How to reuse wastewater

Abstract

To provide a reusing method of waste water capable of reusing the waste water containing a surfactant and an oil by purification in a simple method.SOLUTION: In a reusing method of waste water where (a) a polymer coagulant (hereafter described as (a) component) having spinnability and (b) bentonite (hereafter described as (b) component) are mixed in the waste water and an aqueous layer is reused as water after standing,: the waste water containing a surfactant and an oil is mixed with the (b) component at a ratio of 5 pts.mass or more and 100 pts.mass or less to 1,000 pts.mass of the waste water; and the (a) component and the (b) component are mixed so that a mass ratio (b) / (a) becomes 100 or more and 3,000 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for reusing wastewater. [Background technology]

[0002] Ensuring safe water is one of the most important activities in everyday life. In developed countries, infrastructure for water use is being developed. However, there are still many areas on the planet where sufficient water cannot be secured, and the people living in such areas are forced to make a great effort to secure water. Therefore, there is a strong demand for technology that can easily purify contaminants such as sludge present in river water, lake water, groundwater, rainwater, etc. In addition, water that needs to be treated includes wastewater discharged from washing objects contaminated with oil in everyday life and various industrial fields. Some of these contain oils, such as oily animal and vegetable oils and petroleum-based hydrocarbons, which are sources of contamination, and surfactants contained in cleaning agents, etc.

[0003] Patent Document 1 describes a coagulation and sedimentation treatment method in which bentonite is used alone or in combination with an inorganic or organic precipitant as an adsorbent and coagulation aid for removing water-soluble substances from industrial wastewater. Patent Document 2 describes an agent for treating surfactant-containing wastewater, which contains a formaldehyde condensate obtained by condensation reaction of dihydroxydiphenyl sulfones, an aromatic compound having a sulfonic acid group, and formaldehyde. Patent Document 3 describes a method for treating wastewater containing resin particles (A) having a volume average particle diameter of 0.0005 to 500 μm, a surfactant (B) and / or a water-soluble polymer (C), the method including a step of adding an inorganic flocculant (a), a step of adding a polymer flocculant (b), and a step of adding an organic coagulant (c) as necessary. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 48-40260 [Patent Document 2] JP 2001-96279 A [Patent Document 3] JP 2006-7208 A Summary of the Invention [Problem to be solved by the invention]

[0005] Currently, wastewater discharged from laundry, washing dishes, washing the body, etc. is disposed of as is, and it cannot be said that it is sufficiently reused. This is because wastewater often contains surfactants and oil, and surfactants, oil themselves, and oily dirt emulsified, solubilized, or dispersed by surfactants cannot be easily separated from water. The reuse of wastewater needs to be considered from a different perspective than the reuse of industrial water and waste liquid treatment that meets environmental standards. That is, in order to treat and reuse wastewater in general households, etc., a method is required that allows easy reuse, for example, when flocculating contaminants to form flocs (also called flocs) and separating them, the flocs should settle easily and in a short time, and the supernatant should be usable without filtration. In addition, by purifying wastewater containing surfactants and oil, water resources can be effectively utilized as grey water to be used, for example, for cleaning oily dirt and flushing toilets.

[0006] The present invention provides a method for recycling wastewater, which can purify and reuse wastewater containing a surfactant and oil in a simple manner. [Means for solving the problem]

[0007] The present invention relates to a method for recycling wastewater, which comprises mixing (a) a polymer flocculant having a spinnability (hereinafter referred to as component (a)) and (b) bentonite (hereinafter referred to as component (b)) with the wastewater, allowing the mixture to stand, and then recycling the aqueous layer as water, The wastewater contains a surfactant and an oil, (b) component is mixed in a ratio of 5 parts by mass to 100 parts by mass to 1,000 parts by mass of wastewater; The component (a) and the component (b) are mixed so that the mass ratio of (b) / (a) is 100 or more and 3000 or less. This relates to a method for reusing wastewater. Effect of the Invention

[0008] According to the present invention, there is provided a method for recycling wastewater, which can purify and reuse wastewater containing surfactants and oil in a simple manner. The method of the present invention is excellent in the purification effect of wastewater containing surfactants and oil, and can quickly form coagulates even in wastewater containing surfactants and oil, and can efficiently remove surfactants and oil. Furthermore, the water layer obtained after treatment by the method of the present invention is clear and clean. In other words, the method of recycling wastewater of the present invention can produce reusable water from wastewater. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] As mentioned above, wastewater often contains surfactants and oils. The present invention is directed to reusing wastewater containing surfactants and oils. In the present invention, it is presumed that the (b) component aggregates the surfactants, oils, and other contaminants in the wastewater to form aggregates, and that the (a) component is present between the aggregates to promote the bonding of the aggregates. Since the (a) component has a spinnability, it is presumed that the (a) component is entangled with the aggregates to further promote the bonding of the aggregates. As a result, in the present invention, even in wastewater containing surfactants and oils, it is considered that the aggregates are formed quickly and an excellent purification effect is exhibited. Even if a polymer compound known as a flocculant is used, if it does not have a spinnability, it takes a long time for the aggregates to settle, and the effect of the present invention cannot be obtained.

