System and method for repairing organic polluted site

Abstract

A system for repairing an organic polluted site, comprising: a functional well subsystem, comprising a plurality of aeration wells (1), extraction wells (7), pressure monitoring wells and groundwater sampling and monitoring wells, wherein the aeration wells (1) are arranged in a main polluted region, the extraction wells (7) are arranged to cover an aeration region, and it is ensured that a circle is formed on the periphery to surround all the aeration wells; an aeration subsystem, used for providing aeration for each aeration well (1); an extraction subsystem, used for extracting pollutants from each extraction well (7); a data acquisition subsystem, used for acquiring and monitoring key operating parameters of each subsystem; a PLC controller (6), separately connected to each subsystem, monitoring the key operating parameters, and controlling the operation of each subsystem; and an oxygen slow-release-based microbial enhancement subsystem, arranged in the aeration wells (1) and the groundwater sampling and monitoring wells and used for slowly releasing oxygen into groundwater. The system can improve efficiency, greatly shorten the repair time, and save costs. Also disclosed is a repair method using the system.

Description

A system and method for remediating organically contaminated sites Technical Field

[0001] This invention belongs to the field of environmental pollution control technology, and relates to a system and method for remediating organically contaminated sites, especially suitable for the remediation of organically contaminated soil and groundwater. Background Technology

[0002] Soil and groundwater contamination levels are severely excessive, creating an urgent need for remediation, particularly for sites contaminated with complex organic pollutants such as halogenated hydrocarbons, petroleum hydrocarbons, and polycyclic aromatic hydrocarbons. Groundwater aeration is an effective technology for removing volatile and semi-volatile organic compounds (VOCs) such as petroleum hydrocarbons, benzene compounds, and chlorinated hydrocarbons from organically polluted groundwater. Its main mechanism involves stripping and desorption during the initial aeration phase, followed by enhanced degradation of pollutants through aerobic microbial stimulation during the later stages of aeration. While this technology is simple to operate, convenient to run, highly adaptable to various sites, and has mature equipment, it also suffers from the following technical limitations:

[0003] (1) Using groundwater aeration alone can cause gas blockage after the water in the pores of the underground soil is replaced by gas, which prevents the gas from diffusing further underground. This severely restricts the efficiency of groundwater remediation and the radius of influence of aeration, leading to the failure of remediation. Therefore, aeration needs to be used in conjunction with extraction to form a gas flow balance underground and avoid gas blockage.

[0004] (2) Early aeration-extraction could remove a large amount of organic pollutants from groundwater, resulting in high remediation efficiency and a significant reduction in pollutant concentration. However, with the removal of a large amount of pollutants, the efficiency of aeration remediation decreased rapidly, reaching the technology boundary effect. Even with long-term operation, it was difficult to achieve remediation standards with low pollutant concentrations, exhibiting a "tailing" effect. The inefficient operation of continuous aeration-extraction wastes a large amount of energy.

[0005] (3) Successful remediation requires continuous monitoring and feedback of dynamic parameters during the aeration-extraction process: excessive injection pressure and flow rate can cause localized air blockage or soil fracturing, and soil fissures can lead to gas short-circuiting, resulting in local remediation failure; excessive extraction pressure and flow rate can cause over-extraction, resulting in inefficient equipment operation and extraction of large amounts of external clean gas, causing unnecessary energy waste. Current technology has not solved this technical problem.

[0006] Among the similar technologies disclosed, CN109824140A, "An In-situ Enhanced Bioremediation Method for Groundwater," emphasizes the enhanced stimulation and remediation effect of aeration injection on microorganisms, but it does not solve the problem of gas blockage caused by aeration alone, and the lack of an extraction system with an unsaturated zone leads to the escape of stripped organic pollutants outside the remediation area; CN217972741U, "A Groundwater Chlorinated Hydrocarbon Pollution Remediation System," sets up an extraction system, but it is for groundwater extraction and circulation and reagent injection, without paying attention to the extraction of pollutant gases and the circulation of underground gas paths; CN112429859A, "A Remediation System and Method for Petroleum-Contaminated Groundwater," carries out gas phase extraction, but ignores the "tailing" effect caused by relying solely on gas phase extraction and aeration, resulting in low technical efficiency, and does not pay attention to the dynamic monitoring and balance during the extraction-aeration process.

