Sludge dewatering agent composition, and method for dewatering sludge

Abstract

The present invention provides a sludge dewatering agent composition that exhibits excellent coagulation and dewatering performance, requires a small amount of additive, and can produce a cake with a low water content, as well as a method for dewatering sludge. [Solution] The above problem is solved by a sludge dewatering agent composition comprising at least two types of amphoteric polymers, wherein the value obtained by dividing the cation equivalent value (Cv) of the sludge dewatering agent composition by the anionic equivalent value (Av) is 4.0 to 5.5, and among the at least two types of amphoteric polymers, the top two components with the highest blending ratios are amphoteric polymers having cationic monomer units derived from a tertiary or quaternary salt of dialkylaminoalkyl (meth)acrylate, and the difference in cation equivalent value (Cv) between the top two components with the highest blending ratios among the at least two types of amphoteric polymers is 0.60 to 1.80, and the difference in anionic equivalent value (Av) is 0.10 to 0.70.

Description

Technical Field

[0001] The present invention relates to a sludge dewatering agent composition and a method for dewatering sludge. More specifically, it relates to a sludge dewatering agent composition that has excellent flocculation and dewatering performance and gives a cake with a low water content, and a method for dewatering sludge using the same.

Background Art

[0002] Conventionally, a cationic polymer flocculant has been used alone for sludge dewatering treatment. However, in recent years, due to an increase in the amount of sludge generated and deterioration of sludge properties, the conventional cationic polymer flocculant has limitations in the treatment amount of sludge, and the treatment state is not always satisfactory in terms of the water content of the dewatered cake, the TS recovery rate, and the peelability of the cake from the filter cloth. Improvements in these points are required.

[0003] Patent Document 1 discloses an amphoteric polymer flocculant that has excellent flocculation and dewatering performance, requires a small addition amount, and can give a cake with a low water content, and is composed of two or more amphoteric polymers having different ion equivalents. However, there is still room for improvement in the dewatering performance of this amphoteric polymer flocculant.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem of the present invention is to overcome the drawbacks of conventional sludge dewatering agents, and to provide a sludge dewatering agent composition that has excellent flocculation and dewatering performance, requires a small addition amount, and can give a dewatered cake with a low water content, and a method for dewatering sludge.

Means for Solving the Problems

[0006] As a result of diligent research into the above-mentioned problems, the present inventors have found that a sludge dewatering agent composition comprising two or more amphoteric polymers having different cation equivalent values ​​(Cv) and anion equivalent values ​​(Av) within a predetermined range, and which is obtained by mixing the two or more amphoteric polymers such that the value obtained by dividing the cation equivalent value (Cv) by the anion equivalent value (Av) falls within a predetermined range, exhibits a particularly excellent dewatering effect, and have completed the present invention.

[0007] The present invention, which solves the above problems, is described below.

[0008] [1] A sludge dewatering agent composition comprising at least two types of amphoteric polymers, The cation equivalent value (Cv) of the sludge dewatering agent composition divided by the anionic equivalent value (Av) is 4.0 to 5.5. Of the at least two types of amphoteric polymers mentioned above, the top two components with the highest proportions are amphoteric polymers having cationic monomer units derived from a tertiary or quaternary salt of dialkylaminoalkyl(meth)acrylate, A sludge dewatering agent composition characterized in that, among the at least two types of amphoteric polymers, the difference in cation equivalent value (Cv) between the top two components with the highest blending ratios is 0.60 to 1.80, and the difference in anion equivalent value (Av) is 0.10 to 0.70.

[0009] [2] The sludge dewatering agent composition according to [1], wherein the cationic monomer unit is a dimethylaminoethyl acrylate methyl chloride quaternary salt or a dimethylaminoethyl methacrylate methyl chloride quaternary salt.

[0010] [3] The cationic monomer unit comprises at least one amphoteric polymer having a cationic monomer unit derived from dimethylaminoethyl acrylate methyl chloride quaternary salt, The cationic monomer unit comprises at least one amphoteric polymer having a cationic monomer unit derived from dimethylaminoethyl methacrylate methyl chloride quaternary salt, A sludge dewatering agent composition according to [1] or [2], which is a mixture of the above.

