Immobilized microorganism coupling circulating well in-situ low-carbon remediation system and method

Abstract

The application discloses a kind of immobilized microorganism coupling circulating well in-situ low-carbon remediation system and method, and the remediation medium layer of the system uses PVA-SA-BC double-network hydrogel microspheres immobilized degradation bacterial population, and agricultural waste-derived biochar is used as functional porous filler instead of activated carbon;Multivariable fuzzy controller is arranged in intelligent control layer, and dissolved oxygen deviation, pollutant concentration change rate and upper and lower chamber water level difference are input simultaneously, while water pump frequency adjustment and oxygen release rate adjustment are output, to realize the real-time feedback coupling of circulating well hydraulic parameter and microbial degradation process;Execution layer integrates variable frequency water pump, regulating valve group, oxygen release device and upper and lower packer, to build the trinity low-carbon remediation process dominated by biodegradation, assisted by oxygen release, and linked by hydraulic circulation;The application realizes carrier-hydraulic-biochemical system level cooperation, and degradation bacterial population can be recycled and utilized, and is suitable for in-situ remediation of groundwater organic pollution.

Description

Technical Field

[0001] This invention relates to the field of in-situ remediation technology for organic pollution in soil and groundwater, and particularly to an in-situ low-carbon remediation system and method for immobilized microorganisms coupled with circulating wells. Background Technology

[0002] Groundwater circulation well (GCW) technology creates a three-dimensional circulating flow field of groundwater within an aquifer by forming a vertical hydraulic circulation within a single well, eliminating the need to extract groundwater to the surface for treatment. Existing technologies include, for example, Chinese patent CN121535032A, which discloses an in-situ remediation scheme for GCWs integrating oxygen release, microorganisms, and chemical oxidation modules, with the microbial module employing direct injection of free-state microorganisms into the aquifer; another example is an academic paper reporting experimental research on the coupling of polyvinyl alcohol-sodium alginate-activated carbon hydrogel microspheres immobilized with microorganisms and groundwater circulation wells for the remediation of naphthalene-contaminated aquifers. Furthermore, Chinese patent CN121576285A relates to a method for hydraulic control of pumping-injection balance in GCWs, and CN121449203A relates to a remediation device combining bioelectric Fenton and GCWs.

[0003] First, in schemes employing free-state microorganisms, these microorganisms are prone to aggregation and loss within the aquifer due to groundwater flow, making it difficult to maintain an effective bacterial concentration in the target remediation area. Furthermore, free-state microorganisms cannot be recycled, leading to high remediation costs. Second, the hydraulic control of the circulating well is disconnected from the microbial degradation process. Existing systems typically set fixed hydraulic parameters based on experience or adjust them solely for water level balance, failing to adjust circulation flow and residence time in real time according to actual biochemical responses such as pollutant concentration changes and dissolved oxygen consumption during microbial degradation. This results in a mismatch between hydraulic circulation conditions and the needs of the microbial remediation process, hindering the full realization of their synergistic potential. Third, existing immobilization carrier materials use activated carbon as a functional filler, which has high energy consumption and a large carbon footprint during preparation. Moreover, the relatively simple pore structure of activated carbon limits its adsorption-mass transfer performance for hydrophobic organic pollutants. Fourth, remediation schemes dominated by electrochemical oxidation require continuous consumption of electricity and chemical reagents during operation, resulting in high carbon emissions and potential secondary pollution, which does not align with the development direction of green and low-carbon remediation.

[0004] Therefore, in response to the problems mentioned above, this invention proposes an immobilized microorganism coupled circulation well in-situ low-carbon remediation system and method. Summary of the Invention

[0005] To overcome the problems of lack of real-time feedback coupling between hydraulic regulation and microbial degradation processes in existing technologies, and the failure of various components of the remediation system to achieve synergistic effects, this invention proposes an immobilized microorganism coupled circulating well in-situ low-carbon remediation system and method. This system constructs a closed-loop control link of perception-decision-execution-feedback, and integrates the material properties of the immobilized microbial carrier, the hydraulic regulation of the circulating well, and the biochemical processes of microbial degradation into a synergistic optimization framework, thereby achieving efficient and low-carbon in-situ remediation of organic pollution in groundwater.

