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aquaponics idea: opinions?  RSS feed

 
Gilbert Fritz
Posts: 1319
Location: Denver, CO
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A big downside of aquaponics to me is the electricity needed. Alternative energy tends to be intermittent, and so an aquaponics system utilizing alternative energy directly would perish. Alternative energy can be converted into electricity and stored, but there are two big downsides. First of all, a lot of energy is lost going from motion or radiation, to electricity, to motion (a pump.) Secondly, my focus is on designing and developing truly sustainable, resilient systems for self-sustaining cities. Solar cells are difficult to manufacture; small scale wind power is less productive due to all the buildings around; large scale wind power is not doable on a local level; and micro-hydropower is not universally available.

So, here is my idea of a set up which would use human or animal power directly. (Or other alternative energy sources if available.) The big problem, of course, is that pumping has to be continuous, or nearly so. So there would be a big tank of water, raised maybe five feet above ground level. At two feet above ground level is a grow bed. Sunk into the ground is a large fish tank. It is sufficient to hold all the volume of water held by the grow bed and water tank. Around it, one the same level, are shallow ponds or gravel beds. Water drains steadily out of the water tank into a small holding tank above the grow bed. Every half hour or so, a syphon trips and pours the water into the grow bed. From there it flows into the fish tank. As the fish tank overfills, it overflows through pipes into the shallow ponds or gravel beds. They are busy growing duckweed, azolla, and bog plants to feed the fish. (They are set up to retain an inch or so of water no matter what happens to the fish tank water level.

Then, once a day or so, a bike or treadmill is used to move the water from the fish pond into the water tank. In Asia, large amounts of water are moved into rice paddies by efficient, simple pumps worked by someone on a board, rocking back and forth. Or a windmill could recharge the system, especially in places where there is plenty of wind most of the time. (Like here in Colorado.) The tank of water would even out the energy in the wind.

Am I missing something here? I think this is a great system, especially the duckweed part, since, in combination with a simple solar dryer and the intense sun of the front range, there is a free source of fish feed. Add a few rabbits and some black solder fly, and it would be even better.

Then, as to heating the fish tank and thereby the greenhouse it is in; what about using a compost pile directly to heat water? In between the fish tank and the grow bed, the water could spiral through tubing in a hot compost pile. If a really good pile could heat water to 140 degrees, it should be easy to get nice eighty degree water going into the fish pond after a short tubing run. And all that solar mass and those rabbits would help heat the greenhouse too. The fish and rabbit guts, and the nitrogen rich azolla fern would easily heat up a compost pile.

So, what about it?

Edited to add; is seems that in this system, fish stocking could be slightly higher than normal, if one were only considering the fish tank itself. But I am not sure about this. Which is a bigger concern; cubic inches per fish, or gallons of water per fish?
 
Chris Kott
Posts: 823
Location: Toronto, Ontario
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From what I have read, the concerns with aquaponics systems seem to revolve around even the lowest stocking rates producing too much nutrient for a closed-loop aquaponic system; in order to have the fish, you need the smaller flora and fauna that process the excess nutrients in the system.

My feeling is that you will probably find it useful to create a sedimentation pool for excess solids (whose breakdown takes up oxygen, the real limiting factor in such systems), that could be employed in adjacent garden beds as fertilizer for human or rabbit food.

I suggest you make your setup as modular as possible, so you can tweak the individual components. Relying on your fish tank to act as your thermal mass, adjusting for seasonal and diurnal temperature fluctuations sounds like a good way to kill your fish, unless it's made much larger than I think you're thinking.

Bottom line: beyond keeping things clean so you don't asphyxiate your fish, if you don't modularize your system, it makes diagnosing problems that much harder.

-CK
 
Jeremiah Robinson
Posts: 92
Location: Madison, WI
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Hi Gilbert,

Your idea is really creative. I've been trying to figure out how to integrate aquaponics with a larger permaculture garden for some time and it's not easy. Kudos to you for helping generate some ideas!

The trouble, I think, is that to really use the fish waste effectively for plant growth, you need to move all the water every hour. You can get away with taking a few hours off here or there, such as on a cold night in the winter, but generally you need a good and stable throughput. Unless you live in a place with a consistent source of alternative energy (like a stream), it's hard to see how you can get away from electrical storage.

The bigger use of energy, for most aquapons, is in heating. There's a lot of room for improvement in this area with the systems that are currently out there.
 
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