Separation membrane module state determination method, state determination program, and method for operating desalination system

Abstract

According to the present invention, in a desalination system in which to-be-treated water is filtered through a separation membrane module to obtain treated water, the resistance (filtration resistance R) when water is passed from a primary side of the separation membrane to a secondary side of the separation membrane is computed, and the degree of resistance increase (filtration resistance increase ΔR) is computed from the change over time in the filtration resistance R with respect to the change over time in the total treated water volume. In a separation membrane module that has been cleaned, the state of a separation membrane surface of the separation membrane module is determined from the relationship between both the ratio (A) of the filtration resistance R immediately after resumption of operation with respect to an initial filtration resistance R0 and the ratio (B) of the filtration resistance increase ΔR from immediately after resumption of operation with respect to an initial filtration resistance increase ΔR0.

Description

Separation membrane module state determination method, state determination program, and water production system operation method

[0001] The present invention relates to a state diagnosis method for a separation membrane module that treats natural water such as river water, lake water, or seawater, as well as sewage water and industrial wastewater, a state determination program, and a method for operating a freshwater production system.

[0002] Separation membranes such as microfiltration membranes, ultrafiltration membranes, and reverse osmosis membranes have advantages such as energy savings, space savings, and improved filtered water quality, and as a result, their use is expanding in a variety of fields, including the treatment and reuse of various types of industrial wastewater and sewage, the desalination of seawater and brine, water purification processes to produce drinking water, industrial pure water, and ultrapure water, and in manufacturing processes in the food industry.

[0003] A major problem in the use of these separation membranes is fouling. Fouling occurs when contaminants accumulate on the membrane surface, in the membrane pores, and within the separation membrane module as the amount of treated water increases during membrane filtration. These contaminants clog the flow path of the treated water, creating resistance to water flow and resulting in a decrease in the amount of treated water or an increase in the treatment driving force (differential pressure). Therefore, in water treatment methods using microfiltration or ultrafiltration membranes, membrane filtration and physical cleaning processes are generally performed alternately. In the membrane filtration process, in which the treated water is filtered through a membrane, the filtration resistance increases due to the accumulation of contaminants. In the subsequent physical cleaning process, the accumulated contaminants are removed, restoring the filtration resistance. Physical cleaning methods in practical use include backpressure cleaning, in which clear water such as treated water is forced under pressure in the opposite direction to filtration to remove dirt components that have accumulated on the membrane surface and in the membrane pores, air cleaning, in which air bubbles are introduced into the treated water side of the membrane (primary side) to shake the membrane and generate shear forces to scrape off adherent materials on the membrane surface, simultaneous air backwashing, in which air cleaning and backpressure cleaning are performed simultaneously, and flushing cleaning, in which water is passed in a direction parallel to the membrane surface to remove dirt components on the membrane surface. However, it is difficult to remove all of the accumulated material in the physical cleaning process, and the filtration resistance due to the remaining components continues to gradually increase as operation continues, eventually leading to chemical cleaning using chemicals or replacement of the membrane module itself.

[0004] In order to suppress such an increase in filtration resistance over a long period of time and to perform stable, long-term continuous operation, Patent Document 1 shows that it is effective to use a separation membrane that has the properties of a large increase in filtration resistance in a single filtration step, high physical cleaning recovery, and not too high initial filtration resistance, and proposes a separation membrane that has these properties at an appropriate level.

[0005] Furthermore, in conventional membrane filtration treatment devices, a cleaning method has been adopted in which physical cleaning is uniformly and periodically performed regardless of whether the membrane is only slightly clogged at the beginning of continuous operation or has become clogged over a long period of time since the start of continuous operation.Patent Document 2 proposes a method of changing the frequency of physical cleaning based on the transmembrane pressure and the transmembrane pressure rise rate of a separation membrane module to reduce damage to the membrane caused by cleaning the membrane more than necessary.

[0006] Japanese Patent Publication No. 2008-36574 Japanese Patent No. 3924919

[0007] However, these technologies are based on the premise that the separation membranes in the separation membrane module always exhibit a constant separation function. The accumulation of contaminants impairs the separation function, and operation is continued while physical or chemical cleaning is performed to eliminate the impediment. When the accumulation of contaminants progresses to a level where chemical cleaning is no longer sufficient to restore separation function, the separation membrane module is replaced. However, these technologies do not take into account the fact that the separation function of the separation membrane itself changes over time. In reality, separation membrane modules undergo deterioration over time, such as friction between membranes or damage to the membrane surface by accumulated contaminants, resulting in changes in the size and number of membrane surface pores, resulting in changes in separation function. When pore size or the number of pores decreases, membrane filtration resistance and the degree of increase in filtration resistance increase even with the same water quality, flow rate, and volume of treated water. According to the technology of Patent Document 2, the frequency of physical cleaning increases, accelerating the deterioration of the separation membrane, necessitating the replacement of the separation membrane module and increasing running costs.

[0008] If the surface condition of the separation membrane could be determined, it would be possible to determine when the separation membrane module has reached the end of its replacement life and to set appropriate operating conditions. However, in order to check the membrane surface condition, it is generally necessary to remove the separation membrane module from the membrane treatment device, disassemble the separation membrane module, collect the separation membrane, and observe the separation membrane surface under a magnified field of view using a scanning electron microscope or the like.

[0009] An object of the present invention is to provide a method for determining the state of a separation membrane module, which determines the state of the surface of a separation membrane in a separation membrane module during operation without disassembling the separation membrane module.

[0010] In order to solve the above problems, the present invention has the following features.

[0011] [1] A method for determining the state of a separation membrane module in a freshwater production system in which treated water is filtered using a separation membrane module to obtain treated water, the method comprising: measuring the filtration resistance R0 of the separation membrane module at the beginning of use (hereinafter referred to as initial filtration resistance R0) and the increase in filtration resistance ΔR0 from immediately after the start of operation (hereinafter referred to as initial filtration resistance increase ΔR0); measuring the filtration resistance R immediately after restarting operation and the increase in filtration resistance ΔR from immediately after the restart of operation in the separation membrane module after cleaning; and determining the state of the separation membrane surface of the separation membrane module based on the relationship between the ratio of the filtration resistance R immediately after the restart of operation to the initial filtration resistance R0 (hereinafter referred to as ratio A) and the ratio of the increase in filtration resistance ΔR from immediately after the restart of operation to the initial filtration resistance increase ΔR0 (hereinafter referred to as ratio B).

[0012] [2] The separation membrane module state determination method according to [1], wherein a set value AI, a set value A-II smaller than the set value AI, a set value BI, and a set value B-II smaller than the set value BI are preset as reference values ​​for determining the state of the separation membrane surface, and the separation membrane surface of the separation membrane module after cleaning is determined to be in any of the following states (i) to (vii) based on the ratio A, the ratio B, and the reference values ​​for determining the state of the separation membrane surface. (i) When the ratio A is greater than the set value A-I and the ratio B is greater than the set value B-I, the opening rate of the separation membrane surface is reduced, promoting membrane clogging by the water to be treated in the freshwater production system. (ii) When the ratio A is greater than the set value A-I and the ratio B is smaller than the set value B-II, the opening rate of the separation membrane surface is reduced, suppressing membrane clogging by the water to be treated in the freshwater production system. (iii) When the ratio A is smaller than the set value A-II and the ratio B is greater than the set value B-I, the opening rate of the separation membrane surface is increased, and membrane clogging by the water to be treated in the freshwater production system is progressing, maintaining the separation function of the separation membrane module for the water to be treated in the freshwater production system. (iv) When the ratio A is smaller than the set value A-II and the ratio B is smaller than the set value B-II, the opening rate of the separation membrane surface is increased, and the separation function of the separation membrane module for the water to be treated in the freshwater production system is reduced. (v) When the ratio A is equal to or greater than the set value A-II and equal to or less than the set value A-I, and the ratio B is greater than the set value B-I, the separation function of the separation membrane module for the water to be treated in the freshwater production system is normal, and membrane clogging by the water to be treated in the freshwater production system is progressing. (vi) When the ratio A is equal to or greater than the set value A-II and equal to or less than the set value A-I, and the ratio B is smaller than the set value B-II, the separation function of the separation membrane module for the water to be treated in the freshwater production system is normal, and membrane clogging by the water to be treated in the freshwater production system is suppressed. (vii) When the ratio B is equal to or greater than the set value B-II and equal to or less than the set value B-I, the membrane clogging by the water to be treated in the freshwater production system has not changed significantly.

[0013] [3] In the separation membrane module after the cleaning, the set value AI is 1.25 or more and 3.5 or less, the set value A-II is 0.5 or more and 0.85 or less, the set value BI is 1.5 or more and 5 or less, and the set value B-II is 0.2 or more and 0.7 or less. [2] The method for determining the state of a separation membrane module.

[0014] [4] The method for determining the state of a separation membrane module according to any one of [1] to [3], wherein the filtration resistance R of the separation membrane module after cleaning is measured immediately after the restart of operation, and then cleaning is performed again. The cleaning is repeated until the rate of change V from the filtration resistance R measured after the previous cleaning is less than 5%, and then the filtration resistance increase rate ΔR is measured using water to be treated from the freshwater production system, and the ratio B of the filtration resistance increase rate ΔR to the initial filtration resistance increase rate ΔR0 is calculated.

