JP7797797B2 - Method for purifying soil containing DDTs - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies. Annual Forum 2021, hosted by the Japan Association of Defense Facilities Engineers, April 19, 2021. June 3, 2021. http://www.jsdfe.org/kaishi/2021AnnualForum_Thesis.pdf

The present invention relates to a method for purifying soil containing DDTs.

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.

A method using microorganisms is known as a method for decontaminating soil contaminated with DDTs by converting the DDTs into harmless substances (Patent Document 1).

Special Publication No. 10-507687

The purpose of the present invention is to provide a new method for purifying soil containing DDTs.

As a result of extensive research to solve the above-mentioned problems, the inventors discovered that soil containing DDTs can be purified by adding (A) iron powder and (B) a surfactant to the soil, leading to the completion of the present invention.

That is, the present invention relates to the following inventions.
[1] A method for purifying soil containing DDTs, characterized in that (A) iron powder and (B) a surfactant are added to the soil , and the mass ratio of the amounts of component (A) and component (B) added is 1-10:1-10 .
[2] The method for remediating 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 remediating 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%.

This invention makes it possible to provide a new method for purifying soil containing DDTs.

1 is a graph showing the purification effect when iron powder and an anionic surfactant are added to soil containing DDTs. 1 is a graph showing the purification effect when iron powder and a nonionic surfactant are added to soil containing DDTs. This 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. 1 is a graph showing the change over time in the concentration of DDTs in target soil when iron powder and a nonionic surfactant (HLB value 13.6) were added to soil containing high concentrations of DDTs. 1 is a graph showing the purification effect when iron powder and a nonionic surfactant (HLB value 13.6) are added to soil containing a high concentration of DDTs.

The following describes in detail preferred embodiments of the present invention. However, the present invention is not limited to the following embodiments.

One embodiment of the present invention relates to a method for purifying soil containing DDTs, which is characterized by adding (A) iron powder and (B) a surfactant to soil containing DDTs.

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 decomposition products, including 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).

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

In this embodiment, the soil to be purified is soil containing DDTs, and there are no particular restrictions on the type or quality of the soil.

<Component (A)>
In the method for purifying soil containing DDTs according to this embodiment, iron powder is added as component (A). The iron powder used as component (A) is not particularly limited 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. 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, from the viewpoints of ease of addition and mixing with soil, characteristics of the equipment used for mixing, reactivity with DDTs, and the like. In this specification, the "average particle size" refers to the volume-based median diameter measured using a laser diffraction particle size analyzer.

In the method for purifying soil containing DDTs according to this embodiment, the amount of component (A) added is not particularly limited and is set appropriately 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 above amount of component (A) added is suitable not only from the perspective of uniformly dispersing component (A) in the soil and efficiently purifying DDTs, but also from the perspective of reducing costs.

<(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.

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, acylaminocarboxylates, 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, "non-soap-based anionic surfactants" refers to anionic surfactants that are formed by anionic surfactants containing carboxylates. This refers to anionic surfactants excluding activators. The anionic surfactant used as component (B) is preferably a non-soap anionic surfactant, from the perspective 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. Alpha-olefin sulfonate, alkyl sulfate, polyoxyalkylene alkyl ether sulfate, amide ether sulfate, methyl taurate, or sulfosuccinate is more preferred. These anionic surfactants may be used alone or in any combination of two or more.

Examples of α-olefin sulfonates include tetradecene sulfonate (olefin (C14-16) sulfonate). Examples of alkyl sulfates include lauryl sulfate and alkyl (C6-18) sulfate. Examples of polyoxyalkylene alkyl ether sulfates include polyoxyethylene alkyl ether sulfate (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.

Examples of salts 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).

Commercially available α-olefin sulfonates include Liporan PJ-400CJ, Liporan PJ-400CJ, Liporan LB-440, Liporan LJ-441, Liporan LB-840, and Liporan 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 suitable acrylic adhesives that can be used include: NOF Corp. (manufactured by NOF Corp.), EMAL 0, EMAL 10G, EMAL 2F Paste, EMAL 2FG, EMAL 2F-30, EMAL 40 Paste, EMAL TD, LATEMUL AD-25, EMAL 20C, EMAL E-27C, EMAL 270J, EMAL 20CM, EMAL D-3-D, EMAL D-4-D, LATEMUL E-118B, LATEMUL E-150, LEVENOL WX, LATEMUL WX, EMAL 20T, LATEMUL E-108MB (all trade names manufactured by Kao Corp.), and the like. Commercially available methyl taurate salts include Lipotack TE (trade names, manufactured by Lion Corporation), Diapon S, Diapon LM, Diapon K, Diapon K-SF, Diapon K-SF Powder, and Diapon HF-SF (trade names, manufactured by NOF Corporation). Commercially available sulfosuccinate salts include Ripearl 835I, Ripearl 860K, Ripearl 870P, Ripearl MSC, and Ripearl NTD (trade names, manufactured by Lion Corporation), Sanmorin OT-70 (trade names, manufactured by Sanyo Chemical Industries, Ltd.), Rapisol A-30, and Rapisol A-80 (trade names, manufactured by NOF Corporation).

