Operation method for separation membrane

Abstract

Provided are: a specific method for evaluating the operation performance of a separation membrane; and a method for logically determining, on the basis of the evaluation results of the operation performance, an operation method for use after chemical cleaning. In an operation method for a separation membrane that filters to-be-treated water to obtain treated water, flux is changed to a plurality of conditions and a subsequent operation method is determined on the basis of the operation performance evaluation for each flux, and thereby increases in inter-membrane differential pressure after chemical cleaning can be more effectively suppressed.

Description

Separation membrane operation method

[0001] The present invention relates to a method for operating a separation membrane.

[0002] Membrane separation has advantages such as energy savings, space savings, and improved treated water quality, and is therefore being used in a wide range of fields. For example, precision separation membranes and ultra-separation membranes are used in water purification processes to produce industrial water and tap water from river water, groundwater, and treated sewage water, and reverse osmosis membranes are used in seawater desalination.

[0003] In the membrane bioreactor, which is primarily used for sewage treatment, biological treatment is carried out in a biological reactor, and the activated sludge undergoes solid-liquid separation using a separation membrane immersed in the reactor to obtain clear treated water. During this process, solid matter, such as impurities in the activated sludge itself and in the liquid to be filtered that flows into the reactor, adheres to the surface of the separation membrane, causing clogging (fouling) of the membrane and increasing filtration resistance. Therefore, in the membrane bioreactor, air is diffused using an aeration tube installed below the separation membrane to prevent a decrease in filtration efficiency, and the bubbles and upward flow have an effect of vibrating and stirring the separation membrane, peeling off the deposits on the surface of the separation membrane while filtering.

[0004] When the separation membrane is a hollow fiber modular type, physical cleaning is performed using methods such as air washing (air washing), in which air bubbles are introduced into the separation membrane on the side of the water to be filtered, causing the separation membrane to vibrate and touch each other, thereby scraping off contaminants from the surface of the separation membrane, and backpressure washing (backwashing), in which filtered water or clarified water is forced in the opposite direction of the filtration method of the separation membrane, removing contaminants that have adhered to the surface of the separation membrane and within the membrane pores.

[0005] Although filtration is performed while physically cleaning the membrane surface in this way, it is difficult to sufficiently prevent the progression of membrane clogging over a long period of time under continuous operation. Therefore, when the transmembrane pressure (or filtration resistance) increases or after the membrane module has been operated for a certain period of time, the membrane is chemically cleaned with a chemical solution to restore the membrane's water permeability, i.e., chemical cleaning is performed.

[0006] However, if the operational performance of the separation membrane, such as filtration pressure, transmembrane pressure difference, filtration resistance, and membrane permeability, is not sufficiently restored by chemical cleaning, the differential pressure may rise suddenly immediately after filtration operation is resumed.

[0007] Techniques described in Patent Documents 1 and 2 are known as methods for solving the above-mentioned problems. Patent Document 1 describes determining an appropriate cleaning strength for the next chemical cleaning based on the transmembrane pressure difference or filtration resistance value immediately after chemical cleaning of the separation membrane. Patent Document 2 also describes a method in which, rather than immediately returning to normal filtration operation after chemical cleaning, filtration operation is started at a permeation flux set to a value of 40% or less of the target permeation flux, and the permeation flux is increased stepwise or continuously to the target permeation flux within a predetermined time from the start of filtration. Thereafter, filtration is performed while maintaining the target permeation flux until the next cleaning, thereby suppressing an increase in differential pressure immediately after filtration is resumed.

[0008] Japanese Patent Publication No. 2017-18859 Japanese Patent Publication No. 2005-246283

[0009] However, with the technology described in Patent Document 1, if the membrane fouling state during chemical cleaning is always the same, appropriate chemical cleaning conditions can be determined for each chemical cleaning. However, since the membrane fouling state changes from moment to moment depending on the operating conditions and the properties of the liquid to be filtered, it may be impossible to determine appropriate chemical cleaning conditions. Furthermore, if the chemical cleaning strength is insufficient to determine the next chemical cleaning conditions, fouling may remain, resulting in a decrease in operating performance and a sudden increase in differential pressure after chemical cleaning.

[0010] Even when filtration is resumed at a permeation flux set to a value of 40% or less of the target permeation flux described in Patent Document 2, if fouling remains after chemical cleaning, there is a possibility that the operating performance will deteriorate and the differential pressure will increase rapidly when the target permeation flux is restored.

[0011] The present invention aims to provide a specific method for evaluating the operational performance of separation membranes and a technique for rationally determining the operational method after chemical cleaning based on the results of the operational performance evaluation. Furthermore, the present invention aims to more effectively suppress the increase in differential pressure after chemical cleaning compared to conventional techniques.

[0012] In order to achieve the above object, the present invention has the following configuration.

[0013] (1) A method for operating a separation membrane to filter water to be treated and obtain treated water, characterized in that the method involves filtering water while changing the flux under multiple conditions, creating the operating performance at each flux as a function of the flux, and evaluating the operating performance of the separation membrane from the intercept of the function.

[0014] (2) The method for operating a separation membrane according to (1), wherein the evaluation index for the operational performance is at least one of filtration pressure, transmembrane pressure difference, filtration resistance, and membrane permeability.

[0015] (3) The method for operating a separation membrane according to (1) or (2), wherein the evaluation of the operational performance of the separation membrane is carried out after cleaning with a chemical solution.

[0016] (4) The separation membrane operating method according to (3), characterized in that either A10 or A20 below is determined based on the operational performance evaluation of the separation membrane after the chemical washing. A10: Based on the first operational performance standard, a determination is made as to whether to resume filtration after chemical washing or to determine chemical washing conditions and perform chemical washing again. A20: Based on the second operational performance standard, a determination is made as to whether to change the type of chemical and further determine chemical washing conditions and perform chemical washing again.

[0017] (5) The method for operating a separation membrane according to (4), wherein, in the first operating performance standard, if the evaluation index for the operating performance is any one of filtration pressure, transmembrane pressure difference, and filtration resistance, the following A11 is the standard; and if the evaluation index for the operating performance is membrane water permeability, the following A12 is the standard; if the evaluation result after chemical cleaning is within the first operating standard, filtration is resumed; and if it deviates from the first operating standard, chemical cleaning conditions are determined and it is judged that chemical cleaning should be performed again; and, in the second operating performance standard, if the evaluation index for the operating performance is any one of filtration pressure, transmembrane pressure difference, and filtration resistance, the following A21 is the standard; and if it is membrane water permeability, the following A22 is the standard; if the evaluation result after chemical cleaning is within the second operating standard, the type of chemical is changed, and further chemical cleaning conditions are determined and chemical cleaning is performed again. A11: Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) ≦ 1.3 A12: 0.7 ≦ Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) A21: 1.5 < Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) A22: Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) < 0.5

[0018] (6) The method for operating a separation membrane according to (4) or (5), wherein the chemical cleaning conditions are at least one of a chemical concentration, a chemical immersion time, a chemical temperature, a chemical supply amount, and a chemical supply flow rate.

