JP3141766B2 - Sludge dewatering method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sludge dewatering method capable of efficiently dewatering sludge generated as a residue at a wastewater treatment plant or the like.

[0002]

2. Description of the Related Art Sludge generated from sewage and human waste treatment plants, organic industrial wastewater, etc. is an aggregate of a large number of organic and inorganic substances having a complicated structure, and has a small particle size and a strong affinity with water. It is difficult to efficiently separate water even if it is directly subjected to dehydration treatment such as filtration or centrifugation without treatment. Therefore, usually, a method of increasing the dewatering characteristics of sludge by adding a dehydrating agent (hereinafter also referred to as a flocculant) or the like, and then performing a dehydration treatment is adopted. In addition, as a method for performing dehydration more efficiently,
No. 17760 also proposes a method in which a primary dehydrating agent is added, partial dehydration is performed by gravity dehydration, and then a cationic polymer having a high cohesive force is further added as a secondary dehydrating agent, followed by mechanical dehydration. I have.

[0003]

Generally, in order to dewater sludge using a polymer flocculant, the effect of making the sludge hydrophobic (easy dehydration) by acting on the active point of the sludge and the effect of the sludge particles on the sludge are considered. It is necessary to have the effect of forming large flocs by cross-linking between them and facilitating gravity dewatering. However, in the case of sludge with high organic matter content and sludge that is difficult to dehydrate such as digested sludge, a polymer flocculant is expected. Often these effects are not sufficiently exhibited. In addition, as described above, after the primary dehydrating agent is added, partial dehydration is performed by gravity dehydration, and then a cationic polymer having a high cohesive force is further added to carry out mechanical dehydration. Since it is a system polymer, there is naturally a limit in improving dehydration.

[0004] However, the cationic polymer flocculant is a so-called hardly dewaterable material, as in the case of the conventional dehydration method, such as highly organic sludge, for example, sludge containing a large amount of domestic wastewater or sludge generated from human waste treatment plants. Sludge does not provide sufficient floc strength, and as a result, the dewaterability and peelability of the mechanical dewatered cake cannot be sufficiently improved. This is considered to be due to the fact that the cationic polymer flocculant only exerts a function as a charge neutralizer on the sludge as described above.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide the previously proposed gravity dehydration by adding a primary dehydrating agent and mechanical dehydration after adding a secondary dehydrating agent. The purpose of the present invention is to provide a secondary dewatering agent and a sludge dewatering method that can further improve the dewatering method of the combined dewatering method and further increase the dewatering efficiency of the hardly dewaterable sludge, and can greatly reduce the water content of the cake after mechanical dewatering. is there.

[0006]

The sludge dewatering method according to the present invention, which has achieved the above-mentioned objects, is a method of dewatering sludge by coagulating the sludge with a polymer coagulant and then supplying the sludge to a dehydrator. In the dehydration method of the above, in a pre-process of supplying to the dehydrator, a cationic polymer flocculant is added to the sludge as a primary dehydrating agent to form a coarse floc, which is concentrated by gravity dehydration. The feature is that mechanical dehydration is performed after the addition of the polymer compound.

The amphoteric polymer flocculant used at this time has a cation equivalent value (Cv) of 0.8 to 13.0 meq /.
g, a polymer flocculant having an anion equivalent value (Av) of 0.1 to 6.0 meq / g is preferable, and a carboxyl group-containing polymerizable monomer is indispensable as the amphoteric polymer flocculant. Is a polymer derived from the polymerizable monomer contained in, a part of the carboxyl group in the polymer molecule, 1-3
Polyalkyleneimine-based polymer coagulant present as a monobasic acid addition salt of a secondary aminoalkyl ester,
In particular, the repeating units represented by the following general formulas (1) and (2) may be used in an amount of 0.005 to 0.005 mol per mol of the former.
A polyalkylenimine-based polymer flocculant present in a ratio of 7.5 moles is recommended as a very preferred one.

