JP2009274004A - Treating method of soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid water supply impossibility due to deposition of suspended particles and pump failure and to reduce amount of industrial waste by reducing the amount of precipitates. <P>SOLUTION: The treating method of soil comprises: an indirect heat desorption process 11 for indirectly heating organic halogen compound-containing soil at temperature not lower than the boiling point of the organic halogen compound so as to evaporate water and the organic halogen compound and to obtain dry clarified soil not including moisture; a decomposing process 12 for decomposing the organic halogen compound by heating the evaporated organic halogen compound together with water; a gas cooling process 13 for quenching exhaust gas coming out of the decomposing process to temperature not higher than the boiling point of water so as to condense water contained in the exhaust gas; a water treatment process 14 for performing water treatment so as to remove suspended particles from the condensed water; and a flocculating sedimentation process 15 for subjecting treated water obtained at the water treatment process to water treatment by flocculating sedimentation so as to remove heavy metals and then to discharge the treated water to a sewer or a public water area. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for treating soil, particularly soil contaminated with organic halogen compounds and heavy metals. The present invention also relates to a method for treating soil containing organic halogen compounds such as PCBs (polychlorobiphenyls) or dioxins as at least part of the inclusions.

  PCBs and dioxins are difficult-to-decompose substances and harmful substances that adversely affect the human body, so it is urgent to dispose of these organic halogen compounds that have been produced or produced as by-products. ing. If these substances are stored in pure form, they can be processed relatively easily, but if these substances are present in the soil at low concentrations, such contamination will occur. It was extremely difficult to treat the soil. Until now, as a method for treating contaminated soil containing organic halogen compounds such as PCBs and dioxins, a method of transporting and embedding in a final landfill or enclosing with concrete or the like has been common. Although these means are effective as an emergency means for isolating PCBs and dioxins from the general environment, PCBs and dioxins are persistent substances that do not decompose over a long period of time because they are persistent substances. Will do. Therefore, there is a risk that these substances are eluted from the final landfill or concrete and leached into the general environment.

  FIG. 2 shows an example of a conventional soil treatment method. In FIG. 2, after passing through the indirect thermal desorption process 1, decomposition process 2, gas cooling process 3, storage tank 4 from the contaminated soil, it is led to the coagulation sedimentation process 5, and after treatment, it is drained into sewage or public water areas. .

  First, in the indirect thermal desorption process 1, the contaminated soil containing the organic halogen compound is heated to a predetermined temperature range by an indirect heating device to volatilize the organic halogen compound. In the decomposition step 2, the gas containing the organic halogen compound volatilized in the indirect thermal desorption step 1 is reacted by heating together with the moisture to decompose the organic halogen compound into a substance containing at least hydrogen halide and carbon dioxide, Detoxify halogen compounds.

The gas containing hydrogen halide and carbon dioxide generated in the decomposition step 2 is guided to the next gas cooling step 3. The moisture contained in the contaminated soil is volatilized in the indirect thermal desorption process 1 and condensed in the gas cooling process 3 to return to water. In the decomposition step 2, water vapor is generated by the reaction between the organic hydrocarbon and oxygen, or the reaction between the organic hydrocarbon and water vapor. This water vapor is also condensed in the gas cooling step 3 and returned to water. The PCB concentration of water generated in the gas cooling step 3 and the concentration of dioxins depend on the decomposition performance of the decomposition step 2 and the amount of soil fine particles scattered from the indirect thermal desorption step 1. The concentration of dioxins depends on the amount of soil fine particles scattered from the indirect thermal desorption step 1.
Water generated in the gas cooling step 3 is guided to the storage tank 4. Water from the storage tank 4 is guided to the coagulation sedimentation step 6 by the pump 5. In the coagulation sedimentation step 6, coagulation sedimentation treatment with chemicals is performed to precipitate heavy metals and the like dissolved in water. The precipitate in the coagulation sedimentation process 6 is discarded as industrial waste, and the treated water is drained into sewage or public water.

