Oxidation risk evaluation method for separation membrane, oxidation risk evaluation program, recording medium, and evaluation device

Abstract

A method for evaluating the risk of oxidation of a separation membrane in a water treatment plant, the method being characterized in that deposits on a separation membrane to be used are collected, the deposits are brought into contact with a solution containing a sulfite or a bisulfite, and the solution is separated from the separation membrane. And evaluating the oxidation potential of the deposit on the basis of the generated oxidizing substance.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the oxidation risk of a separation membrane, an oxidation risk evaluation program, a recording medium, and an evaluation device. Background Art

[0002] In recent years, water treatment technologies using various separation membranes such as gas separation membranes, reverse osmosis membranes, nanofiltration membranes, ultrafiltration membranes, and microfiltration membranes have attracted attention as high-precision and energy-saving treatment processes, and their applications in various water treatments have been promoted. For example, in the reverse osmosis separation method using a reverse osmosis membrane, by passing a solution containing solutes such as salts through the reverse osmosis membrane under a pressure above the osmotic pressure of the solution, a liquid with a reduced concentration of solutes such as salts can be obtained, which is widely used in the desalination of seawater and brine, the production of ultrapure water, the concentration and recovery of valuable substances, etc., and has become the core of membrane separation technology for water treatment.

[0003] As the main problems when applying a reverse osmosis membrane to the above uses, surface fouling of the semipermeable membrane called fouling and chemical degradation of the semipermeable membrane can be cited. As a device for suppressing the former, a method of adding an oxidizing substance such as sodium hypochlorite to sterilize microorganisms can be cited. However, the oxidizing substance contained in this pretreatment becomes a factor of oxidative degradation. As a method for detecting an oxidizing substance, oxidation-reduction potential (ORP) measurement, the N,N-diethyl-p-phenylenediamine (DPD) method as a color reaction, the Fujiwara test described in Patent Document 1 and Non-Patent Document 1, etc. are used. On the other hand, as a substance that is not an oxidizing substance but plays an important role in the oxidation reaction process, an oxidation reaction promoting substance represented by a certain transition metal can be cited. The amount of this substance is difficult to evaluate by the aforementioned oxidizing substance detection methods. As another method, a method of investigating the elemental composition of the supply water by high-frequency inductively coupled plasma (ICP) emission analysis, etc. can be cited. However, this spectroscopic analysis method requires highly sophisticated and expensive instruments, requires a professional analysis institution, takes time until the result is obtained, and requires a high cost. In addition, when the amount of the oxidation reaction promoting substance contained in the supply water is below the detection limit value of the spectroscopic analysis method, it is difficult to evaluate the oxidation risk. On the other hand, Patent Document 2 discloses a method for evaluating the oxidation risk of a separation membrane in a water treatment plant by passing membrane-filtered supply water through an oxidizing substance-sensitive member. Among them, when the amount of the oxidation reaction promoting substance contained in the supply water is trace, there is a problem that it is difficult to detect by this method.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2020-6322

[0007] Patent Document 2: Japanese Patent Application Publication No. 2016-190212

[0008] Patent Document 3: Japanese Patent Application Publication No. 2021-63335

[0009] Non-patent literature

[0010] Non-patent literature 1: Journal of Membrane Science, 2010, Vol. 347, P. 159-164. Summary of the invention

[0011] Problems to be solved by the invention

[0012] The present invention uses the deposits on the surface of the separation membrane to evaluate the oxidation potential, and can easily and quickly evaluate the oxidation risk that is difficult to evaluate by the previous method. In addition, since it can be easily and quickly implemented and the amount of deposits required is small, it is useful in risk avoidance and early resolution of operating failures in water treatment plants.

[0013] Means for solving problems

[0014] The present invention is an oxidation risk assessment method characterized by recovering deposits on the surface of a separation membrane, bringing the membrane into contact with a solution containing sulfite or bisulfite, and evaluating the oxidation potential of the deposits based on generated oxidizing substances.

[0015] In order to solve the above-mentioned problems, the present invention has the following features.

[0016] (1) A method for evaluating the oxidation risk of a separation membrane, which is a method for evaluating the oxidation risk of a separation membrane in a water treatment plant, the method comprising bringing deposits recovered from a used separation membrane into contact with a solution containing sulfite or bisulfite, and evaluating the oxidation potential of the deposits based on the generated oxidizing substances.

[0017] (2) The method for evaluating oxidation risk of a separation membrane according to (1), wherein a deposit extract is used instead of the deposit.

[0018] (3) The method for evaluating oxidation risk of a separation membrane according to (1) or (2), wherein the separation membrane is any one of the following:

[0019] A: The separation membrane collected from the semipermeable membrane element, which separates the feed water into permeate and concentrate in the water treatment plant.

[0020] B: A separation membrane installed inside a water-passing member installed in a water supply line of a water treatment plant

[0021] C: A separation membrane disposed inside a water-passing member. The water-passing member uses a semi-permeable membrane element and is disposed in a concentrated water pipeline. The semi-permeable membrane element separates supplied water into permeate water and concentrated water in a water treatment equipment set.

[0022] (4) The method for evaluating the oxidation risk of the separation membrane according to any one of (1) to (3), characterized in that the method for evaluating the oxidation risk of the separation membrane is a method for evaluating the oxidation risk based on a catalytic reaction, and the method for evaluating the oxidation potential of the attachment is a method for measuring the change over time of the oxidation power index value of the solution in contact with the attachment, and any one of the following is evaluated:

[0023] A: The maximum value of the oxidation power index value

[0024] B: The rate of change of the oxidation power index value per unit time

[0025] C: The maximum value of the moving average of the oxidation power index value

[0026] D: The rate of change of the moving average of the oxidation power index value per unit time.

[0027] (5) The method for evaluating the oxidation risk of the separation membrane according to any one of (1) to (4), characterized in that the method for evaluating the oxidation potential of the attachment is a method for changing the concentration of sulfite or bisulfite in the solution in contact with the attachment by adding sulfite or bisulfite and measuring the oxidation power index value when the attachment is in contact.

[0028] (6) The method for evaluating the oxidation risk of the separation membrane according to any one of (1) to (5), characterized in that the method for evaluating the oxidation potential of the attachment is: using two or more solutions with different concentrations of sulfite or bisulfite solution as the solution in contact with the attachment and measuring the oxidation power index value when the attachment is in contact.

[0029] (7) The method for evaluating the oxidation risk of the separation membrane according to (5) or (6), characterized in that the method for evaluating the oxidation potential of the attachment in (5) or (6) evaluates any one of the following:

[0030] A: The maximum value of the oxidation power index value

[0031] B: The rate of change of the oxidation power index value with respect to the concentration of sulfite or bisulfite.

[0032] (8) The method for evaluating the oxidation risk of a separation membrane according to any one of (5) to (7), characterized in that this method is a method of further adding a sulfite or bisulfite after the oxidation power index value reaches the maximum and measuring the oxidation power index value at this time.

[0033] (9) The method for evaluating the oxidation risk of a separation membrane according to any one of (5) to (7), characterized in that this method is a method of using a different solution with a higher concentration after the oxidation power index value reaches the maximum and measuring the oxidation power index value when the attachment is in contact.

[0034] (10) The method for evaluating the oxidation risk of a separation membrane according to (7) or (8), characterized in that the method for evaluating the oxidation potential of the attachment described in (7) or (8) is a method of evaluating at least any one of the following,

[0035] A: The concentration of sulfite or bisulfite whose oxidation power index value is below that before the attachment is in contact

[0036] B: The rate of change of the oxidation power index value with respect to the concentration of sulfite or bisulfite.

[0037] (11) The method for evaluating the oxidation risk of a separation membrane according to any one of (1) to (10), characterized in that the attachment is brought into contact with the aforementioned solution containing sulfite or bisulfite having a hydrogen ion concentration index (pH) of 9.0 or more.

[0038] (12) An oxidation risk evaluation program, which is an oxidation risk evaluation program for a separation membrane in a water treatment equipment set. In this program, in order to evaluate the oxidation risk, a computer functions as a data recording device that records the input data in the computer and a device that evaluates the oxidation potential of the attachment based on the recorded data. The input data is the conditions and the oxidation power index value when the attachment recovered from the used separation membrane is brought into contact with a solution containing sulfite or bisulfite. This oxidation risk evaluation program utilizes the oxidation risk evaluation method described in (1).

[0039] (13) The oxidation risk evaluation program according to (12), characterized in that the oxidation risk evaluation method of the water treatment equipment set is an oxidation risk evaluation method based on a catalytic reaction. The aforementioned device for evaluating the oxidation potential of the attachment is a device that evaluates at least any one of the following based on the time-dependent data of the oxidation power index value,

[0040] A: The maximum value of the oxidation power index value

[0041] B: The rate of change of the oxidation power index value per unit time

[0042] C: The maximum value of the moving average of the oxidation power index value

[0043] D: Rate of change of the moving average of the oxidation power index value per unit time.

[0044] (14) The oxidation risk evaluation procedure according to (12), characterized in that the device for evaluating the oxidation potential of the attachment is a device for evaluating any one of the following based on the relationship between the oxidation power index value and the concentration of sulfite or bisulfite,

[0045] A: Maximum value of the oxidation power index value

[0046] B: Rate of change of the oxidation power index value with respect to the concentration of sulfite or bisulfite.

