Valorization of biorefinery residues for sustainable fertilizer production: a comprehensive review

AbstractThe management of biowaste and agricultural solid waste is gaining attention due to rising landfill disposal costs and the need for locally available agricultural feedstocks. The biorefinery concept aims to achieve zero waste through valorizing residues as fertilizers. Despite containing NPK macronutrients, residues may not promote plant growth due to limited nutrient availability and phytotoxic compounds. The production of valuable organic, mineral-organic, or mineral fertilizers with confirmed agronomic properties as marketable biorefinery products remains understudied. This comprehensive review broadens our understanding of fertilizer production in biorefineries, which complements the energy (thermal, biogas, biodiesel) and chemical compounds (e.g., succinic acid, propanediol, protein concentrates) that are also generated within biorefineries. It is among the first reviews to investigate the importance of valorizing biorefinery residues as fertilizers, emphasizing methods leading to commercial products and the rationale behind this process. The findings confirm that directly applying unprocessed residues to the soil does not fully exploit their value as by-products. This study contributes to the practical analysis of barriers (legal, chemical, biological, technological) and opportunities (rising prices and reduced global availability of mineral fertilizers) related to fertilizer production in the biorefining process.