Sludge dewatering agent, method for dewatering sludge, and method for producing dewatered sludge

Abstract

Provided are: a sludge dewatering agent characterized by comprising a polyalkylene imine with a number average molecular weight of 2,000-200,000; a method for dewatering sludge, the method characterized by using, in combination, the sludge dewatering agent (first sludge dewatering agent) and a second sludge dewatering agent comprising a polymeric flocculant other than the polyalkylene imine described above; and a method for producing dewatered sludge, the method characterized by comprising a dewatering step in which the above method for dewatering sludge is used. The abovementioned polymeric flocculant is preferably a cationic polymer.

Description

Sludge dehydration agent, sludge dehydration method, and method for producing dehydrated sludge

[0001] The present invention relates to a sludge dehydrating agent, a method for dehydrating sludge, and a method for producing dehydrated sludge.

[0002] In general, in sewage and industrial wastewater treatment, raw sewage and industrial wastewater is first pretreated before being subjected to activated sludge treatment. The products of these treatments are excess sludge, primary sludge, or a mixed, thickened sludge of these, which are dewatered and then disposed of (incineration, etc.). In order to efficiently dewater excess sludge, primary sludge, or a mixed, thickened sludge of these, polymer flocculants have traditionally been added to the excess sludge, primary sludge, or a mixed, thickened sludge as a sludge dewatering agent. The addition of polymer flocculants causes the formation of flocs, and the properties of these flocs have a significant impact on dewatering efficiency.

[0003] As the sludge dewatering agent, a cationic polyacrylic acid ester polymer is used. Patent Document 1 describes a sludge dewatering method using a flocculant, in which a flocculant is added to sludge produced by wastewater treatment, followed by filtration and dewatering, characterized in that a part of the flocculant to be added is added to excess sludge, the mixture is stirred to homogenize, and then the remainder is added and stirred, and the flocculant used is a cationic polymer flocculant such as polyacrylic acid ester.

[0004] However, if the dewatering rate of sludge is low, a large amount of fuel is required for incineration of the dewatered sludge. Therefore, there is a need for a sludge dewatering agent that can further improve dewatering efficiency, thereby reducing fuel consumption or, conversely, enabling energy generation using the sludge itself as fuel.

[0005] Japanese Unexamined Patent Publication No. 64-27700

[0006] Therefore, an object of the present invention is to provide a sludge dehydration agent having high dehydration efficiency, a sludge dehydration method that can easily increase the dehydration rate of sludge, and a method for producing dehydrated sludge having a high dehydration rate.

[0007] The present inventors have discovered that a sludge dehydration agent containing a polyalkyleneimine having a number average molecular weight (Mn) within a specific range, a method for dehydrating sludge characterized by using the sludge dehydration agent (first sludge dehydration agent) in combination with a second sludge dehydration agent containing a polymer flocculant other than the polyalkyleneimine, and a method for producing dehydrated sludge characterized by including a dehydration step using the sludge dehydration method can provide a sludge dehydration agent with high dehydration efficiency, a method for dehydrating sludge that can easily increase the dehydration rate of sludge, and a method for producing dehydrated sludge with a high dehydration rate, and have completed the present invention.

[0008] That is, the sludge dewatering agent of the present invention is characterized by containing a polyalkyleneimine having a number average molecular weight of 2,000 to 200,000. The sludge dewatering agent does not necessarily contain any polymer flocculant other than the polyalkyleneimine.

[0009] The present invention also provides a method for dehydrating sludge, characterized in that the sludge dehydration agent is used. The amount of polyalkyleneimine added to the sludge (solid content) is preferably 0.04 to 6 mass % based on the solid content of the sludge.

[0010] Another sludge dewatering method of the present invention is characterized by using in combination the sludge dewatering agent (first sludge dewatering agent) that does not contain any polymer flocculant other than the polyalkyleneimine and a second sludge dewatering agent that contains a polymer flocculant other than the polyalkyleneimine. The polymer flocculant is preferably a cationic polymer. The amount of the polyalkyleneimine added to the sludge (solid content) is preferably 0.1 to 0.3 mass% based on the solid content of the sludge. The amount of the polyalkyleneimine added to the sludge (solid content) is preferably 0.04 to 0.09 mass% based on the solid content of the sludge. The mass ratio of the solid content of the first sludge dewatering agent to the second sludge dewatering agent is preferably 1.0 to 1.0 to 15.0.

