Water quality prediction system and water quality prediction method for water treatment systems

Abstract

To predict a quality of pure water obtained by a target pure water production system using an evaluation system that is a smaller pure water production system.SOLUTION: A water quality prediction system 10 that predicts water quality when pure water is produced by supplying raw water containing unknown TOC components to a pure water production system 50 that includes at least a reverse osmosis membrane device 52, includes: an evaluation system 20 equipped with at least a reverse osmosis membrane device 22 and supplied with the same raw water; a measuring device 25 that measures a TOC concentration of the raw water and a TOC concentration in the evaluation system; and an evaluation calculation unit 26. The evaluation calculation unit 26 calculates the TOC concentration in the pure water production system 50 based on each TOC concentration measured by the measuring device 25, operating parameters of the pure water production system 50, and operating parameters of the evaluation system 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a system and method for predicting the water quality of treated water obtained by a water treatment system. [Background technology]

[0002] Pure water and ultrapure water are used for cleaning purposes in fields such as semiconductor equipment manufacturing. When producing pure water or ultrapure water from raw water, ionic or organic impurities (TOC (Total Organic Carbon) components) contained in the raw water are removed from the raw water in a pure water production system or ultrapure water production system consisting of ion exchange devices, reverse osmosis membrane devices, ultraviolet irradiation devices, etc. In the following explanation, "pure water" includes ultrapure water, and "pure water production system" includes ultrapure water production systems.

[0003] Traditionally, river water, well water, and surface water have been used as raw water for pure water production. However, in response to the recent trend of water resource depletion, the use of recovered water obtained by treating factory wastewater and domestic wastewater as raw water is increasing. It is known that the concentration, component composition, and ratio of ions, TOC, etc. in recovered water differ significantly from those of river water. For example, recovered water may contain persistent TOC components. Persistent TOC components are organic components that are difficult to remove by reverse osmosis membrane treatment, ion exchange treatment, or ultraviolet oxidation treatment using ultraviolet irradiation. If persistent TOC is present in the raw water, when producing pure water from that raw water using an existing pure water production system, the quality of the resulting pure water may decrease, specifically, the TOC concentration in the resulting pure water may increase. Depending on the quality of the raw water, it is necessary to change whether or not to accept the raw water and the operating conditions of the pure water production system. In the case of high-capacity pure water production systems, it takes time for changes in the quality of the raw water supplied to the system to have an impact on the outlet. Therefore, it is not appropriate to respond to changes in the raw water quality only after detecting changes in the quality of the treated water obtained from the outlet. For this reason, it has been proposed to set up a small-scale pure water production system, or evaluation system, for evaluating the quality of the raw water, separate from the pure water production system (main pure water production system) that produces pure water supplied to the point of use. The quality of the pure water produced by the evaluation system is then measured to evaluate the quality of the raw water.

[0004] Patent Document 1 discloses an evaluation pure water production unit separate from the water treatment system, which is equipped with a TOC removal device that performs unit operations used to remove TOC components from the water to be supplied to the water treatment system, with the target water being the target water, and the TOC concentration is measured at multiple measurement points in the evaluation pure water production unit, and these TOC concentration values ​​are analyzed to evaluate the target water. The technology described in Patent Document 1 allows the supply of raw water to the water treatment system to be controlled according to the evaluation results, for example, if the target water, which is the raw water, is evaluated to contain recalcitrant TOC components, the raw water can not be supplied to the water treatment system.

[0005] Patent Document 2 discloses the provision of a secondary ultrapure water production system for monitoring and controlling the quality of raw water, in addition to a main ultrapure water production system that produces ultrapure water to be supplied from raw water to a point of use. The secondary ultrapure water production system has an equivalent configuration to the main ultrapure water production system and produces ultrapure water of similar quality. The TOC concentration of the ultrapure water obtained from the secondary ultrapure water production system is measured, the quality of the raw water is evaluated based on this TOC concentration, and the amount of raw water supplied to the main ultrapure water production system is controlled based on the evaluation results. In the system described in Patent Document 2, for example, if the TOC concentration of the ultrapure water obtained from the secondary ultrapure water production system is high, the supply of raw water to the main ultrapure water production system is stopped, or the raw water is supplied to the main ultrapure water production system via a urea removal device, or the amount of ultraviolet irradiation from the ultraviolet irradiation device is increased.

[0006] Although it concerns reverse osmosis membrane systems used for seawater desalination rather than TOC removal, Patent Document 3 discloses accurately predicting the transport parameters of a reverse osmosis membrane and the operating state of the reverse osmosis membrane system by considering concentration polarization phenomena. Similarly, Patent Document 4 discloses predicting the concentration of a specific component in the permeate from the total salt concentration in the permeate of a reverse osmosis membrane, and setting or controlling the operating conditions of the reverse osmosis membrane system according to the predicted value. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2019-155275 [Patent Document 2] Japanese Patent Publication No. 2016-107249 [Patent Document 3] Japanese Patent Publication No. 2001-62255 [Patent Document 4] Japanese Patent Publication No. 2001-129365 [Overview of the project] [Problems that the invention aims to solve]

[0008] The evaluation system used to assess the quality of raw water needs to be able to quickly and easily evaluate the impact of the raw water on the main pure water production system using a small amount of raw water. Therefore, the evaluation system needs to be as small as possible compared to the main pure water production system. However, due to the small size, the specifications and operating conditions of the evaluation system must differ from those of the main pure water production system. For example, regarding the reverse osmosis membrane system, the main pure water production system uses a combination of several dozen 8-inch (20 cm) reverse osmosis (RO) spiral elements, employing conditions that result in a high recovery rate of 80-95%. In contrast, the evaluation system preferably uses one or two small membrane elements of 2-4 inches (5-10 cm). Furthermore, it is not always possible to obtain small membrane elements using the same brand of reverse osmosis membrane as those used in the main pure water production system, and it may be necessary to select a reverse osmosis membrane with different performance characteristics than those used in the main pure water production system. Furthermore, due to limitations on the amount of raw water that can be used for evaluation, and the amount of water supplied to the equipment installed downstream of the evaluation system, the recovery rate and flux in the reverse osmosis membrane system are also limited.

[0009] The same applies to UV irradiation equipment used for UV oxidation treatment; it is not always possible to find a small UV irradiation device with the same performance as the UV lamp used in the main pure water production system, and it may be necessary to select a small UV irradiation device with different performance than that used in the main pure water production system. In the main pure water production system, membrane degassing devices and oxidizing agent addition devices may be installed to improve the TOC removal rate in UV oxidation treatment, but installing such devices in the evaluation system would lead to a larger and more complex system, and is not necessarily appropriate. Moreover, the water quality supplied from the reverse osmosis membrane device to the UV irradiation device differs between the main pure water production system and the evaluation system, and this difference in water quality has a significant impact on the water quality of the treated water from UV oxidation treatment.

[0010] Thus, while existing evaluation systems can estimate the behavior of TOC components in treated water (i.e., pure water) obtained from the main pure water production system, they cannot predict detailed TOC concentration values. Patent documents 1 and 2 also do not address the prediction of TOC concentration in pure water obtained from the main pure water production system.

[0011] The above describes the challenges related to predicting water quality in pure water production systems. These challenges are not limited to predicting water quality in pure water production systems. Similar challenges arise when a water treatment system performs some kind of treatment on water to obtain treated water, and an evaluation system is set up in conjunction with that water treatment system to measure the water quality in the evaluation system and evaluate the water quality of the water to be treated supplied to the water treatment system based on these measurement results.

[0012] The object of the present invention is to provide a system and method for predicting the water quality of treated water obtained by a target water treatment system using an evaluation system, which is a smaller water treatment system. [Means for solving the problem]

[0013] The present invention provides a water quality prediction system that predicts the water quality of treated water in a water treatment system when treated water is supplied to a water treatment system equipped with a first water treatment device that performs unit operations on treated water, and the water treatment system is operated based on first operating parameters. The system includes an evaluation system equipped with a second water treatment device that performs unit operations similar to those of the first water treatment device, to which treated water to be supplied to the water treatment system is supplied and which is operated based on second operating parameters, and a calculation means that calculates a predicted value of the solute concentration of treated water in the water treatment system based on the water quality of the treated water, the water quality of the treated water in the evaluation system, first operating parameters, and second operating parameters.

