Water treatment method, water treatment device, and coagulant

Abstract

To provide a water treatment method that can effectively flocculate suspended matters contained in water being treated, automatically determine an injection ratio of a flocculant and perform purification treatment.SOLUTION: A water treatment method includes injecting a flocculant into target water containing suspended matter, agitating the target water into which the flocculant has been injected, and purifying the agitated target water in a purifier 20. The flocculant has an alkalinity of 65-80%, and contains poly aluminum chloride having a particle size of 0.5 μm-1 μm in more than 120,000 particles per 1 mL.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a water treatment method and a water treatment apparatus for purifying water containing suspended solids. Furthermore, this invention relates to a coagulant used in such a water treatment method. [Background technology]

[0002] Aquariums and other facilities that display and breed aquatic life such as fish and marine mammals, as well as those used in aquaculture, require the use of clean seawater in their tanks. Since transporting clean seawater from offshore is not practical, purified seawater or brackish water from harbors or coastal areas, which are generally of lower purity, is typically used.

[0003] One method for purifying seawater with low purity (hereinafter also referred to as treated water) involves injecting a coagulant such as polyaluminum chloride into the treated water to coagulate the suspended solids contained in the treated water, and then purifying the treated water using a sand filter or the like. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-49442 [Patent Document 2] Japanese Patent Publication No. 2021-20165 [Overview of the project] [Problems that the invention aims to solve]

[0005] The water quality of the treated water (turbidity, amount of suspended solids, etc.) fluctuates significantly with changes in the environment. Therefore, it is necessary to adjust the injection rate of the coagulant to the appropriate level according to the water quality of the treated water. If the amount of coagulant is excessive compared to the appropriate injection rate, the aluminum component of the coagulant, which does not contribute to the coagulation of suspended solids, will leach into the treated water after purification. Conversely, if the amount of coagulant is insufficient compared to the appropriate injection rate, the suspended solids will not coagulate sufficiently, and the treated water cannot be purified.

[0006] Aquariums and fish farms require 24-hour water purification treatment to maintain the water in their tanks. However, it is difficult for workers to constantly monitor the water quality and adjust the coagulant injection rate to the appropriate level due to cost and other issues.

[0007] Therefore, the present invention aims to provide a water treatment method and a water treatment apparatus that can effectively coagulate suspended solids contained in water to be treated and purify the water to be treated. Furthermore, the present invention aims to provide a coagulant that can effectively coagulate suspended solids used in such a water treatment method. [Means for solving the problem]

[0008] In one embodiment, a water treatment method for purifying water to be treated containing suspended solids is provided, comprising injecting a coagulant into the water to be treated, stirring the water to be treated into which the coagulant has been injected, and purifying the stirred water to be treated with a purification device, wherein the coagulant has a basicity of 65-80% and contains 120,000 or more polyaluminum chloride particles per 1 mL with a particle size of 0.5 μm-1 μm. In one embodiment, the water treatment method further includes obtaining a property index value of the water to be treated, determining the injection rate of the coagulant based on the property index value, and injecting the coagulant at the determined injection rate.

[0009] In one embodiment, the property index value is at least one of the turbidity of the treated water, the SS concentration, and the number of fine particles per unit volume. In one embodiment, the water treatment method further includes obtaining in advance the correlation between the turbidity and the SS concentration, and obtaining the property index value means calculating the turbidity based on the measured SS concentration and the correlation, or calculating the SS concentration based on the measured turbidity and the correlation. In one embodiment, the purification device includes a sand filtration device. In one embodiment, the chloride ion concentration of the treated water is in the range of 1,000 to 22,000 mg / L.

[0010] In one embodiment, a water treatment apparatus for purifying water to be treated containing suspended solids is provided, comprising: a coagulant injection device for injecting a coagulant into the water to be treated; a stirrer for stirring the water to be treated into which the coagulant has been injected; and a purification device for purifying the stirred water to be treated, wherein the coagulant has a basicity of 65-80% and contains 120,000 or more polyaluminum chloride particles per 1 mL with a particle size of 0.5 μm-1 μm. In one embodiment, the water treatment apparatus further includes a property measuring device that acquires property index values ​​of the water to be treated, and a control device that determines the injection rate of the coagulant based on the property index values. In one embodiment, the property measuring device is at least one of a turbidity measuring device, a SS concentration measuring device, and a fine particle counter. In one embodiment, the purification device includes a sand filtration device. In one embodiment, the chloride ion concentration of the treated water is in the range of 1,000 to 22,000 mg / L.

