ABSTRACT
This research focuses on achieving a
substantial improvement in the performance of microbial fuel cell by exploring
a wide range of local alternative materials suitable for the construction of
its critical components in the economic perspective as against the use of the
conventional and expensive ones. Albeit several efforts have been made in this
direction further reduction in the production cost is necessary to make the
technology economically viable for commercialization. The operational efficiency of MFCs is actually dependent on a number
of factors which may include: differences in temperature, electron acceptor, pH, electrode surface
areas, type and volume of substrate, cation or proton exchange membrane (PEM), electrode,
reactor size, presence of absence of exogenous mediators, and operation time.
TABLE OF CONTENTS
Title page i
Certification
page ii
Dedication iii
Acknowledgements iv
Abstract v
Table of
Contents vi
CHAPTER ONE:
INTRODUCTION 6
Statement of the
Problem 14
Objectives of the Study 14
Scope of the Study 16
CHAPTER TWO
LITERATURE
REVIEW
Study of Microbial Fuel Cells (MFCs) 18
A Brief History of MFC Technology 18
MFC
applications in Recent Times 19
Biofuels and their types
24
Disadvantages of Bio-oil and Bioethanol alternatives as Fuel 27
MFC as an Electrical Energy Producing Device. 30
Advantages of MFC over Fuel Cells
31
Electrocoagulation technique
in wastewater treatment 65
CHAPTER THREE
MATERIALS AND METHODS
Research design focus 68
Chloride by Argentometric Titration
(APHA 4500-CT B; 1995) – Salinity 86
Determination of alkalinity using
phenolphthalein indicator: 87
Determination of Chloride ion (Cl-):
88
Anode Feedstock
Preparation and Inoculation. 89
MFC Proton Exchange Membrane (PEM) 90
Akaso Clay physicochemical characterization
procedure. 94
Determination of Exchangeable Ca, Mg, K, Na,
Mn, and Effective CEC in clay Soil. 96
MFC
Electrodes and External Load 104
MFC Design
and Construction Procedure and Operation 106
Determination of coulombic
efficiency 109
CHAPTER FOUR
RESULTS AND DISCUSSION
111
Physicochemical Analysis of Akaso Clay 111
Optimization
Results of MFC Performance using Response Surface Methodology 114
Power
generation in microbial fuel cell, mfc 123
Synergistic Effect
of Starch-clay composite (PEM) on
MFC performance 136
Cumulative Quantity
of Electricity Generated 139
Wastewater bioremediation using microbial fuel cell 147
Electrocoagulation in microbial fuel cell (MFC) 168
CHAPTER FIVE
SUMMARY, CONCLUSION AND RECOMMENDATION
Summary 169
Conclusion 171
Recommendations, Suggestions for
improved MFC model and performance 171
Contribution to
Knowledge 173
References 174
Artificial
neural network CODES 1 204
CHAPTER
ONE
The global
socio-economic expansion and exponential growth in industrialization result in
a corresponding growing demand for energy. These activities of man incidentally
generate unwanted materials with negative environmental effect and as such
constitute major challenges to researchers and engineers as such processes
increasingly mount pressure on energy resource and transportation systems (Rosenbaum, 2007; Cheng et al, 2011;
GOTS, 2013). The quality of waste water discharged into the receiving waters in
the environment determines to a very large extent the functions and state of
biodiversity. Management of our
wastewater should not be such that involves a costly or complex process or
technology. To this end, it is pertinent
and economically reasonable to employ a simple and cost-effective way to treat these
wastewaters and so reduce their deleterious effects on the receiving human
environment to the barest minimum.
Microbial
fuel cell is a simple scalable technology that operates in a manner as to
provide the necessary and favourable biochemical condition that promotes
biodegradation of biomass to generate electrical energy (Barua and Deka, 2010).