[0011] Furthermore, the method for producing dewatered sludge of the present invention is characterized by including a dewatering step using the above-mentioned method for dewatering sludge.

[0012] According to the present invention, it is possible to provide a sludge dehydration agent having high dehydration efficiency, a sludge dehydration method that can easily increase the dehydration rate of sludge, and a method for producing dehydrated sludge having a high dehydration rate.

[0013] 1 is a diagram showing a schematic diagram of a CST test device. 2 is a photograph showing a dehydration cell used in a centrifugal dehydration test.

[0014] 1. Sludge Dehydration Agent The sludge dehydration agent of the present invention is characterized by containing a polyalkyleneimine having a number-average molecular weight of 2,000 to 200,000. The number-average molecular weight of the polyalkyleneimine is preferably 10,000 to 150,000, and more preferably 20,000 to 120,000. By ensuring that the number-average molecular weight of the polyalkyleneimine contained in the sludge dehydration agent of the present invention falls within the above range, flocs that can be efficiently dewatered can be obtained.

[0015] The sludge dehydration agent of the present invention may be an aqueous solution of the polyalkyleneimine. The content of the polyalkyleneimine in the sludge dehydration agent of the present invention is preferably 0.01% by mass to 95% by mass, and more preferably 0.05% by mass to 90% by mass, relative to 100% by mass of the sludge dehydration agent. By setting the content of the polyalkyleneimine within the above range, flocs that can be dewatered more efficiently can be obtained.

[0016] The polyalkyleneimine is not particularly limited as long as it has the above number-average molecular weight, and examples thereof include polyethyleneimine and polypropyleneimine. For practical purposes, polyethyleneimine is preferred, and specifically, commercially available Epomin (registered trademark) SP-200 (polyethyleneimine having a number-average molecular weight of 10,000, manufactured by Nippon Shokubai Co., Ltd.), Epomin (registered trademark) P-1000 (polyethyleneimine having a number-average molecular weight of 70,000, manufactured by Nippon Shokubai Co., Ltd.), and Epomin (registered trademark) P-3000 (polyethyleneimine having a number-average molecular weight of 100,000, manufactured by Nippon Shokubai Co., Ltd.) can be used.

[0017] The number-average molecular weight of a polyalkyleneimine can be measured, for example, by gel permeation chromatography (GPC) using pullulan, polyethylene glycol, or the like as a standard substance. As an example, it can be measured by the following method. <Method for Measuring Number-Average Molecular Weight> The number-average molecular weight is determined by separating a sample containing a polyalkyleneimine at a concentration of 0.1 wt % using a Shimadzu Corporation HPLC system Prominence and connecting Showa Denko K.K. Shodex SB-806M and SB-807 in series, measuring with an RI detector, and analyzing with a GPC application. An aqueous solution containing 0.5 mol / L acetic acid and 0.5 mol / L sodium nitrate is used as the eluent. A calibration curve is created using pullulan (Shodex GPC standard sample P-82).

[0018] The sludge to which the sludge dehydrating agent of the present invention can be added includes sludge generated when high-BOD wastewater is subjected to biological treatment, etc., and can be applied to, for example, sludge generated in sewage and night soil treatment plants, excess sludge and primary sludge generated by activated sludge treatment of sewage and wastewater generated in food factories, livestock farms, chemical factories, etc., or mixed concentrated sludge thereof.

[0019] The amount of the sludge dehydrating agent added to the sludge (solid content) is not particularly limited, but a typical suitable amount can be about 0.05 to 10 mass % of the solid content of the sludge. If the amount added is too small, the flocculation performance may decrease, and if it is too large, the sludge may redisperse, making it impossible to obtain satisfactory flocculation performance.

[0020] The amount (solid content) of the polyalkyleneimine contained in the sludge dehydration agent to be added to the sludge is not particularly limited, but a typical preferred amount is about 0.05 to 10 mass % based on the solid content of the sludge. If the amount is too small, the flocculation performance may decrease, and if the amount is too large, the sludge may redisperse, making it impossible to obtain satisfactory flocculation performance.

[0021] In this specification, the solid content can be measured by the following method. Approximately 0.3 g of the object is weighed out and placed in an aluminum cup, and allowed to dry naturally at room temperature. Then, using a hot air dryer (for example, Espec Corporation, product name "PHH-101"), the object is dried at 140°C for 3 hours, and then allowed to cool in a desiccator, and the mass is measured. The solid content of the object is calculated from the amount of mass loss.

