20320130406024

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –

6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME

198

EFFECT OF COD ON OCV, POWER PRODUCTION AND COULOMBIC

EFFICIENCY OF SINGLE-CHAMBERED MICROBIAL FUEL CELLS

T. Opoku-Donkor, R. Y. Tamakloe, R. K. Nkum, K. Singh

Department of Physics, Kwame Nkrumah University of Science and Technology,

Kumasi, Ghana (West Africa)

ABSTRACT

An attempt has been made to find the effect of Chemical Oxygen Demand (COD) on the

Open Circuit Voltage (OCV), Power production and Coulombic efficiency of single – chambered

Microbial Fuel Cells (MFCs). Three different MFCs of similar design have been fabricated using

carbon paper doped with platinum as cathode and graphite as anode separated by Proton Exchange

Membrane (PEM).It has been found that the Open Circuit Voltage (OCV), power production and

Coulombic efficiency obtained are in direct proportion with COD level.

Keywords: MFC = Microbial Fuel Cell; SC-MFC = Single Chambered MFC;

Ecell = Total Cell Potential; OCV = Open Circuit Voltage

GGBL = Guinness Ghana Brewery Limited

INTRODUCTION

Power generation from MFCs using anaerobic microbes is a novel technology with great

potential for alternative energy generation and environmental pollution reduction. Microbial fuel cell

is a system that drives a current to generate electricity using bacteria found in nature. Organic

substances are degraded by micro-organisms through anaerobic metabolism liberating electrons and

protons in a biochemical cell using anode and cathode separated by proton exchange membrane

(PEM). For example, nutrient such as glucose is broken down into carbon dioxide, hydrogen ions

and electrons.

C12H22O11 + 13H2O -> 12CO2 + 48H+ +48e

-

INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING

AND TECHNOLOGY (IJARET)

ISSN 0976 - 6480 (Print)

ISSN 0976 - 6499 (Online)

Volume 4, Issue 7, November - December 2013, pp. 198-206

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The current is generated through the flow of electrons via a complete electric circuit. In 1910,

Potter had proposed the idea of production of EMF during fermentation of organic compounds by

yeast. However the first known patent of MFC was in 1967. Since then, different researchers worked

on the development of MFCs with different setups. For example, dual chambered cell with a proton

exchange membrane or single chambered cell with anode and cathode separated by cotton cloth,

were successful [1].

There are two main components of the fuel cell; cathode and anode compartments along with

a cation specific membrane. In the anode compartment, microorganism oxidizes substrates which

generate electrons and protons. Electrons are then transferred to the cathode compartment via an

external electric circuit. Protons are transferred to the cathode compartment through the cation

specific membrane. Consumption of electrons and protons in the cathode compartment with oxygen

results in formation of water. As stated by Logan et al [2] virtually any biodegradable organic matter

can be used in an MFC, including volatile acids, carbohydrates, proteins, alcohols, and even

relatively recalcitrant materials like cellulose.

A large amount of beer brewery wastewater is produced from cooling (eg. saccharification

cooling, fermentation) and washing units in brewery industry and often causes several environmental

problems. The wastewater is non-toxic, but has high Biological Oxygen Demand (BOD) compared

with other industrial wastewater. Generally, biological methods used for the beer brewery

wastewater treatment are reported to perform well in COD removal [3]. Domestic wastewater is also

reported in electricity generation in several MFC configurations (Liu et al. 2004; Liu & Logan 2004;

Min & Logan 2004) [4]. Beer brewery wastewater might be good source for electricity generation in

MFCs due to its nature of high carbohydrate and low ammonium-nitrogen concentration.

In this study, we have successfully verified the potential of brewery wastewater (Malta

Guinness - brewed from barley, hops, and water) to be used as fuel to generate electricity in a single-

chamber MFCs. All the experiments have been performed at temperature between 25 oC and 26

oC.

The scope of this study comprises two aspects: (i) to examine the possibility of direct power

generation from brewery wastewater; (ii) to investigate effect of different loading of COD on OCV

and Coulombic efficiency (CE). Besides, the main purpose of the study was also to validate

workability of a novel MFC design in terms of current generation and cheap materials, hence

showing current generation could be increased with multiple anodes sharing a common cathode and

also providing possibility for serial connectivity for increasing voltage output.

