JP4404645B2 - Organic sludge dewatering method - Google Patents

Description

The present invention relates to a method for dewatering organic sludge, and more specifically, when dewatering organic sludge, a monomer mixture containing a cationic water-soluble monomer and an anionic water-soluble monomer as essential components is used as a salt aqueous solution. A cation equivalent consisting of a dispersion produced by a dispersion polymerization method in which a polymer dispersant soluble in the aqueous salt solution is coexisted to produce polymer particles having a particle size of 100 μm or less insoluble in the aqueous salt solution. The present invention relates to an organic sludge dewatering method in which an amphoteric water-soluble polymer (A) having the same number or higher than an equivalent value and an amphoteric water-soluble polymer (B) having an anion equivalent value higher than a cation equivalent value are added in combination and dehydrated.

  Conventionally, cationic polymer flocculants have been used for the dehydration of various sludges, but amphoteric polymer flocculants have become widespread for the purpose of reducing the moisture content of dehydrated cake and improving filter cloth peelability. . However, due to the recent increase in sludge generation and deterioration of sludge properties, there is a limit to the amount of sludge treated, the water content of the dehydrated cake, the SS recovery rate, the peelability of the cake from the filter cloth, etc. Improvement is demanded.

  On the other hand, for the purpose of reducing the moisture content of the dehydrated cake and improving the peelability from the filter cloth, Patent Document 1 and Patent Document 2 disclose crosslinkable ionic polymer flocculants. As described above, the crosslinkable water-soluble polymer has various characteristics and functions. However, when the polymer is applied to a sludge dehydrating agent, the molecular spread in the aqueous solution is relatively small. There is a problem that the amount of addition increases compared to the above. In order to improve such disadvantages of the crosslinkable water-soluble polymer, Patent Document 3 or Patent Document 4 contains a quaternary ammonium base, a methacrylate monomer, an acrylate monomer and an anion. An amphoteric polymer dehydrating agent obtained by copolymerizing an ionic monomer at a certain ratio is disclosed. However, these still do not satisfy the purpose enough.

  As a new and improved method, the amphoteric water-soluble polymer and the anionic monomer molar ratio are higher than the molar ratio of the cationic monomer. A combination with a water-soluble polymer (Patent Document 5). However, the product form of this amphoteric water-soluble polymer is a powder or water-in-oil emulsion, and the dissolution time is long because of the powder, and there is concern that the solvent and activator may affect the environment because of the water-in-oil emulsion. Is done.

Japanese Patent Laid-Open No. 2-219887 Japanese Patent Publication No. 8-164 JP 7-256299 A JP 7-256300 A JP 2003-175302 A

  When a crosslinkable water-soluble ionic polymer is used as a sludge dewatering agent, excellent points such as a decrease in the moisture content of the dehydrated cake are manifested, but on the other hand, the amount of addition is inevitably increased until the effect is manifested. As a result, there arises a problem of an increase in cost. Further, as in Patent Document 5, the molar ratio of the amphoteric water-soluble polymer and the anionic monomer is higher than the molar ratio of the cationic monomer. The method combining with a high amphoteric water-soluble polymer is expected to improve the dehydration property, but causes problems of product solubility and environmental impact. Therefore, an object of the present invention is to propose a sludge dewatering method that leaves the advantages of a crosslinkable water-soluble ionic polymer, solves the problem of reducing the addition amount, and further solves the problems of product solubility and environmental impact. There is.

In order to solve the above-mentioned problems, the present inventor has intensively studied and as a result, has reached the following invention. That is, according to the first aspect of the present invention, when dewatering organic sludge, a monomer mixture containing a cationic water-soluble monomer and an anionic water-soluble monomer as essential components can be added to the salt aqueous solution in a salt aqueous solution. The cation equivalent value of the dispersion produced by the dispersion polymerization method in which a soluble polymer dispersant is coexistent to produce polymer particles having a particle size of 100 μm or less insoluble in the salt aqueous solution is equal to or higher than the anion equivalent value. The present invention relates to a method for dewatering organic sludge, comprising adding and dehydrating an amphoteric water-soluble polymer (A) and an amphoteric water-soluble polymer (B) having an anion equivalent value higher than the cation equivalent value.

