Valorization of post-consumer food leftovers by black soldier fly (Hermetia illucens) bioconversion into protein feed and organic fertilizer

Introduction Organic waste presents a significant environmental challenge, causing environmental issues, such as landfill accumulation, greenhouse gas emissions, and water pollution. Food leftovers from restaurants, which are rich in fats and other elements, are among the most threatening organic waste materials in Saudi Arabia. This study evaluated the potential of black soldier fly (BSF) larvae, Hermetia illucens, to bioactive post-consumer food leftovers from restaurants into valuable protein-rich feed and organic fertilizer. Methods Three substrates were tested: 100% poultry feed (PF) as a control, 100% food leftovers from restaurants (LF 100%), and a 50:50 mixture of PF and LF (LF 50%). Larval growth performance, survival rate, proximate chemical composition, amino acid content, mineral profile, and toxic elements were assessed, alongside the safety of residual frass. Results Larvae fed the LF 50% achieved the highest growth and survival rates. Both larvae and frass contained essential amino acids and key macro- and micro-minerals, with heavy metal concentrations remaining below hazardous thresholds. The residual frass also showed potential as a plant growth-promoting fertilizer due to its amino acid composition. Therefore, these findings demonstrate that BSF bioconversion is an effective and sustainable approach for valorizing high-fat restaurant waste, an underexplored substrate in the region. Conclusion This study presents insights into the benefits of producing insect protein for feed and nutrient-rich frass, which can support agriculture from high-fat restaurant waste, an underexplored substrate in the region, contribute to food security, and align with environmental objectives under the Saudi Green Initiative. Further research should focus on optimizing the substrates, exploring the long-term applications of BSF larvae frass in agriculture, and scaling up the BSF larvae systems using various waste streams.