Method for treating wastewater containing hydrocolloids

Abstract

An object of the present invention is to provide a method for efficiently treating wastewater containing hydrocolloids. [Solution] A method for treating wastewater containing hydrocolloids, comprising: a pH adjustment step for adjusting the pH of the wastewater; and an active ingredient addition step for adding an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient to the wastewater whose pH has been adjusted in the pH adjustment step, wherein in the pH adjustment step, the pH of the wastewater is adjusted to be within a pH range of ±0.5 of the pH value of the aqueous solution.

Description

[Technical Field]

[0001] The present invention relates to a method for treating wastewater containing hydrocolloids. [Background technology]

[0002] BACKGROUND ART Various technologies have been proposed for treating wastewater containing dispersed organic polymeric substances, which is discharged from factories (plants) producing textiles, paints, paper, adhesives, synthetic resins, rubber, etc. For example, Patent Document 1 discloses a wastewater treatment method for coagulation and sedimentation treatment of wastewater discharged from chemical plants, semiconductor plants, food factories, paper and pulp factories, printing factories, automobile factories, etc., and biologically treated water from sewage treatment plants and sewage treatment plants, in which one or more water-soluble polymers having a phenolic hydroxyl group, such as (i) a homopolymer of vinylphenol, (ii) a homopolymer of modified vinylphenol, (iii) a copolymer of vinylphenol and / or modified vinylphenol with a hydrophobic vinyl monomer, or (iv) an addition condensate of phenol and formaldehyde, are added to the wastewater, and then an inorganic coagulant is added to perform coagulation treatment, characterized in that the pH of the wastewater is adjusted to 9 or higher prior to the addition of the water-soluble polymer having a phenolic hydroxyl group.

[0003] Furthermore, for example, Patent Document 2 discloses a technique for removing SS components and COD components in wastewater by adjusting the pH of wastewater containing vinyl acetate polymer to 8 or higher and adding 500 to 1000 ppm of ferrous sulfate to perform coagulation treatment. Patent Document 3 discloses a technique in which a flocculant is added to an aqueous dispersion containing an organic polymer substance in the form of an emulsion, latex, suspension, or the like, and the mixture is flocculated, precipitated, heated, and then filtered. Patent Document 4 discloses a technology in which bacteria of the genus Neisseria and Pseudomonas are added to water containing a polyvinyl alcohol resin, and the water is treated by an aerobic biological treatment method.

[0004] Furthermore, Patent Document 5 discloses a technique in which a mixed composition of a pyrolysis product made of a CaO-MgO-SiO2 system having a specific mass ratio and a metal salt made of an iron salt or a magnesium salt is added to a waste liquid containing a polymer emulsion or latex, thereby flocculating and separating particles whose main component is resin in the waste liquid. Patent Document 6 discloses a technique in which waste liquid containing a polymer emulsion or latex is mixed with a pyrolysis product made of a CaO-MgO-SiO2 system having a specific mass ratio and an aluminum-based inorganic flocculant, or an aluminum-based inorganic flocculant and a polymer flocculant, to flocculate and separate particles whose main component is resin in the waste liquid. Patent Document 7 discloses a technique in which a polyhydric phenol compound such as tannic acid is added to acidic vinyl chloride resin polymerization wastewater to carry out a coagulation and sedimentation treatment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-210613 [Patent Document 2] Japanese Patent Application Publication No. 52-155859 [Patent Document 3] Special Publication No. 56-046915 [Patent Document 4] Special Publication No. 57-046914 [Patent Document 5] Special Publication No. 06-073666 [Patent Document 6] Special Publication No. 07-106355 [Patent Document 7] Japanese Patent Application Publication No. 10-244278 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the prior art techniques proposed in Patent Documents 1 to 7 sometimes fail to achieve a sufficient solid-liquid separation effect for special wastewater containing hydrocolloids. Furthermore, with growing environmental awareness worldwide, regulations and standards surrounding factories are becoming stricter, creating a demand for more efficient and environmentally friendly wastewater treatment.

[0007] Therefore, an object of the present invention is to provide a method for efficiently treating wastewater containing hydrocolloids. [Means for solving the problem]

[0008] As a result of extensive research to solve the above problems, the present inventors have discovered that, by adjusting the pH of wastewater containing hydrocolloids to the pH of an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient before adding the aqueous solution to the wastewater, the treatment effect of wastewater containing hydrocolloids can be improved, i.e., excellent solid-liquid separation effect can be obtained, and the water quality of the wastewater after treatment can be improved, which led to the completion of the present invention.

