JP6728835B2 - Method of operating pure water production equipment - Google Patents

Description

The present invention relates to a pure water production apparatus and a method for operating the pure water production apparatus, and more particularly to a pure water production apparatus having a reverse osmosis membrane separation device (RO apparatus) and an electric deionization apparatus and operation of the pure water production apparatus. Regarding the method.

Conventionally, ultrapure water used as semiconductor cleaning water is an ultrapure water production system including a pretreatment system 12, a primary pure water system 13, and a subsystem (secondary pure water system) 14 as shown in FIG. It is produced by treating raw water (industrial water, city water, well water, etc.) W in the device 11. The role of each system in FIG. 2 is as follows.

In the pretreatment system 12 including a flocculation, pressure floating (precipitation), filtration (membrane filtration) device, etc., suspended substances and colloidal substances in the raw water W are removed. Further, in this process, it is possible to remove high molecular organic matter, hydrophobic organic matter and the like.

The primary pure water system 13 includes a tank 15, low-pressure or ultra-low pressure type reverse osmosis membrane separation (RO) devices 16 and 17, an electric deionization device 18, and a deaeration device 19 such as a deaeration membrane, and pretreated water. Ions and organic components in W1 are removed. The reverse osmosis membrane separation devices 16 and 17 remove salts, as well as ionic and colloidal TOC. The electric deionization device 18 removes salts and also removes TOC components that are adsorbed or ion-exchanged by an ion exchange action. Further, the deaerator 19 removes dissolved gas such as carbon dioxide and oxygen from the treated water of the electric deionizer 18. The primary pure water system 13 may be equipped with a regenerative ion exchange device or the like, if necessary.

The subsystem 14 includes a low-pressure ultraviolet oxidation device, an ion-exchange pure water device, and an ultrafiltration membrane separation device. In this subsystem 14, the purity of the primary pure water W2 obtained by the primary pure water system 13 is further enhanced. To make ultrapure water W3. In the low-pressure ultraviolet oxidizer, TOC is decomposed to organic acid and further to CO ₂ by ultraviolet rays having a wavelength of 185 nm emitted from a low-pressure ultraviolet lamp. The organic matter and CO ₂ generated by the decomposition are removed by the ion exchange resin in the subsequent stage. In the ultrafiltration membrane separator, fine particles are removed and outflow particles of the ion exchange resin are also removed.

Since the primary deionized water system 13 in the ultrapure water production system 11 uses the electric deionization device 18, it has advantages such as no need for regeneration treatment unlike a regenerative ion exchange device. It is attracting attention as the most general-purpose system that can be used not only for pure water applications, but also for applications such as pharmaceuticals and foods where it is not necessary to use a subsystem to obtain water with a purity level of ultrapure water. .. In recent years, for example, a small-sized and low-cost general-purpose type electric deionization device in which cells each having a height and a width of about 50 cm or less are stacked has become widespread, and the primary pure water system 13 has been made compact.

However, since such a small-sized electrodeionization apparatus is small in size and therefore has a large membrane area load with respect to the amount of water, it tends to be easily affected by scale and dirt. Therefore, when using a small-sized electric deionization device for the primary pure water system 13, low-pressure or ultra-low pressure type reverse osmosis membrane separation devices are arranged in series in two stages, and calcium, silica, or an organic substance that is a scale component is previously arranged. Although the reverse osmosis membrane separators 16 and 17 consume a large amount of power and require securing an installation space and a power source, the reverse osmosis membrane separators 16 and 17 can be configured with a single-stage RO membrane device if possible. desirable.

In addition, since the small-sized electrodeionization device is small in size, the current density between the electrodes is higher than that of the large-sized electrodeionization device in order to achieve the desired performance, and the water in the deionization chamber is There is a concern that OH ⁻ will increase due to the increased dissociation, the scale tendency will increase, and damage inside the electric deionization apparatus will accumulate, adversely affecting the life of the apparatus. Furthermore, the removal rate of weak ions such as silica is inevitably lower than that of a large-scale electric deionization device. High purity has recently been required for the primary pure water W2, and the silica concentration of the primary pure water W2 may be 0.3 ppb or less, and it is desirable to maintain this.

