Title of Invention

A method of conditioning mixed liquor in a membrane biological reactor

Abstract A method of conditioning mixed liquor having a mixed liquor suspended solids loading of about 5 g/L to about 30 g/L in a membrane biological reactor comprising adding to the mixed liquor an effective coagulating and flocculating amount of one or more water soluble cationic, antiphoteric or zwitterionic polymers, or combination thereof.
Full Text METHOD OF USING WATER SOLUBLE POLYMERS IN A MEMBRANE
BIOLOGICAL REACTOR
TECHNICAL FIELD
This invention concerns the use of water soluble cationic, amphoteric or
zwitterionic polymers to condition mixed liquor in membrane biological reactors
resulting in reduced fouling and increased water flux through the membrane. This
invention is also a method of using the polymers to reduce sludge production in the
bioreactor.
BACKGROUND OF THE INVENTION
Biological treatment of wastewater for removal of dissolved organics is well
known and is widely practiced in both municipal and industrial plants. This aerobic
biological process is generally known as the "activated sludge" process in which micro-
organisms consume the organic compounds through their growth. The process
necessarily includes sedimentation of the micro-organisms or "biomass" to separate it
from the water and complete the process of reducing Biological Oxygen Demand
(BOD) and TSS (Total Suspended Solids) in the final effluent. The sedimentation step
is typically done in a clarifier unit. Thus, the biological process is constrained by the
need to produce biomass that has good settling properties. These conditions are
especially difficult to maintain during intermittent periods of high organic loading and
the appearance of contaminants that are toxic to the biomass.
Typically, this activated sludge treatment has a conversion ratio of organic
materials to sludge of about 0.5 kg sludge/kg COD (chemical oxygen demand), thereby
resulting in the generation of a considerable amount of excess sludge that must to be
disposed of. The expense for the excess sludge treatment has been estimated at 40-60
percent of the total expense of wastewater treatment plant. Moreover, the conventional
disposal method of landfilling may cause secondary pollution problems. Therefore,
interest in methods to reduce the volume and mass of the excess sludge has been
growing rapidly.
Membranes coupled with biological reactors for the treatment of wastewater are
well known, but are not widely practiced. In these systems, ultrafiltration (UF),
microfiltration (MF) or nanofiltration (NF) membranes replace sedimentation of
biomass for solids-liquid separation. The membrane can be installed in the bioreactor
tank or in an adjacent tank where the mixed liquor is continuously pumped from the
bioreactor tank and back producing effluent with much lower total suspended solids
(TSS), typically less than 5 mg/L, compared to 20 to 50 mg/L from a clarifier. More
importantly, MBRs (membrane biological reactors) de-couple the biological process
from the need to settle the biomass, since the membrane sieves the biomass from the
water. This allows operation of the biological process at conditions that would be
untenable in a conventional system including: 1) high MLSS (bacteria loading) of 10-30
g/L, 2) extended sludge retention time, and 3) short hydraulic retention time. In a
conventional system, such conditions could lead to sludge bulking and poor
settleability.
The benefits of the MBR operation include low sludge production, complete
solids removal from the effluent, effluent disinfection, combined COD, solids and
nutrient removal in a single unit, high loading rate capability, no problems with sludge
bulking, and small footprint. Disadvantages include aeration limitations, membrane
fouling, and membrane costs.
Membrane costs are directly related to the membrane area needed for a given
volumetric flow through the membrane, or "flux." Flux is expressed as liters/hour/m2
(LMH) or gallons/day/ft (GFD). Typical flux rates vary from approximately 10 LMH
to about 50 LMH. These relatively low flux rates, due largely to fouling of the
membranes, have slowed the growth of MBR systems for wastewater treatment.
The MBR membrane interfaces with so-called "mixed liquor" which is
composed of water, dissolved solids such as proteins, polysaccharides, suspended solids
such as colloidal and particulate material, aggregates of bacteria or "flocs", free
bacteria, protozoa, and various dissolved metabolites and cell components. In
operation, the colloidal and particulate solids and dissolved organics deposit on the
surface of the membrane. Colloidal particles form layer on the surface of the
membrane called a "cake layer." Cake layer formation is especially problematic in
MBRs operated, in the "dead end" mode where there is no cross flow; i.e., flow
tangential to the membrane. Depending on the porosity of the cake layer, hydraulic
resistance increases and flux declines.
In addition to the cake formation on the membrane, small particles can plug the
membrane pores, a fouling condition that may not be reversible. Compared to a
conventional activated sludge process, floc (particle) size is reportedly much smaller in
typical MBR units. Since MBR membrane pore size varies from about 0.04 to about
0.4 micrometers, particles smaller than this can cause pore plugging. Pore plugging
increases resistance and decreases flux.
Therefore, there is an ongoing need to develop improved methods of
conditioning the mixed liquor in MBR units to increase flux and reduce fouling of the
i membranes.
SUMMARY OF THE INVENTION
Polymeric water-soluble coagulants and flocculants have not been used in MBR
units, as it is generally understood that excess polymer fouls membrane surfaces,
resulting in dramatic decreases in membrane flux.
However, we have discovered that using certain water soluble cationic,
amphoteric and zwitterionic polymers in the MBR to coagulate and flocculate the
biomass in the mixed liquor and to precipitate the soluble biopolymer substantially
reduces fouling of the membrane and can result in an increase of up to 500 percent in
membrane flux while leaving virtually no excess polymer in the treated wastewater at
the effective dose. This increase in membrane flux permits the use of smaller systems,
with a concomitant reduction in capital costs, or alternatively, increases treated
wastewater volumetric flow from an existing system, with a corresponding reduction in
cost of operation.
Accordingly, this invention is a method of conditioning the mixed liquor in a
membrane biological reactor comprising adding to the mixed liquor an effective
coagulating and flocculating amount of one or more water soluble cationic, amphoteric
or zwitterionic polymers, or combination thereof.
In another aspect, this invention is a method of clarifying wastewater in a
membrane biological reactor where microorganisms consume organic material in the
wastewater to form a mixed liquor comprising water, the microorganisms and dissolved
and suspended solids comprising
(i) adding to the mixed liquor an effective coagulating and flocculating amount of
one or more cationic, amphoteric or zwitterionic polymers, or a mixture thereof, to form
a mixture comprising water, the microorganisms and coagulated and flocculated solids;
and
(ii) separating clarified water from the microorganisms and the coagulated and
flocculated solids by filtration through a membrane.
In another aspect, this invention is a method of preventing fouling of a filtration
membrane in a membrane biological reactor where microorganisms consume organic
material in the wastewater in a mixed liquor comprising water, the microorganisms and
dissolved, colloidal and suspended solids and wherein clarified water is separated from
the mixed liquor by filtration through the filtration membrane comprising adding to the
mixed liquor an amount of one or more cationic, amphoteric or zwitterionic polymers,