一般式（１）
Ｒ１は水素又はメチル基、Ｒ２、Ｒ３は炭素数１〜３のアルキル基、アルコキシ基あるいはベンジル基、Ｒ４は水素、炭素数１〜３のアルキル基、アルコキシ基あるいはベンジル基であり、同種でも異種でも良い。Ａは酸素またはＮＨ、Ｂは炭素数２〜４のアルキレン基またはアルコキシレン基、Ｘ１は陰イオンをそれぞれ表わす

一般式（２）
Ｒ５は水素又はメチル基、Ｒ６、Ｒ７は炭素数１〜３のアルキル基、アルコキシ基あるいはベンジル基、Ｘ２は陰イオンをそれぞれ表わす

一般式（３）
Ｒ８は水素またはＣＨ２ＣＯＯＹ２、ＱはＳＯ３、Ｃ６Ｈ４ＳＯ３、
ＣＯＮＨＣ（ＣＨ３）２ＣＨ２ＳＯ３、Ｃ６Ｈ４ＣＯＯあるいはＣＯＯ、Ｒ９は水素、メチル基またはＣＯＯＹ３であり、Ｙ１、Ｙ２、Ｙ３は水素または陽イオン In the invention of claim 2, the amphoteric water-soluble polymer (A) is represented by 15 to 95 mol% of a monomer represented by the following general formula (1) and / or (2), and (3). It is obtained by polymerizing a monomer mixture comprising 5 to 50 mol% of a monomer and 0 to 80 mol% of a nonionic monomer, and the amphoteric water-soluble polymer (B) has the following general formula: From 5 to 50 mol% of the monomer represented by (1) and / or (2), from 15 to 60 mol% of the monomer represented by (3) and from 0 to 80 mol% of the nonionic monomer The method for dewatering organic sludge according to claim 1, which is obtained by polymerizing a monomer mixture.

General formula (1)
R1 is hydrogen or a methyl group, R2 and R3 are alkyl groups having 1 to 3 carbon atoms, alkoxy groups or benzyl groups, R4 is hydrogen, an alkyl group having 1 to 3 carbon atoms, alkoxy groups or benzyl groups. But it ’s okay. A represents oxygen or NH, B represents an alkylene group or alkoxylene group having 2 to 4 carbon atoms, and X1 represents an anion.

General formula (2)
R5 represents hydrogen or a methyl group, R6 and R7 each represent an alkyl group having 1 to 3 carbon atoms, an alkoxy group or a benzyl group, and X2 represents an anion.

General formula (3)
R8 is hydrogen or CH2COOY2, Q is SO3, C6H4SO3,
CONHC (CH3) 2CH2SO3, C6H4COO or COO, R9 is hydrogen, methyl group or COOY3, Y1, Y2, Y3 are hydrogen or cation

The invention of claim 3 is characterized in that the anionic group of the amphoteric water-soluble polymer (A) and the amphoteric water-soluble polymer (B) is composed only of a carboxyl group. This is a method for dewatering organic sludge.

  When two types of amphoteric water-soluble polymers are added in combination, it is considered that efficient dehydration is realized by the following actions. That is, when added sequentially, the amphoteric water-soluble polymer (A) having a cation equivalent value equal to or higher than the anion equivalent value first acts on the sludge suspended particles, and flocs are generated by agglomeration reaction. Next, the addition of the amphoteric water-soluble polymer (B) having an anion equivalent value higher than the cation equivalent value causes the reaction to adsorb to the cationic sites of floc and reaggregate in parallel. This action results in a strong and dehydrated floc that is high in strength and does not contain excess moisture, resulting in improved dewatering efficiency. On the other hand, when two types of amphoteric water-soluble polymers are mixed and added, an ion complex is formed by most of the polymers when they are added to the sludge, and agglutination occurs. In this case, it is presumed that an ion complex is generated more efficiently than one type of amphoteric water-soluble polymer, and this enhances the aggregation effect.

