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Definition of Water Terms

(You can double click on any word on this page to get a full dictionary description)

This Day in History

AAMI: Association for the Advancement of Medical Instrumentation – sets the standards for kidney dialysis-grade water.

Absolute: When referring to filters is used in reference to the micron rating of cartridge or disc filters, indicating that all particles larger than a specified size will be trapped within or on the filter and will not pass through.

Absorb: The process by which a liquid penetrates the solid structure of the absorbent’s fibers or particles, which then swell in size to accommodate the liquid.

Absorption: The process of taking up a substance into the physical structure of a liquid or solid by physical or chemical action, but without chemical reaction.

ACFM: ACFM means actual cubic feet per minute. In air and gas streams the ACFM is the actual flow. When corrected for pressure and temperature, ACFM can be correlated to SCFM (standard cubic feet per minute).

Acid rain: Rainfall below the natural pH range, caused by contact with atmospheric pollutants such as nitric and sulfuric oxides and carbon monoxide.

Activated carbon: Granulated activated carbon used to remove tastes, odor, chlorine, chloramines, and some organics from water.

Activated clay: An adsorbent clay that removes color, odor, free fatty acids, etc., from oils and tallow.

Admix: Medium that is added directly into the batch tank of pre-coat to create a permeable filter cake. Usually used in place of body feed.

Adsorb: The act of selectively attracting and holding a gas, vapor, liquid, chemical or colloid onto the surface of a solid.

Adsorption: The process by which molecules, colloids, or particles adhere to the surfaces by physical action but without chemical reaction.

Aeration: The process of adding air to a water supply for the purpose of oxidizing or mixing.

Aerosols: Liquid droplets or solid particles dispersed in air or gases, of fine enough particle size (0.01 to 100 μm) to remain so dispersed for a period of time. Generally removed by coalescing filters.

Agglomerate: The process of bringing together smaller divisions into a larger mass.

Alkalinity: Capacity for neutralizing acid, usually due to presence of bicarbonate or carbonate ions. Hydroxide, borate, silicate, or phosphate ions may contribute to alkalinity in treated waters.

Angstrom: A unit of length equaling 10-10 meters, 10-4 microns, 10-8 centimeters, and 4 x 10-9 inches. The symbol is Å.

Anion: Negatively-charged ion in a solution.

Antimicrobial: An additive, material, fluid or chemical that inhibits and kills the growth of micro-organisms on contact.

Aquifer: Natural, underground porous formation where mineral-bearing water flows or is stored. Source of well water.

ASAIO: American Society for Artificial Internal Organs.

Asbestos: A fibrous silicate material, chiefly calcium magnesium silicate; a noncombustible, nonconducting, and chemical-resistant material; a known lung carcinogen.

ASME code: Used in relation to filter vessels. ASME=American Society of Mechanical Engineers, Boiler and Pressure Vessels. Sections VIII and X apply to pressure vessels.

ASTM: American Society for Testing and Materials – sets the standards for laboratory and electronics water.

Atmosphere: A unit measurement of pressure. The air pressure at sea level: 14.7 psi. (1 atm = 14.7 psi).

Backwash: Reversal of a solution’s flow through a filtration system. Often used as a cleansing mechanism in sand and dual-media filters.

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 nonliving organic material already present in the environment), or parasitic (deriving nutrition from another living organism). Often symbiotic in man, but sometimes pathogenic.

Bactericide: Agent capable of destroying bacteria.

Bacteriostat: Substance that inhibits bacterial growth and metabolism but does not necessarily kill the cell.

Baffle: A plate or deflector to provide flow distribution in a filter housing. Primary functions are to provide uniform flow and to prevent erosion of pre-coat or bed and setting of body feed.

Bar: Designation of pressure units. 1 bar = psi ÷ 14.5.

Beta of a cartridge or element: The filtration ratio (beta rating) number of particles size x μm and larger in the feed divided by the number of particles in the filtrate.

Binders: In reference to cartridge filters, chemicals used to hold or “bind” short fibers together in a filter.

Blind spots: Any place on a filter septum where liquid cannot flow through due to blinding or plugging.

Blinding: In depth and surface filtration, a buildup of particulates on or within the filter, preventing fluid flow through the filter at normal pressures.

Blowdown: In reference to boiler technology, the purge from the system of a small portion of concentrated boiler water in order to maintain the level of dissolved and suspended solids in the system below the maximum.

BOD: (Biochemical Oxygen Demand) – a measure of the amount of oxygen required for the biochemical degradation of organic material in a water sample.

Body feed: The pre-coat medium that is continuously added to the filter while it is on stream. Its purpose is to create a permeable filter cake.

Bottled water: Commercial products sold in containers as pure water for drinking and domestic use.

Bridging: The act of particles forming an arch over the openings on a septum. Also filter cakes that have grown to a size where they actually touch each other in the filter.

Bubble: The differential gas pressure that when applied to a filter element submerged in the test fluid causes the first steady emission of gas (air) from the filter element being tested. This is a means of verifying the micrometer rating of the test element.

Burst: The ability of the filter medium to resist disruption by pressure applied in the direction of normal flow.

Cake: The accumulation of solids on the medium, on the surface of the pre-coat or on the septum.

Cake space: The volumetric space available in a filter to support the formation of a cake.

Candle turbidimeter: A device principally used to measure high turbidity water with results expressed in Jackson Turbidity Units (JTU) or Formazine Turbidity Units (FTU). The JTU is measured with light scattering.

CAP: College of American Pathologists, which has set water purification standards for laboratory use

CAPD: Continuous ambulatory peritoneal dialysis

Carbonate hardness: The hardness caused by carbonates and bicarbonates of calcium and magnesium in water. The amount of hardness equivalent to the alkalinity formed and deposited when water is boiled. In boilers, carbonate hardness is readily removed by blowdown.

