Journal of Power Sources 204 (2012) 34–39 Contents lists available at SciVerse ScienceDirect Journal of Power Sources jou rn al h om epa ge: www.elsevier.com/locate/jpowsour Simultaneous reduction of vanadium (V) and chromium (VI) with enhanced energy recovery based on microbial fuel cell technology Baogang Zhang a , Chuanping Feng a,∗ , Jinren Ni b , Jing Zhang a , Wenli Huang a a School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing Key Laboratory of Water Resources & Environmental Engineering, Beijing 100083, China b Department of Environmental Engineering, Peking University, Beijing 100871, China a r t i c l e i n f o Article history: Received 30 September 2011 Received in revised form 27 December 2011 Accepted 1 January 2012 Available online 9 January 2012 Keywords: Microbial fuel cells Vanadium (V) Chromium (VI) Wastewater treatment Electricity generation a b s t r a c t Vanadium (V) and chromium (VI) are the main metals found in vanadium containing wastewater with large amount and great toxicity. In present study, reduction of V(V) and Cr(VI) together with electricity generation is successfully achieved in double chamber microbial fuel cells (MFCs) by employing vanadium containing wastewater as the cathodic electron acceptor. The V(V) and Cr(VI) reduction efficiencies for 240 h operation approach up to 67.9 ± 3.1% and 75.4 ± 1.9%, respectively, with a maximum power density of 970.2 ± 20.6 mW m -2 . The power output is enhanced, compared with the results from MFCs with V(V) as the sole electron acceptor, while the decrease of the cathode efficiency caused by deposits from Cr(VI) reduction process can also be mitigated. After reduction, chromium is mainly deposited on the cathode surface in the form of Cr(III), while most of vanadium can be precipitated from the exhausted catholyte by adjusting pH, thus treating vanadium containing wastewater successfully with energy harvest based on MFC technology. The operating principles of MFCs with two different electron acceptors are also reported for the first time. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Vanadium containing wastewater with low pH from vanadium mining and vanadium pentoxide manufacture is often produced in large quantities and can be greatly toxic [1]. Vanadium (V) and chromium (VI) are the main metals found in wastewater discharged after vanadium precipitation, with concentrations usually in the range from 100 to 400 mg L -1 and pH of 2–4 [2]. Vanadium is harm- ful to people, and sometimes can be fatal. The toxicity of vanadium depends on its oxidation state, with V(V) being more toxic than other species [3]. Cr(VI), identified as one of 17 chemicals posing the greatest threat to human health, is a well-known mutagen, ter- atogen, and carcinogen besides being highly corrosive [4]. Previous methods for Cr(VI) removal from wastewater have included the use of cationic and anionic ion-exchange resins, chemical and elec- trochemical precipitation, membrane filtration and sorption [5], which may be operated with high cost. Moreover, these methods also generate large amount of sludge that is difficult to dispose and can hardly recover valuable metals from the treatment process [4]. Nowadays, few publications are presently available that address technologies for removal and recovery of V(V) from vanadium con- ∗ Corresponding author. Tel.: +86 10 8232 2281; fax: +86 10 8232 1081. E-mail address: fengchuanping@gmail.com (C. Feng). taining wastewater without sludge generation [6], especially when V(V) and Cr(VI) occur together. Microbial fuel cells (MFCs) are devices that use bacteria as catalysts to oxidize organic or inorganic matter and generate elec- tricity [7–9]. MFCs are capable of simultaneous biological electricity generation and wastewater treatment, and so offer an economic pathway to a sustainable energy future [10–12]. Electron acceptors in the cathode compartment play an important role in MFC per- formance. Oxygen and ferricyanide (K 3 [Fe(CN) 6 ]) are most widely used for laboratory-based research on MFCs [13–15]. Recently, cer- tain pollutants with high electrochemical redox potentials that are present in wastewater have been applied as electron acceptors in MFCs, while being reduced at the same time [16]. To the authors’ knowledge, our research group was the first to report on the reduc- tion and recovery of V(V) by means of MFC technology employing V(V) as the electron acceptor [2]. V(V) acted as the sole electron acceptor in our previous research, which is not the case in practice for vanadium containing wastewater discharged after vanadium precipitation. At the same time, little attention has been paid to the principle of the MFCs operated with multiple electron acceptors in MFC research field at present. This issue is worth investigat- ing and the principles should be revealed as electron acceptors from wastewaters may be presented together in the actual circum- stances. In the present study, V(V) and Cr(VI) are considered together. Both have high electrochemical redox potentials (Eqs. (1) and (2)) 0378-7753/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2012.01.013