Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Bac~g~und ~ftheIn~ention
Floccl~lation is a rnethod ~f dewaterin~ susp~nd~ solids by agglomerating the sotids.
Flocculation mat~rially improves the de~Natering rate of rnany types of suspended solids,
including thos~ used in m~neral, pap~rm~kin~, waste water treating and oil ,ield applicatlons.
Synthètic polymer flocculants ha~/e been utiliz~d in tt:e in~ustry slnce th~ 1950's ~s
flccculatin~ agents in the tr~atment of susper:~ed s~ s H¢wever, due to rnoderrl concerns
with e:lvircnmental prot~ction, slu~Qe ,rlc3nerati~n~ tr~nsportc,ti~n and dis~osal costs, It has
become increasingly desirable to impr~ve on the performance of conventional linear polymer
flocculants ~ protAding ~ flocculating ~ent w~ich ac~ievss gr~ter dew2tering at a siven
1G polymer dose, or equiYalent dewatering at a 14wer polyrner dose.
~he pr~s~nt invention provides com~ositions and me~hods for dewatering suspendedsolic!s, including thos~ 'r~quently enco;lnter~r~ in the waste Wate! ~reatin3, mining and
papermaking in~ustries, ~Ising high mGlecular weight, w~e~-solu~le or~at~r-s~hellable.
branche~, cationic, polymer fiGcGularlts, as well as rnetho~s fcr mai<lng said compocitions
1~ ~he co~r,posltions and metho~s of :he instart Invention ,~rovir~e ~or superior aewatering lNh~r~
ccmpared to t~ose previGusly used in the art.
Linear polymer flccculan~s have been ~'struetured'' in the art thro~Jgh the US2 of
~ranching or crossiin~lng ayer~ls. Polymer str..cturing is ~iscussed by J.E~. rholr9an et al., ~dv.
Chem. Ser., Voi 187. pp. 23~-52 ~19~Q~ U.S. Patenls ~los. 4.720,3~B an~ 4,~43,378
~0 de~oribe th~ use of cros~iinked ~atlonic polymer part.cles having a d~ particle si2e h610w t G
micrornetefs (um). U.S. Patent Nos. 5,152,903 and ~ 65 dieclose a method of
flocc~latin.3 using cross-linlced cationic poly~.er rnicroparticles. U.S. Patent hJo. ~,235,45
describe~ a ~loc~u~aticn methcd wilioh utilizes crc~ssilnk~ poiyacrylarnide. I J.S. Patent Nc.
3,~8,~37 t~ac~es a methcd of relea$ing water from activate~l sewa~e s!udge usinrcS crosslinked catiani~ emuision polymers. Methods and c~mpo~itions us~ful for thickening
aqueous media ~re given in U.S. ~ater,~ Nos. 4,359,~5~; and 4,172,066. Gopen~ingapp~ications hios. Q8~02~,9t6, 08/028,001, 0814~7,25~, 0~8/45~,g74 and 0~4~,41~, ~nich are
assign~d to assignee ~f this inven~ian and are all hereby in~orporated nerein by retr~renc~,
~escri~e me~hods fo~ Rocculatin~ suspe~cled solids Using Cationic, h~gh n~oiecu~ar weight,
30 water-soluble, ~r~nched polymers.
Water-solub~e polymers tT~y ba charac~erlzed by dete~rrninin~ the solution visco~ity o~
dilu~e e.g. ~.05% to 1~,~o, soluffons of the polymers in pure ~Nater and ir~ sal~ solutions. Herein,
all p~rcentages ~re ~iven as weight percent based on tota~i ~,veight. The dilute solution
visc~sity o~ a linear~ cationic. higl~ moiec~iar wei~ht w~ter solu~e polymer is
AhlENl)ED SHE~T
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typically much higher in pure water than in, for instance, 1 molar (M) NaCI solution. For our
purposes, the "bulk viscosity" of a polymer is defined as the viscosity of a 0.2% solution of
polymer in pure water, measured using a rotating cylinder viscometer, e.g., Brookfield
viscometer, under the conditions described in the Examples. As used herein, "standard
viscosity" is the viscosity of a 0.1% solution of polymer in 1 M NaCI solution, also measured
using a rotating cylinder viscometer, e.g., Brookfield viscometer, under the conditions
described in the Examples. The ratio of the bulk viscosity to the standard viscosity, BV/SV,
tends to vary as a function of the degree of structuring present in the polymer.The "sedimentation value" also varies as a function of the degree of structuringpresent in the polymer. The "sedimentation value" is a sensitive indicum of the settling rate
of a water-soluble or water-swellable polymer in salt solution. A sedimentation value of less
than 10% means that there is little or no tendency for the polymer to sediment in salt
solution. A sedimentation value is determined by preparing a 0.05% solution of a particular
polymer in 0.001M NaCI, centrifuging part of the solution for about 60 minutes at about
18,000 X G (gravity) and 22~ C, and measuring the ultraviolet (UV) absorbance, at 215
nanometers (nm), of the uncentrifuged part and of the supernatant of the centrifuged part.
