JP3460469B2 - Polymer dehydrating agent and wastewater treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a suitable polymeric dehydrating agent used in waste water treatment, also such a polymer removal
The present invention relates to a wastewater treatment method using a liquid medication .

[0002]

2. Description of the Related Art Currently, there is great interest worldwide in environmental problems, and securing water resources is one of the most important issues. In this situation,
From the viewpoint of preventing water and environmental pollution, the Water Pollution Control Law, etc.
The legal restrictions on wastewater discharged from factories and households are becoming more stringent.

As a measure against waste water, cleaning treatment of waste water with various polymer coagulants is performed. At present, the commonly used polymer flocculants include nonionic / anionic flocculants for treating industrial wastewater and cationic flocculants for treating sewage / human waste. These aggregating agents are used properly depending on the application, but in any case, they are required to have excellent clarification, concentration and dehydration rate of the suspension. Especially, regarding the clarification ability of the suspension, the filtrate after coagulation treatment is discharged as it is to general rivers, seas, lakes and marshes, and thus the demand level tends to be particularly severe from the viewpoint of environmental protection.

Under these circumstances, attempts have been made to reduce the turbidity in the filtrate by combining two types of polymer coagulants or by using a metal compound and a polymer coagulant together. There is.

[0005]

By the way, as the above-described polymer flocculant, there is one using a styrene polymer. It has been difficult for the polymer flocculant using such a styrene-based polymer to sufficiently flocculate the suspended substance in the suspension. Therefore, this polymer flocculant has a problem that the clarification ability of the suspension is insufficient.

Further, in such a polymer flocculant, a large amount of water is contained in the cake produced by aggregating the suspended substances in the suspension. As described above, the conventional polymer flocculant has a problem that a cake having a high water content is formed and the amount of waste increases. Further, it has been troublesome to perform post-treatment such as incineration treatment on a cake having a high water content.

On the other hand, such a styrenic polymer is
For example, even if it is used in combination with another polymer flocculant, the above-mentioned characteristics are not changed.

That is, the conventional polymer flocculants have insufficient ability as additives for treating suspensions, and further excellent techniques are desired.

Therefore, in the present invention, the clarification ability of the suspension is high, and the water content of the cake formed is reduced.
An object is to provide a polymeric dehydrating agent . It is another object of the present invention to provide a wastewater treatment method having a high effect of clarifying a suspension using such a polymer dehydrating agent .

[0010]

The present inventor has conducted extensive studies as to achieve the above-mentioned object, and as a result, by using a styrene-based polymer having a relatively large molecular weight, the clarification effect of the suspension can be improved. It has been found that it is possible to increase and reduce the water content of the cake produced.

That is, the polymer dehydrating agent according to the present invention is mainly composed of a sulfonated styrene polymer, and the weight average molecular weight of the styrene polymer is 150,000 to 600,000.
It is characterized in that the suspended matter is aggregated and the water content of the aggregate is reduced.

Further, the wastewater treatment method according to the present invention comprises adding to the wastewater a macromolecular dehydrating agent mainly composed of a sulfonated styrene polymer and having a weight molecular weight of 150,000 to 600,000. It is characterized in that the suspended matter is aggregated from the wastewater and the water content of the aggregate is reduced.

Here, in the wastewater treatment method according to the present invention, even when the above-mentioned polymer dehydrating agent and the nonionic and / or anionic acrylamide polymer are used in combination, the above-mentioned polymer dehydrating agent and cationic polymer are used. You may use together with.
Also, these may be used in combination.

[0014] High frequency according to the present invention configured as described above
As a coagulant, the child dehydration agent enhances the clarification effect of the suspension.
Decreases the water content of the cake produced as it works
It is a dehydrating agent, and the molecular weight of the styrene-based polymer is 15 to
By setting it to 600,000, the clarification effect of the suspension can be enhanced and the water content of the cake to be produced can be reduced. When the molecular weight of the styrene-based polymer is 150,000 or less, not only the aggregation effect on the suspended substance in the suspension is lowered, but also the suspended substance is dispersed. On the other hand, when the molecular weight of the styrene-based polymer is 600,000 or more, the suspended substance aggregates as coarse flocs, a good clarification effect cannot be obtained, and the water content of the cake produced becomes high. Will end up.

