JP4073699B2 - Method for decomposing harmful substances present in air and apparatus therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION The present invention relates to a method for decomposing harmful substances present in air and an apparatus therefor.
[0002]
Background Art The use of microorganisms in the decomposition treatment of harmful substances present in the air has been conventionally performed. However, in the method using microorganisms, at present, a sufficient treatment effect cannot be obtained due to a slow degradation rate by microorganisms.
[0003]
As a method of using microorganisms, when composting waste such as manure from poultry farms and pig houses, odorous exhaust gas exhausted from the composting facility is introduced into the ground, and odor components are decomposed by soil microorganisms. Has been put to practical use. However, in this method, there have been reports of cases where the nitrification / denitrification process of nitrogen components in the treated soil does not work, and nitrate nitrogen penetrates into the groundwater and the groundwater is contaminated.
[0004]
Deodorizing filters using microorganisms have also been put into practical use. However, the application range is limited to a case where the odor component is small, and it is difficult to apply to a large amount of odorous exhaust gas exhausted from a large garbage disposal device or a large compost manufacturing facility. .
[0005]
On the other hand, attempts to apply the electrolysis method to the decomposition treatment of harmful substances present in the air have been made conventionally. An initial attempt is oxidative decomposition of odorous components by ozone generated from electrodes or electric wires. However, this method has a practical level for decomposing odorous components exhausted in large quantities from large compost production equipment, garbage processing equipment, etc., such as ammonia, H ₂ S, acetaldehyde, trimethylamine, methyl mercaptan, etc. It is difficult to cause an oxidation reaction.
[0006]
As an improved method to increase the oxidative decomposition efficiency of the target substances in solution, hypochlorite is generated by adding sodium chloride to the target wastewater and electrolyzing it, and it is processed by the oxidizing power of the hypochlorous acid. An indirect electrolysis method in which a target substance is oxidatively decomposed has been proposed (Japanese Patent Laid-Open No. 10-85750). However, there are harmful substances that cannot be sufficiently decomposed by the oxidizing power of hypochlorous acid.
[0007]
Japanese Patent Laid-Open No. 5-261374 discloses that an electrolyte salt (for example, MnSO ₄ ) is added to produce manganese oxide (MnOx) by an electrolysis reaction, and the oxidative decomposition of organic matter is promoted by an oxygen donating catalytic action. An indirect electrolysis method has been proposed. However, as described in the examples of this publication, this method requires a processing time of 3 hours to decompose about 90% of a 0.1% solution of oxalic acid, an easily biodegradable substance. Yes.
[0008]
Therefore, there is still a need for a method for decomposing harmful substances present in the air.
[0009]
SUMMARY OF THE INVENTION
The present inventors have recently dissolved a harmful substance present in the air in an electrolytic solution containing a high concentration of a halogen compound and a metal ion, and energized the obtained solution to be treated, thereby allowing the metal oxide to be dissolved. It has been found that an effective amount can be generated, whereby a harmful substance contained in the solution to be treated can be decomposed. The present invention is based on such knowledge.
[0010]
Accordingly, an object of the present invention is to provide a method and apparatus for efficiently decomposing harmful substances present in the air.
[0011]
And the hazardous substance decomposition method according to the present invention comprises:
A method for decomposing harmful substances present in the air,
A solution to be treated is prepared by dissolving the harmful substance in an electrolytic solution containing at least a halogen compound and a metal ion,
Energizing the solution to be treated to form a metal oxide by the energization, and at least comprising oxidatively decomposing harmful substances in the solution to be treated by the metal oxide;
Here, the halogen compound is capable of forming a halogen molecule by the energization, the solution to be treated has a pH in a range where the halogen molecule becomes a hypohalite ion, and the halogen compound and The metal ion is contained at a concentration necessary to form an amount of metal oxide effective for oxidative decomposition of harmful substances.
[0012]
Moreover, the hazardous substance decomposition apparatus according to the present invention comprises:
An apparatus for carrying out the hazardous substance decomposition method according to the present invention,
Means for dissolving harmful substances present in the air in an electrolytic solution comprising at least a halogen compound and metal ions;
Means for adjusting the pH of the electrolytic solution to a range in which halogen molecules become hypohalite ions, and a tank for holding the solution to be treated;
Energizing means capable of energizing the solution to be treated in the tank;
At least.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
According to the harmful substance decomposition method of the present invention, it is possible to efficiently decompose harmful substances dissolved in the electrolytic solution from the air, whereby the air purification process can be performed efficiently. In particular, according to this method, it is possible to purify a large amount of air.
