Membrane separation technology is basically a means to separate solutes from the solvent. Membranes that achieve separation by using pressure difference as a driving force include reverse osmosis (RO), ultrafiltration (UF), and microfiltration (MF) membranes. They are used to separate colloids, small molecules, and ions in liquid as well as for purification and concentration. Typical uses of reverse osmosis membrane include seawater desalination, where fresh water is obtained by applying high pressure of about 6 MPa to seawater, the concentration of fruit juice, and wastewater treatmen

Typical uses of ultrafiltration membranes are diverse and include the separation of not only polymers but also viruses, bacteria, yeast, colloid, fine particles, etc., purification, and concentration. Because membrane filtration can take place even below room temperature, it is useful for pharmaceutical and food processes, which are susceptible to deterioration, and is used for removing endotoxins and filtering sake spoilage lactic acid bacteria from unpasteurized sake.

Typical uses of microfiltration membranes include precise and efficient removal of suspended substances, colloid particles, and microbial cells from water, organic solvent, and liquid chemicals as well as of airborne particles and bacteria from gas, such as air and other gases, purification, and separation.

In addition, there is dialysis membrane, where separation is achieved by using concentration difference across the membrane as the driving force, and electrodialysis, where the electric potential difference is used as the driving force to separate molecules in a solution by using electrochemical characteristics and molecular size. A concrete example of dialysis membrane filtration is blood purification, where impurities are removed from the blood of a patient with chronic renal failure by passing dialysate through the dialysis membrane. A hollow fiber membrane module is widely used for this purpose due to its small size and high reliability.

Cited from Japan Water Research Center, “Membrane Filtration in Water Supply, with Q&A, Glossary of Filtration Methods in Water Supply” (partially modified)