[0019] (7) The method for operating a separation membrane according to (1) or (2), wherein the evaluation of the operational performance of the separation membrane is an evaluation of the initial operational performance immediately after the start of operation.

[0020] (8) The method for operating a separation membrane according to any one of (1) to (7), wherein the separation membrane is a microfiltration membrane or an ultrafiltration membrane.

[0021] (9) A separation membrane operating condition determination program for evaluating the membrane performance of a separation membrane that filters water to be treated to obtain treated water, which causes a computer to function as a filtration flux changing means that filters by changing the flux under multiple conditions, and as an operating performance evaluation means that creates operating performance at each flux as a function of the flux and evaluates the operating performance of the separation membrane using the intercept of the function.

[0022] (10) The program for determining operating conditions for a separation membrane according to (9), wherein the evaluation index of the operational performance evaluation means is at least one of filtration pressure, transmembrane pressure difference, filtration resistance, and membrane permeability.

[0023] (11) The separation membrane operating condition determination program according to (9) or (10), wherein the separation membrane operating performance evaluation means is operated after chemical washing.

[0024] (12) The separation membrane operating condition determination program according to (10), characterized in that it functions as operating condition control means for determining and executing one of the following, based on the means for evaluating the separation membrane operating performance after chemical washing: A10: Based on a first operating performance standard, it determines and executes whether to resume filtration after chemical washing or whether to determine chemical washing conditions and perform chemical washing again; A11: Based on a second operating performance standard, it determines and executes whether to change the type of chemical, determine chemical washing conditions, and perform chemical washing again.

[0025] (13) The separation membrane operating condition determination program according to (4), characterized in that, in the first operating performance standard, if the evaluation index of the operating performance is any one of filtration pressure, transmembrane pressure difference, and filtration resistance, the following A11 is the standard, and if the evaluation index of the operating performance is membrane water permeability, the following A12 is the standard; if the evaluation result after chemical cleaning is within the first operating standard, filtration is resumed; if the evaluation result deviates from the first operating standard, chemical cleaning conditions are determined and a decision is made to perform chemical cleaning again, and the chemical cleaning is carried out; and in the second operating performance standard in the operating condition control means, if the evaluation index of the operating performance is any one of filtration pressure, transmembrane pressure difference, and filtration resistance, the following A21 is the standard; if the evaluation result after chemical cleaning is within the second operating standard, the following A22 is the standard; A11: Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) ≦ 1.3 A12: 0.7 ≦ Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) A21: 1.5 < Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) A22: Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) < 0.5

[0026] (14) The separation membrane operating condition determination program according to (12) or (13), wherein the chemical cleaning conditions in the operating condition control means are at least one of chemical concentration, chemical immersion time, chemical temperature, chemical supply amount, and chemical supply flow rate.

[0027] (15) The separation membrane operating condition determination program according to (9) or (10), wherein the separation membrane operating performance evaluation means functions as an evaluation means for initial operating performance at the start of operation.

[0028] (16) A computer-readable recording medium having recorded thereon the separation membrane operating condition determination program according to any one of (9) to (15).

[0029] According to the present invention, the operating performance of a separation membrane can be evaluated, and particularly after chemical cleaning, stable operation after chemical cleaning can be achieved by determining the subsequent operating method of the separation membrane based on the evaluation results of the operating performance after chemical cleaning.

[0030] Fig. 1 is a schematic device flow diagram showing an example of a membrane separation device to which the present invention is applied. Fig. 2 is a schematic device flow diagram showing another example of a membrane separation device to which the present invention is applied. Fig. 3 is a conceptual diagram of fouling of a separation membrane to which the present invention is applied. Fig. 4 is a graph showing an example of the tendency of transmembrane pressure when the flux is changed under multiple conditions to which the present invention is applied as described in Example 1. Fig. 5 is a graph showing an example of the tendency of transmembrane pressure when the flux is changed under multiple conditions to which the present invention is applied as described in Example 2.

[0031] 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.

[0032] The separation membrane operating method of the present invention relates to a separation membrane operating method in which filtration is performed while changing the flux under multiple conditions, an approximation equation is created that approximates the operating performance at each flux as a function of the flux, and the operating performance of the separation membrane is evaluated from the intercept of the approximation equation.

[0033] A membrane separation apparatus to which the present invention is applied is provided with a submerged membrane separation unit 2, as shown in Fig. 1. In this embodiment, in order to filter the liquid to be filtered in the submerged membrane separation unit 2, a pump or the like may be provided between the submerged membrane separation unit 2 and the filtrate storage tank 5, and since filtration is performed using a head pressure difference as a driving force, the filtrate level in the filtrate storage tank 5 may be set lower than the liquid level in the liquid to be filtrated tank 3. In Fig. 1, filtration is performed by a suction pump 11.

[0034] In another example of a membrane separation apparatus to which the operating method of the membrane separation apparatus of the present invention can be applied, for example, as shown in FIG. 2, a filtrate supply pump 1 that supplies water to be filtered, a separation membrane module 12 that filters the liquid to be filtered, a filtrate storage tank 5 that stores the filtrate, a backwash pump 14 that supplies the filtrate to the separation membrane module 12 for backwashing, a chemical supply pump 13 that supplies a chemical to the water to be filtered or the separation membrane module, a chemical storage tank 6 that stores the chemical, an air blower 7 that is an air supply source for air washing of the separation membrane module 12, a filtrate flow meter 8, a filtrate flow meter 9, and an air flow meter 10 are provided.

[0035] Here, the liquid to be filtered is a liquid containing suspended solids and is subjected to membrane filtration, and is not particularly limited, but may be a liquid containing microorganisms such as a microbial culture solution or activated sludge. The membrane filtration method may be a dead-end filtration method in which membrane filtration is performed while concentrating the liquid to be filtered, or a cross-flow method in which membrane filtration is performed while generating a flow of the liquid to be filtered on the membrane surface.

[0036] Furthermore, a separation membrane has the function of capturing substances with a certain particle size or larger contained in the liquid to be filtered by applying pressure to the liquid to be filtered or by suction from the permeation side. Depending on the captured particle size, there are various names such as dynamic separation membranes, precision separation membranes, and ultraseparation membranes. The separation membranes used in the present disclosure are preferably precision separation membranes and ultraseparation membranes. The shape of the separation membrane may be a hollow fiber membrane, a flat membrane, a tubular membrane, a monolith membrane, or the like, but the shape is not particularly limited. The membrane structure is also not particularly limited, but any porous membrane such as a precision separation membrane or an ultraseparation membrane may be used. The membrane material is also not particularly limited. Specific examples of the membrane include porous membranes such as polyacrylonitrile porous membranes, polyimide porous membranes, polyethersulfone porous membranes, polyphenylene sulfide sulfone porous membranes, polytetrafluoroethylene porous membranes, polyvinylidene fluoride porous membranes, polypropylene porous membranes, and polyethylene porous membranes. However, polyvinylidene fluoride porous membranes and polytetrafluoroethylene porous membranes are particularly preferred due to their high chemical resistance. 1 shows a separation membrane device using flat membranes, and FIG. 2 shows a separation membrane device using hollow fiber membranes.

