Modular Farming of Black Soldier Fly (BSF) | Scaling Up - Schematic Overviewby Terry Green on 10/31/16
It is very difficult for anyone interested in starting up or planning to build a scaled up BSF production facility to find information on what needs to be addressed in the construction of a viable operating plant. Building and operating a large commercial BSF facility poses many challenges (see, for example, On the Road to Commercial Production of BSFL |Sorting Out the Chaff and Commercial Black Soldier Fly (BSF) Production in 2016 | Where Are We Today?). I recently commented on the dearth of information regarding scaling up production, and the very real need for a more open exchange of in-depth scientific, engineering, and economic disclosures concerning the production of BSF larvae on an industrial scale, and for more transparency and vetting in the reporting of achievements (see Black Soldier Fly industry: more enthusiasm than scientific know-how?). This blog describes in some depth critical steps to consider in operating a large scale modular BSF production facility including disclosure of information on how to reduce the footprint needed in scaling up a production facility by vertically stacking larval bioreactors in a central work area and integration of the layout to maximize the output of larval harvests and byproducts while streamlining the throughput of spent waste.
At the present time there is no blue print on how to set up and operate a plant facility. Because the technology of growing larvae on a large scale off organic wastes is new, and because there is presently no vetted evidence that any company has yet succeeded in commercially scaling up and sustaining larval harvests over any lengthy period, there are obvious risks in time and capital outlay in scaling up a commercial operation that at best must be mitigated as best possible under the circumstances. For these reasons, the most practical approach in scaling up larval production is to build a plant facility based on a modular albeit scalable design. This provides for flexibility and adjustments in the operating system in step with technological changes likely to occur over the next several years.
Planning the logistics of the operation ahead of time is important. All operations in handling waste and growing larvae in a plant facility should be done on an enclosed concrete pad so as to keep predators (insects, rodents, birds, herps, etc.) out of the work area. If allowed access, such predators, aside from the problem of reducing larval yields, must be viewed as vectors in transferring potential pathogens and parasites into the process stream. Common predatory insects, in particular, given the chance, seek out young larvae growing in decaying wastes, and BSF eggs deposited near the waste. Beetles from the Cleridae family such as Necrobia rufipes, and a number of Hister beetles from the Histeridae family, specialized in detecting the presence of fly larvae in decaying wastes, can easily bore up through soil in gaining access to wastes in the absence of a concrete pad blocking their access to the waste.
Provisions need to be made for allowing natural sunlight to pass into the facility through insulated windows, skylights, or solar tubes, or in tropical regions through netting, to help induce mating of BSF adults bred indoors in sustaining larval production. If it is not possible to bring natural light into an enclosure, LED lighting of high intensity having an emission spectrum around 450 nm can induce some mating in the absence of natural sunlight, though less than that induced in natural light.
The scaling up process in farming larvae, itself, can be distilled down to a very specific set of core tasks - waste input and output, larval propagation and harvesting, and collection of byproducts, all collectively integrated into a “Processing Train” as outlined in the flowchart shown in Fig. 1.
Fig. 1. Flowchart summarizing varying processing steps needing to be addressed in commercially farming BSF larvae grown off biodegradable wastes (Copyright © 2016, Terry Green, All rights reserved).
Choosing the waste best suited to the task of scaling up production is of particular importance early on in planning the start up of a plant facility. Whether or not it will need to be presorted into biodegradable and non-biodegradable wastes, whether it will need to be shredded, whether or not its properties as larval feedstock will require the addition of a bulking (aerating) agent, its availability over the long run while operating the facility, environmental or health risk issues associated with processing it on site, the planned use of harvested larvae and byproducts relative to the source and nature of the waste used in growing the larvae, etc. - all need to be taken into consideration.
Incoming waste for growing larvae should be stockpiled in a “Waste Input” center (Fig. 1). It should be stockpiled in covered, corrosion resistant bins, drums or dumpsters. Because of its restricted access to air, the waste will begin to ferment. This drives the pH of the waste downward into a range of about 3.5 to 4.0, low enough to discourage the growth of pathogenic bacteria. The low oxygen tension in the waste combined with the lower pH is furthermore effective in killing off many “filth” flies including the larvae, for example, of the common housefly, Musca domestica, blow flies (Calliphoridae spp.), flesh flies (Sarcophagidae spp.), fruit flies (Drosophila spp.), phorid flies (Phoridae spp.), etc., all commonly found in decaying wastes.
