Method for purifying soil containing DDTs

Abstract

To provide a novel method for purifying soil containing DDTs.SOLUTION: This method for purifying soil containing DDTs is configured such that (A) iron powders and (B) a surface active agent are added to the soil.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for remediating soil containing DDTs. [Background technology]

[0002] One method of treating soil contaminated with DDTs is to use controlled or isolated final disposal sites or incineration facilities. However, the number of final disposal sites and incineration facilities is limited in Japan. Furthermore, both methods have the problem of placing a heavy burden on the environment and being expensive to treat.

[0003] A method using microorganisms is known as a method for decontaminating soil contaminated with DDTs by converting DDTs into harmless substances (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 10-507687 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a novel method for purifying soil containing DDTs. [Means for solving the problem]

[0006] As a result of extensive research to solve the above problems, the present inventors have discovered that soil containing DDTs can be purified by adding (A) iron powder and (B) a surfactant to the soil, and have thus completed the present invention.

[0007] That is, the present invention relates to the following inventions. [1] A method for purifying soil containing DDTs, characterized by adding (A) iron powder and (B) a surfactant to the soil. The mass ratio of the amounts of component (A) and component (B) added is 1-10:1-10. How to purify soil. [2] The method for purifying soil according to [1], wherein component (B) is an anionic surfactant. [3] The method for remediating soil according to [1] or [2], wherein component (B) is a non-soap anionic surfactant. [4] The method for purifying soil according to any one of [1] to [3], wherein component (B) is at least one anionic surfactant selected from the group consisting of α-olefin sulfonates, alkyl sulfates, polyoxyalkylene alkyl ether sulfates, amide ether sulfates, methyl taurates, and sulfosuccinates. [5] The method for purifying soil according to [1], wherein component (B) is a nonionic surfactant. [6] The method for purifying soil according to [1] or [5], wherein component (B) is at least one nonionic surfactant selected from the group consisting of polyoxyalkylene alkyl ethers, polyoxyalkylene alkyl esters, sorbitan fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene sorbitol fatty acid esters, alkylamines, and polyoxyalkylene alkylamines. [7] The method for remediating soil according to [1], [5] or [6], wherein component (B) is a nonionic surfactant having an HLB value of 8.1 to 16.9. [8] The method for purifying soil according to any one of [1] to [7], wherein the component (A) is added so that the content of the component (A) in the soil is 0.1 to 30 mass %. [9] The method for purifying soil according to any one of [1] to [8], wherein the component (B) is added so that the content of the component (B) in the soil is 1 to 15 mass %. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a novel method for purifying soil containing DDTs. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a graph showing the purification effect when iron powder and an anionic surfactant are added to soil containing DDTs. [Figure 2] 1 is a graph showing the purification effect when iron powder and a nonionic surfactant are added to soil containing DDTs. [Figure 3] 1 is a graph showing the purification effect when iron powder and a nonionic surfactant with an HLB value in the range of 8.1 to 16.9 are added to soil containing DDTs. [Figure 4] This is a graph showing the change in the concentration of DDTs in target soil over time when iron powder and a nonionic surfactant (HLB value 13.6) were added to soil containing high concentrations of DDTs. [Figure 5] This is a graph showing the purification effect when iron powder and a nonionic surfactant (HLB value 13.6) were added to soil containing high concentrations of DDTs. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will be described in detail below, but the present invention is not limited to the following embodiments.

[0011] A method for purifying soil containing DDTs according to one embodiment of the present invention is characterized by adding (A) iron powder and (B) a surfactant to soil containing DDTs.

[0012] In this specification, "DDTs" refers to 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (p,p'-DDT), 1,1,1-trichloro-2-(2-chlorophenyl)-2-(4-chlorophenyl)ethane (o,p'-DDT), 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (p,p'-DDD), 1,1-dichloro-2-(2-chlorophenyl)-2-(4-chlorophenyl)ethane (o,p'-DDT), 1,1-bis(4-chlorophenyl)-2,2-dichloroethene (p,p'- This refers to DDT and its degradation products, including DDT, 1,1-dichloro-2-(2-chlorophenyl)-2-(4-chlorophenyl)ethene (o,p'-DDE), 1-chloro-2,2-bis(4-chlorophenyl)ethene (p,p'-DDMU), 1-chloro-2-(2-chlorophenyl)-2-(4-chlorophenyl)ethene (o,p'-DDMU), 2,2-bis(4-chlorophenyl)ethanol (p,p'-DDOH), and 2-(2-chlorophenyl)-2-(4-chlorophenyl)ethanol (o,p'-DDOH).

[0013] In this specification, "purification" means reducing the concentration of DDTs in the soil.

