Water treatment method, water treatment apparatus, and flocculant for water purification

Abstract

To provide a water treatment method capable of efficiently removing a contaminant in water to be treated by utilizing a chitosan based flocculant, a water treatment apparatus and a flocculant for water purification.SOLUTION: In the water treatment method, a chitosan based flocculant and an inorganic flocculant are simultaneously added to water to be treated or the inorganic flocculant is added after the chitosan based flocculant is added to the water to be treated to form flocs in the water to be treated.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a water treatment method, a water treatment device, and a flocculant for water purification. [Background technology]

[0002] A commonly known method for neutralizing and flocculating colloidal particles, which are suspended components in water, is to add an inorganic flocculant such as aluminum or iron to generate fine flocs, and then add a polymer flocculant to generate coarse flocs. This method generates fine flocs in water using an inorganic flocculant, and then generates coarse flocs using a polymer flocculant, thereby increasing the settling rate of the flocs and enabling efficient solid-liquid separation.

[0003] However, when applied to water purification treatment for producing drinking water, concerns remain about the toxicity of acrylamide and other substances contained in polymer flocculants, and currently, most water purification facilities still use only inorganic flocculants for flocculation treatment. In such water purification facilities, when poor flocculation occurs due to the inorganic flocculant, they are forced to wastefully inject excessive amounts of inorganic flocculant to improve the settling rate. As a result, water purification facilities that use only inorganic flocculants face the problem of increased chemical usage due to poor flocculation.

[0004] Japanese Patent Publication No. 1959-610 describes a technique for improving the settling and separation of fine suspended matter contained in raw water by adding chitosan to general industrial wastewater or general polluted liquid, or by further adding calcium chloride and caustic soda to separate and settle suspended impurities in the wastewater or polluted liquid. Japanese Patent Application Laid-Open No. 2008-216168 also discloses a method for coagulating and settling wastewater, in which a coagulant containing chitosan derived from natural substances and a coagulant containing sodium alginate derived from natural substances are added to the wastewater in a 1:1 ratio. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 34-610 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-216168 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the inventions described in Patent Documents 1 and 2 are intended to treat industrial wastewater or polluted liquids that are significantly colored and polluted, and do not suggest application to water to be treated that is introduced into water purification facilities. Furthermore, the chitosan described in Patent Documents 1 and 2 is considered to be insufficient in its effectiveness compared to conventional inorganic flocculants in completely separating turbid components from water to be treated that is introduced into water purification facilities.

[0007] In view of the above problems, the present invention provides a water treatment method, a water treatment device, and a flocculant for purified water that can efficiently remove pollutants from water to be treated by using a chitosan-based flocculant. [Means for solving the problem]

[0008] As a result of intensive research to solve the above problems, the inventors have discovered that by using a specific chitosan-based flocculant under specific conditions, it is possible to efficiently remove pollutants from the water to be treated.

[0009] In order to solve the above problems, in one aspect, the present invention provides a water treatment method in which a chitosan-based flocculant and an inorganic flocculant are added simultaneously to the water to be treated, or a chitosan-based flocculant is added to the water to be treated and then an inorganic flocculant is added, thereby forming flocs in the water to be treated.

[0010] In one embodiment of the water treatment method according to the present invention, a polymer flocculant is further added to the water to be treated after the flocs have been formed.

[0011] In another embodiment of the water treatment method according to the present invention, the polymer flocculant is an anionic polymer flocculant.

[0012] In yet another embodiment of the water treatment method according to the present invention, the chitosan-based flocculant has a 1% salt viscosity of 50 to 1500 mPa·s and a colloidal charge of 3.8 meq / g or more.

[0013] In yet another embodiment of the water treatment method according to the present invention, 0.01 to 100 mg / L of a chitosan-based flocculant is added to the water to be treated.

[0014] In yet another embodiment of the water treatment method according to the present invention, the chitosan-based flocculant contains 0.1 to 5.0% chitosan.

[0015] In yet another embodiment of the water treatment method according to the present invention, the water to be treated is raw water for water purification treatment.

