JP2006043507A - Hollow fiber membrane module filter system of water tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the hollow fiber membrane module filter system of a water tank using a hollow fiber membrane module having hollow fiber membranes having a relatively large pore size, capable of being miniaturized and capable of easily keeping the disinfection of stored water. <P>SOLUTION: Since stored water is filtered by the hollow fiber membrane module A which has the hollow fiber membranes having the relatively large pore size and water passing resistance is low, the filtering of a large flow amount of water becomes possible and the miniaturization of the hollow fiber membrane module filter system can be achieved. Since a disinfectant is supplied to the water tank even during physical washing or chemical washing by bypassing a raw liquid at the time of physical washing or chemical washing, the disinfection of stored water can be kept easily. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hollow fiber membrane module filtration system having a module made of a hollow fiber membrane having a relatively large pore diameter and circulatingly filtering the water stored in the water storage tank, and more particularly, to a water storage tank during physical cleaning of a hollow fiber membrane and chemical cleaning. To disinfectant injection into

  2. Description of the Related Art Conventionally, devices that use cartridge (pincushion) filtration in addition to sand filtration and diatomaceous earth filtration are known as devices for filtering water stored in water storage tanks such as pools, baths, and jet baths. However, each filtration device has a problem that sand filtration requires a large amount of water for backwashing, diatomite filtration is troublesome to wash, and cartridge (pincushion) filtration has a short lifespan. There is also a problem of waste disposal. On the other hand, in recent years, the technique of separation operation using a separation membrane having selective permeability has been remarkably advanced, and an apparatus for treating pool water or the like using a separation membrane such as a hollow fiber membrane is known (for example, And Patent Documents 1 to 3).

A system using a separation membrane such as a hollow fiber membrane has the following advantages. That is, (a) Since the separation accuracy is sharp, a stable filtrate is obtained regardless of the quality of raw water, and the safety is high. (B) Less troublesome maintenance such as sand replacement and less waste. (C) In the case of sand filtration, a coagulation sedimentation process is required to improve the fractionation accuracy, but in the case of membrane filtration, the coagulation sedimentation process can be omitted or simplified, and the system can be saved in space. And simplification of processing steps. (D) Since the filtrate recovery rate is high and the backwash wastewater is small, the backwash waste liquid treatment is simplified.
JP 59-206091 A JP-A-8-323396 JP 2000-5582 A

  However, in a system using a conventional separation membrane in which a microfiltration membrane having a fractional particle size of 0.2 μm or less or an ultrafiltration membrane of 1 μm or less is the mainstream, the membrane area is increased in order to treat a large amount of water. There is a problem that the system is increased in size and cost.

  On the other hand, in the process of filtration using a separation membrane, the permeation flow rate decreases with time due to contamination of the membrane surface called clogging or clogging of micropores. On the other hand, it is necessary to periodically perform physical cleaning such as gas backwashing and chemical cleaning such as acid.

  Further, in the filtration of pool water, it is necessary to supply a disinfectant such as sodium hypochlorite so as to maintain the chlorine concentration for sterilization. However, in the above physical cleaning and chemical cleaning, the membrane filtration is stopped. However, since the disinfectant supply port is usually provided in the membrane filtration line, the disinfectant supply is also stopped and the physical cleaning is performed. There is also a problem that it is difficult to maintain a chlorine concentration for disinfecting pool water during chemical cleaning.

  In view of the above-described problems, the present invention provides a hollow storage tank that allows a system to be miniaturized using a hollow fiber membrane module having a hollow fiber membrane having a relatively large pore diameter and that can easily maintain disinfection of stored water. An object is to provide a thread membrane module filtration system.

