EXPLORING MICROBES FOR THEIR BIOELECTRICITY
GENERATING POTENTIAL: A REVIEW
Pratibha Jadhav*, Suprabha Kumbhar, Priyanka Patiland Madhuri Gaykwad
Department of Microbiology, Abeda Inamdar Senior College,2390-B K.B. Hidayatullah
Road, Azam Campus, Camp Pune, Maharashtra 411001, India.
ABSTRACT
The need to develop and improve sustainable energy resources is of
eminent importance due to the finite nature of our fossil fuels.
Renewable energy is an increasing need in our society. Microbial fuel
cell (MFC) technology represents a new form of renewable energy by
generating electricity from what would otherwise be considered waste.
Ability of different waste: waste water from paper industry, soap lake
sample, sewage sludge from hostel, marine sediment, soil, waste water,
fresh water were reviewed. Halophiles, alkalophiles, anaerobic
bacteria, electricigens, Proteus vulgaris etc. has been found to serve as
an alternative source of generating electricity to the conventional
method. Electricity generation is possible by separating bacteria from
oxygen, but allowing the bacterial growth on an anode to transfer
electrons to the counter electron (cathode) that is exposed to air.
Electrons can harvested to produce current. This review represents the potential of different
microbes isolated from various waste material in generating bioelectricity.
KEYWORDS: Microbial fuel cells, Microorganisms, Bioelectricity, Organic matter.
INTRODUCTION
The microbial fuel cell[MFC] has gained much attention because of ability to generate
electricity from organic or inorganic compound by microorganisms. Around one hundred
years ago, the technology of generating electricity through bacteria was found, but it did not
gain much attention. MFC have many potential applications, such as biohydrogen production,
electricity generation, wastewater treatment and biosensor. This is possible due to the ability
of MFC to convert chemical energy to the electrical energy. In a MFC, microorganisms
Volume 7, Issue 4, 422-437. Conference Article ISSN 2277– 7105
Article Received on 02 Jan. 2018,
Revised on 23 Jan. 2018, Accepted on 13 Feb. 2018,
DOI: 10.20959/wjpr20184-10793
*Corresponding Author
Pratibha Jadhav
Department of
Microbiology, Abeda
Inamdar Senior College,
2390-B K.B. Hidayatullah
Road, Azam Campus,
Camp Pune, Maharashtra
411001, India.
interact with electrodes using electrons, which are either removed or supplied through an
electrical circuit (Rabaey et.al. 2007). Inside the electrode compartment of the
electrochemical cell, the organisms acts as a source of electrons, initially trapped as reduced
intermediates from the degradation of substrate, but available for transfer to the anode. This
transfer is effect by a redox mediator that diverts electrons from the reduced intermediate
and, via the anode, to the external circuit, which is completed by a suitable cathode. For the
oxidation of glucose,
C6H12O6 + 6H2O = 6CO2 + 24e- + 24H+
(Ref. impact of salt bridge on Electricity Generation From Hostel Sewage Sludge Using
Double Chamber microbial FuelCell, Anand Prakash* Department of Chemical Engineering,
Mehran University of Engineering and Technology, Jamshoro, pakistan)
General protocol for generating bioelectricity from microbes
Sample used
Soap, lake sample, sewage sludge from hostel, waste water from breweries paper industry,
soil etc.
↓ Media used
Soap lake basal medium (SLBM),basal salt medium plus nitrate etc.
↓
Isolate microbes (Bacillus, Clostridium, Halophiles, Saccharomyces etc.) for the
bioelectricity production.
Substrate collection
Sewage was collected from hostel or soap lake sample.
MFC component majorly constitutes electrodes, anodic and cathodic chamber, salt bridge.
↓
The anodic chamber (anaerobic chamber) which holds the substrate and the biocatalysts
microorganisms.
↓
The cathodic chamber is in aerobic chamber.
↓
The transfer of ions (protons) is facilitated by the salt bridge that forms a bridge between
cathodic and anodic chamber.