The device operates with virtually any biodegradable organic matters which
includes human, animal and industrial wastewaters, while simultaneously
accomplishing wastewater treatment. The operation of MFC leverages the
potential of microorganisms to achieve extracellular electron transfer (EET) to
an artificial electrode during organic matter biodegradation and respiration. As
a consequence of MFC operation, the process of reduction or removal of
biochemical oxygen demand from wastewater system via anaerobic digestion,
fundamentally brings about the release of elementary particles (protons and
electrons) which also destabilize and settle suspended, colloidal and dissolve
particles by neutralizing its surface charges. This process is referred to as electrocoagulation (Bello et al, 2014; Brahmi
et al, 2014) . By this way, investment in microbial fuel cell as a
biotechnological device would be a meaningful contribution to global energy and
industrialization.
The search for alternative sources of energy has
increased due to current prediction of the global energy depletion (Karmakar et al, 2010; Haslett,
2012). There is a clear call for sustenance of the worldwide energy
demand and a balance of the effect of energy demand chain operation on the
environment. The challenge therefore, is that fossil fuel as the hub of world
energy supply is exhaustible implying that several centralized power plants
probably may become redundant due to lack of fuel. Hence the focus is now on
the increase for tailored solutions designed to meet world energy demand (Sørensen, 2004).
The current status of world energy put dependence on
fossil fuel at 80±5% (Sørensen, 2004) while renewable and
nuclear energy completes the balance. The resultant effect of this is that many
countries are in short supply of energy due to cost and technology. It is also
important to note that transportation alone gulps 58% of the world fossil fuel
supply (Sørensen, 2004; Nigam and Singh, 2011; Kuye and Edeh, 2013).
The
handling of anthropogenic waste in an environmentally friendly manner gives
tremendous challenges to researchers, inventors, engineers, scientists, policy
makers and economist alike (Pharm et al., 2006; Mohan et al., 2007). More so these materials may be made into a resource
to support energy supply type like the off-grid as they are not feed stocks
having competitive demand but they can be turned into valuable energy resources
(Cheng, et al 2011). Thus, the worries caused by fast depleting fossil fuel have
heightened the search for high and efficient energy transformations with
leakage on the utilization of renewable energy sources as a lee-way (Kuye and
Edeh, 2013). Therefore, a major shift in energy sources for more efficient renewable energy
sources is desirable due to a gradual obsolescence of fossil fuels including
coal and petroleum (Rosenbaum,
2007). The increasing
complementary role of the renewable energy sourced is graphically shown on Figure.
1.1
Figure 1.1: Global Energy Supply
by Source (Tverberg, 2012)
The
other negative effects of the dependence on fossil fuel for energy supply
include the generation of greenhouse gases and other pollution challenges which
are of global environmental concern. Therefore, for the irresistible need for
“greener” and cleaner energy source to combat climate change, electric
producing cell commonly called microbial fuel cell is one promising significant
aspect of renewable energies that has been on high priority of contemporary
research as a complimentary energy supply source (Logan, 2005; Mohan et al.,
2007; Karmakar et al., 2010; Majumder et al., 2014). Vehicle manufacturers are designing vehicles that
are less dependent on fossil fuel. Houses, recreational buildings and other
structures are also designed and redesigned to function on green and renewable
energy sources. Funding and investment projects are further scrutinized to suit
the sustainability and environmental friendly policies and high demand for the
cut-down on emissions on existing projects.
Microbial Fuel Cell takes advantage of the fact
that energy can be recovered from biodegradation of organic via electrochemical
reaction where active microbial activity produces proton and electron with
carbondioxide and biomass being the final products (Ann and Logan, 2010). The
components of MFC include: the anode and cathode chambers, the proton exchange
membrane and the external circuit. The treatment level, however, does not get
to the point were the treated water becomes consumable or fit for domestic use
but rather could get to a point where it has little or no deleterious effect on
the ecosystem when discharged into the environment. Improvement in the performance of this device
hinges on a combination of factors among
which are: electrode material and surface area, temperature, type of microorganism used, proton exchange
membrane used, mass transfer, type of electron transfer mechanism (mediated or
non-mediated), over-potential at the
electrode, kinetics of microorganisms (slow or fast), the amount of external
load, and the geometry of the reactor relative to the concentration and
condition of substrate in the solution (Rabaey and Verstraete, 2005., Wang,
2006, Cheng and Logan, 2011).
