JP2005177744A - Producing apparatus of reclaimed water and producing method of reclaimed water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a producing apparatus of reclaimed water and a producing method of the reclaimed water by which a disinfectant can be effectively utilized by a simple method and thereby lowering of penetration performance and separation performance of a reverse osmosis membrane due to propagation of microorganisms or adhesion or the like of the microorganism and its metabolite on a reverse osmosis membrane surface can be effectively prevented. <P>SOLUTION: Water to be treated is filtered by using a dipping type membrane filtration apparatus equipped with a filtration membrane which is arranged by dipping in a treating tank and which filters the water to be filtered and a filtered water tank for storing filtered water obtained by filtration of the water to be treated with the filtration membrane and then the filtered water obtained by filtration is sterilized and is subjected to reverse osmosis treatment using the reverse osmosis membrane. In this producing method of the reclaimed water, a part of concentrated water obtained by the reverse osmosis treatment is returned to the filtered water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reclaimed water production apparatus and a reclaimed water production method. Specifically, the present invention relates to a reclaimed water production apparatus and a reclaimed water production method obtained by regenerating wastewater such as sewers and industrial wastewater.

  Conventionally, wastewater such as sewage and industrial wastewater has been constructed and treated with a sand filtration method, a coagulation sedimentation method, and chlorine addition as main processes. However, the sand filtration method and the coagulation sedimentation method require a large facility area, and depending on the raw water conditions, problems such as sufficient separation cannot be performed unless strict operation management is performed, have been highlighted. As a technique capable of eliminating the drawbacks, a membrane separation method, in particular, a submerged membrane separation method in which a membrane separation module including a membrane element and a membrane element case is immersed in water to be treated has been widely used.

  In addition, against the background of the water shortage problem, there is a growing movement to further process wastewater into reclaimed water and reuse this reclaimed water. As a method for purifying wastewater such as sewers and industrial wastewater, a method of further treating a filtrate obtained by a submerged membrane separation method with a reverse osmosis membrane has been proposed (for example, see Patent Document 1).

  However, in this method, some of the microorganisms present in the treated water pass through the membrane immersed in the treated water, or some of the metabolites of the microorganisms present in the treated water are in the treated water. Permeation performance and separation of reverse osmosis membranes by passing through the immersed membrane and using it as a nutrient source, such as microbial growth on the reverse osmosis membrane surface or adhesion of microorganisms and their metabolites to the membrane surface There was a disadvantage that it caused a decrease in performance.

On the other hand, in order to avoid such a problem, a membrane sterilization method characterized by having an acidic water treatment step in which the pH of the liquid supplied to the reverse osmosis membrane is 4 or less has been proposed (for example, Patent Documents). 2). However, in this method, part of the acidic water is not used for sterilization of microorganisms, but is discarded as part of the reverse osmosis membrane concentrated water and cannot be said to be used effectively.
JP-A-4-305287 JP 2000-237555 A

  The present invention solves the above-mentioned problems of the prior art and regenerates wastewater such as sewers and industrial wastewater to obtain reclaimed water that can be used as middle water such as water spray or toilet water, or as drinking water. It is possible to effectively use a bactericidal agent added to filtered water by a simple method, and the reverse osmosis membrane by the growth of microorganisms on the surface of the reverse osmosis membrane or the adhesion of microorganisms and their metabolites to the membrane surface. An object of the present invention is to provide a reclaimed water production apparatus and a reclaimed water production method capable of effectively preventing a decrease in permeation performance and separation performance.

In order to solve the above problems, the present invention adopts the following configuration. That is,
(1) A treatment tank, a filtration membrane for filtering the treated water immersed in the treatment tank, and a filtered water tank for storing the filtrate obtained by filtering the treated water through the filtration membrane are provided. A reclaimed water production apparatus comprising: a pump for taking out and pressurizing filtered water from the filtered water tank; a reverse osmosis membrane for reverse osmosis treatment of the pressurized filtered water; and a disinfectant adding device for sterilizing the filtered water; An apparatus for producing reclaimed water, comprising: the filtered water tank and / or a device for returning a part of the concentrated water obtained by reverse osmosis treatment of the filtered water between the filtered water tank and the pump. .

