Dewatering promoter composition for wet sludge

Abstract

To provide a dewatering accelerator composition for water-containing sludge with excellent stability, such as efficiently producing a sludge concentrate with low water content and uniform appearance from water-containing sludge.SOLUTION: A dewatering accelerator composition for hydrous sludge containing (A), a nonionic surfactant, and (B) an anionic surfactant with a molecular weight of 200 to 1000.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dewatering promoter composition for wet sludge and a method for producing a sludge concentrate. [Background technology]

[0002] Sludge is a sediment containing various substances that is produced in various fields, such as sewage treatment, industrial wastewater treatment, and soil excavation. For disposal or reuse, it is sometimes desirable to turn sludge into a concentrated product with as little water content as possible to improve its handleability. To thicken or dewater sludge, for example, a flocculant (coagulant) is added to the sludge to be treated. The flocculant has the effect of converting particles dispersed in water into concentrated organic matter in the form of flocs. The generated flocs are separated from the water produced by the separation operation. Various chemicals used in thickening and dewatering sludge have been studied.

[0003] Patent Document 1 discloses a method for dehydrating a wet particulate polymer mass, which comprises adding a surface-active polymer to the wet particulate polymer mass in an amount sufficient to aid in dehydration of the polymer mass, and then subjecting the polymer mass to a mechanical dehydration operation. In the examples, a homopolymer of diallyldimethylammonium chloride, polyethylene glycol 400 diolate, and a mixture of 3-alkoxy(C11-C15)-2-hydroxy-n-propyltrimethylammonium chloride are used as surface-active polymers.

[0004] Patent Document 2 discloses a method for producing calcium carbonate slurry from lime sludge produced when green liquor obtained in a pulp manufacturing process by the Kraft method is causticized, in which at least two types of dispersants are used. The two types of dispersants are a polycarboxylate-based anionic surfactant and a polyoxyalkylene alkyl ether-based nonionic surfactant.

[0005] Patent Document 3 discloses a method for dehydrating muddy water, which includes adding a surfactant to muddy water containing soil whose particle size has been reduced to 75 μm or less by classification, concentrating the muddy water after the surfactant causes the soil to coagulate and precipitate, adding a flocculant to the concentrated muddy water, concentrating the muddy water after the coagulation and precipitation of the soil by the flocculant, and compressing and dehydrating the soil that has coagulated and precipitated by the flocculant. In the examples, a cationic surfactant is used as the surfactant.

[0006] Patent Document 4 discloses a method for dehydrating organic sludge by treating it with a flocculant and then dehydrating it, in which one or more cationic surfactants, an anionic surfactant, and an organic polymer flocculant are added to the organic sludge and then treated.

[0007] Patent Document 5 discloses a method for treating wet excavation waste, in which an amine surfactant is added to wet excavation waste, the mixture is kneaded, the resulting mixture is dehydrated under pressure, and then crushed.

[0008] Furthermore, Non-Patent Document 1 discloses that the use of a surfactant when reducing the residual moisture in lime sludge by centrifugation results in lime sludge that is easy to handle and has a plastic limit or less. The surfactant used is sodium dodecylbenzenesulfonate. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 3-6205 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-84279 [Patent Document 3] Patent Publication No. 2021-109113 [Patent Document 4] Japanese Patent Application Publication No. 62-11600 [Patent Document 5] Japanese Patent Application Laid-Open No. 2001-40351 [Non-patent literature]

[0010] [Non-Patent Document 1] Oi et al., "Reduction of Residual Moisture in Lime Sludge by Centrifugal Dewatering," Journal of the Japan Mining Association, Japan Mining Association, 1988, Vol. 104, No. 1203, pp. 283-288 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention provides a dehydration accelerator composition for water-containing sludge, which can efficiently produce a sludge concentrate having a low water content from water-containing sludge and has excellent stability (hereinafter also referred to as one-component stability), such as exhibiting a uniform appearance, and a method for producing the sludge concentrate. [Means for solving the problem]

[0012] The present invention relates to a dewatering accelerator composition for wet sludge, which contains (A) a nonionic surfactant and (B) an anionic surfactant having a molecular weight of 200 or more and 1,000 or less.

