Microfoam remediation system and method for organic contaminated soil

Abstract

The invention discloses a microfoam remediation system and method for organic contaminated soil, and belongs to the technical field of soil contamination remediation. The micro-foam generating unit is formed by connecting a micro-foaming matrix and a stand column type air stone device in series, an outlet of the micro-foaming matrix is divided into two paths through a second two-position three-way electromagnetic valve, liquid is supplied to different sets of air stone devices alternately, the liquid extraction pump and the micro-foam generating unit are made to operate continuously, the shutdown waiting time of a traditional intermittent pump is eliminated, and the production efficiency is improved. And the repairing efficiency is obviously improved. In the soil remediation process, double-way alternate injection is executed, and boiling type microfoam is generated; and the foam pump is controlled to continuously convey clear water, and intermittent blowing and final drying are performed in combination with compressed air. The micro-foam generated by the method is uniform in particle size and high in stability, can remarkably improve the desorption efficiency of organic pollutants such as polycyclic aromatic hydrocarbon, has system self-cleaning capability, is free of secondary pollution, and is particularly suitable for repairing complicated organic polluted soil such as coking sites.

Description

Technical Field

[0001] This invention relates to the field of soil pollution remediation technology, specifically to a microfoam remediation system and method for organically polluted soil, which is particularly suitable for in-situ or ex-situ remediation of soils contaminated with recalcitrant organic pollutants such as polycyclic aromatic hydrocarbons (PAHs), petroleum hydrocarbons, and phenols, especially for the refined treatment of heavily polluted sites such as coking plants and chemical plants. Background Technology

[0002] With the acceleration of global industrialization, soil pollution from legacy industrial sites has become increasingly serious, posing a key factor restricting sustainable urban development and threatening human health. Soils from sites such as coking plants, petrochemical plants, and gas plants are rich in toxic and harmful substances such as polycyclic aromatic hydrocarbons (PAHs), benzene compounds (BTEX), phenols, and cyanides. These organic pollutants are characterized by strong hydrophobicity, high octanol-water partition coefficient (Kow), easy adsorption into soil organic matter and micropores, and difficulty in biodegradation, and are thus known as "stubborn pollutants."

[0003] Traditional soil remediation technologies have significant limitations when dealing with such complex pollution: 1. Thermal desorption method: Although it has high removal efficiency, it consumes a lot of energy (usually requires heating to 300-500℃), has high operating costs, and high temperature will destroy the soil aggregate structure and microbial community, resulting in the loss of soil ecological function. The soil needs to be improved again before it can be used after remediation.

[0004] 2. Chemical Leaching: This method involves injecting chemical solutions to leach the soil. However, traditional leachate solutions are mostly macroscopic fluids, making it difficult to penetrate the soil's micropores (<50 micrometers), resulting in insufficient contact between the chemicals and pollutants and limited removal rates. Furthermore, the use of large amounts of chemicals can alter the soil pH, causing secondary pollution, and wastewater treatment is challenging.

[0005] 3. Bioremediation: This method uses microorganisms to degrade pollutants. Although it is low-cost and environmentally friendly, the reaction cycle is extremely long (often several years), and high concentrations of toxic pollutants can inhibit microbial activity, making it difficult to meet the urgent needs of site redevelopment.

[0006] 4. Ordinary aeration method: Air or oxygen is introduced into the soil, but the resulting bubbles have large particle size (millimeter level), fast rising speed, small specific surface area, low gas-liquid mass transfer efficiency, poor reagent carrying capacity, and are difficult to effectively emulsify and remove strongly adsorbed organic pollutants.

[0007] In recent years, micro- and nano-bubble technology has emerged as a promising field in environmental remediation due to its unique physicochemical properties (such as large specific surface area, long residence time, high surface negative potential, and free radical generation). Microbubble remediation technology utilizes microbubbles as carriers to deliver surfactants (such as the biosurfactant rhamnolipid) into soil micropores, removing pollutants through solubilization, emulsification, and desorption. However, existing microbubble generation devices and processes still face the following key bottlenecks: 1. Uneven bubble size distribution: Single-stage foaming devices cannot simultaneously achieve bubble miniaturization and homogenization. The generated bubbles are often of mixed sizes, with large bubbles escaping rapidly, which not only reduces the utilization rate of the pesticide but may also lead to soil structure damage (gas channeling).

[0008] 2. System Piping Residue and Blockage: Rhamnose lipolipids and other biosurfactants have certain viscosity and colloidal properties, easily adhering to the inner walls of pipes, valves, and the surfaces of precision foaming elements (such as microporous ceramics). Existing systems lack efficient and automated online cleaning mechanisms, which can easily lead to micropore blockage, reduced flow rate, and even cross-contamination of different batches of repair sites after long-term operation.

[0009] 3. Rigid operating mode and low efficiency: Traditional systems mostly adopt a continuous constant flow injection mode, which cannot adapt to the resistance changes caused by soil heterogeneity. Some intermittent systems adopt a "pump stop-wait-pump start" mode. During the pump stop, the entire system is in a static state, which not only causes equipment idleness and wasted time (intermittent waiting time is as long as 15-20 minutes), but also causes the sudden disappearance of the pressure field, which is not conducive to the lateral diffusion and deep penetration of microfoam in the soil.

[0010] 4. Lack of multi-level synergistic foaming mechanism: A single foaming stage cannot balance the generation of bubble nuclei and the stable growth of bubbles, resulting in poor stability of the micro foam injected into the soil, which is prone to agglomeration and breakage during the transport process.