  (2) A filtration membrane for filtering the water to be treated immersed in the treatment tank and a filtration water tank for storing the filtered water obtained by filtering the water to be treated by the filtration membrane In the method for producing reclaimed water, which is filtered using a submerged membrane filtration device and sterilized filtered water obtained by filtration and then reverse osmosis treated using a reverse osmosis membrane, the concentration obtained by reverse osmosis treatment A method for producing reclaimed water, characterized in that a part of water is refluxed to filtered water.

  (3) The method for producing reclaimed water according to (2) above, wherein the ratio of the concentrated water that is refluxed to the filtered water is in the range of 10 to 50%.

  According to the present invention, it is possible to regenerate waste water such as sewage and industrial waste water, and to obtain reclaimed water that can be used as middle water such as water spray or toilet water, or as drinking water. It is possible to effectively use the fungicide added to the surface of the reverse osmosis membrane and effectively reduce the permeation and separation performance of the reverse osmosis membrane due to the growth of microorganisms on the surface of the reverse osmosis membrane or adhesion of microorganisms and metabolites to the membrane surface An apparatus for producing reclaimed water and a method for producing reclaimed water can be provided.

  Hereinafter, the manufacturing apparatus of the reclaimed water in this invention is demonstrated based on the embodiment shown in FIG.

  FIG. 1 is a schematic flow diagram showing one embodiment of the apparatus for producing reclaimed water according to the present invention.

  The reclaimed water production apparatus shown in FIG. 1 includes a filtration membrane 2 for filtering the treated water 1 to obtain filtered water, a treatment tank 3 for immersing the filtered membrane 2 in the treated water, and a filtration membrane 2. The filtered water tank 4 for storing the filtered water obtained by filtering the water 1 to be treated by the above, the pump 5 for taking out the pressurized water from the filtered water tank 4 and pressurizing it, and the reverse osmosis for performing the reverse osmosis treatment of the pressurized filtered water Between the membrane 6, the disinfectant addition device 7 for sterilizing the filtered water, and a part of the concentrated water obtained by reverse osmosis treatment of the filtered water between the filtered water tank 4 and the pump 5 for pressurizing the filtered water. And a recirculating pipe 8. Reclaimed water is obtained from 9 and discarded concentrated water is obtained from 10.

  Here, the filtration membrane 2 has a flat membrane element structure in which, for example, the filtration membrane is bonded to both sides of the frame with the filtration water channel material interposed therebetween in order to improve the handling property and physical durability of the filtration membrane. This structure is not particularly limited, and an element using a hollow fiber membrane may be used. However, the flat membrane element structure is effective in removing dirt due to shear force when a flow velocity parallel to the membrane surface is applied. Is suitable for the present invention. The flat membrane element structure includes a rotating flat membrane structure.

  Examples of the membrane structure of the filtration membrane 2 include a porous membrane and a composite membrane in which a functional layer is combined with the porous membrane, but is not particularly limited. Specific examples of these membranes include polyacrylonitrile porous membrane, polyimide porous membrane, polyethersulfone porous membrane, polyphenylene sulfide sulfone porous membrane, polytetrafluoroethylene porous membrane, polyvinylidene fluoride porous membrane, polypropylene Examples of the porous film include a porous film and a polyethylene porous film, and a polyvinylidene fluoride porous film and a polytetrafluoroethylene porous film are particularly preferable because of high chemical resistance. Furthermore, a composite film in which a rubbery polymer such as cross-linked silicone, polybutadiene, polyacrylonitrile butadiene, ethylene propylene rubber, or neoprene rubber is compounded as a functional layer can be given as a functional layer.

  The treatment tank 3 is not particularly limited as long as it can store the water to be treated and the filter membrane 2 can be immersed in the water to be treated, and a concrete tank, a fiber reinforced plastic tank, or the like is preferably used. Moreover, the inside of the treatment tank 3 may be divided into a plurality of tanks, and a part of the plurality of divided tanks may be used as a tank for immersing the filtration membrane 2 and the other may be used as a denitrification tank. May be circulated between the tanks divided from each other.

  The filtered water tank 4 is not particularly limited as long as it can store filtered water, and a concrete tank, a fiber reinforced plastic tank, or the like is preferably used. Moreover, in order to filter to-be-processed water with the filtration membrane 2, you may provide a pump etc. between the filtration membrane 2 and the filtration water tank 4, and in order to apply a head pressure difference, the filtration in the filtration water tank 4 is sufficient. The water level may be lower than the water level to be treated in the treatment tank 3.

