Muddy water treatment apparatus and muddy water treatment method

Abstract

To provide a turbid water treatment apparatus capable of realizing an optimum treatment method (pH range) using magnetic particles and a method for suppressing the use amount of a neutralizing agent when turbid water is mixed with cement and is alkaline, and a turbid water treatment method.SOLUTION: A muddy water treatment apparatus 1 according to the present invention includes a reaction tank 4 that coagulates suspended solids in cement muddy water to which an inorganic coagulant and magnetic particles are added, a coagulation tank 5 that is provided downstream of the reaction tank 4 and coagulates the suspended solids in the cement muddy water to which a polymer coagulant is added to form magnetic floc, a sedimentation tank 6 that is provided downstream of the coagulation tank 5 and sediments the coagulated magnetic floc to obtain supernatant water and sludge containing the magnetic particles, a recovery unit 8 that recovers the magnetic particles from the sludge, and a supply unit 9 that supplies the recovered magnetic particles to the cement muddy water.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to a turbid water treatment device and a turbid water treatment method. [Background technology]

[0002] FIG. 22 is a schematic diagram illustrating the configuration of a typical coagulation-sedimentation device. As shown in FIG. 22, a typical coagulation-sedimentation device 221 includes a pH adjustment tank 222, a reaction tank 223, a coagulation tank 224, and a settling tank 225. In the pH adjustment tank 222, a pH adjuster (neutralizer) is added to the raw water (turbid water) to adjust the pH of the turbid water. In the reaction tank 223, an inorganic coagulant is added to the pH-adjusted turbid water and thoroughly mixed with the suspended solids in the turbid water to form basic flocs. In the coagulation tank 224, a polymer coagulant is added, and coarse flocs are formed by the cross-linking action of the polymer coagulant. In the settling tank 225, the flocs are precipitated to form sediments (suspended solids) and separated from the supernatant water. The supernatant water is then discharged as treated water, and the sediments are discharged as sludge. If the pH of the supernatant water does not meet the discharge regulation value, the pH of the supernatant water is neutralized in a neutralization treatment tank (not shown) before being discharged.

[0003] The above-mentioned common coagulation and sedimentation devices have the problem that it takes time for flocs to settle, and the larger the treatment volume, the larger the device becomes. Furthermore, because the preferred application range for commonly used inorganic coagulants (e.g., polyaluminum chloride (PAC)) is a pH range of 6 to 9, coagulation and sedimentation is generally performed on raw water in the neutral range. Therefore, for alkaline (e.g., pH 9 or higher) turbid water, such as turbid water containing cement (cement turbid water), which is often generated in tunnel drainage, neutralization is first performed using a neutralizing agent such as dilute sulfuric acid or carbon dioxide before coagulation and sedimentation. However, this treatment requires large amounts of dilute sulfuric acid, carbon dioxide, etc., which is a factor in increasing costs.

[0004] Among the above-mentioned problems, with regard to the settling of flocs, attempts have been made to shorten the settling time by adding granular materials (sand, etc.) to coarsen the flocs, as described in, for example, Patent Documents 1 to 3. The techniques described in these documents coarsen the flocs using the added granular materials as nuclei, thereby promoting settling.

[0005] Furthermore, in recent years, a technology has been proposed for floc precipitation, as described in Patent Document 4, for example. Patent Document 4 describes a purification device that includes a coagulation tank that adds a coagulant and magnetic powder (magnetic particles / magnetic bodies) to raw water to perform coagulation treatment, a sludge blanket-type settling tank into which effluent from the coagulation tank is introduced, and a means for extracting sludge from below the sludge blanket in the settling tank and transporting it to a sludge decomposition device. Patent Document 4 states that when a coagulation settling method using magnetic powder as a seed agent is adopted for this purification device, the settling rate increases, thereby increasing the removal rate, and the magnetic powder can be easily reused, improving the efficiency of continuous operation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3866054 [Patent Document 2] Patent No. 4073116 [Patent Document 3] Patent No. 6725316 [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-170404 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technology described in Patent Document 4 leaves room for improvement in terms of the optimal treatment method (pH range) using magnetic particles. Furthermore, the technology described in Patent Document 4 is unable to reduce the amount of neutralizer used when the turbid water is alkaline and contains cement. This is because the technology described in Patent Document 4 does not consider the idea of ​​performing coagulation and sedimentation treatment without adjusting the pH when the turbid water is alkaline and contains cement, and then neutralizing the supernatant water after the treatment.

[0008] The present invention has been made in view of the above circumstances. An object of the present invention is to provide a turbid water treatment device and a turbid water treatment method that can realize an optimal treatment method (pH range) using magnetic particles and a method for reducing the amount of neutralizing agent used when the turbid water is alkaline due to the presence of cement. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention has the following means. The present invention provides a turbid water treatment device comprising: a reaction tank for flocculating suspended matter in turbid cement water to which an inorganic flocculant and magnetic particles have been added; a coagulation tank located downstream of the reaction tank for flocculating the suspended matter in the turbid cement water to which a polymer flocculant has been added to form magnetic flocs; a settling tank located downstream of the coagulation tank for settling the flocculated magnetic flocs to obtain supernatant water and sludge containing the magnetic particles; recovery means for recovering the magnetic particles from the sludge; and supply means for supplying the recovered magnetic particles to the turbid cement water.

[0010] The present invention also provides a turbid water treatment method comprising the steps of: adding an inorganic flocculant and magnetic particles to cement turbid water; a reaction step of flocculating suspended matter in the cement turbid water using the inorganic flocculant and the magnetic particles; a flocculation step of further flocculating the flocculated suspended matter to form magnetic flocs by adding a polymer flocculant; a precipitation step of precipitating the flocculated magnetic flocs to obtain supernatant water and sludge containing the magnetic particles; a recovery step of recovering the magnetic particles from the sludge; and a supply step of supplying the recovered magnetic particles to the cement turbid water.

[0011] Because cement turbid water has a pH of 9 or higher, conventional coagulation and sedimentation treatment (using PAC and polymer flocculants) requires neutralization of the cement turbid water before the coagulation and sedimentation treatment, requiring a large amount of neutralizing agent. In contrast, the turbid water treatment device and turbid water treatment method of the present invention add magnetic particles in addition to conventional coagulation and sedimentation treatment, allowing for coagulation and sedimentation (forming and precipitating magnetic flocs) without neutralizing the turbid water while the water remains alkaline. This eliminates the need for pH adjustment of the cement turbid water before flocculation. Therefore, the turbid water treatment device and turbid water treatment method of the present invention significantly reduce the amount of neutralizing agent added to the supernatant water after treatment (i.e., supernatant water with low levels of suspended solids, such as soil particles, that have pH buffering properties) compared to adding neutralizing agent to turbid water with high levels of suspended solids, thereby reducing costs and achieving efficient treatment. Furthermore, the turbid water treatment device and turbid water treatment method of the present invention have a simple configuration, thereby reducing the manufacturing costs of the device.

[0012] In the turbid water treatment device of the present invention, it is preferable to provide a discharge reservoir tank downstream of the settling tank for storing the supernatant water. Furthermore, the turbid water treatment method of the present invention preferably includes a discharge storage step of storing the supernatant water after the sedimentation step. By doing this, while the supernatant water is being stored, it is possible to check whether the supernatant water contains suspended solids or particles before being discharged, whether the turbidity meets the discharge regulation value, etc. Furthermore, if an unforeseen event occurs that makes discharge inappropriate, the discharge of the supernatant water can be stopped.

[0013] In the turbid water treatment device of the present invention, it is preferable to provide a first separation means between the settling tank and the discharge storage tank for separating the magnetic particles from the supernatant water. In addition, in the turbid water treatment method of the present invention, it is preferable to carry out a first separation step of separating the magnetic particles from the supernatant water between the sedimentation step and the storage step for discharge. Magnetic particles with small particle sizes (fine magnetic particles) are light and therefore do not settle easily. Therefore, fine magnetic particles may be contained in the supernatant water. Even in such cases, the first separation means or the first separation step can effectively separate and recover the fine magnetic particles from the supernatant water. This also allows the removal of fine magnetic particles from the supernatant water, thereby reducing the amount of suspended solids (weight of suspended solids per unit water volume; SS) in the discharged water and reducing factors that could lead to exceeding emission regulations. Furthermore, the magnetic particles become smaller due to wear caused by repeated use, and fine magnetic particles that do not settle in the sedimentation tank but instead float in the supernatant water can be removed.

[0014] The turbid water treatment device of the present invention preferably includes an extracting means for extracting the sludge that has accumulated at the bottom of the reaction tank from the reaction tank. Magnetic particles with large particle diameters (coarse magnetic particles) are heavy and therefore settle easily. Therefore, the coarse magnetic particles settle quickly without contributing to the formation of flocs. A considerable amount of such coarse magnetic particles is contained in the sludge obtained by retention at the bottom of the reaction tank. Even in such cases, by removing the sludge from the reaction tank, it is possible to prevent the coarse magnetic particles from remaining in the reaction tank and reducing its effective capacity. Furthermore, because the coarse magnetic particles are removed from the reaction tank, it is possible to prevent a decrease in the floc coagulation performance and mixing effect that would otherwise occur due to a reduction in the effective capacity.

[0015] In the turbid water treatment device of the present invention, the reaction tank preferably has a stirring strength that makes it difficult for the magnetic particles having a particle size of 75 μm or less to settle. If the magnetic particles have a particle size of 75 μm or less, the magnetic particles can be prevented from settling in the reaction tank without requiring excessive stirring strength. In the turbid water treatment device of the present invention, the first separating means is preferably a magnetic separator, which makes it possible to recover almost all of the magnetic particles from the supernatant water.

[0016] In the turbid water treatment device of the present invention, the removal means preferably includes a bottom section provided at the bottom of the reaction tank, the cross-sectional area of ​​which decreases downward in the reaction tank. This allows sludge to settle by gravity and accumulate below the bottom section. The sludge accumulated below the bottom section can then be easily removed from the reaction tank.

[0017] In the turbid water treatment device of the present invention, a turbid water storage tank for storing the cement turbid water is provided upstream of the reaction tank, and the extraction means is provided with a second separation means for separating the magnetic particles from the extracted sludge, and it is preferable that the sludge from which the magnetic particles have been separated by the second separation means is returned to the turbid water storage tank. Furthermore, in the turbid water treatment method of the present invention, it is preferable to have a turbid water storage step in which the cement turbid water is stored before the adding step, and in the reaction step, a second separation step is carried out in which, at an appropriate time, sludge remaining at the bottom of the reaction tank that coagulates the suspended matter in the cement turbid water is removed, the sludge is separated from the magnetic particles in the sludge, and the sludge from which the magnetic particles have been separated is returned to the turbid water storage step. In this way, the coarse magnetic particles contained in the sludge can be suitably separated and recovered by the second separation means or the second separation step. The sludge from which the magnetic particles have been separated is returned to the turbid water storage tank or the turbid water storage step, and is subjected to turbid water treatment again.

