Cold Season Aquaponics in Underutilized Greenhouses– How to Improve the Livelihood of the Family Farmer

Now that I’m dealing with agriculture and aquaculture extension people and the USDA Sustainable Agriculture Research & Education program, I’ve decided to remove “Lunatic Farmer” from my article titles. For my regular readers (all three of you), I promise that this will be my last “thinking out loud” article. You will soon be rewarded for your loyalty with the gut-wrenching story of my involvement in the demise of 750 baby tilapia. But, first, I need somewhere that I can point people to.

Living in one of the world’s least developed countries, it’s been difficult to get used to the idea of potentially doing things in a mostly developed country like the USA. At first I thought I’d just heat water by filling a used steel barrel and building a fire under it, just like they do here.  Anyway, as this has evolved, and with the modest chance of the US taxpayer footing part of the bill, I’ve come up with some common-sense changes and improvements which I’ll discuss below. But it doesn’t have to be expensive. The coordinator for a project in Hawaii (a professor at the University of Hawaii) confirmed this via a personal communication I received from him:

. . . Please note that when most people build aquaponics systems they want one or two more bells and whistles than someone else has.  We started off on a different foot.  We started off from the point of view of the farmer where capital costs and operating costs must be subtracted from gross sales. Our system is 4-8 times cheaper than other systems around here.

Statement of Purpose (Modified)

Underutilized greenhouse in Massachusetts-- look at all that space!

The importance of local, family 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.

The possibility of increasing gross earnings through aquaponics for family farms is not limited to those with existing greenhouses such as my brother. In fact, it may be the deciding factor in a farmer’s decision to build a greenhouse in the first place. I suspect my brother spent many sleepless nights wondering if he was doing the right thing by making such a heavy investment. But if it can be shown that with a little ingenuity a greenhouse in a cold climate could function as a multipurpose facility, improving the family farmer’s livelihood, then it should be taken into consideration.

Indeed, this could be of benefit to both the family farm and the nerdy aquaponics enthusiast in town with the small backyard. The aspiring non-traditional farmer could inquire about the possibility of renting some area in the conventional farmer’s greenhouse while he’s not using it, promising not to break anything, of course. What is there to lose for either of them? Could this be the start of a new cottage industry of nerds producing local, fresh crops for us in the cold season?

This is a proposal for a low-cost prototype system which would aid greatly in determining the potential and limitations of such a venture.

Why Aquaponics?

Both aquaponics and hydroponics are proven methods for high density production of plants in enclosures. Startup and running costs are the limiting factors, especially for year-round production. Hydroponics is by far the more mainstream method, but aquaponics is catching up quickly. Aquaponics is the natural choice for a family farmer who believes in the concept of organic farming whether certified or not. It is organic be default. A myriad of microorganisms form a symbiotic army tasked with converting fish waste and excess feed into the nutrients that the plants require while making the system water safe for its return to the fish. Hydroponics is sterile. The nutrients are produced in factories and transported to the farm in trucks, whereas in aquaponics they are produced on site within the system itself. Also, an aquaponics system does not need to have its system water changed; just top it off now and then when it starts getting low. With hydroponics, system water must periodically be completely discharged and replaced because of the build up of salts. Lastly, studies have shown that aquaponics is significantly more productive than inorganic hydroponics for production of food plants in greenhouses.

Summary of System Modifications

  • Heat source– At first I considered an inexpensive wood-fired spa heater, but since this project can now be loosely defined as a scientific experiment, I’ve decided to use a tankless “on-demand” liquid propane water heater. The EZ101 is rated at 42,000 btu and at $145 it seems like a good deal. Liquid propane is considered a “green” alternative energy source. Unlike wood, it would allow us to keep track of how much heat energy is put into the system by keeping records of usage.
  • Fish tanks– Although fabricating one big rectangular one out of plywood and framing materials and lining it with greenhouse plastic would work, I don’t think it’s wise to skimp in this area. First of all, two is better than one in terms of redundancy. That’s why each circular, fiberglass tank will have its own pump. If one pump fails, stop feeding the fish and alternate flow with one pump until a replacement is found. Also, circular tanks are, to a degree, self-cleaning, and solids are more easily removed. Plus, a modest current can be generated and rainbow trout are said to appreciate that. The tanks are small enough that they could be moved out of the greenhouse when the space becomes needed.
  • Insulation for fish tanks and hydroponic troughs– Shredded newspaper was a pretty crappy idea. It would turn to mush with the slightest condensation. I was very pleasantly surprised to learn about sheep wool insulation. I didn’t even know it existed. Not only does it absorb and buffer moisture, it releases heat as it does so. The 4″ (10cm) thick material has an R-value of 13. Presto, potential condensation problems mostly solved.
  • Insulation board for the enclosure– beefier, r-5, 1-inch boards, painted white on the inside to reflect and diffuse natural light. Update: See “The Straw Bale Solution,” below.
  • Enclosure for the barrel clarifiers/passive solar heating units– Shiny, corrugated aluminum or steel partial enclosure with clear plastic cover. Still working on the design here.
  • Hydroponic trough water depth– stopped trying to fix things that aren’t broken by lowering the water depth from 50cm to the more commonplace 30cm. Still plenty of head room for the Australian red claw crayfish.
  • Sump water depth– lowered to 15cm, still plenty of volume.
  • 2013/14 winter experiment– it would be extremely useful to remotely monitor and record the relevant environmental conditions (air temps, water temp, humidity, natural light, etc.) that occur in a mini-prototype before the bigger one is build for winter 2014/15 (no fish or plants).
  • Update: Contingency plan– It’s been pointed out that trout are tricky, so I’ve added a contingency plan in case I kill them all. I’ve also decided to increase the capacity of the fish tanks in order to lower the stocking density.