[0011] [4] The sludge dewatering agent composition according to [1] or [2], wherein the total blending ratio of the top two amphoteric polymers with the highest blending ratios among the at least two types of amphoteric polymers is 80% by mass or more.

[0012] [5] The sludge dewatering agent composition according to [1] or [2], wherein the mixing ratio of the top two amphoteric polymers with the highest mixing ratios among the at least two types of amphoteric polymers is in the range of 30 / 70 to 70 / 30 by mass ratio.

[0013] [6] A sludge dewatering agent composition according to [1] or [2], in the form of a powder.

[0014] [7] A method for dewatering sludge, characterized by adding the sludge dewatering agent composition described in [1] to the sludge and then performing solid-liquid separation.

[0015] [8] The method for dewatering sludge according to [7], wherein the loss on ignition of the sludge is 70% by mass or less. [Effects of the Invention]

[0016] The present invention provides a sludge dewatering agent composition that exhibits excellent sludge coagulation and dewatering performance, requires a small amount of additive, and can produce a dewatered cake with a low water content, as well as a method for dewatering sludge. [Modes for carrying out the invention]

[0017] The present invention will be described in detail below. In this specification, acrylates and / or methacrylates may be referred to as (meth)acrylate; acrylamides and / or methacrylamides as (meth)acrylamide; and acrylic acid and / or methacrylic acid as (meth)acrylic acid. Furthermore, acrylic acid and / or its salts may be referred to as acrylic acid (salt). Unless otherwise specified, each physical property value is the value at 25°C and atmospheric pressure.

[0018] 1. Amphoteric polymer The sludge dewatering agent composition of the present invention comprises at least two kinds of amphoteric polymers. Among the amphoteric polymers constituting the sludge dewatering agent composition of the present invention, the top two components with a high blending ratio (mass%) may be copolymers having a cationic monomer unit derived from a tertiary salt or quaternary salt of a dialkylaminoalkyl (meth)acrylate and an anionic monomer unit as essential constituent monomer units.

[0019] Examples of the cationic monomer include tertiary salts such as hydrochloride and sulfate of dialkylaminoalkyl (meth)acrylate such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate and diethylamino-2-hydroxypropyl (meth)acrylate; quaternary salts such as alkyl halide adducts such as methyl chloride adduct of dialkylaminoalkyl (meth)acrylate and aryl halide adducts such as benzyl chloride adduct; tertiary salts such as hydrochloride and sulfate of dialkyl (meth)acrylamide such as N,N-dimethyl (meth)acrylamide; quaternary salts such as alkyl halide adducts such as methyl chloride adduct of dialkyl (meth)acrylamide and aryl halide adducts such as benzyl chloride adduct.

[0020] Examples of the anionic monomer include alkali metal salts or ammonium salts such as (meth)acrylic acid and its sodium salt; maleic acid and its alkali metal salts; acrylamidealkylalkanesulfonic acids such as acrylamide-2-methylpropanesulfonic acid and its alkali metal salts or ammonium salts; and vinylsulfonic acid and its alkali metal salts or ammonium salts.

[0021] As the amphoteric polymer, monomers other than the above-mentioned monomers, specifically nonionic monomers, may be used in combination as necessary. Examples of the nonionic monomers include (meth)acrylamide, dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl (meth)acrylate, dialkylaminoalkyl (meth)acrylamides such as dialkylaminopropyl (meth)acrylamide, styrene, acrylonitrile, vinyl acetate, alkyl acrylates, alkyl methacrylates, vinyl pyridine, vinyl imidazanol, and allylamine. Among these, (meth)acrylamide is preferred.

[0022] Any of the monomers can be used alone or in combination of two or more.

