ASTM D6161-19

Standard Terminology Used for Microfiltration, Ultrafiltration, Nanofiltration, and Reverse Osmosis Membrane Processes

SIGNIFICANCE AND USE
4.1 The need to understand the relationships found in membrane unit processes for water treatment increases with the continuing demand for these separation systems. Defining the terms common to microfiltration, ultrafiltration, nanofiltration, and reverse osmosis processes assist the manufacturer, consultant, and end-user in eliminating inter-process terminology confusion. This standard expands the definitions found in Terminology D1129.
SCOPE
1.1 This terminology covers the use of microfiltration, ultrafiltration, nanofiltration, and reverse osmosis for membrane separation processes.  
1.2 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Jun-2019
• ICS: 01.040.17 - Metrology and measurement. Physical phenomena (Vocabularies)
• ICS: 17.060 - Measurement of volume, mass, density, viscosity
• Technical Committee: D19 - Water
• Drafting Committee: D19.08 - Membranes and Ion Exchange Materials

Relations

• Replaces: ASTM D6161-10 - Standard Terminology Used for Microfiltration, Ultrafiltration, Nanofiltration and Reverse Osmosis Membrane Processes (Withdrawn 2019)
• Effective Date: 01-Jul-2019
• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D3739-19 - Standard Practice for Calculation and Adjustment of the Langelier Saturation Index for Reverse Osmosis
• Effective Date: 01-Jul-2019
• Refers: ASTM D2035-19 - Standard Practice for Coagulation-Flocculation Jar Test of Water
• Effective Date: 01-Mar-2019
• Refers: ASTM D2035-13 - Standard Practice for Coagulation-Flocculation Jar Test of Water
• Effective Date: 01-Jan-2013
• Refers: ASTM D3739-06(2010) - Standard Practice for Calculation and Adjustment of the Langelier Saturation Index for Reverse Osmosis (Withdrawn 2019)
• Effective Date: 01-May-2010
• Refers: ASTM D1129-10 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2010
• Refers: ASTM D2035-08 - Standard Practice for Coagulation-Flocculation Jar Test of Water
• Effective Date: 01-May-2008
• Refers: ASTM D3739-06 - Standard Practice for Calculation and Adjustment of the Langelier Saturation Index for Reverse Osmosis
• Effective Date: 15-Dec-2006
• Refers: ASTM D1129-06a - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006
• Refers: ASTM D1129-06ae1 - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006
• Refers: ASTM D1129-06 - Standard Terminology Relating to Water
• Effective Date: 15-Feb-2006
• Refers: ASTM D4582-05 - Standard Practice for Calculation and Adjustment of the Stiff and Davis Stability Index for Reverse Osmosis
• Effective Date: 01-Jan-2005
• Refers: ASTM D3739-05 - Standard Practice for Calculation and Adjustment of the Langelier Saturation Index for Reverse Osmosis
• Effective Date: 01-Jan-2005
• Refers: ASTM D1129-04 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2004

Overview

ASTM D6161-19: Standard Terminology Used for Microfiltration, Ultrafiltration, Nanofiltration, and Reverse Osmosis Membrane Processes was developed by ASTM International to provide comprehensive, standardized definitions for terminology associated with membrane separation processes. These processes-including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO)-are increasingly critical in water treatment and purification worldwide. The standard serves as a reference to harmonize terms and eliminate confusion, supporting manufacturers, consultants, and end-users in understanding and applying membrane technologies consistently.

This terminology expands upon existing definitions in ASTM D1129 (Terminology Relating to Water), aligning with internationally recognized standards principles under the WTO Technical Barriers to Trade (TBT) Committee.

Key Topics

ASTM D6161-19 covers key terminology relevant to:

• Membrane Process Types: Clear definitions for MF, UF, NF, and RO, which are essential membrane separation processes distinguished by pore size and separation characteristics.
• Membrane Components and Configurations: Terms related to membrane elements (e.g., hollow fiber, flat sheet, spiral wound cartridge), membrane materials (e.g., ceramic, polymeric), and system arrangements (e.g., array, cassette, module).
• Operational Parameters: Definitions of flux, recovery (conversion), differential pressure, concentration polarization, and permeate, among others, which are necessary for system design and operation.
• Water Chemistry and Quality: Standard terms for water quality indicators and contaminants such as dissolved solids (TDS), alkalinity, hardness, bacteria (e.g., E. coli, total bacterial count), and coagulants like alum or ferric salts.
• Maintenance and Fouling: Terminology on fouling, cleaning-in-place (CIP), integrity testing (bubble point test), and cleaning chemicals.
• Auxiliary Equipment: Definitions for manifolds (headers), pressure vessels, accumulators, and related process instrumentation.

Applications

ASTM D6161-19 terminology supports various real-world applications, notably in:

• Water and Wastewater Treatment: Standardized language is crucial for municipal and industrial treatment facilities employing MF, UF, NF, or RO systems for contaminant removal and water purification.
• Desalination Operations: Accurate terms are necessary for designing and operating desalination plants, especially those using RO for seawater and brackish water treatment.
• Manufacturing and Procurement: Consistent terminology helps membrane manufacturers, system integrators, and buyers communicate requirements, product specifications, and operational guidelines effectively.
• Regulatory Compliance: Adherence to standardized terminology streamlines documentation and reporting for compliance with national and international water quality standards.
• Consulting and Training: Consultants, engineers, and operators depend on unified definitions to conduct training, troubleshoot systems, and draft technical documentation.
• Research and Development: Researchers benefit from a shared vocabulary when comparing studies, reporting results, and developing new membrane materials or configurations.

Related Standards

For comprehensive understanding and effective application, ASTM D6161-19 should be used alongside related standards:

• ASTM D1129: Terminology Relating to Water - foundational terms referenced within D6161-19.
• ASTM D2035: Practice for Coagulation-Flocculation Jar Test of Water - relevant to pretreatment of feed water for membrane systems.
• ASTM D3739: Practice for Calculation and Adjustment of the Langelier Saturation Index for Reverse Osmosis.
• Other Membrane and Water Quality Standards: Additional ASTM, ISO, and AWWA standards may further specify methods for testing, performance, and material safety.