[0016] In another aspect, the present invention is a water treatment device comprising a chitosan-based flocculant adding means for adding a chitosan-based flocculant to the water to be treated, an inorganic flocculant adding means for adding an inorganic flocculant to the water to be treated, and a mixing means connected to the chitosan-based flocculant adding means and the inorganic flocculant adding means for mixing the water to be treated with the chitosan-based flocculant and the inorganic flocculant to form flocs in the water to be treated, wherein the chitosan-based flocculant adding means is connected upstream of the inorganic flocculant adding means in the direction in which the water to be treated is introduced.

[0017] In one embodiment, the water treatment device of the present invention further comprises a control means for controlling the amount of chitosan-based flocculant added to the water to be treated so that 0.01 to 100 mg / L of chitosan-based flocculant having a 1% salt viscosity of 50 to 1500 mPa·s and a colloidal charge of 3.8 meq / g or more is added to the water to be treated.

[0018] In yet another aspect, the present invention provides a flocculant for water purification, which comprises chitosan, has a 1% salt viscosity of 50 to 1500 mPa·s, and a colloidal charge of 3.8 meq / g or more, and is a chitosan-based flocculant to be added to raw water for water purification treatment simultaneously with or before an inorganic flocculant. [Effects of the Invention]

[0019] According to the present invention, there are provided a water treatment method, a water treatment apparatus, and a flocculant for water purification that can efficiently remove pollutants from water to be treated by using a chitosan-based flocculant. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram illustrating a water treatment method according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating a water treatment device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification, "%" used for components means % by weight unless otherwise specified. The water treatment method according to an embodiment of the present invention includes simultaneously adding a chitosan-based flocculant and an inorganic flocculant to the water to be treated, or adding a chitosan-based flocculant to the water to be treated and then adding an inorganic flocculant to form flocs in the water to be treated.

[0022] The water to be treated is preferably raw water for water purification treatment. Raw water for water purification treatment is, for example, tap water or service water (industrial water, industrial water, agricultural and livestock water), and specifically refers to one or more types of fresh water or seawater, particularly river water, groundwater (well water), lake water, rainwater, etc. The water to be treated is not limited to raw water for water purification treatment, and for example, one or more types of water from factories, households, mining, construction sites, agricultural and livestock wastewater, commercial facilities, human waste, and other wastewater (so-called sewage, including rainwater) can be used in the present invention.

[0023] Specifically, raw water for water purification treatment can be suitably used that has a pH of 3 to 11, preferably 4 to 10, and more preferably 5 to 9, a turbidity of 0.1 to 300 degrees, preferably 0.5 to 200 degrees, and more preferably 1 to 50 degrees, and a color of 1 to 100 degrees, preferably 2 to 50 degrees, and more preferably 5 to 20 degrees. In particular, unlike water to be treated that contains a large amount of pollutants such as excess sludge, the water treatment method according to this embodiment can efficiently remove turbid components, particularly from low-turbidity raw water for water purification treatment that is difficult to remove turbid components from simply by injecting a large amount of a conventional inorganic flocculant.

[0024] Chitosan-based flocculants are flocculants containing chitosan. Chitosan is obtained by deacetylating chitin, which is found in crustaceans such as crabs and shrimp. Chitin is usually deacetylated using caustic soda, but by adjusting the caustic soda concentration, reaction temperature, and reaction time, various acetylation rates and viscosities can be produced.

[0025] For ease of handling, powdered (flake) chitosan is preferably used. For example, powdered chitosan having a particle size of 3.0 mm or less, an ash content of 2.0% or less, a viscosity of a 0.5-1.0% solution at 20°C of about 5.0 mPa·s to several thousand mPa·s, and a deacetylation degree of 95% or more can be suitably used as the chitosan according to this embodiment.

[0026] Chitosan itself is insoluble in water, but when treated with an acid or dissolved in an acid solution, a chitosan salt is formed and dissolved. Examples of acids include formic acid, acetic acid, propionic acid, maleic acid, benzoic acid, tartaric acid, malic acid, citric acid, lactic acid, sulfamic acid, hydrochloric acid, and nitric acid. Among these, it is preferable to use a chitosan solution in which powdered chitosan is dissolved in acetic acid as the chitosan-based flocculant in this embodiment.

