Method for diagnosing state of separating membrane module

Abstract

Test water containing, as solutes, at least two kinds of ionic substances having different valences or substances having different molecular weights is supplied to a separating membrane module, or at least two kinds of test water containing one kind of solute, obtained by changing the valence of the ionic substance or changing the molecular weight of the substance, are individually supplied to the separating membrane module, permeated water is collected at a plurality of positions, namely two or more positions, in a permeated water collecting tube, and separation performances of the at least two kinds of solutes, obtained on the basis of differences between the solute concentration in the permeated water collected at each water collection position and the solute concentration attributable to the permeated water on the upstream side of the water collection position are compared with each other to determine any of the type of an abnormality, the degree of the abnormality, and the occurrence position of the abnormality in the permeated water collection pipe length direction in the separating membrane module.

Description

Diagnosis method for separation membrane module

[0001] The present invention relates to a method for diagnosing the state of a separation membrane module.

[0002] In recent years, the depletion of water resources has become a serious problem, and efforts are being made to utilize previously untapped water resources. To address this issue, new technologies, such as microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, and ion exchange membranes, which offer significantly higher separation efficiency than conventional methods such as sand filtration and evaporation, have begun to be applied to water treatment. In particular, the application of separation membranes, particularly reverse osmosis membranes, has attracted considerable attention in seawater desalination, a technology for producing drinking water from seawater, which is the most familiar but otherwise unusable source of water, as well as in the purification of sewage wastewater and the reuse of treated water.

[0003] Seawater desalination has traditionally been carried out mainly using evaporation methods in the Middle East, where water resources are extremely scarce and heat resources from petroleum are abundant.Recently, technological advances in reverse osmosis have improved reliability and reduced costs, and reverse osmosis seawater desalination plants are now being put into practical use in the Middle East.

[0004] In the case of sewage and wastewater reuse, reverse osmosis membranes are used in inland and coastal urban and industrial areas, areas with no water sources, areas where discharge volume is restricted due to wastewater regulations, etc. In particular, Singapore deals with water shortages by treating domestic sewage and then using reverse osmosis membranes to regenerate it to drinking water quality.

[0005] The reverse osmosis membrane process, which is used in seawater desalination and sewage wastewater reuse, is a method of producing desalinated water by applying a pressure greater than the osmotic pressure to water containing solutes such as salt, causing it to pass through a reverse osmosis membrane. This technology can be used to produce drinking water from seawater or brine, for example, and has also been used to produce ultrapure water for industrial use, treat wastewater, and recover valuable resources.

[0006] However, during normal operation in various water treatment plants, reverse osmosis membranes can undergo chemical degradation due to contact with the membrane surface of disinfectants used to disinfect raw water, coagulants used in pretreatment, and other residues, as well as chemical cleaning with strong acids or strong alkalis, which is commonly performed when the membrane is contaminated. Even when pretreatment appropriate for the raw water quality is applied, physical degradation can occur on the membrane surface due to contact with residual foreign matter in the treated water or scale and foulants generated during operation. Furthermore, physical degradation can occur when wrinkles on the membrane surface caused by sudden changes in operating conditions during use of a reverse osmosis membrane element module come into strong contact with the flow path material. Furthermore, performance changes can occur when reverse osmosis membranes are exposed to high pressure for long periods of time during normal operation in various water treatment plants, or when foulants coat the membrane surface. Therefore, reverse osmosis membrane performance must be periodically inspected, and appropriate countermeasures must be taken immediately if performance degradation is detected.

[0007] A known method for examining whether or not a reverse osmosis membrane is physically damaged involves disassembling a reverse osmosis membrane element to be examined, extracting a membrane fragment, and passing a pressurized dye solution (for example, a solution of Basic Violet 1 (manufactured by Tokyo Chemical Industry Co., Ltd.)) through the skin layer side, which has a reverse osmosis function, of the membrane fragment at a linear velocity of 0.1 to 0.2 cm / sec at an operating pressure of 1.5 MPa for 30 minutes or more, and visually observing whether or not a dyed region is present in the evaluation membrane (Patent Document 1).

[0008] Another known method for investigating whether or not a reverse osmosis membrane is chemically deteriorated involves disassembling the reverse osmosis membrane element to be investigated, immersing the membrane pieces extracted from the element in question in a solution containing a mixture of an alkaline aqueous solution and pyridine, and identifying chemical deterioration, particularly oxidative deterioration, based on whether or not the solution changes color (Non-Patent Document 1).

[0009] On the other hand, chemical and physical degradation are often problems for membranes other than reverse osmosis membranes. For example, when the water to be treated contains oxidizing substances, such as groundwater or industrial wastewater, separation membranes made of organic polymers are oxidized by the oxidizing substances, resulting in chemical degradation. Furthermore, when the water to be treated contains high hardness substances, separation membranes undergo physical degradation. Regarding such degradation, tests known for physical degradation include the PDT (Pressure Decay Test) (Non-Patent Document 2) and air leak tests, and tests for examining degradation of separation performance due to chemical degradation, such as the bubble point test (Non-Patent Document 3), and at the laboratory level, the molecular weight cutoff test (Non-Patent Document 4).

[0010] International Publication No. 2015 / 063975 International Publication No. 2020 / 071507

[0011] R. Sandin et al. / Desalination and Water Treatment 51 (2013) 318-327 "Reverse osmosis membranes oxidation by hypochlorite and chlorine dioxide: spectroscopic techniques vs. Fujiwara test" United States Environmental Agency / MEMBRANE FILTRATION GUIDANCE MANUAL (2005), p. 183 Japanese Industrial Standards, JIS K3832-1990, Bubble point test method for microfiltration membrane elements and modules Haruhiko Oya et al., Membrane, Vol. 16, No. 1, 1991, p. 34 Journal of Membrane Science, Vol. 183, 2000, pp. 259-267 Journal of Membrane Science, Vol. 183, 2000, pp. 249-258

[0012] However, according to the investigations of the present inventors, conventional methods have the problem that in order to diagnose the cause of performance degradation of separation membrane modules used in various water treatment plants, the separation membrane modules must be disassembled, and membrane pieces must be removed and analyzed, which requires time to diagnose the cause of the problem and delays the implementation of countermeasures.

[0013] The present invention has been made in view of the above-mentioned conventional circumstances, and provides a separation membrane module condition diagnosis method that can extremely simply and quickly diagnose the cause of performance degradation of a separation membrane module.

[0014] In order to solve the above problems, the present invention has the following configuration: (1) A method for diagnosing the condition of a separation membrane module equipped with a permeate collection pipe having a plurality of collection holes for obtaining permeate from water to be treated, comprising: supplying test water containing two or more types of solutes to the separation membrane module, the two or more types of solutes in the test water including ionic substances with different valences or two or more types of substances with different molecular weights, or alternatively, changing the valence or molecular weight of one solute in test water containing a single solute so that the two or more types of solutes are supplied individually to the separation membrane module; sampling permeate at at least two or more positions in the permeate collection pipe; and comparing the separation performances of the at least two types of solutes calculated based on the difference between the solute concentrations in the permeate sampled at each sampling position and the solute concentration resulting from the permeate upstream of the sampling positions, thereby determining the type, degree, or location of an abnormality along the length of the permeate collection pipe within the separation membrane module. (2) The method for diagnosing the condition of a separation membrane module according to (1), further comprising: preparing a chemical degradation profile in which the separation performance of the at least two solutes is deteriorated by contacting the separation membrane module with a chemical; and preparing a physical degradation profile in which the separation performance of the at least two solutes is deteriorated by physically damaging the supply side of the separation membrane module; comparing the separation performances of the at least two solutes calculated based on the difference between the solute concentration in the permeate collected at each water sampling position and the solute concentration resulting from the permeate upstream of the water sampling position; calculating the contribution ratios of chemical degradation and physical degradation along the length of the permeate collection pipe in the separation membrane module from the chemical degradation profile, the physical degradation profile, and the separation performances of the at least two solutes; and determining at least the cause of degradation, the location of degradation, and the extent of degradation. (3) The method for diagnosing the condition of a separation membrane module according to (1) or (2), further comprising: comparing the separation performances based on a concentration index of the permeate, a concentration converted from the concentration index, a standard separation performance converted based on operating conditions, and a solute permeability coefficient calculated based on operating data.(4) The separation membrane module condition diagnosis method according to any one of (1) to (3), wherein the ionic substances of different valences are at least a substance composed of monovalent cations and a substance composed of divalent cations. (5) The separation membrane module condition diagnosis method according to any one of (1) to (3), wherein the ionic substances of different valences are at least a substance composed of monovalent anions and a substance composed of divalent anions. (6) The separation membrane module condition diagnosis method according to any one of (1) to (5), wherein the permeate concentration indicator is any one of electrical conductivity, total dissolved solids concentration, TOC, refractive index, turbidity, absorbance, luminescence intensity, chromaticity, IR spectrum, mass spectrometry spectrum, ion chromatography, inorganic substance concentration by ICP-AES mass spectrometry, and pH. (7) The method for diagnosing the state of a separation membrane module according to any one of (1) to (6), wherein the method for collecting permeate water at at least two or more positions in the permeate water collection pipe is a method for measuring the permeate water quality by measuring the permeate water quality by collecting permeate water at different positions in the separation membrane module through a thin tube having an outer diameter smaller than the inner diameter of the permeate water collection pipe. (8) The method for diagnosing the state of a separation membrane module according to any one of (1) to (7), wherein the separation performance of the test water in a pre-use state of the separation membrane module is measured or predicted in advance, and the state of the separation membrane module is determined based on the deviation from that value.

