1Fundamentals of Water TreatmentI. INTRODUCTION

Throughout history, the importance of differentmaterials, utilized for the advancement ofcivilization, change as new technologies evolve. From the Stone Age to the Computer Age onlyone material has remained the most preciousand the most unique. Life, as we know it,cannot go on without it. The early Greekphilosophers believed that it was the originalsubstance of the universe, out of whicheverything had been made. It consists of twoelements that are gases at ordinarytemperatures. One will burn, while the other isnecessary for combustion, yet combined it isused to put out fires. What is the precious,unique material? It is ordinary water and is thesubject of our story.

The purpose of this paper is to explore anddelineate the properties and processes throughwhich water passes in commercial and industrialwater treatment environments. Our primaryfocus will be those processes used in controllingscale formation experienced in the larger flowre-circulating water systems. The commonchemical and the advancing physicochemicalwater conditioning methods available in themarketplace will be covered. The fundamentalforce associated with electric charges and theirresulting fields that control all chemicalreaction will be utilized in exploring theseprocesses. This paper is not intended to be arigorous scientific treatment of the subject, butrather aimed at gaining a conceptualunderstanding of possible phenomena.

As the human population increases andtechnology advances, more and more water isused. In ancient times, when the worldpopulation was a fraction of what it is now, theaverage person used from three to five gallonsof water daily. In the nineteenth century, in theWestern nations where technology wasdeveloping, the water consumption per capita

increased to approximately ten to fifteen gallonsdaily. Since 1900, both the population and theper capita consumption have made enormousleaps. In the U.S. according to one article, theper capita consumption of water has increasedto 100 to 200 gal/day. This number representsour reliance not only from an industrial andcommercial aspect but our personal demand aswell, what with our automatic washers, dryers,dishwashers, air conditioning systems, garbagedisposals, and so on. Overall it is estimated thatAmerica uses more than 400 billion gallons ofwater daily. In Europe, per capita waterconsumption is only 25 to 35% of that in theU.S., partially due to the higher cost of waterand environmental pressures.

Some of this water can be used over and overagain, but a significant portion of it cannotbecause it is lost as steam or polluted with wastematerials or chemicals. Because of our demand,there is a steady lowering of the ground watertables, requiring deeper and deeper wells. Thepollution of lakes and rivers by sewage andindustrial wastes is becoming a more seriousproblem every year and one that is moreexpensive to solve.

On a global basis man has had the greatestimpact on his environment, more than any otherspecies, and this will increase as we continuallydevelop technologies benefiting futuregenerations. It is these modifications, whichhave produced increasingly acute waterproblems. At the present time our main line ofattack upon this problem involvesimprovements in water economy, i.e.,improvement in pollution prevention and/or itsremoval and the efficiency with which availablesupplies are used.

At this point we should reiterate that science isbased on facts, and is the foundation from whichwe should review various water-relatedprocesses. From these, facts hypotheses are

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formed. A successful hypothesis is notnecessarily a permanent hypothesis, but it is onethat stimulates additional research, opens upnew fields, or explains and coordinatespreviously unrelated facts. This accumulatedknowledge concerning physical facts is in effectthe general truths and laws by which the factsare systematically related to one another. Tothis we must add that scientific truths or finalanswers are never achieved. We mustcontinually search for better answers. So it iswith our treatment of water.

II. ATOMIC FORCES

At the end of the nineteenth century, an Englishchemist named John Dalton did experimentsthat suggested that elements were composed oftiny particles called atoms. By the early part ofthe twentieth century, experiments had shownthat atoms were made up of even smaller bits ofmatter called subatomic particles. Presentlyscientists are unlocking the secrets of subatomicparticles and are finding still other layers of thesubatomic building blocks.

Atoms are made up of positively chargedcenters with negatively changed electronscircling about their centers. Atoms come indifferent sizes and form bonds of greater orlesser strengths and directionality with oneanother, resulting in great diversity in materialproperties. Atoms assemble themselves intodifferent atomic structures depending on theirrelative size and the nature of the bond thatengages them. Of primary importance indetermining interatomic forces and the resultingatomic structure, is the arrangement of theatoms outer electrons, which strongly affects thenearest neighboring atoms in the structure.

There are four main types of bonds that playmajor roles in chemical reactions. In ionicbonds, the atoms have either lost or gained oneor more electrons so that their outer electronshell is complete. Thus, they cannot share

electrons, but since they are electrically chargedby virtue of having gained or lost an electron,they are attracted to atoms of the oppositecharge. In covalent bonds, atoms share one ormore pairs of outer electrons in filling theirouter shells. In metallic bonds all the atomsshare all the outer electrons. The molecularbond, also known as a van der Waals bond,arises from the displacement of the electronswithin electrically neutral atoms that produce aweak attractive force between theatoms/molecules as they approach each other. Another molecular bond known as thehydrogen bond is the result of the fact thatelectrons can be easily displaced due to theatoms small size. All these bonds are idealizedand all chemical interactions involve somecombination of them. Note that all chemicalreactions are based on the electroniccharacteristics of the various atoms.

III. WATER

Water is the only substance that commonlyoccurs in nature as solid, liquid, and vapors. Each of the elements combining to form waterexists independently as molecules containingtwo atoms (H2, O2) held together by covalentbonds. It is the covalent bond that also holdstogether the molecules of water (H2O).

Figure 1

3The distribution of the electrons in H2 and O2determines the shape of the water molecule andits electronic structure. The resultant moleculeof H2O is what is called a polar moleculebecause its positive and negative charges are notspread evenly around a center but are insteaddistributed asymmetrically to form positive andnegative poles. The two hydrogen atoms arearranged approximately 0.95 or 0.95x10-10mfrom the oxygen nucleus and separated formone another by 104.5 degrees (see Figure 1).

Water molecules may be said to have a greatdeal of integrity in that they maintain theiridentity in circumstances that causes other kindsof molecules to split into ions. It has beencalculated that a ton of pure water contains onlyabout 0.1 milligrams of H+ and 1.7 milligramsof OH- ions. This means that pure water is avery poor conductor of electricity, since itprovides very few charged particles to constitutea current between two electrodes. However,this atomic arrangement gives it a strongtendency to orient itself (or to be oriented) in anelectrical field with its negative end toward thepositive plate and its negative end toward thepositive plate. Water is therefore said to havean unusually large dipole moment whosebehavior in an electric field may be illustratedas in Figure 2 & 3.

