Method and device for repairing polluted soil through electrodynamic force

Abstract

The invention relates to the field of contaminated soil remediation, and particularly discloses a method and device for electrodynamic remediation of contaminated soil, the device comprises a power source, a perforated conductive tube, a drainage pipe, a vacuum pump and an adsorption device, the adsorption device comprises a cathode chamber, an anode chamber and an adsorption chamber, and the cathode chamber is communicated with the drainage pipe in the cathode perforated conductive tube; and the anode chamber is communicated with a drain pipe in the anode perforated conductive tube. The method comprises a device preparation step, a polluted soil electroosmosis remediation step and a water body circulation step. By arranging the adsorption device, pollutants can be removed, in-situ remediation of the polluted soil is achieved, acid-base neutralization of a cathode and an anode can be achieved, the soil water body is kept neutral, and precipitation is avoided; the adsorption device is arranged outside the soil, so that an adsorbent does not need to be buried in the soil, meanwhile, the adsorbent is convenient to replace, and the operation convenience is improved.

Description

Technical Field

[0001] The present application relates to the field of contaminated soil remediation, and in particular to a method and device for electrodynamic remediation of contaminated soil. Background Art

[0002] There are five main electrical phenomena in soil, namely: flow potential, migration potential, electroosmosis, ion migration and electrophoresis. The soil electrokinetic technology developed by using soil electrical phenomena is a platform technology that realizes water migration, ion migration, electrochemical reaction, etc. in the soil by passing direct current into the soil. This technology can be applied to many fields, such as: sludge dehydration, soft foundation treatment, contaminated soil remediation, mud and water co-control, saline-alkali land control, rare earth green mining, etc.

[0003] The principle of using electrokinetic methods to remediate contaminated soil is as follows: under the action of an external electric field, the pore water in the soil flows from the anode to the cathode, the uncharged pollutants migrate with the pore water and are enriched near the cathode, and the charged pollutant ions or complex ions migrate to the electrode of opposite charge under the action of the electric field (for example, heavy metal cations migrate to the cathode), and then the water containing the pollutants is treated.

[0004] Currently, there is a method of using an adsorbent buried in the soil near the electrode to adsorb pollutants. Since it involves the burial of the adsorbent, the operation is relatively cumbersome and it is not easy to replace the adsorbent. Summary of the invention

[0005] In view of the shortcomings of the prior art in using buried adsorbents to adsorb pollutants, the present application provides a method and device for electrodynamic remediation of contaminated soil.

[0006] The present application provides an electrodynamic device for remediating contaminated soil using the following technical solution: A device for electrodynamic remediation of contaminated soil, comprising: power supply; A plurality of perforated conductive tubes are buried in the soil; each of the perforated conductive tubes is connected to the anode or cathode of the power supply, and the anode perforated conductive tube and the cathode perforated conductive tube are arranged at intervals; liquid level gauges are respectively installed at two different depths in the perforated conductive tubes; A plurality of drain pipes corresponding to the perforated conductive tubes one by one, the water inlet end of the drain pipe is located in the perforated conductive tube, and a first control valve is installed on the drain pipe; the drain pipes in the plurality of cathode perforated conductive tubes are connected to the cathode busbar, and the drain pipes in the plurality of anode perforated conductive tubes are connected to the anode busbar; Two vacuum pumps are respectively arranged on the cathode manifold and the anode manifold; The adsorption device is arranged outside the soil, and comprises a cathode chamber, an anode chamber and an adsorption chamber connected between the cathode chamber and the anode chamber, wherein an adsorbent for adsorbing pollutants is arranged in the adsorption chamber; the cathode chamber and the anode chamber are respectively connected to the cathode manifold and the anode manifold.

[0007] The working principle of the device for electrodynamic remediation of contaminated soil provided in the present application is: under the action of an external electric field, for uncharged pollutants, as the pore water in the soil flows from the anode to the cathode, the water containing the pollutants migrates to the vicinity of the cathode and enters the cathode perforated conductive tube; for positively charged pollutants, under the combined action of ion migration and electroosmosis, as the pore water in the soil flows from the cathode to the cathode, the water enters the cathode perforated conductive tube; for negatively charged pollutants, since the electromigration rate is often greater than the electroosmosis rate, the positively charged pollutants will be enriched at the anode and enter the anode perforated conductive tube.