[0047] (15) The oxidation risk evaluation procedure according to (12), characterized in that the method for evaluating the oxidation potential of the attachment is a method for evaluating any one of the following based on the relationship between the oxidation power index value after reaching the maximum and the concentration of sulfite or bisulfite,

[0048] A: Concentration of sulfite or bisulfite at which the oxidation power index value is below that before the attachment contacts

[0049] B: Rate of change of the oxidation power index value with respect to the concentration of sulfite or bisulfite.

[0050] (16) A recording medium that stores the oxidation risk evaluation procedure according to any one of (12) to (15).

[0051] (17) An oxidation risk evaluation device, which is an oxidation risk evaluation device for a separation membrane in a water treatment equipment set, and includes: a data input device that causes a computer to input, for evaluating oxidation risk, the conditions and the oxidation power index value when an attachment recovered from the used separation membrane is brought into contact with a solution containing sulfite or bisulfite into the computer; a data recording device that records the foregoing conditions and the oxidation power index value in the computer; and a device for evaluating the oxidation potential using any one of the methods described in (1) to (11).

[0052] Advantages of the Invention

[0053] According to the present invention, it is possible to perform a simple and rapid evaluation of the oxidation risk of a separation membrane that is difficult to determine by conventional evaluation methods. Brief Description of the Drawings

[0054] Figure 1 : An example of the flow of a water treatment equipment set is shown.

[0055] Figure 2 : A schematic diagram showing an example of a water passage member used in the present invention.

[0056] Figure 3: An example of a water-permeable container (unit water-permeable member) that constitutes the water-permeable member used in the present invention and is divisible.

[0057] Figure 4 : A graph showing an example of a method for evaluating the relationship between the elapsed time since contact with the attachment and the oxidation power index value, and the maximum value of the oxidation power index value by the first method for evaluating the oxidation potential of the present invention.

[0058] Figure 5 : A graph showing an example of a method for evaluating the relationship between the elapsed time since contact with the attachment and the oxidation power index value, and the rate of change of the oxidation power index value per unit time by the first method for evaluating the oxidation potential of the present invention.

[0059] Figure 6 : A graph showing an example of a method for evaluating the relationship between the sulfite or bisulfite concentration and the oxidation power index value, and the maximum value of the oxidation power index value by the second or third method for evaluating the oxidation potential of the present invention.

[0060] Figure 7 : A graph showing an example of a method for evaluating the relationship between the sulfite or bisulfite concentration and the oxidation power index value, and the rate of change of the oxidation power index value with respect to the sulfite or bisulfite concentration by the second or third method for evaluating the oxidation potential of the present invention.

[0061] Figure 8 : A graph showing an example of a method for evaluating the relationship between the sulfite or bisulfite concentration and the oxidation power index value, and the sulfite or bisulfite concentration below the oxidation power index value before contact with the attachment by the fourth or fifth method for evaluating the oxidation potential of the present invention.

[0062] Figure 9 : A graph showing an example of a method for evaluating the relationship between the sulfite or bisulfite concentration and the oxidation power index value, and the rate of change of the oxidation power index value with respect to the sulfite or bisulfite concentration by the fourth or fifth method for evaluating the oxidation potential of the present invention.

[0063] Figure 10 : An example of a program for performing oxidation risk determination using the first method of the present invention in a computer.

[0064] Figure 11 : An example of a program for performing oxidation risk determination using the second or third method of the present invention in a computer.

[0065] Figure 12: It is an example of a program for performing oxidation risk determination in a computer using the fourth method of the present invention with a sulfite or bisulfite concentration where the oxidation power index value is below that before contact with the attachment.

[0066] Figure 13 : It is an example of a program for performing oxidation risk determination in a computer using the rate of change of the oxidation power index value with respect to sulfite or bisulfite in the fourth method of the present invention.

[0067] Figure 14 : It is an example of a program for performing oxidation risk determination in a computer using the first method of the present invention.

[0068] Figure 15 : It is an example of a program for performing oxidation risk determination in a computer using the second or third method of the present invention.

[0069] Figure 16 : It is an example of a program for performing oxidation risk determination in a computer using the fourth method of the present invention with a sulfite or bisulfite concentration where the oxidation power index value is below that before contact with the attachment.

[0070] Figure 17 : It is an example of a program for performing oxidation risk determination in a computer using the rate of change of the oxidation power index value with respect to sulfite or bisulfite in the fourth method of the present invention.

[0071] Figure 18 : It is a graph showing the relationship between the elapsed time from the start of contact with sulfite or bisulfite and the oxidation-reduction potential in Example 1 of the present invention.

[0072] Figure 19 : It is a graph showing the relationship between the elapsed time from the start of contact with sulfite or bisulfite and the oxidation-reduction potential in Example 3-1 of the present invention.

[0073] Figure 20 : It is a graph showing the relationship between the sulfite or bisulfite concentration and the oxidation-reduction potential in Example 3-2 of the present invention.

[0074] Figure 21 : It is a graph showing the relationship between the elapsed time from the start of contact with sulfite or bisulfite and the oxidation-reduction potential in Example 4 of the present invention. Detailed implementation mode

[0075] To solve the above problems, the present invention has the following features. Hereinafter, the detailed content of the present invention will be illustrated with reference to the accompanying drawings, and the content of the present invention is not limited by the drawings.

[0076] The present invention is a method for evaluating oxidation risk of a separation membrane, and as one embodiment, it is characterized in that the deposits on the surface of the separation membrane are recovered, brought into contact with a solution containing sulfite or bisulfite, and the oxidation potential of the deposits is evaluated based on the generated oxidizing substances. The deposits accumulate on the surface of the separation membrane, thereby replenishing the oxidizing substances and oxidation reaction promoting substances in the feed water and accumulating on the surface of the separation membrane. As a result, the substances exist at a high concentration on the surface of the separation membrane compared with the feed water and the concentrated water. Therefore, even if the content in the feed water is small, the oxidation risk can be evaluated by evaluating the oxidation potential of the deposits.

[0077] It should be noted that the catalytic reaction in one embodiment of the present invention refers to the reaction of the oxidizing substance and the oxidation reaction accelerating substance described above and in the background art with sulfite or bisulfite.

[0078] As an example of the separation membrane in one embodiment of the present invention, there can be mentioned a separation membrane provided in a water treatment plant.

[0079] For example, Figure 1 An example of the flow of a water treatment plant is shown in FIG. Figure 1 The water treatment equipment shown in the figure is composed of a raw water storage tank 1 for storing water to be treated (hereinafter referred to as raw water), a raw water supply pump 2 for supplying raw water, a pretreatment membrane filtration unit 3 for filtering the raw water, a pretreatment membrane filtration water storage tank 4 for storing filtered water of the pretreatment membrane filtration unit 3, a separation membrane filtration unit 5, a booster pump 6 for supplying the filtered water of the pretreatment membrane filtration unit 3 to the separation membrane filtration unit 5, and a booster pump 7 for boosting the pressure of the filtered water of the pretreatment membrane filtration unit 3 in order to separate it into permeate water and concentrated water through the separation membrane filtration unit 5.

[0080] In addition, the raw water storage tank 1 is connected to the pretreatment membrane filtration unit 3 through a raw water pipe 8, the pretreatment membrane filtration unit 3 is connected to the pretreatment membrane filtration water storage tank 4 through a pretreatment membrane filtration water pipe 9, and the pretreatment membrane filtration water storage tank 4 is connected to the separation membrane filtration unit 5 through a separation membrane filtration supply water pipe 10. In the water treatment plant, the raw water is treated by the pretreatment membrane filtration unit 3, and the pretreatment membrane filtration water is temporarily stored in the pretreatment membrane filtration water storage tank 4, and then supplied to the booster pump 7 by the booster pump 6, and after being boosted by the booster pump 7, it is supplied to the separation membrane filtration unit 5, and separated into permeate water from which solutes such as salt are removed and concentrated water from which solutes such as salt are concentrated, and discharged through the separation membrane filtration permeate water pipe 11 and the separation membrane filtration concentrated water pipe 12, respectively.

[0081] As an example of the separation membrane in an embodiment of the present invention, there can be mentioned the separation membrane taken from the components provided in the separation membrane filtration unit, and the separation membrane within the components provided in the piping within the equipment, such as raw water piping 8, pre-treatment filtered water piping 9, separation membrane filtration supply water piping 10, separation membrane filtration permeated water piping 11, separation membrane filtration concentrated water piping 12, etc.

[0082] As the separation membrane in an embodiment of the present invention, it can also be applied to, for example, microfiltration membranes (MF), ultrafiltration membranes (UF membranes), etc. applicable in the pre-treatment filtration unit 3. It is particularly preferably used in equipment for separating and concentrating solute components using semi-permeable membranes such as nanofiltration membranes (NF membranes), reverse osmosis membranes (RO membranes), etc., and is preferably used for desalination of seawater and brine, production of industrial water, concentration of fruit juices, etc., and advanced treatment of tap water. In addition, when the separation membrane of the present invention is a semi-permeable membrane, the oxidation reaction promoting substance does not permeate and is concentrated and accumulated on the surface of the semi-permeable membrane, so it becomes a higher concentration compared to the raw water or concentrated water, and the evaluation accuracy based on the present invention is improved, so it is more preferred. They are usually provided in the separation membrane filtration unit 5.

