Elevated effect of hydrothermal treatment on phosphorus transition between solid-liquid phase in swine manure

The morphology and composition of phosphorus in biomass wastes are key factors in determining its potential for utilization. However, the morphological distribution and evolutionary mechanism of phosphorus during the hydrothermal conversion of biomass wastes are still unclear. In this study, swine manure was investigated as the research subject, and the changes in its solid-phase organic components, such as lignocellulose, and inorganic constituents, including metals and phosphorus, during the hydrothermal carbonization (HTC) processes were analyzed in relation to hydrothermal reaction severity (LnR₀). A significant linear correlation in Phase II was observed between the solid-phase yield of swine manure and the LnR₀. The rapid decline in the solid-phase yield during the initial phase (LnR₀ < 9.72) was primarily attributed to the hydrolysis of hemicellulose and similar components. Similarly, solid phase phosphorus showed a very significant phase II with the decrease of solid phase yield. In the first stage, inorganic phosphorus and metal ions (calcium ions, magnesium ions) transferred to the liquid phase (LnR₀<9.41). When LnR₀ > 9.41, and the driving force of inorganic phosphorus and metal ions into solid phase is enhanced. As the LnR₀ was further increased, the HTC could fix over 90 % of the total phosphorus content. XANES analysis indicated that hydroxyapatite emerged as the predominant phosphorus fraction in the solid-phase products, comprising more than 60 %, while magnesium ammonium phosphate components also appeared. This research elucidates the underlying mechanisms of component interaction and phosphorus transformation, providing a solid foundation for enhancing the reuse efficiency of phosphorus in wastes.