[0011] Therefore, developing a soil remediation system and method that can generate ultrafine, uniform, and highly stable microfoams, possess efficient self-cleaning capabilities, and eliminate intermittent waiting time through an innovative dual-path alternation liquid replacement mechanism to achieve continuous and efficient remediation is a major technical challenge that urgently needs to be solved in the field of soil remediation. Summary of the Invention

[0012] The purpose of this invention is to provide a microfoam remediation system and method for organically contaminated soil, aiming to completely solve the technical bottlenecks in the prior art, such as uneven microfoam particle size distribution, low gas-liquid mass transfer efficiency, serious agent residue in system pipelines, and low remediation efficiency due to excessively long intermittent waiting time in continuous remediation operations.

[0013] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a microfoam remediation system and method for organically contaminated soil, comprising: The drug supply unit includes a high-concentration rhamnolipin solution tank (1), a clear water tank (2), a diluted rhamnolipin solution tank (3), and a liquid preparation pipeline connecting the above tanks; The power delivery unit includes a pump (4) and a multi-channel selection solenoid valve (6), wherein the pump (4) selectively connects to a high-concentration rhamnolipin solution tank (1), a clear water tank (2), or a diluted rhamnolipin solution tank (3) through the multi-channel selection solenoid valve (6). The microfoam generating unit includes a rhamnolipin microfoaming matrix (5) and a column-type air stone device (10) installed in the soil remediation tank (8); the inlet of the rhamnolipin microfoaming matrix (5) is connected to the outlet of the liquid pump (4) through a first two-position three-way solenoid valve (7), and its outlet is connected to the soil remediation tank (8); The air supply unit includes a compressed air source (9), the air outlet of the compressed air source (9) is divided into at least two branches, one branch is connected to the inlet of the rhamnolipin microfoam matrix (5), and the other branch is connected to the column-type air stone device (10) in the soil remediation pool (8). The control unit is equipped with dual-process automated control logic to switch between executing the soil remediation process and the equipment cleaning process; In the soil remediation process, the pump (4) is configured to work continuously or according to a preset time sequence, and to pump the diluted rhamnolipin solution into the rhamnolipin microfoaming matrix (5) and mix it with compressed air to form primary microfoam. The primary microfoam enters the soil remediation pool (8) and then undergoes secondary foaming through the column-type air stone device (10). The outlet pipe of the rhamnolipin microfoaming matrix (5) is connected to a second two-position three-way solenoid valve (11), which divides the microfoam fluid into at least two independent branches (branch A and branch B), which are respectively connected to the column-type gas stone device groups (group A and group B) distributed in different spaces in the soil remediation pool (8). In the soil remediation process, the control unit is configured to execute a dual-path alternating fluid replacement logic: controlling the second two-position three-way solenoid valve (11) to seamlessly switch between branch A and branch B, so that the pump (4) and rhamnolipin microfoaming matrix (5) continue to operate, while the microfoam fluid is alternately injected into the gas stone devices of group A and group B, eliminating the intermittent waiting time caused by the pump start-up and shutdown.

[0014] Furthermore, the rhamnolipin microfoaming matrix (5) is provided with an array of multiple foam generating devices, with a spacing of 10 micrometers between adjacent foam generating devices, which is used to achieve preliminary and sufficient mixing of gas and liquid phases and generation of micro bubble nuclei under high pressure.

[0015] Furthermore, the column-type gas stone device (10) is a cylindrical porous structure with a pore size range of 40 to 60 mesh, used to cut and refine the gas-liquid mixture from the rhamnolipin microfoaming matrix (5) to generate a main microfoam with a particle size between 50 and 200 micrometers.

[0016] Furthermore, a third two-position three-way solenoid valve (92) and a one-way valve (91) are provided on the branch connecting the compressed air source (9) to the column-type air stone device (10). In the soil remediation process, this branch is opened to assist secondary foaming, and the third two-position three-way solenoid valve (92) is linked with the second two-position three-way solenoid valve (11). When supplying liquid to group A, it mainly supplies gas to group A, and when supplying liquid to group B, it mainly supplies gas to group B. In the equipment cleaning process, this branch is used to introduce compressed air to purge the column-type air stone device (10).

[0017] Furthermore, the dual-process automated control logic specifically includes: Soil remediation process: Control the continuous operation of the liquid pump (4), control the second two-position three-way solenoid valve (11) to switch between branch A and branch B at preset time intervals (30-50 minutes); at the same time, control the compressed air source (9) to provide a constant pressure air source; Equipment cleaning process: Control the multi-channel selection solenoid valve (6) to switch to the clean water tank (2), control the liquid pump (4) to run continuously to pump clean water into the system; then control the compressed air source (9) to work in the intermittent mode of "purge-stop", and finally continuously introduce compressed air to purge the system pipeline from wet to dry.

[0018] Furthermore, in the soil remediation process, when the soil pressure in a certain branch reaches a preset upper limit, the control unit triggers the second two-position three-way solenoid valve (11) in advance to switch.

[0019] Furthermore, in the equipment cleaning process, the intermittent purging mode of compressed air is set as follows: working for 8-12 minutes, stopping for 3-5 minutes, with a total cleaning time of not less than 2 hours; the final stage of the cleaning process includes a continuous ventilation and drying process lasting not less than 30 minutes.

[0020] Furthermore, adjustable float flowmeters (93) are installed on both branches of the compressed air source (9) outlet pipeline to adjust the gas flow rate entering the rhamnolipin microfoaming matrix (5) and the column-type air stone device (10), respectively.

[0021] Furthermore, it also includes a distributed sensor network, including a pore water pressure sensor, a redox potential probe, a temperature sensor, and an online volatile organic compound monitor. The sensor network is connected to the control unit to monitor the repair process in real time and provide feedback to adjust operating parameters.

