BIOSORPTION OF HEAVY-METALS

Only within the past decade has the potential of metal. biosorption by biomass materials been well established. For economic reasons, of par ticular interest are abundant biomass types generated as st waste bypr oduct of large-scale industrial fermentations or certain metal-binding algae found in large quantities in the sea. These biomass types serve as a basis for newly developed metal biosorption processes foreseen p articularly as a very competitive means for the detoxification of meta l-bearing industrial effluents. The assessment of the metal-binding ca pacity of some new biosorbents is discussed. Lead and cadmium, for ins tance, have been effectively removed from very dilute solutions by the dried biomass of some ubiquitous species of brown marine algae such a s Ascophyllum and Sargassum, which accumulate more than 30% of biomass dry weight in the metal. Mycelia of the industrial steroid transformi ng fungi Rhizopus and Absidia are excellent biosorbents for lead, cadm ium, copper, zinc, and uranium and also bind other heavy metals up to 25% of the biomass dry weight. Biosorption isotherm curves, derived fr om equilibrium batch sorption experiments, are used in the evaluation of metal uptake by different biosorbents. Further studies are focusing on the assessment of biosorbent performance in dynamic continuous-flo w sorption systems. In the course of this work, new methodologies are being developed that are aimed at mathematical modeling of biosorption systems and their effective optimization. Elucidation of mechanisms a ctive in metal biosorption is essential for successful exploitation of the phenomenon and for regeneration of biosorbent materials in multip le reuse cycles. The complex nature of biosorbent materials makes this task particularly challenging. Discussion focuses on the composition of marine algae polysaccharide structures, which seem instrumental in metal uptake and binding. The state of the art in the field of biosorp tion is reviewed in this article, with many references to recent revie ws and key individual contributions.