Pure water production equipment and pure water production method

Abstract

The present invention provides a pure water production apparatus that can ensure good water quality and is economical. The pure water production apparatus (1) includes: a sulfur compound addition unit (19) for adding a sulfur compound containing a peroxy group to the water to be treated containing organic matter; an ultraviolet irradiation device (15) for irradiating the water to be treated with added sulfur compound with ultraviolet light; a reverse osmosis membrane device (16) for passing water through the water to be treated after being irradiated with ultraviolet light; and an ion exchange resin filling device (17) for passing water through the water to be treated by the reverse osmosis membrane device (16).

Description

Technical Field

[0001] This application is based on and claims priority to Japanese Application No. 2021-101147, filed on June 17, 2021. The entire application of that application is incorporated herein by reference.

[0002] This invention relates to a pure water manufacturing apparatus and a pure water manufacturing method. Background Technology

[0003] With the increasing demand for high-quality pure water, various methods for decomposing and removing trace amounts of organic matter contained in pure water have been studied in recent years. As a representative of such methods, a process for decomposing and removing organic matter using ultraviolet (UV) oxidation treatment is known. Japanese Patent Application Publication No. 2008-229417 discloses a technique in which sulfur compounds containing peroxide groups are added to the water to be treated, and then the water is irradiated with UV light, thereby decomposing and removing the organic matter contained in the water. Furthermore, Japanese Patent Application Publication No. 2008-229417 discloses a method for removing residual sulfur compounds containing peroxide groups from water treated by UV irradiation, followed by deionization treatment using an ion exchange resin packed apparatus. By pre-removing sulfur compounds, oxidative degradation of the resin in the ion exchange resin packed apparatus can be prevented. Methods for removing sulfur compounds include the addition of a reducing agent, the installation of an activated carbon tower, and the installation of a catalyst tower supported on palladium, platinum, etc. Summary of the Invention

[0004] When using activated carbon and catalysts as the removal unit for sulfur compounds, the activated carbon and catalysts themselves may deteriorate due to the oxidant, leading to a deterioration in the quality of the treated water. Furthermore, when using reducing agents, large quantities of reducing agents are required to reduce residual peroxyl-containing sulfur compounds in the water treated by ultraviolet irradiation, increasing chemical costs.

[0005] The purpose of this invention is to provide a pure water production apparatus that can ensure good water quality and is economical.

[0006] The pure water production apparatus of the present invention comprises: a sulfur compound addition unit, which adds a sulfur compound containing a peroxy group to water to be treated containing organic matter; an ultraviolet irradiation device, which irradiates the water to be treated with added sulfur compound with ultraviolet light; a reverse osmosis membrane device, which supplies water to the water to be treated after being irradiated with ultraviolet light; and an ion exchange resin filling device, which supplies water to the water to be treated by the reverse osmosis membrane device.

[0007] According to the present invention, a pure water production apparatus that can ensure good water quality and is economical can be provided.

[0008] The foregoing and other objectives, features, and advantages of this application will become clear from the following detailed description, which is illustrated with reference to the accompanying drawings. Attached Figure Description

[0009] Figure 1A This is a schematic structural diagram of a pure water production apparatus according to the first embodiment of the present invention.

[0010] Figure 1B This is a schematic structural diagram of a pure water production apparatus according to the second embodiment of the present invention. Detailed Implementation

[0011] Hereinafter, embodiments of the pure water manufacturing apparatus and pure water manufacturing method of the present invention will be described with reference to the accompanying drawings. Figure 1A This diagram illustrates the schematic structure of a pure water production apparatus 1 according to the first embodiment of the present invention. The pure water production apparatus 1 (primary system) and its downstream subsystem (secondary system) together constitute an ultrapure water production apparatus. The raw water supplied to the pure water production apparatus 1 (hereinafter referred to as the treated water) contains organic matter.