  A feature of the present invention is that when dewatering organic sludge, a monomer mixture containing a cationic water-soluble monomer and an anionic water-soluble monomer as an essential component is soluble in the aqueous salt solution in the aqueous salt solution. An amphoteric aqueous solution having a cation equivalent value equal to or higher than the anion equivalent value of a dispersion prepared by a dispersion polymerization method in which a polymer dispersant is present to produce polymer particles having a particle size of 100 μm or less that is insoluble in the aqueous salt solution. The hydrophilic polymer (A) and the amphoteric water-soluble polymer (B) having an anion equivalent value higher than the cation equivalent value.

  That is, since the amphoteric water-soluble polymer has a cationic group and an anionic group in the molecule, an intramolecular or intermolecular ion complex is formed, and when added to sludge, the apparent molecular weight is increased and the aggregation effect is improved. In addition, the cationic group alone has a high possibility of redispersion and tends to cause a decrease in the aggregation effect, but is considered to have a function of preventing the cause. This is the basic concept of amphoteric water-soluble polymers. It is presumed that the action mechanism is slightly different between the case where two types of amphoteric water-soluble polymers are mixed and added and the case where they are added sequentially.

  When two types of amphoteric water-soluble polymers are added sequentially, the amphoteric water-soluble polymer (A) whose cation equivalent value is equal to or higher than the anion equivalent value acts on sludge suspended particles first, and flocs due to agglomeration reaction. When the amphoteric water-soluble polymer (B) having the same or higher anion equivalent value than the cation equivalent value is added, and the amphoteric water-soluble polymer (B) is floc A reaction that adsorbs to the cationic sites and reaggregates occurs in parallel. This action results in a strong and dehydrated floc that is high in strength and does not contain excess moisture, resulting in improved dewatering efficiency. On the other hand, when two types of amphoteric water-soluble polymers are mixed and added, an ion complex is formed by most of the polymers when they are added to the sludge, and agglutination occurs. In this case, it is considered that an ion complex is generated more efficiently than one type of amphoteric water-soluble polymer, and this enhances the aggregation effect.

  A water-soluble polymer comprising a polymer fine particle dispersion dispersed in an aqueous salt solution can be produced according to Japanese Patent Application Laid-Open No. 62-15251. In this method, a cationic monomer or a cationic monomer and a nonionic monomer are stirred in a salt aqueous solution in the presence of a dispersant composed of an ionic polymer soluble in the salt aqueous solution. It consists of a dispersion of polymer fine particles having a particle size of 100 mμ or less. When polymerizing an amphoteric water-soluble polymer, an anionic monomer is allowed to coexist during polymerization. As the polymer dispersing agent, a homopolymer of dimethyldiallylammonium chloride or (meth) acryloyloxyethyltrimethylammonium chloride or a copolymer with a nonionic monomer is used. Alternatively, nonionic polyvinyl pyrrolidone can also be used. The addition amount is 1 to 20% by mass, preferably 3 to 15% by mass, based on the monomer mass. The inorganic salts constituting the aqueous salt solution are more preferably polyvalent anion salts, and sulfates or phosphates are suitable. Specifically, ammonium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, ammonium hydrogen phosphate, sodium hydrogen phosphate And potassium hydrogen phosphate. These salts are preferably used as an aqueous solution having a concentration of 15% or more.