The styrene-based polymer may be not only a virgin material but also a waste material. Therefore, the present invention is very effective as a method for reusing polystyrene resin products produced in large quantities as general-purpose resins.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments to which the present invention is applied will be described in detail below.

The present invention is mainly composed of a sulfonated styrenic polymer and has a molecular weight of 150,000 to 600,000.
Mainly composed of high molecular weight dehydrating agent and sulfonated styrenic polymer, and its molecular weight is high from 150,000 to 600,000.
It is a wastewater treatment method of treating wastewater using a molecular dehydrating agent .

Examples of the styrenic polymer used in this polymer dehydrating agent include styrene-butadiene and styrene-
Acrylonitrile, styrene-butadiene-acrylonitrile, styrene- (meth) acrylic acid, styrene-
(Meth) acrylic acid ester (aliphatic hydrocarbon having 1 to 4 carbon atoms), styrene-acrylonitrile- (meth) acrylic acid ester (aliphatic hydrocarbon having 1 to 4 carbon atoms), styrene-butadiene- (meth ) Acrylic ester (aliphatic hydrocarbon having 1 to 4 carbon atoms), styrene-
Maleic anhydride, styrene-itaconic anhydride, etc. may be mentioned. Among these, preferably, styrene-butadiene, styrene-acrylonitrile, styrene-butadiene-acrylonitrile, styrene-maleic anhydride, styrene-acrylonitrile- (meth) acrylic acid ester (aliphatic hydrocarbon having 1 to 4 carbon atoms), Styrene-butadiene- (meth) acrylic acid ester (C1-C1
4 aliphatic hydrocarbons). More preferably, styrene-butadiene, styrene-acrylonitrile, styrene-butadiene-acrylonitrile, and styrene-maleic anhydride are mentioned.

The above-mentioned styrenic polymer is a polymer depolymerized
It may be a new product (virgin material) created to produce a liquid formulation , or may be waste (waste material) from a factory, a store, a household, or the like. You may use together. From the viewpoint of preserving the global environment by reusing polystyrene resin products produced in large quantities as general-purpose resins, it is preferable to use scrap materials rather than virgin materials as styrene polymers.

When the waste material is used, other polymer may be contained in addition to the above-mentioned styrene polymer. Examples of other polymers include polyphenylene ether, polycarbonate, polyphenylene sulfide, and polyethylene terephthalate. In addition, polyphenylene ether and polycarbonate are preferable. At this time, other polymers
It is preferably about 60% by weight or less.

The styrenic polymer as described above is sulfonated in a solvent containing a sulfonating agent. After that, the sulfonated styrene-based polymer becomes a polymer dehydrating agent by neutralizing the sulfone group and then distilling off the solvent and the sulfonating agent.

Examples of the sulfonating agent include anhydrous sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, concentrated sulfuric acid and the like. These sulfonating agents may be used alone or in combination of two or more. The addition amount of the sulfonating agent is 1 mol of an aromatic ring contained in the styrene-based polymer (benzene ring in the side chain of styrene-based resin, polyphenylene ether, benzene ring in the main chain of polycarbonate-based resin) It is preferable to use 0.5 to 2.0 mol, and more preferably 0.7 to 1.
Used in the range of 5 mol. If the addition amount of the sulfonating agent is small, the styrene-based polymer cannot be sufficiently sulfonated. Therefore, in this case, the polymer does not exhibit the function as a polyelectrolyte. On the other hand, if the sulfonating agent is added in a large amount, it may cause gelation during the sulfonation reaction,
A large amount of by-products such as salts are generated in the reaction system.
Therefore, in this case, the polymer contains a large amount of impurities, resulting in low purity.

For the sulfonation of the styrene polymer, the above-mentioned sulfonating agent and Lewis base may be used in combination. Examples of the Lewis base include alkyl phosphates (triethyl phosphate, trimethyl phosphate), dioxane, acetic anhydride, ethyl acetate, ethyl palmitate, diethyl ether, thioxane and the like. The amount of these Lewis bases added is 0 with respect to 1 mol of an aromatic ring unit (a benzene ring in a side chain or a polyphenylene ether in a styrene resin or a benzene ring in a main chain in a polycarbonate resin) contained in a styrene-based polymer. 0.01-2.0 mol, preferably 0.02-1.0
It is a mole. If the Lewis base is added in a small amount, a gelled product is likely to be generated during the sulfonation reaction. On the other hand, when the addition amount is large, the sulfonation reaction itself does not easily proceed, the yield of the polymer decreases, and the cost increases.

