My recent article about this was basically a “thinking out loud” kind of thing which my readers are used to and have hence by now almost entirely stopped reading my blog. I think I’ve made leaps and bounds in terms of coming up with a prototype that is neither too large nor too small and more efficient, as well. I’ve even priced it out.
Statement of Purpose
The importance of local, family operated farms such as Applefield Farm can be likened to the importance of local farmers’ markets. They are not only places where people stop by on their way home from work to pick up fresh, safe produce for their dinner table, they are also meeting places, of sorts, for like-minded community members. By supporting these farmers, the community is getting more value for their “food dollar” and helping to circulate the money within the community rather than sending it to distant places. Applefield Farm is currently open from April until late October. For the next five months the community must rely on supermarkets and their questionable produce which, it is often said, travels an average of 1,500 miles to get there. By utilizing a temporary aquaponics system in a greenhouse enclosure within their 12,000 square foot existing greenhouse, Applefield Farm could stay open longer in the fall and open earlier in the spring—in fact, they could probably open a few days a week in the winter to provide fresh, healthy produce to the determined locavores in the community year-round. This is a proposal for a low-cost prototype system which would aid greatly in determining the limitations and potential of such a venture.
The prototype shown here would temporarily occupy approximately 1,550 square feet (144 square meters), or roughly 13% of the existing greenhouse floor area. Since the enclosure is protected from the wind and other elements, it can be made of lightweight materials. In this prototype, the enclosure is designed using simple 8′ x 8′ panels made from 8-foot lengths of 1 x 3 furring strip boards to which 4′ x 8′ sheets of insulation board are applied. The wall panels would be bolted together and the ceiling panels would be suspended from the existing structure, resting also on the top edges of the wall panels. The fish tank, 5 hydroponic troughs, and sump would be framed using 8-foot lengths of 2 x 4 lumber. The panels that form these vessels would have plywood applied only to the inside, enabling one to bolt the panels together for ease of assembly and disassembly. The vessels would be wrapped in agricultural grade burlap to hold shredded newspaper or another such insulation material in the voids between the studs. Solar energy would be captured passively using the fifteen 52-gallon barrels which also serve as solids settling tanks (clarifiers). Additional water heating will be supplied as necessary by a wood-fired 35,000 BTU outdoor water heater.
Aquaponic System Overview
The objective here is not to explore the limits of commercial aquaponics, but to have a simple system that is inexpensive to set up and run by a conventional farmer who’s just getting his feet wet, so to speak, in aquaponics. The stocking density maximum, at 23kg (51lbs) fish per cubic meter (264 gallons), will be a little less than 30% of the 80kg (176lbs) that a commercial recirculating operation would try to achieve. That’s 500 fish at an average plate-size weight of 250 to 300g (9 to 11 ounces). Water in the system shown here is lifted only once, about 3′ (90cm). All further movement is courtesy of gravity. The only plumbing necessary is from the water pumps located in the sump to the adjacent fish tank and from there to the solids settling barrels (clarifiers). The 150 gallon (570 liter) combined capacity of the three barrels is a fairly robust volume of water. The choice of 3 barrels per trough instead of two was driven by a desire to maximize the capture of solar energy. I actually want some solids to make it into the troughs as that will be the sole source of feed for the red claw crayfish that will be stocked there. Water from the troughs will simply spill over into, in the case of the first trough, the sump, or into a gutter that feeds the sump in the case of the other four. This will be facilitated by simply draping the plastic liner material over the spill-side edge. As this is a prototype, ordinary greenhouse plastic will line all water-holding vessels, but a better removable liner solution should be sought in the future if the project shows prospect. Here is some basic system information:
- Fish tank water volume = 6 cubic meters (1,579 gallons)
- Hydroponic component = 5 troughs with an area of 5.6 square meters (60 square feet) each. The water depth is 50cm (19.5 inches).
- Total clarifier volume = 2.85 cubic meters (750 gallons)
- Total system volume = approximately 24 cubic meters (6,340 gallons)
- Flow rate = 2,850 LPH (750 GPH) per pump (2 pumps, so about 1 fish tank water exchange per hour is possible)
Ideally, rainbow trout eyed eggs that are certified free of listed pathogens should be obtained from a reliable supplier such as Troutlodge and Dabie Fish Hatchery (who generously provided this photo) in early August, hatched out, and reared in a small flow-through system for a month or two before the fingerlings are stocked in the aquaponic system. This would require little space and the groundwater in Massachusetts is cold enough to make this feasible without a negative impact on the environment. For purposes of this experiment, however, fingerlings will likely need to be purchased from a hatchery. When they reach plate-size, about an average of 275g (10 ounces), the system should be able to support 500 fish consuming 1.9% of their body weight per day. With 28 square meters (300 square feet) of hydroponic grow area, that will put the amount of feed consumed each day at just under 100g per square meter of grow area. My strategy would be to stock twice that number, 1,000 fingerlings, so as to halve the time it takes for the system to begin producing greens. It will also halve the time it takes to get all the hydroponic troughs producing. When the 1,000 fish reach a weight of about 140g (5 ounces) they will have to be removed, gradually, keeping the system feed rate at about 2.8kg (a little over 6 pounds) per day. This system can be on the high side of the feed/area ratio because the stocking density will be lower and the hydroponic troughs are deeper than in most deep water culture aquaponic systems (i.e. a greater total system water volume). Total fish production is estimated to be between 200 and 250kg (440 to 550 pounds).
