Introduction: MFC: Sustainable Energy Source

Picture of MFC: Sustainable Energy Source

Have you ever thought about microbes generating electricity? Well with the proper organic compounds a
microbe can convert chemical energy into electrical energy. This is referred to as a microbial fuel cell (MFC) which breaks down organic substances to produce electrical energy without emitting carbon dioxide into the environment. Since organic waste can be converted into energy, human waste can be used as a potential energy source producing approximately 34 billion kWh of energy each year. Microbial fuel cells can be fueled by organic compounds in the sediment as well allowing it to create electricity constantly without recharging. MFC is a great alternative fuel because it generates sustainable energy and decreases production costs

Step 1: Components of MFC

Picture of Components of MFC

A MFC consists of anodic and cathodic chambers each with an electrode inside. The chambers can either be separated by a proton permeable membrane or have a salt bridge for the transportation of ions from the anode to the cathode chamber. Microbe substrates are oxidized anaerobically in the anode chamber creating both electrons and protons. The electrons flow from the anode to the cathode via electrical circuit to generate electricity. Some bacteria may require a mediator to be present to transport electrons from microbial cell to anode because the microbe is incapable of releasing electrons directly to anode. Electrons and protons bind in the cathode to lessen the terminal electron acceptor by separating the microbe from it physically. The protons bind to the oxygen to produce water. The terminal electron acceptor used must be rid of in order to steal electrons for electrical purposes. The power production depends on the concentration of the terminal electron acceptor.

Step 2: Materials

Picture of Materials

o 2 Styrofoam cups- anodic and cathodic chamber

o 2 straws filled with agar- salt bridges

o 2 graphite rods- electrodes

o 10 grams of yogurt- microbe

o 450 mL of dirty pond water- fuel source

o 450 mL of 0.1 M sodium phosphate buffer
(pH 5.8)- maintain pH of microbial fuel cell

o Methylene blue chloride- mediator

o Potassium ferricyanide- terminal
electron acceptor

o Beaker

o Scale

o Pipette

o Erlenmeyer flask

o Tape

o Saran wrap

o Silicon

o Tray

o pH strips

o Deionized (DI) water

o Agarose powder

o Salt

o Red and black wire

o Voltage meter

Step 3: Method

Picture of Method

Take a straw and twist it into both cups (one at a time) to make the holes where the salt bridges will go (2 holes per cup). Cut the straw in half equaling both salt bridges.

Agar solution

Mix the ingredients below in a flask and boil in microwave until completely dissolved to make the agar solution to fill the straws.

o 250 mL deionized water

o 2 grams agarose powder

o 15 grams of salt

Saran wrap and tape one end on both straws so that when pouring agar into the straws it will not come out other end. Tape the straws to the inside of a beaker so they are standing straight up. Use pipette to pour agar into straws and allow solidifying. Takes approximately 20 minutes for agar to become solid.
Put agar filled straws into the holes on the cups and use silicon to seal the straws in place. Allow 10 minutes for silicon to completely dry and seal.

Phosphate buffer

When determining what pH to make the sodium phosphate buffer the pH of the yogurt was taken into account.

o Mix a sample of yogurt with DI water and insert pH strip to obtain the pH which was 5.8.

o Mix 7.9 mL Na2HPO4 + 92.1 mL NaH2PO4 + 900 mL of DI water to make 1 L of sodium phosphate buffer with the pH of 5.8.
Mix 10 grams of yogurt and 450 mL of dirty pond water in the left (anodic) chamber. Pour 450 mL of sodium phosphate buffer into the right (cathodic) chamber.
Attach the red wire to one of the electrodes and insert the electrode into the cathodic chamber. Do the same with
the black wire and the other electrode except insert it into the anodic chamber. Put MFC in tray in case of leakage. Plug both wires into the voltage meter and start collecting data (24 hour run).
Add 5 drops of potassium ferricyanide to the cathodic chamber after the initial run of 24 hours to observe if voltage will increase.
Add 3 drops of methylene blue chloride to the anodic chamber after the second 24 hour run to observe if the voltage will increase even more.

Step 4: Data

Picture of Data

Run #1

The microbial fuel cell was set up to run three test trials each time collecting voltages with different ingredients
incorporated. The voltages were recorded from the voltage meter for the beginning, middle, and end hours of the run. The first run was with the yogurt and pond water mixture in the anodic chamber and the phosphate buffer in the cathodic chamber for which voltages were collected for 24 hours. The highest voltage of 0.061 V was obtained after 8 hours of run with the lowest voltage of 0.021 V after 22 hours and 25 minutes.

Run #2

The second run with potassium ferricyanide incorporated into the MFC cathode chamber ran for a 24 hour period as well. The addition of potassium ferricyanide resulted in the voltages steadily increasing over time and start to decrease within last hour of run. The highest voltage obtained was 0.143 V after 23 hours and 45 minutes, more than doubling the highest voltage from the initial run. 0.037 V was recorded after 5 minutes of second run being the lowest voltage for that run.

