In-situ remediation method for contaminated soil
By implanting electrode arrays in low-permeability soil and applying direct current and alternating current, combined with thermally activated oxidants, the problems of low efficiency and environmental risks in VOCs treatment in low-permeability soil are solved, achieving efficient and controllable in-situ remediation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-12
- Publication Date
- 2026-04-14
AI Technical Summary
Existing technologies are inefficient at treating volatile organic pollutants (VOCs) in low-permeability soils. Traditional methods may damage soil structure or produce byproducts and are not suitable for low-permeability soils.
Electrode arrays are implanted in low-permeability soil using electric technology. Direct current and alternating current are applied alternately, combined with thermally activated oxidants (such as persulfate) to oxidize and degrade VOCs. Electromigration and electroosmosis are used to achieve uniform distribution and heating of the oxidant.
It enables in-situ remediation of VOCs in low-permeability soil, saving time and costs, reducing the risk of secondary environmental pollution, improving remediation efficiency and controllability, and is applicable to recalcitrant organic pollutants.
Smart Images
Figure CN121847577A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of environmental remediation technology, specifically relating to an in-situ remediation method for contaminated soil. Background Technology
[0002] Volatile organic pollutants (VOCs) are a class of chemical substances that pose potential hazards to health and the environment. Common VOCs include benzene, toluene, xylene, and vinyl chloride, which are widely found in various sources such as industrial production, vehicle exhaust, paints, and cleaning agents. These chemicals are characterized by their volatility, toxicity, and flammability, posing a potential threat to human health and the natural environment.
[0003] Treating VOCs in low-permeability soils requires comprehensive consideration of soil characteristics, pollutant types, and pollution levels, necessitating the use of appropriate remediation methods. One possible solution is bioremediation, which involves introducing microorganisms adapted to low-permeability soil environments to degrade VOCs. These microorganisms can grow in the soil and utilize VOCs as a carbon source for metabolism, thereby reducing or eliminating pollutant concentrations.
[0004] Another method is to use adsorbents or adsorbent materials to adsorb VOCs and remove them from the soil. This method can effectively remove VOCs without damaging the soil structure, but the selection and regeneration of the adsorbent need to be considered.
[0005] In addition, chemical oxidation or advanced oxidation techniques can also degrade VOCs to some extent. These methods introduce oxidants to oxidize VOCs, converting them into harmless substances. However, these methods may produce byproducts that require careful handling. Summary of the Invention
[0006] To address these challenges, this invention proposes a method for treating VOCs in low-permeability soil based on electrodynamic technology. This method utilizes electrodynamics to deliver persulfate oxidant to the pollutants in low-permeability soil, achieving on-site treatment and degradation. Compared to traditional remediation methods, this method offers several advantages.
[0007] The technical solution adopted in this invention is: a method for remediating contaminated soil, comprising: adding an oxidant to low-permeability soil containing pore water; exposing the soil to direct current through an electrode assembly implanted in the soil, allowing the oxidant to migrate through the soil and pore water; exposing the soil to alternating current through the electrode assembly implanted in the soil to heat the soil, thereby activating the oxidant; and alternating the exposure of the soil to direct current and alternating current for one or more cycles.
[0008] Preferably, the oxidant is persulfate, or a mixture of persulfate and one or more of permanganate, ozone, and hydrogen peroxide.
[0009] Preferably, the soil is exposed to alternating current until the soil temperature rises above 30°C.
[0010] Preferably, the electrode assembly is implanted into the soil in a substantially vertical direction.
[0011] Preferably, the electrode assembly is implanted in the soil in a substantially horizontal orientation.
[0012] Preferably, one part of the electrode assembly is implanted into the soil in a vertical direction, and the other part is implanted into the soil in a horizontal direction.
[0013] Preferably, the electrode assembly is implanted into the soil in a grid pattern arrangement.
[0014] Preferably, the electrode is made of a rod-shaped conductive material.
[0015] Preferably, the electrode is made of a conductive particulate material.
[0016] Preferably, the oxidant is injected into the implantation site of the electrode or into a supply well; the supply well is located between the positive and negative electrodes of the electrode.
[0017] The beneficial effects of this invention compared to the prior art are reflected in: 1. In-situ remediation: Compared with traditional soil remediation methods, this invention can directly remediate contaminated soil without transferring it to other locations. This saves time and costs and reduces the risk of secondary pollution to the environment.
[0018] 2. Enhanced efficacy of thermally activated oxidants: Adding thermally activated oxidants (such as persulfates) can improve remediation effectiveness. These oxidants generate high temperatures and free radicals upon contact with contaminants, further promoting the degradation and removal of contaminants.
[0019] 3. Use of electrode sets: By using electrode sets, direct current and alternating current can be applied to the soil to promote the migration and activation of oxidants. This electro-hydraulic technology can improve the distribution of oxidants in the soil and their efficiency in contacting pollutants, thereby enhancing the remediation effect.
