Separation membrane operation method

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

[Technical Field]

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

[0002] Membrane separation is being used in a wide range of fields due to its advantages of energy savings, space savings, and improved treated water quality. 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, 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 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 being 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 vibration and agitation effects of the separation membrane caused by the air bubbles and upward flow remove the deposits from 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 water side of the separation membrane to shake the separation membrane and bring the membranes into contact with each other, thereby scraping off contaminants from the surface of the separation membrane, or back pressure washing (backwashing), in which filtered water or clarified water is forced in the opposite direction of the filtration method of the separation membrane to remove contaminants that have adhered to the surface of the separation membrane or 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 operating 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] Patent Documents 1 and 2 describe known methods for solving the above-mentioned problems. Patent Document 1 describes determining an appropriate cleaning intensity 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 not greater than 40% 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, and then 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. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2017-18859 [Patent Document 2] Japanese Patent Publication No. 2005-246283 Summary of the Invention [Problem to be solved by the invention]

[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, because 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 not be possible 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 equal to or less than 40% of the target permeation flux described in Patent Document 2, if fouling remains after chemical cleaning, the operational performance may deteriorate, resulting in a sudden increase in differential pressure 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. [Means for solving the problem]

[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, comprising the steps of: After cleaning the separation membrane with a chemical solution, set filtration Flux Contains 40% or less of multiple Flux of Change the conditions and filter, The relationship between the flux ratio to the set filtration flux and the magnitude of the evaluation index of operational performance is as a function of flux Create an approximate formula to approximate the filtration flux. When the flux ratio to the set filtration flux in the approximate formula is 0%, The separation membrane from the section Caused by non-peeling cake The method for operating a separation membrane is characterized by evaluating its operating performance.

[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.

[0016] ( 3 ) Based on the operational performance evaluation of the separation membrane after the chemical cleaning, a judgment is made as to whether A10 or A20 below applies. 1 ) is a method for operating the separation membrane described in 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 solution is changed, and further chemical cleaning conditions are determined to determine whether chemical cleaning should be performed again.

[0017] ( 4 ) In the first operational performance standard, if the operational performance evaluation index is any one of filtration pressure, transmembrane pressure difference, and filtration resistance, the following A11 is the standard, and if the operational performance evaluation index is membrane water permeability, the following A12 is the standard, and if the evaluation result after chemical cleaning is within the first operational standard, filtration is resumed, and if it deviates, chemical cleaning conditions are determined and chemical cleaning is judged to be performed again, and in the second operational performance standard, if the operational performance evaluation index 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, and if the evaluation result after chemical cleaning is within the second operational standard, the type of chemical is changed, and further chemical cleaning conditions are determined and chemical cleaning is performed again. 3 ) is a method for operating the separation membrane described in 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 results after chemical cleaning (intercept) / Evaluation results 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] ( 5 The chemical cleaning conditions are at least one of the chemical concentration, the chemical immersion time, the chemical temperature, the chemical supply amount, and the chemical supply flow rate. 3 )or( 4 ) is a method for operating the separation membrane described in

[0019] ( 6 ) The separation membrane Caused by non-peeling cake Driving performance of The method for operating a separation membrane according to (1) or (2) is characterized in that the evaluation is an evaluation of the initial operating performance immediately after the start of operation.

[0020] ( 7 ) The separation membrane is a microfiltration membrane or an ultrafiltration membrane (1) or (2) 1. A method for operating a separation membrane according to any one of the preceding claims.

[0021] ( 8 ) In order to evaluate the membrane performance of the separation membrane that filters the water to be treated and obtains the treated water, After the separation membrane is washed with a chemical solution, Computer, Setting Filtration Flux Contains 40% or less of A filtration flux changing means for filtering under a plurality of conditions; The relationship between the flux ratio to the set filtration flux and the magnitude of the evaluation index of operational performance is as a function of flux, When the set filtration flux is 0% The separation membrane from the section Caused by non-peeling cake This is a separation membrane operating condition determination program that functions as an operating performance evaluation means for evaluating operating performance.

[0022] ( 9 The evaluation index of the operational performance evaluation means is at least one of filtration pressure, transmembrane pressure difference, filtration resistance, and membrane water permeability. 8 ) is a program for determining operating conditions for a separation membrane according to the present invention.