Carcinogenic materials: A substance or agent producing, or inciting cancer.

Cartridge filter: A filter device, usually disposable, filtering in the, range of 0.1 micron to 100 microns, and usually 2 inches to 4 inches (51 to 102 mm) in diameter and 6 inches to 60 inches (152 to 1524 mm) in length.

Cation: Positively-charged ion in a solution.

Caustic soda: Sodium hydroxide (NaOH), commonly known as lye. A commonly-used chemical in water treatment.

Cellulose: A fibrous material of vegetable origin used as a filter medium.

CFM: Cubic feet per minute

Chelating agent: A molecule, usually organic, which is soluble in water and undergoes reactions with metal ions to hold them in solution. A number of naturally-occurring organic materials in water have chelating ability, such as humic acid and lignin. Due to their chelating abilities, some organic materials interfere with water-softening processes.

Chemical solution feeder: A pump used to meter chemicals such as acid, chlorine or polyphosphate into a feedwater supply.

Chloramine: A compound consisting of chlorine and ammonia gas which retains its bactericidal qualities for a longer time than does free chlorine.

Chlorination: The addition of small amounts of free chlorine, usually 0.2 to 2.0 ppm, to render water bacteriostatic in a water supply.

Chlorine: Chemical used for its qualities as a bleaching, oxidizing or disinfecting agent in water purification.

Clarity: The clearness of a liquid as measured by a variety of methods.

Cloth: A type of woven filter septum made from natural or synthetic yarns.

Coagulant: Chemical added in water and wastewater applications to cause the formation of flocs that adsorb, entrap, or otherwise bring together suspended matter defined as colloidal. Compounds of iron and aluminum are generally used to form flocs to allow removal of turbidity, bacteria, color, and other finely-divided matter from water and wastewater.

Coalescing: The separation of mixtures of immiscible fluids (such as oil and water) with different specific gravities. Can occur whenever two or more droplets collide and remain in contact and then become larger by passing through a coalescer. The enlarged drops then separate out of solution more rapidly.

COD: Chemical Oxygen Demand – a measure of the oxygen required to oxidize chemicals contained in a sample.

Colloid: A substance of very fine particle size, typically between 0.1 and 0.001 microns in diameter suspended in liquid or dispersed in gas. Typically removable only by reverse osmosis, distillation, or ultrafiltration.

Compaction: In crossflow filtration, the result of applied pressure compressing a reverse osmosis or ultrafiltration membrane which may result in a decline in flux.

Compound: Chemical bonding or union of separate elements, ingredients, or parts.

Compressibility: Degree of physical change in volume when subject to pressure.

Concentrate: In crossflow filtration, the portion of a feed stream which does not permeate the medium but retains and is increased in the amount of ions, organics, and suspended particles which are rejected by the medium.

Concentration: The amount of material contained in a unit volume of fluid; the process of increasing the dissolved material per unit volume.

Concentration polarization: In crossflow filtration, the formation of a more concentrated gradient of rejected material near the surface of the membrane causing either increased resistance to solvent transport, or an increase in local osmotic pressure, and possibly a change in rejection characteristics of the membrane.

Condensate: Water obtained through evaporation and subsequent condensation. Normally the water resulting from condensing plant steam originally generated in a boiler. Water condensed in a water still operation is usually called distillate.

Conductivity: The property of a substance’s (in this case, water) ability to transmit electricity. The inverse of resistivity. Measured by a conductivity meter, and described in microSiemens/cm.

Contact time: The length of time an absorbent or adsorbent is in contact with a liquid prior to being removed by the filter or to the occurrence of a chemical change.

Contaminant: A source of contamination, an impurity. Any substance in water other than H2O.

Convoluting: The accordion pleating of filter media to obtain a large effective filtration area in a minimum volume.

Crossflow membrane filtration: A separation of the components of a fluid by semipermeable membranes through the application of pressure and parallel flow to the membrane surface. Includes the processes of reverse osmosis, ultrafiltration, nanofiltration, and microfiltration.

Crypto: An abbreviation for Cryptosporidium, a parasite found in water; sometimes found in drinking water, municipal water systems and private wells. It is detrimental to the digestive system, causes diarrhea, cramps and in severe cases even death.

Cycle: The length of time a filter is “on-stream” before cleaning is needed. Frequently meant to include cleaning time as well.

Dalton: A unit of mass 1/12 the mass of Carbon12. Named after John Dalton (1766-1844), founder of atomic theory and the first theorist since, Democritus (Greek, 5th century BC) to describe matter in terms of small particles

DE: The commonly-used abbreviation for Diatomaceous Earth. Diatomaceous Earth is the fossilized skeletons of minute, prehistoric aquatic plants. Insoluble in water.

Decarbonation: The process of removing CO2 from water, typically using contact towers or air scrubbers.

Degasification: The process of removing dissolved gasses from water, typically using vacuum or heat.

Deionization (DI): Process utilizing specially-manufactured ion exchange resins which remove ionized salts from water. Can theoretically remove 100% of salts. Deionization typically does not remove organics, virus or bacteria, except through “accidental” trapping in the resin and specially made strong base anion resins which will remove gram-negative bacteria.

Delta P: A commonly-used term denoting the pressure drop across a filter.

Demineralization: The process of removing minerals from water, usually through deionization, reverse osmosis, or distillation.

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.

Differential pressure: The difference in pressure between the upstream and downstream sides of a filter. It can also be the difference in pressure between two points in a system or of a component in such system.

Dirt capacity: The weight of a specified artificial contaminant which must be added to the influent to produce a given differential pressure across a filter at specified conditions. Used as an indication of the relative service life.

Disinfectant: A fluid or gas used to disinfect filters, demineralized (DI) water systems, pipe, pipelines, systems, vessels, etc.

