Ultrafiltration (UF) is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semi permeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane. Ultrafiltration is not fundamentally different from reverse osmosis, microfiltration or nanofiltration, except in terms of the size of the molecules it retains.

A membrane or, more properly, a semi permeable membrane, is a thin layer of material capable of separating substances when a driving force is applied across the membrane. Once considered a viable technology only for desalination, membrane processes are increasingly employed for removal of bacteria and other microorganisms, particulate material, and natural organic material, which can impart color, tastes, and odors to the water and react with disinfectants to form disinfection byproducts (DBP).

Advantage of filtration system:
1. No phase change occurs in the separation process. The separation process can be performed at normal temperature, which is suitable for the concentration or purification of some heat-sensitive substances such as juice, biological agents and certain drugs;
2. The equipment covers a small area, is easy to modularize design, and has strong expansion ability;
3. The separation process uses only low pressure as the driving force and consumes less energy;
4. The equipment and process are simple and easy to operate, manage and maintain;
5. Wide application range. Ultrafiltration separation technology can be used for Dalton or solute size around 0.001 ~ 0.1μm.