Biosorption of Cadmium from Aqueous Solution by Free and Immobilized Dry Biomass of Chlorella vulgaris

Biosorption by algae is an effective process for the removal of heavy metals from the aqueous solutions. The present work deals with the biosorption of Cd(II) by Chlorella vulgaris in a batch system. The biosorption efficiency of Cd(II) removal was studied at different pH (3–8), initial metal concentrations (20–100 ppm), agitation time (5–120 min.), agitation speed (50–250 rpm), and biomass dosage (0.01–0.1 g/50 ml of metal solution). The optimum conditions for maximum biosorption capacity for C. vulgaris were at pH 6, initial Cd(II) concentration 75 mg/l, biomass dosage 0.08 g/50 ml metal solution, temperature 25 °C, agitation speed 250 rpm, and agitation time 30 min. The cadmium removal efficiency of the raw and pretreated algal biomass was studied under the optimum conditions. The results showed that pretreatment with acetic acid gave 99.346% as compared with raw biomass. Different algal weights (0.2, 0.15, 0.1, 0.05, and 0.025 g) were immobilized with 10 ml of 4% calcium alginate. The results showed that the highest cadmium biosorption efficiency was 76.448% for 0.025 g as compared with the control. The biosorption mechanisms were examined by Fourier-transform infrared analysis and scanning electron microscopy for raw and pretreated algal biomasses before and after cadmium biosorption. It was found that hydroxyl, amide with hydrogen bond, and carbonyl stretching in carboxyl groups played an important role in biosorption.