JP2001038360A - Underground type purification structure and purification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove contaminants while preventing their diffusion by providing a wall-shaped structure extending from the earth's surface to a water-impermeable layer and a pair of electrodes which is attachably/detachably disposed on the upstream side of the underground water flow, also extending from the earth's surface to the water-impermeable layer and made adjacent to the wall-shaped structure. SOLUTION: This underground type purification structure is provided with an underground continuous water stop wall 3 as the wall-shaped structure extending from the earth's surface 1 to the water-impermeable layer 2 and the pair of electrodes 4 adjacent to the wall 3. The pair of electrodes 4 is attachably/detachably housed in a housing part 6 formed adjacently to the wall 3 on the upstream side. The positively charged particles M+ of heavy metal element-containing colloidal particles contained in the contaminated underground water 5 are moved to the electrode member 20 side being the lower potential side (-) and concentrated. Meanwhile the negatively charged particles M- are moved to the electrode member 19 side being the higher potential side and concentrated. The heavy metal elements are removed from the underground water 5 by exchanging the pair of electrodes 4 together with a water-holding material 13 containing the concentrated M+ and M- with new electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the purification of groundwater, and more particularly to the purification of contaminants such as heavy metals while preventing the diffusion of contaminants such as heavy metals from underground pollution sources. Buried purification structure and purification method capable of providing permanent countermeasures against pollutants and further purifying soil and groundwater generated from the pollution source without providing purification treatment facilities on the ground About.

[0002]

2. Description of the Related Art In recent years, in Japan, as awareness of environmental problems has increased, it has been required in society to actively take measures and purify soil and groundwater pollution.
In an underground environment, since the movement of substances is relatively small as compared with the case on the ground, once the contaminants contaminate groundwater or the like, the pollutants tend to accumulate more easily than on the ground. For this reason, pollutants buried several decades ago may now be a source of pollution causing pollution. In such a case, in order to isolate the pollution source, a continuous underground wall capable of containing the pollutant has been formed in the ground.

[0003] Also, purification of pollutants that have similarly penetrated into the underground may be required at industrial waste disposal sites and general waste disposal sites. In a waste disposal site such as an industrial waste disposal site or a general waste disposal site, waste is dumped in a waste dumping portion in a water-impervious structure formed along a recess formed in the ground. When the discarded waste is exposed to rainwater, heavy metals and the like are released from the waste to generate sewage. Such sewage is normally prevented from leaking to the surrounding environment by a water-blocking sheet or the like forming a water-blocking structure. However, if the impermeable sheet or the like is damaged for any reason, such sewage leaks into the surrounding environment and is contaminated. In order to prepare for such a situation, in order to isolate the pollution source generated by the sewage in the same manner as described above, an underground continuous wall constructed separately from the impermeable structure may be required.

[0004] In addition, even in the case of an underground dam that accumulates rainwater that flows into the sea as groundwater and that is used as domestic water, such as being built on an isolated island, even when sewage is not generated, such underground dams are also used. A continuous wall is used. As described above, the underground continuous wall is frequently used to block groundwater, and the underground continuous wall is one of the countermeasure techniques for containing pollution such as heavy metals including soil and groundwater as described above. In the method, the diffusion of pollution is prevented by forming a structure surrounding the pollution source together with the impermeable layer of the ground, using the underground continuous wall as a water blocking wall.

In the conventional countermeasures against heavy metal pollution using a continuous underground continuous wall, the underground continuous wall is used only for preventing the diffusion of the pollution and does not purify the pollution itself. Nevertheless, the source remains. For this reason, when performing purification after preventing diffusion of contamination by the underground continuous wall, a separate purification technique is required.

Conventionally, as such a purification technique of a pollution source, for example, an excavation removal method of excavating and removing contaminated soil, and a heat treatment method of partially volatilizing and removing and stabilizing underground pollutants by heating. A washing / classifying method has been proposed in which contaminated soil is washed with a solvent such as a surfactant, and clean soil and contaminated soil are separated based on differences in the size and physical properties of soil particles.

[0007] The above-mentioned excavation and removal method requires a step of transporting excavated contaminated soil to the outside of the site and disposing it as industrial waste, and requires a measure for preventing the contaminated soil from scattering during transportation. There is a problem that it is becoming difficult to dispose of a large amount of contaminated soil due to the shortage of the final disposal site ahead.