[0007] To address the shortcomings of existing technologies, this invention, based on the scientific design of a combined aeration and extraction system, installs monitoring sensors for flow rate, pressure, and exhaust gas concentration within the remediation area. A data acquisition system monitors key operating parameters such as flow rate, pressure, and exhaust gas concentration, and a PLC controller performs logical control of the aeration-extraction system, developing a highly efficient control method. Simultaneously, the efficient aeration-extraction operation in the early stages significantly reduces operating time. After the pollutant "tailing" effect becomes apparent, slow-release oxygen materials are added to the groundwater well to create a long-term microbial stimulation environment for enhanced remediation. This method can greatly shorten the operating time required for conventional aeration-extraction, avoid problems such as localized air blockage and over-extraction through real-time monitoring, achieve highly efficient remediation results, fully utilize the microbial remediation process mechanism, and simultaneously achieve energy conservation, consumption reduction, and high-efficiency remediation compliance. Summary of the Invention

[0008] The purpose of this application is to provide a system and method for remediating organically contaminated sites, so as to at least solve one of the problems of existing conventional aeration-extraction methods, such as long operating time, "tailing" effect, inability to achieve energy saving and consumption reduction and efficient remediation to meet standards.

[0009] To achieve the above objectives, this application adopts the following technical solution:

[0010] In a first aspect, this application provides a system for remediating organically contaminated sites, comprising:

[0011] The functional well subsystem includes several aeration wells, extraction wells, pressure monitoring wells, and groundwater sampling monitoring wells. Among them, aeration wells are arranged at equal intervals in the main pollution areas; extraction wells are arranged to cover the aeration area and ensure that a ring surrounds all aeration wells; pressure monitoring wells and groundwater sampling monitoring wells are arranged to cover the entire remediation area.

[0012] The aeration subsystem is used to provide aeration to each aeration well;

[0013] The extraction subsystem is used to extract gas from each extraction well;

[0014] The data acquisition subsystem is used to collect and monitor key operating parameters of each subsystem, including flow rate, pressure, exhaust gas concentration, groundwater quality, and concentration of characteristic pollutants.

[0015] The PLC controller is connected to the functional well subsystem, aeration subsystem, extraction subsystem and data acquisition subsystem respectively, and controls the operation of each subsystem according to key operating parameters.

[0016] The slow-release oxygen microbial stimulation enhanced remediation subsystem includes calcium peroxide slow-release oxygen material, which is installed in aeration wells and groundwater sampling and monitoring wells to slowly release oxygen into the groundwater.

[0017] In a preferred embodiment, the aforementioned system for remediating organically contaminated sites includes an aeration subsystem comprising a first connecting pipeline and an aeration control unit. The aeration control unit includes an air tank and an air compressor, which are connected to a PLC controller. The first connecting pipeline includes a main air outlet pipe and various outlet air pipes. One end of the main air outlet pipe is connected to the air tank, and the other end is connected to each outlet air pipe. Each outlet air pipe is connected to each aeration well. Flow meters are installed on both the main air outlet pipe and each outlet air pipe. Pressure sensors and control valve switches are also installed on each outlet air pipe.

[0018] In a preferred embodiment of the above-mentioned system for remediating organically contaminated sites, the extraction subsystem includes a second connecting pipeline and an extraction control unit. The extraction control unit comprises an extraction fan, an activated carbon tank, and a chimney connected in sequence. The second connecting pipeline includes a main extraction pipe and extraction branch pipes. One end of the main extraction pipe is connected to the extraction fan, and the other end is connected to each extraction branch pipe. Each extraction branch pipe is connected to an extraction well. Flow meters are installed on the main outlet pipe and each outlet pipe. An online VOC monitoring sensor for exhaust gas is installed on the main extraction pipe. Pressure sensors and control valve switches are also installed on each extraction branch pipe.

[0019] In the above-mentioned system for remediating organically contaminated sites, as a preferred embodiment, the horizontal spacing between aeration wells in the functional well subsystem is 3-5m, and the horizontal spacing between extraction wells is 4-8m.

[0020] In the above-mentioned system for remediating organically contaminated sites, as a preferred embodiment, the aeration well has a terminal hole that extends to a depth of 3m below the groundwater level, with the well located 1m-2.5m below the groundwater level being the perforated section, and the remaining part of the well being the plain section.

[0021] The final hole of the extraction well is 1m above the groundwater level. The section of the well with a perforated pipe is 1.5m-4.5m above the groundwater level, and the rest of the well is a plain pipe. If the groundwater level is less than 5m deep, the top of the perforated pipe must be at least 0.5m above the ground.

[0022] The perforated section of the pressure monitoring well is located at ±1m below the groundwater level.

[0023] In a first aspect, this application provides a method for remediating organically contaminated sites. The method, implemented systematically, includes an extraction-aeration stage and a slow-release oxygen microbial stimulation enhancement treatment stage. The extraction-aeration stage comprises the following steps:

[0024] (1) The system is started up as a whole, and aeration and extraction are performed. The initial settings are: aeration pressure ≥ 0.2 MPa and extraction air volume ≥ 2000 m³ / h. 3 / h;

[0025] (2) Monitor the VOC concentration in the exhaust gas and determine the duration for which the current system reaches the preset VOC concentration in the exhaust gas;

[0026] (3) If the current system reaches the preset value of VOC concentration in the exhaust gas and the duration exceeds 72 hours, the extraction-aeration stage will be terminated, and it will be examined whether the conditions are sufficient to enter the slow-release oxygen microbial stimulation enhancement treatment stage.