The hollow fiber membrane module filtration system for a water storage tank according to the present invention includes a module made of a porous hollow fiber membrane having a fractional particle diameter of 1 to 10 μm, and circulates and filters the water stored in the water storage tank through the module. The filtration is stopped every predetermined time, and the hollow fiber membrane is physically and chemically washed. When the filtration is stopped and the physical or chemical washing is performed, the water storage is not performed via the hollow fiber membrane module. A water storage bypass device that circulates and supplies a disinfectant to the water tank is provided. As used herein, the fractional particle size refers to the particle size (S) of particles having a rejection rate of 90% due to the hollow fiber membrane, and measures the rejection rate of at least two types of particles having different particle sizes, Based on the measured value, in the following approximate expression (1), the value of S at which R is 90 is obtained, and this is the fractional particle diameter.
R = 100 / (1−m × exp (−a × log (s))) (1)
In the above formula (1), a and m are constants determined by the hollow fiber membrane, and are calculated based on measured values of two or more types of rejection.

  The fractional particle diameter of the hollow fiber membrane is important to be in the range of 1 to 10 μm and preferably in the range of 2 to 5 μm from the viewpoint of enabling filtration at a large flow rate and reducing the size of the apparatus.

  According to this configuration, the stored water is filtered by the hollow fiber membrane module having a hollow fiber membrane having a relatively large pore diameter, so that the water flow resistance is small, so that a large flow rate can be filtered and the apparatus can be downsized. Since the disinfectant is supplied to the water storage tank even during the physical cleaning and chemical cleaning, it becomes possible to easily maintain the disinfection of the water storage.

  The material of the hollow fiber membrane of the present invention is not particularly limited. For example, a polysulfone resin hydrophilized with a polyvinyl alcohol resin, a polysulfone resin to which a crosslinked or non-crosslinked hydrophilic polymer is added, and a polyvinyl alcohol resin. Examples thereof include resins, polyacrylonitrile resins, cellulose resins, hydrophilic polyolefin resins, and fluorine resins.

  From the viewpoint of the mechanical properties of the hollow fiber membrane and the membrane area as a module, the outer diameter of the hollow fiber membrane is preferably set in the range of 200 to 3000 μm, and more preferably in the range of 500 to 2000 μm.

  The thickness of the hollow fiber membrane is preferably in the range of 50 to 700 μm, and more preferably in the range of 100 to 600 μm.

  A method for producing the above porous hollow fiber membrane will be described. This manufacturing method is realized by improving and devising the composition of the stock solution based on the technology of the manufacturing method of the hollow fiber membrane according to Japanese Patent Application Laid-Open No. 2002-79066 by the applicant. This method for producing a porous hollow fiber membrane has an average particle diameter of 1 which is insoluble in the common solvent and the base polymer of the material constituting the porous hollow fiber membrane, the additive, these common solvents and the common solvent. A step of forming a hollow fiber by a dry-wet spinning method or a wet spinning method using a stock solution composed of fine powder of ˜20 μm and an injection solution for forming a hollow fiber, and dissolving the base polymer in the hollow fiber after spinning First, it is produced by a method including a step of immersing the fine powder in an extract that dissolves the fine powder and extracting and removing the fine powder.

  The concentration of the base polymer is determined in a range where sufficient strength can be obtained as a hollow fiber membrane and through-holes can be formed. Although it varies depending on the type of the base polymer, it is generally 5 to 40 wt%, preferably 15 to 25 wt%.

  By adding the additive, a hollow fiber membrane having a large pore diameter can be obtained by promoting phase separation of the stock solution. The additive may be liquid or solid, for example, water, glycols such as ethylene glycol, propylene glycol and polyethylene glycol, esters such as methyl acetate and ethyl acetate, alcohols such as ethanol, propanol and glycerin, butanediol and the like. Examples thereof include inorganic salts such as diols, lithium chloride and magnesium sulfate, and mixtures thereof. The amount of additive varies depending on the type of additive, but phase separation occurs when only the base polymer, additive, and a common solvent for both are dissolved, but mixing this with fine powder suppresses phase separation. The added amount is preferably a uniform stock solution that can be spun.

  There are no particular restrictions on the type of common solvent as long as it can dissolve both the base polymer and the additive. For example, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, N-vinylpyrrolidone, dimethyl Examples thereof include sulfoxide and sulfolane.

