Make a Microbial Fuel Cell (MFC) - Part II

Step 5 Charging and Operating

Dayyum, that septic tank stuff stinks...You're going to want to do this outside or in a well ventilated area.

Pick on chamber to be the anode (microbe) chamber and one to the cathode chamber.

Fill a measuring cup with about 2 ozs of warm water and add salt to it until no more will dissolve ( a saturated solution ). Stirring and shaking will help. Allow the water to completely cool. Remove the sponge slices from the cathode assembly and make sure they are thoroughly soaked in the salt solution. Pour the rest into the cathode chamber until only the salt slurry remains. Place the carbon electrode on top of one sponge, cover gently with the slurry and then use the remaining slice to complete the sandwich. Place this gently back into its connector and insert into the cathode tube. The tube will overflow as the cathode is inserted, That's okay we want the carbon electrode to come into contact with the air so pour off a bit of water as well.

Fill the anode chamber 1/2-3/4 full of the septic tank treatment. I also added a couple of teaspoons of sugar and some shredded paper to provide carbon and nitrogen. Fill the chamber the rest of the way with pure, dechloronated water. Inser the anode assembly fully into the anode tube.

I began measuring voltage on the open circuit. Within 15 minutes I was generating measurable voltage (82 mA). Once the output voltage seems to stabilize I will measure under load and update.

Comments

[krishnamohan]

Hi,I prepared a micobial fuel cell of approx 1.7 lts with agar salt bridge and carbon/grapite electrodes and waste milk as fuel. I started watching the current from the 2 day of setup with a peak voltage of 0.6 V and 0.5 mA. Could you please suggest me how to optimize it interms of salt bridge , should I go for Nafion membrane. The agar bridge is of 2 inch thickness,so will it make difference if I switch to nafion and do it affect if I add Hydrogen Peroxide to cathode chamber.Please help me out any other ideas if u have.Thank you!!

[egbertfitzwilly]

Measure the total resistance across the circuit, including the media. See how different widths of the salt bridge affect that.

What are you using for electrodes? Probably the best way to increase current flow is to provide more surface area for the electrodes, you might consider one of the Fluval aquarium carbon filters as an electrode.It's not all clear to me that switching to Nafion will impact your performance significantly, but I could be wrong about that.

You could try adding a small amount of hydrogen peroxide, chlorine bleach or sodium hydroxide for increased oxygenation HOWEVER if you are bubbling air through the chamber this probably isn't your problem.

Also it sounds like you are relying on the natural bacteria of milk spoilage, these may not be an effedtive current producer ( I haven't seen anything one way or the other ). You might consider seeding your tank either with Septic tank starter or a small amount of waste effluvient from your local municipal water recycling plant. Yeast is another good choice, as long as the chamber is sealed ( Yeast will switch anaerobic mode in the absence of oxygen ).

[krishnamohan]

Hello sir
As you suggested to use YEAST, I have a doubt that , whether it requires a MEDIATOR or not.If yes, please let me know, which one is the best.

An interesting thing, I observed in my setup is, it  produced peak voltage and current with in 5 days of setting it up, and it started reducing.For 30 days it showed the reducing phase, but for the past one week it started rising again and now to my surprise, it gave me a voltage if  0.5 v and 0.8 mA ( on march 11, 2010 ) , which is highest of my reading till now, I hope it is going to increase more.

[sattarga]

hello sir,
i'm from from and i want to do project in my college in mfc. as you've done experiment in mfc it will be so kind of u if you tell me what are the thing necessary to create an mfc what is the bacteria you used and where can i get it.please help me sir thank you.........

[leecho0]

hi would you be able to make something like this:
http://www.economist.com/sciencetechnology/displayStory.cfm?story_id=14743791

with this 'ible? what would you need to change to make the salt bridges semipermeable to only one kind of ion?

[egbertfitzwilly]

You would need to change the salt bridge which is an electron bridge to an ion bridge. The most common and easy to handle material is Nafion which is used in a large number of fuel cells, including hydrogen cells.

Other ion bridges include Teflon. There may be room for investigation of a teflon coated steel pan being used as a membrane with the steel portion serving as an electrode.

