Technical Info

Desal Supplies

Unit 4, Fletcher Street

Rochdale, Lancs, OL11 1AE

Tel: +44 (0)1706 869777 / Email:

AAS Atomic Absorption Spectroscopy.
AOC Assimiable Organic Carbon.
Anionic polyelectrolyte Usually acrylamide and acrylamide and acrylic copolymers, negatively charged, used for coagulation/flocculation, see Polyelectrolyte’s.
Anthracite A granular hard coal used as a filtration media, commonly used as the coarser layer in dual and multimedia filters.
Antifoulant See antiscalant.
Antiscalant A compound added to a water which inhibits the precipitation of sparingly soluble inorganic salts.
Anti-telescoping device A plastic or metal device attached to the ends of a spiral wound cartridge to prevent movement of the cartridge leaves in the feed flow direction, due to high feed flows.
Array An arrangement of devices connected to common feed, product and reject headers; that is, a 2:1 array.
ATD See anti-telescoping device.
ATP Adenosine triphosphate.
Autopsy The dissection of a membrane module or element to investigate causes of unsatisfactory performance.
Availability The on-stream time or rated operating capacity of a water treatment system.
A-value Membrane water permeability coefficient. The coefficient is defined as the amount of water produced per unit area of membrane when net driving pressure (NDP) is unity, a unit of measurement is m3/hr/m2 /kPa.
Backwash Reverse the flow of water with/without air either across or through a medium designed to remove the collected foreign material from the bed.
Bacteria Any of a class of microscopic single-celled organisms reproducing by fission or by spores. Characterized by round, rod-like spiral or filamentous bodies, often aggregated into colonies or mobile by means of flagella. Widely dispersed in soil, water, organic matter, and the bodies of plants and animals. Either autotrophic (self-sustaining, self-generative), saprophytic (derives nutrition from non-living organic material already present in the environment), or parasitic (deriving nutrition from another living organism). Often symbiotic (advantageous) in man, but sometimes pathogenic.
Bactericide Agent capable of killing bacteria.
Bacteriostat Substance that prevents bacterial growth and metabolism but does not necessarily kill them.
Bank A grouping of devices. See array, block, train, RO train.
Bar Unit of pressure; 14.50 lbs/in2, 1.020 kg/cm2, 0.987 atm, 0.1 MPa.
BDOC Biodegradable Dissolved Organic Carbon.
Bed depth The depth of the filter medium or ion exchange resin in a vessel.
Biocide A substance that kills all living organisms.
Biological deposits The debris left by organisms as a result of their life processes.
Biomass Any material which is or was a living organism or excreted from a micro-organism.
Biostat A substance that inhibits biological growth.
Block A grouping of devices in a single unit having common control. See array, bank, train.
BOD Biological Oxygen Demand. The amount of dissolved oxygen utilized by natural agencies in water in stabilizing organic matter at specified test conditions.
Boundary layer A thin layer at the membrane surface where water velocities deviate significantly less than those in the bulk flow.
Brackish water Water with an approximate concentration of total dissolved solids ranging from 1,000 to 10,000 mg/L. See high brackish water, seawater.
Breakpoint chlorination The point at which the water chlorine demand is satisfied and any further chlorine is the chlorine residual, the 'free' chlorine species.
Break tank A storage device used for hydraulic isolation and surge protection.
Brine The concentrate (reject) stream from a crossflow membrane device performing desalination. Portion of the feed stream which does not pass through the membrane. See Concentrate.
Brine (concentrate) seal A rubber lip seal on the outside of a spiral wound cartridge which prevents feed by-pass between the cartridge and the inside pressure vessel wall.
Brine system staging A process in which the concentrate, under pressure, of a group of membrane devices is fed directly to another set of membrane devices to improve the efficiency of the water separation.
B-value. Salt diffusion The coefficient is defined as the amount of salt transferred per unit area of membrane when the difference in salt concentration across the membrane is unity. A unit of measurement is m/h.
BWRO Brackish Water Reverse Osmosis
CAC Combined Available Chlorine.
