How to Desalinate Water: 9 Steps (with Pictures) - wikiHow How to Desalinate Water Two Parts: Gathering Your Materials Making the Desalination Device Community Q&A When you desalinate water, you remove dissolved salts from the water. Desalination or desalting technologies can be used to produce drinkable water from seawater or brackish water, and it can also be used in the oil and gas industry. 97.5% of the world’s water is salt water from its oceans and only 2.5 percent is freshwater. Scientists are currently looking at ways to use desalination to make the world’s seawater a viable source of drinking water, but you can try to desalinate water on a smaller scale at home by building a simple desalination device. Steps Gathering Your Materials 1 Use bottled drinking water and iodized salt. Before you can desalinate the water, you will need to create salinate water, or salt water. Do this by buying a bottle of drinking water and iodized salt from your local grocery store. You can also use a bottle of tap water if you do not want to buy a bottle of water.

[1] If you happen to live near an ocean, you can skip these materials and fill a bottle with seawater. Seawater is full of salt and great for use in the desalination process. 2 Get a heavy ceramic mug and a large glass bowl. You will use the ceramic mug as a container for the desalinated water and the large glass bowl will act as a receptacle for the salt during the desalination process. The glass bowl should be big enough to fit the mug. [2] You will also need a piece of plastic cling wrap, enough to go over the glass bowl, and a small weight like a rock. 3 Make sure you have access to a spot with direct sunlight, like a window sill. You will need to place your desalination device in direct sunlight to warm up the water in the device and create humid air. The humid air will then condense into water droplets that you can drink. [3] Part 2 Making the Desalination Device 1 Pour 1 inch of drinking water into the mug. You do not want to fill the mug up too much, just until it appears 1 inch deep with water. [4] Mix enough salt into the water so it tastes salty.

Start with a small amount of iodized salt and taste it to ensure it is salty. Make sure you fill the mug with more water if you drink some of it, as you want there to be a depth of about 1 inch of water in the mug. 2 Put the salt water into the large glass bowl. You will then need to rinse and dry the mug to ensure there is not salt residue in the mug. [5] Once you have rinsed and dried the mug, you can put it in the center of the glass bowl in the 1 inch of salt water. 3 Cover the glass bowl with plastic cling wrap. Make sure the cling wrap is stretched tightly over the mug and the sides of the bowl, with no open areas around the rim of the bowl. 4 Place the bowl in direct sunlight. Look for a window sill or a spot on your deck outside that gets lots of direct sunlight and make sure the bowl is on a nice, even surface in the sun. [6] Place the small weight or rock on the top of the plastic wrap, right above the cup. The plastic wrap should sag in the center of the cup due to the weight of the rock. This will ensure the condensed water falls into the cup so you can drink it.

5 Leave the bowl in the sun for three to four hours. After several hours in the sun, there will be a build up of humid air in the bowl. This will lead to the formation of water condensation on the plastic wrap. The water droplets should then flow downward into the cup. 6 Check the cup for fresh water. After the bowl has been in the sun for three to four hours, check the cup for a small amount of water. Remove the plastic wrap and drink the water in the cup. You should taste pure, clean fresh water that has been desalinated. [7] This desalination device works by using the sun to warm up the salt water. The plastic wrap helps to trap the water vapors in the bowl as the salt water evaporates. Because the top of the plastic wrap is much cooler than the rest of the bowl, the humid air in the bowl condenses on the top of the plastic wrap and forms water droplets. Over time, the water droplets on the plastic wrap grow larger and start to flow to the center of the bowl due to the weight of the rock. As the water droplets build up, they grow heavier and eventually fall into the cup.

