Proceedings of ICEE 2009 3rd International Conference on Energy and Environment, 7-8 December 2009, Malacca, Malaysia

978-1-4244-5145-6/09/$26.00 ©2009 IEEE 59

Performance of Air-Cathode Microbial Fuel Cell with wood charcoal as electrodes

Li Fen Chai, Lay Ching Chai, Son Radu Dept. of Food Technology, Faculty of Food Science and

Technology, Universiti Putra Malaysia, 43400 UPM Serdang,

Selangor, Malaysia. yona1437@hotmail.com

Abstract— A cheap and locally available wood charcoal was used as the main electrode component of an air cathode MFC. The air cathode was build with fine charcoal powder and cement plaster as binder; while anode is a packed bed of charcoal granules. Mangrove estuary brackish water was inoculated in the anodic chamber as the fuel and source of exoelectrogens. The constructed fuel cell was monitored by measuring the potential. The MFC generated a stable power density at 33mW/m2 (0.5V) under load 200Ω after 72 hours operation. An open circuit voltage (OCV) of 0.7mV was obtained after 15 hours operating under open circuit. The result of power generation by the constructed fuel cell indicating that wood charcoal was able to be used as electrode in MFC and brackish water contained potential exoelectrogens. Further investigation and modification is required to increase the performance of the fuel cell.

Keywords- MFC; air-cathode; wood charcoal; brackish water

I. INTRODUCTION

In recent years, microbial fuel cell (MFC) technology is evolving rapidly because there is a great potential of MFC as an alternative renewable energy resources and cause no pollution to environment. They used the available substrates from renewable sources such as wastewater and convert them into harmless by-product with simultaneously production of electricity [14]. MFCs are bio-electrochemical devices which convert biomass into electricity through the metabolic activity of the microorganisms [8]. In MFC, microorganisms work as biocatalyst to breakdown the biomass into electrons protons. Electrons were shuttled to anode and transferred to cathode where electrons, oxygen and protons combine to produce water [15].

Previously, the study on carbon, graphite, metal and metal coating [1, 2] and modified electrode with linked mediator onto the electrode [5, 10] have done to investigate their performance in MFC. However, the cost of these materials was found expensive and uncommon in Malaysia. Therefore, the necessary to find a locally available and relatively cheap material is significant for the development of microbial fuel cell technology in Malaysia. Besides, the structure of the reactor is one of the factors that affect the performance and also the capital cost of constructing the reactor. Instead of

Suhaimi Napis

Dept. of Cell and Molecular Biology, Faculty of biotechnology and molecular sciences

Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia.

sediment MFC, air-cathode MFC is one of the most effective improvements in the construction of MFCs. Compared to liquid-state electron acceptor such as dissolved oxygen [3, 4], potassium ferricyanide [9, 11, 13] and potassium manganate [12], membrane-less air-cathode utilized the oxygen freely available in the air as the electron acceptor [6, 7] and therefore decreased the costs of the cells and improve the process sustainability.

The main objectives of current study were to investigate the potential application of wood charcoal, a cheaper material for electrodes in microbial fuel cell and up-scaling of the air-cathode MFC with wood charcoal.

II. METHODOLOGY

A. Brackish water Brackish water was collected from mangrove estuary in

Kuala Sepetang, Perak and kept in 4oC until use. The brackish water was used as the inoculum for all MFC tests as it is without any modification such as pH adjustment or addition of nutrients.

B. MFC design and operation Both of the MFC chambers were designed to have similar

structure but with different volume capacity of 50ml and 450ml. The MFC consisted of an anode, an air-cathode and an anodic chamber. The former MFC with 50ml working volume, namely MFC-I, was used in the initial operation (Fig. 2.1A). The anode of the chamber was a piece of wood charcoal of 8cm x 1.2cm x 1.2cm, whereas the cathode was made of finely grounded wood charcoal powder and cement plaster mixture in 2:1 ratio.

MFC with larger capacity was term MFC-II (Fig. 2.1B). It had a working volume of 450ml and wood charcoal beads (average diameter: 1cm; total volume: 130cm3) as the anode. The construction of the air cathode was similar to MFC-I.