[0009] That is, the present invention relates to the following processing methods, although the present invention is not limited thereto. [1] A method for treating wastewater containing hydrocolloids, comprising: a pH adjustment step of adjusting the pH of the wastewater; and an active ingredient addition step of adding an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient to the wastewater whose pH has been adjusted in the pH adjustment step, wherein in the pH adjustment step, the pH of the wastewater is adjusted to be within a pH range of ±0.5 of the pH value of the aqueous solution. [2] The method for treating wastewater according to [1] above, further comprising, after the active ingredient addition step, a flocculation step of adding an inorganic flocculating agent to flocculate the hydrocolloid. [3] The method for treating wastewater according to [1] or [2] above, wherein the compound having a chain structure containing two or more aromatic rings is a polyphenol compound. [4] The method for treating wastewater according to [3] above, wherein the polyphenol compound has the chain structure as a main chain. [5] The method for treating wastewater according to [3] above, wherein the polyphenol compound is a phenolic resin which may have a substituent or tannic acid. [Effects of the Invention]

[0010] According to the present invention, a method for efficiently treating wastewater containing hydrocolloids can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0011] The method for treating wastewater containing a hydrocolloid of the present invention comprises a pH adjustment step of adjusting the pH of the wastewater, and an active ingredient addition step of adding an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient to the wastewater whose pH has been adjusted in the pH adjustment step, wherein the pH of the wastewater is adjusted in the pH adjustment step to fall within a pH range of ±0.5 of the pH of the aqueous solution. Here, adjusting the pH of the wastewater in the pH adjustment step to fall within a pH range of ±0.5 of the pH of the aqueous solution means adjusting the pH of the wastewater in the pH adjustment step to be between minus 0.5 and plus 0.5 of the pH of the aqueous solution containing the compound having a chain structure containing two or more aromatic rings as an active ingredient. For example, if the pH of the aqueous solution is 10, the pH of the wastewater is adjusted to be between 9.5 and 10.5. In the treatment method of the present invention, the pH of the wastewater is preferably adjusted in the pH adjustment step to fall within a pH range of ±0.4 of the pH of the aqueous solution, more preferably within a pH range of ±0.3. The pH value of an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient refers to the pH value of an aqueous solution in which a compound having a chain structure containing two or more aromatic rings as an active ingredient is dissolved in a water solvent, and means the original pH of the aqueous solution that is not affected by acidic or alkaline components.

[0012] The treatment method of the present invention is used to treat wastewater containing hydrocolloids. Because hydrocolloids have a high affinity for water, a known method for precipitating and removing hydrocolloids is to use a large amount of electrolyte to cause salting out. Another known method for treating wastewater containing general colloid particles is to coagulate colloid particles using inorganic and organic coagulants. However, there is room for further research into methods for effectively coagulating hydrocolloids in wastewater containing hydrocolloids. As a result of extensive research, the present inventors have found that in treating wastewater containing hydrocolloids, the hydrocolloids in the wastewater to be treated can be efficiently coagulated by adjusting the pH of the wastewater to fall within a pH range of ±0.5 of the pH value of an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient, which is added to the wastewater.

[0013] [Wastewater to be treated] The wastewater to be treated in the present invention is not particularly limited as long as it contains hydrocolloids as fine solids. Examples of hydrocolloids include hydrophilic particles, such as particles of synthetic resins such as vinyl acetate resins, epoxy resins, and polyvinyl alcohol, and particles of organic polymeric substances such as rosin (pine resin) and natural rubber derived from animals and plants. These particles are contained in wastewater from, for example, the production and / or processing of textiles, and the production processes of paints, paper, adhesives, synthetic resins, rubber, etc.

[0014] The hydrocolloid may also be hydrophobic particles that have been made hydrophilic by surface modification with a surfactant or the like. Examples of hydrophobic particles include particles of synthetic resins such as vinyl chloride resins and olefin resins, and particles of organic polymeric substances such as natural rubber. These particles are contained in wastewater from, for example, the production and / or processing of fibers, and the production processes of paints, paper, adhesives, synthetic resins, rubber, etc.

[0015] The wastewater treatment method of the present invention can suitably treat wastewater containing a hydrocolloid, which is a colloid comprising hydrophilic particles and / or a colloid comprising hydrophobic particles hydrophilized with a surfactant. Furthermore, the wastewater treatment method of the present invention can suitably treat wastewater in which the hydrophilic particles and / or hydrophobic particles are resin particles, and the wastewater may be mixed wastewater containing two or more types of resin particles. Examples of mixed wastewater include wastewater containing hydrophilic vinyl acetate resin particles and hydrophilized hydrophobic vinyl chloride resin particles, and wastewater containing hydrophilic epoxy resin particles and hydrophilized hydrophobic olefin resin particles.

[0016] If the hydrocolloid concentration in the wastewater to be treated is high (the hydrocolloid content is high), the wastewater to be treated may be diluted with industrial water or wastewater from other systems within the factory before the coagulation treatment in order to promote the coagulation of the hydrocolloid.

[0017] In the treatment method of the present invention, the pH adjustment method in the pH adjustment step of the wastewater to be treated is not particularly limited, and can be carried out using a commonly used pH adjuster.

