JP5878409B2 - Wastewater treatment method using organic coagulant - Google Patents

Description

  The present invention relates to a method for treating papermaking wastewater using an organic coagulant.

  Conventionally, as a wastewater treatment method, there is a method of coagulating and precipitating a suspension in wastewater by adding and mixing an inorganic coagulant to the wastewater and further adding and mixing a polymer flocculant. In this wastewater treatment method, the surface charge of the suspension in the wastewater is neutralized by the charge neutralization action of the coagulant, and the repulsive force between the suspensions is reduced. As a result, the suspension is condensed to form primary agglomerated flocs, and the secondary agglomerated flocs generated by adding a polymer coagulant are solid-liquid separated to remove the suspensions from the waste water. However, since this method requires a large amount of an inorganic coagulant, the amount of sludge generated by solid-liquid separation after wastewater treatment becomes large, and the sludge treatment cost increases.

  In order to reduce the amount of coagulant added, the use of organic coagulants instead of inorganic coagulants has been studied. Patent Document 1 describes a deinking wastewater treatment method using polydimethylaminoalkyl (meth) acrylate or the like having an intrinsic viscosity of 0.05 to 1.0 dl / g (Claim 1). Patent Document 2 describes a wastewater treatment method using polydiallyldimethylammonium chloride as an organic coagulant (Claim 2). Patent Document 3 describes wastewater treatment with an organic coagulant obtained by reacting alkylenediamines with epihalohydrin (Claim 1). Patent Document 4 describes a method of treating purified water in which an organic coagulant such as polyamine or an inorganic coagulant and an organic coagulant are added to and mixed with raw water, and then a polymer flocculant is added and mixed. (wrap up).

  When using an organic coagulant, the amount added to the wastewater is small compared to when using an inorganic coagulant. However, when the coagulation performance evaluated by the floc diameter and sedimentation rate of flocs formed by the addition of organic coagulant and the clarity of treated water (turbidity, suspension (SS) mass) are evaluated, the organic coagulant is still Cannot be said to have sufficient agglomeration performance. In addition, when a large amount of an organic coagulant that is more expensive than an inorganic coagulant is used, there is a problem in cost. Therefore, in wastewater treatment methods that use organic coagulants, it is necessary to further suppress the amount of organic coagulant added and improve coagulation performance and clarity of treated water (turbidity, suspension (SS) mass). It has been.

JP-A-10-118660 JP 2001-38104 A JP 2009-125649 A JP 2002-346572 A

  An object of the present invention is to solve the above-described problems, and to provide a wastewater treatment method capable of reducing the amount of inorganic coagulant added and obtaining treated water with high clarity.

The inventors of the present invention have continued intensive studies in view of the above-mentioned problems, and by adding an organic coagulant composed of a water-soluble polymer having predetermined physical properties to waste water, the amount of the inorganic coagulant is suppressed to a small amount. And found that excellent agglomeration performance can be obtained.
Since the coagulation action of inorganic coagulants such as PAC (polyaluminum chloride) and sulfuric acid band is mainly due to charge neutralization based on the cationic nature, conventional organic coagulants are highly cationic and relatively Research and development have been conducted on low-molecular weight water-soluble polymers. However, when the present inventors investigated the performance as an organic coagulant for a water-soluble polymer having various structures and physical properties, a low cationic water-soluble polymer having a specific structure is high as an organic coagulant. It was found to show performance. In the case of a water-soluble polymer, this is not only the charge neutralization effect that is the main coagulation action of inorganic coagulants, but also the adsorption to suspensions and the cross-linking action between suspensions caused by being a polymer substance. It is thought to contribute.

Based on this knowledge, as a result of investigating the correlation between the physical properties of the organic coagulant with high coagulation performance and the coagulation performance, 0.5% solution viscosity when having a predetermined composition and measured at 25 ° C. A low cationic water-soluble polymer having a value divided by 0.5% salt viscosity of 5 to 50 and a 0.5% salt viscosity of 5 to 30 mPa · s when measured at 25 ° C. It has been found that it exhibits excellent coagulation action compared to organic coagulants.
The above-mentioned water-soluble polymer having the prescribed composition and physical properties has good molecular spread even when salts are dissolved in the addition target, and effectively cross-links with the suspension in the wastewater to aggregate the suspension. Contribute to.
Based on the knowledge about the organic coagulant comprising the above-mentioned water-soluble polymer, the present inventors complete a wastewater treatment method capable of suppressing the amount of inorganic coagulant added and obtaining treated water with high clarity. It came to.

  The present invention is a wastewater treatment method in which at least a primary flocculation step and a secondary flocculation step are performed on industrial wastewater, inorganic substance suspension wastewater, and the like. In the primary flocculation step, a predetermined organic coagulant is added to and mixed with waste water to form primary flocculation flocks. In the secondary flocculation step, a secondary flocculation floc is formed by adding and mixing a polymer flocculant to the waste water in which the primary flocculation floc is formed. In the present invention, a clear treated water can be obtained by solid-liquid separation of the formed secondary aggregation floc.

