Solvent-free biorefinery of leather fleshing waste into FAMEs and nitrogen-rich co-products

This study presents a solvent-free method for converting bovine and ovine fleshing waste into biodiesel-compatible compounds and a nitrogen-rich solid by-product. The process combines mechanical lipid separation using Tricanter® centrifugation with an optimized alkaline conversion step. Lipid recovery exceeded 92 %, and under optimal reaction conditions, conversion yields surpassed 95 % without the need for pre-treatment. Bovine-derived esters complied with international biodiesel standards, while ovine esters showed promising properties for thermal energy storage applications. The solid fraction, containing up to 9.3 % nitrogen and no regulated heavy metals, met European requirements for use as fertilizer. The process consumed approximately 23 % less energy than conventional methods, and techno-economic analysis supports its industrial feasibility. Overall, this integrated approach offers a scalable, sustainable solution for tannery waste valorization aligned with circular bioeconomy goals. Valorization of leather fleshing waste through solvent-free lipid extraction using Tricanter® centrifugation and optimized alkaline transesterification. The process yields FAMEs for biofuels/PCMs and nitrogen-rich solids for potential agronomic applications.