JP3305688B2 - Polymer flocculant, method for producing the same, and method for dehydrating organic sludge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer flocculant mainly used for dehydrating organic sludge discharged from a sewage treatment plant, human waste treatment plant, or wastewater treatment plant of a general factory, and a method for producing the same. The present invention also relates to a method for efficiently dehydrating organic sludge using the polymer flocculant.

[0002]

2. Description of the Related Art In order to treat organic sludge discharged from a sewage treatment facility, human waste treatment facility, or wastewater treatment facility of a general factory, a large amount of an inorganic electrolyte mainly composed of ferric chloride and lime is added. However, the treatment was carried out using a dehydrator such as an Oliver filter or a filter press, but the inorganic chemicals required a large amount of addition, resulting in an increase in the amount of dewatered cake after dehydration and problems in handling chemicals. Alternatively, there is a problem of corrosion of processing equipment and the like, and therefore, an organic polymer flocculant has been used instead of an inorganic chemical.

That is, after adding a polymer flocculant to organic sludge and conditioning (adjusting) the sludge,
A method of dehydrating with a centrifugal separator, a belt press, a screw press, or a similar dehydrator has become mainstream as a means for treating organic sludge. The sludge after dewatering is called dewatered cake and is disposed of by landfill or incineration. In recent years, it is often incinerated, and fuel is used for incineration. It is desired to reduce the water content, increase the dehydration processing speed, increase the throughput, increase the efficiency, and reduce the running cost in the incineration process. For this reason, it is conceivable to increase the rotation speed of the centrifuge to increase the speed, increase the pressure of the belt press, or increase the energy mechanically and physically. Conditioning of sludge by the agent has a weak floc strength and insufficient drainage of water, so that the solid content leaks to the separated liquid or the filtrate and the recovery rate decreases, or the water content of the dewatered cake is high and dehydration is difficult. In many cases, the treatment is insufficient and the filter fabric is poor in releasability, so that satisfactory treatment cannot be performed.

[0004] In recent years, the number of days of storage of sludge before dehydration has increased and the content of organic substances has increased, so that sludge which is difficult to coagulate due to decay has increased. Pretreatment of sludge with an oxidizing agent and pretreatment of sludge with an enzyme have been proposed, and there is a background that the properties of sludge are changing.

The present invention solves these problems, and when a polymer flocculant is added to sludge for conditioning, a significantly larger floc is produced than before, and the floc can maintain sufficient floc strength and can be dewatered. Another object of the present invention is to increase the throughput and reduce the water content of the dewatered cake, thereby improving the efficiency of sludge treatment.

[0006]

Means for Solving the Problems The present invention has been made as a result of intensive studies to achieve the above object,

[0007]

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[0008]

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[0009]

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[0010]

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The above object has been attained with respect to organic sludge which is a substance represented by the general formulas (E), (F) and (G) and a mixture thereof with the substance represented by the general formula (H). The inventors have found that the present invention has been completed.

In the general formula (E), a, b, and c are arbitrary positive numbers, R is (CH ₂ —CH ₂ —O) n (n is zero or any positive number), R ¹ , R ² is an alkyl group having 1 to 4 carbon atoms; R ³ is hydrogen or an alkyl group having 1 to 4 carbon atoms;
⁴ , R ⁵ are a hydrogen atom or a methyl group, X ⁻ is an anionic counter ion, M is a hydrogen atom or an alkali metal ion,
In (F), a, b, and c are arbitrary positive numbers, and R is (CH
₂ -CH ₂ -O) n [n is zero or any positive number], R
¹ and R ² are an alkyl group having 1 to 4 carbon atoms, R ³ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ⁴ and R ⁵ are a hydrogen atom or a methyl group, X ⁻ is an anionic counter ion, and M is A hydrogen atom or an alkali metal ion;
b and c are arbitrary positive numbers, and R is (CH ₂ —CH ₂ —O) n
[N is zero or any positive number], and R ¹ and R ² have 1 to 1 carbon atoms.
An alkyl group of 4, R ³ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ⁴ and R ⁵ are a hydrogen atom or a methyl group, X ⁻ is an anionic counter ion, and M is a hydrogen atom or an alkali metal ion.