[0014]
The reason why the harmful substance in the electrolytic solution can be decomposed by the harmful substance decomposition method according to the present invention is considered as follows. First, a halogen compound present in the electrolytic solution is oxidized into a halogen molecule (X ₂ ) by electrolysis, and the halogen molecule is quickly converted into a hypohalite ion (XO ⁻ ). The presence of a high concentration of hypohalous acid places the metal ions in a redox atmosphere, and the oxidation is strongly promoted on the electrolysis cathode, so that the metal ions present in the electrolyte are oxidized. It is efficiently converted into a product. Oxidation decomposition of the harmful substances present in the electrolyte into CO ₂ , H ₂ O, SO ₄ (sulfuric acid), NO ₃ (nitric acid), N _2, etc. by the oxygen donating catalytic action of the high concentration metal oxide thus obtained. can do.
[0015]
In this specification, the term “decomposition” used for harmful substances is not limited to the complete removal of the harmful substances in the electrolyte solution, but the concentration of the harmful substances is reduced. Preferably, reducing to a concentration acceptable for preventing water pollution. Also, the term “purification” used for air is not limited to the complete removal of harmful substances in the air, the concentration of the harmful substances being reduced, preferably air pollution or Including reducing the concentration to an acceptable level to prevent air pollution.
[0016]
Solution to be treated A solution to be energized in the present invention (referred to as "treatment solution" in the present invention) is an electrolytic solution containing a halogen compound and metal ions in which harmful substances in the air are dissolved. It is a liquid. The harmful substances in the air can be dissolved in the electrolytic solution by a method known to those skilled in the art as a method for dissolving the gas in the liquid, for example, a method using a scrubber. At that time, it is possible to increase the amount of gas in contact with the electrolytic solution within a predetermined time by using an air flow generating means such as a fan, whereby the harmful substance can be efficiently dissolved in the electrolytic solution. Air is purified by the dissolution of harmful substances in the electrolyte.
[0017]
The toxic substance decomposition method according to the present invention is a method for decomposing toxic substances by electrolysis by energization treatment into a solution to be treated. Therefore, according to the present invention, the solution to be treated has electrical conductivity that enables electrolysis. For this reason, the electrolytic solution for dissolving the harmful substance has an electric conductivity that enables energization, and preferably has an electric conductivity of 1 mS / cm to 50 mS / cm. Such electric conductivity can be achieved by dissolving a required amount of electrolyte (for example, salt) in the electrolytic solution in advance. Further, the electrical conductivity of the electrolytic solution may be adjusted by adding an electrolyte at any stage before energization. Here, 1 mS / cm corresponds to the electrical conductivity of about 0.05% saline.
[0018]
In the hazardous substance decomposition method according to the present invention, metal oxide can be efficiently generated by the action of hypohalite ions. Accordingly, the solution to be treated has a pH in a range where the halogen molecule (X ₂ ) becomes a hypohalite ion (XO ⁻ ). The pH at which halogen molecules can be converted to and maintained in the wastewater is generally on the alkali side, preferably in the range of pH 7-12, more preferably pH 8-10. It is a range. Such pH can be achieved by adjusting the pH of the electrolytic solution in the above range in advance. Also, if the pH of the electrolyte is not within the above range, or if the pH of the electrolyte deviates from the above range due to dissolution of harmful substances, addition of metal ions, halogen compounds, electrolytes, etc. The pH of the liquid can be adjusted to the above range to make a solution to be treated.
[0019]
In the hazardous substance decomposition method according to the present invention, the solution to be treated after energization may be reused as an electrolytic solution for preparing the solution to be treated before energization. At that time, if necessary, the pH of the electrolytic solution can be adjusted to the above-mentioned range in which the halogen molecules become hypohalite ions.
