Enhanced Cr reduction and bioelectricity production in microbial fuel cells using polypyrrole-coated MnO2 on carbon cloth

Hexavalent chromium (Cr(VI)) is a carcinogenic pollutant that can be transformed into less toxic trivalent chromium (III). Microbial fuel cells can be used simultaneously to reduce wastewater Cr(VI) and to generate bioelectricity, yet actual cell cathodes are not well-optimized for high performance. Here, we tested the reduction of Cr(VI) using an abiotic cathode made of carbon cloth coated by polypyrrole-coated turf-like manganese dioxide in a two-chamber cell. Results show a 100% Cr(VI) removal within 32 h using an initial catholyte at pH 2 and 50 mg L-1 Cr(VI). The reduction rate of 1.56 mg L-3 h(-1) is 175% higher than for the bare carbon cloth cathode, of 0.89 mg L-3 h(-1). The maximum power density of 1429 mW m(-2) was higher than that for the polypyrrole cathode, of 1017 +/- 65 mW m(-2), the MnO2 cathode, of 648 mW m(-2), and the carbon cloth cathode, of 595 mW m(-2). Noteworthy, Cr reduction was efficient without the use of electron transfer mediators such as anthraquinone-2,6-disulfonate. Moreover, polypyrrole allowed an excellent stability of the electrode under acidic conditions.