The present invention relates to the following general formula (1)
_{^{CH 2 = CR 1 -CO-X}} -Q-N + R 2 R 3 R 4 · Z - (1)
[In Formula (1), X is O or NH; Q is an alkylene group having 1 to 4 carbon atoms or a hydroxyalkylene group having 2 to 4 carbon atoms; R ¹ is H or a methyl group; R ² is 1 to 3 carbon atoms; Alkyl group, benzyl group, R ³ and R ⁴ each independently represent H, an alkyl group having 1 to 3 carbon atoms, and Z ⁻ represents a counter anion. ]
5 to 40 mol% of structural units derived from the cationic monomer represented by the following general formula (2)
R ⁵ CH = CR ⁶ -AB ¹ (2)
[In the formula (2), R ⁵ is hydrogen, methyl group, or COOB ² , R ⁶ is hydrogen, methyl group, or CH ₂ COOB ² , A is COO, SO ₃ , C ₆ H ₅ SO ₃ , CONHC (CH ₃ ) ₂ CH ₂ SO ₃ and C ₆ H ₅ COO, where B ¹ and B ² each represent hydrogen or a cation. ]
Containing 0 to 10 mol% of structural units derived from an anionic monomer represented by the formula (1) and 60 to 95 mol% of structural units derived from other monomers, and 0.5 when measured at 25 ° C. % Organic solution consisting of a water-soluble polymer having a value obtained by dividing the solution viscosity by 0.5% salt viscosity is 5-50, and the 0.5% salt viscosity is 5-30 mPa · s when measured at 25 ° C. A primary flocculation step in which a coagulant is added to and mixed with waste water to form primary flocculation flocs, and a polymer flocculant is further added to and mixed with the waste water in which the primary flocculation flocs are formed to form secondary flocculation flocs. And a secondary coagulation step. The water-soluble polymer is preferably an amphoteric or cationic water-soluble polymer. In the present invention, an inorganic coagulant is preferably added and mixed in the primary aggregation process. The cationic monomer is preferably a methyl chloride quaternized product of dimethylaminoethyl (meth) acrylate. The present invention is preferred as a method for treating papermaking wastewater.

  In the present invention, when treating wastewater, the amount of inorganic coagulant added can be suppressed to a small amount, and treated water with high clarity can be obtained.

Hereinafter, the details of the method for treating wastewater of the present invention will be described.
Waste water to be treated in the present invention includes industrial waste water, inorganic substance suspended waste water, and the like. The wastewater will be explained in detail later.

(1) Primary coagulation step In the primary coagulation step of the present invention, a predetermined organic coagulant described in detail later is added to and mixed with the waste water.
By adding a predetermined organic coagulant to the wastewater and stirring in the same manner as in the ordinary coagulation precipitation method, SS and the like in the wastewater are aggregated to form a primary coagulation floc.

(1-1) Organic coagulant The organic coagulant used in the present invention is represented by 5 to 40 mol% of a structural unit derived from the cationic monomer represented by the above formula (1) and the above formula (2). It consists of a water-soluble polymer containing 0 to 10 mol% of structural units derived from an anionic monomer and 60 to 95 mol% of structural units derived from other monomers.
The water-soluble polymer has a value obtained by dividing 0.5% solution viscosity by 0.5% salt viscosity when measured at 25 ° C., 5 to 50, more preferably 7 to 40, More preferably, it is 8-35. When “the value obtained by dividing the 0.5% solution viscosity by the 0.5% salt viscosity” exceeds 50, the processability of the wastewater deteriorates, the fine SS cannot be removed, and the clarity of the process water deteriorates.

  Moreover, the 0.5% salt viscosity when measured at 25 ° C. in the water-soluble polymer is 5 to 30 mPa · s, more preferably 7 to 25 mPa · s, and particularly preferably 10 to 20 mPa · s. If it exceeds 30 mPa · s, the fine SS cannot be removed and the clarity of the treated water deteriorates. If it is less than 5 mPa · s, the contribution of adsorption to the suspension and the cross-linking action between the suspensions, which are caused by the polymer substance, is reduced, so that the aggregation performance is deteriorated.

  The “value obtained by dividing the 0.5% solution viscosity by the 0.5% salt viscosity” is an index indicating the molecular spread of the water-soluble polymer molecules in the wastewater. The smaller this value is, the more difficult it is to reduce the molecular spread of the polymer when the water-soluble polymer is added to the wastewater.

The methods for measuring “0.5% solution viscosity” and “0.5% salt viscosity” will be described in detail later, but the water-soluble polymer was added to ion-exchanged water and a 4% by mass sodium chloride aqueous solution in a solid content conversion of 0. It calculates based on the viscosity at the time of adding and dissolving so that it may become 5 mass%, and measuring at 25 degreeC.
It is known that the molecular shape of a water-soluble polymer is affected by the salt concentration in water. When a water-soluble polymer is added to an aqueous solution in which salts are dissolved, the molecular spread is greatly reduced as compared with pure water.
There are various types of wastewater containing various salts. Therefore, when a normal water-soluble polymer is added to a waste liquid containing salts, the molecular spread is reduced.
The organic coagulant used in the present invention consists of a water-soluble polymer that exhibits the above-mentioned predetermined values with respect to 0.5% solution viscosity and 0.5% salt viscosity and whose molecular spread is difficult to reduce in waste water. As a result, the organic coagulant used in the present invention sufficiently performs charge neutralization and adsorption / crosslinking reactions on substances such as organic substances, suspensions, and inorganic substances in the waste liquid, and has good coagulation performance.