[0008]

Embedded image

[0009]

DETAILED DESCRIPTION OF THE INVENTION As described above, in the dehydration method according to the present invention, a polymer flocculant is added to sludge to coagulate it, and then the sludge is subjected to a dehydrator to remove water. In a pre-dehydration step, a sludge is added with a cationic polymer flocculant as a primary dehydrating agent (also referred to as a primary flocculant) to form a coarse floc and then concentrated by gravity dehydration.
Next, an amphoteric polymer flocculant is added to the concentrated sludge as a secondary dehydrating agent (also referred to as a secondary flocculant), and then mechanical dehydration is performed. By using, the dewatering efficiency can be significantly increased.

The amphoteric polymer flocculant of the present invention used herein has a cation equivalent value (Cv) of 0.8 to 13.
0 meq / g, more preferably 4.0 to 13.0 meq / g,
A polymer flocculant having an anion equivalent value (Av) in the range of 0.1 to 6.0 meq / g, more preferably 0.2 to 3.0 meq / g, is preferred. A polymer derived from a polymerizable monomer essentially including a polymerizable monomer, wherein a part of the carboxyl groups in the molecule is present as a monobasic acid addition salt of a primary to tertiary aminoalkyl ester. Polyalkylenimine-based polymer flocculants are preferred.

Among the above-mentioned amphoteric polymer flocculants, it is particularly preferable that the repeating units represented by the above-mentioned general formulas (1) and (2) are present in an amount of 0.005-7.
It is a polyalkylenimine polymer flocculant present in a ratio of 5 mol, more preferably 0.02 to 1.0 mol.

The above-mentioned polyalkyleneimine polymer flocculant is usually composed of an anionic monomer (I) and a nonionic monomer (II).
Carboxyl group-containing polymer (II
It is produced by reacting I) with an alkylene imine. There is no particular limitation on the polymerization method at this time, and an aqueous solution polymerization method, a water-in-oil emulsion polymerization method, or the like can be adopted.A general radical polymerization catalyst can be used as a polymerization initiator used in this case. Good. The hydrophobic organic solvent, activator, water and the like used when adopting the water-in-oil emulsion polymerization method can be used at any ratio according to a known method. The type and amount of the polymerization initiator are preferably set so that the molecular weight of the obtained polyalkylenimine-based polymer flocculant falls within the range of 1 to 8,000,000, and is used in the case of water-in-oil emulsion polymerization. Preferred examples of the polymerization initiator include azobisisobutyronitrile and dimethyl azobisbutyrate.

Preferred anionic monomers used in producing the above-mentioned polyalkyleneimine polymer flocculant
Examples of (I) include acrylic acid, methacrylic acid, maleic acid and the like, among which acrylic acid is particularly preferred.

As the nonionic monomer (II), any nonionic monomer (II) copolymerizable with the anionic monomer (I) can be used. , Acrylamide, methacrylamide, N, N-
Examples include dimethylacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and the like, and acrylonitrile. These nonionic monomers (II) are used for the main purpose of adjusting the molecular weight and ion equivalent of the polyalkyleneimine-based polymer coagulant, and usually,
It is preferable to control the proportion of the carboxyl group-containing polymer (III) obtained by the polymerization to 50 mol% or less.

In preparing the polyalkyleneimine polymer flocculant, the cation equivalent value (Cv) of the polyalkylamine polymer is 0.8 to 13.0.
meq / g, anion equivalent value (Av) of 0.1 to 6.0.
Carboxyl group-containing polymer so as to be in the range of meq / g
It is desirable to determine the amount of the anionic monomer (I) or nonionic monomer (II) used in the production of (III), and at the time of aminoalkylation, the carboxyl group-containing polymer (III ) And the amount of alkylene imine used are preferably determined in each case. The alkyleneimine used herein is 1,2-alkyleneimine (aziridine)
Among them, 1,2-propyleneimine and ethyleneimine are preferably used because they are relatively inexpensive and can be easily obtained.

When the cation equivalent value (Cv) of the polyalkyleneimine polymer is less than 0.8 meq / g, the amphoteric properties are not sufficiently exhibited, and a satisfactory dehydration property is obtained due to insufficient cohesive force on sludge. Difficult, 13.0
If the amount exceeds meq / g, the anion is relatively insufficient, and the amphoteric property is hardly exhibited effectively. Further, the anion equivalent value (Av) is 6.0 meq / g.
If it exceeds, the solubility in water is reduced, and it becomes difficult to effectively exert the coagulation action, which is not preferable.

