JP2010162521A - Method and apparatus for treating hardly degradable organic compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus for treating a hardly degradable organic compound for efficiently degrading a hardly degradable organic compound (in particular, PFOA or PFOS) such as a fluorine-based organic compound at a normal temperature and a normal pressure, in the treatment of a solution including the hardly degradable organic compound such as a fluorine-based organic compound, in particular, PFOA or PFOS. <P>SOLUTION: The method for treating hardly degradable organic compound includes a process of adding a persulfate and a chelated iron to the hardly degradable organic compound to degrade the hardly degradable organic compound. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and apparatus for safely and efficiently treating a hardly decomposable organic compound.

  Fluorine-based organic compounds known as typical hardly decomposable substances have a very chemically stable property, and are therefore widely used in various applications such as water repellents, surface treatment agents, and coating agents. In particular, perfluorocarboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids are used in many industries. However, in recent years, it has become clear that perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are present in wildlife and environmental water.

  From such a background, a technique for decomposing and detoxifying a trace amount of a fluorine-based organic compound discharged from a factory or the like is desired. However, fluorinated organic compounds such as PFCAs and perfluoroalkyl sulfonic acids are hardly decomposable substances. In particular, PFOS and PFOA are very stable substances, and are usually used for the treatment of hardly decomposable substances. It is known that the accelerated oxidation treatment (ozone, ozone / UV, hydrogen peroxide / UV, titanium oxide photocatalyst, Fenton method) does not decompose at all (for example, see Non-Patent Documents 1 and 2).

  In recent years, a method of photochemically decomposing these substances using a heteropolyacid photocatalyst (see, for example, Patent Document 1), an aqueous layer containing a photocatalyst in the presence of a chemical species that generates active oxygen, and a fluorine-based polymer compound A method of decomposing these substances by irradiating light while mixing with a carbon dioxide layer in a supercritical state or a liquid state containing liquid (see, for example, Patent Document 2), or a high temperature such as subcritical or supercritical water A method for decomposing these substances under high pressure (for example, see Non-Patent Document 1) has been proposed. Also, a method of hydrothermal treatment at 200 to 370 ° C. in the presence of iron powder (see, for example, Patent Document 3), a method of decomposing by light irradiation in the presence of trivalent iron ions (see, for example, Patent Document 4) ) Has also been proposed. As a decomposition method using persulfate, a decomposition method combining light irradiation (for example, see Patent Document 5) or hot water at 100 to 200 ° C. (for example, see Patent Document 6) has been proposed.

  In addition, as a method for adsorbing these substances, a method using an ion exchange resin (see, for example, Patent Document 7), a method using activated carbon, and the like have been proposed.

Japanese Patent No. 3937006 Japanese Patent No. 3837468 JP 2006-306736 A JP 2007-83096 A JP 2005-225785 A JP 2008-285449 A JP 2002-59160 A

Environmental Purification Technology, Vol.7, No.8, p31-36 Journal of Chromatography, No. 1082 (2005), p110-119

  However, the methods of Patent Documents 1 and 2 are intended for decomposing fluorinated organic compounds having about 1 to 5 carbon atoms, typically trifluoroacetic acid, and are the most widely used among the fluorinated organic compounds. It is not intended to decompose PFOA and PFOS having 8 carbon atoms.

  In addition, in the method of Non-Patent Document 1 using subcritical and supercritical water, when a very small amount of a fluorine-based organic compound is decomposed, the efficiency is very poor, and there are also problems in terms of economy and safety. A technique for decomposing at normal temperature and normal pressure is desired.

  Moreover, in the method of patent document 3, 6, all need to heat to 100 degreeC or more, and there exists a subject in the safety on the energy cost and the operation management of an apparatus.

  Further, in the method of Patent Document 4, the target is a fluorocarboxylic acid, and perfluoroalkyl sulfone such as PFOS which is very difficult to decompose is not a target. Examples of PFCAs are intended for trifluoroacetic acids having 5 or less carbon atoms and fluorinated carboxylic acids such as nonafluoropentanoic acid. Not shown.

  Further, in the method of Patent Document 5, a method of generating and decomposing sulfuric acid radicals by persulfuric acid and light irradiation has been proposed, but perfluoroalkyl sulfonic acids such as PFOS which are very difficult to decompose into the target substance are targeted. However, the examples of PFCAs are directed to fluorinated carboxylic acids such as trifluoroacetic acid and pentafluoropropylene acid having a relatively small carbon number. In addition, the decomposition effect on the target substance having a large carbon number such as PFOA is not specifically shown.