[0006] The technical solution of this invention is: an immobilized microorganism coupled circulating well in-situ low-carbon remediation system, comprising: The real-time sensing layer includes multi-parameter sensors deployed in the upper and lower chambers of the circulation well and the aquifer monitoring well, including at least dissolved oxygen sensors, pollutant concentration sensors, redox potential / pH sensors and water level sensors, for collecting water quality parameters and water level parameters of the aquifer. The intelligent control layer includes a multivariate fuzzy controller and its subordinate pumping balance adjustment module and oxygen release rate adjustment module. The multivariate fuzzy controller takes three variables as inputs: dissolved oxygen deviation, pollutant concentration change rate, and water level difference between the upper and lower chambers. Based on a predefined fuzzy rule base and membership function, it outputs the pump operating frequency adjustment and oxygen release rate adjustment. The domain of the dissolved oxygen deviation is [-5, 5] mg / L, the domain of the pollutant concentration change rate is [-20, 20]% / h, and the domain of the water level difference between the upper and lower chambers is [-30, 30] cm. The domain of the output variable pump frequency adjustment is [-20, 20] Hz, and the domain of the oxygen release rate adjustment is [-5, 5] mg / (L·min). The fuzzy inference adopts the Mamdani type, and the centroid method is used for defuzzification. The execution layer includes a variable frequency water pump, a regulating valve group, an oxygen release device, and upper and lower packers. The variable frequency water pump runs through the upper and lower packers, pumping water from the lower chamber to the upper chamber or vice versa, generating a vertical hydraulic gradient and driving the formation of a three-dimensional circulating flow field in the aquifer. The regulating valve group assists the water pump in achieving precise matching of pumping and injection flow rates. The oxygen release device is installed in the upper chamber or the outlet section of the circulating well, releasing dissolved oxygen into the circulating water in the form of micro-nano aeration heads or calcium peroxide slow-release devices. The upper and lower packers divide the circulating well into an upper chamber and a lower chamber, with corresponding well walls equipped with sieves that communicate with the ambient groundwater. The remediation medium layer comprises PVA-SA-BC immobilized microbial microspheres placed in the aquifer. These microspheres utilize polyvinyl alcohol (PVA) and sodium alginate (SA) as a dual-network gel framework and biochar (BC) derived from agricultural waste as a functional porous filler. They form an interpenetrating network hydrogel structure through chemical and ionic cross-linking, and are internally loaded with degrading bacteria. The preferred formulation is: 6-10% (w / v) polyvinyl alcohol, 1-3% (w / v) sodium alginate, 2-5% (w / v) biochar, and 5-15% (v / v) bacterial suspension. The biochar has a particle size of 50-200 μm, and the microspheres have a particle size of 2-5 mm.

[0007] In the above system, the multivariate fuzzy controller is used for: When dissolved oxygen is below the minimum threshold required for microbial degradation and the rate of decrease in pollutant concentration is lower than expected, the oxygen release rate is increased and the pump speed is reduced to prolong the hydraulic residence time. When the water level difference between the upper and lower chambers exceeds the limit, the pump speed should be reduced or the valve group should be adjusted to ensure pumping balance. When dissolved oxygen is sufficient but pollutant concentration decreases slowly, increase pump speed to expand the circulation radius while maintaining the current oxygen release rate.

