Glossary of Terms
Absorption—The process of one substance actually penetrating into the structure of another substance. activated alumina—A medium made by treating aluminum ore so that it becomes porous and highly adsorptive. Activated alumina will remove several contaminants including fluoride, arsenic, and selenium. Activated alumina medium requires periodic cleaning with an appropriate regenerant such as alum, acid, and/or caustic.
Activated carbon—A water treatment medium, found in block, granulated, or powdered form, which is produced by heating carbonaceous substances (bituminous coal or cellulose-based substances such as wood or coconut shell) to 700ºC or less in the absence of air to form a carbonized char, and then activating (oxidizing) at 800ºC to 1000ºC with oxidizing gases such as steam and carbon dioxide (oxygen is never used as the oxidizing gas because its reaction with the carbon surface is too rapid and violent) to form pores, thus creating a highly porous adsorbent material.
Activated carbon is commonly used for dechlorination and for reducing trace and soluble materials such as organic chemicals and radon from water.
Activated carbon block filter—Activated carbon block is a blend of fine activated carbon (e.g., 80 X 325 mesh activated carbon), water, and a suitable binder (such as polyethylene or a similar material) that is mixed and molded and hardened or extruded to a cartridge filter of any size and shape. Sometimes specialized media are added along with activated carbon to provide customized performances for specific contaminants. The binder is particularly designed and chosen to hold the carbon and other media in a fixed solid matrix, yet, not to plug up the pores of the activated carbon.
Even though the binder does occlude a portion of the adsorption sites, the finer mesh size gives activated carbon block filters faster adsorption kinetics and generally two to four times greater adsorption capacity than equivalent volumes of loose granular activated carbon. Activated carbon block filters typically have a 0.5 to one micron filtration capability, making it also helpful for particulate filtration, insoluble lead reduction, and demonstrating, in some cases, removal of Giardia and Cryptosporidium.
Activated silica—A negatively-charged colloidal substance generally formed by combining a dilute sodium silicate solution with a dilute acidic solution (or other activant). Generally used as a coagulant aid.
This is different from adsorption in which one substance adheres to the surface of another.
Air check—A device which allows water, but not air, to pass through it. An air check is a typical component of a treatment system using a regenerant eductor.
air gap—A clear vertical space between the end of the water treatment device’s drain line and the flood level rim of a receptacle which holds water. An air gap is used to prevent cross connection between the water treatment device and a possible source of waste water thereby preventing a reverse flow of water from the sewer into the water supply system. Without an air gap, such reverse flow could occur due to an increase in the pressure in the sewer system or the creation of a negative pressure in the water supply line. Local plumbing codes indicate how wide the air gap needs
Alkaline—The condition of water or soil which contains a sufficient amount of alkali substances to raise the pH above 7.0.
Alkalinity— A measure of concentration of all species in water capable of neutralizing an acid by binding a hydrogen ion, expressed as mg/L or ppm of calcium carbonate equivalents. Alkalinity is measured by titration and is not equivalent to pH.
The most common alkalinity components in naturally occurring surface and groundwater are bicarbonate, carbonate ions and hydroxide ions. As bicarbonate and carbonate ions typically occur in the greatest concentration, the contribution by other species to the measured alkalinity is negligible and often ignored for the purposes of sizing water treatment equipment. SEE ALSO alkalinity tests; pH.
Alkalinity tests—There are three different tests used for testing alkalinity. They are usually done in this order:
1. The pH alkalinity test will indicate the presence or absence of hydroxide alkalinity. A pH reading of 8.3 or above indicates the presence of hydroxide alkalinity.
2. The phenolphthalein test measures “P alkalinity” which is made up of all hydroxide alkalinity plus 1/2 of the carbonate alkalinity. P alkalinity is that portion of alkalinity above pH 8.3. Phenolphthalein in water changes color from pink above pH 8.3 to clear at pH 8.3.
3. The Methyl Orange test measures the “M alkalinity” which is the remaining ½ of the carbonate alkalinity plus all of the bicarbonate alkalinity. Methyl orange alkalinity measures total alkalinity of water. The methyl orange endpoint is pH 4.5; no alkalinity exists in water below pH 4.5.
Note: Free carbon dioxide (CO2) gas can exist dissolved in water between pH 4.5 and pH 8.3. Below pH 4.5, CO2 escapes quickly into the environment and above pH 8.3 CO2 becomes carbonate (CO32-) alkalinity. SEE ALSO alkalinity.
Alternating system—A dual automatic softener system functioning with one unit in service and one on standby. When a predetermined gallonage of softened water has passed or when a monitor detects hard water breakthrough, the idle or standby unit automatically goes into service. The spent unit then regenerates and becomes the idle/standby unit.
Alum—The common name for aluminum sulfate [Al2(SO4)3 • 14H2O] which is often used as a coagulant in water treatment.
Anaerobic—A condition in which there is no air or no available free oxygen.
Artesian (aquifer or well)—Water held under pressure in porous rock or soil confined by impermeable geologic formations. An artesian well is free-flowing. SEE ALSO confined aquifer.
Oxidizing agent—helps break down protein soils like egg and milk, aids in removing such stains as coffee or tea, and lessens spotting of glassware.
Automatic water softener (or automatic filter)—A water softener (or filter) that is equipped with a clock timer which automatically initiates the backwash and/or regeneration process at certain preset intervals of time. All operations, including bypass of treated or untreated water (depending upon design), backwashing, brining, rinsing, and returning the unit to service are performed automatically.
Backwash A form of backflow which occurs due to negative pressure.
Calcite 1. Calcium carbonate (CaCO3). 2. A trade name for finely ground grades of marble or limestone, very high in calcium carbonate, which are used to raise the pH reading (reduce the acidity) of low pH (acidic) water or to filter out sediment.
Bacteria Single-celled organisms (singular form=bacterium) which lack well-defined nuclear membranes and other specialized functional cell parts and reproduce by cell division or spores. Bacteria may be free-living organisms or parasites. Bacteria (along with fungi) are decomposers that break down the wastes and bodies of dead organisms, making their components available for reuse. Bacterial cells range from about 1 to 10 microns in length and from 0.2 to 1 micron in width. They exist almost everywhere on earth. Despite their small size, the total weight of all bacteria in the world likely exceeds that of all other organisms combined. Some bacteria are helpful to man, others harmful.
Bacteriacide Any substance or agent which kills bacteria, both disease causing and non-disease causing. Spores and nonbacterial microorganisms (e.g., algae, fungi, and viruses) are not necessarily killed by a bactericide.
Bacteriostat Having the ability to inhibit the growth of bacteria without destroying the bacteria. For example, silver-impregnated activated carbon will reduce bacterial colonization in a bed but not eliminate it.
Barium Fouling In ion exchange deionization, a condition where the cation exchanger resin becomes coated with a very insoluble coating of barium sulfate. This occurs in the decationization unit when regenerated with sulfuric acid, where a barium-bearing water is being processed. Generally, the remedy must be to replace the cation resin and install upstream water softening to remove the barium prior to the deionization treatment.
Bead (resin bead )In water processing, refers to the spherical shape of individual particles of ion exchange resin products, as compared to the irregular shaped particles of most other granular media products.
Bed The mass or volume of ion exchange resin or other media through which the water passes in the process of water treatment.
Bed depth The height of the resin or other media (excluding support material) in a bed, usually expressed in inches or centimeters.
Bicarbonate hardness The hardness of a water due to the presence of calcium and magnesium bicarbonates, usually the major component of carbonate hardness or total hardness. Bicarbonate hardness is often referred to simply as carbonate hardness.
Birm The trade name for a manganese dioxide-coated volcanic aluminum silicate (pumicite) used as an oxidizing-catalyst filter for iron and manganese reduction.
Black Water Liquid and solid human body waste and the carriage water generated through toilet usage.
Block carbon Activated carbon block is a blend of fine activated carbon (e.g., 80 X 325 mesh activated carbon), water, and a suitable binder (such as polyethylene or a similar material) that is mixed and molded and hardened or extruded to a cartridge filter of any size and shape. Sometimes specialized media are added along with activated carbon to provide customized performances for specific contaminants. The binder is particularly designed and chosen to hold the carbon and other media in a fixed solid matrix, yet, not to plug up the pores of the activated carbon. Even though the binder does occlude a portion of the adsorption sites, the finer mesh size gives activated carbon block filters faster adsorption kinetics and generally two to four times greater adsorption capacity than equivalent volumes of loose granular activated carbon. Activated carbon block filters typically have a 0.5 to 1 micron filtration capability, making it also helpful for particulate filtration, insoluble lead reduction, and demonstrating, in some cases, removal of <i>Giardia</i> and <i>Cryptosporidium</i>.
Blue Green Algae -Single-celled organisms (singular=cyanobacterium) similar to bacteria, except cyanobacteria contain the green pigment chlorophyll (as well as other pigments), which traps the energy of sunlight and enables these organisms to carry on photosynthesis. Cyanobacteria are autotrophic producers of their own food from simple raw materials, whereas bacteria are heterotrophic decomposers of the wastes and bodies of other organisms. Cyanobacteria were formerly known as blue-green algae. Blooms or population explosions of cyanobacteria cause water pollution. Some cyanobacteria-like bodies (CLBs) have been associated with causing waterborne diarrheal illnesses.
Bottled Mineral Water Bottled water containing fluoride. The label shall specify whether the fluoride is naturally occurring or added. Any water which meets the definition of bottled fluoridated water shall contain not less than 0.8 milligrams per liter fluoride ion and otherwise comply with the Food and Drug Administration (FDA) quality standards in Section 103.35(d)(2) of Title 21 of the Code of Federal Regulations (CFR).
