Glossary of Terms 

The entrapment of a particle or gas within the body of a filtering material – therefore only strictly applicable to liquids, but also used of entrapment within the depth of a thick filter medium.

The energizing of the surface of (usually granular) carbon to render it capable of efficient removal of, e.g. odours from a gas or a colour from a liquid by adsorption

Retention of gas, liquid or solid on a surface of a solid filtering material which thus needs to be finely granular or fibrous to present the highest possible surface area per unit volume

Organisms which require oxygen to live.

A dispersion of small liquid particles in a gas.

A backward surge of pressure from downstream to upstream of the filter. Can be the result of closing a valve or air entrapped in a liquid system.

Reversal of a fluid flow through the filtration media, as an attempt to clean or “regenerate” a filter.

A unit of pressure. One bar = 14.5 psi.

Measurement of filter retention efficiency. Ratio of particles exposed to a filter (as feed stream) to particles present in the filtrate.

A test to determine the maximum pore size openings of a filter. The differential gas pressure at which a wetting liquid (usually deionised water) is pushed out of the largest pores and a steady stream of gas bubbles is emitted from a wetted filter under specific test conditions. Used as filter integrity test with specific, validated, pressure values for specific pore-size of filters.

A Nitrile rubber seal compound. This is a generic term covering many formulations.

Solids deposited on the filter media.

Negative pole or electrode of an electrolytic system.

A centrifuge in which the separation of solids from liquids is achieved through a filter medium which will be basically cylindrical in shape, with the filtrate draining outwards from the centre, under the centrifugal force.

The difference in pressure between the upstream and downstream sides of the filter. May be modified with applied, available, clean, dirty, initial, or maximum.

Deionized water; water processed through an ion exchange process by passing through both cation and anion exchange resin beds, or a mixed resin bed to remove both positive and negative ions. The purity of water is measured by its electric resistance.

Filtration of suspended solids within the thickness of the filter medium rather than at its surface.

Amount of dirt or debris retained by a filter in grams per unit area of the filter medium.

Food and Drug Administration.

In the present context, a filter is the mechanical device that achieves the required separation by filtration and that hold the filter media

A measurement of how well a filter retains particles. Usually expressed as the percentage of retention of particles of a specific size by a filter.

The permeable material that removes particles from a fluid being filtered.

The effluent of a filtration process. The filtered product.

The process by which particles are removed from a fluid by passing the fluid through a permeable material.

It is the speed at which a liquid flow’s and is measured in gallons or litres per minute. Flow rate of a liquid can be affected by the liquids’ viscosity, differential pressure, temperature and type of filter used.

Material inserted between contact surfaces of a joint to ensure a fluid-tight seal.

Filter medium produced in the form of minute tubes, which are bundled together to allow sufficient filter area to be built into a sensibly sized filter.

The pressure entering the inlet side of the filter. Also called upstream pressure or line pressure.

A non-destructive test which is used to predict the functional performance of a filter. The valid use of this test requires that it be correlated to standardized bacterial or particle retention test. Examples: Bubble Point Test, Diffusion Test, Forward Flow Test, Pressure Hold Test.

The average diameter of all the pores passing through filter medium, used the same as effective pore size.

In filtration, the material through which fluid passes in the process of filtration and which retains particles. Also, the nutrients containing solutions in which cells or microorganisms are grown.

Migration of the materials making up the filter medium. May cause contamination of the filtrate.

A continuous matrix with pores of defined size.

Separation of particles ranging from 0.1µm to 10µm from a fluid by passing the fluid through a membrane. Used for clarification, sterilization or to detect or analyze bacteria and other organisms and particulate matter.

Also referred to as minimum critical bubble point pressure, it is a filter specification derived from diffusional flow – bubble point curves for a few filters. It is a diffusional flow pressure just before the onset of bulk flow.

The pressure exiting the outlet side of the filter. Also called downstream pressure.

Any discrete unit of material structure; a discernible mass having an observable length, width, thickness, size and shape.

The degree to which a fluid will pass through a permeable substance under specified conditions. The space or void volume between molecules allowing fluid flow.

The inverse (negative) logarithm to the base 10 of hydrogen ion concentration. Measure of a substance’s acidity or alkalinity with 7 being neutral. Measure of hydrogen ion concentration.

A thermoplastic polymeric material which is resistant to a broad range of chemicals. When used as a membrane, polypropylene is hydrophobic.

Commonly used membrane material. Has excellent flow rates, high mechanical strength, resistant to a broad range of temperatures (can be sterilized) and is hydrophilic. Is not resistant to exposure to many organic solvents.

Diameter of pore in membrane.

Polytetrafluoroethylene; More commonly known as Teflon. Highly durable and resistant to a broad range of temperatures and chemicals. PTFE is hydrophobic.

Ability of a filter to recover bacteria (or other defined particles) from a solution. In Membrane Filtration Technique, expressed as percent of bacteria originally present or observed on a comparable pour plate.

Ability of a filter to retain particles (total number or those of a specific size) suspended in a gas or liquid. Expressed as a percent of particles originally present.

A filtration separation method (usually crossflow or stirred cell type) operating at 200-1500 psi to overcome osmotic pressure. Pore sizes are typically in the order of 10-10meters (107mm). Efficiency is usually described in terms of percent salt rejection with 90% being common.

A filter with straight-though capillary pores with identical dimension, e.g. a screen filter.

The process by which steam, compressed air, or gas is forced into a liquid through perforations or nozzles in a pipe as part of fermentation.

To make or be free of any viable microorganisms. Demonstrated by testing to show the absence of microorganisms.

A non-fiber releasing filter which produces an effluent in which no microorganisms are demonstrable when tested by the method specified in the current edition of the United States Pharmocopeia. Usually accepted as 0.2µm pore-size absolute rating.

Also “interfacial tension.” Tendency of the surface of a liquid to contract to the smallest area possible under the existing circumstances. Defined as a force in dynes acting on a line 1 cm long lying in the surface of the liquid.

A soluble compound that reduces the surface tension of a liquid or reduces interfacial tension between two liquids (causing formation or micelles) or between a liquid and a solid, thereby functioning as a wetting agent.

A membrane filtration process that deals with large molecules, lying between microfiltration and nanofiltration in both degree of fineness of filtration and operating pressure.

The depression of pressure below atmospheric pressure.

Demonstration that a process or product does what it is supposed to do by challenging the system and providing complete documentation.vv

A resistance to flow as a function of force, or gradual yielding of force. Viscosity is in units of centipoises or centistokes. For a given filter and differential pressure, flow rate will decrease as viscosity increases; e.g. oil will have a flow rate much slower than water. The viscosity of water is 1 centipoise.

A surfactant added to a membrane to assure complete intrusion (wetting) by a high surface tension fluid such as water.