  The pump 5 is not particularly limited as long as the filtered water can be pressurized, and is a centrifugal pump, a diffuser pump, a spiral mixed flow pump, a mixed flow pump, a piston pump, a plunger pump, a diaphragm pump, a gear pump, a screw pump, Vane pumps, cascade pumps, jet pumps, etc. can be used, but because they can be easily pressurized to the pressure required for reverse osmosis treatment, centrifugal pumps, diffuser pumps, piston pumps, plunger pumps, cascade pumps, jet pumps Etc. are preferably used.

  The reverse osmosis membrane 6 is not particularly problematic as long as it has a performance capable of reducing solutes and suspended substances in filtered water to a concentration that can be used as reclaimed water, but dissolved organic substances adhere to the membrane surface. A low-fouling reverse osmosis membrane that is resistant to chemical fouling (chemical fouling) and biofouling (biological fouling) in which microorganisms grow and adhere to the membrane surface using dissolved organic matter as nutrients is preferable. . Examples of low-fouling reverse osmosis membranes include TML20 manufactured by Toray Industries, Inc. and LF10 manufactured by Nitto Denko Corporation (the surface of the membrane is neutral, a hydrophilic group is introduced, adsorption of charged substances and heavy metals such as iron colloids) MFC), Hydranautic LFC1, LFC3, Dow BW30-365FR, and the like. In addition, if the concentration of solutes and suspended substances in filtered water is low, there is a particular problem even if a nanofiltration membrane that is a liquid separation membrane that blocks particles and polymers smaller than about 2 nm is used as a reverse osmosis membrane. Absent.

  The disinfectant addition device 7 is durable to the disinfectant and there is no particular problem as long as the disinfectant can be supplied quantitatively, and usually a hard vinyl chloride or polyethylene chemical tank and a diaphragm type or plan. A combination with a jar-type liquid metering infusion pump is used. The disinfectant addition device also includes a water electrolytic disinfection device that activates chlorine ions contained in filtered water to hypochlorite ions.

  The pipe 8 for returning a part of the concentrated water to the filtered water is not particularly problematic as long as it has durability against the sterilizing agent, and usually a pipe made of hard vinyl chloride or stainless steel is used. Moreover, it is preferable that a cock or a valve capable of controlling the flow rate is provided in the middle of the pipe 8 and / or on the concentrated water side to be discarded so that the ratio of the concentrated water to be recirculated can be arbitrarily set. The connection position of the pipe 8 for returning a part of the concentrated water obtained by reverse osmosis treatment of the filtered water to the filtered water is connected to the pipe between the filtered water tank 4 and the filtration membrane 2 and circulates to the filtered water. Alternatively, it may be connected to the filtered water tank 4 and recirculated to the filtered water, or may be between the filtered water tank 4 and the pump 5 for pressurizing the filtered water as shown in FIG.

  In the above-described reclaimed water production apparatus, reclaimed water is produced as follows.

  That is, the water to be treated treated in the treatment tank 3 is filtered by the filtration membrane 2 immersed in the treatment tank 3, and the filtered water is stored in the filtered water tank 4. In order to store the filtered water in the filtered water tank 4, the filtered water may be sucked using a pump or the like, and the filtered water level in the filtered water tank 4 is made lower than the treated water level in the processing tank 3. Therefore, it is possible to apply a water head pressure difference. The stored filtered water is pressurized by the pump 5 and supplied to the reverse osmosis membrane 6 after being added with the sterilizing agent by the sterilizing agent adding device 7, and is subjected to reverse osmosis treatment.

  Here, as the bactericidal agent, those having an effect of preventing microbial growth on the reverse osmosis membrane surface or adhesion of microorganisms and their metabolites to the membrane surface can be used. Organic acids, inorganic acids, sodium hypochlorite, chloramine, chlorine dioxide, ozone, hydrogen peroxide, formaldehyde, peracetic acid, sodium hydrogen sulfite and the like are preferable because they have a high bactericidal effect. As the organic acid or inorganic acid, sulfuric acid which is inexpensive and has a high bactericidal effect in a small amount is particularly preferable. Moreover, a bactericidal agent can also be used in mixture of several types. Mixing and using sulfuric acid and sodium hydrogen sulfite is also a preferred embodiment.

