Heavy Metals: Toxicity and Removal by Biosorption

Abstract

Industrialization, urbanization and various anthropogenic activities such as mining and agriculture have increased releases of toxic heavy metals into the natural environment such as soils, lakes, rivers, groundwaters and oceans. The release of heavy metals in biologically available forms alter both natural and man–made ecosystems. Although some heavy metal ions are essential micronutrients for plant metabolism, they become highly toxic when they occur at high concentrations in soils, groundwaters and waste streams. Moreover, heavy metals are not biodegradable and persist in the environment. Conventional methods for the removal of the heavy metals ions from contaminated wasters and wastewaters include chemical precipitation, electroflotation, ion exchange, reverse osmosis and adsorption onto activated carbon. Recently, pioneering research on biosorption of heavy metals has led to the identification of microbes that are extremely effective in bioconcentrating metals. Biosorption is the binding and concentration of an element from aqueous solutions by organic materials such as microbial biomass. The major advantages of biosorption over conventional treatment methods include low cost, high efficiency, minimization of chemical or biological sludge, regeneration of biosorbents and possible metal recovery. Due to their humic acid content, vermicomposts are a novel and effective variety of biosorbent for removing metallic ions such as Pb, Ni, Cr, Cd and V from wastewaters. The types of biosorbents surveyed in this chapter are fungal biomass, biomass of nonliving, dried brown marine algae, agricultural wastes and residues, composite chitosan biosorbent prepared by coating chitosan, cellulose based sorbents, and bacterial strains.