Disinfection: The process of killing pathogenic organisms in a water supply or distribution system by means of heat, chemicals, or UV light .

Disposable: Quality describing a filter which is intended to be discarded and replaced after each service cycle.

Dissolved solids: The residual material remaining from a filtered source after evaporating the solution to a dry state.

Distillate: The product water from distillation formed by condensing vapors.

Distillation: The process of condensing steam from boiling water on a cool surface. Most contaminants do not vaporize and therefore do not pass to the distillate. Removes nearly 100% of all impurities.

Doctor Blade (knife): A sharp, hard blade that cuts the cake off the surface of a filter. Usually found on a rotary vacuum pre-coat or metal edge-type filter.

Effective area: The total area of the medium exposed to flow in a filter element.

Efficiency: The ability, expressed as a percent, of a filter to remove a specified artificial contaminant at a given contaminant concentration under specified test conditions.

Effluent: The output stream exiting a treatment system.

Electrodialysis: Dialysis that is conducted with the aid of an electromotive force applied to electrodes adjacent to both sides of the membrane.

Element: Any structural member in a filter on which the septum is supported. May be round, rectangular or cylindrical.

End cap: A ported or closed cover for the end of a cartridge, pipe or housing.

Endotoxin: A heat-resistant pyrogen, specifically a lipopolysaccharide found in the cell walls of viable and nonviable bacteria.

Endotoxin Units (EDU): Unit of measurement for pyrogen levels.

EPA: Environmental Protection Agency (USA) – an organization that has set the potable water standards.

Evaporation: Process in which water passes from a liquid to a vapor state.

Exhaustion: In water softening or ion exchange, the point where the resin can no longer exchange additional ions of the type the process was designed for.

FDA: U.S. Food and Drug Administration.

Feed/feedwater: The input solution to a treatment/purification system, including the raw water supply prior to any treatment.

Filter aid: Any material that assists in the separation of solids from liquids. Usually used on difficult filter applications.

Filter cake: The accumulated particles on a filter surface, usually from a slurry mixture, to enhance the filtering characteristics of a filter medium.

Filter medium: The permeable material that separates particles from a fluid passing through it.

Filter system: The combination of a filter and associated hardware required for the filtration process.

Filtrate: Any liquid that has passed through the filter medium. Sometimes erroneously called effluent. Also known as the clarified effluent from a filter.

Filtration: The process by which solid particles are separated from a liquid by passing the liquid through a permeable material. Also, the physical or mechanical process of separating insoluble particulate matter from a fluid, such as air or liquid, by passing the fluid through a filter medium that will not let the particulates through.

Filtration rate: The volume of liquid that passes through a given area in a specified time. Usually expressed as gallons per square foot per minute (or hour).

Floc: Coagulated groupings of formerly suspended particles which then settle by gravity.

Flocculant: Chemical(s) which, when added to water, cause suspended particles to coagulate into larger groupings (flocs) which then settle by gravity.

Flocculation: The process of agglomerating particles into larger groupings called flocs, which then settle by gravity.

Flow fatigue resistance: The ability of a filter element to resist structural failure due to flexing caused by differential pressures.

Fluid compatibility: The suitability of filtration medium and seal materials for service with the fluid involved.

Flux: In crossflow filtration, the unit membrane throughput, usually expressed in volume per unit time per area, such as gallons per day per ft2 or liters per hour per m2.

Fouling: In crossflow filtration, the reduction of flux that is attributed to a buildup of solids on the surface of the membrane.

Frazier: A test to measure the air permeability of filter septums. Usually expressed in CFM of air at a Delta P of 1/2-inch WC (water column).

FTU: Formazine Turbidity Units – a measure of turbidity, by a nephelometer.

Fuller’s Earth: A sorptive clay, also called Attapulgus Clay (Attapulgite), Bentonite (Montmorillonite) and Kaolin (Kaolinite). Generally used for filtration, acid removal, bleaching, decolorizing, clarifying agents, filter aids, floor adsorbents, animal litter, pesticide carriers, components or non carbon papers, catalysts, and refining aids. Also removal of surfactants from gasoline, kerosene, diesel and jet fuels. Not to be confused with DE.

Gauge: Thickness of steel sheet or wire diameter. The lower the gauge, the thicker the steel or larger the wire diameter. Also a device for measuring thicknesses, pressures, temperatures, etc.

Giardia cyst: A parasite found in water. Very detrimental to the digestive system, causing diarrhea, cramps and in severe cases death.

Glassing: A form for silica scaling at high temperatures, usually in high pressure boilers or stills.

gpd: Gallons per day

Grains per gallon (gpg): A unit of concentration equal to 17.1 milligrams per liter (17.1 ppm).

GRAS: Materials “Generally Regarded As Safe,” as listed by the FDA.

Groundwater: Water confined in permeable sand layers or cavities between rock or clay. All subsurface water.

Hardness: The concentration of calcium and magnesium salts in water.

Head: An end closure for the filter case or bowl which contains one or more ports. Also the measurement of pressure in a column of water expressed in feet of liquid depth x 0.433 = pounds per square inch.

Heavy metals: Metals having a high density or specific gravity of approximately 5.0 or higher. The elemental weight is also high. A generic term used to describe contaminants such as cadmium, lead, and mercury. In low concentrations most are toxic to humans.

Heel: The liquid left in the filter at the end of a cycle. Also the pre-coat left on an R.V.P.F. (Rotary Vacuum Pre-coat Filter) at the end of its cycle.

Hemodialysis: The process of purifying a kidney patient’s blood by means of dialysis membranes.

Hemolysis: Rupturing of red blood cells sometimes occurring during hemodialysis. May be caused by the presence of chloramines in the dialysis water supply.

