Team:Bielefeld-Germany/Project/MFC Efficiency

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<h1>MFC Efficiency</h1>
<h1>MFC Efficiency</h1>
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<p><a href="https://2013.igem.org/Team:Bielefeld-Germany/Project/Abstract">Projects <br>Overview</a></p></div>
<p><a href="https://2013.igem.org/Team:Bielefeld-Germany/Project/Abstract">Projects <br>Overview</a></p></div>
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<a href="https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC">MFC Overview</a></div>
<a href="https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC">MFC Overview</a></div>
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<a href="https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Construction">MFC Construction</a></div>
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<a href="https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#Verification.2C_comparison_and_appraisal_of_measurement_results">Calculation</a></div>
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<a href="https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#Feasibility_study_for_MFC_in_sewage_and_waste_treatment">Feasibility Study</a></div>
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==Overview==
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In order to get a better evaluation of our Microbial Fuel Cell, we calculated several characteristic numbers. Furthermore, we searched and found a feasibility study and compared it with our results.
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[[File:MFC-Principle.png|250px|left|thumb|MFC-Principle|'''Figure 1:''' Schematic illustration of the general microbial fuel cell functional principle, showing the flow of charged species during operation.]]
 
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<p align="justify">
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==Verification, comparison and appraisal of measurement results==
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To determine how well the different BioBricks we create really work in the designated environment, the design and construction of a suitable microbial fuel cell was necessary. This fuel cell has to meet several requirements. As explained [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#General_design previously] it should consist of two chambers, separated by a material that is only traversable for cations. Both chambers have to contain an electrode, which has to be electrically conductive. Also, they should have a large surface area, in order to allow contact to a high number of electron donors at the same time. Both the anode and the cathode chamber also have to be air-tight, since the reaction has to take place under anaerobic conditions. For obvious reasons, we aim at keeping the costs for the cell low by using materials which cost as little as possible while still performing well.<br>
 
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Construction of a first prototype began in May. After initial testing, the design underwent significant changes over the course of the project. Important stages of this process are shown below, along with a description of their design and the flaws that led to the planning of a new model.
 
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</p>
 
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<br><br>
 
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==Theory==
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*<p align="justify">After consultation with expert Dr. Falk Harnisch and the productive feedback of our presentation and poster session during the European Jamboree in Lyon the need for verifying our measurement system and a technical and economic appraisal of the results became very obvious.</p>
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===General design===
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*<p align="justify">As the overall cell-voltage represents the difference between anode and cathode potential, it was not clear whether the measured voltage values were influenced by the biocatalytic activity in the anode chamber only, or by a combination of potential changes in both chambers. For independent consideration of the anode or cathode compartments potential, a Ag/AgCl [http://www.meinsberger-elektroden.de/labor/bezug.html#se10 reference electrode] was ordered and the [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#The_Gen3plus_Fuel_Cell Gen3<sup>''plus''</sup> MFC] was designed and constructed to make the new electrode usable. The circuit diagram, including a schematic illustration of the entire measurement setup is shown in Figure 1.</p>
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<div style="margin-right: auto;">
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[[File:IGEM_Bielefeld2013_MFCframe.png|left|300px|thumb|Figure 2: Schematical illustration of a typical MFC design used in research environments.]]
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</div>
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<p align="justify">
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The general design of a microbial fuel cell is mainly influenced by the shape of the electrode chambers. A very simple design is called the “H” shape, which usually consists of two bottles or other vessels, connected by a tube containing a suitable separation material. Further investigations underlined the general usability of this system to test materials or parameters, but the power gain seems rather low. This is most likely the case because of the slow proton exchange through the tubes and because of a high internal resistance  ([https://2013.igem.org/wiki/index.php?title=Team:Bielefeld-Germany/Project/MFC&action=submit#References Oh ''et al.'', 2004; Oh and Logan, 2006]).<br><br>
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</p>
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<br>
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[[Image:IGEM_Bielefeld2013_ReferenceElectrodeSchematic.png|500px|thumb|center|<p align="justify"> '''Figure 1: Schematic illustration of the [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#The_Gen3plus_Fuel_Cell Gen3<sup>''plus''</sup> MFC] measurement setup, using a Ag/AgCl reference electrode. '''</p>]]
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<p align="justify">
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There are many other possible shapes, like a cylindrical reactor with a concentric inner tube that acts as the cathode to enable a continuous flow. One specific design, proposed by H. P. Bennetto ([https://2013.igem.org/wiki/index.php?title=Team:Bielefeld-Germany/Project/MFC&action=submit#References Bennetto, 1990]), is often used for research purposes. The system consists of plastic elements in form of two solid plates and two frames, as shown in Figure 2. The frames are placed between the plates and form two reaction compartments, separated by a cation exchange membrane. Furthermore, every compartment is equipped with electrodes to enable a flow of electrons. To create a system with the option for anaerobic cultivation with simultaneous aeration and the possibility to add or remove liquid, the elements are fitted with ports. To ensure the system is air-tight, rubber gaskets are fitted between the plastic parts. The endplates are held together by four threaded rods.
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</p>
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<br>
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*'''Requirements:'''
 
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** formation of a closed system
 
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** possibility for axenic cultivation
 
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** possibility for anaerobic conditions
 
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**large internal surface
 
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<br>
 
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<br>
 
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<br>
 
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===Anode===
 
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<p align="justify">
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*Using this setup the parallel measurement of both the overall cell potential and the potential of the cathode were measured. The according data, including the c anode potential, calculated from P<sub>cell</sub>= P<sub>cathode</sub> - P<sub>anode</sub> are plotted in Figure 2.
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In order to be used as an anode, a material has to be highly conductive, biocompatible and chemically stable under the conditions present inside the fuel cell. Many traditional materials like copper are not suitable, because of the highly toxic effect of heavy-metal ions to bacteria. Platinum works excellent, but is extremely expensive. Several carbon-based materials provide a cheap but practical alternative. Regarding this, the surface area is a very important factor for high current production. Previous investigations showed that current increases with the overall internal surface in the following order: carbon felt > carbon foam > graphite ([https://2013.igem.org/wiki/index.php?title=Team:Bielefeld-Germany/Project/MFC&action=submit#References Chaudhuri and Lovley, 2003]).
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</p><br>
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<br>
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*'''Requirements:'''
 
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**high conductivity
 
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**good biocompatibility
 
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**long-term physical and chemical stability
 