On the other hand, the solvent used in the sulfonation of the above-mentioned styrene-based polymer has 1 to 2 carbon atoms.
Aliphatic halogenated hydrocarbons (preferably 1,2-dichloroethane, chloroform, dichloromethane, 1,1
-Dichloroethane), aliphatic cyclic hydrocarbons (preferably cyclohexane, methylcyclohexane, cyclopentane) and the like. These solvents may be used alone or as a mixture of two or more. In mixing the solvents, the mixing ratio is not particularly limited.

The above-mentioned solvent may be used by mixing with other solvent. At this time, other solvents that can be mixed and used include paraffin hydrocarbons (having 1 to 7 carbon atoms), acetonitrile, carbon disulfide, tetrahydrofuran, tetrahydropyran, 1,2-dimethoxyethane, acetone, Examples include methyl ethyl ketone and thiophene. Of these, preferred as other solvents are paraffin hydrocarbons (having 1 to 7 carbon atoms), tetrahydrofuran, acetone, and acetonitrile. The mixing ratio with these other solvents is not particularly limited, but is preferably in the range of 1 to 100% by volume. In addition, the above-mentioned solvent may be recovered by a method such as extraction or distillation after the completion of the sulfonation reaction of the styrene-based polymer and used again in the sulfonation reaction.

The polymeric dehydrating agent is obtained by mixing the above-mentioned styrene polymer, sulfonating agent and solvent in a predetermined amount to proceed the sulfonation reaction.

In this sulfonation reaction, the concentration of the styrene polymer is preferably 0.1 to 30% by weight, more preferably 0.5 to 20% by weight.
If the concentration of the styrene-based polymer is lower than the above range, it becomes difficult to introduce the sulfone group. On the other hand, when the concentration is lower than the above range, a gelled substance is likely to be generated during the sulfonation reaction, or a large amount of unreacted substance is generated.

In this sulfonation reaction, the reaction temperature is 0 to 100 ° C, preferably 15 to 80 ° C.
In the sulfonation reaction, if the reaction temperature is lower than this range, the sulfonation reaction becomes difficult to occur, and the yield of the polymer decreases.

Further, in this sulfonation reaction, the reaction time (excluding the dropping time of the sulfonating agent) is 10 minutes to.
It is set to 10 hours, preferably 30 minutes to 5 hours.

As described above, the solution in which the sulfonation reaction has been completed is subjected to neutralization of the sulfone group with the neutralizing agent and then the solvent is distilled off. This produces the desired polymeric dehydrating agent.

At this time, as the neutralizing agent, basic compounds such as oxides, hydroxides, carbonates of alkali metals (sodium, lithium, potassium, etc.) and alkaline earth metals (magnesium, calcium, etc.), Compounds such as acetate, sulfate and phosphate, ammonia and various compounds (1 to 3
Primary alkyl) amine compounds and the like. Then, this neutralizing agent is gradually added to the reaction system in a solid state or an aqueous solution state to neutralize the sulfone group introduced into the styrene polymer. As a method for distilling off the solvent, a method such as liquid separation or distillation is used.

According to the present invention obtained as described aboveHigh
Molecular dehydrating agentThen, its molecular weight (Mw) is 150,000-600,000
Needs to be done. The molecular weight (Mw) is 2
It is more preferably from 0 to 500,000.Polymeric dehydrating agent
Is a sulfonated styrenic polymer having a molecular weight of 1
When it is 50,000 or less, the coagulation effect on the suspended substance in the suspension is
It not only reduces the fruit, but also disperses suspended substances.
Become. On the other hand, the content of sulfonated styrenic polymer
If the molecular weight is more than 600,000, the flocculated substance is coarse.
As a result, it does not obtain a good clarification effect,
In addition, the water content of the cake produced is also high.
I will

On the other hand, in this polymer dehydrating agent , the styrene group contains 40 mol% or more, preferably 50 mol% or more, of a sulfone group. When the sulfonic group in the styrenic polymer is less than 40 mol%, the polymer flocculant has a reduced solubility in water, and the flocculation effect on suspended substances in the suspension is significantly reduced. .