Figure 2 Dipole Moment

By orienting themselves in this way, watermolecules tend to neutralize an electrical field--a fact expressed in technical language by sayingthat water's large dipole moment gives it anabnormally large dielectric constant. If weassume the dielectric constant of a vacuum to beone, then the dielectric constant of water is 80,which is to say that two electrically chargedparticles will attract or repel on another withonly 1/80 as much strength in water as theywould in a vacuum.

These structural and electrical characteristicsaccount in part for water's remarkable ability todissolve substances, and particularly thosesubstances whose molecules are held togetherby ionic bonding. The negative ions of asubstance are attracted to the partially positivehydrogen atoms of the water molecules. Thisweakens and overcomes the attraction of thenegative ion for the positive ions in thesubstances (salts), and the negative ion is pulledinto solution. Likewise, the positive ions areattracted to the partially negative oxygen atomsof the water molecules. As the ion moves intosolution they are surrounded by more watermolecules, a process called hydration, and thusan ionized solution is formed. Since, theattraction between the dissociated, oppositelycharged ions is reduced by water's highdielectric constant to a fraction of what it wouldbe in air, or to just 1/80 of its strength in avacuum. The attraction is so slight that it can becompletely nullified by mild thermal agitationand turbulence.

Figure 3 Water in an Electrical Field

The electrical charges of the polar watermolecules cause water molecules to be attracted

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to each other. In solid and liquid states, bondsform between water molecules. The oxygen ofone water molecule is attracted to hydrogen ofanother water molecule. This interaction iscalled the hydrogen bond and is electrostatic innature. It holds many water molecules together. Although hydrogen bonds are not as strong aseither ionic or covalent bonds, they do play amajor role in the chemical and physicalproperties of water.

We usually consider pure water as non-electrolytic (no ions) that contains onlymolecules of water. However, if we were tomeasure very carefully, we would find that thereare a few water molecules that do ionize. Onewater molecule in 10 million ionizes to producea hydrogen ion (H+) and a hydroxide ion (OH-).Note that the hydrogen ion, which is just aproton, cannot exist by itself and is present as ahydronium ion (H3O+). The collision of twowater molecules transfers a proton to form ahydronium ion (H3O+) and a hydroxide ion (OH-):

H20 + H20 H3O+ + OH-or to simplify

H20 H+ + OH-.In pure water at 250C, the concentration of H+ is1 x 10-7, which is equal to the concentration ofthe hydroxide ion, (OH-). When the H+ and theOH- concentrations are the same (equal) and thesolution shows no acidic or basic properties, wesay that the water is neutral (pH = 7).

The product of the H+ and OH- concentrationsgives a value called the ion product for water,which is 1 x 10-14. The ion product is aconstant, i.e., always 1 x 10-14 for pure water aswell as for any other kind of aqueous solution,acidic or basic. In acids, the hydrogen ionconcentration will be greater than the hydroxideion concentration. When a base is added towater, the hydroxide ion becomes greater thanthe hydrogen ion concentration. The acidity or

basicity of a solution is indicated by its pH. Thevalue of pH is defined as pH = -log [H+]. Hence, the pH scale is a way of describing theH3O+ concentration, or [H+], by using theexponential of the concentration. This scaleranges form 0 to 14, where as a solution with apH of zero is strongly acidic and a pH of 14 is avery strong basic solution.

IV. THERMAL ENERGY

Energy is defined as the ability to do work. This energy can take many forms. The energyavailable from the bonds of a chemicalcompound is chemical energy. The burning ofwood converts chemical energy into thermalenergy. The energy of electromagneticradiation may take the form of light, whileelectrical energy in your home is yet anotherform of energy that can be converted into lightor to thermal energy. Thermal energy, or heat,is an energy form with which you are probablymost familiar and is associated with the motionof particles in a substance. This thermal energyis associated with the kinetic energy of the atomwithin the solid, liquid, or gas.

The English botanist Robert Brown observedthe motion of pollen grains and othermicroscopic objects (such as colloidal particles)suspended in a liquid. This 'Brownian motion'constitutes a visual confirmation of the randomkinetic motion of molecules, which is the directresult of thermal vibration. Two points toconsider here are that all atoms do not have thesame energy as they are constantly exchangingenergy with one another. This distribution ofenergy is shown in Figure 4. The otherconsideration is that atoms / molecules in thebulk of a liquid or solid have fewer degrees offreedom (of movement) to break all their bonds,as do the atoms on the surface. There are manyexamples of atoms breaking their bonds andleaving the surface of the liquid, even thoughthe average temperature is below the boilingpoint, e.g., steam rising from a cup of coffee.

5However, the most germane example is thebeloved cooling tower. In a cooling towerwater enters at a temperature below the boilingpoint. The construction of the cooling tower issuch that the surface area of the incoming wateris increased tremendously affording the atomsthat have obtained sufficient thermal energy theopportunity to break their liquid bonds and form

vapor. In doing so, these vapor atoms take withthem the energy associated with their bonds,(latent heat) thereby decreasing the temperatureof the remaining water.

Figure 4 Boltzman Distribution of Energies

V. NUCLEATION AND GROWTH

Nucleation and growth are complex subjectsand require understanding of Brownian motionand diffusion, surface energy and surfacecharge, as well as, solubility characteristics, andthe rudiments of physical and colloidalchemistry. However, these subjects are easier tograsp by focusing on only the concepts requiredto understand them in relation to our primarysubject, water and scale formation.

Since, this paper, is primarily concerned withthe solid (crystalline or scale) to liquid (watersolution) interface, we will focus on thatinterface. Note that in this discussion the atomsand molecules in solution (minerals) areconsidered to be ionic.

It is assumed, for this discussion, that thecrystal, (in our case scale or colloidal particles)is undistorted right up to its surface, and that allthe atomic bonds have the same energy

distribution as the bonds within the crystal. Theatoms at the surface, however, will naturallyhave fewer, nearest neighbors, therefore, fewercrystalline bonds. The energies of these surfaceatoms are higher than that of atoms in theinterior of the crystal, in proportion to thenumber of missing bonds. One can easilyvisualize that on a smooth crystalline surface itwould require more energy to remove an atomfrom that surface than for removing an atomthat rests on top of this surface (one notsurrounded by other atoms). A detaileddiscussion of this case would not be appropriatefor this paper. However, the basis of theargument is as follows: an ion (a single atom ormolecule) from solution arriving at the solidcrystal surface (scale) may 'stick' in the sensethat it loses part of its latent heat of solution byforming one or more atomic bonds. It is thenable to move about on the surface, through theaid of thermal energy, until one of three eventsoccurs: 1) It acquires sufficient thermal energyto go back into solution, 2) It finds a site, on theedge of an existing crystalline step where thenumber of neighbors is sufficient to 'trap' theatom / ion by lowering its energy, (by formingadditional bonds), Or, 3) it encountesrsufficient other adsorbed mobile atoms / ions tostabilize each other by the formation of an'island' of a new layer. Theory shows that thelast can occur only if the concentration of ions/atoms at the surface is high. This requires highsupersaturation, or driving force, otherwise therate of arrival of ions / atoms would be too low. Event #2 above is the method most likely andeasily visualized since crystalline defects, suchas, dislocations, and grain boundaries can lowerthe energy required to 'trap' incoming ions oratoms.

