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A novel microbial fuel cell stack for continuous productionof clean energy

M. Rahimnejad a, A.A. Ghoreyshi a,*, G.D. Najafpour a, H. Younesi b, M. Shakeri c

aBiotechnology Research Lab., Faculty of Chemical Engineering, Noshirvani University, Babol, IranbDepartment of Environmental Science, Faculty of Natural Resources and Marine Science, Tarbiat Modares University, Noor, Iranc Faculty of Mechanical Engineering, Noshirvani University, Babol, Iran

a r t i c l e i n f o

Article history:

Received 8 November 2011

Received in revised form

25 December 2011

Accepted 28 December 2011

Available online 28 January 2012

Keywords:

Microbial fuel cell

Stack

Columbic efficiency

Electricity generation

Saccharomyces cerevisiae

* Corresponding author. Tel.: þ98 111 323 42E-mail address: aa_ghoreyshi@nit.ac.ir (A

0360-3199/$ e see front matter Copyright ªdoi:10.1016/j.ijhydene.2011.12.154

a b s t r a c t

Production of sustainable and clean energy through oxidation of biodegradable materials

was carried out in a novel stack of microbial fuel cells (MFCs). Saccharomyces cerevisiae as an

active biocatalyst was used for power generation. The novel stack of MFCs consist of four

units was fabricated and operated in continuous mode. Pure glucose as substrate was used

with concentration of 30 g l�1 along with 200 mmol l�1 of natural red (NR) as a mediator in

the anode and 400 mmol l�1 of potassium permanganate as oxidizing agent in the cathode.

Polarimetry technique was employed to analyze the single cell as well as stack electrical

performance. Performance of the MFCs stack was evaluated with respect to amount of

electricity generation. Maximum current and power generation in the stack of MFC were

6447 mA.m�2 and 2003 mW.m�2, respectively. Columbic efficiency of 22 percent was

achieved at parallel connection. At the end of process, image of the outer surface of

graphite electrode was taken by Atomic Force Microscope at magnification of 5000. The

high electrical performance of MFCs was attributed to the uniform growth of microor-

ganism on the graphite surface which was confirmed by the obtained images.

Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

1. Introduction (BFCs) are a subset of fuel cells which employ active bio-

Consumption of fossil fuels has created serious threats for

human being, such as global warming and environment

pollution. In addition, proven reserves of fossil fuels are finite

and world may be faced with serious shortage of energy in

a near future. These crucial issues have encouraged

researchers to seek alternatives for conventional fossil fuels

[1,2]. Fuel cells are known as renewable and environmental-

friendly sources of energy [3]. Fuel cells are electrochemical

engines that convert directly the chemical energy existing in

the chemical bonds into electricity [4]. Biological fuel cells

04; fax: þ98 111 321 0975..A. Ghoreyshi).2012, Hydrogen Energy P

catalysts for production of bioelectricity instead of expensive

metal catalysts used in conventional fuel cells such as proton

exchange membrane fuel cell (PEMFC). The main types of

BFCs are defined by the biocatalyst used in anode compart-

ment. Microbial fuel cells (MFCs) employ living cells for

oxidation of organic substrate, whereas enzymatic fuel cells

use active enzymes for the same purposes [5,6]. MFCs have

been considered as new alternatives to conventional

batteries for electricity generation in power sources [7]. The

main advantage of MFCs is that they typically have long

lifetimes (up to five years) [8,9]. MFCs are capable to oxidize

ublications, LLC. Published by Elsevier Ltd. All rights reserved.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 5 9 9 2e6 0 0 0 5993

simple carbohydrates to carbon dioxide via biochemical

reactions [10].

Recently, great attentions have been paid to MFCs due to

their mild operating conditions and using variety of biode-

gradable substrates as fuel [11]. Traditional MFCs consist of

two separate compartments named as cathode and anode

[12]. Some microorganisms such as Saccharomyces species and

Escherichia coli are unable to transfer directly the produced

electrons to anode surface [13,14]. Therefore, such bio-

catalysts require electron shuttles in anode chamber of MFCs

[15]. The performance of MFCs mainly depend on several

important factors, such as system architecture, electrode

material, electrode surface area, bacterial species, types of

organic matter, operating conditions (solution conductivity,

pH), and type of catholyte [14,16e20].