[0020]
The method according to the invention applies to harmful substances present in the air. In the present invention, the term “hazardous substance” broadly means not only substances that adversely affect the environment and the health of animals, particularly humans, but also substances that are not preferably present in the air. Accordingly, the “hazardous substance” includes substances that cause discomfort to humans due to their presence, such as odor components. Examples of harmful substances include odor components, environmental hormones such as polychlorinated biphenyl (PCB) and dioxins, nitrogen oxides, sulfur oxides, and exhaust particulates.
[0021]
According to a preferred embodiment of the present invention, the harmful substance is an odor component. Here, the odor component means a substance that causes gaseous odor, and examples thereof include ammonia (NH ₃ ), hydrogen sulfide (H ₂ S), acetaldehyde, trimethylamine, and methyl mercaptan.
[0022]
In the method according to the present invention, harmful substances to be treated are dissolved from the air into the electrolyte. Therefore, the harmful substances are preferably water-soluble.
[0023]
Specific examples of air containing harmful substances as described above include indoor air in general households, business establishments, research laboratories, factories, etc., industrial waste treatment equipment, garbage incineration equipment, garbage disposal equipment, compost production equipment, sewage Examples include exhaust gas exhausted from treatment facilities. According to a preferred embodiment of the present invention, the air containing harmful substances is exhaust gas.
[0024]
Metal ion In the present invention, the metal ion is oxidized on the cathode in the presence of hypohalous acid during the energization treatment of the solution to be treated, and can oxidatively decompose harmful substances contained in the solution to be treated. It means a metal ion that can be a metal oxide. That is, in the present invention, the metal oxide functions as an oxygen donating catalyst. According to a preferred embodiment of the present invention, the metal ion is preferably a heavy metal ion, more preferably a metal ion having a specific gravity of 4 or more, more preferably a metal ion having a specific gravity of 5 or more. . Specific examples of preferred metal ions in the present invention include metal ions such as iron, manganese, chromium, copper, lead, cobalt, nickel, zinc, titanium, molybdenum, silver, cadmium, platinum, and mercury. Copper, zinc, silver and chromium are preferred.
[0025]
In the present invention, the amount of metal ions in the solution to be treated is an amount that can provide an amount of metal oxide capable of decomposing harmful substances contained in the solution to be treated. Therefore, the amount of metal ions in the electrolytic solution is not limited as long as the metal ion concentration in the solution to be treated is provided, but is preferably about 1 μmol / l to 1 mol / l, more preferably 50 μmol / l. It is about 1-50 mmol / l. Such a metal ion concentration in the electrolytic solution can be achieved by dissolving a necessary amount of metal ions in the electrolytic solution in advance. Moreover, you may achieve said metal ion density | concentration by adding a metal ion to electrolyte solution in any step before electricity supply.
[0026]
In the present invention, the metal compound added to supply metal ions is not particularly limited, but a water-soluble metal salt is preferable.
[0027]
Halogen compounds <br/> halogen compound in the present invention are those capable of forming a corresponding halogen molecule (X ₂₎ by energizing the solution to be treated containing the same. All or part of the formed halogen molecules (X ₂ ) are converted into hypohalite ions (XO ⁻ ) in the solution to be treated. Alternatively, when the halogen compound is a halogen molecule (X ₂ ), a hypohalite ion (XO ⁻ ) is present in the solution to be treated without energization.
[0028]
According to a preferred embodiment of the present invention, the halogen compound is preferably a chlorine compound, a bromine compound, or an iodine compound. According to a more preferred embodiment of the present invention, the halogen compound is preferably a chlorine compound or a bromine compound. Moreover, as such a halogen compound, a water-soluble halogen compound is preferable.
[0029]
In the present invention, the concentration of the halogen compound in the solution to be treated is set such that an amount of metal oxide capable of decomposing harmful substances contained in the solution to be treated can be provided. Therefore, the amount of the halogen compound in the electrolytic solution is not limited as long as the concentration of the halogen compound in the solution to be treated is provided, but when converted as a halide ion (X ⁻ ), preferably 1 mmol / l to It is about 1 mol / l, more preferably about 0.01 mol / l to 0.3 mol / l. Such a halogen compound concentration in the electrolytic solution can be achieved by dissolving a necessary amount of the halogen compound in the electrolytic solution in advance. Moreover, you may achieve said halogen compound density | concentration by adding a halogen compound to electrolyte solution in any step before electricity supply.