As described above, in order to introduce a desired amount of sulfone groups in this polymeric dehydrating agent, 60 mol% or more of styrene unit is added to the styrene polymer.
It is preferable that the content is 80 mol% or more.
60 mol% of styrene unit in styrene-based polymer
When the amount is less, it is difficult to obtain the polymer dehydrating agent having the above-mentioned amount of the sulfone group by the sulfonation reaction.

Polymer according to the present invention manufactured as described above
As the dehydrating agent , a nonionic and / or anionic acrylamide polymer can be used in combination as another aggregating agent when performing wastewater treatment. Similarly, it is possible to use a cationic polymer in combination as another aggregating agent.

Examples of nonionic polymer flocculants, anionic polymer flocculants, and cationic polymer flocculants are given below.

<Nonionic polymer flocculant> Polyacrylamide, polymethacrylamide. Preferably polyacrylamide.

<Anionic Polymer Flocculant> As the (meth) acrylic acid-based resin, a partial hydrolyzate of polyacrylamide or polymethacrylamide, a copolymer of acrylic acid or methacrylic acid with acrylamide or methacrylamide, and a product thereof A terpolymer of salts, acrylic acid or methacrylic acid, acrylamide or methacrylamide, and 2-acrylamide-methylpropanesulfonic acid or vinylsulfonic acid or vinylmethylsulfonic acid, and salts thereof. Preferably, a partial hydrolyzate of polyacrylamide, a copolymer of acrylic acid and acrylamide and salts thereof, a terpolymer of acrylic acid, acrylamide and 2-acrylamido-methylpropanesulfonic acid and salts thereof.

<Cationic polymer flocculant> quaternized product of dialkylaminoalkyl (meth) acrylate (as a quaternizing agent, methyl chloride, benzyl chloride, etc.) or acid salt (as an acid salt, a hydrochloride, Inorganic acid salts such as sulfates and organic acid salts such as acetates), or polymers or copolymers of these with (meth) acrylamide. For example, a methyl chloride quaternary product of dimethylaminoethyl acrylate, or a polymer or copolymer of this and acrylamide.

A quaternary compound or acid salt of dialkylaminoalkyl (meth) acrylamide, or a polymer or copolymer of these and (meth) acrylamide. For example,
A copolymer of dimethylaminopropyl acrylamide quaternary methyl chloride and acrylamide.

A cationized modification of polyacrylamide. For example, Mannich modified products of polyacrylamide and Hoffmann degradation products.

An epihalohydrin-amine condensate. For example, a polycondensate of epihalohydrin and an alkylenediamine having 2 to 8 carbon atoms.

Polydimethyldiallylammonium chloride.

Dicyandiamide condensate. For example, a formalin condensate of dicyandiamide and ammonium chloride.

-Polyethyleneimine.

The various polymer flocculants as described above may be a mixture of a plurality of the same ionic species, or different ionic properties such as anionic-nonionic and cationic-nonionic. You may mix and use several kinds.

Further, the polymeric dehydrating agent may be used by premixing with the above-mentioned other aggregating agent, or may be sequentially added and used. In particular, when a cationic polymer flocculant is used in combination, it is preferable to add them sequentially.

The polymeric dehydrating agent according to the present invention may be used in combination with various conventionally known inorganic coagulants and inorganic coagulants.

[0049]

EXAMPLES Here, the wastewater treatment was actually carried out using the polymer dehydrating agent according to the present invention, and the ability thereof was evaluated.

[0050] As the polymer dehydrating agent according to Example 1 Example 1, as a sulfonated styrene polymer, sodium polystyrene sulfonate (manufactured by Scientific Polymer Co.) was used. In this Example 1, the molecular weight of sodium polystyrene sulfonate is set to 175,000.

[0051] As the polymer dehydrating agent according to Example 2 Example 2, molecular weight 50.
Sodium polystyrene sulfonate (manufactured by Scientific Polymer Co., Ltd.) which is considered to be 0,000 was used.

[0052] polymeric dehydrating agent according to Example 3 Example 3 was prepared as follows.

