Scaling Up Black Soldier Fly Food Scrap Processing | Phase III : The Life and Times of BSF (Black Soldier Flies)
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Scaling Up Black Soldier Fly Food Scrap Processing | Phase III

by Terry Green on 11/26/12

In Phase I and Phase II we described the layout and initial construction of a Black Soldier fly (BSF) shed  constructed for researching scaling up, propagation and management of BSF larvae used for recycling food scrap and agricultural wastes. The shed has a footprint 10 x 24 ft, stands approximately 10 ft high on its North side, and has a roof sloping South to the opposite wall (approximately 8 ft in height). The shed, because it is in a Northern temperate zone too cold for propagation of BSF outdoors during the winter months, was designed to deal with temperature fluctuations between summer and winter months by installing insulation throughout the walls, subfloors and roof, making it practical to operate it in propagating BSF and maintaining recycling operations year round.

Fig. 1 shows a close-up view on how the skylights were installed in the roof to maximize natural light entering the shed that is necessary for breeding and propagation of BSF.

image of BSF shed skylight
Fig. 1. Close up view of skylight installed in roof of Black Soldier fly propagation and recycling shed. Copyright (c) 2012, Terry Green, All rights reserved.

Fig. 2 shows the completed shed viewed from the East end where double doors were installed for easy access in moving materials in and out of the shed. A tarp hangs just inside the double door from the ridge of the doors to the floor to discourage adult BSF from flying out of the shed while the doors are opened up to move materials in and out of the shed.

image of East end of DipTerra BSF food scrap recycling shed
Fig. 2. East end view of Black Soldier fly propagation and recycling shed showing double door entrance for moving materials in and out of recycling shed. Copyright (c) 2012, Terry Green, All rights reserved.

In scaling up the processing of degradable wastes such as food scrap, drainage of the BSF processing bin (the reservoir used to contain the decomposing waste) is extremely important. Inadequate drainage quickly leads to the formation of a heavy mud-like sludge which shuts down efficient decomposition of the waste and efficient larval processing of the waste. Additionally, the mud-like composition of the waste tends to promote anaerobic fermentation and stasis as the pH of the decomposing waste becomes progressively more acidic due to formation of large amounts of organic acids attributable to acidogenic anaerobic activity.

The same problems encountered with BSF larval processing of food scraps attributable to inadequate drainage of the decomposing waste is also commonly encountered in the aerobic composting  of food scrap. We will be discussing this issue in another blog to follow concerning the use of bulking agents as a strategy for improving drainage and gas exchange which serves to markedly accelerate BSF-mediated decomposition of food scrap and other readily biodegradable wastes.

image of DipTerra drainage system inside BSF food scrap processing bin
Fig. 3. View of drain system set up in 2 square meter fiberglass worm bin converted to Black Soldier fly food scrap recycling bin by installation of 1.5” drain tubes at the bottom base of the bin through which leachate drains into a bottom collection bin (not shown). Copyright (c) 2012, Terry Green, All rights reserved.

Figure 3 shows one type of drainage set-up in converting 2 square meter worm bins into useful BSF larval food scrap recycling bins of intermediate size used in our BSF recycling shed. The bottom of the bin was fitted with elbow adapters made of PVC of 1.5” internal ID fitted to PVC pipes of similar dimension extending outward approximately 1.5 to 2 ft horizontally with the approximately 1 – 2 inches above the bottom of the bin, closed off on the far end with PVC end caps, and with multiple drain holes in the horizontal pipes covered with plastic netting secured in place with tie-down nylon straps. The drains can be easily dismantled at the elbow fitting for quick cleaning and inspection, if desired, even after the processing bin is up and running.

A gutter constructed of 3” corrugated drain pipe with a “T”-insert (Fig. 4) affixed to the ends of the processing bins allows for harvesting of prepupae exiting the processing bin. Metal flashing (1.5”) strips were also fitted along the top long edges of the processing bins, and bent inward toward the center of the bin, as barriers, causing prepupae attempting to exit over the long axis side of the bins to instead migrate to the ends where they were channeled into the side gutters which then feed them into receiving vessels to simplify collection and harvesting of prepupae.

image of BSF gutter for harvesting BSF exiting food scrap recycling bin.
Fig. 4. View of Black Soldier fly (BSF)  PVC prepupae harvesting gutter secured to side walls of BSF food scrap processing bin (not shown) with “T” insert used to capture and channel prepupae into collection vessels (not shown) housed beneath processing bin. Copyright (c) 2012, Terry Green, All rights reserved.