[0018] The turbid water treatment device of the present invention is provided with a pH adjusting device that adjusts the pH of the supernatant water immediately before or after the discharge storage tank. The turbid water treatment method of the present invention also includes a pH adjustment step of adjusting the pH of the supernatant water immediately before or after the storage step for discharge. By doing these things, the pH of turbid cement water is often 9 or higher, so neutralization treatment can clear the emission regulations. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a turbid water treatment device and a turbid water treatment method that can realize an optimal treatment method (pH range) using magnetic particles and a method for reducing the amount of neutralizing agent used when the turbid water contains cement and is alkaline. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram illustrating the configuration of a turbid water treatment device according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a magnetic separator. [Figure 3] 2 is a flowchart illustrating a method for treating muddy water according to the first embodiment. [Figure 4A]1 is a graph showing the test results of investigating the effect of turbid water pH on coagulation performance. In this figure, the horizontal axis is pH and the vertical axis is turbidity [NTU]. [Figure 4B] 1 is a graph showing the test results of investigating the effect of turbid water pH on coagulation performance. In this figure, the horizontal axis is pH and the vertical axis is turbidity [NTU]. [Figure 5] FIG. 10 is a schematic diagram illustrating sampling positions in Test 2. [Figure 6A] 1 is a graph showing the relationship between the amount of magnetic particles present and particle size during rapid stirring, in which the horizontal axis represents the particle size range and the vertical axis represents the amount of magnetic particles present [wt %]. [Figure 6B] 1 is a graph showing the relationship between the amount of magnetic particles present and particle size during slow stirring, in which the horizontal axis represents the particle size range and the vertical axis represents the amount of magnetic particles present [wt %]. [Figure 7] 1 is a graph showing the effect of magnetic particle size on the turbidity of treated water, where the horizontal axis represents the particle size range and the vertical axis represents turbidity [NTU]. [Figure 8] 1 is a graph showing the amount of 5% diluted sulfuric acid added to the turbid water and the supernatant water after treatment until the pH reached 8.6. In this figure, the horizontal axis is the pH of the turbid water, and the vertical axis is the amount of 5% diluted sulfuric acid added [mL / L]. [Figure 9] FIG. 1 is an explanatory diagram illustrating a method for a magnetic particle recovery test. [Figure 10] Photographs (left) and (right) show the state of turbid water A (on-site generated raw water) in Test 5 before coagulation and sedimentation treatment, respectively, a photograph (center) showing the state after coagulation and sedimentation treatment without adding iron powder, and a photograph (right) showing the state after coagulation and sedimentation treatment with iron powder added. [Figure 11] FIG. 10 is a schematic diagram illustrating the configuration of a turbid water treatment device according to a second embodiment. [Figure 12] FIG. 10 is a schematic diagram showing an example of a preferred embodiment of a turbid water treatment device according to the second embodiment. [Figure 13] FIG. 2 is a schematic diagram illustrating an embodiment of the extraction means and the magnetic separator. [Figure 14] 10 is a flowchart illustrating a method for treating muddy water according to a second embodiment. [Figure 15] 10 is a flowchart illustrating a method for treating turbid water according to a preferred aspect of the second embodiment. [Figure 16] 10 is a flowchart illustrating a method for treating turbid water according to another preferred aspect of the second embodiment. [Figure 17] 10 is an explanatory photograph showing a full view of a demonstration test device (corresponding to a turbid water treatment device) in an example related to the second embodiment. [Figure 18] FIG. 1 is a schematic diagram illustrating the high-speed coagulation and sedimentation apparatus used in Test 6. [Figure 19] 1 is a graph showing the turbidity in the settling tank 8 minutes, 12 minutes, 16 minutes, and 20 minutes after the start of the test. [Figure 20] 1 is a graph and a table showing the results of SS in the supernatant water (treated water) of the settling tank 8 minutes, 12 minutes, 16 minutes, and 20 minutes after the start of the test. [Figure 21] 1 is a graph showing the results of measuring the particle size distribution of two common types of commercially available iron powder. [Figure 22] FIG. 1 is a schematic diagram illustrating the configuration of a general coagulation and sedimentation device. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of a turbid water treatment device and a turbid water treatment method according to the present invention will be described in detail with reference to the accompanying drawings. In the description of each embodiment, the same components will be denoted by the same names and symbols, and duplicate descriptions may be omitted.

[0022] First Embodiment (Muddy water treatment equipment) FIG. 1 is a schematic diagram illustrating the configuration of a turbid water treatment device 1 according to the first embodiment. As shown in Figure 1, the turbid water treatment device 1 of the first embodiment includes a turbid water storage tank 2, a pH adjustment tank 3, a reaction tank 4, a coagulation tank 5, a sedimentation tank 6, a neutralization treatment tank 7, a recovery means 8, and a supply means 9. This turbid water treatment device 1 treats turbid water containing suspended solids to obtain supernatant water, which is then discharged outside the device as treated water. Examples of turbid water include, but are not limited to, wastewater from construction and civil engineering projects, as well as sewage, rainwater, river water, lake water, and seawater. Turbid water can be of any origin as long as it contains suspended solids. The pH of the turbid water may be acidic (e.g., pH less than 3.0), weakly acidic (e.g., pH 3.0 to less than 6.0), neutral (e.g., pH 6.0 to 8.0), weakly alkaline (e.g., pH greater than 8.0 to 11.0), or alkaline (e.g., pH greater than 11.0). Note that, in this specification, weakly alkaline and alkaline are sometimes collectively referred to as alkaline. Furthermore, as will be described later in this embodiment, the treatment procedures performed by the device vary depending on whether the turbid water is cement turbid water and whether the pH of the turbid water measured in the turbid water storage tank 2 is 9 or higher. When the turbid water is cement turbid water, the pH is often 9 or higher, and often 11 or higher. Each component of the turbid water treatment device 1 will be described below.

[0023] The turbid water storage tank 2 takes in and stores turbid water. The turbid water storage tank 2 is equipped with a pH meter 21 that measures the pH of the turbid water. The pH meter 21 measures the pH of the turbid water continuously or intermittently. A commercially available pH meter 21 can be used. The pH adjustment tank 3 is provided downstream of the turbid water storage tank 2. When the pH of the turbid water measured in the turbid water storage tank 2 is less than 6, the pH adjustment tank 3 adjusts the pH of the turbid water to between 6 and 9. When the pH of the turbid water measured in the turbid water storage tank 2 is 9 or more but is not cement turbid water, the pH adjustment tank 3 adjusts the pH of the turbid water to between 6 and 9. Since the preferred application range of the inorganic flocculant added in the reaction tank 4 is pH 6 to 9, the pH adjustment tank 3 adjusts the pH of the turbid water of less than pH 6 to within the preferred application range of the inorganic flocculant. When the pH of the turbid water measured in the turbid water storage tank 2 is equal to or greater than 6 but less than 9, or when the pH is 9 or greater and the turbid water is cement turbid water, the turbid water is sent from the turbid water storage tank 2 to the reaction tank 4 without passing through the pH adjustment tank 3.

[0024] Here, for turbid water with a pH of 6 or more and less than 9 (regardless of whether it is cement turbid water), an inorganic flocculant is added in the reaction tank 4, and a polymer flocculant is added in the coagulation tank 5 to coagulate suspended matter in the turbid water. Furthermore, when the pH is 9 or more and the water is cement turbid water, an inorganic flocculant and magnetic particles are added in the reaction tank 4, and a polymer flocculant is added in the coagulation tank 5 to coagulate suspended matter in the turbid water. In this embodiment, magnetic particles are used when the water is cement turbid water and the pH is 9 or more, so even if the water has a pH of 9 or more, it is not necessary to adjust the pH of the turbid water to 6 or more and less than 9 before coagulation. The pH adjustment tank 3 may be any tank capable of taking in and storing turbid water and adjusting the pH, and there are no limitations on its shape, size, or material. The pH adjustment tank 3 may be equipped with an agitation means (not shown), such as an agitator blade or bubbling agitator, to quickly adjust the pH of the turbid water. An appropriate pH adjustment tank 3 can be used depending on the properties of the turbid water (e.g., whether it is cement turbid water, acidic, neutral, etc.) and the amount of water. Neutralizing agents that can be used in the pH adjustment tank 3 include, but are not limited to, sodium hydroxide for acidic turbid water and dilute sulfuric acid or carbon dioxide gas for alkaline turbid water.

[0025] The reaction tank 4 is provided downstream of the turbid water storage tank 2 (downstream of the pH adjustment tank 3). The reaction tank 4 is equipped with inorganic flocculant addition means 41 that adds an inorganic flocculant to the turbid water. The reaction tank 4 is equipped with magnetic particle addition means 42 that adds magnetic particles to the turbid water. In the reaction tank 4, suspended matter in the turbid water is flocculated (forming basal flocs) by the inorganic flocculant and magnetic particles. The reaction tank 4 may be equipped with agitation means (not shown) such as a stirring blade or bubbling agitation to efficiently flocculate the suspended matter in the turbid water. Commercially available transport loader devices, feeder devices, screw conveyors, powder and granular material supply devices, etc. can be used for the inorganic flocculant adding means 41 and the magnetic particle adding means 42. The addition of the inorganic flocculant by the inorganic flocculant adding means 41 and the addition of the magnetic particles by the magnetic particle adding means 42 may be performed manually by an operator without using any device. The inorganic flocculant adding means 41 may be operated at an appropriate time when turbid water is taken in. Magnetic particles are administered to the magnetic particle administration means 42 when the turbid water treatment device 1 is used for the first time, when recovered magnetic particles are reused, or when lost magnetic particles are replenished, and the administered magnetic particles are added to the reaction tank 4.

[0026] Examples of inorganic flocculants that can be used include polyaluminum chloride (PAC), aluminum sulfate, ferric chloride, polyferric sulfate, ferrous sulfate, hydrated lime, low molecular weight cationic polymer flocculants, etc. The inorganic flocculant is not limited to those described above, and any flocculant can be used. The magnetic particles used have a specific gravity greater than that of suspended matter such as organic particles and inorganic particles contained in the turbid water. Iron powder is preferably used as the magnetic particles, but is not limited to this.

