Conductive polymer-mediated Cr(VI) reduction in a dual-chamber microbial fuel cell under neutral conditions

Microbial fuel cell (MFC) technology for Cr(VI) removal offers the advantage of simultaneous electricity generation and Cr-laden wastewater treatment, but Cr(VI) removal at neutral pH proceeds with slow kinetics. We herein report the use of conductive polymer as a mediator shuttling electron transfer from the cathode to Cr(VI), facilitating Cr(VI) reduction in MFCs under neutral conditions. It has been found that PPy films synthesized by electropolymerization on the graphite felt cathode considerably improved Cr(VI) removal from the aqueous solution. The surface morphology of PPy, which is correlated to performance of the PPy-modified cathode, was highly dependent on the type of dopants that were incorporated during electropolymerization. The PPy/AQS(9,10-anthraquinone-2-sulfonic acid sodium salt)-modified cathode with nanowire structure enabled higher Cr(VI) removal rate and exhibited larger power output than the PPy/ClO4−-modified cathode with compact globular structure. These results are attributed to the increased surface area of electrode and the presence of AQS that is electrochemically active for reaction with Cr(VI). Cr(III) precipitates were the primary end-products of Cr(VI) reduction under neutral conditions, with no soluble Cr(III) detected.