Single MFCs were used by many researchers for the

purpose of power generation by means of pure and mixed

cultures of active biocatalysts [21e23]. A series of attempts

has been made to improve MFCs’ performance using suitable

substrates and microorganisms by application of process

optimization [16,24e26]. Maximum power density of

10.2 mW.m�2 was obtained by Park and Zeikus using She-

wanella putrefacians and lactate as a substrate in an MFC [13].

Power generation by a pure culture of Geobacter metal-

lireducens in a dual chambered MFC was investigated. It was

found that maximum power was about the same value ob-

tained in a mixed culture originated from wastewater

(38 mW.m�2) [27]. Cheng and his coworkers have achieved

maximum power of 462 mW.m�2 in a cubic MFC [28]. The

obtained results from others researchers have demonstrated

that the produced power from single MFC was too low to be

used even in low consumption devices. Therefore, a number

of single MFC has to be connected in parallel or series to

provide enough power for a specific application such as

a vehicle or an uninterruptible power supply. Any desired

voltage or current can be obtained by series or parallel

connection of a few single cells. A combination of single MFC

connected in parallel and/or series is called a fuel cell stack

[28,29].

Connecting several individual cells in series adds the

voltages, while a unique current flows through all MFCs.

When several single cells are connected in parallel, the voltage

averages and the currents are added [29]. Wilkinson has used

six individual cells named ‘gastrobots’ for a digester of food

residues [30]. Also Aelterman and his research teamhave used

six anode and cathode in their stack. They have reported the

stack in series or in parallel had increased voltage and current,

respectively [29]. Oh and Logan have reported that the oper-

ation of MFCs in series connection had the risk of voltage

reversal [31]. The above discussion reveals that a stack of

MFCs is required to obtain higher electrical outputs.

Liu et al. have conducted similar research in fed batch

system. They have combined two single MFCs as stack. Their

systemhad significantly high power outputs; where the anode

and cathode were sandwiched between two proton exchange

membranes [32]. The polarization curves obtained in their

experiments were almost identical for all cells; as there was

nomass transfer limitation in their anode chamber. However,

fed batch system may not be suitable for continuous power

generation.

The main objective of present research was to assemble

a number of individual MFCs in a specially designed stack to

enhance electrical output for practical applications. In this

research, a new design of MFCs stack composed of four

anodes and three cathodes compartments were used .All

experiments were conducted in continuousmode at optimum

hydraulic residence time (HRT) as well as glucose concentra-

tion determined based our pervious results [33,34]. The

uniformity of electricity generation at each individual MFC

was investigated. The collective current and voltage produc-

tion in series and parallel connections of MFCs was also

studied. Results of present research demonstrated that the

novel fabricated stack was remarkably enhanced current and

power at optimum conditions which can be used for low

consumption electrical devices.

2. Materials and methods

2.1. Microorganism and cultivation

The systemwas inoculated with pure culture of Saccharomyces

cerevisiae PTCC 5269. The yeast was supplied by Iranian

Research Organization for Science and Technology (Tehran,

Iran). Themicroorganismwas grown at anaerobic condition in

an anaerobic jar. The prepared medium for the seed culture

consisted of glucose, yeast extract, NH4Cl, NaH2PO4, MgSO4

and MnSO4: 10, 3, 0.2, 0.6, 0.2 and 0.05 g.l�1, respectively. The

medium was autoclaved at 121 �C and 15 psig for 20 min.

The medium pH was initially adjusted to 6.5 and the

inoculums were introduced into the media at ambient

temperature. The inoculated cultures were incubated at 30 �C.The organism was fully grown in a 100 ml flask without any

agitation for the duration of 24 h.

2.2. Stacked MFCs set up

The cubic stack of MFCs was fabricated from Plexiglas mate-

rial and used for power generation in laboratory scale. Stacked

MFCs was assembled from four individual anodes and three

cathodes compartments. Schematic diagram and photo image

of the fabricated cells are shown in Fig. 1a and b, receptively.

The volume of each chamber (anodes and cathodes chambers)

was 460 ml with a working volume of 350 ml. The sample port

was provided for each anode chamber with wire point input

and inlet port. The selected electrodes for all separated cell

were unpolished graphite plates, size of 40 � 60 � 1.2 mm.

