JPH10249399A - Method for dehydrating sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drastically decrease the water content in the two-stage dehydration method for successively adding first and second high molecular flocculants to sludge and mechanically dehydrating the sludge by using a high-mol.wt. cationic or amphoteric high molecular flocculant as the first flocculant and a low-mol.wt. anionic high molecular flocculant as the second flocculant. SOLUTION: A high-mol.wt. cationic or amphoteric high molecular flocculant is used as the primary dehydrating agent used in the two-stage dehydration method, and further an inorg. polyelectrolyte such as a calcium salt, magnesium salt and iron salt is jointly used to decrease the water content more effectively. The primary dehydrating agent should have >=1,500,000 weight average mol.wt. Meanwhile, a low-mol.wt. anionic high molecular flocculant is used as the secondary dehydrating agent, and the weight average mol.wt. is preferably controlled less than that of the primary dehydrating agent. Further, the difference in weight average mol.wt. between the primary and secondary dehydrating agents is preferably controlled to >=500,000.

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 in various industrial wastewaters, sewage treatment, human waste treatment and the like.

[0002]

2. Description of the Related Art Sludge generated from sewage and human waste treatment plants, organic industrial wastewater, and the like 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.

[0003] As a method for more efficiently performing dehydration, Japanese Patent Publication No. 17760/1991 discloses that a cationic polymer is added as a primary dehydrating agent, and then partial dehydration is performed by gravity dehydration. There has also been proposed a method of performing mechanical dehydration after further adding a cationic polymer as a secondary dehydrating agent.

[0004]

Generally, when dewatering sludge using a polymer flocculant, the effect of hydrophobizing (dewatering easily) by acting on the active point of the sludge and the effect between the sludge particles are considered. It is necessary to have an effect of forming coarse flocs by cross-linking 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, it is expected to be a polymer flocculant. In many cases, 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 the secondary dehydrating agent having a high cohesive force is further added to perform a mechanical dehydration. Since it is a cationic polymer that does not limit the physical properties of the agent and the secondary dehydrating agent is a cationic polymer that does not limit the physical properties of the agent, there is naturally a limit in improving the dehydration properties.

[0005] The performance required as a primary dehydrating agent is mainly gravity dehydration, and it is necessary to make the floc correlated with gravity dehydration as strong as possible. As described above, when a cationic polymer that does not limit the physical properties is used as the primary dehydrating agent, sludge having a high organic property, for example, sludge containing a large amount of domestic wastewater or sludge generated from a human waste treatment plant, as in the case of the conventional dehydration method. As described above, a so-called hardly dewaterable sludge cannot provide sufficient floc strength, and due to them, the dewaterability and peelability of a mechanically dewatered cake cannot be sufficiently improved. As a cause, due to the influence of the structure of the flocculant, the weight average molecular weight, etc., the cationic charge is insufficiently neutralized with negative particles of sludge and / or the crosslinking between polymers is insufficient, so that sufficient floc strength is obtained. I do not think that it is.

When a cationic polymer is used as the secondary dewatering agent, the hydrophobization of sludge after gravity dewatering is insufficient, and as a result, the dewatering property and peelability of the mechanical dewatering cake cannot be sufficiently improved.

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. Provide a primary dehydrating agent, a secondary dehydrating agent and a sludge dewatering method capable of further improving the combined dewatering method, further increasing the sludge efficiency of hardly dewaterable sludge, and greatly reducing the water content of the cake after mechanical dewatering. What you want to do.

[0008]

Means for Solving the Problems The sludge dewatering method according to the present invention, which has achieved the above-mentioned objects, is a step of supplying a first polymer flocculant to sludge in a pre-process of supplying the sludge to a dewatering machine. In a two-stage dehydration method in which a coarse floc is formed and then a second polymer flocculant is added and mechanically dewatered, the first polymer flocculant is a high molecular weight cationic or amphoteric polymer flocculant, and the second polymer flocculant is The coagulant is a low molecular weight anionic polymer coagulant. At this time, the presence or absence of solid-liquid separation after the addition of the first polymer flocculant does not matter, but the solid-liquid separation is preferably performed.

The first polymer flocculant used at this time has a weight average molecular weight of 1.5 million or more, a cation equivalent value (Cv) of 0 to 13.0 meq / g, and an anion equivalent value (Av) of 0 to 6 A 0.0 meq / g cationic or amphoteric polymeric flocculant is preferred. Further, an inorganic polyelectrolyte may be used in combination.