or a combination thereof, sufficient to prevent fouling of the membrane.
In another aspect, this invention is a method of enhancing flux through a
filtration membrane in a membrane biological reactor where microorganisms consume
organic material in the wastewater in a mixed liquor comprising water, the
microorganisms and dissolved, colloidal and suspended solids and wherein clarified
water is separated from the mixed liquor by filtration through the filtration membrane
comprising adding to the mixed liquor an effective flux enhancing amount of one or
more cationic, amphoteric or zwitterionic polymers, or a combination thereof.
In another aspect, this invention is a method of reducing sludge formation in a
membrane biological reactor where microorganisms consume organic material in the
wastewater to form a mixed liquor comprising water, the microorganisms and a sludge
comprising dissolved, colloidal and suspended solids and wherein clarified water is
separated from the mixed liquor by filtration through a membrane comprising
1) adding to the mixed liquor an effective coagulating and flocculating amount of
one or more cationic, amphoteric or zwitterionic polymers, or a combination thereof;
and
2) increasing the concentration of microorganisms in the mixed liquor.
In another aspect, this invention is a method of reducing sludge formation in a
membrane biological reactor where microorganisms consume organic material in the
wastewater to form a mixed liquor comprising water, the microorganisms and a sludge
comprising dissolved, colloidal and suspended solids and wherein clarified water is
separated from the mixed liquor by filtration through a membrane comprising
1) adding to the mixed liquor an effective coagulating and flocculating amount of
one or more cationic, amphoteric or zwitterionic polymers, or a combination thereof;
and
2) increasing the amount of time that the microorganisms remain in contact with
the wastewater.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram of a typical membrane bioreactor system for the
biological treatment of wastewater comprising an aeration tank 1, submerged
membrane module 2, suction pump 3, aeration means 4 for membrane scouring,
aeration means 5 for the bioreaction and optional sludge disintegrator 6.
Figure 2 shows sludge build-up curves calculated by simultaneously solving
Equations 1 and 2 below. The parameters and constants used in this calculation were
summarized in Tables 1 and 2. The sludge production rate at a particular mixed liquor
suspended solids (MLSS) value (for example 18,000 mg L-1) can be obtained from the
slope of a tangent line. Therefore 'zero slope' means 'no sludge production'.
In Figure 2, the slope of tangent line 1) decreases with higher hydraulic
retention time (HRT) while MLSS is constant and 2) decreases with higher MLSS while
HRT is constant. For the first case, in which MLSS is constant, for example 14,000
mg/L, no excess sludge will be produced by increasing the HRT to 12 hours. For the
second case in which HRT is fixed, for example 10 hours, no sludge will be produced
by increasing the MLSS to 17,000 mg/L.
Sludge retention time (SRT) is calculated by dividing the total amount of sludge
in the bioreactor (kg) by sludge removal rate (kg/day). Therefore SRT will increase
with less excess sludge production until it finally becomes 'infinite' without excess
sludge production.
In a biological wastewater treatment process, microorganisms in the bioreactor
grow with the consumption of organic substrate contained in wastewater. In addition,
the microorganisms respire endogenously, consuming themselves. These phenomena
are described by Eq (1), where microbial growth is expressed by the Monod equation
minus endogenous respiration represented by the first order kinetic equation ( kd x) on
the far the right side of the equation.
Here, nm is the maximum specific growth rate (day1), Ks is the half saturation
constant (mg L-1), kd is the endogenous decay constant (day-1), Se is the substrate
concentration in mixed liquor (mg L-1), x is the MLSS (mg L-1) and t is the time
(days).
While microorganisms are growing, the majority of the substrate (organic
pollutants in the influent) is consumed and some is going out with effluent. This
balance can be described as Eq (2) where the first term on the right side expresses the
organic mass balance between influent and effluent and the second term substrate
consumption by microorganisms.
Where Q is the influent flow rate (m3 day-1) and Y is the yield coefficient (kg
MLSS kg COD-1), V is the reactor volume (m3) and 5, is the influent COD (mg L-1). All
constants and parameters used in the foregoing calculations are summarized in Tables 1
and 2.
1Nagaoka H., Yamanishi S. and Miya A. (1998) Modeling of biofouling by extracellular polymers in a
membrane separation activated sludge system. Water Science and Technology 38(4-5) 497-504.
2Henze M., Grady C.P.L., Gujer W., Marais G.V.R. and Matsuo T. (1987) A general model for single-
sludge wastewater treatment systems. Water Research 21(5) 505-515.
3Grady C.P. L., Daigger G.T. and Lim H.C., (1999) Biological Wastewater Treatment. pp61 -125, Marcel
Dekker, NY.
DETAILED DESCRIPTION OF THE INVENTION
Definitions of Terms
As used herein, the following abbreviations and terms have the following
meanings:
AcAm for acrylamide; DMAEA BCQ for dimethylaminoethylacrylate benzyl chloride
quaternary salt; DMAEA MCQ for dimethylaminoethylacrylate methyl chloride
quaternary salt; Epi-DMA for epichlorohydrin-dimethylamine; DADMAC for
diallyldimethylammonium chloride; pDADMAC for poly(diallyldimethylammonium
chloride); and PEI for polyethyleneimine.
"Amphoteric polymer" means a polymer derived from both cationic monomers
and anionic monomers, and, possibly, other non-ionic monomer(s). Amphoteric
polymers can have a net positive or negative charge. Representative amphoteric
polymers include acrylic acid/DMAEA MCQ copolymer, DADMAC/acrylic acid
copolymer, DADMAC/acrylic acid/acrylamide terpolymer, and the like.
The amphoteric polymer may also be derived from zwitterionic monomers and
cationic or anionic monomers and possibly nonionic monomers. Representative
amphoteric polymers containing zwitterionic monomers include DMAEA MCQ/N,N-
dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine copolymer,
acrylic acid/N,N-dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-arnmonium
betaine copolymer, DMAEAMCQ/Acrylic acid/N,N-dimethyl-N-
methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine terpolymer, and the like.
"Anionic monomer" means a monomer as defined herein which possesses a
negative charge above a certain pH range. Representative anionic monomers include
acrylic acid, and it's salts, including, but not limited to sodium acrylate, and ammonium
acrylate, methacrylic acid, and it's salts, including, but not limited to sodium
methacrylate, and ammonium methacrylate,
2-acrylamido-2-methylpropanesuIfonic acid (AMPS), the sodium salt of AMPS,
sodium vinyl sulfonate, styrene sulfonate, maleic acid, and it's salts, including, but not
limited to the sodium salt, and ammonium salt, sulfonate, itaconate, sulfopropyl
acrylate or methacrylate or other water-soluble forms of these or other polymerisable
carboxylic or sulphonic acids. Sulfomethylated acrylamide, allyl sulfonate, sodium
vinyl sulfonate, itaconic acid, acrylamidomethylbutanoic acid, fumaric acid,
vinylphosphonic acid, vinylsulfonic acid, allylphosphonic acid, sulfomethylated
acrylamide, phosphonomethylated acrylamide, and the like.
"Cationic polymer" means a polymer having an overall positive charge. The
cationic polymers of this invention include polymers composed entirely of cationic
monomers and polymers composed of cationic and nonionic monomers. Cationic
polymers also include condensation polymers of epichlorohydrin and a dialkyl
monoamine or polyamine and condensation polymers of ethylenedichloride and
