Water treatment method and water treatment device

Abstract

To provide a water treatment method and a water treatment device capable of obtaining safe and secure treatment water free from foreign odor while reducing an injection ratio of a coagulant to target water containing musty odor-producing bioorganisms.SOLUTION: A water treatment method for removing musty odor-producing bioorganisms from target water includes the steps of: injecting an inorganic coagulant into target water containing musty odor-producing bioorganism; injecting 0.05-2.0 mg / L of a polymer coagulant with an acrylamide monomer content of 0.05 wt% or under, or free from acrylamide; and performing coagulation settling.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water treatment method and a water treatment device, and more particularly to a water treatment method and a water treatment device that can be used in water purification plants that produce tap water, industrial water, and the like. [Background technology]

[0002] The raw water used in water treatment facilities such as water purification plants is generally dam water, lake water, river water, etc., but due to various reasons including the progression of eutrophication, abnormal proliferation of organisms such as algae and blue-green algae has been causing problems in water purification. Furthermore, in recent years, problems such as the moldy odor of treated water caused by algae and blue-green algae that produce a moldy odor have been observed all over Japan, regardless of the season.

[0003] The main moldy odor substances in water are geosmin and 2-methylisoborneol (2-MIB), which are the causes of the unpleasant odor and taste of tap water. These substances are required to be below a certain concentration in tap water quality standards. In order to remove such moldy odor substances, most water purification plants add powdered activated carbon to the raw water before coagulation and sedimentation treatment, and various studies are being conducted to optimize the amount of powdered activated carbon added.

[0004] For example, JP 2022-187271 A (Patent Document 1) describes an example of a powdered activated carbon injection control system that includes an algae detection and determination means for detecting algae contained in raw water and determining the type of algae, an odorant estimation means for estimating the type of odorant emitted by the algae, an odorant concentration measurement means for measuring the concentration of odorants contained in the raw water or treated water after powdered activated carbon injection treatment, and a powdered activated carbon injection control means for calculating an odorant-specific powdered activated carbon injection rate for adjusting the concentration of odorants contained in the treated water in the receiving well to a target concentration using the odorant concentration measured by the odorant concentration measurement means, and controlling the amount of powdered activated carbon injected into the treated water in the receiving well or the treated water in the coagulant mixing pond based on the odorant-specific powdered activated carbon injection rate.

[0005] Japanese Patent Publication No. 2015-157239 (Patent Document 2) describes an example of a water treatment process control method that can achieve both a reduction in the chemical injection rate and a reduction in the moldy odor value of the treated water, in which a basic injection rate of coagulant to be injected in coagulant treatment is determined based on the raw water turbidity, and a maximum injection rate of coagulant to be injected in coagulation sedimentation treatment is determined based on the raw water moldy odor value, and multiple coagulant injection rates are selected within the range between the basic injection rate and the maximum injection rate.

[0006] JP 2022-26969 A (Patent Document 3) describes an example of a water treatment method in which a first coagulant injection rate, which is the injection rate of coagulant required for coagulation and sedimentation of turbidity in the raw water, is calculated based on the water quality of the raw water, and a first powdered activated carbon injection rate, which is the injection rate of powdered activated carbon required to remove odorous substances in the raw water, is calculated based on the odorous substance concentration in the raw water and at least one of the ultraviolet absorbance, fluorescence intensity, and soluble organic carbon concentration of the raw water, as well as the first coagulant injection rate. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2022-187271 A [Patent Document 2] JP 2015-157239 A [Patent Document 3] Patent Publication No. 2022-26969 Summary of the Invention [Problem to be solved by the invention]

[0008] In the invention described in Patent Document 1, the powdered activated carbon treatment removes most of the moldy odor substances in the raw water before the coagulation treatment. However, the organisms that produce the moldy odor, which are the source of the odor, cannot be removed by the powdered activated carbon treatment, and are removed by settling together with the turbidity from the raw water containing the powdered activated carbon in the subsequent coagulation treatment. Therefore, it is necessary to set new coagulation conditions, such as the coagulant injection rate, in order to more reliably remove the moldy odor-producing organisms, and the amount of coagulant required for the coagulation treatment may increase.

[0009] The invention described in Patent Document 2 does not mention removing organisms that produce moldy odors in raw water. In order to remove the moldy odor generated from the treated water, a method of increasing the injection rate of inorganic coagulants is generally used, but increasing the injection rate of inorganic coagulants increases the cost of using chemicals as well as the cost of sludge treatment due to the increase in the amount of settled sludge. In addition, the invention described in Patent Document 3 can optimize the injection rate of powdered activated carbon, but does not provide detailed consideration on reducing the injection rate of coagulants.

[0010] In view of the above problems, the present invention provides a water treatment method and a water treatment device that can produce safe and secure treated water free of unpleasant odors and tastes while reducing the injection rate of coagulant into the treated water containing organisms that produce a moldy odor. [Means for solving the problem]

[0011] As a result of intensive research into solving the above problems, the inventors discovered that it is useful to add an appropriate amount of a specific polymer flocculant, in addition to an inorganic flocculant, to the treatment water containing organisms that produce a moldy odor.