  Moreover, in the method of patent document 7 using adsorption agents, such as resin and activated carbon, there exists a subject in the processing of the adsorption agent after adsorption | suction.

  Therefore, the present invention is effective in treating a hardly decomposable organic compound such as a fluorinated organic compound, particularly a refractory organic compound such as a fluorinated organic compound (especially PFOA) efficiently at room temperature and normal pressure in the treatment of a solution containing PFOA and PFOS. , PFOS) is intended to provide a processing method and a processing apparatus capable of decomposing.

  In the method for treating a hardly decomposable organic compound of the present invention, a persulfate and chelated iron are added to the hardly decomposable organic compound to decompose the hardly decomposable organic compound.

  In the method for treating a hardly decomposable organic compound, it is preferable that the hardly decomposable organic compound is a fluorine-based organic compound.

  Moreover, in the processing method of the said hardly decomposable organic compound, it is preferable that the said chelate iron is organic acid iron.

  Moreover, in the processing method of the said hard-to-decompose organic compound, it is preferable that the said organic acid iron is iron citrate, and it prepares by mixing a citric acid and an iron salt.

  In the method for treating a hardly decomposable organic compound, the solution after the hardly decomposable organic compound treatment is preferably treated with activated carbon.

  Moreover, the processing apparatus for the hardly decomposable organic compound of the present invention includes a decomposition reaction tank for adding a persulfate and chelated iron to the hardly decomposable organic compound to decompose the hardly decomposable organic compound, Persulfate addition means for adding the persulfate to the decomposition reaction tank and chelate iron addition means for adding the chelate iron to the decomposition reaction tank.

  Moreover, in the processing apparatus for the hardly decomposable organic compound, it is preferable that the hardly decomposable organic compound is a fluorine organic compound.

  Moreover, in the processing apparatus of the said hardly decomposable organic compound, it is preferable that the said chelate iron is organic acid iron.

  Moreover, in the processing apparatus of the said hard-to-decompose organic compound, the said organic acid iron is iron citrate, It has a production | generation reaction tank for mixing a citric acid and an iron salt and producing | generating the said iron citrate. preferable.

  Moreover, it is preferable that the processing apparatus of the said hardly decomposable organic compound is equipped with the activated carbon apparatus which carries out activated carbon treatment of the solution after the said hardly decomposable organic compound process.

  According to the present invention, in the treatment of a solution containing a hardly decomposable organic compound such as a fluorinated organic compound, particularly a PFOA or PFOS, the hardly decomposable organic compound such as a fluorinated organic compound (especially PFOA in particular) at room temperature and normal pressure. , PFOS).

It is a schematic diagram which shows an example of a structure of the processing apparatus of the fluorine-type organic compound which concerns on embodiment of this invention. It is a schematic diagram which shows an example of a structure of the processing apparatus of the fluorine-type organic compound which concerns on other embodiment of this invention. It is a schematic diagram which shows an example of a structure of the processing apparatus of the fluorine-type organic compound which concerns on other embodiment of this invention.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment. In the following embodiment, among the hardly decomposable organic compounds, a fluorine-based organic compound will be described as a substance to be decomposed, but this embodiment is not limited to the fluorine-based organic compound.

  FIG. 1 is a schematic diagram showing an example of a configuration of a fluorine-based organic compound processing apparatus according to an embodiment of the present invention. As shown in FIG. 1, the fluorine-containing organic compound treatment apparatus 1 includes a decomposition reaction tank 10 for decomposing a fluorine-based organic compound, a persulfate pump 12, and a persulfate supply line 14. Chelate iron addition means comprising a salt addition means, a persulfate tank 16, a chelate iron pump 18 and a chelate iron supply line 20, a chelate iron tank 22, a treated water inflow line 24, and a treated water discharge line 26.

  A treated water inflow line 24 is connected to the treated water supply port (not shown) of the decomposition reaction tank 10, and the treated water discharge line 26 is connected to the treated water discharge port (not shown) of the decomposition reaction tank 10. Is connected. The persulfate supply port (not shown) of the decomposition reaction tank 10 and the persulfate tank 16 are connected by a persulfate supply line 14. Further, a chelate iron supply line 20 connects the chelate iron supply port (not shown) of the decomposition reaction tank 10 and the chelate iron tank 22. The persulfate supply line 14 is provided with a persulfate pump 12, and the chelate iron supply line 20 is provided with a chelate iron pump 18.