Bottled Water Artisian Bottled water from a well tapping a confined aquifer in which the water level stands above the water table. Bottled artesian water shall meet the requirements of bottled natural water.
Brackish Water Water containing dissolved solids in the range of 1,000 to less than 15,000 parts per million.
Bridging. Bridging occurs in water softening when salt sticks together to form one large solid mass of pellets, or by the salt caking in a dry-salt brine tank which causes failure of the liquid or brine beneath the dry salt to become saturated. The result of bridging is insufficient salt in the regenerant solution to properly regenerate the cation resin. 2. The ability of particles to form a crustlike film over void spaces within a filter medium or membrane.
Brine A strong solution of salt(s) (usually sodium chloride and other salts too) with total dissolved solids concentrations in the range of 40,000 to 300,000 or more milligrams per liter. Potassium or sodium chloride brine is used in the regeneration stage of cation and/or anion exchange water treatment equipment. Sodium chloride brine saturation in an ion exchange softening brine tank is about 26 percent NaCl by weight at 60 degrees Fahrenheit.
Brine draw Usually means the process of drawing a brine solution into a cation or anion exchange water treatment device during regeneration.
Bromine A nonmetallic usually univalent or pentavalent element that lies between chlorine and iodine in the halogen group of the periodic table. Bromine has been used in swimming pools for disinfection and in cooling towers as a biocide, but its use in drinking water as a primary disinfectant has been limited because of uncertain effectiveness in the presence of organic material, ammonia, and other amines.
Cartridge Filter A device often used for single faucet water treatment, made up of a housing and a removable cartridge (element). In high flow rate commercial applications, the elements are clustered in a large housing, and the elements are cleanable and reusable. In residential use, disposable elements are used.
Catalyst media Those filter media which can cause certain reactions to occur in water treatment, such as activated carbon, calcite, manganese greensand, magnesium oxides, and dissimilar metal alloys.
Catalyst Oxidizing Filter A class of media bed filters which contain manganese treated greensand, zeolites, or pumicites.
Catalytic Activated carbon Activated carbon with modified surface properties that enhance the functionality of the activated carbon in converting the oxidation state of various elements. For example, with hydrogen sulfide (H2S), the sulfide ion (S-) is adsorbed and then converted on the catalytic carbon to elemental sulfur (S0) and sulfate ion (SO4 --). Once the sulfide is adsorbed and converted, it is desorbed and the site is restored. For these reactions to occur, excess dissolved oxygen is required in the water and a minimum empty bed contact time (EBCT) of five minutes may be necessary.
Cation Exchange The ion exchange process in which cations in solution are exchanged for other cations available from an ion exchange product. Formerly called base exchange.
Cation Exchange Resin An ion exchange material possessing reverse exchange ability for cations. Sulfonated polystyrene copolymer divinylbenzene exchange resin is used almost exclusively today in ion exchange water softeners. A cation exchange resin may be called a cation exchanger or a base exchanger.
Channeling The higher and unbalanced flow of water or regenerant through a limited number of passages in a filter or ion exchanger bed, as opposed to an evenly distributed flow through all passages in the bed. Channeling results in the greater flow of liquid through passages of lower resistance which can occur in fixed beds or columns of media particles due to nonuniform packing, irregular sizes and shapes of the particles, gas pockets, wall effects, fouling of the bed and resulting plugging of many passages, poor distributor design, low flow rates, faulty operations procedures, insufficient backwash, and other causes.
Chloramines Chemical complexes formed from the reaction between ammonia and chlorine being used to disinfect many municipal water supplies. Unlike chlorine, chloramines do not combine with organics in the water to form potentially dangerous trihalomethanes (THMs). Chloramines can exist in three forms: 1. monochloramine (NH2Cl) 2. dichloramine (NHCl2) 3. nitrogen trichloride (NCl3). The proportions of the chloramines depend on the physical and chemical properties of the water. Water containing chloramines may not be used for fish or for kidney dialysis applications.
Chlorination The treatment process in which chlorine gas or a chlorine solution is added to water for disinfection and control of microorganisms. Chlorination is also used in the oxidation of dissolved iron, manganese, and hydrogen sulfide impurities.
Chloroform Bacteria A particular group of bacteria primarily found in human and animal intestines and wastes. These bacteria are widely used as indicator organisms to show the presence of such wastes in water and the possible presence of pathogenic (disease-producing) bacteria. Escherichia coli (E. coli) is one of the fecal coliform bacteria widely used for this purpose.
Colloids Very fine solid particles, typically between 0.1 and 0.001 microns in diameter, which are suspended in a liquid or gas and will not settle out of a solution and cannot be removed by conventional filtration alone. When in sufficient concentrations, colloidal matter may give a grayish cast to a standing water sample. The removal of colloidal particles usually requires coagulation to form larger particles which may then be removed by sedimentation and/or filtration.
Combined Available Residual Chlorine The concentration of residual chlorine which is combined with ammonia (NH3) and/or organic nitrogen in water as chloramine (or other chloro derivative) yet is still available to oxidize organic matter and utilize its bactericidal properties. The combined chlorine compounds are more stable than free chlorine forms, but are somewhat slower in reactions.
Compensated Hardness A calculated value based upon the total hardness, the magnesium-to-calcium ratio, and the sodium, iron, and manganese concentrations in a water. This value is used to correct for the reduction in hardness removal capacity of a cation exchange water softener which is caused by the presence of these substances. No single method of calculation has been uniformly accurate.
Composite Membrane A semipermeable membrane used in water treatment, consisting of a rejecting barrier layer of one chemical composition (usually a type of polymer) supported by one or more layers of porous materials with different composition(s).
Conditioned Water Any water which has been treated by one or more processes (adsorption, deionization, filtration, softening, reverse osmosis, etc.) to improve the water's usefulness and/or aesthetic quality by reducing undesirable substances (iron, hardness etc.) or undesirable conditions (color, taste, odor, etc.)
Cross-linked Polyethylene (XLPE or PEX) Polyethylene that, by cross-linking via irradiation of linear polyethylene with an electron beam or gamma radiation, or with a chemical cross-linking agent, such as benzoyl peroxide, is made to be a non-toxic thermosetting (remains solid upon heating) white solid with superior strength and durability, high temperature and pressure resistance, and inertness toward chemical attack and corrosion. Cross-linked polyethylene pipe and tubing is accepted by many plumbing codes for potable water distribution with buildings. It is flexible (bend radii of six times or greater the outside pipe/tubing diameter) and can be used in place of polybutylene (PB) water pipe.
Cryptosporidium (crip-toe-spor-ID-ee-um) A waterbourne protozoan that forms oocysts and causes acute gastrointestinal illness in humans. Several species of cryptosporidium exist, but only one, C. parvum, is known to be infective to humans. In the environment, the organism's fertilized eggs are protected by an outer shell form called an oocyst (OH-oh-cist). Once injested, the organism emerges from the shell and infects the lining of the small intestines. Cryptosporidium is commonly found in unfiltered surface water and is resistant to disinfectants such as chlorine and ultraviolet light, but C. parvum oocysts, generally being three to five microns in diameter, can be removed by filters that capture all particles of one micron and greater in size.
Cyst A capsule or protective sac produced about themselves by many protozoans (as well as some bacteria and algae) as preparation for entering a resting or a specialized reproductive stage. Similar to spores, cysts tend to be more resistant to destruction by disinfection. Fortunately, protozoan cysts are typically 2 to 50 microns in diameter and can be removed from water by fine filtration.
Dealkalization The dealkalization of water refers to the removal of alkalinity ions from the feed stream. This is readily done with chloride cycle anion exchange whereby the alkalinity (bicarbonate or carbonate) is removed in exchange for chloride. The resin can be regenerated with salt (NaCl).
In a boiler, alkalinity decomposes under heat to produce CO2 so the steam that is produced contains carbonic acid (H2CO3) and can be highly corrosive. Dealkalization avoids this. In addition, the removal of alkalinity avoids the formation of boiler scale (CaCO3) because the chloride salt of calcium is very soluble and does not form deposits
Deionization The removal of all ionized minerals and salts (both organic and inorganic) from a solution by a two-phase ion exchange procedure: First, positively-charged ions are removed by a cation exchange resin in exchange for a chemically equivalent amount of hydrogen ions. Second, negatively-charged ions are removed by an anion exchange resin for a chemically equivalent amount of hydroxide ions. The hydrogen and hydroxide ions introduced in this process unite to form water molecules. This process is also called demineralization by ion exchange.
Drinking Water Standards Standards that define allowable water quality limits for potable and domestic water supplies. The U.S. Environmental Protection Agency (EPA) is responsible for the National Primary Drinking Water Regulations, which are health-related standards that establish the Maximum Contaminant Levels (MCLs) for regulated substances in drinking water. An MCL is the highest permissible level of a contaminant allowed in water delivered to the consumer's tap. MCLs are enforceable at public water systems under the Safe Drinking Water Act. The EPA also has set Maximum Contaminant Level Goals (MCLGs) at levels which no known or anticipated adverse effects on the health of persons occur and which allow an adequate margin of safety. The enforceable MCL is set as close to the MCLG as reasonable, taking into consideration the costs and treatment techniques available to public water systems. National Secondary Drinking Water Regulations, also issued by the EPA, pertain to aesthetic characteristics of water and are advised, but not enforceable, by the Federal government.
Exchange Sites Locations on each bead of ion exchange resin which hold mobile ions that are available for exchange with other ions in the solution that passes through the resin bed. In cation water softening, for example, mobile sodium ions located at the various exchange sites are exchanged for calcium, magnesium, iron, or other polyvalvent cations in the water being softened. Exchange sites are also called functional groups.