The present invention has been made in view of the above problems, suppresses the generation of scale of the electrodeionization device, a reverse osmosis membrane separation device and an electrodeionization device with high removal performance of weak ionic components such as silica. An object of the present invention is to provide a pure water producing apparatus having the same and a method of operating the pure water producing apparatus.

The present invention is, firstly, a pure water producing apparatus having a high pressure type reverse osmosis membrane separation device provided in a single stage and an electric deionization device arranged in two stages in series, wherein the high pressure type reverse osmosis membrane separation device is provided. The invention provides a pure water production apparatus having a pH adjusting agent supply means in the preceding stage (Invention 1).

The high-pressure type reverse osmosis membrane separation device exhibits a high removal rate equivalent to that of a normally used low-pressure or ultra-low pressure type reverse osmosis membrane separation device even if it has only one stage. It was said that the contamination would significantly reduce the removal rate as compared with the low pressure type reverse osmosis membrane separation device, so that it was not suitable to be combined with an electric deionization device that is weak against scale. Therefore, the present inventor has studied the cause of the reduction in the removal rate of the high-pressure type reverse osmosis membrane separation device, and as a result of the contamination on the membrane surface, the concentration on the concentration side tends to affect the treated water side. It was found that the contamination of the film surface was due to the fact that the Al concentration in the raw water was 0.5 ppb or more, and the film surface was easily attached. According to the invention (Invention 1), the pH is adjusted to 5 or less by supplying the pH adjusting agent to the front stage of the high-pressure type reverse osmosis membrane separator, thereby ionizing aluminum and suppressing the contamination of the membrane surface. Furthermore, by arranging the electric deionizers in two stages in series, operating the former electric deionizer at a low current density and operating the latter electric deionizer at a high current density, the treated water silica concentration was 0.3 ppb. The following can be achieved and the shortening of the service life of the electrodeionization device can be avoided.

In the above invention (Invention 1), in the electric deionization device arranged in two stages in series, the electric deionization device having high current efficiency is arranged in the front stage, and the electric deionization device having low current efficiency is arranged in the rear stage. Is preferred (Invention 2).

According to this invention (Invention 2), the electrodeionization device with high current efficiency exhibits removal performance at low current density even in wastewater with high silica concentration, while the electrodeionization device with low current efficiency has silica concentration. Silica scale is liable to be generated in wastewater having a high concentration, but exhibits a high removal rate at a high current density even with a low silica concentration. Therefore, by combining the electric deionization devices having such different characteristics, first, by treating the treated water with a low current density in the electric deionization device having high current efficiency, silica and the like in the treated water are removed to some extent. Then, by subsequently treating this water having a low silica concentration with an electric deionization apparatus having a low current efficiency at a high current density, it is possible to stably produce water having a reduced silica concentration.

In the above inventions (Inventions 1 and 2), it is preferable to use the electrodeionization device having a membrane area load of 0.08 L/h/cm ² or more (Invention 3).

According to this invention (invention 3), it is possible to prevent scales and dirt from adhering to the film surface of the electrodeionization device.

Secondly, the present invention relates to a method for operating a pure water producing apparatus having a high-pressure type reverse osmosis membrane separation device provided in a single stage and an electric deionization device arranged in two stages in series, with a pH of 5 or less. There is provided a method for operating a pure water producing device, in which the adjusted water to be treated is passed through the high-pressure reverse osmosis membrane separation device and then treated by an electric deionization device arranged in two stages in series (invention 4).

According to this invention (Invention 4), a pH adjusting agent is supplied to the preceding stage of the high pressure type reverse osmosis membrane separation device to adjust the pH of the water to be treated to 5 or less, and then the high pressure type reverse osmosis membrane separation device is treated. As a result, the aluminum in the raw water is ionized to suppress the contamination of the membrane surface of the high pressure type reverse osmosis membrane separation device. Further, by arranging the electric deionization devices in two stages in series, operating the electric deionization device in the front stage at a low current density and operating the electric deionization device in the rear stage at a high current density, the treated water silica concentration was 0.3 ppb. The following can be achieved and the adverse effect of the life of the electrodeionization device can be avoided and it can be used for a long time.

