JP7226418B2 - Sludge dewatering agent and sludge dewatering method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sludge dehydrating agent suitable for dewatering sludge, particularly difficult-to-dewater sludge, and a sludge dehydrating method using the same.

Cationic polymer flocculants are generally used as sludge dehydrating agents for dehydration of sludge, mainly excess sludge generated in food factories, chemical factories, human waste treatment plants, and the like. However, in recent years, with the diversification of sludge, such as an increase in the amount of sludge generated and changes in its properties, sludge that is difficult to dewater is increasing, and sludge dewatering agents with better dewatering performance for various sludge are needed. It has been demanded.

Conventionally, dimethylaminoethyl (meth)acrylate or its methyl chloride quaternary product was mainly used as a sludge dewatering agent using a cationic polymer flocculant. Various sludge dewatering agents other than cationic polymer flocculants have also been proposed.

For example, in Patent Document 1, an aqueous solution of a monomer mixture essentially containing a cationic monomer and a polyfunctional monomer having a plurality of unsaturated double bonds is emulsion-polymerized to form a dispersed phase in oil. It describes the use of an ionic water-soluble polymer having a charge encapsulation rate of 35 to 90% obtained by obtaining a water droplet emulsion (W/O emulsion) liquid, drying it, and granulating it for dehydration of sludge.
In Patent Documents 2 and 3, aggregates obtained by combining a water-soluble ionic polymer with a high charge inclusion rate and a water-soluble ionic polymer with a low charge inclusion rate, which contain structural units derived from cationic monomers Treatment agents are described for use in dewatering sludge.

JP 2009-280649 A JP 2005-144346 A WO2008/015769

Conventionally, it was believed that the cationic degree of the polymer of the sludge dehydrating agent affects the dewatering performance of sludge, and that the higher the cationic degree, the higher the charge neutralization power and the better the dewatering performance.
However, with the recent diversification of sludge as described above, the dehydration effect may vary greatly due to differences in properties such as the electrical conductivity of the sludge and the concentration of organic substances contained in the sludge. Dehydrating agents do not necessarily have good dehydrating performance.

The present invention has been made under such circumstances, and a sludge dehydrating agent that exhibits a stable dewatering effect on various sludges and enables efficient dehydration treatment, and sludge using the same It is an object of the present invention to provide a dehydration method.

The present invention provides a sludge dehydration comprising a polymer having a predetermined amount of structural units derived from a predetermined cationic monomer and a structural unit derived from a crosslinkable monomer, and having a predetermined colloid equivalent value. This is based on the discovery that the agent exerts a stable dehydration effect on various sludges and enables efficient dehydration treatment.

That is, the present invention provides the following [1] to [9].
[1] A sludge dewatering agent containing a polymer having a structural unit derived from a cationic monomer and a structural unit derived from a crosslinkable monomer,
The cationic monomer is a cationic monomer (a) represented by the following formula (A), or a cationic monomer (a) represented by the following formula (A) and the following formula (B ) containing a cationic monomer (b) represented by
The cationic monomer is 60 mol% or more with respect to a total of 100 mol% of the monomers that are the constituent units of the polymer (excluding the crosslinkable monomer), and the cationic monomer (b) is 35 mol% or less, and the crosslinkable monomer is 0.001 mol% or more and 0.025 mol% or less,
A sludge dewatering agent in which the colloid equivalent value of the polymer satisfies the following formula (1).

（式（Ａ）中、Ｒ^１及びＲ^２は、それぞれ独立に、水素原子又は炭素数１～３のアルキル基であり、Ｒ^３は、水素原子、炭素数１～３のアルキル基又はベンジル基である。Ａ^１は、酸素原子又はイミノ基であり、Ｂ^１は炭素数２～４のアルキレン基である。Ｘ^－は陰イオンである。）

(In formula (A), R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R ³ is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or a benzyl group. A ¹ is an oxygen atom or an imino group, B ¹ is an alkylene group having 2 to 4 carbon atoms, and X ^- is an anion.)

（式（Ｂ）中、Ｒ^４及びＲ^５は、それぞれ独立に、水素原子又は炭素数１～３のアルキル基であり、Ｒ^６は、水素原子、炭素数１～３のアルキル基又はベンジル基である。Ａ^２は、酸素原子又はイミノ基であり、Ｂ^２は炭素数２～４のアルキレン基である。Ｙ^－は陰イオンである。）
ｐＨ７におけるコロイド当量値（Ｉ）／ｐＨ５におけるコロイド当量値（ＩＩ）×１００≧９２（％） （１）
［２］前記ポリマーの構成単位となる単量体（ただし、架橋性単量体を除く）の合計１００モル％に対して、前記カチオン性単量体（ｂ）が２５モル％以下である、上記［１］に記載の汚泥脱水剤。
［３］前記ポリマーが、非イオン性単量体に由来する構成単位を含む、上記［１］又は［２］に記載の汚泥脱水剤。
［４］前記カチオン性単量体が、前記カチオン性単量体（ａ）及び前記カチオン性単量体（ｂ）を含む、上記［１］～［３］のいずれかに記載の汚泥脱水剤。
［５］前記ポリマーが、アニオン性単量体に由来する構成単位を含む上記［４］に記載の汚泥脱水剤。
［６］前記カチオン性単量体（ａ）と、前記カチオン性単量体（ｂ）とのモル比率［カチオン性単量体（ａ）／カチオン性単量体（ｂ）］が、５０／５０以上８５／１５以下である、上記［４］又は［５］に記載の汚泥脱水剤。
［７］前記式（Ａ）で表されるカチオン性単量体が、２－（アクリロイルオキシ）エチルトリメチルアンモニウムクロライドである、上記［１］～［６］のいずれかに記載の汚泥脱水剤。
［８］前記ポリマーが、油中水滴エマルション型、又は粉末状である、上記［１］～［７］のいずれかに記載の汚泥脱水剤。
［９］上記［１］～［８］のいずれか１項に記載の汚泥脱水剤を汚泥に添加して、前記汚泥を脱水する、汚泥脱水方法。

(In formula (B), R ⁴ and R ⁵ are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R ⁶ is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or a benzyl group. A ² is an oxygen atom or an imino group, B ² is an alkylene group having 2 to 4 carbon atoms, and Y ^— is an anion.)
Colloid equivalent value at pH 7 (I) / Colloid equivalent value at pH 5 (II) × 100 ≥ 92 (%) (1)
[2] The cationic monomer (b) is 25 mol% or less with respect to a total of 100 mol% of the monomers (excluding crosslinkable monomers) that constitute the constituent units of the polymer. The sludge dewatering agent according to [1] above.
[3] The sludge dewatering agent according to [1] or [2] above, wherein the polymer contains a structural unit derived from a nonionic monomer.
[4] The sludge dewatering agent according to any one of [1] to [3] above, wherein the cationic monomer comprises the cationic monomer (a) and the cationic monomer (b). .
[5] The sludge dewatering agent according to [4] above, wherein the polymer contains a structural unit derived from an anionic monomer.
[6] The molar ratio of the cationic monomer (a) and the cationic monomer (b) [cationic monomer (a)/cationic monomer (b)] is 50/ The sludge dewatering agent according to the above [4] or [5], which is 50 or more and 85/15 or less.
[7] The sludge dewatering agent according to any one of [1] to [6] above, wherein the cationic monomer represented by formula (A) is 2-(acryloyloxy)ethyltrimethylammonium chloride.
[8] The sludge dewatering agent according to any one of [1] to [7] above, wherein the polymer is a water-in-oil emulsion type or a powder.
[9] A sludge dewatering method, wherein the sludge dehydrating agent according to any one of the above [1] to [8] is added to sludge to dewater the sludge.

