Ultrafiltration membrane separation based on a physical sieving mechanism, selectively retaining macromolecules through pore size restriction while allowing water and small molecules to pass through. Their core characteristics can be systematically summarized as follows:
Principle of Ultrafiltration Membrane Separation
UF membranes feature an asymmetric porous structure, with a dense skin layer pore size of 2-100 nm (ASTM defines <0.1 μm), achieving selective filtration through pressure-driven processes.
Particles (≥10 nm), colloids, bacteria (0.2-5 μm), and viruses (20-400 nm) are retained, while water, minerals (ionic dissolved salts), and small organic molecules (MW ≤1,000 Da) freely pass through.
The ultrafiltration membrane has a bacterial removal rate of ≥ 6 logarithmic units (99.9999%), a virus removal rate of ≥ 4 logarithmic units (99.99%), and a turbidity of < 0.1 NTU.
Operating Parameters and Performance
- Operating Pressure: 0.05-0.6 MPa; typical operating pressure range: 0.1-0.3 MPa.
- Molecular Weight Cut-Off (MWCO): 1,000-500,000 Da, corresponding to a pore size of approximately 0.01-0.1 μm.
- Substance Retention Characteristics: Non-ionized small molecules (e.g., glucose) and inorganic salts (e.g., Na⁺, Ca²⁺) can pass through, maintaining water mineral balance.
- Treatment Efficiency: Critical flux design and cross-flow filtration reduce concentration polarization, stabilizing flux at 50-135 LMH.
Application
- Drinking Water Purification: UF replaces traditional sand filtration, producing water with SDI <3, directly connecting to reverse osmosis systems.
- Wastewater Reuse: MBR coupled with UF achieves SS <1 mg/L and recovery rates of 75-90%.
