Waste-to-fertilizer strategy for circular nutrient recovery from meat and bone meal: Optimization of organo-mineral fertilizer production

Rising mineral fertilizer prices and the environmental impacts of synthetic agrochemicals underline the need for sustainable, circular nutrient-recovery solutions. This study presents an integrated waste-to-fertilizer strategy that converts meat and bone meal (MBM), a nutrient-rich animal by-product, into safe, effective organo-mineral fertilizers that are also rich in amino acids. The process relies on alkaline hydrolysis, statistically optimized with Response Surface Methodology and a Box–Behnken design. Optimal conditions (50 % KOH, 100°C, solid to liquid ratio 1:1) maximized the content of amino acids (up to 1.8 %), including arginine, proline, threonine and glutathione, all known for their biostimulant functions. The hydrolysates were neutralized with phosphoric acid(V) (formulation F1) or sulfuric acid(VI) (formulation F2) and then granulated using dried peat and zinc lignosulfonate as binders. Both formulations were assessed for macro- and micronutrient composition, nutrient-release behavior and compliance with European Union fertilizer regulations. Analytical results confirmed high levels of plant available macronutrients (P, K, Mg, S), low content of heavy metals, and complete microbiological safety. Phytotoxicity assays and pot experiments with cucumber ( Cucumis sativus L. ) showed significant improvements in root development, shoot biomass and flowering relative to unfertilized controls and a commercial reference organo-mineral fertilizers based on chicken manure. These findings demonstrate that fertilizers derived from MBM provide a circular, sustainable and agronomically effective alternative to conventional mineral fertilizers, thereby supporting resource-efficient agricultural practices. • Waste valorized into fertilizers via RSM-optimized alkaline hydrolysis (BBD design). • Organo-mineral granules met EU safety norms and provided bioavailable NPK. • Fertilization enhanced root complexity, biomass, and flowering in cucumber trials. • Process supports circular nutrient reuse and mitigates reliance on synthetic inputs.