The Process of Desalination
adapted from United States Geological Survey
Thirsty? How 'bout a cool, refreshing cup of seawater?
No, don't take us literally! Humans cannot drink saline water. But, saline water can be made into freshwater. The process is called desalination, and it is being used more and more around the world to provide people with needed freshwater. Most of the United States has, or can gain access to, ample supplies of fresh water for drinking purposes. But, fresh water can be in short supply in some parts of the country (and world). And, as the population continues to grow, shortages of fresh water will occur more often, if only in certain locations. In some areas, salt water (from the ocean, for instance) is being turned into freshwater for drinking.
The "simple" hurdle that must be overcome to turn seawater into fresh water is to remove the dissolved salt in seawater. That may seem as easy as just boiling some seawater in a pan, capturing the steam and condensing it back into water (distillation). Other methods are available but these current technological processes must be done on a large scale to be useful to large populations, and the current processes are expensive, energy-intensive, and involve large-scale facilities.
Desalination is not modern science
Solar desalination evaporation is used by nature to produce rain which is the main source of fresh water on earth. All available man-made distillation systems are a duplication on a small scale of this natural process. Desalination/distillation is one of mankind's earliest forms of water treatment, and it is still a popular treatment solution throughout the world today. In ancient times, many civilizations used this process on their ships to convert sea water into drinking water. Today, desalination plants are used to convert sea water to drinking water in many arid regions of the world, and to treat water in other areas that is fouled by natural and unnatural contaminants. Distillation is perhaps the one water treatment technology that most completely reduces the widest range of drinking water contaminants.
The sun supplies energy that causes water to evaporate from surface sources such as lakes, oceans, and streams. The water vapor eventually comes in contact with cooler air, where it recondenses to form dew or rain. This process can be imitated artificially and more rapidly than in nature, using alternative sources of heating and cooling.
Your own personal desalination plant
What if you find yourself in the desert in need of a drink of water? The low-tech approach to accomplish this is to construct a "solar still" which uses heat from the sun to run a distillation process to cause dew to form on something like plastic sheeting. Using seawater or plant material in the body of the distiller creates humid air, which, because of the enclosure created by the plastic sheet, is warmed by the sun. The humid air condenses water droplets on the underside of the plastic sheet, and because of surface tension, the water drops stick to the sheet and move downward into a trough, from which it can be consumed.
Some desalination facts
It is estimated that some 30% of the world's irrigated areas suffer from salinity problems and remediation is seen to be very costly.
In 2002 there were about 12,500 desalination plants around the world in 120 countries. They produce some 14 million cubic meters/day of freshwater, which is less than 1% of total world consumption.
The most important users of desalinated water are in the Middle East, (mainly Saudi Arabia, Kuwait, the United Arab Emirates, Qatar and Bahrain), which uses about 70% of worldwide capacity; and in North Africa (mainly Libya and Algeria), which uses about 6% of worldwide capacity.
Among industrialized countries, the United States is one of the most important users of desalinated water, especially in California and parts of Florida. The cost of desalination has kept desalination from being used more often.
Select ALL the correct answers.
Which two statements from the passage best support the idea that there is a need for new scientific development in the field of desalinization?
The "simple" hurdle that must be overcome to turn seawater into fresh water is to remove the dissolved salt in seawater.
Other methods are available but . . . the current processes are expensive, energy-intensive, and involve large-scale facilities.
It is estimated that some 30% of the world's irrigated areas suffer from salinity problems and remediation is seen to be very costly.
Distillation is perhaps the one water treatment technology that most completely reduces the widest range of drinking water contaminants.
The low-tech approach to accomplish this is to construct a "solar still" which uses heat from the sun to run a distillation process.
Other methods are available but . . . the current processes are expensive, energy-intensive, and involve large-scale facilities.
It is estimated that some 30% of the world's irrigated areas suffer from salinity problems and remediation is seen to be very costly.