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Encyclopedia > Reverse osmosis

Reverse osmosis (RO) is a separation process that uses pressure to force a solution through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane here is semipermeable, meaning it allows the passage of solvent but not of solute. Making a saline water solution by dissolving table salt (NaCl) in water This article is about chemical solutions. ... A semipermeable membrane is a membrane which will allow certain molecules to pass through it by diffusion (sometimes facilitated diffusion). The rate of passage depends on the pressure, concentration and temperature of the molecules (or solutes) on either side, as well as the permeability of the membrane to each kind. ... A substance is soluble in a fluid if it dissolves in the fluid. ... For other uses, see Solvent (disambiguation). ... This article or section does not adequately cite its references or sources. ... Osmosis is the spontaneous net movement of water across a semipermeable membrane from a region of low solute concentration to a solution with a high solute concentration, down a solute concentration gradient. ... For other uses, see Solvent (disambiguation). ... Scheme of semipermeable membrane during hemodialysis. ...

The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs. In most cases the membrane is designed to allow only water to pass through this dense layer while preventing the passage of solutes (such as salt ions). This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 2–17 bar (30–250 psi) for fresh and brackish water, and 40–70 bar (600–1000 psi) for seawater, which has around 24 bar (350 psi) natural osmotic pressure which must be overcome. The bar (symbol bar), decibar (symbol dbar) and the millibar (symbol mbar, also mb) are units of pressure. ... A pressure gauge reading in PSI (red scale) and kPa (black scale) The pound-force per square inch (symbol: lbf/in²) is a non-SI unit of pressure based on avoirdupois units. ...

This process is best known for its use in desalination (removing the salt from sea water to get fresh water), but it has also been used to purify fresh water for medical, industrial and domestic applications since the early 1970s. Shevchenko BN350 desalination unit situated on the shore of the Caspian Sea. ... Sea water is water from a sea or ocean. ... For the village on the Isle of Wight, see Freshwater, Isle of Wight. ...

When two solutions with different concentrations of a solute are mixed, the total amount of solutes in the two solutions will be equally distributed in the total amount of solvent from the two solution.

Instead of mixing the two solutions together, they can be put in two compartments where they are separated from each other by a semipermeable membrane. The semipermeable membrane does not allow the solutes to move from one compartment to the other, but allows the solvent to move. Since equilibrium cannot be achieved by the movement of solutes from the compartment with high solute concentration to the one with low solute concentration, it is instead achieved by the movement of the solvent from areas of low solute concentration to areas of high solute concentration. When the solvent moves away from low concentration areas, it causes these areas to become more concentrated. On the other side, when the solvent moves into areas of high concentration, solute concentration will decrease. This process is termed osmosis. The tendency for solvent to flow through the membrane can be expressed as "osmotic pressure", since it is analogous to flow caused by a pressure differential. Scheme of semipermeable membrane during hemodialysis, where red is blood, blue is the dialysing fluid, and yellow is the membrane. ...

In reverse osmosis, in a similar setup as that in osmosis, pressure is applied to the compartment with high concentration. In this case, there are two forces influencing the movement of water: the pressure caused by the difference in solute concentration between the two compartments (the osmotic pressure) and the externally applied pressure.



Drinking water purification

Around the world, household drinking water purification systems, including a reverse osmosis step, are commonly used for improving water for drinking and cooking. Tap water Mineral Water Water of sufficient quality to serve as drinking water is termed potable water whether it is used as such or not. ... Water purification is the process of removing contaminants from a raw water source. ...

Such systems typically include a number of stages:

  • a sediment filter to trap particles including rust and calcium carbonate
  • optionally a second sediment filter with smaller pores
  • an activated carbon filter to trap organic chemicals, and chlorine which will attack and degrade TFC reverse osmosis membranes
  • a reverse osmosis (RO) filter which is a thin film composite membrane (TFM or TFC)
  • optionally a second carbon filter to capture those chemicals not removed by the RO membrane.
  • optionally an ultra-violet lamp is used for disinfection of any microbes that may escape filtering by the reverse osmosis membrane.

In some systems, the carbon pre-filter is omitted and cellulose triacetate membrane (CTA) is used. The CTA membrane is prone to rotting unless protected by the chlorinated water, while the TFC membrane is prone to breaking down under the influence of chlorine. In CTA systems, a carbon post-filter is needed to remove chlorine from the final product water. Activated carbon Activated carbon, also called activated charcoal or activated coal, is a general term which covers carbon material mostly derived from charcoal. ... Thin film composite membranes (TFC or TFM) are semipermeable membranes manufactured principally for use in water purification or desalination systems. ... For other uses, see Ultraviolet (disambiguation). ... Cellulose triacetate, also known simply as triacetate, is manufactured from cellulose and acetate. ...

