Water quality prediction method and device

Abstract

To predict water quality, such as a concentration of persistent TOC components, typified by urea, in a water treatment system, based on a measured TOC concentration, etc.SOLUTION: Based on an inlet TOC concentration, which is a TOC concentration of inlet water of an ultraviolet irradiation device 52, an outlet TOC concentration, which is a TOC concentration of outlet water of an ion exchange device 53 provided downstream of the ultraviolet irradiation device 52, a concentration of persistent TOC components in water to be treated, and an ultraviolet irradiation amount in the ultraviolet irradiation device 52, a TOC decomposition model expressing a decomposition of the TOC components is created, and the created TOC decomposition model is stored in a model storage unit 15. Thereafter, three of four parameters, namely, the inlet TOC concentration, the outlet TOC concentration, the concentration of persistent TOC components, and the amount of ultraviolet light irradiation, are fitted to the TOC decomposition model to predict a value of a remaining one parameter.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water quality prediction method and device for predicting water quality values ​​such as the concentration of persistent TOC components, typically urea, in a water treatment system that treats water to be treated. [Background technology]

[0002] For example, in water treatment systems such as ultrapure water production systems that produce ultrapure water from raw water, attention must be paid to the quality of the raw water supplied to the water treatment system. For example, in ultrapure water production systems, in order to remove organic substances (TOC (Total Organic Carbon) components) contained in the raw water, ultraviolet oxidation treatment is performed to oxidize the organic components in the raw water by irradiating ultraviolet rays, and ion exchange treatment is performed to remove the carbonic acid components and organic acids generated by the ultraviolet oxidation treatment by ion exchange. However, there are organic components that are easy to remove by these treatments and those that are not. The latter components are also called persistent TOC components, and urea in particular is a component that is difficult to remove by ultraviolet oxidation treatment and the subsequent ion exchange treatment, and it has a significant effect on the quality of the treated water obtained from the water treatment system. In particular, in recent years, reclaimed water and recycled water that have been primarily treated and reused from factory wastewater have come to be used as raw water in order to make effective use of water resources, but reclaimed water and recycled water may contain more urea than tap water, industrial water, etc. When reclaimed water or recovered water is used as raw water for a water treatment system, if the raw water contains a large amount of urea, there is a high possibility that the treated water from the water treatment system will contain urea.

[0003] If the raw water of a water treatment system contains a large amount of urea, the quality of the treated water cannot be maintained, so that, for example, if recovered water or reclaimed water is used as part of the raw water, measures such as stopping the acceptance of the recovered water or reclaimed water must be taken. Therefore, it is desired to be able to accurately evaluate the concentration of urea contained in the raw water supplied to the water treatment system and the concentration of urea contained in the treated water from the water treatment system.

[0004] Patent Document 1 discloses a water treatment management device that evaluates raw water to a water treatment system such as an ultrapure water production system in order to manage the operation of the water treatment system. The water treatment management device includes an evaluation pure water production unit that includes a TOC removal device that performs a unit operation for removing TOC components. The evaluation pure water production unit is provided separately from the water treatment system, and is supplied with raw water to be evaluated. The TOC concentration is measured at multiple measurement points in the evaluation pure water production unit, including the inlet and outlet of the evaluation pure water production unit, and the quality of the raw water can be evaluated by analyzing these multiple TOC concentration measurement values.

[0005] As an analytical device suitable for continuously quantifying the urea concentration in raw water and treated water of a water treatment system, Patent Document 2 discloses an apparatus that performs urea quantification by flow injection analysis using a colorimetric method using diacetyl monoxime. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-155275 A [Patent Document 2] JP 2018-179545 A Summary of the Invention [Problem to be solved by the invention]

[0007] Among the persistent TOC components, urea is one of the compounds that is particularly difficult to decompose, and it has a large effect on the treated water of the water treatment system, so it is important to evaluate the urea concentration in the raw water and the treated water. When the urea concentration is evaluated based on the TOC concentration of the treated water that has been subjected to ultraviolet oxidation treatment and ion exchange treatment as described in Patent Document 1, it cannot be said that the urea concentration can be accurately evaluated because there is a possibility that persistent TOC components other than urea are contained, and when the amount of ultraviolet irradiation is controlled based on the TOC concentration, there is a possibility that excessive ultraviolet irradiation will occur. Even if there is a persistent TOC component other than urea, if the impact on the treated water of the water treatment system is large, it is necessary to evaluate the concentration of the persistent TOC component in the raw water and the treated water. On the other hand, the analytical device for urea determination described in Patent Document 2 consumes a reaction reagent and needs to be refrigerated, and there is a problem that the running cost is high in order to continuously measure the urea concentration.