The following general formula (A) applied in the present invention:

[0014]

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The cationic monomer represented by is a quaternary ammonium salt of dialkylaminoethyl methacrylate, and specific examples thereof include methyl quaternary chloride of dimethylaminoethyl methacrylate, methyl quaternary chloride of diethylaminoethyl methacrylate, and chloride quaternary. It is a benzyl quaternary compound or the like, and may be used alone or a plurality of quaternary compounds may be combined.

Further, the following general formula (B) applied in the present invention:

[0017]

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The cationic monomer represented by is a quaternary ammonium salt of dialkylaminoethyl acrylate. Specific examples thereof include quaternary methyl chloride of dimethylaminoethyl acrylate, similar quaternary diethyl sulfate, and quaternary benzyl chloride. And may be used alone or in combination.

Further, the following general formula (C) applied in the present invention:

[0020]

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Specific examples of the nonionic monomer represented by the above are methacrylamide and acrylamide, and may be used alone or in combination.

Further, the following general formula (D) applied in the present invention:

[0023]

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Specific examples of the anionic monomer represented by (1) include acrylic acid, methacrylic acid and their alkali metal salts or partially neutralized salts, and may be used alone or in combination.

The above-mentioned monomers are mixed to form an aqueous solution of a predetermined concentration, and various known polymerization methods (aqueous solution polymerization, suspension polymerization, reverse phase emulsion polymerization) are carried out in the presence of a polymerization initiator and, in some cases, a chain transfer agent. , Bulk polymerization etc.) to obtain a copolymer.

The composition ratio of each monomer in the copolymer or polymer flocculant represented by the general formulas (E), (F) and (G) can be any ratio, but 50 mol% of anionic monomer Hereinafter, preferably 1 mol% to 15 mol%, 0 to 95 mol% of nonionic monomer, and 1
It is preferably in the range of ~ 99 mol%.

In the present invention, the presence of an anionic monomer is essential, and, for example, a chemical cross-linking is obtained via a carboxyl group of the anionic monomer.

In the chemical cross-linking according to the present invention, the higher the molar ratio of the quaternary ammonium salt cationic monomer in the composition ratio, the slower the generation of the chemical cross-linking reaction, and the lower the composition ratio of the anionic monomer. Is less than 3 mol, the chemical cross-linking reaction similarly becomes difficult to occur.

Generally, fine sludge particles in organic sludge have a negative load on the surface, and in order to obtain flocculated floc, so-called coagulation (coagulation) in which a negative charge on the surface is neutralized with a positive charge, and particles are combined. Although flocculation is required to form a large floc by bonding to the bridge (crosslinking), the polymer flocculant has both functions of coagulation and flocculation, and has the ability to coagulate sludge and form large flocs. In the present invention, of the two functions possessed by the polymer flocculant, the flocculation function, in particular, is achieved by polymerization by chemical cross-linking of the copolymer chain, and simultaneously by physical cross-linking physically occurring, that is, by the Coulomb force of the groups. The resulting polyion complex generates extremely large flocs as compared to a normal polymer flocculant that is linear.

Further, the floc formed by the polymer flocculant of the present invention is not only huge but also very strong, so that when a strong shearing force is applied, for example,
When the pressure of the belt press dehydrator is increased to increase the dehydration rate, or when the centrifugal force of the centrifuge is increased to increase the separation efficiency, the generated floc is less likely to be broken. Contribute to increase.

The organic sludge to be treated in the present invention includes sewage, night soil, raw sludge discharged from wastewater treatment facilities of general industry, excess sludge generated by activated sludge, mixed raw sludge, digested sludge generated from digestion tanks. Floating sludge generated from a coagulating sedimentation tank, and mixed sludge obtained by mixing several kinds of these.