Modified System Overview (Update: See “The Straw Bale Solution,” below)

Aquaponics system showing enclosure and stages of expansion

Nothing much has changed here except improvements to maintain water temperature in the various vessels. Fish tank water is pushed up from the bottom of the center of the tanks and flows by gravity into a 4″ PVC pipe. Not shown, a serviceable manifold will be designed from which 1 flexible hose of suitable diameter will supply, by gravity, the first barrel of each clarifier unit. The system water will pass through the barrels consecutively and spill from the third barrel into the hydroponic trough. The barrels will be equipped with baffles as in sewer systems. Each barrel will have a tap at the bottom for removal of settled solids. From the hydroponic troughs, water will flow by gravity to the sump. From the sump, two pumps, each capable of exchanging one fish tank’s water volume per hour, will return system water to the respective tanks.

  • Fish tanks– 2 cylindrical fiberglass tanks with a capacity of about 2,300 3,000 liters (605 790 gallons) each for a total volume of 4,300 6,000 liters (1,210 1,580 gallons)
  • Pumps– 2 pumps each capable of pumping 2,300 3,000 liters (605 790 gallons)
  • Aeration– A 70 LPM air pump for each fish tank and hydroponic trough
  • Hydroponic component– 5 to 7 (only 5 shown above) troughs with a water depth of 30cm (12 inches) and surface area of 5.6 square meters (60 square feet) each.
  • Total clarifier volume– 3,830 liters (1,008 gallons) @ 7 troughs
  • Sump– 450 liters (118 gallons)
  • Total system water–  approximately 20 21.4 cubic meters (5,250 5,630 gallons) @ 7 troughs

The Straw Bale Solution (New!)

Straw bales for the enclosure-- why did it take me so long to think of that?

If I were doing this in Laos, I would use woven polypropylene “rice bags” with rice husks for insulated walls wherever they would not block the sun. I’ve kind of envied the Western permaculture folks with their straw-bale homes and such, so now’s my chance. Using straw bales is such a good idea for this purpose that I’m surprised how long it took me to think of it. First of all, they are something a family farm can easily obtain if they don’t have a source already. Secondly, compared to 1″ thick rigid insulation board with an R-value of 5, these things rock. And, lastly, they should work well in this application for the very same reasons that they are not recommended for humid locations. Here I’m taking a giant leap of faith in saying that they will have a huge buffering effect to control humidity (my second-most worrisome issue after temperature). A natural material just like the sheep wool insulation mentioned above, if they absorb a lot of moisture from the humid environment, they will deal with it and release heat.

I like the idea so much I've added another view

A stack of 5 bales would give a ceiling height of about 205cm (6’9″). With some buttresses built in here and there, the whole thing could go up an a matter of hours with a small crew and plenty of cold beer. I can almost feel the underside of my forearms itching already. Before establishing Applefield Farm in 1981, my brother, Steve, used to cut people’s hay and I, a teenager at the time, sometimes helped out. Using straw bales would kind of bring things full circle. I suspect that after a season of intense humidity buffering, the straw bales would be getting a bit “mature” with a good bit of aerobic decomposition in progress. But, if they are intended to be used as mulch, they will have actually increased in value.

With such robust insulation for walls, I couldn’t resist upgrading the ceiling insulation to 4″ sheep wool insulation.

