8.6 Thermal Pollution

Solubility of Oxygen and Temperature

The solubility of oxygen in water decreases as temperature increases. This is because as the temperature of water increases, the water molecules move faster, which causes them to collide more frequently and with more energy. This increased movement of the water molecules makes it harder for the oxygen molecules to dissolve in the water, leading to a decrease in solubility.

Real Life Applications (Examples)

• Fish in warm water bodies: Fish and other aquatic organisms rely on dissolved oxygen to survive. As the water temperature rises, the solubility of oxygen in water decreases, making it harder for fish and other aquatic life to get the oxygen they need. This can lead to fish kills and other ecological problems in warm water bodies like lakes and rivers.

• Water treatment: In water treatment plants, oxygen is often added to the water to help remove impurities and to promote the growth of beneficial microorganisms. As the water temperature increases, the solubility of oxygen decreases, making it harder to maintain the desired oxygen levels in the water. This can lead to problems with the treatment process and can make it more difficult to ensure that the water is safe to drink.

• Scuba diving: Scuba divers rely on tanks of compressed air to breathe underwater. As the water temperature increases, the solubility of oxygen decreases, which means that the air in the tanks will contain less oxygen. This can lead to a greater risk of hypoxia (lack of oxygen) for divers and can make it more difficult to plan dives and calculate the amount of air needed.

• Industrial production: industries like paper mills, food process and chemical industries also rely on dissolved oxygen in water to support the aerobic microorganisms that break down organic matter and remove impurities. As water temperature increases, the solubility of oxygen decreases, which can make it harder to maintain the desired oxygen levels and lead to problems with the industrial process.

What is Thermal Pollution?

Thermal pollution refers to the increase in the temperature of a body of water, which can have a variety of negative effects on the ecosystem. One of the effects of thermal pollution is the decrease in the solubility of oxygen in the water. As the temperature of the water increases, the solubility of oxygen decreases, which can lead to a decrease in the amount of oxygen available for aquatic organisms to breathe. This can be harmful to fish and other aquatic life, as they may struggle to survive in water with low oxygen levels. Additionally, the decrease in oxygen levels can also lead to an increase in the growth of harmful algal blooms and other organisms that thrive in low-oxygen environments.

Examples of Thermal Pollution

Thermal pollution can be found in many places around the world, particularly in areas where there is a high concentration of power plants and industrial facilities. Some examples include:

• The United States: Many power plants and industrial facilities in the United States discharge heated water into rivers and lakes, particularly in the Midwest and Northeast regions. The Great Lakes region, for example, has seen a significant decline in fish populations due to thermal pollution from power plants and other industrial sources.
• China: China has a rapidly growing economy and a large number of power plants and industrial facilities. These sources of thermal pollution have led to significant declines in fish populations and other aquatic life in many Chinese rivers and lakes.
• India: India also has a rapidly growing economy and a large number of power plants and industrial facilities. These sources of thermal pollution have led to significant declines in fish populations and other aquatic life in many Indian rivers and lakes.
• Europe: Europe also has a large number of power plants and industrial facilities that discharge heated water into rivers and lakes. This has led to significant declines in fish populations and other aquatic life in many European rivers and lakes.

Thermal pollution can occur anywhere where there is a concentration of power plants and industrial facilities, and it is important to monitor and mitigate its impact on the environment.

Sources of Thermal Pollution

Power plants

Power plants that use fossil fuels or nuclear energy to generate electricity often discharge large amounts of heated water into nearby rivers, lakes, or oceans. This can raise the temperature of the water and harm fish, plants, and other aquatic life.

One example of a power plant leading to thermal pollution is the James A. FitzPatrick Nuclear Power Plant in New York, USA. The plant cools its equipment by drawing in water from Lake Ontario and discharging it back into the lake at a higher temperature. This has led to an increase in the water temperature in the surrounding area, which has harmed fish and other aquatic life. The plant has been under scrutiny for its impact on the lake and the state has implemented several measures to reduce the thermal pollution caused by the plant, such as reducing the intake and discharge of water during certain times of the year and installing cooling towers to reduce the temperature of the water that is discharged back into the lake.

