Патент USA US3097173код для вставки
July 9, 1963 T. M. RIDDICK 3,097,163 TREATMENT OF' WATER IN MUNICIPAL AND INDUSTRIAL WATER SYSTEMS Filed Aug. 25, 1958 United States Patent O ICC l 3,097,163 TREATMENT 0F WATER IN MUNICIPAL AND INDUSTRIAL WATER SYSTEMS Thomas Moore Riddick, 369 E. 149th St., New York 55, N.Y. Filed Aug. 25, 1958, Ser. No. 757,073 8 Claims. (Cl. 210-53) l 3,097,163 Patented July 9, 1963 2 and apparatus lfor the treatment, purification, and filtra tion of natural water wherein optimum alkalinity con trol .for flocculation, chlorination, and filtration are achieved by cooperating chemical reactions of composi tions added to the water. A further object of this invention is to provide compo sitions of the character described for addition to and reaction in natural water in water purification Asystems to obtain therein optimum control of alkalinity ‘and other This invention relates to water «treatment in municipal and industrial Water systems and, more particularly, to a 10 conditions which may variously affect `a number of dif ferent -chemical reactions which it is desired to produce system for the treatment and purification of water whereby in water. enhancing efficiency of chemicals and easier and more The chemical treatment land/or purification of water Still another object of this invention is to provide meth ods of the character described whereby a number of dif ferent and conventionally inconsistent chemical reactions from reservoirs, ponds, lakes, streams, rivers and the are made to occur Kand to go toward completion to an like, conventionally includes attempts to achieve a vari ety of end results by chemical additions to the water prior to distribution thereof through a municipal or industria-l .distribution system. For example, it is conventional to 20 ¿add t-o the water a coagulant or ñocculating agent, such enhanced extent notwithstanding that the optimum con ditions for one reaction may be inimical to the comple tion of another reaction if carried on separately instead of as combined according to this invention. as Ialuminum sulfate or ferrie sulfate, or Kferrie chloride, etc., to form therein a ñocculant precipitation which will remove by adsorption or other mechanics iron and manga following description, the accompanying drawing, and the appended claims. advantageous pH control is ‘achieved with the composi tions, methods, and apparatus for practicing this invention. Other objects and advantages will be lapparent from the The drawing is a diagrammatic or schematic flow sheet nese materials, sand, silt, loam, micro-organisms, etc., 25 representation of »a municipal water purification or treat ment plant embodying and for practicing this invention. which may contaminate, ldiscolor or turbidity the natural Experience indicates that it is usually necessary to ap ply some type of alkaline reagent to practically all natu ral water, either to raise the alkalinity of the lraw water tioccul‘ating reaction but .also for the inhibition of cor rosion on the distribution pipe system, fand, as is well 30 to a poi-nt suflicient for eflicient coagulation purification or to raise the .alkalinity of finished or treated water for known, chlorine may be ladded in a variety of forms for the purpose of inhibiting corrosion in the distribution sys purification or sterilization purposes. tem. For example, rain water as it falls may contain In order to correlate or achieve these several varied carbon dioxide in, perhaps, concentrati-ons of the order goals by the addition of vario-us. chemicals to produce of 0.8 ppm., whereas as the rain water worksy through various Ireactions in the water, diiiiculty may be experi layers of soil, it may pick up from 2O to 50, and from enced from the fact that optimum pH, stoichiometric, and swampy drainage areas sometimes 100 ppm. concentra other conditions in the system, when at Ian optimum for tions of carbon dioxide, which, of course, form carbonio one desired reaction, may be `at a disadvantageous or de or raw water. Similarly, 4but for lother purposes, alkaline materials may be added to the water not only to aid the acid with the water, thus greatly increasing the tendency For example, if aluminum sulfate is` utilized asthe 40 of the water to dissolve mineral-s from the soil. This same coaguliant or ilocculating agent, its optimum effect in this type of reaction also produ-ces a certain, though widely varying, concentration of calcium bicarbonate by reacting regard is achieved by »a reaction with calcium bicarbonate ‘with the alkaline earths through which subsurface water present in the water, and this reaction goes most desir iiows which is essential for the Idesired coagulation reac ;ably to completion if aluminum «hydroxide 1as o-ne result tion with coagulants such as aluminum sulfate. ant thereof is precipitated from solution in the Water. That is, the desired reaction with aluminum sulfate The isoelectric point for the solubility of aluminum hy 45 to produce a flocculant precipitate of the desired materials droxide, however, may be a pH which is readily exceeded from the raw water is as follows: by natural alkalinity fand/ or the addition of other alkaline terring point for other .desired independent reactions. chemicals to the water either for other reasons or to achieve a bicarbonate concentration suñîcient for the de 50 sired fiocculant formation. Similarly, separate additions of chlorine, as may be for completely independent rea sons, may create ancillary problems of