In Summary:
ASTM D6161-19 provides the foundational language for anyone involved in the design, operation, maintenance, or regulation of membrane-based water treatment systems. By unifying terminology, it supports technical clarity, process optimization, and international collaboration in the fast-growing field of water purification technologies.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:D6161 −19
Standard Terminology
Used for Microfiltration, Ultrafiltration, Nanofiltration, and
Reverse Osmosis Membrane Processes
This standard is issued under the fixed designation D6161; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope and reverse osmosis processes assist the manufacturer,
consultant, and end-user in eliminating inter-process terminol-
1.1 This terminology covers the use of microfiltration,
ogy confusion. This standard expands the definitions found in
ultrafiltration, nanofiltration, and reverse osmosis for mem-
Terminology D1129.
brane separation processes.
1.2 This international standard was developed in accor-
5. Terminology
dance with internationally recognized principles on standard-
5.1 Definitions:
ization established in the Decision on Principles for the
absolute filter rating, n—particle size above which 100 % of
Development of International Standards, Guides and Recom-
particles that are trapped on or within the filter medium.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
absorption, n—the release for desorption holding of a sub-
stance within a solid by cohesive or capillary forces.
2. Referenced Documents
accumulator, n—apulsationdampenerinstalledonthesuction
2.1 ASTM Standards:
D1129Terminology Relating to Water and/or discharge lines of pumps, generally plunger type, to
minimize pressure surges and provide uniformity of flow.
D2035Practice for Coagulation-Flocculation Jar Test of
Water
accuracy, n—the closeness of agreement between an observed
D3739Practice for Calculation and Adjustment of the
value and an accepted reference value. Where an accepted
Langelier Saturation Index for Reverse Osmosis
reference value is not available, accuracy is a description of
D4582Practice for Calculation and Adjustment of the Stiff
a measure of the degree of conformity of a value generated
and Davis Stability Index for Reverse Osmosis (With-
3 by a specific procedure to the assumed or accepted true
drawn 2019)
value, including both precision and bias.
3. Summary
acidity, n—the quantitative capacity of aqueous media to react
3.1 This terminology is common to membrane separation
with hydroxyl ions.
processes but independent of the source of manufacture.
activated carbon, n—granulatedorpowderedactivatedcarbon
4. Significance and Use usedtoremovetastes,odor,chlorine,chloramines,andsome
organics from water. A family of carbonaceous substances
4.1 The need to understand the relationships found in
manufactured by processes that develop adsorptive proper-
membraneunitprocessesforwatertreatmentincreaseswiththe
ties.
continuing demand for these separation systems. Defining the
terms common to microfiltration, ultrafiltration, nanofiltration,
adsorption, n—the holding of a substance onto the surface of
a solid by chemical surface forces, without forming new
1 chemical bonds.
This terminology is under the jurisdiction ofASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.08 on Membranes and Ion
aerobic bacteria, n—bacteria that require oxygen for growth.
Exchange Materials.
CurrenteditionapprovedJuly1,2019.PublishedJuly2019.Originallyapproved
See bacteria, aerobes.
in 1997. Last previous edition approved in 2010 as D6161–10, which was
withdrawn January 2019 and reinstated in July 2019. DOI: 10.1520/D6161-19.
aggregate, n—granular material such as sand, gravel, crushed
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
stone.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
aggressive water, n—water having a high tendency to corrode
the ASTM website.
pipes and other equipment. Usually seen as having a
The last approved version of this historical standard is referenced on
www.astm.org. negative Langelier Index value.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
D6161−19
air header, n—the pipe running within a cassette that distrib- antifoulant, n—see antiscalant.
utes the air to the individual modules or aerators.
antiscalant, n—a compound added to a water which inhibits
air scour, n—distributing air over the entire area at the bottom the precipitation of sparingly soluble inorganic salts.
of a filter media flowing upward or immersed membrane to
anti-telescoping device, n—a plastic or metal device attached
improve the effectiveness of filtration or backwashing or to
to the ends of a spiral wound cartridge to prevent movement
permit the use of lower backwash water flow rate, or both.
ofthecartridgeleavesinthefeedflowdirection,duetohigh
air stripping, v—removal of volatile substances from a water feed flows.
solution by passing a gas through the solution.
AOC, n—assimilable organic carbon.
algae, n—a major group of lower plants, generally aquatic,
aquifer, n—awater-bearinggeologicalformationthatprovides
photosynthetic of extremely varied morphology and
a ground water reservoir.
physiology, mono cellular plants with chlorophyll often
masked by a brown or red pigment.
