Method for treating wastewater containing hydrophilic colloids

Abstract

The object of this invention is to provide a method for efficiently treating wastewater containing hydrophilic colloids. [Solution] A method for treating wastewater containing hydrophilic colloids, 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 with 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 fall within a pH range of ±0.5 of the pH value of the aqueous solution.

Description

Technical Field

[0004]

[0001] The present invention relates to a method for treating wastewater containing hydrophilic colloids.

Background Art

[0002] ​​​​​​​​​​​​​​Furthermore, Patent Document 5 discloses a technique for agglomerating and separating resin-based particles in wastewater by adding a mixed composition of a thermal decomposition product consisting of a CaO-MgO-SiO2 system having a specific mass ratio and a metal salt consisting of an iron salt or a magnesium salt to wastewater containing a polymer emulsion or latex. Patent Document 6 discloses a technique for coagulating and separating resin-based particles in wastewater by mixing a thermal decomposition product consisting of a CaO-MgO-SiO2 system having a specific mass ratio with an aluminum-based inorganic flocculant or an aluminum-based inorganic flocculant and a polymer flocculant in wastewater containing a polymer emulsion or latex. Patent Document 7 discloses a technique for coagulation and precipitation treatment of polymerization wastewater of acidic vinyl chloride resin by adding polyhydric phenolic compounds such as tannic acid. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication 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 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, prior art, such as that proposed in Patent Documents 1 to 7, sometimes failed to achieve sufficient solid-liquid separation for special wastewater containing hydrophilic colloids. Furthermore, due to growing global environmental awareness, regulations and standards surrounding factories are becoming stricter, and there is a demand for more efficient and environmentally friendly wastewater treatment.

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

[0008] As a result of diligent research to solve the above problems, the present inventors have found that by adjusting the pH of the wastewater containing hydrophilic colloids to the pH of the aqueous solution before adding the aqueous solution containing a compound having a chain structure with two or more aromatic rings as an active ingredient, the treatment effect of the wastewater containing hydrophilic colloids is improved, that is, an excellent solid-liquid separation effect is obtained, and the water quality of the treated wastewater is improved, thus completing the present invention.

[0009] In other words, the present invention relates to the following processing method, although it is not limited thereto. [1] A method for treating wastewater containing hydrophilic colloids, 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 with 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 fall within a pH range of ±0.5 of the pH value of the aqueous solution. [2] The wastewater treatment method according to [1] above, further comprising a coagulation step of adding an inorganic coagulant after the active ingredient addition step to coagulate the hydrophilic colloid. [3] The wastewater treatment method 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 wastewater treatment method according to [3] above, wherein the polyphenol compound has the chain-like structure as its main chain. [5] The wastewater treatment method according to [3] above, wherein the polyphenol compound is a phenolic resin or tannic acid which may have substituents. [Effects of the Invention]

[0010] According to the present invention, a method for efficiently treating wastewater containing hydrophilic colloids can be provided. [Modes for carrying out the invention]

[0011] The present invention relates to a method for treating wastewater containing hydrophilic colloids, 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 with two or more aromatic rings as an active ingredient to the wastewater whose pH has been adjusted in the pH adjustment step, characterized in that the pH of the wastewater is adjusted in the pH adjustment step to fall within a pH range of ±0.5 of the pH value 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 value of the aqueous solution means adjusting the pH of the wastewater in the pH adjustment step to a pH of -0.5 or more and +0.5 or less of the pH value of the aqueous solution containing a compound having a chain structure with two or more aromatic rings as an active ingredient. For example, if the pH value of the aqueous solution is 10, the pH of the wastewater is adjusted to be between 9.5 and 10.5. In the processing method of the present invention, it is preferable to adjust the pH of the wastewater in the pH adjustment step to fall within a pH range of ±0.4 of the pH value of the aqueous solution, and more preferably to fall within a pH range of ±0.3. Furthermore, the pH value of an aqueous solution containing a compound having a chain structure with two or more aromatic rings as an active ingredient refers to the pH value of an aqueous solution obtained by dissolving the compound having a chain structure with two or more aromatic rings as an active ingredient in an aqueous solvent, and represents the original pH of the aqueous solution that is not affected by acidic or alkaline components.