[0083] A semi-permeable membrane refers to a membrane having semi-permeability that allows a part of the components in the raw water, such as the solvent, to permeate while not allowing solute components such as salts to permeate. Examples include nanofiltration membranes (NF membranes), reverse osmosis membranes (RO membranes), etc. The membrane structure can include an asymmetric membrane having a separation dense layer on one side of the membrane and micropores with gradually increasing pore diameters from the separation dense layer to the inside of the membrane or the other side, and a composite membrane having a very thin separation functional layer formed of other raw materials on the dense layer of the asymmetric membrane, etc. As the membrane form, there are hollow fiber membranes and flat membranes.

[0084] The semi-permeable membrane is usually made into an element of a suitable form according to the membrane form. The semi-permeable membrane element in the present invention is not particularly limited as long as it has substantial liquid chambers on both sides of the semi-permeable membrane and can pressurize and permeate the liquid from one surface of the semi-permeable membrane to the other surface. As an example, there can be mentioned a spiral semi-permeable membrane element having a flat membrane form. The spiral semi-permeable membrane element generally consists of a supply side flow path member that guides the supply water to the surface of the semi-permeable membrane, a semi-permeable membrane, and a permeate side flow path member that guides the liquid (permeated water) that has permeated through the semi-permeable membrane to the collection pipe. The supply side flow path member, the semi-permeable membrane, and the permeate side flow path member are wound spirally around the collection pipe. As described above, as the separation membrane of the present invention, from the viewpoint of improving the evaluation accuracy, the separation membrane taken from the spiral semi-permeable membrane element is preferred.

[0085] In addition, by periodically implementing the evaluation method of an embodiment of the present invention, for example, regularly at a frequency of once a day to once a week, it becomes easy to determine the occurrence period of a sudden increase in oxidation risk, and countermeasures can be taken promptly. At this time, when it is difficult to take the separation membrane from the setting member of the separation membrane filtration unit, such as a semi-permeable membrane element, by using the pipes near the separation membrane filtration unit, such as the separation membrane filtration supply water pipe 10, the separation membrane filtration permeate water pipe 11, or the separation membrane filtration concentrated water pipe 12, the oxidation risk in the separation membrane filtration unit 5 can be evaluated correctly and promptly, so it is preferred. In particular, since the evaluation accuracy of the present invention is improved when the concentration of the oxidation-promoting substance in the solution in the pipe is large, the separation membrane filtration supply water pipe or the separation filtration membrane concentrated water pipe is preferred, and the separation membrane filtration concentrated water pipe is more preferred. As an example of the form of setting the separation membrane on the pipe, a water passage member having a separation membrane inside can be cited as being provided in the pipe.

[0086] The water passage member in one embodiment of the present invention is not particularly limited as long as it has a separation membrane inside and the solution moves from one end of the water passage member to the other end. In addition, as described above, since the oxidation risk evaluation can be performed regularly and at a high frequency, it is desirable that the water passage member is easy to install and remove on the pipes of the water treatment equipment set. As an example, as Figure 2 illustrated, it is preferred that a certain unit structure can be continuously combined and separated via a connecting member of a threaded structure or a fitting structure (such as a joint like the one-touch joint 15), or has a structure such as a hose 13 that can be easily cut with scissors or can be partially separated. As an example, as Figure 2 and Figure 3 shown, a water passage container 19 formed by connecting one or more unit water passage members 19a having a connectable structure provided with a threaded groove and a separation membrane 20 at both ends in the length direction (water passage direction 18) of the water container opening / closing part 16 and the cylindrical unit water passage member 19a, and then connecting to the water passage container opening / closing part 16 can be cited as a preferred mode. It is preferred to implement leakage prevention measures such as gaskets, sealing tapes, and O-rings on the connection part in advance according to the shape. It should be noted that at this time, the area of the separation membrane 20 is not particularly limited, and it is preferably 0.01 m 2 Above, more preferably 0.03 m 2 Above. In addition, the separation membrane 20 is more preferably provided perpendicular to the water passage direction.

[0087] In addition, as a simple water passage container, a member such as a hose as described above can be used. At this time, the water passage container is preferably cylindrical and formed of a soft material. Thereby, the separation membrane inside can be easily cut out with scissors. In addition, a flow meter 14 and a flow control valve 17 can also be inserted into the middle of the hose 13.

[0088] It should be noted that when the water-passing component is arranged in the internal piping of the equipment other than near the aforementioned separation membrane filtration unit, the oxidation risk assessment of each piping and its vicinity can also be carried out.

[0089] The material (component) constituting the separation membrane or semipermeable membrane is not particularly limited. Preferred are cellulose acetate compounds, vinyl polymer compounds, polyamide compounds, polyester compounds, polyimide compounds, etc. Particularly preferred are cellulose acetate compounds and polyamide compounds widely used as semipermeable membrane materials.

[0090] The sulfite or bisulfite is not particularly limited. As examples, sodium sulfite, potassium sulfite, magnesium sulfite, calcium sulfite, sodium bisulfite, potassium bisulfite, magnesium bisulfite, calcium bisulfite, etc. can be cited. They can use ordinary commercially available products. Among them, sodium sulfite, potassium sulfite, sodium bisulfite, and potassium bisulfite are particularly preferred.

[0091] In one embodiment of the present invention, it is characterized in that after the attachment on the surface of the separation membrane is recovered by a physical method, it is supplied for oxidation risk assessment. As the method for recovering the attachment, as long as it has a high recovery rate and is quantitative, there is no particular limitation. For example, a method of immersing the membrane in pure water and dispersing the attachment in pure water by ultrasonic crushing for recovery can be cited. In addition, as a method for reliably peeling and recovering the attachment fixed to the separation membrane, a method of immersing the wiping tool in pure water after recovering the attachment on the surface of the separation membrane with the wiping tool to disperse the attachment in pure water for recovery can be cited. As the wiping tool, cotton swabs, spatulas, scrapers, rubber spatulas, etc. can be cited. It is preferred that they do not contain oxidant-based disinfectants. In addition, in order to prevent damage and peeling of the separation membrane, cotton swabs and silicon tools can be cited as preferred tools, and there is no particular limitation. As the pure water, distilled water, freshly purified reverse osmosis membrane (RO membrane) water, ion-exchanged water, commercially available ultrapure water, etc. are preferred. In addition, a method of drying the separation membrane and then using the aforementioned wiping tool to recover the attachment on the surface of the separation membrane into a container can also be cited as an example. At this time, as the drying method of the separation membrane, as long as it can easily peel the attachment on the surface of the separation membrane, there is no particular limitation. Examples include natural drying at room temperature and drying by placing it in a heated dryer. The recovered attachment is preferably dried at room temperature or by heating. At this time, it is preferably heated to 30°C to 120°C using a constant temperature dryer and dried until its weight change is less than ±0.1 g.

[0092] In one embodiment of the present invention, it is characterized in that an adherend is brought into contact with a solution containing sulfite or bisulfite, and the oxidation potential of the adherend is evaluated based on the generated oxidizing substance. The method of bringing the adherend into contact with the solution containing sulfite or bisulfite is not particularly limited, and examples thereof include a method of putting the recovered adherend into a solution prepared by dissolving sulfite or bisulfite in pure water. At this time, in order to increase the contact area between the adherend and the solution, it is preferable to use a stirring device, a stirrer, an oscillator, etc. to oscillate and stir the solution into which the adherend has been put. Examples of the stirring device, stirrer, and oscillator include a spatula, a spatula, a magnetic stirrer, a stirring rod having a stirring blade at the tip, a stirrer such as a THREE-ONE MOTOR (manufactured by Shinto Kagaku Co., Ltd.), an ultrasonic cleaner, etc.

[0093] In addition, as another example of bringing the adherend into contact with a solution containing sulfite or bisulfite and evaluating the oxidation potential of the adherend based on the generated oxidizing substance, a method of using an adherend extract obtained by treating the adherend with a chemical solution can be cited. By using the adherend extract, the catalytic reaction between the oxidation reaction promoting substance in the adherend and sulfite or bisulfite is promoted, and a more accurate evaluation of the oxidation potential of the adherend can be performed. As a method of treating and extracting the adherend with a chemical solution, ordinary extraction operations can be used. For example, a method of adding the adherend to the chemical solution and allowing it to stand or using a stirring device, stirrer, oscillator described later to stir the chemical solution, and collecting the chemical solution after a certain period of time can be cited. As a method of collecting the chemical solution at this time, as an example, in addition to using an instrument such as a dropper to collect the chemical solution, a method of collecting the chemical solution by removing the adherend through a filtration operation can also be cited. As the chemical solution to be used, an acidic chemical solution is ideal. That is, it is preferable to use a chemical solution with a hydrogen ion concentration of pH 6 or less, more preferably pH 3 or less. Examples thereof include sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, citric acid, oxalic acid, acetic acid, formic acid, etc., and nitric acid, hydrochloric acid, and phosphoric acid are particularly preferred. These chemical solutions are usually commercially available and can be used.

[0094] In addition, the solution containing sulfite or bisulfite in one embodiment of the present invention may contain other inorganic salts to reproduce the state in an actual water treatment equipment. It is particularly preferable to contain sodium chloride. As the sodium chloride concentration, it is preferably 500 to 80000 mg / L, more preferably 1000 to 50000 mg / L.

