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Патент USA US3097173

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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.
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