Because adult BSF females lay their egg clutches (upwards of 500 eggs per clutch) in and around fermented waste, the task of seeding incoming waste with larvae can be left to mating female BSF by transferring incoming waste from the Waste Input section of the plant to a Propagation & Larval Seeding workstation designed into the Processing Train of the plant facility for upwards of about four days (see Figs. 1 and 2). Seeding occurs optimally when the temperature and relative humidity are kept in the range of about 25 to 35 C and 60+%, respectively. A series of modified larval bioreactors (see below), also permanently housed inside this latter workstation, serves in sustaining a continuing supply of mating adult BSF charged with replacing the loss of larvae carried out of this workstation as input waste moves on down the Processing Train to the central core of the plant facility housing a larval Mix Bed and larval bioreactors BR1 and BR2 (see Fig. 1).
Fig. 2. The BSF Propagation & Larval Seeding workstation serves as a waste holding area for seeding incoming waste with newly hatched larvae and eggs. Adult BSF, produced and replenished in this workstation of the plant facility, and adult females, mating in this section, ensure that waste gets seeded with eggs and newly hatched larvae as it travels through this section of the Processing Train designed into the plant facility (Copyright © 2016, Terry Green, All rights reserved).
Fig. 3. View of BSF egg clutches and newly emerging larvae crawling about on the underside of the lid of a waste bin filled with scrap food waste by adult females attracted to the odor of the fermenting waste temporarily housed in a BSF Propagation & Larval Seeding workstation incorporated into the Processing Train of an operating plant facility (Copyright © 2016, Terry Green, All rights reserved).
Waste, seeded with larval eggs and newly hatching larvae (see Fig. 3), moves downstream from the BSF Propagation & Larval Seeding station to a Mix Bin and Bioreactors 1 and 2 (BR1-BR2), the central larval growing workstation of the plant facility (see Fig.4). The Mix Bin (Fig. 4) provides the means for loading incoming larval-seeded waste with waste loaded earlier into BR2 bins stacked in the preceding loading cycle atop BR1.
A commercial compost or soil mixer can be substituted in place of the Mix Bin. If a commercial mixer is not used, incoming larval-seeded waste must be mixed with a front loader or optionally a motor driven auger at the Mix Bin workstation before it is reapportioned into the BR2 bins and the latter again stacked atop BR1.
Fig. 4. Recycling and loading operations carried out in growing and harvesting BSF larvae in stacked bioreactor larval bins (BR1-BR2) in the core bioreactor workstation of a scaled up BSF farming facility (Copyright © 2016, Terry Green, All rights reserved).
Fig. 5. Top down and cutaway side views of BR1 Bioreactor. BR2 bioreactors (not shown) stack and nestle inside the main trough of BR1 (Copyright © 2016, Terry Green, All rights reserved).
Channel Guides (Farming Black Soldier Flies (BSF) | Managing Larval Migration) running parallel with BR1 at ground level capture prepupae self-harvesting from the stacked BR2 bins as larvae drop by gravity into BR1. Leachate released from the waste likewise flows by gravity into BR1 where it drains away through lines housed below grade to a sump pump where it then gets pumped into a storage tank positioned at grade outside the work area (Fig. 5).
Prepupae captured in the Channel Guides can be removed for further processing, for example for washing, drying and incorporation into feed formulations, by dragging an industrial vacuum line through the Channel Guides, or by flushing and washing the newly harvested prepupae through drain pipes and strainers installed downstream from the Channel Guides.
Commercial vented agricultural bins fabricated out of tough plastic polymers, and built specifically for stacking produce in stacks of upwards of 8 to 12 bins per stack, are readily available and used in many industrial applications in agriculture. These same bins can be used as BR2 stacking bins in farming BSF off waste.