[0024] ( 10 ) The operating condition control means is characterized in that it functions as an operating condition control means that determines and executes one of the following based on the operating performance evaluation means for the separation membrane after chemical washing: 9 ) is a program for determining operating conditions for a separation membrane according to the present invention. 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, and then the decision is made. A11: Based on the second operational performance standard, the type of chemical solution is changed, and further chemical cleaning conditions are determined, and a decision is made as to whether to perform chemical cleaning again, and then this is carried out.

[0025] ( 11 ) In the first operational performance standard, if the operational performance evaluation index is any one of filtration pressure, transmembrane pressure difference, and filtration resistance, the following A11 is the standard, and if the operational performance evaluation index is membrane water permeability, the following A12 is the standard, and if the evaluation result after chemical cleaning is within the first operational standard, filtration is resumed, and if it deviates, chemical cleaning conditions are determined and chemical cleaning is judged to be performed again and carried out, and in the second operational performance standard in the operational condition control means, if the operational performance evaluation index 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, and 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 judged to be performed again and carried out, characterized in that it functions as operational condition control means ( 10 ) is a program for determining operating conditions for a separation membrane according to the present invention. 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 results after chemical cleaning (intercept) / Evaluation results 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] ( 12 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. 10 )or( 11) is a program for determining operating conditions for a separation membrane according to the present invention.

[0027] ( 13 The operational performance evaluation means for the separation membrane functions as an evaluation means for the initial operational performance at the start of operation. 8 )or( 9 ) is a program for determining operating conditions for a separation membrane according to the present invention.

[0028] ( 14 ) (8) or (9) and a computer-readable recording medium having recorded thereon a program for determining operating conditions for the separation membrane. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic flow diagram showing an example of a membrane separation device to which the present invention is applied. [Figure 2] FIG. 2 is a schematic flow diagram showing another example of a membrane separation apparatus to which the present invention is applied. [Figure 3] 1 is a conceptual diagram of fouling of a separation membrane to which the present invention is applied. [Figure 4] 1 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 described in Example 1 is applied. [Figure 5] 1 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 described in Example 2 is applied. DETAILED DESCRIPTION OF THE INVENTION

[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, for example. 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 cleaning 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. FIG. 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 for 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 cleaning 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 state of membrane fouling. 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 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 typical chemical solution immersion time is 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 through 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 chemical solution immersion 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 the liquid to be filtered is filtered through a membrane, and is generally defined by equation (1).

[0047]

number

[0048] where 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 can 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 can be calculated from the temperature according to equation (2).

[0050]

number

[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 Celsius temperature is σ [°C], then T = σ + 273.15.

[0052] When the flux is changed under multiple 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, there are no or few membrane modules that 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 changing the flux under multiple 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 filtration conditions that minimize the risk of membrane fouling, such as a set filtration flux of 40% or less, 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 membrane.

[0056] Here, fouling of a separation membrane by components of the liquid to be filtered can be divided into pore blockage 16, which is components of 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 of 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 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 in order to suppress the adhesion of new peelable cake and to accurately obtain 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. In addition, the upper limit of the evaluation time at each flux is preferably about 1 hour.

[0061] In the present disclosure, the operational performance is preferably evaluated by creating an operational performance evaluation approximation equation that approximates the operational performance at each flux as a function of the 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 the following membrane performance evaluation indicators on the vertical axis: filtration pressure, transmembrane pressure difference, filtration resistance, or membrane permeability.

[0062]

number

[0063]

number

[0064] Here, H is the operating performance of the separation membrane at each flux, and can 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 using the least squares method or multiple regression analysis each time 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 operating performance at each flux as a function of flux allows us to obtain the operating performance at a set filtration flux of 0%, i.e., the operating performance resulting from fouling (non-exfoliated cake) adhering to the membrane surface of the separation membrane, and therefore can be calculated as an operating performance evaluation value.

[0067] Second, 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 separation activated sludge method contains a large number of microorganisms, it is also preferable to evaluate it using the following method.

[0069] Here, 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, the capillary suction time (CST), microscope image information, the 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 its treated water dilution, and the ATP (Adenosine triphosphate) concentration.