In the said invention (invention 4), the said electric deionization apparatus arrange|positioned in 2 steps|paragraphs is arrange|positioned combining the electric deionization apparatus with high current efficiency in the front|former stage, respectively, and the electric deionization apparatus with low current efficiency is arrange|positioned in the back|latter stage. cage, the front of the electrodeionization apparatus is operated at a current density of 500~3000mA / dm ^2, preferably to operate the subsequent electrodeionization apparatus at a current density of 3500~10000mA / dm ² (invention 5).

According to the invention (Invention 5), the electrodeionization device having high current efficiency exhibits removal performance at low current density even in wastewater having high silica concentration, while the electrodeionization device having low current efficiency is silica. Silica scale is likely to occur in wastewater having a high concentration, but even if the silica concentration is low, the removal rate is exhibited at a high current density. Therefore, by combining an electric deionization apparatus having such different characteristics, first, by treating with an electric deionization apparatus having a high current efficiency at a current density of 500 to 3000 mA/dm ² , calcium, silica, etc. in the treated water can be treated to some extent. By removing and subsequently treating the water having a low silica concentration with an electric deionization device having a low current efficiency at 3500 to 10000 mA/dm ² , it is possible to stably produce water having a reduced silica concentration.

According to the present invention, the water to be treated whose pH is adjusted to 5 or less is permeated through the high pressure type reverse osmosis membrane separation device and then treated by the electric deionization device arranged in two stages in series. By suppressing the contamination of the membrane surface of the osmosis membrane separation device, it is possible to produce pure water with a treated water silica concentration of 0.3 ppb or less by the electric deionization device arranged in two stages in series and the life of the electric deionization device. It is possible to avoid the adverse effects of and improve the service life.

It is a flow figure showing the pure water manufacturing device by one embodiment of the present invention. It is a flowchart which shows the conventional pure water manufacturing apparatus.

Hereinafter, a pure water producing apparatus and an operating method thereof according to an embodiment of the present invention will be described in detail with reference to FIG.

FIG. 1 is a flow chart showing a pure water producing apparatus according to an embodiment of the present invention. In FIG. 1, the pure water producing apparatus 1 is provided after a pretreatment system 2.

The pretreatment system 2 is composed of a flocculation, pressure floating (precipitation), filtration (membrane filtration) device, etc. to remove suspended substances and colloidal substances in raw water (industrial water, city water, well water, etc.) W. To do. Further, in this process, it is possible to remove high molecular organic matter, hydrophobic organic matter and the like.

The pure water production apparatus 1 has a tank 3, an acid supply mechanism 4 as a pH adjusting agent supply means attached to the tank 3, and a pH meter 5, and a high pressure type reverse osmosis membrane separation ( RO) device 6, a first electrodeionization device 7, a second electrodeionization device 8 and a degasser 9 such as a degasser.

In such an ultrapure water production system 1, the high-pressure type reverse osmosis membrane separation (RO) device 6 is a reverse osmosis membrane separation device conventionally used for seawater desalination and has a standard operating pressure of 5.52 MPa or more. Yes, it has characteristics of pure water flux of 0.5 m3/m2·D or more and NaCl removal rate of 99.5% (NaCl3 2000 mg/L) or more at standard operating pressure. This NaCl removal rate is the removal rate at 25° C. for an NaCl aqueous solution having a NaCl concentration of 32000 mg/L. It should be noted that the reverse osmosis membrane catalog (including technical data) has specifications displayed by the membrane manufacturer, and it can be determined as a catalog value whether it is a high pressure type, a low pressure type or an ultra low pressure type.

In this high-pressure type reverse osmosis membrane, the skin layer on the membrane surface is denser than the low-pressure or ultra-low pressure type reverse osmosis membrane used in the primary pure water system of the conventional ultrapure water production apparatus. Therefore, although the high-pressure type reverse osmosis membrane has a lower amount of water permeated per unit operating pressure than the low-pressure type or ultra-low pressure type reverse osmosis membrane, the organic matter removal rate is extremely high. When the reverse osmosis membrane treatment is performed on the feed water having a salt concentration of 1500 mg/L or less of TDS (total soluble substance), the osmotic pressure applied to the reverse osmosis membrane is about 1.0 MPa at the maximum under operating conditions at a recovery rate of 90%. is there. Therefore, when a high pressure type reverse osmosis membrane separator is used for the treatment of feed water of TDS 1500 mg/L or less, the membrane surface effective pressure (primary side and secondary pressure) of preferably about 1.5 to 3 MPa, particularly preferably about 2 to 3 MPa. It is possible to secure the same amount of water as the low pressure type or ultra low pressure type reverse osmosis membrane due to the pressure difference from the side. As a result, it is possible to obtain the same treated water quality and quantity as the conventional two-stage RO of low-pressure type or ultra-low pressure type reverse osmosis membrane by only one-stage RO membrane treatment. The cost can be reduced, and the cost can be saved and the space can be saved.

