micro farm greenhouse

Hello,

I would like to present and develop my ideas for a micro farm greenhouse (heated) in a temperate climate that I want to build some time next year. It is an integrated system for laying ducks and fish that are fed with black soldier fly larvae, water fern (Azolla) and duckweed (Lemna).

The goal:
I want to create a system that is capable of producing a good amount of mainly calorie-dense food. 100 % self sufficiency is not the goal, more important is reliability in the sense of resilience, easy controlling and self regulation. It should also be rather low tech and function without chemical inputs, no mineral fertilizers (NPK).

The input:
I said no NPK, so the main nutrient input will be food waste, slaughter waste, manure, whatever is available. No human feces, as that would require quite an effort/time to make it safe.
Also, no commercial fish food. I don't want to feed my fish fish meal, soy or any grains as I think it's either unsustainable or unnatural or both.

The output:
Duck eggs, fish, maybe crayfish, maybe snails plus some vegetables and greens. Preferably calorie-dense foods.

The system (rough outline):
The greenhouse will have a pond where duck poo, fish poo and black soldier fly leachate are going into. In this pond there will grow water fern (Azolla) and duckweed (Lemna) and some other Floating plants together. They will remove the nutrients from the water and serve as fodder for ducks, fish and as green manure depending on how fast it will grow. They will also go into a black soldier fly bin, together with food waste, to grow black soldier fly larvae that go directly into the Pond to feed the ducks and fish.

But why???:
Fun, independance, research, because I can.

Description of the components:
The pond:
The pond recieves the manure of the ducks, fish and black soldier fly larvae and serves as heat storage in the greenhouse. It can be as shallow as 10 cm for growing the plants, but a deeper pond would yield more heat storage. The pond will cover all of the surface of the greenhouse for maximum photosynthesis. A metal grid above the pond will support all the other elements. That way, no space for paths is wasted. Both Azolla and Lemna are floating plants that can grow in high nutrient environments, grow very rapidly and can serve as fodder. Azolla seems to be more productive, grows best with only 25 - 50 % sun exposure and fixes nitrogen. Lemna on the other hand seems to have a better fodder value. Under high nutrient conditions it can have 45 % protein (Azolla ~25 %). Studies show that Azolla can substitute 10 % of a commercial Tilapia diet, while Lemna can substitute 40 % before weight gain decreases. So, both have their pros and cons and I want to grow them together. They have to cover the whole pond at all times in order to use as much light as possible. The harvest has to be scooped out daily for maximum productivity.

The fish:
I plan on stocking catfish and tilapia in the greenhouse Pond that feed on Azolla, Lemna and black soldier fly larvae. I prefer a low stocking density, so I don't have to aerate that much.

The ducks:
Most of the daytime, they will forage outside, the rest of the time they will stay in the greenhouse. Inside they feed on Azolla, Lemna, black soldier fly larvae and small fish offspring. They can swim in the pond or stay on the metal grid. The idea is that their poo falls directly into the pond, but I have to check if the grid is ok for their feet.

The black soldier fly bin:
The larvae serve as fodder source, just as Azolla and Lemna. The bin will be installed in a way that the prepupae move up a ramp (which they do naturally) and drop into the pond all by themselves. From my own experience, they eat both Azolla and Lemna and grow at an incredible speed. They will also get all kitchen sraps, slaughter waster (from the fish) and maybe coffee grounds, restaurant waste and so on. The liquid will go into the Pond to fertilize Azolla a and Lemna.

So far the rough outline of the project. Next post will be the beginning of the dimensioning. Looking forward to feedback, postitive or negative!

Here is a raft draft of the greenhouse. It is an earthsheltered greenhouse that is partially buried in the soil to regulate the temperature (the green surfaces in the pictures are supposed to be grass). The interior Pond is connected to an outside Pond to allow for water Exchange, if nutrient loads are getting too high. The outside pond also reflects sunlight into the greenhouse (south side) in winter, when the sun stands low. Along the backside in the greenhouse are laying boxes for the ducks. Behind them is a vertical wicking bed that is filled with charcoal, Perlite, vermiculite and compost und pulls up the nutrient rich pond water upwards, so vegetables can be grown in the backside of the greenhouse, out of reach from the ducks. the black soldier fly box is not shown yet.

This is what a mixture of Azolla and duckweed and some other floating plants looks like. These plants have an enormous capacity to take up nutrients. Azolla is the fastest growing plant on the planet followed by duckweed, both grow at an exponential rate, doubling every 2-3 days under optimal conditions.