aramid, n—a fully aromatic polyamide.
alkalinity, n—the quantitative capacity of aqueous media to
array, n—the overall arrangement of pressure vessels in a
react with hydrogen ions. “M” alkalinity is that which will
crossflow membrane system, including the groupings of
react with acid as the pH of the sample is reduced to the
vessels in parallel and in series.
methylorange endpoint of about 4.5. “P” alkalinity is that
asymmetric membrane, n—membrane which has a change in
which reacts with acid as the pH of the sample is reduced to
pore structure. See anisotropic membranes.
the phenolphthalein end point of 8.3. “M” is the total
alkalinity which is the sum of hydroxide, carbonate, and
ATD, n—see anti-telescoping device.
bicarbonate contents, “P” includes all the hydroxyl and half
atomic weight, n—the relative mass of an atom based on a
the carbonate content.
scaleinwhichaspecificcarbonatom(carbon12)isassigned
alum, n—aluminum sulfate, AL (SO ) XH O (X = 14–18), a
2 4 3 2
a mass value of 12.
coagulant.
ATP, n—adenosine triphosphate.
ambient temperature, n—the temperature of the
autopsy, n—the dissection of a membrane module or element
surroundings, generally assumed to be 20–25°C.
to investigate causes of unsatisfactory performance.
amorphous, n—non crystalline, devoid of regular cohesive
availability, n—the on-stream time or rated operating capacity
structure.
of a water treatment system.
amphoteric, adj—capable of acting as an acid or a base.
a-value, n—membrane water permeability coefficient. The
anaerobic bacteria, n—bacteria that do not use oxygen.
coefficient is defined as the amount of water produced per
Oxygen is toxic to them. See bacteria, anaerobes.
unit area of membrane per unit of net driving pressure
3 2
−10 −4 (NDP); units of measurement are m /hr/m /kPa.
angstrom (A), n—a unit of length equaling 10 m, 10 µm,
−8 −9
10 cm, and 3.937 × 10 in. The symbol is Å, A, or A.U.
AWWA, n—American Water Works Association.
anion, n—negatively charged ion.
AWWARF, n—American Water Works Association Research
Foundation.
anion exchange material, n—amaterialcapableoftherevers-
ible exchange of negatively charged ions.
backflush, n—temporary reversal of the permeate or retentate
flow.
anion exchange membrane, n—membrane containing fixed
cationic charges and mobile anions that can be exchanged
backpulse, n—pumping treated water with or without added
with other anions present in an external fluid in contact with
chemicals in the reversed direction from the lumen to the
the membrane.
feed side of the membrane (inside-out).
anionic polyelectrolyte, n—usually acrylamide or acrylamide
backwash, n—reversing the flow of water with/without air
and acrylic copolymers, negatively charged, used for
either across or through a medium or membrane. Designed
coagulation/flocculation. See polyelectrolyte.
to remove the collected foreign material from the bed or
membranes.
anisotropic membrane, n—a non-uniform structure in cross-
section; typically the support substructure has pores much
bacteria, n—any of a class of microscopic single-celled
larger than the barrier layer. See asymmetric membranes.
organisms reproducing by fission or by spores. Character-
ized by round, rod-like, spiral, or filamentous bodies, often
anode, n—positive electrode.
aggregated into colonies or mobile by means of flagella.
anthracite, n—a granular hard coal used as a filtration media, Widely dispersed in soil, water, organic matter, and the
commonly used as the coarser layer in dual and multimedia bodies of plants and animals. Either autotrophic (self-
filters. sustaining, self-generative), saprophytic (derives nutrition
D6161−19
from non-living organic material already present in the biostat, n—a substance that inhibits biological growth.
environment), or parasitic (deriving nutrition from another
bipolar membrane, n—synthetic membrane containing two
living organism). Often symbiotic (advantageous) in man,
oppositely charged ion-exchange layers that are in contact
but sometimes pathogenic.
with each other.
bactericide, n—agent capable of killing bacteria.
block, n—a grouping of devices in a single unit having
bacteriostat, n—substance that prevents bacterial growth and
common control. See array, bank, train.
metabolism but does not necessarily kill them.
BOD (biochemical oxygen demand), n—the amount of dis-
baffle, n—a deflector plate in a vessel that disperses the inlet
solved oxygen utilized by natural agencies in water in
fluid.
stabilizing organic matter at specified test conditions.
bank, n—a grouping of pressure vessels in parallel, with
body feed, n—the continuous addition of filter medium (for
commonfeed-andconcentrate-streammanifolds;equivalent
example, diatomaceous earth) to sustain the efficacy of the
to stage.
filter.
2 2
bar, n—unit of pressure; 14.50 lbs/in. , 1.020 kg/cm , 0.987
BOO, n—build, own, operate.
atm, 0.1 MPa.
BOOT, n—build, own, operate, and transfer.
BAT, n—best available technology.
boundary layer, n—a thin layer at the membrane surface
battery limit, n—the boundary limits that physically defines a
wherewatervelocitiesaresignificantlylessthanthoseinthe
plant or process; inside the boundary are all the equipment
bulk flow.
and reactions associated with the defined plant or process
brackish water, n—water with an approximate concentration