ammonia or formaldehyde and an amine salt. Cationic polymers of this invention
include solution polymers, emulsion polymers, dispersion polymers and structurally
modified polymers as described in PCT US01/10867.
"Cationic monomer" means a monomer which possesses a net positive charge.
Representative cationic monomers include dialkylaminoalkyl acrylates and
methacrylates and their quaternary or acid salts, including, but not limited to,
dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl
acrylate methyl sulfate quaternary salt, dimethyaminoethyl acrylate benzyl chloride
quaternary salt, dimethylaminoethyl acrylate sulfuric acid salt, dimethylaminoethyl
acrylate hydrochloric acid salt, dimethylaminoethyl methacrylate methyl chloride
quaternary salt, dimethylaminoethyl methacrylate methyl sulfate quaternary salt,
dimethylaminoethyl methacrylate benzyl chloride quaternary salt, dimethylaminoethyl
methacrylate sulfuric acid salt, dimethylaminoethyl methacrylate hydrochloric acid salt,
dialkylaminoalkylacrylamides or methacrylamides and their quaternary or acid salts
such as acrylamidopropyltrimethylammonium chloride, dimethylaminopropyl
acrylamide methyl sulfate quaternary salt, dimethylaminopropyl acrylamide sulfuric
acid salt, dimethylaminopropyl acrylamide hydrochloric acid salt,
methacrylamidopropyltrimethylammonium chloride, dimethylaminopropyl
methacrylamide methyl sulfate quaternary salt, dimethylaminopropyl methacrylamide
sulfuric acid salt, dimethylaminopropyl methacrylamide hydrochloric acid salt,
diethylaminoethylacrylate, diethylarninoethylrnethacrylate, diallyldiethylammonium
chloride and diallyldimethyl ammonium chloride. Alkyl groups are generally C1-4
alkyl.
"Conditioning" means precipitating soluble biopolymer and coagulating and
flocculating the particulate and colloidal organic material in the mixed liquor to form
larger aggregates of particles, resulting in an increase in flux through the membrane
bioreactor filtration membrane and a reduction of fouling of the membrane.
"Hydraulic retention time" (HRT) means the time the wastewater stays in the
bioreactor. It is obtained by dividing the total volume of the bioreactor by the influent
flow rate.
"Mixed Liquor" or "sludge" means a mixture of wastewater, microorganisms
used to degrade organic materials in the wastewater, organic-containing material
derived from cellular species, cellular by-products and/or waste products, or cellular
debris. Mixed liquor can also contain colloidal and particulate material (i.e. biomass /
biosolids) and/ or soluble molecules or biopolymers (i.e. polysaccharides, proteins,
etc.).
"Mixed liquor suspended solids" (MLSS) means the concentration of biomass
which is treating organic material, in the mixed liquor.
"Monomer" means a polymerizable allylic, vinylic or acrylic compound. The
monomer may be anionic, cationic or nonionic. Vinyl monomers are preferred, acrylic
monomers are more preferred.
"Nonionic monomer" means a monomer which is electrically neutral.
Representative nonionic monomers include acrylamide, methacrylamide, N-
methylacrylamide,
N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-
isopropyl(meth)acrylamide,
N,N-butyl(meth)acrylamide, N-(2-hydroxypropyl)methacrylamide, N-
methylolacrylamide,
N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, poly(ethylene
glycol)(meth)acrylate, polyethylene glycol) monomethyl ether mono(meth)acryate,
N-vinyl-2-pyrrolidone, glycerol mono((meth)acrylate), 2-hydroxyethyl(meth)acrylate,
2-hydroxypropyl(meth)acrylate, vinyl methylsulfone, vinyl acetate,
glycidyl(meth)acrylate, and the like.
"Prevention" includes both preventing and inhibiting.
"Sludge Retention time" (SRT) means the amount of time that microorganisms,
which roughly approximates sludge, remain inside the bioreactor. SRT is calculated by
dividing the total sludge in the bioreactor by the sludge removal rate.
"Zwitterionic monomer" means a polymerizable molecule containing cationic
and anionic (charged) functionality in equal proportions, so that the molecule is net
neutral overall. Representative zwitterionic monomers include N,N-dimethyl-N-
acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl -N-
acrylamidopropyl-N-(2-carboxyrnethyI)-ammonium betaine,
N,N-dimethyl-N-acrylamidopropyl-N-(3-sulfopropyl)-arnmonium betaine, N,N-
dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine
(DMMAPSB), N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium
betaine, 2-(methylthio)ethyl methacryloyl-S-(sulfopropyl)-sulfonium betaine, 2-[(2-
acryloylethyl)dimethylammonio]ethyl 2-methyl phosphate, 2-(acryloyloxyethyl)-2'-
(trimethylammonium)ethyl phosphate, [(2-acryloylethyl)dimethylammonio]rnethyl
phosphonic acid, 2-methacryloyloxyethyl phosphorylcholine (MPC), 2-[(3-
acrylamidopropyl)dimethylammonio]ethyl 2'-isopropyl phosphate (AAPI), 1-vinyl-3-
(3-sulfopropyl)imidazolium hydroxide, (2-acryloxyethyl) carboxymethyl
methylsulfonium chloride, 1-(3-sulfopropyl)-2-vinylpyridinium betaine, N-(4-
sulfobutyl)-N-methyl-N,N-diallylamine ammonium betaine (MDABS), N,N-diallyl-N-
methyl-N-(2-suIfoethyl) ammonium betaine, and the like. A preferred zwitterionic
monomer is N,N-dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium
betaine.
"Zwitterionic polymer" means a polymer composed from zwitterionic
monomers and, possibly, other non-ionic monomer(s). Representative zwitterionic
polymers include homopolymers such as the homopolymer of N,N-dimethyl-N-(2-
acryloyloxyethyl)-N-(3-sulfopropyl) ammonium betaine, copolymers such as the
copolymer of acrylamide and N,N-dimethyl-N-(2-acryloyloxyethyl)-N-(3-sulfopropyl)
ammonium betaine, and terpolymers such as the terpolymer of acrylamide, N-vinyl-2-
pyrrolidone, and 1-(3-sulfopropyl)-2-vinylpyridinium betaine. In zwitterionic
polymers, all the polymer chains and segments within those chains are rigorously
electrically neutral. Therefore, zwitterionic polymers represent a subset of amphoteric
polymers, necessarily maintaining charge neutrality across all polymer chains and
segments because both anionic charge and cationic charge are introduced within the
same zwitterionic monomer.
"Reduced Specific Viscosity" (RSV) is an indication of polymer chain length
and average molecular weight. The RSV is measured at a given polymer concentration
and temperature and calculated as follows:
wherein ? = viscosity of polymer solution;
?0 = viscosity of solvent at the same temperature; and
c = concentration of polymer in solution.
As used herein, the units of concentration "c" are (grams/100 ml or g/deciliter).
Therefore, the units of RSV are dl/g. The RSV is measured at 30 °C. The viscosities ?
and ?0 are measured using a Cannon-Ubbelohde semimicro dilution viscometer, size
75. The viscometer is mounted in a perfectly vertical position in a constant temperature
bath adjusted to 30 ± 0.02 °C. The error inherent in the calculation of RSV is about 2
dl/g. Similar RSVs measured for two linear polymers of identical or very similar
composition is one indication that the polymers have similar molecular weights,
provided that the polymer samples are treated identically and that the RSVs are
measured under identical conditions.
IV stands for intrinsic viscosity, which is RSV in the limit of infinite polymer
dilution (i.e. the polymer concentration is equal to zero). The IV, as used herein, is
obtained from the y-intercept of the plot of RSV versus polymer concentration in the
range of 0.015-0.045 wt% polymer.
Preferred Embodiments
The water soluble cationic, amphoteric or zwitterionic polymers of this
invention are added to the MBR unit to promote the incorporation of colloidal panicles,
such as cell fragments and single bacterium, into aggregate or floc structures and/or to
increase the porosity of the cake layer. The water soluble polymers may be solution
polymers, latex polymers, dry polymers or dispersion polymers.
"Latex polymer" means an invertible water-in-oil polymer emulsion comprising
a cationic, amphoteric or zwitterionic polymer according to this invention in the
