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Water Chemistry and Biological Terms

AcidAny substance that donates a proton (H+) when dissolved in a solution. In water treatment, it usually means circulating water with a pH of less than 7.0. Sulfuric acid is the most common acid used to control cooling water pH.
AdsorptionAssimilation of molecules or other substances onto the physical structure of a liquid or solid without chemical reaction.
Aerationblowing or mixing of air through water to sweep out other dissolved gases and to equilibrate the water with primarily nitrogen, oxygen and carbon dioxide.
Aerobean organism that grows only in the presence of free (molecular) oxygen.
Algaea low form of plant life containing chlorophyll that generally requires sunlight and air for existence. Many are microscopic but under favorable conditions can grow sufficiently dense to plug cooling tower distributors on the decks and to interfere with water splashing in the fill. Large masses often slough off the tower and plug heat exchangers or deposit in piping.
Algaecidea toxic material that will kill algae. Some of the more commonly used algaecides are chlorine, copper sulfate and phenolic compounds.
Alkalinityan expression of the total basic anions (hydroxyl groups) that is present in a solution. It also represents, particularly in water analysis, the bicarbonate, carbonate, hydroxyl and occasionally the borate, silicate, and phosphate salts which will react with water to produce acid neutralizable anions.
Ammoniaa water-soluble, colorless, pungent gas with the formula NH3.
Ammoniumpositive ion with the formula NH4+ that forms when ammonia dissolves in water. It adds non-natural alkalinity to the water.
Anaerobe (strict)an organism that grows only in the absence of free oxygen (e.g., sulfate reducing bacteria).
Anaerobe (facultative)an organism that can grow under either aerobic or anaerobic conditions.
Aniona negatively charged ion.
Anodea positively charged electrode that, during electrolysis, attracts anions.
Anodic areaarea on a metal surface where electrons are given up and metal dissolves (corrosion).
Antifoaman agent that prevents foam from forming or reduces its presence.
Atomic numbera number given to each element representing the number of protons in one atom of that element.
Atomic weightweight (in grams) of 6.02x1024 atoms of a particular element. The weight of an atom of any element compared with that of oxygen that is considered to be 16.
Autotrophican organism that is capable of producing its own food through the use of chlorophyll and light.
BacteriaUnicellular microorganisms which reproduce by fission or spores, identified by their shapes: coccus, round; bacillus, rod shaped; and spirillum, curved.
Bicarbonate alkalinityin a water solution, the presence of ions resulting from the hydrolysis of carbonates when these salts react with water. A strong base and a weak acid are produced and the solution is alkaline. Its formula is HCO3-, but its concentration is usually denoted as ppm as CaCO3.
Biocidea chemical that is designed to control the population of troublesome microbes by killing them.
Biological depositwater-formed deposits of organisms or their waste products (example: slimes, barnacles, etc.).
Biostata chemical that is designed to control the population of troublesome microbes by inhibiting their reproduction and subsequent increase in population.
Blowdownwater discharged from the system to control concentration of salts or other impurities in the circulating water.
Carbonate hardnesshardness in water caused by bicarbonates of calcium and magnesium. If alkalinity exceeds total hardness, all hardness is carbonate hardness; if hardness exceeds alkalinity, the carbonate hardness equals the alkalinity.
Cathodea negatively charged electrode (which attracts cations in electrolysis).
Cationa positively charged ion resulting from dissociation of molecules in solution.
Chemical dosagethe amount of chemical added to a system, usually expressed as ppm, or pounds of chemical per million pounds of water.
Chloraminea compound formed when chlorine reacts with ammonia or a chemical containing the ammonium ion. The result is mono-, di-, tri-, and organochloramines. The resulting chloramines are weak oxidants or nonoxidants. They are a component of total chlorine. These are very weak biocides.
Chlorinationadding chlorine or a chlorine derivative to water to prevent the growth of various organisms that cause biofouling.
Chlorination, dechlorinationthe act of removing chlorine from water, usually via a reducing agent or strong aeration.
Chlorinea poisonous yellow gas with chemical symbol Cl2 used for water treatment. It is soluble in water but can be removed by reducing aeration and reaction with sunlight.
Chlorine demandthe relation of the amount of chlorine to be added to a system to react with chlorine-oxidizable material until a free residual in a given system is achieved.
Chlorine dioxidea compound with the symbol ClO2, used mainly for bleaching wood pulp for paper. It is also used for the taste and odor control of phenolic compounds in water and can be used as a disinfectant in cooling towers.
Chlorine, freethe total amount of hypochlorous ion and hypochlorous acid in the system.
