Views: 0 Author: Site Editor Publish Time: 2021-06-30 Origin: Site
desalination of seawater for use as fresh water by reverse osmosis.
Osmosis occurs when two solutions, composed of solute (dissolved inorganic solids, such as salt) mixed with a solvent (in this case, water) are separated by a semipermeable membrane. The solvent molecules move through the membrane in the direction of high solute concentration until the solute/solvent ratios are equal. Osmosis would create two solutions of equally salty water. The seawater reverse osmosis (SWRO) process, as the name implies, reverses natural osmosis. It begins by bringing seawater (feed water) at low pressure through a pretreatment filtering system that removes suspended solids. The pretreated water then is pressurized and pumped through a series of semipermeable reverse osmosis (RO) membrane elements at about 900 to 1,200 psi (60 to 82.5 bar). On the other side of the membrane, fresh water is passed. Because of the pressure, the water molecules in the seawater (the high solute concentrate) pass through the membrane in the direction of the low solute concentrate — in this case, the passing fresh water (the product stream) and joins it — leaving the salt and other dissolved solids behind.
SWRO is expected to dominate and drive the desalination industry in coming years because it requires substantially less energy than other popular desalination technologies, such as multistage flash (MSF) and multieffect distillation (MED). These are high-energy thermal processes that rely on heating the seawater to produce steam. Only the water molecules are gasified, leaving the salt and impurities in the solution. The steam is transported to a cooling tank where the desalinated water condenses. Further, SWRO usually incorporates energy recovery devices that capture hydraulic energy from the process and convert it into rotary power for the high-pressure pumps.