[0014] The present invention provides a water quality prediction method for predicting the water quality of treated water in a water treatment system when water to be treated is supplied to a water treatment system equipped with a first water treatment device that performs unit operations on water to be treated, and the water treatment system is operated based on first operating parameters. The method involves supplying water to be treated to an evaluation system equipped with a second water treatment device that performs unit operations similar to those of the first water treatment device, operating the evaluation system based on second operating parameters, and calculating a predicted value for the solute concentration of the treated water in the water treatment system based on the water quality of the water to be treated, the water quality of the treated water in the evaluation system, the first operating parameters, and the second operating parameters.

[0015] In the present invention, the "second water treatment device that performs the same unit operations as the first water treatment device" means that the types of devices constituting the first water treatment device, which is the target system, and the types of devices constituting the second water treatment device, which is the evaluation system, are the same. If the first water treatment device includes, for example, a reverse osmosis membrane device, an ultraviolet irradiation device, and an ion exchange device in this order as devices for performing unit operations, then the second water treatment device also includes a reverse osmosis membrane device, an ultraviolet irradiation device, and an ion exchange device in this order, even if the models and specifications of the individual devices are different. In the present invention, the solute whose concentration is the prediction target is, for example, a TOC component, but components other than the TOC component, such as boron and ions, can also be used as the solute to be predicted. If TOC is the evaluation target as the solute, the solute permeation coefficient defined in the reverse osmosis membrane at that time is the TOC permeation coefficient.

Advantages of the Invention

[0016] According to the present invention, it becomes possible to accurately predict the water quality of treated water obtained from the target water treatment system using an evaluation system, which is a smaller water treatment system.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram showing an example of the overall configuration including a water quality prediction system and a pure water production system that is the target of water quality prediction. [Figure 2] It is a diagram for explaining water quality prediction in the first embodiment. [Figure 3] It is a diagram for explaining water quality prediction in the second embodiment. [Figure 4] It is a diagram for explaining water quality prediction in the third embodiment. [Figure 5] It is a diagram for explaining water quality prediction in the fourth embodiment. [Figure 6] It is a diagram for explaining water quality prediction in Calculation Examples 1 and 2. [Figure 7] It is a diagram for explaining water quality prediction in Calculation Example 3. [Figure 8] It is a diagram for explaining water quality prediction in Calculation Example 4. [Modes for carrying out the invention]

[0018] Next, embodiments for carrying out the present invention will be described with reference to the drawings. The water quality prediction method according to the present invention involves a water treatment system (referred to as the target system) to which water to be treated is supplied and treated water is produced. An evaluation system is configured as a smaller water treatment system that performs the same processing as the target system, and based on the water quality measurement results of the evaluation system, detailed values ​​of the water quality of the treated water produced in the target system are predicted. More specifically, the water quality prediction method according to the present invention involves supplying water to be treated to a target system equipped with a first processing device that performs unit operations on the water to be treated, and in order to predict the water quality in the target system when the target system is operated based on first operating parameters to obtain treated water, the water to be treated is supplied to an evaluation system equipped with a second processing device that performs the same type of unit operations as those performed in the target system, the evaluation system is operated based on second operating parameters, and the solute concentration in the target system is calculated based on the water quality of the water to be treated, the water quality in the evaluation system, the first operating parameters, and the second operating parameters. The water quality prediction method according to the present invention predicts the water quality of treated water from a target system, and if the predicted value deviates from the target water quality in the target system, the operating parameters of the target system, i.e., the first operating parameters, can be changed so that the water quality of the treated water approaches the target water quality.

[0019] The water treatment system to which the water quality prediction method according to the present invention applies is not particularly limited, but in the following description, the water treatment system will be assumed to be a pure water production system that produces pure water from raw water (water to be treated) and supplies it to a point of use, for example. The water quality to be measured in the evaluation system and to be evaluated in the pure water production system will be the concentration of solutes, which are impurities, more specifically, the concentration of TOC dissolved as a solute in water, which is the solvent. Therefore, in the following, we will describe a case in which, when there is a pure water production system, a water quality prediction system equipped with an evaluation system configured as a pure water production system smaller than the target pure water production system is used, and the detailed value of the TOC concentration of the pure water produced by the target pure water production system is predicted based on the measurement results of the TOC concentration in the evaluation system. Here, "smaller" means that at least one of the devices constituting the evaluation system is smaller than the corresponding device in the target system. If both the target system and the evaluation system are equipped with a reverse osmosis membrane device, an ultraviolet irradiation device, and an ion exchange device in that order, then, for example, if the reverse osmosis membrane device of the evaluation system is smaller than the reverse osmosis membrane device of the target system, then the evaluation system is considered smaller than the target system. Of course, all the devices constituting the evaluation system may be smaller than the corresponding devices in the target system. In the example given here, the reverse osmosis membrane device, ultraviolet irradiation device, and ion exchange device may all be smaller in the evaluation system than in the target system.

[0020] Figure 1 is a diagram illustrating a water quality prediction method according to the present invention, showing an example of the overall configuration of a water quality prediction system 10 and a pure water production system 50, which is a water treatment system to be evaluated. Raw water containing an unknown TOC component is supplied to the water quality prediction system 10 and also to the pure water production system 50 to be evaluated via a valve 11. The pure water production system 50 is a large-scale system configured to supply pure water to a point of use, and includes a tank 51 for temporarily storing raw water, a reverse osmosis membrane device (RO) 52 to which the raw water in the tank 51 is supplied, an ultraviolet irradiation device (UV) 53 to which the permeate water from the reverse osmosis membrane device 52 (RO permeate water) is supplied for ultraviolet oxidation treatment, and an ion exchange device (IER) 54 to which the treated water from the ultraviolet irradiation device 53 is treated for ion exchange treatment, and the treated water from the ion exchange device 54 is supplied to the point of use as pure water. Water that does not permeate the reverse osmosis membrane in the reverse osmosis membrane device 52 (RO concentrated water) is discharged to the outside as is. To increase the TOC removal rate in the UV oxidation treatment, a membrane degasser for degassing RO permeate and a device for adding an oxidizing agent such as hydrogen peroxide may be provided before the UV irradiation device 53, but these devices are not shown in Figure 1. The raw water here may be treated in advance by a device attached to the pure water production system 50. For example, water that has been pretreated by a sand filter, activated carbon treatment device, ion exchange device, or degasser attached to the pure water production system 50 may be branched off and supplied to the evaluation system 10.

[0021] The water quality prediction system 10 includes an evaluation system 20 that receives raw water for evaluation and produces pure water from it. The evaluation system 20 includes a reverse osmosis membrane device (RO) 22 to which raw water is supplied, an ultraviolet irradiation device (UV) 23 to which permeate water (RO permeate) from the reverse osmosis membrane device 22 is supplied and subjected to ultraviolet oxidation treatment, and an ion exchange device (IER) 24 to which the outlet water from the ultraviolet irradiation device 23 is supplied and subjected to ion exchange treatment. The outlet water from the ion exchange device becomes the treated water of the evaluation system 20. The water quality prediction system 10 also includes a measuring instrument 25 for measuring TOC concentration. A portion of the raw water supplied to the evaluation system 20 is branched off and supplied to the measuring instrument 25 via valve 31a, a portion of the RO permeate is branched off and supplied via valve 32a, and a portion of the outlet water from the ion exchange device 24 is supplied via valve 33a. The water quality prediction system 10 can measure the TOC concentration of raw water, RO permeate, and treated water after ion exchange treatment by controlling the opening and closing of valves 31a to 33a. Furthermore, the water quality prediction system 10 is equipped with an evaluation calculation unit 36 ​​that predicts the TOC concentration in the pure water produced by the pure water production system 50 from the raw water, as well as the TOC concentration at various points within the pure water production system 50, based on the measurement results from the measuring instrument 25 and the operating parameters described later. In addition, from the viewpoint of protecting the water quality prediction system and improving prediction accuracy, the raw water may be passed through pretreatment devices such as a heat exchanger, filter, activated carbon treatment device, ion exchange device, and deaeration device before being accepted into the water quality prediction system 10.

