JP2005152733A - Method and system for in situ extracting second-class specified toxic substance, and system for in situ purifying the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for in situ extracting the second-class specified toxic substance, by which soil can efficiently be purified safely. <P>SOLUTION: The second-class specified toxic substance in soil G is extracted by pumping up the water in the soil G. At that time the water in the soil G is heated to lower the pH of the water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an in-situ extraction method, an in-situ extraction system, and an in-situ purification system for a second-type specified harmful substance. More specifically, the present invention relates to a technology for developing a technology for extracting a second-type specific harmful substance by pumping water present in soil.

  Currently, as a method for remediating contaminated soil, there is a method described in “Explanation of technical methods of investigation and measures based on the Soil Contamination Countermeasures Law” (Non-Patent Document 1). The soil pollution control law assumed by this explanation is that the pollutants are classified into Class 1 specified hazardous substances (volatile organic compounds), Class 2 specified hazardous substances (heavy metals, etc.) and Class 3 specified hazardous substances (Agricultural chemicals / Since the physical properties of toxic substances differ greatly depending on this classification, the explanation explains the purification method in consideration of the target pollutants.

  Although various purification methods are described in this commentary, it can be said that the in-situ removal (purification) method is preferable from the viewpoint of permanent countermeasures, maintenance load, purification cost, and the like. This in-situ purification method is a method for purifying soil in-situ without being excavated, and is classified into an in-situ extraction method (in-situ soil washing method), an in-situ decomposition method, and other purification methods. Among these methods, in-situ extraction methods include the “soil gas suction method” in which a suction well installed in the soil is depressurized with a vacuum pump, etc., to vaporize specific hazardous substances, "Groundwater pumping method" to pump water, "air sparging" to inject air into the soil to promote volatilization of specific harmful substances from groundwater, "steam injection" to promote volatilization of specific harmful substances by applying heat Various methods such as “hot gas injection” are exemplified in the description. However, among these methods, the soil gas suction method, air sparging, steam injection, hot gas injection, etc. use the volatility of harmful substances, so the first class specific hazardous substances are the targets. Species-specific hazardous substances (heavy metals, etc.) are not planned and are not currently used. Therefore, in-situ purification of Class II Specified Hazardous Substances is usually performed by the groundwater pumping method, that is, by pumping up saturated groundwater present in the contaminated soil and removing and collecting the specified toxic substances via the groundwater. Will do.

However, this method is based on the premise that the type 2 specified harmful substances are dissolved in the groundwater, and the type 2 specified harmful substances are not so easily eluted in water. Very bad. Therefore, the commentary also states that the in-situ soil cleaning method is basically difficult to apply when the concentration of heavy metals is high. In this regard, there is a method of promoting the elution of the second type specific harmful substance using a chemical solution (chemical substance), but this method is not desirable because there is a new danger of harming the environment.
"Explanation of technical methods for investigation and measures based on the Soil Contamination Countermeasures Law", Soil Environment Center, March 2003, P96-97, P127-128

  The main problem to be solved by the present invention is to provide an in-situ extraction method, an in-situ extraction system and an in-situ purification system capable of efficiently and safely purifying soil. is there.

The present invention that has solved the above problems is as follows.
[Invention of Claim 1]
A method of extracting the second type specific harmful substance in the soil by pumping water in the soil,
An in-situ extraction method of the second type specific harmful substance, characterized in that elution of the second type specific harmful substance into the water is promoted by heating the water to lower the pH.

[Invention of Claim 2]
The in-situ extraction method of the 2nd class specific harmful substance of Claim 1 which heats water to 60-100 degreeC.

[Invention of Claim 3]
The in-situ extraction method of the second type specific harmful substance according to claim 1 or 2, wherein steam is injected into the soil to heat water in the soil.

[Invention of Claim 4]
The in-situ extraction method of the second type specific harmful substance according to any one of claims 1 to 3, wherein the water is pumped up continuously or intermittently in the stage where the heated water has residual heat.

[Invention of Claim 5]
The stage 2 specified harmful substance according to any one of claims 1 to 4, wherein the water is intermittently pumped according to the temperature and elapsed time of the water in the stage where the temperature of the heated water is lowered. In-situ extraction method.

[Invention of Claim 6]
The in-situ extraction method of the second kind specific harmful substance according to any one of claims 1 to 3, wherein when the heated water is lowered to a predetermined temperature, the water is heated again to lower the pH.

[Invention of Claim 7]
The measure according to any one of claims 1 to 6, wherein measures for preventing settlement of the soil are taken based on the temperature distribution of water in the soil, the composition of the soil and the amount of pumped water per hour (m ³ / h). In-situ extraction method for type 2 specified hazardous substances.