The absorbance of the supernatant of the centrifuged part compared to the absorbance of
the uncentrifuged part is c~lc~ ted as [AA(uncentrifuged) - ~A(centrifuged)] /
AA(uncentrifuged), where ~A = A(polymer solution) - A(water) and A is the measured UV
absorbance at 215 nm. The value c~lcll'~ted thereby is multiplied by 100 to give the
sedimentation value, which is expressed as a percentage.
Surprisingly, it has now been found that water-soluble polymers having BV/SV of
from about 300 to about 500 and having sedimentation values of less than 10%, are
superior flocculants for suspended solids. In particular, these polymers give faster
dewatering of waste activated sludge, in particular extended aeration activated sludge, than
polymers of sirnilar molecular weight and cationicity that do not have the BV/SV and
sedimentation values mentioned above.
Summary of ~e l,.,~ n
According to the present invention, there are provided methods of dewatering a
dispersion of suspended solids comprising adding to the dispersion an effective amount of
a cationic, water-soluble or water-swellable polymer to form a mixture of the dispersion and
the polymer, wherein the polymer has a bulk viscosity to standard viscosity ratio of about
300 to about 500, and wherein the polymer has a sedimentation value of about 10% or less,
and then dewatering the mixture.
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This invention provides, as a more pr~fened embodiment, methods of dewatering
a dispersion of suspended solids using a copolymer of acrylamide and quaternizeddialkylaminoalkyl(alk)acrylate, the copolymer having at least about 20 mole percent cationic
units based on the total number of moles of recurring units in said polymer.
In a preferred embodiment, there are provided methods of dewatering a dispersionof suspended solids using a copolymer of acrylamide and acryloxyethyltrimethylammonium
~ chloride, the copolymer having at least about 30 mole percent cationic units based on the
total number of moles of recurring units in said polymer.
There are also provided processes of making a cationic polymer comprising
polymerizing or copolymerizing the monomer components of a mixture comprised of an
ethylenically unsaturated cationic monomer, an effective amount of chain-transfer agent and
an effective amount of a branching agent sufficient to form a water-soluble or water-
swellable cationic polymer having a bulk viscosity to standard viscosity ratio of from about
300 to about 500 and a sedimentation value of about 10% or less.
This invention, in a more preferred embodiment, provides processes of making a
cationic polymer comprising copolymerizing the monomer components of a mixture
comprised of acrylamide and acryloxyethyltrimethylammonium chloride, an effective amount
of isopropanol or lactic acid as a chain-transfer agent and an effective amount of
methylenebisacrylamide as a branching agent to form a water-soluble cationic polymer
containing at least about 30 mole percent acryloxyethyltrimethylammonium chloride based
on the total number of moles of recurring units in the cationic polymer, the copolymer
having a weight average molecular weight of greater than 1,000,000, a bulk viscosity to
standard viscosity ratio in the range of from about 300 to about 400 and a sedimentation
value of about 5 % or less.
In another embodiment, there are provided processes of making a Mannich
acrylamide polymer comprising polymerizing or copolymerizing the monomer components
of a mixture comprised of acrylamide, an effective amount of a chain-transfer agent, and
an effective amount of a branching agent, to form a water-soluble or water-swellable
precursor polymer, and reacting said precursor polymer with an effective amount of a
formaldehyde and a secondary amine or a complex thereof, to form a water-soluble or
water-swellable Mannich acrylamide polymer having a bulk viscosity to standard viscosity
ratio of from about 300 to about 500 and a sedimentation value of about 10% or less.
There is also provided a water-soluble or water-swellable cationic polymer having
a bulk viscosity to standard ratio of from about 300 to about 500 and a sedimentation value
of about 10% or less.
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This invention provides, as a more preferred embodiment, a cationic copolymer
comprised of recurring units of acryiamide and quaternized dialkylaminoalkyl~alk)acrylate
units, the copolymer containing at least about 30 mole percent quaternized
dialkylaminoalkyl(alk)acrylate recurring units, based on the total number of moles of
5 recurring units in the cationic copolymer, the copolymer having a weight average molecular
weight of greater than about 1,000,000, a bulk viscosity to standard viscosity ratio in a
range from about 300 to about 400 and a sedimentation value of about 5 % or less.
In a more preferred embodiment, this invention provides a cationic copolymer
comprised of recurring units of acrylamide and acryloxyethyltrimethylammonium chloride,
10 the copolymer containing at least about 30 mole percent acryloxyethyltrimethylammonium
chloride, based on the total number of moles of recurring units in the cationic copolymer,
the copolymer having a weight average molecular weight of greater than about 1,000,000,
a bulk viscosity to standard viscosity ratio in a range from about 300 to about 400 and a
sedimentation value of about 5 % or less.
Further, in this invention, there is provided a method of dewatering extended aerated
sludge, the method comprising adding to the sludge an effective amount of cationic, water
soluble or water-swellable polymer to form a mixture of the sludge and the polymer, wherein
the polymer has a bulk viscosity to ,lalldard viscosity ratio of from about 300 to about 500,
and wherein the polymer has a sedimentation value of about 10% or less, and dewatering
20 the mixture.
This invention provides, as a preferred embodiment, a method of dewatering
extended aerated sludge, the method comprising adding to the sludge an effective amount
of water soluble copolymer of acrylamide and quaternized dialkylaminoalkyl(alk)acrylate to
form a mixture of sludge and the copolymer, wherein the copolymer has at least about 20
25 mole percent cationic units based on the total number of moles of recurring units in the
polymer, a bulk viscosity to standard viscosity ratio of from about 300 to about 500 and a
sedimentation value of about 5% or less and dewatering the mixture.
