Microbial Fuel Cell

[deleted-313445]

Hi!
Im trying to figure out what variables I will use for this project; I will have 6 microbial fuel cells so I could either do three different experiments (one control and two experiments) with two tests each, or I could do two experiments (one control and one experiment) with three tests each. A variable I'm considering is adding sugar to see if it would lead to the produce of more electricity--- but I'm wondering how I would go about this?- Just mix in a 1/2 cup or so of sugar into the benthic mud? -Do you have any suggestions for how to go about this?- Or other ideas for variables?- Which of the options for experiments do you think would be preferable; the three variables with less tests or two variables with more tests?
thanks for the help
-margo

[deleted-291762]

Hello!

A wonderful project idea!

One thing that will help you decide what variables to include is to first determine what you want to find out, i.e. what is your hypothesis. It sounds like you want to test how sugars affect the electrical output of the fuel cell. Are you more interested in how the type of sugar (ex. sucrose, mannose, glucose) affects the electrical output? Or are you more interested in how the amount of one particular sugar affects the electrical output? Once you nail down your specific question, we can help you with the variables! Let us know what sparks your interest!

Regards,
Surya

[deleted-313445]

hey there!

So I want to determine if adding a substance to the microbial fuel cell will make it produce more electricity- my first thought was sugar although I'm not 100% sure that sugar would be the best stimulator for the bacteria. Do you think that regular cane sugar would make a good variable? I'd love to hear any other suggestions for bacteria stimulants- i have heard ideas such as vegetable scraps or other organic compounds. If I do three experiments (one control and two with variables) I have been thinking of what to compare such as acidic v basic material, or like you said more sugar v less sugar, I pondered temperature but that would have been difficult to control especially since this project will be in the middle of winter. Do you have any suggestions as to comparisons/variables?

thanks so much

[SciB]

Hi,

I noticed you had no replies to your question about what to use as a fuel cell bacteria stimulant, so I thought i would suggest using a commercial fertilizer. To grow well, bacteria need a carbon source like sugar but they also need a nitrogen source. Nitrogen, or more accurately nitrate, can be supplied by manure, compost, or a commercial fertilizer. The fertilizer you buy at the garden store is easy to use and has a defined amount of nitrate. You could get the kind that dissolves in water and then add various amounts to your fuel cell and measure the effect on electrical output.

One thing I would like to emphasize considering what you said about it being winter and maybe cool inside the house, that bacteria need to be warm to grow and metabolize and hopefully make electrons for your fuel cell. How warm? I don't know what their optimum temperature is but if the place where you have the fuel cells is much lower than 20 C [68 F] you might want to move them to some place warmer.

If you have more questions, let us know.

Good luck!

Sybee

[deleted-313445]

hi,
Our house stays about 69 degrees so it may be a bit on edge but I'm not sure what we could do about that. (a heat lamp could of course be an option but I am not sure my dad would be too keen about that seeing as this project has been a bit more expensive than was expected.)
The variable that a teacher recommended was yeast... What would you say about that? Would just regular store-bought yeast work, the kind used in cooking or would it require a more specific type?

Thanks for the help!!

[SciB]

If you can find a warmer place--near the water heater or furnace--keep your bioelectric cells there. You could put the cells inside a large box with a 15 watt incandescent lamp. That would use only pennies worth of electricity and keep them warm. Put a thermometer inside to monitor the temperature.

The organism that powers this bioelectric cell is a species of bacteria. Yeast would not produce electrons, so no power to light an LED, and it would poison the soil with too much carbon dioxide and eventually ethanol so you would have to start over. Just stick with the conditions as outlined in the project guide and add different types and amounts of carbon (sugars) and nitrogen (nitrate fertilizer). The soil bacteria need moisture, warmth and food and these should be the variables you choose from. You might also want to test mud from several different locations to see which gives the most power.

Keep asking questions--that's why we're here!

