New sludge dewatering method

Abstract

To solve the problems that municipal sludge is difficult to treat because its composition can change significantly in a short period of time, and it is also difficult to transport because the sludge is often highly concentrated.SOLUTION: The present invention is a sludge dewatering method, comprising 1) dissolving at least one particulate flocculant polymer P1 in water to obtain a polymer solution; and 2) adding the polymer solution to the sludge to be treated; 3) transporting the treated sludge to the solid-liquid separator by a conveying system and adding at least one oil-in-water emulsion flocculant polymer P2 to the treated sludge within the conveying system at least 2 meters from the polymer solution addition position; and 4) dewatering the sludge using a solid-liquid separator.SELECTED DRAWING: None

Description

[Technical field]

[0001] In large cities and industries, very large volumes of wastewater are generated and need to be discharged. Discharge of wastewater requires the treatment of very large volumes of sludge before it can be discharged into the natural environment. Generally, a first step, mechanical dewatering, is performed to minimize the volume occupied by the sludge. For this purpose, polymeric flocculants are used, which artificially increase the size of the particles that compose the sludge and the cohesiveness of the particle flocs. This allows the sludge to be separated into solid and liquid phases. [Background technology]

[0002] From the patent document JP 5622263, it is known that by combining particulate flocculant polymer P1 with water-in-oil emulsion type polymer flocculant, dewatering performance can be improved and foaming can be prevented if foaming is present. However, when two polymer flocculants are added simultaneously, it is difficult to control / adjust the amount of flocculant to the variation of sludge composition. Powdered flocculant polymer is difficult to dissolve. When adding water-in-oil emulsion and powder at the same time, it is necessary to dissolve all the powder, which makes the adjustment to the variation of sludge composition slow and cannot cope with the heterogeneous sludge composition such as in big cities and industries. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-194348 A (Japanese Patent No. 5622263) Summary of the Invention [Problem to be solved by the invention]

[0004] Municipal sludge is difficult to treat because its composition changes dramatically over a short period of time, and the sludge is often highly concentrated, making it difficult to transport. [Means for solving the problem]

[0005] A sludge dewatering method, comprising the steps of adding dissolved particulate flocculant polymer P1 to the sludge to be treated and then adding water-in-oil emulsion type flocculant polymer directly to the means of transporting the sludge to the solid-liquid separator at different injection points. Effect of the Invention

[0006] As a result of extensive research, the inventors have found that the method of the present invention allows for more appropriate control of the amount of coagulant added and allows for real-time adaptation to the sludge composition, resulting in better dewatering effects and at the same time reducing the amount of polymer used, thereby reducing CO2 emissions.

[0007] Furthermore, it was found that adding the water-in-oil emulsion flocculant polymer directly to the sludge transport to the solid-liquid separation device reduced the energy required to transport the sludge because the oil acted as a lubricant, an effect that was not observed when the water-in-oil emulsion flocculant polymer P2 was added together with the particulate flocculant polymer P1.

[0008] Furthermore, it has been found that adding the flocculant polymer at two different locations reduces the time required to treat the sludge, and without wishing to be bound by theory, the applicant believes that this reduction in time may be related to better mixing of the polymer with the sludge.

[0009] Finally, by using a mixer to inject the water-in-oil emulsion flocculant polymer P2, the user avoids the need for a tank to invert the emulsion.

[0010] Application of the method of the present invention reduces the energy costs and environmental impact of sludge dewatering and improves process efficiency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] As used herein, the term "polymer" refers to an aqueous solution (concentration 10 g L at 25 °C) that is free of insoluble particles after moderate mixing with water. -1 ) is meant to indicate the polymer obtained.

[0012] As used herein, the term "polymer" refers to a homopolymer prepared from one type of monomer, or a copolymer prepared from at least two different monomers, i.e., copolymers of at least two monomers selected from anionic hydrophilic monomers, cationic hydrophilic monomers, nonionic hydrophilic monomers, hydrophobic monomers, and mixtures thereof.

[0013] As used herein, the term "hydrophilic monomer" refers to a monomer having an octanol / water partition coefficient, K ow K is equal to or less than 1. ow The partition coefficients are determined at 25° C. in octanol / water mixtures with a volume ratio of 1 / 1 at pH values ​​between 6 and 8.

[0014] As used herein, the term "hydrophobic monomer" refers to a monomer having an octanol / water partition coefficient, K ow K is greater than 1. ow The partition coefficients are determined at 25° C. in octanol / water mixtures with a volume ratio of 1 / 1 at pH values ​​between 6 and 8.

[0015] Octanol / water partition coefficient K ow represents the ratio of monomer concentration (g / L) between the octanol phase and the aqueous phase. ow is defined as follows:

[0016]

number

[0017] As used herein, the term "sludge" means a residue having a level of dry matter of at least 0.1% by weight, and often 5% by weight or more, based on the total weight of the sludge. Sludge may be mineral, organic or oily.

[0018] As used herein, the term "particulate" means powders, beads, or mixtures thereof. The particles may be of regular or irregular size and may be spherical or non-spherical.

[0019] "X and / or Y" refers to "X", "Y", or "X and Y".

[0020] All possible combinations between the different disclosed embodiments are likewise part of the present invention, regardless of whether they are preferred embodiments or given as examples. Furthermore, when ranges of values ​​are given, the endpoint values ​​are included in these ranges. The disclosure also includes the endpoint values ​​and all combinations of ranges between these values. For example, the numerical range "1-20, preferably 5-15" includes the ranges "1-5", "1-15", "5-20", "15-20", and the disclosure of the numerical values ​​"1", "5", "15", and "20".

[0021] According to the invention, the weight average molecular weight is determined by the intrinsic viscosity. The intrinsic viscosity can be measured by methods known to those skilled in the art. As already explained in connection with the Huggins coefficient, the intrinsic viscosity can in particular be calculated from the reduced viscosity values ​​for different concentrations by a graphical method consisting in plotting the reduced viscosity values ​​(vertical axis) against the concentration (horizontal axis) and extrapolating the curve to zero concentration. The intrinsic viscosity values ​​are read off the vertical axis or by using the least squares method. The weight average molecular weight is then calculated according to the Mark-Houwink formula: [η]=K M α [In the formula, [η] is the intrinsic viscosity of the polymer as determined by solution viscometry; K is an empirical constant, M is the molecular weight of the polymer, α is the Mark-Houwink coefficient. α and K depend on the particular polymer-solvent system. There are tables showing the values ​​of α and K for different polymer-solvent systems.

