Microbial Biosorption of metal contaminants: An Environment friendly process

Abstract

Heavy metal contamination of the natural water streams is increasingly observed because of the anthropogenic activity of human beings in terms of metal mining, mineral beneficiation and metal production, and application in different industrial processes. In view of the limitations of heavy metal decontamination by conventional treatment such as chemical precipitation, ion exchange or flotation: the microbial bio-sorption is perceived to be an attractive alternative which is emerging as the frontier option for the remediation of effluents/streams. This article summarizes various aspects of bio-sorption of metals with emphasis on the types of microbial species used, mechanism of the process and factors affecting the metal sorption on different microorganisms. A brief account of the isotherms / models applicable to the metal uptake and kinetics of bio-sorption, are also presented. The important of bio-sorption lies in its transfer a substance from the liquid phase to the solid surface/cell wall which is bound by physical and/or chemical interactions. Metal bio-sorption and bio-accumulation may or may not depend on the microbial metabolic activity; since the form of metals associated with the microbe remains unchanged (valence state, size, and shape) even if the cells are living, denatured or dead unless extraneous conditions prevail. Bio-sorption has also been discussed using various microbes such as bacteria, microalgae and fungi, particularly that of binding of metals on the cell surface and its interaction with the polysaccharides (PS) and related functional groups.