When dewatering these organic sludges, usually, a polymer coagulant is made into an aqueous solution of 0.1 to 0.2% in terms of a polymer, and it is added to the sludge at a rate of 1 to 2% / ss. The mixture is slowly stirred in the adjusting tank to form flocculated flocs, and then dewatered by a dehydrator such as a centrifuge or a belt press.

In recent years, the content of organic matter in sludge has increased,
The sludge concentration is high, and the sludge that has decayed due to a long residence time and has a small particle size is increasing.

For such sludge, the floc cannot be sufficiently increased only with the conventional cationic polymer flocculant,
Further, when the amount of addition is increased, a redistribution phenomenon occurs, and there is a problem that the floc is conversely reduced.

According to the treatment method of the present invention, a remarkably large and strong floc is generated compared to the conventional method, and the redispersion phenomenon due to the fluctuation of the sludge concentration and the amount of the polymer flocculant hardly occurs. In addition, the amount of treatment increases and the water content decreases.

The present treatment method can be applied to the above-mentioned various sludges, but may also be applied to sludge obtained by adding an inorganic polyvalent metal salt such as an iron salt or an aluminum salt to the organic sludge in the preceding step.

It is necessary to select an optimum polymer coagulant for each target sludge. In the case of the coagulants of claims 1 to 3, it is sufficient to select the copolymerization ratio. What is necessary is just to select a polymerization ratio and a mixing ratio.

The partial crosslinking of the copolymer applied in the present invention is as follows:
There are both chemical cross-linking in which a chemical reaction is caused by adding a cross-linking agent to cause cross-linking, and physical cross-linking between polymer chains by a hydrogen bond or an ionic bond or by physical bonding in a polymer chain.

The physical cross-linking referred to in the present invention is a bonding between an anionic group and a cationic group in a copolymer chain between polymer chains and in a polymer chain. Thus, the chemical cross-linking is irreversible.

The crosslinking agent used in the present invention may be any crosslinking agent capable of crosslinking by chemically reacting with a carboxyl group in a copolymer having a carboxyl group, such as a diepoxy compound and a cyclic compound. Epoxy compounds, di- and polyisocyanate compounds, di- and polymethylol phenolic resins, aziridine compounds, amine compounds, dialdehyde compounds, and the like are particularly preferable. Among these, diepoxy compounds that are more water-soluble are practically preferable. Specific examples thereof include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and glycerin triglycidyl ether.

These crosslinking agents may be used alone or in combination of two or more. Furthermore, as a crosslinking method other than the crosslinking agent, effective crosslinking may be generated by radiation crosslinking, photocrosslinking, or plasma crosslinking.

The cross-linking agent of the present invention may cause a cross-linking reaction at the same time as the polymerization, or may react the cross-linking agent with the formed polymer after the polymerization.

The polymerization operation according to the present invention may be any of an aqueous solution polymerization, a bulk polymerization, a suspension polymerization and an inverse emulsion polymerization, and the product form may be any of emulsion, powder, aqueous solution and the like. It is.

However, when the ratio of partial chemical cross-linking in the composition increases, the solubility of the product in the form of an aqueous solution or powder becomes extremely slow as a product. Is most preferred.
Since the emulsion product has a very small polymer particle size of 0.1 to several microns, when the emulsion product (latex polymer) is diluted and dissolved in water, a uniform solution can be obtained in a very short time. Therefore, in the case of powdery products and aqueous products, even partially chemically crosslinked polymers that are practically impossible to dilute and dissolve in water,
With an emulsion product (latex polymer), a uniform diluted solution can be obtained in a very short time, and the object of the present invention can be more easily achieved.

[0045]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

[0046]

[First Embodiment] 50% in a 500 ml separable flask
Acrylamide 53.29 parts by weight, 78% dimethylaminoethyl methacrylate methyl chloride quaternary (DM
C) 19.97 parts by weight, 80% acrylic acid 4.50 parts by weight, 50% NaOH 4.0 parts by weight, azo initiator 0.0
After 3 parts by weight and 392.47 parts by weight of deionized water were charged and replaced with nitrogen under stirring, polymerization was carried out at 36 ° C. for 24 hours in a closed and sealed state, and further kept at 50 ° C. for 24 hours to terminate the reaction.