Ferric Iron Small solid iron particles containing trivalent iron, usually as gelatinous ferric hydroxide [Fe(OH)<sub>3</sub>] or ferric oxide (Fe<sub>2</sub>O<sub>3</sub>), which are suspended in water and visible as "rusty water." Ferric iron can normally be removed by filtration. Also called <i>precipitated iron</i>.
Ferrous Iron A divalent iron ion, usually as ferrous bicarbonate [Fe(HCO<sub>3</sub>)<sub>2</sub>] which, when dissolved in water, produces a clear solution. It is usually removed by cation exchange water softening. Also called <i>clear water iron</i>.
Giardia A common waterborne protozoan that forms cysts and is resistant to disinfectants such as chlorine and ultraviolet light. Giardia can be removed by filters that capture all particles of four microns and greater in size.
Green Sand A naturally-occurring mineral that consists largely of dark greenish grains of glauconite and which possesses ion exchange properties. Greensand was the original product used in commercial and home cation exchange water softening units and was the base product for manufacturing manganese greensand zeolite products.
Hardness Hardness is a measurable property of water brought about by the presence of calcium and magnesium ions (and other multivalent metallic ions) that can cause scale formation, soap curd, water spotting, and harshness in fabrics laundered in such water. The term was colloquially used to describe certain waters that caused difficulty in using soap; i.e. “this water makes soap hard to lather”.
Hardness is expressed in grains per US gallon (gpg) where 1 grain equals 17.1 ppm as calcium carbonate equivalent. The degree of hardness expressed in gpg that is generally accepted:
Less than 1 gpg is termed as soft water
1.0 to 3.5 gpg is slightly hard
3.5 to 7.0 gpg is moderately hard
7.0 to 10.5 gpg is termed as hard
Above 10.5 gpg is very hard.
Hydrogen Sulfide (H2S) While many divalent and trivalent metallic cations can potentially contribute to “hard water” symptoms, the most commonly referenced “hardness” contaminants are calcium and magnesium ions in water, expressed as calcium carbonate (CaCO3).
In practice, when sizing a water conditioner for the removal of hardness in residential applications, it is common to count only the calcium and magnesium content in calculating the hardness load. “Total” hardness would include iron, manganese, strontium, barium and radium plus the common hardness. In certain applications requiring very low hardness residuals, if the total hardness exceeds the common hardness by more than 1 percent, specific design treatment or pretreatment and/or regeneration schemes are employed to prevent fouling of the system as a result of the marginal solubility of the heavier elements.
A corrosive and flammable gas often found dissolved in well water and often accompanied by iron and low pH values. Hydrogen sulfide develops from decaying organic matter, from sulfate-reducing bacteria, and from petroleum refining. H2S formation can be catalyzed by a magnesium anode rod in a hot water heater; anaerobic sulfate-reducing bacteria can live in a hot water heater so long as water temperatures are below 140° Fahrenheit, and to produce H<sub>2</sub>S the SRB need only a ready source of sulfate ions in the incoming water supply and a ready source of electrons as provided by the water heater's anode rod. The odor of water with as little as 0.5 milligrams per liter (mg/L) of hydrogen sulfide concentration is detectable by most people. Concentrations less than one mg/L give the water a "musty" or "swampy" odor. Over one mg/L hydrogen sulfide concentration gives water a very disagreeable "rotten egg" odor and makes the water corrosive to plumbing. Generally, hydrogen sulfide levels are less than 10 mg/L, but occasionally amounts of 50 to 75 mg/L are found. At higher pH levels hydrogen sulfides present in the ionized alkaline sulfide (HS<sub>-</sub> and S<sup>2-</sup>) forms, and at low pH levels it is present in the H<sub>2</sub>S gaseous form. At pH 5.0 about 90 percent is present as gaseous H<sub>2</sub>S and 10 percent as sulfide. At pH 8 only six percent is present as a gas. Hydrogen sulfide concentrations up to about six mg/L can be removed from water using an oxidizing filter (same as an iron filter). Hydrogen sulfide concentrations exceeding six mg/L can be removed by injecting an oxidizing chemical such as household bleach or potassium permanganate and using a filter. The oxidizing chemical should be thoroughly mixed into the water upstream from a retention tank to provide at least 20 minutes of contact time between the chemical and water. Sulfur particles can then be removed by activated carbon filtration. When potassium permanganate is used a manganese greensand filter is recommended. Other oxidants such as ozone and hydrogen peroxide are also excellent for oxidizing hydrogen sulfide to precipitate sulfur and even to innocuous sulfate.
Ion Exchange A reversible chemical process in which ions from an insoluble permanent solid medium (the "ion exchanger"--usually a resin) are exchanged for ions in a solution or fluid mixture surrounding the insoluble medium. The superficial physical structure of the solid is not affected. The direction of the exchange depends upon the selective attraction of the ion exchanger resin for the certain ions present and the concentrations of the ions in the solution. Both cation and anion exchange are used in water conditioning. Cation exchange is commonly used for water softening.
Iron (Fe) A very common element often present in groundwater in amounts ranging from 0.01 to 10.0 ppm (mg/L). Iron may be found in three forms: In soluble form such as in ferrous bicarbonate; Bound with a soluble organic compound; and As suspended ferric iron particles. Iron above 0.3 mg/L is objectionable in water because of staining of laundry and plumbing fixtures caused by the oxidation and precipitation of ferric hydroxide and/or ferric oxide (ferric iron) into small solid iron particles. Iron can also give a metallic or distorted flavor to beverages. Iron also occurs in water as ferric iron.
Iron Bacteria Bacteria which thrive on iron and are able to actually use ferrous iron (as found in water or steel pipes) in their metabolic processes, to incorporate ferric iron in their cell structure, and to deposit gelatinous ferric hydroxide iron compounds in their life processes. Iron bacteria are found in several varieties including Crenothrix, Lepothrix, and Gallionella. Iron bacteria can cause staining, plugging, and taste and odor problems in a water system.
Iron Fouled The accumulation of iron on or within an ion exchange resin bed or filter medium in such amounts that the capacity of the medium is reduced.
Grains Per Gallon (gpg) A common method of reporting water analysis results in the United States and Canada. One grain per gallon equals 17.1 parts per million (ppm) or 17.1 milligrams per liter. Grains per Imperial gallon equals 14.3 mg/L (or ppm).
KDF The trade name for a patened medium composed of high purity copper and zinc granules. KDF is capable of removing chlorine, soluble heavy metals, and other inorganic contaminents from water through the chemical reduction/oxidation (redox) process.
Magnesium One of the elements that make up the earth's crust as part of many rock-forming minerals such as dolomite. Magnesium and calcium dissolved in water constitute hardness. The presence of magnesium in water contributes to the formation of scale and the insoluble soap curds which identify hard water.
Manganese (Mn) An element sometimes found dissolved in groundwater, usually in combination with - but in lower concentrations than- iron. Manganese is noticeable because in concentrations above 0.05 mg/L it causes black staining of laundry and plumbing fixtures. Important ores of manganese are pyrolusite, manganite, psilomelane, and rhodochrosite.
Membrane A thin sheet or surface film, either natural or man-made, of microporous structure that performs as an efficient filter of particles down to the size range of chemical molecules and ions. Such membranes are termed "semipermeable" because some substances will pass through, but others will not. Usually small ions, water, solvents, gases, and other very small molecules can pass through a membrane, but other ions and macromolecules such as proteins and colloids are barred from passage. Man-made (synthetic) membranes are highly engineered polymer films about 100 angstroms thick and with controlled distributions of pores ranging from 5 to 5,000 angstroms in diameter. Membranes are used in reverse osmosis, electrodialysis, nanofiltration, ultrafiltration, and as pleated final filter cartridges in water treatment. SEE ALSO cellulose acetate (CA); cellulose triacetate (CTA); charged polysulfone membrane.
Methemoglobinemia A serious condition, found mostly in young infants under six months of age (or newborn animals), in which the oxygen-carrying capacity of the blood is reduced as a result of a reaction with nitrite (NO2-), which changes the healthy hemoglobin to an inactive methemoglobin form. As a result of the higher pH conditions in the gastrointestinal tract of infants and newborn animals, nitrate (NO3-), which is consumed in food or water, can be transformed into nitrite more readily than would occur with adults.
Nanofiltration A membrane treatment process which falls between reverse osmosis and ultrafiltration on the filtration/separation spectrum. The nanofiltration process can pass more water at lower pressure operations than reverse osmosis, can remove particles in the 300 to 1,000 molecular weight range such as humic acid and organic color bodies present in water, and can reject selected (typically polyvalent) salts. Nanofiltration may be used for selective removal of hardness ions in a process known as membrane softening.
Packed Bed A bed of filter or ion exchange medium which is completely retained so that no bed expansion can occur, and no backwash step is used to reclassify the filter or resin. Packed beds are usually part of the design features in ion exchange water softeners used to obtain high capacity and increased regeneration efficiency.
Parts per million A measure of proportion by weight which is equivalent to one unit of weight of solute (dissolved substance) per million weights of solution. Since one liter of water weighs one million milligrams, one ppm is equal to one milligram per liter (mg/L). Milligram per liter is the preferred unit of measure in water or waste water analysis.
Percent Rejection (reverse osmosis/ultrafiltration) The percentage of TDS in the feedwater that is prevented from passing the membrane with the permeate. The formula used is: the difference obtained from the TDS in feedwater minus TDS in permeate divided by TDS in feedwater; then multiply the answer obtained by 100 to obtain a percent
pH The degree of the acidity or basicity of a solution as measured on a scale ("pH scale") of 0 to 14. The midpoint of 7.0 on the pH scale represents neutrality--that is, a "neutral" solution is neither acidic nor basic. Numbers below 7.0 indicate acidity; numbers above 7.0 indicate basicity. Substances that when dissolved in water cause the pH to be less than 7.0 often create a sour taste and may sting when in contact with skin. The resulting solution will turn litmus paper red. Substances that when dissolved in water cause pH to be greater than 7.0 create a bitter taste and a slippery feel and will turn litmus paper blue. Water with a high pH tends to cause drying of the skin.
