BACKPRESSURE:
A positive pressure applied to the output of a filter on either filtrate or
retentate streams.
BACK-PULSE:
An intermittent application of high pressure clean filtrate momentarily forced
back through the membrane/filter media to clear the membrane from coatings.
BACKWASH:
Reversal of clean fluid flow through the filter media, as an attempt to clean,
unblock or "regenerate" a filter.
BACTERIA:
Free living simple celled, microscopic organisms having a cell wall and
characteristic shape.
BAR:
A unit of pressure. One bar = 14.7 psi = 100kpa.
BIOLOGICAL OXYGEN DEMAND (BOD):
The amount of oxygen required by aerobic micro-organisms to decompose the
organic matter in a sample of water, such as that polluted by sewage. It is
used as a measure of the degree of water pollution. Also called biochemical
oxygen demand.
BUBBLE POINT PRESSURE:
A test to determine the pore size openings of a filter membrane. The
differential gas pressure at which a wetting liquid (usually 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.
CAKE:
Solids deposited on the filter media from the stream being filtered. These can
become a filter in themselves.
CENTIPOISE (cP):
(N s/m2; N = Newton) A unit of absolute viscosity. One centipoises equals 0.01
stoke.
CENTISTOKE (cSt):
A unit of kinematic viscosity (m2/s). One centistokes equals 0.01 stoke.
CENTRIFUGATION:
Process of separating two substances of differing densities by high speed
spinning to create centrifugal force. Typically used to separate suspended
particles from liquid. Ineffective if the solids/fluid are “neutral” density.
CHEMICAL OXYGEN DEMAND (COD):
The quantity of a specified oxidant that reacts with a sample under controlled
conditions. The quantity of oxidant consumed is expressed in terms of its
oxygen equivalence. COD is expressed in mg/L 02. COD is often measured as a
rapid indicator of organic pollutant in water. It is normally measured in both
municipal and industrial wastewater treatment plants and gives an indication of
the efficiency of the treatment process.
CLARIFICATION:
To clear a liquid by filtration, by the addition of agents to precipitate
solids, or by other means.
CLEAN IN PLACE (CIP):
CIP is a term used within the Food & Beverage industry for the chemical
cleaning of process lines and equipment. Normally the cleaning system is
permanently piped into place. It can be either, or both acid and alkali wash.
Alkali wash is typically caustic soda at a temperature above 65 degrees
centigrade.
COLD STERILIZATION:
Removal of all bacteria by filtration through a sterilizing grade 0.2µm
absolute filter.
COMPATIBILITY:
Term used in relation to the non-reactivity of filter materials with the
substance to be filtered.
CONCENTRATOR:
An apparatus or method for removing some of the water from a sample to
concentrate the substances dissolved or suspended in it; usually used to
concentrate solutions of biological macromolecules, e.g., proteins and nucleic
acids.
CROSS-FLOW (TANGENTIAL FLOW) FILTRATION:
A filtration system in which the feed and retentate streams flow typically at
90 degrees to the filtrate stream. The retentate stream is returned to merge
into the feed stream, while a portion of it (filtrate) passes through the
filter media, resulting in concentration of the feed stream (ie: a semi-closed
system)
DIA-FILTRATION:
A crossflow filtration process allowing for the transfer of low molecular
weight species, water and/or solvents through a membrane without changing the
solution volume. This process is used for purifying retained large molecular
weight species, increasing the recovery of low molecular weight species, buffer
exchange and simply changing the properties of a given solution.
DIATOMACEOUS EARTH FILTRATION:
A filtration method that employs a medium consisting of microscopic shells of
single celled plants known as diatoms. Typically used in wine making as a
coating to rotary drum vacuum filters.
DEAD END (CONVENTIONAL) FILTRATION:
Feed stream flows into the filter medium under pressure. Filtrate will pass
through the media and exit while retentate needs to be cleared with a
disruption to the filter feed flow.
DEPTH FILTER:
A matrix of filter media creating an extended and tortuous path with pores of
undefined size and shape, so to capture the “particles” within the membrane or
filter media. A depth filter is more commonly used for streams with low solids
loadings, as cleaning of the depth filter can become an issue.
