definition 112 causes, effects and control measures of

5.2.6 Thermal Pollution

Sources

: The discharge of warm water into a

river is usually called a 

thermal pollution. 

It

occurs when an industry removes water from a

source, uses the water for cooling purposes and

then returns the heated water to its source.

Power plants heat water to convert it into steam,

to drive the turbines that generate electricity.

For efficient functioning of the steam turbines,

the steam is condensed into water after it leaves

the turbines. This condensation is done by tak-

ing water from a water body to absorb the heat.

This heated water, which is at least 15oC higher

than the normal is discharged back into the

water body.

Effects: 

The warmer temperature decreases the

solubility of oxygen and increases the metabo-

lism of fish. This changes the ecological balance

of the river. Within certain limits thermal addi-

tions can promote the growth of certain fish

and the fish catch may be high in the vicinity of

a power plant. However sudden changes in tem-

perature caused by periodic plant shutdowns

both planned and unintentional can change re-

sult in death of these fish that are acclimatized

to living in warmer waters.

Tropical marine animals are generally unable to

withstand a temperature increase of 2 to 3

0

C

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Pollution

and most sponges, mollusks and crustaceans are

eliminated at temperatures above 37

0

C. This

results in a change in the diversity of fauna as

only those species that can live in warmer wa-

ter survive.