[0012] The pure water production apparatus 1 includes a raw water tank 11, a filter 12, an activated carbon tower 13, an ion exchange device 14, an ultraviolet irradiation device (ultraviolet oxidation device) 15, a reverse osmosis membrane device 16, an ion exchange resin filling device 17, and a degassing device 18, which are connected in series from upstream to downstream along the main pipe L1 in the direction of water flow D. The water to be treated, stored in the raw water tank 11, is pressurized by a raw water pump (not shown), then passes through the filter 12 to remove larger particles such as dust, and through the activated carbon tower 13 to remove impurities such as high-molecular-weight organic matter. The structure of the filter 12 is not limited; in this embodiment, a sand filter is used. The ion exchange device 14 includes a cation exchange tower (not shown) filled with cation exchange resin, a decarbonation tower (not shown), and an anion exchange tower (not shown) filled with anion exchange resin, which are connected in series from upstream to downstream. The cation exchange tower removes cationic components from the water being treated, the decarbonation tower removes carbonic acid from the water being treated, and the anion exchange tower removes anionic components from the water being treated.

[0013] Between the ion exchange unit 14 and the ultraviolet irradiation unit 15, a sulfur compound addition unit 19 is provided for adding sulfur compounds containing peroxy groups (hereinafter, sometimes simply referred to as sulfur compounds) to the water being treated. The sulfur compound addition unit 19 includes a sulfur compound addition line 19a, a sulfur compound storage tank 19b connected to one end of the addition line 19a, and a sulfur compound transfer pump 19c. The other end of the addition line 19a is connected to a main pipe L1 between the ion exchange unit 14 and the ultraviolet irradiation unit 15. Examples of sulfur compounds containing peroxy groups include sodium persulfate (Na₂S₂O₈), ammonium persulfate ((NH₄)₂S₄O₈), and potassium persulfate (K₂S₂O₈), which can be used alone or in combination.

[0014] The concentration of sulfur compounds relative to the TOC of the treated water (more precisely, the TOC of the treated water in the region between the connection point of the addition line 19a and the main pipe L1 and the ion exchange unit 14) (hereinafter referred to as the concentration ratio) is preferably about 50 to 5000 times. When the concentration ratio is less than 50, the generation of sulfate free radicals is insufficient, and the decomposition efficiency of organic matter in the treated water decreases. When the concentration ratio is greater than 5000, the concentration of residual sulfur compounds that are not used in the decomposition of organic matter increases, resulting in a waste of sulfur compounds. In addition, the increased concentration of sulfur compounds in the treated water of the reverse osmosis membrane unit 16 may increase damage to the ion exchange resin filling unit 17.

[0015] Ultraviolet irradiation device 15 irradiates the water to be treated with ultraviolet light. As the ultraviolet irradiation device 15, for example, an ultraviolet lamp containing at least one wavelength selected from 365 nm, 254 nm, 185 nm, and 172 nm can be used. Sulfur compounds containing peroxides generate sulfate radicals in the water to be treated through ultraviolet irradiation. Sulfate radicals, for example, decompose organic matter faster and more efficiently than hydroxyl radicals generated by irradiating water with ultraviolet light.

[0016] The reverse osmosis membrane unit 16 removes sulfur compounds containing peroxy groups from the treated water remaining in the ultraviolet irradiation unit 15. These sulfur compounds have strong oxidizing power. Therefore, if treated water from the ultraviolet irradiation unit 15 containing a high concentration of sulfur compounds is supplied to the ion exchange resin filling unit 17, it leads to oxidative degradation of the ion exchange resin and the resulting leaching of organic matter, increasing the TOC of the treated water in the ion exchange resin filling unit 17. In this embodiment, since the treated water with a low concentration of sulfur compounds is supplied to the ion exchange resin filling unit 17, the increase in TOC of the treated water in the ion exchange resin filling unit 17 can be prevented.

[0017] The ion exchange resin filling unit 17 is a regenerable ion exchange resin tower filled with anion exchange resin and cation exchange resin. Decomposition products of organic matter generated in the treated water by ultraviolet irradiation are removed through the ion exchange resin filling unit 17. Then, dissolved oxygen, carbonic acid, etc., are removed from the treated water by the degassing unit 18. Although not shown in the figure, an electro-deionized water (EDI) unit can be installed instead of the ion exchange resin filling unit 17. EDI is a continuous regeneration system, therefore a regeneration process for the ion exchangers is not required.