[0037] Although the method of injecting the chemical solution is not limited in the present disclosure, in a membrane separation apparatus using a submerged membrane separation unit as shown in Figure 1, it is preferable to inject the chemical solution from the permeation side (secondary side) of the separation membrane to the liquid to be filtered (primary side) while the membrane module is immersed in the liquid to be filtered after stopping the filtration operation. Methods of contacting the separation membrane with the chemical solution include removing the entire membrane module from the membrane separation tank and immersing it in a chemical solution washing tank, or emptying the membrane separation tank and then storing the chemical solution in the tank to contact the membrane, but this is because the required auxiliary equipment is large and not economical.

[0038] The chemical solution is stored in a chemical solution tank 6 and is supplied to the permeate side of the membrane module using a head difference or a pump. Alternatively, a chemical solution storage tank may be provided above ground and the chemical solution supplied to the chemical solution tank. The chemical solution used for cleaning may be selected according to the membrane fouling condition. For organic fouling, sodium hypochlorite with an effective chlorine concentration of approximately 500 mg / L to 6000 mg / L is typically used, while for inorganic fouling, organic acids with a chelating effect, such as oxalic acid or citric acid, with a concentration of approximately 1 to 3% by mass, are preferably used, as these are effective in restoring operational performance.

[0039] The timing for chemical cleaning is generally when the transmembrane pressure difference (or filtration resistance) rises to a certain value or above, or after the membrane module has been operated for a certain period of time, but chemical cleaning does not necessarily have to be performed at these times and may be performed at any timing.

[0040] After the injection of the chemical solution into the secondary side of the membrane element is completed, the chemical solution immersion time for removing (cleaning) the contaminants clogging the membrane through chemical reaction by decomposition and dissolution can be set appropriately depending on the degree of membrane clogging (increase in differential pressure) during chemical cleaning and the water temperature, but a suitable chemical solution immersion time is typically in the range of 30 minutes to 4 hours, more preferably 1 to 2 hours. Since the concentration of the injected chemical solution decreases on the membrane surface due to consumption by reaction and diffusion, an excessively long chemical solution immersion time is less effective. On the other hand, if the chemical solution immersion time is too short, it is undesirable because it increases the amount of unreacted and undecomposed foulants remaining on the membrane, so a time of 30 minutes or more is preferable.

[0041] In the present disclosure, filtration is performed while changing the flux under multiple conditions, the operational performance for each flux is calculated as a function of the flux, and the operational performance of the separation membrane is evaluated based on the intercept of the function. Furthermore, the operational performance of the separation membrane may be evaluated at the beginning of operation, such as when the separation membrane module is installed or replaced, or preferably after chemical cleaning. It is also preferable to evaluate the operational performance at the beginning of operation to compare the operational performance after chemical cleaning. Furthermore, the frequency of operational performance evaluation after chemical cleaning is not particularly limited, but because accurately understanding the performance after chemical cleaning has a significant impact on subsequent operational performance (differential pressure increase), it is preferable to evaluate the operational performance after each chemical cleaning.

[0042] Here, the process corresponding to chemical cleaning is defined as the period from the completion of chemical injection into the membrane element to the resumption of normal filtration operation of the membrane module.

[0043] Further, examples of the evaluation of driving performance include (A) filtering the flux under multiple conditions and obtaining a driving performance evaluation index for each flux, (B) creating an approximation formula (described later) based on the driving performance evaluation index obtained from the flux under the multiple conditions, and (C) evaluating driving performance based on the intercept of the approximation line.

[0044] In the present disclosure, the indicator for evaluating operational performance is preferably at least one of filtration pressure, transmembrane pressure difference, filtration resistance, and membrane permeability.

[0045] Here, the transmembrane pressure is the pressure difference between the filtrate side and the permeate side of a separation membrane, and means for generating this pressure include, for example, pressurizing the filtrate side with a pump, suctioning from the permeate side with a pump, and utilizing the hydraulic head difference between the filtrate side and the permeate side. The transmembrane pressure is generally measured as the difference between the pressure measured on the filtrate side of the separation membrane and the pressure measured on the permeate side. In this case, it is preferable to measure or calculate the pressure loss caused by hydraulic flow and subtract the pressure loss from the difference between the pressure measured on the filtrate side of the separation membrane and the pressure measured on the permeate side. In the membrane bioreactor activated sludge process, when suctioning from the permeate side with a pump, the transmembrane pressure is generally measured as the difference between the pressure measured on the permeate side during filtration and the pressure measured when filtration is stopped.

[0046] The filtration resistance is the resistance that occurs when a liquid to be filtered is filtered through a membrane, and is generally defined by equation (1).

[0047]

[0048] Here, ΔP is the transmembrane pressure difference [Pa], μ is the viscosity of the membrane filtrate [Pa·s], R is the filtration resistance [1 / m], and J is the membrane filtration flux [m / s].

[0049] Here, μ may be determined by directly measuring the viscosity of the membrane filtrate, but when the membrane filtrate is water or an aqueous liquid containing a small amount of solute, μ may be calculated from the temperature according to equation (2).

[0050]

[0051] Here, F = 0.01257187, B = -0.005806436, C = 0.001130911, D = -0.000005723952, and T is the absolute temperature [K]. In other words, if the Celsius temperature is σ [°C], then T = σ + 273.15.

[0052] When the flux is changed under a plurality of conditions, it is preferable that the flux contains 40% or less of the set filtration flux.

[0053] Here, the set filtration flux refers to the flux when, for example, no or few membrane modules are stopped for chemical cleaning or maintenance in the entire wastewater treatment plant that treats sewage, industrial wastewater, etc., and all or most of the membrane modules installed in the plant are being used for wastewater treatment and filtering the required amount of water, and is usually equivalent to the average filtration flux before chemical cleaning is performed. When it is necessary to clarify the definition, for convenience, the set filtration flux is defined as the value obtained by dividing the average amount of filtered water (amount of treated water) in the most recent month before chemical cleaning is performed by the total membrane area of ​​the membrane modules used in the plant.

[0054] When the flux is changed under a plurality of conditions, it is preferable to include a flux that is 40% or less of the set filtration flux, because this has the following effect.

[0055] By setting the filtration conditions to 40% or less of the set filtration flux, which reduces the risk of fouling on the separation membrane, it is possible to evaluate the filtration pressure, transmembrane pressure difference, filtration resistance, and membrane permeability resulting from fouling adhering to the surface of the separation membrane.