The sludge dehydrating agent of the present invention exerts a stable dewatering effect on various types of sludge, enabling efficient dehydration. Therefore, according to the sludge dewatering method of the present invention using the sludge dehydrating agent, it is possible to stably and efficiently dewater various types of sludge.

The sludge dehydrating agent of the present invention and the sludge dewatering method using the sludge dehydrating agent will be described in detail below.
In this specification, "(meth)acryl" means acryl and/or methacryl, and the same applies to notations of "(meth)acrylate" and "(meth)acryloyl".

[Sludge dewatering agent]
The sludge dewatering agent of the present invention contains a polymer having a structural unit derived from a cationic monomer and a structural unit derived from a crosslinkable monomer.
The cationic monomer is a cationic monomer (a) represented by the following formula (A), or a cationic monomer (a) represented by the following formula (A) and the following formula (B ) contains a cationic monomer (b) represented by

In the above formula (A), R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R ³ is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms or a benzyl group. is. A ¹ is an oxygen atom or an imino group, and B ¹ is an alkylene group having 2 to 4 carbon atoms. X ⁻ is an anion.

In the above formula (B), R ⁴ and R ⁵ are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R ⁶ is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms or a benzyl group. is. A ² is an oxygen atom or an imino group, and B ² is an alkylene group having 2 to 4 carbon atoms. Y ⁻ is an anion.

The cationic monomer is 60 mol% or more with respect to a total of 100 mol% of the monomers that are the constituent units of the polymer (excluding the crosslinkable monomer), and the cationic monomer (b) is 35 mol % or less, and the crosslinkable monomer is 0.001 mol % or more and 0.025 mol % or less.

And the colloid equivalent value of the polymer satisfies the following formula (1).
Colloid equivalent value at pH 7 (I) / Colloid equivalent value at pH 5 (II) × 100 ≥ 92 (%) (1)

<Polymer>
The sludge dewatering agent of the present invention contains a polymer having a structural unit derived from a cationic monomer and a structural unit derived from a crosslinkable monomer.
The monomers that constitute the constituent units of the polymer essentially include a cationic monomer and a crosslinkable monomer, and may further contain a nonionic monomer and/or an anionic monomer. From the viewpoint of improving the dehydration performance by forming coarse aggregated flocs, the monomers that are the constituent units of the polymer include a cationic monomer, a crosslinkable monomer, and a nonionic monomer. It preferably contains a cationic monomer, a crosslinkable monomer, a nonionic monomer and an anionic monomer.

(Cationic monomer)
The cationic monomer is a cationic monomer (a) represented by the following formula (A), or a cationic monomer (a) represented by the following formula (A) and the following formula (B ) contains a cationic monomer (b) represented by

In formula (A), R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, preferably a methyl group.
R ³ is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms or a benzyl group, preferably a methyl group.
A ¹ is an oxygen atom or an imino group, preferably an oxygen atom.
B ¹ is an alkylene group having 2 to 4 carbon atoms, preferably an ethyl group.
^X- is an anion, preferably chloride, bromide, iodide, 1/2.SO ₄ ^- , HSO ₄ ^- or CH ₃ SO ₄ ^- .
The cationic monomer contains the cationic monomer (a) represented by the formula (A), so that the sludge dehydrating agent can form coarse flocculated flocs. It becomes easy to perform more efficient dehydration treatment.

In formula (B), R ⁴ and R ⁵ are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, preferably a methyl group.
R ⁶ is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms or a benzyl group, preferably a methyl group.
^A2 is an oxygen atom or an imino group, preferably an oxygen atom.
^B2 is an alkylene group having 2 to 4 carbon atoms, preferably an ethyl group.
^Y- is an anion, preferably chloride, bromide, iodide, 1/2.SO ₄ ^- , HSO ₄ ^- or CH ₃ SO ₄ ^- .
When the cationic monomer contains the cationic monomer (b) represented by the formula (B), the hydrolysis of the polymer contained in the sludge dewatering agent during sludge dehydration is suppressed, and the polymer is It is possible to suppress the decrease in cationic degree, and the sludge dehydrating agent can exert a stable dewatering effect on various sludges. It is also possible to reduce the water content (cake water content) of the dewatered sludge after the sludge dehydration treatment.

In the present invention, the cationic monomer contains cationic monomer (a) as an essential component. The polymer contained in the sludge dewatering agent has a structural unit derived from a cationic monomer containing a cationic monomer (a) and a structural unit derived from a crosslinkable monomer described later, and the polymer The cationic monomer is 60 mol% or more with respect to a total of 100 mol% of the monomers that are the constituent units of (excluding the crosslinkable monomer), and the crosslinkable monomer is 0 001 mol % or more and 0.025 mol % or less, and a polymer that satisfies the above formula (1) exhibits a stable dehydration effect on various sludges, enabling efficient dehydration treatment. Therefore, the cationic monomer (b) may not be contained.
In the present invention, from the viewpoint of exhibiting a more stable dehydration effect on various sludges and performing more efficient dehydration treatment, the cationic monomer is a cation represented by the formula (A) It preferably contains a cationic monomer and a cationic monomer represented by the formula (B).

Examples of the cationic monomer represented by the formula (A) and the cationic monomer represented by the following formula (B) include 2-((meth)acryloyloxy)ethyltrimethylammonium chloride, 2- ((meth)acryloyloxy)ethyldimethylbenzylammonium chloride and other (meth)acryloyloxyalkyl quaternary ammonium salts; 2-((meth)acryloyloxy)ethyldimethylamine sulfate or hydrochloride; 3-((meth) (Meth)acryloyloxyalkyl tertiary amine salts such as acryloyloxy)propyldimethylamine hydrochloride; 3-((meth)acryloylamino)propyltrimethylammonium chloride, 3-((meth)acryloylamino)propyltrimethylammonium methylsulfate (meth)acryloylaminoalkyl quaternary ammonium salts such as These may be used individually by 1 type, or may use 2 or more types together.
Among the cationic monomers, the cationic monomer represented by the formula (A) is preferably an acryloyloxyalkyl quaternary ammonium salt from the viewpoint of polymerizability and formation of coarse aggregated flocs. , 2-(acryloyloxy)ethyltrimethylammonium chloride are more preferred. The cationic monomer represented by the formula (B) suppresses the hydrolysis of the polymer, exhibits a stable dehydration effect on various sludges, and from the viewpoint of reducing the moisture content of the cake, methacryloyl Oxyalkyl quaternary ammonium salts and methacryloyloxyalkyl tertiary amine salts are preferred, and 2-(methacryloyloxy)ethyltrimethylammonium chloride and 2-(methacryloyloxy)ethyldimethylamine hydrochloride are more preferred.