The result of this simple desalination device is a cup of fresh drinking water that does not contain any salt. Community Q&A What happens to the salt? wikiHow Contributor The salt remains in solution in the larger bowl, just in greater concentrations. If the concentration becomes high enough, it will precipitate (i.e., form solid salt) in the bottom of the bowl. Does the bowl have to be glass? wikiHow Contributor No, for example if you were on the beach, you can dig a round whole down to the wet sand and put a bowl in the middle with a tarp over the whole and you will get the same results. Is desalination a feasible way to purify water when camping? Can stream water be collected in a bowl and heated in a similar fashion to yield potable water? wikiHow Contributor You can provide water for camping this way, but it will take a long time for the water to evaporate in a bowl out in the sun. Try using a cooker or a bonfire to heat the water. Or you can simply bring water with you, or use one of the many water purification products designed for hikers and campers such as pumps, filters, and tablets. Would a source of heat work?

wikiHow Contributor Steam it and capture the gassed water. In the original container will be the salt from the water you just steamed. Can I follow the same steps with a non-glass bowl? wikiHow Contributor This is unlikely, as glass has a property to allow in the heat from sunlight and contain it. (Think greenhouses). You may only be able to achieve this result with a non-glass bowl if an external source heats the water till condensation occurs, like a pot on a stove. If using this method, keep in mind that you'll need to find a safe alternative to plastic wrap to replace that function in this diagram. Instead of letting the sun do all the work, can I boil the water? wikiHow Contributor That's essentially what large desalination plants do. Just keep in mind the heat so you don't melt any plastic. Would a focus light such as a lamp work instead of sunlight? wikiHow Contributor Probably not, unless it were of a higher wattage, or a heat lamp. The reason being, it has to generate enough heat to make the water evaporate so it can re-condense on the plastic wrap (leaving the salt behind).

You could try it, though but you can't be certain of the results. Desalting - 18 Category Salinity of produced brine The salinity of produced brine varies widely, but for most produced water, it ranges from 5,000 to 250,000 ppm of equivalent NaCl. Crude oil that contains only 1.0% water with a 15,000-ppm salt content has 55 lbm of salt per 1,000 bbl of water-free crude. The chemical composition of these salts varies, but nearly always is mostly NaCl, with lesser amounts of calcium and magnesium chloride. Salt content limits might be by either of the following: transportation requirements in the production field or shipping terminal concerns over corrosion, fouling, or catalyst degradation in the refinery Purpose of a desalting system The purpose of a desalting system is to reduce the salt content of the treated oil to acceptable levels. When the salinity of the produced brine is not too high, merely ensuring that there is a low fraction of water in the oil can reduce salt content.

In that case, the terms desalting and emulsion treating effectively have the same meaning, and the concepts and equipment can be used. Salt specification The required maximum concentration of water in oil to meet a known salt specification can be derived from Eq. 1: (Eq. 1) Cso = the salt content of the oil, lbm/1,000 bbl Csw = the concentration of salt in produced water, ppm γw = the specific gravity of produced water fw = the volume fraction of water in crude oil Desalter In produced brine with a high salt concentration, it might not be possible to treat the oil to a low enough water content ( < 0.2% is difficult to guarantee). A desalting system such as the one shown schematically in Fig. 1 consists of a mixing device (in which fresh water is used to wash the crude oil) and any of the electrostatic treating systems described below (which then are used to dehydrate the oil to a low water content). Mixing dilution water with the produced water lowers the effective value of Csw in Eq. 1.

If a single-stage desalting system requires too much dilution water or is unable to reach the desired salt concentration, then a two-stage system is used, such as the one shown schematically in Fig. 2. Fig. 1—Typical flow diagram for a single-stage desalter. (Courtesy of Natco Group Inc.) Fig. 2—Typical flow diagram for a two-stage desalter. (Courtesy of Natco Group Inc.) Mixing efficiency The mixing efficiency is the fraction of wash water that actually mixes with the produced water. In effect, the remainder of the water bypasses the desalting stage and is disposed of as free water. A mixing efficiency of 70 to 85% is considered the highest attainable. Because mixing efficiency depends on the probability of contact between the dilution water and entrained brine, it varies with the drop population in the crude oil.

The effectiveness of this dilution reaction is determined by a variety of influences, e.g.: mixing intensity and duration interdrop-collision frequency Dilution water Enough dilution water must be available to satisfy mass-balance requirements for diluting the dispersed brine enough that the salt specification can be met while considering the residual basic sediment and water (BS&W) in the oil. Dilution-water quality also must be considered and can be a problem because of high pH, the presence of surfactants, and other conditions that can lead to increased emulsion stability. [1] Obviously, to remove salt, the dilution water must have low enough salt content to achieve the required equilibrium concentration in the residual entrained water. Less obvious but also important is the need for dilution water to be of sufficient quality to avoid contributing to emulsification. Streams that contain considerable amounts of the following materials should not be used: coke particles and/or emulsified oil Neither should streams contain traces of surfactant chemicals or excess caustic soda. Limiting ammonia to < 200 ppm avoids fouling and corrosion in the crude-distillation unit overhead and limits pH excursions.

