Thermal pollution and thermal pollution control
Thermal pollution refers to the introduction of excess heat into aquatic environments, primarily caused by fossil-fuel and nuclear power plants. This additional heat can negatively impact marine life, as higher temperatures reduce oxygen levels critical for survival, increase the metabolic rates of cold-blooded species, and elevate the toxicity of existing pollutants. As a result, fish like salmon and trout are particularly vulnerable, facing rapid mortality when water temperatures exceed 26° Celsius, especially during sudden temperature shifts associated with power plant operations.
To mitigate thermal pollution, various control measures can be implemented. Waste heat can be harnessed for beneficial uses, such as agricultural irrigation or preheating seawater for distillation in areas with freshwater shortages. When beneficial uses are not available, cooling ponds serve as a cost-effective solution, allowing heated water to release heat into the atmosphere before being recycled. Alternatively, cooling towers function as large radiators to dissipate heat, although they require more investment and can increase electricity costs. Understanding these dynamics is crucial for balancing energy production with environmental preservation and marine ecosystem health.
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Thermal pollution and thermal pollution control
Thermoelectric power plants remove large quantities of water from the environment, use it to condense steam exiting a turbine, and return warmer water. Although the water is heated only slightly, there are environmental consequences.
Definition
Thermal pollution is waste heat that has been dumped into an aquatic environment. The main sources of thermal pollution are fossil-fuel and nuclear power plants.
Overview
The oxygen content of the heated water, critical for most marine life, decreases as the temperature increases, while concurrently plankton multiply more rapidly, putting a further demand on the available oxygen. Since fish are cold-blooded and cannot maintain a constant body temperature, their metabolic rate increases with temperature: More oxygen is needed, and less is available.
Also, the toxicity of chemical pollutants present in a lake or river increases with temperature. Extra heat in the water can also raise the temperature beyond the lethal temperature for fish. Cold-water species such as salmon and trout die quickly when the water temperature reaches 26° Celsius. Although fish can adapt to warmer water if the change occurs slowly, the rapid changes that occur when power plants shut down for maintenance are usually fatal. Furthermore, warm water can block cold-water species from reaching their spawning areas, and entire food chains can be disrupted when higher temperatures alter a local ecological balance.
Thermal pollution can be controlled either by using the waste heat or by alleviating it through other means when it cannot be used. Waste heat could be utilized to irrigate fields in cold, dry climates so as to extend the growing season. Waste heat can preheat for distillation in coastal regions where is scarce, such as in Southern California. A large pond could be used to contain the heat, and the pond could be stocked with catfish, a source of food, which thrive in 34° Celsius water. Combining a sewage treatment plant with an electric power plant, the waste heat could be employed to help evaporate water from treated sewage. In winter, waste heat could be used to heat factories located near the power plant. Finally, rivers such as the St. Lawrence that often freeze in winter perhaps could, with a sufficient number of power plants along its bank, be kept open for navigation.
There are two methods for alleviating thermal pollution when no useful means of using the heat can be found. The simpler method is a cooling pond. The warmed water flows into a large artificial pond, where it releases its heat into the atmosphere. After cooling, the water may be reused or flow back into a river. Although relatively inexpensive to construct and maintain, this method requires a large amount of land—approximately 800 hectares for a typical small power plant producing 1,000 megawatts. Obviously this is not feasible in a densely populated region.
The main way that thermal pollution is alleviated is by means of the cooling tower, essentially a very large radiator. The heated water flows through finned tubes, transferring its heat to the atmosphere. If the system is closed, no water is lost through evaporation. For a typical small, 1,000-megawatt plant, at least one tower 76 meters in diameter and 98 meters high is required. Although not much land area is covered, the towers are much more expensive than cooling ponds. Each tower adds approximately 10 percent to the cost of constructing the power plant, which causes electricity rates to be about 5 percent higher.
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"What Is Thermal Pollution?" Collective Clean Energy Fund, 9 Apr. 2024, cocleanenergyfund.com/what-is-thermal-pollution/. Accessed 6 Jan. 2025.
"What Is Thermal Pollution?" Inspire Clean Energy, 29 June 2021, www.inspirecleanenergy.com/blog/clean-energy-101/what-is-thermal-pollution. Accessed 6 Jan. 2025.