[0022] The sludge dehydration method of the present invention is characterized by using the above-mentioned sludge dehydration agent. The amount of the polyalkyleneimine added to the sludge (solid content) is preferably 0.04 to 6 mass %, more preferably 4 to 6 mass %, based on the solid content of the sludge.

[0023] Another sludge dewatering method of the present invention is characterized by using the above-mentioned sludge dewatering agent (first sludge dewatering agent) in combination with a second sludge dewatering agent containing a polymer flocculant other than the polyalkyleneimine. Examples of the polymer flocculant include cationic polymers, anionic polymers, nonionic polymers, and amphoteric polymers, with cationic polymers being preferred. In this case, the sludge dewatering agent (first sludge dewatering agent) of the present invention preferably does not contain a polymer flocculant other than the polyalkyleneimine.

[0024] Examples of the cationic polymer include polyacrylic acid esters, polyacrylamide (salts / quaternary salts), and chitosan (salts), among which polyacrylic acid esters are preferred. The polyacrylic acid ester preferably has a weight-average molecular weight of 500,000 to 10,000,000, more preferably 750,000 to 9,500,000, and even more preferably 1,000,000 to 9,000,000. Examples of the polyacrylic acid ester include polymers of alkylaminoethyl (meth)acrylates, copolymers of these with (meth)acrylamide, and quaternary ammonium salts thereof. Specific examples include polymers of dimethylaminoethyl (meth)acrylates, copolymers of these with acrylamide, and quaternary ammonium salts thereof. The cationic polymers may be used alone or in combination. The cationic polymer preferably has a cation equivalent value (Cv) of 1 to 15 meq / g, more preferably 2 to 10 meq / g.

[0025] The content of the polymer flocculant other than the polyalkyleneimine in the second sludge dehydration agent is preferably 0.01% by mass to 95% by mass, and more preferably 0.05% by mass to 90% by mass, relative to 100% by mass of the sludge dehydration agent. By setting the content of the polymer flocculant other than the polyalkyleneimine within the above range, flocs that can be dewatered more efficiently can be obtained.

[0026] When the first sludge dehydration agent and the second sludge dehydration agent are used in combination, the amount (solid content) of the first sludge dehydration agent added to the sludge is not particularly limited, but a typical suitable amount can be about 0.05 to 10 mass% of the solid content in the sludge. If the amount added is too small, the flocculation performance may decrease, and if it is too large, the sludge may redisperse, making it impossible to obtain satisfactory flocculation performance.

[0027] Furthermore, when the first sludge dehydration agent and the second sludge dehydration agent are used in combination, the amount of the polyalkyleneimine added to the sludge (solid content) is not particularly limited, but a standard suitable amount is preferably about 0.04 to 10 mass %, more preferably 0.04 to 5 mass %, even more preferably 0.04 to 1.0 mass %, and particularly preferably 0.04 to 0.09 mass % or 0.1 to 0.3 mass % based on the solid content of the sludge. If the amount added is too small, the flocculation performance may decrease, and if it is too large, the sludge may redisperse, making it impossible to obtain satisfactory flocculation performance.

[0028] The method for adding the first sludge dehydration agent and the second sludge dehydration agent to the sludge is not particularly limited. One method is to add each of them almost simultaneously and allow them to act on the sludge, for example, by dissolving each of them separately in water and adding them to the sludge almost simultaneously and stirring and mixing, or by mixing them in advance and adding this to the sludge-containing liquid to be treated.Another method is to first add either the first sludge dehydration agent or the second sludge dehydration agent to the sludge-containing liquid to be treated and mix well, and then add the other agent to act on the excess sludge.

[0029] The optimum conditions for the use ratio of the first sludge dehydration agent and the second sludge dehydration agent and the amount to be added to the sludge vary depending on the properties of the sludge, etc., so it is advisable to collect the sludge-containing liquid in a beaker or the like before putting it into practical use, add various amounts of the first sludge dehydration agent and the second sludge dehydration agent to the liquid, and select the conditions under which the best flocculation performance and dewatering properties are obtained. The mass ratio of the first sludge dehydration agent (solid content) to the second sludge dehydration agent (solid content) can be appropriately selected and determined from a range of 95:5 to 5:95, so as to obtain the ratio that exhibits the best flocculation and dewatering performance. The mass ratio of the solid content of the first sludge dehydration agent to the second sludge dehydration agent is preferably 1.0 to 1.0 to 15.0, more preferably 1.5 to 14.5, and even more preferably 2.0 to 14.0.

