An assessment of hydrothermal treatment of dairy waste as a tool for a sustainable phosphorus supply chain in comparison with commercial phosphatic fertilizers

Hydrothermal treatment has been proven efficient in immobilizing phosphorus and other macronutrients from animal waste; however, there are still gaps in understanding the best end-use applications for nutrient-dense biochars. In this research, aqueous phase phosphorus availability (P (aq)) of biochars produced at various temperatures and residence times was determined in pH 5.5 citric acid for 8 weeks. Further, P (aq) of commercially available composted manure and fertilizers was also determined for comparison. P (aq) was found to plateau after 4 weeks in aqueous phase. Hydrothermal treatment temperature and residence time were found to improve nutrient immobilization efficiency, while conversely lowering P (aq). Comparing to commercially available fertilizers, biochars produced from hydrothermal treatment are low in P (aq), despite high P2O5% found in the solids. A preliminary process study evaluating energy consumption and CO2 emissions associated with recycled P2O5 recovered from the process operating at 200 A degrees C was conducted, indicating CO2 emissions with respect to soluble phosphorus are significantly higher in comparison with commercial phosphatic fertilizers. Further recommendations regarding life cycle analysis of the phosphorus supply chain are also discussed.