[0018] [pH adjuster] The pH adjuster is not particularly limited, and examples thereof include alkaline agents such as sodium hydroxide and potassium hydroxide when adjusting the pH of acidic or nearly neutral wastewater to the alkaline side, which can be used in the form of an aqueous solution when used. Also, examples thereof include oxidizing agents such as hydrochloric acid, sulfuric acid, and phosphoric acid when adjusting the pH of alkaline or nearly neutral wastewater to the acidic side, which can be used in the form of an aqueous solution when used. It is believed that by adjusting the pH of the wastewater to be treated to fall within a pH range of ±0.5 of the pH of an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient, and then adding the aqueous solution to the wastewater to be treated, the compound having a chain structure containing two or more aromatic rings as an active ingredient can be used as a coagulant to efficiently coagulate (form flocs) the hydrocolloids in the wastewater to be treated while maintaining the stability of the compound having a chain structure containing two or more aromatic rings as an active ingredient in the wastewater. Note that the mechanism by which the hydrocolloids in the wastewater to be treated can be efficiently separated and removed by adjusting the pH of the wastewater to fall within a pH range of ±0.5 of the pH of the aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient in the wastewater to be treated is not limited to the above.

[0019] [Compounds with a chain structure containing two or more aromatic rings] The aromatic ring of the compound having a chain structure containing two or more aromatic rings may be either a monocyclic ring or a fused polycyclic ring. Examples include a monocyclic aromatic ring such as a benzene ring, and a condensed polycyclic aromatic ring such as a naphthalene ring, an anthracene ring, and a phenanthrene ring, with a benzene ring being preferred among these. The chain structure is a structure in which aromatic rings are linked directly or indirectly, and is preferably a structure in which the aromatic rings are linked via at least one group selected from the group consisting of an ester group, an ether group, a thioether group, a sulfonyl group, and a hydrocarbon group.

[0020] Examples of the hydrocarbon group include linear or branched chain hydrocarbon groups or cyclic hydrocarbon groups having 1 to 10, preferably 1 to 6, carbon atoms. Examples of cyclic hydrocarbon groups include divalent or higher groups derived from monocyclic hydrocarbons such as cyclopentane, cyclohexane, cyclopentene, and cyclohexene, and divalent or higher groups derived from heteromonocyclic compounds such as oxolane, oxanethiolane, and thiane. Of these hydrocarbon groups, groups derived from oxane are more preferred. The chain may be either a straight chain or a branched chain, and for example, aromatic rings may be linked directly or indirectly via two or more hydrocarbon groups. The aromatic ring preferably has at least one type of group selected from the group consisting of a hydroxy group, an amino group, a carbonyl group, a carboxy group, a sulfo group, a nitro group, an alkyl group such as a methyl group, an ethyl group, a propyl group, or a butyl group, and an alkoxy group such as a methoxy group, an ethoxy group, a propoxy group, or a butoxy group. Of these, a hydroxy group is more preferred, and it is more preferred that the aromatic ring has two or more hydroxy groups.

[0021] The compound having a chain structure containing two or more aromatic rings is preferably a polyphenol compound having two or more phenolic hydroxy groups (i.e., hydroxy groups bonded to an aromatic ring such as a benzene ring, a naphthalene ring, an anthracene ring, or a biphenyl ring). The phenol structure having a phenolic hydroxy group may have two or more hydroxy groups, or may have a polar group such as those described above in addition to the hydroxy group on the aromatic ring.

[0022] The compound having a chain structure containing two or more aromatic rings is preferably a polyphenol compound having a chain structure containing two or more, preferably five or more, more preferably ten or more, aromatic rings having a phenolic hydroxy group. Furthermore, the polyphenol compound preferably has a chain structure as the main chain. The polyphenol compound preferably has a benzene ring as the aromatic ring and 10 or more phenolic hydroxy groups.

[0023] The polyphenol compound of the present invention is not particularly limited, but examples thereof include phenolic resins which may have a substituent and tannic acid. Among phenolic resins, water-soluble phenolic resins are preferred, and specific examples thereof include water-soluble resol resins.

[0024] The water-soluble resol resin can be obtained by reacting a phenol with an aldehyde in the presence of an alkali catalyst. Examples of phenols include phenol, cresol, xylenol, nonylphenol, p-tert-butylphenol, p-sec-butylphenol, naphtholcatechol, hydroquinone, methylhydroquinone, dimethylhydroquinone, etc., and these can be used alone or in combination of two or more. Among these, phenol is preferred. Examples of aldehydes include formaldehyde, paraformaldehyde, and trioxane (metaformaldehyde), and these can be used alone or in combination of two or more. Among these, paraformaldehyde is preferred.

[0025] The ratio of phenols to aldehydes is, for example, 40 to 100 parts by weight of 92% paraformaldehyde to 100 parts by weight of phenols. Examples of alkali catalysts include hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, and these can be used alone or in combination of two or more. Among these, potassium hydroxide and sodium hydroxide are preferred because of their good catalytic activity. The reaction conditions for the phenols and aldehydes may be set appropriately, and for example, the molecular weight of the resol resin can be adjusted by setting the conditions.

[0026] An aqueous solution containing a compound having a chain structure containing two or more aromatic rings can usually be prepared by dissolving the compound having a chain structure containing two or more aromatic rings in tap water or industrial water. The concentration of the aqueous solution containing the compound having a chain structure containing two or more aromatic rings is not limited, but from the viewpoint of ease of handling, it may be, for example, about 0.1 to 5 mass %.