[0027] If the current system reaches the preset value of exhaust gas VOC concentration but the duration does not exceed 72 hours, then the extraction-aeration stage will continue to operate.

[0028] (4) If the conditions are met, the treatment will proceed to the stage of slow-release oxygen microbial stimulation enhancement.

[0029] Preferably, the preset value is 100 ppm VOC concentration in the exhaust gas;

[0030] Preferably, in step (2), at the initial stage of the extraction-aeration phase, the system dynamically adjusts the pressure and flow rate of extraction and aeration to ensure balance. After the system adjusts adaptively, it enters a stable operating state of start-stop rotation. The "system adjustment adaptively" means that when one or more pressure and flow rate parameters are detected to have numerical drift characteristics, the PLC controller automatically adjusts the opening and closing of one or more aeration subsystems to achieve balance, that is, the pressure and flow rate of each aeration well are relatively consistent without significant deviation. Further, the stable operating state of start-stop rotation is as follows: after extraction and aeration every 8 hours, aeration and extraction are paused, and after 8 hours, the initial settings are restored to start extraction and aeration.

[0031] Preferably, in step (3), maintaining the extraction-aeration phase means: if the current system concentration is greater than the preset value of the exhaust gas VOC concentration, then maintain aeration and extraction; otherwise, stop aeration and extraction, and restore the initial settings to start aeration and extraction after 8 hours.

[0032] In a preferred embodiment of the above-described method for remediating organically contaminated sites, the extraction-aeration stage further includes monitoring the extraction flow rate and pressure well pressure, and the PLC controller performs the following control accordingly:

[0033] a. If the extraction flow rate is less than 500m³ 3 If the pressure monitoring well pressure drops below -0.2 kPa, stop extraction and continue aeration until the pressure monitoring well pressure is 0, then resume extraction.

[0034] b. If the positive pressure of the pressure monitoring well is higher than 0.2 kPa, stop aeration until the pressure of the pressure monitoring well is -0.1 kPa and then resume aeration.

[0035] The above-mentioned method for remediating organically contaminated sites, as a preferred embodiment, includes step (3) of examining whether the conditions are sufficient to enter the slow-release oxygen microbial stimulation enhancement treatment stage, which includes: further determining whether the conditions for slow-release oxygen microbial stimulation enhancement treatment are met by sampling and analyzing the groundwater quality parameters DO, ORP, and characteristic pollutant concentrations; preferably, the conditions for meeting the slow-release oxygen microbial stimulation enhancement treatment are: groundwater dissolved oxygen concentration DO>2mg / L, oxidation-reduction potential ORP>0mV, and groundwater characteristic pollutant concentration removal rate reduced by more than 95% compared to aeration-extraction, but still not reaching the remediation target.

[0036] In the above-mentioned method for remediating organically contaminated sites, as a preferred embodiment, step (4) includes the following steps: using existing aeration wells and groundwater sampling monitoring wells, calcium peroxide slow-release oxygen material is placed into geotextile bags and suspended in the groundwater to slowly release oxygen into the groundwater, forming a long-lasting aerobic environment for microorganisms; preferably, the dissolved oxygen concentration in the groundwater is monitored during this stage, and a batch of calcium peroxide slow-release oxygen material is replaced whenever DO < 2 mg / L.

[0037] In the above-described method for remediating organically contaminated sites, as a preferred embodiment, the organically contaminated site is groundwater contaminated with petroleum hydrocarbons.

[0038] Compared with the prior art, the beneficial effects of this application include, but are not limited to:

[0039] 1. Using a PLC controller as the system control center, the system dynamically judges the process operation effect in real time based on changes in parameters such as pressure, gas flow rate, and exhaust gas VOC concentration. Through automation, the system achieves operational balance in the extraction-aeration stage, avoiding local air blockage or airflow dominance channels caused by soil heterogeneity and early airflow imbalance during the extraction-aeration process. This improves the effective operating efficiency of the process and greatly reduces remediation energy consumption and operating costs.

[0040] 2. In the later stages of the remediation phase, the microbial stimulation enhancement based on slow-release oxygen materials can effectively solve the "tailing" effect in the later stages of remediation caused by the single aeration-extraction process, improve technical efficiency, greatly shorten the overall remediation time, and further save operating costs. Attached Figure Description

[0041] Figure 1 is a schematic diagram of the functional well layout in the system for remediating organically contaminated sites provided in Example 1;

[0042] Figure 2 is a schematic diagram of the connection process of the aeration well, extraction well, aeration control unit, extraction control unit, and PLC controller in the system for remediating organically contaminated sites provided in Example 1.

[0043] Figure 3 is a graph showing the time variation of VOC concentration in exhaust gas in the method for remediating organically contaminated sites provided in Example 1.

