Detailed Explanation of the Filtration Principle of Industrial Ultrapure Water Microfiltration

Microfiltration (MF), along with reverse osmosis and ultrafiltration, belongs to pressure-driven membrane separation technologies. Microfiltration is a membrane process that uses hydrostatic pressure difference as the driving force, utilizing the "sieving" effect of a sieve-like filter medium membrane for separation. Its principle is similar to ordinary filtration, but the filtered particles are between 0.05 and 15 μm, hence it is also called precision filtration and represents the latest development in filtration technology. It primarily removes particulate, submicron, and fine particles. Under hydrostatic pressure, solvents, water, salts, and macromolecules are widely used to explain the separation mechanism of microfiltration. This theory posits that microfiltration membranes have countless micropores. These existing pores of varying sizes, under the action of hydrostatic pressure difference, act like a sieve, trapping solutes and particles larger than the pore size, thus separating components of different sizes and achieving the separation purpose. Since each square centimeter of filter membrane contains tens of millions or even hundreds of millions of micropores, with a porosity accounting for 70%-80% of the total volume, the resistance is very low, and the filtration speed is relatively fast. Its operating pressure is generally around 0.7-7 kPa.

Microfiltration primarily removes micron- and submicron-sized suspended solids from gaseous and liquid phases to achieve purification, separation, and concentration. It focuses on separating particles larger than 0.05 μm from solutions, cutting off particles with relative molecular masses greater than one million. During microfiltration, the filter media does not detach, no impurities dissolve, it is non-toxic, easy to use and replace, and has a long lifespan; it is also known as absolute filtration and is well-suited for filtering suspended particles and microorganisms. Microfiltration demonstrates unique efficacy in water purification, removal of bacteria and particles from pharmaceuticals, detection of bacteria and microorganisms, laboratory analysis, and medical diagnosis, thus its applications are very wide-ranging. Currently, it is mainly used in the production of sterile liquids, the separation of biological agents, the preparation of ultrapure water, and the detection and analysis of biological and microbial substances in air filtration.