Picture of Make a Microbial Fuel Cell (MFC) - Part II
This instructable provides detailed directions for building your own microbial fuel cell using Jello, Saltwater and Septic Tank treatment. It's based on the information provided in Make a Microbial Fuel Cell (MFC) - Part 1

This is a true fuel cell in that both the anaerobic and electrolyte media are replaceable and the salt bridge may be serviced as needed. The fuel cell consumes organic material and produces electricity and methane ( or more properly biogas include CO2 and other gasses ). These are captured in a methane store for further processing....Okay, it's a balloon and I have no idea what you should do with the biogas except be careful and experiment with it.

We'll be using a traditional two cell design with a gelatin/salt bridge. Most commonly agar is used but we'll be trying both traditional unflavored gelatin as well as hide glue. Yes, you can actually use Jello brand flavored gelatin and I would be very interested in your results.

I also intend to experiment with gelatinous nutrient medium in the anode chamber. It seems to me a gel based replaceable anode would be a significant enhancement to the utility of this technology.

The device has two relatively small chambers (approximately 100 mL). In theory microbe population densities are primarily a function of nutrients and not space and we should be able to obtain (more or less) the same charge out of a 100 mL cell as we would from a 1L cell with the same population.

Now let's take a look at the materials we'll be using.
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jinfante116 days ago

What will i do if i want to widen the voltage output.. Thanks for the answer.. :D

ThrovinL7 months ago

There is a similar experiment on Sciencebuddies that uses a 220 Ohm resistor when measuring the output voltage of the microbial fuel cell. In many of these pictures and many other experiments online, I see that the user does not use a resistor to measure the voltage. When I do not use a resistor to measure the voltage, I read around 0.3 millivolts. However, when I connect the ends of the voltmeter to the wires directly, I read around 150 millivolts (this is after an hour or so). Do you know if the resistors are necessary to read the voltage?

egbertfitzwilly (author)  ThrovinL4 months ago

It depends on whether you are doing science or actual work. Without a resistor ( or load of some sort ) across the circuit you get the actual output voltage which is what one measures in, say, a science fair project. Once a load is applied (which represents actual work) you are measuring the current, not the output voltage.

ahirdstudent8 months ago
How big a system could you make with this process?
Could you actually make a sceptic tank into a power cell, say on a rural property that has no access to mains power?
And if so would the generation be more efficient or productive?
egbertfitzwilly (author)  ahirdstudent8 months ago

Yes, you could. It would require some modifications. A septic tank would be a single model more similar to some of my other projects. The tank would have to be drained and cleaned so that carbon paint could be applied to use as electrodes. There would need to be air flow across the top of the tank so a methane capture system of some sort would be required which could be used supplement LNG in a generator. Energy output is a function of water volume ( primarily ). However its always going to be trickle charge level current, not direct tap generator style so its potentially valuable as a supplemental source. Possibly stand alone for 12V batteries or to supplement a solar or wind system.

Cool thanx for that.

How would it work, if you tried to adapt a biogas digester to also produce current. Could that work as well, producing some charge as well as methane production? Or does the process of a digester make a power cell adaptation too complicated to be feasible?
egbertfitzwilly (author)  ahirdstudent7 months ago

if you can figure out how to tap the digester tank in a way similar to the one outlined above you should be able to get some current out.

cjthedad3 years ago
I was going to purchase some Nafion and found it in three different thickness what is the corelation of effectiveness to thickness
egbertfitzwilly (author)  cjthedad3 years ago
I have absolutely no idea.I've never used a Nafion membrane, my areas of research use electron rather than proton bridges.

Hi, please tell me more about the electron bridge theory? Would that cause an MFC to run backwards? I may have accidentally made an electron bridge.

