Method for synchronously remediating organically contaminated soil and groundwater by means of electrokinetic coupled multiphase extraction

Abstract

A method for synchronously remediating organically contaminated soil and groundwater by means of electrokinetic coupled multiphase extraction. Cathode wells and anode wells are distributed in a staggered manner in an area to be remediated; a pipe filled with an electrolyte is inserted into each of the cathode wells and the anode wells; an extraction pipe is inserted into each cathode well; electrodes are connected to an electrokinetic remediation system; the extraction pipes are connected to a multiphase extraction system; by means of electrokinetic remediation, persulfate anions in a catholyte are injected into a stratum from the cathode wells and are then migrated to an anode by means of the action of electromigration, iron ions released by a sacrificial anode in an anolyte are migrated to a cathode by means of the action of electromigration and electrodialysis, and persulfate in soil and groundwater are activated during "opposite-direction" migration; then, the direction of an electric field is switched, and at the same time, electrolytes are added to corresponding electrode wells for "opposite-direction" migration, and remediation treatment is performed according to the above electrode-based remediation method and an electrode-based remediation method in which an electrode direction is switched, until organically contaminated soil and groundwater in the area to be treated are completely remediated at the same time; and the multiphase extraction system is started after the electrode-based remediation, and the electrolytes in the electrode wells are depleted. Further disclosed is the use of the method for synchronously remediating organically contaminated soil and groundwater by means of electrokinetic coupled multiphase extraction in in-situ remediation of organically contaminated soil.

Description

A method for synchronous remediation of organically contaminated soil and groundwater by electrokinetic coupled multiphase extraction Technical Field

[0001] The present invention belongs to the technical field of in-situ remediation of organic contaminated soil, and in particular relates to a method for synchronously remediating organic contaminated soil and groundwater by electrokinetic coupling multiphase extraction. Background Art

[0002] Vacuum enhanced extraction technology, also known as multiphase extraction technology (MPE), is an in-situ remediation technology that can simultaneously extract underground gas and liquid. Under vacuum conditions, the fluid in the formation responds to the pressure gradient and continuously flows into the extraction well. The dissolved pollutants and floating oil layer (light non-aqueous phase liquid) in the groundwater are extracted and removed; the decrease in soil pore pressure accelerates the transfer of volatile organic pollutants (VOCs) and semi-volatile organic pollutants (SVOCs) to the soil gas phase, and are extracted from the soil along with the air flow. At the same time, the improvement of soil permeability and the increase in pore oxygen content can also effectively promote the degradation of aerobic microorganisms. In addition, the vacuum dehydration effect will also reduce the groundwater level around the extraction well and increase the air permeability of the formation. The VOCs and SVOCs retained in the soil will be redistributed to the gas phase, thereby improving the efficiency of pollution remediation.

[0003] MPE technology has the advantages of minimal site disturbance and the ability to remove pollutants from both the vadose zone and aquifers. However, its application effect is greatly affected by the hydrogeological conditions of the site, mainly the extraction flow of soil gas and groundwater. The applicable formation permeability coefficient (K) of MPE technology is in the range of 10 -5 -10 -3 cm·s-1, corresponding to medium and low permeability soil layers (sand-silty clay layers), applied to clay layers (K<10 -6 cm·s-), it is difficult to achieve the ideal remediation effect, and the pollutant concentration changes tend to be slow in the later stage of remediation ("tailing" phenomenon), which seriously affects the remediation effect. MPE technology can effectively remove organic pollutants with small molecular weight, high volatility and good water solubility. On the contrary, it has poor removal effect on organic pollutants with large molecular weight, low volatility and poor water solubility. Generally, MPE technology is suitable for the removal of organic pollutants with saturated vapor pressure >0.133kPa (20℃), Henry coefficient >0.01 (20℃), and boiling point 250-300℃. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of limited application of MPE technology in low permeability formations, low efficiency in remediation of macromolecular organic pollutants, and severe "tailing" in the later stage of remediation, and to propose a method for synchronous remediation of organically contaminated soil and groundwater by electrokinetic coupled multiphase extraction.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for synchronously remediating organically contaminated soil and groundwater by electrokinetic coupling multiphase extraction comprises: staggered cathode and anode wells are arranged in an area to be remediated; tubes filled with electrolyte are inserted into the cathode and anode wells; an extraction tube is inserted into the cathode well; the electrodes are connected to an electrokinetic remediation system; and the extraction tube is connected to a multiphase extraction system; through electrokinetic remediation, persulfate anions in the cathode electrolyte are injected into the formation from the cathode well and migrate to the anode through electromigration; iron ions released from the sacrificial anode in the anolyte migrate toward the cathode through electromigration and electrodialysis, activating persulfate in the soil and groundwater during the "counter-directional" migration; then, the direction of the electric field is switched and electrolyte is simultaneously added to the corresponding electrode wells for "counter-directional" migration; and remediation treatment is performed according to the aforementioned electrode remediation and electrode remediation with switched electrode directions until the organically contaminated soil and groundwater in the area to be remediated are completely and simultaneously remediated; and after the electrode remediation, the multiphase extraction system is started to deplete the electrolyte in the electrode wells.

