Microfiltration can intercept particles between 0.1 and 1 micron. The microfiltration membrane allows large molecular organic matter and soluble solids (inorganic salts) to pass through, but can block the penetration of suspended matter, bacteria, some viruses and large-scale colloids. The operating pressure difference (effective driving force) on both sides of the microfiltration membrane is generally 0.7 bar.

Ultrafiltration can intercept particles and impurities between 0.002 and 0.1 microns. The ultrafiltration membrane allows small molecules and soluble solids (inorganic salts) to pass through, but will effectively block colloids, proteins, microorganisms and macromolecular organic matter. The cut-off molecular weight used to characterize the ultrafiltration membrane is generally between 1,000 and 100,000. The operating pressure on both sides of the ultrafiltration membrane is generally 0.2 to 7 bar.

Nanofiltration is a special type of separation membrane. It is named because it can retain substances of about 1 nanometer (0.001 micron). The operating range of nanofiltration is between ultrafiltration and reverse osmosis. It retains organic matter with a molecular weight of about 200~400, and its ability to retain soluble salts is between 20~98%. The removal rate of monovalent anion salt solution is lower than that of high-valent anion salt solution. For example, the removal rate of sodium chloride and calcium chloride is 20~80%, while the removal rate of magnesium sulfate and sodium sulfate is 90~98%. Nanofiltration membranes are generally used to remove organic matter and color from surface water, remove hardness and radioactive radium from well water, partially remove soluble salts, concentrate food, and separate useful substances in medicines. The operating pressure of nanofiltration membranes is generally 3.5~16bar.

Reverse osmosis is the most sophisticated membrane liquid separation technology. It can block almost all soluble salts and organic matter with a molecular weight greater than 100, but allows water molecules to pass through. The desalination rate of cellulose acetate reverse osmosis membrane is generally greater than 95%, and the desalination rate of reverse osmosis composite membrane is generally greater than 98%. They are widely used in seawater and brackish water desalination, boiler feed water, industrial pure water and electronic grade ultrapure water preparation, drinking pure water production, wastewater treatment and special separation processes. Using reverse osmosis before ion exchange can greatly reduce operating costs and wastewater discharge. The operating pressure of the reverse osmosis membrane is generally greater than 5bar when the inlet water is brackish water, and is generally less than 84bar when the inlet water is seawater.