Utilization of fly ash as pH adjustment for efficient immobilization and reutilization of nutrients from swine manure using hydrothermal treatment

Hydrothermal treatment has been proven an effective process for immobilization of phosphorus and other macronutrients from animal wastes. Recent research has shown biochars generated from hydrothermal treatment are relatively low in phosphorus availability to be used as a fast release fertilizer substitute. In this research, basic (>7 pH) environment was evaluated at 250-400 °C to determine its impacts on nutrient immobilization and mobility from solid products generated from swine manure. Both fly ash and 0.1 M NaOH were used to adjust hydrothermal treatment environment pH and compared with DI water. Macronutrients were found to be more efficiently immobilized in the basic environments, particularly with addition of fly ash. Further, fly ash altered crystal phases formed at the treatment temperatures resulting in differences of biochar nutrient mobility. Further, post-treatment products were evaluated for heavy metal release for potential use in agricultural applications.