[0007] The electrodes in the cathode well and the anode well are made of iron or stainless steel; the electrolyte in the cathode well is a persulfate aqueous solution with a concentration of 50-100 g / L, preferably 50-100 g / L, more preferably 50 g / L or 100 g / L; the electrolyte in the anode well is water.

[0008] The electrode well is a cavity dug in the area to be repaired, a supporting screen is inserted into the cavity, and electrodes, electrolyte injection pipes and extraction pipes are inserted into the screen. The depth of the electrode well is 0.5-1.5m below the groundwater pollution depth, and 10-30cm above the ground is used as a well platform, and the wellhead valve is sealed.

[0009] Conductive particles are filled between the electrode well wall and the outer wall of the support screen tube.

[0010] Furthermore, the electrode well has a diameter of 45-108 mm, and the well wall is supported by a porous PVC screen tube (screen hole diameter 3-5 mm) with an outer diameter of 40 mm-98 mm (smaller than the electrode well aperture 10 mm); the screen tube and the well wall are filled with conductive particles such as iron carbon and petroleum coke (diameter 6-15 mm).

[0011] The electrodes are made of iron or stainless steel with a diameter of 27-42 mm; the extraction tube is made of PVC or HDPE with a diameter of 22-34 mm, and the filter tube (cut slit 0.2-0.4 mm) has a length that covers the depth of groundwater pollution; the electrolyte injection tube is made of PVC or HDPE with a diameter of 18-27 mm, and a pipe valve is installed outside the wellhead to control the pipeline sealing.

[0012] Specifically:

[0013] 1) Set up electrode wells in a matrix-like staggered distribution in the repair area, fix the electrodes, extraction tubes, and electrolyte injection tubes in the electrode wells, and seal the wellheads;

[0014] 2) Water and persulfate aqueous solution are pumped into the anode well and cathode well as electrolytes, respectively. The electrodes are connected to the output end of the electric repair system, and the extraction pipe is connected to the multiphase extraction system.

[0015] 3) Setting the operating voltage and starting the electric repair system, after completing the transport of persulfate in the cathode well and iron ions released by the electrode in the anode well, starting the multiphase extraction system in the cathode well;

[0016] 4) After the electrolyte in the cathode well is completely extracted, the electric repair device and the extraction device are disconnected, and the electrolyte in the anode well is pumped to the cathode well and then replenished with a persulfate aqueous solution;

[0017] 5) Switching the direction of the electric field, the initial anode well becomes the cathode well, and the initial cathode well becomes the anode well, and starting the multiphase extraction system of the cathode well;

[0018] 6) Repeat steps 3) to 5) until the repair target is achieved.

[0019] The wellhead is sealed with a rubber pad in combination with cement and bentonite. The rubber pad is provided with a plurality of reserved through holes for the electrodes, electrolyte injection pipes and extraction pipes to be inserted. Then cement and bentonite are used for masonry to seal the above-ground part of the electrode well to ensure the airtightness of the extraction system.

[0020] The electric repair system consists of a DC power supply (constant voltage output, 0-220V), a relay (coil voltage 240V), a digital voltmeter (DC 0-500V), a digital ammeter (DC 0-10A), and a time-controlled switch (DC 220V), which are connected in sequence through wires to realize the setting of working voltage and automatic switching of electrode polarity.

[0021] The operating voltage range of the electric repair system in step 3) is 15-150V, corresponding to a potential gradient of 0.1-1V / cm, preferably 0.5V / cm or 1V / cm; the transport time of the persulfate in the cathode well and the iron ions released by the sacrificial anode in the anode well is 7-30d, preferably 15d;

[0022] The multiphase extraction system is a single-pump system, which is composed of a high-vacuum vacuum pump (maximum vacuum degree -101kPa), a gas-liquid separator (DN150-200), a waste gas processor (activated carbon adsorption tank), and a wastewater treatment device (Fenton oxidation tower) connected in sequence through connecting pipes, wherein the vacuum pump is connected to the extraction pipe through a connecting section.

[0023] In step 4), the vacuum pump pressure parameters of the multiphase extraction system are set to -20 to -90 kPa; the influence radius of the extraction system is 0.5-1.5 m, the wellhead vacuum is -0.01 to -0.06 MPa, preferably -0.04 MPa, the gas extraction rate of a single well is 0.5-10 m3 / h, preferably 3 m3 / h, and the liquid extraction rate of a single well is 0.005-0.1 m3 / h, preferably 0.02 m3 / h; the operation time of the extraction system is 5-7 days, preferably 5 days;

[0024] The activated carbon adsorption tank has a filling capacity of 10-50kg; the wastewater treatment capacity of the Fenton oxidation tower is 0.05-0.2m 3 / h, hydrogen peroxide (≥27.5%) added in an amount of 0.5-5L, and iron ion dosage of 40-500g;

[0025] In step 5), the direction of the electric field is switched by the electric repair control system with the same voltage parameters as in step 3), and the switching period is set to 7-30 days, preferably 15 days.