Fig. 5 shows a fully operational BSF food scrap bin installed and up and running inside the BSF processing shed. Processing bins are mounted on stands containing a leachate collection bin which captures leachate generated during the BSF-mediated degradation of food scrap added to the upper bin. The bins additionally have lids (opened up in Fig. 5) mounted above each bin that swing on hinges which allow for closing off the upper area of the bin from direct light, and on which plastic grids and lids are affixed to encourage egg laying by adults as they fly in and out of the bins inside the shed. This arrangement allows the food scrap bins to operate as recycling units as the BSF larvae grow off of and self-harvest from the waste while also serving as a larval nursery in ensuring continual production of new larvae year round.

image of Black Soldier fly food scrap recycling bin
Fig. 5. View of Black Soldier fly food scrap processing bin (2 square meters) installed and operating inside DipTerra’s (www.dipterra.com) BSF processing shed.

In future blogs we will be following up on additional metrics of the scaled up processing bins in recycling food scrap waste, and other relevant topics relating to the recycling of biodegradable wastes. Comments on this blog, or any of our other blogs, are always welcome. Follow us through our RSS feed. For additional information or follow-up questions, visit our Forums page, or Contact Us (www.dipterra.com).

Comments (33)

1. pixelrie said on 1/3/13 - 04:34PM
Good job guys! I bought one of your books, trying to propagate BSF. I built the enclosure and I have about 1000 prepupae now. Some of the flies emerged already but are not mating. Room temp is 73F. I am rethinking my strategy, is it possible to force these prepupae to hibernate. At what temp do they go dormant and can I keep them in that state until late April. I'm in south east VA. Thank you.
2. Terry Green said on 1/3/13 - 05:35PM
Thank you. Glad to hear of your success in getting your nursery going. Re your question about the flies not mating, 73F is just on the border and rather marginal for good mating activity. If you can bring the temperature up another 10 degrees mating activity should increase noticeably. Also make certain that they have good exposure to natural light during the day, and access to water. Temperature, light and some source of available water are all critical. They will go dormant if you store the prepupae around 45 to 50 F. You should be able to delay emergence for many weeks this way. Even on entering the prepupae stage, they can take upwards to 3 to 4 weeks to emerge left at room temperature. Good luck and keep us posted. We appreciate hearing from you.
3. Bob Segraves-Collis said on 1/23/13 - 03:46AM
The remediation of food waste in a commercial scale facilities will face some amount of fluctuation in the amount of feedstock that arrives at the plant door. How do BSF react to such variations both as short term a few days or less and seasonally?
4. Bob Segraves-Collis said on 1/23/13 - 04:00AM
As I read I find more to ask about! Leachate - does it have an odor? Can it be stored - how? Are there other byproducts beyond the larvae and leachate - what and how can they be used? I have seen biopods with their escape ramps, is it necessary for the critters to leave the growth facility or can I just leave them in the bin and add more feedstock?
5. Bob Segraves-Collis said on 1/23/13 - 04:03AM
I promise this will be the last one for the day! You remark about how there is a nominal temp that is needed for mating of BSF and a low temp yields to dormancy. Is there a high temp that will result in death of the either the flies or the larvae>
6. Terry Green said on 1/23/13 - 06:49AM
Variations in the supply or availability of food waste over a period of a few days or less has no effect on BSF larval survival or behavior. They tolerate environmental extremes remarkably well. In the absence of feed, they slow down their rate of maturation until more feedstock becomes available. We have placed them in tap water (devoid of feedstock) maintained at 86 F (30 C) for a period of one week, and observed them resume feeding on reintroduction to food scrap with no apparent ill effects on their viability. In temperate zones they winter over to the next spring, a period of upwards of three months or longer, under conditions too cold for them to feed and crawl about with no apparent adverse effects. They do not survive freezing, however. So under the latter winter conditions they apparently must find places outdoors that are insulated from freezing temperatures in getting through the winter months so that they are able to resume their natural cycle the following year.
7. Terry Green said on 1/23/13 - 07:07AM
Larvae and adults do well up to about 115 F (~45 C). If left above this threshold temperature over a period of several days they will start to die off due to heat stress. At these higher temperatures young larvae exhibit heat stress by crawling to the surface of the bin and crawling up and out of the bins in large numbers.
8. Terry Green said on 1/23/13 - 09:32AM