More specifically, pH is the negative of the base 10 logarithm of the hydrogen ion concentration of a solution, -log10[H+], where “p” is the short hand notation for “-log10”. The hydrogen ion concentration, [H+], is the moles of hydrogen ions per liter of solution. In neutral water, for example, the hydrogen ion concentration is 1x10-7 mol/L; the pH is therefore 7. Because both letters in the term pH are representative notations, the term must be written with a lower case “p” and an upper case “H”.
pH is an exponential function. A pH of 10 is ten times as basic as a pH of 9 and one hundred times as basic as a pH of 8. Similarly, a pH of 2 is one hundred times as acidic as a pH of 4 and one thousand times as acidic as a pH of 5.
In the field, pH is measured with a pH meter, which must be properly calibrated for accuracy. As pH in a water sample can change with time due to fluctuation of carbon dioxide concentration, pH should be measured quickly after sample collection.
Phosphate A salt of phosphoric acid. In the water industry, polyphosphates are used as sequestering agents to control iron and hardness, and as coating agents to control corrosion by formation of a thin passivating film on metal surfaces. The complex phosphates also are a group of sequestering agents widely used in detergent formulations (except where phosphates are banned by law) because of their superiority in chemical water softening, sequestering, and other builder functions. Sodium tripolyphosphate was the original builder upon which modern laundry detergent technology developed, and is used in laundry granules, automatic dishwasher detergents, and cleansers. It is adaptable to the spray drying process by which granules are made. Tetrasodium pyrophosphate is also used in detergent granules, but since it does not rank as high in overall performance as sodium tripolyphosphate, its application is more limited. Highly soluble tetrapotassium pyrophosphate is used in liquid laundry detergents and in hard surface cleaners, where it serves as a builder, water softener, and source of alkalinity. Another complex phosphate, sodium metaphosphate, is marketed as a packaged water softener. The most widely used sodium metaphosphate is sodium hexametaphosphate (SHMP), which softens by sequestering. The orthophosphate form of phosphates, trisodium phosphate (also called sodium orthophosphate), is a water softener that inactivates hardness minerals by precipitation. It is used to a limited extent in soap and detergent formulations as a builder, as a source of alkalinity, and for its water-softening properties. It is also used in powdered hard surface cleaners and cleansers to supply alkaline cleaning power. Chlorinated trisodium phosphate is a dry chlorine bleach that, in water, acts much like sodium hypochlorite (liquid chlorine bleach). It provides a means of incorporating chlorine bleach effectively in dry products, and for this reason is used in cleansers and automatic dishwasher detergents. It also provides alkalinity that aids in cleaning. Waters containing concentrations of iron, manganese, calcium, or magnesium sometimes can be treated with a sequestrant such as polyphosphate and kept from depositing these mineral precipitates or scales for a period of time. However, polyphosphate sequestering is not permanent, and therefore may not be as effective as actually removing the iron, manganese, and hardness minerals, as is done with iron filters and ion exchange water softening, for example. The sequestering value of polyphosphates is destroyed when they revert (hydrate) to orthophosphate. Polyphosphate reversion or hydration to orthophosphate occurs naturally in water with time. Intentions would be for this reversion not to happen and not to drop the sequestered water hardness, iron, and manganese out until after it reaches the wastewater. But, the polyphosphate reversion process can be accelerated by various uncontrolled conditions, such as low pH, high temperature, and the presence of the oxides of certain heavy metals, including iron, calcium, copper, and zinc in water. It is important in phosphate feed water treatment operations to: 1)maintain a stable pH within the phosphate product's performance rage. 2) determine the polyphosphate composition or blend that is most compatible with the specific water quality objectives and conditions, and 3) apply the appropriate dosage of phosphate to accomodate the system demand. Because of the difficulty in maintaining phosphate stabilities in the presence of varying pH, time, temperature, and metal oxides in most natural water supplies, the actual removal of iron, manganese, and water hardness is generally a more assuredly effective water treatment method. Municipal applications of polyphosphates to water supplies can interfere with home water treatment technologies. A portion of any water hardness, iron,
Potassium Permanganate (KMnO4) Dark purple, odorless crystals (with a blue metallic sheen) that dissolve in water to produce a purple-red color. Potassium permanganate is a powerful oxidizing agent that is used in water treatment as both an oxidizer and a disinfectant. It is also an effective regenerant for manganese oxidizing filters.
POU Point of Use
POE Point of Entry
Raw Water Water, usually from wells or surface sources, which has had no previous treatment and is entering a water processing system or device. 2. Water at the inlet side of any water treatment system or device.
Regenerant In ion exchange or softening applications, a regenerant is the chemical solution used to restore an exhausted bed of ion exchange resin to the fully ionic (regenerated) form necessary for the desired ion exchange to again take place effectively. Regenerants are also used in a similar fashion to restore catalyst (e.g., iron and manganese removal) media for reuse. Sodium chloride brine is normally used to regenerate cation exchange water softeners and for some dealkalizer systems. Hydrochloric and sulfuric acids are used for hydrogen-form cation deionizations units. Sodium hydroxide is normally used to regenerate OH- form anion deionizations systems. Potassium permangante regenerant is used to regenerate a manganese greensand iron and manganese removal filter.
Reverse Osmosis A water treatment process that removes undesirable materials from water by using pressure to force the water molecules through a semipermeable membrane. This process is called "reverse" osmosis because the pressure forces the water to flow in the reverse direction (from the concentrated solution to the dilute solution) to the flow direction (from the dilute to the concentrated) in the process of natural osmosis. RO removes ionized salts, colloids, and organic molecules down to a molecular weight of 100. May be called hyperfiltration.
Salt Bridging The creation of salt encrustment and cementing together of salt particles in dry storage brine tanks which causes tight bonding of the entire salt mass to the walls of the brine tank and prevents the salt from dropping into the incoming water for brine makeup.
Sequestration A chemical reaction in which certain ions are bound into a stable water-soluble compound so that they (ions) are prevented from certain normal but undesirable actions. For example, the sequestration of iron to prevent it from oxidizing, precipitating, and staining. The same as sequesterin
Tannin Any of a group of water soluble, natural organic phenolic compounds that are produced by metabolism in trees andplants, and are part of the degredation-resistant fulvic acid materials formed during the decomposition of vegetation. Tannins occur in water in almost any location where large quantities of vegetation have decayed. Tannins can impart a faintly yellowish to brown color to water. Tannin molecules tend to form anions in water above pH 6 and can then be treated with anion exchange resins. Below pH 5, tannins are better treated with activated carbon.
TDS- Total Dissolved Solids, The total weight of the solids that are dissolved in the water, give in ppm per unit volume of water. TDS is determined by filtering a given volume of water (usually through a 0.45 micron filter), evaporating it at a defined temperature (usually 103-105 degrees Celsius), and then weighing the residue. Note: A test measuring the electrical conductivity of the water provides only an estimate of the TDS present, as conductivity is not precisely proportional to the weight of an ion and nonconductive substances cannot be measured by electrical tests.
TDS Creep The appearance of salt in RO product water which sometimes occurs as a result of the reduction of differential pressure across the membrane as can occur when the RO unit has been shut down for a period of time. Water flow will cease to permeate through the membrane when there is insufficient differential water pressure across the membrane. However TDS permeates through the membrane as a function of the TDS concentration difference across the membrane.
TFC Membrane A class of reverse osmosis membranes made with polyamide-based polymer and fabricated with different materials in the separation and support layers.
Trihalomethanes (THMs) A group of organic chemicals, suspected of being carcinogenic, which are formed in water when chlorine being used as a disinfectant reacts with natural organic matter such as humic acids from decayed vegetation. Humic acids are present in all natural water used as sources of drinking water supplies. Chloroform is one of the most common THMs formed in this type of reaction.
Ultraviolet (UV) Light Radiation (light) having a wavelength shorter than 3900 angstroms, the wavelengths of visible light, and longer than 100 angstroms, the wavelengths of x-rays. This wavelength puts ultraviolet light at the invisible violet end of the light spectrum. Ultraviolet light is used as a disinfectant.
Upflow Brining Is a means of forcing the brine solution upward through the cation exchanger for regenerating the resin. Where the softening flow is downward and the regenerating brine flow is upward, the mode is also called countercurrent flow. Countercurrent flow means regeneration flows and service flows are in the opposite directions.
Upflow Softening A pattern of water flow used in softeners in which the service water flows upward through the ion exchange bed; the media is restricted in movement, usually because of a packed bed. The regeneration brine usually flows downward in such systems. Upflow softening is normally used to achieve higher operating efficiency.
Water Softener A device, product, or equipment that reduces the presence of water hardness to less than 1 gpg expressed as calcium carbonate (CaCO3) equivalent via chemical, physical, or other means. In residential and commercial applications, the most common water softener consists of a pressurized water treatment device in which hard water is passed through a bed of cation exchange media (either inorganic or synthetic organic) for the purpose of exchanging calcium and magnesium ions for sodium or potassium ions, thus producing a softened water which is more desirable for laundering, bathing, and dishwashing. This cation exchange process was originally called zeolite softening or the Permutit Process. Most modern water softeners use a sulfonated bead form of styrene/divinylbenzene (DVB) cation resin. Distillation, electrodialysis, nanofiltration, deionization, and reverse osmosis water treatment systems are also capable of measurably removing calcium and magnesium ions from water and therefore act as water softeners. SEE ALSO no-salt water softener; physical water treatment device.
