Final Microbial Fuel Cell Report

Description
Microbial Fuel Cells (MFC) work because some of the bacteria (exoelectrogens) found in creek and marine sediment can produce free electrons and these can generate electricity. The microbial activity in my fuel cell continued to be much more significant and interesting than in my spring Winogradsky column. The fuel cell was created using my most active Winogradsky column from last fall. The entire process has been interesting and I would definately do this with a class. Even smaller children enjoy it, as my son, who is in 2nd grade, helped me with the measurements and was able to understand the basic idea that tiny organisms in the mud were creating small amounts of electric current.

Materials and Methods
I used the methods described by Josh McCready and Tess Edmonds at the Geobacter Website: http://www.emunsing.com/portfolio/portfolio_content/44_designLab/MFC_Report.pdf to build my fuel cell with some minor adjustments due to materials availability.*

It is important to note that there are many different configurations and materials employed in constructing an MFC and new methods are being developed all over the world. For the purposes of this class and any use for younger children, I thought it would be best to follow a simple design with the fewest and simplest materials. I therefore followed the idea from the Geobactor site of constructing a sediment MFC, which simply uses sediment as a biomass and bacteria source (anodechamber), the overlying water as a substrate (cathode chamber), and the finer top sediment as a membrane to separate these two ‘chambers’.

Materials used:

• Mud and water originally taken from Bear Creak
• One 24 ounce spaghetti sauce jar
• The anode and cathodes were made with graphite pencils from the art store (the research paper called for carbon paper, but the graphite pencils were cheap and easy to obtain). I used the graphite bricks, as opposed to the thinner pencils.
• Two common metal nuts and bots
• Insulated electrical wire
• Common household sealant
• 1/2 teaspoon of sugar
• 1k-Ohm Metal-Oxide Resistor

We drilled all the way through the graphite and used a nut and bolt to connect the electrical wire. We then coated this area with sealant to help protect against corrosion, this has worked fairly well. Since we had used a nut and bot to connect the wire, we did not use an additional connective epoxy. My MFC did not experience any graphite erosion. The anode section was placed in the sediment and covered at the bottom of the jar. I mixed about a 1/2 teaspoon of sugar into the mud while doing this. The water from the column was added to the jar until it filled the jar to the surface. The Cathode was placed in immediately after. It was made in the same way as the anode.
Results
The MFC has not ever shown a significant voltage, however it has consistently maintained a small voltage since the beginning. By adding sugur or vinager throughout the nine weeks of this experiment, I have seen increased activity on a consistent basis. The most recent results for the voltage are:
4.03.09 0.950 V (immediately after adding vinegar to the MFC)
4.04.09 0.050 V
4.07.09 0.060 V
4.12.09 0.050 V
4.16.09 0.025 V
4.23.09 0.023 V
4.30.09 0.027 V
5.04.09 0.028 V

Conclusion
While there was a slight increase in voltage once the MFC was moved outside and vinager added, my MFC did not display what Josh McCready and Tess Edmonds describe as the results of a "true" fuel cell which include, 1. gradual increased voltage over time as the bacteria populate the electrode, 2. I did not take measurements within any 24 hour period, so I can not varify that the measurements would have oscillated during a 24 hour period as McCready and Edmonds suggest they should (indicating that the microbes go through natural daily cycles of activity), finally, they suggest completely sterilizing the MFC to prove that it will go to zero, validating that the microbes were generating electrical current while alive. I did not do this either.

However, my results due seem to indicate that with further effort, including day and night sampling, regular feeding of the bacteria, and having more than one cell to compare, I may have been able to provide a stronger argument that the fuel cell is an effective generator of electricity. I would also like to attempt to connect it to a small light or toy to prove its effectiveness.

This would be a terrific activity for a class, perhaps creating Winogradsky columns in the first semester and then making them into MFCs in the second semester as a way to complete a unit. I would definately want to havemore MFCs to compare results with and have at least a full three months time to demonstrate the activity with a class.

* The site referenced above is no longer active, but here is a good substitute on the Instructables website: http://www.instructables.com/id/Microbial-Fuel-Cells-A-Way-to-Generate-Clean-Elect/

Final Spring Winogradsky Column Report

Column description
My spring Winogradsky column has left a lot to be desired. There has been very little noticible activity after the cheese turned white, other than a very strong odor coming from the column and forcing me to put it outside. Unlike my previous columns from the fall, this column resulted in few changes in color throughout the ten weeks of the experiment.

Materials and Methods
I used the method described from the Penn State profile: http://www.personal.psu.edu/faculty/j/e/jel5/biofilms/winogradsky.html.

• One column constructed of soil or mud from virtually any source
• Water from the same or a different source
• To these natural components, are added supplemental carbon and sulfur.
• Above the soil is a layer of water and the column is usually covered to retard evaporation.
• The entire column is then illuminated to encourage the growth of phototrophs.

For materials, I used:

• Mud from a backyard puddle
• Puddle water
• Glass vase
• Cut grasses for the carbon source
• Cheese for the sulfer source

Results
Amost immediately the cheese in the middle of the column turned extemely white and has remained so for the entire 10 week experiment. I suggested that these might be some form of fungi - or some form of chemoorganoheterotrophs because they are feeding on organic carbon, light as well as the carbon, and using the carbon for their e- source. I saw no sign of the green or rust colored activity that was so prevalent in my column last semester.

On the surface of the water a thin layer of white biofilm and strong oder began within the first three weeks. Since, the water in the column has overflowed once and the film has turned green with a spiderweb-like subsistance. According to the Microbial World website by Jim Deacon, the layer of biofilm on the surface should be sheathed bacteria.

Conclusion
Considering that there were few other signs of life beyond the cheese fungus, the environment in my column might have been too extreme. I did not take a ph sample, but this might have given me an idea of what the reasons for such little activity were. Possibly the sheathed bacteria were better protected to survive in my tiny extreme environment. For a classroom activity, I liked using a smaller container for myself, but I think that the larger columns would be easier to deal with with children. Also, I would want to have one or more controls available and mud from different environments as well as other carbon and sulfer sources. Possibly I simply did not provide enough cut grass for carbon nutrients.