It can be shown that the crystal growth processis primarily the result of single atoms / ionsarriving at and departing from the surface of thesolid. The probability that a small crystal(floating) would be 'in register' with the surfaceof a growing crystal (e.g., at a pipe wall) isextremely small. In addition, the driving force

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or attraction of a small colloid particle to a likecrystalline substrate would not be favorable (tobe discussed in further detail later). The growthof a crystal in this single ion or atomisticapproach can take place, only when the rate ofarrival is much higher that it would be forequilibrium, such that there is a high probabilityof a number of neighboring sites being filledsimultaneously and thereby stabilizing eachother. This departure from equilibrium is thedegree of supersaturation, i.e., driving force thatis required for precipitation or scale build-up. Note that equilibrium conditions exist if thediffusion or flux of the arriving and leaving ionsfrom a crystal surface is equal.

It is logical that the incoming ions that obtainthe largest number of nearest neighbor bondsare more likely to remain on the solid side of theinterface, whereas, atoms more exposed, onesthat have only one or two nearest neighborbonds, are more likely to go back into solution. One must always remember that thedistribution of thermal energy can causevariations in ionic concentration in the liquidand allow for the movement of atoms/moleculesacross the crystal (scale) liquid (water)interface. This phenomenon continually allowscrystal like 'clusters' to form in the liquid withvarious numbers of atoms and then theydissociates, going back into solution. Theaverage number of atoms in these crystal'clusters' will increase as the degree ofsaturation increases for a given solution, i.e.,larger driving force, therefore larger probabilityof ions forming crystal like clusters. Hence, ifthe variation in the degree of supersaturation islarge enough the 'critical radius' or volume ofone of these 'clusters' will become large enoughto be stable and continue to grow. Thiscondition is known as 'HomogeneousNucleation'. Therefore, for a given degree ofsupersaturation a critical size crystal must bereached before a crystal will continue to grow. If the crystal is smaller than this critical radius,they will go back into solution. However,

homogeneous nucleation does not normallyoccur in industry settings.

We find that it is not necessary for the initialcrystal to be a complete sphere; any part of itssurface that is in contact with the liquid and hasa sufficiently large radius of curvature will havea better chance of growing. Therefore a 'cluster'containing a given number of atoms can form aspherical cap on a substrate that has a muchlarger radius of curvature than a sphere of equalvolume as shown in Figure 5. From this it canbe readily seen that a nucleus of critical size canbe catalyzed by a suitable surface in contactwith the liquid (water solution). The process iscalled 'Heterogeneous Nucleation.' The'nucleation catalyst' or 'nucleant' may be eithera solid particle (dust / dirt) suspended in theliquid, or the surface of a container (pipe /chiller).

Figure 5 Embryo on Substrate

The point here is that heterogeneous nucleationcan take place on a surface to which these small(less than the critical radius) clusters wet orstick. The stability of the nuclei on a substratedepends upon the radius of curvature facing theliquid. However, at a surface, the atoms ormolecules are pulled inward, drawing thesurface atoms or molecules tighter together toform a 'skin' on the surface. This physicalproperty at the surface is called surface tension.

7 Also, since the surface atoms are notsurrounded by other atoms there are unsatisfiedbonds. These unsatisfied or incomplete bondsare sometime referred to as dangling bonds. These incomplete or dangling bonds can giverise to a surface charge, whereas metalsnormally have a positive surface charge andmaterials made up of molecules with oxygenwill generally have a negative surface charge.

The departure from equilibrium, i.e., solubilityor saturation limit, in either direction is thedriving force for dissolving a material(concentration below the saturation limit) orprecipitation (nucleation and growth if abovethe solubility limit, i.e., supersaturated). Thedegree of departure from equilibrium controls inpart the kinetic or speeds of the scaling orcrystallization process. Note that heterogeneousnucleation requires a much lower degree ofsupersaturation or driving force. There are,however, other factors that come into play:viscosity, temperature, nucleation siteavailability and characteristics, pressure, sizeand charge of the molecules in solution, surfacecharge, etc. We will consider some of thesefactors affecting nucleation enhancement andcrystal growth control as we continue, but let'sdiscuss some of the parameters affecting water-formed scale deposits.

VI. SCALE FORMATION

Water is always in the process of dissolving ordepositing solids. We will call these depositedsolids scale. Scale, the term generally used inindustry, refers to any deposit on equipmentsurfaces. The general usage of the term scaledenotes hard, adherent deposits of inorganicmineral constituents of water that formed inplace. Sludges, sediments, foulants, etc. alldescribe less adherent deposits that may beformed in place or may be transported fromsome other source and redeposit. The worddescaling is normally used to describe theremoval of a previously formed scale. Theimportant thing to remember is that many

substances will dissolve to some extent in water. Therefore, we have a constant flow of atoms orions across the solid / liquid interface.

The impact that mineral scale and other depositshave on industrial operations, range from: thereduction in pipe carrying capacity, theimpedance of heat transfer capability, theincrease in operational safety hazards, thelocalization of corrosion attack, the increase inoperating costs due to inefficiencies, in additionto increased downtime and maintenance, amongothers.

Scale is formed by precipitation of primarily,calcium carbonate that becomes insoluble athigher temperature decreasing the efficiency ofboth boilers and chillers. This scale has beenshown to be a very effective thermal insulator. The following are examples of how muchadditional energy consumption is required for agiven scale thickness:

Thickness of Scale Boiler Chiller

1/64" ~5% ~11%1/32" ~9% ~26%1/16" ~15% >50%1/8" ~30% --N/A---1/4" ~50% --N/A---

This data was taken from several sources,averaged and rounded off, to demonstrate thetrend of scale build-up. Generally, in mostindustrial cases, mineral scale deposits are aproblem. Prevention, control, and treatment ofmineral scale are the objectives of watertreatment.