↓
MFC construction: Salt bridge immersed air cathode MFC consists of a plastic container
which serves as the anodic chamber which contain substrate and also the copper electrode.
↓
The copper electrode which also served as cathode.
↓
The salt cathode was immersed in the salt bridge when it was in molten stage to ensure
complete surface contact.
↓
The 50% cathode surface was exposed to atmospheric air and proper precautions were taken
to ensure anaerobic conditions in anodic chamber by applying epoxy.
↓
MFC operation:substrate (sewage sludge) was added in the anode chamber and was
completely settle and keeps anaerobic condition.
↓
A batch configuration was employed and reading were taken for a period of 20 days. The
reading were taken on a daily basis.
GOALS AND OBJECTIVES
Microbial fuel cell generate electricity directly from microorganisms grown on an electrode
surface. An increase in ionic strength may enhance current density; however, such an
increase would require microbes that can survive high salinity. Microbes having hyper saline
environment and the low solubility of oxygen in that environment are used in MFCs would
encourage consistent production of power. (Oren 2002). Efficient current output would
depend on determination of the possible electron donors and electrons acceptors and on the
Microbial Fuel Cell
A microbial fuel cell (MFC) is an emerging technology that converts chemical energy to
electrical energy by the action of microorganisms. A microbial fuel cell (MFC), or biological
fuel cell, is a bio-electrochemical system that drives an electric current by using bacteria and
mimicking bacterial interaction found in nature. These electrochemical cells are constructed
using either a bioanode and biocathode. Most MFCs contain a membrane to separate the
compartments of the anode (where oxidation takes place) and the cathode (where reduction
takes place). The electrons produced during oxidation are transferred directly to an electrode.
The electron flux is moved to the cathode. The charge balance of the system is compensated
by ionic movement inside the cell, usually across an ionic membrane. Most MFCs use an
organic electron donor that is oxidized to produce CO2, protons and electrons. The cathode
reaction uses a variety of electron acceptors that include the reduction of oxygen as the most
studied process.
Electricity generation by microorganisms is known since long, but only in the past few years
vigorous work has started in this area (Barua and Deka, 2010). Microbial fuel cells (MFCs)
are unique in promising sustainable energy biotechnology to utilize microorganisms as
catalysts for converting the chemical energy of feedstock directly into electricity in their
metabolism which would otherwiae be considered as waste (Gruning et al.2014;Mahendra
and Mahavarkar, 2013), saline water (Cao et al.2009), sediment(Jung et al.,2014). MFCs
present a complex microbial ecosystem similar to classical fuel cells, where the redox
reaction is part of the microbial metabolism rather than mediated by an inorganic catalyst
(Gruning el at., 2014). Extensive research has been performed throughout the world on
bioelectricity production from a range of fermentation products and organic materials (Regan
and Logan, 2006). Studies of MFCs have focused on the attachment and growth of the
biofilm of anode respiring bacteria (ARB) and the means of transferring electrons to the
surface of anode.
History
The idea of using microbes to produce electricity was conceived in the early twentieth
century. M.C. Potter initiated the subject in 111. Potter managed to generate electricity from
Saccharomyces cerevisiae, but the work received little coverage. In 1931, Branet Cohen
created microbial half fuel cells that, when connected in series, were capable of producing
Fermentation of glucose by Clostridium butyricum resulted in production of Hydrogen, which
acts as reactant at the anode of a hydrogen and air fuel cell. (DelDuca et al). Though the cell
functioned, it was unreliable owing to the unstable nature of hydrogen production by the
microorganisms. This issue was resolved by Suzuki et al. in 1976, who produced a successful
MFC design a year later.
Design of Microbial Fuel Cell
Researchers have proposed a variety of scalable designs for constructing an MFC. In most
studies, the configuration commonly adopted was the traditional, dual chambered (H-shaped)
MFC, in which two bottles or chambers are connected by means of a tube containing a
separator membrane (Logan et al., 2006). Initially, reactors used a salt bridge (Min et al.,
2005) as the ion exchange channel between the anode and the cathode chambers.