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<br>
 
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<br>
 
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===Cathode===
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[[Image:IGEM_Bielefeld2013_ReferenceElectrodeCurves.jpg|500px|thumb|center|<p align="justify"> '''Figure 2: Plot of the overall cell potential, cathode potential against Ag/AgCl reference electrode and the calculated data for the anode potential for a measurement of wild type'' E. coli'' KRX, OD<sub> 600</sub> : 1,66 in the [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#The_Gen3plus_Fuel_Cell Gen3<sup>''plus''</sup> MFC]. Methylene blue was added after 15 minutes with an end concentration of 232,56 µM.</p>]]
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<p align="justify">
 
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Because of its low overpotential in combination with carbon electrodes and the resulting working potential, which is close to its open circuit potential, potassium ferricyanide (K<sub>3</sub>)[Fe(CN) <sub>6</sub>]) is the most frequently used electron acceptor in microbial fuel cells in research scenarios ([https://2013.igem.org/wiki/index.php?title=Team:Bielefeld-Germany/Project/MFC&action=submit#References Logan ''et al.'', 2006]). However, one has to consider that the reoxidation by oxygen is very low and the diffusion through the PEM is not negligible, so that the oxidation of this substance can affect the performance of the MFC when operated for long periods of time ([https://2013.igem.org/wiki/index.php?title=Team:Bielefeld-Germany/Project/MFC&action=submit#References Rabaey ''et al.'', 2005]). Alternatively oxygen can be used as a very effective electron acceptor in combination with an open-air electrode. For an effective oxygen reduction, however, high-cost platinum catalysts are necessary. For this reason, this option is rarely used ([https://2013.igem.org/wiki/index.php?title=Team:Bielefeld-Germany/Project/MFC&action=submit#References Sell ''et al.'', 1989]). <br>
 
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<br>
 
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</p>
 
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*'''Requirements:'''
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*<p align="justify">The depicted data show the expected results. In the beginning the cell potential is very low, because the cells cannot transport the produced electrons to the anode. After addition of the mediator solution the cell potential shows a characteristic increase and reaches its maximum of 325 mV. The cathode potential against Ag/AgCl amounts about –360 mV at the start of the measurement, what was expected by calculating the potential using Nernst equation. The course of the measured potential values also shows a significant effect of mediator addition because of a polarization of both electrodes regarded to the resulting current flow, but it reach a stable value of -240 mV quickly. This and the calculated anode potential data show, that the anode potential is mainly responsible for the overall cell potential, so that the measurement of this value is suitable for the analysis of different bacteria strains or even enzymes, placed in the anode chamber.</p>
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**good reduction performance
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*<p align="justify">As the detailed description of the [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#The_Gen3plus_Fuel_Cell Gen3<sup>''plus''</sup> MFC] indicates, the cell is furthermore optimized for a better power output in terms of a larger volume, higher N<sub>2</sub> aeration and an adapted mediator concentration. To generate different operating numbers for the established microbial fuel cell generation three plus the determination of the used substrate amounts was necessary. Because of the incompatibility between the mediator methylene blue and the separation column used for sugar analysis, a new purification method was established. The methylene blue containing samples were blended with a spatula tip of activated carbon to bind the mediator, inverted for two minutes and centrifuged at 10000 x g for 5 minutes. To exclude an effect on the substrate concentration standard samples, containing different amounts of mediator and activated carbon, were analyzed using the [https://2013.igem.org/Team:Bielefeld-Germany/Labjournal/Molecular#Substrate_HPLC substrate HPLC method]. As the results showed no differences for methylene blue containing standard samples treated with activated carbon and the untreated sample, the applicability of the method could be verified.</p>
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**good reoxidation
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**high long term stability
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<br>
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===Compartment separation===
 
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<p align="justify">
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*<p align="justify">The relevant data for calculating the subsequent operation numbers based on the experiment presented in Figure 2 are presented in Table 1.</p>
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Although almost all microbial fuel cells use proton exchange membranes as the separation element between anode and cathode compartment, it is possible to use more simple constructions like salt or agarose bridges. These basic separation systems, however, do not reach the power output of membrane based systems because of the high internal resistance. Cation exchange membranes offer very defined properties and ensure a better current output because of their high selectivity for the passage of positive charged ions. However, in this context it has to be considered that the PEM could be permeable to chemicals and oxygen, which could influence the long term performance of the cell ([https://2013.igem.org/wiki/index.php?title=Team:Bielefeld-Germany/Project/MFC&action=submit#References Logan ''et al.'',2006]).
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</p><br>
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<br>
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*'''Requirements: '''
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**high selectivity for positive ions
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**impermeability for chemicals and oxygen
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<br>
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==MFC-Evolution==
 
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===The Film Canister Cell===
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[[Image:IGEM_Bielefeld2013_TableValues.jpg|600px|thumb|center|<p align="justify"> '''Table 1: '''Measurement values recorded and calculated from the experiment presented in Figure 2 and further data needed for operation number calculation. ([https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Bastos ''et al''.], 1988 and [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Gomes ''et al''.], 2013).</p>]]
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<p align="justify">
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*<p align="justify">To compare the power output of the [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#The_Gen3plus_Fuel_Cell Gen3<sup>''plus''</sup> MFC], containing ''E. coli'' KRX (OD<sub>600</sub>=1.66) in M9 medium and using 232.56 µM methylene blue as mediator with other Microbial Fuel Cell systems the power density is normalized to technical characteristics ([https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Logan ''et al''., 2006]). Because the anode is the part of the Fuel Cell where the biocatalytical reaction occurs, its projected surface area is an often used parameter for normalization:</p>
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This is a model designed to gain better understanding about the general concept of galvanic cells and microbial fuel cells. It was used with different chemicals, yeast and the <i>E. coli</i> KRX strain. It also allowed to gather experience with the equipment used for measurement. The anode and cathode chambers are film canisters. Both have holes in their walls which are connected by roughly 2 cm long part of a 15 mL centrifugation tube. The individual parts are held together by hot-melt glue. The centrifugation tube is filled with 3 % agarose, which acts as a salt bridge to allow protons to pass from anode to cathode chamber. In both chambers, pieces of carbon tissue (see Figure 4) act as the electrode.<br><br>
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</p>
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<div style="float:left; margin-right:1px; width:48%">
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[[File:IGEM_Bielefeld2013_Carbontissue.jpg|270px|left|thumb|Figure 4: Carbon tissue.]]<br>
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[[File:IGEM_Bielefeld2013_Carboncloth.png|265px|left|thumb|Figure 5: Carbon cloth.]]
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<p align="justify"; style="clear:both">
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The biggest problem of this design is the salt bridge connecting both chambers. After being submerged in liquid for a while, it tends to become loose and glide out of the centrifugation tube. Furthermore, the construction does not allow for anaerobic operating of the fuel cell.<br>
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</p>
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*Dimensions per Chamber:
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**height: 50 mm
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**diameter: 32 mm
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**volume: 40.2 mL<br><br>
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<div style="float:left; margin-right:1px; width:45%">
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[[File:IGEM_Bielefeld2013_VerificationFormel1.jpg|center]]
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[[File:IGEM_Bielefeld2013_Filmcannister.jpg|270px|left|thumb|Figure 6: The Film Canister Cell.]]<br>
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[[File:IGEM_Bielefeld2013_FilmCellAnim.gif|281px|left|thumb|Figure 7: Exploded view of the Film Canister Cell.]]
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<br><br><br>
 