[0008] If the pollutant is negatively charged, since the direction of its ion migration is opposite to the direction of electroosmosis (ions migrate toward the anode and electroosmosis flows toward the cathode), one of the following methods needs to be used: 1) Add a chelating agent or complexing agent (such as EDTA) through the anode to chelate or complex the pollutant and the additive, changing the electrical properties to positive or uncharged; 2) Add an organic acid (such as acetic acid, citric acid) to change the direction of electroosmosis of soil pore water so that it is consistent with the direction of ion migration.

[0009] Regardless of whether the pollutants reach the anode or the cathode, the treatment method is similar. The following is an example of the pollutants reaching the cathode. When the water level in the cathode perforated conductive tube is higher than the first design water level, the first control valve of the drainage pipe in the perforated conductive tube is opened, so that the accumulated water in the perforated conductive tube can be pumped into the cathode chamber in time. When the water level in the cathode perforated conductive tube is not higher than the second design water level (the second design water level is lower than the first design water level), the first control valve of the drainage pipe in the perforated conductive tube is closed, thereby preventing the drainage pipe from affecting the vacuum degree of the entire drainage pipeline due to air intake, which is beneficial to ensure drainage efficiency.

[0010] The water with pollutants in the cathode chamber enters the adsorption chamber, the pollutants in the water are adsorbed by the adsorbent, and the water without pollutants enters the anode chamber. Start the vacuum pump on the anode manifold, keep the first control valve on the drainage pipe in the anode perforated conductive pipe open, so that the water in the anode chamber enters the anode perforated conductive pipe and returns to the soil near the anode, achieving acid-base neutralization between the cathode and cathode, keeping the soil water neutral, and avoiding precipitation.

[0011] Furthermore, a second control valve is provided at one end of the drain pipe located inside the perforated conductive pipe.

[0012] Furthermore, it also includes a controller for controlling the opening and closing states of the corresponding first control valve and the second control valve according to the water level in the perforated conductive tube.

[0013] When the drain pipe is pumping water, the first control valve and the second control valve are opened at the same time. When the drain pipe is not pumping water, the first control valve is closed to block the air connection between the vacuum pump and the drain pipe; at this time, the second control valve is also closed, the purpose is to keep the drain pipe full of water, so that when the drain pipe is vacuumed again, the pumping effect will not be affected by air entering the drain pipe.

[0014] Furthermore, a filter layer is provided on the inner wall of the perforated conductive tube.

[0015] The filter layer helps prevent the silt in the soil from entering the perforated conductive pipe and causing the drainage pipe to be blocked. If the filter layer is set on the outer wall of the perforated conductive pipe, the resistance between the perforated conductive pipe and the soil is very large, which affects the electroosmosis effect; therefore, the filter layer needs to be set on the inner wall of the perforated conductive pipe.

[0016] Furthermore, valves are provided between the cathode chamber and the adsorption chamber, and between the anode chamber and the adsorption chamber.

[0017] The valve between the cathode chamber and the adsorption chamber is used to control the connection or isolation between the cathode chamber and the adsorption chamber, and the valve between the anode chamber and the adsorption chamber is used to control the connection or isolation between the anode chamber and the adsorption chamber. Usually, the cathode chamber and the adsorption chamber, and the anode chamber and the adsorption chamber are both in a connected state.

[0018] When it is necessary to use the solution in the cathode chamber or the anode chamber to perform in-situ leaching and regeneration of the adsorbent, the corresponding valve is closed to isolate the anode chamber or the cathode chamber from the adsorption chamber.

[0019] When it is necessary to inject a reaction liquid such as a complexing agent into the soil, the corresponding valve can be closed to isolate the anode chamber or cathode chamber from the adsorption chamber, store the reaction liquid in the anode chamber or cathode chamber, and then inject the reaction liquid into the soil.