As other methods for detoxifying organic halogen compounds, several methods for separating and treating PCBs and dioxins from soil by heating have been proposed. For example, Patent Document 1 describes a method for decomposing gaseous PCBs and dioxins with a catalyst as a method for decomposing extracted PCBs and dioxins. Patent Document 2 describes a decomposition method in which gaseous PCBs and dioxins are subjected to secondary combustion with an afterburner at around 1000 ° C.
JP-A-7-328595 Japanese Patent Laid-Open No. 11-148631

  By the way, since the soil generally contains 10% by mass or more of moisture, when the PCBs and dioxins are separated by heating, the moisture in the soil also evaporates together with the PCBs and dioxins. In addition, when the water content is 30% by mass or more, it is desired to dry in advance, but in that case, wastewater containing a small amount of PCBs and dioxins is generated. Since the exhaust gas coming out of the heating furnace is rapidly cooled to a predetermined temperature below the boiling point of water, the water evaporated in the above process is condensed and waste water is generated.

  Since these drains may contain heavy metals, etc. depending on the components in the soil, it is necessary to perform water treatment below the drainage standard value in order to drain into sewage or public waters. As a general water treatment for removing heavy metals, a coagulation sedimentation treatment is performed. However, since these wastewaters have a high SS concentration, the amount of precipitates becomes large. This deposit is discarded as industrial waste, and there is a problem that the amount of waste becomes large.

Further, since SS (Suspended Solid) in these wastewaters has good sedimentation properties, there is a problem that when they are stored in a storage tank, SS precipitates and accumulates at the bottom.
Furthermore, a pump is required to guide this waste water from the storage tank to the water treatment process. However, since the SS concentration in the wastewater is high, there is a problem that the suspended particles make the sealing function of the pump structure impossible and cause a failure of the pump.

  The present invention has been made to solve the above problems, and wastewater generated by moisture contained in the contaminated soil is directly stored in the storage tank without being stored in the storage tank, so that suspended particles in the tank can be obtained. First, water treatment that removes SS in the wastewater is performed, and it is effectively used as wet water for the purified soil discharged from the indirect thermal desorption device, and secondly, sewage Alternatively, the water drained to public water areas is subjected to coagulation sedimentation treatment, but by removing SS in advance, a soil treatment method is provided that can reduce the amount of sediment and reduce the amount of industrial waste. For the purpose.

  The soil treatment method according to the present invention is a soil treatment method for detoxifying an organic halogen compound contained in soil, wherein the soil containing the organic halogen compound is indirectly heated to a temperature equal to or higher than the boiling point of the organic halogen compound. Indirect thermal desorption step of volatilizing moisture and organic halogen compound to make dry purified soil free from moisture, decomposition step of decomposing the organic halogen compound by heating the volatilized organic halogen compound together with the moisture, A gas cooling step of rapidly cooling the exhaust gas coming out of the decomposition step to a temperature below the boiling point of water to condense moisture contained in the exhaust gas, a water treatment step of performing water treatment to remove suspended particles from the condensed water, The coagulation sedimentation process which performs the water treatment by the coagulation sedimentation of the treated water obtained in the water treatment process, removes heavy metals, and then drains it into sewage or public water area Characterized in that it comprises.

  According to the present invention, PCB-contaminated soil and the like are indirectly heated to volatilize PCBs and dioxins, and the water volatilized with the PCBs and dioxins is directly led to the water treatment process without going through the storage tank and the pump. By treating the treated water with coagulation sedimentation, the heavy metals dissolved in the surplus water are made to be below the sewage drainage standard and drained into sewage or public water areas.

