WO2025005078A1 - Method for diagnosing state of separating membrane module - Google Patents

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

Method for diagnosing the condition of a separation membrane module

The present invention relates to a method for diagnosing the condition of a separation membrane module.

In recent years, the depletion of water resources has become a serious problem, and the utilization of water resources that have not been used until now is being considered. In addition, as a new technology for this purpose, separation membranes with extremely high separation efficiency compared to conventional sand filtration and evaporation methods, such as microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, and ion exchange membranes, are being applied to water treatment. In particular, the application of separation membranes, especially reverse osmosis membranes, has attracted much attention in the technology of producing drinking water from seawater, which is the most familiar but cannot be used as is, so-called seawater desalination, and in the reuse technology of purifying sewage wastewater and regenerating treated water.

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

In the case of sewage and wastewater reuse, reverse osmosis is used in inland and coastal urban and industrial areas, areas with no water sources, and areas where discharge volumes are restricted due to wastewater regulations. In particular, Singapore deals with water shortages by treating sewage generated within the country and then using reverse osmosis to regenerate it to drinking water quality.

The reverse osmosis membrane process, which is used in seawater desalinization 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 brackish water, for example, and has also been used to produce ultrapure water for industrial use, treat wastewater, and recover valuable materials.

However, chemical deterioration of the reverse osmosis membrane may occur when the disinfectant used to sterilize the raw water taken during normal operation in various water treatment plants, the coagulant used in pretreatment, and other residues come into contact with the reverse osmosis membrane surface, and when the reverse osmosis membrane is contaminated, chemical cleaning with strong acids or strong alkalis is generally performed. Even if pretreatment according to the raw water quality is applied, physical deterioration may occur on the reverse osmosis membrane surface when foreign matter remaining in the treated water or scale and foulants generated during operation come into contact with the reverse osmosis membrane surface, or when wrinkles generated on the membrane surface due to a sudden change in operating conditions during use of the reverse osmosis membrane element module come into strong contact with the flow path material, causing physical deterioration. In addition, performance changes may occur when the reverse osmosis membrane is exposed to high pressure for a long period of time during normal operation in various water treatment plants, or when foulants cover the membrane surface of the reverse osmosis membrane. Therefore, it is necessary to periodically check the performance of the reverse osmosis membrane, and if performance deterioration occurs, it is necessary to take appropriate measures to address the problem immediately.

A known method for investigating whether or not there is physical damage to a reverse osmosis membrane is to disassemble the reverse osmosis membrane element under investigation, extract a piece of membrane, and pressurize the skin layer side, which has a reverse osmosis function, with a dye solution (for example, a solution of Basic Violet 1 (manufactured by Tokyo Chemical Industry Co., Ltd.)) at a linear velocity of 0.1 to 0.2 cm/sec by cross-flow at an operating pressure of 1.5 MPa for 30 minutes or more, and then visually observe whether or not there is any dyed area on the evaluation membrane (Patent Document 1).

A method for investigating whether or not a reverse osmosis membrane has chemically deteriorated is known in which the reverse osmosis membrane element under investigation is disassembled, the membrane pieces are removed, and immersed in a solution containing a mixture of an alkaline aqueous solution and pyridine, and chemical deterioration, particularly oxidative deterioration, is identified based on the presence or absence of color change in the solution (Non-Patent Document 1).

Meanwhile, chemical and physical deterioration is often an issue for membranes other than reverse osmosis membranes. For example, when the water to be treated contains oxidizing substances, such as groundwater or industrial wastewater, the separation membrane made of organic polymers is oxidized by the oxidizing substances, causing chemical deterioration. Furthermore, when the water to be treated contains substances with high hardness, the separation membrane undergoes physical deterioration. Regarding such deterioration, tests such as the PDT (Pressure Decay Test) (Non-Patent Document 2) and air leak tests are known for physical deterioration, as are bubble point tests (Non-Patent Document 3) as tests to check for deterioration in separation performance due to chemical deterioration, and at the laboratory level, the molecular weight cutoff test (Non-Patent Document 4).

International Publication No. 2015/063975 International Publication No. 2020/071507

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), p183 Japanese Industrial Standards, JIS K3832-1990, Bubble point test method for microfiltration membrane elements and modules Haruhiko Ohya 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)

However, according to the inventors' investigations, in conventional methods, in order to diagnose the cause of performance degradation in separation membrane modules used in various water treatment plants, it was necessary to dismantle the separation membrane modules and remove and analyze the membrane pieces, which resulted in the problem that it took time to diagnose the cause of the trouble and delayed countermeasures.

The present invention was made in consideration of the above-mentioned conventional situation, and provides a method for diagnosing the condition of a separation membrane module that can diagnose the causes of performance degradation of the separation membrane module extremely simply and quickly.

In order to solve the above problems, the present invention has the following configuration.
(1) A method for diagnosing the state of a separation membrane module having a permeate collection pipe having a plurality of water collection holes for obtaining permeate from water to be treated, comprising the steps of:
Test water containing two or more types of solutes is supplied to a separation membrane module, and the test water contains, as the two or more types of solutes, 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 individually supplied to the separation membrane module by changing the valence or molecular weight of the one type of solute in test water containing the one type of solute;
Permeate water is collected at at least two or more positions in the permeate collection pipe;
By comparing the separation performances of the at least two types of solutes, which are calculated based on the difference between the solute concentration in the permeated water collected at each water collection position and the solute concentration due to the permeated water upstream of the water collection position,
A method for diagnosing the condition of a separation membrane module, comprising determining the type of abnormality, the degree of abnormality, or the location of the abnormality in the longitudinal direction of a permeate collection pipe in a separation membrane module.
(2) creating in advance a chemical deterioration profile in which the separation performance of the at least two 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 solutes is deteriorated by physically scratching the supply side of the separation membrane module;
comparing the separation performances of the at least two types of solutes obtained based on a difference between a solute concentration in the permeated water sampled at each of the water sampling positions and a solute concentration originating from the permeated water upstream of the water sampling positions;
The method for diagnosing the condition of a separation membrane module described in (1), further comprising calculating a contribution rate of chemical deterioration and physical deterioration in a longitudinal direction of a permeate collection pipe in a separation membrane module from the chemical deterioration profile, the physical deterioration profile, and the separation performance of each of the at least two types of solutes, and determining at least any one of a cause of deterioration, a position of deterioration, and an extent of deterioration.
(3) The method for diagnosing the state of a separation membrane module according to (1) or (2), in which the comparison of the 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) The method for diagnosing the state of a separation membrane module according to any one of (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) The method for diagnosing the state of a separation membrane module according to any one of (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) The permeate concentration indicator is an inorganic concentration measured by electrical conductivity, total dissolved solids concentration, TOC, refractive index, turbidity, absorbance, luminous intensity, chromaticity, IR spectrum, mass spectrometry spectrum, ion chromatography, or ICP emission mass spectrometry;
The method for diagnosing a state of a separation membrane module according to any one of (1) to (5), wherein the state of the separation membrane module is either pH or 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 collecting 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 collecting pipe.
(8) A method for diagnosing the state of a separation membrane module according to any one of (1) to (7), in which the separation performance of the test water in a state before use of the separation membrane module is measured or predicted in advance, and the state of the separation membrane module is judged based on the deviation from the measured value.

