Phosphorus recovery from aqueous solutions using Bioclastic Granules (Lithothamnium calcareum)

Against the growing world demand for food and the possibility of recovering some nutrients, this work focused on the evaluation of the use of Bioclastic Granules (BG) from the algae Lithothamnium calcareum as sorbent material for the removal/recovery of phosphorus from aqueous solutions. The main variables that affect the sorption process, pH, initial concentration of phosphate, and GB, as well as the contact time, were evaluated. The effect of pH was very significant, obtaining the best results of PO₄^3- removal at pH 5. In the coarser granulometric fractions (+ 106 - 150 and + 210 - 300 μm), the best removals were observed (around 75%). Regarding the initial PO₄^3- concentration in the solutions, the highest removal (in the range of 74 to 78%) was observed in the lowest concentrations (5 to 70 mg L^-1) and the best uptake (10 to 14 mg g^-1) at higher concentrations (200 to 420 mg L^-1). The PO₄^3- sorption data fitted the Freundlich model well, with k_F of 1.35 L mg^-1 and n of 2.43. A q_max of 14.35 mg g^-1 was obtained using the Langmuir model. Regarding the sorption data over time, a better fit to the pseudo-first-order kinetic model was observed, obtaining a calculated q_eq of 6.56 mg g^-1 and a k₁ of 0.0073 min^-1. The incorporation of PO₄^3- ions in the GB structure was confirmed through the characterization results before and after the sorption experiments using X-ray fluorescence (FRX) and scanning electron microscopy (SEM) techniques.