[0012] The treatment method of the invention is used for treating wastewater containing hydrophilic colloids. Since hydrophilic colloids have a high affinity for water, in order to precipitate hydrophilic colloids, a method of causing salting out by using a large amount of electrolyte to precipitate and remove hydrophilic colloids is known. Also, as a method for treating wastewater containing general colloidal particles, a method of coagulating colloidal particles using an inorganic coagulant and an organic coagulant is also known. However, for wastewater containing hydrophilic colloids, there is room for further study on a method for effectively coagulating hydrophilic colloids in the wastewater. As a result of intensive studies by the inventors, in the treatment of wastewater containing hydrophilic colloids, by adjusting the pH of the above wastewater to fall within the 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 added to the above wastewater, it was found that the hydrophilic colloids in the wastewater to be treated can be efficiently coagulated.

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

[0014] Also, the hydrophilic colloid may be hydrophobic particles hydrophilized 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 polymer substances such as natural rubber. These particles are contained in wastewater from, for example, the manufacturing and / or processing processes of fibers, and the manufacturing processes of paints, papers, adhesives, synthetic resins, rubbers, etc. <0​​The wastewater treatment method of the present invention can preferably treat wastewater containing a hydrophilic colloid composed of a colloid containing hydrophilic particles and / or a colloid composed of hydrophobic particles hydrophilized with a surfactant. Further, the wastewater treatment method of the present invention can preferably 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 kinds of resin particles. Examples of the mixed wastewater include wastewater containing hydrophilic vinyl acetate resin-based resin particles and hydrophilized hydrophobic vinyl chloride resin-based resin particles, and wastewater containing hydrophilic epoxy resin particles and hydrophilized hydrophobic olefin resin particles.

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

[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 it can be carried out using a commonly used pH adjuster.

[0018] [pH adjuster] The pH adjuster is not particularly limited. For example, when adjusting the pH of wastewater near acidic or neutral to the alkaline side, alkaline agents such as sodium hydroxide and potassium hydroxide can be mentioned, and these can be used in the form of an aqueous solution during use. Also, for example, when adjusting the pH of wastewater near alkaline or neutral to the acidic side, oxidizing agents such as hydrochloric acid, sulfuric acid, and phosphoric acid can be mentioned, and these can be used in the form of an aqueous solution during use. By adjusting the pH of the wastewater to be treated to fall within ±0.5 of the pH value of an aqueous solution containing a compound having a chain structure with two or more aromatic rings as an active ingredient, and then adding the aqueous solution to the wastewater, it is believed that the stability of the compound having a chain structure with two or more aromatic rings as an active ingredient in the wastewater is maintained, while the compound acting as a coagulant efficiently promotes the coagulation (floc formation) of hydrophilic colloids in the wastewater. However, the mechanism by which hydrophilic colloids in the wastewater can be efficiently separated and removed from the water by adjusting the pH of the wastewater to be treated to fall within ±0.5 of the pH value of an aqueous solution containing a compound having a chain structure with two or more aromatic rings as an active ingredient is not limited to the above.

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

[0020] Examples of hydrocarbon groups include linear or branched chain hydrocarbon groups or cyclic hydrocarbon groups having 1 to 10 carbon atoms, 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, oxanthiolane, and thian. Among these hydrocarbon groups, groups derived from oxane are more preferred. Furthermore, the chain structure may be either linear or branched, and for example, aromatic rings may be directly or indirectly linked via two or more hydrocarbon groups. The aromatic ring preferably has at least one alkyl group such as a hydroxyl group, amino group, carbonyl group, carboxyl group, sulfo group, nitro group, methyl group, ethyl group, propyl group, or butyl group, or an alkoxy group such as a methoxy group, ethoxy group, propoxy group, or butoxy group. Among these, it is more preferable to have a hydroxyl group, and it is even more preferable for the aromatic ring to have two or more hydroxyl groups.

[0021] Compounds having a chain-like structure containing two or more aromatic rings are preferably polyphenol compounds having two or more phenolic hydroxyl groups (i.e., hydroxyl groups bonded to aromatic rings such as benzene rings, naphthalene rings, anthracene rings, and biphenyl rings). A phenolic structure having a phenolic hydroxyl group may have two or more hydroxyl groups, or it may have polar groups other than hydroxyl groups on the aromatic ring as described above.