Would the indoor pond be fully lined with insulation underneath to thermally separate it from the earth underneath? I'm wondering that as Tilapia require rather warm water to be productive and survive, relative to catfish. Depending how deep the pond is, the earth underneath will be a heat sink and draw heat from the water, possibly making it too cold for the tropical fish (depending on location).

You might find some other species which are more tolerant of varied conditions similar to catfish, or if the pond is deep enough a colder variety may work better.

Mark Tudor wrote:Would the indoor pond be fully lined with insulation underneath to thermally separate it from the earth underneath? I'm wondering that as Tilapia require rather warm water to be productive and survive, relative to catfish. Depending how deep the pond is, the earth underneath will be a heat sink and draw heat from the water, possibly making it too cold for the tropical fish (depending on location).

You might find some other species which are more tolerant of varied conditions similar to catfish, or if the pond is deep enough a colder variety may work better.

Good point! I'm not planning to insulate the interior pond. The local average temperature is 8,5°C, which is what the deeper soil layer will have then more or less. Tilapia start dying below 10°C. I think it's quite hard to predict what the minimum water temperature will be like in the coldest months as a lot of factors are contributing. I guess I'll start with just catfish to be on the safe side and see what the first winter will be like. The emphasis is on the ducks anyway and most breeds are surprisingly tough.

What temperature do the water plants need in order to proliferate at the needed rate?

Will you insulate the part of the E, W and North walls that are within 4' of the surface of the surrounding soil?  I can understand the concept of not insulating the bottom of the pond so that it harnesses the semi-deep earth temps.  Just don't forget that any soil near the surface and touching your greenhouse will be frozen in the winter and will suck the heat out.

One idea that comes to mind is that you could dig the pond extra deep in a couple spots to tie into warmer/deeper temperatures.  Steep pond sides are a challenge but I'm imagining a 2-4' diameter pipe or culvert standing on end.  It would hold back the dirt and the water inside it could "mine" heat from below.  I'm not sure if the convection of that heat would be sufficient to actually help heat the building...

That idea of having deeper parts of the pond is really cool Mike!
I'll have to look into that myself.
John,if the fish have free access to the plants and the ducks free access to the fish and the plants,you might find yourself without either fish or plants.
On the other hand, allowing ducks access to a pond without filters or water changes of some sort is probably asking for trouble.
You could segregate the plants with floating cages , but im not sure what would allow ducks and fish to coexist in a pond at this scale.
Floating your structure on the pond might be cheaper and easier than building a steel span.
Floating duck roots are well known,for other stuff, steel "Metro" style shelves are strong enough to walk on ,and modular.

Mike Jay wrote:What temperature do the water plants need in order to proliferate at the needed rate?

Some duckweeds are supposed to grow even below 10°C. But I don't think there will be any significant growth below 15°C.

Will you insulate the part of the E, W and North walls that are within 4' of the surface of the surrounding soil?  I can understand the concept of not insulating the bottom of the pond so that it harnesses the semi-deep earth temps.  Just don't forget that any soil near the surface and touching your greenhouse will be frozen in the winter and will suck the heat out.

You're right about the heat loss at the upper soil layers. However, I think that amount is negligible compared to the amount I will lose through the sheet at the whole front. Therefore I plan to roll down an insulation over the whole front, when it gets really cold. Otherwise I will probably not use any insulation to keep it simple.

One idea that comes to mind is that you could dig the pond extra deep in a couple spots to tie into warmer/deeper temperatures.  Steep pond sides are a challenge but I'm imagining a 2-4' diameter pipe or culvert standing on end.  It would hold back the dirt and the water inside it could "mine" heat from below.  I'm not sure if the convection of that heat would be sufficient to actually help heat the building...

You mean geothermal heating? I just googled that, you would need to dig 33 m deep for a 1°C increase in temperature on average. Sounds like a lot of digging to me or I misunderstood your idea.

William Bronson wrote:John,if the fish have free access to the plants and the ducks free access to the fish and the plants,you might find yourself without either fish or plants.
On the other hand, allowing ducks access to a pond without filters or water changes of some sort is probably asking for trouble.

That depends on how much plants, how much fish and how much ducks there are. The components need to be kept in balance. I will post some calculations on that soon.

You could segregate the plants with floating cages , but im not sure what would allow ducks and fish to coexist in a pond at this scale.

