Fate of phosphorous after thermochemical treatment of algal biomass

Autoflocculation can remove algal cell at a high pH while simultaneously can precipitate out more than 90% of the soluble phosphorous as different mineral species of calcium and magnesium (inorganic-P). Hydrothermal liquefaction (HTL) then can be applied to convert the algal solids cultivated from wastewater (WW) to biofuel and fertilizer. To find out the impact of harvest on HTL reaction products the growth stage at which the algae were harvested and the total Ca:P ratio in algal solids were varied, resulting in different quantities of biologically assimilated-P and inorganic-P. The X-ray diffraction (XRD) pattern for algal solids harvested at high pH was amorphous or CaCO3. The dominant crystal species for the HTL biochar was HAp for algal solids harvested during the exponential phase and with a total Ca:P ratio of 1.17. Adding lime to increase the total Ca:P ratio to 1.67, the stoichiometric Ca:P ratio for HAp, caused a shift to have equal amounts of HAp and TCP in the HTL biochar.