[0008] This invention also provides a method for in-situ low-carbon remediation of immobilized microorganisms coupled with circulating wells, comprising the following steps: S1. Based on the site hydrogeological survey results and the distribution of the pollution plume, determine the well location, well depth, screen section location, and packer installation depth of the circulating well; prepare PVA-SA-BC immobilized microbial microspheres according to the above formula, and release them into the target aquifer area through the injection well or the circulating well itself before circulation is started; start the circulating well system and initially run it at a pump speed of 60-80% of the design flow rate to establish a three-dimensional circulating flow field in the aquifer; S2, the multi-parameter sensors of the real-time sensing layer collect dissolved oxygen, pollutant concentration trends, oxidation-reduction potential, pH and water level data of the upper and lower chambers at preset time intervals (5-15 minutes) and transmit them to the multivariable fuzzy controller. S3, the multivariate fuzzy controller takes three variables as input: dissolved oxygen deviation, pollutant concentration change rate, and water level difference between the upper and lower chambers. Based on a predefined fuzzy rule base and membership function, it simultaneously outputs the pump operating frequency adjustment and oxygen release rate adjustment, which are then issued to the frequency converter and oxygen release device for execution. Specifically, when the dissolved oxygen concentration is sufficient (≥2.0mg / L) and the pollutant decrease rate is normal, a higher pump speed is output to expand the circulation radius. When the dissolved oxygen concentration is low, the pump speed is reduced while the oxygen release rate is increased to prolong the residence time of dissolved oxygen-containing water in the immobilized microsphere area. When the pollutant concentration enters a plateau period and the concentration decrease rate is consistently below the preset threshold, the circulation direction is switched (from "downward pumping and upward injection" to "upward pumping and downward injection" or vice versa), changing the water flow path to contact new polluted areas. S4, circulating water containing dissolved oxygen flows through the immobilized microsphere distribution area in the aquifer. The multi-level porous structure of biochar in the microspheres adsorbs and enriches dissolved organic pollutants. The loaded degrading bacteria use dissolved oxygen for aerobic degradation. The changes in pollutant concentration caused by degradation are continuously monitored by the sensing layer and fed back to the control layer. S5, repeat S2 to S4 until the pollutant concentration drops below the remediation target value; S6, reduce the system operating power to the maintenance level or shut down, capture the immobilized microspheres through the in-well recovery device (net or backwash trap), and reload the recovered microspheres with bacteria after activity testing and reuse them.

[0009] In the above method, the basic oxygen release rate of the oxygen release device is 0.5-2.0 mg / (L·min), and the emergency enhanced oxygen release rate is 3.0-5.0 mg / (L·min); the circulation flow rate of the circulation well is 10-200 L / min, the injection-extraction ratio is dynamically adjusted to 0.95-1.05 by a fuzzy controller, the hydraulic retention time is 2-24 h, and the radius of influence is 5-50 m; The preparation method of the PVA-SA-BC immobilized microbial microspheres includes: mixing polyvinyl alcohol, sodium alginate, biochar and bacterial suspension evenly, dropping them into a crosslinking solution of saturated boric acid and 1-2% (w / v) calcium chloride, crosslinking at room temperature for 4 hours, and then washing with deionized water to obtain the microspheres.

[0010] The beneficial effects of this invention are: 1. This invention uses PVA-SA-BC dual-network hydrogel microspheres to immobilize microorganisms and uses biochar derived from agricultural waste to replace traditional activated carbon as a functional porous filler, overcoming the problems of easy loss and non-recyclability of free microorganisms.

[0011] 2. This invention introduces a multivariate fuzzy controller into a circulating well remediation system for the first time. It uses dissolved oxygen deviation, pollutant concentration change rate, and water level difference between the upper and lower chambers as joint input variables, and simultaneously outputs pump frequency and oxygen release rate adjustment. This realizes real-time bidirectional feedback coupling between circulating well hydraulic parameters and microbial degradation process, enabling hydraulic circulation conditions to be adaptively adjusted according to the actual biochemical needs of microorganisms. This solves the long-standing problem of separation between hydraulic control and degradation process, and significantly improves the system's synergistic efficiency.

[0012] 3. This invention uses biochar instead of activated carbon to construct an immobilized carrier. The multi-level porous structure of biochar is more conducive to microbial attachment and pollutant mass transfer than the single microporous structure of activated carbon. Moreover, the raw material of biochar is agricultural waste, and the preparation temperature is lower than that of activated carbon. While improving the adsorption-degradation performance of the carrier, it reduces the energy consumption and carbon footprint of material preparation, thus achieving carbon reduction at the source in the remediation process.