  Examples of fine powders insoluble in common solvents include metal oxides such as silicon oxide, zinc oxide and aluminum oxide, metal fine particles such as silicon, zinc, copper, iron and aluminum, sodium chloride, sodium acetate, sodium phosphate and calcium carbonate. Examples thereof include inorganic compounds such as calcium hydroxide. Depending on the type of base polymer, additive, etc., the type and amount of fine powder may be appropriately determined. It is preferable to select a fine powder that has a strong intermolecular force between the fine powders in the solution and easily causes an aggregating action. Among these, silicon oxide fine powder (silica powder) is commercially available with a small average particle diameter and various particle diameters, and is best in that it is easy to disperse in the spinning dope and has cohesive properties. The average particle size of the fine powder is preferably in the range of 1 to 20 μm, and more preferably in the range of 2 to 10 μm. When the average particle size of the fine powder is less than 1 μm, it is difficult to obtain a hollow fiber membrane having a large fractional particle size. When a large fine powder having an average particle size exceeding 5 μm is used, the agglomeration action of the fine powders becomes weaker as the average particle size increases, so that it becomes easier to form a heterogeneous hollow fiber membrane with large voids. Become a trend. For this reason, it is necessary to make preparations such as appropriately mixing particles having a small average particle diameter or increasing the amount added to more effectively utilize the agglomeration action of the fine powder. Here, “insoluble” means that the solubility is 0.1 g (fine powder) / 100 cc (solvent) or less at the dissolution temperature of the spinning dope.

  The spinning dope having the above composition is usually defoamed and then discharged from a nozzle having a double ring structure, and then immersed in a coagulation bath to form a hollow fiber membrane. As for the film forming method, the spinning solution discharged from the nozzle is directly passed through the coagulation bath even in the dry-wet spinning method in which the spinning solution discharged from the nozzle is once passed through a certain length of air and then introduced into the coagulation bath. Any of the wet spinning methods introduced into the inside may be used. The dry / wet spinning method is preferable in that the outer surface structure of the hollow fiber membrane can be easily controlled and a hollow fiber membrane having high water permeability can be produced.

  In spinning the hollow fiber membrane, an injection solution is usually introduced inside the double ring structure nozzle for the purpose of maintaining the shape of the spinning solution discharged from the nozzle in a hollow fiber shape. The inner surface structure of the hollow fiber membrane can be controlled by controlling the coagulation rate of the injection solution. The injection solution is not particularly limited as long as it is miscible with the solvent of the stock solution and has a coagulation ability with respect to the base polymer. Water, an aqueous solution of water and a solvent, alcohols, glycols, esters, water and a solvent Of the mixture. Also, by adding a water-soluble hydrophilic polymer such as polyvinyl alcohol or polyvinyl pyrrolidone to the injection solution, the hydrophilic polymer is coated on the inner surface of the hollow fiber membrane or the entire hollow fiber membrane by diffusion in the coagulation stage. It is possible. As the coagulation liquid, a liquid having the same composition as the injection liquid is used.

  In the dry-wet spinning method, the outer surface structure of the hollow fiber membrane obtained is determined by the length, temperature, humidity, etc. of the dry zone. When the length of the dry zone is increased or the temperature or humidity of the dry zone is increased, the phase separation proceeds and the pore diameter of the micropores formed on the outer surface tends to increase. Even if the length of the dry zone is short, for example, 0.1 cm, a hollow fiber membrane having an outer surface structure completely different from that obtained by the wet spinning method without passing through the dry zone can be obtained. Note that if the dry zone is too long, spinning stability is affected, and therefore it is usually set in the range of 0.1 to 200 cm, preferably 0.1 to 50 cm.

  The hollow fiber membrane coagulated in the coagulation bath contains a common solvent, additives and a large amount of fine powder. These are removed from the hollow fiber membrane during the spinning process or once wound up by the following operation. First, the common solvent and additives remaining in the hollow fiber membrane are extracted and removed by washing with water or washing with warm water at 40 to 90 ° C. When the hydrophilic polymer remains in the hollow fiber membrane, the hydrophilic polymer is physically or scientifically cross-linked as necessary after the above washing operation. A known cross-linking method may be selected as the cross-linking structuring method depending on the type of the hydrophilic polymer. For example, when the hydrophilic polymer is polyvinyl alcohol, a method of acetalizing with an aldehyde such as glutaraldehyde in the presence of a sulfuric acid catalyst is convenient.