  The 0.5% solution viscosity and 0.5% salt viscosity vary depending on the composition and molecular weight of the water-soluble polymer. Therefore, by adjusting the composition and polymerization conditions of the amphoteric or cationic water-soluble polymer as described below, the 0.5% salt viscosity when measured at 25 ° C. of the water-soluble polymer used in the present invention. Is adjusted to 5-30 mPa · s, and the value obtained by dividing the 0.5% solution viscosity by the 0.5% salt viscosity can be adjusted to 5-50.

  Hereinafter, the amphoteric water-soluble polymer and the cationic water-soluble polymer, which are water-soluble polymers used as the organic coagulant in the present invention, will be described focusing on the composition.

(1-2) Amphoteric water-soluble polymer The amphoteric water-soluble polymer used in the present invention is a structural unit derived from the cationic monomer represented by the above formula (1) with respect to all structural units of the amphoteric water-soluble polymer. 5 to 40 mol%, more preferably 20 to 40 mol%. Furthermore, 1-10 mol% of structural units derived from the anionic monomer represented by the above formula (2) are contained, more preferably 5-10 mol%. Further, it contains 60 to 94 mol% of structural units derived from other monomers.
When the content of the cationic monomer is less than 5 mol%, the primary aggregation floc cannot be formed effectively without sufficient charge neutralization performance.

  In the structure represented by the above formula (1) serving as a structural unit for polymerization, examples of the counter anion include halogen ions such as chlorine ions, sulfate ions, nitrate ions, phosphate ions, and methylsulfonate ions. Examples of the cationic monomer represented by the above formula (1) include dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate (hereinafter, both are represented as dimethylaminoethyl (meth) acrylate. Hereinafter, other monomers have the same structure. The analog is represented by (meth)), a quaternized product such as methyl chloride or benzyl chloride, and the like, and a methyl chloride quaternized product of dimethylaminoethyl (meth) acrylate is more preferable.

  Specific examples of anionic monomers include (meth) acrylic acid and salts thereof; unsaturated carboxylic acids and salts thereof such as crotonic acid, itaconic acid and maleic acid; and acrylamide alkyls such as acrylamide-2-methylpropanesulfonic acid. And alkanesulfonic acid and its salt; and vinylsulfonic acid and its salt and 4-vinylbenzoic acid and its salt. Examples of the salt include ammonium salts and alkali metal salts such as sodium and potassium. Among these, (meth) acrylic acid is preferable.

  The amphoteric water-soluble polymer of the present invention can be obtained by polymerizing a monomer mixture containing at least one of the above cationic monomer and anionic monomer. Furthermore, you may copolymerize with another monomer.

Examples of other monomers include nonionic monomers and hydrophobic monomers.
As the nonionic monomer, various compounds can be used as long as they have radical polymerizability. Specifically, dialkyl (meth) acrylamides such as (meth) acrylamide, dimethyl (meth) acrylamide and diethyl (meth) acrylamide are used. , Hydroxyalkyl (meth) acrylates such as hydroxylethyl (meth) acrylate, dialkylaminoalkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate, dialkylaminoalkyl (meth) acrylamides such as dialkylaminopropyl (meth) acrylamide, etc. Can be mentioned. Among these, (meth) acrylamide is preferable.

Also, other hydrophobic monomers can be used as long as the effects of the present invention are not impaired.
As the hydrophobic monomer, various compounds can be used as long as they have radical polymerizability. Specifically, methoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, ethyl carbitol (meth) acrylate, methyl (Meth) acrylate, ethyl (meth) acrylate, vinyl acetate and the like can be mentioned.
These other monomers may be used alone or in combination of two or more.

As the polymerization method, radical polymerization is preferred. As the radical polymerization method, conventionally known radical polymerization methods such as bulk polymerization, suspension polymerization, dispersion polymerization, emulsion polymerization, aqueous solution polymerization, aqueous solution gel polymerization and the like can be used. Among these radical polymerization methods, aqueous solution gel polymerization and emulsion polymerization are preferred from the viewpoint of production cost and ease of handling of the polymer.
Which polymerization method is used is appropriately selected depending on the physical properties required for the organic coagulant. When the degree of crosslinking is high, it is preferable to select emulsion polymerization, and when it is low, aqueous gel polymerization is selected.

  Examples of the polymerization initiator in radical polymerization include peroxides such as potassium persulfate, ammonium persulfate, hydrogen peroxide, peracetic acid, t-butyl hydroxide, benzoyl peroxide, and di-t-butyl peroxide. , 2'-azobis (2-methylpropionamidine) dihydrochloride, azobiscyanovaleric acid, 2,2'-azobisisobutyronitrile and 2,2'-azobis [2-methyl-N- (2- Hydroxyethyl) -propionamide, azo initiators such as azobiscyanovaleronitrile, azobisisobutyronitrile, peroxides such as hydrogen peroxide and sodium persulfate, sodium bisulfite, potassium bisulfite, sulfuric acid A redox initiator composed of a combination with a reducing agent such as ferrous iron and ascorbic acid, and a photopolymerization initiator Depending can be appropriately utilized. The amount of the polymerization initiator used is preferably 0.001 to 5% with respect to the total mass of the monomers.

