Reverse osmosis

Reverse osmosis uses pressure to drive solvent through a selectively permeable membrane from a concentrated solution toward a more dilute one, rejecting many dissolved substances.

Osmosis: The net movement of solvent across a selectively permeable membrane toward a solution with higher solute concentration. Reverse osmosis applies pressure to oppose and reverse this natural solvent flow.
Seawater desalination: The removal of dissolved salts from seawater to produce fresh water. Reverse osmosis is a widely used method for turning seawater into drinking water.
Nanofiltration: A pressure-driven membrane process that typically rejects multivalent ions and larger organic molecules while passing more monovalent salts. It often operates at lower pressure but provides less complete salt removal.
Jean-Antoine Nollet: An eighteenth-century French physicist who observed water moving through animal bladder membranes. His observations of osmosis established an early basis for understanding membrane transport.
Semipermeable membrane: A barrier that permits some substances to pass while restricting others. Its selective transport lets water pass while retaining many dissolved solutes.
Brackish water desalination: The treatment of moderately saline groundwater or surface water to reduce its dissolved salts. Its lower salinity generally requires less pressure than seawater treatment.
Ultrafiltration: A membrane process that removes suspended particles and many macromolecules while allowing dissolved salts to pass. Unlike reverse osmosis, it does not substantially remove ordinary dissolved ions.
Sidney Loeb: An engineer and chemist who helped develop practical asymmetric membranes for reverse-osmosis desalination. His membrane work made high-throughput desalination technically feasible.
Osmotic pressure: The pressure required to stop net solvent flow across a selectively permeable membrane. Feed pressure must exceed the osmotic-pressure difference to produce net water flow.
Water purification: The removal of unwanted substances from water to make it suitable for a particular use. Reverse osmosis is one membrane-based method within the broader practice of water purification.

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