[0010] Component (a) is a polymer flocculant having spinnability.

[0011] In the present disclosure, "spinnability" refers to the property of "pulling threads" in which the elongation characteristics of an object appear, and one example of this is "natto threading". In one or more embodiments, spinnability refers to the property of exhibiting a continuous thread-like structure without breaking to form droplets when a liquid composition is dropped at a low speed or stretched by holding one end of the liquid composition, and one example of this is "the threading of animal and plant mucus". Spinnability is one of the elastic relaxation phenomena of a liquid composition, and is generally known to be a physical property completely independent of surface tension and viscosity. The presence or absence of spinnability of component (a) can be determined by the following method. For example, a polymer flocculant is dissolved in purified water to a predetermined concentration (e.g., 10% by mass) to obtain an aqueous solution, and the result is determined by the method described below in [Method for determining spinnability]. If the polymer flocculant has spinnability, it can be determined that the polymer flocculant has spinnability.

[0012] [Threadability determination method] When gently dropped from a Pasteur pipette (glass, for example, ASAHITECHNOGLASS, IK-PAS-5P) with an inner tip diameter of 1 mm, an aqueous solution that forms threads can be considered to be an aqueous solution exhibiting spinnability in the present disclosure.

[0013] Component (a) is preferably a polymer flocculant that exhibits spinnability in an aqueous solution having a concentration of 30 g / L or less, more preferably a polymer flocculant that exhibits spinnability in an aqueous solution having a concentration of 10 g / L or less, and even more preferably a polymer flocculant that exhibits spinnability in an aqueous solution having a concentration of 5 g / L or less.

[0014] The weight average molecular weight of component (a) is preferably 500,000 or more, more preferably 800,000 or more, even more preferably 2 million or more, and preferably 15 million or less, more preferably 12 million or less, even more preferably 10 million or less. The weight average molecular weight of component (a) is calculated from the intrinsic viscosity for polyethylene oxide, and is calculated from gel permeation chromatography (GPC) for the others.

[0015] (a) As the polymer flocculant component, there may be mentioned a water-soluble (co)polymer having a water-soluble monomer (a1) as a constituent unit and comprising a water-soluble (co)polymer having drawability. The water-soluble monomer (a1) includes the following nonionic monomer (a11), cationic monomer (a12), anionic monomer (a13), and a mixture of two or more of these. The water-soluble monomer is preferably a water-soluble unsaturated monomer. As the monomer constituting the water-soluble (co)polymer, a water-insoluble unsaturated monomer (x) and a crosslinkable monomer (y) may be used in combination with the water-soluble monomer (a1) as necessary, as long as the effects of the present invention are not inhibited. Among the water-soluble copolymers having the following water-soluble monomers as constituent units, those having drawability can be used as the component (a) of the present invention.

[0016] Here, the water-soluble monomer or water-soluble (co)polymer means a monomer or (co)polymer having a solubility in water (20 °C) of 1 g / 100 g of water or more, and the water-insoluble monomer means a monomer having a solubility in water (20 °C) of less than 1 g / 100 g of water.

[0017] In the following, the number average molecular weight measured by gel permeation chromatography (GPC) method is abbreviated as GMn, and the weight average molecular weight is abbreviated as GMw. The GMn and GMw are determined under the following GPC measurement conditions. GPC measurement conditions <GPC measurement conditions> Apparatus: HLC-802A, manufactured by Tosoh Corporation Column: TSKgel GMH6 (two columns) Measurement temperature: 40 °C Sample solution: 0.5 mass% tetrahydrofuran solution Solution injection volume: 200 μl Detector: Refractive index detector Standard: Polyethylene glycol

