Author: Site Editor Publish Time: 2023-01-26 Origin: Site
Reverse osmosis is currently the most sophisticated liquid filtration technology, reverse osmosis membrane for dissolved salts and other inorganic molecules and molecular weight greater than 100 organic substances to play a retention role, on the other hand, water molecules can freely through the reverse osmosis membrane, typical soluble salt removal rate of > 95 ~ 99%. Operating pressures range from 7 bar (100 psi) for brackish feed water to 69 bar (1,000 psi) for seawater.
Nanofiltration removes impurities with particles of 1 nm (10Å) and organic matter with a molecular weight greater than 200 to 400. The removal rate of dissolved solids is 20 to 98%, the removal rate of salts containing monovalent anions (such as NaCl or CaCl2) is 20 to 80%, while the removal rate of salts containing divalent anions (such as MgSO4) is higher at 90 to 98%.
Ultrafiltration is useful for the separation of large molecules larger than 100 to 1,000 Å (0.01 to 0.1 µm). All dissolved salts and small molecules can pass through ultrafiltration membranes, removing substances such as colloids, proteins, microorganisms and macromolecular organics. Most ultrafiltration membranes have a cut-off molecular weight of 1,000 to 100,000.
Microfiltration removes particles in the range of approximately 0.1 to 1 micron. Typically, suspended matter and large colloids can be retained while macromolecules and dissolved salts are free to pass through the microfiltration membrane, which is used to remove bacteria, microflocs or total suspended solids TSS, typically at a pressure of 1 to 3 bar on both sides of the membrane.
Water treatment companies can provide special membrane cleaning agents and cleaning services, users can buy cleaning agents for membrane cleaning according to the recommendations of membrane companies or equipment suppliers.
What is the maximum permissible silica concentration in the reverse osmosis membrane feed water?
The maximum permissible silica concentration depends on temperature, pH and scale inhibitor, usually the maximum permissible concentration at the concentrated water end is 100ppm without scale inhibitor, some scale inhibitors can allow the concentration of silica in concentrated water up to 240ppm, please consult the scale inhibitor supplier.
Some heavy metals such as chromium can play a catalytic role in the oxidation of chlorine, which in turn causes irreversible performance degradation of the membrane. This is because Cr6+ is less stable in water than Cr3+. It seems that this damaging effect is stronger with metal ions of high oxidation valence. Therefore, the concentration of chromium should be reduced or at least Cr6+ should be reduced to Cr3+ in the pretreatment section.
