Biological Chromium(VI) Reduction in the Cathode of a Microbial Fuel Cell

Abstract

The biocathode of a microbial fuel cell (MFC) offers a promising potential for the reductive treatment of oxidized pollutants. In this study, we demonstrated biological Cr(VI) reduction in the cathode of a MFC and identified putative Cr(VI) reducing microorganisms. The MFC was continuously monitored for Cr(VI) reduction and power generation. Acetate was provided to the anode compartment as substrate and bicarbonate was added to the cathode compartment as the sole external carbon source. 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 generated from the oxidation of acetate in the anode compartment. Relatively fast Cr(VI) reduction was observed at initial Cr(VI) concentrations below 80 mg/L. However, at 80 mg Cr(VI)/L, Cr(VI) reduction was extremely slow. 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/m(2) and 55.5 mW/m(2), respectively. The reduced chromium was nondetectable in the supernatant of the catholyte which indicated complete removal of chromium as Cr(OH)(3) precipitate. 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, the putative Cr(VI) reducers.

Enhanced Performance of Hexavalent Chromium Reducing Cathodes in the Presence ofShewanella oneidensisMR-1 and Lactate

“…The maximum current produced by "+Lac+Shew" occurred after the first addition and was comparable to the 46.6 mA/m 2 observed by Tandukar et al 11 , who used a mixed culture biocathode with a similar configuration (electrode TASA to working volume ratio: 16 m 2 /m 3 [vs.…”

“…It has been shown, however, that efficiency can be enhanced by utilizing Cr(VI)-reducing bacterial biofilms as biocatalysts (biocathodes) [8][9][10][11] . In this case, the bacteria used must be able to obtain a metabolic gain from the electron transfer process, and prospective candidates for this task are electrophilic bacteria that have been extensively tested in MFC anodes 12 .…”

“…At low pH values where H + is abundant, cathodic Cr(VI) reduction has been demonstrated at relatively fast rates and without the use of a catalyst 5,6 . In the neutral pH region, however, the reaction kinetics are slower due to low H + availability:CrO 4 2-+ 8H + + 3e -= Cr 3+ + 4H 2 O (1) At neutral pH, Cr(VI) reduction takes place under lower cathode potentials and is also severely inhibited by Cr(III) oxyhydroxide monolayers which form progressively on the cathode surface 7 .It has been shown, however, that efficiency can be enhanced by utilizing Cr(VI)-reducing bacterial biofilms as biocatalysts (biocathodes) [8][9][10][11] . In this case, the bacteria used must be able to obtain a metabolic gain from the electron transfer process, and prospective candidates for this task are electrophilic bacteria that have been extensively tested in MFC anodes 12 .…”

Impact of Fe(III) as an effective electron-shuttle mediator for enhanced Cr(VI) reduction in microbial fuel cells: Reduction of diffusional resistances and cathode overpotentials

“…However, since the Cr(VI) species (Cr 2 O 7 2-or CrO 4 2-) are electronegative and mutually exclusive against the negatively charged cathodes, the reduction of Cr(VI) and the electrochemical reaction kinetics are usually slow. The development of biocathodes based on the electrotrophic mediation between cathode electrode and Cr(VI) [12][13][15][16][17][18][19] appears to be a promising method for the reduction of Cr(VI) in…”

Bioelectrochemical recovery of Cu, Pb, Cd, and Zn from dilute solutions

“…Regarding metal recovery, copper (Cu 2+ ) [9][10][11] and hexavalent chromium (Cr 2 O 7 2-) [12,13] have been used as electron acceptors in the cathode of MFCs. Both Cu 2+ and Cr 2 O 7 2-have high reduction potentials (0.340 V and 0.365 V, respectively), which means that electrical energy production and metal recovery can be achieved simultaneously.…”