[0011] In one embodiment, a coagulant is provided for treating water containing suspended solids, wherein the coagulant has a basicity of 65-80% and contains 120,000 or more polyaluminum chloride particles per 1 mL with a particle size of 0.5 μm-1 μm. [Effects of the Invention]

[0012] According to the present invention, suspended solids contained in the water to be treated can be effectively and stably coagulated by using a coagulant containing 120,000 or more polyaluminum chloride particles per 1 mL with a basicity of 65-80% and a particle size of 0.5 μm-1 μm. Furthermore, according to the present invention, the property index value of the water to be treated is obtained, and the injection rate of the coagulant is determined based on the obtained property index value, so the injection rate of the coagulant can be automatically determined and the purification treatment can be performed. [Brief explanation of the drawing]

[0013] [Figure 1] It is a diagram showing one embodiment of a water treatment apparatus. [Figure 2] It is a graph showing the correlation between the turbidity and SS concentration of the water to be treated. [Figure 3] It is a table showing the results of a jar test. [Figure 4] It is a table showing the test results using a water treatment apparatus.

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing one embodiment of a water treatment apparatus 1. The water treatment apparatus 1 according to the present embodiment is an apparatus for purifying water to be treated containing suspended substances. The water to be treated in the present embodiment is seawater or brackish water in a relatively unclean harbor or coastal area. The chloride ion concentration of the water to be treated is in the range of 1,000 to 22,000 mg / L. However, the water to be treated is not limited to this as long as it contains suspended substances, and for example, it may be fresh water.

[0015] The water treatment apparatus 1 includes a water to be treated supply pipe 2, a property measurement device 3, a flocculant supply pipe 5, a stirrer 10, a purification device 20, and a control device 30. The water to be treated supply pipe 2 is arranged on the most upstream side of the water treatment apparatus 1. The water to be treated supply pipe 2 may be connected to an introduction pipe (not shown) for introducing the water to be treated from a harbor or coastal area adjacent to the water treatment apparatus 1, or may be connected to a storage tank (not shown) for storing the water to be treated. The water to be treated supplied from the introduction pipe or the storage tank flows through the water to be treated supply pipe 2.

[0016] The property measuring device 3 is located in the treated water supply piping 2. As described later, the property measuring device 3 is configured to acquire property index values ​​of the treated water flowing through the treated water supply piping 2. The coagulant supply piping 5 is connected to the treated water supply piping 2 at a location downstream of the property measuring device 3. The coagulant supply piping 5 is connected to the coagulant storage tank 7, which stores the coagulant. The coagulant supply piping 5 is equipped with a coagulant injection device 8 that injects the coagulant into the treated water containing suspended solids at a predetermined injection rate. The coagulant injection device 8 is, for example, a pump, a valve, or a combination of a pump and a valve.

[0017] The flocculant used in this embodiment is a polyaluminum chloride with a high basicity of 65-80% and a particle size of 0.5 μm-1 μm, containing 120,000 or more polyaluminum chloride (PAC) particles per 1 mL. The general formula for polyaluminum chloride is [Al2(OH) n ·Cl 6-n ] m It is expressed as (1 ≤ n ≤ 5, m ≤ 10), and basicity is defined as n / 6 × 100%. Details about flocculants will be described later.

[0018] The water to be treated supply pipe 2 is connected to the agitator 10 at a position downstream of the coagulant supply pipe 5. The water to be treated into which the coagulant has been injected by the coagulant injection device 8 is supplied to the agitator 10. In one embodiment, the coagulant supply pipe 5 may be connected to the agitator 10 instead of the water to be treated supply pipe 2, and the coagulant may be injected into the water to be treated in the agitator 10.

