Pure water production device and pure water production method

Abstract

To provide an economical pure water production apparatus capable of ensuring good quality of treated water.SOLUTION: A pure water production apparatus 1 includes sulfur compound adding means 19 for adding a sulfur compound containing a peroxide group to treated water containing organic matter, an ultraviolet light irradiation device 15 for irradiating ultraviolet light to treated water to which the sulfur compound has been added, an inverse osmosis membrane device 16 by which treated water to which the ultraviolet light has been irradiated is passed, and an ion exchange resin filling device 17 into which treated water treated by the reverse osmosis membrane device 16 is passed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pure water production apparatus and a pure water production method. [Background technology]

[0002] As the demand for higher quality pure water becomes more apparent, various methods for decomposing and removing trace amounts of organic matter contained in pure water have been investigated in recent years. A representative example of such a method is the decomposition and removal of organic matter using ultraviolet oxidation treatment. Patent Document 1 discloses a technology for decomposing and removing organic matter contained in the water by adding sulfur compounds containing peroxide groups to the water to be treated and then irradiating the water with ultraviolet light. Patent Document 1 also discloses removing sulfur compounds containing peroxide groups remaining in the treated water after ultraviolet irradiation, followed by deionization using an ion exchange resin filling device. Removing sulfur compounds in advance can prevent oxidative degradation of the resin in the ion exchange resin filling device. Methods for removing sulfur compounds have been disclosed, including the addition of a reducing agent, the installation of an activated carbon tower, and the installation of a catalyst tower supporting palladium, platinum, or the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-229417 Summary of the Invention [Problem to be solved by the invention]

[0004] When activated carbon or a catalyst is used as a means for removing sulfur compounds, the activated carbon or catalyst itself may be deteriorated by the oxidizing agent, which may deteriorate the quality of the treated water. Also, when a reducing agent is used, a large amount of reducing agent must be used to reduce the sulfur compounds containing peroxide groups remaining in the UV-irradiated treated water, which increases the chemical cost.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide an economical pure water production system that can ensure good quality of treated water. [Means for solving the problem]

[0006] The pure water production system of the present invention comprises a sulfur compound addition means for adding a sulfur compound containing a peroxide group to water to be treated that contains organic matter, an ultraviolet irradiation device for irradiating the water to be treated with ultraviolet light to which the sulfur compound has been added, a reverse osmosis membrane device through which the water to be treated that has been irradiated with ultraviolet light is passed, and an ion exchange resin filling device through which the water to be treated that has been treated in the reverse osmosis membrane device is passed. In one embodiment, the pure water production system has a control device that controls at least one of the amount of sulfur compounds added by the sulfur compound adding means, the operating conditions of the reverse osmosis membrane device, and the operating conditions of the ultraviolet irradiation device based on at least one of the TOC of the feed water to the ultraviolet irradiation device, the TOC of the treated water from the ultraviolet irradiation device, the concentration of sulfur compounds in the feed water to the reverse osmosis membrane device, and the concentration of sulfur compounds in the feed water to the ion exchange resin charging device. In another embodiment, the pure water production system has a sulfur compound removing means installed between the reverse osmosis membrane device and the ion exchange resin charging device. In yet another embodiment, the pure water production system has a second reverse osmosis membrane device installed between the reverse osmosis membrane device and the ion exchange resin charging device. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an economical pure water production system that can ensure good water quality of treated water. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a pure water producing apparatus according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the pure water production system and method of the present invention will be described with reference to the drawings. Figure 1(a) shows the schematic configuration of a pure water production system 1 according to a first embodiment of the present invention. The pure water production system 1 (primary system) and a downstream subsystem (secondary system) constitute an ultrapure water production system. The raw water (hereinafter referred to as water to be treated) supplied to the pure water production system 1 contains organic matter.