[0027] The amount of a compound having a chain structure containing two or more aromatic rings as an active ingredient (hereinafter simply referred to as an organic compound) added to the wastewater to be treated can be appropriately set depending on the type of compound, the properties and amount of hydrocolloid contained in the wastewater to be treated, and is not particularly limited, but may be, for example, in the range of 1 to 1000 mg / L of the wastewater, preferably in the range of 50 to 1000 mg / L of the wastewater. The amount of the organic compound added to the wastewater is preferably 50 mg / L or more, more preferably 100 mg / L or more, and even more preferably 200 mg / L or more. The amount of the organic compound added to the wastewater is preferably 900 mg / L or less, more preferably 800 mg / L or less, and even more preferably 600 mg / L or less. In the present disclosure, the amount of the chemical agent such as the organic compound to be added to the wastewater can be selected by appropriately combining a suitable lower limit and an upper limit.

[0028] The wastewater treatment method of the present invention preferably further comprises an inorganic coagulant addition step of adding an inorganic coagulant. By further adding the inorganic coagulant to the wastewater to be treated, the total dosage of the compound having a chain structure containing two or more aromatic rings as an active ingredient and the inorganic coagulant, i.e., the amount of chemicals used in the wastewater treatment method, can be reduced, and the amount of coagulated material recovered by the wastewater treatment method of the present invention can be reduced.

[0029] [Inorganic coagulant] In the wastewater treatment method of the present invention, the hydrocolloid can be further coagulated by further using an inorganic coagulant. When an inorganic coagulant is further used in the present invention, the amount of the compound having a chain structure containing two or more aromatic rings used as an active ingredient can be reduced.From another point of view, by using the compound having a chain structure containing two or more aromatic rings as an active ingredient in combination with the inorganic coagulant, the amount of the inorganic coagulant used can be significantly reduced compared to the amount of the inorganic coagulant used in the conventional treatment method.

[0030] The inorganic coagulant is not particularly limited, but examples thereof include inorganic metal salts such as polyaluminum chloride (PAC), aluminum sulfate (aluminum sulfate), and ferric chloride, which can be used alone or in combination of two or more. These can be used in the form of an aqueous solution when used. The concentration of the aqueous solution of the inorganic coagulant is usually about 5 to 50 mass %.

[0031] Among the above inorganic coagulants, polyaluminum chloride (PAC) and aluminum sulfate (aluminum sulfate) are preferred because of their coagulation effect and ease of industrial availability.

[0032] The coagulation pH range of inorganic coagulants is usually pH 6 to 8, but because the coagulation effect can be obtained over a wide pH range, the pH of the wastewater to be treated when the inorganic coagulant is added may be pH 3 to 11. When the treatment method of the present invention includes an inorganic coagulant addition step in which an inorganic coagulant is added, the inorganic coagulant is preferably added to wastewater to be treated having a pH of 3 to 11, more preferably to wastewater to be treated having a pH of 4 to 10, and even more preferably to wastewater to be treated having a pH of 6 to 8. Furthermore, as a preliminary step to the inorganic coagulant addition step, a pH adjustment step in which the pH of the wastewater to be treated in the inorganic coagulant addition step may be included. The pH adjustment step in which the pH of the wastewater to be treated in the inorganic coagulant addition step is adjusted is a step in which the pH of the wastewater to be introduced into the inorganic coagulant addition step or the wastewater to be treated in the inorganic coagulant addition step before the inorganic coagulant is added is adjusted, and the pH of the wastewater to be treated in the inorganic coagulant addition step is preferably adjusted to 4 to 10, more preferably to 6 to 8. In the pH adjustment step of adjusting the pH of the wastewater in the inorganic coagulant addition step, the above-mentioned pH adjusters can be used.

[0033] The amount of inorganic coagulant to be added can be appropriately set depending on the type of inorganic coagulant, the properties and amount of hydrocolloid contained in the wastewater to be treated, the amount of coagulant to be added, etc., and is preferably 100 to 3000 mg / L of wastewater, for example. The amount of inorganic coagulant added to the wastewater (also referred to as the concentration (mg / L)) is preferably 150 mg / L or more, more preferably 200 mg / L or more. The amount of inorganic coagulant added to the wastewater is preferably 800 mg / L or less, more preferably 600 mg / L or less, and even more preferably 500 mg / L or less.

[0034] When an inorganic coagulant is used in combination, the amount of the compound having a chain structure containing two or more aromatic rings as an active ingredient added to the wastewater and the amount of the inorganic coagulant added to the wastewater may be 1:9 to 9:1, 1:6 to 6:1, or 2:5 to 5:2, and within these ranges, it is preferable that the amount of the compound having a chain structure containing two or more aromatic rings as an active ingredient added to the wastewater is large.