[0018] (a11) (Meth)acrylate The following, and mixtures thereof are included. (a11-1) (Meth)acrylic acid ester The number of carbon atoms (hereinafter abbreviated as C) is 4 or more and the number average molecular weight (measured by gel permeation chromatography (GPC), hereinafter abbreviated as GMn) is 5,000 or less, for example, hydroxyl group-containing (meth)acrylates (e.g., hydroxyethyl-, diethylene glycol mono-, polyethylene glycol (polymerization degree 3 to 50) mono-, and polyglycerol (polymerization degree 1 to 10) mono(meth)acrylates) and alkyl acrylates (alkyl group is C1 to 2) esters (C4 to 5, for example, methyl acrylate, ethyl acrylate). (a11-2) (Meth)acrylamide and its derivatives C3 to 30, for example, (meth)acrylamide, N-alkyl (C1 to 3) (meth)acrylamide [N-methyl and isopropyl (meth)acrylamide, etc.], N-alkylol (meth)acrylamide [N-methylol (meth)acrylamide, etc.] (a11-3) Nitrogen-containing ethylenically unsaturated compounds other than those mentioned above C3 to 30, such as acrylonitrile, N-vinylformamide, N-vinyl-2-pyrrolidone, N-vinylimidazole, N-vinylsuccinimide, N-vinylcarbazole, and 2-cyanoethyl (meth)acrylate. (a11-4) Alkylene oxide Ethylene oxide, propylene oxide

[0019] (a12) Cationic monomer Examples of such compounds include the following, their salts (for example, inorganic acid salts (hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, etc.), methyl chloride salt, dimethyl sulfate salt, benzyl chloride salt, etc.), and mixtures thereof. (a12-1) Nitrogen atom-containing (meth)acrylate C5 to 30, for example, aminoalkyl (C2 to 3) (meth)acrylate, N,N-dialkyl (C1 to 2) aminoalkyl (C2 to 3) (meth)acrylate [N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-diethylaminopropyl (meth)acrylate, etc.], heterocycle-containing (meth)acrylate [N-morpholinoethyl (meth)acrylate, etc.] (a12-2) Nitrogen atom-containing (meth)acrylamide derivatives C5 or more and 30 or less, for example, N,N-dialkyl (C1 or more and 2 or less) aminoalkyl (C2 or more and 3 or less) (meth)acrylamide [N,N-dimethylaminoethyl (meth)acrylamide, etc.]; (a12-3) Ethylenically unsaturated compounds having an amino group C5 to 30, e.g., vinylamine, vinylaniline, (meth)allylamine, p-aminostyrene, etc. (a12-4) Compounds having an amine imide group C5 or more and 30 or less, for example, 1,1,1-trimethylamine (meth)acrylamide, 1,1-dimethyl-1-ethylamine (meth)acrylamide, 1,1-dimethyl-1-(2'-phenyl-2'-hydroxyethyl)amine (meth)acrylamide, etc. (a12-5) Nitrogen-containing vinyl monomers other than those mentioned above C5 to 30, e.g., 2-vinylpyridine, 3-vinylpiperidine, vinylpyrazine, vinylmorpholine

[0020] (a13) Anionic monomer Examples include the following acids, their salts [alkali metal (lithium, sodium, potassium, etc., same below) salts, alkaline earth metal (magnesium, calcium, etc., same below) salts, ammonium salts and amine (C1 to 20) salts, etc.], and mixtures of these. (a13-1) Unsaturated carboxylic acid C3 to 30, e.g. (meth)acrylic acid, (anhydrous) maleic acid, fumaric acid, (anhydrous) itaconic acid, vinyl benzoic acid, allyl acetic acid (a13-2) Unsaturated sulfonic acid Aliphatic unsaturated sulfonic acids with C2 to 20 (vinyl sulfonic acid, etc.), aromatic unsaturated sulfonic acids with C6 to 20 (styrene sulfonic acid, etc.), sulfonic acid group-containing (meth)acrylates [sulfoalkyl (C2 to 20) (meth)acrylates [2-(meth)acryloyloxyethanesulfonic acid, 2-(meth)acryloyloxypropanesulfonic acid, 3-(meth)acryloyloxypropanesulfonic acid, 2-(meth)acryloyloxybutanesulfonic acid, 4-(meth)acryloyloxybutanesulfonic acid, 2-(meth)acryloyloxy-2,2-dimethylethanesulfonic acid, p-(meth)acryloyloxymethylbenzenesulfonic acid, etc.], sulfonyl (meth)acrylamide containing an isopropyl group [2-(meth)acryloylaminoethanesulfonic acid, 2- and 3-(meth)acryloylaminopropanesulfonic acid, 2- and 4-(meth)acryloylaminobutanesulfonic acid, 2-(meth)acryloylamino-2,2-dimethylethanesulfonic acid, p-(meth)acryloylaminomethylbenzenesulfonic acid, etc.], alkyl (C1 to 20) (meth)allyl sulfosuccinate [methyl (meth)allyl sulfosuccinate, etc.], etc. (a13-3) (meth)acryloyl polyoxyalkylene (C1 to 6) sulfate ester, (meth)acryloyl polyoxyethylene (degree of polymerization 2 to 50) sulfate ester, etc.

