Analysis method, analysis system, and water treatment system

Abstract

This analysis system (1) for quantifying a low-molecular-weight component contained in sample water comprises: a reverse osmosis membrane device (10) to which sample water is supplied and which includes a reverse osmosis membrane (11) having a permeability coefficient in which a pure water permeation flux for each 1 MPa of effective pressure at a water temperature of 25ºC is at most 0.7 m / d; an analysis device (30) to which concentrated water discharged from the reverse osmosis membrane device (10) is supplied and which quantifies a low-molecular-weight component; and an arithmetic device (40) for calculating the concentration of the low-molecular-weight component in the sample water on the basis of the concentration ratio of the low-molecular-weight component in the reverse osmosis membrane device (10) and the measured value in the analysis device (30).

Description

Analysis method, analysis system, and water treatment system

[0001] The present invention relates to an analytical method and analytical system for quantifying low molecular weight components contained in water, and a water treatment system that is controlled in accordance with the results of quantifying the low molecular weight components.

[0002] Pure water and ultrapure water are used, for example, in the manufacture of semiconductor devices and pharmaceuticals. At semiconductor device and pharmaceutical manufacturing sites, the concentrations of impurities contained in pure water and ultrapure water are continuously monitored using online analyzers. In recent years, there has been a demand for reducing the impurity concentrations in pure water and ultrapure water to the utmost. Because it is difficult to accurately quantify ultratrace amounts of impurities in water as analytes using online analyzers, it has been proposed to concentrate the analytes in sample water by passing only the water through a reverse osmosis membrane (RO membrane) before performing quantification using the online analyzer. For example, Patent Documents 1 to 3 disclose a method in which sample water is supplied to a reverse osmosis membrane device, and a portion of the water that does not pass through the RO membrane (i.e., concentrated water) is supplied to the analyzer, and the remaining concentrated water is combined with the sample water and returned to the inlet of the RO membrane device, thereby increasing the concentration ratio when concentrating the analyte using the RO membrane device. Patent Document 4 discloses that in order to further increase the concentration ratio in the techniques disclosed in Patent Documents 1 to 3, a plurality of reverse osmosis membrane devices are connected in series so that water that has permeated the reverse osmosis membrane in a first-stage reverse osmosis membrane device (i.e., permeated water) is supplied to a second-stage reverse osmosis membrane device, and a portion of the concentrated water from the first-stage reverse osmosis membrane device is supplied to an analyzer and the remainder is returned to the inlet of the first-stage reverse osmosis membrane device, and the concentrated water from the second-stage and subsequent reverse osmosis membrane devices is also returned to the inlet of the first-stage reverse osmosis membrane device.

[0003] Urea is an example of an impurity contained in pure water or ultrapure water, and the urea concentration in pure water or ultrapure water used in semiconductor manufacturing is required to be below a certain value. Patent Document 5 discloses a method for online quantification of urea contained in pure water or ultrapure water, in which sample water is pretreated with a reverse osmosis membrane device to remove interfering substances, and the absorbance of the permeated water from the reverse osmosis membrane device is measured by flow injection analysis based on a colorimetric method using diacetyl monoxime to quantify urea.

[0004] JP 2008-209396 A JP 2009-156692 A JP 2010-44022 A JP 2020-124687 A JP 2019-284436 A

[0005] As described in Patent Documents 1 to 4, the concentration ratio can be increased by returning concentrated water from a reverse osmosis membrane device to the inlet of the reverse osmosis membrane device. However, in this case, it becomes difficult to follow the water quality fluctuations when there are sudden changes in the water quality of the sample water, resulting in a decrease in responsiveness in quantifying the analyte. Furthermore, when using a reverse osmosis membrane device to concentrate analyte components contained in water, analyte components with relatively small molecular weights, such as urea and boron, tend to easily permeate the reverse osmosis membrane, making it difficult to sufficiently concentrate such analyte components.

[0006] The object of the present invention is to provide an analytical method and system that can quickly and reliably obtain analytical results when quantifying trace amounts of low-molecular-weight components contained in sample water that undergoes water quality fluctuations as the analytical target components, and a water treatment system that can be controlled in accordance with such analytical results.

[0007] One embodiment of the analytical method of the present invention is an analytical method for quantifying low molecular weight components contained in sample water, in which the sample water is supplied to a reverse osmosis membrane device equipped with a reverse osmosis membrane having a permeability coefficient such that the pure water permeation flux per effective pressure of 1 MPa at a water temperature of 25°C is 0.7 m / day or less, the concentrated water discharged from the reverse osmosis membrane device is supplied to an analytical device that quantifies the low molecular weight components, and the concentration of the low molecular weight components in the sample water is calculated based on the concentration ratio of the low molecular weight components in the reverse osmosis membrane device and the measured value in the analytical device.