First, high-impact polystyrene (used VHS cassette tape housing material, Mw = 1
77,000) was dissolved in 1,2-dichloroethane, and sulfuric acid anhydride was added dropwise at 20 to 25 ° C to carry out a sulfonation reaction. Then, after adding an aqueous solution of sodium hydroxide in an equimolar amount to anhydrous sulfuric acid to neutralize the sulfone group,
By distilling off the solvent by heating distillation, an aqueous solution of the polymer dehydrating agent according to Example 3 was obtained.

In the polymer dehydrating agent according to Example 3, the molecular weight of sodium polystyrene sulfonate is set to 350,000.

[0055] polymeric dehydrating agent according to Example 4 Example 4 is used for TV housing materials as high-impact polystyrene (Mw = 2
It was obtained in the same manner as in Example 3 except that 24,000) was used. In the polymer dehydrating agent according to Example 4, the molecular weight of sodium polystyrene sulfonate is set to 450,000.

[0056] polymeric dehydrating agent according to Example 5 Example 5, a polymer dehydration of Example 3
Agent to a weight ratio of polyacrylamide partial hydrolyzate is obtained as that added to a 1-to-1 as the anionic polymer flocculant.

Example 6 In Example 6, the polymeric dehydrating agent was a cationic polymeric flocculant, methyl chloride quaternary product of dimethylaminoethyl acrylate, and the polymeric dehydrating agent of Example 3,
Was mixed with the suspension for aggregation evaluation by the method described below.

Example 7 In Example 7, the polymeric dehydrating agent was a cationized polymeric flocculant quaternary methyl chloride of dimethylaminoethyl acrylate, and the polymeric dehydrating agent of Example 5
Was mixed with the suspension for aggregation evaluation by the method described below.

[0059] polymeric dehydrating agent according to Comparative Example 1 Comparative Example 1 used a sodium polystyrene sulfonate having a molecular weight are 70,000 (manufactured by Scientific Polymer Co.).

[0060] polymeric dehydrating agent according to Comparative Example 2 Comparative Example 2, using polystyrene sulfonate soda molecular weight is 1.2 million (manufactured by Scientific Polymer Co.).

[0061] In Comparative Example 3 Comparative Example 3, polymeric dehydrating agent, and methyl chloride quaternary product of dimethylaminoethyl acrylate as a cationic polymer flocculant, a polymeric dehydrating agent Comparative Example 1,
Was mixed with the suspension for aggregation evaluation by the method described below.

Comparative Example 4 In Example 4, the polymeric dehydrating agent was a dimethylaminoethyl acrylate quaternary methyl chloride as a cationic polymeric flocculant, and a polymeric dehydrating agent of Comparative Example 2.
Was mixed with the suspension for aggregation evaluation by the method described below.

With respect to Examples 1 to 7 and Comparative Examples 1 to 4 as described above, the following effects were examined in order to examine the wastewater treatment capacity.

Examination of Effects A suspension for evaluating aggregation was prepared by adding 500 ppm of aluminum sulfate to wastewater (pH 4.8, suspension substance (SS) concentration 1.2% by weight) of an electronic component factory. And 100 ml of this suspension for aggregation evaluation was put into a 200 ml graduated cylinder with a stopper, and each sample of Examples 1-5 and Comparative Examples 1-2 was put into it, and the polymer concentration in the suspension for aggregation evaluation was measured. An amount of 10.0 ppm was added. Immediately thereafter, the graduated cylinder was stirred up and down 10 times and then allowed to stand, and the sedimentation rate of suspended particles, the turbidity of the filtrate after aggregation,
The water content of the cake after dehydration was measured. The results of this measurement are shown in Table 1.

[0065]

[Table 1]

[0066] From Table 1, samples Examples 1 to 5 each have basic characteristics as the polymer coagulant, in particular, for the effect of reducing the turbidity of the filtrate after aggregation, a polymer
It is significantly superior to Comparative Example 2 in which the molecular weight of the dehydrating agent is outside the range of 150,000 to 600,000. Thus, by using a polymer dehydrating agent mainly composed of a sulfonated styrene-based polymer and having a molecular weight of 150,000 to 600,000, the wastewater treatment ability, particularly the clarification ability of the suspension is significantly improved. You can see that you can.