[0015] [5] The method for determining the state of a separation membrane module according to any one of [1] to [4], wherein, in the separation membrane module after the cleaning, clear water is used to measure the filtration resistance R immediately after the restart of operation, and the water to be treated in the freshwater production system is used to measure the filtration resistance increase rate ΔR immediately after the restart of operation.

[0016] [6] The method for determining the state of a separation membrane module according to any one of [1] to [5], wherein the separation membrane module is a separation membrane module having a separation membrane with an asymmetric structure.

[0017] [7] A method for operating a freshwater production system in which treated water is obtained by filtering water to be treated using a separation membrane module, the method comprising: determining a state of a separation membrane surface of the separation membrane module using the method for determining the state of a separation membrane module according to any one of [1] to [6]; and performing any one of the following operational controls (1) to (6). (1) Operational control for determining that the separation membrane module has reached the end of its replacement life and replacing the separation membrane module when it is determined that the aperture ratio of the separation membrane surface has decreased and that this is promoting membrane clogging due to the water to be treated in the freshwater production system, or when it is determined that the aperture ratio of the separation membrane surface has increased and that the separation function of the separation membrane module for the water to be treated in the freshwater production system has deteriorated. (2) Operational control for performing at least one of the following controls (a) to (d) when it is determined that the surface aperture ratio of the separation membrane has decreased and that membrane clogging due to the water to be treated in the freshwater production system is being suppressed. (3) Operational control for performing at least one of the following controls (e) to (g) when it is determined that the aperture ratio of the separation membrane surface has increased and that membrane clogging due to the water to be treated is progressing, thereby maintaining the separation function of the separation membrane module. (4) Operational control for performing at least one of the following controls (e) to (k) when it is determined that the separation function of the separation membrane module for the water to be treated in the freshwater production system is normal and that membrane clogging due to the water to be treated in the freshwater production system is progressing. (5) Operational control that performs at least one of the following (a) to (d), (l), and (m) when it is determined that the separation function of the separation membrane module for the water to be treated in the freshwater production system is normal and that membrane blockage due to the water to be treated in the freshwater production system is suppressed. (6) Operational control that continues the current control when it is determined that membrane blockage due to the water to be treated in the freshwater production system has not changed significantly. Here, (a) to (m) are as follows.(a) Control to shorten at least one of the back pressure cleaning time and the air washing time. (b) Control to reduce at least one of the water supply flow rate during the water supply process, the back pressure cleaning flow rate during the back pressure cleaning process, and the air supply flow rate during the air washing process. (c) Control to extend the filtration time of the filtration process in one cycle to reduce the frequency of the back pressure cleaning process and the air washing process per unit treated water amount. (d) Control to omit at least one of the back pressure cleaning process and the air washing process. (e) Control to supply a chemical solution to the separation membrane module to perform enhanced chemical cleaning of the separation membrane module. (f) Control to reduce the treated water flow rate in one cycle of the filtration process. (g) Control to increase at least one of the chemical solution supply flow rate, chemical solution concentration, and contact time between the chemical solution and the separation membrane in the enhanced chemical cleaning. (h) Control to extend at least one of the water supply time, back pressure cleaning time, and air washing time. (i) Control to increase at least one of the water supply flow rate during the water supply process, the back washing flow rate during the back pressure cleaning process, and the air supply flow rate during the air washing process. (j) Control to shorten the filtration time of the filtration process in one cycle and increase the frequency of the back pressure cleaning process and the air washing process per day. (k) Control to perform at least one of the back pressure cleaning process and the air washing process two or more times in one cycle. (l) Control to increase the flow rate of treated water in one cycle of the filtration process. (m) Control to reduce at least one of the flow rate of the chemical solution, the chemical solution concentration, and the contact time between the chemical solution and the separation membrane in an operation to supply a chemical solution to the separation membrane module and clean the separation membrane module.

[0018] [8] A separation membrane module state determination program for a desalination system in which treated water is filtered using a separation membrane module to obtain treated water, the separation membrane module state determination program causing a computer to function as a separation membrane module state determination means that determines the state of the separation membrane surface of the separation membrane module based on the relationship between the filtration resistance R0 at the beginning of use of the separation membrane module (hereinafter referred to as initial filtration resistance R0), the filtration resistance increase ΔR0 from immediately after the start of operation (hereinafter referred to as initial filtration resistance increase ΔR0), the filtration resistance R immediately after restarting operation of the separation membrane module after cleaning, and the filtration resistance increase ΔR immediately after restarting operation of the separation membrane module after cleaning, obtained by the calculation means, to the initial filtration resistance R0 (hereinafter referred to as ratio A), and the ratio of the filtration resistance increase ΔR from immediately after restarting operation obtained by the calculation means to the initial filtration resistance increase ΔR0 (hereinafter referred to as ratio B).

[0019] [9] In the separation membrane module state determination means described in [8], a set value AI, a set value A-II smaller than the set value AI, a set value BI, and a set value B-II smaller than the set value BI are preset as reference values ​​for determining the state of the separation membrane surface, and a separation membrane module state determination program is provided which determines whether the separation membrane surface of the separation membrane module after cleaning is in any of the following states (i) to (vii) based on the ratio A, the ratio B, and the reference values ​​for determining the state of the separation membrane surface: (i) When the ratio A is greater than the set value A-I and the ratio B is greater than the set value B-I, the opening rate of the separation membrane surface is reduced, promoting membrane clogging by the water to be treated in the freshwater production system. (ii) When the ratio A is greater than the set value A-I and the ratio B is smaller than the set value B-II, the opening rate of the separation membrane surface is reduced, suppressing membrane clogging by the water to be treated in the freshwater production system. (iii) When the ratio A is smaller than the set value A-II and the ratio B is greater than the set value B-I, the opening rate of the separation membrane surface is increased, and membrane clogging by the water to be treated in the freshwater production system is progressing, maintaining the separation function of the separation membrane module for the water to be treated in the freshwater production system. (iv) When the ratio A is smaller than the set value A-II and the ratio B is smaller than the set value B-II, the opening rate of the separation membrane surface is increased, and the separation function of the separation membrane module for the water to be treated in the freshwater production system is reduced. (v) When the ratio A is equal to or greater than the set value A-II and equal to or less than the set value A-I, and the ratio B is greater than the set value B-I, the separation function of the separation membrane module for the water to be treated in the freshwater production system is normal, and membrane clogging by the water to be treated in the freshwater production system is progressing. (vi) When the ratio A is equal to or greater than the set value A-II and equal to or less than the set value A-I, and the ratio B is smaller than the set value B-II, the separation function of the separation membrane module for the water to be treated in the freshwater production system is normal, and membrane clogging by the water to be treated in the freshwater production system is suppressed. (vii) When the ratio B is equal to or greater than the set value B-II and equal to or less than the set value B-I, the membrane clogging by the water to be treated in the freshwater production system has not changed significantly.

[0020]

[10] A computer-readable recording medium having recorded thereon the separation membrane module state determination program according to [8] or [9].

[0021] According to the present invention, the condition of the separation membrane surface can be accurately determined without dismantling the separation membrane module during operation. Furthermore, by controlling the operation of the freshwater production system while accurately determining the lifespan of the separation membrane module, running costs can be reduced.

[0022] 1 is a schematic diagram of an apparatus flow chart showing an example of a fresh water production system to which the present invention is applied. 2 is a schematic diagram showing an example of a separation membrane module to which the present invention is applied. 3 is a schematic diagram showing one embodiment of the present invention. 4 is a schematic diagram showing one embodiment of the present invention.

[0023] The present invention will be described in more detail below based on the embodiments shown in the drawings, but the present invention is not limited to the following embodiments.

[0024] The present invention relates to a method for operating a separation membrane module, an operating device, a management program, and a freshwater production system for reducing running costs, and includes a method for determining the condition of the separation membrane surface of a separation membrane module. A freshwater production system 100 to which the present invention is applied includes, for example, as shown in Figure 1, a treated water supply pump 1 for supplying treated water, a treated water supply valve 2 that opens when the treated water is supplied, a separation membrane module 3 that filters the treated water, a backwash drain valve 4 that opens when backwashing or air washing is performed, a treated water discharge valve 5 that opens during membrane filtration, a treated water storage tank 6 for storing treated water, a backwash pump 7 that supplies treated water to the separation membrane module 3 for backwashing, a backwash valve 8 that opens during backwashing, a chemical solution supply pump 9 for supplying a chemical solution to the treated water or the separation membrane module, a chemical solution storage tank 10 for storing the chemical solution, and an air supply source for air washing of the separation membrane module 3. The system includes a blower 11, an air cleaning valve 12 that opens when air is supplied to the bottom of the separation membrane module 3 to clean the air, a drain valve 13 that opens when the treated water or cleaning wastewater is discharged from the primary side of the separation membrane module 3, a treated water supply valve 14 to the primary side, a treated water bypass valve 15, a primary side supply pressure sensor 16 that measures the pressure (P1) of the treated water supply section, a primary side outlet pressure sensor 17 that measures the pressure (P3) of the backwash wastewater discharge section, a secondary side pressure sensor 18 that measures the pressure (P2) of the treated water discharge section, a discharge treated water flow rate sensor 19 that measures the treated water flow rate F1 discharged to the secondary side, and a treated water temperature sensor 20 that measures the treated water temperature (T1). The treated water is a solution or suspension to be treated using a separation membrane module, and examples include river water, groundwater, seawater, sewage treatment water, industrial wastewater, and culture solution. The "primary side" refers to the side of the space separated by the separation membrane to which the treated water is supplied, and the "secondary side" refers to the opposite side of the separation membrane, the side containing the treated water after filtering the treated water through the separation membrane.