baume scale, Be, n—a measure of the density of a solution
of total dissolved solids ranging from 500 to 10 000 mg/L.
relative to water.
See high brackish water, potable water, sea water.
•
BE 5145 2
breakpoint chlorination, n—the point at which the water
specificgravity*
chlorine demand is satisfied and any further chlorine is the
United States for densities greater than unity.
chlorine residual, the “free” chlorine species.
•
BE 5 2130
break tank, n—a storage device used for hydraulic isolation
specificgravity*
and surge protection.
For densities less than unity.
brine, n—the concentrate (reject) stream from a crossflow
*at 60°F
membrane device performing desalination. Portion of the
bed depth, n—the depth of the filter medium or ion exchange
feed stream which does not pass through the membrane.
resin in a vessel.
brine (concentrate) seal, n—arubberlipsealontheoutsideof
bed expansion, n—the depth increase of filter medium or ion
a spiral wound cartridge which prevents feed by-pass be-
exchange resin that occurs during backwashing.
tween the cartridge and the inside pressure vessel wall.
beta (value), n—a design parameter indicating the ratio of the
brine seal carrier, n—see ATD.
ion concentrations at the membrane surface to the concen-
tration in the bulk stream for spiral wound RO/NF. brine system staging, n—a process in which the concentrate,
under pressure, of a group of membrane devices is fed
binders, n—in reference to cartridge filters, chemicals used to
directly to another set of membrane devices to improve the
hold, or ‘bind,’short fibers together in a filter.
efficiency of the water separation.
binding, n—in surface filtration, a build-up of particulates on
bubble point, n—pressure differential at which bubbles first
the filter, restricting fluid flow through the filter at normal
appear on one surface of an immersed porous membrane as
pressures.
gas pressure is applied to the other side.
biocide, n—a substance that kills all living organisms.
bubble point pressure, n—the pressure differential necessary
to displace a liquid held by surface tension forces from the
biological deposits, n—the debris left by organisms as a result
largest equivalent capillaries in a membrane filter.
of their life processes.
biomass, n—anymaterialwhichisorwasalivingorganismor bubble point test, n—a nondestructive membrane filter test
used to assess filter integrity and proper installation.
excreted from a micro-organism.
bioremediation, n—the biological degradation treatment of buffer, n—a substance in solution that accepts hydrogen or
waste sludge and soils to breakdown organic and hydrocar- hydroxyl ions added to the solution minimizing a change in
bons. pH.
D6161−19
bundle, n—a general term for a collection of parallel filaments cation, n—positively charged ion.
or fibres.
cation exchange material, n—a material capable of the
B-value—salt diffusion coefficient, n—defined as the amount
reversible exchange of positively charged ions.
of salt transferred per unit area of membrane per unit of
cation exchange membrane, n—membrane containing fixed
concentration difference across the membrane. A unit of
3 2
anionic charges and mobile cations that can be exchanged
measurement is m/h or more specifically, m /m /h.
withothercationspresentinanexternalfluidincontactwith
BWRO, n—brackish water reverse osmosis.
the membrane.
CAC, n—combined available chlorine.
cationic polyelectrolyte, n—a polymer containing positively
charged groups used for coagulation/flocculation, usually
cage, n—a structural fabrication fitted around the perimeter of
dimethyl-aminoethyl methacrylate or dimethyl-aminoethyl
the cassette with one or more lifting eye suitable for
acrylate. See polyelectrolyte.
installingorremovingthecassetter.Thefourbottomcorners
of the cage rest within the frame in the tank.
cellulose, n—anamorphouscarbohydrate(C H O )thatisthe
6 10 5
cake layer, n—layer comprised of particulate materials resid- principal constituent of wood and plants.
ing on the upstream face of a membrane.
cellulose acetate (CA), n—in the broad sense, any of several
calcium carbonate equivalents (mg/L as CaCO ), n—a
3 esters of cellulose and acetic acid.
method for expressing mg/L as ion in terms of calcium
Celsius (°C), n—the designation of the degree on the Interna-
carbonate.Concentrationincalciumcarbonateequivalentsis
tional Practical Temperature Scale. Formerly called
calculated by multiplying concentration in mg/L of the ion
centigrade, °C = °K minus 273.15. K = Kelvin. °C= (°F –
by the equivalent weight of calcium carbonate (50) and
32) * 0.556.
dividing by the equivalent weight of the ion. (See Table 1).
centigrade, n—since 1948, now called Celsius, a temperature
calcium hypochlorite, n—Ca(HClO) , a disinfection agent.
scale.
carbonate hardness, n—the hardness in a water caused by
carbonatesandbicarbonatesofcalciumandmagnesium.The
ceramic membrane, n—generally a glass, silica, alumina, or
amount of hardness equivalent to the alkalinity formed and
carbon based membrane. Generally used in micro and
deposited when water is boiled. In boilers, carbonate hard-
ultrafiltration.They tend to withstand high temperatures and
ness is readily removed by blowdown.
widepHrangesandbemorechemicallyinertthanpolymeric
membranes.
cartridge, n—see spiral wound cartridge.
CFU, n—colonyformingunit;unitusedinthemeasureoftotal
cassette, n—an assembly of membrane elements (or modules),
bacteria count (TBC).
membrane aerators, air and permeate manifolds, and hard-
ware in the cage; this is how the membranes are installed or
channeling, n—unequal flow distribution in the desalination
removed from the process tank.
bundle or filter bed.
catalyst, n—a substance whose presence initiates or changes
charge-mosaic membranes, n—synthetic membranes com-
the rate of a chemical reaction, but does not itself enter into
posed of two-dimensional or three dimensional alternating
the reaction.
cation and anion exchange channels throughout the mem-
cathode, n—negative electrode. brane.
A,B
TABLE 1 Conversion Factors
Clark or English Grain per U.S. French German
mg/L as Ion mg/L as CaCO EPM MEQ/L Atomic Weight
Degree Gallon Degree Degree
++
Ca 2.495 0.175 0.0583 0.250 0.140 0.0499 40.08
++
Mg 4.112 0.288 0.0583 0.411 0.231 0.0823 24.32
+
Na 2.175 0.152 0.0583 0.218 0.122 0.0435 22.99
+
K 1.279 0.089 0.0583 0.128 0.072 0.0256 39.10
++
Sr 1.141 0.080 0.0583 0.114 0.064 0.0288 87.63
++
Ba 0.728 0.051 0.0583 0.073 0.041 0.0146 137.36
++
Fe 1.791 0.125 0.0583 0.179 0.101 0.0358 55.85
–
HCO 0.819 0.057 0.0583 0.082 0.046 0.0164 61.02
SO 1.041 0.073 0.0583 0.104 0.058 0.0208 96.07
4–
–
Cl 1.410 0.098 0.0583 0.141 0.079 0.0282 35.46
–
F 2.632 0.184 0.0583 0.263 0.148 0.0526 19.00
–