[0022] The sludge dewatering method of the present invention A sludge dewatering method comprising the steps of: 1) dissolving at least one particulate flocculant polymer P1 in water to obtain a polymer solution; 2) adding a polymer solution to the sludge to be treated; 3) transporting the sludge to be treated by a transport system to a solid-liquid separator and adding at least one water-in-oil emulsion type flocculant polymer P2 to the sludge to be treated in the transport system at least 2 meters from the adding point of the polymer solution; 4) Dewatering the sludge using a solid-liquid separator; A sludge dewatering method comprising:

[0023] Process 1) In a first step of the process, the particulate flocculant polymer P1 can be partially or completely dissolved, preferably the particulate flocculant polymer P1 is completely dissolved.

[0024] If the particulate flocculant polymer P1 is not completely dissolved, then no more than 5% by weight, preferably no more than 2.5% by weight, based on the total weight of the particulate flocculant polymer P1, is undissolved.

[0025] The particulate flocculant polymer P1 may be a mixture of two or more flocculant polymers.

[0026] The polymer solution may contain additional additives commonly used in sludge dewatering methods, including, but not limited to, coagulants, antifoaming agents, non-aqueous media, and organic and / or inorganic salts that can be used as pH buffers, diluents, fluidizing agents, stabilizers, dissolution promoters, etc. Non-aqueous media may include hydrophilic organic solvents such as C1-C8 lower alcohols, e.g., methanol, ethanol, propanol, etc.

[0027] Preferred salts are urea, ammonium sulfate or chloride, adipic acid, sodium formate, succinic acid.

[0028] The resulting polymer solution preferably contains polymer at a concentration of between 0.05 and 4% by weight, more preferably between 0.1 and 2% by weight, based on the total weight of the polymer solution.

[0029] Process 2) In the second step, the polymer solution may be added all at once, or in several portions, or continuously, but is preferably added continuously.

[0030] The sludge to be treated is, for example, municipal or industrial sludge.

[0031] The amount of polymer solution added to the sludge for treatment depends on the amount of flocculant polymer P1. The amount of flocculant polymer P1 added to the sludge for treatment depends on many parameters (sludge composition, pH, etc.). Preferably, in the case of the method of the present invention, the particulate flocculant polymer P1 is added to the sludge to be treated in an amount ranging from 10 to 10,000 ppm relative to the sludge. The skilled person can determine and adjust the amount of flocculant polymer P1 to be added depending on the sludge composition and variations to achieve sufficient sludge dewatering. Thus, the amount of polymer solution P1 added to the sludge may range from 0.5 to 40 L / t relative to the sludge.

[0032] Process 3) In the third step, the means of the sludge transport system can be any means capable of moving the sludge from one place to another, examples of which can include, but are not limited to, pipes, waterways, and conveyor belts.

[0033] The transport speed of the sludge is not particularly limited, but may generally be in the range of 1 km / h to 20 km / h, preferably 2 km / h to 15 km / h, and more preferably 3 km / h to 10 km / h.

[0034] The water-in-oil emulsion flocculant polymer P2 may be a mixture of two or more flocculant polymers.

[0035] The water-in-oil emulsion type flocculant polymer P2 can be added all at once, in several portions, or continuously, but is preferably added continuously.

[0036] The water-in-oil emulsion flocculant polymer P2 is added at a different injection location from the polymer solution of particulate flocculant polymer P1. Advantageously, the water-in-oil emulsion flocculant polymer P2 is added at least 2.5 meters, preferably at least 3 meters, from the addition location of the polymer solution.

[0037] The water-in-oil emulsion type flocculant polymer P2 is advantageously added at a distance of not more than 25 meters, preferably not more than 22 meters, more preferably not more than 20 meters from the addition point of the polymer solution.

[0038] In one embodiment of the present invention, the adding position of the polymer solution is the same as the starting position of the transport of the sludge to which the polymer solution is added.Therefore, in one embodiment, the water-in-oil emulsion type flocculant polymer P2 is added at least 2 meters, preferably at least 2.5 meters, more preferably at least 3 meters from the starting position of the transport, and / or at most 25 meters, preferably at most 22 meters, more preferably at most 20 meters from the starting position of the transport.

[0039] The water-in-oil emulsion flocculant polymer P2 can be added at multiple injection locations, for example, two or more injection locations, with at least one of the injection locations being at least 2 meters from the injection location of the particulate flocculant polymer P1 and no more than 25 meters from the injection location of the flocculant polymer. Preferably, when multiple injection locations are used, they are all at least 2 meters from the injection location of the particulate flocculant polymer P1 and at least one of the injection locations being no more than 25 meters from the injection location of the flocculant polymer.

[0040] Without wishing to be bound by theory, the applicant believes that a distance of at least 2 meters and no more than 2 meters from the injection location of the particulate flocculant polymer P1 polymer solution is important to achieve good homogeneity and synergistic effect of the two flocculant polymers. Addition before the 2 meter limit does not provide good homogeneity because the powdered polymer flocculant P1 does not have enough time to properly interact with the sludge, and addition after 25 meters does not provide a lubricating effect. It is believed that if added after 25 meters, the flow is already too turbulent for the polymer to act as a lubricant to achieve laminar flow.

[0041] The water-in-oil flocculant polymer P2 can be added directly without inverting, or it can be added in water to invert before injection into the sludge to be treated to form a flocculant polymer solution of P2. Preferably, P2 is added in invert before injection.

[0042] The water-in-oil flocculant polymer P2 can be inverted using, by way of example and not limitation, tanks, mixers and pumps.

[0043] The mixer may be, for example, a static mixer or a dynamic mixer. Preferably, a static mixer is used to inject the water-in-oil flocculant polymer P2.

[0044] The amount of water-in-oil emulsion type flocculant polymer P2 to be added to the sludge for treatment depends on many parameters (sludge composition, pH, etc.). Preferably, in the case of the method of the present invention, the water-in-oil emulsion type flocculant polymer is added to the sludge to be treated in an amount ranging from 10 to 10,000 ppm relative to the sludge. The skilled person can determine and adjust the amount of polymer flocculant depending on the sludge composition and variations to achieve sufficient sludge dewatering. The skilled person can determine and adjust the amount of flocculant polymer P2 to be added depending on the sludge composition and variations to achieve sufficient sludge dewatering. Thus, the amount of polymer solution P2 to be added to the sludge may be in the range of 0.5 to 40 L / t relative to the sludge.