Preferably, the pH of the dilution water should be < 9.0, and provision for acid injection for pH control should be made if higher values are expected. High pH might enhance the formation of stable emulsions, whereas pH values < 6.5 might raise concerns about corrosion within the desalter vessel. The dilution water should contain < 0.02 ppm oxygen and < 1 ppm fluoride and should be low in: sodium salts hardness ions Water recycle Contact efficiency, or collision frequency, between drops of dispersed brine and dilution water is proportional to the drop populations. Increasing the number of dilution-water drops yields more efficient contact. Because quantities of available dilution water usually are limited, the effluent water often is recycled to increase drop population. Effluent water from the second-stage desalter is much less saline than the dispersed brine, so that it can be used for dilution water for the first stage, as shown in Fig. 2. This is known as interstage recycling.

Another recycle scheme, intrastage recycling, was previously limited because it requires mixing of the recycle water and the fresh water, thereby lessening the effectiveness of the fresh water; however, the advent of counterflow desalting made it feasible to inject recycle water ahead of the mixing valve of a single-stage desalter and to inject the fresh water into the counterflow distributors, thereby increasing the drop population without raising the salinity of the fresh dilution water. With all recycle streams, be careful as to the quality of the water: if interface sludge or mud-wash solids are allowed to recycle, they might produce stable emulsions and cause rapid buildup of the interface-sludge layer. If this problem appears likely to occur, the recycle should be taken after an effluent water-cleaning device. Effluent-water quality The effluent water from a properly operating desalter, exclusive of mud-wash cycles, is frequently < 250 ppm oil in water. Field dehydrators might carry more oil in their effluent water, depending on the conditions of the crude oil being treated. Further clarifying the water requires additional retention time and different chemical treatment, both of which are more economically provided externally to the desalter vessel.

Water solubility in crude oil Water exhibits an appreciable solubility in crude oil at elevated temperatures. A rule of thumb is that approximately 0.4% water might be dissolved at temperatures of approximately 300°F, as shown in Fig. 3.12 for a variety of crude oils. A desalter or dehydrator can separate only dispersed water and has no effect on water that is soluble at operating conditions; however, a significant quantity of soluble water can precipitate when the output is sampled through a sample cooler and the sample is further cooled while awaiting analysis. This precipitated water might be erroneously assumed to be dispersed water in the effluent oil. A more insidious aspect of water solubilization occurs in the preheat train ahead of a desalter. As the oil is heated to operating temperature, water from the dispersed brine is solubilized into the oil phase while leaving behind precipitated salts. This can cause the formation of crystalline salt, which is very difficult to remove from the oil. Injecting fresh water ahead of the preheat train can help offset this problem and can alleviate heat exchanger fouling.

Incompatibilities of oils Crude oils might contain semisoluble organic materials (e.g., waxes and asphaltenes), which can precipitate during processing and cause the production of troublesome sludges or the stabilization of emulsions. Wax precipitation can be controlled through temperature and chemicals, but asphaltenes are more troublesome. By definition, asphaltenes precipitate in hydrocarbons of the molecular weight of pentane; therefore, if light hydrocarbons are recycled as slop oil into a vessel that is processing asphaltic crude oil, serious sludge precipitation might result. Analytical methods Several procedures are currently in use, depending on: the values to be measured the accuracy required the equipment available BS&W measurements BS&W measurements usually are done by centrifugation, as discussed in Sampling and Analyzing Crude Oil Emulsions and as described in ASTM D-96 [2] and ASTM D-4007. [3] Salt analysis by conductivity, as described in ASTM D-3230, [4] is a widely used technique for process monitoring and quality control.

