Microbial fuel cell: a new approach of wastewater treatment

MICROBIAL FUEL CELL: A NEW APPROACH OF WASTEWATER
TREATMENT WITH POWER GENERATION
M.M. GHANGREKAR 1 AND V.B. SHINDE 2
ABSTRACT: Application of Microbial Fuel Cells (MFCs) may represent a completely
new approach to wastewater treatment with production of sustainable clean energy.
In recent years, researchers have shown that MFCs can be used to produce
electricity from water containing glucose, acetate or lactate. Studies on electricity
generation using organic matter from the wastewater as substrate are in progress.
The performance of the MFCs as reported in literature with different substrate is
presented in this paper. Under different conditions such as inoculum culture (pure or
mixed), substrate sources, and external loads, the MFCs are reported to produce
power density in the range 0.3 to 3600 mW/m 2 . Performance of the laboratory scale
membrane less MFC using synthetic wastewater was evaluated for its effectiveness
for organic matter removal and electricity production. It was observed that this
membrane less MFC was capable to give COD reduction greater than 90 percent,
with maximum power production 6.73 mW/m 2 . If power generation in MFC can be
increased, this technology may provide a new method to offset wastewater treatment
plant operating costs, with less excess sludge production.
KEYWORDS: Microbial Fuel Cell, Wastewater Treatment, Electric power production
INTRODUCTION
The high energy requirement of conventional sewage treatment systems are
demanding for the alternative treatment technology which will be cost effective and
require less energy for its efficient operation. In past two decades, high rate
anaerobic processes are finding increasing application for the treatment of domestic
as well as industrial wastewaters. The major advantages these systems offer over
conventional aerobic treatment are no energy requirement for oxygen supply, less
sludge production, and recovery of methane gas. While treating sewage, particularly
in small capacity treatment plant recovery of methane may not be attractive, because
most of the methane produced in the reactor is lost through effluent of the reactor.
The methane concentration of about 16 mg/L (equivalent COD 64 mg/L) is expected
in the effluent of the reactor due to high partial pressure of methane gas inside the
reactor 1 . Hence, while treating low strength wastewater major fraction of the
methane gas may be lost through effluents, reducing the energy recovery.
In addition, due to global environmental concerns and energy insecurity, there
is emergent interest to find out sustainable and clean energy source with minimal or
zero use of hydrocarbons. Electricity can be produced in different types of power
1 Assistant Professor, Department of Civil Engineering, Indian Institute of Technology, Kharagpur – 721302.
India. (Phone No. 03222 – 283440 (O) 283441 (R); E-mail: ghangrekar@civil.iitkgp.ernet.in)
2 M.Tech. (Environmental Engineering & Management) Student. Department of Civil Engineering, Indian Institute
of Technology, Kharagpur – 721302. India.

