Note: Descriptions are shown in the official language in which they were submitted.
-` 1085S22
26,
TITLE: PROCESS FOR-CLA~IFICATION OF RAW WATER
This ~nvention relates to an improved process for
clarifying raw waters. More particularly, this invention
relates to such a process wherein a low molecular weight
~uaternized dimethylaminomethyl acrylamide polymer is employed
as clarifying agent.
Recent developments in the field of water-solu~le
polymers have led to materials that are effective in water
treatment to remove undesirable materials suspended therein.
The separation of suspended particles from aqueous suspen-
ions thereof is generally referred to as "flocculation".
Such general term can include a wide range of aqueous systems
varying from a minor amount of inorganic solids in aqueous
, ~uspension, such as raw water, to high concentrations of or-
: ! ` ganic wastes in aqueous suspension, such as sewage sludges.
Because of this widely diverse nature of the various solids-
-water systems, the agents provided for such utility are
;I generally provided in a form that offers versatile perform-
j ance, i.e., suitable for use with a wide variety of solids-
; , water systems.
-l For certain solids-water systems, such as raw wa-
` ~ ters, these polymeric agents are used to clarify the water
5~ by removal of inorganic solids suspended therein. For other
solids-water systems, such as sewage sludges, the polymeric
~ ~ agents are used primarily to dewater the sludge so that the
f.'~ olids may be readily disposed of without prohibitive amounts
o~ water being associated therewith. These distinct appli-
;~ cations of the polymeric agents give rise to different
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1085S22
requirements as to the nature of the agents employed.
One teaching with respect to certain prior art
flocculants is that, in general, increased effectiveness
arises with increased molecular weight of the polymeric agent
employed, see U.S. Patent 3,738,945 for example. Another
teaching with respect to another type of prior art floccu-
lants is that there is a certain high molecular weight value
at which maximum effectiveness occurs and above which effec-
tiVeness remains essentially unchanged, see U.S. Patent
3,897,333 for example. Accordingly, one seeking an effective
flocculant for the various solids-water systems contemplated
by such application of polymeric agents would provide such
agent in high molecular weight range.
Typically, polymeric agents that are used in floc-
culation applications have molecular weights in excess of
about 200,000, usually in the range of about 500,000 to
several million, and in difficult solids-water systems, such
as sewage sludges, frequently higher, depending upon the
chemical nature of the polymeric agent. Most products that
have been available for commercial use have been in the high
molecular weight range so as to provide versatile utility in
the wide variety of applications in which they are useful.
Although the commercial products possess some degree of ver-
satility as to usage, they do not necessarily provide the
optimum performance in any given application.
Certain polymeric flocculants can be made directly
from suitable reactants, such as reaction products of epi-
chlorohydrin and dimethylamine or free-radical polymerization
products of such monomers as diallyldimethylammonium chlor-
ide. Other polymeric flocculants may be made by preparing
a polymer from a reactive monomer not containing certain
desired functionalities and subsequently modifying the pre-
formed polymer to provide the functionalities desired. In
this procedure, the functionality of the pre-formed polymer
can be varied in a number of respects, but the degree of
polymerization as it affects molecular weight of the modi-
fied polymer is determined by the polymer pre-formed.
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Acrylamide is a highly reactive monomer that is
widely used to provide pre-formed polymers that can be read-
~ly modified chemically to provide alternative or additional
functionality for specific end-uses. Thus, acrylamide poly-
mers may be controllably hydrolyzed to provide acrylic acid
functions on the polymer structure and provide an anionic
polymer. Alternatively, formaldehyde and dimethylamine can
be reacted with the amide groups of the polymer to provide
substituent dimethylaminomethyl functionality thereon and
prov~de a cationic polymer. Because of the high reactivity
of acrylamide monomer, however, the pre-formed polyacryl-
amide used for subse~uent chemical modification is usually
in the molecular weight range of about 200,0~0 to 5,000,000,
since such is the degree of polymerization normally obtained.
To obtain polyacrylamides of molecular weights outside this
range, special preparative procedures are necessary. For
higher molecular weight polyacrylamides, for example, highly
purified monomer is required. Although procedures for ob-
taining lower molecular weight polyacrylamides are available,
use of such techniques is not generally considered with re-
spect to flocculation applications because of the preference
for high molecular weight polymers.