[0015] The method for diagnosing a separation membrane module of the present invention makes it possible to diagnose the cause of performance degradation of a separation membrane module extremely simply and quickly without dismantling the separation membrane module. As a result, by taking immediate countermeasures for the water treatment plant based on the diagnosis results, stable operation of the separation membranes in the water treatment plant becomes possible, and fresh water or purified water can be obtained stably and inexpensively.

[0016] FIG. 1 is a partially exploded perspective view of a typical spiral-wound reverse osmosis membrane element. FIG. 2 is a side cross-sectional view of a reverse osmosis membrane module in which spiral-wound reverse osmosis membrane elements are loaded into a pressure-resistant vessel. FIG. 3 is a side cross-sectional view of a typical hollow-fiber microfiltration membrane module. FIG. 4 is a schematic diagram showing an example of a method for measuring local permeate quality through a tube from a permeate piping of a reverse osmosis membrane module. FIG. 5 is a schematic diagram showing an example of a method for measuring local permeate quality through a tube from a permeate piping with a plurality of reverse osmosis membrane modules connected in series. FIG. 6 is a schematic diagram of a reverse osmosis membrane element performance evaluation device equipped with a separation membrane module having two or more permeate intake ports. FIG. 7 is an image diagram of a differential method for determining the rate of change in separation performance relative to initial performance from the difference between the permeate concentration at water sampling position n and the permeate concentration sampled at a water sampling position upstream (on the feedwater side) of water sampling position n. FIG. 8 is a graph showing the change in separation performance and the contribution rates of chemical and physical deterioration in Example 1. FIG. 9 is a graph showing the distribution of ionic substance concentrations in the permeate along the length of the permeate collecting pipe in Example 2. FIG. 10 is a graph showing the rate of change in separation performance along the length of the permeate collecting pipe and the contribution rates of chemical and physical deterioration along the length of the permeate collecting pipe in Example 2. FIG. 11 is a graph (differential method) showing the rate of change in separation performance along the length of the permeate collecting pipe and the contribution rates of chemical and physical deterioration along the length of the permeate collecting pipe in Example 2. FIG. 12 is a graph showing the change in separation performance and the contribution rates of chemical and physical deterioration in Example 3. FIG. 13 is a graph showing the distribution of ionic substance concentrations in the permeate along the length of the permeate collecting pipe in Example 4. FIG. 14 is a graph showing the rate of change in separation performance along the length of the permeate collecting pipe and the contribution rates of chemical and physical deterioration along the length of the permeate collecting pipe in Example 4. Fig. 15 is a graph (differential method) showing the rate of change in separation performance in the length direction of the permeate collecting pipe and the contribution rates of chemical and physical deterioration in the length direction of the permeate collecting pipe in Example 4. Fig. 16 is a graph showing the change in separation performance and the contribution rates of chemical and physical deterioration in Example 5. Fig. 17 is a graph showing the distribution of the concentration of each ionic substance in the permeate in the length direction of the permeate collecting pipe in Example 6.FIG. 18 is a graph showing the rate of change in separation performance along the length of the permeate collecting pipe and the contribution rates of chemical and physical deterioration along the length of the pipe in Example 6. FIG. 19 is a graph (differential calculus) showing the rate of change in separation performance along the length of the permeate collecting pipe and the contribution rates of chemical and physical deterioration along the length of the pipe in Example 6. FIG. 20 is a graph showing the change in separation performance and the contribution rates of chemical and physical deterioration along the length of the pipe in Example 7. FIG. 21 is a graph showing the distribution of the concentration of each ionic substance in the permeate along the length of the permeate collecting pipe in Example 8. FIG. 22 is a graph showing the rate of change in separation performance along the length of the permeate collecting pipe and the contribution rates of chemical and physical deterioration along the length of the pipe in Example 8. FIG. 23 is a graph (differential calculus) showing the rate of change in separation performance along the length of the permeate collecting pipe and the contribution rates of chemical and physical deterioration along the length of the pipe in Example 8.

[0017] The present invention will be described in detail below, but these are merely examples of preferred embodiments, and the present invention is not limited to these details. When simply referring to the present invention, it refers to a concept including the first, second, and third embodiments described below. Furthermore, the "to" in a numerical range refers to a range including the preceding and following numerical values, for example, "50 to 70,000" refers to a range of 50 or more and 70,000 or less.

[0018] [Method for diagnosing a separation membrane module] A diagnostic method according to a first embodiment of the present invention (hereinafter sometimes simply referred to as the first embodiment) is a method for diagnosing the condition of a separation membrane module for obtaining permeate from water to be treated, in which test water containing two or more types of solutes is supplied to the separation membrane module. The two or more types of solutes in the test water include ionic substances with different valences or two or more substances with different molecular weights, or two or more types of solutes are supplied individually to the separation membrane module by changing the valence or molecular weight of one solute in test water containing one solute. It is sufficient to measure the separation performance of at least two types of solutes based on the concentration of the solute contained in the permeate, and one type of test water or two or more types of test water may be supplied to the separation membrane module. The separation performance of the test water in a state before use of the separation membrane module is measured or predicted in advance, and a chemical degradation profile in which separation performance deteriorates when the separation membrane module is exposed to chemicals and a physical degradation profile in which separation performance deteriorates when physical damage is caused to the supply side of the separation membrane module are created in advance. The degree of chemical and physical degradation of the separation membrane module is determined by comparing the separation performance of the test water before and after degradation of the separation membrane module with the chemical degradation profile and the physical degradation profile. Specifically, the separation performance of the first solute and the second solute is determined to have a certain ratio based on the characteristics of the separation membrane. This separation performance is generally expressed as a rejection rate. For example, in the case of a reverse osmosis membrane module, as exemplified in the literature "Toray TSW-LE Series Catalog," a NaCl rejection rate of 99.6% and a boron rejection rate of 90% are described. As mentioned above, the major factors that cause a decrease in separation performance of a separation membrane module are chemical degradation and physical degradation, and the relationship between the separation performance decline due to each type of degradation is different. The chemical deterioration in this case may be, for example, the chemical deterioration that occurs when the separating functional layer of the reverse osmosis membrane comes into contact with chemicals and begins to deteriorate.

[0019] The chemical deterioration in the present invention is, for example, a change in the molecular chain arrangement of the polymer component of the separating functional layer, scission, or loss of low molecular weight components, and the form of chemical deterioration is not particularly limited.

[0020] In plants using reverse osmosis membrane elements, an oxidant is often used in the pretreatment of raw water supplied to the reverse osmosis membrane elements, and it is known that some of the oxidant leaks into the reverse osmosis membrane elements, causing oxidative degradation. While the present invention is not particularly limited to the oxidant used in pretreatment, the main cause of chemical degradation is often oxidative degradation caused by hypochlorous acid used in sterilizing raw water and hypobromous acid produced by conversion of hypochlorous acid.

[0021] In the case of chemical degradation, the removal performance of two types of solutes declines in a certain relationship. Specifically, as shown in, for example, Non-Patent Document 5 (Journal of Membrane Science, Vol. 183, 2000, pp. 259-267), it has been found that there is a constant, nearly proportional relationship between the decline in NaCl removal performance and the decline in boron removal performance. The inventors of the present application have confirmed through extensive research that this relationship is also true for other solutes. That is, the changes in the removal performance of two types of solutes follow a certain relationship, and in many cases, the performance declines in a linear relationship from the performance at the time of new to a certain level. That is, by measuring or predicting the separation performance of the test water of the separation membrane module before chemical and physical degradation occur, and judging the state of the separation membrane module based on the deviation from that value, abnormalities can be detected and diagnosed. The separation performance for two types of solutes before deterioration may be, for example, the performance when new, the initial performance at the start of the plant, the performance immediately after chemical cleaning, or the performance immediately after a long-term shutdown of the plant due to trouble or equipment maintenance, and may be set appropriately depending on the trouble that occurs in the plant. Regarding deterioration of a separation membrane module that occurs during the Nth use, for example, the separation performance before the Nth use may be measured in advance, and the state of the separation membrane module may be determined based on the deviation from the value of the state before use. Regarding deterioration of a separation membrane module that progresses between the first and Nth uses, the separation performance immediately after the first use may be measured or predicted, and the state of the separation membrane module may be determined based on the deviation from the separation performance measured or predicted during the Nth use.