[0014] The soil to be purified in this embodiment is soil containing DDTs, and there are no particular limitations on the type or quality of the soil.

[0015] <Component (A)> In the method for purifying soil containing DDTs according to this embodiment, iron powder is added as component (A). There are no particular limitations on the iron powder used as component (A), as long as it has a reducing effect. Examples of iron powder include commercially available ordinary iron powder, atomized iron powder, reduced iron powder, electrolytic iron powder, sponge iron powder, cast iron powder, and alloy iron powder. From the viewpoints of ease of addition and mixing with soil, the characteristics of the equipment used for mixing, and reactivity with DDTs, the average particle size of the iron powder is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. In this specification, the "average particle size" refers to the volume-based median diameter measured using a laser diffraction particle size analyzer.

[0016] In the method for purifying soil containing DDTs according to this embodiment, the amount of component (A) added is not particularly limited and is appropriately determined depending on the concentration of DDTs in the soil to be purified, the type of soil, the soil quality, etc. When component (A) is added to the soil, the amount of component (A) added is preferably such that the content relative to the soil is 0.1 to 30% by mass, more preferably 0.1 to 15% by mass, and even more preferably 0.5 to 10% by mass. The amount of component (A) added is suitable not only from the viewpoint of uniformly dispersing component (A) in the soil and efficiently purifying DDTs, but also from the viewpoint of reducing costs.

[0017] <(B) component> In the method for purifying soil containing DDTs according to this embodiment, a surfactant is added as component (B). Examples of surfactants used as component (B) include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. Component (B) is preferably anionic or nonionic surfactants.

[0018] The anionic surfactant used as component (B) is not particularly limited as long as it has the effect of promoting the cleaning action of iron powder. Examples of anionic surfactants include soap-based anionic surfactants (higher fatty acid salts, alkyl ether carboxylates, polyoxyalkylene ether carboxylates, alkyl (or alkenyl) amide ether carboxylates, acylamino carboxylates, etc.), non-soap-based anionic surfactants (sulfonates (linear alkylbenzene sulfonates (LAS), α-olefin sulfonates (AOS), methyl taurates, sulfosuccinates, etc.), sulfates (alkyl sulfates (AS), polyoxyalkylene alkyl ether sulfates (AES), amide ether sulfates, etc.), etc. In this specification, the term "non-soap-based anionic surfactant" refers to an anionic surfactant having an anionic bond consisting of a carboxylate. This refers to anionic surfactants excluding surfactants. The anionic surfactant used as component (B) is preferably a non-soap anionic surfactant, from the viewpoint of maintaining the reducing action on the iron powder surface and promoting the purification action of the iron powder, i.e., improving the dispersion of soil particles and iron powder, and reducing the formation of cations and precipitates in the soil, thereby promoting the purification action of the iron powder. More preferred examples include α-olefin sulfonates, alkyl sulfates, polyoxyalkylene alkyl ether sulfates, amide ether sulfates, methyl taurines, and sulfosuccinates. These anionic surfactants may be used alone or in any combination of two or more.

[0019] Examples of α-olefin sulfonates include tetradecene sulfonates (olefin (C14-16) sulfonates). Examples of alkyl sulfates include lauryl sulfate and alkyl (C6-18) sulfate. Examples of polyoxyalkylene alkyl ether sulfates include polyoxyethylene alkyl ether sulfates (e.g., polyoxyethylene alkyl (C8-18) ether sulfate, laureth sulfate (polyoxyethylene lauryl ether sulfate)). Examples of amide ether sulfates include fatty acid (C12-14) amide ether sulfate and alkyl amide ether sulfate. Examples of methyl taurine salts include coconut oil fatty acid methyl taurine and N-myristoyl-N-methyl taurine. Examples of sulfosuccinates include dialkyl (C6-18) sulfosuccinates (such as dioctyl sulfosuccinate, etc.), polyoxyethylene dialkyl (C8-18) sulfosuccinates (such as di-polyoxyethylene lauryl sulfosuccinate, etc.), and the like. Here, for example, (C14-16) means that the alkyl group has 14 to 16 carbon atoms.

[0020] Examples of the salt include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as magnesium salts and calcium salts; alkanolamine salts such as monoethanolamine salt (monoethanolammonium), diethanolamine salt (diethanolammonium), and triethanolamine salt (triethanolammonium); and ammonium salts such as triethylamine salt (triethylammonium). Specific examples include sodium α-olefin sulfonate, sodium tetradecene sulfonate, sodium dioctyl sulfosuccinate, polyoxyethylene lauryl ether sodium sulfate, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene alkyl ether sulfate ester triethanolamine, fatty acid amide ether sulfate ester triethanolamine, sodium coconut oil fatty acid methyl taurate, sodium N-decanoyl-N-methyl taurate, triethanolamine lauryl sulfate, and polyoxyethylene lauryl ether sulfate triethanolamine, all of which can be suitably used as the anionic surfactant for component (B).