　By using the separation membrane module diagnostic method of the present invention, the cause of performance degradation of the separation membrane module can be diagnosed very simply and quickly without dismantling the separation membrane module. As a result, by taking immediate measures for the water treatment plant based on the diagnostic results, it becomes possible to stably operate the separation membranes in the water treatment plant and obtain fresh water and clear water stably and inexpensively.

FIG. 1 is a partially exploded perspective view of a most typical spiral-wound reverse osmosis membrane element. FIG. 2 is a side cross-sectional view of a reverse osmosis membrane module in which a spiral-type reverse osmosis membrane element is 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 permeated water quality through a tube from a permeated water piping of a reverse osmosis membrane module. FIG. 5 is a schematic diagram showing an example of a method for measuring local permeated water quality through a tube from a permeated water piping in a state where a plurality of reverse osmosis membrane modules are 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 the initial performance from the difference between the permeate concentration at the water sampling position n and the permeate concentration sampled at a water sampling position upstream (supply water side) of the water sampling position n. FIG. 8 is a graph showing the change in separation performance and the contribution rates of chemical deterioration and physical deterioration in Example 1. FIG. 9 is a graph showing the distribution of the concentration of each ionic substance in the permeated water in the length direction of the permeated water collecting pipe in Example 2. FIG. 10 is a graph showing the rate of change in separation performance in the length direction of the permeate collecting tube in Example 2 and the contribution rates of chemical deterioration and physical deterioration in the length direction of the permeate collecting tube. FIG. 11 is a graph (differential method) showing the rate of change in separation performance in the length direction of the permeate collecting tube in Example 2 and the contribution rates of chemical deterioration and physical deterioration in the length direction of the permeate collecting tube. FIG. 12 is a graph showing the change in separation performance and the contribution rates of chemical deterioration and physical deterioration in Example 3. FIG. 13 is a graph showing the distribution of the concentration of each ionic substance in the permeated water in the length direction of the permeated water collecting pipe in Example 4. FIG. 14 is a graph showing the rate of change in separation performance in the length direction of the permeate collecting tube in Example 4 and the contribution rates of chemical deterioration and physical deterioration in the length direction of the permeate collecting tube. FIG. 15 is a graph (differential method) showing the rate of change in separation performance in the length direction of the permeate collecting tube in Example 4 and the contribution rates of chemical deterioration and physical deterioration in the length direction of the permeate collecting tube. FIG. 16 is a graph showing the change in separation performance and the contribution rates of chemical deterioration and physical deterioration in Example 5. FIG. 17 is a graph showing the distribution of the concentration of each ionic substance in the permeated water in the length direction of the permeated water collecting pipe in Example 6. FIG. 18 is a graph showing the rate of change in separation performance in the length direction of the permeate collecting pipe in Example 6 and the contribution rates of chemical deterioration and physical deterioration in the length direction of the collecting pipe. FIG. 19 is a graph (differential method) showing the rate of change in separation performance in the length direction of the permeate collecting pipe in Example 6 and the contribution rates of chemical deterioration and physical deterioration in the length direction of the collecting pipe. FIG. 20 is a graph showing the change in separation performance and the contribution rates of chemical deterioration and physical deterioration in Example 7. FIG. 21 is a graph showing the distribution of the concentration of each ionic substance in the permeated water in the length direction of the permeated water collecting pipe in Example 8. FIG. 22 is a graph showing the rate of change in separation performance in the length direction of the permeate collecting pipe in Example 8 and the contribution rates of chemical deterioration and physical deterioration in the length direction of the collecting pipe. FIG. 23 is a graph (differential method) showing the rate of change in separation performance in the length direction of the permeate collecting pipe in Example 8 and the contribution rates of chemical deterioration and physical deterioration in the length direction of the collecting pipe.

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 contents. When simply referring to the present invention, it means a concept including the first, second, and third embodiments described below. Furthermore, "to" in a numerical range means a range including the numerical values before and after it, for example, "50 to 70,000" means a range of 50 or more and 70,000 or less.

[Method for diagnosing 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 state of a separation membrane module for obtaining permeate water from water to be treated, in which test water containing two or more types of solutes is supplied to the separation membrane module. The test water contains, as the two or more types of solutes, ionic substances with different valences or two or more types of 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 type of solute in test water containing one type of solute. It is sufficient to measure the separation performance of each of the at least two types of solutes based on the concentration of the solute contained in the permeate water, and the test water supplied to the separation membrane module may be one type or two or more types. 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 deterioration profile in which the separation performance is deteriorated by contacting the separation membrane module with a chemical and a physical deterioration profile in which the separation performance is deteriorated by physically scratching the supply side of the separation membrane module are prepared in advance. The separation performance of the test water before and after deterioration of the separation membrane module, the chemical deterioration profile, and the physical deterioration profile are compared to determine the degree of chemical deterioration and physical deterioration of the separation membrane module. Specifically, the separation performance of the first solute and the separation performance of the second solute are in a certain ratio based on the characteristics of the separation membrane. This separation performance is generally expressed as a removal rate. For example, in the case of a reverse osmosis membrane module, as exemplified in the document "Toray TSW-LE Series Catalog", it is described that the NaCl removal rate is 99.6% and the boron removal rate is 90%. The major factors that cause the separation performance deterioration of the separation membrane module are chemical deterioration and physical deterioration as described above, and the relationship between the separation performance deterioration due to each type of deterioration 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 a chemical agent and begins to deteriorate.

