Hydrothermal recovery of phosphorus from organic solid waste: Mechanisms, transformation pathways, and product applications

With the increasing scarcity of global phosphorus resources and the massive generation of organic solid waste (OSW), the efficient recovery and resource utilization of phosphorus (P) have become critical issues for sustainable development. Hydrothermal technology, due to its high efficiency and environmental friendliness, has been widely applied in the recovery of P from OSW and the preparation of P-enriched products. This review systematically analyzes the occurrence characteristics of P in OSW, the migration and transformation pathways of P during hydrothermal processes, and the application potential of P-enriched products (such as struvite, calcium phosphate salts, and P-enriched hydrochar). Comprehensive analysis results indicate that the P content in OSW varies significantly depending on its source, with inorganic phosphorus (IP) being the dominant form (maximum proportion can reach over 90 %) and organic phosphorus (OP) as the secondary form. The release and transformation of P, as well as its distribution in solid and liquid phases, are collaboratively influenced by factors such as feedstock characteristics, hydrothermal temperature, holding time, pH, and additives, with the conversion to IP being the ultimate trend. The primary application of P-enriched products is as slow-release P fertilizers, which have shown excellent fertilization effects in crop production. However, their P release behavior is significantly affected by preparation conditions and environmental factors. This review aims to provide theoretical guidance and suggestions for the development of efficient P recovery and resource utilization from OSW, promoting the deep integration of sustainable P resource utilization and green agricultural development, with significant environmental and economic implications.