  The addition amount of the bactericide may be appropriately determined according to the type of bactericide, the bactericidal effect of the bactericide, and the durability of the reverse osmosis membrane with respect to the bactericide. When an organic acid or an inorganic acid is used as the bactericidal agent, the addition amount is preferably such that the pH of the filtered water is 4 or less, and in order to develop a high bactericidal effect, the addition amount is such that the pH is 3 or less. Is more preferable, but since the reverse osmosis membrane deteriorates even if the pH is too low, the addition amount is preferably such that the pH is 2 or more. When sodium hypochlorite is used, the amount of free residual chlorine is preferably 0.01 ppm or more in order to exhibit a bactericidal effect, but the reverse osmosis membrane deteriorates even if the concentration is too high. Therefore, the addition amount is preferably 1.0 ppm or less. When chloramine is used, it is preferable that the chloramine concentration is 0.1 ppm or more in order to exhibit a bactericidal effect, but the reverse osmosis membrane deteriorates even if the concentration is too high, so that it becomes 10 ppm or less. The addition amount is preferable. In the case of using a mixture of sulfuric acid and sodium hydrogen sulfite, in addition to the pH conditions in the case of using an organic acid or an inorganic acid as the bactericidal agent, sodium hydrogen sulfite is 10 ppm or more in order to develop a bactericidal effect. The addition amount is preferable, but since the reverse osmosis membrane deteriorates even if the addition amount is too large, the addition amount is preferably 1000 ppm or less.

  As a method for adding a bactericidal agent, either a method of constantly adding to filtered water or a method of adding intermittently can be used, but sulfuric acid, sodium hypochlorite, chlorine dioxide, ozone, hydrogen peroxide, etc. are used. In some cases, the intermittent addition method is preferable in order to make the reverse osmosis membrane difficult to deteriorate, and when chloramine is used, the method of always adding a high bactericidal effect is preferable.

  Of the filtered water that has been subjected to the reverse osmosis treatment, a part of the concentrated water is returned to the filtered water. By doing in this way, the disinfectant which remains in concentrated water can be used effectively, and the addition amount of a disinfectant can be reduced.

  Of the concentrated water, the ratio of reflux to filtered water is too high, but the reverse osmosis membrane permeation performance and separation due to microorganism growth on the surface of the reverse osmosis membrane or adhesion of microorganisms and their metabolites to the membrane surface. A decrease in performance is not preferable, and if it is too small, it is not preferable because the effect of reducing the addition amount of the bactericide is low. Concentrated water that has not been refluxed to other filtered water is discarded.

  Water produced by reverse osmosis treatment by the above method is used as reclaimed water.

Example 1
A composite flat membrane (polypore diameter 0.1 μm, thickness 200 μm, initial pure water permeability 4 × 10 ⁻⁸ m ³ / m ² / s / Pa) coated on a polyester nonwoven fabric with a polyvinylidene fluoride film on both sides of the frame Ten bonded flat membrane elements 2 (effective membrane portion: length 250 mm, width 200 mm, effective membrane area 0.1 m ² ) were immersed in the treatment tank 3 of the immersion membrane filtration apparatus shown in FIG. As treated water 1, artificial sewage composed of glucose 0.1 g / L, peptone 0.1 g / L, dipotassium hydrogen phosphate 7.8 mg / L, monopotassium phosphate 3.9 mg / L (biological oxygen demand) An amount (BOD) of 160 mg / L, a total nitrogen concentration of 13.6 mg / L, and a total phosphorus concentration of 2.3 mg / L were supplied to the treatment tank 3 at a rate of 550 L / day. The treated water was filtered by the flat membrane element 2 at a rate of 550 L / day and supplied to the filtered water tank 4. From the lower part of the flat membrane element 2, air was supplied at a rate of 200 L / min for biological treatment of water to be treated and to prevent microorganisms from adhering to the membrane surface of the flat membrane element 2. The filtered water was taken out from the filtered water tank 4 at a rate of 70 mL / min, pressurized to 1.0 MPa using the pump 5, and supplied to the reverse osmosis membrane 6 having an effective membrane area of 9.42 cm ² . 30% by weight sulfuric acid aqueous solution was intermittently added to the filtered water from the disinfectant addition device 7 at a rate of 0.050 mL / min for 24 minutes per day. 30 mL / min (30%) of the concentrated water obtained by the reverse osmosis treatment was refluxed between the filtered water tank 4 and the pump 5. The pH of the filtrate supplied to the reverse osmosis membrane 6 was 7.0 when the sulfuric acid aqueous solution was not added and 2.5 when it was added. The amount of reclaimed water obtained by reverse osmosis treatment at 25 ° C. was 0.8 g / min at the start of reverse osmosis treatment, but halved after 55 days.

