Saturday, March 24, 2012

Short Article on Water Pollution by Shanti

This diagram shows the many things that can pollute the water.

Water pollution is usually defined as the addition of materials to water in such quantity as to lessen its suitability for the life of aquatic organisms, for irrigation, for recreation, or for drinking. Some water pollutants are inherently toxic to one or more forms of life. While seldom intrinsically toxic, nutrients may be toxic in high concentrations or may produce so much growth of bacteria or other aquatic life as to make life impossible for other aquatic organisms.

Sources of water pollution include human wastes; runoffs of industrial processes, farmlands, feedlots, and mines, air pollutants that find their way into lakes and rivers; accidental and deliberate discharges of petroleum; and radioactive wastes. Farm runoffs include fertilizer, manure, insecticides, and herbicides.

The volume of water pollutants in the United States is huge, Runoffs into the Ohio River from mines in Pennsylvania and West Virginia, for example account for a daily outpouring of 200,000 tons of sulphuric acid.

The Detroit River alone dumps 20 million tons of miscellaneous waste into Lake Erie every day. Cleveland, Buffalo, and Toledo all add their sewage effluent and industrial discharges to the same lake. By 1980, 11 regions along the shores of the Great Lakes alone had been designated areas of major pollutions.

Several major water pollutants are considered in the sections that follow:

Biodegradable, Nontoxic Organic Wastes. The ways that sewage is usually treated in American cities tells something of the nature of the problem of pollution by biodegradable, nontoxic organic wastes.

After secondary treatment has greatly reduced biological oxygen demand (BOD); this sewage effluent is allowed to enter a river, lake, or ocean.

The BOD of water is defined as the amount of oxygen that is removed from the water by the respiration of sewage bacteria in the course of 5 days at 20°C as they decompose its organic matter; as such, it is an index of the water's content of biodegradable organic matter. Thus, the greater the bacterial growth in a water sample, the more oxygen is used, and the greater it's BOD.

A high BOD and consequent high depletion of oxygen will slow the process of sewage degradation. Secondary treatment usually reduces the BOD by 60 to 90 percent. The remaining organic matter in the effluent then decomposes in the lake or river into which the effluent is discharged, usually without promoting enough bacterial growth or using enough of the water's oxygen to jeopardize its aquatic life.

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