[0008] An analytical system according to one embodiment of the present invention is an analytical system for quantifying low molecular weight components contained in sample water, and includes a reverse osmosis membrane device equipped with a reverse osmosis membrane having a permeability coefficient such that the pure water permeation flux per effective pressure of 1 MPa at a water temperature of 25°C is 0.7 m / day or less and to which sample water is supplied, an analytical device that is supplied with concentrated water discharged from the reverse osmosis membrane device and quantifies the low molecular weight components, and a computing device that calculates the concentration of the low molecular weight components in the sample water based on the concentration factor of the low molecular weight components in the reverse osmosis membrane device and the measured value in the analytical device.

[0009] One embodiment of the water treatment system of the present invention is a water treatment system that treats raw water to produce treated water, and is equipped with the above-mentioned analysis system and a low molecular weight component reduction means that reduces low molecular weight components contained in the water in the water treatment system, wherein water from a predetermined location in the water treatment system is supplied to the analysis system as sample water, and the operating conditions of the low molecular weight component reduction means are controlled according to the concentration of the low molecular weight components quantified by the analysis system.

[0010] According to the present invention, when quantifying trace amounts of low molecular weight components contained in sample water that undergoes water quality fluctuations as analysis target components, analysis results can be obtained quickly and reliably.

[0011] FIG. 1 is a diagram explaining the principle of concentration of an analyte component by a reverse osmosis membrane. FIG. 2 is a flow sheet showing the configuration of an analysis system of an embodiment. FIG. 3 is a graph showing the relationship between the permeability coefficient of a reverse osmosis membrane and the concentration ratio of urea. FIG. 4 is a flow sheet showing the configuration of an analysis system of another embodiment. FIG. 5 is a graph showing the relationship between the recovery rate of a reverse osmosis membrane device and the concentration ratio of urea. FIG. 6 is a flow sheet showing the configuration of an analysis system of another embodiment. FIG. 7 is a diagram showing an example of the configuration of a water treatment system incorporating an analysis system.

[0012] Next, preferred embodiments of the present invention will be described with reference to the drawings. First, the principle of concentrating a trace amount of a target component in sample water using a reverse osmosis membrane for quantitative determination of the target component will be described. Figure 1 is a diagram illustrating the principle of concentrating a target component.

[0013] A reverse osmosis membrane device 10 equipped with a reverse osmosis membrane 11 is provided for concentrating the components to be analyzed, and a sample water pipe 12 for supplying sample water is connected to the reverse osmosis membrane device 10. The sample water pipe 12 is provided with a pump 13 for pressure-feeding the sample water toward the reverse osmosis membrane device 10. Furthermore, the reverse osmosis membrane device 10 is connected to a concentrated water pipe 14 for discharging water that did not permeate the reverse osmosis membrane 11, i.e., concentrated water, and a permeated water pipe 15 for discharging water that permeated the reverse osmosis membrane 11, i.e., permeated water. The flow rate of the feed water (i.e., sample water) supplied to the reverse osmosis membrane device 10 is defined as Q f , the flow rate of the concentrated water discharged from the reverse osmosis membrane device 10 is Q b , the flow rate of the permeated water discharged from the reverse osmosis membrane device 10 is Q p Then, the formula (1) is established, and the water recovery rate f in the reverse osmosis membrane device 10 is defined by the formula (2).

[0014] Q f = Q b + Q p (1) f = Q p / (Q b + Q p ) = Q p / Q f (2)

[0015] Since the components to be analyzed generally do not permeate the reverse osmosis membrane 11, the components to be analyzed appear in the concentrated water. If the recovery rate f is increased, the flow rate Q of the concentrated water becomes relatively b If the concentration of the analyte in the concentrated water increases by a factor of 1 compared to the concentration in the feed water, the concentration factor k in the reverse osmosis membrane device 10 is expressed by equation (3) when the rejection rate of the analyte in the reverse osmosis membrane 11 is sufficiently high.

