JP2002086129A - Method for purifying contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reform soil a surface layer of which is contaminated with low concentration of dioxins to soil with lower concentration of the dioxins by simple treatment of low cost. SOLUTION: In a method for purifying contaminated soil, the soil with lower concentration of dioxins is obtained via a stage in which the soil contaminated with the dioxins is gathered from an original position and is washed with hot water and a stage in which muddy water accompanied with the dioxins is separated from the soil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for purifying soil contaminated with dioxins.

[0002]

2. Description of the Related Art Dioxins generated from garbage incineration plants are not only highly toxic substances but also so-called environmental hormones that cause physiological harm to the human body, and their generation is a serious social problem. . There is a national regulation on incinerator emissions, and future incineration will be curbed by improvements to incinerators. However, soil contaminated by dioxins that have already scattered into the environment will The purification process is necessary.

Hitherto, high-temperature heat treatment has been widely used as a detoxification technique for soil contaminated with dioxins. Recently, however, an electrode has been inserted into contaminated soil to generate high heat, and soil has been removed like lava. Melt-solidification method (melt-solidification method) and method of adding catalyst or alkali to contaminated soil to decompose dioxin by applying high heat (alkali-catalyzed chemical decomposition method) have been developed. Classification can be made almost completely harmless.

[0004]

The above-mentioned melt-solidification method and alkali-catalyzed chemical decomposition method can be said to be advanced technologies in that dioxins can be almost completely rendered harmless. Therefore, the present invention is effective for soil having a high dioxin concentration and a small area. However, if this technique is applied to a soil where the dioxin concentration is low and is widely and shallowly distributed, there is a problem that the treatment cost becomes extremely high. In addition, those treated by these methods can no longer be called soil in terms of morphology or function, so they are not suitable for growing plants, and if there is no use that can reuse the treated soil. In addition, the waste must be treated again and the cost is further increased.

[0005] Further, the purification of dioxin-contaminated soil up to now has mainly involved thermal energy, electric energy,
Furthermore, since a large amount of medicine is required, the equipment must be large.

However, the form of dioxin contamination is almost always low-level surface pollution in the area near the incineration plant, and low-level dioxins distributed over a wide range of surface soil are further reduced to below the standard value. The conventional technology for reducing the concentration is not always suitable because it is too large or requires high cost.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve such a problem of the prior art, and a method for purifying dioxin-contaminated soil that can easily and inexpensively treat low-contamination concentration soil is provided. It is something to offer.

[0008]

Means for Solving the Problems The present inventors have carried out various tests and studies to solve the above-mentioned problems. (1) The solubility of dioxins in water greatly depends on the temperature and the temperature is high. (2) Fine particles accompanying the water side when the soil is washed with hot water (fine suspension)
It is highly probable that dioxins are attached to the soil, so if this fine fraction is separated from the soil together with the wash water,
Utilizing the phenomenon that most dioxins can be separated from soil, concretely, if the soil contaminated with dioxins is washed with hot water and the dioxin accompanying sewage is separated, I found that the purpose could be achieved advantageously.

Therefore, according to the present invention, the dioxin-contaminated soil is collected from the original position and washed with hot water, and the dioxin-contaminated mud is separated from the soil through the dioxin-concentration process. Provided is a method for purifying contaminated soil to obtain reduced soil.

As a more specific means for solving the above problems, the present invention provides a method for transporting soil contaminated with dioxins by means of a transfer means (for example, a conveyor) and then transferring the soil (for example, at 25 to 100 ° C.). B) Hot water is sprinkled, and mud accompanying dioxins is discharged from the soil by its own weight to obtain soil with a reduced concentration of dioxins. Purification method of contaminated soil: Put the soil contaminated with dioxins into a container ( After contacting with hot water (for example, at 25 to 100 ° C.), a method for purifying contaminated soil in which dioxin-entrained mud is separated from the soil to obtain a soil with a reduced concentration of dioxins:
Soil contaminated with dioxins (eg, 25-10
By discharging the contents obliquely upward from a container containing hot water (at 0 ° C.) by a transfer means (for example, a screw conveyor), mud water accompanying dioxins is left in the container, and soil having a reduced dioxin concentration is removed from the container. Purification method for contaminated soil discharged to the outside:

[0011] In any of the methods, the soil treated with hot water often kills the bacteria living in the soil. Therefore, when dioxin-decomposing bacteria are added to the soil, the bacteria are removed. Became the priority species and became easier to grow, increasing the efficiency of decomposing dioxins remaining in the soil. Therefore, according to the present invention, as a means for solving the problem more advantageously, a method for purifying contaminated soil, which comprises adding dioxin-decomposing bacteria to soil having a reduced concentration of dioxins obtained by the above method. I will provide a.