In the present invention, chemical deterioration refers to, for example, changes in the molecular chain arrangement of the polymer components of the separation functional layer, breakage, or loss of low molecular weight molecules, and there are no particular limitations on the form of chemical deterioration.

In plants that use reverse osmosis membrane elements, an oxidizing agent is often used in the pretreatment of the raw water supplied to the reverse osmosis membrane elements, and it is known that some of the oxidizing agent leaks into the reverse osmosis membrane elements, causing oxidative deterioration. In the present invention, the oxidizing agent is not particularly limited to the oxidizing agent used in the pretreatment, but the main cause of chemical deterioration is often oxidative deterioration caused by hypochlorous acid used to disinfect the raw water and hypobromous acid generated by conversion of hypochlorous acid.

In the case of chemical deterioration, the removal performance of the two solutes decreases in a certain relationship. Specifically, for example, as shown in Non-Patent Document 5 (Journal of Membrane Science, Vol. 183, 2000, pp. 259-267), it is known that there is a certain relationship that is nearly proportional to the decrease in NaCl removal performance and boron removal performance. The inventors of the present application have confirmed through intensive research that this relationship is similar for other solutes. That is, the change in the removal performance of the two solutes is in a certain relationship, and in many cases, the performance decreases in a linear relationship from the performance when new to a certain level. In other words, the separation performance of the test water of the separation membrane module before chemical deterioration and physical deterioration occur is measured or predicted in advance, and the state of the separation membrane module is judged based on the deviation from that value, so that abnormalities can be detected and diagnosed. The separation performance of two types of solutes before deterioration may be, for example, the performance when new, the initial performance when the plant is started up, the performance immediately after chemical cleaning, or the performance immediately after a long-term shutdown of the plant due to a problem or equipment maintenance, and may be set appropriately depending on the problem that occurs in the plant. Regarding deterioration of the 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 the 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.

In addition, when chemical deterioration begins to occur in a reverse osmosis membrane, the amount of monovalent ionic substances that permeates increases before the amount of divalent ionic substances that permeates, and as chemical deterioration progresses further, the amount of divalent ionic substances that permeates also increases, and the difference between the amount of monovalent ionic substances that permeates decreases. Therefore, the degree of deterioration in the separation performance of monovalent ionic substances and divalent ionic substances can also be used to diagnose the early stage of chemical deterioration due to contact with chemicals (minor deterioration).

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% by 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 permeated water in the permeated water collection pipe is 0.2% by 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.

On the other hand, in the case of physical deterioration, it is possible to obtain a relational equation by measuring the characteristics of a separation membrane module without leakage and a separation membrane module with leakage, but basically, the membrane is damaged, has large holes, or has gaps in the adhesive or other areas, causing leakage of test water, water to be treated, or other feed water. In other words, the phenomenon is that the permeate concentration deteriorates depending on the feed water composition regardless of the membrane's separation performance, so it can also be roughly calculated. For example, if the Na ion concentration of the feed water is 32,000 mg/L and the boron concentration is 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, and if chemically deteriorated, the performance will decrease in a relationship of, for example, 150 mg/L and 0.75 mg/L. However, if there is physical deterioration, for example, if 0.1% of the feed water leaks, the permeate concentration will be 132 mg/L and 0.505 mg/L, and the decrease in Na ion separation performance will be significant. In such cases, it can be determined that physical deterioration has occurred.

After creating and acquiring a relationship profile in advance between chemical deterioration due to contact with chemicals and physical deterioration due to scratches, etc., it is possible to compare it with the measured separation performance of the separation membrane module and determine the contribution of chemical deterioration and physical deterioration by decomposing it into two arrows, the relationship between the rate of change of monovalent ions and divalent ions in the case of chemical deterioration and the relationship between the rate of change of monovalent ions and divalent ions in the case of physical deterioration, as shown in the vector diagram of chemical deterioration and physical deterioration in Figure 8. In this way, by being able to determine whether chemical deterioration or physical deterioration is the main cause of deterioration, appropriate measures can be taken in response to problems.

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 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.

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 a first treated water containing monovalent ionic substances to a spiral reverse osmosis membrane element equipped with a permeate collection pipe having a plurality of collection holes under pressure at a pressure equal to or greater than the osmotic pressure of the first treated water, 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 supply water side to the concentrated water side, and, before or after sampling the first permeate, supplying a second treated water containing divalent ionic substances to a spiral reverse osmosis membrane element equipped with a permeate collection pipe having a plurality of collection holes 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 with a pressure force, the second treated water is separated into a second concentrated water and a second permeate, the second permeate is collected at multiple 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 concentration of the monovalent ionic substance and the concentration of the divalent ionic substance.

Furthermore, by determining the rate of change in separation performance relative to the initial performance from the concentrations of the monovalent ionic substances and the divalent ionic substances in the permeate at each water sampling position in the permeate collection pipe of the reverse osmosis membrane element, and decomposing this into two arrows representing the relationship between the rate of change of monovalent ions and divalent ions in the case of chemical deterioration and the relationship between the rate of change of monovalent ions and divalent ions in the case of physical deterioration, it becomes possible to determine the contribution of chemical deterioration and physical deterioration at each water sampling position. By combining these, the rate of change in separation performance in the length direction within the reverse osmosis membrane element and the contribution rates of chemical deterioration and physical deterioration can be calculated, making the degree and location of chemical deterioration and physical deterioration of the separation membrane module clear, enabling more appropriate measures to be taken against problems.