[0016] k = Q f / Q b (3)

[0017] However, typical reverse osmosis membranes used in applications such as pure water production, such as those with a pure water permeation flux of more than 0.7 m / d per 1 MPa effective pressure at a water temperature of 25°C, do not have sufficient rejection rates for low-molecular-weight components such as urea and boron. In other words, even if a reverse osmosis membrane is used to concentrate low-molecular-weight components, it is not possible to achieve a large concentration ratio as expressed by equation (3), making efficient concentration impossible. To achieve a high concentration ratio, it is possible to supply a portion of the concentrated water to an analytical device and return the remainder to the inlet of the reverse osmosis membrane device. However, this configuration makes it impossible to analyze the rapid concentration fluctuations of the components to be analyzed in the sample water. Here, low-molecular-weight components refer to components with a molecular weight of less than 100. The pure water permeation flux (flux) per unit effective pressure at a given temperature (usually 25°C) through a reverse osmosis membrane is called the permeability coefficient of the reverse osmosis membrane. The pure water permeation flux is calculated by dividing the amount of pure water permeating by the membrane area. "Effective pressure" is the effective pressure acting on a membrane, calculated by subtracting the osmotic pressure difference and the secondary pressure from the average operating pressure, as described in JIS (Japanese Industrial Standards) K3802:2015 "Membrane Terminology." The average operating pressure is the average value of the pressure of the membrane feed water (operating pressure) and the pressure of the concentrated water (concentrated water outlet pressure) on the primary side of the membrane, and is expressed by the following formula (4):

[0018] Average operating pressure = (operating pressure + concentrated water outlet pressure) / 2 (4)

[0019] The present inventors have studied the relationship between the permeability coefficient of a reverse osmosis membrane and the concentration ratio of low molecular weight components, and have found that a reverse osmosis membrane having a permeability coefficient smaller than that of a typical reverse osmosis membrane used in the production of pure water, etc., can achieve a sufficient concentration ratio of low molecular weight components without refluxing the concentrated water, thereby completing the present invention. Figure 2 shows the configuration of an analytical system 1 according to one embodiment of the present invention.

[0020] The analytical system 1 shown in Fig. 2 is for quantifying trace amounts of low-molecular-weight components contained in pure water or ultrapure water used in the manufacture of semiconductor devices, etc. Although there are no restrictions on the water to be analyzed or the water supplied to the analytical device, it is preferable that the water satisfy the following conditions regarding water quality. The TDS (Total Dissolved Solids) concentration is 500 ppm or less, preferably 10 ppm or less, and more preferably 1 ppm or less; the TOC (Total Organic Carbon) concentration is 1 ppm or less, preferably 200 ppb or less, and more preferably 2 ppb or less; the silica concentration is 20 ppm or less, preferably 2 ppm or less, and more preferably 0.2 ppm; the calcium concentration is 10 ppm or less, preferably 1 ppm or less, and more preferably 0.1 ppm or less; the aluminum concentration is 0.05 ppm or less, and preferably 0.01 ppm or less; and the inorganic carbonate concentration is 100 ppm or less, preferably 10 ppm or less, and more preferably 1 ppm or less. High silica, aluminum, calcium, or inorganic carbonate concentrations in the analyte not only cause blockage of the reverse osmosis membrane used to concentrate the analyte water, but also cause bubbles and blockages on the concentrating side of the reverse osmosis membrane to disrupt the flow rate balance, resulting in fluctuations in the concentration ratio. Furthermore, by analyzing water with a low TDS concentration, the osmotic pressure can be considered to be zero when calculating the effective pressure, improving calculation accuracy. Pure water and ultrapure water used in the manufacture of semiconductor devices generally meet the water quality requirements described herein, and are therefore suitable for application of the analytical method based on this invention.

[0021] The analysis system 1 shown in FIG. 2 broadly comprises a reverse osmosis membrane device 10 that concentrates low-molecular-weight components to be quantified, an analysis device 30 that analyzes the low-molecular-weight components to be quantified, and a computing device 40 that calculates the quantitative values ​​of the low-molecular-weight components in the water to be analyzed based on the measurements made by the analysis device 30. The reverse osmosis membrane device 10 comprises a reverse osmosis membrane 11, which has a permeability coefficient of 0.7 m / d / MPa or less. The reverse osmosis membrane 11 is made of, for example, a polyamide as a base material. Examples of such reverse osmosis membranes 11 that can be used include those commercially available for seawater desalination. The low-molecular-weight components to be analyzed are components with a molecular weight of less than 100, such as urea and boron components. However, the following description will be given assuming that urea is being quantified.