  In the present embodiment, the persulfate addition means is configured by the persulfate pump 12 and the persulfate supply line 14. However, as long as the persulfate can be supplied to the decomposition reaction tank 10. However, it is not necessarily limited to the above configuration. Similarly, the chelate iron adding means is constituted by the chelate iron pump 18 and the chelate iron supply line 20. However, if the chelate iron can be supplied to the decomposition reaction tank 10, the chelate iron addition means is not necessarily configured as described above. It is not limited.

  If the decomposition reaction tank 10 is a tank for adding a persulfate and chelated iron to a solution containing a fluorine organic compound to decompose the fluorine organic compound, its structure is not particularly limited. However, it is preferable to provide a stirrer (a stirrer, a diffuser, a submersible pump, etc.) in the decomposition reaction tank 10 in terms of increasing the decomposition efficiency of the fluorine-based organic compound. The pH during the reaction in the decomposition reaction tank 10 is 7 or less, preferably in the range of 2-5. Moreover, although the temperature at the time of reaction can be implemented at normal temperature of 15-30 degreeC, it is also possible to heat and implement as needed.

  Below, the process of the fluorine-type organic compound using the processing apparatus 1 which concerns on this embodiment is demonstrated.

  The treated water flows into the decomposition reaction tank 10 from the treated water inflow line 24. Persulfate is supplied to the treated water by the persulfate pump 12. Further, the chelate iron is supplied by the chelate iron pump 18, whereby the decomposition treatment of the fluorine-based organic compound is performed in the decomposition reaction tank 10. In the decomposition reaction tank 10, it is preferable to mix the oxidizing agent and the substance to be decomposed with a stirrer, a mixer, a submersible pump, an aeration, or the like. Further, the residence time (reaction time) of water is preferably at least 5 minutes. Furthermore, when the decomposition target substance has a low concentration of 1 mg / L or less, it is more efficient to perform the multistage treatment by connecting the decomposition reaction tanks 10 in two or three stages in series. As a result, the fluorine-based organic compound can be efficiently decomposed at normal temperature and normal pressure.

  In the Fenton treatment that generates hydroxy radicals having a stronger oxidizing power than sulfuric acid radicals and accelerated oxidation treatments such as ozone / UV and ozone / hydrogen peroxide, no decomposition of PFOS was observed (Journal of Chromatography, No. 1082 ( 2005), p110-119), as in the present embodiment, the PFOS decomposition is observed for the first time by the present inventors' diligent study that sulfate radicals are generated by adding chelated iron to persulfate. It is the obtained result.

  On the other hand, as a general method for generating sulfate radicals, there are known methods of adding an iron salt to persulfuric acid and methods of irradiating persulfuric acid with light, and it is also proposed to actually apply these to fluorinated organic compounds. (Japanese Patent Laid-Open No. 2005-225785).

  However, the present inventors have arrived at the present invention by finding for the first time that the decomposition rate of PFOS and PFOA varies depending on the method of generating sulfate radicals. In other words, rather than adding divalent iron to persulfate and decomposing it, chelating iron, especially organic acid iron (iron citrate, iron gluconate, etc.) is added to persulfate to decompose PFOS and PFOA. By doing so, the decomposition rate can be increased. In particular, in PFOA, although a clear decomposition reaction was not confirmed in a system in which persulfuric acid and iron salt were added to persulfuric acid, decomposition could be clearly confirmed in the present invention (the following, See Examples). Although the mechanism involved in this phenomenon has not been clarified, the addition of chelating iron such as iron citrate only promotes the generation of sulfuric acid radicals effective in the decomposition of fluorine-based organic compounds resulting from the decomposition of persulfuric acid. However, it is considered that the fluorine-based organic compound is efficiently decomposed at room temperature and normal pressure by releasing sulfuric acid radicals in a controlled manner.