[0008] An object of the present invention is to provide a water quality prediction method and apparatus capable of predicting water quality, such as the concentration of persistent TOC components, typified by urea, in a water treatment system based on measured TOC concentration values, etc. [Means for solving the problem]

[0009] In the present invention, a model is constructed that describes the relationship between four parameters, namely, (a) TOC concentration in the inlet water of the ultraviolet oxidation treatment, (b) TOC concentration in the outlet water of the ion exchange treatment, (c) the amount of ultraviolet irradiation in the ultraviolet oxidation treatment, and (d) concentration of persistent TOC components, in correspondence with a water treatment system that performs ultraviolet oxidation treatment and ion exchange treatment on the outlet water of the ultraviolet oxidation treatment. This model is a TOC decomposition model that models the decomposition of TOC components by ultraviolet oxidation treatment and ion exchange treatment. If such a model is constructed, it becomes possible to predict the concentration of persistent TOC components such as urea, since the remaining one parameter can be determined if three of the four parameters are given. Here, the concentration of the persistent TOC component is the concentration of the component in at least one of the inlet water of the ultraviolet oxidation treatment and the outlet water of the ion exchange treatment.

[0010] Therefore, the water quality prediction method of the present invention is a water quality prediction method for predicting water quality in a water treatment system that treats water to be treated, and generates a TOC decomposition model that represents the decomposition of TOC components in the ultraviolet irradiation device and the ion exchange device based on actual measured values ​​of the inlet TOC concentration, which is the TOC concentration of the inlet water of the ultraviolet irradiation device to which the water to be treated is supplied, the outlet TOC concentration, which is the TOC concentration of the outlet water of an ion exchange device provided downstream of the ultraviolet irradiation device, the concentration of persistent TOC components in at least one of the inlet water of the ultraviolet irradiation device and the outlet water of the ion exchange device, and the ultraviolet irradiation dose in the ultraviolet irradiation device, and after generating the TOC decomposition model, three of the four parameters, namely the inlet TOC concentration, outlet TOC concentration, concentration of persistent TOC components, and ultraviolet irradiation dose, are applied to the TOC decomposition model to predict the value of the remaining parameter.

[0011] The water quality prediction device of the present invention is a water quality prediction device that predicts the water quality in a water treatment system that treats water to be treated, and is equipped with an inlet TOC concentration, which is the TOC concentration of the inlet water of an ultraviolet irradiation device to which the water to be treated is supplied, an outlet TOC concentration, which is the TOC concentration of the outlet water of an ion exchange device provided downstream of the ultraviolet irradiation device, the concentration of persistent TOC components in at least one of the inlet water of the ultraviolet irradiation device and the outlet water of the ion exchange device, and the amount of ultraviolet light irradiation in the ultraviolet irradiation device, and a water quality prediction unit that applies three parameters of the four parameters, namely the inlet TOC concentration, the outlet TOC concentration, the concentration of persistent TOC components, and the amount of ultraviolet light irradiation to the TOC decomposition model to predict the value of the remaining parameter. Effect of the Invention

[0012] According to the present invention, the water quality, such as the urea concentration, in a water treatment system can be easily predicted based on the measured TOC concentration value, etc. [Brief description of the drawings]

[0013] [Figure 1] 1 is a block diagram showing a water quality prediction device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing another application example of the water quality prediction device of the first embodiment. [Diagram 3] FIG. 4 is a block diagram showing a water quality prediction device according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] [First embodiment] Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a water quality prediction device according to a first embodiment of the present invention. The water quality prediction device 10 performs prediction of the concentration of persistent TOC components in a water treatment system in order to manage the operation of the water treatment system. The water treatment system must perform an ultraviolet oxidation process in which ultraviolet rays are irradiated onto the water to be treated, and an ion exchange process on the outlet water of the ultraviolet oxidation process. In the following description, the water treatment system is assumed to be an ultrapure water production system 50, and the persistent TOC component to be predicted is assumed to be urea.

[0015] The ultrapure water production system 50 produces ultrapure water from water to be treated stored in a raw water tank 31. In the example shown here, industrial water is supplied to the raw water tank 31 via a valve 32, and recovered water is supplied via a valve 33. Industrial water contains almost no urea and has stable water quality. In contrast, recovered water may contain a large amount of urea. The ultrapure water production system 50 is composed of a pretreatment section 51 that receives the water to be treated from the raw water tank 31 via a pipe 35 and performs pretreatment, a primary pure water system 55 that receives the water to be treated that has been pretreated in the pretreatment section 51 and produces primary pure water from the water to be treated, and a subsystem 60 (also called a secondary pure water system) that further refines the primary pure water produced in the primary pure water system 55 to produce ultrapure water. The pretreatment section 51 is composed of, for example, an activated carbon device, a filtration device, etc. The primary pure water system 55 is composed of, for example, a membrane filtration device, a membrane degassing device, a reverse osmosis membrane device, etc.

