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 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 degrees C). Serial analysis, including transmission/scanning electron microscopy and X-ray/selected area electron diffraction, confirmed that the biogenically synthesized nanostructures were iron nanospheres (similar to 100 nm) for hematite and nanostars (similar to 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 microbial fuel cells in a soil environment, along with physiological characters of microbes (i.e., iron-reducing bacteria), for in situ applications in sustainable energy research.

Automated summary

This study investigated the biogenic mineral transformation of poorly crystalline ferrihydrite in the presence of an acclimated microbial consortium in a soil environment. The microbial consortia were able to transform the ferrihydrite into crystallized hematite and goethite, and the resulting nanostructures were iron nanospheres and nanostars. Fe(II) ion production was higher in the anode electrode sample, and the microbial isolates were more abundant and diverse at the anode.