[0027] The chitosan-based flocculant preferably contains 0.01 to 5.0% chitosan, more preferably 0.1 to 5.0%, even more preferably 0.1 to 3.0%, and even more preferably 0.2 to 2.0%. If the chitosan concentration in the chitosan-based flocculant is too high, dissolution may become difficult. If the chitosan concentration in the chitosan-based flocculant is too low, it may become difficult to appropriately control the settling rate of turbid components in the treated water and the turbidity reduction effect.

[0028] There is a correlation between the molecular weight and viscosity of chitosan. Chitosan-based flocculants suitable for water treatment, particularly for water to be treated in water purification, preferably have a 1% salt viscosity of 50 to 1500 mPa·s, more preferably 75 to 1400 mPa·s, and even more preferably 100 to 1300 mPa·s. If the 1% salt viscosity of chitosan is less than 50 mPa·s, a sufficient crosslinking effect may not be achieved, making it difficult to form large flocs with good solid-liquid separability. If the 1% salt viscosity of chitosan exceeds 1500 mPa·s, the flocs and separated water may become viscous or clog pipes, resulting in poor handleability. The salt concentration is measured using a B-type rotational viscometer at 25°C with a spin rotor No. 3 at a rotation speed of 30 rpm using the chitosan-based flocculant of this embodiment.

[0029] In the chitosan-based flocculant according to this embodiment, the colloidal charge of the chitosan is preferably 3.8 meq / g or more. If the colloidal charge is less than 3.8 meq / g, it may be difficult to efficiently remove pollutants from the water to be treated. A higher colloidal charge is preferable, and although there is no particular upper limit, a value of about 5.5 meq / g is generally feasible for production. Note that the "colloidal charge" in this embodiment refers to a 0.2% colloidal charge measured by colloid titration.

[0030] The chitosan-based flocculant is preferably added to the water to be treated in an amount of 0.01 to 100 mg / L, more preferably 0.05 to 50 mg / L. If the amount added is less than 0.01 mg / L, it is difficult to efficiently remove pollutants from the water to be treated, and if it exceeds 100 mg / L, chitosan is expensive and the treatment may not be considered efficient from an economical standpoint.

[0031] Inorganic flocculants that can be used include aluminum sulfate, polyaluminum chloride (PAC), polyferric sulfate (polyiron), ferric chloride, or a mixture of these. Because all of these inorganic flocculants have a flocculating effect through charge neutralization, they are particularly effective when used in combination with other flocculants, such as chitosan-based flocculants. The type of inorganic flocculant can be varied as appropriate. The amount of inorganic flocculant added can also be varied as appropriate depending on the type and quality of the water being treated.

[0032] Furthermore, inorganic flocculants with any basicity (approximately 50 to 80%) can be used as the inorganic flocculant. For example, for raw water to be purified, it is preferable to use high-basicity polyaluminum chloride with a basicity of 65 to 80%. By using high-basicity polyaluminum chloride with a basicity of 65 to 80%, various suspended solids contained in the raw water to be purified can be sufficiently flocculated to form good flocs while maintaining the stability of the polyaluminum chloride. The basicity of the inorganic flocculant used for raw water to be purified may be 68 to 80%, or 70 to 80%.

[0033] Although not limited to the following, the inorganic flocculant is preferably added to the water to be treated at 1 to 200 mg / L, more preferably 5 to 150 mg / L, and even more preferably 10 to 100 mg / L. According to this embodiment, by adding a chitosan-based flocculant and an inorganic flocculant to the water to be treated at a predetermined weight ratio, the settling rate of pollutants in the water to be treated can be adjusted within a suitable range, and a sufficient turbidity reduction effect can be obtained with a small amount of flocculant.

[0034] In place of inorganic flocculants, commonly used organic coagulants can also be used, such as condensation polyamines, dicyandiamide-formaldehyde condensates, polyethyleneimine, polyvinyl imidaline, polyvinylpyridine, diallylamine salt-sulfur dioxide copolymers, polydimethyldiallylammonium salts, polydimethyldiallylammonium salt-sulfur dioxide copolymers, polydimethyldiallylammonium salt-acrylamide copolymers, polydimethyldiallylammonium salt-diallylamine hydrochloride derivative copolymers, and allylamine salt polymers.