[0044] Figure 4 is a graph showing the benzene concentration in groundwater and the benzene removal efficiency-time in the method for remediating organically contaminated sites provided in Example 1.

[0045] Figure 5 shows the groundwater DO and ORP variation curves in the method for remediating organically contaminated sites provided in Example 1.

[0046] Figure 6 shows the groundwater DO curve during the slow-release oxygen microbial stimulation enhancement stage of the method for remediating organically contaminated sites provided in Example 1.

[0047] The following labels are used in the attached diagram: 1. Aeration well; 2. Pressure sensor; 3. Flow meter; 4. Control valve switch; 15. First connecting line pipeline; 25. Second connecting line pipeline; 6. PLC controller; 7. Extraction well; 8. Aeration main control unit; 9. Extraction main control unit. Detailed Implementation

[0048] This application provides a system and method for remediating organically contaminated sites, the specific implementation of which is as follows:

[0049] 1. Repair the system structure

[0050] (1) Well layout

[0051] Based on the site's hydrogeological characteristics, aeration wells 1 and extraction wells 7 were installed on the contaminated site. The horizontal spacing between aeration wells 1 was 3-5m, and the horizontal spacing between extraction wells 7 was 4-8m. Aeration wells 1 were mainly located in the main contaminated areas (i.e., areas with high pollution concentrations). Extraction wells 7 needed to cover the aeration area and ensure that a ring of wells 1 surrounded the aeration area. Pressure monitoring wells and groundwater sampling monitoring wells covered the entire remediation area according to process requirements. In a specific deployment example, see Figure 1. Red represents aeration well 1, green represents extraction well 7, blue represents groundwater sampling well, and purple represents pressure monitoring well. Aeration well 1 is deployed within the main contaminated area (orange hexagonal area), positioned at the corners and center of the hexagon, with a horizontal spacing of 3m. Extraction well 7 covers the aeration area, forming a ring that surrounds all aeration well 1. This ensures that all pollutants stripped by aeration treatment can be extracted. The horizontal spacing of extraction well 7 varies from 4m to 8m. Pressure monitoring wells and groundwater sampling monitoring wells cover the entire remediation area.

[0052] (2) Vertical depth requirements of the well

[0053] The final hole of aeration well 1 needs to be 3m below the groundwater level. The section of the well located 1m-2.5m below the groundwater level is the perforated pipe (screen pipe) part, and the rest of the well is the white pipe.

[0054] The final hole of extraction well 7 needs to be above the groundwater level by 1m. The section of the well located 1.5m-4.5m above the groundwater level is the perforated pipe (screen pipe) section, and the rest of the well is the white pipe. If the groundwater level is less than 5m deep, the top of the perforated pipe (screen pipe) must be at least 0.5m above the ground.

[0055] The perforated pipe (screen pipe) of the pressure monitoring well should be located at ±1m below the groundwater level.

[0056] (3) Connection between well and equipment / instruments

[0057] Aeration well 1 is connected to an air compressor, the maximum pressure of which is not less than 0.2 MPa. Flow meters 3 are installed on the main outlet pipe and each outlet pipe to monitor the aeration flow rate in real time.

[0058] The extraction well 7 is connected to an extraction fan (such as the centrifugal fan in Figure 2), and the extraction air volume is not less than 2000 m³ / s. 3 / h. An online VOC monitoring sensor is installed on the main extraction pipe to monitor the VOC concentration in the exhaust gas in real time; flow meters are installed on the main extraction pipe and each extraction branch pipe to monitor the extraction flow rate in real time. An activated carbon tank is connected after the extraction fan to treat the exhaust gas.

[0059] A pressure sensor is installed at the head of the pressure monitoring well (i.e., the top / upper end of the pressure monitoring well) to monitor the pressure inside the well in real time.

[0060] Groundwater sampling and monitoring wells are equipped with relevant equipment to sample, analyze, and detect groundwater quality parameters (DO, ORP) and the concentration of characteristic petroleum hydrocarbon pollutants (such as benzene concentration).

[0061] The flow meter 3, the exhaust gas VOC online monitoring sensor, and the pressure sensor 2 are all connected to the PLC controller, and the relevant data are adjusted and started / stopped by the PLC controller.

