Membrane filtration

Membrane filtration separates substances by passing a mixture across a semipermeable barrier that allows selected components through while retaining others.

Semipermeable membrane: A barrier that permits some substances to pass while restricting others. Its selective permeability is the defining feature that makes membrane separation possible.
Microfiltration: Membrane filtration that removes suspended particles and many microorganisms using relatively large pores. It occupies the coarse-retention end of pressure-driven membrane processes.
Desalination: The removal of dissolved salts from seawater or brackish water. Reverse osmosis membranes make desalination widely practical.
Centrifugation: A separation technique that uses rotation to sort components by density and sedimentation behavior. It can separate suspended material without requiring selective membrane transport.
Transmembrane pressure: The pressure difference across a membrane that drives fluid through it. Pressure supplies the driving force in many filtration systems.
Ultrafiltration: Membrane filtration that retains macromolecules and colloids while allowing smaller solutes to pass. It separates larger dissolved and dispersed matter through size exclusion.
Wastewater treatment: Processes that remove contaminants from used water before reuse or environmental release. Membranes retain suspended solids and can support high-quality treated effluent.
Sedimentation: The settling of suspended particles under gravity or another applied acceleration. It removes settleable solids by motion through a fluid rather than membrane retention.
Concentration polarization: The buildup of retained solutes near a membrane surface during filtration. This boundary layer reduces effective transport and can promote fouling.
Nanofiltration: Pressure-driven membrane separation that rejects many multivalent ions and small organic molecules. It bridges size-based filtration and the stronger ion rejection of reverse osmosis.

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