Developments in Microbial Fuel Cell System for Electricity Generation

Abstract

Over the last few years, world is facing problem of alternate energy source that has to be environmental friendly also. Microbes are present everywhere in environment that can oxidize different organic material and converts their chemical energy into electrical energy with the help of Microbial Fuel Cell (MFC) system through different catalytic reactions. Several cultures of microorganism like E.coli, Enterobacter aerogene, Geobacter sulfurreducens, Shewanella putrefaciens etc. have been tested for this and showed that energy can be obtained by them usng MFC system. Apart from the pure cultures waste water samples also showed to produce electrical energy with waste water treatment that improved the application of MFC. In this article several components and materials have been discussed that play key role for the performance of this system so that applications of MFC can be improved much and practical use of MFC can be a preferred option for the sustainable bioenergy source.

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Trends in Biosciences 6 (6): 701-704, 2013
MINI REVIEW
Developments in Microbial Fuel Cell System for Electricity Generation
SAM A MASIH AND MERCY DEVASAHAYAM
Centre for Transgenic Studies, Sam Higginbottom Institute of Agriculture, Technology and Sciences, Naini,
Allahabad 211007, Uttar Pradesh, India
email: horton037@yahoo.co.in
ABSTRACT
Over the last few years, world is facing problem of alternate
energy source that has to be environmental friendly also.
Microbes are present everywhere in environment that can
oxidize different organic material and converts their chemical
energy into electrical energy with the help of Microbial Fuel
Cell (MFC) system through different catalytic reactions. Several
cultures of microorganism like E.coli, Enterobacter aerogene,
Geobacter sulfurreducens, Shewanella putrefaciens etc. have been
tested for this and showed that energy can be obtained by them
usng MFC system. Apart from the pure cultures waste water
samples also showed to produce electrical energy with waste
water treatment that improved the application of MFC. In this
article several components and materials have been discussed
that play key role for the performance of this system so that
applications of MFC can be improved much and practical use of
MFC can be a preferred option for the sustainable bioenergy
source.
Key words Microbial Fuel Cell, Bioelectricity, Microbes,
Remediation.
The world wrestles with the energy crisis for a long
time. There is need for different alternatives to provide energy
in various situations. Recently discoveries imply that microbes
can be used as viable option to make electricity. Such a system
using microbes as a source for electricity generation is called
Microbial Fuel Cell System. According to TIMES magazine,
Microbial Fuel Cells (MFC) is among the top 50 most important
inventions in 2009.
Microbial Fuel cell is a bio-electrochemical system which
converts the chemical energy present in the organic
compounds to electrical energy by microorganisms in the
anaerobic conditions through catalytic reactions. The first
idea of using Microbial fuel cell in an attempt to produce
electricity was conceived in 1911. A real breakthrough was
made when some microbes were found to transfer electrons
directly to the anode Geobacteraceae metalloreducens (Min,
et al., 2005) are all bioelectrochemically active and can form a
biofilm on the anode surface and transfer electrons directly
by conductance through the membrane the anode will act as
the final electron acceptor in the dissimilatory (Table 1).
A MFC uses bacteria to catalyze the conversion of
organic matter into electricity by transferring electrons to a
developed circuit. When microorganisms consume a substrate
such as sugar in aerobic conditions they produce carbon
dioxide and water
Microbial cultures used in MFC:
Earlier it was thought only few microorganisms can be
used to produce electricity. But recently it was observed that
most of the microorganisms can be utilized in MFCs. MFC
concept was demonstrated as early in 1910 where Escherechia
coli and Saccharomyces sp. were used to generate electricity
using Platinum electrodes. Microorganisms do not use the
energy produced by the flow of electrons in a direct way, the
flow of electrons is used to create a proton gradient across
the cell membrane.
There are three categories of microbes that can be used
in MFCs:
(a) Those that can directly transfer electrons to anode using
anode as terminal electron acceptor;
(b) Those that can’t directly but use mediators to transfer
electrons to anode;
(c) Those who can accept electron from cathode.
Presently several microorganisms have been tested for
the generation of electricity using microbial fuel cell systems.
We have used Enterobacter cloacae and Enterobacter
aerogene with 0.5, 1.0 optical density (O.D.) and two different
substrate i.e. sucrose and sodium acetate in same amount
(0.4%) to check the electricity generation using dual
chambered MFC and showed that 0.5 O.D. of Enterobacter
cloacae produced maximum power density of 440 mW/cm2
(Fig. 1) using 0.4% sodium acetate as compare to same optical
density of Enterobacter aerogene and E.coli that produced
356.40 mW/cm2 and 222.60 mW/cm2 respectively (Fig.1 ) using
equal amount of same substrate (Masih et al., 2012a, Masih
et al., 2012b). In another study we have compared electricity
generation using different water samples (pond, canal,
untreated and primary treated sewage water samples) at two
different pH values i.e. 4.5 and 5.5 with 0.4% sucrose as
substrate. Our results showed that 5.5 pH showed best results
for all the samples and among them pond gave highest voltage
value of 724 mV as compare to other samples i.e. canal (538
mV), untreated sewage water (492 mV) and primary treated
sewage water that showed 705 mV (Masih et al., 2011, Masih