[0012] In order to solve the above problems, in one aspect, the present invention is a water treatment method which includes injecting an inorganic coagulant into the water to be treated which contains organisms producing a moldy odor, and then injecting 0.05 to 2.0 mg / L of a polymer coagulant having an acrylamide monomer content of 0.05 wt% or less or which does not contain acrylamide, thereby removing organisms producing a moldy odor from the water to be treated by coagulation and sedimentation treatment.

[0013] In one embodiment of the water treatment method according to the present invention, the acrylamide-free polymer flocculant contains a polyacrylate.

[0014] In another embodiment of the water treatment method according to the present invention, 15 to 50 mg / L of inorganic flocculant and 0.05 to 2.0 mg / L of polymer flocculant are injected.

[0015] In yet another embodiment of the water treatment method according to the present invention, the polymer flocculant is injected so that the injection rate ratio of the polymer flocculant to the inorganic flocculant (polymer flocculant injection rate [mg / L] / inorganic flocculant injection rate [mg / L]) is 0.001 to 0.13.

[0016] In still another embodiment of the water treatment method according to the present invention, a polymer flocculant is dissolved to prepare an aqueous solution having a dissolution concentration of more than 0.2 wt % and not more than 0.4 wt %, and then the aqueous solution is injected into the water to be treated.

[0017] In yet another embodiment of the water treatment method of the present invention, the injection rate of the polymer coagulant is determined based on the injection rate of the predetermined inorganic coagulant and the concentration of mold odor-producing organisms in the treated water, without increasing the injection rate of the predetermined inorganic coagulant.

[0018] In yet another embodiment of the water treatment method according to the present invention, the musty odor producing organisms include cyanobacteria that produce geosmin or 2-methylisoborneol.

[0019] In another aspect, the present invention is a water treatment device comprising a mixing tank into which water to be treated containing organisms producing a moldy odor is introduced, an inorganic flocculant injection means for injecting an inorganic flocculant into the water to be treated in the mixing tank, a flocculation tank for forming flocs in the water to be treated after the inorganic flocculant has been injected, a polymer flocculant injection means for injecting an acrylamide monomer content of 0.05 wt% or less or an acrylamide-free polymer flocculant at 0.05 to 2.0 mg / L into the water to be treated, and a solid-liquid separation tank for removing organisms producing a moldy odor from the water to be treated by performing solid-liquid separation of the water to be treated after the injection of the polymer flocculant.

[0020] In one embodiment of the water treatment device according to the present invention, the flocculation tank includes a plurality of tanks, and the polymer flocculant injection means is connected to at least the first or second stage flocculation tank.

[0021] In another embodiment of the water treatment device of the present invention, the polymer flocculant injection means includes a dissolution tank that dissolves powdered polymer flocculant to prepare an aqueous solution of polymer flocculant having a dissolution concentration of more than 0.2 wt% and not more than 0.4 wt%, and an injection pump that injects the polymer flocculant into the water to be treated so that the injection rate ratio between the polymer flocculant and the inorganic flocculant (polymer flocculant injection rate [mg / L] / inorganic flocculant injection rate [mg / L]) is 0.001 to 0.13. Effect of the Invention

[0022] According to the present invention, a water treatment method and a water treatment device are provided that can reduce the injection rate of a coagulant into the treated water containing organisms that produce a moldy odor, while producing safe and secure treated water that is free of unpleasant odors and tastes. [Brief description of the drawings]

[0023] [Figure 1] 1 is an explanatory diagram illustrating an example of a water treatment device according to an embodiment of the present invention. [Diagram 2] 1 is a graph showing an example of the relationship between the dissolved concentration of a polymer flocculant and the supernatant turbidity when a flocculation precipitation process is carried out using a polymer flocculant containing an acrylamide monomer and a polymer flocculant not containing acrylamide. [Diagram 3] 1 is a graph showing an example of the relationship between the dissolved concentration of a polymer flocculant and the floc settling velocity when a flocculation and sedimentation treatment is carried out using a polymer flocculant containing an acrylamide monomer and a polymer flocculant not containing acrylamide. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. Note that the embodiment shown below is an example of an apparatus and method for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not limit the structure, arrangement, etc. of the components to those described below.

[0025] (Water treatment method) In the water treatment method according to the embodiment of the present invention, the water to be treated is not particularly limited as long as it contains a mold odor producing organism. In this embodiment, the term "mold odor producing organism" refers to an organism including cyanobacteria that produces geosmin or 2-methylisoborneol, which are causative substances of mold odor, and specifically refers to an organism that causes damage classified as cyanobacteria, diatoms, etc. in the water purification test method (Japan Water Works Association, "Water Supply Test Method 2020 Edition IV. Microorganisms V. Organisms", pages 310-316). Typical examples of cyanobacteria contained in mold odor producing organisms include Phormidium. Such mold odor producing organisms are microorganisms that cause odor and taste disorders such as mold odor in treated water such as tap water, and can rapidly grow due to various external factors such as the amount of sunlight, hours of sunlight, and temperature in water treatment facilities such as water purification plants.

