Osmosis<br /> When two solutions of differing concentrations of dissolved materials are separated by a semi-permeable membrane, the liquid component will tend to flow from the lower to the more highly concentrated side. In a sense, the concentration difference will tend to equilibrate across the membrane.<br />*The semi-permeable membrane does not allow the solutes to move from one compartment to the other, but allows the solvent to move.<br />
Reverse Osmosis<br /> If the liquid on the more concentrated side is maintained at a higher pressure, however, this process can be reversed: the solvent will flow from the concentrated side to the less concentrated side. Since the membrane blocks the passage of the dissolved waste constituents, the concentrated solution becomes even more concentrated.<br />
Dependent on the following factors:<br />Influent Solute Concentration<br />Water Flux Rate<br />Pressure<br /><ul><li> Pressure caused by the difference in solute concentration between the two compartments (the osmotic pressure)
The externally applied pressure (in excess of the osmotic pressure.)</li></li></ul><li>Required Pressure Amount (high concentrated side):<br />For fresh and brackish water: 15.5 to 26 bar (225 to 375 psi) <br />For seawater: 55 to 81.5 bar (800 to 1,180 psi), overcome 24 bar (350 psi) natural osmotic pressure<br />
Drinking water purification<br />Portable reverse osmosis (RO) water processors <br />Best be under some pressure (40 psi or greater is the norm)<br />Production of bottled mineral water<br />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.)<br />United States military, R.O.W.P.U.'s (Reverse Osmosis Water Purification Unit, pronounced "roh-poo")<br />Can purify salt water and water contaminated with N.B.C. (Nuclear/Biological/Chemical) agents from the water. A single ROWPU can sustain a force of a battalion size element or roughly 1,000 to 6,000 soldiers.<br />
Food Industry<br /><ul><li> More economical operation for concentrating food liquids (such as fruit juices) than conventional heat-treatment processes</li></ul>Dairy industry <br /><ul><li>For the concentration of milk to reduce shipping costs. </li></li></ul><li>Desalination<br /><ul><li>Useful for areas that have either no or limited surface water or groundwater.
Reverse osmosis is the most common method of desalination, although 85 percent of desalinated water is produced in multistage flash plants.
Sea Water Reverse Osmosis (SWRO) : No heating or phase changes are needed, energy requirements are low in comparison to other processes of desalination, but are still much higher than those required for other forms of water supply (including reverse osmosis treatment of wastewater).
The Ashkelon seawater reverse osmosis (SWRO) desalination plant in Israel is the largest in the world.</li></li></ul><li>RO Disadvantages<br />Household RO units use a lot of water because they have low back pressure. As a result, they recover only 5 to 15 percent of the water entering the system. The remainder is discharged as waste water. An RO unit delivering 5 gallons of treated water per day may discharge 40 to 90 gallons of waste water per day to the septic system.<br /> Large scale industrial/municipal systems have a production efficiency of closer to 48% because they can generate the high pressure needed for RO filtration.<br />