It is reliable at salt concentrations > 5 lbm/1,000 bbl and, with care, can be used at concentrations of from 2 to 5 lbm/1,000 bbl. At low salt levels, oil conductivity becomes a function of water content and pH, as well as of salt content. Because the ions responsible for pH changes are 2.6 to 4.6 times as conductive as chloride, the effects of minor pH changes far outweigh those of chloride-concentration changes. Other problems (e.g., variation in the composition of the salt mix in oils) also help to preclude the use of this method as a reliable indicator of absolute desalter performance at low effluent salt contents unless exacting calibration procedures are followed. Laboratory results usually are obtained by analyzing total chloride ion, converting it to equivalent sodium chloride, and reporting it in lbm/1,000 bbl. At salt levels of 2 lbm/1,000 bbl and below, achieving meaningful and reproducible results requires great care. Of the several available salt-analysis methods, extraction and analysis of soluble salts has proved to be the most reliable, the one least subject to interference from other constituents.

Extraction and analysis Extraction and analysis of soluble salts involves diluting an oil sample with xylene and extracting the mixture with boiling deionized water. The extraction funnels then are placed in a water bath at 140 to 160°F for phase separation. If necessary, one the following methods may be used to enhance separation: acidification chloride-free emulsion breaker Aqueous layer The aqueous layer is removed and filtered if it is cloudy or if entrained oil is present. Then it is titrated with dilute silver nitrate (0.01N), using a chromate indicator under incandescent lighting. The titration procedure is known as the Mohr method and is described in API RP 45. [5] Endpoint recognition requires a practiced eye when using dilute titrant. If available, ion chromatography also may be used for chloride determination. Ion chromatography is extremely accurate for determining small quantities of chloride, but its equipment is more expensive than titration equipment. Because of the widespread occurrence of chloride in nature and the very small quantity being measured in this method, take care to avoid contaminating the sample during handling.

Spectrophotometric determination Another commonly used method is the spectrophotometric determination of the following metals: sodium calcium magnesium These techniques use atomic absorption or inductively coupled plasma and are accurate and highly automated; however, they do not distinguish between water-soluble salts and those that exist primarily in the oil phase (e.g., metal-organic compounds or mineral precipitates), so their results might relate poorly to desalter performance. Nomenclature the volume fraction of water in crude oil References ↑ Warren, K.W. 1993. Reduction of Corrosion through Improvements in Desalting. Paper presented at the Benelux Refinery Symposium, Lanaken, Belgium, 2–3 December. ↑ ASTM D-96-88 (withdrawn 2000), Standard Test Methods for Water and Sediment in Crude Oil by Centrifuge Method (Field Procedure). 1988. West Conshohocken, Pennsylvania: ASTM. ↑ ASTM D-4007-02, Standard Test Methods for Water and Sediment in Crude Oil by Centrifuge Method (Laboratory Procedure). 2002. West Conshohocken, Pennsylvania: ASTM.

↑ ASTM D-3230-05, Test Method for Salts in Crude Oil (Electrometric Method). 2005. West Conshohocken, Pennsylvania: ASTM. ↑ API RP-45, Recommended Practice for Analysis of Oilfield Waters, third edition. 1998. Washington, DC: API. Noteworthy papers in OnePetro Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read External links Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro See also Desalination | SSWM Desalination Félicien Mazille (Aquasis, cewas, international centre for water management services) , Dorothee Spuhler (seecon international gmbh) Adapted from: Executive Summary The chemical process of changing seawater into potable or fresh water is called desalination. Thermal distillation and membrane processes are the two main approaches used around the world to desalinise water. Desalination processes may be used in municipal, industrial, or commercial applications.

With improvements in technology, desalination processes are becoming cost-competitive with other methods of producing usable water to respond to a growing demand. Stand-alone desalination plants can use renewable to operate. The pure water that is obtained after desalination must be re-mineralised to be adequate for human consumption. The concentrated brine produced in desalination processes needs to be disposed of properly. In freshwater when other sources and treatment procedures are uneconomical or not environmentally responsible is becoming more and more common. Desalination is any process that removes excess salts and other minerals from water. In most desalination processes, saltwater (also called “feed water”) is treated and two streams of water are produced: that has low concentrations of salts and minerals. Concentrate or brine, which has salt and mineral concentrations higher than that of the feed water. Main inputs and outputs in a desalination process. Source: CLAYTON (2007) The feed water for desalination processes can be seawater or , which are stores of water underground. Two technologies are primarily used around the world for desalination: thermal distillation and .

