Bioremoval of zinc ions by Scenedesmus obliquus and Scenedesmus quadricauda and its effect on growth and metabolism

Zinc biosorption by two green algae, Scenedesmus obliquus and Scenedesmus quadricauda, was investigated. Data show that, at concentrates between 0.5 and 8 ppm, zinc adsorption by algae increased with increasing metal ion concentration. The maximum specific adsorptive capacity of zinc ions obtained from the Langmuir adsorption isotherms was higher for S. obliquus (6.67) and lower for S. quadricauda (5.03). These S. obliquus appears to be more efficient than S. quadricauda for removing zinc ions. However, the affinity constant of zinc on the biomass of both algae were 0.19 and 0.27 indicating that S. obliquus is more tolerant to zinc phytotoxicity than S. quadricauda. Algal growth, pigment fractions, total amino acids, and the activities of some phosphatases enzyme (acid phosphatase, alkaline phosphatase, and ATPase) in the algal cells were measured in the exponential growth phase after exposure to various concentrations of zinc. Lower concentrations of zinc increased dry weight, chlorophyll a, b, carotenoids, and total amino acid contents in both algae. On the other hand, higher concentrations of zinc were inhibitory for growth and the other metabolic activities.