JP2013034938A - Method for washing membrane module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an effective washing method and an effective washing device of a membrane module and a method for stably operating the membrane module for a long period.SOLUTION: The method for washing the membrane module in a membrane filtering method obtaining filtrate by filtrating water to be treated with the membrane module is characterized in that a primary side and a secondary side of the membrane module are immersed in chemical for washing, the chemical for washing of the primary side of the membrane module is discharged to the outside of the system of the membrane module, the water to be treated is supplied to the membrane module, the membrane filtration is restarted, the filtrate of an initial period for restarting the membrane filtraion is stored in a chemical residual water tank, the filtrate of an initial period for restarting the membrane filtraion stored in the chemical residual water tank is used in reverse pressure water washing compressedly sending the washing water from the secondary side to the primary side of the membrane module.

Description

  The present invention relates to a method for cleaning a membrane module for water treatment. More specifically, the present invention relates to a method of cleaning a membrane module for water treatment used in the field of water purification in waterworks, the field of industrial water production such as industrial water, food, and medical process water, and the field of sewage water such as sewage and industrial wastewater. .

  The membrane separation method has features such as energy saving, space saving, labor saving, and product quality improvement, and therefore, its use in various fields is expanding. For example, microfiltration membranes and ultrafiltration membranes can be applied to water purification processes for producing industrial water and tap water from river water, groundwater, and sewage treated water. Separation membranes used in water treatment are broadly divided into two types: nanofiltration membranes (NF membranes) / reverse osmosis membranes (RO membranes), microfiltration membranes (MF membranes) / ultrafiltration membranes (UF membranes). It is used for desalination and ion removal from seawater and brine, while the latter is used in water purification processes that produce industrial water and tap water from river water, groundwater, and sewage water. Furthermore, a treatment called “Membrane Bioreactor (MBR)” in which sewage or industrial wastewater that has been treated by the activated sludge method is treated with an MF membrane / UF membrane directly immersed in the activated sludge tank. Has also been active.

  Due to the recent situation where water shortages are screamed, water treatment methods using these membranes have been further developed. In recent years, MF membranes / UF membranes have been used to remove organic matter and fine particles from seawater or brine, or sewage or After the pretreatment such as purifying industrial wastewater with MBR, it is filtered by RO membrane, and the method called “Integrated Membrane System (IMS)” is adopted to produce fresh water efficiently. Many water facilities have been constructed in the Middle East and Asia, which suffer from water shortages.

  Such a membrane module for water treatment (hereinafter referred to as a membrane module) is roughly divided into a pressure membrane module and an immersion membrane module. The pressurization type membrane module has a shape in which a large number of membranes are accommodated in a container and both ends or one end of the container are bonded with various adhesives. This is a membrane module of the type in which the introduced water to be treated is in a pressurized state and is filtered by the membrane surface. On the other hand, the submerged membrane module has a shape in which the membrane is exposed to the atmosphere. The membrane module is a type of membrane module in which the membrane module is immersed in a treatment tank opened to the atmosphere and filtered by suctioning the filtered water side. It is.

  The pressure membrane module can set the filtration pressure higher than the submerged membrane module, so the processing amount per membrane area increases, so the number of membrane modules required for processing can be reduced, the installation area can be reduced, etc. Has advantages. On the other hand, the submerged membrane module does not require a pressure-resistant cylindrical case and is used by immersing the membrane in the water to be treated. There is an advantage that membrane filtration can be performed even with treated water. Moreover, since the filtration method is simple and there are few incidental piping, there also exists an advantage which can reduce installation cost.

  As described above, the submerged membrane module performs the filtration by immersing the membrane module in the water to be treated in the treatment tank open to the atmosphere and sucking the filtered water side. In the case of suction filtration, the inside of the filtrate pipe from the filtrate outlet of the submerged membrane module to the suction means (suction pump, etc.) that sucks the filtrate water side of the membrane module must be sucked during the filtration process. Therefore, it has a feature that it becomes a negative pressure state or a state close thereto.

  When these membrane modules are used to filter the water to be treated, removal objects such as turbidity and organic matter contained in the water to be treated accumulate on the membrane surface, resulting in a membrane clogging phenomenon. As a result, it becomes impossible to perform filtration. Therefore, in order to maintain the membrane filtration performance, it is common to periodically stop the membrane filtration and perform physical cleaning. Usually, the filtration process and the physical cleaning process described above are automatically and repeatedly performed.