The ;ntrinsic viscosity of a polymer is obtained
by measuring the viscosity of varying concentrations of the
polymer in a specific solvent and extrapolating to a value
of zero concentration, which is the value designated as
nintrinsic viscosity". The viscosity is the resistance of
liquid forms of the polymer to flow and ;s a characteristic
property measuring the combined effects of adhesion and co-
hesion. From the intrinsic viscosity can be calculated the
molecular weight of a polymer by use of appropriate equa-
t~ons. As i`s apparent, the intrinsic viscosity-molecular
~e;`ght relationship of one polymer type will differ from
that of another polymer type. Accordingly, the intrinsic
viscosity of a polyacrylamide of a specific degree of poly-
.....
merization will differ from that of a chemically modified
polyacrylamide of the same degree of polymerization. The
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fact remains, however, that as the molecular weight, or de-
gree of polymerization of a polymer increases, the intrinsic
viscosity thereof also increases in any particular series.
A quaternized dimethylaminomethyl polyacrylamide
has been previously disclosed for the treatment of sewage
sludges, see U.S. Patent 3,897,333. The useful polymer dis-
closed is one stated to have an intrinsic viscosity of at
least 0.5 deciliters per gram and the examples used to il-
lustrate the invention employ polymers having intrinsic
viscosit~es of l.0 and 2.5 deciliters per gram. For a qua-
ternarized dimethylaminomethyl polyacrylamide containing at
least 50 mole percent of such quaternarized groups to have
an intrinsic viscosity of at least 0.5 deciliters per gram,
the pre-formed polyacrylamide must have a molecular weight
of about 130,000 as a minimum and to conform to exemplified
species must have a molecular weight of about 350,000 to
1,500,000. The degree of polymerization for such polymers
would be at least l,800 and, as exemplified, from about
5,000 to 20,000, At this range of degrees of polymerization,
the polymers of the reference are said to exhibit eqivalent
performance in dewatering of sewage sludges, regardless of
the actual degree of polymerization in such range. Absent
any further teaching by the reference, one would be led to
believe that the same range of intrinsic viscosities would
be the most effective range for other flocculation applica-
tions.
In accordance with the present invention, there
is provided a polyacrylamide chemically modified to provide
a polymer consisting essentially of repeating units of the
8tructure:
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'10855Z2
C 1 H
CH3 x Y 1l
wherein A is an anion, R i5 an alkyl of 1-3 carbons or hy-
droxyalkyl of 2-3 carbons, x is a mol fraction of at least
about 50 percent, y is a mol fraction of up to about 50 per-
cent and represents unmodified acrylamide units and n is an
; ~nteger in the range of about 100 to about 1,600 to provide
the chemically-modified polyacrylamide with an intrinsic
viscosity in the range of about 0.1 to 0.45 deciliters per
gram.
There is further provided a process for clarifica-
tion of raw water containing up to about 10,000 ppm of sus-
pended inorganic solids of a particular size up to about 2
microns wh~ch compr~ses: mixing with said water from about
0.1 to 20 ppm of a polyacrylam~de having a content of at
least about 50 mole percent of amide groups chemically-
modified to contain dimethylaminomethyl groups, the dimethy-
~ aminomethyl groups being further modified by quaternization
. with an alkylating agent, the chemically-modified polyacryl-
amide having an intrinsic viscosity in the range of about
0.1 to 0.45 deciliters per gram measured in 3 molar NaCl at
l 30~C., to form suspendible flocs from a portion of the
` ~ solids present; maintaining the suspendible flocs in suspen-
. ~ion in said water until a substantial portion of the re-
- mai~ing solids is adsorbed thereto; and thereafter settling
:~ the resulting flo~s formed.
: ~ The present invention provides a polyacrylamide
:. chemically modified to contain quaternized dimethylamino-
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methyl groups and of low molecular weight. Unexpectedly,
such polymer type exhibi~ts optimum performance ~n raw water
clar~ficat~on at lower molecular we~ght values than do other
polymer types and than do higher molecular weight polymers
of the same type. Because the highly effective polymers of
the present invention are of low molecular weight, numerous
advantages arise, which include the following:
1. The polymers of the present invention develop
max~mum effect~veness in raw water clarification at low
molecular weight, thus eliminating d;sadvantages associated
with providing high molecular weight polymers.