[0021] Examples of the water-insoluble unsaturated monomer (x) that may be used in combination with (a) if necessary include the following (x1) to (x5) and mixtures thereof.

[0022] (x1) (Meth)acrylate with C6 or more and C23 or less Aliphatic or alicyclic alcohol (C3 to 20) (meth)acrylates [propyl, butyl, lauryl, octadecyl, and cyclohexyl (meth)acrylate, etc.] and epoxy group-containing (meth)acrylates (C4 to 20) [glycidyl (meth)acrylate, etc.]

[0023] (x2) Unsaturated carboxylic acid monoester of [monoalkoxy (C1 to 20)-, monocycloalkoxy (C3 to 12)-, or monophenoxy]polypropylene glycol (hereinafter abbreviated as PPG) (degree of polymerization 2 to 50) (Meth)acrylic acid esters of propylene oxide (hereinafter abbreviated as PO) adducts of monools (C1 to 20) or monohydric phenols (C6 to 20) [ω-methoxy PPG mono(meth)acrylate, ω-ethoxy PPG mono(meth)acrylate, ω-propoxy PPG mono(meth)acrylate, ω-butoxy PPG mono(meth)acrylate, ω-cyclohexyl PPG mono(meth)acrylate, ω-phenoxy PPG mono(meth)acrylate, etc.] and (meth)acrylic acid esters of PO adducts of diols (C2 to 20) or dihydric phenols (C6 to 20) [ω-hydroxyethyl (poly)oxypropylene mono(meth)acrylate, etc.], etc.

[0024] (x3) Unsaturated hydrocarbons with C2 to 30 Ethylene, nonene, styrene, 1-methylstyrene, etc. (x4) Carboxylic acid (C2 to 30) esters of unsaturated alcohols [C2 to 4, e.g., vinyl alcohol, (meth)allyl alcohol] (e.g., vinyl acetate) (x5) Halogen-containing monomers (C2 to 30, e.g., vinyl chloride)

[0025] Examples of the crosslinkable monomer (y) include the following (y1) to (y5), their salts (for example, for basic monomers, inorganic acid salts (hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, sulfurous acid, phosphoric acid, nitric acid, etc.), methyl chloride salt, dimethyl sulfate salt, benzyl chloride salt, etc., and for acidic monomers, alkali metal salts, alkaline earth metal salts, and amine (C1 to 20, for example methylamine, ethylamine, cyclohexylamine) salts) and mixtures thereof).

[0026] (y1) Bispoly(2 to 4)(meth)acrylamide C5 to 30, e.g., N,N'-methylenebisacrylamide

[0027] (y2) Poly(2 to 4) (meth)acrylate C8 to 30, e.g., ethylene glycol di(meth)acrylate, pentaerythritol [poly(2 to 4)] (meth)acrylate

[0028] (y3) Monomer containing vinyl groups (2 to 20) C4 or more and GMn 6,000 or less, such as divinylamine, polyhydric (2 to 5) amines [C2 or more and GMn 3,000 or less, such as ethylenediamine, polyethyleneimine (C4 or more and GMn 3,000 or less)] poly(2 to 20) vinylamines, divinyl ethers, polyhydric alcohols [C2 or more and GMn 3,000 or less, such as alkylene (C2 to 6) glycols [ethylene glycol, propylene glycol, 1,6-hexanediol (hereinafter abbreviated as EG, PG, and HD, respectively)], polyoxyalkylenes [GMn 2,000 or more and 3,000 or less, such as For example, polyethylene glycol (hereinafter abbreviated as PEG) (molecular weight 106 or more and GMn 3,000 or less), PPG (molecular weight 134 or more and GMn 3,000 or less), polyoxyethylene (molecular weight 106 or more and GMn 3,000 or less) / polyoxypropylene (molecular weight 134 or more and GMn 3,000 or less) block copolymer, trimethylolethane, trimethylolpropane, (poly)(2 or more and 50 or less) glycerin, pentaerythritol, sorbitol (hereinafter abbreviated as TME, TMP, GR, PE, and SO, respectively), poly(2 or more and 20 or less) vinyl ether of starch, etc.