[0022] In the configuration shown in Figure 1, the evaluation system 20 within the water quality prediction system 10 and the pure water production system 50 under evaluation are the same in that they treat raw water by passing it through reverse osmosis membrane devices 22, 52, ultraviolet irradiation devices 23, 53, and ion exchange devices 24, 54 in that order to produce pure water. The main difference between the evaluation system 20 and the pure water production system 50 is that the pure water production system 50 is a large-scale system for supplying a large amount of pure water to the point of use, while the evaluation system 20 is a small-scale system equipped with measuring instruments 25 and an evaluation calculation unit 26, and is used to predict the water quality (especially TOC concentration) in the pure water production system 50.

[0023] [First Embodiment] Next, we will explain water quality prediction in the configuration shown in Figure 1. The ultimate goal of water quality prediction is to quickly predict the water quality (especially TOC concentration) of the pure water produced by the pure water production system 50, which is large-scale and has a slow response to fluctuations in the quality of the raw water, from the measurement results of the evaluation system 20. In both the evaluation system 20 and the pure water production system 50, the raw water is passed through the reverse osmosis membrane devices 22, 52, ultraviolet irradiation devices 23, 53, and ion exchange devices 24, 54 in that order, thereby removing the TOC components from the raw water. In the reverse osmosis membrane devices 22, 52, TOC components with large molecular weights or that are electrically charged are removed, and the remaining TOC components are converted into components such as organic acids and carbonic acid by ultraviolet oxidation treatment in the ultraviolet irradiation devices 23, 53, and these components such as organic acids and carbonic acid are removed along with other remaining ionic impurities in the ion exchange devices 24, 54. From the perspective of removing TOC components, the series of processes can be broadly divided into processing in the reverse osmosis membrane devices 22 and 52, and processing in the ultraviolet irradiation devices 23 and 53 and ion exchange devices 24 and 54. The TOC concentration in the pure water ultimately obtained in the pure water production system 50 depends on how much TOC component is removed in each of these processes. In the first embodiment, using Figure 2, we will explain an example of predicting the TOC concentration of the treated water, i.e., RO permeate, from the treated water, i.e., RO permeate, of the reverse osmosis membrane device 22 of the evaluation system 20.

[0024] The configuration of the reverse osmosis membrane apparatus 22 in evaluation system 20 (such as membrane area and number of membrane elements) and the type of reverse osmosis membrane used (membrane type) are known, and the operating conditions (recovery rate and flux) are also known. Here, flux refers to the permeation flux in the reverse osmosis membrane. If the membrane type is known, the water permeation coefficient A2 (unit: m / d / MPa), which is the solvent permeation coefficient specific to that reverse osmosis membrane, is also known. Similarly, the configuration and membrane type of the reverse osmosis membrane apparatus 52 in pure water production system 50 are known, the operating conditions are known, and the water permeation coefficient A1 in the reverse osmosis membrane is also known. Naturally, the operating conditions can be set as appropriate. In evaluation system 20, the TOC concentration of the inlet water, i.e., the raw water, and the TOC concentration of the RO permeate water are also known by measurement using the measuring instrument 25. On the other hand, in the pure water production system 50, the reverse osmosis membrane device 52 is supplied with the same raw water as the evaluation system 20, so the TOC concentration of the inlet water of the reverse osmosis membrane device 52 is known. What we want to determine in this embodiment is the TOC concentration of the RO permeate (treated water) from the reverse osmosis membrane device 52 of the pure water production system 50. This TOC concentration is the TOC concentration derived from an unknown TOC component contained in the raw water. Membrane type, membrane area, number of membrane elements, operating conditions, water permeability coefficient, etc., are collectively called the operating parameters of the reverse osmosis membrane device.

[0025] First, the TOC permeation coefficient B2 (unit: m / d), which is the permeation coefficient (solute permeation coefficient) of the TOC component in the reverse osmosis membrane of the reverse osmosis membrane apparatus 22 of the evaluation system 20, is determined. The TOC permeation coefficient B2 can be calculated from the TOC concentration on both sides of the reverse osmosis membrane (i.e., the TOC concentration in the inlet water and the RO permeate) and the flux by membrane transport parameter calculation using a concentration polarization model, as described in, for example, Patent Documents 3 and 4. Next, assuming that the TOC permeation coefficient B2 in the reverse osmosis membrane apparatus 22 of the evaluation system 20 and the TOC permeation coefficient B1 in the reverse osmosis membrane apparatus 52 of the pure water production system 50 are the same, the TOC concentration of the RO permeate from the reverse osmosis membrane apparatus 52 of the pure water production system 50 is calculated from the TOC concentration of the inlet water, membrane area, recovery rate, and flux of the pure water production system 50. If the reverse osmosis membrane used in the pure water production system and the reverse osmosis membrane used in the evaluation system 20 have equivalent membrane performance, it is reasonable to assume that the TOC permeation coefficients B1 and B2 of both membranes are the same for the unknown TOC component to be predicted. This allows the TOC concentration in the RO permeate from the reverse osmosis membrane device 52 of the pure water production system 50 to be predicted from the measurements taken in the evaluation system 20. In this embodiment, parameters due to the mechanical structure of the reverse osmosis membrane devices 22 and 52 may be further considered.

[0026] In the water quality prediction system shown in Figure 1, the evaluation calculation unit 26 is pre-configured with the operating parameters of the reverse osmosis membrane device 22 of the evaluation system 20 and the operating parameters of the pure water production system 50. When the evaluation calculation unit 26 receives measured values ​​of the TOC concentration of the raw water and the TOC concentration of the RO permeate from the reverse osmosis membrane device 22 from the measuring instrument 25, it calculates and outputs a predicted value of the TOC concentration in the RO permeate from the reverse osmosis membrane device 52 of the pure water production system 50 as described above.

[0027] [Second Embodiment] The water quality prediction method of the second embodiment will be explained using Figure 3. When the reverse osmosis membrane apparatus 52 of the pure water production system 50 and the reverse osmosis membrane apparatus 22 of the evaluation system 20 use different membrane types, especially when the physical or chemical properties of the reverse osmosis membranes differ significantly, the assumption that the TOC permeability coefficient B1 in the reverse osmosis membrane apparatus 52 and the TOC permeability coefficient B2 in the reverse osmosis membrane apparatus 22 are the same no longer holds. Figure 3 is a diagram illustrating the water quality prediction method in such a case. When the membrane types are different, a conversion coefficient c for the membrane type used in the evaluation system 20 is determined for each membrane type that may be used in the pure water production system 50, and these conversion coefficients c are stored in advance in the form of a conversion table 41 (see Figure 3) in a database provided in the evaluation calculation unit 26. Then, after determining the TOC permeation coefficient B2 in the evaluation system 20, the calculation B1 = c·B2 is performed to determine the TOC permeation coefficient B1 in the pure water production system 50. After that, by performing the same procedure as in the first embodiment, the TOC concentration in the RO permeate from the reverse osmosis membrane device 52 of the pure water production system 50 can be predicted. In this embodiment, when the combination of membrane types used in the evaluation system 20 and the membrane types used in the pure water production system 50 is input, the evaluation calculation unit 26 searches the built-in conversion table 41 to read the corresponding conversion coefficient c, and uses the conversion coefficient c to perform a prediction calculation of the TOC concentration of the RO permeate from the pure water production system 50. Since the first embodiment described above is equivalent to the case where c=1 in the second embodiment, if c=1 is specified in the conversion table 41 when the same membrane type is used in the evaluation system 20 and the pure water production system 50, it becomes possible to perform water quality prediction based on the second embodiment in a form that encompasses the first embodiment.

