Biosorption of Cd2+ from Water Using Rhodotorula sp. Immobilized on Rice Husk

Cadmium (Cd2+) is a potentially toxic element that is a health and environmental risk agent, especially when found in water bodies. The objective of this study was to evaluate the removal efficiency of untreated rice husk as a biosorbent and the yeast Rhodotorula sp., immobilized on the same fiber, for Cd2+ removal from an aqueous solution. Micrographs and biosorption assays were performed in batch systems, comparing the efficiency of the unmodified fiber and the fiber with the immobilized microorganism. The percentage of removal and the biosorption capacity were also determined, and the experimental data were analyzed using kinetic models and adsorption isotherms. The immobilization of the microorganism increased the Cd2+ (1 mg/L) removal efficiency to 99.79%, compared to untreated rice husk, which was removed to 92.99%; however, no difference was observed in the biosorption capacity of the untreated fiber (3.54 mg/g) versus the yeast-immobilized material (3.52 mg/g). Both materials fit better to the Sips model (R2 = 0.9977–0.9989) and pseudo-second-order kinetics (R2 = 0.9826–0.9944). The results suggest that knowing the Cd concentration is important for selecting the most suitable removal system; nevertheless, both alternatives could be used to remove this contaminant from water.