[0021] Commercially available α-olefin sulfonates include Lipolan PJ-400CJ, Lipolan PJ-400CJ, Lipolan LB-440, Lipolan LJ-441, Lipolan LB-840, and Lipolan PB-800CJ (all trade names, manufactured by Lion Corporation). Commercially available alkyl ether sulfates include Sannol LMT-1430 and Sannol TD-3130 (all trade names, manufactured by Lion Corporation), Syntrex EH-R, Persoft SP, Persoft SK, Persoft SF-T, Nissan Trax K-40, Nissan Trax K-300, Persoft EF, Persoft EDO, Persoft EL, Persoft EK, Persoft EF-T, Persoft EL-T, Sanamide CF-3, and Sanamide CF-10 (all trade names, manufactured by Lion Corporation). Examples of commercially available methyl taurate salts include those listed under the trade names Lipotack TE (manufactured by Lion Corporation), Diapon S, Diapon LM, Diapon K, Diapon K-SF, Diapon K-SF Powder, and Diapon HF-SF (manufactured by NOF Corporation). Commercially available sulfosuccinates include, for example, Repearl 835I, Repearl 860K, Repearl 870P, Repearl MSC, and Repearl NTD (all trade names manufactured by Lion Corporation), Sunmorin OT-70 (all trade names manufactured by Sanyo Chemical Industries, Ltd.), Lapisol A-30, and Lapisol A-80 (all trade names manufactured by NOF Corporation).

[0022] The nonionic surfactant used as component (B) is not particularly limited as long as it promotes the cleaning action of iron powder. Examples of nonionic surfactants include polyoxyalkylene alkyl ethers, polyoxyalkylene alkyl esters, sorbitan fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyalkylene fatty acid esters, polyoxyalkylene hydrogenated castor oil, alkylamines, and polyoxyalkylene alkylamines. From the viewpoint of promoting the reducing action on the iron powder surface, i.e., improving the dispersion of soil particles and iron powder to promote the cleaning action of iron powder, the nonionic surfactant used as component (B) is preferably polyoxyalkylene alkyl ethers, polyoxyalkylene alkyl esters, sorbitan fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene sorbitol fatty acid esters, alkylamines, or polyoxyalkylene alkylamines. These nonionic surfactants may be used alone or in any combination of two or more.

[0023] Examples of polyoxyalkylene alkyl ethers include polyoxyethylene alkyl ethers (polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene oleyl ether, polyoxyethylene behenyl ether, polyoxyethylene-2-ethylhexyl ether, polyoxyethylene isodecyl ether, polyoxyethylene branched alkyl ethers, etc.), polyoxyethylene polyoxypropylene alkyl ethers, polyoxypropylene alkyl ethers (polyoxypropylene stearyl ether, etc.). Examples of polyoxyalkylene alkyl esters include polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, etc. Examples of sorbitan fatty acid esters include sorbitan monocaprylate, sorbitan monolaurate, sorbitan monomyristate, sorbitan monopalmitate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate, sorbitan sesquioleate, etc. Examples of polyoxyalkylene sorbitan fatty acid esters include polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan triisostearate, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan trioleate. Examples of polyoxyalkylene sorbitol fatty acid esters include polyoxyethylene sorbitan tetraoleate. Examples of alkylamines include bis(2-hydroxyethyl)alkyl(coconut)amine, bis(2-hydroxyethyl)oleylamine, bis(2-hydroxyethyl)alkyl(beef tallow)amine, and bis(2-hydroxyethyl)alkyl(hardened beef tallow)amine.Examples of polyoxyalkylene alkylamines include polyoxyethylene alkylamines (polyoxyethylene laurylamine, polyoxyethylene alkyl(coconut)amine, polyoxyethylene stearylamine, polyoxyethylene oleylamine, polyoxyethylene alkyl(beef tallow)amine, polyoxyethylene alkyl(hardened beef tallow)amine).