[0022] A pipe 20 is provided for supplying the target water, which is pure water or ultrapure water, to the location where it is to be used, and a sample water pipe 12 branches off from the pipe 20. The sample water pipe 12 supplies sample water, which is continuously collected from the target water for quantitative determination of the target components, to the reverse osmosis membrane device 10. A pump 13 is provided in the sample water pipe 12 to pressurize the sample water and supply it to the reverse osmosis membrane device 10. A drive circuit 21 is provided for driving the pump 13. The drive circuit 21 includes an inverter circuit and the like that electrically drives a motor (not shown) provided in the pump 13.

[0023] The concentrated water from the reverse osmosis membrane device 10 is supplied to the analyzer 30 via the concentrated water pipe 14. The concentrated water pipe 14 is also provided with a pressure control valve 22 for adjusting the pressure at the concentrated water outlet of the reverse osmosis membrane device 10. The analyzer 30 for analyzing urea can be an analyzer capable of continuously quantifying urea online, such as the urea analyzer described in Patent Document 5. The entire amount of concentrated water may be supplied to the analyzer 30, or a portion of the concentrated water may be diverted and supplied. When a portion of the concentrated water is supplied to the analyzer 30, the remaining concentrated water is directly discharged to the outside as wastewater. The portion of the concentrated water is not returned to the inlet side of the reverse osmosis membrane device 10. The permeated water from the reverse osmosis membrane device 10 is directly discharged to the outside via the permeated water pipe 15. The water recovery rate in the reverse osmosis membrane device 10 can be adjusted by adjusting the rotation speed of the motor (not shown) of the pump 13 using the drive circuit 21 and adjusting the pressure control valve 22. The reverse osmosis membrane device 10 is preferably operated so that the recovery rate f is 80% or more, more preferably 90% or more, and even more preferably 95% or more.

[0024] By pretreating the sample water using the reverse osmosis membrane device 10, water in which the analyte component is concentrated by a concentration factor k is supplied to the analyzer 30. Therefore, the measured value of the concentration of the analyte component obtained by the analyzer 30 is expressed as C m The concentration of the target component in the sample water is C s Then, the concentration of the target component in the sample water is C s is expressed by equation (5).

[0025] C s = C m / k (5)

[0026] As described above, low molecular weight components in the sample water are not completely blocked by the reverse osmosis membrane 11, and some of them pass through the reverse osmosis membrane 11. Therefore, the concentration factor k of the low molecular weight components in the reverse osmosis membrane device 10 cannot be determined based on formula (3). According to the studies of the present inventors, the concentration factor is determined depending on the reverse osmosis membrane 11, although it is affected by the water recovery rate in the reverse osmosis membrane device 10, and the smaller the permeability coefficient of the reverse osmosis membrane 11, the larger the concentration factor k. In the analysis system 1 shown in FIG. 2, the measured value C obtained by the analysis device 30 m is input to the calculation device 40. The calculation device 40 calculates the concentration C of the component to be analyzed in the sample water based on the formula (5). s as a quantitative value and outputs it, and a concentration factor storage unit 42 that stores the concentration factor k of the component to be analyzed in the reverse osmosis membrane device 10, and the arithmetic device 40 calculates the quantitative value based on the concentration factor k stored in the concentration factor storage unit 42. As will be described later, the concentration factor k also depends on the water temperature, so the arithmetic device 40 may have a function of acquiring the water temperature in the reverse osmosis membrane device 10 and correcting the concentration factor k based on this water temperature.

[0027] In the analysis system 1 shown in FIG. 2 , as a pretreatment, the water to be analyzed may be passed through a separately provided water treatment device (not shown) to remove TDS components, TOC components, silica, calcium, aluminum, inorganic carbonates, and other interfering substances contained in the water to adjust the water quality. The interfering substances here refer to substances that interfere with measurement by the analyzer 30. Alternatively, the concentrated water from the reverse osmosis membrane device 10 may be passed through a similar water treatment device to remove TDS components, TOC components, silica, calcium, aluminum, inorganic carbonates, and other interfering substances contained in the concentrated water, thereby adjusting the concentrated water to a water quality more suitable for measurement by the analyzer 30. In either case, the water treatment device may be a filter, an activated carbon device, a regenerative ion exchange resin tower, a reverse osmosis membrane device, an ultraviolet oxidation device, a degassing device, or the like.