Next, the amphoteric water-soluble polymer (A) and the amphoteric water-soluble polymer (B) will be described. These amphoteric water-soluble polymers are copolymers obtained by polymerizing a monomer mixture essentially comprising a cationic water-soluble monomer and an anionic water-soluble monomer. For example, the cationic water-soluble monomer is a salt of inorganic acid or organic acid such as dimethylaminoethyl (meth) acrylate or dimethylaminopropyl (meth) acrylamide represented by the general formula (1), or methyl chloride or benzyl chloride. Is a copolymer of quaternary ammonium salt and acrylamide. That is, (meth) acryloyloxyethyltrimethylammonium chloride, (meth) acryloyloxy 2-hydroxypropyltrimethylammonium chloride, (meth) acryloylaminopropyltrimethylammonium chloride, (meth) acryloyloxyethyldimethylbenzylammonium chloride, ( Examples thereof include (meth) acryloyloxy 2-hydroxypropyldimethylbenzylammonium chloride and (meth) acryloylaminopropyldimethylbenzylammonium chloride. Also, diallylammonium salts such as dimethyldiallylammonium chloride represented by the general formula (2) can be used.

  The anionic water-soluble monomer is represented by the general formula (3). For example, acrylamide 2-methylpropanesulfonic acid, styrenesulfonic acid, (meth) allylsulfonic acid, vinylsulfonic acid, (meth) acrylic acid And itaconic acid, which is maleic acid, and the like are copolymerized using one or more of them.

A nonionic water-soluble monomer may be copolymerized with these ionic water-soluble monomers. For example, (meth) acrylamide, N, N-dimethylacrylamide, vinyl acetate, acrylonitrile, methyl acrylate, 2-hydroxyethyl (meth) acrylate, diacetone acrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide Acrylamide is preferable.

The ratio of each monomer of these amphoteric water-soluble polymers (A) and (B) is as follows. The amphoteric water-soluble polymer (A) whose cation equivalent value is the same or higher than the anion equivalent value is 15 to 95 mol% of the cationic water-soluble monomer, 5 to 50 mol% of the anionic water-soluble monomer, and nonionic. 0 to 80 mol% of the water-soluble monomer, preferably 20 to 90 mol% of the cationic water-soluble monomer, 10 to 50 mol% of the anionic water-soluble monomer, and the nonionic water-soluble monomer It is 0-70 mol%. Further, the amphoteric water-soluble polymer (B) having an anion equivalent value higher than the cation equivalent value is 5 to 50 mol% of the cationic water-soluble monomer, 15 to 60 mol% of the anionic water-soluble monomer, and nonionic. 0 to 80 mol% of water-soluble monomer, preferably 10 to 50 mol% of cationic water-soluble monomer, 20 to 50 mol% of anionic water-soluble monomer, and 0 to nonionic water-soluble monomer -70 mol%.

  The amphoteric water-soluble polymer used in the present invention may be either a carboxyl group or a sulfone group as an anionic group, or may coexist, but it is preferably composed of only a carboxyl group. The reason for this is considered that the dissociation degree of the carboxyl group changes depending on the pH, so that an agglutination reaction corresponding to the surrounding environment is generated, and as a result, the agglomeration performance is also improved. In addition, the sulfone group-containing monomer generally has a high price and a large influence on the cost, and it is economically expensive to use a carboxyl group-containing monomer at a lower price.

The ratio of the combination of the two types of amphoteric water-soluble polymers (A) and (B) is such that when the ion equivalent per unit mass is not the same (cation equivalent per unit mass of the amphoteric water-soluble polymer (A)) The ratio of anion equivalent) / (anion equivalent-cation equivalent per unit mass of the amphoteric water-soluble polymer (B)) is 0.5 to 10, preferably 0.6 to 8. When the ion equivalent per unit mass is the same amount, the ratio of (cation equivalent per unit mass of amphoteric water-soluble polymer (A)) / (anion equivalent per unit mass of amphoteric water-soluble polymer (B)) ratio = It is 0.5-15, Preferably it is 0.8-1.2. As for the addition method, either one of the amphoteric water-soluble polymers (A) and (B) may be added first, and the other may be added sequentially, or both may be mixed and added.