[0025] The pore size of the separation membrane used in the separation membrane module 3 is not particularly limited as long as it is porous. However, depending on the properties and amount of the desired water to be treated, an MF membrane (microfiltration membrane), a UF membrane (ultrafiltration membrane), or a combination of both may be used. For example, if it is desired to remove turbid components, E. coli, yeast, Cryptosporidium, etc., either an MF membrane or a UF membrane may be used. On the other hand, if it is desired to also remove viruses, high molecular weight organic matter, etc., a UF membrane is preferred. Separation membrane structures include symmetrical separation membranes in which the pore size is uniform from the inner surface to the outer surface of the membrane, and asymmetrical separation membranes in which the pore size varies in the membrane thickness direction from the inner surface to the outer surface of the membrane. In embodiments of the present invention, either symmetrical or asymmetrical separation membranes may be used, but asymmetrical structures generally have superior performance to symmetrical separation membranes. For example, in an asymmetric membrane having a dense layer with small pores on the outer surface side of the separation membrane and a support layer with large pores on the inner surface side of the membrane, the dense layer performs the separation function, and the support layer can maintain low water resistance while maintaining the strength of the separation membrane, thereby achieving both high separation function and low water resistance. The shape of the separation membrane may be any commonly used shape, such as a hollow fiber membrane, a flat membrane, a tubular membrane, or a monolithic membrane.

[0026] The material of the separation membrane preferably contains at least one selected from the group consisting of polyethylene, polypropylene, polyacrylonitrile, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, polytetrafluoroethylene, polyvinyl fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride, polysulfone, cellulose acetate, polyvinyl alcohol, and inorganic materials such as polyethersulfone and ceramics. Furthermore, polyvinylidene fluoride (PVDF) is more preferable from the viewpoints of membrane strength and chemical resistance, and polyacrylonitrile is more preferable from the viewpoints of high hydrophilicity and strong stain resistance.

[0027] The separation membrane module 3 has a case in which a separation membrane is inserted, and has at least a water supply section to be treated, a backwash wastewater discharge section, and a treated water discharge section. The case may have any shape, such as a cylindrical shape or a polygonal shape. The separation membrane module 3 may either be completely covered by the case around the separation membrane, or the separation membrane may be exposed from the case. However, if the separation membrane is exposed from the case, an immersion tank is required to immerse the separation membrane module in the water to be treated.

[0028] FIG. 2 shows an example of a separation membrane module to which the present invention is applicable. Multiple hollow fiber membranes are inserted into a cylindrical case 30 as separation membranes 31, and the hollow fiber membranes are adhesively fixed at both ends of the cylindrical case 30 with potting material 32. At the upper adhesive fixing portion of the membrane module, the hollow portions of the hollow fiber membranes are open, and removable caps 33 are attached. Meanwhile, at the lower adhesive fixing portion of the membrane module, the ends of the hollow fiber membranes are closed with potting material 32. A lower side nozzle 34 and an upper side nozzle 35 are provided on the side of the cylindrical case 30, inside the adhesive fixing portions at both ends of the cylindrical case 30, and communicate with the outside of the hollow fiber membranes. The lower side nozzle 34 serves as a water supply port, and the upper side nozzle 35 serves as an air vent, water discharge port, and backwash wastewater discharge port during backpressure cleaning. The lower nozzle 37 serves as an air supply port for air cleaning and a backwash wastewater discharge port, and thus has a through-hole 38 in the lower adhesive fixing portion of the membrane module. During filtration operation, the supplied untreated water is filtered through the hollow fiber membrane, and treated water can be obtained from the upper nozzle 36 (treated water discharge section). Note that when operating without using the lower side nozzle or in a module configuration without a lower side nozzle, the lower nozzle 37 can be used not only as an air supply section and backwash wastewater discharge section, but also as a untreated water supply section. Figure 1 illustrates a configuration in which the lower nozzle is used as the untreated water supply section.

[0029] The state determination of a separation membrane module in an embodiment of the present invention is characterized by having the following means, as shown in FIG. 3 . First, an operating data recording means 40 and a membrane module state determination program 210 are installed in a computer 200 that acquires operating data from a freshwater production system 100. In the freshwater production system 100 illustrated in FIG. 1 , the water to be treated is supplied to the primary side of a separation membrane module 3 by operating the water to be treated supply pump 1 and opening the water to be treated supply valve 2 and backwash drain valve 4. After the primary side is filled with the water to be treated during this water supply process, the backwash drain valve 4 is closed and the treated water discharge valve 5 is opened, thereby moving on to the filtration process, in which the water is filtered using the separation membranes provided in the separation membrane module 3. Note that the water supply process can be omitted. Although not shown, if an exhaust valve is provided between the backwash drain valve 4 and the upper side nozzle 35 of the separation membrane module, air can be automatically expelled through the exhaust valve even when the filtration process is started by closing the backwash drain valve 4 and opening the treated water discharge valve 5 while air is present on the primary side of the separation membrane module 3. During the filtration process, treated water is transferred from the secondary side of the separation membrane module 3 to the treated water storage tank 6 via the treated water discharge valve 5. Although not shown, as an alternative or additional means to the treated water supply pump 1, a treated water suction pump can be installed in the secondary piping between the secondary pressure sensor 18 and the treated water discharge valve 5 to lower the secondary pressure below the primary pressure, thereby generating a liquid transport driving force and transferring the treated water to the treated water storage tank 6. In the case of dead-end filtration, the backwash drain valve 4, backpressure washing valve 8, air wash valve 12, and drain valve 13 are all closed. The pressures on the primary and secondary sides of the separation membrane module during the filtration process are measured using the primary supply pressure sensor 16, the primary outlet pressure sensor 17, and the secondary pressure sensor 18, respectively, and recorded in the operating data recording means 40. The treated water flow rate F1 is measured using the treated water flow rate sensor 19, and the treated water temperature (T1) is measured using the treated water temperature sensor 20, and recorded in the operating data recording means 40.

[0030] In a freshwater production system without a treated water flow sensor 19, the treated water flow rate (F1) may be calculated by manually measuring the amount of treated water (q1) discharged within a predetermined time (s1) and dividing the measured amount of discharged treated water by the measurement time, or by measuring the time required to discharge a predetermined amount of treated water and dividing the measured amount of discharged treated water by the measurement time. The amount of discharged treated water can be measured by volume or mass. Furthermore, if a treated water temperature sensor 20 is not provided, treated water may be manually sampled and measured with a thermometer. Alternatively, the water temperature in the storage tank 6 or the supply water temperature may be measured and used as the treated water temperature (T1), although this provides less accurate results. The records are periodically recorded over time, and are recorded at least three times during the filtration process: at the start, middle, and end of the filtration process. Although not shown, operational data such as the treated water flow rate and temperature may also be measured and recorded in the operational data recording means 40. Filtration methods include dead-end filtration and cross-flow filtration. In the cross-flow filtration method, the backwash drain valve 4 is not fully closed during the filtration process, but the opening is adjusted to drain a portion of the water to be treated. Either filtration method is acceptable, but the dead-end filtration method is preferred in terms of low energy consumption.

[0031] As the filtration process progresses, membrane clogging progresses, and the filtration resistance of the separation membrane module increases. In other words, in the case of constant flow rate filtration operation, the pressure difference between the primary and secondary sides of the membrane module (generally "P2 - P1") increases. To suppress this increase, physical cleaning is performed periodically, and operation is generally performed while repeating filtration and physical cleaning. It is preferable to set the filtration time appropriately depending on the properties of the water to be treated and the membrane filtration flux. Common methods include periodically performing physical cleaning once every 10 to 120 minutes of filtration time, or continuing the filtration time until a predetermined membrane filtration differential pressure is reached.

[0032] In physical cleaning, filtration is generally suspended and the steps are carried out in the following order: backpressure cleaning, air washing, drainage, and water supply, but it is also possible to carry out the backpressure cleaning and air washing steps simultaneously, to carry out the backpressure cleaning step after the drainage step, or to omit any of the steps or to carry out any of the steps multiple times. Physical cleaning is not particularly limited to the cleaning methods described above, and may be any method that physically cleans the membrane or the inside of the module, such as ultrasonic cleaning, high-pressure water cleaning, pulse cleaning, hot water cleaning, vibration / rotation cleaning, turbulent cleaning, or cleaning with a cleaning member such as a ball.

[0033] After the filtration process is completed, the process moves to the backpressure washing process, in which the treated water supply pump 1 is stopped, the treated water supply valve 2 and the treated water discharge valve 5 are closed, the backpressure washing valve 8 and the backwash drain valve 4 are opened, and the backpressure washing pump 7 is operated to pump the water from the secondary side to the primary side of the separation membrane module. As the backpressure washing water, it is preferable to use treated water obtained by filtering the water to be treated through the separation membrane module as in this embodiment, but this is not particularly limited, and industrial water, purified water, tap water, RO membrane permeate water, pure water, etc. may also be used. The backpressure washing time is not particularly limited, but is preferably within the range of 1 to 120 seconds. By setting the backpressure washing time to 1 second or more, a sufficient cleaning effect can be obtained, and by setting it to 120 seconds or less, the operating rate and water recovery rate of the separation membrane module can be improved.