Calcium Carbonate equivalents A method for expressing mg/L as ion in terms of calcium carbonate. Concentration in calcium carbonate equivalents is calculated by multiplying concentration in mg/L of the ion by the equivalent weight of calcium carbonate (50) and dividing by the equivalent weight of the ion.
Carbonate hardness The hardness in a water caused by carbonates and bicarbonates of calcium and magnesium. The amount of hardness equivalent to the alkalinity formed and deposited when water is boiled. In boilers, carbonate hardness is readily removed by blowdown.
Cationic polyelectrolyte A polymer containing positively charged groups used for coagulation/flocculation, usually dimethyl - aminoethyl methacrylate or dimethyl-aminoethyl acrylate. Seepolyelectrolyte.
CFU Colony forming unit; unit used in the measure of total bacteria count (TBC).
Channelling Unequal flow distribution in the desalination bundle or filter bed.
Chelating agents A sequestering or complexing agent that, in aqueous solution, renders a metallic ion inactive through the formation of an inner ring structure with the ion.
Chemical feed pump A pump used to meter chemicals, such as chlorine of polyphosphate, into a feed water supply.
Chloramine A combination of chlorine and ammonia in water which has bactericidal qualities for a longer time than does free chlorine.
Chlorine Chemical used for its qualities as a bleaching or oxidizing agent and disinfectant in water purification.
Chlorine demand The amount of chlorine used up by reacting with oxidizable substances in water before chlorine residual can be measured.
Chlorine, residual The amount of available chlorine present in water at any specified time.
Chlorine, free available The chlorine (Cl2), hypochlorite ions (OCl-), hypochlorous acid (OHCl) or the combination thereof present in water.
Chlorine, total available The sum of free available chlorine plus chloramines present in water.
CIP Cleaning-in-place.
Citric acid C3H4(OH)(CO2H)3, membrane cleaning chemical.
Clarifier A tank in which precipitate settles and supernatant overflows, a liquid-solids separation unit using gravity to remove solids by sedimentation.
Coagulant Chemical added in water and wastewater applications to cause destalization of suspended particles and subsequent formation of flocs that adsorb, entrap, or otherwise bring together suspended matter that is so fine, it is defined as colloidal. Compounds of iron and aluminium are generally used to form flocs to allow removal of turbidity, bacteria, colour, and other finely divided matter from water and waste water.
COD-chemical oxygen demand The amount of oxygen required under specified test conditions for the oxidation of water borne organic and inorganic matter.
Colloid A substance of very fine particle size, typically between 0.1 and 0.001 pin in diameter suspended in liquid or dispersed in gas. A system of at least two phases, including a continuous liquid plus solid, liquid or gaseous particles so small that they remain in dispersion for a practicable time.
Colony forming unit (CFU) Unit used in the measure of total bacterial count (TBC).
Compaction In crossflow filtration, the result of applied pressure and temperature compressing a polymeric membrane which may result in a decline in flux.
Composite membrane A membrane having two or more layers with different physical or chemical properties. Membrane manufactured by forming a thin desalinating barrier layer on a porous carrier membrane.
Concentrate The stream exiting a crossflow membrane device which has increased concentration of solutes and particles over the feed stream. Portion of the feed stream which does not pass through the membrane. The stream in which dissolved solids or particulates, or both, are concentrated in a membrane separation process.
Concentration Factor, CF The ratio of the feed quantity (or feed stream) over the concentrate quantity (or concentrate stream). CF = CB/CF
Concentration polarization The increase of the solute concentration over the bulk feed solution which occurs in a thin boundary layer at the feed side of the membrane surface, resulting from the removal of the solvent.
Concentrate recycle A technique for improving recovery in which a fraction of the concentrate is recycled through the membrane system.
Conductivity The property of a substance's (in this case, water and dissolved ons) ability to transmit lectricity. The inverse of resistivity. Measured by a conductivity meter, and described in microsiemens/cm or microohms/cm, µS/cm.
Contaminant Any foreign substance present which will adversely affect performance or quality.
Corrosion products Products that result from chemical or electrochemical reaction between a metal and its environment.
CPU Chloroplatinate unit (colour indicator).