There are basic components of MFCs which are important in constructions. Electrodes,
wirings, glass cell and salt bridge have an important role. In PEM fuel cell Salt bridge is
replaced with proton exchange membrane. Though it enhances the cost but handling and the
power generation both get enhanced, thus increasing the portability and efficiency of the
system. Apart from the fuel cells can be classified intwo types on the basis of number of
compartments or chambers.
1. Single-chambered fuel cells.
2. Double-chambered fuel cells.
3. Stacked-microbial fuel cells.
1. Single-chambered microbial fuel cells
A single chambered MFC, an anaerobic chamber that is linked to porous cathode exposed to
air and is separated by a proton exchange membrane (PEM). Electrons are transferred to the
cathode to complete the circuit. A single chambered MFC does not require recharging with
an oxidative media and aeration makes the single chamber MFC more versatile and
inexpensive to setup due to the absence of expensive membrane and cathodic chambers this
creates flexible application in wastewater treatment and power generation.
2. Double-chambered microbial fuel cell
A double chambered MFC this type of MFC contains an anodic and cathodic chamber
the cathode all while blocking the diffusion of oxygen into the anode, this system is generally
used for waste treatment and energy generation.
Two chambered MFC was constructed with batch operation. The purposes of proton
exchange membrane, such as Nafion 117, are to separate the liquids in each chamber and
allow protons to flow from anode to cathode. Sometimes, PEM can be replaced by cation
exchange membrane (CEM), as it is less expensive and stronger. Furthermore, the CEM in
two chamber MFCs could be replaced by a salt bridge, which consisted of a tube filled with
and salt and then capped with porous caps, but the power output was as low as 2.2 mW/m2,
which was due to the very high internal resistance. Liu and Logan demonstrated that if PEM
was removed in a single-chamber MFCs, the oxygen diffusion increased, although the
internal resistance was reduced. Cathodes used in MFCs are either catalyst coated carbon
electrodes immersed in water, or they are plain carbon electrodes in a ferricyanide solution. If
a catalyst coated carbon electrode is used, the dissolved oxygen is the electron acceptor, and
the cathodic reaction is,
O2 + 4H+ + 4e- = 2H2O.
3. Stacked-microbial fuel cell
These are another type of construction in which fuel cells are stacked to form battery of fuel
cell. This type of construction doesn’t affect each cells individual Coulombic efficiency but
in together it increases the output of overall battery to be comparable to normal power
sources. These can be either stacked in series or stacked in parallel. Both have their own
importance and are high in power efficiency and can be practically utilized as power source.
Air-chambered MFCs
Power output of two-chamber MFCs can be improved by increasing the efficiency of the
cathode, such as using ferricyanide. But two-chambers MFCs are primarily used in laboratory
scale and cannot be adapted for continuous treatment of organic matter due to the demand of
oxygenated water. In the air-cathode MFCs, the earliest air-cathode MFC architecture was
designed and reported that an oxygen gas diffusion electrode could be used as a cathode in
bioelectro-chemical fuel cell. In this study, they developed the air-cathode configuration with
presence and absence of PEM.
The architecture of air-chamber MFCs is aimed to optimize some characteristics of
membranes, energy requirement for intensive air/oxygen sparging. Another advantage of air
-cathode over the two-chamber is the reduction of the high internal resistance of MFCs.
Other designs of MFCs
Liu et al. demonstrated MFCs could produce electricity from domestic wastewater with
removal of chemical oxygen demand. Many types of wastewater can be used as substratein
MFCs, because the production of intermediates in wastewater helps in electricity generation.
Effect of conditions and construction on MFC operation
Electrode materials, proton exchange membranes or salt bridge and operation conditions of
anode and cathode have important effect on MFCs. The electrode material determines the
diffusivity of oxygen in single chambered MFCs. If the electodes are more porous, it allows
diffusion of oxygen to anode which reduces the efficiency of fuel cells. The electrode
material also determines the power loss of fuel cell in terms of internal resistance. The
longevity of electrode is also a important criterion. But the most important criterion is cost.