2. Because preparation of low molecular weight
polymers takes less time than does preparation of high mole-
cular we~ght polymers, greater productivity is obtained for
a reactor of given capacity in a specific time period
3. Because low molecular weight polymers provide
low solution viscosity, chemical modification can be achieved
at h~gher polymer concentrations than in the case of high
molecular weight polymers.
4. Because chemical modification can be achieved
at hi`gh polymer concentration, chemical modif~cation is more
read~ly and completely effected.
5. Because the polymer of the present invention
~s provided at high polymer concentration, shipping costs
per unit weight of polymer are reduced.
6. The low molecular weight polymers of the pre-
~ent invention provide small, absorbent flocs which adsorb
additional suspended solids of the raw water and provide
greater clarification than do high molecular weight polymers
which provide large, non-absorbent flocs.
7. The polymers of the present invention of~er
cost-performance advantages over other polymeric flocculants
~ecause of their processing advantages.
In order to prepare polymers of the present inven-
~ion, lt is first necessary to prepare a low molecular
weight polyacrylamide in aqueous solution. By n polyacryl-
amide" is meant a polymer whic~ co~sists essentially of
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repeating units of acrylamide. Although it is generally pre-
ferred to provide a homopolymer of acrylamide for optimum
results in use, it is also possible to replace part of the
acrylamide units with another monomer in amounts which do
not interfere with the advantageous performance of the poly-
mer in raw water clar~fication. Other monomers that may
replace part of the acrylamide monomer include acrylonitrile,
methyl methacrylate, styrene, diallyldimethylammonium
chloride, methacrylamide, N,N-dîmethacrylamide, and acrylic
acid. If an ac~dic monomer is used, it should constitute
less than 10 mol percent of the polymer. It is generally
preferable to introduce a high degree of chemical modifica-
tion in the polyacrylamide and, therefore, the amount of
comonomer employed should be minimized in order to achieve
such preference. The polyacrylamide, accordingly, will con-
sist essentially of at least 50 mol percent of acrylamide
groups that have been chemically modified to provide quater-
nized dimethylaminomethyl groups thereon and preferably the
balance of unmodified acrylamide groups or of comonomer
un~ts that do not adversely affect the performance of the
polymer in the clarification of raw water. Both unmodified
acrylamide units and units derived from another comonomer
may be present with the re~uired content of quaternized di-
methylaminomethyl acrylamide groups.
In preparing the polyacrylamide, an aqueous solu-
tion of about 10 to 50, preferably 15 to 30, more preferably
20 to 25 weight percent of acrylamide, or monomer mixture,
is employed. A number of techniques are known which can be
employed to provide the desired low molecular polymer. Use
of initiator contents of at least about 0.1 weight percent
are effective. The use of high reaction temperatures such
as at least 50C., preferably about 70C. to 100C., is
also effective using the initiator concentration stated. A
chain transfer agent, such as isopropanol, is also effective
but is not necessary. In instances wherein an impurity,
such as ionic copper is present, a chelating agent, such as
ethylenediamine tetracetic acid may be used to combine with
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th~s impurity. However, the presence of impurities and use
of chelating agents is not necessary to prepare the low mol-
ecular weight polymer,
Free radical initiators useful at the concentration
specified include, for example, ammonium persulfate, potas-
sium persulfate, benzoyl peroxide, bromobenzoyl peroxide,
t-butyl hydroperoxide, and hydrogen peroxide in the presence
of ferrous ion.
As indicated, the init;ated polymer solution is
heated to 50C. or higher and held at the selected temperature
until the polyacrylamide of desired molecular weight is ob-
tained. The polyacrylamide should have a degree of polymer-
ization in the range of about 100 to 1,600. In the case of
a homopolymer of acrylamide this will correspond to a molecu-
lar weight of about 7,000 to 110,000. After the desired
polyacrylamide is provided, the reaction solution is cooled
to about 40C. to effect chemical modification with formal-
dehyde and dimethylamine.