alkalinity control and otherwise which are inimical to achieving the de sired coagulant results in the most efficient and most eco nomical manner. According «to this invention, however, it has been dis covered that optimum pH control is obtained for the vari Pure crystalline aluminum sulfate lhas 18 molecules of water of crystallization and a molecular weight of 666. The commercial form 0f alum, however, usually employed for water treatment contains approximately 14.2 mole cules of water of crystallization and has a molecular weight of approximately 600. Accordingly, considering alkalinity in this respect as in terms of calcium carbonate equivalents, it appears lfrom Equation l that 1 ppm. tems and that, indeed, by the synergistic -adm-ixture and 60 aluminum sulfate requires 0.5 ppm. calcium bicarbonate, and upon reacting produces 0.68 p.p.m. calcium sulfate interaction of various compositions upon being .added to (which remains in solution), 0.26 p.p.m. aluminum hy the raw or untreated water, the independent effects` of droxide (the basis of the gelatinous lloc which settles out conventionally separate reactions can be coordinated and in the sedimentation basin carrying with it the various combined to produce enhanced results and greater econ impurities it is desired to remove), and 0.44 p.p.m. carbon omy of chemical use with the elimination or control of 65 factors heretofore considered inconsistent among the , _ dioxide. In such a system, then it would appear necessary to various -desired reactions. ÁOne object of this invention is to provide a »system oi have at least half as much calcium bicarbonate as alum. the Icharacter described for interrelated chemical treat Considering, then, a conventional alum dosage of 30 ppm. and l5 ppm. bicarbonate to be required, according to ment to achieve liocculation, chlorination, tand alkalinity 70 control of natural water in water purification systems. the law of mass action, the reaction rate is proportional to the molecular concentration of each reacting substance, Another object of this invention is to provide a system ous independent reactions desired in water purification sys 3,097,163 4 so the reaction of Equation 1 would not be expectedl to Considering the carbon dioxide formed by the reaction of go to completion unless an excess of about 5 p.p.m. car Equation 5 as also reacting with excess calcite present, the l p.p.m. chlorine reacts with 1.42 calcite, providing an increase in alkalinity of about 0.71 p.p.m. for each part of bonate were present. Thus, a dosage of 30 p.p.m. alum would require at least 20 p.p.m. calcium carbonate. When the raw water alkalinity is less than about 20 chlorine added, as indicated as follows: p.p.m., some type of alkali is required to be added to augment this ydeficiency and usually is chosen from among the commercial alkalis available, so that soda ash and As will be understood, the reaction of Equation 5 may be expected to go substantially to completion, whereas the reaction of Equation 6 probably only goes part way to completion perhaps approximately 50%, thereby re sulting in practical concentration adjustments to achieve lime have been conventionally employed. Regardless of the cost or rate of application, some difficulty may be experienced using either lime (which is a hydrate) or soda ash (a carbonate), primarily because the alkalinity for the reaction according to Equation 1 is desired to be in the situation where 1 p.p.m. chlorine utilizes about l p.p.m. bicarbonate rather than carbonate Ior hydrate form. 1of calcite and raises the alkalinity about 0.3 to 0.4 p.p.m. Furthermore, bicarbonate concentrations can adequate 15 Also, some of the carbon dioxide formed by the reaction ly be maintained when there is an excess of carbon «di of Equation 5 is undoubtedly given off to the atmosphere oxide, by bicarbonate alkalinity in the range of 20 to 80 -before it has time to react with excess calcite according p.p.m., with an excess of carbon dioxide of about 2 to '10 to Equation 6. Similarly, also, some chlorine gas is p.p.m., but produces pH values in the range of about 6.5 volatilized and evolved in the course of these reactions. to 7.2. The isoelectric point or point of minimum solu 20 Regarding t-he coagulant reaction of aluminum sul bility, however, of aluminum hydroxide (which it is de fate and calcite, it may be indicated as follows: sired to precipitate) is about pH 6.0 to 7.0. Desirably, then, the pH of treated water (after the addition of alum and any primarily augmenting alkali) should be in this range. Thus, the addition of lime to obtain an adequate 25 Thus 1 p.p.m. of commercial alum requires about 0.5 bicarbonate concentration for the reaction in Equation 1 p.p.m. calcite and forms 0.26 p.p.m. aluminum hydroxide may have a tendency of raising the pH of the raw water ‘and 3 molecules of carbon dioxide. 