  In general, the soil contains 10% by mass or more of moisture, but in the conventional treatment method, the moisture separated from the soil during the treatment is pumped to remove heavy metals etc. in the drainage through the storage tank. It was led to a coagulation sedimentation tank and all the wastewater was treated. Therefore, there is a problem that suspended particles accumulate at the bottom of the storage tank. At the same time, there was a problem that the sealing function of the pump became impossible due to suspended particles, but in the present invention, wastewater from the soil is directly led to the water treatment process, thus avoiding the inability to feed water due to sediment removal work and pump failure can do. In addition, since the wastewater is conventionally coagulated and precipitated, there is a problem that the amount of the precipitate is increased due to suspended particles. However, in the present invention, the water treatment for removing suspended particles from the condensed water is performed before the coagulation sedimentation, so that the amount of precipitates in the coagulation sedimentation treatment can be reduced and the amount of industrial waste can be reduced. .

  Moreover, if the density | concentration of the suspended particle of the treated water from the said water treatment process is 1000 mg / L or less, the treated water can be reused as the moist water of the purification | cleaning soil from which PCB and dioxins were isolate | separated. Since the wet water is added so that the moisture content of the purified soil is about 10% by mass, excess water is generated when the moisture content of the soil is higher than 10% by mass. Therefore, the surplus water is subjected to water treatment by coagulation sedimentation treatment and drained into sewage or public water areas.

Hereinafter, the soil treatment method of the present invention will be described in more detail.
As described above, the soil treatment method according to the present invention includes the indirect thermal desorption step (a), the decomposition step (b), the gas cooling step (c), the water treatment step (d), and the condensation precipitation step. (E) is performed.
In the indirect thermal desorption step (a), the soil can be indirectly heated to a temperature range of 400 ° C. or higher using an indirect thermal desorption method. Here, the indirect heating of the soil refers to a method in which a flame is heated by heat transfer from a heat source outside the apparatus containing the contaminated soil without direct contact of the flame with the contaminated soil. Examples of the organic halogen compound to be treated in the present invention include various compounds such as PCB, dioxins which are hardly decomposable compounds, and trichlorethylene which is a volatile compound.

  In this invention, it is preferable that the temperature of the indirect thermal desorption process which volatilizes an organic halogen compound from contaminated soil shall be 400-600 degreeC. Here, when the contaminated soil is treated at a temperature of less than 400 ° C., PCBs and dioxins contained in the contaminated soil may not completely volatilize and remain in the soil. Moreover, since the quality of soil will change if it heats exceeding 600 degreeC, it may become difficult to reproduce | regenerate this soil. Therefore, the heating temperature for volatilizing PCBs and dioxins from contaminated soil is preferably 400 to 600 ° C. Furthermore, the higher the temperature in this step, the shorter the treatment time is, but a temperature range of 400 to 600 ° C. is desirable in order to volatilize 99% of the organic halogen compound within a heating time of one hour or less.

  Moreover, it is desirable to use either the steam decomposition method or the combustion decomposition method as the decomposition step (b) for decomposing the organic halogen compound volatilized after the indirect thermal desorption step. Further, by maintaining the heating temperature in the decomposition step (b) at 900 ° C. or higher, PCBs and dioxins can be decomposed into carbon dioxide and hydrogen chloride by steam, thermal decomposition reaction or oxidation reaction. The higher the set temperature in the decomposition step (b), the higher the decomposition rate of the organic halogen compound. The relationship between the temperature and the decomposition rate depends on the residence time of the gas. When the residence time is 5 seconds, the decomposition rate is 12% at a heating temperature of 600 ° C, the decomposition rate is 15% at a temperature of 700 ° C, and the decomposition rate is at a temperature of 800 ° C. When the temperature is 31% and the temperature is 900%, the decomposition rate is 83%. At 1000 ° C, the decomposition rate is 99.99%. At 1100 ° C, the decomposition rate is 99.999%. Therefore, in order to set the gas residence time in the decomposition step (b) to about 5 seconds and the decomposition rate of the organic halogen compound to 99% or more, a temperature range of 1000 to 1200 ° C. is desirable.