As mentioned earlier, the mineral that remain inthe water may be controlled by dividing theseminerals into three groups; materials that are insolution (ionic), precipitate out as smallsuspended colloidal particles, or deposits asscale on surfaces.

Practically speaking, no chemical is pure,whether naturally occurring or artificial. Most

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industrial chemicals have a level of impurityusual measured in percentage, or parts permillion (ppm). Anything in water that is notH2O, (plus H+ & OH-) is a contaminant orimpurity, and all water is impure. Generally acontaminant is considered a pollutant when itsconcentration reaches a level that may beharmful to aquatic life or to the public health.

The amount of water man has been able to useis limited; and throughout the past few centurieswe have not been able to add significantly to theamount of available fresh water. Since theworld has experienced an increase in populationand technological growth, the available water isinsufficient for future needs and is becomingincreasingly polluted. The causes are by andlarge due to dissolved solids. As we havediscussed, water is almost designed to becomecontaminated.

The ability to dissolve, transport, and depositsolids are the primary roles that water plays inthe scaling process. Because of its dissolvingpower, water can leach significantconcentrations of mineral matter as well asother material, with which it comes in contact. In some cases the dissolving power is enhancedby the nature of the constituents. The solubilityof a given material in water is controlled byvariations of temperature, pressure, pH, redoxpotential, and the relative concentrations ofother substances in solution. These variablesare related in such a complex manner that exactsolubilities cannot always be predicted, but insome cases these estimates are helpful inunderstanding the relationship and behavior ofcertain minerals.

Generally, the solubility of most mineralsincreases as the pH of the water is loweredirrespective of how the acidity occurs. Themain natural cause for acidification is thebonding of carbon dioxide from the air withrainwater. Carbonic acid (H2CO3) then forms. Similar processes can occur with sulfur dioxide

and nitric oxides. Both oxides are dissolved inrainwater and sulfuric, and nitric acids areformed. As the acidic water passes throughlime deposits, larger amounts of lime are takeninto solution. If lime is absent, the waterremains acidic and may absorb other materialsuch as heavy metals. Most metallic elementsare soluble as cations (positive ions) in acidicground water but will precipitate as hydroxidesor basic salts with an increase of pH.

We have listed some of the chemical reactionsbetween water, carbonic acid and calcium andmagnesium, the so-called water hardeners, asshown here:

1. H20 H+ + OH- plus2. CO2 + H20 H2CO3 then3. H2CO3- HCO3- + H+ or4. HCO3- CO32- + H+ and5. CaHCO3+ Ca2+ + HCO3-and6. CaCO3 Ca2+ + CO32- or7. H2CO3- + OH- HCO3- + H20 or

reverse #3, or with heat8. Ca(HCO3)2 + heat CO2 + CaCO3

+ H209. CaSO4 Ca2+ + SO4- and, etc.,10. MgHCO3+ Mg2+ + HCO3, 11. MgCO3 Mg2+ + CO32-, 12. MgSO4 Mg2+ + SO4-

and so on. (Note that reaction 3 & 4make up the carbonic acid - bicarbonatebuffer system.)

These reactions are all reversible equilibriumreactions and are interrelated to each other. Carbonic acid (H2CO3) is formed by thedissolution of carbon dioxide (CO2) in water. Carbonic acid dissociates into hydrogen ions(H+, the actual acid ion) and hydrogen carbonateions HCO3-. Hydrogen carbonate ions, in turn,can release another H+, forming carbonate ions,CO32-. It is the concentration of H+ ions, (thepH value), that mainly determines in whichdirection the reaction actually takes place. A

9lowering of the pH value, that is, an increase ofthe H+ concentration, will shift the reactions 3and 4 towards the left of the equations. Alowering of the H+ concentration (increase ofthe pH value) will push the reactions towardsthe right, which would result in an increasedconcentration of CO32-pushing reaction 6 to theleft, i.e., precipitating CaCO3. Generally, if youincrease the concentration of one of thecomponents on the right the reaction will moveto the left.

Calcium may be present in water as Ca2+, or itmay exist as Ca(HCO3)+, or Ca(OH)+. Moreover, remember that the water moleculeitself can take part in these reactions, as we havenoted, by surrounding the ions and is usuallyassociating with metal cations in a ratio of 4:1or 6:1 to form hydrates. For example, severalhydrate forms of CaCO3 are found withhexahydrate being the most common. Hydratesare thought be associated with initialcrystallization process.

As calcium carbonate is formed from ions insolution we find three distinct crystalline forms:calcite, (the most stable) aragonite and vaterite(metastable forms) all of which have differentsolubilities. The conditions affectingprecipitation of calcite, aragonite and vateritedepends primarily upon temperature, pH,pressure and impurities present. It has beenreported that when CaCO3 precipitates, a gelcan form (a hydrate?) and its lifetime dependson temperature and pH. Generally, CaCO3 isnegatively charged, however, under varyingconditions of formation, CaCO3 may have adifferent charge. One of the major controllingfactors for calcium carbonate precipitation andthe resulting predominant crystalline form istemperature. Generally, calcite forms attemperatures below 30oC and aragonite ispredominant above 50oC. The crystal structureof the aragonite is dendritic, dense, and isreported to be more adherent than calcite. Thecrystalline structure, the conditions under whichthey form and the surface charge of small

colloidal particles will come into play duringscale deposit prevention and control.

VII. CHEMICAL TREATMENT

As one can readily see, the reactions affectingthe solubility of minerals such as calciumcarbonate in water is complicated and moredifficult to predict than the solubility datasuggests. There are numerous equilibriumreactions occurring in the water that affects theinterpretation of simple chemical data. Onemust rely on empirical data based on plantexperiences to estimate the scalingcharacteristics of a water system.

Minerals can be kept in solution using acids;lower the pH, or they must be removed orcontrolled as a precipitate (usually in a higherpH environment). In a low pH environment, theemphasis shifts from controlling scale tocorrosion and biological control considerations. If we move toward an alkaline system (higherpH) we must focus on: a) removal of ions orsuspended solids before water is used; or b)leaving the dissolved and suspended solids inthe water and treating the water chemically orphysically in order to control scale buildup. The removal of both suspended and/or dissolvedsolids from waters can be accomplished bywater softening, ion exchange, filtration,sedimentation, coagulation, flocculation, reverseosmosis, etc. We will discuss the increasedsolubility and removal techniques to help inunderstanding the overall 'water / scale' system. However, in this paper, our main emphasis willbe placed on techniques that inhibit suspendedand dissolved solids from forming scale.