  Moreover, you may use a chain transfer agent as needed. Examples of chain transfer agents include alcohols such as methanol, isopropyl alcohol, ethylene glycol and propylene glycol, amines such as methylamine and dimethylamine, thiols such as methanethiol and ethanethiol, methallylsulfonic acid and salts thereof Etc.

  Moreover, you may use a crosslinking agent as needed. Examples of the crosslinking agent include N, N-methylenebis (meth) acrylamide, glycidyl acrylate, ethylene glycol dimethacrylate, N-vinylacrylamide and the like.

When the water-soluble polymer used in the present invention is produced by aqueous gel polymerization or emulsion polymerization, it can be produced under known polymerization conditions.
In the case of aqueous gel polymerization, the polymerization initiation temperature is preferably 0 to 35 ° C. The polymerization time is preferably from 0.1 to 3 hours. The polymerization reaction is preferably carried out in an inert atmosphere in the absence of oxygen. After completion of the polymerization reaction, heat treatment or drying is appropriately performed as necessary.

  In the case of emulsion polymerization, an aqueous phase containing a predetermined monomer, radical initiator, chain transfer agent and the like used in the present invention, an oily substance composed of immiscible hydrocarbons, and a water-in-oil emulsion are formed. An effective amount of surfactant is used to form a water-in-oil emulsion. A water-soluble polymer used in the present invention can be synthesized by polymerizing the formed water-in-oil emulsion.

  Examples of oily substances include paraffins, various mineral oils, hydrocarbon oils having the same characteristics as these, and mixtures thereof. The content of the oily substance is 20% by mass to 50% by mass, preferably 25% by mass to 40% by mass with respect to the total amount of the water-in-oil emulsion.

  The surfactant for forming the water-in-oil emulsion preferably has an HLB of 3-11. Examples of such surfactants include nonionic surfactants such as sorbitan monooleate and sorbitan monostearate. The effective addition amount of these surfactants is preferably 0.5 to 10% by mass, more preferably 1 to 5% by mass with respect to the total amount of the water-in-oil emulsion.

  When emulsion polymerization is performed, the polymerization conditions are appropriately set according to the monomers and initiators used and the physical properties of the polymer. Polymerization temperature is 0-100 degreeC, 20-80 degreeC is preferable and 20-60 degreeC is more preferable. The polymerization concentration of the monomer is preferably 20 to 50% by mass, and more preferably 25 to 40% by mass. The polymerization reaction is preferably performed in an inert atmosphere free of oxygen. The polymerization time is preferably 1 to 10 hours, more preferably 2 to 6 hours.

  The 0.5% salt viscosity of the amphoteric water-soluble polymer of the present invention is 5 to 30 mPa · s, preferably 7 to 25 mPa · s, and more preferably 10 to 20 mPa · s. The degree of polymerization can be adjusted by a known method such as the use of a polymerization catalyst concentration, a crosslinking agent, or a chain transfer agent. By adjusting the degree of crosslinking and the degree of polymerization, the value obtained by dividing 0.5% solution viscosity by 0.5% salt viscosity when measured at 25 ° C. is 5-50, and the salt viscosity is 5-30 mPa · An amphoteric water-soluble polymer that is s can be obtained. By adding such an amphoteric water-soluble polymer to waste water, primary aggregated flocs can be effectively formed.

(1-3) Cationic water-soluble polymer The cationic water-soluble polymer used as the organic coagulant in the present invention contains at least 5 to 40 structural units derived from the cationic monomer represented by the above formula (1). It contains in mol%, preferably 10-30 mol%, more preferably 15-30 mol%. The cationic water-soluble polymer may contain structural units derived from other monomers. The constitutional unit of the other monomer is 60 to 95 mol%, preferably 70 to 90 mol%, more preferably 70 to 85 mol%.
As the cationic monomer represented by the above formula (1) and other monomers as the structural unit of the polymer, the same cationic monomers and other monomers used for the production of the amphoteric water-soluble polymer may be used. it can.

  The cationic water-soluble polymer can be obtained by polymerizing a composition containing at least the cationic monomer represented by the above formula (1) using a known polymerization method. The known polymerization method is as described above.

  The 0.5% salt viscosity of the cationic water-soluble polymer of the present invention is 5 to 30 mPa · s, preferably 7 to 25 mPa · s, and more preferably 10 to 20 mPa · s. The degree of polymerization can be adjusted by a known method such as the use of a polymerization catalyst concentration, a crosslinking agent, or a chain transfer agent. The same crosslinking agent and chain transfer agent as those used for the polymerization of the amphoteric water-soluble polymer of the present invention can be used.

  By adjusting the degree of crosslinking and the degree of polymerization, the value obtained by dividing the 0.5% solution viscosity when measured at 25 ° C. by the 0.5% salt viscosity is 5-50, and the 0.5% salt viscosity is A cationic water-soluble polymer of 5 to 30 mPa · s can be obtained. By adding such a cationic water-soluble polymer to waste water, primary aggregated flocs can be effectively formed.