Run #3

The final run incorporated methylene blue chloride into the anode chamber, noting
that potassium ferricyanide was not taken away. This run was recorded over a 16 hour time period instead of 24 hours due to sharing voltage meters with other microbiologists. This run showed an instant increase in voltage after 10 minutes with a voltage of 0.173 V and stayed constant throughout the 16 hours ending with the highest
voltage of 0.179 V.

Granted if allowed to run for 24 hours like the other two trials the voltage possibly would have started to decrease towards the end hours.

Step 5: Conclusion

Microbial fuel cells are great alternative fuel sources to ensure a sustainable future for the world because they are ecofriendly and need little to no maintenance, reducing production costs. They emit absolutely no carbon dioxide into the environment resulting in less pollution. MFCs are not just limited to generating electricity but can also produce hydrogen as a renewable source, treat wastewater by turning it into reclaimed water, and acting as a BOD sensor to measure organic pollution. While the microbial fuel cell is treating wastewater it can also generate electricity doing more than one job at once. The efficiency of MFCs can be improved by adjusting numerous components utilized. The type of microbe used matters because they have different respiration requirements, the fuel source needs to match the nutritional requirement of the microbe, and how the MFC is arranged are just a few things that determines how well the MFC will generate power. It is just amazing how microbial fuel cells can use toxic matters to produce power while breaking the matter down into nontoxic substances. Once they world comes to term with using microbial fuel cells as an widely used fuel source the better the environment and public health will be.

Comments

JyotismanR (author)2015-03-28

What is the current produced by these cells??? Can you please tell me...

tytower (author)2014-12-16

You say "The electrons flow from the anode to the cathode via electrical circuit to generate electricity."

This is strange . Electrons normally flow from the negative-cathode to the positive -anode terminals. Do you perhaps have this wrong ? Or am I not understanding ?

jasrenee (author)tytower2014-12-16

Actually the anode is the negative terminal and cathode is positive terminal so you are right electron flow from negative to positive.

tytower (author)jasrenee2014-12-16

en.wikipedia.org/wiki/Anode

tytower (author)tytower2014-12-18

I suggest you make some adjustments in the write up then you have it wrong !

anthonyo2 (author)tytower2014-12-31

I think that the issue here is that the term anode has different
meanings depending on the context (unfortunately for us).The terms used for microbial fuel cells are
the same terms used for galvanic (voltaic) cells since they use redox reactions
to generate electricity.A distinction is that in the context of the
MFC, the electrons are flowing into
the device at the anode.

Here is a link to UC Davis’ chemwiki, which explains voltaic
cells and uses the anode/cathode terminology in the same manner that it is being
used in this instructable:

http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Voltaic_Cells

Here are a couple of links to some peer-reviewed literature,
so you can see the terminology usage for microbial fuel cells:

http://132.235.17.4/Paper-gu/MFCreview.pdf

http://nopr.niscair.res.in/bitstream/123456789/10294/1/JSIR%2069%2810%29%20727-731.pdf?utm_source=The_Journal_Database&trk=right_banner&id=1401393248&ref=083a50db4ac9ba7073d816c1ee783c22

http://www.microbemagazine.org/index.php?option=com_content&view=article&id=307:microbial-fuel-cells-plug-in-and-power-on-microbiology&catid=132&Itemid=305

tytower (author)anthonyo22014-12-31

Thank you anthonyo2 . It makes more sense now . This is the production or generation of electrons being discussed .On a galvanic cell they would build up on the cathode plates eventually stopping the reaction . Thats interesting The salt bridge allows electrons to flow back the normal way Cathode to Anode. so I guess there would be a way to measure that flow also.

Importantly though without it there is no circuit and no electrons flow.

So now my question is ,can electricity be harvested from the anode/cathode bridge and also from the salt bridge.? Is there any way to do this? I guess they are the same electrons going through both lines

tytower (author)tytower2014-12-31

And I would suspect the voltage pressure would be the same on both lines so no extra useable current could be extracted

forge tech (author)2014-12-22

came here thinking MFC meant microfusion cell. too much fallout

gmendez3 (author)2014-12-16

Great instructable, im just worry that I could mess up the experiment by using the wrong amount of chemicals, but I will love to try ift out....

brianchadorourke (author)2014-12-14

This is so cool. Scale this up and power your house. LEDs!!

russ_hensel (author)2014-12-14

Nice.

Could you focus a bit more on the Energy produced. It should not be measured either in watts ( power ) or volts ( electric potential ) ?

One choice is voltage * current * time ( in metric most commonly the watt second or joule )

rsinton (author)2014-12-14

Beautiful Instructable! I've often wondered about the feasibility of using microbes at home for recycling waste and generating energy! I wonder which species of Lactobacillus you ended up with from your yogurt and if other yogurts/inoculum/species offer more or less efficiency. It's also possible that you ended up with multiple species of bacteria from your yogurt. Great job!

collins1470 (author)2014-12-13

Very well done!

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