NO 0.806 0.056 0.0583 0.081 0.045 0.0161 62.00
––
CO 1.666 0.117 0.0583 0.167 0.094 0.0323 60.01
–––
PO 1.579 0.110 0.0583 0.158 0.089 0.0316 94.98
A
To convert from mg/L as ion to any other unit multiply by factor.
B
To convert to mg/L as ion from any other unit divide by factor.
D6161−19
check valve, n—a valve that will allow water to pass in one clark degree, n—numberofgrainsofsubstanceperoneBritish
direction but will close and prevent flow in the opposite imperial gallon of water expressed CaCO . Concentration in
direction. Clark or English degree is calculated by dividing concentra-
tion in calcium carbonate equivalents by 14.3. One grain
chelating agents, n—a sequestering or complexing agent that,
weighs1/7000lbandoneimperialgallonofwaterweighs10
in aqueous solution, renders a metallic ion inactive through
lbs at 25°C. (See Table 1.)
the formation of an inner ring structure with the ion.
clear well, n—acollectionbasinthathousesfilteredorclarified
chemical feed pump, n—a pump used to meter chemicals,
water.
such as chlorine of polyphosphate, into a feed water supply.
coagulant, n—chemical added in water and wastewater appli-
chemically enhanced backwash, CEB, n—chemicaladditions
cations to cause destablization of suspended particles and
used to backwash membranes.
subsequent formation of flocs that adsorb, entrap, or other-
chloramine, n—a combination of chlorine and ammonia in
wise bring together suspended matter that is so fine, it is
water which has bactericidal qualities for a longer time than
defined as colloidal. Compounds of iron and aluminum are
does free chlorine.
generally used to form flocs to allow removal of turbidity,
bacteria, color, and other finely divided matter from water
chlorine, n—chemical used for its qualities as a bleaching or
and waste water.
oxidizing agent and disinfectant in water purification.
coalescing, v—the separation of mixtures of immiscible fluids
chlorine, free available, n—the chlorine (Cl ), hypochlorite
– (such as oil and water) based on different specific gravities
ions (OCl ), hypochlorous acid (HOCl), or the combination
and surface tensions. Coalescence occurs whenever two or
thereof present in water.
moredropletscollideandremainincontactandthenbecome
chlorine, residual, n—theamountofavailablechlorinepresent
larger by passing through a coalescer. The enlarged drops
in water at any specified time.
then separate out of solution more rapidly.
chlorine, total available, n—thesumoffreeavailablechlorine
co-current flow, n—flowpatternthroughamembraneinwhich
plus chloramines present in water.
the fluids on the upstream and downstream sides of the
membranemoveparalleltothemembranesurfaceandinthe
chlorine demand, n—the amount of chlorine used up by
same directions. (See Fig. 1.)
reacting with oxidizable substances in water before chlorine
residual can be measured.
COD—chemical oxygen demand, n—the amount of oxygen
required under specified test conditions for the oxidation of
CIP, n—cleaning-in-place.
water borne organic and inorganic matter.
citric acid, n—C H (OH)(CO H) ,membranecleaningchemi-
3 4 2 3
coliform bacteria, n—a particular group of bacteria primarily
cal.
found in human and animal intestines and wastes.
clarifier, n—a tank in which precipitate settles and supernatant
overflows, a liquid-solids separation unit using gravity to colloid, n—a substance of very fine particle size, typically
remove solids by sedimentation. between0.1and0.001µmindiametersuspendedinliquidor
FIG. 1Types of Ideal Continuous Flows Used in Membrane-Based Separations
D6161−19
dispersed in gas.Asystem of at least two phases, including manently charged ion exchange media; CEDI is a subset of
a continuous liquid plus solid, liquid or gaseous particles so EDI and is a continuous process.
small that they remain in dispersion for a practicable time.
control block, n—a group of devices having a common piping
colony forming unit (CFU), n—unit used in the measure of
and control system.
total bacterial count (TBC).
conversion (Y), n—product water flow rate divided by feed
compaction, n—in crossflow filtration, the result of applied
water flow rate. Also called recovery; given as fraction or
pressure and temperature compressing a polymeric mem-
decimal. See recovery.
brane which may result in a decline in flux.
conversion factors, n—see Table 1.
completely mixed (perfectly mixed) flow, n—flow through a
corrosion products, n—products that result from chemical or
membrane module in which fluids on both the upstream and
electrochemical reaction between a metal and its environ-
downstream sides of the membrane are individually well-
ment.
mixed. (See Fig. 1.)
counter-current flow, n—flowthroughamembranemodulein
composite membrane, n—a membrane having two or more
whichthefluidontheupstreamanddownstreamsidesofthe
layers with different physical or chemical properties. Mem-
membrane move parallel to the membrane surface but in the
brane manufactured by forming a thin desalinating barrier
opposite direction. (See Fig. 1.)
layer on a porous carrier membrane.
concentrate, n—the stream exiting a crossflow membrane CPU, n—chloroplatinate unit (color indicator).
device which has increased concentration of solutes and
cross flow, n—flow through a membrane module in which the
particles over the feed stream; portion of the feed stream
fluidontheupstreamsideofthemembranemovesparallelto
which does not pass through the membrane. The stream in
the membrane surface and the fluid on the downstream side
which dissolved solids or particulates, or both, are concen-
of the membrane moves away from the membrane in the
trated in a membrane separation process.
direction normal to the membrane surface. (See Fig. 1.)
concentrate recycle, n—atechniqueforimprovingrecoveryin
crossflow membrane filtration, n—a separation of the com-
which a fraction of the concentrate is recycled through the
ponentsofafluidbysemipermeablemembranesthroughthe
membrane system.
application of pressure and flow parallel to the membrane
concentration factor, CF, n—the ratio of the concentration of
surface. Includes the processes of reverse osmosis,
a component in the retenate (concentrate, brine) to the
utrafiltration, nanofiltration, and microfiltration.
concentration of the same component in the feed:
cryptosporidium, n—a waterborne protozoan that forms cysts
C ~brinewater concentration!
B
and causes acute gastrointestinal illness in humans.
CF 5
C feedwater concentration
~ !
F
Dalton, n—an arbitrary unit of molecular weight, one twelfth
5 ~approximation!
the mass of the nuclide of carbon 12.
1 2conversion
DBP, n—disinfection by-products (a rule as part of the
concentration polarization, n—the increase of the solute
SDWA).
concentration over the bulk feed solution which occurs in a
