Phosphorus recovered from digestate by hydrothermal processes with struvite crystallization and its potential as a fertilizer

Phosphorus (P) recovery from digestate has attracted considerable interest. In this study, hydrothermal processes in combination with struvite crystallization were performed to promote P solubilization and capture from digestate; its potential as a phosphate-based fertilizer was also investigated. Hydrothermal treatment with HCl and H2O2 showed good results for the solubilization of organic and slightly soluble P, and achieved the lowest input energy need (768 kWhkg-1P). Struvite crystallization reached 99.3% (Mg2+:PO43-1.84:1, pH 9.98). X-ray diffractometry and energy dispersive X-ray spectrometer mapping demonstrated the main precipitate component was struvite. For the fertilization of maize, P utilization from struvite was 19.0%. Light microscope analysis revealed that appropriate amounts of struvite may have an influence on the growth of the primary root. Overall, 16.6% of total P was recovered after P was solubilized, captured and made available.