Filtration is a process of separating solid phase particles from a liquid, where the particles form a suspended matter in that liquid. The product of filtration is a liquid purified to the required level and condensed solid phase, separated from that liquid. The suspention of the solid phase is characterized by the mass concentration of the solid phase the size of the particles that create the suspension.
Taking into consideration the properties of the suspension and the requirements of its separation, the following types of filtration are distinguished:
- cake filtration,
- dynamic filtration,
- membrane filtration,
- depth filtration,
The first two types of filtration are usually used for the preseparating of the suspension. They are often used for the systems with high concentration of particles of a large size (over 100 µm).
The membrane filtration is used for the removing of small amounts of particles of submicron and nanoparticles (ultra and nanofiltration). It is generalny used for such special tasks as clean Technologies and medical purposes.
Depth filtration is used for removing solid phase particles from liquids, with mass concentration of those particles of 10 mg/l, by filtering suspended matter against a deposit layer, composed of grains or fibers. While passing through the layer, the particles deposit on grain or fibers, creating an agglomerate of removed particles. Pure liquid leaves the filter.
fig.1 Particles deposited on the fibers
Depth filtration is used for puryfying liquids that include particles of the size of 0.5 - 100 µm. It is applied in the systems for puryfying drinking and technological water, and other liquids. The depth filtration is often combined with membrane filtration as a pre-stage of the cleaning and as protection of the membrane filters against its fouling. |