(MFC-Microbial Fuel Cell)

egbertfitzwilly (author)  TimW68 months ago

I'm not sure what you mean about the electron bridge theory. An electron bridge is something that allows electrons (current) to flow. I'm not sure how one would accidentally make an electron bridge. If the current is running backwards its more likely you've reversed the leads on your output.

adinoffi1 year ago

I am student in Nigeria intending to perform this protocol. please how can i get some these materials over to me in Nigeria... Pleas help me

I am a student that will be conducting this protocol and was hoping you would tell me what type of carbon brush you used. Each carbon brush has a different size,etc. So if you can tell me where you brought yours, I'd appreciate it.
egbertfitzwilly (author)  ehernandez261 year ago

Sorry it took so long to reply. I got these at my local Ace hardware store. They had quite a selection so I picked the one with the largest surface area that would fit inside the apparatus.

I am a student that will be conducting this protocol and was hoping you would tell me what type of carbon brush you used. Each carbon brush has a different size,etc. So if you can tell me where you brought yours, I'd appreciate it.
bobtannica6 years ago
Fascinating 'able you have here. Can I suggest a few more pictures re the charging and operating section? Could these be hooked to others for more power? (in series or parallel?) Are there temperature parameters? (Min/Max) Approximately how long will this last overall, not just between "feedings". Really interesting and thought provoking. Thanks for your effort and sharing!
egbertfitzwilly (author)  bobtannica6 years ago
Thank you for your kind words. This is alpha rollout, the charging was primitive to say the least. I'm very interested in looking into this more, particularly energy which might be released during fermentation as well. The nutrient medium is pretty ad-hoc, I'm working on a formalization. Optimizing the nutrient/species/feedstock mix is left as an excercise for the reader... Lifetime borders on infinite. Like a septic tank the MFC must be cleaned of sludge (exhausted biomass) periodically (probably annually) but if well fed should continue along their merry way as they have for the last few hundred thousand years. I'm not sure what the optimum range is, its septic tank treatment so it's going to be pretty broad. I wouldn't leave it in a parked car with the windows rolled up in Death Valley or the Arctic circle for extended periods. Multiple cells can be arranged in series or in parallel to increase voltage/current. I asked Dr. Logan of Penn State about this, he said that multiple cells could be put into a single septic tank with separate cathode assemblies ( a closed pipe with a salt bridge at one end and a vented aeration chamber at the other ). He would recommend a Nafion bridge and suggest using a catalyst such as Platinum or Cobalt. If you google platinum coated wire you'll find scitoys has a 1 foot section of platinum coated nickel wire for $14.
I guess my only concern with using nafion is sourced at the same place as my "affection" for the gelatin salt bridge that you concocted. It is readily available to the common man, such as myself. I certainly applaud any and all efforts at scaling this up and making it usable for the general population, however, I love the instructability of your alpha. Thanks again.
egbertfitzwilly (author)  bobtannica6 years ago
I agree about the Nafion. This is also the reason i published the "Easy Carbon Electrode" 'ible. The bridge as constructed as too deep. I tested another bridge in a bowl of water and it seems to be holding up fairly well, but then it doesn't have microbes eating away at it. More experimentation needs to be done to determine the minimum mechanically stable depth. Interestingly enough the bridge swells in water. I think hide glue is more promising, if one can find it. That's unrefined gelatin and more stable at room temperature. It's available cheaply on the net (actually so is Nafion) although, as I said, the gelatin is doing fine. Make sure you get the flakes that need to be melted and not the liquid type. I think there's a great deal of electrical loss in the current design. I'm working on two revisions. Dr. Logan is very, very big on single cell designs with an exposed electrode. So I've got a consolidated two cell 'tee' design with a smaller cathode chamber and a single chamber design with an exposed cathode. I'm also experimenting with using silk screen material. Soak it in salt slurry and allow it to evaporate. The crystals should form on the silk screen and a few layers should form a stable, highly conductive salt bridge. This is a variation of the sponge design I used for aluminum air batteries.
FYI, hide glue can be found at any reasonably stocked woodworker's supply store
egbertfitzwilly (author)  Stickboy752 years ago
Not, as it turns out, in the SF Bay Area. However it is amusing to see the look of horror on the clerks face when one inquires about it. One was a PETA supporter who didn't know where glue came from and quit the job....
Seems that hide glue can be easily made by simmering shavings/cuttings from animal hide,fish bladders etc. and straining the broth afterwards. A search on google reveals many interesting sites.
egbertfitzwilly (author)  bobtannica6 years ago
This is an example of Dry Hide Glue I pulled at random off the net as an example of what to look for.
Slicerr22 years ago
would nutrient agar work i have some extra from petri dishes i was making
Could you run the biogas through the algae CO2 scrubber?
egbertfitzwilly (author)  colinroberts6 years ago
Indeed, you have stumbled onto the subject of my next instructable. Ideally the cycle works from algae->MFC->biogas->methane->generator->algae. The carbonated waste water from the MFC is used to provide supplemental CO2 for the primary algae generators while the biogas and generator exhaust is scrubbed by the algae feeder reactor. The exhausted sludge from the MFC is used as fertilizer or biomass for carbonization.
Great Job brother ... I have been studying this stuff for a few weeks now wondering if someone has done this with a septic tank .... I have not tested my unprofessional design as if it would work :) however my idea came from a candy wrapper that was stuck to my hand because it was magnetically charged ... so the reason the wrapper was so important was because I was trying to think of how to collect ions instead of producing them in a second solution ... that was the only way I could incorporate the septic tank without a second tank for the ions to transfer from ... my thought was that if i could increase or control the amount of ions then bottlenecking in the current would not occur. Peace Brother. Some day I hope you visit our project in Niagara Falls, Ontario. "Sustainable Christian Ministry"
Been thinking about this septic tank coating problem. if it was electrically grounded you could use a static generator (i.e. vann de graff or the like) to adhere carbon to the walls or even aluminium foil if that works better.
essentially powder coating.
egbertfitzwilly (author)  pleng13 years ago
My proposal for a septic tank solution is in the process of being tested in a 5 gallon bucket but I will share it with you. It derives from this design:


Which is also one of mine.

A septic tank requires what is called a single cell design, that is a cell which is deep enough to provide an anaerobic area ( oxygen free) and allows for oxygen to be absorbed from the air near the surface.

A septic tank is perfectly suited to this requirement. First the tank is generally sealed. The liquid media within has a broad surface area which allows more oxygen to be absorbed. Since gas uptake from air only penetrates about 6 cm the lower area provides an anaerobic chamber. There is plenty of food and bacterial activity here which can be trapped.

The challenge of a septic design is in the electrodes. For this I propose two variants on a novel solution. In the commercial world there are many products design to control electro-magnetic radiation in laboratory and development areas. Among these products are various paints which contain carbon. This is used to paint the walls and ceilings to capture stray EMF.

Do not immediately drain your septic tank, try this with a 5 gallon plastic bucket first.

This paint can be used to provide an electrode surface. The tank must be drained and cleaned. Paint the bottom and a foot or so up the side with carbon paint. Use a standard "grounding plate" from the same source to tap the carbon and run a lead out of the tank.

Paint the upper portion of the walls similarly. Make sure to go a foot or so below the low water mark of the tank. Attach a grounding plate to this section and run that lead out of the tank.

Refill the tank and resume use. Once bacterial activity begins in earnest power should begin emitting from the leads. This should provide sufficient energy to continuously trickle charge a series of batteries for use in specific applications.

From the same sources ( I use lessemf.com, I am not affiliated with them but have had good experience with their products ) one can obtain conductive cloth made from vapor deposition silver over nylon. This can be floated on the surface and may increase power output. That's the point of the current experiment cycle.