More preferably, for example, as shown in FIG. 7, the separation performance change rate relative to the initial performance is calculated from the difference between the concentration of the monovalent ionic substance and the concentration of the divalent ionic substance in the permeated water at the water collection position n in the permeated water collection pipe of the reverse osmosis membrane element and the concentration of the monovalent ionic substance and the divalent ionic substance resulting from the permeated water collected at the water collection position upstream (supply water side) of the water collection position n, and the contribution of chemical deterioration and physical deterioration at each water collection position can be determined by decomposing into two arrows representing the relationship between the change rate of monovalent ions and divalent ions in the case of chemical deterioration and the relationship between the change rate of monovalent ions and divalent ions in the case of physical deterioration. By combining these, the separation performance change rate in the length direction within the reverse osmosis membrane element and the contribution rate of chemical deterioration and physical deterioration can be calculated more accurately, the degree and the location of chemical deterioration and physical deterioration of the separation membrane module become clear, and more appropriate measures against troubles can be taken. By using this method of analysis, 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 upstream (supply water side) of the reverse osmosis membrane element.

The permeate concentration C _p (n) of the collection hole (nth) at the water sampling position n can be calculated from the amount of solute material.
in particular,
F(n)×C(n)=F(n-1)×C(n-1)+F _p (n)×C _p (n) ... (1)
F(1) = _Fp (1)
C(1) = _Cp (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, _Cp (n) = C(n) + (n-1) x ΔC(n)
In addition,
F _p (n): Permeation rate of the water collecting hole (nth) [m ³ /d]
C _p (n): Permeate concentration of the collection hole (nth) [mg/L]
F _p (n-1): Permeation rate of the water collecting hole (n-1th) [m ³ /d]
C _p (n-1): Permeate concentration of the collection hole (n-1th) [mg/L]
F(n): Permeate volume at 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 collection pipe [mg/L]
F(n-1): Amount of permeated water at the water collection position (n-1th) in the water collection pipe [m ³ /d]
C(n-1): Permeate concentration at the water collection position (n-1th) in the collection pipe [mg/L]
It is.

For simplicity, C _p (n) may be calculated by subtracting the permeate concentration at the nearest water sampling position (n-1th) in the water collection pipe from the permeate concentration at the nth water sampling position in the water collection pipe.

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.

The first treated water can be obtained, for example, by mixing a monovalent ionic substance with pure water. The second treated water can be obtained, for example, by mixing a divalent ionic substance with pure water.

　The reverse osmosis membrane element is as described above.

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

The flow rate of the first treated water when separating the first treated water into the first concentrated water 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 about 201 mm (about 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, since chemical deterioration occurs when the pH becomes close to a strong acid or strong alkali.

The flow rate of the second treated water when separating the second treated water into the second concentrated water 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 about 201 mm (about 8 inches). The temperature of the second treated water at this time is preferably 5 to 45°C, and more preferably 20 to 35°C. The pH of the second treated water at this time is preferably 2 to 11, and more preferably 6 to 8.5, since chemical deterioration occurs when the pH becomes close to a strong acid or strong alkali.

In addition, the concentration of monovalent ionic substances in the first permeated water is determined by measuring the water quality of the first permeated water. The concentration of divalent ionic substances in the second permeated water is determined by measuring the water quality of the second permeated water.

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

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.

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 pressurized and 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.

In the first embodiment described above, Na (a strong monovalent cationic substance) and boron (a weak trivalent anionic substance) are used, but it is also preferable to use ionic substances with different valences, and it is also preferable for substances to have different molecular weights. Furthermore, it is good to target components that have a large difference in removal performance or are easy to measure. Also, 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, a monovalent cation and a divalent cation, or a monovalent anion and a divalent anion.

The monovalent ionic substance used in the present invention is not particularly limited, but is preferably completely dissociated and neutral when dissolved in water such as pure water. For example, Na and Mg, Cl and SO4 are very preferable because they are abundant in nature, easy to handle, and relatively low cost. Furthermore, in water treatment separation membranes for treating natural water such as seawater and river water, natural organic matter is generally weak anion, so the membrane surface is often negatively charged, and in that case, it is preferable to apply Na and _Mg , which are cations. In particular, sodium chloride is preferably used as the monovalent ionic substance. In addition, the divalent ionic substance used in the present invention is not particularly limited, but is preferably used for the same reason as long as it is completely dissociated and neutral when dissolved in water such as pure water. Magnesium sulfate is preferably used for the same reason. It is very preferable to select these simultaneously, because the cations and anions have different properties.

The concentrations in the test water are preferably set to conditions that make them easy to measure, but are not subject to any particular restrictions. In general, the concentration of monovalent ionic substances is preferably 50 to 70,000 mg/L, more preferably 500 to 35,000 mg/L, and the concentration of divalent ionic substances is preferably 50 to 10,000 mg/L, more preferably 500 to 4,000 mg/L.

In the present invention, the "at least two types of test water" basically have different solutes, but it is also possible to use the same solute and change the pH or temperature to create substantially different solutes. For example, if the pH of a solute containing carbon dioxide is changed, it will dissociate, i.e., its valence will change, resulting in a solute with different properties. Changing the temperature can also change the properties of solutes, particularly polymeric solutes, so this is an applicable method. When the pH or temperature is changed, the membrane performance may also change, making it easier to determine chemical changes. On the other hand, in the case of physical deterioration, changes in membrane performance generally have no effect. However, care must be taken as changing the pH or temperature requires chemicals and thermal energy, as well as the time and effort required for this.

In addition, it is preferable that the test water contains only the components to be measured, as this increases analytical accuracy, but if it is desired to diagnose a separation membrane module that is in use (while the plant is operating), it is necessary to stop the supply of treated water and switch to test water, or to remove the separation membrane module from the facility and load it into a diagnostic device. If it is desired to carry out this diagnosis while the actual plant is operating, it is possible to use the treated water as the test water while the plant is in operation. However, since solutes other than the solutes to be compared and evaluated are often contained, it is necessary to be aware that this will affect analytical accuracy. If there are problems with the accuracy of the concentration analysis of the treated water and permeate during operation, one preferred method is to increase sensitivity by adding two types of solutes to be compared and evaluated in a pulsed manner to the treated water.

The separation performance of a membrane module is generally measured in terms of removal rate (= 1 - permeate concentration / feed water concentration), permeability (= permeate concentration / feed water concentration), permeability coefficient, etc.

