Method for treating water containing calcium hardness

Abstract

To provide a method of treating water containing Ca hardness, capable of downsizing a packed column while preventing a hardness component from leaking into treated water side.SOLUTION: The method of treating water containing Ca hardness for removing Ca hardness by allowing water containing Ca hardness to pass through a packed column packed with a cation exchanger is characterized in that the Ca hardness in the water containing Ca hardness is 5 mg-CaCO3 / L or below, and a space velocity (SV) of the water containing Ca hardness is from 100 to 300 h-1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a technique for treating water containing Ca hardness. [Background technology]

[0002] In the past, in water treatment, packed towers filled with ion exchangers have been widely used to remove various ionic components. When the water to be treated supplied to this packed tower comes into contact with the ion exchangers in the packed tower, the target ionic components contained in the water to be treated are adsorbed onto the ion exchangers and removed, thereby increasing the purity. For example, calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ When removing hardness components such as sulphur dioxide using an ion exchanger, the space velocity (SV) of the water being treated passing through the packed tower is 20 to 80 h -1 (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-3675 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the space velocity (SV) is 80h -1 If the SV is too high, there is a problem that hardness components leak into the treated water. In addition, when treating a large amount of water to be treated, if the space velocity (SV) cannot be increased, a large amount of ion exchanger is required, which increases the size of the packed tower and is disadvantageous in terms of cost.

[0005] Therefore, an object of the present disclosure is to provide a method for treating water containing hardness components, which can reduce the size of a packed tower while suppressing leakage of hardness components, particularly Ca hardness, into the treated water. [Means for solving the problem]

[0006] The present disclosure provides a method for treating Ca hardness-containing water, in which Ca hardness is removed by passing the Ca hardness-containing water through a packed column filled with a cation exchanger, The Ca hardness-containing water includes wastewater from a detoxification system, The concentration of Ca hardness in the Ca hardness-containing water is 5 mg-CaCO3 / L or less, and the space velocity (SV) of the Ca hardness-containing water passing through the packed tower is 100 to 300 h -1 It is characterized in that:

[0007] In the above-mentioned method for treating Ca-containing water, the cation exchanger is preferably a weakly acidic cation exchanger.

[0008] In addition, in the above-mentioned method for treating Ca hardness-containing water, it is preferable that the Ca hardness-containing water contains silica, and the treated water from which the Ca hardness has been removed by the cation exchanger is passed through a reverse osmosis membrane under alkaline conditions.

[0009] In the above-mentioned method for treating water containing Ca hardness, the water containing Ca hardness preferably contains fluorine.

[0011] In the above-mentioned method for treating Ca hardness-containing water, it is preferable that the cation exchanger is regenerated or washed at a frequency of not more than once every seven days and not less than once every 21 days. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to provide a method for treating water containing Ca hardness, which can reduce the size of a packed tower while suppressing leakage of Ca hardness into the treated water. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a processing apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present embodiment will be described below. The present embodiment is an example of implementing the present disclosure, and the present disclosure is not limited to the present embodiment.

[0015] FIG. 1 is a schematic diagram showing an example of a treatment device according to this embodiment. The treatment device 1 according to this embodiment is a device for treating Ca hardness-containing water. Hardness components are known in the field of water treatment, and typically include Ca. 2+ and Mg 2+ are divalent cations, such as:

[0016] The treatment device 1 shown in FIG. 1 includes a softening treatment device 3, a regeneration treatment device 5, and a membrane filtration device .

[0017] 1 includes a raw water tank 10 for storing Ca hardness-containing water, a packed tower 12 filled with a cation exchanger, a treated water tank 14, pipes 16a and 16b, and a raw water pump 18. The raw water pump 18 is installed in the pipe 16a. One end of the pipe 16a is connected to the outlet of the raw water tank 10, and the other end of the pipe 16a is connected to the raw water inlet of the packed tower 12. One end of the pipe 16b is connected to the treated water outlet of the packed tower 12, and the other end of the pipe 16b is connected to the inlet of the treated water tank 14.

[0018] 1 includes a regenerant tank 20 for storing a regenerant, pipes 22c and 22d, and a regenerant pump 24. The regenerant pump 24 is installed in the pipe 22c. One end of the pipe 22c is connected to the outlet of the regenerant tank 20, and the other end of the pipe 22c is connected to the regenerant inlet of the packed tower 12. The pipe 22d is connected to the regenerant outlet of the packed tower 12.