The shape of the reverse osmosis membrane is not particularly limited, and may be, for example, a spiral type, a hollow element type, a 4-inch RO membrane, an 8-inch RO membrane, a 16-inch RO membrane, or the like. However, the raw water spacers are preferably 20-40 inches wide.

The first electrodeionization apparatus 7 preferably has a membrane area load of 0.08 L/h/cm ² or more, particularly 0.1 L/h/cm ² or more. Here, the membrane area load is the flow rate (L/h) of the deionization chamber to the effective area (cm ² ) of the ion exchange membrane on one side of the deionization chamber of the electric deionization apparatus, and this membrane area load is 0. If it is less than 08 L/h/cm ² , the device will be left unmounted and downsizing cannot be achieved. If the upper limit of the membrane area load is too large, it is easily affected by scales and stains, so the upper limit may be less than 0.2 L/h/cm ² .

The first electrodeionization apparatus 7 is of a high current efficiency during operation type, de-specifically 500~3000mA / dm ^2, in particular at a relatively low current density of 1000~2500mA / dm ² It is preferable to use the one that exhibits the ionic performance. Such a first electric deionization apparatus 7 has a smaller removal rate of weak ionic components such as silica and boron as compared with a type having a low current efficiency during operation (operated at a high current density). Although low, it has the advantage of being less prone to scale.

The second electrodeionization device 8 preferably has a membrane area load of 0.08 L/h/cm ² or more, particularly 0.1 L/h/cm ² or more. The second electrodeionization apparatus 8 is of current efficiency is low type, specifically 3000~10000mA / dm ^2, deionized performance especially at relatively high current densities of 3500~5000mA / dm ² It is preferable to use a material that exhibits a suitable effect. Such a second electric deionization device 8 has a high removal rate of weak ion components such as boron as compared with a type having a high current efficiency during operation (operated at a low current density), while having a scale. It is easy to occur.

Furthermore, the acid added from the acid supply mechanism 4 attached to the tank 3 is not particularly limited, and hydrochloric acid, sulfuric acid, nitric acid or the like can be used, and hydrochloric acid is preferable. In addition, an optional scale inhibitor can be added to the tank 3 as needed.

Next, a method of operating the pure water producing apparatus 1 having the above-described configuration will be described. The raw water W is treated by the pretreatment system 2 to be pretreated water (water to be treated) W1, and the pretreated water W1 is stored in the tank 3. At this time, it is preferable to add hydrochloric acid from the acid supply mechanism 4 as a pH adjusting agent supply means and monitor the pH of the pretreated water W1 with the pH meter 5 to adjust the pretreated water W1 to pH 5 or less. By setting the pH of the pretreated water W1 to 5 or less, silica in the pretreated water W1 is easily precipitated, while Al is ionized to adhere to the membrane surface of the high pressure type reverse osmosis membrane separation device 6 in the subsequent stage. Can be suppressed. In addition, it is preferable to add a scale inhibitor as necessary for the purpose of preventing the scale from adhering to the membrane surface of the high-pressure type reverse osmosis membrane separation device 6.

Next, this pretreated water W1 is treated by the high pressure type reverse osmosis membrane separation device 6. The high-pressure reverse osmosis membrane separation device 6 removes ionic and colloidal TOC in addition to removing salts, calcium, silica and the like. The high pressure type reverse osmosis membrane separation device 6 exhibits the removal rate equivalent to that of the low pressure type or ultra low pressure type reverse osmosis membrane in one stage.

