When considering my design to use aquaponics to remove excess nutrient and other pollutants from our river system and reduce apoxia levels and the dead zones at the mouth of our rivers one of big questions was how to ensure enough nutrient density to grow cash crops and make the system financially self sustaining. Being that most aquaponic systems are closed loops with controlled nutrient inputs in the form of fish food, this isn’t typically a problem. In our case there is a special piece of irony as too much nutrient is the problem we are endeavoring to solve with this system. The current issue is density though.
So how do we ensure nutrient density?
It turns out, there is a relatively simple solution. we evaporate the water. This works because the nutrients don’t become airborne at anywhere near the rate of the hydrogen and oxygen that make up water vapor.
But this does lead us to another consideration. The main purpose of the system is to clean the water…so we need to recapture that water vapor to return it to its original source (the river). So we built that into the system.
Another major consideration is keeping operating costs low. So we dove deep into the most basic of Permaculture design principles and asked how we could use natural processes to make this function. The only external power input needed for this greenhouse is to pump the water to the top of the system.
Which brings us to the actual design. Below you will find an explanation of the drawing at the head of this article.
Principle of Operation– In this greenhouse we want to encourage as much evaporation as we can. This means we want heavy but disrupted water flow, high heat, and air movement. All design elements are based on those ends.
A. Air intake vents. These should be along the lower portion of what we will refer to as the head of the greenhouse. The purpose of its location is to bring cool air into the greenhouse which will move across the greenhouse and form a light breeze to item L, which is venting for the hot air to escape.
B. Water intake pipe and riser pump. This comes from the storage tanks and/or water tower that are fed from the river. Water should receive its initial quality tests at those storage tanks, prior to entering this part of the system. Water should be pumped at a heavy enough rate to maximize flow from the spray heads at item C.
C. “Rain shower heads”. It is important that these allow the water to be diffused as much as possible to maximize aeration of the water flow and to encourage the evaporation process.
D. Filter trays. These layered trays are to continue spreading the water and diffusing it further to continue maximizing evaporation. The bottoms should be porous enough so as not to inhibit water flow, but merely break it up as it descends to item E. They should be dark in color and preferably of a metal construction to absorb heat to transfer to to the water.
E. Water accumulation bin. This bin should be filled with river rock and made of concrete. The river rock is to create massive surface area to provide homes to the first stages of bacteria that will process the various wastes in the water into nitrates and nitrites for the plants to consume later in the process. River rock is preferred to other media as it is more dense to hold heat AND it will provide some mineralization which will benefit plant production in the grow stations. This design feature will be implemented at several stages of the full system to allow for as much plant uptake as possible.
F. Fog Curtain. Following the lead of water harvesters in the desert, our system will employee fog curtains to recapture evaporated pure water to return to the river system.
G. Accumulation tray and water line. All fog curtains should feed into this tray and line, which will feed Item H, where water will be accumulated and mixed with water leaving the grow areas, to be quality tested and returned to the river.
H. Return water merge and testing tank. All water going back to river will be merged here for testing, and then allowed to flow back into river.
I. River Feed Line. Gravity fed pipe returning water to source.
J. Waterline from grow operation. As noted, this line comes from the grow operation and is returning water to the merge tank for testing.
K. Waterline to grow operation. This line takes water from Item E and routes it to the grow operation via a refugium room, where tanks will be set up to provide addition aeration and bacteria processing to prepare nutrient rich water for plant uptake.
L. Exhaust vent. This venting should be at the highest point at the foot of the greenhouse, large enough to allow heavy air flow, but small enough to not allow too much heat to escape. This combined with the heat capturing elements of the design and the air intake at Item A, should provide adequate breeze to encourage evaporation sufficiently and to pull the moist air back across the fog curtains for recapture.
Summary- These elements will be scaled to work together to ensure maximum evaporation and recapture while preparing the nutrient rich water for its most efficient uptake by the production plants.
For more information on how to fix Dead Zones in the Gulf of Mexico and the mouth of other rivers, follow this link –>
