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Let me know if you need any help building one of your own. My name is Paul Nylund, and my partner on the project was Marcia Rojas if you need to cite this.

Blueprint: http://goo.gl/Z3Nuf

During our testing, we occasionally saw spikes of up to 6 volts while adjusting the apparatus. We were not able to stabilize the output to the extent that we were able to stabilize it to approximately 220 millivolts. I recommend experimenting with the size of the containers and the position of the air pump and electrodes.


Abstract

The goal of the project was to construct a working two-chamber microbial fuel cell with a maximum output of 300 millivolts (mV), or 0.3 volts (V).  A microbial fuel cell, or MFC, is a fuel cell in which the naturally occurring electrochemical processes of anaerobic bacteria breaking down food, are harnessed to generate electricity.

The chosen source of bacteria and organic substance in the cell was sludge retrieved from the bottom of Bluff Creek behind Playa Vista Park in Los Angeles, California. This was chosen as the ideal resource for the microbial fuel cell because it lay in still water, which provides a good environment for anaerobic bacteria growth.


Materials

- 2 1l Plastic Containers
- Cotton rope
- Aluminum mesh
- Paper clips
- Copper wire
- Alligator clips
- Electrical tape
- Glue gun
- Glue sticks
- Aquarium air pump
- Duct tape
- Sludge
- Hand spade
- Bucket
- Water
- Salt
- Small Pot
- Spoon
- Voltmeter
- Drill gun


Procedure

Collect sludge from the bottom of a still creek or pond into a bucket. Such a source will most likely have plenty of anaerobic bacteria.

Drill one hole for copper wire on lids of containers. On one of the two lids, drill one hole for the air pump tube and one small hole for ventilation (this will not be sealed). Drill one hole on one side to both containers for salt bridge.

Prepare the electrodes. Fold aluminum mesh a few times over and bind with large paper clips. Strip ends off of copper wire and attach to both electrodes.

Insert copper wire and air pump tube into drilled holes on lids. Seal with hot glue or caulk.

Prepare the salt bridge. Heat water over stovetop and dissolve in as much salt as possible. Twist a long rope around itself to create a thicker rope. If necessary, cut the   rope to approx. 15 cm. Soak the rope in the salt water. Once damp, wrap the rope in one layer of electrical tape and one of duct tape, but keep the ends exposed.

Insert each end of the salt bridge into the drilled holes on the sides of the containers. Seal with hot glue or caulk and extra tape (as needed).

Fill one container almost to the rim with sludge and the other with water.

Submerge the electrodes into the sludge and water. Close the lids of the containers, and make sure the one over the sludge is airtight.

Anaerobic bacteria should be exposed to as little oxygen as possible.

Attach alligator clips to each loose end of copper wire. Clamp the alligator clips onto the voltmeter probes. Make sure the red probe is attached electrically to the electrode in the water. The black probe should connect to the electrode submerged in the sludge.

Turn on the aquarium air pump.

Turn the dial on the voltmeter to 20 VDC (can also be marked by the symbol,      ) to measure the force of electricity moving through the circuit in terms of volts. Turn the dial to 2000m to measure it in terms of millivolts, a thousandth of a volt, to observe a more accurate reading.

Turn the dial to 10A. This number is the flow of current the microbial fuel cell is generating, measured in amps.

To calculate the rate of transfer energy as one joule per second, also known as one watt, use the formula below.

watts (W) = amps (I) x volts (V)


Results

The results were significantly more successful than anticipated. The microbial fuel cell generated 221 mV at its peak efficiency when measured with a voltmeter and occasionally peaked at 6 V when we messed with the positioning of the electrodes and water pump tube. Something especially interesting occurred when the air pump was unplugged, which stopped extra oxygen from flowing throughout the container. It was observed that the current generated by the cell rapidly  dropped down to a low of 168 mV. The lack of oxygen slowed down the reduction reaction and consequently slowed down the current, as well.


Background

The salt bridge allows for current to flow of hydrogen ions in a circuit. If it did not exist, there would be a pileup of electrons, and the current would stop, rendering the cell useless. The anode of the microbial fuel cell depends on a potential that causes the current to flow, and therefore, the oxidation reaction in its chamber is also dependent on a potential. In this case, the potential element is the cathode in the chamber filled with oxygenated water, because it helps to complete a reduction reaction in that chamber. Oxidation and reduction reactions always have to occur together (called a redox reaction), and in a microbial fuel cell, they are absolutely necessary. Electrons emitted by an oxidation reaction must be accepted by atoms or ions of another substance.