[0028] In the second embodiment, the conversion factor c for each film type can be determined, for example, by measuring the TOC permeability coefficient for each film type using known TOC components and determining the result based on the measurement. As known TOC components for determining the TOC permeability coefficient, low molecular weight organic substances with a molecular weight of about 100 or less, such as isopropyl alcohol, urea, and ethanol, can be used. Instead of these low molecular weight organic substances, boron compounds such as boric acid, although not strictly organic substances, can also be used.

[0029] [Third Embodiment] In the second embodiment, a conversion factor c was determined for each membrane type, or more precisely, for each combination of membrane types used in the pure water production system 50 and the evaluation system 20. The TOC permeation coefficient B2 obtained in the reverse osmosis membrane apparatus 22 of the evaluation system 20 was linked to the TOC permeation coefficient B1 in the reverse osmosis membrane apparatus 52 of the pure water production system 50 via the conversion factor c. However, when the performance of the reverse osmosis membrane changes from its initial performance, for example, when the reverse osmosis membrane deteriorates or becomes blocked, it may become inappropriate to apply the conversion factor c predetermined for each membrane type. Furthermore, if the membrane type of the reverse osmosis membrane used in the pure water production system 50 is unknown, it is impossible to know the conversion factor c in the first place. Here, the case where the performance of the reverse osmosis membrane changes from its initial performance is included in the case where the membrane type is unknown. In the third embodiment, the TOC concentration of RO permeate is predicted when it is inappropriate or impossible to use the existing conversion factor c. Figure 4 is a diagram illustrating the process of the third embodiment. The third embodiment is no different from the second embodiment in that it uses the TOC removal rate B1 in the reverse osmosis membrane apparatus 52 of the pure water production system 50, which is obtained by multiplying the TOC removal rate B2 in the reverse osmosis membrane apparatus 22 of the evaluation system 20 by a conversion factor c. The difference between the third embodiment and the second embodiment is that the value of the conversion factor c is estimated.

[0030] In the third embodiment, first, the water permeability coefficient A1 in the reverse osmosis membrane apparatus 52 of the pure water production system 50 is calculated. When the membrane type is unknown, of course, but also when deterioration or blockage of the reverse osmosis membrane occurs, the water permeability coefficient A1 itself will change, so it is necessary to calculate the water permeability coefficient A1. The water permeability coefficient A1 can be determined using operating parameters of the reverse osmosis membrane apparatus 52, such as flux, as well as the conductivity and pressure of the inlet water, RO permeate, and RO concentrated water, respectively. Once the water permeability coefficient A1 is calculated, the ratio of this water permeability coefficient A1 to the water permeability coefficient A2 in the evaluation system 20 (A1 / A2) is determined, a conversion factor c is determined based on the ratio (A1 / A2), and the TOC concentration of the RO permeate in the pure water production system 50 is calculated using the determined conversion factor c. According to the inventors' findings, when there are two types of reverse osmosis membranes, there is a correlation between the ratio of water permeability coefficients (A1 / A2) and the ratio of TOC permeability coefficients (B1 / B2), i.e., the conversion factor c, between those membranes. Therefore, this correlation is determined in advance and stored in a database provided in the evaluation calculation unit 26 of the water quality prediction system 10. In the third embodiment, instead of the membrane type, the water permeability coefficient A1 measured for the reverse osmosis membrane device 52 of the pure water production system 50 is input to the evaluation calculation unit 26. The evaluation calculation unit 26 then calculates the ratio (A1 / A2) of the water permeability coefficients mentioned above, applies this ratio (A1 / A2) to the correlation relationship stored in advance to obtain a conversion coefficient c, and then calculates the TOC concentration of RO permeate water in the pure water production system 50 in the same manner as in the second embodiment.

[0031] In Figure 4, graph 62 shows an example of the correlation between the ratio of water permeability coefficients (A1 / A2) and the conversion factor c. This correlation is determined by prior experiments. For example, the correlation can be determined by passing water containing an indicator substance as a TOC component through the reverse osmosis membrane 22 of the evaluation system 20 and multiple reverse osmosis membrane elements equipped with reverse osmosis membranes having different TOC permeability coefficients than those in the evaluation system 22, and then determining the TOC permeability coefficients. As the indicator substance, low-molecular-weight organic substances with a molecular weight of about 100 or less are preferably used.

[0032] [Fourth Embodiment] The first to third embodiments predict the TOC concentration in RO permeate discharged from the reverse osmosis membrane device 52 of the pure water production system 50. In order to predict the TOC concentration in the pure water ultimately obtained from the pure water production system 50, it is necessary to estimate the TOC removal rate in the ultraviolet oxidation treatment and subsequent ion exchange treatment to which the RO treated water is supplied, and then apply the TOC removal rate to the TOC concentration in the RO permeate to calculate the final TOC concentration. The fourth embodiment concerns treating the ultraviolet oxidation treatment and the ion exchange treatment as a single treatment (ultraviolet oxidation / ion exchange treatment) and predicting the TOC removal rate therein. Figure 5 is a diagram illustrating the fourth embodiment.

[0033] Regarding the ultraviolet oxidation / ion exchange treatment, the operating parameters for the evaluation system 20 include the type and specifications of the ultraviolet (UV) lamp used in the ultraviolet irradiation device 23, the amount of ultraviolet irradiation, the dissolved oxygen (DO) concentration in the inlet water, the concentration of the oxidizing agent in the inlet water after the addition of the oxidizing agent (if such as hydrogen peroxide is added to the inlet water), the brand of the ion exchange resin (IER) used in the ion exchange device 24, and the space velocity (SV) of the water flowing through the ion exchange resin. Other items may also be included as operating parameters. For example, the dissolved carbon dioxide (CO2) concentration in the inlet water may be included as an operating parameter. If multiple ion exchange resins are mixed and used in the ion exchange device 24, their mixing ratio will also be included as an operating parameter. The inlet water referred to here is the RO permeate from the preceding reverse osmosis membrane device 22, which is supplied to the ultraviolet irradiation device 23. The outlet water of the ultraviolet oxidation / ion exchange treatment is the treated water (pure water) from the ion exchange device 24. In the fourth embodiment, first, the TOC removal rate for an unknown TOC component originating from the raw water in the UV oxidation / ion exchange treatment is calculated from the TOC concentration of the inlet water and the TOC concentration of the outlet water in the UV oxidation / ion exchange treatment of the evaluation system 20.

[0034] By performing the methods described in the first to third embodiments, a predicted value for the TOC concentration in the RO permeate from the reverse osmosis membrane device 52 in the pure water production system 50 is obtained. Then, the TOC removal rate obtained in the UV oxidation / ion exchange treatment in the evaluation system 20 is applied to this predicted value for the TOC concentration of the RO permeate to predict the TOC concentration of the treated water (pure water) from the UV oxidation / ion exchange treatment in the pure water production system 50. At this time, considering the differences in configuration between the evaluation system 20 and the pure water production system 50, the TOC removal rate used is corrected, for example, as follows: (1) For example, if the UV lamps are from different manufacturers or have different model numbers and therefore have different UV irradiation efficiencies, obtain a correction factor for the irradiation efficiency of each lamp in advance and multiply the TOC removal rate by that correction factor; (2) Generally, the removal efficiency of TOC in UV oxidation / ion exchange treatment tends to decrease as the TOC concentration in the inlet water increases. Therefore, if the predicted TOC concentration in the RO permeate from the pure water production system 50 is higher than the measured TOC concentration in the RO permeate from the evaluation system 20, the TOC removal rate should be revised downward. (3) Since it is known that the removal efficiency of TOC in ultraviolet oxidation / ion exchange treatment changes depending on the dissolved oxygen concentration, a correction factor between the dissolved oxygen concentration and the removal efficiency is obtained in advance, and if the dissolved oxygen concentration differs between the evaluation system 20 and the pure water production system 50, the TOC removal rate is multiplied by a correction factor corresponding to the difference in dissolved oxygen concentration; (4) Since it is known that the removal efficiency of TOC in the UV oxidation / ion exchange treatment changes depending on the oxidizing agent concentration, a correction coefficient between the oxidizing agent concentration and the removal efficiency is obtained in advance, and if the oxidizing agent concentration differs between the evaluation system 20 and the pure water production system 50, the TOC removal rate is multiplied by a correction coefficient corresponding to the difference in oxidizing agent concentration.