[0018] Sulfur compounds containing peroxy groups act as oxidants, thus causing oxidative degradation of the resin in the ion exchange resin filling unit 17. Therefore, sulfur compounds are removed from the treated water before it is passed through the ion exchange resin filling unit 17. Sulfur compound removal can be achieved not only by the reverse osmosis membrane unit 16, but also by activated carbon, platinum group metal supported catalysts, etc. However, in the case of activated carbon and catalysts, they themselves may oxidize and degrade, leading to a decrease in water quality. In contrast, the inventors of this application have discovered that the oxidative degradation behavior of the sulfur compound removal unit differs in each unit, and that the reverse osmosis membrane unit 16 is less susceptible to oxidative degradation.

[0019] Furthermore, the inventors of this application have discovered that while the ion exchange resin filling device 17 is more susceptible to oxidative degradation caused by sulfur compounds compared to the reverse osmosis membrane device 16, it is less affected by oxidative degradation if the concentration of sulfur compounds is sufficiently low. As will also be described in the embodiments, the sulfur compound concentration of the treated water of the reverse osmosis membrane device 16, i.e., the inlet water of the ion exchange resin filling device 17, is preferably 0.5 mg / L or less. This prevents oxidative degradation of the ion exchange resin and efficiently removes ionized organic matter. When the sulfur compound concentration is greater than 0.5 mg / L, the TOC increases due to oxidative degradation of the ion exchange resin, increasing the likelihood of a decrease in the quality of the treated water. By using the reverse osmosis membrane device 16 to reduce the sulfur compound concentration to below 0.5 mg / L, the increase in TOC of the treated water caused by oxidative degradation of the resin in the ion exchange resin filling device 17 can be suppressed. The concentration of sulfur compounds in the treated water fed into the ion exchange resin filling device 17 can be set, for example, to below 0.5 mg / L. Based on at least one of the following: the TOC of the supply water to the UV irradiation device 15, the TOC of the treated water to the UV irradiation device 15, the concentration of sulfur compounds in the supply water to the reverse osmosis membrane unit 16, and the concentration of sulfur compounds in the supply water to the ion exchange resin filling unit 17, at least one of the following: the amount of sulfur compound added in the sulfur compound addition unit 19, the operating conditions of the reverse osmosis membrane unit 16 (recovery rate, etc.), and the operating conditions of the UV irradiation device 15 (irradiation intensity, etc.). Control can be performed using only one of the aforementioned TOC and sulfur compound concentrations, or multiple concentrations can be used. Furthermore, there are no restrictions on the method for obtaining the sulfur compound concentration; for example, conductivity measured with a conductivity meter can be converted into sulfur compound concentration. As an example, conductivity measured with a conductivity meter can be converted into sulfur compound concentration based on a pre-obtained formula relating conductivity and sulfur compound concentration. The above control can be performed using a specified control device (not shown).

[0020] Sulfur compounds can also be removed by adding reducing agents such as sodium bisulfite. However, since a reducing agent needs to be continuously supplied to the inlet water of the ion exchange resin filling device 17, the cost of chemicals increases, the ion load increases, and the regeneration frequency of the ion exchange resin in the ion exchange resin filling device 17 increases. In this embodiment, by utilizing a novel structure such as the reverse osmosis membrane device 16 in the removal of sulfur compounds containing peroxy groups, a pure water production device 1 can be realized that can suppress the oxidative degradation of the resin in the ion exchange resin filling device 17 and suppress operating costs (chemical costs).

[0021] The concentration of sulfur compounds in the treated water fed into the reverse osmosis membrane unit 16 is not particularly limited, but is preferably 400 mg / L or less. From the viewpoint of suppressing the load on the ion exchange resin filling unit 17, it is more preferably 100 mg / L or less, and even more preferably 20 mg / L or less. If the sulfur compound concentration is greater than 400 mg / L, oxidative deterioration of the reverse osmosis membrane unit 16 may occur, and the load on the ion exchange resin filling unit 17 may also increase. The concentration of sulfur compounds in the treated water fed into the reverse osmosis membrane unit 16 can be set to 400 mg / L or less, for example, as described below. Based on at least one of the TOC of the supply water of the ultraviolet irradiation device 15, the TOC of the treated water of the ultraviolet irradiation device 15, the concentration of sulfur compounds in the supply water of the reverse osmosis membrane unit 16, and the concentration of sulfur compounds in the supply water of the ion exchange resin filling unit 17, at least one of the following is controlled: the amount of sulfur compounds added in the sulfur compound addition unit 19, the operating conditions of the reverse osmosis membrane unit 16 (recovery rate, etc.), and the operating conditions of the ultraviolet irradiation device 15 (irradiation intensity, etc.). Control can be performed using only one of the aforementioned TOC and sulfur compound concentrations, or multiple concentrations can be used. Furthermore, there are no restrictions on the method for obtaining the sulfur compound concentration; for example, conductivity measured with a conductivity meter can be converted into sulfur compound concentration. As an example, conductivity measured with a conductivity meter can be converted into sulfur compound concentration based on a pre-established relationship between conductivity and sulfur compound concentration. The above control can be performed using a specified control device (not shown).

