OUTLOOK OF SEDIMENT MICROBIAL FUEL CELL FOR POWER GENERATION AND BIOREMEDIATION OF CONTAMINANTS

Abstract

Due to lack of a membrane and completely anoxic, sediment microbial fuel cells (SMFCs) are different from
microbial fuel cells. The simultaneous production of renewable energy, bioremediation of contaminants and moderate functioning parameters, SMFCs have attracted the attention of many researchers. For power generation, many exoelectrogens in SMFCs have the ability to transfer electrons from electrodes by using four ways of natural electron shuttles. The most dominant mechanism is long-range electron transfer via conductive pili. The powering by microbes is an emerging technique for the remediation of contaminants from sediments. The pathways for transferring electrons in electrotrophs operate in the opposite direction from those in exoelectrogens.This review briefly targets on the SMFC prototype, power generation and contaminants remediation.

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International Journal of Advances in Science Engineering and Technology, ISSN: 2321-9009 Volume-5, Issue-3, Jul.-2017
http://iraj.in
Outlook of Sediment Microbial Fuel Cell For Power Generation and Bioremediation of Contaminants
45
OUTLOOK OF SEDIMENT MICROBIAL FUEL CELL FOR POWER
GENERATION AND BIOREMEDIATION OF CONTAMINANTS
1SYED ZAGHUM ABBAS, 2MOHDRAFATULLAH, 3NORLI ISMAIL,
4MUHAMMAD IZZUDDINSYAKIR
Division of Environmental Technology, School of Industrial Technology, UniversitiSains Malaysia, Penang, Malaysia
E-mail address: zaghum2009@gmail.com
Abstract - Due to lack of a membrane and completely anoxic, sediment microbial fuel cells (SMFCs) are different from
microbial fuel cells. The simultaneous production of renewable energy, bioremediation of contaminants and moderate
functioning parameters, SMFCs have attracted the attention of many researchers. For power generation, many
exoelectrogens in SMFCs have the ability to transfer electrons from electrodes by using four ways of natural electron
shuttles. The most dominant mechanism is long-range electron transfer via conductive pili. The powering by microbes is an
emerging technique for the remediation of contaminants from sediments. The pathways for transferring electrons in
electrotrophs operate in the opposite direction from those in exoelectrogens.This review briefly targets on the SMFC
prototype, power generation and contaminants remediation.
Keywords - Electrodes, Electrotrophs, Exoelectrogens, Power generation
I. INTRODUCTION
In general, sediment is recognized a major “sink” for
contaminants, specifically for some persistent organic
pollutants and heavy metals. These pollutants may
accumulate to concentrations many fold above than
those in the water column. In recent years, the
pollution of the aquatic environment has become a
global problem because of its toxic effects on living
organisms. Due to their bio-accumulation in the
ecosystem and their toxic effects, heavy metals are of
particular concern among environmental pollutants
[1]. Many conventional methods have been used for
the remediation of sediments, such as ozonation,
dredging, and electro-chemical degradation, but their
high cost and harsh nature limits their widespread
application [2]. Thus, the natural degradation of
sediments by microorganisms, including methods
such as immobilization, degradation, and
decomposition, has received much interest due to its
reduced cost and environmentally benign nature. The
microorganisms have many diverse metabolic routes
by which they can easily degrade/transform the
sediment pollutants into less toxic forms [3].
However, the natural degradation/transformation of
sediment heavy metals by microorganisms is a very
slow process because there is a lack of proper
electron donors and acceptors. Thus, to boost this
metabolic process, a system is needed that can easily
provide a proper electron acceptor and donor for
simultaneous sediments heavy metal remediation and
electricity generation.
There are many types of fuels cells. Many reports that
environmental microbes can easily build
electrochemical signaling with solid electrodes have
rapidly led to the microbial fuel cells (MFCs)
development [4]. An MFC is a device that converts
the chemical energy of organic and inorganic
compounds into electricity using bacteria, and in this
device, pollutant treatment and electricity generation
are simultaneously achieved [5]. Sediment microbial
fuel cells (SMFCs) are a special application of MFCs
for sediment remediation and electricity production.
There are many advantages of SMFCs for sediment
remediation to remove various contaminants while
producing renewable energy: 1) for the natural
bioconversion mechanisms, the electrode can provide
a less aggressive, inexhaustible, clean and flexibly
portableelectron acceptor or donor; 2) SMFCs cause
minimum distraction to the native aquatic habitat; and
3) controllable electrochemical parameters can be
easily monitored for the remediation processes [6].
II. SEDIMENT MICROBIAL FUEL CELLS
(SMFCs)
Electricity production by bacteria was first observed
by Potter. Very few practical advances were achieved
in the field of MFC for the next 55 years. In the early
1990s, researchers were primarily using exogenous
chemical mediators (natural red, methyl viologen,
potassium ferricyanide, thonin, anthraquinone 2-6,
disulfonate, and others) for the transfer of electrons
from inside bacteria to electrodes, but these
exogenous chemical mediators (electron shuttles) are
often toxic and unstable . Kim et al. achieved the first
breakthrough in the field of MFCs when they found
that without the addition of exogenous mediators, the
bacteria could transfer the electrons to electrodes [7].
The prototype SMFCs consist of a graphite anode
placed in an anaerobic sediment and a graphite
cathode placed in water containing dissolved oxygen.
The performance of SMFCs depends on the potential
gradient of the sediment-water interface. Around both
the anode and cathode, copper wires are tangled
because they are very good electrical conductors. To
make the SMFCs efficient, a multi-anode system is
typically used; approximately 11 anodes are sufficient