[0024] Commercially available polyoxyalkylene alkyl ethers include, for example, Nonion K-204, Nonion K-220, Nonion K-230, Nonion K-2100W, Persoft NK-60, Persoft NH-90C, Persoft NK-100, Persoft NK-100C, Nonion P-208, Nonion P-210, Nonion P-213, Nonion E-202, Nonion E-202S, Nonion E-205, Nonion E-205S, Nonion E-212, Nonion E-215, Nonion E-230, Nonion S-202, Nonion S-207, and Nonion E-215. S-215, Nonion S-220, Nonion B-250, Nonion EH-204, Nonion EH-208, Nonion ID-203, Nonion ID-206, Nonion ID-209, Dispanol TOC, Nonion HT-505, Nonion HT-507, Nonion HT-510, Nonion HT-512, Nonion HT-515, Nonion HT-518 (all trade names manufactured by NOF Corporation), Leox CL-30, Leocol NL-30C, Leocol TD-50, Leocol TD-70, Leocol TD-90, Leocol TD-90D, Leocol TDA -90-25, Leocal TDN-90-80, Leocal TD-120, Leocal TD-150, Leocal TD-200, Leocal TDA-400-75, Leocal SC-50, Leocal SC-70, Leocal SC-80, Leocal SC-90, Leocal SC-120, Leocal SC-150, Leocal SC-200, Leocal SC-300, Leocal SC-400, Rheox CL-2008, Lionol L-535, Lionol L-745, Lionol L-785, Lionol L-950, Lionol NH-1 509, Lionol TD-730, Lionol TD-2180, Lionol TDL-20, Lionol TDL-30, Lionol TDL-50 (all trade names / manufactured by Lion Corporation), Emulgen 102KG, Emulgen 103, Emulgen 104P, Emulgen 105, Emulgen 106, Emulgen 108, Emulgen 109P, Emulgen 120, Emulgen 123P, Emulgen 130K, Emulgen 147, Emulgen 150, Emulgen 210P, Emulgen 220, Emulgen 306P, Emulgen 320P, Emulgen 350,Emulgen 404, Emulgen 408, Emulgen 409PV, Emulgen 420, Emulgen 430, Emulgen 705, Emulgen 707, Emulgen 709, Emulgen 1108, Emulgen 1118S-70, Emulgen 1135S-70, Emulgen 1150S-60, Emulgen 4085, Emulgen 2020G-HA, Emulgen 2025G (all trade names / manufactured by Kao Corporation), Emulmin CC-100, Emulmin CC-130, Emulmin CC-150, Emulmin CC-200, Emulmin CO-50, Emulmin CO-100, Emulmin NL-70, Emulmin LS-80, Emulmin NL-80, Emulmin NL-90, Emulmin LS-90 Emulmin NL-100, Emulmin NL-110, Emulmin L-380, Sannonic SS-70, Sannonic SS-90, Sannonic SS-120, Sannonic SS-50, Sannonic FN-80, Sannonic FN-100, Sannonic FN-140, Naroacty CL-40, Naroacty CL-50, Naroacty CL-70, Naroacty CL-85, Naroacty CL-95, Naroacty CL-100, Naroacty CL-120, Naroacty CL-140, Naroacty CL-160, Naroacty CL-200, Naroacty CL-400 (all trade names manufactured by Sanyo Chemical Industries, Ltd.) and the like can be used. Commercially available polyoxyalkylene alkyl esters that can be used include, for example, Nonion L-2, Nonion L-4, Nonion S-2, Nonion S-4, Nonion S-6, Nonion S-15, Nonion S-15K, Nonion S-15.4, Nonion S-15.4V, Nonion S-40, Nonion O-2, Nonion O-3, Nonion O-4, and Nonion O-6 (hereinafter referred to as trade names, manufactured by NOF Corporation). Examples of sorbitan fatty acid esters include Nonion CP-08R, Nonion LP-20R, Nonion MP-30R, Nonion PP-40R pellets, Nonion SP-60R pellets, Nonion OP-80R, Nonion OP-83RAT, Nonion OP-85R (all trade names manufactured by NOF Corporation), Cadenax SO-83M (all trade names manufactured by Lion Corporation), Rheodol SP-L10, Rheodol SP-P10, Rheodol SP-S10V, Rheodol SP-S20,Rheodor SP-S30V, Rheodor SP-O10V, Rheodor SP-O30V, Rheodor Super SP-L10, Rheodor AS-10V, Rheodor AO-10V, Rheodor AO-15V (all trade names manufactured by Kao Corporation) and the like can be used. Commercially available polyoxyalkylene sorbitan fatty acid esters that can be used include, for example, Nonion LT-221, Nonion LT-280, Nonion LT-280W, Nonion ST-221, Nonion OT-221, and Nonion OT-521 (all trade names, manufactured by NOF Corporation), Rheodol TW-L120, Rheodol TW-L106, Rheodol TW-P120, Rheodol TW-S120V, Rheodol TW-S106V, Rheodol TW-S320V, Rheodol TW-O120V, Rheodol TW-O106V, Rheodol TW-O320V, Rheodol TW-IS399C, and Rheodol Super TW-L120 (all trade names, manufactured by Kao Corporation). Commercially available polyoxyalkylene sorbitol fatty acid esters include, for example, Uniox ST-30E, Uniox ST-40E, and Uniox ST-60E (all trade names, manufactured by NOF Corporation), Rheodol 430V, Rheodol 440V, and Rheodol 460V (all trade names, manufactured by Kao Corporation), etc. Commercially available alkylamines include, for example, Liponol C / 12, Liponol O / 12, Liponol T / 12, and Liponol HT / 12 (all trade names, manufactured by Lion Corporation), etc. Commercially available polyoxyalkylene alkylamines include, for example, Nymeen L-201, Nymeen L-202, Nymeen L-207, Nymeen F-202, Nymeen F-215, Nymeen T2-202, Nymeen T2-210, Nymeen T2-230, Nymeen S-202, Nymeen S-204, Nymeen S-210, Nymeen S-215, and Nymeen S-216. Nine S-220, Nymeen O-205 (all trade names / manufactured by NOF Corporation), Liponol C / 15, Liponol C / 25, Liponol O / 15, Liponol O / 25, Liponol T / 15, Liponol T / 25, Liponol HT / 14, Liponol C / 18-18 (all trade names / manufactured by Lion Corporation), Amite 102, Amite 105, Amite 105A, Amite 302,Amit 320 (trade name, manufactured by Kao Corporation) and the like can be used.