[0019] The membrane filtration device 7 shown in Fig. 1 includes a membrane module 26 equipped with a reverse osmosis membrane (hereinafter sometimes referred to as an RO membrane), a pipe 28e, a permeate pipe 28f, a concentrate pipe 28g, and a booster pump 30. The membrane module 26 includes, for example, a membrane element formed of a reverse osmosis membrane and a pressure-resistant container for housing the membrane element. The booster pump 30 is installed in the pipe 28e. One end of the pipe 28e is connected to the outlet of the treated water tank 14, and the other end of the pipe 28e is connected to the inlet of the membrane module 26. The permeate pipe 28f is connected to the outlet on the permeate side of the membrane module 26, and the concentrate pipe 28g is connected to the outlet on the concentrate side of the membrane module 26.

[0020] An example of a method for treating water containing Ca hardness using the treatment device 1 shown in FIG. 1 will be described.

[0021] <Softening treatment> When the raw water pump 18 is operated, the Ca hardness-containing water in the raw water tank 10 is supplied to the packed tower 12 through the pipe 16a. The Ca hardness-containing water flows downward through the packed tower 12 and comes into contact with the cation exchanger in the packed tower 12, where hardness components are removed from the Ca hardness-containing water (softening treatment). The treated water from which the hardness components have been removed flows from the packed tower 12 through the pipe 16b and is stored in the treated water tank 14.

[0022] Here, the calcium hardness-containing water to be softened is 5mg-CaCo 3 / L or less. And the Ca hardness is 5mg-CaCo 3 When softening water containing Ca hardness of 1 / L or less, the space velocity (SV) of the water containing Ca hardness passing through the packed tower 12 is set to 100 to 300 h -1 Here, the space velocity means how many times the volume of the ion exchanger packed in the packed tower 12 is treated per unit time, and is the flow rate (m 3 / h) was calculated by dividing the amount of ion exchanger (volume: m 3) in the treatment device 1 shown in FIG. 1, the space velocity (SV) of the Ca hardness-containing water passing through the packed tower 12 is 100 to 300 h -1 The output of the raw water pump 18 is controlled to adjust the flow rate of the Ca hardness-containing water passed through the packed tower 12 so that the above-mentioned condition is satisfied.

[0023] The amount of Ca hardness leaking from the packed tower 12 is affected not only by the space velocity (SV) but also by coexisting ions (e.g., sodium ions) in the Ca hardness-containing water. When Ca hardness-containing water containing a large amount of coexisting ions is softened, the cation exchanger adsorbs not only Ca hardness but also sodium ions, etc., so that the time when Ca hardness leaks into the treated water is earlier. Therefore, in the case of raw water with low Ca hardness, it is not easy to simply think that the space velocity (SV) can be increased. However, after extensive research by the present inventors, it was found that when the Ca hardness of the Ca hardness-containing water is 5 mg-CaCo 3 Under specific conditions of 0.15g / L or less, the space velocity (SV) of the Ca hardness-containing water passing through the packed tower 12 is set to 100 to 300 h -1 It was found that even when the reactor was operated at this temperature, leakage of calcium hardness into the treated water could be suppressed. In addition, the space velocity (SV) of the calcium hardness-containing water was set in a much higher range (100 to 300 h -1 ), the amount of cation exchanger can be reduced, allowing for the design of a compact packed column.

[0024] By the way, the Ca hardness of the Ca hardness-containing water stored in the raw water tank 10 is 5 mg-CaCo 3 / L, for example, the treated water stored in the treated water tank 14 is returned to the raw water tank 10, and the Ca hardness-containing water is diluted to reduce the Ca hardness to 5 mg-CaCo 3 / L or less. During dilution, for example, the operation of the softening treatment is stopped. Then, the Ca hardness of the Ca hardness-containing water stored in the raw water tank 10 is reduced to 5 mg-CaCo 3 When the hardness of the Ca-containing water is reduced to 100 to 300 h / L or less, the space velocity (SV) of the Ca-containing water passing through the packed tower 12 is increased to 100 to 300 h / L. -1In addition, when the Ca hardness of the Ca hardness-containing water stored in the raw water tank 10 is 5 mg-CaCo 3 / L, for example, the space velocity (SV) of the Ca hardness-containing water passing through the packed tower 12 is set to 100 h -1 Set it to less than, for example, 20 to 50 hours. -1 The softening treatment may be performed by setting the temperature to 100°C.