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<p align="justify">
 
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===The Film Canister Stack===
 
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Connecting single batteries in series can be used to increase the output voltage. Likewise, the film canister stack consists of five film canister cells connected with copper wires in series. Because of the higher voltage generated, it was possible to operate a single low power light-emitting diode, using a high concentrated baker's yeast suspension and methylene blue in the anode chamber.
 
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<div style="float:left; margin-right:1px; width:55%">
 
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[[File:IGEM_Bielefeld2013_Filmstack.png|300px|left|thumb|Figure 8: The Film Canister Stack.]]
 
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</div>
 
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<div style="float:left; margin-right:1px; width:40%">
 
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*Dimensions per chamber <br>(10 total):
 
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**height: 50 mm
 
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**diameter: 32 mm
 
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**volume: 201 mL total
 
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<br>
 
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===The Second Generation Fuel Cell===
 
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<p align="justify">
 
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This cell was designed with anaerobic operation in mind. The plastic parts needed were ordered from the workshop of the Faculty of Biology at Bielefeld University. The overall design is inspired by the fuel cell proposed by Benetto (Bennetto, 1990). Two frames make up the anode and cathode chamber. They are enclosed by two flat plates, which each have four bores. Threaded rods are put through the bores. The construction is held together by these rods, which have tightly fastened nuts on their ends.<br>
 
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All plastic parts are separated by thin rubber gaskets. A Nafion N117 membrane is placed between the two frames to allow cations to travel between the chambers. The two electrodes were initially cut out of the same carbon tissue as the ones used in the film canister cells. The rims were sown together with extra durable yarn to prevent the material from frazzling. These electrodes were held in place by two plastic pars plugged in each chamber. The copper wire connecting the electrode runs through two holes on the top of each plastic frame.<br>
 
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Initial testing revealed that the carbon cloth electrodes did not seem to be as conductive as expected. For this reason, they were replaced with electrodes made from another kind of carbon material, which were obtained from University of Readings [http://www.ncbe.reading.ac.uk/ National Centre for Biotechnology Education ]. However, the material is not very strong and easily ruptures, especially when wet. This made it difficult to connect the copper wires and to hold the electrodes in place within the chambers. The design also lacked means to drive out the oxygen from medium with nitrogen, an important prerequisite to establish anaerobic conditions within the fuel cell.
 
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</p><br>
 
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*Dimensions per chamber:
 
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**height: 40mm
 
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**width: 40mm
 
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**depth: 14mm
 
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**volume 22,4 mL<br>
 
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<div style="float:left; margin-right:1px; width:45%">
 
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[[File:IGEM_Bielefeld2013_Mfcevolution.png|262px|left|thumb|'''Figure 9:''' The Second Generation Fuel Cell.]]<br>
 
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<div style="float:left; margin-right:1px; width:45%">
 
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[[File:IGEM_Bielefeld2013_1stGenCellAnim.gif|310px|left|thumb|'''Figure 10:''' Detailed schematic view of the second generation cells plastic parts and threaded rods. Click to view animation.]]
 
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<br><br>
 
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===The Third Generation Fuel Cell===
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*<p align="justify">To compare the system related to economic considerations like reactor size and material costs the power output is also normalized to the total volume of the Fuel Cell:</p>
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<p align="justify">
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The fuel cell consists of six plastic parts. The overall design is similar to 2<sup>nd</sup> generation cell, but the frames are split up into two parts each. This allows for the carbon electrodes to be mounted between two frames, as was already the case for the membrane before. This ensures the fragile carbon cloth is fixed in the centre of each chamber and can be tapped by squeezing a wire between the gaskets. Since the material is extremely thin, bacteria and medium can diffuse through the electrode and travel between both halves of a single chamber.<br>
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The second important change from the previous design is the introduction of four tube connectors on each frame. This allows aeration of the anode chamber with nitrogen gas and, e.g., introducing fresh medium in the system. The copper wire connecting the electrodes is replaced with platinum, because of the rapid copper-oxidation, resulting in a decreased conductivity.<br>
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*Dimensions per chamber:
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[[File:IGEM_Bielefeld2013_Mfcrevolution.png|262px|left|thumb|'''Figure 11:''' The Third Generation Fuel Cell.]]
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[[File:IGEM_Bielefeld2013_2ndGenCellAnim.gif|267px|left|thumb|'''Figure 12:''' Detailed schematic view of the third generation cells plastic parts and threaded rods. Click to view animation.]]
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===The iGEM-York Cell===
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<p align="justify">
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Since the iGEM Team York_UK is also doing work related to microbial fuel cells this year, we [https://2013.igem.org/Team:Bielefeld-Germany/Collaborations#iGEM-Team_York_UK offered to send] them one of our fuel cells to conduct their experiments in. Our design did not fully meet their requirements, especially since it was too large. After consulting with two of their team members, we build a small fuel cell based on the 3<sup>rd</sup> generation design and sent it to York.
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<div style="float:left; margin-right:1px; width:55%">
 
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[[File:IGEM_Bielefeld2013_Mfcyork.jpg|280px|left|thumb|'''Figure 13:''' The Fuel Cell designed for the iGEM-Team York.]]
 
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<div style="float:left; margin-right:1px; width:40%">
 
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*Dimensions per chamber:
 
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**height: 25mm
 
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**width: 25mm
 
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**depth: 12 mm
 
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**volume: 7,5 mL
 
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</div>
 
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<br>
 
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<br>
 
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===The Stack===
 
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<p align="justify">
 
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In order to increase the power output of the fuel cell, a fuel cell stack was built based on the third generation design. It consists of alternating anode and cathode chambers, five of each, placed between two cover plates. Using copper wiring, the five chamber-pairs are connected in series. Physically, they are separated by 1 mm thick stainless steel tiles, which act as bipolar plates.
 
