Industrial Water Use
Industrial Water Use
Water (H2O) is essential to most industries. It is used for a variety of purposes, such as cleaning or dissolving substances. The amount of water a country needs for industrial purposes varies widely and is low in mainly rural economies. Most of the water used by industry is not consumed and can be returned to the water supply. However, it has usually been degraded to some extent by the processes with which it has been in contact. Environmental legislation provides for treatment of this wastewater so it can be safely re-used by the population.
Some industrial wastewater contains hazardous material such as heavy metals or acids. This needs treatment before entering the water supply. Often, this will be done on site and may involve filtration or neutralization. In recent years, industries and their products have been rated according to the amount of water they use. Water is, increasingly, a precious resource and industries need to conserve it wherever possible.
Historical Background and Scientific Foundations
Industries use water in many different ways. It could be a raw material, as in the food industry or pharmaceutical manufacturing. Water is said to be the universal solvent, so it is used for dissolving and diluting, and it also has a high specific heat capacity, so is useful as a coolant for its ability to absorb the waste heat that is produced by many industrial processes. Around half of all industrial water withdrawals are used for cooling purposes. It can also be heated to form steam, which can generate electricity, and so can be used as a local source of power. In industries making products intended for human consumption, such as pharmaceuticals or cosmetics, the grade of water used is important, with various levels of purification being required to remove toxins and bacteria. Water is also used to transport products and for general sanitation within an industrial plant.
According to the United Nations World Water Development Report, industry accounts for 22% of all global water withdrawals. This varies from 59% in high-income countries, to 8% in low-income countries. This is not as much as is used by agriculture, which accounts for about 50% of freshwater use. Agriculture consumes water, mainly in irrigation, returning little of it to the supply. Industry, however, tends to consume far less of its water withdrawals. Industry tends to use mainly freshwater, as saltwater is unsuitable for most applications because it corrodes the metal parts used in machinery. By 2025, industry will probably account for 24% of global freshwater withdrawals. Although much industrial water is available for reuse, it is usually degraded by the processes it has been involved in, and this type of wastewater will require treatment before its return to the water supply.
The electric power production industry, comprising hydroelectric, nuclear, and coal and oil-fired power stations, account for 50% to 70% of industrial water use. Paper and pulp production, chemicals, mining and metal processing, and petroleum refining all use substantial amounts of water in their operations. The amount of water used in producing various goods and services is called water intensity. Manufacture of a pound of paper takes about 3,000 gallons (11,400 liters) of water, while producing one car takes, on average, about 65,000 gallons (246,000 liters). A pound of aluminum takes about 200,000 gallons (757,000 liters) of water to produce and a hamburger around 1,300 gallons (4,999 liters).
WORDS TO KNOW
DEGRADED WATER: Water that has reduced in quality through industrial use.
ORGANIC WATER POLLUTANT: Organic materials from farm or food waste that increase the nutrient content of water.
THERMAL PLUME: A discharge of heated wastewater into the water supply.
WATER INTENSITY: The amount of water used to produce specific goods or services.
Impacts and Issues
Much of the water produced by industry can be returned to the water supply. However, the water coming out of an industrial process is usually lower in quality than the water that went into it. According to the United Nations World Water Development Report, industry produces 300 to 500 million tons (272 to 545 million metric tons) of toxic heavy metals, organic solvents, sludge, and other wastes, much of which finds its way into the freshwater supply. In the United States, the 1972 Clean Water Act was established to control the quality of water dumped back into the public supply by industry. Companies need a permit to discharge their wastewater and must disclose its content. The Clean Water Act and similar legislation in other developed countries has significantly reduced, although not eliminated, water pollution from industry. In developing countries, where legislation is weak or nonexistent, 70% of industrial wastewater is dumped untreated into the water supply and is therefore a significant source of pollution of drinking water.
Many different chemicals enter the water supply from industrial processes and some are harmful to both aquatic systems and human health. For instance, heavy metals, such as lead (Pb), mercury (Hg), cadmium (Cd), and tin (Sn), can be very polluting in a water supply, even at low levels, because they do not break down and they accumulate in food webs over time. In North America, the main toxic metal contamination comes from mercury released from coal-burning power plants. A survey carried out by the U.S. Environmental Protection Agency found unacceptably high levels of mercury in more than half of the fish surveyed in 260 lakes across the nation. Therefore, states have frequently needed to issue warnings about eating fish because of mercury contamination. Mine drainage and leaching of mining waste also leads to metal pollution in water above safe levels.
Over the last 50 years, the number of synthetic organic chemicals used in and produced by industry has grown dramatically, particularly in the manufacture of paints, plastics, pharmaceuticals, and pesticides. Many of these chemicals are very toxic with exposure to even minute amounts potentially causing birth defects or cancer. Some of these compounds are very resistant to environmental degradation and may contaminate groundwater or surface water for many years. The danger of these xenobiotics was first noted through the study of how the insecticide DDT accumulates in aquatic systems, causing deformities in fish and birds. There is increasing concern that many of these compounds act as endocrine disruptors, because they mimic the effect of the female hormone estrogen, and could have long-term effects on human health due to their ubiquity, albeit at low levels, in the water supply.
The food industry contributes 40% of organic pollutants in water in high-income countries and 54% in low-income countries. These increase the nutrient content of water and encourage the growth of algal blooms, which can reduce the oxygen (O) content of water and kill fish and other aquatic organisms.
Many industrial processes generate heat and require large amounts of cooling water, which may then be discharged at a higher temperature than the receiving water supply. Industries draw cool water from the ocean or a lake and run it through a heat exchanger to extract the excess heat. Then a discharge of heated water called a thermal plume is dumped back into the water supply. This artificial warming may have a harmful impact on local ecosystems, because aquatic organisms are not well adapted to rapid temperature change. Oxygen solubility decreases with rising temperature, putting species requiring high oxygen levels at risk. Electric power plants, petroleum refineries, paper mills, food-processing works, and chemical manufacturing all use and release large amounts of cooling water.
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United Nations World Water Development Report. “World Water Assessment Programme.” http://www.unesco.org/water/wwap/facts_figures/water_industry.shtml (accessed April 20, 2008)
U.S. Geological Survey. “Industrial Water Use.” August 30, 2005. http://ga.water.usgs.gov/edu/wuin.html (accessed April 20, 2008).