JP3567412B2 - How to clean contaminated soil by groundwater circulation - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for cleaning contaminated soil by groundwater circulation.
[0002]
[Prior art]
Hazardous substances may accumulate in the ground and groundwater due to landfill of waste and leakage of industrial wastewater, and it is necessary to take measures against pollution when using contaminated ground for land or groundwater.
[0003]
There are two types of soil and groundwater pollution that require such pollution control: soil pollution in which pollutants are retained in soil, and groundwater pollution in which pollutants are contained in soil water. Further, when the pollutant is a volatile organic chlorine compound such as trichlorethylene which is hardly adsorbed to the soil, the pollutant may be present not only in the groundwater but also in a gas state in the soil void.
[0004]
As a countermeasure against such contaminated soil, a method of removing contaminants is typical, and the method includes replacement of contaminated soil. In addition, as a method of treating without removing contaminants from the contaminated area, there are techniques such as a concrete solidification method, insolubilization and detoxification of contaminants using chemicals, and containment by impermeable works.
[0005]
[Problems to be solved by the invention]
However, the replacement of contaminated soil has problems in that it is difficult to secure land at the disposal site, and that excavation and transportation costs are also high. In particular, when the contaminated area is deep, the cost increases. In addition, it is difficult to completely contaminate the contaminated area by the method of injecting and solidifying concrete or the like. Further, the method of insolubilizing and detoxifying contaminants using chemicals is not effective when the depth of the contaminated area is large because the chemicals are sprayed from the ground surface or penetrated from shallow trenches or the like.
[0006]
In consideration of the above circumstances, the present invention can be widely applied to various types of pollution situations, and can be applied particularly to a pollution area having a large depth, and can efficiently purify contaminated soil without cost. It is an object of the present invention to provide a method for cleaning contaminated soil by groundwater circulation.
[0007]
[Means for Solving the Problems]
In the cleaning method according to the first aspect of the present invention, a water injection well is provided in the ground so as to surround the contaminated area, a pumping well is provided so that water injected from the water injection well passes through the contaminated area, and pumped from the pumping well. A method for cleaning contaminated soil by circulating groundwater through a pollution treatment device installed on the ground and returning the groundwater from an injection well into the ground , wherein the pollution treatment device forcibly removes heavy metal ions in the groundwater. Heavy metal ion treatment means for chemically changing to oxides and hydroxides, suspension pretreatment means for separating suspended matter in groundwater that has undergone the heavy metal ion treatment, and groundwater that has passed the suspension pretreatment. Membrane filtration treatment means for separating and removing suspended substances and impurities in the water, organic matter / microorganism treatment means for adding a chlorine-based chemical to groundwater that has passed through the membrane filtration treatment to remove factors for the growth of microorganisms, Material soil A chemical adding means for adding a chemical that promotes the separation of a chemical or a chemical that causes a chemical reaction with a harmful substance to groundwater that has undergone the organic / microbial treatment, and a wastewater generated in the suspension pretreatment and the membrane filtration treatment. It is characterized by comprising a wastewater treatment means for treating and a water supply means for supplying water lost by the wastewater .
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the basic concept of a method for cleaning contaminated soil by groundwater circulation. In this method, first, a plurality of injection wells 2 are provided so as to surround the contaminated area 1 in a plane, and a pumping well 3 is provided so that the injection water from the injection well 2 passes through the contaminated area 1. Then, the groundwater pumped from the pumping well 3 is passed through a pollution treatment device (hereinafter abbreviated as “ground device”) installed on the ground, returned from the injection well 2 to the ground, and the groundwater is circulated. The arrow in the figure indicates the flow of groundwater, and 8 indicates the groundwater level.
[0012]
In this case, due to the head difference (energy difference) between the injection well 2 and the pumping well 3, the circulation of the injection water having a superior horizontal direction occurs, and the harmful substances in the groundwater and the harmful substances separated from the soil are removed together with the pumping water from the ground equipment 5. Collected and processed. Therefore, by continuing the circulation, the purification of the contaminated area 1 gradually progresses. Also, when detoxification is to be achieved by injection of chemicals, since the injection water containing the chemicals easily reaches the contaminated area 1 between the injection well 2 and the pumping well 3, it is only necessary to continuously circulate the groundwater. The detoxification of the contaminated area 1 is completed. In the illustrated example, the injection well 2 is inserted into the poorly permeable layer 4 in order to prevent leakage of the contaminated groundwater to the surroundings. However, the injection well 2 does not necessarily need to be inserted into the poorly permeable layer 4.
[0013]
Next, the ground device 5 will be described.
The ground device 5 is a device for injecting groundwater pumped into the ground while suppressing occurrence of clogging of the groundwater. As shown in FIG. 2, the heavy metal ion treatment device 11, the suspension pretreatment device 12, the membrane filtration device 13, an organic / microorganism treatment device 14, a wastewater treatment device 16, a water replenishment device 17, and a chemical aqueous solution adjusting tank 15. The pump is omitted.
[0014]
The heavy metal ion treatment device 11 chemically converts heavy metal ions into heavy metal oxides and hydroxides by aeration of ozone and addition of an oxidizing agent, thereby increasing the size of the substance and facilitating the removal by filtration in a subsequent step. Means. However, when the heavy metal ion concentration is high and the treatment is difficult by ozone aeration or addition of an oxidizing agent, a forced oxidation device 11A, a preliminary filter 11B, and a heavy metal adsorption device 11C are further provided. The forced oxidizing device 11A is for aerating ozone and adding an oxidizing agent, the preliminary filter 11B is a filtering device of about 10 μm, and the heavy metal adsorbing device 11C is a forced oxidizing device 11A applying an ion exchange resin method or a chelating resin method. This is to deal with heavy metal ions that have not been deposited.