(Crosslinkable monomer)
The polymer has structural units derived from crosslinkable monomers. When the polymer has a structural unit derived from the cationic monomer and a structural unit derived from the crosslinkable monomer, the polymer is three-dimensionally structured and has an intricate and complicated structure. As a result, the cationic groups contained in the polymer can be retained inside the polymer, the contact between the cationic groups and hydroxide ions in the sludge can be suppressed, and the hydrolysis reaction of the cationic groups can be suppressed. As a result, it becomes possible to suppress the decrease in cationicity accompanying the reaction. For the above reasons, a stable dehydration effect can be exhibited for various types of sludge.
Examples of crosslinkable monomers include N,N'-methylenebis(meth)acrylamide, triallylamine, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth) acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, triallylammonium chloride and the like. These may be used individually by 1 type, or may use 2 or more types together.
Among the crosslinkable monomers, N,N'-methylenebis(meth)acrylamide, ethoxylated isocyanuric acid tri(meth)acrylate, 1,3 from the viewpoint of exerting a stable dewatering effect on various sludges. ,5-triacryloylhexahydro-1,3,5-triazine, triallylammonium chloride are preferred, N,N′-methylenebis(meth)acrylamide, 1,3,5-triacryloylhexahydro-1,3,5 -triazine is more preferred, and N,N'-methylenebis(meth)acrylamide is even more preferred.

(nonionic monomer)
Examples of nonionic monomers include amides such as (meth)acrylamide and N,N-dimethyl(meth)acrylamide; vinyl cyanide compounds such as (meth)acrylonitrile; methyl (meth)acrylate; (Meth)acrylic acid alkyl esters such as ethyl methacrylate; vinyl esters such as vinyl acetate; and aromatic vinyl compounds such as styrene, α-methylstyrene and p-methylstyrene. These may be used individually by 1 type, or may use 2 or more types together.
Among the nonionic monomers, amides are preferable because they are excellent in water solubility, easy to adjust the monomer composition ratio in the polymer, and easy to obtain good sludge dewatering performance. Meta)acrylamide is more preferred, and acrylamide is even more preferred.
In the present invention, the polymer preferably contains structural units derived from nonionic monomers. Since the polymer contains structural units derived from nonionic monomers, the cationic monomer units are not densely packed, the uniformity of the polymer is improved, and cations can act effectively, resulting in coarse aggregation. Flocs are easily obtained.

(anionic monomer)
Examples of anionic monomers include vinylsulfonic acid, vinylbenzenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, (meth)acrylic acid, itaconic acid, maleic acid, and alkali metal salts thereof. mentioned. These may be used individually by 1 type, or may use 2 or more types together.
In the present invention, the polymer preferably contains structural units derived from anionic monomers. When the polymer contains a structural unit derived from an anionic monomer, when the polymer dissolves in water, a reaction between cations and anions in the polymer also occurs, which complicates the structure of the polymer and causes the sludge to aggregate. Coarse flocs are easily obtained when flocculated flocs are formed.

In the present invention, the content of the cationic monomer is 60 mol % or more with respect to the total 100 mol % of the monomers constituting the constituent units of the polymer. By using a polymer having structural units derived from such cationic monomers, the reaction with the sludge anion becomes dense and strong, so it is possible to form flocculated flocs with excellent gravity filtration properties. Become.
In the present invention, in the monomer composition in the polymer, when the amount of the "monomer that becomes the structural unit of the polymer" is indicated, the "monomer that becomes the structural unit of the polymer" includes: The crosslinkable monomer is not included. Further, in the present invention, the blending composition ratio of the monomers at the time of polymerization of the polymer is regarded as the composition ratio of the monomers forming the constituent units of the polymer.
With respect to a total of 100 mol% of the monomers constituting the polymer, the cationic monomer is preferably 60 mol% or more from the viewpoint of forming aggregated flocs with excellent gravity filterability. More preferably 65 mol % or more, still more preferably 70 mol % or more.

In the present invention, the content of the cationic monomer (b) is 35 mol% or less with respect to the total 100 mol% of the monomers constituting the constituent units of the polymer. By using a polymer having structural units derived from such cationic monomers, the resulting sludge dewatering agent can form flocculated flocs with excellent gravity filterability without deteriorating dehydration performance. becomes.
When the cationic monomer contains the cationic monomer (a) and the cationic monomer (b), the above The cationic monomer (b) is preferably 10 mol% or more from the viewpoint of suppressing hydrolysis of the polymer and exerting a stable dehydration effect on various sludges, and from the viewpoint of reducing the moisture content of the cake. , More preferably 15 mol% or more, more preferably 18 mol% or more, and from the viewpoint of forming aggregated flocs with excellent gravity filterability, preferably 35 mol% or less, more preferably 30 mol% or less, and still more preferably is 25 mol % or less.

In the present invention, when the cationic monomer contains the cationic monomer (a) and the cationic monomer (b), the cationic monomer (a) and the cationic monomer The molar ratio [cationic monomer (a) / cationic monomer (b)] with the monomer (b) suppresses the hydrolysis of the polymer and provides a stable dehydration effect for various sludges. From the viewpoint of performance and the reduction of cake moisture content, etc., it is preferably 50/50 or more and 85/15 or less, more preferably 60/40 or more and 82/18 or less, further preferably 70/30 or more and 80/20 It is below.

In the present invention, the content of the crosslinkable monomer is 0.001 mol % or more and 0.025 mol % or less with respect to a total of 100 mol % of the monomers constituting the constituent units of the polymer. By having a structural unit derived from a crosslinkable monomer in such a range, it is possible to efficiently reduce contact with hydroxide ions in sludge and suppress hydrolysis of the polymer. It is also possible to more efficiently suppress the reaction between the cations of the polymer and the hydroxide ions in the sludge. As a result, a stable dehydration effect can be exhibited for various types of sludge.
With respect to a total of 100 mol% of the monomers constituting the polymer unit, the crosslinkable monomer is selected according to the type of the cationic monomer, the type of the crosslinkable monomer, polymerization conditions, etc. However, from the viewpoint of exhibiting a stable dehydration effect for more various sludges, it is preferably 0.0013 mol% or more, more preferably 0.0015 mol% or more, and 0.0017 mol% or more. From the viewpoint of forming aggregated flocs with excellent gravity filterability, the content is preferably 0.020 mol% or less, more preferably 0.010 mol% or less, and still more preferably 0.005 mol% or less.

In the present invention, the polymer contains 1 mol% of a nonionic monomer with respect to a total of 100 mol% of the monomers constituting the polymer, from the viewpoint of forming coarse aggregated flocs. It is preferably contained in an amount of at least 3 mol %, more preferably 4 mol % or more. From the viewpoint of dehydration performance, the content is preferably 30 mol% or less, more preferably 25 mol% or less, and still more preferably 23 mol% or less, in order to suppress a decrease in the cationic degree of the polymer.