E. coli:
Escherichia coli; The most prevalent bacteria in the gastro-intestinal tract of
humans and animals. It occurs in solids and water as a result of fecal
contamination.
EFFECTIVE FILTRATION AREA:
The portion of filter that fluid flows through during the filtration (EFA)
process.
EFFLUENT:
The fluid which has passed through a filter (syn: filtrate or product stream);
also, outflow from other types of treatments such as wastewater treatment
plants.
FERMENTATION:
Generally referred to as enzymatically controlled breakdown of an energy rich
compound (as a sugar to produce ethyl alcohol, carbon dioxide, and energy) by
the action of yeasts which carry the necessary enzymes (bacterial fermentations
also occur).
FILTER (noun):
A device for carrying out filtration/separation which consists of the filter
medium and suitable holder for constraining and supporting the filter in the
fluid path.
FILTER (verb):
To pass a fluid containing particles through a filter medium whereby particles
are removed from the fluid.
FILTER MEDIUM:
The permeable material that removes particles from a fluid being filtered.
FILTRATE:
The filtered product.
FILTRATION:
The process by which particles are removed from a fluid by passing the fluid
through a permeable material.
FLOW DECAY:
Decrease in flow rate as a result of filter plugging or clogging.
FLOW RATE:
It is the volumetric rate at which a liquid flows. Flow rate of a liquid can be
affected by the liquids' viscosity, differential pressure, temperature and type
of filter used.
FLUX RATE:
The volumetric rate of which filtrate is “produced” through a filter. Typically
it is measured in volume passed per area of filter media per hour, eg: litres
per square metre per hour.
GAUGE PRESSURE:
The pressure measured by a pressure gauge or sensor. Pressure above ambient
pressure. Symbolized as psig when the pressure is expressed in psi units.
GEL LAYER:
Thin layer of retained molecules that forms on a membrane surface during
filtration.
HOLD-UP VOLUME:
Also called Retention Volume. Volume of fluid retained in a filter and/or
housing after purging the assemble with air or suitable gas.
HYDROPHILIC:
Having an affinity for water; a membrane which will wet with aqueous solutions.
HYDROPHOBIC:
Literally, fearing water; a membrane which cannot be wetted by and repels
aqueous and other high surface tension fluids; when pre-wetted with low surface
tension fluid, such as alcohol, the filter will then wet with water. INERT:
Chemical inactivity; unable to move; totally unreactive.
ION EXCHANGE COLUMNS:
Vessels filled with ion exchange resin (anion, cation, or mixed) for producing
conditioned or DI Water. Also, type of column used for Ion Exchange
Chromatography (IEC).
MEDIA:
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.
MEDIA MIGRATION:
Migration of the materials making up the filter medium. May cause contamination
of the filtrate.
MEMBRANE FILTER:
A continuous matrix with pores of defined size.
MICRO-FILTRATION:
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.
MICROMETER (m)/ MICRON:
Also referred to as "micron." It is a 1/1,000,000 of a meter (1µm = 10-6µm =
.000039 in); 25.4µm = 0.001 inch; 60µm = approximately the diameter of a human
hair.
MINIMUM BUBBLE POINT PRESSURE:
Also referred to as minimum critical bubble point pressure, it is a filter
specification derived from diffusional flow – bubble point curves for a number
of filters. It is a diffusional flow, or “break-through” pressure just before
the onset of bulk flow.
NANO-FILTRATION:
Filtration that removes both particles and small dissolved molecules and ions.
Finer than ultrafiltration, not as fine as reverse osmosis.
NTU:
Measured units of turbidity; nephelometric turbidity units.
PARTICLE:
Any discrete unit of material structure; a discernible mass having an
observable length, width, thickness, size and shape.
PARTICULATE:
Relating to or occurring in the form of fine particles.
PASTEURIZATION:
Partial sterilization of a substance and especially a liquid (as milk) at a
temperature and time of exposure that destroys objectionable organisms without
a major chemical alteration of the substance. Maintaining the high temperature
for only a short period of time is referred to as 'flash' pasteurization.
PERMEABILITY:
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.
PERMEATE:
The fluid which passes through a membrane. Also known as Filtrate.
pH:
The inverse logarithm to the base 10 of hydrogen ion concentration.