CRC Combined Residual Chlorine. 
Crossflow membrane filtration A separation of the components of a fluid by semi permeable membranes through the application of pressure and flow parallel to the membrane surface. Includes the processes of reverse osmosis, ultrafiltration, nanofiltration, and microfiltration.
Dalton An arbitrary unit of molecular weight, 1 1/2 the mass of the nuclide of carbon 12. Unit of measure for the smallest, size of the molecular retained by an ultrafilter.
Dead end filtration A process in which water is forced through a media which captures the retained particles on and within it, where the process involves one influent and one effluent stream.
Deionization (Dl) The removal of ions from a solution by ion exchange.
Demineralization The process of removing minerals from water.
Desalination See demineralization.
Detergent A cleansing agent; any of numerous synthetic water soluble or liquid-organic preparations that are chemically different from soaps but resemble them in the ability to emulsify oils and hold dirt in suspension.
Disinfection The process of killing organisms in a water supply or distribution system by means of heat, chemicals, or UV light.
Dissolved solids The residual material remaining after filtering the suspended material from a solution and evaporating the solution to a dry state at a specified temperature. That matter, exclusive of gases, which is dissolved in water to give a single homogeneous liquid phase.
Double pass RO system RO system in which the permeate is further desalinated by a subsequent RO system.
Element The component containing the membrane, generally replaceable, such as a spiral wound cartridge.
ERD Energy recovery device.
ERT Energy recovery turbine.
FAC Free Available Chlorine.
FDA Food and Drug Administration (USA).
Feed The input solution to a treatment/purification system or device, including the raw water supply prior to any treatment. The liquid entering the module.
Feed channel spacer A plastic netting between membrane leaves which provides the flow channel for the fluid passing over the surface of the membrane and increases the turbulence of the feed-brine stream.
Feed water That water entering a device or process.
Ferric chloride A coagulant, solid as FeCl3 or liquid as FeCl3 · 6H2O.
Ferric sulphate Fe2(SO4)3 · 9H2O, a coagulant.
Ferrous sulphate FeSO4 · 7H2O, a coagulant.
FI Fouling Index.
Filtrate The portion of the feed stream which has passed through a filter.
Floc A loose, open-structured mass produced by the aggregation of minute particles.
Flocculent Chemical(s) which, when added to water, form bridges between suspended particles causing them to agglomerate into larger groupings (flocs) which then settle or float by specific gravity differences.
Flocculation The process of agglomerating fine particles into larger groupings called flocs.
Flux The membrane throughput, usually expressed in volume of permeate per unit time per unit area, such as gallons per day per ft2 or litres per hour per m2.
Fouling The reduction of flux due to a build-up of solids on the surface or within the pores of the membrane, resulting in changed element performance.
Fouling index (FI) See SDI.
FRC Free Residual Chlorine.
Freeboard The space above a filter bed in a filtration vessel to allow forexpansion of the bed during back washing.
Free (available) chlorine Chlorine existing as hypochlorous acid or its dissociated ions. Chlorine remaining after the demand has been satisfied.
FRP Fiberglass reinforced plastic.
Fungus Primitive plants distinguished from algae by the absence of chlorophyll.
GAC Granular Activated Carbon.
GD Gallons per day. See GPD.
GFD (GPDSF) Unit of permeate rate or flux; gallons per day per square foot of effective membrane area.
GPD Unit of flow rate; gallons per day. See GD.
Gravity filter A filter through which water flows through it by gravity.
Greensand A mineral (glauconite), used as a filtration medium. See manganese greensand.
Groundwater-water Confined in permeable sand layers between rock or clay; that part of the subsurface water that is in the saturated zone.
Halogen Any element of the family of the elements fluorine, chlorine, bromine and iodine (definition for purpose of this standard).
Hardness The polyvalent-cation concentration of water (generally calcium and magnesium). Usually expressed as mg/L as CaCO3.
Header See manifold.
Head loss The reduction in liquid pressure usually associated with the passage of a solution through a filter media bed.