3 molecules of car to a point so high that the desired precipitation of alumi bon dioxide then combining with excess calcite (instead num hydroxide will not occur to a suflìcient extent and/or of being evolved as a gas -and lost) produces a situation may inhibit the adsorptive properties of the precipitant 30 where 1 p.p.m. aluminum sulfate reacts with 1 p.p.m. particularly in color removal. calcite, «forming as their products of the reaction cal Quite apart Ifrom the effect of alkalinity in the reaction cium sulfate, aluminum hydroxide and calcium bicar of Equation l, the addition of chlorine may produce sep bonate. Actually, because of inevitable practical con arate and distinct difficulties. Thus, chlorination which siderations, satisfactory results have been obtained con is desirable Áfor a number of reasons in water treatment, 35 sidering that l p.p.m. alum reacts with or requires about has its own effect on alkalinity. The chemical reactions 0.50 to 0.75 p.p.m. calcite. involved in the chlorination of water may be represented The degree of completion )of the various reactions somewhat as follows: . is, of course, a function of the contact time between alum and calcite, the temperature of the solution sus 40 pension, as well as being a function of the ñneness of the calcite particles. Thus, the finer the grind of calcite, the quicker -w‘ill be the reaction, and the longer the contact From the above equations, it appears, that, for example, time, the more complete will ’be the reaction. The re l p.p.m. applied chlorine forms 0.51 p.p.m. hydrochloric actions involved, also, occur quite slowly and almost in acid which, in turn, requires 0.71 p.p.m. bicarbonate al 45 appreciably if alum and calcite are added separately to kalinity for neutralization. Thus, the application of 10 the raw water because the tremendous dilution of the p.p.m. primary chlorine as could be in the excess-chlorine chemicals markedly lowers the mass action effect. With 'type of treatment would reduce the alkalinity of raw water mixing of only a few minutes, adding the two materials by 7 p.p.m. and would add 0.63 p.p.m. carbon dioxide. separately to raw water may result in more than 50% Since it may be desired that, for corrosion inhibition, 50 of the calcite dropping out ineffectively at the entrance the alkalinity of the finished water should be at least 25 to` the sedimentation basin. p.p.m. and preferably 35 to 40 p.p.m., the chlorination reaction would Ihave an adverse effect. if, on the other hand, a solution of alum and a sus pension :of calcite are combined in normal proportions According to this invention, however, it has been dis covered that the aforementioned disadvantageous effects 55 from commercial chemical feeding machinery (discharg ing of the order :of 7 to l0 gallons per minute) :the mass can be substantially controlled and the over all water »treat action conditions force the reactions to a :rather advanced ment system enhanced by utilizing calcite-_a finely ground state. Mixing of the solutions prior to addition to the crystalline carbonate, principally calcium carbonate-«as water 'for l0 or 15 minutes, «for example, produces a a preferred material for controlling` alkalinity, and, fur copious aluminum hydroxide precipitate or ñoc with the thermore, that calcite has a synergistic effect in collecting 60 size of each floc particle almost at its maximum obtain and enhancing the efficiency of both chlorination and able. From the standpoint of water purification, how flocculation steps. ever, this may not be desirable. That is, the function ìFor example, a substantial drop in raw water alkalinity of the aluminum hydroxide precipitate is that of adsorb resulting from heavy dosages of chlorine is satisfactorily prevented or controlled by first reacting a concentrated 65 ing color, iron, manganese and colloidal turbidity, and this adsorption begins most effectively when the floc suspension of calcite with a concentrated chlorine water particle is microscopic or sub-microscopic in size. The solution prior vto the introduction of either to the raw water. The reaction is indicated as follows: As appears from the above, l p.p.m. chlorine would re quire 0.71 p.p.m. calcite, with the formation of 0.31 p.p.m. carbon dioxide. This amount, however, would addition to raw lwater of maximum size ‘floc particles actually reduces the efficiency of removal of the desired impurities, and may result in the heavy ñoc being broken 70 up, peptized or dispersed into particles of smaller size which will not again readily reform into adsorptive pre deplete the natural calcium bicarbonate alkalinity of water. 75. cipitate .particles )of a size which will `settle as desired and not penetrate or clog a filter bed through which the treated water is subsequently passed. Preferably, then, a concentrated solution of alum is 3,097,163 6 5 clarification. From the filters 39, the treated Water drops mixed withla concentrated suspension of calcite (each directly from an automatic feeding machine) and with «to a conventional filtered water flume 40 and then to a agitation for a very short period of the :order of about conventional clea-r water basin 41, which is preferably 30 seconds to two minutes so that the reaction is accom provided with agitaiting and «aerlating Äapparatus (not plished vvith the formation of only very fine lloc par shown) where a final adjustment of the chemical compo sition of the water is made as by adding as conventional, ' lime, sodium silicate, additional chlorine, :and/or other ticles. This mixture, then, is immediately added to the raw water and is there slowly agitated for a .period of corrosion retarding, etc., materials. This final chemical 20 to 30 minutes. In this way minute aluminum hy addition fis indicated «generally by a feeder 45 leading droxide or alum floc particles build up during agitation to large size but under circumstances where they have 10 through feed line r‘t6 into the lclear water basin 41, from enhanced efliciency in adsorption of the desired impuri ties, and absorption or enmeshing of suspended matter including silt, micro-organisms, precipitated