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</p><br>
 
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<div style="float:left; margin-right:1px; width:55%">
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[[File:IGEM_Bielefeld2013_VerificationFormel2.jpg|center]]
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[[File:IGEM_Bielefeld2013_Mfcstackboss.png|280px|left|thumb|'''Figure 14:''' The Fuel Cell Stack.]]
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*Dimensions per chamber <br>(10 total):
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**height: 50mm
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**width: 50mm
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**depth: 12mm
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**volume: 150mL total
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==3D printing==
 
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<p align="justify">
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*<p align="justify">In comparison to measurements by [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Liu ''et al''.], performed in a single-chamber Microbial Fuel Cell the calculated values are in the same dimension. In their measurement the power generated with acetate as substrate was 506 mW m<sup>-2</sup> or 12.7 mW L<sup>-1</sup> and 305 mW m<sup>-2</sup> or 7.6 mW L<sup>-1</sup> using butyrate ([https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Liu ''et al''., 2005]). Although the values reached with the [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#The_Gen3plus_Fuel_Cell Gen3<sup>''plus''</sup> MFC] are little lower, they can be described as positive results since [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Liu ''et al.''] used domestic wastewater to inoculate their cell with a mixed culture of bacteria which are naturally adapted to anaerobic respiration ([https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Liu ''et al''., 2005]). Since the results of the genetic optimized ''E. coli'' strains illustrate the potential of genetic optimization in regard to a higher power output, a further increase in power output using ''E. coli'' can be assumed upon further research.</p>
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To make the microbial fuel cell accessible to everyone, an additional model was developed which can be produced using a 3D printer. 3D printers are becoming more and more common and if none is available, the model can be ordered online from a 3D printing shop.<br>
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For our 3D printed microbial fuel cell it was important to apply material that does not inhibit microbial growth. To make sure this is the case, <i>E. coli</i> KRX was cultivated in the presence of two different kinds of plastic commonly used for 3D printing. These materials were acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA), which are both thermoplastics that become moldable when heated and return to solid once the temperature drops.<br>
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A proper material for gaskets is essential as well, so different kinds of polysiloxane were tested in the same way. The rubber gaskets used in second and [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#The_Third_Generation_Fuel_Cell third generation MFC] designs were also probed.
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<div style="float:left; margin-right:5px; width:50%">
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*'''Acrylonitrile butadiene styrene'''<br><br><br><br>
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[[File:IGEM_Bielefeld2013_ABS.PNG|150px|center|thumb|'''Figure: NACHTBLAUER WEIßKOPFSEEADLER''' Lewis structure of ABS.]]<br><br>
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*ABS as a polymer can take many forms and can be engineered to have many properties. In general, it is a strong plastic with mild flexibility (compared to PLA).
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<br><br>
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*It's strength, shapeability and higher temperature resistance make it often a preferred plastic by engineers and those with mechanical uses in mind.<br><br>
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*ABS can be smelted down and recycled very easily provided it is available in suitable purity. Sorting methods do exist to separate ABS from mixed wastes with high efficiency.
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<div style="float:left; margin-right:5px; width:45%">
+
-
*'''Polylactic acid'''<br><br>
+
-
[[File:IGEM_Bielefeld2013_PLA.png|150px|center|thumb|'''Figure CAMOUFLAGE CHAMÄLEON:''' Lewis structure of PLA.]]<br><br>
+
-
*Created from processing any number of plant products including corn, potatoes or sugar-beets, PLA is considered a more 'environmental friendly' plastic compared to petroleum based ABS. <br><br>
+
-
*When properly cooled, PLA seems to have higher maximum printing speeds, lower layer heights, and sharper printed corners.<br><br>
+
-
*PLA is biodegradable, having a typical lifetime of about 6 months to 2 years until microorganisms break it down into water and carbon dioxide.
+
-
<br><br>
+
-
<br>
+
-
</div>
+
-
<br><br>
+
*<p align="justify">Further important operation numbers to characterize the efficiency of a Microbial Fuel Cell are the maximum possible electric charge and the theoretical amount of energy. The so called Coulombic efficiency describes the ratio of electric charge which is actually transferred from substrate to the anode to the theoretical maximum of produced Coulombs. Based upon the following reaction, the maximum number of electrons produced per substrate is 14 ([https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Gomes ''et al''., 2013]).</p>
-
<p align="justify">
 
-
To assess the issue of possible growth retardation, we cultivated <i>E. coli </i>with each material and compared the measured growth curves to a control cultivation without added plastics.
 
-
</p>
 
-
<br>
 
-
[[File:IGEM_Bielefeld2013_PLATEST.jpg|400px|center|thumb|'''Figure BRONZE NARWAL:''' Testing of ABS and PLA plastics for biocompatibility.]]
 
-
<br>
 
-
<br>
 
-
<br>
 
-
<p align="justify" style="clear:both">
+
[[File:IGEM_Bielefeld2013_VerificationFormel10.jpg|center]]
-
The results shown in in figure LILA PAVIAN and figure UMBRA SEEPFERDCHEN demonstrate, that both ABS and PLA are biocompatible. Also, all brands of polysiloxane except B1 and the rubber are suitable as gasket material.
+
-
</p>
+
-
<br>
+
-
<div style="float:left; margin-right:15px; width:45%">
 
-
[[File:IGEM_Bielefeld2013_PlasticTest.jpg|270px|left|thumb|'''Figure LILA PAVIAN:''' Results of <i>E. coli</i> KRX cultivation in the presence of different kinds of plastic.]]
 
-
</div>
 
-
<div style="float:left; margin-right:15px; width:45%">
 
-
[[File:IGEM_Bielefeld2013_Polysiloxane.jpg|270px|center|thumb|'''Figure UMBRA SEEPFERDCHEN:''' Results of <i>E. coli</i> KRX cultivation in the presence of different kinds of polysiloxane and rubber.]]
 