[0010] The pure water production system 1 includes a raw water tank 11, a filter 12, an activated carbon tower 13, an ion exchanger 14, an ultraviolet irradiation device (ultraviolet oxidation device) 15, a reverse osmosis membrane device 16, an ion exchange resin packing device 17, and a degassing device 18, which are arranged in series in this order along a mother pipe L1 from upstream to downstream in the flow direction D of the water to be treated. The water to be treated stored in the raw water tank 11 is pressurized by a raw water pump (not shown), after which relatively large particles such as dust are removed by the filter 12, and impurities such as high molecular weight organic matter are removed by the activated carbon tower 13. The configuration of the filter 12 is not limited, but in this embodiment, a sand filter is used. The ion exchanger 14 includes a cation tower (not shown) filled with a cation exchange resin, a decarbonation tower (not shown), and an anion tower (not shown) filled with anion exchange resin, which are arranged in series in this order from upstream to downstream. The cation tower removes cationic components from the water to be treated, the decarbonation tower removes carbon dioxide from the water to be treated, and the anion tower removes anionic components from the water to be treated.

[0011] Between the ion exchange device 14 and the ultraviolet irradiation device 15, there is provided a sulfur compound adding means 19 that adds a sulfur compound containing a peroxide group (hereinafter, sometimes simply referred to as a sulfur compound) to the water to be treated. The sulfur compound adding means 19 has a sulfur compound adding line 19a, a sulfur compound storage tank 19b connected to one end of the adding line 19a, and a sulfur compound transfer pump 19c, and the other end of the adding line 19a is connected to a mother pipe L1 between the ion exchange device 14 and the ultraviolet irradiation device 15. Examples of sulfur compounds containing a peroxide group include sodium peroxodisulfate (NaSO), ammonium peroxodisulfate ((NH)SO), potassium peroxodisulfate (KSO), etc., which may be used alone or in combination.

[0012] The ratio of the concentration of sulfur compounds to the TOC of the water to be treated (more precisely, the TOC of the water to be treated in the section between the junction of the addition line 19a with the main pipe L1 and the ion exchange device 14) (hereinafter referred to as the concentration ratio) is preferably about 50 to 5000 times. If the concentration ratio is less than 50, the generation of sulfate radicals is insufficient, and the decomposition efficiency of organic matter in the water to be treated decreases. If the concentration ratio is more than 5000, the concentration of remaining sulfur compounds that are not used to decompose organic matter increases, resulting in a waste of sulfur compounds. Furthermore, the concentration of sulfur compounds in the treated water from the reverse osmosis membrane device 16 increases, which may increase damage to the ion exchange resin filling device 17.

[0013] The ultraviolet irradiation device 15 irradiates the water to be treated with ultraviolet light. For example, an ultraviolet lamp that emits at least one of the wavelengths of 365 nm, 254 nm, 185 nm, and 172 nm can be used as the ultraviolet irradiation device 15. Sulfur compounds containing peroxide groups generate sulfate radicals in the water to be treated by ultraviolet irradiation. Sulfate radicals decompose organic matter more quickly than, for example, hydroxyl radicals generated by irradiating water with ultraviolet light, and thus efficiently decompose the organic matter contained in the water to be treated.

[0014] The reverse osmosis membrane device 16 removes sulfur compounds containing peroxide groups remaining in the treated water from the ultraviolet irradiation device 15. Sulfur compounds containing peroxide groups have strong oxidizing power. Therefore, if treated water from the ultraviolet irradiation device 15 containing a high concentration of sulfur compounds is supplied to the ion exchange resin charging device 17, it will cause oxidative deterioration of the ion exchange resin, resulting in the elution of organic matter, and the TOC of the treated water from the ion exchange resin charging device 17 will increase. In this embodiment, the water to be treated, in which the concentration of sulfur compounds has been reduced, is supplied to the ion exchange resin charging device 17, thereby preventing an increase in the TOC of the treated water from the ion exchange resin charging device 17.

[0015] The ion exchange resin packing device 17 is a regenerative ion exchange resin tower packed with anion exchange resin and cation exchange resin. Decomposition products of organic matter generated in the water to be treated by ultraviolet irradiation are removed by the ion exchange resin packing device 17. Thereafter, dissolved oxygen, carbon dioxide, etc. in the water to be treated are removed by a degassing device 18. Although not shown, an electrodeionized water production device (EDI) can also be provided instead of the ion exchange resin packing device 17. Because the EDI is a continuous regeneration type, a regeneration process for the ion exchanger is not required.

