Biomass ash: a neglected source of phosphorus recovery

Abstract Phosphorus, essential for plant growth and fertilizers, faces depletion as global phosphate rock reserves dwindle. Recovering phosphorus from secondary resources, like biomass ash, has gained focus, as it contains 1–4 % phosphorus and offers potential as a sustainable source. Biomass ash, a by-product of energy generation from biomass, is typically treated as waste despite its nutrient value. Annually, 47,000 kilotons of phosphorus pentoxide (P 2 O 5 ) are used worldwide in fertilizers. This review examines phosphorus recovery from biomass ash, including biogenic sources, the phosphorus soil cycle, and recovery technologies such as thermochemical treatments, acid/base leaching, bioleaching, struvite precipitation, hydrothermal treatment and emerging technologies like electrochemical treatment, ion-exchange and adsorption. Efficiency, environmental impacts, and chemical speciation influencing phosphorus extractability are analyzed. Additionally, policy frameworks and circular economy strategies for phosphorus recycling are discussed, highlighting challenges like solubilizing insoluble phosphorus compounds. The study emphasizes recent advances in recovery technologies and life cycle assessments to improve sustainability and economic viability, proposing future research directions to address these challenges. By optimizing phosphorus recovery from biomass ash, this approach aligns with sustainable agriculture and resource management goals, reducing dependence on finite phosphate rock reserves.