Enhanced Performance for Treatment of Cr (VI)-Containing Wastewater by Microbial Fuel Cells with Natural Pyrrhotite-Coated Cathode

Here we reported the investigation of enhanced performance for the removal of hexavalent chromium (Cr (VI)) by a new microbial fuel cell (MFC) with natural pyrrhotite-coated cathode. By comparisons of the graphite-cathode, the MFCs equipped with a pyrrhotite-coated cathode generated the maximum power density of 45.4 mW·m−2 that was 1.3 times higher than that of with bare graphite cathode (35.5 mW·m−2). Moreover, the Cr (VI) removal efficiency of 97.5% achieved after 4.5 h compared with only 46.1% by graphite cathode MFC. In addition, Cr (VI) removal rate with different initial Cr (VI) concentrations for 10 mg/L and 30 mg/L was investigated and a decreased removal percentage with increasing Cr (VI) concentration was observed. Batches of experiments of different pH values from 3.0 to 9.0 in catholyte were carried out to optimize system performance. The complete Cr (VI) removal was achieved at pH 3.0 and 99.59% of Cr (VI) was removed after 10.5 h, which met the requirement of the Cr (VI) National Emission Standard. When the value of pH was decreasing, the removal rate was obviously increased and Cr (VI) could be removed successfully with a broad pH range indicating pyrrhotite-coated cathode MFC had more extensive usage scope. Furthermore, cathode treatment products were studied by X-ray photoelectron spectroscopy (XPS), Cr2O3, Cr (III)-acetate were detected on the cathode by the XPS Cr2p spectra and no Cr (VI) founded, indicating that the Cr on the surface of cathode was Cr (III) and Cr (VI) were reduced. On cathode, pyrrhotite not only played a significant role for catalyst of MFCs, but also acted as reactive sites for Cr (VI) reduction. Our research demonstrated that pyrrhotite, an earth-abundant and low-cost natural mineral was promised as an effective cathode material. Which had great potential applications in MFCs for reduction of wastewater containing heavy metals and other environmental contaminants in the future.