[0035] Specific examples of condensation polyamines include condensates of alkylene dichloride and alkylene polyamine, condensates of aniline and formalin, condensates of alkylene diamine and epichlorohydrin, condensates of ammonia and epichlorohydrin, etc. Examples of alkylene diamines that can be condensed with epichlorohydrin include dimethylamine, diethylamine, methylpropylamine, methylbutylamine, and dibutylamine.

[0036] In order to efficiently remove pollutants from the water to be treated by using a chitosan-based flocculant and an inorganic flocculant in combination, the order in which the chitosan-based flocculant and the inorganic flocculant are added is important. In this embodiment, as shown in Figure 1(a), the chitosan-based flocculant and the inorganic flocculant are added simultaneously to the water to be treated, or as shown in Figure 1(b), the inorganic flocculant is added after the chitosan-based flocculant is added to the water to be treated. If the inorganic flocculant is added before the chitosan-based flocculant for flocculation treatment, the floc diameter becomes smaller and the settling rate becomes slower than when the inorganic flocculant is used alone, and the turbidity of the treated water may actually increase.

[0037] In this specification, the term "simultaneous addition" refers not only to the simultaneous addition of a chitosan-based flocculant and an inorganic flocculant to one reaction tank, but also to the addition of a certain time interval to account for the treatment process. For example, the chitosan-based flocculant and the inorganic flocculant may be mixed in one mixing tank connected to a chitosan-based flocculant supply port and an inorganic flocculant supply port before the water to be treated is discharged into another treatment tank. According to this embodiment, by adjusting the order of addition of the flocculants so that the chitosan-based flocculant and the inorganic flocculant are added simultaneously or before the inorganic flocculant, relatively large flocs can be formed even in low-turbidity water to be treated. This increases the settling rate and shortens the flocculation treatment time, and improves the turbidity removal effect compared to when the chitosan-based flocculant or the inorganic flocculant is used alone.

[0038] In one embodiment, it is preferable to further add a polymer flocculant to the water to be treated after adding a chitosan-based flocculant and an inorganic flocculant to the water to be treated to form flocs. By further adding a polymer flocculant to the water to be treated, the floc diameter can be further increased, thereby accelerating the settling speed of the flocs and further improving the flocculation and sedimentation effect.

[0039] The polymer flocculant to be added after the addition of the inorganic flocculant and chitosan can be one or more selected from anionic polymer flocculants, nonionic polymer flocculants, cationic polymer flocculants, and amphoteric polymer flocculants.

[0040] Preferred examples of anionic polymer flocculants include polyacrylamide partial hydrolysates, copolymers of anionic monomers, and copolymers of anionic monomers and nonionic monomers. Preferred examples of anionic monomers include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-allylamidoethanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamidoethanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid, 4-acryloyloxybutanesulfonic acid, 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfonic acid, and metal salts or ammonium salts thereof, such as alkali metals and alkaline earth metals.

[0041] Preferred examples of the copolymer of an anionic monomer and a nonionic monomer include an acrylamide-acrylic acid copolymer and an acrylamide-2-acrylamido-2-methylpropanesulfonic acid copolymer.

[0042] As the nonionic polymer flocculant, a homopolymer or copolymer of a nonionic monomer can be preferably used, such as acrylamide, methacrylamide, methacrylonitrile, vinyl acetate, etc., or a combination thereof, and more preferably polyacrylamide can be used.

[0043] In the polymer flocculant addition step, it is also possible to use a two-component method in which the above-mentioned cationic polymer flocculant is added, and then the above-mentioned anionic polymer flocculant is added. As the cationic polymer flocculant, a cationic polymer flocculant having a cationic monomer as an essential component, and consisting of a homopolymer or copolymer of a cationic monomer, or a copolymer of a cationic monomer and a nonionic monomer, and a cationic polymer flocculant having an amidine unit in the molecule can be preferably used.

[0044] Preferred examples of the cationic monomer include dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, or neutralized salts or quaternary salts thereof, and combinations thereof.

