Backyard Aquaponics
A place to discuss aquaponics

I needed a good excuse to take a break from washing media. So when Fishbits told us about urine and cellphones I got curious and went off on a tangent . Googling came up with some info that looks interesting;

http://en.wikipedia.org/wiki/Microbial_fuel_cell

Down the page they start talking about using aquatic plants to generate electricity. Even mentioned tomato plants.

Now, where in the world is Bullwinkle ? If he can make an extruder molding apparatus maybe he could come up with an " MFC" prototype in his spare time

Dag Nab it Dave, now you got me all worked up again!

BTW Dave, the wife and I will be visiting # 2 son and his tribe come end of September.

Maybe I can pick your brain again

I just Googled "microbial fuel cells aquaponics" and found this thread. I had hoped you guys would be well on your way with this so that I could ride your coat tails.

Has anyone done anymore with this idea?

I'll bet a microbial fuel cell can be made with 1 electrode in fish tank and one in bottom of grow medium. The only concern of mine is will trace metals be shed from the electrodes due to electrolysis. I suppose a single IBC system could be used with a water tight sheathed conductor so if the cable rots it only takes a small amount of copper or aluminum with it. Improved results can likely be achieved by using electrically differing materials for your 2 conductors ie anode and cathode legs. I would suggest trying stainless steel leg in the grow media and aluminum in the tank.
This idea is very interesting to say the least, I would try it out if I had a large setup, and condsidering I use a DC powered pump the fuel cell would possibly make a self sustaining system. My system is a small prototype right now and with only 25 gallons or so any electrolysis would have a major impact on it.

I would also suggest writing down the voltage generated with the leads in that configuration. After you know the voltage generated by a single electrode pair I would suggest swapping them so the alum is in the media instead and then observing the second voltage. This could be a very promising experiment.

Right now I think there is no way they generate enough oomph to power much worthwhile. Maybe a really large AP system could power a pump someday.

First thing: Cool!

Second thing: but.

On the principle that there is no such thing as a free lunch if you incorporate one of these with tomatoes (as mentioned in one of the links) then wouldn't you be taking energy from the plants and hence be reducing your yeild?

Lots of other similar points. Yes they sound cool but is it really worth it even if it works?

You are indeed right there is no such thing as a free lunch, and I am not too sure whether this could work well enough to run a pump without adding metals to the environment. The truth is with enough fish running in a system you could generate pretty nice power. My real questions are how many fish would it take, and what are the aqueous byproducts.

How about this?

Run a methane digester off of your effluent waste and plant waste. Generate electricity from there as well as methane. No harm to fish, no nutrients taken from the plants that aren't already being removed from the system anyway.

I did some research and found that only 0.8W per m2 can be expected. The preferred material for the anode is carbon fiber cloth. The cathode can be stainless steel. Copper was found to perform poorly but we would not use copper in an AP system anyhow.

I found a small piece of carbon fiber cloth on ebay and ordered it for the experiment. Larger pieces 50" wide by as long as you wish are available for about $24/linear yard. I ordered the small piece for less than $8 to see how well it works before investing more.

Assuming that it does work my plan would be to lay the cloth in the bottom of a media bed and place the cathode on the surface. Hopefully the cathode does not require the same surface area. But since the bacteria exchange the ions on the anode I would expect the is the area that needs to be large.
http://www.ebay.com/itm/Carbon-Fiber-Cloth-Fabric-Plain-Weave-3K-5-8-oz-50-W-/321155897278?pt=LH_DefaultDomain_0&hash=item4ac66217be

leave it to BobCampbell to test out the ideas. It might be a good idea to make a small side system for the experiment though. If either electrode deposits metal it will contaminate your crops/fish and anyone who eats of them. My system is a very small one for now because I do not plan to stay at this house or even Texas much longer.

I just lost interest.

0.8W/m2?

So 8kW per hectare?

You could do better by putting solar panel strips on all the structural members of your greenhouse.

I received the small roll of carbon fiber cloth yesterday and immediately placed it in the water. In a few weeks when the bacteria have a chance to populate the cloth I will use a stainless steel cathode and let you know what I find.

http://www.ebay.com/itm/Carbon-Fiber-Cloth-Fabric-Unidirectional-Tape-12K-4-Wide-/390639924372?pt=LH_DefaultDomain_0&hash=item5af3f43494