogenic mineral transformation of poorly crystalline ferrihydrite in the presence of an acclimated microbial consortium after confirming successful soil/sediment microbial fuel cell optimization. The acclimated microbial consortia in the electrodes distinctly transformed amorphous ferrihydrite into crystallized hematite (cathode) and goethite (anode) under ambient culture conditions (30 °C). X-ray diffraction and selected area electron diffraction analyses confirmed that the biogenically synthesized nanostructures were iron nanospheres (~100 nm) for hematite and nanostars (~300 nm) for goethite. Fe(II) ion production with acetate oxidation via anaerobic respiration was much higher in the anode electrode sample (3.2- to 17.8-fold) than for the cathode electrode or soil samples. Regarding the culturable bacteria from the acclimated microbial consortium, the microbial isolates were more abundant and diverse at the anode. These results provide new insights into the biogeochemistry of iron minerals and fuel cells in a soil environment, along with microbes (i.e., iron-reducing bacteria), for future applications in sustainable energy research.