[0013] The present invention also relates to a method for producing a sludge concentrate, comprising the following steps 1 and 2: Step 1: A step of mixing a sludge containing water with (A) a nonionic surfactant (hereinafter referred to as component (A)) and (B) an anionic surfactant having a molecular weight of 200 to 1,000 (hereinafter referred to as component (B)), thereby obtaining a sludge containing component (A) and component (B). Step 2: A step of separating water from sludge containing component (A) and component (B) to obtain a sludge concentrate. [Effects of the Invention]

[0014] According to the present invention, a dehydration promoter composition for water-containing sludge, which can efficiently produce a sludge concentrate having a low water content from water-containing sludge and has excellent one-component stability (appearance), and a method for producing the sludge concentrate are provided. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Drainage accelerator composition for wet sludge] The present invention relates to a dewatering accelerator composition for wet sludge, containing components (A) and (B). The present invention concentrates sludge and increases its solids content by adding two specific surfactants, components (A) and (B), to the sludge. Water in sludge can be broadly divided into free water and water bound in interparticle spaces. While free water can be relatively easily dewatered using mechanical dewatering, water bound in interparticle spaces is difficult to dewater. Furthermore, the smaller the particle size, the greater the interparticle capillary pressure, making dewatering even more difficult. In this invention, the capillary force acting between particles is reduced by the surface tension reduction of the two surfactants, and the interparticle force is weakened by the particle dispersion force of component (B). This is thought to reduce water migration (water backflow phenomenon) after the dewatering process, improve dewatering efficiency, and enable the efficient production of concentrates.

[0016] The dehydration accelerator composition for wet sludge of the present invention has excellent one-component stability (appearance). The dewatering promoter composition for wet sludge of the present invention may be a dewatering promoter composition that is mixed with water-containing sludge to promote separation of water and solids.

[0017] Examples of the nonionic surfactant of component (A) include polyoxyalkylene alkyl ethers, polyoxyalkylene alkenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, fatty acid monoglycerides, polyethylene glycol fatty acid esters, etc. These can be used alone or in combination of two or more.

[0018] The component (A) is preferably one or more nonionic surfactants selected from polyoxyalkylene alkyl ethers and polyoxyalkylene alkenyl ethers, and more preferably one or more nonionic surfactants selected from polyoxyalkylene alkyl ethers.

[0019] The polyoxyalkylene alkyl ether has an average number of moles of oxyalkylene groups added of preferably 3 or more, more preferably 5 or more, from the viewpoint of water solubility, and preferably 12 or less, more preferably 10 or less, from the viewpoint of reducing surface tension. Examples of the oxyalkylene group include oxyalkylene groups having from 2 to 4 carbon atoms, and an oxyalkylene group having 2 carbon atoms, i.e., an oxyethylene group, is preferred. Furthermore, the polyoxyalkylene alkyl ether has an alkyl group with preferably 8 or more, more preferably 10 or more, from the viewpoint of reducing surface tension, and preferably 20 or less, more preferably 18 or less, from the viewpoint of water solubility.

[0020] In the polyoxyalkylene alkenyl ether, from the viewpoint of water solubility, the average number of moles of oxyalkylene groups added is preferably 3 or more, more preferably 5 or more, and from the viewpoint of reducing surface tension, it is preferably 12 or less, more preferably 10 or less. In addition, in the polyoxyalkylene alkenyl ether, from the viewpoint of reducing surface tension, the number of carbon atoms in the alkenyl group is preferably 8 or more, more preferably 10 or more, and from the viewpoint of water solubility, it is preferably 20 or less, more preferably 18 or less.

[0021] From the viewpoint of water solubility, component (A) has an HLB value of preferably 8.0 or more, more preferably 9.0 or more, and from the viewpoint of reducing surface tension, preferably 14.0 or less, more preferably 13.0 or less. This HLB value is determined by the Griffin method.

[0022] Component (B) is an anionic surfactant having a molecular weight of 200 or more and 1,000 or less. From the viewpoint of forming mixed micelles with component (A), the molecular weight of component (B) is 200 or more, preferably 250 or more, and 1000 or less, preferably 600 or less. The molecular weight of the anionic surfactant of component (B) is calculated in terms of an acid compound, i.e., based on a compound in which the anionic group is acid.

[0023] The anionic surfactant of component (B) may be an anionic surfactant having a molecular weight of 200 or more and 1,000 or less, selected from sulfate ester salts, sulfonate salts, fatty acid salts, and phosphate ester salts.