[0027] The magnetic particles preferably have a particle size of 106 μm or less. This size allows the magnetic particles to be distributed uniformly throughout the turbid water in the coagulation tank 5, thereby enabling efficient and effective coagulation of suspended solids in the turbid water. The particle size of the magnetic particles can be adjusted to any size, for example, by sieving using one or more sieves with a specified mesh size. The particle size of the magnetic particles is more preferably 75 μm or less, and even more preferably 45 μm or less. The smaller the particle size of the magnetic particles, the more uniformly they can be distributed throughout the turbid water, improving the coagulation effect of suspended solids in the turbid water. Methods for obtaining magnetic particles with small particle sizes include adding magnetic particles to a water tank, collecting the supernatant immediately after stirring, and then recovering the magnetic particles in the water using a magnetic separator. The particle size of the magnetic particles can be measured, for example, in accordance with JIS Z 8815-1994 (General Rules for Sieving Test Methods).

[0028] The coagulation tank 5 is provided downstream of the reaction tank 4. In the coagulation tank 5, a polymer coagulant is added to further coagulate the suspended solids into coarse magnetic flocs (in the case of treatment without using magnetic particles, ordinary coarse flocs are formed). Magnetic flocs are formed by flocculating suspended matter in turbid water using magnetic particles and inorganic flocculants, and then assembling these aggregates to form larger aggregates (aggregates). Polymer flocculants are also called organic flocculants. Examples of polymer flocculants that can be used include anionic flocculants, cationic flocculants, and nonionic flocculants. Examples of anionic and nonionic flocculants that can be used include polyacrylamide flocculants and sodium polyacrylate. Examples of cationic flocculants that can be used include polyacrylic acid ester flocculants and polymethacrylic acid ester flocculants. In addition to the above-mentioned polymer flocculants, other examples that can be used include polyamine flocculants and dicyandiamide flocculants. Organic flocculants are not limited to those mentioned above, and any flocculant can be used. The polymer flocculant can be added by polymer flocculant adding means 51 provided in the flocculation tank 5. As with the inorganic flocculant adding means 41 and the magnetic particle adding means 42, the polymer flocculant adding means 51 can be a commercially available transport loader device, feeder device, screw conveyor, powder and granular material supply device, etc. The polymer flocculant can be added by the polymer flocculant adding means 51 manually by an operator, regardless of the device used.

[0029] The settling tank 6 is provided downstream of the coagulation tank 5. In the settling tank 6, the coagulated magnetic flocs are allowed to settle, yielding supernatant water and sludge containing magnetic particles (ordinary sludge in the case of treatment without magnetic particles). The magnetic flocs and flocs can be settled by gravity settling, but if rapid treatment is desired, other methods such as centrifugation can be used. The settling tank 6 is equipped with a recovery means 8. The settling tank 6 sends settled sludge to the recovery means 8. The recovery means 8 then recovers magnetic particles from the sludge. The recovery means 8 can be, for example, a simple, widely used magnetic separator 81 (magnetic separator). FIG. 2 is a schematic diagram illustrating the configuration of the magnetic separator 81. As shown in FIG. 2, the magnetic separator 81 is equipped with a magnetic core 82, an outer cylinder 83 that covers the outer periphery of the magnetic core 82, a roller 84 that squeezes water out of the magnetic particles attached to the outer cylinder 83, and a scraper 85 that peels off the magnetic particles from which the water has been squeezed by the roller 84 from the outer cylinder 83. With such a recovery means 8, it is possible to recover almost all of the magnetic particles from the sludge. It should be noted that a magnet having a surface magnetic flux density of, for example, 2000 to 13000 gauss, preferably 4000 gauss or more, and more preferably 10000 gauss or more can be used as the magnet core 82. Specifically, a permanent magnet such as a ferrite (isotropic or anisotropic) magnet, a neodymium magnet, a samarium-cobalt magnet, or an alnico magnet can be used as the magnet core 82.

[0030] The sludge recovered from the recovery means 8 is composted, incinerated, or disposed of in a landfill. On the other hand, as will be described later, if the turbid water is not cement turbid water, or if it is cement turbid water but the pH is not 9 or higher, and the magnetic particle adding means 42, recovery means 8, and supply means 9 are stopped, no magnetic particles are used and therefore the sludge does not contain magnetic particles, so there is no need to recover or reuse the magnetic particles. Therefore, in this case, the sludge recovered in the settling tank 6 can be disposed of as is in the same manner as above, without going through the recovery means 8.

[0031] The supply means 9 supplies the magnetic particles collected by the collection means 8 to the magnetic particle adding means 42. The supply means 9 can be, for example, a belt conveyor or a screw conveyor, but a method in which the collection means 8 (magnetic separator 81) is placed above the reaction vessel 4 and the separated magnetic particles are directly introduced into the reaction vessel 4 reduces the loss of magnetic particles compared to transport by a conveyor or the like. Note that when the collection means 8 employs the method of directly introducing the separated magnetic particles into the reaction vessel 4, the collection means 8 serves both as the supply means 9 and the magnetic particle adding means 42.

[0032] The neutralization treatment tank 7 is located downstream of the settling tank 6. If the pH of the supernatant water obtained in the settling tank 6 is outside the discharge regulation value, the neutralization treatment tank 7 supplies a neutralizing agent to the supernatant water to neutralize it. The neutralization treatment tank 7 is equipped with a pH meter 71 for measuring the pH of the supernatant water. The pH meter 71 measures the pH of the supernatant water continuously or intermittently. As with the pH meter 21 described above, a commercially available pH meter can be used for the pH meter 71. The discharge regulation value can be, for example, a value set by the national or local government for the turbid water and treated water to be treated, or a voluntary value. The neutralizing agent used in the neutralization treatment tank 7 may be, for example, dilute sulfuric acid or carbon dioxide gas, but is not limited to these. Any neutralizing agent can be used as long as it can neutralize the pH of the supernatant water.

[0033] The above-described turbid water storage tank 2, reaction tank 4, flocculation tank 5, settling tank 6, and neutralization treatment tank 7 may be any tank capable of taking in and storing turbid water and supernatant water, and there are no limitations on their shape, size, or material. Any of these tanks can be used appropriately depending on the properties of the turbid water and supernatant water (for example, whether it is cement turbid water, acidic, neutral, alkaline, etc.) and the amount of water.

[0034] In this embodiment, in the turbid water treatment device 1 configured as described above, if the turbid water taken into the turbid water storage tank 2 is cement turbid water and the pH of the turbid water measured in the turbid water storage tank 2 is 9 or higher (this may be referred to as the former case in the description of this embodiment), the pH adjustment tank 3 is stopped, and the magnetic particle addition means 42, recovery means 8 and supply means 9 are operated, while the inorganic coagulant addition means 41, reaction tank 4, coagulation tank 5, sedimentation tank 6 and neutralization treatment tank 7 are operated.

[0035] In the former case, the turbid water treatment device 1 forms magnetic flocs by adding and reusing magnetic particles in addition to the normal coagulation and sedimentation treatment. In other words, in the former case, the turbid water treatment device 1 can perform coagulation and sedimentation treatment while the turbid water remains alkaline, without neutralizing the turbid water. As a result, the turbid water treatment device 1 can significantly reduce the amount of neutralizing agent added to the supernatant water after treatment compared to when a neutralizing agent is added to the turbid water, making it more efficient and cost-effective. Furthermore, because the turbid water treatment device 1 does not perform neutralization treatment of the turbid water, the treatment time of the entire device can be shortened, thereby reducing costs.

[0036] On the other hand, when the pH of the turbid water measured in the turbid water storage tank 2 is not 9 or higher, or when the turbid water taken into the turbid water storage tank 2 is not cement turbid water (sometimes referred to as the latter case in the description of this embodiment), the turbid water treatment device 1 stops the magnetic particle addition means 42, recovery means 8, and supply means 9, and operates the pH adjustment tank 3, inorganic coagulant addition means 41, reaction tank 4, coagulation tank 5, sedimentation tank 6, and neutralization treatment tank 7.

[0037] Specifically, if the pH of the turbid water measured in the turbid water storage tank 2 is between 6 and 9, the turbid water is within the preferred range for inorganic flocculants, and is therefore sent directly to the reaction tank 4 for floc formation. Alternatively, if the pH of the turbid water measured in the turbid water storage tank 2 is not between 6 and 9 (i.e., the pH is less than 6), or if the pH is 9 or greater but not cement turbid water, the turbid water is not within the preferred range for inorganic flocculants. Therefore, the turbid water is first sent to the pH adjustment tank 3, where the pH is adjusted to between 6 and 9, as described above, and then sent to the reaction tank 4 for floc formation. Therefore, in the latter case, the turbid water treatment device 1 stops the recovery of magnetic particles from the sludge and the addition of the recovered magnetic particles to the turbid water, and can perform a normal coagulation and sedimentation treatment. Furthermore, in the latter case, the magnetic particle addition means 42, the recovery means 8, and the supply means 9 are stopped, thereby reducing running costs. In addition, in this case, since the magnetic particles are not recovered or reused, there is no loss of magnetic particles, and the cost and effort of replenishing magnetic particles can be reduced compared to conventional technology (e.g., Patent Document 4), in which the magnetic particle addition means 42, recovery means 8, and supply means 9 are operated at all times. In this way, the turbid water treatment device 1 according to this embodiment can easily switch operations even when there is a change in the type or pH of the turbid water, and can perform efficient treatment.

[0038] (Muddy water treatment method) Next, a turbid water treatment method according to the first embodiment will be described with reference to Figure 3. In the following description, the same components as those in the turbid water treatment device 1 will be given the same reference numerals, and their description may be omitted. Furthermore, in this turbid water treatment method, the same magnetic particles as those in the turbid water treatment device 1 can be used. FIG. 3 is a flowchart illustrating the method for treating muddy water according to the first embodiment. As shown in Figure 3, this turbid water treatment method includes a turbid water storage step S1, a judgment step S2, a pH adjustment step S3, an inorganic coagulant addition step S4, a magnetic particle addition step S5, a reaction step S6, a coagulation step S7, a precipitation step S8, a neutralization treatment step S9, a recovery step S10, and a supply step S11.