[0070] After careful investigation, it was found that the turbidity of the activated sludge liquor filtered through a filter paper, microscopic image information, filtration resistance (calculated from the results of membrane filtration tests using membrane pieces), TOC concentration of the filtered paper liquor, and TOC concentration of the membrane filtrate are particularly effective indicators for determining the membrane filtration characteristics of activated sludge liquor in terms 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 filter paper filtrate contains information reflecting the abundance of biopolymers, such as proteins and polysaccharides, that are generated by chemical damage and have sizes smaller than the filter paper pore size (1 μm). These components are substances that easily foul membranes with pore sizes between 0.01 μm and 1 μm, which are used in membrane bioreactors. In other words, the turbidity of sludge filter paper filtrate is not only easy to measure, but can also be used as a highly accurate and reliable indicator of the sludge's filtration characteristics. It is particularly suitable as a characteristic to use when determining operating methods after chemical cleaning.

[0075] Microscopic 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 activated sludge liquid is observed with an optical microscope at 100 to 400 magnifications (when observed through an eyepiece), as well as 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, combining a system that automatically supplies sludge to the microscope field of view at a fixed frequency with an image analysis system makes it easy to obtain continuous data unattended. Therefore, a control system may be provided that continuously measures the microscopic image information of the activated sludge liquid after chemical cleaning, and automatically returns the membrane bioreactor to the set filtration flux when the measurement results meet a predetermined standard (absolute value or rate of change).

[0076] When obtaining image information about 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 or 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 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. 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] A TOC analyzer is particularly preferred for this measurement because it can measure scientifically accurate values ​​in a short time (generally within a few minutes of being injected into the analyzer). When using the TOC concentration of membrane filtrate from activated sludge as an indicator, treated water from the membrane module can be used instead of membrane filtrate during normal filtration before chemical cleaning or during filtration after chemical cleaning. In this case, 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. After chemical cleaning, it is preferable to resume filtration operation after the activated sludge has recovered based on the standards established for each plant, as described below. Before resuming filtration operation, a warm-up operation may be performed at a flux set to 40% to 80% of the target 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] The criteria for determining the characteristics of activated sludge liquid when restarting filtration operation at a set filtration flux or at a flux set at 40% to 80% of the set filtration flux vary depending on the type of wastewater and the flux value during filtration operation designed for each plant, so it is desirable to establish conditions and set the criteria for each plant site. Specifically, these criteria can 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 can be evaluated over time, and filtration operation at the set filtration flux or at a flux of 40% to 80% of that 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.

[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, it is recommended to set the filtration flux at 0.5 to 0.7 m. 3 / m 2 In the sewage treatment plant in d, the turbidity of the activated sludge filtrate must satisfy the condition "turbidity value of the filtrate before chemical cleaning + 4" (unit: NTU). In the case of microscope image information, the turbidity value of the filtrate must satisfy the condition "area 200 μm 2 The sum of the area 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 restarting filtration operation at the set filtration flux is that the following condition is met: "total area of ​​flocs / area of ​​microscope field of view) × 1.3"; and in the case of filtration resistance calculated from the results of membrane filtration tests using membrane pieces, the condition "value of increase in filtration resistance ≦ value of increase in filtration resistance before chemical cleaning × 2.5" is met. 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, more detailed sludge monitoring and determination of operating methods become possible. After chemical cleaning of the membrane is completed and aeration is resumed, or aeration is resumed and filtration operation is resumed at a flux set to a value of 40% or less of the set filtration flux, and 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 a sewage treatment plant such as 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 judgments is made based on an evaluation of the operational performance of the separation membrane after 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 solution is changed, and further chemical cleaning conditions are determined to determine whether chemical cleaning should be performed again.

