Microbial Fuel Cells (Essay Sample)

MICROBIAL FUEL CELLS
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Executive Summary
Microbial Fuel Cells (MFC) research is one of the most rapidly and evolving fields of science which lacks both in established terminology and the ways or methods for its analysis and the performance of their systems. This therefore complicates work for researchers in the field in clearly comparing devices on a uniform level. Analysis and construction the MFCs needs grounding various fields of science covering biology, chemistry, physics and other materials sciences. In this paper we provide a detailed history and background analysis of the MFCs, the mechanism behind the generation of the MFC as well as the principle on which the MFC generated electricity flows in the cathode. We also in detail consider some secondary generation of fuel and its application to treatment of wastewater. We also examine the MFC technological advancement, concluding with recommendations on further research in the field before it can finally be relied upon.
Abstract
Two of the most recent challenges are environmental protection and energy crisis and economic growth today depends crucially on sustained availability of energy accessed from eco – friendly, but most importantly affordable sources. In recent times, Bio Electrochemical systems (BESs) have emerged as a very exciting technology in which, an electron from bacteria interacts with electrodes. The most popular type of BES is the Microbial Fuel Cells (MFCs) which acting as devices uses bacteria to catalyze oxidization of both organic and inorganic matters. In such systems, electrons produced by bacteria from the substrates flow to the anode, through to the electrode linked by a material which is conductor although under some external resistance. Anodes of the MFCs act like bacteria’s typical electrons receptor and therefore flow of electrons to the cathode of through a resistor through MFCs generate considerable electricity. During construction and analysis of MFCs knowledge of various scientific fields is a prerequisite. This ranges from biology to engineering. This report tries to define and explain the MFCs, as well analyze the mechanisms behind the fuel production, and how the mechanisms can be used as treatment of water.
Introduction
Today alternative energy sources are very high on demand for the reason that developing as well as the developed world is facing a serious energy crisis and besides high energy requirement in conventional treatment of sewage systems also are demanding for alternate technology treatment (Catal, et al., 2008). Furthermore, because of the concerns of the environment globally and energy insecurity concerns, there are also emerging interest to getting a sustainable but clean sources of energy with very little or no use of hydrocarbons (Manohar et al., 2008). In that respect bio electrochemical systems (BES) have recently emerged interacting with electrodes through electrons, either removed or supplied by an electrical circuit. The most popular of the BES being the Microbial Fuel Cells (MFCs) in which bacteria is used in the fuel cells to act as reagent to convert organic matter which are found in waste water into useful electricity.
Scientists have for a long time known about the connection of biology, chemistry and electricity to the fact that in the late 1700s, an Italian scientist, Luigi Galvani noted from his observations that a detached leg of a frog could twitch due to electrical charges existing in the atmosphere. These findings helped a lot to create the field of electrochemistry and as late as 1911, English scientists published one of the original papers on generating electricity by use of bacteria. Today the advances have zeroed on MFCs which are receiving increased attention as because they are expected to have more potential for solutions to energy demands and yet they could provide clean as well renewable sources of energy.
Microbiology
Our knowledge of electrochemically active microbes is still emerging but an entire new field of microbial ecology is now also emerging which is based on “anodophilic” bacteria as well as possible transfer of electrons (Li et al., 2013). Such bacteria can be called exoelectrogens because of their ability to externally release electrons. The original understanding of flow of electrons through bacteria to electrodes originated from dissimilatory studies Geobacter or Shewanella species which can produce electricity in MFCs (Bond and Lovely, 2003). The biochemical and properties as indicated can also be involved in extra transfer of electrons. We also note that some bacteria leads to and uses soluble electron shuttles which minimize the need for direct contact between the cells and electron acceptors, an example is phenazine production given by a strain of pseudomonas aeruginosa stimulated bacteria strain transfer (Rabaey et al., 2005). The following figure displays microbial community, electrically connected by nanowires.


Figure 1 – An electronically connected microbial community in a vast network of nanowires (Keego Technologies, LLC, 2011)
Microbial Fuel Cells
The microbial fuel cells as devices use bacteria to catalyze organic and inorganic matter oxidization to generate electricity with the produced electrons from substrates flowing to the anode, flowing to the cathode connected by a conductor which contains a resistor operating a load. The electrons as produced can be transferred by electron mediators to the anode or through direct membrane related to electron flow or nanowire which also produced by bacteria or by other means that are yet to be discovered. The chemical mediators which include neutral red, anthraquinone – 2.6 are added to the set system to permit electricity production from bacteria to support the use of the electrode (Yuan et al., 2011). Where there are exogenous mediators of electron added to the system, the MFC are classified as mediator – less even when the mechanism of transfer of electron may not clearly be known. A simple cell is shown in the following graphic


Figure 2: A Microbial Fuel Cell with Slurry and Drain water (Sulonen et al., 2015)
The microbial catalyzed electrons which are liberated at the anode are subsequently consumed at the cathode when the process are sustained and are defining properties of the MFCs. Using a sacrificial anode which is made of an alloy from magnesium slab does not qualify the system as an MFC since there no added bacteria for canalization of oxidization of the fuel. The MFCs which are operated with mixed cultures presently achieve a substantial density of power as compared to the pure cultures and in some of the recent tests, an MFC show high voltage power generation on pure culture as much as the same device has not been tested on an acclimated mixed culture with cells which has grown away from the device.
Microbial Fuel Cell Development
The analysis of microorganisms existing in MFCs has revealed diversity in composition and it is believed that several forms of bacteria may be found which have capability to anodophilic or interspecies electrons flow (Jiang et al., 2009). There is capability to produce clean energy with use of MFC for treatment of water and the benefits include clean, lower emissions, safe and quite performance, direct electricity recovery with a higher energy efficiency. Today the MFCs are built with a variety of materials in diversity of configurations and these systems are operate with a range of conditions among which are temperature, electron receptor, pH, reactor size, electrons surface areas and the time of operation. The potentials in the systems are report with various reference states, sometimes under a single load or resistance but in some cases.
TECHNICAL SETUP AND THE PRINCIPLE ELECTRICITY GENERATION
Generation
Bacteria requires energy to survive just as humans need food for their survival but bacteria acquires this energy in two steps the first one requiring removing electrons from a given source of organic matter a process called oxidization and the next step of energy acquisition involves emission of electrons to an acceptor like “oxygen”. Now for some bacteria grow under some conditions in absence of oxygen, they transfer the electrons to a carbon electrode called an anode. At this moment the electrons then move across a given wire under some resistance to the cathode at which they combine with protons with oxygen to form water. When the effect is the flow of electrons from the anode to the cathode is realized, there is generation of current together with a voltage that makes electricity.
Technical Principle of Generation
An ideal MFC apparatus has two “chambers” for anode and cathode respectively which are made of glass, Plexiglas or polycarbonate, with a respective electrode made of graphite, graphite felt, carbon – cloth, carbon paper, platinum, platinum black or reticulated vitreous carbon (RVC) and these chambers are clearly separated by Nafion or Ultrex (PEM). The chamber which acts as the anode is filled with an organic substrate that is metabolized using microbes for its growth and production of energy while it generates protons and electrons (Watanabe, 2008). The chamber which is a cathode is filled with a very high potential acceptor of electrons to complete an electric circuit (Karube et al., 1981). Here an ideal electron receptor is not to interfere with the microbes in any way and should also be a sustainable compound that has no toxic effects. In this process oxygen serves an in ideal acceptor of electrons because of its non – toxic effect and thus preferred as an oxidizing reagent because it simplifies the operation of an MFC, otherwise the reference media which has suitable electron ...