This invention also provides, as a more preferred embodiment, a method of
dewatering extended aerated sludge, the method comprising adding to the sludge an
30 effective amount of water soluble copolymer of acrylamide and acryloxyethyl
trimethylammonium chloride to form a mixture of sludge and the copolymer, wherein the
copolymer has at least about 30 mole percent acryloxyethyl trimethylammonium chloride
units based on the total number of moles of recurring units in the polymer, a bulk viscosity
to standard viscosity ratio of from about 300 to about 400 and a sedimentation value of
35 about ~% or less and dewatering the mixture.
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ne~ ' Description c~ ~e r.~ E..~ Y~
The high molecular weight, cationic, water-soluble or water sv.el'qhle, polymeric
floccl ~Iqrlts of the instant invention are formed by the polymerization of cationic ethylenically
unsaturated monomers, alone or with comonomers, in the presence of a branching agent
5 and a chain-transfer agent in optimum proportions. High molecular weight, cationic, water
~ soluble or water-sw6"~~'o polymers are also formed by polymerizing or copolymerizing
nonionic monomers, e.g., acrylamide, to form nonionic polymers, e.g., polyacrylamide, and
functionalizing nonionic polymers to impart cationic groups to the polymer, preferably tertiary
aminomethyl group which may be quaternized.
10Cationic monomers useful in the practice of this invention include
diallyldimethylammonium chloride; acryloxyethyltrimethylammonium chloride;
methacryloxyethyltrimethylammonium chloride; dialkylaminoalkyl(alk)acrylate compounds;
and quaternaries and salts thereof, such as N,N-dimethylaminoethylmethacrylate
methylchloride salt; monomers of N,N-dialkylaminoalkyl (meth)acrylamides; and salts and
15 quaternaries thereof, such as N,N-dialkylaminoethylacrylamides;
methacrylamidopropyltrimethylammonium chloride; 1-methacryloyl-4-methyl piperazine and
the like. Quaternized dialkylaminoalkyl(alk)acrylate monomers are preferred, andacryloxyethylL,ill,~lllylammonium chloride and methacryloxyethyltrimethylammonium chloride
are most preferred. Cationic monomers are generally of the following formulae:
1 1
CH2= lC
C=O
A
R2--r--R3
R4
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where R1 is hydrogen or methyl; R2 is lower alkyl of C1 to C4; R3 is lower alkyl of C1 to C4;
R4 is hydrogen, alkyl of C, to C12, aryl or hydroxyethyl and R2 and R3 or R2 and R4 can
combine to form a cyclic ring conlai.lillg one or more hetero atoms, and X is the conjugate
base of an acid, A is oxygen or -NR,- wherein Rl is as defined above, and B is an alkylene
group of C1 to Cl2; or
15 ~7 ~6
CH2=C--CH2-1,CH2-C=CH2
R8 X-
where R5 and R6 are hydrogen or methyl, R7 is hydrogen, alkyl of C1 to C12, benzyl or
hydroxyethyl; and X is defined above.
Nonionic monomers, suitable in the practice of this invention, generally comprise
acrylamides; methacrylamides; and N-alkylacrylamides, such as N-methylacrylamide; and
N,N-dialkylacrylamides, such as N,N-dimethylacrylamide. Acrylamide and methacrylamide
are preferred. Small amounts, e.g., 10 mole % or less, based on total moles of recurring
units in the polymer, of sparingly soluble nonionic monomers such as methyl acrylate,
methyl methacrylate, ethyl acrylate, acrylonitrile, etc. and the like may also be suitable.
Cationic homopolymers having recurring units of one or more cationic monomers
may be employed in this invention. Preferably, one or more nonionic monomers, e.g.,
acrylamide, may be copolymerized with one or more cationic monomers, e.g.,
acryloxyethyltrimethylammonium chloride to produce cationic copolymer. Preferably,
cationic copolymers are comprised of at least about 20 mole % of recurring units of cationic
monomer, based on the total number of moles of recurring units in the polymer. Herein,
when referring to the mole % of recurring units in a polymer, all mole % are based on the
total number of moles of recurring units in the copolymer. More preferably, the copolymers
are comprised of at least about 25 mole % of recurring units of cationic monomer; most
preferably, the copolymers are comprised of at least about 30 mole % of recurring units of
cationic monomer.
Cationic charge may also be imparted to a polymer by functionalizing nonionic
recurring units of the polymer. For instance, acrylamide units in the polymer backbone may
be reacted with an effective amount of a formaldehyde and a secondary amine or acomplex thereof in a manner known per se to form Mannich acrylamides having pendant
tertiary aminomethyl groups that are cationic at low pH, or the tertiary aminomethyl groups
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can be quaternized to form cationic pendant groups following procedures known to those
skilled in the art, e.g., see U.S. Patent No.5,037,881,4,956,399, and 4,956,400, which are
incorporated herein by reference. Formaldehydes useful in the practice of this invention are
selected from formaldehyde, paraformaldehyde, trioxane, or aqueous formalin, etc. Useful
secondary amines are selected from dimethylamine, methylethylamine, diethylamine,
amylmethylamine, dibutylamine, dibenzylamine, piperidine, morpholine, ethanolmethylamine,
diethanolamine, or mixtures thereof. Especially preferred is a process wherein the
formaldehyde comprises formalin and the secondary amine comprises dimethylamine. It
is also contemplated to employ a formaldehyde-secondary amine complex such as N,N-
dimethylaminomethanol.