  Next, the fine powder remaining in the hollow fiber membrane is extracted and removed with an extraction solvent that dissolves the fine powder but does not dissolve the base polymer of the hollow fiber membrane. Micropores are formed in the trace of the powder being extracted and removed. The extraction conditions for the fine powder must be set so that 95% or more, preferably 100%, of the fine powder is extracted. Since the fine powder is present in the polysulfone matrix, it varies depending on the type of fine powder and the solubility of the extraction solvent, but it is set to be much stricter than the dissolution conditions of the fine powder alone, and the extraction temperature and solvent concentration are increased. Moreover, it is necessary to lengthen the extraction time. For example, in the case of extracting silicon oxide, a hollow fiber membrane is used under the condition that 5 to 20% by weight sodium hydroxide aqueous solution is used as an extraction solvent, the extraction temperature is 60 ° C. or more, and the extraction time is 30 minutes or more. It is necessary to process. The fine powder may be extracted and removed by a spinning process, or may be performed in the state of the module after forming the hollow fiber as a module.

  The porous hollow fiber membrane according to the present invention has a fine porous structure such as a network structure, a honeycomb structure, or a fine gap structure. There may be a so-called finger-like structure or void structure inside the hollow fiber membrane. The fine porous structure inside the hollow fiber membrane determines the fractional particle size and the pure water permeation rate.

  The porous hollow fiber membrane produced as described above is dried after being wound, for example, on a frame or a cassette. A hollow fiber membrane module can be obtained by bundling a predetermined number of hollow fiber membranes after drying and storing the hollow fiber membranes in a case having a predetermined shape, and then fixing the ends with urethane resin, epoxy resin, or the like. The hollow fiber membrane module is a type in which both ends of the hollow fiber membrane are fixed open, the hollow fiber membrane is fixed so that one end of the hollow fiber membrane opens, and the other end is sealed but not fixed Various types are known, such as types. The hollow fiber membrane module is mounted on a filtration device and used for liquid separation and purification such as water purification.

  Examples of the filtration method using the hollow fiber membrane module used in the present invention include external pressure total filtration, external pressure circulation filtration, and internal pressure circulation filtration, and can be appropriately selected according to desired treatment conditions and treatment performance. From the viewpoint of membrane life, a circulation system capable of simultaneously cleaning the separation membrane surface is preferable, and a total filtration system is preferable from the viewpoint of simplicity of equipment, installation cost, and operation cost.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1: is a schematic block diagram and process chart which show the hollow fiber membrane module filtration system of the water tank which concerns on 1st Embodiment of this invention. This system circulates and filters the water (raw solution) of a water storage tank such as the pool W through the hollow fiber membrane module A. In addition to the hollow fiber membrane module A, the raw solution supply pump P1, the chemical solution supply pump P2, A disinfectant supply pump P3, valves AV1 to AV9, an air compressor 8, a hair catcher 9, a chemical tank 10 and a neutralization tank 11 are provided.

  A hollow fiber membrane module A shown in FIG. 2 is, for example, an external pressure total filtration type, and includes a plurality of hollow fiber membrane elements 1 and a housing (case) 2. The hollow fiber membrane module A is partitioned into a stock solution side S1 and a membrane filtrate water side S2 by a partition plate 7, and the stock solution side S1 has a stock solution introduction port 3, a gas discharge port 4, and a concentrated solution discharge port 5, The membrane filtrate side S2 is provided with a membrane filtrate outlet (also used as a pressurized gas inlet) 6 to filter the stock solution introduced from the stock solution inlet 3 and discharge the membrane filtrate from the membrane filtrate outlet 6 To do.

