Black Soldier Fly Hydroponics

 
Overview:
A family sized food growing system utilizing only food waste to then produce fresh vegetables. Through very fast composting via black soldier fly (BSF) larva (similar to vermiculture quality composting), an individual or families generated food waste is quickly recycled into high quality hydroponic nutrient base to grow all of their own vegetables. Piggybacking this technology, earthworms are living in the hydroponic trays with the plant roots, and guppies living in the compost tea, along with the beneficial bacteria. The system is off-grid, using a solar panel (no batteries) to run a ebb/flow 45/15 minute cycle during the daytime hours. In the ebb/45 minutes, an aerator provides oxygenation for the beneficial bacteria and guppies in the compost tea tank. (Click the image for a 1.4mb PDF overview of how the system works.)
 
System Output:
I am regularly growing and harvesting:
Tomatoes, cucumbers, carrots, beets, lettuce, arugula, green beans, peas, strawberries, onions, zucchini, bell peppers, celery, various herbs, and others.
 
Nutrient Sources:
Food waste only. Which consists of any edible foods, including meats. Any waste like chicken parts are encouraged. The more diverse the food waste, the more complete the nutrient base. No bulking materials should be added (no grass, leaves, etc). No woody parts like grape stems, or they will remain as the larvae will not process them. Egg shells are fine, but are not processed fully and add to some bulk material which will eventually build up to be removed from the bins and is excellent around trees or a soil garden. Normal amounts of food waste from preparing meals is all that is required since the system recirculates the nutrients until they are used by a plant (none lost as with dirt farming). If you eat out most of your meals, and don't have food waste, this is a problem. Feel free to collect additional waste from work or neighbors.
You will NEVER use traditional hydroponics chemicals EVER. This is a complete ecosystem, and chemicals/fertilizers would be detrimental to the beneficial bacteria, guppies, earth worms, etc. and are unnecessary.
 
Ongoing Maintenance:
  • At least once per week add your food waste to the active bin (there are active and resting bins)
  • Once every two weeks, rinse the resting compost bin, which adds the nutrients to the hydroponics, this is now the active bin where you will add your food waste, the other becomes the resting bin. (This assumes you use compost bins with screen bottoms, mounted directly over the water trough)
  • Add seeds as you harvest for plants like carrots.
  • Top off the hydroponics system with water usually every 1-2 weeks. My 29 sqft system uses about 5 gallons per week.

Once constructed, ongoing maintenance is extremely limited. Simply add food waste as available (I do so about every 4-5 days), add vegetable seeds where desired (most seeds germinate fine directly), and harvest as appropriate. Depending on the environment and the size of the system, some water may need to be added every 1-2 weeks. In my design, a rain gutter terminating at a 5 gallon bucket keeps water handy as needed. There are 2 food compost/BSF bins over the water tank with screen bottoms to allow for nutrient release as the BSF make it available (and for later rinsing). Usage of the 2 bins is rotated about every 2 weeks (or when the active bin waste is 3" deep). When ready to switch, simply rinse the resting bin compost, this rinsed bin becomes the active bin, allow the previous active bin to rest for two weeks and the BSF to complete processing.
The system is designed to be a "life long" system, particularly when redwood is used. The clear agricultural sheet roofing is rated at 5-7 years life, and is the only ongoing expected repair. This sheet roofing is used on a system in Colorado currently and easily supports 18" of snow. You could use more substantial clear roofing panels, but this would require additional roofing structure, and may limit the sunlight/UV that the plants need or want.
 
Construction & Costs:
My home system uses redwood due to significant rot & termite issues in Hawaii, so this increases the price of the unit as designed. The price using typical white/construction lumber for my design using three 3x3 trays is about $1,000. Using redwood, about $1,400. The unit I built on the University of Hawaii campus is three 4x4 trays (48 sqft w/ 3-4x4 vs. 29 sqft with 3-3x3) in redwood is $2,500. Most likely these prices will be lower outside of Hawaii since things just cost more here (shipped in). With my design you can also use zip-on walls with reversible black/white so that even in winter in some areas, the system is still productive year round. In more severe winter areas, you could have a BSF composting system setup in the garage (with some heat in winter) to continue to process food waste, for immediate start up in spring. Using the zip-on walls in this case allows for a much longer growing season.
 
For my design, it takes 3 full days for one construction talented person to build assuming you have all materials on hand. Here is the wiring diagram of the solar panels, regulator, timer, pump & aerator.
 