[0030] The total amount (solid content) of the first sludge dehydration agent and the second sludge dehydration agent to be added to the sludge is not particularly limited, but a typical suitable amount to be added can be approximately 0.1 to 10 mass %, preferably 0.15 to 5 mass %, and more preferably 0.2 to 1.5 mass %, based on the solid content of the sludge. If the amount added is too small, the flocculation performance may decrease, and if it is too large, the sludge may redisperse, making it impossible to obtain satisfactory flocculation performance.

[0031] 3. Manufacturing Method of Dewatered Sludge The manufacturing method of dewatered sludge of the present invention is characterized by including a dewatering step using the above-described sludge dewatering method. In the dewatering step, the above-described sludge dewatering agent (first sludge dewatering agent) is used in combination with a second sludge dewatering agent containing a polymer flocculant other than the polyalkyleneimine. The method of using these agents in combination is the same as that described in the section on the sludge dewatering method. By using the first sludge dewatering agent and the second sludge dewatering agent in combination with the sludge, the total amount of the first sludge dewatering agent and the second sludge dewatering agent added can be reduced. This allows the production of dewatered sludge with a high dewatering rate. Therefore, the dewatered sludge produced by the manufacturing method of dewatered sludge of the present invention can reduce fuel consumption during incineration or, conversely, enable energy generation using the sludge itself as fuel.

[0032] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0033] [Regarding the Samples Used] The polymers contained in the sludge dewatering agents used in the Examples and Comparative Examples are as follows. Nippon Shokubai's Epomin (registered trademark): SP-006, SP-018, SP-200, P-1000, and P-3000 were used as polyethyleneimines. The number-average molecular weights of the polymers were 600, 1,800, 10,000, 70,000, and 100,000, respectively (listed values ​​in the catalog). The polymer flocculant used was a cationic polyacrylic acid ester: a copolymer of dimethylaminoethyl (meth)acrylate and acrylamide with an estimated molecular weight of 3,000,000 (catalog value).

[0034] [About the sludge used] Mixed thickened sludge sampled from sewage treatment plant A or sewage treatment plant B was used. The mixed thickened sludge from sewage treatment plant A was a mixture of gravity-thickened primary sludge and flotation-pressurized thickened excess sludge. The mixed thickened sludge from sewage treatment plant B was a mixture of gravity-thickened primary sludge and centrifugal thickened excess sludge.

[0035] [Capillary Suction Time Measurement Test (CST Test)] The CST test apparatus is shown in Figure 1. In the CST test, a small amount of flocculated sludge is placed in a tube on filter paper. As the water in the sludge is drawn into the filter paper by capillary suction and expands circumferentially, the time it takes for the water in the sludge to pass between two concentric points (A-B in Figure 1) is measured, which can determine the dewaterability of the sludge. The smaller this value, the better the dewaterability. Measurements were performed using a CST meter (Yamato Scientific Co., Ltd.: Capillary Suction Time Measurement Device CST-1). Filter paper (cellulose chromatography paper, 69 mm x 90 mm) was placed on a plastic base, a plastic cover was placed on top of it, and a stainless steel cylinder was placed in the center, tightly contacting the base. A sludge sample was then placed in a beaker, and the appropriate sludge dehydration agent was added so that the polymer solids content relative to the sludge solids reached the specified amount shown in the table below. The mixture was stirred to form flocs. 6.4 mL of the completed sludge floc sample was measured and added via a cylinder, and the CST value [sec] was read.

[0036] [Number Average Molecular Weight] The number average molecular weight of polyalkyleneimine was measured by gel permeation chromatography (GPC) using pullulan as a standard substance according to the following method. <Measurement of Number Average Molecular Weight> The number average molecular weight was determined by separating a sample containing a polyalkyleneimine at a concentration of 0.1 wt % using a Shimadzu Corporation HPLC system Prominence and Showa Denko K.K. Shodex SB-806M and SB-807 connected in series, measuring with an RI detector, and analyzing using a GPC application. The eluent used was an aqueous solution containing 0.5 mol / L acetic acid and 0.5 mol / L sodium nitrate. A calibration curve was created using pullulan (Shodex GPC standard sample P-82).