[0095] As a first method for evaluating the oxidation potential of the present invention, a method can be cited in which an adherend recovered from the surface of a separation membrane is brought into contact with a solution containing sulfite or bisulfite, and the time-dependent change in the oxidation power index value of the solution is measured. As an example of the first method, as Figure 4 or Figure 5As shown, a method for evaluating at least any one of the following can be cited. At this time, the magnitude of the oxidation risk is as described later and is determined according to the determination method in the oxidation power index value measurement method used. However, generally, in any of the following cases, the larger the value, the greater the oxidation potential and the higher the oxidation risk.

[0096] A: The maximum value of the oxidation power index value

[0097] B: The change rate of the oxidation power index value per unit time

[0098] C: The maximum value of the moving average of the oxidation power index value

[0099] D: The change rate of the moving average of the oxidation power index value per unit time.

[0100] It should be noted that the change rate of the oxidation power index value per unit time is calculated by dividing the difference in the oxidation power index value by the difference in the elapsed time from the start of contact of the adherend. For example, Figure 5 in the case of, it is calculated by Equation 1.

[0101] (Change rate of oxidation power index value per unit time) = (y2 - y1) ÷ (t2 - t1) (Equation 1)

[0102] In Equation 1, y1 represents the oxidation power index value when the elapsed time from the start of contact of the adherend is t1, and y2 represents the oxidation power index value when the elapsed time from the start of contact of the adherend is y2. Here, it is assumed that t2 > t1. It should be noted that in a single evaluation where the adherend is contacted once, when calculating for multiple t2 and t1, the maximum value calculated by Equation 1 is adopted. In addition, the moving average of the oxidation power index value refers to the arithmetic average of the oxidation power index values of the most recent N (an integer of 2 or more) points. As a second method for evaluating the oxidation potential of the present invention, a method can be cited in which two or more solutions with different concentrations of sulfite or bisulfite are used, and the oxidation power index values when the adherend recovered from the surface of the separation membrane comes into contact with each of them are measured. As an example of the second method, as Figure 6 or Figure 7 shown, a method for evaluating at least any one of the following can be cited. At this time, the magnitude of the oxidation risk is as described later and is determined according to the determination method in the oxidation power index value measurement method used. However, generally, in any of the following cases, the larger the value, the greater the oxidation potential and the higher the oxidation risk.

[0103] A: The maximum value of the oxidation power index value

[0104] B: The change rate of the oxidation power index value with respect to the concentration of sulfite or bisulfite.

[0105] It should be noted that the change rate of the oxidation power index value with respect to the concentration of sulfite or bisulfite is calculated by dividing the difference in the oxidation power index value by the difference in the corresponding sulfite or bisulfite concentration. For example, Figure 8 In the case of

[0106] (Change rate of oxidation power index value with respect to sulfite or bisulfite concentration)

[0107] =(y4 - y3)÷(c4 - c3) (Formula 2)

[0108] In Formula 2, y3 represents the oxidation power index value when the sulfite or bisulfite concentration is c3, and y4 represents the oxidation power index value when the sulfite or bisulfite concentration is c4. It is assumed that c4 > c3.

[0109] It should be noted that in a single evaluation where the attachment is made to contact once, when calculating multiple c4 and c3, the maximum value among the values calculated by Formula 2 is adopted. In addition, when measuring the oxidation power index value over time under each concentration condition, the oxidation power index value under each concentration condition uses any one of the following.

[0110] A: Maximum value of oxidation power index value

[0111] B: Change rate of oxidation power index value per unit time

[0112] C: Maximum value of moving average of oxidation power index value

[0113] D: Change rate of moving average of oxidation power index value per unit time.

[0114] As the third method for evaluating the oxidation potential of the present invention, there can be cited a method of changing the sulfite or bisulfite concentration of the solution by further adding sulfite or bisulfite to the solution containing sulfite or bisulfite in which the attachment is contacted, and measuring the oxidation power index value when the attachment is contacted. As an example of the third method, as Figure 6 or Figure 7 shown, there can be cited a method of evaluating at least any one of the following. At this time, the magnitude of the oxidation risk is as described later, in accordance with the determination method in the oxidation power index value measurement method used, but generally in any of the following cases, the larger the value, the greater the oxidation potential and the higher the oxidation risk.

[0115] A: Maximum value of oxidation power index value

[0116] B: Change rate of oxidation power index value with respect to sulfite or bisulfite concentration.

[0117] It should be noted that the change rate of the oxidation power index value with respect to the sulfite or bisulfite concentration is calculated by dividing the difference in the oxidation power index value by the difference in the corresponding sulfite or bisulfite concentration. For example, as described above, Figure 7 In the case of, it is calculated by Equation 2.

[0118] As the fourth method for evaluating the oxidation potential of the present invention, there can be mentioned a method of measuring the oxidation power index value when contacting a solution containing sulfite or bisulfite in which the adherends are in contact with each other and having a higher concentration than the solution described in any one of the first to third methods. As an example of the fourth method, as Figure 8 or Figure 9 shown, there can be mentioned a method of evaluating at least any one of the following. At this time, the magnitude of the oxidation risk is as described later and follows the determination method in the oxidation power index value measurement method used, but generally, in any of the following cases, the larger the value, the greater the oxidation potential and the higher the oxidation risk.

[0119] A: The sulfite or sulfite concentration at which the oxidation power index value is below that before contact of the adherend

[0120] B: The change rate of the oxidation power index value with respect to the sulfite or bisulfite concentration.

[0121] It should be noted that the change rate of the oxidation power index value with respect to the sulfite or bisulfite concentration is calculated by dividing the difference in the oxidation power index value by the difference in the corresponding sulfite or bisulfite concentration. For example, Figure 9 In the case of, it is calculated by Equation 3.

[0122] (Change rate of oxidation power index value with respect to sulfite or bisulfite concentration)

[0123] =(y6 - y5)÷(c6 - c5) (Equation 3)

[0124] In Equation 3, y5 represents the oxidation power index value when the sulfite or bisulfite concentration is c5, and y6 represents the oxidation power index value when the sulfite or bisulfite concentration is c6. It is assumed that c6 > c5. Usually, y6 < y5, so the value calculated by Equation 3 is negative, and the larger the absolute value, the smaller the value.

[0125] It should be noted that in a single evaluation in which the adherend is contacted once, when calculating multiple c5 and c6, the maximum value among the values calculated by Equation 3 is adopted.

[0126] In addition, when measuring the oxidation power index value over time under each concentration condition, the oxidation power index value under each concentration condition uses any one of the following.

[0127] A: The maximum value of the oxidation power index value

[0128] B: Rate of change of the oxidation power index value per unit time

[0129] C: Maximum value of the moving average of the oxidation power index value

[0130] D: Rate of change of the moving average of the oxidation power index value per unit time.

[0131] In addition, as a fifth method for evaluating the oxidation potential of the present invention, there can be mentioned a method in which, in the method described in any one of the first to third methods, after the oxidation power index value of a solution containing sulfite or bisulfite in contact with the adherend reaches the maximum, sulfite or bisulfite is further added and the oxidation power index value at this time is measured. As an example of the fifth method, as shown in Figure 8 or Figure 9 There can be mentioned a method for evaluating at least any one of the following. At this time, the magnitude of the oxidation risk is as described later and follows the determination method in the oxidation power index value measurement method used, but generally, in any of the following cases, the larger the value, the greater the oxidation potential and the higher the oxidation risk are judged.

[0132] A: Sulfite or sulfite concentration at which the oxidation power index value is below that before contact with the adherend

[0133] B: Rate of change of the oxidation power index value with respect to the sulfite or bisulfite concentration.

[0134] It should be noted that the rate of change of the oxidation power index value with respect to the sulfite or bisulfite concentration is calculated by dividing the difference in the oxidation power index value by the difference in the corresponding sulfite or bisulfite concentration, and is usually negative. For example, as described above, in the case of Figure 9 It is calculated by Equation 3.

[0135] By using any one of the first to third methods, the oxidation potential can be evaluated quickly and simply. For example, when evaluating the oxidation risk at a specified concentration or amount such as the sulfite or bisulfite concentration used in an actual equipment set, the first method is preferred. On the other hand, when wanting to know the maximum oxidation risk to be worried about, the second or third method is preferred. In addition, if the fourth or fifth method is used, the sulfite or bisulfite concentration required to sufficiently eliminate the oxidation potential can be known.

[0136] Furthermore, in the first to fifth embodiments, when it is possible to grasp the membrane area used in the collection of the adherent substance and the number of years of use (operation) of the element or water passage member containing the membrane, if the value obtained by dividing the index obtained by each embodiment by the membrane area and / or the number of years of use is used, the oxidation risk of the actual equipment can be evaluated more accurately. For example, when using the first embodiment, if the value calculated by Equation 4 is used, a more accurate oxidation risk evaluation can be performed.

[0137] (Oxidation force index value per unit area · number of years of use)

[0138] = z ÷ ((membrane area used in the collection of the adherent substance) × (number of years of use of the membrane)) (Equation 4)

[0139] Here, z is the oxidation risk index value evaluated by the first embodiment, that is, any one of the following.