[0045] Advantageously, the mass ratio between the particulate polymeric flocculant and the water-in-oil polymeric flocculant is comprised between 90:10 and 10:90, preferably between 70:30 and 30:70.

[0046] Step 4) The solid-liquid separation device can be, by way of example and without limitation, a belt filter, a filter press, a rotary press filter, a centrifuge, a screw press, a multi-disk dewatering machine, or any device capable of separating water from sludge. Preferably, the solid-liquid separation device is selected from a belt filter, a screw press, and a centrifuge, and more preferably, the solid-liquid separation device is a centrifuge.

[0047] The solid-liquid separator is preferably at a distance comprised between 5 and 150 m, more preferably between 7.5 and 120 m, more preferably between 10 and 100 m from the injection point of the water-in-oil emulsion type flocculant polymer.

[0048] The method of the present invention may include additional steps such as, for example, the addition of one or more different flocculant polymers or coagulants.

[0049] The coagulant may be organic or inorganic. An example of an inorganic coagulant is polyaluminium chloride (PAC).

[0050] A preferred organic coagulant is poly(diallyldimethylammonium chloride) having a weight average molecular weight of less than 2 million g / mol. Another preferred coagulant is polyvinylamidine. The weight average molecular weight can be measured in the same manner as the weight average molecular weight of the polymer of the present invention.

[0051] Flocculant polymer composition The particulate flocculant polymer P1 and the water-in-oil flocculant polymer P2 may be the same polymer or may be different, but are preferably different.

[0052] By different, it is meant that the two flocculant polymers have at least one difference, which may be in monomer composition, ionicity, molecular weight, structure, or the like.

[0053] The flocculant polymers of the present invention may be natural, synthetic, or semi-synthetic. Preferably, the flocculant polymers are synthetic.

[0054] Semi-synthetic polymers refer to natural polymers that have undergone chemical reactions to graft different synthetic substituents, a type of reaction known to those skilled in the art as such, which is a classical chemical reaction applied to natural polymers.

[0055] The particulate flocculant polymer P1 and the water-in-oil flocculant polymer P2 are advantageously prepared from monomers selected from cationic hydrophilic monomers, non-ionic hydrophilic monomers, anionic hydrophilic monomers, hydrophobic monomers and mixtures thereof.

[0056] Advantageously, the cationic hydrophilic monomers may be chosen in particular from vinylic monomers, in particular acrylamide, acrylic, allylic or maleic monomers carrying an ammonium function, advantageously quaternary ammonium. Non-limiting examples include diallyldialkylammonium salts such as diallyldimethylammonium chloride (DADMAC); acidified or quaternized salts of dialkylaminoalkyl(meth)acrylamides; acidified or quaternized salts of dialkyl-aminoalkyl(meth)acrylamides such as methacrylamide-propyltrimethylammonium chloride (MAPTAC), acrylamido-propyltrimethylammonium chloride (APTAC); acidified or quaternized salts of dialkyl-aminoalkylacrylates such as quaternized or chlorinated dimethylaminoethylacrylate (DMAEA); acidified or quaternized salts of dialkylaminoalkylmethacrylates such as quaternized or chlorinated dimethylaminoethylmethacrylate (DMAEMA), N,N-dimethylallylamine, diallylmethylamine, diallylamine, vinylamines obtained by hydrolysis (basic or acidic) of the amide group -N(R2)-CO-R1 (R1 and R2 are independently hydrogen atoms or alkyl chains having 1 to 6 carbon atoms), vinylamines obtained by Hofmann degradation, and mixtures thereof. Advantageously, the alkyl groups are C1 to C7, preferably C1 to C3, and may be linear, cyclic, saturated or unsaturated. Preferably, the flocculant polymer comprises at least one cationic hydrophilic monomer that is a quaternized dimethylaminoethyl acrylate (DMAEA).

[0057] Those skilled in the art will know how to prepare quaternized monomers, for example using RX type quaternizing agents, where R is an alkyl group and X is a halogen or sulfate.

[0058] The term "quaternizing agent" refers to a molecule capable of alkylating a tertiary amine.

[0059] The quaternizing agent may be selected from dialkyl sulfates containing 1-6 carbon atoms, or alkyl halides containing 1-6 carbon atoms. Preferably, the quaternizing agent is selected from methyl chloride, benzyl chloride, dimethyl sulfate, or diethyl sulfate. Furthermore, the present invention is also directed to DADMAC, APTAC, and MAPTAC monomers in which the counter ion is sulfate, fluoride, bromide, or iodide instead of chloride.

[0060] The flocculant polymer generally comprises between 1 and 100 mol % of cationic hydrophilic monomer, based on the total moles of monomer in the polymer. The flocculant polymer preferably comprises 30 mol % or more, preferably 50 mol % or more, more preferably 70 mol % or more, and even more preferably 90 mol % or more of cationic hydrophilic monomer.

[0061] Advantageously, the non-ionic hydrophilic monomer or monomers are in particular water-soluble vinyl monomers, such as acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N,N-dialkylacrylamide (e.g. N,N-dimethylacrylamide or N,N-diethylacrylamide), N,N-dialkylmethacrylamide, alkoxylated acrylic acid esters, alkoxylated methacrylic acid esters, N-vinylpyrrolidone, N-methylol(meth)acrylamide, N-vinylcaprolactam, N-vinylformamide (NVF), N-vinylacetamide. , N-vinylimidazole, N-vinylsuccinimide, acryloylmorpholine (ACMO), glycidyl methacrylate, glyceryl methacrylate, diacetone acrylamide, methacrylic anhydride, acrylonitrile, maleic anhydride, itaconic anhydride, hydroxyalkyl (meth)acrylates, thioalkyl (meth)acrylates, isoprenol and its alkoxylated derivatives, hydroxyethyl (meth)acrylate and its alkoxylated derivatives, hydroxypropyl acrylate and its alkoxylated derivatives, vinyl acetate, and mixtures thereof. Among these nonionic monomers, the alkyl group is advantageously C1-C5, more advantageously C1-C3. Linear alkyl groups are preferred. Preferably, the flocculant polymer comprises at least one nonionic hydrophilic monomer which is an acrylamide.