[0056] Here, fouling of the separation membrane by components of the liquid to be filtered can be divided into pore blockages 16, which are components in the liquid to be filtered that are smaller than the pore diameter and have penetrated into the pores of the membrane, and cake, which is components in the liquid to be filtered that adhere to the surface of the separation membrane, as shown in Figure 3. Furthermore, if the amount of components or filtration resistance of the liquid to be filtered that can be removed with a specified physical washing strength and the amount of components or filtration resistance of the liquid to be filtered that cannot be removed with a specified physical washing strength are further divided, the cake amount and cake resistance can be divided into peelable cake 17 and non-peeled cake 18, and the peelable cake 17 that adheres to the surface of the separation membrane is consolidated by the applied pressure and converted into non-peeled cake 18.

[0057] Although it is possible to evaluate the operational performance at the set filtration flux or at a flux of 40% or more of the set filtration flux, it is more preferable to operate at 40% or less of the set filtration flux from the viewpoint of suppressing adhesion of new peelable cake and obtaining with high accuracy the filtration pressure, transmembrane pressure difference, filtration resistance, and membrane permeability mainly of the non-peeled cake remaining on the surface of the separation membrane.

[0058] Furthermore, as a result of extensive investigation, it was found that the filtration pressure, transmembrane pressure difference, filtration resistance, and membrane permeability of the non-exfoliated cake can be calculated using the evaluation methods described below.

[0059] The aforementioned "specified physical cleaning strength" is not limited, but is preferably the physical cleaning strength when an unpeeled cake is formed, and if the physical cleaning strength fluctuates, it is preferable to use the average value.

[0060] The method for changing the flux is not limited, but in order to obtain the effect of suppressing the risk of fouling, it is preferable to increase the flux stepwise or continuously within a flux range of 100% or less of the set filtration flux, or to operate in a combination of these. More preferably, it is preferable to change the flux within a flux range of 20 to 80% of the set filtration flux. Furthermore, the upper limit of the evaluation time at each flux is preferably about 1 hour.

[0061] In the present disclosure, the evaluation of operational performance is preferably carried out by creating an operational performance evaluation approximation equation that approximates operational performance at each flux as a function of flux, and evaluating the performance based on the intercept of the approximation line. The approximation line may be determined by least squares or multiple regression analysis. The shape of the approximation line is not limited, and may be linear or curved, as in equations (3) and (4). Here, the intercept is defined as the intersection of the operational performance evaluation approximation equation with the vertical axis when the flux ratio relative to the set filtration flux is 0%. For example, in a plane coordinate system in which the flux ratio relative to the set filtration flux is plotted on the horizontal axis, the intersection of the vertical axis and the approximation line when the set filtration flux is 0% is the intercept. It is preferable to set one of filtration pressure, transmembrane pressure difference, filtration resistance, and membrane permeability as a membrane performance evaluation index on the vertical axis.

[0062]

[0063]

[0064] Here, H is the operating performance of the separation membrane at each flux, and may be any of transmembrane pressure difference [kPa], filtration resistance [1 / m], or membrane permeability [m / s / Pa]. L, N, and K are parameters that depend on the operating performance of the separation membrane and the filtration characteristics of the liquid to be filtered, and are calculated by the least squares method or multiple regression analysis each time the operating performance is evaluated.

[0065] The reason for creating the approximation line is that it has the following effects.

[0066] First, the intercept of the approximation equation obtained by calculating the operational performance at each flux as a function of the flux allows the operational performance at a set filtration flux of 0%, i.e., the operational performance resulting from fouling (non-exfoliated cake) adhering to the membrane surface of the separation membrane, to be obtained, and therefore can be calculated as an operational performance evaluation value.

[0067] Secondly, the operational performance evaluation index for each flux changes depending on the filtration characteristics of the liquid to be filtered. Specifically, the slope of the approximation line changes, and the filtration characteristics of the liquid to be filtered can be calculated from the slope.

[0068] The evaluation of the filtration characteristics of the liquid to be filtered is not limited to the above evaluation method. For example, when the liquid to be filtered (activated sludge liquid) in a membrane bioreactor process contains a large number of microorganisms, it is also preferable to evaluate it by the following method.

[0069] Here, examples of the characteristics of activated sludge liquid include the viscosity of activated sludge liquid, the volume of filter paper filtrate, the turbidity of the filter paper filtrate, capillary suction time (CST), microscope image information, oxygen consumption rate, foaming power, filtration resistance, the organic matter concentration in the centrifugal supernatant of activated sludge liquid (methods for measuring organic matter concentration include TOC (Total Organic Carbon) concentration, COD (Chemical Oxygen Demand) concentration, and BOD (Biological Oxygen Demand) concentration), the organic matter concentration in the filter paper filtrate of activated sludge liquid, the organic matter concentration in the membrane filtrate of activated sludge liquid, the sludge volume index (SVI), the SV (activated sludge settling rate) of activated sludge liquid or a diluted solution of the activated sludge liquid or its treated water, and the ATP (Adenosine triphosphate) concentration.

[0070] After careful investigation, it was found that the turbidity of activated sludge liquor filtered through a filter paper, microscope image information, filtration resistance (calculated from the results of membrane filtration tests using membrane pieces), TOC concentration of the filter paper filtrate, and TOC concentration of the membrane filtrate are particularly effective indicators for determining the membrane filtration characteristics of activated sludge liquor from the standpoints of measurement accuracy, measurement time, reliability, and simplicity.

[0071] Here, turbidity indicates the degree of cloudiness of water, and the turbidity equivalent to 1 mg / L of formazin in 1 liter of water is expressed as 1 degree (NTU: Nephelometric Turbidity Unit). The turbidity of a filter paper filtrate of activated sludge liquid refers to the turbidity of the filtrate obtained when a predetermined amount of activated sludge is filtered through filter paper. Although the evaluation method is not particularly limited, a suitable index can be the turbidity of the filtrate obtained when 50 ml of activated sludge liquid is filtered using filter paper equivalent to JIS P 3801 Chemical Analysis Filter Paper Type 5C (particle retention capacity 1 micron).

[0072] When this evaluation method is applied to sludge near the membrane module before chemical cleaning, for example, the turbidity of the filtrate is about 3 NTU. However, after chemical cleaning, sludge-derived components damaged by the chemical solution are released into the activated sludge liquid, causing the turbidity of the filter paper filtrate of the sludge near the membrane module to temporarily increase to, for example, about 15 NTU.

[0073] Here, by using this evaluation method, the behavior of improvement in sludge filtration characteristics due to the dilution effect of turbidity components by mixing activated sludge liquid and the adsorption, decomposition, and coagulation effects of turbidity components by activated sludge can be confirmed from the behavior of reduction in turbidity of the filter paper filtrate during operation after chemical cleaning.

[0074] The turbidity of the filter paper filtrate contains information reflecting the abundance of biopolymers, such as proteins and polysaccharides, that are generated by chemical damage and have a size equal to or smaller than the pore size (1 μm) of the filter paper. These components are substances that easily foul membranes with pore sizes of 0.01 μm or larger and less than 1 μm, which are used in membrane bioreactors. In other words, the turbidity of the sludge filter paper filtrate is easy to measure and can be used as an indicator of the sludge's filtration characteristics with high accuracy and reliability. It is particularly preferable as a characteristic to use when determining the operating method after chemical cleaning.