[0026] The number of moldy odor producing organisms contained in the water to be treated is not particularly limited, but the present treatment method can be applied to water containing at least 1 organism / mL of moldy odor producing organism. In this embodiment, effective treatment can be performed on water containing 7 organisms / mL or more of moldy odor producing organisms, more effective treatment can be performed on water containing 10 organisms / mL or more of moldy odor producing organisms, more effective treatment can be performed on water containing 15 organisms / mL or more of moldy odor producing organisms, and more effective treatment can be performed on water containing 20 organisms / mL or more of moldy odor producing organisms. There is no particular upper limit on the number of moldy odor producing organisms, but effective treatment can be performed on water containing, for example, about 100 organisms / mL, or even about 1000 organisms / mL of moldy odor producing organisms that can be actually contained in the water to be treated.

[0027] In this embodiment, the number of moldy odor producing organisms is measured in accordance with the method for measuring the counting unit of the target organism based on the description on page 311 of the Japan Water Works Association's "Water Supply Testing Methods 2020 Edition IV. Microorganisms V. Organisms". For example, for filamentous Phormidium, one of the moldy odor producing organisms, a colony of 100 μm in length is counted as one unit (one organism) using a biological microscope.

[0028] In order to efficiently remove such moldy odor producing organisms, in this embodiment, an inorganic flocculant is injected into the water to be treated, and then 0.05 to 2.0 mg / L of a polymer flocculant containing no acrylamide monomer or no acrylamide is injected to perform a flocculation and precipitation treatment. This results in a flocculation and precipitation treated water with a moldy odor producing organism count of 10 organisms / mL or less, preferably 7 organisms / mL or less, more preferably 5 organisms / mL or less, and even more preferably 1 organism / mL or less.

[0029] The injection rate of the inorganic flocculant can be set to a predetermined injection rate, and the value can be set by performing a jar test or the like on the water to be treated. Although not limited to the following, in this embodiment, for example, the injection rate of the inorganic flocculant can be 15 to 50 mg / L, more preferably 15 to 25 mg / L, and even more preferably 15 to 20 mg / L. Examples of inorganic flocculants include polyferric sulfate, ferric chloride, PAC (polyaluminum chloride), and aluminum sulfate. Among them, it is preferable to use PAC as a flocculant that is highly versatile, low-cost, and efficiently removable. In addition to the inorganic flocculant, a known flocculation aid, an organic coagulant, an inorganic coagulant, or a flocculation improver may be added.

[0030] The injection rate of the inorganic coagulant may be adjusted as appropriate to be optimal for the water to be treated, based on the measurement results, by measuring the turbidity of the water to be treated at predetermined intervals. By adjusting the injection rate of the inorganic coagulant according to the fluctuation of the turbidity of the water to be treated, the addition rate of the inorganic coagulant required for the coagulation and settling treatment of the turbidity in the water to be treated can be optimized, and the amount of coagulant used can be reduced overall for the treatment.

[0031] After the inorganic flocculant is injected into the water to be treated, the water containing the inorganic flocculant is rapidly stirred to form fine flocs in the water to be treated. A small amount of polymer flocculant is then injected into the water to be treated in which the fine flocs have formed, to carry out a coagulation and sedimentation treatment. As the polymer flocculant, a polymer flocculant with an acrylamide monomer content of 0.05 wt% or less (hereinafter also referred to as an "acrylamide-containing polymer flocculant") or a polymer flocculant that does not contain acrylamide (hereinafter also referred to as an "acrylamide-free polymer flocculant") is used.

[0032] An acrylamide-containing polymer flocculant is a polymer produced using an acrylamide monomer, and refers to a polyacrylamide polymer flocculant in which only acrylamide is homopolymerized, or an acrylamide polymer flocculant in which acrylamide is copolymerized with another monomer component, with an acrylamide monomer content of 0.05 wt% or less.

[0033] If the acrylamide monomer content in the polymer flocculant is too high, the concentration of acrylamide remaining in the treated water may exceed a predetermined standard value. On the other hand, if the acrylamide monomer content is too low, the appropriate coagulation and sedimentation treatment effect for the turbidity in the treated water may not be obtained. Therefore, the acrylamide monomer content in the acrylamide-containing polymer flocculant is 0.05 wt% or less, preferably 0.01 wt% or less, and more preferably 0.005 wt% or less. Although not limited to the following, the lower limit of the acrylamide monomer content in the acrylamide-containing polymer flocculant can be, for example, 0.001 wt% or more.

[0034] The acrylamide monomer content indicates the mass of acrylamide contained in the acrylamide-containing polymer flocculant, and the content can be measured in accordance with the method described in "Polyacrylamide for Water Supply, JWWA K 126-1980, enacted on June 28, 1980, reviewed by the Japan Water Works Association, Standing Sanitation Investigation Committee."

