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Abstract I’ Increased emphasis on the efficient and effective treatment of waste water, has led to a revived interest in the effect of various toxic inorganic materials. These toxic materials may find their ways into waste water. The problem of the presence of toxic materials in wastes has two equally important parts: 1) The deleterious effects which a given toxic substance may exert on biological waste treatment processes; 2) The possibility of harmful effects to aquatic and terrestrial organisms downstream from the waste treatment plant. Therefore, there is an interest not only in the ability of process to withstand the presence of toxic material, but also in the ability to remove these materials from the waste. Metals are introduced into the environment from various sources, e.g., from industrial processes and during the mining and refining of metal ores (Table 1.1). The rapid expansion of industry and the increase in domestic activities in the past century had caused a concomitant increase in the quantities of metals that are being released to the environment. The natural recycling of some metals, that generally occurred in biogeochemical cycles, had been disrupted as a result of the large quantities of metals and pollutants that are currently entering the environment from various sources (Moulton and Directo, 1962; Mcdermott et al, 1963). The presence of heavy metals, especially many of those included in the first transition series of the periodic chart, is of particular importance. Due to the following reasons: a)Their wide use in metal finishing industries with the ubsequent discharge of significant quantities of metallic ions in the wastes from these industries. b) The observation that many of these common metals can have a pronounced toxic effect on the biological systems at extremely low concentrations. (Mance, 1987) |