Most substrate utilizations
that result in the production of electrons take place near or at the surface of
the anode where they form biofilm. The electrons from microbial activity taking
place in the anolyte at a distant point from the anode may require an exogenous
mediator for faster transport. Mediators are chemical substances which act as electronophore to assist electron
recovery during substrate utilization reaction in a mediated microbial fuel
cell. A non-mediated case utilizes only the electrochemical activity of the
microbial community or isolated microbe to produce and achieve transfer of
electrons to the anode. Some examples of chemical mediators are: thionine (C12H10N3S+),
methylene blue (C16H18ClN3S.3H2O),
pyocyanin (C13H10N2O) (Rabaey et al, 2005),
2-hydroxy-1,4-naphthoquinone (HNQ), neutral red (C15H17ClN4),
Meldola’s blue (MelB) (C18H15Cl3N2OZn)
(Ieropoulos et al, 2005), TMPD co-substrate (2,3,5,6-tetramethyl-1,4-phenylenediamine,
C10H16N2.2HCl ) (Haslett, 2012). The general equation for the electrogenetic
reaction at the anode is represented by the following reaction;
The application of mediators
has been reported to improve power generation but could cause inhibit cell
growth in the long run due to its poisonous nature (Park and Zeikus, 2000). Although
previous studies have shown the possibility of improving the performance of
MFCs by introducing different materials (such as nafion, agar-agar) to function
as the proton exchange membrane, in this research study we will show that under
certain conditions and controlled operating variables, a the less expensive option in MFC production (incorporating
clay) is possible so as to achieve this critical potentials (wastewater
treatment and bioenergy production) at minimum operating cost.
The
human life indispensably depends of clean and quality water. However, only
about 2-3% of the water available all over the earth is clean and fresh. The
remaining volume of water is either salty or contains various degrees of
contaminants (Kuokkanen, 2016). This situation therefore calls for emergency
response from researchers all over the world to seek the most viable solution.
On the same vein, the current society of ours is largely
energy-based. The whole lot of industrial and economic activities taking place
come along with waste containing organic load which constitute environmental
pollution. This organic load (OL) in waste water is no longer considered as
waste but rather a valuable source of renewable energy (Mathuriya and Sharma, 2009). Microbial fuel cell being a
bifunctional device therefore finds a suitable medium to exploit these
biological substrates by degrading them to produce electricity.
The terms renewable energy, regenerative
energy, green energy and
supplementary energy” have been used interchangeably to mean the collective
name for a number of energy resources available to man on Earth (Sørensen,
2004). These include energy
that originates from properties that are inherent in flowing water bodies
(hydro energy) and other natural sources like the sunlight
and wind (Wikipedia, 2013). A very important change in energy sources seems
inevitable and is likely to be the usage of biomass, as a renewable energy. Research
into and the adaption of renewable energy sources is in the increase with the
aim of using renewable energy sources to meet the
growing global energy demand (Pike, 2008).
The processes employed for the
production of bioenergy include production of vegetable oils through trans-esterification
which can also yield other products including esters and methyl fatty acids (Pike,
2008). Further is the alcohol production of alcohols from starch through
fermentation with ethanol as the major produce.
Further bioenergy involves the production of ketones from cellulose
using anaerobic digestion processes. Pyrolysis is also employed including gasification
producing ash and char and partial combustion of biomass that produces synthesis
gas (Pike, 2008).
Microbial fuel cell employs microbes to generate biochemical
energy using various organic biomass as substrates (See Figure. 1.2). Besides flexibility of
fuel consumption, MFC has advantage over batteries in that batteries are
completely polarized ( stop producing electricity) as soon as the stored
chemical reactants are exhausted, whereas MFC runs on renewable energy
continually as long the fuel (organic substrates which include all human,
animal and plant wastes, compost, sludge, algal bloom, estuarine sediments,
among others) are in constant supply to the anode electrode. The operation of microbial fuel cell (MFC) leverages the
possibility of biochemical conversion of biomass by microbe to produces
electricity from the anaerobic oxidation of biodegradable organic substrates.