The permeability coefficient can be calculated simply as the permeation amount per membrane area, pressure and time, for example, as expressed in units of kg/ ^m2 /Pa/s. More precisely, however, it can be determined by a calculation method taking into account the osmotic pressure and concentration polarization shown in Non-Patent Document 6, "Journal of Membrane Science, Vol. 183, 2000, pp. 249-258," and further taking into account the temperature change of membrane performance.

in particular,
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)
In addition,
J _v : Pure water permeation flux [m ³ /m ²・s]
J _s : 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]
It is.

Here, the solute mass transfer coefficient k is a value determined by the separation membrane module structure and the evaluation cell, but can be obtained as a function of the membrane surface flow rate Q [m ³ /s] or the membrane surface flow rate u [m/s] by the osmotic pressure method or flow rate change method shown in Non-Patent Document 5 (Journal of Membrane Science, Vol. 183, 2000, pp. 259-267).

In the case of the flat membrane cell shown in Reference 2,
k=1.63×10 ^-3・Q ^0.4053
It is.

Therefore, the unknowns _Lp , P, and _Cm can be calculated from the above formula. In the case of a separation membrane module, _Lp and P can be calculated by fitting while integrating in the longitudinal direction of the membrane element, as shown in Reference 1, if the unknowns can be obtained as average values for the entire module.

The separation membrane module to which the present invention is applied can be used with a variety of separation membranes, including reverse osmosis membranes, nanofiltration membranes, ultrafiltration membranes, microfiltration membranes, ion exchange membranes, gas separation membranes, and filter cloths. In particular, application to microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes for water treatment, which treat seawater or river water to produce drinking water or various types of water, is highly preferable, as it contributes to reducing water treatment costs. The module shape is also not particularly limited, and may be a spiral type, hollow fiber type, or flat membrane parallel plate plate and frame type.

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

In addition, examples of ultrafiltration membranes and precision filtration membranes include porous membranes such as polyacrylonitrile, polyimide, polyethersulfone, polyphenylene sulfide sulfone, polytetrafluoroethylene, polypropylene, and polyethylene.

Furthermore, by compounding these porous membranes with rubber-like 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 as a highly permeable composite separation membrane.

The structure of a separation membrane module varies depending on the application of the membrane, but in the case of reverse osmosis 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.

This spiral-type reverse osmosis membrane element generally consists of a reverse osmosis membrane unit including a reverse osmosis membrane 1, a permeate flow path material 2, and a treated water flow path material (net spacer) 3 wound in a spiral shape around a permeate collection pipe 4 with a collection hole, the outside of the reverse osmosis membrane unit is covered with a film or glass fiber impregnated with a hardening resin, etc., and a telescope prevention plate 5 is attached to at least one end of the fluid separation element.

For the treated water flow path material, net-like or mesh-like lattice flow path material, grooved sheets, corrugated sheets, etc. can be used. For the permeate water flow path material, net-like or mesh-like lattice flow path material, grooved sheets, corrugated sheets, 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.

The water 6 to be treated is supplied from the telescope prevention 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 a hole 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.

When the reverse osmosis membrane is a flat membrane, the type known as the spiral type mentioned above is common, and 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.

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

The flow rate of the mixed treated water when separating the mixed treated water into the mixed retentate 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 treated water in this case is preferably 5 to 45°C, and more preferably 20 to 35°C. The pH of the mixed treated water in this case is preferably 2 to 11, and more preferably 6 to 8.5, since chemical deterioration occurs when the pH becomes close to a strong acid or strong alkali.

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

On the other hand, the hollow fiber membrane module to which the present invention is applied generally has an opening that is airtightly sealed (potted) between the hollow fiber membranes and between the hollow fiber membranes and the module container. This allows the outside and inside of the hollow fiber membrane to be isolated by the hollow fiber membrane itself, and separation processing can be performed through the membrane. The structure of the hollow fiber membrane module can be a "double-ended open type" in which both ends of the hollow fiber membrane are potted and then opened from both ends, a "single-ended open type" in which only one end is opened after both ends are potted, a "U-shaped" in which the hollow fiber membrane is 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. As for the filtration direction, there are cases where the raw water to be treated flows inside the hollow fiber membrane (internal pressure type) and cases where it flows outside (external pressure type), and the present invention can be applied to all of these.

There are no particular restrictions on the measurement of test water and permeate concentration, and various measurement methods can be used, such as electrical conductivity, total dissolved solids concentration, TOC, refractive index, turbidity, absorbance, luminescence intensity, color, IR spectrum, mass spectrometry spectrum, ion chromatography, inorganic 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 method that allows easy measurement, such as electrical conductivity for ionic substances, and refractive index, absorbance, and luminescence intensity for polymers.

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 electrical conductivity can be determined in advance using a conventionally known method. By determining the relationship between the concentration of each ionic substance and electrical conductivity in advance, electrical conductivity can be converted into concentration.

When test water contains two or more types of solutes, multiple components can be measured at once by using a chromatograph or absorbance to resolve the retention time or wavelength, scanning, and then detecting and measuring with a detector. It is also a preferred method to connect two different detectors simultaneously to measure two different water quality indicators. In particular, these methods are highly preferred when measuring water quality online, in terms of the complexity of the measurement and the accuracy.

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. In other words, 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 inside the module.

As a specific example of the second embodiment, a side cross-sectional view of an example using a spiral-type reverse osmosis membrane module is shown in Figure 4. Here, the mixed permeate is collected at multiple points in the permeate collection tube, and the separation performance of the collection points is obtained. As a method of identifying the content and location of the abnormality, for example, a thin tube 10 is passed through the permeate collection tube, one end of the tube 10 is fastened at a predetermined position in the permeate collection tube, and the mixed permeate at that position is collected from the other end of the tube 10.

In this case, 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 and 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.

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.

In other words, when using a tube to measure the electrical conductivity of each permeate, the tube is passed through the permeate collection pipe, one end of the tube is secured at a predetermined position in the permeate collection pipe, and the permeate at that position is sampled from the other end of the tube to measure the electrical conductivity.