COULOMBIC AND ENERGY EFFICIENCY OF MFC

The generation of power is a main goal of MFC operation, but there is a need to extract as

much of the electrons stored in the biomass as possible as current, and to recover as much energy as

possible from the system. The recovery of electrons is defined as the fraction (or percent) of

electrons recovered as current versus that in the starting organic matter and referred as Coulombic

efficiency(CE) [5].

CE = Coulombs recovered/Total coulombs in the substrate

The energy eficiency of an MFC is based on energy recovered in the system compared to the

energy content of the starting material. The energy efficiency, ηMFC, is the ratio of power produced

by the cell over a time interval ‘t’ divided by the heat of combustion of the organic substrate, or

ηMFC = ∫ EMFC I dt / ∆H ns

where ∆H is the heat of combustion n (J mol-1

) and n, is the amount (mol) of substrate added.



200

POWER PRODUCTION BY MFC

From the graph, we read off a peak power in mW/cm2. Converting this to just power production from

the system as given below

P = PAN AAN

Where PAN is the peak power in mW/cm2 and AAN is the area of PEM.

EXPERIMENTAL PROCEDURES

Preparation of PEM: Nafion 117 of area 12.6 cm2 was taken through the normal cleaning process

[distilled water → 3% hydrogen peroxide → dilute sulfuric acid → distilled water ].

Fabrication of MFCs: Figures 1 – 6 show the necessary steps for the fabrication of MFCs.

- 2 Perspex slabs were cut, shaped and dilled for each cell (Fig 1).

- Carbon paper doped with platinum was cut and shaped (Fig 2).

- PEM (Nafion 117 – Fig 3)

- Cupper conductor was cut and shaped (Fig 4).

- Graphite electrode (Fig 5)

- A plastic container of 2 liters capacity served as the anodic chamber (Fig 6). The anode

chamber contains the wastewater and the graphite electrode. The carbon paper tightens onto

the PEM served as the cathode.

Types of Wastewater for MFCs: Following three types of wastewater of different COD and pH

from GGBL (Kumasi, Ghana) were used as Fuel for these cells. The characteristics of the wastewater

are listed in Table 1:

Table 1

Wastewater COD[mg/L] pH

Influent 3790.0 11.18

Anaerobic 748.0 6.80

Balance 4330.0 6.01

Fig 1: Perspex slabs Fig 2: Carbon paper



201

Fig 3: Nafion 117 Fig 4: Cupper plate and wire

Fig 5: Graphite electrode

Fig 6: a) Block diagram of finished cell Fig 6: b) Finished cell



202

Fig 7: Operational Cells setup with Campbell Scientific Ltd Datalogger CR10X, Logger to PC

adapter, USB to RS232 Cable and 12 V Battery to power the logger. The Datalogger stores data

every minute. We programmed the logger using Shortcut (CS PC200W 4.1 Datalogger Support

Software –CR10X)

Operation

The cells were kept at 25 oC (+- 0.5

oC). The anode was immersed in the wastewater such that

the cupper conductor did not touch the water in order to avoid corrosion. The anode chamber was

sealed to maintain anaerobic system throughout the experiment. OCV readings were taken for 35

days with the CR10X datalogger which stores the differential voltage every one minute. A

multimeter (Peak Tech 2010DMM) was used in the reading of the load voltage and the current

through a resistance box ranging from 0 to 10,000 ohms.

RESULTS AND DISCUSSION

The experiment was operational for 35 days. A constant increment of OCV was observed

from day one of the operation of MFCs until it got to their peak values of OCV. These values were

maintained for about 10 days. The graph of OCV against time is shown in Fig 8. Also their pH and

COD values at the end experiment are given in Table 2. The experiments were performed with the

wastewater as collected in order to check the viability of the cells without adding inoculants and

other chemicals.

Table 2

Wastewater Starting COD Ending COD Starting pH Ending pH

Influent 3790.0 133 11.18 8.3

Anaerobic 748.0 59 6.8 8.9

Balance 4330.0 267 6.01 8.6



203

Fig 8: Open circuit voltage (OCV) as a function of time as measured (stored every munite) by the

Datalogger. The lines shown are actual measured throughout the experimental period

The red line indicated that the Balance produced very high voltage for a long period and thus

maintains that for the period compare to Anaerobic and Influent substrates. This may be attributed to

the high value of COD.