During the period the economics of oil coupled with global warming, makes renewable
energy from biomass and other areas appeared as viable sources of sustainable alternative
energy that has advantage of easing the effect of greenhouse gas impact. The organic load of industrial, agro and municipal wastewater from
sewage, dairy, brewery or sugar is exceptionally energy-rich and this has found
application in outsourcing for alternative energy.
Figure 1.2: Biomass Raw Materials
(Pike, 2008): a) crop straw. b) Cob and Husk crop. C) Grains and steak. d) Stem and
peels
Microbial
fuel cell has some advantages over the other sources due to its ability to
produces energy without initial energy requirement (Das and Mangwani, 2010).
The unit costs of some bio-based feedstock are set by their alternate use; an instance
is fermentation of corn for ethanol with this feedstock produced from organic fertilizers
that originates from hydrocarbon sources like the fossil fuels. The greenhouse
gas from ethanol sources produces 22% emissions less than the gasoline (Pike,
2008). Microbial fuel cell (MFC) sources for its feedstock from biomass wastes
which has little or no alternative uses or processing energies. MFCs are amongst the utmost looked-at region of investigation for
renewable energy sourcing for quite a long time now (Logan, 2005; Lovley and
Nevin, 2008). Research on MFC technology is concentrated on developing ways of
transforming natural chemical form of energy in feedstock to electricity. In addition,
substantial attention is been given to harvesting and harnessing
the advantages of MFCs to help preserve the ecosystem resulting to
environmentally appropriate form of energy. This has made MFC a topical process
aimed at improving the potential to concurrently treat waste and produce electricity
from electrolyte from variety of wastewaters (Mohan et al., 2007).
The employed
technique in an MFC is centered on catalytic action of microbes (especially
bacteria) which converts biological constituent in an environment free of
oxygen called the anode chamber generating protons and electrons (Das and
Mangwani, 2010). The transfer of protons to the cathode chamber through the PEM
generates the potential difference between the anode and cathode required to
cause electron flow. The electrons then flow to the cathode chamber with a load
connected across the two chambers, the cathode chamber is the sink where the protons
that pass through the Proton exchange membrane (PEM), react with oxygen to
produce water. At the cathode, the protons are reduced by accepting an electron,
mainly from oxygen (or other oxidizing or neutralizing agents) (Figure. 1.3).
The use of organic feeds as electrolytes
in the anode chamber of MFCs has found success in common application with so
many organic matter as listed in section 2.5 (Table 2.0); Further to these,
inorganic chemicals use as anode electrolyte has been severally researched (Logan,
2005).
Extensive multiplicities
of feedstock has been established as MFC substrate including simple sugars, aldehydes, brewery
wastewater, agro wastewater, petrochemical wastewater, paper industry
wastewater, municipal wastewater, food processing wastewater (Liu et al., 2005a;
Logan et al., 2005; Heilmann and Logan, 2006; Yazdi et al., 2007; Oh and Logan,
2005). Other wastewater sources including Starch processed, Abattoir, Leachate
from Landfill, effluent from Palm oil mill
(Min et al., 2005; You et al., 2006b ; Heilmann et al., 2006; You et
al., 2006a; Rodrigo et al., 2007; Scott and Murano, 2007 ; Lefebvre et al.,
2008; Jung et al., 2008; Wang et al., 2008; Mohan et al., 2008; Huang et al.,
2009; Lu et al., 2009; Wagner et al., 2009 ; Cheng et al., 2010).