The backbone polymer which contains the nonionic groups may be comprised
completely of nonionic groups, or may be comprised partly of nonionic groups and partly
of cationic groups prior to the functionalization reaction that imparts the cationic groups.
Preferably, a polyacrylamide emulsion or microemulsion polymer is polymerized in a known
manner to form a precursor polymer, subjected to Mannich reaction conditions, and,
optionally, quaternized, as in U.S. Patent Nos.5,037,881; 4,956,399; and 4,g56,400; which
are hereby incorporated herein by reference. Preferably, at least about 20 mole % of the
recurring units are cationically charged. More preferably, at least about 30 mole % of the
recurring units are cationically charged.
Polymerization of the monomers is generally conducted in the presence of a
branching agent or cn~ ing agent to form branched, or crosslinked, homopolymer or
copolymer. The branching agent generally comprises compounds having either at least two
double bonds, or at least a double bond and a reactive group, or at least two reactive
groups. Polyfunctional branching agents should have at least some water-solubility.
Preferred polyfunctional branching agents include compounds containing at least two double
bonds, e.g., methylenebisacrylal l :'e; methylenebismethacrylamide; polyethyleneglycol
diacrylate; polyethyleneglycol dimethacrylate; N-vinyl acrylamide; divinylbenzene;
triallylammonium salts; N-methylallylacrylamide; and the like. Also preferred are
polyfunctional branching agents containing at least one double bond and at least one
reactive group including glycidyl acrylate; acrolein; methylolacrylamide; and the like.
Polyfunctional branching agents containing at least two reactive groups include aldehydes,
such as glyoxal; diepoxy compounds and epichlorohydrin and the like.
Methylenebisacrylamide ("MBA") is a preferred branching agent.
Essential to the practice of this invention is the presence of, in optimum
concentration, a molecular weight modifying or chain-transfer agent to provide the proper
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polymer structure. In the absence of a chain-transfer agent, the incorporation of even
extremely small amounts of branching agent, e.g., 10 parts per million may causecrosslinking that is so extensive as to render the polymer less effective as a flocculant.
However, branched cationic polymers are obtained in accordance with the present invention
when a chain-transfer agent is used, in optimum concentration, in conjunction with said
branching agent. Many such chain t~ansfer agents are well known in the art. These include
lactic acid and alcohols such as isopropyl alcohol; mercaptans such as 2-mercaptoethanol;
thioacids; phosphites and sulfites, such as sodium hypophosphite, although many different
chain-transfer agents may be employed. Preferred chain transfer agents are isopropyl
alcohol and lactic acid.
The weight average molecular weights of the polymers of the instant invention are
generally greater than 500,000, preferably greater than 1,000,000. Weight average
molecular weights may be determined by using light scattering methods well known to those
skilled in the art.
The polymers of the instant invention are characterized by BV/SV of at least about
300, preferably at least about 320, and the BVtSV is generally no greater than about 500,
preferably less than about 450, more preferably less than about 400.
It is important that optimum concenll~tions of chain-transfer agent and branching
agent be employed in order to produce polymers having BV/SV of from about 300 to about
500, preferably about 300 to about 400, and sedimentation values of about 10% or less,
preferably about 5% or less. The optimum amounts of chain-transfer agent and branching
agent depend on the relative efficiencies of the particular chain-transfer agent and
branching agent and will vary depending on the polymerization conditions. It is therefore,
difficult to set specific amounts of chain-lldns~er agents and cross linking agents for all
polymers and types of chain-transfer agents and cross linking agents. Routine experimental
methods are particularly useful for delt:rl,lil,i,lg optimum levels of branching agent and
chain-transfer agent because the polymerization conditions will obviously affect branching
and molecular weight. It is known that the usual constituents of polymerization, e.g.,
surfactant, polymer, monomer, solvent, etc. may act as chain transfer agents and that
impurities in monomers may act as branching or crosslinking agents. Therefore, it is difficult
to specify the appropriate amounts of added chain transfer agent and branching agent that
will result in a polymer having a desired BV/SV and sedimentation value without knowledge
of the polymerization conditions. Nevertheless, for the purpose of this invention, the general
range of the concentration of chain-transfer agent may range from 0.01% to 5%, and the
branching agent may range from 0.001% to 0.1%.
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For a given polymer, polymerization condition, chain-transfer agent and branching
agent, the optimum ratio of chain transfer agent to branching agent tends to fall in a rather
narrow range. For instance, for the emulsion copolymerization of acrylamide and
acryloxyethyltrimethylammonium chloride in which the branching agent MBA and the chain
6 transfer agent lactic acid are used, the weight ratio of lactic acid to MBA should be in the
range of about 40 to about 90, preferably about 50 to about 80, most preferably about 60
to about 70. ~he ratio tends to be much different if a more efficient chain-transfer agent,
e.g., 2-mercaptoethanol were to be used. Optimum levels of chain-transfer agent and
branching agent may be determined for each type of cationic polymer by routine
experimental methods known to those skilled in the art. For instance, a matrix of
polymerizations encompassing various combinations of different levels of chain transfer
agent and branching agent could be carried out, following by determination of the BV/SV
and sedimentation values of each resulting polymer.