[0028] FIG. 3 shows the results of an investigation into the relationship between the permeability coefficient A of a reverse osmosis membrane and the concentration factor k for urea for several different types of reverse osmosis membranes when the water recovery rate in the reverse osmosis membrane device 10 was 95%. Polyamide reverse osmosis membranes were used for all of the several types of reverse osmosis membranes. When the permeability coefficient A of the reverse osmosis membrane was greater than 0.7 m / d / MPa, the concentration factor k was approximately 2 regardless of the permeability coefficient A. However, when the permeability coefficient A was 0.7 m / d / MPa or less, the concentration factor k for urea was 2 or greater, and the smaller the permeability coefficient A, the greater the concentration factor k. If a concentration factor of 2 or greater is considered practical, it can be seen that the permeability coefficient A of the reverse osmosis membrane 11 should be 0.7 m / d / MPa or less. The permeability coefficient A of the reverse osmosis membrane 11 is preferably 0.6 m / d / MPa or less, and more preferably 0.4 m / d / MPa or less. If the permeability coefficient A is 0.4 m / d / MPa, a concentration factor k of about 4.5 can be obtained.

[0029] In the analysis system 1 shown in FIG. 2, the permeate flow rate Q p and concentrated water flow rate Q b f varies due to external factors such as fluctuations in the water temperature and pressure of the water to be analyzed, clogging of the reverse osmosis membrane, and fluctuations in the opening of the pressure control valve 22 due to precipitates and generated gas, which in turn cause fluctuations in the recovery rate f and concentration factor k. In particular, when the recovery rate f in the reverse osmosis membrane device 10 is 80% or higher, the concentration factor k may change significantly due to changes in the flow rate in the reverse osmosis membrane device 10. Therefore, the analysis system 1 measures the recovery rate f in the reverse osmosis membrane device 10 and calculates the concentration C of the component to be analyzed in the sample water. s The concentration factor k used to calculate the concentration of the analyte component is corrected by the recovery rate f. s 4 shows the configuration of an analysis system 1 in which the concentration factor k is changed according to the recovery rate f.

[0030] The analytical system 1 shown in FIG. 4 is the same as the analytical system 1 shown in FIG. 2 except that the concentrated water flow rate Q b and a flow rate sensor 23 attached to the permeate pipe 15 for measuring the flow rate Q of the permeate. pIn the calculation device 40, instead of the concentration rate storage unit 42, the flow rate Q measured by the flow rate sensors 23 and 24 is stored. b , Q p and a concentration factor calculation unit 44 that calculates the concentration factor k from the calculated recovery factor f based on the relationship between the recovery factor f and the concentration factor k that is previously determined for the reverse osmosis membrane 11, and outputs the concentration factor k to the concentration calculation unit 41. In the analysis system 1 shown in FIG. 4, the concentration factor k is calculated based on the current recovery factor f in the reverse osmosis membrane device 10, so that the concentration C of the analyte component in the sample water can be calculated based on the current operating status of the reverse osmosis membrane device 10. s In this analysis system 1, the flow rate Q measured by the flow rate sensors 23 and 24 is calculated so that the recovery rate f becomes a predetermined value. b , Q p The drive circuit 21 and the pressure control valve 22 may be controlled based on the above. Due to the characteristics of the reverse osmosis membrane 11, as the water temperature increases, concentration of components tends to become more difficult. In other words, even if the recovery rate f is constant, the concentration factor k tends to decrease as the water temperature increases. Therefore, the concentration factor calculation unit 44 may have a function to acquire the water temperature in the reverse osmosis membrane device 10 and correct the calculated concentration factor k based on the water temperature.

[0031] FIG. 5 shows an example of an actual measurement of the relationship between the recovery rate f and the concentration factor k in the reverse osmosis membrane device 10. FIG. 5 shows the results of examining the relationship between the recovery rate f and the concentration factor k for a polyamide reverse osmosis membrane for seawater desalination, with a permeability coefficient A of 0.35 m / d / MPa. From FIG. 5, it can be seen that in order to obtain a high concentration factor k, the recovery rate f is preferably 80% or higher, more preferably 90% or higher, and even more preferably 95% or higher. The concentration factor calculation unit 44 has a built-in table that represents the relationship shown in FIG. 5, and when the recovery rate f is input, it outputs the corresponding concentration factor k.

[0032] In the above description, it has been assumed that the permeability coefficient A of the reverse osmosis membrane 11 is constant. However, in reality, the permeability coefficient A changes due to factors such as deterioration in performance of the reverse osmosis membrane 11 over time due to long-term use and the influence of the manufacturing lot of the reverse osmosis membrane 11. Changes in the permeability coefficient A have a significant impact on the concentration factor k for low-molecular-weight components. Therefore, it is conceivable to actually measure the permeability coefficient A of the reverse osmosis membrane 11 and change the concentration factor k according to the permeability coefficient A. Figure 6 shows the configuration of an analysis system 1 in which the concentration factor k is changed according to the permeability coefficient A.