Figure 1.3: Two-Chamber Microbial
fuel cell (Du et al., 2007)
The viability of MFC is being heightened by its simplicity in
terms of technology, its competitive edge of using wide variety of wastewater
making it sustainable (Zuo et al., 2008). The recent trend makes Microbial fuel
cells capable of producing current directly from intricate organic effluent
such as benthic sediment organic matter making it useful and capable of
delivering sound ecological energy with ability to re-condition contaminated
soil (remediation), assessing, and/or controlling of the water and soil environment
using endogenous microbes as catalyze for energy development (Franks and Navin,
2010; Cao et al., 2010). Factors relevant for the effective performance of a
MFC unit include nature of electrode materials, nature of proton exchange membrane (PEM) and
operating environments that the cathode and the anode is kept including pH,
temperature, conductivity, salinity etc. Contemporary materials being used as
MFC electrode includes solid graphite, platinum coated graphite and graphite
felt (Das and Mangwani, 2010). Certain anode materials
have variously been used in MFCs, such may include plain graphite, carbon
paper, carbon cloth, felt, or foam, reticulated vitreous carbon (RVC), or graphite
granules (Logan et al, 2007). These materials though have shown to improve the relative power
performance of MFCs but their relative expensive nature limits their use. The
electrode material to a large extent determines the diffusivity of oxygen in MFCs
unit (Karmakar et al., 2010). When the electrode is not
effective, it causes over potential and this can result to oxygen going back to
the anode chamber through the cathode chamber reducing the overall effectiveness
of the MFC. The electrode material (the material used for the production) has
influent on the flow of current in the MFC. Some material gives rise to high
resistance resulting to low potential energy on in the MFC (Oh and Logan,
2005). Also the longevity and cost of electrodes are important criteria to its
effectiveness (Cheng et al., 2006). This was asserted
by Banik et al., (2012) who reported significance of MFC electrode
configuration on electricity production.
Figure 1.4: Orientation of graphite brushes
in the circuit (Banik et al., 2012)
The Proton exchange membranes
(PEM) are semi-permeable membranes which facilitate the transfer of ions but
impede the flow of water and oxygen. Commonly applied PEM in microbial fuel
cells includes Nafion, Ultrex, Agar-agar salt bridge
and starch-alginate mixture (Bond and Lovely, 2003; Obasi et al.,
2012). The effect of operating conditions (temperature and pH) of anode
and cathode electrolyte will be discussed in chapter two of this thesis. The most obvious use of
MFCs is for energy supply (Karmakar et al., 2010). This makes them future source of off grid supply of electricity
in rural and remote areas. MFC had found applications for power in reusable
cell; small voltage remotely operated units, remote sensing and lighting
sources. Frank and Nevin, (2010) in a
review suggested supply of power to pace makers or body implants utilizing MFC
as a form of remote energy source (Ieropoulos et al., 2003).
Researchers
have faulted direct application waste from animal production to the soil as a
source of polluting the environment including the ground water and emission of
gases. The distance of this facility make the capturing and using the energy
from these sources used of MFC as a potential source preventing release to air
and cost effective environmental operation(Williams et al., 1999; Volterra and
Conti, 2000)
This research focuses on achieving a
substantial improvement in the performance of microbial fuel cell by exploring
a wide range of local alternative materials suitable for the construction of
its critical components in the economic perspective as against the use of the
conventional and expensive ones. Albeit several efforts have been made in this
direction further reduction in the production cost
is necessary to make the technology economically viable for commercialization. The operational efficiency of MFCs is
actually dependent on a number of factors which may include: differences in temperature, electron acceptor, pH, electrode surface
areas, type and volume of substrate, cation or proton exchange membrane (PEM), electrode,
reactor size, presence of absence of exogenous mediators, and operation time.
The challenges in controlling these factors summarily determine the overall
output of this device as discussed below:
- There
exist several technical challenges that limit MFC technology feasibility
for widespread application: power densities should be increased, at
reduced cost of its construction materials, and also the architectural
design must be scalable to allow treatment of large volume of wastewater.
This can be achieved by identifying and incorporating locally sourced and
low cost materials for each of the unit component. Hence, this study
focuses on finding suitable alternatives for polymer nafion or ultrex as
salt bridge and graphite as electrode.