Proton exchangemembrane (cross-sectional area: 32 cm2) was

used to separate two compartments. Table 1 shows a list of

components and the materials used for fabrication of stacked

MFCs. Proton exchange membrane, Nafion 117, was subjected

to a course of pretreatment to take off any impurities. For this

purpose, it was boiled for 1 h in 3 percent H2O2, washed with

deionized water, 0.5 M H2SO4, and finally washed with

deionized water. In order to maintain a good conductivity for

membrane, the anode and cathode compartments were filled

with deionized water when the microbial fuel cell was not

in use. NR (200 mmol.l�1) and potassium permanganate

(400 mmol.l�1) supplied by Merck Company (Darmstadt,

Germany) were used as mediator and oxidizing agent,

Fig. 1 e Fabricated cell (a) Schematic diagram (b) cell picture. Stacked MFC (c) Schematic diagram of the stacked assembly, (d)

Stacked picture with the auxiliary equipments.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 5 9 9 2e6 0 0 05994

respectively. The schematic diagram, photographic images

and auxiliary equipments of the fabricated stacked MFC

systems have been shown in Fig. 1c and d. In continuous

operation, all anode chambers were continuously fed with the

Table 1 e Basic component was used for staked MFC.

Item Materials Company

Anode electrodes Graphite plate ENTEGRIS, INC.

FCBLK-508305-00004, USA

Cathode electrodes Graphite plate ENTEGRIS, INC.

FCBLK-508305-00004, USA

Anode Chambers Plexiglas Neonperse, Iran

Cathode chambers Plexiglas Neonperse, Iran

Proton exchange

Membranes

Nafion 117 SigmaeAldrich, USA

Connection the cells Copper wire Khazar Electric, Iran

prepared media in an up-flow mode using an adjustable

peristaltic pump (THOMAS, Germany) and the oxygen needed

at the cathode side was provided by an air sparger.

2.3. Chemical and analysis

All chemicals and reagents used for the experiments were

analytical grades and supplied by Merck (Darmstadt, Ger-

many). The pH meter, HANA 211 (Romania) model glass-

electrode was employed to measure pH values of the

aqueous phase. The initial pH of the working solution was

adjusted by addition of diluted HNO3 or 0.1 M NaOH solutions.

The surface images of the graphite plate electrodes before and

after each experimental run were obtained by Atomic Force

Microscope (AFM) at magnifications of 5000 (Easyscan2 Flex

AFM, Swiss). The sample specimen size was 1 cm � 1 cm for

AFM analysis. AFM images were used to demonstrate the

Fig. 2 e Open circuit voltage produced in a first individual

MFC (cells 1 and 2) using S. cerevisiae as the active

biocatalyst and 200 mmol.lL1 NR as mediators in anode

chamber and 200 mmol.lL1 potassium permanganate in

cathode chamber.

Current (mA.m-2)0 200 400 600 800 1000

Vol

tage

(m

V)

0

200

400

600

800

1000

Pow

er (

mW

.m-2

)

0

50

100

150

200

250

300Voltage

Power

Fig. 3 e Results of batch operated MFCwith 30 g.lL1 glucose

as the substrate. power density and voltage as function of

current density in a cubic MFC (cell 1 and 2) using S.

cerevisiae as the active biocatalyst, 200 mmol.lL1 NR as

mediators and 400 mmol.lL1 potassium permanganate as

oxidizing agent.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 5 9 9 2e6 0 0 0 5995

physical characteristics of the electrode surface and to

examine the growth of yeast on the anode surface.

Dinitrosalicylic acid [3, 5(NO2)2C6H2e2OHeCOONa.H2O]

(DNS) method was employed to detect and measure substrate

consumption using colorimetric method [35]. Before analysis,

liquid samples were filtered by a 0.45 mm syringe membrane

(Sartorius Minisart).

Polarimetry technique was adapted to analyze the cell

electrical performance. Polarization curves were obtained

using an adjustable external resistance. Power and current

were calculated based on following equations:

P ¼ I�E (1)

I ¼ ðE=RextÞ (2)

where P is generated power and E measured cell voltage; Rext

denotes external resistance and I indicates produced current.

Theonline recordedcurrentandpowerwerenormalizedby the

surface area of the used membrane. Analog digital data

acquisition was fabricated to record data point in every 4 min.