[0088] The criteria vary depending on factors such as the type of wastewater and the flux values ​​during filtration operation designed for each plant. Therefore, it is desirable to establish conditions and set 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 the set filtration flux or at fluxes lower than the set filtration flux can be started at different times for multiple membrane module systems. The criteria can then 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, it is recommended to set the filtration flux to 0.5 to 0.7 m. 3 / m 2 In the case of sewage treatment plants (membrane separation activated sludge treatment equipment) in d, the following can be given as examples:

[0090] The present disclosure is characterized in that, in the first operational performance standard, if the operational performance evaluation index is any one of filtration pressure, transmembrane pressure difference, and filtration resistance, the following A11 is the standard, and if the operational performance evaluation index is membrane permeability, the following A12 is the standard, and if the evaluation result after chemical cleaning is within the first operational standard, filtration is resumed, and if it deviates, 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 operational performance evaluation index is any one of filtration pressure, transmembrane pressure difference, and filtration resistance, the following A21 is the standard, and if it is membrane permeability, the following A22 is the standard, and 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 results after chemical cleaning (intercept) / Evaluation results 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 operational performance is within the first operational performance standard and also satisfies the "first filtration characteristic standard," it can be determined that the filtration characteristics of the liquid to be filtered are also in a good state, and it is preferable to immediately start filtration operation at the set filtration flux. However, it is not always necessary to resume operation at the set filtration flux, and it is also preferable to resume filtration operation at a flux set to 40% to 80% of the set filtration flux or to a value of 40% or less.

[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 fouling on the membrane surface 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 re-chemically wash the separation membrane. At this time, the chemical washing may be carried out under the same chemical washing conditions or under different chemical washing conditions.

[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, more preferably 1 to 2 hours, for example.

[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 driving 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 it is therefore 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 organic acids 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 immersion time in the chemical solution is usually in the range of 30 minutes to 4 hours, and more preferably 1 to 2 hours, for example. The concentration of the injected chemical solution on the membrane surface decreases due to consumption by reaction and diffusion, so extending the immersion time too long is not effective. On the other hand, immersion time that is too short is not desirable because it increases the amount of unreacted and undecomposed foulants remaining on the membrane, so a immersion 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 based on the operating performance evaluation means for the separation membrane after 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, and then the decision is made. A11: Based on the second operational performance standard, the type of chemical solution is changed, and further chemical cleaning conditions are determined, and a decision is made as to whether to perform chemical cleaning again, and then this is carried out.

[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. [Example]

[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 Tests were conducted using wastewater treatment equipment with the configuration shown in Figure 1. The sludge concentration was controlled so that the MLSS concentration was approximately 8000 mg / L in the activated sludge tank where a membrane module (a flat membrane module was used) was installed, and intermittent filtration operation (9 minutes of filtration, 1 minute of filtration stop) was performed at an average flux of 0.7 m / d while aeration was performed over 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 (during filtration - when filtration is stopped) reached the point where chemical cleaning was required (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 solution with an effective chlorine concentration of 5000 mg / L. The solution was injected into the membrane module from the inlet of the filtrate water piping of the flat membrane module so that just over 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 cleaning.

[0109] To evaluate 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 difference. An approximate equation was created as a function of the operational performance at each flux. As shown in Figure 4, a comparison of the intercept obtained from the evaluation results after initial chemical cleaning (dashed line) and the intercept obtained from the evaluation results after chemical cleaning (solid line) confirmed that the operational performance was equivalent. Filtration operation was then resumed at the set filtration flux, and even 30 days after the resumption of normal filtration operation, the transmembrane pressure difference did not reach the point where chemical cleaning was required, allowing stable operation to continue for an extended period of time.

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

[0111] To evaluate 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 difference. 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 in the membrane bioreactor tank reached or below a value calculated by adding 4.0 to the turbidity measurement of the filter paper filtrate of activated sludge liquid near the membrane module in 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 after the start of membrane surface aeration. The turbidity of the filter paper filtrate of activated sludge liquid measured before chemical cleaning (before chemical injection) 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] for the turbidity of the filter paper filtrate of activated sludge liquid near the membrane module in the membrane bioreactor tank. 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 at 5.8 [NTU] or less. As a result, the operational performance evaluation confirmed that the system was better than the first operational performance criterion, "1.3 < evaluation result (intercept) after chemical cleaning / evaluation result (intercept) of initial chemical cleaning after operation start-up ≦ 1.5." Regarding filtration characteristics, the turbidity of the activated sludge filtrate reached 5.2 NTU approximately one hour after the start of sludge mixing, confirming the first filtration characteristic criterion (5.8 NTU or less) was met. Following the above criteria, 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 threshold for chemical cleaning, 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 chemical cleaning in the initial stage after 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. [Explanation of symbols]