aqueous phase, a hydrocarbon oil for the oil phase, a water-in-oil emulsifying agent
and, potentially, an inverting surfactant. Inverse emulsion polymers are hydrocarbon
continuous with the water-soluble polymers dispersed as micron sized particles within
the hydrocarbon matrix. The latex polymers are then "inverted" or activated for use by
releasing the polymer from the particles using shear, dilution, and, generally, another
surfactant, which may or may not be a component of the inverse emulsion.
The preparation of water-in-oil emulsion polymers has been described in, for
example, U.S. Patent Nos. 2,982,749; 3,284,393; and 3,734,873. See also Hunkeler et
al., "Mechanism, Kinetics and Modeling of the Inverse-Microsuspension
Homopolymerization of Acrylamide", Polymer (1989). 30(1), 127-42; and Hunkeler et
al., "Mechanism, Kinetics and Modeling of Inverse-Microsuspension Polymerization: 2.
Copolymerization of Acrylamide with Quaternary Ammonium Cationic Monomers",
Polymer (1991), 32(14), 2626-40.
Latex polymers are prepared by dissolving the desired monomers in the aqueous
phase, dissolving the emulsifying agent(s) in the oil phase, emulsifying the water phase
in the oil phase to prepare a water-in-oil emulsion, in some cases, homogenizing the
water-in-oil emulsion, polymerizing the monomers dissolved in the water phase of the
water-in-oil emulsion to obtain the polymer as a water-in-oil emulsion. If so desired, a
self-inverting surfactant can be added after the polymerization is complete in order to
obtain the water-in-oil self-inverting emulsion.
"Dispersion polymer" means a water-soluble polymer dispersed in an aqueous
continuous phase containing one or more inorganic/organic salts. Representative
examples of polymers prepared by dispersion polymerization of water-soluble
monomers in an aqueous continuous phase are found in, for example U.S. Patent Nos.
4,929,655; 5,006,590; 5,597,859; and 5,597,858, in European Patent Nos. 657,478; and
630,909 and in PCT/US01/09060.
A general procedure for the manufacture of dispersion polymers is as follows.
The types and quantities of specific components in the formula (salts and stabilizer
polymers, for example) will vary depending upon the particular polymer that is being
synthesized.
An aqueous solution containing one or more inorganic salts, one or more
monomers and any additional water-soluble monomers, any polymerization additives
such as chelants, pH buffers, chain transfer agents, branching or cross-linking agents
and one or more water-soluble stabilizer polymers is charged to a reactor equipped with
a mixer, a thermocouple, a nitrogen purging tube, and a water condenser.
The monomer solution is mixed vigorously, heated to the desired temperature,
and then a water-soluble initiator is added. The solution is purged with nitrogen while
maintaining temperature and mixing for several hours. After this time, the products are
cooled to room temperature, and any post-polymerization additives are charged to the
reactor. Water continuous dispersions of water-soluble polymers are free flowing
liquids with product viscosities generally 100-10,000 cP, measured at low shear.
"Solution polymer" means a water soluble polymer in a water continuous
solution.
In a solution polymerization process, one or more monomers are added to a
vessel followed by neutralization with a suitable base. Water is then added to the
reaction vessel, which is then heated and purged. Polymerization catalysts may also be
added to the vessel initially or fed in gradually during the course of the reaction. Water
soluble polymerization initiators such as any azo or redox initiator or combination
thereof are added along with the monomer solution to the reaction mixture in separate
feeds over the same amount of time. Heating or cooling may be used as necessary to
control the reaction rate. Additional initiator may be used after addition is complete to
reduce residual monomer levels.
"Dry polymer" means a polymer prepared by gel polymerization. In a gel
polymerization process, an aqueous solution of water-soluble monomers, generally 20-
60 percent concentration by weight, along with any polymerization or process additives
such as chain transfer agents, chelants, pH buffers, or surfactants, is placed in an
insulated reaction vessel equipped with a nitrogen purging tube. A polymerization
initiator is added, the solution is purged with nitrogen, and the temperature of the
reaction is allowed to rise uncontrolled. When the polymerized mass is cooled, the
resultant gel is removed from the reactor, shredded, dried, and ground to the desired
particle size.
In a preferred aspect of this invention, the water soluble cation ic, amphoteric or
zwirterionic polymers have a molecular weight of about 2,000 to about 10,000,000
dalton.
In another preferred aspect, the cationic polymer is a copolymer of acrylamide
and one or more cationic monomers selected from diallyldimethylammonium chloride,
dimethylaminoethylacrylate methyl chloride quaternary salt,
dimethylaminoethylmethacrylate methyl chloride quaternary salt and
dimethylaminoethylacrylate benzyl chloride quaternary salt.
In another preferred aspect, the cationic polymer has a cationic charge of at least
about 5 mole percent.
In another preferred aspect, the cationic polymer is diallyldimethylammonium
chloride/acrylamide copolymer.
In another preferred aspect, the amphoteric polymer is selected from
dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylic acid copolymer,
diallyldimethylammonium chloride/acrylic acid copolymer, dimethylaminoethyl
acrylate methyl chloride salt N,N-dimethyl-N-methacryamidopropyl-N-(3-sulfopropyl)-
ammonium betaine copolymer, acrylic acid N,N-dimethyl-N-methacrylamidopropyl-N-
(3-sulfopropyl)-ammonium betaine copolymer and DMAEAMCQ/Acrylic acid N,N-
dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine terpolymer.
In another preferred aspect, the amphoteric polymer has a molecular weight of
about 5,000 to about 2,000,000 dalton.
In another preferred aspect, the amphoteric polymer has a cationic charge
equivalent to anionic charge equivalent ratio of about 0.2:9.8 to about 9.8:0.2.
In another preferred aspect, the cationic polymer has a cationic charge of 100
mole percent.
In another preferred aspect, the cationic polymer has a molecular weight of
about 2,000 to about 500,000 dalton.
In another preferred aspect, the cationic polymer is selected from the group
consisting of polydiallyldimethylammonium chloride, polyethyleneimine,
polyepiamine, polyepiamine crosslinked with ammonia or ethylenediamine,
condensation polymer of ethylenedichloride and ammonia, condensation polymer of
triethanolamine and tall oil fatty acid, poly(dimethylarninoethylrnethacrylate sulfuric
acid salt) and poly(dimethylaminoethylacrylate methyl chloride quaternary salt).
In another preferred aspect, the water soluble zwitterionic polymer is composed
of about 1 to about 99 mole percent of N,N-dimethyl-N-methacrylamidopropyl-N-(3-
sulfopropyl)-ammonium betaine and about 99 to about 1 mole percent of one or more
nonionic monomers.
In another preferred aspect, the nonionic monomer is acrylamide.
The MBR unit combines two basic processes: biological degradation and
membrane separation-into a single process where suspended solids and microorganisms
responsible for biodegradation are separated from the treated water by a membrane
filtration unit. See Water Treatment Membrane Processes, McGraw-Hill, 1996, p 17.2.
The entire biomass is confined within the system, providing for both control of the
residence time for the microorganisms in the reactor (sludge age) and the disinfection of
the effluent.
In a typical MBR unit, influent wastewater 7 is pumped or gravity flowed into
the aeration tank 1 where it is brought into contact with the biomass, which biodegrades
organic material in the wastewater. Aeration means 5 such as blowers provide oxygen