[0035] As such an acrylamide-containing polymer flocculant, various commonly available anionic polymer flocculants, such as polyacrylamide, polyacrylic acid, or a copolymer of polyacrylamide partial hydrolysate or acrylamide acid, can be used. The acrylamide-containing polymer flocculant according to the present embodiment not only has high flocculation properties, but also has an acrylamide content of 0.05 wt% or less, so it can be used in water purification treatment, wastewater treatment after water purification treatment, etc.

[0036] On the other hand, the acrylamide-free polymer flocculant refers to a polymer flocculant whose acrylamide monomer content is below the detection limit, preferably whose acrylamide monomer content is substantially zero. Therefore, it can be used more safely and securely in water purification treatment and wastewater treatment after water purification treatment. Among them, it is preferable to use polyacrylate.

[0037] As the polyacrylic acid salt, for example, it is preferable to use one or more selected from the group consisting of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, polymethacrylic acid, sodium polymethacrylate, potassium polymethacrylate, and ammonium polymethacrylate. Among them, it is more preferable to use sodium polyacrylate or one containing sodium polyacrylate as the main component (content of 50 wt% or more). The molecular weight of the polyacrylic acid salt is preferably 2 to 10 million in weight average molecular weight, and more preferably 4 million or more in weight average molecular weight.

[0038] The acrylamide-containing polymer flocculant and the acrylamide-free polymer flocculant may contain one or more additives such as surfactants, preservatives, colorants, buffers, pH adjusters, etc. There are no limitations on the type of additive, but it is preferable to use additives that do not cause acrylamide to remain in the treated water and that do not decompose the acrylamide-containing polymer flocculant.

[0039] If the injection rate of the polymer flocculant is too high, it may affect the quality of the treated water, while if it is too low, the desired coagulation and sedimentation treatment effect may not be obtained. The injection rate of the polymer flocculant is 0.05 to 2.0 mg / L of the water to be treated, more preferably 0.05 to 1.0 mg / L, and even more preferably 0.05 to 0.5 mg / L.

[0040] If the injection rate ratio of the polymer flocculant to the inorganic flocculant is too high, the injection rate of the inorganic flocculant increases and efficient treatment cannot be performed, while if it is too low, the effect of removing moldy odor-producing organisms may not be obtained. The injection rate ratio of the polymer flocculant to the inorganic flocculant (polymer flocculant injection rate [mg / L] / inorganic flocculant injection rate [mg / L]) is preferably 0.001 to 0.13, more preferably 0.001 to 0.05, and even more preferably 0.001 to 0.01.

[0041] It is preferable to adjust the injection rate of the polymer flocculant to an appropriate injection rate based on the predetermined injection rate of the inorganic flocculant and the concentration of mold odor producing organisms in the water to be treated, without increasing the predetermined injection rate of the inorganic flocculant. That is, in this embodiment, the injection rate of the inorganic flocculant is maintained at a predetermined injection rate, for example, the injection rate required for coagulation and sedimentation of the turbidity of the water to be treated without increasing the injection rate of the inorganic flocculant, while the injection rate of the polymer flocculant is adjusted based on the injection rate of the inorganic flocculant and the number of mold odor producing organisms in the water to be treated. The injection rate of the polymer flocculant requires a smaller injection amount than the injection rate of the inorganic flocculant that must be further added to obtain the same effect, so the amount of flocculant used can be significantly reduced.

[0042] The injection rate of the polymer coagulant may be determined in advance by a jar test or the like to determine an appropriate value based on the injection rate of the inorganic coagulant and the number of mold odor producing organisms in the water to be treated, or it may be determined by using machine learning using past water quality data and test data as learning data, with the injection rate of the inorganic coagulant and the number of mold odor producing organisms in the water to be treated as explanatory variables, and the injection rate of the polymer coagulant as the objective variable.

[0043] Polymer flocculants generally contain acrylamide monomers and have high viscosity, so rapid stirring is required to efficiently disperse them in the water to be treated and form coarse flocs. In addition, acrylamide monomers are a carcinogenic substance, and there is concern that the use of polymer flocculants in water purification treatment may result in acrylamide monomers remaining in the treated water. Therefore, polymer flocculants have not been used in general water purification treatment applications in Japan.

[0044] According to this embodiment, a polymer flocculant containing no acrylamide monomer or having a low concentration of 0.05 wt% or less is used. The polymer flocculant according to this embodiment has a lower viscosity when dissolved than a general polymer flocculant containing an acrylamide monomer, so that it is easily dispersed uniformly in the water to be treated and a rapid flocculation reaction can be performed. For example, the polymer flocculant according to this embodiment has a 0.1% solution viscosity at 25°C of 2 to 5 mPa·s, or even 2 to 3 mPa·s, and the dissolved concentration can be increased.