[0019] The agitator 10 comprises a stirring tank 12 that contains the water to be treated supplied from the water to be treated supply pipe 2, a stirring blade 13 that stirs the water to be treated, and a motor 15 as a drive device for rotating the stirring blade 13. The water to be treated supply pipe 2 is connected to the stirring tank 12, and the water to be treated to which the coagulant has been injected is supplied into the stirring tank 12. In this embodiment, the agitator 10 has a stirring blade 13 with a rotation speed of 30 to 220 min⁻¹. -1It is configured as an agitator. The rotation speed of the agitator blade 13 is adjusted based on the properties of the treated water containing suspended solids (e.g., turbidity, SS (Suspended Solids) concentration, number of particles per unit volume, viscosity, etc.).

[0020] When the water to be treated, into which the coagulant has been injected, is stirred in the stirring tank 12, the coagulant is uniformly dispersed in the water. The surface charge of suspended solids contained in the water is neutralized by the dispersed coagulant, and flocs of suspended solids are formed in the water. Hereinafter, this process may be referred to as "coagulation treatment".

[0021] In one embodiment, a line mixer may be used as the agitator 10. A line mixer is a mixer incorporated into the piping. The advantage of a line mixer is that, because the mixer is sealed, the water to be treated can be sent downstream of the line mixer with just two pumps: one for the water to be treated and another for the coagulant, both located upstream of the line mixer. On the other hand, in the case of an agitator 10 in which a stirring blade 13 is installed inside a stirring tank 12, the top of the stirring tank 12 is open, so an additional pump or equivalent equipment is required to send the liquid downstream of the agitator 10. For this reason, it is generally common to send the liquid downstream using the difference in elevation without installing a pump. In another embodiment, without providing an agitator and a line mixer, the coagulant may be injected directly into the line through which the water to be treated flows, and the water to be treated and the coagulant may be mixed by the flow of the water in the line.

[0022] The agitator 10 is connected to the purification device 20. The purification device 20 includes agitated water transfer piping 21, a sand filter 25, and purified water transfer piping 26. The agitated water transfer piping 21 is connected to the agitator tank 12 of the agitator 10 on the upstream side and to the sand filter 25 on the downstream side. The water to be treated, agitated by the agitator 10 and with flocs formed, flows through the agitated water transfer piping 21 and is supplied to the sand filter 25.

[0023] The water to be treated, on which flocs have formed, is separated into flocs and filtrate by passing through the sand filter 25. The purified water transfer pipe 26 is connected to the downstream side of the sand filter 25. The filtrate separated by the sand filter 25 is supplied as clean water to the water tank 50 through the purified water transfer pipe 26. In this way, the water treatment device 1 purifies the water to be treated, which contains suspended solids, and supplies clean water to the water tank 50.

[0024] The sand filtration device 25 may be a single-layer filtration device having a single sand filtration layer. Alternatively, the sand filtration device 25 may be a multi-layer filtration device having multiple layers of sand filtration media, such as anthracite or garnet, which have different densities and particle sizes, configured so that the grains progress from coarse to fine in the direction of water flow.

[0025] The sandy filter media of the sand filtration device 25 may have a uniformity coefficient (the ratio of the grain size of sand that 60% of the total sample passes through to the grain size of sand that 10% of the total sample passes through, on the grain size distribution curve of the sand) of 1.7 or less. A uniformity coefficient of 1 for the sandy filter media indicates that all the grain sizes of the sandy filter media are the same. The closer the uniformity coefficient of the sandy filter media is to 1, the larger the porosity of the filtration layer and the greater the amount of turbidity retained (for example, the amount of floc retained). In other words, the closer the uniformity coefficient of the sandy filter media is to 1, the higher the purification performance of the sand filtration device 25.

[0026] Furthermore, repeated purification treatment can cause the sandy filter media to break down and wear away, leading to leakage and changes in the particle size composition and thickness of the sand filtration layer. Therefore, it is preferable that the sandy filter media of the sand filtration device 25 contains few impurities and is resistant to wear. More specifically, the specific gravity of the sandy filter media may be in the range of 2.57 to 2.67. Sandy filter media with a specific gravity lower than 2.57 may contain organic substances or porous sand, and sandy filter media with a specific gravity higher than 2.67 may contain limestone or heavy metal ores, which are undesirable.