[0024] Examples of the sulfate salts include salts of sulfate esters having an alkyl or alkenyl group having from 10 to 20 carbon atoms. Specific examples of the sulfate salts include sulfate ester salts (AS) having an alkyl or alkenyl group having from 10 to 20 carbon atoms, polyoxyalkylene alkyl (or alkenyl) ether sulfate ester salts (AES) (for example, alkyl or alkenyl ether sulfate ester salts having an average added mole number of alkylene oxide having from 2 to 4 carbon atoms of from 0.5 to 10 moles and having a linear or branched alkyl or alkenyl group having from 10 to 20 carbon atoms), polyoxyalkylene alkyl or alkenyl phenyl ether sulfate ester salts having a linear or branched alkyl or alkenyl group having from 10 to 20 carbon atoms, and castor oil sulfate ester salts.

[0025] Specific examples of the sulfonate salts include alkanesulfonates (SAS) having from 10 to 20 carbon atoms, linear or branched alkylbenzenesulfonates (LAS or ABS) having an alkyl group having from 8 to 18 carbon atoms, α-olefinsulfonates (AOS) having from 10 to 20 carbon atoms, di- or mono-alkyl sulfosuccinates (e.g., sodium di(2-ethylhexyl) sulfosuccinate (AOT)), saturated or unsaturated α-sulfofatty acids having from 8 to 20 carbon atoms, or methyl, ethyl, or propyl ester salts thereof.

[0026] The number of carbon atoms of the fatty acid in the fatty acid salt is preferably from 10 to 18. Specific examples of the fatty acid salt include alkali metal salts and organic amine salts of capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, and mixtures thereof.

[0027] Examples of the phosphate ester salts include salts of phosphate esters having an alkyl or alkenyl group having from 10 to 20 carbon atoms. Specific examples of the phosphate ester salts include polyoxyalkylene alkyl ether phosphates, polyoxyalkylene alkyl phenyl ether phosphates, and long-chain alkyl phosphates. Examples of the phosphate salts that can be used include monoesters, diesters, and any mixtures of mono- and di-phosphates (sesquiesters).

[0028] The component (B) is preferably one or more anionic surfactants selected from alkyl sulfates and alkyl ether sulfates, and more preferably one or more anionic surfactants selected from alkyl sulfates.

[0029] The alkyl sulfate salt is preferably an alkyl sulfate salt having an alkyl group with 10 to 18 carbon atoms. The polyoxyethylene alkyl ether sulfate is preferably a polyoxyethylene alkyl ether sulfate having an alkyl group with 10 to 18 carbon atoms and an average number of moles of ethylene oxide added of 0.5 to 5.0.

[0030] Examples of the salt of the anionic surfactant of component (B) include alkali metal salts, alkaline earth metal salts, amine salts, ammonium salts, and alkanolamine salts. The salt is preferably a salt selected from alkali metal salts and alkanolamine salts, more preferably a sodium salt or alkanolamine salt. The alkanolamine salt is preferably a salt of an alkanolamine having from 1 to 3 alkanol groups each having from 1 to 3 carbon atoms.

[0031] From the viewpoint of the one-component stability (appearance) of the dewatering accelerator composition for wet sludge, component (B) preferably has an HLB value of 10 or more, more preferably 15 or more, even more preferably 25 or more, and 40 or less, even more preferably 35 or less, as measured by the Davis method. In the present invention, the HLB value of component (B) is calculated based on a compound in which the salt is replaced with a sodium salt. In this case, when component (B) is a polymeric salt, such as a compound such as an alkaline earth metal salt of a fatty acid, the sodium salt of the monomer that constitutes the compound is taken as the HLB value of that compound.

[0032] The dewatering promoter composition for wet sludge of the present invention may have a mass ratio (A) / (B) of the content of the component (A) to the content of the component (B) of, for example, 95 / 5 or less, further 90 / 10 or less, further 80 / 20 or less, further 70 / 30 or less, and may be 30 / 70 or more, further 40 / 60 or more, or further 50 / 50 or more.

[0033] The dewatering promoter composition for wet sludge of the present invention contains, for example, 5% by mass or more, further 10% by mass or more, and 80% by mass or less, further 70% by mass or less of component (A) based on the solid content. Here, the solid content refers to the components other than water in the dewatering promoter composition for wet sludge of the present invention. The dewatering accelerator composition for wet sludge of the present invention contains, for example, 0.5 mass % or more, preferably 1 mass % or more, and 20 mass % or less, preferably 10 mass % or less of the component (B) based on the solid content.

