Functions of a Semipermeable Membrane

When it comes to water filtration, the type of membrane used counts for a lot. A permeable membrane is a biological membrane with a pore size that allows just about every ion, particle, and water molecule to pass through. A selectively permeable membrane, on the other hand, filters larger molecules and ions such as Na+, Ca++, Cl- and does not permit them to cross the layer.

A semipermeable membrane is a necessary component in reverse osmosis, which is a standard water purification process. The artificial membrane filters out unwanted substances and chemicals from the water, making it safe for human consumption. Aside from desalinating seawater and purifying well water, a semipermeable membrane can also be utilized for medical purposes. In particular, semipermeable membranes filter out waste products during dialysis, helping to cleanse the blood from impurities when the kidneys are unable to function.

While a semipermeable membrane can be constructed out of various materials, artificial semipermeable membranes used for reverse osmosis systems are typically made from polyamide resins and cellulose acetate. Polyamide may be water permeable, but it is designed to block small ions and molecules that are usually hard to filter. For this reason, polyamide is considered a suitable material for water purification systems.