Acid (solubility)

In the 'good old days', acid was added to thecooling system in sufficient quantity to depressthe re-circulating water's pH to the point wherescale would not readily form. In turn thecorrosion was controlled, in the early days(1920 - 1945), by adding inorganic

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polyphosphates. Chromates were used inconjunction with phosphate-based programs atpH values below 6.5 - 7.0. The chromateinhibited microbiological growth due to thetoxicity of the chromates. This toxicity wouldlater be the cause of legislation against thecontinued discharge of chromate to publicwaterways and wastewater treatment plants. Over the years a wide variety of anti-scalingcontrol compounds have evolved. Somesystems use acid, but control the pH such that abalanced system is obtained, inhibiting scalingand minimizing corrosion and bio fouling byadditional chemical agents.

Acid or special chemicals (polyphosphate, etc.)can be added to increase the water solubility ofscale forming constituents. Sulfuric acid ismost often used since it is the least expensive,but hydrochloric, citric or other acids are alsosuitable. Acid systems can reduce thebicarbonate, forming calcium and magnesiumsulfate or phosphate that is more soluble thanthe carbonates. Acid salts are more applicableto smaller cooling systems for improved pHcontrol but in all acid systems fluctuations infeed rates can produce widely varying pH levelsand corrosion inhibitors are needed.

Polymeric organic phosphorus compounds, e.g.,phosphonates, polyacrylates, polynaleics, etc.,are commonly used to prevent calcium-basedscales. Polyacrylate in the cooling water cankeep calcium carbonate and calcium phosphatescale from forming, by keeping it in solution.

Alkalinity (solubility)

As discussed, scale deposits result from the ionsin the water consisting of positive chargedmetallic ions such as calcium, magnesium andiron in combination with negative charged ionssuch as sulfate, carbonate, silica and oxygen. Atechnology being offered by Terlyn IndustriesInc. consists of adding chemicals with anextremely strong negative nucleus to attract

cations from the solution. The chemicaladditive attracts positive metallic ions with asignificantly strong bond such that the negativeions remain as free radicals (ions). Thischemical (thought to be a polymer) can attractseveral thousand calcium or positive metal ionsper molecule.

With this advanced chemical technology,corrosion is controlled as a result of a reducedbleed (zero blowdown claimed) allowing the pHto rise above 8.3 so a natural passivating filmwill develop. In addition, biological foulingneeds metallic ions to grow. With the newchemical a complex metallic ion is formed withstrong bonds removing them from the foodchain, hence growth is hindered. Their fieldexperience supports these claims.

Briefly, let us again turn our attention fromminerals in solution (ionic) to suspended solidsand colloidal particles. Those solids that arelarge and heavy will settle out. Theconcentration of the intermediate suspendedsolids can be determined by filtration, andweighting the collected solids if the particles areof sufficient size to allow filtration. Theremaining solids are very fine and result inturbidity. Turbidity in water is measured by theeffect of the fine suspended particles on a lightbeam. The very fine suspended minerals orcolloidal particles causing turbidity usuallycarry a negative charge, as discussed earlier. These surface charges result in a repulsion forcebetween the particles preventing them fromcoagulating into larger particles and are kept insuspension by thermal energy (Brownianmotion). We will discuss this phenomenon inmore detail later when 'zeta potential' isexplored.

The crux of the scale problem is that there hasbeen neither a simple nor a sophisticatedchemical process that has totally eliminatedscale formation without some side effects. Increasingly stringent ecological requirements

11

have complicated the once simple decisionsregarding water management problems;particularly those concerned with deposits. Projects that once were merely return-on-investment decisions have become necessitiesby legislation, and management is frequentlyconfronted with major economic decisions as towhere and how to best handle potential depositproblems. Thus, the more one understands thesignificance and costs of deposit-causing solids,the more likely that sound economic judgmentscan be made. Therefore, a discussion of thecurrent practices employed to minimize orprevent scale deposition must include therelevant interdisciplinary theories on themechanism of scale inhibition, for only througha coalition of disciplines can the best solutionsfor preventing scale formation be selected.

The use of trace amounts of certain types ofchemical additives has long been known to havea profound effect on the solubility as well as thegrowth rate of crystals formed in aqueousmedia. The exact mechanisms of all theseadditives are not completely understood. Thereis, however, general agreement that adsorptionof the additives must take place. Scale controlagents generally work by interfering with thegrowing face(s) of a crystal. Therefore, theinterest will be on the effect these additiveshave on the nucleation, precipitation, and thegrowth of adherent scale.

Crystal Modifiers (suspension and removal)

Chemical additives can be used to distort thecrystal structure, changing scale to a non-adherent sludge. It is also effective at highertemperatures. Two different types of chemicalsare effective as crystal modifiers; they are thepolymaleic acids and sulfonated polystyrenes. These synthetically produced polymers areclassified as water-soluble. The resultingsludge can be allowed to settle out, removed byblowdown or by side-stream filtration. Treatedcooling water will appear turbid, indicating thatthe crystal modifiers are working.

Lime (removal)

One of the oldest methods in the softening ofwater is with lime. The following reactions areexpected:

CaO (lime)+H20 Ca(OH)2Ca(HCO3)2+Ca(OH)2 2CaCO3 +2H20Mg(HCO3)2 + 2Ca(OH)2 Mg(OH)2 + 2CaCO3 + _2H2ORemoving most of both calcium and magnesiumfrom solution.

Coagulation and Flocculation (removal)

For coagulation to take place the energy barrierof growth should be lowered or removed. Compressing the double layer or reducing thesurface charge can do this. See informationunder Zeta Potential for details on thesecharacteristics. Double layer compressioninvolves adding salts to the system. As theionic concentration increases, the double layerand the repulsion energy curves are compressedsufficiently so that the van der Waals forces(attractive) predominate and coagulation takesplace. Salting out compresses the colloid'ssphere of influence and does not necessarilyreduce its charge.

Charge neutralization results when a positivelycharged coagulant, such as alum or a cationicpolymer, is adsorbed on the surface of thecolloidal particle. These coagulant additionswill lower the surface charge and the repulsiveenergy curve. More coagulants can be added tocompletely eliminate the energy barrier. Coagulation destabilizes these colloids byneutralizing the forces that keep them apart.Generally, collision between particles isaccomplished by applying mixing energy, i.e.,supplying the opportunity and the kinetic energyfor collision to overcome the energy barrier.

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Ion Exchange (removal)

Another solution to the problem is to get rid ofthe calcium and magnesium in solution. Oneprocess is through the use of ion exchange. Ionexchange is the process of removing unwantedions from a solution in an equivalent exchangefor preferred ions supplied by a solid having aspecial structure to do this.