[0062] The flocculant polymer preferably comprises between 0 and 99 mol % of non-ionic hydrophilic monomers, preferably 70 mol % or less, preferably 50 mol % or less, more preferably 30 mol % or less, and even more preferably 10 mol % or less, based on the total moles of monomers in the polymer.

[0063] Advantageously, the other anionic hydrophilic monomers can be selected from a wide range of groups. These monomers may have a vinyl functionality, in particular an acrylic, maleic, fumaric, malonic, itaconic or allylic functionality. These monomers may also contain carboxylate, phosphonate, phosphate, sulfonate or other negatively charged groups. Suitable monomers belonging to this class are, for example, acrylic acid; methacrylic acid; dimethylacrylic acid; itaconic acid; C1-C 22 Itaconic acid hemiesters; itaconamide; acryloyl chloride; crotonic acid; maleic acid; fumaric acid; acrylamidoundecanoic acid; 3-acrylamido-3-methylbutanoic acid; for example, strong acid monomers having sulfonic or phosphonic acid functional groups, such as vinyl sulfonic acid, vinyl phosphonic acid, allyl sulfonic acid, methallyl sulfonic acid, 2-methylidenepropane-1,3-disulfonic acid, 2-sulfoethyl methacrylate, sulfopropyl methacrylate, sulfopropyl acrylate, allyl phosphonic acid, ethylene glycol methacrylate phosphate, styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid (ATBS), 2-acrylamido-2-methylpropanedisulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, diethyl allylphosphonate, carboxyethyl acrylate; water-soluble salts of all these monomers, such as their alkali metal, alkaline earth metal or ammonium salts; and mixtures thereof. Preferably, the anionic hydrophilic monomer is acrylic acid and its salts.

[0064] In certain embodiments, the anionic hydrophilic monomer can be salified.

[0065] Salification means the replacement of the proton of at least one acid functional group of the -R(=O)-OH type (R=P, S or C) of the anionic hydrophilic monomer with a metal or ammonium cation to form a salt of the -R(=O)-OX type (X is a metal or ammonium cation). In other words, the non-salted form corresponds to the acid form of the monomer, e.g., in the case of a carboxylic acid functional group, the non-salted form is RC(=O)-OH and the salified form of the monomer is RC(=O)-OX. + Type(X + corresponds to an alkali or ammonium cation). The salification of the acid functions of the polymer may be partial or total.

[0066] The salt forms advantageously correspond to alkali metal salts (Li, Na, K...), alkaline earth metal salts (Ca, Mg...) or ammonium salts (for example ammonium ions or tertiary ammonium). Preferred salts are the sodium salts.

[0067] The salification can be carried out before or after the polymerization.

[0068] The flocculant polymer comprises between 0 and 99 mol % anionic monomers, based on the total moles of monomers in the polymer, preferably 70 mol % or less, preferably 50 mol % or less, more preferably 30 mol % or less, and even more preferably 10 mol % or less.

[0069] The flocculant polymer can include a hydrophobic monomer. If a hydrophobic monomer is used, the hydrophobic monomer is less than 5 mol % based on the total moles of monomers in the polymer.

[0070] When a hydrophobic monomer is used, it is used in an amount that maintains the water solubility of the flocculant polymer.

[0071] Those skilled in the art know that the monomers in the polymer composition should not exceed 100 mol %, and therefore adjust the amount of said monomers so that they do not exceed 100 mol %.

[0072] According to the present invention, the flocculant polymer can have linear, branched, star, comb, block, microblock structure, or controlled polydispersity of molecular weight. These properties can be obtained by the selection of one or more of the initiator, transfer agent, polymerization techniques such as template polymerization, controlled radical polymerization known as RAFT (reversible chain transfer by addition-fragmentation), NMP (Nitroxide Mediated Polymerization) or ATRP (Atom Transfer Radical Polymerization), incorporation of structural monomers, and monomer concentration. The general knowledge of the person skilled in the art allows the preparation of water-soluble polymers with any of these types of structures. The flocculant polymer of the present invention with the specific morphology as described above maintains water solubility.

[0073] The flocculant polymer can be structured with a crosslinker. A structured polymer is a non-linear polymer with side chains.

[0074] The crosslinking agent is advantageously chosen from: - structuring agents which may be selected from the group comprising polyethylenically unsaturated monomers (having at least two unsaturated functions, such as vinyl functions, and in particular allyl or acrylic functions), such as methylenebisacrylamide (MBA), triallylamine, or tetraallylammonium chloride or 1,2 dihydroxyethylenebis-(N-acrylamide), - a monomer having at least two epoxy functional groups, - a monomer having at least one unsaturated functional group and one epoxy functional group, - Polymer initiators such as polyperoxides and polyazides, transfer agents such as polymercaptants and polyols, - functionalized polysaccharides, - * Trivalent or higher metals, such as, but not limited to, aluminum, boron, zirconium, titanium, and the like; * A water-soluble metal complex composed of a ligand having a hydroxyl functional group.

[0075] Suitable crosslinking agents are selected from methylenebisacrylamide (MBA), ethylene glycol diacrylate, tetraallyl ammonium chloride polyethylene glycol dimethacrylate, diacrylamide, cyanomethyl acrylate, vinyloxyethyl acrylate, vinyloxymethacrylate, triallylamine, formaldehyde, glyoxal, glycidyl ethers such as ethylene glycol diglycidyl ether, and epoxy, triallylamine, tetraallyl ammonium chloride (TAAC) and mixtures thereof.

[0076] The flocculant polymer advantageously contains between 0.1 and 1000 ppm, preferably between 1 and 100 ppm crosslinks, based on the total weight of the flocculant polymer.

[0077] In crosslinked cationic polymers, the measured cationic degree is lower than the theoretical cationic degree. Cationic regain is the increase in cationic degree between the theoretical cationic degree and the measured cationic degree.

[0078] In reality, the measured degree of cationization (unit: meq g -1 ) is 5g·L -1 Determined by colorimetric titration of the polymer solution. Theoretical degree of cationization (meq g -1 ) is 5g·L -1 The polymer solution was sheared at high shear rate (12,000 rpm, 7-8 min) and then determined by colorimetric titration. That is, cationic regain is the ratio of the degree of cationization (meq g -1 ) is the increase in

[0079] When crosslinked, the flocculant polymer advantageously has a cationic regain of between 20% and 300%, preferably between 40% and 200%, more preferably between 50% and 150%.