[0016] The subsystem 60 includes a tank 61 for temporarily storing the primary pure water sent from the primary pure water system 55, an ultraviolet irradiation device (UV) 62 for irradiating the primary pure water in the tank 61 with ultraviolet light to perform ultraviolet oxidation treatment, and an ion exchange device (CP) 63 for performing ion exchange treatment by receiving the outlet water of the ultraviolet irradiation device 62. The ion exchange device 63 is, for example, a non-regenerative ion exchange device (also called a cartridge polisher) filled with a mixed bed of anion exchange resin and cation exchange resin, and the outlet water of the ion exchange device 63 is the outlet water of the subsystem 60, which is treated water from the ultrapure water production system 50, i.e., ultrapure water. The generated ultrapure water is supplied to the place where the ultrapure water is used, but the ultrapure water that is not supplied to the place where the ultrapure water is used is returned to the tank 61. The ultrapure water returned to the tank 61 circulates within the subsystem 60 and is further purified while circulating. In the figure, subsystem 60 is equipped with only an ultraviolet irradiation device 62 and an ion exchange device 63, but subsystem 60 may also be equipped with other equipment that performs some kind of treatment on the water to be treated, such as a membrane filtration device or a membrane degassing device.

[0017] 1 is itself a water treatment system, and the subsystem 60 also includes an ultraviolet irradiation device 62 and an ion exchange device 63, so it can be said to be a water treatment system that is the subject of water quality prediction based on the present invention. The primary pure water system 55 and the subsystem 60 can be controlled independently. Therefore, the following will explain the case where water quality prediction is performed with a focus on the subsystem 60.

[0018] The water quality prediction device 10 includes a TOC measurement unit 11 for measuring the concentration of TOC components in water, a urea measurement unit 12 for measuring the concentration of urea in water, a processing unit 13 for performing data processing based on the detection values ​​of the TOC measurement unit 11 and the urea measurement unit 12, and an irradiation amount control unit 17 for controlling the amount of ultraviolet irradiation in the ultraviolet irradiation device 62 based on the processing result of the processing unit 13. The TOC measurement unit 11 is supplied with water (water to be treated) supplied from a tank 61 to the ultraviolet irradiation device 62, i.e., the inlet water of the ultraviolet irradiation device 62, via a valve 21, and further with outlet water of the ion exchange device 63, i.e., the treated water of the ultrapure water production system 50, via a valve 22. By alternately opening and closing the valves 21 and 22, the TOC measurement unit 11 can continuously measure the TOC concentration of the inlet water of the ultraviolet irradiation device 62 and the TOC concentration of the outlet water of the ion exchange device 63. In the following description, the TOC concentration of the inlet water of the ultraviolet irradiation device 62 is called the inlet TOC concentration, and the TOC concentration of the outlet water of the ion exchange device 63 is called the outlet TOC concentration. A commercially available TOC concentration meter can be used as the TOC measurement section 11. Here, one TOC measurement section 11 is provided, but two TOC concentration meters may be used, and the inlet TOC concentration and the outlet TOC concentration may be measured by different TOC concentration meters.

[0019] The urea measuring unit 12 measures the urea concentration of at least one of the inlet water of the ultraviolet irradiation device 62 and the outlet water of the ion exchange device 63, and is supplied with the inlet water of the ultraviolet irradiation device 62 via the valve 23 and the outlet water of the ion exchange device 63 via the valve 24. Since it can be considered that urea cannot be almost removed by the ultraviolet oxidation treatment and the ion exchange treatment, the urea concentration may be measured for either the inlet water of the ultraviolet irradiation device 62 or the outlet water of the ion exchange device 63, and in that case, it is preferable to measure the urea concentration of the outlet water of the ion exchange device 63. When the urea measuring unit 12 measures only the urea concentration of the outlet water of the ion exchange device 63, the valve 23 and the piping in which the valve 23 is provided are not necessary. As the urea measuring unit 12, for example, a urea concentration meter based on the measurement principle described in Patent Document 2 can be used.

[0020] The processing unit 13 is configured as a general computer system, and includes a model creation unit 14, a model storage unit 15, and a water quality prediction unit 16. The model creation unit 14 and the water quality prediction unit 16 are realized by a software program executed by the processing unit 13, which is a computer system. The model storage unit 15 is secured as a storage area in the processing unit 13. The model creation unit 14 creates a TOC decomposition model that represents the decomposition of the TOC components in the subsystem 60, based on the ultraviolet irradiation amount in the ultraviolet irradiation device 62, the TOC concentration measurement value obtained in the TOC measurement unit 11, and the urea concentration measurement value obtained in the urea measurement unit 12. The created TOC decomposition model is stored in the model storage unit 15. Once the TOC decomposition model is created and stored in the model storage unit 15, the water quality prediction unit 16 obtains a predicted value of the urea concentration, particularly the urea concentration of the outlet water of the ion exchange device 63, i.e., the treated water of the subsystem 60, by applying the TOC concentration measurement value and the ultraviolet irradiation amount to the TOC decomposition model.

