Thermal pollution is defined as the addition of excess of undesirable heat to water thereby making it harmful to man, animal or aquatic life.

Sources of Thermal Pollution

1. Nuclear power plants:

Nuclear power plants including drainage from hospitals, research institutions, nuclear experiments and explosions discharge a lot of heat that is not utilized.

2.Coal-fired power plants:

Coal fired power plants constitute a major source of thermal pollution. The condenser coils in such plants are cooled with water from nearby lakes or rivers. The resulting heated water is discharged into streams thereby raising the water temperature by 15C.

3. Industrial effluents:

Industries like textile, paper, pulp and sugar manufacturing release huge amounts of cooling water along with effluents into nearby natural water bodies.

4. Domestic Sewage:

Domestic sewage is discharged into rivers, lakes, canals or streams with minimal treatment or without any treatment. These wastes have a higher organic temperature and organic load.

5. Hydro-electric power:

Generation of hydroelectric power sometimes leads to negative thermal loading in water systems.

Effects of Thermal pollution

1. Reduction in dissolved oxygen: Concentration of Dissolved Oxygen (DO) decreases with increase in temperature.

2. Increase in toxicity The concentrated pollutant causes the rise in the temperature of water which increases the toxicity of the poison present in water. The toxicity in water will increase the death rate in marine life.

3. Disruption of Biological activities Temperature changes disrupt the entire marine ecosystem because changes in temperature causes change in physiology, metabolism and biological process like respiration rate, digestion, excretion and development of an aquatic organism.

4. Interference in reproduction: In fishes, several activities like nest building, spawning, hatching, migration and reproduction depend on optimum temperature.

Control measures for thermal pollution

The following measures can be taken to prevent or control high temperature caused by thermal pollution:

1. Heated water from the industries can treated before discharging directly to the water bodies.

2. Heated water from the industries can be treated by the installation of cooling ponds and cooling towers.

3. Industrial treated water can be recycled for domestic use or industrial heating.

4. Through artificial lakes: In this lake Industries can discharge their used or heated water at one end and water for cooling purposes may be withdrawn from the other end. The heat is eventually dissipated through evaporation.