Electrodes can be replaced if they are corroded or saturated and it doesn’t affect the
conditions much if the microbes are non-film making and are present in liquid analyte.
Proton exchange membranes also play an important part but they are very costly and needed
proper installation procedures for limiting the dangers of clogging and drying. But they make
the assembly very robust and thus usable in practical conditions. The ratio of membrane
surface area to system volume is critical to the system performance. Alternative membranes
such as porous polymers and glass wools have been tested but are not utilized by researchers
most of the time. Some researchers prepared their own polymer using polyethylene by
sulphonation with chlorosulphonic acid in 1,2-dichloroethane. But none of them were as
efficient as nafion.
Operating condition such as Dissolved Oxygen (DO) content is important parameter. Anode
uses low DO but cathode uses high DO. But higher DO facilitates diffusion of more oxygen
into anode compartment through the porous membrane. Oxygen saturated catholytes are
found to be the optimum. Increasing the DO more than that doesn’t give any considerable
change in efficiency of the system. Fuel or substrate concentration also plays an important
role. Though higher fuels are preferable but most of the time it is inhibitory to
microorganism. So a proper feed rate should be maintained in continuous systems and proper
Effect of anode in MFCs
Microorganisms play important roles in anode chamber and generated electrons. These
generated electrons are utilized to reduce electron acceptors in cathode once they passed
through external circuit. Likewise, so as to complete the circuit produced protons must bore
into PEM from anode to the cathode. An anaerobic anode compartment is one of the main
part of MFCs. All the essential conditions to degrade the biomass are provided in the anode
chamber. The compartment is filled with substrate, microorganisms and the anode electrode
as electron acceptor. It is necessary to point out that activation energy required for anodic
reaction must be lowered by means of commensurate catalysts. Available bacteria in the
anode chamber usually function as catalysts. Ideal electrode materials should be of ensuing
features;
1. Good electrical conductivity and low resistance.
2. Strong biocompatibility.
3. Chemical stability and anti-corrosion.
4. Large surface area.
5. Appropriate mechanical strength and toughness.
Modification of anode electrode could be useful in promoting the performance of MFCs. One
feasible manner to improve MFC output power is using modified carbon and metal-based
anodes with conductive polymers. For the oxidation of glucose, the anode reaction is written
effectively below:
C6H12O6 + 6H2O = 6CO2 + 24e- + 24H+
Mediator action results in a dramatic increase in the current and electrical yields obtainable.
The facility for a substantial degree of oxidation is one of the important advantages that the
present approach to biomass-energy conversion holds over other methods.
Effect of cathode in MFCs
Protons produced in the anode chamber migrate into the cathode through the proton exchange
membrane which complete the electrical circuit. The electrons generated at the anode site
travels to cathode chamber and transmit onto oxygen. This radical oxygen and produced
positive ions in the anode participate in the following reaction to form water which spreads
by the way of the ion permeable membrane on the cathode along with the assistance of
A steady current is generated by the process with the wire connecting the anode and cathode.
Catalysis is needed in anodic and cathodic reactions. Oxygen has usually been a final electron
acceptor in the cathode due to its accessibility, intense oxidation potential, and not being a
chemical waste product (water is formed as the only end product), being free and producing
no poisonous end products. The presence of Co as a catalysts on the air side of cathode is
able to improve MFC performance. If oxygen diffusion of membrane to the anode could be
controlled, power output of MFC would be enhanced by raising the air pressure of cathode. A
biocathode, in which cathodic reactions are catalyzed using microorganisms, has been used to
improve electricity production in a MFC, as a result, it can be adopted into MFC to enhance
the cathode performance instead of catalysts using nitrate, sulfate, fumarate, CO2, H+ as
electron acceptor and without the help of exogenous.
The performance of cathode is considered the main limitation. To make an MFC scalable, the
design of cathode is the immense challenge.