[0013] 4. This invention constructs a three-in-one low-carbon remediation process with biodegradation as the main component, oxygen release as an auxiliary component, and hydraulic circulation as the transmission link. When dissolved oxygen is insufficient, the fuzzy controller automatically executes a combined strategy of increasing oxygen release and reducing pump speed to extend residence time and improve oxygen utilization efficiency. During the plateau period of pollutant decline, the circulation flow direction is automatically switched to break the mass transfer limitation. No chemical oxidizing agents are required throughout the process, avoiding the secondary pollution risk of chemical oxidation schemes and the carbon emissions caused by continuous consumption of chemical reagents. Attached Figure Description

[0014] Figure 1 The diagram shown is a structural block diagram of the repair system of the present invention; Figure 2 The diagram shown is a schematic representation of the overall process of the method of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Please see Figure 1 and Figure 2 The present invention provides an embodiment: This system first requires determining the well location, depth, screen section location, and packer installation depth of the circulation well based on the site's hydrogeological survey results and pollution plume distribution characteristics. After the circulation well is completed, upper and lower packers are installed at a predetermined depth within the well, dividing the well body into an upper and lower chamber. Screens communicating with the ambient groundwater are installed on the corresponding well walls. A variable frequency pump is installed through the upper and lower packers, enabling it to pump water from the lower chamber to the upper chamber, and can also operate in reverse to achieve a "pumping from the bottom and injecting from the top" mode. The regulating valve group works in conjunction with the pump to ensure dynamic matching of pumping and injecting flow rates. An oxygen release device is installed in the upper chamber or the outflow section of the circulation well, which can use micro-nano aerators or calcium peroxide slow-release devices to release dissolved oxygen into the circulating water.

[0017] Simultaneously with the deployment of the circulating well system, it is necessary to prepare PVA-SA-BC immobilized microbial microspheres. Preparation methods include: The first step is to source biochar from agricultural waste, including but not limited to rice husks, sawdust, corn stalks, and wheat stalks.

[0018] This example uses rice husk biochar: After washing the rice husks with deionized water to remove surface impurities, they are dried in an oven at 80℃ for 24 hours until constant weight. The dried rice husks are then placed in a tube furnace and heated to 500℃ at a rate of 10℃ / min under a nitrogen atmosphere. The pyrolysis is maintained for 2 hours, and the husks are then allowed to cool naturally to room temperature. The resulting biochar is ground and sieved, and the fraction with a particle size of 50-200μm is collected for later use. The preparation temperature of the biochar can be adjusted within the range of 400-700℃ depending on the source of the raw materials and the type of target pollutant. When treating polycyclic aromatic hydrocarbons (PAHs), biochar prepared from sawdust pyrolysis at 600℃ can be used, as it has a higher degree of aromatization and a stronger affinity for hydrophobic organic pollutants.

[0019] The second step is to weigh the following components according to the formula: polyvinyl alcohol (PVA, degree of alcoholysis ≥98%, degree of polymerization approximately 1750±50) 6-10% (w / v), sodium alginate (SA, viscosity ≥200mPa·s) 1-3% (w / v), and biochar (BC, particle size 50-200μm) 2-5% (w / v).

[0020] During preparation, the calculated amount of PVA is slowly added to deionized water and heated and stirred in a 90°C water bath until completely dissolved, forming a transparent, viscous PVA solution. Once the PVA solution cools to 40-50°C, sodium alginate powder is added, and stirring continues until completely dissolved, forming a PVA-SA mixed solution. The pretreated biochar powder is then added to the above mixed solution and stirred at 300-500 rpm for 30 minutes to ensure uniform dispersion of the biochar in the solution. The mixed solution is then cooled to room temperature (25-30°C) for later use.

[0021] The third step involves selecting highly efficient degrading bacterial cultures that have been enriched and acclimatized, based on the target pollutant type. For petroleum hydrocarbon pollution, a complex bacterial culture containing Pseudomonas spp. and Acinetobacter spp. can be used; for polycyclic aromatic hydrocarbon pollution, a naphthalene-degrading bacterial culture enriched and acclimatized on a medium containing naphthalene inorganic salts can be used. The activated bacterial strains are inoculated into liquid culture medium and cultured to the logarithmic growth phase under suitable temperature (25-30℃) and shaking conditions. The bacterial cells are collected by centrifugation, resuspended in sterile physiological saline, and the concentration of the bacterial suspension is adjusted to the OD value. 600 =1.0-2.0. The bacterial suspension should be stored at 4°C before use, and the storage time should not exceed 24 hours.