[0022] Furthermore, when chemical degradation begins to occur in a reverse osmosis membrane, the permeation rate of monovalent ionic substances increases before the permeation rate of divalent ionic substances, and as chemical degradation progresses, the permeation rate of divalent ionic substances also increases, and the difference between the permeation rate of monovalent ionic substances and the permeation rate of divalent ionic substances decreases. Therefore, the degree of deterioration in the separation performance of monovalent ionic substances and divalent ionic substances can be used to diagnose the early stage of chemical degradation (minor degradation) due to contact with chemicals.

[0023] Simply put, for example, when diagnosing a reverse osmosis membrane using monovalent ionic substances and divalent ionic substances, if the concentration of the monovalent ionic substances is 0.9 mass% or more of the concentration of the monovalent ionic substances in the raw water and the concentration of the divalent ionic substances in the permeate in the permeate collection pipe is 0.2 mass% or less of the concentration of the divalent ionic substances in the raw water, it can be diagnosed that the main cause of deterioration of the reverse osmosis membrane element is chemical deterioration.

[0024] On the other hand, in the case of physical degradation, a relationship can be established by measuring the characteristics of a leak-free separation membrane module and a leaking separation membrane module. However, because physical degradation essentially involves the occurrence of scratches, large holes, adhesive joints, or other gaps in the membrane, resulting in leakage of feed water (such as test water or treated water), i.e., the permeate concentration deteriorates depending on the feed water composition, regardless of the membrane's separation performance, the relationship can also be roughly determined by calculation. For example, if the feed water has a Na ion concentration of 32,000 mg / L and a boron concentration of 5 mg / L, a normal new separation membrane module will have permeate concentrations of, for example, 100 mg / L and 0.5 mg / L, respectively. In the case of chemical degradation, the performance will deteriorate in a relationship of, for example, 150 mg / L and 0.75 mg / L. In the case of physical degradation, for example, if 0.1% of the feed water leaks, the permeate concentrations will be 132 mg / L and 0.505 mg / L, resulting in a significant deterioration in Na ion separation performance. In such cases, it can be determined that physical degradation has occurred.

[0025] After creating and acquiring a relationship profile between chemical deterioration due to contact with chemicals and physical deterioration due to scratches, etc., it is possible to determine the contribution of chemical deterioration and physical deterioration by comparing it with the measured separation performance of the separation membrane module and breaking it down into two arrows: the relationship between the rate of change between monovalent and divalent ions in the case of chemical deterioration and the relationship between the rate of change between monovalent and divalent ions in the case of physical deterioration, as shown in the vector diagram of chemical and physical deterioration in Figure 8. In this way, being able to determine whether chemical or physical deterioration is the main cause of deterioration makes it possible to take appropriate measures to deal with the problem.

[0026] In the first embodiment, test water containing a mixture of two types of ions with different valences is used, but it is also possible to prepare two types of test water containing only one type of different solute, supply each test water separately to the separation membrane module, collect the permeate, and obtain two types of separation performance, after which the separation membrane module can be diagnosed.

[0027] A second embodiment of the present invention (hereinafter, sometimes simply referred to as the second embodiment) will be described below. The diagnostic method for a spiral reverse osmosis membrane element according to the second embodiment includes: supplying first treated water containing monovalent ionic substances under pressure at a pressure equal to or greater than the osmotic pressure of the first treated water to a spiral reverse osmosis membrane element equipped with a permeate collection pipe having a plurality of collection holes; separating the first treated water into a first concentrated water and a first permeate; sampling the first permeate at a plurality of positions within the permeate collection pipe from the feed water side to the concentrated water side; and before or after sampling the first permeate, supplying second treated water containing divalent ionic substances under pressure at a pressure equal to or greater than the osmotic pressure of the second treated water. The second treated water is pressurized and supplied to the reverse osmosis membrane element using a pressure force, the second treated water is separated into a second concentrated water and a second permeate, the second permeate is sampled at a plurality of locations in the permeate collection pipe, and the concentration of the monovalent ionic substance in the first permeate is determined by measuring the water quality of the first permeate, and the concentration of the divalent ionic substance in the second permeate is determined by measuring the water quality of the second permeate, and the deterioration state of the reverse osmosis membrane element is diagnosed from changes in the concentrations of the monovalent ionic substance and the divalent ionic substance.

[0028] Furthermore, the rate of change in separation performance relative to the initial performance is calculated from the concentrations of the monovalent ionic substances and the divalent ionic substances in the permeate at each water sampling point in the permeate collection pipe of the reverse osmosis membrane element, and this is broken down into two arrows representing the relationship between the rate of change between monovalent ions and divalent ions in the case of chemical degradation and the relationship between the rate of change between monovalent ions and divalent ions in the case of physical degradation, making it possible to determine the contribution of chemical and physical deterioration at each water sampling point. Combining these results allows the rate of change in separation performance along the length of the reverse osmosis membrane element and the contribution rates of chemical and physical deterioration to be calculated, clarifying the extent and location of chemical and physical deterioration in the separation membrane module and enabling more appropriate countermeasures to be taken against problems.

[0029] 7, the rate of change in separation performance relative to the initial performance is calculated from the difference between the concentrations of the monovalent ionic substances and the divalent ionic substances in the permeate at a water sampling point n in the permeate collection pipe of the reverse osmosis membrane element and the concentrations of the monovalent ionic substances and the divalent ionic substances in the permeate sampled at a water sampling point upstream (on the feedwater side) of the water sampling point n, and the rate of change in separation performance relative to the initial performance is calculated from the difference between the concentrations of the monovalent ionic substances and the divalent ionic substances in the permeate sampled at a water sampling point upstream (on the feedwater side) of the water sampling point n. This is then broken down into two arrows representing the relationship between the rate of change between monovalent ions and divalent ions in the case of chemical degradation and the rate of change between monovalent ions and divalent ions in the case of physical degradation, thereby making it possible to determine the contribution of chemical and physical deterioration at each water sampling point. By combining these, the rate of change in separation performance along the length of the reverse osmosis membrane element and the contribution rates of chemical and physical deterioration can be calculated more accurately, thereby clarifying the extent and location of chemical and physical deterioration in the separation membrane module and enabling more appropriate countermeasures to be taken against problems. By using this analysis method, it is possible to more accurately identify the cause, location, and extent of deterioration, particularly when localized physical deterioration such as membrane scratches, wrinkles, or leakage from the membrane edge or woven area occurs, without being affected by the performance of the upstream side (feed water side) of the reverse osmosis membrane element.

[0030] The permeate concentration C of the collection hole (nth) at the water sampling position n ｐ(n) can be calculated from the amount of solute material. Specifically, F(n) × C(n) = F(n-1) × C(n-1) + F ｐ (n) × C ｐ (n) ...(1) F(1)=F ｐ (1) C(1) = C ｐ (1) ΔC(n)=C(n)-C(n-1) (1) Rearranging the equation, C ｐ (n)=(F(n)×C(n)−F(n−1)×C(n−1)) / F ｐ (n) ... (2) F ｐ (1) = F ｐ (2) = ... = F ｐ (N)=F(N) / N...(3) F(n)=n×F ｐ (1) = n × F(N) / N ... (4) C(1) = C(2) = ... = C(N) ... (5) From (2) to (5) above, C ｐ (n) = C(n) + (n-1) × ΔC(n) where F ｐ (n): Permeation volume of the collecting hole (nth hole) [m ３ / d] C ｐ (n): Permeate concentration of the collection hole (nth) [mg / L] F ｐ (n-1): Permeation volume of the water collection hole (n-1th) [m ３ / d] C ｐ (n-1): Permeate concentration of the water collection hole (n-1th) [mg / L] F(n): Permeate volume of the water collection position (nth) in the water collection pipe [m ３ / d] C(n): Permeate concentration at the water collection position (nth) in the water collection pipe [mg / L] F(n-1): Permeate volume at the water collection position (n-1th) in the water collection pipe [m ３ / d] C(n-1): Permeate concentration [mg / L] at the water sampling position (n-1th) in the collection pipe.

[0031] Simply put, the value obtained by subtracting the permeate concentration at the nearest water sampling position (n-1th) in the water collection pipe from the permeate concentration at the water sampling position (nth) in the water collection pipe is C ｐ (n) may also be used.

[0032] The concentration of monovalent ionic substances in the first treated water is preferably 50 to 70,000 mg / L, more preferably 500 to 35,000 mg / L. The concentration of divalent ionic substances in the second treated water is preferably 50 to 10,000 mg / L, more preferably 50 to 4,000 mg / L.