[0026] After the electrode direction is switched, the electrolyte (water) in the original anode well is pumped to the original cathode well by a self-priming pump (lift 10-40m, flow rate 0.5-2m 3 / h) is connected to the extraction tube to complete the process, and the concentration of the persulfate aqueous solution added after the electrode well is emptied is 50-100 g / L.

[0027] An application of the method for synchronously repairing organically contaminated soil and groundwater by electrokinetic coupling multiphase extraction in in-situ remediation of organically contaminated soil.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] The present invention realizes the transport of persulfate in the cathode well to the soil and groundwater in the direction of the anode based on the electromigration effect. The iron ions released by the sacrificial anode are transported to the soil and groundwater in the direction of the cathode under the dual effects of electrodialysis and electromigration, which can effectively activate persulfate and realize the oxidative degradation of pollutants. At the same time, the weak DC electric field can stimulate the biodegradation of indigenous microorganisms in the soil and groundwater, further improving the removal efficiency of pollutants. Under the strengthening effect of the stable electrodialysis flow, the extraction efficiency of MPE for groundwater in low permeability formations is further improved. The alternating operation of the electric field can not only avoid the drastic changes in soil acid-base conditions caused by water electrolysis, but also eliminate the differences in activation efficiency and pollutant removal efficiency caused by the differences in the transport efficiency of persulfate ions and iron ions, significantly improving the spatial uniformity of pollutant removal. In addition, the DC electric field can further improve the pollutant extraction efficiency of MPE by promoting desorption and mass transfer of pollutants. The EK-MPE coupling technology can effectively solve the bottleneck of MPE technology in low permeability formation applications, effectively solve the "tailing" problem in the late extraction period, and realize the synchronous and efficient remediation and detoxification of complex organic contaminated soil and groundwater. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0031] FIG1 shows the change of the iron ion release amount of the sacrificial anode of the present invention over time;

[0032] FIG2 is a simulated experimental setup for persulfate and sacrificial anode iron ion release according to the present invention; in the figure, 1-DC power supply; 2-cathode chamber electrolyte recovery tank; 3-cathode chamber; 4-cathode; 5-porous sieve plate; 6-soil chamber; 7-anode; 8-anode chamber; 9-peristaltic pump; 10-anode chamber electrolyte storage tank; 11-soil sampling point location;

[0033] FIG3 shows the distribution of persulfate in soil when the cathode injection method is used in the present invention;

[0034] FIG4 shows the distribution of iron ions released by the sacrificial anode of the present invention in the soil;

[0035] FIG5 is a laboratory verification device for the electrokinetic coupled multiphase extraction method of the present invention; in the figure, (a) laboratory simulation verification device; (b) sampling point arrangement;

[0036] FIG6 is a schematic diagram of an electrode well provided in an embodiment of the present invention; in the figure, (a) an anode well; (b) a cathode well;

[0037] FIG7 shows the laboratory verification results of the electrokinetic coupled multiphase extraction method of the present invention; in the figure, (a) the spatial distribution of benzene pollutants; (b) the spatial distribution of petroleum hydrocarbon pollutants;

[0038] FIG8 is a schematic diagram of a method for implementing the present invention in actual field application; in the figure, (a) is a schematic diagram of the on-site layout of the implementation process; (b) is a schematic diagram of the plan layout;

[0039] FIG9 shows the results of field application of the electrokinetic coupled multiphase extraction method of the present invention for soil remediation. In the figure, (a) the residual amount of chloroform in the soil; (b) the residual amount of cis-1,2-dichloroethylene in the soil; (c) the residual amount of benzene in the soil; and (d) the residual amount of petroleum hydrocarbons in the soil.

[0040] FIG10 shows the results of groundwater remediation using the electrokinetic coupled multiphase extraction method of the present invention. In the figure, (a) the residual amount of chloroform in the groundwater; (b) the residual amount of cis-1,2-dichloroethylene in the groundwater; and (c) the residual amount of benzene in the groundwater. DETAILED DESCRIPTION

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0043] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0044] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0045] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0046] The raw materials used in the following examples of the present invention are all commercially available.