[Invention of Claim 8]
An in-situ extraction system for type 2 specified hazardous substances with a well for pumping up water in soil,
An in-situ extraction system for a second-type specified harmful substance, comprising a well for injecting the heat source of water into the soil.

[Invention of Claim 9]
An in-situ purification system for type 2 specified hazardous substances with a well for pumping up water in the soil,
A well for injecting the heat source of water into the soil is provided, and the well also serves as a bioremediation well for injecting any one or more of microorganisms, oxygen, and nutrients into the soil. In-situ purification system for type 2 specified hazardous substances.

  According to the present invention, it is possible to purify the soil containing the second type specific harmful substance efficiently and safely.

Embodiments of the present invention will be described below.
[Target of purification]
In the present invention, the second type specified harmful substances (heavy metals, etc.) defined by Article 2, Paragraph 1 of the Soil Contamination Countermeasures Law are subject to purification. Specifically, cadmium and its compounds, hexavalent chromium compounds, cyanide compounds, mercury and its compounds, selenium and its compounds, lead and its compounds, arsenic and its compounds, fluorine and its compounds, and boron and its compounds The target of.

[Extraction method]
In the in-situ extraction method of the second type specified harmful substance of the present embodiment, when extracting the second type specified harmful substance in the soil by pumping up the water in the soil, the water in the soil is heated. By lowering the pH, elution of the second type specific harmful substance into water in the soil is promoted. By heating the water in the soil to lower the pH, elution of the second type specific harmful substance into the water in the soil is promoted, so that extraction (purification) is performed efficiently. Moreover, since no chemical solution is used for promoting the elution of the second type specific hazardous substance into water, there is no risk of environmental danger and the safety is excellent. Furthermore, when a chemical solution is used, the elution promotion effect remains after the extraction treatment, whereas according to the method of the present invention, when the temperature of water in the soil returns to the original temperature, the pH also returns to the original temperature. The elution promotion effect disappears, reducing the burden of post management. The reason why the heating of water in the soil, the decrease in pH, and the promotion of elution are used as described above is as follows.

  That is, the present inventors have proposed the Steam Enhanced Remediation (SER) invented in the United States from the inventors, Mr. Kent S. Udell and Mr. Sita Nicholas (Nicholas Sitar). I learned directly and conducted full-scale experiments. The steam-accelerated purification method is an in-situ purification method in which water vapor is injected into the ground from an injection well to promote volatilization and migration of pollutants and collect pollutant gas and contaminated groundwater in the extraction well. The target pollutants in this method are substances whose volatilization is promoted by heating. Recently, volatile organic compounds such as tetrachloroethylene and trichlorethylene (type 1 specified) have been regarded as a problem of soil and groundwater pollutants. Hazardous substances) and petroleum hydrocarbons such as gasoline and heavy oil.

  However, in the course of the design study of the experiment, the present inventors recalled that the pH of water suddenly changed with temperature. For example, water at a room temperature of 25 ° C. and pH = 7.00 decreases as the temperature rises and becomes pH = 4.70 at 100 ° C., and the pH rises as the temperature decreases and reaches 0 ° C. = 7.47 (see Table 1).

  On the other hand, as one of the purification techniques for contaminated soil, there is a method for insolubilizing heavy metals using cement or the like. In this method, however, it is important that pH control of soil (water) is very important. Crossed. This is because, since the solubility of heavy metal hydroxides varies greatly depending on the pH value, even if it is once insolubilized, it may be eluted due to subsequent fluctuations in pH (see FIG. 3).

  Therefore, the present inventors have noticed that the steam-accelerated purification method, which has been invented and developed as an in-situ purification method for volatile substances, can also be used for heavy metals and the like (second type specified harmful substances). Since the pH change of the water corresponds to the temperature change, it is sufficient to heat the water, and it is noticed that the same effect can be obtained by heating with hot air, high temperature water, etc. instead of heating with steam. It has been completed. However, since steam has latent heat and has a large amount of heat, it has an advantage that water in soil can be heated more effectively than hot air or high-temperature water.