Formaldehyde may be used as a 20 to 60 weight
percent aqueous solution and dimethylamine is used as a 20
to 65 weight percent aqueous solution. The molar amount
of formaldehyde employed must be suficient to chemically
modify enough acylamide groups to provide at least 50 mole
percent of modified acrylamide groups in the final polymer
but the amount of formaldehyde used may be sufficient to
obtain a polymer consisting essentially of modified acryl-
amide groups, preferably a polymer containing 60-90 mole
percent of modified acrylamide groups. The amount of di-
methylamine employed in the chemical modification of the
acrylamide groups will constitute the molar equivalent
amount of dimethylamine plus about a 1 to 10 mole percent
excess, preferably about 5 mole percent excess. The reac-
tion to provide chemical modification is preferably con-
ducted at about 40C. for sufficient time to complete the
reaction, generally in about two hours. Temperature and
appropriate time modifications may be made in accordance
with conventional procedures for providing this chemical
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modificatlon, which is also called Mannich base formation.
After the reaction with formaldehyde and dimethyl-
amine is complete, the reaction product is quaternized with
an alkylating agent to a pH in the range of about 4 to 7.
Preferred alkylating agents are dimethyl sulfate and methyl
chloride but other alkylating agents may be used. The qua-
ternization is preferably carried out to involve essentially
all of the dimethylaminomethyl groups provided but complete
reaction is not required so long as the minimum quantity of
quaternized groups is provided. In the event that all of
the dimethylaminomethyl acrylamide groups are not quaternized,
the unquaternized dimethylaminomethyl acrylamide will repre-
sent a part of the polymer composition.
With respect to the ind~vidual steps of polymer
preparation, chemical modification of the polyacrylamide to
`provide Mannich base modification, and quaternization of the
reaction product, the conditions of reaction and useful re-
actants are known. The process of preparation of the pro-
duct, however, is the specific combination of the individual
steps involving a low molecular weight polyacrylamide as the
polymer undergoing chemical modification which results in a
no~el polymer possessing unexpected properties when used in
raw water clarification and provides unexpected processing
advantages not possible when the conventional high molecular
we~ght polyacrylamides are suitably processed.
The product obtained by the process of the present
invention is a stable product which contains from about 50
to 100 mole percent of quaternized dimethylaminomethyl acryl-
amide groups. The degree of polymerization of the chemically
modified polyacrylamide will be substantially the same as
that of the starting polyacrylamide since no increase in
polymer backbone molecular weight is known to arise as a
result of the chemical modification effected. Accordingly,
the degree of polymerization of the product polymer of the
present invention will range from about 100 to 1,600. As a
result of the chemical modification of the polyacrylamide,
the molecular weight of the repeating units will be increased
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depending upon the extent to which chemical modification is
effected and, accordingly, the product polymer will have a
higher molecular weight than the starting polyacrylamide al-
though the degree of polymerization is unchanged. Also, as
a result of the chemical modification of the polyacrylamide,
the resulting product will have different rheological proper-
ties from those of the starting polyacrylamide and conse-
quently the intrinsic viscosity values of the starting and
product polymers will differ. The intrinsic viscosity of
the polymer of the invention will be in the range of about
0.1 to about 0.45, preferably about 0.2 to 0.4, deciliters
per gram when measured in 3 molar sodium chloride at 30C.
The raw waters for which the product of the pre-
sent invention is a superior clarification agent are those
which contain up to about 10,000 parts of suspended inorganic
solids of particle size of up to about 2 microns. This
should cover most raw waters encountered since gravitational
setting generally occurs with waters of higher solids con-
tents.
In carrying out clarification of raw water as de-
fined, an effective amount of the product of the present
invention i8 mixed with the water to be clarified. By "an
effective amount" is meant that amount which produces a de-
sirable clarification of the water being treated. Such
amount will vary widely depending upon the nature of the
water being clarified, the nature of the chemically-modified
polymer of the present invention employed, the specific
degree of~clarification agents may be used in the range of
about 0.1 to 1,000 parts per million (ppm) based on the
quantity of water being treated. The polymer of the present
invention has generally been found to be effective in the
range of about 0.1 to 20 ppm.