Bulk viscosity (BV) of a polymer is determined by diluting a polymer or polymer
emulsion to a concentration of 0.2% in pure water, stirring to dissolve the polymer, and
measuring the viscosity using a rotating cylinder viscometer, specifically a Brookfield LVT
viscometer, with a #2 spindle at 30 revolutions per minute (rpm). Standard viscosity of a
polymer is determined by dissolving a polymer or polymer emulsion in deionized water, then
adding NaCI solution to give a polymer concentration of 0.1% and a NaCI concentration of
1.0 M, and measuring the viscosity of the polymer solution by using a rotating cylinder
viscometer, specifically a Brookfield LVT viscometer, with a #00 spindle at 60 revolutions
per minute (rpm). In the case of long dissolution times, the pH may need to be adjusted
to be in the range of aboul 3 to about 4 to stabilize the polymer.
A sedimentation value is deter,llilled by first isolating a polymer sample by
precipitating the polymer emulsion or polymer solution into an organic solvent e.g., acetone,
to remove ultraviolet (UV) absorbing substances e.g. surfactants, then collecting and drying
the polymer. A solution of the polymer is then prepared by stirring the isolated polymer in
deionized water until it dissolves and adding NaCI solution to give a polymer solution having
a polymer concentration of 0.05% and a NaCI concentration of 0.001M. Part of thepolymer solution is then centrifuged for about 60 minutes at about 18,000 X G (gravity) and
22~ C, and the UV absorbance, at 215 nanometers (nm), of the uncentrifuged part and of
the supernatant of the centrifuged part are measured. The sedimentation value is equal to
A/~A, which is equal to [AA(uncentrifuged) - AA(centrifuged)] / AA(uncentrifuged), where
AA = A(polymer solution) - A(water) and A is the measured UV absorbance at 215 nm. A
convenient centrifuge is a Labnet ZK380 centrifuge with a fixed angle rotor spinning at
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13,000 rpm and a constant temperature of ZZ~ C. The UV absorbance measurements may
~e performed using a flow-through UV detector (ABI model 875A), drawing the solutions
through the detector using a Harvard syringe pump in a withdraw mode at about 0.5
milliliters per minute. Other types of equipment substantially equivalent to that used herein
are well known to those skilled in the art.
Polymerization may be carried out using microemulsion or emulsion polymerizationtechniques. These techniques are widely known to those skilled in the art. For instance,
emulsion polymerization procedures generally involve the preparation of two phases as
described in U.S. Patent No. 3,284,393, which is incorporated herein by reference. The
aqueous phase is comprised of the monomer(s), branching agent and chain-transfer agent
dissolved in deionized water, and other additives well known to those skilled in the art, such
as stabilizers and pH adjusters. The oil phase usually comprises a water-insoluble
hydrocarbon solution of surfactant(s). The aqueous phase and oil phase are mixed and
homogenized in a conventional apparatus to form an emulsion, sparged with inert gas or
otherwise deoxygenated, then polymerization initiated in the usual manner. Polymerization
may also be carried out by using microemulsion techniques well known in the art as in U.S.
Patent Nos.5,037,881; 4,956,399; 4,956,400; and 4,521,317 which are hereby incorporated
herein by reference.
Polymerization may also be carried out by solution polymerization techniques. The
monomer(s), branching agent, and chain-transfer agent are added to water, deoxygenated
as above, and polymerized by any conventional initiator. Viscous solutions of structured
polymers, useful in the present invention, are produced when the amounts and types of
branching agent and chain transfer agent are selected, via routine experimentation, to
produce polymer with BV/SV of from about 300 to about 500 and sedimentation value of
about 10% or less.
Any conventional additives may be used for stabilization purposes. Suitable
additives include ammonium sulfate, ethylene diaminetetraacetic acid (disodium salt) and
diethylene triaminepentaacetate (pentasodium salt). See Modern Plastics Encyclopedia/88,
McGraw Hill, October 1987, pp. 147-8.
Any conventional initiator may be employed to initiate polymerization, includingthermal, redox and ultraviolet radiation. Suitable for use in this invention areazobisisobutyronitrile; sodium sulfite; sodium metabisulfite; 2,2'-azobis(2-methyl-2-
amidinopropane~ dihydrochloride; ammonium persulfate and ferrous ammonium sulfate
hexahydrate, and the like. Organic peroxides may also be employed for polymerizing
ethylenically unsaturated monomers. A particularly preferred initiator for the purpose of this
CA 02235006 1998-04-16
inven~on is suifur dioxi~eJso~ium ~romate See Modern Plastics ~ncyc!opedia/88, McC3raw
Hill, October 1g87, pp. 165-168.