Subsequently, the obtained RO-treated water is treated with the first electric deionization apparatus 7 to remove weak ions such as calcium, silica, and boron and salts, and TOC components that are adsorbed or ion-exchanged by the ion-exchange action. Is removed. In the present embodiment, as the first electric deionization device 7, a type that suitably exhibits deionization performance at a relatively low current density is used, so that a current density of 500 to 3000 mA/dm ² , particularly 1000 It is preferred to operate at relatively low current densities of ˜2500 mA/dm ² . Also the current density exceeds 3000 mA / dm ² during operation, not only the efficiency of removal of such higher silica not obtained, due such as the silica component contained in the RO membrane treated water, first electrodeionization It is not preferable because the electric resistance of the device 7 is greatly increased and the life of the device is adversely affected. On the other hand, when the current density during operation is less than 500 mA/dm ² , the removal rate of weak ionic components such as silica and boron decreases.

Subsequently, the treated water of the first electrodeionization device 7 is further treated by the second electrodeionization device 8 to further remove trace amounts of residual weak ions such as silica and boron and salts, and to perform ion exchange action. The TOC component adsorbed or ion-exchanged by is further removed. Here, since the silica concentration of the water to be treated by the second electrodeionization device 8 has already been largely reduced by the first electrodeionization device 7, the water density is higher than that of the first electrodeionization device 7. Little increase in electrical resistance even when driving. Therefore, in the present embodiment, as the second electric deionization device 8, a type that suitably exhibits deionization performance at high current density is used, and the current density is 3000 to 10000 mA/dm ² , particularly 3500 to 5000 mA. It is preferable to operate at a relatively high current density of /dm ² . Even if the current density during operation exceeds 10000 mA/dm ^2, not only is silica removal efficiency higher than that, but also the electrical resistance of the second electrodeionization device 8 rises, which adversely affects the device life. Not preferable. On the other hand, when the current density during operation is less than 3000 mA/dm ² , the removal rate of weak ionic components such as silica and boron decreases.

Since the first electrodeionization device 7 and the second electrodeionization device 8 are not airtight, a small amount of carbonic acid, oxygen, etc. dissolves during the treatment. Therefore, the treated water of the second electric deionization device 8 is treated by the degassing device 9 to remove these dissolved gases to obtain pure water W2.

By thus treating with the pure water producing apparatus 1, pure water W2 having a silica concentration of 0.3 ppb or less can be stably produced. Further, the adhesion of contaminants to the high-pressure type reverse osmosis membrane separation (RO) device 6 is suppressed, and it is caused by calcium, silica, etc. to the first electrodeionization device 7 and the second electrodeionization device 8. Since the scale can be suppressed, the service life of the device can be improved.

Although one embodiment of the present invention has been described above with reference to the accompanying drawings, the present invention is not limited to the above-mentioned embodiment, and an electric deionization device is provided at a stage subsequent to the high pressure type reverse osmosis membrane separation (RO) device. Various elements can be added to the deionized water device if they are provided in series and the pH is adjusted before the high pressure type reverse osmosis membrane separation (RO) device. For example, a membrane type deaerator or a decarbonation tower may be provided in front of the first electric deionization apparatus 7, or a regenerative mixed bed type ion exchange apparatus may be provided if necessary. Furthermore, the pretreatment system 2 does not necessarily have to be provided, and tap water may be directly supplied to the pure water producing apparatus 1. Further, an ultrapure water producing apparatus may be configured by providing a subsystem in the latter stage of the pure water producing apparatus and using pure water W2 as primary pure water.

Hereinafter, the present invention will be described more specifically with reference to Comparative Examples and Examples, but the present invention is not limited to the following Examples.

[Example 1]
In FIG. 1, the pretreatment system 2 was composed of only an activated carbon tower. In addition, as the high pressure type reverse osmosis membrane device 6, a high pressure type reverse osmosis membrane (KROA-20XU-FX) manufactured by Kurita Industry Co., Ltd. is used, and VNX is used as a first electric deionization device 7 of a high current efficiency operation type. (Manufactured by EVOQUA WATER TECHNOLOGIES), and VNX-EX (manufactured by EVOQUA WATER TECHNOLOGIES) was used as the second electric deionization device 8 of the operation type having low current efficiency to configure the pure water producing device 1. Further, hydrochloric acid and a scale inhibitor (N500, manufactured by Kurita Water Industries Ltd.) can be added from the acid supply mechanism 4.

The city water of Yokohama (silica concentration 20 ppm) was used as raw water W and treated with the pure water producing apparatus 1 described above to produce 15 m ³ /h of pure water. At this time, hydrochloric acid and a scale inhibitor were added from the acid supply mechanism 4 to adjust the pH of the pretreated water W1 to 4.9, and water was passed through the first electrodeionization device 7 at a current density of 2000 mA/dm ^2. Water was passed through the ^second electrodeionization device 8 at a current density of 4000 mA/dm ² .