[0012]

DETAILED DESCRIPTION OF THE INVENTION Dioxin has many isomers. In particular, 2,3,7,8-dibenzo-para-dioxin (2,3,7,8-TCDD), a type of dioxin, is the most toxic. For this reason, the dioxin standard value notified by the Environment Agency uses the value converted to the toxicity of 2,3,7,8-TCDD.
Also in this specification, the term "dioxins" is used to mean various isomers as in the notification of the Environment Agency. Note that 2,
It is said that the solubility of 3,7,8-TCDD in water at 25 ° C. is very small, about 8 to 200 ng / L.

[0013] Soil contamination of dioxins is often found in the surface soil near the incineration plant. In particular, it is localized in the extreme surface layer up to a depth of 10 cm, and in some cases up to about 5 cm, and its concentration is usually extremely reduced in deeper ground.

[0014] This is because dioxins accompanied by ash scattered from the incineration plant fall directly to the surface of the ground or adhere to various plants, etc., and then become scattered with organic substances on the surface of the ground over time. Since dioxins have a very low solubility in water, it is considered that the permeation into the ground using water as a medium is relatively difficult to proceed. However, if the water path is formed naturally during rainfall, a portion of the water that is carried by the water and accumulates at a high concentration will occur, and it is conceivable that a portion exceeding the reference value may be localized. Therefore, even though the soil is contaminated with dioxins, the standard value of 1000 pg-TEQ
/ G in many cases is scattered, and in the soil near the ground or its underground ground, it is often lower than the reference value.

In view of the distribution form of such dioxin contamination, it is not necessarily a rational measure to completely purify a wide area to a high depth by applying a solidification method or an alkali-catalyzed chemical decomposition method. I can say.

In view of the above, according to the present invention, the dioxin-contaminated soil is preferably stripped of the contaminated soil in the surface layer, and preferably has a depth of 50 cm in the contaminated zone.
The purpose of this study is to wash the surface soil with hot water while stripping the soil up to the point where the solubility of dioxins in water increases rapidly with increasing temperature. It is advantageous to take advantage of the phenomenon that the soil is often attached to the fine particles that accompany the washing water. The soil contaminated with dioxins is collected in situ and washed with hot water. And obtaining a soil having a reduced concentration of dioxins through a step of separating mud water accompanying dioxins from the soil.

Here, the hot water is water having a temperature of from normal temperature to 100 ° C. (25 to 100 ° C.). The step of washing the soil with this hot water depends on the contamination area and the type and properties of the soil. It is carried out in various preferred embodiments as described below, but basically, the dioxins are dissolved in the hot water by washing the contaminated soil with the hot water, The purpose of the present invention is to suspend fine particles (fine suspensions, regardless of organic and inorganic substances, which accompany water after washing) toward the hot water side.

At this time, an organic solvent can be added to hot water, and the dioxins can be dissolved in the organic solvent. For example, the solubility of 2,3,7,8-TCDD in various organic solvents (per liter) dissolves in the order of mg to the order of ng in water, so the use of solvent promotes the transfer of dioxins to the wash water side. Can be done. Examples of organic solvents and their solubility are as follows: benzene (solubility = 570 mg / L), chloroform (370 mg / L), acetone (110 mg / L), n-octanol (50 mg / L),
Methanol (same as 10 mg / L).

In any case, in the step of washing the soil with hot water, the target soil is contaminated with dioxins, so that water vapor, fine particles, mist and the like generated by the treatment are scattered around. It may cause unexpected danger. For this reason, it is preferable that the washing with hot water be performed in a closed system as much as possible, or in equipment that takes exhaust treatment into consideration.

Next, following the washing step, a step of separating "dioxin-entrained muddy water" from the soil is performed, in which hot water after washing is separated from the soil. The simplest method of this separation is to allow the washing water to flow naturally out of the soil using its own weight. In this case, pore water remains in the soil, but there is no particular problem if the amount of hot water used for washing is sufficient because dioxins remaining in the pore water will be very small.

In the washing water separation step, the amount and the particle size of the fine particles flowing out differ depending on the degree of solid-liquid separation, but when the washing water (hot water) is naturally released from the soil using its own weight. , A phenomenon occurs in which fine particles in the soil flow out along with the washing water. In the present invention, the fine particles that flow out naturally are transferred to the washing water side regardless of the solid-liquid separation means employed. One feature of the present invention is that dioxins accompanying or adhering to the fine particles are transferred to the washing water side by transferring the fine particles to the washing water side. Therefore, “mud with dioxins” means a mixture of fine particles with or attached dioxins and washing water (hot water) in which dioxins are dissolved, and this mixture is usually muddy. is there. The mud accompanying dioxins separated from the soil is preferably at a temperature above normal temperature (25 ° C or higher).
Separate from soil while retaining (heat).