High Efficiency Particulate Absolute (HEPA): A filter which removes from air 99.97% or more monodisperse dioctyl phthalate (DOP) particles having a mean particle diameter of 0.3 μm. Common use: “HEPA filter” high efficiency particulate air filter.

High-purity water: Highly-treated water with attention to microbiological reduction or elimination; the term commonly used in the pharmaceutical industry.

Housing: A ported chamber with closure, which directs the flow of fluid through the filter element.

Humic acid: A water-soluble organic compound composed of decayed vegetable matter which is leached into a water source by runoff. Present in most surface waters. Higher concentrations cause a brownish tint. Difficult to remove except by ultrafiltration or reverse osmosis.

Hydrocarbon: An organic compound containing only carbon and hydrogen and often occurring in petroleum, natural gas, coal, and bitumens. Most successfully removed from water by coalescing for large volumes or by using activated carbon for small volumes.

Hydrogen sulfide: A toxic gas (H2S) that is detectable by a strong “rotten egg” odor. A common by-product of anaerobic bacteria.

Hydrologic cycle: The natural cycle of water as it passes through the environment by evaporation, condensation, precipitation, and retention in the oceans or on land.

Hydrophilic: Water-accepting.

Hydrophobic: Water-rejecting.

Influent: The fluid entering the filter.

Injection: In water treatment, the introduction of a chemical or medium into the process water for the purpose of altering its chemistry or filtering specific compounds.

In-line filter: A filter assembly in which the inlet, outlet and filter element axes are in a straight line.

Inside-out flow: Fluid flow through a filter element outward from and perpendicular to its longitudinal axis. This is not the normal direction of flow for most filter elements (See outside-in flow).

Ion: An atom or molecule which has lost or gained one or more electrons, thereby acquiring a net electric charge.

Ion exchange: A process in which ions are preferentially based on equilibrium, adsorbed from a solution for equivalently-charged ions attached to small solid structures called resin.

JTU: Jackson Turbidity Units – turbidity test units of measurement registered on a candle turbidimeter.

LAL: Limulus Amoebocyte Lysate – a reagent used in the detection of endotoxin, the pyrogen of greatest concern to the pharmaceutical industry. The LAL reagent is made from the blood of the horseshoe crab, Limulus polyphemum.

Laminar flow: A flow in which rapid random fluctuations are absent, nonturbulent.

Leaf: Any flat filter element that holds or supports the filter septum.

LSI: Langelier Saturation Index – an expression of a calculation that allows the prediction of calcium carbonate precipitation at a specific condition, temperature, pH, TDS, hardness, and alkalinity.

L-Type filter: A filter assembly in which the inlet and outlet ports are at 90 degrees to each other.

Manifold: A set of ports that come together to form a common port.

Mean filtration rating: A measurement of the average size of the pores of the filter medium.

Media: The material that performs the actual separation of solids from liquids. Sometimes erroneously used to mean septum.

Media migration: Release of filtration media particles into the effluent of the filter.

Medical device manufacturer: A manufacturer that, according to the FDA, has specific manufacturing and recordkeeping which allows the manufacturer to be certified as a medical device manufacturer. The purpose is to assure physicians and patients that strict controls have been used and that component traceability is assured.

Medium: The porous material that performs the actual process of filtration. The plural of this word is “media.”

Membrane (polymeric): Highly-engineered polymer film containing controlled distribution of pores. Membranes serve as a barrier permitting the passage of materials only up to a certain size, shape, or character. Membranes are used as the separation mechanism in reverse osmosis, electrodialysis, ultrafiltration, nanofiltration, and microfiltration, as disc filters in laboratories, and as pleated final filter cartridges, particularly in pharmaceutical and electronic applications.

Mesh: Number of strands in a linear inch of woven filter fabric, usually wire. It is also used as a septum.

mg/L: Milligrams of an element per liter of water; approximately equal to ppm (See page 15).

Microfiltration (MF): Filtration designed to remove particles and bacteria in the range of 0.1 to 3 microns in diameter.

Micron: A metric unit of measurement equivalent to 106 meters, 104centimeters. Symbol is μ.

Mixed-bed: An ion exchange tank consisting of both cation and anion resin mixed together. Provides the most complete deionization of water, up to 18.3 megohm/cm resistivity. Commonly used to polish water already treated by two-bed ion exchange tanks or reverse osmosis.

Module: A membrane element combined with the membrane element housing.

Molecular weight (MW): The sum of the atomic weights of the constituents which make up a molecule. Often used to indicate size when referring to ultrafiltration of saccharide compounds (See dalton).

Molecule: The smallest physical unit of a compound or chemical, composed of one or more atoms, that retains the properties of that substance.

Multi-pass test: The test used to determine the Beta-ratio of an element. A destructive test.

Multifilament: A number of continuous fiber strands that are twisted together to form a yarn; used in weaving filter cloths.

Multiple-effect evaporation: Series-operation energy economizer system where heat from the steam generated (evaporated liquid) in the first stage is used to evaporate additional liquid in the second stage (by reducing system pressure), and so on, up to 10 or more effects.

Nanofiltration (NF): A crossflow membrane separation process which removes particles in the 250 to 1000 molecular weight range, selected salts and most organics; sometimes referred to as a softening membrane process.

NCCLS: National Committee for Clinical Laboratory Standards – a committee that has promulgated purified water standards.

Nephelometer: A device used to measure mainly low-turbidity water with results expressed in Nephelometric Turbidity Units (NTU).

Nominal: With regard to the micron rating of cartridge filters, refers to an approximate size particle, the vast majority of which will not pass through the filter. A small amount of particles this size or larger may pass through the filter.

Nominal rating: An arbitrary micrometer value indicated by various filter manufacturers.

Noncarbonate hardness: Hardness caused by chlorides, sulfates, and nitrates of calcium and magnesium. Evaporation of waters containing these ions makes the water highly corrosive.