-
</div>
 
-
<br><br><br>
 
-
<br>
 
-
<br>
 
 +
*<p align="justify">The total electric charge was determined by integration of current, calculated from voltage using Ohms law over time:</p>
-
===Models===
 
-
<br>
+
[[File:IGEM_Bielefeld2013_VerificationFormel3.jpg|center]]
-
<br>
+
 
-
<div style="float:left; margin-right:15px; width:50%">
+
 
-
[[File:IGEM_Bielefeld2013_Blackmodel.jpg|320px|left|thumb|'''Figure 17:''' A print of one of the earlier models.]]
+
*<p align="justify">For calculating the energy efficiency, defined as the ratio of power production to the heat of combustion of the organic substrate, the power production was integrated over time:</p>
-
</div>
+
 
-
<div style="float:left; margin-right:15px; width:40%">
+
 
-
[[File:IGEM_Bielefeld2013_Earlymodel.png|239px|left|thumb|'''Figure 18:''' An early model that was designed but never actually printed.]]
+
[[File:IGEM_Bielefeld2013_VerificationFormel4.jpg|center]]
-
</div>
+
 
 +
 
 +
*<p align="justify">The calculated values of 1.56 % for the Coulombic efficiency and 0.308 % energy efficiency are located at the lower end of the available literature values ([https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Liu ''et al''., 2005]; [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Logan ''et al''., 2006]). The exact cause cannot be determined accurately because of the multitude of factors affecting the power output in a Microbial Fuel Cell. Relevant reasons might be the high energy amount of glycerol in contrast to wastewater, the Microbial Fuel Cell setup which is optimized for measurement value generation, or the organism ''E. coli''. As stated previously ''E. coli'' is not adapted for anaerobic respiration and because of this fact a long term power output which is necessary for a high efficiency has not been possible right now and further genetic optimization is needed.</p>
 +
*<p align="justify">Since the mediator is an important factor, in regard to its essential function as the electron shuttle between ''E. coli'' and the anode, the  mediator functionality was characterized. For that purpose the mediator turnover number was calculated which is defined as the ratio between the amount of transported electrons and the amount of mediator:</p>
 +
 
 +
 
 +
[[File:IGEM_Bielefeld2013_VerificationFormel5.jpg|center]]
-
<br><br>
 
-
<p align="justify" style="clear:both">
 
-
3D models were programmed with the software [http://www.openscad.org/ openSCAD], exported as .stl-files and translated into G-Code using [http://slic3r.org/ Slic3r].<br>
 
-
Initially, slicing and printing took place at the local [http://hackerspace-bielefeld.de/ hackerspace] with counseling by experienced members of the groups. The printer, a [http://printrbot.com/ Printrbot Plus v2] was made available by the hackerspace community as well. After a total of roughly 34 hours of work, a first model was successfully printed from ABS. Like the models described in the [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#MFC-Evolution MFC-Evolution paragraph], the design was changed several times. Some of the results can be seen in Figure 17. In early August, Bielefeld Universities Faculty of Physics offered their help. They printed out all subsequent designs with their [http://www.reprappro.com/products/mono-mendel/ RepRapPro Mono-Mendel] using PLA plastic and also executed the slicing process.
 
-
</p>
+
*<p align="justify">The obtained turn over number of about 13 illustrates, that methylene blue is used as a reversible redox mediator. During the 200-minute experiment each mediator molecule transports on average 13 electrons from the bacterium to the anode. As this value corresponds to a turnover of 0.065 min<sup>-1</sup> the mediator activity of methylene blue could be a limiting factor in regard to the low efficiencies, too. To elucidate this hypothesis, a further investigation of the redox system is necessary, because the corresponding potential differences are essential for the efficient transfer of electrons between the substances used.</p>
-
<br><br>
+
*<p align="justify">All in all the calculation of different operation numbers illustrate the general functionality of the [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#The_Gen3plus_Fuel_Cell Gen3<sup>''plus''</sup> MFC]. The comparison with literature data for related systems is problematically because mixed cultures are used in most cases, but first achievements highlight the potentials using methods of synthetic biology to optimize the biocatalytic process.</p>
-
<div style="float:left; margin-right:15px; width:35%">
+
 
-
[[File:IGEM_Bielefeld2013_Greenmodel.png|219px|left|thumb|'''Figure 19:''' The final model for the 3D-print printed out using PLA plastic.]]
+
 
-
</div>
+
 
-
<div style="float:left; margin-right:15px; width:55%">
+
 
-
[[File:IGEM_Bielefeld2013_DIYFigger195.gif|300px|left|thumb|'''Figure WEINROTER KOMODOWARAN:''' The final model for the 3D-print. Click to view animation]]
+
 
-
</div>
+
 
 +
==Feasibility study for MFC in sewage and waste treatment==
 +
<p align="justify">To assess the usability of our MFC regarding potential applications, we searched for a feasibility study and compared it to our results. It shows, that our currently achieved efficiencies have the potential for efficient energy production in real world applications.</p>
 +
 
 +
 
 +
===The study===
 +
'''Feasibility study for the application of a Microbial Fuel Cell in sewage and waste treatment''' ([http://www.dbu.de/projekt_26580/_db_1036.html AZ 26580-31])
 +
 
 +
'''Funded by''' the ‘Deutschen Bundesstiftung Umwelt – Osnabrück‘
 +
 
 +
'''Reporting period''': 16.12.2008 – 31.08.2010
 +
 
 +
'''Author''':
 +
*Prof. Dr.-Ing. Michael Sievers<sup>1</sup>
 +
*Dr. Ottmar Schläfer<sup>1</sup>
 +
*Dipl.-Ing. Hinnerk Bormann<sup>1</sup>
 +
*Dipl.-Ing. Michael Niedermeiser<sup>1</sup>
 +
*Prof. Dr. Detlef Bahnemann<sup>2</sup>
 +
*Dr. Ralf Dillert<sup>2</sup>
 +
**<sup>1</sup>  Clausthaler Umwelttechnik-Institut GmbH – CUTEC-Institut GmbH
 +
**<sup>2</sup>  Leibniz Universität Hannover
 +
 
 +
 
 +
===Summary===
 +
*<p align="justify">Since the first investigations on mediatorless MFCs in 1999, the maximum power densities increased from 0.05 mW/m<sup>2</sup> in 1999 to 2700 mW/m<sup>2</sup> in 2008. Therefore, this feasibility study refers to a power density of 2 W/m<sup>2</sup>.</p>
 +
*<p align="justify">An estimation of the power generation potential shows, that the usage of an MFC could produce around 20 kW for a 10,000 PE (population equivalent) sewage treatment plant. The integration of an MFC would generate an electricity production and saving potential, which provides the opportunity to enable nearly energy self-sufficient sewage treatment plants. This is based on a low cost production with low cost materials of the MFC. Especially electrode and membrane materials have to be cost-saving.</p>
 +
 