Well, ducks can only eat what fits in their beak, so with bigger fish, I don't see a problem. The same goes the other way round.

Floating your structure on the pond might be cheaper and easier than building a steel span.

Yeah, true, but I want to be able to use as much light as possible and grow floating plants even below the steel span. I will need to do some calculations there.

Last January I scraped aside 12" of snow in my yard and dug a hole.  It had been 10F for the high and -5F for the low for the month.  The ground wasn't frozen but it was close.  When I got down to 7' deep it warmed up to 47F.  So I saw about a 12 degree F temperature increase from 0 to 7 feet.  I doubt that increase would continue for the next 7' but temperature did climb a fair bit.

The concept I'm thinking for "geothermal" would be to dig the equivalent of a hand dug well about 8' deep.  Or however deep you can safely and easily do.  Or do several.  Then support the sides with stone work, block or a piece of road culvert.  The top of the well or culvert would be at the bottom of your pond depth so the pond is sitting on top and connected to the water in the deep well.  

If you have a high water table and that hand dug well connects to the water table, that could work for or against you.

Regarding the heat loss to the cold ground, I would not assume it is negligible.  Now, I am assuming that you get frost in your soil and that it is frozen for the first foot or two below grade.  That could be a very bad assumption on my part.  But if that soil is frozen (or in some climates, well below 0C), that is a very cold surface up against your wall.  While your glazing has poor R value and is fighting off the exterior air temp, at least for some of the daytime it could be above freezing.  On the other hand, the walls will be fighting this constant frozen dirt temperature all day long.    

In my greenhouse design I planned on R20 for the first 4 feet underground.  By doing that, the ensuing heat loss was indeed negligible.  If your design counted on a lot of snow to insulate the ground for you, that could work in your favor.  As long as it doesn't block light in the South side.

Mike Jay wrote:The concept I'm thinking for "geothermal" would be to dig the equivalent of a hand dug well about 8' deep.  Or however deep you can safely and easily do.  Or do several.  Then support the sides with stone work, block or a piece of road culvert.  The top of the well or culvert would be at the bottom of your pond depth so the pond is sitting on top and connected to the water in the deep well.

 
Are there some example of that concept or is it your own idea?

In my greenhouse design I planned on R20 for the first 4 feet underground.  By doing that, the ensuing heat loss was indeed negligible.

Sounds reasonable. But you're in zone 4, I'm in 7, maybe 8. However, if a little insulation can extend the productive season it probably pays for itself.

I'm still unsure how I would construct the walls. With the interior pond, I'm afraid any wood will rot easily. I thought about covering the earth walls with liner from the inside and just putting in some vertical steel rebars, connecting them with horizontal steel rebars to press the liner onto the earth.

I believe it is my idea or something I inadvertently stole from someone else on permies.  I haven't seen it in actual use, it is just an idea that seems like it should work.

As for the walls, have you seen the wofati construction method?  Logs and boards form the walls with bracing to keep them from tipping in.  They have plastic on the earthen side to keep them from rotting as quickly.  The pond would have to not touch the logs so a small walkway around the perimeter of the pond could ensure separation.  

I'd echo William's concern about the ducks eating all the vegetation. I have three very young ducks and they gobble up duckweed faster than I can get it in the pond which has about a 1000 sq ft surface. Looking forward to seeing your calculations on that as they may help me out!

Mike Jay wrote:
As for the walls, have you seen the wofati construction method?  Logs and boards form the walls with bracing to keep them from tipping in.  They have plastic on the earthen side to keep them from rotting as quickly.  The pond would have to not touch the logs so a small walkway around the perimeter of the pond could ensure separation.  

Just looked into it. It says it is mainly based on Mike Oehler's concepts. I read his book about earth-sheltered solar greenhouses, it was a huge inspiration for me. Nevertheless, I am concerned about the longevity of the wood, as I assume, I will have very high humidity inside coming from the pond.

John Natoli wrote:I'd echo William's concern about the ducks eating all the vegetation. I have three very young ducks and they gobble up duckweed faster than I can get it in the pond which has about a 1000 sq ft surface. Looking forward to seeing your calculations on that as they may help me out!

I'm just guessing, but probably your pond has very little nutrients in it.