However, even in the case of using steam in the same manner, the SER method is intended to effectively extract (purify) by promoting volatilization / migration of pollutants, whereas the method of the present invention. Since effective extraction (purification) is promoted by promoting the elution of the second type specific harmful substance, the range of usable temperatures is different.
That is, the SER method requires heating above the temperature at which the contaminant is volatilized, generally above the boiling point. On the other hand, since the method of the present invention uses a change in pH, heating up to 60 to 100 ° C. is sufficient, and even if the temperature is lower than that, the pH is proportional to the temperature. It can be used because it is changing.
More specifically, the soil (water) once heated to near 100 ° C. takes a long time of about six months to one year to return to the original temperature (for example, normal temperature 25 ° C.). During this period (stage with residual heat), the pH of the soil (water) is lowered according to the temperature, so that the elution of the second type of specific harmful substances is promoted and intermittently or continuously in the soil. If the water is pumped up, purification will proceed even more.

  In addition, this method uses residual heat and is excellent in terms of cost. However, pumping water in the soil is naturally expensive, so water pumping is intermittent rather than continuous. It is better to go there. In addition, the elution of type 2 specified hazardous substances depends not only on the temperature and pH of water, but also on the concentration of type 2 specified hazardous substances in water, and the temperature of water also decreases with the passage of time. Therefore, it is necessary to analyze in advance when it is most effective to pump up the water in the soil from the temperature and elapsed time of the water, and intermittently based on this analysis value. It is better to pump water.

  On the other hand, when extraction (purification) is desired more quickly than cost reduction, when the heated water is lowered to a predetermined temperature, it is preferably heated again, and then this reheating is repeated as necessary. The temperature at which the predetermined temperature is set is not particularly limited, and may be appropriately determined based on factors such as elution efficiency and cost.

By the way, the above extraction method utilizes the physical property that “the pH is lowered by heating” of water, but water also has the physical property that “the viscosity is lowered by heating”. For example, the viscosity coefficient of water is expressed as 0.1794 / (1 + 0.03702 × temperature + 0.0001638 × temperature ² ). When water at 16 to 17 ° C. is heated to about 100 ° C., the viscosity coefficient is 3 minutes. It becomes about 1 of. Therefore, according to the above extraction method, the water in the soil improves as the water is heated, so that the extraction efficiency can be improved. However, it is more positive that the viscosity of the water decreases due to the heating. Can also be used.
That is, when the water in the soil is heated, the passage of the water at the heated portion is improved, which means that the heated portion is liable to cause settlement of the soil. Therefore, by measuring the temperature distribution of water in the soil, it is possible to detect areas where soil settlement is likely to occur, and to take measures to prevent soil settlement, focusing on the detected areas. Will be prevented. However, in addition to the temperature distribution of the water in the soil, the influence of the water composition in the soil (for example, whether it is sandy or clayey) and the amount of pumped water per hour (m ³ / h) Since it is large, it is more preferable to take measures against soil settlement in consideration of these factors.

  The temperature distribution measurement system is not particularly limited, and can be an appropriate system. For example, a plurality of temperature detectors are arranged at appropriate intervals in the depth direction in each injection well, pumping well, arbitrarily provided well, or the like. It is possible to use a system provided with a gap.

[Extraction and purification system]
Next, an in-situ extraction system for the second type specific harmful substance and a purification system that combines this extraction system with another system will be described.
The in-situ extraction system of the present invention includes at least one well (injection well) for injecting a heating source of water in the soil into the soil, and at least one well (pumping well) for pumping the water in the soil. Has mainly. The heating mode of water includes not only a direct heating mode for directly heating water but also an indirect heating mode for heating water through heating of soil such as sand and gravel.

  The heating source of water in the soil is not particularly limited, and for example, steam, hot air, high-temperature water, quicklime, etc. can be used, but steam and high-temperature water are used from the viewpoint of preventing land subsidence due to pumping water. In addition to this, it is preferable to use steam from the viewpoint of effectively heating water in the soil. In addition, when using hot air, it is good to aim at prevention of ground subsidence, for example by sprinkling water (natural infiltration method) on the ground surface. The method for effectively preventing land subsidence is as described above.

  When steam is used as a heating source, how to inject steam and pump water in the soil is not particularly limited, but since it has many achievements, it is suitable for volatile organic substances. It is preferable to apply the SER method that has been used (for example, Japanese Patent No. 2660307). This will be specifically described below.

  As shown in FIG. 1, in the system of the present embodiment, injection wells 43, 43... For injecting a gas such as water vapor horizontally into soil G in the region to be treated, and a large-capacity vacuum pump (not shown). The pumping wells 44, 44... For pumping the water in the soil G are provided vertically. In FIG. 1, the injection wells 43, 43... And the pumping wells 44, 44... Are not shown in a circular shape or a triangular shape. , A triangle, a quadrangle, a polygon more than that, and the like.