[0016] Sulfur compounds containing peroxide groups are oxidizing agents that oxidize and deteriorate the resin in the ion exchange resin packing device 17. Therefore, sulfur compounds are removed from the water to be treated before the water is passed through the ion exchange resin packing device 17. Sulfur compounds can be removed not only by the reverse osmosis membrane device 16, but also by activated carbon, platinum group metal-supported catalysts, and other methods. However, activated carbon and catalysts themselves can be subject to oxidative deterioration, leading to a decline in water quality. In response to this, the inventors of the present application have discovered that the oxidative deterioration behavior of sulfur compound removal means differs depending on the means, and that the reverse osmosis membrane device 16 is less susceptible to oxidative deterioration.

[0017] The present inventors also discovered that, although the ion exchange resin charging device 17 is more susceptible to oxidative degradation by sulfur compounds than the reverse osmosis membrane device 16, it is less susceptible to oxidative degradation if the sulfur compound concentration is sufficiently low. As described in the Examples, it is preferable to keep the sulfur compound concentration of the treated water from the reverse osmosis membrane device 16, i.e., the inlet water of the ion exchange resin charging device 17, at 0.5 mg / L or less. This allows for efficient removal of ionized organic matter while preventing oxidative degradation of the ion exchange resin. If the sulfur compound concentration exceeds 0.5 mg / L, the TOC increases due to oxidative degradation of the ion exchange resin, increasing the likelihood of a deterioration in the quality of the treated water. By reducing the sulfur compound concentration to 0.5 mg / L or less in the reverse osmosis membrane device 16, it is possible to suppress an increase in TOC in the treated water due to oxidative degradation of the resin in the ion exchange resin charging device 17. The sulfur compound concentration of the water to be treated flowing through the ion exchange resin charging device 17 can be kept at 0.5 mg / L or less, for example, as follows. Based on at least one of the TOC of the feed water to the ultraviolet irradiation device 15, the TOC of the treated water from the ultraviolet irradiation device 15, the sulfur compound concentration in the feed water to the reverse osmosis membrane device 16, and the sulfur compound concentration in the feed water to the ion exchange resin charging device 17, at least one of the amount of sulfur compounds added by the sulfur compound adding means 19, the operating conditions (e.g., recovery rate) of the reverse osmosis membrane device 16, and the operating conditions (e.g., irradiation dose) of the ultraviolet irradiation device 15 is controlled. The control may be performed using only one of the TOC and sulfur compound concentrations, or multiple of them. Furthermore, the method for acquiring the sulfur compound concentration is not limited. For example, the conductivity measured by a conductivity meter can be converted to the sulfur compound concentration. As an example, the conductivity measured by the conductivity meter can be converted to the sulfur compound concentration using a relationship between the conductivity and the sulfur compound concentration acquired in advance. The above control can be performed by a predetermined control device (not shown).

[0018] Sulfur compounds can also be removed by adding a reducing agent such as sodium bisulfite. However, this requires a constant supply of a reducing agent to the inlet water of the ion exchange resin-filling device 17, which increases chemical costs, the ionic load, and the frequency of regeneration of the ion exchange resin in the ion exchange resin-filling device 17. In this embodiment, a novel configuration is used in which a reverse osmosis membrane device 16 is used to remove sulfur compounds containing peroxide groups, thereby realizing a pure water production system 1 that can suppress oxidative degradation of the resin in the ion exchange resin-filling device 17 and reduce operating costs (chemical costs).