[0080] In certain embodiments, the polymer may include a transfer agent.

[0081] The transfer agent is advantageously selected from the group consisting of methanol, isopropyl alcohol, sodium hypophosphite, calcium hypophosphite, magnesium hypophosphite, potassium hypophosphite, ammonium hypophosphite, formic acid, sodium formate, calcium formate, magnesium formate, potassium formate, ammonium formate, 2-mercaptoethanol, 3-mercaptopropanol, dithiopropylene glycol, thioglycerol, thioglycolic acid, thiohydroacrylic acid, thiolactic acid, thiomalic acid, cysteine, aminoethanethiol, thioglycolic acid salts, allyl phosphites, allyl mercaptans, such as n-dodecyl mercaptan, sodium methallylsulfonate, calcium methallylsulfonate, magnesium methallylsulfonate, potassium methallylsulfonate, ammonium methallylsulfonate, alkyl phosphites, such as trialkyl(C 12 ~C 15 ) phosphites, dioleyl-hydrogen phosphite, dibutyl phosphite, dialkyl dithiophosphites such as dioctyl phosphonate, tertiary nonyl mercaptan, 2-ethylhexyl thioglycolate, n-octyl mercaptan, n-dodecyl mercaptan, tertiary dodecyl mercaptan, isooctyl thioglycolate, 2-ethylhexyl thioglycolate, 2-ethylhexyl mercaptoacetate, polythiols, and mixtures thereof. Preferably, it is sodium hypophosphite or sodium formate.

[0082] When the flocculant polymer comprises a chain transfer agent, its amount is advantageously comprised between 1 and 1000, preferably between 1 and 100, based on the total mass of the flocculant polymer.

[0083] In a preferred embodiment, the flocculant polymer does not include a chain transfer agent.

[0084] The polymerization is a free radical polymerization, which in the sense of the present invention means a free radical polymerization using at least one UV, azo, redox or thermal initiator, or a controlled radical polymerization technique (CRP) or a matrix polymerization technique.

[0085] Examples of controlled radical polymerization techniques include, but are not limited to, iodine transfer polymerization (ITP), nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT) including MADIX technology (MAcromolecular Design by Interchange of Xanthates), various variations of polymerization using organometallic compounds ("Organometallic Mediated Radical Polymerization" (OMRP)), and heteroatom-controlled radical polymerization ("OrganoHeteroatom-mediated Radical Polymerization" (OHRP).

[0086] In a preferred embodiment, the polymerization is carried out by reversible addition-fragmentation chain transfer polymerization (RAFT).

[0087] RAFT polymerization is a reversible deactivation radical polymerization (RDRP) technique that combines the ease of implementation of conventional radical polymerization with the liveliness of ionic polymerization.

[0088] RAFT polymerization relies on a reversible activation-deactivation equilibrium between dormant and active species (growing macroradicals). This activation-deactivation process allows the chains to grow at the same rate until the monomer is completely consumed, allowing control of polymer molecular weight and narrow molecular weight distribution. This also minimizes compositional heterogeneity. Reversible deactivation of the growing chains minimizes irreversible termination reactions. The majority of polymer chains remain dormant and can be reactivated. Then, functionalization of the chain ends can initiate other polymerization modes or extend the chains. This is the key to achieving high molecular weight, controlled composition and architecture.

[0089] Therefore, controlled radical polymerization has the following characteristics: 1. The number of polymer chains remains constant throughout the reaction. 2. All polymer chains grow at the same rate, so - The molecular weight increases linearly, - Narrow molecular weight distribution. 3. The average molecular weight is controlled by the monomer / precursor molar ratio.

[0090] The controlled nature of the process is even more pronounced when the rate of radical chain reactivation is greater than the rate of chain propagation. However, in some cases, the rate of radical chain reactivation is equal to or greater than the rate of propagation. In such cases, conditions 1 and 2 are not observed, and as a result, molecular weight control is not possible.

[0091] Reversible addition-fragmentation chain transfer polymerization requires the use of a control agent.

[0092] In the context of the present invention, the water-soluble control agent has the formula (I):

[0093] [ka]

[0094] [In the formula, - Z=O, S or NR3, R1 and R2, and R3 may be identical or different; *(i) an optionally substituted alkyl, acyl, alkenyl or alkynyl group, or * (ii) a carbocyclic ring, which is saturated or unsaturated, optionally substituted or aromatic, or * (iii) Heterocyclic rings, which are saturated or unsaturated, optionally substituted or aromatic. wherein these groups and rings (i), (ii) and (iii) may be substituted with substituted aromatic groups, alkoxycarbonyl or aryloxycarbonyl (-COOR), carboxy (-COOH), acyloxy (-OCR), carbamoyl (-CON(R)), cyano (-CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, phthalimido, maleimido, succinimido, amidino, guanidimo, hydroxy (-OH), amino (-N(R)), halogen, allyl, epoxy, alkoxy (-OR), S-alkyl, S-aryl, hydrophilic or ionic groups, such as alkali salts of carboxylic acids, alkali salts of sulfonic acids, polyalkylene oxide chains (POE, POP), cationic substituents (quaternary ammonium salts), R is C2~C 20 represents an alkyl group or an aryl group, R3 may also represent a hydrogen atom, Q is a linear or structured polymer chain comprising n identical or different hydrophilic monomers containing at least one ethylenic functional group, - n is an integer between 0 and 500, advantageously between 1 and 500. has.

[0095] The monomer or monomers used to form Q are advantageously selected from the same hydrophilic monomers as described for the formation of the block polymers in the remainder of this specification.

[0096] In the N(R)2 functional group, the two R groups may be the same or different from each other.

[0097] According to a preferred embodiment, the water-soluble control agent has formula (I) where Z=O.

[0098] According to another preferred embodiment, the water-soluble control agent has the formula (I): [In the formula, - Z=O, - Q is a linear or structured polymer chain derived from 0 to 100 monomers, including at least one nonionic hydrophilic monomer and / or at least one anionic hydrophilic monomer and / or at least one cationic hydrophilic monomer. has.