[0035] As described above, the amount of the compound having a chain structure containing two or more aromatic rings as an active ingredient and the amount of the inorganic coagulant added to the wastewater can be appropriately determined depending on the type of these additives, the properties and amount of the hydrocolloid contained in the wastewater to be treated, etc., and are not particularly limited. For example, when an inorganic coagulant is used in combination, the total amount of the compound having a chain structure containing two or more aromatic rings as an active ingredient and the inorganic coagulant added to the wastewater is preferably 1000 mg / L or less, more preferably 900 mg / L or less, and even more preferably 700 mg / L or less. According to the present invention, hydrocolloid particles in wastewater containing hydrocolloids are efficiently treated, and excellent solid-liquid separation effects are obtained, so the amount of inorganic coagulant added can be reduced, and even considering the total amount of the compound having a chain structure containing two or more aromatic rings as an active ingredient and the inorganic coagulant added, it tends to be lower than the amount of conventional inorganic coagulants added.

[0036] [Organic flocculant] In the wastewater treatment method of the present invention, an organic flocculant can also be used to flocculate the coagulated hydrocolloid. In the present invention, when an organic flocculant is further used, the coagulated matter of the hydrocolloid can be flocculated, and solid-liquid separation of the wastewater can be efficiently carried out.

[0037] The organic flocculant is not particularly limited as long as it can flocculate flocs formed by coagulation of a compound having a chain structure containing two or more aromatic rings as an active ingredient, or flocs formed by coagulation of the above compound and an inorganic coagulant. Examples include known polymer flocculants of the anionic, cationic, nonionic, and amphoteric types. Among these polymer flocculants, anionic polymer flocculants are preferred in terms of flocculation effect. Examples of anionic polymer flocculants include polyacrylamide partial hydrolysates obtained by partially hydrolyzing nonionic polyacrylamide, copolymers of polyacrylamide and sodium acrylate, copolymers of acrylamide, sodium acrylate, and sodium 2-acryloylamino-2-methylpropanesulfonate, and sodium polyacrylate. Specific examples include the anionic polymer flocculants used in the test examples. 。 The coagulant can be used in the form of an aqueous solution when used. The weight average molecular weight thereof is preferably about 50,000 to 30,000,000, and more preferably about 5,000,000 to 20,000,000.

[0038] The concentration of the aqueous solution of the organic flocculant is usually about 0.01 to 0.5% by mass. The flocculation pH range of the organic flocculant is usually pH 6 to 8, and it is preferable to adjust the pH of the wastewater to be treated to 6 to 8 before adding the organic flocculant to the wastewater to be treated. When the treatment method of the present invention includes an organic flocculant addition step of adding an organic flocculant, the organic flocculant is preferably added to wastewater to be treated having a pH of 6 or more and 8 or less. Furthermore, a pH adjustment step of adjusting the pH of the wastewater in the organic flocculant addition step may be included as a preliminary step to the organic flocculant addition step. The pH adjustment step of adjusting the pH of the wastewater in the organic flocculant addition step is a step of adjusting the pH of the wastewater to 6 to 8 before being introduced into the organic flocculant addition step, or the wastewater in the organic flocculant addition step before the organic flocculant is added. The pH adjustment agent described above can be used in the pH adjustment step of adjusting the pH of the wastewater in the organic flocculant addition step.

[0039] The amount of organic flocculant to be added can be appropriately determined depending on the properties and amount of the coagulated hydrocolloid (floc) contained in the wastewater to be treated, and is preferably 0.5 to 3 mg / L of the wastewater, for example. The amount of the flocculant to be added is more preferably 0.5 to 2 mg / L, and particularly preferably 0.5 to 1 mg / L.

[0040] [Processing equipment / processing operations] In the wastewater treatment method of the present invention, unit operations such as adding an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient to the wastewater, adding an inorganic coagulant or an organic flocculant, and stirring the treated wastewater during addition may be carried out using existing equipment. The selection of the equipment and the conditions for carrying out the unit operations may be determined appropriately depending on the status of the existing equipment. When adding the chemicals, it is preferable to stir the wastewater to increase the chance of contact between the hydrocolloids in the wastewater and the chemicals. The temperature of the wastewater to be treated may normally be the temperature of the water system in the factory, preferably about 10 to 80° C. If the water temperature is too low or too high, the coagulation and flocculation effects may decrease.

[0041] When an inorganic coagulant and an organic flocculant are further used, the order of treatment by adding (a) an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient, (b) an inorganic coagulant, and (c) an organic flocculant may be appropriately determined depending on the material type of each component, the properties and amount of the hydrocolloid contained in the wastewater to be treated, etc. The respective agents may be added simultaneously or separately for treatment. The order of addition of each agent may be, for example, (a) → (b) → (c) as in the test example described below, or (a) + (b) (simultaneous addition) → (c). Among these, the order of (a) → (b) → (c) is preferred in terms of the coagulation effect and aggregation effect.

[0042] The wastewater to be treated may have a pH within ±0.5 of the pH of the aqueous solution containing at least (a) a compound having a chain structure with two or more aromatic rings as an active ingredient when added. Specifically, in either case of the addition order (a) → (b) or (a) + (b) (simultaneous addition), the wastewater to be treated may be adjusted to a pH within ±0.5 of the pH of the aqueous solution containing the compound having a chain structure with two or more aromatic rings as an active ingredient before adding (a). (c) Before the addition, it is preferable to adjust the pH of the wastewater to be treated to 6 to 8, for example, as in the test examples described below.