Chlorine, residualthe amount of available chlorine present in water at any given time subsequent to the addition of chlorine.
Circulating water ratequantity of water pumped from the tower basin to the equipment to be cooled, usually expressed as gallons per minute (gpm).
Combined Chlorine (new)the amount of chloramine or chloro-organic compounds present in water.
Compoundssubstances formed from the chemical bonding of two or more atoms.
Concentrationthe process of increasing solids per unit volume of solution, usually by evaporation of the liquid; also, the amount of material dissolved in a unit volume of solution. This occurs in a cooling tower due to evaporation that cools the water. It is normally expressed directly as ppm or indirectly as mhos conductivity.
Conductivitythe ability of water to conduct electricity. When measured with a standard apparatus, it is called specific conductivity and is a function of the total ionic dissolved solids. As a rule of thumb, TDS = 2/3 specific conductance measured as micromhos.
Cooling waterwater circulated through a cooling system to remove heat from certain areas.
Copper alloysmetals made from a mixture of copper and another metal (Example brass = copper + zinc).
Corrosionto be dissolved away, usually by oxidation or acidification. This usually refers to metal loss in cooling systems, often recognized by the local reaction of the dissolved metal with oxygen, carbon dioxide, acids or galvanic action. May result in general (widespread) or pitting loss of the metal.
Corrosion coupona small piece of metal that is inserted into a circulating system that can be analyzed to find the corrosive nature of the system's water.
Corrosion fatiguethe weakening of a pipe or similar piece of metal due to corrosion acting on it.
Corrosion inhibitorchemical used in a system to prevent corrosion.
Cycles of Concentrationcompares dissolved solids in makeup water with solids concentrated through evaporation in the circulating water. Since chlorides are soluble in water, for example, the cycles of concentration are equal to the ratio of chlorides in circulating water to chlorides in makeup water.
Deflocculationthe ability of some materials such as polyphosphides to peptize and disperse suspensions of colloidal particles.
Delignificationthe dissolving of the lignin portion of cooling water wood usually by strong alkaline and/or oxidizing agents.
Denitrificationthe removal of nitrogen from a system. This may be done chemically or biologically.
Disinfectingto remove microorganisms from a particular surface or liquid.
Dispersanta chemical that causes particulates in a water system to remain in or be placed into suspension.
Dissolved gasestotal gases dissolved in a liquid.
Dissolved solidstotal solids that have been dissolved into a liquid. They may be ionic and/or polar in nature.
Driftwater lost from a cooling tower as liquid droplets entrained in the exhaust air. It is independent of water lost by evaporation. Units may be in lbs./hr. or percentage of circulating water flow. Drift eliminators control this loss from the tower.
Electrodeconductor that carries an electrical charge.
Electrolytea chemical compound that dissociates or ionizes in water to produce a solution that will conduct an electric current; an acid, base, or salt.
Elementssubstances that cannot be divided into smaller units without nuclear destruction.
Equivalent weightmolecular or atomic weight divided by the valence of the substance being considered.
Evaporation losswater evaporated from the circulating water into the atmosphere by the cooling process.
Evaporation ratethe rate at which a liquid turns into gas and leaves a system.
Fatigue, corrosionThe weakening of a piece of metal or pipe due to corrosion.
Ferrobacillusa type of iron-reducing bacteria.
Filamentous bacteriabacteria with a long, threadlike shape.
Float valvea valve that is actuated by a float, generally used to control makeup water supply to a cooling system.
Flocculationthe process of agglomerating coagulated particles into settleable flocs, usually of a gelatinous nature.
Flow control valvea manually controlled valve generally located in the hot water supply line used to increase or decrease the flow of a liquid in a system.
Fungisimple, plant-like life forms that lack true roots, stems, leaves, and chlorophyll. They are filamentous in structure (e.g., mushrooms, mildews, molds, and yeasts).
Galvanic attackcorrosion behavior caused by the current generated when one metal type is in contact with a different metal type.
Galvanic corrosioncorrosion formed from galvanic attack.
Galvanic couplethe contact of one metal type with another as seen with a steel bolt in an aluminum sheet or a copper joint on an iron pipe, which allows a differential current to be generated.
Groundwaterwater pumped from underground rivers, wells and lakes.
Half lifein water treatment, the time it takes to lose " of a slug fed product from the system through blowdown, drift and windage when taking into account its continuous concentration by evaporation and dilution by fresh makeup.
Hardness, calciumthe calcium compounds dissolved in water, usually expressed as calcium carbonate.