After the chemically-modified polymer has been
mixed with the raw water being treated, small absorbent
flocs involving part of the suspended solids will immediately
form. These flocs, because of their nature can be kept in
~uspension by application of suitable agitation, usually
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~085SZZ
-- 11
slow speed, and while in suspension will adsorb addit~onal
su6pended solids~ to effect a greater degree of clarification
than would be the case if the initial flocs were immediately
settled and the supernatant liquor separated. The duration
of time over whi`ch the initial flocs are maintained in sus-
pension will vary widely depending upon the nature of the
water being clarified and the content of solids therein, the
particular polymer employed in clar~fication, the extent to
which clarification is desired, and the like. It is gener-
ally desired to remove a substantial amount of the suspended
solids remaining in the water being clarified by adsorption
upon the initial flocs formed. Prefera~ly, the suspendible
flocs are maintained in suspension until the turbidity of
the treated water is less than about 20~ of that of the un-
treated water.
After the suspendible flocs have adsorbed a suit-
able amount of the remaining solids in suspension, the
resulting flocs are allowed to settle, thus providing super-
natant clarified water and a sediment of flocculated inor-
ganic solids. The clarified water may be decanted or other-
wise recovered from the sediment in accordance with conven-
tional procedures involving the processing equipment employed.
The clarified water obtained by use of the clar;ficat;on
process of the present invention will have a lower residual
turbidity than water clarified by equal amounts of other
polymeric flocculants an equal residual turbidity at a lower
dosage of polymeric flocculant than required with other
polymeric flocculants, or the cost-performance requirements
for the desired level of clarification will be substantial-
ly lower for the process of the present invention than for
other processes.
The invention is more fully illustrated in the
examples which follow wherein all parts and percentages are
by wei~ht unless otherwise specified. ~he following examples
are preferred embodiments and are not to be construed as
limitations on the scope of the claims,
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EXAMPLE 1
The following example illustrates a process for
manufacturing a polymer contain~ng aminomethylated acrylamide
groups quaternized with dimethylsulfate.
226 Pounds of deionized water, 0.087 pounds of
ethylene diamine tetraacetic acid, disodium d~hydrate salt
and 0.87 pounds of isopropyl alcohol are charged to a clean
reactor which is then sealed. Agitation is started and the
charge is heated to 70 + 2C. under a stream of nitrogen.
At 70C., a 5.16 weight percent aqueous solution of ammonium
persulfate ~i.e., 15,000 ppm based on acrylamide) ~s added as
rapidly as possible, the temperature is readjusted to 70C.
if necessary, and then a 50 weight percent aq-ueous acrylamide
solution is metered in during 2 hours, while maintaining the
temperature at 70 ~ 2C. The amount of acrylamide charged
is calculated to give a 20 weight percent aqueous polymer
solution. After all the acrylamide has been added, the
batch is held at 70C. for another hour in order to complete
the polymerization, then the nitrogen flow is stopped and
l~opropyl alcohol is distilled off at a batch temperature of
70-75C. and a pressure of 225 mm. Hg. Distilling off 0.8
to 0. 9 weight percent of the batch load removes 90-95 weight
percent of the isopropyl alcohol as a 22 weight percent aque-
OU8 solution (Sp, Gr. 0.9671. After reducing the batch to
a temperature below 50C., the batch weight is adjusted by
adding an amount of deionized water equal to the weight of
i~opropyl alcohol solution removed during stripping. Then
a premixed solution of 100 mole percent each of formaldehyde
and dimethylamine based on the amount of acrylamide contain-
ing 5 mole percent excess dimethylamine is added as rapidly
as possible. The dimethylamine-formaldehyde solution should
be premixed and cooled below 40C. After holding for two
hours, the batch temperature is readjusted to 35C. and
then 100 mole percent of dimethylsulfate based on the amount
of dimethylamine is pumped in as rapidly as possible while
maintaining the batch at 35 to 40C. to a final pH of 6.0 +
0.2. After the d~methylsulfate has been added and the pH
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is stable at pH 6.0 + 0.2, the batch is drummed off,
EXAMPLE 2
The following example illustrates another process
for manufacturing a polymer of this invention without the
use of a chain transfer agent and without purginq the reac-
tor with nitrogen.
