Fecal sludge management using black soldier fly larvae and product safety

Abstract

Black soldier fly larvae, Hermetia illucens L., (BSFL) convert organic waste material into insect biomass, which can then be processed into a profitable and sustainable protein and fat ingredient in animal feeds. In areas where sanitation remains a challenge, the potential to valorise fecal waste material, using the BSFL technology would increase stakeholder participation in improving sanitation and encourage entrepreneurial opportunities. However, remaining barriers still exist, such as product safety. Therefore, the main objectives of this study were to evaluate BSFL development on varying ratios and combinations of differing types of human fecal waste and organic waste material, and to assess if the use of a novel non-thermal treatment technology, low energy electron beam (LEEB), could lead to safe BSFL products. The first part of the study was conducted in Durban, South Africa, where a public private partnership exists between the Ethekwini Municipality and The BioCycle, to innovatively manage fecal sludge from urine diversion toilets (UD). However, BSFL develop poorly on UD fecal sludge, due to the low nutritional quality. Therefore, the substrates tested in this study were: UD fecal sludge, ventilated improved pit latrine fecal sludge (VIP), primary sludge (PS), restaurant food waste (FW), and brewers’ spent grain (SG). To evaluate this, BSFL development (mass), survivability, bioconversion and waste reduction efficiency were measured. Four-day old BSFL were reared on 250 g wet mass of the specified substrate at the start of the experiment, based on an assumed feeding rate of 100 mg of substrate larvae-1day-1. Experiments were conducted under controlled environmental conditions with a temperature of 30 ± 2°C and relative humidity of 60 ± 5 % for 11 days. Results demonstrated BSFL grown on the substrate combination of 37.5% PS, 37.5% VIP and 25% FW (% m/m) had a high dry bioconversion rate of 18.69 ± 2.11% compared to 3.33 ± 2.78% on 100% VIP. To effectively inactivate pathogens that may be present in BSFL reared on human fecal waste, BSFL were inoculated with Escherichia coli (E. coli, strain K-12 MG1655) and passed through continous LEEB at a specified dose to achieve a 3 to 5-log10 inactivation. The attractiveness of using this non-thermal treatment technology is the potential in reducing microbial concentrations without product damage, in addition to extending the shelf life.