  The number and arrangement of the injection wells 43, 43... And the pumping wells 44, 44 are not particularly limited. However, as in the present embodiment, the pumping wells 44, 44. It is preferable to provide six wells (FIG. 1A) or four places (FIG. 1B) and injection wells 43, 43. According to this form, the steam spreads evenly over the entire target area, and the water in the soil from which the second type specific harmful substances are effectively eluted can be pumped up. The interval between the injection wells 43 adjacent to each other can be appropriately determined according to the injection pressure of steam, the water permeability of the soil, and the like. In this embodiment, the interval is 7 m. Further, the pumping wells 44, 44... Are preferably extended to a deeper position than the deepest position where the second type specific harmful substance is suspected to exist.

  In this system, as shown in FIG. 2, a steam generator 10 such as a boiler supplied with fuel such as gasoline and oil, water and air is provided with a liquid trap 12 and a pressure regulator 13, respectively. .. Are supplied to the respective injection wells 43, 43... Through the plurality of lines 11, 11. The condensate collected in the liquid traps 12, 12... Is returned to the steam generator 10 via the line 16. When steam is injected into the injection wells 43, 43... Using this system, the water vapor heats the soil and moisture in the soil G while moving horizontally in the contaminated area. Thereby, the pH of water falls and elution of a 2nd type specific harmful substance is accelerated | stimulated.

  The water in the soil from which the second type specific harmful substances are eluted (hereinafter also referred to as contaminated water) is pumped from the bottom of the pumping wells 44, 44. In the line 20, the flow rate is controlled based on the flow meter 21. Liquids other than water, such as gasoline and oil, contained in the contaminated water are extracted from the separation tank and are pumped to the storage tank 23 via the line 22. On the other hand, the contaminated water is pumped through the line 24 to a contaminated water treatment system 50 described later.

  In collecting the contaminated water, volatile gas can also be collected, but this volatile gas is sent to the condenser 27 from the pumping well 44 through the line 26 together with the contaminated water. The volatile matter (liquid) liquefied by the condenser 27 is sent to the separation tank 28, and is pumped from the separation tank 28 to the storage tank 23, and is mixed with a liquid other than water contained in the previous contaminated water. The However, the volatile matter (liquid) in the separation tank 28 also includes contaminated water, and this contaminated water is pumped to the contaminated water treatment system 50 described later via the line 29.

  The cooling tower 30 as an air / water heat exchanger is for cooling water as a cooling source for liquefying volatile gas. Water is supplied to the cooling tower 30 via a line 31 to supply water as a cooling source lost as water vapor when the cooling tower 30 is used.

  Volatile gas and volatile components that have passed through the condenser 27 and the separation tank 28 contain air, but this air still contains vaporized mercury that has not been completely liquefied. . Therefore, the air containing the contaminants is passed through a carbon canister (activated carbon tank) 33, 33. The carbon canisters 33, 33... Are for adsorbing and removing contaminants present in the air, and may include one, two, three, or more. The air from which the contaminants are adsorbed and removed can be discharged into the atmosphere via the line 34, or sent to the steam generator 10 via the line 32 and used as air. In addition, a part of the steam sent from the steam generator 10 to the injection wells 43, 43... May be supplied to the carbon canisters 33, 33. This is because when the steam is circulated, the activated carbon is regenerated by the heat and pressure of the circulated steam. The gas containing contaminants generated by this regeneration is sent to the condenser 27 via the line 36 and treated in the same manner as the volatile gas from the pumping well.

Next, the contaminated water treatment system 50 will be described.
The contaminated water treatment system 50 is for recovering heavy metals and the like in the contaminated water, and is designed according to the type of heavy metals and the like. Below, the case where hexavalent chromium is collect | recovered as an example is demonstrated.

  The contaminated water from the lines 24 and 29 is first subjected to reduction treatment in a reduction tank 37 in order to change hexavalent chromium to trivalent chromium, and sludge and flocculant are added in a neutralization precipitation tank 38 to add heavy metal (trivalent). Chromium) is recovered as a precipitate. Next, since the contaminated water from which heavy metals have been recovered in the neutralization sedimentation tank 38 is treated in the separation tank 28 described above, the volatile matter (volatile organic compound) may be dissolved therein. Hydrogen peroxide water is added to generate OH radicals in the liquid, and the volatile organic compound is decomposed in the ultraviolet decomposition tank 40. Next, the hydrogen peroxide solution remaining in the contaminated water that has exited the ultraviolet decomposition tank 40 is adsorbed in an absorption tank 41 made of activated carbon or the like, and the pH is adjusted by adding alkali in the next pH adjustment tank 42. Release into rivers and rivers.