[0045] Usually, the dissolution concentration of the polymer flocculant is 0.2wt% at most. When using the polymer flocculant according to this embodiment, the dissolution concentration can be adjusted in a wide range of 0.1 to 0.4wt%, so that various aqueous solutions can be prepared according to the application. For example, by adjusting the polymer flocculant to a high-concentration aqueous solution with a dissolution concentration of more than 0.2wt% and 0.4wt% or less, or even 0.3 to 0.4wt%, the capacity of the tank required for adjusting the aqueous solution can be reduced compared to the conventional method, and the water treatment equipment can be made compact. In addition, the performance deterioration of the aqueous solution in which the polymer flocculant is dissolved can be suppressed by increasing the dissolution concentration.

[0046] The aqueous solution of the polymer flocculant according to this embodiment has a lower viscosity than general polymer flocculants as described above, and therefore does not require rapid stirring. Therefore, the polymer flocculant can bring the moldy odor producing organisms in the treated water into contact with or incorporate them into the flocs, coarsening them and improving the settling speed of the flocs. Therefore, the flocs containing the moldy odor producing organisms can be quickly settled and removed in the subsequent settling separation treatment, and the moldy odor producing organisms can be more reliably separated and removed from the treated water.

[0047] In the conventional method for removing moldy odor from treated water that combines activated carbon treatment and an inorganic flocculant, depending on the properties of the treated water, the flocculation effect of the inorganic flocculant may be small, and the flocs generated in the treated water may be small. As a result, the settling speed of the flocs is slow, and the amount of suspended matter in the solid-liquid separation liquid increases, and good treated water quality may not be obtained. According to this embodiment, a polymer flocculant having a cross-linking adsorption effect is used to form coarser flocs from the flocs generated by the inorganic flocculant, so that moldy odor producing organisms can be more reliably captured in the flocs and can be easily separated by settling, so that the moldy odor producing organisms can be more reliably removed from the treated water.

[0048] The pollutants contained in the water to be treated include suspended solids such as suspended solids and those having colloidal properties. Among them, substances that do not naturally settle, such as colloids, mainly have negative charges, and exist in a stable state in the water to be treated by repelling each other. Since these substances repel each other and float in the raw water, and do not cause coagulation, a coagulation and sedimentation treatment is performed by adding an inorganic coagulant having a positive charge to neutralize the charge. However, depending on the properties of the water to be treated, even if a large amount of inorganic coagulant is injected, the coagulation and sedimentation treatment effect may not be significantly improved. According to this embodiment, even for such water to be treated in which the coagulation and sedimentation treatment effect is small even by adding an inorganic coagulant, small flocs in the water to be treated can be coarsened by injecting a small amount of polymer coagulant, so that the settling speed of the flocs can be improved and a higher coagulation and sedimentation treatment effect can be obtained. This allows the amount of coagulant used in the entire treatment to be reduced, and the treatment efficiency to be improved.

[0049] (Water treatment equipment) As shown in FIG. 1, a water treatment device according to an embodiment of the present invention includes a raw water tank 1 for accommodating water to be treated that contains moldy odor producing organisms, a mixing tank 2 into which the water to be treated is introduced, an inorganic flocculant injection means 3 for injecting an inorganic flocculant into the water to be treated in the mixing tank 2, a flocculation tank 4 for forming flocs in the water to be treated after the inorganic flocculant is injected, a polymer flocculant injection means 6 for injecting a polymer flocculant having an acrylamide monomer content of 0.05 wt% or less or containing no acrylamide into the water to be treated at 0.05 to 2.0 mg / L, and a solid-liquid separation tank 7 for removing the moldy odor producing organisms from the water to be treated by performing solid-liquid separation of the water to be treated after the injection of the polymer flocculant.

[0050] The raw water tank 1 is a tank for storing the water to be treated. In the case of a water purification facility, a receiving well or the like can be suitably used to store the raw water to be treated, which is the raw water conveyed from a water intake tower or the like, and to adjust the amount and level of the taken-in water to be treated and to grasp the water quality of the water to be treated. The raw water tank 1 may be connected to various measuring instruments such as a water level gauge for measuring the water level, a pH meter, a conductivity meter, a turbidity meter, an alkalinity meter, a flow meter, a water temperature meter, a color meter, and a particle meter. When the raw water tank 1 is a receiving well or the like, moldy odor producing organisms in the water to be treated may rapidly grow when the water level drops, when the inflow amount of the water to be treated decreases, when the sunshine hours become longer, when the temperature exceeds a certain level, and the like. Therefore, in order to optimize the injection rate of the coagulant, it is preferable to sample a certain amount of the water to be treated in the raw water tank 1 at predetermined time intervals and measure the number of moldy odor producing organisms in the water to be treated at predetermined time intervals.