The lump obtained was roughly crushed by a meat chopper, dried by a reduced pressure drier so that the product temperature did not rise to 50 ° C. or higher, and then pulverized by a fine pulverizer to obtain a powdery polymer.

A sample was prepared in the same manner as above except for changing only the composition ratio.

The samples are shown in Table 1.

[0050]

[Table 1]

Each sample in Table 1 was 0.1% by polymer
Was dissolved in pure water, and a predetermined amount was added to sludge collected from a sewage treatment plant, and the amount of polymer added and the size and strength of the generated floc were compared.

Put 200 sludge in a 300 ml tall beaker.
g. Accurately weigh and add a predetermined amount of polymer, and use a jar tester (a rectangular plate blade 45 mm in length × 20 mm in width) attached to a stirring shaft in duplicate to rotate at 60 rpm. p. m. The size of the floc after stirring for 30 seconds was measured. Thereafter, the generated flocks are rotated at a rotational speed of 200 r. p. m. For 30 seconds, the size of the floc was measured, and the floc strength was determined.

[0053]

[Table 2]

The size of the floc is based on the “floc particle size determination table” in FIG. 1 as in Tables 3, 5 and 7, and “SP” in each table indicates a large floc particle size of 8 mm or more. Flock means.

[0055]

[Table 3]

As described above, Examples 1 to 4 correspond to Comparative Example 1.
Compared with Comparative Examples 4 to 4, a large floc that cannot be obtained with the conventional commercial polymer flocculant can be obtained, and the flocculation effect is excellent without redispersion phenomenon caused by increasing the addition amount as in the comparative example. It is recognized that.

[0057]

Second Example The copolymer constituting the coagulant of Example 1 and a commercially available copolymer were mixed to obtain a polymer coagulant (sample) of Example 5 as Comparative Examples 5- (1) and Comparative Examples 5- (2) was compared.

[0058]

[Table 4]

The sludge collected from the sewage treatment plant C was compared and evaluated in the same manner as in the first experimental example.

[0060]

[Table 5]

Also in the case of the fifth embodiment, the redispersion phenomenon does not occur.
In addition, it was found that a huge floc, which cannot be obtained with a conventional commercial polymer flocculant, was obtained and the flocculant effect was excellent.

[0062]

Third Example The flocculant samples shown in Table 6 were evaluated.

[0063]

[Table 6]

Evaluation method D A predetermined amount of commercially available PAC (aqueous solution of polyaluminum chloride) was added to excess sludge (pH 7.25 alkalinity 1990 SS 23040 TS 2.55% organic matter 73.0%) in a sewage treatment plant and uniformly added. After mixing, a polymer flocculant was added and mixed well in a sludge adjusting tank to form flocs, and then dehydrated with a screw decanter.

In Example 6, a stronger floc was formed than in Comparative Example 6, and the result was that both the water content and the recovery of the dehydrated cake were excellent.

[0066]

[Table 7]

[0067]

[Functions and Effects of the Present Invention] The present invention relates to a method of forming a bridge in a polymer chain by a chemical reaction (chemical cross-linking) and a method of forming a polymer (polymer) chain by forming a bridge by hydrogen bond or ionic bond (polyion complex). Both the physical entanglement (physical cross-linking) and the physical entanglement enable the formation of extremely large and strong aggregate flocs. Accordingly, it is possible to increase the sludge treatment amount and reduce the water content in the sludge dewatering step, and it can effectively act on hardly dewaterable sludge.