[0023] Preferred monomer combinations in the present invention include copolymers composed of a tertiary or quaternary salt of dialkylaminoalkyl acrylate as a cationic monomer, acrylate as an anionic monomer, and acrylamide as a nonionic monomer; copolymers composed of a tertiary or quaternary salt of dialkylaminoalkyl methacrylate as a cationic monomer, acrylate as an anionic monomer, and acrylamide as a nonionic monomer; and copolymers composed of a tertiary or quaternary salt of dialkylaminoalkyl methacrylate as a cationic monomer, a tertiary or quaternary salt of dialkylaminoalkyl acrylate, acrylate as an anionic monomer, and acrylamide as a nonionic monomer.

[0024] The ion equivalents of the top two amphoteric polymer components with high proportions are preferably 0.5 to 4.8 meq / g, more preferably 1.0 to 4.8 meq / g, even more preferably 1.5 to 4.8 meq / g, and particularly preferably 2.0 to 4.8 meq / g. Furthermore, the anion equivalents (hereinafter referred to as Av) are preferably 0.2 to 2.5 meq / g, more preferably 0.3 to 2.2 meq / g, even more preferably 0.3 to 2.0 meq / g, and particularly preferably 0.3 to 1.9 meq / g. The above Cv and Av values ​​are determined comprehensively, taking into account the solubility of the coagulant in water, its coagulation performance on sludge, and the dewatering properties of the coagulated flocs. Generally, if Cv and Av become too low, the coagulation performance decreases, and if they become too high, the coagulation performance itself may be good, but the dewatering properties of the flocs tend to deteriorate.

[0025] The 0.5% salt viscosity of the top two amphoteric polymer components with the highest proportions is preferably 10 to 100 mPa·s, more preferably 15 to 90 mPa·s, and particularly preferably 20 to 80 mPa·s. If it exceeds 100 mPa·s, solubility in water tends to decrease, and the flocculation effect may become uneven. If it is less than 10 mPa·s, it may not be possible to form flocs of sufficient size.

[0026] There are no particular restrictions on the method for producing this amphoteric polymer, and general polymerization methods can be employed. For example, in aqueous solution polymerization, peroxides such as potassium persulfate, ammonium persulfate, hydrogen peroxide, peracetic acid, and t-butyl hydrate peroxide, azo-based initiators such as 2,2'-azobis(2-methylpropionamidine) dihydrochloride and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], redox initiators consisting of combinations of peroxides such as hydrogen peroxide and sodium persulfate with reducing agents such as sodium bisulfite, potassium bisulfite, ferrous sulfate, and ascorbic acid, and photopolymerization initiators can be appropriately used depending on the polymerization method. Furthermore, in reverse-phase emulsion polymerization, in addition to the aforementioned polymerization initiators, water-insoluble initiators such as azobisisobutyronitrile and benzoyl peroxide may be used for polymerization.

[0027] 2. Sludge dewatering agent composition The cation equivalent value (Cv) divided by the anionic equivalent value (Av) of the sludge dewatering agent composition of the present invention (Cv / Av) is 4.0 to 5.5, preferably 4.1 to 5.4, more preferably 4.2 to 5.3, and particularly preferably 4.3 to 5.2. If it is less than 4.0, the amount of cations will be small, making it easy for the reaction with anionic substances in the sludge to be insufficient. This can lead to a decrease in sludge flocculation and dewatering efficiency, deterioration of the sludge's filtration characteristics, insufficient dewatering, longer processing times, and a higher moisture content in the dewatered cake. If it exceeds 5.5, the amount of cations is too high, causing excessive sludge flocculation and trapping moisture within the sludge flocs, which can conversely decrease dewatering efficiency.