[0027] Furthermore, the effective diameter of the granular filter medium (the particle diameter of the sand through which 10% of the total sample passes on the sand particle size accumulation curve) may be within the range of 0.45 to 0.70 mm in order to correspond to the turbidity blocking rate, filtration duration, and backwashing rate, as well as the properties of a wide range of raw water to be treated. For a granular filter medium with an effective diameter smaller than 0.45 mm, there is a risk that the filter medium may flow out into the purified water transfer pipe 26 in the subsequent stage, and for a granular filter medium with an effective diameter larger than 0.70 mm, the ability to capture (block) flocs is low, and sufficient purification performance cannot be obtained, which is not preferable.

[0028] In this embodiment, the purification device 20 includes a sand filtration device 25 that uses a granular filter medium as the filter medium, but the type (material, size, shape, etc.) of the filter medium used in the filtration device is not particularly limited. Examples of the filter medium material include anthracite, urethane foam, activated carbon, polystyrene, polypropylene, etc. In one embodiment, the purification device 20 may include, in addition to or instead of the sand filtration device 25, at least one of various filtration devices such as a floating filtration device, a fiber filtration device, a membrane filtration device, a foam separation treatment device, an ozone treatment device, a UV treatment device, and a contact oxidation treatment device.

[0029] The water tank 50 is not particularly limited and may be water tanks of various shapes and sizes such as an aquarium display tank, a aquaculture water tank, and a live fish tank etc. The water treatment device 1 of this embodiment is particularly preferably used when supplying water to a display water tank 50 that requires a high degree of cleanliness.

[0030] Aquatic organisms including fish, shellfish, marine mammals, aquatic plants, seaweeds, etc. can be accommodated in the water tank 50. The capacity of the water tank 50 is not particularly limited, and water tanks 50 with a capacity of several m 3 ~ tens of thousands of m 3 can be used. For example, water tanks 50 with a capacity of 1 m 3 or more, further 1000 m 3 or more, further 5000 m 3 or more can be used.

[0031] Next, the method for determining the injection rate of the coagulant will be explained. If the amount of coagulant is excessive compared to the appropriate injection rate, the aluminum component of the coagulant, which does not contribute to the coagulation of suspended solids, will leach into the treated water after the purification treatment. Conversely, if the amount of coagulant is insufficient compared to the appropriate injection rate, the suspended solids will not coagulate sufficiently, and water of the desired quality cannot be obtained after the purification treatment. Therefore, the water treatment device 1 of this embodiment determines the injection rate of the coagulant based on the property index value of the treated water obtained by the property measuring device 3.

[0032] The property measuring device 3 is at least one of a turbidity measuring device for measuring the turbidity of the treated water, a SS concentration measuring device, and a particulate counter. The turbidity measuring device acquires the turbidity of the treated water as a property index value. The SS concentration measuring device acquires the SS concentration of the treated water as a property index value. The particulate counter acquires the number of particulates per unit volume of the treated water as a property index value. Commercially available products can be used for the turbidity measuring device, SS concentration measuring device, and particulate counter.

[0033] The appropriate injection rate of a coagulant is the rate at which flocs of suspended solids contained in the treated water are formed effectively during the coagulation process. Turbidity, SS concentration, and number of particulate matter per unit volume of the treated water are all numerical values ​​that indicate the state of suspended solids contained in the treated water. Therefore, the appropriate injection rate of a coagulant can be determined based on at least one of the property indicators among the turbidity, SS concentration, and number of particulate matter per unit volume of the treated water.

[0034] As shown in Figure 1, the property measuring device 3 and the coagulant injection device 8 are electrically connected to the control device 30. The control device 30 is configured to determine the coagulant injection rate based on the property index values ​​obtained by the property measuring device 3. The control device 30 consists of at least one computer. The control device 30 includes a storage device 30a that stores a program and an arithmetic unit 30b that performs calculations according to the instructions contained in the program stored in the storage device 30a.

[0035] The storage device 30a stores appropriate injection rate data that shows at least one of the following relationships: the relationship between the turbidity of the water to be treated and the appropriate injection rate of the coagulant; the relationship between the SS concentration of the water to be treated and the appropriate injection rate of the coagulant; and the relationship between the number of fine particles per unit volume of the water to be treated and the appropriate injection rate of the coagulant. The property index values ​​of the water to be treated obtained by the property measuring device 3 are sent to the control device 30. The calculation device 30b is configured to determine the injection rate of the coagulant based on the property index values ​​of the water to be treated obtained by the property measuring device 3 and the appropriate injection rate data stored in the storage device 30a. The determined injection rate is sent to the coagulant injection device 8, and the coagulant injection device 8 injects the coagulant at the determined injection rate.