[0033] The first treated water can be obtained, for example, by blending a monovalent ionic substance with pure water, and the second treated water can be obtained, for example, by blending a divalent ionic substance with pure water.

[0034] The reverse osmosis membrane element is as described above.

[0035] The pressure at which the mixed water to be treated is supplied to the reverse osmosis membrane element under pressure is preferably 0.5 to 10 MPa, and more preferably 0.75 to 6 MPa.

[0036] The flow rate of the first treated water when separating the first treated water into the first concentrate and the first permeate is preferably 50 to 1000 L / min, and more preferably 120 to 500 L / min, for example, when the reverse osmosis membrane element has an outer diameter of approximately 201 mm (approximately 8 inches). The temperature of the first treated water at this time is preferably 5 to 45°C, and more preferably 20 to 35°C. The pH of the first treated water at this time is preferably 2 to 11, and more preferably 6 to 8.5, because chemical degradation occurs when the pH becomes close to a strong acid or strong alkali.

[0037] The flow rate of the second treated water when separating the second treated water into the second concentrate and the second permeate is preferably 50 to 1000 L / min, and more preferably 120 to 500 L / min, for example, when the reverse osmosis membrane element has an outer diameter of approximately 201 mm (approximately 8 inches). The temperature of the second treated water in this case is preferably 5 to 45°C, and more preferably 20 to 35°C. The pH of the second treated water in this case is preferably 2 to 11, and more preferably 6 to 8.5, because chemical degradation occurs when the pH becomes close to a strong acid or strong alkali.

[0038] The concentration of monovalent ionic substances in the first permeated water can be determined by measuring the quality of the first permeated water, and the concentration of divalent ionic substances in the second permeated water can be determined by measuring the quality of the second permeated water.

[0039] Specific examples of the water quality of the first permeate and the second permeate include the electrical conductivity, ion concentration, or total dissolved solids concentration of the first permeate and the second permeate.

[0040] Furthermore, it is preferable that the concentration of the monovalent ionic substance is a value determined from the electrical conductivity of the first permeated water, and the concentration of the divalent ionic substance is a value determined from the electrical conductivity of the second permeated water. By determining the concentration of each ionic substance from the electrical conductivity of each permeated water, measurements such as ion chromatography and titration can be omitted.

[0041] In the second embodiment, the order in which the first treated water and the second treated water are pressurized and supplied is not limited, and either may be supplied first. For example, if the first treated water is pressurized and supplied first, the first treated water may be converted to water such as pure water and supplied to the reverse osmosis membrane element before the second treated water is pressurized and supplied, and the first treated water may be washed out.

[0042] In the first embodiment described above, Na (a monovalent strong cationic substance) and boron (a trivalent weak anionic substance) are used, but it is also preferable to use ionic substances with different valences, and it is also preferable to use substances with different molecular weights. Furthermore, it is good to target components that have large differences in removal performance or are easy to measure. In addition, since the surface of the separation membrane is often charged, it is also preferable that the two types of ions are the same type but with different valences. That is, for example, monovalent cations and divalent cations, or monovalent anions and divalent anions.

[0043] The monovalent ionic substance used in the present invention is not particularly limited, but it is preferable that it completely dissociates and becomes neutral when dissolved in water such as pure water. For example, Na and Mg, Cl and SO are particularly preferred because they exist in large quantities in nature, are easy to handle, and are relatively inexpensive. ４is highly preferred. Furthermore, separation membranes for water treatment treating natural water such as seawater or river water are often negatively charged on the membrane surface because natural organic matter is generally weak anions. In such cases, it is preferable to use cations such as Na and Mg. In particular, sodium chloride is preferably used as the monovalent ionic substance. Furthermore, the divalent ionic substance used in the present invention is not particularly limited as long as it completely dissociates and becomes neutral when dissolved in water such as pure water, but for the same reason, magnesium sulfate is preferably used. Selecting these simultaneously is highly preferred because the cations and anions have different properties.

[0044] The concentrations in the test water are preferably set to conditions that facilitate measurement, but are not particularly limited. In general, the concentrations of monovalent ionic substances are preferably 50 to 70,000 mg / L, more preferably 500 to 35,000 mg / L, and the concentrations of divalent ionic substances are preferably 50 to 10,000 mg / L, more preferably 500 to 4,000 mg / L.

[0045] While the "at least two types of test water" in this invention essentially have different solutes, it is also possible to obtain substantially different solutes by changing the pH or temperature of the same solute. For example, changing the pH of a solute containing carbonate dissociates, i.e., changes its valence, resulting in a solute with different properties. Changing the temperature also changes the properties of solutes, particularly polymeric solutes, so this method is applicable. Changing the pH or temperature can also change membrane performance, making it easier to determine chemical changes. On the other hand, physical deterioration generally does not affect membrane performance. However, changing the pH or temperature requires chemicals, thermal energy, and the time and effort required, so care must be taken.

[0046] Furthermore, it is preferable for the test water to contain only the components to be measured, as this increases analytical accuracy. However, if one wishes to diagnose a separation membrane module in use (during plant operation), it is necessary to either stop the supply of treated water and switch to test water, or remove the separation membrane module from the equipment and load it into a diagnostic device. If one wishes to perform this diagnosis during actual plant operation, it is also possible to use the treated water as test water during operation. However, since solutes other than those targeted for comparative evaluation are often contained, it is important to note that this will affect analytical accuracy. If the accuracy of concentration analysis of the treated water and permeate during operation is poor, one preferable method is to increase sensitivity by pulse-adding the two solutes targeted for comparative evaluation to the treated water.

[0047] Generally, the separation performance of a membrane module is expressed in terms of removal rate (=1-permeate concentration / feed water concentration), permeability (=permeate concentration / feed water concentration), permeability coefficient, etc.

[0048] The permeability coefficient can be expressed simply as, for example, kg / m ２ As expressed in units of .times. ...

[0049] Specifically, J ｖ =L ｐ (ΔP-Δπ) J ｓ = P(C ｍ -C ｐ ) Δπ = π(C ｍ )-π(C ｐ ) (C ｍ -C ｐ ) / (C ｆ -C ｐ ) = exp(J ｖ / k) Note that J ｖ : Pure water permeation flux [m ３ / m ２ ・s] Jｓ : Solute permeation flux [kg / m ２ ・s] L ｐ : Pure water permeability coefficient [m ３ / m ２ ・Pa・s] P: TDS permeability coefficient [m / s] π: Osmotic pressure [Pa] Δπ: Osmotic pressure difference [Pa] ΔP: Operating pressure difference [Pa] C ｍ : Supply water film surface concentration [kg / m ３ ] C ｆ : supply water bulk concentration [kg / m ３ ] C ｐ : Permeated water concentration [kg / m ３ ] k : solute mass transfer coefficient [m / s]

[0050] Here, the solute mass transfer coefficient k is a value determined by the separation membrane module structure and the evaluation cell, but it can be calculated as the membrane surface flow rate Q [m ３ / s] or the membrane surface flow velocity u [m / s].

[0051] For the flat membrane cell shown in Reference 2, k = 1.63 × 10 －３ ・Q ０．４０５３ is.

[0052] Therefore, from the above equation, the unknown L ｐ , P.C. ｍ In the case of a separation membrane module, it is possible to obtain the average value of the entire module, or, as shown in Reference 1, to calculate L by integrating in the length direction of the membrane element. ｐ , P can be calculated by fitting.

[0053] The separation membrane module to which the present invention is applied can be used with various separation membranes such as reverse osmosis membranes, nanofiltration membranes, ultrafiltration membranes, microfiltration membranes, ion exchange membranes, gas separation membranes, and filter cloths, but is particularly preferred when applied to microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes for water treatment used to treat seawater, river water, etc. to produce drinking water and various types of water, as this contributes to reducing water treatment costs. The module shape is also not particularly limited, and may be a spiral type, hollow fiber type, flat membrane parallel plate type, or plate and frame type.

[0054] Materials that can be used for reverse osmosis membranes and nanofiltration membranes include polymeric materials such as cellulose acetate polymers, polyamides, polyesters, polyimides, vinyl polymers, etc. The membrane structure may be either an asymmetric membrane having a dense layer on at least one side of the membrane and gradually increasing micropores in size from the dense layer toward the interior of the membrane or toward the other side, or a composite membrane having a very thin functional layer made of a different material on the dense layer of the asymmetric membrane.

[0055] Examples of ultrafiltration membranes and microfiltration membranes include porous membranes such as polyacrylonitrile, polyimide, polyethersulfone, polyphenylene sulfide sulfone, polytetrafluoroethylene, polypropylene, and polyethylene.