  For physical cleaning, air is blown into the lower part of the membrane module and the membrane is vibrated in water, so that the suspended matter adhering to the membrane surface is shaken off (air washing) and the filtration direction of the membrane module is reversed. Reverse pressure water that pushes water (wash water) such as filtered water under pressure in the direction, that is, from the filtered water side (secondary side) to the treated water side (primary side) There is washing (back washing). In the normal operation of the membrane module, after each of these steps is performed once, a drainage step of discharging the suspended matter separated from the membrane out of the system is performed.

  However, if the membrane filtration operation lasts for a long time, impurities that cannot be removed even by the above-mentioned physical cleaning adhere to and accumulate on the membrane surface and between the membranes, so that chemical cleaning that dissolves and removes these impurities using chemicals is necessary. Come. The chemical cleaning is composed of a chemical cleaning process for dissolving or removing impurities deposited and accumulated on the film by the chemical and a rinsing process for washing away the chemical in the membrane module.

  There are generally two methods for on-line chemical cleaning of the membrane module: a method of immersing the membrane module in the chemical for a fixed time and a method of circulating the chemical in the membrane module for a fixed time.

  The on-line chemical cleaning method of the membrane module will be described by taking the pressure membrane module as an example. In the method of immersing in the chemical, the chemical is supplied into the membrane module from the primary side or the secondary side of the membrane module, and the membrane module When the primary side and the secondary side are filled with chemicals, the supply is stopped, and after immersing for about several hours, the chemicals are discharged from the membrane module and a rinsing step is performed. On the other hand, in the method of circulating the chemical, the operation of supplying the chemical into the membrane module from the primary side or the secondary side of the membrane module and continuing to supply the chemical discharged from the membrane module to the membrane module for several hours is continued. Later, chemicals are discharged from the membrane module and a rinsing process is performed.

  However, when chemical cleaning is performed by the method described above, since the chemical remains in the membrane module in any method, the rinsing process is performed. There is a problem that a large amount of washing water is required and a large amount of waste water containing chemicals is generated, and another chemical is used for neutralization of the pH of the washing waste water. .

  As means for reducing the wastewater treatment cost of chemicals used in chemical cleaning, in Patent Document 1, a chemical is passed from a chemical storage tank toward the primary side from the secondary side of the membrane module, and the chemical storage tank A chemical cleaning method has been proposed in which a chemical is filtered with a filter installed in the middle of a pipe connecting the membrane module to the membrane module and then supplied again to the secondary side of the membrane module to circulate the chemical. This method is suitable for a pressurized membrane module where the inside of the membrane module is a closed space and pipes are connected to the upper and lower parts of the membrane module, but it is installed in an immersion tank and performs membrane filtration. When applied to membrane modules, it is necessary to fill a large immersion tank, so it is necessary to use a large amount of both chemicals and rinsing water. After all, wastewater treatment after cleaning is costly and can be applied to all membrane modules It cannot be said that it is a simple chemical cleaning method.

  Therefore, in Patent Document 2, the rinse water is collected in a recovery rinse water tank, and is turbidized with the first recovery membrane and then reused in the rinse water or concentrated with the second recovery membrane. A method has been proposed in which the water is reused as rinse water, and the concentrated water is reused as a chemical for chemical cleaning. In addition, a method has been proposed in which a chemical discharged from the membrane module after the chemical liquid cleaning step is completed is filtered through a membrane module for chemical purification and reused. Certainly, in this method, wastewater treatment costs can be reduced because the rinse water is membrane filtered and used again as rinse water. However, since a new membrane filtration facility is provided, the space for the entire treatment facility is expanded. Will lead to

  On the other hand, in Patent Document 3, the pretreatment membrane is washed with concentrated water in which the salinity generated from the RO membrane device that produces fresh water by removing the salt content of the filtered water obtained from the pretreatment device having the pretreatment membrane. A method for use in water has been proposed. Conventionally, since the concentrated water is drained, the wastewater treatment costs are certainly reduced by using it for cleaning the pretreatment membrane. However, this method is a method realized only by an apparatus that performs processing using an RO membrane, and is not applicable to the field of processing using only a pretreatment membrane (referred to as MF membrane or UF membrane in Patent Document 2).

  Further, although any patent document proposes a technique for reducing the wastewater treatment cost, even when the proposed technique is applied, the chemical cleaning frequency of the membrane module cannot be lowered.