[0034] The dehydration promoter composition for wet sludge of the present invention may contain, as optional components, for example, alcohol-based antigelling agents, glycol-based antigelling agents, thickeners, fragrances, dyes, pigments, disinfectants, preservatives, pH adjusters, etc.

[0035] The dewatering promoter composition for wet sludge of the present invention may be a composition containing water, and may have a pH at 20°C of 5 or more, preferably 6 or more, and 9 or less, preferably 8 or less.

[0036] When the drainage promoter composition for wet sludge of the present invention contains component (A), component (B), and water, water is used as the remainder of the composition (amount that makes the total 100% by mass). When the drainage promoter composition for wet sludge of the present invention contains water, the content of component (A) in the composition may be, for example, 3% by mass or more, or even 5% by mass or more, and 30% by mass or less, or even 20% by mass or less, from the viewpoint of the effect of reducing capillary force by reducing surface tension. In this case, the content of component (B) in the composition may be, for example, 0.3% by mass or more, or even 0.5% by mass or more, and 8% by mass or less, or even 5% by mass or less, from the viewpoint of particle dispersion force.

[0037] [Method for producing sludge concentrate] The method for producing a sludge concentrate of the present invention includes the following steps 1 and 2. Step 1: A step of mixing water-containing sludge with component (A) and component (B) to obtain sludge containing component (A) and component (B). Step 2: A step of separating water from sludge containing component (A) and component (B) to obtain a sludge concentrate. The matters described for the dewatering promoter composition for wet sludge of the present invention can be appropriately applied to the method for producing a sludge concentrate of the present invention. Specific examples and preferred examples of components (A) and (B) in the method for producing a sludge concentrate of the present invention are the same as those for the dewatering promoter composition for wet sludge of the present invention.

[0038] In step 1 of the present invention, sludge containing water is mixed with component (A) and component (B) to obtain sludge containing component (A) and component (B).

[0039] Aqueous sludge is a mixture containing various substances and water, which is generated in various fields such as sewage treatment, industrial wastewater treatment, and soil excavation. For example, aqueous sludge may be clay, soil, or even excavated soil. That is, in the present invention, aqueous sludge may be sludge containing soil and water. Other aqueous sludges include papermaking sludge containing coated inorganic materials such as kaolinite and calcium carbonate, cement-containing sludge generated at concrete manufacturing and civil engineering construction sites, sludge containing aluminum hydroxide and other substances generated from coagulants in water purification plants and wastewater treatment facilities, heavy metal sludge generated during the detoxification of heavy metal-containing wastewater from the water washing step in plating processes, and other industrial wastes such as car wash sludge, waste alumina, waste diatomaceous earth, wastewater treatment filter media, cooling tower sludge, sludge containing alumina-based catalysts, silica-based catalysts, iron-containing sludge, polishing sludge, painting sludge, paint wastewater sludge, and slurries containing other inorganic fine particles such as calcium hydroxide.

[0040] In step 1, the components (A) and (B) are mixed in a mass ratio (A) / (B) of the component (A) to the component (B) of, for example, 95 / 5 or less, further 90 / 10 or less, further 80 / 20 or less, further 70 / 30 or less, further 30 / 70 or more, further 40 / 60 or more, or further 50 / 50 or more.

[0041] In step 1, the total amount of the components (A) and (B) may be mixed with the water-containing sludge in an amount of, for example, 0.05 mass% or more, further 0.1 mass% or more, further 0.2 mass% or more, and 2.0 mass% or less, further 1.0 mass% or less, and further 0.5 mass% or less.

[0042] In step 2 of the present invention, water is separated from the sludge containing component (A) and component (B) obtained in step 1 to obtain a sludge concentrate. Separation of water from sludge can be carried out using gravity, centrifugal force, compression, or the like. In the present invention, in step 2, water can be separated from sludge preferably by gravity or centrifugal force, more preferably by centrifugal force. Conditions for centrifugation include, for example, a centrifugal acceleration of 800 G or more and 1200 G or less, and a treatment time of 1 minute or more and 10 minutes or less. Centrifugal separation promotes separation of the sludge from the liquid phase, facilitating recovery and reuse (backfilling) of the sludge. The sludge concentrate obtained in step 2 can be reused or disposed of depending on the source of the sludge. [Example]

[0043] (1) Dehydration test (1-1) Preparation of simulated sludge water A 100 ml Erlenmeyer flask was charged with 16.7 g of finely powdered civil engineering clay (Sumiclée, Sumitomo Osaka Cement Co., Ltd.) and 83.3 g of water to prepare a mixture with a specific gravity of 1.2. After preparation, the mixture was stirred for 30 minutes with a magnetic stirrer to prepare simulated sludge water, which is a sludge containing water. The finely powdered civil engineering clay used here had a fine particle content of 0.075 mm or less and a D10 of 0.0023 mm.