  Note that the present inventors have disclosed a method for purifying organic pollutants using persulfate after Fenton treatment with iron containing hydrogen peroxide and chelated iron (Japanese Patent Laid-Open No. 2006-341195), and persulfate and peroxidation. A method for purifying organic pollutants in the presence of iron containing hydrogen and chelated iron (Japanese Patent Laid-Open No. 2006-75469) has been proposed. However, Japanese Patent Application Laid-Open No. 2006-341195 discloses a method of decomposing by the oxidizing power of persulfuric acid after decomposing by a hydroxy radical generated by Fenton treatment, and not a method using sulfuric acid radical. Further, in Japanese Patent Application Laid-Open No. 2006-75469, the presence of hydrogen peroxide is an essential technique, and specific examples of specific promotion effects using chelated iron, particularly organic acid iron, are also available regarding the form of iron. Not shown. In both methods, the decomposition target is trichlorethylene or the like which is decomposed at normal temperature and normal pressure with ozone, hydroxy radicals, etc., which are conventionally known, and is different from the present embodiment. Furthermore, this embodiment does not require an apparatus for adding hydrogen peroxide, has a low chemical cost, and is also applicable to substances that were previously considered not to be decomposed at normal temperature and normal pressure. It is effective for.

  The fluorine-based organic compound can be decomposed to fluoride ions by the method using the persulfate of this embodiment and chelate iron, particularly organic acid iron (iron citrate, iron gluconate, etc.). Therefore, in the present embodiment, in the subsequent treatment, for example, fluoride ions can be converted into environmentally harmless calcium fluoride by an existing calcium treatment method or the like. Furthermore, since calcium fluoride becomes hydrofluoric acid which is a raw material of the fluorine-based organic compound by acid treatment, it can be reused.

  The persulfate concentration in the decomposition reaction tank 10 is not particularly limited, but is preferably at least 10 times the concentration of the fluorine-based organic compound, and more preferably at least 10 mg / L or more. preferable. Moreover, regarding the reaction pH in the decomposition reaction tank 10, it is not necessary to prepare in particular, However, It is preferable to make it react at pH 7 or less. Further, the mixing ratio of persulfate and chelate iron is not particularly limited, but a large amount of persulfate is preferable, and persulfate: chelate iron is 2: 1 to 50: 1 in molar mixing ratio. More preferably, it is the range.

  In the present embodiment, the treated water is discharged from the treated water discharge line 26 after the completion of the decomposition reaction of the fluorinated organic compound. The pH of the treated water passing through the treated water discharge line 26 may become acidic due to sulfuric acid generated by the decomposition of persulfuric acid in the decomposition reaction tank 10. Therefore, it is preferable to neutralize by injecting an alkaline agent such as caustic soda into the decomposition reaction tank 10 or the treated water discharge line 26 (during or after the reaction). In addition, since unreacted persulfate may remain in the treated water, in order to treat the persulfate, for example, sodium sulfite, sodium thiosulfate solution, etc. It is preferable to inject a reducing agent to reduce the persulfate.

  FIG. 2 is a schematic diagram showing an example of the configuration of a fluorine-based organic compound processing apparatus according to another embodiment of the present invention. In the fluorinated organic compound processing apparatus 2 shown in FIG. 2, the same components as those of the fluorinated organic compound processing apparatus 1 shown in FIG.

  The fluorine-containing organic compound treatment apparatus 2 shown in FIG. 2 includes a decomposition reaction tank 10 for decomposing the fluorine-containing organic compound, a persulfate pump 12 and a persulfate supply line 14. A chelate iron addition means comprising a persulfate tank 16, a chelate iron pump 18 and a chelate iron supply line 20, a production reaction tank 28 for producing chelate iron, a treated water inflow line 24, A treated water discharge line 26, a citric acid supply line 30 as a citric acid addition means, and an iron salt supply line 32 as an iron salt addition means are provided.

  A citric acid supply line 30 is connected to a citric acid supply port (not shown) of the production reaction tank 28, and an iron salt supply line 32 is connected to an iron salt supply port (not shown) of the production reaction tank 28. Has been. A chelate iron supply line 20 connects the chelate iron discharge port (not shown) of the production reaction tank 28 and the chelate iron supply port (not shown) of the decomposition reaction tank 10. Other configurations are the same as those of the fluorine-containing organic compound processing apparatus 1 shown in FIG.

  The production reaction tank 28 is a tank for producing iron citrate, and a stirrer (stirrer, air diffuser, submersible pump, etc.) is provided in the production reaction tank 28 in order to increase the production efficiency of iron citrate. It is preferable.