[0037] Example 1 A sludge dewatering test was conducted on mixed concentrated sludge sampled at a sewage treatment plant A, using an aqueous solution (solid content 0.2% by mass) of polyethyleneimine [Epomin (registered trademark): SP-200 (number average molecular weight 10,000) manufactured by Nippon Shokubai] as a sludge dehydration agent, such that the amount of polymer (solid content) relative to the sludge (solid content) was 5% by mass, and the above-mentioned capillary suction time measurement test results were obtained.

[0038] Examples 2 to 3, Comparative Examples 1 to 3 A sludge dewatering test was carried out in the same manner as in Example 1, except that an aqueous solution (solids content 0.2% by mass) of polyethyleneimine [Epomin (registered trademark) manufactured by Nippon Shokubai: SP-006, SP-018, P-1000, P-3000] shown in Table 1 below and an aqueous solution (solids content 0.2% by mass) of cationic polyacrylic acid ester [a copolymer of dimethylaminoethyl (meth)acrylate and acrylamide having an estimated weight average molecular weight of 3,000,000 (catalog value)] were used as the sludge dewatering agent, and the capillary suction time measurement test results were obtained.

[0039] Example 4: A sludge dewatering test was conducted on mixed concentrated sludge sampled at Sewage Treatment Plant B using an aqueous solution (solids content: 0.2% by mass) of polyethyleneimine [Epomin (registered trademark): P-1000 (number average molecular weight: 70,000) manufactured by Nippon Shokubai] as the first sludge dehydration agent, and an aqueous solution (solids content: 0.2% by mass) of cationic polyacrylic acid ester [a copolymer of dimethylaminoethyl (meth)acrylate and acrylamide with an estimated weight average molecular weight of 3,000,000 (catalog value)] as the second sludge dehydration agent, and the results of the capillary suction time measurement test were obtained. The amounts of polymer (solids content) used relative to the sludge (solids content) were 0.2% by mass for the polyethyleneimine and 0.8% by mass for the polyacrylic acid ester.

[0040] [Examples 5 to 9] As the first sludge dehydration agent, an aqueous solution (solid content 0.2% by mass) of polyethyleneimine [Epomin (registered trademark): P-1000, P-3000 manufactured by Nippon Shokubai] shown in Table 2 below was used, and as the second sludge dehydration agent, an aqueous solution (solid content 0.2% by mass) of cationic polyacrylic acid ester [a copolymer of dimethylaminoethyl (meth)acrylate and acrylamide having an estimated weight average molecular weight of 3,000,000 (catalog value)] was used. Except for the amount of polymer (solid content) used relative to the sludge (solid content) shown in Table 2, a sludge dehydration test was performed in the same manner as in Example 4, and the capillary suction time measurement test results were obtained.

[0041] The results of the CST test are shown in Tables 1 and 2 below. It was confirmed that sludge dehydration agents containing SP-200, P-1000, and P-3000, which are polyethyleneimines having a number-average molecular weight of 2,000 to 200,000, exhibit better dehydration properties than sludge dehydration agents containing polyacrylic acid esters or SP-006 and SP-018, which are polyethyleneimines having a number-average molecular weight of less than 2,000. It was also confirmed that when a first sludge dehydration agent containing polyethyleneimine [Epomin (registered trademark): P-1000 and P-3000, manufactured by Nippon Shokubai] was used in combination with a second sludge dehydration agent containing polyacrylic acid ester, good dehydration properties were exhibited even when the total amount used was small.

[0042]

[0043]

[0044] Example 10 A mixed concentrated sludge sampled at a sewage treatment plant A was subjected to a centrifugal dehydration test using an aqueous solution (solid content 0.2% by mass) of polyethyleneimine [Epomin (registered trademark): P-1000 (number average molecular weight 70,000) manufactured by Nippon Shokubai] as a sludge dehydration agent, such that the amount of polymer (solid content) relative to the sludge (solid content) was 1.7% by mass, and the moisture content of the dehydrated cake was calculated.

[0045] [Centrifugal dehydration test] Sludge was placed in a centrifuge tube, and the above-mentioned sludge dehydrating agent was added at 1.7 mass% (as polymer solids) / TS (solids in the target sludge). The mixture was stirred with a spoon and centrifuged at 2,100 G for 3 minutes to perform solid-liquid separation. The remaining solids were wrapped in nylon gauze as shown in Figure 2, placed in a dehydration cell, and centrifuged at 2,100 G for 12 minutes. The moisture content of the resulting dehydrated cake was calculated by measuring the weight of the dehydrated cake.