[0056] Furthermore, by combining these porous membranes with rubbery polymers such as cross-linked silicone, polybutadiene, polyacrylonitrile butadiene, ethylene propylene rubber, and neoprene rubber as a functional layer, the present invention can be applied to form highly permeable composite separation membranes.

[0057] The structure of a separation membrane module varies depending on the application of the membrane, but in the case of reverse osmosis membranes and nanofiltration membranes, the spiral type is common. Figure 1 shows a partially exploded perspective view of an element used in the most typical reverse osmosis membrane module.

[0058] This spiral-type reverse osmosis membrane element generally has a reverse osmosis membrane unit including a reverse osmosis membrane 1, a permeate flow path material 2, and a water-to-be-treated flow path material (net spacer) 3 wound in a spiral shape around a permeate collection pipe 4 having water collection holes, and the outside of the reverse osmosis membrane unit is covered with a film or glass fiber impregnated with a curable resin, and an anti-telescope plate 5 is attached to at least one end of this fluid separation element.

[0059] For the water-to-be-treated flow path material, a net-like or mesh-like lattice flow path material, a grooved sheet, a corrugated sheet, etc. can be used. For the permeate flow path material, a net-like or mesh-like lattice flow path material, a grooved sheet, a corrugated sheet, etc. can be used. In either case, the net or sheet may be independent of the separation membrane, or may be integrated by bonding or fusion.

[0060] The water 6 to be treated is supplied through the anti-telescope plate 5 and passes through the water flow path material 3 to the reverse osmosis membrane, where it is separated by membrane separation into permeate 7 and concentrated water 8. The permeate 7 is collected inside the permeate collection pipe 4 through holes in the side of the pipe, passes through the pipe, and is collected from the opening of the pipe. This spiral element can be used by loading it into a pressure vessel 9 as shown in Figure 2.

[0061] When the reverse osmosis membrane is a flat membrane, the type known as the spiral type described above is generally used. These elements can be placed in a cylindrical housing such as a pressure vessel and connected to pipes for feed water, permeate water, and concentrated water for use.

[0062] The pressure at which the mixed water to be treated is supplied to the reverse osmosis membrane element under pressure is preferably 0.5 to 10 MPa, and more preferably 0.75 to 6 MPa.

[0063] The flow rate of the mixed water to be treated when separating the mixed water to be treated into the mixed concentrate and the mixed permeate is preferably 50 to 1000 L / min, and more preferably 120 to 500 L / min, for example, when the reverse osmosis membrane element has an outer diameter of about 201 mm (about 8 inches). The temperature of the mixed water to be treated in this case is preferably 5 to 45°C, and more preferably 20 to 35°C. The pH of the mixed water to be treated in this case is preferably 2 to 11, and more preferably 6 to 8.5, because chemical degradation occurs when the pH becomes close to a strong acid or strong alkali.

[0064] In this embodiment, the permeate may be collected from the right side (concentrate outlet side) of the permeate collection pipe of the pressure vessel 9 as shown in FIG. 2, or from the left side (feed water inlet side) of the permeate collection pipe, which is sealed in FIG. 2.

[0065] On the other hand, hollow fiber membrane modules to which the present invention is applied generally have a shape in which the spaces between the hollow fiber membranes and between the hollow fiber membranes and the module container are airtightly sealed (potted) to create openings. This allows the hollow fiber membranes themselves to isolate the outside and inside of the hollow fiber membranes, allowing separation processing to be performed through the membranes. Hollow fiber membrane module structures include a "double-ended open-type" in which both ends of the hollow fiber membranes are potted and then opened from both ends, a "single-ended open-type" in which both ends are potted and then only one end is opened, a "U-shaped" module in which the hollow fiber membranes are U-shaped and only one end of the hollow fiber membrane is open, and a "comb-shaped" module in which the U-shaped portion is cut and each hollow fiber membrane is individually sealed. The filtration direction can be either one in which the raw water to be treated flows inside the hollow fiber membranes (internal pressure type) or one in which it flows outside (external pressure type), and the present invention can be applied to all of these.

[0066] There are no particular restrictions on the measurement of the test water or permeate concentration, and various measurement methods can be used, such as electrical conductivity, total dissolved solids concentration, TOC, refractive index, turbidity, absorbance, luminescence intensity, chromaticity, IR spectrum, mass spectrometry spectrum, ion chromatography, inorganic substance concentration by ICP optical emission mass spectrometry, pH, and radiation. However, when using two types of test water consisting of one type of solute, it is preferable to use a simple measurement method such as electrical conductivity for ionic substances, and refractive index, absorbance, and luminescence intensity for polymers.

[0067] To determine the concentration of each ionic substance from the electrical conductivity of each permeate, the relationship between the concentration of each ionic substance and the electrical conductivity may be determined in advance using a conventionally known method. By determining the relationship between the concentration of each ionic substance and the electrical conductivity in advance, the electrical conductivity can be converted into the concentration.

[0068] In the case of test water containing two or more solutes, multiple components can be measured at once by resolving retention times or wavelengths using a chromatograph or absorbance, scanning, and then detecting and measuring with a detector. It is also a preferable method to connect two different detectors simultaneously to measure two different water quality indicators. These methods are particularly preferable when measuring water quality online, in terms of the complexity and accuracy of the measurement.

[0069] In the first embodiment, the separation performance of the entire separation membrane module is measured and diagnosed, but the method of the present invention can also be used to detect local abnormalities in the separation membrane module. That is, by taking permeate water from at least two locations in the module and comparing the separation performance, it becomes possible to diagnose what type of abnormality has occurred and at what location within the module.

[0070] As a specific example, a spiral-type reverse osmosis membrane module is used as a second embodiment, and its side cross-sectional view is shown in Figure 4. In this example, the mixed permeate is sampled at multiple locations in the permeate collection pipe, the separation performance of the sampling points is acquired, and the nature and location of the abnormality can be identified by, for example, passing a thin tube 10 through the permeate collection pipe, fastening one end of the tube 10 at a predetermined position in the permeate collection pipe, and sampling the mixed permeate at that position from the other end of the tube 10.

[0071] During this process, the tube 10 is gradually moved to collect mixed permeate at multiple locations, and the concentrations of monovalent ionic substances and divalent ionic substances in the resulting mixed permeate are measured using techniques such as ion chromatography or titration. The deterioration state of the separation membrane module can be diagnosed from the changes in the concentrations of monovalent ionic substances and divalent ionic substances.

[0072] When using a tube as described above, by marking length scales on the tube 10 in advance, it is possible to identify where the end of the tube 10 is located within the permeate collection pipe of the separation membrane module.

[0073] That is, when measuring the electrical conductivity of each permeate using a tube, the tube is passed through the permeate collecting pipe, one end of the tube is fastened at a predetermined position in the permeate collecting pipe, and the permeate at that position is sampled from the other end of the tube to measure the electrical conductivity.

[0074] Here, if a tube is passed through the permeate piping of the pressure vessel and the tip of the tube is fastened at a predetermined position, and permeate is sampled at multiple locations, water samples can be taken from both ends of the permeate collection pipe, the feed water side and the concentrate side, at approximately equal intervals between them. The spacing width is not particularly limited, but for evaluation of a single reverse osmosis membrane element with a total length of approximately 1 m, intervals of approximately 5 cm are preferred. Also, while Figure 4 shows the tube 10 inserted from the downstream side of the permeate collection pipe, it is also possible to insert the tube with the upstream side open. Furthermore, while Figure 4 shows the application of the present invention to a single membrane module, in the case of a spiral-wound module, multiple modules can be connected in series with permeate collection pipes, as illustrated in Figure 5, making it possible to sample and evaluate multiple modules at the same time.

[0075] Alternatively, the electrical conductivity of each permeate may be measured by installing a plurality of electrical conductivity sensors at a plurality of locations in the permeate collection pipe.

[0076] There are no particular limitations on the separation membrane module to which the second embodiment can be applied. However, as illustrated in FIG. 2 , a flat membrane module into which a thin tube can be easily inserted, particularly a spiral reverse osmosis membrane module into which a permeate collection pipe can be easily inserted in a straight line, is preferred.

[0077] In the case of spiral reverse osmosis membranes, raw water may occasionally be mixed in due to deterioration of a seal such as an O-ring sealing one end of the permeate collection pipe, which may result in a high concentration of the divalent ionic substances within approximately 30 cm from the sealed end of the permeate collection pipe. Therefore, if an abnormality is found in the concentration of the divalent ionic substances from a point 30 cm away from one sealed end of the permeate collection pipe to the other end of the permeate collection pipe, it can be determined that a problem with the seal has occurred.

[0078] Of course, in the second embodiment, it is also possible to extract the separation membrane module from the pressure vessel of an actual plant and diagnose the degradation state of the separation membrane module using another evaluation device and the above-mentioned method.

