Types of Filtration
Filtration is widely used in biotechnology for separating substances based on relative particle size. Types of filtration most commonly used include:
- Microfiltration (MF)
- Ultrafiltration (UF)
- Reverse Osmosis and nanofiltration (RO/NF)
Microfiltration
Microfiltration (MF) is the physical retention of particles behind a filter medium while the liquid they were suspended in passes through the filter. Particles are retained because they are larger than the pores in the filter. Other factors affecting retention are fluid viscosity and chemical interactions between the membrane and the particles in the solution. Microfiltration removes particles with a pore size of .05 and 5.0 µm.Ultrafiltration
Ultrafiltration (UF) works basically that same way as microfiltration, except that the pore sizes are considerably smaller. Solutes are retained behind the filter on the basis of molecular size while the bulk of the liquid and dissolved salts pass through. A pressure gradient across the membrane, known as transmembrane pressure, drives the filtration process. Ultrafiltration membranes are designed for the concentration and separation of complex protein mixtures.Reverse osmosis (RO) and nanofiltration (NF)
Reverse osmosis (RO) and nanofiltration (NF) are the processes of separating very low molecular weight molecules (typically <1500 Daltons) from solvents, most often water. The primary basis for separation is rejection of solutes by the membrane on the basis of size and charge. Unlike UF membranes, RO and NF membranes retain most salts, as well as uncharged solutes. NF membranes are a class of RO membranes which allow passage of monovalent salts but retain polyvalent salts and uncharged solutes > ~400 Daltons. Reverse osmosis membranes (RO) have very small pore sizes and are designed to separate ions from each other.Scaling from analytical to industrial
For most high volume filtration applications, the properties of membrane and depth filters are clearly complementary. Depth filtration allows the removal of a bulk of particles economically. Composite filtration combines relatively high dirt-holding capacity with clearly defined retention characteristics.Membrane filtration permits complete removal of particles and microorganisms above a certain size as qualified by pre-established specifications and testing regimens.
Type of Filters