[0033] The analytical system 1 shown in FIG. 6 is the same as the analytical system 1 shown in FIG. 2 except that the flow rate Q of the permeated water is p and a pressure sensor 25 attached to the sample water pipe 12 to measure the effective pressure applied to the reverse osmosis membrane 11. In the computing device 40, instead of the concentration ratio storage unit 42, the flow rate Q measured by the flow rate sensor 24 is stored. b and the effective pressure measured by the pressure sensor 25, and a concentration factor calculation unit 46 is provided to calculate a concentration factor k from the permeability coefficient A and output the calculated concentration factor k to the concentration calculation unit 41. Since the effective membrane area of ​​each reverse osmosis membrane 11 is known, the permeate flow rate Q p and the effective pressure applied to the reverse osmosis membrane 11. As described above, when the relationship between the permeability coefficient A and the concentration factor k for each of a plurality of different reverse osmosis membranes is examined, the relationship shown in Figure 3 is obtained. The concentration factor calculation unit 46 has a built-in table showing the relationship between the permeability coefficient A and the concentration factor k, and when the permeability coefficient A is input, it outputs the corresponding concentration factor k. In the analysis system 1 shown in Figure 6, the concentration factor k is calculated based on the current permeability coefficient A in the reverse osmosis membrane device 10, so the concentration C of the analyte component in the sample water can be calculated based on the current state of the reverse osmosis membrane 11. s In this analysis system 1, the concentrated water flow rate Q is calculated in the same manner as in the analysis system 1 shown in FIG. b A flow rate sensor 23 is also provided to measure the concentrated water flow rate Q b and permeate flow rate Q pThe recovery rate f may also be calculated from the permeability coefficient A, and the concentration factor k may be corrected in accordance with the permeability coefficient A and the recovery rate f. The analysis system 1 shown in FIG. 6 may also be provided with a function for correcting the concentration factor k in accordance with the water temperature in the reverse osmosis membrane device 10.

[0034] The analysis system 1 of each of the above-described embodiments can be incorporated into a water treatment system that treats raw water to produce treated water to control the system. Such a water treatment system includes the above-described analysis system 1 and a low-molecular-weight component reduction means for reducing low-molecular-weight components contained in the water in the water treatment system. Water from a predetermined location in the water treatment system is supplied to the analysis system 1 as sample water, and the operating conditions of the low-molecular-weight component reduction means are controlled according to the concentration of the low-molecular-weight components quantified by the analysis system 1. Examples of the low-molecular-weight component reduction means include a chemical addition means for adding a chemical to decompose and remove the target low-molecular-weight component. For example, if the low-molecular-weight component is urea, a chemical generating hypobromous acid may be added to oxidize and decompose the urea with the hypobromous acid. If the target low-molecular-weight component is decomposed by ultraviolet oxidation in the presence of an oxidizing agent, a chemical addition means may be provided as a means for adding an oxidizing agent upstream of the ultraviolet oxidation device installed in the water treatment system. In addition, when raw water is supplied to a water treatment system from different water sources, a mechanism for switching piping so that raw water from a water source that is thought to have a lower concentration of low molecular weight components is supplied to the water treatment system is also included in the category of low molecular weight component reduction means.

[0035] Fig. 7 shows an example of the configuration of a water treatment system including an analysis system 1 and a chemical addition means as a low-molecular-weight component reduction means, in which the amount of chemical addition is controlled in accordance with the data obtained by the analysis system 1. The water treatment system shown in Fig. 7 treats raw water containing urea to produce treated water (primary pure water or ultrapure water) with a reduced urea concentration. The raw water may be, for example, city water, well water, river water, industrial water, reclaimed water obtained by treating domestic or industrial wastewater, or desalinated seawater, either singly or in combination.

[0036] The water treatment system includes a raw water tank 111 for temporarily storing raw water, the above-described analysis system 1 for measuring the concentration of urea as a low-molecular-weight component, and a chemical dosing device 140 as a chemical dosing means. To obtain primary pure water, the water treatment system includes a sand filter (SF) 112, an activated carbon (AC) 114, an ion exchanger (IE) 115, and a reverse osmosis membrane device (RO) 120, which are provided in this order at the outlet of the raw water tank 111. Furthermore, an ultraviolet oxidation device (UV) 132, an ion exchanger (IE) 133, and a membrane degassing device 134 (MD) are provided in this order at the permeate outlet of the reverse osmosis membrane device 120. The reverse osmosis membrane device 120 includes a reverse osmosis membrane 125. Primary pure water is discharged from the membrane degassing device 134. Intermediate storage tanks may be provided between the water treatment devices as needed. For example, an intermediate storage tank can be provided between the sand filtration device 112 and the activated carbon device 114, between the ion exchange device 115 and the reverse osmosis membrane device 120, or between the permeate outlet of the reverse osmosis membrane device 120 and the ultraviolet oxidation device 132. The primary pure water discharged from the membrane degassing device 134 can be used as treated water in this water treatment system. In the water treatment system, other water treatment devices may be provided as needed, some water treatment devices may be omitted, or the arrangement order of the water treatment devices may be changed.