  Furthermore, by providing the gas cooling step (c) for cooling the gas after the decomposition step (b), water in the soil volatilized in the indirect thermal desorption step (a) can be condensed and efficiently recovered. . The PCB and dioxins of the condensed water have different contents depending on the decomposition performance in the decomposition step (b). Here, when the SS concentration of the condensed water is set to 0 mg / L, heavy metals are mostly excluded from the condensed water, so that there is an advantage that the amount of precipitates discarded in the coagulating precipitation step can be remarkably reduced. In addition, when the SS concentration of condensed water is processed at 1000 mg / L or less, the treated water obtained in the water treatment process is reused as wet water in the purified soil obtained in the indirect thermal desorption process, thereby reducing waste water. It has already been found that not only effective use of water by water, but also three effects of reduction of dust generation and prevention of resynthesis of dioxins can be obtained.

  That is, in the water treatment step (d), solid-liquid separation is performed to remove suspended fine particles from the condensed water. The method of the water treatment step (d) for setting the SS concentration to 1000 mg / L or less can be appropriately selected from centrifugation, gravity sedimentation, filter press, membrane treatment and the like. As a method of the water treatment step (d) for reducing the SS concentration to 0 mg / L or less, a membrane treatment or the like can be considered, but a method of passing a filter having a pore diameter of 0.1 to 1 μm reduces the apparatus size and suppresses energy consumption. Is particularly preferable. The water obtained in the water treatment step (d) leads to the coagulation precipitation step (e) to remove heavy metals.

  Here, since the water in which the coagulation sedimentation is performed increases in the SS concentration, the amount of the precipitate increases. Therefore, in the water treatment step (d), the SS concentration is 1000 mg / L or less, preferably 100 mg / L or less. The amount of sediment can be reduced and the amount of industrial waste can be reduced. Moreover, since the SS concentration is 1000 mg / L or less, dioxins are not re-synthesized.

(Embodiment)
A soil treatment method according to an embodiment of the present invention will be described with reference to FIG. Note that the present embodiment is not limited to the following description.
In this embodiment, the moisture obtained through the indirect thermal desorption process 11, the decomposition process 12, the gas cooling process 13, and the water treatment process 14 from the contaminated soil C is returned to the purified soil obtained in the indirect thermal desorption process 11, The initial moisture originally contained in the contaminated soil C is effectively reused. However, the water | moisture content which can be returned to the purification | cleaning soil P here is only the quantity from which the moisture content of the purification | cleaning soil P will be about 10 mass%. Therefore, the water | moisture content which became surplus in the water treatment process 14 is guide | induced to the coagulation sedimentation process 15, is drained to a sewer or a public water area after passing through a process. In addition, the number 16 in a figure shows a pump.

  First, in the indirect thermal desorption process 11, the contaminated soil C containing an organic halogen compound is heated to a temperature range of 400 to 600 ° C. by an indirect heating device, and the organic halogen compound is volatilized to obtain the purified soil P. The indirect heating apparatus used in the indirect heat desorption step 11 includes a soil heating unit main body, a soil charging unit for supplying soil into the soil heating unit main body, heating means provided outside the soil heating unit main body, and the soil A temperature measurement unit that measures the temperature of the heating unit body, a temperature control device that controls a heating unit that heats the soil heating unit body based on temperature information output from the temperature measurement unit, and a process performed in the soil heating unit body And a generated gas discharge port for discharging a gas generated as a result of being heated in the main body of the soil heating unit.

  A device such as a rotary screw feeder or a rotary kiln can be used for the soil heating unit main body. By using these devices, it is possible to effectively volatilize organic halogen compounds such as PCB and dioxins while heating the soil indirectly without directly contacting the soil and suppressing the amount of exhaust gas. As the heating means, a known general-purpose heating device such as an electric resistance heating device or a combustion heating device can be used, but the combustion heating device is most suitable from the viewpoint of economy. Furthermore, as the temperature measuring device, a known general-purpose measuring instrument such as a thermocouple can be used.