[0020] The present application also provides a method for electrodynamic remediation of contaminated soil, using the above-mentioned electrodynamic remediation device for contaminated soil, the method comprises the following steps: Device preparation: bury several perforated conductive pipes in the area to be treated, complete the installation of the liquid level meter, drainage pipe, first control valve and adsorption device, and complete the connection between the perforated conductive pipes and the power supply; Electro-osmosis remediation of contaminated soil: When power is turned on, the first control valve of the drainage pipe in the cathode perforated conductive pipe controls the opening and closing state according to the water level in the cathode perforated conductive pipe, and the vacuum pump pumps the accumulated water in the cathode perforated conductive pipe to the cathode chamber. The water in the cathode chamber enters the adsorption chamber for pollutant adsorption, and the water without pollutants enters the anode chamber; Water circulation: The water in the anode chamber is injected into the anode perforated conductive tube and returned to the soil near the anode to achieve acid-base neutralization of the cathode and cathode.

[0021] Furthermore, the electro-osmosis remediation of contaminated soil step also includes: when the water level in the cathode perforated conductive tube is higher than the first design water level, the first control valve of the drainage pipe in the perforated conductive tube is opened; when the water level in the cathode perforated conductive tube is not higher than the second design water level, the first control valve of the drainage pipe in the perforated conductive tube is closed; the first design water level is higher than the second design water level.

[0022] Furthermore, the device preparation step also includes: installing a second control valve at one end of the drain pipe located in the perforated conductive pipe, and the opening and closing states of the second control valve and the first control valve are kept consistent.

[0023] Furthermore, the device preparation step also includes: injecting a buffer solution into the cathode chamber or the anode chamber to adjust the pH of the water returned to the soil body in the water circulation step.

[0024] Furthermore, the device preparation step also includes: installing a valve between the cathode chamber and the adsorption chamber to control the connection or isolation between the cathode chamber and the adsorption chamber; installing a valve between the anode chamber and the adsorption chamber to control the connection or isolation between the anode chamber and the adsorption chamber.

[0025] In summary, the present application includes at least one of the following beneficial technical effects: 1. The present application sets the adsorption device outside the soil, and there is no need to bury the adsorbent in the soil. It is also convenient to replace the adsorbent, which improves the convenience of operation; 2. By setting up an adsorption device, not only can the pollutants be removed and the contaminated soil be repaired in situ, but also the acid-base neutralization of the cathode and anode can be achieved, so that the soil water body remains neutral and precipitation is avoided; 3. Buffer solution, complexing agent solution, etc. can be added to the cathode chamber and anode chamber in the adsorption device according to actual needs to meet various usage requirements; 4. Use perforated conductive pipes and drainage pipes in conjunction with vacuum pumps to achieve automatic extraction of polluted water, which is beneficial to improving the efficiency of extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the overall structure of a device for electrodynamic remediation of contaminated soil according to an embodiment of the present application.

[0027] Figure numerals: 1. perforated conductive tube; 2. drain pipe; 3. vacuum pump; 4. first control valve; 5. first liquid level gauge; 6. second control valve; 7. filter layer; 8. cathode manifold; 9. anode manifold; 10. cathode chamber; 11. anode chamber; 12. adsorption chamber; 13. valve; 14. second liquid level gauge. DETAILED DESCRIPTION

[0028] The following is combined with Figure 1 This application is described in further detail.

[0029] The present application discloses a device for electrodynamic remediation of contaminated soil. Figure 1 The device for electrodynamic remediation of contaminated soil includes a power source (not shown in the figure), a plurality of perforated conductive pipes 1, a plurality of drainage pipes 2, two vacuum pumps 3, and also includes an adsorption device and a controller.

[0030] Reference Figure 1 A plurality of perforated conductive tubes 1 are buried in the soil in an array, each perforated conductive tube 1 is connected to the anode or cathode of the power source, and the anode perforated conductive tube 1 is arranged at intervals from the cathode perforated conductive tube 1. A filter layer 7 is arranged on the inner wall of the perforated conductive tube 1, and the filter layer 7 can be a geotextile.