[0025] The Ca hardness-containing water is preferably passed through the packed tower 12 in a downward flow manner, as in the treatment device 1 shown in FIG. 1, in order to efficiently remove the Ca hardness, but this is not limited thereto and an upward flow manner is also acceptable.

[0026] The cation exchanger is preferably a weakly acidic cation exchanger, more preferably a Na-type weakly acidic cation exchanger, because it can efficiently remove hardness components. Strongly acidic cation exchangers, which are commonly used for softening, have lower regeneration efficiency than weakly acidic cation exchangers, and repeated regeneration may result in leakage of hardness components accumulated in the packed tower 12. This tendency is particularly pronounced at high space velocities (SV). Therefore, in order to prevent leakage of hardness components, it is particularly advantageous to use a weakly acidic cation exchanger to perform softening treatment on Ca-hardness-containing water with low Ca hardness.

[0027] Examples of the cation exchanger include granular macroporous cation exchange resins, gel-type cation exchange resins, monolithic organic porous cation exchangers, ion adsorption membranes having cation exchange groups, and chelating resins.

[0028] The gel type and the macroporous type can be distinguished by the following method. (1) When ion exchange resins exposed to light are observed under an optical microscope, those that transmit light are classified as "gel type" and those that do not transmit light are classified as "macroporous type." (2) The "gel type" and "macroporous type" are distinguished from each other by the specific surface area or pore volume of the ion exchange resin measured by the adsorption method (BET method) using nitrogen gas, etc. Generally, the specific surface area of ​​the gel type ion exchange resin is very small, and the pore volume is also very small. For example, the specific surface area of ​​the gel type ion exchange resin is 0.1 m 2 / g (dry resin), and the pore volume of gel-type ion exchange resins is 0.001 to 0.008 ml / ml (dry resin). Macroporous ion exchange resins have a relatively large specific surface area and a relatively large pore volume. For example, the specific surface area of ​​macroporous ion exchange resins is 2 to 125 m 2 / g (dry resin), and the pore volume of macroporous ion exchange resin is 0.17 to 0.50 ml / ml (dry resin).

[0029] As for the cation exchange resin, a macroporous type cation exchange resin is preferable to a gel type cation exchange resin in terms of stain resistance, strength, reaction rate, etc.

[0030] The average particle size of the macroporous cation exchange resin is not particularly limited, but is preferably in the range of 200 to 1000 μm, more preferably in the range of 200 to 500 μm, for example. The average particle size of the cation exchange resin is a value measured by a laser diffraction particle size distribution analyzer.

[0031] The monolithic organic porous cation exchanger is prepared by uniformly introducing ion exchange groups into the surface and interior of the skeleton of the monolithic organic porous material after production, and has an ion exchange capacity per volume in a water-wet state of 0.1 mg equivalent / ml or more, preferably 0.15 to 5.0 mg equivalent / ml. In the case of a weakly acidic cation exchange resin, carboxylic acid groups are introduced.

[0032] <Membrane treatment> The treated water stored in the treated water tank 14 is supplied to the membrane module 26 through the pipe 28e by the pressure pump 30. The treated water is separated into permeate, from which impurities have been removed by passing through the RO membrane in the membrane module 26, and concentrated water, which does not pass through the RO membrane and contains impurities. The permeate is discharged from the permeate pipe 28f, and the concentrated water is discharged from the concentrated water pipe 28g.

[0033] In the treatment device 1 of FIG. 1, the treated water contains almost no Ca hardness, so Ca hardness-derived scale is unlikely to form on the RO membrane in the membrane module 26. However, if the Ca hardness-containing water contains silica, some of the silica may be captured by the cation exchanger, but some silica leaks into the treated water, making silica-derived scale likely to form on the RO membrane. Therefore, when the Ca hardness-containing water contains silica, it is preferable to pass the treated water through the RO membrane under alkaline conditions to prevent scale formation on the RO membrane. For example, the alkaline conditions are preferably such that the pH of the treated water is 10 or higher. That is, if the pH of the treated water is less than 10, it is preferable to add an alkaline agent to the treated water tank 14 to raise the pH of the treated water to 10 or higher before passing the water through the RO membrane.

[0034] Furthermore, if fluorine is contained in Ca hardness-containing water, calcium fluoride may be generated, potentially clogging the RO membrane. However, according to the present embodiment, the leakage of Ca hardness into the treated water is kept low, thereby suppressing the generation of calcium fluoride and preventing RO membrane clogging. Examples of fluorine-containing Ca hardness-containing water include wastewater from detoxification systems. Detoxification system wastewater is wastewater discharged from semiconductor manufacturing processes by treating harmful gases used in scrubbers or the like, and contains highly volatile components such as fluorine, ammonia, and organic components. While the Ca hardness in this wastewater is usually extremely low, it has been found that trace amounts of Ca hardness may be present due to leaching from treatment equipment, etc.