In the present invention, the polymer contains 8 mol% or less of the anionic monomer with respect to the total 100 mol% of the monomers constituting the polymer, from the viewpoint of forming coarse aggregated flocs. It is preferably contained, more preferably 5 mol % or less, still more preferably 3 mol % or less.

The polymer contained in the sludge dehydrating agent may be of the water-in-oil emulsion type (W/O emulsion) or powdery. Whether the polymer is in the form of a water-in-oil emulsion or in the form of a powder, the same effect can be obtained.

Moreover, the said polymer contained in the said sludge dehydrating agent may be used individually by 1 type, or 2 or more types may be used together. For example, when two types of polymers are used, each polymer may be mixed to form a single dosage form, or each polymer may be a separate liquid formulation or the like to be used together to form a two dosage form.

<Colloid equivalent value>
In general, floc is generated by electrostatically interacting the charge (e.g., positive charge) of the polymer as a sludge dewatering agent with the charge (e.g., negative charge) of the sludge component, and the charge of the polymer and the charge of the sludge component. formed by neutralizing the The charge possessed by the polymer is obtained by measuring the colloidal equivalent value. Here, "colloid equivalent value" refers to the charge density (meq/g) possessed by the polymer determined by colloid titration, and for example, when the polymer is a cationic polymer, it refers to the cation density. In the present invention, the colloidal equivalent value of a polymer refers to cation density and is an indicator of "cationicity."
A polymer with a high colloidal equivalent value can be said to have a high charge-neutralizing ability. However, as described above, with the recent diversification of sludge, even if a sludge dehydrating agent containing a polymer with a high colloid equivalent value is used, the dehydration effect may vary greatly depending on the sludge, and the colloid equivalent value is high. A sludge dehydrating agent containing a polymer does not necessarily have good dewatering performance as a sludge dehydrating agent for any kind of sludge. As a result of detailed examination of the cause, it was found that conventional polymers sometimes cannot exhibit good dehydration performance for the following reasons.
As described above, polymers contained in conventional sludge dewatering agents generally contain ester-based cationic polymers. In the aqueous solution containing this polymer, the colloid equivalent value is maximized in the pH range of 3 to 5, and when the pH of the aqueous solution exceeds 5, the colloid equivalent value tends to decrease. This is because the hydroxide ions in the aqueous solution increase as the pH value increases, and the increased hydroxide ions promote hydrolysis of the polymer, which is an ester, and lower the cationic degree of the polymer. In addition, it is considered that the cation degree of the polymer is lowered due to the reaction between the cations of the polymer and the hydroxide ions. Such a decrease in colloid equivalent value results in a decrease in charge neutralization ability, leading to a decrease in dehydration performance.
On the other hand, the pH of most sludge is around 5-7. Therefore, with conventional sludge dehydrating agents, the higher the pH of the sludge, the lower the colloid equivalent value of the polymer contained in the sludge dehydrating agent. presumably occurred.

Therefore, the present inventors focused on the fact that the pH of the aqueous solution containing the polymer contained in the sludge dehydrating agent affects the dehydration performance, and conducted extensive studies. A sludge dehydrating agent containing a polymer whose value does not change greatly, that is, a polymer satisfying the following formula (1), exerts a more stable dewatering effect on various sludges than before, and enables efficient dehydration treatment. and completed the present invention.
Colloid equivalent value at pH 7 (I) / Colloid equivalent value at pH 5 (II) × 100 ≥ 92 (%) (1)
In the above formula (1), the colloid equivalent value (I) at pH 7 is a value calculated from the titration amount obtained by preparing an aqueous solution containing the polymer having a pH of 7 and determining the titration amount by colloid titration. be.
In the above formula (1), the colloid equivalent value (I) at pH 5 is obtained by preparing an aqueous solution containing the polymer having a pH of 5, determining the titration amount by colloid titration, and calculating from the titration amount. value.
Although the indicator used for colloidal titration is not particularly limited, toluidine blue is preferably used. The titrant used for colloidal titration is not particularly limited, but a polyvinyl potassium sulfate standard solution is preferably used.

In the present invention, the polymer that satisfies the formula (1) has a structural unit derived from the cationic monomer described above and a structural unit derived from the crosslinkable monomer described above. The cationic monomer is 60 mol% or more with respect to a total of 100 mol% of the unit monomers (excluding the crosslinkable monomer), and the cation represented by the formula (B) is 35 mol% or less, and the crosslinkable monomer is not particularly limited as long as it is 0.001 mol% or more and 0.025 mol% or less. It can be appropriately prepared by considering the type and amount of the monomer and polymerization initiator, the composition ratio of the monomers constituting the polymer, the reaction heat during polymer synthesis, the polymer synthesis method and synthesis conditions, etc. .

In the present invention, the value obtained by dividing the colloid equivalent value (I) at pH 7 by the colloid equivalent value (II) at pH 5 and multiplying it by 100 is a more stable dehydration effect for various sludges. It is preferably 92.5(%) or more, more preferably 92.8(%) or more.

<Intrinsic viscosity>
Intrinsic viscosity [η] is a polymer physical property that is an index of the extent of polymer chain expansion and contraction.
In addition, the intrinsic viscosity [η] tends to increase as the molecular weight of the polymer increases, and can be used as a tentative measure of the molecular weight. However, the intrinsic viscosity [η] is influenced by the structure of the monomers that are the constituent units of the polymer, the polymerization conditions, etc., and does not necessarily correspond to the size of the molecular weight.
In the present invention, the polymer preferably has an intrinsic viscosity [η] of 0.5 to 5.0 dL/g, more preferably 1.0 to 4.0 dL/g in a 1 mol/L sodium nitrate aqueous solution at 30°C. 5 dL/g, more preferably 1.5 to 4.0 dL/g.
If the polymer has an intrinsic viscosity [η] within the above numerical range, the polymer chains can spread appropriately in various sludges, and coarse aggregated flocs are easily formed.

In the present invention, the intrinsic viscosity [η] is a value calculated using the Huggins formula shown in formula (2) below.
η _SP /C=[η]+k′[η] ² C (2)
In formula (2), η _SP : specific viscosity (=η _rel −1), k′: Huggins constant, C: polymer concentration, η _rel : relative viscosity.
The Huggins constant k' is a constant determined by the type of _polymer and the type of solvent. can be obtained as the slope of Specifically, a plurality of polymer solution samples with different polymer concentrations are prepared, the specific viscosity η _SP of the polymer solution samples at each concentration is determined, and plotted on a graph with η _SP /C as the vertical axis and C as the horizontal axis. , C is extrapolated to 0 and the value of the intercept is the intrinsic viscosity [η].
The specific viscosity η _SP can be obtained by a method as shown in Examples described later.

The sludge dehydrating agent may contain, in addition to the polymer, other components such as sulfamic acid, sodium sulfate, sodium hydrogensulfate, a solvent, etc., within a range that does not impair the effects of the present invention. However, the content of the other components is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 0% by mass, based on 100% by mass of the sludge dehydrating agent.
The solvent is used to allow the polymer to exist in the sludge dewatering agent at an appropriate concentration, to maintain the polymer in a stable and uniform state, and to facilitate handling of the sludge dewatering agent. can be included in terms of The solvent is usually water, but also includes organic solvents such as oily solvents resulting from the production method of the polymer described later.