  Below, the process of the fluorine-type organic compound using the processing apparatus 2 which concerns on this embodiment is demonstrated.

  First, citric acid is supplied from the citric acid supply line 30 and iron salt is supplied from the iron salt supply line 32 to the production reaction tank 28 and mixed to produce iron citrate. The treated water flows into the decomposition reaction tank 10 from the treated water inflow line 24. Persulfate and iron citrate are supplied to the water to be treated by the persulfate pump 12 and the chelate iron pump 18. Also by such a method, it is possible to decompose the fluorine-based organic compound as described above. In addition, it is possible to generate iron citrate from citric acid and iron salts, and use the generated iron citrate for the decomposition of fluorine-based organic compounds, significantly reducing processing costs compared to purchasing commercially available iron citrate. can do. However, when citric acid and an iron salt are mixed as in this embodiment, it is preferable to supply iron citrate to the decomposition reaction tank 10 after sufficiently generating iron citrate. It should be noted that the citric acid supply line 30 and the iron salt supply line 32 are not necessarily required if citric acid and iron salt can be mixed in the production reaction tank 28 to produce iron citrate.

  As the persulfate used in the present embodiment, potassium persulfate or sodium persulfate can be preferably used, but is not limited thereto. As the citric acid used in the present embodiment, citric acid, sodium citrate or the like can be preferably used, but is not limited thereto. The iron salt used in the present embodiment can be divalent iron, trivalent iron chloride, iron sulfate or the like, but is not limited thereto.

  FIG. 3 is a schematic view showing an example of the configuration of a fluorine-based organic compound processing apparatus according to another embodiment of the present invention. In the fluorinated organic compound processing apparatus 3 shown in FIG. 3, the same components as those of the fluorinated organic compound processing apparatus 1 shown in FIG.

  3 is a persulfate addition means comprising a decomposition reaction tank 10 for decomposing a fluorine-based organic compound, a persulfate pump 12 and a persulfate supply line 14. A chelate iron addition means comprising a persulfate tank 16, a chelate iron pump 18 and a chelate iron supply line 20, a chelate iron tank 22, a treated water inflow line 24, and treated water discharge lines 26 and 27. And an activated carbon device 34. The decomposition reaction tank 10 and the activated carbon device 34 are connected by a treated water discharge line 26.

  The treated water treated by the decomposition reaction tank 10 may contain unreacted persulfate or a fluorine-based organic compound. Therefore, in the present embodiment, the unreacted persulfate and the fluorine-based organic compound can be treated by passing the treated water through the activated carbon device 34 and performing the activated carbon treatment. Examples of the activated carbon treatment by the activated carbon device 34 include activated carbon treatment by a complete mixing tank using powdered activated carbon, treatment by a fixed bed of granular activated carbon using an activated carbon tower, treatment by a fluidized bed using granular activated carbon, and the like. . However, it is not necessarily limited to these.

  When the treated water is passed through the activated carbon device 34, a pH adjuster such as caustic soda is injected into the treated water discharge line 26 to neutralize the treated water or the treated water. It is preferable to adjust the pH in the range of 5.5 to 7.5. The superficial velocity at the time of water flow to the activated carbon device 34 is preferably in the range of 1 to 20 (1 / hr).

  Furthermore, it is more preferable to reduce the remaining persulfate by injecting a reducing agent such as sodium sulfite, sodium thiosulfate, and hydrogen peroxide into the treated water discharge line 26 in terms of extending the life of the activated carbon.

Examples of the hardly decomposable organic compounds to be treated in this embodiment include fluorine-based organic compounds, organic chlorine compounds, agricultural chemicals, petroleums, and the like. Examples of the organic chlorine compound include tetrachloroethylene, trichloroethylene, cis-dichloroethylene, trichloroethane, and the like. Examples of the agrochemicals include dichlorodiphenyltrichloroethane (DDT), benzenehexachloride (BHC), cresol, thiuram, simazine, isoxathion, diazinon, fenitrothion, chlorpyripos, trichlorfone, butahomis, propyzamide, and the like. Examples of petroleums include crude oil, heavy oil, light oil, kerosene, and lubricating oil. The fluorine-based organic compound is not particularly limited as long as it is an organic compound containing a fluorine atom in the molecule. For example, perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA), perfluorooctanesulfonic acid. (PFOS), perfluorobutanesulfonic acid (PFBS), etc., an alkyl group in which all hydrogen atoms are substituted with fluorine atoms, a sulfo group (SO ₃ H group), a carboxyl group (COOH group), an amino group (NH ₂ group) Fluorine organic compounds such as perfluoroalkyl sulfonic acids, perfluoroalkyl carboxylic acids, perfluoroalkyl amines, etc., to which at least one group selected from (1) is bonded, and all hydrogen atoms are replaced by fluorine atoms Obtained from a sulfo group, a carboxyl group, and an amino group. More preferably at least fluorine-based organic compound in which one group is attached barrel. In the present specification, the fluorine-based organic compound to which at least one group selected from a sulfo group, a carboxyl group, and an amino group is bonded includes those salts.