[0051] The mixing tank 2 is a tank in which small flocs are formed in the water to be treated by injecting an inorganic coagulant and rapidly stirring it, and in the case of a water purification facility, a mixing basin in which the inorganic coagulant is injected and mixed can be suitably used. The mixing tank 2 has multiple tanks, each of which is provided with an agitator 21 for stirring the water to be treated to which the inorganic coagulant has been added. The water to be treated to which the inorganic coagulant has been mixed in the mixing tank 2 is sent to the flocculation tank 4.

[0052] The flocculation tank 4 is a tank in which flocs are formed in the water to be treated, and in the case of a water purification facility, a flocculation pond or the like can be suitably used. The flocculation tank 4 has a plurality of tanks, typically about 3 to 4 tanks, each of which is provided with an agitator 31 for stirring under slower stirring conditions than those in the mixing tank 2. When the flocculation tank 4 is a bypass type, the agitator 31 can be omitted. In the flocculation tank 4, it is preferable to employ a tapered flocculation type in which the stirring speed of the water to be treated gradually decreases toward the latter stage.

[0053] The polymer flocculant injection means 6 is a device for injecting a polymer flocculant into the water to be treated into which an inorganic flocculant has been injected. The polymer flocculant injection means 6 includes, for example, a dissolution tank (not shown) for dissolving a powdered polymer flocculant in water, and an injection pump (not shown) for injecting the polymer flocculant into the water to be treated at a predetermined injection rate.

[0054] The polymer flocculant is in powder form and is dissolved in water in a dissolution tank to prepare an aqueous solution with a predetermined dissolution concentration. According to this embodiment, a polymer flocculant with an acrylamide monomer content of 0.05 wt% or less or a polymer flocculant that does not contain acrylamide is used as the polymer flocculant, so that the dissolution concentration can be increased. For example, a dissolution tank for preparing a high-concentration aqueous solution of a polymer flocculant with a dissolution concentration of more than 0.2 wt% and 0.4 wt% or less can be smaller in volume than a conventional dissolution tank, so that the equipment can be made smaller. In addition, the polymer flocculant can be injected into the water to be treated by the injection pump so that the injection rate ratio of the polymer flocculant to the inorganic flocculant (polymer flocculant injection rate [mg / L] / inorganic flocculant injection rate [mg / L]) is 0.001 to 0.13, so that coarse flocculants that capture moldy odor-producing organisms can be efficiently formed in the water to be treated, and the coagulation and sedimentation treatment effect is improved. The injection rate ratio of the polymer flocculant to the inorganic flocculant may be adjusted to an optimal value by a control device (not shown) or the like depending on the properties of the water to be treated.

[0055] The polymer flocculant injection means 6 is preferably connected to the rear of the mixing tank 2, the piping on the outlet side of the mixing tank 2, the inlet of the flocculation tank 4, or the front of the flocculation tank 4, for example, the first or second tank. By connecting the polymer flocculant injection means 6 to the rear of the mixing tank 2 or the front of the flocculation tank 4, the polymer flocculant can be efficiently brought into contact with the water to be treated in which small flocs have been formed by rapid stirring after the inorganic flocculant has been injected, thereby coarsening the flocs. In the example of FIG. 1, an example is shown in which the flocculation tank 4 is composed of four tanks. In such a case, the polymer flocculant injection means 6 is connected to at least the front part of the flocculation tank 4, for example, the first and / or second tanks, so that coarse flocs can be more efficiently formed in the water to be treated while ensuring the residence time required for mixing the water to be treated and the polymer flocculant. The water to be treated in which flocs have been formed by the inorganic flocculant and the polymer flocculant is sent to the solid-liquid separation tank 7.

[0056] The solid-liquid separation tank 7 is a device for removing flocs grown in the coagulation and sedimentation treatment by, for example, gravitational settling to obtain treated water, and in the case of a water purification facility, a settling tank or the like can be suitably used. According to this embodiment, the coagulation and sedimentation treatment is performed using an inorganic coagulant and a small amount of polymer coagulant without using activated carbon as in the conventional treatment, so that in the sedimentation separation treatment, flocs containing musty odor producing organisms are more reliably removed and the amount of coagulant injected can be significantly reduced, compared to the conventional treatment using activated carbon.

[0057] As described above, the present invention has been described with reference to the above-mentioned embodiment, but the description and drawings forming a part of this disclosure should not be understood as limiting the present invention. The present disclosure is not limited to the above-mentioned embodiment, and the components can be combined and modified to be embodied without departing from the spirit of the present disclosure.

[0058] In the above embodiment, an example of a water treatment device shown in Fig. 1 is described assuming a lateral flow type coagulation sedimentation facility, but the water treatment facility is not limited to a lateral flow type coagulation sedimentation facility, and can be applied to various facilities that are in practical use. For example, the present invention can be widely applied to water treatment facilities having a slurry circulation type or sludge blanket type high-speed coagulation sedimentation facility. EXAMPLES

[0059] 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.

[0060] (Continuous water flow test) A coagulation and sedimentation treatment test with continuous water flow was conducted in a water purification plant equipped with the water treatment device shown in Figure 1. The outline of the test device and the test conditions are shown in Table 1.