Sybee

[deleted-313445]

Hi there,

okay, thanks for the info on the temperature, I think that will be able to work out nicely
I miss remembered what my teacher suggested- I told you yeast instead of yeast-extract. I have done a bit of research on it and it seems like the yeast extract should do a better job than sugar since the bacteria found in mud will be more likely to respond to it. My teacher suggested I use about a 2% volume of the mud for the yeast extract. How does all of this sound to you?

thanks- margo

[SciB]

Hi Margo,

That makes more sense--yeast extract! Yeah, that should work. It's a common ingredient in bacterial growth media.

Can you explain better what you mean by 2%? Will you be adding powdered yeast extract or a solution? I would use a solution so you can add it without disturbing the mud. But, I don't know how much you should add. I would start by adding a relatively small amount and see what affect that has on power output. You can always add more.

I would also test other things as well like sugar solution and liquid fertilizer. The more data you can get from your experiments the better. You don't know what is going to happen, so if you get an unexpected result it helps to have other results to compare it with.

Remember what I said about using different kinds of mud. Try to find some that works well and get your cells going nicely before you start adding test compounds.

Good luck! We'll be here when you have more questions.

Sybee

[deleted-313445]

hey!

thanks that all sound good- I will try to test as much as i can!
I will be using the yeast extract solution instead of the powdered version.
It was in an email that I asked how much to use and they said "about 2% of the liquid/mud. Volume percent." I am hoping you could clarify this but if not I will simply ask again. My thinking was just two percent of the quart but I am also not sure how one would go about finding that about...

thanks!!
Margo

[SciB]

Hi again,

I think you should try to find out how much yeast extract is in the solution that you will use because that concentration is really the important one. You are probably right that the 2% means one-fiftieth of the volume of the mud. So, if you have 32 ounces of mud by volume then you would add about 0.6 oz of yeast extract which would be--if my kitchen measurements are correct--a little more than one tablespoon.

As I said, how much you should add to the mud really depends on how concentrated the yeast extract is. In other words, how much yeast extract was added to what volume of water. In the lab, this would usually be expressed as grams of YE per milliliter, g/mL, so you probably should use metric measurements when doing the calculations.

Remember that YE contains mostly amino acids and peptides and is a nitrogen source. Your mud bacteria still need a carbon source like glucose or sucrose. You can test YE alone, but you should also test YE plus sugar. Here is the recipe for a commonly used medium called Luria broth that is used to grow bacteria such as E coli:
http://cshprotocols.cshlp.org/content/2 ... _only=true

Luria broth contains 5 g of YE per liter which would be 0.5%. But the recipe calls for powdered YE, not a solution. If, for example, you had a 10% solution of YE, how much would you have to add to one liter to be equivalent to 5 g? A 10%, weight to volume solution, has 10 g per 100 mL of water so you would have to add 50 mL of 10% YE to make one liter of Luria broth.

What I am trying to do is make a comparison between how much YE is in a common bacterial growth medium and how much YE you would be adding to the mud if you added 2% of the mud's volume. Once you find out the YE concentration then you can work from that to calculate the amount of YE being added to the mud and see how it compares to the amount in Luria broth.

I hope I haven't confused you with all this math! These are the kinds of calculations scientists have to do every day, so we are used to it. Getting the concentrations of things right is critical and many experiments have failed because someone made a solution wrong or wrote down milligrams when they meant micrograms!

Keep us posted on your progress and don't hesitate to ask any question. We want you to understand why you are doing things a certain way and not just follow a recipe.

Good luck!

Sybee

[deleted-313445]

Hello!

I will need a bit of time to think about all of that^^ but for the most part it all sound good! I really appreciate you helping me out!
For the salt bridge part of the MFC we bought a plastic tubing (still the recommended 1/2 inch width) but I am not sure how long to make them...? I was guessing at around six inches but I am really not sure. Also the tubing is slightly curved, do you think any problems could come from this? I just wanted to double check before I made them.
Thanks so much!
Margo

[SciB]

Hi Margo,

I'm glad you found my info helpful. If there's anything unclear, don't hesitate to ask. I want you to understand what you are doing and why.

I assume that you are building the microbial fuel cell that Scibuddies described here: https://www.sciencebuddies.org/science- ... #procedure

Is that the procedure you are following?

They don't say how long the salt bridge fittings are but I would guess 4-6" is OK. I would build ONE complete fuel cell first and test it to make sure the cell generates power before buying six fittings.