  The chelated iron used in the present embodiment includes organic acid irons such as EDTA-iron, iron citrate, and iron gluconate. Among them, iron citrate is more preferable from the viewpoint of cost, decomposition effect, and handling. .

  The treatment method of the present embodiment is suitably used for treatment of water, drainage, soil, sediment, sludge, groundwater, and the like containing the hardly decomposable organic compound.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

Example 1
Using the apparatus shown in FIG. 1, a PFOS decomposition test was performed. In Example 1, waste water containing PFOS having a concentration of 100 μg / L was used as the solution containing the fluorine-based organic compound. The effluent containing PFOS was mixed with 5,000 mg / L sodium persulfate, 86 mg / L citric acid and 249 mg / L iron sulfate heptahydrate (50 mg / L as divalent iron). Iron acid was added. The pH during the PFOS decomposition reaction was in the range of 2-5. Two days after the start of the reaction, excess oxidizing agent such as persulfate was reduced with sodium thiosulfate. And the PFOS density | concentration in waste_water | drain was measured by LC-MS. In addition, the water temperature in a decomposition test was implemented in the range of 15-20 degreeC.

(Example 2)
In Example 2, a fluorine-based organic compound decomposition test was performed under the same conditions as in Example 1 except that the excess oxidizing agent was removed with activated carbon instead of reducing with sodium thiosulfate two days after the start of the reaction. It was.

(Comparative Example 1)
In Comparative Example 1, wastewater containing PFOS having a concentration of 100 μg / L was left as a solution containing a fluorine-based organic compound for 2 days, and then the PFOS concentration in the wastewater was measured by LC-MS.

(Comparative Example 2)
In Comparative Example 2, sodium persulfate having a concentration of 5000 mg / L was added to wastewater containing PFOS having a concentration of 100 μg / L, and excess oxidizer such as persulfate was reduced with sodium thiosulfate two days after the start of the reaction. . And the PFOS density | concentration in waste_water | drain was measured by LC-MS.

(Comparative Example 3)
In Comparative Example 3, sodium persulfate having a concentration of 5000 mg / L and iron sulfate heptahydrate having a concentration of 249 mg / L (50 mg / L as divalent iron) were added to wastewater containing PFOS having a concentration of 100 μg / L. Two days after the start, excess oxidizing agent such as persulfate was reduced with sodium thiosulfate. And the PFOS density | concentration in waste_water | drain was measured by LC-MS.

  Table 1 summarizes the PFOS concentrations of Examples 1 and 2 and Comparative Examples 1 to 3. As can be seen from Table 1, in Examples 1 and 2 in which sodium persulfate and iron citrate were added to a solution containing PFOS, Comparative Example 2 in which only sodium persulfate was added, and sodium persulfate and iron sulfate were added. From Comparative Example 3, the decomposition efficiency of PFOS could be improved. Even in the combination of sodium persulfate and iron sulfate of Comparative Example 3, sulfuric acid radicals were generated, but no improvement in decomposition efficiency was observed compared to the persulfuric acid of Comparative Example 2 alone. Although the mechanism for promoting decomposition by using iron citrate is not clear, Examples 1 and 2 supply iron or sulfate radicals in a controlled manner in such a manner that fluorine organic compounds can be decomposed more efficiently. As a result of the effective action of the generation of organic radicals by adding an organic acid, etc., the decomposition efficiency of PFOS was improved at room temperature and normal pressure.