The mud accompanying dioxins separated from the soil is guided to a sedimentation tank or a solid-liquid separator if necessary, to separate mud, and the mud is subjected to a secondary treatment for removing dioxins. At the same time, the water from which mud has been separated can be reused as hot water for washing the soil again.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the embodiment shown in FIG. 1, soil contaminated with dioxins is transported on a conveyor while 25
As one form of the method of the present invention in which hot water of -100 ° C is sprinkled and mud accompanying dioxins is allowed to flow out of the soil by its own weight to obtain soil with a reduced concentration of dioxins, this method is carried out by a traveling purification apparatus. Is shown.

In FIG. 1, reference numeral 1 designates a dioxin-contaminated soil at an in-situ surface layer. The contaminated soil 1 is peeled off from the surface layer by a backhoe 2, and the contaminated soil 1 is mounted on a caterpillar. And put into the hopper 4. The traveling purification device 3 is provided with a system capable of continuously cleaning and separating contaminated soil by hot water on a caterpillar, and is configured as follows.
1A is a schematic view of the traveling purifier 3 as viewed in plan, and FIG. 1B is a schematic view of the inside of the cleaning tank as viewed from the side.

From the hopper 4 to the first screw conveyor 6
Then, the soil is transported to the washing tank 5 through the second screw conveyor 7. A third screw conveyor 8 is installed in the washing tank 5 with the discharge end 9 facing the rear side, and a hot water injector 10 is installed above the washing tank 5. , Hot water is sprayed on the soil on the third screw conveyor 8. The third screw conveyor 8 is shown in FIG.
As shown in FIG. 3, the soil received along the bottom of the gutter hopper 11 from the second screw conveyor 7 into the gutter hopper 11 is disposed along the third screw conveyor 8.
While being stirred by hot water, it is sprayed with hot water and transported toward the discharge end 9. During this transport, the water is drained naturally and becomes muddy water 12 accompanied by dioxins and falls from the third screw conveyor 8 And accumulates in the lower part of the washing tank 5.
On the other hand, by separating the muddy water 12 accompanying the dioxins, the soil 13 having a reduced concentration of the dioxins is discharged from the discharge end 9 and returned to the surface as treated soil 14.

On the other hand, a heating tank 15 is installed at an appropriate position (on the washing tank 5 in the illustrated example), and the hot water produced in the heating tank 15 is sent to the hot water injector 10. At that time, an organic solvent is added from the additive tank 16 (FIG. A) to the heating tank 15 as needed. The muddy water 12 accompanying dioxins accumulated at the bottom of the washing tank 5 is removed by a pump 17 into a solid-liquid separation tank 18 (FIG. A).
The water separated here is returned to the heating tank 15 together with inevitable mud. Mud accumulates in the solid-liquid separation tank 18 as the treatment proceeds, but this is separately collected and stored for secondary treatment for removing dioxins.

As a heat source of the heating tank 15, engine exhaust gas from a self-propelled device can be used. When a centrifugal separator is applied as the solid-liquid separation tank 18, a self-propelled engine can be used as the rotational power, and a self-propelled engine can also be used for the screw conveyor and pump power.

Reference numeral 19 in FIG. 1A denotes a driver's cab. The driver's cab 19 controls the operation of the screw conveyor and the control of the heating tank together with the self-propelled operation of the purification device 3. Can be continuously purified, and by operating this apparatus, backfilling of the treated soil 14 can be performed with good workability.

If dioxin-decomposing bacteria are added before returning the “soil 13 with reduced dioxin concentration” from the discharge end 9 to the ground surface, the soil 13 is treated with hot water to kill various bacteria. Alternatively, dioxin-degrading bacteria are cultivated as a priority species due to a decrease in the number of bacteria.
The dioxins unavoidably remaining in the waste are easily decomposed, and the purification purpose is more advantageously achieved. That is, when inoculated into the soil 14 treated according to the present invention, the decomposition efficiency by the decomposed bacteria can be remarkably improved as compared with the case where the decomposed bacteria are inoculated into the soil 1 before the hot water treatment.

FIG. 2 shows another embodiment of the present invention, that is, a method in which soil contaminated with dioxins is placed in a container,
1 is a diagram schematically illustrating a method for purifying contaminated soil in which mud accompanying dioxins is separated from the soil after contact with hot water at 00 ° C. to obtain soil with a reduced concentration of dioxins.

