Evaluating the feasibility of using screw conveyors as a means to continuously grow black soldier fly larvae

Abstract

This research attempted to assess the feasibility of using screw conveyors as a means of continuously rearing black soldier fly larvae. Farming of the black soldier fly (BSF) has gained popularity in recent years as means to supply protein for animal feed and recycle food waste. However current methods for BSF farming are labor intensive and costly. This is due partly from the batch system in which BSFs are grown. It is also a factor of space inefficiency, as BSF larvae can only live in the first 7-10 cm of the substrate they are grown in due to oxygen depletion. Screw conveyors in theory could solve both these problems by allowing for continuous production and mixing which could aerate the substrate preventing oxygen depletion. In order to test the feasibility of using screw conveyors an analysis was done to predicted energy cost. Based on the calculations done in this work energy cost would be trivial, on the order of 0.01 US dollars or less per pound of dry weight BSF larvae. Physical experiments were also done on the effectiveness of mixing in aerating the substrate and allowing BSF larvae to live deeper. This involved filling a tube with substrate and BSF larvae to various depth between 15 and 45 cm and measuring oxygen levels at the bottom depth. The tube was also flipped to simulate mixing. While there is a high level of uncertainty, the results in general indicate oxygen was depleted in the substrate on the order of 5-10 minutes for depths bellow 15 cm. This does not support the feasibility of using screw conveyors for BSF farming as the conveyor would have to be running almost constantly to prevent the development of anaerobic conditions. However many factors in this research where high conservative and the development of anaerobic zones in BSF substrate and the effects of mixing warrant further research.