plant systems, batteries or fuel cells. Bacteria can be used to catalyze the
conversion of organic matter into electricity 2,3,4,5,6,7 . Fuel cells that use bacteria are
classified as two different types: biofuel cells that generate electricity from the
addition of artificial electron shuttles (mediators) and microbial fuel cells (MFCs) that
do not require the addition of mediator 8 . Unlike a battery, a fuel cell does not store
energy. Instead, it converts energy from one form to another (much like an engine)
and will continue to operate as long as fuel is fed to it. However, unlike internal
combustion generators, fuel cells convert chemical energy directly into electricity
without an intermediate conversion into mechanical power. Fuel cells, if used for
wastewater treatment, can provide clean energy for people, apart from effective
treatment of wastewater. The benefits of using fuel cells include: clean, safe, quiet
performance; high energy efficiency; low emissions; and ease in operating.
Biofuel cells use biocatalysts for the conversion of chemical energy to
electrical energy. It is a device that directly converts microbial metabolic or enzyme
catalytic energy into electricity by using conventional electrochemical technology 2 .
The biocatalysts participate in the electron transfer chain between the fuel-substrate
(organic or inorganic) and the electrode surfaces 9 . That is, microorganisms or redoxenzymes
facilitate the electron transfer between the fuel substrate and the electrode
interface, thereby enhancing the cell current. It has been shown that, direct electron
transfer from microbial cells to electrodes occurs only at very low efficiency 10 . Most
of the redox-enzymes lack in direct electron transfer with conductive supports and a
variety of electron mediators (electron relays) are used for electrical contacting of the
biocatalysts and the electrode. Since, most microbial cells are electrochemically
inactive; electron transfer from microbial cells to the electrode is facilitated by the
help of mediators such as thionine, methyl viologen, humic acid, etc. Enzyme
catalyzed generation of NADH (dihydro-nicotinamide adenine dinucleotide) from
alcohol, lactic acid, amino acids, formate or other abundant substrates could provide
the bio-transformations that activate the anodic compartment of the fuel cell 9 .
Theoretically, any organic or inorganic compound or a mixture can serve as a fuel,
provided it is oxidized by the appropriate organism, e.g., the reaction for glucose is 11 :
C 6 H 12 O 6 + 6H 2 O 6CO 2 + 24e - + 24 H + ….(1)
Mediator Less MFC
It has recently been shown that certain metal-reducing bacteria, belonging
primarily to the family Geobacteraceae can directly transfer electrons to electrodes

using electrochemically active redox enzymes, such as cytochromes on their outer
membrane 12,13 . These microbial fuel cells does not need mediator for electron
transfer to electrodes and are called as mediator less MFCs. Mediator less MFCs
are considered to have more commercial application potential, because mediators
used in Biofuel cells are expensive and can be toxic to the microorganisms 7 .
The schematic diagram of mediator less MFC is shown in the Figure 1. In a
MFC, two electrodes (anode and cathode) are placed in water in two compartments
separated by a proton exchange membrane (PEM). Most studies have used
electrodes of solid graphite 7 , graphite-felt 14 , carbon cloth 15 and platinum coated
graphite cathode electrode 16 . Microbes in the anode compartment oxidize fuel
(electron donor) generating electrons and protons. Electrons are transferred to the
cathode compartment through the external circuit, and the protons through the
membrane. Electrons and protons are consumed in the cathode compartment
reducing oxygen to water.
Rate Limiting Steps: (1) Oxidation of Fuel, (2) Electron transfer from the microbial cells to the
electrode, (3) Electric load in the circuit, (4) Proton supply into the cathode compartment, (5) Oxygen
supply and reduction at the cathode [Gil et al. 6 ].
Figure 1: Mediator Less Microbial Fuel Cell with rate limiting steps
In addition to microorganisms that can transfer electrons to the anode, the
presence of other organisms appears to benefit MFC performance. It is reported
that, a mixed culture generated a current that was six fold higher that that generated
by a pure culture 17 . Hence, the microbial communities that develop in the anode
chamber may have a similar function as those found in methanogenic anaerobic
digesters, except that microorganisms that can transfer electrons to the electrode
surface replace methanogens. Rabaey et al. 18 referred to such microbial
communities as adapted anodophilic consortia. Anodophilic bacteria from different