  A stock solution inlet valve AV1 is connected between the stock solution supply pump P1 and the stock solution introduction port 3, a gas discharge port AV3 and a chemical solution outlet valve AV8 are connected to the gas discharge port 4, and a concentrate discharge port valve AV4 is connected to the concentrate discharge port 5. And the chemical | medical solution outlet valve AV9 is connected. The chemical solution from the chemical solution outlet valves AV8 and AV9 is discharged to the chemical solution tank 10. A membrane filtrate outlet valve AV2 is connected to the membrane filtrate outlet 6, a pressurized gas inlet valve AV5 is connected between the membrane filtrate outlet (pressurized gas inlet) 6 and the air compressor 8, and the chemical solution supply pump P2 and the stock solution A chemical solution inlet valve AV7 is connected between the introduction ports 3. A chemical circulation device 15 is configured by the chemical liquid supply pump P2, the chemical liquid inlet valve AV7, the chemical liquid outlet valves AV8 and AV9, and the chemical liquid tank 10.

  A bypass line L1 is provided between the stock solution supply pump P1 and the membrane filtrate outlet valve AV2, and a bypass valve AV6 is provided in the bypass line L1. The water storage bypass device 17 according to the present invention includes the stock solution supply pump P1, the bypass line L1, and the bypass valve AV6.

The operation of this system will be described below based on the process chart of FIG.
Membrane filtration process
(No. 1) Water filling process From the state where all the valves are closed, the gas outlet valve AV3, the stock solution inlet valve AV1, and the membrane filtrate outlet valve AV2 are opened, and the stock solution supply pump P1 is operated. The stock solution of the pool W is separated into hairs and the like by the hair catcher 9 and then introduced into the stock solution side S1 of the hollow fiber membrane module A, and the stock solution overflows from the gas outlet valve AV3. The water filling is performed for several seconds, for example.
(No. 2) Filtration Step After the stock solution overflows from the gas outlet valve AV3, the gas outlet valve AV3 is closed and the filtration is started with the stock solution inlet valve AV1 and the membrane filtrate outlet valve AV2 open. Filtration is performed for about 30 minutes to 1 hour. For example, when a hollow fiber membrane module A having a fractional particle size of 2.5 μm is used, a filtration treatment with a membrane area of 0.5 to ² m ³ / H per 1 m ² can be performed.

  During this membrane filtration step (No.1-No.2), the disinfectant supply pump P3 is in operation, and a disinfectant such as sodium hypochlorite is added together with the membrane filtrate from the hollow fiber membrane module A. It is supplied in the pool W.

Physical washing (back washing) process
(No.3) Backwashing process As the filtration time elapses, dissolved substances and SS (suspension substances) adhere to the membrane surface of the hollow fiber membrane element 1 and the filtration capacity decreases. Stop and perform physical washing (back washing) of the hollow fiber membrane. That is, the stock solution inlet valve AV1 and the membrane filtrate outlet valve AV2 opened in the membrane filtration step are closed to stop the filtration, and then the gas outlet valve AV3 and the pressurized gas inlet valve AV5 are operated while the air compressor 8 is operated. open. Then, the pressurized air introduced into the membrane filtrate side S2 of the hollow fiber membrane is supplied with pressurized air having a pressure larger than the pressure that passes through the hollow fiber membrane and escapes to the stock solution side. Introduced into S2, gas back washing operation is performed for about 3 to 5 seconds, for example. In this example, gas (gas) backwashing is performed, but liquid backwashing using liquid (membrane filtered water) instead of gas, bubbling cleaning, or the like may be performed.
(No.4) Drainage process After backwashing, the pressurized gas inlet valve AV5 is closed, and then the concentrated liquid outlet valve AV4 is opened to discharge the concentrated liquid retained in the stock solution side S1 to the outside of the system. . This drainage is performed for about 30 seconds, for example.

  The disinfectant supply pump P3 is operating even during the physical cleaning process (No.3-No.4). In the present invention, the stock solution supply pump P1 continues to operate. During the physical cleaning process, the bypass valve AV6 is opened, and the stock solution is supplied and circulated directly to the pool through the bypass line L1 without passing through the hollow fiber membrane module A because the stock solution inlet valve AV1 is closed. At the same time, a disinfectant is supplied into the pool W by the disinfectant supply pump P3. Thereby, even during the physical cleaning, the disinfectant is supplied to the pool W, so that the stock solution (pool water) can be easily maintained.