to the biomass. The resulting mixed liquor is pumped from the aeration tank into the
membrane module 2 where it is filtered through a membrane under pressure or is drawn
through a membrane under low vacuum. The effluent 11 is discharged from the system
while the concentrated mixed liquor is returned to the bioreactor. Excess sludge 9 is
pumped out in order to maintain a constant sludge age, and the membrane is regularly
cleaned by backwashing, chemical washing, or both.
Membranes used in the MBR unit include ultra-, micro- and nanofiltration,
inner and outer skin, hollow fiber, tubular, and flat, organic, metallic, ceramic, and the
like. Preferred membranes for commercial application include hollow fiber with an
outer skin ultrafilter, flat sheet (in stacks) microfilter and hollow fiber with an outer
skin microfilter.
Preferred membrane materials include chlorinated polyethylene (PVC),
polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polysulfone (PSF),
polyethersulfone (PES), polyvinylalcohol (PVA), cellulose acetate (CA), regenerated
cellulose (RC) as well as inorganics.
Additional sludge disintegration devices 6 can be attached to the MBR to
enhance sludge decay. Excess sludge 9 from the aeration tank 1 is pumped into the
disintegration device for further degradation. The liquified sludge 8 exiting the
disintegration devices is recycled to bioreactor again and will be used as feed.
Examples of sludge disintegration devices include ozonation, alkaline treatment, heat
treatment, ultrasound, and the like. In this case protoplasmic materials contained in the
disintegrated sludge will contribute to increased biopolymer (i.e. proteins,
polysaccharides) levels in the mixed liquor. This additional biopolymer is removed by
the polymer treatment described herein.
The wastewater may be pretreated before entering the MBR. For example, a bar
screen, grit chamber or rotary drum screen may be used to achieve coarse solids
removal.
In industrial plants where synthetic oils are present in the untreated wastewater,
such as an oil refinery, pretreatment to remove oil is accomplished in units such as the
inclined plate separator and the induced air flotation unit (LAF). Often, a cationic
flocculant, such as a co-polymer of DMAEM and AcAm, is used in the LAF unit to
increase oil removal. Also, excess phosphate is sometimes precipitated in the
bioreactor by the addition of metal salts such as ferric chloride, so that the phosphate
does not pass through the membrane and into the final effluent.
Depending on the ultimate use of the water and the purity of the MBR permeate,
the clarified wastewater may also be subjected to post treatment. For instance, in water
reclamation where treated wastewater is ultimately recharged into an aquifer used as a
source for drinking water, the permeate may be further treated with reverse osmosis
(RO) to reduce the dissolved mineral content. If the water is to be recycled into a
process, then the requirements of that process may necessitate further treatment of the
permeate for removal of recalcitrant organics not removed by the MBR. Processes such
as nanofiltration or carbon adsorption might be used in these cases. Finally, all
biologically treated wastewater may be further disinfected prior to discharge into a
receiving stream, generally by addition of sodium hypochlorite, although this is not
required for discharge into a municipal sewer.
As discussed above, in the MBR process complete retention of the biomass by
the membrane process makes it possible to maintain high MLSS in bioreactor, and this
high MLSS allows for a longer solid retention time (SRT). Consequently, the MBR
sludge production rate, which is inversely proportional to the SRT, is much reduced
compared to the conventional activated sludge process, to about 0.3 kg sludge/kg COD.
However, the expense for sludge treatment in the MBR plant is still estimated to be
30~40% of the total expense.
As discussed above, sludge production can be much reduced simply by
increasing HRT or target MLSS of bioreactor. However, this method will accelerate
membrane fouling and may finally increase 'membrane cleaning frequency'.
In fact high HRT and high MLSS cause high SRT. Under these conditions,
microorganisms remain in the bioreactor for an extended period, during which time
some old microorganisms decay automatically. During this decay process, substantial
amounts of miscellaneous protoplasmic materials such as polysaccharides, proteins etc
are produced. These materials are commonly referred to as 'biopolymer'. This
biopolymer will be added to the background biopolymer, so called extra-cellular
polymer (ECP) secreted by microorganisms. Consequently high SRT causes a high
level of biopolymer which is a major membrane foulant.
Therefore, sludge reduction by increasing HRT and/or MLSS is limited by
accelerated membrane fouling by biopolymer. The high level of soluble biopolymer in
mixed liquor can be reduced by using the polymers of this invention to react with and
coagulate and flocculate the biopolymer forming insoluble precipitate into larger
particles.
In practice, in a new MBR facility sludge production can be decreased by about
50-90 percent as use of polymers as described herein allows for increasing HRT to
about 10-15 hours without an increase in MLSS.
In the case of an existing facility where HRT is fixed, sludge production can be
decreased by about 30-50 percent as use of polymers as described herein permits
increasing MLSS by about 2-2.5 percent.
The cationic, amphoteric or zwitterionic polymers are introduced into the
aeration basin/bioreactor by various means, for example by dosing into the wastewater
feed line ahead of the bioreactor or by dosing directly into the bioreactor.
In all cases, the polymer should be thoroughly mixed with the mixed liquor in
the bioreactor to maximize adsorption. This may be accomplished by feeding the
polymer into an area of the bioreactor where an aeration nozzle is located. So-called
"dead" zones in the bioreactor having little to no flow should be avoided. In some
cases, a submerged propeller mixer may be needed to increase mixing in the basin, or
the sludge can be re-circulated through a side arm loop.
Solution polymers can be dosed using a chemical metering pump such as the
LMI Model 121 from Milton Roy (Acton, MA).
The recommended polymer dosage, based on mixed liquor in the bioreactor, is
about 1 to about 2000 ppm on active basis, at MLSS (mixed liquor suspended solids) of
approximately 1-2%. If the MLSS is lower than 1%, a proportionately lower dosage of
polymer may be used. The polymer can be periodically pumped directly to the
bioreactor mixed liquor or into the wastewater feed line The polymer may be pumped
intermittently ("slug fed") or continuously to the wastewater.. If polymer is fed
continuously to the wastewater feed, then dosage would be considerably lower, about
0.25 to about 10 ppm.
Overdosing polymer may result in reduced biological activity and organics
removal in the bioreactor. For this reason, a low polymer dosage should be used
initially: for example about 25 to about 100 ppm in the mixed liquor. Additional
polymer can then be fed to increase flux while maintaining biological activity.
Permeate TOC (total organic carbon), COD (chemical oxygen demand), or BOD
(biological oxygen demand) can be monitored to ascertain biological activity.
Alternately, a jar test can be conducted with samples of mixed liquor. Using a
four paddle mixer, the sample jars are dosed with sequentially higher amounts of
polymer; one jar is left untreated. After mixing, the samples are allowed to sit for
several hours, so that the solids can settle to the bottom of the jar. The turbidity of the
water on top of the settled solids (supernatant) is measured to ascertain the
effectiveness of the polymer dosage. A turbidimeter from Hach Company (Loveland,
Co) could be used. A dosage that gives lower turbidity in the jar than the untreated
sample will usually increase flux in the MBR.