Here, if a tube is passed through the permeate piping of the pressure vessel and the tip of the tube is fixed at a predetermined position, and permeate is collected at multiple locations, water should be collected from both ends of the permeate collection tube, the supply water side and the concentrated water side, and water should be collected at approximately equal intervals between them. There is no particular limit to the width of the interval, but when evaluating one reverse osmosis membrane element with a total length of about 1 m, an interval of about 5 cm is preferable. Also, in Figure 4, the tube 10 is inserted from the downstream direction of the permeate collection tube, but it is also possible to insert the tube with the upstream side open. Furthermore, while Figure 4 shows the case where the present invention is applied to one membrane module, in the case of a spiral-type module, it is possible to connect multiple modules in series with the permeate collection tube, as exemplified in Figure 5, so that water can be collected and evaluated from multiple modules at once.

In addition, the electrical conductivity of each permeate can be measured by installing multiple electrical conductivity sensors at multiple locations in the permeate collection pipe.

There are no particular limitations on the separation membrane module to which the second embodiment can be applied, but as shown in FIG. 2, flat membrane modules into which thin tubes can be easily inserted, and in particular spiral reverse osmosis membrane modules into which permeate collection pipes can be easily inserted in a straight line, are preferred.

In the case of spiral reverse osmosis membranes, raw water may occasionally get mixed in due to deterioration of the sealing material, such as an O-ring, that seals the outlet on one side of the permeate collection pipe, and the concentration of the divalent ionic substances may become high up to about 30 cm from the sealed end of the permeate collection pipe. Therefore, if an abnormality is confirmed in the concentration of the divalent ionic substances from 30 cm away from the 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 sealing material has occurred.

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

As a third embodiment, when the 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 the permeate to be taken in from at least two locations, and the flow rate ratio of the permeate can be changed to obtain results similar to those of the second embodiment.

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 perform constant abnormality diagnosis, including the contribution rates of physical and chemical deterioration. This method is a preferable embodiment because it makes it possible to detect abnormal positions without inserting tubes into the separation membrane module.

However, because this method can cause errors if there is a localized distribution of permeability, a method has been proposed to increase accuracy by combining it with a method of inserting a tube into the permeate collection pipe, as described in Japanese Patent Publication No. 2023-20636.

The deterioration diagnosis device according to the 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-type reverse osmosis membrane element is used as a separation membrane module, and test water containing a monovalent ionic substance and a divalent ionic substance is used as two different types of test water.

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 for separating treated water, which contains at least one of a first treated water containing monovalent ionic substances and a second treated water containing divalent ionic substances, into concentrated water and permeate water, and a water collection pipe for collecting the permeate water, and includes inputting into the computer the operating conditions of the reverse osmosis membrane element during operation, the water quality of the first permeate water containing the monovalent ionic substances, and the water quality of the second permeate water containing the divalent ionic substances, into the computer to diagnose the deterioration state of the reverse osmosis membrane element. The data input means inputs the data, the operating conditions, the water quality of the first permeate, and the water quality of the second permeate into a computer, and the data on 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 the 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 are used to function as a deterioration diagnosis calculation means for diagnosing the occurrence or non-occurrence of deterioration of the reverse osmosis membrane element based on a predetermined deterioration diagnosis criterion for the reverse osmosis membrane element.

In the third embodiment, a computer having the above means is made to function to diagnose the deterioration state of a reverse osmosis membrane element. The third embodiment can be recorded in a recording device such as a computer memory or a hard disk, and the form of recording is not particularly limited.

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.

The data recorded in the data recording means is used to diagnose whether or not deterioration of the reverse osmosis membrane element has occurred based on predetermined deterioration diagnosis criteria for the reverse osmosis membrane element.

The data recorded in the data recording means may include, for example, 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.

The third embodiment makes it possible to diagnose the causes of performance degradation of a reverse osmosis membrane element extremely simply and quickly.

In addition, specific examples of the water to be treated, the structure of the reverse osmosis membrane element, and the water quality of the first permeate and the second permeate in the third embodiment are the same as those in the first and second embodiments.

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

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

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 its separation performance was measured using a performance evaluation device.

Sodium chloride was dissolved in pure water to prepare test water with a concentration of 1500 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 treated water, 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.

Then, the test water was changed to pure water and supplied to the membrane element loaded in the pressure vessel, the sodium chloride was washed out, and 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 treated water. Using the same method as for sodium chloride, the electrical conductivity of the permeate containing magnesium sulfate in the permeate collection pipe was measured, and the concentration was calculated from the relationship between magnesium sulfate concentration and electrical conductivity.

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%). Note that the performance of this reverse osmosis membrane element as produced, measured under the same conditions, was 99.74% sodium chloride removal rate (transmittance 0.26%) and 99.97% magnesium sulfate removal rate (transmittance 0.03%). The rates of decline in separation performance were 4.6 and 2.7 times the initial rates, respectively. As the rate of decline in magnesium sulfate separation performance was not large compared to the rate of decline in sodium chloride separation performance, at least indications were confirmed that chemical degradation was the main cause.

Furthermore, as a relational expression for chemical deterioration, a relational expression (1) for the analyzed 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 deteriorated by immersing it in hypochlorous acid in advance. In addition, as a relational expression for physical deterioration, a relational expression (2) for the permeability of sodium chloride and magnesium sulfate was created, which was obtained by assuming that as the damage became larger, the supply water leaked and mixed in small amounts. When each of these relational expressions was plotted in Figure 8, and the initial (before deterioration) and post-deterioration permeability were further plotted, the contribution ratio of chemical deterioration to physical deterioration was calculated to be 97:3, and it was determined that the decrease in separation performance was almost entirely due to chemical deterioration.

Example 2
The same reverse osmosis membrane element as in Example 1 was evaluated under the same conditions as in Example 1. However, since a tendency for the quality of the produced water to deteriorate was observed in an ultrapure water production plant, the 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. However, as shown in Figure 4, the permeated water was passed through a tube from the permeated water piping of the pressure vessel, and the 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 collection pipe from the feed water side to the concentrated water side was measured, and the sodium chloride concentration and magnesium sulfate concentration were calculated from the relationship between the concentration and electrical conductivity.