During the first (oxidation) reaction, which takes place in the sludge-filled container on the anode, the bacteria consume glucose for energy and water. They then yield carbon dioxide, positive hydrogen ions, and electrons. The positive hydrogen ions and the electrons are attracted to compounds in the second container and will take part in a reduction reaction. The electrons travel up through the aluminum mesh and copper wire to the cathode in the second container. The positive hydrogen ions make their way across the salt bridge to the second container. This is where the second part of the redox reaction takes place.

During the reduction reaction, the positive hydrogen ions combine with the electrons leftover from the oxidation reaction and oxygen from within the water to yield water. The redox reaction ends here. Therefore, the lifetime of the microbial fuel cell is limited by the lifetime of the bacteria within the sample of sludge.

The salt bridge can also be called a proton exchange membrane, or PEM. It allows for hydrogen protons yielded  by the bacteria to pass through.

The aquarium pump provides extra oxygen to the reaction yielding water.
Because the bacteria are not exposed to oxygen, they produce carbon dioxide, protons, and electrons instead of carbon dioxide and water.


Conclusion

Any organic waste material should be compatible with the microbial fuel cell. As long as there is a good enough balance of bacteria and organic material, it should work. This type of cell is a relatively new invention. The very first idea of it was formed in 1911, and the first design was conceived in 1977. There are still ways to go in terms of further developing the technology, and people involved in related projects are still unsure whether it would ever catch on, given its current state of relative inefficiency. However, like any new development, there is only a matter of time before someone is able to improve on its design. Then, it stands as a viable option for energy generation in waste treatment plants.


Sources

http://www.research.psu.edu/capabilities/documents/MFC_QandA.pdf

http://web.eng.fiu.edu/~licz/2012fallNanomed/Biosensors/Lecture%203-4/saltbridge.pdf

http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Ions-in-Solution-Electrolytes-598.html

http://chem.wisc.edu/deptfiles/genchem/lab/labdocs/modules/echem/echemsalt.htm

https://www.instructables.com/id/Simple-Algae-Home-CO2-Scrubber-Part-III-An-Algae/