[0031] Reference Figure 1 A first liquid level gauge 5 is installed near the bottom of the perforated conductive tube 1 , and a second liquid level gauge 14 is installed near the top of the perforated conductive tube 1 . The first liquid level gauge 5 and the second liquid level gauge 14 are used to monitor the water level in the perforated conductive tube 1 .

[0032] Reference Figure 1 , multiple drain pipes 2 correspond to the perforated conductive tubes 1 one by one, the water inlet end of the drain pipe 2 is located near the bottom of the perforated conductive tube 1 and lower than the position of the first liquid level gauge 5, the upper part of the drain pipe 2 is installed with a first control valve 4, and one end of the drain pipe 2 located in the perforated conductive tube 1 is installed with a second control valve 6. The drain pipes 2 in the multiple cathode perforated conductive tubes 1 are connected to the cathode bus 8, and the drain pipes 2 in the multiple anode perforated conductive tubes 1 are connected to the anode bus 9, and two vacuum pumps 3 are respectively arranged on the cathode bus 8 and the anode bus 9.

[0033] Reference Figure 1 The adsorption device is arranged outside the soil, and includes a cathode chamber 10, an anode chamber 11, and an adsorption chamber 12 connected between the cathode chamber 10 and the anode chamber 11. The adsorption chamber 12 is provided with an adsorbent for adsorbing pollutants. A valve 13 is arranged between the cathode chamber 10 and the adsorption chamber 12, and between the anode chamber 11 and the adsorption chamber 12. The valve 13 is used to control the connection or isolation between the adsorption chamber 12 and the cathode chamber 10 or the anode chamber 11. The cathode chamber 10 and the anode chamber 11 are connected to the cathode manifold 8 and the anode manifold 9, respectively.

[0034] The first liquid level meter 5 , the second liquid level meter 14 , the first control valve 4 and the second control valve 6 are all connected to a controller, and the controller is used to control the opening and closing states of the corresponding first control valve 4 and the second control valve 6 according to the water level in the perforated conductive tube 1 .

[0035] A method for electrodynamically repairing contaminated soil is implemented by using the above-mentioned device for electrodynamically repairing contaminated soil, and the method comprises the following steps: Step 1: Device preparation: Several perforated conductive pipes 1 are buried in an array in the area to be treated. A filter layer 7 is laid on the inner wall of the perforated conductive pipe 1, and a first liquid level gauge 5 and a second liquid level gauge 14 are installed in each perforated conductive pipe 1. A drainage pipe 2 is inserted into each perforated conductive pipe 1, a first control valve 4 is installed on the upper part of the drainage pipe 2, and a second control valve 6 is installed on the bottom end of the drainage pipe 2.

[0036] The anode and cathode of the power supply are respectively connected to the corresponding perforated conductive tubes 1, so that the anode perforated conductive tubes 1 and the cathode perforated conductive tubes 1 are arranged alternately. The water outlet ends of the drain pipes 2 in all the cathode perforated conductive tubes 1 are connected to the cathode manifold 8, and the water outlet ends of the drain pipes 2 in all the anode perforated conductive tubes 1 are connected to the anode manifold 9.

[0037] An adsorption device is arranged outside the soil, an adsorbent is filled in the adsorption chamber 12, and valves 13 are respectively installed between the cathode chamber 10 and the adsorption chamber 12, and between the anode chamber 11 and the adsorption chamber 12. The cathode manifold 8 and the anode manifold 9 are respectively connected to the cathode chamber 10 and the anode chamber 11, and vacuum pumps 3 are respectively installed on the cathode manifold 8 and the anode manifold 9.