[0019] The sulfur compound concentration in the water to be treated passed through the reverse osmosis membrane device 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 charging device 17, 100 mg / L or less is more preferable, and 20 mg / L or less is even more preferable. If the sulfur compound concentration exceeds 400 mg / L, oxidation degradation of the reverse osmosis membrane device 16 may occur, and the load on the ion exchange resin charging device 17 may also increase. The sulfur compound concentration in the water to be treated passed through the reverse osmosis membrane device 16 can be reduced to 400 mg / L or less, for example, as follows. Based on at least one of the TOC of the feed water to the ultraviolet irradiation device 15, the TOC of the treated water from the ultraviolet irradiation device 15, the sulfur compound concentration in the feed water to the reverse osmosis membrane device 16, and the sulfur compound concentration in the feed water to the ion exchange resin charging device 17, at least one of the amount of sulfur compounds added by the sulfur compound adding means 19, the operating conditions (e.g., recovery rate) of the reverse osmosis membrane device 16, and the operating conditions (e.g., irradiation dose) of the ultraviolet irradiation device 15 is controlled. The control may be performed using only one of the TOC and sulfur compound concentrations, or may be performed using a combination of these. The method for acquiring the sulfur compound concentration is not limited, but for example, the conductivity measured with a conductivity meter can be converted to the sulfur compound concentration. As an example, the conductivity measured with a conductivity meter can be converted to the sulfur compound concentration using a relationship between the conductivity and sulfur compound concentration acquired in advance. The above control can be performed by a predetermined control device (not shown).

[0020] FIG. 1(b) shows a schematic configuration of a pure water production system 1 according to a second embodiment of the present invention. The pure water production system 1 according to this embodiment is the same as the pure water production system 1 according to the first embodiment, except that it includes a means for removing sulfur compounds containing peroxide groups 20 between a reverse osmosis membrane device 16 and an ion exchange resin filling device 17. For configurations and effects not described here, please refer to the description of the first embodiment. The type of the sulfur compound removal means 20 is not particularly limited, and various means commonly used for removing oxidizing agents, such as a reducing agent, activated carbon, or a platinum group metal-supported catalyst, can be used.

[0021] The sulfur compound removal means 20 is preferably provided between the reverse osmosis membrane device 16 and the ion exchange resin filling device 17. The sulfur compound removal means 20 can also be provided between the ultraviolet irradiation device 15 and the reverse osmosis membrane device 16, but in that case, the load on the sulfur compound removal means 20 increases. If the removal means 20 is activated carbon or a catalyst, these may be oxidized and deteriorated by the sulfur compounds, resulting in the leakage of TOC and other compounds into the treated water, potentially degrading the quality of the treated water. If the removal means 20 is a reducing agent, a larger amount of reducing agent must be added, potentially increasing chemical costs. In this embodiment, after most of the sulfur compounds are removed by the reverse osmosis membrane device 16, the remaining sulfur compounds are removed by the removal means 20, leading to improved performance and reduced operating costs for the pure water production system 1.

[0022] Although several embodiments of the present invention have been described above, the present invention is not limited to these embodiments. For example, a metal ion adding means can be provided upstream of the ultraviolet irradiation device 15. The metal ions are not limited to any metal other than alkali metals, and examples include ions of iron, copper, silver, gold, and manganese. The presence of metal ions in the water to be treated promotes activation of sulfur compounds and improves organic matter treatment performance.

[0023] Furthermore, the sulfur compound concentration in the treated water from the ultraviolet irradiation device 15 may vary depending on the TOC of the water at the inlet to the ultraviolet irradiation device 15. That is, if the TOC of the water at the inlet to the ultraviolet irradiation device 15 is low, a large amount of sulfur compounds may flow out of the ultraviolet irradiation device 15 without being consumed. Increasing the sulfur compound concentration to improve the decomposition efficiency of organic matter may also increase the sulfur compound concentration in the treated water from the ultraviolet irradiation device 15. Even in such cases, two or more reverse osmosis membrane devices 16 may be arranged in series to suppress oxidative degradation of the resin in the ion exchange resin charging device 17. 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 charging device 17. By providing the reverse osmosis membrane devices 16 in series, the sulfur compound removal performance can be improved and the load on the ion exchange resin charging device 17 can be reduced. In the second embodiment, the sulfur compound removal means 20 may be arranged between the reverse osmosis membrane devices 16 arranged in series.