[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, and more preferably ten or more aromatic rings having phenolic hydroxyl groups. Furthermore, it is preferable that the polyphenol compound has a chain-like structure as its main chain. The polyphenol compound is preferably one in which the aromatic ring is a benzene ring and has 10 or more phenolic hydroxyl groups.

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

[0024] Water-soluble resol resins can be obtained by reacting phenols and aldehydes in the presence of an alkaline catalyst. Examples of phenols include phenol, cresol, xylenol, nonylphenol, p-tert-butylphenol, p-sec-butylphenol, naphtholcatechol, hydroquinone, methylhydroquinone, and dimethylhydroquinone. These can be used individually 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 individually 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 per 100 parts by weight of phenols. Examples of alkaline catalysts include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide. These can be used individually or in combination of two or more. Among these, potassium hydroxide and sodium hydroxide are preferred due to their good catalytic activity. The reaction conditions between phenols and aldehydes can be set as appropriate; for example, the molecular weight of the resol resin can be adjusted by changing the conditions.

[0026] Aqueous solutions containing compounds having a chain-like structure with two or more aromatic rings can usually be prepared by dissolving such compounds in tap water or industrial water. The concentration of an aqueous solution containing a compound having a chain-like structure with 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% by mass.

[0027] The amount of a compound having a chain structure containing two or more aromatic rings (hereinafter also simply referred to as an organic compound) added to the wastewater to be treated can be appropriately set depending on the material type of the compound, the properties and amount of hydrophilic colloids contained in the wastewater to be treated, etc., and is not particularly limited, but for example it may be in the range of 1 to 1000 mg / L of wastewater, and preferably in the range of 50 to 1000 mg / L of 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. Furthermore, 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 this disclosure, the amount of the above-mentioned organic compound or other chemicals added to the wastewater can be appropriately combined to determine suitable lower and upper limits.

[0028] The wastewater treatment method of the present invention preferably further includes an inorganic coagulant addition step. This is because by further adding an inorganic coagulant to the wastewater to be treated, the total amount 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, thereby reducing the amount of coagulated material recovered by the wastewater treatment method of the present invention.

[0029] [Inorganic coagulant] The wastewater treatment method of the present invention can further coagulate hydrophilic colloids by using an inorganic coagulant. In the present invention, when an inorganic coagulant is further used, the amount of compound having a chain structure containing two or more aromatic rings as an active ingredient can be reduced. From another viewpoint, by using a compound having a chain structure containing two or more aromatic rings as an active ingredient in combination with an inorganic coagulant, the amount of inorganic coagulant used can be significantly reduced compared to the amount of inorganic coagulant used in conventional processing methods.

[0030] While not particularly limited, inorganic metal salts such as polyaluminum chloride (PAC), aluminum sulfate, and ferric chloride can be used individually or in combination of two or more. These can be used in aqueous solution form at the time of use. The concentration of an aqueous solution of an inorganic coagulant is typically around 5-50% by mass.

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

[0032] The pH range for the coagulation of inorganic coagulants is usually pH 6 to 8, but since a coagulation effect can be obtained over a wide pH range, the wastewater to be treated when adding the inorganic coagulant may have a pH of 3 to 11. When the treatment method of the present invention includes an inorganic coagulant addition step, the inorganic coagulant addition step is preferably performed on wastewater with a pH of 3 to 11, more preferably on wastewater with a pH of 4 to 10, and even more preferably on wastewater with a pH of 6 to 8. Furthermore, as a preliminary step to the inorganic coagulant addition step, there may be a pH adjustment step to adjust the pH of the wastewater in the inorganic coagulant addition step. The pH adjustment step to adjust the pH of the wastewater in the inorganic coagulant addition step is a step to adjust the pH of the wastewater introduced into the inorganic coagulant addition step, or the wastewater in the inorganic coagulant addition step before the inorganic coagulant is added, and it is preferable to adjust the pH of the wastewater in the inorganic coagulant addition step to 4 to 10, and more preferably to 6 to 8. In the pH adjustment step, which adjusts the pH of the wastewater in the inorganic coagulant addition step, the above-mentioned pH adjusting agent can be used.