[0061] [Table 1]

[0062] The equipment conditions were the same for both the comparative example and the example, and the raw water flow rate and the injection rate of the inorganic flocculant were the same. The inorganic flocculant used was polyaluminum chloride (PAC250A (registered trademark)) manufactured by Taki Chemical Co., Ltd. The polymer flocculant used was WA-600 manufactured by Suing Co., Ltd., which is a polyacrylate salt-based acrylamide-free polymer flocculant that does not contain acrylamide monomers. In the comparative example, no polymer flocculant was injected, and in the example, the polymer flocculant was injected into the slow stirring tank (floc formation tank) at an injection rate of 0.2 mg / L. The slow stirring tank has four tanks as shown in FIG. 1, and in the example, the polymer flocculant was injected into the most upstream tank. The position where the coagulation and sedimentation treated water was collected was the upper part of the settling tank where the water surface load was 10 mm / min.

[0063] The musty odor producing organisms used in the test were wild strains of Phormidium that actually release the odorous substance 2-MIB present in raw water, without adding any new culture strains. Phormidium were counted according to the measurement method for the count unit of the target organism based on the description on page 311 of the Japan Water Works Association's "Water Supply Test Methods 2020 Edition IV. Microorganisms V. Biological Organisms", after placing 1 mL of the target water on a clinical examination glass (interface slide glass) manufactured by Matsunami Glass Industry Co., Ltd., and counting visually using a biological microscope (Biological microscope BM2000 manufactured by AS ONE Corporation). Note that since Phormidium has a filamentous appearance and is not uniform in length, it was counted as 1 organism per 100 μm in length.

[0064] In both the examples and the comparative examples, one day of continuous water flow test was defined as one RUN, and three RUNs (RUN1-RUN3, RUN4-RUN6) of continuous water flow test were performed. Since it takes a certain amount of time from the start of actual water flow until the treatment becomes stable, the water flow time and total water flow time are set to 0 (zero) two hours after the start of water flow in the examples and the comparative examples, and the water flow time and total water flow time are recorded. That is, in RUN1 in Table 2, the actual water flow time is 7.5 hours in total, but the 2.4 hours when the treatment becomes stable are recorded as "total water flow time 0.4 hr". The test results in the comparative examples are shown in Table 2, and the test results in the examples are shown in Table 3. In Tables 2 and 3, cases in which the number of Phormidium in the raw water or the coagulation sedimentation treated water could not be counted or evaluated due to the continuous water flow test and the convenience of the water purification plant are recorded as non-analysis (NA).

[0065] [Table 2]

[0066] As shown in Table 2, in RUNs 1 to 3 of the comparative example, the number of phormidium in the coagulation sedimentation treated water was 0 to 19 particles / mL, with an average of 8 particles / mL, and the turbidity was 0.55 to 1.2 degrees, with an average of 0.78 degrees. In the comparative example, a relatively good treated water turbidity was obtained, but it was confirmed that more than 8 particles / mL of phormidium, a substance that causes a moldy odor, remained in the coagulation sedimentation treated water.

[0067] [Table 3]

[0068] As shown in Table 3, in Runs 4 to 6 of the embodiment, the number of phormidium in the coagulation sedimentation treated water was 0 to 3 particles / mL, with an average of 1 particle / mL, and the turbidity was 0.29 to 1.6 degrees, with an average of 0.79 degrees. The treated water had a similar turbidity to the comparative example, but it was confirmed that by injecting a polymer flocculant, the number of phormidium in the coagulation sedimentation treated water was significantly reduced to 3 particles / mL or less.

[0069] (Study on the relationship between the dissolved concentration of polymer flocculants and flocculation performance) In this test, two types of polymer flocculants were prepared: one that did not contain acrylamide monomer and one that contained more than 0.05 wt% acrylamide monomer. The dissolved concentration and flocculation performance of each polymer flocculant were evaluated by a jar test. The polymer flocculant that did not contain acrylamide was WA-600 manufactured by Suing Co., Ltd., as described above, and the polymer flocculant that contained more than 0.05 wt% acrylamide monomer was WA-142 manufactured by Suing Co., Ltd. In the jar test, an inorganic flocculant was injected into the raw water at 20 mg / L and rapidly stirred, and then a polymer flocculant was injected at 0.2 mg / L and slowly stirred, and then the mixture was left to stand for 10 minutes. The turbidity of the supernatant water after standing was measured. The raw water used was the same as that used in Tables 1 to 3. The turbidity of the supernatant water was measured using a turbidimeter WA6000 manufactured by Nippon Denshoku Kogyo Co., Ltd. The floc settling velocity was calculated as the settling distance per hour after measuring the settling distance of the flocs with a ruler in 5- or 10-second intervals. The test conditions are shown in Table 4.

