Valorising Organic Waste using the Black Soldier Fly (Hermetia illucens), in Ghana

Abstract: Ghana as a rapidly growing and urbanizing middle-income country is facing a number of challenges, including (1) implementing a sanitary, environmental-friendly, and economically-sound waste management system; (2) increasing its agricultural productivity in a sustainable way to meet the growing domestic food demand; and (3) providing livelihood opportunities in both rural and urban areas. Using the black soldier fly (BSF), a particularly beneficial insect, to locally and cost-effectively valorise abundant, high-impacting, and nutrient rich organic waste streams, such as food waste (FW) and faecal sludge (FS), into affordable and sustainable farming inputs like organic fertilizer and animal feed products, could tackle all these challenges at the same time. Therefore, this study aimed at (1) providing a comprehensive overview of BSF technology; (2) investigating the technical feasibility of valorising food waste and faecal sludge using a low-tech BSF bioconversion system; and (3) assessing the economic viability of such system in the Ghanaian context. First, through an extensive literature review and field visits of BSF units, the different dimensions of the BSF technology were discussed, BSF waste treatment method was compared to other options for organic waste valorisation, case studies of implementation were documented, the status of the research was highlighted, and research gaps were identified. In a second step, a 10-week field work consisting of establishing a BSF colony and recording rearing performance in the one hand, and running two waste treatment trials using a low-tech BSF system on the other hand, enabled demonstrating the technical feasibility of co-digesting FW and FS with the BSF, as well as artificially rearing the BSF in Ghana using a low-tech system. However, further research is needed to characterize the bioconversion products, determine the optimal FW/FS ratio, and optimize the rearing performance of the system. Finally, a costbenefit analysis was conducted to compare three scenarios: (1) co-composting FW and FS into fertilizer; (2) co-digesting FW and FS with BSF into only animal feed; and (3) co-digesting FW and FS with BSF into both animal feed and fertilizer. By building financial models for each scenario and performing a sensitivity analysis, it was established that, in the Ghanaian context, scenario (3) was the most likely to be viable, as well as the most profitable, followed by scenario (1).  On the other hand, scenario (2) was associated with a much lower likelihood to be viable. Eventually, the choice of the optimal valorisation option for FW and FS should consider the local context and priorities.