thinboundarylayeratthefeedsideofthemembranesurface,
dead end filtration, n—a process in which water is forced
resulting from the removal of the solvent. Concentration
throughamediawhichcapturestheretainedparticlesonand
profile that has a higher level of solute nearest to the
within it, where the process involves one influent and one
upstreammembranesurfacecomparedwiththemore-or-less
effluent stream.
mixed bulk fluid far from the membrane surface.
dead end flow, n—flow through a membrane module in which
conductivity, n—the property of a substance’s (in this case,
the only outlet for the upstream fluid is through the mem-
water and dissolved ions) ability to transmit electricity. The
brane. (See Fig. 1.)
inverse of resistivity. Measured by a conductivity meter, and
described in microsiemens/cm or micromhos/cm, µS/cm.
deaerator, n—a device to remove air from water.
contaminant, n—any foreign substance present which will
decarbonator, n—a device to remove carbon dioxide from
adversely affect performance or quality.
water.
continuous deionization, n—a deionization process that does
degasification, n—the process of removing dissolved gasses
notrequireregularinterruptionsinservicetodischargeionic
from water.
materials collected from the water being processed.
deionization (DI), n—the removal of ions from a solution by
continuous electrodeionization (CEDI), n—removal of ion-
ion exchange.
ized and ionizable species from liquids using both electric
active media and electrical potential; ion transport typically demineralization, n—the process of removing minerals from
comprise semipermeable ion-exchange membrane and per- water.
D6161−19
denitrification, n—aqueous nitrate reduction or removal. E. coli, n—one of the members of the coliform bacterium
associated with animal and human waste.
dense (non-porous) membrane, n—membrane with no de-
effluent, n—exit stream from a unit/vessel.
tectable pores.
electrodialysis (ED), n—a process in which ions are trans-
desalination, n—see demineralization.
ferred through membranes from a less concentrated to a
desorption, n—opposite of absorption. See absorption.
more concentrated solution using direct current electric
power as the driving force.
detergent, n—a cleansing agent; any of numerous synthetic
water soluble or liquid-organic preparations that are chemi-
electrodialysis reversal (EDR), n—same as ED with the
callydifferentfromsoapsbutresemblethemintheabilityto
addition of a polarity reversal step added to improve
emulsify oils and hold dirt in suspension.
performance.
dialysis, n—a separation process dependent on different diffu-
electrolyte, n—a substance that dissociates into two or more
sion rates of solutes across a permeable membrane without
ions when dissolved in water.
an applied hydraulic driving force. It is a process in which
element, n—the component containing the membrane, gener-
transport is driven primarily by concentration differences,
allyreplaceable,suchasaspiralwoundcartridgeorcassette.
rather than by pressure or electrical potential differences,
across the thickness of a membrane.
element housing, n—the vessel containing one or more mem-
brane elements connected in series or parallel, with feed
dialysis permeability coefficient, n—permeability coefficient
stream inlet, and permeate and concentrate-stream outlet
on a transmembrane driving force expressed in terms of the
ports; with backflush elements, housings may also have a
concentration difference of a given component.
backflush stream inlet and discharge ports. See pressure
vessel.
diatom, n—singlecellmarineanimalhavingacoatingconsist-
ing principally of silica.
English degree, n—number of grains of substance per one
British imperial gallon of water. (See Table 1.)
diatomaceous earth (DE) filtration, n—filtration using an
amphorous, lightweight siliceous earth medium occurring
EPA—Environmental Protection Agency (USA), n—an or-
naturally as the fossil remains of diatoms.
ganization that has set the potable water standards.
differential pressure (∆P, dP), n—the difference in pressure
EPS, n—extra-cellular polysaccharide produced by bacteria to
between two points.
form a protective coating especially after attaching to the
membrane surface.
disinfection, n—the process of killing organisms in a water
supplyordistributionsystembymeansofheat,chemicals,or
equivalent per million (EPM), n—a unit chemical equivalent
UV light.
weight of solute per million unit weights of solution.
Concentration in equivalents per million is calculated by
dissolved organic matter (DOM), n—the amount of organic
dividing concentration in ppm by the equivalent weight of
matter in a water sample passing through a 0.45-µm filter,
the substance or ion. Equivalent weight is the atomic weight
reported as percent or fraction.
of the substance divided by the valence of the substance.
dissolved oxygen (DO), n—the gas, oxygen, which is dis-
equivalent weight, n—the weight of an ion determined by
solved in a liquid, mg/L.
dividing the sum of the atomic weights of its component
dissolved solids, n—the residual material remaining after atoms by its valence.
filtering the suspended material from a solution and evapo-
ERD, n—energy recovery device.
rating the solution to a dry state at a specified temperature.
That matter, exclusive of gases, which is dissolved in water
ERT, n—energy recovery turbine.
to give a single homogeneous liquid phase.
Escherichia colia, n—see E. coli.
distillation, n—the process of condensing steam from boiling
ESWTR, n—enhanced surface water treatment rule.
water on a cool surface.
evaporation, n—process where a liquid (water) passes from a
Donnan exclusion, n—reduction in concentration of mobile
liquid to a gaseous state.
ions within an ion exchange membrane due to the presence
of fixed ions of the same sign as the mobile ions.
FAC, n—free available chlorine.
downstream, n—side of a membrane from which permeate
facultative organisms, n—microbes capable of adapting to
emerges.
either aerobic or anaerobic environments.
dynamic membrane formation, n—process in which an Fahrenheit (°F), n—designation of a degree on the Fahrenheit
active layer is formed on the membrane surface by the temperaturescalethatisrelatedtotheInternationalPractical
depositionofsubstancescontainedinthefluidbeingtreated. Temperature Scale.
D6161−19
FDA, n—Food and Drug Administration (USA). unitoftimethroughaunitofmembranesurfaceareanormal
to the thickness direction.
feed, n—theinputsolutiontoatreatment/purificationsystemor
device, including the raw water supply prior to any treat-
fouling, n—the reduction of flux due to a build-up of solids on
ment. The liquid entering the module. thesurfaceorwithintheporesofthemembrane,resultingin