Heavy metals Elements having a high density or specific gravity of approximately 5.0 or higher. A generic term used to describe contaminants such as cadmium, lead, mercury, etc. Most are toxic to humans in low concentration.
High brackish water Water with an approximate concentration of total dissolved solids ranging from 10,000 to 30,000 mg/L. See brackish water and seawater.
High-purity water Highly treated water with attention to microbiological, particle, organics and mineral reduction or elimination.
HPC Heterotrophic plate count. Formerly called SPC.
HPW High Purity Water.
Humic acid A variety of water-soluble organic compounds, formed by the decayed vegetable matter, which is leached into a water source by runoff or percolation. Present in most surface and some ground waters. Higher concentrations cause a brownish tint. Difficult to remove except by adsorption, ultrafiltration, nanofiltration or reverse osmosis.
In-line coagulation  A filtration process performed by continually adding a coagulant to the raw feedwater and then passing the water through a filter to remove the microfloc which has been formed.
Interconnector A device to connect adjacent membrane elements in series and to seal the product channel from the feed brine channel.
Ion exchange A reversible process by which ions are interchanged between a solid and a liquid with no substantial structural changes in the solid; ions removed from a liquid by chemical bonding to the media.
Ionic strength Measure of the overall electrolytic potential of a solution, the strength of a solution based on both the concentrations and valencies of the ions present.
Ionization The disassociation of molecules into charged particles (ions).
Langellier Saturation Index, LSI An index calculated from total dissolved solids, calcium concentration, total alkalinity, pH, and solution temperature that shows the tendency of a water solution to precipitate or dissolve calcium carbonate.
Leaf The sandwich layer of flat-sheet membrane/product channel spacer/flat-sheet membrane, glued together on the sides and across the outer end in a spiral wound element.
Lime soda softening Use of lime and Na2CO3 for softening water.
LSI Langellier Saturation Index, measure of CaCO3 solubility in brackish waters. See S&DSI.
Manganese greensand A manganese dioxide coated greensand used as a filter medium for removal of manganese and iron. See greensand.
Manifold An enlarged pipe with connections available to the individual feed, brine and product ports of a desalination device.
Mass Transfer Coefficient (MTC) Mass (or volume) transfer through a membrane based on driving force.
Membrane Engineered thin semi permeable film which serves as a barrier permitting the passage of materials only up to a certain size, shape, or electro-chemical character. Membranes are used as the separation agent in reverse osmosis, electro dialysis, ultrafiltration, nanofiltration, and microfiltration, as disc filters in laboratories, and as pleated filter cartridges, particularly for microfiltration.
Membrane area The active area available for micro, nano and ultrafiltration and reverse osmosis.
Membrane compaction See compaction.
Membrane configuration The design and shape of a given membrane element (cartridge) such as tubular, spiral wound or hollow fibre.
Membrane element A bundle of spiral membrane envelopes bound together as a discrete entity.
Membrane filter Geometrically regular porous matrix; removes particles above pore size rating by physical size exclusion.
Membrane salt passage SPm is the concentration of a compound in the permeate related to its average concentration on the feed/concentrate side.
Membrane softening Use of crossflow membrane to substantially reduce hardness ions in water. See nanofiltration.
MF Microfiltration.
MFI Modified Fouling Index.
MGD (MGPD) Millions of gallons per day.
Microfiltration (MF) Filtration designed to remove particles in the approximate range of 0.05 to 2 µm.
Microbe Bacteria and other organisms that require the aid of a microscope to be seen.
Microorganism See microbe.
Microsiemens Unit of measurement of water purity by electrical conductivity; one microohm; reciprocal of resistivity. See megohm, ohm.
Milliequivalent per litre (meq/L) A weight-volume measurement obtained by dividing the concentration expressed in milligrams per litre by the equivalent weight of the substance or ion. If specific gravity is unity meq/L is the same as epm.
Milligram per litre (mg/L) A weight-volume measurement which expresses the concentration of a solute in milligrams per litre of solution. When specific gravity is unity mg/L = ppm. When specific gravity is not unity, mg/L divided by specific gravity of solution equals ppm.
Mixed-bed A physical mixture of anion-exchange and cation-exchange materials.