[0140] A: Maximum value of the oxidation force index value

[0141] B: Rate of change of the oxidation force index value per unit time

[0142] C: Maximum value of the moving average of the oxidation force index value

[0143] D: Rate of change of the moving average of the oxidation force index value per unit time.

[0144] Similarly, in other embodiments, by setting the oxidation risk index value evaluated by each method as z and using the value calculated by Equation 4, a more accurate oxidation risk evaluation can be performed.

[0145] As the method for measuring the oxidation force index value, there is no particular limitation, and a method that reacts sensitively to oxidizing substances is preferred. As a general method, for example, oxidation-reduction potential (ORP) measurement, measurement of free residual chlorine concentration or combined and / or total chlorine concentration based on the N,N-diethyl-p-phenylenediamine (hereinafter referred to as DPD) method, Fujiwara test described in Patent Document 1 and Non-Patent Document 1, dissolved oxygen (DO) measurement, etc. can be cited. In particular, from the viewpoint of measurement simplicity, ORP measurement, measurement of free residual chlorine concentration, combined and / or total chlorine concentration based on the DPD method are preferred.

[0146] It should be noted that the oxidation-reduction potential (ORP) is an index indicating the oxidizing or reducing property of a solution, which is determined by the equilibrium state of electron donation and acceptance between the oxidant and reductant coexisting in the solution. It is usually measured as the potential difference between a metal electrode and a reference electrode based on the Nernst equation. As a method for measuring this index, there is a method using an oxidation-reduction potentiometer. The oxidation-reduction potentiometer is not particularly limited, and preferably an oxidation-reduction potentiometer that uses a platinum electrode and a reference electrode, or a composite electrode of a platinum electrode and a reference electrode to measure the oxidation-reduction potential based on the Nernst equation, and preferably a saturated calomel electrode or a saturated silver / silver chloride electrode, etc. is used as the reference electrode, and more preferably a 3.3 mol / L silver chloride electrode is used as the reference electrode for measurement.

[0147] In addition, the DPD method is a method for measuring the free residual chlorine concentration and the combined / total chlorine concentration based on the color reaction of the oxidizing substances present in water with the DPD reagent. When measuring this index, commercially available measuring instruments and DPD reagents can be used.

[0148] When using an index value affected by the measurement conditions as the oxidation power index value, it is preferable to use the value under any one condition, or a value obtained by making an unambiguously corrected value for the influence of the measurement conditions. For example, when using the oxidation-reduction potential (ORP) as the aforementioned index, it is preferable to use the value under any measurement conditions, especially at a certain arbitrary solution temperature and pH. It is preferable to use the value under any one condition where the solution temperature is 20 to 35 °C and the pH is 1 to 8. Hereinafter, when there is no particular description of the oxidation-reduction potential, the value at a solution temperature of 25 °C and a pH of 7 is described.

[0149] As an example of the method for determining the oxidation risk, when evaluating the oxidation potential by the maximum value of the oxidation power index value in the first to third methods, or the maximum value of the moving average value of the oxidation power index value, for example, when using the oxidation-reduction potential as the oxidation power index value, if it is less than 300 mV, it can be judged that the oxidation risk is low (mild), if it is 300 mV or more and less than 600 mV, it can be judged that there is an oxidation risk (moderate), and if it is 600 mV or more, it can be judged that the oxidation risk is high (severe). When using the free residual chlorine concentration or the total chlorine concentration as the oxidation power index value, if it is less than 0.01 mg / L, it can be judged that the oxidation risk is low (mild), if it is 0.01 mg / L or more and less than 0.5 mg / L, it can be judged that there is an oxidation risk (moderate), and if it is 0.5 mg / L or more, it can be judged that the oxidation risk is high (severe).

[0150] In addition, as an example of the oxidation risk determination method, when evaluating the oxidation potential by the rate of change of the oxidation power index value per unit time and the rate of change of the moving average value of the oxidation power index value in the first method, for example, when using the oxidation-reduction potential as the oxidation power index value, if it is less than 50 mV / minute, it can be judged that the oxidation risk is low (mild); if it is 50 mV / minute or more and less than 300 mV / minute, it can be judged that there is an oxidation risk (moderate); if it is 300 mV / minute or more, it can be judged that the oxidation risk is high (severe). When using the free residual chlorine concentration or the total chlorine concentration as the oxidation power index value, if it is 0.1 mg / L / minute, it can be judged that the oxidation risk is low (mild); if it is 0.1 mg / L / minute or more and less than 0.5 mg / L / minute, it can be judged that there is an oxidation risk (moderate); if it is 0.5 mg / L / minute or more, it can be judged that the oxidation risk is high (severe).

[0151] In addition, when judging the oxidation potential by the rate of change of the oxidation power index value with respect to the concentration in the second or third method, for example, when using the oxidation-reduction potential as the oxidation power index value, if it is less than 50 mV / (mg / L), it can be judged that the oxidation risk is low (mild); if it is 50 mV / (mg / L) or more and less than 100 mV / (mg / L), it can be judged that there is an oxidation risk (moderate); if it is 100 mV / (mg / L) or more, it can be judged that the oxidation risk is high (severe). When using the free residual chlorine concentration or the total chlorine concentration as the oxidation power index value, if it is 0.1 mg / L / (mg / L), it can be judged that the oxidation risk is low (mild); if it is 0.1 mg / L / (mg / L) or more and less than 0.5 mg / L / (mg / L), it can be judged that there is an oxidation risk (moderate); if it is 0.5 mg / L / (mg / L) or more, it can be judged that the oxidation risk is high (severe).

[0152] In addition, in the fourth or fifth method, when evaluating the oxidation potential by the concentration of sulfite or bisulfite below the value before contact with the attachment, if it is less than 5 mg / L, it can be judged that the oxidation risk is low (mild); if it is 5 mg / L or more and less than 100 mg / L, it can be judged that there is an oxidation risk (moderate); if it is 100 mg / L or more, it can be judged that the oxidation risk is high (severe). In addition, when evaluating the oxidation potential by the change rate of the oxidation power index value with respect to the concentration of sulfite or bisulfite, for example, in the case of using the oxidation-reduction potential as the oxidation power index value, if it is less than -100 mV / (mg / L), it can be judged that the oxidation risk is low (mild); if it is -100 mV / (mg / L) or more and less than -5 mV / (mg / L), it can be judged that there is an oxidation risk (moderate); if it is -5 mV / (mg / L) or more, it can be judged that the oxidation risk is high (severe). In the case of using the free residual chlorine concentration or the total chlorine concentration as the oxidation power index value, if it is less than -0.01 mg / L / (mg / L), it can be judged that the oxidation risk is low (mild); if it is -0.01 mg / L / (mg / L) or more and less than -5.0×10 -3 mg / L / (mg / L), it can be judged that there is an oxidation risk (moderate); if it is -5.0×10 -3 mg / L / (mg / L) or more, it can be judged that the oxidation risk is high (severe).

[0153] When the attachment is brought into contact with a solution containing sulfite or bisulfite, when the hydrogen ion concentration index (pH) of the contacting solution is 9.0 or more, the generation of oxidizing substances is promoted. Thereby, in order to be able to evaluate the oxidation power potential of the attachment quickly and with high precision, it is preferable to bring the attachment into contact with a solution containing sulfite or bisulfite having a hydrogen ion concentration index (pH) of 9.0 or more.

[0154] As a method for making the hydrogen ion concentration index (pH) of a solution containing sulfite or bisulfite 9.0 or more, a method of adding an alkaline substance to the solution can be cited. There is no particular limitation on the alkaline substance, and examples thereof include sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, etc.

[0155] In addition, the solution containing sulfite or bisulfite in one embodiment of the present invention preferably contains chloride ions and / or bromide ions. If these ions are present, oxidizing substances such as hypochlorite ions and hypobromite ions will be generated, increasing the oxidation risk. Therefore, the oxidation potential in the water treatment equipment can be estimated more accurately. In addition, by making the solution containing sulfite or bisulfite have a composition close to the raw water and supply water used in the actual water treatment equipment, the oxidation risk in the water treatment equipment can be evaluated more accurately.

[0156] As an application example of the present invention, it is possible to cite determining the oxidation risk in a certain water treatment equipment based on the oxidation potential evaluated by any one of the first to fifth methods of the present invention. At this time, the magnitude of the oxidation risk depends on the determination method in the measurement method of the oxidation power index value used. For example, in the ORP and DPD methods, the greater the measured value, the greater the judged oxidation risk. In the Fujiwara test described in Patent Document 1 and Non-Patent Document 1, it is judged that the oxidation risk is high when coloring. Further, as an application example of the present invention, it is possible to cite: comparing the oxidation potentials evaluated by the same method in any one of the first to fifth methods of the present invention using a certain amount of adherends to judge the oxidation risks of different water treatment equipment, piping positions, and different times. For example, when recovering adherends from a water passage member having a semipermeable membrane element or a separation membrane used in different equipment and evaluating the oxidation potentials of each adherend by the same method in any one of the first to fifth methods using the same amount of each adherend, the magnitude of the oxidation risk in each equipment can be compared according to their magnitudes. In addition, for example, by providing a water passage member having a separation membrane in different pipes within the same equipment and evaluating the oxidation potential for the adherends recovered from each separation membrane by the same method in any one of the first to fifth methods using the same amount of each adherend, the magnitude of the oxidation risk in each pipe can be judged. Thereby, for example, when the oxidation risk in the equipment increases, it becomes easy to determine the cause location. In addition, by regularly evaluating the oxidation potential of the adherends in the same equipment by any one of the first to fifth methods of the present invention, the oxidation risk of the equipment can be monitored, and rapid response can also be carried out when the oxidation risk increases. For example, it is possible to detect the excessive addition of a reducing agent in the supply pipeline and the increase in oxidation risk caused by a failure in the previous process. In addition, it is possible to find the presence or absence of an oxidation risk (a failure in which an oxidation reaction-promoting substance mixes into the permeated water) in the permeation pipeline due to deterioration of the semipermeable membrane and component breakage. In this way, the present invention can achieve a simple and rapid oxidation risk determination that is difficult with conventional methods, which is useful for risk avoidance and early resolution of operation failures.