[0035] The filtration membrane used in the membrane module 26 is preferably a reverse osmosis membrane (RO membrane), but may also be, for example, a nanofiltration membrane (NF membrane). Also, for example, a membrane module equipped with a nanofiltration membrane may be installed in the upstream stage, and a membrane module equipped with a reverse osmosis membrane may be installed in the downstream stage.

[0036] <Recycling process> When regenerating the cation exchanger, the raw water pump 18 is stopped and the regenerant pump 24 is operated. The regenerant in the regenerant tank 20 is supplied to the packed tower 12 through pipe 22c. The regenerant is passed through the packed tower 12 in an upward flow and comes into contact with the cation exchanger in the packed tower 12, whereby hardness components and the like adsorbed on the cation exchanger are removed from the cation exchanger (regeneration treatment). The wastewater used in the regeneration treatment is discharged from the packed tower 12 through pipe 22d to the outside of the system. The regenerant varies depending on the type of cation exchanger, but examples include sodium chloride, potassium chloride, hydrochloric acid, and sulfuric acid.

[0037] In this embodiment, a cleaning treatment may be performed in which cleaning water is passed through the cation exchanger to clean it. In this embodiment, the cleaning treatment may be performed instead of the regeneration treatment, or the regeneration treatment and cleaning treatment may be combined by alternately performing the regeneration treatment and the cleaning treatment, performing the cleaning treatment multiple times followed by the regeneration treatment, or performing the regeneration treatment multiple times followed by the cleaning treatment. The configuration of the cleaning device that performs the cleaning treatment may be similar to that of the regeneration treatment device 5. Although not shown in the figures, for example, a pump is operated to supply cleaning water from a tank through a pipe to the packed tower 12, and the water is passed through the packed tower 12 in an upward flow to clean the cation exchanger in the packed tower 12. The wastewater used for cleaning is discharged from the packed tower 12 through a pipe to the outside of the system. The cleaning water may be tap water, pure water, treated water stored in a treated water tank, or the like.

[0038] The regenerant and wash water are preferably passed through the packed tower 12 in an upward flow manner, as in the treatment device 1 shown in FIG. 1, in terms of, for example, regeneration efficiency and washing efficiency, but this is not limited thereto and a downward flow manner is also acceptable.

[0039] When the Ca hardness of the Ca hardness-containing water is low, at 5 mg-CaCO3 / L or less, it may seem that the frequency of regeneration or cleaning of the cation exchanger can be extremely low, for example, once a month. However, such a low frequency may result in clogging of the packed tower 12 due to slime formation. Therefore, in order to prevent clogging of the packed tower 12 due to slime formation, the regeneration or cleaning treatment is preferably carried out at least once every 21 days, and more preferably at least once every 14 days. Note that if the space velocity (SV) is too low, the cation exchanger will be regenerated or cleaned while still having some exchange capacity, resulting in waste. However, the space velocity (SV) in this embodiment is set to 100 to 300 h -1 Therefore, even if the regeneration or washing frequency is set to once every 21 days or more, it is possible to avoid regeneration or washing while leaving some exchange capacity of the cation exchanger, and appropriate regeneration or washing is performed. Furthermore, the lower limit of the frequency of regeneration or washing of the ion exchanger is preferably once every 7 days or less, for example, from the viewpoint of processing costs. [Example]

[0040] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited thereto.

[0041] In the examples and comparative examples, Ca hardness-containing water was passed through an acrylic column packed with a weakly acidic cation exchange resin in a downward flow to perform a softening treatment. The test conditions for this softening treatment were as follows: Weakly acidic cation exchange resin: Amberlite HPR8400 (trade name), manufactured by Organo Corporation Resin amount: 225ml Column used: Φ (diameter) 21.5 mm x H (height) 1.5 m Water containing hardness components: Add CaCl2 to the wastewater from the detoxification system, and Ca = 5mg-CaCO3 / L Adjust to Space velocity (SV): as shown in Table 1

[0042] Table 1 shows the space velocity (SV) and the concentration of hardness components in the treated water after passing the water for 50 to 300 hours for each example and comparative example.