Activated carbon—A water treatment medium, found in block, granulated, or powdered form, which is produced by heating carbonaceous substances (bituminous coal or cellulose-based substances such as wood or coconut shell) to 700ºC or less in the absence of air to form a carbonized char, and then activating (oxidizing) at 800ºC to 1000ºC with oxidizing gases such as steam and carbon dioxide (oxygen is never used as the oxidizing gas because its reaction with the carbon surface is too rapid and violent) to form pores, thus creating a highly porous adsorbent material.
Activated carbon is commonly used for dechlorination and for reducing trace and soluble materials such as organic chemicals and radon from water.
Activated carbon block filter—Activated carbon block is a blend of fine activated carbon (e.g., 80 X 325 mesh activated carbon), water, and a suitable binder (such as polyethylene or a similar material) that is mixed and molded and hardened or extruded to a cartridge filter of any size and shape. Sometimes specialized media are added along with activated carbon to provide customized performances for specific contaminants. The binder is particularly designed and chosen to hold the carbon and other media in a fixed solid matrix, yet, not to plug up the pores of the activated carbon.
Even though the binder does occlude a portion of the adsorption sites, the finer mesh size gives activated carbon block filters faster adsorption kinetics and generally two to four times greater adsorption capacity than equivalent volumes of loose granular activated carbon. Activated carbon block filters typically have a 0.5 to one micron filtration capability, making it also helpful for particulate filtration, insoluble lead reduction, and demonstrating, in some cases, removal of Giardia and Cryptosporidium.
Activated silica—A negatively-charged colloidal substance generally formed by combining a dilute sodium silicate solution with a dilute acidic solution (or other activant). Generally used as a coagulant aid.
This is different from adsorption in which one substance adheres to the surface of another.
Air check—A device which allows water, but not air, to pass through it. An air check is a typical component of a treatment system using a regenerant eductor.
air gap—A clear vertical space between the end of the water treatment device’s drain line and the flood level rim of a receptacle which holds water. An air gap is used to prevent cross connection between the water treatment device and a possible source of waste water thereby preventing a reverse flow of water from the sewer into the water supply system. Without an air gap, such reverse flow could occur due to an increase in the pressure in the sewer system or the creation of a negative pressure in the water supply line. Local plumbing codes indicate how wide the air gap needs
Alkaline—The condition of water or soil which contains a sufficient amount of alkali substances to raise the pH above 7.0.
Alkalinity— A measure of concentration of all species in water capable of neutralizing an acid by binding a hydrogen ion, expressed as mg/L or ppm of calcium carbonate equivalents. Alkalinity is measured by titration and is not equivalent to pH.
The most common alkalinity components in naturally occurring surface and groundwater are bicarbonate, carbonate ions and hydroxide ions. As bicarbonate and carbonate ions typically occur in the greatest concentration, the contribution by other species to the measured alkalinity is negligible and often ignored for the purposes of sizing water treatment equipment. SEE ALSO alkalinity tests; pH.
Alkalinity tests—There are three different tests used for testing alkalinity. They are usually done in this order:
1. The pH alkalinity test will indicate the presence or absence of hydroxide alkalinity. A pH reading of 8.3 or above indicates the presence of hydroxide alkalinity.
2. The phenolphthalein test measures “P alkalinity” which is made up of all hydroxide alkalinity plus 1/2 of the carbonate alkalinity. P alkalinity is that portion of alkalinity above pH 8.3. Phenolphthalein in water changes color from pink above pH 8.3 to clear at pH 8.3.
3. The Methyl Orange test measures the “M alkalinity” which is the remaining ½ of the carbonate alkalinity plus all of the bicarbonate alkalinity. Methyl orange alkalinity measures total alkalinity of water. The methyl orange endpoint is pH 4.5; no alkalinity exists in water below pH 4.5.
Note: Free carbon dioxide (CO2) gas can exist dissolved in water between pH 4.5 and pH 8.3. Below pH 4.5, CO2 escapes quickly into the environment and above pH 8.3 CO2 becomes carbonate (CO32-) alkalinity. SEE ALSO alkalinity.
Alternating system—A dual automatic softener system functioning with one unit in service and one on standby. When a predetermined gallonage of softened water has passed or when a monitor detects hard water breakthrough, the idle or standby unit automatically goes into service. The spent unit then regenerates and becomes the idle/standby unit.
Alum—The common name for aluminum sulfate [Al2(SO4)3 • 14H2O] which is often used as a coagulant in water treatment.
Anaerobic—A condition in which there is no air or no available free oxygen.
Artesian (aquifer or well)—Water held under pressure in porous rock or soil confined by impermeable geologic formations. An artesian well is free-flowing. SEE ALSO confined aquifer.
Oxidizing agent—helps break down protein soils like egg and milk, aids in removing such stains as coffee or tea, and lessens spotting of glassware.
Automatic water softener (or automatic filter)—A water softener (or filter) that is equipped with a clock timer which automatically initiates the backwash and/or regeneration process at certain preset intervals of time. All operations, including bypass of treated or untreated water (depending upon design), backwashing, brining, rinsing, and returning the unit to service are performed automatically.
Backwash A form of backflow which occurs due to negative pressure.
Calcite 1. Calcium carbonate (CaCO3). 2. A trade name for finely ground grades of marble or limestone, very high in calcium carbonate, which are used to raise the pH reading (reduce the acidity) of low pH (acidic) water or to filter out sediment.
Bacteria Single-celled organisms (singular form=bacterium) which lack well-defined nuclear membranes and other specialized functional cell parts and reproduce by cell division or spores. Bacteria may be free-living organisms or parasites. Bacteria (along with fungi) are decomposers that break down the wastes and bodies of dead organisms, making their components available for reuse. Bacterial cells range from about 1 to 10 microns in length and from 0.2 to 1 micron in width. They exist almost everywhere on earth. Despite their small size, the total weight of all bacteria in the world likely exceeds that of all other organisms combined. Some bacteria are helpful to man, others harmful.
Bacteriacide Any substance or agent which kills bacteria, both disease causing and non-disease causing. Spores and nonbacterial microorganisms (e.g., algae, fungi, and viruses) are not necessarily killed by a bactericide.
Bacteriostat Having the ability to inhibit the growth of bacteria without destroying the bacteria. For example, silver-impregnated activated carbon will reduce bacterial colonization in a bed but not eliminate it.
Barium Fouling In ion exchange deionization, a condition where the cation exchanger resin becomes coated with a very insoluble coating of barium sulfate. This occurs in the decationization unit when regenerated with sulfuric acid, where a barium-bearing water is being processed. Generally, the remedy must be to replace the cation resin and install upstream water softening to remove the barium prior to the deionization treatment.
Bead (resin bead )In water processing, refers to the spherical shape of individual particles of ion exchange resin products, as compared to the irregular shaped particles of most other granular media products.
Bed The mass or volume of ion exchange resin or other media through which the water passes in the process of water treatment.
Bed depth The height of the resin or other media (excluding support material) in a bed, usually expressed in inches or centimeters.
Bicarbonate hardness The hardness of a water due to the presence of calcium and magnesium bicarbonates, usually the major component of carbonate hardness or total hardness. Bicarbonate hardness is often referred to simply as carbonate hardness.
Birm The trade name for a manganese dioxide-coated volcanic aluminum silicate (pumicite) used as an oxidizing-catalyst filter for iron and manganese reduction.
Black Water Liquid and solid human body waste and the carriage water generated through toilet usage.
Block carbon Activated carbon block is a blend of fine activated carbon (e.g., 80 X 325 mesh activated carbon), water, and a suitable binder (such as polyethylene or a similar material) that is mixed and molded and hardened or extruded to a cartridge filter of any size and shape. Sometimes specialized media are added along with activated carbon to provide customized performances for specific contaminants. The binder is particularly designed and chosen to hold the carbon and other media in a fixed solid matrix, yet, not to plug up the pores of the activated carbon. Even though the binder does occlude a portion of the adsorption sites, the finer mesh size gives activated carbon block filters faster adsorption kinetics and generally two to four times greater adsorption capacity than equivalent volumes of loose granular activated carbon. Activated carbon block filters typically have a 0.5 to 1 micron filtration capability, making it also helpful for particulate filtration, insoluble lead reduction, and demonstrating, in some cases, removal of <i>Giardia</i> and <i>Cryptosporidium</i>.
Blue Green Algae -Single-celled organisms (singular=cyanobacterium) similar to bacteria, except cyanobacteria contain the green pigment chlorophyll (as well as other pigments), which traps the energy of sunlight and enables these organisms to carry on photosynthesis. Cyanobacteria are autotrophic producers of their own food from simple raw materials, whereas bacteria are heterotrophic decomposers of the wastes and bodies of other organisms. Cyanobacteria were formerly known as blue-green algae. Blooms or population explosions of cyanobacteria cause water pollution. Some cyanobacteria-like bodies (CLBs) have been associated with causing waterborne diarrheal illnesses.
Bottled Mineral Water Bottled water containing fluoride. The label shall specify whether the fluoride is naturally occurring or added. Any water which meets the definition of bottled fluoridated water shall contain not less than 0.8 milligrams per liter fluoride ion and otherwise comply with the Food and Drug Administration (FDA) quality standards in Section 103.35(d)(2) of Title 21 of the Code of Federal Regulations (CFR).
Bottled Water Artisian Bottled water from a well tapping a confined aquifer in which the water level stands above the water table. Bottled artesian water shall meet the requirements of bottled natural water.
