Meaning Term
The test procedure for determining the bubble point of a microfiltration membrane.
Bubble point test
The term cartridge refers to hollow fiber filter unit, for either microfiltration or ultrafiltration.
Cartridge or cartridge filter
The term cassette refers to a filter unit containing stacked flat sheets of membrane separated by support screens. Cassette
Cassettes from GE are exclusively used for ultrafiltration. The height of the path that the feed/retentate solution must pass through for a flat membrane cassette. Channel height
Also called retentate. The part of the process solution that does not pass through a cross flow filter.
Concentrate
In cross flow filtration, the feed solution flows parallel to the surface of the membrane. Driven by pressure, some of the feed solution passes through the membrane filter. The remainder is circulated back to the feed tank. The move- ment of the feed solution across the membrane surface helps to prevent the buildup of materials on the surface. Cross flow filtration
(CFF)
Also called retentate flow rate. Cross flow rate
The flow rate of feed solution that flows across the surface of the filter and exits the filter as retentate. Higher cross flow rates help "sweep away" material that otherwise ac- cumulates on the surface of the filter. Cross flow rate is most often measured at the retentate outlet.
See Nominal molecular weight cutoff (NMWC). Cutoff
See normal flow filtration. Dead-end filtration
Pressure differential between the feed and retentate lines. The ΔP equals the feed pressure minus the retentate pressure.
ΔP
An operation that uses ultrafiltration filters to remove salts or other microsolutes from a solution. Small molecules pass into the permeate while larger molecules are retained in the retentate.
Diafiltration
Microsolutes are generally so easily washed through the filter that for a fully permeated species about three volumes
A Abbreviations and glossary
Meaning Term
Diafiltration exchange factor = Diafiltration buffer volume / Sample volume
Diafiltration exchange factor
See ΔP. Differential pressure
See normal flow filtration. Direct flow filtration
The active area of the membrane exposed to flow. Effective filtration area
Substances that may dissolve or leach from a membrane filter during filtration and contaminate the process solution. For example, these might include wetting agents in the membrane, membrane cleaning solutions or substances from the materials used to encase the membrane. Extractables
Material or solution that is fed into the filter. Feed
The pressure measured at the inlet port of a cartridge or cassette.
Feed pressure
The surface area of filter membrane inside a membrane filter.
Filter area
Filter efficiency represents the percentage of a given size particle removed from the fluid by the filter.
Filter efficiency
The total length that a feed solution travels from inlet to outlet. Flow path length is an important parameter to consider when doing any process development, system design or scale-up or scale-down experiments. Flow path length, nom-
inal flow path length
The flow path length and other fluid channel geometries such as lumen diameter or channel height can affect the fluid dynamics of the system and will directly affect pump requirements and differential pressure of the filtration step. Flux represents the volume of solution flowing through a given membrane area during a given time. Expressed as LMH (liters per square meter per hour).
Flux
A build up of material on the membrane surface that re- duces the filtration rate. Unlike the gel layer, this material is not redispersed in the bulk stream by higher cross flow rates.
Fouling
Meaning Term
During the filtration process, a thin layer of particles or molecules may build up at the membrane surface. Under extreme circumstances this concentrated layer may form a gel, blocking flux across the membrane and potentially resulting in increased TMP.
Gel layer
Operating at a higher cross flow may reduce the thickness of the gel layer.
Volume of fluid in the system tubing and filter. Hold-up volume
A tube of membrane, sealed inside a cross flow cartridge. The feed stream flows into the lumen of one end of the hollow fiber and the retentate (the material that does not permeate through the walls of the hollow fiber) flows out of the other end. The material that passes through the membrane (walls of the hollow fiber) is called the permeate. Hollow fiber
The mechanical structure that surrounds and supports the membrane or filter element. The housing normally has feed, retentate and permeate ports that direct the flow of process fluids into and out of the filter assembly.
Housing
The pressure of a fluid at the feed port of a membrane filter. Inlet pressure
The volume of solution that will pass through a membrane filter before the permeate output drops to an unacceptable level.
Loading
The degree to which the original performance of a mem- brane can be restored by cleaning.
Membrane recovery
The process of removing particles from a liquid by passing it through a porous membrane under pressure. Microfiltra- tion usually refers to removing submicron-sized particles. Microfiltration
A thin, porous film or hollow fiber having pores ranging from 0.1 to 10 μm. Cross flow microfilters typically have pores ranging from 0.1 to 1.0 μm.
Microporous mem- brane
Also called minimum operating volume. The least amount of fluid able to be handled effectively by a filtration system. Minimum process vol-
ume
A rating that indicates the percentage of particles of a specific size or molecules of a specific molecular weight that will be removed by a filter. No industry standard exists; Nominal filter rating
Meaning Term
The pore size designation, usually in kiloDaltons (kD), for ultrafiltration membranes. No industry standard exists; hence the NMWC ratings of different manufacturers are not always comparable.
Nominal molecular weight cut off (NMWC)
In normal flow filtration, liquid flows perpendicular to the filter media. Material that does not pass through the filter remains on the filter surface.
Normal flow filtration
See Flow path length. Nominal flow path
length
The water flux at 20°C divided by pressure. Common units LMH/psi, LMH/bar.
Normalized water per- meability (NWP)
Also called filtrate. Any components of the feed solution that passes through the membrane.
Permeate
A measurement of the open space in a membrane. The higher the membrane porosity, the more pores there are, and hence a higher flow rate is expected.
Porosity
The portion of the feed solution that does not pass through the filter. Any component that does not pass through the membrane flows out of the filter and back to the feed container.
Retentate
The ability of a membrane filter to retain an entity of a given size.
Retention
The ratio of velocity and distance expressed in units of s-1. The shear rate for a hollow fiber cartridge is based on the flow rate through the fiber lumen and is used to control cross flow.
Shear rate
Disruptive force that arises in connection with a steep flow gradient. Shear stress can disrupt cells and denature pro- teins.
Shear stress
The process of sterilizing a filter unit, such as a hollow fiber cartridge, with steam without removing the unit from the separation system.
Steam-in-place (SIP)
Mechanism for removing particles from a feed stream based strictly on the size of the particles. Retained particles are held back because they are larger than the pore opening.
Size exclusion
Meaning Term
See Cross flow filtration. Tangential flow filtra-
tion
The pressure drop across the filtration membrane. Transmembrane pres-
sure
The separation of macrosolutes based on their molecular weight or size.
Ultrafiltration
The feed side of a separation process. Upstream
Measurement of the amount of water that flows through a given membrane surface area in a set time. See also Flux. The water flux test is commonly used to assess cleaning efficacy.
Water flux
A Abbreviations and glossary
Index
A
abbreviations, 73 air diffusion test, 29 air sensors, 11
ÄKTACrossflow system, 15 ÄKTA flux system, 15 application areas, 8
B
basic configuration, 10 bubble point test, 29