[0034] After the backpressure washing step is completed, the backpressure washing pump 7 is stopped, the backpressure washing valve 8 is closed, the air washing valve 12 is opened, and the air blower 11 is operated to supply air to the separation membrane module 3 for washing, and the process moves to the air washing step. There are no particular restrictions on the air washing time, but it is preferably within the range of 1 to 120 seconds. By setting the time for one backpressure washing to 1 second or more, a sufficient washing effect can be obtained, and by setting it to 120 seconds or less, the operating availability of the separation membrane module can be improved. Furthermore, during the backpressure washing step, the air washing valve 12 may be opened and the air blower 11 may be operated to perform backpressure washing and air washing simultaneously.

[0035] After the air cleaning process is completed, the air blower 11 is stopped, the air cleaning valve 12 is closed, and the drain valve 13 is opened, and the process moves to the drainage process, in which all of the cleaning wastewater accumulated in the separation membrane module 3 is drained. In the drainage process, the backwash drain valve 4 and the drainage valve 13 are opened, and the water to be treated on the primary side is discharged from the bottom of the separation membrane module. After that, the process returns to the water supply process for the water to be treated, and membrane filtration operation continues. The above-mentioned water to be treated supply process, filtration process, backpressure cleaning process, air cleaning process, and drainage process constitute one filtration cycle, and the filtration cycle is repeated to perform continuous operation.

[0036] The back pressure cleaning process and air cleaning process cannot remove the clogging substances that remain in the membrane, and as a result, the filtration resistance continues to gradually increase as operation continues. Therefore, the separation membrane module 3 is finally cleaned with a chemical solution or thoroughly subjected to the physical cleaning described above to eliminate the accumulation of clogging substances. Then, membrane filtration operation to filter the water to be treated is resumed. If repeated water production and cleaning results in an increase in filtration resistance that cannot be eliminated by cleaning or a significant decrease in separation function, the membrane is deemed to have reached the end of its life, and the separation membrane module 3 is replaced with a new one.

[0037] The chemical used for chemical cleaning can be selected by appropriately setting the concentration, temperature, and contact time to a level that does not deteriorate the membrane. Examples of cleaning chemicals include acids, alkalis, oxidizers, surfactants, and chelating agents. An appropriate chemical must be selected depending on the type of clogging substance. Examples of oxidizers include sodium hypochlorite, chlorine dioxide, hydrogen peroxide, and ozone, which are effective for cleaning organic substances. Examples of acids include hydrochloric acid, sulfuric acid, nitric acid, citric acid, and oxalic acid, which are effective for cleaning inorganic substances such as aluminum, iron, and manganese. The chemical concentration is preferably 5 mg / L to 100 g / L, which is preferably higher than the concentration used in the enhanced chemical cleaning described below. The appropriate chemical concentration varies depending on the type of chemical, the fouling state, and the type of membrane. While not particularly limited, for example, the effective chlorine concentration for sodium hypochlorite is preferably 1,000 mg / L to 10,000 mg / L, and for hydrochloric acid and citric acid, it is preferably 5 g / L to 100 g / L. By setting the temperature in an appropriate range, it is possible to achieve a cleaning effect while keeping chemical costs within an economical range and to prevent deterioration of the separation membrane or separation membrane module components. It is preferable to use two or more chemical solutions in sequence rather than one type; for example, it is more preferable to use acid and sodium hypochlorite alternately. From the viewpoint of chemical reactions, the higher the temperature of the cleaning chemical solution, the greater the cleaning effect, and keeping it below 40°C prevents deterioration of the separation membrane or separation membrane module components from being accelerated.

[0038] In chemical cleaning, a chemical solution is supplied to the separation membrane module at a timing different from the filtration cycle of the freshwater production system (the water supply process, filtration process, backpressure cleaning process, air cleaning process, and drainage process), and the separation membrane is brought into contact with the chemical solution for a predetermined period of time. Here, enhanced chemical cleaning, which will be described later, differs in that a chemical solution is supplied to the separation membrane module during the filtration cycle of the freshwater production system, and the separation membrane is brought into contact with the chemical solution for a predetermined period of time. The contact time between the separation membrane and the chemical solution is preferably set longer than that for enhanced chemical cleaning. Furthermore, the cleaning effect is enhanced by providing a fixed contact time after adding the chemical solution, and 1 to 5 hours is preferable. Furthermore, by setting the contact time between the membrane and the chemical solution within a certain range, the cleaning effect can be obtained while keeping the operating efficiency within an economical range. Chemical cleaning can be performed, for example, by the following method. A chemical solution is supplied from the lower side nozzle 34 and / or the lower nozzle 37 of the separation membrane module 3, discharged from the upper side nozzle 35 of the separation membrane module 3, and again supplied from the lower side nozzle 34 and / or the lower nozzle 37, and circulated for approximately 30 minutes to 3 hours. Thereafter, the chemical solution is supplied from the lower side nozzle 34 and / or the lower nozzle 37 of the separation membrane module 3, discharged from the upper nozzle 36 (treated water discharge section) of the separation membrane module 3, and again supplied from the lower side nozzle 34 and / or the lower nozzle 37, and circulated for approximately 30 minutes to 3 hours. Thereafter, the chemical solution is discharged, and a rinsing operation is performed to wash away any remaining chemical solution in the separation membrane module 3. The rinsing operation is performed in the same manner as the chemical solution washing method described above, except that the chemical solution is replaced with clear water. Treated water obtained by filtering water to be treated through a separation membrane module is preferably used as the clear water, but industrial water, purified water, tap water, RO membrane permeate water, pure water, etc. may also be used. Furthermore, if a continuously operated freshwater production system is configured in such a way that chemical cleaning of the separation membrane module cannot be performed, the separation membrane module can be chemically cleaned by replacing it with another separation membrane module chemical cleaning system once every few weeks to several years. In this case, a system that integrates the above-mentioned chemical cleaning system with a separation membrane module inspection system described below can also be used.

[0039] Although not shown, the operation data recording means 40 is not particularly limited as long as it is data related to operation, and for example, pressure data and flow rate data in the back pressure cleaning process may also be recorded in the operation data recording means 40. However, if the amount of operation data to be recorded becomes enormous, the load on recording increases.

[0040] In one embodiment of the present invention, as illustrated in FIG. 3, the operating data recorded in the operating data recording means 40 is processed by a calculation means 41 included in a separation membrane module state determination program 210, and the state of the separation function of the membrane surface of the separation membrane module can be identified by a separation membrane module state determination means 42.

[0041] Specific methods included in the calculation means 41 include calculation methods 1 and 2, for example.

[0042] Calculation method 1 obtains the filtration resistance R at the start of the filtration process after cleaning based on the pressure difference across the separation membrane module. The filtration resistance R is calculated from the pressure difference between the primary and secondary sides of the separation membrane module, i.e., the transmembrane pressure (ΔP). The filtration resistance R refers to the resistance when water flows from the primary side to the secondary side. The transmembrane pressure ΔP can be calculated using the values ​​of the pressure (P1) in the treated water supply section, the pressure (P3) in the backwash wastewater discharge section, and the pressure (P2) in the treated water discharge section, as follows: (P1-P2), (P3-P2), or {(P1+P3) / 2-P2}. Note that P3 is preferably a static pressure. Furthermore, if the pressure gauges measuring pressures P1 to P3 are installed at different heights, it is preferable to perform a correction that takes into account the head difference. If only primary pressure data is available, the primary pressure may be used in place of ΔP, although the accuracy of the determination will be reduced. Even in this case, it is more desirable to make corrections that take into account the difference in head between the installation height of the pressure gauge and the treated water discharge outlet of the secondary piping (opening to the treated water storage tank 6), as well as corrections that take into account the piping pressure loss in the secondary piping.

[0043] When the treated water flow rate and water temperature of the freshwater production system are constant, the above-mentioned transmembrane pressure difference ΔP may be used as a simple substitute for the filtration resistance R. More accurately, to enable comparison under the same preconditions even when the measurement conditions (treated water flow rate, water temperature) are different, the filtration resistance R is calculated using the following formula based on the transmembrane pressure difference ΔP, treated water flow rate F1, and treated water temperature (T1).

[0044] Filtration resistance R (1 / m) = transmembrane pressure difference ΔP (Pa) × membrane area of ​​separation membrane module (m ２ ) / Treated water flow rate F1 (m ３ / s) / treated water viscosity (Pa s) × temperature correction coefficient (-) The "membrane area" here refers to the surface area of ​​the membrane at the location used for separation, that is, the surface area of ​​the membrane on the primary side of the exposed portion that is not covered on the outer periphery with potting material. The membrane area of ​​a separation membrane module may be measured, or a nominal value may be set. Generally, it is difficult to measure the membrane area of ​​each individual module, so a nominal value is used. In addition, the "temperature correction coefficient" is used to correct viscosity between different water temperatures, and is calculated from the ratio of the viscosity of water at a reference water temperature to the viscosity of the treated water temperature (T1). The reference water temperature may be determined appropriately depending on the initial value data and the water temperature of the freshwater production system, but a temperature between 20°C and 25°C is generally used.

[0045] In calculation method 2, the filtration resistance increase rate ΔR is obtained based on the amount of change in the filtration resistance R over time that increases in one filtration process cycle and the integrated value of the treated water flow rate F1 (total treated water volume) in one filtration process cycle, and the filtration resistance increase rate ΔR is calculated using the following formula: ２ ) = Change in filtration resistance R over time in one filtration cycle (1 / m) / (total amount of treated water in one filtration cycle (m ３ ) / membrane area of ​​separation membrane module (m ２ ))

[0046] In order to obtain the degree of increase in filtration resistance ΔR more accurately, it is calculated from a linear approximation using the least squares method as follows.

