Efficient and safe substrates for black soldier fly biowaste treatment along circular economy principles

Black soldier fly larvae (BSFL) treatment is an emerging technology for the valorisation of nutrients from biowaste. Selecting suitable substrates for BSFL treatment is a frequent challenge for researchers and practitioners. We conducted a systematic assessment of BSFL treatment substrates in Nairobi, Kenya to source more substrate for upscaling an existing BSFL treatment facility. The applied approach is universal and considers four criteria: 1) substrate availability and costs, 2) BSFL process performance, 3) product safety, and 4) waste recovery hierarchy. Data were collected from previous waste assessments or semi-structured key informant interviews and sight tours of waste producers. Waste nutritional composition and BSFL process performance metrics were summarised in the “BSFL Substrate Explorer”, an open-access web application that should facilitate the replication of such assessments. We show that most biowaste in Nairobi is currently not available for facility upscaling due to contamination with inorganics and a lack of affordable waste collection services. A mixture of human faeces, animal manure, fruit/vegetable waste, and food waste (with inorganics) should be pursued for upscaling. These wastes tend to have a lower treatment performance, but in contrast to cereal-based byproducts, food industry byproducts, and segregated food waste, there is no conflict with animal feed utilization. The traceability of substrates, source control, and post-harvest processing of larvae are required to ensure feed safety. The criteria presented here ensures the design of BSFL treatment facilities based on realistic performance estimates, the production of safe insect-based products, and environmental benefits of products compared to the status quo.