Environmental contamination by toxic heavy metal ions is a significant worldwide phenomenon affecting all most every aspect of living beings. These heavy metals are the main constituent of inorganic contaminants. Though, trace of these heavy metals is essential for normal growth and metabolism of living organisms, but its excessive level can be detrimental. Various anthropogenic activities, such as mining, electroplating industries etc, are responsible for heavy metal contamination of environment. Unlike organic pollutants, which in most cases are eventually destroyed, the inorganic pollutants, metallic species released in to the environment tend to persist, circulate and in the long run accumulate in the food chain, thus posing a series of threats to animal and human life (Volesky, 1994). The effects of heavy metal contamination on ecosystem are of large economic and public health concern as the increased amount of these heavy metals has resulted in the toxicity of soil, air and water (the incidence of mercury poisoning through fish from Minimata Bay in Japan is a glaring example). As everything finally goes in to the aqueous bodies, therefore it is most affected among all three systems. Hence, it is necessary to produce an efficient, cost effective and nontoxic method for removing heavy metals from the aquatic environment.
The commonly used procedures for removing metallic pollutants from aqueous streams include chemical precipitation, lime coagulation, ion exchange, reverse osmosis and solvent extraction (Rich and Cherry, 1987). These procedures are expensive, effective in the case of higher metal concentrations in water and some produces toxic waste (metal hydroxide sludge) with an additional disposal cost (Crusberg et al., 1989).
To overcome these limitations, biosorption is an emerging and cost effective technique to remove the toxic heavy metal from aqueous system. The biosorption process utilizes metal binding capacities of biomaterials and micro-organisms, such as bacteria (Hartmeier and Berends, 1995), yeast (Sugawara et al., 1997), and fungi (Luef et al., 1991).
The living microbes have unlimited capacities of cleaving organo-metallic complexes, degrading organic compounds, and accumulating other inorganic ions such as ammonium, nitrate and phosphate (Kumar, 2016). These cells are the better option due to their ability of self-replenishment, continuous metabolic uptake after physical adsorption, and potential for optimization through development of resistant species and cell surface modification (Sandau et al., 1996). This makes biosorption simple, cost effective, self sustainable, no secondary pollutant producing method with the possibility of metal recovery (Kratochvil and Volesky, 1998).
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