Environmental Engineering Reference
In-Depth Information
36.1 Water and Water Pollutants
Water is indispensable for life. In fact, it can be considered as
the molecule of life
. The daily
requirement of water may vary from one person to another; however, there is a certain
minimum daily uptake of pure water that is essential for sustaining the natural growth
of human life [1]. Therefore, providing pure and fresh water, free of toxic solutes, is indis-
pensable for healthy living, and providing safe drinking water to every resident is the top
priority of any government.
Groundwater often has high amounts of inorganic constituents because of the dissolu-
tion of rock-forming minerals and the release of industrial efluents. Fluoride and arsenic
ions are the most commonly occurring inorganic contaminants in groundwater. The pres-
ence of these ions in drinking water, in excess of permissible limits, results in undesirable
health effects. Unfortunately, a signiicant increase in the levels of arsenic and luoride in
surface water has been reported in several regions in India and its neighboring countries
during the past decade [2]. The primary reason for this increase is the rapid decline in the
water table with increasing use of surface water for agricultural purposes and for urban
water supplies. The risks to human health have increased with the increased concentra-
tions of these solutes in potable water.
Fluoride is considered to be a reactive element. It may combine with other elements by
forming covalent and ionic bonds. It is mainly found in alkaline rocks, alkaline soils, and
industrial efluents, such as pharmaceuticals, semiconductor waste, cosmetics, coal power
plants, and fertilizer manufacturing plants. According to the World Health Organization
(WHO) norms, the upper limit for the luoride concentration in drinking water is 1.5 mg/l.
Small quantities of luoride can protect against dental cavities and the weakening of bones;
however, large amounts can impair health by causing dental luorosis and damage to the
bones (skeletal luorosis). As many as 200 million people worldwide are affected by luo-
ride contamination of drinking water [3].
The contamination of groundwater by arsenic also affects vast regions in India,
Bangladesh, China, Mexico, the United States, Cambodia, and Argentina. The maximum
arsenic level allowed in drinking water has been set at 10 μg/l (WHO, 2001) since 1993,
whereas the permitted limit for industrial efluents is <0.2 mg/l. Drinking arsenic-rich
water over a long period results in various adverse health effects, including skin prob-
lems; cancers of the bladder, kidney, and lung; disease in the blood vessels of the legs and
feet; and possibly diabetes, high blood pressure, and reproductive disorders. A study in
2007 found that >137 million people in >70 countries are most likely affected by arsenic-
contaminated drinking water. Wastewater efluents from a few metallurgical industries,
such as gold, silver, copper and zinc, electronics, and pharmaceuticals, may contain
>1 mg/l of arsenic [2,4].
36.2 Wastewater Treatment and Adsorption
Various methods are in place for the treatment of wastewater containing inorganic con-
taminants, including luoride and arsenic. The methods are based on the principles of
precipitation and coagulation, chemical oxidation, sedimentation, iltration, adsorption,
osmosis, ion exchange, etc. Currently, adsorption is being used extensively for the removal
