Effects of cathodic electron acceptors and potassium ferricyanide concentrations on the performance of microbial fuel cell
Highlights
► Enriched hydrogen-producing mixed bacteria were first used in fed-batch MFC. ► Effects of different cathodic electron acceptors on MFC performance were discussed. ► Optimum electron acceptor and potassium ferricyanide concentration were available. ► In addition, the major metabolites produced by the mixed culture were observed.
Introduction
With the rapid growth of the world's population and economy, demands for energy are increasing significantly. At the same time, industrial effluent and domestic wastewater are also constantly increasing. The simultaneous production of energy and the degradation of contaminants in wastewater can provide economic and environmental benefits from microbial fuel cells (MFCs) [1], [2], [3].
MFC is an electrochemical device that can directly convert the chemical energy contained in organic matter into electricity by means of the catalytic activity of living microorganisms. Organic matter in an anolyte used as a fuel is oxidized by bacteria and electrons are transferred to the anode. Electrons that pass along the circuit combine with protons and oxygen to form water. Thus, the biological electrochemical process and energy conversion are completed [2], [3], [4], [5], [6], [7].
As an important component of MFC, the cathode has a great effect on the electricity generation characteristics. At present, research is focused on studies of the cathodic electron acceptor, the nature and type of the electrode and the catalyst on the electrode [8], [9], [10], [11], [12]. Dissolved oxygen, ferricyanide, potassium permanganate, or manganese dioxide have often been used as cathodic electron acceptors in two-chambered MFCs. In two-chambered MFC tests, Oh and Logan [13] found that replacing the aqueous cathode using oxygen with ferricyanide increased power by 1.5–1.8 times. Thus, potassium ferricyanide was widely used as an electron acceptor in studies of the two-chambered MFC. The electricity-generation characteristics of MFC using potassium ferricyanide catholyte sparged with air as electron acceptor have been investigated in the previous study [14]. And there have been no reports about a comparison of the performances of MFCs with potassium ferricyanide catholyte sparged with air, aerated catholyte, and potassium ferricyanide catholyte, respectively. Thus, it does not know which one is a promising electron acceptor for a two-chambered MFC. In addition, it is necessary to choose an appropriate concentration to improve power generation because changes in electron acceptor concentration affect the performance of MFC from Nernst equation and the kinetics of redox reaction. Based on above-mentioned reasons, the effects of various cathodic electron acceptors and potassium ferricyanide concentrations on the performance of a two-chambered MFC (with unmodified carbon paper electrodes) were studied in this work.
Section snippets
MFC configuration
A two-chambered MFC, which is as shown in Fig. 1, was used in this study. The MFC consisted of two plexiglass bottles, which served as an anode and a cathode, each with an operating volume of 1 L. The carbon paper (5 × 5 cm each), proton exchange membrane (PEM), adjustable resistor and data acquisition system (DAS) were used in the system as previously described [14].
MFC inoculation and operation
The mixed cultures used here were enriched from cracked cereals and were dominated by Clostridium pasteurianum following
Effect of different cathodic electron acceptors on voltage output
The two-chambered MFC exhibited rapid start-up and continuous and stable power output over a long period [14]. The variation of voltage using different cathodic electron acceptors in the MFC is shown in Fig. 2. After 72 h of operation, the voltage output values of M1 and M3 were ca. 500 mV, much higher than that of M2. After the exhaustion of carbon source in the feed, a marked drop in the voltages of M1, M2 and M3 was observed and the total sugar degradation efficiency (TSDE) of all MFCs were
Conclusions
Potassium ferricyanide is an excellent cathodic electron acceptor for the two-chambered MFCs. The maximum power density of the system with potassium ferricyanide was slightly higher than that using potassium ferricyanide catholyte sparged with air, which was 8-fold higher than that with aerated catholyte. The potassium ferricyanide concentration had little effect on MFC performance at start-up. The optimum concentration of potassium ferricyanide was 0.1 M, and the maximum voltage output of
Acknowledgments
The authors would like to thank the Chinese Academy of Sciences for financial support (KJCX2-YW-H21).
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