Biosorption of heavy metals by fungal biomass and modeling of fungal biosorption: A review

The wastewaters discharged from chemical industries which may contain heavy metal ions have toxic effect on all the living organisms. Because of this, disposal of them to the environment is a major threat to both human health and ecosystem. So the development of new technologies is required to treat wastewaters as an alternative to traditional physicochemical processes. Bi osorption, the process of passive cation binding by dead or Living biomass, represents a potentially cost-effective way of eliminating toxic heavy met als from industrial waste waters. While the abilities of microorganisms ro remove metal ions in solution have been extensively studied, fungi have bee n recognized as a promising class of low-cost adsorbents for removal of hea vy-metal ions from aqueous waste streams. Algae, fungi and bacteria differ from each other in their constitution, giving rise to different mechanisms of metal biosorption. The paper reviews the biosorption capacities of vario us fungi (free or immobilized or subjected to physical and chemical treatme nts) and, chitin and chitosan, important fungal cell wall components, in di fferent reactor systems for heavy metal ions and discusses the fungal bioso rption mechanisms. To explore the biosorption mechanisms, it is necessary t o identify the functional groups involved in the biosorption process. As si ngle toxic metallic species rarely exist in natural and waste waters, any a pproach that attempts to removal heavy metals from multi-component systems using fungi would be more realistic. The effects of various combinations of the metal ions on the biosorption capacity of various fungi are discussed and the actions of the metal ion combinations synergistic or antagonistic a re identified. Equilibria and capacity relationships for mono-component sys tems are well established and quantitatively expressed by various types of adsorption isotherms. In the case of multi-metal systems, models should be modified in order to take into account all metals and cover experimental da ta over a wide range of solution concentrations. The researcher is often pu zzled as to what are the basic differences or similarities between the isot herms and what isotherm to select for practical use to predict adsorption c apacities or to incorporate it in predicting breakthrough of columnar opera tions. The paper reviews the range of equilibrium sorption models, and diff usion and sorption models in different reactor systems used by different re searchers to correlate experimental data for fungal biosorption.