[0035] In the water quality prediction system 10, the evaluation calculation unit 26 calculates the TOC removal rate of the ultraviolet oxidation / ion exchange treatment in the evaluation system 20 based on the measurement results from the measuring instrument 25, calculates a predicted value of the TOC concentration in the RO permeate water of the reverse osmosis membrane device 52 of the pure water production system 50 using the method described in the first to third embodiments, and applies the thus calculated TOC removal rate to the predicted value of the TOC concentration in the treated water (pure water) of the pure water production system 50 after correcting it as described above. Note that, including the case where reverse osmosis membrane devices 22 and 52 are not provided, if the water quality of the inlet water of the ultraviolet irradiation device 23 of the evaluation system 20 and the water quality of the inlet water of the ultraviolet irradiation device 53 of the pure water production system 50 are considered to be equivalent, it is not necessary to perform the correction for RO permeate water as shown in the first to third embodiments. Alternatively, instead of using the predicted TOC concentration for the RO permeate from the reverse osmosis membrane device 52 of the pure water production system 50, the treated water quality of the ion exchange device 54 of the evaluation system 20 may be calculated from the water quality of the treated water from the ion exchange device 24 of the evaluation system 20, the first operating parameter, and the second operating parameter.

[0036] In the above explanation, an ion exchange device filled with ion exchange resin (IER) is used for ion exchange treatment. However, in both the evaluation system 20 and the pure water production system 50, an electrodeionized water generator (EDI) may be used instead of an ion exchange device. With conventional ion exchange devices, prolonged use can cause breakthrough of the ion exchange resin, leading to a decrease in water quality, requiring replacement of the ion exchange device or regeneration of the ion exchange resin. However, with an electrodeionized water generator, the ion exchange treatment and the regeneration of the ion exchange material proceed simultaneously, eliminating the risk of water quality deterioration. Furthermore, while it was explained that the pure water production system 50 may be equipped with a membrane degasser in addition to the reverse osmosis membrane device 52, ultraviolet irradiation device 53, and ion exchange device 54, in the evaluation system 20, a membrane degasser or electrodeionized water generator may also be placed before the ultraviolet irradiation device 23 to reduce the dissolved oxygen and dissolved carbon dioxide concentrations in the inlet water for ultraviolet oxidation treatment. By sufficiently lowering the dissolved oxygen and dissolved carbon dioxide concentrations in the inlet water for ultraviolet oxidation treatment, the accuracy of predicting the TOC concentration in the treated water of the pure water production system 50 can be improved.

[0037] The water quality prediction system and method based on the present invention can be suitably used in the production of pure water and ultrapure water, and can also be used in wastewater recovery systems that recover and use various types of wastewater generated from factories as non-potable water or equipment water after desalination treatment and TOC component removal treatment. By applying the present invention, it becomes possible to evaluate fluctuations in treated water quality early in wastewater recovery systems where water quality fluctuates depending on the type and amount of wastewater being collected. Furthermore, the water treatment system to which the present invention is applied does not necessarily need to be equipped with all of the reverse osmosis membrane device, ultraviolet irradiation device and ion exchange device, and may be equipped with only some of these devices. Moreover, it may not be equipped with any of these devices at all, but may be equipped with other devices that perform some kind of treatment (i.e., unit operation) on the water to be treated. In short, the water treatment system to which the present invention is applied only needs to be equipped with one or more of the following devices: reverse osmosis membrane device, ultraviolet irradiation device, ion exchange device, degasser, activated carbon device, distillation device, etc.

[0038] For example, if the pure water production system 50, which is a water treatment system, is equipped only with a reverse osmosis membrane device 52 and does not have an ultraviolet irradiation device 53 or an ion exchange device 54, then the evaluation system 20 will also be equipped only with a reverse osmosis membrane device 22. By applying any of the first to third embodiments described above, the TOC concentration in the permeate (i.e., treated water) from the reverse osmosis membrane device 52 of the pure water production system 50 can be predicted. Also, if the pure water production system 50, which is a water treatment system, is equipped with an ultraviolet irradiation device 53 and an ion exchange device 54 provided thereafter, but does not have a reverse osmosis membrane device 52, then the evaluation system 20 will also be composed of an ultraviolet irradiation device 23 and an ion exchange device 24 provided thereafter. In this case, in the fourth embodiment, the water supplied to the ultraviolet irradiation devices 23 and 53 is treated as raw water, and by measuring the water quality of the raw water, the TOC concentration in the outlet water (i.e., treated water) from the ion exchange device 54 of the pure water production system 50 can be predicted even if the reverse osmosis membrane devices 22 and 52 are not provided.

[0039] In each of the embodiments described above, the water quality evaluation system 10 was used to predict the water quality of the treated water of the pure water production system 50 under evaluation. Such water quality prediction is usually performed to maintain the water quality of the treated water of the pure water production system 50 within a desired range. Therefore, when the predicted water quality for the pure water production system 50 deviates from the target water quality of the pure water production system 50, the operations to be performed on each operating parameter of the pure water production system 50 will be described. For example, if the predicted value of the TOC concentration of the treated water of the reverse osmosis membrane device 52 of the pure water production system 50 is higher than the target value, i.e., the water quality is poor, the recovery rate of the reverse osmosis membrane device 52 can be reduced or the supply water temperature can be lowered to bring the predicted TOC concentration of the treated water of the reverse osmosis membrane device 52 closer to the target value. Conversely, if the predicted value of the TOC concentration of the treated water of the reverse osmosis membrane device 52 is lower than the target value, the recovery rate can be increased or the degree of cooling of the supplied water can be reduced to save energy.

[0040] Similarly, if the predicted TOC concentration of the treated water from the ultraviolet irradiation device 53 of the pure water production system 50 is also high compared to the target value, the amount of ultraviolet irradiation in the ultraviolet irradiation device 53 can be increased, the dissolved oxygen concentration of the water supplied to the ultraviolet irradiation device 53 can be reduced, the concentration of the oxidizing agent added to the water can be increased, the recovery rate in the preceding reverse osmosis membrane device 52 can be reduced, or the temperature of the water supplied to the preceding reverse osmosis membrane device 52 can be reduced to bring the predicted TOC concentration of the treated water from the ultraviolet irradiation device 53 closer to the target value. Conversely, if the predicted TOC concentration of the treated water from the ultraviolet irradiation device 53 is lower than the target value, the operating parameters can be adjusted to increase the TOC concentration in order to save energy. [Examples]

[0041] Next, the present invention will be explained in more detail with actual calculation examples. In the following description, the supply flow rate, concentrated water volume, and permeate volume of the feed water (inlet water) of the reverse osmosis membrane apparatus are denoted by Qf, Qc, and Qp, respectively. Similarly, the concentrations of solute (in this case, TOC component) in the feed water, concentrated water, and permeate of the reverse osmosis membrane apparatus are denoted by Cf, Cc, and Cp, respectively. The flux of the solvent (in this case, water) in the reverse osmosis membrane apparatus is denoted by Jv, the solute permeation coefficient by P, and the solvent permeation coefficient by Lp. Assuming that a concentration polarization model is applied to the reverse osmosis membrane as shown in Patent Documents 3 and 4, the solute concentration at the feed side membrane surface of the reverse osmosis membrane is denoted by Cm. Re, Sc, and Sh are the Reynolds number, Schmidt number, and Sherwood number, respectively. Let ρ be the density of the liquid, η be the viscosity coefficient, d be the channel thickness, u be the flow velocity, D be the solute diffusion coefficient, and k be the mass transfer coefficient across the membrane. Re=ρ·u·d / η Sc = η / (ρ·D) Sh = k·d / D It is represented as follows.