[0029] (y4) Monomer containing an allyl group (2 to 20) C6 or more and GMn 3,000 or less, for example, di(meth)allylamine, N-alkyl (C1 to 20) di(meth)allylamine, poly(2 to 20) (meth)allylamine of polyvalent amines (above), di(meth)allyl ether, poly(2 to 20) (meth)allyl ether of polyhydric alcohols (above), poly(2 to 20) (meth)allyloxyalkane (C1 to 20) (tetraallyloxyethane, etc.)

[0030] (y5) Epoxy group-containing monomer C8 or more and GMn 6,000 or less, e.g. EG diglycidyl ether, PEG diglycidyl ether, GR triglycidyl ether

[0031] Examples of the component (a) include polymer flocculants having spinnability, which are composed of water-soluble (co)polymers having as constituent units one or more water-soluble monomers selected from the nonionic monomer (a11) and the anionic monomer (a13). Examples of the component (a) include polymer flocculants having spinnability, which are composed of one or more water-soluble (co)polymers selected from the group consisting of water-soluble (co)polymers having the nonionic monomer (a11) as a constituent unit and water-soluble (co)polymers having the anionic monomer (a13) as a constituent unit. Examples of the water-soluble (co)polymer having the nonionic monomer (a11) as a constituent unit include (a11-2) (meth)acrylamide and derivatives thereof, and (a11-4) one or more nonionic monomers selected from the alkylene oxides, and further (a11-4) one or more nonionic monomers selected from the alkylene oxides. Examples of the water-soluble (co)polymer having an anionic monomer (a13) as a constituent unit include (a13-1) a water-soluble (co)polymer having an unsaturated carboxylic acid as a constituent unit. The component (a) is preferably one or more polymeric flocculants having a spinnability selected from nonionic polymeric flocculants having a spinnability and anionic polymeric flocculants having a spinnability. The component (a) is more preferably a nonionic polymeric flocculant having a spinnability. The component (a) is preferably one or more polymeric flocculants having a spinnability selected from polyalkylene oxides, polyacrylamides, and polyacrylic acids or salts thereof. The component (a) is preferably a polyalkylene oxide having a spinnability, and more preferably a polyethylene oxide having a spinnability.

[0032] The polyalkylene oxide preferably contains ethylene oxide as a polymer unit. The polyalkylene oxide is preferably polyethylene oxide having a weight average molecular weight of 500,000 or more.

[0033] Component (b) is bentonite. Bentonite, component (b), is a general term for clays whose main component is montmorillonite. Bentonite has high water absorption and ion exchange properties because it contains a lot of layered aluminum phyllosilicate. Some bentonites contain sodium, calcium, potassium, and other cations in addition to aluminum, and are classified according to the type of cation, such as sodium bentonite and calcium bentonite.

[0034] In the present invention, from the viewpoints of improving the flocculation performance and handling, the swelling degree of the bentonite of component (b) is 5 mL / 2 g or more, preferably 10 mL / 2 g or more, and 50 mL / 2 g or less, preferably 40 mL / 2 g or less, more preferably 35 mL / 2 g or less.

[0035] The degree of swelling is measured according to the swelling test method for bentonite (powdered) in JBAS104:77 of the Japan Bentonite Industry Association. That is, 2.0 g of sample adjusted to 8.0 mass% moisture is added in about 10 separate additions to a 100 ml stoppered measuring cylinder containing 100 ml of distilled water. The next addition is made after the previous addition has settled at the bottom of the measuring cylinder. After the last addition, the sample is left to stand for 24 hours at 25°C ± 0.5°C. The apparent volume of the swollen sample mass at the bottom of the measuring cylinder is read from the graduations on the measuring cylinder and expressed as the degree of swelling (mL / 2 g).

[0036] In the present invention, from the viewpoints of improving flocculation performance and handling, the (b) component is mixed in an amount of 5 parts by mass or more, preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, and 100 parts by mass or less, preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less, per 1,000 parts by mass of wastewater.

[0037] In the present invention, from the viewpoints of improving the aggregation performance and handling, the components (a) and (b) are mixed so that the mass ratio of (b) / (a) is 100 or more, preferably 300 or more, more preferably 500 or more, even more preferably 800 or more, and is 3000 or less, preferably 2500 or less, more preferably 2000 or less, even more preferably 1500 or less.

[0038] In the present invention, while satisfying the mass ratio (b) / (a), the (a) component can be mixed so that the concentration of the (a) component in the wastewater to be treated is, for example, 1 ppm or more, further 5 ppm or more, further 10 ppm or more, and 500 ppm or less, further 100 ppm or less, further 50 ppm or less.

