Ultrafiltration is a membrane separation technology whose membrane has a porous asymmetric structure. The ultrafiltration filtration process is a solution separation process driven by the pressure difference on both sides of the membrane and based on the principle of mechanical sieving. The operating pressure is usually 0.01~0.3 MPa, the sieving pore size is from 0.002~0.1μm, and the molecular weight cutoff is Around 1000~100,000 daltons.

★  The separation process does not undergo phase change and consumes less energy;

★  The separation process can be carried out at normal temperature, which is suitable for the concentration or purification of some heat-sensitive substances such as juices, biological preparations and certain pharmaceuticals;

★  The separation process only uses low pressure as the driving force. The equipment and process flow are simple and easy to operate, manage and maintain;

★  It has a wide range of applications. Ultrafiltration separation technology can be used for any solute molecular weight between 1000 and 500,000 Daltons or solute size between 0.005 and 0.1μm. In addition, by using a series of membranes with different molecular weight cutoffs, each component in a mixture of solutes with different molecular weights can be classified by molecular weight.

Ultrafiltration can operate in three operating modes: full flow or dead-end filtration, cross-flow filtration and concentrated water discharge filtration (Concentrate Bleed).

The cleaning process of ultrafiltration includes air scrubbing, water backwashing and forward washing of physical cleaning process, as well as chemical enhanced backwash and chemical cleaning (Cleaning In Place) of chemical cleaning process. Among them, air scrubbing uses compressed air to form strong turbulence in the water to loosen the particle pollutants trapped on the membrane surface, while water backwashing uses the direction of the water flow opposite to the direction of water production. The water flow passes through the membrane pores, which can remove the deep layers of the membrane pores and The positive wash removes pollutants on the membrane surface and removes the remaining pollutants from the backwash, and discharges the gas in the membrane module. Chemically enhanced backwashing and chemical cleaning use chemicals to remove contamination formed on the surface and interior of the ultrafiltration membrane such as colloids, organic matter, and inorganic salts. Increased cleaning frequency and cleaning intensity will help to remove various pollutants more thoroughly.

There are many materials that can be used to make ultrafiltration membranes, including polyvinylidene fluoride (PVDF), polyethersulfone (PES), polypropylene (PP), polyethylene (PE), polysulfone (PS), polyacrylonitrile (PAN) ), polyvinyl chloride (PVC), etc. In the early 1990s, polyethersulfone materials were commercially used; and in the late 1990s, polyvinylidene fluoride ultrafiltration membranes with better performance began to be widely used in the water treatment industry. Polyvinylidene fluoride and polyethersulfone have become the most widely used ultrafiltration membrane materials. When ultrafiltration is used for water treatment, the chemical stability and hydrophilicity of its materials are the two most important properties. Chemical stability determines the service life of membrane materials under the action of acids, alkalis, oxidants, microorganisms, etc., and is also directly related to the choice of cleaning processes; hydrophilicity determines the anti-pollution ability of membrane materials against pollutants in water, affecting the membrane of flux.