[0042] [Calculation example 1] A calculation example corresponding to the first embodiment will be described. Pure water is produced by supplying raw water containing an unknown TOC component as a solute to the evaluation system 20 and the pure water production system 50, respectively. Figure 6 illustrates the calculation in Calculation Example 1, where (a) shows the flow rate and concentration in the reverse osmosis membrane device 22 of the evaluation system 20, (b) shows the configuration of the reverse osmosis membrane device 52 of the pure water production system 50, and (c) shows another calculation example of the concentration in the reverse osmosis membrane device 52 of the pure water production system 50. The reverse osmosis membrane device 22 of the evaluation system 20 was equipped with one 4-inch element, Nitto Denko ESPA2-4021. The membrane area was 3.5 m². 2 This system was operated under conditions of a 50% recovery rate and a flux Jv of 0.82 m / d. The water supply rate Qf to the reverse osmosis membrane apparatus 22 was 240 L / h, the concentrated water rate Qc was 120 L / h, and the permeate rate Qp was also 120 L / h. The solute concentrations Cf of the supply water, concentrated water, and permeate in the reverse osmosis membrane apparatus 22 were 40 ppb, 72 ppb, and 8 ppb, respectively, as TOC concentrations.

[0043] First, the solute (TOC) concentration Cm at the membrane surface is calculated. This calculation requires the mass transfer coefficient k, which can be calculated from the Sherwood number Sh, the channel thickness d, and the solute diffusion constant D. Regarding the Sherwood number Sh, Deisler's equation is known, using the Reynolds number Re and the Schmidt number Sc, and assuming α, β, and γ are experimentally determined constants. Sh=α×Re β ·Sc γ This can be done. Also, as described in Patent Document 3, (Cm-Cp) / (Cf-Cp)=exp(Jv / k) (1) The following holds true. As mentioned above, since the concentrations Cf, Cc, and Cp are known, the solute concentration Cm on the membrane surface can be determined. And, Jv·Cp=P(Cm-Cp) (2) Since the relationship holds, the solute permeation coefficient P (i.e., the TOC permeation coefficient B2) was calculated using equations (1) and (2), and the result was P = 5.32 × 10 -7 m / d was obtained.

[0044] The reverse osmosis membrane apparatus 52 of the pure water production system 50 was equipped with eight 8-inch elements, Nitto Denko ES20-D8, and as shown in Figure 6(b), two parallel systems of four membrane elements connected in a cascade were used. The membrane area was 37 m². 2 The reverse osmosis membrane apparatus 52 was operated with a recovery rate of 90% and a flux Jv of 0.72 m / d. The water supply volume Qf of the reverse osmosis membrane apparatus 52 was 10 m 3 / h, concentrated water volume Qc is 1m 3 / h, permeation rate 9m 3 It was / h. The solute concentration Cf of the supply water was the same as in evaluation system 22, and the TOC concentration was 40 ppb. The reverse osmosis membrane used in evaluation system 20 and the reverse osmosis membrane used in pure water production system 50 have almost the same membrane performance. In this case, the solute permeability coefficient P (i.e., TOC permeability coefficient B2) obtained in evaluation system 20 for the unknown TOC component contained in the raw water can be used directly in the concentration calculation for the aforementioned unknown TOC component in pure water production system 50. Combining the above equations (1) and (2), Jv·Cp / P=(Cf-Cp)·exp(Jv / k) (3) The mass transfer coefficient k was determined in the same way as in the evaluation system 20, and the solute concentration Cp was calculated from the known values ​​Jv, P, and Cf, and Cp was found to be 6.5 ppb. In other words, 6.5 ppb was obtained as the predicted value of the TOC concentration of the RO permeate water from the reverse osmosis membrane device 52 of the pure water production system 50.

[0045] The above calculation example is an example in which the calculation was performed by treating the eight membrane elements of the reverse osmosis membrane device 52 of the pure water production system 50 as one unit. However, as shown in Fig. 6(c), the above calculation can be performed for each membrane element, and the calculation results can be reflected in the calculation for the next-stage membrane element. Using the subscript n for the nth-stage membrane element, first, when calculating for the first-stage membrane element as described above, the solute concentrations Cp1 and Cc1 in the permeated water and the concentrated water of the first-stage membrane element are calculated respectively. Since the concentrated water of the first-stage element is supplied to the second-stage membrane element, the relationships Qc1 = Qf2 and Cc1 = Cf2 hold. Calculation can be performed in this way up to the final-stage membrane element. From the permeated water volume and quality of each stage, the flow rate and quality when the permeated water of each stage is combined can be calculated.

[0046] [Calculation Example 2] In the case of the second embodiment, that is, a calculation example will be described when the membrane performance is different between the reverse osmosis membrane used in the evaluation system 20 and the reverse osmosis membrane used in the pure water production system 50, and the solute permeation coefficient (TOC permeation coefficient) cannot be directly applied. The same evaluation system 20 as in Calculation Example 1 was operated under the same operating conditions. Therefore, the solute permeation coefficient P (i.e., the TOC permeation coefficient B2) in the evaluation system 20 for the unknown TOC components contained in the raw water is 5.32×10 -7 m / d. On the other hand, as the reverse osmosis membrane device 52 of the pure water production system 50, although it is the same as in Calculation Example 1 in that eight membrane elements are connected as shown in Fig. 6(b), a different one was used in that the CPA5-LD manufactured by Nitto Denko, which is an 8-inch element, was used for each membrane element. The membrane area is 37 m 2 and the reverse osmosis membrane device 52 was operated with a recovery rate of 90% and a flux Jv of 0.72 m / d.

[0047] Let P1 and P2 be the solute permeation coefficients for the pure water production system 50 and the evaluation system 20, respectively. This calculation example is for cases where the solute permeation coefficient P2 (i.e., TOC permeation coefficient B2) cannot be directly used as the solute permeation coefficient P1 (i.e., TOC permeation coefficient B1). In such cases, the solute permeation coefficient for a simulated substance, which is a known TOC component, is measured in advance for each reverse osmosis membrane. For example, isopropyl alcohol can be used as the simulated substance. Sample water containing isopropyl alcohol at a TOC concentration of, for example, 100 ppb-C is passed through each reverse osmosis membrane under similar conditions, for example, a flux of 0.6 m / d and a recovery rate of 15%, and the IPA concentration of the RO permeate is measured. Then, for each reverse osmosis membrane, the solute permeation coefficients P1 and P2 are calculated using the same procedure as described in Calculation Example 1. Since the conversion factor c explained in the second embodiment is expressed as c = P1 / P2, by performing the calculation with P1 = c·P2, the predicted value of the TOC concentration in the RO permeate water from the reverse osmosis membrane device 52 of the pure water production system 50 can be calculated.

[0048] [Calculation example 3] A calculation example corresponding to the third embodiment will be described. Figure 7 illustrates the calculation in Calculation Example 3, where (a) shows the pressure, flow rate, and concentration in the reverse osmosis membrane apparatus 22 of the evaluation system 20, (b) shows the configuration, pressure, flow rate, and concentration of the reverse osmosis membrane apparatus 52 of the pure water production system 50, and (c) shows an example of the correlation between the solvent permeability coefficient and the solute permeability coefficient. Calculation Example 3 describes a calculation for estimating the TOC concentration of RO permeate when the membrane type of the reverse osmosis membrane in the reverse osmosis membrane apparatus 52 of the pure water production system 50 is unknown. The evaluation system 20 was the same as in Calculation Example 1 and operated under the same operating conditions. Therefore, the solute permeability coefficient P (i.e., TOC permeability coefficient B2) in the evaluation system 20 is 5.32 × 10⁻⁶. -7 The ratio is m / d. As shown in Figure 7(a), the supply pressure Pf to the reverse osmosis membrane apparatus 22 of the evaluation system 20 was 0.8 MPa, the pressure Pc at the concentrated water outlet was 0.78 MPa, and the pressure at the permeate water outlet was 0 MPa. If the pressure difference is ΔP and the osmotic pressure with respect to the solute concentration C is π(C), then, as described in Patent Document 3, Jv = Lp[ΔP - π(Cm) - π(Cp)] (4) The following holds true. In dilute systems, Cp=0 may be treated as such for calculations. The solvent permeability coefficient Lp2 (water permeability coefficient A2) in the evaluation system 20 is calculated using equation (4).