[0021] The creation of a TOC decomposition model will be described below. First, the removal of TOC components by the ultraviolet oxidation treatment in the ultraviolet irradiation device 62 and the ion exchange treatment in the ion exchange device 63 will be described using mathematical expressions.

[0022] It is considered that the inlet water to the ultraviolet oxidation process contains multiple TOC components, i.e., multiple organic chemical species, but the TOC concentration value obtained by the TOC measurement unit 11 is the total concentration value of all TOC components, i.e., the total TOC concentration. in The total TOC concentration in the outlet water of the ion exchange treatment is TOC out Let the ratio of each TOC component to the total TOC components in the inlet water of the UV oxidation treatment be p i Here, i is a subscript to distinguish each TOC component. The concentration of each TOC component in the inlet water of the UV oxidation treatment is C i given that, C i =p i *TOC in (1) holds true.

[0023] The remaining rate of each TOC component after UV oxidation and ion exchange treatment is expressed as y i The survival rate y i is the concentration of the TOC component in the outlet water of the ion exchange treatment and the concentration C i The UV irradiation amount is R, and the reaction rate coefficient for the TOC component of interest is k i Then, the survival rate y i teeth, y i =exp(-k i *R) (2) It is expressed as k i is the concentration C of the TOC component at the inlet of the UV oxidation treatment i It can be said that the function is a linear function of k i =a i *C i +b i (3) It can be put as follows. i and b i is a parameter determined for each TOC component. i If we define the ratio of individual TOC components in the inlet water of the UV oxidation process, p i Therefore, equation (4) is established. The TOC decomposition model uses the parameters a i ,b i The TOC decomposition model assumes that the decomposition of each TOC species is independent of the others, i.e., the decomposition of one TOC species does not change the decomposition rate of other TOC species.

[0024]

number

[0025] Among the TOC components that may be contained in the raw water supplied to the ultrapure water production system 50 as the water to be treated, urea is a component that is difficult to remove by ultraviolet oxidation treatment and ion exchange treatment, while TOC components other than urea are easily decomposed and removed by ultraviolet oxidation treatment and ion exchange treatment. Even if TOC components are removed from the raw water in the primary pure water system 55, the primary pure water still contains TOC components. In this embodiment, a TOC decomposition model is created assuming that the TOC components contained in the water to be treated, which is the primary pure water, are two types: urea and model TOC species that are easily decomposable. Although the TOC components other than urea are lumped together as model TOC species, the decomposability of urea and the other TOC components is significantly different, so that even a model using only these two types of TOC components can accurately represent the removal of TOC components in an actual ultrapure water production system. In the following, the subscript indicating urea among the TOC components is designated as u, and the subscript indicating the model TOC species is designated as x. For ease of calculation, it is assumed that urea, a persistent TOC component, is not decomposed by UV oxidation treatment. The urea concentration is the same between the inlet water of the UV oxidation treatment and the outlet water of the ion exchange treatment, regardless of the amount of UV irradiation. The residual rate y u is 100%, i.e., 1. In this case, from equations (2) and (3), the reaction rate constant k for urea is identically 0, and a u =b u =0.

[0026] In creating the model, pure water in which urea and model TOC species are dissolved is used as the water to be treated. Methyl alcohol, for example, can be used as the model TOC species. This water to be treated is supplied to the ultrapure water production system 50, and the TOC concentration (inlet TOC concentration) of the water at the inlet of the ultraviolet irradiation device 62 is measured by the TOC measurement unit 11, while the TOC concentration (outlet TOC concentration) and urea concentration of the water at the outlet of the ion exchange device 63 are measured by the TOC measurement unit 11 and the urea measurement unit 12, respectively. Using the same water to be treated, measurements of the outlet TOC concentration and urea concentration are repeated at two or more points in the ultraviolet irradiation device 62 with different amounts of ultraviolet radiation. For urea, the parameter a u ,bu Since both are assumed to be 0, the parameters a x ,b x All that is required is to determine the following.

[0027] Parameter a for model TOC species x ,b x is the ratio p of urea in the TOC components in the inlet water of the ultraviolet irradiation device 62 u and these parameters a x ,b x The concentration TOC is calculated based on Eq. (4) using and as fitting parameters. out The TOC concentration can be determined by fitting the model so that the error between the actual measured value of the outlet TOC concentration is minimized. It is preferable to use the square error as the error.