[0039] In the present invention, while satisfying the above-mentioned mixing amount relative to the wastewater and the above-mentioned mass ratio (b) / (a), the (b) component can be mixed so that the concentration of the (b) component in the wastewater to be treated is, for example, 3000 ppm or more, further 5000 ppm or more, further 10000 ppm or more, and 80,000 ppm or less, further 50,000 ppm or less, further 30,000 ppm or less.

[0040] In the present invention, optional components such as water-soluble inorganic compounds, bleaching agents, disinfectants, antibacterial agents, preservatives, pH adjusters, and anti-redeposition agents (excluding components (a) and (b)) can be mixed.

[0041] The wastewater targeted by the present invention contains a surfactant and oil. For example, the wastewater may be wastewater discharged after an object contaminated with oil is washed with a detergent containing a surfactant. The wastewater may be discharged as domestic wastewater, urban wastewater, industrial wastewater, etc. Domestic wastewater and other wastewater generally contains various pollutants. The pollutants contained in the wastewater may be formed of organic matter, inorganic matter, or a composite of these. Other than surfactants and oils, examples of the dirt components include soil (meaning that it may include clay, mud, etc.), bacteria, heavy metals and their ions, sebum, lipids, dyes, keratin, hair, dyes, pigments, food, fibers, etc. The dirt components contained in the wastewater other than surfactants and oils may be determined depending on the use of the water after treatment, etc.

[0042] The present invention is directed to wastewater containing a surfactant and oil. The present invention has been discovered by finding that an excellent water purification effect can be obtained by using component (a) and component (b) under conditions in which surfactant and oil coexist in the wastewater. The surfactant and oil may be contained in the wastewater as contaminant components and / or as components added separately.

[0043] The surfactant contained in the wastewater may be one or more surfactants selected from anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants. The surfactant may be a surfactant having a molecular weight of less than 500,000. From the viewpoint of a high removal effect from the wastewater according to the present invention, it is preferable that the wastewater contains a nonionic surfactant as a surfactant. Examples of nonionic surfactants include polyoxyalkylene alkyl or alkenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, fatty acid monoglycerides, and polyethylene glycol fatty acid esters. Examples of the anionic surfactant include an anionic surfactant having a hydrocarbon group having 8 to 24 carbon atoms and a sulfonic acid group or a sulfate ester group. The sulfonic acid group or the sulfate ester group may be a salt. Examples of the anionic surfactant having a sulfate ester group include an alkyl or alkenyl sulfate ester salt, and a polyoxyalkylene alkyl or alkenyl ether sulfate ester salt. Examples of the anionic surfactant having a sulfonate group include an alkylbenzene sulfonate salt. Other examples of the anionic surfactant include a fatty acid having 12 to 24 carbon atoms or a salt thereof. The cationic surfactant may be a quaternary ammonium surfactant or a tertiary amine surfactant. The amphoteric surfactant is not particularly limited, and examples thereof include N-alkyl-N,N-dimethylamine oxide having an alkyl group with 8 or more carbon atoms, preferably 10 or more, and 18 or less, preferably 16 or less carbon atoms, N-alkylcarbonylaminopropyl-N,N-dimethylamine oxide having an alkyl group with a carbon number within the above range, N-alkyl-N,N-dimethylaminoacetic acid betaine having an alkyl group with a carbon number within the above range, N-alkylcarbonylaminopropyl-N,N-dimethylaminoacetic acid betaine having an alkyl group with a carbon number within the above range, and N-alkyl-N,N-dimethyl-N-(2-hydroxysulfopropyl)ammonium sulfobetaine having an alkyl group with a carbon number within the above range.

[0044] The concentration of the surfactant in the wastewater is, for example, 1 ppm or more, further 10 ppm or more, further 50 ppm or more, further 100 ppm or more, further 500 ppm or more, and 50,000 ppm or less, further 10,000 ppm or less, further 5,000 ppm or less, further 3,000 ppm or less. The wastewater before adding the (a) component and the (b) component may contain the surfactant at this concentration. Also, the surfactant may be added to the wastewater containing or not containing the surfactant to adjust the concentration to this concentration.

[0045] The oil contained in the wastewater may be selected from animal and vegetable oils and petroleum hydrocarbons. Examples of animal and vegetable oils include drying oils (iodine value 130 or more) such as linseed oil and sunflower oil, semi-drying oils (iodine value 100-130) such as soybean oil, sesame oil, and rapeseed oil, and non-drying oils (iodine value 100 or less) such as castor oil, olive oil, palm oil, and coconut oil. Petroleum-based hydrocarbons include compounds contained in products derived from petroleum, such as gasoline, diesel, heavy oil, and mineral oil.

