The Operating Principle of the Hollow Fiber Ultrafiltration Membrane

The operating principle of hollow fiber ultrafiltration membranes is to use a certain pressure and flow rate to allow raw water to pass through the membrane, where impurities in the water cannot pass through the membrane pores, achieving the purpose of separation.

Figure 1 Ultrafiltration Membrane

The basic principle is to use an asymmetric microporous structure and a semi-permeable membrane medium at normal temperature, relying on the pressure difference on both sides of the membrane as the driving force and using a cross-flow filtration mode to allow solvents and small molecular substances to pass through while retaining large molecular substances and particles such as proteins, water-soluble polymers, and bacteria.

There are approximately 6 billion 0.01-micrometer micropores on the tube wall of the ultrafiltration membrane, and only water molecules, beneficial mineral elements in water, and trace elements can pass through the pore size. Bacteria, as well as colloids, rust, suspended solids, sediment, and large molecular organic substances larger than bacteria, can be retained by the ultrafiltration membrane, thus achieving the purification process.

Figure 2 Hollow Fiber UF Membrane

Hollow fiber ultrafiltration membranes are a relatively mature and advanced form of ultrafiltration technology. The outer diameter of the hollow fiber is 0.5-2.0mm, and the inner diameter is 0.3-1.4mm. The tube wall of the hollow fiber is covered with micropores, and the pore size is expressed by the molecular weight of the intercepted substance.

The intercepted molecular weight can reach several thousand to several hundred thousand. Raw water flows under pressure on the outside or inside of the hollow fiber, constituting external pressure and internal pressure types. 

Ultrafiltration is a dynamic filtration process, and the intercepted substances can be removed with concentration, without clogging the membrane surface, and can operate continuously for a long time.

Figure 3 Ultrafiltration process

Advantages of Hollow Fiber Ultrafiltration Membranes

Figure 4 Advantages of hollow fiber ultrafiltration membranes

High strength: Advanced membrane formation technology and unique module structure can provide excellent filtration efficiency and durability, and the tensile strength of a single membrane can reach 6N.

Good rigidity: The membrane is designed to operate at a pressure as low as 0.02MPa to permeate enough water, with a maximum TMP of more than 2.5 bars and a highly compressible structure.

Excellent extensibility: The elongation rate of the membrane is as high as 300%, and the membrane fiber avoids the phenomenon of stretching and breaking.

High crystallinity: Compared with similar domestic products, the membrane has good chemical resistance, mechanical strength, and longer service life.

Large flow rate: The permeation flux exceeds 100OLMH at 25℃ and 0.1MPa.

Low-pressure drop: Due to its asymmetrical and gradually narrowing structure, the membrane is easy to backwash.

Issues to Note for Hollow Fiber Ultrafiltration Membranes

1. The raw water should be sterilized with a bactericide before filtration, and a suitable residual chlorine level should be maintained because bacteria and microorganisms have a strong pollution capacity and can produce more impurities and foreign substances.

2. Pre-filtering to remove solid particles and suspended solids, and coagulation and sedimentation.

3. Pre-treatment should be used when the colloid content is high, otherwise, it will increase the working pressure of the hollow fiber membrane and cause unnecessary damage.

4. Timely backwashing, rapid washing, and periodic chemical cleaning are helpful to ensure the cleanliness of the membrane, and the quality of the membrane treatment work, and extend the service life of the membrane.

Figure 5 Backwashing

5. Dynamic filtration should also be performed regularly.

6. When starting and shutting down the device, raise and lower the pressure slowly to prevent strong impacts that can cause excessive pressure on the membrane and result in damage to the membrane.

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