When first establishing a system, you will need likely several months worth of BSF food processing to create the initial level of nutrients to begin using your system. You can start your BSF processing and composting before you build a system. If you live in a particularly cold climate, or high altitude, this is especially a good idea to handle any BSF challenges before investing in a full system. (see the section on my desired future research)
 
It absolutely is possible to build a less interesting (less expensive) frame/cover and be successful since the important factors are using the BSF compost with a hydroponics system.
 
For questions, please contact [ Wesley Owens ]
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Pictures

Below is my home system with three 3'x3' trays - withstood a category one hurricane with no damage what so ever.

 
Below is the University of Hawaii system with three 4'x4' trays
Here is my AG 230 class project paper on this system.


 
Below is a close up of the University of Hawaii system BSF captive compost bins mounted over the 150 gallon reservoir. There are doors to close the front not shown here.

 

 
I'm currently (Dec 2017) living & traveling in a 36' motorhome, and traveling the US & Mexico, and so I build a BSFHydro system on my tow car trailer.
Below is a pic of my garden 9 weeks after starting from seeds.

 
About the BSF compost bins
The most important factor on the BSF bins is capture of the liquids created while the BSF are processing your food waste, and then to rinse the finished compost materials with the water from the reservoir so that the nutrients end up in the nutrient water in the reservoir.
Usually you will have 2 compost bins, one active (where you add your food waste currently) and one resting (which rests for 2 weeks while you use the other bin, giving the BSF additional time to fully process)
After 2 weeks (or when the active bin waste is 3" deep), the resting bin will need to be processed to get the nutrients into your reservoir. There are a few ways to do this (see below).
 
A few notes that apply to all methods:
  • Your reservoir pump will need a screen on it (window screen size holes) to avoid clogging up with debris, and to avoid pumping your guppies or small fish into the system.
  • I've found that crunched (not powdered) eggshells in the bins acts as a filler which greatly helps the nutrient drainage. If you have only food waste, the bottom may still plug up too easily, and the egg shells really help prevent this. I've also used papaya seeds (lots) for this purpose.
  • Do NOT wash or add your compost to the reservoir if it STINKS. (see problems & solutions section)
  • If you add meat/animal parts to your bins, then never wash or add the compost to the reservoir unless these items are fully processed by the BSF.
  • Since this is mesophilic compost (70-90 degrees), the solids that you remove from the system with seeds are likely to germinate still, so if you have a traditional thermophilic compost pile (100 degrees+), then it may be good to add there so that the seeds are destroyed (composted).

 
You can do your bins in number of ways:
  • Two bins on the ground - this is more labor intensive and requires you handle the compost
    You can have a bin with many 1/8" holes in the bottom (like a large plastic planter), with a tray underneath to capture the liquids. The bin must not be sitting on the bottom of the tray since this will make the bottom of the compost soggy (anaerobic). It's important for the compost bin to be able to drain of liquids. Usually you will have a lid that has openings in it for the BSF to both emerge as maggots to pupate into the flies, and for the flies to enter and lay their eggs on the lid so that they will fall into the compost when they hatch. Ideally you will have 2 of these bins, so that you can have a bin you are adding food waste into (active bin), and one resting, where the BSF are completing processing for 2 weeks (or until done). If you do it this method, then you will have to then do one of:
    • Dump the compost into the reservoir and stir it up well.
        then either
      • use a screen or small hole fish net to remove all the remaining debris. If you have guppies or fish in the reservoir, this can be a problematic way to do it and not accidentally remove the fish.
      • Leave the materials in the reservoir, knowing that at some point it will build up and need removal as indicated above.
      • This newly emptied bin now becomes the active bin, and the other you were using before the resting bin.
    • either way here, the BSF larvae will float, so be sure to use a small fish net to save them from drowning, and put them back into the active bin. Check the reservoir again within 8 hours to fish the BSF larvae out again. BSF seem to not drown unless left in water for over 8 hours.
  • Two bins with screen bottoms, mounted directly over the reservoir - much less labor, and you rarely will need to handle the compost
    • The liquids automatically drip through the bottom screen into the reservoir.
    • You will need a hose from the pump so that you can rinse the completed resting bin several different times. The liquids will return through the bottom screen to the reservoir taking the nutrients and small particles with it. Depending on what food you have added to your system, you may have almost nothing left in the bin when finished washing. If you have remaining stuff like fruit seeds, etc, then eventually you will need to scoop these out and use as compost elsewhere in your garden.
    • When you rinse this bin, the BSF will not drown and you don't need to do anything with them.
    • If your screen is plugged up with particles, and the bin fills up with water, still well while full, then just leave it full, it will drain. Check the later or the next day, and turn over the compost, getting down to the screen bottom. But be sure you do not puncture your screen bottom! Then rinse again.
    • Rinse the compost up to 4 times (once or more each day), until it looks like the small particles are all gone.
    • This newly rinsed bin now becomes the active bin, and the other you were using before the resting bin.