A. Preparation of the Polyacrylamide Backbone
738 lb. deionized water and 0,38 lb. EDTA (diso-
dium dihydrate, 1000 ppm on monomer) are charged to a clean
reactor and the pH is adjusted to 4.5 with 10% sulfuric
acid solution. The reactor is sealed and the batch is heated
to reflux during 1 hr, After 1 hr., 0.22 lb. of ammonium
~ persulfate initiator is added and then 2.02 lb. of the ini-
j ator and 941 lb. of 39.7~ acrylamide monomer solution (at
pH 4.3) are metered in simultaneously during 90 mins. while
maintaining steady reflux. After the monomer and initiator
solutions have been added, the batch is held at reflux for
~ 30 minutes to complete the polymerization and then the batch
5 ~ temperature is reduced to 35-40C.
B. Preparation of the Aminomethylated
Polyacrylamide Quaternized Polymer
t At 35C., a premixed solution of 532.75 lb. of a
37 weight percent formaldehyde solution and 779.88 lb. of a
40 weight percent dimethylamine solution (1:1:1.05 mole ratio
of amide:formaldehyde:amine) is added as rapidly as possible
~ , with no cooling. The batch is held 3 hours. Then the batch
temperature is reduced to 20C. and 698 lb. of dimethylsul-
~5: ' fate is metered in at a temperature of 35C. until the pH
5 , i8 reduced to 5 + 0.5. After the dimethylsulfate has been
added and the pH is stable the batch may be drummed off.
X~OLIN FLOCCULATION TEST
The determination of relative normalized dosage
( ~RD20) for the cationic flocculants was by the Kaolin floc-
i culation test, also known as the jar test. This test re-
presents a simulation of the actual use of the cationic
, flocculants as primary coagulants in the treatment of raw
-1 water from natural waterways. The turbidity present in
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most natural waters is similar to that represented by the
suspensions used in this test. The accuracy of this test is
within + 5 percent.
A measure of the degree of quaternization of a
cationic polymer may be obtained by flocculating suspensions
with chlorine present. The presence of chlor~ne inhibits
the action of the tertiary amine functions within the polymer,
while the quaternary sites are unaffected by the presence
of chlorine. The necessary presence of chlorine to conduct
this test can be obtained with sodium hypochlor;`te.
The water used in the test is only mildly buffered
and day to day variations will occur due to uptake of atmos-
pheric carbon dioxide. A control should therefore be run
with each day's tests to account for variation in water qual-
ity.
The results obtained are described in Examples 3
and 4 ~elow.
~XAMPLE 3
The following illustrates the effectiveness of the
cationic flocculants of this invention when clarifying raw
water containing kaolin clay.
The polymer prepared by the process of Example 1
is used. A suspension of kaolin clay with negative charges
on the particles in water is used as a standard test medium
as this closely approaches many river waters. A stock sus-
pension of clay is made by mixing 25 grams of kaolin in a
liter of deionized water for 24 hours and then allowing
settling in a graduated cylinder for 24 hours. The upper
portion is decanted, such that the particle size of this
fraction is not substantially in excess of 2 microns. This
concentration is then diluted with water to yield a test
water containing 70 ppm of kaolin. One liter samples of the
test water are placed in a six-place laboratory stirrer and
varying amounts of the standard compound diluted to 30 ml.
added, mixing being maintained at 100 r.p,m, for one minute,
This is followed by flocculation at 40 r.p.m, for 15 minutes
and settling for 15 minutes, The supernatant liquid is
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`` 108552Z
drawn off and analyzed for residual turbidity and electro-
phoretic mobility. The turbidities are plotted and the dos-
age taken where the turbidity is 20% of that for the untrea-
ted water. A similar series of tests is run on the sample
of the product of interest and the relative dosage compared
to the standard is calculated. The dosage is that quantity
of flocculant needed to produce a turbidity which is 20% of
that of the untreated water and varies with the different
flocculants. The dosage of standard flocculant divided by
the dosage required of the flocculant of interest and ,multi-
plied by 100 represents the relative efficiency of the pro-
duct of interest at a dosage level, producing the turbidity
of 20% of the untreated water RD20.
Results are as follows:
Intrinsic Viscosity (dl/gm.) RD20
0.7 (control) 1.00
0 33 0.81
- 0 25 0.79
0.12 0~89
0.06 (comparative) 1.01
These results show that unexpectedly quaternized
, dimethylaminomethylacrylamide polymers of the range of in-
i trinsic viscosity values of the present invention are super-
ior in dosage requirements for providing a specific level of
clarification of raw waters than are similar polymers of
intrins~c viscosity outside this range.
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