[0025] For nonionic surfactants, the HLB (Hydrophilic-Lipophilic Balance) value is sometimes used to represent the degree of affinity for water and oil. In this specification, the "HLB" value refers to a value calculated by the Griffin method. When two or more nonionic surfactants are used in combination, the "HLB" value refers to the weighted average of the HLB values ​​of the individual nonionic surfactants. The HLB value of the nonionic surfactant used as component (B) is not particularly limited, as long as it maintains the reducing action on the iron powder surface and promotes the purification action of the iron powder, i.e., improves the dispersion of soil particles and iron powder to promote the purification action of the iron powder. The HLB value of the surfactant used as component (B) is preferably 8.1 to 16.9, more preferably 10.5 to 12.1, from the perspective of facilitating contact of DDTs with the iron powder surface and promoting the purification action of the iron powder, i.e., improving the dispersion of soil particles and iron powder to promote the purification action of the iron powder.

[0026] In the method for remediating soil containing DDTs according to this embodiment, the amount of component (B) added is not particularly limited and is appropriately determined depending on the concentration of DDTs in the soil to be remediated, the type and quality of the soil, the amount of component (A) added, and other factors. When component (B) is added to the soil, the amount of component (B) added is preferably 1 to 15% by mass, more preferably 1 to 10% by mass, and even more preferably 2 to 8% by mass relative to the soil. The amount of component (B) added is suitable from the perspective of facilitating contact of DDTs with the surface of iron powder and promoting the remediation action of the iron powder, i.e., improving the dispersion of soil particles and iron powder and promoting the remediation action of the iron powder.

[0027] In the method for remediating soil containing DDTs according to this embodiment, the mass ratio of component (A) to component (B) added to the soil is not particularly limited and is appropriately determined depending on the concentration of DDTs in the soil to be remediated, the type and quality of the soil, the types of component (A) and component (B), etc. The mass ratio of component (A) to component (B) added to the soil is preferably component (A):component (B)=1-10:1-10, more preferably component (A):component (B)=1-6:1-6, and even more preferably component (A):component (B)=2-6:3-6, from the viewpoint of maintaining the reducing action on the surface of the iron powder and facilitating contact of the DDTs with the iron powder, i.e., from the viewpoint of improving the dispersion of the soil particles and iron powder and promoting the remediation action of the iron powder.

[0028] The method for remediating soil containing DDTs according to this embodiment can be carried out, for example, by adding component (A) and component (B) to excavated soil at a remediation facility. In this case, the remediated soil can be returned to its original location (i.e., the excavated location). Alternatively, the method for remediating soil containing DDTs according to this embodiment can be carried out by directly adding component (A) and component (B) to the soil containing DDTs in situ, without transporting the soil to a remediation facility.

[0029] Methods for adding component (A) and component (B) to soil containing DDTs include mixing component (A) and component (B) with water to form a slurry and then adding the slurry to the soil, or mixing the soil to form a slurry with water and then adding component (A) and component (B). The amount of water used when adding component (A) and component (B) is not particularly limited and is appropriately determined depending on the type and quality of the soil to be purified, the amount of water contained in the soil, and the amounts of component (A) and component (B) to be added. The water content is preferably 0 to 300% by mass, more preferably 5 to 250% by mass, and even more preferably 10 to 200% by mass, of the soil to be purified. This water content is suitable from the perspective of efficiently mixing and uniformly dispersing component (A) and component (B) in the soil to be purified.