The second polymer flocculant is preferably an anionic polymer flocculant having a weight average molecular weight less than the weight average molecular weight of the first polymer flocculant.

It is recommended that the difference in molecular weight between the first polymer flocculant and the second polymer flocculant is 500,000 or more, and it is particularly preferable that the difference in molecular weight is 700,000 to 1.5 million.

It is preferable that the first polymer flocculant and the second polymer flocculant are used in combination at a weight ratio of 90:10 to 50:50, particularly at a ratio of 80:20 to 70:30. It is highly recommended that

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in the dehydration method according to the present invention, a polymer flocculant is added to sludge to cause coagulation, and the sludge is subjected to a dehydrator to remove water. In the pre-dehydration step, a sludge is added with a cationic or amphoteric polymer flocculant as a primary dehydrating agent (also referred to as a primary flocculant) to form a coarse floc, and then a secondary dehydrating agent (secondary flocculant) The mechanical dehydration is performed after the addition of an anionic polymer flocculant. At this time, the presence or absence of solid-liquid separation after the addition of the first polymer flocculant does not matter, but the solid-liquid separation is preferably performed.

As the primary dehydrating agent of the present invention, a high molecular weight cationic or amphoteric polymer flocculant is used, and the effect of lowering the water content is exhibited even when used together with an inorganic polyelectrolyte. Is done. The primary dehydrating agent must have a weight average molecular weight of 1.5 million or more, and have a cation equivalent value (Cv) of 0 to 13.0 meq / g and an anion equivalent value (Av) of 0 to 6.0 meq / g. When the weight average molecular weight is less than 1.5 million, the amount added is excessively large or the water content is significantly increased due to insufficient cohesion due to insufficient molecular weight. As the inorganic polyelectrolyte, calcium salt, magnesium salt,
Iron salt, aluminum salt, specifically, for example, sulfate band, polyaluminum chloride, ferric chloride, ferrous sulfate,
Examples thereof include polyiron sulfate. The type of the primary dehydrating agent conforms to the above physical properties, but depending on the properties of the sludge, the type of the dehydrator, etc., appropriately select appropriate ones of the cation strength, molecular weight, and viscosity within the range of the above physical properties. used.

As the secondary dehydrating agent, a low molecular weight anionic polymer flocculant is used, and the weight average molecular weight is preferably less than the weight average molecular weight of the primary dehydrating agent. It is recommended that the difference in molecular weight between the primary dehydrating agent and the secondary dehydrating agent be 500,000 or more, which is extremely preferable.

There is no particular limitation on the polymerization method of the primary dehydrating agent and the secondary dehydrating agent, and an aqueous solution polymerization method or a water-in-oil emulsion polymerization method can be employed. A general radical polymerization catalyst may be used. 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 as to be the target molecular weight of the obtained polymer flocculant. As a preferable polymerization initiator used in the case of water-in-oil emulsion polymerization, azobisisopropane is used. Examples include butyronitrile and dimethyl azobisbutyrate.

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

The nonionic monomer (II) includes:
Any nonionic monomer (II) copolymerizable with the anionic monomer (I) can be used, and is preferably, for example, (meth) acrylamide, N, N-dimethylacrylamide, or the like. Ethyl (meth) acrylate, hydroxypropyl (meth) acrylate and the like, or acrylonitrile and the like. These nonionic monomers (II) are used mainly for the purpose of controlling the molecular weight and ion equivalent of the polymer flocculant, and are usually 50 mol% or less in the polymer. It is preferable to suppress.

As the cationic monomer (III), any cationic monomer (III) copolymerizable with the anionic monomer (I) can be used. The type of is not particularly limited, but preferred are monomers selected from alkylaminoethyl methacrylate, alkylaminoethyl acrylate and the like, and quaternary salts thereof. Among these cationic monomers, It may be appropriately selected and used so as to obtain the optimum cation strength and molecular weight. Usually, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl (meth)
Acrylamide 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.

In general, the primary dehydrating agent contains the above (III) as an essential component, and the secondary dehydrating agent contains the above (I) as an essential component. The primary dehydrating agent and the secondary dehydrating agent can be obtained by adjusting the molecular weight to an appropriate value depending on the amount of the polymerization initiator and the like.
(II) may be introduced, and the secondary dehydrating agent may be introduced (II).