Hardness, carbonatethe calcium and magnesium carbonate and bicarbonate dissolved in water, expressed as calcium carbonate. Other metallic cations such as ferrous iron, barium, zinc and manganous ions are also included.
Hardness, magnesiummagnesium compounds dissolved in water, expressed as calcium carbonate.
Hardness, noncarbonatethe difference between the total hardness and the total alkalinity of a water.
Hardness, permanentthe hardness that cannot be removed from water by precipitation reactions. Essentially, the same thing as the non-carbonate hardness.
Hardness, temporarythe hardness that can be removed from water by precipitation. Essentially, the same as the carbonate hardness.
Hardness, totalthe sum of the calcium and the magnesium hardness. Also the sum of the permanent hardness and temporary hardness. The U.S. Geological Survey hardness criteria for potable water are: soft water 0-60 ppm, moderately hard water 61-120 ppm, hard water 121-180 ppm, very hard water >180 ppm.
Heat exchangera device for transferring heat from one substance to another. Heat transfer can be by direct contact, as in a cooling tower, or indirect, as in a shell and tube condenser. Can also be the tube or fin tubed bundles in a wet/dry tower.
Heat loadheat removed from the circulating water within the tower. It may be calculated from the range and the circulating water flow.
Impuritiesany substance that contaminates another.
Iron bacteriaoxidative bacteria that cause taste, staining, and odor problems in water. The precipitation of iron by the bacteria can build up in piping and heat exchangers to restrict water flow. Although they are not a direct cause of corrosion, differential aeration cells will form under deposits and localized corrosion will appear.
Langelier's Indexa formula for predicting whether water will tend to dissolve or precipitate calcium carbonate.
Makeupwater added to the circulating water system to replace water lost from the system by evaporation, drift, blowdown, and leakage.
Microorganisman organism that is too small to be studied without the aid of a microscope.
Molluscicidea material that will kill molluscs.
Nonoxidizing biocidea biocide whose effectiveness depends on some property other than its ability to oxidize organic material (i.e., systematic poisons and surface activity).
pHthe logarithm of the reciprocal of the hydrogen ion concentration. Water with a pH of 7 is neutral at room temperature. A pH greater than 7 indicates alkaline water. A pH less than 7 indicates acidic water.
Phosphatesinorganic ions comprised of phosphorous and oxygen.
Photosynthesisthe process by which plants use sunlight to produce energy by consuming CO2 and releasing O2.
Residual chlorine(see chlorine, free) the amount of available chlorine present in water at any specified period, subsequent to the addition of chlorine.
Ryznar Indexan empirical method, often used in combination with the Langelier's Index, to predict the scaling tendencies of water. It is based on a study of operating results with water of various saturation indices.
Scalethe deposition on heat transfer surfaces of material normally in solution, as opposed to fouling, which is deposition of material normally in suspension.
Slimea deposit build-up directly related to the excessive growth of microorganisms that secrete or form thick, sticky material. These slimes cause tube pluggage, reduce heat transfer, entrap migratory suspended solids and can result in underdeposit corrosion.
Solubilitythe ability of one material (the solute) to dissolve in another (the solvent).
Solutionsliquid mixtures that are uniform throughout.
Sulfate-reducing bacteriagroup of anaerobic bacteria capable of reducing sulfates to sulfides, especially hydrogen sulfide, a very corrosive gas.
Surfactantin water, any molecule that modifies the interfacial tension of a liquid and the surface it contacts (surfaces can be air, metal, biomass, etc.).
Suspended solidsinsoluble particles suspended in water
Synergismthe condition existing where the effect of two or more materials added to water is greater than the sum of their individual effects
Thermophilica type of bacteria that thrives in very high temperatures.
Total Chlorine (new)the total amount of all types of chlorine compounds present. This includes Cl2, hypochlorous acid, hypochlorite ion, and all the chloramine compounds. Free Chlorine + Combined Chlorine = Total Chlorine.
Total Dissolved Solidsthe sum of the organic and inorganic materials dissolved in water.
Tuberculationlocalized attack typified by the formation of inverted pliable conical structures. In water systems, tuberculation is more commonly associated with localized corrosion of iron and the conical structures are predominately made up of several oxidation states of iron (Fe2O3, Fe3O4, etc.). Pitting is normal result.
Turbiditythe interference to light transmission caused by suspended solids usually colloidal in nature.
Water-formed depositany accumulation of insoluble material derived from water or formed by the reaction of water upon surfaces, including scale, sludge, foulants, sediments, corrosion products or biological deposits.