The product so prepared is a cathnic, high molecular weight, p~lymer that is general.y
solu~le in pure water In wa~ers commonly cncourltered in ~pplication, e.g. harr~ w-ate,s or
5 waters containing varicus amounts o~ min~rals, the palymre7r may br water-swellable. The
poiymers o~ the instant invention are p~rticularly useful as chemical flocculating agents.
The f!occulation and dewa~ring stages cf this invf~ntion, to release water frorn a
dispersion ot suspended solids, are carried out by aoding the cat~onic, branched. high
mo~ .lar weight, w~ter-solu~le or water-swellable, polymeric floc~ulant, either in solution or
0 directly as an ~mulsian or microemulsion, t~ the suspend~d sal5ds. mixing the suspended
solids and polymer to tlccculate ~he solids, and then de~ateriny, preferably u sing a
conventional dewatering app~ratus e.g. centrifu~o, belt press, piston press, tilter, et~. to
temove ~ater from the sus~ensi~n. The producfs of this invention are useful in facilitating a
wide range of solids/liquids separations, ir.c!uding industrial s,ud~e3. dewatering suspende~
1 S solid in wastewater treating applications, for t~e draina~e of c~llulo~ic suspensions suc~ as
tnose found in paper prod~ction, %nd for the settlement of various inorganic suspensions.
The optimum ~GSe of the polymer is de~ermined by routi~e experimentation, well known
to ~flose ski~led in the art. Cationic. wat~r-solubl~ or water-swellable. branche~ pol~m~rs of
the ins,ant invention, llaving ~VJS~ of from about 300 to about 500 and hav~ng a20 sadirnentation value of less than lO~a~ perform su~stantial~y ~etter than p~lymels that d~ nGt
have these BV/SV ar,d se~iment~tion values. For instance, Ta~le 3 shows th~ results ot
labor~tory testing on stispen~ed solids in ~he form of waste a~tiva~e~ s~wa~e slud~e. In thls
tes~, the dewatoring rat~ of the sludge after being flocculate~ ~;th polymer flocculants A
throu~h G is shown as a functlon of polymer dose. The 8VISV values of th~ flccculan~s are
25 shown in Tabl~ 1. Nate that sludges tlocculat~d with polymers B, C, and G, which h~ve B'JJSV
greater than 3Cl~. dewatered si~nificantly taster than ttle slud~es treated with Fo!ymers A, C},
E ~nd F. Tne sludge treated with polymer C dewatered at a rate subst~ntial!y slmilar to the
slu~ges treat~d with polyme~s G and 8, ~Ut a much higher dose o~ polyrner was require~. Th2
sedi,~nl.3t;.~" ~Jalues of p~mers B, ~ and G are shown in Table 2. Note that pclymer C; hac
30 a seaimentation value gre~ter than 1 0~/o. Thus, the poly ners which gave the highest rates of
dew~tering, n~ely p~lymers ~, C and G, all had BV/SV values th~t were in the ran~e of 300
to 500. P~ymers a and G, which dewatered at a dose significant~y lower than C, als~ had
sedim~ntation values below 1 ~C/~ ese
AMENDED St~EE~
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results show that polymers having BV/SV in the range of about 300 to about 500, and
having sedimentation values of 10% or less performed si,~,-iticantly better than polymers
which did not have these BV/SV and sedimentation attributes.
This invention is particularly suitable for dewatering sludge, particularly sludge
comprising biologically treated suspensions. Generally, sludge is any thick, viscous mass,
usually a sediment or filtered waste product. Waste activated sludge refers to sludge which
has undergone aerobic, suspended growth and biological treatment using the metabolic
reactions of microorganisms to produce a high quality effluent by converting and removing
substances having a high oxygen demand. This process for producing waste activated
sludge reduces the concentration of dissolved, particulate and colloidal organic pollutants
in the wastcwdt~r. Additionally, this process also reduces the ammonia concentration in
the wastewater (nil~itication). Ammonia is an inorganic pollutant toxic to aquatic life at high
concentrations and exerts an oxygen demand on the receiving water.
Extended aeration is a waste activated sludge process that retains the waste water
in the aeration tank for 18 hours or more and operates in a medium which deprives the
microorganisms of enough food to support all of them. The microorganisms therefore
compete actively for the limited food supply and even use their own cell mass for food.
This highly competitive situation results in a highly treated effluent with low sludge
production. See Operation of Municipal Wastewater Treatment Plants, Manual of Practice,
MOP 11, Vol 11, 1990, pp.418-419 and 501-516, which is hereby incorporated herein by
reference. As used herein, extended aerated sludge refers to waste activated sludge that
has been subjected to the conditions for extended aeration. Alternatively, for the purposes
of this invention, extended aerated sludge refers to sludge that has similar chemicai and/or
physical characteristics typically associated with extended aerated activated sludge.
26 An aspect of the instant invenffon relates to a method of dewatering sludge. More
preferably, this invention relates to a method of dewatering waste activated sludge. Most
preferably, this invention is directed to a rnethod of dewatering extended aerated sludge.
The following Examples illustrate the present invention. They are not to be
construed to limit the claims in any manner whatsoever.
Polymers A, C, D, E, and F are believed to be copolymers of acrylamide and
cationic monomers and are all available commercially. Polymer A is SD-2081TM, available
commercially from Cytec Industries, Inc. Polymer C is EM840TPDTM, available commercially
from SNF Floerger. Polymer D is Percol 778FS25TM, Polymer E is Percol 778FS40TM, and
12
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Polymer F is Percol 775FS25TM; all are available commercially from Allied Colloids, Inc.