[0046] The concentration of oil in the wastewater is, for example, 0.1 ppm or more, further 1 ppm or more, further 5 ppm or more, further 10 ppm or more, further 50 ppm or more, and 10,000 ppm or less, further 5,000 ppm or less, further 1,000 ppm or less, further 500 ppm or less. The wastewater before adding the (a) component and the (b) component may contain animal and vegetable oils and petroleum hydrocarbons at this concentration. In addition, the concentration may be adjusted to this concentration by adding animal and vegetable oils and petroleum hydrocarbons to wastewater containing animal and vegetable oils and petroleum hydrocarbons or wastewater not containing animal and vegetable oils and petroleum hydrocarbons.

[0047] The wastewater may contain soil as a contaminant component. The concentration of soil in the wastewater before the addition of the components (a) and (b) is, for example, 0.1 ppm or more, further 1 ppm or more, further 10 ppm or more, and 100,000 ppm or less, further 10,000 ppm or less, further 5,000 ppm or less.

[0048] In the present invention, the order and form in which components (a) and (b) are added to wastewater are not important, but it is preferable to add component (a) after adding component (b).

[0049] In the present invention, components (a) and (b) are mixed in a predetermined ratio with wastewater, and after standing, the aqueous layer is reused as water. In the present invention, it is preferable that the surfactant concentration and oil concentration in the wastewater after mixing components (a) and (b) and before standing are within the above-mentioned ranges.

[0050] In the present invention, the pH of the wastewater containing the components (a) and (b) is preferably 4 or more, more preferably 5 or more, and 9 or less, even more preferably 8.5 or less. That is, it is preferable to adjust the pH of the wastewater to the above range and then allow it to stand. The pH can be adjusted with an alkali agent such as caustic soda, sodium carbonate, sodium hydrogen carbonate, sodium silicate, or monoethanolamine, or an acid agent such as an organic acid such as sodium hydrogen sulfate, citric acid, or lactic acid.

[0051] The mixing may be carried out with stirring. The standing can be performed by leaving the mixture after mixing. The standing time can be, for example, 1 minute or more, further 5 minutes or more, and 60 minutes or less, further 30 minutes or less. The standing temperature can be, for example, 5°C or more and 80°C or less. By leaving the solution at rest, the flocculants settle, and the aqueous layer is reused as water, for example, as water for domestic use, industrial use, etc. After leaving the solution at rest, the wastewater in which the flocculants have settled can be subjected to a method such as filtration, decantation, or removal of the flocculant layer at the bottom, as necessary, to obtain the aqueous layer. The water from the obtained water layer can be used, for example, as grey water for cleaning oil stains, flushing toilets, and the like. EXAMPLES

[0052] (1) Preparation method of model domestic wastewater A 1000 ml glass beaker was charged with 450 g of ion-exchanged water, and the surfactants shown in Table 1 were added so that the concentrations in the model domestic wastewater were the values ​​shown in Table 1, followed by stirring for 1 minute with a magnetic stirrer. Next, mineral oil [Mobil DTE 22 manufactured by Mobil Corporation, dyed with 0.4 mass% Sudan IV (manufactured by Fujifilm Wako Pure Chemical Industries)] was added so that the concentrations in the model domestic wastewater were the values ​​shown in Table 1, followed by stirring for 60 minutes with a magnetic stirrer to prepare the model domestic wastewater.

[0053] (2) Evaluation The purification effect of the model domestic wastewater prepared above was evaluated. The results are shown in Table 1. (2-1) Settling time of aggregates While stirring the model domestic wastewater with a magnetic stirrer, component (b) was added so that the concentration in the model domestic wastewater for evaluation would be the value shown in Table 1. After 15 minutes, an aqueous solution prepared with ion-exchanged water so that the concentration of component (a) would be 1,000 ppm was added so that the concentration in the model domestic wastewater for evaluation would be the value shown in Table 1 as component (a). Finally, ion-exchanged water was added so that the total liquid volume was 1000 g, and the mixture was stirred for a total of 25 minutes to obtain the model domestic wastewater for evaluation. After stirring, the mixture was left to stand in a room adjusted to a temperature of 25°C. After standing, the aggregates were observed, and the time until the volume of the aggregates reached 500 ml was measured, which was taken as the settling time of the aggregates.

[0054] (2-2) Surface tension of the supernatant 20 ml of the supernatant was collected at the time when the settling time of the aggregates was determined in (2-1) above, and the surface tension was measured using a surface tensiometer (AN-526P, manufactured by Nippon Oil Testing Machinery Co., Ltd.) and calculated as a value corrected with distilled water (literature value: 72.75 mN / m) and ethanol (literature value: 22.55 mN / m). The higher the surface tension, the smaller the amount of surfactant in the supernatant and the better the surfactant removal effect.