[0030]
Further, according to another preferred embodiment of the present invention, when halogen gas is generated by an energization operation to be described later, the halogen gas is circulated and dissolved in the electrolyte before or during energization to supply the halogen compound. May be a source. According to a preferred embodiment of the present invention, the circulation of the halogen gas is preferably performed in the electrolyte before energization, and if necessary, the electrolyte is brought into a range where the dissolved halogen gas becomes hypohalite ions. Adjust the pH.
[0031]
Electrolysis In the present invention, energization of the solution to be treated is performed by immersing the electrode in the solution to be treated and applying a voltage thereto. The distance between the electrodes may be determined in consideration of the electrical conductivity of the solution to be treated. For example, when the electrical conductivity is 1 mS / cm or more, the distance is preferably 1.0 cm to 2.0 cm. . The voltage may be determined in consideration of the type of the solution to be treated, the size of the electrode, etc., but is preferably about 1V to 100V, more preferably about 5V to 30V.
[0032]
The energizing step for the solution to be treated may be performed by a so-called batch method in which the solution to be treated is once stored in a tank and then processed, and then all the solution to be treated is discharged from the tank. May be carried out by a continuous operation in which the solution to be treated is discharged continuously.
[0033]
The energization of the solution to be treated may be performed until a desired degree of decomposition can be realized. According to a preferred embodiment of the present invention, harmful substances in the solution to be treated can be reduced to the order of 10 ⁻¹ to 10 ¹ ppm, and extremely high harmful substance removal can be achieved.
[0034]
Hazardous substance decomposing apparatus The present invention also relates to an apparatus for carrying out the above detrimental substance decomposing method, the apparatus comprising at least a halogen compound and a metal ion as a detrimental substance present in the air. Means for dissolving in the electrolyte, means for adjusting the pH of the electrolyte to a range in which the halogen molecules become hypohalite ions, a tank for holding the solution to be treated, and a solution to be treated in the tank And at least an energizing means capable of energizing.
[0035]
Further, in the above hazardous substance decomposition method, when the treated solution after energization is reused as an electrolytic solution for preparing the treated solution before energization, the hazardous substance decomposing apparatus according to the present invention is Electrolytic solution circulation means is further provided.
[0036]
Furthermore, in the above hazardous substance decomposition method, when the halogen gas generated by energization is dissolved in the electrolyte before or during energization, the hazardous substance decomposition apparatus according to the present invention further comprises a halogen gas circulation means for this purpose. Prepare.
[0037]
As a harmful substance decomposition apparatus according to a preferred embodiment of the present invention, for example, an apparatus shown in FIG. In FIG. 1, a scrubber 1 is a harmful substance dissolving means, an electrolysis tank 2 is a solution holding tank, and an anode panel 9 and a cathode panel 10 are energizing means. For the anode panel, titanium sintered with platinum is used, and for the cathode panel, stainless steel is used. Further, this apparatus includes a pH sensor 5, a pH control sequencer 4, an alkaline tank 3, a pump 6 and a supply means 15 as pH adjusting means. Further, this apparatus includes a pump 16 and a pipe 13 as electrolyte solution circulation means. Further, this apparatus includes a fan 8, a pipe 14, and a scrubber 1 as a halogen gas circulation means. Hereinafter, the harmful substance removal process using the apparatus shown in FIG. 1 will be described.
[0038]
Air is first introduced into the scrubber 1. The scrubber 1 stores an electrolytic solution in advance, and the electrolytic solution contains an effective amount of metal ions and an effective amount of a halogen compound for oxidizing and decomposing harmful substances. The stored electrolyte is sent to the watering nozzle by the pump 7 and the pipe 12 which are circulation means, and is sprayed to the filler for gas-liquid mixing. In this filler, the electrolytic solution and the air rising from the lower portion of the scrubber 1 are mixed, and the water-soluble component of the harmful substances is dissolved in the electrolytic solution. This electrolytic solution is circulated in the scrubber 1 by the pump 7 and the pipe 12.
[0039]
Further, as the energization process proceeds, the halogen gas generated by the energization process is introduced into the scrubber 1 by the fan 8 and the pipe 14, and the solution to be treated after the energization process is introduced by the pump 16 and the pipe 13. This solution to be treated is reused as an electrolytic solution and dissolves harmful substances in the air as described above. At that time, the halogen gas is also dissolved in the electrolytic solution in the same manner as harmful substances.