Measure of a substance's acidity or alkalinity with 7 being neutral. pH below 7
is acid, above 7 is alkali or base. Measure of hydrogen ion concentration.
POLYPROPYLENE:
A thermoplastic polymeric material which is resistant to a broad range of
chemicals. When used as a membrane, polypropylene is hydrophobic.
POLYSULFONE:
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. PORE SIZE:
Diameter of pore in membrane.
PORE SIZE-ABSOLUTE RATING:
The rated pore size of a filter at which particles equal or larger than the
rated pore size are retained with 100% efficiency.
POROSITY:
The percentage of the filter volume which is void space (syn. Void volume).
Also, number of pores per square centimeter of filter area.
PTFE:
Polytetrafluoroethylene; More commonly known as Teflon. Highly durable and
resistant to a broad range of temperatures and chemicals. PTFE is hydrophobic.
RETENTATE:
The fluid and particles retained by the filter. The incoming feed stream is
separated into filtrate (passed through the filter media) and the retentate
(retained/blocked by the filter media). Also known as concentrate.
RETENTION:
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.
RETENTION VOLUME:
See "Hold-up Volume."
REVERSE OSMOSIS (RO):
A filtration separation method (usually crossflow) operating at 200-1500 psi to
overcome osmotic pressure. Pore sizes are typically in the order of 10-10
meters (107mm). Efficiency is usually described in terms of percent salt
rejection with 90% being common.
SERIAL FILTRATION:
Filtration through two or more filters of decreasing pore size one after the
other to increase throughput, filtration efficiency, or to protect the final
filter.
SIEVE:
A filter with straight-though capillary pores with identical dimension, e.g. a
screen filter.
SINTERED MEMBRANE:
Sintering is a method for making filter membrane from powder, increasing the
adhesion between particles as they are heated. Partial sintering ensures voids
and gaps between powder particles are left open thus creating a “tight path”
which can act as a filter medium. Sintered metallic membranes have been
developed from the field of powder metallurgy.
SPARGING:
The introduction of gas into a liquid.
STANDARD (NORMAL) PRESSURE:
A pressure of 1 atmosphere (14.70 psi or 760 mm of mercury) to which
measurements of quantities dependent on pressure are often referred.
STERILE:
To make or be free of any viable micro-organisms. Demonstrated by testing to
show the absence of micro-organisms.
SURFACE FILTER:
The membrane wall is the point where filtration/separation occurs. Any fluid
passing through the surface membrane will pass on out of the filter media as
filtrate. In many instances a “cake” of solids will form at the membrane
surface and can become a form of depth filter. Surface filters are usually used
for filtering streams with high solids loadings, but if a “cake” forms flux
rates can be expected to be low.
SURFACE TENSION:
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.
SURFACTANT:
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.
THROUGHPUT:
The amount of solution which will pass through a filter prior to clogging.
TOTAL DISSOLVED SOLIDS (TDS):
Is the portion of the total solids in the sample that passes through the filter
and is indicated by the increase in weight in the vessel after the filtrate has
been dried at 180şC.
TOTAL SOLIDS:
The material residue left in the vessel after evaporation of a sample and its
subsequent drying in an oven at 103-105şC. The increase in weight over that of
the empty vessel represents the total solids.
TOTAL SUSPENDED SOLIDS (TSS):
Is the portion retained on the filter and indicated by an increase in the
weight of the filter after drying at 103-105şC.
TURBIDITY:
The amount of solid particles that are suspended in water and that cause light
rays shining through the water to scatter. Thus, turbidity makes the water
cloudy or even opaque in extreme cases. Turbidity is measured in nephelometric
turbidity units (NTU).
ULTRAFILTRATION (UF):
Filtration of liquids via a membrane under pressure. Liquids are forced through
a membrane with extremely fine pores to filter colloids and molecules between
0.002 and 0.1 microns in size. Ultrafiltration is capable of removing solids,
bacteria and viruses. UPSTREAM SIDE (of filter): The feed side of the filter.
VACUUM:
The depression of pressure below atmospheric pressure.
VISCOSITY:
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.
VOLATILE:
Evaporates easily, converts easily from liquid form to gas.
WETTING AGENT:
A surfactant added to a membrane to assure complete intrusion (wetting) by a
high surface tension fluid such as water.
