CADMIUM ADSORPTION BY NONLIVING BIOMASS OF THE SEMI-MACROSCOPIC BROWNALGA, ECTOCARPUS-SILICULOSUS, GROWN IN AXENIC MASS-CULTURE AND LOCALIZATION OF THE ADSORBED CD BY TRANSMISSION ELECTRON-MICROSCOPY

Non-living, freeze-dried material of the brown alga Ectocarpus silicul osus (Phaeophyceae) demonstrated high equilibrium uptake of Cd from aq ueous solutions (Fehrmann and Pohl, 1993). The alga was grown in 250-L photobioreactors under various growth conditions (light, salinity and nutrient concentrations) in order to obtain larger quantities of biom ass and to improve its Cd adsorption capacity. To derive further knowl edge on the biosorbant phenomenon different adsorption parameters such as pH for the sorption process and kinetics of Cd adsorption were tes ted. The maximum adsorption capacity of the freeze-dried biomass excee ded 41 mg Cd per g biomass. After repeated addition of low Cd concentr ations the maximum adsorption capacity was lower (31.4 mg Cd per g bio mass). In comparison with other adsorbing materials (activated carbon, silica gel, siliceous earth) E. siliculosus showed significantly high er adsorption capacity. Desorption of deposited Cd with 0.1 M HCl resu lted in no changes of the adsorption capacity through five subsequent adsorption-/desorption-cycles. Hence, dried E. siliculosus appears to be an efficient material for the elimination of Cd from industrial was te water. Transmission electron microscopic investigations showed an e lectron dense area in the outer surface layers of the cell wall after Cd adsorption indicating the most likely location of Cd fixation.