The presence or absence of gravity dehydration after coagulation using the primary dehydrating agent is not limited, but gravity dehydration is more preferred. In the case of gravity dewatering, as a device for concentrating the coarse floc sludge capable of gravity dewatering to be generated, for example, a solid material in the sludge is basically used, such as a screen device, a vacuum filter, a centrifugal separator or a belt press type dehydrator. A method of performing solid-liquid separation by utilizing gravity should be adopted. However, equipment that mechanically applies pressure is disadvantageous in terms of cost, and when sludge is dewatered with a normal mechanical dehydrator, it becomes difficult to mix the polymer flocculant into the generated coarse floc-like sludge, resulting in secondary dewatering. In the present invention, a solid-liquid separation method by gravity is used for the concentration of the coarse floc, because the excellent effect of increasing the water content brought about by using the flocculant as the agent 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 in addition to a screen device, and any device may be used. In the case where 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 dehydration of sludge is fundamentally achieved by a combination of coarse flocking with a high molecular weight type polymer flocculant and concentration by gravity dehydration, and addition of a low molecular weight type polymer flocculant to the concentrated sludge. Since it is improved, it is of course possible to apply a mechanical dehydrator other than the above without any problem.

The amounts of the primary dehydrating agent and the secondary dehydrating agent vary depending on the type of sludge and the composition of each flocculant, and therefore cannot be determined uniformly. 0.05% by weight or more is sufficient. In the case of the primary dehydrating agent, it is not necessary to add more than an appropriate amount when the one-liquid coagulation method is employed, and it is preferable to add 0.1% from the viewpoint of an increase in treatment cost and a decrease in water content.
It is added in the range of about 2 to 2% by weight. On the other hand, the more the added amount of the secondary dehydrating agent 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% by weight.

It is more effective to use an appropriate amount of an inorganic polyelectrolyte together with a cationic or amphoteric polymer flocculant as a primary dehydrating agent. As the inorganic polyelectrolyte, calcium salt, magnesium salt, iron salt, aluminum salt, etc.
Specifically, a sulfate band, polyaluminum chloride, ferric chloride, ferrous sulfate, polyiron sulfate, etc. are exemplified.These inorganic polyelectrolytes are added to sludge simultaneously with the amphoteric polymer flocculant. These may be added separately or separately, but it is more effective to add the inorganic polyelectrolyte prior to the addition of the amphoteric polymer flocculant. The addition amount of the inorganic polyelectrolyte is in the range of 0.5 to 10% by weight based on the solid content of the sludge in consideration of the balance between the effect on the amphoteric polymer coagulant used in combination, the treatment cost, and the effect of reducing the water content. It is better to choose from.

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 excess 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 primary dehydrating agent (high molecular weight type polymer flocculant) is added to sludge, the sludge is coarsely dewatered by gravity due to the excellent flocculating action of the flocculant. When floc-like sludge is formed, the coarse floc-like sludge is concentrated, and then a secondary dehydrating agent (a low molecular weight type polymer flocculant) is added. And further agglomerates, and is dehydrated very efficiently by subsequent mechanical dehydration.

Although the reason why the present invention improves the dewatering property of sludge is not necessarily clear, the pretreatment of the sludge with a primary dehydrating agent followed by concentration allows the electrolyte in the coarse floc-like sludge to be concentrated. Factors that inhibit coagulation and dehydration such as organic acidic substances such as colloids and colloids are reduced, and the cross-linking between the functional groups of the secondary dehydrating agent and the non-adsorbed cationic groups enhances the floc strength and reduces the mechanical dehydration cake. It is thought that the effect of enhancing dehydration and peelability was exhibited.

[0029]

EXAMPLES Hereinafter, the present invention will be described more specifically 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 Example of Polymer Coagulant] Quaternized dimethylaminoethyl methacrylate (4DAM), quaternized dimethylaminoethyl acrylate (4DAA), dimethylaminoethyl methacrylate (3DAM), dimethylaminoethyl acrylate (3DAA), It was obtained by polymerizing or copolymerizing acrylamide (AAm) and acrylic acid (AA) by a known method. Also, polyamidine was obtained by copolymerizing and hydrolyzing poly-N-vinylformamide (PNVF) and acrylonitrile (AN) by a known method. Table 1 shows the composition, Cv value, Av value, and molecular weight of the obtained polymer flocculant.

[0031]

[Table 1]

In Table 1, AAm; Acrylamide, AA; Acrylic acid 4DAM; Dimethylaminoethyl methacrylate quaternary 3DAM; Dimethylaminoethyl methacrylate tertiary salt The compositions are the weight percentages of the monomers, and the cation equivalent values are the values at pH3. is there.