Brackish Water Water containing dissolved solids in the range of 1,000 to less than 15,000 parts per million.
Bridging. Bridging occurs in water softening when salt sticks together to form one large solid mass of pellets, or by the salt caking in a dry-salt brine tank which causes failure of the liquid or brine beneath the dry salt to become saturated. The result of bridging is insufficient salt in the regenerant solution to properly regenerate the cation resin. 2. The ability of particles to form a crustlike film over void spaces within a filter medium or membrane.
Brine A strong solution of salt(s) (usually sodium chloride and other salts too) with total dissolved solids concentrations in the range of 40,000 to 300,000 or more milligrams per liter. Potassium or sodium chloride brine is used in the regeneration stage of cation and/or anion exchange water treatment equipment. Sodium chloride brine saturation in an ion exchange softening brine tank is about 26 percent NaCl by weight at 60 degrees Fahrenheit.
Brine draw Usually means the process of drawing a brine solution into a cation or anion exchange water treatment device during regeneration.
Bromine A nonmetallic usually univalent or pentavalent element that lies between chlorine and iodine in the halogen group of the periodic table. Bromine has been used in swimming pools for disinfection and in cooling towers as a biocide, but its use in drinking water as a primary disinfectant has been limited because of uncertain effectiveness in the presence of organic material, ammonia, and other amines.
Cartridge Filter A device often used for single faucet water treatment, made up of a housing and a removable cartridge (element). In high flow rate commercial applications, the elements are clustered in a large housing, and the elements are cleanable and reusable. In residential use, disposable elements are used.
Catalyst media Those filter media which can cause certain reactions to occur in water treatment, such as activated carbon, calcite, manganese greensand, magnesium oxides, and dissimilar metal alloys.
Catalyst Oxidizing Filter A class of media bed filters which contain manganese treated greensand, zeolites, or pumicites.
Catalytic Activated carbon Activated carbon with modified surface properties that enhance the functionality of the activated carbon in converting the oxidation state of various elements. For example, with hydrogen sulfide (H2S), the sulfide ion (S-) is adsorbed and then converted on the catalytic carbon to elemental sulfur (S0) and sulfate ion (SO4 --). Once the sulfide is adsorbed and converted, it is desorbed and the site is restored. For these reactions to occur, excess dissolved oxygen is required in the water and a minimum empty bed contact time (EBCT) of five minutes may be necessary.
Cation Exchange The ion exchange process in which cations in solution are exchanged for other cations available from an ion exchange product. Formerly called base exchange.
Cation Exchange Resin An ion exchange material possessing reverse exchange ability for cations. Sulfonated polystyrene copolymer divinylbenzene exchange resin is used almost exclusively today in ion exchange water softeners. A cation exchange resin may be called a cation exchanger or a base exchanger.
Channeling The higher and unbalanced flow of water or regenerant through a limited number of passages in a filter or ion exchanger bed, as opposed to an evenly distributed flow through all passages in the bed. Channeling results in the greater flow of liquid through passages of lower resistance which can occur in fixed beds or columns of media particles due to nonuniform packing, irregular sizes and shapes of the particles, gas pockets, wall effects, fouling of the bed and resulting plugging of many passages, poor distributor design, low flow rates, faulty operations procedures, insufficient backwash, and other causes.
Chloramines Chemical complexes formed from the reaction between ammonia and chlorine being used to disinfect many municipal water supplies. Unlike chlorine, chloramines do not combine with organics in the water to form potentially dangerous trihalomethanes (THMs). Chloramines can exist in three forms: 1. monochloramine (NH2Cl) 2. dichloramine (NHCl2) 3. nitrogen trichloride (NCl3). The proportions of the chloramines depend on the physical and chemical properties of the water. Water containing chloramines may not be used for fish or for kidney dialysis applications.
Chlorination The treatment process in which chlorine gas or a chlorine solution is added to water for disinfection and control of microorganisms. Chlorination is also used in the oxidation of dissolved iron, manganese, and hydrogen sulfide impurities.
Chloroform Bacteria A particular group of bacteria primarily found in human and animal intestines and wastes. These bacteria are widely used as indicator organisms to show the presence of such wastes in water and the possible presence of pathogenic (disease-producing) bacteria. Escherichia coli (E. coli) is one of the fecal coliform bacteria widely used for this purpose.
Colloids Very fine solid particles, typically between 0.1 and 0.001 microns in diameter, which are suspended in a liquid or gas and will not settle out of a solution and cannot be removed by conventional filtration alone. When in sufficient concentrations, colloidal matter may give a grayish cast to a standing water sample. The removal of colloidal particles usually requires coagulation to form larger particles which may then be removed by sedimentation and/or filtration.
Combined Available Residual Chlorine The concentration of residual chlorine which is combined with ammonia (NH3) and/or organic nitrogen in water as chloramine (or other chloro derivative) yet is still available to oxidize organic matter and utilize its bactericidal properties. The combined chlorine compounds are more stable than free chlorine forms, but are somewhat slower in reactions.
Compensated Hardness A calculated value based upon the total hardness, the magnesium-to-calcium ratio, and the sodium, iron, and manganese concentrations in a water. This value is used to correct for the reduction in hardness removal capacity of a cation exchange water softener which is caused by the presence of these substances. No single method of calculation has been uniformly accurate.
Composite Membrane A semipermeable membrane used in water treatment, consisting of a rejecting barrier layer of one chemical composition (usually a type of polymer) supported by one or more layers of porous materials with different composition(s).
Conditioned Water Any water which has been treated by one or more processes (adsorption, deionization, filtration, softening, reverse osmosis, etc.) to improve the water's usefulness and/or aesthetic quality by reducing undesirable substances (iron, hardness etc.) or undesirable conditions (color, taste, odor, etc.)
Cross-linked Polyethylene (XLPE or PEX) Polyethylene that, by cross-linking via irradiation of linear polyethylene with an electron beam or gamma radiation, or with a chemical cross-linking agent, such as benzoyl peroxide, is made to be a non-toxic thermosetting (remains solid upon heating) white solid with superior strength and durability, high temperature and pressure resistance, and inertness toward chemical attack and corrosion. Cross-linked polyethylene pipe and tubing is accepted by many plumbing codes for potable water distribution with buildings. It is flexible (bend radii of six times or greater the outside pipe/tubing diameter) and can be used in place of polybutylene (PB) water pipe.
Cryptosporidium (crip-toe-spor-ID-ee-um) A waterbourne protozoan that forms oocysts and causes acute gastrointestinal illness in humans. Several species of cryptosporidium exist, but only one, C. parvum, is known to be infective to humans. In the environment, the organism's fertilized eggs are protected by an outer shell form called an oocyst (OH-oh-cist). Once injested, the organism emerges from the shell and infects the lining of the small intestines. Cryptosporidium is commonly found in unfiltered surface water and is resistant to disinfectants such as chlorine and ultraviolet light, but C. parvum oocysts, generally being three to five microns in diameter, can be removed by filters that capture all particles of one micron and greater in size.
Cyst A capsule or protective sac produced about themselves by many protozoans (as well as some bacteria and algae) as preparation for entering a resting or a specialized reproductive stage. Similar to spores, cysts tend to be more resistant to destruction by disinfection. Fortunately, protozoan cysts are typically 2 to 50 microns in diameter and can be removed from water by fine filtration.
Dealkalization The dealkalization of water refers to the removal of alkalinity ions from the feed stream. This is readily done with chloride cycle anion exchange whereby the alkalinity (bicarbonate or carbonate) is removed in exchange for chloride. The resin can be regenerated with salt (NaCl).
In a boiler, alkalinity decomposes under heat to produce CO2 so the steam that is produced contains carbonic acid (H2CO3) and can be highly corrosive. Dealkalization avoids this. In addition, the removal of alkalinity avoids the formation of boiler scale (CaCO3) because the chloride salt of calcium is very soluble and does not form deposits
Deionization The removal of all ionized minerals and salts (both organic and inorganic) from a solution by a two-phase ion exchange procedure: First, positively-charged ions are removed by a cation exchange resin in exchange for a chemically equivalent amount of hydrogen ions. Second, negatively-charged ions are removed by an anion exchange resin for a chemically equivalent amount of hydroxide ions. The hydrogen and hydroxide ions introduced in this process unite to form water molecules. This process is also called demineralization by ion exchange.
Drinking Water Standards Standards that define allowable water quality limits for potable and domestic water supplies. The U.S. Environmental Protection Agency (EPA) is responsible for the National Primary Drinking Water Regulations, which are health-related standards that establish the Maximum Contaminant Levels (MCLs) for regulated substances in drinking water. An MCL is the highest permissible level of a contaminant allowed in water delivered to the consumer's tap. MCLs are enforceable at public water systems under the Safe Drinking Water Act. The EPA also has set Maximum Contaminant Level Goals (MCLGs) at levels which no known or anticipated adverse effects on the health of persons occur and which allow an adequate margin of safety. The enforceable MCL is set as close to the MCLG as reasonable, taking into consideration the costs and treatment techniques available to public water systems. National Secondary Drinking Water Regulations, also issued by the EPA, pertain to aesthetic characteristics of water and are advised, but not enforceable, by the Federal government.
Exchange Sites Locations on each bead of ion exchange resin which hold mobile ions that are available for exchange with other ions in the solution that passes through the resin bed. In cation water softening, for example, mobile sodium ions located at the various exchange sites are exchanged for calcium, magnesium, iron, or other polyvalvent cations in the water being softened. Exchange sites are also called functional groups.
Ferric Iron Small solid iron particles containing trivalent iron, usually as gelatinous ferric hydroxide [Fe(OH)<sub>3</sub>] or ferric oxide (Fe<sub>2</sub>O<sub>3</sub>), which are suspended in water and visible as "rusty water." Ferric iron can normally be removed by filtration. Also called <i>precipitated iron</i>.