[0047] First, the filtration resistance R is calculated using calculation method 1 for all data in one cycle of the filtration process recorded in the operation data recording means 40. Next, the total treated water volume (m ３ / m ２ ) is defined as x, and the estimated filtration resistance R' (1 / m) obtained from the linear equation y = ax + b is defined as y. Then, a is calculated by the least squares method so that the sum of all errors between R and R' is minimized. The calculated linear coefficient a is then used as the filtration resistance increase rate ΔR.

[0048] The inventors have discovered that the state of a separation membrane module, such as separation function, membrane clogging, and surface open area ratio, can be determined from changes in the filtration resistance R and the filtration resistance increase rate ΔR obtained by the above-mentioned calculation process. Here, "separation function" refers to the function of removing substances from the water being treated and clarifying it, and "membrane clogging" refers to a state in which substances in the water being treated accumulate on the surface or inside the separation membrane, causing clogging. As separation membranes operate, they may rub against each other or substances in the water being treated may collide or rub against the membrane surface, resulting in the collapse of the separation membrane openings, reducing the membrane surface pore size and the number of surface pores, resulting in a decrease in the surface open area ratio, or the surface pore size may become coarser, resulting in an increase in the surface open area ratio. Here, the surface open area ratio is calculated by taking an electron microscope photograph of the membrane surface to determine the area S of the pores, dividing it by the area S of the entire photographed image, and multiplying the result by 100.

[0049] A decrease in the surface porosity increases filtration resistance, but because filtration resistance also increases due to membrane clogging, it is generally difficult to distinguish between the two phenomena. If a decrease in the surface porosity over time is mistaken for membrane clogging and physical cleaning is intensified to resolve the membrane clogging, there is a risk that this will increase friction between membranes and collisions and friction between substances, shortening the membrane's lifespan. Furthermore, if the water quality of the treated water in a water production system is constant, a decrease in the membrane surface porosity makes it easier for substances in the treated water to be captured by the separation membrane, synergistically promoting membrane pore clogging, ultimately reaching the end of the separation membrane module's lifespan and forcing replacement with a new separation membrane module.

[0050] As the surface pores become coarser, the minimum size of substances that can be captured by the separation membrane surface generally increases, resulting in a decrease in separation function. Substances not captured by the membrane permeate to the secondary side, deteriorating the quality of the treated water, necessitating replacement of the separation membrane module. However, depending on the quality of the water being treated in the freshwater production system, substances may penetrate into the membrane, or a collection of substances previously captured and deposited on the membrane surface (called a "cake") may capture other substances, thereby maintaining the separation function. Therefore, an increase in the surface porosity alone cannot be used to determine the deterioration of the separation function of the separation membrane module, or the replacement life of the separation membrane module in the freshwater production system. When assessing the separation function of a separation membrane module, the quality of the water being treated in the freshwater production system should also be taken into account. Typically, to check the quality of the water being treated, one must go to the site and either collect and analyze the water or install a measuring sensor to measure the values ​​of specific water quality items. However, this requires labor and equipment costs, and various substances in the water being treated interact with the separation function of the separation membrane module, making it difficult to use this method as a means of making a comprehensive judgment about the separation membrane.

[0051] According to the present invention, in a separation membrane module after cleaning, the state of the separation membrane module is determined from the relationship between the rate of change of the filtration resistance R from its initial value immediately after restarting operation after cleaning and the rate of change of the filtration resistance increase ΔR from its initial value immediately after restarting operation after chemical cleaning, and by determining the replacement life of the separation membrane module and performing module replacement at an appropriate time, running costs can be reduced and appropriate operation control of the separation membrane module can be performed while maintaining the life of the separation membrane module. Furthermore, if the operating records can be obtained via the Internet, it can be determined even from a remote location whether the separation membrane module has a separation function appropriate for the water quality being treated.

[0052] The state of the separation membrane module is determined by recording the rates of change (ratios) from the initial values ​​of the two indicators (filtration resistance R and filtration resistance increase rate ΔR) obtained by calculation methods 1 and 2 in a rate of change recording means 43-a and comparing the rates of change using a rate of change comparison means 44-a. Here, the initial values ​​refer to measurement data obtained when the separation membrane module is manufactured or measurement data obtained when an unused separation membrane module is installed in a freshwater production system and operation is started.

[0053] For example, in the case of filtration resistance R, the initial value refers to the filtration resistance R0 (hereinafter referred to as the initial filtration resistance R0) at the beginning of use of the separation membrane module, which is obtained by measuring data measured during module manufacture or by loading an unused separation membrane module into a freshwater production system and starting operation. In the case of filtration resistance increase ΔR, the initial value refers to the filtration resistance increase ΔR0 (hereinafter referred to as the initial filtration resistance increase ΔR0) immediately after the start of operation, which is obtained by loading an unused separation membrane module into a freshwater production system and starting operation. Furthermore, when measuring filtration resistance R0, filtration resistance increase ΔR0, etc., data may be obtained using another separation membrane module having a separation membrane with the same composition as the separation membrane installed in the freshwater production system. The unused separation membrane module is not limited to a separation membrane module unused after manufacture. A separation membrane module equivalent to an unused separation membrane module can also be used, as long as the separation membrane does not deteriorate due to use and the separation membrane performance, such as the treated water volume, water quality, and treatment driving force, does not change. For example, if the initial filtration resistance R0 and the initial filtration resistance ΔR0 are equivalent to those of an unused separation membrane module, it can be said to be an unused separation membrane module. Methods for confirming whether it is in an unused state include checking the usage history, measuring the filtration resistance R etc. and comparing it with the measurement data at the time of manufacture (to within approximately 10%), and confirming that there is no foreign matter such as turbidity in the separation membrane module.

[0054] Note that when setting the initial value, it is necessary to take into consideration the acquisition conditions and calculation conditions of the transmembrane pressure data to be acquired. For example, if the acquisition conditions (flux, water temperature conditions, etc.) of the pressure difference data to be assessed are the same as the initial value, there is no problem in comparing the pressure difference data as is with the initial value as the filtration resistance R. However, if the flux or water temperature is different, it is preferable to set the pressure difference data or resistance value corrected taking these into consideration as the initial value. Furthermore, as shown in Figure 4, the amount of change may be recorded in the amount of change recording means 43-b, and the respective amounts of change may be compared with each other using the amount of change comparison means 44-b.

[0055] As described above, in the present invention, the filtration resistance R immediately after restarting operation and the increase in filtration resistance ΔR from immediately after restarting operation are measured in a separation membrane module after cleaning, and the state of the separation membrane surface of the separation membrane module can be determined based on the relationship between the ratio of the filtration resistance R immediately after restarting operation to the initial filtration resistance R0 (hereinafter referred to as ratio A) and the ratio of the increase in filtration resistance ΔR from immediately after restarting operation after cleaning to the initial filtration resistance increase ΔR0 (hereinafter referred to as ratio B).

[0056] Table 1 shows an outline of a method for determining the state of a separation membrane module in one embodiment of the present invention.

[0057]

[0058] Here, since both the ratio A and the ratio B may increase or decrease depending on the state of the separation membrane surface, it is preferable to previously set a set value AI, a set value A-II smaller than the set value AI, a set value BI, and a set value B-II smaller than the set value BI as reference values ​​for determining the state of the separation membrane surface for the ratio A and the ratio B, and to determine the state of the separation membrane surface of the separation membrane module after the cleaning based on the ratio A, the ratio B, and the reference values ​​for determining the state of the separation membrane surface.

[0059] As a result of extensive research in light of the above-mentioned problems, the present inventors have found a relationship between the set values ​​of ratio A and ratio B and the surface state of the separation membrane by focusing on the relationship between both ratios A and B.

[0060] The set values ​​A-I and A-II can be set based on the relationship between the surface state of the separation membrane and the filtration resistance R. Once the set values ​​A-I and A-II are set, these set values ​​may be used in another freshwater production system equipped with the same type of separation membrane module. When A-I is 1.25, that is, when the filtration resistance R of the separation membrane module increases by 1.25 times or more relative to R0, it can be determined that the aperture ratio of the separation membrane surface has decreased and the water permeability has decreased. On the other hand, when A-II is 0.85, that is, when the filtration resistance R of the separation membrane module is 0.85 times or less relative to R0, it can be determined that the aperture ratio of the separation membrane surface has increased and the water permeability has increased. In other words, it can be determined that the membrane surface state has changed from the initial state.

[0061] The set values ​​B-I and B-II can be set based on the relationship between the surface condition of the separation membrane and the filtration resistance increase ΔR for the water to be treated in the freshwater production system. Once the set values ​​B-I and B-II are set, these set values ​​can be used in another freshwater production system using the same type of separation membrane module for the same type of water to be treated. If B-I is 1.5, that is, if the filtration resistance increase ΔR for the water to be treated in the freshwater production system is 1.5 times or more greater than ΔR0, it can be determined that membrane clogging by the water to be treated is progressing. On the other hand, if B-II is 0.7, that is, if the filtration resistance increase ΔR for the water to be treated in the freshwater production system using the separation membrane module is 0.7 times or less greater than ΔR0, it can be determined that membrane clogging by the water to be treated is suppressed, that is, the membrane surface condition has changed from its initial state.