[0028] The sludge dewatering agent composition of the present invention comprises at least two amphoteric polymers, but the top two components, the amphoteric polymers, are preferably present in the sludge dewatering agent composition in amounts of 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, and particularly preferably 40% by mass or more. If the amount is less than 10% by mass, it becomes necessary to increase the amount of the sludge dewatering agent composition used in order to obtain an appropriate dewatering effect. This not only increases costs but also raises concerns about secondary effects due to over-administration. The sludge dewatering agent composition of the present invention comprises at least two amphoteric polymers, but the top two components with the highest proportions of the amphoteric polymers are preferably present in the sludge dewatering agent composition in a total of 20% by mass or more, preferably 40% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. It may also be 100% by mass. If it is less than 20% by mass, it will be necessary to increase the amount of sludge dewatering agent composition used in order to obtain an appropriate dewatering effect. This will not only increase costs but also raise concerns about secondary effects due to over-administration.

[0029] The sludge dewatering agent composition of the present invention comprises two or more amphoteric polymers with different ion equivalents. The difference in Cv between the top two amphoteric polymers with the highest blending ratios is 0.60 to 1.80 meq / g, more preferably 0.80 to 1.80 meq / g, even more preferably 1.00 to 1.80 meq / g, and particularly preferably 1.20 to 1.70 meq / g. The difference in Av is 0.10 to 0.70 meq / g, more preferably 0.20 to 0.70 meq / g, even more preferably 0.30 to 0.70 meq / g, and particularly preferably 0.40 to 0.70 meq / g. If the difference in Cv or Av is below the above lower limits, both amphoteric polymers may exhibit similar effects, resulting in a coagulation effect that is not significantly different from that obtained with only one amphoteric polymer. If the difference between Cv and Av exceeds the above upper limit, the flocculation effect may become uneven, resulting in stronger flocculation for certain substances while insufficient flocculation for others. As a result, the uniformity of sludge dewatering treatment may decrease, potentially leading to a reduction in dewatering efficiency.

[0030] The sludge dewatering agent composition of the present invention comprises two or more amphoteric polymers with different ion equivalents. The mixing ratio of the top two components with the highest mixing ratios among the amphoteric polymers is preferably 30 / 70 to 70 / 30 by mass ratio, more preferably 35 / 65 to 65 / 35, and even more preferably 40 / 60 to 60 / 40. If the mixing ratio of one of the amphoteric polymers falls below 30, the properties of the less abundant amphoteric polymer may not be fully reflected, and the overall sludge dewatering performance may be insufficient.

[0031] The sludge dewatering agent composition of the present invention can be produced by mixing two or more amphoteric polymers with different ion equivalents as described above. Alternatively, each component can be added separately during sludge dewatering. Even when three or more amphoteric polymers are blended, it is preferable that the amphoteric polymers have ion equivalents within a range similar to that of the preferred amphoteric polymers described above. Furthermore, the sludge dewatering agent composition of the present invention may contain known additives such as sodium bisulfate, sodium sulfate, and sulfamic acid, as long as they do not adversely affect the dewatering treatment. The sludge dewatering agent composition of the present invention is preferably in powder form.

[0032] 3. Dewatering method using a sludge dewatering agent composition

[0033] In the dewatering method using the sludge dewatering agent composition of the present invention, the sludge to be treated is not particularly limited. Various types of sludge can be treated, including sludge generated in sewage treatment, human waste treatment, and domestic wastewater treatment, as well as sludge generated in various industrial wastewater treatments such as food processing plants, meat processing plants, and chemical plants, raw manure and sludge generated in livestock farming such as pig farms and in the treatment of its wastewater, and sludge generated in the pulp or paper industry. There are also no restrictions on the type of sludge, and primary sedimentation sludge, excess sludge and mixed sludge thereof, concentrated sludge, and digested sludge treated with anaerobic microorganisms can all be treated.

[0034] The following are specific examples of dewatering methods using the sludge dewatering agent composition of the present invention. Specifically, an inorganic flocculant or an organic cationic compound is added to the sludge as needed, and the pH is preferably adjusted to 4-8. Then, the sludge dewatering agent composition of the present invention is added to this sludge, and the mixture is stirred and / or mixed by known methods to allow the suspended matter in the sludge to react with the amphoteric polymer and form sludge flocs. The formed sludge flocs are then mechanically dewatered by known means to separate them into treated water and dewatered cake. Furthermore, when the purpose is deodorization, dephosphorization, and denitrification, it is preferable to set the pH of the sludge to less than 5.