In the event of a polymer overdose, dosing of polymer should be halted until
biological activity returns to normal levels. It may also be necessary to discharge more
sludge from the bioreactor to assist in recovery of bioactivity. Addition of
bioaugmentation products containing appropriate bacteria may also be helpful in
recovering activity after polymer overdose.
The foregoing may be better understood by reference to the following
Examples, which are presented for purposes of illustration and are not intended to limit
the scope of this invention.
Representative cationic, amphoteric and zwittenonic polymers of this invention
are listed in Table 3. Polymers B and C are from Ciba (Tarrytown, NY); Polymers M
and N are from BASF (Mount Olive, NJ). All other polymers are from Ondeo Nalco
Company, Naperville, IL.
Example 1
Sample of aerobically digested mixed liquor from a midwestern municipal
wastewater treatment plant (TSS about 10-1.5%) is mixed with representative water
soluble polymer of this invention using a paddle stirrer at 110 rpm for 5 minutes. The
mixture is then placed in an Amicon Model 8400 Stirred Cell (Millipore Corporation,
Bedford, MA) and forced through a Durapore® polyvinylidenedifluoride membrane
with a nominal pore size of 0.1 micron and effective membrane area of 0.0039 m2 (
Millipore Corporation, Bedford, MA), at a constant pressure of 26 lbs/in2 (psi). Flux is
determined by weighing permeate at timed intervals on a Mettler Toledo Model
PG5002S top loading balance. Weight is recorded in 2 or 6 second intervals by
computer. Volume is calculated assuming density of 1.00 g/mL, and no temperature
correction for density is made. Flux is calculated as follows:
J = 913.7 ?W/?t
where J = flux (L/m2/hour);
AW = difference between 2 weight measurements (in grams); and
At difference between 2 time measurements (in seconds).
The results are shown in Table 4.
Additional tests are performed on mixed liquor from the same municipal plant.
In these tests the mixed liquor samples with and without polymer are mixed at 275RPM
for 15 minutes before testing in the Amicon cell. Feed pressure to the cell is 15 psi.
The results are shown in Table 5.
The data in Tables 4 and 5 clearly show a significant increase in flux through
the membrane using water soluble cationic polymers to treat the sludge. In particular,
NH3-crosslinked Epi-DMA shows as much as a 700% increase in flux, and PEI shows
about a 1500% increase. Other cationic polymers, including linear epi-DMA and
pDADMAC) also show increased flux relative to no treatment of the sludge.
Example 2
Excess soluble cationic polymer is measured by adding varying amounts of a
representative cationic polymer (Epi-DMA) to mixed liquor from a midwestern
municipal wastewater treatment plant, stirring the mixture at 110 rpm, centrifuging the
mixture at 20,000 rpm for 25 minutes and then measuring the residual polymer in the
centrate by colloid titration with a 0.001M solution of the potassium salt of
polyvinylsulfuric acid (PVSK). The results are summarized in Table 6.
As shown in Table 6, no residual polymer is detected in the centrifuge water
centrate at polymer dosages that result in substantial increases in membrane flux.
Dosages 30 times more than optimum are required for excess residual polymer to begin
to appear in the centrate. This is very important discovery because excess polymer is
known to foul membrane surfaces resulting in dramatic decreases in membrane flux.
Example 3
Five gallon buckets of mixed liquor are taken from a western United States
MBR unit treating municipal wastewater, air-freighted overnight and tested the next
day. The sample is refrigerated overnight and then warmed to room temperature for
testing on subsequent days. Cationic polymer (2.0 g of a 1% polymer solution) and 198
g of mixed liquor are added to a 400 ml beaker. The mixture is stirred on a motorized
stirrer for 15 minutes at 275 rpm to redisperse the solids. This mixed sludge is
transferred to the Amicon cell with a polyvinylidenedifluoride membrane with nominal
pore size of 0.2 microns just before the filtration test is performed.
The mixture is forced through the membrane at a constant pressure of either 15
or 8 psi. Flux was determined by weighing permeate at timed intervals on a Mettler
Toledo Model PG5002S top loading balance. Weight is recorded in 2 second intervals
by computer. Volume was calculated assuming density of 1.00 g/mL, and no
temperature corrections for density were made. Flux was calculated as explained in
Example 1.
At the end of the sludge sample test, the membrane is discarded. All tests with
polymer treatment include a test in which no polymer is dosed to establish the baseline
conditions. This test compares polymer-treated sludge flux rates to untreated mixed
liquor flux rates. This is done for quantification of the effects of dosage, chemistry,
pressure, etc., on flux. The results are shown in Table 7.
The data in Table 7 clearly show a significant increase in flux through the
membrane at both pressures of 8 and 15 psi using cationic polymers A and M. to
condition the sludge before the test.
Example 4
Mixed liquor from a midwestern United States MBR unit treating municipal
wastewater MBR is mixed with amphoteric polymer Q at different dosages and then
filtered through a flat sheet Kubota membrane using a dead-end filtration cell at 15 psig
with stirring of the treated mixed liquor (300 rpm) at 22 °C. The control mixed liquor
without polymer treatment is also filtered under similar conditions. The percent
enhancement in the permeate flux after treatment with amphoteric polymer at different
dosages is shown in Table 8.
The data in Table 8 clearly show a significant increase in flux through the
membrane relative to control using a representative amphoteric polymer to condition
the mixed liquor before the test.
Example 5
Mixed liquor from a western United States MBR unit treating municipal
wastewater is mixed with amphoteric polymer Q and membrane flux is measured using
the method of Example 4. The results are shown in Table 9 below.
The data in Table 9 clearly show a significant increase in flux through the
membrane relative to control using a representative amphoteric polymer to condition
the mixed liquor before the test.
Example 6
Mixed liquor from a western United States MBR unit treating municipal
wastewater is mixed with amphoteric polymer R and membrane flux is measured using
the method of Example 4. The results are shown in Table 10 below.
The data in Table 10 clearly show a significant increase in flux through the
membrane relative to control using a representative amphoteric polymer to condition
the mixed liquor before the test.
Example 7
In order to confirm the complexation of polysaccharide from the mixed liquor
with the amphoteric polymer, the colorimetric test for polysaccharide level is conducted
on the centrate of mixed liquor obtained after polymer addition to the mixed liquor and
subsequent centrifugation.
Table 11 shows the amount of residual glucose (a direct measure of
polysaccharide) in the mixed liquor after complexation with amphoteric polymer Q for
MBR mixed liquor from a western USA MBR unit treating municipal wastewater.
As shown in Table 11, conditioning of mixed liquor with a representative
polymer of this invention results in a substantial decrease in the polysaccharide level in
the MBR mixed liquor, resulting in significant flux enhancement, shown in Table 9.
In addition, no residual polymer is detected in the centrate of the mixed liquor
from a Midwestern USA MBR after addition of up to 2000 ppm-active of amphoteric
polymer Q and centrifugation of this treated mixed liquor. This indicates almost
complete consumption of added polymer for coagulation of suspended solids and
complexation with soluble biopolymer. Therefore it is unlikely that the added
amphoteric polymer will contribute itself to the membrane fouling, while yielding the
higher permeate fluxes.