JP 2006-281022 A JP 2005-246361 A JP 2011-31121 A

  An object of the present invention is to provide an efficient cleaning method for a membrane module, to provide a method for stably operating the membrane module for a long period of time, and reducing wastewater treatment costs.

  In order to solve the above problems, the present invention has the following configuration.

  (1) A membrane module cleaning method in a membrane filtration method in which water to be treated is filtered with a membrane module to obtain filtered water, wherein the primary side and the secondary side of the membrane module are immersed in cleaning chemicals, The cleaning chemical on the primary side of the membrane module is discharged out of the system of the membrane module, the water to be treated is supplied to the membrane module, the membrane filtration is restarted, and the filtered water at the initial stage of the membrane filtration restart is put into the chemical residue water tank. The membrane module which is stored and used in the reverse pressure water cleaning in which the filtered water stored in the chemical residual water tank at the initial stage of the membrane filtration restart is pumped from the secondary side to the primary side of the membrane module. Cleaning method.

  (2) The membrane module cleaning method according to (1), wherein the primary side of the membrane module is flushed with the water to be treated before the membrane filtration is restarted.

  (3) The method for cleaning a membrane module according to (2), wherein when flushing the primary side of the membrane module with the water to be treated, air is supplied to the primary side of the membrane module.

  (4) Water mixed with the filtered water at the initial stage of resumption of membrane filtration stored in the chemical residual water tank and normal filtered water stored in the filtered water tank is used for back pressure water cleaning (1) The washing | cleaning method of the membrane module in any one of-(3).

  According to the present invention, it becomes possible to efficiently remove the contaminants from the membrane module even during normal operation, and it is possible to continue stable operation for a long period of time and to reduce the frequency of chemical cleaning. Therefore, the amount of chemicals to be used can be reduced, and low processing cost operation can be realized.

It is an apparatus schematic flowchart which shows an example of the membrane filtration apparatus with which this invention is applied. It is an apparatus general | schematic flowchart which shows another example of the membrane filtration apparatus with which this invention is applied.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings, taking as an example a filtration device for a pressurized hollow fiber membrane module. However, the scope of the present invention is not limited to these.

  FIG. 1 is an apparatus schematic flowchart showing an example of a membrane filtration apparatus to which the present invention is applied.

  In normal membrane filtration operation, the water to be treated in the membrane module 1 is continuously supplied from the water pipe 2 to be treated to the primary side of the membrane module 1 by the treated water supply pump 3. The membrane is filtered to the secondary side of the membrane module 1 by the membrane. Since the membrane filtration flux is determined by the amount of water to be treated supplied to the primary side of the membrane module 1, the amount of water to be treated is adjusted by the degree of opening and closing of the water valve 4 to be treated. The filtrate obtained by membrane filtration in the membrane module 1 then flows into the filtrate tank 7 through the filtrate pipe 5 and the filtrate valve 6, and the filtrate is stored (membrane filtration step).

  After the membrane filtration step, the treated water supply pump 3 is stopped, the treated water valve 4 and the filtered water valve 6 are closed, and physical cleaning is started. In backwashing, filtered water is usually used as washing water, and the washing water is supplied from the backwashing water pipe 8 to the secondary side of the membrane module 1 by the backwashing pump 9 and accumulated on the membrane surface and inside the membrane. Remove dirt material. In general, the backwashing flux is about 1 to 2 times the membrane filtration flux, and the amount of washing water supplied to the membrane module 1 is adjusted by the degree of opening and closing of the backwashing valve 10. The backwashing is performed while opening the backwash drain valve 12 and discharging the backwash drainage through the backwash drain pipe 11 to the outside of the system. In addition, an oxidizing agent such as sodium hypochlorite or an acid such as sulfuric acid may be added to the backwash water in order to efficiently remove dirt substances on the membrane surface and inside the membrane. Moreover, the same effect can be expected even if the backwash water is heated. The warming of the backwash water is preferably about 30 to 40 ° C. by providing heating equipment such as a heater in the filtered water tank 7 or the backwash water pipe 8.

  Subsequently, air washing such as supplying a gas such as air from the lower part of the membrane module 1 into the membrane module 1 to wash the membrane surface is performed. A gas such as air is preferably supplied from the treated water supply pipe 2 or the drain pipe 13. In addition, there is no problem with empty washing separately from backwashing at any timing before or after backwashing or simultaneously with backwashing. The simultaneous implementation that can be expected to have both the effect of removing and shaking off the suspended solids by air washing is a preferred mode.