[0036] The property measurement device 3 automatically acquires property index values ​​of the treated water at predetermined intervals, allowing for continuous monitoring of the treated water's properties. Furthermore, the control device 30 can automatically determine the coagulant injection rate based on the acquired property measurements of the treated water. This eliminates the need for operators to constantly monitor the water quality and adjust the coagulant injection rate, enabling proper purification treatment in response to changes in the treated water's properties. As a result, costs such as labor expenses can be reduced, and maintenance can be simplified.

[0037] Figure 2 is a graph showing the correlation between the turbidity and SS concentration of the treated water. In Figure 2, the vertical axis represents turbidity, and the horizontal axis represents SS concentration. As shown in Figure 2, there is a correlation between the turbidity and SS concentration of the treated water. Therefore, in one embodiment, the property measuring device 3 may acquire the correlation (calibration curve) between the turbidity and SS concentration of the treated water in advance, calculate the turbidity of the treated water from the measured SS concentration and the correlation, and acquire it as a property index value. Alternatively, the property measuring device 3 may calculate the SS concentration of the treated water from the measured turbidity and the correlation, and acquire it as a property index value.

[0038] The control device 30 determines the injection rate of the coagulant based on the turbidity or SS concentration, which are property indicator values ​​of the water to be treated, obtained in this manner. In other embodiments, the correlation between the turbidity and SS concentration of the water to be treated may be stored in the storage device 30a of the control device 30. In this case, the calculation device 30b may calculate the turbidity of the water to be treated from the SS concentration of the water to be treated measured by the property measuring device 3 and the correlation stored in the storage device 30a. Alternatively, the calculation device 30b may calculate the SS concentration of the water to be treated from the turbidity of the water to be treated measured by the property measuring device 3 and the correlation stored in the storage device 30a.

[0039] In one embodiment, the control device 30 may determine the injection rate of the coagulant based on two or more property indicator values ​​from among the turbidity of the water to be treated, the SS concentration, and the number of fine particles per unit volume. In this case, the property measuring device 3 may consist of two or more of the turbidity measuring device, the SS concentration measuring device, and the fine particle counter. Alternatively, two property indicator values ​​may be used: a measured value of the turbidity of the water to be treated and the SS concentration of the water to be treated calculated from the correlation between the turbidity and SS concentration of the water to be treated, or a measured value of the SS concentration of the water to be treated and two property indicator values ​​of the turbidity of the water to be treated calculated from the correlation between the turbidity and SS concentration of the water to be treated. By using multiple property indicator values, the injection rate of the coagulant can be determined with greater accuracy.

[0040] In one embodiment, a predetermined lower or upper limit value for the coagulant injection rate is stored in the storage device 30a, and even if the property index value of the treated water decreases or increases significantly, the control device 30 may be configured to determine the coagulant injection rate within the range of the lower and / or upper limit values.

[0041] Next, the flocculant used in the flocculation treatment will be described. Generally, inorganic flocculants such as polyaluminum chloride, polyaluminum sulfate, ferric chloride, polyferric sulfate, ferric sulfate, and polysilica iron, as well as organic flocculants and polymer flocculants, are used. In this embodiment, a flocculant is used that contains 120,000 or more polyaluminum chloride (PAC) particles per 1 mL, which have a high basicity of 65-80% and a particle size of 0.5 μm-1 μm.

[0042] The inventors conducted the following tests on this embodiment. The water to be treated used in the tests had a pH of 7.9, a particulate matter count of 18,700 particles / mL per unit volume, an electrical conductivity of 4,000 mS / m, and an acid consumption of 79 CaCO3 mg / L. Using this water to be treated, jar tests for coagulation treatment and purification treatment, and tests using the water treatment device 1 were performed.

[0043] Figure 3 is a table showing the results of the jar test. The jar test was performed using the following procedure.

