The classification of membranes filters is based on 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 pores of the membrane are from coarse to finely, microfiltration membranes, for example, its pore diameter is 0.05um or more, or the molecular weight is 1000 or more.
NF membranes have particle pore sizes ranging from 100 to 1000 molecular weight. While for RO membranes, the size is 10 moles.
These four kinds of membrane filters have different applications as their separate particle size ranges show. MF membrane filter is to remove the colloid and high molecular organic matter. NF, as a transition, is responsible for removing substances between UF and RO, such as rihalomethane, odor, chroma, pesticides, soluble organic matter, Ca, Mg, etc. RO’s duty is the removal of salt and inorganic salt. Not as verstile as the NF membrane, but it still plays a significant role in the membrane filtering field.
In addition to the above four, there are ion-exchange membranes and gas permeation membranes. MF, UF, NF, and RO separate solids from the liquids because of pressure. However, Ion exchange membranes are driven by electricity to separate salt molecules and promote the desalination of seawater. A gas permeation membrane is a new type of membrane that can concentrate ethanol and desalinate seawater through the gas.