Interactions between zinc and cadmium uptake by free and immobilized cells of Scenedesmus quadricauda (Turp.) Breb.

Biological treatment of heavy metals is an effective technology for the treatment of low concentration industrial wastewater. The purpose of this study was to evaluate the zinc and cadmium removal capacities through absorption (active) and adsorption (passive) by free and alginate-immobilized cells of Scenedesmus quadricauda. Immobilized cells have high capacities for uptake of both the heavy metal tested and the kinetics under the conditions studied were relatively fast. About 90% of the biosorption (adsorption) occurred within 10 min and equilibrium was reached within 30 minutes in both free and immobilized cells. However, a different pattern was observed for absorption. Maximum absorption by immobilized cells was found to be around 6.6 mmol Zn(2+) and 8.0 mmol Cd(2+) per mg protein, these values being approximately 1.4 and 1.6 fold higher than those of the free cells. Statistical analysis (ANOVA) confirmed the superiority of immobilized cells for metal absorption but not for adsorption. Free cells were equally good for adsorption. The results obtained on the patterns of metal/metal interactions showed either antagonistic, or non-interaction type of behaviour for both adsorption and absorption. However, no synergistic type of behaviour was observed during treatment.