[0022] Fourth, after cooling the above PVA-SA-BC mixed solution to room temperature, add the prepared bacterial suspension at a ratio of 5-15% (v / v) of the bacterial suspension. Gently stir to ensure that the bacterial suspension and the mixed solution are fully mixed and homogeneous. Note that the stirring speed should not be too fast (preferably 100-200 rpm) to avoid mechanical damage to the bacteria.

[0023] This example uses a dropwise method to prepare microspheres. Specifically, a mixed solution containing bacterial suspension is placed in a constant-pressure dropping device and dropped into a cross-linking solution at a constant rate through a needle with an appropriate orifice (0.8-1.2 mm inner diameter). The cross-linking solution is a mixture of saturated boric acid and 1%-2% (w / v) calcium chloride (CaCl2). After the droplets enter the cross-linking solution, sodium alginate undergoes ionic cross-linking with calcium ions to form a gel network, while polyvinyl alcohol undergoes chemical cross-linking with boric acid to form another network. Together, they construct an interpenetrating hydrogel structure. The microspheres are cross-linked in the cross-linking solution at room temperature for 4 hours to ensure the cross-linking reaction is complete. After cross-linking, the microspheres are repeatedly washed with deionized water 35 times to remove residual cross-linking agent and unreacted substances from the surface. The resulting microspheres have a particle size of 2-5 mm, which can be controlled by adjusting the needle orifice size and dropping rate according to the aquifer permeability coefficient. The prepared immobilized microspheres should be stored under humid conditions at 4°C and used within 48 hours to ensure the activity of the bacterial community.

[0024] Furthermore, the present invention will describe this system in detail: After the circulating well system is deployed and the immobilized microspheres are released into the target aquifer area via injection wells or the circulating wells themselves before circulation begins, the system enters its initial operating state. The initial pump speed is set to 60-80% of the design flow rate to establish a three-dimensional circulating flow field in the aquifer while avoiding excessive hydraulic shear that could adversely affect the microorganisms during the initial attachment period. The oxygen release device operates at a basic oxygen release rate of 0.5-2.0 mg / (L·min), with the specific initial value determined based on the background dissolved oxygen concentration of the groundwater at the site.

[0025] The multi-parameter sensors in the real-time sensing layer begin operating upon system startup. A set of sensors (including at least a dissolved oxygen sensor, an ORP / pH sensor, and a water level sensor) is deployed in both the upper and lower chambers of the circulation well. Additional pollutant concentration sensors (which can employ indirect sensing methods such as UV fluorescence and conductivity, combined with periodic sampling verification) are installed in downstream and surrounding aquifer monitoring wells. Each sensor collects data at preset time intervals (5-15 minutes) and uploads it to the multivariate fuzzy controller in the intelligent control layer via a closed-loop data link.

[0026] Multivariable fuzzy controller with dissolved oxygen deviation e DO The input consists of three variables: (domain of discourse [-5,5] mg / L), pollutant concentration change rate rc (domain of discourse [-20,20] % / h), and water level difference between the upper and lower chambers Δh (domain of discourse [-30,30] cm). Based on a predefined fuzzy rule base and membership function (triangular / trapezoidal membership function, Mamdani-type fuzzy inference, centroid method for fuzzification), the output is the water pump operating frequency adjustment Δf (domain of discourse [-20,20] Hz) and the oxygen release rate adjustment ΔO2 (domain of discourse [-5,5] mg / (L·min)).

