Scaling Up Black Soldier Fly Food Scrap Processing | Phase IIIby 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.
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.
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.
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.
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.
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).