(No.5) Repeat process The membrane filtration process and physical washing process (No.1-No.4) are repeated. This repeating step is performed, for example, about 5 to 50 times.

Chemical cleaning process
(No.6) Chemical solution circulation process Chemical cleaning is carried out by stopping the filtration every predetermined time when the hollow fiber membrane is clogged to some extent. That is, first, the chemical tank 10 is filled with a predetermined chemical such as oxalic acid at a predetermined concentration (0.5 to 5% by weight), then all the water in the hollow fiber membrane module A is discharged, and all the valves are closed. From the state, the chemical solution inlet valve AV7 and the chemical solution outlet valve AV8 are opened, the chemical solution supply pump P2 is started, the chemical solution is introduced into the raw solution side S1 of the hollow fiber membrane module A, overflows from the chemical solution outlet valve AV8, and returned to the chemical solution tank 10. Circulate for a predetermined time (for example, 15 minutes). Thus, since the chemical | medical agent used for washing | cleaning is used repeatedly, cost reduction can be achieved. At this time, the chemical liquid supply pump P2 is stopped, the chemical liquid inlet valve AV7 is closed to stop the circulation, and the immersion can be left standing for a predetermined time, or the circulation and the immersion still can be combined. is there. It is also possible to filter and wash a part or all of the chemical solution. Furthermore, it is also possible to carry out a combination of circulation and immersion standing and physical washing operations such as gas backwashing.

(No. 7) Liquid Discharge Step After the chemical liquid is circulated, the chemical liquid outlet valve AV9 is opened, and the chemical liquid from the concentrated liquid discharge port 5 is discharged to the chemical liquid tank 10. This draining is performed for about 30 seconds.

  During this chemical cleaning process (No.6-No.7), as in the physical cleaning process (No.3-No.4), the disinfectant supply pump P3 operates and the stock solution supply pump P1 continues to operate. is doing. During the chemical cleaning process, the bypass valve AV6 is opened and the stock solution is supplied and circulated directly to the pool W through the bypass line L1 without passing through the hollow fiber membrane module A because the stock solution inlet valve AV1 is closed. The disinfectant is supplied into the pool W by the disinfectant supply pump P3 together with the stock solution. Accordingly, since the disinfectant is supplied to the pool W even during the chemical cleaning, the stock solution (pool water) can be easily disinfected.

  As described above, in the present invention, even when physical cleaning or chemical cleaning is performed, the stock solution is bypassed and the disinfectant is injected, so that the chlorine concentration in the pool W can be maintained. Further, since the stock solution supply pump P1 is not stopped, pump failure due to repeated ON / OFF can be avoided.

(No. 8) Repeating Steps The chemical cleaning effect may be increased by repeating the chemical solution circulation step and the draining step (No. 6-No. 7), for example, two or more times.

  Various chemicals known in the art can be used as the chemicals used in the chemical cleaning step, and can be appropriately selected according to the membrane adhesion substance to be removed and the chemical resistance of the hollow fiber membrane module A. It is. For example, in acid chemicals, inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, etc. In addition to the aforementioned oxalic acid, organic acids include acetic acid, citric acid, ascorbic acid, etc., and alkaline chemicals include sodium hydroxide, Examples thereof include potassium hydroxide, examples of the oxidizing agent include hydrogen peroxide and sodium hypochlorite, and examples of the chelating agent include ethylenediaminetetraacetic acid and salts thereof. Various other cleaning agents can also be used.

  Conditions such as concentration of chemical used, contact time with hollow fiber membrane, temperature, etc., can be selected as appropriate depending on the type and amount of the substance adhering to the membrane, chemical used, chemical resistance of the hollow fiber membrane module, etc. It is.