[0062] Therefore, the values ​​of the set values ​​AI, A-II, B-I, and B-II may be appropriately set according to the characteristics of the separation membrane module used, the target water quality, the target chemical cleaning frequency, etc., but AI is preferably a value of 1.25 or more and 3.5 or less, the set value A-II is a value of 0.5 or more and 0.85 or less, the set value B-I is a value of 1.5 or more and 5 or less, and the set value B-II is a value of 0.2 or more and 0.7 or less. More preferably, the set value AI is a value of 2 or more and 3.5 or less, the set value A-II is a value of 0.65 or more and 0.85 or less, the set value B-I is a value of 1.5 or more and 3.5 or less, and the set value B-II is a value of 0.5 or more and 0.7 or less. By setting each of the above set values ​​A-I, A-II, B-I, and B-II within the respective preferred ranges, they become appropriate reference values ​​for capturing changes in the target water quality, target chemical cleaning frequency, etc., and the state of the separation membrane surface can be appropriately determined. For example, for set value A-I, if the filtration resistance R of the separation membrane module is 3.5 times or less than R0, changes in the aperture ratio of the separation membrane surface can be appropriately determined, and this is suitable for operational control as a standard for the target water quality, target chemical cleaning frequency, etc. In this way, by setting the values ​​within the respective preferred ranges, the state of the separation membrane surface can be appropriately determined with high sensitivity.

[0063] For the filtration resistance R, an index of the separation function and flow resistance of the separation membrane module can be obtained by using data obtained immediately after the start of operation after cleaning, for example, data obtained within 5 minutes after the start of the filtration process in a predetermined filtration cycle within one day after the freshwater production system was restored after chemical cleaning.

[0064] The water to be treated in measuring the filtration resistance R may be water from a freshwater production system, but for more precise measurements, it is preferable to use clear water. The clear water is preferably treated water obtained by filtering the water to be treated through a separation membrane module, but industrial water, purified water, tap water, RO membrane permeate water, pure water, etc. may also be used. In cases where it is not possible to secure a sufficient amount of clear water in the freshwater production system to measure the filtration resistance R, the filtration resistance R may be measured using a separately provided chemical cleaning system. In this case, after chemical cleaning and rinsing operations, clear water is supplied from the primary side as the water to be treated, and measurement is performed in the same manner as in the filtration process. Alternatively, the rinsing operation and measurement of the filtration resistance R may not be performed intermittently, and the filtration resistance R may be measured at the final stage of the rinsing operation.

[0065] Alternatively, after measuring the filtration resistance R, chemical cleaning may be performed again and the filtration resistance R may be measured again. By comparing the filtration resistances R before and after the chemical cleaning, it is possible to determine whether clogging that can be eliminated by chemical cleaning still exists. As a guideline, if the filtration resistance R measured later differs from the filtration resistance R measured earlier by 5% or more, it can be said that the remaining clogging has been eliminated by the chemical cleaning performed again. If clogging remains, it will affect the aperture ratio of the separation membrane surface, making it difficult to properly determine the surface condition of the separation membrane. Therefore, from the perspective of eliminating clogging, it is preferable to perform the cleaning until the rate of change V of the filtration resistance R before and after cleaning is less than 5%.

[0066] Since an increase in chemical cleaning operations will result in a postponement of the restart of the freshwater production system, the number of times chemical cleaning is performed and the number of times filtration resistance R is measured should be determined taking into consideration the time limit until restart. Furthermore, when chemical cleaning and measurement of filtration resistance R are repeated many times in this way, it is preferable to use the value of filtration resistance R measured at the end of the repeated operations to calculate the ratio to the initial value.

[0067] The filtration resistance increase rate ΔR can be used to obtain an index of the separation function of the separation membrane module for the water to be treated by using data from one cycle of the filtration process immediately after the start of operation after cleaning, for example, data from one cycle of the filtration process within one day of the restoration of the freshwater production system after chemical cleaning. By using the water to be treated in the freshwater production system as the water to be treated used to measure the filtration resistance increase rate ΔR, an index of the separation function of the separation membrane module for the water to be treated can be obtained. Therefore, in the separation membrane module after cleaning, it is preferable to measure the filtration resistance R using clear water as described above, and then, when measuring the filtration resistance increase rate ΔR immediately after the resumption of operation, to measure it using the water to be treated from the freshwater production system. As will be described in detail later, when the filtration resistance increase rate ΔR is obtained using a separate inspection system for the separation membrane module, the water to be treated can be sampled from the freshwater production system.

[0068] In a separation membrane module after cleaning, if the ratio A of the filtration resistance R immediately after restarting operation to the initial filtration resistance R0 is greater than a set value A-I, and the ratio B of the filtration resistance increase rate ΔR from immediately after restarting operation to the initial filtration resistance increase rate ΔR0 is greater than a set value B-I, it is determined that the aperture ratio of the separation membrane surface has decreased, promoting membrane clogging by the water to be treated in the freshwater production system. In this state of the separation membrane module, the decrease in the aperture ratio of the separation membrane surface increases the resistance to liquid flow, and substances in the water to be treated are more likely to be captured on the surface or inside of the separation membrane, which synergistically promotes membrane clogging and promotes an increase in filtration resistance. Even if chemical cleaning is performed once, another chemical cleaning will be required soon, increasing running costs. Therefore, the separation membrane module is deemed to have reached the end of its life, and the separation membrane module is replaced with a new one.

[0069] In a separation membrane module after cleaning, if the ratio A of the filtration resistance R immediately after restarting operation to the initial filtration resistance R0 is greater than a set value A-I, and the ratio B of the filtration resistance increase rate ΔR from immediately after restarting operation to the initial filtration resistance increase rate ΔR0 is less than a set value B-II, it is determined that the aperture ratio of the separation membrane surface has decreased and membrane blockage by the water to be treated in the freshwater production system has been suppressed. In this state of the separation membrane module, although the separation membrane has deteriorated, the increase rate of filtration resistance has decreased, so it appears to be operating stably. However, by weakening and optimizing the intensity of the physical cleaning, the replacement life of the separation membrane module can be extended. That is, in order to reduce running costs while maintaining the life of the separation membrane module, it is effective for the control means 45 to implement at least one of the following controls: control a, which shortens at least one of the back pressure cleaning time during the back pressure cleaning process and the air washing time during the air washing process; control b, which reduces at least one of the water supply flow rate during the water supply process, the backwash flow rate during the back pressure cleaning process, and the air supply flow rate during the air washing process; control c, which extends the filtration time of the filtration process in one cycle to reduce the frequency of the back pressure cleaning process and the air washing process per unit treated water amount; and control d, which omits at least one of the back pressure cleaning process and the air washing process.

[0070] In the separation membrane module after cleaning, if the ratio A of the filtration resistance R to the initial filtration resistance R0 immediately after restarting operation is smaller than the set value A-II, and the ratio B of the filtration resistance increase rate ΔR from immediately after restarting operation to the initial filtration resistance increase rate ΔR0 is greater than the set value B-I, it is determined that the aperture ratio of the separation membrane surface has increased, and membrane clogging by the water to be treated in the freshwater production system is progressing, thereby maintaining the separation function of the separation membrane module for the water to be treated in the freshwater production system. In order to suppress membrane clogging while maintaining the life of the separation membrane module, it is effective to perform at least one of the following controls by the control means 45: control e: operating the chemical supply pump 9 during the backpressure cleaning process to supply the chemical solution from the secondary side to the separation membrane module 3; control f: reducing the flow rate of treated water in one cycle of the filtration process; and control g: increasing at least one of the chemical solution supply flow rate, chemical solution concentration, and contact time between the chemical solution and the separation membrane during the chemical solution enhanced cleaning. In this state of the separation membrane module, physical cleaning should be avoided in order to suppress the filtration resistance, as this would accelerate damage to the separation membrane surface.

[0071] In chemical-enhanced cleaning, the contact time between the chemical solution and the separation membrane may be set to enhance the cleaning effect. The contact time is preferably about 10 seconds to 3 hours, but is not particularly limited. For example, if the contact is performed every time backwashing is performed, it may be set to 10 to 60 seconds, and if the contact is performed once a day, it may be set to 10 to 60 minutes. In some cases, chemical-enhanced cleaning may be performed for a time outside the preferred contact time range. The chemical solution used for cleaning can be selected by appropriately setting the concentration and contact time so that the membrane does not deteriorate. It is preferable for the chemical solution to contain at least one of sodium hypochlorite, chlorine dioxide, hydrogen peroxide, ozone, etc., as this enhances the cleaning effect on organic matter. It is also preferable for the chemical solution to contain at least one of hydrochloric acid, sulfuric acid, nitric acid, citric acid, oxalic acid, etc., as this enhances the cleaning effect on aluminum, iron, manganese, etc. The chemical concentration is preferably 5 mg / L to 10,000 mg / L, which is preferably lower than the concentration of the chemical cleaning described above. The appropriate chemical concentration varies depending on the type of chemical, the fouling state, and the type of membrane. While not particularly limited, for example, when chemical cleaning is performed using 3000 mg / L of sodium hypochlorite, the chemical concentration in enhanced chemical cleaning is preferably 10 mg / L to 20 mg / L if performed during each backpressure cleaning, and preferably 300 mg / L to 600 mg / L if performed during backpressure cleaning once a day. In some cases, enhanced chemical cleaning may be performed at a concentration lower than the preferred chemical concentration. It is preferable to use two or more chemicals in sequence rather than one type; for example, it is more preferable to use acid and sodium hypochlorite alternately. While it is preferable to supply the chemical to the separation membrane module 3 from the secondary side as in this embodiment, the chemical may also be supplied to the separation membrane module 3 from the primary side. By performing enhanced chemical cleaning, membrane blockage can be easily and efficiently eliminated, and the number of days until the chemical cleaning is completed can be extended.