changed element performance.
feed channel spacer, n—a plastic netting between membrane
leaves which provides the flow channel for the fluid passing fouling index (FI), n—see SDI.
over the surface of the membrane and increases the turbu-
Francis turbine, n—a centrifugal turbine ERD like a reverse-
lence of the feed-brine stream.
running pump.
feed distributor, n—theplasticmeshcylinderatthecoreofthe
FRC, n—free residual chlorine.
fiber bundle which distributes the feed evenly.
free (available) chlorine, n—chlorine existing as hypochlo-
feed pretreatment, n—process carried out on a crude (raw)
rousacidoritsdissociatedions.Chlorineremainingafterthe
feed stream prior to feeding to a membrane separation
demand has been satisfied.
system to eliminate objectionable components such as bio-
logical agents and colloids that might impede the stable
freeboard, n—the space above a filter bed in a filtration vessel
operation of the membrane.
to allow for expansion of the bed during back washing.
feed water, n—that water entering a device or process.
French degree, n—calciumcarbonateequivalentsexpressedin
parts per hundred thousand. Concentration in French degree
ferric chloride, n—crystalline form of FeCl 6H O, a coagu-
3 2
is calculated by dividing concentration in calcium carbonate
lant.
equivalents by ten. (See Table 1.)
ferric sulfate, n—Fe (SO ) -9H O, a coagulant.
2 4 3 2
FRP, n—fiberglass reinforced plastic.
ferrous sulfate, n—FeSO -7H O, a coagulant.
4 2
fungus, n—primitive plants distinguished from algae by the
fiber bundle, n—the heart of the permeator consisting of the
absence of chlorophyll.
hollow fiber polymer membrane, epoxy tube sheet, nub and
GAC, n—granular activated carbon.
feed distributor.
galvanic corrosion, n—accelerated corrosion of a metal be-
filter cake, n—the accumulated particles on a filter surface,
causeofanelectricalcontactwithamorenoblemetalornon
usually from a slurry mixture.
metallic conductor in an electrolyte.
filtrate, n—the portion of the feed stream which has passed
GD, n—gallons per day. See GPD.
through a filter.
gel fouling layer, n—highly swollen fouling layer comprising
fixed matter, n—residues from the ignition of particulate or
a three-dimensional. Possibly network, structure residing at
dissolved matter, or both.
the surface of a membrane.
flat sheet membrane, n—a sheet type membrane may be
German degree, n—calcium oxide equivalents expressed in
coated onto a fabric substrate.
partsperhundredthousand.ConcentrationinGermandegree
floc, n—a loose, open-structured mass produced by the aggre-
is calculated by dividing concentration in calcium carbonate
gation of minute particles.
equivalents by 17.86. (See Table 1.)
flocculation, n—the process of agglomerating fine particles
GFD (GPDSF), n—unit of permeate rate or flux; gallons per
into larger groupings called flocs.
day per square foot of effective membrane area.
flocculent, n—chemical(s) which, when added to water, form
GPD, n—unit of flow rate; gallons per day. See GD.
bridges between suspended particles causing them to ag-
glomerate into larger groupings (flocs) which then settle or grain, n—unit of weight, 0.648 g, 0.000143 lb.
float by specific gravity differences.
grains per U.S. gallon (GPG), n—number of grains of
flow balancing, n—the use of an imposed pressure drop (flow substance per one U.S. gallon of water. Concentration in
balancing tube), to minimize conversion differences of GPG is calculated by dividing concentration in ppm of the
modules operating in parallel. ionby17.1.Onegrainweighs1/7000lbandoneU.S.gallon
weighs 8.3 lb.
flow balancing tube, n—see flow balancing.
GRAS, n—materials “generally regarded as safe,” as listed by
flux, n—the membrane throughput, usually expressed in vol-
the FDA.
ume of permeate per unit time per unit area, such as gallons
2 2
per day per ft or litres per hour per m . Number of moles, gravity filter, n—a filter through which water flows through it
volume,ormassofaspecifiedcomponentthatispassingper by gravity.
D6161−19
greensand, n—a mineral (glauconite), used as a filtration hydrated lime, n—dry calcium hydroxide.
medium. See manganese greensand.
hydrophilic, adj—having an affinity for water.
groundwater, n—water confined in permeable sand layers
hydrophobic, adj—lacking an affinity to water.
between rock or clay; that part of the subsurface water that
is in the saturated zone.
hydroxyl alkalinity, n—see alkalinity.
HAA, n—agroupofsixhaloaceticacidsregulatedindrinking
hyperfiltration, n—separation of dissolved ions from a feed
water (mono-, di-, and tri-chloroacetic acid; mono- and
stream as in nanofiltration and reverse osmosis.
di-bromoacetic acid; and chlorobromoacetic acid).
immersed membrane, n—MF/UF membranes immersed in
halogen, n—anyelementofthefamilyoftheelementsfluorine,
thewatertobefiltered,wherethetransmembranepressureis
chlorine, bromine and iodine (definition for purpose of this
applied by suction to the permeate side.
standard).
imperial gallon (IG), n—1.2 times U.S. gallon.
hardness, n—the polyvalent-cation concentration of water
(generally calcium and magnesium). Usually expressed as
impulse turbine, n—anERDsometimesreferredtoasaPelton
mg/L as CaCO .
3 Wheel.
head loss, n—the reduction in liquid pressure usually associ-
in-line coagulation, n—a filtration process performed by
ated with the passage of a solution through a filter media
continuallyaddingacoagulanttotherawfeedwaterandthen
bed.
passing the water through a filter(s) to remove the microfloc
which has been formed.
header, n—see manifold.
integrity, n—measure of the degree to which a membrane
heavy metals, n—elements having a high density or specific
gravity of approximately 5.0 or higher.Ageneric term used system rejects particles of interest.
to describe contaminants such as cadmium, lead, mercury,
interconnector, n—a device to connect adjacent membrane
etc. Most are toxic to humans in low concentration.
elements in series and to seal the product channel from the
high brackish water, n—water with an approximate concen- feed-brine channel.
tration of total dissolved solids ranging from 10 000 to 30
ion, n—a charged portion of matter of atomic or molecular
000 mg/L. See brackish water and sea water.
dimensions.
high-purity water, n—highly treated water with attention to
ion exchange, n—a reversible process by which ions are
microbiological, particle, organics, and mineral reduction or
interchangedbetweenasolidandaliquidwithnosubstantial
elimination.
structural changes in the solid; ions removed from a liquid
hollow fiber (HF) membrane, n—self-supporting membrane
by chemical bonding to the media.
fibers which have a hollow bore like a cylinder. In reverse
ion-exchange capacity (volume basis), n—the number of