[0043] When the wastewater treatment method of the present invention involves the addition of multiple chemicals, it may be a batch treatment in which chemicals are added sequentially in one reaction tank for treatment, or a continuous treatment in which the wastewater to be treated is transferred to the next reaction tank for treatment after each chemical addition.

[0044] In the wastewater treatment method of the present invention, the wastewater to be treated is adjusted to a pH range of ±0.5 of the pH of an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient, and after adding the aqueous solution containing the compound having a chain structure containing two or more aromatic rings as an active ingredient, it is preferable to adjust the pH of the treated water to near neutral (pH 6 to 8) using the above-mentioned known pH adjuster as appropriate, as in known wastewater treatments. The neutralized treated water can be subjected to other treatments as necessary and then discharged outside the factory as wastewater, or can be used as recycled water. [Example]

[0045] The present invention will be specifically explained below with reference to test examples, but the present invention is not limited to these examples.

[0046] The following compounds were used in the test examples: [Organic compounds] Phenolic resin with a chain structure containing two or more aromatic rings (sold by Katayama Nalco Co., Ltd.) Co., Ltd., product name: Floclan (registered trademark) C69, aqueous solution: pH 10) Compounds with a chain structure containing two or more aromatic rings (sold by Katayama Nalco Corporation, product name: Floclan (registered trademark) AC89, aqueous solution: pH 7) Compounds with a chain structure containing two or more aromatic rings (Kishida Chemical Co., Ltd., product name: 020-76012 Tannic acid, aqueous solution: pH 3)

[0047] [Other organic compounds] CAT-FLOC (registered trademark) 8793 PLUS (aqueous solution: pH 7), marketed by Katade Nalco Corporation as a water purification aid NALCOLYTE 8105 (aqueous solution: pH 7), marketed by Katayama Nalco Corporation as an "organic coagulant"

[0048] [Inorganic coagulant] Polyaluminum chloride (PAC) Aluminum sulfate (aluminum sulfate)

[0049] [Organic flocculant] Anionic polymer flocculant (sold by Katayama Nalco Corporation, product name: Floclan (registered trademark) A1205) In the table below, organic compounds, inorganic coagulants and organic flocculants are listed by abbreviation or product name.

[0050] (Test Example 1) In Test Examples 1-1 to 1-13, wastewater containing vinyl acetate resin particles and vinyl chloride resin particles (pH: 3.9) from a certain resin factory was used as wastewater containing hydrocolloids, and each test example was carried out according to the test procedures below.

[0051] (1) 300 mL of the above wastewater (pH: 3.9) was dispensed into a 300 mL glass beaker as wastewater containing hydrocolloid. (2) The pH of an aqueous solution of a compound having a chain structure containing two or more aromatic rings (also called an organic compound) was measured. The measurement results are shown in Tables 1 and 2 below. (3) Depending on the test conditions, sodium hydroxide solution is used as the alkaline component. DissolveThe pH of the wastewater was adjusted to the pH value of the wastewater at the time of adding the organic compound shown in Tables 1 and 2 below using the solution. (4) Depending on the test conditions, an aqueous solution containing an organic compound (an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient) was added to wastewater whose pH had been adjusted so that the amount of organic compound added to the wastewater was the amount shown in Tables 1 and 2 below, and the solution was stirred at 200 rpm for 1 minute using a mixer (manufactured by Miyamoto Seisakusho Co., Ltd. (now Daido Kogyosho Co., Ltd.), model: Jar Tester MJS-4H). (5) The inorganic coagulants shown in Tables 1 and 2 below were added to the wastewater in the amounts shown in Tables 1 and 2, and the mixture was stirred at 200 rpm for 1 minute using the above-mentioned stirrer. (6) The pH of the wastewater was adjusted to 7 using an aqueous sulfuric acid solution as the acid component (neutralization treatment). (7) The organic flocculants shown in Tables 1 to 4 were added to the wastewater in the amounts shown in Tables 1 to 4, and the mixture was stirred at 200 rpm for 1 minute using the stirrer. (8) The treated wastewater was allowed to stand for 5 minutes, and the appearance of the solid-liquid separation was visually observed. (9) In visual observation, the floc diameter was evaluated by comparing the flocs in the wastewater with several diagrams showing flocs of different diameters shown in a standard diagram showing floc diameter. (10) After standing for 5 minutes, the turbidity (NTU) of the wastewater was measured using a turbidity meter (manufactured by Kyoritsu Chemical Research Institute, Model: Lambda 9000) and a formazin standard solution in accordance with JIS K0101 "Testing Methods for Industrial Water." Note that the measurement limit for turbidity (NTU) is 100, so test examples with turbidity exceeding 100 are indicated as "over" in the table. The results obtained are shown in Tables 1 and 2.