[0037] 7 also includes a subsystem 150 that receives primary pure water and generates it to obtain ultrapure water with an extremely low urea concentration. Subsystem 150 includes a tank 151 for temporarily storing the primary pure water, and an ultraviolet oxidation device (UV) 152, a non-regenerative ion exchange device (CP) 153, also known as a cartridge polisher, and an ultrafiltration membrane device (UF) 154, which are provided in this order at the outlet of tank 151. Ultrapure water is discharged from ultrafiltration membrane device 154 and supplied to points of use, but any ultrapure water not supplied to points of use is circulated back to tank 151 via circulation piping 155.

[0038] In this water treatment system, the sand filter 112, activated carbon device 114, ion exchange devices 115 and 133, ultraviolet oxidation device 132, and membrane degassing device 134 are unable to remove much urea. As a result, if the urea concentration in the raw water is high, the urea concentration in the treated primary pure water will also be high. Because it is difficult to remove urea in the subsystem 150, the urea concentration in the ultrapure water obtained from the subsystem 150 will also be high. Therefore, in this water treatment system, the chemical additive device 140 adds a chemical to the raw water tank 111 or a location upstream of the raw water tank 111 that decomposes the urea in the raw water, thereby promoting the urea decomposition reaction in the raw water tank 111. In the example shown in FIG. 7 , the chemical additive device 140 adds, for example, hypochlorous acid or hypochlorite and alkali bromide to the raw water to decompose urea through an oxidation reaction with hypobromous acid. As indicated by "HClO or NaClO" and "NaBr" in the figure, an aqueous solution of hypochlorous acid or sodium hypochlorite and an aqueous solution of sodium bromide are supplied to a raw water tank 111 via pumps 141 and 142, respectively. In the raw water tank 111, hypochlorous acid or sodium hypochlorite reacts with sodium bromide to produce hypobromous acid, which then oxidizes and decomposes urea. The raw water tank 111 functions as a urea decomposition tank, where the oxidative decomposition of urea progresses. Water with a reduced urea concentration is discharged from the raw water tank 111, and as a result, the urea concentration in the treated primary pure water or ultrapure water is also reduced.

[0039] To optimize the amount of chemical added by the chemical addition device 140 while sufficiently reducing the urea concentration in the treated water, i.e., to add the correct amount of chemical, it is necessary to measure the urea concentration in the raw water or the treated water and determine the amount of chemical to be added. Therefore, an analysis system 1 based on any of the above-described embodiments configured to measure the urea concentration in the water to be analyzed measures the urea concentration in the water flowing through the water treatment system. Pumps 141, 142 used to deliver the chemical to be added to the raw water are controlled according to the urea quantification results obtained by the analysis system 1. In Figure 7, as shown at position C, the analysis system 1 is provided branching off from the piping connecting the sand filter device 112 and the activated carbon device 114. However, the installation location of the analysis system 1 is not limited thereto. For example, the analysis system 1 may be provided so as to branch off at position A from a pipe supplying raw water to the raw water tank 111, or so as to branch off at position B from a pipe connected to the outlet of the raw water tank 111, or so as to branch off at position D from a pipe carrying concentrated water from the reverse osmosis membrane device 120, or so as to branch off at position E from a pipe carrying permeated water from the reverse osmosis membrane device 120. Furthermore, the analysis system 1 may be provided so as to branch off at position F from a pipe carrying primary pure water discharged from the membrane degassing device 134, or so as to branch off at position G from a pipe carrying ultrapure water generated by the subsystem 150. Position A is a position upstream of the raw water tank 111 where the urea concentration in the raw water is measured, and positions B to G are positions downstream of the raw water tank 111 where the urea concentration in water obtained by carrying out an oxidative decomposition reaction of urea is measured. In the water treatment system shown in FIG. 7 , the amount of chemicals added is controlled based on the urea concentration actually measured in the water treatment system. Therefore, even when the urea concentration in the treated water (primary pure water and ultrapure water) from the water treatment system is reduced to the minimum, the amount of chemicals added to decompose urea can be made appropriate.