[0033] The amount of inorganic coagulant added can be appropriately determined depending on the type of inorganic coagulant material, the properties and amount of hydrophilic colloids contained in the wastewater to be treated, and the amount of the above-mentioned coagulant added. For example, it is preferable that the amount is 100 to 3000 mg / L relative to the wastewater. The amount of inorganic coagulant added to the wastewater (also called the concentration (mg / L)) is preferably 150 mg / L or more, and more preferably 200 mg / L or more. Furthermore, 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 ratio of the amount of the compound having a chain structure containing two or more aromatic rings as an active ingredient added to the wastewater to 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. 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 greater.

[0035] As described above, the amount of compound having a chain structure containing two or more aromatic rings as an active ingredient added to the wastewater, and the amount of inorganic coagulant added, can be appropriately set depending on the material type of these additives, the properties and amount of hydrophilic colloids contained in the wastewater to be treated, etc., and are not particularly limited. However, for example, when an inorganic coagulant is used in combination, the total amount of compound having a chain structure containing two or more aromatic rings as an active ingredient added to the wastewater and the amount of 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, hydrophilic colloid particles in wastewater containing hydrophilic colloids are efficiently treated and an excellent solid-liquid separation effect is obtained, so the amount of inorganic coagulant added can be reduced, and even considering the total amount of compound having a chain structure containing two or more aromatic rings as an active ingredient added and the amount of inorganic coagulant added, it tends to be lower than the amount of conventional inorganic coagulant added.

[0036] [Organic flocculant] The wastewater treatment method of the present invention can also be used to further coagulate the coagulated hydrophilic colloid by using an organic coagulant. In the present invention, if an organic coagulant is further used, the hydrophilic colloidal aggregates can be coagulated, enabling efficient solid-liquid separation of wastewater.

[0037] The organic flocculant is not particularly limited as long as it can flocculate flocs formed by coagulation with a compound having a chain structure containing two or more aromatic rings as an active ingredient, or flocs formed by coagulation with the above compound and an inorganic flocculant. 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 their flocculation effect. Examples of anionic polymer flocculants include polyacrylamide partially hydrolyzed products 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. Specifically, the anionic polymer flocculant used in the test example can be used in aqueous solution form. Its weight-average molecular weight is preferably around 50,000 to 30 million, and more preferably around 5 million to 20 million.

[0038] The concentration of an aqueous solution of an organic flocculant is typically around 0.01 to 0.5% by mass. The pH range for flocculation of organic flocculants is typically pH 6 to 8, and it is preferable to adjust the pH of the wastewater to be treated to pH 6 to 8 before adding the organic flocculant to the wastewater. If the treatment method of the present invention includes an organic coagulant addition step in which an organic coagulant is added, it is preferable that the organic coagulant addition step be performed on wastewater to be treated having a pH of 6 or more and 8 or less. Furthermore, as a preliminary step to the organic coagulant addition step, there may be a pH adjustment step to adjust the pH of the wastewater in the organic coagulant addition step. The pH adjustment step to adjust the pH of the wastewater in the organic coagulant addition step is a step of adjusting the pH of the wastewater introduced into the organic coagulant addition step, or the wastewater in the organic coagulant addition step before the organic coagulant is added, to 6 to 8. The above-mentioned pH adjusting agent can be used in the pH adjustment step to adjust the pH of the wastewater in the organic coagulant addition step.

[0039] The amount of organic coagulant added can be appropriately determined depending on the properties and amount of the coagulated hydrophilic colloid (floc) contained in the wastewater to be treated, and is preferably 0.5 to 3 mg / L relative to the wastewater. A more preferable amount of flocculant to be added is 0.5 to 2 mg / L, with 0.5 to 1 mg / L being particularly preferable.

[0040] [Processing device / processing operation] In the wastewater treatment method of the present invention, unit operations such as adding an aqueous solution containing a compound having a chain structure with 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 the addition process can be carried out using existing equipment. The selection of these pieces of equipment and the conditions for performing their unit operations should be determined appropriately according to the existing equipment situation. When adding the drug, it is preferable to stir the mixture to increase the opportunity for the drug to come into contact with the hydrophilic colloids in the wastewater. Furthermore, the water temperature of the wastewater to be treated can usually be the same as the water temperature in the factory's water system, preferably around 10-80°C. If the water temperature is too low or too high, the coagulation and flocculation effects may decrease.