[0045] Preferred examples of the nonionic monomer include acrylamide, methacrylamide, methacrylonitrile, vinyl acetate, and combinations thereof. Preferred examples of the cationic polymer flocculant that can be used in the present invention and is made of a copolymer of a cationic monomer and a nonionic monomer include a copolymer of acrylamide and at least one of dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate (both of which are preferably quaternized methyl chloride).

[0046] Furthermore, as a cationic polymer flocculant having an amidine unit in the molecule that can be used in the present invention, for example, an amidinized product of an N-vinylformamide / acrylonitrile copolymer can be preferably mentioned.

[0047] As the amphoteric polymer flocculant, a copolymer of a cationic monomer unit, an anionic monomer unit and a nonionic monomer unit can be preferably used.

[0048] Preferred examples of amphoteric polymer flocculants that can be used in the present invention include copolymers of at least one of dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate (both of which are preferably quaternized methyl chloride), acrylamide, and acrylic acid. Cationic starch, cationic cellulose, and cationic guar gum can also be used.

[0049] According to this embodiment, by using a polymer flocculant in addition to a chitosan-based flocculant and an inorganic flocculant, it is possible to more efficiently remove turbid substances from low-turbidity treated water that were previously difficult to remove even with the addition of large amounts of flocculant, thereby achieving the effect of stably obtaining clear treated water over a relatively long period of time, regardless of fluctuations in the raw water quality due to changes in the natural environment.

[0050] Although not limited to the following, chitosan-based flocculants and inorganic flocculants are often positively charged, so when using a polymer flocculant in combination with these chitosan-based flocculants or inorganic flocculants, it is preferable to use an anionic polymer flocculant.

[0051] Although not limited to the following, the polymer flocculant is preferably added to the water to be treated in an amount of 0 to 100 mg / L, more preferably 0.05 to 50 mg / L, and even more preferably 0.1 to 10 mg / L. According to this embodiment, by adding a chitosan-based flocculant, an inorganic flocculant, and a polymer flocculant to the water to be treated in a predetermined weight ratio, the settling velocity of pollutants in the water to be treated can be adjusted within a suitable range, and a sufficient turbidity reduction effect can be obtained with a small amount of flocculant.

[0052] 2 shows an example of a water purification facility used for water treatment, as a water treatment device 10 suitable for application of the water treatment method according to an embodiment of the present invention. The water treatment device 10 according to the embodiment of the present invention includes chitosan-based flocculant adding means 1 that adds a chitosan-based flocculant to the water to be treated, inorganic flocculant adding means 2 that adds an inorganic flocculant to the water to be treated, and mixing means 5 that is connected to the chitosan-based flocculant adding means 1 and the inorganic flocculant adding means 2 and mixes the water to be treated with the chitosan-based flocculant and the inorganic flocculant to form flocs in the water to be treated, and the chitosan-based flocculant adding means 1 is connected upstream of the inorganic flocculant adding means 2 in the direction in which the water to be treated is introduced.

[0053] The chitosan-based flocculant addition means 1, inorganic flocculant addition means 2, and polymer flocculant addition means 3 each include a container for storing the chitosan-based flocculant, inorganic flocculant, and polymer flocculant, respectively, and a pump for delivering each flocculant from the container to each reaction tank. The chitosan-based flocculant addition means 1, inorganic flocculant addition means 2, and polymer flocculant addition means 3 may be connected to control means 4 for controlling the amount of chitosan-based flocculant, inorganic flocculant, and polymer flocculant added. The control means 4 is a device for adjusting the amount of chitosan-based flocculant, inorganic flocculant, and polymer flocculant added from the chitosan-based flocculant addition means 1, inorganic flocculant addition means 2, and polymer flocculant addition means 3 according to the properties of the raw water. For example, the control means 4 controls the amount of chitosan-based flocculant to be added to the water to be treated so that 0.01 to 100 mg / L of chitosan-based flocculant with a 1% salt viscosity of 50 to 1500 mPa·s and a colloidal charge of 3.8 meq / g or more is added to the water to be treated. Although not shown, the control means 4 may be connected to a measuring device for measuring the pH, color, turbidity, etc. of the water to be treated (raw water), and may be configured to control the amount of flocculant to be added so that the amount of each flocculant is within an optimal range based on the measurement results of the measuring device.