  Next, in the decomposition step 12, the gas containing the organic halogen compound volatilized in the indirect thermal desorption step 11 is reacted by heating to a predetermined temperature, and the organic halogen compound is converted into a substance containing at least hydrogen halide and carbon dioxide. Decomposes and detoxifies organic halogen compounds. A steam cracking furnace, a combustion cracking furnace, etc. can be used for such a cracking process 12. As the heating means, as in the indirect thermal desorption step 11 described above, an electric resistance heating device or a combustion heating device can be used. The decomposition rate of the organic halogen compound is determined by the heating temperature and the residence time. When the residence time is 5 seconds, the decomposition rate is 12% at a heating temperature of 600 ° C., the decomposition rate is 15% at a temperature of 700 ° C., and the decomposition rate at a temperature of 800 ° C. At 31% and a temperature of 900 ° C., the decomposition rate is 83%, at 1000 ° C., the decomposition rate is 99.99%, and at 1100 ° C., the decomposition rate is 99.999%. Therefore, in order to set the gas residence time in the decomposition step to about 5 seconds and to set the decomposition rate of the organic halogen compound to 99% or more, a temperature range of 1000 to 1200 ° C. is desirable.

  The gas containing hydrogen halide and carbon dioxide generated in the decomposition step 12 is guided to the next gas cooling step 13. As the gas cooling means, it is possible to use a quencher device that sprays water into the gas to quench the gas, or an indirect heat exchange device that guides the gas to the indirect heat exchange plate in which the cooling water is circulating and quenches it. . The water contained in the contaminated soil C is volatilized in the indirect thermal desorption process 11 and condensed in the gas cooling process 13 to return to water. Further, in the decomposition step 12, water vapor is generated by the reaction between the organic hydrocarbon and oxygen, or the reaction between the organic hydrocarbon and water vapor. This water vapor is also condensed in the gas cooling step 13 and returned to water.

The amount of water generated in the gas cooling step 13 is approximately equal to the moisture content of the contaminated soil C. For example, when the moisture content of the contaminated soil C is 20% by mass and the input speed of the contaminated soil C is 2000 kg / hour, the amount of water generated in the gas cooling step 13 is about 400 kg / hour.
The PCB concentration of water generated in the gas cooling step 13 and the concentration of dioxins depend on the decomposition performance of the decomposition step 12 and the amount of soil fine particles scattered from the indirect thermal desorption step 11. When the temperature in the decomposition step 12 is 1100 ° C. and the residence time is 5 seconds, the PCB concentration is always below the discharge standard value (0.003 mg / L). The concentration of dioxins depends on the amount of soil fine particles scattered from the indirect thermal desorption step 11. The dioxin density | concentration of soil particulates is the same level as the purification | cleaning soil P, and is set to 10pg-TEQ / L.

The water generated in the gas cooling step 13 is guided to the next water treatment step 14. While being guided to the water treatment step 14, since it does not go through a storage tank as in the prior art, fine particles accumulate in the tank and the work of removing it can be omitted. Moreover, although the pump 16 is used to guide to the coagulation sedimentation step 15, it is possible to avoid the failure of the pump due to the fine particles and the inability to feed water because there is no accumulation of the fine particles.
In the water treatment step 14, the fine particles (SS concentration) scattered from the indirect thermal desorption step 11 are set to 100 mg / L or less. As a means for removing SS, centrifugal separation, gravity sedimentation, filter press, membrane separation can be used. Since the dioxin concentration in SS is about 10 pg-TEQ / g, which is the same level as that of the purified soil P, it can be handled in the same manner as the purified soil P. The water whose SS is 100 mg / L or less can be used as wet water for the purified soil P discharged from the indirect thermal desorption step 11.

  The temperature of the purified soil P discharged from the indirect thermal desorption step 11 is as high as around 500 ° C., and the moisture content is 0% by mass. Handling soil with a moisture content of 0% by weight is not preferable because dust rises in the air and deteriorates the working environment. Moreover, when metals, such as copper and iron, are contained in the soil, dioxins may be re-synthesized in the cooling stage of the purified soil P. Therefore, using it for the wet water of the purification soil P has not only effective use of water by reducing waste water, but also three effects of reducing dust generation and preventing resynthesis of dioxins.