[0099] According to another preferred embodiment, the water-soluble control agent has the formula (I): [In the formula, - Z=O, - Q is a linear or structured polymer chain obtained from 0 to 100 monomers, including at least one non-ionic hydrophilic monomer and / or at least one anionic hydrophilic monomer and / or at least one LCST group-containing monomer. has.

[0100] According to another preferred embodiment, the water-soluble control agent has the formula (II):

[0101] [ka]

[0102] [wherein n is an integer between 0 and 100, preferably between 1 and 50] has.

[0103] In a further preferred embodiment, the control agent has the formula (I) where Z=S.

[0104] In a further preferred embodiment, the control agent has the formula (III):

[0105] [ka]

[0106] [In the formula, - the R3 groups are identical or different and independently represent H or CH3 or a cation, the latter advantageously being chosen from alkali metal (Li, Na, K...), alkaline earth metal (Ca, Mg...) or ammonium (for example ammonium ion or tertiary ammonium) cations, preferably sodium. has.

[0107] In another preferred embodiment, the control agent has the formula (IV):

[0108] [ka]

[0109] [In the formula, the R groups are identical or different and independently represent H or CH or a cation, the latter advantageously chosen from alkali metal (Li, Na, K...), alkaline earth metal (Ca, Mg...) or ammonium (for example ammonium ion or tertiary ammonium) cations, preferably sodium; n and n' are independent integers between 0 and 100, preferably between 1 and 50. has.

[0110] In another preferred embodiment, the control agent has the formula (V):

[0111] [ka]

[0112] [In the formula, R3 are identical or different and independently represent H or CH3 or a cation, the cation being advantageously chosen from alkali metal (Li, Na, K...), alkaline earth metal (Ca, Mg...) or ammonium (for example ammonium ion or tertiary ammonium) cations, preferably sodium. has.

[0113] In another preferred embodiment, the control agent has the formula (VI):

[0114] [ka]

[0115] [In the formula, the R groups are identical or different and independently represent H or CH or a cation, the latter advantageously chosen from alkali metal (Li, Na, K...), alkaline earth metal (Ca, Mg...) or ammonium (for example ammonium ion or tertiary ammonium) cations, preferably sodium; n is an even number between 0 and 100, preferably between 1 and 50. has.

[0116] Particulate flocculant polymer P1 The particulate flocculant polymer P1 can be obtained by gel polymerization followed by a drying and grinding step; precipitation polymerization; solution polymerization followed by a spray drying step; inverse emulsion polymerization followed by a spray drying step; inverse suspension polymerization to obtain microbeads, micellar polymerization optionally followed by a precipitation step. Preferably, the particulate flocculant polymer P1 is obtained by gel polymerization.

[0117] The particulate flocculant polymer P1 according to the invention preferably has a particle size comprised between 100 μm and 2 mm, preferably between 150 μm and 1.7 mm.

[0118] The average size of the water-soluble polymer particles is the average size of the largest dimension, for example the diameter of a spherical particle. The average particle size is advantageously measured by a laser measuring device using conventional techniques known to those skilled in the art. As an example, a device of the Mastersizer type from Malvern, for example MS2000, can be used for this purpose. This type of device makes it possible to measure the particle size distribution in a liquid medium or in a solid state by laser diffraction.

[0119] The size of the polymer particles may vary depending on the polymerization method, and a person skilled in the art will know how to adapt the polymerization method to produce the desired particle size.

[0120] The flocculant polymer according to the invention preferably has a weight average molecular weight of at least 1 million g / mol, more preferably at least 2 million g / mol, more preferably at least 3 million g / mol, more preferably at least 5 million g / mol. There is no upper limit to the weight average molecular weight of the star polymer, but generally the particulate flocculant polymer P1 has a weight average molecular weight of 30 million g / mol or less.

[0121] In a preferred embodiment, the particulate flocculant polymer P1 is linear.

[0122] In a preferred embodiment, the particulate flocculant polymer P1 is prepared by controlled radical polymerization known as RAFT (Reversible Chain Transfer by Addition-Fragmentation).

[0123] In a preferred embodiment, the particulate flocculant polymer P1 is a cationic polymer.

[0124] In a preferred embodiment, the particulate flocculant polymer P1 is composed of cationic hydrophilic monomers and optionally non-ionic hydrophilic monomers.

[0125] In a preferred embodiment, the particulate flocculant polymer P1 comprises at least 30 mol %, preferably at least 50 mol %, more preferably at least 70 mol %, even more preferably at least 80 mol % of cationic hydrophilic monomers.

[0126] In a preferred embodiment, the particulate flocculant polymer P1 comprises at least quaternized dimethylaminoethyl acrylate (DMAEA) as cationic hydrophilic monomer, more preferably the only cationic hydrophilic monomer is quaternized dimethylaminoethyl acrylate (DMAEA).

[0127] In a preferred embodiment, the particulate flocculant polymer P1 is a polymer of quaternized dimethylaminoethyl acrylate (DMAEA) and acrylamide monomers.

[0128] In a preferred embodiment, the particulate flocculant polymer P1 is a polymer consisting of at least 30 mol% quaternized dimethylaminoethyl acrylate (DMAEA) and not more than 70 mol% acrylamide, more preferably a polymer consisting of at least 50 mol% quaternized dimethylaminoethyl acrylate (DMAEA) and not more than 50 mol% acrylamide, even more preferably a polymer consisting of at least 70 mol% quaternized dimethylaminoethyl acrylate (DMAEA) and not more than 30 mol% acrylamide, even more preferably a polymer consisting of at least 80 mol% quaternized dimethylaminoethyl acrylate (DMAEA) and not more than 20 mol% acrylamide.

[0129] Water-in-oil flocculant polymer P2 The water-in-oil emulsion type flocculant polymer is obtained by inverse emulsion polymerization.

[0130] The term "reverse emulsion" refers to both reverse emulsions and reverse microemulsions. Reverse emulsions are water-in-oil emulsions in which droplets of an aqueous phase are dispersed in an organic phase.

[0131] Inverse emulsions are two-phase media. Inverse emulsions can be unstable in the absence of surfactants (surfactants include water-in-oil emulsifiers and oil-in-water emulsifiers). Under stirring, the particles of the hydrophilic phase are dispersed in the lipophilic phase, with a wide range of particle size distributions and average particle size in the micrometer range. During inverse emulsion polymerization, the monomers are dispersed in large droplets of the emulsion (diameter: about 50 nm to 50 μm) and small emulsifier micelles (diameter: about 5 to 10 nm).