[0054] In FIG. 2, raw water to be treated is mixed in a mixing means 5 consisting of one or more tanks, where a chitosan-based flocculant and an inorganic flocculant are added, and the mixture is stirred by a stirring means M to form flocs. After the flocs have formed, a polymer flocculant is further added to the raw water in a flocculation means 6 consisting of one or more tanks connected downstream of the mixing means 5, and the mixture is stirred by the stirring means M to form flocs that are coarser than the flocs formed in the mixing means 5. The raw water containing the coarse flocs formed in the flocculation means 6 is subjected to solid-liquid separation by gravity settling or the like in a settling means 7 consisting of a settling tank or the like. The solid-liquid separated treated water obtained by solid-liquid separation in the settling means 7 is sent to a filtration means 8 such as a sand filter basin connected downstream of the precipitation means 7, where it is filtered to obtain filtered water (treated water). The filtered water is then subjected to a predetermined sterilization treatment to obtain purified water (tap water).

[0055] 2, in a water treatment device 10 according to an embodiment of the present invention, the chitosan-based flocculant adding means 1 is connected upstream of the inorganic flocculant adding means 2 in the direction of introduction of the water to be treated, i.e., closer to the supply port through which raw water is supplied to the mixing means 5. This allows the mixing means 5 to mix the chitosan flocculant into the raw water after mixing the inorganic flocculant, thereby making it possible to increase the diameter of flocs formed in the raw water compared to when the inorganic flocculant is mixed into the raw water before the chitosan flocculant. As a result, the settling speed of the flocs during the flocculation and sedimentation treatment can be increased, and the pollution removal effect can be improved.

[0056] As shown in Fig. 2, the chitosan-based flocculant adding means 1 may be connected to the mixing means 5 and / or may have multiple supply ports connected to a supply pipe for supplying raw water to the mixing means 5 so that the chitosan-based flocculant can be injected into the middle of the supply pipe. When the mixing means 5 is composed of multiple tanks, the chitosan-based flocculant adding means 1 may be connected so that the chitosan-based flocculant is injected into the first reaction tank, and the inorganic flocculant adding means 2 may be connected so that the inorganic flocculant is injected into the second reaction tank. Furthermore, when the flocculation means 6 is composed of multiple tanks as shown in Fig. 2, the polymer flocculant adding means 3 may be connected to each tank individually, or may be connected to the last reaction tank of the mixing means 5 to which the flocculation means 6 is connected.

[0057] (Flocculant for water purification) The water purification flocculant according to an embodiment of the present invention can be a chitosan-based flocculant containing chitosan. This chitosan-based flocculant is prepared by dissolving powdered chitosan in an acid or acid solution. Specifically, the chitosan-based flocculant contains chitosan, has a 1% salt viscosity of 50 to 1500 mPa·s, and a colloidal charge of 3.8 meq / g or greater, and is added to raw water for water purification treatment simultaneously with or before an inorganic flocculant. While the raw water to be treated is not particularly limited, the chitosan-based flocculant according to this embodiment is particularly advantageous in that it can exert the desired effect even on raw water with relatively low turbidity when applied to raw water for water purification treatment, and can consistently produce clear treated water over a relatively long period of time, regardless of fluctuations in raw water quality due to recent changes in the natural environment.

[0058] This chitosan-based flocculant preferably contains 0.01 to 5.0% chitosan, more preferably 0.1 to 5.0%, even more preferably 0.1 to 3.0%, and even more preferably 0.2 to 2.0%. The 1% salt viscosity of the chitosan-based flocculant is preferably 50 to 1500 mPa·s, more preferably 75 to 1400 mPa·s, and even more preferably 100 to 1300 mPa·s. In the chitosan-based flocculant according to this embodiment, the colloidal charge of the chitosan is preferably 3.8 meq / g or more. This chitosan-based flocculant can be prepared, for example, by dissolving powdered chitosan having a particle size of 3.0 mm or less, an ash content of 2.0% or less, a viscosity of a 0.5-1.0% solution of 5.0 mPa·s to several thousand mPa·s at 20°C, and a degree of deacetylation of 95% or more in the above-mentioned acid or acid solution, and then diluting with water to adjust to the desired chitosan concentration.

