Basic knowledge of membranes

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Release Date:

2023-09-08

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The main membrane separation processes include:Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), dialysis (DA), electrodialysis (ED), electrodesalination (EDI), pervaporation (PV), membrane extraction (ME), membrane distillation (MD), liquid membrane technology (LM), gas separation (GS), etc.

Commonly used water treatment separation membrane products:The main difference between microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) is the size of the pore size. The pore size of RO membrane, NF membrane, UF membrane, and MF membrane increases sequentially. Each membrane plays a different interception role in different application environments. RO and NF membranes can separate ion grade substances from water, UF membranes are usually used to separate larger molecules, and microfiltration membranes are mainly used to intercept suspended particles, bacteria, viruses, algae, etc.

 

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Microfiltration(MF)

Microfiltration can intercept particles between 0.1 and 1 micrometer, and the microfiltration membrane allows the passage of macromolecular organic matter and soluble solids (inorganic salts), blocking the passage of suspended solids, bacteria, some viruses, and large-scale colloids.

 

Ultrafiltration (UF)

Ultrafiltration can intercept particles and impurities between 0.002 and 0. l micrometers. Ultrafiltration membranes allow small molecule substances and soluble solids (inorganic salts) to pass through, effectively blocking colloids, proteins, microorganisms, and macromolecular organic matter. The cutting molecular weight used to characterize ultrafiltration membranes is generally between l, 000 and 200000 (DALTON).

 

Nanofiltration (NF)

Nanofiltration is a special and promising separation membrane, named after its ability to retain substances of approximately 1 nanometer (0.001 micrometer) in size. The operating range of nanofiltration is between ultrafiltration and reverse osmosis, with a molecular weight of about 100-1000DA to retain organic matter and a capacity to retain soluble salts ranging from 20-99%. The removal rate of monovalent anionic salt solutions is lower than that of high valent anionic salt solutions, such as sodium chloride and calcium chloride, with a removal rate of 20-80%, The removal rate of magnesium sulfate and sodium sulfate is 90-99%.

Nanofiltration membranes are generally used to remove organic matter and chromaticity from surface water, remove hardness and radioactive substances from groundwater, partially remove soluble salts, and concentrate and separate special components in food and medicine.

 

Reverse osmosis(RO)

Reverse osmosis is one of the most precise membrane liquid separation technologies, which can block almost 99.99% of soluble salts and organic compounds with a molecular weight greater than 100 (DALTON), but allows water molecules to penetrate. The desalination rate of reverse osmosis membranes can generally exceed 99%. RO membrane is widely used for seawater and brackish water desalination, boiler makeup water, industrial pure water and electronic grade ultra pure water preparation, production of drinking pure water, advanced wastewater treatment, special concentration and separation, and zero and near zero discharge

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