Each bin stacked vertically atop BR1 increases by an incremental ~1.2 square meters the bioreactor’s footprint above the footprint occupied by BR1. This is advantageous. Consider, for example, a rectangular bin having a total footprint of 200 square feet (18.6 square meters) loaded with food waste at a rate of approximately 5 Kg per square meter per day. Based upon the current metrics in producing larvae per unit area, and load rate (see Scaling Up BSF Production | Theoretical and Practical Effect of BSF Bin Space Surface Area and Food Scrap Load Rate on Larval Yield), assuming efficient growth conditions are maintained on a sustained basis, the annual larval harvest projects out at approximately 2.2 metric tons per year. Stacking BR2 bins vertically (12 per column) atop a BR1 having the same footprint at its base projects out, on the other hand, to approximately 27 metric tons per year, about a 12-fold increase in production capacity over that of the footprint occupied by BR1 lacking bins stacked atop its base.
BR2 bins stacked in this manner furthermore provide a means of maintaining a steady input of new waste, and removal of spent waste (that already broken down and used by growing larvae which must removed to make room for incoming fresh larval-seeded waste). This can be achieved by staggering the loading of larval-seeded waste added to the stacked BR2 bins, namely by loading BR2 bins in the first column, then the second the following loading day, then the third on the third day, etc. in a round-robin pattern. Only that stack which is the oldest in the series of column stacks atop BR1 gets emptied in any cycle as it becomes filled and it becomes necessary to discharge spent waste, preserving larvae in the remaining column stacks for subsequent harvest and reloading with fresh larval-seeded waste. Fig. 6 outlines a flowchart that can be used in managing waste as it becomes spent in this manner.
Fig. 6. Flowchart decision tree providing guidance on how to recycle larvae and waste through the BR1-BR2 workstation of a scaled up BSF pilot plant facility (Copyright © 2016, Terry Green, All rights reserved).
This round-robin loading regimen insures that only the oldest waste, namely that which is the most depleted of nutrients, moves out of the processing train and on to the composting site where it then gets “polished off” as compost. Overlay (residue debris not broken down during the composting operation), recovered after passing the finished compost through metal screens, can be reused as bulking agent as needed in managing newly collected waste entering the Processing Train (see Fig. 1).
Lastly, it is important in scaling up larval production to deal with odors given off during operation of the plant. Advanced composting technologies now routinely deal with odors efficiently using biofilters. Noxious volatiles get drawn into plastic inlet pipes and sent through finely shredded wood wetted and spread in windrows (the biofilter), and in the process noxious volatiles get scrubbed from the air by microbes growing in the biofilter as the air exits from the windrow. Fig. 7 shows a large biofilter in operation on a composting facility designed for handling upwards of 1000 tons of food waste per day.
The same kind of biofilter albeit constructed on a smaller scale can be situated inside a BSF plant facility to scrub the air of nuisance odors. Blowers with screens secured over the air intake ports to prevent adult BSF from being drawn in to the venting pipes leading to the biofilters must be used, but this is not a problem and can be done simply and economically in addressing issues relating to nuisance odors associated with scaling up a production facility.
Fig. 7. Picture of a large scale biofilter operating in an open air composting facility which cleans air of noxious odors. The biofilter works by drawing air using blowers positioned so as to create a negative pressure and move air down through windrows (on the left) consisting of decaying food waste and other decomposing waste stacked over plastic pipes placed at the center of the each windrow and sends the air and noxious odors through vented pipes overlayed with wetted wood chips (the biofilter – see windrow on the right side of the blowers). Microbes growing and seeded on the wetted wood chips making up the biofilter scrub the air of noxious volatile fumes before they escape from the filter as the air exits the filter eliminating nuisance odors generated by the decaying waste (Copyright© 2016, Terry Green, All rights reserved).
The layout design described here can be tested on a pilot plant scale in a modular format by limiting construction and operations to one or two BR1 bioreactors and choosing a convenient number of BR2 bins as desired to test and compare actual larval yields against projections based on the footprint of the modular units put into action.
A useful model in getting started is to decide on a target annual larval harvest rate as a test run in operating a facility, and to build accordingly with the goal of vetting output performance. I will follow up on projecting and calculating larval harvest rates, waste input and byproduct outputs in a separate blog to follow – stay tuned.
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