  After the physical cleaning is completed, the cleaning waste water remaining in the membrane module 1 is discharged outside the system through the drain pipe 13 by opening the drain valve 14.

  After draining the washing wastewater from the membrane module 1, normally the drainage valve 14 is closed and the membrane filtration process is restarted, but the backwash drainage valve 12 is opened and flushing is performed for several seconds to several tens of seconds. The membrane filtration process may be resumed. By performing the flushing for several seconds to several tens of seconds, it becomes possible to discharge the contaminants remaining on the primary side of the membrane module 1 out of the system of the membrane module 1. Here, the flushing is a cleaning method that removes deposits between the membrane surface and the membrane by flowing water to be treated into the membrane module at a high flux.

  The chemical cleaning performed after the normal membrane filtration operation is continued for a long time is performed in the membrane module 1 from the chemical storage tank (not shown) from the primary or secondary side of the membrane module 1 by the chemical supply pump (not shown). When the primary side and the secondary side in the membrane module 1 are filled with chemicals, the supply is stopped and immersed for several hours, or the chemical storage tank (from the primary side or secondary side of the membrane module 1 ( The chemical is supplied into the membrane module 1 by a chemical supply pump (not shown) from the not shown), the chemical discharged from the membrane module 1 is returned again to the chemical storage tank, and the chemical discharged from the membrane module 1 is again supplied. The operation of supplying the membrane module 1 is continued for several hours (the case where the chemical is circulated is also included in the “immersion” of the present invention). In addition, if the chemical | medical agent supplied to a membrane module is heated, the cleaning effect can be expected further. It is preferable that the chemical is heated to about 30 to 40 ° C. by providing a chemical storage tank (not shown) or a heating facility such as a heater in the pipe. In addition, a method of intermittently supplying a gas such as air from the lower part of the membrane module 1 while immersing the chemical to promote scraping off of the dirt substance adhering to the membrane surface is also preferably used. After the membrane in the membrane module 1 is sufficiently washed with chemicals, the drain valve 14 is opened, and the cleaning chemical on the primary side of the membrane module 1 is discharged out of the membrane module 1 through the drain pipe 13. To do. Further, a method of supplying a gas such as air from the lower part of the membrane module 1 at the time of discharging the chemicals and promoting the scraping of the dirt substance adhering to the membrane surface is also preferably used.

  In the membrane filtration operation, the membrane filtration operation is temporarily stopped once every 1 to 3 days, and the chemical cleaning using a chemical having a concentration of about 1/10 of the chemical concentration used in the above chemical cleaning is performed. May be implemented. The chemical cleaning is the same as the chemical cleaning described above except that the immersion time is shorter than that of the chemical cleaning described above and is about 15 to 30 minutes.

  Further, when the membrane filtration device is a device that further treats the filtered water of the membrane module 1 with a reverse osmosis membrane, such as a device used in seawater desalination or sewage reuse (so-called “MF / UF + RO”). In order to dilute chemicals when carrying out normal physical washing and flushing with concentrated water generated during treatment with reverse osmosis membranes and performing chemical washing, a method using fresh water obtained by treatment with reverse osmosis membranes It is also possible to adopt.

  In the present invention, after the chemical is discharged from the primary side of the membrane module 1 (that is, after the chemical cleaning step is completed), the rinsing step is performed as follows. The treated water is continuously supplied from the treated water pipe 2 to the primary side of the membrane module 1 by the treated water supply pump 3, and the membrane in the membrane module 1 is membrane filtered to the secondary side of the membrane module 1. Then, the chemical residual water inflow valve 16 is opened, and the filtered water in which the chemical remains in the chemical residual water tank 17 is stored through the chemical residual water inflow pipe 15. In this operation, the pH in the membrane module 1, the oxidation-reduction potential (ORP), and the water quality such as residual chlorine concentration are normal values (standard values are pH: 6.5 to 8.0, ORP: +200 to +700 mV, residual chlorine Concentration: 0.1 mg / L or less) and when it reaches a normal value, the chemical residual water inflow valve 16 is closed, the filtered water valve 6 is opened, and the filtered water is stored again in the filtered water tank 7. .