[0041] When inorganic coagulants and organic flocculants are used further, the order of treatment by adding (a) an aqueous solution containing a compound having a chain structure with 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 hydrophilic colloids contained in the wastewater to be treated, etc. Each drug may be added and treated simultaneously, or they may be added and treated separately. The order in which each agent is added may be, for example, (a) → (b) → (c) as in the test example described later, or (a) + (b) (simultaneous addition) → (c). Among these, the order (a) → (b) → (c) is preferred in terms of coagulation and flocculation effects.

[0042] The wastewater to be treated should have a pH of ±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 the aqueous solution is added. Specifically, in either the addition order (a) → (b) or (a) + (b) (simultaneous addition), the wastewater to be treated should be adjusted to a pH of ±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 adding the substance, it is preferable to adjust the pH of the wastewater to be treated to 6-8, for example, as shown in the test example described later.

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

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

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

[0046] The following compounds were used in the test examples. [Organic compounds] • Phenolic resin having a chain-like structure containing two or more aromatic rings (Distributor: Katayama Naruko Co., Ltd.) Company, Product name: Floclan (registered trademark) C69, Aqueous solution: pH 10) • Compounds having a chain-like structure containing two or more aromatic rings (Distributor: Katayama Naruko Co., Ltd., Product name: Floclan® AC89, Aqueous solution: pH 7) • Compounds having a chain-like structure containing two or more aromatic rings (manufactured by Kishida Chemical Co., Ltd., product name: 020-76012 Tannic acid, aqueous solution: pH 3)

[0047] [Other organic compounds] CAT-FLOC(registered trademark) 8793PLUS (aqueous solution: pH 7), marketed by Katade Naruko Co., Ltd. as a "water purification aid." • NALCOLYTE8105 (aqueous solution: pH 7), marketed as an "organic coagulant" by Katayama Naruko Co., Ltd.

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

[0049] [Organic flocculant] • Anionic polymer flocculant (Distributor: Katayama Naruko Co., Ltd., Product name: Floclan (registered trademark) A1205) In the table below, organic compounds, inorganic coagulants, and organic flocculants are indicated by their abbreviations or product names.

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

[0051] (1) 300 mL of the wastewater (pH: 3.9) containing hydrophilic colloids was taken out and placed in a 300 mL glass beaker. (2) The pH of aqueous solutions of compounds (also called organic compounds) having a chain structure containing two or more aromatic rings was measured. The measurement results are shown in Tables 1 and 2 below. (3) Depending on the test conditions, a sodium hydroxide aqueous bath solution was used as the alkaline component, and the pH of the wastewater was adjusted to the pH value of the wastewater when organic compounds were added, as shown in Tables 1 and 2 below. (4) Depending on the test conditions, an aqueous solution containing an organic compound (an aqueous solution having a chain structure containing two or more aromatic rings as an active ingredient) was added to pH-adjusted wastewater so that the amount of organic compound added to the wastewater was as shown in Tables 1 and 2 below, and the mixture was stirred for 1 minute at a rotation speed of 200 rpm using a stirrer (Miyamoto Seisakusho Co., Ltd. (now Daido Kogyosho Co., Ltd.), model: Jar Tester MJS-4H). (5) The inorganic coagulants listed in Tables 1 and 2 below were added to the wastewater in the amounts listed in Tables 1 and 2, and the mixture was stirred for 1 minute at a rotation speed of 200 rpm using the above-mentioned agitator. (6) A sulfuric acid solution was used as the acid component to adjust the pH of the wastewater to 7 (neutralization treatment). (7) The organic flocculants listed in Tables 1 to 4 were added to the wastewater in the amounts listed in Tables 1 to 4, and the mixture was stirred for 1 minute at a rotation speed of 200 rpm using the above-mentioned agitator. (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 multiple diagrams showing flocs of different diameters, as shown in the standard diagram representing floc diameter, with the flocs in the wastewater. (10) For wastewater treated by standing for 5 minutes, the turbidity (NTU) was measured in accordance with JIS K0101 "Test Methods for Industrial Water" using a turbidimeter (manufactured by Kyoritsu Chemical Research Institute Co., Ltd., model: Lambda 9000) and formazin standard solution. Since the detection limit for turbidity (NTU) is 100, test examples where the turbidity exceeds 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 floc diameter obtained by measurement. 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 1.5mm or more and less than 2.25mm D6: Floc diameter is 2.25 mm or more and less than 3.0 mm D7: Floc diameter of 3.0 mm 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, along with the processing conditions, are shown in Tables 1-4.