Nonwoven: A filter cloth or paper that is formed of synthetic fibers that are randomly oriented in the media. Usually held together by a binder.

Normal flow: The flow of the entire feedwater stream in a single direction directly through the filter medium. The flow is generally “normal,” or perpendicular, to the medium.

NTU: Nephelometric Turbidity Units – the result of passing a light beam through a water sample with a nephelometer to quantify low-turbidity water. The NTU is measured by light scattering.

On-stream: Describes when a filter system is producing a filtered product while in operation.

Osmosis: The spontaneous flow of water from a less concentrated solution to a more concentrated solution through a semipermeable membrane until energy equilibrium is achieved.

Osmotic pressure: A measurement of the potential energy difference between solutions on either side of a semipermeable membrane. A factor in designing reverse osmosis equipment. The applied pressure must first overcome the osmotic pressure inherent in the chemical solution in order to get good purification and flux.

Outside-in flow: Fluid flow is through a filter element perpendicular to and toward the axis of the element on most filters today. Exception is the coalescing element which always flows from inside to outside to remove the accumulated water from the fuel stream.

ORP: Oxidation Reduction Potential. It is the oxidizing potential of free oxidizers in water that is measured by electrical current of a volt meter. The combination of voltage (potential) and pH give us a standard of ORP or oxidizers available for sanitation for several different types of water.

Oxidation: Process by which electrons are lost to an oxidizing agent in order to increase a molecule or ion in positive valence.

Oxidizing filters: Filters that use a catalytic medium such as manganous oxide to oxidize iron and manganese and then filter the impurities from the water after they have been oxidized.

Ozonator: A device which generates ozone by passing a high-voltage current through a chamber containing air or oxygen. Used as a disinfection system.

Ozone (03): An unstable, highly reactive state of the oxygen formed by passing air or oxygen through a high-voltage electric charge or strong light source. An excellent oxidizing agent and bactericide.

Particle filtration (PF): Filtration rated in the range of 1 to 75 microns. Typically handled by cartridge filters.

Particulate: Minute, separate pieces of matter.

Permeable: Allowing some material to pass through.

Permeate: That portion of the feed stream which passes through a membrane, leaving behind a more concentrated stream.

Permeator: A hollow fine-fiber membrane element itself consisting of thousands of hollow fibers.

pH: An expression of hydrogen ion concentration; specifically, the negative logarithm of the hydrogen ion concentration. The range is from 0 to 14, with 7 as neutral, 0 to less than 7 as acidic, and 7 to 14 as alkaline (basic).

Phase: A state of matter, either solid, gaseous, or liquid.

Polymer: A chemical compound with many repeating structural units produced by uniting many primary units called monomers.

Pore: An opening in a membrane or filter matrix.

Porous: The ability of certain substances to pass fluids due to an open physical structure.

ppb: Parts per billion, commonly considered equivalent to micrograms per liter (μg/L).

ppm: Parts per million, commonly considered equivalent to milligrams per liter (mg/L).

ppt: Parts per trillion, commonly considered equivalent to nanograms per liter (ng/L).

Precipitate: An insoluble product that is in the solution or liquid mixture.

Precipitation: The process of producing an insoluble reaction product from a chemical reaction, usually a crystalline compound that grows in size to be settleable.

Precursors: Compounds such as humic acid which may lead to the creation of other compounds, such as THM.

psi: Pounds per square inch (pressure).

psid: Pounds per square inch differential.

psig: Pounds per square inch gauge.

Pyrogen: Any substance capable of producing a fever in mammals. Often an organic substance shed by bacteria during cell growth. Chemically and physically stable, pyrogens are not necessarily destroyed by conditions that kill bacteria.

Reagent-grade water (ASTM): Water that meets the standards for reagent use promulgated by American Society for Testing and Materials. Four ASTM reagent-grades, I through IV, have been established depending upon intended use. See Appendix for specific quality requirements.

Recirculation: a) In crossflow membrane systems, the recycling of a portion of the stream to maintain a desirable flow. b) In water system design, the continuous operation of the transfer pump to keep water flowing through the system above the use rate, to reduce the hazard of bacterial growth. A portion of the water continuously goes back to the break tank.

Regeneration: The displacement from the ion exchange resin of the ions removed from the process water or waste stream.

Rejection: In crossflow membrane systems, the process of retaining at the membrane contaminants that are larger than the membrane’s pore sizes or are repelled by an electrical charge. In a membrane system, expressed as a percent of the total presence of those contaminants.

Resins (ion exchange): Specially manufactured polymer beads used in the ion exchange process to remove dissolved salts from water.

Resistivity: The property of a substance (in this case, water) to resist the flow of electricity; the measurement of that resistance. The inverse of conductivity. Measured by a resistivity monitor and described in megohmcm.

Reverse osmosis (RO): The separation of one component of a solution from another component by flowing the feed stream under pressure across a semipermeable membrane. RO concentrates ionized salts, colloids, and organics down to 150 molecular weight in the concentrate stream and provides a purified stream of water. May also be called hyperfiltration.

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.

Scaling: The buildup of precipitated salts on such surfaces as pipes, tanks and boiler condensate tubes.

Scavenger: A filter, or element in the bottom of a filter, that recovers the liquid heel that remains in the filter tank at the end of a cycle.

Screen: A term commonly used for septum. Also a wire mesh screen used to screen out large-sized particles that would clog a filter cartridge. Usually installed on the suction side of a pump.

SDI: Silt Density Index – test used to measure the level of suspended solids in feedwater for a reverse osmosis system.

SEMI: Semiconductor Equipment and Materials International – has set the electronics-grade purified water standards.

Semipermeable: In membranes, a membrane which allows a solvent such as water to pass through, while rejecting certain dssolved or colloidal substances.