[0022] This invention relates to a microfoam remediation method for organically contaminated soil, comprising the following steps performed sequentially: S1. System pretreatment and deployment: Prepare a diluted rhamnolipin solution of a set concentration, complete the deployment of injection wells and monitoring sensors, and divide the injection wells into at least two groups (Group A and Group B). S2. Start the dual-path alternating repair process: Start the liquid pump (4) and compressed air source (9) through the control unit to generate micro foam; control the second two-position three-way solenoid valve (11) to first introduce the micro foam into the group A gas stone device for injection; S3. Seamless switching: When the preset time or pressure threshold is reached, the second two-position three-way solenoid valve (11) is controlled to quickly switch to the gas stone device of group B for injection without stopping the liquid pump (4), while group A enters the relaxation reaction period. S4. Cyclic Operation: Repeat step S3, alternately injecting microfoam into group A and group B until the repair is complete; S5. Perform equipment cleaning process: After the repair is completed, switch to cleaning mode, use clean water to flush the system pipelines and components, and then use compressed air for intermittent purging and final drying until there is no chemical residue inside the system and it is dry.

[0023] This system adopts a modular integrated design, mainly comprising a reagent supply unit, a power delivery unit, a micro-foam generation unit, a gas supply unit, a dual-path alternating deployment unit, and an intelligent control unit. Each unit is connected to a high-speed signal line via precision fluid pipelines, forming a closed-loop feedback control system.

[0024] The reagent supply unit not only includes traditional tanks for high-concentration rhamnolipin solution, clear water solution, and diluted rhamnolipin solution, but also innovatively introduces an online concentration monitoring and dynamic proportioning module. This module monitors the concentration of the mixed solution in real time using a high-precision conductivity sensor and a densitometer, feeding the signal back to the intelligent control unit. This dynamically adjusts the opening of the multi-channel selection solenoid valve, ensuring that the concentration fluctuation of the rhamnolipin solution entering the microfoam generation unit is controlled within ±0.05 g / L. Furthermore, the solution tanks are equipped with an ultrasonic anti-precipitation device and a constant-temperature heating jacket to prevent the precipitation or stratification of high-viscosity surfactants at low temperatures, ensuring the uniformity and flowability of the reagent solution.

[0025] The core of this system lies in its unique "two-stage fine foaming" structure. Specifically: Primary foaming (microfoaming matrix): The rhamnolipin microfoaming matrix integrates an array of microporous ceramic or sintered metal filter elements, with the spacing between adjacent foam generating devices precisely controlled at 10 micrometers. When the diluted rhamnolipin solution encounters high-pressure compressed air at this point, the gas and liquid phases undergo violent turbulent mixing under extremely high shear rates. The tiny 10-micrometer spacing forces the gas to be cut into initial bubble nuclei, with diameters ranging from 10 to 50 micrometers. The key to this stage is utilizing the rapid adsorption characteristics of rhamnolipin molecules to form a stable double-layer structure at the instant of bubble nucleus formation, preventing immediate bubble aggregation.

[0026] Secondary foaming (vertical airstone device): The gas-liquid mixture after primary foaming is not directly injected into the soil, but instead enters a vertical airstone device installed within the soil remediation tank. This device is made of high-strength porous material with a mesh size of 40-60 and features a unique gradient pore structure (larger inside and smaller outside). When the mixture containing primary microbubbles flows through the airstone wall, it undergoes secondary mechanical cutting and dispersion. Simultaneously, the auxiliary air path of the gas supply unit directly supplements the airstone with high-pressure airflow, forming a synergistic effect of "air-encapsulated air" or "air-push-liquid," further refining the bubbles into a main microfoam range of 50-200 micrometers. This two-stage series design ensures that the microfoam ultimately injected into the soil has an extremely narrow particle size distribution standard deviation, significantly improving specific surface area and pore penetration capacity.

[0027] In response to the problems of stagnant soil remediation reaction and low equipment utilization when the pump stops working in traditional intermittent remediation processes, this invention creatively proposes a dual-path alternating fluid replacement and zero-wait continuous remediation technology.

[0028] 1. At the outlet end of the rhamnolipin microfoaming matrix, a high-precision second two-position three-way solenoid valve (or a more advanced multi-way distribution valve group) is installed. This valve group divides the microfoam fluid after primary foaming treatment into at least two independent delivery branches (branch A and branch B), which are respectively connected to column-type gas stone device groups (group A and group B) distributed in different spaces within the soil remediation pool.

[0029] Branch A: Connects to the gas stone device group A on the left side or deep within the repair area.

[0030] Branch B: Connects to the right side of the repair area or the shallow layer of the gas stone device group B.

[0031] 2. The intelligent control unit has a built-in dedicated "alternating timing control algorithm", the workflow of which is as follows: Phase 1 (A-line in operation, B-line pressure holding / standby): The liquid pump starts, the first two-position three-way solenoid valve switches to repair mode, and the micro-foam fluid is guided to branch A via the second two-position three-way solenoid valve. At this time, the group A pneumatic stone device injects micro-foam into the soil for high-intensity repair work. Meanwhile, branch B is in a closed or low-flow pressure holding state to prevent soil back pressure from causing pipeline blockage, but the auxiliary air supply line can continue to introduce a small amount of air into the group B pneumatic stone to maintain pore patency.

[0032] Phase Two (Seamless Switching): When the preset working time (e.g., 35 minutes) is reached, or when the pressure in area A is detected to reach the threshold, the control unit does not stop the pump, but directly drives the second two-position three-way solenoid valve to complete the switching within milliseconds. The fluid flow instantly changes from branch A to branch B.

[0033] Phase 3 (B-path operation, A-path exhaust / relaxation): Micro-foam fluid immediately enters the B-path gas stone device to begin injection. At this time, the liquid intake in the A-path area stops, and the pollutant desorption reaction continues using the soil's own permeability and capillary force. Simultaneously, the system can perform a brief low-pressure purging of the A-path pipeline to prevent residue deposition.