Fabrication and Underlying Principles

Except for the 2 fiberglass fish tanks which are small enough to be moved without the use of any heavy equipment, all components will be designed such that they can simply be placed upon the existing greenhouse’s concrete floor and bolted together. The hydroponic troughs and sump will be lined with 2 layers of greenhouse plastic. All water holding vessels will be insulated with condensation-proof sheep wool insulation held in place by breathable agriculture grade burlap. The system and its enclosure will be designed for quick and easy assembly in the fall and dismantling in the spring. It will grow (expand) as the fish consume more and more feed until it reaches an equilibrium. It is difficult to predict how quickly this will happen and how many hydroponic troughs the fish will be able to support. Indeed, discerning this is one of the purposes of the experiment. However, certain broad assumptions may be made based on what is known about rainbow trout growth and feed rates. And, it has been established that 60 to 100g of feed put into the system daily can support 1 square meter of growing plants in deep channel culture. From this, we can anticipate something like the following scenario.

Stage I

It is estimated that it will take 8 months from receipt of 1,000 eyed rainbow trout eggs (minimum order quantity) to fully pan-size, 275g (10oz) fish. That means getting started in mid-July if the entire system is to be dismantled and removed from the greenhouse by mid-March. For the first 2 months, only space for 1 fish tank is required. During this period, no system enclosure is necessary; the existing, permanent greenhouse will do the job. In fact, in order to maintain water temperature at between 16 and 18C (60 to 65F), shade cloth during the day and the addition of 8.5C (47F) groundwater may be required. Since the one fish tank will be well insulated and shaded, and will have a volume of about 2,300 3,000 liters (605 790 gallons), any temperature changes would not be sudden and could be corrected accordingly. The first hydroponic trough could be added to the fledgling system any time there is space. The sooner the better, because naturally forming bacteria will begin to colonize and multiply on its surfaces (a good thing). The troughs will also contain substrate (hiding places for the Australian red claw crayfish in the form of PVC pipe cutoffs) which will increase the surface area for the microorganisms. In principle, deep water culture (raft) aquaponics does not need a separate bio-filtration unit. Depending on the feed consumption of the fish, the first 4′ x 4′ raft (Dow blue board) may be set afloat on the first hydroponic trough as early as the 1st of September.

Stages II through V to VII

The existing greenhouse will probably provide enough of a greenhouse effect until mid- to late-fall. Daily replenishment of system water losses through transpiration and evaporation (and solids removal), estimated at 1 to 2% per day, with heated groundwater may be sufficient to keep the system water at the target temperature. When this is no longer sufficient, it would probably be about the time that the temporary enclosure should go up. The decision when to begin putting it up should be based on observation and common sense. It should be fabricated and ready to be put in place well in advance.

It’s impossible to estimate accurately when the system will be at or exceeding Stage V. What we do know, however, is that when the fish reach an average weight of about 140g (5oz), the system will likely be maxed out. It is possible, however, that the fish could by then be supporting a Stage VI or even VII. But, regardless of how much the hydroponic component has expanded, the fish will simply be running out of room. The stocking density will be approximately 60 46kg per cubic meter (1/2 1/3 pound per gallon). In the worst case scenario, we could begin eating them.

I will know in more detail when I get information from the eyed egg supplier about the growth rate of their rainbow trout at 17C. It’s unusual to have a controlled water temperature, a luxury reserved for recirculating (RAD) systems. Regardless, I think it is entirely likely that the system will be supporting 5 to 7 hydroponic troughs growing lettuce by mid-November to mid-December.

Heating and Ventilation– Why It Will Work

Twenty 21.4 cubic meters (5,250 5,630 gallons) of insulated warm water in an enclosure covering 190 square meters (2,024 square feet) is a significant, if not tremendous, heat sink, as is the exposed concrete floor. But the ingenious, if I may say so myself, component in this design is the passive solar barrel heaters that also function as solids settling tanks. Admittedly, a better, more efficient design may be called for. The contribution that this component will make to heating and environmental conditions within an enclosure will be studied over the winter of 2013/14. See “The Mini-Experiment” below.

Additional water heating will, however, be required, and, tentatively, I believe a liquid propane “on-demand” tankless water heater is the way to go. The one I’m considering would be installed just outside the system enclosure and would be controlled by a thermostat to heat water to a certain temperature at night. Likewise, its venting duct will be enclosed in a box made of metal or other suitable material so that the dry heat that it radiates can be injected into the enclosure (a large computer fan should be sufficient.