evolutionary lineages from the families of Geobacteraceae, Desulfuromonaceae,
Alteromonadaceae, Enterobacteriaceae, Pasteurellaceae, Clostridiaceae,
Aeromonadaceae, and Comamonadaceae were able to transfer electrons to
electrodes 19 . Methanogens also reported to have a capacity to transfer electrons 20 .
Because the power output of MFCs is low relative to other types of fuel cells,
reducing their cost is essential, if power generation using this technology is to be an
economical method of energy production. The overall limiting steps to enhance the
power production are showed in the Figure 1. Further research is required to
enhance the power production by overcoming these limitations. The main
disadvantage of a two chamber MFC is that the solution cathode must be aerated to
provide oxygen to the cathode 8 . The power output of an MFC can be improved by
increasing the efficiency of the cathode, e.g. power is increased by adding
ferricyanide to the cathode chamber 21 .
The effects of operational conditions of a microbial fuel cell were investigated
and optimized for the best performance of a mediator-less microbial fuel cell by Gil et
al. 6 . The optimal pH reported was 7. The resistance higher than 500 Ω was the ratedetermining
factor by limiting electron flow from anode to cathode. At the resistance
lower than 200 Ω, proton and oxygen supplies to the cathode were limited. For the
construction of an efficient microbial fuel cell, a non-compartmentalized fuel cell with
an electrode having a high oxygen reducing activity should be developed. Since the
concentration of fuel determines the amount of electricity generation from the fuel
cell, the device can be used as a BOD sensor.
It is possible to design a MFC that does not require the cathodes to be placed
in water. In hydrogen fuel cells, the cathode is bonded directly to the PEM so that
oxygen in air can directly react at the electrode 22 . This technique was successfully
used to produce electricity from wastewater in a single chamber MFC 15 . However, a
maximum of 788 mW/m 2 power density was reported by Park and Zeikus 21 with a
Mn 4+ graphite anode and a direct air Fe 3+ graphite cathode.
Membrane Less MFC
In a meditor less MFC, the membrane separates the anode from the cathode
as in other MFCs, and the membrane functions as an electrolyte that plays the role
of an electric insulator and allows protons to move through 16 . However, the use of
membrane can limit the application of MFC to wastewater treatment. Proton transfer

through the membrane can be a rate limiting factor especially with fouling expected
due to suspended solids and soluble contaminants in a large scale wastewater
treatment process. In addition, membranes are expensive and hence may limit its
application. A membrane-less microbial fuel cell (ML-MFC) was developed by Jang
et al. 16 and used successfully to enrich electrochemically active microbes that
converted organic contaminants to electricity. The COD removal rate of 526.67 g/m 3
day was reported with maximum power production 1.3 mW/m 2 and current density
6.9 mA/m 2 . The design used in the study showed poor cathode reaction allowing a
large quantity of oxygen to diffuse toward the anode. Further studies are required to
improve the design of ML-MFC to improve current yield and COD removal efficiency.
Power production of MFC and Further Development Required
The major limitations to implementation of MFCs for treatment of wastewater
are their power density is still relatively low and the technology is only in the
laboratory phase. Based on the potential difference, ∆E, between the electron donor
and acceptor, a maximum potential of nearly 1 V can be expected in MFCs, which is
not much greater than the 0.7 V that is currently being produced 21 . However, by
linking several MFCs together, the voltage can be increased. Current and power
densities are lower than what is theoretically possible, and system performance
varies considerably as shown in Table 1. The maximum power density reported in
the literature, 3600 mW/m 2 , was observed in a dual-chamber fuel cell treating
glucose with an adapted anaerobic consortium in the anode chamber and a
continuously aerated cathode chamber containing an electrolyte solution that was
formulated to improve oxygen transfer to cathode 18 .
Cost of the MFC can be minimized by using plain graphite electrodes without
exogenous electron shuttles and a commercially available membrane 19 . Further
improvement in the power density is required, and the rates of electron transfer to
the anode are the major limiting factor. Optimization of MFCs is required, which
involves investigation of a variety of aspects such as, anodophilic consortium
selection for efficient electron transfer to electrode; cathode performance, oxygen
supply and oxidation of fuel; MFC configuration, external resistance and electrodes
(material and surface area); specific inoculum and concentration of bacteria; types of
organic material in the wastewater, and electron shuttles.