[0028] The TOC decomposition model created in this way assumes that there are only two TOC components: urea and model TOC species, and describes the relationship between the inlet TOC concentration, outlet TOC concentration, UV irradiation dose, and urea concentration. Therefore, the urea concentration can be estimated by applying the inlet TOC concentration and outlet TOC concentration actually measured in the ultrapure water production system 50 and the UV irradiation dose at that time to the model. Once the urea concentration has been estimated in this way, the ratio of recovered water in the water supplied to the raw water tank 31 can be controlled or the acceptance of recovered water can be refused depending on the urea concentration, thereby reducing the impact of urea in the water to be treated on the quality of the treated water from the ultrapure water production system.

[0029] In addition, when the urea concentration is estimated as described above or measured, the urea concentration and the measured inlet TOC concentration are used, a target outlet TOC concentration is set, and the target outlet TOC concentration is applied to the model to calculate the ultraviolet irradiation amount for achieving the target outlet TOC concentration. The irradiation amount control unit 17 may control the ultraviolet irradiation amount of the ultraviolet irradiation device 62 based on the calculated ultraviolet irradiation amount.

[0030] In this embodiment, once the TOC decomposition model is created, the actual measured value of the urea concentration is not necessary for predicting the urea concentration or controlling the amount of ultraviolet irradiation, so the urea measurement unit 12 can be removed. In other words, if a TOC decomposition model is created and stored in the model storage unit 15, the water quality prediction device 10 does not need to be provided with the urea measurement unit 12. The processing unit 13 also does not need to be provided with the model creation unit 14. In addition, if there are multiple ultrapure water production systems 50 that have the same configuration and specifications and are supplied with water to be treated from the same water source, and a TOC decomposition model is created in one of them, the created TOC decomposition model can be incorporated in the water quality prediction device 10 connected to the other ultrapure water production systems 50 to predict the urea concentration and control the amount of ultraviolet irradiation in the other ultrapure water production systems 50. Although the inlet water to the ultraviolet irradiation device 62 is supplied to the TOC measurement section 11 and the urea measurement section 12, the inlet water to the primary pure water system 55, i.e., the outlet water of the pretreatment section 51, may be supplied to the TOC measurement section 11 and the urea measurement section 12.

[0031] In the ultrapure water manufacturing system 50, it is also possible to carry out ultraviolet oxidation treatment and ion exchange treatment on the outlet water of the ultraviolet oxidation treatment in the primary pure water system 55. In this case, the primary pure water system 55 can be said to be a water treatment system to which the water quality prediction method based on the present invention is applied, and the water quality prediction device 10 described above can be used to predict the quality of the primary pure water and control the amount of ultraviolet irradiation in the primary pure water system 55. Figure 2 shows a configuration when the water quality prediction device 10 is used to control the amount of ultraviolet irradiation in the primary pure water system 55.

[0032] In the ultrapure water production system 50, the primary pure water system 55 includes an ultraviolet irradiation device (UV) 57 which is supplied with the water to be treated that has been pretreated in the pretreatment device 51 and irradiates the water to be treated with ultraviolet light to perform ultraviolet oxidation treatment, and an ion exchange resin tower (IER) 58 which is supplied with the outlet water of the ultraviolet irradiation device 57 and performs ion exchange treatment. The ion exchange resin tower 58 is filled with, for example, anion exchange resin and cation exchange resin in a mixed bed or multiple beds. The ion exchange resin tower 58 may be configured so that the ion exchange resin filled therein is regenerative or exchangeable. The outlet water of the ion exchange resin tower 58 is primary pure water which is the outlet water of the primary pure water system 55, and this primary pure water is supplied to the subsystem 60. In addition to the ultraviolet irradiation device 57 and the ion exchange resin tower 58, the primary pure water system 55 may include a reverse osmosis membrane device, a membrane filtration device, a membrane degassing device, etc.

[0033] In the ultrapure water production system 50, it is preferable that the urea concentration in the primary pure water supplied to the subsystem 60 is as low as possible, so in the configuration shown in Fig. 2, the water quality prediction device 10 described with reference to Fig. 1 is connected to the primary pure water system 55. The outlet water of the pretreatment unit 51, i.e., the inlet water of the ultraviolet ray irradiation device 57, is supplied to the TOC measurement unit 11 via the valve 21 and also to the urea measurement unit 12 via the valve 23, and the outlet water of the ion exchange resin tower 58, i.e., the treated water (primary pure water) of the primary pure water system 55, is supplied to the TOC measurement unit 11 via the valve 22 and also to the urea measurement unit 12 via the valve 24. When the water quality prediction device 10 is connected to the primary pure water system 55, the processing unit 13 processes data based on the detection values ​​in the TOC measurement unit 11 and the urea measurement unit 12 in the same manner as in the case described with reference to Fig. 1, and the irradiation amount control unit 17 controls the ultraviolet ray irradiation amount in the ultraviolet ray irradiation device 57 in the primary pure water system 55 based on the processing result in the processing unit 13.