Ferrous Iron A divalent iron ion, usually as ferrous bicarbonate [Fe(HCO<sub>3</sub>)<sub>2</sub>] which, when dissolved in water, produces a clear solution. It is usually removed by cation exchange water softening. Also called <i>clear water iron</i>.
Giardia A common waterborne protozoan that forms cysts and is resistant to disinfectants such as chlorine and ultraviolet light. Giardia can be removed by filters that capture all particles of four microns and greater in size.
Green Sand A naturally-occurring mineral that consists largely of dark greenish grains of glauconite and which possesses ion exchange properties. Greensand was the original product used in commercial and home cation exchange water softening units and was the base product for manufacturing manganese greensand zeolite products.
Hardness Hardness is a measurable property of water brought about by the presence of calcium and magnesium ions (and other multivalent metallic ions) that can cause scale formation, soap curd, water spotting, and harshness in fabrics laundered in such water. The term was colloquially used to describe certain waters that caused difficulty in using soap; i.e. “this water makes soap hard to lather”.
Hardness is expressed in grains per US gallon (gpg) where 1 grain equals 17.1 ppm as calcium carbonate equivalent. The degree of hardness expressed in gpg that is generally accepted:
Less than 1 gpg is termed as soft water
1.0 to 3.5 gpg is slightly hard
3.5 to 7.0 gpg is moderately hard
7.0 to 10.5 gpg is termed as hard
Above 10.5 gpg is very hard.
Hydrogen Sulfide (H2S) While many divalent and trivalent metallic cations can potentially contribute to “hard water” symptoms, the most commonly referenced “hardness” contaminants are calcium and magnesium ions in water, expressed as calcium carbonate (CaCO3).
In practice, when sizing a water conditioner for the removal of hardness in residential applications, it is common to count only the calcium and magnesium content in calculating the hardness load. “Total” hardness would include iron, manganese, strontium, barium and radium plus the common hardness. In certain applications requiring very low hardness residuals, if the total hardness exceeds the common hardness by more than 1 percent, specific design treatment or pretreatment and/or regeneration schemes are employed to prevent fouling of the system as a result of the marginal solubility of the heavier elements.
A corrosive and flammable gas often found dissolved in well water and often accompanied by iron and low pH values. Hydrogen sulfide develops from decaying organic matter, from sulfate-reducing bacteria, and from petroleum refining. H2S formation can be catalyzed by a magnesium anode rod in a hot water heater; anaerobic sulfate-reducing bacteria can live in a hot water heater so long as water temperatures are below 140° Fahrenheit, and to produce H<sub>2</sub>S the SRB need only a ready source of sulfate ions in the incoming water supply and a ready source of electrons as provided by the water heater's anode rod. The odor of water with as little as 0.5 milligrams per liter (mg/L) of hydrogen sulfide concentration is detectable by most people. Concentrations less than one mg/L give the water a "musty" or "swampy" odor. Over one mg/L hydrogen sulfide concentration gives water a very disagreeable "rotten egg" odor and makes the water corrosive to plumbing. Generally, hydrogen sulfide levels are less than 10 mg/L, but occasionally amounts of 50 to 75 mg/L are found. At higher pH levels hydrogen sulfides present in the ionized alkaline sulfide (HS<sub>-</sub> and S<sup>2-</sup>) forms, and at low pH levels it is present in the H<sub>2</sub>S gaseous form. At pH 5.0 about 90 percent is present as gaseous H<sub>2</sub>S and 10 percent as sulfide. At pH 8 only six percent is present as a gas. Hydrogen sulfide concentrations up to about six mg/L can be removed from water using an oxidizing filter (same as an iron filter). Hydrogen sulfide concentrations exceeding six mg/L can be removed by injecting an oxidizing chemical such as household bleach or potassium permanganate and using a filter. The oxidizing chemical should be thoroughly mixed into the water upstream from a retention tank to provide at least 20 minutes of contact time between the chemical and water. Sulfur particles can then be removed by activated carbon filtration. When potassium permanganate is used a manganese greensand filter is recommended. Other oxidants such as ozone and hydrogen peroxide are also excellent for oxidizing hydrogen sulfide to precipitate sulfur and even to innocuous sulfate.
Ion Exchange A reversible chemical process in which ions from an insoluble permanent solid medium (the "ion exchanger"--usually a resin) are exchanged for ions in a solution or fluid mixture surrounding the insoluble medium. The superficial physical structure of the solid is not affected. The direction of the exchange depends upon the selective attraction of the ion exchanger resin for the certain ions present and the concentrations of the ions in the solution. Both cation and anion exchange are used in water conditioning. Cation exchange is commonly used for water softening.
Iron (Fe) A very common element often present in groundwater in amounts ranging from 0.01 to 10.0 ppm (mg/L). Iron may be found in three forms: In soluble form such as in ferrous bicarbonate; Bound with a soluble organic compound; and As suspended ferric iron particles. Iron above 0.3 mg/L is objectionable in water because of staining of laundry and plumbing fixtures caused by the oxidation and precipitation of ferric hydroxide and/or ferric oxide (ferric iron) into small solid iron particles. Iron can also give a metallic or distorted flavor to beverages. Iron also occurs in water as ferric iron.
Iron Bacteria Bacteria which thrive on iron and are able to actually use ferrous iron (as found in water or steel pipes) in their metabolic processes, to incorporate ferric iron in their cell structure, and to deposit gelatinous ferric hydroxide iron compounds in their life processes. Iron bacteria are found in several varieties including Crenothrix, Lepothrix, and Gallionella. Iron bacteria can cause staining, plugging, and taste and odor problems in a water system.
Iron Fouled The accumulation of iron on or within an ion exchange resin bed or filter medium in such amounts that the capacity of the medium is reduced.
Grains Per Gallon (gpg) A common method of reporting water analysis results in the United States and Canada. One grain per gallon equals 17.1 parts per million (ppm) or 17.1 milligrams per liter. Grains per Imperial gallon equals 14.3 mg/L (or ppm).
KDF The trade name for a patened medium composed of high purity copper and zinc granules. KDF is capable of removing chlorine, soluble heavy metals, and other inorganic contaminents from water through the chemical reduction/oxidation (redox) process.
Magnesium One of the elements that make up the earth's crust as part of many rock-forming minerals such as dolomite. Magnesium and calcium dissolved in water constitute hardness. The presence of magnesium in water contributes to the formation of scale and the insoluble soap curds which identify hard water.
Manganese (Mn) An element sometimes found dissolved in groundwater, usually in combination with - but in lower concentrations than- iron. Manganese is noticeable because in concentrations above 0.05 mg/L it causes black staining of laundry and plumbing fixtures. Important ores of manganese are pyrolusite, manganite, psilomelane, and rhodochrosite.
Membrane A thin sheet or surface film, either natural or man-made, of microporous structure that performs as an efficient filter of particles down to the size range of chemical molecules and ions. Such membranes are termed "semipermeable" because some substances will pass through, but others will not. Usually small ions, water, solvents, gases, and other very small molecules can pass through a membrane, but other ions and macromolecules such as proteins and colloids are barred from passage. Man-made (synthetic) membranes are highly engineered polymer films about 100 angstroms thick and with controlled distributions of pores ranging from 5 to 5,000 angstroms in diameter. Membranes are used in reverse osmosis, electrodialysis, nanofiltration, ultrafiltration, and as pleated final filter cartridges in water treatment. SEE ALSO cellulose acetate (CA); cellulose triacetate (CTA); charged polysulfone membrane.
Methemoglobinemia A serious condition, found mostly in young infants under six months of age (or newborn animals), in which the oxygen-carrying capacity of the blood is reduced as a result of a reaction with nitrite (NO2-), which changes the healthy hemoglobin to an inactive methemoglobin form. As a result of the higher pH conditions in the gastrointestinal tract of infants and newborn animals, nitrate (NO3-), which is consumed in food or water, can be transformed into nitrite more readily than would occur with adults.
Nanofiltration A membrane treatment process which falls between reverse osmosis and ultrafiltration on the filtration/separation spectrum. The nanofiltration process can pass more water at lower pressure operations than reverse osmosis, can remove particles in the 300 to 1,000 molecular weight range such as humic acid and organic color bodies present in water, and can reject selected (typically polyvalent) salts. Nanofiltration may be used for selective removal of hardness ions in a process known as membrane softening.
Packed Bed A bed of filter or ion exchange medium which is completely retained so that no bed expansion can occur, and no backwash step is used to reclassify the filter or resin. Packed beds are usually part of the design features in ion exchange water softeners used to obtain high capacity and increased regeneration efficiency.
Parts per million A measure of proportion by weight which is equivalent to one unit of weight of solute (dissolved substance) per million weights of solution. Since one liter of water weighs one million milligrams, one ppm is equal to one milligram per liter (mg/L). Milligram per liter is the preferred unit of measure in water or waste water analysis.
Percent Rejection (reverse osmosis/ultrafiltration) The percentage of TDS in the feedwater that is prevented from passing the membrane with the permeate. The formula used is: the difference obtained from the TDS in feedwater minus TDS in permeate divided by TDS in feedwater; then multiply the answer obtained by 100 to obtain a percent
pH The degree of the acidity or basicity of a solution as measured on a scale ("pH scale") of 0 to 14. The midpoint of 7.0 on the pH scale represents neutrality--that is, a "neutral" solution is neither acidic nor basic. Numbers below 7.0 indicate acidity; numbers above 7.0 indicate basicity. Substances that when dissolved in water cause the pH to be less than 7.0 often create a sour taste and may sting when in contact with skin. The resulting solution will turn litmus paper red. Substances that when dissolved in water cause pH to be greater than 7.0 create a bitter taste and a slippery feel and will turn litmus paper blue. Water with a high pH tends to cause drying of the skin.