Be careful to follow all the instructions and if you aren't sure about some part of the procedure, send us a quick post and we will get back to your right away.

Good luck!

Sybee

[deleted-313445]

Hey there

We altered the design given in science buddies procedure just a tad to make it cheaper and hopefully easier- I'll outline the differences

-We used tupperware containers in place of acrylic boxes (I looked up a few examples and this seemed fine)
-We used 1/2 inch plastic tubing in lieu of the 1/2 inch compression fittings
-and then in order to connect the tupperware and tubing we are using a sort of tubing that screws into the box and then fits inside of the plastic tubing-I have already put these in place and they seem to work very well! [Do you have an Email that I could send the some pictures of it to? I know it is hard to picture/describe. I tried to add it to this message but it doesn't seem to be working]
For the most part I am following ScienceBuddie's procedure, these are the main exceptions^^

I really wish that I could do as you've suggested and build one fuel cell, test it and see how it goes. However I'm on a time constraint- the science fair itself is on the 27th of February so by then I need to have completed not only my project (which will take thirty days just on its own) but also all of my layouts like my science board/presentation with all of my information, data, etc- you know the drill. So I will need time to process my results and figure out my conclusion and what not. So if I go as planned and begin my experiment on January 3rd, I will have a few weeks still to put together everything.

I made the electrodes this morning and my plan is to make my salt bridges today as well, get the mud sample tomorrow, and finally start the experiment on Sunday.

Thanks for helping me out & sorry for my confusion!

[SciB]

Hi again and thanks for the very clear description of what you are doing. If all the students would take the time to tell us the details of their project it would make it so much easier for us to answer their questions accurately!

I know what you mean about the time constraint. Building six cells is going to take a while. Be sure all the electrode wires are making good contact and the salt bridge connections are not leaking.

Where are you planning to get soil from? Most instructions say you can use garden soil if no chemical fertilizers or pesticides have been used on it. You can buy topsoil at the home store, but I think soil from your yard or the woods would be more likely to have a healthier microbial population. There is also evidence that mud from the bottom of a pond or stream gives the best results in the fuel cell: https://www.google.com/url?sa=t&rct=j&q ... Fg&cad=rja

Let us know how the project is coming and post again if you have any questions. Your feedback on this project is very important to us. The more we hear from students who have tried these projects, the better we can answer the questions of others.

Good luck!

Sybee

[deleted-313445]

hi

So today I go my mud and water from the stream. I also got everything put together and so that part is all done finally

I do however have some questions about the digital multimeter-
I tried to read through science buddies pages about multimeters but it really just confused me even more :/

1-When testing the voltage measurement, I just touch each probe to the resistor correct? (I obviously have never used one before so I'm sorry for all my simple questions...)

2-I know it is supposed to be set to "voltage" and I assume it should be set to 'direct current' but I don't know what level to set it to. I would think that the very smallest would be best but I really can't pretend to know what the range would be.
Here are the options under direct current:
500
200
20
2000m
200m (<this one is my guess)

3-also, there are the two different wires; red (positive) and black (negative) but I don't know which (or if it matters) side of the resistor to touch each probe to. the anode side or the cathode side? When I was just testing them out, switching sides gave me different measurements so...?

4-While I was just messing around/testing them, the numbers on the multimeter's screen changed rapidly between about three different numbers... what should I do/know about this?

thanks for all of your help!

[SciB]

Hi,

Here's my answers:

1. Yes--you want to measure the V across the cell with a resistor connecting them. One thing to make sure of is that you have the resistor connected tightly between the anode and cathode. You are using cables with alligator clips, right? Just make sure that the clips are well attached to the resistor leads. What I do to insure good contact is to hold the jaws of the clip tightly together on the wire and rotate it a little to scrape the teeth on the wire.

2. I know the multimeter instructions can be confusing, but you guessed right--the 200m scale reads in millivolts (mV). One volt equals 1000 mV. So, if you got a reading of 10 mV, that would be 0.010 V. When you calculate the power output of your cell you use the formula P = V^2/R and the voltage has to be in 'volts' not mV. Your results will be in watts, W, but the power of these mud cells is in the microwatt range, uW, so you have to multiply the result by 10^6 in order to convert W to uW.

