Farming Black Soldier Flies (BSF) | Scaling Up & Sustaining Larval Productionby Terry Green on 01/06/16
Growing Black Soldier fly (BSF) larvae off of food scrap as a feedstock is relatively straightforward on a backyard scale (see Black Soldier Fly Processing of Biodegradable Wastes). The same cannot be said regarding scaling up larval production to achieve sustained industrial outputs. This blog discusses scaling up and managing larval production incorporating corrective measures designed to overcome colony collapse (Post-Mortem) and other farming problems typically encountered on scaling up larval yields and the throughput of biodegradable wastes processed by BSF.
Scaling up and sustaining consistent production requires careful management of the waste feedstock starting with its initial presentation to the larvae. It also requires careful observation and prompt corrective action be taken as necessary in addressing the changing physical attributes of the feedstock after its delivery to larval processing bins/troughs (bioreactors) used in raising larvae.
Farming larvae on an industrial scale must foremost be done economically, and to this end harvesting larvae and other end products generated in the farming operation must be handled efficiently to ensure uninterrupted output of product. Several tons of feedstock must be processed, and hundreds of kilograms of larvae must be harvested on a daily basis.
The larval production “train” (the throughput design of the farming operation) from input of larval feedstock to output of product must accordingly accommodate the integration of heavy lifting farming equipment into the production train. This includes, for example, the incorporation and integration of tractors, front loaders, forklifts and industrial waste shredders at various points in the process stream.
Based upon experience in working with BSF larvae at out test pilot plant facility over the last four years, we have identified the following processing steps in the production train to be of upmost importance in improving throughput and management of larval harvests:
Managing Waste Feedstock
- Food scrap (waste feedstock) needs to be shredded into small fragments to maximize surface area; add bulking agent (shredded branches, shredded bark chips, or other recyclable lignocelluloses matter) as necessary to render the feedstock larval penetrable (if necessary add water to dampen down excessive aerobic activity evidenced when the feedstock’s temperature exceeds the optimal range required for healthy larval growth and maturation - see below);
- Store collected feedstock in a fermented state; use passive drainage systems to draw off and collect fluid (leachate) released as the waste feedstock undergoes degradation in larval bioreactors; and
- Ensure that the temperature of the feedstock in larval bioreactors does not fall below approximately 20 C or exceed 45 C (optimal temperature range, approx. 25 to 35 C).
- Whether spent feedstock removed from larval bioreactors is destined for recycling back into soil as a soil amendment, processed further as vermicompost, or subsequently composted, plan the larval bioreactor layout train to ensure there is a continuous input and output of feedstock passing through the processing train so as to avoid interruptions in the production stream;
- Managing multi-ton loading and mixing of feedstocks in bioreactors, and unloading and transferring spent feedstocks, requires heavy equipment - the layout of larval bioreactors, and their construction, must be designed with this in mind; materials used in their construction (for example, concrete) must be strong yet affordable;
- Processing feedstocks in farming larvae includes integrating a dual bioreactor system into the farming operation, one serving to grow larvae on feedstock added early on in the decomposition process, and the other complimentary (secondary) bioreactor serving as a polishing reactor designed to improve feedstock turnover, re-seed and propagate larvae, and improve the physical attributes of feedstock added to the first bioreactor;
- Bioreactor 1 (BR1) receives fresh larval feedstock used in growing larvae from which larvae self-harvest;
- Bioreactor 2 (BR2) serves as an intermediate feedstock polishing unit integrated into the operation of BR1 serving to seed and propagate; BR2 serves to also reduce the larval processing site footprint while sustaining continuous high yield production of larvae, and additionally improves the physical attributes of the feedstock mix in BR1;
- Spent feedstock exits the larval processing train through BR2;
- The vertical depth of each bioreactor works best as follows: BR1, generally less than or equal to 16 inches, maximum; BR2, less than or equal to 48 inches, maximum; and
- The optimal moisture content of feedstocks in BR1 and BR2 is best managed kept at greater than 55% but not more than 70%.
- Spontaneous mating requires maintenance of ambient air temperatures in the range of 25 to 45 C (optimal temperature range, ~ 27 to 40 C), and illumination of the mating area with natural light;
- Efficient larval self-harvesting and migration activity works best when the temperature of the feedstock in BR1 and BR2 exceeds approximately 25 C – at lower operating temperatures larval activity drops off sharply leading to a loss in throughput of feedstock and larval yields;
- Larvae can be propagated in a separate larval nursery separated from the larval harvesting site dedicated to mating and the subsequent transfer of newly hatched larvae into BR1 and BR2; and
- Alternatively, propagation can be done directly inside the larval growing facility by providing adult BSF the opportunity of mating and laying eggs directly in and about BR1 and BR2 processing units.
- Use channel guides (see Farming Black Soldier Flies (BSF) | Managing Larval Migration) aligned parallel with BR1 and BR2 to contain and deliver self-harvesting larvae to a desired common drop off site; harvested larvae picked up from the common drop site may then, depending upon production needs, be subsequently washed, dried and further processed.
Fig. 1 shows the appearance of food scrap retained in our BR1 unit, and a view of larval densities just beneath the surface of food scrap in the processing unit. Larvae exiting BR1 self harvest principally at the prepupae stage largely free of immature larvae (Fig. 2).
Fig. 1. The appearance of food scrap on which BSF larvae are feeding and growing in BR1 viewed top down (Fig. 1a), and larvae residing just beneath the surface of the food scrap feedstock added to BR1 (Fig. 1b). Copyright © Terry Green 2016, all rights reserved.
Fig. 2. Image of self-harvesting BSF prepupae recovered upon exiting BR1. Copyright © Terry Green 2016, all rights reserved.
Stay tuned! Our next blog to follow will discuss some helpful guidelines in observing how larval behavior in response to feedstock conditions, and the appearance of feedstock in the bioreactor, itself, can help alert you ahead of time of an impending colony collapse on scaling up production in sufficient time to intercept and avert the loss of your colony and concomitant losses in larval output.
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