  By carrying out the rinsing step as in the present invention, it is not necessary to use filtered water that is generally used as rinsing water for chemical cleaning. The ratio of the amount of filtered water that can be used as product water) can be increased, and added to the rinse water to bring the pH, ORP, residual chlorine concentration, etc. in the membrane module 1 to normal values in a short time. This eliminates the use of neutralizing agents and reducing agents that can be used, and can contribute to a reduction in processing costs.

  In addition, when a dirt substance adhered to the membrane surface remains on the primary side of the membrane module 1 at the end of the chemical cleaning process, the dirt substance adheres to the membrane surface again during the rinsing process of the present invention. Therefore, it is only necessary to open the backwash drain valve 12, perform flushing for several seconds to several tens of seconds, and then start storing chemical residual water in the chemical residual water tank 17. By performing the flushing for several seconds to several tens of seconds, it becomes possible to prevent the reattachment of the dirt substance that has adhered to the membrane surface remaining on the primary side of the membrane module 1 to the membrane surface. Furthermore, by supplying air from the lower part of the membrane module 1 at the time of the flushing, the remaining dirt substance can be efficiently discharged out of the membrane module 1, and the flushing time can be shortened, which is a preferable mode. .

  By the way, for the purpose of discharging dirt substances adhering to the membrane surface remaining on the primary side of the membrane module 1 from the primary side of the membrane module 1, the secondary side of the membrane module 1 is transferred to the filtered water tank 7. A method of supplying the treated water to the membrane module 1 after supplying the stored filtered water as cleaning water for several seconds to several tens of seconds and discharging the cleaning water through the backwash drainage pipe is conceivable. However, since the filtrate is consumed in a small amount, the recovery rate of the filtrate is lower than that of the present invention, leading to an increase in the processing cost.

  After the chemical cleaning is completed and the process returns to the normal process (repetition of membrane filtration and physical cleaning), in the present invention, the chemical residual water stored in the chemical residual water tank 17 is stored during the chemical cleaning. The chemical residual water supply pump 19 supplies the secondary side of the membrane module 1 through the chemical residual water supply pipe 18 for a certain period of time and discharges the backwash drainage from the system through the backwash drain pipe 11. To do. The supply amount of the chemical residual water to the membrane module 1 is adjusted by the degree of opening / closing of the chemical residual water supply valve 20.

  Subsequent to the air washing performed in the same manner as described above, there is no problem if it is carried out at any timing before or after the back washing, or simultaneously with the back washing. The simultaneous implementation that can be expected to have both the effects of removing the dirt accumulated in the interior and shaking off the suspended solids by rinsing is a preferred mode.

  In addition, since the amount of chemical residual water is limited, it is not used in the initial stage after chemical cleaning, but backwashing with filtered water is performed for a certain period of time, and then dirt substances accumulate on the membrane surface and in the membrane. At this point, backwashing using chemical residual water may be performed. In addition, when performing backwashing with filtered water, an oxidizing agent such as sodium hypochlorite or an acid such as sulfuric acid may be added to the washing water in order to efficiently remove the contaminants on the membrane surface and inside the membrane. However, in order to reduce the processing cost, it is preferable not to add an oxidizing agent or an acid.

  Regardless of which method is employed, filtered water in which chemicals remain during backwashing can be used, so that the membrane module 1 can be efficiently used from the normal process without adding new chemicals or even in a reduced state. This makes it possible to delay the time for starting chemical cleaning as compared to membrane filtration operation by backwashing using filtered water.

  Here, when a relatively high concentration of chemical residual water can be stored in the chemical residual water tank 17, in addition to the back washing method shown in FIG. 1, the chemical residual water is washed with filtered water as shown in FIG. A method of adding to is also applicable. In this method, the consumption amount of chemical residual water in one backwash can be reduced.

  In the present invention, the chemical used for chemical cleaning is selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, citric acid, ascorbic acid, sodium hydroxide, sodium hypochlorite, hydrogen peroxide, and a surfactant. It is preferable that it is a chemical | medical agent containing 1 or more types chosen. If these chemicals are used, it is possible to dissolve or decompose inorganic substances and organic substances contained in the water to be treated, and it is possible to continue the stable operation of the membrane module 1 for a long period of time.

