Thermal pollution, also known as heat pollution, occurs when heat is released into water or air that produces undesirable effects.
This type of pollution may also be referred to as thermal enrichment.
Thermal Pollution Definition
Thermal pollution occurs when there is a sudden increase or decrease in the temperature of a natural body of water.
Merriam-Webster defines thermal pollution as,
“the discharge of heated liquid (such as wastewater from a factory) into natural waters at a temperature harmful to the environment.”
The sudden heat releases that cause adverse effects are usually due to forest fires, volcanic eruptions, or human activities. Volcanic eruptions and forest fires contribute to heat increases; however, thermal pollution is more specifically associated with artificial, human-caused heat releases.
The addition of excessive and undesirable heat can make water harmful to humans, animals, or aquatic life.
The European Environment Agency defines thermal pollution as,
“The excessive raising or lowering of water temperature above or below normal seasonal ranges in streams, lakes, or estuaries or oceans as the result of discharge of hot or cold effluents into such water.”
What Are the Sources of Thermal Pollution?
The discharge of warm water into a water body, such as a river or lake, is usually termed thermal pollution. This happens when an industry or plant uses water from a source, utilizes it for cooling purposes, and then returns the heated water to the source.
There are various sources of thermal pollution. These sources include heat released into the environment from thermal power plants, nuclear power plants, petroleum refineries, steel plants, chemical plants, metallurgical industries, paper mills, etc.
A major source of thermal pollution is coal-fired power plants. Natural gas and oil plants can also cause thermal pollution.
To generate electricity, power plants heat water to create steam that drives turbines. After leaving the turbines, the steam is condensed back into water using cooling methods, often by taking water from a nearby body of water. The heated water, which can be several degrees (usually between 5°C to 15°C) warmer than the intake water, is then discharged back into the water body.
Also Read: Marine Pollution: Causes, Effects, and Solutions
Thermal Pollution of Water
Atomic energy centers, thermal power stations, and various industries require a huge amount of water for cooling purposes. The hot water afterward is released directly into the water source. This results in altering water temperature and thus causes thermal pollution.
Most industries produce heated effluents from different processes that are discharged into water, changing its temperature.
Undesirable polluted water is then discharged into the surrounding area, affecting the natural balance.
Also Read: Eutrophication: Causes, Impacts, and Solutions
Effects of Thermal Pollution
Temperature is important in regulating desired living conditions for living beings.
For instance, birds and mammals need a narrow range of body temperature to survive, whereas aquatic organisms can only survive at a certain range of temperatures.
Disruption of the temperature of water bodies has detrimental effects on aquatic life. Thermal pollution leads to an undesirable rise in water temperature, altering the levels of dissolved oxygen. This rise in overall temperature disrupts the natural decay of plants and aquatic animals.
Warmer water is responsible for the rise in the metabolic rate of fish and other animals in the sea, resulting in decreased life expectancy and causing an increased rate of decay.
Thermal additions can promote the growth of some fish species, and fish catches may increase near power plants. However, sudden temperature changes, such as those caused by plant shutdowns, can lead to the death of fish acclimatized to warmer waters.
Tropical marine animals typically cannot tolerate a temperature increase beyond 2°C to 4°C. Most sponges, mollusks, and crustaceans are eliminated at temperatures above 37°C, leading to a reduction in biodiversity.
In short, some of the major impacts of thermal pollution are:
- Every plant and animal species has a specific level and rate of thermal tolerance. When this level is altered or increased beyond the tolerance limit, they can die or become physiologically damaged. Excessive heat exposure can also damage their reproductive capability.
- Thermal pollution in water bodies can lead to the dominance of heat-resistant algae over normal species of algae. This results in damage to the biological diversity of the area.
- The high temperature of the water causes the deaths of many aquatic animals. Many other species migrate to other, safer water regions.
- A rise in water temperature leads to enhanced chemical reactions, producing changes in the toxicity or breakdown of existing chemicals. The lowered oxygen levels and the concentration of certain toxins can be more harmful.
- An increase in water temperature decreases the solubility of oxygen and other gases, leading to oxygen deficiency.
- Higher water temperature results in increased metabolic activities of animals, which creates a higher oxygen demand.
Also Read: Water Pollution: Sources, Impacts, and Solutions
Control Measures of Thermal Pollution
Thermal pollution can be controlled by cooling heated water before it’s released back into the environment.
One method is using a cooling pond where hot water enters one end and cools before being removed from the other.
Another option is a cooling tower, which takes up less space and cools water by evaporating it as it flows down over sheets, while cool air rises through the tower.
Both methods help reduce thermal pollution, but they also result in water loss due to evaporation.
Thermal pollution can be controlled by the following measures:
- Cooling towers, designed to control water temperature, can transfer heat from the water to the atmosphere by the process of evaporation. For this method, wet cooling towers and dry cooling towers are used. Different types of industries and power stations should install cooling towers best suited for operation.
- Cooling ponds can help dissipate thermal discharges from industries and factories. Heated effluents are cooled down to a certain degree with cooling ponds.
- Manmade bodies of water or artificial lakes can be solid alternatives when heated effluents are discharged into these from one end and cooler water is withdrawn from the other end.
- Industries that release huge amounts of water should be made to maintain their own reservoirs for the purpose of cooling down the hot water before releasing it into the water source.
- New technologies and stricter regulations should be in place to make industries and plants recycle their wastewater in the most efficient ways possible to reduce environmental and economic impacts.