The solids consist of small polystyrene beads,also known as resin or zeolite. These beadscarry a negative charge. In normal operation,hard water moves into the tank that contains theresin beads and the calcium and magnesiumions, both possessing positive charges, move tothe beads, replacing sodium ions. The sodiumions now replace the calcium and magnesiumions to 'soften' the water. Once the resin beadsare saturated with calcium and magnesium, theunit enters a regenerating cycle. Sodium ionsalso have positive charges, albeit not as strongas the charge on the calcium and magnesium. When a very strong brine solution (NaCl) isflushed through the tank that has resin beadsalready saturated with calcium and magnesium,the sheer volume of the sodium ions is enoughto drive the calcium and magnesium ions off thebeads, which in turn goes down the drain. Theion exchange is now ready to remove morecalcium and magnesium from solution. Becauseof the sheer volume of sodium ions required forregeneration, a portion of them are flushed withthe calcium and magnesium ions. Thisincreases the salinity of the back wash and is theprimary environmental concern with the use of'softeners.'

Reverse Osmosis or Membrane Separation(removal)

Reverse osmosis, called hyperfiltration,indicating its relationship to a high-pressurefiltration process. Where as ultrafiltration,

which uses lower applied pressures anddifferent membranes removes only solutes ofintermediate molecular weight. Reverseosmosis can remove low molecular weight ionicspecies. RO uses a membrane that issemipermeable, allowing the fluid that is beingpurified to pass through it, while rejecting thecontaminants. Reverse osmosis is capable ofrejecting bacteria, salts, sugars, proteins,particles, dyes, and other constituents. It isinteresting to note that the separation of ionswith reverse osmosis is aided by chargedparticles. This means that dissolved ions thatcarry a charge, such as salts, are more likely tobe rejected by the membrane than those that arenot charged, such as some organic'. The largerthe charge and the larger the particle, the morelikely it will be rejected

Precipitate / colloidal particles (suspension)

More than forty years ago it was discovered thatsome types of phosphates would preventprecipitation of certain scale-forming materials. In low concentrations, the basic theoryregarding the mechanism of scale inhibition byphosphate addition is that the phosphate servedto hold large concentrations of calciumcarbonate in suspension. The phosphates do notstop the initial formation of scale (crystalnuclei), but keep them in the submicroscopicrange (colloidal) by inhibiting their growth.

To understand, from the atomistic side of things,we need to look at how colloids interact witheach other. Turbidity particles range in sizefrom about 0.01 to 100 microns. The larger sizeparticles tend to settle out or can be filtered outeasily. The smaller sizes, (colloidal particles inthe .01 to 5 microns), have settling times thatare very slow and are not readily filtered. A0.01 micron size particle will contain almost 7million CaCO3 molecules, a 1 micron particlewill contain just under 10 billion.

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Colloidal particles in water, as discussed earlier,carry an electrical charge that is normallynegative. We know that like charges repel eachother and it follows that this would preventeffective agglomeration and flocculation. Therefore, charged colloidal particles tend notto grow in size and remain in suspension ordispersed throughout the liquid.

Zeta Potential (suspension)

To visualize the environment surrounding acharged colloidal particle and demonstrate howthe repulsive forces, as well as, the ionicconcentration varies with distance, a doublelayer model is normally used. At the surface ofthe negative colloidal particle a layer of positiveions will form. This layer of positive ions isknown as the Stern layer. More positive ionswill be attracted by the negative colloid but theyare partially repelled by the positive Stern layer. Conversely to the distribution of positive ionsis the distribution of negative ions, i.e., very fewat the colloid surface and increasing withdistance until equilibrium is reached. SeeFigure 6, (Courtesy of, Zeta-Meter, Inc.).

The region in which the positive ions aredecreasing and the negative ions are increasing,hereby reaching the bulk equilibriumconcentration, is called the diffuse layer. TheStern layer and the charged diffuse layer arereferred to as the double layer. The thickness ofthe double layer depends upon the concentrationof the ions in solution. A higher level of ionsmeans more positive ions are available toneutralize the negative charge of the colloidalparticle, and in turn a thinner double layerleading to an increased probability of intimatecontact or collision between collide particlesand hence coagulation or colloidal particlegrowth. On the other hand, a decrease in theionic concentration reduces the number ofpositive ions resulting in a thicker double layerleading to increased dispersion

Figure 6. The Double Layer

Also, the valence of the positive ion additionhas an impact on the double layer thickness. The concentration of aluminum (Al3+) ions willbe more effective in decreasing the colloidalcharge and its double layer thickness thanwould sodium (Na+). The electrical potential isat its maximum at the surface of the colloid anddrops toward zero as the distance increasesacross the Stern layer and the diffuse layer, i.e.,with increasing distance from the surface of theparticle. The potential curve indicates thestrength of the repulsive force and the distanceat which these forces come into play.

The potential at the junction of the Stern layerand the diffuse layer is known as the Zetapotential. Zeta potential is a tool used forcoagulation control because changes in Zetapotential indicate changes in the repulsive forcebetween colloids. If one looks at the balance offorces between two colloid particles, one findsan electrostatic repulsion and a van der Waalsattraction. The electrostatic repulsion becomessignificant when two particle approach eachother and their electrical double layers begin tooverlap. Energy is required to overcome thisrepulsion and force the particles together. Thisis the energy barrier that must be overcome. The height of the energy barrier indicates howresistant the system is to effective coagulation. For agglomeration to take place two particles

Copyright 2002, Fluid Treatment Solutions, Inc., all rights reserved. 14

must collide with sufficient kinetic energy tojump over this barrier.

VIII. PHYSIOCHEMICAL TREATMENT

Catalytic Processing

In 1836, J. Berzelius defined a catalyst as acompound, which increases the rate of achemical reaction, but which is not consumedby the reaction. The catalyst affects only therate of the reaction; it changes neither thethermodynamics of the reaction nor theequilibrium composition.

The study of catalysis is fascinating in that it islargely an empirical science. The application ofcatalysis has been a necessity for the chemicalindustry for at least 150 years. However, untilabout 25 years ago, the experimental techniquesfor investigating the process of catalysis at theatomic level were not readily available. For thisreason vast amounts of empirical knowledgeexist and await systematic investigation.