[0040]
The pH of the electrolyte circulating in the scrubber 1 is maintained on the alkali side by a series of pH control systems 3, 4, 5, 6 and 15. Thereby, a part of halogen molecule is converted into hypohalous acid.
[0041]
A solution to be treated containing high-concentration hypohalous acid and metal ions is supplied to the electrolysis tank 2 through a pipe 11 that supplies a part of the solution circulating in the scrubber 1 to the electrolysis tank. A plurality of electrodes, that is, an anode panel 9 and a cathode panel 10 are installed in the electrolysis tank 2, and energization processing is continuously performed between these electrodes. The amount of the solution to be treated supplied to the electrolysis tank 2 is determined by the decomposition capacity of the electrolysis tank 2 and can be adjusted by the pump 16.
[0042]
Metal ions placed in an oxidative atmosphere with hypohalous acid by the energization treatment are converted into metal oxides in the cathode panel 10, thereby accumulating metal oxides at a high concentration. High concentration metal oxides can decompose harmful substances into CO ₂ , H ₂ O, SO ₄ , NO ₃ , N _2, etc. due to their strong oxygen supply catalysis.
[0043]
The solution to be treated after the energization process is introduced into the scrubber 1 by the pump 16 and the pipe 13, and the halogen gas generated by the energization process is also introduced into the scrubber 1 by the fan 8 and the pipe 14.
[0044]
Through the above process, the target harmful substance is decomposed and removed in the electrolysis tank 2 while repeating partial circulation. The electrolytic solution in the electrolysis tank can be exchanged through the drain 17.
[0045]
【Example】
The present invention will be described more specifically with reference to the following examples. In the following examples, harmful substances are decomposed and removed by the apparatus shown in FIG. 1 for a large amount of air that is difficult to purify by the conventional method.
[0046]
Example 1
In the present embodiment, the air to be treated is odorous gas exhausted from an apparatus for composting waste at a feeding center. The main component of the odor is ammonia, and it is known that the odor is almost eliminated if the ammonia is removed with a scrubber. The ammonia concentration of the exhaust gas was 80 ppm as a result of measurement with a gas detector tube.
[0047]
As a scrubber for trapping exhaust gas in the electrolyte, a scrubber having a SV value of 100 having a 20 L filler volume and a 50 L electrolyte storage tank was used. The SV value is the amount of air that passes through the filter medium of the scrubber in one minute and the volume of the filter medium when ammonia in the air that is input to the scrubber is removed from the detection limit when it is output from the scrubber. A ratio. As the electrolytic solution, an aqueous solution in which 0.5% sodium chloride, 0.01% bromine chloride and 0.001% manganese chloride were dissolved was used. The anode plate for electrolysis is a 20cm x 20cm, 3mm thick titanium plate with two platinum sintered plates, and the cathode plate is a 20cm x 20cm, 3mm thick stainless steel plate. Three sheets were used. The actual volume of the electrolysis tank was 8.7 L, and cathode plates and anode plates were alternately arranged at an interval of 1.4 cm.
[0048]
The above exhaust gas was introduced into the scrubber for 10 minutes. The resulting electrolyte solution in the scrubber was measured for ammonia concentration by the indophenol method. As a result, 1,600 mg (32 ppm) of ammonia was dissolved. This electrolytic solution was introduced into an electrolysis tank, and a current of 12 A was applied at a voltage of 5 V for 1 hour.
[0049]
As a result, the ammonia odor disappeared from the electrolyte after energization. About the electrolyte solution after electricity supply, the ammonia concentration was measured by the indophenol method, and the nitric acid concentration was measured by cadmium / copper column reduction-naphthylethylenediamine spectrophotometry. As a result, the ammonia concentration was outside the detection limit, and the nitric acid concentration was 1.2 ppm. As a result, it was found that most of ammonia was converted to nitrogen gas, and part of it was oxidized to nitrate nitrogen.
[0050]
Example 2
The air to be treated in this example is an artificial odorous exhaust gas that artificially generates H ₂ S assuming the odor of sewage treatment. This artificial odorous exhaust gas was produced by removing hydrogen sulfide gas from a commercially available hydrogen sulfide filled cylinder and adjusting the concentration to 100 ppm / m ³ .