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702 Trends in Biosciences 6 (6), 2013
Table 1. Details of different bacteria, substrates and mediators used for MFC operation.
Microorganisms
Substrates
Mediators
Actinobacillus succinogenes
Escherichia coli
Geobacter metallireducens
Geobacter sulfurreducens
Shewanella putrefaciens
Shewanella oneidensis
Lactobacillus plantarum
Desulfovibrio desulfuricans
Glucose
Glucose sucrose
Acetate
Acetate
Lactate, pyruvate,
acetate, glucose
Lactate
Glucose
Sucrose
Neutral red or thionin as electron mediator (Park and Zeikus 1999; Park and Zeikus , 2000)
Mediators such as methylene blue needed. (Schroder et al .,2003; Ieropoulos et al., 2005.,
Grzebyk and Pozniak, 2005)
Mediator-less MFC (Min et al., 2005)
Mediator-less MFC (Bond et al., 2002 ; Bond and Lovely ., 2003 )
Mediator-less MFC (Kim et al., 1999) but incorporating an electron mediator like Mn (IV) or NR
into the anode enhanced the electricity production(Park and Zeikus , 2002)
Anthraquinone-2,6-disulfonate (AQDS) as mediator (Ringeisen et al., 2006)
Ferric chelate complex as mediators (Vega and Fernandez, 1987)
Sulphate/sulphideas mediator (Park et al., 1997 ; Ieropoulos et al., 2005)
et al., 2013). There are several other pure microbial cultures
and mixed cultures as well that have been examined to produce
electricity using microbial fuel cell system (Table 2)
Role of electrode in MFC
Electrode materials, Proton exchange membranes and
operation conditions of anode and cathode have important
effect on MFCs. If the electrodes are more porous it allows
diffusion of oxygen to anode which reduces the efficiency of
fuel cells. Electrode modification is actively investigated by
several research groups to improve MFC performance.
Different anode materials results in different activation
polarization losses. The surface area of the electrode is also
important. In the MFC operated by Venkata Mohan, et al.,
2008, the surface area of the plain graphite electrode were
increased from 70cm2 to 83.56cm2 by drilling nine uniform holes
of 0.1 cm diameter to increase .
Experiments have shown that current increases on
increasing the surface area in the order-
Carbon felt®carbon foam ® graphite
Role of Proton Exchange membrane in MFC:
For improving the performance of MFC, the main
challenges are to increase the electrons recovery from the
substrate, i.e., the Columbic Efficiency (CE), and hence
increasing the power. It has been found that decrease in power
was due to increased ohmic resistance from hot-pressing the
membrane (Kim, et al., 2007). The use of Cation (CEMs) and
Anion (AEMs) has been found to increase the CE (Kim et al.,
2007, 2009; Zuo et al., 2008), it also increased the internal
resistance, creates pH gradients, and reduces the power
densities compared to systems that lack membranes (Kim, et
al., 2007; Rozendal, et al., 2007, Masih and Devasahaym, 2013).
Role of substrate for electricity generation:
In MFCs, substrate is regarded as one of the most
important biological factors affecting electricity generation
(Liu, et al., 2009). A great variety of substrates can be used in
MFCs for electricity production ranging from pure compounds
to complex mixtures of organic matter (Table 1). In another
study, the energy conversion efficiency (ECE) of acetate and
glucose as substrates in MFC was compared (Lee, et al., 2008).
Sucrose was used as a fuel in a thionine-mediated
microbial fuel cell containing Proteus vulgaris serving as the
biocatalyst in the anode compartment There are other
substrates like cellulose, most abundant polymer, fructose,
dextrose can be used as substrate for electricity generation in
MFC. Ren, et al., 2007 reported a power density of 153 mW/m2
using carboxymethyl cellulose as substrate. Very recently,
Rezaei, et al., 2009 tested the effect of particle size on maximum
power, power longevity and CE using different sized chitin
particles. In order to benchmark new MFC components, reactor
designs or operational conditions, acetate is commonly used
as a substrate because of its inertness towards alternative
microbial conversions (fermentations and methanogenesis)
at room temperature. Further, acetate is the end product of
several metabolic pathways for higher order carbon sources.
Chae, et al., 2009 compared the performance of four different
substrates in terms of CE and power output.
The benefits of using microbial fuel cells for wastewater
treatment include clean, safe, quiet performance, low
emissions, high efficiency, and direct electricity recovery. With
similar designs of MFC, 506 mW/m2 was produced with acetate
(Liu, et al., 2005, Masih and Devasahaym, 2013).The maximum
Table 2. Details of different microbial cultures producing current and power density.
S. No.
Source
Current (mA)
Power Density
(mW/cm2)
Coulombic
Effeciency (%)
References
1 Chemical waste water 6.08 22.11 62.90 Venkatamohan et al., 2008
2 Enterobacter aerogene 9.9 356.4 83.43 Masih et al., 2012a
3
Enterobacer cloacae
11
440
92.00
Masih
et al., 2012a
4 E.coli 7.79 220.66 69.49 Devasahayam and Masih , 2012
5
Geobacter sulfurreducens
0.24
43.63
---
Trinh
et al
., 2009
6 Klebsella spp. 1.47 0.1209 --- Xia et al., 2010
7
Shewanella oneidensis
0.40
0.50
---
Tront
et al
., 2008