[0075] The microscope image information refers to information such as the total area of ​​non-water objects, such as activated sludge flocs, disintegrated (micronized) flocs, and suspended particles, that are observed in the field of view when the activated sludge liquid is observed with an optical microscope at 100 to 400 magnifications (when observed through an eyepiece), and the total length of the boundary between the non-water objects and the water. This analytical information correlates with the turbidity and filtration resistance of the activated sludge liquid filtered through a filter paper, and also has the advantage of providing information on the activity of microorganisms, such as microorganisms. Furthermore, by combining a system that automatically supplies sludge to the microscope field of view at a constant frequency with an image analysis system, unmanned and continuous data acquisition can be easily achieved. Therefore, the membrane bioreactor may be equipped with a control system that continuously measures the microscope image information of the activated sludge liquid after chemical cleaning, and automatically returns the membrane bioreactor to a set filtration flux when the measurement results meet a predetermined standard (absolute value or rate of change).

[0076] When obtaining image information of activated sludge, if the concentration is too high, the entire field of view will be dominated by sludge flocs, making it difficult to observe disintegrated (micronized) flocs and particles floating in the water, so the MLSS concentration during observation is preferably 10,000 mg / L or less, and more preferably 8,000 mg / L or less.When diluting sludge, it is best to use filtered water from the membrane module of a membrane bioreactor, as this is substantially free of suspended particles that would affect observation, has the same osmotic pressure as the activated sludge liquid, and prevents microorganisms in the sludge from being shocked and exploding due to changes in osmotic pressure.

[0077] The filtration resistance of activated sludge liquid is the filtration resistance calculated from data obtained when the activated sludge liquid is filtered using a microfiltration membrane or an ultrafiltration membrane under specified conditions. The evaluation method is not particularly limited, but it can be calculated from data obtained by loading a membrane piece into a small cell filtration test device, pouring an activated sludge sample into it, and measuring the amount of filtrate over time when the filtrate is filtered under constant pressure or constant flow rate conditions. Here, it is preferable to use a membrane with a pore size of 0.01 μm or more and less than 1 μm, and it is particularly preferable to use a membrane with the same specifications as that used in the membrane separation module, as this increases the reliability of monitoring.

[0078] The TOC concentrations of paper filter filtrate and membrane filtrate from activated sludge can be measured by injecting the filtrate obtained by filtering activated sludge using the paper filtration or membrane filtration methods described above into a TOC analyzer, and there are no particular restrictions on the specifications of the analyzer used. Because membrane filtrate is already a liquid that has been filtered through a membrane, it contains almost no substances that would cause filtration resistance in the membrane. However, damage to sludge caused by chemicals occurs simultaneously on various scales, from an increase in the concentration of soluble organic matter below the pore size of the membrane to an increase in sludge disintegration flocs. Therefore, it is possible to infer information about the associated increase or decrease in filtration resistance substances in the sludge from the TOC measurement results of membrane filtrate.

[0079] Other methods for measuring the organic matter concentration in filter paper filtrate or membrane filtrate include COD and BOD, but these measurements require time. While there are methods for measuring COD and BOD using simple kits, the accuracy of quantification is low because they involve colorimetric evaluation using color reagents. For the evaluation of activated sludge characteristics in the present disclosure, the TOC concentration of the filter paper filtrate and the TOC concentration of the membrane filtrate are preferably used.

[0080] TOC analyzers used for measurement are particularly preferred because they can measure scientifically accurate values ​​in a short time (generally within a few minutes of injection into the analyzer). When using the TOC concentration of membrane filtrate of activated sludge as an indicator, treated water from the membrane module can be used instead of membrane filtrate of activated sludge during normal filtration operation before chemical cleaning or during filtration after chemical cleaning. In this case, using a TOC analyzer capable of automatically measuring TOC concentration continuously or intermittently (e.g., the TNC-200S manufactured by Toray Engineering D Solutions Co., Ltd.) is particularly preferred, as it allows for stable measurement of the characteristics of activated sludge before and after chemical cleaning. Furthermore, resuming operation after chemical cleaning is preferably performed after the activated sludge has recovered based on standards established for each plant, as described below. Furthermore, before resuming filtration operation, a warm-up operation may be performed with a flux set to 40% to 80% of the set filtration flux.

[0081] For example, by setting a standard for the turbidity of the filter paper filtrate, the time for filtration operation with aeration only or with aeration together at a flux set to a value of 40% or less of the set filtration flux, or the time for continuing filtration operation at a flux set to a value of 40% to 80% of the set filtration flux, can be rationally determined based on the turbidity value of the sludge filter paper filtrate, making it possible to efficiently return to normal filtration operation and improving operational stability after normal filtration operation is resumed.

[0082] When filtration operation is resumed at a set filtration flux or at a flux set to 40% to 80% of the set filtration flux, the criteria for determining the characteristics of the activated sludge liquid vary depending on the type of wastewater, the flux value during filtration operation designed for each plant, etc., and therefore it is desirable to establish conditions and set criteria for each plant site. Specifically, these criteria may be established on-site based on the results of initial chemical cleaning after plant startup, or when chemical cleaning is performed, the filtration characteristics of the sludge before and after chemical cleaning are evaluated over time, and filtration operation at the set filtration flux or a flux of 40% to 80% of that flux is started at different times in multiple membrane module systems, and the criteria can be efficiently identified and set based on the transition of the differential pressure in each system after filtration operation.

[0083] Alternatively, a small membrane separation device equipped with multiple membrane modules capable of independent evaluation can be used to treat the same wastewater as the actual device and conduct similar tests. A small membrane separation device would have a capacity of, for example, about 30 L.

[0084] As mentioned above, when deciding on the operating method, it is preferable to verify and prepare the characteristics and standards of the activated sludge liquid on-site. However, if there is no time to carry out the test, the set filtration flux is set to 0.5 to 0.7 m. ３ / m ２ In the sewage treatment plant in d, in the case of the turbidity of the filter paper filtrate of activated sludge liquid, the condition "turbidity value of the filter paper filtrate ≦ turbidity value of the filter paper filtrate before chemical washing + 4" (unit: NTU) is satisfied, and in the case of microscope image information, "area 200 μm ２ The sum of the areas of the following flocs / area of ​​the microscope field of view≦(area before chemical cleaning 200 μm ２ The "first filtration characteristic criterion" suitable for resuming filtration operation at the set filtration flux is one that satisfies the following condition: "total area of ​​flocs / value of area of ​​microscope field of view × 1.3"; and in the case of filtration resistance calculated from the results of a membrane filtration test using membrane pieces, one that satisfies the following condition: "value of increase in filtration resistance≦value of increase in filtration resistance before chemical cleaning × 2.5". The same effect can be obtained whether the indicator used is the turbidity of the filter paper filtrate of the activated sludge liquid, the microscope image information, or the filtration resistance.

