Effect of Different Mediator Concentrations on Power Generation in MFC Using Ti‐TiO2 Electrode

International Journal of Energy Science (IJES) Volume 4 Issue 1, February 2014 Doi: 10.14355/ijes.2014.0401.02

www.ijesci.org

Effect of Different Mediator Concentrations on Power Generation in MFC Using Ti‐TiO2 Electrode Ergin Taskan*1, Bestamin Özkaya2, Halil Hasar1 Firat University, Department of Environmental Engineering, Elazıg‐Turkey.

1

Yildiz Technical University, Faculty of Civil Engineering, Department of Environmental Engineering, Istanbul‐Turkey 2

etaskan@firat.edu.tr; bozkaya@yildiz.edu.tr; hhasar@firat.edu.tr

Abstract In this study, performance of MFC using three different mediators was investigated in terms of power density and internal resistance. Methylene blue (MB), neutral red (NR) and 2‐hydroxy‐1,4‐naphthoquinone (HNQ)mediators were used to increase power generation in MFC with the mediator concentrations of 50, 100, 200, 300 and 400 μM. The maximum power densities were recorded as 36, 31 and 18.7 mW/m2withthe mediators of MB, NR and HNQ corresponding optimal mediator concentrations of 300, 200 and 50 μM, respectively. Further, it was observed that internal resistance changed with mediator concentration.

Keywords Microbial Fuel Cell; Mediator; Ti‐TiO2 Electrode

Introduction Renewable energy requirement has been increased in recent years. Microbial fuel cell (MFC) is a new technology used to obtain electricity energy from wastewater. A conventional MFC consisting of anode and cathode compartments, is separated by using a proton exchange membrane from each other. Many types of wastewaters such as synthetic, domestic and industrial wastewaters have been recently tested (He at al., 2005; Huang et al., 2008; Ahn et al., 2009) considering various parameters; such as micro‐ organism growth, electrode materials, membrane‐ electrode assemblies, microbial metabolism, ions’ transportation, bacterial electron transfer, electrons’ mitigation and acceptance for the overall efficiency (Logan, 2007; Armstrong et al., 2000; Habermuller et al., 2000). Another key factor affecting power generation in MFC is electron transfer from microorganism to electrode. Up to now, two mechanisms have been stated; i) direct electron transfer, ii) mediated electron transfer (MET) (UweSchröder, 2007). In previous studies, different mediators were used to increase

power generation in MFC. Methylene blue (Zhou et al., 2007), neutral red (Park et al., 2000), HNQ (Ho et al., 2011) and thionine (Rahimnejad et al., 2012) were used as an electron mediator. Babanova et al. (2011) used methylene blue (MB), methyl orange (MO), bromocresol green (BG), methyl red (MR), neutral red (NR) in MFC and reported that mediator order was BG<NR<MR< MO<MB considering power generation. Similarly, Ho et al. (2011) used 2‐hydroxy‐l,4‐naphthoquinone and thionin as an electron mediator and they recorded that thionin more effective than 2‐hydroxy‐l,4‐ naphthoquinone. In this study, MB, NR and HNQ mediators were utilized to increase power generation in MFC and optimum mediator concentration was determined with the mediator concentration ranges from 50 to 400 μM.

FIG. 1 PICTURE OF LAB SCALE MICROBIAL FUEL CELL (1: Anode Chamber; 2: Proton Exchange Membrane; 3: Cathode Chamber)

Material and Methods In this study, dual chambered MFC was constructed (Fig. 1) with the working anode and cathode chamber volume of 300 ml. Ultrex CMI 7000 (UltrexTM

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CMI7000, Membranes International Inc., USA) cation exchange membrane was used to separate anode and cathode chamber. Power curves were carried out by using potentiometer. Titanium dioxide coated titanium (Ti‐TiO2) electrode was used as an anode electrode.

Counter electrode was made of platinum coated titanium electrode 5 cm2 projected surface area and connected with copper wire. Anode and cathode electrodes fixed with 10 Ω external resistances.