Further, in the heat treatment method, although it is possible to set up a treatment plant at the site, the treatment is generally performed at a treatment plant outside the site in many cases. Therefore, there is a problem that the cost is high and the processing takes time.

Further, in the above-mentioned cleaning / classifying method, it is possible to install a processing plant on site similarly to the above-mentioned heat treatment method, but in general, the processing is performed in a processing plant outside the site. Because of the large number, a process of excavating and carrying out contaminated soil is required. On the one hand, it has the advantage that the purification cost is cheaper than the heat treatment. However, the applicability of the washing / classifying method depends on the soil and pollutants, and it is not always possible to carry out stable purification, and it is not always sufficient. Further, in order to carry out the above-described purification method in a place where a pollution source exists, usually, a site for installing a treatment plant adjacent to the pollution source is required, and large-scale facilities are required, It is generally difficult to implement because of the need to prevent the spread of environmental pollution to nearby residents.
Therefore, it is necessary to easily, efficiently and permanently remove contaminants such as underground heavy metals.

[0010] Further, if not only pollutants discharged from abandoned polluting sources but also substances such as heavy metals contained in nature can be removed by an underground continuous wall constructed underground, more effective use of rainwater can be achieved. Therefore, it is desired to easily, efficiently and permanently remove substances such as underground heavy metals.

[0011]

Accordingly, the present invention provides
In view of the above-mentioned problems of the prior art, it is possible to purify groundwater, prevent the diffusion of pollutants from a pollution source, purify the pollutants, and provide a permanent countermeasure against heavy metals. No need for the introduction of other purification treatment technologies, and no buried purification equipment on the ground, and it is a buried type that can remove heavy metals from groundwater, such as purifying soil and groundwater pollution generated from pollution sources. It is an object to provide a purification structure and a purification method.

[0012]

SUMMARY OF THE INVENTION The above objects of the present invention are as follows.
This problem is solved by providing an embedded purification structure and a purification method according to the present invention.

That is, in the first aspect of the present invention,
A wall-shaped structure extending from the ground surface to the water-impermeable layer, and a detachable electrode disposed upstream of the groundwater flow direction and extending from the ground surface to the water-impermeable layer and adjacent to the wall-shaped structure. An embedded purification structure is provided.

In the invention of claim 2 of the present invention, the wall-like structure is a continuous underground water stop wall formed surrounding a contaminated region containing at least a heavy metal element, and the electrode is provided in the contaminated region. Buried purifying structure provided on a part of the continuous underground water blocking wall.

According to a third aspect of the present invention, there is provided a buried type purification structure, wherein the buried type purification structure is provided with a groundwater permeable screen upstream of the electrode in the direction of flow of the groundwater. Is done.

According to a fourth aspect of the present invention, a permeable underground continuous wall extending from the ground surface to an impermeable layer and permeating groundwater, and a direction formed in the permeable underground continuous wall and intersecting the direction of groundwater flow. The present invention also provides an embedded purification structure including a slot extending to the water-impermeable layer and an electrode removably inserted into the slot.

According to a fifth aspect of the present invention, there is provided an embedded purifying structure, wherein the electrodes are electrodes for electrophoresis and electroosmosis.

According to the invention of claim 6 of the present invention, there is provided a buried purification structure wherein the groundwater contains at least a heavy metal element.