[0047] The present invention couples and integrates the advantages of MPE technology and EK-ISCO technology. It mainly uses a DC electric field to achieve efficient "counter-directional" transport of oxidants (persulfate, cathode to anode) and activators (iron ions released by sacrificial anode, anode to cathode) in the soil, activates persulfate with iron ions, and effectively degrades pollutants. Switching the direction of the electric field at a specific time can not only avoid drastic fluctuations in the pH of the repaired soil and groundwater, but also effectively avoid oxidant loss caused by increased electrolyte pH during the cathode injection process. The uniform spatial distribution of iron ions and persulfate can further improve the uniformity of pollutant removal. After the persulfate-iron ion-pollutant fully reacts, the cathode well extraction system is started, and the stable electrodialysis flow (anode → cathode) can effectively improve the groundwater extraction efficiency; at the same time, the weakly bound water in the soil breaks away from the double electric layer and becomes free water under the action of the electric field, which can accelerate the mass transfer process of pollutants and also improve the pollutant extraction efficiency of the MPE technology; in addition, the vacuum negative pressure effectively improves the air permeability and water permeability of the soil, which is beneficial to the mass transfer process and electric field stimulated biodegradation process of the next EK-ISCO stage, effectively improving the remediation efficiency and shortening the remediation cycle. The present invention realizes the synchronous and efficient remediation and detoxification of composite organic contaminated soil and groundwater based on the synchronous electrokinetic transport of oxidants and activators, electric field stimulated biodegradation, and negative pressure extraction to improve mass transfer efficiency.

[0048] In the following preferred embodiments of the present invention, the electrode well can be constructed using a Geoprobe, Powerprobe or 30-type drilling rig, etc. The electrode well aperture is 45-108 mm, and the well wall is supported by a porous PVC sieve pipe (sieve aperture 3-5 mm) with an outer diameter of 40 mm-98 mm (less than the electrode well aperture 10 mm).

[0049] The electrodes are made of iron or stainless steel with a diameter of 27-42 mm; the extraction tube is made of PVC or HDPE with a diameter of 22-34 mm, and the filter tube (cut slit 0.2-0.4 mm) has a length that covers the depth of groundwater pollution; the electrolyte injection tube is made of PVC or HDPE with a diameter of 18-27 mm, and a pipe valve is installed outside the wellhead to control the pipeline sealing.

[0050] The electric repair system consists of a DC power supply (constant voltage output, 0-220V), a relay (coil voltage 240V), a digital voltmeter (DC 0-500V), a digital ammeter (DC 0-10A), a time-controlled switch (DC220V), etc., which can realize the setting of working voltage, automatic switching of electrode polarity, etc.; the multiphase extraction system is a single pump system, consisting of a high vacuum pump (maximum vacuum degree -101kPa), a gas-liquid separator (DN150-200), a waste gas processor (activated carbon adsorption tank), a wastewater treatment device (Fenton oxidation tower), etc.

[0051] The following examples serve as further illustrations of the technical solutions of the present invention.

[0052] Example 1

[0053] (1) Changes in iron ion release from sacrificial anode over time

[0054] Three 1L beakers (14 cm diameter) were each filled with a 100 g / L sodium sulfate aqueous solution. The beakers were then covered with a perforated plexiglass plate (12 cm apart, for electrode placement). A stainless steel anode (12 cm long, 1.5 cm diameter) and a graphite cathode (12 cm long, 1.5 cm diameter) were inserted into the holes in the plate and connected to the output of a DC power supply. The power supply voltage was set to 6 V, 12 V, and 24 V (corresponding to potential gradients of 0.5 V / cm, 1 V / cm, and 2 V / cm, respectively). The electrolyte was regularly sampled to measure the iron ion content and investigate the time-dependent changes in iron ion release from the anode. As shown in Figure 1, the ferrous ion content increased with increasing applied voltage and prolonged power-on time. Within one day, iron ion release was minimal due to limited electrode corrosion. As power-on time increased, the electrolyte gradually acidified due to the electrolysis of water at the anode, leading to increasing iron ion release from the sacrificial anode.

[0055] (2) Persulfate cathode injection efficiency based on polarity switching operation

[0056] The experimental apparatus (Figure 2) consisted of a digitally controlled DC power supply, electrode connection cables, electrodes, an electrode well, a soil chamber, an electrolyte storage tank, an electrolyte recovery tank, and a peristaltic pump. Clay soil was wet-packed into the soil chamber (50 cm long × 10 cm wide × 10 cm high). The soil moisture content was adjusted to saturation (40.0%, w / w). The filling height was 8.0 cm, and the soil density was 1.96 g / cm³ (approximately 7.9 kg). To prevent soil from entering the electrode well through the holes, the outer wall of the electrode well in contact with the soil was covered with 100-mesh nylon mesh. Electrodes (graphite, 12 cm long, 1.5 cm diameter) were installed in the electrode well (10 cm long × 10 cm wide).

[0057] In the first operation phase, the initial anode and initial cathode were connected to the corresponding output ports of a DC power supply. The DC power supply voltage was set to 25 V (corresponding to a potential gradient of 0.5 V / cm). Tap water was injected into the initial anode well as the electrolyte (liquid level 8.0 cm), and a persulfate solution (100 g / L) was pumped into the initial cathode well as the electrolyte (liquid level 8.0 cm). The DC power supply was activated and the cycle lasted for 15 days. In the second operation phase, the initial anode was connected to the cathode output terminal of the DC power supply, and the initial cathode was connected to the anode output terminal of the DC power supply (switching the electric field direction from initial anode to cathode and then from initial cathode to anode). The electrolyte in the electrode wells from the previous phase was emptied, and tap water and a persulfate solution (100 g / L) were injected into the current anode well and the current cathode well. The DC power supply was activated and the cycle lasted for 15 days.