A catalyst provides an alternate path with alower activation energy by which the reactantscan proceed to form the products. The loweractivation energy means a much higherproportion of the total reactants (ions) will havesufficient energy to react effectively along thecatalyzed path than could have reacted along theuncatalyzed path. Hence, the kinetics, or rate ofthe reaction can be greatly increased by thepresence of the catalyst. However, there is nochange in the free energy of the reaction sincethe catalyst does not affect the energies of theproducts and reactants.

Many processes in nature are influenced byenzyme catalysis. Therefore the use of thecatalysis principle in ways that resemble thoseused in bio-minerialization should not be toosurprising. Honeywell's kaltecpro is such atechnology and is based on a natural process inwhich crystallization takes place as a result of a

surface process, utilizing this catalytic principle,which generates a large number of seed crystals(colloid particles) or nuclei.

To examine this process let's back track a littleand reiterate what we have already discussed,but this time with a slight twist. Hydration is animportant property of dissolved calciumcarbonate, which must be understood toappreciate how scale forms, based on thisnatural principle works. Calcium carbonatedissolved in water mostly takes the 'hydrated'form. This means the calcium (or magnesium)and the carbonate ions are entirely surroundedby loosely attached water molecules. Even ifthe solution is saturated, the driving force maynot be sufficient to allow the combination of thecations and anions in quantities necessary toform critical radius nuclei (stable viahomogeneous nucleation). However, they canprecipitate out on solid metal pipe walls (or dirtparticles etc.) if the supersaturation, i.e., drivingforce, is sufficient. In doing so they lose theirhydrate envelopes, i.e., the barrier separatingthem from the opposite ions and scale depositsstart forming.

Using a container filled with the activatedkaltecpro material, as a catalyst to overcomethe hydrate envelopes, which usually preventthe forming of crystals in water, bio-mineralization takes place. This induces thegrowth of crystals on the kaltecpro materialsurface. Friction forces then shear off the newlyformed crystals from the kaltecpro beads. These crystals are of sufficient size to be stableand serve as 'seed crystals' for furtherprecipitation, e.g., heterogeneous nucleation, ofthe dissolved calcium carbonate. Once thisprocess has started, it continues in the hot watercontainer system. The total surface area of thecolloidal size seed crystals is many timesgreater than that of the system containmentwalls and serves as site for heterogeneousnucleation and scale growth. Hence thedeposition of scale preferentially takes place on

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the colloid size seed crystals rather than formingscale on the system components. Due to thenatural principle of catalysis, the process ofcrystallization needs no energy input and themaintenance of the kaltecpro unit requires thecatalytic material be changed approximatelyevery three years. This technology has passedstringent European water quality standards,which include the German DVGW - W512. The products derived from this technology areprimarily focused toward the residential marketfor potable hot water systems.

Magnetic

Magnetic technology used in the treatment ofwater has been cited in the literature andinvestigated since the turn of the 19th century,when lodestones and naturally occurringmagnetic mineral formations were used todecrease the formation of scale in cooking andlaundry applications. History shows thatEgyptians used permanent magnets two to threethousand years ago in an attempt to reduce scaledeposits in pipes carrying hard water. The useof magnets may be one of the oldest methodsfor the prevention of scaling in heat transfercomponents and the transportation of hardwater. It is believed that permanent magnetswork by precipitation of the ions, similar to thatfound in the chemical arenas.

Hard water contains ions, both positive andnegatively charged, cations and anions. Thegeneral operating principle for the magnetictechnology is a result of a moving ionized fluid(an electric current) through a magnetic field. When ions pass through the magnetic field, aforce is exerted on each ion (Lorentz Force). This force is perpendicular to both the magneticfield and to the direction of motion and isproportional to the velocity. Since the force isat right angles to the velocity, it will not affectthe magnitude of the velocity nor its kineticenergy but will merely alter its direction. Theforces on ions of opposite charges are inopposite directions. The opposing redirection

of the ions tends to increase the frequency withwhich ions of opposite charge collide andcombine to form a mineral precipitate, (acolloidal particle) similar to affect of thermalagitation discussed earlier. Since this reactiontakes place in a low-temperature region of aheat exchange re-circulating system, theprecipitation formed is non-adherent(heterogeneous nucleation) and similar to theeffect of chemical additions as discussed above. Since the removal of calcium carbonatechanges the ionic equilibrium balance in thesolution, the water is now able to reabsorb someexisting scale.

Commercialization of the technology beganafter World War II, with the largest advancescoming in the last 20 years with thedevelopment of high-power, rare-earth elementmagnets advancing the technology to the pointwhere it is more reliable. There are records ofinstallation of the technology in the UnitedStates from about 1950. Manufacturers claim tohave installations operating satisfactorily for aslong as 30 years. It has been estimated thatapproximately 1,000,000 units have been sold. It appears that most of the presently availableunits, based on manufactures' specifications, aredesigned to be used in smaller flowapplications.

Electronic / Induced Electric Field

Electronic descaling (ED) technology,developed by Dr. Cho of Drexel University andfirst offered by York Industries, uses a timevarying electronic current in a solenoid wrappedaround a pipe to create an inducedelectromagnetic field inside the pipe. We knowfrom physics that moving magnets or changingmagnetic fields can produce electrical current asin the generation of electricity. Also movingelectric charges can produce magnetic fields, asin a solenoid. To help quantify this one can referto Faraday's law of induction. Faraday's 'law ofinduction' states that the electromotive forceinduced in a circuit is directly proportional to

Copyright 2002, Fluid Treatment Solutions, Inc., all rights reserved. 16

the rate of change of the magnetic flux throughit. Note that this is merely the principle onwhich a transformer operates, i.e., the primarya-c current, sets up the (changing) magnetic flux(the magnetizing current) inducing an a-ccurrent in the secondary winding.

An applied current flowing in a clockwisedirection in a solenoid wrapped around a pipecreates a magnetic field, which will induce anelectric field inside the pipe. The inducedelectric field is in the counterclockwisedirection and is proportional to the radius. Thedirection of the electric field E changes whenthe direction of current changes. When thecurrent flows in the counterclockwise direction,the induced electric field points to the clockwisedirection.

The distribution of E, the induced electric field,decreases to zero at the center of a solenoid. However, the velocity of the fluid flow is at amaximum at the pipe center and decreases tozero at the pipe wall. To improve the efficiencyof the induced electric field an offset coil isused resulting in an induced electric field E thatis larger than that of a solenoid centered on thepipe diameter. In addition, to the increasesstrength of the induced E, a square-wave currentinput, is used to increase the rate of change ofthe magnetic flux, and therefore the inducedelectric field.