osmosis, the membrane is usually on the outside with the
milliequivalents of exchangeable ions per millilitre of back-
bore conveying the permeate. In ultra and micro filtrations
washed and settled bed of ion-exchange material in its
the membrane may be on the inside or the outside of the
standard form.
fiber.
homogeneous membrane, n—membrane with essentially the ion-exchange capacity (weight basis), n—the number of
samestructuralandtransportpropertiesthroughoutitsthick- milliequivalents of exchangeable ions per dry gram of
ness. ion-exchange material in its standard form.
HPC, n—heterotrophic plate count. Formerly called SPC.
ion-exchange material, n—a water insoluble material that has
the ability to reversibly exchange ions in its structure, or
humic acid, n—avarietyofwater-solubleorganiccompounds,
attached to its surface as functional groups, with ions in a
formed by the decayed vegetable matter, which is leached
surrounding medium.
into a water source by runoff or percolation. Present in most
surface and some ground waters. Higher concentrations
ion-exchange membrane, n—an ion-exchange material in a
cause a brownish tint; difficult to remove except by
form suitable for use as a barrier between two fluids.
adsorption, ultrafiltration, nanofiltration, or reverse osmosis.
ion-exchange particle, n—an ion-exchange material in the
humidity, absolute, n—the mass of water vapor per unit
form of spheroids or granules.
volume of the atmosphere usually measured as grams per
ion-exchange resin, n—an organic ion-exchange material
m .
substrate, usually synthetic.
humidity, relative, n—the ratio of the actual pressure of
existing water vapor to the maximum possible (saturation) ionic strength, n—measureoftheoverallelectrolyticpotential
pressure of water vapor in the atmosphere at the same of a solution, the strength of a solution based on both the
temperature, expressed as a percentage. concentrations and valencies of the ions present.
D6161−19
ionization, n—the disassociation of molecules into charged maximum instantaneous flux, MIF, n—the maximum flux at
particles (ions). anytimeortemperatureduringoperations;unitsofmeasure-
ment usually expressed in volume of permeate per unit time
jackson turbidity unit, JTU, n—unitofmeasureusedwiththe 2
perunitareasuchasgallonsperdayperft orlitresperhour
jackson candle turbidimeter.
per m ; number of moles, volume, or mass of a specified
component that is passing per unit of time through a unit of
jar test, n—a laboratory procedure for the evaluation of a
membrane area normal to the thickness direction.
treatment to reduce dissolved, suspended colloidal and non
settleable matter from water (see Practice D2035).
MCL, n—maximum contaminant level.
Langelier saturation index, LSI, n—anindexcalculatedfrom
megohm, n—unitofmeasurementofwaterpuritybyelectrical
totaldissolvedsolids,calciumconcentration,totalalkalinity,
resistance;onemillionohms;reciprocalofconductivity.See
pH, and solution temperature that shows the tendency of a
microsiemens, ohm.
water solution to precipitate or dissolve calcium carbonate
(see Practice D3739). membrane, n—engineered thin semipermeable film which
serves as a barrier permitting the passage of materials only
Langmuir-Blodgett (LB) membrane, n—syntheticmembrane
up to a certain size, shape, or electro-chemical character.
formed by sequential depositing of one or more monolayers
Membranes are used as the separation agent in reverse
of surface active component onto a porous support.
osmosis, electrodialysis, ultrafiltration, nanofiltration, and
microfiltration, as disc filters in laboratories, and as pleated
LD-50—concentration required for 50% mortality (lethal
filter cartridges, particularly for microfiltration.
dose).
membrane area, n—theareaavailableincontactwiththefeed
leaf, n—the sandwich layer of flat-sheet membrane/product
water.
channel spacer/flat-sheet membrane, glued together on the
sides and across the outer end in a spiral wound element.
membrane-cleaning system, n—tank(s), filtration devices,
pumps and associated equipment and appurtenances that are
lime, n—Ca(OH) , calcium hydroxide, a common water treat-
periodically used to prepare and feed chemical solutions to
ment chemical.
the modules to recover fouling.
lime soda softening, v—use of lime and Na CO for softening
2 3
membrane compaction, n—compression of membrane struc-
water.
ture due to a pressure difference across its thickness. See
compaction.
limestone, n—either calcite limestone (CaCO ) or dolomitic
limestone (CaCO -MgCO ).
3 3
membrane conditioning (pretreatment), n—process carried
limiting current density, n—currentdensityatwhichdramatic out on a membrane after completion of its preparation and
increases in resistance are observed such as in an ion prior to its use in a separation application such as thermal
exchange membrane system under the influence of an annealing.
appliedelectricfieldbetweentheupstreamanddownstream.
membrane configuration, n—the design and shape of a given
Limitingcurrentdensityisthepointwhereliquidphaseionic
membrane element (cartridge) such as tubular, spiral wound
diffusionratelimitationsresultinsubstantialdepletionofion
or hollow fiber.
concentrations at the membrane surface.
membrane distillation, n—distillation process in which the
loose RO, n—see nanofiltration.
fluid and gas phases are separated by a porous membrane.
LRV—Log Reduction Value, n—a measure of the particle
membrane element, n—a bundle of spiral membrane enve-
removalefficiencyofthemembranesystemexpressedasthe
lopes or hollow fiber membranes bound together as a
log of the ratio of the particle concentration in the untreated
discrete entity.
andtreatedfluid.Forexample,a10-foldreductioninparticle
concentration is an LRV of 1.
membrane filter, n—geometrically regular porous matrix;
removes particles above pore size rating by physical size
LSI, n—Langelier saturation index, measure of CaCO solu-
exclusion.
bility in brackish waters. See Practice D3739 and S&DSI.
membrane module, n—manifold assembly containing one or
manganese greensand, n—amanganesedioxidecoatedgreen-
more membranes to separate the streams of feed, permeate
sand used as a filter medium for removal of manganese and
and retenate (brine). See Fig. 2.
iron. See greensand.
membrane partition (distribution) coefficient, n—parameter
manifold, n—an enlarged pipe with connections available to
equal to the equilibrium concentration of a component in a
the individual feed, brine, air, and product ports.
membrane divided by the corresponding equilibrium con-
mass transfer coefficient (MTC), n—mass (or volume) trans- centration of the component in the external phase in
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