Water pollution and energy options
Water pollution and energy options are interlinked topics that highlight the significant role of water in energy production and the environmental challenges associated with various energy sources. Energy extraction and generation processes, such as oil drilling, hydraulic fracturing, and thermoelectric power generation, heavily rely on water for operations like cooling and enhanced recovery. For instance, conventional oil extraction uses minimal water, but methods like oil sands extraction demand significantly more, resulting in environmental concerns related to tailings and potential contamination of local water sources.
Thermoelectric power plants, which are predominant in electricity generation, utilize large quantities of water for cooling, leading to thermal pollution and the alteration of aquatic ecosystems. Additionally, various energy options impact water resources differently; while renewable sources like wind have low water requirements, biofuel production can lead to significant water consumption and pollution. The increasing focus on reducing greenhouse gas emissions is driving investment in technologies such as carbon capture and storage (CCS), which, while promising for emission reductions, can also escalate water usage and potentially increase other pollutant emissions.
Overall, as freshwater resources become scarcer, there is a growing need for more efficient water management and innovative technologies to balance energy production demands with environmental protection. Understanding these interconnections is crucial for developing sustainable energy policies that mitigate water pollution while addressing diverse energy needs.
Water pollution and energy options
Summary: Water is required for the exploration, processing, and distribution of energy. The availability of adequate water supplies has an impact on the type of energy options that are developed.
in Drilling for Oil and
Very little water is used in the extraction of conventional oil. In fact, water is often extracted with the oil. In some cases, the water amounts to more than 40 times the amount of oil extracted. The extracted water is often reinjected into the well in a process called enhanced oil recovery (EOR). EOR increases the pressure in the well and enhances the amount of oil extracted. EOR can use between 50,000 and 90,000 liters of water per gigajoule of oil extracted, whereas traditional recovery processes may use as little as 3 to 7 liters per gigajoule of oil.
The extraction of oil from oil sands uses significantly more water than conventional oil extraction. Estimated requirements of water per gigajoule range from between 70 and 1,800 liters. The water that is not returned to its source is deposited in tailings, which are large slurry ponds of bitumen, water, sand, silt, and fine clay. Processing 3.3 cubic feet (1 cubic meter) of bitumen is estimated to produce 19.6 cubic feet (6 cubic meters) of tailings. These tailings pose environmental risks, as they can leak into local rivers and lakes.
The process of removing unconventional natural gas (tight sands, coal-bed methane, and gas shales) from gas-bearing rocks is called hydraulic fracturing. Unconventional gas is mainly extracted in the United States, with most coming from the Newark East Field in northern Texas. Concerns have been expressed that hydraulic fracturing could be affecting underground drinking water sources. Some countries, such as France, have banned the activity; others, such as South Africa, have placed a moratorium on activities until the potential impacts are better understood. In March 2010, the Environmental Protection Agency launched a study to assess the impact of hydraulic fracturing, or fracking, on drinking water supplies in the United States. The 2016 final report identified several conditions in which fracking could affect drinking water supplies, for example, when extracting water for fracking in low-water areas or periods, or when fracking fluids are spilled or stored incorrectly.
and Water-Cooling Requirements for Thermoelectric Plants
Thermoelectric power plants require cooling to condense steam that exits turbines. Water is the most common source of cooling. In the United States, it is estimated that each kilowatt-hour of electricity generated requires approximately 25 gallons of water. The amount of water required for cooling depends on the cooling technology and fuel type. There are three types of cooling systems: Once-through (or open-loop) cooling systems withdraw large amounts of water, which is returned to the source at a higher temperature. These systems withdraw large amounts of water but consume very little water through evaporation. Closed-loop cooling systems recirculate water and reject excess heat through a cooling tower. Closed-loop systems withdraw less water than once-through systems but, because more water is lost through evaporation, closed-loop cooling systems consume more water. Dry-cooling systems rely on air for cooling, but because air is a less efficient heat sink than water, dry-cooling systems are less efficient and more expensive than water-cooled systems.