[0157] As another aspect of the present invention, there can be cited an oxidation risk evaluation program, which is an oxidation risk evaluation program for a water treatment plant. In this program, in order to evaluate the oxidation risk, a computer is equipped with a data recording device for recording input data in the computer and a device for evaluating the oxidation potential of the deposit based on the input data. The input data is the conditions and oxidation power index value when the deposit recovered from the separation membrane in use is brought into contact with a solution containing sulfite or bisulfite. This aspect enables a computer having each device to function as an evaluation of the oxidation risk of the separation membrane. This aspect can be recorded in a recording device such as a memory or a hard disk of a computer, and the recording method is not particularly limited. In addition, as another aspect of the present invention, there can be cited a recording medium storing the aforementioned evaluation risk evaluation program.

[0158] The computer has a data recording device that records the conditions and oxidation power index value when the deposit recovered from the separation membrane in use is brought into contact with a solution containing sulfite or bisulfite. Further, using the data recorded in the data recording device, an oxidation risk index value is determined or calculated and output. Alternatively, based on a predetermined determination criterion, the oxidation risk of the separation membrane is evaluated and output.

[0159] For example, there can be cited, as Figure 10 or Figure 14 shown, a program for evaluating the oxidation risk based on the time-dependent data of the oxidation power index value. That is, based on the oxidation power index value of the solution containing sulfite or bisulfite with which the deposit is brought into contact and the elapsed time from when the deposit is brought into contact at the time of measuring the oxidation power index value, any one of the following is determined or calculated, thereby evaluating the oxidation potential and outputting an oxidation risk determination result.

[0160] A: The maximum value of the oxidation power index value

[0161] B: The rate of change of the oxidation power index value per unit time

[0162] C: The maximum value of the moving average of the oxidation power index value

[0163] D: The rate of change of the moving average of the oxidation power index value per unit time.

[0164] At this time, in order to grasp the accurate oxidation risk, the output determination result is preferably, as Figure 10 shown, the oxidation potential evaluation result itself as the oxidation risk index value. On the other hand, for simplicity and easy discrimination, it is preferably, as Figure 14The oxidation risk level is determined based on a pre-determined determination criterion (index value), for example, the result of the degree of oxidation deterioration (mild, moderate, severe). As the index value and determination criterion at this time, as described above, values and determination criteria based on the oxidation potential evaluation method such as oxidation-reduction potential, free residual chlorine concentration, or combined (total) chlorine concentration can be used, for example.

[0165] It should be noted that in the aforementioned oxidation potential evaluation method, when a quick determination is desired, it is preferable to use the change rate (B) of the index value of the oxidation power per unit time. On the other hand, from the perspective of determination accuracy, the maximum value (A) of the oxidation power index value is preferable. In addition, for example, when it is desired to accurately grasp the oxidation risk during a certain period, the moving average is calculated based on the recorded time-series data, and the oxidation potential is evaluated by its maximum value (C) and change rate (D), thereby the oxidation risk can be determined. At this time, when a quick result is desired, it is preferable to use the change rate (D) of the moving average, and when an accurate oxidation risk is to be grasped, it is preferable to use the maximum value (C) of the moving average.

[0166] In addition, for example, as Figure 11 or Figure 15 shown, a procedure for evaluating the oxidation risk based on the relationship between the oxidation power index value and the concentration of sulfite or bisulfite can be cited. That is, based on the oxidation power index value of the solution containing sulfite or bisulfite that the adherend contacts and the concentration of sulfite or bisulfite at the time of measuring the oxidation power index value, any one of the following is determined or calculated, thereby the oxidation potential is evaluated and the oxidation risk determination result is output.

[0167] A: The maximum value of the oxidation power index value

[0168] B: The change rate of the oxidation power index value with respect to the concentration of sulfite or bisulfite.

[0169] At this time, in order to grasp the accurate oxidation risk, the output determination result is preferably, as Figure 11 shown, the value itself of the oxidation potential evaluation result indicating the magnitude of the oxidation risk. On the other hand, for simplicity and easy discrimination, it is preferably the result determined based on a pre-determined determination criterion (index value) as Figure 15 shown.

[0170] As the index value at this time, as described above, values and determination criteria based on the oxidation potential evaluation method can be used.

[0171] In addition, similar to the above, when a quick determination is desired, the change rate (B) of the oxidation power index value with respect to sulfite or bisulfite can be utilized. On the other hand, from the perspective of determination accuracy, the maximum value (A) of the oxidation power index value is preferable.

[0172] As other examples, there can be cited a program for evaluating oxidation risk based on the relationship between the oxidation power index value after reaching the maximum and the concentration of sulfite or bisulfite. That is, for example, as Figure 12 shown in or 16, according to the oxidation power index value of the solution containing sulfite or bisulfite that contacts the adherent, the concentration of sulfite or bisulfite at the time of measuring the oxidation power index value, and the oxidation power index value of the solution containing sulfite or bisulfite before the adherent contacts, a program for determining the oxidation risk by the concentration of sulfite or bisulfite at which the oxidation power index value is below that before the adherent contacts. In addition, as other examples, there can be cited as Figure 13 shown in or 17, according to the oxidation power index value of the solution containing sulfite or bisulfite that contacts the adherent and the concentration of sulfite or bisulfite at the time of measuring the oxidation power index value, based on the relationship between the oxidation power index value after reaching the maximum and the concentration of sulfite or bisulfite, calculate the change rate of the concentration of bisulfite or bisulfite, and thereby evaluate the oxidation potential and determine the oxidation risk.

[0173] At this time, in order to grasp the accurate oxidation risk, the output determination result is preferably, as Figure 12 or Figure 13 shown, the value itself of the oxidation potential evaluation result indicating the magnitude of the oxidation risk. On the other hand, for simplicity and easy discrimination, as Figure 16 or Figure 17 shown, it is preferably the result of determining the magnitude of the oxidation risk based on a predetermined index value as the determination criterion.

[0174] In each of the programs using the first to fifth methods, which program to use can be arbitrarily selected according to the situation and purpose as described above.

[0175] In addition, as another aspect of the present invention, there can be cited an oxidation risk evaluation device, which is an oxidation risk evaluation device for a water treatment plant, and includes: a data input device for causing a computer to input the conditions and oxidation power index value when an adherent recovered from a separation membrane in use is brought into contact with a solution containing sulfite or bisulfite for evaluating the oxidation risk into the computer; a data recording device for recording the aforementioned conditions and oxidation power index value in the computer; and a device for evaluating the oxidation potential using the aforementioned method. The evaluation device includes: a data input device for inputting the conditions and oxidation power index value when an adherent recovered from the separation membrane is brought into contact with a solution containing sulfite or bisulfite into the computer for evaluating the oxidation risk; a data recording device for recording the input data in the computer; a data recording device for recording the input data in the computer; and a method for evaluating the oxidation potential of the adherent based on the input data.

[0176] Examples of the conditions when the attached matter comes into contact include the elapsed time since the start of contact, the concentration of sulfite or bisulfite, and the oxidation power index value before the attached matter comes into contact. As a data input device, there can be mentioned a method of inputting, based on the evaluation result, the conditions and the oxidation power index value when the attached matter recovered from the separation membrane in use is brought into contact with a solution containing sulfite or bisulfite, which are numerically input by hand or automatically input by the evaluation device itself having a method for evaluating and measuring these conditions. As an automatic input method, for example, there can be mentioned a method in which the evaluation device has a method for evaluating and measuring the elapsed time since the start of contact and the concentration of sulfite or bisulfite, and records and inputs the results at any time. As such an evaluation and measurement method, for example, there can be mentioned a colorimetric method using a reagent that colors or changes color upon reaction with sulfite or bisulfite, determining the concentration of sulfite or bisulfite based on the prepared standard curve, and further determining the elapsed time since the start of contact from the time.

[0177] As a method for evaluating the oxidation potential, there can be mentioned the present invention, that is, as described above, Figures 10 to 17 as shown, a method for evaluating based on the time-dependent data of the oxidation power index value and the relationship between the oxidation power index value and the concentration of sulfite or bisulfite, and outputting the determined and calculated oxidation risk index value. Or, based on a predetermined determination criterion, evaluating the oxidation risk of the separation membrane and outputting it.

[0178] Examples

[0179] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited by any of these examples.