3. The multimeter probes are red for positive and black for negative. The red should touch the cathode and the black the anode.

4. If the reading jumps around that means something is not making good contact. It could be one of the connections of your wires to the anode or cathode plate but more likely it is intermittent contact between the meter probe and the resistor wire. You need to have a box or some books set up next to the cell so you can support the resistor while you press down hard enough on the wires to make good contact. If you have some extra gator clips you can attach one on the end of each probe so you can clip them onto the wires.

Let me know your power readings from a couple of the resistors. You can get an idea what the readings should be by looking at the graph on the procedure page for a different fuel cell project: https://www.sciencebuddies.org/science- ... #procedure

Good luck!

Sybee

[deleted-313445]

Hello again!
I have just completed my 30 day experiment with this project and I think it went pretty well! [My main problem was that two (out of six) of my fuel cells never produced any electricity but I think a broken circuit is to blame seeing as one was from the control group and one from the experimental- but luckily I used six cells so I can just reject this data.] The measurements on my working fuel cells ranged everywhere from .1 to about 14 which is a pretty wide range so I am not really sure how to compile this data...
I am now working on my research paper and so I wanted to ask some more technical questions if you don't mind:
1) I know that the protons go through the salt-bridge (PEM) into the cathode and that the electrons flow up through the external circuit, but could you explain why/how they separate in this way or what draws them apart?
2) (probably a dumb question...) What happens to the electrons once they go through the external circuit? Similarly, with the protons, once they travel through the salt-bridge to the cathode do they just hang out there or what?
3) Since I took measurements two times a day for 30 days, I have a whole bunch of data- what do you think is the best way to compile this/ what type of graph should I use?
thanks a bunch!
Marg

[SciB]

Hi Marg,

Congratulations on completing the project. The MFC is a challenging gadget to make work properly as you have seen first hand!

To answer your questions, electrons are produced by the bacteria in the anode container and this causes a negative charge to build up. Since the anode is directly connected to the cathode by a wire, the electrons travel through it to the other chamber where there is a relative deficiency of electrons. There they combine with oxygen (O2) from air dissolved in the salt solution and protons (H+) to make water. This depletes the electrons at the cathode so that more can flow over from the anode and continue to produce power. The salt bridge balances the charges between the two chambers.

As to how to plot your data, here is what the procedure suggests (https://www.sciencebuddies.org/science- ... #procedure)

Analyzing Your Data
1. Plot your data on a scatter plot--power vs day. Make three plots--one for each fuel cell.
2. Did the fuel cells produce electricity? Did the fuel cells start producing electricity right away? Did the electricity production ever peak? How did the electricity production vary over one day?

Let us know if you have more questions.

Sybee

[deleted-313445]

hello
Thanks for the answers! Just two more quick questions
-For my project I measured twice-per-day, but for the scatterplot graph you suggested power vs. day so should I average the two measurements and then use it as a single day's measurement? or do something like: day 1 AM *data*, day 1 PM *data*, day 2 AM *data*, day 2 PM *data*, day 3 AM *data*, day 3 PM *data*
-Since two of my MFCs malfunctioned and I am rejecting their data, should I still make graphs for them or is that unecessary?
Sorry, I am not sure if that made any sense ...
Marg

[SciB]

Hi Marg,

You are making perfect sense! From what you said, one MFC out of each set of three produced no V, so just exclude those values. You should mention this in your report, however, and offer an explanation for the malfunction.

So then, take the average of the AM and PM power values for the two good MFCs and plot them on a scatter graph. I don't know what would be the best way to show the points--all together on one graph or separated:

1. Contr - AM and PM
2. Exptal - AM and PM
3. Contr and Exptal - AM
4. Contr and Exptal - PM

It is better for the sake of comparison to have Cont and Exptal on the same graph, but if the points are not well-separated then it might be confusing.

Do you see much difference between the AM and PM values for each pair of MFCs? If the values are very similar then you could explain in your report that you decided to average the readings and then just plot the average for each set on one scatter graph.

Just try the various plots and decide for yourself what conveys the information best.

Let us know how it comes out.

Sybee