What is Filtration?
Filtration is a mechanical or physical operation widely used for separating substances based on relative particle size. The particle or molecule of interest may either be part of what passes through the filter or part of what is retained by the filter. A successful separation may be completed in a single filtration step or may require many steps. The sample may be a liquid, gas, or supercritical fluid.
Filtration can be driven by gravity, vacuum or pressure. Gravity is generally used at a small scale in laboratory applications where filter paper is used to remove particles from a liquid. Gravity filtration is slow and requires filters with fairly large pores. In the majority of applications, a sample is applied to the filter and forced through it under pressure or sucked through it by vacuum. Obviously, filtration requires a housing so that the sample can be isolated to one side of the filter and kept separate from the filtrate.
The types of filtration used in biotechnology include:
- Microfiltration
- Ultrafiltration
- Reverse Osmosis
Microfiltration and ultrafiltration are the most widely used methods and differ according to the size of what is being separated. Microfiltration is used to separate particles ranging from about 0.05 to 10 µm. Ultrafiltration is used to fractionate or concentrate molecules ranging from about 1000 to 1,000,000 Daltons. Reverse osmosis, used largely for water purification, separates very low molecular weight molecules. All three filtration types use membranes as the filtering material.
Developed in Germany in 1935, membrane filters found immediate application in the assessment of safe drinking water and were used in Germany after World War II, where saturation bombing resulted in widespread water contamination.
- History of Membrane Filters
- Types of Filtration
- Depth Filters
- Membrane Filters
- Microporous Filters
- Ultra Filters
- Reverse Osmosis Filters