Module A membrane element combined with the element's housing. Pressure vessel containing membrane element(s).
Molality (-m1) Moles (gram molecular weight) of solute per 1,000 g of solvent.
Molarity (m1) Moles (gram molecular weight) of solute per litre of total solution.
Molecular Weight Cut Off (MWCO) The rating of a membrane for the size of uncharged solutes it will reject. Also referred to as nominal molecular weight cut off (NMWCO).
Multimedia filter Filter with a bed consisting of three or more separate filter media. The coarsest, lowest density at the top and the finest, highest density at the bottom.
NaHMP Sodium hexametaphosphate, an antiscalant.
Nanofiltration (NF) A crossflow process with pore sizes designed to remove selected salts and most organics above about 300 molecular weight range, sometimes referred to as loose RO.
Nephelometer A device used to measure mainly the turbidity of water with results expressed in nephelometric turbidity units (NTU). Measures light at 90°.
Non-ionic polyelectrolyte Neutral charged polymers, usually polyacrylamides, used for coagulation / flocculation. See polyelectrolyte’s.
Normalization Converting actual data to a set of reference conditions in order to 'standardize' operation to common base.
NF Nanofiltration.
NOM Natural Organic Matter.
NTU See nephelometer.
OEM Original equipment manufacturer.
O&M Operation and maintenance.
Operating pressure The gage hydraulic pressure at which feedwater enters a device.
ORP Oxidation-Reduction Potential.
Osmosis The spontaneous flow of water from a less concentrated solution to a more concentrated solution through a semi permeable membrane until chemical potential equilibrium is achieved.
Osmotic pressure A measurement of the potential energy difference between solutions on either side of a semi permeable membrane. A factor in designing the operating pressure of reverse osmosis equipment. The applied pressure must first overcome the osmotic pressure inherent in the chemical solution in order to produce any flux.
Oxidation-reduction potential The electromotive force developed by a noble metal electrode immersed in the water, referred to the standard hydrogen electrode.
Oxygen demand The amount of oxygen required for the oxidation of waterborne organic and inorganic matter under the specified test conditions.
Parts Per Billion (ppb) A measure of proportion by weight, equivalent to a unit weight of solute per billion unit weights of solution (approximate pg/L or mg/m3 in dilute solutions).
Parts Per Million (ppm) A measure of proportion by weight, equivalent to a unit weight of solute per million unit weights of solution (approximate mg/L or g/m3 in dilute solutions).
Pass A treatment step or one of multiple treatment steps producing in a membrane system a product stream.
Permeable Allowing material to pass through.
Permeate The portion of the feed which passes through the membrane, also called product.
Permeate channel spacer Fabric that mechanically supports the membrane and drains the permeate to the permeate tube, see product (permeate) channel spacer.
Permeate collector fabric See Permeate channel spacer.
Permeate flux Permeate flow rate per unit membrane area, expressed commonly as l/m2 h (or GFD).
Plant capacity Manufacture of product per unit time, expressed as m3/day, m3/h, GPD, MGD.
Plugging factor See fouling factor and SDI.
Polarization See concentration polarization.
Polyelectrolyte Synthetic (or natural) molecules, containing multiple ionic groups, used as coagulants and flocculants; available as anionic, cationic and non-ionic.
Polymers A substance consisting of molecules characterized by the repetition of one or more types of monomeric units.
Porosity That portion of a membrane filter volume which is open to fluid flow, also known as void volume.
Post treatment The addition of chemicals to the product or concentrate stream to make it suitable for the desired end use application.
Post treatment Utilization of equipment such as degasifiers to make the product or concentrate stream, or both, suitable for the desired end use application.
Pressure filtration Filtration performed in an enclosed pressurized filter vessel.
Pressure vessel The vessel containing one or more individual membrane elements and designed to withstand safely the hydraulic pressure driving the separation mechanism.
Pre-treatment Processes such as chlorination, filtration, coagulation, clarification, acidification which may be used on feedwater ahead at membrane devices to improve quality, minimize scaling and corrosion potential, control biological activity.
