Swine manure valorization for phosphorus and nitrogen recovery by catalytic–thermal hydrolysis and struvite crystallization

Phosphorus (P) and nitrogen (N) recovery from swine manure has attracted considerable interest for biomass valorization. In this study, a catalytic–thermal hydrolysis (TH) process combined with struvite crystallization was investigated to promote P and N conversion from swine manure. Its potential as a phosphate-based fertilizer was investigated. Two periods for P solubilization and transformation were observed, i.e., an initial increase with reaction time followed by a decrease as treatment continued. Nitrogen conversion efficiency increased with increasing temperature and time. Treatment of swine manure by catalytic–TH with HCl + H₂O₂ showed the best performance for P and N solubilization and transformation. With a Mg²⁺/PO₄ ³⁻ molar ratio of 2.49 and a pH of 9.11, the struvite crystallization efficiency from the supernatant after catalytic–TH with HCl + H₂O₂ reached 99.2%. Hydroculture bioassay showed that struvite had a positive effect on the early growth of wheat. The P concentrations in both root and shoot tissues for struvite treatment were more than two times higher than that of soluble P. These encouraging results warrant further studies on the conversion of biowaste given that recycling nutrients sources may outperform traditional synthetic fertilizers.