(Example 3)
Using the apparatus shown in FIG. 1, a PFOA decomposition test was performed. In Example 3, wastewater containing PFOA having a concentration of 75 μg / L was used as the solution containing the fluorine-based organic compound. A citrate prepared by mixing the effluent containing PFOA with sodium persulfate at a concentration of 5000 mg / L, citric acid at a concentration of 86 mg / L and iron sulfate heptahydrate (50 mg / L as divalent iron) at 249 mg / L. Iron acid was added. The pH during the PFOA decomposition reaction was in the range of 2-5. Two days after the start of the reaction, excess oxidizing agent such as persulfate was reduced with sodium thiosulfate. And the PFOA density | concentration in waste_water | drain was measured by LC-MS. In addition, the water temperature in the decomposition test was implemented in the range of 15-20 degreeC.

(Comparative Example 4)
In Comparative Example 4, wastewater containing 75 μg / L of PFOA as a solution containing a fluorine-based organic compound was allowed to stand for 2 days, and then the PFOA concentration in the wastewater was measured by LC-MS.

(Comparative Example 5)
In Comparative Example 5, sodium persulfate having a concentration of 5000 mg / L and iron sulfate heptahydrate having a concentration of 249 mg / L (50 mg / L as divalent iron) were added to wastewater containing PFOA having a concentration of 100 μg / L. Two days after the start, excess oxidizing agent such as persulfate was reduced with sodium thiosulfate. And the PFOA density | concentration in waste_water | drain was measured by LC-MS.

  Table 2 summarizes the PFOA concentrations of Example 3 and Comparative Examples 4 and 5. As can be seen from Table 2, PFOA was clearly decomposed only in Example 3 in which sodium persulfate and iron citrate were added to the wastewater containing PFOA. Also in this example, decomposition was not observed in the sulfuric acid radical generated from persulfuric acid and iron in Comparative Example 5, and decomposition occurred only in the present invention, confirming the effectiveness of the present invention. As described above, the combination of sodium persulfate and iron citrate is suitable for the decomposition of fluorine-based organic compounds at room temperature and pressure, particularly for the decomposition of highly stable fluorine-based organic compounds such as PFOS and PFOA. It was confirmed that it was very effective.

  1 to 3 treatment apparatus, 10 decomposition reaction tank, 12 persulfate pump, 14 persulfate supply line, 16 persulfate tank, 18 chelate iron pump, 20 chelate iron supply line, 22 chelate iron tank, 24 Treated water inflow line, 26, 27 Treated water discharge line, 28 production reaction tank, 30 citric acid supply line, 32 iron salt supply line, 34 activated carbon device.

Claims (10)

  A method for treating a hardly decomposable organic compound, comprising adding persulfate and chelated iron to a hardly decomposable organic compound to decompose the hardly decomposable organic compound.   The method for treating a hardly decomposable organic compound according to claim 1, wherein the hardly decomposable organic compound is a fluorine organic compound.   The method for treating a hardly decomposable organic compound according to claim 1 or 2, wherein the chelated iron is an organic acid iron.   4. The method for treating a hardly decomposable organic compound according to claim 3, wherein the organic acid iron is iron citrate, and is prepared by mixing citric acid and an iron salt. Organic compound processing method.   The method for treating a hardly decomposable organic compound according to any one of claims 1 to 4, wherein the solution after the treatment of the hardly decomposable organic compound is treated with activated carbon. Processing method. A decomposition reaction tank for adding a persulfate and chelated iron to the hardly decomposable organic compound to decompose the hardly decomposable organic compound;
Persulfate addition means for adding the persulfate to the decomposition reaction tank;
And a chelating iron adding means for adding the chelating iron to the decomposition reaction tank.   7. The processing apparatus for a hardly decomposable organic compound according to claim 6, wherein the hardly decomposable organic compound is a fluorinated organic compound.   8. The processing apparatus for a hardly decomposable organic compound according to claim 6, wherein the chelated iron is an organic acid iron.   The processing apparatus for a hardly decomposable organic compound according to claim 8, wherein the organic acid iron is iron citrate, and the iron citrate is produced by mixing citric acid and an iron salt. An apparatus for treating a hardly decomposable organic compound, comprising:   It is a processing apparatus of the hard-to-decompose organic compound of any one of Claims 6-9, Comprising: The hard-to-decompose characteristic provided with the activated carbon apparatus which carries out the active carbon process of the solution after the said hard-to-decompose organic compound process Equipment for organic organic compounds.

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