According to a seventh aspect of the present invention, groundwater containing at least a heavy metal element is brought into contact with a detachable electrode extending from the ground surface to an impermeable layer and adjacent to an underground continuous wall, and a voltage is applied to the electrode. A method for purifying the colloid containing the heavy metal element, and removing the heavy metal element from the groundwater by electroosmosis of ions obtained from the heavy metal element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention can be widely used for purification of groundwater, but the present invention will be described in detail below by taking removal of heavy metals as an example. FIG. 1 is a sectional view showing a buried type purification structure according to a first embodiment of the present invention installed in the ground. The buried type purification structure shown in FIG. 1 is a continuous underground water blocking wall 3 as a wall-like structure used in the present invention which extends from the ground surface 1 to an impermeable layer 2.
And an electrode 4 adjacent to the underground continuous water stop wall 3. The groundwater 5 contains a heavy metal element as a pollutant, flows in the direction indicated by the arrow A, and the electrode 4 is shown to be arranged on the upstream side in the flow direction of the groundwater 5. Heavy metals in the present invention include, for example,
2nd printing, Volume 4, page 620, refers to metals having a specific gravity of 4 or more and their elements as described in Kyoritsu Shuppan,
Specific examples include mercury, lead, cadmium, chromium, tin, and copper. Further, as ions obtained from heavy metals, ions of any valence of the heavy metals described above,
Examples include ions formed by forming a complex or a chelate with another compound. In the buried type purification structure of the first embodiment of the present invention, the continuous underground water blocking wall 3 is extended to the impermeable layer 2, and one end of the water blocking layer 3 is shown to penetrate into the impermeable layer 2. ing. In addition, the electrode 4 is shown to be stopped at the upstream end in the flow direction of the groundwater 5 toward the water impermeable layer 2 in contact with the water impermeable layer 2. However,
This electrode 4 can be extended to the water-impermeable layer 2 as necessary, similarly to the continuous underground water blocking wall 3. Also,
One end of the underground continuous water stop wall 3 and one end of the underground water permeable screen 7 can be projected from the ground surface 1.

In FIG. 1, the above-described contaminated groundwater 5
Is indicated by B, and does not flow downstream from the underground continuous water stop wall 3.

The underground continuous water stop wall 3 used in the present invention comprises:
As long as it has a sufficient water stopping function, it may be constructed by any conventionally known method, for example, underground continuous reinforced concrete wall method, soil mortar wall method, mud solidified wall method, steel pipe sheet pile method, It can be constructed by a steel sheet pile method, a pillar row method, a method of burying a precast reinforced concrete wall, or the like. Hereinafter, among the above-mentioned construction methods, description will be made assuming that the underground continuous water blocking wall 3 is constructed by the underground continuous reinforced concrete wall construction method.

The electrode 4 in the buried purification structure according to the first embodiment of the present invention shown in FIG. 1 is formed on the upstream side of the continuous underground wall 3 and adjacent to the underground continuous wall 3. It is detachably housed in a housing 6 for the electrode 4. FIG. 2 is a sectional view taken along the line C-- of FIG. 1 showing the buried type purification structure shown in FIG.
A part of the cross section along C is shown. As shown in FIG. 2, the storage section 6 is adjacent to the groundwater 5 containing a heavy metal element so that soil containing the groundwater 5 does not leak into the storage section 6 when the electrode 4 is replaced. And a side wall 8 formed on both sides of the continuous underground water blocking wall 3 and a continuous underground water blocking wall 3 provided on the side facing the underground water transmitting screen 7. Have been. FIG. 2 shows that the electrode 4 is housed in the housing 6 defined in this way. By accommodating the electrode 4 in the accommodating portion 6 in this way, the electrode 4 can be replaced according to the degree of deterioration or the like of the electrode 4.

The groundwater permeable screen 7, which forms a part of the housing 6, prevents the soil from collapsing into the housing 6 when the electrode 4 is replaced. It is made of a water-permeable member so that it can be introduced into the device. As such a water-permeable member, for example, a wire mesh or plate-like metal member having a mesh or a slot formed thereon, an ion exchange resin, a porous ceramic plate, a porous resin plate, a mesh or a slot is formed. A member including a plastic such as a resin composite material can be used. By using the water-permeable member on the groundwater 5 side, the groundwater 5 containing a heavy metal element can be supplied to the electrode 4 while preventing the collapse of the soil. In FIG. 2, such an underground continuous water stop wall 3 is shown in which the underground continuous wall 3 is extended across the flow direction of the underground water vein, and the adjacent underground water permeation screen 9 is formed. It is shown extended. The underground continuous water stop wall 3 also forms a ground water permeable screen 7 and a structure composed of the portion of the underground continuous water stop wall 3 sandwiched between the side walls 8 as segments, and has a required length. Over the groundwater vein.