Thermal Distillation Thermal distillation technologies are widely used in the Middle East, primarily because the region’s petroleum reserves keep costs low. The three major, large-scale thermal processes are multistage flash distillation, multi-effect distillation, and vapour compression distillation. Another thermal method, solar distillation, is typically used for very small production rates. Membrane Technologies Thermal Technologies Multi-Stage Flash Distillation Multi-stage flash distillation is a process that sends the saline feed water through multiple chambers. In these chambers, the water is heated and compressed to a high , is then is condensed and collected. Multi-Effect Distillation Multi-effect distillation employs the same principals as the multi-stage flash distillation process except that instead of using multiple chambers of a single vessel (also known as an“effect”), multi-effect distillation uses successive vessels. A series of evaporator vessels produces water at progressively lower pressures. Water boils at lower temperatures as pressure decreases, so the water vapour of the first vessel serves as the heating medium for the second, and so on. The more vessels there are, the higher the performance ratio will be. The water vapour that is formed when the water boils is condensed and collected.

The use of multiple vessels makes the multi-effect distillation process more efficient. Vapour Compression Distillation Vapour compression distillation can function independently or be used in combination with another thermal distillation process. Vapour compression distillation uses heat from the compression of vapour to evaporate the feed water. Vapour compression distillation units are commonly used to produce for small- to medium-scale purposes such as resorts, industries, and petroleum drilling sites. Solar Distillation Example of a solar distillation process. Source: MECHELL & LESIKAR (2010) Solar desalination is generally used for small-scale operations. Although the designs of solar distillation units vary greatly, the basic principle is the same: that the sun provides -evaporated water left behind in the still basin form the brine solution that must be discarded appropriately. Solar distillation is often used in freshwater , according to their design and geographic location. Recent tests on four solar still designs by the Texas AgriLife Extension Service in College Station, Texas, have shown that a solar still with as little as 0.7 square meter surface area can produce enough water for a person to survive.

Membrane Technologies membranes used in electrodialysis are built to allow the passage of either positively or negatively charged ions, but not both. Common ionic molecules in saline water are sodium, chloride, calcium, and carbonate. Electrodialysis uses the driving force of an electrical potential to attract and move different cations (positively charged ions) or anions (negatively charged ions) through the permeable membranes are placed so that some allow only cations to pass and others allow only anions to pass, the process can effectively remove most of the salts from the water. The electrodialysis reversal process functions like the electrodialysis process; the only difference is that in the reverse process, the charge of the electrodes is switched periodically. This reversal in flow of ions helps remove scaling and other debris from the , which extends the system’s operating life. Reverse Osmosis that prevents the salt ions from passing (see also membrane filtration ). Because the RO has such small pores, the feed water must be pre-treated adequately before being passed through it. The water can be pre-treated chemically, to prevent biological growth and scaling, and physically, to remove any suspended solids. Membrane Distillation sources to heat the feed water.

Alternative Energy Sources Adapted from MATIOULAKIS et al. (2007) Renewable energies and desalination plants are two different technologies that can be combined in various ways. The interface between the renewable are stand-alone systems in locations without an electricity grid. Stand-alone-systems are often hybrid systems, combining more than one type of renewable . In order to ensure continuous or semi-continuous operation independent of weather conditions, stand-alone systems usually include a storage system. Mineralisation of Water After Desalination Adapted from HASSON & BENDRIHEM (2006) The lack of dissolved minerals in the high-purity water produced by desalination processes raises some problems. High-purity water tends to be highly reactive and, unless treated, it can create severe corrosion difficulties during its transport in conventional pipelines. Also, untreated desalinated water cannot be used directly as a source of Minerals contained in “normal” water.