[0034] 3. Through the above-mentioned dual-path alternation mechanism, the following breakthrough effects were achieved: Eliminating intermittent waiting time: In traditional single-channel systems, the entire system is stationary for 15-20 minutes when the pump stops. In this system, although injection is intermittent (simulating boiling effect) in a single area, the pump and micro-foam generation matrix are always operational for the entire system, only the output target rotates between different areas. This improves the equipment's operating efficiency by nearly 100%, eliminating energy loss and mechanical shock caused by pump start-up and shutdown.

[0035] Homogenized remediation field: Alternating injection avoids the soil fissure dominance channel effect caused by long-term high pressure at a single injection point (i.e., the agent only travels through large fissures and ignores micropores). By activating different areas of airstone groups in turn, microfoams are forced to diffuse laterally and redistribute pressure in the soil medium, significantly improving the homogeneity of remediation.

[0036] Extended equipment life: The pump body does not need to be frequently started and stopped, reducing the impact of motor starting current and mechanical wear, thus extending the service life of core power components.

[0037] This invention is equipped with a highly intelligent dual-process automated control logic, which can automatically switch between the "soil remediation process" and the "equipment cleaning process" according to the working conditions.

[0038] 1. In repair mode, the system not only performs basic intermittent / alternating injections, but also has adaptive adjustment capabilities: Pressure feedback regulation: Soil resistance is monitored in real time by pressure sensors installed in each branch. If the pressure in a branch rises abnormally, the system automatically reduces the flow rate in that branch or extends the switching interval to prevent soil structure breakdown; if the pressure is too low, it indicates the possible existence of a short circuit, and the system automatically adjusts the injection strategy.

[0039] Pulse boiling effect: Even during single-circuit operation, the pump can use a high-frequency, low-amplitude pulse mode, or be combined with a pulsed compressed air supply, to create a "boiling" phenomenon at the microscopic scale. This pressure fluctuation can effectively disrupt the van der Waals forces between pollutants and soil particles, accelerating the desorption of hydrophobic organic compounds such as polycyclic aromatic hydrocarbons.

[0040] 2. To address the tendency of rhamnolipids to leave residues, a three-stage deep cleaning strategy of "water washing - air sweeping - drying" was designed: Primary clean water replacement: After the repair is completed, the multi-channel selection solenoid valve automatically switches to the clean water tank, and the liquid pump runs continuously at full speed to completely replace the high-concentration chemical solution out of the pipeline and matrix. This stage continues until the conductivity of the outlet water returns to the level of clean water.

[0041] Secondary intermittent air hammer purging: Close the liquid circuit and start the compressed air source. Use an intermittent mode of "high-pressure purging (8-12 minutes) - depressurization and relaxation (3-5 minutes)". The high-pressure airflow creates an "air hammer" effect in the pipeline, using instantaneous pressure shock waves to peel off colloidal residues adhering to the inner wall of the 10-micron micropores and the surface of the air stone; the depressurization stage allows the residues to be discharged with the airflow, preventing redeposition.

[0042] Three-stage continuous drying: In the final stage, the system enters continuous ventilation mode (for no less than 30 minutes), using dry compressed air to remove all moisture from the pipelines, bringing the system to an absolutely dry state. This not only prevents microbial growth but also ensures that there is no need to drain the accumulated water during the next startup, truly achieving "zero residue and zero cross-contamination".

[0043] Compared with the prior art, the present invention has the following beneficial effects.

[0044] 1. This invention innovatively designs a dual-path alternating fluid replacement mechanism. The microfoam fluid is divided into two paths (Branch A and Branch B) via a second two-position three-way solenoid valve. Under the scheduling of the intelligent control unit, seamless switching between the two gas stone device groups is achieved. While one path is performing high-pressure injection, the other enters the relaxation reaction period, while the core pump and microfoaming matrix maintain continuous operation. In traditional intermittent remediation, the system completely stalls during the 15-20 minute waiting period after the pump stops, resulting in low equipment utilization. This invention eliminates this ineffective time, increasing the effective operating time of the equipment from approximately 60% to over 98%, nearly doubling the reagent processing capacity and contaminant removal efficiency per unit time, and significantly shortening the overall remediation period (estimated to be reduced by 40%-50%).

[0045] 2. The present invention adopts a series coupling structure of "microfoaming matrix (first stage) and column-type gas stone device (second stage)".

[0046] Primary foaming: Using an array of micropores with a 10-micron spacing, initial bubble nuclei of 10-50 microns are generated under high shear force, ensuring the ultrafineness and uniformity of the bubble nuclei.

[0047] Secondary foaming: Using 40-60 mesh gradient pore size air stones for secondary cutting, and with the synergistic effect of "air-in-air" in the auxiliary air path, the particle size of the micro foam finally injected into the soil is stably controlled in the range of 50-200 micrometers.

[0048] This narrowly distributed microbubble has a large specific surface area and a long soil residence time, which can effectively overcome capillary resistance and penetrate deep into soil micropores (<50 micrometers). It solves the problem that traditional large bubbles are easy to escape and cannot reach pollutants in micropores, and significantly improves the emulsification and desorption efficiency of strongly adsorbed pollutants such as polycyclic aromatic hydrocarbons (PAHs) (removal rate can reach more than 95%).

[0049] 3. This invention employs a dual-path alternating injection mode to create a dynamically changing pressure field within the soil. When injection occurs via path A, the pressure is concentrated in area A; upon switching to path B, the pressure in area A is released, causing the micro-foam to diffuse laterally into surrounding low-permeability areas, filling remediation blind spots. This periodic "pressurization-depressurization" process simulates the "breathing" effect, effectively preventing the soil fissure dominance channel phenomenon (i.e., the agent only travels through large fissures) caused by long-term single-point high-pressure injection, resulting in more uniform and thorough remediation.