[0027] The following describes the typical control logic of a fuzzy controller under specific operating conditions: In scenario one, sensor data shows that the dissolved oxygen concentration drops below 1.0 mg / L, while the pollutant concentration decreases at a slower rate than expected. At this point, the multivariate fuzzy controller determines that microbial activity is limited by dissolved oxygen and outputs control commands. On the one hand, it increases the oxygen release rate to an emergency enhancement level of 3.0-5.0 mg / (L·min); on the other hand, it appropriately reduces the pump speed to prolong the hydraulic residence time of the dissolved oxygen-containing water in the immobilized microsphere distribution area, thereby improving oxygen utilization efficiency and the contact time between microorganisms and pollutants.

[0028] In the second scenario, sensor data shows that the water level difference between the upper and lower chambers exceeds the safe threshold (preferably ±30cm). At this time, the fuzzy controller uses the water level difference as a high-priority input variable and prioritizes outputting instructions to reduce the pump speed or adjust the valve group opening to ensure that the injection-extraction ratio is maintained within the range of 0.95-1.05, preventing abnormal fluctuations in the aquifer water level from adversely affecting the site's hydrological conditions.

[0029] In condition three, sensor data shows sufficient dissolved oxygen concentration (≥2.0 mg / L) and a normal rate of pollutant concentration decrease, indicating that the microbial degradation process is in good condition. At this time, the fuzzy controller tends to output a higher pump speed (increase the pump frequency) to expand the circulation radius, allowing more polluted water to be drawn into the circulation flow field and come into contact with the immobilized microspheres, thus accelerating the overall remediation process.

[0030] Condition 4: Sensor data shows that pollutant concentration has entered a plateau phase (concentration decrease rate remains below the preset threshold (preferably 2% / d) for three consecutive days). This indicates that degradable pollutants in the current circulation path coverage area have been largely depleted, and microbial degradation is limited by the substrate. The fuzzy controller outputs a circulation flow direction switching command, changing the circulation mode from "downward pumping and upward injection" to "upward pumping and downward injection" (or vice versa), changing the water flow path to contact new polluted areas and breaking the mass transfer limitation.

[0031] The four operating conditions mentioned above often involve multiple situations occurring simultaneously or alternating. The advantage of a multivariable fuzzy controller lies in its ability to handle the coupling relationships of multiple input variables simultaneously, outputting coordinated control commands and avoiding decision conflicts that may occur with single-variable control. For example, when low dissolved oxygen and large water level differences occur simultaneously, the controller needs to find the optimal compromise between "oxygenation" and "maintaining balance".

[0032] Driven by the execution layer, circulating water containing dissolved oxygen flows vertically through the immobilized microsphere distribution area in the aquifer. The biochar in the PVA-SA-BC immobilized microspheres, with its multi-level porous structure (coexistence of micropores, mesopores, and macropores), efficiently adsorbs and enriches dissolved organic pollutants through hydrophobic interactions and π-π electron donor-acceptor interactions. The adsorbed and enriched pollutants inside and on the surface of the microspheres are in a high-concentration microenvironment, in close contact with the degrading bacteria loaded on the microsphere pores and surface. The bacteria utilize the dissolved oxygen carried by the circulating water as an electron acceptor to aerobically degrade the enriched pollutants, converting organic pollutants into harmless byproducts such as carbon dioxide, water, and microbial biomass.

[0033] The "adsorption and enrichment" of biochar and the "in-situ degradation" of microorganisms form a positive synergistic effect. Specifically, adsorption concentrates low-concentration dissolved pollutants inside the microspheres, providing a high-concentration substrate environment for the degrading bacteria and increasing the degradation reaction rate. Meanwhile, degradation continuously consumes pollutants inside the microspheres, maintaining the concentration gradient between the inside of the microspheres and the external water body, driving the continuous mass transfer of pollutants from the aqueous phase to the inside of the microspheres. This "adsorption-degradation-re-adsorption" cycle enables the immobilized microspheres to maintain stable repair capabilities during long-term operation, avoiding failure caused by adsorption saturation.

[0034] Changes in pollutant concentrations and dissolved oxygen consumption caused by degradation are continuously monitored in real time by the sensing layer. The data is fed back to the control layer, triggering a new round of regulatory decisions, forming a complete closed loop of perception-decision-execution-feedback. This closed loop continues until the pollutant concentrations at each monitoring point drop below the remediation target value.