[0044] <Examples 1-3> For 500 mL of water to be treated, a coagulant containing 160,000 polyaluminum chloride particles per mL with a basicity of 70% and a particle size of 0.5 μm to 1 μm is injected at a predetermined injection rate, and the rotation speed is 150 min. -1 The mixture was stirred for 1 minute. Immediately after stirring, the mixture was filtered using filter paper (JIS P 3801, for chemical analysis, type 5A), and the turbidity, number of particulate matter per unit volume, and aluminum concentration of the filtrate were measured. The injection rates of the coagulant were 2.5 mg / L in Example 1, 5.0 mg / L in Example 2, and 7.5 mg / L in Example 3.

[0045] <Comparative Examples 1-3> For 500 mL of water to be treated, a coagulant containing 93,000 polyaluminum chloride particles per mL with a basicity of 51% and a particle size of 0.5 μm to 1 μm is injected at a predetermined injection rate, and the rotation speed is 150 min. -1The mixture was stirred for 1 minute. Immediately after stirring, the mixture was filtered using filter paper (JIS P 3801, for chemical analysis, type 5A), and the turbidity, number of particulate matter per unit volume, and aluminum concentration of the filtrate were measured. The coagulant injection rates were 2.5 mg / L for Comparative Example 1, 5.0 mg / L for Comparative Example 2, and 7.5 mg / L for Comparative Example 3. Except for the type of coagulant and the coagulant injection rate, the same conditions as in Examples 1 to 3 were used.

[0046] As shown in Figure 3, the test results confirmed that the treated water was most purified in Example 3. Furthermore, comparing Examples 1-3 with Comparative Examples 1-3, it was confirmed that even with the same coagulant injection rate, Examples 1-3, which used a coagulant with a basicity of 70% and containing 160,000 polyaluminum chloride particles per mL with a particle size of 0.5 μm to 1 μm, were able to purify the treated water more effectively.

[0047] Figure 4 is a table showing the test results using water treatment device 1. The test using water treatment device 1 was conducted according to the following procedure.

[0048] <Examples 4-6> The water to be treated has a processing capacity of 120 m³. 3 A flocculant containing 160,000 polyaluminum chloride particles per mL with a basicity of 70% and a particle size of 0.5 μm to 1 μm was injected into a line flowing at a predetermined rate. After the water to be treated and the flocculant were mixed in the line, sand filtration was performed using a purification device 20, and the turbidity, number of particulate matter particles per unit volume, and aluminum concentration of the filtrate were measured. The flocculant injection rates were 6.3 mg / L in Example 4, 7.2 mg / L in Example 5, and 9.0 mg / L in Example 6.

[0049] <Comparative Example 4> The water to be treated has a processing capacity of 120 m³. 3A flocculant containing 93,000 polyaluminum chloride particles per mL with a basicity of 51% and a particle size of 0.5 μm to 1 μm was injected into a line flowing at a rate of 1 / hour at an injection rate of 9.0 mg / L. After the water to be treated and the flocculant were mixed in the line, sand filtration was performed using a purification device 20, and the turbidity, number of particulate matter particles per unit volume, and aluminum concentration of the filtrate were measured. Except for the type of flocculant and the injection rate of the flocculant, the procedure was carried out under the same conditions as in Examples 4 to 6.

[0050] As shown in Figure 4, the test results confirmed that the treated water was effectively purified in all of Examples 4 to 6. In other words, the coagulant used in Examples 4 to 6, which has a basicity of 70% and contains 160,000 polyaluminum chloride particles per mL with a particle size of 0.5 μm to 1 μm, was found to have a wide range of appropriate injection rates, enabling effective and stable coagulation treatment. Furthermore, comparing Example 6 with Comparative Example 4, it was confirmed that even with the same coagulant injection rate, Example 6, which used a coagulant with a basicity of 70% and containing 160,000 polyaluminum chloride particles per mL with a particle size of 0.5 μm to 1 μm, was more effectively able to purify the treated water.

[0051] The inventors discovered that effective and stable flocculation can be achieved by using a flocculant containing more than 120,000 polyaluminum chloride particles per mL, with a high basicity of 65-80% and a particle size of 0.5 μm-1 μm. With polyaluminum chloride with a basicity of less than 65%, suspended solids in the treated water do not flocculate sufficiently, and flocs cannot be formed properly. With polyaluminum chloride with a basicity exceeding 80%, the stability of the polyaluminum chloride decreases.