FIG. 3 shows a front view of the electrode 4 used in the present invention. The electrode 4 used in the present invention is configured as a removable cartridge, and can be replaced as needed. The electrode 4 is formed by arranging a plurality of electrode members 11 facing each other on a frame member 10 that is electrically insulated. These electrode members 11 are also configured as individually removable cartridges as needed. The potential difference is given to the electrode 4 shown in FIG. Of the heavy metal elements, cations move to the lower potential side of the electrode member 11 by electroosmosis, and colloids having a positive charge move by electrophoresis. On the other hand, it is configured such that anions move toward the high potential side by electroosmosis, and colloids having negative charges move by electrophoresis. As a material of the electrode member 11 described above,
Various materials such as corrosion-resistant metal, metal coated with ceramic on the surface, graphite, etc. can be used. Also,
It is also possible to coat the electrode member 11 with an insulator such as Teflon as appropriate. The frame member 10 forming such an electrode 4 can be formed over the length of the continuous underground water blocking wall 3, or as described above, the underground continuous water blocking wall 3 is configured as a plurality of segments, and It may be configured to be continuous along the pulse.

A water-retentive material 13 is filled or arranged between the electrode members 11 shown in FIG. 3 as necessary, and groundwater 5 containing a heavy metal element introduced through the groundwater permeable screen 7 is transferred between the electrode members 11. And the electrode 4
The storage part 6 while retaining the heavy metal component together with the electrode when replacing the
It can be taken out from. Various materials can be used as the water retention material 13 used in the present invention. However, considering that the heavy metal element collected in the electrode member 11 or its vicinity is treated after the replacement of the electrode 4, a porous material can be used. In addition to porous ceramics, non-contaminated soil molded with a polymer substance or the like so as not to be disintegrated, a water-absorbing polymer material can be used in terms of processability that can be easily incinerated.

Examples of such a highly water-absorbing material include a gel of a water-absorbing polymer, and specifically, starch grafted with potassium acrylate or sodium acrylate, polyacrylamide gel, N
-Acrylamide crosslinked product, cellulose-acrylonitrile graft copolymer, carboxymethylcellulose crosslinked product, hyaluronic acid-based polysaccharide derivative, polyvinyl alcohol crosslinked product, polyvinyl alcohol absorbent gel, sodium acrylate-vinyl alcohol copolymer, sodium polyacrylate crosslinked And the like. The voltage or current applied to the electrode member 11 can be appropriately set so that electrophoresis or heavy metal ion deposition can be performed as described later.

FIG. 4 shows a buried purification structure according to a second embodiment of the present invention. As shown in FIG. 4 (a), the buried type purification structure of the second embodiment of the present invention, as shown in FIG. 4 (a), surrounds the contaminated area 14 containing heavy metals in four directions underground continuous water stop walls 3a, 3b, 3b. 3c and 3d are formed, and the inside shows that polluted groundwater 5 formed by dissolving heavy metals for a long period of time is accumulated. The electrode 4 for performing purification according to the present invention is provided on at least the underground continuous water stop wall 3a on the downstream side of the contaminated ground water 5 among these four directions of underground continuous water stop walls to serve as a purification wall. Is shown. As shown in FIG.
By forming the underground continuous water blocking walls 3a, 3b, 3c, 3d, it becomes possible to isolate the contaminated area 14 contaminated by heavy metals from the surroundings, and to continuously convert heavy metals by the buried type purification structure of the present invention. And purify it. FIG. 4 (b) is a side view of an embedded purification apparatus according to a second embodiment of the present invention. The underground continuous water blocking walls 3a and 3c, the electrode 4, and the groundwater permeable screen 7 are shown to be configured as described in FIG.

FIG. 5 shows a buried purification structure according to a third embodiment of the present invention. The buried type purification structure of the third embodiment of the present invention shown in FIG. 5 has the same configuration as the buried type purification structure of the first embodiment of the present invention shown in FIG. Instead of a continuous water barrier 3, a permeable underground continuous wall 1 instead
5 is used. In FIG. 5, the groundwater level of the contaminated groundwater 5 on the upstream side is indicated by a solid line B, and the groundwater level of the purified groundwater 16 on the downstream side is indicated by a solid line D. FIG.
In the buried purification structure shown in Figure 5, the contaminated groundwater 5
Flows in the direction indicated by the arrow A in the figure, and the heavy metal element is removed by the buried type purification structure disposed in the middle thereof, and after being purified, the heavy metal element is further flowed downstream so that purification is performed. Has been.