Nafion is inexpensive and easy to handle. Be careful when shopping for fuell cell components, there are many pseudo-environmentalists hustling a variety of overpriced biodiesel and fuel cell components.

I have no relationship with these guys.

These guys have a $49 15cmX15cm

http://www.cleanfuelcellenergy.com/membrane.html

[leecho0]

 nafion would only work for the cation exchanges, right? what would you use for the anion bridge? 

[lendogg]

i constructed a quick version of this using two mini pie tins as electrodes and cardboard saturated with salt as the salt bridge using river mud id made 0.5v 100-200ma intreastingly i got a simeler output from clear river water taken from the surface

[egbertfitzwilly]

I believe what you have is an aluminum air battery formed by the electrolyte and the aluminum tins. You might want to try again using plastic or other non-reactive containers.

[Javin007]

I would be very interested in seeing what kind of voltage and amperage you get out of one of these units. I ask, because I've only been able to find one place on the internet that mentions voltage and amperage from a Microbial fuel cell, and the amount of energy put out on that one is around 1/72000th of what a AAA puts out. At least for their purposes, the cost of energy used to create the fuel cell (heating the water and the hot glue gun alone, not even taking into account the production of the PVC, chemicals, etc. ad infinum) resulted in one of these cells requiring literal millions of times more energy to create than they would ever produce. I would be interested in seeing if anyone has created one with a decent energy output, or if these are more of a school science experiment type of thing.

[egbertfitzwilly]

Logan at Penn State projects that sustained output for a single MFC can be 6.6 mW/L. The most likely application of this is the production of power in wastewater treatment plants. Variations of this technology are widely used in third world countries to provide a trickle current for driving rechargeable batteries. Although I do dispute your analysis over time, at 6.6 mW/L thats 158.4 mW/day or 1W/week or 57 W/year which is significantly higher than one would get out of a AAA battery. Especially if one tried to run it 24/7 for a year...

[Javin007]

If I'm understanding your math correctly, it would take almost two weeks to produce the same amount of electricity that's in a single AAA. This is also the equivalent of 32 AAA batteries in a year (assuming that this can run non-stop for a year with no additional resources.) I think (just guessing)the electricity used to create the PVC piping (melting plastic, shaping, etc) as well as any other resources used to create the product (chemicals, filters, etc) would significantly outweigh the electricity it produced unless it was kept running non-stop for many, many, many years. Compare the 57W per year with the 3000W per hour of a home generator that runs on gasoline. Even running on a fossil fuel, the home generator would be far, far more "green" than one of these devices. Even more so if the home generator is running on ethanol (which can be made at home). In order to create the same amount of electricity that you would get from a home generator, you would have to build 454,546 of these devices (running at peak efficiency according to Logan at Penn State) running in serial. Half a million of these devices would be many hundreds of times more damaging than a single $300 generator. I think when you consider the impact to output ratio, this device is actually quite "un-green" in the long run. Now, if it were made (which it could not be) 100% out of stuff found in a landfill, it'd be a different story. But the production of the necessary chemicals alone would be enough for me to consider this device (and many like it, I'm not specifically trying to pick on you) to be "dirty" energy.

[egbertfitzwilly]

FirstI don't think I promoted it as a solution to anything other than boredom...and you missed the really clever bit which is using the unflavored gelatin instead of agar. It would seem you haven't fully recognized the potential inherent in this, aside from potential applications in the third world where they can't just run out and buy a backyard generator and the fuel to run it. Or perhaps the inherent scalability isn't apparent. This technology can be leveraged to draw power from every waste water treatment plant and septic tank in America. Half a billion MFCs can readily exist in our extant waste treatment systems. Actually probably more using a single cell floating cathode array as the cells do not need to be physically segregated. Without buildout, without consuming land mass or competing with food for feedstock, without building large mechanical generators and creating the agricultural infrastructure to fuel them, assuming that the land isn't needed for actual food.

[bobtannica]

I will be eagerly watching for further developments! Thanks again for the great 'able.

[egbertfitzwilly]

Last measurement I took showed approximately 30mV@28mA across a 220 ohm resistor.

[bobtannica]

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]

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.

[bobtannica]

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]

This is an example of Dry Hide Glue I pulled at random off the net as an example of what to look for.

[egbertfitzwilly]

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.