Also if one can keep a slight air flow over the surface which does not disturb the water power output will increase from the additional oxygen which is made available.
How would you produce more water in a microbial fuel cell and which catholyte is suitable for that? Thanks!
egbertfitzwilly (author)  kowusu-boateng3 years ago
I'm not sure I understand your question, water is not a byproduct of this fuel cell.
hello egbertfitzwilly......
I m making a microbial fuel cell in which i am using a sulfides as a substrate.. and aerobic bacterial cultures. i made a two nylone made chambers with salt bridge. Now i am about to start my work and my guide told me to staderdize a fuel cell,,, so i am not getting how to standerdize a fuel cell with a use of sulfides as a subsrate. i need a help with every type of actions which carry out a good work. it will be a great help of you if you guide me as any......
proball9593 years ago
Could you please tell me the length of the connector that the salt bridge is made in. The connector I bought actually was 3 yards long so I need to cut it down to the correct size.
egbertfitzwilly (author)  proball9593 years ago
As I recall mine was 2-3 inches long.
Does the knox gelatin in the salt bridge not melt after some time?
egbertfitzwilly (author)  proball9593 years ago
The salt bridge will break down with most materials. This is a test bed, it is not intended for sustained use.

You might try hide glue ( similar to this http://www.bonanza.com/listings/Dry-Hide-Glue-3-Ounces/21111474 ) which should have a much greater structural integrity and is produced by the same process that makes gelatin.
Electricity from wastewater! Amazing! I would like to try this in my school here in Ghana. The bacteria used, where can you get them? We have a lagoon filled with organic matter, good source? And also this the prepared culture really necessary? What can you use as the proton exchange membrane and electrodes, I've seen some MFCs that use carbon cloth. Thanks
egbertfitzwilly (author)  kowusu-boateng4 years ago
Thank you for your kind words.

Yes the material from the bottom of the lagoon can be used although if you have access to a septic tank scheduled to be cleaned that would be very good as well. Carbon cloth can be used but there are other designs better suited to that.

This doesn't use proton exchange, it uses ion exchange with a simple salt bridge with a gelatin medium. The gelatin could readily be replaced by animal hide glue rendered from local sources. Here's a wikipedia link with more information:
http://en.wikipedia.org/wiki/Animal Hide_glue

Using the hide glue as a medium in the salt bridge should provide a significant improvement in stability and life of the cell.

This could be scaled up using two 50 gallon plastic drums and a 6 inch section of PVC pipe to construct the salt bridge between them. I'm not sure metal drums would work well and they would have to be isolated from the ground ( sitting on a table ) and from each other ( except for the salt bridge ).

Some very advanced carbon electrodes could be made using corn or potato plastic. Mix in about 20% carbon ( very finely ground coal ) and you will have some very durable and extremely interesting electrodes.

You could also try steel wool, carbon is not strictly required. Its used in experiments to eliminate false readings from metal creating an electrochemical reaction.

Also it should be possible to aerate the cathode with a small windmill rather than an electric pump. If the windmill pumps water and allows it to fall back down over an inclined plane or slope it should pick up sufficient oxygen to fuel the cell.

Hello again,
I'd like to know if you set up actually produces current that can power a light bulb or you'd have to use a mediator. And how can you adjust your set up to one for large scale water treatment. Thanks for the help
egbertfitzwilly (author)  kowusu-boateng3 years ago
Yes, the power can be directly consumed by anything that will take DC, it should also function reasonably well as a trickle charger for rechargeable batteries. Obviously you'd need a cell ( or possibly multiple cells in series ) to get power for a 1V or more light.

I've been experminenting with larger scale designs. There are two that I've focused in on, both use carbon paint as the electrode. In design the bottom of a tank ( say a septic tank ) is painted with carbon paint, a separate band of paint is applied around the top at the surface area of the media. If the tank is filled with waste water I believe that the basic design will produce measurable output.

In a variation on this I use carbon paint on the bottom and a floating piece of conductive cloth on the top.

The big questions is oxygen uptake at the surface and its affect on the output. I suspect the floating conductive cloth will be more effective but there may need to be fresh air circulated across the top the media to get optimal performance.

The tank must be deep enough to ensure that the anaerobic bacteria at work on the the waste remain undisturbed.

I was able to get carbon paint and conductive cloth from a company called lessEMF.

It may be possible to make carbon paint locally by mixing carbon with a dry acrylic paint before mixing. I have not experimented with that.

I believe you could also use the carbon cloth that is used in making fiberglass as the electrode but again I have not experimented with that.

Contact me privately and we can discuss working together in more detail.
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