The nonionic surfactant used as component (B) is not particularly limited, as long as it promotes the cleaning action of the 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 perspective of promoting the reducing action on the iron powder surface, i.e., improving the dispersion of soil particles and iron powder and promoting the cleaning action of the 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.

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, and polyoxypropylene alkyl ethers (polyoxypropylene stearyl ether, etc.). Examples of polyoxyalkylene alkyl esters include polyoxyethylene monolaurate, polyoxyethylene monostearate, and polyoxyethylene monooleate. 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, and sorbitan sesquioleate. 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, and polyoxyethylene alkyl (hardened beef tallow)amine).

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, and Nonion E -212, Nonion E-215, Nonion E-230, Nonion S-202, Nonion S-207, Nonion 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), Rheox CL-30, Rheocol NL-30C, Rheocol TD-50, Rheocol TD-70, Rheocol TD-90, Rheocol TD-90D, Rheocol TDA-90-25, Rheocol TDN-90-80, Rheocol TD-120, Rheocol TD-150, Rheocol TD-200, Rheocol TDA-400-75, Rheocol SC-50, Rheocol SC-70, Rheocol S C-80, Leocol SC-90, Leocol SC-120, Leocol SC-150, Leocol SC-200, Leocol SC-300, Leocol SC-400, Rheox CL-2008, Lionol L-535, Lionol L-745, Lionol L-785, Lionol L-950, Lionol NH-1509, 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 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 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, Sannonik 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 that can be used include Nonion CP-08R, Nonion LP-20R, Nonion MP-30R, Nonion PP-40R pellets, Nonion SP-60R pellets, Nonion OP-80R, Nonion OP-83RAT, and 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, Rheodol SP-S30V, Rheodol SP-O10V, Rheodol SP-O30V, Rheodol Super SP-L10, Rheodol AS-10V, Rheodol AO-10V, and Rheodol AO-15V (all trade names, manufactured by Kao Corporation). 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, 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 that can be used 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 that can be used 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, Nymeen S-220, and Nymeen O-20. 5 (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), Amit 102, Amit 105, Amit 105A, Amit 302, Amit 320 (all trade names, manufactured by Kao Corporation), etc. can be used.

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 using the Griffin method. Furthermore, when two or more nonionic surfactants are used in combination, the "HLB" value refers to the weighted average of the HLB values of each nonionic surfactant. 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 and promotes the purification action of the iron powder. 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 and promoting the purification action of the iron powder, the HLB value of the surfactant used as component (B) is preferably 8.1 to 16.9, and more preferably 10.5 to 12.1.

In the method for purifying soil containing DDTs according to this embodiment, the amount of component (B) added is not particularly limited and is set appropriately depending on the concentration of DDTs in the soil to be purified, 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 the DDTs with the surface of the iron powder and promoting the purification action of the iron powder, i.e., improving the dispersion of soil particles and iron powder and promoting the purification action of the iron powder.

In the method for purifying soil containing DDTs according to this embodiment, the mass ratio of components (A) and (B) added to the soil is not particularly limited and is set appropriately depending on the concentration of DDTs in the soil to be purified, the type and quality of the soil, and the types of components (A) and (B). From the perspective of maintaining the reducing action on the iron powder surface and facilitating contact of the DDTs with the iron powder, i.e., improving the dispersion of soil particles and iron powder and promoting the purification action of the iron powder, the mass ratio of components (A) and (B) added to the soil is preferably 1-10:1-10, more preferably 1-6:1-6, and even more preferably 2-6:3-6.

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 area). 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 it to a remediation facility.

Methods for adding components (A) and (B) to soil containing DDTs include mixing components (A) and (B) with water to form a slurry and then adding it to the soil, or mixing the soil to form a slurry with water and then adding components (A) and (B). The amount of water used when adding components (A) and (B) is not particularly limited and is set appropriately depending on the type and quality of the soil to be purified, the amount of water contained in the soil, and the amounts of components (A) and (B) added. The water amount 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 amount is suitable from the perspective of efficiently mixing and uniformly dispersing components (A) and (B) in the soil to be purified.

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 leaving 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 above-mentioned standing period, the concentration of DDTs in the soil can be reduced more efficiently.

The method for purifying soil containing DDTs according to this embodiment may further include a mixing step in addition to the step of adding component (A) and component (B) to the soil containing DDTs. The method for mixing the soil containing DDTs with component (A) and component (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 mixing machine, or a power blender. By including the above mixing step, component (A) and component (B) are more uniformly dispersed in the soil to be purified, thereby more efficiently reducing the concentration of DDTs in the soil.