[0020] 4. Suitable for low-permeability soils: This method is suitable for low-permeability soils where traditional remediation methods often fail to achieve the desired results. By combining electrode sets with thermally activated oxidants, the entire volume of contaminated soil can be effectively treated.
[0021] 5. Controllable Repair Results: By adjusting parameters such as current and temperature, the repair process can be precisely controlled to achieve optimal results. This controllability helps achieve effective repairs and reduces unnecessary resource waste.
[0022] Compared to traditional soil remediation methods, this method offers higher remediation efficiency, better controllability, and is suitable for treating low-permeability soils. This will help improve soil environmental quality and reduce potential health and environmental impacts. Furthermore, the combination of electrochemical treatment and thermally activated oxidants employed in this invention can effectively treat recalcitrant organic pollutants, demonstrating promising application prospects. Attached Figure Description
[0023] Figure 1 This is a schematic diagram of a cross-section of contaminated, low-permeability soil. Figure 2 This is a schematic diagram of the cross-section of the electrode and supply well used to treat contaminated soil; Figure 3 This is a schematic diagram of the cross-section of persulfate oxidant migrating from the electrode and supply well through low-permeability soil; Figure 4 This is a schematic cross-sectional view of the ERH system activated after persulfate oxidant migrates in low-permeability soil. Figure 5 This is a schematic diagram of the alternating electrodes and supply well configuration. Detailed Implementation
[0024] The present invention will now be described more completely and clearly with reference to the accompanying drawings and specific embodiments. The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0025] The term "low permeability" refers to soil permeability, which limits the injection of fluids without applying excessive pressure or causing soil rupture.
[0026] In soil terminology, "electromigration" refers to the migration of ionic substances in soil and the generation of pore water under the influence of an electric field.
[0027] The term "electroosmosis" refers to the movement of liquids in a porous material caused by an applied electric field.
[0028] The term "electrokinetic" refers to a series of different effects (electromigration, electroosmosis, electrophoresis) occurring in a porous body filled with fluid. All these effects share a common source—the so-called interfacial "bilayer" of charge. The influence of external forces on the diffusion layer produces tangential motion of the fluid relative to the adjacent charged surface.
[0029] "AC / DC power supply" refers to electrical equipment that can provide direct current and alternating current to an electrode system.
[0030] A “set” is a group of at least one pair.
[0031] In a first embodiment of the invention, a method is provided for oxidizing organic pollutants and their contained pore water in low-permeability soil. The method includes applying direct current through vertical rod-shaped electrodes, supplying an oxidant and electromigration and / or electroosmosis throughout the soil and pore water, these electrodes being arranged in a line within the soil, and then heating the soil and pore water to at least 30°C by applying alternating current using the same electrodes. Optionally, a second set of electrodes can be used to conduct the heating of the soil and pore water. The oxidant is added to the system through supply holes located between the electrodes and the electrode holes themselves.
[0032] In the second embodiment, the soil is first heated to at least 30°C by applying alternating current, for example by using vertical rod-shaped electrodes arranged in lines within the soil, and then an oxidant is electromigrated and / or electroosminated into the entire soil and pore water by applying direct current.
[0033] In some implementations, the electrodes used may be horizontal rather than vertical.
[0034] In some implementations, the electrodes can be a combination of vertical and horizontal.
[0035] In some implementations, the electrodes may be composed of conductive particulate material or rod-shaped material.
[0036] In some implementations, the electrodes may be placed in a grid or other nonlinear configuration to achieve the desired migration and heating.
[0037] In other embodiments, the oxidant is added at the electrode or at the supply well.
[0038] In another embodiment, the oxidant is persulfate, which can be supplemented with other oxidants such as permanganate, ozone, and hydrogen peroxide to allow the degradation of pollutants during the heating process.
[0039] In another embodiment of the invention, a method for oxidizing organic pollutants and their contained pore water in low-permeability soil is provided. Electrodes are implanted into low-permeability soil containing pore water. An oxidant is added to the system through supply holes located between the electrodes and the electrode holes themselves. The soil is exposed to direct current and alternating current, causing the oxidant to undergo electromigration and / or electroosmosis throughout the soil and pore water, and heating the soil and pore water to at least 30°C. Pollutants residing in the low-permeability soil and its contained pore water are degraded through electromigration and / or electroosmosis resulting from the oxidant's interaction with the soil's ERH (Electrical Resistive Heating).
[0040] Reference Figure 1 and Figure 2 This invention provides an in-situ remediation method for low-permeability soil 2 containing organic pollutants 1 and pore water 3. The method involves locating and determining the dimensions of the low-permeability soil 2 located below the groundwater level 4 and below the surface layer 5, and then implanting a set of rod-shaped electrodes, with the positive electrode 6 and the negative electrode 7, into the ground.
[0041] Electrodes are placed in a series of linear arrays to generate an electromagnetic field throughout the contaminated soil. Depending on the size and depth of the contaminant dispersion, the location of the electrodes may include the entire contaminated soil, or, if too large to be practical or effective, soil treatment may be performed on a portion consisting of a smaller soil volume.