Both MFCs were initially connected to an external circuit with a single resistor (1000 Ω) and allowed to operate for a few days. When stable power generation was reached, the circuit was opened until constant potential was obtained; then,

60

polarization test was performed by varying the external resistance over a range of 100Ω-400KΩ. The voltage was recorded. The power density was then calculated for each resistance as a function of the current density and polarization curve was plotted.

(A) (B)

Figure 2.1 MFC-I (A); MFC-II (B)

C. Data capture and calculation The performance of the constructed MFC was monitored

by linking the fuel cell to a pc via an eleven-channels terminal board connected to an ADC-11 converter (Pico Technology Ltd., Cambridgeshire, UK). Real time data was recorded using PicoLog® version 5.16.2 recorder software and retrieval of the data was performed using the PicoLog® version 5.16.2 player software (Pico technology).

The current I in miliAmpere (mA) was calculated using Ohm’s law, I=V/R, where V is the measured voltage (V) and R is the known external load value used for the test. The power density (mW/m2) of the MFC was also calculated base on the following formula, P= (I x V)/A, where A is the surface area of air-cathode.

III. RESULT AND DISCUSSION

A Power generation from brackish water using MFC-I Preliminary experiment was conducted using MFC-I to

demonstrate that wood charcoal can work as an electrode to conduct electricity. Initially, MFC-I was operated across an external load of 1KΩ, an average circuit voltage of 3.69mV was immediately generated within 24 hours. This initial voltage might have been due to both the chemical and biological factors based on the difference of the potential between the anode (brackish water) and cathode (free oxygen in the air). Thereafter, the voltage increased dramatically due to the biological activity and stabilized at average of 11.74mV over the following 11days, resulting in an average power density of 0.014mW/m2 (normalized by the surface area of the cathode) (Fig. 3.1A).

By varying the external resistance, it was determined from the polarization curve that the maximum power that was this system could produce was 0.04mW/m2 (0.6mA/m2) at 10KΩ (Fig. 3.1B). The generation of electricity was gradually decrease after day 16 and dropped lower than 6mV after day 23.

0

50

100

150

200

250

0.0 0.2 0.4 0.6 0.8

Curren density (mA/m2)

volta

ge (m

V)

0.00

0.01

0.02

0.03

0.04

0.05

pow

er d

ensi

ty (m

W/m

2)

Figure 3.1 (A)Power generation with brackish water in the MFC-I (1KΩ). (B) Voltage-current curve and power curve

obtain by using external circuit of 100Ω-400KΩ.

B. Power generation from brackish water using MFC-II. To demonstrate the potential for large-scaled operation, the MFC-II was constructed with a larger capacity volume. It is inoculated with brackish water so as to measure the changes in power generation due to an increase in the working volume of the MFC. After 2 days operation, the fuel cell voltage reached a stable value of 399mV (Fig. 3.2A). The maximum power density was 17.7mW/m2 (200Ω, 44.33mA/m2) (Figure 3.2B). The power density is approximately 1200 times higher than that obtained with MFC-I. The outcome of the experiments implies that the constructed fuel cell has great potential to be up-scaled into larger industrial reactor for generation of greater power density.

0

5

10

15

20

25

0 5 10 15 20 25Time (days)

Pow

er d

ensi

ty (W

/m

0.25

0.20

0.15

0.10

0.00

(mW

/m2 )

(A)

(B)

61

0

50100

150

200250

300

350

400450

500

0 20 40 60 80 100Current density (mA/m2)

Volta

ge (m

V)

0

24

6

810

12

14

1618

20

Pow

er d

ensi

ty (m

W/m

2)

Figure 3.2 (A) Voltage generation with brackish water in the MFC-II. (B) Voltage-current curve and power curve obtained

by using external circuit of 100Ω-400KΩ.

In fact, up-scaling of microbial fuel cell for greater electricity generation is not impossible. However, it is not feasible due to its high-cost in production. Scientists all over the world have yet find out ways to economically scale-up an MFC for commercial application. Capital cost is always one of the issues that stop it from up-scaling. But with the utilization of cheaply available wood charcoal, it brings us one step forward to apply MFC technology into industrial application.