[0022] Figure 1B This diagram illustrates a schematic structure of the pure water production apparatus 1 according to the second embodiment of the present invention. The pure water production apparatus 1 according to this embodiment is identical to the pure water production apparatus 1 according to the first embodiment, except that it has a sulfur compound removal unit 20 containing peroxy groups between the reverse osmosis membrane unit 16 and the ion exchange resin filling unit 17. For details regarding the omitted structures and effects, please refer to the description of the first embodiment. The type of sulfur compound removal unit 20 is not particularly limited; various units commonly used for removing oxidants can be used, such as reducing agents, activated carbon, platinum group metal supported catalysts, etc.

[0023] The sulfur compound removal unit 20 is preferably located between the reverse osmosis membrane unit 16 and the ion exchange resin filling unit 17. Alternatively, the sulfur compound removal unit 20 can be located between the ultraviolet irradiation unit 15 and the reverse osmosis membrane unit 16, but this increases the load on the sulfur compound removal unit 20. If the removal unit 20 is activated carbon or a catalyst, these materials are oxidized and degraded by sulfur compounds, and TOC and other substances leak into the treated water, potentially reducing the quality of the treated water. If the removal unit 20 is a reducing agent, the amount of reducing agent added increases, potentially increasing chemical costs. In this embodiment, after most of the sulfur compounds are removed by the reverse osmosis membrane unit 16, the remaining sulfur compounds are removed by the removal unit 20, thus contributing to improved performance and reduced operating costs of the pure water production unit 1.

[0024] The present invention has been described above with reference to several embodiments, but the present invention is not limited to these embodiments. For example, a metal ion addition unit may be provided upstream of the ultraviolet irradiation device 15. The metal ions are not limited as long as they are not alkali metals; examples include ions of iron, copper, silver, gold, and manganese. By the presence of metal ions in the water being treated, the activation of sulfur compounds is promoted, thereby improving the organic matter treatment performance.

[0025] Furthermore, the sulfur compound concentration in the treated water of the UV irradiation device 15 may vary depending on the TOC of the inlet water of the UV irradiation device 15. That is, if the TOC of the inlet water of the UV irradiation device 15 is low, more sulfur compounds may not be consumed and may flow out of the UV irradiation device 15. When the sulfur compound concentration is increased to improve the decomposition efficiency of organic matter, the sulfur compound concentration in the treated water of the UV irradiation device 15 may also become high. Even in such cases, in order to suppress the oxidative degradation of the resin in the ion exchange resin filling device 17, two or more reverse osmosis membrane devices 16 can be arranged in series. That is, a second reverse osmosis membrane device (not shown) may be provided between the reverse osmosis membrane device 16 and the ion exchange resin filling device 17. By arranging the reverse osmosis membrane devices 16 in series, the sulfur compound removal performance is improved, and the load on the ion exchange resin filling device 17 can be reduced. It should be noted that, in the case of the second embodiment, the sulfur compound removal unit 20 may also be arranged between the reverse osmosis membrane devices 16 arranged in series.