TABLE 1: POWER GENERATION RATES REPORTED IN THE LITERATURE 8
Substrate Description Power (mW/m 2 )
Complex Anaerobic sediments 16
Starch wastewater 19
Starch wastewater 20
Domestic Wastewater 24
Anaerobic sediments 28
Domestic wastewater, CE-PEM 28
Domestic wastewater, CE no PEM 146
Defined Lactate 0.6 – 15
Lactate, Peptone, and yeast extract 788
Acetate (salt Bridge) 0.3
Acetate 14 - 49
Glucose 33 – 3600
Glucose – CE-PEM 262
Glucose – CE (no PEM) 494
The basic disadvantages of microbial fuel cells are their generally low
coulombic yields and low power outputs. Many more improvements will be
necessary, before biological fuel cell production and use can be commercialized. A
membrane less MFC could improve the economic feasibility of the process to treat
wastewater by reducing not only the capital investment, by eliminating costly
membrane, but also the operational cost for the membrane maintenance. The
objective of this study was to evaluate the electricity production potential and
treatment efficiency of mediator less microbial fuel cell without membrane, using
synthetic wastewater and mixed anaerobic microbial culture as inoculum.
MATERIAL AND METHODS
Membrane-less microbial fuel cell
Figure 2 shows the schematic diagram of the membrane-less microbial fuel
cell (ML-MFC) used in this study. The anode was at the bottom, and the cathode at
the top of cylinder-shaped reactor made of polyacrylic having internal diameter of 10
cm. Glass wool (4 cm depth) and glass bead (4 cm depth) was placed at the upper
portion of the anode. Graphite rod, as roll form, was used for both anode and
cathode. Total height of the reactor was 60 cm, and distance between the anode
and cathode was 20 cm, including glass wool and glass bead. The apparent surface
area of each anode and cathode was 46.65 cm 2 . The fuel was supplied to the bottom
of the anode and the effluent left through the cathode compartment at the top. The
electrodes were connected with copper wire through a resistance ranging from 10 Ω

to 100 Ω, including the resistance of copper wire and a multimeter. The internal
resistance of the MFC was ranging from 3 MΩ to 4.5 MΩ.
Figure 2: Membrane Less Microbial Fuel Cell used in the study
Wastewater
The wastewater was applied at the rate of 5.011 L/d making hydraulic
retention time (HRT) in the MFC of 24 h. The cathode compartment was aerated at
rate of 60 mL/min for the cathode reaction. A synthetic sewage containing sucrose
as a carbon source was used throughout the study. The composition of the synthetic
wastewater used is provided in Table 2. The COD of synthetic wastewater used was
in the range 312 to 446 mg/l and influent pH was maintained in the range 7.2 to 7.6.
TABLE 2: THE COMPOSITION OF THE SYNTHETIC WASTEWATER
Component Sucrose NaHCO 3 NH 4 Cl K 2 HPO 4 KH 2 PO 4 CaCl 2 .2H 2 O MgSO 4 .7H 2 O
mg/ L 300-450 480 95.5 10.5 5.25 63.1 19.2
Note: Trace metals were added as FeSO 4 .7H 2 O = 10 mg/L, NiSO 4 .6H 2 O = 0.526 mg/l,
MnSO 4 .H 2 O = 0.526 mg/l, ZnSO 4 .7H 2 O = 0.106 mg/l, H 3 BO 3 = 0.106 mg/l, CoCl 2 .6H 2 O = 52.6
µg/L, CuSO 4 .5H 2 O = 4.5 µg/L, and (NH 4 ) 6 Mo 7 O 24 .4H 2 O = 52.6 µg/L.
Enrichment of electrochemically active microbes for operating MFC
The ML-MFC was inoculated with sludge (1.0 L) collected from septic tank
bottom. All experiments were conducted at room temperature ranging from 29 to
33 o C. For the first fifteen days of operation the MFC was operated without any
pretreatment of the inoculum sludge. After fifteen days, the sludge form the MFC
was removed, heated and inoculated. The sludge was heated at 100 o C for 15
minutes to suppress the methanogens, cooled at room temperature and 1 L volume
of sludge was added to the reactor in the anode compartment. No microbial addition
was carried out in cathode compartment in both the cases.