[0180] <Example 1>

[0181] In the water treatment equipment set A that had been operating for about 2 months, a tendency for the quality of the produced water to deteriorate was observed. The semipermeable membrane element TM820C-400 (manufactured by Toray Industries, Inc.) used in this equipment set was disassembled, and the separation membrane was collected. The separation membrane was dried at room temperature for 24 hours, the attached matter was recovered using a silicon utensil, and placed in a glass petri dish. It was dried in a dryer set at 120 °C for 2 hours. This was designated as attached matter A-1.

[0182] To prepare 400 mL of an aqueous solution with a sodium bisulfite concentration of 20 mg / L in a 1 L beaker, seawater, sodium bisulfite, and a stir bar were added, and it was stirred with a magnetic stirrer to dissolve. Further, 1 mol / L sodium hydroxide aqueous solution and 1 mol / L sulfuric acid were added to adjust the pH to 7. 10 mg of the above-mentioned attached matter A-1 was put into this solution, and the time-dependent change in the oxidation-reduction potential was measured using an oxidation-reduction potentiometer while stirring. In addition, the pH and the solution temperature were measured using a hydrogen ion concentration (pH) meter and an alcohol thermometer. The results are shown inFigure 18 The maximum value of the redox potential is 459 mV. In addition, the pH at this time is 7, and the solution temperature is 25 °C. Since the redox potential is above 300 mV, it is considered that the oxidation potential of the attachment is high and the oxidation risk in this equipment set is high.

[0183] To investigate the presence or absence of oxidative degradation of the separation membrane, 6 g of pyridine and 2 g of 3 mol / L aqueous sodium hydroxide solution were put into a 20 mL glass bottle and mixed. A 10 cm square piece was cut out from the separation membrane disassembled and collected from the above-mentioned component, washed with pure water, and the substrate was peeled off and removed. It was put into the aforementioned pyridine-sodium hydroxide aqueous solution and left standing at room temperature for 8 hours. As a result, the solution turned red. According to this result, as described in Non-Patent Document 1, it is considered that the separation membrane has undergone oxidative degradation. In addition, the elemental composition of the aforementioned attachment was investigated by high-frequency inductively coupled plasma (ICP) emission analysis, and it was found that it contains copper (1.1 wt%) and manganese (32 wt%).

[0184] <Comparative Example 1>

[0185] At the same time as Example 1, the filter material (sand) of the gravity filter (DMF) used in the water treatment equipment set A was immersed in concentrated nitric acid for 20 hours to obtain a DMF filter material extract. To prepare 400 mL of an aqueous solution with a sodium bisulfite concentration of 20 mg / L in a 1 L beaker, seawater, sodium bisulfite, and a stir bar were added and stirred with a magnetic stirrer to dissolve it. 5 g of the aforementioned DMF filter material extract was put into this solution, and the change in redox potential over time was measured while stirring. The results are shown together in Figure 18 The maximum value of the redox potential is 220 mV.

[0186] Based on the results of Example 1 and Comparative Example 1, it is considered that the separation membrane element used in the water treatment equipment set A has undergone oxidative degradation and the oxidation risk in the water treatment equipment set A is high. As described above, the fact that the oxidation risk in the water treatment equipment set A is high can be quickly judged by evaluating the oxidation potential using the attachment of the separation membrane used. Further, a large amount of copper and manganese were detected in the elemental composition analysis result of the attachment. Therefore, it is speculated that they have caused the high oxidation risk state of the separation membrane as described above. On the other hand, when evaluating using the extract of the filter material of DMF, the oxidation potential is low and the oxidation risk of the water treatment equipment set A cannot be correctly evaluated. However, by using the attachment of the separation membrane, this oxidation risk can be evaluated.

[0187] <Example 2>

[0188] The separation membrane was collected from the same semipermeable membrane element TM820C-400 (manufactured by Toray Industries, Inc.) as in Example 1. The separation membrane was dried at room temperature for 24 hours, the attached substances were recovered using a silicon utensil, and placed in a glass petri dish. It was dried in a dryer set at 120 °C for 2 hours. It was designated as the attached substance A-2.

[0189] To prepare 400 mL of an aqueous solution with a sodium bisulfite concentration of 20 mg / L in a 1 L beaker, seawater, sodium bisulfite, and a stir bar were added, and it was stirred with a magnetic stirrer to dissolve. Further, 1 mol / L sodium hydroxide aqueous solution and 1 mol / L sulfuric acid were added to adjust the pH to 7. 10 mg of the attached substance A-2 was added to this solution and stirred for 15 minutes. The free chlorine concentration of this solution was measured using a residual chlorine meter, and the result was 4.34 mg / L.

[0190] Since the free chlorine concentration was 0.5 mg / L or more, it was determined in the same manner as in Example 1 that the oxidation potential of this attached substance was high and the oxidation risk in this equipment set was high.

[0191] <Example 3-1>

[0192] For the water treatment equipment set B that had been operating for about 0.5 months, in order to confirm the operating condition of the equipment set, the oxidation risk was investigated using an oxidation risk evaluation method based on a catalytic reaction. The semipermeable membrane element TML10D (manufactured by Toray Industries, Inc.) used in this equipment set was disassembled, and the separation membrane was collected. The attached substances were recovered from this separation membrane using a silicon utensil and placed in a glass petri dish. It was dried in a dryer set at 120 °C for 2 hours. It was designated as the attached substance B.

[0193] 20 mL of 1 mol / L nitric acid aqueous solution was added to a sealable glass bottle, and further 1.0 g of the attached substance B was added, sealed, and allowed to stand at room temperature. After one night, the supernatant was collected into another glass bottle using a dropper. It was designated as the attached substance extract B.

[0194] To prepare 500 mL of a sodium chloride aqueous solution with a sodium bisulfite concentration of 10 mg / L and a sodium chloride concentration of 32000 mg / L, sodium chloride, sodium bisulfite, pure water, and a stir bar were added to a 1 L beaker and stirred with a magnetic stirrer to dissolve. While stirring the solution, 5 mL of the attached substance extract was added, and the time-dependent change in the oxidation-reduction potential was measured for 8 minutes using an oxidation-reduction potentiometer. At this time, the pH and temperature of the solution were measured using a hydrogen ion concentration (pH) meter and an alcohol thermometer. The maximum value of the oxidation-reduction potential for 8 minutes was 436 mV.

[0195] On the other hand, 5 mL of 1 mol / L nitric acid was added to an aqueous sodium chloride solution with a sodium bisulfite concentration of 10 mg / L and a sodium chloride concentration of 32000 mg / L, and the redox potential, pH, and temperature were measured. As a result, it was 338 mV at pH 2 and 26 °C.

[0196] The above results are shown in Figure 19 . It should be noted that in any case, the hydrogen ion concentration (pH) of the aqueous sodium bisulfite solution during the measurement of the change over time was 2, and the solution temperature was 26 °C.

[0197] Based on these results, the oxidation potential of the adherent extract B was 98 mV higher than that when 1 mol / L nitric acid was added only to the aqueous sodium bisulfite solution without using the adherent. Therefore, it was determined that the oxidation potential of the adherent B was high and there was an oxidation risk.

[0198] <Example 3-2>

[0199] In the aqueous sodium bisulfite solution containing the adherent extract of Example 3-1, sodium bisulfite was further added to make the sodium bisulfite concentration 50 mg / L, and the measurement was carried out for 8 minutes in the same manner as in Example 3-1. In addition, sodium bisulfite was further added to make the sodium bisulfite concentration 100 mg / L and the measurement was carried out in the same manner. As a result, the maximum values of the redox potential at 8 minutes were 344 mV and 329 mV, respectively. In addition, in any case, the hydrogen ion concentration (pH) of the aqueous sodium bisulfite solution during the measurement of the change over time was 2, and the solution temperature was 26 °C.

[0200] The relationship between the concentration of the bisulfite (sodium bisulfite) and the maximum value of the redox potential obtained from the above results is shown in Figure 20 .

[0201] Based on the above results, the maximum values of each bisulfite concentration are as shown in Figure 20As shown, the maximum value is 436 mV when the concentration of bisulfite is 10 mg / L, and this result is set as the oxidation potential of the adherent. It is the same as the oxidation potential obtained in Example 3-1. It is determined that the oxidation potential of adherent B is high and there is an oxidation risk. On the other hand, it is a value lower than 600 mV at which the oxidation risk is judged to be severe at pH 7. Generally, it is considered that the redox potential becomes higher at lower pH. Based on this, the oxidation risk is judged to be moderate. In addition, when considering the pH change before and after the addition of the adherent extract, when only the pH is changed in the case of adding the extract without the adherent, it is considered that the redox potential of the aqueous solution is the same as the value of the redox potential under the condition of 1 mol / L nitric acid in Example 3-1, and this value is 338 mV. When the adherent extract is used, the oxidation potential at a bisulfite concentration of 100 mg / L is the same as this value. Therefore, it is presumed that in order to sufficiently reduce the oxidation risk of adherent B, the bisulfite concentration needs to be 100 mg / L.

[0202] <Example 4>

[0203] For the water treatment equipment set C that has been operating for about 2 months, due to concerns about the increase in the differential pressure of the RO module and the oxidation risk associated with the increase in the adherents on the membrane surface, the oxidation risk assessment method based on the catalytic reaction is used to investigate the oxidation risk. The semi-permeable membrane element SU-720 (manufactured by Toray Industries, Inc.) used in this equipment set is disassembled, and the separation membrane is collected. The adherent is recovered from this separation membrane using a silicon utensil and placed in a glass petri dish. It is dried in a dryer set at 120 °C for 2 hours. It is set as adherent C.