When the pure water W2 was continuously produced for 6 months by the pure water producing apparatus 1, the silica concentration of the pure water W2 was stable at 0.3 ppb or less with respect to the silica concentration of the raw water W of 20 ppm. The voltage during the operation of the electric deionization device 7 increased from 80V to 90V, and the voltage during the operation of the second electric deionization device 8 slightly increased from 60V to 65V, but this does not hinder the operation of the device. It was

[Comparative Example 1]
Pure water W2 was obtained in the same manner as in Example 1, except that hydrochloric acid and scale inhibitor were not added from the acid supply mechanism 4 before the high pressure type reverse osmosis membrane device 6 and pretreated water W1 having a pH of 7.0 was treated. Manufactured.

When the pure water W2 was continuously produced for 6 months by the pure water producing apparatus 1, the silica concentration of the pure water W2 was 1.1 ppb with respect to the silica concentration of the raw water W of 20 ppm. The operating voltage of 7 greatly increases from 80V to 250V, and the operating voltage of the second electrodeionization device 8 greatly increases from 60V to 88V. If this state continues, the useful life of the device is 1 to 2 years. It was at the level of the year.

[Example 2]
Pure water was prepared in the same manner as in Example 1, except that the pure water producing apparatus 1 was constructed by using VNX (manufactured by EVOQUA WATER TECHNOLOGIES) as both the first electrodeionization device 7 and the second electrodeionization device 8. The production apparatus 1 was configured to produce pure water W2.

When the pure water W2 was continuously produced for 6 months by the pure water producing apparatus 1, the silica concentration of the pure water W2 was stable at 0.3 ppb or less with respect to the silica concentration of the raw water W of 20 ppm. The voltage during the operation of the electric deionization device 7 increased from 80V to 90V, and the voltage during the operation of the second electric deionization device 8 slightly increased from 60V to 70V, but this does not hinder the operation of the device. It was However, a reduction in the removal rate of other weak ionic components such as boron was observed.

[Example 3]
In the same manner as in Example 1, except that the pure water producing apparatus 1 was configured using both VNX-EX (manufactured by EVOQUA WATER TECHNOLOGIES) as the first electrodeionization apparatus 7 and the second electrodeionization apparatus 8. The pure water producing apparatus 1 was configured to produce pure water W2.

When the pure water W2 was continuously produced for 6 months by the pure water producing apparatus 1, the silica concentration of the pure water W2 was stable at 0.3 ppb or less with respect to the silica concentration of the raw water W of 20 ppm. The voltage during the operation of the electric deionization device 7 increased from 80 V to 90 V, and the voltage during the operation of the second electric deionization device 8 slightly increased from 60 V to 65 V, but this does not hinder the operation of the device. It was However, a slight scale tendency was observed in the first electric deionization apparatus 7, and it was a level requiring caution for long-term continuous operation.

1 Pure Water Production Device 2 Pretreatment System 3 Tank 4 Acid Supply Mechanism (pH Adjusting Agent Supply Means)
5 pH meter 6 High pressure type reverse osmosis membrane separation (RO) device 7 First electric deionization device 8 Second electric deionization device 9 Degassing device W Raw water W1 Pretreatment water W2 Pure water (primary pure water)

Claims (1)

A method for operating a pure water production apparatus having a high-pressure type reverse osmosis membrane separation device provided in a single stage and an electric deionization device arranged in two stages in series,
After permeating the water to be treated whose pH has been adjusted to 5 or less through the high pressure type reverse osmosis membrane separation device, it is treated with an electric deionization device arranged in two stages in series ,
In electrodeionization apparatus disposed in the two-stage series, the first electrodeionization apparatus which exhibits deionized performance at a current density of 500~3000mA / dm ² in front, a current density of 3000~10000mA / dm ² in a subsequent stage The second electric deionization device that exhibits the deionization performance at
Said first electrodeionization apparatus was operated at a current density of 500~3000mA / dm ^2, the method operating in the pure water production device for operating said second electrodeionization apparatus at a current density of 3500~10000mA / dm ^2.

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