  The amount of the organic coagulant made of the amphoteric or cationic water-soluble polymer is adjusted according to the pH of the waste water, the properties of the waste water such as SS and TS, and the amount of the inorganic coagulant when used in combination. . The addition amount of the organic coagulant is usually 0.1 to 20 mg / l, preferably 0.5 to 10 mg / l in terms of solid content with respect to the amount of waste water.

When an inorganic coagulant is used in combination, the amount of inorganic coagulant added is also taken into consideration. For example, the addition amount of the organic coagulant is preferably 0.1 to 20 parts by mass with respect to 100 parts by mass of the inorganic coagulant reduced by using the organic coagulant. More preferably, it is a part. The inorganic coagulant will be described in detail later.
The mode of the organic coagulant added to the waste water is not particularly limited, but is preferably an aqueous solution, such as a solution, a powder, and an emulsion.
The organic coagulant of the present invention may be added with additives such as an antifoaming agent, an antioxidant and a pH adjuster as long as the effects of the present invention are not impaired.

(1-4) Other coagulants In the present invention, in order to improve the coagulation action in the primary agglomeration step, a known inorganic coagulant or the above-described predetermined coagulant may be used as long as the effect of the present invention is not impaired. Another organic coagulant different from the organic coagulant can be used in combination.
Examples of known inorganic coagulants include sulfuric acid bands, polyaluminum chloride (PAC), aluminum chloride, ferric chloride, ferrous sulfate, polyiron, and polysilica iron. These inorganic coagulants may be used alone or in combination of two or more.

When the inorganic coagulant is used in combination, the amount added is adjusted according to the properties of the wastewater, such as pH, SS, TS, etc. of the wastewater. The amount of the inorganic coagulant added is usually 10 to 2000 mg / l, preferably 50 to 2000 mg / l in terms of solid content with respect to the amount of waste water.
The form of the inorganic coagulant added to the waste water is not particularly limited, but is preferably an aqueous solution.

  Examples of other organic coagulants include condensates of epichlorohydrin and dimethylamine, polyethyleneimine hydrochloride, polyallylamine hydrochloride, polydimethyldiallylammonium chloride, and the like.

  When the organic coagulant of the present invention is used in combination with another organic coagulant or inorganic coagulant in the primary coagulation step, the order of addition to the wastewater is not particularly limited. The organic coagulant of the present invention and other organic coagulants or inorganic coagulants may be added individually to the waste water, or may be added in advance by mixing. When the organic coagulant and the inorganic coagulant of the present invention are used in combination, it is preferable to add and mix the organic coagulant after adding and mixing the inorganic coagulant.

  In the present invention, since the organic coagulant described in the above (1-1), (1-2), and (1-3) is added to waste water, it is not necessary to add a large amount of inorganic coagulant. Due to the charge neutralization action and the adsorption / crosslinking action of the organic coagulant, the coagulation performance is sufficiently exhibited even when the amount of the inorganic coagulant added is suppressed to a small amount, and treated water with good clarity can be obtained.

(1-5) Wastewater Wastewater to be treated in the present invention includes industrial wastewater, inorganic substance suspended wastewater, and the like.
Specific examples include industrial wastewater from the automobile industry, steel industry, etc., cleaning wastewater, and wastewater from the metal processing industry. Examples of the waste liquid in the metal processing industry include a waste liquid containing a water-soluble or water-dispersible treatment liquid, a lubricant, cutting oil, and the like used in die casting and hot forging.
Other examples include electronic industry wastewater generated in the development process, stripping process, etching process, cleaning process, etc. in semiconductor manufacturing and liquid crystal panel manufacturing, organic wastewater generated in painting and dyeing plants, chemical factory wastewater, and sewage treatment plants. There is sewage pollution wastewater. In addition, there are wastewater from meat processing plants and wastewater from food processing plants. Food processing factory wastewater is rich in organic matter and oil.
Other examples include livestock treated water containing animal and fish blood, human waste and organic industrial wastewater.
Other examples include ground improvement, tunnel excavation, construction / contamination wastewater generated at building construction sites, gravel collection, gravel crushed stones, dredged mud generated at construction sites such as rivers and harbors. Generally, these wastewaters contain a large amount of inorganic suspension.

  The present invention is particularly effective for the treatment of papermaking wastewater generated in the papermaking industry. Papermaking wastewater is used paper pulp manufacturing wastewater discharged when manufacturing wastepaper pulp, kraft pulp manufacturing wastewater discharged when manufacturing kraft pulp (KP), and mechanical pulp discharged when manufacturing mechanical pulp. Manufacturing wastewater, coating solution wastewater discharged when coating paint on paper, papermaking process wastewater discharged when making pulp, bleaching wastewater discharged when bleaching with chlorine, etc. . Further, waste water obtained by treating these papermaking wastewater with activated sludge, clarifier treated water, wastewater obtained by treating these with aluminum sulfate or the like, and further, general wastewater composed of the above-mentioned various papermaking wastewater, cooling wastewater, or the like may be used. Generally, the papermaking wastewater contains suspended substances such as fibers, fillers, and pigments.