 
Captive vs. Non-captive
I suggest a captive system where the bins are contained in a screen enclosure so that the flies (or larva) are unable to escape. I've had geckos, lizards, frogs and birds all simultaneously having their way with my BSF larva and flies in a non-captive scenario, creating a problem for reproduction. As well high winds may blow flies too far for them to return to mate and lay eggs. If you build a captive system, make sure you create enough space for them to fly around.
 
Commercially available BSF bins
So far, all the commercially available BSF bins focus on harvesting the larva for feed stock. Every design I've seen likely is routinely anaerobic (and stinky), and since they are sold as single units, are surely fraught with problems. I've seen many using different materials in the bottom of the bins, to facilitate draining of liquids, but all have issues. I myself tried coconut matting, which worked well for drainage, but became compacted with larva which eventually died in place. Basically, the commercial BSF systems I've seen will cause more problems than the benefit of their purpose. However, I have not used any of the commercially available bins, and this is based on my experience with various methods I tried, and my best guesstimate of how the commercial bins work based on exterior photos. The screen bottom as I propose and have used works well, and appears to be a good hole size for the processed particles to pass without much clogging. The clogging I did get cleared up when filled with water, eventually self clearing.
 
Getting your BSF bins started
When you first start, you will likely order or get a limited number of BSF larva from someone. The trick is to not overwhelm your limited number of larva with food waste. You will need to feed them in smaller amounts, just enough that they can consume in a few days. Avoid meat while getting the colony started since it may go off-bad before they have a chance to process it all. I'd suggest starting with a batch of around 1,000 larva. This is around 2 measured cups of adult larva. As well, choose older (larger) larva over smaller, younger larva if you can. The reason being that they live so long as larva eating, that if you start with very young larva, it may be 4-6 months before they mature, pupate into flies, and then lay eggs. What you want is those batches of eggs as soon as possible, so that you can build the colony quickly and then process all your food waste without any issues. During this time, if you live in a colder environment, you will also need to make sure that the bins don't get too cold at night (guessing no lower than 50 degrees). Once the colony is established, they actually maintain their temperature to some degree. As well, once you have been processing food for a while, some non-processed organics in the bins may act as insulation.
 

Problems & Solutions

Common problems with compost:
  • STINKY compost- means that it's gone anaerobic (no oxygen) and has "bad" bacteria. The compost should almost always smell earthy, and never stinky. If it is very wet, then you don't have enough drainage. Or if your compost is very deep (more than 4") it may compact and not get enough air to the bottom. If you add a bunch of anaerobic compost to the reservoir, you may kill the fish.
      Solution
    • If stinky like sewage, you need to turn over the compost in the bin well each day to add oxygen and be sure that it can drain until it's no longer stinky.
    • If stinky like rotting food, it is possible to overload your BSF with food, so build up your colony slowly, and only provide enough food that they can process it in 2 days.
  • No BSF eggs or eggs not hatching (egg clutch remains for more than a week) - The eggs will usually hatch in 2-5 days, and if they do not, then there is maybe a problem.
      Solutions
    • No enough moisture - be sure to use a lid on your BSF compost bin to hold in moisture, but still allows BSF flies to come and go. Some research has indicated 85% humidity is ideal.
    • Not warm enough - The eggs like to be around 80 degrees F to hatch. Cooler evenings are OK, but if the eggs aren't able to warm up, they won't hatch.
    • It is possible they just weren't fertilized. So if most of the egg clutches are hatching, don't worry about a few that don't.

 

Research on Black Soldier Flies

These are all copyrighted by their owners, and are not for commercial use.
Reduction of Escherichia coli O157:H7 and Salmonella enterica Serovar Enteritidis in Chicken Manure by Larvae of the Black Soldier Fly
A Survey of Bacterial Diversity From Successive Life Stages of Black Soldier Fly (Diptera: Stratiomyidae) by Using 16S rDNA Pyrosequencing
Black Soldier Fly (Diptera: Stratiomyidae) Larvae Reduce Escherichia coli in Dairy Manure
Rearing Methods for the Black Soldier Fly (Diptera: Stratiomyidae)

