THERMALPOLLUTION

ENGR. MAHESH KUMAR

What is Thermal Pollution?

Increase in the normal temperatures of natural waters

caused by intervention of human activities.

It is the degradation of water quality by any process

that changes ambient water temperature.

Temperature is a physical characteristic of water which is

characteristic of water which is regulated under the

Clean Water Act.

Causes

The major sources of thermal pollution are electric power plants

and industrial factories.

Another cause is the use of water as a coolant by power plants

and industrial manufacturers. When water used as a coolant is

returned to the natural environment at a higher temperature,

the change in temperature decreases oxygen supply, and

affects ecosystem composition.

When a power plant first opens or shuts down for repair or other

causes, fish and other organisms adapted to particular

temperature range can be killed by the abrupt change in water

temperature known as "thermal shock."

Causes

Streams and small lakes are naturally kept cool by trees and

other tall plants that block sunlight. People often remove

this shading vegetation in order to harvest the wood in the

trees, to make room for crops, or to construct buildings,

roads, and other structures.

Even the removal of vegetation far away from a stream or

lake can contribute to thermal pollution by speeding up the

erosion of soil into the water, making it muddy.

Thermal Pollution

Waste Heat from Power Plants

Major Causes

Nuclear power plants

Deforestation

Soil erosion

Nuclear Power Plants

Nuclear power plants use water as a cooling agent.

After the water is used, it is put back into a water supply

at 9-20oC warmer

Deforestation

The decrease in vegetation increases the amount of light

that hits the water, which increases the temperature of

the water

Deforestation also increases erosion

IMPACTS

All plant and animal species that live in water are adapted to

temperatures within a certain range.

Thermal pollution may also increase the metabolic rate of

aquatic animals, as enzyme activity, resulting in these

organisms consuming more food in a shorter time than if their

environment were not changed.

Some organisms do thrive in warm water, often with

undesirable effects. Algae and other plants grow more rapidly

in warm water than in cold, but they also die more rapidly.

Effects of Increased Water

Temperature

Thermal shock aquatic life adapted to a certain water

temperature can go into shock when the temp is

changed even 1 or 2 degrees.

Oxygen dissolved in water decreases

Increases the rate of photosynthesis, which increases the

amount of plant growth

Increases the metabolic rate of fish, which increases

their need for oxygen

Changes in the environment may also result in migration

of organisms to another, more suitable environment, and

to in-migration of organisms that normally only live in

warmer waters elsewhere.

As a result one has the problem of compromising food

chains of the old and new environments.

Biodiversity can be decreased as a result.

Biotic Effects of Thermal Pollution

DISOLVED OXYGEN VS TEMPERATURE

CONTROLS

Thermal pollution from power plants and factories is

relatively easy to control. Instead of discharging

heated water into lakes and streams, power plants and

factories can pass the heated water through cooling

towers or cooling ponds, where evaporation cools the

water before it is discharged.

Alternatively, power plants can be designed or refitted

to be more efficient and to produce less waste heat in

the first place.

Control of thermal pollution

Cooling towers, which transfer waste heat tothe atmosphere through evaporation and/or heattransfer

Cogeneration, a process where waste heat isrecycled for domestic and/or industrial heatingpurposes

CONTROLS

Thermal pollution from devegetation is quite hard tocontrol because it is caused by the cumulative effectof many peoples actions, most of which areindividually minor.

There should be implemented laws that will helpcontrol, conserve, and protect resources to counterthermal pollution.

To prevent thermal pollution due to devegetation, theprescription is simple: do not devegetate. All efforts tocontrol erosion also have the effect of keeping waterclearer and, thus, cooler.

Uses of Waste Heat

Cogeneration

Aquaculture

Greenhouse heating

Desalination of seawater

Increase crop growth in cold season

Preheat air

Others

Natural Draft Cooling Tower

Mechanical Draft Cooling

Tower

Air to Liquid Heat Exchanger