[0034] [Second embodiment] The water quality prediction device 10 shown in FIG. 1 or FIG. 2 predicts the urea concentration using the actual measured values ​​of the inlet TOC concentration and the outlet TOC concentration in the ultrapure water production system 50, which is a water treatment system. However, if the water treatment system, which is the ultrapure water production system 50, is large-scale, even if the type of raw water supplied to the water treatment system is changed based on the predicted urea concentration in the treated water, it may take time for the effect of the change to appear in the treated water. Therefore, as in the case of the water quality treatment management device shown in Patent Document 1, a pure water production unit for evaluation is provided separately from the water treatment system, and a TOC decomposition model is created based on the TOC concentration and urea concentration measured in the pure water production unit for evaluation. After the TOC decomposition model is created, the urea concentration in the water treatment system can be predicted based on the ultraviolet irradiation amount and TOC concentration in the pure water production unit for evaluation. FIG. 3 shows the water quality prediction device 10 of the second embodiment of the present invention. The water quality prediction device 10 shown in FIG. 3 is obtained by adding a pure water production unit for evaluation 40 to the water quality prediction device 10 shown in FIG. 2. The primary pure water system 50 of the ultrapure water production system 50 includes at least an ultraviolet irradiation device 57 and an ion exchange resin tower 58 to which the outlet water of the ultraviolet irradiation device 57 is supplied and which performs ion exchange processing, and the subsystem 60 includes an ultraviolet irradiation device 62 and an ion exchange device 63 to which the outlet water of the ultraviolet irradiation device 62 is supplied and which performs ion exchange processing.

[0035] The evaluation pure water production unit 40 is configured to be supplied with the same water to be treated as the ultrapure water production system 50, which is a water treatment system, and to simulate the decomposition and removal process of TOC components in the ultrapure water production system 50, but is a smaller-scale system than the ultrapure water production system 50. That is, the evaluation pure water production unit 40 includes a pretreatment unit 41 to which the water to be treated is supplied via a pipe 36 branched from a pipe 35 that supplies the water to be treated from a raw water tank 31 to the ultrapure water production system 50 and performs pretreatment, an ultraviolet irradiation device (UV) 42 to which the water to be treated pretreated in the pretreatment unit 41 is supplied and which irradiates the water to be treated with ultraviolet rays to perform ultraviolet oxidation treatment, and an ion exchange device (CP) 43 to which the outlet water of the ultraviolet irradiation device 42 is supplied and which performs ion exchange treatment. The pretreatment unit 41 is configured, for example, by a reverse osmosis membrane device, and the ion exchange device 43 is, for example, a non-regenerative ion exchange device filled with a mixed bed of anion exchange resin and cation exchange resin. The outlet water of the ion exchange device 43 is discharged to the outside as wastewater.

[0036] In the water quality prediction device 10 of the second embodiment, the TOC measurement unit 11 is supplied with the water to be treated that has been pretreated by the pretreatment unit 41 of the evaluation pure water production unit 40, i.e., the inlet water of the ultraviolet irradiation device 42, via the valve 21, and further with the outlet water of the ion exchange device 43, via the valve 22. By alternately opening and closing the valves 21 and 22, the TOC measurement unit 11 can continuously measure the TOC concentration of the inlet water of the ultraviolet irradiation device 42 (inlet TOC concentration) and the TOC concentration of the outlet water of the ion exchange device 43 (outlet TOC concentration). Similarly, the urea measurement unit 12 is supplied with the inlet water of the ultraviolet irradiation device 42 of the evaluation pure water production unit 40 via the valve 23 and with the outlet water of the ion exchange device 43 via the valve 24, and measures the urea concentration of at least one of the inlet water of the ultraviolet irradiation device 42 and the outlet water of the ion exchange device 43.