III. CONCLUSSION

Electricity was generated using brackish water, at a power density that depends greatly on the volume capacity of the MFC. The power density generated with MFC-I was 0.014mW/m2, while 1200 times more power (17.7mW/m2) was generated using MFC-II. The findings from this study imply that wood charcoal could be used as the electrodes of the MFC. The high availability and lower cost of wood charcoal in this country have solved one of the issue in economically scale-up of MFC by greatly cut down the capital cost of constructing a microbial fuel cell. This paper presented a preliminary study on the performance of microbial fuel cell using wood charcoal and brackish water as the electrodes and inoculum, respectively. Further studies are required to

determine the limiting factors and modifications in order to improve the performance of the air-cathode microbial fuel cell with wood charcoal as electrodes.

ACKNOWLEDGMENT This research was financially supported by the Research University Grants (RUGS) (XXXXXX) from Universiti Putra Malaysia.

REFERENCES

[1] A. L. Walker and C. W. Walker Jr., “Biological fuel cell and an application as a reserve power source,” J. Power Sources, vol 160, pp. 123-129, 2006.

[2] A. T. Heijne, H. V. M. Hamelersa, M. Saakes, C. J. N. Buisman, “Performance of non-porous graphite and titanium-based anodes in microbial fuel cells,” Electrochimica Acta, vol 53, pp. 5697–5703, 2008.

[3] B. E. Logan, C. Murano, K. Scott, N. D. Gray, I. M. Head. “Electricity generation by microbial fuel cell,” Water Res., vol 39, pp. 942-952, 2005.

[4] B. Min, J. R. Kim, S. E. Oh, J. M. Regan, B. E. Logan. “Electricity generation from swine water using microbial fuel cell,” Water Res., vol 39, pp. 4961-4968, 2005.

[5] D. H. Park, J. G. Zeikus, “Improved Fuel Cell and Electrode Designs for Producing Electricity from Microbial Degradation,” Biotech. and Bioengineering, vol 81, pp. 348- 355, Feb 2003.

[6] H. Liu and B. E. Logan. “Electricity generation using an air-cathode single chamber micreobial fuel cell in the presence and absence of a proton exchange membrane,” Environ. Sci. Technol., vol 38, pp. 4040-4046, 2004.

[7] H. Liu, S. Cheng, B. E. Logan. “Scale-up of memebrane –free single chamber microbial fuel cells,” J. Power Sources, vol 179, pp. 274-279, 2008.

[8] I. A. Ieoropulos., J. Greenman, C. Melhuish, J. Hart. “Comparative study of three types of microbial fuel cell,” Enzyme Microb Technol, vol 37, pp. 238-245, 2005.

[9] K. Rabaey, G. Lissens, S. D. Siciliano, W. Verstraete. “A microbial fuel cell capable of converting glucose to electricity at high rate and efficiency,” Biotechnol, Lett., vol 25, pp. 1531-1535, 2003.

[10] Pham, T. Hai, J. K. Jang, I. S. Chang, B. H. Kim, “Improvement of Cathode reaction of a Mediator-less Microbial Fuel Cell,” J. Microbial. Biotechnol., vol 14(2), pp. 324-329, 2004.

[11] S. E. Oh, B. Min, B. E. Logan. “Cathode performance as a factor in electricity generation in microbial fuel cell,” Environ. Sci. Technol., vol 38, pp. 4900-4904, 2004.

[12] S. You, Q. Zhao, J. Zhang, J. jiang, S. Zhao. “A microbial fuel cell using pwrmanganate as the cathodic electron acceptor.” J. Power Sources, vol 162, pp. 1409-1415, 2006.

[13] U. Schroder, J. Nieben, R. Scholz. “A generation of microbial fuel cell with current outputs boosted by more than one order of magnitude,” Angew. Chem. Int. Ed. Engl. Vol 42, pp. 2880-2883, 2003.

[14] Y. Mohan, S. Manoj Muthu Kumar, D. Das. “Electricity generation using microbial fuel cells,” International Journal of Hydrogen Energy, vol 33, pp. 423- 426, 2008.

[15] Z. J. Li, X. W. Zhang, Y. X. Zeng, L. C. Lei. “Electricity Production by an overflow-type wetted-wall microbial fuel cell,” Bioresource Techynology, vol 100, pp. 2552-2555, 2009.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0 10 20 30 40 50Time (hours)

Volta

ge (m

V

700

600

500

400

300

200

100

0

Vol

tage

(mV

)

(B)

(A)