  The moistening of the purified soil P is performed until the water content becomes about 10% by mass. Therefore, when the moisture content of the soil is higher than 10% by mass, the amount of treated water in the water treatment step 14 is larger than the amount of water used for wetting the purified soil P. In that case, surplus water in the water treatment step 14 is guided to the coagulation sedimentation step 15. In the coagulation sedimentation step 15, coagulation sedimentation treatment with chemicals is performed to precipitate heavy metals and the like dissolved in water. The precipitate in the coagulation sedimentation treatment step 15 is discarded as industrial waste. However, since the fine particles are reduced to 100 mg / L or less in the water treatment step 14 in advance, the precipitate is almost a floc such as heavy metals caused by chemicals. Only effective in reducing industrial waste.

(Specific examples)
Targeting soil with a PCB concentration of 14,000 mg / kg, dioxins concentration of 280,000 pg-TEQ / g, and a moisture content of 15% by mass, the soil heating means is a rotary screw feeder with a combustion-type indirect thermal desorption device. Adopted. The example which processed by making the introduction speed | rate of the contaminated soil C into 300 kg / hour is shown.

The temperature of the soil heating unit body was controlled by a temperature control device so that the soil temperature was 600 ° C., and the contaminated soil C was subjected to indirect thermal desorption treatment so that the residence time of the soil in the soil heating unit body was about 60 minutes. The amount of gas generated from the indirect thermal desorption step 1 was about 90 Nm ³ / hour, and water vapor was the main composition. As a result of measuring the concentrations of PCB and dioxins in the purified soil P, the PCB concentration was <0.05 mg / kg, and 99.999% or more of PCBs could be separated from the soil. The dioxins concentration was 12 pg-TEQ / g, and 99.995% of dioxins could be separated from the soil.

The gas generated in the indirect thermal desorption step 11 was heated in the decomposition step 12. The heating means indirectly heated the gas with an electric resistance heating device. The gas heating temperature was 1100 ° C., and the gas residence time was 5 seconds. As a result of measuring the PCB concentration and dioxin concentration of the outlet gas in the decomposition step 12, the PCB concentration was 0.0003 mg / Nm ³ , the dioxin concentration was 0.013 ng-TEQ / Nm ³ , and the PCB was 99.9999% or more. And was able to decompose dioxins.

  Next, the exhaust gas in the decomposition step 12 was rapidly cooled to a gas temperature of 35 ° C. in the gas cooling step 13. For quenching the gas, a quencher method in which water was sprayed into the gas was adopted. The sprayed water circulated, and the quencher circulated water was cooled with a plate heat exchanger in order to suppress the rise in water temperature. The water in the gas cooling step 13 continued to increase with soil treatment, and the increase rate was 45 L / hour, which was the same as the moisture content 45 L / hour calculated from the contaminated soil input rate of 300 kg / hour and the moisture content of 15% by mass. As a result of measuring PCB and dioxins of quencher water, the PCB concentration was <0.003 mg / L below the emission standard value. Dioxins were 24 pg-TEQ / L and exceeded the effluent standard value of 10 pg-TEQ / L. The SS concentration was 2000 mg / L.

  It led to the water treatment process 14 at 45 L / hour equivalent to the generation amount of the gas cooling process 13. A membrane separation method was adopted as a means for removing SS. By passing through a membrane having a pore diameter of 0.2 μm, the water in the gas cooling step having an SS concentration of 2000 mg / L could be removed to an SS concentration of 1 mg / L or less. Moreover, as a result of measuring the dioxin density | concentration after removing SS, it was 0.099pg-TEQ / L and was fully lower than 10pg-TEQ / L of a waste_water | drain standard. Furthermore, as a result of drying SS and measuring dioxin density | concentration, it was 11pg-TEQ / g of the same level as the purification | cleaning soil P.