The purification structure according to the third embodiment of the present invention shown in FIG. 5 is formed from a permeable underground continuous wall 15 extending from the ground surface 1 to the impermeable layer 2 and permeable to groundwater. Inside the continuous underground continuous wall 15, there are provided a slot 17 extending to the water-impermeable layer 2 in a direction transverse to the flow direction of the groundwaters 5 and 16, and the electrode 4 attached so as to be insertable into the slot 17. I have. As described in FIG. 1, one end of the permeable underground continuous wall 15 extends to the water-impermeable layer 2, and the electrode 4 inserted therebetween is stopped at a portion adjacent to the water-impermeable layer 2. Is shown.

FIG. 6 is a sectional view of the arrangement of the permeable underground continuous wall 15 and the electrode 4 used in the third embodiment of the present invention, taken along a section line EE in FIG. It is sectional drawing which showed. The permeable underground continuous wall 15 described above is
It can be formed by containing a water-permeable material inside.
The electrode 4 similar to that described with reference to FIG. 3 is detachably accommodated in the slot 17 between the permeable underground continuous walls 15 thus formed, while maintaining electrical insulation. As the material for forming the permeable underground continuous wall 15, any material can be used as long as it is a porous material. For example, it can be formed of the same material as the above-described underground water permeable screen 7. The strength can be appropriately set so as to withstand the earth pressure, and a reinforcing means such as a reinforcing bar or a steel material (not shown) can be appropriately used.

In FIG. 6, the electrode 4 can be formed into a plurality of segments so as to correspond to the permeable underground continuous wall 15 in consideration of handleability. In addition, by arranging a plurality of permeable underground continuous walls 15 adjacent to each other by using the structure shown in FIG. 6 as a segment, a necessary length can be secured. By controlling the permeability of the permeable underground continuous wall 15,
The residence time of the contaminated groundwater 5 inside the embedded purification structure of the third embodiment of the present invention can be controlled. The residence time of the contaminated groundwater 5 can be appropriately set in consideration of the degree of purification.

Hereinafter, the purification method of the present invention will be described with reference to FIG. FIG. 7 is an enlarged view showing a space between the electrode members 11 of the electrode 4 used in the present invention. The shape of the electrode member 11 shown in FIG. 7 can be a plate shape, a rod shape, or another shape as required, and various coatings can be applied as needed. Of the colloid particles that move using groundwater as a medium and contain heavy metal elements and ions obtained from the heavy metal elements, a charged body having a positive charge is indicated by M +, and a charged body having a negative charge is indicated by M-. I have. In the present invention, these M + and M− are removed from the contaminated groundwater 5 by using an electrophoresis method or an electroosmosis method. In FIG. 7, arrows F and G indicate the direction of movement of the charged body by electrophoresis or electroosmosis. In the electrophoresis method or electroosmosis method used in the present invention, M + contained in the contaminated groundwater 5 is moved from the electrode member 19 on the high potential side (+) to the electrode member 20 on the low potential side (−). To concentrate on the electrode member 20 side,
Is moved from the electrode member 20 on the low potential side (−) to the electrode member 19 on the high potential side (+), and the electrode member 1 is moved.
Concentrate on the 9 side. By replacing the electrode 4 together with the water retaining material 13 containing the concentrated M + and M−, it becomes possible to remove heavy metal elements from the contaminated groundwater 5.

The method of the present invention will be further described with reference to FIG.
And M + and M- are absorbed into the water retention material 13 through the permeable underground continuous wall 15. At this time, the electrode members 19 and 2
0, a voltage is applied from the power supply 21 so as to generate a potential difference, and M + and M−
Will be electrophoresed or electroosmotic.

In the purification method of the present invention, when a sufficient amount of M + and M− is removed from the contaminated groundwater 5 by performing electrophoresis or electroosmosis appropriately, the electrode is replaced with a new electrode 4.
The next purification process is performed. By repeating this, heavy metals from the contaminated groundwater 5 are M +, M
-Can be removed particularly on site. The water retention material 13 containing the heavy metal element is removed by incineration or the like, and the heavy metal is removed by collecting the ash containing the heavy metal element.