When the sludge dehydrating agent contains a W/O emulsion type polymer as described later, the polymer concentration in the sludge dehydrating agent is preferably 30 to 60% by mass, more preferably 32 to 55% by mass, More preferably, it is 35 to 50% by mass. The sludge dehydrating agent may be prepared as an additive solution by appropriately diluting it with a solvent such as water so that the polymer has a predetermined concentration depending on the properties of the sludge to be added at the time of use.

<Method for producing polymer>
The polymer can be produced by polymerizing a monomer and a crosslinkable monomer, which are constituent units of the polymer, using a polymerization initiator or the like.

(Polymerization initiator)
Polymerization initiators used for polymerization of the polymer include, for example, persulfates such as ammonium persulfate and potassium persulfate; organic oxides such as benzoyl peroxide; azobisisobutyronitrile, azobiscyanovaleric acid; , 2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) , 2,2′-azobis(2-methylamidinopropane) dihydrochloride, 2,2′-azobis(2-methylpropionamidine) dihydrochloride, 2,2′-azobis[2-(2-imidazoline-2 -yl) propane] dihydrochloride and other azo compounds. These may be used individually by 1 type, or may use 2 or more types together. Among these, 2,2'-azobis(2-amidinopropane) dihydrochloride is preferred.
The amount of the polymerization initiator to be added can be appropriately set according to the composition of the monomers that form the constituent units of the polymer. 001 to 0.5 parts by mass.

(Polymerization method)
Examples of the polymerization method include an emulsion polymerization method, an aqueous solution polymerization method, a suspension polymerization method, and the like. Among these polymerization methods, the emulsion polymerization method, in which the polymer is obtained in the form of a W/O emulsion, is preferable from the viewpoints of ease of production, ease of handling of the produced polymer as a sludge dehydrating agent, solubility in sludge, and the like.
A known emulsion polymerization method can be used. For example, an oil phase containing an oily solvent and a surfactant is prepared, and an aqueous solution of a monomer to be a constituent unit of the polymer is added to the oil phase. It is added, stirred and mixed, emulsified, and polymerized. When the polymerization initiator is water-soluble, it may be mixed with the aqueous solution of the monomer. When it is oil-soluble, it may be added after emulsification.
Examples of the oil-based solvent include mineral oils such as kerosene and light oil, and their refined products such as normal paraffin, isoparaffin, and naphthenic oil. , animal oils or mixtures thereof can also be used.
Examples of the surfactant include sorbitan fatty acid esters such as sorbitan monooleate and sorbitan monostearate; nonionic surfactants such as polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and pentaoxyethylene oleyl ether. It is preferably used.

In the present invention, the temperature during emulsion polymerization is preferably 0 to 70° C., more preferably 5 to 60° C., even more preferably, from the viewpoint of exhibiting a more stable dehydration effect on various sludges. 10 to 58°C, more preferably 15 to 55°C.
The emulsion polymerization time is preferably 2 to 24 hours, more preferably 4 to 12 hours, still more preferably 6 to 10 hours, from the viewpoint of exhibiting a more stable dehydration effect on various sludges. .

[Sludge dehydration method]
The sludge dewatering method of the present invention is a method of adding the sludge dewatering agent to sludge to dewater the sludge.
Sludge to which the sludge dehydration method is applied includes, for example, surplus sludge of sewage, raw mixed sludge, digested sludge, surplus sludge and coagulated mixed sludge from food factories and chemical factories, mixed sludge from human waste treatment plants, and the like. is mentioned.
According to the sludge dehydration method using the sludge dehydrating agent of the present invention, various sludges can be dewatered stably and efficiently.

For example, when the content of suspended solids (SS) in the sludge is about 0.5 to 4.0% by mass, the amount of the sludge dehydrating agent added is preferably 20 to 500 mg / L, More preferably 30 to 300 mg/L, still more preferably 40 to 200 mg/L.
The content of SS referred to here is a value determined by the analysis method described in the Examples below.

A method for adding the sludge dehydrating agent to the sludge is not particularly limited, and a known method can be applied. For example, the sludge dehydrating agent can be added to sludge after being diluted with a solvent such as water so that the polymer in the sludge dehydrating agent has a predetermined concentration.
The concentration of the polymer in the additive liquid when adding the sludge dehydrating agent is preferably 0.01 to 1.0% by mass from the viewpoint of uniformly dispersing the polymer in the sludge, and more It is preferably 0.03 to 0.6% by mass, more preferably 0.05 to 0.4% by mass.

The sludge to which the sludge dehydrating agent has been added can be stirred in a coagulation reaction tank with a stirring blade under predetermined stirring conditions (eg, 180 rpm for 30 seconds) to form coagulated flocs.
Then, a dewatered cake is obtained by dehydrating the flocculated flocs with a dehydrator and separating solid and liquid.
Examples of the dehydrator include, but are not particularly limited to, a belt press filter, a screw press dehydrator, a multi-disc dehydrator, a centrifugal dehydrator, and the like.

The dehydrated cake is disposed of in landfills or reused as horticultural soil or raw material for cement.
From the viewpoint of making the dehydrated cake easy to handle in transportation, disposal, reuse processing, etc., it is preferable that the lumpy cake shape does not collapse and the water content is as low as possible. According to the sludge dewatering method of the present invention, such a dehydrated cake with good handleability can be obtained.

In addition, in the sludge dehydration method of the present invention, by using the sludge dehydrating agent of the present invention, various sludges can be stably and efficiently dewatered. In addition, other sludge dehydrating agent containing a polymer different from the polymer in the sludge dehydrating agent may be used in combination. Polymers in other sludge dewatering agents used in combination include, for example, polymers having cationic functional groups or anionic polymers. The polymer having a cationic functional group includes not only cationic polymers but also amphoteric polymers. In addition, these polymers may be crosslinked or non-crosslinked such as linear.
The other sludge dehydrating agent is also preferably added by the same addition method as the addition of the sludge dehydrating agent of the present invention.

EXAMPLES The present invention will be described below based on examples, but the present invention is not limited to the following examples.
Various polymers were prepared, and evaluation tests of sludge dehydrating agent samples using the polymers were conducted.