[0026] (Example)

[0027] <Example 1>

[0028] Adding 10 mg / L potassium persulfate (K₂S₂O₈) to the treated water containing 80 μg / L urea, and then using an ultraviolet irradiation device to achieve an output of 0.73 kWh / m³ 3The water is irradiated with ultraviolet light, and then water is passed through a reverse osmosis membrane unit (Nitto Denko ESPA2-4040) for treatment. The water flow rate through the reverse osmosis membrane unit is 1.0 m³ / h. 3 The reverse osmosis membrane unit has a treated water flow rate of 200 L / h and a concentrated water flow rate of 800 L / h. The treated water from the reverse osmosis membrane unit is passed through an ion exchange resin (Organo Corporation ESP-2) packed unit at SV120 ( / h). The K2S2O8 concentration and TOC of the inlet water of the ion exchange resin packed unit, and the urea concentration and TOC of the treated water of the ion exchange resin packed unit are measured.

[0029] <Example 2>

[0030] In Example 1, 40 mg / L of K2S2O2 was added, and the determination was carried out under the same conditions.

[0031] <Example 3>

[0032] In Example 1, a reducing agent was added to the treated water of the reverse osmosis membrane unit, and the water was then passed through the ion exchange resin filling unit. Sodium sulfite (Na₂SO₃) was used as the reducing agent, and its mass was increased to twice the amount of persulfate relative to the concentration of the treated water in the reverse osmosis membrane unit.

[0033] <Example 4>

[0034] In Example 1, a reducing agent was added to the treated water of the ultraviolet irradiation device, and water treatment was carried out in the order of reverse osmosis membrane device and ion exchange resin filling device. The reducing agent used was Na2SO3, added at twice the amount of persulfate relative to the concentration of the treated water in the ultraviolet irradiation device.

[0035] <Comparative Example 1>

[0036] In Example 1, the treated water from the ultraviolet irradiation device is not passed to the reverse osmosis membrane device, but is instead passed to the ion exchange resin filling device.

[0037] Table 1 shows the measurement results. In Comparative Example 1, the TOC of the treated water was high. This is believed to be because the residual persulfate in the UV irradiation device caused oxidative degradation of the ion exchange resin. In Example 1, which included a structure with a reverse osmosis membrane device, the TOC of the treated water was less than 1 μg / L. This is believed to be because the concentration of persulfate was reduced to 0.1 mg / L by utilizing the reverse osmosis membrane device, thereby suppressing the oxidative degradation of the ion exchange resin. In Example 2, the concentration of persulfate in the inlet water of the ion exchange resin filling device was 0.5 mg / L, but the TOC of the treated water of the ion exchange resin filling device was 1 μg / L, less than that of Comparative Example 1. This is believed to be because the amount of leached ion exchange resin was low, suppressing the effect of oxidative degradation. Therefore, when the concentration of sulfur compounds in the treated water flowing into the ion exchange resin filling device is less than 0.5 mg / L, it is believed that there is no significant impact on the quality of the treated water. Examples 3 and 4, which added a reducing agent, achieved the same treatment performance. However, the case where the reducing agent was added upstream of the reverse osmosis membrane unit (Example 4) required more reducing agent compared to the case where it was added downstream of the reverse osmosis membrane unit (Example 3). Therefore, it is preferable to add the reducing agent downstream of the reverse osmosis membrane unit.

[0038] [Table 1]

[0039]

[0040] <Example 5>

[0041] A solution containing 5 mg / L NaCl, 100 μg / L IPA, and 400 mg / L K₂S₂O₈ was added to pure water and passed through a reverse osmosis membrane unit (Nitto Denko ESPA2-4040) for 800 hours. The permeation coefficient, intermembrane pressure difference ((raw water pressure + concentrate pressure) / 2 - permeate pressure), and rejection rates of Na, Cl, and IPA were calculated after 800 hours. The rejection rate was calculated as {(raw water concentration + concentrate concentration) / 2 - permeate concentration} / {(raw water concentration + concentrate concentration) / 2} × 100. Accelerated tests were conducted with K₂S₂O₈ concentrations set to 4000 times that of Example 1 and 800 times that of Example 2, allowing for evaluation over a time span comparable to the replacement frequency of the reverse osmosis membrane unit. The flow rate through the reverse osmosis membrane unit was 1 m³ / L. 3 The reverse osmosis membrane unit had a treatment flow rate of 200 L / h and a concentration flow rate of 800 L / h. The results are shown in Table 2. After 800 hours, no tendency for deterioration of either value was observed. Therefore, it can be concluded that the performance of the reverse osmosis membrane unit will not decrease when the K₂S₂O₈ concentration is below 400 mg / L.