The leachate fraction has an odor which varies depending upon how it is processed and stored. If large volumes of food scrap are processed, the leachate fraction will contain trace levels of volatile fatty acids carried into the leachate fraction. These byproducts are commonly formed in all organic wastes undergoing degradation. The odor problem can be addressed by collecting the leachate in containers closed off from exposure to the atmosphere and is easily resolved by mixing the leachate fraction into soil. Nutrients and residual solids (~ 3 to 8 % at most) recovered in the leachate fraction are highly beneficial in promoting establishment of a healthy soil microflora. Some of our other posted blogs may also help answer questions on the leachate fraction (see, for example: "Are Waste Products in Your Recycled Food Scrap Inhibiting Plant Growth"; "Recycling Food Scrap? | What’s with the Stink?"; and "Black Soldier Fly Processed Food Scrap | Foliant and Soil Applications").
9. Terry Green said on 1/23/13 - 10:03AM
Other byproducts of processing food scrap with BSF besides larvae and the leachate fraction include using the residual processed solid residue left behind which is of value as a soil conditioner for improving soil structure, retention of important soil microbes beneficial for the growth of healthy plants, and water retention. Additionally, although at the present time little work has been done in this area, adult flies, after laying eggs and having died, are also likely to be a valuable byproduct in supplementing the nutritional quality of feedstocks. Concerning the construction of escape ramps in processing bins, making provisions for larvae to escape through escape ramps is not necessary. Larvae spontaneously climb up and out of bins, including even vertical side walls without assistance as they enter their prepupa stage. Feedstock can be metered into processing bins without having to be concerned about providing larvae an escape route from the feedstock added to bins.
10. Glen said on 4/28/13 - 03:51AM
Terry, can you explain the purpose/function of the PVC pipe on the underside of the lids? What is the amount of daily pre-pupa harvest you expect and how much food scrapes will each of these units process daily? Thanks for your good work!
11. Terry Green said on 4/29/13 - 11:45AM
The purpose of the PVC pipe is to drain the beds of leachate. Fresh food scrap has a water content in the range of 80 to 90%. Yard waste is around 70% water. Too much water released as cellular structures break down during the degradation process, left unchecked, will shut off air from accessing the waste in the bin. This reduces the efficiency of larval access to the waste. Additionally, too much retention shifts the process too far toward anaerobic fermentation, throwing the whole process of degradation out of balance (see our blog "Recycling Food Scrap? | What’s with the Stink?). On a wet weight basis under optimal operating conditions pre-pupae yields run about 5% of the wet weight of food scrap added to the bins. Turnover of food scrap is about 10 Kg per square meter per day (approx. 2 lbs per sq ft per day). This rate will vary depending upon the operating temperature of the bin, the larval density and nature of waste added to the processing bin.
12. James Robert said on 10/11/13 - 04:47PM
This blog is extremely helpful. Where did you get the digester? I have had difficulty finding an affordable plastic rectangulary grow bed. I really like your design. Love to know where you got it. Thank you in advance.
13. Terry Green said on 10/12/13 - 01:22PM
Our fiberglass bins were obtained second hand. Commercial prefabricated fish ponds made of fiberglass can be purchased from supply houses of comparable size for ~ $1000. Custom fabricators can produce the same size bins for ~ $600 to $700. Bins at ground level using EPDM pond liner can also be used. These are less expensive, but they require planning the drain system ahead of time. Leachate needs to be drained to an underground collection tank where it can be recovered using a sump pump. EPDM retails at ~ $70 per 10 ft x 10 ft section. Bins can also be built out of concrete. In bins set at ground level, harvesting prepupae differs from bins set above ground level, but this is also very doable. The key in scaling up is to plan for strength, easy access, flexibility and durability in the design of the bins, drainage and harvesting units.
14. Holly Canan said on 5/10/14 - 06:21AM
In your 10 x 24 feet building facility how much profit would you expect to make or expect to produce?
15. Terry Green said on 5/12/14 - 06:03AM
We are still looking closely at the economic potential and profitability of raising and using BSF to process food scrap and agricultural waste. There are several very important factors involved in identifying the economical benefits of using BSF in waste management. Profitability is very much linked to the scale of an operation. Even for a small farmer working with a 10 x 24 foot building facility, with organic waste readily available off the farm or nearby, profitability can be linked with integration of BSF into the farming operation in offsetting the cost of purchasing outside animal feed for chickens, pigs, fish, etc., savings in fertilizer costs, income from specialty retail sales of BSF larvae to homeowners who recycle backyard wastes (food scrap and compost piles), etc. We plan on posting more blogs on the economics of BSF production soon – stay tuned!