Portable reverse osmosis (RO) water processors are sold for personal water purification in various locations. To work effectively, the water feeding to these units should best be under some pressure (40 psi or greater is the norm). Portable RO water processors can be used by people who live in rural areas without clean water, far away from the city's water pipes. Rural people filter river or ocean water themselves, as the device is easy to use (Saline water may need special membranes). Some travelers on long boating trips, fishing, island camping, or in countries where the local water supply is polluted or substandard, use RO water processors coupled with one or more UV sterilizers. RO systems are also now extensively used by marine aquarium enthusiasts. In the production of bottled mineral water, the water passes through an RO water processor to remove pollutants and microorganisms. In European countries, though, such processing of Natural Mineral Water (as defined by a European Directive) is not allowed under European law.(In practice, a fraction of the living bacteria can and do pass through RO membranes through minor imperfections, or bypass the membrane entirely through tiny leaks in surrounding seals. Thus, complete RO systems may include additional water treatment stages that use ultraviolet light or ozone to prevent microbiological contamination.) For other uses, see Ozone (disambiguation). ...

In the water treatment industry there is a chart of types of contaminants, their sizes and which ones pass through the various types of membranes.[1] Membrane pore sizes can vary from 1 to 50,000 angstroms depending on filter type. "Particle filtration" removes particles of 10,000 angstroms or larger. Microfiltration removes particles of 500 angstroms or larger. "Ultrafiltration" removes particles of roughly 30 angstroms or larger. "Nanofiltration" removes particles of 10 angstroms or larger. Reverse osmosis is in the final category of membrane filtration, "Hyperfiltration", and removes particles larger than 1 angstrom. An angstrom, angström, or ångström (symbol Å) is a unit of length. ... Microfiltration is a filtration process which removes contaminants from a fluid or gas by passage through a microporous membrane. ...

In the United States military, R.O.W.P.U.'s (Reverse Osmosis Water Purification Unit, pronounced ROW-PEW) are used on the battlefield and in training. They come ranging from 1500 GPD (gallons per day) to 150,000 GPD and bigger depending on the need. The most common of these are the 600 GPH (gallons per hour) and the 3,000 GPH. Both are able to purify salt water and water contaminated with N.B.C. (Nuclear/Biological/Chemical) agents from the water. During a normal 24 hour period, one unit can produce anywhere from 12,000 to 60,000 gallons of water, with a required 4 hour maintenance window to check systems, pumps, R.O. elements and the engine generator. A single ROWPU can sustain a force of a battalion size element or roughly 1,000 to 6,000 soldiers.

Water and wastewater purification

Rain water collected from storm drains is purified with reverse osmosis water processors and used for landscape irrigation and industrial cooling in Los Angeles and other cities, as a solution to the problem of water shortages.

In industry, reverse osmosis removes minerals from boiler water at power plants. The water is boiled and condensed repeatedly. It must be as pure as possible so that it does not leave deposits on the machinery or cause corrosion. It is also used to clean effluent and brackish groundwater. A power station (also power plant) is a facility for the generation of electric power. ...

Reverse osmosis product can be used for the production of deionized water. Deionized water (DI water or de-ionized water; also spelled deionised water, see spelling differences) is water that lacks ions, such as cations from sodium, calcium, iron, copper and anions such as chloride and bromide. ...

In July 2002, Singapore announced that a process named NEWater would be a significant part of its future water plans. It involves using reverse osmosis to treat domestic wastewater before discharging the NEWater back into the reservoirs. Bottles of NEWater for distribution during the National Day Parade celebrations of 2005 at Marina South NEWater is the brand name given to reclaimed water produced by Singapores public utilities. ...


Reverse osmosis is the technique used in dialysis, which is used by people with kidney failure. The kidneys filter the blood, removing waste products (e.g. urea) and water, which is then excreted as urine. A dialysis machine mimics the function of the kidneys. The blood passes from the body via a catheter to the dialysis machine, across an osmotic filter. In medicine, dialysis is a type of renal replacement therapy which is used to provide an artificial replacement for lost kidney function due to renal failure. ... The kidneys are the organs that filter wastes (such as urea) from the blood and excrete them, along with water, as urine. ... This article is about the urine of animals generally. ... In medicine, dialysis is a type of renal replacement therapy which is used to provide an artificial replacement for lost kidney function due to renal failure. ...