Next, a system combined with the above-described in-situ extraction system for the second type specific harmful substance will be described.
As described above, the in-situ extraction system of the present embodiment has a long-term residual heat even after heating, and this is in a state suitable for the activity of microorganisms (for example, about 70 ° C. to about 35 ° C.) for a long time. Means. Therefore, in the in-situ extraction system according to the present embodiment, one or more of microorganisms, oxygen, and nutrients are injected into the soil from the injection well (43) used in the in-situ extraction system (bioremediation). Mediation). As a result, degradable pollutants are decomposed by microorganisms, and purification is further promoted. Note that the in-situ extraction system of this embodiment does not use chemicals to acidify water (soil), temporarily lowers the pH by heating the water, and returns the pH by returning the temperature. Therefore, chemicals do not remain in the soil after treatment, and a smooth transition to bioremediation is possible.

[Others]
(1) In carrying out the in-situ extraction and in-situ purification of the present invention, it is preferable to use a containment method or the like in combination so that the specified harmful substance does not diffuse around.

(2) Cadmium and its compounds, hexavalent chromium compounds, cyanide compounds, mercury and its compounds, lead and its compounds, and arsenic acid and its compounds are said to have water-soluble materials originally, and chemical insolubilization treatment It is targeted. In addition, selenium and its compounds, fluorine and its compounds, and boron and its compounds are said to be relatively insoluble in water, but are soluble in water as specified by the Soil Contamination Countermeasures Law. It ’s not something you do n’t want.

It is an example of formation of a well. It is a system flow figure of a steam promotion purification method. It is a figure which shows the relationship between pH value and the elution amount of heavy metals.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Steam generator, 11 ... Steam injection line, 12 ... Liquid trap, 13 ... Pressure regulator, 15 ... Manifold, 16 ... Condensate recovery line, 17 ... Vacuum pump, 19 ... Gas-liquid separation tank, 20 ... Pumping line, 21 ... Flow meter, 22 ... Contaminant recovery line, 23 ... Storage tank, 24 ... Contaminated water line, 26 ... Liquid recovery line, 27 ... Condenser, 28 ... Separation tank, 29 ... Contaminated water line, 30 ... Cooling tower 31 ... Water supply line, 32 ... Gas recovery line, 33 ... Carbon canister, 34 ... Exhaust line, 35 ... Steam line for carbon regeneration, 36 ... Condensate introduction line for gas and liquid during carbon canister regeneration, 37 ... Reduction Tank, 38 ... neutralization precipitation tank, 39 ... hydrogen peroxide injection valve, 40 ... ultraviolet reaction tank, 41 ... residual hydrogen peroxide decomposition tank, 42 ... pH adjustment tank, 43 ... injection well, 44 ... lifting Well, 45 ... thermometer, 50 ... contaminated water treatment system, G ... soil.

Claims (9)

A method of extracting the second type specific harmful substance in the soil by pumping water in the soil,
An in-situ extraction method of the second type specific harmful substance, characterized in that elution of the second type specific harmful substance into the water is promoted by heating the water to lower the pH. The in-situ extraction method of the 2nd class specific harmful substance of Claim 1 which heats water to 60-100 degreeC. The in-situ extraction method of the second type specific harmful substance according to claim 1 or 2, wherein steam is injected into the soil to heat water in the soil. The in-situ extraction method of the second type specific harmful substance according to any one of claims 1 to 3, wherein the water is pumped up continuously or intermittently in the stage where the heated water has residual heat. The stage 2 specified harmful substance according to any one of claims 1 to 4, wherein the water is intermittently pumped according to the temperature and elapsed time of the water in the stage where the temperature of the heated water is lowered. In-situ extraction method. The in-situ extraction method of the second kind specific harmful substance according to any one of claims 1 to 3, wherein when the heated water is lowered to a predetermined temperature, the water is heated again to lower the pH. The measure according to any one of claims 1 to 6, wherein measures for preventing settlement of the soil are taken based on the temperature distribution of water in the soil, the composition of the soil and the amount of pumped water per hour (m ³ / h). In-situ extraction method for type 2 specified hazardous substances. An in-situ extraction system for type 2 specified hazardous substances with a well for pumping up water in soil,
An in-situ extraction system for a second-type specified harmful substance, comprising a well for injecting the heat source of water into the soil. An in-situ purification system for type 2 specified hazardous substances with a well for pumping up water in the soil,
A well for injecting the heat source of water into the soil is provided, and the well also serves as a bioremediation well for injecting any one or more of microorganisms, oxygen, and nutrients into the soil. In-situ purification system for type 2 specified hazardous substances.

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