[0030] When adding components (A) and (B) to soil containing DDTs, the specified amounts of each can be added all at once or in multiple installments. Furthermore, by adding components (A) and (B) to soil containing DDTs and then allowing the soil to stand for 1 to 12 weeks, the concentration of DDTs in the soil can be reduced. By adding components (A) and (B) in multiple installments during the standstill period, the concentration of DDTs in the soil can be reduced more efficiently.

[0031] The method for remediating soil containing DDTs according to this embodiment may further include a step of mixing components (A) and (B) in addition to the step of adding them to the soil containing DDTs. The method for mixing the soil containing DDTs with components (A) and (B) is not particularly limited, and mixing can be performed using equipment commonly used in plant mixing, such as a backhoe, a backhoe equipped with a mixing bucket, a stabilizer, a self-propelled soil improvement machine, a stationary mixer, a trencher-type agitator / mixer, a deep mixer, or a power blender. By including the mixing step, components (A) and (B) are more uniformly dispersed in the soil to be remediated, thereby more efficiently reducing the concentration of DDTs in the soil.

[0032] According to the remediation method of the embodiment described above, soil containing DDTs can be remediated inexpensively and simply. [Example]

[0033] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0034] In the present examples, "% by mass" refers to the mass % relative to the soil containing DDTs.

[0035] [Test Example 1: Measurement of DDT concentrations in soil] Soil samples (hereinafter referred to as "sample soil No. 1" and "sample soil No. 2") were collected from two sites contaminated with DDTs, and the concentrations of DDTs in each soil were measured. Measurements of DDT concentrations in the sample soil were carried out in accordance with the method described in "IV Soil Section," "1. Analysis of Organochlorine Compounds, Octachlorostyrene, and Benzo(a)pyrene" (GC / MS method) in the official "Survey and Analysis Methods for the Actual Status of Environmental Residues of Pesticides, etc." (October 1999, Soil and Pesticides Division, Water Quality Conservation Bureau, Environment Agency).

[0036] Specifically, in this example, the concentrations (mg / kg) of p,p'-DDT, o,p'-DDT, p,p'-DDD, o,p'-DDD, p,p'-DDE, and o,p'-DDE among the DDTs contained in sample soils No. 1 and 2 were measured according to the method described above. The results are shown in Table 1.

[0037] [Table 1]

[0038] Table 1 shows that sample soil No. 1 contains a higher concentration of DDTs than sample soil No. 2.

[0039] [Test Example 2: Amount of iron powder added and purification effect] The purification effect of adding only iron powder to sample soil No. 2 containing DDTs was evaluated using the following method. 40 g of sample soil No. 2 was placed in a 100 ml glass bottle, and 60 ml of water was added. To the glass bottle, no iron powder was added as a control in Study Example 1, 0.8 g (2 mass%) of iron powder was added in Study Example 2, 1.6 g (4 mass%) of iron powder was added in Study Example 3, and 2.4 g (6 mass%) of iron powder was added in Study Example 4. Each sample was stirred and mixed, and then allowed to stand for one week. The DDT concentrations in Study Examples 1 to 4 after standing for one week were measured using the same method as in Test Example 1. The results are shown in Table 2.

[0040] [Table 2]

[0041] Table 2 shows that the addition of iron powder reduced the concentration of DDTs in the sample soil after one week of standing. It also shows that increasing the amount of iron powder further reduced the concentration of DDTs in the sample soil after one week of standing. In other words, increasing the amount of iron powder strengthened the purification effect. Table 2 also shows that the enhancement of the purification effect was smaller when the amount of iron powder added was increased from 1.6 g (4 mass%) (Example 3) to 2.4 g (6 mass%) (Example 4) than when the amount of iron powder added was increased from 0.8 g (2 mass%) (Example 2) to 1.6 g (4 mass%) (Example 3). For these reasons, in Test Examples 3 to 5, the amount of iron powder added was set to 4 mass% of the sample soil.

[0042] [Test Example 3: Purifying effect of iron powder and anionic surfactant] The purification effect of adding iron powder and an anionic surfactant to sample soil No. 2 was evaluated using the following method. 40 g of sample soil No. 2 was placed in a 100 ml glass bottle, followed by the addition of 60 ml of water. In Examples 1-1 to 1-10, 1.6 g (4 mass%) of iron powder and 1.2 g (3 mass%) of anionic surfactant were added and mixed by stirring. The components and classifications of the anionic surfactants added in Examples 1-1 to 1-10 are shown in Table 3. In contrast, Comparative Example 1-1 contained only sample soil No. 2 and water, and Comparative Example 1-2 contained sample soil No. 2, water, and 1.6 g (4 mass%) of iron powder, mixed by stirring. In Comparative Examples 1-1 and 1-2 and Examples 1-1 to 1-10, the DDT concentrations after standing for two weeks were measured using the same method as in Test Example 1. The results are shown in Figure 1. For example, "polyoxyethylene (3)" means that the average number of repeating oxyethylene groups is 3 (the average number of moles of ethylene oxide added is 3).