[0049] On the other hand, the reverse osmosis membrane apparatus 52 of the pure water production system 50, as shown in Figure 7(b), is equipped with eight 8-inch membrane elements, and as shown in Figure 7(b), two systems of four membrane elements connected in a cascade are provided in parallel. The membrane area is 37 m². 3 It is known that this is the case, but the type of membrane element is unknown. This reverse osmosis membrane apparatus 52 was operated under operating conditions of a recovery rate of 90% and a flux Jv of 0.72 m / d. At this time, the water supply Qf of the reverse osmosis membrane apparatus 52 was 10 m 3 The supply pressure Pf is 0.95 MPa and the concentrated water volume Qc is 1 m³ / h. 3 The pressure Pc is 0.9 MPa and the permeate Qp is 9 m 3 The flow rate was / h and the pressure Pp was 0.3 MPa. The solute concentration (TOC concentration) Cf in the feedwater was 40 ppb, the same as in evaluation system 20. For the pure water production system 50, the solvent permeability coefficient Lp1 (water permeability coefficient A1) was also calculated using equation (4).

[0050] To calculate the TOC concentration of RO permeate from the pure water production system 50, it is necessary to know the solute permeation coefficient (TOC permeation coefficient). However, in this calculation example, the membrane type is unknown, and therefore the solute permeation coefficient is also unknown. Therefore, the correlation between the solvent permeation coefficient Lp (water permeation coefficient) and the solute permeation coefficient P (TOC permeation coefficient) is determined in advance. The solvent permeation coefficient Lp1 of the pure water production system 50 is applied to this correlation to determine the solute permeation coefficient P1 (TOC permeation coefficient B1) in the pure water production system 50. Then, by performing calculations similar to those in Calculation Example 1, the predicted value of the TOC concentration in the RO permeate from the reverse osmosis membrane device 52 can be calculated. The correlation between the solvent permeation coefficient Lp and the solute permeation coefficient P can be determined for various types of reverse osmosis membranes by passing a sample water containing a simulated substance through the reverse osmosis membrane and calculating the solvent permeation coefficient Lp and solute permeation coefficient P at that time. Specifically, isopropyl alcohol is used as a simulated substance, and sample water containing isopropyl alcohol at a TOC concentration of, for example, 100 ppb-C is passed through each reverse osmosis membrane under similar conditions, for example, with a flux of 0.6 m / d and a recovery rate of 15%. Figure 7(c) shows a correlation diagram 43 plotting the calculated solvent permeability coefficient Lp and solute permeability coefficient P. This correlation diagram 43 shows the correlation between the solvent permeability coefficient Lp and the solute permeability coefficient P. The relationship between the solvent permeability coefficient Lp and the solute permeability coefficient P is not necessarily linear, but there is a relationship in which the solute permeability coefficient P decreases as the solvent permeability coefficient Lp decreases.

[0051] [Calculation example 4] A calculation example corresponding to the fourth embodiment will be described. Figure 8 illustrates the calculation in Calculation Example 1, where (a) shows the ultraviolet irradiation device 23 and ion exchange device 24 of the evaluation system 20, (b) shows the ultraviolet irradiation device 53 and ion exchange device 54 of the pure water production system 50, (c) shows the relationship between ultraviolet (UV) irradiation amount and TOC removal rate, and (d) shows the effect of dissolved carbon dioxide (CO2) concentration, dissolved oxygen (DO) concentration, ion concentration and TOC concentration on the TOC removal rate. The ultraviolet irradiation device 23 of the evaluation system 20 is an evaluation ultraviolet irradiation device, and the ultraviolet irradiation amount is 0.1 kWh / m 3The ion exchange device 24 used an Organo cartridge polisher ESP-2, and its space velocity (SV) of water flow was 50h -1 The dissolved amino acid (CO2) concentration in the inlet water of the ultraviolet irradiation device 23 (RO permeate from the preceding reverse osmosis membrane device 22) was 5 ppm, the dissolved oxygen (DO) concentration was 8 ppm, the total dissolved solids (TDS) was 2 ppm, and the TOC concentration was 8 ppb-C. In addition, the TOC concentration in the treated water (pure water) of the ion exchange device 24 was 4.0 ppb-C, and the TOC removal rate R was calculated to be 50%. The TOC concentration here refers to an unknown TOC component originating from the raw water.

[0052] The ultraviolet irradiation device 53 of the pure water production system 50 uses JPW manufactured by Nippon Photo Science, and the ultraviolet irradiation dose is 0.1 kWh / m². 3 The ion exchange device 54 used an Organo cartridge polisher ESP-2, and its spatial velocity (SV) of water flow was 50h -1 In this example, the RO permeate discharged from the reverse osmosis membrane device 52 in calculation example 1 is supplied to the ultraviolet irradiation device 53, so the TOC concentration value (predicted value) at the inlet water of the ultraviolet irradiation device 53 is 6.5 ppb-C. The objective of calculation example 4 is to predict the TOC concentration of an unknown TOC component originating from the raw water in the treated water (pure water) of the ion exchange device 54 of the pure water production system 50.

[0053] In the example shown here, although the UV irradiation dose is the same for the evaluation system 20 and the pure water production system 50, the models of the UV irradiation devices are different. As a result, the TOC removal efficiency in relation to the UV irradiation dose also differs, and the TOC removal rate R2 of 50% calculated for the evaluation system 20 cannot be directly applied to the pure water production system 50. Therefore, a correction is made to the TOC removal rate based on the difference in UV irradiation devices. The relationship between the UV irradiation dose and the TOC removal chamber is determined by passing sample water containing a simulated substance that is a TOC component through the UV irradiation devices 23 and 53 of the evaluation system 20 and the pure water production system 50, respectively, while varying the UV irradiation dose. For example, for sample water containing 10 ppb-C of isopropyl alcohol as a simulated substance, 0.1~1 kWh / m³ 3 The ultraviolet oxidation treatment is performed while varying the amount of ultraviolet irradiation within the specified range. Figure 8(c) shows the relationship between the amount of ultraviolet irradiation obtained in this way and the TOC removal rate. The graph of TOC removal rate R1 was obtained for the pure water production system 50, and the graph of TOC removal rate R2 was obtained for the evaluation system 20. The ratio of the TOC removal rates R1 and R2 for the simulated substance obtained in this way (R1 / R2) is used as a correction factor, and by multiplying the TOC removal rate R2, which was previously determined for the evaluation system 20, by this correction factor, the TOC removal rate R1' for the unknown TOC component originating from the raw water can be determined. In the example shown here, the TOC removal rate R1' is 75%, and the TOC concentration in the treated water of the pure water production system 50 is predicted to be 1.6 ppb.