 +
 
 +
===Previous development of the maximal achieved power densities with MFCs===
 +
*<p align="justify">Since the first investigations on mediatorless MFCs in 1999, the maximum power densities increased. Figure 3 ([https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#References Logan, 2008]) shows the development of the power density from 0.05 mW/m<sup>2</sup> in 1999 to 2700 mW/m<sup>2</sup> in 2008.</p>
 +
 
 +
[[Image:IGEM_Bielefeld2013_DevelopmentPowerDensity.jpg|500px|thumb|center|<p align="justify"> '''Figure 3:''' The development of the power density of the MFC from 1999-2008.</p>]]
 +
 
 +
*<p align="justify">Pure chemicals (glucose or glycerol) are much better usable than organic wastewater components. Furthermore, the conductivity of the organic liquid is usually much higher. Consequently, power densities achieved with wastewater tests are lower. On closer examination of the cathode, we can observe a higher power density for air cathodes (wastewater treatment) in comparison to water cathodes (degradation of pure chemicals). Air cathodes are additionally fumigated.</p>  
 +
 
 +
 
 +
===Assessment of the potential for applications===
 +
*<p align="justify">The energy content of waste water is about 20 W per population equivalent (PE). Therefore, a 10,000 PE plant could generate a power of 200 kW. Table 2 shows an overview of the electricity production potential for various wastewater treatment plant sizes with an extrapolation for 80 million people (Number of inhabitants of Germany). The energy content of the water is defined by the COD (Chemical oxygen demand). COD is commonly used to indirectly measure the amount of organic compounds in water.</p>
 +
 
 +
[[Image:IGEM_Bielefeld2013_Feasibility_Table1.jpg|500px|thumb|center|<p align="justify"> '''Table 2:''' Electricity production potential for various wastewater treatment plant sizes.</p>]]
 +
 
 +
*<p align="justify">Table 3 summarizes the electricity savings potential for various wastewater treatment plant sizes with an extrapolation for 80 million people (number of inhabitants of Germany).</p>
 +
 
 +
[[Image:IGEM_Bielefeld2013_Feasibility_Table3.jpg|500px|thumb|center|<p align="justify"> '''Table 3:''' Electricity savings potential for various wastewater treatment plant sizes.</p>]]
 +
 
 +
*<p align="justify">In comparison, a fully optimized plant for 100,000 inhabitants has an average power consumption of 285 kW. The integration of an MFC would generate an electricity production potential and electricity savings potential of up to total 246 kW. Thus, the Microbial Fuel Cell provides the opportunity to enable energy self-sufficient sewage treatment plants.</p>
 +
 
 +
 
 +
===Assessment of our Microbial Fuel Cell===
 +
*<p align="justify">With our self-designed and constructed Microbial Fuel Cell we achieved a power density of 231 mW/m<sup>2</sup>. ([https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC_Efficiency#Verification.2C_comparison_and_appraisal_of_measurement_results Calculation of the power density]). In contrast to the assumed power density for the feasibility study, which was 2000 mW/m<sup>2</sup>, we have still a ten times lower power density. That means the total electricity saving potential would be 25 kW, which shows a reduction for the required energy of 8% for a fully optimized sewage plant for 100,000 inhabitants with an average power consumption of 285 kW.</p>
<br>
<br>
-
<br>
+
*<p align="justify">In conclusion, while our MFC has quite some potential for improvements, even now our system might be usable to realize significant energy savings.
-
<p align="justify" style="clear:both">
+
-
The final model, illustrated in Figure 19, was finished in September. It features a 4-part design like the [https://2013.igem.org/Team:Bielefeld-Germany/Project/MFC#The_Second_Generation_Fuel_Cell second generation model] described in the MFC-Evolution section and has tube connectors for aeration of each individual chamber. Polysiloxane is used instead of rubber gaskets, the membrane and electrodes are fixed between the four frames of the reaction chambers. The end plates are held together by M3 threaded rods with M3 nuts. The materials necessary for building this fuel cells chassis cost less than 4€ an the cell is biodegradable. The .stl-file is [https://static.igem.org/mediawiki/2013/9/96/IGEM_Bielefeld2013_DIYcell.zip available for download here].
+
</p>
</p>
-
<br>
+
 
-
<br>
+
Line 381: Line 213:
==References==
==References==
-
*Bennetto, H. P. (1990). Electricity generation by microorganisms. [http://www.ncbe.reading.ac.uk/NCBE/MATERIALS/METABOLISM/PDF/bennetto.pdf ''Biotechnology Education, 1''](4), 163-168.<br><br>
+
*<p align="justify">Bastos M, Nilsson SO, Ribeiro da Silva MD, Ribeiro da Silva MA, Wadsö I (1988) Thermodynamic properties of glycerol enthalpies of combustion and vaporization and the heat capacity at 298.15 K. Enthalpies of solution in water at 288.15, 298.15, and 308.15 K. ''The Journal of Chemical Thermodynamics'' 20(11): 1353-1359.</p>
-
 
+
-
*Chaudhuri, S. K., & Lovley, D. R. (2003). Electricity generation by direct oxidation of glucose in mediatorless microbial fuel cells. [http://www.nature.com/nbt/journal/v21/n10/abs/nbt867.html ''Nature biotechnology, 21''](10), 1229-1232.<br><br>
+
-
*Logan, B. E., Hamelers, B., Rozendal, R., Schröder, U., Keller, J., Freguia, S., ... & Rabaey, K. (2006). Microbial fuel cells: methodology and technology. [http://pubs.acs.org/doi/abs/10.1021/es0605016 ''Environmental science & technology, 40''](17), 5181-5192.<br><br>
+
*<p align="justify">Gomes JF, Gasparotto LH, Tremiliosi-Filho G (2013) Glycerol electro-oxidation over glassy-carbon-supported Au nanoparticles: direct influence of the carbon support on the electrode catalytic activity. ''Phys. Chem. Chem. Phys.''</p>
-
*Oh, S., Min, B., & Logan, B. E. (2004). Cathode performance as a factor in electricity generation in microbial fuel cells. [http://pubs.acs.org/doi/abs/10.1021/es049422p ''Environmental science & technology, 38''](18), 4900-4904.<br><br>
+
*<p align="justify">Liu H, Cheng S, Logan BE (2005) Production of electricity from acetate or butyrate using a single-chamber microbial fuel cell. ''Environmental science & technology'' 39(2): 658-662.</p>
-
*Rabaey, K., Clauwaert, P., Aelterman, P., & Verstraete, W. (2005). Tubular microbial fuel cells for efficient electricity generation. [http://pubs.acs.org/doi/abs/10.1021/es050986i ''Environmental science & technology, 39''](20), 8077-8082.<br><br>
+
*<p align="justify">Logan BE, Hameler B, Rozendal R, Schröder U, Keller J, Freguia S, ... & Rabaey K (2006) Microbial fuel cells: methodology and technology. ''Environmental science & technology'' 40(17): 5181-5192.</p>
-
*Sell, D., Krämer, P., & Kreysa, G. (1989). Use of an oxygen gas diffusion cathode and a three-dimensional packed bed anode in a bioelectrochemical fuel cell. [http://link.springer.com/article/10.1007/BF00262465 ''Applied microbiology and biotechnology, 31''](2), 211-213.<br><br>
+
*<p align="justify">Logan BE (2008): Microbial Fuel Cells. ''John Wiley & Sons Inc''., New Jersey.</p>