The preferred molecular weight of the polyalkyleneimine polymer flocculant is 1 to 8,000,000, more preferably 20.
When the molecular weight is less than 1,000,000, the cohesive strength becomes insufficient and a satisfactory dehydration effect cannot be obtained, or the amount of addition must be excessively increased, and conversely, the molecular weight exceeds 8,000,000. If it is too large, it will be difficult to uniformly disperse the sludge in the coarse floc, and it will be difficult to exhibit a favorable effect of lowering the water content.

Preferred examples of the hydrophobic organic solvent used when adopting the water-in-oil emulsion polymerization method include alicyclic solvents such as isoparaffin and cyclohexane, and kerosene. As the monobasic acid, mineral acids such as hydrochloric acid and nitric acid, and carboxylic acids such as acetic acid and formic acid can be used. These monobasic acids are usually in the range of 50 to 100 mol% based on the added alkyleneimine. Used.

The amphoteric polymer flocculants other than those described above according to the present invention can be obtained by using a cationic monomer and an anionic monomer and polymerizing them by a known method. The kind of the cationic monomer used at that time is not particularly limited, but preferred examples include a monomer selected from alkylaminoethyl methacrylate, alkylaminoethyl acrylate, and the like, or a quaternary ammonium salt thereof. Any of these cationic monomers may be appropriately selected and used so as to obtain the optimum cation strength. Usually, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate or dimethylaminopropyl (meth) acrylamide is used. And their quaternary ammonium salts are preferably used.
In the case of primary to tertiary amino groups, an acid for neutralization is usually required. Examples of the acid used in this case include mineral acids such as hydrochloric acid and nitric acid and carboxylic acids such as acetic acid and formic acid. Basic acids are preferably used. On the other hand, the anionic monomer can be arbitrarily selected from those copolymerizable with the above-mentioned cationic monomer, and particularly preferred are acrylic acid, methacrylic acid and maleic acid.

In producing the above amphoteric polymer flocculant, any other nonionic monomer copolymerizable with the above cationic monomer and anionic monomer can be used as another component. Examples of such nonionic monomers include acrylamide, methacrylamide, N, N-dimethylacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, etc., and acrylonitrile. These nonionic monomers are used mainly for controlling the molecular weight and ion equivalent of the amphoteric polymer flocculant.

Next, when the dehydration method of the present invention is carried out, the cationic polymer constituting the cationic polymer flocculant used as the primary dehydrating agent (primary flocculant) is not limited to the type of cation. That is, a cationic polymer usually used for refining organic sludge can be used, for example, polyalkylaminoethyl methacrylate, polyalkylaminoethyl acrylate, a copolymer of these with polyacrylamide, or 4 Examples thereof include a quaternary ammonium salt, and a modified polyacrylamide cation. Among them, the most common ones are dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl (meth) acrylamide, and quaternary ammonium salts thereof. 1 to
In the case of a tertiary amino group, a neutralizing acid is usually required, but preferred acids used in this case include the above-mentioned monobasic acids. From among these cationic polymers,
Depending on the properties of the organic sludge, the type of dehydrator, and the like, those having an appropriate cation strength and molecular weight are appropriately selected and used.
In addition, any cationic polymer other than those exemplified above can be used as the cationic polymer flocculant as long as it is a cationic polymer capable of forming a coarse floc sludge capable of gravity dewatering.

The above cationic polymer flocculant has a cation equivalent value Cv of 1.0 in consideration of cohesiveness and dehydration.
It is preferably at least meq / g, more preferably at least 2.0 meq / g, and if the Cv value is less than 1.0 meq / g, it will be difficult for the sludge coagulation performance and dewatering performance to be exhibited satisfactorily. The upper limit of the Cv value is not particularly limited, and the higher the Cv value, the higher the cohesiveness and dehydration property. However, in the ordinary case, the limit is inevitably about 12 meq / g in relation to the molecular weight. The preferred molecular weight is 1,000,000 to 8,000,000, more preferably 30
When the molecular weight is less than 1,000,000, it is necessary to increase the amount of cohesion with sludge which is insufficient. On the other hand, when the molecular weight is excessively higher than 8,000,000,
It becomes difficult to disperse uniformly in organic sludge.