Food Industry

In addition to desalination, reverse osmosis is a more economical operation for concentrating food liquids (such as fruit juices) than conventional heat-treatment processes. Research has been done on concentration of orange juice and tomato juice. Its advantages include a low operating cost and the ability to avoid heat treatment processes, which makes it suitable for heat-sensitive substances like the protein and enzymes found in most food products. A representation of the 3D structure of myoglobin showing coloured alpha helices. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ...

Reverse osmosis is extensively used in the dairy industry for the production of whey protein powders and for the concentration of milk to reduce shipping costs. In whey applications, the whey (liquid remaining after cheese manufacture) is pre-concentrated with RO from 6% total solids to 10-20% total solids before UF (ultrafiltration) processing. The UF retentate can then be used to make various whey powders including WPI (whey protein isolate) used in bodybuilding formulations. Additionally, the UF permeate, which contains lactose, is concentrated by RO from 5% total solids to 18–22% total solids to reduce crystallization and drying costs of the lactose powder. Whey protein is the name for a collection of globular proteins that can be isolated from whey, a by-product of cheese manufactured from cows milk. ...

Although use of the process was once frowned upon in the wine industry, it is now widely understood and used. An estimated 60 reverse osmosis machines were in use in Bordeaux, France in 2002. Known users include many of the elite classed growths (Kramer) such as Château Léoville-Las Cases in Bordeaux. For other uses, see Bordeaux (disambiguation). ... Château Léoville-Las Cases is a Second Growth in the Bordeaux Wine Official Classification of 1855. ... For other uses, see Bordeaux (disambiguation). ...

Reverse osmosis is used globally throughout the wine industry for many practices including wine and juice concentration, taint removal; such as acetic acid, smoke taint and brettanomyces taint; and alcohol removal. The patent holder for these processes, Vinovation, Inc., claims to have served over 1000 wineries worldwide, either directly or through one if its licensed partners, in the last 15 years. Its use has become so widely accepted that patent infringers have sprung up on several continents. R-phrases , S-phrases , , , Flash point 43 °C Related Compounds Related carboxylic; acids Formic acid; Propionic acid; Butyric acid Related compounds acetamide; ethyl acetate; acetyl chloride; acetic anhydride; acetonitrile; acetaldehyde; ethanol; thioacetic acid; acetylcholine; acetylcholinesterase Supplementary data page Structure and properties n, εr, etc. ... This article does not cite any references or sources. ... [[|Diversity]] Binomial name Trinomial name Type Species Species [[Image: ]] Synonyms Brettanomyces is a single-celled fungus that is important in brewing and winemaking as it is resistant to alcohol so can grow even after fermentation starts. ... This article does not cite any references or sources. ...

Car Washing

Because of its lower mineral content, Reverse Osmosis water is often used in car washes during the final vehicle rinse to prevent water spotting on the vehicle. Reverse osmosis water displaces the mineral heavy reclamation water (municipal water). Reverse Osmosis water also enables the car wash operators to reduce the demands on the vehicle drying equipment such as air blowers.

Maple Syrup Production

Starting in the 1970s, some maple syrup producers started using reverse osmosis to remove water from sap before being further boiled down to syrup. The use of reverse osmosis allows approximately 75–80% of the water to be removed from the sap, reducing energy consumption and exposure of the syrup to high temperatures. Microbial contamination and degradation of the membranes has to be monitored. Bottled maple syrup produced in Quebec. ... Leafhoppers and many other insects feed off plant sap Sap is the fluid transported in xylem cells (tracheids or vessel elements) or phloem sieve tube elements of a plant. ... In cooking, a syrup (from Arabic شراب sharab, beverage, via Latin siropus) is a thick, viscous liquid, containing a large amount of dissolved sugars, but showing little tendency to deposit crystals. ...

Hydrogen production

For small scale production of hydrogen, reverse osmosis is sometimes used to prevent formation of minerals on the surface of electrodes and to remove organics and chlorine from drinking water. Hydrogen production is commonly completed from hydrocarbon fossil fuels via a chemical path. ... For other uses, see Electrode (disambiguation). ... General Name, symbol, number chlorine, Cl, 17 Chemical series nonmetals Group, period, block 17, 3, p Appearance yellowish green Standard atomic weight 35. ...