iron and the which »the finally treated Water passes to a finished water basin 48 and, thence, through 'line 49 into the distribution system. A further sensing venturi is indicated in line 49 at 50 to measure and detect the volume of finished water like. fiow which sensing is received by an »additional controller As an additional advantage, it should be noted that 5i and transmitted to regulate automatically the propor the particles of calcite are hard and crystalline in na tioning and feed rate of final »chemical addition from ture. When treated according to this invention, about feeder 45 as required by the volume of finished water be -50 percent of the particles are not ‘completely dissolved ing withdrawn «from basin 48. either in the mixing or in addition to the raw water but As will #be understood, -calcite is primarily calcium car remain as discrete calcite particles of microscopic or 20 bonate, the principal constituent of limestone. Satisfac semi-microscopic size where they serve, as such, as nuclei tory results according to this invention have been achieved for ñoc formation and as materials which will “Weight” using as the icalcite component that obtained from highly the floc to increase its specific gravity and increase the calcareous limestone with relatively lfow silica and other desired tendency and speed of lsettling out of the floc and its adsorbed and absorbed impurities. «It is also be 25 insolu-ble components and, particularly, la ground calcite sold by Limestone Products Company, of Newton, New lieved that undissolved calcite which does not enter into Jersey, under the name “Aqua Treat” which is under the foregoing reactions has a deterring effect as a neu stood -to be air separated and yground so that about 95% tralizing agent to combine with dissolved 0r evolved car passes a 325 mesh sieve. bon dioxide to decrease the extent to »which such dis Also, in connection with the foregoing description, it solved gases might tend to buoy up or float the lioc and 30 should be noted that, Whereas the fioc or precipitate re retard sedimentation. fer-red to may be Iconsidered generally aluminum hydrox Referring to the drawing, which sho-Ws a fiow sheet ide, the lioc actually produced according to .this invention type of representation yfor a Water treatment plant em appears to 1be a much more complex substance. For bodying or for practicing this invention, there is illus trated the raw water entering the system at lill and the 35 example, it has been found that the sulfate and other ions various treating chemicals entering through the alum »feeder il, calcite feeder Al2 and chlorinator 13. 'Iïhese in ,the water being treated decidedly infiuence lthe pH at which a desirably full-bodied highly :adsorptive and tough Hoc will be produced. For example, whereas the iso pieces of apparatus are of conventional and well-known electric point for pure ‘or commercial grade aluminum design. These three materials are then combined and/or mixed in a reaction chamber or crock 15, which 40 hydroxide has been determined within 1a very lnar-now pH range about 6.() to 7.0, it has lbeen found that the pH may .be of any suitable corrosion-resistant material and of Iwater ltreated according to this invention, in order to has satisfactorily been formed as a rubber lined 55 obtain optimum effectiveness of coagulant impurity re gallon steel drum, Where the chlorine-calcite and alum `calcite rea-ctions occur. ' moval, should desirably «be above 6.0 and, indeed, is pref size Without excessive agglomerating. A sensing -ventur-i in Ítwo ways: by lowering the natural `alkalinity and by tional fiow controller and proportioning device is pro mit proportioning control to the automatic feeders 1-1 and tion, it may be that the carbon dioxide formed is partly eliminated during aeration resulting in a higher pH than if the alum were `applied following aeration, in which in provided so that the feeding and proportioning of` alum, filters. In any case, it is appadent that coagulan-t dosages calcite and chlorine are -automatically controlled in ac cordance -with the quantity of lioW of raw water into the pH of the water rather than 'being proportioned to the y An agitator 16 is preferably provided .toV enhance the 45 erably controlled to la fairly constant value within the range of pH 6.8 to 7.2. Also, the application of alumi mixing and reaction and to insure that any flocculating num sulfate tto natural water may depress the pH thereof precipitate which forms will remain of a small'particle the formation of carbron dioxide which itself depresses arrangement 20 is provided in the water line 21 to sense or measure the flow of Water therethrough. A conven 50 pH. `If the alum is applied to the raw water before aera vided at 25 to detect the flow from venturi 20 and trans stance a substantial 'amount of carbon dioxide (perhaps 12 and the chlorinator 13 as is indicated by the dotted lines in FIG. l. Such apparatus »and circuits are conventional 55 5 -to 15 ppm.) will remain in solution during passage of the `treated water through the sedimentation basin and and well-known and not further described here and are system througth venturi 20. A feed pump 26 pumps the reaction mixture from chamber 15 through feed line 27 into the raw water in line 2.1 where it is mixed with the water as it passes to conventional spray aerators 30. 