[0039] In the turbid water storage step S1, turbid water is taken in and stored, and the pH of the turbid water is measured by the pH measuring device 21. This step can be performed in the turbid water storage tank 2 described above. In decision step S2, it is determined whether the turbid water taken into the turbid water storage tank 2 is cement turbid water and has a pH of 9 or higher. This step is generally determined based on whether cement-containing mortar or concrete has been poured at the location where the turbid water is generated. At the time of this determination, if there is a trace amount of cement, the pH of the turbid water may be low, and in that case, normal treatment is carried out even if the turbid water contains cement (normal coagulation and sedimentation treatment is carried out).

[0040] A specific example of the decision step S2 will be described. In the decision step S2, first, it is determined whether the pH of the turbid water is 9 or higher (step S21). If the pH of the turbid water is 9 or higher (Yes in step S21), it is then determined whether the turbid water is cement turbid water (step S22). If the turbid water is cement turbid water (Yes in step S22), the reaction step S6 is carried out. If the pH of the turbid water is not 9 or higher in step S21 (No in step S21), it is then determined whether the pH of the turbid water is 6 or higher and lower than 9 (step S23). If the pH of the turbid water is 6 or higher and lower than 9 (Yes in step S23), reaction step S6 is carried out. Then, if the pH of the turbid water is not greater than 6 and less than 9 in step S23 (i.e., if the pH of the turbid water is less than 6) (No in step S23), and if the pH of the turbid water is 9 or greater but is not cement turbid water (Yes in step S21, No in step S22), pH adjustment step S3 is performed.

[0041] In the pH adjustment step S3, when the pH of the turbid water is less than 6, or when the pH of the turbid water is 9 or more but is not cement turbid water, the pH of the turbid water is adjusted to 6 or more and less than 9. This step can be performed by the pH adjustment tank 3 described above. In the inorganic flocculant addition step S4, an inorganic flocculant is added to the turbid water. This step can be performed by the inorganic flocculant addition means 41 described above. In the magnetic particle addition step S5, magnetic particles are added to the turbid water. This step can be performed by the magnetic particle addition means 42 described above. In the reaction step S6, suspended matter in the turbid water is flocculated (basal flocs are formed) by the inorganic flocculant and magnetic particles. This step can be carried out in the reaction tank 4 described above.

[0042] In the flocculation step S7, a polymer flocculant is added to further flocculate the flocculated suspended matter into magnetic flocs. This step can be performed in the flocculation tank 5 described above. The polymer flocculant can be added in the polymer flocculant addition step S71. This step can be performed by the polymer flocculant addition means 51 described above. In the settling step S8, the flocculated magnetic flocs are allowed to settle to obtain supernatant water and sludge containing magnetic particles. This step can be carried out in the settling tank 6 described above. In the neutralization step S9, if the pH of the supernatant water obtained in the settling tank 6 is outside the discharge regulation value, a neutralizing agent is supplied to the supernatant water to perform neutralization. The pH of the supernatant water can be measured using a pH meter 71. This step can be performed in the neutralization tank 7 described above. In the recovery step S10, the magnetic particles are recovered from the sludge. This step can be performed by the recovery means 8 described above. In the supply step S11, the collected magnetic particles are supplied to the magnetic particle addition step S5, which can be performed by the supply means 9 described above.

[0043] In this embodiment, in the turbid water treatment method configured as described above, if it is determined in judgment step S2 that the turbid water is cement turbid water and the pH is 9 or higher, that is, if the answer is Yes in step S21 and Yes in step S22 (this may be referred to as the former case in the description of this embodiment), the pH adjustment step S3 is not performed, and instead the magnetic particle addition step S5, recovery step S10 and supply step S11 are performed, as well as the inorganic flocculant addition step S4, reaction step S6, flocculation step S7, precipitation step S8 and neutralization treatment step S9.

[0044] In the former case, this turbid water treatment method forms magnetic flocs by adding and reusing magnetic particles in addition to the usual coagulation and sedimentation treatment. In other words, in the former case, this turbid water treatment method can perform coagulation and sedimentation treatment while the turbid water remains alkaline, without neutralizing it. As a result, this turbid water treatment method can significantly reduce the amount of neutralizing agent added to the supernatant water after treatment compared to adding a neutralizing agent to the turbid water, making it more efficient and cost-effective. Furthermore, because this turbid water treatment method does not require neutralizing the turbid water, the overall treatment time can be shortened, resulting in lower costs.

[0045] On the other hand, if the judgment step S2 determines that the pH of the turbid water is not 9 or higher, or if the turbid water is determined to be not cement turbid water, that is, if the answer is No in step S21 or No in step S22 (this may be referred to as the latter case in the description of this embodiment), the magnetic particle addition step S5, recovery step S10, and supply step S11 are not performed, and instead the pH adjustment step S3, inorganic flocculant addition step S4, reaction step S6, flocculation step S7, precipitation step S8, and neutralization treatment step S9 are performed.

[0046] In the latter case, a pH adjustment step S3 is performed according to the pH of the turbid water. Specifically, if the pH of the turbid water measured in the turbid water storage step S1 is between 6 and 9, the pH of the turbid water is within the preferred range for inorganic flocculants, and the reaction step S6 is then performed to form flocs. In addition, if the pH of the turbid water measured in the turbid water storage step S1 is not between 6 and 9 (i.e., the pH is less than 6), or if the pH of the turbid water is 9 or greater but not cement turbid water, the pH of the turbid water is not within the preferred range for inorganic flocculants, and the pH adjustment step S3 is first performed as described above to adjust the pH of the turbid water to between 6 and 9, and then the reaction step S6 is performed to form flocs. Therefore, in the latter case, the turbid water treatment method can stop the recovery of magnetic particles from the sludge and the addition of the recovered magnetic particles to the turbid water, and perform a normal coagulation and sedimentation treatment. In the latter case, the magnetic particle addition step S5, the recovery step S10, and the supply step S11 are stopped, thereby reducing the running costs. In addition, in this case, since the magnetic particles are not recovered or reused, there is no loss of magnetic particles, and the cost and effort of replenishing magnetic particles can be reduced compared to conventional technology (e.g., Patent Document 4), in which the magnetic particle addition step S5, recovery step S10, and supply step S11 are constantly performed.

[0047] Furthermore, the turbid water treatment device 1 and turbid water treatment method according to the present embodiment described above are useful in civil engineering work, particularly tunnel construction. In civil engineering work, particularly tunnel construction, the turbid water discharged contains cement, has low turbidity, and is highly alkaline (pH of approximately 11 to 12). Therefore, conventional methods require large amounts of neutralizing agent for the turbid water. In this embodiment, the use of magnetic particles enables rapid formation and precipitation of magnetic flocs without adjusting the pH of the turbid water, thereby improving treatment speed. This also enables the device to take up less space than conventional devices.

[0048] Furthermore, the turbid water treatment device 1 and turbid water treatment method according to this embodiment can reduce the amount of neutralizing agent added compared to conventional methods. That is, typical turbid water treatment devices and methods use inorganic and polymer flocculants to form flocs. Since the preferred application range for inorganic flocculants is the neutral range, the pH of the turbid water is adjusted to that range using a neutralizing agent such as dilute sulfuric acid before coagulation and precipitation. Neutralizing turbid water containing a large amount of suspended solids, such as soil particles, requires a large amount of neutralizing agent due to the pH buffering effect of the suspended solids. In contrast, the turbid water treatment device 1 and turbid water treatment method according to this embodiment add magnetic particles, enabling floc formation and precipitation even in cement turbid water. Therefore, the turbid water treatment device 1 and turbid water treatment method according to this embodiment do not require pH adjustment of the turbid water before flocculation, even if the turbid water is cement turbid water and the pH of the turbid water measured in the turbid water storage tank 2 is 9 or higher. In the turbid water treatment device 1 and turbid water treatment method according to this embodiment, it is only necessary to adjust the pH of the supernatant water obtained by floc formation and precipitation (i.e., the water contains little suspended matter such as soil particles) to a level that conforms to the discharge regulation value, which allows for a significant reduction in the amount and cost of neutralizing agent added compared to conventional methods. The amount of neutralizing agent added can be reduced to, for example, 1 / 6 to 1 / 3 of the conventional amount.

[0049] Furthermore, in the turbid water treatment device 1 and turbid water treatment method according to this embodiment, magnetic particles are not used when the turbid water is not cement turbid water or when the pH of the turbid water is less than 9, but are used when the turbid water is cement turbid water and the pH of the turbid water measured in the turbid water storage tank 2 is 9 or higher. In the turbid water treatment device 1 and turbid water treatment method according to this embodiment, when the turbid water is cement turbid water and the pH of the turbid water measured in the turbid water storage tank 2 is 9 or higher and magnetic particles are used, the recovery means 8 (recovery step S10) is used to separate the magnetic particles from the sludge recovered. This allows almost all of the added magnetic particles to be recovered, and they can be reused by returning them to the coagulation tank 5 (coagulation step S7). As mentioned above, magnetic particles are not used when the turbid water is not cement turbid water or when the pH of the turbid water is less than 9, and magnetic particles are only used repeatedly when the turbid water is cement turbid water or when the pH of the turbid water measured in the turbid water storage tank 2 is 9 or higher. Therefore, magnetic particles are less likely to be lost than in conventional technology (e.g., Patent Document 4), and the cost of replenishing magnetic particles can be reduced.

[0050] (Muddy water treatment device according to a modification of the first embodiment) One aspect of the turbid water treatment device 1 according to this embodiment is its application to construction work using cement, such as tunnel construction. In this case, the turbid water generated at the construction site is cement turbid water, with a pH of 9 or higher. Therefore, as described above, the turbid water can be treated by adding magnetic particles without measuring the pH in the turbid water storage tank 2, adjusting the pH in the pH adjustment tank 3, or determining whether the water is cement turbid water or whether the pH is 9 or higher. In other words, in this case, the turbid water treatment device 1 according to this embodiment can treat cement turbid water without measuring the pH in the turbid water storage tank 2 or adjusting the pH using the pH adjustment tank 3.

[0051] In this case, the configuration of the turbid water treatment device 1 of this embodiment specifically includes a turbid water storage tank 2, a reaction tank 4, a coagulation tank 5, a sedimentation tank 6, a neutralization treatment tank 7, a recovery means 8, and a supply means 9. Of these, the reaction tank 4, flocculation tank 5, settling tank 6, recovery means 8, and supply means 9 are the same as those in the above-mentioned embodiment. Also, the reaction tank 4 is similarly provided with inorganic flocculant addition means 41 and magnetic particle addition means 42, and suspended solids in the cement turbid water are similarly flocculated by the inorganic flocculant and magnetic particles.