Electrical parameters were measured by using multimeter (Fluke 8846A). Domestic wastewater was used as a substrate. Table 1 summarizes the operation periods of dual chambered MFC.

stage, despite the increase of mediator concentration, power density decreased. Internal resistance of MFC decreased from 5391 Ω to 2885 Ω with addition of 50 μm HNQ. It was concluded that adsorption of mediators to the electrode surface effected the internal resistance of MFC. Obtained results showed that HNQ has more adsorption capacity than MB and NR mediators. Also, two‐fold maximum power generation was observed with addition of mediator. The maximum power density and internal resistance of MFC under different mediator and concentrations are shown in Fig 2.

TABLE 1 OPERATION PERIODS OF DOUBLE CHAMBER MFC.

Periods Mediator type

Mediator concentrations

I

MB

Mediator‐less 50 100 200 300 400

II

NR

Mediator‐less 50 100 200 300 400

III

HNQ

Mediator‐less 50 100 200 300 400

Result and Discussion Power generation performance by using MB, NR and HNQ was examined in double chamber MFC system.

Firstly, MFC was operated mediator‐less to determine effect of mediator addition on performance of MFC. With this purpose, MFC was operated with domestic wastewater. Maximum power densities were determined by using power curves in each period.

In the first period, MFC was operated with 50, 100, 200, 300 and 400 μM methylene blue mediator, respectively.

The maximum power density was 17.9 mW/m2 in mediator‐less operation before methylene blue addition. Then 50 μM MB was added and max power density wasincreased to 21.1 mW/m2. The max power density reached 36 mW/m2 with 300 μM MB addition.

When MB concentration increased from 300 to 400 μM, the max power density decreased to 26 mW/m2. The maximum power density increased 2 fold with 300 μM MB in comparison with mediator‐less operation.

Internal resistance was 5382 Ω in mediator‐less operation. After 300 μM MB addition, internal resistance decreased 3785 Ω.

In the second period, MFC produced 13.7 mW/m2 power density in the absence of mediator addition.

The max power density achieved 31 mW/m2 with 200 μM NR. On the other hand, internal resistance decreased from 5363 Ω to 2802 Ω with addition of 200 μM NR. In the third period, the max power density obtained 18.7 mW/m2 with 50 μM HNQ addition. After this

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FIG. 2 MAXIMUM POWER DENSITY AND INTERNAL RESİSTANCE OF MFC

Conclusions Performance of MFC using Ti‐TiO2 as anode electrode was investigated under variable mediators. Two fold power density was obtained by using mediator. Our results have indicated that optimum concentrations of mediators were 300, 200 and 50 μM for MB, NR and HNQ, respectively.

ACKNOWLEDGMENT

This paper includes a part of PhD thesis data of Ergin TASKAN. The authors gracefully acknowledge the financial support from FUBAP, Project Number MF. 12.10.

International Journal of Energy Science (IJES) Volume 4 Issue 1, February 2014

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HalilHasar is professor in the Department of Environmental Engineering at the Firat University (Elazıg). He received his B.S. degree in Environmental engineering from Firat University in 1994. Halil Hasar completed his MSc and Ph.D. degrees at Firat University in 1997 and 2001 respectively. His research interests include microbial fuel cell, environmental biotechnology, membrane bioreactors, and membrane biofilm reactor.

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Bestamin Ozkaya is an associate professor in the Department of Environmental Engineering at the Yıldız Technical University (Istanbul). He received his B.S. degree in Environmental engineering from Firat University in 1998.

Bestamin Ozkaya completed his MSc and Ph.D. degrees at Yildız Technical University in 2001 and 2004 respectively. His research interests include microbial fuel cell, solid wastes, biofuel production technologies, and environmental biotechnology.

Ergin Taşkan is a research assistant in the Department of Environmental Engineering at the Firat University (Elazıg) where he has been a faculty member since 2009. He received his B.S. degree in Environmental engineering from Firat University in 2006.

Ergin Taşkan completed his MSc and Ph.D. degrees at Firat University in 2009 and 2013 respectively. His research interests include microbial fuel cell, membrane bioreactors and membrane biofilm reactors.

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