[0055] (2-3) Oil content in the supernatant (ppm) 10 ml of the supernatant collected in (2-2) above was sampled and the absorbance at 260 nm was calculated using a UV-visible spectrophotometer (Shimadzu Corporation UV-160A). A calibration curve was prepared using a sample in which mineral oil was dissolved in n-hexane.

[0056] [Table 1]

[0057] The components in the table are as follows. POE in the surfactant is an abbreviation for polyoxyethylene, and the number in parentheses is the average number of moles added. The number in parentheses for component (a) is the weight average molecular weight. (a) Ingredients PEO (7 million): Polyethylene oxide, Alcox E-300, manufactured by Meisei Chemical Industry Co., Ltd., spinnable PEO (5 million): Polyethylene oxide, Alcox E-240, manufactured by Meisei Chemical Industry Co., Ltd., spinnable PEO (2 million): Polyethylene oxide, Alcox E-75, manufactured by Meisei Chemical Industry Co., Ltd., spinnable PEO (800,000): Polyethylene oxide, Alcox E-45, manufactured by Meisei Chemical Industry Co., Ltd., spinnable AAm (5 million): Polyacrylamide, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., spinnable (b) Component Bentonite: TB-250, manufactured by Tachibana Material Co., Ltd. Swelling ratio: 14mL / 2g Component (b') (comparison component of component (b)) Kasaoka clay: Kasaoka clay, manufactured by Kasanen Kogyo Co., Ltd. Swelling ratio 2mL / 2g Fine powder clay for civil engineering: Sumiclair, manufactured by Sumitomo Osaka Cement Co., Ltd.

[0058] From the surface tension values ​​of the supernatants of Examples 1-1 to 1-13, it is estimated that the concentration of the surfactant in the supernatant is equal to or lower than the critical micelle concentration (CMC). For example, in Example 1-12, the surfactant is polyoxyethylene (EO=6) lauryl ether, and the surface tension value of the supernatant is 46.2 mN / m. Here, the relationship between the concentration of the polyoxyethylene (EO=6) lauryl ether aqueous solution and the surface tension is 0.0002 mass% (68.3 mN / m), 0.0005 mass% (56.9 mN / m), and 0.0008 mass% (52.3 mN / m). From this, it was confirmed that at least 99 mass% or more of the surfactant was removed in these Examples 1-1 to 1-13. In addition, from the oil content of the supernatants of Examples 1-1 to 1-13, it was confirmed that 94.5 mass% or more of the oil was removed in these Examples. That is, it was confirmed that the Examples had high effects of removing both surfactants and oil.

Claims

1. A method for recycling wastewater, comprising the steps of: (a) dissolving a polymer flocculant in purified water to a concentration of 10% by mass; mixing the resulting aqueous solution with a polymer flocculant having spinnability as determined by the following spinnability determination method [hereinafter referred to as component (a)] and (b) bentonite [hereinafter referred to as component (b)]; allowing the solution to stand for 1 to 60 minutes, and then recycling the aqueous layer as water; The wastewater contains a surfactant and an oil, (b) component is mixed in a ratio of 5 parts by mass to 100 parts by mass per 1,000 parts by mass of wastewater; The component (a) and the component (b) are mixed so that the mass ratio of (b) / (a) is 100 or more and 3000 or less. How to reuse wastewater. [Threadability determination method] When gently dripped from a Pasteur pipette (glass) with a tip inner diameter of 1 mm, the solution that forms threads is considered to be a spinnable solution.

2. The method for reusing wastewater according to claim 1, wherein the wastewater contains a surfactant in an amount of 10 ppm or more and 10,000 ppm or less.

3. The method for reusing wastewater according to claim 1 or 2, wherein the wastewater contains oil in an amount of 10 ppm or more and 10,000 ppm or less.

4. The method for reusing wastewater according to any one of claims 1 to 3, wherein the wastewater contains an oil selected from animal and vegetable oils and petroleum hydrocarbons.

5. The method for reusing wastewater according to any one of claims 1 to 4, wherein the component (a) is a polymer flocculant having a weight average molecular weight of 500,000 or more.

6. The method for reusing wastewater according to any one of claims 1 to 5, wherein the wastewater contains a nonionic surfactant.

7. The method for reusing wastewater according to any one of claims 1 to 6, wherein the wastewater is mixed with the component (b) and then mixed with the component (a).

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