Characteristics of Anode Respiring Bacteria
Investigators in the field of biological electricity production have taken up the task of
identifying and isolating those bacteria that have the capability of transferring the electrons to
an electrode. In the absence of oxygen, dissimilatory metal reducing bacteria (DMRB)
transfer their electrons to a metal such as iron or manganese, which acts as a terminal electron
acceptor (Lovley, 1993). Electrons can be transferred to the anode in any of the following
ways: direct transfer by means of bacterial structures called nanowires, indirect transfer using
intermediate electron shuttles, conduction through the biofilm matrix; or a combination of
these mechanisms (Lovley, 2008; Rittmann, 2008; Logan et al., 2006). A recent study used
MFCs to understand the electron transfer abilities and terminal electron accepting processes
in a highly alkaline and salty environment (Miller & Oremland, 2008). A few other bacteria
from extreme environments have been reported to generate electricity. For example,
thermophilic bacteria.
Working principles in MFCs
Working principles in MFCs is related to microorganisms oxidise organic matter in the anode
chamber (anaerobic condition) producing electrons and protons. Electrons transfer via the
external circuit to the cathode chamber where electrons, protons, and electrons acceptor
(mainly oxygen) combine to produce water. In a two-chamber set up, the anode and cathode
anode to cathode and preventing oxygen diffusion to the cathode chamber. In the single
chamber MFC the cathode is exposed directly to air. Despite of this there are also mediator
MFCs and mediator less MFCs, microorganisms that require a mediator do not have
electrochemically active surface proteins to transfer electrons to the anode electrode. Whether
the fuel cells are single culture or not MFCs that don’t use mediators still require some form
of carbohydrate to function. In comparison to mediator MFCs, mediator less MFCs is more
important. Examples of mediator less MFCs is marine environment have created a fuel cell
using the different sediments on the sea floor.
Microorganisms Inoculated in microbial fuel cells
Fuel cells are able to generate electricity from many different chemicals by oxidation of the
chemicals at the anode and reduction at the cathode. MFCs do not need to use metal catalysts
at the anode; instead, they use microorganisms that biologically oxidize organic matter and
transfer electrons to the electrode. Logan defined the microorganisms as exoelectrogens due
to their capability of exocellular electron transfer. The microorganisms, which can be
inoculated in MFCs for electricity generation, are found in marine sediments, soil,
wastewater and fresh water sediment or activated sludge. A number of species, such as
Geobacter, Shewanella, Pseudomonas, Clostridium, are often inoculated into MFCs or MFCs
for electricity and hydrogen productions, and they are able to oxidize acetate, ethanol, lactate,
butyrate as substrate. Therefore, the electron transfer mechanisms in anode chamber of MFCs
are a crucial issue of studying MFCs working principles. The performance of MFCs is
impacted not only by types of microorganisms presented, but also by mechanisms of
electrons transfer to anode. Several mechanisms are involved in mediator-less MFCs: bacteria
can transfer electrons through self produced mediators; electrons transfer is related to
nanowires produced by bacteria; in an absence of nanowires, electrons can be transferred via
Fig: Schematic representation of the production of bioelectricity from microbes.
Commercialization of MFC
MFC deals with production of electricity by employing waste materials, it commercialization
will offer several advantages such as:
1. Production of low-cost electricity from waste materials.
2. The electricity will be produced all round the year since waste and xenobiotic are readily
available.
3. People would be able to produce electricity in their homes.
4. This technology will be helpful for the people living in poor countries such as Africa
where huge infrastructure required for set of energy production plants is not available.
5. MFC will lead to clean up of waste. So, it can be used as an alternate method for
Diagrammatic representation of bioelectricity generation from microbes
RESULTS AND DISCUSSION
Analysis of various strong salts: In the experiments conducted by employing 1M, 2M, 3M
KCl based salt bridges, the maximum current produced was 2 volts.