16. Luke and Kathryn said on 7/31/14 - 03:19PM
Love this blog! I am also interested in the economics of this, we have perfect climate year round for bsfl! I would like to scale up from my bio pod in a back yard operation and would love to see more on the bin design, this is one of the few designs i have seen without ramps. I see in your pictures the blue barrel system and the IBC pallet containers. I was thinking about them as a cost effective backyard semi commercial BSFL bin set up. Any tips on how i should go about this would be appreciated? thanks Luke also did i say how much i love this blog!
17. Terry Green said on 8/4/14 - 10:31AM
Thank you! It is important in scaling up to address issues on the economics and practicality of managing BSF on a sustained basis. This includes critically examining the long term goals of the operation, capital outlay required upfront, labor requirements, equipment needs, drainage, collection of leachate byproduct, etc. These issues are not trivial. We plan to discuss in upcoming blogs some of these aspects – please stay tuned. Re your question about using 55 gallon blue barrel drums on a semi-commercial basis as BSF bins, we believe they are too small. There are alternatives to the general idea of using bins in designing scaled up BSF production. Bins fabricated from plastics or barrels, in particular, are in our experience too expensive in terms of capital outlay, upkeep and management, relative to the return on the investment, and far too limited in holding capacity, to work on a practical scale in getting up to commercial BSF scale production.
18. kim g said on 3/15/15 - 10:13AM
i just have an old chest freezer with a space heater in it and a small bsfl compost bin in it and the little bugs seem to climb into the pails quite nicely. I live in cold climate and its not expensive to hear such a small insulated area. Then i will move the bsfl into a heated, lighted area to see if i can get them to breed.
19. Terry Green said on 3/15/15 - 02:39PM
That should work. Just take a portion of the prepupae crawling out of your bin and move them into a heated net enclosure with access to sunlight through a window or skylight. Prepupae can be collected in a clean plastic container covered with a rim so that they cannot crawl out. Skip adding dirt, wood chips or any other cover material inside the container. They don’t need it to pupate. They will emerge as adults, mate and lay eggs on the walls or lid of a nearby waste can containing a small amount of decaying waste, for example, stored in another small plastic pale in the same enclosure. Transfer the egg clutches and newly hatched larvae back to your other bin. Natural sunlight is very important in inducing the adults to mate. The net enclosure should be not less than about 3 x 3 x 6 ft or larger.
20. Eduardo^Pérez said on 6/26/15 - 11:56AM
Hi, congratulations on such a good blog. I bought one of yours books and I found it very enlightening. I have a question: What substrate was used in the bin? How thick is the substrate layer? regards
21. Terry Green said on 6/26/15 - 09:17PM
Thank you, Eduardo. With reference to this particular bin set up, we usually layer about 2 inches(~3 cm)of coarse bark mulch on the bottom of the bin around the drain tubes and layer food scrap waste over top of the bark mulch. The mulch serves as a bulking agent, improves drainage and gets mixed up with the food scrap added to the bin as the larvae feed and grow off of the waste.
22. Eduardo Pérez said on 8/30/15 - 10:08PM
Dr. Green, I wonder if the larvae try to escape through the slot in the harvesting gutter? The gutter is completely horizontal or slightly inclined to favor that prepupae fall into collection vessels? Thank you
23. Terry Green said on 8/31/15 - 10:53AM
Your point is well taken, Eduardo. We learned since posting this blog now going on almost 3 years ago that some larvae indeed can escape through the slot from the harvesting gutter. We discovered after posting the blog a better method of capturing larvae using standard rain gutters constructed with right-angle overhangs which prevent the larvae from pulling themselves up and out of the gutter. Larvae are extremely adept at climbing up and pulling themselves over vertical walls, even if the walls curve inward at less than a right angle as is the case in the slotted gutters shown in the picture. Larvae appear incapable of climbing out of gutters designed with the top edge projecting about 1 inch or more inward at a right (or more acute) angle from the vertical wall. I will soon be posting an updated blog covering this topic in more depth re design changes in the harvesting gutter and drain system.
24. Juan Langlois said on 5/24/16 - 07:20PM
Hello, congratulations on the blog. I am currently trying to grow my own larvae, and would like to know if there is an optimum amount of waste to put in the bins (height-wise, should I cover, for example, the bin to half its height?). Thanks in advance!