[0054] [Table 1]

[0055] [Table 2]

[0056] According to Tables 1 and 2 above, although test examples 1-1 to 1-3 added inorganic coagulants and organic flocculants, similar to conventional wastewater treatment methods containing colloids, the turbidity (NTU) of the treated wastewater exceeded 100 in all cases, indicating that the hydrophilic colloidal 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 chain-like compound with two or more aromatic rings (organic compounds in the table) as an active ingredient, and then the above aqueous solution was added, the turbidity (NTU) of the treated wastewater became 100 or less, and hydrophilic colloidal 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 above aqueous solution containing a chain-like compound with two or more aromatic rings (organic compounds in the table) was added without adjusting the pH of the wastewater to match that of the aqueous solution, the turbidity (NTU) of the treated wastewater exceeded 100, indicating that the hydrophilic colloidal particles in the wastewater could not be effectively coagulated and removed. According to Tables 1 and 2 above, Test Examples 1-6 and 1-7 received a "◎" rating for wastewater evaluation after treatment, confirming particularly excellent coagulation effects of hydrophilic colloids. Although Test Examples 1-6, 1-7, and 1-5 all share the same total concentration of 700 mg / L for the addition of a chain-like compound containing two or more aromatic rings as an active ingredient (organic compound in the table) and the addition of an inorganic coagulant, the evaluation results of the wastewater after treatment shown in Test Examples 1-6 and 1-7 were superior to those shown in Test Example 1-5. Based on these results, it is considered that a ratio of 1:9 to 9:1 (excluding 1:1) for the addition of a chain-like compound containing two or more aromatic rings as an active ingredient (organic compound in the table) to the addition of an inorganic coagulant is more preferable for wastewater.

[0057] (Test Example 2) In Test Examples 2-1 to 2-8, the wastewater used in Test Example 1, i.e., wastewater containing hydrophilic colloids, was wastewater containing vinyl acetate resin particles and vinyl chloride resin particles (pH: 3.9) from a certain resin factory. Except for adjusting the pH of the aqueous solution containing a compound with a chain structure containing two or more aromatic rings as the active ingredient in some Test Examples, and using other organic compounds that do not contain a compound with a chain structure containing two or more aromatic rings as the active ingredient in some Test Examples, each Test Example was carried out according to the same test procedure.

