Biological Chromium(VI) Reduction in Microbial Fuel Cell: A Three in One Approach

Chromium(VI) reduction in the cathode of a microbial fuel cell (MFC) was investigated. An Htype MFC was operated with anaerobic anode and cathode compartments. The anode compartment was inoculated with an acetate-oxidizing mixed culture and the cathode compartment was inoculated with a mixture of denitrifying and anaerobic cultures enriched in the presence of Cr(VI). Acetate was provided to the anode compartment as substrate and bicarbonate was added to the cathode compartment as the sole inorganic carbon source. Fast Cr(VI) removal in the cathode compartment was observed along with acetate oxidation in the anode chamber and current generation. A maximum Cr(VI) reduction rate of 0.46 mg Cr(VI)/g VSS·h was achieved, which resulted in a current and power density of 123.4 mA/m2 and 55.5 mW/m2, respectively. The reduced chromium was non-detectable in the supernatant of the catholyte, which indicates complete removal of chromium as Cr(OH)3 precipitate. The contribution of biomass decay and abiotic processes on Cr(VI) reduction was minimal, confirming that most of the Cr(VI) reduction was assisted by microbial activity in the cathode, which utilizes electrons and protons from the oxidation of acetate in the anode compartment. Analysis of the 16S rRNA gene based clone-library revealed that the cathode biomass was largely dominated by phylotypes closely related to Trichococcus pasteurii and Pseudomonas aeruginosa.