[0050] 4. Addressing the issue of rhamnolipid residue, this invention employs a three-stage automated cleaning process: water washing and replacement, intermittent air hammer purging, and continuous drying. The intermittent air hammer purging technology, in particular, utilizes the dramatic fluctuations in air pressure to generate shock waves, effectively removing colloidal residues adhering to the inner walls of the 10-micron micropores and the surface of the air stones. Subsequent deep drying ensures the system reaches an absolutely dry state. This not only prevents micropore clogging and guarantees the long-term stability of the equipment but also completely avoids cross-contamination of chemicals between different batches of repair tasks, achieving "zero residue" reuse of the equipment.

[0051] 5. Because this invention adopts a continuous operation and valve switching mode, the core power component (liquid pump) does not need to be frequently started and stopped. This eliminates the mechanical damage to the pipeline system caused by the huge current surge and water hammer effect during motor startup, significantly extending the service life of the pump body and valves. At the same time, the equipment always operates at its most efficient operating point, avoiding energy loss during start-up and shutdown, resulting in an overall energy consumption reduction of approximately 15%. Attached Figure Description

[0052] The present invention will now be further described with reference to the accompanying drawings.

[0053] Figure 1 This is a schematic diagram of the structure of the present invention.

[0054] In the diagram, 1 is a high-concentration rhamnolipin solution tank, 2 is a clear water tank, 3 is a diluted rhamnolipin solution tank, 4 is a pump, 5 is a rhamnolipin microfoaming matrix, 6 is a multi-channel selection solenoid valve, 7 is a first two-position three-way solenoid valve, 8 is a soil remediation tank, 9 is a compressed air source, 91 is a check valve, 92 is a third two-position three-way solenoid valve, 93 is an adjustable float flow meter, 10 is a column-type air stone device, and 11 is a second two-position three-way solenoid valve. Detailed Implementation

[0055] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0056] like Figure 1As shown in the figure, this embodiment constructs a complete microfoam remediation system for organically contaminated soil. This system is particularly suitable for in-situ or ex-situ remediation of sites contaminated with high concentrations of polycyclic aromatic hydrocarbons (PAHs), such as coking plants and chemical plants.

[0057] 1. Detailed System Hardware Configuration Pharmaceutical supply unit: High-concentration rhamnolipin solution tank 1: 500L capacity, made of food-grade PE or 304 stainless steel, with a built-in propeller stirrer and PTC heating rod, storing rhamnolipin mother liquor with a concentration of 20g / L. An air drain valve is located at the bottom of the tank, and level and temperature sensors are mounted on the sides.

[0058] Clean water tank 2: 1000L capacity, connected to municipal water supply or independent water source, used for solution preparation and cleaning. The tank is equipped with a pre-filter to prevent particulate matter from entering the system.

[0059] Diluted rhamnolipid solution tank 3: 800L volume, serving as a buffer tank. A level sensor is installed at the bottom of the tank, and an online conductivity meter (accuracy ±1μS / cm) and a density meter are mounted on the side to monitor the concentration of the mixed solution in real time.

[0060] Liquid preparation piping: Constructed of corrosion-resistant UPVC or PVDF material, with a diameter of DN50. The piping is equipped with a precision metering pump (adjustable stroke), which automatically mixes the mother liquor with water according to a set ratio (e.g., 1:15) and pumps it into the diluted rhamnolipid solution tank 3. The liquid preparation process is automatically monitored by the control unit to ensure accurate concentration.

[0061] Power delivery and flow path control unit: Liquid pump 4: A variable frequency screw pump with a maximum flow rate of 5 m³ / h and a head of 60 m, made of 316L stainless steel. The frequency converter receives signals from the control unit and can achieve stepless speed regulation from 0-100% and soft start, and has overload protection and dry running protection functions.

[0062] Multi-channel selectable solenoid valve 6: Three-position four-way electric ball valve, with a valve body made of PVC or stainless steel, connecting to tank 1, tank 2, tank 3, and waste liquid discharge port respectively. Valve response time < 2 seconds, excellent sealing performance, preventing cross-contamination.

[0063] The first two-position three-way solenoid valve 7 is installed at the pump outlet and is used to switch between "reflux dispensing mode" (outlet leads to tank 3 inlet for circulation homogenization) and "repair / cleaning mode" (outlet leads to microfoaming matrix 5).

[0064] The second two-position three-way solenoid valve 11 is the core component of this embodiment. It is installed at the outlet of the microfoaming matrix 5, and adopts a quick-opening pneumatic ball valve with a switching time of <0.5 seconds and a pressure resistance of 1.0MPa. Its outlet is divided into branch A and branch B, which are laid to different areas of the soil remediation pool respectively.

[0065] Microfoam generation unit: Rhamnose lipolipin microfoaming matrix 5: The shell is made of 316L stainless steel, and the interior is encapsulated with 12 parallel arrays of microporous ceramic filter elements. Each filter element consists of hundreds of micropores with a diameter of 10 micrometers, with a total filtration area of ​​2.5㎡. The matrix is ​​designed to withstand a pressure of 1.0MPa, maintaining the microporous structure without deformation under high pressure and ensuring the stability of bubble nucleus formation. Pressure gauges and flow meters are installed at the matrix inlet and outlet for monitoring the operating status.

[0066] Vertical airstone device 10: Two sets (Set A and Set B) are set up, each set containing 4 vertical columns, arranged in a quincunx pattern at the bottom of the soil remediation tank 8. The airstone is made of porous corundum ceramic with a pore size of 40-60 mesh (approximately 250-380 micrometers), possessing extremely high mechanical strength and resistance to acid and alkali corrosion. The height of each column can be customized according to the soil thickness (2.5 meters in this example), with an air inlet at the bottom and an anti-clogging cap at the top.