[0035] While there are no particular limitations on the inorganic flocculant, examples include aluminum sulfate, polyaluminum chloride, ferric chloride, ferrous sulfate, and polyferric sulfate.

[0036] Examples of organic cationic compounds include polymer polyamines, polyamidines, and cationic surfactants.

[0037] While there are no particular limitations on the dewatering equipment, examples include screw press type dewaterers, belt press type dewaterers, filter press type dewaterers, screw decanters, and multi-disc dewaterers.

[0038] The amount of sludge dewatering agent composition, inorganic flocculant, and cationic compound added, as well as the stirring speed and stirring time, should follow conventional dewatering conditions. Furthermore, it can be used in combination with other cationic or anionic polymers, or added to the dewatering agent to be used as a single mixed liquid.

[0039] The sludge dewatering agent composition of the present invention is also applicable to dewatering methods using a granulation and thickening tank having a filtration section. Specifically, examples include a method in which an inorganic coagulant is added to the sludge, and then the sludge dewatering agent composition is added, or introduced together with the sludge dewatering agent composition, into a granulation and thickening tank having a filtration section for the sludge, the filtrate is extracted from the filtration section and granulated, and the granulated material is dewatered using a dewatering machine. [Examples]

[0040] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring various physical properties are as follows. Unless otherwise specified, the temperature condition for measuring various physical properties is 25°C. Physical properties for which the measurement method is not described were measured in accordance with JIS K 0101 or JIS K 0102.

[0041] [0.5% salt viscosity] 500 g of pure water was placed in a 500 mL conical beaker, and 20.8 g of precisely weighed reagent-grade sodium chloride powder was added and dissolved. While stirring with a magnetic stirrer, the sample was added in an amount that resulted in a concentration of 0.5 mass% in terms of solid content after dissolution. The mixture was stirred at 200 rpm for 4 hours, and then allowed to stand to dissolve completely to prepare a 0.5 mass% solution. The viscosity was measured using a BM type viscometer manufactured by Tokyo Keiki Co., Ltd. under the conditions of 25°C, 60 rpm, and after 5 minutes.

[0042] [Measurement of cationic equivalent (Cv)] (Preparation of a 500 ppm aqueous solution of the sample) 0.2 g of the sample (not converted to dry weight) was accurately weighed and placed in a stoppered Erlenmeyer container, then dissolved in 100 mL of deionized water. 25 mL of this solution was then diluted with deionized water in a 100 mL volumetric flask. (titration) 90 mL of deionized water was placed in a conical beaker, 10 mL of a 500 ppm aqueous solution of the sample was added, and the pH was adjusted to 3.0 with hydrochloric acid solution. The mixture was then stirred for approximately 1 minute. Next, 2-3 drops of toluidine blue indicator were added, and the mixture was titrated with N / 400 potassium polyvinyl sulfate reagent (hereinafter referred to as N / 400PVSK). The titration rate was 2 mL / min, and the endpoint was defined as the point at which the sample changed color from blue to reddish-purple and remained so for 10 seconds or more. (calculation method) The cationic equivalent (Cv) was calculated using the following formula.

[0043]

number

[0044] [Measurement of anionic equivalent (Av)] (Preparation of a 500 ppm aqueous solution of the sample) 0.2 g of the sample (not converted to dry weight) was accurately weighed and placed in a stoppered Erlenmeyer container, then dissolved in 100 mL of deionized water. 25 mL of this solution was then diluted with deionized water in a 100 mL volumetric flask. (titration method) 90 mL of deionized water was placed in a conical beaker, 10 mL of a 500 ppm aqueous solution of the sample was added, and the pH was adjusted to 7.0 with a caustic soda solution. The mixture was then stirred for approximately 1 minute. Next, 2-3 drops of toluidine blue indicator were added, and the mixture was titrated with N / 400 potassium polyvinyl sulfate reagent (hereinafter referred to as N / 400PVSK). The titration rate was 2 mL / min, and the endpoint was defined as the point at which the sample changed color from blue to reddish-purple and remained so for 10 seconds or more. (calculation method) The anionic equivalent (Av) was calculated using the following formula.