[0058] After the experiment was completed, the persulfate content in the soil was tested using UV spectrophotometry. Specifically, deionized water, NaHCO3, and KI were mixed in a ratio of 40:0.2:4 (mL:g:g) to form Reagent A. Persulfate in the soil (soil:water = 1:10) was extracted with deionized water (150 rpm, room temperature, oscillation for 30 minutes). The supernatant after centrifugation (6000 rpm, 3 minutes) was used as the test solution. 100 μL of the test solution was mixed evenly with 40 mL of Reagent A, allowed to stand for 15 minutes, and the absorbance was measured at a wavelength of 352 nm. Persulfate solutions of varying concentrations were mixed with Reagent A and the absorbance was measured to create a standard curve.

[0059] The results show (Figure 3) that the cathode well injection method based on polarity switching operation can achieve relatively uniform distribution of persulfate in low-permeability soil. At the end of the experiment (30 days), the persulfate concentrations in the soil S1-S5 profiles ranged from 16.8 to 19.2 g / kg, with an average content of 17.88 g / kg and an injection efficiency of approximately 70%.

[0060] (3) Distribution of iron ions released from sacrificial anodes in soil based on polarity switching operation

[0061] The experimental setup, soil loading, and experimental parameters were the same as in (2), except that the graphite electrode was replaced with an iron electrode (12 cm long, 1.5 cm in diameter). The results (Figure 4) showed that the electrokinetic transport method based on the release of iron ions by the sacrificial anode via polarity switching operation can achieve efficient production and spatial distribution of ferrous ions. At the end of the experiment (30 days), the iron ion content of soil sections S1-S5 ranged from 10.2 to 11.9 g / kg, with an average content of 10.96 g / kg.

[0062] Example 2

[0063] Based on the electrokinetic transport parameters of persulfate cathode well injection and iron ion release at the sacrificial anode under the polarity switching operating conditions obtained in Example 1, laboratory verification of the electrokinetic coupled multiphase extraction method was carried out.

[0064] The device consists of a digitally controlled direct current power supply, electric wires, a PVC soil tank, an electrode well, electrodes, a peristaltic pump, a water electrolyte storage tank, a persulfate electrolyte storage tank, an electrolyte injection pipeline, an extraction pipeline, a vacuum pump, and the like.

[0065] The specific simulation device (Figure 5) is staggered in the area to be repaired (soil chamber) to set up cathode and anode wells (see Figure 6), that is, a row of cathode wells is arranged between two rows of symmetrically distributed anode wells, and the spacing between the anode wells and the opposite cathode wells is equal. Tubes filled with electrolyte are inserted into the cathode and anode wells, and an extraction tube is inserted into the cathode well. The electrodes are connected to the electric repair system, and the extraction tube is connected to the multiphase extraction system.

[0066] The electrodes were connected to the anode and cathode output ports of a digitally controlled DC power supply, respectively. A simulated composite contaminated clay soil (benzene content 7.8 mg / kg, petroleum hydrocarbon content 1570.6 mg / kg) was placed in a soil chamber (120 cm long × 120 cm wide × 50 cm high) using a wet packing method. The soil moisture content was adjusted to saturation (40.0%, w / w). The filling height was 45 cm, and the soil density was 1.96 g / cm. 3 To prevent soil from entering the electrode well through the hole, the outer wall of the electrode well (50 cm high, 6 cm inner diameter) in contact with the soil was covered with 100-mesh nylon mesh. The well wall was supported by a porous PVC sieve (3 mm pore size) with an outer diameter of 5 cm (1 cm smaller than the electrode well aperture). The space between the sieve and the well wall was filled with petroleum coke conductive particles (6 mm diameter). A wellhead sealing cap (a perforated rubber plug, 5 cm thick) was installed, and an electrode (52 cm long, 2 cm diameter, iron), an electrolyte injection tube (1 cm diameter), and an extraction tube (2 cm diameter) were inserted into the electrode well through the hole in the rubber sealing cap.

[0067] The extraction pipe is connected to the vacuum pump, which is connected to the gas-liquid separator (DN15-DN25, rated flow rate 0.3-0.5m 3 / min The capacity of this embodiment is set to 0.3m 3 / min), activated carbon adsorption purifier (processing air volume 5-20m3 / h, the set capacity of this embodiment is 5m3 / h, the amount of activated carbon added is 30kg), Fenton reactor (wastewater treatment capacity 0.05-0.5m 3 / h. This embodiment sets the capacity to be 0.5L of H2O2 (≥27.5%) and 40g of iron ions, allowing for further treatment of the extracted waste gas and wastewater. The activated carbon adsorption purifier has a loading capacity of 30-60kg; the Fenton reactor has a loading capacity of 0.5L of H2O2 (≥27.5%) and 40g of iron ions.