[0052] The floc sizes shown in the table are classified as follows according to the measured floc diameter. D1: Floc diameter is 0.3 mm or more and less than 0.5 mm D2: Floc diameter is 0.5 mm or more and less than 0.75 mm D3: Floc diameter is 0.75 mm or more and less than 1.0 mm D4: Floc diameter is 1.0 mm or more and less than 1.5 mm D5: Floc diameter is 1.5 mm or more and less than 2.25 mm D6: Floc diameter is 2.25mm or more and less than 3.0mm D7: Flock diameter 3.0mm or more

[0053] (Evaluation criteria) ◎: Turbidity (NTU) is less than 50 and floc size is D5 or larger ○: Turbidity (NTU) is less than 50 and floc size is between D3 and D4 △: Turbidity (NTU) is between 50 and 100, or floc size is D2 or less ×: Turbidity (NTU) exceeds 100 The results obtained are shown in Tables 1 to 4 together with the treatment conditions.

[0054] [Table 1]

[0055] [Table 2]

[0056] According to Tables 1 and 2 above, in Test Examples 1-1 to 1-3, inorganic coagulants and organic flocculants were added, as in conventional methods for treating wastewater containing colloids, but in all cases the turbidity (NTU) of the treated wastewater exceeded 100, and the hydrocolloid particles in the wastewater could not be effectively coagulated and removed. As can be seen from Test Examples 1-4 to 1-7, 1-12, and 1-13, when the pH of the wastewater was adjusted to match the pH of an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient (organic compound in the table), and then the aqueous solution was added, the turbidity (NTU) of the treated wastewater was 100 or less, and the hydrocolloid particles in the wastewater were effectively coagulated. On the other hand, as can be seen from Test Examples 1-8 to 1-11, when the pH of the wastewater was not adjusted to match the pH of an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient (organic compound in the table), the turbidity (NTU) of the treated wastewater exceeded 100, and the hydrocolloid particles in the wastewater could not be effectively coagulated and removed. According to Tables 1 and 2, Test Examples 1-6 and 1-7 were evaluated as "Excellent" after treatment, confirming the particularly excellent coagulation effect of the hydrocolloid. Test Examples 1-6, 1-7, and Test Example 1-5 all had the same total concentration (mg / L) of the compound having a chain structure containing two or more aromatic rings as an active ingredient (organic compound in the table) and the inorganic coagulant (mg / L), both of which were 700 mg / L. However, the evaluation results of the treated wastewater shown in Test Examples 1-6 and 1-7 were superior to the evaluation results of the treated wastewater shown in Test Example 1-5. Based on these results, it is believed that a ratio of the concentration of the compound having a chain structure containing two or more aromatic rings as an active ingredient (organic compound in the table) to the concentration of the inorganic coagulant added to the wastewater of 1:9 to 9:1 (excluding 1:1) is more preferable.

[0057] (Test Example 2) In Test Examples 2-1 to 2-8, wastewater containing vinyl acetate resin particles and vinyl chloride resin particles (pH: 3.9) from a certain resin factory was used as the wastewater used in Test Example 1 above, i.e., wastewater containing hydrocolloid. Each Test Example was carried out according to the same test procedure as Test Example 1 above, except that in some Test Examples, the pH of an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient was adjusted, and in some Test Examples, an organic compound other than the compound having a chain structure containing two or more aromatic rings was used as an active ingredient.

[0058] (1) 300 mL of the above wastewater (pH: 3.9) was dispensed into a 300 mL glass beaker as wastewater containing hydrocolloid. (2) The pH of an aqueous solution containing an organic compound shown in Table 3 below (aqueous solution containing an organic compound) was measured. The measurement results are shown in Table 3 below. (3) Depending on the test conditions, use a sulfuric acid solution as the acid component or a sodium hydroxide solution as the alkaline component. Dissolve The pH of the wastewater was adjusted to the pH value of the wastewater at the time of adding the organic compound shown in Table 3 below using the solution. (4) Depending on the test conditions, the pH of the aqueous solution containing organic compounds is adjusted by using a sulfuric acid solution as the acid component or a sodium hydroxide solution as the alkaline component. Dissolve The aqueous solutions were adjusted to the pH shown in Table 3 below using the aqueous solutions. In Test Examples 2-1, 2-3, 2-5, and 2-7, the pH of the aqueous solutions containing organic compounds (compounds having a chain structure containing two or more aromatic rings as an active ingredient, or other organic compounds) was not adjusted, and the original pH of the aqueous solutions was used. (5) An aqueous solution containing an organic compound (an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient, or an aqueous solution containing other organic compounds) was added to the wastewater whose pH had been adjusted so that the amount of organic compound added to the wastewater was the amount shown in Table 3 below, and the solution was stirred at 200 rpm for 1 minute using an agitator (manufactured by Miyamoto Seisakusho Co., Ltd. (now Daido Kogyosho Co., Ltd.), model: Jar Tester MJS-4H). (6) The inorganic coagulant shown in Table 3 below was added to the wastewater in the amount shown in Table 3, and the mixture was stirred at 200 rpm for 1 minute using the above-mentioned stirrer. (7) Depending on the test conditions, a sulfuric acid solution was used as the acid component and a sodium hydroxide solution was used as the alkaline component, and the pH of the wastewater was adjusted to 7 (neutralization treatment). (8) The organic flocculant shown in Table 3 was added to the wastewater in the amount shown in Table 3, and the mixture was stirred at 200 rpm for 1 minute using the above stirrer. (9) The treated wastewater was allowed to stand for 5 minutes, and the appearance of the solid-liquid separation was visually observed. (10) In visual observation, the floc diameter was evaluated by comparing the flocs in the wastewater with several diagrams showing flocs of different diameters shown in a standard diagram showing floc diameter. (11) After standing for 5 minutes, the turbidity (NTU) of the wastewater was measured using a turbidity meter (manufactured by Kyoritsu Chemical Research Institute, Model: Lambda 9000) and a formazin standard solution in accordance with JIS K0101 "Testing Methods for Industrial Water." Note that the measurement limit for turbidity (NTU) is 100, so test examples with turbidity exceeding 100 are indicated as "over" in the table. The results obtained are shown in Table 3. The results obtained and the evaluation results according to the above evaluation criteria are shown in Table 3 below.