Latest revision as of 23:27, 28 October 2013



MFC Efficiency


In order to get a better evaluation of our Microbial Fuel Cell, we calculated several characteristic numbers. Furthermore, we searched and found a feasibility study and compared it with our results.


Verification, comparison and appraisal of measurement results

  • After consultation with expert Dr. Falk Harnisch and the productive feedback of our presentation and poster session during the European Jamboree in Lyon the need for verifying our measurement system and a technical and economic appraisal of the results became very obvious.

  • As the overall cell-voltage represents the difference between anode and cathode potential, it was not clear whether the measured voltage values were influenced by the biocatalytic activity in the anode chamber only, or by a combination of potential changes in both chambers. For independent consideration of the anode or cathode compartments potential, a Ag/AgCl [http://www.meinsberger-elektroden.de/labor/bezug.html#se10 reference electrode] was ordered and the Gen3plus MFC was designed and constructed to make the new electrode usable. The circuit diagram, including a schematic illustration of the entire measurement setup is shown in Figure 1.


Figure 1: Schematic illustration of the Gen3plus MFC measurement setup, using a Ag/AgCl reference electrode.


  • Using this setup the parallel measurement of both the overall cell potential and the potential of the cathode were measured. The according data, including the c anode potential, calculated from Pcell= Pcathode - Panode are plotted in Figure 2.


Figure 2: Plot of the overall cell potential, cathode potential against Ag/AgCl reference electrode and the calculated data for the anode potential for a measurement of wild type E. coli KRX, OD 600 : 1,66 in the Gen3plus MFC. Methylene blue was added after 15 minutes with an end concentration of 232,56 µM.


  • The depicted data show the expected results. In the beginning the cell potential is very low, because the cells cannot transport the produced electrons to the anode. After addition of the mediator solution the cell potential shows a characteristic increase and reaches its maximum of 325 mV. The cathode potential against Ag/AgCl amounts about –360 mV at the start of the measurement, what was expected by calculating the potential using Nernst equation. The course of the measured potential values also shows a significant effect of mediator addition because of a polarization of both electrodes regarded to the resulting current flow, but it reach a stable value of -240 mV quickly. This and the calculated anode potential data show, that the anode potential is mainly responsible for the overall cell potential, so that the measurement of this value is suitable for the analysis of different bacteria strains or even enzymes, placed in the anode chamber.

  • As the detailed description of the Gen3plus MFC indicates, the cell is furthermore optimized for a better power output in terms of a larger volume, higher N2 aeration and an adapted mediator concentration. To generate different operating numbers for the established microbial fuel cell generation three plus the determination of the used substrate amounts was necessary. Because of the incompatibility between the mediator methylene blue and the separation column used for sugar analysis, a new purification method was established. The methylene blue containing samples were blended with a spatula tip of activated carbon to bind the mediator, inverted for two minutes and centrifuged at 10000 x g for 5 minutes. To exclude an effect on the substrate concentration standard samples, containing different amounts of mediator and activated carbon, were analyzed using the substrate HPLC method. As the results showed no differences for methylene blue containing standard samples treated with activated carbon and the untreated sample, the applicability of the method could be verified.


  • The relevant data for calculating the subsequent operation numbers based on the experiment presented in Figure 2 are presented in Table 1.


Table 1: Measurement values recorded and calculated from the experiment presented in Figure 2 and further data needed for operation number calculation. (Bastos et al., 1988 and Gomes et al., 2013).


  • To compare the power output of the Gen3plus MFC, containing E. coli KRX (OD600=1.66) in M9 medium and using 232.56 µM methylene blue as mediator with other Microbial Fuel Cell systems the power density is normalized to technical characteristics (Logan et al., 2006). Because the anode is the part of the Fuel Cell where the biocatalytical reaction occurs, its projected surface area is an often used parameter for normalization:


IGEM Bielefeld2013 VerificationFormel1.jpg


  • To compare the system related to economic considerations like reactor size and material costs the power output is also normalized to the total volume of the Fuel Cell:


IGEM Bielefeld2013 VerificationFormel2.jpg


  • In comparison to measurements by Liu et al., performed in a single-chamber Microbial Fuel Cell the calculated values are in the same dimension. In their measurement the power generated with acetate as substrate was 506 mW m-2 or 12.7 mW L-1 and 305 mW m-2 or 7.6 mW L-1 using butyrate (Liu et al., 2005). Although the values reached with the Gen3plus MFC are little lower, they can be described as positive results since Liu et al. used domestic wastewater to inoculate their cell with a mixed culture of bacteria which are naturally adapted to anaerobic respiration (Liu et al., 2005). Since the results of the genetic optimized E. coli strains illustrate the potential of genetic optimization in regard to a higher power output, a further increase in power output using E. coli can be assumed upon further research.

  • Further important operation numbers to characterize the efficiency of a Microbial Fuel Cell are the maximum possible electric charge and the theoretical amount of energy. The so called Coulombic efficiency describes the ratio of electric charge which is actually transferred from substrate to the anode to the theoretical maximum of produced Coulombs. Based upon the following reaction, the maximum number of electrons produced per substrate is 14 (Gomes et al., 2013).


