In Southern California, much of the water we use here is imported from the San Francisco Bay-Delta area, the Owens Valley, and the Colorado River. Southern California is experiencing its driest year on record, and water resources throughout California and across the Southwest are being impacted by a persistent drought, global warming, and continued population growth. The shutdown of the pumps in the Delta that feed the State Water Project highlight the vulnerability of Southern California to disruptions in it's water supply.
With 20 desalination projects proposed for the California coast, desalination is being considered as an answer to California’s dwindling water supply. Desalination would provide a reliable, drought-proof water supply from a seemingly endless source and would give local control to municipalities who are located far from fresh water sources. But is desalination truly the answer to California’s water shortage?
There are two main processes for desalinating water: thermal evaporation or reverse osmosis. Thermal evaporation uses heat to produce water vapor, which is then condensed into fresh water. Thermal evaporation is the method used most widely in the Middle East, where energy is abundant and fresh water is not. On the other hand, reverse osmosis uses a membrane to separate the salts and other contaminants. Reverse osmosis is mostly used here in the United States.
Both of these methods require an enormous amount of energy to treat the water, with energy costs accounting for at least half the cost. Due to these high energy costs, the costs to produce desalinated seawater continues to be at least twice as much as other water supply options.
Desalinated water is especially vulnerable to escalating costs during times of drought; since a major portion of California’s energy comes from hydropower; in drier periods, power output of hydroelectric plants is reduced and power costs increase, thereby increasing the cost. Recent advances in wind-powered and wave-powered desalination plants have shown promise in some parts of the world, but can only be implemented in areas where the weather conditions are appropriate.
The method of water intake is a major area of concern. Seawater is a habitat that contains an entire ecosystem. Larger fish and aquatic life are killed on the intake screen; the smaller organisms are killed during the processing of the water. These organisms are then disposed of in the ocean, and the decomposition of these organisms can reduce oxygen content and have an adverse impact on the environment near the discharge point. Subsurface intake wells can be an alternative, but limit intake volumes of water and cause salt water intrusion into freshwater aquifers and degradation of the beach environment.
The desalination process can introduce new contaminants at many stages. The intake water may contain biological contaminants, such as viruses, protozoa and bacteria, as well as chemical contaminants from urban and agricultural run-off, which may or may not be removed by the filter. During pre-treatment, the water is treated with chemicals to prevent membrane fouling. As the water goes through the membrane, minerals, such as magnesium and calcium, are removed; this is a health concern because ingestion of low-mineral water can leach vital nutrients from the body. The treated water also tends to be acidic, which leads to corrosion of the distribution system. To minimize these effects, calcium carbonate is added in the post-treatment process. Chlorination may also be required, and careful monitoring and management is necessary.
The by-product of desalination is brine, which contains a higher density and concentration of salt, manganese, lead, iodine, pollutants from urban and agricultural runoff, as well as the aquatic life that was killed in the process. Chemicals used in the process may be discharged with the brine, and corrosion of equipment may cause leaching of heavy metals into the waste stream. The brine is usually discharged into the ocean, and can impact the marine environment at the discharge point. Certain habitats and aquatic life are more at risk than others, and there is a need for more comprehensive analysis and studies.
Desalination may seem like the answer to our needs: a reliable, endless source of water, but the energy required to produce it and the impact on the marine environment present significant challenges to a state concerned with electrical shortages, global warming, and continued degradation of the environment. The energy-intensive desalination process does not produce abundant amounts of water; if all of the 20 desalination facilities proposed were built, their combined capacity would have provided only 6% of California’s water use in the year 2000. If the City of Santa Barbara's desalination plant were operational, it would supply about 15,000 homes with water, and yet consume the same amount of energy as a small steel mill. It would take six of these desalination plants to supply enough water for Santa Barbara's needs.
Research and development has been focusing on improving reverse-osmosis membranes for increased efficiency and reliability; but despite these advances, the cost of desalinated water remains at least twice as expensive as conventional water supplies. Recent advances in renewable energy sources show some promise in areas where the proper weather conditions exist; however, these technologies are still unproven, and it is questionnable as to whether they can be implemented on a large-scale basis that would be able to supply a meaningful amount of water for California.
But perhaps the greatest risk of all would be to the ocean environment. Few studies have performed or any comprehensive analysis done on the effects of brine discharge on the marine environment. Historically, coastal development has been restricted by many factors, one of them being a limited fresh water supply. Desalination would provide a new, abundant water source for coastal communities, thereby encouraging development in fragile areas. The California Coastal Commission noted in its 2004 report that “a desalination facility’s most significant effect could be its potential for inducing growth”.
For more information on desalination:
“Seawater Desalination and the California Coastal Act”, California Coastal Commission, March, 2004. Visit: http://www.coastal.ca.gov/energy/14a-3-2004-desalination.pdf
“Desalination: With a Grain of Salt – A California Perspective”, The Pacific Insitute, June 2006. Visit: http://www.pacinst.org/reports/desalination/desalination_report.pdf
For more information on wave-powered desalination barges, click here.
For more information on wind-powered desalination, click here.
For more information on Southern California water issues, visit http://aquafornia.com
Is Desalination the Answer to Southern California's Water Supply Issues?
Is Desalination the Answer to Southern California's Water Supply Issues?
Attributed to Jeff Wilson (editor-supplied)
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