Molar conc of salt
Maximum current of 2 volts was obtained when using 1M concentration of KCl in salt
bridge. The current study proved that the number of salt bridge which conducts protons to the
anode plays a role in different designs of MFCs salt bridges, the MFC with four salt bridges
produced 2 volts. The two major problems that have played havoc; with our lives are; one is
protection and conservation of our environment and the other is energy crises. In recent years
peoples are moving towards biotechnology and microbiology to sort out the solution. MFC is
an essential part in the research. MFC can be utilized for diverse purposes, Eg-Power
production, Bio-hydrogen production, Biosensor. The majority of the research performed on
the MFCs is concerned with the enhancement of the power density of the system with respect
to the anode surface area.
Utilization of substrate (sewage sludge) by microorganisms oxygen over whelming condition
turn out dioxide and water. In this experiment conducted by employing strong salt like KCl in
1M, 2M, 3M concentrations were used for fabricating salt bridge. The results obtained were
showed that KCl was most efficient in transporting H+ ions in the cathodic chamber. During
the study, it was noted that initially the voltage rises rapidly but, soon voltage starts falling
study showed that KCl salt is more efficient for the generation of voltage from different bio
wastes by using MFCs.
Applications of MFCs
The most obvious use of MFCs are the source of electricity. They can be utilized in rural
sector and urban sectors. Though till now the electricity generation via fuel cells is not that
efficient in small scale but large scale use can be efficient. Low power wireless systems can
also be powered with MFCs. There has been reported study of using the MFC to utilize the
body glucose to power implanted medical devices. Robotics has also high usage of MFCs for
sustaining self-sustainable autonomous robots.
Future prospects
The development and utilization is still in infancy of MFCs. There is a wide scope for
development of MFCs as the power density is too low for deployment in automobiles and
other industrial applications. The microorganisms can be genetically modified to form high
reducing recombinant strains producing more available electron at anode. Materials of
construction can also be studied to lower the internal resistance and corrosion. The
implementation and operation cost can also be lowered with better designs of single
chambered microbial fuel cells and upflow mode of fuel cells to be scaled up for wastewater
treatment facility.
MFCs developed in recent decades are classified in different forms.
Education
Soil-based microbial fuel cells serve as educational tools, as they encompass multiple
scientific disciplines (microbiology, geochemistry, electrical engineering, etc) and can be
made using commonly available materials, such as soils and items from the refrigerator. Kits
for home science projects and classrooms are available. One example of microbial fuel cell
being used in the classroom is in the IBET (Integrated Biology, English, and Technology)
Biosensor
Using MFC technology as sensor for pollutant analysis and process monitoring is another
application of biofuel cell. Batteries have restricted lifetime and must be changed or
telemetry systems to transmit obtained signals to remote receivers. It is possible to use MFCs
as biological oxygen demand (BOD) sensor.
Bio-hydrogen production
MFCs can be readily adjusted to the harvest of biohydrogen, instead of producing electricity.
Hydrogen can be accumulated for later applications. MFCs supply a renewable hydrogen
source that can be donated to the overall hydrogen demand in a hydrogen economy. We can
generate hydrogen gas in typical MFC.
Generation of bioelectricity
MFC is a fantastic technology that can use a wide variety of substrate, materials and system
architectures with bacteria to achieve bioenergy production despite the fact that power levels
in all these systems were relatively low. It is particularly preffered for sustainable long term
power applications, with potential health and safely issue. The main objective of MFC is to
achieve a suitable current and power for the applications in a small electrical device.
Waste water treatment
As energy source, large potential is kept in waste water including diverse types of organic
substrate. Different kinds of waste water such as sanitary waste, food processing waste
water.swine wastewater and corn stover contain energy in the form of biodegradable organic
matter. MFCs technology that was considered to be used for wastewater treatment is
favourable as a completely different method because; of capturing energy in the form of
electricity or hydrogen gas.
CONCLUSION
As petroleum source is depleted, energy crises encouraged researches in the world to consider
for alternative sources of energy. Using of fossil fuels may cause environmental pollution.
Clean fuels significantly fuel cells and biofuels, as new sources of energy without any
pollution are suitable replacements of traditional fossil fuels.
ACKNOWLEDGEMENT
We are very thankful to our Principal Dr. Shaila Bootwala. We are also thankful to our HOD
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