Examples of the apparatus for concentrating the coarse floc sludge capable of gravity dehydration generated by adding the above cationic polymer flocculant include a screen apparatus, a vacuum filter, a centrifugal separator and a belt press type dehydrator. As described above, basically, a method of performing solid-liquid separation using the gravity of solid matter in sludge should be adopted. However, it is disadvantageous in terms of cost for a device that mechanically applies pressure, and when the sludge is dewatered by a normal mechanical dehydrator, it becomes difficult to mix the amphoteric polymer flocculant into the generated coarse floc-like sludge. In the present invention, a solid-liquid separation method by gravity is used for the concentration of coarse floc-like sludge, because the excellent effect of improving the dehydration rate provided by using the polymer flocculant cannot be effectively utilized.

As a solid-liquid separation device by gravity, there is a rotary drum screen or a rotary cylindrical granulation dewatering device other than a screen device, and any device may be used. When a belt press type dehydrator is used as the mechanical dehydrator, the dehydrator is usually provided with a solid-liquid separation unit by gravity, so that there is no need to provide a separate solid-liquid separation device. You can enjoy.

The type of the mechanical dehydrator used in the present invention is not particularly limited. For example, a belt press, a filter press, a screw press, a vacuum filter, a centrifugal separator and the like can be used. Since the solid-liquid separation section by gravity is provided in the apparatus as described above, it is recommended as a mechanical dehydrator particularly suitable for implementing the present invention. However, according to the present invention, the dewatering property of sludge is fundamentally improved by a combination of coarse flocking with a cationic polymer flocculant, concentration by gravity dehydration, and addition of an amphoteric polymer flocculant to the concentrated sludge. Therefore, it is of course possible to apply a mechanical dehydrator other than those described above without any problem.

The addition amount of the cationic polymer flocculant and the amphoteric polymer flocculant cannot be determined uniformly because it varies depending on the type of sludge and the composition of each flocculant. It is sufficient if the content is 0.05% by weight or more based on the solid content (TS). In the case of a cationic polymer flocculant, it is not necessary to add more than an appropriate addition amount when the one-package flocculation method is employed, and preferably 0.2 to 2% in view of a balance between an increase in treatment cost and a decrease in water content. It is added in the range of about. On the other hand, the more the added amount of the amphoteric polymer flocculant is, the more effective it is. However, from the balance between the increase in the treatment cost and the decrease in the water content, the added amount is preferably 0.4 to 1%.

It is more effective to use an appropriate amount of an inorganic polyelectrolyte together with the cationic polymer flocculant. As the inorganic polyelectrolyte, calcium salt, magnesium salt, iron salt, aluminum salt, etc., specifically, polyiron sulfate, ferric chloride, polyaluminum chloride, aluminum sulfate (sulfate band), ferrous sulfate, etc. For example, these inorganic polyelectrolytes may be added to the sludge simultaneously with the cationic polymer flocculant, or may be added separately. Preferably, the inorganic polyelectrolyte is added to the cationic polymer flocculant. It is more effective to add it before adding the agent. The addition amount of the inorganic polyelectrolyte is 0.5 to 10% by weight based on the solid content of the sludge in consideration of the effect on the cationic polymer flocculant used in combination, the treatment cost, and the balance of the effect of reducing the water content. It is better to choose from a range.

In the present invention, the sludge to be treated refers to sludge generated when high-BOD wastewater is subjected to biological treatment or the like, and examples thereof include sludge generated in a sewage and human waste treatment plant; Sewage generated from chemical plants, etc.
It refers to sludge of a general concept including surplus sludge and primary sludge generated by activated sludge treatment of wastewater; mixed raw sludge mixed with them; digested sludge generated by anaerobic digestion of wastewater and wastewater; Among them, the effect of the present invention is extremely effectively exerted on hardly dewaterable sludge.