[0068] Specifically:

[0069] 1) Set up electrode wells in a matrix-like staggered pattern in the remediation area (soil chamber), fix the electrodes, extraction tubes, and electrolyte injection tubes in the electrode wells, and seal the wellheads;

[0070] 2) Water and persulfate aqueous solution are pumped into the anode well and cathode well as electrolytes, respectively. The electrodes are connected to the output end of the electric repair system, and the extraction pipe is connected to the multiphase extraction system.

[0071] 3) Setting the operating voltage and starting the electric repair system, after completing the transport of persulfate in the cathode well and iron ions released by the electrode in the anode well, starting the multiphase extraction system in the cathode well;

[0072] 4) After the electrolyte in the cathode well is completely extracted, the electric repair device and the extraction device are disconnected, and the electrolyte in the anode well is pumped to the cathode well and then replenished with a persulfate aqueous solution;

[0073] 5) Switching the direction of the electric field, the initial anode well becomes the cathode well, and the initial cathode well becomes the anode well, and starting the multiphase extraction system of the cathode well;

[0074] 6) Repeat steps 3) to 5) until the repair target is achieved.

[0075] Step 3) is the first operating stage: the initial anode and the initial cathode are respectively connected to the corresponding output ports of the DC power supply; the DC power supply voltage is set to 25 V (corresponding to a potential gradient of 0.5 V / cm); tap water is injected into the initial anode well as the electrolyte (liquid level 45 cm), and a persulfate solution (100 g / L) is pumped into the initial cathode well as the electrolyte (liquid level 45 cm); the DC power supply is started and the duration is 15 days.

[0076] The extraction system parameters in step 4) are as follows: the extraction well influence radius is set to 0.5 m, the wellhead vacuum is -0.01 MPa, and the single well gas extraction volume is 0.5 m 3 / h, liquid extraction volume 0.005m 3 / h; extraction system operation time 5d.

[0077] The step 5) is the second operation stage: the initial anode is connected to the cathode output terminal of the DC power supply, and the initial cathode is connected to the anode output terminal of the DC power supply (switching the direction of the electric field, initial anode → cathode, initial cathode → anode); the electrolyte in the electrode well of the previous stage is emptied, and tap water (liquid level 45cm) is injected into the anode well, and persulfate solution (100g / L) is injected into the cathode well (liquid level 45cm); the DC power supply is started and the duration is 15d. Extraction system parameters: the influence radius of the extraction well is set to 0.5m, the wellhead vacuum is -0.01MPa, and the gas extraction volume of a single well is 0.5m 3 / h, liquid extraction volume 0.005m 3 / h; extraction system operation time 5d.

[0078] After the operation ended (40 days), the average contents of benzene (0.41-0.72 mg / kg) and petroleum hydrocarbons (539.8-624.8 mg / kg) in the soil at different sampling points were 0.56 mg / kg and 584.6 mg / kg, respectively (Figure 7), both lower than the first category of land screening values ​​in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018) (benzene 1 mg / kg, petroleum hydrocarbons C10-C40: 826 mg / kg).

[0079] Example 3

[0080] The electrokinetic coupled multiphase extraction method was applied on-site. A chemical plant relic site, with a production history primarily involving pesticides and other chemical reagents, was selected. The soil in the test area was contaminated with a combination of chloroform (4.7-12.5 mg / kg), cis-1,2-dichloroethylene (105.8-620.3 mg / kg), benzene (1.7-23.9 mg / kg), and petroleum hydrocarbons (975.4-1986.5 mg / kg). The groundwater was also contaminated with a combination of chloroform (783.9-4657.2 μg / L), cis-1,2-dichloroethylene (83.7-143.8 μg / L), and benzene (650.4-9806.1 μg / L). The maximum contamination depth reached 7 meters.

[0081] The specific implementation method is shown in Figure 8. Anode and cathode wells are staggered in the area to be remediated (soil chamber) (see Figure 6). That is, a row of cathode wells is placed between two symmetrically distributed rows of anode wells, with the anode wells and the opposing cathode wells spaced equidistant. Electrolyte-filled tubes are inserted into the cathode and cathode wells, and an extraction tube is inserted into the cathode well. The electrodes are connected to the electric remediation system, and the extraction tube is connected to the multiphase extraction system.

[0082] First, a Type 30 drilling rig was used to construct electrode wells (aperture 108 mm) within the selected test range, with a spacing of 1.5 m between wells and a depth of 8 m. The well walls were supported by porous PVC screen tubes (aperture 98 mm, sieve aperture 5 mm), with 20 cm exposed above the ground. The space between the screen tubes and the well walls was filled with 10 mm diameter iron-carbon particles. Stainless steel (tube) electrodes (DN25, diameter 3.4 cm), PVC extraction tubes (3.4 cm diameter, 0.4 mm slotted filter tubes, length 5 m), and PVC electrolyte injection tubes (1.8 cm diameter) were inserted through reserved holes in a rubber mat (113 mm diameter, 40 mm thick) and fixed in the electrode wells. The well platform was built with cement and bentonite, and the above-ground portion of the electrode well was sealed.