'I‘hen the treated raw Water is collected in a conventional trough indicated at 31 and is led into conventional iiocculators 35. Floc culators 35 are essentially, a series of chambers in which the treated water is detain-ed for some 20 or 30 minutes may ywell be governed to a large extent by the effect on the 60 amount tof color or ‘other impurities -which it is desired to remove unless the pH control, as explained heretofore, is achieved according 'to this invention With calcite ma terials. . It should also be noted that the forma-tion of desirably 65 adsorptive floc, after the original precipitation of alumi num hydroxide, is inliuenced, .among other sources, by the type `of nucleus upon which the floc »particles agglomerate and, particularly, by the electrical charge of the cations and `anions in -the original nucleus-e.-g., whether the nu while being agitated slowly by paddle agitators 36 to complete the agglomeration of the floc particles and the 70 clei yare silt, .artificial ‘turbidity such as bentonite, other iioc particles, undissolved calcite crystals, etc. Also, the adsorption thereby of the impurities it is ydesired to re move. . From the flocculators 35, the water passes to one or more sedimentation basins indicated at 33 where the floc role tof the sulfate ion in floc agglomeration, may not now be completely understood, but it has -been discovered that sul-fates :are a part «of the complex substance which has precipitate settles, Iand thence to filters 39 for the final 75 been'collectively referred toas lioc. 3,097,163 It should >also 'be noted that, particularly with water treatment plants designed without the special provision of separate flocculating basins such as 36, enhanced results S As will be understood, of course, it may be desired to utilize other flocculating agents in place of or in ìaddition to the alum described in the foregoing illustrative disclo are lachieved according to this invention lby utilizing the sure, with, :of course, `a calcite reactant for preliminary standard catch basin 3‘1 which receives the effluent from formation or reaction las described. spray aerates as la `detention area where the -water êbein-g other ñocculating agents ‘may -be noted, for example, ferrie chloride. This material, already known as a flocculating treated may be held for a suflicient length of time for ñoc As illustrative of coagulation, the necessary agitation being inherently fin agent `for the treatment of water 4in water purification sys ished as a result of the spray aeration. èIn this connection, tems of the character described, is also Within the purview of this invention, and the efliciency thereof in both quan tity and quality of »floc formation is also enhanced by the it should :be recalled that »agitator 16 is provided in the reaction chamber l5 to `give violent agitation at `the mo ment off lmixing of the 'calcite and coagulant to prevent as much as possible build up of lloc particles during .the combination therewith of lan addition of calcite, `as is the spray aeration will have an inhibiting result in lloc ag found that the addition of no more than 15 ppm. calcite case with alum. Thus, the quality of flocculation with, vreaction and »before addition to the raw Water so that the for example, the addition of 40 ppm. ferrie chloride is precipitate actually added tto ‘the raw water comprises mi 15 tremendou-‘sly'enhanced and time for appropriate floccula nute lloc particles which `later will perform the coagulation tion tremendously Idecreased with the addition, for ex function. By «the `same token, the mechanical elïect of ample, of 20 to 30 ppm. calcite. Actually, it has been glomeration so that, with proper control according to this along with 30 p.p.'m. ferric chloride produces tremen invention, the basin 3l of the spray aerator is ythe first 20 dously enhanced characteristics of quality of ñocculation place in the system where agglomeration or coagulation and diminution of flocculating time as desired. of the ñoc particle is permitted to occur, las »also will be It should also be noted that the controlled reaction of understood, the additive materials are preferably retained calcite with flocculating materials, whether alum or iron in the chamber for no more »than about 30` to 60 seconds, salts or others, has been found to give satisfactory results and are added therefrom to the raw Water line immedi 25 even in water purification plants where -alum alone for ately prior to spray aeration for the purpose, among purification had previously been considered unsatisfac others, of avoiding lloc agglomeration until after the w-ater tory, and has been vfound to give highly enhanced results is passed to a point in the system Where detention with in flocculation or coagulation in plants where conventional but mild »agitation will provide the desired coagulation alum techniques have proved, at least, operable. It .and consequent impurity removal. 