Make a Microbial Fuel Cell (MFC) - Part III

This 5 gallon single chamber microbial fuel cell uses inexpensive conductive cloth to provide a silver catalyst and a styrofoam permeable membrane.

Operation of a single chamber MFC is complicated by oxygen poisoning resulting from the conflicting requirements of the anaerobic population and the cathode requirement for dissolved O2. This design attempts to limit oxygen poisoning by using a brush type carbon electrode combined conventional carbon paper to provide a gas barrier without limiting free flow of the microbial medium.

The use of styrofoam as the permeable membrane is novel as far as I can tell.

Conductive cloth is used to provide an inexpensive silver catalyst to promote oxidation at the cathode. We use silver plated conductive cloth from lesseremf but any silver plated material should do. The use of silver as a catalyst is based on the research done for the air cathode in an aluminum air battery and is experimental in an MFC.


As you can see from the picture I got about 90 mV across the open circuit after charging and assembling the cell. The extraction of power from an MFC scales directly in proportion to two things, population density and surface area of the electrode surface at the cathode and anode.
Power will continue to rise as the population density increases.

Step 1 Bill of Materials

This is a simple bill of materials and assembly. Because we are building a single chamber MFC we won't need to create a salt bridge or anything like that.

1 5 gallon plastic pail with lid - I got my mine at Home Depot on sale for $2.97 plus the lid
8 in styrofoam disc - Cut out of packing material or I'm using one I got at Michael's
Use loose styrofoam if you can get it. You want air to pass easily through
Anaerobic Microbial Culture - I'm using "Microbe Lift" brand Septic Tank and Cesspool Treatment
Yeast should also work
1 Package of large aquarium charcoal filter pads. I'm using Fluval brand 4 PLUS filters
Silver coated conductive cloth - http://www.lessemf.com/fabric.html I'm using the "Stretchy silver coated sheer nylon weave". This is used as a catalyst to facilitate oxyidation at the air cathode. It also as the electron collection grid.
A couple of wire leads with clips or some way to attach them to the carbon pads.
Two sheets of carbon paper. This is used to get good mechanical connectivity between the pads.

Comments

[Dr Qui]

Please don't take this question the wrong way, I'm not trying to disprove the concept just curious.

Is it possible to power any electronics as is or would you need bigger or more of them?

Is there a large scale application?

[egbertfitzwilly]

First let me say I'm not really a scientist I just play one on Instructables...You might also like my Jello and Yeast project. Yes, this technology can produce production levels of power. My next generation cell will be a significant improvement over this and well suited to septic tank or municipal waste storage tanks. My personal target application is the 66% of the world who have no electricity at all. Scalability seems to be double vectored,multiple cells in series or larger quantities of media. The leading researcher in the field is Logan at Penn State and Hui up at Oregon State has done some fascinating work. Both have published in the Journal of Power Sources Additional information as well as links to other researchers in the field can be found at microbialfuelcell.org.

[Dr Qui]

I'm kinda baffled by it.

Does the yeast culture feeding on the paper and sugar from the soda make an electrolyte type substance that powers the cell?

Would it be more efficient at the equator than saw Canada or Ireland?

You are indeed a scientist, you work is pure science, much cooler than anything they ever showed us at school.

The best science and technology comes from men in sheds who often make groundbreaking discoveries.

[egbertfitzwilly]

Thank you for these kind words. What forms the electrolyte has been discussed in some detail. I'm of the opinion that the sugar in Jello serves a dual role as electrolyte and feed with the jello acting as an agar like bridge. I don't know that the carbon paper decomposes fast enough to provide nitrogen to the yeast, its possible that supplemental nitrogen of some form might increase the yield. The barbon paper will, of course, eventually decompose leaving no trace of its existance. Output will also be affected by the environment. The happier the yeast are the higher the output. I noticed that power dropped overnight and resumed in the morning, this correlates nicely with the ambient temperature.

[egbertfitzwilly]

Voltage dropped significantly overnight the first night. It varies quite a bit during the day but is steadily rising. I have no idea how long it will take a container of this size to reach peak output. At the moment I'm seeing a steady 60 mV and rising.

[CoolKoon]

How about the current? And since many months have passed since this assembly, how much energy have you managed to extract from it (Wh or something)?

