MICROBIAL FUEL CELLS

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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

1.0              INTRODUCTION

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.

1.1              Motivation and Background of the Study

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)

1.2              Statement of the Problem

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.

1.3              Objectives of Study

 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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