30 should also `be understood that other coagulation or ñoc Satisfactory results have been achieved by mechani culation aids such as activated silica and the like, .as pres cally Ifeeding and proportioning the chemicals into the re ently utilized, may @also -be employed Without detrimental action chamber, ‘as noted in the drawing, or by a regular results in the enhanced results of Processes embodying `gravity feed. A suction blower or equivalent apparatus and for practicing this invention and, that, also, addi is preferably provided to remove from the reaction cham 35 tional alkali may be added, :as is conventionally done with ber any chlorine gas >which may Ibe volatized therein. Sat ilsfactory results have been ‘achieved by adding the various some systems, to raise Vthe pH in extraordinary cases to a level for optimum liocculaiion in the water being treated. chemicals to the raw Water under such circumstances that It should also ‘be noted that any additional amount of there is a lapse of about 2` to 4 minutes between chemical “hardness” resulting in the water being treated from the addition and entrance of the Water into its iloccul‘ation 40 addition of calcite thereto (and/ or from the faddition of a detention apparatus, by, as noted, the provision of :agita tion in the reaction chamber, pumping through the raw ñocculating agent thereto) does not «appreciably affect the desired puriñcation and coagulation results, -even with periods of extended detention in the several basins. Ap venting formation of lloc particles of appreciable size parently this has to do with the law of mass action, and, during this period, as 2a result of which, increased fioc 45 of course, with the fact that reaction of the calcite and, formation appears to occur upon the entrance of the for example, alum occurs in the mixing crock 1S without treated water into the íirst ñoccul‘ator 36. Although the »attributing a substantial or undesirably excessive amount calcite preferred, as noted, is of about 325 mesh particle of hardness to the water being treated as measured, for size, microorganic examination of the treated water dis example, as additional calcium sulfate produced therein. 50 closes a substantial amount of the undissolved excess cal For example, when 10 g.p.l. alum and 10 g.p.l. calcite water flume, and at spray aeration all intentionally pre cite has Ibeen reduced to particles of 'about half their original size during passage to the flocculator thereby forming the `desired increased quantity of available nuclei were added, it was found that, after 30 minutes contact time, the hardness (as calcium sulfate) amount to only 4900 ppm. which is only 98% of that which 10 gpl. to aid in lloc agglomeration. alum -alone would be expected t-o form, thus indicating 55 Satisfactory results are achieved, according to this in that, Whereas enhanced results in quality of lloc and de vention, with calcite dosages being added to the raw Water crease of flocking time are experienced with the use of a within the range of 25% to 75% of the coagulant dosage -oalcite process embodying and for practicing this inven added, «and a ratio of 50% to 75 % is preferred. Within tion, still substantially no increase in water hardness 'of these ranges it has been found that the removal of color the treated water is experienced, as might otherwise be impurities (originally present Iat from 20 to 40 ppm.) is 60 expected, by the intentional addition to the treated Water complete and that iron impurities, even if present in con of substantial proportions of calcite and/or la reaction centrations up to 5 ppm., is also complete. As -Will be product of calcite with the ilocculating agent. understood, however, the greater the ratio of calcite to As will be understood, of course, there are some aluminum sulfate the higher will be the resulting pH of the natural Waters in this country (particularly, those stem treated water in the flocculators. Considering lloc for ming from the Great Lakes watersheds where a high mation as instigated primarily by bicarbonate alkalinity limestone content is prevalent in the area) Where the the pH range may optionally be considered at 6.0 to 6.7 natural alkalinity may be in the range of, more or less, for a dosage of 'approximately 25 p.p.m. Íaluminum sul 80 to 120 ppm., as compared to a desirable range of fate. It has been discovered in connection with this in natural alkalinity in raw Water to be treated with various vention, however, that excellent floc formation is obtained coagulants in 'the range of, generally, 35 to 65 p.p.m. at values as high as 7.3 which pH range can be obtained Obviously, in instances of such excess alkalinity some dif with an >alum dosage of 20 to 25 p.p.m. plus 60 to 70% ferent factors rnay be obtained in the application of the of calcite. Higher calcite ratios, of course, markedly en processes embodying the present invention to ysuch raw hance precipitation in view of the excess calcite present water. For example, -since alum (or other similar agglom to serve as a weighting agent in the agglomerated floc. erates or coagulants) reacts almost instantaneously with 3,097,163 10 the alkalinity factor of raw water, it may well beV that it is preferable to add alum, in some proportions, directly excess of «that which will react With said fiocculating agent providing a source of finely divided and undissolved crys talline nuclei for enhancing the formation of coagulated fioc, intimately admixing said added materials with said to the Water to be treated ahead of any calcite Iaddition, because, among other reasons, the alum will react with the natural alkalinity of the raw Water to reduce the alka Water to be treated for said precipitation of said precipi linity thereof and, thereafter, the addition of calcite (per haps 5 to 30 seconds «after the addition of Ialum alone) will produce a situation whereby only »a minor portion of ing said thus treated water in a still pool for the agglom eration and coagulation of said flocculant precipitate to the calcite Will be «dissolved so that there is a substantial remove therefrom said impurities. pot of the added crystalline calcite available for enmesh 