(2) Secondary flocculation step In the secondary flocculation step, a polymer flocculant is further added to and mixed with the waste water in which the primary flocculation flocs are formed. A secondary agglomerated floc in which the primary agglomerated floc is further coarsened is formed.
In this step, a known anionic or nonionic polymer flocculant can be used. Examples of the anionic polymer flocculant include a copolymer of acrylamide and sodium acrylate, a copolymer of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, sodium acrylate and 2-acrylamido-2-methylpropane. Examples include sulfonic acid copolymers, sodium polyacrylate, and polyacrylamide partial hydrolysates. Nonionic polymer flocculants include polyacrylamide, copolymers of acrylamide and other nonionic monomers, and the like.

The preferred weight average molecular weight of the polymer flocculant is 2 million to 20 million.
The amount of the polymer flocculant added is adjusted depending on the properties of the waste water after the primary flocculation step. The addition amount is preferably 0.05 to 20 mg / l, more preferably 0.1 to 10 mg / l in terms of solid content with respect to the amount of wastewater in the wastewater treated in the primary flocculation step.
By adding and mixing the polymer flocculant in the secondary flocculation step, a coarsened secondary flocculation floc is formed in the waste water.

(3) Treatment after the secondary flocculation step By subjecting the secondary flocculation floc formed in the secondary flocculation step to solid-liquid separation, clear treated water can be obtained.
The solid-liquid separation method can be performed by a conventionally known method. For example, solid-liquid separation can be performed by sedimentation separation, pressurized flotation, filtration, or the like, and preferably sedimentation separation is performed. By subjecting the secondary flocculated floc and other suspensions to solid-liquid separation, treated water with good clarity can be obtained.
The wastewater treatment method of the present invention may be performed while appropriately adding a pH adjuster to the wastewater.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
(Organic coagulant)
A 0.1% by mass aqueous solution of water-soluble polymers A1 to A11 and B1 to B4 obtained by polymerizing monomers having the compositions shown in Table 1 was used. The abbreviations DMC, DAB, DAC, AcA and AMD in Table 1 mean the following.
DMC: Methyl chloride quaternized product of dimethylaminoethyl methacrylate DAB: Benzyl chloride quaternized product of dimethylaminoethyl acrylate DAC: Methyl chloride quaternized product of dimethylaminoethyl acrylate AcA: Acrylic acid AMD: Acrylamide

(Production Example 1: Emulsion polymerization)
Organic coagulant A5 was synthesized by the steps described below.
In a 1000 ml four-necked separable flask, 284.4 g of 50% acrylamide aqueous solution, 86.5 g of 79% dimethylaminoethyl acrylate methyl chloride quaternary solution, 0.42 g of sodium methallyl sulfonate as a chain transfer agent (0 to monomer) 2 mass%) and distilled water, and after adjusting the pH to 4 with concentrated sulfuric acid, 20 g of an aqueous solution containing 0.4 g of 2,2′-azobis (2-methylpropionamidine) dihydrochloride as an initiator was added. The total amount of the monomer aqueous solution was 400 g. Further, this monomer aqueous solution was added to 160 g of paraffin oil in which 11.2 g of HLB4.2 nonionic surfactant was dissolved, and the mixture was emulsified by stirring at high speed with a homogenizer. Attach a nitrogen gas blowing tube, a reflux condenser, and a thermometer to the flask, replace the stirrer with an ordinary stirrer for chemical reaction, and degas by passing nitrogen gas through the emulsion for 30 minutes while stirring. The temperature was raised, and polymerization was carried out in a nitrogen gas atmosphere for 4 hours. After completion of the polymerization, 16.0 g of a nonionic surfactant having an HLB of 13.0 was added to obtain an organic coagulant A5 as an emulsion. A sample of the obtained organic coagulant A5 was taken, and 0.5% salt viscosity was measured with a B-type viscometer. The 0.5% salt viscosity was 11.6 mPa · s.

(Production Example 2: Aqueous Gel Polymerization)
Into a stainless steel reaction vessel, put 88.3 g of 79% dimethylaminoethyl acrylate methyl chloride quaternized aqueous solution and 460.6 g of 50% acrylamide aqueous solution so that the total weight is 1 kg and the total monomer concentration is 30% by mass. Distilled water was added and then adjusted to pH = 4 with hydrochloric acid. Subsequently, the temperature of the solution was adjusted to 20 ° C. while blowing nitrogen gas into the solution for 60 minutes, thereby obtaining an aqueous monomer mixture solution for polymerization. Furthermore, 2300 ppm of 2,2′-azobis (2-methylpropionamidine) dihydrochloride and 110 ppm of sodium bisulfite were added on the basis of the total monomer weight, and 13W black light was used from above the reaction vessel. Polymerization was performed by irradiation for 60 minutes at an irradiation intensity of 0.4 mW / cm ² to obtain a water-containing gel-like water-soluble copolymer. The water-containing gel-like water-soluble copolymer was taken out of the container and chopped, dried at a temperature of 80 ° C. for 5 hours and then pulverized to obtain a powdery organic coagulant A7. A sample of the obtained organic coagulant A7 was taken, and 0.5% salt viscosity was measured with a B-type viscometer. The 0.5% salt viscosity was 12.6 mPa · s.
Other organic coagulants were obtained by appropriately adjusting the reaction conditions in the same manner as in Production Example 1 or 2.

(Inorganic coagulant)
A 0.8% by mass aqueous solution of sulfuric acid band or an 8% by mass aqueous solution of aluminum chloride was used.