Furthermore, the permeate quality is not compromised by the polymer treatment
as evidenced by a permeate turbidity that is generally below 0.5 NTU for both the
Western and Midwestern USA MBR sludge mixed liquor after polymer treatment.
Example 7
Western USA mixed liquor is treated with a representative amphoteric polymer
as described in example 4, except using a flow through cell with submerged
membranes. The extent of flux enhancement is reflected from the amount of suction
pressure required for a constant permeate flux. Thus, the higher the suction pressure
that is required for a given permeate flux, the higher the membrane fouling. The
suction pressure profile is measured over a period of 24 hours for control and polymer
treated mixed liquor for a constant permeate flux of 30 LMH. The sludge volume is 8
L and the air-flow rate for membrane scouring is 10 l/min (LPM). The results are
shown in Table 12.
Example 8
Biopolymer removal efficacy by cationic polymer is also determined by IR
analysis as follows. Mixed liquor of MBR is spun down and supernatant is obtained.
A representative cationic polymer P is then added. IR analysis of the precipitate and
supernatant revealed that the majority of biopolymer originally contained in the
supernatant is found in the precipitate while only a trace is found in bulk. Moreover
there has not been any evidence that cationic polymer causes membrane fouling at a
concentration of up to 100 ppm in the mixed liquor.
A three-month pilot experiment further reveals that membrane fouling is
delayed with polymer P. In the case of batch experiment performed with a stirred cell,
flux decline is not observed even with 1,000 ppm of polymer P. Additionally, bio-
activity also is not affected by cationic polymers such as polymer P and polymer A at an
extremely high polymer concentration of 3,000 ppm.
Although this invention has been described in detail for the purpose of
illustration, it is to be understood that such detail is solely for that purpose and that
numerous modifications, alterations and changes can be made therein by those skilled
in the art without departing from the spirit and scope of the invention except as it may
be limited by the claims. All changes which come within the meaning and range of
equivalency of the claims are to be embraced within their scope.
We Claim:
1. A method of conditioning mixed liquor having a mixed liquor
suspended solids loading of about 5 g/L to about 30 g/L in a
membrane biological reactor comprising adding to the mixed
liquor an effective coagulating and flocculating amount of one or
more water soluble cationic, antiphoteric or zwitterionic polymers,
or combination thereof.
2. The method as claimed in claim 1 wherein the water soluble
cationic, amphoteric or zwitterionic polymers have a molecular
weight of about 2,000 to about 10,000,000 dalton.
3. The method as claimed in claim 1 wherein the cationic polymer is
copolymer of acrylamide and one or more cationic monomers
selected from diallyldimethylammonium chloride,
dimethylaminoethylacrylate methyl chloride quaternary salt,
dimethylaminoethylmethacrylate methyl chloride quaternary salt
and dimethylaminoethylacrylate benzyl chloride quaternary salt.
4. The method as claimed in claim 3 wherein the cationic polymer
has a cationic charge of at least about 5 mole percent.
5. The method as claimed in claim 3 wherein the cationic polymer is
diallyldimethylammonium chloride/acrylamide copolymer.
6. The method as claimed in claim 1 wherein the amphoteric polymer
is selected from dimethylaminoethyl acrylate methyl chloride
quaternary salt/acrylic acid copolymer, diallyldimethylammonium
chloride/acrylic acid copolymer, dimethylaminoethyl acrylate
methyl chloride salt/N,N-dimethyl-N-methacrylamidopropyl-N-(3-
sulfopropyl)-ammonium betaine copolymer, acrylic acid/N,N-
dimethyl-N-methyacrylamidopropyl-N-(3-sulfopropyl)-ammonium
betaine copolymer and DMAEA.MCQ/Acrylic acid/N,N-dimethyl-
N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine
terpolymer.
7. The method as claimed in claim 6, wherein the amphoteric
polymer has a molecular weight of about 5,000 to about 2,000,000
dalton.
8. The method as claimed in claim 6 wherein the amphoteric polymer
has a cationic charge equivalent to amionic charge equivalent ratio
of about 0.2:9.8 to about 9.8:2.
9. The method as claimed in claim 6 wherein the cationic polymer
has a cationic charge of 100 mole percent.
10. The method as claimed in claim 9 wherein the cationic polymer
has a molecular weight of about 2,000 to about 500,000 dalton.
11. The method as claimed in claim 9 wherein the water soluble
cationic polymer is selected from the group consisting of
polydiallyldimethylammonium chloride, polyethyleneimine,
polycpiamine, polyepiamine crosslinked with ammonia or
ethylenediamine, condensation polymer of ethylenedichloride and
ammonia, condensation polymer of triethanolamine an tall oil fatty
acid, poly (dimethylaminoethylmethacrylate sulfuric acid salt) and
poly(dimethylaminoethylacrylate methyl chloride quaternary salt).
12. The method as claimed in claim 1 wherein the water soluble
zwitterionic polymer is a composed of about 1 to about 99 mole
percent of N,N-dimethyl-N-methacrylamidopropyl-N-(3-
sulfopropyl)-ammonium betaine and about 99 to about 1 mole
percent of one or more nonionic monomers.
13. The method as claimed in claim 12 wherein the nonionic monomer
is acrylamide.
14. A method of clarifying wastewater in a membrane biological
reactor where microorganisms consume organic material in the
wastewater to form a mixed liquor comprising water having a
mixed liquor suspended solids loading of about 5 g/L to about 30
g/L, the microorganisms and dissolved and suspended solids
comprising
(i) adding to the mixed liquor an effective coagulating and
flocculating amount of one or more cationic, amphoteric or
zwitterionic polymers, or a mixture thereof, to form a
mixture comprising water, the microorganisms and
coagulated and flocculated solids; and
(ii) separating clarified water from the microorganisms and the
coagulated and flocculated solids by filtration through a
membrane.
15. A method of preventing fouling of a filtration membrane in a
membrane biological reactor where microorganisms consume
organic material in the wastewater in a mixed liquor comprising
water having a mixed liquor suspended solids loading of about 5
g/L to about 30 g/L, the microorganisms and dissolved, colloidal
and suspended solids and wherein clarified water is separated from
the mixed liquor by filtration through the filtration membrane
comprising adding to the mixed liquor an amount of one or more
cationic, amphoteric or zwitterionic polymers, or a combination
thereof, sufficient to prevent fouling of the membrane.
16. A method of enhancing flux through a filtration membrane in a
membrane biological reactor where microorganisms consume
organic material in the wastewater in a mixed liquor comprising
water having a mixed liquor suspended solids loading of about 5
g/L to about 30 g/L, the microorganisms and dissolved, colloidal
and suspended solids and wherein clarified water is separated from
the mixed liquor by filtration through the filtration membrane
comprising adding to the mixed liquor an effective flux enhancing
amount of one or more cationic, amphoteric or zwitterionic
polymers, or a combination thereof.
17. A method of reducing sludge formation in a membrane biological
reactor where microorganisms consume organic material in the
wastewater to form a mixed liquor comprising water having a
mixed liquor suspended solids loading of about 5 g/L to about 30
g/L, the microorganisms and a sludge comprising dissolved,
colloidal and suspended solids and wherein clarified water is
separated from the mixed liquor by filtration through a membrane
comprising
adding to the mixed liquor an effective sludge reducing amount of
one or more cationic, amphoteric or zwitterionic polymers, or a
combination thereof.

