Step 8: Assembling the Reactor - Part III Assembling the anode

Now we turn our attention back to the we obtained earlier. The collected water will be used as culture media and the mud in the pipe will be used to provide the culture.

We'll be diverging from Abbie's design a bit. Where Abbie used the actual mud we're going to try to extract a sample and culture the bacterium.

I have been advised by Dr. Logan at Penn State that they do not de-gas the influent since the bacteria will handle it due to the low solubility of oxygen. The material in italics may be bypassed but I left it in case anyone ever wants to de-gasify water for some reason.

"'To do that we're going to de-gas the water using nitrogen, argon or other inert gas. Strictly speaking you don't have to do this but it will give our bacteria a better chance to breed.

We're going to do it slowly. Since the options for obtaining gas range from inner tube to pressure tank I give you the following simple instruction. Connect a section of aquarium air tube to the end of a hose that is connected to the gas reserve. Hopefully you have some way to regulate the gas. If you're using an inner tube I suggest filling a balloon (insert it over the valve and push the valve in) and using that to dispense the gas by inserting the air hose into the end and letting the gas slowly out of the balloon. Yeah, I know, it ain't easy being that cheap. Get over it or spend some money for a tank with a valve.

Now having arranged by some mechanism to regulate the gas flow of the nitrogen into the air tube attach the bubbler stone to it. Fill the anode chamber (one bottle) with the culture media water. Agitate well. Insert the bubbler stone into it and slowly bubble nitrogen through the solution.

How much nitrogen to bubble and for how long? A very, very good question and as soon as I have an answer I'll update this. I've asked the folks at Penn State so its not impossible this will be updated. Try to stretch it out, say 15 minutes maybe stirring occassionally.

If you've got the nitrogen do both bottles since we'll be topping off the culture media.

Once you've de-gassified the water or not its time to introduce the culture (mud).

This is also the time to put in some algae sludge if you have some.

See I said it was an algae fuel cell....

Grab the sample pipe and place the mud end in the anode chamber preferably under water before removing the slip cap. You might need to push it off with a long screwdriver or kitchen fork. Pull the slip cap off of the other end and slowly begin pushing mud out with a dowel or broom handle. You want to push out the bottom 2-3 inches of mud then take out the pipe. This should give you a solid culture of primarily anaerobic bacteria. Top off the culture media if needed from the second jar and add 2 drops of vinegar for each quart of culture media in the jar to supplement the natural nutrients.

Now place the anode cap and electrode in the anode jar and seal the edge with hot glue. The anode should be air tight and is not designed to be recharged at this time. Once the food is exhausted the bacteria will die. This will be indicated by a drop off in the output voltages.

Because the MFC cannot be recharged it is properly called a battery. To rectify this (get, a little electrical joke...very little) use a container which gives a solid, air tight seal and add a feeder hole and tube to it. Remember to seal the feeder tube when not in use and preferably flush with nitrogen.

<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>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>http://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?
In the current design the anode is sealed, the design would have to be modified to vent and capture the biogas. This could be post processed by an algae scrubber to produce biomethane suitable for any number of uses.
What's your connection with Bruce &amp; Abigail?<br/>For the amount of text I'd expect pictures of this <em>being made</em>, can you get some?<br/><br/>L<br/>

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