[egbertfitzwilly]

This device was disassembled long ago. All of these devices are experimental in nature and rarely survive more than a few weeks. Overall my results from this design were disappointing and did not compare well with the two chamber model.

I believe the 5 gallon pail ( and larger tanks ) are best suited for a single cell approach where chamber "seperation" into aerobic and anaerobic portions is controlled primarily by depth.

[CoolKoon]

Yeah, I'm even kinda surprised you've managed to separate the two processes, as that's kinda hard to do with off-the-shelf materials. This reminds me of the process of making sour cabbage (a local delicacy I guess), where you shred the cabbage, but it into a barrel/vat, add some salty water, cover the whole thing with a plastic bag and press it down for better seal (my grandma used a big rock for this). I know that the fermentantion process that takes place there is anaerobic (the bacteria involved use nitrogen in their metabolism instead of oxygen IIRC), and it's relatively slow (it takes a few weeks for the cabbage to turn sour). What I still don't get though is the need for dissolved O2. I thought that the only thing you need in an electrolyte are ions (molecules that will act as charge carriers) or am I missing something?
How did this two chamber model of yours perform then?

[egbertfitzwilly]

As I understand it, and it is by no means clear that I do, the salt bridge provides transport for hydrogen ions which carry a negative charge. These combine with dissolved O2 to produce water and release an electron or two. The dissolved oxygen can be provided by a number of sources including chemicals, algae byproducts or "gas uptake in a liquid" which is the long way to say the surface absorbs oxygen from the air.

I suspect that if a salt bridge were connected to the cabbage bucket a charge could be generated and multiple cells could be wired in series. Grandma would be proud....

[CoolKoon]

Hmmmm.......this goes contrary to much of the stuff I've learned about the chemical reaction involved in my chemistry class (hmmm........quite a few years ago). I mean water is a dipole molecule, which is caused by the big electronegativity of the oxygen atom (it almost strips the H atoms of their lonely electrons and keeps them for itself, making the O part negative). Therefore when you dissolve something in water, it's actually "disassembled" by the water molecules into positively and negatively charged ions. Take for example table salt: the water molecules separe it to H+ and Cl-. This separation remains while the water molecules are present.
A salt bridge is usually used to facilitate ion exchange between two separate electrolytes. You see the charge carriers are not the water constituents but the ions dissolved in it, otherwise some distilled water could work as an electrolyte too (without prior charging, of course). I'd say that the charge carriers (ions) give up their electrons by merging with the materials of the electrodes itself. Now I'm sure things are a bit different when microbes are involved, but I don't know much about the mechanics involved. So the question remains: if the microbes can survive only in an oxygen-free environment, what's the O2 there for?
As for the sour cabbage electricity thing I thought about that too. Unfortunately my grandma passed away about a year ago as the result of a final stroke. She never recovered fully even from their second one though (wasn't the same person anymore), but have I tried that before (attaching electrodes to sour cabbage and testing it with my multimeter) she would've surely been convinced that I've gone crazy and banned me from the basement (by hiding the key) :P No sour cabbage has been for a long time (probably for practical reasons as well, because it wouldn't be eaten I guess) so I don't think I could try it out (especially because none of my parents like my experiments either :S). Still, it's a really interesting idea that's worth a try.....

[AwesomeD]

where does the 1st lead go

[egbertfitzwilly]

There are two electrodes in the chamber, one in the bottom under the paper and the other attached to the styrofoam. One lead goes to each electrode.

[bobtannica]

Egbertfitzwilly, you have done it again. Fascinating! A corollary question to AwesomeD's... I am assuming that the leads connect to the silver mesh but in the top electrode there are two layers of mesh... In this case, is it one or both pieces of mesh? If one, does it matter which one?
  I also have another pair of linked questions. Re the shredded paper; you state to "put in the rest of the shredded paper" but haven't told us to add paper before that. Did I miss a step? In all, about how much paper do you want us to add?
  I am just full of...er...questions. Are you using the liquid or granular microbe lift? And finally, what kind of power output did you see with this?
  Thank you for all your hard work! Again, fascinating!
  Wait....one more..."next generation wind turbine"??? Haven't seen you post THAT on here!!!

[egbertfitzwilly]

Oh yeah, the next generation wind turbine ( using 3L bottle fan blades ) is bound by mechanical challenges. The primary problem is solving the balance so that the windmill can be connected to a CPU fan acting as a generator.