Source: HASSON & BENDRIHEM (2006) The most common processes for the remineralisation of desalinated water are as follows: Dosage of chemical solutions based on calcium chloride and sodium bicarbonate Limestone dissolution by carbon dioxide Limestone dissolution is the simplest and most widely used process. Operation and Maintenance require trained technicians to operate and maintain the plants, whereas solar desalination requires very low maintenance. Brine Management membrane desalination processes produce a stream of brine water that has a high concentration of salt and other minerals or chemicals that were either removed during the desalination process or added to help pre-treat the feed water. For all of the processes, the brine must be disposed of in an economical and environmentally friendly way. Options for discharging the brine include discharge into the ocean, injection through a well into a saline Costs Adapted from ZHOU & TOF (2004) The costs of desalination vary significantly depending on the size and type of the desalination plant, the source and quality of incoming feed water, the plant location, site conditions, qualified labour, energy consumption. As with all new technologies, progress in desalinating water has been rapid.

Whereas it cost about $9.0/m3 to desalinate seawater around 1960, the costs are now around $1.0/m3 for the multi-stage flash distillation process. For brackish water desalination. There is no reason to believe that the trend will not continue in the future. However, it should be noted that the costs of desalination still remain higher than other alternatives for most regions of the world. At a Glance are the two most widely used techniques. Capacity/Adequacy Technologies available are adapted to many scales from small to large communities. Performance Very efficient to produce deionised water. Costs Relatively high costs but are tending to decrease. Self-help Compatibility Depends on the process used. Reliability Highly reliable if plant is properly maintained. Main strength from very abundant source (oceans). Main weakness drinking water supply processes. Consequently, desalination should be applied if it is the only option. Pure water produced by desalination processes is corrosive and not appropriate for human consumption. Thus, remineralisation (e.g. limestone dissolution) is required before distribution and consumption.

Advantages Uses an abundant water source (seawater) Allows drinking water production in arid, coastal regions Many processes available can be adapted to different local contexts Disadvantages High energy consumption or investment costs Production of highly concentrated salty water is a by-product that has to be discharged properly Desalinated water has to be remineralised before it becomes drinking water References ZHOU, Y.; TOF, R.S.J. (2004): Evaluating the Costs of Desalination and Water transport . Hamburg: International Max Planck Research School of Earth Systems Modeling. URL [Accessed: 04.07.2012]. Further Readings ADU-RES (Editor) (2005): Desalination Units Powered by Renewable Energy Systems . Hammamet: ADU-RES. URL [Accessed: 04.07.2012]. PDF This paper reports the proceedings of the Autonomous Desalination Units Based on Renewable Energy (ADU-RES) International Seminar held in Hammaet, Tunisia, focusing on the water supply situation in Tunisia and analysing different solutions based on desalination. EL-NASHAR, A.M.

(n.y.): The Economics and Performance of Desalination Plants . Paris: Encyclopedia of Life Support Systems (EOLSS). URL [Accessed: 05.03.2012]. PDF In this paper, the technical and economic features of the major seawater desalination processes are reviewed. Each process is described in some detail and the basic mathematical relations used for estimating its performance are outlined. Economic models are also introduced which were developed for the purpose of estimating the water cost for each process. GARCIA-RODRIGUEZ, L. (2007): Assessment of most Promising Developments in Solar Desalination . In: RIZZUTI (2007): Solar Desalination for the 21th Century. Heidelberg, 355-369. URL [Accessed: 04.07.2012]. PDF Indirect solar desalination systems consist of a conventional desalination unit coupled to a solar conversion system. Their most significant possibilities of development in the near future are assessed in this paper.

Particular emphasis is given to the efficiency of such systems since their cost mainly depends on the maturity of the technology and the production scale. KOSCHIKOWSKI, J.; WIEGHAUS, M.; ROMMEL, M. (2003): Solar Driven Desalination Plants Based on Membrane Distillation . In: Elsevier Desalination 156, 298-304. URL [Accessed: 05.03.2012]. PDF This paper describes the use of solar thermally driven stand-alone desalination systems adapted to remote areas based on membrane distillation. The aim is to develop systems for a capacity ranging from 0.2 to 20 m3/day. Technical simplicity, long maintenance-free operation periods and high quality output are the important parameters that will enable successful application of the systems. MATIOULAKIS, E.; BELESSIOTIS, V.; DELYANNIS, E. (2007): Desalination by using Alternative Energy: Review of State of the Art . In: Elsevier Desalination 203, 346-365.