[0052] Furthermore, in polyaluminum chloride with a basicity of 65-80%, if the number of polyaluminum chloride particles with a particle size of 0.5 μm to 1 μm is less than 120,000 per mL, it will contain a large amount of polyaluminum chloride particles that are either smaller than 0.5 μm or larger than 1 μm. If the amount of polyaluminum chloride particles smaller than 0.5 μm is large, it will not effectively act to coagulate suspended solids, and flocs cannot be formed properly. In addition, there is a risk of polyaluminum chloride leaching into the treated water after purification. If the amount of polyaluminum chloride particles larger than 1 μm is large, it may affect the turbidity of the treated water, making it unsuitable as a coagulant.

[0053] In one embodiment, in addition to the flocculant containing 120,000 or more polyaluminum chloride particles per mL with a high basicity of 65-80% and a particle size of 0.5 μm-1 μm, known inorganic flocculants or organic flocculants may be used in combination.

[0054] The embodiments described above are intended to enable persons with ordinary skill in the art to implement the present invention. Various modifications of the above embodiments can be made naturally by those skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments as well. Therefore, the present invention is not limited to the embodiments described, but is to be interpreted in the broadest sense according to the technical idea defined by the claims. [Explanation of symbols]

[0055] 1. Water treatment equipment 2. Water supply piping for treated water 3 Property measuring device 5. Coagulant supply piping 7. Coagulant storage tank 8. Coagulant injection device 10. Agitator 12 Agitation tank 13. Agitator blades 15 Motor 20 Purification device 21. Agitated water transfer piping 25 Sand filter equipment 26. Purified water transfer piping 30 Control device 50 aquariums

Claims

1. A water treatment method for purifying water to be treated that contains suspended solids, The property index value of the treated water is obtained, which is at least one of the turbidity, SS concentration, and number of fine particles per unit volume of the treated water. Based on the appropriate injection rate data, which shows the relationship between the property index value and the appropriate injection rate of the flocculant and is pre-stored in the control device, and the acquired property index value, the control device determines the injection rate of the flocculant. The coagulant is injected into the water to be treated at the injection rate determined above. The water to be treated, into which the coagulant has been injected, is stirred. This includes purifying the agitated water to be treated using a purification device, A water treatment method comprising the coagulant having a basicity of 65-80% and containing 120,000 or more polyaluminum chloride particles per 1 mL, with a particle size of 0.5 μm to 1 μm present in aqueous solution.

2. This further includes obtaining in advance the correlation between the turbidity and the SS concentration. The water treatment method according to claim 1, wherein obtaining the property index value is to calculate turbidity based on the measured SS concentration and the correlation, or to calculate the SS concentration based on the measured turbidity and the correlation.

3. The water treatment method according to claim 1, wherein the purification device comprises a sand filtration device.

4. The water treatment method according to any one of claims 1 to 3, wherein the chloride ion concentration of the water to be treated is in the range of 1,000 to 22,000 mg / L.

5. A water treatment device for purifying water to be treated that contains suspended solids, A property measuring device that acquires a property index value of the treated water, which is at least one of the turbidity, SS concentration, and number of fine particles per unit volume of the treated water, Appropriate injection rate data showing the relationship between the property index value and the appropriate injection rate of the flocculant, and a control device that determines the injection rate of the flocculant based on the acquired property index value, A coagulant injection device that injects the coagulant into the water to be treated at the injection rate determined above, A stirrer for stirring the water to be treated into which the coagulant has been injected, The system includes a purification device for purifying the agitated water to be treated, The property measuring device is at least one of a turbidity measuring device, a SS concentration measuring device, and a fine particle counter. The control device has the appropriate injection rate data stored in advance. The aforementioned flocculant contains 120,000 or more polyaluminum chloride particles per 1 mL, having a basicity of 65-80% and a particle size of 0.5 μm-1 μm in an aqueous solution.

6. The water treatment apparatus according to claim 5, wherein the purification apparatus comprises a sand filtration apparatus.

7. The water treatment apparatus according to any one of claims 5 or 6, wherein the chloride ion concentration of the treated water is in the range of 1,000 to 22,000 mg / L.

8. A coagulant for treating water containing suspended solids, A flocculant containing 120,000 or more polyaluminum chloride particles per 1 mL, having a basicity of 65-80% and a particle size of 0.5 μm-1 μm in an aqueous solution.

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