Glossary of Water Treatment Terms

Some license has been taken with the strict semantic interpretation of the following words and anagrams.

A

Absorb:
To soak up, as would a sponge. GAC does not absorb.

Acid: A compound which dissociates in water solution to furnish hydrogen ions.

Acidity: An expression of the concentration of hydrogen ions present in a solution.

Acid Radical: The anion in equilibrium with the hydrogen ion of an acid.

Activated Carbon: Carbon or charcoal that has undergone further heat and steam etching to increase its pore sizes and number.

Adsorb:
To adhere to or on. GAC takes up organics by attractive forces.

Adsorbate: That which is taken up or adsorbed by GAC.

Adsorbent: A synthetic resin possessing the ability to attract and to hold charged particles.

Adsorption: The attachment of charged particles to the chemically active groups on the surface and in the pores of an ion exchanger.

Alkalinity:
An expression of the total basic anions (hydroxyl groups) present in a solution. It also represents, particularly in water analysis, the bicarbonate, carbonate, and occasionally, the borate, silicate, and phosphate salts which will react with water to produce the hydroxyl groups.

Anion: Negatively charged ion, such as CO2-, SO42-, HCO3-, Cl-, NO3-,

Anion Interchange: The displacement of one negatively charged particle by another on an anion exchange material.

Atomic Weight:
Relative weight of an atom of an element as compared to the weight of an atom of carbon, taken as 12.

Attrition: The rubbing of one particle against another in a resin bed; frictional wear that will affect the size of resin particles.

B

Backwash:
The counter-current flow of water through a resin bed (i.e., in at the bottom of the exchange unit, out at the top) to clean and reclassify the bed after exhaustion.

Base-Exchange:
The property of the trading of cations shown by certain insoluble naturally occurring materials (zeolites) and developed to a high degree of specificity and efficiency in synthetic resin adsorbents.

Batch Operation:
The utilization of ion exchange resins to treat a solution in a container wherein the removal of ions is accomplished by agitation of the solution and subsequent decanting of the treated liquid.

Bed:
A mass of ion exchange resin particles contained in a column.

Bed Depth: The height of the resinous material in the column after the exchanger has been properly conditioned for effective operation.

Bed Expansion:
The effect produced during back washing: the resin particles become separated and rise in the column. The expansion of the bed due to the increase in the space between resin particles may be controlled by regulating backwash flow.

Bicarbonate Alkalinity:
The presence in a solution of hydroxyl (OH-) ions resulting from the hydrolysis of carbonates or bicarbonates. When these salts react with water, a strong base and a weak acid are produced, and the solution is alkaline.

Breakthrough:
The first appearance in the solution flowing from an ion exchange unit of unabsorbed ion similar to those which are depleting the activity of the resin bed. Breakthrough is an indication that regeneration of the resin is necessary.

C

Conversion: Percent of feed converted into permeate. Also known as recovery.

Capacity:
The adsorption activity possessed in varying degree by ion exchange materials. This quality may be expressed as kilograins per cubic foot, gram-milli-equivalents per gram, pound-equivalents per pound, gram-milli-equivalents per milliliter, etc., where the numerators of these ratios represent the weight of the ions adsorbed and the denominators, the weight or volume of the adsorbent.

Carbonaceous Exchangers: Ion exchange materials of limited capacity prepared by the sulfonation of coal, lignite, peat, etc.

Carbonate Hardness:
That hardness caused by bicarbonates and carbonates of calcium and magnesium, see Non carbonate Hardness

Carboxylic: A term describing a specific acidic group (COOH) that contributes cation exchange ability to some resins.

Cation: Positively charged ion, such as Ca2+, Mg2+, Fe3+, Na+, K+, etc.

Channeling:
Cleavage and furrowing of the bed due to faulty operational procedures, in which the solution being treated follows the path of least resistance, runs through these furrows, and fails to contact active groups in other parts of the bed.

Chemical Stability: Resistance to chemical change which ion exchange resins must possess despite contact with aggressive solutions.

Colloidal Matter:
Matter of very fine particulate size, usually in the range of 10-5 to 10-7 cm in diameter. It forms dispersions intermediate in character between a true solution and a suspension.