URL [Accessed: 05.03.2012]. PDF This paper presents a review of the highlights that have been achieved during the recent years and the state-of-the-art for most important efforts in the field of desalination by renewable energy, with emphasis on solar energy applications. PURNAMA, A.; AL-BARWANI, H.H.; SMITH, R. (2005): Calculating the Environmental Cost of Seawater Desalination in the Arabian Marginal Seas . In: Elsevier Desalination 185 185, 79-86. URL [Accessed: 05.03.2012]. PDF In this paper, a mathematical model is presented to calculate the impact of desalination plants on salinity within a semi-enclosed sea of simple geometry. SALAZAR, J.; TADEO, F.; PRADA, C. (2010): Renewable Energy for Desalination using Reverse Osmosis . Valladolid: Deparment of Systems Engineering and Automatic Control, University of Valladolid. URL [Accessed: 05.03.2012].

PDF This paper presents a proposal for fulfilling the energy demands of small desalination facilities in remote areas by using a combination of renewable energies. The integrated system consists of photovoltaic modules as well as a wind turbine, diesel generator, battery bank for energy storage and a reverse osmosis desalinisation unit. Drink Up: Taking the Salt out of Seawater - Scientific American Scientific American Drink Up: Taking the Salt out of Seawater Removing the salt from briny water is becoming more affordable By Steven Ashley on March 19, 2009 Advertisement | Report Ad Almost three quarters of Earth's surface is covered with water, but most of it is too salty to drink. And the 2.5 percent that is freshwater is locked up either in soil, remote snowpacks and glaciers or in deep aquifers. That leaves less than 1 percent of all freshwater for humans and animals to drink and for farmers to use to raise crops—and that remnant is shrinking as rising global temperatures trigger more droughts. The upshot: it's becoming increasingly difficult to slake the world's thirst as the population grows and water supplies dwindle. Analysts at the investment bank Goldman Sachs estimate that worldwide water use doubles every 20 years.

So the search for new water sources is on. One proved candidate is desalinization—technologies that extract the salt from brine drawn from the oceans or saline aquifers to create potable water . But the historically high price of desalinization has largely kept it at bay, a situation that's changing as technology improves and growing demand squeezes freshwater supplies . "The two main desalinization techniques are distillation and reverse osmosis , or RO," says Menachem Elimelech, an environmental engineer at Yale University. "Distillation, in which the raw water is evaporated and then condensed as freshwater, is energy-intensive, so it's mainly used in the Middle East where oil is abundant." Thermal salt-removing processes require high temperatures so they tend to be expensive (more than $1 per cubic meter of freshwater), but the use of rejected "waste" heat from other industrial or power plant operations for co-generation can cut energy expenditure. More commonly, however, desalinization plants rely on RO, which is based on high-tech polymer membranes that are permeable to water, but reject the passage of dissolved salts, Elimelich says.

When a saline solution sits on one side of a semipermeable membrane and a less salty solution is on the other, he explains, water diffuses through the membrane from the less concentrated to the more concentrated side. Scientists call this phenomenon osmosis, which tends to equalize the salinity of the two solutions. In the 1950s and '60s researchers realized that they could reverse the process by applying pressure to the more concentrated solution, causing water molecules there to traverse the membrane, leaving behind a condensed brine. To counter the osmotic pressure that arises between the solutions and force water back through the membrane, desalinization plants must utilize high pressures of 7,000 to 8,300 kilopascals (71 to 86.5 kilogram-force per square centimeter or 1,000 to 1,200 pounds per square inch), he notes. Common RO membranes are thin-film composites that combine a mechanically robust support layer made of microporous polysulfone with a micron-thick polyamide "filter" layer through which water molecules can pass but nothing else.

The latter substance is "a second cousin to DuPont's Kevlar —the super-strong aramid polymer fiber used in lightweight body armor," says Bill Mickols, senior research scientist at Dow Water Solutions (DWS) of Edina, Minn., the biggest supplier of such products. RO membranes have matured during the past two decades, he says, with marked improvements in water permeability, salt-rejection capability, operating life (now as long as three to five years) and cost. These advances, in combination with energy-recovery devices that take pressure from the concentrated brine stream and transfer most of it to the incoming water flow, have made desalinization more affordable. Current RO facilities desalinize seawater for 68 to 90 cents per cubic meter. The average delivery price of municipal water in the U.S. is around 60 cents a cubic meter, according to the American Water Works Association. Other improvements currently in the works include measures to maintain process flow. RO plants must filter seawater and inject chemicals to eliminate particles that could cause clogging, and the membranes are washed regularly to lessen scale formation and biofilm fouling, says Benny Freeman, a chemical engineer at the University of Texas at Austin.

