Phosphorus Recovery from Aqueous Solutions using Bioclastic Granules (Lithothamnium calcareum)

Abstract

Against of 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, such as 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 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 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 sorption data fitted the Freundlich model well, with kF of 1.35 L mg-1 and n of 2.43. Using the Langmuir model, a qmax of 14.35 mg g-1 was obtained. Regarding the sorption data over time, a better fit to the pseudo-first order kinetic model was observed, obtaining a calculated qeq of 6.56 mg g-1 and a k1 of 0.0073 min-1. The incorporation of PO4 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.