A method of conditioning mixed liquor having a mixed liquor suspended
solids loading of about 5 g/L to about 30 g/L in a membrane biological
reactor comprising adding to the mixed liquor an effective coagulating and
flocculating amount of one or more water soluble cationic, antiphoteric or
zwitterionic polymers, or combination thereof.

Documents:

921-kolnp-2004-abstract.pdf

921-kolnp-2004-claims.pdf

921-kolnp-2004-correspondence.pdf

921-kolnp-2004-description (complete).pdf

921-kolnp-2004-drawings.pdf

921-kolnp-2004-examination report.pdf

921-kolnp-2004-form 1.pdf

921-kolnp-2004-form 18.pdf

921-kolnp-2004-form 2.pdf

921-kolnp-2004-form 26.pdf

921-kolnp-2004-form 3.pdf

921-kolnp-2004-form 5.pdf

921-KOLNP-2004-FORM-27.pdf

921-kolnp-2004-reply to examination report.pdf

921-kolnp-2004-specification.pdf


Patent Number 237550
Indian Patent Application Number 921/KOLNP/2004
PG Journal Number 1/2010
Publication Date 01-Jan-2010
Grant Date 29-Dec-2009
Date of Filing 30-Jun-2004
Name of Patentee NALCO COMPANY
Applicant Address 1601 DIEHL ROAD, NAPERVILLE, ILLINOIS
Inventors:
# Inventor's Name Inventor's Address
1 COLLINS, JOHN, H 389 MEADOWLARK ROAD, BLOOMINGDALE IL 60108
2 MUSALE, DEEPAK, A. 950 FAIRWAY DRIVE APT. 108, NAPERVILLE IL 60563
3 YOON, SEONG-HOON 31603 VILLAGE GREEN BLVD., WARRENVILLE IL 60555
4 WARD, WILLAM, J. 23W 305 EDGEWOOD COURT, GLEN ELLYN, IL 60137
5 SALMEN, KRISSTINE, S 23W042 KINGS COURT, GLEN ELLYN, IL 60137
PCT International Classification Number B01D 65/08
PCT International Application Number PCT/US2003/00301
PCT International Filing date 2003-01-06
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10/035,785 2002-01-04 U.S.A.