Comparative Example 1
Concentrated water obtained by reverse osmosis treatment of Example 1 was operated without reflux between the filtered water tank 4 and the pump 5. The amount of reclaimed water obtained by reverse osmosis treatment at 25 ° C. was 0.8 g / min, the same amount as in Example 1 at the start of reverse osmosis treatment. In order to operate the reduction rate of the amount of the reclaimed water to be halved after 55 days in the same manner as in Example 1, 30 wt% aqueous sulfuric acid solution was added to the filtered water from the disinfectant addition device 7 to 0.064 mL / min. It was necessary to add intermittently for 24 minutes per day, and more bactericides were needed than in Example 1.

Example 2
For Example 1, 15 mL / min (15%) of the concentrated water obtained by removing the filtered water from the filtered water tank 4 at a rate of 85 mL / min and the reverse osmosis treatment was obtained with the filtered water tank 4 and the pump 5. The operation was performed under the same conditions as in Example 1 except that the mixture was refluxed during the period. The amount of reclaimed water obtained by reverse osmosis treatment at 25 ° C. was 0.8 g / min, the same amount as in Example 1 at the start of reverse osmosis treatment, but halved after 50 days.

Example 3
For Example 1, 45 mL / min (45%) of the concentrated water obtained by removing the filtered water from the filtered water tank 4 at a rate of 55 mL / min and the reverse osmosis treatment, The operation was performed under the same conditions as in Example 1 except that the mixture was refluxed during the period. The amount of reclaimed water obtained by reverse osmosis treatment at 25 ° C. was 0.8 g / min, the same amount as in Example 1 at the start of reverse osmosis treatment, but halved after 50 days.

Example 4
Compared to Example 1, the filtered water was taken out from the filtered water tank 4 at a rate of 95 mL / min, and 5 mL / min (5%) of the concentrated water obtained by reverse osmosis treatment was filtered with the filtered water tank 4 and the pump 5. The operation was performed under the same conditions as in Example 1 except that the mixture was refluxed during the period. The amount of reclaimed water obtained by reverse osmosis treatment at 25 ° C. was 0.8 g / min, the same amount as in Example 1 at the start of reverse osmosis treatment, but halved after 45 days.

Example 5
With respect to Example 1, the filtered water is taken out from the filtered water tank 4 at a rate of 45 mL / min, and 55 mL / min (55%) of the concentrated water obtained by the reverse osmosis treatment is supplied to the filtered water tank 4 and the pump 5. The operation was performed under the same conditions as in Example 1 except that the mixture was refluxed during the period. The amount of reclaimed water obtained by reverse osmosis treatment at 25 ° C. was 0.8 g / min, the same amount as in Example 1 at the start of reverse osmosis treatment, but halved after 45 days.