In this embodiment, as shown in FIG. 2, a soil 20 contaminated with dioxins is formed by a slit 21
The hot water is sprayed from a hot water sprayer 23 installed on the upper part of the container 20 into the closed container 22 having. Hot water is in the soil on slit 21
It flows down in the soil while being in contact with 20, and in the meantime, falls from the slit 21 into the mud pool 24 at the bottom of the container while washing the soil 20. That is, the slit 21 serves as a solid-liquid separator, and the mud accompanying dioxins is separated from the soil 20 and collected in the mud pool 24. Depending on the size of the opening of the slit 21, the size of the fine particles accompanying the muddy water will also differ. Since the clogging occurs naturally, the muddy water with fine accompanying substances is slit in the same way that excess water is naturally released from the side and underside of the heaped soil by its own weight.
21 and the passage of coarse particles is hardly observed.

Hot water is produced in a heating tank 26 having a heater 25,
The hot water is sent to the hot water injector 23 by the hot water pump 27. On the other hand,
The mud accumulated in the mud pool 24 of the container 22 is supplied to a mud pump 28.
Is fed into the solid-liquid separation tank 29, where the mud is settled and separated. The mud 30 at the bottom of the tank is discharged as appropriate by opening the cock 31 at the mud outlet, and is stored for secondary processing of dioxins removal. On the other hand, the supernatant liquid of the tank 29 is returned from the overflow port 34 to the heating tank 26, heated again, and used as hot water for washing. An organic solvent 33 is added to the heating tank 26 from an addition tank 32 as necessary.

FIG. 3 shows yet another embodiment of the present invention, namely, soil contaminated with dioxins and 25-100 ° C.
Purification of contaminated soil by discharging dirt and dioxin-bearing mud in the container by discharging the contents diagonally upward from the container containing hot water with a screw conveyor, and discharging soil with reduced dioxin concentration out of the container 1 schematically illustrates a main part of the method.

In this example, a screw conveyor 37 is installed at an angle to the container 35 so as to have a receiving end at the bottom of the container and a discharge end outside the container, and a mixture of soil and hot water stored in the container 35 is provided. From 38, the sediment 41 that is scraped up by the screw of the conveyor 37 is paid out of the container, and mud water that cannot be scraped up by the screw is left in the container 35.

A container 35 is charged with soil 40 contaminated with dioxins from a hopper 39, and is filled with hot water from a heating tank 26, and a stirring screw machine installed in the container.
The mixture 38 in the container is stirred and mixed by driving the 42. The earth and sand 41 discharged from the discharge end of the screw conveyor 37 to the outside of the container is soil that has been washed with hot water and has a reduced concentration of dioxins, and is used as a treated soil 43 for backfilling and other purposes. On the other hand, the mud water remaining in the container 35 is drawn out from the muddy water discharge port 44 to the solid-liquid separation tank 29 in the same manner as in FIG. 2, where the mud 30 is settled and separated, and When the cock 31 is opened, it is discharged as appropriate, and is stored for secondary processing of dioxin removal. Hot water is produced in a heating tank 26 having a heater 25 and sent to a vessel 35 by a hot water pump 27. In this heating tank 26, the supernatant liquid of the solid-liquid separation tank 29 is returned through an overflow port 34, It is heated again and used for hot water for cleaning. An organic solvent 33 is added to the heating tank 26 from an addition tank 32 as necessary.

In any of the embodiments, the soil contaminated with dioxins is transferred from the original position into a container or a conveyor, where it is brought into contact with hot water or mixed with stirring to be washed with hot water. After washing with hot water, the dioxin-containing mud accompanying mud is separated as a post-wash liquid, and the soil with a reduced dioxin concentration is recovered by separating the mud. Separation can be performed easily and efficiently. And
Since the collected dioxin-concentrated soil has been drained and fine particles removed at the same time, it has the property of being able to easily pass air while maintaining appropriate humidity. For this reason, the water and oxygen supply are good and the soil is suitable for the inhabitation of microorganisms. Therefore, when this soil is inoculated with dioxin-decomposing bacteria, the decomposition efficiency of dioxins by the decomposing bacteria increases. In particular, dioxins which are firmly attached to fine particles (organic and inorganic substances) are difficult to decompose by microorganisms in the soil, but such fine particles have been removed by hot water washing, and thus can be obtained by the present invention. The soil is suitable for biodegradation.

Although the method of the present invention for dioxin-contaminated soil has been described above, in addition to dioxin, oils, organic solvents such as benzene, toluene, xylene, various agricultural chemicals, PCBs The method of the present invention can be similarly applied to soil contaminated with sulfur, mercury, cyanide, and the like.