[Preparation of polymer]
Various polymers used for the sludge dehydrating agent samples of the following examples and comparative examples were prepared according to the synthesis examples shown below.
Various constituent monomers in each polymer are abbreviated as follows.
<Cationic monomer (a)>
-DAA: 2-(acryloyloxy)ethyltrimethylammonium chloride; molecular weight 193.7
<Cationic monomer (b)>
- DAM-1: 2-(methacryloyloxy)ethyltrimethylammonium chloride; molecular weight 207.7
- DAM-2: 2-(methacryloyloxy)ethyldimethylamine hydrochloride; molecular weight 193.67
<Nonionic monomer>
- AAM: acrylamide; molecular weight 71.1
<Anionic monomer>
- AA: acrylic acid; 72.1
<Crosslinkable monomer>
(i): N,N'-methylenebisacrylamide; molecular weight 154.17
(ii): 1,3,5-triacryloyl hexahydro-1,3,5-triazine; molecular weight 249.27
(iii): ethoxylated isocyanuric acid triacrylate; molecular weight 423.37
(iv): triallyl ammonium chloride; molecular weight 173.686

(Synthesis example 1)
301 g of normal paraffin, 40 g of pentaoxyethylene oleyl ether, and 12 g of sorbitan monooleate were charged into a 1 L four-neck separable flask equipped with a stirrer, condenser, nitrogen inlet tube, and thermometer, and stirred and mixed to prepare an oil layer mixture. bottom.
Next, a mixed aqueous solution of 384 g of an 80% by mass aqueous solution of DAA, 110 g of an 80% by mass aqueous solution of DAM-1, 7.5 g of AAM, 0.5 g of AA, 0.0065 g of N,N'-methylenebisacrylamide, and 150 g of water was added to the oil layer mixture. and emulsified by stirring with a homogenizer. This was adjusted to 50° C. under stirring, and nitrogen gas was bubbled for 30 minutes. Under a nitrogen gas stream, 1.0 g of a 4% by mass toluene solution of 2,2′-azobis(2-methylpropionamidine) dihydrochloride was added as a polymerization initiator, polymerized at 45 to 55° C. for 8 hours, and W/O An emulsion type polymer (Polymer 1) was obtained.

The polymer concentration was determined as follows.
About 10 g of the W/O emulsion polymer (Polymer 1) was placed in a beaker and weighed accurately, then acetone was added in an amount of 10 times or more by weight of the W/O emulsion polymer to precipitate the polymer, and the supernatant was removed. . Acetone was added again to remove the supernatant, and this operation was repeated a total of three times to purify the polymer, which was then dried in a vacuum dryer at room temperature (25°C) for 48 hours to obtain a powdery polymer. rice field.
The obtained powdery polymer was accurately weighed, and the ratio of the mass of the powdery polymer to the mass of the W/O emulsion type polymer measured first was calculated, and this value was defined as the polymer concentration [% by mass].

(Synthesis Examples 2-10, Comparative Synthesis Examples 1-5)
In Synthesis Example 1, the constituent monomers and polymerization initiator used as synthetic raw materials were changed to those shown in each synthesis example in Table 1 below, and in the same manner as in Synthesis Example 1, each W / O emulsion type polymer (Polymers 2-10, Comparative Polymers 1-5) were obtained.

<Colloid equivalent value>
For the W/O emulsion type polymers (polymers 1 to 10, comparative polymers 1 to 5) obtained in Synthesis Examples 1 to 10 and Comparative Synthesis Examples 1 to 5, according to the following procedures (1) to (9). , pH 5 and pH 7, and the colloid equivalent value (I) at pH 7 was divided by the colloid equivalent value (II) at pH 5 and multiplied by 100 to calculate a value.
(1) At room temperature of 25° C., deionized water is stirred at 1500 rpm using a magnetic stirrer, and the W/O emulsion type polymer is rapidly spread along the inner surface of the vortex so that the polymer concentration becomes 0.2% by mass. Charged and stirred for 1 hour. If the solution was not sufficiently dissolved, the mixture was stirred for an additional hour. Then, it was allowed to stand overnight at room temperature to dissolve.
(2) Measure 25 mL of the aqueous solution having a polymer concentration of 0.2% by mass prepared in (1) with a whole pipette, place it in a 200 mL graduated cylinder, fill it up with deionized water, and invert and stir to obtain a polymer concentration. A 250 mg/L aqueous solution (measurement sample) was prepared.
(3) Prepare four conical beakers, put 80 mL of deionized water in each conical beaker, add 20 mL of the measurement sample prepared in (2), stir thoroughly with a magnetic stirrer, and titrate each sample and
(4) The pH of each sample to be titrated was adjusted by adding an aqueous solution of hydrochloric acid or an aqueous solution of sodium hydroxide while checking with a pH meter so that the sample to be titrated had a pH of 3, 5, 7, or 9.
(5) To each sample to be titrated adjusted to pH 3, 5, 7 and 9, 1 to 2 drops of toluidine blue was immediately added in advance as an indicator and stirred for 10 seconds.
(6) Then, immediately titrate with stirring at a rate of 2 mL / min using 0.0025 mol / L (1 / 400 N) polyvinyl potassium sulfate standard solution as a titrant, changing from blue to pink to pink was defined as the end point and the titer AmL was determined.
(7) On the other hand, deionized water was also titrated in the same manner as the sample to be titrated to determine the blank titer BmL. The colloid equivalent values of the samples to be titrated adjusted to pH 3, 5, 7 and 9 were calculated from the results of the titration amount AmL and the blank titration amount BmL using the following formula (3).

なお、上記の式（３）における滴定剤とはポリビニル硫酸カリウムを指す。
（８）ｐＨ３、５、７、９に調整した滴定対象試料のそれぞれは、滴定終了後にｐＨ値を計測し、計測したｐＨ値をグラフのＸ軸に、上記の式（３）より算出したコロイド当量値をグラフのＹ軸にそれぞれプロットした。
グラフにプロットした４点を結んだ曲線からｐＨ５及びｐＨ７に相当する値におけるコロイド当量値を読み取り、ｐＨ５及びｐＨ７におけるコロイド当量値（ｍｅｑ／ｇ）とした。
（９）（８）で得られたｐＨ７におけるコロイド当量値（Ｉ）とｐＨ５におけるコロイド当量値（ＩＩ）から、ｐＨ７におけるコロイド当量値（Ｉ）をｐＨ５におけるコロイド当量値（ＩＩ）で除して１００を乗じた値を算出した。その値を表１に示す。

The titrant in the above formula (3) refers to potassium polyvinyl sulfate.
(8) For each of the samples to be titrated adjusted to pH 3, 5, 7, and 9, the pH value was measured after the titration was completed, and the measured pH value was plotted on the X axis of the graph, and the colloid calculated from the above formula (3) Equivalence values were plotted respectively on the Y-axis of the graph.
The colloid equivalent values at the values corresponding to pH 5 and pH 7 were read from the curve connecting the four points plotted on the graph and used as the colloid equivalent values (meq/g) at pH 5 and pH 7.
(9) From the colloid equivalent value (I) at pH 7 and the colloid equivalent value (II) at pH 5 obtained in (8), divide the colloid equivalent value (I) at pH 7 by the colloid equivalent value (II) at pH 5. A value multiplied by 100 was calculated. The values are shown in Table 1.