(Polymer flocculant)
Polyacrylamide flocculant A (AcNa / AMD = 12/88 (mol / mol), 0.1% salt viscosity = 6.4), or polyacrylamide flocculant B (AcNa / AMD = 20/88 (mol / mol) mol), 0.1% salt viscosity = 6.8). AcNa is an abbreviation for sodium acrylate. AMD is an abbreviation for acrylamide.

(Waste water)
Comprehensive wastewater (wastewater A, wastewater B) discharged from different paper mills was treated.
The properties of waste water A and waste water B are as follows.
Wastewater A: pH = 6.70, SS = 700 mg / l, TS = 2000 mg / l
Wastewater B: pH = 7.02, SS = 6400 mg / l, TS = 10100 mg / l
Here, SS is an abbreviation for suspended matter, and TS is an abbreviation for total evaporation residue. Each was measured according to the JIS K0102 factory drainage test method.

(Measurement of 0.5% salt viscosity and 0.5% solution viscosity of water-soluble polymer)
Samples of the water-soluble polymers A1 to 11 and B1 to 4 in Table 1 are 0.5% by mass in terms of solid content in 500 ml of a 4% by mass sodium chloride aqueous solution prepared with ion-exchanged water in a 500 ml tall beaker. Added as follows. The sample was stirred at 200 rpm using a screw blade (about 6 cmφ) in a constant temperature water bath at 25 ± 1 ° C. until the sample was completely dissolved. The viscosity of this sample solution was read for 3 minutes at 60 rpm and 25 ± 1 ° C. using a TV-10M type B viscometer manufactured by Toki Sangyo Co., Ltd. with an M1 rotor. The salt viscosity was used. When the viscosity exceeded the measurement upper limit of the M1 rotor, the M2 rotor was used.
Samples of water-soluble polymers A1 to 11 and B1 to 4 in Table 1 are added to 500 ml of ion-exchanged water so as to be 0.5% by mass in terms of solid content, and the above-mentioned measurement solution for 0.5% salt viscosity and A 0.5% by mass solution was prepared by dissolving in the same manner. The viscosity of this sample solution was read for 3 minutes at 30 rpm and 25 ± 1 ° C. using a TV-10M type B viscometer manufactured by Toki Sangyo Co., Ltd. with an M1 rotor. It was set as the solution viscosity. When the viscosity exceeded the measurement upper limit of the M1 rotor, the M2 rotor was used.

(Settling time)
After the secondary flocculation step, after the stirring was stopped, the time until the secondary flocculation floc settled at the bottom of the 500 ml beaker was measured and set as the sedimentation time.

(Transparency)
According to the JIS K0102 factory drainage test method, it measured visually using the transparency meter.

(Examples 1-11, Comparative Examples 1-6)
500 ml of waste water A was collected in a 500 ml beaker, and the pH was adjusted to 6.1 with 1N sulfuric acid. A 0.8% by mass aqueous solution of a sulfuric acid band as an inorganic coagulant was added to this waste water in the addition amount shown in Table 2, and the mixture was stirred at 120 rpm × 30 seconds. Subsequently, 0.1% aqueous solutions of organic coagulants A1 to 11 and B1 to 4 shown in Table 1 were added in the addition amounts shown in Table 2, and stirred at 120 rpm for 60 seconds. Thereafter, 1.0 mg / l of polymer flocculant A was further added and stirred at 120 rpm × 60 seconds, followed by stirring at 60 rpm × 60 seconds to form an aggregated floc. After the stirring was stopped, the floc settled on the bottom of the 500 ml beaker. The sedimentation time until measurement was measured. After standing for 1 minute, the floc diameter and transparency were measured. Table 2 shows the floc diameter, settling time, and transparency of the floc formed in each example and comparative example.

Comparative Example 1 is a conventional wastewater treatment method in which only the inorganic coagulant is added in the primary coagulation step. In Examples 1 to 11, the predetermined organic coagulant and inorganic coagulant of the present invention were added. Although the addition amount of the inorganic coagulant was 1/3 of that of Comparative Example 1, good aggregation performance was exhibited. The transparency of wastewater was also improved as compared with Comparative Example 1.
In Comparative Example 2, no organic coagulant was added. As a result, compared with Examples 1-11 and Comparative Example 1, the agglomeration performance was lowered, and the transparency of wastewater was also inferior.
In Comparative Example 3, the proportion of the cationic monomer in the organic coagulant exceeded the specified range of the present invention. The results were inferior to Examples 1-11 in both aggregation performance and clarity.
In Comparative Example 4, the 0.5% salt viscosity of the water-soluble polymer used exceeded the upper limit of the specified range of the present invention. The results were inferior to Examples 1-11 in both aggregation performance and clarity.
In Comparative Example 5, the value obtained by dividing the 0.5% solution viscosity by the 0.5% salt viscosity of the water-soluble polymer used exceeded the upper limit of the specified range of the present invention. As a result, the clarity of treated water was inferior compared with Examples 1-11.
In Comparative Example 6, the value obtained by dividing the 0.5% solution viscosity by the 0.5% salt viscosity of the water-soluble polymer used was below the lower limit of the specified range of the present invention. As a result, the clarity of treated water was inferior compared with Examples 1-11.

