BeanHillierWater2010

Jonathan Bean Craig Hillier

= Desalination =


 * What is the problem at hand?**

There is a limited supply of fresh water and with an increasing human population a “water crisis” developing. Water crisis is term use to describe the worldwide water shortage by the United Nations and other world organizations is the problem at hand. What is the driving force?

“Lawrence Smith, the president of the population institute, asserts that although a majority of the planet is composed of water, 97% of this water is constituted of saltwater; the freshwater used to sustain humans is only 3% of the total amount of water on Earth. Therefore, Smith believes that the competition for water in an overpopulated world would pose a major threat to human stability; indeed, world wars may be fought over the control of thinning ice sheets and nearly desiccated reservoirs. “There are many other countries of the world that are severely impacted with regard to human health and inadequate drinking water. The following is a partial list of some of the countries with significant populations whose only consumption is of contaminated water”
 * Sudan -12.3 million
 * Venezuela - 5.0 million
 * Zimbabwe - 2.7 million
 * Tunisia - 2.1 million
 * Cuba -1.2 million (Wikipedia)

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 * What is currently being done to solve the problem?**

Much of the modern interest in desalination is focused on developing cost-effective ways of providing fresh water for human use in regions where the availability of fresh water is, or is becoming, limited. This is big in Saudi Arabia and other Arab countries. Water desalinization is used aboard ships and submarines to provide sailors with suitable drinking water. This technology is now a reality it is no longer "If we could ever competitively, at a cheap rate, get fresh water form salt water, that would be in the long-range interest of humanity which would really dwarf any other scientific accomplishments." -John F Kennedy, 1962- New water users supply.org Now is the time for desalinization "Ten years ago, desalination was the crazy aunt in attic. Thats changed. It is now entering the main stream and being taken seriously." - Barry Nelson, Natural Resources Defense Council, 2003 Just think about how expansion of desalination can cure much of the worlds problem.


 * How does it work?**

There are several ways in which salt water can be desalinated and made fit for human consumption. The primary way it is done is through thermal desalination. This can be done using vapor distillation, multi-stage distillation or multiple-effect distillation. Another popular method is membrane desalination, which is either reverse osmosis or electrodialysis.

= Thermal Distillation =

Thermal distillation is a fairly simple method of producing clean water. It is based on the fact that covalently bonded water has a much lower boiling point than the ionic bonded salt present in saltwater. The water can be turned to steam and removed from the mixture. The water vapor is then cooled and the condensed fresh water is collected. To cut down on the amount of energy required to vaporize the water, many plants distil at very low pressures. This allows the water to boil at temperatures less than 100 C. This is because a substance boils when the vapor pressure is equal to the atmospheric pressure. By lowering the atmospheric pressure, the temperature at which the vapor pressure is equal to the atmospheric pressure is less.



A typical plant is located on the shoreline near an ocean. It takes in the warmer water from the surface to a flash chamber. This chamber is maintained at a very low pressure and is heated using warm water. Water turns to steam and migrates towards the condenser. Cool water, from the lower depths of the ocean, is pumped through coils surrounding the water vapor. The vapor condenses, is collected, and ready for drinking.



= Membrane Desalination =



Water can also be desalinated using reverse osmosis. Osmosis is a natural process, in which solvent moves from an area of low solute concentration, through a semipermeable membrane to an area of high solute concentration. A semipermeable membrane is something that allows the solvent to flow freely through its pores, but blocks other molecules. Reverse osmosis uses high pressure, to forcing the solvent to flow in the opposite of its natural direction and thus removes the salt from the water. In order for this to work the applied pressure must be greater than the natural osmotic pressure.

A typical plant utilizes high pressure pumps to achieve reverse osmosis. Water is pumped into a chamber containing a semipermeable membrane. This membrane is designed to allow water to flow through it, but blocks the flow of salts. High pressure pumps pull ocean water into the chamber. Water passes through the membrane, is desalinated, and is collected. Highly concentrated salt water on the other side of the membrane is removed from the system.




 * How much water can be produced by desalination?**

It depends largely on the size and type of plant. There are portable systems that only produce enough water for a single person. The world’s largest desalination plant is capable of producing 300 million cubic meters per year.


 * What are the advantages of desalination?**

The biggest advantage for desalination is that there is virtually an endless supply of salt water. 97% of water on earth is salt water.


 * What are the disadvantages of desalination?**

Water desalination is extremely energy intensive. This energy is costly in two ways: monetarily and environmentally. Energy, regardless of what type, costs money. The current cost of producing drinkable water is 50 cents per cubic meter using desalination. Energy production also takes a toll on the environment. Depending on the type, it releases, either toxic or greenhouse vapors, as well as radioactive waste.

Salt water is only available in coastal areas. Most of the regions with the most acute water shortages are in inland areas. It would cost a lot to import water for them.

Wildlife is also affected by the process. Thermal pollution is released into the water, which changes temperatures for the area. Highly concentrated salt water is also released into the ocean. Plankton and other wildlife are sucked into the chambers and killed.

These desalination plants are also visually unpleasing. Much like the wind turbine debate on Cape Cod, some people located in these regions do not want these plants on their coasts.
 * Who uses this technology?**

This technology is used worldwide. There are plants located in the United Arab Emirates, Aruba, Australia, Cyprus, Israel, the United Kingdom, and the United States.
 * Why it is not used more?**

Desalination is expensive and the areas that need water, cannot afford this technology.
 * What would I do to change it?**

After reading about this process I would like to see the plants rely more on renewable resources. They could heat the water using geothermal or solar energy. Plants might also be able to recycle the heat energy created by the process, and use it again. I think that as water consumption increases around the world, we will need more and more desalination plants. I also believe that the cost of production will decrease as more plants are built and become more efficient.