Measurements were carried out at variable resistances

imposed to theMFC. The current in theMFCwas automatically

calculated and recorded dividing the obtained voltage by the

specified resistance. Then, the system provides power calcu-

lation bymultiplication of voltage and current. The provisions

were provided for online observation of polarization curve

showing the variation of power density and MFC voltage with

respect to current. The online systemhad the ability to operate

automatically ormanually.While it operates inauto-mode, the

assembled relays were able to regulate automatically the

resistances. Voltage of MFC was amplified and then data were

transmitted to a microcontroller by an accurate analog to

digital converter. Themicrocontrollerwas also able to send the

primary data to a computer by serial connection. In addition,

a special functionofMATLABsoftware (7.4, 2007a,MathWorks,

US) was used to store and display synchronically the obtained

data. The power, current and voltage were automatically

recorded by the computer connected to the system.

Columbic efficiency (CE) was calculated by division of total

coulombs obtained from the cell by theoretical amount of

coulombs that can be produced from glucose (Eq. (3)):

CE ¼ �Cp=CT

�� 100 (3)

Total coulombs are obtained by integrating the current

variation over time (Cp), where CT is the theoretical amount of

coulombs that can be produced from carbon source. For

continuous flow through the system, CE can be calculated on

the basis of generated current at steady state conditions as

follows [23]:

CE ¼ MI=FbqDS (4)

In Eq. (4), F is Faraday’s constant; b is the number ofmoles of

electrons produced per mole of substrate (24 mol of electrons

were produced in glucose oxidation in anaerobic anode

chamber); S is the substrate concentration; q is flow rate of

substrate and M is the molecular weight of used substrate

(M ¼ 180.155 g.mol�1) [36,37].

In batch mode of operation, polarization curves were ob-

tained at steady state condition while setting an adjustable

resistance in data logger. When the MFC was operated in

continuous mode, the concentration of glucose in the feed

tank solution was kept constant (30 g.l�1). HRT was fixed at

6.7 h by means of peristaltic pump in each anode chamber.

The HRT was measured from the volume of medium and the

input flow rate to the anode compartment.

3. Results and discussion

Batch mode of operation is necessary to determine the best

operating conditions to achieve maximum electrical output.

The optimum conditions for power generation in a single cell

MFC was found in our recent research [35]. To test the

reproducibility of the results, batch mode of operation was

replicated at the predetermined condition. After inoculation

Current (mA.m-2)

0 500 1000 1500 2000 2500

Vol

tage

(m

V)

0

200

400

600

800

1000

1200

Pow

er (

mW

.m-2

)

0

100

200

300

400

500

600Voltage current

Fig. 4 e Results of continuous operated MFC with 30 g.lL1

glucose as the substrate. power density and voltage as

function of current density in a cubic MFC (cells 1 and 2)

using S. cerevisiae as the active biocatalyst, 200 mmol.lL1 NR

as mediators, 400 mmol.lL1 potassium permanganate as

oxidizing agent and 6.7 h HRT.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 5 9 9 2e6 0 0 05996

of 30 g l�1 glucose in anode chamber with S. cerevisiae, data

logger was set to record open circuit voltage (OCV) until

steady state condition. An infinite resistance was used to

obtain OCV in batch mode in presence of 200 mmol l�1 of NR

and 400 mmol l�1 of potassium permanganate as mediator and

Current (mA.m-2)

0 500 1000 1500 2000 2500

Vol

tage

(mV

)

0

200

400

600

800

1000

1200

1400

Pow

er (m

W.m

-2)

0

100

200

300

400

500

600Voltage current

Chamber 3 and 4

Current (mA.m-2)

0 500 1000 1500 2000 2500 3000

Vol

tage

(m

V)

0

200

400

600

800

1000

1200

Pow

er (

mW

.m-2

)

0

100

200

300

400

500Voltage current

Chamber 6 and 7

Fig. 5 e Results of continuous operated MFC with 30 g.lL1 glucos

current density in different individual cells. Experiment conditi

oxidizer in anode and cathode, respectively. The initial volt-

ages for all individual cells were nearby 330 mV, which

confirmed the reproducibility of electrical output with respect

to our previous experiments. Continuous generation of elec-

trons and protons along with substrate consumption by the

biocatalyst, led to enhancement of bioelectricity production.

The time required to reach steady state is quiet different for

systems using various substrates, concentration and micro-

organism. Fig. 2 depicts MFC performance in terms of OCV

improvement with respect to time. The cell voltage gradually

increased and reached to 847 mV after 38 h. The data were

recorded for duration of 75 h of operation.