According to the purification method of the present invention, the contaminated soil
By adjusting the pH of the groundwater, the insoluble heavy metal compound or the heavy metal alone contained in the soil without being eluted in the groundwater can be eluted, thereby improving the decontamination efficiency of the present method. Further, an organic compound such as phenol that dissolves in water at normal temperature can be moved to the electrode member as the groundwater moves by electroosmosis and concentrated. Furthermore, since it is possible to cause a current to flow between the electrode members 11, harmful volatile organic compounds such as trichloroethylene and tetrachloroethylene that may be contained in the contaminated groundwater 5 can be vaporized by the heat generated by the flowing current. It is also possible to do. By doing so, it is possible to efficiently remove volatile harmful substances such as trichlorethylene and tetrachloroethylene, which normally require several months to several years with the soil gas suction method, while purifying the contaminated groundwater 5. It becomes possible. In this case, a suction facility can be provided on the ground surface corresponding to the electrode 4 and exhaust can be performed through a filter such as an activated carbon tower.

[0036]

According to the present invention, since the electrode is a detachable cartridge, replacement and maintenance of the electrode are easy, and it is possible to purify soil and groundwater particularly in a place where a contaminated area exists, and There is no need to set up a large-scale treatment plant, so no site is required, and it is possible to concentrate and extract contaminants without the risk of contaminating the surrounding environment, and reduce the amount of industrial waste. It is possible to provide a buried purification structure and a purification method capable of reducing transportation costs and disposal costs associated therewith and enabling permanent pollution control.

[Brief description of the drawings]

FIG. 1 is a view showing an embedded purification structure according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing an underground continuous water stop wall and electrodes of the present invention.

FIG. 3 is a plan view of the electrode of the present invention.

FIG. 4 is a view showing an embedded purification structure according to a second embodiment of the present invention.

FIG. 5 is a view showing a buried type purification structure according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a permeable underground continuous wall according to a third embodiment of the present invention.

FIG. 7 is a view showing a purification method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ground surface 2 ... Impervious layer 3 ... Underground continuous water blocking wall 4 ... Electrode device 5 ... Contaminated groundwater 6 ... Housing part 7 ... Groundwater permeable screen 8 ... Side wall 9 ... Segment adjacent to groundwater permeable screen 10 ... Frame member 11 ... Electrode member 12 ... Power supply 13 ... Water retention material 14 ... Contaminated area 15 ... Permeable underground continuous wall 16 ... Purified ground water 17 ... Slot 18 ... Space 19,20 ... Electrode member 21 ... Power supply

 ──────────────────────────────────────────────────続 き Continued from the front page F term (reference) 2D043 CA13 2D049 EA01 EA05 GB01 4D004 AA41 AB03 AC07 CA44 4D061 DA10 DB19 DC21 DC23 DC25 DC26 DC27 DC28 EA01 EA10 EA11 EB31 EB20 EB29 EB31

Claims (7)

[Claims] 1. A wall-like structure extending from the ground surface to an impermeable layer, and a detachable structure disposed upstream of a groundwater flow direction and extending from the ground surface to the impermeable layer and adjacent to the wall-like structure. Embedded type purification structure comprising: 2. The underground continuous water stop wall formed so as to surround a contaminated region containing at least a heavy metal element, wherein the electrode faces the contaminated region. The embedded purification structure according to claim 1, wherein the purification structure is provided on a part of a water wall. 3. The buried type purification structure according to claim 1, wherein the buried type purification structure is provided with a groundwater permeable screen upstream of the electrode in the direction of flow of the groundwater. 4. A permeable underground continuous wall extending from the surface of the ground to an impermeable layer and permeating groundwater; and a permeable underground continuous wall formed on the permeable underground continuous wall and extending to the impermeable layer in a direction transverse to the flow direction of groundwater. An buried purification structure comprising a flattened slot and an electrode removably inserted into the slot. 5. The buried purification structure according to claim 1, wherein said electrodes are electrodes for electrophoresis and electroosmosis. 6. The buried purification structure according to claim 1, wherein the groundwater contains at least a heavy metal element. 7. Groundwater containing at least a heavy metal element,
The electrode extends from the ground surface to the water-impermeable layer and comes into contact with a detachable electrode adjacent to the underground continuous wall, a voltage is applied to the electrode, the colloid containing the heavy metal element is electrophoresed, and ions obtained from the heavy metal element are electrolyzed. A purification method, characterized in that the heavy metal element is removed from the groundwater by infiltration.