Bioresource Technology 114 (2012) 308–313

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Electricity generation from a floating microbial fuel cell Yuelong Huang a, Zhen He b, Jinjun Kan c, Aswin K. Manohar a, Kenneth H. Nealson d, Florian Mansfeld a,⇑ a Corrosion and Environmental Effects Laboratory (CEEL), The Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-0241, USA b Department of Civil Engineering and Mechanics, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA c Stroud Water Research Center, Avondale, PA 19311, USA d Department of Earth Science, University of Southern California, Los Angeles, CA 90089, USA

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Article history: Received 30 November 2011 Received in revised form 28 February 2012 Accepted 29 February 2012 Available online 7 March 2012 Keywords: Microbial fuel cell Electrochemical impedance spectroscopy Electricity production Internal resistance Seawater

a b s t r a c t A floating microbial fuel cell (FMFC) has been designed and its performance has been evaluated for 153 days. The power output gradually increased to a maximum value of 390 mW/m3 at 125 days. The polarization resistance of the anode ðRap Þ changed with operating time reaching a minimum value at 125 days, while the polarization resistance of the cathode ðRcp Þ was relatively constant and much smaller than Rap . It has been demonstrated that the observed changes of the internal resistance (Rint) and the maximum power (Pmax) with exposure time were mainly due to the changes of Rap . Compared with sediment MFCs for which the anode is embedded in marine or river sediments, the application of the FMFC, which could be installed in a buoy, is not limited by the depth of the ocean. The FMFC has the potential to supply electricity to low-power consuming electronic devices at remote locations. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction Electrical energy can be harvested using sediment microbial fuel cells (SMFCs) that consist of an anode embedded in marine or river sediment and a cathode suspended in the aerobic water column above the anode (Dumas et al., 2007; Girguis et al., 2010; Nielsen et al., 2008; Schamphelaire et al., 2008). Bacteria inhabiting the sediment oxidize organic compounds and supply electrons to the anode, while at the cathode oxygen is reduced (Dumas et al., 2007; Girguis et al., 2010; Nielsen et al., 2008; Schamphelaire et al., 2008). Holmes et al. (2004) have shown that among the different electrochemically active bacteria, Desulfuromonas spp. are rich in marine sediments, while Geobacter spp. become predominate in freshwater sediments. Current technologies provide electric power to remote sensors or other electronic devices via batteries, which require periodic replacement at a high cost, in addition to the cost of the batteries themselves. SMFCs have been studied and developed to operate low-power consuming electronic devices installed in marine or river environments (Dumas et al., 2007; Logan et al., 2006; Lowy et al., 2006; Schamphelaire et al., 2008; Tender et al., 2008). Tender et al. (2008) demonstrated that a benthic microbial fuel cell (BMFC) can be used as an alternative to batteries for a meteorological buoy. SMFCs are potentially advantageous over current technologies (e.g. batteries) for powering remote sensors or other ⇑ Corresponding author. Tel.: +1 213 740 3016; fax: +1 213 740 7797. E-mail address: [email protected] (F. Mansfeld). 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.02.142

electronic devices because of low cost and less frequent maintenance (e.g. periodic replacement). SMFCs are commonly installed in marine or river sediment (Dumas et al., 2007; Girguis et al., 2010; Logan et al., 2006; Lowy and Tender, 2008; Lowy et al., 2006; Nielsen et al., 2008; Schamphelaire et al., 2008; Tender et al., 2008). The cathode should be deployed close to the water surface to ensure sufficient oxygen supply. The distance between the anode and the cathode cannot be too large due to increased installation difficulties and Ohmic drop. Hence, it is questionable whether the traditional SMFCs could be applied in deep waters at remote areas. To overcome the limitation due to water depth, the floating MFC (FMFC) was designed for potential applications at remote locations. A single-chamber tubular FMFC has been evaluated during exposure at Long Beach Harbor, CA for 153 days. Previous studies have investigated floating-type MFCs that were significantly different from the present FMFC in reactor configuration and operation (An et al., 2009; Song et al., 2010). The obtained results in the present study have demonstrated that electricity was constantly produced from the FMFC which in the future may be installed with a buoy floating in ocean water. 2. Experimental approach 2.1. FMFC configuration and operation A schematic of the FMFC developed in this project is shown in Fig. 1. The FMFC was constructed using a tube made of cation exchange membrane (Ultrex CMI7000, Membranes International,

Y. Huang et al. / Bioresource Technology 114 (2012) 308–313

USA). The tube had a diameter of 9 cm and a length of 70 cm with a total anode volume of 4.5 L. The top and bottom of the tube were covered with rubber stoppers. Each rubber stopper had a small hole with a diameter of 8 mm to allow circulation of ocean water through the FMFC while preventing excessive oxygen flux into the anode chamber. Granular graphite (diameter about 10 mm, Carbon Activated Corp., Compton, CA, USA) was used to fill the tube and function as the anode resulting in an anode liquid volume of 2.3 L. Three titanium wires were inserted into the granular graphite as current collectors. Before being deployed in the ocean, the FMFC was operated in the laboratory to examine its electricity generation from organic compounds. It was fed continuously with a solution containing NaC2H3O23H2O (3 g/L); yeast extract (0.2 g/ L); NH4Cl (1 g/L); MgSO4 (0.25 g/L); NaCl (0.5 g/L); CaCl2 (15 mg/ L); trace solution (1 mL/L) (He et al., 2006) and phosphate buffered nutrient medium (100 mL/L) containing NaH2PO4 (50 g/L) and Na2HPO4 (107 g/L). Forty milliliter of a mixture of anaerobic and aerobic sludge (50/50), that was collected from a wastewater treatment plant (Joint Water Pollution Plant, CA), were injected into the anode chamber as inoculum. The cathode consisted of Ni-coated carbon fibers (TenaXÒ-J, Toho Tenax Co., Ltd., grade HTS 40, Irvine, CA, USA) and two catalyst layers. To make a catalyst layer, Pt/C powder (10% Pt, Etek, Somerset, NJ, USA) was mixed with tap water to form a paste that was applied to the outer surface of the membrane tube using a brush. This layer was then covered with carbon fibers. The second catalyst layer with the same composition as the first catalyst layer, but mixed with a Nafion solution was applied to the outside of the carbon fibers. The catalysts layers were air dried for 48 h at room temperature before operation. Before deployment of the FMFC the feeding had been stopped for a few days to allow the voltage to drop to very low levels (