[0079] As a third embodiment, when a separation membrane module has two or more permeate intake ports, in order to obtain more detailed information, a device such as that shown in FIG. 6 is applied, and as in Patent Document 2 "WO 2020 / 071507: Method for creating a water quality profile, method for inspecting a separation membrane module, and water treatment device," the separation membrane module has a structure that allows permeate to be taken in from at least two locations, and by changing the flow rate ratio of the permeate, it is possible to obtain results similar to those of the second embodiment.

[0080] This method is highly preferable because it uses an online water quality detector to automatically and continuously obtain operating conditions and concentration indicators, calculate standard separation performance and solute permeability coefficients, and enable constant abnormality diagnosis, including the contribution rates of physical and chemical deterioration. This method is a preferable embodiment because it enables detection of abnormal positions without inserting a tube into the separation membrane module.

[0081] However, since this method may cause errors if there is a local distribution of permeability, a method has been proposed in which accuracy is improved by using this method in combination with a method of inserting a tube into the permeate collection pipe, as in Japanese Patent Application Laid-Open No. 2023-20636.

[0082] A deterioration diagnosis device according to a third embodiment of the present invention (hereinafter sometimes simply referred to as the third embodiment) will be described using an example in which a spiral reverse osmosis membrane element is used as a separation membrane module and test water containing two different types of test water, one containing a monovalent ionic substance and the other containing a divalent ionic substance, is used.

[0083] The deterioration diagnosis device for a reverse osmosis membrane element according to the third embodiment is a deterioration diagnosis device for a reverse osmosis membrane element having a separation membrane that separates water to be treated, which contains at least one of first water to be treated containing monovalent ionic substances and second water to be treated containing divalent ionic substances, into concentrated water and permeated water, and a water collection pipe that collects the permeated water, and the deterioration state of the reverse osmosis membrane element is diagnosed by inputting into the computer the operating conditions of the reverse osmosis membrane element during operation, and the water quality of the first permeated water containing the monovalent ionic substances and the water quality of the second permeated water containing the divalent ionic substances. The computer functions as a deterioration diagnosis calculation means that uses a data input means, a data recording means that records the operating conditions, the water quality of the first permeate, and the water quality of the second permeate in a computer, the performance of the reverse osmosis membrane element determined from the operating conditions, the water quality of the first permeate, and the water quality of the second permeate, and data on the rate of change between the concentration of the monovalent ionic substance in the first permeate and the concentration of the divalent ionic substance in the second permeate, based on predetermined deterioration diagnosis criteria for the reverse osmosis membrane element.

[0084] In the third embodiment, a computer having the above-described means is operated to diagnose the deterioration state of a reverse osmosis membrane element. The third embodiment can be recorded in a recording device such as the computer's memory or a hard disk, and the recording format is not particularly limited.

[0085] The computer has a data input means for extracting and inputting data relating to the operating conditions of the reverse osmosis membrane element during operation and the water quality of the first permeate and the water quality of the second permeate for each process, and the measured values ​​for each process obtained by the data input means are recorded in the data recording means.

[0086] Using the data recorded in the data recording means, the presence or absence of deterioration of the reverse osmosis membrane element is diagnosed based on the predetermined deterioration diagnosis criteria for the reverse osmosis membrane element.

[0087] Examples of the data recorded in the data recording means include the performance of the reverse osmosis membrane element determined based on the operating conditions, the water quality of the first permeate, and the water quality of the second permeate, and data on the rate of change between the concentration of the monovalent ionic substance in the first permeate and the concentration of the divalent ionic substance in the second permeate.

[0088] According to the third embodiment, the cause of performance degradation of a reverse osmosis membrane element can be diagnosed extremely simply and quickly.

[0089] Specific examples of the water to be treated, the structure of the reverse osmosis membrane element, and the water qualities of the first permeate and second permeate in the third embodiment are the same as those in the first and second embodiments.

[0090] In the third embodiment, the diagnostic criteria for determining whether the primary cause of deterioration of a reverse osmosis membrane element is chemical deterioration or physical deterioration are the same as those in the first and second embodiments. The third embodiment can be recorded on a computer-readable recording medium and used.

[0091] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0092] Example 1 Because a tendency for the quality of the produced water to deteriorate was observed at an ultrapure water production plant, a reverse osmosis membrane element in use was removed from a vessel, and one reverse osmosis membrane element was loaded into a pressure vessel as shown in Figure 2, and the separation performance was measured using a performance evaluation device.

[0093] Test water with a concentration of 1500 mg / L was prepared by dissolving sodium chloride in pure water, and the system was operated with a supply pressure of 1.5 MPa, a concentrated water flow rate of 80 L / min, a water temperature of 25°C, and a pH of the water to be treated of 7, and permeated water was obtained from the pressure vessel. Permeated water 7 was taken out and its electrical conductivity was measured, and the concentration was calculated from the relationship between sodium chloride and electrical conductivity.

[0094] Thereafter, the test water was changed to pure water and supplied to the membrane element loaded in the pressure vessel. After washing out the sodium chloride, magnesium sulfate was dissolved in the pure water to prepare a solution with a concentration of 2000 mg / L. The system was operated with a supply pressure of 1.5 MPa, a concentrated water flow rate of 80 L / min, a water temperature of 25°C, and a pH of 7 for the water to be treated. The electrical conductivity of the permeate containing magnesium sulfate in the permeate collection pipe was measured in the same manner as for sodium chloride, and the concentration was determined from the relationship between the magnesium sulfate concentration and electrical conductivity.

[0095] As a result, the sodium chloride removal rate was 98.80% (transmittance 1.20%) and the magnesium sulfate removal rate was 99.93% (transmittance 0.07%). The performance of this reverse osmosis membrane element as produced, measured under the same conditions, was 99.74% (transmittance 0.26%) for sodium chloride and 99.97% (transmittance 0.03%) for magnesium sulfate, and the rates of decline in separation performance were 4.6 and 2.7 times, respectively, compared to the initial rates. Since the rate of decline in magnesium sulfate separation performance was not significant compared to the rate of decline in sodium chloride separation performance, this confirmed at least an indication that chemical degradation was the primary cause.

[0096] Furthermore, as a relational expression for chemical degradation, a relational expression (1) for the permeability of sodium chloride and magnesium sulfate was created based on the separation performance (permeability) of sodium chloride and magnesium sulfate created using a reverse osmosis membrane that had been forcibly chemically degraded by immersing it in hypochlorous acid. Furthermore, as a relational expression for physical degradation, a relational expression (2) for the permeability of sodium chloride and magnesium sulfate was created, assuming that as the damage grew, a small amount of feed water was mixed due to leakage. Each relational expression is shown in Figure 8, and when the initial (before degradation) and post-degradation permeability were plotted, the contribution ratio of chemical degradation to physical degradation was calculated to be 97:3, indicating that the deterioration in separation performance was almost entirely due to chemical degradation.

[0097] Example 2 The same reverse osmosis membrane element as in Example 1 was evaluated under the same conditions as in Example 1. However, because a tendency for the quality of the produced water to deteriorate was observed at an ultrapure water production plant, a reverse osmosis membrane element in use was removed from the vessel, and one reverse osmosis membrane element was loaded into a pressure vessel as shown in Figure 2 and subjected to measurement of separation performance using a performance evaluation device. However, as shown in Figure 4, permeated water was sampled from the permeate collection pipe of the reverse osmosis membrane element through a tube passed from the permeate piping of the pressure vessel. The electrical conductivity of the permeated water sampled at multiple positions in the collection pipe from the feed water side to the concentrated water side was measured, and the sodium chloride concentration and magnesium sulfate concentration were determined from the relationship between the electrical conductivity and the concentration.

[0098] The results are shown in Figure 9. Based on these results, the rate of change in separation performance calculated in the longitudinal direction in the same manner as in Example 1, and the contribution rate at each position calculated in the same manner as in Figure 8, are shown in Figures 10 and 11. From these results, it was determined that the rate of change in separation performance for magnesium sulfate at the front and rear was small, and that the occurrence of physical deterioration was minor.

[0099] From the above, it was determined that the main cause of deterioration of the reverse osmosis membrane elements was chemical degradation. When the chemical usage process of the plant was checked, it was found that the sodium hypochlorite added in the raw water disinfection process had been in excess of the prescribed amount, and it was presumed that it had leaked into the raw water. Therefore, the operational management of the chemical addition process was quickly improved, which prevented serious trouble at the plant and allowed water production to continue.

[0100] Example 3 A tendency for the quality of the produced water to deteriorate was observed in a pure water manufacturing plant that periodically performs hot water sterilization. Therefore, a reverse osmosis membrane element that was in use was removed from a vessel, and one reverse osmosis membrane element was loaded into a reverse osmosis membrane element evaluation device.