[0083] The extraction pipe is connected to the vacuum pump, which is connected to the gas-liquid separator (DN15-DN25, rated flow rate 0.3-0.5m 3 / min The capacity of this embodiment is set to 0.5m 3 / min), activated carbon adsorption purifier (processing air volume 5-20m 3 / h In this embodiment, the capacity is set to 5m3 / min, and the amount of activated carbon added is 50kg), Fenton reactor (wastewater treatment capacity 0.05-0.5m 3 / h. This embodiment sets the capacity to be 1.5L of H2O2 (≥27.5%) and 120g of iron ions, allowing for further treatment of the extracted waste gas and wastewater. The activated carbon adsorption purifier has a loading capacity of 30-60kg; the Fenton reactor has a loading capacity of 1.5L of H2O2 (≥27.5%) and 120g of iron ions.

[0084] Specifically:

[0085] 1) Set up electrode wells in a matrix-like staggered pattern in the remediation area (soil chamber), fix the electrodes, extraction tubes, and electrolyte injection tubes in the electrode wells, and seal the wellheads;

[0086] 2) Water and persulfate aqueous solution are pumped into the anode well and cathode well as electrolytes, respectively. The electrodes are connected to the output end of the electric repair system, and the extraction pipe is connected to the multiphase extraction system.

[0087] 3) Setting the operating voltage and starting the electric repair system, after completing the transport of persulfate in the cathode well and iron ions released by the electrode in the anode well, starting the multiphase extraction system in the cathode well;

[0088] 4) After the electrolyte in the cathode well is completely extracted, the electric repair device and the extraction device are disconnected, and the electrolyte in the anode well is pumped to the cathode well and then replenished with a persulfate aqueous solution;

[0089] 5) Switching the direction of the electric field, the initial anode well becomes the cathode well, and the initial cathode well becomes the anode well, and starting the multiphase extraction system of the cathode well;

[0090] 6) Repeat steps 3) to 5) until the repair target is achieved.

[0091] The step 3) is the first operation stage: the initial anode and the initial cathode are respectively connected to the corresponding output ports of the DC power supply of the electric repair system; water is pumped into the initial anode well, and a persulfate aqueous solution (100 g / L) is pumped into the initial cathode well as the electrolyte; the electric field potential gradient is set to 0.5 V / cm (the DC power supply operating voltage is set to 75 V), and the transportation time is 15 days.

[0092] The extraction system parameters in step 4) are as follows: the extraction well influence radius is set to 1.5 m, the wellhead vacuum is -0.04 MPa, and the single well gas extraction volume is 3 m 3 / h, liquid extraction volume 0.02m 3 / h; extraction system operation time 5d.

[0093] Step 5) is the second operation phase: switch the direction of the electric field (initial anode → cathode, initial cathode → anode); empty the electrolyte in the electrode wells of the previous phase, inject tap water into the anode well, and inject persulfate solution (100g / L) into the cathode well; start the DC power supply and continue for 15 days. Extraction system parameters: the extraction well influence radius is set to 1.5m, the wellhead vacuum is -0.04MPa, and the single well gas extraction volume is 3m 3 / h, liquid extraction volume 0.02m 3 / h; extraction system operation time 5d.

[0094] The first and second operation phases were repeated. After the operation (total operation time 80 days), the average contents of chloroform (0.16-0.24 mg / kg), cis-1,2-dichloroethylene (37.8-57.4 mg / kg), benzene (0.52-0.85 mg / kg), and petroleum hydrocarbons (632.8-705.0 mg / kg) in the soil of the remediation area were 0.21 mg / kg, 49.5 mg / kg, 0.74 mg / kg, and 680.3 mg / kg, respectively (Figure 9). These values ​​were all lower than the first-category screening value for land use (chloroform 0. The average contents of chloroform (111.5-167.5 μg / L) and benzene (51.2-83.9 μg / L) in groundwater were 149.5 μg / L and 70.7 μg / L, respectively (Figure 9), meeting the Class IV water quality standard of the Groundwater Quality Standard (GB / T 14848-2017) (chloroform ≤ 300 μg / L, benzene ≤ 120 μg / L). The average content of cis-1,2-dichloroethylene (22.7-42.8 μg / L) was 33.4 μg / L (Figure 10), meeting the Class III water quality standard of GB / T 14848-2017 (cis-1,2-dichloroethylene ≤ 60 μg / L).

[0095] In summary, persulfate anions can be injected into the formation from the cathode well via electromigration (cathode to anode). Iron ions released from the sacrificial anode migrate toward the cathode via electromigration and electrodialysis (anode to cathode), effectively activating persulfate in the soil and groundwater. Simultaneously, the microbial degradation of pollutants is further enhanced by the stimulation of a weak DC electric field. After the transport of persulfate and iron ions and the activation of persulfate, the MPE device in the cathode well is activated. The stable electrodialysis flow (anode to cathode) further improves the extraction efficiency of groundwater from low-permeability formations. VOCs in soil gas, incompletely degraded organic pollutants in groundwater, and degradation products dissolved in water are extracted and disposed of at depth by the MPE, achieving simultaneous and efficient remediation and detoxification of complex organic-contaminated soil and groundwater.