[0132] This polymerization technique is well known to those skilled in the art. Inverse emulsion polymerization involves emulsifying a hydrophilic phase containing one or more monomers in a lipophilic phase. This emulsification is accomplished using a water-in-oil emulsifier.

[0133] Inverse emulsions generally include at least: - a hydrophilic phase comprising at least one water-soluble polymer; - with a lipophilic phase. - at least one water-in-oil emulsifier; - optionally with an oil-in-water emulsifier; Includes.

[0134] The weight ratio of the hydrophilic phase to the lipophilic phase during the polymerization is preferably between 50 / 50 and 90 / 10, more preferably between 70 / 30 and 80 / 20.

[0135] A "water-in-oil emulsifier" is a compound capable of emulsifying water in oil, and an "oil-in-water emulsifier" is a compound capable of emulsifying oil in water. Generally speaking, water-in-oil emulsifiers are surfactants with an HLB strictly less than 8, and oil-in-water emulsifiers are surfactants with an HLB of 10 or more. Surfactants with an HLB between 8 and 10 are considered wetting agents. Those skilled in the art may refer, if necessary, to Chapter 11 of K. Holmberg's "Handbook of Applied Surface and Colloid Chemistry."

[0136] The hydrophilic-lipophilic balance (HLB) of a compound is a measure of the hydrophilicity and / or lipophilicity of a compound, determined by calculating values ​​for different regions of the molecule, as described by Griffin in 1949.

[0137] In the present invention, we have adopted the method of Griffin, which is based on the calculation of values ​​based on the chemical groups of the molecule. Griffin assigned a dimensionless number between 0 and 20 to give information on the solubility of water and oil.

[0138] The HLB value of a substance having a total molecular weight M and a hydrophilic portion with a molecular weight Mh is given by the following formula: HLB=20(Mh / M)

[0139] The water-in-oil emulsifiers are advantageously selected from the following list: polyesters with a molecular weight between 1000 and 3000 g / mol, condensation products of poly(isobutenyl)succinic acid or its anhydride with polyethylene glycol, block polymers with a molecular weight between 2500 and 3500 g / mol, such as those sold under the trade name Hypermer®, sorbitan extracts, such as sorbitan mono- or polyoleate, sorbitan isostearate or sorbitan sesquioleate, polyethoxylated sorbitan esters, or diethoxylated oleoacetyl alcohol or tetraethoxylated lauryl acrylate, condensation products of aliphatic alcohols higher than ethylene, such as the reaction product of oleic alcohol with two ethylene oxide units; condensation products of alkylphenols with ethylene oxide, such as the reaction product of nonylphenol with four ethylene oxide units. Ethoxylated fatty amines, such as Witcamide® 511, alkylated phosphate esters, betaine-based products, and ethoxylated amines are also good candidates for water-in-oil emulsifiers.

[0140] The amount of oil-in-water emulsifier in the inverse emulsion is advantageously between 0.1 and 10% by weight, preferably between 1 and 10% by weight, based on the total weight of the inverse emulsion.

[0141] The process of the present invention may include the addition of at least one oil-in-water emulsifier.

[0142] The oil-in-water emulsifiers are advantageously selected from ethoxylated nonylphenols, preferably having an ethoxylation of 4 to 10 (i.e. preferably having an ethoxylation degree ranging from 4 to 10); ethoxylated / propoxylated alcohols, preferably having an ethoxylation / propoxylation containing from 12 to 25 carbon atoms; ethoxylated tridecyl alcohols; ethoxylated / propoxylated fatty alcohols; ethoxylated sorbitan esters, advantageously having 20 molar equivalents of ethylene oxide; polyethoxylated sorbitan laurates, advantageously having 20 molar equivalents of ethylene oxide; polyethoxylated castor oils, advantageously having 40 molar equivalents of ethylene oxide; decaethoxylated oleodecyl alcohols; heptaethoxylated lauryl alcohols; polyethoxylated sorbitan monostearates, advantageously having 20 molar equivalents of ethylene oxide; polyethoxylated alkyl phenols, advantageously having 20 molar equivalents of ethylene oxide; The emulsifiers are preferably selected from the group consisting of: cetyl ether of alcohols (advantageously having 10 molar equivalents of ethylene oxide); polyethylene oxide alkylaryl ethers; N-ketyl-N-ethylmorpholinium ethosulfate; sodium lauryl sulfate; condensation products of fatty alcohols with ethylene oxide (advantageously having 10 molar equivalents of ethylene oxide); condensation products of alkylphenols with ethylene oxide (advantageously having 12 molar equivalents of ethylene oxide); condensation products of fatty amines with 5 or more molar equivalents of ethylene oxide (advantageously 5 to 50 equivalents); ethoxylated tristyrylphenols; condensation products of ethylene oxide with polyhydric alcohols partially esterified with fatty chains, and their anhydrides; amine oxides, preferably with alkyl polyglucosides; glucamides; phosphoric acid esters; alkylbenzene sulfonic acids and their salts; surfactant block polymers, and mixtures thereof. The alkyl groups of these oil-in-water emulsifiers are preferably linear or branched groups containing 1 to 20 carbon atoms, more preferably 3 to 15 carbon atoms. Furthermore, the aryl groups of these oil-in-water emulsifiers preferably contain from 6 to 20 carbon atoms, more preferably from 6 to 12 carbon atoms.

[0143] Typically, the inverse emulsion comprises between 0.1 and 10% by weight, preferably between 1 and 10% by weight, of an oil-in-water emulsifier based on the total weight of the inverse emulsion.

[0144] The oil-in-water emulsifier can be added before, during or after the polymerization. Preferably, the oil-in-water emulsifier is added after the polymerization.

[0145] Generally, the polymer concentration in the inverse emulsion is between 5 and 50% by weight, preferably between 15 and 40% by weight, based on the total weight of the inverse emulsion.

[0146] The flocculant polymer according to the invention preferably has a weight average molecular weight of at least 1 million g / mol, more preferably at least 2 million g / mol, more preferably at least 3 million g / mol, more preferably at least 5 million g / mol. There is no upper limit to the weight average molecular weight of the star polymer, but generally the particulate flocculant polymer P1 has a weight average molecular weight of 30 million g / mol or less.