[0062] Figure 2 illustrates an embodiment of a system for remediating organically contaminated sites, comprising 7 aeration wells 1 and 13 extraction wells 7. Each aeration well 1 is connected to an aeration control unit 8 via a first connecting line pipe 15. The aeration control unit 8 includes an air tank and an air compressor, which is connected to a PLC controller 6. The first connecting line pipe 15 includes a main outlet pipe and various outlet pipes. One end of the main outlet pipe is connected to the air tank, and the other end is connected to each outlet pipe. Each outlet pipe is connected to each aeration well 1. Flow meters 3 are installed on both the main outlet pipe and each outlet pipe to monitor the aeration flow rate in real time. Pressure sensors 2 and control valve switches 4 are also installed on each outlet pipe. Each extraction well 7 is connected to a second connecting line pipe... Pipeline 25 is connected to the extraction control unit 9; the extraction control unit 9 includes an extraction blower (centrifugal blower), a gas-water separation device (which may be omitted in some cases), an activated carbon tank, and a chimney connected in sequence. The extraction control unit 9 is also connected to a PLC controller 6; the second connection line pipeline 25 includes an extraction main pipe and various extraction branch pipes. One end of the extraction main pipe is connected to the extraction blower, and the other end is connected to each extraction branch pipe. Each extraction branch pipe is connected to each extraction well 7. Flow meters 3 are installed on the main outlet pipe and each outlet outlet pipe to monitor the extraction flow rate in real time; an online VOC monitoring sensor for tail gas is installed on the extraction main pipe to monitor the VOC concentration of tail gas in real time; each extraction branch pipe is also equipped with a pressure sensor 2 and a control valve switch 4.

[0063] 2. Execution control logic

[0064] (1) The system is started up as a whole, with the initial aeration pressure set at 0.2 MPa and the extraction air volume at 2000 m³ / h. 3 / h; In the initial stage of extraction, the system dynamically adjusts the pressure and flow rate of extraction and aeration to ensure balance. After the system adapts, it enters a stable operating state of extraction-stop alternation, during which the VOC concentration in the exhaust gas steadily and continuously decreases. The so-called "system adaptive adjustment" means that when one or more pressure and flow rate parameters are detected to have numerical drift characteristics, the PLC controller automatically adjusts the opening and closing of one or more corresponding aeration subsystems to ultimately achieve balance, that is, the pressure and flow rate of each aeration well are relatively consistent with no large deviation.

[0065] (2) If the VOC concentration in the exhaust gas is greater than 100ppm, continue running; otherwise, stop the system and restart after 8 hours at the initial settings.

[0066] (3) If the extraction flow rate is less than 500 m³ / h 3 If the pressure monitoring well pressure is below -0.2 kPa, the extraction fan will be stopped, while the aeration air compressor will continue to run until the pressure monitoring well pressure is 0, at which point the extraction fan will be restarted.

[0067] (4) If the positive pressure of the pressure monitoring well is higher than 0.2 kPa, stop the operation of the aeration air compressor until the pressure of the pressure monitoring well is -0.1 kPa and then resume aeration.

[0068] (5) If the system maintains normal operation for 8 hours, aeration and extraction will be suspended, and the initial settings will be restored after 8 hours.

[0069] (6) If the system cannot reach the start-up state within 72 hours (i.e., the VOC concentration is less than 100ppm after each restart within 72 hours), the extraction-aeration stage is judged to be over and the slow-release oxygen microbial stimulation enhancement treatment stage is entered.

[0070] 3. Enhanced microbial stimulation with slow-release oxygen

[0071] If the extraction-aeration system fails to reach startup status within 72 hours, further sampling and analysis of groundwater quality parameters (DO, ORP) and the concentration of characteristic petroleum hydrocarbon pollutants (such as benzene concentration) are required to determine whether the conditions for slow-release oxygen microbial stimulation-enhanced treatment have been met. Generally, the conditions for achieving slow-release oxygen microbial stimulation-enhanced treatment are: groundwater dissolved oxygen concentration (DO) > 2 mg / L, oxidation-reduction potential (ORP) > 0 mV, and a reduction in the removal rate of characteristic petroleum hydrocarbon pollutants in the groundwater by more than 95% compared to the aeration-extraction process, but the remediation target has still not been achieved.

[0072] At this stage, if extraction-aeration continues, it would require several times, or even more than ten times, the current operating time to achieve remediation standards, resulting in extremely low technical efficiency and cost-effectiveness. Therefore, by utilizing existing aeration wells and groundwater sampling monitoring wells, slow-release calcium peroxide material (commercially available calcium peroxide, purchased from Foshan Nongxin Biotechnology Co., Ltd., with a calcium peroxide content of 50-60%) is placed in geotextile bags and suspended in the groundwater. This slowly releases oxygen into the groundwater, creating a long-lasting aerobic microbial environment. This achieves low-energy, low-cost, and sustainable aerobic bioremediation of petroleum hydrocarbons, ultimately achieving long-term remediation standards.

[0073] No additional energy is required during the slow-release oxygen microbial stimulation and enhanced remediation process. Only the dissolved oxygen concentration in the groundwater needs to be monitored. When DO < 2 mg / L, a batch of slow-release calcium peroxide material can be replaced.

[0074] The following embodiments are provided to facilitate a better understanding of this application, but are not intended to limit the scope of this application.

[0075] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0076] Unless otherwise specified, all other experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0077] Example 1

[0078] This embodiment provides a system and method for remediating organically contaminated sites, specifically for in-situ treatment of petroleum hydrocarbon-contaminated groundwater.