[0067] Gas supply unit: Compressed air source 9: Composed of a screw air compressor (power 7.5kW), an air tank (1m³), a refrigerated dryer (dew point -40℃) and a precision filter, providing stable pressure (0.6-0.8MPa), oil-free and water-free clean compressed air.

[0068] Main gas path: After passing through a pressure reducing valve, a one-way valve 91, and an adjustable float flowmeter 93, the gas enters the gas-liquid mixing chamber at the bottom of the microfoaming matrix 5. The flowmeter accuracy is ±1.5%, allowing for precise control of the gas-liquid ratio.

[0069] Auxiliary gas path: After passing through the third two-position three-way solenoid valve 92, check valve 91, and flow meter 93, it splits into two streams that connect to the bottom air inlets of the gas stone devices in groups A and B, respectively. This branch is independently controlled and can maintain continuous gas flow or independent purging during liquid path switching.

[0070] Soil remediation pond 8 and monitoring network: The remediation tank is a closed reinforced concrete structure or a large stainless steel tank, and its volume can be adjusted according to the site size (50m³ in this example). An impermeable membrane is laid at the bottom of the tank to prevent pollutant leakage.

[0071] A distributed sensor network is deployed within the pool, including: Pore ​​water pressure sensor: buried at different depths (0.5m, 1.0m, 1.5m, 2.0m) to monitor the injection pressure distribution.

[0072] Oxidation-reduction potential (ORP) probe: to monitor changes in soil redox environment and assess remediation progress.

[0073] Temperature sensor: monitors reaction temperature to prevent overheating from affecting microbial activity (if combined with bioremediation).

[0074] Volatile organic compounds (VOCs) online monitoring instrument: Real-time detection of pollutant concentrations in the gas phase of soil.

[0075] All sensor data is transmitted to the intelligent control unit in real time via RS485 bus.

[0076] Intelligent control unit: It adopts an industrial-grade PLC controller (such as the Siemens S7-1200 series) and is equipped with a 10-inch color touch screen human-machine interface (HMI).

[0077] It has built-in "dual-path alternating repair algorithm", "self-cleaning logic library", "fault diagnosis module" and "data recording and analysis system".

[0078] It supports remote monitoring (via 4G / 5G module), allowing operators to view the operating status, adjust parameters, and receive alarm information in real time via mobile app or computer.

[0079] 2. Detailed Work Process The working process of this embodiment is divided into three main stages: system preparation, dual-path alternating repair operation, and equipment self-cleaning.

[0080] Phase 1: System Preparation and Parameter Initialization Solution preparation: Start the solution preparation program. Connect the high-concentration rhamnolipin solution tank 1 and the clear water tank 2 using the multi-channel selection solenoid valve 6. Dilute the rhamnolipin stock solution to 1.2-1.5 g / L according to the set ratio (e.g., 1:15) and pump it into the diluted rhamnolipin solution tank 3. Confirm the concentration meets the standard using an online conductivity meter (conductivity range set to 1200-1500 μS / cm).

[0081] Self-test: The system automatically detects the status of each valve, pump insulation, air pressure, and sensor signals to confirm there are no fault alarms. It also checks the emergency stop button and safety valve for proper functioning.

[0082] Parameter settings: The operator enters the repair parameters on the HMI: Single-circuit working time: 40 minutes (can be adjusted according to soil permeability, ranging from 30 to 50 minutes).

[0083] Switching interval: 0 seconds (seamless switching).

[0084] Target injection pressure: 0.45MPa (upper limit 0.55MPa, lower limit 0.35MPa).

[0085] Gas-liquid ratio: 15:1 (volume ratio, air flow rate approximately 1.25 m³ / min, liquid flow rate approximately 5 m³ / h).

[0086] Total repair period: 30 days.

[0087] Cleaning trigger conditions: Repair completed or manually triggered.

[0088] Phase Two: Dual-path replacement fluid repair and operation Through precise timing control, the continuous generation of microbubbles and alternating injection in zones are achieved, completely eliminating the downtime waiting time of traditional intermittent pumps.

[0089] Step S2.1: Start and inject via A-path The control unit issues a command, and the first and second two-position three-way solenoid valves 7 switch to "repair mode".

[0090] The pump 4 is started at its rated speed (or set frequency) to pump the diluted rhamnolipid solution into the microfoaming matrix 5.

[0091] Simultaneously, the main air path is opened, and compressed air enters matrix 5 at a set flow rate (adjusted by flow meter 93). Inside the matrix, the gas and liquid phases undergo intense shearing at 10-micron micropores, generating a large number of primary microfoam particles with a diameter <50μm. At this time, the gas-liquid mixture appears milky white, and its density is significantly reduced. The second two-position three-way solenoid valve 11 is initially set to connect to branch A. The primary microfoam fluid enters the group A column-type air stone device in the soil remediation tank 8 via branch A.

[0092] Meanwhile, the third and second position three-way solenoid valve 92 in the auxiliary air path controls the airflow mainly to the group A gas stone to assist in secondary foaming; the group B gas stone is only supplied with a small amount of maintenance airflow (about 0.1 m³ / min) or is in a closed pressure-maintaining state to prevent soil particles from backflowing. The microfoam forms a "boiling" upward flow in the group A area, penetrating the soil pores. Due to the small particle size (50-200 μm) and large specific surface area of ​​the microfoam, it can carry high concentrations of rhamnolipin deep into the soil micropores, emulsifying and desorbing PAHs pollutants. This process continues for 40 minutes. During this period, the liquid pump and matrix maintain full-load, high-efficiency operation without any interruptions, and the system pressure remains stable at approximately 0.45 MPa.