  The molecular weight of these amphoteric water-soluble polymers (A) or (B) is 100,000 to 20 million, preferably 1 million to 15 million. If it is less than 100,000, the cohesive force is insufficient and the yield rate is lowered, and if it is 20 million or more, the cohesive force is too high and the flocs become enormous and dehydration is reduced, and the solution viscosity becomes too high and the dispersibility becomes poor. In addition, the handling of the aqueous solution also becomes worse.

Applicable sludge is surplus sludge generated during biological treatment such as papermaking wastewater, chemical industry wastewater, food industry wastewater, or organic sludge such as raw sludge, mixed raw sludge, surplus sludge, digested sludge, etc. . The amount of the amphoteric water-soluble polymer (A) or (B) used in the present invention to the organic sludge is 0.1 to 1.5 in terms of the total amount of (A) and (B) to the sludge solids. It is mass%, Preferably it is 0.2-1.0 mass%.

(Synthesis Example 1) Metacloyl in a 500 mL four-necked flask equipped with a thermometer, a stirrer, a nitrogen inlet tube, a monomer supply pipe connected to a peristaltic pump (SMP-21 type, manufactured by Tokyo Rika Kikai Co., Ltd.) and a condenser 46.3 g of 80 wt% aqueous solution of oxyethyltrimethylammonium chloride (hereinafter abbreviated as DMC), 60.5 g of 80 wt% aqueous solution of acryloyloxyethyltrimethylammonium chloride (hereinafter abbreviated as DMQ), acrylic acid (hereinafter abbreviated as AAC) ) (20.6 g), 50% aqueous solution of acrylamide (hereinafter abbreviated as AAM) 36.5 g, 173.1 g of ion-exchanged water, 125.0 g of ammonium sulfate, acryloyloxyethyltrimethylammonium chloride homopolymer as a dispersant 30.0 g (20 wt% liquid, viscosity 6450 mPa · s ) And the pH was adjusted to 3.3. At this time, the mol% of each monomer is DMC / DMQ / AAC / AAM = 25/35/20/20. Next, the temperature in the reactor was kept at 30 ± 2 ° C., and after replacing with nitrogen for 30 minutes, 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] as an initiator was used. Polymerization was initiated by adding 1.0 g of a 1% aqueous solution of dihydrochloride (0.01% monomer). When the internal temperature was kept at 30 ± 2 ° C. and the reaction was carried out for 7 hours from the start of polymerization, 0.01% of the initiator was added to the above monomer, and the reaction was further completed for 7 hours. The resulting dispersion had a squeeze monomer concentration of 20%, a polymer particle size of 10 μm or less, and a viscosity of the dispersion of 710 mPa · s. Moreover, the weight average molecular weight was measured with the molecular weight measuring device (DLS-7000 by Otsuka Electronics) by a static light scattering method. This sample is designated as Sample-1. The composition is shown in Table 1 and the results are shown in Table 2.

(Synthesis Example 2) By the same operation as in Synthesis Example 1, a dispersion polymerized product DMQ / AAC / acrylamido 2-methylpropanesulfonic acid / AAM = 40/10/5/45 (sample-2) in an aqueous salt solution was synthesized. The composition is shown in Table 1 and the results are shown in Table 2.