[0051]
This artificial odorous exhaust gas was treated in the same manner as in Example 1. The hydrogen sulfide concentration in the electrolyte before energization was 38 ppm as measured by the mixed diamine colorimetric method, indicating that most of the hydrogen sulfide in the artificial odorous exhaust gas was trapped in the electrolyte by the scrubber. . The concentration of hydrogen sulfide in the electrolyte after energization for 1 hour was outside the detection limit. As a result of measuring the sulfate ion concentration of the electrolytic solution after energization by the method of Iwasaki and Utsumi (The Chemical Society of Japan, 79, 38, 1958), SO ₄ -S was 35 ppm. This means that most of the hydrogen sulfide has been converted to sulfate ions by electrooxidation, and therefore it has been found that hydrogen sulfide, which is a harmful substance, is decomposed by an electrochemical method and the exhaust gas is purified.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a preferable hazardous substance decomposition apparatus for carrying out a hazardous substance decomposition method according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Scrubber 2 Electrolysis tank 3 Alkali tank 4 pH control sequencer 5 pH sensor 6 Pump for supplying alkaline solution of alkali tank to scrubber under control of pH sequencer 7 Pump for supplying solution to scrubber 8 Electrolysis Fan 9 for blowing halogen gas generated in the tank to the scrubber 9 Anode panel 10 Cathode panel 11 Pipe for supplying a part of the solution circulating in the scrubber to the electrolysis tank 12 Pipe for circulating the solution in the scrubber 13 Pipe for sending the electrolytic solution treated in the electrolysis tank to the scrubber 14 Pipe for sending the halogen gas generated in the electrolysis tank to the scrubber 15 Means for supplying an alkaline solution to the circulation pipe in the scrubber 16 Electrolysis Sending the electrolytic solution treated in the tank to the scrubber Pump 17 for draining to replace the electrolyte

Claims (10)

A method for decomposing harmful substances present in the air,
A solution to be treated is prepared by dissolving the harmful substance in an electrolytic solution containing at least a halogen compound and a metal ion,
Energizing the solution to be treated to form a metal oxide by the energization, and at least comprising oxidatively decomposing harmful substances in the solution to be treated by the metal oxide;
Here, the halogen compound is capable of forming a halogen molecule by the energization, and the solution to be treated has a pH in a range where the halogen molecule becomes a hypohalite ion, and the halogen compound and A method comprising containing the metal ions at a concentration necessary to form an amount of a metal oxide effective for oxidative decomposition of harmful substances. The solution to be treated after energization is reused as an electrolyte for preparing the solution to be treated before energization, and if necessary, the pH of the electrolyte is adjusted to a range in which halogen molecules become hypohalite ions. The method of claim 1, comprising the step of adjusting. In order to form a metal oxide in an effective amount for oxidative decomposition of harmful substances, the halogen gas generated by the energization is circulated and dissolved in the electrolyte before or during energization. The method according to claim 1 or 2, further comprising a step of adjusting the pH of the electrolytic solution to a range in which halogen molecules become hypohalite ions. The method according to claim 1, wherein the halogen compound is a chlorine compound or a bromine compound. The method according to any one of claims 1 to 4, wherein the metal ion is a manganese ion, a copper ion, a zinc ion, a silver ion, or a chromium ion. The method according to claim 1, wherein the air is exhaust gas. The method according to any one of claims 1 to 6, wherein the harmful substance is an odor component. An apparatus for carrying out the method according to claim 1,
Means for dissolving harmful substances present in the air in an electrolytic solution comprising at least a halogen compound and metal ions;
Means for adjusting the pH of the electrolyte to a range in which halogen molecules become hypohalite ions;
A tank for holding the solution to be treated;
Energizing means capable of energizing the solution to be treated in the tank;
A device comprising at least. The apparatus according to claim 8, further comprising electrolyte solution circulation means for reusing the solution to be treated after energization as an electrolyte for preparing the solution to be treated before energization. The apparatus according to claim 8 or 9, further comprising a halogen gas circulating means for dissolving a halogen gas generated by energization in an electrolyte before or during energization.

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