[0052] As mentioned above, the pH is not measured in the turbid water storage tank 2. In this embodiment, the pH adjustment tank 3 is omitted. In this embodiment, the pH of the cement turbid water is 9 or higher, so the pH of the supernatant water after treatment does not fall within the discharge regulation value. Therefore, in this embodiment, a neutralizing agent is supplied to the supernatant water in the neutralization treatment tank 7 to perform neutralization treatment. In this embodiment, similar to the above-described embodiment, the treatment of turbid cement water is carried out using magnetic particles. Therefore, in this embodiment, it is possible to similarly realize an optimal treatment method (pH range) using magnetic particles and a method for reducing the amount of neutralizing agent used when the turbid water is alkaline due to the presence of cement.

[0053] (Muddy water treatment method according to a modified example of the first embodiment) As described above, one aspect of the turbid water treatment method according to this embodiment is its application to construction work using cement, such as tunnel construction. In this case, the turbid water generated at the construction site is cement turbid water, and the pH is 9 or higher. Therefore, as described above, the turbid water can be treated by adding magnetic particles without measuring the pH in the turbid water storage step S1, adjusting the pH in the pH adjustment step S3, or determining whether the water is cement turbid water or whether the pH is 9 or higher (determination step S2). In other words, in this case, in the turbid water treatment method according to this embodiment, the cement turbid water can be treated without measuring the pH in the turbid water storage step S1, adjusting the pH in the pH adjustment step S3, and judging whether the water is cement turbid water or whether the pH is 9 or higher.

[0054] In this case, the configuration of the turbid water treatment method of this embodiment specifically includes a turbid water storage step S1, an inorganic flocculant addition step S4, a magnetic particle addition step S5, a reaction step S6, a flocculation step S7, a precipitation step S8, a neutralization treatment step S9, a recovery step S10, and a supply step S11. Among these, the inorganic flocculant adding step S4, the magnetic particle adding step S5, the reaction step S6, the flocculation step S7, the precipitation step S8, the recovery step S10 and the supply step S11 are the same as those in the above embodiment.

[0055] As mentioned above, the pH is not measured in the turbid water storage step S1. Furthermore, in this embodiment, the determination step S2 and the pH adjustment step S3 are omitted. Furthermore, in this embodiment, the pH of the cement turbid water is 9 or higher, so the pH of the supernatant water after treatment does not meet the discharge regulation value. Therefore, in this embodiment, a neutralizing agent is supplied to the supernatant water in the neutralization treatment step S9 to perform neutralization treatment. In this embodiment, similar to the above-described embodiment, the treatment of turbid cement water is carried out using magnetic particles. Therefore, in this embodiment, it is possible to similarly realize an optimal treatment method (pH range) using magnetic particles and a method for reducing the amount of neutralizing agent used when the turbid water is alkaline due to the presence of cement.

[0056] [Test Example Related to the First Embodiment] Next, a test example relating to the first embodiment will be described. (Test 1) Effect of pH of turbid water on coagulation performance When magnetic particles are added as a material to promote floc sedimentation, the effectiveness of coagulation and sedimentation depends on the pH of the turbid water. A jar test was conducted to determine the optimum pH for coagulation and sedimentation. Turbid water (cement turbid water) with a pH of 12 and a turbidity of 1900 NTU (Nephelometric Turbidity Unit) discharged from a tunnel excavation site was used for the test.

[0057] In this study, 500 mL of the above turbid water was taken and adjusted to a pH range of 7–12 using a 5% dilute sulfuric acid solution. An inorganic flocculant (70 mg / L) was added to the pH-adjusted turbid water, followed by stirring for 60 seconds using a jar tester (not shown). After stirring was stopped, 7.5 g / L of magnetic particles and 0.5 mg / L of polymer flocculant were added to promote sedimentation. The mixture was rapidly stirred at 250 rpm for 30 seconds, then slowly stirred at 150 rpm for 60 seconds, after which stirring was stopped. The supernatant solution was collected 30 seconds after stirring was stopped, and the turbidity was measured. The turbidity was measured by absorbance at a wavelength of 860 nm using a TBD700 (manufactured by AS ONE Corporation). The inorganic flocculant used was polyaluminum chloride (PAC) (Kyowa Sogyo Co., Ltd., liquid). The polymer flocculant used was Taipolymer TA-360 (anionic type) (manufactured by Taimei Chemical Industry Co., Ltd., powder). The magnetic particles used were Ecomel 53NJ (manufactured by Kobe Steel, Ltd.). For comparison, a test was also conducted using a conventional method without adding magnetic particles. The test results are shown in Figure 4A. Figure 4A is a graph showing the results of a test investigating the effect of the pH of turbid water on flocculation performance. Figure 4A shows the results when magnetic particles, an inorganic flocculant, and a polymer flocculant were added, as well as the results for the conventional method.

[0058] In the case of the conventional method in which no magnetic particles were added (only inorganic flocculants and polymer flocculants were added), the turbidity was 18 NTU at pH 7, as plotted by "x" in Figure 4A, and the turbidity increased as the pH increased. On the other hand, when magnetic particles (particle size adjusted to 45 μm or less by sieving) were added, the turbidity was 12 NTU at pH 9 or higher, as plotted by "◆" in Figure 4A, which was lower than the turbidity when no magnetic particles were added.

[0059] Using the same procedure as above, we also investigated the effect of the pH of turbid water on flocculation performance when only magnetic particles were used (no inorganic flocculant or polymer flocculant was used). Figure 4B is a graph showing the test results of investigating the effect of the pH of turbid water on flocculation performance. Figure 4B shows the results of comparing the addition of magnetic particles alone with the addition of magnetic particles, an inorganic flocculant, and a polymer flocculant. Note that the test results for the latter case in Figure 4B (the test results plotted with "♦" in Figure 4B) are the same as the test results plotted with "♦" in Figure 4A. As shown by the dots in Figure 4B, it was confirmed that the turbidity of turbid water decreased as the pH increased, even with the addition of magnetic particles alone. In other words, it was confirmed that flocs can be formed using magnetic particles alone, without the use of a flocculant.

[0060] (Test 2) Effect of magnetic particle size on mixing efficiency When granular magnetic particles are mixed in the coagulation and sedimentation process, there is a concern that the magnetic particles with a high specific gravity may not mix sufficiently with the suspended matter and chemicals (coagulants), and may become trapped at the bottom of the mixing vessel.In order to investigate the particle size range of magnetic particles that can sufficiently mix the magnetic particles with turbid water, a jar test was conducted using magnetic particles of different particle sizes. First, the magnetic particles were classified using a sieve into four particle size categories: over 106 μm (Case 1), 106 μm to over 75 μm (Case 2), 75 μm to over 45 μm (Case 3), and 45 μm or less (Case 4), and a jar test similar to Test 1 was performed. In Test 2, sampling was performed during rapid and slow stirring from two sampling positions shown in Figure 5, namely, the top and center of the stirring vessel. Figure 5 is a schematic diagram explaining the sampling positions in Test 2.

[0061] The magnetic particles in the sample were then collected and weighed using a magnet bar 94 (see Figure 9) to confirm whether the magnetic particles were uniformly stirred in the turbid water. Figures 6A and 6B show the test results. Figure 6A is a graph showing the relationship between the amount of magnetic particles present and particle size during rapid stirring. Figure 6B is a graph showing the relationship between the amount of magnetic particles present and particle size during slow stirring. 6A and 6B, the smaller the amount of magnetic particles sampled in the upper and middle parts of the stirring vessel, the more the magnetic particles are retained in the lower part of the stirring vessel. Note that in Test 2, 7.5 g of magnetic particles were added to 1 L of turbid water (7.5 g / L), so the amount of magnetic particles present, calculated as "amount of magnetic particles present [wt%] = amount of magnetic particles [g] / amount of turbid water [g] × 100," had a maximum value of 0.75 wt% (see dashed lines in Figures 6A and 6B).

[0062] In particular, most of the magnetic particles with particle diameters exceeding 106 μm (Case 1) remained at the bottom in both the rapid and slow stirring conditions, as shown in FIGS. 6A and 6B. Furthermore, as shown in Figure 6A, when magnetic particles with a particle size of 106 μm or less and over 75 μm (Case 2) were rapidly stirred, approximately half of them were mixed into the turbid water. However, as shown in Figure 6B, when the stirring speed was slow, approximately 85% of the magnetic particles, assuming that they were 100%, settled (i.e., approximately 85% of the 0.75 wt% settled). As shown in Figure 6A, for magnetic particles with a particle size of 75 μm or less and over 45 μm (Case 3), when rapidly stirred, approximately 90% of the added magnetic particles were stirred in the turbid water, assuming that the added magnetic particles were 100%. Also, as shown in Figure 6B, when slowly stirred, approximately 70% of the added magnetic particles were stirred in the turbid water (i.e., approximately 70% of the 0.75 wt% were stirred in the turbid water). As shown in FIGS. 6A and 6B, the magnetic particles with a particle size of 45 μm or less (Case 4) were almost all uniformly stirred.

[0063] Here, Figure 7 is a graph showing the effect of the particle size of magnetic particles on the turbidity of treated water. As shown in Figure 7, under conditions other than when the particle size was over 106 μm (Case 1) (i.e., Cases 2 to 4), the turbidity of treated water was 10 NTU or less. This shows that removing coarse particles with a particle size of over 106 μm from the magnetic particles can improve the flocculation effect. From the two perspectives of uniformity of stirring and turbidity of treated water, it was shown that it is preferable to adjust the particle size of the magnetic particles to 106 μm or less.

[0064] (Test 3) Amount of neutralizer added The use of magnetic particles makes it possible to treat alkaline turbid water, such as cement turbid water, through coagulation and sedimentation. This eliminates the need for neutralization of the turbid water, and simply adjusts the pH of the treated supernatant water to meet discharge regulations as needed before discharging it. When adjusting the pH of turbid water, the pH buffering effect of suspended solids such as soil particles comes into play, requiring a large amount of neutralizing agent. On the other hand, the supernatant water after treatment contains almost no suspended solids, so it is thought that less neutralizing agent will be required compared to neutralizing turbid water. Therefore, the pH of the turbid water and the supernatant water after treatment was adjusted before and after the jar test similar to Test 1, and the amount of neutralizing agent (5% diluted sulfuric acid) added was compared.