(Synthesis Example 3) Acryloyloxy in a 500 mL four-necked flask equipped with a thermometer, a stirrer, a nitrogen introduction tube, a monomer supply tube connected to a peristaltic pump (SMP-21 type, manufactured by Tokyo Rika Kikai Co., Ltd.) and a condenser 49.4 g of 80% by weight aqueous solution of ethyltrimethylammonium chloride (hereinafter abbreviated as DMQ), 36.7 g of 60% by weight aqueous solution of acrylic acid (hereinafter abbreviated as AAC), 50% aqueous solution of acrylamide (hereinafter abbreviated as AAM) 72. 4 g, 150.0 g of ion-exchanged water, 125.0 g of ammonium sulfate, and 30.0 g of acryloyloxyethyltrimethylammonium chloride homopolymer as a dispersant (20 wt% solution, viscosity 6450 mPa · s) were each squeezed to a pH of 3.3. Adjusted. At this time, the mol% of each monomer is DMQ / AAC / AAM = 20/30/50. Next, the temperature in the reactor was kept at 30 ± 2 ° C., and after replacing with nitrogen for 30 minutes, 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] as an initiator was used. Polymerization was initiated by adding 1.0 g of a 1% aqueous solution of dihydrochloride (0.01% monomer). When the internal temperature was kept at 30 ± 2 ° C. and the reaction was carried out for 7 hours from the start of polymerization, 0.01% of the initiator was added to the above monomer, and the reaction was further completed for 7 hours. The dispersion monomer obtained had a squeeze monomer concentration of 20.5%, a polymer particle size of 10 μm or less, and a dispersion viscosity of 550 mPa · s. Moreover, the weight average molecular weight was measured with the molecular weight measuring device (DLS-7000 by Otsuka Electronics) by a static light scattering method. This sample is designated as sample-4. The composition is shown in Table 1 and the results are shown in Table 2.

ＤＭＣ：メタクロルオキシエチルトリメチルアンモニウムクロリド
ＤＭＱ：アクロルオキシエチルトリメチルアンモニウムクロリド、ＡＡＣ：アクリル酸、ＡＡＰＳ：アクリルアミド２−メチルプロパンスルホン酸、ＡＡＭ：アクリルアミド、
（表２）

製品粘度：ｍＰａ・ｓ、分子量：万、製品形態：塩水中分散液 (Synthesis Example 4) By the same operation as in Synthesis Example 3, a dispersion polymerized product DMQ / AAC / acrylamido 2-methylpropanesulfonic acid / AAM = 20/20/10/50 (sample-4) in an aqueous salt solution was synthesized. The composition is shown in Table 1 and the results are shown in Table 2.



(Table 1)

DMC: methacryloxyethyltrimethylammonium chloride DMQ: acryloxyethyltrimethylammonium chloride, AAC: acrylic acid, AAPS: acrylamide 2-methylpropanesulfonic acid, AAM: acrylamide,
(Table 2)

Product viscosity: mPa · s, molecular weight: 10,000, product form: salt water dispersion

Collect 200 mL of raw sewage mixed sludge (pH 5.95, total ss 31,500 mg / L) in a poly-bicker, and use the amphoteric water-soluble polymer (A) sample-1 or sample-2 in Table 2 as a solid sludge Add 3,500 ppm to the beaker, change the beaker and stir 10 times, then add amphoteric water-soluble polymer (B) Sample-3 or Sample-4 of Table 2 to the solid content of 3000 ppm against sludge. -After transferring and stirring 10 times, the mixture was filtered through a T-1179L filter cloth (made of nylon), and the filtrate amount after 20 seconds was measured. The filtered sludge is dehydrated at a press pressure of 3 kg / m 2 for 1 minute. Thereafter, the filter cloth peelability was visually checked, and the cake water content (dried at 105 ° C. for 20 hours) was measured. The results are shown in Table 3.

フロック径：ｍｍ、ケーキ含水率：質量％、薬注濃度：質量％
薬注量：対ｓｓ質量％、濾布剥離性：○＞△＞×の順に良いことを示す。 When only sample-1 of Table 2 is used as a comparative test, when sample-1 and sample-2 are combined, when only sample-2 is used, when only sample-3 is used, and when sample-3 and sample-4 are used Each case was tested in combination.
The results are shown in Table 3.
(Table 3)

Flock diameter: mm, cake moisture content: mass%, chemical concentration: mass%
This indicates that the amount of chemical injection: ss mass%, filter cloth peelability: ○>Δ> × in that order.