Product channel spacer (permeate carrier) The fabric or other material through which permeate water flows after it passes through the flat sheet membrane.
Product staging A process in which the permeate from one membrane plant is used as the feed to another membrane plant in order to further improve product quality.
Product tube The tube at the centre of the spiral wound cartridge which collects permeate water.
Productivity Flow rate of product water.
Product water Purified water produced by a process. See Permeate.
Projection A calculation usually performed by a software package, which predicts the performance of parts or all of a water plant.
Pyrogens Any substance capable of producing a fever in mammals. Often a bacterial endotoxin such as lipo polysaccharide generated by gram negative bacteria at destruction. Chemically and physically stable, pyrogens are not necessarily destroyed by conditions that kill bacteria.
Raw water Water which has not been treated. Untreated water from wells, surface sources, the sea or public water supplies.
Recovery – Y (conversion) The ratio of product quantity (permeate stream flow rate) over the feed quantity (feed stream flow rate), given as fraction or in percent.
Reject Brine, (concentrate) stream from a desalination device. Portion of the feed stream which does not pass through the membrane.
Rejection The ability of the membrane to hinder certain elements from passing through. Expressed as 1 minus the ratio between the concentration in the product and the feed.
Retentate See concentrate.
Reverse Osmosis (RO) The separation process where one component of a solution is removed from another component by flowing the feed stream under pressure across a semi permeable membrane. RO removes ions based on electro chemical forces, colloids, and organics down to 150 molecular weight. May also be called hyper filtration.
RO Reverse Osmosis.
RO train One of two or more complete RO installations, including membranes and high pressure pump operating in parallel.
S&DSI Stiff & Davis Stability Index.
Salinity The concentration of inorganic salts in water.
Salt flux Amount of dissolved salt passing through the membrane, moles per day per square unit of membrane area. salt passage, SP-SP = (CPx100)/CF
Sanitization Reduction in the number of bacterial contaminants to safe levels. Seedisinfection.
Saturation The point at which a solution contains enough of a dissolved solid, liquid, or gas so that no more will dissolve into the solution at a given temperature and pressure.
SBS Sodium bisulphite, NaHSO3.
Scale inhibitor A chemical which inhibits the growth of micro-crystals (inhibits precipitation of sparingly soluble salts). See antiscalant.
Scaling The build-up of precipitated salts on a surface, such as membranes, pipes, tanks, or boiler condensate tubes.
SDI - Salt Density Index An index calculated from the rate of plugging of 0.45 µm membrane filter. It is an indication of the amount of particulate matter in water, sometimes called fouling index.
S&DSI Stiff and Davis saturation index, measure of CaCO3 solubility in seawater or highly saline water. See LSI.
Seawater Water with an approximate concentration of total dissolved solids ranging from 30,000 to 60,000 mg/L. See brackish water, high brackish water.
Sedimentation The precipitation or settling of insoluble materials from a suspension, either by gravity or artificially. For example, centrifuge, pressure.
Semi permeable membrane A membrane which preferentially allows the passage of specific compounds while rejecting others.
SHMP Sodium HexaMetaPhosphate. (NaHMP).
Siemens A measure of electrical conductance in water, equivalent to a mho. See Mho, Ohm. Slime Biological deposits of gelatinous or filamentous matter.
SMBS Sodium MetaBiSulfite, Na2S2O5.
Softening See membrane softening.
Softener Water treatment equipment that uses a sodium based ion-exchange resin principally to remove cations as calcium and magnesium.
Solids contact clarifier Water treating device used in lime softening, waste water treatment and coagulation processes.
Solubility product [M+]a [X-]b/[MX] where the brackets indicate the concentrations of the components of the ionization equilibrium M aXb Æ aM+ + bX. For sparingly soluble salts [MX] is essentially unity.
Solutes Matter dissolved in a solvent.
Solvent Here defined as water.
SPC Standard (heterotrophic) plate count. Measurement method for enumerating bacteria.
Specific flux Flux divided by net pressure driving force.
Spiral wound cartridge A crossflow membrane element design consisting of a product tube, flat membrane leaves, feed channel spacers, anti-telescoping devices, and brine (concentrate) seal.