As for ventilation, since the system must facilitate growth (expansion), extraction fans will have to be mounted on each 8′ x 8′ lightweight panel that serves as the back wall of the enclosure. (Nope, better to stack straw bales for the walls and put the extraction fans in the ceiling panels). These would be controlled such that they turn on at a certain air temperature or humidity level within the system enclosure. In extreme situations, the clear plastic at the front of the enclosure could be manually rolled up to allow maximum relief. Cold nighttime temperatures will not harm the plants as their roots will be comfortable, but humidity and overheating might.

The Living Components

Eyed eggs ship well and are free of pathogens-- they are also all females, which means they grow faster and taste better (photo courtesy of Dabie Fish Hatchery)

Rainbow trout have been chosen over tilapia for the obvious reason that they thrive at cooler water temperatures. I was also pleasantly surprised to read in the literature available that even at a pan size of 275g (10oz), at 16 to 18C (60 to 65F), they can consume as much as 1.9% of their body weight per day. Ideally, eyed eggs that are certified free from listed pathogens should be sought out and hatched out oneself. If this were done in one of the two fish tanks, the natural microorganisms would begin to colonize the system earlier. A simple biofilter could be added to aid in the process. By stocking twice as many fish as the system can handle at full capacity, production of food plants can begin twice as quickly and the system will reach its full potential twice as fast.

With deep water culture aquaponics lettuce grows faster and at greater densities that in the field

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 and ascertain whether or not this is feasible. 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. Based solely on lettuce production, and obviously counting chickens before they’ve hatched, the system is capable of producing over 10,000 heads of lettuce before it is dismantled in the spring.

These fellows are not just tasty, they will clean the hydroponic troughs

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, they will reproduce. If this were the case, they could be reared in ponds outside over late spring and summer and harvested in the fall, and the process could be repeated.

Contingency Plan– What if I Kill the Rainbow Trout?

A professor at the University of Hawaii and grantee of the same grant that I’m likely to apply for commented that “. . . rainbow trout are notorious for being sensitive to less than pristine water quality.  You may have trouble keeping your fish alive if you use trout.  I would suggest cold tolerant tilapia, Oreochromis aureus, the so called blue tilapia.” This is sound advice. I’m determined, however, to give rainbows a try, but I realize the need for a contingency plan in case I send them to their maker before their time. The role of the fish is to metabolize feed and supply the nutrients to the plants via the plethora of microorganisms in the system. For this, any fish will do. If I kill the rainbows at an early stage, I could perhaps invite the fish in my brother’s backyard pond inside for the winter, or I could buy some koi. Koi seem like a good choice. In such a case I’d raise the water temperature to 24C (75F). The Australian red claw crayfish would be happier. It is hoped, however, that the fish harvest will offset the additional propane and electricity costs associated with cold season production, so a pricier fish that requires less water heating is preferred.

The Mini-Experiment (Also See Mini-Experiment II, below)

Let's get an idea what conditions would be in there over the winter of 2013/14

Having a good idea beforehand of roughly what it will be like inside the “greenhouse within the greenhouse” before the bigger project goes ahead over the winter of 2014/15 would be tremendously helpful. As such, I’m considering setting up an experimental hydroponic trough, passive solar barrel array, and enclosure. Remote climate monitoring equipment isn’t that expensive these days. I’d like to know what the temperature is outside, inside the existing greenhouse, and inside the enclosure. Of course, it would also be prudent to monitor the water temperature (it would be circulated with an aquarium pump), humidity, and the quality and quantity of natural light over the winter of 2013/2014. Incidentally, the red shafts in the sketch represent the elevation of the sun at noontime in mid-fall and mid-winter.

Mini-Experiment II– with Modified Passive Solar Component

Mini-Experiment with (possibly) improved passive solar component design

Google Sketchup is an excellent tool for playing around with designs, and it’s free. It let’s you design things that Sir Issac Newton would balk at, though. For those of you who have been wondering why the ceiling appears to be defying gravity, it’s just that I couldn’t be bothered showing it either (a) suspended from the existing structure’s robust steel framework or (b) using simple wooden posts attached where necessary to the hydroponic troughs. Anyway, as I was turning the mini-experiment into one that incorporates straw bales, I also hit on what may be an improved passive solar component design. For all apparent unenclosed areas, imagine battens and draped greenhouse plastic.

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. The availability of light is certainly an issue.

Based on information kindly provided to me, the “consumables” involved in aquaponic lettuce production (seeds, Oasis cubes, etc.) cost about $0.12 per head of lettuce. Considering the retail price of lettuce in the winter, at about 10,000 heads, that would leave a lot of room for propane, labor, and electricity. I suspect the estimated value of the fish ($3,250) would cover the cost of propane and electricity, leaving a healthy reward for the family farmer’s efforts.

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