  200 mL of city sewage digested sludge (pH 7.66, total ss 38,000 mg / mL) was collected in a poly-bicker, and the amphoteric water-soluble polymer (A), Sample-1 or Sample-2 in Table 2 was used as a solid sludge content 4 2,000 ppm was added, the beaker was transferred and stirred 10 times, and then the amphoteric water-soluble polymer (B) Sample-3 or Sample-4 shown in Table 2 was added to the sludge solid content of 4,000 ppm. -After changing and stirring 10 times, the mixture was filtered through a T-1179L filter cloth (made of nylon), and the amount of filtrate after 20 seconds was measured. The filtered sludge is dehydrated at a press pressure of 2 kg / m @ 2 for 1 minute. Thereafter, the filter cloth peelability was visually checked, and the cake water content (dried at 105 ° C. for 20 hours) was measured. The results are shown in Table 4.

フロック径：ｍｍ、ケーキ含水率：質量％、薬注濃度：質量％、薬注量：対ｓｓ質量％、濾布剥離性：○＞△＞×の順に良いことを示す。




When only sample-1 of Table 2 was used as a comparative test, when sample-1 and sample-2 were combined, only when sample-4 was used, and each case where sample-3 and sample-4 were combined was tested. . The results are shown in Table 4.
(Table 4)

Flock diameter: mm, cake moisture content: mass%, chemical injection concentration: mass%, chemical injection amount: ss mass%, filter cloth peelability: ○>Δ> × indicates good order.

Claims (3)

When dewatering organic sludge, a monomer mixture containing a cationic water-soluble monomer and an anionic water-soluble monomer as an essential component coexists with a polymer dispersant soluble in the aqueous salt solution. The amphoteric water-soluble polymer (A) having a cation equivalent value equal to or higher than the anion equivalent value of a dispersion produced by a dispersion polymerization method for producing polymer particles having a particle size of 100 μm or less insoluble in the aqueous salt solution. And an amphoteric water-soluble polymer (B) having an anion equivalent value higher than the cation equivalent value in combination and dehydrating, and dehydrating the organic sludge. The amphoteric water-soluble polymer (A) is a monomer represented by the following general formula (1) and / or (2) 15 to 95 mol%, a monomer represented by (3) 5 to 50 mol % And a nonionic monomer from 0 to 80 mol%, and the amphoteric water-soluble polymer (B) is represented by the following general formula (1) and / or ( 2) The monomer mixture represented by 5 to 50 mol% represented by 2), the monomer mixture represented by (3) 15 to 60 mol% and the nonionic monomer 0 to 80 mol% is polymerized. The method for dewatering organic sludge according to claim 1, wherein the method is obtained.

General formula (1)
R1 is hydrogen or a methyl group, R2 and R3 are alkyl groups having 1 to 3 carbon atoms, alkoxy groups or benzyl groups, R4 is hydrogen, an alkyl group having 1 to 3 carbon atoms, alkoxy groups or benzyl groups. But it ’s okay. A represents oxygen or NH, B represents an alkylene group or alkoxylene group having 2 to 4 carbon atoms, and X1 represents an anion.

General formula (2)
R5 represents hydrogen or a methyl group, R6 and R7 each represent an alkyl group having 1 to 3 carbon atoms, an alkoxy group or a benzyl group, and X2 represents an anion.

General formula (3)
R8 is hydrogen or CH2COOY2, Q is SO3, C6H4SO3,
CONHC (CH3) 2CH2SO3, C6H4COO or COO, R9 is hydrogen, methyl group or COOY3, Y1, Y2, Y3 are hydrogen or cation The method for dewatering organic sludge according to claim 1 or 2, wherein the anionic groups of the amphoteric water-soluble polymer (A) and the amphoteric water-soluble polymer (B) are composed of only carboxyl groups.