Example 6
A composite flat membrane (polypore diameter 0.1 μm, thickness 200 μm, initial pure water permeability 4 × 10 ⁻⁸ m ³ / m ² / s / Pa) coated on a polyester nonwoven fabric with a polyvinylidene fluoride film on both sides of the frame Ten bonded flat membrane elements 2 (effective membrane portion: length 250 mm, width 200 mm, effective membrane area 0.1 m ² ) were immersed in the treatment tank 3 of the immersion membrane filtration apparatus shown in FIG. As treated water 1, artificial sewage composed of glucose 0.1 g / L, peptone 0.1 g / L, dipotassium hydrogen phosphate 7.8 mg / L, monopotassium phosphate 3.9 mg / L (biological oxygen demand) An amount (BOD) of 160 mg / L, a total nitrogen concentration of 13.6 mg / L, and a total phosphorus concentration of 2.3 mg / L were supplied to the treatment tank 3 at a rate of 550 L / day. The treated water was filtered by the flat membrane element 2 at a rate of 550 L / day and supplied to the filtered water tank 4. From the lower part of the flat membrane element 2, air was supplied at a rate of 200 L / min for biological treatment of water to be treated and to prevent microorganisms from adhering to the membrane surface of the flat membrane element 2. The filtered water was taken out from the filtered water tank 4 at a rate of 70 mL / min, pressurized to 1.0 MPa using the pump 5, and supplied to the reverse osmosis membrane 6 having an effective membrane area of 9.42 cm ² . An aqueous solution containing 27% by weight of sulfuric acid and 42% by weight of sodium hydrogen sulfite was intermittently added from the disinfectant addition device 7 to the filtered water at a rate of 0.050 mL / min for 24 minutes per day. 30 mL / min (30%) of the concentrated water obtained by the reverse osmosis treatment was refluxed between the filtered water tank 4 and the pump 5. The pH of the filtered water supplied to the reverse osmosis membrane 6 was 7.0 when an aqueous solution containing sulfuric acid and sodium hydrogen sulfite was not added, and 2.5 when it was added. The concentration of sodium bisulfite in the filtered water supplied to the reverse osmosis membrane 6 was 0 ppm when an aqueous solution containing sulfuric acid and sodium bisulfite was not added, and 300 ppm when it was added. The amount of reclaimed water obtained by reverse osmosis treatment at 25 ° C. was 0.8 g / min at the start of reverse osmosis treatment, but halved after 65 days.

Example 7
Compared to Example 6, operation was performed under the same conditions as Example 6 except that the sulfuric acid in the aqueous solution added to the filtered water from the bactericide addition device 7 was 29% by weight and that sodium bisulfite was 14% by weight. did. The pH of the filtered water supplied to the reverse osmosis membrane 6 was 7.0 when an aqueous solution containing sulfuric acid and sodium hydrogen sulfite was not added, and 2.5 when it was added. The concentration of sodium bisulfite in the filtered water supplied to the reverse osmosis membrane 6 was 0 ppm when an aqueous solution containing sulfuric acid and sodium bisulfite was not added, and 100 ppm when it was added. The amount of reclaimed water obtained by reverse osmosis treatment at 25 ° C. was 0.8 g / min at the start of reverse osmosis treatment, but halved after 60 days.

  The present invention can be suitably used when using wastewater such as sewers and industrial wastewater as reclaimed water.

It is a schematic flowchart which shows one embodiment of the manufacturing apparatus of the reclaimed water which concerns on this invention. FIG. 3 is a schematic flow diagram of the immersion membrane filtration apparatus used in Comparative Example 1.

Explanation of symbols

1: Water to be treated 2: Filtration membrane 3: Treatment tank 4: Filtration water tank 5: Pump 6: Reverse osmosis membrane 7: Disinfectant addition device 8: Piping 9: Reclaimed water 10: Concentrated water

Claims (3)

Reclaimed water comprising a treatment tank, a filtration membrane for filtering the treated water immersed in the treatment tank, and a filtered water tank for storing the filtered water obtained by filtering the treated water through the filtration membrane A production apparatus comprising a pump for taking out and pressurizing filtered water from the filtered water tank, a reverse osmosis membrane for performing reverse osmosis treatment of the pressurized filtered water, a disinfectant adding device for sterilizing the filtered water, and filtered water An apparatus for producing reclaimed water, comprising: the filtered water tank and / or a device for returning a part of the concentrated water obtained by reverse osmosis treatment between the filtered water tank and the pump. A submerged type comprising a filtration membrane for filtering the water to be treated, immersed in the treatment tank, and a filtration water tank for storing the filtrate obtained by filtering the water to be treated by the filtration membrane One of the concentrated water obtained by reverse osmosis treatment in a method for producing reclaimed water that is filtered using a membrane filtration device and sterilized filtered water obtained by filtration and then reverse osmosis treated using a reverse osmosis membrane. A method for producing reclaimed water, characterized in that the part is refluxed to filtered water. The method for producing reclaimed water according to claim 2, wherein a ratio of the concentrated water that is refluxed to the filtered water is within a range of 10 to 50%.

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