Membranes filters are classified according to the size of particles retained in raw water. Membrane holes are divided into microfiltration membranes (MF), ultrafiltration membranes (UF), nanofiltration membranes (NF) and reverse osmosis membranes (RO). The pore size of the MF membrane is more than 0.05um, or its molecular weight is more than 1000. The removal of colloids and macromolecule organic compounds is the object of the MF membrane.
The pore size of NF membranes ranges from 100 to 1000 molecular weight. It removes substances between UF and RO to remove trihalomethane, odor, chroma, pesticides, soluble organic matter, Ca, Mg and so on. The particle size of RO is 10 moles, and the removal of salt and inorganic salt is the object of RO separation.
The pressure of RO seepage water is 1-2 times higher than that of RO seepage water. In addition to the above four, there are ion exchange membranes and gas permeation membranes. MF, UF, NF, and RO are driven by the pressure to separate solids from the liquid. Ion exchange membranes are driven by electricity to separate salt molecules and promote desalination of seawater. Gas permeation membrane is a new type of membrane which can concentrate ethanol and desalinate seawater through the gas.
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