The results are shown in Figure 9. Based on these results, the rate of change in separation performance was calculated in the length 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 8, and these results are shown in Figures 10 and 11. From these results, it was determined that the rate of change in separation performance of magnesium sulfate at the front and rear was small, and that the occurrence of physical deterioration was minor.

　Based on the above, it was determined that the main cause of deterioration of the reverse osmosis membrane elements was chemical degradation. When the plant's chemical usage process was checked, records showed that sodium hypochlorite had been added in excess of the prescribed amount in the raw water sterilization process, and it was presumed that it had leaked into the raw water. As a result, the operational management of the chemical addition process was quickly improved, which allowed the plant to avoid serious trouble and continue producing fresh water.

Example 3
At a pure water manufacturing plant where hot water sterilization is performed periodically, a tendency for the quality of the produced water to deteriorate was observed. 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.

The sodium chloride and magnesium sulfate concentrations of the permeate were determined using the same method as in 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 performance of this reverse osmosis membrane element measured under the same conditions as production was 99.82% (transmittance 0.18%) for sodium chloride removal rate and 99.98% (transmittance 0.02%) for magnesium sulfate removal rate. The rates of decline in separation performance were 8.4 and 59.2 times the initial values, respectively. The rate of decline in sodium chloride separation performance was large, at least 5 times, and the rate of decline in magnesium sulfate separation performance was extremely large, confirming at least indications that physical deterioration was the main cause.

Furthermore, as a relational equation for chemical deterioration, a relational equation (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 deteriorated by first immersing it in hypochlorous acid. Furthermore, as a relational equation for physical deterioration, a relational equation (2) for the permeability of sodium chloride and magnesium sulfate was created, which was obtained by assuming that as the damage became larger, the supply water leaked and mixed in small amounts. When each of these relational equations was plotted in Figure 12, and the initial (before deterioration) and post-deterioration permeability were plotted, the contribution ratio of chemical deterioration to physical deterioration was calculated to be 21:79, and it was determined that physical deterioration was the main cause of the decline in separation performance.

Example 4
The same reverse osmosis membrane element as in Example 3 was evaluated under the same conditions as in Example 2, and the 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 calculated from the relationship between the concentration and electrical conductivity.

The results are shown in Figure 13. Based on these results, the rate of change in separation performance was calculated in the length direction in the same way as in Example 1, and the contribution rate at each position was calculated in the same way as in Figure 12, and these results are shown in Figures 14 and 15. From Figure 14, it was determined that the rate of change in separation performance of magnesium sulfate was greater at the rear than at the front, and that while chemical degradation was occurring, physical degradation was also 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.

　Based on the above, it was determined that physical deterioration was a major factor in the deterioration of the performance of the reverse osmosis membrane elements. When the hot water sterilization process was checked as a part of the plant's operating method, it was discovered that when cooling during the hot water sterilization process, 25°C cooling water was to be introduced only after the water temperature in the plant's piping had dropped to 35°C, but 25°C cooling water had mistakenly been introduced when the water temperature in the plant's piping was 40°C. It was presumed that sudden 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 method of 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.

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 in the same manner as in Example 1. As a result, the sodium chloride removal rate was 99.37% (transmittance 0.63%) and the magnesium sulfate removal rate was 99.93% (transmittance 0.07%). Note that the performance of this reverse osmosis membrane element as produced, measured under the same conditions, was a sodium chloride removal rate of 99.80% (transmittance 0.20%) and a magnesium sulfate removal rate of 99.98% (transmittance 0.02%), and the rates of decline in separation performance were 3.1 and 3.5 times the initial rates, respectively, and the rate of decline in magnesium sulfate separation performance was not significantly different from the rate of decline in sodium chloride separation performance, confirming at least indications that chemical degradation was the main cause.

Furthermore, similar to Example 1, when the initial (before deterioration) and post-deterioration transmittances were plotted in Figure 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 decrease in separation performance.

Example 6
Furthermore, the same reverse osmosis membrane element as in Example 5 was evaluated under the same conditions as in Example 2, and the 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 from the feed water side to the concentrated water side in the permeated water collection pipe was measured, and the sodium chloride concentration and magnesium sulfate concentration were calculated from the relationship between the concentration and electrical conductivity.

The results are shown in Figure 17. Based on these results, the rate of change in separation performance was calculated in the length 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 these results are shown in Figures 18 and 19. These results also confirmed that chemical deterioration was the main cause, and that deterioration occurred overall, not locally.

Example 7
Since deterioration of the water quality of the product water of the ultrapure water production plant became evident, the 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 in the same manner as in Example 1. As a result, the sodium chloride removal performance was 88.24% (transmittance 11.76%), and the magnesium sulfate removal performance was 95.95% (transmittance 4.05%). Note that the performance of this reverse osmosis membrane element measured under the same conditions as when it was produced was 99.82% (transmittance 0.18%) for sodium chloride removal and 99.98% (transmittance 0.02%) for magnesium sulfate removal, and the rates of decline in separation performance were 65.3 and 225.2 times the initial rates, respectively. Since the rates of decline in both sodium chloride separation performance and magnesium sulfate separation performance were large, it was difficult to determine the main cause.

Similar to Example 1, when the initial (before deterioration) and post-deterioration transmittances were plotted in Figure 20, the contribution ratio of chemical deterioration to physical deterioration was calculated to be 67:33, and it was determined that both chemical and physical deterioration were factors, with the contribution of chemical deterioration being slightly greater in the deterioration of separation performance.

Example 8
Furthermore, the same reverse osmosis membrane element as in Example 7 was evaluated under the same conditions as in Example 2, and the 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 calculated from the relationship between the concentration and electrical conductivity.

The results are shown in Figure 21. Based on these results, the rate of change in separation performance was calculated in the lengthwise 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 20, and these results 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 although the contribution of physical deterioration at the rear positions was somewhat greater, physical deterioration and chemical deterioration occurred relatively uniformly. Furthermore, as shown in Figure 23, physical deterioration was significantly greater at around 700 mm in the rear positions, and it was decided to focus on investigating the causes of physical deterioration at the rear positions of around 700 mm in the dismantling investigation.