[0065] The amount of 5% diluted sulfuric acid added to 1 L of turbid water or treated supernatant water until the pH reached 8.6 was measured. The results are shown in Figure 8. Figure 8 is a graph showing the amount of 5% diluted sulfuric acid added to turbid water and treated supernatant water until the pH reached 8.6. As shown in Figure 8, when the pH of the supernatant water after treatment was adjusted, the amount of dilute sulfuric acid added was significantly reduced compared to when the pH of the turbid water was adjusted. The amount of neutralizing agent added to the supernatant water was approximately 1 / 6 when the pH of the turbid water was 9, and approximately 1 / 3 when the pH of the turbid water was 12.

[0066] (Test 4) Confirmation of magnetic particle recovery amount To confirm that magnetic particles can be recovered from the suspended solids by a magnet, a magnetic particle recovery test using a magnetic bar was conducted after the jar test. Figure 9 is an explanatory diagram illustrating the magnetic particle recovery test method. As shown in FIG. 9(a), after the jar test, the sample was allowed to stand, separating supernatant water 91 (treated water) from suspended solids 92 containing magnetic particles that had flocculated and settled. Next, as shown in FIG. 9(b), the supernatant water 91 was discarded, and a magnet bar 94 using a magnet (permanent magnet) similar to that used in magnetic separators was placed in the precipitated slurry 93 of the flocculated and settled suspended solids, and the material attached to the magnet (magnetically attached material 96) was collected. As shown in FIG. 9(b), the magnet bar 94 has a cover 95 that covers the magnet. The magnet bar 94 can eliminate the effect of the magnetic force on the magnetic particles by removing the magnet from the cover 95. Therefore, the magnetically attached material 96, including the magnetic particles that had been attracted by the magnetic force, can be detached and collected via the cover 95.

[0067] Immediately after collection, the magnetized material 96 (collected material) contains a large amount of moisture. Therefore, as shown in Figure 9(c), the collected material was placed in an empty container 97 and vacuum dried. Thereafter, as shown in Figure 9(d), the weight of the collected material was measured. The test results are shown in Table 1. The magnetic particle recovery rate and the entrainment rate of suspended matter were calculated using the following method. Magnetic particle recovery rate [%] = (weight of magnetic particles after vacuum drying [g] / weight of added magnetic particles [g]) × 100 Entrainment rate of suspended matter [%] = {(weight of magnetic material after vacuum drying [g] - weight of added magnetic particles [g]) / weight of added magnetic particles [g]} × 100

[0068] [Table 1]

[0069] The magnetic particle recovery rate was approximately 106%. This result shows that although approximately 6% of the suspended matter in the turbid water was entrained, the added magnetic particles were recovered at approximately 100% and none remained in the turbid water. In a previous study in which arsenic-contaminated muddy water was purified by adding magnetic material (iron powder), it was confirmed that even when the iron powder added to the muddy water was reused approximately 200 times, almost all of the iron powder was recovered and did not flow into the treated muddy water (Reference: Takahata Akira et al.: Study on purification technology using iron powder from arsenic-contaminated muddy water generated by a muddy water shield - Full-scale test introducing a small magnetic separator and iron powder recycling technology -, Geotechnical Journal, Vol. 15, No. 3, pp. 479-486, 2020).

[0070] (Test 5) Comparative test between cement-based and non-cement-based turbid water Coagulation and sedimentation tests were carried out on turbid water containing cement and turbid water without cement (turbid water without added cement), and the results were compared. <Test Method> 1. 100 mL of turbid water A, B, and C shown in Tables 2 and 3 were dispensed into each beaker. 2. 75 mg / L of inorganic coagulant (PAC) was added to each beaker and stirred for 30 seconds. 3. Under the conditions shown in Tables 2 and 3, 10 g / L of iron powder (magnetic particles) was added to each beaker, or the mixture was stirred without adding iron powder, and then 1 mg / L of polymer flocculant was added and stirred for 30 seconds. 4. After standing for 1 minute, the turbidity of the supernatant was measured. The turbidity was measured by measuring absorbance at a wavelength of 860 nm using a TBD700 manufactured by AS ONE Corporation. The inorganic flocculant used was polyaluminum chloride (PAC) (liquid manufactured by Kyowa Sogyo Co., Ltd.). The polymer flocculant used was Thai Polymer TA-360 (anionic type) (powder manufactured by Taimei Chemical Industry Co., Ltd.). The magnetic particles used were Ecomel 53NJ (manufactured by Kobe Steel, Ltd.).

[0071] The results are shown in Tables 2 and 3 and Figure 10. Figure 10 shows a photograph (left) of turbid water A (on-site generated raw water) in Test 5 before coagulation sedimentation treatment, a photograph (center) of the water after coagulation sedimentation treatment without adding iron powder, and a photograph (right) of the water after coagulation sedimentation treatment with iron powder added. In Tables 2 and 3, the on-site generated raw water was collected from a tunnel excavation (NATM) site. Cement was mixed into the on-site generated raw water. The simulated turbid water was prepared by mixing excavation waste at 10 g / L (dry weight) with tap water. No cement was added to the simulated turbid water. As shown in Table 3, depending on the sample conditions, 2 g / L of cement was added to the simulated turbid water to make the pH similar to that of the on-site generated raw water (Turbid Water B and C in Table 3). The "-" in Table 2 indicates that cement was originally added to the on-site generated raw water, and therefore no data is available for the raw water without added cement.

[0072] [Table 2]

[0073] [Table 3]

[0074] Turbid waters B and C in Table 2 show that when the turbid water does not contain cement, there is almost no difference in turbidity depending on whether or not iron powder is present. In contrast, from turbid waters A, B, and C in Table 3, it was found that adding iron powder to turbid water containing cement reduced the turbidity. This shows that adding iron powder is more effective for turbid water containing cement. It was also found that doing so allows for a more advanced purification process. This is also clear from Figure 10.

[0075] That is, as shown in the left diagram of Figure 10, before the turbid water A (raw water generated on-site) was treated with coagulation and sedimentation, it was extremely turbid overall. In contrast, as shown in the center of Figure 10, the turbid water (without iron powder) after coagulation and sedimentation treatment was significantly purified, and the supernatant water was fairly clear, but fine particles could be visually confirmed in the supernatant. Furthermore, as shown in the right diagram of Figure 10, the turbid water (with iron powder) after coagulation and sedimentation treatment was further purified by adding iron powder, and the supernatant water became even clearer. After coagulation and sedimentation treatment, almost no particles remained in the supernatant water of the turbid water (with iron powder). The results shown in the right panel of Figure 10 indicate that when iron powder is added to turbid water containing cement, the supernatant water contains almost no suspended solids, which significantly weakens the pH buffering effect of suspended solids such as soil particles, allowing for a reduction in the amount of neutralizing agent required (see Figure 8). Furthermore, as explained above, it has been confirmed that the present invention can realize an optimal treatment method (pH range) using magnetic particles and a method for reducing the amount of neutralizing agent used when the turbid water contains cement and is alkaline.

[0076] Second Embodiment (Muddy water treatment equipment) As explained in the turbid water treatment device 1 according to one variation of the first embodiment, for example, turbid water generated at a construction site such as a tunnel construction site is cement turbid water, and has a pH of 9 or higher. In this case, as in the above, in the turbid water treatment device 1 according to the second embodiment, it is possible to treat the cement turbid water without measuring the pH in the turbid water storage tank 2 and omitting the pH adjustment tank 3 and the pH adjustment therethrough. In this case, the following embodiment can be adopted. Fig. 11 is a schematic diagram illustrating the configuration of a turbid water treatment device 1 according to the second embodiment. As shown in Fig. 11, the turbid water treatment device 1 according to the second embodiment includes a reaction tank 4, a flocculation tank 5, a settling tank 6, a recovery means 8, a supply means 9, and a pH adjustment device 11b. In the second embodiment, these elements are configured as follows:

[0077] The reaction tank 4 flocculates suspended solids in the turbid cement water to which an inorganic flocculant and magnetic particles have been added. The flocculation tank 5 is located downstream of the reaction tank 4. The flocculation tank 5 flocculates suspended solids in the turbid cement water to which a polymer flocculant has been added to form magnetic flocs. The settling tank 6 is located downstream of the flocculation tank 5. The settling tank 6 settles the flocculated magnetic flocs to obtain supernatant water and sludge containing magnetic particles. The recovery means 8 recovers the magnetic particles from the sludge. The supply means 9 supplies the recovered magnetic particles to the turbid cement water. The pH adjustment device 11b adjusts the pH of the supernatant water obtained in the settling tank 6 (performs neutralization treatment). The pH of the supernatant water can be adjusted by adding the neutralizing agent described above. In the second embodiment, the treatment of turbid cement water is carried out using magnetic particles, as in the first embodiment etc. Therefore, in the second embodiment as well, it is possible to realize an optimal treatment method (pH range) using magnetic particles and a method for reducing the amount of neutralizing agent used when the turbid water is alkaline due to the presence of cement.

[0078] In the second embodiment, it is more preferable to do as follows. FIG. 12 is a schematic diagram showing a preferred embodiment of the turbid water treatment device 1 according to the second embodiment. As shown in FIG. 12, the turbid water treatment device 1 preferably includes a discharge reservoir 11 downstream of the settling tank 6 for storing supernatant water (i.e., treated water). The discharge reservoir 11 is a tank for temporarily storing the supernatant water before discharging it into a river or the like. This allows for confirmation, while the supernatant water is being stored, of whether it contains suspended solids or particles, whether its turbidity satisfies emission regulations, and so on. Furthermore, if an unforeseen event occurs that makes discharging the supernatant water inappropriate, the discharge of the supernatant water can be stopped. The discharge reservoir 11 may also include a pH measuring device 11a.

[0079] The supernatant water stored in the discharge storage tank 11 was turbid cement water before treatment, and therefore has a pH of 9 or higher. Therefore, before discharging the supernatant water, a neutralization treatment (pH adjustment) is performed to lower the pH. The neutralization treatment allows the water to comply with the discharge regulation value. As described above, the neutralization treatment can be performed by adding a neutralizing agent to the supernatant water. As shown in FIG. 12, in the second embodiment, the turbid water treatment device 1 is equipped with a pH adjustment device 11b that adjusts the pH of the supernatant water immediately before or after it enters the discharge storage tank 11.