The aim of this experiment is to reach and maintain a system water temperature of 16 to 18C (about 60 to 65F) even in the dead of winter. Rainbow trout grow quickly at this temperature. There are many cool climate plants that would also do well with a root zone temperature in this area. Watercress is just one of them. West Virginia University did a study on which plants do well in a flow-through aquaponic system using 12C (53.6F) trout effluent water and published a long list of suitable ornamental plants and vegetables including many lettuces. Four of the hydroponic troughs will be devoted to lettuce varieties as these can be considered the cash crop, and the 5th will be a test area for a variety of other plants. Based solely on lettuce production, the hydroponic component of this system, assuming 1 to 2 weeks for seedling production in trays with artificial lighting, 4 weeks on the water with 4 hours of supplemental lighting a day, and 6 crops during a growing season, has a production potential of 7,680 heads.
One more objective is to create a simulated ecosystem with more complete cycling of nutrients and more effective biological controls through the incorporation of more species and phyla– biodiversity. Crayfish and freshwater prawns have been successfully introduced into hydroponic troughs in aquaponic systems at low densities. Stick-Fins Fish Farm in Florida has been breeding Australian red claw crayfish that can reproduce at lower water temperatures which are roughly in the range that this system will be using. They provide “small breeders” that ship 6 males and 12 females to the box. One box will be stocked in each hydroponic trough. Their job will be to consume the fish waste and uneaten feed that does not get removed by the clarifiers, and, hopefully, to reproduce.
The costs listed below are by no means all of the costs associated with fabricating and stocking the prototype system. I suspect there are “hidden” costs in excess of 20% of the total shown below. In the pursuit for financial assistance in the form of a grant of some kind, this is the amount to be used. It is hoped that other costs are recouped through the sale of produce.
- 151 lengths of 1 x 3 furring strip boards, 8′ in length @ $1.53 = $231
- 44 sheets of 4′ x 8′ insulation board @ $10 = $440
- Miscellaneous hardware = $50
- 163 lengths of 2 x 4 lumber, 8′ lengths @ $2.84 = $463
- 20 sheets of 4′ x 8′ plywood @ $21 = $420
- 1 roll agriculture grade burlap = $65
- 15 used 55-gallon drums @ $15 = $225
- Miscellaneous hardware = $50
- 2 Laguna 900 GPH pumps @ $110 = $220
- 4 Hydrofarm 70 LPM air pumps @ $53 = $212
- Miscellaneous hoses, water test kit, etc. = $50
- 10 sheets 4′ x 8′ Dow Styrofoam 1.5″ Blueboard @ $30 = $300
- 14 T5 HO fluorescent lights @ $138 = $1,932
- 1 Chofu wood-fired water heater = $863
- Greenhouse plastic = $200
- Labor for construction = $2,240
Total = $7,961
Conclusion and Discussion
Both the rainbow trout and the cool climate plants can tolerate periods of very low temperatures. The red claw crayfish, however, will likely die at water temperatures of 10C (50F) or less. It would not, therefore, be a catastrophe if water temperatures cannot be maintained at 16 to 18C (about 60 to 65F). The fish would simply eat less, grow more slowly, and provide fewer nutrients to the hydroponic component. The plants would grow more slowly. I am confident, however, that with the large passive solar component for daytime water heating (if only maintaining the morning temperature throughout the day) and the external 35,000 BTU wood-fired water heater, the optimum temperature can be maintained. The temperature of such a large volume of water would not change quickly. The large volume of water also acts as a heat sink. I would be very pleased to find that two systems of this size could, in fact, share one external water heater. Humidity is a foreseeable issue, but I believe it can be tackled in a number of ways, including injection of warm, dry air for ventilation. This would increase cost so it would only be done to keep humidity at a tolerable level.
The running costs (electricity, cord wood, labor, etc.) will be evaluated and a complete cost for production per plant/fish determined after the trial season. The potential gross revenue from the aquaculture component (the rainbow trout), estimated at an average of $2 per fish for the fish that are removed from the system before becoming plate size, and $5 per fish for the plate size fish, is $1,000 and $2,500, respectively. Considering fish losses of 5%, the total retail value would be $3,325. At first glance, one could easily dismiss this as hardly worth the effort. When you view the fish as small nutrient production units, however, a surprise is in store. The fish waste and uneaten feed will have provided most of the nutrients for plant growth (fish feed does not contain sufficient iron, potassium, and calcium), will have fed the red claw crayfish, and the solid waste removed daily from the clarifiers can be used as is for fertilizer or, preferably, converted to worm castings through the gut of composting worms (part of Phase II). The potential gross revenue from the hydroponic component of the system, assuming a yield over a season of 7,680 heads of lettuce at wintertime retail prices of $1.50 per head, would be $11,520. Thus, ignoring the red claw crayfish, the potential gross revenue over the winter would be $14,845. Incidentally, rafts with 1 to 2-week old seedlings are placed at one end of the hydroponic component and, over a four week period, are gradually floated to the other end. This means that the 6 crops can be grown incrementally and harvested weekly over 24 weeks. This is an advantage if the farmer were to open once a week to sell his produce. Weekly production of lettuce in this case would be 320 heads. A weekly gross revenue of $480 might have its own appeal over the long New England (or any cold climate) winter. This all pales, of course, if you consider having 6 of these systems, or, in the case of Applefield Farm, utilize 78% of the existing greenhouse area. This would bring in a gross revenue of nearly $90,000. Now, if I can just track down Mr. Grant. . .