In response to numerous questions about what happens to the collected algae this instructable should help someone to build a microbial fuel cell (MFC) with household items and materials. As its name suggests, an MFC uses microbes to catalyze electricity-producing reactions.

This instructable is based on work done by Bruce Logan and his team at Penn State University and on the microbial fuel cells built by Abbie Groff, a student at Conestoga Valley High School in Lancaster, PA. The research she performed with her MFCs helped her win the Grand Champion Award at the 2005 Lancaster County Science Fair.

Now to be completely honest the fuel cell we will build is not "purely" an algae fuel cell, it is a microbial fuel cell that uses anaerobic bacteria to decompose organic matter, in our case dead algae.

The fuel cell will consume the algae (or other organic material) with two significant by-products, electricity (always useful) and methane gas. In a production system the methane must be captured for further use for instance as fuel for a steam powered generator which processes its exhaust plume through an algae based (or other) exhaust gas scrubber.

In this design its very cleverly captured in the sealed anode and if you come up with some clever way to do something with it, I'd be very pleased to hear it.

Step 1: Bill of Materials


Drill or drill press
Razor knife or scissors
Hot glue gun
Funnel - Optional for filling bottles
Soldering iron
Lead Solder
Materials and where I got them. I have no relationship with any of these stores or products. They are inexpensive and should be commonly available:

  • Two heavy duty plastic bottles with sealable lids. Wide mouth bottles are best choice for ease of inserting broad surface area electrodes.
  • Low power aquarium air pump
I recommend the Hagen Elite 799 available at PetSmart for around $6. Rated at 1.8W.
  • 1 x 2" PVC pipe 1-2 feet long
  • 2 x 1 quart mason jars or similar
  • 1 x 2" PVC Nipple or Sprinkler system riser
  • 4 x PVC slip caps. You can probably get away with two, I use two for storing the salt bridge
  • 2 x 1in square Silkscreen material or other nonconductive mesh
Cut to 2 circles that match the outdiameter of the PVC nipple
  • Agar - 100g per Liter of water
  • Salt - 400g per Liter of water ( 14 oz/Qt ).
  • Carbon cloth or carbon paper
Carbon cloth of various types can be purchased online. These folks http://www.uscomposites.com/carbonpage.html offer it for around $40/yd. I'm using plain old fashioned carbon paper with wire mesh support. Eventually I plan to experiment with alternative designs that use carbon filtration technologies.