[0038] Step 2: Electroosmosis remediation of contaminated soil: When the power is turned on, the vacuum pump 3 on the cathode manifold 8 is started, and the first control valve 4 of the drainage pipe 2 in the cathode perforated conductive tube 1 controls the opening and closing state according to the water level in the cathode perforated conductive tube 1, as follows: When the water level in the cathode perforated conductive tube 1 is higher than the second liquid level gauge 14, the first control valve 4 and the second control valve 6 of the drainage pipe 2 in the perforated conductive tube 1 are both opened, and the vacuum pump 3 pumps the accumulated water in the cathode perforated conductive tube 1 to the cathode chamber 10, and the water in the cathode chamber 10 enters the adsorption chamber 12 for pollutant adsorption, and the water without pollutants enters the anode chamber 11.

[0039] When the water level in the cathode perforated conductive tube 1 is not higher than the first liquid level gauge 5, the first control valve 4 and the second control valve 6 of the drain pipe 2 in the perforated conductive tube 1 are both closed, so that the drain pipe 2 remains full of water, so that when the drain pipe 2 is vacuumed again, the pumping effect will not be affected by the air intake into the drain pipe 2.

[0040] Step 3: Water circulation: Open the first control valve 4 of the drainage pipe 2 in the anode perforated conductive tube 1 to allow the water in the anode chamber 11 to enter the anode perforated conductive tube 1 and return to the soil near the anode, thereby achieving acid-base neutralization between the cathode and cathode, maintaining the soil water body neutral, and avoiding precipitation.

[0041] Cathode pumping and anode water injection can be performed simultaneously or separately. If cathode pumping and anode water injection are performed simultaneously, the first control valve 4 and the second control valve 6 of the drainage pipe 2 in the anode perforated conductive tube 1 are kept open while the cathode pumping, and the vacuum pump 3 on the anode manifold 9 is started. If cathode pumping and anode water injection are performed separately, the first control valve 4 and the second control valve 6 of the drainage pipe 2 in the anode perforated conductive tube 1 are kept closed while the cathode pumping, and the vacuum pump 3 on the anode manifold 9 is turned off; when the cathode pumping is completed, a sufficient amount of water is stored in the anode chamber 11, and the first control valve 4 and the second control valve 6 of the drainage pipe 2 in the anode perforated conductive tube 1 and the vacuum pump 3 on the anode manifold 9 are opened to inject the water in the anode chamber 11 into the soil.

[0042] During the power-on period, the current decreases exponentially with time. When the current decreases to a constant, the polarity of the power supply is changed so that the original cathode perforated conductive tube 1 is converted to the anode perforated conductive tube 1, and the original anode perforated conductive tube 1 is converted to the cathode perforated conductive tube 1. After the polarity conversion, the power is turned on again, and the electro-osmosis remediation of contaminated soil and the water circulation steps are repeated until the current decreases to a constant value close to zero or the current residual constant, and the power is stopped, and the remediation of contaminated soil in the area is completed.

[0043] The purpose of changing polarity is that as electromigration and electroosmosis proceed, the positive and negative electrodes become polarized, and precipitation may form at the cathode, resulting in a decrease in electromigration efficiency. Changing the polarity of the electrodes eliminates polarization, dissolves precipitation, and thus reduces resistance and increases the effective electric field strength of the soil, which is beneficial to improving electromigration and electroosmosis efficiency.

[0044] In some feasible implementations, a buffer solution may be injected into the cathode chamber 10 or the anode chamber 11 to adjust the pH of the water returned to the soil in the water circulation step.

[0045] In some feasible embodiments, the corresponding valve 13 may be closed to isolate the adsorption chamber 12 from the anode chamber 11 or the cathode chamber 10 , and then the adsorbent may be regenerated by in-situ leaching using the solution in the cathode chamber 10 or the anode chamber 11 .

[0046] In some feasible implementations, the corresponding valve 13 can be closed to isolate the adsorption chamber 12 from the anode chamber 11 or the cathode chamber 10, and the reaction solution such as the complexing agent can be stored in the anode chamber 11 or the cathode chamber 10, and then the reaction solution can be injected into the soil.