[Brief description of the drawings]

FIG. 1 is a floc particle size determination table for determining the size of floc.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 21/01 C02F 11/00-11/20

Claims (6)

(57) [Claims] 1. A monomer which is represented by the following general formulas (C) and (D) and one or both of the monomers represented by the general formulas (A) and (B), and is partially cross-linked so as to be capable of being dissolved and dissolved. A polymer flocculant comprising a copolymer represented by the following general formula (E). Embedded image Embedded image Embedded image Embedded image Embedded image In the formula, a, b, and c are arbitrary positive numbers, and R is (CH ₂
—CH ₂ —O) n (n is zero or any positive number), R
¹ , R ² is an alkyl group having 1 to 4 carbon atoms, R ³ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ⁴ and R ⁵ are a hydrogen atom or a methyl group, X ⁻ is an anionic counter ion, and M is Indicates a hydrogen atom or an alkali metal ion. 2. Each of the monomers represented by the following general formulas (C) and (D) and one or both of the monomers represented by the general formulas (A) and (B), and partially cross-linked so as to be capable of being dissolved and dissolved. A polymer flocculant comprising a copolymer represented by the following general formula (F). Embedded image Embedded image Embedded image Embedded image Embedded image In the formula, a, b, and c are arbitrary positive numbers, and R is (CH ₂
—CH ₂ —O) n (n is zero or any positive number), R
¹ , R ² is an alkyl group having 1 to 4 carbon atoms, R ³ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ⁴ and R ⁵ are a hydrogen atom or a methyl group, X ⁻ is an anionic counter ion, and M is Indicates a hydrogen atom or an alkali metal ion. 3. Each of the monomers represented by the following general formulas (C) and (D) and one or both of the monomers represented by the general formulas (A) and (B), and partially cross-linked so as to be capable of being dissolved and dissolved. A polymer flocculant comprising a copolymer represented by the following general formula (G). Embedded image Embedded image Embedded image Embedded image Embedded image In the formula, a, b, c, and d are arbitrary positive numbers, and R is (CH
₂ -CH ₂ -O) n [n is zero or any positive number], R
¹ , R ² is an alkyl group having 1 to 4 carbon atoms, R ³ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ⁴ and R ⁵ are a hydrogen atom or a methyl group, X ⁻ is an anionic counter ion, and M is Indicates a hydrogen atom or an alkali metal ion. 4. Polymer aggregation obtained by mixing all or a part of the copolymer represented by the following general formulas (E), (F) and (G) with the copolymer represented by the following general formula (H) at an arbitrary ratio. Agent. Embedded image In the formula, a, b, and c are arbitrary positive numbers, and R is (CH ₂
—CH ₂ —O) n (n is zero or any positive number), R
¹ , R ² is an alkyl group having 1 to 4 carbon atoms, R ³ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ⁴ and R ⁵ are a hydrogen atom or a methyl group, X ⁻ is an anionic counter ion, and M is Indicates a hydrogen atom or an alkali metal ion. Embedded image In the formula, a, b, and c are arbitrary positive numbers, and R is (CH ₂
—CH ₂ —O) n (n is zero or any positive number), R
¹ , R ² is an alkyl group having 1 to 4 carbon atoms, R ³ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ⁴ and R ⁵ are a hydrogen atom or a methyl group, X ⁻ is an anionic counter ion, and M is Indicates a hydrogen atom or an alkali metal ion. Embedded image In the formula, a, b, c, and d are arbitrary positive numbers, and R is (CH
₂ -CH ₂ -O) n [n is zero or any positive number], R
¹ , R ² is an alkyl group having 1 to 4 carbon atoms, R ³ is hydrogen or an alkyl group having 1 to 4 carbon atoms, R ⁴ and R ⁵ are a hydrogen atom or a methyl group, X ⁻ is an anionic counter ion, and M is Indicates a hydrogen atom or an alkali metal ion. Embedded image 5. The coagulation treatment of organic sludge by adding the polymer coagulant according to any one of claims 1 to 4 alone or together with an inorganic chemical such as a sulfate band, ferric chloride, and PAC. A method for dehydrating organic sludge, comprising dehydrating using a dehydrator. 6. A copolymer of each monomer represented by the following general formulas (C) and (D) and one or both of the monomers represented by the general formulas (A) and (B) in the presence of a crosslinking agent represented by the general formula (I) A method for producing a polymer flocculant, comprising reacting or copolymerizing and then subjecting it to a crosslinking reaction with a crosslinking agent represented by the general formula (I). Embedded image Embedded image Embedded image Embedded image Embedded image