[0080] As shown in FIG. 12, the turbid water treatment device 1 preferably includes a first separation means 10 between the settling tank 6 and the discharge storage tank 11 to separate magnetic particles from the supernatant water. Magnetic particles with small particle sizes (fine magnetic particles) are light and therefore difficult to settle (see Test 2 above). Therefore, fine magnetic particles may be contained in the supernatant water. Even in such cases, the first separation means 10 can be used to effectively separate and recover the fine magnetic particles from the supernatant water. This also allows the removal of fine magnetic particles from the supernatant water, thereby reducing the amount of suspended solids (the weight of suspended solids per unit water volume; SS) in the discharge water and reducing the risk of exceeding the emission regulation value. Furthermore, the magnetic particles become smaller due to wear caused by repeated use, and fine magnetic particles that do not settle in the settling tank 6 but instead float in the supernatant water can be removed. The first separation means 10 is preferably a magnetic separator (magnetic separator 81 (FIG. 2)). In this way, it is possible to separate and recover almost all of the fine magnetic particles from the supernatant water. Furthermore, if the magnetic separator is placed above the discharge storage tank 11, recovery of the supernatant water and transfer from the settling tank 6 to the discharge storage tank 11 can be carried out in one step. The fine magnetic particles separated and recovered by the first separation means 10 are stored in the magnetic particle storage tank 10a.

[0081] Furthermore, the turbid water treatment device 1 preferably includes an extraction means 12 for extracting the sludge that has accumulated at the bottom of the reaction tank 4 from the reaction tank 4. Magnetic particles with large particle diameters (coarse magnetic particles) are heavy and therefore settle easily (see Test 2 above). Therefore, the coarse magnetic particles settle quickly without contributing to the formation of flocs. A considerable amount of such coarse magnetic particles is contained in the sludge that has accumulated at the bottom of the reaction tank 4. Even in such cases, by extracting the sludge from the reaction tank 4, it is possible to prevent the coarse magnetic particles from remaining in the reaction tank 4 and reducing the effective capacity. Furthermore, because the coarse magnetic particles are extracted from the reaction tank 4, it is possible to prevent a decrease in the flocculation performance of the flocs and a decrease in the stirring effect that would otherwise occur due to a decrease in the effective capacity.

[0082] Although not particularly limited, one embodiment of the extraction means 12 is preferably, for example, as shown in FIG. 13, a bottom section 121 is formed in the lower part of the reaction tank 4. The bottom section 121 has a shape (e.g., an inverted cone shape, an inverted pyramid shape, etc.) in which the area of ​​its horizontal cross section decreases toward the bottom of the reaction tank 4. A pipe 122 and a valve 123 for extracting sludge are connected to the lower end of the bottom section 121. FIG. 13 is a schematic diagram illustrating one embodiment of the extraction means 12 and the magnetic separator 81. In this configuration, the sludge settles due to gravity and accumulates below the bottom section 121. The sludge accumulated below the bottom section 121 can then be extracted from the reaction tank 4 via the pipe 122 and the valve 123 and introduced into the magnetic separator 81.

[0083] In the second embodiment, a turbid water storage tank 2 for storing cement turbid water is provided upstream of the reaction tank 4, and the extraction means 12 preferably includes a second separation means 13 for separating magnetic particles from the extracted sludge. The second separation means 13 preferably returns the sludge from which the magnetic particles have been separated to the turbid water storage tank 2. In this manner, the second separation means 13 can effectively separate and recover coarse magnetic particles contained in the sludge. The coarse magnetic particles separated and recovered by the second separation means 13 are stored in a magnetic particle storage tank 14. Examples of coarse magnetic particles include, but are not limited to, particles with a particle size exceeding 75 μm. The sludge from which the magnetic particles have been separated is returned to the turbid water storage tank 2 and subjected to turbid water treatment again. A permanent magnet or a magnetic separator (e.g., the magnetic separator 81 shown in FIG. 13) can be used as the second separation means 13. The sludge containing the magnetic particles extracted by the extracting means 12 can be composted, incinerated or disposed of in a landfill as it is (that is, without passing through the second separating means 13).

[0084] The inventors' investigation revealed that commercially available magnetic particles are generally aggregates of magnetic particles ranging in size from 20 to 200 μm. While the particle size of the magnetic particles themselves varies widely depending on their manufacturing method, the particle size was generally less than 1 mm, with an average particle size of 65 to 150 μm (see Test 7 below). Japanese Patent Application Publication No. 2003-136051 discloses the use of magnetic particles ranging in size from approximately 1 to 500 μm, and Japanese Patent Application Publication No. 2006-326561 indicates that the average particle size of the magnetic particles used in the test was approximately 65 μm. Since commercially available magnetic particles typically contain particles exceeding 75 μm, it is preferable to remove particles exceeding 75 μm by sieving beforehand in order to use the particles as a sedimentation accelerator in turbid water coagulation and sedimentation treatments. However, the sieving process is costly and time-consuming.

[0085] In light of these considerations, it is preferable that the turbid water treatment device 1 according to the second embodiment, which includes both a first separation means 10 and a second separation means 13, is equipped with both a first separation means 10 and a second separation means 13, as shown in FIG. 12. This arrangement allows fine magnetic particles to be removed from the turbid water treatment device 1 by the first separation means 10, while coarse magnetic particles are removed by the second separation means 13. As a result, magnetic particles of an appropriate size remain within the turbid water treatment device 1. Furthermore, this embodiment eliminates the need for the costly and laborious prior sieving process required for magnetic particles used as a sedimentation promoter. In other words, commercially available magnetic particles can be used as a sedimentation promoter in coagulation and sedimentation treatments immediately after delivery without any pretreatment, such as sieving. This reduces the cost of pretreatment. Furthermore, if a large amount of pre-screening is performed to reduce particle size to 75 μm or less, it is possible that magnetic particles (iron powder) with particle sizes of 53 μm or less, as specified by the Fire Service Act, may be contained at 50% by mass or more. However, in this embodiment, such pre-screening is not performed, and therefore safety in storage and handling in accordance with the Fire Service Act is improved.

[0086] The reaction vessel 4 preferably has a stirring strength that prevents magnetic particles with a particle size of 75 μm or less from settling. For magnetic particles with a particle size of 75 μm or less, the magnetic particles can be prevented from settling in the reaction vessel 4 without an excessive stirring strength (see Test 2 above). Such a stirring strength can be achieved by changing the shape of the stirring blades or controlling the stirring speed. These differ depending on the equipment used, so it is advisable to conduct tests and simulations in advance and replace the stirring blades or set the stirring speed to achieve the above-mentioned stirring strength.

[0087] (Muddy water treatment method) Next, a muddy water treatment method according to the second embodiment will be described with reference to Fig. 14. Fig. 14 is a flowchart illustrating the muddy water treatment method according to the second embodiment. As shown in FIG. 14, this turbid water treatment method includes an adding step S40, a reacting step S6, a flocculating step S7, a precipitating step S8, a recovering step S10, a supplying step S11, and a pH adjusting step S12.

[0088] In the adding step S40, an inorganic flocculant and magnetic particles are added to the cement turbid water. This step can be performed by the inorganic flocculant adding means 41 and the magnetic particle adding means 42 described above. In the reaction step S6, the suspended matter in the cement turbid water is flocculated (basal flocs are formed) by the inorganic flocculant and the magnetic particles. This step can be carried out in the reaction tank 4 described above. In the flocculation step S7, a polymer flocculant is added to further flocculate the flocculated suspended matter into magnetic flocs. This step can be performed in the flocculation tank 5 described above. In the settling step S8, the flocculated magnetic flocs are allowed to settle to obtain supernatant water and sludge containing magnetic particles. This step can be carried out in the settling tank 6 described above. In the recovery step S10, the magnetic particles are recovered from the sludge. This step can be performed by the recovery means 8 described above. In the supply step S11, the recovered magnetic particles are supplied to the turbid cement water, specifically, to the turbid cement water in the adding step S40. This step can be performed by the supply means 9 described above. In the pH adjustment step S12, the pH of the supernatant water obtained in the precipitation step S8 is adjusted (neutralized). This step can be performed by the pH adjustment device 11b described above. The recovery step S10 and the supply step S11 can be performed in one step if the magnetic separator 81 described above is used.

[0089] This turbid water treatment method forms magnetic flocs by adding and reusing magnetic particles in addition to the usual coagulation and sedimentation process. In other words, this turbid water treatment method can perform coagulation and sedimentation treatment while the turbid water remains alkaline, without neutralizing it. As a result, this turbid water treatment method can significantly reduce the amount of neutralizing agent added to the supernatant water after treatment compared to adding a neutralizing agent to the turbid water, making it more efficient and cost-effective. Furthermore, because this turbid water treatment method does not involve neutralizing the cement turbid water, the overall treatment time can be shortened and costs can be reduced.

[0090] FIG. 15 is a flowchart illustrating a method for treating turbid water according to a preferred aspect of the second embodiment. 15, the present turbid water treatment method includes a discharge storage step S90 for storing supernatant water after the sedimentation step S8 in the second embodiment. This step can be performed by the discharge storage tank 11 described above. As described above, the target of treatment in the second embodiment is cement turbid water. As described above, cement turbid water has a pH of 9 or higher, so before discharging the supernatant water, a neutralization treatment (pH adjustment) is performed to lower the pH. This neutralization treatment makes it possible to comply with the discharge regulation value. As described above, the neutralization treatment can be performed by adding a neutralizing agent to the supernatant water. In order to perform the neutralization treatment, a preferred aspect of the second embodiment includes a pH adjustment step S12 in which the pH of the supernatant water is adjusted immediately before or after the storage step for discharge S90, as shown in FIG. 15. The pH adjustment step S12 can be performed by the pH adjustment device 11b described above.

[0091] FIG. 16 is a flowchart illustrating a method for treating turbid water according to another preferred aspect of the second embodiment. As shown in FIG. 16, in this method for treating turbid water, a first separation step S91 for separating magnetic particles from supernatant water is performed between the settling step S8 and the storage for discharge step S90. This turbid water treatment method also includes a turbid water storage step S1 in which cement turbid water is stored before the adding step S40. Additionally, this turbid water treatment method also includes a second separation step S92 in the reaction step S6. In the second separation step S92, sludge remaining at the bottom of the reaction tank 4, which aggregates suspended solids in the cement turbid water, is removed as needed, and the sludge is separated from the magnetic particles in the sludge. The sludge from which the magnetic particles have been separated is then returned to the turbid water storage step S1. The sludge can be extracted by the extraction means 12 described above. The turbid water storage step S1 can be performed by the turbid water storage tank 2 described above. The first separation step S91 can be performed by the first separation means 10 described above. The second separation step S92 can be performed by the second separation means 13 described above. [Example]

[0092] Next, examples relating to the second embodiment will be described. (Test 6) Demonstration test of coagulation and sedimentation of alkaline turbid water using a high-speed coagulation and sedimentation device A demonstration test was conducted using iron powder (magnetic particles) as a sedimentation accelerator in the coagulation and sedimentation treatment of alkaline turbid water, with a standard treatment volume of approximately 10 m 3 The experiment was carried out using a high-speed coagulation and sedimentation equipment with a capacity of 1000 kJ / h. Figure 17 is an explanatory photograph showing a full view of the demonstration test equipment (corresponding to turbid water treatment equipment 1) in an example related to the second embodiment. As shown in Figure 17, the main components of this equipment are a raw water tank (corresponding to turbid water storage tank 2) for storing alkaline turbid water used in the test, a high-speed coagulation and sedimentation equipment (corresponding to reaction tank 4, coagulation tank 5, and sedimentation tank 6) that performs coagulation and sedimentation treatment on the turbid water sent from the raw water tank, a treated water tank (corresponding to neutralization treatment tank 7 or discharge storage tank 11) for storing the supernatant water after solid-liquid separation, and a sludge tank for storing sludge. Carbon dioxide gas is supplied to the treated water tank to neutralize the treated water.