Sepralator: A spiral-wound membrane element in crossflow membrane systems. Modular and replaceable.

Septum: A binding wall or membrane.

Side seal: The longitudinal seam of the filter medium in a pleated filter element.

Solutes: Matter dissolved in a solvent.

Sparger: A device to introduce compressed air or gas into a liquid to agitate it or to dissolve the air or gas in this liquid. Spargers are made of porous ceramic or stainless steel in various grades (porosities) to provide a specific-sized “bubble.”

Strainer: A coarse filter element (pore size over 40 μm); also a unit that screens out large particles, normally on the suction side of a pump.

Suspended solids (SS): Solid organic and inorganic particles that are held in suspension in a solution.

TDS: Total Dissolved Solids – See dissolved solids.

THM: Trihalogenated Methane Compound – Initiated by contact between free chlorine and certain organics to form materials similar to certain organic solvents. Considered a carcinogen.

TOC: Total Organic Carbon – The amount of carbon bound in organic compounds in a water sample as determined by a standard laboratory test. The CO2 is measured when a water sample is atomized in a combustion chamber.

Traceability: In medical and pharmaceutical device manufacturing, the stringent recordkeeping on the use and origin of component materials.

Transpires: The process of a plant giving off water directly to the air.

TS: Total Solids – The sum of total dissolved solids and total suspended solids.

TSS: Total Suspended Solids – The residual matter which can be removed from a solution by filtration.

Turbidity: A suspension of fine particles in water that cause cloudiness and will not readily settle due to small particle size.

Turbidity units: Measurement of the relative ability of a solution to allow a light beam to pass through it.

Two-bed: A pairing of cation and anion ion exchange tanks, typically operating in series. Best used for the deionization of relatively high volumes of water. Capable of product water resistivity of up to 4 megohm/cm.

Ultrafiltration (UF): Separation of one component of a solution from another component by means of pressure and flow exerted on a semipermeable membrane, with membrane pore sizes ranging from 10Å to 0.2 micron. Typically rejects organics over 1000 MW while passing ions and small organics.

Ultrapure water: Highly-treated water of high resistivity and no organics; usually used in the semiconductor and pharmaceutical industries.

Ultraviolet (UV): Radiation having a wave length shorter than visible light but no longer than X-rays. Ultraviolet light with a wave length of 254 nm is used to kill bacteria and destroy ozone.

Unloading: The release of contaminant that was originally captured by the filter medium.

USP: United States Pharmacopoeia which publishes standards for the pharmaceutical industry, including those for water quality. Was established by the US Congress in 1884 to control drug makeup.

Validation: In the pharmaceutical industry, the mandating of specific testing and recordkeeping procedures to ensure compliance not only with a specific quality but with a specific means to achieve that quality.

Vaporize: To convert a liquid into a vapor.

Velocity: Free air passing through a filter panel and measured in feet per minute (fpm). It is determined by the volume of air/min (ft3/m) divided by the area of the panel (ft2). It is expressed in this case as ft/min divided by feet per minute (fpm).

Virus: Any of a large group of submicroscopic infective agents capable of growth and multiplication only in living cells of a host.

Viscosity: That property of fluids by which they offer resistance to flow. Measured in poise, kinematic viscosity, centistokes, saybolt universal seconds (SUS), seconds saybolt, degree Engler and degree Barbey, Gardner-Holt, etc.

VOC: Volatile organic compound – synthetic organic compounds which easily volatilize. Many are suspected carcinogens.

Voids: The openings or pores in a filter medium.

Wash filter: A filter in which a larger unfiltered portion of the fluid flowing parallel to the filter element axis is utilized to continuously clean the influent surface which filters the lesser flow.

WFI: Water For Injection – high-purity water intended for use as a solvent for the preparation of parenteral (injectable) solutions. Must meet specifications as listed in the USP.

WHO: World Health Organization – part of the United Nations which has set the standards for potable water.

Alkalinity: Alkalinity is comprised primarily of carbon dioxide, bicarbonate, carbonate and hydroxides. Naturally occurring alkalinity is the earth’s natural buffering system in that small doses of strong acids (e.g. acid rain) react with alkalinity and result in relatively small changes in pH. Carbon dioxide and bicarbonate are in a balance between the pH range of 4.4 and 8.2. At a pH of 4.4 or lower, all alkalinity is in the form of carbon dioxide. At a pH of 8.2, there is no carbon dioxide and all alkalinity is bicarbonate. Bicarbonate and carbonate are in a balance between the pH range of 8.2 and 9.6. At a pH of 9.6, there is no carbon dioxide or bicarbonate and all alkalinity is carbonate. As the pH increases above 9.6, hydroxyl alkalinity due to the presence of the hydroxide ion starts to occur. Most naturally occurring water sources have a pH between 6 and 8.4, so the presence of hydroxides is the result of man-made activity. Alkalinity, especially by boiler water chemists, can be reported as M-Alkalinity and P-Alkalinity. M-Alkalinity measures the Total Alkalinity in a water in terms of “ppm as calcium carbonate” based on an acid titration to a pH of 4.2 using a Methyl orange indicator endpoint. P-Alkalinity measures the amount of bicarbonate, carbonate and hydroxyl alkalinity based on an acid titration to a pH of 8.2 using a Phenolphthalein pink indicator endpoint.

Barium (Ba): A divalent cation. The solubility of barium sulfate (BaSO4) is low and can cause a RO scaling problem in the back-end of a RO. Barium sulfate solubility is lower with increasing sulfate levels and decreasing temperatures. Typically, barium can be found in some well waters, with typical concentrations less than 0.05 ppm to 0.2 ppm. It is important that barium be measured with instruments capable of 0.01 ppm (10 ppb) minimum detection levels. With saturation at 100%, super-saturation up to 6000% is typical with an antiscalant.