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MASIH AND DEVASAHAYAM, Developments in Microbial Fuel Cell System for Electricity Generation 703
power density produced appears to be related to the complexity
of the substrate (i.e. single compound versus several
compounds). Heilmann and Logan, 2006 reported that with
substrates like peptone and meat processing wastewater
containing many different amino acids and proteins, lower
power was produced than achieved using single compound
like bovine serum albumin (BSA). Recently, while evaluating
the potential of various eco-systems in harnessing
bioelectricity through benthic fuel cells, Venkata Mohan, et
al., 2009 reported that the substrate concentration of the water
body showed significant influence on the power generation
as they act as carbon source (electron donor) for the benthic
metabolic activity. Water bodies containing higher organic
matter were able to generate higher power output.
Effect of resistance in MFC
There are several different methods to evaluate the
internal resistance of an MFC. These include polarization slope,
power density peak, electrochemical impedance spectroscopy
(EIS) using a Nyquist plot, and current interrupt methods.
The microorganism oxidizing the substrate release electrons
onto the anode surface and should thus be considered a
current. However, this current source is not constant, but
affected the amount of resistance in the system. There is not
a linear relationship between voltage and current in this case.
It is plausible that under the conditions of limited electron
disposal through the circuit with a high resistance, the
electrons are consumed in the anode to reduce other electron
acceptors such as sulfate and nitrate. There are some electrical
parameters on which electrical conductance of MFC depend.
An extremely high Columbic efficiency of 97% was reported
during the oxidation of formate with the catalysis of Pt black
(Rosenbaum, et al., 2006.
Electrical parameters:
Open circuit voltage is the voltage measured in the
absence of any resistor. By definition it is the difference of
electrical potential between the two electrodes i.e. anode and
cathode of a cell in the absence of any resistor. Theoretically
open circuit voltage should be almost close to the electromotive
force of a cell but in practice it does not happen generally. The
probable reason for this disparity between the two is the large
energy losses at the cathode, which is called the overpotential.
Overpotential is directly related to current density and
generally include:
Activation losses- To carry out the oxidation-reduction
reaction at the electrode bacteria need to cross an energy
barrier that results in large activation losses. But
increasing the electrode surface area can minimize this
loss. Other measures taken to overcome this loss are
increasing temperature and by enrichment of biofilm on
the anode surface (Logan, et al., 2006).
Metabolic losses- This is because of the large difference
of redox potential between the substrate and anode
(Logan, et al., 2006).
Concentration losses -These occurs at the high current
density and are due to rate of mass transport of a species
to or from the electrode. And these losses limit the current
production.
Ohmic losses- Impedence to the flow of electrons at the
electrodes and interconnections and to the protons at
the membrane and electrolytes is the cause of these
losses. Keeping the electrodes in close proximity to each
other i.e. at the closest distance and using the electrolytes
of higher conductivity can overcome these losses.
Power and power density-Power can be calculated as
P =E2cell/ Rex
where Ecell / Rext is calculated by Ohm’law. Thus power
density is calculated as amount of power per unit surface area
of the electrode. To enhance power density it is preferred to
use anode with the projected surface area. Surface area of
anode can be enhanced greatly by using porous electrodes.
Other measures are using electrodes in sieve or brush form
but in these cases it is difficult to measure surface area of
each and every unit of the anode. Therefore using porous
anode with defined surface area of the plate and of each pore
as well is advantageous over others.
In many instances, however, the cathode reaction is
thought to limit overall power generation or the anode consists
of a material which can be difficult to express in terms of surface
area (i.e., granular material. Work by several researchers have
shown that MFC can be used for power generation but still
Fig. 1 Comparison of Power Density and Current
Density: Polarization curve of Power Density and
Current Density has been plotted in between pure
cultures of E.aerogens(dark line), E.cloacae(dotted line)
and E.coli(dashed line)

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704 Trends in Biosciences 6 (6), 2013
ways has to be find to make the system economical. Power
density still needs to be increased under realistic conditions.
Materials and different methods have to be examined in terms
of power generation and cost. More information is needed on
the flow of nutrients and methods to control these in MFC
based system. Overall there is much exciting work has to be
done on better understanding the response of bacterial culture
with substrate and the conductivity of different electrode
materials that helps to harvest electrical conductance from
MFC.
ACKNOWLEDGEMENT
The authors wish to acknowledge with gratitude the
support of Prof Dr Rajendra B Lal, Vice Chancellor, Sam
Higginbottom Institute of Agriculture, Technology and
Sciences for his encouragement. The authors wish to express
their gratitude to the Director (Research), SHIATS for financial
support.
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Recieved on 05-09-2013 Accepted on 15-1 0-2013