[0043] [Table 1]

[0044] In Examples 1 to 4, the space velocity (SV) was 100 to 300 h -1 Even under high SV conditions, the calcium hardness in the treated water was maintained at a low concentration even after 300 hours. 3 / h, and redesigning the amount of resin packed in the packed tower, the amounts are 300, 200, 150, and 100 L in Examples 1 to 4, respectively. On the other hand, as in Comparative Examples 1 and 2, when the space velocity (SV) is set to 20 to 50 h -1 Even so, it was possible to maintain a low concentration of Ca hardness in the treated water after 300 hours. However, if the amount of resin packed in the packed tower is redesigned as in the Examples, the amounts become 1500 and 600 L in Comparative Examples 1 and 2, respectively. From these results, it can be seen that when softening Ca hardness-containing water with a Ca hardness of 5 mg-CaCO3 / L or less, as in the Examples, the space velocity (SV) of the Ca hardness-containing water passing through the packed tower should be set to 100 to 300 h -1 By doing so, it is possible to reduce the size of the packed tower while suppressing leakage of hardness components into the treated water.

[0045] In Example 5, water containing hardness components was passed downward through an acrylic column packed with a weakly acidic cation exchange resin to perform a softening treatment. The softened treated water was then passed through an RO membrane to perform membrane treatment. The softened treated water was passed through the RO membrane at 940 L / h, yielding approximately 140 L / h of permeate and 800 L / h of concentrate. The test conditions for the softening treatment and membrane treatment were as follows: (Softening treatment conditions) Weakly acidic cation exchange resin: Amberlite HPR8400 (trade name), manufactured by Organo Corporation Resin amount: 10L Column used: Φ (diameter) Φ 250 mm x H (height) 2.0 m Water containing hardness components: Add CaCl2 to pure water to adjust the Ca content to 5 mg-CaCO3 / L, and add sodium silicate solution to adjust the SiO2 content to 120 mg / L. Space velocity (SV): 100 (1 / h) (Membrane treatment conditions) RO membrane: Nitto Denko Corporation, CPA-5LD pH of treated water after softening: 10.2 to 10.5 Operating pressure: 0.5 to 0.6 MPa

[0046] In Comparative Example 3, the resin tower was bypassed and the Ca hardness-containing water was introduced directly into the RO membrane.

[0047] In Example 5, the RO membrane was not clogged with scale even after 1,300 hours of continuous operation of the softening treatment and membrane filtration treatment. The Ca concentration of the treated water in the resin tower was kept low at <0.05 mg / L, and the RO membrane in the subsequent stage was not clogged. The RO membrane permeability coefficient retention rate (the retention rate of the permeate volume per unit pressure, assuming that the initial water flow rate is 100%) was always 96% or higher. On the other hand, in Comparative Example 3, the permeability coefficient fell below 80% after 24 hours of continuous operation of the membrane filtration treatment, and the RO membrane was clogged with scale, making it difficult to continue operation. [Explanation of symbols]

[0048] 1 treatment device, 3 softening treatment device, 5 regeneration treatment device, 7 membrane filtration device, 10 raw water tank, 12 packed tower, 14 treated water tank, 16a, 16b, 22c, 22d, 28e piping, 18 raw water pump, 20 regenerant tank, 24 regenerant pump, 26 membrane module, 28f permeate piping, 28g concentrated water piping, 30 pressure pump.

Claims

1. A method for treating water containing hard components, comprising passing water containing Ca hardness through a packed column filled with a cation exchanger to remove Ca hardness, The Ca hardness-containing water includes wastewater from a detoxification system, The Ca hardness in the Ca hardness-containing water is 5 mg-CaCO ３ / L or less, and the space velocity (SV) of the Ca hardness-containing water passing through the packed tower is 100 to 300 h －１ A method for treating water containing Ca hardness, characterized by:

2. 2. The method for treating water containing calcium hardness according to claim 1, wherein the cation exchanger is a weakly acidic cation exchanger.

3. The Ca hardness-containing water contains silica, 3. The method for treating water containing Ca hardness according to claim 1, wherein the treated water from which the Ca hardness has been removed by the cation exchanger is passed through a reverse osmosis membrane under alkaline conditions.

4. 4. The method for treating Ca-hardness-containing water according to claim 1, wherein the Ca-hardness-containing water contains fluorine.

5. The method for treating Ca-hardness-containing water according to any one of claims 1 to 4, characterized in that the cation exchanger is subjected to a regeneration treatment or a cleaning treatment at a frequency of not more than once every 7 days and not less than once every 21 days.

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