The effect of external load on the voltage is shown in Fig 9. This characteristic curves show

wide variation in the three substrates indicating the dominance of Balance type of wastewater. As

expected, the power generation was observed to be highest when the COD was higher and the pH

skews towards acidity. Using the potential drop as function of load we calculated the current density

in mA/cm2 and the power. The polarization curve is shown in Fig 10.

According to Logan [5] the determination of power produced varied depending on the

relative sizes of the anode, cathode and PEM. We therefore, chose to normalize the current density

by the PEM surface area. To obtain a polarization curve we used a series of different resistances

from 0 to 10,000 Ω on the circuit, measuring the voltage at each resistance, as shown in Fig. 9 and

10.

INTERNAL RESISTANCE

According to Logan [5] the maximum power occurs when the internal and external

resistances are equal. From the graph shown in Fig. 11 the peak occurred at (8.04, 31.01) and this

corresponds to an external resistance of 3,000 Ω. Consequently the internal resistance for Balance is

equal to 3,000 Ω in the anode system (6 cm separation between anode and PEM). The peak for

Influent occurred at 8,000 Ω and that for Anaerobic occurred at 10,000 Ω. The high values of the

internal resistances may be due to the fact that the conductivities of the substrates were not tempered

with.



204

Fig 9: This depicts the potential dropped verses load (external resistance). We obtained a data set as

a function of resistance for the three systems

Fig 10: Polarization Curves for the Three Cells



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Fig 11: Power Density Curves

Power Production by MFC From Fig. 11 we read off a peak power of 31.01 mW/cm2. Converting this to power

production from the system we obtain

P = 31.01 (mW/cm2) x (12.6 cm

2) = 30 x 10

-4 W

Coulombic Efficiency (CE) The recovery of electrons is referred to as Coulombic efficiency, defined as the fraction

(or percent) of electrons recovered as current versus that in the starting organic matter [6].

That is

Where tb = Total cycle (s)

I = Current (A)

F = Faraday’s constant (C/mole)

VAn = volume of liquid in the anode compartment (L)

∆COD = Change in COD (g/L)

CE = 11.3 %

Partition Surface Area of PEM per Volume = 0.7 m2/m

3



206

CONCLUSION

It has been found that the Balance wastewater produced power most significantly than the

other two. It has been observed that the current generation of the cells increased for a higher COD

and lower pH. Characterization curves for Influent and Anaerobic wastewaters are insignificant

compared to that of Balance wastewater. The removal of COD of observed to be highest for the cell

which produces higher current. The COD for Balance dropped from 4386 to 267mg/L for the 36

days of running.

Summary of other Generated Parameters

Substrate Max. OCV

(mV)

Max Current

(mA)

Power

Density

(mW/cm2)

Current

Density

(mA/cm2)

Internal

Resistance

(Ω)

Balance 782 0.330 246 8.04 3 k

Influent 345 0.021 37.9 0.34 8 k

Anaerobic 66 0.003 10.7 0.028 10 k

ACKNOWLEDGEMENTS

Authors would like to thank Dr. Young-Gi Yoo of Korea Institute of Energy Research for

providing Carbon paper doped with platinum. We would also like to thank the Head of Physics

Department, KNUST and Guinness Ghana Brewery Limited for necessary facilities for this work.

REFERENCES

[1] Banik et al, 2012 Greener Journal of Biological Sciences ISSN: 2276-7762 Vol. 2 (2),

pp. 013-019, October 2012.

[2] Logan, B.E. 2008, Microbial Fuel Cells pp. 6.

[3] X. Wang; Y. J. Feng, H. Lee 2008, Electricity production from beer brewery wastewater

using single chamber microbial fuel cell – Water Science & Technology – WST, 57.7, 1117.

[4] Liu, H., Cheng S. and Logan, B.E. 2005b, Production of Electricity from acetate or butyrate

in a single chamber microbial fuel cell, Environ. Sci. Techno, 39(2), 658 -662.

[5] Logan, B.E. 2008, Microbial Fuel Cells, pp 46 – 48.

[6] Chonde Sonal G, Mishra A. S. and Raut P.D., “Bioelectricity Production from Wastewater

using Microbial Fuel Cell (MFC)”, International Journal of Advanced Research in

Engineering & Technology (IJARET), Volume 4, Issue 6, 2013, pp. 62 - 69, ISSN Print:

0976-6480, ISSN Online: 0976-6499.

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