[0059] [Table 3]

[0060] From the results in Table 3 above, in Test Examples 2-1 to 2-4, when other organic compounds that do not contain a compound having a chain structure containing two or more aromatic rings as an active ingredient were used, even if the pH of the wastewater was adjusted to the pH of the aqueous solution containing the organic compound, the turbidity (NTU) of the treated wastewater exceeded 100, and an efficient coagulation effect of the hydrocolloids in the wastewater was not obtained. As shown in Test Examples 2-5 and 2-7, whether the aqueous solution containing a compound having a chain structure with two or more aromatic rings as an active ingredient is in the neutral range (pH 7) (Test Example 2-5) or the acidic range (pH 3) (Test Example 2-7), when the pH of the wastewater to be treated is adjusted to the pH of the original aqueous solution containing the compound having a chain structure with two or more aromatic rings as an active ingredient and then the aqueous solution is added, the turbidity (NTU) of the treated wastewater is less than 50, the floc size is D5, and it has been confirmed that the solution exhibits an excellent coagulation effect on the hydrocolloids in the wastewater. On the other hand, as shown in Test Examples 2-6 and 2-8, even when the pH of an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient was adjusted using an acidic or alkaline component, the pH of the wastewater to be treated was adjusted to a value similar to the pH of the adjusted aqueous solution, and the pH-adjusted aqueous solution was added to the pH-adjusted wastewater to be treated, the turbidity (NTU) of the treated wastewater exceeded 100 and the floc size was D1, and therefore an efficient coagulation effect of the hydrocolloids in the wastewater was not obtained.

[0061] (Test Example 3) In Test Examples 3-1 to 3-4, wastewater containing vinyl acetate resin particles and vinyl chloride resin particles (pH: 3.9) from a certain resin factory was used as the wastewater used in Test Example 1 above, i.e., wastewater containing hydrocolloid. Each test example was carried out using the same test procedure as Test Example 1 above, except that the amounts of a compound (organic compound) having a chain structure containing two or more aromatic rings as the active ingredient and an inorganic coagulant added were as shown in Table 4 below, and the pH of the wastewater when each agent was added was adjusted to the pH shown in Table 4 below. The results obtained and the evaluation results according to the above evaluation criteria are shown in Table 4 below.

[0062] [Table 4]

[0063] According to Table 4 above, the wastewater evaluation after treatment for Test Examples 3-1 to 3-4 was "Fair to Good," confirming the coagulation effect of the hydrocolloid for Test Example 3. Based on these results, it can be said that the ratio of the concentration of the compound having a chain structure containing two or more aromatic rings (organic compound in the table) added to the wastewater as an active ingredient to the concentration of the inorganic coagulant added is preferably 1:9 to 9:1, and more preferably 1:6 to 6:1. These results are similar to the discussion of the results of Test Examples 1-5 to 1-7 in Test Example 1 above.

Claims

1. A method for treating wastewater containing hydrocolloids, comprising: a pH adjustment step of adjusting the pH of the wastewater; an active ingredient addition step of adding an aqueous solution containing a compound having a chain structure containing two or more aromatic rings as an active ingredient to the wastewater whose pH has been adjusted in the pH adjustment step; In the pH adjustment step, the pH of the wastewater is adjusted to be within a pH range of ±0.5 of the pH value of the aqueous solution, The hydrocolloid includes a colloid containing hydrophilic particles and a colloid containing hydrophobic particles hydrophilized with a surfactant, the hydrophilic particles are vinyl acetate resins, the hydrophobic particles are made of a vinyl chloride resin, The compound having a chain structure containing two or more aromatic rings is a structure in which the aromatic ring is at least one type selected from the group consisting of a benzene ring and a naphthalene, and the chain structure is a structure in which the aromatic rings are linked via at least one group selected from the group consisting of an ester group and a hydrocarbon group.

2. 2. The method for treating wastewater according to claim 1, further comprising, after the step of adding the active ingredient, a coagulation step of adding an inorganic coagulant to coagulate the hydrocolloid.

3. The amount of the compound having a chain structure containing two or more aromatic rings as an active ingredient added to the wastewater and the amount of the inorganic coagulant added to the wastewater are 1:1.4 to 1:

9. The method for treating wastewater according to claim 2.

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