Color-Throw:
Discoloration of the liquid passing through an ion exchange material; the flushing from the resin interstices of traces of colored organic reaction intermediates.

Column Operation:
Conventional utilization of ion exchange resins in columns through which pass (either up flow or down flow) the solution to be treated.

Concentrate (Reject):
Concentrated portion of the feed remaining outside the membrane, which is discarded.

Conductivity:
A measure of salt concentration due to the ability of dissolved solids (ions) to conduct electricity, usually expressed as mhos/cm, or microseimens per cm, S/cm.

Contact Time:
The time in minutes that the bed is in contact with GAC. Assumes 7.5 gal per cu. ft. of GAC. Divide gpm flow into 7.5 times total cu. ft. to get contact time in minutes.

Cycle:
A complete course of ion exchange operation. For instance, a complete cycle of cation exchange would involve: regeneration of the resin with acid, rinse to remove excess acid, exhaustion, backwash, and finally regeneration.

D

Deashing:
The removal from solution of inorganic salts by means of adsorption by ion exchange resins of both the cations and the anions that comprise the salts. See deionization.

Dechlorination:
Removal of free chlorine from water by catalytic reduction. GAC has the ability to remove nearly 5 lbs. of chlorine per 1 lbs. of GAC.

Deionization:
See deashing. Deionization, a more general term than, deashing, embraces the removal of all charged constituents or ionizable salts (both inorganic and organic) from solution.

Demineralizing: See deashing.

Density:
The weight of a given volume of exchange material, back-washed and in place in the column.

Differential Pressure: Pressure drop measured between inlet and outlet streams.

Dissociation: Ionization.

Down Flow:
Conventional direction of solutions to be processed in ion exchange column operation, i.e., in at the top, out at the bottom of the column.

Dynamic System:
An ion exchange operation wherein a flow of the solution to be treated is involved.

E

Effective Size:
Taken from the particle distribution profile. It is the size screen which allows 10% of the sample to pass through.

Efficiency:
The effectiveness of the operational performance of an ion exchanger. Efficiency in the adsorption of ions is expressed as the quantity of regenerant required to effect the removal of a specified unit weight of adsorbed material, e.g., pounds of acid per kilogram of salt removed.

Effluent: The solution which emerges from an ion exchange column.

Electrolyte: A chemical compound which dissociates or ionizes in water to produce a solution which will conduct an electric current; an acid, base, or salt.

Elution: The stripping of adsorbed ions from an ion exchange material by the use of solutions containing other ions in concentrations higher than those of the ions to be stripped.

Equilibrium Reactions:
The interaction of ionizable compounds in which the products obtained tend to revert to the substances from which they were formed until a balance is reached in which both reactants and products are present in definite ratios.

Equivalent Weight: The molecular weight of any element or radical expressed as grams, pounds, etc., divided by the valence.

Equivalents Per Million:
A unit chemical equivalent weight of solute ( the substance dissolved) per million unit weights of solution. Concentration in epm is calculated by dividing the concentration in parts per million by the equivalent weight (combining weight) of the ion or substance.

Exchange Velocity: The rate with which one ion is displaced from an exchanger in favor of another.

Exhaustion:
The state in which the adsorbent is no longer capable of useful ion exchange; the depletion of the exchanger's supply of available ions. The exhaustion point is determined arbitrarily in terms of: (a) a value in parts per million of ions in the effluent solution; (b) the reduction in quality of the effluent water determined by a conductivity bridge which measures the resistance of the water to electric current.

F

Feed: The feed water pumped into a permeator under high pressure.

Fines:
Extremely small particles of ion exchange materials.

Flow Rate:
The volume of solution which passes through a given quantity of resin within a given time. Flow rate is usually expressed in terms of gallons per minute per cubic foot of resin, or as milliliters per minute per milliliter of resin.

Freeboard: The space provided above the resin bed in an ion exchange column to allow for expansion of the bed during back washing.

Free Mineral Acidity:
(FMA) Is the actual acidity in a hydrogen cycle cation exchanger effluent and is usually expressed as PPM of hydrogen.(as CaCO3.)

G

Grain:
A unit of weight; 0.0648 grams; 0.000143 pounds.

