Purification of sea water In the late 20th century, more than 8,000,000 cubic m (2,112,000,000 gallons) of fresh water were produced each day by several thousand desalination plants throughout the world. Distillation processes are used in about half of all the plants and account for roughly three-quarters of the worlds desalted water. Most of the other plants employ membrane processes. The worlds desalination capacity expanded rapidly during the 1970s and 80s as the oil-rich countries of the Middle East improved their standard of living, with attendant changes greatly increasing the consumption of fresh water. The Middle Eastern countries produce about 75 percent of all the worlds desalinated water. The United States produces about 10 percent, and Europe and Africa each account for approximately 5 percent.
The worlds largest desalination plants are in the Arabian Peninsula. Desalination is very important, because in many places on out planet fresh water is a problem, while it is the most important thing for a human being to survive. Although water desalination is expensive, it is sometimes cheaper than shipping freshwater long distances. Desalted water provides the primary source of municipal supply in many areas of the world, and its use is increasing in the United States. (Abulnour 54) Some techniques for desalination are already used widely, while others are now being developed and refined. There are four main methods of desalination: electrodialysis, reverse osmosis, flash distillation, and solar humidification. Some methods are more effective in different parts of the world.
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Also, some methods are only used to treat brackish water as they do not remove very much salinity. If a liquid rich in ions is subjected to an electrical field be means of two electrodes with a continuous potential difference applied between them, the cations will be attracted to the cathode and the anions will be attracted to the anode. (Cumberland 34) In the electrodialysis process, the water to be treated is placed in a large tray. A series of membranes (some negative and only permeable by cations, others positive and permeable by anions) are arranged alternately in the trough to trap the separate ions. So, the water rich in salt is forced in one section of the tray, while the freshwater is in another section. However, salinity can hardly be reduced by more than 50% be movement through one electrodialysis cell without a loss in efficiency.
Consequently, most units comprise several stages in series, and the required reduction in salinity is achieved by successive stages. (Aswed 297) The United States has electrodialysis plants converting 2.25 million liters of brackish water per day. Electrodialysis is more effective on water with a lower salt content. This method can easily and efficiently convert brackish water that contains 3,000 mg/L. New membranes are being studied to help make this process better for desalting sea water. Reverse osmosis is the second most common way to desalt water, behind flash distillation. In reverse osmosis, salty water of two different concentrations is separated by a semi permeable membrane.
This membrane allows the passage of solvent, but not dissolved substances. Naturally, osmosis will come into play and the two concentrations will start to even out; meaning the dilute side will start to flow to the concentrated side. The difference in pressure between the solutions of different concentration is the osmotic pressure. (Degremont 306) What happens in this reverse osmosis method is that a high pressure, greater than the osmotic pressure, is applied to the membrane and pure water passes through. A major advantage to this method is the rather simple method that is used. The most common membranes used in reverse osmosis desalination are made of a treated cellulose acetate.
There are many reasons why we need to treat our water, and there are also many different ways we can treat our water. Water is very important to our survival. Regulations are set so that our water is healthy for us to drink. Without those regulations there could be things in our water to cause us to be sick. Some problems in parts of the country are heavy metals. One of the best ways to see if you ...
Using this membrane, 98-99% of the original salinity is removed at a rate of 150 to 200 liters per day. New research is concentrated on increasing the flow through the membrane, and increasing the reduction in salinity. Flash distillation is the most widely used method of desalination. It works using evaporation at low pressures. First, hot sea water passes into an area of lower pressure where some of the water evaporates quickly. This instantaneous boiling and the generation of vapor without a heat supply is known as flashing. Distillation takes place and the hot sea water is cooled in the process. Further flash steam can be released at a lower pressure and temperature in a series of stages.
Usually, a flash distillation plant is consisted of a series of chambers that are running at lower temperatures than the previous one. There are also condensing coils that are banks of tinned tubes. The heat that starts the process is steam that has already completed a job, such as a steam turbine in another part of the facility. The sea water flows from one chamber to the next producing water vapor. The vapor is condensed and the freshwater falls into collecting trays. Then the water is put into bulk storage. Some very large plants have been built for this type of desalination.
One, in Tijuana, Mexico, was built in 1970. It uses local sea water and produces 27 million liters of distilled water per day. Abu Dhabi has six facilities distilling nine million liters of water per day. This method is cheaper and more effective than reverse osmosis or electrodialysis. There have been problems with membrane breakage in those methods, hampering production. The last method of desalination is solar humidification.
Thesis Statement: Water is the most crucial part of life its self, and must never go unnoticed. I. People frequently overlook the importance of water in the body. In order to keep the body healthy, people must consume water. A healthy body is a well-hydrated body. Without the constant consumption of water the body becomes dehydrated. Perhaps people overlook waters importance, simply because its ...
This is a very cheap and simple method, but production is limited. Sea water is placed in shallow trays with black lining. Black lining is used because it collects heat better than any other color. Over the trays is a roof constructed of glass or plastic. Sunlight passing through the roof heats the water. Then, the water evaporates and condenses on the cooler under-side of the roof. The condensed water then runs down the slope of the roof and is collected in troughs. It is known that one square meter of water surface is needed to produce 4.5 liters of water per day.
The energy to use complete this process is free, so it is almost ideal. The only problem is the small amount of desalted water that is produced. This method is used in small communities that cannot afford expensive equipment and do not need a great supply of potable water. The desalination of water is something that will be researched feverishly in the future. On the average, a human in the United States uses 70 gallons of water per day. If we continue this, our freshwater supply will be gone. One method that can be easily used is flash distillation.
Larger and more efficient facilities are being constructed that will yield well over 30 million liters of desalted water per day. We will never run out of water as long as these new methods are being improved upon.
Abulnour, A.M., Sorour, M.H., Squeezing Desalted Water Costs by Proper Choice of the Desalting Technology and Water Management, Desalination, May 1983, vol. 44, 189-198 Aswed, M., El Hares, H., Cost Comparison of Effectively Produced Desalted Water by Different Processes in a Developing Country Desalination, vol. 23, no. 1-3, Dec.
1977, 285-290 Cumberland, J. H., Effects of Economic Development on Water Resources, Water Resources Research Center, College Park, MD, 1977.