(Examples 12-22, Comparative Examples 7-12)
500 ml of waste water B was collected in a 500 ml beaker, and an 8 mass% aqueous solution of aluminum chloride as an inorganic coagulant was added in the addition amount shown in Table 3, and stirred at 120 rpm × 60 seconds. Subsequently, 0.1% aqueous solutions of organic coagulants A1 to 11 and B1 to 4 shown in Table 1 were added in the addition amounts shown in Table 3, and stirred at 120 rpm for 60 seconds. Thereafter, 3.0 mg / l of polymer flocculant B was further added and stirred at 120 rpm × 60 seconds, followed by stirring at 60 rpm × 60 seconds to form an aggregated floc. After the stirring was stopped, the floc settled on the bottom of the 500 ml beaker. The sedimentation time until measurement was measured. After standing for 1 minute, the floc diameter and transparency were measured. Table 3 shows the floc diameter, settling time, and transparency of the floc formed in each example and comparative example.

Comparative Example 7 is a conventional wastewater treatment method in which only the inorganic coagulant is added in the primary coagulation step. In Examples 12 to 22, the predetermined organic coagulant and inorganic coagulant of the present invention were added. The amount of the inorganic coagulant added was 2/3 that of Comparative Example 7, but good coagulation performance was exhibited. The transparency of wastewater was also improved as compared with Comparative Example 7.
In Comparative Example 8, no organic coagulant was added. As a result, compared with Examples 12-22 and Comparative Example 7, the agglomeration performance was lowered, and the transparency of wastewater was also inferior.
In Comparative Example 9, the proportion of the cationic monomer in the organic coagulant exceeded the specified range of the present invention. The results were inferior to Examples 12-22 in both aggregation performance and clarity.
In Comparative Example 10, the 0.5% salt viscosity of the water-soluble polymer used exceeded the upper limit of the specified range of the present invention. The results were inferior to Examples 12-22 in both aggregation performance and clarity.
In Comparative Example 11, the value obtained by dividing the 0.5% solution viscosity by the 0.5% salt viscosity of the water-soluble polymer used exceeded the upper limit of the specified range of the present invention. As a result, the clarity of treated water was inferior compared with Examples 12-22.
In Comparative Example 12, the value obtained by dividing the 0.5% solution viscosity by the 0.5% salt viscosity of the water-soluble polymer used was below the lower limit of the specified range of the present invention. As a result, the clarity of treated water was inferior compared with Examples 12-22.

In the above examples, the amount of the inorganic coagulant could be reduced from the conventional addition amount to at least 2/3 or less. The addition amount of the organic coagulant is 1/200 or less of the addition amount of the reduced inorganic coagulant.
That is, the present invention exhibits good agglomeration performance while greatly reducing the amount of inorganic coagulant added as compared with the prior art. Thereby, the waste water treatment method which obtains treated water with high clarity is realized.

  The wastewater treatment method using an organic coagulant in the present invention is an industrially excellent wastewater treatment method that can reduce the amount of inorganic coagulant added compared to the prior art.

Claims (4)

The following general formula (1)
_{^{CH 2 = CR 1 -CO-X}} -Q-N + R 2 R 3 R 4 · Z - (1)
[In Formula (1), X is O or NH; Q is an alkylene group having 1 to 4 carbon atoms or a hydroxyalkylene group having 2 to 4 carbon atoms; R ¹ is H or a methyl group; R ² is 1 to 3 carbon atoms; Alkyl group, benzyl group, R ³ and R ⁴ each independently represent H, an alkyl group having 1 to 3 carbon atoms, and Z ⁻ represents a counter anion. ]
5 to 40 mol% of structural units derived from the cationic monomer represented by the following general formula (2)
R ⁵ CH = CR ⁶ -AB ¹ (2)
[In the formula (2), R ⁵ is hydrogen, methyl group, or COOB ² , R ⁶ is hydrogen, methyl group or CH ₂ COOB ² , A is COO, SO ₃ , C ₆ H ₅ SO ₃ , CONHC (CH ₃ ) ₂ CH ₂ SO ₃ and C ₆ H ₅ COO, and B ¹ and B ² each represent hydrogen or a cation. ]
0 to 10 mol% of a structural unit derived from an anionic monomer represented by the formula (1), and 60 to 95 mol% of a structural unit derived from (meth) acrylamide , and 0. A value obtained by dividing 5% solution viscosity by 0.5% salt viscosity is 5 to 50, and consists of a water-soluble polymer having a 0.5% salt viscosity of 5 to 30 mPa · s when measured at 25 ° C. A primary agglomeration step in which an organic coagulant is added to and mixed with waste water to form a primary agglomeration floc;
A waste water treatment method comprising: a secondary flocculation step of further adding and mixing a polymer flocculant to the waste water in which the primary flocculation floc is formed to form a secondary flocculation floc.   The method for treating wastewater according to claim 1, wherein an inorganic coagulant is further added and mixed in the primary coagulation step.   The wastewater treatment method according to claim 1, wherein the cationic monomer is a methyl chloride quaternized product of dimethylaminoethyl (meth) acrylate. The wastewater treatment method according to any one of claims 1 to 3, wherein the wastewater is papermaking wastewater.