[0204] Add 20 mL of 1 mol / L nitric acid to a sealable glass bottle, and then add 4.0 g of adherent C. Seal it and let it stand at room temperature. After about 70 hours, use a dropper to collect the supernatant into another glass bottle. It is set as adherent extract C.

[0205] To prepare 400 mL of an aqueous solution with a sodium bisulfite concentration of 10 mg / L and a sodium chloride concentration of 32000 mg / L, add sodium chloride, sodium bisulfite, pure water, and a stir bar to a 1 L beaker, and stir with a magnetic stirrer to dissolve. Add 5 mL of the above adherent extract C to this solution, and while stirring, measure the redox potential with a redox potentiometer for 10 minutes, and measure the change over time by measuring every 1 minute. In addition, use a hydrogen ion concentration (pH) meter and an alcohol thermometer to measure the pH and the solution temperature. The results are shown in Figure 21 . The maximum value of the redox potential is 633 mV. In addition, the pH at this time is 2, and the solution temperature is 25 °C.

[0206] Based on the above and the results of Example 3-1, it was determined that the oxidation potential of the adherent C is high and higher than that of the adherent B, and the oxidation risk is severe.

[0207] The above describes various embodiments, but the present invention is of course not limited to these examples. Obviously, those skilled in the art can conceive of various modification examples or correction examples within the scope described in the claims, and it should be understood that they also belong to the technical scope of the present invention. In addition, within the scope not departing from the gist of the invention, the constituent elements in the above embodiments can be arbitrarily combined.

[0208] It should be noted that this application is based on the Japanese patent application (Japanese Patent Application No. 2022-188059) filed on November 25, 2022, the content of which is incorporated herein by reference.

[0209] Industrial Applicability

[0210] According to the present invention, it is possible to evaluate the oxidation risk of a separation membrane that is difficult to determine by conventional evaluation methods. In addition, since the oxidation risk can be grasped simply and quickly, it becomes easier to determine the cause of deterioration and select countermeasures, so an actual improvement in the operating conditions of the water treatment equipment is expected.

[0211] Symbol Explanation

[0212] 1: Raw water storage tank

[0213] 2: Raw water supply pump

[0214] 3: Pretreatment membrane filtration unit

[0215] 4: Pretreatment membrane filtered water storage tank

[0216] 5: Separation membrane filtration unit

[0217] 6: Booster pump

[0218] 7: Step-up pump

[0219] 8: Raw water pipe

[0220] 9: Pretreatment membrane filtered water pipe

[0221] 10: Separation membrane filtration supply water pipe

[0222] 11: Separation membrane filtration permeate water pipe

[0223] 12: Separation membrane filtration concentrated water pipe

[0224] 13: Hose

[0225] 14: Flowmeter

[0226] 15: Quick-connect fitting

[0227] 16: Water-passing container opening / closing part

[0228] 17: Flow rate regulating valve

[0229] 18: Water-passing direction

[0230] 19: Water-passing container

[0231] 19a: Unit water-passing member

[0232] 20: Separation membrane.

Claims

1. A method for evaluating the oxidation risk of a separation membrane, which is a method for evaluating the oxidation risk of a separation membrane in a water treatment plant, wherein deposits on the used separation membrane are recovered, the deposits are brought into contact with a solution containing sulfite or bisulfite, and the oxidation potential of the deposits is evaluated based on the generated oxidizing substances.

2. The method for evaluating the oxidation risk of the separation membrane according to claim 1, wherein The attachment extract is used instead of the attachment.

3. The method for evaluating the oxidation risk of the separation membrane according to claim 1 or 2, characterized in that, The separation membrane is any one of the following, A: The separation membrane collected from the semipermeable membrane element, which separates the feed water into permeate and concentrate in the water treatment plant. B: A separation membrane installed inside a water-passing member installed in a water supply line of a water treatment plant C: A separation membrane provided inside a water-passing member, wherein the water-passing member uses a semipermeable membrane element and is provided in a concentrated water line. The semipermeable membrane element membrane-separates the feed water into permeated water and concentrated water in a water treatment plant.

4. The method for evaluating the oxidation risk of the separation membrane according to any one of claims 1 to 3, characterized in that, The oxidation risk assessment method of the separation membrane is an oxidation risk assessment method based on a catalytic reaction, and the method for evaluating the oxidation potential of the deposit is a method for measuring the change over time in the oxidizing power index value of a solution with which the deposit is brought into contact, and any of the following is evaluated: A: Maximum value of the oxidation index B: Change rate of the oxidation index value per unit time C: Maximum value of the moving average of the oxidation index value D: Change rate of the moving average value of the oxidizing power index value per unit time.

5. The method for evaluating the oxidation risk of the separation membrane according to any one of claims 1 to 4, characterized in that, The method for evaluating the oxidation potential of the deposit is to add sulfite or bisulfite to a solution to be brought into contact with the deposit to change the sulfite or bisulfite concentration of the solution and measure an oxidizing power index value when the deposit is brought into contact.

6. The method for evaluating the oxidation risk of the separation membrane according to any one of claims 1 to 5, characterized in that, The method for evaluating the oxidation potential of the deposit is a method of using two or more solutions having different concentrations of sulfite or bisulfite solutions as a solution for the deposit to contact, and measuring an oxidizing power index value of the deposit in contact.

7. The method for evaluating the oxidation risk of the separation membrane according to claim 5 or 6, characterized in that, The method for evaluating the oxidation potential of deposits according to claim 5 or 6 is to evaluate at least any one of the following: A: Maximum value of the oxidation index B: Change rate of the oxidizing power index value relative to the sulfite or bisulfite concentration.

8. The method for evaluating the oxidation risk of the separation membrane according to any one of claims 5 to 7, characterized in that, This method is a method of further adding sulfite or bisulfite after the above-mentioned oxidizing power index value reaches a maximum, and measuring the oxidizing power index value at this time.

9. The method for evaluating the oxidation risk of the separation membrane according to any one of claims 5 to 7, characterized in that, This method is a method in which, after the aforementioned oxidizing power index value reaches a maximum, a different solution having a higher concentration is used to measure the oxidizing power index value when the deposit is brought into contact with the solution.

10. The method for evaluating the oxidation risk of the separation membrane according to claim 8 or 9, characterized in that, The method for evaluating the oxidation potential of deposits according to claim 8 or 9 is a method for evaluating at least any one of the following: A: The oxidizing index value is the concentration of sulfite or bisulfite before contact with the attached material. B: Change rate of the oxidizing power index value relative to the sulfite or bisulfite concentration.

11. The method for evaluating the oxidation risk of the separation membrane according to any one of claims 1 to 10, characterized in that, The deposit is brought into contact with the solution containing the sulfite or bisulfite having a hydrogen ion concentration index (pH) of 9.0 or more.

12. Oxidation risk assessment procedure, which is an oxidation risk assessment procedure for the separation membrane in the complete water treatment equipment, wherein, The computer functions as a data recording device that records input data in the computer and a device that evaluates the oxidation potential of an adherend based on the recorded data. The input data is the conditions and the oxidation power index value when the adherend recovered from the separation membrane in use is brought into contact with a solution containing sulfite or bisulfite. This oxidation risk evaluation program utilizes the oxidation risk evaluation method described in claim 1.

13. The oxidation risk assessment program according to claim 12, characterized in that, The oxidation risk evaluation method for a water treatment equipment set is an oxidation risk evaluation method based on a catalytic reaction. The device for evaluating the oxidation potential of the adherend is a device that evaluates at least any one of the following based on the time-dependent data of the oxidation power index value. A: The maximum value of the oxidation power index value B: The change rate of the oxidation power index value per unit time C: The maximum value of the moving average of the oxidation power index value D: The change rate of the moving average of the oxidation power index value per unit time.

14. The oxidation risk assessment program according to claim 12, characterized in that, The device for evaluating the oxidation potential of the adherend is a device that evaluates any one of the following based on the relationship between the oxidation power index value and the sulfite or bisulfite concentration. A: The maximum value of the oxidation power index value B: The change rate of the oxidation power index value with respect to the sulfite or bisulfite concentration.

15. The oxidation risk assessment program according to claim 12, characterized in that, The device for evaluating the oxidation potential of the adherend is a device that evaluates any one of the following based on the relationship between the oxidation power index value after reaching the maximum and the sulfite or bisulfite concentration. A: The sulfite or bisulfite concentration at which the oxidation power index value is below that before the adherend contact B: The change rate of the oxidation power index value with respect to the sulfite or bisulfite concentration.

16. A recording medium that stores the oxidation risk evaluation program according to any one of claims 12 to 15.

17. An oxidation risk evaluation device, which is an oxidation risk evaluation device for a separation membrane in a water treatment equipment set, and includes: a data input device that inputs the conditions and the oxidation power index value when the adherend recovered from the separation membrane in use is brought into contact with a solution containing sulfite or bisulfite into a computer; a data recording device that records the above conditions and the oxidation power index value in the computer; and a device that evaluates the oxidation potential using any one of the methods described in claims 1 to 11.

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