Industrial facilities

Many industrial facilities, such as factories, refineries, and chemical plants, use large amounts of water in their operations. The water is often heated during the process and then discharged into nearby waterways. This can raise the temperature of the water and harm fish, plants, and other aquatic life.

The James River Power Station in Virginia, USA is an example of industrial facilities leading to thermal pollution. The power station is a coal-fired power plant that uses large amounts of water for cooling. The water used in the cooling process is then released back into the James River at a temperature that is significantly higher than the natural temperature of the river. This thermal pollution can have a range of negative impacts on the ecosystem of the James River, including changes in the behavior and reproduction of fish, and reductions in the dissolved oxygen levels of the water. The thermal pollution can also harm the aquatic life and make it difficult for them to survive in that area.

Urbanization

Urbanization, where the expansion of cities and towns leads to the paving over of natural areas, also plays a role in thermal pollution. Urbanization causes heat island effect, where surfaces like roads, buildings, and parking lots absorb and retain heat, raising the temperature of the surrounding air and water, which can harm fish, plants, and other aquatic life.

An example of urbanization leading to thermal pollution is in the city of Los Angeles, California, USA. The city has a large urban heat island effect due to its high density of concrete and asphalt surfaces, as well as a lack of vegetation. This has led to temperatures in the city being significantly higher than in surrounding rural areas. This increased heat can have a range of negative impacts on the environment and human health, including increased air conditioning usage which leads to more energy consumption and more power plants are needed to meet the demand, which in turn leads to thermal pollution as a byproduct of power generation. Additionally, higher temperatures can also lead to increased smog and air pollution, which can have negative impacts on human health.

Agriculture 

In agriculture, irrigation and other farming activities can contribute to thermal pollution by increasing the temperature of water in nearby waterways. This can be caused by excess water from irrigation or from the use of water to cool equipment.

We can see that agriculture led to thermal pollution through the use of irrigation systems in large-scale agriculture. Irrigation systems, such as center-pivot and flood irrigation, use large amounts of water to cultivate crops, and this water is often taken from rivers or other bodies of water. This can lead to thermal pollution if the water is returned to the source at a higher temperature than it was taken. For example, in Central Valley of California, USA, many farmers use center-pivot irrigation systems to water their crops. The water is pumped from the Sacramento-San Joaquin Delta and returned at a much higher temperature, which can harm the aquatic life in the delta and reduce the dissolved oxygen levels in the water. This thermal pollution can also have a negative impact on the environment and the ecosystem of the area.

Recreational activities

Activities like boating, swimming and water skiing can also contribute to thermal pollution by raising the temperature of the water. When large numbers of people and boats congregate in a small area, the water can become quite warm and harm fish, plants, and other aquatic life.

One specific example of recreational activities leading to thermal pollution is the use of personal watercraft, such as jet skis and wave runners, in lakes and other bodies of water. These vehicles are powered by internal combustion engines, which can release warm exhaust into the water. This can lead to thermal pollution, especially in smaller bodies of water where the water is not able to dissipate the heat quickly.

For example, in Lake Havasu, Arizona, USA, which is a popular spot for personal watercraft, the high number of these vehicles on the lake during peak season can raise the water temperature significantly, which can harm the aquatic life and affect the ecosystem of the lake. This thermal pollution can also have a negative impact on the recreational activities, such as swimming and fishing, that rely on the lake being at a healthy temperature.

Cooling Towers

Cooling towers are structures commonly used in industrial facilities, power plants and HVAC systems to reject waste heat to the atmosphere. They work by using a process called evaporative cooling, where water is pumped to the top of the tower and allowed to flow over a large surface area, such as fill media or a heat exchanger. As the water flows over this surface, it evaporates, which cools the water. This cooled water can then be recycled back into the industrial process or HVAC system to absorb more heat.

Cooling towers can also release warm water as a byproduct of their cooling systems, leading to thermal pollution. This can happen when the cooled water is released into nearby rivers or oceans, or when the water vapor produced by the cooling tower is released into the atmosphere.

It's worth noting that regulations exist to minimize the thermal pollution caused by cooling towers, such as limiting the temperature of the water released and setting standards for drift emissions (small droplets of water that are carried away by wind from the tower).