[0045]

number

[0046] [Floc diameter, and liquid volume after 10 seconds] 200 mL of sludge was collected in a 300 mL beaker, a predetermined amount of a sludge dewatering agent composition dissolved at 0.2% by mass was added, and the mixture was stirred at 200 rpm for 1 minute using a jar tester to generate sludge flocs. The particle size of the flocs was then measured visually. The aggregated sludge was poured all at once into a stainless steel sieve with an inner diameter of 75 mm, a depth of 100 mm, and an opening of 80 meshes, and gravity filtration was performed. The volume of the filtrate after 10 seconds was measured using a graduated cylinder.

[0047] [Moisture content of dehydrated cake] The aggregated sludge was dewatered using a laboratory mini-belt press, dried overnight in a 110°C dryer, and then the moisture content of the dewatered cake was measured.

[0048] [Turbidity of the filtrate] The turbidity of the filtrate after dewatering the sludge was measured using a Lovibond Turbidimeter TB 250WL. In some examples, the following evaluations were made based on turbidity measurements. ○: Turbidity 60NTU or less △: Turbidity more than 60NTU, less than 80NTU ×: Turbidity over 80NTU

[0049] <Manufacturing Example 1> In a stainless steel reaction vessel (Teflon is a registered trademark) with a Teflon coating on the inside, a 78% by mass aqueous solution of dimethylaminoethyl acrylate methyl quaternary salt (hereinafter abbreviated as "DAC"), a 79% by mass aqueous solution of dimethylaminoethyl methacrylate methyl quaternary salt (hereinafter abbreviated as "DMC"), acrylic acid (hereinafter abbreviated as "AA"), and a 50% by mass aqueous solution of acrylamide (hereinafter abbreviated as "AMD") were weighed, and pure water was added to make a total mass of 1,000 g. At this time, the molar composition (mol%) of each monomer in this solution was DAC / DMC / AA / AMD = 60 / 0.8 / 5 / 34.2, and the total concentration of each monomer was approximately 40% by mass. The pH of this solution was adjusted to 4, and the solution temperature was adjusted to 5°C while blowing nitrogen gas into the solution for 60 minutes. Subsequently, 2,2'-azobis(2-methylpropionamidine) dihydrochloride (hereinafter abbreviated as "V-50") and NaHSO3 were added in amounts of 1500 ppm and 20 ppm, respectively, based on solid content relative to the total mass of each monomer. Then, polymerization was carried out by irradiating this solution with light from above the reaction vessel to obtain a hydrated gel polymer. A 13W black light was used for light irradiation. The irradiation intensity was 0.4 mW / cm². 2 The irradiation time was 60 minutes. The resulting water-containing gel-like polymer was removed from the container and shredded. This was dried at 80°C for 5 hours, then pulverized to obtain a powdered polymer (hereinafter referred to as "polymer A"). Various physical properties of this polymer were measured. The results are shown in Table 1.

[0050] <Manufacturing Examples 2-5> Polymers B to F were obtained in the same manner as in Production Example 1, except that the mixing ratios shown in Table 1 were changed.

[0051] <Manufacturing Examples 6-10> Polymers I to V were obtained in the same manner as in Production Example 1, except that the blending ratios shown in Table 2 were changed.

[0052] [Table 1]

[0053] [Table 2]

[0054] <Example 1 of the synthesis of a sludge dewatering agent composition> A sludge dewatering agent composition was prepared by mixing polymer A and polymer I, manufactured in the above production example, in a mass ratio of 1:1. Various physical properties of this sludge dewatering agent composition were measured.

[0055] <Examples of sludge dewatering agent compositions 2-5> As shown in Table 3, a sludge dewatering agent composition was prepared in the same manner as in Synthesis Example 1, except that the type and blending ratio of the polymer were changed. Various physical properties of this sludge dewatering agent composition were measured.