[0101] The sodium chloride and magnesium sulfate concentrations of the permeate were determined in the same manner as in Example 1. The sodium chloride removal rate was 98.50% (transmittance 1.50%) and the magnesium sulfate removal rate was 98.93% (transmittance 1.07%). The performance of this reverse osmosis membrane element as produced, measured under the same conditions, was 99.82% (transmittance 0.18%) for sodium chloride and 99.98% (transmittance 0.02%) for magnesium sulfate. The rates of decline in separation performance were 8.4 and 59.2 times, respectively, compared to the initial rates. The decline in sodium chloride separation performance was significant, at least five-fold. Furthermore, the rate of decline in magnesium sulfate separation performance was extremely significant, confirming indications that physical deterioration was at least the primary cause.

[0102] Furthermore, as a relational expression for chemical degradation, a relational expression (1) for the permeability of sodium chloride and magnesium sulfate was created based on the separation performance (permeability) of sodium chloride and magnesium sulfate created using a reverse osmosis membrane that had been forcibly chemically degraded by immersing it in hypochlorous acid. Furthermore, as a relational expression for physical degradation, a relational expression (2) for the permeability of sodium chloride and magnesium sulfate was created, assuming that as the damage grew, a small amount of feed water was mixed due to leakage. When each of these relational expressions was plotted in Figure 12, and the initial (before degradation) and post-degradation permeability were plotted, the contribution ratio of chemical degradation to physical degradation was calculated to be 21:79, and it was determined that physical degradation was the main cause of the deterioration in separation performance.

[0103] Example 4 The same reverse osmosis membrane element as in Example 3 was evaluated under the same conditions as in Example 2, and permeated water was sampled from the permeated water collection pipe of the reverse osmosis membrane element. The electrical conductivity of the permeated water sampled at multiple positions in the permeated water collection pipe from the feed water side to the concentrated water side was measured, and the sodium chloride concentration and magnesium sulfate concentration were determined from the relationship between the electrical conductivity and the concentration.

[0104] The results are shown in Figure 13. Based on these results, the rate of change in separation performance was calculated in the longitudinal direction in the same manner as in Example 1, and the contribution rate at each position was calculated using the same method as in Figure 12. These results are shown in Figures 14 and 15. From Figure 14, it was determined that the rate of change in separation performance for magnesium sulfate was greater at the rear than at the front, and that not only chemical degradation was occurring but also physical degradation was occurring, with physical degradation being particularly significant in the central portion from 300 mm to 700 mm. Furthermore, as shown in Figure 15, it was determined that physical degradation was occurring primarily in the central portion from 300 mm to 700 mm.

[0105] Based on the above, it was determined that physical deterioration contributed significantly to the performance degradation of the reverse osmosis membrane elements. An inspection of the hot water sterilization process as part of the plant's operating procedures revealed that, during cooling during the hot water sterilization process, 25°C cooling water was supposed to be introduced after the water temperature in the plant piping had dropped to 35°C. However, 25°C cooling water was mistakenly introduced when the water temperature in the plant piping was 40°C. It was assumed that rapid cooling from a water temperature of over 35°C had caused wrinkles on the separation membrane surface, resulting in physical deterioration. By quickly improving the operating procedures for the hot water sterilization process and replacing the affected reverse osmosis membrane elements, the plant was able to avoid serious trouble and continue producing water.

[0106] Example 5 During a periodic inspection of an ultrapure water production plant, a reverse osmosis membrane element in use was removed from the vessel, and the sodium chloride and magnesium sulfate concentrations of the permeate at multiple positions in the permeate collection pipe were determined using the same method as in Example 1. The sodium chloride removal rate was 99.37% (permeability 0.63%) and the magnesium sulfate removal rate was 99.93% (permeability 0.07%). The as-manufactured performance of this reverse osmosis membrane element, measured under the same conditions, was 99.80% (permeability 0.20%) for sodium chloride and 99.98% (permeability 0.02%) for magnesium sulfate. The rates of decline in separation performance were 3.1 and 3.5 times, respectively, compared to the initial values. The rates of decline in magnesium sulfate separation performance were not significantly different from the rate of decline in sodium chloride separation performance, confirming at least indications that chemical degradation was the primary cause.

[0107] Furthermore, similarly to Example 1, when the initial (before deterioration) and post-deterioration transmittances were plotted in FIG. 16, the contribution ratio of chemical deterioration to physical deterioration was calculated to be 90:10, and it was determined that chemical deterioration was the main cause of the deterioration in separation performance.

[0108] Example 6 Furthermore, the same reverse osmosis membrane element as in Example 5 was evaluated under the same conditions as in Example 2, and permeated water was sampled from the permeated water collection pipe of the reverse osmosis membrane element. The electrical conductivity of the permeated water sampled at multiple positions in the permeated water collection pipe from the feed water side to the concentrated water side was measured, and the sodium chloride concentration and magnesium sulfate concentration were determined from the relationship between the electrical conductivity and the concentration.

[0109] The results are shown in Figure 17. Based on these results, the rate of change in separation performance was calculated in the longitudinal direction in the same manner as in Example 1, and the contribution rate at each position was calculated in the same manner as in Figure 16, and the results are shown in Figures 18 and 19. These results also confirmed that chemical degradation was the main cause and that degradation occurred not locally but overall.

[0110] Example 7: When deterioration in the quality of water produced by an ultrapure water production plant became apparent, a reverse osmosis membrane element in use was removed from the vessel, and the sodium chloride and magnesium sulfate concentrations of the permeate at multiple positions in the permeate collection pipe were determined using the same method as in Example 1. The sodium chloride removal rate was 88.24% (transmittance 11.76%), and the magnesium sulfate removal rate was 95.95% (transmittance 4.05%). The performance of this reverse osmosis membrane element measured under the same conditions as in production was 99.82% (transmittance 0.18%) for sodium chloride and 99.98% (transmittance 0.02%) for magnesium sulfate. The separation performance declined by 65.3 and 225.2 times compared to the initial values, respectively. Because the declines in both sodium chloride separation performance and magnesium sulfate separation performance were significant, it was difficult to determine the primary cause.

[0111] Therefore, similarly to Example 1, when the initial (before deterioration) and post-deterioration permeabilities were plotted in FIG. 20 , the contribution ratio of chemical deterioration to physical deterioration was calculated to be 67:33, and it was determined that the deterioration in separation performance was due to both chemical and physical deterioration, with chemical deterioration contributing slightly more.

[0112] Example 8 Furthermore, the same reverse osmosis membrane element as in Example 7 was evaluated under the same conditions as in Example 2, and permeated water was sampled from the permeated water collection pipe of the reverse osmosis membrane element. The electrical conductivity of the permeated water sampled at multiple positions in the permeated water collection pipe from the feed water side to the concentrated water side was measured, and the sodium chloride concentration and magnesium sulfate concentration were determined from the relationship between the electrical conductivity and the concentration.

[0113] The results are shown in Figure 21. Based on these results, the rate of change in separation performance calculated in the longitudinal direction, as in Example 1, and the contribution rate at each position calculated using the same method as in Figure 20, are shown in Figures 22 and 23. From Figure 22, it was determined that the rate of change in magnesium sulfate separation performance was greater at the rear than at the front, and that the contribution of physical deterioration was somewhat greater at the rear positions, but that physical deterioration and chemical deterioration occurred relatively uniformly. Furthermore, as shown in Figure 23, physical deterioration was significantly greater at the rear positions around 700 mm, and a policy was decided to focus on investigating the causes of physical deterioration at the rear position around 700 mm in the disassembly investigation.

[0114] Later, the reverse osmosis membrane element was disassembled to confirm the cause of deterioration, and when the membrane surface was observed, crystalline deposits were found on the entire membrane surface. From the results of staining the membrane, it was assumed that scratches had occurred on the entire membrane surface due to precipitated crystalline salts.

[0115] <Comparative Example 1> As shown in Example 1, a tendency for the quality of the produced water to deteriorate was observed at an ultrapure water production plant. Therefore, a reverse osmosis membrane element in use was removed from the vessel, and one reverse osmosis membrane element was loaded into a pressure vessel as shown in Figure 2, and the separation performance was measured using a performance evaluation device.

[0116] Sodium chloride was dissolved in pure water to prepare test water with a concentration of 1500 mg / L. The system was operated at a supply pressure of 1.5 MPa, a concentrate flow rate of 80 L / min, a water temperature of 25°C, and a pH of 7 for the treated water, and permeate was obtained from the pressure vessel. Permeate 7 was taken out and its electrical conductivity was measured. The concentration was calculated from the relationship between sodium chloride concentration and electrical conductivity. The resulting sodium chloride removal rate was 98.80% (transmittance 1.20%). The sodium chloride removal rate of this reverse osmosis membrane element measured under the same conditions as when it was produced was 99.74% (transmittance 0.26%), indicating a 4.6-fold decrease in separation performance. However, it was unclear whether this was due to chemical or physical degradation, and appropriate countermeasures for the problem could not be developed.