[0037] In this embodiment, the model creation section 14 in the processing section 13 of the water quality prediction device 10 creates a TOC decomposition model based on the inlet TOC concentration, outlet TOC concentration, urea concentration, and ultraviolet irradiation dose in the evaluation pure water production section 40. The procedure for creating the TOC decomposition model is the same as in the first embodiment. Then, by using the created TOC decomposition model, the urea concentration in the outlet water of the ion exchange device 43 can be predicted based on the inlet TOC concentration, outlet TOC concentration, and ultraviolet irradiation dose in the evaluation pure water production section 40, which can be considered as the urea concentration in the inlet water of the ultraviolet irradiation device 42, and therefore, the urea concentration in the treated water supplied to the ultrapure water production system 50 can be predicted. In addition, when comparing the ultraviolet irradiation devices 57 and 62 of the ultrapure water production system 50 with the ultraviolet irradiation device 42 of the pure water production section for evaluation 40, the ultraviolet irradiation doses that achieve the same TOC removal rate are proportional to each other between these ultraviolet irradiation devices 42, 57, and 62, and the proportionality coefficient k is considered to be determined by the size and water flow rate of the ultraviolet irradiation devices 42, 57, and 62, the specifications of the ultraviolet lamps used, and the like. Therefore, when controlling the outlet TOC concentration of the ultrapure water production system 50 to a desired value, it is sufficient to control the ultraviolet irradiation devices 57 and 62 of the ultrapure water production system 50 so that the ultraviolet irradiation dose is the ultraviolet irradiation dose of the ultraviolet irradiation device 42 when controlling the outlet TOC concentration of the pure water production section for evaluation 40 to the same desired value multiplied by the proportionality coefficient k. Such control of the ultraviolet irradiation devices 57 and 62 is performed by the irradiation amount control section 17. In this case, the irradiation amount may be controlled for either the ultraviolet irradiation device 57 in the primary pure water system 55 or the ultraviolet irradiation device 62 in the subsystem 60.

[0038] In the second embodiment, after creating a TOC decomposition model based on the measurement results in the evaluation pure water production unit 40, it is possible to predict the urea concentration based on the inlet TOC concentration, outlet TOC concentration, and ultraviolet ray irradiation dose in the ultrapure water production system 50 while taking into account the above-mentioned proportionality coefficient k for the ultraviolet ray irradiation dose, and to control the ultraviolet ray irradiation dose in the ultraviolet ray irradiation devices 57, 62.

[0039] In the above-described embodiments, urea cannot be decomposed and removed by the ultraviolet oxidation treatment and the ion exchange treatment. u =b u However, when the decomposition of urea by the ultraviolet oxidation treatment and the ion exchange treatment cannot be ignored, the urea concentration is measured for both the inlet water of the ultraviolet oxidation treatment and the outlet water of the ion exchange treatment, and the parameter a u ,b u It is also possible to create a TOC decomposition model by performing fitting for urea. Although one model TOC species, which is a TOC component other than urea, is used, it is also possible to use multiple model TOC species.

[0040] In each embodiment described above, the persistent TOC component to be predicted is urea, but the persistent TOC component to be predicted in the water quality prediction method of the present invention is not limited to urea. For example, chemical species such as isopropyl alcohol are also known as organic chemical species that are difficult to decompose by ultraviolet oxidation treatment, and these can be the persistent TOC components to be predicted based on the present invention. When isopropyl alcohol or the like is to be predicted, a measurement unit that measures the concentration of isopropyl alcohol or the like may be provided instead of the urea measurement unit 12. [Explanation of symbols]

[0041] 10 Water quality prediction device 11 TOC measurement section 12 Urea measuring section 13 Processing section 14 Model Creation Department 15 Model Storage 16 Water Quality Prediction Division 17 Radiation amount control section 40 Evaluation Pure Water Production Department 41,51 Pretreatment section 42,57,62 Ultraviolet irradiation device (UV) 43,63 Ion exchange device (CP) 50 Ultrapure water production system 55 Primary Pure Water System 58 Ion exchange resin tower (IER) 60 Subsystems

Claims

1. A water quality prediction method for predicting water quality in a water treatment system that treats water to be treated, comprising: a TOC decomposition model is generated based on actual measurements of an inlet TOC concentration, which is the TOC concentration of the inlet water of an ultraviolet irradiation device to which the water to be treated is supplied, an outlet TOC concentration, which is the TOC concentration of the outlet water of an ion exchange device provided downstream of the ultraviolet irradiation device, the concentration of persistent TOC components in at least one of the inlet water of the ultraviolet irradiation device and the outlet water of the ion exchange device, and the amount of ultraviolet light irradiation in the ultraviolet irradiation device; After generating the TOC decomposition model, three of the four parameters, namely the inlet TOC concentration, the outlet TOC concentration, the concentration of the persistent TOC components, and the ultraviolet light exposure dose, are applied to the TOC decomposition model to predict the value of the remaining parameter.

2. the TOC decomposition model is a model that represents decomposition of TOC components including the persistent TOC components and at least one model TOC species other than the persistent TOC components, assuming that the decomposition of each TOC species is independent of each other; In the TOC decomposition model, k is a reaction rate constant, R is the ultraviolet ray irradiation dose, and the reaction rate constant k for each TOC species is expressed as a linear function of the concentration of the TOC species in the inlet water of the ultraviolet ray irradiation device; The residual rate y of each TOC species is y=exp(-k*R) The water quality prediction method according to claim 1, wherein the water quality prediction method is expressed as follows:

3. The water quality prediction method according to claim 1 or 2, wherein the water treatment system is provided with the ultraviolet irradiation device and the ion exchange device.

