Cr(VI) was reduced in-situ at a carbon felt cathode in an air-cathode dual-chamber microbial fuel cell (MFC). The reduction of Cr(VI) was proven to be strongly associated with the electrogenerated H(2)O(2) at the cathode driven by iron-reducing bacteria. At pH 2.0, only 42.5% of Cr(VI) was reduced after 12 h in the nitrogen-bubbling-cathode MFC, while complete reduction of Cr(VI) was achieved in 4 h in the air-bubbling-cathode MFC in which the reduction of oxygen to H(2)O(2) was confirmed. Conditions that affected the efficiency of the reduction of Cr(VI) were evaluated experimentally, including the cathodic electrolyte pH, the type of iron-reducing species, and the addition of redox mediators. The results showed that the efficient reduction of Cr(VI) could be achieved with an air-bubbling-cathode MFC. (C) 2010 Elsevier Ltd. All rights reserved.