The fabricated stack was operated in batch mode at room

temperature (25 � 1 �C). Then, performance of the microbial

fuel cell was evaluated by the polarization curve. Once all

individual cells have stabilized at maximum steady voltage,

the polarization curves were obtained using an adjustable

external resistance to determine variation of voltage with

respect to current density. Fig. 3 demonstrates polarization

curve for the first MFC (between chambers 1 and 2). The

maximum generated power and current density were

241mW.m�2 and 930mA.m�2, respectively. Similar results for

other cells in stack were recorded; the obtained data are

summarized in Table 1.

Once stable voltage was established in each cell, the

batch operation was switched to continuous mode. In

continuous operation, the prepared substrate was injected

from the feed tank to anode compartment with a defined

Current (mA.m-2)

0 500 1000 1500 2000 2500

Vol

tage

(m

V)

0

200

400

600

800

1000

1200

Pow

er (

mW

.m-2

)0

100

200

300

400

500

600Voltage current

Chamber 2 and 3

Current (mA.m-2)

0 500 1000 1500 2000 2500 3000

Vol

tage

(m

V)

0

200

400

600

800

1000

1200

Pow

er (

mW

.m-2

)

0

100

200

300

400

500

600Voltage current

Chamber 4 and 5

e as the substrate. Power density and voltage as function of

on was similar to Fig. 4.

Table 2 e Optimum condition obtained from eachindividual cell without feeding.

Single cellnumber

Pmax

(mW.m�2)Imax in Pmax

(mA.m�2)OCV at S.S. condition

(mV)

1e2 241 630 847

2e3 246 645 850

3e4 243 639 849

4e5 244 641 849

5e6 244 644 851

6e7 235 621 841

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flow rate (HRT of 6 h). Substrate with initial glucose

concentration of 30 g.l�1 and the same mediator and oxidizer

concentration were continuously transferred through

uniform flow distributors by means of peristaltic pump.

Effect of HRT on performance of continuous MFC was

investigated in our previous research [33]. Polarization data

were obtained when the stable voltage output was estab-

lished in continuous mode (after 3 days). Polarization curve

for the first MFC is shown in Fig. 4. The maximum generated

current and power density were 2100 mA.m�2 and

490 mW.m�2, respectively.

Polarization curves for other individual MFCs were plotted

in Fig. 5. The polarization curves obtained for different single

MFCs indicated that the maximum current density and power

density for all individual cells were almost similar. However,

the generated power and current in the last cell (cell 6 and 7)

was slightly less than the others. This may be attributed to

insufficient flow distribution inside the last cell (also see the

reported values of power density in Table 2).

Combining appropriate number of single fuel cells may

provide adequate power source. In present work, four anodes

and three cathodes chambers were connected to each other to

make a stack of MFCs. All anodes, except the first and last

anode (cells 1 and 7), were connected with two cathodes. To

enhance voltage or current, all individual cells were con-

nected in series and parallel, respectively. These special

configurations led to OCV of 3230 and 1005 mV for series

connection and the parallel connection, respectively. The

Current (mA.m-2)

0 2000 4000 6000 8000 10000

Vol

tage

(m

V)

0

200

400

600

800

1000

1200

Pow

er (

mW

.m-2

)

0

500

1000

1500

2000

2500

Voltage current

Fig. 6 e Results of parallel staked MFC with initial 30 g.lL1

glucose as the substrate. Power density and voltage as

function of current density in different individual cells.

Other experimental conditions were similar to Fig. 4.

performance of MFCs stack with parallel connection was also

investigated by polarization curve. Fig. 6 depicts variation

of voltage and power density as function of current density

(polarization curve). The maximum current and power

density for parallel connection were 2003 mW.m�2 and

6447mA.m�2, respectively. MFCs stack operated continuously

for duration of 3 days and polarization data indicated that the

power generation was stable.

OCV represents the highest voltage which is obtained in an

MFC. In an actual condition, there is a resistance in external

circuit. In order to obtain close circuit voltage, a 1 KU resis-

tance was fixed in external circuit and the system worked

at this situation for the period of 148 h. Fig. 7 shows the close

circuit voltage and generated power was stable like open

circuit voltage for the entire period of operation. Table 3

compares results obtained for stacked MFCs in this work

with the similar works reported in literature for different

substrates and microorganisms.