The present invention is constituted as described above. First, when a cationic polymer flocculant is added to the sludge, the sludge forms a coarse floc-like sludge which can be gravity-dewatered by the excellent flocculating action of the flocculant. If the amphoteric polymer flocculant is added after concentrating the coarse floc-like sludge, the surface hydrophilic layer is efficiently hydrophobized by the action of the amphoteric polymer flocculant and further flocculated. Dewatered efficiently.

Although the reason why the present invention improves the dewatering property of sludge is not always clear, the sludge is pretreated with a cationic polymer flocculant and then concentrated to obtain a coarse floc-like sludge. Factors that inhibit aggregation and dehydration, such as organic acidic substances such as electrolytes and colloids, are reduced, and the cation and anion groups in the amphoteric polymer flocculant form hydrophobic salts. The water-soluble salt enhances the water separation and the floc strength to enhance the dewatering and peeling properties of the mechanical dewatered cake, and has an excellent water content lowering effect that cannot be obtained by using a cationic polymer flocculant. It is considered that the performance of the amphoteric polymer flocculant excellent in versatility for sludge was extremely effectively exhibited.

[0031]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention is not limited thereto. Of course, the present invention can be implemented with modifications, and all of them are included in the technical scope of the present invention.

[Synthesis of polyalkyleneimine-based polymer flocculant] The polyalkyleneimine-based polymer flocculant is prepared by using acrylic acid and acrylamide in the presence of an activator ("Nonion OP-80" manufactured by NOF Corporation). A water-in-oil emulsion polymerization was carried out using dimethyl azobisisobutyrate as a polymerization initiator in an aliphatic hydrocarbon ("Exol D-80", manufactured by Exxon Chemical Co., Ltd.) to obtain a carboxyl group-containing polymer (III). Aminoethylation with ethyleneimine and then acidification with nitric acid gave a 20% by weight active ingredient as a water-in-oil emulsion. Table 1 shows the composition, Cv value, Av value, and molecular weight of the synthesized polyalkyleneimine-based polymer flocculant.

Similarly, the cationic polymer flocculant and the other amphoteric polymer flocculant are quaternary ammonium salt of dimethylaminoethyl methacrylate (4DAM) and quaternary ammonium salt of dimethylaminoethyl acrylate (4DAM).
A), dimethylaminoethyl methacrylate (3DA
M), acrylamide (AAm) and acrylic acid (A
It was obtained by polymerization or copolymerization in a known manner using A). The composition and physical properties are also shown in Table 1.

[0034]

[Table 1]

Example 1 Digested sludge A generated from an urban sewage treatment plant (pH: 7.
3, TS: 1.8%, M alkalinity: 3000 ppm)
Was dehydrated using a belt press type dehydrator. The cationic polymer flocculant (C-1) and the polyalkylenimine polymer flocculant (R-1) were both used as 0.2% by weight aqueous solutions. The amount of each of these flocculants was shown as a percentage by weight of the sludge relative to TS.

The cationic polymer flocculant (C-1) was added and mixed in an amount of 0.7% by weight per TS of the digested sludge to form a coarse floc-like sludge. After the solid-liquid separation of the resulting concentrated sludge, a polyalkyleneimine-based polymer coagulant (R-1) was added to and mixed with 0.7% by weight of the resulting TS and mechanically pressed and dewatered by a belt. The water content of the obtained mechanical dewatered cake was 76%, and the removability of the dewatered cake from the belt was good.

Comparative Examples 1a to 1d As a comparative example, when the use of the polyalkyleneimine polymer flocculant was omitted (Comparative Example 1a), a cationic polymer having a high cation strength was used instead of the polyalkyleneimine polymer flocculant. When polyethyleneimine is used as the polymer (Comparative Example 1b), when the cationic polymer flocculant and the polyalkyleneimine polymer flocculant are added to the digested sludge simultaneously (Comparative Example 1c), the polyalkyleneimine polymer flocculant is used. The same experiment was performed for each case where dehydration was performed after aggregation using only (Comparative Example 1d).

The results are as shown in Table 2. According to the present invention, a coarse floc-like sludge was formed by adding a cationic polymer flocculant, followed by gravity dehydration, and then an amphoteric polymer flocculant was added. From the results, it can be seen that the moisture content of the cake of the example in which the mechanical dewatering was performed was lower than that of the comparative examples 1a to 1d, and the sludge treatment capacity was higher.