[0059] The chitosan-based flocculant according to the embodiment of the present invention can be used in combination with an inorganic flocculant and added to the water to be treated simultaneously with or before the inorganic flocculant, thereby forming relatively large flocs even in low-turbidity water to be treated, thereby increasing the settling rate and shortening the flocculation treatment time. Furthermore, the chitosan-based flocculant according to the embodiment of the present invention can improve the turbidity removal effect compared to when the chitosan-based flocculant or the inorganic flocculant is used alone.

[0060] Although the present invention has been described with reference to the above-described embodiments, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. The present disclosure is not limited to the above-described embodiments, and components can be combined and modified to be embodied within the scope of the gist of the present disclosure. [Example]

[0061] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0062] (Comparative Example 1) Tests were conducted using raw water (pH: 8.1, turbidity: 6.3, color: 19.2) from a certain water purification plant. 70 mg / L of high-basicity polyaluminum chloride (PAC) with a basicity of 70% was added to 1 liter of raw water. The water was rapidly stirred in a jar tester at 150 rpm for 3 minutes, followed by slow stirring at 50 rpm for 5 minutes, and the floc diameter was visually observed. After stirring, the settling velocity of the flocs was measured visually, and the supernatant water was left to stand for 5 minutes, after which the turbidity and color were measured. The results are shown in Table 1. In the following examples and comparative examples, turbidity and color were measured using a turbidity / colorimeter (WA 6000) manufactured by Nippon Denshoku Industries Co., Ltd. The results are shown in Table 1. In Table 1, "chitosan" refers to a chitosan-based flocculant.

[0063] Example 1 5 mg / L of chitosan-based flocculant (dissolved at 10 g / L; the same amount of acetic acid was added during dissolution; 1% salt viscosity: 1250 mPa·s; 0.2% colloidal charge: 4.10 meq / g) was added to the same raw water as in Comparative Example 1, and the mixture was rapidly stirred at 150 rpm in a jar tester for 3 minutes. One minute after the start of stirring, 70 mg / L of PAC was added, followed by slow stirring at 50 rpm for 5 minutes. After stirring was completed, the floc diameter, settling velocity, turbidity, and color were measured in the same way as in Comparative Example 1. The results are shown in Table 1.

[0064] (Comparative Example 2) In Comparative Example 2, the order of injection of the chitosan-based flocculant and PAC was reversed. That is, PAC was injected first and rapidly stirred in a jar tester at 150 rpm for 3 minutes. One minute after the start of stirring, the chitosan-based flocculant was injected and slowly stirred at 50 rpm for 5 minutes. Measurements after stirring were completed were the same as in Comparative Example 1 and Example 1. The results are shown in Table 1.

[0065] [Table 1]

[0066] Treatment with only a conventional inorganic coagulant (PAC) resulted in a low settling rate and high turbidity and color of the supernatant (Comparative Example 1). Furthermore, when a chitosan-based coagulant was used in combination with the inorganic coagulant, the floc diameter was small and the turbidity and color of the supernatant increased when the inorganic coagulant was added before the chitosan-based coagulant (Comparative Example 2).

[0067] (Example 2, Comparative Examples 3 and 4) For the above Example 1 and Comparative Examples 1 and 2, 0.2 mg / L of an anionic polymer flocculant, an acrylamide-sodium acrylate copolymer (Evagrose WA-142, manufactured by Suing Co., Ltd., adjusted to a 0.1% aqueous solution), was further added at the start of slow stirring. Measurements after stirring were completed were the same as for Example 1 and Comparative Examples 1 and 2. The results are shown in Table 2.

[0068] Example 3 The same chitosan-based flocculant as in Example 1 and PAC were simultaneously added to the same raw water as in Comparative Example 1, and the mixture was rapidly stirred in a jar tester at 150 rpm for 3 minutes. Then, 0.2 mg / L of the same anionic polymer flocculant as in Examples 2, Comparative Examples 3, and 4 was further added, and the mixture was slowly stirred at 50 rpm for 5 minutes. Measurements after stirring were performed were the same as in Examples 1-2 and Comparative Examples 1-4. The results are shown in Table 2.