[0056] [Table 3]

[0057] (Examples 1-3, Comparative Examples 1-3) (Dewatering test of pig farm sludge) A coagulation test was conducted using sludge from a pig farm. The physical properties of the sludge were pH=7.5, TS (total evaporation residue)=11,200 (mg / L), and VTS (loss on ignition)=66.0%. 200 mL of sludge was taken into a 300 mL beaker, and a predetermined amount (100 ppm relative to the total sludge volume) of sludge dewatering agent dissolved at 0.2% by mass was added. The mixture was stirred for 30 seconds in a jar tester to induce a coagulation reaction. After that, various physical properties were measured.

[0058] [Table 4]

[0059] Examples 1-3 showed better floc diameter, greater liquid volume after 10 seconds, better turbidity, lower dewatered cake water content, and superior flocculation performance compared to Comparative Examples 1-3.

[0060] (Examples 4-6, Comparative Examples 4-6) (Sludge from a sewage treatment plant) A coagulation test was conducted using sludge from a sewage treatment plant. The physical properties of the sludge were pH=7.85, TS (total evaporation residue)=12,200 (mg / L), and VTS (loss on ignition)=57.4%. 200 mL of sludge was taken into a 300 mL beaker, and a predetermined amount (150 ppm relative to the total sludge volume) of sludge dewatering agent dissolved at 0.2% by mass was added. The mixture was stirred for 30 seconds in a jar tester to induce a coagulation reaction. After that, various physical properties were measured.

[0061] [Table 5]

[0062] Examples 4-6, and especially Example 5, showed large floc diameters, high liquid volume after 10 seconds, good turbidity, and low water content in the dewatered cake, resulting in excellent flocculation performance.

Claims

1. A sludge dewatering agent composition comprising at least two types of amphoteric polymers, The cation equivalent value (Cv) of the sludge dewatering agent composition divided by the anion equivalent value (Av) is between 4.0 and 5.

5. Of the at least two types of amphoteric polymers mentioned above, the top two components with the highest proportions are amphoteric polymers having cationic monomer units derived from a tertiary or quaternary salt of dialkylaminoalkyl (meth)acrylate, A sludge dewatering agent composition characterized in that, among the at least two types of amphoteric polymers, the difference in cation equivalent value (Cv) between the top two components with the highest blending ratios is 0.60 to 1.80, and the difference in anion equivalent value (Av) is 0.10 to 0.

70.

2. The sludge dewatering agent composition according to claim 1, wherein the cationic monomer unit is a dimethylaminoethyl acrylate methyl chloride quaternary salt or a dimethylaminoethyl methacrylate methyl chloride quaternary salt.

3. The cationic monomer unit comprises at least one amphoteric polymer having a cationic monomer unit derived from dimethylaminoethyl acrylate methyl chloride quaternary salt, The cationic monomer unit comprises at least one amphoteric polymer having a cationic monomer unit derived from dimethylaminoethyl methacrylate methyl chloride quaternary salt, A sludge dewatering agent composition according to claim 1 or 2, which is a mixture of the above.

4. The sludge dewatering agent composition according to claim 1 or 2, wherein the total blending ratio of the top two amphoteric polymers with the highest blending ratios among the at least two types of amphoteric polymers is 80% by mass or more.

5. The sludge dewatering agent composition according to claim 1 or 2, wherein the blending ratio of the top two amphoteric polymers with the highest blending ratios among the at least two types of amphoteric polymers is in the range of 30 / 70 to 70 / 30 by mass ratio.

6. A sludge dewatering agent composition according to claim 1 or 2, which is in the form of a powder.

7. A method for dewatering sludge, characterized by adding the sludge dewatering agent composition described in claim 1 to the sludge and then performing solid-liquid separation.

8. The method for dewatering sludge according to claim 7, wherein the loss on ignition of the sludge is 70% by mass or less.

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