Here are the calculations. I can provide references for most numbers, if anyone is interested, just ask! All the masses are referring to the dry mass! So, 32 t/ha/y of duckweed yield means about 640 t/ha/y of fresh weight, because it's about 95 % water. The same goes for food waste, duck eggs, larvae, it's all specified in dry mass! Have a look at the attachment first as an orientation.

One duck needs on average: 125 g of dry feed per day with 18 % Protein, which equals 22,5 g Protein, which equals 3,6 g N. It lays 0,66 eggs per day (80 % laying ducks, each having 300 eggs per year) having 5,9 g protein which equals 0,9 g N. The duck poo contains 2,5 g N then. However, the ducks will spent 50 % of their time outside of the greenhouse, so only 50 %, 1,3 g N go into the interior pond. I would feed one duck 10 g of larvae per day. For that I need to put in 67 g of food waste (12 % protein) which would result in the production of leachate with 0,6 g N entering the pond.

Together one duck and the larvae rearing for this one duck would put 1,9 g N per day into the pond. Duckweed can take up 4,4 g N per day per m² under favorable conditions. The trick here is to keep them at the perfect density at all times: thick enough to cover the whole surface to make use of all the sunlight hitting the surface and to suppress competing algal growth underneath, but not too thick to induce crowding, which inhibits or even stops the growth of duckweed. Let’s assume, I would have a removal of 2,2 g N/m²/d with all the floating plants, then I could get 115 ducks plus the respective larvae rearing without accumulation of N in the pond.
115 ducks would produce 76 eggs having 108 g N per day, which would be the system’s output. The system’s input would be 7,7 kg of food waste for the larvae rearing with 148 g N. In this case I would have a surplus of 40 g N per day. However, I did not take into account any losses of N, like denitrification, sedimentation and volatilization of ammonia, which can be higher than 70 % of all N under high N conditions. The system buffers itself, so to say.

The area of 100 m² would produce 877 g of floating plants per day (32 t/ha/y). For one duck out of 115 that would be 7,6 g per day. That’s rather low, even when they can forage outside. However, this is based on a productivity of 32 t/ha/y of floating plants. The highest yield under lab conditions for duckweed is 183 t/ha/y, for Azolla it's 360 t/ha/y, so there is still room for improvement.

As I made many assumptions and all of this just serves as a rough estimation, I will start with a small number of ducks and fish and larvae and slowly increase their numbers while keeping dissolved oxygen, temperature and salinity (as an indirect measurement of N) of the pond in check. No pumps, no aerators, and no need to rush it.

On that basis I have to regulate the system by observing these three main parameters and readjusting them:
Dissolved oxygen too low: reduce the number of fish, put less leachate from the larvae in the pond
Dissolved oxygen too high: unlikely
Temperature too low: improve insulation, heat (I’m thinking about a thermo siphon stove with an inside copper coil tubing that lets the pond water run through it)
Temperature too high: increase ventilation, exchange water with exterior pond
Salinity too low: put more food waste into the larvae rearing, get more fish/ducks
Salinity too high: exchange water with exterior pond, put less food waste into the larvae rearing, reduce the number of fish/ducks

One of the most interesting studies I found regarding duckweed research is this one:
"Nutrient recovery from swine waste and protein biomass production using duckweed ponds (Landoltia punctata): southern Brazil" https://www.ncbi.nlm.nih.gov/pubmed/22592476
The authors grew duckweed in anaerobically digested swine manure in ponds for one year and managed to produce a yield of 64 t/ha/y dry mass with an average protein content of 35 %. They concluded that this type of duckweed farming produced 20 times more protein than soy in the same time period on the same surface area under the same climatic conditions.

So, I'm guessing, an integrated system with duckweed cultivation might be the most efficient way of farming. The highest yield obtained with duckweeds is 183 t/ha/y under lab conditions, so there is even potential for further improvement! Additionally, the protein content can be 45 %, when the nitrogen content in the pond is maintained at very high levels. http://www.fao.org/ag/aga/agap/frg/lrrd/lrrd7/1/3.htm
In contrast to using swine manure as nutrient source, with ducks that have acces to the duckweed pond, there is no need to transport their feces from A to B as they directly crap into the pond.

Here's a video explaining how a thermo siphon works: https://www.youtube.com/watch?v=5IRLVCJ1olA&t=
I would like to use that to heat the pond inside the greenhouse with firewood. The method could be combined with a rocket mass heater, whereby the exhaust would be going through the pond before exiting the greenhouse. I imagine, it's a lot more efficient to heat water than to heat air, as water can store much more heat.