10 ment in the fioc as a Weighting agent. It should be noted, as will be understood, that the alum-calcite reaction is quite desirable, as disclosed, for addition to raw water of tate, mechanically :agitating said admixture, and retain ` 3. In a water purification procedure fof the character described for removal of impurities from water by precipi tation in a coagulated flocculant, Vthe steps Which comprise adding to said Water to be purified a chemical ñorcculating agent in combination with finely divided calcite for re fect of a Weighting agent or nuclei forming agent for the 15 action with said fiocculating agent, said agent being se~ lected »from the group consisting of alum and ferrie chlo fioc may be additionally achieved, particularly in raw Water of very high alkalinity, by a separate addition of ride fiocculants and mixtures thereof, reacting said calcite with said fiocculating :agent before addition to said water, calcite, since the alum Ácalcite added according to the fore said calcite ibeing added in an amount in excess of that going suggested raugcs, leaving only about half of the calcite to be active as a Weighting agent. 20 which will react with said fiocculating agent providing a source of finely divided and undissolved crystalline In the past, a number of clays have been employed in various degrees of alkalinity, but that, the additional ef water treatment programs as a weighting `agent or a sub~ stance added t-o the water for the purpose of `forming a nuclei »for enhancing the formation ‘of coagulated floc, and intimately admixing said added materials with said Water to be treated for said precipitation of said precipi~ large number of nuclei for fioc formation lchereover. Such a step has not, in all cases, given beneficial results-per 25 tate. 4. In a Water purification process of the character haps because such clays have a specific gravity of no more described for removal of impurities ‘from water by precipi than 1.7 so that, as compared Witlh the normal specific gravity of calcite of 2:7 the weighting agent function has ltation in a coagulated fiocculant, the steps which comprise admixing for reaction a fiocculating agent, selected from been diminished. Additionally, apart from being, per haps, too light for a good Weighting agent, such clays 30 the group «consisting of alum and ferric chloride flocculants :and mixtures thereof, and a finely divided crystalline min are, frequently, too fine to enhance formation in treated eral, maintaining said admixed materials in initimate con Water. tact for a predetermined time for chemical reaction there In such instances when a Weighting agent is desired, it between, adding the reaction product of said admixed has been found that satisfactory results are achieved ac cording to this invention if barium sulfate is used as a 35 flooculating agent and crystalline mineral to said Water to be purified, the amount :of said' crystalline mineral being Weighting agent to promote flocculation according to this in excess of tha-t Which completely reacts with said fioc invention. Barium sulfate, being almost completely in culating agent effecting direct laddition to said Water to be soluble in Water, has a specific gravity oi about 4.6, and, puriñed of finely divided crystalline mineral for provid in sufficiently finely divided size, is a useful and satisfac tory weighting agent for the flocculant precipitate pro~ 40 ing fiocculati-on and agglomeration nuclei for coagulation of ra flocculant precipitate formed in said water by said 1duced by the alum or ferrie chloride or other fiocculating ladd‘ed reaction product, and intimately admixing said re~ agent in conjunction with calcite. action product and said excess crystalline mineral with While the processes and apparatus described herein said water to be purified for agglomeration and settling constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these 45 and precipitation of said precipitate. 5. In a water purification process of the character precise processes and apparatus and that changes may ‘be described for removal of impurities from Water by pre made therein Without departing from the scope of the cipitation in a coagulated fiocculant, the steps which com invention as defined in the accompanying claims. prise admixing a flocculating agent and finely divided What is claimed is: 1. In a Water purification procedure of the character 50 crystalline calcium carbonate, said flocculating agent be ing seìected from the group consisting of alum and ferrie described -for removal of impurities from Water by precipi chloride iiocculants and mixtures thereof, maintaining said tation in a coagulated fiocculan-t, the steps which comprise admixed materials in intimate contact with mechanical adding to said water to be purified a chemical ñocculating agitation for chemical reaction therebetween, adding the 'agent in combination with finely divided calcite after reaction with said fiocculating agent, said flocculating 55 react-ion product of said admixed flocculating agent and crystalline calcium carbonate to said water to be purified, agent yhaving a cation of the type which forms with the amount of said crystalline calcium carbonate being in said calcite a hydrous oxide gel fiocculant precipitate and excess of that which completely reacts with said fiocculat said finely divided calcite being added in an amount in ing agent effecting direct addition to said Water to be excess of tha-t which Will react with said fiocculating agent providing fa source of finely divided and undissolved crys 60 purified of finely divided crystalline calcium carbo-nate for providing floccul'ation and agglomeration nuclei for talline nuclei for enhancing the formation «of coagulated coagulation of a fiocculant precipitate formed in said fioc, intimately admixing said added materials with said Water by said added reaction product, and intimately ad Water to be treated for said precipitation, ‘and retaining mixing said reaction product `and said excess crystalline said thus treated water in a still pool for the agglomera tion 'and coagulation ‘of said fiocculant precipitate to re 65 calcium carbonate with said Water to be purified with mechanical agitation for agglomeration :and settling and move therefrom said impurities. precipitation of said precipitate. 