[0117] Therefore, the reverse osmosis membrane element was disassembled at great effort and the membrane was stained, but no noticeable scratches were found on the membrane surface, and it was not possible to conclude that physical deterioration was the main cause of the deterioration. Furthermore, when a piece of the reverse osmosis membrane was immersed in a solution containing an alkaline aqueous solution and pyridine, coloring was observed, confirming the occurrence of oxidative deterioration, and it was concluded that chemical deterioration was the main cause of the deterioration. However, it was not possible to estimate the contribution ratio between chemical and physical deterioration.

[0118] <Comparative Example 2> As shown in Example 3, a tendency for the quality of the produced water to deteriorate was observed in a pure water production plant that periodically performs hot water sterilization. Therefore, a reverse osmosis membrane element that was in use was removed from the vessel, and one reverse osmosis membrane element was loaded into a reverse osmosis membrane element evaluation device.

[0119] The sodium chloride removal performance was measured using the same method as in Comparative Example 1, and the sodium chloride removal rate was 98.50% (transmittance 1.50%) and the magnesium sulfate removal rate was 98.93% (transmittance 1.07%). The sodium chloride removal rate of this reverse osmosis membrane element measured under the same conditions as at the time of production was 99.82% (transmittance 0.18%), indicating that the separation performance had decreased by 8.4 times. However, it was not possible to determine whether this was chemical or physical degradation, and appropriate countermeasures for the problem could not be taken.

[0120] Therefore, after going to the trouble of disassembling this reverse osmosis membrane element, wrinkles were found on the membrane surface. Furthermore, when the disassembled membrane was stained, numerous scratches were found on the membrane surface, confirming that significant physical deterioration had occurred, but it was not possible to determine whether chemical deterioration had occurred. Furthermore, when a piece of reverse osmosis membrane was immersed in a solution containing a mixture of an alkaline aqueous solution and pyridine, coloring was observed, confirming the occurrence of oxidative degradation. It was concluded that the performance decline was due to both chemical and physical degradation. However, it was not possible to estimate the contribution ratios of chemical and physical degradation.

[0121] Comparative Example 3 As shown in Example 5, during a periodic inspection of an ultrapure water production plant, a reverse osmosis membrane element in use was removed from a vessel, and one reverse osmosis membrane element was loaded into a reverse osmosis membrane element evaluation device.

[0122] The sodium chloride removal performance was measured using the same method as in Comparative Example 1, and the sodium chloride removal rate was 98.50% (transmittance 1.50%). Note that the sodium chloride removal rate of this reverse osmosis membrane element measured under the same conditions as at the time of production was 99.82% (transmittance 0.18%), indicating that the separation performance had decreased by 3.1 times. However, it was not possible to determine whether this was chemical or physical degradation, and appropriate measures to address the problem could not be taken.

[0123] Therefore, after taking the time and effort to disassemble the reverse osmosis membrane element, they found no abnormalities in appearance, and staining revealed almost no scratches on the membrane surface, and no signs of physical deterioration were found. Therefore, it was assumed that chemical deterioration was the main cause, but surface observation was unable to determine the cause. Furthermore, when a piece of reverse osmosis membrane was immersed in a solution containing a mixture of alkaline aqueous solution and pyridine, coloring was observed, confirming the occurrence of oxidative deterioration. It was concluded that chemical deterioration was the main cause of deterioration. However, it was not possible to estimate the contribution ratio between chemical and physical deterioration.

[0124] Comparative Example 4 Because deterioration in the quality of water produced at an ultrapure water production plant became apparent, a reverse osmosis membrane element in use was removed from a vessel, and one reverse osmosis membrane element was loaded into a reverse osmosis membrane element evaluation device.

[0125] The sodium chloride concentration of the permeate at multiple positions in the permeate collection pipe was determined using the same method as in Example 1, and the sodium chloride removal rate was found to be 88.24% (transmittance 11.76%). Note that the performance of this reverse osmosis membrane element as produced, measured under the same conditions, was found to be 99.82% sodium chloride removal rate (transmittance 0.18%), indicating a 65.3-fold decrease in separation performance. However, it was not possible to determine whether this was chemical or physical degradation, and appropriate countermeasures for the problem could not be devised.

[0126] Therefore, the reverse osmosis membrane element was disassembled at great effort and the membrane surface was observed. Crystalline deposits were found on the entire membrane surface, and staining of the membrane suggested that precipitated crystalline salts had caused numerous scratches on the entire membrane surface. However, these results did not allow for the determination of chemical degradation. Furthermore, when the reverse osmosis membrane piece was immersed in a solution containing an alkaline aqueous solution and pyridine, no coloring was observed, and the occurrence of oxidative degradation could not be detected.

[0127] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0128] This application is based on a Japanese patent application (Patent Application No. 2023-104395) filed on June 26, 2023, the contents of which are incorporated herein by reference.

[0129] 1: Reverse osmosis membrane 2: Permeate flow path material 3: Untreated water flow path material (net spacer) 4: Permeate water collection pipe 5: Anti-telescope plate 6, 6': Untreated water 7, 7': Permeate water 8: Concentrated water 9: Pressure vessel 10: Tube 11: Conductivity meter 12: Permeate water collection pipe connector 21: Hollow fiber membrane 22: Potting 23: Filtrate water side cap 24: Backwash water outlet 25: Feed water outlet 26: Filtrate water outlet nozzle 27: Feed water inlet nozzle 28: Feed water inlet

Claims

1. A method for diagnosing the condition of a separation membrane module equipped with a permeate collection pipe having a plurality of collection holes for obtaining permeate from water to be treated, comprising: supplying test water containing two or more types of solutes to a separation membrane module, the two or more types of solutes in the test water including ionic substances with different valences, or two or more types of substances with different molecular weights, or the two or more types of solutes are supplied individually to the separation membrane module by changing the valence or molecular weight of one type of solute in test water containing one type of solute; sampling the permeate at at least two or more positions in the permeate collection pipe; and comparing the separation performances of the at least two types of solutes calculated based on the difference between the solute concentration in the permeate sampled at each sampling position and the solute concentration resulting from the permeate upstream of the sampling positions, thereby determining the type of abnormality, the degree of abnormality, or the location of the abnormality along the length of the permeate collection pipe in the separation membrane module.

2. A method for diagnosing the condition of a separation membrane module as described in claim 1, which comprises: preparing in advance a chemical deterioration profile in which the separation performance of the at least two types of solutes is deteriorated by contacting the separation membrane module with a chemical; and a physical deterioration profile in which the separation performance of the at least two types of solutes is deteriorated by physically damaging the supply side of the separation membrane module; obtaining the separation performance of each of the at least two types of solutes based on the difference between the solute concentration in the permeate collected at each of the water sampling positions and the solute concentration caused by the permeate upstream of the water sampling positions; and calculating the contribution rate of chemical deterioration and physical deterioration in the length direction of the permeate collection pipe in the separation membrane module from the chemical deterioration profile, the physical deterioration profile, and each separation performance of the at least two types of solutes, and determining at least one of the cause of deterioration, the location of deterioration, and the extent of deterioration.

3. A method for diagnosing the condition of a separation membrane module according to claim 1 or 2, in which the comparison of separation performance is carried out based on a concentration index of the permeate, a concentration converted from the concentration index, a standard separation performance converted based on operating conditions, and a solute permeability coefficient calculated based on operating data.

4. A method for diagnosing the condition of a separation membrane module described in any one of claims 1 to 3, wherein the ionic substances having different valences are at least a substance composed of monovalent cations and a substance composed of divalent cations.

5. A method for diagnosing the condition of a separation membrane module described in any one of claims 1 to 3, wherein the ionic substances having different valences are at least a substance composed of monovalent anions and a substance composed of divalent anions.

6. A method for diagnosing the condition of a separation membrane module described in any one of claims 1 to 5, wherein the permeate concentration indicator is any one of electrical conductivity, total dissolved solids concentration, TOC, refractive index, turbidity, absorbance, luminous intensity, chromaticity, IR spectrum, mass spectrometry spectrum, ion chromatography, inorganic concentration by ICP optical emission mass spectrometry, and pH.

7. A method for diagnosing the condition of a separation membrane module described in any one of claims 1 to 6, wherein the method for collecting permeate water at at least two or more positions within the permeate water collection pipe is a method for measuring the permeate water quality by collecting permeate water at different positions in the separation membrane module through a thin tube having an outer diameter smaller than the inner diameter of the permeate water collection pipe and measuring the permeate water quality.

8. A method for diagnosing the condition of a separation membrane module described in any one of claims 1 to 7, in which the separation performance of the test water in the pre-use state of the separation membrane module is measured or predicted in advance, and the condition of the separation membrane module is judged based on the deviation from that value.

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