The type of fuel and technology used in power plants affect the amount of water required for cooling. For cooling towers using generic technology (that is, not combined cycle or including combined carbon and sequestration, CCS), nuclear plants consume between 581 and 845 gallons per megawatt-hour, while coal plants using similar technology consume 480 to 1,100 gallons per megawatt-hour. Consumption levels can be reduced significantly with improved technology. Natural gas plants using combined cycle technology and once-through cooling can consume between 20 and 100 gallons per megawatt-hour. Increasing pressure on available freshwater resources is leading to increased interest in more efficient water-cooling technologies, such as nontraditional water (saline or salt water), combined cycle technology, and dry cooling towers. However, because of the increased costs involved, the application of these technologies remains limited. More research and development are required to improve the economic viability of more efficient cooling technologies.
Water that is released from a power plant is usually of a higher temperature than the water received. This results in thermal pollution. Thermal pollution alters the chemical composition of the water into which the heated water is released, resulting in a rapid increase in levels of nutrients such as nitrogen and phosphorus and leading to increased growth in certain aquatic plant species and overall reduced water quality.
Thermoelectric power plants also contribute indirectly to water pollution through air pollution. In 2023, American power plants were estimated to emit about 747,000 tons of sulfur dioxide, 640,000 tons of nitrogen oxides, and 2.4 million tons of mercury, representing reductions from the previous year of 24 percent, 15 percent, and 17 percent, respectively. In 2023, they also released 107,000 tons of particulate matter and 1.56 billion tons of carbon dioxide. The latter represents a 19 percent reduction over 2022. These emissions reduce the pH of precipitation, resulting in what is commonly known as acid rain, with negative effects on surface waters and forest soils. Acid rain has been a major environmental issue in northern Europe and eastern North America and has been observed in western North America, Japan, China, the Soviet Union, and South America. Heavy metals, including mercury, arsenic, and selenium, are also often present at trace levels in power plants’ flue gas and wastewater. Technology to remove and treat these pollutants, and thereby reduce their accumulation in the natural environment, is improving.
Water Use for Generation
Hydroelectric power consumes water through evaporative losses from the surfaces of reservoirs. Estimates of water losses from reservoirs vary widely; some estimates are significantly higher than the water required to cool a closed-loop, thermoelectric power plant. Reservoirs for hydroelectric power can have an impact on aquatic ecosystems by blocking migration patterns of fish and other animals, changing sediment loads in rivers, and altering flow regimes. These effects may have a negative impact on riverine communities that rely on aquatic ecosystems. However, the impacts of hydropower are often balanced by other benefits, including improved water storage for agriculture and human consumption. Some types of hydropower (such as pumped-storage schemes) can also act as a power “battery.” Water is pumped to an upper reservoir and then released through the turbines when electricity demands are higher and other variable supply options, such as wind and solar, may not be available. This allows hydropower to act as a base-load supply in conjunction with less water-intensive renewable options.
Water Use and Technologies
The negative impact of greenhouse gas emissions is increasing investment in alternative energy technologies. Some of these alternative options, such as wind, require very little water and have minimal water-pollution effects. However, some emerging technologies have a significant impact on water resources. For example, the growing of crops for biofuels requires large amounts of water and can lead to increased pollution. A comparison of water consumption across 11 different energy options (including nuclear, hydropower, and coal with CCS) found that corn-based ethanol was the largest-ranked consumer of water. CCS is seen as a possible technical innovation to reduce carbon dioxide emissions. Utilizing this technology requires more water per energy output. Depending on the technology and fuel used, water use in power plants can increase from about 46 percent to as much as 90 percent when combined with CCS. CCS may also result in an overall increase in emissions of sulfur dioxide and ammonia, which are the main gases contributing to acid rain pollution.
In April 2024, the US Environmental Protection Agency announced new regulations to cut pollution from coal-fired power plants. New standards addressed carbon dioxide, mercury, wastewater, and coal ash disposal. The carbon dioxide emission standards applied to existing coal plants and future natural gas plants.
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