2. In a Water purification procedure of the character 6. In a Water purification process of the character described for removal of impurities from water by precipi described for removal of impurities from Water by pre tation in a coagulated ilocculant, the steps which comprise adding to said Water to be purified 1a chemical flocculating 70 cipitation in a coagulated fiocculant, the steps which com prise admixing for reaction a fiocculating «agent and finely agent in combination with a finely divided crystalline min divided calcit'e, said iiocculating agent being selected from eral after reaction with said fiocculating agent, said agent the group consisting of alum and ferric ychloride fioccu being selected from the group consisting of ialum `and lants and mixtures thereof, maintaining sai-d admixed ma ferrie chloride fiocculants and mixtures thereof, said finely divided crystalline mineral being added in an amount in 75 terials in intimate contact with mechanical agitation for '3,097,163 1T va predetermined time for chemical reaction therebetween, adding the reaction product of said admixed >iioicculating agent and calcitel ‘to said Water to be puriiied, the amount of said 'calcite being in excess of that which completely reacts with said flocculating agent effecting y'direct addition -to said Water to be purified of íinely divided oalcite for providing ñocculation and agglomeration nucleil for co agulation of -a iiocculant precipitate formed in said water 12 cipitation ina coagulated ilocculant, die steps which com prise adding to said Water to be purified a chemical floc »culating agent and íinely divided calcite ‘for reaction there in, said calcite being added in substantial excess yor the amount thereof which reacts With said iiocculating agent and said i'locculating agent being selected from the group consisting of alum and ferrie chloride flocculants and mix tures thereof, additionally adding .to said thus treated by said added reaction product, intimately admixing said water íinely divided barium sulfate »as a Weighting agent to reaction product and said excess ca'lcite with said Water to 10 form a plurality tot nuclei for coagulation and agglomera be purified, and thereafter retaining said thus treated water tion `of said iiofcculant precipitate, intimately admixing said in a substantially still pool for agglomeration and settling added materials with said water to be treated, and retain and precipitation of said coagulated ñocculant precipitate. ing said -thus treated water for agglomeration and coagula 7. In a water purification process of the character tion of said ñocculant precipitate on said barium sulfate «described for removal of impurities yfrom Water by pre nuclei for removal from said Water of said impurities cipitation in a coagulated flocculant, the steps which com therein. ' prise adding to said Water to be purified a chemical Íioc culating agent in ‘combination with a finely -divided calcite ReferenceseCited in the file of this patent material for reaction With said flocculating agent, said UNITED STATES PATENTS `calcite material being added in excess of the amount which 20 354,650 yMorrison et al ________ __ Dec, 21, 1886 reacts with said 'ñocculating agent and said iiocculating agent having a cati-on Which ¿forms with :said calcite a hydnous oxide gel ñocculant precipitate, intimately adm-ix iug said added materials with said water to be treated for `said precipitation of said precipitate, additionally «adding 25 to said .treated Water another insoluble Íinely divided min eral material as a weighting agent for said iiocculant pre cipitate tand essentially inert and non-reactive 'with said flocculating agent and said oalcite mineral for enhancing the precipitation and settling out of said iiooculant pre 30 cipitate, and retaining said thus treated water in a still pool for agglomeration and coagulation of said iiocculant precipitate and said Weighting agent to remove from said Water said impurities. 1,535,709 1,619,036 1,930,792 2,234,285 2,310,009 2,326,395 2,362,409 Booth ______________ __ Apr. 28, Ravnestad ___________ __ Mar. 1, Evans ______________ __ Oct. 17, Schworm et al ________ __ Mar. 11, Baker et al. __________ __ Feb. 2, Samuel _____________ __ Aug. 10, Samuel _____________ __ Nov. 7, 1925 1927 1933 1941 1943 1943 1944 FOREIGN PATENTS 891,625 France ______________ __ Dec. 11, 1943 OTHER REFERENCES “Principles of Industrial Waste Treatment,” by C. Fred 'Gurnhanr John Wiley and Sons, Inc., New York (1955), 8. In a water purification process of the character 35 pages 226. to 228. described for removal of impurities from Water by pre Chemical Abstracts, vol. 50, co1. 2900~2901.