"Chlorine is added to sterilize the water ," he says, "but operators usually need to dechlorinate it afterwards to protect the membrane from chemical degradation." Freeman and James McGrath, a polymer scientist at Virginia Polytechnic Institute and State University in Blacksburg have modified chlorine-resistant polysulfone to serve as a desalinization membrane. Researchers elsewhere are meanwhile attempting to work around the RO's reliance on high pressure. Elimelech and entrepreneur Robert McGinnis have advanced a process called forward osmosis (FO) that could reduce the energy needed to purify water by 90 percent. FO takes advantage of the osmotic pressure difference between a concentrated "draw" solution and a raw water stream to drive water through a semipermeable membrane. "The right draw solution means you don't have to do all the work with pressure," McGinnis notes, who recently formed a start-up company called Oasys to commercialize the technology. The main challenge, he adds, is to select a nontoxic draw solute that may be simply and economically removed. Oasys plans to use an ammonia and carbon dioxide mixture as a draw solute.

When the solution is heated, the dissolved ammonium carbonate and related salts decompose into their precursor gases, enabling easy removal. Oasys' process, McGinnis says, can run efficiently on small quantities of electrical power combined with "waste" heat (less than 120 degrees Fahrenheit, or 50 degrees Celsius) from industrial operations. When fully scaled up, FO desalinization is expected to cost only 37 to 44 cents a cubic meter. More speculative desalinization research aims to create "superflux" membranes that allow water to pass through more easily, says Mark Shannon, director of the Center of Advanced Materials for the Purification of Water with Systems (CAMPWS) at the University of Illinois at Urbana–Champaign. Investigators have shown, for example, that carbon nanotubes can convey water at unexpectedly high flow rates. These so-called water wires may be able to pass a greater volume of water at a given pressure than existing membranes while still blocking out hydrated salts. Biomimetic membrane technologies are also under development, Shannon says. These materials try to imitate the ability of the minute pores in biological cell membranes to selectively allow water to flow through while preventing the passage of salt ions.

The Danish firm Aquaporin, for instance, is embedding natural aquaporins (water channels) extracted from green plants in membranes that it hopes to market this year. Others, including CAMPWS scientists, are working on artificial active nanopore structures. Recently, the Madrid Institute for Advanced Studies agreed to collaborate with Valladolid, Spain–based engineering company, PROINGESA, to design a capacitive de-ionization process that applies an electrical potential to raw water to attract dissolved salt ions toward oppositely charged electrodes, where they are adsorbed and later removed. Some 13,000 desalinization plants capable of producing 52.3 million cubic meters (13.8 billion gallons) of potable water a day are currently in operation, according to the International Desalination Association (IDA). But that is only a half a percent of global daily water use, a figure that would grow faster if process costs could be further reduced. Nevertheless, construction of desalinization facilities rose at an annual clip of 17 percent since 1990, the IDA reports.

The trend worries many local environmental groups, such as California's Surfrider Foundation or Australia's Nature Conservation Council of NSW, which are concerned about protecting nearby ecosystems by safely disposing the concentrated brine left from the process as well as increased fossil-fuel use and the resulting greenhouse gas emissions . In any case, a new market analysis by Lux Research forecasts that the global desalinated water supply will grow at a compound annual growth rate of 9.5 percent during the next decade as Australia, Israel, Singapore, California and others build desalinization plants for seawater and inland brackish water as well as for water recycling. This means that output will reach 54 billion cubic meters a year (54 trillion liters/year) by 2020, or triple what it had been in 2008. CAMPWS's Shannon agrees, predicting, "We're going to see exponential growth in desalinization over the next few decades."

Question: The removal of salt from brine to produce fresh water is commonly named what?
Answer: Desalination