  • Nitrogen for removing oxygen from water. This can be readily obtained from several sources locally and online.
    • Welding supply places will have Nitrogen and Argon in tanks for various sizes. Around $35 for a small tank here.
    • Local tire dealers. Local tire dealers often replace air in tires with nitrogen (for a fee). They will happily fill up your inner tube or inexpensive pressure tank (for a fee).
    • Bacteria for a MFC can be obtained from several sources.
    • Shultz Liquid Plant food
Most likely, wastewater or anaerobic sediments will initially contain enough organic matter to serve as food for the bacteria, but this will eventually run out. Algae will provide the food source (substrate) used to maintain the MFC. The liquid plant food and soil water will provide trace minerals and nutriets.
<p>how many volts produced?</p>
<p>Hi, I am going to make a mfc. I used 10 lit containers for anode and cathode chambers and 3 inch dia. pvc pipe for salt bridge. Now i am unable to get graphite electrodes. Kindly guide me, what should I do? Can I use carbon brushes for this purpose?</p><p>If yes then what shuold be its size. ? Kindly help me as soon as possible. </p>
<p>Carbon brushes used in washing machines and large dc motors should be good enough for 10 litres setup . Also i would recommend using 3 containers of about 3-4 litre capacity and they can be connected externally in parallel </p>
<p>HI, I am wiki. I am going to make a mfc with 10 lit chambers i.e anode and cathode with 3 inch dia. pvc pipe as a salt bridge. Now i am unable to find graphite electrodes.</p><p>kindly guide me as soon as possibe.</p><p>Can i use carbon burshes as electrodes? if yes then what should be its size?</p>
<p>Great instructions. I'm planning to give it a go.</p><p>I'm trying to understand the step: &quot;Once the electrodes have been assembled the exposed metal mesh should be protected with a good coating of hot glue.&quot;</p><p>A picture would have been helpful.</p><p>Do you completely cover both sides of the mesh (as in trying to completely seal it to make sure not water gets in), or do you only do one side of the electrode, or do you leave an opening in it for the solution to make contact? </p><p>Please explain a wee bit more. </p>
<p>This was a very early prototype and you might find some of the other designs more efficient. I switch to using various types of carbon electrodes.</p><p>The hot glue is to seal the electrode around the edges and cover any projecting metal bits that stick out past the solder. The main body must be exposed to the medium.</p>
<p>Can this wire be used as electrodes in the above MFC?</p><p><a href="http://www.amazon.com/Plastic-Coated-Value-Coils-24-Translucent/dp/B003K7AINE/ref=pd_sim_ac_2?ie=UTF8&refRID=0HFMH4R2WEZ14MCPN2D8" rel="nofollow">http://www.amazon.com/Plastic-Coated-Value-Coils-2...</a></p><p>Thanks.</p>
That link doesn't seem to be working any more. From the text of the link I would expect the plastic coating to insulate the wires and prevent the MFC from working properly.<br><br>The electrode(s) must be conductive, however they do not need to be carbon. Carbon is used by the scientific community to prevent any secondary reactions from interfering with the measurements but that is not a production requirement.
<p>Can you explain how electrons are generated from the bacteria and then transferred from the bacteria to the electrode?</p><p>Thanks!</p>
<p>The last time I checked the research the process was not well understood. From what I understand certain types of anaerobic bacteria generate electricity as a side effect of biological processes. The research has, as far as I know, focused primarily on identifying the strains that demonstrate this the most.</p>
<p>How long will this experiment take approximately?</p>
<p>Initial energy production should begin within a few days and will run as long as there are nutrients to feed the organisms. The salt bridge is subject to breakdown over time and the electrolyte could eventually be depleted and need replacement.</p>
<p>I'm a student who tried to build an mfc at home. I used waste water as the anode substance, and carbon electrodes, in both anode and cathode. but im not getting any voltage reading. is their something wrong?</p>
<p>There's not enough information for me to make any sort of an informed guess. What sort of waste water did you use and what did you use to create the individual cells? There are more detailed instructions in Part II.</p>
Does electric current is obtained spontaneously or take some hours for the process? <br>
It takes a while for current to ramp up. Its a function of volume and colony size.
Hi. i want to do a project on the MFCs, the problem im facing now is with the length of agar-salt bridge. so I want to know the length of the agar-salt bridge for a working volume of 1 lit or 2 lit inoculum and it retention time also. how long did a agar-salt bridge is capable of holding a MFC??
What kind of waste does the MCF produce?
It seems to me that a resistor is necessary to a fuel cell's operation. What resistance, in this manner, should be applied?
As you probably know resistance is a function of load. This design, as with many others, are designed for scientific purposes ( such as science fair projects ). Due to natural variation in resistor manufacturing ( normally +- 10% ) the only scientifically reproduceable voltage is the open circuit voltage. Obviously once a load is applied current and voltage vary.<br><br>Generally speaking this sort of design is best suited to trickle charge applications.
Ok thanks.
hello egbertfitzwilly......<br> 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......<br>
Try this design:<br><br>https://www.instructables.com/id/Make-a-Microbial-Fuel-Cell-MFC-Part-II/
Do you have to use agar.
No, if you you look at my other instructables I've substituted Knox unflavored gelatin.
Hi,<br> I'm a student who tried to build an mfc at home. I used waste water as the anode substance, and graphite electrodes, in both anode and cathode. But my multimeter is showing a negative voltage reading. What have I done wrong?<br>
If you are showing a negative non-zero voltage you have connected your voltmeter backwards.
A couple of thoughts on de-gassing:<br><br>One quick way to degas a solution is to boil it for a few minutes. Gas solubility decreases a lot with temperature. Of course you won't be able to boil your culture, but sterilizing the media might help to keep stray yeasts out of it.<br>Other gases will work as well, such as helium, which is more readily available for party ballons in smaller disposable cylinders. <br><br>You can also remove the oxygen specifically by electrolyzing the solution since you have nice electrodes and a very fine salt bridge. During the electrolysis of salt water, at the cathode (-) side dissolved oxygen is reduced to hydroxide, OH-, and hydrogen gas is evolved. In the other compartment, the anode(+), oxygen gas is evolved, while acidifying the adjacent solution.
Thank you for this excellent input. I will experiment with this for my other &quot;How to make Sodium Hydroxide&quot; instructable series...