  In addition, as a method for cleaning the membrane module 1 using chemicals, it is also preferable to use two different types of chemicals and continuously perform cleaning with each chemical. The method is not particularly limited. For example, the membrane module 1 is prepared by dissolving or decomposing organic matter-derived contaminants accumulated on the membrane surface and in the membrane by first washing with sodium hypochlorite. There is also a method of discharging out of the system of the membrane module 1 and then dissolving or decomposing the inorganic material-derived soil substances accumulated on the surface of the membrane and in the membrane by washing with citric acid and discharging it out of the system of the membrane module 1. Furthermore, when cleaning with a chemical is performed, it is more preferable to maintain the state after all the membrane module 1 is filled with cleaning water containing the chemical, that is, to perform immersion for a certain period of time. Adopted. By performing cleaning using these methods, almost all of the contaminants derived from the water to be treated can be discharged out of the membrane module 1, and the membrane module 1 can be stably operated for a long time. Is possible. In this way, when performing chemical cleaning using two different types of chemicals, two chemical residual water tanks 17 may be installed, each chemical residual water may be stored, or one chemical residual water tank 17 may be stored. It may be installed to store any chemical residual water.

  Examples of the shape of the membrane module 1 used in the present invention include a hollow fiber membrane, a tubular membrane, and a flat membrane. Here, the hollow fiber membrane refers to a cylindrical separation membrane having a diameter of less than 2 mm, and the tubular membrane refers to a tubular separation membrane having a diameter of 2 mm or more. In the present invention, any shape membrane module may be used, but it is sufficiently more than a flat membrane shape membrane module which is generally a structure that cannot be backwashed with a high membrane filtration flux. It is preferable to use a hollow fiber membrane or a tubular membrane membrane module that can be backwashed with a high membrane filtration flux because the surface of the membrane and the contaminants in the membrane are easily dissolved or decomposed during chemical cleaning.

  The separation membrane may be any membrane from the gist of the present invention, but in general, a microfiltration membrane or an ultrafiltration membrane used for turbidity is preferred.

  The material of the membrane used for the microfiltration membrane and the ultrafiltration membrane is not particularly limited, but polyacrylonitrile, polyphenylene sulfone, polyphenylene sulfide sulfone, polyvinylidene fluoride, polypropylene, polyethylene, polysulfone, polyvinyl alcohol, cellulose acetate, ceramic, etc. It is preferable that at least one selected from the group consisting of these inorganic materials is included. Further, from the viewpoint of film strength and chemical resistance, a resin film mainly composed of polyvinylidene fluoride is more preferable.

  The pore diameter on the membrane surface is not particularly limited, but can be appropriately selected within the range of 0.001 μm to 1 μm.

  The treated water in the present invention is not particularly limited, and may be any water such as river water, lake water, ground water, industrial water, municipal sewage, industrial wastewater, etc. Water that has been subjected to treatment such as precipitation, filtration, adsorption, or biological treatment may also be used.

  Three pressure-type membrane modules (HFU-2008 manufactured by Toray Industries, Inc.) made of polyvinylidene fluoride hollow fiber UF membrane having a nominal molecular weight cut off of 150 kDa were prepared and shown in FIG. Membrane filtration operation was performed using a flow membrane filtration device. In addition, in the implementation of the examples and comparative examples, surface water with a turbidity of 2 to 3 NTU was used as raw water. In Examples and Comparative Examples, the membrane filtration operation is temporarily stopped once / day, and 300 mg / L sodium hypochlorite is supplied from the secondary side of the membrane module. Supply was continued until the secondary side and the secondary side were filled with sodium hypochlorite. After the supply of sodium hypochlorite was stopped, chemical cleaning was performed in which the membrane module was immersed for 20 minutes.

  <Example 1> After performing chemical cleaning with sodium hypochlorite performed once a day, sodium hypochlorite on the primary side of the membrane module is discharged out of the system of the membrane module. Treated water was supplied to the primary side of the membrane module, membrane filtration was resumed, and filtered water was stored in the chemical residual water tank until the residual chlorine concentration became 0.1 mg / L or less. Then, by continuing the membrane filtration operation, filtered water was stored in the filtered water tank, and after filtration was continued for 30 minutes, backwashing was performed for 1 minute using sodium hypochlorite-containing water stored in the chemical residual water tank. . After that, washing with air was performed for 1 minute, and washing waste water was discharged from the inside of the membrane module. Thereafter, the water to be treated was supplied to the membrane module, and the membrane filtration operation was started again.

  As a result, the water permeability of the membrane module two months after the start of operation was 63.8% of the initial value ratio. Moreover, the recovery rate of the filtrate at that time was 99.6%.