If I can get the windmill more or less balanced I can use a vacuum cleaner belt and a couple of hubs out of a CD drive to spin the fan and get power out the cables.

I'll take all the help I can get.

[egbertfitzwilly]

Thank you for your kind words. Let's see if I can answer your questions.

That's not two pieces of mesh, that's overlapping ends of one piece of mesh. If you are using multiple pieces as long as they connect it should be okay.

You are correct, that should say "put in the shredded paper so that the anode is covered" A couple of handfuls out of your office shredder should be sufficient.

I used the liquid septic tank treatment which stinks to high heaven. I didn't see a crystal form and if I need some more I will certainly look for it. Ordinary yeast can be used for experimental purposes as it will grow anaerobically if deprived of oxygen. You could experiment with some vinegar as a substrate with either yeast or septic tank starter.

Overall the output from this design was disappointing. Although the styrofoam is porous I don't think there was enough air circulation. I know from my work with algae that gas uptake only affects about 6 cm or so ( still water/still air ) so I suspect the additional protection is unnecessary. I have a refined open top design that, well, stinks....The problem to be solved is air circulation across the surface of the water in a closed tank. I'm hoping the windmill will provide a solution for that.

[bobtannica]

Well, I am indeed missing something. To quote you from step 2, when you are constructing the top or Styrofoam cathode you say,  "As you can see in the picture it is a sandwich. The bottom layer is Styrofoam, next is a layer of conductive cloth, then two carbon pads laid side by side. This is followed by another layer of conductive cloth, then the carbon paper. "  You seem to be indicating two layers of conductive cloth(mesh) on this top layer. Do you connect the alligator clip to one or both? Thanks.

[egbertfitzwilly]

You are correct, it does seem to indicate two layers but actually does not. I used one piece of cloth long enough to cover both faces by wrapping around. If two pieces are used they should be placed on the brush so that they overlap.

What I was trying to emphasize is that both faces should be covered for optimal catalyzation by the silver,

[mhkabir]

how much voltage does it pump out?

[egbertfitzwilly]

Dr. Hui up at Oregon State published an interesting paper on cathode placement in a single cell MFC using conductive cloth. I got in a shipment of cloth so I tore that one down to experiment with her new design. It may provide a good way to address the problem of buoyancy in the carbon filters. It seems to me her design is really a two chamber MFC using conductive cloth as the salt bridge and water flow as the ion bridge. But I'm not prepared to challenge her paper. I'm actually inclined to return to the original two chamber design which I consider more scalable. I'm very encouraged by your reported results. I actually think that the single chamber is intrinsically suited to waste water pipe flow in an industrialized sewage system. That's an elegant energy tap but not a problem I find particularly interesting.

[puppylinux]

(removed by author or community request)

[egbertfitzwilly]

I'm not really a scientist, I just play one on the internet.... This is an expermental technology that can be exploited in a number of ways, generally left as an exercise for the reader.

[conrad2468]

I sure wish these werent so inefficient! Great instructable i just wish the technology was a little more advanced!

[egbertfitzwilly]

There's a number of groups looking at scaling this in a number of directions. Logan at Penn State, Hiu at Oregon State ( Dr. Who? ), some lads up at Humboldt are all looking hard at extracting power in volume from wastewater, although nobody thinks it will be significant in terms of quads. The Aussies I think have a pilot project in a brewery which is interesting. In the other direction a group has developed a micro-MFC using yeast and glucose in blood that might be used to power implanted devices. I'm working with an associate who has a septic tank system. We're hoping to come up with a design that we can implement at the next cleaning using carbon paint in the anode. However the real power of this technology is in areas of extreme energy poverty. To understand this let me put it this way, in a recent presentation the head of the African Energy Unit of the World Bank said their goal is that 50% of the households in Africa should have a working 150W light bulb by 2020.

[puppylinux]

(removed by author or community request)

[egbertfitzwilly]

I'd be interested in getting those links if you have them handy.... Mine is special because its posted on instructables....Other than that, and experimental use of styrofoam as the permeable membrane, its just your run of the mill 5 gallon single chamber microbial fuel cell....

[hopenui]

This is awesome. First time here. Reading all other know-how