The Sources, Environmental Impact, and Control of Water Pollution

Water pollution is one of the most serious environmental challenges.

It occurs when water is contaminated by such substances as human and

animal wastes, toxic chemicals, metals and oils. Pollution can affect

rain, rivers, lakes, oceans and the water beneath the earth, called

ground water.

Polluted water may look clean or dirty, but it all contains bacteria,

viruses, chemicals or other chemicals than can cause illness or even

death. Impurities must be removed before such water can be used safely

for drinking, cooking or washing. Some industries must clean the water

before it can be used in their manufacturing processes.

Water pollution has become a serious problem in most countries. As a

result, governments have passed laws limiting the amounts and kinds of

wastes that can be dumped into water. In many parts of the world,

cities and towns release untreated sewage into rivers, lakes and

coastal waters. Also, pollution that does not come from a direct

point, such as a sewerage outlet or factory drain, is largely

uncontrolled.

Sources of water pollution

There are three main sources of water pollution. These sources are (1)

industrial wastes, (2) sewage and (3) agricultural chemicals and

wastes.

· Industrial wastes. In many countries industries discharge pollutants

that include many toxic chemicals. Industries discharge much chemical

waste directly into natural bodies of water. In addition, the burning

of coal, oil and other fuels by power plants, factories and motor

vehicles releases sulphur and nitrogen oxides into the air. These

pollutants cause acid rain, which enters streams and lakes.

High levels of mercury...

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...r-than-normal water can kill some kinds

of plants and fish.

Control of water pollution

· Sewage treatment. The most efficient sewage treatment plants use

three processes- primary, secondary and tertiary treatment. Primary

and secondary treatment can remove up to 95 percent of the waste in

sewage. Tertiary treatment removes even more impurities. Many plants

use primary and secondary processes, and some use tertiary processes

as well. However, most treated sewage still contains nutrients and

toxic chemicals because secondary processes cannot remove them all.

· Pretreatment of wastes. Industries can reduce pollution by treating

wastes to remove harmful chemicals before dumping the wastes into

water. Industrial wastes can also be reduced by using manufacturing

processes that recover and reuse polluting chemicals.