[0035] After the repair is completed and the standards are met, reduce the system operating power to a maintenance level or shut down completely. The deployed immobilized microspheres are collected and recovered using in-well recovery devices (such as nets and backwash traps). After being washed with deionized water, samples are taken for activity testing. If more than 70% of the original activity is retained, the microbial community can be reloaded and reused, achieving the recycling of the carrier material and significantly reducing the total life-cycle cost.

[0036] To further verify the effectiveness of this invention, the following comparative experiment was designed. The experiment was conducted in a simulated aquifer sand box with dimensions of 200cm × 100cm × 80cm, filled with quartz sand with a particle size of 0.2-0.5mm and a permeability coefficient of approximately 5 × 10⁻⁶. -4 m / s, simulating the environment of a loose porous aquifer.

[0037] This example sets up four experimental groups, each with three parallel samples. The results are averaged. Specifically: Experimental group 1, using the present invention, PVA-SA-BC immobilized microbial microspheres (PVA 8% + SA 2% + rice husk biochar 3%, bacterial suspension OD 600 =1.5), and the multivariable fuzzy controller intelligently regulates and coordinates with the oxygen release module.

[0038] Experimental group 2 used PVA-SA-activated carbon immobilization carrier to immobilize the same bacterial population. The circulating well was operated at a fixed pump speed (40 rpm), without an oxygen release module or multivariate fuzzy intelligent control.

[0039] Experimental group 3 adopted the method of directly injecting free microorganisms into the aquifer, with the circulating well operating at a fixed pump speed, without setting up an oxygen release module, and without introducing multivariate fuzzy intelligent control.

[0040] Experimental group 4 served as a blank control group, with only the circulating well running hydraulically without the addition of any microorganisms or carrier materials, in order to deduct the decrease in pollutant concentration caused by factors such as hydraulic dilution and volatilization.

[0041] This experiment simulated naphthalene (polycyclic aromatic hydrocarbon) as the pollutant, with an initial concentration of 30 mg / L. The aquifer temperature was controlled at 20±1℃, pH at 7.0±0.2, and salinity at 0.5%. The fuzzy controller settings for Experiment 1 were as follows: dissolved oxygen threshold 1.0 mg / L, pollutant concentration change rate plateau threshold 2% / d, and water level difference safety threshold ±30 cm. The sensor collected data every 10 minutes. The experiment ran continuously for 72 hours, with periodic sampling and monitoring of naphthalene concentration, dissolved oxygen concentration, and microbial activity indicators. The experimental results are shown in the table below: Table 1 Comparison Results

[0042] As shown in Table 1, experimental group 1 achieved a naphthalene removal rate of 97.3% within 72 hours, and only 48 hours were needed to reach a 90% removal rate. The removal rate of experimental group 3 was 42.6%, far lower than that of the two immobilized microbial groups. This verifies the problem that free-state microorganisms are easily lost in aquifers and it is difficult to maintain an effective bacterial concentration. The 12.1% removal rate of experimental group 4 mainly came from the dilution and volatilization caused by hydraulic circulation, further confirming the contribution of biodegradation to the remediation effect of this invention.

[0043] The PVA-SA-BC dual-network hydrogel microspheres of this invention exhibited a breakage rate of only 2.3% under 72 hours of hydraulic scouring, significantly lower than the 6.8% breakage rate of the PVA-SA-activated carbon carrier. This is because the interpenetrating network structure formed by the chemical cross-linking of PVA and the ionic cross-linking of SA endows the microspheres with higher mechanical strength and elasticity, enabling them to maintain good structural integrity under the hydraulic shearing and particle collision conditions of the circulating well, thus reducing the loss and replenishment frequency of the carrier material.