[0070] [Table 4]

[0071] The measurement results of the supernatant water turbidity are shown in Figure 2, and the measurement results of the floc settling velocity are shown in Figure 3. As shown in Figure 2, the supernatant water turbidity shows a slight tendency to increase with increasing dissolution concentration in polymer flocculants containing more than 0.05 wt% of acrylamide monomer, but no increase in turbidity was observed with increasing dissolution concentration in polymer flocculants not containing acrylamide. In other words, according to the examples, it can be seen that a good turbidity removal effect is obtained even when the dissolution concentration of the polymer flocculant is increased.

[0072] As shown in Figure 3, when the floc settling velocity was evaluated, the floc settling velocity of the polymer flocculant containing more than 0.05 wt% of acrylamide monomer dropped rapidly with an increase in the dissolved concentration, resulting in poor flocculation, whereas the acrylamide-free polymer flocculant obtained a stable high floc settling velocity. In other words, the results of Figures 2 and 3 show that the acrylamide-free polymer flocculant maintains good flocculation performance in terms of supernatant turbidity and floc settling velocity, even when the dissolved concentration is increased compared to the conventional acrylamide-containing polymer flocculant.

[0073] That is, according to the water treatment method and water treatment device of the embodiment of the present invention, it is possible to shorten the dissolution time of the polymer flocculant, and especially after the polymer flocculant is injected, it is possible for the polymer flocculant to come into contact with the flocs and moldy odor producing organisms in the water to be treated quickly and reliably. This improves the settling speed of the flocs and the removal of the moldy odor producing organisms. Furthermore, according to the water treatment method and water treatment device of the embodiment of the present invention, since the viscosity of the polymer flocculant is lower than that of conventional polymer flocculants, it is possible to set the dissolution concentration high and make the dissolution tank compact. As a result, it is possible to reduce the initial cost and increase the freedom of installation space. [Explanation of symbols]

[0074] 1: Raw water tank 2: Mixing tank 3: Inorganic coagulant injection means 4: Flocculation tank 6: Polymer coagulant injection means 7: Solid-liquid separation tank 21, 31: Stirrer

Claims

1. A water treatment method comprising the steps of injecting an inorganic flocculant into water to be treated that contains organisms producing a moldy odor, and then injecting 0.05 to 2.0 mg / L of a polymer flocculant having an acrylamide monomer content of 0.05 wt % or less or containing no acrylamide, thereby removing the organisms producing a moldy odor from the water to be treated.

2. 2. The water treatment method according to claim 1, wherein the acrylamide-free polymer flocculant contains a polyacrylate.

3. 2. The water treatment method according to claim 1, wherein the inorganic flocculant is injected at 15 to 50 mg / L, and the polymer flocculant is injected at 0.05 to 2.0 mg / L.

4. The water treatment method according to any one of claims 1 to 3, characterized in that the polymer flocculant is injected so that the injection rate ratio of the polymer flocculant to the inorganic flocculant (polymer flocculant injection rate [mg / L] / inorganic flocculant injection rate [mg / L]) is 0.001 to 0.

13.

5. The water treatment method according to any one of claims 1 to 3, characterized in that the polymer flocculant is dissolved to form an aqueous solution having a dissolution concentration of more than 0.2 wt% and not more than 0.4 wt%, and then the aqueous solution is injected into the water to be treated.

6. The water treatment method according to any one of claims 1 to 3, characterized in that the injection rate of the polymer coagulant is determined based on the predetermined injection rate of the inorganic coagulant and the concentration of the mold odor producing organisms in the treated water, without increasing the predetermined injection rate of the inorganic coagulant.

7. 4. The water treatment method according to claim 1, wherein the musty odor producing organisms include cyanobacteria that produce geosmin or 2-methylisoborneol.

8. A mixing tank into which water to be treated containing mold odor producing organisms is introduced; an inorganic flocculant injection means for injecting an inorganic flocculant into the water to be treated in the mixing tank; a flocculation tank for forming flocs in the water to be treated after the inorganic coagulant is injected; A polymer flocculant injection means for injecting a polymer flocculant having an acrylamide monomer content of 0.05 wt % or less or containing no acrylamide into the water to be treated at 0.05 to 2.0 mg / L; a solid-liquid separation tank for removing the moldy odor producing organisms from the treated water by performing solid-liquid separation of the treated water after the injection of the polymer flocculant; A water treatment device comprising:

9. 9. The water treatment device according to claim 8, wherein the flocculation tank includes a plurality of tanks, and the polymer flocculant injection means is connected to at least the first or second stage of the flocculation tank.

10. The polymer flocculant injection means is A dissolution tank for dissolving the powdered polymer flocculant to prepare an aqueous solution of the polymer flocculant having a dissolution concentration of more than 0.2 wt % and not more than 0.4 wt %; An injection pump that injects the polymer flocculant into the treated water so that the injection rate ratio of the polymer flocculant to the inorganic flocculant (polymer flocculant injection rate [mg / L] / inorganic flocculant injection rate [mg / L]) is 0.001 to 0.13; The water treatment device according to claim 8 or 9, further comprising:

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