Bicarbonate (HCO3): A monovalent anion. The solubility of calcium bicarbonate is low and can cause a RO scaling problem in the back-end of a RO. Calcium bicarbonate solubility is measured using LSI (Langlier Saturation Index) for brackish waters or the Stiff-Davis Index for seawaters and is lower with increasing temperature and increasing pH. Bicarbonate is one component of alkalinity and its concentration is in a balance with carbon dioxide between the pH range of 4.4 and 8.2 and in a balance with carbonate between the pH range of 8.2 and 9.6.

Calcium (Ca): A divalent cation. Calcium, along with magnesium, is a major component of hardness in brackish water. The solubility of calcium sulfate (CaSO4)(gypsum) is typically limited to 230% with the use of an antiscalant. The solubility of calcium carbonate is typically limited to a LSI (Langlier Saturation Index) value of positive 1.8 to 2.5.

Carbon Dioxide (CO2): Carbon dioxide is a gas that when dissolved in water reacts with the water to form weak carbonic acid (H2CO3). If a pure water was completely saturated with carbon dioxide, its concentration would be about 1600 ppm and the pH would be about 4.0. A typical source for carbon dioxide in natural waters is the result of a balance with bicarbonate alkalinity based on the pH of the water. The concentration of carbon dioxide in water is typically indirectly determined by graphical comparison to the bicarbonate concentration and pH. Carbon dioxide and the bicarbonate ion are in a balance between the pH range of 4.4 and 8.2. The alkalinity is all carbon dioxide at pH 4.4 and is all bicarbonate at pH 8.4. The RO design program calculates the carbon dioxide level based on the bicarbonate level and pH of the water. Carbon dioxide, being a gas, is not rejected or concentrated by a RO membrane, therefore its concentration will be the same in the feed, permeate and concentrate. Acidifying the RO feed water will lower pH by converting bicarbonate to carbon dioxide.

Carbonate (CO3): A divalent anion. The solubility of calcium carbonate is low and can cause a RO scaling problem in the back-end of a RO. Calcium carbonate solubility is measured using LSI (Langlier Saturation Index) for brackish waters or SDSI (Stiff-Davis Index) for seawaters and is lower with increasing temperature and increasing pH. Carbonate is one component of alkalinity and its concentration is in a balance with bicarbonate between the pH range of 8.2 and 9.6. At a pH of 9.6 and higher, there is no carbon dioxide or bicarbonate, with all alkalinity being in the carbonate form.

Ionic Strength: The solubility of sparingly soluble salts increases with increasing feed TDS. To account for this effect in calculating the solubility of a salt (e.g. calcium sulfate, barium sulfate, strontium sulfate or SDSI), the Ionic Strength of a water is calculated. The Ionic Strength of each ion is derived by taking the ppm concentration of each ion (as calcium carbonate) and multiplying each monovalent ion by 1 x 10-5 and each divalent ion by 2 x 10-5. Summing the Ionic Strength of each ion then derives the total Ionic Strength of the water.

Iron (Fe): Iron is a water contaminant that takes two major forms. The water-soluble form is known as the ferrous state and has a + 2 valence state. In non-aerated well waters ferrous iron behaves much like calcium or magnesium hardness in that it can be removed by softeners or its precipitation in the back end of the RO system can be controlled by the use of a dispersant chemical in an RO feed water. The water-insoluble form is known as the ferric state and has a + 3 valence state. Typically, RO manufacturers will recommend that combined iron levels be less than 0.05 ppm in the RO feed. If all iron is in the soluble ferrous form, iron levels up to 0.5 ppm in the feed can be tolerated if the pH is less than 7.0 (though an iron dispersant is recommended). The introduction of air into water with soluble ferrous iron will result in the oxidation to insoluble ferric iron. Soluble iron can be found in deep wells, but can be converted into the more troublesome insoluble iron by the introduction of air by being placed in tanks or by leaky pump seals. Soluble iron can be treated with dispersants or can be removed by iron filters, softeners or lime softening. Insoluble ferric iron oxides or ferric hydroxides, being colloidal in nature, will foul the front end of the RO system. Sources of insoluble iron are aerated well waters, surface sources, and iron scale from unlined pipe and tanks. Insoluble iron can be removed by iron filters, lime softening, softeners (with limits), ultrafiltration (with limits) and multimedia filtration with polyelectrolyte feed (with limits). Precautions are required with the use of potassium permanganate in manganese greensand iron filters in that potassium permanganate is an oxidant that could damage any polyamide membrane. Precautions are also required with a cationic polyelectrolyte in that they can irreversibly foul a negatively charged polyamide membrane. Corrosion proof vessels and piping (e.g. FRP, PVC or stainless steels) are recommended for all RO systems, RO pretreatment, and distribution piping coming to the RO system. Iron as foulant will quickly increase RO feed pressure requirements and increase permeate TDS. In some cases, the presence of iron can create a bio-fouling problem by being the energy source for iron-reducing bacteria. Iron-reducing bacteria can cause the formation of a slimy biofilm that can plug the RO feed path.

