Advances in biosorption of metals: selection of biomass types

Within the past decade, the potential of metal biosorption has been well established. For economic reasons, of particular interest are abundant biomass types either generated as a waste by-product of large-scale industrial fermentations or certain metal-binding algae found in large quantities in the sea. Some of these high metal-sorbing biomass types serve as a basis for newly developed metal biosorption processes foreseen particularly as a very competitive means for detoxification of metal-bearing industrial effluents. Ions of lead and cadmium, for instance, have been found to be bound very efficiently from very dilute solutions by the dried biomass of some ubiquitous brown marine algae such as Ascophyllum and Sargassum which accumulate more than 30% of biomass dry weight in the metal. Mycelia of industrially steroid-transforming fungi Rhizopus and Absidia are excellent biosorbents for lead, cadmium, copper, zinc, and uranium, binding also other heavy metals up to 25% of the biomass dry weight. The common yeast Saccharomyces cerevisiae is a 'mediocre' metal biosorbent. Construction of biosorption isotherm curves serves as a basic technique assisting in evaluation of the metal uptake by different biosorbents. The methodology is based on batch equilibrium sorption experiments extensively used for screening and quantitative comparison of new biosorbent materials. Experimental methodologies used in the study of biosorption and selected recent research results demonstrate the route to novel biosorbent materials some of which can even be repeatedly regenerated for re-use.