[0072] In a separation membrane module after cleaning, if the ratio A of the filtration resistance R immediately after restarting operation to the initial filtration resistance R0 is smaller than the set value A-II, and the ratio B of the filtration resistance increase rate ΔR from immediately after restarting operation to the initial filtration resistance increase rate ΔR0 is smaller than the set value B-II, it is determined that the surface opening rate of the separation membrane has increased and the separation function of the separation membrane module for the water to be treated in the freshwater production system has deteriorated. In this state of the separation membrane module, there is a possibility that substances in the water to be treated are not removed and are permeating into the treated water, so the water quality of the treated water is checked, and if the water quality of the treated water does not meet the target water quality, it is determined that the separation membrane module has reached the end of its life, and the separation membrane module is replaced with a new one.

[0073] In the separation membrane module after cleaning, if the ratio A of the filtration resistance R to the initial filtration resistance R0 immediately after restarting operation is equal to or greater than a set value A-II and equal to or less than a set value AI, and the ratio B of the filtration resistance increase rate ΔR from immediately after restarting operation to the initial filtration resistance increase rate ΔR0 is greater than a set value BI, it is determined that the separation function of the separation membrane module for the water to be treated in the freshwater production system is normal, and that membrane blockage by the water to be treated in the freshwater production system is progressing. In this state of the separation membrane module, in order to suppress the progression of membrane blockage, it is effective to implement at least one of the following controls: control e, in which the control means 45 operates the chemical supply pump 9 during the backpressure cleaning process to supply the chemical from the secondary side to the separation membrane module 3; control f, in which the treated water flow rate in one cycle of the filtration process is reduced; control g, in which, in the enhanced chemical cleaning, the chemical supply flow rate, the chemical concentration, and the contact time between the chemical and the separation membrane are increased; control h, in which the water supply time, the backpressure cleaning time during the backpressure cleaning process, and the air washing time during the air washing process are extended; control i, in which at least one of the water supply flow rate during the water supply process, the backwash flow rate during the backpressure cleaning process, and the air supply flow rate during the air washing process is increased; control j, in which the filtration time of the filtration process in one cycle is shortened to increase the frequency of the backpressure cleaning process and the air washing process per day; and control k, in which at least one of the backpressure cleaning process and the air washing process is performed two or more times within one cycle.

[0074] In the separation membrane module after cleaning, if the ratio A of the filtration resistance R to the initial filtration resistance R0 immediately after restarting operation is equal to or greater than the set value A-II and equal to or less than the set value A-I, and the ratio B of the filtration resistance increase rate ΔR from immediately after restarting operation to the initial filtration resistance increase rate ΔR0 is smaller than the set value B-II, it is determined that the separation function of the separation membrane module for the water to be treated in the freshwater production system is normal and membrane blockage by the water to be treated in the freshwater production system is suppressed. In this state of the separation membrane module, in order to reduce running costs, it is effective to use the control means 45 to implement at least one of the following controls: control a, which shortens at least one of the backwashing time during the backwashing process and the air washing time during the air washing process; control b, which reduces at least one of the backwash flow rate during the backwashing process and the air supply flow rate during the air washing process; control c, which extends the filtration time of the filtration process in one cycle to reduce the frequency of the backwashing process and the air washing process per unit treated water amount; control d, which omits at least one of the backwashing process and the air washing process; control l, which increases the treated water flow rate in one filtration process cycle; and control m, which reduces at least one of the chemical supply flow rate, chemical concentration, and contact time between the chemical and the separation membrane in the enhanced chemical washing.

[0075] In the separation membrane module after cleaning, if the ratio B of the filtration resistance increase rate ΔR immediately after restarting operation to the initial filtration resistance increase rate ΔR0 is equal to or greater than a set value B-II and equal to or less than a set value BI, it is determined that the membrane blockage caused by the water to be treated in the freshwater production system has not changed significantly. In this state of the separation membrane module, it is effective to carry out operational control to continue the current control.

[0076] In determining the state of the above-mentioned separation membrane module, in a separation membrane module having a separation membrane with an asymmetric structure, the surface layer of the separation membrane is scraped, the surface pore size changes significantly, and the ratios A and B change significantly, making it easier to determine the state than a separation membrane with a symmetric structure.

[0077] The frequency of the status assessment and cleaning method assessment in the separation membrane module operation method described above is not particularly limited. However, in the case of a continuously operated freshwater production system, it is preferable to perform the assessment each time cleaning is performed, as this allows for immediate detection of any deterioration in separation function. Furthermore, if a continuously operated freshwater production system is configured in such a way that it is not possible to acquire the operational data necessary to assess the status of the separation membrane module, the degree of deterioration in separation function and the progression of membrane blockage can be assessed by replacing the separation membrane module with a separate separation membrane module inspection system once every few weeks to several years. In other words, the present invention is preferably applied not only to automated freshwater production systems, but also to offline inspection systems operated manually. In this case, it is sufficient to perform the minimum necessary operational steps to assess the status. Then, countermeasures based on the status assessment results are reflected in the freshwater production system. The number of operational steps required to assess the status of the separation membrane module is fewer than in conventional technology, and the calculation of operational data is simplified, thereby reducing the work time of on-site operators and the time required for data calculation.

[0078] The recording period of the recording period setting means may be set arbitrarily in units of several tens of seconds to several hours for the filtration process, but is preferably set to one minute or more to prevent strain on server capacity. By minimizing the amount of operating data acquired, an increase in server capacity can be prevented, and in the case of acquiring operating data via the Internet, communication costs can also be reduced. Furthermore, the operating data used for filtration resistance R is preferably data acquired immediately after the start of the filtration process, for example, operating data acquired within five minutes of the start of the filtration process.

[0079] It should be noted that each of the above-mentioned recording means may not only record the data itself as indicated by the name, but may also record other information that allows the data of the name to be calculated. For example, the "change rate recording means" may not only record the change rate itself, but also record the time measurement interval and the amount of change therebetween, and therefore may be used as the change rate recording means, since the change rate can be calculated from these.

[0080] In one embodiment of the present invention, the separation membrane module state determination method for determining the state of the separation membrane surface of the separation membrane module as described above and functioning as a separation membrane module state determination means may be stored as a computer-readable program on a computer-readable recording medium on which the program is recorded. In this case, the separation membrane module state determination program is stored on a recording medium such as a computer hard disk.

[0081] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0082] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0083] This application is based on a Japanese patent application (Patent Application No. 2023-218932) filed on December 26, 2023, the contents of which are incorporated herein by reference.

[0084] 1: Untreated water supply pump 2: Untreated water supply valve 3: Separation membrane module 4: Backwash drain valve 5: Treated water discharge valve 6: Treated water storage tank 7: Backpressure cleaning pump 8: Backpressure cleaning valve 9: Chemical solution supply pump 10: Chemical solution storage tank 11: Air blower 12: Air cleaning valve 13: Drain valve 14: Treated water supply valve to primary side 15: Untreated water bypass valve 16: Primary side supply pressure sensor 17: Primary side outlet pressure sensor 18: Secondary side pressure sensor 19: Treated water flow rate sensor 20: Treated water temperature sensor 30: Cylindrical case 31: Separation membrane (hollow fiber membrane) 32: Potting material 33: Cap 34: Lower side nozzle 35: Upper side nozzle (backwash wastewater discharge section) 36: Upper nozzle (treated water discharge section) 37: Lower nozzle (untreated water supply section) 38: Through-hole 100: Fresh water production system 200: Computer 210: Separation membrane module state determination program 40: Operation data recording means 41: Calculation means 42: Separation membrane module state determination means 43-a: Change rate recording means 43-b: Change amount recording means 44-a: Change rate comparison means 44-b: Change amount comparison means 45: Control means

Claims

1. A method for determining the state of a separation membrane module in a water production system that filters raw water with the separation membrane module to obtain treated water, the method comprising: measuring an initial filtration resistance R0 (hereinafter referred to as the initial filtration resistance R0) at the initial stage of starting the use of the separation membrane module and a filtration resistance increase rate ΔR0 (hereinafter referred to as the initial filtration resistance increase rate ΔR0) from immediately after the start of operation; measuring a filtration resistance R immediately after restarting operation and a filtration resistance increase rate ΔR from immediately after restarting operation in the separation membrane module after cleaning; and determining the state of the surface of the separation membrane of the separation membrane module based on the relationship between both a ratio of the filtration resistance R immediately after restarting operation to the initial filtration resistance R0 (hereinafter referred to as ratio A) and a ratio of the filtration resistance increase rate ΔR from immediately after restarting operation to the initial filtration resistance increase rate ΔR0 (hereinafter referred to as ratio B).