More specifically, pH is the negative of the base 10 logarithm of the hydrogen ion concentration of a solution, -log10[H+], where “p” is the short hand notation for “-log10”. The hydrogen ion concentration, [H+], is the moles of hydrogen ions per liter of solution. In neutral water, for example, the hydrogen ion concentration is 1x10-7 mol/L; the pH is therefore 7. Because both letters in the term pH are representative notations, the term must be written with a lower case “p” and an upper case “H”.
pH is an exponential function. A pH of 10 is ten times as basic as a pH of 9 and one hundred times as basic as a pH of 8. Similarly, a pH of 2 is one hundred times as acidic as a pH of 4 and one thousand times as acidic as a pH of 5.
In the field, pH is measured with a pH meter, which must be properly calibrated for accuracy. As pH in a water sample can change with time due to fluctuation of carbon dioxide concentration, pH should be measured quickly after sample collection.
Phosphate A salt of phosphoric acid. In the water industry, polyphosphates are used as sequestering agents to control iron and hardness, and as coating agents to control corrosion by formation of a thin passivating film on metal surfaces. The complex phosphates also are a group of sequestering agents widely used in detergent formulations (except where phosphates are banned by law) because of their superiority in chemical water softening, sequestering, and other builder functions. Sodium tripolyphosphate was the original builder upon which modern laundry detergent technology developed, and is used in laundry granules, automatic dishwasher detergents, and cleansers. It is adaptable to the spray drying process by which granules are made. Tetrasodium pyrophosphate is also used in detergent granules, but since it does not rank as high in overall performance as sodium tripolyphosphate, its application is more limited. Highly soluble tetrapotassium pyrophosphate is used in liquid laundry detergents and in hard surface cleaners, where it serves as a builder, water softener, and source of alkalinity. Another complex phosphate, sodium metaphosphate, is marketed as a packaged water softener. The most widely used sodium metaphosphate is sodium hexametaphosphate (SHMP), which softens by sequestering. The orthophosphate form of phosphates, trisodium phosphate (also called sodium orthophosphate), is a water softener that inactivates hardness minerals by precipitation. It is used to a limited extent in soap and detergent formulations as a builder, as a source of alkalinity, and for its water-softening properties. It is also used in powdered hard surface cleaners and cleansers to supply alkaline cleaning power. Chlorinated trisodium phosphate is a dry chlorine bleach that, in water, acts much like sodium hypochlorite (liquid chlorine bleach). It provides a means of incorporating chlorine bleach effectively in dry products, and for this reason is used in cleansers and automatic dishwasher detergents. It also provides alkalinity that aids in cleaning. Waters containing concentrations of iron, manganese, calcium, or magnesium sometimes can be treated with a sequestrant such as polyphosphate and kept from depositing these mineral precipitates or scales for a period of time. However, polyphosphate sequestering is not permanent, and therefore may not be as effective as actually removing the iron, manganese, and hardness minerals, as is done with iron filters and ion exchange water softening, for example. The sequestering value of polyphosphates is destroyed when they revert (hydrate) to orthophosphate. Polyphosphate reversion or hydration to orthophosphate occurs naturally in water with time. Intentions would be for this reversion not to happen and not to drop the sequestered water hardness, iron, and manganese out until after it reaches the wastewater. But, the polyphosphate reversion process can be accelerated by various uncontrolled conditions, such as low pH, high temperature, and the presence of the oxides of certain heavy metals, including iron, calcium, copper, and zinc in water. It is important in phosphate feed water treatment operations to: 1)maintain a stable pH within the phosphate product's performance rage. 2) determine the polyphosphate composition or blend that is most compatible with the specific water quality objectives and conditions, and 3) apply the appropriate dosage of phosphate to accomodate the system demand. Because of the difficulty in maintaining phosphate stabilities in the presence of varying pH, time, temperature, and metal oxides in most natural water supplies, the actual removal of iron, manganese, and water hardness is generally a more assuredly effective water treatment method. Municipal applications of polyphosphates to water supplies can interfere with home water treatment technologies. A portion of any water hardness, iron,
Potassium Permanganate (KMnO4) Dark purple, odorless crystals (with a blue metallic sheen) that dissolve in water to produce a purple-red color. Potassium permanganate is a powerful oxidizing agent that is used in water treatment as both an oxidizer and a disinfectant. It is also an effective regenerant for manganese oxidizing filters.
POU Point of Use
POE Point of Entry
Raw Water Water, usually from wells or surface sources, which has had no previous treatment and is entering a water processing system or device. 2. Water at the inlet side of any water treatment system or device.
Regenerant In ion exchange or softening applications, a regenerant is the chemical solution used to restore an exhausted bed of ion exchange resin to the fully ionic (regenerated) form necessary for the desired ion exchange to again take place effectively. Regenerants are also used in a similar fashion to restore catalyst (e.g., iron and manganese removal) media for reuse. Sodium chloride brine is normally used to regenerate cation exchange water softeners and for some dealkalizer systems. Hydrochloric and sulfuric acids are used for hydrogen-form cation deionizations units. Sodium hydroxide is normally used to regenerate OH- form anion deionizations systems. Potassium permangante regenerant is used to regenerate a manganese greensand iron and manganese removal filter.
Reverse Osmosis A water treatment process that removes undesirable materials from water by using pressure to force the water molecules through a semipermeable membrane. This process is called "reverse" osmosis because the pressure forces the water to flow in the reverse direction (from the concentrated solution to the dilute solution) to the flow direction (from the dilute to the concentrated) in the process of natural osmosis. RO removes ionized salts, colloids, and organic molecules down to a molecular weight of 100. May be called hyperfiltration.
Salt Bridging The creation of salt encrustment and cementing together of salt particles in dry storage brine tanks which causes tight bonding of the entire salt mass to the walls of the brine tank and prevents the salt from dropping into the incoming water for brine makeup.
Sequestration A chemical reaction in which certain ions are bound into a stable water-soluble compound so that they (ions) are prevented from certain normal but undesirable actions. For example, the sequestration of iron to prevent it from oxidizing, precipitating, and staining. The same as sequesterin
Tannin Any of a group of water soluble, natural organic phenolic compounds that are produced by metabolism in trees andplants, and are part of the degredation-resistant fulvic acid materials formed during the decomposition of vegetation. Tannins occur in water in almost any location where large quantities of vegetation have decayed. Tannins can impart a faintly yellowish to brown color to water. Tannin molecules tend to form anions in water above pH 6 and can then be treated with anion exchange resins. Below pH 5, tannins are better treated with activated carbon.
TDS- Total Dissolved Solids, The total weight of the solids that are dissolved in the water, give in ppm per unit volume of water. TDS is determined by filtering a given volume of water (usually through a 0.45 micron filter), evaporating it at a defined temperature (usually 103-105 degrees Celsius), and then weighing the residue. Note: A test measuring the electrical conductivity of the water provides only an estimate of the TDS present, as conductivity is not precisely proportional to the weight of an ion and nonconductive substances cannot be measured by electrical tests.
TDS Creep The appearance of salt in RO product water which sometimes occurs as a result of the reduction of differential pressure across the membrane as can occur when the RO unit has been shut down for a period of time. Water flow will cease to permeate through the membrane when there is insufficient differential water pressure across the membrane. However TDS permeates through the membrane as a function of the TDS concentration difference across the membrane.
TFC Membrane A class of reverse osmosis membranes made with polyamide-based polymer and fabricated with different materials in the separation and support layers.
Trihalomethanes (THMs) A group of organic chemicals, suspected of being carcinogenic, which are formed in water when chlorine being used as a disinfectant reacts with natural organic matter such as humic acids from decayed vegetation. Humic acids are present in all natural water used as sources of drinking water supplies. Chloroform is one of the most common THMs formed in this type of reaction.
Ultraviolet (UV) Light Radiation (light) having a wavelength shorter than 3900 angstroms, the wavelengths of visible light, and longer than 100 angstroms, the wavelengths of x-rays. This wavelength puts ultraviolet light at the invisible violet end of the light spectrum. Ultraviolet light is used as a disinfectant.
Upflow Brining Is a means of forcing the brine solution upward through the cation exchanger for regenerating the resin. Where the softening flow is downward and the regenerating brine flow is upward, the mode is also called countercurrent flow. Countercurrent flow means regeneration flows and service flows are in the opposite directions.
Upflow Softening A pattern of water flow used in softeners in which the service water flows upward through the ion exchange bed; the media is restricted in movement, usually because of a packed bed. The regeneration brine usually flows downward in such systems. Upflow softening is normally used to achieve higher operating efficiency.
Water Softener A device, product, or equipment that reduces the presence of water hardness to less than 1 gpg expressed as calcium carbonate (CaCO3) equivalent via chemical, physical, or other means. In residential and commercial applications, the most common water softener consists of a pressurized water treatment device in which hard water is passed through a bed of cation exchange media (either inorganic or synthetic organic) for the purpose of exchanging calcium and magnesium ions for sodium or potassium ions, thus producing a softened water which is more desirable for laundering, bathing, and dishwashing. This cation exchange process was originally called zeolite softening or the Permutit Process. Most modern water softeners use a sulfonated bead form of styrene/divinylbenzene (DVB) cation resin. Distillation, electrodialysis, nanofiltration, deionization, and reverse osmosis water treatment systems are also capable of measurably removing calcium and magnesium ions from water and therefore act as water softeners. SEE ALSO no-salt water softener; physical water treatment device.