[0040] In the above description, the chemical additive device 140 is provided as the low-molecular-weight component reduction means, and both the amount of hypochlorous acid or sodium hypochlorite and the amount of sodium bromide added are controlled in accordance with the urea quantification value in the analysis system 1. However, it is also possible to control the amount of either one of the chemicals added. By controlling the amount of these chemicals added, the concentration of the chemicals in the raw water can be varied. Because the urea decomposition reaction is also affected by water temperature and pH, the amount of pH adjuster (acid or alkali) added to the raw water may be controlled in accordance with the urea concentration measurement results in the analysis system 1, or the water temperature (raw water temperature) in the raw water tank 111 may be controlled. Furthermore, the low-molecular-weight component reduction means provided in the water treatment system is not limited to adding hypochlorous acid or sodium hypochlorite and sodium bromide to the raw water. The low-molecular-weight component reduction means may, for example, switch piping so that raw water from a water source believed to have a low urea concentration is supplied to the water treatment system, or may add an oxidizing agent to the permeate from the reverse osmosis membrane device 120 upstream of the ultraviolet oxidation device 132. The operating conditions of these low molecular weight component reducing means are also controlled in accordance with the urea measurement results in the analysis system 1.

[0041] REFERENCE SIGNS LIST 1 Analysis system 10 Reverse osmosis membrane device 11 Reverse osmosis membrane 13, 52, 53 Pump 21 Drive circuit 22 Pressure control valve 23, 24 Flow rate sensor 25 Pressure sensor 30 Analysis device 40 Arithmetic device 41 Concentration calculation unit 42 Concentration ratio storage unit 43 Recovery rate calculation unit 44, 46 Concentration ratio calculation unit 45 Permeability coefficient calculation unit 110 Raw water tank 140 Chemical addition device

Claims

1. An analytical method for quantifying low molecular weight components contained in sample water, comprising: supplying the sample water to a reverse osmosis membrane device equipped with a reverse osmosis membrane having a permeability coefficient of 0.7 m / d or less in pure water permeation flux per 1 MPa effective pressure at a water temperature of 25°C; supplying concentrated water discharged from the reverse osmosis membrane device to an analyzer that quantifies the low molecular weight components; and calculating the concentration of the low molecular weight components in the sample water based on the concentration ratio of the low molecular weight components in the reverse osmosis membrane device and the measurement value in the analyzer.

2. The analytical method according to claim 1, wherein the concentrated water discharged from the reverse osmosis membrane device is supplied to the analytical device without being returned to the inlet of the reverse osmosis membrane device.

3. The analytical method according to claim 1 or 2, wherein the concentration ratio is determined by obtaining at least one of the water temperature in the reverse osmosis membrane device, the water recovery rate, and the permeability coefficient of the reverse osmosis membrane.

4. The analytical method according to claim 1 or 2, wherein the reverse osmosis membrane device is operated so that the water recovery rate is 80% or more.

5. The analytical method according to claim 1 or 2, wherein the low molecular weight component is urea.

6. The analytical method according to claim 1 or 2, wherein the analytical device is an online analytical device that continuously performs the quantitative determination of the low molecular weight components.

7. An analytical system for quantifying low molecular weight components contained in sample water, comprising: a reverse osmosis membrane device equipped with a reverse osmosis membrane having a permeability coefficient of 0.7 m / d or less in pure water permeation flux per 1 MPa effective pressure at a water temperature of 25°C, and to which the sample water is supplied; an analytical device that is supplied with concentrated water discharged from the reverse osmosis membrane device and quantifies the low molecular weight components; and a computing device that calculates the concentration of the low molecular weight components in the sample water based on the concentration ratio of the low molecular weight components in the reverse osmosis membrane device and the measurement value in the analytical device.

8. The analytical system according to claim 7, wherein the computing device acquires at least one of the water temperature in the reverse osmosis membrane device, the water recovery rate, and the permeability coefficient of the reverse osmosis membrane, and determines the concentration ratio.

9. A water treatment system that treats raw water to produce treated water, comprising: an analysis system as described in claim 7 or 8; and a low molecular weight component reduction means that reduces the low molecular weight components contained in the water in the water treatment system, wherein water from a predetermined location in the water treatment system is supplied to the analysis system as the sample water, and the operating conditions of the low molecular weight component reduction means are controlled according to the concentration of the low molecular weight components quantified by the analysis system.

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