The remediation method according to the embodiment described above allows for the inexpensive and easy remediation of soil containing DDTs.

The present invention will be explained in more detail below based on examples. However, the present invention is not limited to the following examples.

In this example, "mass %" refers to the mass % of the soil containing DDTs.

[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. The concentrations of DDTs in the sample soil were measured according to the method described in "IV Soil""1. Analysis of organochlorine compounds, octachlorostyrene, and benzo(a)pyrene" (GC/MS method) in the official "Survey and Analysis Method for the Actual State of Environmental Residues of Pesticides, etc." (October 1999, Soil and Pesticides Division, Water Quality Conservation Bureau, Environment Agency).

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

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

[Test Example 2: Amount of Iron Powder Added and Purifying 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, followed by 60 ml of water. 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 mixture was stirred and mixed, and then allowed to stand for one week. The concentrations of DDTs in Study Examples 1 to 4 after one week of standing were measured using the same method as in Test Example 1. The results are shown in Table 2.

Table 2 shows that adding iron powder reduces the concentration of DDTs in the sample soil after one week of standing. It also shows that increasing the amount of iron powder added further reduces the concentration of DDTs in the sample soil after one week of standing. In other words, increasing the amount of iron powder added strengthens the purification effect. Table 2 also shows that increasing the amount of iron powder added from 1.6 g (4 mass%) (Study Example 3) to 2.4 g (6 mass%) (Study Example 4) reduces the purification effect to a lesser extent than increasing the amount of iron powder added from 0.8 g (2 mass%) (Study Example 2) to 1.6 g (4 mass%) (Study 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.

Test Example 3: Purifying Action 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 stirred. 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, while Comparative Example 1-2 contained Sample Soil No. 2, water, and 1.6 g (4 mass%) of iron powder, which were then stirred and mixed. In Comparative Examples 1-1 and 1-2 and Examples 1-1 to 1-10, 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 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).

Figure 1 shows that the concentration of DDTs in the sample soil after two weeks of standing was reduced when iron powder and 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 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 carboxylic acid-based anionic surfactants improve the dispersion of soil particles and iron powder, and also reduce the formation of cations and precipitates in the soil, making it difficult for them to exhibit the effect of promoting the purification effect of iron powder.

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, classification, 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, while 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. In Comparative Examples 2-1 and 2-2, as well as 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.

Figure 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).

Test Example 5: HLB value and purifying action of nonionic surfactants
The effect of the HLB value of the nonionic surfactant on the purification activity when iron powder and a nonionic surfactant were added 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 3-1 to 3-6, 1.6 g (4% by mass) of iron powder and 1.2 g (3% by mass) of 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, while Comparative Example 3-2 contained Sample Soil No. 2, water, and 1.6 g (4% by mass) of iron powder, which were then 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.

Figure 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).

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 contains a high concentration of DDTs, was evaluated by measuring the change in the concentration of DDTs 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 added, and HLB values of the nonionic surfactants added in Examples 4-1 to 4-4 are as shown in Table 6. In contrast, 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 mass%) of iron powder, which were then stirred and mixed. Furthermore, in Comparative Example 4-2 and Examples 4-1 to 4-4, after 7 weeks of standing, 1.6 g (4 mass%) of iron powder was added to Comparative Example 4-2, and in Examples 4-1 to 4-4, the same amounts of iron powder and nonionic surfactant as those initially added were added and then stirred and mixed. 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 week of standing, 2 weeks of standing, 3 weeks of standing, and 10 weeks of standing, measured using the same method as in Test Example 1. FIG. 5 shows the concentrations of DDTs after 10 weeks of standing in Comparative Examples 4-1 and 4-2 and Examples 4-1 to 4-4.

Figures 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). It also shows that the reduction effect of the iron powder was maintained for a longer period of time and the purification effect was sustained 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). It also shows that 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 was enhanced when 1.6g (4% by mass) of iron powder and 2.4g (6% by mass) of nonionic surfactant were added (Example 4-2) compared to when 2.4g (6% by mass) of iron powder and 1.2g (3% by mass) of nonionic surfactant were added (Example 4-3). From this, it is presumed that the mass ratio of the added amounts of iron powder and nonionic surfactant maintains the reduction activity of DDTs on the iron powder surface and affects the effect of facilitating contact between the iron powder and DDTs.

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 (8)

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. The method for remediating soil according to claim 1 , wherein component (B) is a non-soap anionic surfactant. 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. 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. 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. 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 claim 1 , wherein the component (A) is added so that the content of the component (A) in the soil is 0.1 to 30 mass %. 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 %.