Grains Per Gallon: An expression of concentration of material in solution. One grain per gallon is equivalent to 17.1 parts per million.

Gram:
A unit of weight; 15.432 grains; 0.0022 pounds.

Gram-Milliequivalents: The equivalent weight in grams, divided by 1000.

Granulated Activated Carbon: (GAC) See activated carbon.

Greensand:
Naturally-occurring materials, composed primarily of complex silicates, which possess ion exchange properties.

H

Hardness:
The scale-forming and lather-inhibiting qualities which water, high in calcium and magnesium ions, possesses. Temporary hardness, caused by the presence of magnesium or calcium bicarbonate, is so called because it may be removed by boiling the water to convert the bicarbonates to the insoluble carbonates. Calcium sulfate, magnesium sulfate, and the chlorides of these two metals cause permanent hardness.

Hardness As Calcium Carbonate:
The expression described to the value obtained when the hardness-forming salts are calculated in terms of equivalent quantities of calcium carbonate; a convenient method of reducing all salts to a common basis for comparison.

Head Loss:
The reduction in liquid pressure associated with the passage of a solution through a bed of exchange material; a measure of the resistance of a resin bed to the flow of the liquid passing through it.

Hydraulic Classification:
The rearrangement of resin particles in an ion exchange unit. As the backwash water flows up through the resin bed, the particles are placed in a mobile condition wherein the larger particles settle and the smaller particles rise to the top of the bed.

Hydrogen Cycle: A complete course of cation exchange operation in which the adsorbent is employed in the hydrogen or free acid form.

Hydroxyl:
The term used to describe the anionic radical (OH-) which is responsible for the alkalinity of a solution.

I

Influent:
The solution which enters an ion exchange unit.

Ion: Any particle of less than colloidal size possessing either a positive or a negative electric charge.

Ionization: The dissociation of molecules into charged particles.

Ionization Constant: An expression in absolute units of the extent of dissociation into ions of a chemical compound in solution.

J

K

Kilograin: A unit of weight; one thousand grains.

L

Leakage:
The phenomenon in which some of the influent ions are not adsorbed and appear in the effluent when a solution is passed through an under - regenerated exchange resin bed.

M

Mean Particle Diameter: Refers to the size profile of a given GAC. Reported in mm. Does not affect the adsorptive performance but does affect hydraulic performance.

Molecular Weight:
The sum of the atomic weights of the atoms of a molecule

N

Neat: Free from admixture or dilution, Straight.

Negative Charge: The electrical potential which an atom acquires when it gains one or more electrons; a characteristic of an anion.

Neutralization:
Reaction of acid or alkali with the opposite reagent until the hydrogen ions are approximately equal to the hydroxyl ion in solution.

Non Carbonate Hardness:
Hardness in water caused by chlorides, sulfates and nitrates of calcium and magnesium, see Carbonate Hardness.

Normal Solution:
A solution containing an equivalent weight of a solute in one liter of solution, e.g. 1 N/HCl solution contains 36.5g HCl per liter.

O

Osmosis:
Movement of a solvent through a semipermeable membrane into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane.

Osmotic Equalization:
Osmotic equalization is reached when no further solute transport takes place due to equalization of the solute concentration on both sides of the membrane.

Osmotic Head (Pressure):
The maximum pressure that develops in a solution separated from a solvent by a membrane permeable only to the solvent. The pressure that must be applied to a solution to just prevent osmosis.

size="+1">P

Passage: Ratio of permeate to feed concentration of a particular dissolved material, expressed in percent.

Permeate (Product):
The purified portion of the feed passing through the membrane.

pH: An expression of the acidity of a solution; the negative logarithm of the hydrogen ion concentration (pH 1 very acidic; pH 14, very basic; pH 7, neutral).

Physical Stability: The quality which an ion exchange resin must possess to resist changes that might be caused by attrition, high temperatures, and other physical conditions.

pK:
An expression of the extent of dissociation of an electrolyte; the negative logarithm of the ionization constant of a compound.

pOH:
An expression of the alkalinity of a solution; the negative logarithm of the hydroxyl ion concentration.