Example 1
Preparation of polymer G: An aqueous phase was prepared by mixing together the
following: 210 parts 50% aqueous acrylamide, 238.74 parts 80%
~ 5 acryloxyethyltrimethylammonium chloride, t 20 parts deionized water,17.76 parts citric acid,
0.74 parts 40% diethylenetriaminepentaacetic acid, pentasodium salt (chelating agent),0.67
parts 89% lactic acid (chain-transfer agent), 0.0089 parts methylenebisacrylamide
(branching agent), and 0.015 parts sodium bromate. The pH was adjusted to about 3.5
using 2.3 parts 29% aqueous ammonia, then deionized water was added to give a total of
612 parts.
An oil phase was prepared by adding 11.13 parts of sorbitan monooleate and 10.29parts of a nonionic surfactant made of ethoxylated linear alcohols, HLB = 12.0, to 148.58
parts of a paraffinic solvent (mixture of branched and cyclic hydrocarbons, boiling point
range of 408 to 442 F) in a mixing vessel. The aqueous phase was added to the oil phase
with mixing; the crude emulsion was then mechanically homogenized to give a monomer
emulsion. The monomer emulsion was transferred to suitable reaction vessel equipped with
stirring means, gas dip tube, vent line and thermometer; the mixing vessel was rinsed with
10 parts of paraffinic solvent, which was also added to the emulsion. The mixture was
sparged with nitrogen for 30 minutes.
The polymerization was initiated at 24~ C using sulfur dioxide gas (4000 ppm in
nitrogen); the flow rate was conl,~"~d such that the mixture exothermed to 40~ C over a
35 minute period; a temperature of 40-42~ C was then maintained by active cooling of the
reaction vessel, as the sulfur dioxide flow rate was graduaily increased over a 20 minute
period. After the exotherm had completed, the temperature was maintained at 40-42~ C
for 3.5 hours by heating. After the polymerization was complete, the nitrogen and sulfur
dioxide were turned off. About 8.0 parts of a nonionic surfactant made of ethoxylated linear
alcohols, HLB = 12.0, was added over a 15 minute period; the emulsion was allowed to mix
for 1.5 hours and cool to ambient temperature.
Example 2
Preparation of polymer B: An aqueous phase was prepared by mixing together the
following: 13413 parts 52.5% aqueous acrylamide, 13200 parts 80%
13
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acryloxyethyltrimethylammonium chloride, 7643 parts deionized water, 151 parts 17%
sulfuric acid, 18 parts 40% ethylenediaminetetraacetic acid, disodium salt, 650 parts
isopropanol (chain-transfer agent), 0.44 parts methylenebisacrylamide, and 1 part 70% t-
butylhydroperoxide.
An oil phase was prepared by adding 572 parts of a surfactant containing
predominately dihydroxyethyl oleamide and 308 parts of polyoxyethylene monooleate, ~ILB
= 11.4, to 12814 parts of a paraffinic solvent (mixture of branched and cyclic hydrocarbons,
boiling point range of 408 - 442~ F) in a mixing vessel. The aqueous phase was added to
the oil phase with mixing; the crude emulsion was homogenized to give a monomer
emulsion. The monomer emulsion was transferred to suitable reaction vessel equipped with
stirring means, gas dip tube, vent line and thermometer. The mixture was sparged with
nitrogen for 30 minutes.
The polymerization was initiated at 24~ C using sulfur dioxide gas (4000 ppm in
nitrogen); the flow rate was controlled such that the mixture exothermed to 40~ C over a
35 minute period; a temperature of 40 to 42~ C was then maintained by active cooling of
the reaction vessel, as the sulfur dioxide flow rate was gradually increased over a 20 minute
period. After the exotherm had completed, the temperature was maintained at 40 to 42~
C for 3.5 hours by heating. After the polymerization was complete, the nitrogen and sulfur
dioxide were turned off. About 940 parts of polyoxyethylene monooleate, HLB = 11.4 were
added over a 15 minute period; the emulsion was allowed to mix for 1.5 hours and cool to
ambient temperature.
EA~ S 3-1 6
Bulk viscosities (BV) of Polymers A through G were determined as follows:
Polymer or polymer emulsion was diluted in deionized water and stirred until the polymer
dissolved, so that the polymer concentration was 0.2%. The bulk viscosity (BV) was
determined at 25~ C + 1~ C using a Brookfield viscometer (LVT model) with a #2 spindle
at 30 rpm.
Standard viscosities (SV) of Polymers A through G were determined as follows:
Polymer or polymer emulsion was diluted in deionized water and stirred until the polymer
dissolved, then NaCI solution added so that the polymer concentration was 0.1 % and the
NaCI concentration was 1.0 M. The standard viscosity (SV) was determined at 25~ C +
1 ~ C using a Brookfield viscometer ~LVT model) with a #00 spindle at 60 rpm. The BV, SV
and BV/SV of Polymers A-G are shown in Table 1. In the case of long dissolution times,
14
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e.g overnight, the pH was adjusted to be in the range of about 3 to about 4 to st~hili~e the
polymer.