  In the chemical cleaning step, for example, the chemical cleaning operation is performed under the above-described conditions, and then the chemical liquid in the hollow fiber membrane module is discharged. Thereafter, the chemical cleaning operation may be repeated again in the same manner. As the number of repetitions, any number can be selected from two or more times, and the first and second chemical cleaning times may be the same or different. For example, when circulating for 2 hours and / or standing soaked, for example, the chemical solution is once drained after 1 hour and then washed again for 1 hour. Thus, the cleaning effect can be remarkably improved. Further, for example, each chemical cleaning step may be the same operation or different operations, such as a chemical solution circulation in the first chemical cleaning operation and a stationary immersion in the second chemical operation.

  Furthermore, in the above chemical cleaning process, a chemical or high-concentration chemical solution is added as necessary and repeatedly used twice or more without discarding the chemical solution used for chemical cleaning once or more. Since it can be used for a long time without discharging the chemical solution for each cleaning, the amount of waste liquid can be greatly reduced.

  The chemical solution used for chemical cleaning generally consumes active ingredients when used for chemical cleaning, and the amount of dissolved and suspended substances increases and the cleaning performance decreases due to the migration of membrane-adhering substances into the chemical solution. To do. In this chemical cleaning method, the chemical liquid used for chemical cleaning once or more is repeatedly used twice or more without being discarded, but it is desirable to evaluate the cleaning ability of the chemical liquid by some method. Most directly, it can be judged by evaluating the recoverability in chemical cleaning. For example, pH (hydrogen ion concentration) for acid chemicals and alkaline chemicals, effective chlorine concentration for sodium hypochlorite, etc. It is also possible to make a judgment by performing an appropriate analysis accordingly. A chemical solution that has been used for chemical cleaning once or more and has deteriorated cleaning ability or reduced active ingredient concentration can be replaced with a new chemical solution. It is also possible to add and use them.

  When the chemical solution is repeatedly used in the chemical cleaning step (No. 6-No. 7), the chemical solution in the chemical solution tank 10 overflows in the (No. 7) draining step due to mixing of pool water into the chemical solution. There is a case. In this case, since the chemical solution is often an acid or an alkali, it is preferable to carry out a neutralization treatment in the neutralization tank 11 when discharging.

Physical washing (back washing) process
(No. 9) Backwashing process After chemical cleaning, the pressurized gas inlet valve AV5 and the chemical solution outlet valve AV8 are opened, and backwashing is performed in the same manner as described above.
(No. 10) Drainage step After backwashing, the pressurized gas inlet valve AV5 is closed, and then the chemical solution outlet valve AV9 is opened to discharge the concentrated solution remaining in the stock solution side S1 out of the system.
(No.11)
Return to (No.1) and repeat steps No.1-No.10. In order to dilute the acid or the like, if necessary (No. 10), a washing operation such as washing may be performed after the draining step.

  A series of steps such as membrane filtration, physical cleaning, and chemical cleaning described above can be automatically performed by performing sequence control with a control device. In addition, the membrane filtration process and the physical cleaning process can be repeated continuously by sequence control, and when the clogging becomes large, the chemical cleaning is manually performed. It is.

It is a schematic block diagram and process chart which show the hollow fiber membrane module filtration system of the water storage tank which concerns on one Embodiment of this invention. It is a schematic block diagram which shows the hollow fiber membrane module of FIG.

Explanation of symbols

A: Hollow fiber membrane module W: Pool 1: Hollow fiber membrane element 2: Case 3: Space portion 3: Stock solution inlet 4: Gas outlet 5: Concentrate outlet 6: Membrane filtrate outlet 8: Air compressor 10: Chemical tank 15: Chemical circulation device 17: Water storage bypass device

Claims (2)

A module comprising a porous hollow fiber membrane with a fractional particle size of 1 to 10 μm is provided, and the water stored in the water tank is circulated and filtered through the module, and the filtration is stopped at predetermined intervals to physically remove the hollow fiber membrane. Water tank filtration system for washing and chemical washing,
Reservoir hollow fiber membrane module filtration with a water storage bypass device that circulates water without going through the hollow fiber membrane module and supplies the disinfectant to the water tank when filtration is stopped and physical or chemical cleaning is performed system. In claim 1,
A hollow fiber membrane module filtration system for a water storage tank, wherein the porous hollow fiber membrane has a fractional particle diameter of 2 to 5 µm.

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