IGEM Bielefeld2013 VerificationFormel10.jpg


  • The total electric charge was determined by integration of current, calculated from voltage using Ohms law over time:


IGEM Bielefeld2013 VerificationFormel3.jpg


  • For calculating the energy efficiency, defined as the ratio of power production to the heat of combustion of the organic substrate, the power production was integrated over time:


IGEM Bielefeld2013 VerificationFormel4.jpg


  • The calculated values of 1.56 % for the Coulombic efficiency and 0.308 % energy efficiency are located at the lower end of the available literature values (Liu et al., 2005; Logan et al., 2006). The exact cause cannot be determined accurately because of the multitude of factors affecting the power output in a Microbial Fuel Cell. Relevant reasons might be the high energy amount of glycerol in contrast to wastewater, the Microbial Fuel Cell setup which is optimized for measurement value generation, or the organism E. coli. As stated previously E. coli is not adapted for anaerobic respiration and because of this fact a long term power output which is necessary for a high efficiency has not been possible right now and further genetic optimization is needed.

  • Since the mediator is an important factor, in regard to its essential function as the electron shuttle between E. coli and the anode, the mediator functionality was characterized. For that purpose the mediator turnover number was calculated which is defined as the ratio between the amount of transported electrons and the amount of mediator:


IGEM Bielefeld2013 VerificationFormel5.jpg


  • The obtained turn over number of about 13 illustrates, that methylene blue is used as a reversible redox mediator. During the 200-minute experiment each mediator molecule transports on average 13 electrons from the bacterium to the anode. As this value corresponds to a turnover of 0.065 min-1 the mediator activity of methylene blue could be a limiting factor in regard to the low efficiencies, too. To elucidate this hypothesis, a further investigation of the redox system is necessary, because the corresponding potential differences are essential for the efficient transfer of electrons between the substances used.

  • All in all the calculation of different operation numbers illustrate the general functionality of the Gen3plus MFC. The comparison with literature data for related systems is problematically because mixed cultures are used in most cases, but first achievements highlight the potentials using methods of synthetic biology to optimize the biocatalytic process.




Feasibility study for MFC in sewage and waste treatment

To assess the usability of our MFC regarding potential applications, we searched for a feasibility study and compared it to our results. It shows, that our currently achieved efficiencies have the potential for efficient energy production in real world applications.


The study

Feasibility study for the application of a Microbial Fuel Cell in sewage and waste treatment ([http://www.dbu.de/projekt_26580/_db_1036.html AZ 26580-31])

Funded by the ‘Deutschen Bundesstiftung Umwelt – Osnabrück‘

Reporting period: 16.12.2008 – 31.08.2010

Author:

  • Prof. Dr.-Ing. Michael Sievers1
  • Dr. Ottmar Schläfer1
  • Dipl.-Ing. Hinnerk Bormann1
  • Dipl.-Ing. Michael Niedermeiser1
  • Prof. Dr. Detlef Bahnemann2
  • Dr. Ralf Dillert2
    • 1 Clausthaler Umwelttechnik-Institut GmbH – CUTEC-Institut GmbH
    • 2 Leibniz Universität Hannover


Summary

  • Since the first investigations on mediatorless MFCs in 1999, the maximum power densities increased from 0.05 mW/m2 in 1999 to 2700 mW/m2 in 2008. Therefore, this feasibility study refers to a power density of 2 W/m2.

  • An estimation of the power generation potential shows, that the usage of an MFC could produce around 20 kW for a 10,000 PE (population equivalent) sewage treatment plant. The integration of an MFC would generate an electricity production and saving potential, which provides the opportunity to enable nearly energy self-sufficient sewage treatment plants. This is based on a low cost production with low cost materials of the MFC. Especially electrode and membrane materials have to be cost-saving.


Previous development of the maximal achieved power densities with MFCs

  • Since the first investigations on mediatorless MFCs in 1999, the maximum power densities increased. Figure 3 (Logan, 2008) shows the development of the power density from 0.05 mW/m2 in 1999 to 2700 mW/m2 in 2008.

Figure 3: The development of the power density of the MFC from 1999-2008.

  • Pure chemicals (glucose or glycerol) are much better usable than organic wastewater components. Furthermore, the conductivity of the organic liquid is usually much higher. Consequently, power densities achieved with wastewater tests are lower. On closer examination of the cathode, we can observe a higher power density for air cathodes (wastewater treatment) in comparison to water cathodes (degradation of pure chemicals). Air cathodes are additionally fumigated.


Assessment of the potential for applications

  • The energy content of waste water is about 20 W per population equivalent (PE). Therefore, a 10,000 PE plant could generate a power of 200 kW. Table 2 shows an overview of the electricity production potential for various wastewater treatment plant sizes with an extrapolation for 80 million people (Number of inhabitants of Germany). The energy content of the water is defined by the COD (Chemical oxygen demand). COD is commonly used to indirectly measure the amount of organic compounds in water.

Table 2: Electricity production potential for various wastewater treatment plant sizes.

  • Table 3 summarizes the electricity savings potential for various wastewater treatment plant sizes with an extrapolation for 80 million people (number of inhabitants of Germany).

Table 3: Electricity savings potential for various wastewater treatment plant sizes.

  • In comparison, a fully optimized plant for 100,000 inhabitants has an average power consumption of 285 kW. The integration of an MFC would generate an electricity production potential and electricity savings potential of up to total 246 kW. Thus, the Microbial Fuel Cell provides the opportunity to enable energy self-sufficient sewage treatment plants.


Assessment of our Microbial Fuel Cell

  • With our self-designed and constructed Microbial Fuel Cell we achieved a power density of 231 mW/m2. (Calculation of the power density). In contrast to the assumed power density for the feasibility study, which was 2000 mW/m2, we have still a ten times lower power density. That means the total electricity saving potential would be 25 kW, which shows a reduction for the required energy of 8% for a fully optimized sewage plant for 100,000 inhabitants with an average power consumption of 285 kW.


  • In conclusion, while our MFC has quite some potential for improvements, even now our system might be usable to realize significant energy savings.



References

  • Bastos M, Nilsson SO, Ribeiro da Silva MD, Ribeiro da Silva MA, Wadsö I (1988) Thermodynamic properties of glycerol enthalpies of combustion and vaporization and the heat capacity at 298.15 K. Enthalpies of solution in water at 288.15, 298.15, and 308.15 K. The Journal of Chemical Thermodynamics 20(11): 1353-1359.

  • Gomes JF, Gasparotto LH, Tremiliosi-Filho G (2013) Glycerol electro-oxidation over glassy-carbon-supported Au nanoparticles: direct influence of the carbon support on the electrode catalytic activity. Phys. Chem. Chem. Phys.

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