[0147] In a preferred embodiment, the water-in-oil emulsion flocculant polymer is crosslinked.

[0148] In a preferred embodiment, the water-in-oil emulsion flocculant polymer is crosslinked and has a cationic regain of between 20% and 300%, more preferably between 40% and 200%, and even more preferably between 50% and 150%.

[0149] In a preferred embodiment, the water-in-oil flocculant polymer P2 is prepared by controlled radical polymerization known as RAFT (Reversible Chain Transfer by Addition-Fragmentation).

[0150] In a preferred embodiment, the water-in-oil emulsion flocculant polymer P2 is a cationic polymer.

[0151] In a preferred embodiment, the water-in-oil flocculant polymer P2 is composed of cationic hydrophilic monomers and optionally non-ionic hydrophilic monomers.

[0152] In a preferred embodiment the water-in-oil flocculant polymer P2 comprises at least 30 mol %, preferably at least 50 mol %, more preferably at least 70 mol %, even more preferably at least 80 mol % of cationic hydrophilic monomers.

[0153] In a preferred embodiment, the water-in-oil flocculant polymer P2 comprises at least quaternized dimethylaminoethyl acrylate (DMAEA) as a cationic hydrophilic monomer, more preferably the only cationic hydrophilic monomer is quaternized dimethylaminoethyl acrylate (DMAEA).

[0154] In a preferred embodiment, the water-in-oil flocculant polymer P2 is a polymer consisting of quaternized dimethylaminoethyl acrylate (DMAEA) and acrylamide monomers.

[0155] In a preferred embodiment, the water-in-oil flocculant polymer P2 is a polymer consisting of at least 30 mol% quaternized dimethylaminoethyl acrylate (DMAEA) and not more than 70 mol% acrylamide, more preferably a polymer consisting of at least 50 mol% quaternized dimethylaminoethyl acrylate (DMAEA) and not more than 50 mol% acrylamide, even more preferably a polymer consisting of at least 70 mol% quaternized dimethylaminoethyl acrylate (DMAEA) and not more than 30 mol% acrylamide, even more preferably a polymer consisting of at least 80 mol% quaternized dimethylaminoethyl acrylate (DMAEA) and not more than 20 mol% acrylamide.

[0156] The invention will now be further described with reference to the following examples.

[0157] The following examples are merely illustrative of the invention and are not intended to be limiting. EXAMPLES

[0158] List of abbreviations: AM: Acrylamide AA: Acrylic acid DMAEA: Dimethylaminoethyl acrylate, ammonium chloride MBA: Methylenebisacrylamide SH: Sodium hypophosphite DADMAC: Diallyldimethylammonium chloride APTAC: Acrylamidopropyltrimethylammonium chloride Characteristics of sludge

[0159] [Table 1]

[0160] The polymers used in the examples are summarized in Table 2 (polymer P1) and Table 3 (polymer P2).

[0161] [Table 2]

[0162] [Table 3]

[0163] Dehydration method Unless otherwise noted, all examples were generated using the following method:

[0164] The powdered flocculant polymer P1 was dissolved in water in a dissolution tank and added to the sludge to be treated. Then, a belt conveyor was used to transport the sludge to the solid-liquid separator at a transport speed of 3 km / h. The water-in-oil emulsion flocculant polymer P2 was inverted in water and added to the sludge to be treated using a static mixer at X meters after the injection position (summarized in Table 5). The sludge sample was taken just before the sludge reached the solid-liquid separator (centrifuge). The ratio of the powdered flocculant polymer P1 to the water-in-oil flocculant polymer P2 was 70:30.

[0165] (Example 1) The powdered flocculant polymer P1 was dissolved in water in a dissolver and added to the sludge to be treated. The water-in-oil emulsion flocculant polymer P2 was added directly to the dissolver of P1 and the mixture of the two polymers was added to the sludge to be treated. The sludge samples were taken just before the sludge reached the dewatering unit.

[0166] (Example 14) The same procedure was used for all other polymers, except that the water-in-oil emulsion flocculant polymer P2 was not inverted using a static mixer prior to addition to the sludge.

[0167] (Examples 24-28) The same procedure was used as for all other polymers, but the solid-liquid separation equipment was modified according to Table 4.

[0168] [Table 4]

[0169] The results are summarized in Table 5.

[0170] [Table 5A]

[0171] [Table 5B]

[0172] In these instances, the methods of the present invention provide superior dewatering performance than those known in the prior art.

[0173] Lubrication effect The lubrication effect was calculated by measuring the pressure difference immediately after the addition of the water-in-oil emulsion flocculant polymer and in the solid-liquid separator. For this test, the solid-liquid separator was installed at different distances from the injection position of the water-in-oil emulsion flocculant polymer, and the results are summarized in Table 6.

[0174] The results are expressed as friction reduction rate (%), with the higher the percentage, the better the lubrication effect.

[0175] [Table 6]

[0176] This test demonstrates that the method of the present invention provides lubricating benefits not otherwise observed.

Claims

1. A sludge dewatering method comprising the steps of: 1) dissolving at least one particulate flocculant polymer P1 in water to obtain a polymer solution; 2) adding a polymer solution to the sludge to be treated; 3) transporting the sludge to be treated by a transport system to a solid-liquid separator and adding at least one water-in-oil emulsion type flocculant polymer P2 to the sludge to be treated in the transport system at least 2 meters from the adding point of the polymer solution; 4) Dewatering the sludge using a solid-liquid separator; A sludge dewatering method comprising:

2. 2. The sludge dewatering method according to claim 1, wherein the water-in-oil emulsion type flocculant polymer P2 is added at least 2.5 meters from the addition point of the polymer solution.

3. 3. A sludge dewatering method according to claim 1 or 2, wherein the water-in-oil emulsion type flocculant polymer is inverted in water before injection into the sludge to be treated using a static mixer prior to addition.

4. 2. The sludge dewatering method according to claim 1, wherein the ratio of particulate flocculant polymer P1 to water-in-oil flocculant polymer P2 is comprised between 10:90 and 90:

10.

5. 2. The sludge dewatering method according to claim 1, wherein the particulate flocculant polymer P1 is a linear polymer.

6. 2. The sludge dewatering method according to claim 1, wherein the water-in-oil emulsion type flocculant polymer P2 is a crosslinked polymer.

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