[0039]

[Table 2]

Example 2 Excess sludge B generated from an urban sewage treatment plant (pH: 6.
7, TS: 1.4%) was subjected to a dehydration treatment using a belt press dehydrator. Both the cationic polymer flocculant (C-2) and the polyalkylenimine polymer flocculant (R-2) were used as 0.2% by weight aqueous solutions. The amount of each of these flocculants was shown as a percentage by weight of the sludge relative to TS.

The cationic polymer flocculant (C-2) was added and mixed in an amount of 0.6% by weight per TS of the above excess sludge to form coarse floc-like sludge. After the solid-liquid separation was performed, 0.8% by weight of a polyalkyleneimine-based polymer flocculant (R-2) was added to and mixed with the obtained concentrated sludge per TS, and the mixture was mechanically pressed and dewatered by a belt. The water content of the obtained mechanical dewatered cake was 78%, and the removability of the dewatered cake from the belt was good.

Comparative Examples 2a to 2d As comparative examples, when the use of the polyalkyleneimine polymer flocculant was omitted (Comparative Example 2a), a cationic polymer having a high cation strength was used instead of the polyalkyleneimine polymer flocculant. When polyethyleneimine is used as the polymer (Comparative Example 2b), when the cationic polymer flocculant and the polyalkyleneimine polymer flocculant are added to excess sludge simultaneously (Comparative Example 2c), the polyalkyleneimine polymer flocculant is used. The same experiment was performed for each of the cases where dehydration was performed after coagulation using only (Comparative Example 2d).

The results are as shown in Table 3. According to the present invention, a coarse floc-like sludge was formed by adding a cationic polymer flocculant, followed by gravity dehydration, and then adding an amphoteric polymer flocculant. It can be seen that the moisture content of the cake of the example in which mechanical dehydration was performed was lower than that of Comparative Examples 2a to 2d, and the sludge treatment capacity was higher.

[0044]

[Table 3]

Examples 3, 3a Digested sludge C generated from an urban sewage treatment plant (pH: 7.
2, TS: 1.7%, M alkalinity: 2900 ppm)
Was dehydrated by a belt press type dehydrator. The cationic polymer flocculant (C-2) and the polyalkylenimine polymer flocculant (R-3) were both used as 0.2% by weight aqueous solutions. The amount of each of these flocculants was shown as a percentage by weight of the sludge relative to TS.

The cationic polymer flocculant (C-2) was added and mixed in an amount of 0.6% by weight per TS of the digested sludge to form a coarse floc-like sludge. After the solid-liquid separation of the resulting concentrated sludge, a polyalkyleneimine-based polymer coagulant (R-3) was added to and mixed with 0.8% by weight of TS in the obtained concentrated sludge, and mechanically pressed and dewatered by a belt. The water content of the obtained mechanical dewatered cake was 78%, and the removability of the dewatered cake from the belt was good (Example 3).

Further, a cationic polymer flocculant (C-2)
Before adding and mixing, the experiment was performed in exactly the same manner as above except that 2% by weight of polyiron sulfate was added as an inorganic polyelectrolyte to the digested sludge per TS of the sludge. The water content of the mechanically dehydrated cake obtained by the running was 74.1%, which was even lower than that of Example 3, and the dewaterability of the dewatered cake from the belt was good (Example 3a).

Comparative Examples 3a to 3d As comparative examples, when the use of the polyalkyleneimine polymer flocculant was omitted (Comparative Example 3a), a cationic polymer having a high cation strength was used instead of the polyalkyleneimine polymer flocculant. When polyethyleneimine is used as the polymer (Comparative Example 3b), when the cationic polymer flocculant and the polyalkyleneimine polymer flocculant are simultaneously added to the digested sludge (Comparative Example 3c), the polyalkyleneimine polymer flocculant is used. The same experiment was performed for each of the cases where dehydration was performed after coagulation using only (Comparative Example 3d).