[0069] [Table 2]

[0070] (Examples 4 to 7, Comparative Examples 5 to 9) Instead of the raw water used in Examples 1 to 3 and Comparative Examples 1 to 4, simulated raw water (pH: 7.9, turbidity 7.7) prepared by dispersing kaolin in tap water was used as the raw water. Furthermore, tests were conducted by changing the PAC added to the raw water to one with a basicity of 50%. In Examples 4 to 6, the chitosan-based flocculant was added before the inorganic flocculant, as in Examples 1 and 2. In Example 7, the chitosan-based flocculant and the inorganic flocculant were added simultaneously, as in Example 3. In Comparative Examples 4 to 6, only PAC was added to the raw water, as in Comparative Example 1, and in Comparative Example 7, PAC was added first to the raw water, as in Comparative Example 2. The results are shown in Table 3. Note that, since simulated raw water was used in Examples 4 to 7 and Comparative Examples 5 to 9, color measurement was not performed.

[0071] Example 8 In Example 8, 0.2 mg / L of an anionic polymer flocculant, which is an acrylamide-sodium acrylate copolymer (Evagrose A-151, manufactured by Suing Co., Ltd., adjusted to a 0.1% aqueous solution), was further added at the start of slow stirring in Example 6, and the test was carried out. As a result, good results were obtained: floc diameter: more than 3 mm, settling velocity: 140 mm / min, and supernatant water turbidity: 0.2 degrees.

[0072] [Table 3]

[0073] As shown above, the experimental results of Examples 1 to 8 demonstrated that, compared with Comparative Examples 1 to 8, the floc diameter can be increased, the settling velocity can be increased, and the turbidity and color of the supernatant water can be reduced. [Explanation of symbols]

[0074] 1: Chitosan-based flocculant addition method 2: Means of adding inorganic coagulant 3: Polymer flocculant addition method 4: Control means 5: Mixing means 6: Floc forming means 7: Precipitation means 8:Filtration means 10: Water treatment equipment

Claims

1. A water treatment method characterized by simultaneously adding a chitosan-based flocculant and an inorganic flocculant to the water to be treated, or by adding the chitosan-based flocculant to the water to be treated and then adding the inorganic flocculant to form flocs in the water to be treated.

2. 2. The water treatment method according to claim 1, further comprising adding a polymer flocculant to the water to be treated after the flocs have been formed.

3. 3. The water treatment method according to claim 2, wherein the polymer flocculant is an anionic polymer flocculant.

4. 4. The water treatment method according to claim 1, wherein the chitosan-based flocculant has a 1% salt viscosity of 50 to 1500 mPa·s and a colloidal charge of 3.8 meq / g or more.

5. 4. The water treatment method according to claim 1, wherein the chitosan-based flocculant is added to the water to be treated in an amount of 0.01 to 100 mg / L.

6. 4. The water treatment method according to claim 1, wherein the chitosan-based flocculant contains 0.1 to 5.0% chitosan.

7. 4. The water treatment method according to claim 1, wherein the water to be treated is raw water for water purification treatment.

8. a chitosan-based flocculant adding means for adding a chitosan-based flocculant to the water to be treated; an inorganic flocculant adding means for adding an inorganic flocculant to the water to be treated; a mixing means connected to the chitosan-based flocculant adding means and the inorganic flocculant adding means, for mixing the water to be treated with the chitosan-based flocculant and the inorganic flocculant to form flocs in the water to be treated; Equipped with 10. A water treatment device, wherein the chitosan-based flocculant adding means is connected upstream of the inorganic flocculant adding means in the direction in which the water to be treated is introduced.

9. The water treatment device according to claim 8, further comprising a control means for controlling the amount of chitosan-based flocculant added to the water to be treated so that 0.01 to 100 mg / L of chitosan-based flocculant having a 1% salt viscosity of 50 to 1500 mPa·s and a colloidal charge of 3.8 meq / g or more is added to the water to be treated.

10. containing chitosan, having a 1% salt viscosity of 50 to 1500 mPa s and a colloidal charge of 3.8 meq / g or more; A flocculant for water purification comprising a chitosan-based flocculant which is added to raw water for water purification treatment simultaneously with an inorganic flocculant or before the inorganic flocculant is added to the raw water.

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