[0079] Firstly, the system for remediating petroleum hydrocarbon-contaminated groundwater includes: aeration well 1, extraction well 7, pressure monitoring well, and groundwater sampling monitoring well. The aeration well 1 is arranged horizontally at intervals of 3-5m in the main contaminated area, and the extraction well 7 is arranged horizontally at intervals of 4-8m covering the aeration area, ensuring that a ring surrounds the aeration well 1. The pressure monitoring well and groundwater sampling monitoring well cover the entire remediation area.

[0080] The aeration well 1 terminates at a depth 3m below the groundwater level. The section of the well 1m-2.5m below the groundwater level is a perforated pipe, and the rest of the well is a plain pipe. The extraction well 7 terminates at a depth 1m above the groundwater level. The section of the well 1.5-4.5m above the groundwater level is a perforated pipe, and the rest of the well is a plain pipe. If the groundwater level is less than 5m deep, the top of the perforated pipe must be at least 0.5m above the ground. The perforated pipe section of the pressure monitoring well is located at ±1m below the groundwater level.

[0081] Aeration well 1 is connected to an air compressor with a maximum pressure of not less than 0.2 MPa. Electronic flow meters and electronic pressure sensors are installed on the main outlet pipe and each outlet pipe to monitor the aeration flow rate and pressure in real time.

[0082] Extraction well 7 is connected to an extraction fan, with an extraction air volume of not less than 2000 m³ / h. 3 / h. The main extraction pipe is equipped with an online VOC monitoring sensor, electronic flow meter, and electronic pressure sensor for the exhaust gas. Each extraction pipe is equipped with an electronic flow meter and electronic pressure sensor to monitor the VOC concentration, extraction flow rate, and pressure of the exhaust gas in real time. An activated carbon tank is connected after the extraction fan to treat the exhaust gas.

[0083] An electronic pressure sensor is installed at the head of the pressure monitoring well to monitor the pressure inside the well in real time.

[0084] The electronic flow meter, exhaust gas VOC online monitoring sensor, and electronic pressure sensor are all connected to the PLC controller, and the relevant data are adjusted and started / stopped by the PLC controller.

[0085] Secondly, the method for remediating petroleum hydrocarbon-contaminated groundwater is implemented through the aforementioned system and includes the following steps:

[0086] (I) Extraction-Aeration Stage:

[0087] (1) Obtain the pollution status through site investigation, and design according to the pollution status and theoretical calculations to determine the location of aeration wells and extraction wells (see Figure 1).

[0088] (2) Aeration well 1 and extraction well 7 are installed in the polluted area. Each aeration well 1 and extraction well 7 is equipped with a pressure sensor, flow meter and control valve (see Figure 2).

[0089] (3) The pressure sensor, flow meter, and control valve are all connected to the PLC controller.

[0090] (4) Start the aeration and extraction device to perform aeration and extraction;

[0091] (5) In practice, the initial extraction tail gas VOC concentration reached 1400ppm, which is greater than the 100ppm judgment value. The PLC controller judged that aeration and extraction needed to be carried out (see Figure 3).

[0092] (6) In the initial stage of extraction, the system dynamically adjusts the pressure and flow rate of extraction and aeration. After the system adjusts and adapts, it enters a stable operating state of 8 hours of extraction and 8 hours of shutdown. The VOC concentration in the exhaust gas decreases steadily and continuously during this stage, and begins to decrease to below 100 ppm after about 40 days (see Figure 3).

[0093] (7) After entering the low concentration range (i.e., below 100 ppm), the system intermittently starts and stops according to the VOC concentration in the exhaust gas until it triggers a state where the VOC concentration in the exhaust gas is below 100 ppm for 72 consecutive hours after day 63, thus ending the extraction-aeration stage. The so-called "state where the exhaust gas concentration is below 100 ppm for 72 consecutive hours" means that the system cannot reach the start-up state within 72 hours, that is, the VOC concentration is less than 100 ppm after each restart of the system within 72 hours.

[0094] (8) According to process monitoring data (see Figure 4), the benzene concentration in the groundwater decreased significantly within the first 20 days of operation, resulting in a sharp drop in daily benzene removal efficiency and a severe reduction in technical efficiency (see Figure 4). However, although the benzene concentration in the groundwater decreased significantly, it exhibited a stable low-concentration tailing state. According to design calculations, it would still take 240 days of operation to reach the remediation target value of 10 μg / L. Therefore, the technical efficiency and cost-effectiveness of the extraction-aeration process were significantly reduced.

[0095] (II) Slow-release oxygen microbial stimulation enhancement stage

[0096] In the pilot-scale experiment, after 90 days of operation using the extraction-aeration stage method, the groundwater DO concentration reached 2 mg / L and ORP reached 0 mV or higher (see Figure 5), and slow-release oxygen microbial stimulation was used to enhance remediation.