The results are shown in Table 4. According to the present invention, a coarse floc-like sludge was formed by adding a cationic polymer flocculant, followed by gravity dehydration, and then an amphoteric polymer flocculant was added. Alternatively, the water content of the cake in the example in which mechanical dehydration was performed by further adding an inorganic polyelectrolyte was determined in Comparative Example 3
It turns out that it is low compared with a-3d, and sludge processing capacity is high.

[0050]

[Table 4]

Example 4 Mixed raw sludge C generated from an urban sewage treatment plant (pH: 5.
6, TS: 1.9%) was dehydrated by a belt press dehydrator. Cationic polymer flocculant (C-2)
And an amphoteric polymer flocculant (R-4) synthesized by an ordinary method
Was used as a 0.2% by weight aqueous solution. The amount of each of these flocculants was shown as a percentage by weight of the sludge relative to TS.

The cationic polymer flocculant (C-2) was added and mixed in an amount of 0.5% by weight per TS of the mixed raw sludge to form a coarse floc-like sludge. After solid-liquid separation by gravity, the obtained concentrated sludge was mixed with an amphoteric polymer flocculant (R-4) at a ratio of 0.6 per TS.
By weight, the mixture was mixed and mechanically pressed and dewatered by a belt. The water content of the obtained mechanical dewatered cake was 71%, and the removability of the dewatered cake from the belt was good.

Comparative Examples 4a to 4d As comparative examples, when the use of the amphoteric polymer flocculant was omitted (Comparative Example 4a), polydiallylammonium chloride was used instead of the amphoteric polymer flocculant as a cationic polymer having a high cation strength. Is used (Comparative Example 4b), when the cationic polymer flocculant and the amphoteric polymer flocculant are simultaneously added to the mixed raw sludge (Comparative Example 4c), the amphoteric polymer flocculant (R
The same experiment was performed for each case of dehydration after aggregation using only -4) (Comparative Example 4d).

The results are as shown in Table 5. According to the present invention, a coarse floc-like sludge was formed by adding a cationic polymer flocculant, followed by gravity dehydration, and then an amphoteric polymer flocculant was added. It can be seen that the moisture content of the cake of the example in which the mechanical dewatering was performed was lower than that of Comparative Examples 4a to 4d, and the sludge treatment capacity was higher.

[0055]

[Table 5]

[0056]

The present invention is configured as described above and employs a procedure in which a cationic coagulant is first added to sludge, followed by gravity dehydration, and then a mechanically dehydrated by adding an amphoteric polymer coagulant. By doing so, it is possible to exert an excellent coagulation action on various sludges including hardly dewaterable sludge, thereby significantly increasing the dewatering efficiency of the dewatered cake and contributing to the improvement of the sludge treatment efficiency. be able to.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-223000 (JP, A) JP-B-59-49080 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 11/14 B01D 21/01 107

Claims (4)

(57) [Claims] In a method of dewatering sludge, in which sludge is coagulated with a polymer coagulant and then supplied to a dehydrator to be dewatered, a cationic polymer coagulant is added to the sludge in a pre-step of supplying the sludge to the dewaterer. A sludge dewatering method comprising the steps of: forming a coarse floc shape; concentrating the floc by gravity dehydration; and adding amphoteric polymer flocculant to the concentrated sludge, followed by mechanical dehydration. 2. An amphoteric polymer flocculant having a cation equivalent value (Cv) of 0.8 to 13.0 meq / g and an anion equivalent value (Av) of 0.1 to 6.0 meq / g. The dehydration method according to claim 1, wherein 3. The amphoteric polymer flocculant is a polymer derived from a polymerizable monomer essentially containing a carboxyl group-containing polymerizable monomer, and a part of the carboxyl group in the polymer molecule. Is a polyalkyleneimine-based polymer coagulant present as a monobasic acid addition salt of a primary to tertiary aminoalkyl ester, the dehydration method according to claim 1 or 2. 4. An amphoteric polymer flocculant represented by the following general formula (1):
And a repeating unit represented by the general formula (2) is a polyalkyleneimine polymer flocculant present in a ratio of 0.005 to 7.5 mol per 1 mol of the former.
The dehydration method according to any one of the above. Embedded image