LSI (Langlier Saturation Index): LSI is a method of reporting the scaling or corrosive potential of low TDS brackish water based on the level of saturation of calcium carbonate. LSI is important in RO water chemistry in determining whether a water will or will not form calcium carbonate scale. Water with a negative LSI is considered corrosive to metal piping and will not form calcium carbonate scale. Water with a positive LSI is not corrosive, but it will tend to form calcium carbonate scale. LSI is important to RO chemists as a measurement of the scaling potential for calcium carbonate. The LSI value is calculated by subtracting the calculated pH of saturation of calcium carbonate from the actual feed pH. Calcium carbonate solubility decreases with increasing temperature (as evidenced by the liming of a teakettle), higher pH, higher calcium concentration, and higher alkalinity levels. The LSI value can be lowered by reducing pH by the injection of an acid (typically sulfuric or hydrochloric) into the RO feed water. A recommended target LSI in the RO concentrate is negative 0.2 (which indicates that the concentrate is 0.2 pH units below the point of calcium carbonate saturation). A negative 0.2 LSI allows for pH excursions in actual plant operation. A polymer-based antiscalant can also be used to inhibit the precipitation of calcium carbonate. Some antiscalant suppliers have claimed the efficacy of their product up to a positive LSI value of 2.5 in the RO concentrate (though a more conservative design LSI level is +1.8). Sodium hexametaphosphate, an inorganic antiscalant, was used in the early days of RO but the maximum concentrate LSI was + 0.5 and it had to be made in short-lived batches as the air easily oxidized it.

Magnesium (Mg): A divalent cation. Magnesium can account for about a third of the hardness in a brackish water, but can have a concentration five times higher than calcium in sea water. The solubility of magnesium salts is high and typically does not cause a scaling problem in RO systems.

Manganese (Mn): Manganese is a water contaminant present in both well and surface waters, with levels up to 3 ppm. Manganese, like iron, can be found in organic complexes in surface waters. In oxygen-free water, it is soluble. In the oxidized state, it is insoluble and usually in the form of black manganese dioxide (MnO2) precipitate. An alert level for potential manganese fouling in a RO aerated RO feed waters is 0.05 ppm. Drinking water regulations limit manganese to 0.05 ppm due to its ability to cause black stains. Dispersants used to control iron fouling can be used to help control manganese fouling.

pH: The pH of the feed water measures the acidity or basicity. A pH of 7.0 is considered neutral. A pH between 0.0 and 7.0 is acidic. A pH between 7.0 and 14.0 is basic. To the analytical chemist, pH is a method of expressing hydrogen ion concentration in terms of the power of 10 with the pH value being the negative logarithm of the hydrogen ion concentration. To the water chemist, pH is important in defining the alkalinity equilibrium levels of carbon dioxide, bicarbonate, carbonate and hydroxide ions. The concentrate pH is typically higher than the feed due to the higher concentration of bicarbonate/carbonate ions relative to the concentration of carbon dioxide. The RODESIGN program allows the user to adjust the pH of the feed water using hydrochloric and sulfuric acid. Lowering the feed pH with acid results in a lower LSI (Langlier Saturation Index) value, which reduces the scaling potential for calcium carbonate. Feed and concentrate (reject) pH can also effect the solubility and fouling potential of silica, aluminum, organics and oil. Variations in feed pH can also affect the rejection of ions. For example, fluoride, boron and silica rejection are lower when the pH becomes more acidic.

SDSI (Stiff Davis Saturation Index): SDSI, in similar fashion as LSI, is a method of reporting the scaling or corrosion potential of high TDS seawater based on the level of saturation of calcium carbonate. The primary difference between SDSI for high TDS seawater and LSI for low TDS brackish water is the effect that increasing ionic strength has on increasing solubility. The solubility of sparingly soluble salts increase with higher TDS and ionic strength, based on the theory that a denser ion population interferes in the formation and/or precipitation of the sparingly soluble salt.

Silica (SiO2): Silica (silicon dioxide), in some cases, is an anion. The chemistry of silica is a complex and somewhat unpredictable subject. In similar fashion as TOC reports the total concentration of organics (as carbon) without detailing what the organic compounds are, silica reports the total concentration of silicon (as silica) without detailing what the silicon compounds are. The “Total Silica” content of water is composed of “Reactive Silica” and “Unreactive Silica”. Reactive silica (e.g. silicates SiO4) is dissolved silica that is slightly ionized and has not been polymerized into a long chain. Reactive silica is the form that RO and ion exchange chemists hope for. Reactive silica is the form of silica to be used in RO projection programs. Reactive silica, though it has anionic characteristics, is not counted as an anion in terms of balancing a water analysis but it is counted as a part of total TDS. Unreactive silica is polymerized or colloidal silica, acting more like a solid than a dissolved ion. Silica, in the colloidal form, can be removed by a RO but it can cause colloidal fouling of the front-end of a RO. Colloidal silica, with sizes as small as 0.008 micron can be measured empirically by the SDI (Silt Density Index) test, but only that portion that is larger than 0.45 micron or larger. Particulate silica compounds (e.g. clays, silts and sand) are usually 1 micron or larger and can be measured using the SDI test. Polymerized silica, which uses silicon dioxide as the building block, exists in nature (e.g. quartzes and agates). Silica, in the polymerized form, also results from exceeding the reactive silica saturation level. The solubility of reactive silica is typically limited to 200-300% with the use of a silica dispersant. Reactive silica solubility increases with increasing temperature, increases at a pH less than 7.0 or more than 7.8, and decreases in the presence of iron which acts as a catalyst in the polymerization of silica. Silica rejection is pH sensitive, with increasing rejection at a more basic pH as the reactive silica exists more in the salt form than in the acidic form.

Strontium (Sr): A divalent cation. The solubility of strontium sulfate is low and can cause a RO scaling problem in the back-end of a RO. Strontium sulfate solubility is lower with increasing sulfate levels and decreasing temperatures. Typically, strontium can be found in some well waters where lead ores are also present, with typical concentrations less than 15 ppm. With saturation at 100%, super-saturation up to 800% is typical with an antiscalant.

Sulfate (SO4): A divalent anion. The solubility of calcium, barium and strontium sulfate is low and can cause a RO scaling problem at the concentrate end of a RO. The solubility of these sparingly soluble salts is lower with decreasing temperature. The recommended upper limit for sulfate in potable water is 250 ppm based on taste issues.



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