[0042] [Table 2]

[0043]

[0044] The foregoing and other objectives, features, and advantages of this application will become clear from the following detailed description, which is illustrated with reference to the accompanying drawings.

[0045] Explanation of reference numerals in the attached figures

[0046] 1 Pure water production equipment

[0047] 11 Raw Water Tank

[0048] 12 Filters

[0049] 13 Activated Carbon Tower

[0050] 14 Ion exchange device

[0051] 15. Ultraviolet irradiation device (ultraviolet oxidation device)

[0052] 16 Reverse osmosis membrane unit

[0053] 17. Ion exchange resin packing device

[0054] 18 Degassing device

[0055] 19 Sulfur compound addition unit

[0056] 20. Unit for the removal of sulfur compounds.

Claims

1. A pure water producing apparatus characterized by comprising: have: A sulfur compound addition unit that adds a peroxy group-containing sulfur compound to the treated water containing organic matter; An ultraviolet irradiation device that irradiates treated water containing added sulfur compounds with ultraviolet light. A reverse osmosis membrane device, through which water that has been irradiated with ultraviolet light is passed; An ion exchange resin filling device is used to pass in water that has been treated by the reverse osmosis membrane device. as well as A control device, based on at least one of the following: the TOC of the supply water of the ultraviolet irradiation device, the TOC of the treated water of the ultraviolet irradiation device, the concentration of sulfur compounds in the supply water of the reverse osmosis membrane device, and the concentration of sulfur compounds in the supply water of the ion exchange resin filling device, controls at least one of the following: the amount of sulfur compounds added in the sulfur compound addition unit, the operating conditions of the reverse osmosis membrane device, and the operating conditions of the ultraviolet irradiation device, so that the concentration of sulfur compounds in the treated water is below 0.5 mg / L. A sulfur compound removal unit is provided between the reverse osmosis membrane device and the ion exchange resin filling device.

2. The pure water producing apparatus according to claim 1, wherein The concentration of sulfur compounds in the water treated by the reverse osmosis membrane device is below 400 mg / L.

3. The pure water manufacturing apparatus according to claim 2, wherein, The pure water production apparatus has a control device that controls at least one of the following: the TOC of the supply water of the ultraviolet irradiation device, the TOC of the treated water of the ultraviolet irradiation device, the concentration of sulfur compounds in the supply water of the reverse osmosis membrane device, and the concentration of sulfur compounds in the supply water of the ion exchange resin filling device. The control device controls the amount of sulfur compounds added in the sulfur compound addition unit, the operating conditions of the reverse osmosis membrane device, and the operating conditions of the ultraviolet irradiation device, so that the concentration of sulfur compounds in the treated water treated by the reverse osmosis membrane device is below 400 mg / L.

4. The pure water production apparatus according to claim 1 or 2, wherein, The pure water production apparatus has a second reverse osmosis membrane device disposed between the reverse osmosis membrane device and the ion exchange resin filling device.

5. A method for producing pure water, characterized in that, The process includes the following steps: A sulfur compound containing peroxy groups is added to the treated water containing organic matter using a sulfur compound addition unit. The treated water containing added sulfur compounds was irradiated with ultraviolet light using an ultraviolet irradiation device. The treated water, after being irradiated with ultraviolet light, is passed into the reverse osmosis membrane device. The treated water after being processed by the reverse osmosis membrane device is passed into the sulfur compound removal unit, and the treated water after being processed by the sulfur compound removal unit is passed into the ion exchange resin filling device. as well as Based on at least one of the TOC of the supply water of the ultraviolet irradiation device, the TOC of the treated water of the ultraviolet irradiation device, the concentration of sulfur compounds in the supply water of the reverse osmosis membrane device, and the concentration of sulfur compounds in the supply water of the ion exchange resin filling device, at least one of the following is controlled: the amount of sulfur compounds added in the sulfur compound addition unit, the operating conditions of the reverse osmosis membrane device, and the operating conditions of the ultraviolet irradiation device, so that the concentration of sulfur compounds in the treated water is below 0.5 mg / L.

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