[0054] While we have explained an example of correcting the TOC removal rate based on differences in the configuration of the ultraviolet irradiation device, it is known that the TOC removal rate in ultraviolet oxidation / ion exchange treatment is also affected by the concentrations of each component in the raw water, such as dissolved carbon dioxide (CO2 concentration), dissolved oxygen (DO) concentration, ionic impurity concentration, and TOC concentration. Therefore, similar to correcting the TOC removal rate based on the configuration of the ultraviolet irradiation device, it is preferable to keep the amount of ultraviolet irradiation the same for each concentration item, determine the relationship between the concentration and the TOC removal rate R in advance using a simulated substance, and then correct the TOC removal rate used for the pure water production system 50 based on the obtained relationship. Figure 8(d) shows an example of the relationship between the concentration and the TOC removal rate for each concentration item obtained in this way. As an example, to explain the correction of the TOC removal rate due to the dissolved carbon dioxide concentration, suppose the dissolved carbon dioxide concentration in the pure water production system 50 is 1 ppm and the dissolved carbon dioxide concentration in the evaluation system 20 is 10 ppm. From the graph of dissolved carbon dioxide concentration and TOC removal rate (for a simulated substance) shown in Figure 8(d), the TOC removal rate Rα for 1 ppm and the TOC removal rate Rβ for 10 ppm are determined. Rα / Rβ is used as a correction coefficient for dissolved carbon dioxide concentration, and the TOC removal rate R1' after correction for the ultraviolet irradiation device is further multiplied by this correction coefficient to obtain the TOC removal rate R1''. Using this TOC removal rate R1'', the TOC concentration in the treated water of the pure water production system 50 can be predicted, taking into account the difference in dissolved carbon dioxide concentration. Here, the correction coefficient was calculated based only on the dissolved carbon dioxide concentration, but one or more of multiple concentration items such as dissolved carbon dioxide, dissolved oxygen concentration, ionic impurity concentration, and TOC concentration can be used to calculate the correction coefficient. [Explanation of symbols]

[0055] 10 Water Quality Prediction Systems 20 Evaluation System 22,52 Reverse osmosis membrane device (RO) 23,53 Ultraviolet irradiation device (UV) 24,54 Ion exchange equipment (IER) 25 Measuring Instruments 26 Evaluation Calculation Unit 50 Pure Water Production Systems 51 Raw water tank

Claims

1. A water quality prediction system that predicts the water quality of treated water in a water treatment system when water to be treated is supplied to a water treatment system equipped with a first water treatment device that performs unit operations on water to be treated, and the water treatment system is operated based on first operating parameters, An evaluation system comprising a second water treatment apparatus that performs unit operations similar to those of the first water treatment apparatus, to which water to be treated is supplied to the water treatment system, and which is operated based on second operating parameters, A calculation means for calculating a predicted value of the solute concentration of the treated water in the water treatment system based on the water quality of the water to be treated, the water quality of the treated water in the evaluation system, the first operating parameter, and the second operating parameter. It has, The first water treatment apparatus is a first reverse osmosis membrane apparatus equipped with a first reverse osmosis membrane, The water quality prediction system is a second reverse osmosis membrane apparatus that is smaller than the first reverse osmosis membrane apparatus and includes a second reverse osmosis membrane apparatus.

2. The calculation means is Based on the water quality of the treated water, the water quality of the permeate from the second reverse osmosis membrane, and the second operating parameters, the solute permeation coefficient in the second reverse osmosis membrane is obtained. Based on the solute permeability coefficient in the second reverse osmosis membrane, the solute permeability coefficient in the first reverse osmosis membrane is estimated. A water quality prediction system according to claim 1, which calculates a predicted value of the solute concentration of the permeate from the first reverse osmosis membrane based on the solute permeation coefficient of the first reverse osmosis membrane, the water quality of the water to be treated, and the first operating parameters.

3. The water quality prediction system according to claim 2, wherein the calculation means multiplies the solute permeability coefficient of the second reverse osmosis membrane by a conversion coefficient corresponding to the combination of the membrane type of the first reverse osmosis membrane and the membrane type of the second reverse osmosis membrane, and the result is the solute permeability coefficient of the first reverse osmosis membrane.

4. The aforementioned calculation means The water permeability coefficient of the first reverse osmosis membrane and the water permeability coefficient of the second reverse osmosis membrane are obtained. A water quality prediction system according to claim 2, wherein the solute permeability coefficient of the first reverse osmosis membrane is estimated from the water permeability coefficient of the first reverse osmosis membrane, the water permeability coefficient of the second reverse osmosis membrane, and the solute permeability coefficient of the second reverse osmosis membrane, based on the correlation between the ratio of the water permeability coefficient of the first reverse osmosis membrane to the water permeability coefficient of the second reverse osmosis membrane and the ratio of the solute permeability coefficient of the first reverse osmosis membrane to the solute permeability coefficient of the second reverse osmosis membrane.

5. The water treatment system comprises a first ultraviolet irradiation device provided downstream of the first reverse osmosis membrane, and a first ion exchange device provided downstream of the first ultraviolet irradiation device. The evaluation system comprises a second ultraviolet irradiation device provided downstream of the second reverse osmosis membrane, and a second ion exchange device provided downstream of the second ultraviolet irradiation device. The aforementioned calculation means The solute removal rate of the second ultraviolet irradiation device and the second ion exchange device is obtained. Based on the first operating parameter and the second operating parameter, the solute removal rate is corrected. A water quality prediction system according to any one of claims 2 to 4, wherein a predicted value of the solute concentration of the treated water of the first ion exchange device is calculated from the corrected solute removal rate.

6. The water quality prediction system according to claim 5, wherein the calculation means calculates a predicted value of the solute concentration of the treated water of the first ion exchange device using the corrected solute removal rate in addition to the predicted value of the solute concentration of the permeate water of the first reverse osmosis membrane.

7. A water quality prediction system that predicts the water quality of treated water in a water treatment system when water to be treated is supplied to a water treatment system equipped with a first water treatment device that performs unit operations on water to be treated, and the water treatment system is operated based on first operating parameters, An evaluation system comprising a second water treatment apparatus that performs unit operations similar to those of the first water treatment apparatus, to which water to be treated is supplied to the water treatment system, and which is operated based on second operating parameters, A calculation means for calculating a predicted value of the solute concentration of the treated water in the water treatment system based on the water quality of the water to be treated, the water quality of the treated water in the evaluation system, the first operating parameter, and the second operating parameter. It has, The first water treatment apparatus comprises a first ultraviolet irradiation device and a first ion exchange device located downstream of the first ultraviolet irradiation device. The second water treatment apparatus comprises a second ultraviolet irradiation device and a second ion exchange device located downstream of the second ultraviolet irradiation device. The first condition is that the second ultraviolet irradiation device is smaller than the first ultraviolet irradiation device, and the second condition is that the second ion exchange device is smaller than the first ion exchange device. At least one of the first and second conditions is met. The aforementioned calculation means The solute removal rate of the second ultraviolet irradiation device and the second ion exchange device is obtained. Based on the first operating parameter and the second operating parameter, the solute removal rate is corrected. A water quality prediction system that calculates a predicted value for the solute concentration of the treated water of the first ion exchange device using the corrected solute removal rate.

8. The water quality prediction system according to any one of claims 5 to 7, wherein the calculation means performs the correction of the solute removal rate based on the relationship between the amount of ultraviolet irradiation obtained by passing sample water containing a simulated substance which is a known solute component through the first ultraviolet irradiation device and the second ultraviolet irradiation device and the solute removal rate.

9. A water quality prediction method for predicting the water quality of treated water in a water treatment system, which is equipped with a first water treatment device that performs unit operations on water to be treated, and which is operated based on first operating parameters, wherein water to be treated is supplied to the water treatment system, and the water treatment system is operated based on first operating parameters, An evaluation system is provided with a second water treatment device that performs unit operations similar to those of the first water treatment device, and the water to be treated is supplied to the water treatment system, and the evaluation system is operated based on the second operating parameters. Based on the water quality of the water to be treated, the water quality of the treated water in the evaluation system, the first operating parameter, and the second operating parameter, a predicted value for the solute concentration of the treated water in the water treatment system is calculated. The first water treatment apparatus is a first reverse osmosis membrane apparatus equipped with a first reverse osmosis membrane, A water quality prediction method, wherein the second water treatment apparatus is a second reverse osmosis apparatus that is smaller than the first reverse osmosis apparatus and includes a second reverse osmosis membrane.

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