Spiral wound membrane A flat sheet membrane with one or more feed channel spacers and barrier layers, all of which are rolled into a spiral configuration.
Stage A sequestial arrangement of pressure vessels, usually reject staged such as 2:1 array, sometimes permeate staged as in double pass RO.
Staging See brine staging and product staging.
Standard test conditions The parameters under which a membrane manufacturer tests devices for flow and salt rejection.
Sterilization Destruction or removal of all viable organisms.
Stiff & Davis Stability Index, S&DSI An index calculated from total dissolved solids, calcium concentration, total alkalinity, pH and solution temperature that shows the tendency of a water solution to precipitate or dissolve calcium carbonate. S&DSI is used primarily for seawater RO applications.
STP Sodium triphosphate - Na5P3O10, a cleaning agent.
STPP Sodium tripolyphosphate. See STP.
Supersaturation A state in which the inorganic salt(s) are in solution at a level higher than the respective solubility product.
Suspended solids (SS) Solid organic and inorganic particles that are held in suspension in a liquid.
SWRO Seawater reverse osmosis.
System salt passage SPS is the concentration of a compound in the permeate related to its concentration in the feed water, also called apparent salt passage.
TBC Total Bacteria Count, the total number of viable microorganisms present in the sample, excluding anaerobic organisms.
TDS Total Dissolved Solids, usually expressed as mg/l or ppm (parts per million).
Telescoping The movement of the outer layers of a spiral wound cartridge in the direction of the feed flow caused by excessive pressure drop through the feed channel spacer.
Temperature correction factor (TCF) Defines the effect of temperature on permeate flow relative to a base temperature (25°C), is mainly a function of fluid characteristics but also membrane polymer.
Thin film composite (TFC) See composite membrane.
Threshold treatment The process of stopping precipitation at the start of occurrence; usually does not stop the formation of nuclei but does inhibit growth. See antiscalant.
THM Trihalomethanes; a group of low molecular weight molecules which can result from chlorination of organics typically found in surface water.
THMP Trihalomethane precursors; organic molecules found in water which have the potential of reacting with chlorine to form THMs.
Thrust collar A plastic cylinder placed between the last spiral wound cartridge and vessel end plate to support the last cartridge in a pressure vessel against telescoping.
TOC Total Organic Carbon, a measure of the level of organic constituents in water.
TOCI Total organic chlorine.
TOX Total organic halides.
TOXFP Total organic halide formation potential.
Train A grouping of devices. See array, bank, block.
Transmembrane pressure The net driving force across the membrane. The hydraulic pressure differential from the feed side to permeate side less the osmotic pressure differential on each side.
Trisodium phosphate (TSP) Na3PO4 · 12H2O, a cleaning agent.
TRC Total Residual Chlorine.
TSS Total suspended solids. Concentration of undissolved solids in a liquid, usually expressed in mg/L or ppm.
Turbidity A suspension of fine particles that scatters or absorbs light rays.
Turbidity, nephelometric (NTU) An empirical measure of turbidity based on a measurement of the light-scattering characteristics (tyndall effect) of the particulate matter in the sample.
Ultrafiltration UF A process employing semi permeable membrane under a hydraulic pressure gradient for the separation of components in a solution. The pores of the membrane are of a size which allow passage of the solvent(s) but will retain non-ionic solutes based primarily on physical size, not chemical potential.
UPW - ultra pure water Water generally used in semiconductor industry having specifications (chemical, physical and biological) for extremely low contaminant levels.
Ultraviolet (UV) radiation Wavelengths between 200 to 300 nm. These wave lengths have a strong germicidal effect. The maximum effect is at 253.7 min.
Viable Ability to live or grow. For example, bacteria, plants.
VOC (Viable Organism Count) A measure of biological activity (living or growing) in water.
VOC (Volatile Organic Compound) An organic compound with a vapour pressure higher than water.
Water softener A vessel having a cation resin in the sodium form that removes cations such as calcium and magnesium from water and releases another ion such as sodium. The resin is usually regenerated. See softener.
Y Conversion, recovery.