Reef aquariums

Typical RO/DI unit used for an aquarium
Typical RO/DI unit used for an aquarium

Many reef aquarium keepers use reverse osmosis systems for their artificial mixture of seawater. Ordinary tap water can often contain excessive chlorine, chloramines, copper, nitrogen, phosphates, silicates, or many other chemicals detrimental to the sensitive organisms in a reef environment. Contaminants such as nitrogen compounds and phosphates can lead to excessive, and unwanted, algae growth. An effective combination of both reverse osmosis and deionization (RO/DI) is the most popular among reef aquarium keepers and is preferred above other water purification processes due to the low cost of ownership and minimal running costs. (Where chlorine and chloramines are found in the water carbon filterion is needed before the membrane as the common residential membrane used by reef keepers does not cope with these compounds.) Deionized water (DI water or de-ionized water; also spelled deionised water, see spelling differences) is water that lacks ions, such as cations from sodium, calcium, iron, copper and anions such as chloride and bromide. ...


Areas that have no or limited surface water or groundwater may choose to desalinate seawater or brackish water to obtain drinking water. Reverse osmosis is the most common method of desalination, although 85 percent of desalinated water is produced in multistage flash plants.[2] Large reverse osmosis and multistage flash desalination plants are used in the Middle East, especially Saudi Arabia. The energy requirements of the plants are large, but electricity can be produced relatively cheaply with the abundant oil reserves in the region. The desalination plants are often located adjacent to the power plants, which reduces energy losses in transmission and allows waste heat to be used in the desalination process of multistage flash plants, reducing the amount of energy needed to desalinate the water and providing cooling for the power plant. Shevchenko BN350 desalination unit situated on the shore of the Caspian Sea. ... Tap water Mineral Water Water of sufficient quality to serve as drinking water is termed potable water whether it is used as such or not. ... A map showing countries commonly considered to be part of the Middle East The Middle East is a region comprising the lands around the southern and eastern parts of the Mediterranean Sea, a territory that extends from the eastern Mediterranean Sea to the Persian Gulf. ... Electricity (from New Latin Ä“lectricus, amberlike) is a general term for a variety of phenomena resulting from the presence and flow of electric charge. ... Petro redirects here. ... A power station (also power plant) is a facility for the generation of electric power. ...

Sea Water Reverse Osmosis (SWRO) is a reverse osmosis desalination membrane process that has been commercially used since the early 1970s. Its first practical demonstration was done by Sidney Loeb and Srinivasa Sourirajan from UCLA in Coalinga, California. Because no heating or phase changes are needed, energy requirements are low in comparison to other processes of desalination, though still much higher than other forms of water supply (including reverse osmosis treatment of wastewater).[citation needed] Binomial name Ucla xenogrammus Holleman, 1993 The largemouth triplefin, Ucla xenogrammus, is a fish of the family Tripterygiidae and only member of the genus Ucla, found in the Pacific Ocean from Viet Nam, the Philippines, Palau and the Caroline Islands to Papua New Guinea, Australia (including Christmas Island), and the... Coalinga is a city located in Fresno County, California. ... This article is about the U.S. state. ...

The typical single pass SWRO system consists of the following components:

  • Intake
  • Pre-treatment
  • High-pressure pump
  • Membrane assembly
  • Remineralization and pH adjustment
  • Disinfection

In biogeochemistry, remineralisation refers to the transformation of organic molecules to inorganic forms, typically mediated by biological activity. ...


Pre-treatment is important when working with RO and nanofiltration (NF) membranes due to the nature of their spiral wound design. The material is engineered in such a fashion to allow only one way flow through the system. As such the spiral wound design doesn't allow for backpulsing with water or air agitation to scour its surface and remove solids. Since accumulated material cannot be removed from the membrane surface systems they are highly susceptible to fouling (loss of production capacity). Therefore, pretreatment is a necessity for any RO or NF system. Pretreatment in SWRO system has four major components:

Screening of solids
Solids within the water must be removed and the water treated to prevent fouling of the membranes by fine particle or biological growth, and reduce the risk of damage to high-pressure pump components.
Screening of biologicals
Prefiltration pH adjustment
If the pH of upstream salinwater is above 5.8 in the acidic-alkaline measurement scale, sulfuric acid or other acidic solution is used to adjust the pH of water at 5.5 to 5.8.
Cartridge filtrationation

High pressure pump

The pump supplies the pressure needed to push water through the membrane, even as the membrane rejects the passage of salt through it. Typical pressures for brackish water range from 225 to 375 lbf/in² (1.6 to 2.6 MPa). In the case of seawater, they range from 800 to 1,180 lbf/in² (6 to 8 MPa). Brackish redirects here. ...

