Heavy Metal Pollution Essay

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1.1 Background of study

Water pollution is a major problem in the global context. Several industrial wastewater streams may contain heavy metals such as Cr, Cu, Pb, Zn, Ni, etc. including the waste liquids generated by metal finishing or the mineral processing industries. The toxic metals, probably existing in high concentrations, must be effectively treated/ removed from the wastewaters. If the wastewaters were discharged directly into natural waters, it will constitute a great risk for the aquatic ecosystem, whilst the direct discharge into the sewerage system may affect negatively the subsequent biological wastewater treatment. In recent years, the removal of toxic heavy metal ions from sewage, industrial and mining waste effluents has been widely studied. Among the many methods available to reduce heavy metal concentration from wastewater, the most common ones are chemical precipitation, ion-exchange, adsorption and reverse osmosis (Chao et al., 2005). Heavy metals are the non-degradable
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These enter into the water resources through both natural and anthropogenic sources. More attention is being given to the potential health hazards posed by heavy metals. The term heavy metal refers to any metallic chemical element that has a relatively high density. The density of heavy metals is usually more than 5.0 g/cm3. Examples of heavy metals include mercury(Hg), cadmium (Cd), arsenic (As), chromium (Cr), thallium (Tl), lead (Pb), Copper (Cu), Zinc (Zn), Cobalt (Co), Nickel (Ni), and Iron (Fe). These metals are classified in to three categories: toxic metals (such as Hg, Cr, Pb, Zn, Cu, Ni, Cd, As, Co, Sn, etc), precious metals (such as Pd, Pt, Ag, Au, Ru etc.) and radionuclides (suchas U, Th, Ra, Am, etc.) (Volesky, 1990; Bishop, 2002). Toxic metals cause toxicity to organisms even at ppm level of

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