  <Example 2> After performing chemical cleaning with sodium hypochlorite carried out once / day as in Example 1, the sodium hypochlorite on the primary side of the membrane module was replaced with the membrane module system. The water to be treated was supplied to the primary side of the membrane module, the membrane filtration was resumed, and the filtrate was stored in the chemical residual water tank until the residual chlorine concentration became 0.1 mg / L or less. After that, filtered water is stored in the filtered water tank by continuing the membrane filtration operation, and after filtration is continued for 30 minutes, the sodium hypochlorite-containing filter stored in the chemical residual water tank is stored in the filtered water stored in the filtered water tank. Backwashing was carried out for 1 minute using water supplied to 1/10 of the backwashing supply. Then, it washed with air for 1 minute and discharged | emitted washing waste_water | drain from the inside of a membrane module. Thereafter, the water to be treated was supplied to the membrane module, and the membrane filtration operation was started again.

  As a result, the water permeability of the membrane module 2 months after the start of operation was 42.5% of the initial value ratio. Moreover, the recovery rate of the filtrate at that time was 96.4%.

  <Comparative Example 1> After performing chemical cleaning with sodium hypochlorite performed once / day, sodium hypochlorite on the primary side of the membrane module is discharged out of the membrane module and filtered. A rinsing process in which the filtered water stored in the water tank was pumped from the secondary side to the primary side of the membrane module was performed, and the rinsing process was continued until the residual chlorine concentration in the rinsing water reached 0.1 mg / L. Thereafter, the membrane filtration operation was resumed, and filtration was continued for 30 minutes, and then backwashing was performed for 1 minute using the filtrate stored in the filtrate tank. After that, washing with air was performed for 1 minute, and washing waste water was discharged from the inside of the membrane module. Thereafter, the water to be treated was supplied to the membrane module, and the membrane filtration operation was started again.

  As a result, the water permeability of the membrane module after 2 months from the start of operation was 23.7% of the initial value ratio. Moreover, the recovery rate of the filtrate at that time was 90.3%.

  From the above, the initial value ratio of the water permeability of the membrane module 2 months after the start of operation in Examples 1 and 2 and the recovery rate of filtrate water are both the initial values of the water permeability of the membrane module 2 months after the start of operation in the comparative example. It was shown to be superior to the value ratio and the recovered rate of filtered water. In addition, among the examples, the example in which the chemical residual water is used as it is for the backwash water is more effective than the example in which the chemical residual water is added to the backwash water using the filtered water. Both are excellent.

  The present invention is a method for cleaning membrane modules efficiently and at low processing costs in the field of water purification in waterworks, the field of industrial water production such as industrial water, food, and medical processes, and the field of sewage such as sewage and industrial wastewater. Can be used.

1: membrane module 2: treated water pipe 3: treated water supply pump 4: treated water valve 5: filtered water pipe 6: filtered water valve 7: filtered water tank 8: backwash water pipe 9: backwash pump 10: Backwash valve 11: Backwash drain pipe 12: Backwash drain valve 13: Drain pipe 14: Drain valve 15: Chemical residual water inlet pipe 16: Chemical residual water inlet valve 17: Chemical residual water tank 18: Chemical residual water supply pipe 19 : Chemical residual water supply pump 20: Chemical residual water supply valve 21: Check valve

Claims (4)

  A membrane module cleaning method in a membrane filtration method in which water to be treated is subjected to membrane filtration with a membrane module to obtain filtered water, wherein a primary side and a secondary side of the membrane module are immersed in a cleaning chemical. The primary side cleaning chemical is discharged out of the system of the membrane module, the water to be treated is supplied to the membrane module, the membrane filtration is restarted, and the filtrate water at the beginning of the membrane filtration restart is stored in the chemical residual water tank, The membrane module cleaning method, wherein the filtered water stored in the chemical residue water tank is used at the time of reverse pressure water cleaning in which cleaning water is pumped from the secondary side to the primary side of the membrane module. .   The membrane module cleaning method according to claim 1, wherein before the membrane filtration is restarted, the primary side of the membrane module is flushed with the water to be treated.   The method for cleaning a membrane module according to claim 2, wherein when flushing the primary side of the membrane module with the treated water, air is supplied to the primary side of the membrane module.   The water mixed with the filtered water at the initial stage of resuming the membrane filtration stored in the chemical residual water tank and the normal filtered water stored in the filtered water tank is used at the time of reverse pressure water cleaning. The method for cleaning a membrane module according to any one of the above.

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