[0117] 1: Filtrate supply pump 2: Submerged membrane separation unit 3: Filtrate tank 4: Diffuser pipe 5: Filtrate storage tank 6: Chemical storage tank 7: Air blower 8:Filtered liquid 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: Drainage line 16: Pore blockage 17: Peelable cake 18: Non-peeling cake 19: Separation membrane

Claims

1. A method for operating a separation membrane to filter water to be treated and obtain treated water, comprising: 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 approximate equation is created that approximates the relationship between the flux ratio to the set filtration flux and the magnitude of an evaluation index of operational performance, which is one of transmembrane pressure difference, filtration resistance, and membrane permeability, as a function of flux; An evaluation index of operational performance caused by non-exfoliated cake that cannot be removed by physical cleaning strength performed during operation is calculated from the intercept when the flux ratio to the set filtration flux is 0% in the approximation formula, The evaluation index after the chemical cleaning is compared with the evaluation index obtained during initial operation at the start of operation to evaluate the operational performance of the separation membrane after the chemical cleaning; When the evaluation index of the operational performance is either the transmembrane pressure or the filtration resistance, the following A11 is used as the first operational performance standard, When the evaluation index of the operational performance is membrane water permeability, the following A12 is used as the first operational performance standard: If the evaluation result after the chemical cleaning is within the first operating standard, filtration is resumed, and if the evaluation result is outside the first operating standard, chemical cleaning conditions are determined and chemical cleaning is to be performed again; When the evaluation index of the operational performance is either the transmembrane pressure or the filtration resistance, the following A21 is used as the second operational performance standard, When the evaluation index of the operational performance is membrane water permeability, the following A22 is used as the second operational performance standard: A method for operating a separation membrane, comprising: changing the type of chemical if the evaluation result after chemical cleaning is within a second operating standard; determining chemical cleaning conditions; and performing chemical cleaning 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

2. 2. The method for operating a separation membrane according to claim 1, wherein the chemical cleaning conditions are at least one of chemical concentration, chemical immersion time, chemical temperature, chemical supply amount, and chemical supply flow rate.

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

4. In order to evaluate the membrane performance of a separation membrane that filters water to be treated to obtain treated water, a filtration flux changing means is provided for chemically cleaning the separation membrane and then filtering under a plurality of conditions including 40% or less of a set filtration flux by a computer; an approximation formula is prepared that approximates the relationship between the flux ratio to the set filtration flux and the magnitude of an evaluation index of operational performance, which is any one of transmembrane pressure difference, filtration resistance, and membrane permeability, as a function of flux; An evaluation index of operational performance caused by non-exfoliated cake that cannot be removed by physical cleaning strength performed during operation is calculated from the intercept when the flux ratio to the set filtration flux is 0% in the approximation formula, The evaluation index after the chemical cleaning is compared with the evaluation index obtained during initial operation at the start of operation to evaluate the operational performance of the separation membrane after the chemical cleaning; Based on the evaluation of the operational performance of the separation membrane after the chemical cleaning, When the evaluation index of the operational performance is either the transmembrane pressure or the filtration resistance, the following A11 is used as the first operational performance standard, When the evaluation index of the operational performance is membrane water permeability, the following A12 is used as the first operational performance standard: If the evaluation result after the chemical cleaning is within the first operating standard, filtration is resumed, and if the evaluation result is outside the first operating standard, chemical cleaning conditions are determined and chemical cleaning is determined to be performed again, and then the chemical cleaning is performed. When the evaluation index of the operational performance is either the transmembrane pressure or the filtration resistance, the following A21 is used as the second operational performance standard, When the evaluation index of the operational performance is membrane water permeability, the following A22 is used as the second operational performance standard: A separation membrane operating condition determination program characterized by functioning as an operating condition control means that, if the evaluation result after chemical cleaning is within a second operating standard, changes the type of chemical, determines the chemical cleaning conditions, and determines that chemical cleaning should be performed again and executes it. 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 separation membrane operating condition determination program according to claim 4, 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.

6. 6. The separation membrane operating condition determination program according to claim 4, wherein the separation membrane operating performance evaluation means functions as an evaluation means for initial operating performance at the start of operation.

7. A computer-readable recording medium having recorded thereon the separation membrane operating condition determination program according to claim 4 or 5.

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