----------------------      VOCAL EXPLANATION


<p>this is going to be awesome for our project. We got about .3 volts. Thank you so much.</p>
<p>Hey would you mind emailing me at TreshaunReed@yahoo.com. </p><p>I'm having some difficulty and I hope you can help me with it!</p>
<p>Thank YOU! Awesome work, and great results!</p>
<p>THANK YOU SO MUCH.</p>
<p>I'm doing this project for science fair, and have built the MFC. However, my meter is only showing resistance. I have no idea if I did something wrong, and if I did, I have no idea what I did wrong. Can anyone offer advice on things I should check to make sure it's built correctly? Thanks.</p>
<p>Hi Paul! We just completed our project and were wondering what interevals should we test our volts.</p>
<p>Hi Paul... thanks for your site...its awesome and informative. I have been doing various experiments with MFCs and last year successfully connected a LED using a hacker board. However, this year I wanted to connect a low wattage light bulb but I'm not sure on how to connect it...would I need a capsitor? or do I just connect the bulb directly to my dual chambered MFC using a lightbulb holder with wires? Any information would be helpful. Thank you!</p>
<p>Does it need an air pump or just a hole to expose it to oxygen.</p>
<p>Here is an improved video of my second attempt without oxygen. Its a double fuel cell. I am thinking of using gold plated wire and stainless steel as an electrode. Air from a air pump that splits into three sections to give air to both the bottles will be better.</p>
Hello is it safe to leave my microbial fuel cell plugged in with my aquarium air pump overnight?
Yes it is Probably safe but you may have to do more research. As along as the device doesnot get too wet everything SHOULD be ok.
<p>Yep, everything went fine while the aquarium air pump was plugged in overnight. Thank you so much for replying!</p>
Your idea inspired me to use as my science fair project but am I allowed to keep the aquarium air pump plugged to keep on malting energy overnight? I'm scared it might explode because the energy isn't going anywhere.
<p>Without air exposure the total voltage came to 131-136 mV. Improvements are needed as well as better electrodes.</p>
<p>For the salt bridge does the rope have to be made from cotton or would something like nylon or polyethylene work?</p>
<p>Is an aquarium air pump necessary to receive voltage, or would something like a straw work </p>
<p>Worked great! Except my first was a failure, kept leaking everywhere. I moved the salt bridge to the lid after that, and it worked wonderfully yielding a steady ~240mV! Thank-you for this great instructable; this will be awesome for my science project.</p>
<p>Also, I used yeast in the anode, not mud. </p>
<p>Also, I used yeast in the anode, not mud. </p>
<p>Hi! Really like this, especially because of the video! Just one question, how long did you have to wait for the mfc to start producing voltage?</p>
<p>finally</p>
awesome! nice work :)
<p>Thank you. I am doing my science fair, and this website helped me a lot.</p>
<p>I live in a very cold area. Outside everything is all covered in snow for a few months. Is it OK to collect mud sample in such conditions? Does the freezing temperature kills bacteria in the mud? I tried this experiment with my own MFC, but the voltage is negative (the connections are all correct!). What could be wrong? I'm wondering if the cold/ freezing temperature kills bacteria in the mud/ sludge? If so, where I can get the mud from? Please let me know! Thank you!!</p>
<p>it's ok if you live in a cold area. if the voltage is negative, try reconnect but another side of the multimeter, then the voltage may be positive</p>
<p>it's ok if you live in a cold area. if the voltage is negative, try reconnect but another side of the multimeter, then the voltage may be positive </p>
<p>it's ok if you live in a cold area. if the voltage is negative, try reconnect but another side of the multimeter, then the votage may be positive </p>
<p>did you use tube agar and salt to make salt bridge??</p>
<p>How long did you document the experiment, such as over a period of weeks or? </p>
<p>I Need some advice on how to attach the aluminum mesh to the copper wire, can i attach it using alligator clips?</p><p>Also can i add salt in the water in one chamber to help the salt bridge?</p><p>Thank You, Sarvesh </p><p>Sarveshrbabu@yahoo.com</p>
<p>Correction it can hold 4 L but I only put in 1000 ml or 1L</p>
<p>I have not shown the air pump but it is there.</p>
<p>I have just made a 4 L glass Pyrex bowl with a lid. The lid has holes that place two electrodes copper strapping and stainless steel. Another hole is designed to pump oxygen into the solution. Finally a magnetic stirrer and heater is used. I only use the stirrer for low stirring. </p>
<p>Half a day latter and little oxygen exposure the current went from 12 uA to approx 600 uA.</p>
<p>I don't know but I think that salt MAY effect the outcome. The salt solution is a bonus so only one type of bacteria (for my project will grow). The salt must be measured with probes before adding the bacteria!! Then you can compare the readings. This is a salt/bacteria bio battery.</p>
<p>I know for a fact that Lactobacillus r can tolerate up to 20%. This is from my memory of my project.</p>
<p>This includes using a graduated flask 100 ml and weighing out 10 grams of salt and 5 g of glucose.</p>
<p>I have just ordered a good air pump for 25 dollars instead of 60 dollars Canadian. It will be used to pump air into the container. Also high salt levels will prevent growth of unwanted bacteria Bacillus Lentamorpus. The concentration of salt is 10 grams sodium chloride per 100 ml of tap water. The Lactobacillus bacteria can tolerate high concentrations of salt. This is perfect!!!</p>
<p>Ooops 12 uW.</p>
<p>Here is a very simple bacteria culture. it consists of 5 million cultures of L. retuni. </p><p>This is a simple bioreactor with air coming from a fan. The voltage after 1 day was 0.778 V and 0.016 mA.</p><p>Total power. 12 uA! I know not very much but still it proves your theries. </p>
<p>Hey would this work with lactobacillus bacteria if they react with sugars to produce weak acids? I now have access with several cultures at home of non toxic bacteria like Lactobacillus reuteni, Bacillus Lentamorphis.</p>
<p>I am doing a microbial fuel cell for my science project, the cotton rope salt bridge does it need to be attached immediately or can it be attached to the MFC around 24 hours or is that too late</p><p> Late?</p>
I have already made the thing. Power output is .3 volts . Can you please tell me how to light a bulb or do any &quot;Action&quot; with the electricity used other than displaying the output in the multimeter?
<p>Approximately how much would this project cost?</p>
Is there ny other options other than sludge
<p>Great project guys! I was trying to do your experiment for my class and I was wondering, Did you use an specific type of aquarium air pump?</p>
<p>How thick is the copper wire used?</p>
<p>could you use a bigger containment for the sludge thing, with plants and stuff to recover bacterias continously?</p>
<p>Try it!</p>

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