[0047] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A device for electrodynamic remediation of contaminated soil, characterized in that: include: power supply; A plurality of perforated conductive tubes are buried in the soil; each of the perforated conductive tubes is connected to the anode or cathode of the power supply, and the anode perforated conductive tube and the cathode perforated conductive tube are arranged at intervals; liquid level gauges are respectively installed at two different depths in the perforated conductive tubes; A plurality of drain pipes corresponding to the perforated conductive tubes one by one, the water inlet end of the drain pipe is located in the perforated conductive tube, and a first control valve is installed on the drain pipe; the drain pipes in the plurality of cathode perforated conductive tubes are connected to the cathode busbar, and the drain pipes in the plurality of anode perforated conductive tubes are connected to the anode busbar; Two vacuum pumps are respectively arranged on the cathode manifold and the anode manifold; The adsorption device is arranged outside the soil, and comprises a cathode chamber, an anode chamber and an adsorption chamber connected between the cathode chamber and the anode chamber, wherein an adsorbent for adsorbing pollutants is arranged in the adsorption chamber; the cathode chamber and the anode chamber are respectively connected to the cathode manifold and the anode manifold.

2. The device for electrodynamic remediation of contaminated soil according to claim 1, characterized in that: A second control valve is arranged at one end of the drainage pipe located in the perforated conductive pipe.

3. The device for electrodynamic remediation of contaminated soil according to claim 2, characterized in that: It also includes a controller for controlling the opening and closing states of the corresponding first control valve and the second control valve according to the water level in the perforated conductive tube.

4. The device for electrodynamic remediation of contaminated soil according to claim 1, characterized in that: The inner wall of the perforated conductive tube is provided with a filter layer.

5. The device for electrodynamic remediation of contaminated soil according to claim 1, characterized in that: Valves are arranged between the cathode chamber and the adsorption chamber, and between the anode chamber and the adsorption chamber.

6. A method for electrodynamic remediation of contaminated soil, using the electrodynamic remediation device for contaminated soil according to any one of claims 1 to 5, characterized in that: The following steps are involved: Device preparation: bury several perforated conductive pipes in the area to be treated, complete the installation of the liquid level meter, drainage pipe, first control valve and adsorption device, and complete the connection between the perforated conductive pipes and the power supply; Electro-osmosis remediation of contaminated soil: When power is turned on, the first control valve of the drainage pipe in the cathode perforated conductive pipe controls the opening and closing state according to the water level in the cathode perforated conductive pipe, and the vacuum pump pumps the accumulated water in the cathode perforated conductive pipe to the cathode chamber. The water in the cathode chamber enters the adsorption chamber for pollutant adsorption, and the water without pollutants enters the anode chamber; Water circulation: The water in the anode chamber is injected into the anode perforated conductive tube and returned to the soil near the anode to achieve acid-base neutralization of the cathode and anode.

7. The method for electrodynamic remediation of contaminated soil according to claim 6, characterized in that: The electro-osmosis repair of contaminated soil step also includes: when the water level in the cathode perforated conductive tube is higher than the first design water level, the first control valve of the drainage pipe in the perforated conductive tube is opened; when the water level in the cathode perforated conductive tube is not higher than the second design water level, the first control valve of the drainage pipe in the perforated conductive tube is closed; the first design water level is higher than the second design water level.

8. The method for electrodynamic remediation of contaminated soil according to claim 7, characterized in that: The device preparation step also includes: installing a second control valve at one end of the drain pipe located in the perforated conductive pipe, and the opening and closing states of the second control valve and the first control valve are kept consistent.

9. The method for electrodynamic remediation of contaminated soil according to claim 6, characterized in that: The device preparation step also includes: injecting a buffer solution into the cathode chamber or the anode chamber to adjust the pH of the water returned to the soil body in the water body circulation step.

10. The method for electrodynamic remediation of contaminated soil according to claim 6, characterized in that: The device preparation step also includes: installing a valve between the cathode chamber and the adsorption chamber to control the connection or isolation between the cathode chamber and the adsorption chamber; installing a valve between the anode chamber and the adsorption chamber to control the connection or isolation between the anode chamber and the adsorption chamber.

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