Table 1
Polymer BV, centipoise SV, centipoise BV/SV
A~ 453 3.32 136
B 708 2.09 339
C~ 585 1.53 382
D* 284 2.37 120
E~ 411 2.29 179
F~ 397 2.42 164
G 705 1.94 363
Comparative Examples
Examples 17-19
The sedimentation values of Polymers B, C, and G were determined as follows:
15 Hydrocarbon oil was added to the polymer emulsions to reduce the viscosity of the
emulsion, and the emuisions were added dropwise, with stirring, to an excess of acetone
to precipitate the polymer. The polymer was collected and dried. A polymer solution was
prepared by stirring the dried polymer in deionized water until it dissolved, then adding NaCI
solution to give a polymer solution having a polymer concentration of 0.05% and a NaCI
20 concenl,~lion of 0.001M. In the case of long ~~sSo~.ltion times, e.g overnight, the pH was
adjusted to be in the range of about 3 to about 4 to stabilize the polymer. Part of the
solution was centrifuged for about 60 minutes at about 18,000 X G and 22~ C. The
ultraviolet (UV) absorbance, at 215 nanometers (nm), of the uncentrifuged part and of the
supernatant of the centrifuged part were determined. The sedimentation value is e~ual to
25 ~A/AA, which is equal to ~f~A(ullcer,l"fl-ged) - /~A(centrifuged)] / AA(uncentrifuged), where
~A = A(polymer solution) - A(water) and A is the absorbance value measured by UV
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absorbance at 215 nm. A Labnet ZK380 centrifuge with a fixed angle rotor was used,
spinning at 13,000 rpm and at a constant temperature of 22~ C. The UV absorbancemeasurements were performed using a flow-through UV detector (ABI model 875A),
drawing the solutions through the detector using a Harvard syringe pump in a withdraw
5 mode at about 0.5 milliliters per minute. The sedimentation values of Polymers B, C and
G are shown in Table 2.
Table 2
Polymer Sedimentation
Value
B 0
C~ 23
G 3
Comparative Examples
16
CA 0223~006 1998-04-16
Examples 2~-26
So~uticns o~ Polyf~rs A through G were prepi~red i~t polym~r ~oncentration of ~.2%.
Various amounts of polymer solutians wer6 m~x~d with 200 gram samples of suspended sc~id~
(waste activ~te~ sew~e sludge, about 1 .~~,~o sali~s) ~.o achieve a range of polymer 'dos~s."
5 The polymerlsludge mixtures were s'tirred ~igorously an~ ~iltere~ throuigh a ~l~nnel ~iitte~ with
a 3~ mesh stalnless str~l screen. Tha volume in rnillilit~rs ~ml ) of water dr2inin~ throug~ the
screen during the first ten se~ionds oF filtration was reciorded ~s the drainia~e ~o!ume. Th~
dose and dra~na~e volurne for e~cll polymer are given ~n Ta~ie 3. The ~rainage vo~ume l~f
each sample of each polymer is shown ir~ T~b!e 3 ~s a f:~nction of the polymer close. where
10 the dose is in units Ct pounds of polymer per d~ t~n o' sludg~ so~ids. ~ hi~h dr~inage ~olume
means th2~ ~he sl~id~e dewatered rapid~y. Ta~l~ 3 ~how~ii th~t ;'Giymers B and G both
flaccl!!ated ~he susp~nded sewag~ slud~e solids more efficiently thi~n the other polyr;~ers,
giving highef dewatering ~a~as than Polymers A, ), E, and F, an~ giving ~ubstaf~tial~y
e~uiva'ent perrormance tc PGjYnnerC, ~l;t at much lower pol~mer do~es ~han Polyrner C.
lr~~
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Table 3
Polymer Dose (poundstdry ton) Drainage Volume (mL)
A* 3.4 89
6.7 109
10.1 107
13.4 112
16.8 108
B 10.1 t~
13.4 154
16.8 154
20.2 1 65
C* 13.4 117
16.8 160
20 ~ 166
23.5 1 68
26.9 1 66
D* 6.7 114
10.1 1 2:;'
13.4 127
16.8 133
~:~.5 1 32
F~ 6.7 101
10.1 114
13.4 119
16.8 124
26.9 109
F* 3.4 P'~
6.7 1 24
10.1 128
16.8 ' 120
G 6.7 87
10.1 140
13.4 161
16.8 165
* Comparative Examples
18
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E~..., ' s 27-33
Solutions of Polymers A through G were prepared at polymer concentration of 0.2%.
Various amounts of polymer solutions were mixed with 200 gram samples of suspended
solids (extended aerated sewage sludge) to achieve a range of polymer "doses." The
5 polymer/sludge mixtures were stirred vigorously and filtered through a funnel fitted with a
35 mesh stainless steel screen. The volume in milliliters (mL) of water draining through the
screen during the first ten seconds of filtration was recorded as the drainage volume.
Polymers B and G both flocc~ ted the suspended extended aerated sewage sludge solids
more efficiently than the other polymers, giving higher dewatering rates than Polymers A,
10 D, E, and F, and giving substantially equivalent performance to Polynner C, but at much
lower polymer doses than Polymer C.
~ ' . . 1g