4. The water quality prediction method of claim 3, further comprising applying the target value of the outlet TOC concentration, the inlet TOC concentration, and the concentration of the persistent TOC components to the TOC decomposition model to calculate the ultraviolet irradiation amount, and operating the ultraviolet irradiation device at the calculated ultraviolet irradiation amount.

5. a pure water producing section for evaluation, which is provided separately from the water treatment system and to which the water to be treated is supplied, is provided with the ultraviolet irradiation device and the ion exchange device; The water quality prediction method according to claim 1 or 2, wherein the water treatment system comprises an ultraviolet irradiation device for water treatment to which the water to be treated is supplied, and an ion exchange device for water treatment provided downstream of the ultraviolet irradiation device for water treatment.

6. The water quality prediction method of claim 5, further comprising: applying a target value of the TOC concentration in the outlet water of the water treatment ion exchange device, the inlet TOC concentration, and the concentration of the persistent TOC components to the TOC decomposition model to calculate the ultraviolet irradiation amount; converting the calculated ultraviolet irradiation amount into an ultraviolet irradiation amount in the water treatment ultraviolet irradiation device; and operating the water treatment ultraviolet irradiation device based on the converted ultraviolet irradiation amount.

7. A water quality prediction device for predicting water quality in a water treatment system that treats water to be treated, a model storage unit for storing a TOC decomposition model that expresses the decomposition of TOC components in the ultraviolet irradiation device and the ion exchange device based on an inlet TOC concentration, which is the TOC concentration of inlet water of an ultraviolet irradiation device to which the water to be treated is supplied, an outlet TOC concentration, which is the TOC concentration of outlet water of an ion exchange device provided downstream of the ultraviolet irradiation device, a concentration of persistent TOC components in at least one of the inlet water of the ultraviolet irradiation device and the outlet water of the ion exchange device, and an ultraviolet irradiation amount in the ultraviolet irradiation device; a water quality prediction unit that predicts the value of the remaining parameter by applying three parameters out of the four parameters, namely, the inlet TOC concentration, the outlet TOC concentration, the concentration of the persistent TOC component, and the ultraviolet ray irradiation dose, to the TOC decomposition model; A water quality prediction device comprising:

8. The water quality prediction device according to claim 7, further comprising a model creation unit that creates the TOC decomposition model based on the actual measured values ​​of the inlet TOC concentration, the outlet TOC concentration, the concentration of the persistent TOC components, and the ultraviolet irradiance.

9. the TOC decomposition model is a model that represents decomposition of TOC components including the persistent TOC components and at least one model TOC species other than the persistent TOC components, assuming that the decomposition of each TOC species is independent of each other; In the TOC decomposition model, k is a reaction rate constant, R is the ultraviolet ray irradiation dose, and the reaction rate constant k for each TOC species is expressed as a linear function of the concentration of the TOC species in the inlet water of the ultraviolet ray irradiation device; The residual rate y of each TOC species is y=exp(-k*R) The water quality prediction device according to claim 8, wherein the water quality prediction device is expressed as follows:

10. The water quality prediction device according to claim 7 , wherein the water treatment system is provided with the ultraviolet irradiation device and the ion exchange device.

11. The water quality prediction device of claim 10, further comprising an irradiation amount control unit that controls the ultraviolet irradiation device to operate at the ultraviolet irradiation amount calculated by applying the target value of the outlet TOC concentration, the inlet TOC concentration, and the concentration of the persistent TOC components to the TOC decomposition model.

12. The apparatus further includes a pure water producing unit for evaluation, which is provided separately from the water treatment system and to which the water to be treated is supplied, the ultraviolet irradiating device and the ion exchange device are provided in the evaluation pure water producing section, The water treatment system comprises an ultraviolet irradiation device for water treatment to which the water to be treated is supplied, and an ion exchange device for water treatment provided downstream of the ultraviolet irradiation device for water treatment. The water quality prediction device described in any one of claims 7 to 9.

13. The water quality prediction device of claim 12 further comprises an irradiation amount control unit that converts the ultraviolet irradiation amount calculated by applying a target value of the TOC concentration of the outlet water of the water treatment ion exchange device, the inlet TOC concentration, and the concentration of the persistent TOC components to the TOC decomposition model into an ultraviolet irradiation amount in the water treatment ultraviolet irradiation device, and controls the water treatment ultraviolet irradiation device to operate according to the converted ultraviolet irradiation amount.

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