- A wide range of substrate materials
which are waste water from industrial activities whose pollution
parameters have been pre-determined via sample laboratory analysis, and
the results compared with the effect of MFC operation with the same waste
waters.
- Locally
sourced polymeric and traditional ceramic raw materials (such as starches,
clay, that are subjected to treatment using high temperature pyrolysis and
other high temperature treatments to impart improved conductivity and stability
to the substances.
- The
reduction in the cost of electrical power needed to run small and medium
scale industrial and public facilities is in focus. This device, which
operates on ‘waste to energy philosophy’, would invariably guarantee this
result at minimum cost implication and equally reduce the effect of the
potential hazards associated with such wastes, emanating from the same
facility, on the environment.
·
In all industrial operations, waste
water generated from a chain of activities and processes are harmful to both
land and aquatic flora and fauna, when they are discharged without pre-treatment. Conventional pre-treatment methods of
composting will require dedicated space and additional cost due to aeration and
transportation. These wastewaters should be deployed to provide the required energy
based on their organic matter content (substrate) in the production of
electricity through using MFC technology and by extension reduce their toxicity
and high concentrations of organic load before disposal.
This study is an experimental research work
that is aimed at establishing the potentiality of industrial effluent
wastewater to drive the operation of microbial fuel cell, MFC, to generate
electricity while itself being treated in the process. The cell under study
operates with proton exchange membrane produced from locally sourced materials
with specific study on starch and clay based PEMs at various preparation temperatures as well as
investigate the effect of proton conductivity on the overall waste water
treatment efficiency of MFC and power generation. In order to achieve this aim and further
address the above identified challenges, an investigative procedure was set up
via experimentation. The objectives of the research work include:
1.
To characterize a
mediatorless Microbial Fuel cell functioning on wastewaters from various
sources.
2.
To review the basic principles of MFC technology
and its applications with the use of organic substrates/ effluents in a dual
chamber H-type MFC configuration for
power generation.
3.
To investigate the effect of thermal
treatment at various temperatures on the proton conductivity of locally sourced
biomass on current produced and level of waste water treatment by MFC.
4.
To examine the interplay among the
various factors affecting the performance of a MFC as a power generating device
(e.g substrate concentration, pH, PEM material composition and condition of
preparation.
5.
To optimize the performance of MFC by
examining its behaviours under different conditions.
6.
To propose a model relating
the voltage generated against time
7.
To examine the Coulombic Efficiency (Ec)
of electron production and transfer in a MFC from the bacteria to the anode
using various modifications of clay-starch composite as the proton exchange
membrane.
1.4 Scope of Study
This research work
shall focus on the development, operation and application of a microbial fuel
cell in wastewater treatment and electrical power generation. A H-type, dual
chamber mediatorless MFC would be constructed using locally sourced materials
to develop the components. Hence the system would deploy a direct electron
transfer mechanism (DET). Effort will also be made to discover local
alternative materials for proton exchange and further enhance its performance
via modification. It is however, not an attempt to carry out microbiological
analysis of the effluent waste water solution as the study of MFC is mainly
classified under the broad areas of specialization including; Microbiology, Industrial
Biotechnology, Process Engineering and Electrical engineering (Frank and Nevin, 2010). There will also be no attempt to discover suitable alternative
materials for carbon (graphite) as material for electron transfer. The
substrate to be used shall include industrial and agro waste waters. The study
shall also be looking at Chemical Engineering application of the MFC in the tapping
of electricity and waste water treatment in comparison with the conventional
chemical treatment methods. The stepping up of the power generation capacity of
the cell shall also not be covered.
Governing Models for MFC operation and analyses
(1) The BOD removal efficiency of the MFC is
determined using the procedure.
(2) Power and current generated
are calculated using the equations
(3)The performance of the MFC will be calculated
by estimating the COD removal efficiency of the substrate
during the cycle of operation using the equation
(4) where Cso represent
the initial COD and Cs represents the final COD in mg/l.
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