This is really cool. Just wondering how many amps are you able to pull out of it and in that condition what was the output voltage. In other words what's the maximun output power you're able to achieve? <br><br>Does the algae have to have sunlight in order to do its thing?<br><br>Keep rocking this kind of cool stuff.
Thank you for these kind words.<br><br>There is no relationship between microbial fuel cells and algae scrubbers. The output voltage from an MFC varies according to volume, microbe type and available food.
side topic: New application for MFCs - desalination. This might interest you:<br/><br/>&#8220;Water desalination can be accomplished without electrical energy input or high water pressure by using a source of organic matter as the fuel to desalinate water,&#8221; reported in a recent online issue of Environmental Science and Technology. Please read more at <br/><br/><a rel="nofollow" href="http://earthalternate.blogspot.com/2009/08/electricity-and-desalination-from.html">http://earthalternate.blogspot.com/2009/08/electricity-and-desalination-from.html</a><br/>
tell me more<br>i was looking for this kind of solution for months<br>wow is this a miracle or what ?
I'd say its more in the &quot;or what&quot; category.....
the blog isnt showing up !!!
"Later on the research team modified the microbial fuel cell by adding a third chamber between the two existing chambers. They also put certain ion specific membranes between the central chamber and the positive and negative electrodes. The ion specific membranes permit either positive or negative ions to pass but not both. Now they place salty water to be desalinated in the central chamber." I wonder what they used for membranes? I'll take a look at Logan's site and see if he's published anything on this. It's the first I've heard of this application or a 3 chamber cell. Thanks for the info
Idea on methane collection: Add a valved aquarium tube ended in an interface with attachable valved end connected to a lightweight &quot;bag&quot;. Put on empty - remove when full, vacuum empty, replace. Make 2 for efficiency.
a species of bacteria known as Methanobacterium palustre can convert CO2 to methane. will it work in this setup??
I'm not really a scientist, I just play one on instructables...-)<br> <br> Here's a link to the base article:<br> <br> <a href="http://pubs.acs.org/doi/abs/10.1021/es803531g" rel="nofollow">Direct Biological Conversion of Electrical Current into Methane by Electromethanogenesis</a><br> <br> I would recommend the Jello based design as a test platform. It is much more adaptable and a number of configurations can be tested at once. Current can readily be applied across the electrodes or through the media depending on the experimental model.<br> <br> If your goal is the production of methane I would suggest that you will get better results with an algae farm. There are numerous tank designs that will scale up extremely well. The energy input cost, even with pumps, is lower. The Chinese have reported ( in peer reviewed journals, see the Journal of Power Sources ) that get 1L of methane for each liter of algae sludge mixed with approximately 50% paper pulp.<br> <br> The sludge and pulp is placed into an anaerobic digester and the methane captured. The exhausted sludge is dried and used as a high grade fertilizer.<br> <br> All of these technologies are low-tech and within the grasp of virtually anyone.<br>
I want to make an electrolytic cell which uses carbon and produces methane as explained in this article: http://www.azonano.com/news.asp?NewsID=17238 The problem is that I don't know how to proceed with this idea. Some Help Please!
&nbsp;I'm a little confused as to exactly what &quot;silkscreen material&quot; means. If its a nonconducive mesh, how will the electrons produced by the anaerobic bacteria get to the cathode?
Silkscreen material is a fine mesh fabric used in silkscreening. It is inexpensive and readily available so it can be used to provide mechanical support to the bridge while allowing the free flow of electrolyte solution ( and the associated ions ) through the mesh.<br /> <br /> Without it the agar (or other salt bridge media) will break down and collapse quite rapidly (eventually it will completely degrade in any event). A mechanical support ( such as silkscreen material ) can delay that.<br /> <br />
&nbsp;Are there some alternatives I could use to replace silkscreen material?<br /> <br /> I'm not sure where exactly to go to get access to it. Also, should the agar be touching this material when its actually placed over the pipe?<br /> <br /> Sorry for taking your time.<br />
I'm always pleased to answer questions. There are many things you can try such as pantyhose material. Silkscreen material will be available at most art supply stores.<br /> <br /> I would place it over the end when I poured in the gelatin/electrolyte mixture,&nbsp; This will bind the agar and the mesh together.<br /> <br /> Also consider possibly cutting out a circle or two that will fit in the pipe and can be manipulated down onto the interior surface.<br /> <br /> You might try one or two without worrying about the mesh just to work out the rest of the process details and get an idea of expected voltages over, say, a week or two.<br />
what kind of voltage is it capable of putting out?
I got an update from a kid doing some classroom work. He's reporting .120V (maybe a typo) from 1-2 ml of E. Coli innoculant.<br/><br/><a rel="nofollow" href="http://groups.google.com/group/DIYbio-SF/browse_thread/thread/f2178d7f12c053a7">http://groups.google.com/group/DIYbio-SF/browse_thread/thread/f2178d7f12c053a7</a><br/>
That's a very good question. If you get a good answer please share it with the rest of us...:-) Current flow is going to be controlled by the bacterial population which is not optimized by sticking a pipe into a riverbed. I asked Dr. Logan about populations and he suggested a mixed population but didn't give me a detailed recommendation. I'm hoping to experiment a great deal in selectively breeding a population optimized for algae sludge by feeding them, well, algae sludge and let the best germs win... It's also not clear to me what the theoretical limits are, if any. A metal oxide battery/fuel cell has a theoretical max of 1.2V, I don't know if an MFC has a similar limitation or how far it can be scaled up. The folks at PS are wastewater specialists and speak glowingly of scalability but I haven't investigated that in any detail. I'm actually interested, at this point, in finding out what the cell volume/sunlight/nutrient ratio to determine the smallest functional cell that can be configured into a power grid is. Putting a bunch of them together is a sure fire way to scale up, but to what I cannot say at this time...
How has the methane been captured in the anode? In certain cases even carbon dioxide will be given out as a byproduct in the anode. How can these gases be obtained as an an output from the cell?

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