[0024] (Example) Example 1 Potassium peroxodisulfate (K2S2O8) was added at 10mg / L to the water to be treated, which contained 80μg / L of urea, and the output of the ultraviolet irradiation device was 0.73kWh / m 3 The water was then irradiated with ultraviolet light at 1.0 m saturation, and then passed through a reverse osmosis membrane device (Nitto Denko ESPA2-4040) for treatment. 3 The treated water flow rate of the reverse osmosis membrane device was 200 L / h, and the concentrated water flow rate was 800 L / h. The treated water from the reverse osmosis membrane device was passed through an ion exchange resin (ESP-2 manufactured by Organo Corporation) packing device at SV120 ( / h), and the K2S2O8 concentration and TOC of the inlet water of the ion exchange resin packing device, and the urea concentration and TOC of the treated water from the ion exchange resin packing device were measured.

[0025] <Example 2> In Example 1, 40 mg / L of K2S2O2 was added, and measurements were carried out under the same conditions.

[0026] Example 3 In Example 1, a reducing agent was added to the treated water from the reverse osmosis membrane device, and the water was passed through an ion exchange resin packing device. Sodium sulfite (NaSO) was used as the reducing agent, and the amount of the substance added was twice the peroxodisulfate concentration of the treated water from the reverse osmosis membrane device.

[0027] Example 4 In Example 1, a reducing agent was added to the treated water from the ultraviolet irradiation device, and the water was passed through a reverse osmosis membrane device and an ion exchange resin filling device in that order. Na2SO3 was used as the reducing agent, and the amount of the substance added was twice the peroxodisulfate concentration of the treated water from the ultraviolet irradiation device.

[0028] <Comparative Example 1> In Example 1, the treated water from the ultraviolet irradiation device was passed through the ion exchange resin packing device without being passed through the reverse osmosis membrane device.

[0029] The measurement results are shown in Table 1. In Comparative Example 1, the TOC of the treated water was high. This is thought to be due to the residual peroxodisulfuric acid in the UV irradiation device oxidizing and deteriorating the ion exchange resin. In Example 1, which was configured by adding a reverse osmosis membrane device to Comparative Example 1, the TOC of the treated water was less than 1 μg / L. This is thought to be due to the reverse osmosis membrane device reducing the peroxodisulfuric acid concentration to 0.1 mg / L, thereby suppressing oxidative degradation of the ion exchange resin. In Example 2, the peroxodisulfuric acid concentration in the inlet water of the ion exchange resin-filled device was 0.5 mg / L, but the TOC of the treated water from the ion exchange resin-filled device was 1 μg / L, which was lower than in Comparative Example 1. This is thought to be due to the low amount of elution from the ion exchange resin, thereby suppressing the effects of oxidative degradation. Therefore, if the concentration of sulfur compounds in the treated water passing through the ion exchange resin-filled device is 0.5 mg / L or less, it is thought that there will be no significant impact on the treated water quality. Although the same treatment performance was obtained in Examples 3 and 4 in which a reducing agent was added, a larger amount of reducing agent was required when the reducing agent was added upstream of the reverse osmosis membrane device (Example 4) compared to when the reducing agent was added downstream of the reverse osmosis membrane device (Example 3). This shows that it is preferable to add the reducing agent downstream of the reverse osmosis membrane device.

[0030] [Table 1]

[0031] <Example 5> The treated water, which was made by adding 5 mg / L of NaCl, 100 μg / L of IPA, and 400 mg / L of K2S2O8 to pure water, was passed through a reverse osmosis membrane device (Nitto Denko ESPA2-4040) for 800 hours. After 800 hours, the permeability coefficient of the reverse osmosis membrane device, the transmembrane pressure difference ((raw water pressure + concentrated water pressure) / 2 - permeate pressure), and the rejection rates of Na, Cl, and IPA were calculated. The rejection rate was calculated as {(raw water concentration + concentrated water concentration) / 2 - permeate concentration} / {(raw water concentration + concentrated water concentration) / 2} × 100. Accelerated testing was performed with the K2S2O8 concentration set at 4,000 times that of Example 1 and 800 times that of Example 2, enabling evaluation over a time span equivalent to the replacement frequency of the reverse osmosis membrane device. The flow rate of water passing through the reverse osmosis membrane device was 1 m 3 The reverse osmosis membrane device had a treated water flow rate of 200 L / h and a concentrated water flow rate of 800 L / h. The results are shown in Table 2. Even after 800 hours, no deterioration in any of these values ​​was observed. This indicates that the performance of the reverse osmosis membrane device does not deteriorate when the K2S2O8 concentration is 400 mg / L or less.