[0058] (1) 300 mL of the wastewater (pH: 3.9) containing hydrophilic colloids was taken out and placed in a 300 mL glass beaker. (2) The pH of aqueous solutions containing the organic compounds shown in Table 3 below was measured. The measurement results are shown in Table 3 below. (3) Depending on the test conditions, an aqueous sulfuric acid solution was used as the acid component, or a sodium hydroxide aqueous bath solution was used as the alkaline component, and the pH of the wastewater was adjusted to the pH value of the wastewater when organic compounds were added as shown in Table 3 below. (4) Depending on the test conditions, the pH of the aqueous solution containing the organic compound was adjusted to the pH shown in Table 3 below by using an aqueous sulfuric acid solution as the acid component or a sodium hydroxide aqueous bath solution as the alkaline component. In Test Examples 2-1, 2-3, 2-5, and 2-7, the pH of the aqueous solution containing the organic compound (a compound 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 solution was used. (5) An aqueous solution containing an organic compound (an aqueous solution containing a compound having a chain structure with two or more aromatic rings as an active ingredient, or an aqueous solution containing other organic compounds) was added to pH-adjusted wastewater so that the amount of organic compound added to the wastewater was as shown in Table 3 below, and the mixture was stirred for 1 minute at a rotation speed of 200 rpm using a stirrer (Miyamoto Seisakusho Co., Ltd. (now Daido Kogyosho Co., Ltd.), model: Jar Tester MJS-4H). (6) The inorganic coagulants listed in Table 3 below were added to the wastewater in the amounts listed in Table 3, and the mixture was stirred for 1 minute at a rotation speed of 200 rpm using the above-mentioned agitator. (7) Depending on the test conditions, an aqueous sulfuric acid solution was used as the acid component and an aqueous sodium hydroxide solution as the alkaline component to adjust the pH of the wastewater to 7 (neutralization treatment). (8) The organic flocculants listed in Table 3 were added to the wastewater in the amounts listed in Table 3, and the mixture was stirred for 1 minute at a rotation speed of 200 rpm using the above-mentioned agitator. (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 multiple diagrams showing flocs of different diameters, as shown in the standard diagram representing floc diameter, with the flocs in the wastewater. (11) For wastewater treated by standing for 5 minutes, the turbidity (NTU) was measured using a turbidimeter (manufactured by Kyoritsu Chemical Research Institute Co., Ltd., model: Lambda 9000) and formazin standard solution in accordance with JIS K0101 "Test Methods for Industrial Water". Since the detection limit for turbidity (NTU) is 100, test examples where the turbidity exceeds 100 are indicated as "over" in the table. The results obtained are shown in Table 3. The results obtained and the evaluation results in accordance with 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 compounds with a chain structure containing two or more aromatic rings were used as active ingredients, even if the pH of the wastewater was adjusted to match the pH of the aqueous solution containing the organic compound, the turbidity (NTU) of the treated wastewater exceeded 100, indicating that an efficient coagulation effect of hydrophilic colloids in the wastewater could not be obtained. As shown in Test Examples 2-5 and 2-7, when an aqueous solution containing a chain-like compound with two or more aromatic rings as an active ingredient is added after adjusting the pH of the wastewater to be treated to match the pH of the original aqueous solution containing the chain-like compound with two or more aromatic rings as an active ingredient, regardless of whether the aqueous solution is in the neutral range (pH 7) (Test Example 2-5) or the acidic range (pH 3) (Test Example 2-7), the turbidity (NTU) of the treated wastewater is less than 50, the floc size is D5, and it was confirmed that the aqueous solution exhibits an excellent coagulation effect on hydrophilic colloids in the wastewater. On the other hand, as shown in Test Examples 2-6 and 2-8, even after adjusting the pH of an aqueous solution containing a compound having a chain structure with two or more aromatic rings as an active ingredient using an acidic or alkaline component, and then adjusting the pH of the wastewater to be treated to a value similar to that of the adjusted aqueous solution, and adding the pH-adjusted aqueous solution to the pH-adjusted wastewater, the turbidity (NTU) of the treated wastewater exceeded 100, and the floc size was D1, indicating that an efficient coagulation effect of hydrophilic colloids in the wastewater could not be obtained.

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

[0062] [Table 4]

[0063] According to Table 4 above, the wastewater evaluation after treatment in Test Examples 3-1 to 3-4 was "△ to ○", and the coagulation effect of the hydrophilic colloid was confirmed in Test Example 3. Based on these results, the 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) added to the wastewater 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 hydrophilic colloids, A pH adjustment step to adjust the pH of the wastewater, The process includes an active ingredient addition step, in which an aqueous solution containing a compound having a chain-like structure with two or more aromatic rings as an active ingredient is added 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 fall within a pH range of ±0.5 of the pH value of the aqueous solution. Methods for treating wastewater.

2. The wastewater treatment method according to claim 1, further comprising a coagulation step of adding an inorganic coagulant after the active ingredient addition step to coagulate the hydrophilic colloid.

3. The wastewater treatment method according to claim 1 or 2, wherein the compound having a chain-like structure containing two or more aromatic rings is a polyphenol compound.

4. The wastewater treatment method according to claim 3, wherein the polyphenol compound has the chain-like structure as its main chain.

5. The wastewater treatment method according to claim 3, wherein the polyphenol compound is a phenolic resin or tannic acid which may have substituents.

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