25. Terry Green said on 5/26/16 - 08:39AM
Thank you, Juan. Re loading a bin to an optimum depth, BSF feed and grow best over a relatively shallow range. Up to about 3 to 4 inches (approx. 7.5 to 14 cm) larvae will grow very well. Although larvae can be grown in waste piled even deeper in a bin, even double this height, the efficiency begins to drop off sharply when too much waste is piled into a bin. This is especially true as excess waste (feedstock) starts accumulating in the bottom of the bin. This fall in efficiency appears to be linked to compaction of waste near the bottom of the bin in combination with inadequate ventilation of the waste. Larvae can become trapped inside the waste if it is too dense and suffocate under these latter conditions. Waste added to your bin should be turned over on a frequent basis to ensure adequate ventilation and to also render it accessible for larvae to easily access.
26. Dai Ara said on 6/30/16 - 05:23AM
Hi there, thanks for the great work. I am trying to maintain the colony of BSF in a small heated greenhouse in a winter down south. about a month ago, adult flies started to disappear and I added heater to keep inside around 30 C. I have thousand of black pre-pupa in a container that I put dirt and large brick for them to stay under. but no hatching so far. Do you have any advise on the condition favourable for pupa to hatch? more heat and humidity maybe? thanks!
27. Terry Green said on 6/30/16 - 08:43PM
Thank you, Dai Ara. Re problems with the fall off in prepupae and emerging adults, measure and make certain that the temperature in the greenhouse, the waste on which you are growing larvae, and the ground/ soil/brick container where you have the prepupae are all well below 43 - 45 C. BSF die off rapidly at these higher temperatures. Even though your air temperature may be 30 C, you need to verify that the actual waste and any surfaces the larvae and prepupae reside on or pass through are also within a viable temperature range. Prepupae don’t need any dirt or rocks to emerge as adults. They do fine added to an empty container with just a containment lid (see our Blog, Farming Black Soldier Flies (BSF) | Managing Larval Migration). Optimal conditions for good results are temperatures ranging from about 25 to 35 C and a relative humidity from 50 to about 70%.
28. Dai Ara said on 8/25/16 - 08:05PM
Hi, many thanks for your previous comments, now I can see the adults emerging constantly. however, in the past months, I can not find any eggs deposited in the harvesting container that I prepared basically based on your publication. I added empty larval puparia shells mixed with BSF/food scrap leachate that I have kept from last summer. Temperature and humidity should be within the range(temperature sometime drop down to 15c degree in the early morning). I thought there maybe something that discourage mating in the first place. maybe I should increase resting/hiding area. Do you have any advise on conditions that may influence mating? thank you very much for your great work!
29. Terry Green said on 8/26/16 - 11:01AM
Thank you, Dai Ara. Do you see evidence of mating adults? Optimal mating occurs between 25 and 35 C in natural light, and primarily in the morning. Adults pretty much cease mating at temperatures below 20 C. Make certain also that there are no predatory insects feeding off eggs laid in the containers. Beetles, ants and spiders seek out eggs. Some seeking fly larvae and eggs feed at night. Isolate your containers from predators. A small amount of decaying nutrient waste should also be mixed in with the pupae shells and leachate in drawing female adults to the containers. If you don’t have fresh pupae shells, or want to get away from using the latter, use a leachate-wetted grain such as wheat bran in place of the pupa shells (see http://www.dipterra.com/blog.html?entry=farming-bsf-general-guidelines-that). Work though these steps and you should begin to see good results.
30. Johnny Chavez said on 10/7/16 - 07:54PM
What is the dimension of the bin and how many lbs of food can this size of pod digest in a 24 hour period
31. Terry Green said on 10/9/16 - 02:03PM
The bin in the picture is approximately 21.5 sq ft (2 m) x 1.5 ft (0.46 m) in depth. It is simplest to think of loading waste into a BSF bioreactor in terms of load per unit surface area per day excluding any depth calculation. The loading rate depends somewhat on the type and composition of the food waste fed to larvae. Larvae generally grow well using a loading rate in the range of about 0.25 to 0.5 lbs per sq ft per day (about 2.5 to 5 Kg per sq meter per day).
32. Ali Bio said on 3/30/18 - 04:16AM
Dear Terry, thank you very much for this blog. I would like to know how to harvest digestate (larvae processed food waste) in a steady-state installation.
33. Terry Green said on 3/31/18 - 06:08PM
Ali Bio, please see a more recent blog titled Steady-State Farming of BSF Larvae that I posted on this subject at http://www.dipterra.com/blog.html?entry=steady-state-farming-of-bsf.


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