 
Some general tips on using the system: (to be organized and categorized as this list is developed)
  • In the trays, don't grow plants with lots of roots on the opposite side of the tray from the overflow ebb/flow fitting. There is a bottom mounted inlet, and roots can plug it up. I usually plant things like carrots, beets and onions around the inlet side.
  • When you harvest, try to remove all the roots you can. Leaving behind root is not helping and will eventually lead to plugging up of the hyDroton with organic matter. I will usually uproot the entire plant, then gently shake out some of the hyDrotron (so as to not loose them outside the trays), then clip off the top of the plant, and leave the roots lying on top of the hyDroton for a few days so that the earthworms will migrate out of them back into the trays. After this, work the roots well with your hands to remove all the hyDroton. I usually then rinse the roots in the nutrient solution before discarding since they are usually well coated with dried solution. BSF will not eat plant roots, so don't put them in the BSF bin.
  • Start vining plants either against the tray wall by the lattice, or against the wall by a vertical roof support. Tie up the plants to either as they are growing.
  • Do not use water hose water to refill the system. If you do need to use city water, fill the five gallon pail(s) and let them sit for 24 hours before pouring them into the trays or reservoir (trays drain to the reservoir, so sorta the same either way).
  • Most seeds will start just fine directly in the trays, but try not to place them very deep, like no more than two hyDroton pebbles deep, but enough so they will be wet when the tray fills. Once sprouted, most are easy to transplant and divide to disperse better. Wait until they are big enough that you don't damage them, but small enough that they don't have significant roots yet. When you do transplant, bring your hand in from the side, and come up from underneath, allowing the hyDroton to roll away.
  • Don't plant things like carrots and beets right in a dense root area like near the base of a established tomato plant. The dense roots will hang onto the hyDroton pebbles, and prevent carrots and beets from being able to easily move them as they get bigger.
  • Do not put raw eggs in your system. I'm not sure why, but it killed all the guppies when I did this. The amount of raw egg on egg shells is OK, but I don't recommend egg shells since they are not broken down by the BSF.
  • BSF systems have generally be developed to harvest the larva for fish or chicken feed, and you can still do this in the BSF Hydro type system, just be sure that you are seeing enough egg clutches and hatching to support your desired food processing colony size.
  • The earthworms are optional. I grew everything fine before introducing earthworms, and after introducing them my seeds seem less likely to germinate in the trays. Dr. N. Arancon at the University of Hawaii has research that shows that earthworms can harvest and relocate seeds, but I'm not sure if this is the case here. I definitely had no problems starting seeds directly before the earthworms, but that is correlation not causation. You can of course start your seeds elsewhere, and then transplant them into the trays. I have not experienced any shock or seedling death as long as careful to inflict the least damage possible when transplanting.
  • I have experienced occasional drops in nitrogen levels by watching the intensity of the green color in the cucumber leaves. When this occurs, I've simply added about 2 cups of composted chicken manure (which is very high in nitrates) directly to the nutrient water 100 gallon reservoir. This has not caused any issue with the guppies. I also have found rhizobia on the roots of plants in the system (a symbiotic bacteria that creates root nodules that provides plants with nitrogen).

 
My Desired Future Research
  • Simplified timer - DONE. I've located a timer available on ebay for about $8. I generally coat the entire circuit card in silicone or e-6000 to make it weatherproof.
  • Cold weather BSF life cycle system - I've built a system at 9,000 ft above sea level in Colorado, and was able to get BSF to pupate into flies. I was unsuccessful in mating and egg laying in what was a brief test in a non-captive environment, and it was not likely ever 80 degrees. I'll be building a enclosed, insulated BSF hatchery which could be kept in a garage or similar space, and use some heat source and artificial light. Ideally this system will incorporate bins mounted over water, with a switched pump for rinsing as needed over the winter. Once it warms up enough inside the hydroponics enclosure, this nutrient concentrated water would be added to the system, as well regularly during the growing season.
  • With and with-out earthworms - I like the earthworms in the system, but since the seeds sprouted significantly better in my system before the earthworms, I'd like to make a determination if the two are related, and if so, how they are related.
  • How small can it get - I'd like to work on a apartment patio sized system (likely south facing only) and see how well it could work. With only an individuals food waste, I was able to have 27 square feet of growing space filled and producing, perhaps there could be 2 levels of trays along the railing with less sqft, but more concentrating growing...
  • Restaurant - I'd like to work with a restaurant who likely already uses a garden for some of their stocks, and solve both a waste disposal problem, and provide fresh vegetables and herbs at the same time. If they already use soil farming, this would also be a incredibly significant labor savings.
  • Indoor system - likely this would be similar to the cold weather system, where the BSF bins are in a alternate location, with the trays located indoors along south facing windows. The solution doesn't really have an odor to it, so I think this is a viable situation.
  • Top of high rise housing building. Residents could recycle their food on the roof.
  • ... and others, but this is the big ticket items I'd like to work on.

These images are of food grown in a BSF Hydro system at home, or at the system I built at the University of Hawaii @ Hilo.
Just place your mouse pointer over a thumbnail to view the image larger.