[0097] At this point, a calcium peroxide slow-release oxygen reaction device (i.e., commercially available calcium peroxide, purchased from Foshan Nongxin Biotechnology Co., Ltd., with a calcium peroxide content of 50-60%, filled into geotextile bags and suspended in the groundwater) was installed in the aeration wells and groundwater sampling monitoring wells where conditions permit on-site, and the site was continuously operated and monitored. After the addition of the slow-release oxygen material, the dissolved oxygen in the groundwater remained at a concentration greater than 2 mg / L for more than 20 days (see Figure 6). The groundwater in a high dissolved oxygen state promoted the degradation of low-concentration organic pollutants by aerobic microorganisms. After 60 days of stimulation by slow-release oxygen microorganisms, the remediation target of stable benzene concentration below 10 μg / L in the groundwater was achieved, which was much shorter than the 240 days required by aeration-extraction alone. Moreover, under the operational scale of this embodiment, if the aeration-extraction operation were still carried out for 240 days, the energy consumption and labor operation costs would be about 100,000 yuan. By using the calcium peroxide slow-release oxygen material, the total material cost was only 800 yuan, and no labor or energy consumption was required. Therefore, the remediation method provided in this embodiment has a significantly reduced cost.

[0098] As can be seen from the above embodiments:

[0099] 1. The remediation system and method of the present invention uses a PLC controller as the system control center. It dynamically judges the process operation effect in real time based on changes in parameters such as pressure and gas flow rate. It achieves operational balance in the site extraction-aeration stage through automation, avoiding local air blockage or airflow dominance channels caused by soil heterogeneity and early airflow imbalance during the extraction-aeration process. This improves the effective operating efficiency of the process and greatly reduces remediation energy consumption and operating costs.

[0100] 2. The remediation system and method of the present invention can effectively solve the "tailing" effect in the later stage of remediation caused by the single aeration-extraction process by strengthening microbial stimulation based on slow-release oxygen materials in the later stage of the remediation stage, thereby improving technical efficiency, greatly shortening the overall remediation time, and further saving operating costs.

[0101] Finally, it should be noted that, if any, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0102] Although this application has been disclosed above with reference to specific embodiments, it should be understood that those skilled in the art can devise various modifications, improvements, or equivalents to this application within the spirit and scope of the appended solutions. Such modifications, improvements, or equivalents should also be considered to be included within the scope of protection claimed in this application.

Claims

1. A system for remediating an organically contaminated site, characterized by, include: The functional well subsystem includes several aeration wells, extraction wells, pressure monitoring wells, and groundwater sampling monitoring wells. Among them, aeration wells are arranged at equal intervals in the main pollution areas; extraction wells are arranged to cover the aeration area and ensure that a ring surrounds all aeration wells; pressure monitoring wells and groundwater sampling monitoring wells are arranged to cover the entire remediation area. The aeration subsystem is used to provide aeration to each aeration well; The extraction subsystem is used to extract gas from each extraction well; The data acquisition subsystem is used to collect and monitor key operating parameters of each subsystem, including flow rate, pressure, exhaust gas concentration, groundwater quality, and concentration of characteristic pollutants. The PLC controller is connected to the functional well subsystem, aeration subsystem, extraction subsystem and data acquisition subsystem respectively, and controls the operation of each subsystem according to key operating parameters. The slow-release oxygen microbial stimulation enhanced remediation subsystem includes calcium peroxide slow-release oxygen material, which is installed in aeration wells and groundwater sampling and monitoring wells to slowly release oxygen into the groundwater.

2. The system for remediating an organically contaminated site of claim 1, wherein, The aeration subsystem includes a first connecting pipeline and an aeration control unit. The aeration control unit includes an air tank and an air compressor, which is connected to a PLC controller. The first connecting pipeline includes a main air outlet pipe and various outlet air pipes. One end of the main air outlet pipe is connected to the air tank, and the other end is connected to each outlet air pipe. Each outlet air pipe is connected to each aeration well. Flow meters are installed on the main air outlet pipe and each outlet air pipe. Pressure sensors and control valve switches are also installed on each outlet air pipe.

3. The system for remediating an organically contaminated site according to claim 1 or 2, characterized in that, The extraction subsystem includes a second connecting pipeline and an extraction control unit; the extraction control unit includes an extraction fan, an activated carbon tank, and a chimney connected in sequence; the second connecting pipeline includes an extraction main pipe and various extraction branch pipes, one end of the extraction main pipe is connected to the extraction fan, and the other end is connected to each extraction branch pipe, each extraction branch pipe is connected to each extraction well, and flow meters are installed on the main outlet pipe and each outlet outlet pipe; an online VOC monitoring sensor for exhaust gas is installed on the extraction main pipe; and pressure sensors and control valve switches are also installed on each extraction branch pipe.

4. The system for remediating an organically contaminated site according to any one of claims 1-3, wherein, In the functional well subsystem, the horizontal spacing between aeration wells is 3-5m, and the horizontal spacing between extraction wells is 4-8m.