Further, from Table 1, the samples of Examples 1 to 5 also have the effect of reducing the water content of the cake after dehydration in Comparative Examples in which the molecular weight of the polymer dehydrating agent is outside the range of 150,000 to 600,000. 1 and Comparative Example 2 are superior. From this, a polymer depolymerized mainly composed of a sulfonated styrene-based polymer and having a molecular weight of 150,000 to 600,000.
It is understood that the use of the liquid medicine can significantly improve the wastewater treatment capacity, particularly the recovery rate of water that can be reused from the suspension.

Further, it was found that the polymer dehydrating agent can be used in combination with the polyacrylamide partial hydrolyzate, and the polystyrene sulfonate soda can also be the one produced from the used polystyrene resin.

Next, mixed sludge (pH 6.
6. Suspended substance (SS) concentration 2.8% by weight) was prepared as a suspension for aggregation evaluation. Then, Example 6, Example 7,
Each sample of Comparative Example 3 and Comparative Example 4 was added to the suspension for aggregation evaluation being stirred by a jar tester. At this time, as an addition method, first, 0.6% by weight per SS of dimethylaminoethyl acrylate quaternary chloride of dimethylaminoethyl acrylate, which is common to each sample, is added to the suspension for aggregation evaluation. After that, to each suspension for aggregation evaluation, sodium polystyrene sulfonate unique to each of Example 6, Example 7, Comparative Example 3 and Comparative Example 4 was added per SS of 0.
Added 15% by weight. Then, after stirring, the mixture was allowed to stand and the sedimentation rate of suspended particles, the turbidity of the filtrate after aggregation, and the water content of the cake after dehydration were measured. The results are shown in Table 2.

[0070]

[Table 2]

From Table 2, as in the case of the wastewater of the electronic parts factory described above, by using a polymer dehydrating agent mainly composed of sulfonated styrene-based polymer and having a molecular weight of 150,000 to 600,000, The effect of reducing the turbidity of the filtrate after coagulation and the effect of reducing the water content of the cake after dehydration are significantly superior to those of Comparative Examples 3 and 4.

Further, as the polymer dehydrating agent, it is possible to use in combination with dimethylaminoethyl acrylate quaternary methyl chloride, and as the polystyrene sulfonic acid soda, that produced from the used polystyrene resin can also be used. all right.

[0073]

As is clear from the above results, by applying the present invention, it is possible to treat wastewater having a high effect of clarifying the suspension, which contributes to prevention of water and environmental pollution. In addition, when the present invention is applied, the suspended solids are aggregated and the water content of the aggregates is reduced, so that wastewater treatment with a good recovery rate of water that can be reused from the suspension can be performed.

Since this polymer dehydrating agent can also be produced by using a used polystyrene resin,
Effective use of resources and reduction of waste can be achieved.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Miyuki Kuromiya 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Within Sony Corporation (56) References JP-A-52-68245 (JP, A) JP-A 2-298304 (JP, A) JP-A-3-14803 (JP, A) JP-A-59-16510 (JP, A) JP-A-52-33993 (JP, A) JP-B-44-32419 (JP, A) B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08F 8/00-8/50 B01D 21/01

Claims (6)

(57) [Claims] 1. A styrene-based polymer which is sulfonated as a main component, and the styrene-based polymer has a weight average molecular weight of 1
5 to 600,000 , which aggregates suspended solids and aggregates
A polymeric dehydrating agent which lowers the water content of a substance. 2. The polymer dehydrating agent according to claim 1, wherein the styrene-based polymer contains 40 mol% or more of sulfo groups with respect to all monomer units by sulfonation. 3. A suspension substance is coagulated from the wastewater by adding to the wastewater a macromolecular dehydrating agent having a sulfonated styrene polymer as a main component and the styrene polymer having a weight molecular weight of 150,000 to 600,000. Rutotomoni aggregation was allowed to
A method for treating wastewater , which comprises reducing the water content of water . 4. The method for treating wastewater according to claim 3, wherein the styrene-based polymer contains 40 mol% or more of sulfone groups with respect to all monomer units by sulfonation. 5. The method for treating wastewater according to claim 3, wherein the styrene polymer and a nonionic and / or anionic acrylamide polymer are added to the wastewater. 6. The method for treating wastewater according to claim 3, wherein the styrene polymer and the cation polymer are added to the wastewater.