2. In the method for determining the state of the separation membrane module according to claim 1, as reference values for determining the state of the separation membrane surface, set values A-I, set value A-II smaller than the set value A-I, set value B-I, and set value B-II smaller than the set value B-I are set in advance. Based on the ratio A, the ratio B, and the reference values for determining the state of the separation membrane surface, it is determined whether the separation membrane surface of the separation membrane module after cleaning is in any of the following states (i) to (vii). (i) When the ratio A is greater than the set value A-I and the ratio B is greater than the set value B-I; the aperture ratio of the separation membrane surface decreases, promoting membrane fouling by the water to be treated in the water production system. (ii) When the ratio A is greater than the set value A-I and the ratio B is smaller than the set value B-II; the aperture ratio of the separation membrane surface decreases, and membrane fouling by the water to be treated in the water production system is suppressed. (iii) When the ratio A is smaller than the set value A-II and the ratio B is greater than the set value B-I; the aperture ratio of the separation membrane surface increases, and the separation function of the separation membrane module with respect to the water to be treated in the water production system is maintained due to the progress of membrane fouling by the water to be treated in the water production system. (iv) When the ratio A is smaller than the set value A-II and the ratio B is smaller than the set value B-II; the aperture ratio of the separation membrane surface increases, and the separation function of the separation membrane module with respect to the water to be treated in the water production system decreases. (v) When the ratio A is equal to or greater than the set value A-II and equal to or less than the set value A-I, and the ratio B is greater than the set value B-I; the separation function of the separation membrane module with respect to the water to be treated in the water production system is normal, and membrane fouling by the water to be treated in the water production system is progressing. (vi) When the ratio A is equal to or greater than the set value A-II and equal to or less than the set value A-I, and the ratio B is smaller than the set value B-II; the separation function of the separation membrane module with respect to the water to be treated in the water production system is normal, and membrane fouling by the water to be treated in the water production system is suppressed. (vii) When the ratio B is equal to or greater than the set value B-II and equal to or less than the set value B-I; the change in membrane fouling by the water to be treated in the water production system is not significant 3. In the separated membrane module after the cleaning, the set value A-I is a value of 1.25 or more and 3.5 or less, the set value A-II is a value of 0.5 or more and 0.85 or less, the set value B-I is a value of 1.5 or more and 5 or less, and the set value B-II is a value of 0.2 or more and 0.7 or less. The method for determining the state of the separated membrane module according to claim 2.

4. In the separated membrane module after the cleaning, after measuring the filtration resistance R immediately after restarting the operation, cleaning is performed again, and the cleaning is repeated until the change rate V from the filtration resistance R measured after the previous cleaning becomes less than 5%. Thereafter, the increase rate ΔR of the filtration resistance is measured using the water to be treated of the water production system, and the ratio B of the increase rate ΔR of the filtration resistance to the initial increase rate ΔR0 of the filtration resistance is calculated. The method for determining the state of the separated membrane module according to any one of claims 1 to 3.

5. In the separated membrane module after the cleaning, clarified water is used for measuring the filtration resistance R immediately after restarting the operation, and the water to be treated of the water production system is used for measuring the increase rate ΔR of the filtration resistance immediately after restarting the operation. The method for determining the state of the separated membrane module according to any one of claims 1 to 4.

6. The separated membrane module is a separated membrane module having an asymmetric structure. The method for determining the state of the separated membrane module according to any one of claims 1 to 5.

7. A method for operating a water production system that filters raw water with a separation membrane module to obtain treated water, wherein the state of the separation membrane surface of the separation membrane module is determined using the method for determining the state of the separation membrane module according to any one of claims 1 to 6, and one of the following operations (1) to (6) is performed. (1) When it is determined that the aperture ratio of the separation membrane surface has decreased and the membrane fouling of the raw water in the water production system is being promoted, or when it is determined that the aperture ratio of the separation membrane surface has increased and the separation function of the separation membrane module with respect to the raw water in the water production system has deteriorated, it is determined as the replacement life of the separation membrane module, and the operation control for replacing the separation membrane module. (2) When it is determined that the surface aperture ratio of the separation membrane has decreased and the membrane fouling by the raw water in the water production system is being suppressed, the operation control for performing at least one of the following (a) to (d). (3) When it is determined that the aperture ratio of the separation membrane surface has increased and the separation function of the separation membrane module is maintained due to the progress of membrane fouling by the raw water, the operation control for performing at least one of the following (e) to (g). (4) When it is determined that the separation function of the separation membrane module with respect to the raw water in the water production system is normal and the membrane fouling by the raw water in the water production system is progressing, the operation control for performing at least one of the following (e) to (k). (5) When it is determined that the separation function of the separation membrane module with respect to the raw water in the water production system is normal and the membrane fouling by the raw water in the water production system is being suppressed, the operation control for performing at least one of the following (a) to (d) and (l), (m). (6) When it is determined that the membrane fouling by the raw water in the water production system has not changed significantly, the operation control for continuing the current control. Here, (a) to (m) are as follows.(a) Control to shorten at least one of the backpressure washing time and the air washing time; (b) Control to reduce at least one of the water supply flow rate during the water supply process, the backpressure washing flow rate during the backpressure washing process, and the air supply flow rate during the air washing process; (c) Control to extend the filtration time of the filtration process in one cycle and reduce the frequency of the backpressure washing process and the air washing process per unit treated water volume; (d) Control to omit at least one of the backpressure washing process and the air washing process; (e) Control to supply a chemical solution to the separation membrane module and perform chemical solution enhanced washing of the separation membrane module; (f) Control to reduce the treated water flow rate in the filtration process of one cycle; (g) Control to increase at least one of the supply flow rate of the chemical solution, the chemical solution concentration, and the contact time between the chemical solution and the separation membrane in the chemical solution enhanced washing; (h) Control to extend at least one of the water supply time, the backpressure washing time, and the air washing time; (i) Control to increase at least one of the water supply flow rate during the water supply process, the backwashing flow rate during the backpressure washing process, and the air supply flow rate during the air washing process; (j) Control to shorten the filtration time of the filtration process in one cycle and increase the frequency of the backpressure washing process and the air washing process per day; (k) Control to perform at least one of the backpressure washing process and the air washing process two or more times within one cycle; (l) Control to increase the treated water flow rate in the filtration process of one cycle; (m) Control to reduce at least one of the supply flow rate of the chemical solution, the chemical solution concentration, and the contact time between the chemical solution and the separation membrane in the operation of supplying a chemical solution to the separation membrane module and performing washing of the separation membrane module.

8. A program for determining the state of a separated membrane module in a water production system that filters water to be treated with a separated membrane module to obtain treated water, causing a computer to measure the filtration resistance R0 (hereinafter referred to as the initial filtration resistance R0) at the initial stage of starting the use of the separated membrane module, the increase rate ΔR0 of the filtration resistance from immediately after starting the operation (hereinafter referred to as the initial increase rate ΔR0 of the filtration resistance), the filtration resistance R immediately after restarting the operation in the separated membrane module after cleaning, and the increase rate ΔR of the filtration resistance immediately after restarting the operation in the separated membrane module after cleaning, and based on the relationship between both the ratio (hereinafter referred to as ratio A) of the filtration resistance R immediately after restarting the operation obtained by the calculation means to the initial filtration resistance R0 and the ratio (hereinafter referred to as ratio B) of the increase rate ΔR of the filtration resistance from immediately after restarting the operation obtained by the calculation means to the initial increase rate ΔR0 of the filtration resistance, a program for determining the state of the separated membrane module, which functions as a means for determining the state of the surface of the separated membrane of the separated membrane module.

9. In the state determination means of the separation membrane module according to claim 8, as reference values for determining the state of the separation membrane surface, set values A-I, set value A-II smaller than the set value A-I, set value B-I, and set value B-II smaller than the set value B-I are set in advance. Based on the ratio A, the ratio B, and the reference values for determining the state of the separation membrane surface, determine whether the separation membrane surface of the separation membrane module after cleaning is in any of the following states (i) to (vii). A state determination program for a separation membrane module. (i) When the ratio A is greater than the set value A-I and the ratio B is greater than the set value B-I; the aperture ratio of the separation membrane surface decreases, promoting membrane fouling by the water to be treated in the water production system. (ii) When the ratio A is greater than the set value A-I and the ratio B is smaller than the set value B-II; the aperture ratio of the separation membrane surface decreases, and membrane fouling by the water to be treated in the water production system is suppressed. (iii) When the ratio A is smaller than the set value A-II and the ratio B is greater than the set value B-I; the aperture ratio of the separation membrane surface increases, and the separation function of the separation membrane module with respect to the water to be treated in the water production system is maintained due to the progress of membrane fouling by the water to be treated in the water production system. (iv) When the ratio A is smaller than the set value A-II and the ratio B is smaller than the set value B-II; the aperture ratio of the separation membrane surface increases, and the separation function of the separation membrane module with respect to the water to be treated in the water production system decreases. (v) When the ratio A is equal to or greater than the set value A-II and equal to or less than the set value A-I, and the ratio B is greater than the set value B-I; the separation function of the separation membrane module with respect to the water to be treated in the water production system is normal, and membrane fouling by the water to be treated in the water production system is progressing. (vi) When the ratio A is equal to or greater than the set value A-II and equal to or less than the set value A-I, and the ratio B is smaller than the set value B-II; the separation function of the separation membrane module with respect to the water to be treated in the water production system is normal, and membrane fouling by the water to be treated in the water production system is suppressed. (vii) When the ratio B is equal to or greater than the set value B-II and equal to or less than the set value B-I; the membrane fouling by the water to be treated in the water production system has not changed significantly 10. A computer-readable recording medium recording the state determination program for the separation membrane module according to claim 8 or 9.

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