الفهرس 
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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)