Example 1 Digested sludge A generated from an urban sewage treatment plant (pH: 7.
3, TS: 2.2%, M-alkalinity: 2700 pp
m) was dewatered using a belt press dehydrator.

The cationic polymer flocculant (C-1) and the anionic polymer flocculant (A-2) were 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-1) was added and mixed in an amount of 0.9% by weight per TS of the digested sludge to form a coarse floc-like sludge. After the solid-liquid separation, anionic polymer coagulant (A-2) was added to the obtained concentrated sludge in an amount of 0.1% per TS.
7% by weight was added and mixed, and mechanically pressed and dewatered by a belt. The obtained mechanical dewatered cake was 75.3%, and the removability of the dewatered cake from the belt was good.

COMPARATIVE EXAMPLE 1 As a comparative example, a similar experiment was conducted when the difference in molecular weight between the first polymer flocculant (C-1) and the second polymer flocculant (A-1) was less than 500,000. Was.

The results are as shown in Table 2. According to the present invention, the cationic polymer flocculant is added to form a coarse floc-like sludge and then gravity dewatered, and then the cake water content of the example in which the anionic polymer flocculant is added and then mechanically dewatered. Is lower than Comparative Example 1 and the sludge treatment capacity is higher.

[0038]

[Table 2]

Example 2 Excess sludge B generated from an urban sewage treatment plant (pH: 6.
4, TS: 1.9%) was dehydrated using a belt press dehydrator.

The amphoteric polymer flocculant (R-1) and the anionic polymer flocculant (A-2) 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 amphoteric polymer flocculant (R-1) was added and mixed in an amount of 0.7% by weight per TS of the above-mentioned digested sludge to form a coarse floc-like sludge. After the solid-liquid separation, the obtained concentrated sludge was mixed with 0.7% by weight of anionic polymer coagulant (A-2) per TS, and the mixture was mechanically pressed and dewatered by a belt. The obtained mechanical dewatered cake was 77.0%, and the removability of the dewatered cake from the belt was good.

COMPARATIVE EXAMPLE 2 As a comparative example, a similar experiment was conducted when the difference in molecular weight between the first polymer flocculant (R-1) and the second polymer flocculant (A-1) was less than 500,000. Was.

The results are as shown in Table 2. According to the present invention, the water content of the cake of the example in which the amphoteric polymer flocculant is added to form a coarse floc-like sludge and then gravity dewatered, and then the mechanical dehydration is performed after the anionic polymer flocculant is added. It can be seen that, compared to Comparative Example 2, the sludge treatment capacity was high.

[0044]

[Table 3]

[0045]

The present invention is constituted as described above. First, a cationic or amphoteric polymer flocculant is added to sludge, and after mixing, gravity dehydration is performed. By adopting the dewatering procedure, 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 sludge treatment efficiency. Can also be improved.

Claims (4)

[Claims] 1. A two-stage dewatering method in which a first polymer flocculant is added to sludge and then a second polymer flocculant is added and mechanically dewatered, wherein a high molecular weight cationic or amphoteric polymer flocculant is A low molecular weight anionic polymer coagulant is used in combination, and the weight average molecular weight of the cationic or amphoteric polymer coagulant is 1
A method for dewatering sludge, wherein the weight average molecular weight of the anionic polymer coagulant is 500,000 or more and less than the weight average molecular weight of the cationic or amphoteric polymer coagulant. 2. A two-stage dewatering method in which a first polymer flocculant is added to sludge and then a second polymer flocculant is added and mechanically dewatered, wherein a high molecular weight cationic or amphoteric polymer flocculant is The dehydration method according to claim 1, wherein a low molecular weight type anionic polymer flocculant is used in combination, and a difference in weight average molecular weight between the high molecular weight type polymer flocculant and the low molecular weight type polymer flocculant is 500,000 or more. 3. A two-stage dehydration method in which a first polymer flocculant is added to sludge, gravity dewatered, then a second polymer flocculant is added, and mechanical dehydration is performed, wherein the weight average molecular weight is used as the first polymer flocculant. The use of a high molecular weight cationic or amphoteric polymer coagulant of 1.5 million or more, and the use of a low molecular weight anionic polymer coagulant having a weight average molecular weight less than that of the first polymer coagulant as the second polymer coagulant. Characteristic sludge dewatering method. 4. The method according to claim 3, wherein the difference in weight average molecular weight between the first polymer flocculant and the second polymer flocculant is 500,000 or more.