Team:Bielefeld-CeBiTec/Results/rMFC/Construction
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<h6>Chronoamperometry - current consumption</h6> | <h6>Chronoamperometry - current consumption</h6> | ||
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+ | <font size="2" style="text-align:left;"><b>Figure 2</b>: Cultivation of the <i>E. coli</i> ΔdcuB::oprF strain in M9 minimal media with 100 µM neutral red added. During the cultivation there was set a potential of -400 mV on the H-cell achieved by the chronoamperometric method.</font> | ||
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Revision as of 14:48, 17 October 2014
Module I - reverse microbial fuel cell (rMFC)
Construction of an electrobiochemical reactor
We planned to design a reactor system that is suitable to investigate the electrochemical behaviour in bioprocesses. That includes the possibility to characterize mediators and different electrode materials on the one hand and the electron uptake into the cells on the other.
During our research we discovered the H-cell reactor that seemed to meet with our needs. (Park et al., 1999)
We approached two different concepts to realize the reactor construction. One of our H-cell reactors was constructed with the possibilities given to us by the facillities of our university. We instructed the glass workshop to modify two glass bottles by adding a glass-flange. Besides that the technical workshop build the lids from stainless steel. This approach had the advantage that we could influenze the design and had to make precise design drawings especially for the connections in the lids.
The second H-cell reactor was a commercially available system by Adams & Chittenden scientific glass. The commercial system had a smaller volume and the benefit of a larger flange diameter. The necessary lids for that system were also custom design by our workshop. In figure 1 you can see both reactors in comparison.
In addition to the H-cell design we thought of an alternative reactor design that meets with the requirements of direct electron transfer. To enable direct electron transfer it is necessary that there is a large electrode surface provided to the microorganisms. Furthermore substrate limitation should be avoided. To meet with these requirements it is favourable to have an reactor that can be continiously driven. Our proposed solution is a flow cell reactor (FCR) which could be driven continiously.
Testing the set up
Our first experiments were carried out with a constant power supply and we measured the voltage input and the current. The set up is shown in figure 2.
It turned out that we could not use the pH-electrode and the pO2-electrode during our cultivations, because they affected the measurement. Especially the pO2-electrode was not suitable in this set up, due to the fact that it is completely made of steel. It turned out that the electrode achieved a grounding of the system which set the lid under electric power. This resulted in a couple of unwanted oxidation processes at the weldseam of the lid. The consequence was to remove both electrodes from the system.
Different electrode materials
We tested different electrode materials for their potential to work in our reactor. We decided to investigate fabric carbon, fabric fleece als platinum electrodes. The different materials are shown in figure 3.
Carbon fabric is made up of individual fibres and has therefore a good stability. Another advantage is that the fibres consist of one piece and therefore has a good electrical conductivity.
The carbon fleece instead is thicker and provides a larger surface for the microorganisms to attach to the electrode material. This advantage goes at expense of stability.
Cultivation - constant voltage
The first experiments in the H-cell reactor were performed under constant direct voltage. These experiments were performed to test the set up. We investigated if E. coli was able to grow in the needed voltage range and if the different mediators influence the cells if a small electric current is applied.
Cyclic voltammetry - mediator characterization
During our experiments we used a Ag/AgCl reference electrode for measuring the working electrode potential. The counter electrode, which completes the cell circuit, was made from platinum wire. Platinum has the advantage that it is an inert conducter.
Parameter | Value |
---|---|
Mediator | Neutral red |
Scan rate [mV-s] | 35 |
Step size [mV] | 1 |
Scan limit E1 [V] | 0.3 |
Scan limit E2 [V] | -0.6 |
Electrode material | Platinum |
Aeriation | Oxygen free by aeriation with nitrogen |
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Parameter | Value |
---|---|
Mediator | Bromphenole blue |
Scan rate [mV-s] | 10 |
Step size [mV] | 1 |
Scan limit E1 [V] | 0.4 |
Scan limit E2 [V] | -0.85 |
Electrode material | Platinum |
Aeriation | Oxygen is present |
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Parameter | Value |
---|---|
Mediator | Neutral red |
Scan rate [mV-s] | 10 |
Step size [mV] | 2 |
Scan limit E1 [V] | 0.5 |
Scan limit E2 [V] | -0.6 |
Electrode material | Platinum |
Aeriation | Oxygen is present |
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Parameter | Value |
---|---|
Mediator | Neutral red |
Scan rate [mV-s] | 20 |
Step size [mV] | 1 |
Scan limit E1 [V] | 0.51 |
Scan limit E2 [V] | -0.8 |
Electrode material | Platinum |
Aeriation | Oxygen is present |
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Parameter | Value |
---|---|
Mediator | Neutral red |
Scan rate [mV-s] | 10 |
Step size [mV] | 1 |
Scan limit E1 [V] | 0.1 |
Scan limit E2 [V] | -0.6 |
Electrode material | Platinum |
Aeriation | Oxygen free by aeriation with nitrogen |
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Parameter | Value |
---|---|
Mediator | Neutral red in M9 minimal media with neutral red |
Scan rate [mV-s] | 10 |
Step size [mV] | 1 |
Scan limit E1 [V] | 0.7 |
Scan limit E2 [V] | -0.6 |
Electrode material | Platinum |
Aeriation | Oxygen present |
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Chronoamperometry - current consumption
Flow Cell
References
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Park, D. H.,Laivenieks, M., Guettler, M. V., Jain, M. K. & Zeikus, J.G. (1999) Microbial utilization of electrically reduced neutral red as the sole electron donor for growth and metabolic production. In: Appl. Environ. Microbiol., 65 (7), pp. 2912 - 2917.