Pediastrum boryanum Immobilized on Rice Husk Ash Silica as Biosorbent for Fluoride Removal from Drinking Water

Objectives: Biosorption is an environmentally friendly approach for the removal of organic and inorganic compounds from aqueous solutions. Fluoride concentration in drinking water above 1.5 mg∙L-1 is harmful to human health. The aim of this study was to develop analgae immobilization method using silica gel extracted from renewable rice husk ash and test the biosorbent in defluoridation of water. Methods: Pediastrumboryanum was immobilized using sodium silicate extracted from rice husk ash. The method involved suspending the biomass in a sodium silicate rich filtrate prepared through alkaline leaching of rice husk ash. The immobilization was achieved through acid precipitation of silica. The biosorbent was used in the defluoridation of water and had improved mechanical properties. Findings: The maximum adsorption capacity was 25.641 mg∙g-1 at pH 5. Experimental data fitted well into the Langmuir adsorption isotherm (R2 = 0.9987) although Freundlich adsorption isotherm (R2=0.9898) could also be used to describe biosorption processes. The biosorption process was of the pseudo-second order kinetics with R2 ≥ 0.9988. FT-IR spectra revealed the presence of –OH, -NH, C-O-C and –C=O functional groups. Application: This study demonstrate the feasibility to immobilize Pediastrumboryanum using sodium silicate extracted from renewable bio-waste instead of using commercially available sodium silicate. Experimental results present the possibility to application of the biosorbent in the defluoridation of water.