In addition, for Polymers 1 to 10 and Comparative Polymers 1 to 5, the theoretical value of the colloid equivalent was calculated from the following formula (4). The values are shown in Table 1.
Theoretical value of colloidal equivalent value [meq/g] = [ratio of cationic monomer to total 100 mol% of monomers (excluding crosslinkable monomers) constituting units of polymer [mol%] x 1000 ]/[X _(a) ×Mw _(a) +X _(b) ×Mw _(b) +X _(c) ×Mw _(c) +X _(d) ×Mw _(d) ](4)
X _(a) : Ratio of cationic monomer (a) to total 100 mol% of monomers (excluding crosslinkable monomers) constituting units of polymer [mol%]
Mw _(a) : molecular weight of cationic monomer (a) X _(b) : cationic monomer ( Ratio of b) [mol%]
Mw _(b) : Molecular weight of cationic monomer (b) X _(c) : Nonionic monomer relative to total 100 mol% of monomers (excluding crosslinkable monomers) constituting units of polymer Proportion of (c) [mol%]
Mw _(c) : Molecular weight of nonionic monomer (c) X _(d) : Anionic monomer with respect to total 100 mol% of monomers (excluding crosslinkable monomers) constituting the constituent units of the polymer Proportion of (d) [mol%]
Mw _(d) : molecular weight of anionic monomer (d)

<Intrinsic viscosity>
The W/O emulsion type polymers (polymers 1 to 10, comparative polymers 1 to 5) obtained in Synthesis Examples 1 to 10 and Comparative Synthesis Examples 1 to 5 were prepared according to the following procedures (I) to (VI). , the intrinsic viscosity was determined.
(I) Five Canon Fenske viscometers (manufactured by Kusano Kagaku Co., Ltd. No. 75) were immersed in a neutral detergent for glassware for 1 day or longer, then sufficiently washed with water and dried.
(II) The W/O emulsion type polymer was diluted with water to prepare an aqueous solution having a polymer concentration of 0.2% by mass in the same procedure as the operation for measuring the colloid equivalent value described above.
(III) Add 50 mL of a 2 mol/L sodium nitrate aqueous solution to 50 mL of the aqueous solution having a polymer concentration of 0.2% by mass prepared in (II), stir with a magnetic stirrer at 500 rpm for 20 minutes, and obtain a polymer concentration of 0.1% by mass. A 1 mol/L sodium nitrate aqueous solution was obtained. This was diluted with a 1 mol/L sodium nitrate aqueous solution to prepare polymer solution samples with five levels of polymer concentrations of 0.02, 0.04, 0.06, 0.08 and 0.1% by mass. A 1 mol/L sodium nitrate aqueous solution to which no polymer was added was used as a blank solution.
(IV) Five viscometers prepared in (I) were vertically installed in a constant temperature water bath adjusted to a temperature of 30°C (within ±0.02°C). After 10 mL of the blank liquid was put into each viscometer with a whole pipette, it was allowed to stand still for about 30 minutes in order to keep the temperature constant. After that, the liquid was sucked up using a dropper plug, allowed to drop naturally, and the time taken to pass the marked line was measured with a stopwatch to the nearest 1/100th of a second. This measurement was repeated 5 times for each viscometer, and the average value was taken as the blank value (t ₀ ).
(V) 10 mL each of polymer solution samples having five levels of polymer concentrations prepared in (III) were placed in five viscometers used for blank solution measurement, and allowed to stand for about 30 minutes to keep the temperature constant. After that, the same operation as the measurement of the blank solution was repeated three times, and the average value of the transit time for each concentration was taken as the measured value (t).
The relative _viscosity η _rel , specific viscosity η _SP and reduced viscosity η _SP /C [dL/g] were determined.
η _rel =t/t ₀ (5)
η _SP =(t−t ₀ )/t ₀ =η _rel −1 (6)
From these values, the intrinsic viscosity [η] of each polymer was determined according to the method of determining the intrinsic viscosity based on the above-mentioned Huggins equation.
(VI) In (III), the concentration of the sodium nitrate aqueous solution was changed to prepare a 0.01 mol/L sodium nitrate aqueous solution with a polymer concentration of 0.1% by mass. This was diluted with a 0.01 mol/L sodium nitrate aqueous solution to prepare polymer solution samples with five levels of polymer concentration in the same manner as in (III) above, and follow the procedures of (III) to (V) for each The intrinsic viscosity [η] of the polymer was obtained.

[Sludge]
Details of the sludge used in the evaluation test of the sludge dehydrating agent sample are shown in Table 2 below. The abbreviations and analysis methods (according to the sewage test method) of the items representing the properties of the sludge shown in Table 2 are as follows.

(1) SS
After weighing 100 mL of sludge, it was centrifuged at 3000 rpm for 10 minutes to remove the supernatant. The precipitate was washed with water and poured into a weighed crucible, dried at a temperature in the range of 105 to 110° C. for 15 hours, weighed, and the mass of the residue in the crucible after drying was determined.
The ratio of the mass of the residue to the mass of 100 mL of sludge before drying was defined as the content [% by mass] of suspended solids (SS) in 100 mL of sludge.

(2) VSS
After determining the mass of the residue (SS) in the crucible in (1) above, ignite for 2 hours at a temperature within the range of 600 ± 25 ° C. with the residue (SS) in the crucible, After standing to cool, it was weighed to determine the mass of the residue in the crucible after ignition.
The difference in mass between the residue (SS) in the crucible before ignition and the residue in the crucible after ignition is the mass of volatile suspended solids (VSS) in 100 mL of sludge. . The ratio of the mass of the residue (VSS) after ignition to the mass of SS was determined as the content of VSS [mass %/SS].

(3) TS
100 mL of sludge was weighed, placed in a weighed crucible, dried at a temperature within the range of 105 to 110° C. for 15 hours, weighed, and the mass of the residue in the crucible after drying was determined.
The ratio of the mass of the residue to the mass of 100 mL of sludge before drying was determined as the content [% by mass] of evaporation residue (TS: Total Solids) in 100 mL of sludge.

(4) VTS
After determining the mass of the residue (TS) in the crucible in (3) above, ignite the residue (TS) in the crucible at a temperature within the range of 600 ± 25 ° C. for 2 hours, After standing to cool, it was weighed to determine the mass of the residue in the crucible after ignition.
The difference in mass between the residue (TS) in the crucible before ignition and the residue in the crucible after ignition is the mass of volatile suspended solids (VTS: Volatile Total Solids) in 100 mL of sludge. . The ratio of the mass of the residue (VTS) after ignition to the mass of TS was determined as the content of VTS [% by mass/TS].

(5) Fiber content 100 mL of sludge is filtered through a 100-mesh (149 μm opening) sieve, washed with water, poured into a weighed crucible, and dried at a temperature within the range of 105 to 110 ° C. for 15 hours. After drying, it was weighed to determine the mass of the residue in the crucible after drying.
Thereafter, the residue in the crucible was ignited at a temperature within the range of 600±25° C. for 2 hours, allowed to cool, and then weighed to determine the mass of the residue in the crucible after ignition.
The difference in mass between the residue in the crucible before ignition and the residue in the crucible after ignition is the mass of volatile suspended matter with a particle size of about 149 μm or more in 100 mL of sludge, mainly volatilizing It is the mass of the natural fiber content. The ratio of the mass of the residue after ignition (volatile suspended solids having a particle size of about 149 μm or more) to the mass of SS was determined as the fiber content [mass %/SS].