When charged ions such as calcium andcarbonate ions pass through the ED coil, theyexperience an induced pulsing electrical field. The induced electric field provides necessarymolecular (ion) opposing redirection of thecharged mineral ions, increasing the number ofcollisions such that, nucleation and precipitationoccurs. The ions are converted to insolublecalcite crystals at room temperature. Theparticles are powdery and fluffy, easily removedby turbulence and routine blow down. Thelevel of saturation of the water significantly

decreases; thus, new scale deposits on the heattransfer surface are prevented.

Electrolysis / Electrostatic

A unique design concept by BWT has evolvedout of Europe and is based on electrostaticforces resulting from a low voltage appliedacross a set of electrodes (low current,

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Europe than in North America. The Europeanresidential and commercial market purchased45,000 units in a three-year period. This BWTtechnology has passed stringent European waterquality standards, which include the GermanDVGW-W512 guidelines as well asindependent laboratory testing in the UnitedStates.

Electrostatic

Electrostatic water treatment technology got itsstart in North American in 1957 when Roy C.McMahon started his company, ElectrostaticEquipment Company. The major NorthAmerican suppliers of electrostatic watertreatment technology can trace their roots toMcMahon's basic technology. ElectroStaticTechnologies, Inc. is a direct descendent of theElectrostatic Equipment Company while ZetaCorporation (1994) and York EnergyConservation (1978) where fathered later.

Electrostatic water treatment technology isbased on the formation of a strong electrostaticfield between an electrode (an anode in mostcases) and ground (second electrode) similar tothat found in a capacitor. The capacitance of asystem is equal to the charge on the electrodedivided by the applied voltage (primary field). The original (McMahon) applied voltagestarted at 3kV and has evolved upward through5kV to, as high as, 30kV. Various dielectric-insulating materials isolate the anode (positivelycharged) from the fluid (water in our case). Thedielectric material, the electrode design, and itsplacement in the re-circulating hot water systemall play a role in its effectiveness.

The hypothesis explaining the operatingprinciples of an electrostatic water treatmentsystem must follow the same physical andchemical fundamental concepts used for othertreatment systems. Industrial water, as we havediscussed, has not only the hydronium (H3O+)and hydroxide (OH-) ions, but alsoconcentrations the calcium, magnesium,

carbonate, and sulfate ions. In the presence ofan electric field an attractive or repulsive forcewill be imposed on these charged ions. Therefore, the positive ions will be attractedtoward the negative electrode and repelled bythe positive. Conversely, the negative ions willbe attracted to the positive surfaces and repelledby the negative. This electrostatic force fieldcauses movement or diffusion of the ionstoward their respective electrodes. Thisdiffusion will cause localized concentrationgradients within the moving water, changing thelocalized chemical equilibrium. In parallel withthe build up of a localized concentration, theopposing movement of ions increases theirrespective kinetic energy and the frequency ofcollision between cations and anions. Thesetwo phenomena create a condition favorable fornucleation and the formation of colloidalparticles. Furthermore, an electrostatic treatmentsystem uses a directly applied electric field asopposed to an induced electric field and can bestronger using less energy and is more focused,increasing its effectiveness.

It has been noted, both in the literature and inthe development of this technology, that anelectrostatic field can increase the surfacecharge of the colloidal particles thereforeincreasing the zeta potential. As discussedearlier the zeta potential provides a measure ofthe repulsive force between colloids. Thissecondary effect, the enhanced zeta potential,retards the growth of the suspended colloidalparticles, preventing agglomeration andsedimentation. However, if the colloidalparticles are formed in the cooler portion of there-circulating system, the decreased solubility inthe warmer section will give the necessarydriving force for possible additionalprecipitation. Due to the much larger surfacearea of the now existing colloidal particlescompared to the walls of the heat exchanger thescale growth on these surfaces will beminimized. Conversely, if the degree ofsaturation is small or negative, descaling cantake place. In a cooling tower environment this

Copyright 2002, Fluid Treatment Solutions, Inc., all rights reserved. 18

enhanced nucleation and subsequent growthcontrol allows for a slightly elevated pHnormally between 8.2 and 9.5, leading to animproved corrosion and bio-foulingenvironment.

Field experience has shown that corrosion andbiological consideration are usually minimalwhen accompanied by electrostatic treatment. This is thought to be the result of the fact thatthe free metallic ions are significantly reducedin concentration. This reduces the foodavailable for the microscopic cells that causefouling such that growth is impeded. Corrosionis minimized due to the positive pH levels andthe tendency for the formation of a pacificationlayer on metal component

Electrostatic treatment systems by their designare capable of handling a wide variation ofwater qualities and fluid flows. This allows theapplication of these products across thespectrum to include commercial and heavyindustrial installations.

IX. SUMMATION

We have viewed water treatment from theprimary factors that affect the scaling process. The interconnectivity of the various chemical,electrical, and magnetic phenomena have beendiscussed. As noted, chemical reactions arecontrolled by the electrical charges containedwithin atoms and how these electricalcharacteristics affect the behavior of water andthe minerals in solution or suspension. That theinitiation of nucleation and resulting stablecolloidal particles go through various transitionsdue to the interplay of surface tension andsurface charge. We have also pointed out thatan intimate relationships exist betweenmagnetic and electrical fields and that anelectrical field, induce or applied directly, cancreate stable changes in a water / mineralsolution through the formation of smallcolloidal particles. Finally, these interrelated

phenomena affect the scaling processes in waterrecirculating heat transfer systems.

In all cases, monitoring of the system isnecessary to ensure that both its mechanical andchemical components are operating withindesired limits. Mineral scales consisting ofcalcium sulfate, barium sulfate and high silicacontent may create special local problems andmay or may not have to be treated as a specialcase depending on characteristics of the processenvironment and the water / mineral solution.

The road to truly understanding, the overallscaling process is complex and fraught withmany twists and turns (variables). We haveopened the door to some of the secondary orsupporting phenomena. For instance, thebipolar nature of water leading to its highdielectric constant, its surface tension, itshydration effect, its electrical conductivity, theimpact of pressure and secondary ions, etc., hasbeen relegated a secondary or supporting role inthe overall chemical and physical watertreatment arena. These supporting phenomenaare of interest but will be addressed, as moreinformation becomes available.

This paper was written by David McLachlan. Dr.McLachlan holds his PhD from Iowa StateUniversity in Meturaligical Engineering. Hecurrently holds the position of V.P. TechnicalDevelopment for Fluid Treatment Solutions, Inc. Ifyou have further questions you may contact Dr.McLachlan at dml@estatusa.com.