Table 4.13 lists the most commonly encountered pollutants in water; however, in many industrial applications various heavy metals are frequently combined in the process discharge.
Some heavy metals are essential to life at low concentrations but are dangerous to animal and plant life in higher concentrations. Generally, it is the free metal ion that is the most toxic; however, with Hg and Sn certain organic forms have a greater toxicity.
The WHO, the CEN, and the Environmental Protection Agency in the United States specify the maximum permissible concentrations of these metals and other pollutants in the environment.
Due to the many variables involved, no attempt is made at this stage to cover the various methods used to remove these pollutants before the water is released into the environment. Table 4.14 lists the common heavy metals in water.
TABLE 4.14 Heavy Metals
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