  The water of the water treatment process 14 collected under the above conditions was sprayed as wet water of the purified soil P discharged from the indirect thermal desorption process 11. The discharge rate of the purified soil P was about 250 kg / hour because the moisture content was 0% by mass, and about 30 L / hour was sprayed with wet water, and the moisture content of the purified soil P was 10% by mass. . Wetting was performed by spraying moist water from the upper part where the purified soil P was stirred with a mixer. Moreover, as a result of measuring PCB and dioxin concentrations in the purified soil after wetting, the PCB concentration was <0.05 mg / kg, dioxins were 12 pg-TEQ / g, and it was reduced by waste water by adding wet water In addition to the effective use of water, three effects were obtained: reduction of dust generation and prevention of dioxin resynthesis.

  About 15 L / hour of surplus water due to the above conditions is drained into sewage or public water after removing heavy metals in the coagulation sedimentation step 15. Here, the amount of sludge generated in the coagulation sedimentation step 15 is 0.16 L / hour and the water content is 98% by mass. In the conventional method, the amount of sludge generated in the coagulation sedimentation step 15 is 4.6 L / hour. Since the water content was 98%, the amount of sludge could be greatly reduced.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment. Specifically, in the above-described embodiment, the case where the water in the water treatment process is sprayed on the purified soil as wet water and the excess water is removed in the coagulation sedimentation process and then drained into sewage or the like is described. If there is no surplus water, the water in the water treatment process may be used only as wet water.

The flowchart which shows the processing method of the soil which concerns on embodiment of this invention. The flowchart which shows the processing method of the soil which concerns on the past.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Indirect thermal desorption process, 12 ... Decomposition process, 13 ... Gas cooling process, 14 ... Water treatment process, 15 ... Coagulation sedimentation process, 16 ... Pump.

Claims (6)

In a soil treatment method for detoxifying organic halogen compounds contained in soil,
An indirect thermal desorption process in which the soil containing the organic halogen compound is indirectly heated to a temperature equal to or higher than the boiling point of the organic halogen compound to volatilize the water and the organic halogen compound, thereby obtaining a dry purified soil containing no water;
A decomposition step of decomposing the organic halogen compound by heating the volatilized organic halogen compound together with the water;
A gas cooling step of rapidly cooling the exhaust gas coming out of the decomposition step to a temperature below the boiling point of water to condense moisture contained in the exhaust gas;
A water treatment step for performing water treatment for removing suspended particles from the condensed water;
A method for treating soil, comprising a coagulation-precipitation step in which the treated water obtained in the water treatment step is subjected to water treatment by coagulation sedimentation to remove heavy metals and then drained into sewage or public water. The soil treatment method according to claim 1, wherein the concentration of suspended particles contained in the treated water obtained in the water treatment step is 0 mg / L. Reuse in which the concentration of suspended particles contained in the treated water obtained in the water treatment step is 1000 mg / L or less, and the treated water is returned to the purified soil obtained in the indirect thermal desorption step as wet water for reuse. And when the amount of treated water obtained in the water treatment step is larger than the amount of wet water used in the reuse step, the excess water is led to the coagulation precipitation step. The method for treating soil according to 1. The method for treating soil according to claim 1, wherein the condensed water in the gas cooling step is directly transferred to the water treatment step. 2. The suspended water having a diameter of 1000 μm or less is removed from the condensed water using any one of a centrifugal separation method, a gravity sedimentation method, a filter press method, and a membrane separation method in the water treatment step. Soil treatment method. In the indirect thermal desorption step, the soil is indirectly heated to a temperature of 400 ° C. or higher and 600 ° C. or lower using an indirect thermal desorption method, and
The soil treatment method according to claim 1, wherein in the decomposition step, the organic halogen compound is heated to a temperature of 900 ° C. or more by volatilization using either a steam decomposition method or a combustion decomposition method.

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