5. The system for remediating an organically contaminated site according to any one of claims 1-4, wherein, The aeration well reaches a depth of 3m below the groundwater level at its final borehole. The section of the well with the perforated pipe is located 1m-2.5m below the groundwater level, while the rest of the well is a plain pipe. The final hole of the extraction well is 1m above the groundwater level. The section of the well with a perforated pipe is 1.5m-4.5m above the groundwater level, and the rest of the well is a plain pipe. If the groundwater level is less than 5m deep, the top of the perforated pipe must be at least 0.5m above the ground. The perforated section of the pressure monitoring well is located at ±1m below the groundwater level.

6. A method of remediating an organically contaminated site, characterized in that, The system implementation as described in any one of claims 1-5 sequentially includes an extraction-aeration stage and a slow-release oxygen microbial stimulation enhancement treatment stage, wherein the extraction-aeration stage comprises the following steps: (1) System overall start, aeration and extraction, initial setting for aeration pressure ≥ 0.2 MPa, extraction air volume ≥ 2000 m 3 / h; (2) Monitor the VOC concentration in the exhaust gas and determine the duration for which the current system reaches the preset VOC concentration in the exhaust gas; (3) If the current system reaches the preset value of VOC concentration in the exhaust gas and the duration exceeds 72 hours, the extraction-aeration stage will be terminated, and it will be examined whether the conditions are sufficient to enter the slow-release oxygen microbial stimulation enhancement treatment stage. If the current system reaches the preset value of exhaust gas VOC concentration but the duration does not exceed 72 hours, then the extraction-aeration stage will continue to operate. (4) If the conditions are met, the treatment will proceed to the stage of slow-release oxygen microbial stimulation enhancement. Preferably, the preset value is 100 ppm VOC concentration in the exhaust gas; Preferably, in step (2), at the initial stage of the extraction-aeration phase, the system dynamically adjusts the pressure and flow rate of extraction and aeration to ensure balance. After the system adjusts adaptively, it enters a stable operating state of start-stop rotation. The "system adjustment adaptively" means that when one or more pressure and flow rate parameters are detected to have numerical drift characteristics, the PLC controller automatically adjusts the opening and closing of one or more aeration subsystems to achieve balance, that is, the pressure and flow rate of each aeration well are relatively consistent without significant deviation. Further, the stable operating state of start-stop rotation is as follows: after extraction and aeration every 8 hours, aeration and extraction are paused, and after 8 hours, the initial settings are restored to start extraction and aeration. Preferably, in step (3), maintaining the extraction-aeration phase means: if the current system concentration is greater than the preset value of the exhaust gas VOC concentration, then maintain aeration and extraction; otherwise, stop aeration and extraction, and restore the initial settings to start aeration and extraction after 8 hours.

7. The method of remediating an organically contaminated site according to claim 6, wherein, The extraction-aeration stage also includes monitoring the extraction flow rate and pressure in the well, and the PLC controller implements the following control accordingly: a. If the extraction flow is less than 500 m 3 / h or the pressure in the pressure monitoring well is less than -0.2 kPa, then the extraction is stopped, during which aeration is maintained, until the extraction is resumed when the pressure in the pressure monitoring well is 0 kPa. b. If the positive pressure of the pressure monitoring well is higher than 0.2 kPa, stop aeration until the pressure of the pressure monitoring well is -0.1 kPa and then resume aeration.

8. The method of remediating an organically contaminated site according to claim 6, wherein, The assessment of whether the conditions described in step (3) are sufficient to enter the slow-release oxygen microbial stimulation enhancement treatment stage includes: further determining whether the conditions for slow-release oxygen microbial stimulation enhancement treatment are met by sampling and analyzing the groundwater quality parameters DO, ORP, and characteristic pollutant concentrations; preferably, the conditions for meeting the slow-release oxygen microbial stimulation enhancement treatment are: groundwater dissolved oxygen concentration DO>2mg / L, oxidation-reduction potential ORP>0mV, and groundwater characteristic pollutant concentration removal rate reduced by more than 95% compared to aeration-extraction, but still not reaching the remediation target.

9. The method of remediating an organically contaminated site according to any one of claims 6-8, wherein, In step (4), the slow-release oxygen microbial stimulation enhancement treatment stage includes: using existing aeration wells and groundwater sampling monitoring wells, putting calcium peroxide slow-release oxygen material into geotextile bags and hanging them in the groundwater to slowly release oxygen into the groundwater, forming a long-lasting aerobic microbial stimulation environment; preferably, during this stage, the dissolved oxygen concentration in the groundwater is monitored, and whenever DO < 2 mg / L, a batch of calcium peroxide slow-release oxygen material is replaced.

10. The method of remediating an organically contaminated site according to any one of claims 6-8, wherein, The organically contaminated site is groundwater contaminated with petroleum hydrocarbons.

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