[0093] In this test, a high-speed coagulation sedimentation device (Actiflo AFJ-10T, standard treatment capacity: 10 m) owned by Actio Co., Ltd. 3 / h) was used (Figure 18). Figure 18 is a schematic diagram explaining the high-speed coagulation and sedimentation equipment used in Test 6. The dimensions of this equipment are W 2.8m x D 0.9m x H 2.6m. This equipment consists of a reaction tank and coagulation tank where flocs are generated by stirring, and a settling tank where the flocs are allowed to settle and undergo solid-liquid separation. In this Test 6, a branch pipe was installed midway through the piping that sends the sludge separated in the settling tank to the cyclone, and a magnetic separator was connected to the end of this branch pipe.

[0094] (Test Method) The muddy water used in the test was mud (fine particle ratio: 70-80%) discharged during the excavation of a mountain tunnel. After the gravel was removed using a 4.75 mm mesh sieve, 1.8 kg of the muddy water was added to the raw water tank for every 1 kL of water. The water used was groundwater (pH: 7.7) collected on-site. 1.0 kg of ordinary Portland cement (manufactured by Taiheiyo Cement Corporation) was added to 1 kL of the prepared turbid water, and the mixture was thoroughly stirred with a screw pump to prepare the test muddy water (pH 11.5-11.8). In conducting the following tests, the turbid water treatment speed of the high-speed coagulation sedimentation device was set at 15 m 3 / h, and the turbid water used for one test was 5m 3 The test time for one batch (turbid water treatment time) was 20 minutes.

[0095] (Test conditions) The coagulation and sedimentation treatment was carried out under two conditions: one in which only PAC and polymer coagulant were used as coagulants and no precipitation accelerator (iron powder) was used (Case 1: no iron powder), and the other in which PAC and polymer coagulant were used as coagulants and iron powder, which is a magnetic particle, was used as a precipitation accelerator (Case 2: with iron powder). Three batches of tests were carried out under each condition. The PAC (manufactured by Asada Chemical Industry Co., Ltd.) continuously supplied the raw solution to the reaction tank at 0.9 L / h. A 1 g / L diluted solution of an anionic polymer flocculant (Taipolymer TA-360, manufactured by Taimei Chemical Industry Co., Ltd.) was continuously supplied to the coagulation tank at 3.75 L / h. Iron powder (atomized iron powder manufactured by Kobe Steel, Ltd.) was manually added to the reactor at 1.67 kg every 40 seconds from the start of the test. Taking into consideration sedimentation characteristics based on Figure 6 of Japanese Patent Application No. 2023-018287, iron powder that had passed through a sieve with 75 μm openings was used.

[0096] The alkaline turbid water used in each test showed generally similar properties, with a pH of 11.5 to 11.8 (average: 11.6), SS of 1470 to 1840 mg / L (average: 1600 mg / L), and turbidity of 410 to 500 NTU (average: 440 NTU). The turbidity in the settling tank, the SS of the supernatant water (treated water), and the weight of iron powder contained in the treated water were measured 8, 12, 16, and 20 minutes after the start of the test.

[0097] (Test results) Figure 19 is a graph showing the turbidity (average values) in the settling tank 8, 12, 16, and 20 minutes after the start of the test. Figure 20 is a graph showing the SS (average values) in the supernatant water (treated water) of the settling tank 8, 12, 16, and 20 minutes after the start of the test. In addition to Case 1 and Case 2, Figure 20 also shows Case 3 (iron particles present) as SS data for the treated water after a magnet was used to remove fine iron particles (approximately 14% of the input amount) from the SS in the supernatant water. In other words, the data obtained by subtracting the 14% fine iron particle contamination rate from the Case 2 data.

[0098] As shown in Figure 19, it was confirmed that in Case 2, where iron powder was used, the turbidity in the settling tank was reduced to approximately 20 NTU. On the other hand, in Case 1, where iron powder was not used, the turbidity in the settling tank was approximately 70 NTU. Furthermore, as shown in Figure 20, it was confirmed that in Case 2, in which iron powder was used, the SS of the treated water was below the discharge regulation value (Water Turbidity Act standard) of 150 mg / L. On the other hand, in Case 1, in which iron powder was not used, the SS of the treated water was approximately 400 to 500 mg / L. Furthermore, in Case 3, by removing the magnetic particles from the supernatant water, the SS of the treated water was reduced by roughly 10 to 20% compared to Case 2, and it was confirmed that clearer treated water was obtained.

[0099] (Test 7) ​​Particle size distribution of commercially available iron powder The present inventors measured the particle size distribution of two common types of commercially available iron powder. Figure 21 is a graph showing the results of measuring the particle size distribution of two common types of iron powders available on the market. As shown in Figure 21, it was confirmed that the particle size of the two common types of iron powders was less than 1 mm, with an average particle size of approximately 65 to 150 μm. Iron powder A is cast iron powder manufactured by Kanto Chemical Co., Ltd., and iron powder B is atomized iron powder manufactured by Kobe Steel, Ltd.

[0100] The above describes the embodiments and examples of the present invention, but the present invention is not limited to the above-described embodiments and examples, and each of the above-described components can be modified as appropriate within the scope of the present invention. [Explanation of symbols]

[0101] 1. Turbid water treatment equipment 2 Turbid water storage tank 21 pH measuring device 3 pH adjustment tank 4 Reactor 41 Means of adding inorganic coagulant 42 Magnetic particle addition means 5 Coagulation tank 51 Polymer flocculant addition method 6 Settling tank 7 Neutralization tank 71 pH measuring instrument 8. Recovery Methods 81 Magnetic Separator 82 Magnet core 83 Outer cylinder 84 Roller 85 Scraper 9 Means of supply 10 First Separation Means 11 Discharge storage tank 11b pH adjustment device 12 Extraction Method 13 Second Separation Measures S1 Turbid water storage step S2 Decision Step S3 pH adjustment step S4 Inorganic coagulant addition step S5 Magnetic particle addition step S6 Reaction step S7 Aggregation step S71 Polymer flocculant addition step S8 Precipitation step S9 Neutralization step S10 Collection step S11 Supply step S12 pH adjustment step S40 Addition Step S90 Discharge storage step S91 First Separation Step S92 Second Separation Step

Claims

1. a reaction tank for flocculating suspended matter in turbid cement water to which an inorganic flocculant and magnetic particles have been added; a coagulation tank provided downstream of the reaction tank for coagulating the suspended solids in the turbid cement water to which a polymer coagulant has been added to form magnetic flocs; a settling tank provided downstream of the coagulation tank for settling the coagulated magnetic flocs to obtain supernatant water and sludge containing the magnetic particles; a recovery means for recovering the magnetic particles from the sludge; a supply means for supplying the recovered magnetic particles to the turbid cement water; A turbid water treatment device comprising:

2. 2. The turbid water treatment device according to claim 1, further comprising a discharge reservoir downstream of the settling tank for storing the supernatant water.

3. 3. The turbid water treatment device according to claim 2, further comprising a first separation means for separating the magnetic particles from the supernatant water, the first separation means being disposed between the settling tank and the discharge storage tank.

4. 2. The turbid water treatment apparatus according to claim 1, further comprising an extracting means for extracting the sludge retained at the bottom of the reaction tank from the reaction tank.

5. The turbid water treatment device according to claim 1, characterized in that the reaction tank has a stirring strength that makes it difficult for magnetic particles of 75 μm or less in diameter to settle out.

6. 4. The apparatus for treating muddy water according to claim 3, wherein the first separating means is a magnetic separator.

7. 5. The turbid water treatment device according to claim 4, wherein the extraction means comprises a bottom portion provided at the bottom of the reaction tank, the bottom portion having a shape in which the area of ​​its horizontal cross section decreases downward in the reaction tank.

8. A turbid water storage tank for storing the cement turbid water is provided upstream of the reaction tank, The turbid water treatment device described in claim 4, characterized in that the extraction means is equipped with a second separation means for separating the magnetic particles from the extracted sludge, and the sludge from which the magnetic particles have been separated by the second separation means is returned to the turbid water storage tank.

9. 3. The turbid water treatment device according to claim 2, further comprising a pH adjusting device for adjusting the pH of the supernatant water immediately before or after the discharge storage tank.

10. an adding step of adding an inorganic flocculant and magnetic particles to the cement turbid water; a reaction step of flocculating suspended matter in the cement turbid water by the inorganic flocculant and the magnetic particles; a flocculation step in which the flocculated suspended matter is further flocculated into magnetic flocs by adding a polymer flocculant; a settling step of settling the flocculated magnetic flocs to obtain supernatant water and sludge containing the magnetic particles; a recovery step of recovering the magnetic particles from the sludge; a supply step of supplying the recovered magnetic particles to the turbid cement water; A method for treating turbid water, comprising:

11. The turbid water treatment method according to claim 10, further comprising a discharge storage step of storing the supernatant water after the settling step.

12. The turbid water treatment method according to claim 11, characterized in that a first separation step of separating the magnetic particles from the supernatant water is carried out between the settling step and the discharge storage step.

13. A turbid water storage step of storing the cement turbid water before the adding step, The turbid water treatment method described in claim 10, characterized in that in the reaction step, a second separation step is carried out in which sludge remaining at the bottom of the reaction tank that coagulates the suspended matter in the cement turbid water is removed at appropriate times, the sludge is separated from the magnetic particles in the sludge, and the sludge from which the magnetic particles have been separated is returned to the turbid water storage step.

14. The turbid water treatment method according to claim 11, further comprising a pH adjustment step of adjusting the pH of the supernatant water immediately before or after the discharge storage step.

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