Positive Charge: The electrical potential acquired by an atom which has lost one or more electrons; a characteristic of a cation.

Q

R

Raw Water: Untreated water from wells or from surface sources.

Recovery:
Percent of total inlet flow passing through membrane as permeate. Equal to permeate flow / (permeate flow + concentrate flow). Calculated when RO is in rinse or service steps. Range is 0-100 percent.

Regenerant:
The solution used to restore the activity of an ion exchanger. Acids are employed to restore a cation exchanger to its hydrogen form; brine solutions may be used to convert the cation exchanger to the sodium form. The anion exchanger may be rejuvenated by treatment with an alkaline solution.

Regeneration: Restoration of the activity of an ion exchanger by replacing the ions adsorbed from the treated solution by ions that were adsorbed initially on the resin.

Rejection:
Percent of inlet Total Dissolved Solids (TDS) rejected by RO membranes. Equal to permeate conductivity / inlet conductivity. Calculated when RO is in rinse or service steps. Range is 0-100 percent.

Rejuvenation: See Regeneration.

Reverse Deionization: The use of an anion exchange unit and a cation exchange unit, in that order, to remove all ions from solution.

Reverse Osmosis:
The process by which solute (feed) is forced under high pressure (a pressure in excess of the osmotic pressure) through a semi-permeable membrane. A portion of the fluid with concentrated ionic materials (concentrate) does not pass through the membrane and is discarded (unless it is of interest in a particular application). The purified portion (permeate) which passed through the membrane is then collected for use (as in a water purification application).

Reverse Osmosis (RO) Membrane:
An RO membrane is a semi-permeable membrane generally in sheet or hollow fiber form which rejects not only dissolved materials, but also organics, sub micron size membranes are defined by their rejection characteristics.

RO System Pressures:

Concentrate: Outlet gage pressure at concentrate line (waste).

Differential 1 (Cross 1): Differential pressure across first stage RO (Feed - Transition).

Differential 2 (Cross 2):
Differential pressure across second stage RO (Transition - Concentrate).

Membrane Feed: Inlet stream gage pressure (outlet of pump).

Permeate: Outlet stream gage pressure (product or effluent).

Suction:
City or the incoming House Pressure (inlet of pump).

Driving 1 (Thru 1): Differential pressure through the first stage RO membrane (Feed - Permeate) Note: Net driving pressure would deduct half of differential 1 pressure.


Driving 2 (Thru 2): Differential pressure through 2nd stage RO membrane (Transition - Permeate). Note: Net driving pressure would deduct half of differential 1 pressure.

Transition:
Outlet gage pressure of first stage RO concentrate line.

Rinse: The operation which follows regeneration; a flushing out of excess regenerant solution.

S

Silicous Gel Zeolite: A synthetic, inorganic exchanger produced by the aqueous reaction of alkali with aluminum salts.

Solute: Material (salts) dissolved by solvent (water).

Solution: A solid, liquid, or gaseous substance which is homogeneously mixed with a liquid.

Solvent:
A liquid substance capable of dissolving or dispersing one or more other substances, thereby producing a solution.

Static System:
The batch-wise employment of ion exchange resins, wherein (since ion exchange is an equilibrium reaction) a definite end-point is reached in which a finite quantity of all the ions involved is present. Opposed to a dynamic, column-type operation.

Sulfonic: A specific acidic group (SO3H) on which depends the exchange activity of certain cation adsorbents.

Surface Loading: Refers to the hydraulic flow rate of the column in gpm.

Swelling:
The expansion of an ion exchange bed which occurs when the reactive groups on the resin are converted from one form to another.

T

Throughput Volume:
The amount of solution passed through an exchange bed before exhaustion of the resin is reached.

(TDS) Total Dissolved Solids: Total dissolved inorganic salts present in any fluid stream.

(TOC) Total Organic Carbon: Total organic carbon content of the fluid stream.

U

Up Flow:
The operation of an ion exchange unit in which solutions are passed in at the bottom and out at the top of the container.

V

 Voids:
The space between the resinous particles in an ion exchange bed.

W

X

Y

Z

 Zeolite:
Naturally-occurring hydrous silicates exhibiting limited base exchange.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z