THERMAL POLLUTION

THERMAL POLLUTION

Thermal pollution is defined as sudden increase or decrease in temperature of a natural body of water which may be ocean, lake, river or pond by human influence. This normally occurs when a plant or facility takes in water from a natural resource and puts it back with an altered temperature. Usually, these facilities use it as a cooling method for their machinery or to help better produce their products.

Plants that produce different products or waste water facilities are often the culprits of this massive exodus of thermal pollution. In order to properly control and maintain thermal pollution, humans and governments have been taking many steps to effectively manage how plants are able to use the water. However, the effects are still lasting today.

Effects: 

Many organisms are killed instantly by the hot water resulting into a high mor­tality. It may bring other disturbance in the ecosystem. The egg of fish may hatch early or fail to hatch at all. It may change the diurnal and seasonal be­haviour and metabolic responses of organisms. It may lead to unplanned mi­gration of aquatic animals.

Macro-phytic population may also be changed. As temperature is an important limiting factor, serious changes may be brought about even by a slight increase in temperature in a population. For minimising thermal pollution, hot water should be cooled before release from factories and removal of forest canopies and irrigation return flows should be prohibited.

Causes or Sources of Thermal Pollution:

The various causes of thermal pollution are as follows:

(1) Coal-fired Power Plants:

Some thermal power plants use coal as fuel. Coal-fired power plants constitute the major source of the thermal pollution.

(2) Industrial Effluents:

Industries generating electricity require large amount of Cooling water for heat removal. Other industries like textile, paper, and pulp and sugar industry also re­lease heat in water, but to a lesser extent.

(3) Nuclear Power Plants:

Nuclear power plants emit a large amount of unutilized heat and traces of toxic radio nuclear into nearby water streams. Emissions from nuclear reactors and processing installations are also responsible for increasing the temperature of water bodies.

(4) Hydro Electric Power:

Generation of hydro-electric power also results in negative thermal loading of water bodies.

(5) Domestic Sewage:

Domestic sewage is often discharged into rivers, lakes, canals or streams with­out waste treatment. The municipal water sewage normally has a higher tem­perature than receiving water. With the increase in temperature of the receiv­ing water the dissolved oxygen content (DO) decreases and the demand of oxy­gen increases and anaerobic conditions occur.

Control of Thermal Pollution: 

Control of thermal pollution is necessary as its detrimental effects on aquatic ecosystem may be detrimental in the future. Viable solutions to chronic ther­mal discharge into water bodies are as follows:

(1) Cooling Ponds:

Cooling ponds or reservoirs constitute the simplest method of controlling ther­mal discharges. Heated effluents on the surface of water in cooling ponds maximize dissipation of heat to the atmosphere and minimize the water area and volume. This is the simplest and cheapest method which cools the water to a considerable low tem­perature. However, the technique alone is less desirable and inefficient in terms of air-water contact.

(2) Cooling Towers:

Using water from water sources for cooling purposes, with subsequent return to the water body after passing through the condenser is termed as cooling process. In order to make the cooling process more effective, cooling towers are designed to control the temperature of water. In-fact, cooling towers are used to dissipate the recovered waste heat so as to eliminate the problems of thermal pollution.

(3) Artificial Lake:

Artificial lakes are man-made bodies of water which offer possible alternative to once through cooling. The heated effluents may be discharged into the lake at one end and the water for cooling purposes may be withdrawn from the other end. The heat is eventually dissipated through evaporation.

These lakes have to be rejuvenated continuously. A number of methods have been suggested and developed for converting the thermal effluents from power plants into useful heat resources for maximing the benefits.