[0038]

As described above, according to the present invention,
Dioxin-contaminated soil can be improved to a soil with reduced dioxin concentration by a simple treatment method called hot water washing. In addition, many of these improved soils have reduced or died microbial concentrations due to washing with hot water, and have appropriate moisture and air permeability, so that they have an excellent growth environment for dioxin-degrading bacteria. Has also been modified. Therefore, the concentration of dioxins can be further reduced by microbial decomposition.

Further, since the method of the present invention comprises a combination of simple treatments of hot water washing and hot water separation, the method is applied to the treatment of a large area for surface contaminated soil in which dioxins are distributed at a low concentration. However, it can be treated at a low cost, which is almost impossible with the melt-solidification method or the alkali-catalyzed chemical decomposition method, and it can be said that it is an economical and efficient method according to the distribution of dioxins. .

[Brief description of the drawings]

FIG. 1 is an operation state diagram showing an example in which the method of the present invention is implemented in a traveling purification device.

FIG. 2 is an equipment layout system diagram showing an example in which the method of the present invention is implemented in a fixed facility.

FIG. 3 is an equipment arrangement system diagram showing an example in which the method of the present invention is carried out by a sediment discharging machine. 1 In-situ dioxin-contaminated soil 3 Self-propelled cleaning device 5 Cleaning tank 6 First screw conveyor 7 Second screw conveyor 8 Third screw conveyor in cleaning tank 10 Hot water injector 12 Mud water accompanied by dioxins 13 Dioxins Soil with reduced concentration 14 Treated soil 15 Heating tank 16 Additive tank 18 Solid-liquid separation tank 19 Cab 21 Slit 22 Vessel 23 Hot water injector 24 Mud with dioxins 29 Solid-liquid separation tank 26 Heating tank 32 Organic solvent Addition tank 35 Vessel 37 Screw conveyor for dispensing earth and sand 38 Mixture of dioxin-contaminated soil and hot water 40 Dioxin-contaminated soil 41 Dioxin-concentrated soil 42 Stirring screw

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C12N 1/00 B09B 5/00 S // C07D 319/24 (72) Inventor Hiroyuki Yamamoto Minato-ku, Tokyo 1-2-7 Akasaka, Kashima Construction Co., Ltd. (72) Inventor Go Tsuyoshi Sakura 1-2-7, Moto, Akasaka, Minato-ku, Tokyo Inside Kashima Construction Co., Ltd. (72) Inventor Michitaka Okamoto, Minato-ku, Tokyo 1-7-2 Akasaka, Kashima Construction Co., Ltd. (72) Inventor Tatsushi Kawai 1-2-7, Moto Akasaka, Minato-ku, Tokyo Kashima Construction Co., Ltd. F-term (reference) 2E191 BA15 BB01 BC05 BD00 BD20 4B065 AA01X AC20 BB04 BB13 CA56 4D004 AA41 AB07 AC07 CA18 CA22 CA40 CA41 CB04 CB31 CC03 CC04

Claims (8)

[Claims] 1. A method for obtaining soil having a reduced concentration of dioxins through a step of collecting dioxin-contaminated soil from an in-situ site and washing it with hot water, and a step of separating dioxin-entrained mud from the soil. How to clean the soil. 2. Soil contaminated with dioxins is conveyed by a transfer means while hot water is sprinkled thereon, and mud accompanying dioxins is allowed to flow out of the soil by its own weight to remove the soil having a reduced concentration of dioxins. How to purify the contaminated soil you get. 3. A method for purifying contaminated soil in which dioxin-contaminated soil is put into a container and brought into contact with hot water, and then mud water accompanying dioxins is separated from the soil to obtain soil with a reduced dioxin concentration. Method. 4. A dioxin-contaminated muddy water is discharged obliquely upward from a container containing dioxin-contaminated soil and hot water by a transfer means, so that dioxin-enriched muddy water is left in the container to lower the dioxin concentration. Of contaminated soil by discharging polluted soil outside the container. 5. The method according to claim 1, wherein the soil contaminated with dioxins is a surface soil in a contaminated area. 6. An organic solvent is added to the hot water.
6. The method for purifying contaminated soil according to any one of claims 5 to 5. 7. The method according to claim 1, wherein a soil having a reduced dioxin concentration is obtained, and a dioxin-degrading bacterium is added to the soil.
7. The method for purifying contaminated soil according to any one of claims 6 to 6. 8. The method for purifying contaminated soil according to claim 1, wherein the mud accompanying dioxins is separated from the soil while retaining heat.