[0093] Step S2.2: Seamless switchover (T=40min) When the timer reaches 40 minutes, or when the pressure sensor reading in Group A reaches the preset upper limit (0.55 MPa, indicating that the pores in this area are fully saturated or the resistance has increased), the control unit immediately executes the switching logic.

[0094] The second two-position three-way solenoid valve (11) operates rapidly within 0.5 seconds, cutting off branch A and connecting branch B. At the moment of valve switching, the pressure fluctuation in the pipeline is <0.02MPa, with no impact. The continuous microfoam flow from the microfoaming matrix (5) instantly changes direction and flows into the column-type air stone device of group B. The third two-position three-way solenoid valve (92) operates synchronously, switching the main auxiliary compressed air to the air stone of group B to enhance the secondary foaming effect; the main liquid flow of the air stone of group A stops, and the auxiliary air volume is reduced to the maintenance mode or switched to the low-pressure purging mode (0.2MPa, lasting for 2 minutes) to prevent the air stone orifice from being blocked by soil particles.

[0095] Throughout the switching process, the liquid pump (4) never stopped, and the gas-liquid mixing state within the microfoaming matrix (5) was never interrupted. The system did not undergo the "pump stop-depressurization-restart" process of the traditional mode, thus avoiding the water hammer effect and the impact on the motor. More importantly, it eliminated the 15-20 minute ineffective waiting time, which nearly doubled the amount of reagent processed per unit time and the efficiency of pollutant removal.

[0096] Step S2.3: Injection via B and relaxation reaction via A The microfoam began high-intensity repair work in area B and continued for 40 minutes.

[0097] Meanwhile, area A entered a "relaxation reaction period." Although active injection ceased, the microfoam already injected into the soil continued to slowly rise and break down, releasing surfactants to continue reacting with pollutants. The release of pressure also facilitated the lateral diffusion of the microfoam into surrounding low-permeability areas, repairing any potential blind spots.

[0098] Optional operation: During the relaxation period of Group A, the control unit can control the auxiliary air circuit to perform a short-term low-pressure pulse purging of Group A (purging for 30 seconds every 5 minutes) to prevent the gas stone orifice from being blocked by soil particles and to prepare for the next round of injection.

[0099] Step S2.4: Repeat the process When the running time of branch B reaches the set value (or the pressure reaches the threshold), the system performs a seamless switch again, and the fluid flows back to branch A.

[0100] This process repeats continuously, forming a cycle of "Route A work - Route B work - Route A work...", until the set total number of repair days is reached or monitoring data shows that the pollutant concentration meets the standards.

[0101] The intelligent control unit can dynamically adjust the single-channel working time (e.g., to 30min / 30min or 50min / 30min), gas-liquid ratio, and injection pressure based on real-time monitoring of soil ORP values, VOC concentrations, and pore water pressure, achieving adaptive remediation. For example, when a slow decrease in VOC concentration is detected in a certain area, the working time of the corresponding branch in that area can be extended or the injection pressure increased.

[0102] Phase 3: Equipment Self-Cleaning Process After the repair task is completed (or during regular maintenance), the system automatically enters deep cleaning mode to ensure no chemical residue remains.

[0103] Clean water replacement flushing: Multi-channel selector solenoid valve 6 switches to clean water tank 2.

[0104] Pump 4 operates continuously (100% frequency) to pump clean water into the system. The second two-position three-way solenoid valve 11 is set to either "dual-path simultaneous opening" or rapid rotation mode (switching every 10 seconds) to ensure that both branch A and branch B are thoroughly flushed. Flushing continues for 30 minutes, or until the outlet water is clear and the conductivity is close to the inlet clean water value (<50 μS / cm). This stage removes more than 90% of residual chemicals.

[0105] Intermittent pneumatic hammer purging: Turn off the liquid pump and cut off the liquid circuit. Switch the first and second position three-way solenoid valve 7 to the venting position.

[0106] The compressed air source is activated, and the third and second position three-way solenoid valves 92 control the airflow to sequentially purge the air stones of group A and group B under high pressure. An intermittent cycle of "purge for 10 minutes (0.6 MPa) - stop for 5 minutes (pressure relief)" is used, with a total duration of 2 hours. The "air hammer" effect generated by the intense pressure fluctuations powerfully peels away the sticky colloids adhering to the inner wall of the 10-micron microporous matrix and the surface of the air stones. During the stop phase, the residue is discharged with the airflow to prevent redeposition.

[0107] Deep Drying: After purging, the system enters continuous ventilation drying mode. Compressed air is continuously supplied to all pipelines and components at a pressure of 0.4 MPa for at least 30 minutes. The system is considered dry when the dew point temperature drops below -10°C, as monitored by the humidity sensor at the exhaust port. The system automatically shuts down, all valves return to their normally closed state, and the equipment enters standby mode. At this point, the system is completely dry, eliminating the risk of microbial growth, and the next repair task can be initiated at any time.