[0085] Furthermore, among the characteristics of activated sludge liquid, the turbidity of the activated sludge liquid filtered through a filter paper is particularly easy to measure and has high accuracy, so when this indicator is used, it becomes possible to monitor the sludge more precisely and to determine the operating method. After the chemical cleaning of the membrane is completed and aeration is resumed, or after aeration is resumed and filtration operation is resumed at a flux set to a value of 40% or less of the set filtration flux, once the characteristics of the activated sludge liquid satisfy the "second filtration characteristic criterion" described below, filtration operation can be changed to a flux set to a value of 40% to 80% of the normal set filtration flux, and once the characteristics of the activated sludge liquid satisfy the previously set "first filtration characteristic criterion," filtration operation at the set filtration flux can be resumed.

[0086] As mentioned above, when changing the operation, it is preferable to verify and prepare the characteristics of the activated sludge liquid and its judgment criteria on-site. As a guideline, ３ / m ２ In the case of sewage treatment plants d, a suitable "second filtration characteristic standard" can be "turbidity value of filter paper filtrate ≦ turbidity value of filter paper filtrate before chemical cleaning + 8" (unit: NTU).

[0087] The present disclosure is characterized in that one of the following decisions is made based on an operational performance evaluation of the separation membrane after chemical cleaning: A10: Based on a first operational performance standard, a decision is made as to whether to resume filtration after chemical cleaning or to determine chemical cleaning conditions and perform chemical cleaning again; A20: Based on a second operational performance standard, a decision is made as to whether to change the type of chemical and further determine chemical cleaning conditions and perform chemical cleaning again.

[0088] Since the evaluation criteria vary depending on factors such as the type of wastewater and the flux values ​​during filtration operation designed for each plant, it is desirable to establish conditions and set evaluation criteria for each plant site. Specifically, these criteria can be established on-site based on the results of initial chemical cleaning after start-up. Alternatively, when chemical cleaning is performed, operational performance before and after chemical cleaning can be evaluated over time. Filtration operations at a set filtration flux or a flux lower than the set filtration flux can be started at different times in multiple membrane module systems, and the criteria can be efficiently identified and set based on the changes in differential pressure in each system after filtration operation. Alternatively, similar tests can be performed using a small membrane separation device equipped with multiple membrane modules capable of independent evaluation, treating the same wastewater as the actual system. A small membrane separation device, for example, has a capacity of approximately 30 L.

[0089] As mentioned above, when changing the operation, it is preferable to verify and prepare the filtration characteristics of the liquid to be filtered and the criteria for judgment on site. However, if there is no time to carry out the test, the set filtration flux is set to 0.5 to 0.7 m ３ / m ２ In the sewage treatment plant (membrane separation activated sludge treatment device) of d, the following can be exemplified:

[0090] In the present disclosure, in the first operational performance standard, if the evaluation index for the operational performance is any one of filtration pressure, transmembrane pressure difference, and filtration resistance, the following A11 is the standard; if the evaluation index for the operational performance is membrane water permeability, the following A12 is the standard; if the evaluation result after chemical cleaning is within the first operational standard, filtration is resumed; if it deviates from the first operational standard, chemical cleaning conditions are determined and it is judged that chemical cleaning should be performed again; and in the second operational performance standard, if the evaluation index for the operational performance is any one of filtration pressure, transmembrane pressure difference, and filtration resistance, the following A21 is the standard; if it is membrane water permeability, the following A22 is the standard; if the evaluation result after chemical cleaning is within the second operational standard, the type of chemical solution is changed, and further chemical cleaning conditions are determined and chemical cleaning is performed again. A11: Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) ≦ 1.3 A12: 0.7 ≦ Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) A21: 1.5 < Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) A22: Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) < 0.5 If the operating performance is within the first operating performance criterion and also simultaneously satisfies the "first filtration characteristic criterion," it can be determined that the filtration characteristics of the liquid to be filtered are also in good condition, and it is also preferable to immediately start filtration operation at the set filtration flux. However, it is not necessarily necessary to resume operation at the set filtration flux, and it is also preferable to resume filtration operation at a flux set to a value of 40% to 80% of the set filtration flux or a value below 40%.

[0091] Furthermore, if the "first filtration characteristic criterion" is not met, it is preferable to resume filtration operation at a flux lower than the set filtration flux in order to reduce the risk of membrane surface fouling due to deterioration of the filtration characteristics of the liquid to be filtered. Here, a flux lower than the set filtration flux is preferably a flux set to a value of 40% to 80% or a value of 40% or less. Even if filtration operation is resumed at a set value lower than the set filtration flux, it may be possible to change to the set filtration flux if it is confirmed that the filtration characteristics of the liquid to be filtered satisfy the first filtration characteristic criterion.

[0092] If the first performance standard is not satisfied, it is preferable to perform chemical cleaning of the separation membrane again. At this time, the chemical cleaning may be performed again under the same chemical cleaning conditions, or the chemical cleaning conditions may be changed.

[0093] Although there are no limitations on the concentration of the chemical solution, it is preferable to use sodium hypochlorite with an effective chlorine concentration of about 500 mg / L to 6000 mg / L. The immersion time in the chemical solution can be set appropriately depending on the water temperature during chemical cleaning, and is typically in the range of 30 minutes to 4 hours, and more preferably 1 to 2 hours.

[0094] It is also preferable to perform another chemical cleaning and then evaluate the operability again. If the result of the operability evaluation shows that the operability deviates from the first operability standard even after the chemical cleaning is performed again, it can be determined that the chemical cleaning effect has been reduced due to inorganic fouling, and therefore it is preferable to change the chemical cleaning conditions and perform chemical cleaning of the separation membrane again. The changed chemical cleaning conditions are preferably at least one of the chemical concentration, chemical immersion time, chemical temperature, chemical supply amount, and chemical supply flow rate.

[0095] The chemical solution used is an organic acid with a chelating effect, such as oxalic acid or citric acid, with a concentration of about 1 to 3% by mass, which is effective in restoring operating performance.

[0096] If the operational performance still deviates from the first operational performance standard after the chemical cleaning conditions are changed and the separation membrane is again chemically cleaned, it is preferable to inspect and replace the membrane module.

[0097] If the performance is within the second operating performance standard, it can be determined that the effectiveness of the chemical washing has been reduced due to inorganic fouling, and therefore it is preferable to change the chemical washing conditions and perform chemical washing of the separation membrane again.

[0098] There are no limitations on the type or concentration of the chemical solution, but sodium hypochlorite with an effective chlorine concentration of about 500 mg / L to 6000 mg / L, or an organic acid with a chelating effect such as oxalic acid or citric acid with a concentration of about 1 to 3 mass % are effective in restoring operating performance and are preferably used.