Based on obtained data, columbic efficiency (CE) for the

parallel and series connections were 22 and 6.5 percent. Low

CE may be due to the breakdown of sugars by the microor-

ganism resulted in production of some intermediate prod-

ucts that may play a significant role in decrease of CE

[38,39]. Aelterman et al. have achieved CE of 12.4 and 77.8

percent in series and parallel connections, receptively. They

have used 6 units of MFC in their stack; acetate as substrate

and ulterex as the proton exchange membrane [29]. Differ-

ences in CE of the parallel and series connected stacks were

reported [29]. Since both types of stacks operated at the

same HRT; the difference in CE values was caused by the

higher current generated in parallel connection compared to

that of series connection. Thus, connection of MFCs in

series to form a stack of MFCs may not allow high current

densities [29]. The obtained results from the stacked MFCs

also proved its potential for scale up to achieve higher

electrical outputs.

AFM technique has been widely applied to provide elec-

trode surface and morphological information. The outer

surfaces of the anode electrode before and after experiments

were examinedwith AFM. Fig. 8 depicts the AFM images of the

shape and surface characteristic of the anode electrode

Fig. 7 e Close circuit voltage and produced power from

staked MFC at parallel mode with 1 KU resistances in

external circuit for 148 h.

Table 3 e Production of bioelectricity in stacked MFC with different configuration were used.

Substrate Type Numberof anode

Numberof cathode

Maximumproduced power

Microorganisms Reference

Sodium acetate H-type 2 2 460 mw.m�2 Mixed culture [31]

Glucose Cubic 2 2 256 mW Mixed culture [32]

Sodium acetate Cubic 6 6 258 W.m�3 Mixed culture [29]

Acetate & Glucose H-type 2 2 460 mW.m�2 Mixed culture [31]

Brewery wastewater Tubular 2 2 1.2 W.m�3 Mixed culture [40]

Glucose Cubic 4 3 2003 mW.m�2 Pure culture This work

Fig. 8 e AFM images from outer surface of anode electrode before (a) and after (b) using in anode compartment.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 5 9 9 2e6 0 0 05998

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 5 9 9 2e6 0 0 0 5999

(graphite). A small piece of electrode (1 � 1cm) before use in

anode chamber was analyzed by AFM. Two and three-

dimensional images of the graphite anode surface before

and after use withmagnification 5000 are shown in Fig. 8a and

b. The obtained image demonstrated the microorganisms

have well grown and formed uniform biofilm on all anode

surfaces. This factor justifies the uniform electrical perfor-

mance of all units.

The main objective of present research was to achieve

a suitable current and power for the application in small

electrical devices. As a demonstration, ten LED lumps and one

digital clock used the fabricated stacked MFC as power source

and both devices were successfully operated for the duration

of 2 days.

4. Conclusion

A new stack of MFCs was designed, fabricated and operated

successfully in continuous mode of operation to enhance the

power generation. The system used pure glucose as substrate

at concentration of 30 g l�1 and S. cerevisiae, as biocatalyst.

Potassium permanganate was used as oxidizing agent in

cathode chamber to enhance the voltage. NR as electron

mediator with low concentration (200 mmol.l�1) was selected

as electron mediator in anode side. The produced current and

power by a single MFC was not sufficient for practical appli-

cations even for use in low consumption electrical devices.

Therefore, the electrical outputs were enhanced using a novel

combination of four single MFCs in series and parallel

connection as a stacked MFCs. The obtained results from

present study demonstrated that MFCs with anodes and

cathodes sandwiched between two proton exchange

membranes can be used as stack of MFCs. The maximum

voltage was 3230 mV for the series connection, with initial

glucose concentration of 30 g.l�1. Since, most of small elec-

trical devices required high currents rather than high voltage;

therefore parallel connections are preferred in this regard. The

maximum received power and current density based on peak

point in polarization curve were 2003 mW.m�2 and

6447 mA.m�2, respectively. The results indicated almost

similar electrical performances for all individual cells which

showed a uniform power generation in the system. The result

of study also demonstrated that the scale up of the system is

possible by the use of more number of single MFC in stack.

Acknowledgments

The authors wish to acknowledge Biotechnology Research

Center, Noshirvani University of Technology (Babol, Iran) for

the facilities provided to accomplish the present research.

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