(6) pH
Based on JIS Z 8802:2011, pH was measured based on operation of the glass electrode method. For pH calibration, commercially available pH standard solutions of phthalate, neutral phosphate and carbonate were used.

(7) Electrical conductivity Electrical conductivity was measured according to JIS K 0102:2016.

[Evaluation test of sludge dehydrating agent sample]
Using the sludge dehydrating agent samples prepared above (polymers 1 to 10, comparative polymers 1 to 5), a desktop test of sludge treatment was performed, and the sludge dewatering performance of the sludge dehydrating agent samples was evaluated by the following evaluation method. was evaluated.

(Example 1)
The W/O emulsion type polymer (Polymer 1) obtained in Synthesis Example 1 was diluted with water to prepare an aqueous solution having a polymer concentration of 0.2% by mass.
200 mL of sludge A was collected in a 300 mL beaker, sludge dehydrating agent sample 1 was added to an additive concentration of 80 mg/L, and stirred at 180 rpm for 30 seconds to form flocculated flocs to obtain treated sludge.

(Examples 2 to 30 and Comparative Examples 1 to 5)
In Example 1, the sludge, the sludge dehydrating agent sample, and the addition concentration thereof were changed as shown in Table 3 below, and the sludge dehydrating agent sample was added to the sludge in the same manner as in Example 1, except for the above, to form flocculated flocs. formed to obtain treated sludge.

<Evaluation method>
The treated sludge in the above examples and comparative examples was evaluated for each item shown below. These evaluation results are summarized in Table 3 below.

(1) Floc diameter Of the aggregated flocs in the beaker, about 100 arbitrary aggregated flocs that can be observed from above the beaker were measured with a tape measure for the maximum diameter of each aggregated floc, and the average value was taken as the floc diameter. .
The floc diameter is an index of floc forming ability of the sludge dewatering agent. As the floc diameter is larger, it can be evaluated that coarse aggregated flocs are formed, and it can be said that the sludge dehydrating agent sample has a high floc forming ability. However, when the floc diameter is too large, the moisture content of the cake, which will be described later, tends to increase. The floc diameter is preferably 4.5 mm or more.

(2) Filtration volume for 20 seconds A Buchner funnel (inner diameter 80 mm, pore diameter about 1 mm) is placed on a 200 mL graduated cylinder, and then a polyvinyl chloride cylinder with a diameter of 50 mm is placed above the filtration surface of the Buchner funnel. bottom. The treated sludge was poured into the cylinder all at once, and the filtrate was sampled with a measuring cylinder until 20 seconds after the start of pouring.
The 20-second filtration rate is an index of gravity filterability. It can be evaluated that the larger the 20-second filtration amount, the more excellent the gravity filterability of the flocculated flocs formed. However, even if the 20-second filtration amount is large, if the SS leak amount described later is large, it cannot be said that the treated sludge is dehydrated in a good state. It is necessary to determine both the 20-second filtration amount and the SS leak amount.

(3) SS leak amount After measuring the 20-second filtration amount in (2), 40 seconds later, the graduated cylinder is replaced with another graduated cylinder, and after 60 seconds from the start of pouring the treated sludge, the Buchner The amount of liquid collected through the holes in the funnel was read from the scale on the graduated cylinder. The read liquid amount was taken as the SS leak amount.
The SS leak amount referred to here is a numerical value that serves as a guideline for the amount of suspended solids (SS) such as fine flocs that have not formed coarse flocs or collapsed fine flocs in the treated sludge.
It can be evaluated that the smaller the SS leak amount, the more coarse aggregated flocs were formed.

(4) Moisture Content of Cake After measuring the SS leak amount in (3) above, the aggregated flocs remaining on the Buchner funnel were packed in a polyvinyl chloride column (inner diameter: 30 mm, height: 17.5 mm). The column was removed, and the aggregated flocs with a bottom surface of approximately 30 mm were pressed from the top surface at 0.1 MPa for 60 seconds to obtain a dehydrated cake.
The mass of the dehydrated cake and the mass of the dehydrated cake after drying the dehydrated cake at 105°C for 15 hours were measured. The difference between the mass of the dehydrated cake before drying and after drying was regarded as the moisture content of the dehydrated cake. The ratio of the water content to the weight of the dehydrated cake before drying was obtained as cake water content [% by mass]. From the viewpoint of handleability in disposal of the dehydrated cake, etc., it is preferable that the moisture content of the cake is low.

From the results shown in Table 3, it can be seen that even a sludge dehydrating agent with a high theoretical colloid equivalent value does not necessarily exhibit a stable dehydrating effect on various types of sludge.
In addition, as can be seen from the results shown in Table 3, according to the sludge dehydrating agent of the present invention, the floc diameter, 20-second filtration amount, SS leak amount, and cake moisture content in the treated sludge were all favorable. That is, it was confirmed that the sludge dehydrating agent of the present invention exerts a stable dewatering effect on various types of sludge.

Claims (6)

A sludge dewatering agent comprising a polymer having a structural unit derived from a cationic monomer, a structural unit derived from a crosslinkable monomer, and a structural unit derived from a nonionic monomer,
The cationic monomer includes a cationic monomer (a) and a cationic monomer (b),
the cross-linking monomer is selected from N,N'-methylenebisacrylamide, 1,3,5-triacryloylhexahydro-1,3,5-triazine, ethoxylated isocyanuric acid triacrylate, and triallylammonium chloride; is at least one
the nonionic monomer is acrylamide,
the cationic monomer (a) is 2-(acryloyloxy)ethyltrimethylammonium chloride,
The cationic monomer (b) is at least one selected from 2-(methacryloyloxy)ethyltrimethylammonium chloride and 2-(methacryloyloxy)ethyldimethylamine hydrochloride,
The cationic monomer is 60 mol% or more with respect to a total of 100 mol% of the monomers that are the constituent units of the polymer (excluding the crosslinkable monomer), and the cationic monomer (b) is 35 mol% or less, the crosslinkable monomer is 0.001 mol% or more and 0.025 mol% or less, and the nonionic monomer is 1 mol% or more and 30 mol% or less can be,
A sludge dewatering agent in which the colloid equivalent value of the polymer satisfies the following formula (1).
Colloid equivalent value at pH 7 (I) / Colloid equivalent value at pH 5 (II) × 100 ≥ 92 (%) (1) Claim 1, wherein the cationic monomer (b) is 25 mol% or less with respect to a total of 100 mol% of the monomers (excluding crosslinkable monomers) that constitute the constituent units of the polymer. The sludge dewatering agent described in . The sludge dewatering agent according to claim 2 , wherein the polymer contains structural units derived from anionic monomers. The molar ratio of the cationic monomer (a) and the cationic monomer (b) [cationic monomer (a)/cationic monomer (b)] is 50/50 or more 85 /15 or less, the sludge dewatering agent according to any one of claims 1 to 3 . The sludge dewatering agent according to any one of claims 1 to 4 , wherein the polymer is a water-in-oil emulsion type or a powder. A sludge dewatering method, comprising adding the sludge dehydrating agent according to any one of claims 1 to 5 to sludge and dehydrating the sludge.