[0099] The chemical immersion time is typically in the range of 30 minutes to 4 hours, more preferably 1 to 2 hours. Since the concentration of the injected chemical on the membrane surface decreases due to consumption by reaction and diffusion, prolonged immersion is less effective. On the other hand, if the chemical immersion time is too short, the amount of unreacted and undecomposed foulants remaining on the membrane increases, which is undesirable. Therefore, a time of 30 minutes or more is preferable.

[0100] Since the suitable ranges of the chemical supply amount and chemical supply flow rate vary depending on the capacity of the chemical tank and the performance of the chemical supply pump installed in the plant, the membrane area of ​​the separation membrane, and the number of separation membranes, it is desirable to establish conditions and set criteria for each plant site. Specifically, these criteria may be established on-site based on the results of initial chemical cleaning after start-up of operation, or may be determined by evaluating the operating performance over time before and after chemical cleaning when chemical cleaning is performed.

[0101] If the operational performance still deviates from the first standard after the chemical cleaning conditions are changed and the separation membrane is again chemically cleaned, it is preferable to inspect and replace the membrane module.

[0102] Filtration may be performed on-site by changing the flux under multiple conditions, preparing operational performance at each flux as a function of flux, and evaluating the operational performance of the separation membrane from the intercept of the function. Alternatively, it is also preferable to have a means installed at a remote location connected by a communication device function as a filtration flux changing means for filtering by changing the flux under multiple conditions, and as an operational performance evaluation means for preparing operational performance at each flux as a function of flux and evaluating the operational performance of the separation membrane from the intercept of the function.

[0103] The present disclosure is characterized in that the operating condition control means functions as an operating condition control means that determines and executes one of the following actions based on the means for evaluating the operational performance of the separation membrane after chemical cleaning. A10: Based on the first operational performance standard, it determines and executes whether to resume filtration after chemical cleaning or whether to determine chemical cleaning conditions and perform chemical cleaning again. A11: Based on the second operational performance standard, it determines and executes whether to change the type of chemical and further determine chemical cleaning conditions and perform chemical cleaning again.

[0104] Furthermore, the computer may be operated as a filtration flux changing means, an operational performance evaluation means that creates operational performance at each flux as a function of the flux and evaluates the operational performance of the separation membrane from the intercept of the function, and an operational condition control means that determines and executes one of the following based on the operational performance evaluation means for the separation membrane after chemical cleaning, and these may be performed automatically using a management program, or may be incorporated into the water treatment system as a computer-readable recording medium.

[0105] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0106] Example 1 A test was carried out using wastewater treatment equipment having the configuration shown in Figure 1. The sludge concentration was controlled so that the concentration of the activated sludge mixed liquor (MLSS) was approximately 8000 mg / L in an activated sludge tank equipped with a membrane module (a flat membrane module was used), and intermittent filtration operation (filtration for 9 minutes, filtration stopped for 1 minute) was carried out at an average flux of 0.7 m / d while aeration was performed on the membrane surface of the membrane module from a fine bubble aeration tube at the required air volume.

[0107] After the start of operation, the filtration differential pressure (filtration minus filtration pause) reached the point where chemical cleaning was necessary (an increase of 5 kPa from the beginning of operation at the same flux). The equipment, including filtration and aeration from the aeration means, was stopped, and chemical cleaning was performed with the membrane module immersed in the activated sludge tank.

[0108] The chemical solution used was a sodium hypochlorite aqueous solution with an effective chlorine concentration of 5000 mg / L. The solution was injected into the membrane module from the inlet of the filtrate piping of the flat membrane module so that a little more than half of the injected solution permeated from the inside to the outside of the flat membrane, and the solution was held for approximately 100 minutes to perform chemical solution cleaning.

[0109] As for the operational performance of the separation membrane, the flux was changed every 30 minutes under three conditions (100%, 60%, and 40% of the set filtration flux) and the evaluation index focused on the transmembrane pressure. An approximate equation was created as a function of the operational performance at each flux. As shown in Figure 4, the intercept obtained from the evaluation results after initial chemical cleaning (dashed line) after operation startup was compared with the intercept obtained from the evaluation results after chemical cleaning (solid line). It was confirmed that the operational performance was equivalent. Therefore, filtration operation was resumed at the set filtration flux. Even 30 days after the resumption of normal filtration operation, the transmembrane pressure did not reach the point where chemical cleaning was required, and stable operation was possible for a long period of time.

[0110] Example 2 After a filtration operation was performed under the same conditions as in the example using the same equipment as in the example, chemical cleaning was performed under the same conditions as in the example 1 at the timing when chemical cleaning was performed.

[0111] As for the operational performance of the separation membrane, the flux was changed every 30 minutes under three conditions, and the evaluation index focused on the transmembrane pressure. As shown in Figure 5, the evaluation results for the initial chemical cleaning after start-up were compared with the evaluation results after chemical cleaning, and it was confirmed that the first operational performance criterion, "evaluation result after chemical cleaning (intercept) / evaluation result for the initial chemical cleaning after start-up (intercept) ≦ 1.3," was met.

[0112] Furthermore, we focused on the turbidity of the activated sludge filtrate as the filtration characteristics of the liquid to be filtered, i.e., the filtration characteristics of the activated sludge liquid. First, we restarted the aeration that had been stopped during the chemical cleaning of the membrane, and after the "first filtration characteristic standard" was met, we resumed filtration operation.

[0113] In Example 2, aeration was performed from an aeration pipe installed below the membrane module, and the sludge was mixed until the turbidity of the filter paper filtrate of activated sludge liquid near the membrane module of the membrane bioreactor tank was equal to or less than the value obtained by adding 4.0 to the measured turbidity of the filter paper filtrate of activated sludge liquid near the membrane module of the membrane bioreactor tank measured before chemical injection on the day of chemical cleaning. After chemical cleaning, the state of the activated sludge was evaluated by measuring the turbidity of the filter paper filtrate of activated sludge liquid at intervals of time since the start of membrane surface aeration. The turbidity value of the filter paper filtrate of activated sludge liquid measured before chemical cleaning (before chemical injection began) on the day of chemical cleaning was 1.8 NTU. Based on this result, the "first filtration characteristic standard" was determined to be 1.8 + 4.0 = 5.8 [NTU]. Therefore, from the perspective of filtration characteristics, the criterion for restarting filtration operation at the set filtration flux (average flux 0.7 m / d) was set to 5.8 [NTU] or less. As a result, the operational performance evaluation confirmed that the results were better than the first operational performance criterion, "1.3 < evaluation result (intercept) after chemical cleaning / evaluation result (intercept) at the initial stage of chemical cleaning after operation start-up ≦ 1.5." Regarding filtration characteristics, the turbidity of the activated sludge liquor filtered from the filter paper reached 5.2 NTU approximately one hour after the start of sludge mixing, confirming that the filtration characteristics met the "first filtration characteristic criterion (5.8 NTU or less)." Following the above criteria, filtration operation was resumed at the set filtration flux. As a result, even 30 days after the resumption of normal filtration operation, the transmembrane pressure did not reach the point where chemical cleaning was required, and stable operation was possible over a long period of time.