[0044] (1-2) Evaluation of dehydration The dehydration accelerator composition for wet sludge shown in the table was further added to the simulated sludge water prepared in (1-1) so that the total amount of component (A) and component (B) relative to the simulated sludge water was the amount shown in the table, and then stirred with a magnetic stirrer for 30 minutes. Here, the dehydration accelerator composition for wet sludge contained a total of 10 mass% of component (A) and component (B), with the remainder being water. All of the dehydration accelerator compositions for wet sludge of the examples in the table had a pH at 20°C in the range of 6 to 8. In addition, in the table, the HLB of component (A) is the HLB determined by the Griffin method, and the HLB of component (B) is the HLB determined by the Davis method. The HLB of component (B) was calculated based on a compound in which the salt was replaced with a sodium salt. The stirring by the magnetic stirrer was stopped, and the mixture was divided into two 50 ml Violamo centrifuge tubes and centrifuged at 1000 G for 5 minutes in a multi-rack centrifuge H-80F manufactured by Kokusan Co., Ltd. After centrifugation, the supernatant was immediately removed, the precipitate was stirred uniformly, and approximately 3 g was weighed out into a 30 ml screw tube. It was then dried in a 105°C oven for 18 hours, cooled in a desiccator, and then weighed accurately to determine the moisture content of the precipitate. The results are shown in Table 1. The lower the moisture content, the better the dewatering effect, meaning that sludge concentrate with a low moisture content can be produced more efficiently.

[0045] (1-3) One-component stability (appearance) The components (A) and (B) in the table were mixed with water in the mass ratios shown in the table to a total concentration of 10 mass % to prepare a water-containing dehydration accelerator composition for wet sludge. The composition was allowed to stand at 20 to 22°C for 24 hours, after which the appearance was visually observed and the condition was evaluated. The results are shown in Table 1.

[0046] [Table 1]

[0047] In Table 1, for component (A), the number following C is the number of carbon atoms in the alkyl or alkenyl group, and F indicates the number of unsaturated bonds. EO is an ethyleneoxy group, and the number in parentheses is the average number of moles added. For example, C10(EO)3 means a polyoxyethylene alkyl ether with an alkyl group having 10 carbon atoms and an average number of moles of ethylene oxide added of 3. In addition, in Table 1, component (B) is as follows. C12OSO3·Na: Sodium salt of alkyl sulfate ester with alkyl group having 12 carbon atoms C12OSO3·TEA: Triethanolamine salt of alkyl sulfate ester with alkyl group having 12 carbon atoms C12(EO)2OSO3·Na: Sodium salt of polyoxyethylene alkyl ether sulfate ester with an alkyl group of 12 carbon atoms and an average number of moles of ethylene oxide added of 2. PAA·Na(1): Sodium polyacrylate, weight average molecular weight of acid compound: 9000 PAA·Na(2): Sodium polyacrylate, weight average molecular weight of acid compound: 3000

Claims

1. A method for producing a sludge concentrate, comprising the following steps 1 and 2: Step 1: A step of obtaining a sludge containing the component (A) and the component (B), by mixing a sludge containing soil and water with (A) a nonionic surfactant which is a polyoxyethylene alkyl or alkenyl ether having an alkyl or alkenyl group with 10 to 18 carbon atoms and an average number of moles of ethylene oxide added of 3 to 10 (hereinafter referred to as component (A)), and (B) one or more anionic surfactants selected from alkyl sulfates and alkyl ether sulfates with a molecular weight of 200 to 1,000 (hereinafter referred to as component (B)), in such a manner that the mass ratio (A) / (B) of the component (A) to the component (B) is 50 / 50 or more and 95 / 5 or less, and the total of the component (A) and the component (B) relative to the sludge containing soil and water is 0.05% by mass to 2.0% by mass, Step 2: A step of separating water from sludge containing component (A) and component (B) to obtain a sludge concentrate.

2. 2. The method for producing a sludge concentrate according to claim 1, wherein in step 2, water is separated from the sludge by centrifugal force.

3. A method for producing a sludge concentrate as described in claim 1 or 2, wherein the soil contains fine particles having a particle size of 0.075 mm or less.

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