Page 189 - Industrial Ventilation Design Guidebook

4,4 WATER PROPERTIES AND TREATMENT I 5 1

pharmaceutical industry and silicon chip manufacturers require the greatest
purity in the water used.

4.4.2. i Heavy Metals
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 dan-
gerous 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

Chemical
Constituent formula Problems caused

Antimony Sb Moderately toxic
Arsenic As Highly toxic, corrosive, carcinogen
Beryllium Be High toxicity, long-term effects
Cadmium Cd Highly toxic, carcinogen
Chromium Cr Compounds may be highly toxic
Cobalt Co Moderate toxic
Copper Cu Highly toxic
Lead Pb A cumulative poison
Mercury Hg Very highly toxic
Molybdenum Mo Compounds are highly toxic
Nickel Ni Highly toxic, carcinogenic
Selenium Se Highly toxic
Silver Ag Low toxicity
Tellurium Te Highly toxic
Thallium Tl Sulfates highly toxic
Tin Sn Irritation of skin, eyes, lungs, and
stomach
Titanium Ti Chlorides are moderately toxic
Uranium U Toxic, insoluble in water
Vanadium Va Oxides and chlorides have a high tox-
icity
Zinc Zn Moderately toxic, carcinogenic