Later, the reverse osmosis membrane element was dismantled to confirm the cause of deterioration, and the membrane surface was observed. Crystalline deposits were found all over the membrane, and staining of the membrane suggested that scratches had occurred all over the membrane due to precipitated crystalline salt.

<Comparative Example 1>
As shown in Example 1, a tendency for the quality of the produced water to deteriorate was observed in an ultrapure water production plant, so 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 FIG. 2, and the separation performance was measured using a performance evaluation device.

Sodium chloride was dissolved in pure water to prepare test water with a concentration of 1500 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 treated water, 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 concentration and electrical conductivity. As a result, the sodium chloride removal rate was 98.80% (transmittance 1.20%). The sodium chloride removal rate of this reverse osmosis membrane element at the time of production, measured under the same conditions, was 99.74% (transmittance 0.26%), indicating that the separation performance had decreased by 4.6 times. However, it was not clear whether this was due to chemical or physical deterioration, and appropriate measures to deal with the problem could not be taken.

So, they took the time to dismantle the reverse osmosis membrane element and dyed the membrane, but there were no noticeable scratches 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 a mixture of 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, they were unable to estimate the contribution ratio between chemical and physical deterioration.

<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 where hot water sterilization was performed periodically, so 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.

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%). 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 8.4 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.

So, after going to the trouble of dismantling the reverse osmosis membrane element, wrinkles were found on the membrane surface, and when the dismantled 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 also occurred. Furthermore, when a piece of the reverse osmosis membrane was immersed in a solution made up of a mixture of an alkaline aqueous solution and pyridine, coloring was observed, confirming the occurrence of oxidative deterioration, and it was concluded that the decline in performance was due to both chemical and physical deterioration. However, it was not possible to estimate the contribution ratios of chemical and physical deterioration.

<Comparative Example 3>
As shown in Example 5, during regular 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.

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 at the time of production, measured under the same conditions, 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.

　So, after going to the trouble of dismantling the reverse osmosis membrane element, they found nothing abnormal in appearance, and dyed the membrane surface to have had almost no scratches, and no signs of physical deterioration were found, so it was assumed that chemical deterioration was the main cause, but surface observations were unable to determine the cause. Furthermore, when a piece of the reverse osmosis membrane was immersed in a solution made up of a mixture of 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 deterioration. However, it was not possible to estimate the contribution ratio between chemical and physical deterioration.

<Comparative Example 4>
Since deterioration in the quality of water produced at an ultrapure water manufacturing plant became evident, 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.

The sodium chloride concentration of the permeate at multiple positions in the permeate collection pipe was determined using a method similar to that used in Example 1, and the sodium chloride removal rate was 88.24% (transmittance 11.76%). The performance of this reverse osmosis membrane element measured under the same conditions as at the time of production was a sodium chloride removal rate of 99.82% (transmittance 0.18%), indicating that the separation performance had decreased by 65.3 times. However, it was not clear whether this was chemical or physical degradation, and appropriate measures to address the problem could not be taken.

So, after going to the trouble of dismantling the reverse osmosis membrane element and observing the membrane surface, they found crystalline deposits all over the membrane, and dyeing the membrane suggested that precipitated crystalline salts had caused numerous scratches all over the membrane. However, this result did not allow them to determine whether chemical deterioration had occurred. Furthermore, when a piece of the reverse osmosis membrane was immersed in a solution made up of a mixture of an alkaline aqueous solution and pyridine, no coloring was observed, and it was not possible to detect the occurrence of oxidative deterioration.

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 come up with various modified or revised examples 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 in the above embodiments may be combined in any manner as long as it does not deviate from the spirit of the invention.

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 by reference into this application.

1: reverse osmosis membrane 2: permeate flow path material 3: treated water flow path material (net spacer)
4: Permeate water collection pipe 5: Telescope prevention plate 6, 6': Water to be treated 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 (8)

A method for diagnosing the state of a separation membrane module having a permeate collection pipe having a plurality of water collection holes for obtaining permeate from water to be treated, comprising:
Test water containing two or more types of solutes is supplied to a separation membrane module, and the test water contains, as the two or more types of solutes, 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 individually supplied to the separation membrane module by changing the valence or molecular weight of the one type of solute in test water containing the one type of solute;
Permeate water is collected at at least two or more positions in the permeate collection pipe;
By comparing the separation performances of the at least two types of solutes, which are calculated based on the difference between the solute concentration in the permeated water collected at each water collection position and the solute concentration due to the permeated water upstream of the water collection position,
A method for diagnosing the condition of a separation membrane module, comprising determining the type of abnormality, the degree of abnormality, or the location of the abnormality in the longitudinal direction of a permeate collection pipe in a separation membrane module. A chemical deterioration profile in which the separation performance of the at least two 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 solutes is deteriorated by physically scratching the supply side of the separation membrane module are prepared in advance;
obtaining a separation performance for each of the at least two types of solutes based on a difference between a solute concentration in the permeated water sampled at each of the water sampling positions and a solute concentration resulting from the permeated water upstream of the water sampling positions;
2. The method for diagnosing the condition of a separation membrane module according to claim 1, further comprising: calculating a contribution rate of chemical deterioration and physical deterioration in the longitudinal direction of a permeate collection pipe in a separation membrane module from the chemical deterioration profile, the physical deterioration profile, and the separation performance of each of the at least two types of solutes; and determining at least any one of the cause of deterioration, the location of deterioration, and the extent of deterioration. The separation membrane module condition diagnosis method according to claim 1 or 2, in which the comparison of separation performance is carried out based on the concentration index of the permeate, the concentration converted from the concentration index, the standard separation performance converted based on the operating conditions, and the solute permeability coefficient calculated based on the operating data. The separation membrane module condition diagnosis method according to 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. The separation membrane module condition diagnosis method according to 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. The method for diagnosing the state of a separation membrane module according to 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 emission mass spectrometry, and pH. The method for diagnosing the state of a separation membrane module according to any one of claims 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 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. The separation membrane module condition diagnosis method according to 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 state of the separation membrane module is judged based on the deviation from that value.

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