[0046] Example 11, Comparative Example 4 A centrifugal dehydration test of sludge was carried out in the same manner as in Example 10, except that an aqueous solution (solids content 0.2% by mass) of polyethyleneimine [Epomin (registered trademark): P-3000 manufactured by Nippon Shokubai] shown in Table 3 below, or an aqueous solution (solids content 0.2% by mass) of cationic polyacrylic acid ester [a copolymer of dimethylaminoethyl (meth)acrylate and acrylamide having an estimated weight average molecular weight of 3,000,000 (catalog value)] was used as the sludge dehydrating agent, and the moisture content of the dehydrated cake was calculated.

[0047] The results of the centrifugal dewatering test are shown in Table 3 below. When P-1000 and P-3000 were used, the water content in the sludge was lower than when polyacrylic ester was used, confirming that dewatering was improved.

[0048]

[0049] Example 12: A mixed concentrated sludge sampled at Sewage Treatment Plant B was subjected to a sludge dewatering test using an aqueous solution (solids content 0.2% by mass) of polyethyleneimine [Epomin (registered trademark): P-1000 (number average molecular weight 70,000) manufactured by Nippon Shokubai] as the first sludge dehydration agent, and an aqueous solution (solids content 0.2% by mass) of cationic polyacrylic acid ester [a copolymer of dimethylaminoethyl (meth)acrylate and acrylamide with an estimated weight average molecular weight of 3,000,000 (catalog value)] as the second sludge dehydration agent, and the capillary suction time measurement test results were obtained. The amounts of polymer (solids content) used relative to the sludge (solids content) were 0.06% by mass of polyethyleneimine and 0.8% by mass of polyacrylic acid ester.

[0050] [Examples 13 to 17] As the first sludge dehydration agent, an aqueous solution (solid content 0.2% by mass) of polyethyleneimine [Epomin (registered trademark): P-1000, P-3000 manufactured by Nippon Shokubai] shown in Table 4 below was used, and as the second sludge dehydration agent, an aqueous solution (solid content 0.2% by mass) of cationic polyacrylic acid ester [a copolymer of dimethylaminoethyl (meth)acrylate and acrylamide having an estimated weight average molecular weight of 3,000,000 (catalog value)] was used. Except for the amount of polymer (solid content) used relative to the sludge (solid content) shown in Table 4, a sludge dehydration test was performed in the same manner as in Example 12, and the capillary suction time measurement test results were obtained.

[0051] The results of the CST test are shown in Table 4 below. It was confirmed that when a first sludge dehydration agent containing polyethyleneimine [Epomin (registered trademark): P-1000, P-3000 manufactured by Nippon Shokubai] and a second sludge dehydration agent containing polyacrylic acid ester were used in combination, good dehydration properties were observed even when the total amount used was very small.

[0052]

[0053] The sludge dehydration agent of the present invention can provide a sludge dehydration agent with high dehydration efficiency, a sludge dehydration method that can easily increase the dehydration rate of sludge, and a method for producing dehydrated sludge with a high dehydration rate.

Claims

1. a first sludge dewatering agent containing a polyalkyleneimine having a number average molecular weight of 20,000 to 200,000 and not containing any polymer flocculant other than the polyalkyleneimine; a second sludge dewatering agent containing a polymer flocculant that is a cationic polymer other than the polyalkyleneimine; The method for dewatering sludge, wherein the mass ratio of the solid content of the first sludge dewatering agent to the second sludge dewatering agent is 1.0:1.0 to 15.

0.

2. 2. The method for dewatering sludge according to claim 1, wherein the amount (solid content) of the polyalkyleneimine added to the sludge is 0.04 to 5 mass % based on the solid content of the sludge.

3. A method for dewatering sludge as described in claim 1 or 2, wherein the cationic polymer has a cation equivalent value (Cv) of 1 to 15 meq / g.

4. A method for dehydrating sludge as described in claim 1 or 2, wherein the cationic polymer is a polyacrylic acid ester having a weight average molecular weight of 500,000 to 10,000,000.

5. A method for producing dehydrated sludge, characterized by including a dehydration step using the sludge dehydration method described in claim 1 or 2.