Analyses
The potential was measured using a digital multimeter (MASTECH M-830B,
Russia) and converted to power according to P= iV, where P = power (W), i = current
(A), and V = voltage (V). The influent and effluent characteristics such as, COD, pH,
dissolve oxygen (DO), were monitored according to Standard Methods 23 .
Biochemical oxygen demand (BOD) was determined for three days at 27 o C.
RESULT AND DISCUSSION
Enrichment
The ML-MFC, inoculated with septic tank sludge, was operated on batch
mode for first four days and from fifth day onward with continuous mode. The electric
current production of 0.3 mA was observed at external load of 10 Ω for first five days
of continuous operation, but latter gradual decrease in current production was
observed and it was 0.1 mA after 15 days. This decrease could be attributed to the
growth of methanogens in the anode chamber, reducing the availability of electron
and proton, hence reducing current. The sludge from the anode chamber of MFC
was heated at 100 ºC and re-inoculated. This method was found effective to obtain
an enriched culture of hydrogen producers 24 . The current slowly increased for the
first week, and it was 0.1 mA at external load of 100 Ω. The maximum current of
0.175 mA was observed at external load of 10 Ω with voltage 0.19 V. The open
circuit potential was about 0.3 V after fifteen days of operation. Power density of 6.73
mW/m 2 was observed in this experiment which is higher than the value 1.3 mW/m 2
reported earlier 16 .
COD Removal Efficiency
The ML-MFC was operated at four different external resistance (10 to 100 Ω)
and influent COD concentration ranging from 312 mg/l to 446 mg/l as presented in
Table 3 and Figure 3. After 55 days of operation the COD and BOD removal
efficiency of ML-MFC was 90.86% and 90.67%, respectively. The steady state
condition for COD removal efficiency was observed after 55 days of operation with
COD removal capacity of 0.406 kg/m 3 .d. The specific organic removal rate, with
respect to anode chamber, of 0.08 kg COD/ kg VSS.d was observed. Studies are in
progress to increase the loading capacity. The COD removal in the anode
compartment was 46.36%. After achieving steady state, the effluent COD was 40.8
mg/l and BOD 3 at 27 o C was 25 mg/L. These values demonstrate the capacity of ML-

MFC for wastewater treatment. The COD and BOD values reported are for unsettled
effluent containing SS and VSS concentration of 40 mg/L and 6.2 mg/L, respectively.
Further improvement in the effluent quality is expected by employing settling tank
after MFC. The COD removal efficiency observed is on the higher side of the
maximum efficiency reported in literature as 80 to 90 percent 15,16 . However, the
organic loading rate as high as 27.02 kg COD/m 3 .d is reported with specific organic
load as 18.63 kg glucose/ kg VSS.d for hydrogen production in CSTR type reactor 25 .
TABLE 3: PERFORMANCE OF THE MEMBRANE LESS MICROBIAL FULE CELL
A] COD AND BOD REMOVAL
Days External
Resistance
(Ω)
COD
(Inlet)
(mg/L)
0-15 100 329.17
(±45.43)
16-35 10 399.90
(±34.33)
36-55 25 312.33
(±16.74)
56-78 50 446.50
(±36.08)
COD
(middle)
(mg/L)
248.50
(±19.09)
312.30
(±22.60)
208.17
(±55.53)
239.50
(±17.67)
B] ELECTRICITY PRODUCTION
COD
(outlet)
(mg/L)
162.50
(±24.74)
72.4
(±20.90)
56.30
(±11)
40.8
(±3.26)
Efficiency
(%)
50.63
BOD
(Inlet)
(mg/L)
BOD
(middle)
(mg/L)
BOD
(outlet)
(mg/L)
DO
(Inlet)
(mg/L)
DO
(outlet)
(mg/L)
------ ------ ----- ----- ------
81.89 280 175 48 5.4 4.33
(±15) (±10) (±5) (±1.0) (±0.25)
81.97 240 158 35 5.5 3.75
(±20) (±12) (±5) (±1.0) (±0.35)
90.86 268 162 25 5.4 4.14
(±18) (±13) (±5) (±1.0) (±0.39)
Days Current
(mA)
0-15 0.091
(±0.011)
16-35 0.175
(±0.007)
36-55 0.148
(±0.007)
56-78 0.121
(±0.008)
Voltage
(V)
0.116
(±0.007)
0.188
(±0.003)
0.175
(±0.007)
0.151
(±0.005)
Resistance Power
(ohm) (mW/m 2 )
100 2.29
(±0.39)
10 6.73
(±0.44)
25 5.46
(±0.39)
50 3.96
(±0.46)
Jule
(J/d)
HRT
(hrs)
0.92 24
2.72 24
2.20 24
1.597 24
Effect of External Resistance
It was observed that at lower external resistance the current production is
higher and vice versa. Even for same wastewater COD concentration the production
of current is decreases due to increase in resistance shown in Figure 3. At same
COD concentration when resistance was increased to 25 Ω and 50 Ω, the production
of current decreased to 0.148 mA and 0.121 mA, respectively. These results show
that the resistance becomes the rate-limiting step (step 3 in Figure 1). Even at lower
resistance, low current production could be attributed to the lower electron
consumption rate at the cathode than transfer rate from the external circuit. This
might be due to limited supply of proton or oxygen (steps 4 and 5 in Figure 1). The