[0096] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for synchronously remediating organically contaminated soil and groundwater by electrokinetic coupling multiphase extraction, characterized in that: In the area to be repaired, cathode and anode wells are arranged in a staggered distribution, tubes filled with electrolyte are inserted into the cathode and anode wells, an extraction tube is inserted into the cathode well, the electrodes are connected to the electric repair system, and the extraction tube is connected to the multiphase extraction system. Through electric repair, the persulfate anions in the cathode electrolyte are injected into the formation from the cathode well and migrate to the anode through electromigration. The iron ions released by the sacrificial anode in the anolyte migrate to the cathode through electromigration and electrodialysis. The persulfate in the soil and groundwater is activated in the "counter" migration, and then the direction of the electric field is switched and the electrolyte is added to the corresponding electrode wells at the same time for "counter" migration. The repair treatment is carried out in accordance with the aforementioned electrode repair and electrode repair method of switching the electrode direction until the organic contaminated soil and groundwater in the area to be treated are completely and simultaneously repaired; After the electrode is repaired, the multiphase extraction system is started to exhaust the electrolyte in the electrode well.

2. The method for synchronous remediation of organically contaminated soil and groundwater by electrokinetic coupling multiphase extraction according to claim 1 is characterized in that: The electrodes in the cathode well and the anode well are made of iron or stainless steel; the electrolyte in the cathode well is a persulfate aqueous solution with a concentration of 50-100 g / L; and the electrolyte in the anode well is water.

3. The method for synchronous remediation of organically contaminated soil and groundwater by electrokinetic coupling multiphase extraction according to claim 1 is characterized in that: The electrode well is a cavity dug in the area to be repaired, a supporting screen is inserted into the cavity, electrodes, electrolyte injection pipes and extraction pipes are inserted into the screen, the depth of the electrode well is 0.5-1.5m below the groundwater pollution depth, 10-30cm above the ground as the well platform, and the wellhead is sealed with a valve.

4. The method for synchronous remediation of organically contaminated soil and groundwater by electrokinetic coupling multiphase extraction according to claim 3 is characterized in that: Conductive particles are filled between the electrode well wall and the outer wall of the supporting screen tube.

5. The method for synchronously remediating organically contaminated soil and groundwater by electrokinetic coupling multiphase extraction according to any one of claims 1 to 4, characterized in that: 1) Set up electrode wells in a matrix-like staggered distribution in the repair area, fix the electrodes, extraction tubes, and electrolyte injection tubes in the electrode wells, and seal the wellheads; 2) Water and persulfate aqueous solution are pumped into the anode well and cathode well as electrolytes respectively, the electrodes are connected to the output end of the electric repair system, and the extraction pipe is connected to the multiphase extraction system; 3) Setting the working voltage and starting the electric repair system, after completing the transport of persulfate in the cathode well and iron ions released by the electrode in the anode well, starting the multiphase extraction system of the cathode well; 4) After the electrolyte in the cathode well is completely extracted, the electric repair device and the extraction device are disconnected, and the electrolyte in the anode well is pumped to the cathode well and then supplemented with a persulfate aqueous solution; 5) Switching the direction of the electric field, the initial anode well becomes the cathode well, and the initial cathode well becomes the anode well, and starting the multiphase extraction system of the cathode well; 6) Repeat steps 3) to 5) until the repair target is reached.

6. The method for synchronous remediation of organically contaminated soil and groundwater by electrokinetic coupling multiphase extraction according to claim 5, characterized in that: The wellhead is sealed with a rubber pad in combination with cement and bentonite. The rubber pad is provided with a plurality of reserved through holes for the electrodes, electrolyte injection pipes and extraction pipes to be inserted in series, and then cement and bentonite are used for masonry to seal the above-ground part of the electrode well to ensure the airtightness of the extraction system.

7. The method for synchronous remediation of organically contaminated soil and groundwater by electrokinetic coupling multiphase extraction according to claim 1 or 5, characterized in that: The working voltage range of the electric repair system in step 3) is 15-150V, and the corresponding potential gradient is 0.1-1V / cm; the transportation time of persulfate in the cathode well and the sacrificial anode in the anode well to release iron ions is 7-30d; the vacuum pump pressure parameter of the multiphase extraction system in step 4) is set to -20 to -90kPa; the influence radius of the extraction system is 0.5-1.5m, the wellhead vacuum degree is -0.01 to -0.06MPa, and the gas extraction volume of a single well is 0.5-10m 3 / h, single well liquid extraction volume 0.005-0.1m 3 / h; extraction system operation time 5-7d; said step 5) switching the electric field direction by the electric repair control system voltage parameters and step 3) the same, the switching cycle is set to 7-30d.

8. Use of the method for synchronous remediation of organic contaminated soil and groundwater by electrokinetic coupling multiphase extraction as described in claim 1 in in-situ remediation of organic contaminated soil.