Unlocking the phosphorus reservoir in wet waste: Speciation, circular recovery strategies, and inter-phase migration

The looming depletion of global phosphate rock reserves necessitates an urgent transition to phosphorus (P) recovery from secondary resources. Wet waste represents a massive yet largely untapped reservoir of P in China. However, efficient P extraction is constrained by the complex and heterogeneous speciation of P within these waste matrices. This review comprehensively examined P speciation in wet waste, emphasizing the predominance of inorganic fractions and the structural challenges posed by organic forms, particularly phytate and phosphate esters. Advanced analytical techniques were summarized to bridge the knowledge gap between speciation and practical recovery. Building on this foundation, recovery approaches-including liquid-phase crystallization, pyrolysis, biochar adsorption, and bioconversion-were discussed, and the operational efficacy of targeted extraction methods (hydrothermal, chemical, electrochemical, and biological) was specifically summarized. Quantitative comparisons show that mono-digestion of fiber-rich waste achieves only 26.2% P recovery versus 40.8% for protein-rich substrates, whereas co-digestion can elevate recovery to 88.3%. Additionally, pyrolysis retains > 90% total P, microalgae remove 93.4%, electrodialysis achieves > 90%, and liquid-phase crystallization enables near-complete (∼100%) recovery under optimized conditions. Crucially, the thermodynamic mechanisms underlying P migration during recovery were explored. Through evaluation of each technology's performance against both labile and recalcitrant P fractions, the main challenges were identified as low recovery from fiber-rich substrates and economic scalability barriers. Priority future directions centered on plant-available P recovery and integrated multi-technology coupling were proposed. This study offers a theoretical basis and technical reference for sustainable P reclamation from wet waste, contributing to alleviating global P scarcity and achieving environmental protection.