lower current production means that some electrons are consumed by mechanism(s)
other than the cathode reaction. At this point it is not known how this is possible. 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 6 , or oxygen diffused from cathode compartment
or dissolved oxygen present in the influent. At low resistance the electrons move
more easily through the external circuit than at high resistance, oxidizing electron
carriers of the microbes in the anode. Higher fuel oxidation by the microbes is
expected with high ratio of oxidized electron carriers of the culture at a low
resistance to remove organic contaminants at a high rate 16 .
Influent COD, mg/L
COD at outlet of anode chamber, mg/L
0.25
600
Efflent COD, mg/L
Current,mA
Resistance, Ohm
Voltage, V
0.23
COD (mg/L) & Resistance (ohm)
500
400
300
200
100
0.21
0.19
0.17
0.15
0.13
0.11
0.09
0.07
Current (mA), Voltage (V)
0
0.05
0 20 40 60 80
Time (days)
Figure 3. Time course of performance of membrane less microbial fuel cell
Effect of Dissolved oxygen monitoring of cathode compartment
The microbial cell was operated with aeration in the cathode compartment.
The current and DO concentration measured under different external load are
provided in Table 3. When the cathode compartment was aerated, the current
increased sharply, and so did DO slowly. When the aeration was stopped the current
decreased, whilst the decrease in DO was less significant. These results show that
DO is the major limiting factor for the operation of a microbial fuel cell with graphite
electrode. Probably, due to poor catalytic activity of graphite to reduce oxygen, which
can be explained better by analyzing proton compensation in cathode chamber 6 .

CONCLUSIONS
Under present investigation, the membrane less MFC was used effectively for
synthetic wastewater treatment with COD and BOD removal about 90%. The power
production of this MFC observed was 6.73 mW/m 2 . If power generation in these
systems can be increased, MFC technology may provide a new method to offset
wastewater treatment plant operating cost, making wastewater treatment more
affordable for developing and developed nations. The possibility of direct conversion
of organic material in wastewater to bio-electricity is exciting, but fundamental
understanding of the microbiology and further development of technology is required.
With continuous improvements in microbial fuel cell, it may be possible to
increase power generation rates and lower their production and operating cost.
Thus, the combination of wastewater treatment along with electricity production may
help in saving of millions of rupees as a cost of wastewater treatment at present.
ACKNOWLEDGEMENT
The grants provided by University Grants Commission, New Delhi (F. No. 14-10/2003 (SR)) under the
head Major Research Project, to undertake this research work, are duly acknowledged.
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