[0015]
The suspension pretreatment device 12 is a device capable of separating a suspension of about 100 μm in order to reduce the load on the next membrane filtration device 13. Further, the membrane filtration device 13 is a device comprising an ultra-precision membrane or an ultrafiltration membrane for separating impurities and suspensions of about 1 to 0.001 μm, and can remove substances except for extremely small organic substances.
[0016]
The organic matter / microorganism treatment device 14 removes a factor for the growth of microorganisms by adding a chlorine-based chemical to the injection water.
[0017]
By these means, clogging is prevented and groundwater circulation is possible while purifying pollutants. Further, in the case of groundwater contamination such as heavy metal ions and organic substances, the pollutants are removed by the operation of the wastewater treatment device 16 in particular.
[0018]
Next, measures for harmful substances adhering to soil will be described. As a countermeasure, there are two methods: separating harmful substances from soil and collecting and removing them by pumping groundwater, or infiltrating chemicals into the contaminated area to cause harmful substances to react chemically and make them harmless. . The former method can be implemented by adding a low-pH acidic substance, a powdered ion-exchange resin, or the like to the chemical aqueous solution adjusting tank 15.
[0019]
The latter method of detoxification by a chemical reaction can be carried out by adding a drug appropriately selected according to the type of harmful substance to the drug aqueous solution adjusting tank 15.
Here, an example of a drug to be selected and a chemical reaction to make it harmless will be illustrated using an example of contamination with lead or cadmium. As described below, when sodium sulfide is used as a chemical, insoluble lead sulfide and cadmium sulfide are generated by a chemical reaction, and contaminants are rendered harmless.
Pb ²⁺ + Na ₂ S → PbS ↓ + 2Na ⁺
Cd ²⁺ + Na ₂ S → CdS ↓ + 2Na ⁺
[0020]
In these processes, the circulating water is reduced by discharging a part of the pumped water in the ground apparatus 5, but the shortage is compensated by appropriately replenishing the water with the water replenishing device 17.
[0021]
FIG. 3 shows another embodiment. In this embodiment, a water blocking wall 6 is provided around the contaminated area 1 to further ensure cleaning. That is, by surrounding the contaminated area 1 with the water blocking wall 6, the injected water can be reliably circulated between the injection well 2 and the pumping well 3 under the condition that the leakage of harmful substances to the surroundings is prevented. Therefore, the contaminated groundwater can be reliably recovered, and can be cleaned by the ground apparatus 5. Further, similarly to the first embodiment, harmful substances attached to the soil can be effectively separated and recovered, and detoxification can be performed by a chemical reaction. Further, in the case of this embodiment, it is possible to cope with the case where the polluted area 1 is in an unsaturated area at a position higher than the current groundwater level. For example, after pouring water from a water supply facility on the ground to raise the groundwater level in the water stop wall 6, the pumping well 3 and the pouring well 2 are operated to circulate the groundwater, thereby causing harm in the unsaturated region. Separation of substances and detoxification by chemical reaction can also be performed effectively.
[0022]
【The invention's effect】
As described above, according to the present invention, by using the injection well and the pumping well, the groundwater is circulated, and the pollution treatment is performed by the pollution treatment device installed on the ground. Can also be cleaned. For this reason, the method can be widely applied to various kinds of pollution conditions, can be cleaned even when the depth of the pollution area is large, and the processing cost can be reduced as compared with the excavation and collection of the contaminated soil.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view of a first embodiment of the present invention, wherein (a) is a plan view and (b) is a side sectional view.
FIG. 2 is a block diagram illustrating a configuration of a ground apparatus (contamination processing apparatus) used in the first embodiment of the present invention.
3A and 3B are schematic explanatory views of a second embodiment of the present invention, wherein FIG. 3A is a plan view and FIG. 3B is a side sectional view.
[Explanation of symbols]
Reference Signs List 1 Contaminated area 2 Injection well 3 Pumping well 5 Pollution treatment device 11 Heavy metal ion treatment device 12 Suspension pretreatment device 13 Membrane filtration device 14 Organic / microorganism treatment device 15 Chemical aqueous solution adjustment tank 16 Drainage treatment device 17 Water supply device

Claims (1)

A pollution well is provided in the ground so as to surround the contaminated area, a pumping well is provided so that the injection water from the pouring well passes through the contaminated area, and groundwater pumped from the pumping well is installed on the ground. A method of cleaning contaminated soil by groundwater circulation returning from the injection well to the ground after passing through
A heavy metal ion treatment unit for chemically transforming the heavy metal ions in the groundwater into oxides and hydroxides, and a suspension for separating a suspension in the groundwater that has undergone the heavy metal ion treatment. Pretreatment means, membrane filtration treatment means for separating and removing suspended matter and impurities in the groundwater subjected to the suspension pretreatment, and adding chlorine-based chemicals to the groundwater subjected to the membrane filtration treatment to remove microorganisms. Organic matter / microorganism treatment means for removing factors for growth,
An agent for promoting the separation of contaminants from the soil, or an agent for causing a chemical reaction with a harmful substance, and adding the agent to groundwater that has undergone the organic matter / microbial treatment,
Wastewater treatment means for treating wastewater generated in the suspension pretreatment and the membrane filtration treatment, and water replenishment means for replenishing water lost by the wastewater, wherein the soil is contaminated by groundwater circulation. Cleaning method.

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