Membrane assembly

The membrane assembly consists of a pressure vessel with a membrane that allows feedwater to be pressed against it. The membrane must be strong enough to withstand whatever pressure is applied against it. RO membranes are made in a variety of configurations, with the two most common configurations being spiral-wound and a hollow-fiber.

Reinmineralisation and pH adjustment

The desalinated water is very corrosive and is "stabilized" to protect downstream pipelines and storages usually by adding lime and carbon dioxide to prevent corrosion of concrete or cement lined surfaces. Liming material is used in order to adjust pH at 6.8 to 8.1 to meet the potable water specifications, primarily for effective disinfection and for corrosion control.


Post-treatment consists of stabilizing the water and preparing for distribution. Desalination processes are very effective barriers to pathogenic organisms, however disinfection is used to ensure a "safe" water supply. Disinfection (sometimes called germicidal or bactericidal) is employed to kill the any bacteria protozoa and virus that have bypassed the desalination process into the product water. Disinfection may be by means of ultraviolet radiation, using UV lamps directly on the product, or by chlorination or chloramination (chlorine and ammonia). In many countries either chlorination or chloramination is used to provide a "residual" disinfection agent in the water supply system to protect against infection of the water supply by contamination entering the system. Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ...


Reverse osmosis units sold for residential purposes offer water filtration at the cost of large quantities of waste water. For every 5 gallons of output, a typical residential reverse osmosis filter will send around 10–20 gallons of water down the drain although it may be captured and used for watering plants and lawns.[citation needed]

New developments

Prefiltration of high fouling waters with another, larger-pore membrane with less hydraulic energy requirement, has been evaluated and sometimes used since the 1970s. However, this means the water passes through two membranes and is often repressurized, requiring more energy input in the system, increasing the cost.

Other recent development work[3] has focused on integrating RO with electrodialysis in order to improve recovery of valuable deionized products or minimize concentrate volume requiring discharge or disposal. Electrodialysis (ED) is used to transport salt ions from one solution through ion-exchange membranes to another solution under the influence of an applied electric potential difference. ...

See also

Hydrogen production is commonly completed from hydrocarbon fossil fuels via a chemical path. ... Microfiltration is a filtration process which removes contaminants from a fluid or gas by passage through a microporous membrane. ... It has been suggested that Anoxic sea water, Oxygen minimum zone, and Hypoxic zone be merged into this article or section. ... Sediment from the Mississippi River carries fertilizer to the Gulf of Mexico Dead zones are hypoxic (low-oxygen) areas in the worlds oceans, the observed incidences of which have been increasing since oceanographers began noting them in the 1970s. ... Particle (ecology) is the term for small objects of nonbiological kind. ... Ship pollution is the pollution of water by shipping! It is a problem that has been accelerating as trade has become increasingly globalized. ... Raw sewage and industrial waste flows into the U.S. from Mexico as the New River passes from Mexicali, Baja California to Calexico, California Water pollution is the contamination of water bodies such as lakes, rivers, oceans, and groundwater caused by human activities, which can be harmful to organisms and... Water quality is the physical, chemical and biological characteristics of water, characterized through the methods of hydrometry. ... Blue energy is the energy retrieved from the difference in the salt concentration between seawater and river water with the use of osmosis or reverse electro dialysis (RED) with ion specific membranes. ...

Notes and references

  1. ^ Membrane Systems from 1.2 to 100 gpm, HF Pure Water.
  2. ^ Water Technology - Shuaiba Desalination Plant
  3. ^ How Does HEEPM™ Work?
  • Kramer, Matt. Making Sense of Wine. Philadelphia: Running Press, 2003.

External links

  Results from FactBites:
Reverse osmosis - Wikipedia, the free encyclopedia (1448 words)
Reverse osmosis is the process of pushing a solution through a filter that traps the solute on one side and allows the pure solvent to be obtained from the other side.
This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied.
The use of reverse osmosis allows approximately 75 to 80% of the water to be removed from the sap, reducing energy consumption and exposure of the syrup to high temperatures.
Reverse osmosis (678 words)
Reverse Osmosis (RO) is a filtration technique where you add pressure to the fluid with the highest salt concentration and then press this fluid a very fine membrane (0.001-0.0001 µm) which can filter both ions and dissolved matters in the water.
The principle of reverse osmosis is that the saline raw water is led in across a membrane.
In a reverse osmosis plant only a certain percentage of the inlet water is utilised, normally between 75 and 80 %, if the plant is equipped with pre-treatment, and between 40 and 50 % without pre-treatment - the rest is discharged as concentrate.
  More results at FactBites »



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