[0043] [Table 3]

[0044] FIG. 1 shows that the concentration of DDTs in the sample soil after two weeks of standing was reduced when iron powder and an anionic surfactant were added (Examples 1-1 to 1-10) compared to when neither was added (Comparative Example 1-1). It also shows that the purification effect was enhanced when iron powder and an anionic surfactant were added (Examples 1-1 to 1-6, 1-9, and 1-10) compared to when only iron powder was added (Comparative Example 1-2). In contrast, the results of Examples 1-7 and 1-8 show that the purification effect was not enhanced when a carboxylic acid-based anionic surfactant was used as the anionic surfactant. This is presumably because the carboxylic acid-based anionic surfactant improved the dispersion of soil particles and iron powder and prevented the formation of cations and precipitates in the soil, thereby making it difficult for the carboxylic acid-based anionic surfactant to exhibit the effect of promoting the purification effect of iron powder.

[0045] [Test Example 4: Purifying Action of Iron Powder and Nonionic Surfactant] The purification effect of adding iron powder and a nonionic surfactant to sample soil No. 2 was evaluated using the following method. 40 g of sample soil No. 2 was placed in a 100 ml glass bottle, followed by 60 ml of water. In Examples 2-1 to 2-10, 1.6 g (4% by mass) of iron powder and 1.2 g (3% by mass) of nonionic surfactant were added and stirred. The components, classifications, and HLB values ​​of the nonionic surfactants added in Examples 2-1 to 2-10 are shown in Table 4. In contrast, Comparative Example 2-1 contained only sample soil No. 2 and water, and Comparative Example 2-2 contained sample soil No. 2, water, and 1.6 g (4% by mass) of iron powder, which were then stirred and mixed. For Comparative Examples 2-1 and 2-2 and Examples 2-1 to 2-10, the DDT concentrations after two weeks of standing were measured using the same method as in Test Example 1. The results are shown in Figure 2.

[0046] [Table 4]

[0047] 2 shows that the concentration of DDTs in the sample soil after standing for two weeks was reduced when iron powder and a nonionic surfactant were added (Examples 2-1 to 2-10) compared to when neither was added (Comparative Example 2-1).It also shows that the purification effect was enhanced when iron powder and a nonionic surfactant were added (Examples 2-1 to 2-10) compared to when only iron powder was added (Comparative Example 2-2).

[0048] [Test Example 5: HLB value and purification effect of nonionic surfactants] The effect of the HLB value of the nonionic surfactant on the purification activity of sample soil No. 2 when iron powder and a nonionic surfactant were added was evaluated using the following method. 40 g of sample soil No. 2 was placed in a 100 ml glass bottle, followed by 60 ml of water. In Examples 3-1 to 3-6, 1.6 g (4 mass%) of iron powder and 1.2 g (3 mass%) of a nonionic surfactant were added and mixed by stirring. The types and HLB values ​​of the nonionic surfactants added in Examples 3-1 to 3-6 are shown in Table 5. In contrast, Comparative Example 3-1 contained only sample No. 2 and water, and Comparative Example 3-2 contained sample No. 2, water, and 1.6 g (4 mass%) of iron powder, mixed by stirring. In Comparative Examples 3-1 and 3-2 and Examples 3-1 to 3-6, the concentrations of DDTs after standing for two weeks were measured using the same method as in Test Example 1. The results are shown in Figure 3.

[0049] [Table 5]

[0050] 3 shows that the concentration of DDTs in the sample soil after standing for two weeks was reduced when iron powder and a nonionic surfactant with an HLB value in the range of 8.1 to 16.9 were added (Examples 3-1 to 3-6) compared to when neither was added (Comparative Example 3-1). It also shows that the purification effect was enhanced when iron powder and a nonionic surfactant with an HLB value in the range of 8.1 to 16.9 were added (Examples 3-1 to 3-6) compared to when only iron powder was added (Comparative Example 3-2).