[0032] [Table 2] [Explanation of symbols]

[0033] 1 Pure water production equipment 11 Raw water tank 12 Filter 13 Activated carbon tower 14 Ion exchange unit 15 Ultraviolet irradiation equipment (ultraviolet oxidation equipment) 16 Reverse osmosis membrane equipment 17 Ion exchange resin filling device 18 Degassing device 19 Means of adding sulfur compounds 20. Means for removing sulfur compounds

Claims

1. a sulfur compound adding means for adding a sulfur compound containing a peroxide group to the water to be treated that contains organic matter; an ultraviolet irradiation device that irradiates ultraviolet light onto the water to be treated to which sulfur compounds have been added; a reverse osmosis membrane device through which the water to be treated irradiated with ultraviolet light passes; an ion exchange resin filling device through which the water to be treated that has been treated by the reverse osmosis membrane device is passed; a control device that controls at least one of the amount of sulfur compounds added by the sulfur compound adding means, the operating conditions of the reverse osmosis membrane device, and the operating conditions of the ultraviolet irradiation device based on at least one of the TOC of the supply water to the ultraviolet irradiation device, the TOC of the treated water from the ultraviolet irradiation device, the concentration of sulfur compounds in the supply water to the reverse osmosis membrane device, and the concentration of sulfur compounds in the supply water to the ion exchange resin filling device; A pure water production apparatus having the above.

2. A sulfur compound adding means for adding a sulfur compound containing a peroxide group to the water to be treated that contains organic matter; an ultraviolet irradiation device that irradiates ultraviolet light onto the water to be treated to which sulfur compounds have been added; a reverse osmosis membrane device through which the water to be treated irradiated with ultraviolet light passes; an ion exchange resin filling device through which the water to be treated that has been treated by the reverse osmosis membrane device is passed; a sulfur compound removal means provided between the reverse osmosis membrane device and the ion exchange resin filling device; A pure water production device having the above structure.

3. A sulfur compound adding means for adding a sulfur compound containing a peroxide group to the water to be treated that contains organic matter; an ultraviolet irradiation device that irradiates ultraviolet light onto the water to be treated to which sulfur compounds have been added; a reverse osmosis membrane device through which the water to be treated irradiated with ultraviolet light passes; an ion exchange resin filling device through which the water to be treated that has been treated by the reverse osmosis membrane device is passed; a second reverse osmosis membrane device provided between the reverse osmosis membrane device and the ion exchange resin filling device; A pure water production device having the above structure.

4. 4. The pure water producing apparatus according to claim 1, wherein the concentration of the sulfur compounds in the water to be treated that is passed through the ion exchange resin-filled device is 0.5 mg / L or less.

5. 5. The water purifying apparatus according to claim 1, wherein the concentration of the sulfur compounds in the water to be treated by the reverse osmosis membrane device is 400 mg / L or less.

6. adding a sulfur compound containing a peroxide group to the water to be treated containing organic matter by a sulfur compound adding means; Irradiating the water to be treated with added sulfur compounds with ultraviolet light using an ultraviolet irradiation device; passing the ultraviolet-irradiated water through a reverse osmosis membrane device; passing the water to be treated that has been treated in the reverse osmosis membrane device through an ion exchange resin filling device; controlling at least one of the amount of sulfur compounds added by the sulfur compound adding means, the operating conditions of the reverse osmosis membrane device, and the operating conditions of the ultraviolet irradiation device based on at least one of the TOC of the supply water to the ultraviolet irradiation device, the TOC of the treated water from the ultraviolet irradiation device, the concentration of sulfur compounds in the supply water to the reverse osmosis membrane device, and the concentration of sulfur compounds in the supply water to the ion exchange resin filling device; A method for producing pure water comprising the steps of:

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