A comparatively short definition of membrane filter could be just like this: membrane filters are something to separate and enrich solutes in solution, and separate colloidal suspensions.
Principle of membrane filter
Microfiltration is also called a microporous filtration membrane. Microporous filtration membrane is a refined filter material that can retain large solid particles and other particles, microorganisms and some bacteria in the solution, and solvents and small molecular substances. These substances can be separated through the membrane mixture. The principle of the membrane filter is the screening process. The raw material liquid passes through a microporous membrane material to separate specific substances under the action of static pressure difference.
Membrane filter is to use the sieving mechanism of the microfiltration membrane, driven by pressure, to trap particles with a diameter between 0.1-1μm, such as suspended solids, bacteria, some viruses, and large-sized colloids.
Water flow through the membrane is not very fast, so in order to pass the required amount of water, the monomer area of the membrane device should be large, and many thin membrane tubes should be filled in a small space.
In addition, the membrane with a thickness of less than 100um must have the ability to withstand high pressure, so we should try to make various kinds of pressure-resistant films.
There are five types of membrane filter: plate-frame type, spiral type, bridge type, tubular type, and hollow fiber type. Porous materials should be used for the plate-and-frame membranes. The spiral type is coiled, and the bridge type is to insert a large area of the membrane into a small folded volume.
Tube membranes also need porous materials. Raw water passes through the inner side of the pipe and seepage flows out of the pipe. This kind of membrane filter is commonly used for passengers, but also for externally pressurized ones. The outer diameter of the hollow system is several hundred um, and most fiber tubes are packed in the system.