[0114] (Comparative Example 1) After filtration operation was performed under the same conditions as in Example 1 using the same equipment, chemical cleaning was performed under the same conditions as in Example 1. In Comparative Example 1, the aeration that had been stopped during chemical cleaning of the membrane was restarted, and after one hour had passed, the filtration operation was resumed at the set filtration flux without evaluating the operational performance of the separation membrane after chemical cleaning. After the filtration operation was resumed, a higher transmembrane pressure was observed than after the initial chemical cleaning after operation start-up, and about three days after the start of operation, the transmembrane pressure reached the point where chemical cleaning was required.

[0115] 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.

[0116] This application is based on a Japanese patent application (Patent Application No. 2023-42732) filed on March 17, 2023, the contents of which are incorporated herein by reference.

[0117] 1: Filtrate supply pump 2: Submerged membrane separation unit 3: Filtrate tank 4: Aeration pipe 5: Filtrate storage tank 6: Chemical storage tank 7: Air blower 8: Filtrate flow meter 9: Filtrate flow meter 10: Air flow meter 11: Suction pump 12: Separation membrane module 13: Chemical supply pump 14: Backwash pump 15: Drain line 16: Pore blockage 17: Peelable cake 18: Non-peelable cake 19: Separation membrane

Claims

1. A method for operating a separation membrane for filtering water to be treated to obtain treated water, comprising the steps of: After the separation membrane is washed with a chemical solution, Filtration is performed under a variety of flux conditions, including 40% or less of the set filtration flux. An approximation equation is created that approximates the relationship between the flux ratio to the set filtration flux and the magnitude of the evaluation index of the operational performance as a function of the flux; A method for operating a separation membrane, comprising: evaluating operational performance caused by non-exfoliated cake of the separation membrane from an intercept at a flux ratio of 0% relative to a set filtration flux in the approximation formula.

2. 2. The method for operating a separation membrane according to claim 1, wherein the evaluation index for operational performance is at least one of filtration pressure, transmembrane pressure difference, filtration resistance, and membrane permeability.

3. The method for operating a separation membrane according to claim 1, further comprising the step of: determining whether A10 or A20 below is true based on the evaluation of the operational performance of the separation membrane after the chemical cleaning. A10: Based on the first operational performance standard, it is determined whether to resume filtration after chemical cleaning, or to determine the chemical cleaning conditions and perform chemical cleaning again. A20: Based on the second operational performance standard, the type of chemical is changed, and further, the chemical cleaning conditions are determined, and it is determined whether or not to perform chemical cleaning again.

4. The method for operating a separation membrane according to claim 3, wherein, in the first operating performance standard, if the evaluation index of the operating performance is any one of filtration pressure, transmembrane pressure, and filtration resistance, the following A11 is the standard, and if the evaluation index of the operating performance is membrane permeability, the following A12 is the standard; if the evaluation result after chemical cleaning is within the first operating standard, filtration is resumed, and if it deviates from the first operating standard, chemical cleaning conditions are determined and it is determined that chemical cleaning is performed again; and, in the second operating performance standard, if the evaluation index of the operating performance is any one of filtration pressure, transmembrane pressure, and filtration resistance, the following A21 is the standard, and if it is membrane permeability, the following A22 is the standard; if the evaluation result after chemical cleaning is within the second operating standard, the type of chemical solution is changed, and further chemical cleaning conditions are determined and chemical cleaning is performed again. A11: Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) ≦ 1.3 A12: 0.7≦Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) A21: 1.5 < Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) A22: Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) < 0.5

5. 5. The method for operating a separation membrane according to claim 3, wherein the chemical cleaning conditions are at least one of a chemical concentration, a chemical immersion time, a chemical temperature, a chemical supply amount, and a chemical supply flow rate.

6. 3. The method for operating a separation membrane according to claim 1 or 2, wherein the evaluation of operational performance caused by the non-exfoliated cake of the separation membrane is evaluation of initial operational performance at the start of operation.

7. 3. The method for operating a separation membrane according to claim 1 or 2, wherein the separation membrane is a microfiltration membrane or an ultrafiltration membrane.

8. A separation membrane operating condition determination program for functioning as an operating performance evaluation means for evaluating the operating performance caused by non-peeled cake of the separation membrane from the intercept of the function when the set filtration flux is 0%, the operation ...

9. 9. The program for determining operating conditions for a separation membrane according to claim 8, wherein the evaluation index of the operational performance evaluation means is at least one of filtration pressure, transmembrane pressure difference, filtration resistance, and membrane permeability.

10. The separation membrane operating condition determination program according to claim 9, characterized in that the separation membrane operating condition determination program functions as an operating condition control program that determines and executes one of the following based on the means for evaluating the operating performance of the separation membrane after the chemical cleaning. A10: Based on the first operational performance standard, a decision is made as to whether to resume filtration after chemical cleaning, or to determine chemical cleaning conditions and perform chemical cleaning again, and then this is carried out. A11: Based on the second operational performance standard, the type of chemical is changed, and further, the chemical cleaning conditions are determined, and it is determined whether or not to perform chemical cleaning again, and then the chemical cleaning is performed.

11. 11. The separation membrane operating condition determination program according to claim 10, wherein, in the first operating performance standard, if the evaluation index of the operating performance is any one of filtration pressure, transmembrane pressure, and filtration resistance, the following A11 is the standard, and if the evaluation index of the operating performance is membrane permeability, the following A12 is the standard; if the evaluation result after chemical cleaning is within the first operating standard, filtration is resumed, and if it deviates from the first operating standard, chemical cleaning conditions are determined and chemical cleaning is determined to be performed again and executed; and, in the second operating performance standard in the operating condition control means, if the evaluation index of the operating performance is any one of filtration pressure, transmembrane pressure, and filtration resistance, the following A21 is the standard, and if it is membrane permeability, the following A22 is the standard; if the evaluation result after chemical cleaning is within the second operating standard, the type of chemical solution is changed, and further chemical cleaning conditions are determined and chemical cleaning is determined to be performed again and executed. A11: Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) ≦ 1.3 A12: 0.7≦Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) A21: 1.5 < Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) A22: Evaluation result after chemical cleaning (intercept) / Evaluation result of chemical cleaning at the beginning of operation (intercept) < 0.5

12. The separation membrane operating condition determination program according to claim 10 or 11, characterized in that the chemical cleaning conditions in the operating condition control means are at least one of chemical concentration, chemical immersion time, chemical temperature, chemical supply amount, and chemical supply flow rate.

13. 10. The separation membrane operating condition determination program according to claim 8, wherein the separation membrane operating performance evaluation means functions as an evaluation means for evaluating initial operating performance at the start of operation.

14. A computer-readable recording medium having recorded thereon the separation membrane operating condition determination program according to claim 8 or 9.