[0051] [Test Example 6: Purification of soil containing high concentrations of DDTs] The purification effect of adding iron powder and a nonionic surfactant (HLB value 13.6) to sample soil No. 1, which contained a high concentration of DDTs, was evaluated by measuring the change in DDT concentration in the sample soil over time. 40 g of sample soil No. 1 was placed in a 100 ml glass bottle, followed by 60 ml of water. In Example 4-1, 1.6 g (4 mass%) of iron powder and 1.2 g (3 mass%) of nonionic surfactant were added. In Example 4-2, 1.6 g (4 mass%) of iron powder and 2.4 g (6 mass%) of nonionic surfactant were added. In Example 4-3, 0.8 g (2 mass%) of iron powder and 1.2 g (3 mass%) of nonionic surfactant were added. In Example 4-4, 2.4 g (6 mass%) of iron powder and 1.2 g (3 mass%) of nonionic surfactant were added and stirred. The components, amounts, and HLB values ​​of the nonionic surfactants added in Examples 4-1 to 4-4 are shown in Table 6. Comparative Example 4-1 contained only sample soil No. 1 and water, while Comparative Example 4-2 contained sample soil No. 1, water, and 1.6 g (4% by mass) of iron powder, which were then stirred and mixed. After 7 weeks of standing, Comparative Example 4-2 added 1.6 g (4% by mass) of iron powder, and Examples 4-1 to 4-4 added the same amounts of iron powder and nonionic surfactant as those initially added, followed by stirring and mixing. Figure 4 shows the results of measurements of DDT concentrations in Comparative Examples 4-1 and 4-2 and Examples 4-1 to 4-4 after 1, 2, 3, and 10 weeks of standing, using the same method as in Test Example 1. FIG. 5 shows the concentrations of DDTs after standing for 10 weeks in Comparative Examples 4-1 and 4-2 and Examples 4-1 to 4-4.

[0052] [Table 6]

[0053] 4 and 5 show that the concentration of DDTs in the sample soil after 10 weeks of standing was reduced when iron powder and a nonionic surfactant were added (Examples 4-1 to 4-4) compared to when neither was added (Comparative Example 4-1). Furthermore, the reduction effect of iron powder was maintained for a longer period of time when iron powder and a nonionic surfactant were added (Examples 4-1 to 4-4) compared to when only iron powder was added (Comparative Example 4-2). Furthermore, the purification effect was enhanced when 1.6 g of iron powder (4% by mass) and 2.4 g of nonionic surfactant (6% by mass) were added (Example 4-2) compared to when 1.6 g of iron powder (4% by mass) and 1.2 g of nonionic surfactant (3% by mass) were added (Example 4-1). Furthermore, it can be seen that the purification effect is stronger when 1.6g (4% by mass) of iron powder and 2.4g (6% by mass) of nonionic surfactant are added (Example 4-2) than when 2.4g (6% by mass) of iron powder and 1.2g (3% by mass) of nonionic surfactant are added (Example 4-3). From this, it is presumed that the mass ratio of the added amounts of iron powder and nonionic surfactant affects the effect of maintaining the reduction action of DDTs on the iron powder surface and facilitating contact between the iron powder and DDTs.

[0054] Furthermore, Figures 4 and 5 show that the concentration of DDTs in sample soil No. 1, which contains a high concentration of DDTs, can be significantly reduced by adding iron powder and a nonionic surfactant (Examples 4-1 to 4-4).

Claims

1. A method for purifying soil containing DDTs, comprising: (A) iron powder and (B) a surfactant are added to the soil, the mass ratio of the amounts of the (A) component and the (B) component added is 1 to 10:1 to 10; A method for purifying soil, wherein the component (B) is an anionic surfactant.

2. 2. The method for remediating soil according to claim 1, wherein component (B) is a non-soap anionic surfactant.

3. 3. The soil purification method according to claim 1 or 2, wherein component (B) is at least one anionic surfactant selected from the group consisting of α-olefin sulfonate, alkyl sulfate ester salt, polyoxyalkylene alkyl ether sulfate ester salt, amide ether sulfate ester salt, methyl taurine salt, and sulfosuccinate.

4. A method for purifying soil containing DDTs, comprising: (A) iron powder and (B) a surfactant are added to the soil, the mass ratio of the amounts of the (A) component and the (B) component added is 1 to 10:1 to 10; A method for purifying soil, wherein the component (B) is a nonionic surfactant.

5. 5. The method for purifying soil according to claim 4, wherein component (B) is at least one nonionic surfactant selected from the group consisting of polyoxyalkylene alkyl ethers, polyoxyalkylene alkyl esters, sorbitan fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene sorbitol fatty acid esters, alkylamines, and polyoxyalkylene alkylamines.

6. 6. The method for remediating soil according to claim 4, wherein component (B) is a nonionic surfactant having an HLB value of 8.1 to 16.

9.

7. The method for remediating soil according to any one of claims 1 to 6, wherein the component (A) is added so that the content of the component (A) in the soil is 0.1 to 30 mass%.

8. The method for remediating soil according to any one of claims 1 to 7, wherein the component (B) is added so that the content of the component (B) in the soil is 1 to 15 mass%.

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