[0042] refer to Figure 2 and Figure 3 One or more holes 8 are drilled across the entire cross-section between the positive electrode 6 and the negative electrode 7, optionally including holes near the electrodes, as supply wells for supplying oxidant 10. Treatment of the soil and pore water 3 begins with the addition of oxidant 10 to the supply wells, and the oxidant 10 is distributed throughout the soil and pore water using direct current from a power source 9 between the positive and negative electrodes. (Reference) Figure 4 Once the oxidant 10 is dispersed, it is activated by heating the soil and pore water to at least 30°C using alternating current applied by the same set of electrodes or a new set of electrodes.
[0043] The soil is first heated to at least 30°C by applying alternating current to linearly arranged electrodes placed within it, and then an oxidant is electromigrated and / or electroosmotically absorbed into the entire soil and pore water by applying direct current. This process can be repeated in multiple portions of the total soil volume to be treated, or multiple times on the same portion or both.
[0044] The electrodes used can be placed in a horizontal or vertical position. Furthermore, the electrodes can be placed in a combination of vertical and horizontal positions. (Reference) Figure 5The electrodes can be placed in the gate or other nonlinear configurations to achieve the desired migration and heating.
[0045] Electrodes can also be made of conductive particulate material instead of rod-shaped material.
[0046] The oxidant is preferably a compound that can be activated, or a compound whose properties are enhanced by heating to allow for the degradation of pollutants during heating, such as persulfate. Persulfate can be added alone or in combination with other oxidants, such as permanganate, ozone, and hydrogen peroxide, or a mixture thereof.
[0047] The power supply used in this process is commercially available and is capable of supplying the required current to the electrodes as individual units, which operate with a switch that converts current from DC to AC, or as separate units, one DC and one AC.
[0048] A saturated, low-permeability subsurface layer composed of silt and clay, located approximately 5 meters below the surface, 3 meters thick, and with a radius of 30 meters, was designated for remediation due to contamination from dissolved chlorinated solvents (such as trichloroethylene-TCE) released from the surface into the subsurface. Electrode wells, installed in a remediation-appropriate configuration (appropriate spacing between wells ranging from 1 to 8 meters), consist of mixed metal oxide electrodes suspended within 4-inch PVC well casings shielded within the low-permeability layer. Oxidant supply wells, installed between the electrode wells and consisting of 4-inch PVC perforated casings shielded over the low-permeability layer, are also installed. Monitoring infrastructure, including pH meters, level gauges, and voltmeters, is installed within the electrodes and supply wells. A thermally activated oxidant (such as persulfate) is supplied to the remediation system via peristaltic pumps through the supply and cathode electrode wells at a rate sufficient to maintain the target oxidant concentration in the wells. The target concentration is based on the degree of contamination and the system's natural oxidant requirements. Direct current (DC) is then applied to the electrodes to promote electromigration and electroosmosis of the oxidant from the cathode electrode orifices and supply orifices. Direct current (DC) is applied via a rack-mounted DC power supply, ranging from 0.5 to 5 A / m² (or 1–2 V / cm), until a volume equivalent to the pore volume of the contaminated zone migrates from the electrodes and supply well to the contaminated zone. The power is then switched to alternating current (AC) and operated at 480 V for 2 to 8 weeks until the soil and groundwater temperature in the contaminated zone exceeds 60 degrees Celsius. The oxidant migration phase is then repeated by switching back to DC and migrating the pore volume of the oxidant again.
[0049] The embodiments described above are for reference only; many variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the invention as defined in any of the appended claims.
Claims
1. A method for remediating contaminated soil, characterized in that, include: An oxidant is added to a low-permeability soil containing pore water; the soil is exposed to direct current through an electrode assembly implanted in the soil, allowing the oxidant to migrate through the soil and pore water; the soil is then exposed to alternating current through the same electrode assembly to heat the soil and activate the oxidant; the soil is then exposed to direct current and alternating current for one or more cycles.
2. The method according to claim 1, characterized in that, The oxidant is persulfate, or a mixture of persulfate and one or more of permanganate, ozone, and hydrogen peroxide.
3. The method according to claim 1, characterized in that, Expose the soil to alternating current until the soil temperature rises above 30°C.
4. The method according to claim 1, characterized in that: The electrode assembly was implanted into the soil in a vertical direction.
5. The method according to claim 1, characterized in that: The electrode assembly was implanted in the soil in a horizontal direction.
6. The method according to claim 1, characterized in that: One part of the electrode assembly is implanted into the soil vertically, and the other part is implanted into the soil horizontally.
7. The method according to claim 1, characterized in that, The electrode array is implanted into the soil in a grid pattern.
8. The method according to claim 1, characterized in that: The electrodes are made of rod-shaped conductive material.
9. The method according to claim 1, characterized in that, The electrodes are made of conductive particulate material.
10. The method according to claim 1, characterized in that, The oxidant is injected into the implantation site of the electrode or into the supply well; the supply well is located between the positive and negative electrodes of the electrode.