[0108] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A microfoam remediation system and method for organically contaminated soil, characterized in that, include: The drug supply unit includes a high-concentration rhamnolipin solution tank (1), a clear water tank (2), a diluted rhamnolipin solution tank (3), and a liquid preparation pipeline connecting the above tanks; The power delivery unit includes a pump (4) and a multi-channel selection solenoid valve (6), wherein the pump (4) selectively connects to a high-concentration rhamnolipin solution tank (1), a clear water tank (2), or a diluted rhamnolipin solution tank (3) through the multi-channel selection solenoid valve (6). The microfoam generating unit includes a rhamnolipin microfoaming matrix (5) and a column-type air stone device (10) installed in the soil remediation tank (8); the inlet of the rhamnolipin microfoaming matrix (5) is connected to the outlet of the liquid pump (4) through a first two-position three-way solenoid valve (7), and its outlet is connected to the soil remediation tank (8); The air supply unit includes a compressed air source (9), the air outlet of the compressed air source (9) is divided into at least two branches, one branch is connected to the inlet of the rhamnolipin microfoam matrix (5), and the other branch is connected to the column-type air stone device (10) in the soil remediation pool (8). The control unit is equipped with dual-process automated control logic to switch between executing the soil remediation process and the equipment cleaning process; In the soil remediation process, the pump (4) is configured to work continuously or according to a preset time sequence, and to pump the diluted rhamnolipin solution into the rhamnolipin microfoaming matrix (5) and mix it with compressed air to form primary microfoam. The primary microfoam enters the soil remediation pool (8) and then undergoes secondary foaming through the column-type air stone device (10). The outlet pipe of the rhamnolipin microfoaming matrix (5) is connected to a second two-position three-way solenoid valve (11). The second two-position three-way solenoid valve (11) divides the microfoam fluid into at least two independent branches, designated as branch A and branch B, which are respectively connected to the column-type gas stone device groups with different spatial distributions in the soil remediation pool (8), designated as group A and group B. In the soil remediation process, the control unit is configured to execute a dual-path alternating fluid replacement logic: controlling the second two-position three-way solenoid valve (11) to seamlessly switch between branch A and branch B, so that the pump (4) and rhamnolipin microfoaming matrix (5) continue to operate, while the microfoam fluid is alternately injected into the gas stone devices of group A and group B, eliminating the intermittent waiting time caused by the pump start-up and shutdown.

2. The microfoam remediation system and method for organically contaminated soil according to claim 1, characterized in that, The rhamnolipin microfoaming matrix (5) is equipped with multiple foam generating devices arranged in an array, with a spacing of 10 micrometers between adjacent foam generating devices, which is used to achieve preliminary and sufficient mixing of gas and liquid phases and generation of micro bubble nuclei under high pressure.

3. The microfoam remediation system and method for organically contaminated soil according to claim 1, characterized in that, The column-type gas stone device (10) is a cylindrical porous structure with a pore size range of 40 to 60 mesh. It is used to cut and refine the gas-liquid mixture from the rhamnolipin microfoaming matrix (5) to generate a main microfoam with a particle size between 50 and 200 micrometers.

4. The microfoam remediation system and method for organically contaminated soil according to claim 1, characterized in that, A third two-position three-way solenoid valve (92) and a one-way valve (91) are provided on the branch connecting the compressed air source (9) to the column-type air stone device (10). In the soil remediation process, this branch is opened to assist secondary foaming, and the third two-position three-way solenoid valve (92) is linked with the second two-position three-way solenoid valve (11). When supplying liquid to group A, it mainly supplies gas to group A, and when supplying liquid to group B, it mainly supplies gas to group B. In the equipment cleaning process, this branch is used to introduce compressed air to purge the column-type air stone device (10).

5. The microfoam remediation system and method for organically contaminated soil according to claim 1, characterized in that, The dual-process automated control logic specifically includes: Soil remediation process: Control the continuous operation of the liquid pump (4), control the second two-position three-way solenoid valve (11) to switch between branch A and branch B at preset time intervals; at the same time, control the compressed air source (9) to provide a constant pressure air source; Equipment cleaning process: Control the multi-channel selection solenoid valve (6) to switch to the clean water tank (2), control the liquid pump (4) to run continuously to pump clean water into the system; then control the compressed air source (9) to work in the intermittent mode of "purge-stop", and finally continuously introduce compressed air to purge the system pipeline from wet to dry.

6. The microfoam remediation system and method for organically contaminated soil according to claim 5, characterized in that, In the soil remediation process, when the soil pressure in a certain branch reaches a preset upper limit, the control unit triggers the second two-position three-way solenoid valve (11) in advance to switch.

7. The microfoam remediation system and method for organically contaminated soil according to claim 5, characterized in that, In the equipment cleaning process, the intermittent purging mode of compressed air is set as follows: working for 8-12 minutes, stopping for 3-5 minutes, with a total cleaning time of not less than 2 hours; the final stage of the cleaning process includes a continuous ventilation and drying process lasting not less than 30 minutes.

8. The microfoam remediation system and method for organically contaminated soil according to claim 1, characterized in that, An adjustable float flowmeter (93) is installed on each of the two branches of the compressed air source (9) outlet pipeline to adjust the gas flow rate entering the rhamnolipin microfoaming matrix (5) and the column-type air stone device (10), respectively.

9. The microfoam remediation system and method for organically contaminated soil according to claim 1, characterized in that, It also includes a distributed sensor network, including a pore water pressure sensor, a redox potential probe, a temperature sensor, and an online volatile organic compound monitor. The sensor network is connected to the control unit to monitor the repair process in real time and provide feedback to adjust the operating parameters.

10. A microfoam remediation method for organically contaminated soil using any one of claims 1-9, characterized in that, This includes the following steps performed sequentially: S1. System pretreatment and deployment: Configure a diluted rhamnolipin solution of a set concentration, complete the deployment of injection wells and monitoring sensors, and divide the injection wells into at least two groups, designated as Group A and Group B; S2. Start the dual-path alternating repair process: Start the liquid pump (4) and compressed air source (9) through the control unit to generate micro foam; control the second two-position three-way solenoid valve (11) to first introduce the micro foam into the group A gas stone device for injection; S3. Seamless switching: When the preset time or pressure threshold is reached, the second two-position three-way solenoid valve (11) is controlled to quickly switch to the gas stone device of group B for injection without stopping the liquid pump (4), while group A enters the relaxation reaction period. S4. Cyclic Operation: Repeat step S3, alternately injecting microfoam into group A and group B until the repair is complete; S5. Perform equipment cleaning process: After the repair is completed, switch to cleaning mode, use clean water to flush the system pipelines and components, and then use compressed air for intermittent purging and final drying until there is no chemical residue inside the system and it is dry.

Images