International Journal of Advances in Science Engineering and Technology, ISSN: 2321-9009 Volume-5, Issue-3, Jul.-2017
http://iraj.in
Outlook of Sediment Microbial Fuel Cell For Power Generation and Bioremediation of Contaminants
46
for a single cathode [8]. Thus, both electrodes are
connected with the external circuit that is attached to
a multi-meter data logger to monitor the system.
SMFCs provide an appropriate model to examine
how energy flows through microbial consortia and
how we can collect the energy from a natural system;
their potential role in power generation and the
bioremediation of contaminants in the environment
can be explored. Some potential SMFC types that can
easily degrade/transform sediments containing heavy
metals with simultaneous electricity production are
discussed in the next sections. The prototype of
general SMFCs is shown in Figure 1. Following are
the possible forms of SMFCs.
2.1. Aerobic non-stimulated SMFCs
The prototype for this SMFC is the same as
mentioned above. This SMFC type is very similar to
a natural aquatic environment because it is not
stimulated externally, and an oxygen sparger is
inserted in the cathode chamber to create the aerobic
environment [9].
2.2. Aerobic stimulated SMFCs
This SMFC is stimulated by an external battery, and
the main difference is that the multi-cathode system is
developed by opposing the direction of the external
battery terminals because heavy metals normally
require high potential for reduction or degradation
[10].
2.3. Anaerobic non-stimulated SMFCs
The prototype of this SMFC is the same as for the
aerobic SMFC with the only difference that there is
no external oxygen supply [11]. The entire system is
tightly closed, which prevents the introduction of
oxygen into the system and maintains an anaerobic
environment for the fermentation activities of
anaerobic bacteria.
2.4.Anaerobic stimulated SMFCs
The structure of this SMFC is the same as for the
non-stimulated anaerobic SMFC except that it is
stimulated by an external battery, and a multi-anode
system is created by opposing the direction of the
external battery terminals. This step is used because
the initial current in the external battery from the
positive terminal and heavy metals in the sediments is
easily reduced by the external current due to the
integration of the cathode into sediments [12].
Fig.1. The schematic prototype of a general double-chamber SMFC.
III. EXOELECTROGENS
Many exoelectrogenic bacterial strains are known that
can easily transfer electrons to electrodes, e.g.,
Rhodopseudomonaspalustris,
Geobactersulfurreducens, Geobacterloveleyi,
Anaeromyxobacterdehalogenas, Pseudomonas
aeruginosa, Geothrixfermentas,
Thermincolacarboxydophila, Shewanellaoneidensis,
Shewanellaputrefaciens, Escherichia coli, and
Thermincolapotens. Recently, some pathogenic
bacterial strains, such asOchrobactrum anthropic and
Klebsiella pneumonia [13], have been reported to
produce current in SMFCs.The electrons are
transferred from bacteria to SMFC electrodes through
four mechanisms like Electron transfer by soluble
electron-shuttling molecules, short-range direct
electron transfer by redox-active proteins, long-range
electron transport through conductive pili and direct
interspecies electron transfer.
IV. ELECTROTROPHS
Microbes that have ability to accept electrons from
electrodes are called electrotrophs. The electrotrophs
discovery opened a new research direction for the
remediation of heavy metals through reduction. To
date, many microbial consortia have shown the
properties of electrotrophs. Many bacteria such as
Staphylococcus carnosus, Enterococcus faecalis,
Lactobacillus farciminis, Kingelladenitrificans,
Shigellaflexneri, Streptococcus Mutans,
Dechlorospirillum anomalous, Clostridium
ljungdahlii[14], and Acinetobactercalcoaceticus have

International Journal of Advances in Science Engineering and Technology, ISSN: 2321-9009 Volume-5, Issue-3, Jul.-2017
http://iraj.in
Outlook of Sediment Microbial Fuel Cell For Power Generation and Bioremediation of Contaminants
47
different redox-active molecules that can act as
electrons shuttles, accept the electrons from
electrodes, and deliver them to bacteria to promote
the reduction of inorganic substrates and
fermentation.
CONCLUSIONS
SMFCs have created a new research direction that
may prove to be environmentally sustainable and
more controllable and cost-effective for power
generation and the bioremediation of contaminated
sediments. The electron transfer mechanisms of
exoelectrogens and electrotrophs are well
investigated mostly in Shewanella spp. and
Geobacterspp.; so research about electron transfer
mechanisms in other exoelectrogens and
electrotrophs are also needed. The challenges of
SMFCs will be overcome by joint endeavors from
researchers in many disciplines such as
environmental studies, biotechnology,
electrochemistry, computer science, electronics,
materials science, and biology.
ACKNOWLEDGEMENTS
The authors would like to express their appreciation
to UniversitiSains Malaysia Global Fellowship
(USMGF) for the support and research facilities for
this project.
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