[0044] To further verify the reusability of the immobilized microspheres of this invention, after completing the 72-hour experiment, the microspheres were recovered from experimental group 1, washed with deionized water, and their activity was measured (TTC-dehydrogenase activity method). The microbial community was then reloaded, and a second round of testing was conducted under the same experimental conditions. A total of 6 rounds of cyclic reuse experiments were performed, and the results are shown in the table below: Table 2 Results of Recycling Performance

[0045] As shown in Table 2, after 6 cycles, the PVA-SA-BC immobilized microspheres of this invention maintained a naphthalene removal rate of over 90% after 72 hours, retaining over 75% of the initial activity. The microsphere breakage rate slightly increased from 2.3% to 3.4% after 6 cycles, indicating that the dual-network hydrogel structure has excellent durability. This property allows the carrier material to be recycled multiple times, significantly reducing the material cost and waste generation in remediation projects.

[0046] Furthermore, the following examples illustrate this further: Example 1: In experiments simulating BTEX-contaminated aquifers, the initial total concentration of benzene series compounds was 5-50 mg / L (benzene 10 mg / L, toluene 15 mg / L, ethylbenzene 10 mg / L, xylene 15 mg / L), the simulated aquifer depth was 15-30 m, and the permeability coefficient was 5 × 10⁻⁶. -4 m / s. The system of this invention uses a petroleum hydrocarbon degradation complex microbial community (including Pseudomonas and Acinetobacter). The circulation well adopts the initial mode of "bottom pumping and top injection", with an initial circulation flow rate of 50 L / min and a basic oxygen release rate of 1.0 mg / (L·min).

[0047] On day 7 of operation, the sensor detected a decrease in DO to 0.8 mg / L, and the fuzzy controller automatically increased the oxygen release rate to 2.0 mg / (L·min), while the pump speed decreased to 35 L / min. On day 14 of operation, the BTEX concentration in the downstream 5m monitoring well decreased from 25 mg / L to 8 mg / L. On day 30 of operation, the BTEX concentration in the downstream 5m monitoring well decreased to 1.2 mg / L, and the concentration in the downstream 10m monitoring well decreased to 3.5 mg / L. On day 45 of operation, the BTEX concentration in both monitoring wells was below 0.5 mg / L, achieving the remediation target. The overall removal rate exceeded 95%. Compared with a chemical oxidation scheme of the same scale (Fenton reagent injection), the carbon emissions of this invention are reduced by approximately 60% (mainly due to biochar replacing activated carbon and reducing carbon emissions from chemical reagent production and transportation). The microsphere recovery rate exceeded 85%, and the recovered microspheres retained more than 70% of their original activity after activity testing.

[0048] Example 2: In experiments simulating PAHs-contaminated aquifers at a coking plant site, the initial total PAH concentration was 1-10 mg / L (naphthalene as the main component, phenanthrene as the minor component), and the aquifer depth was 10-25 m. The microbial strain was replaced with naphthalene-degrading bacteria (enriched and acclimatized using a naphthalene-containing inorganic salt culture medium), and the biochar source was adjusted to 600℃ pyrolysis of sawdust (resulting in higher aromaticity and stronger affinity for hydrophobic PAHs). The circulating wells employed a "top-pump, bottom-injection" model, utilizing the vertical distribution characteristic of higher PAH concentrations in the upper part of the aquifer.

[0049] The initial circulation flow rate was 30 L / min, and the baseline oxygen release rate was 0.8 mg / (L·min). On day 21 of operation, the fuzzy controller detected a plateau in the pollutant concentration (concentration decrease rate less than 2% / d for three consecutive days) and automatically switched the circulation direction to "bottom pumping and top injection," while simultaneously increasing the pump speed to 45 L / min. This altered the water flow path to reach new contaminated areas and overcome mass transfer limitations. On day 56 of operation, the total PAH concentration dropped below the remediation target value, with a total removal rate exceeding 92%. The circulation direction switch shortened the plateau period duration by approximately 40%, validating the effectiveness of the multivariate fuzzy controller's circulation direction switching strategy in real-world pollution scenarios.

[0050] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An immobilized microorganism coupled with circulating well in-situ low-carbon remediation system, characterized in that, include: The real-time sensing layer includes multi-parameter sensors deployed in the upper and lower chambers of the circulation well and the aquifer monitoring well. These multi-parameter sensors include at least a dissolved oxygen sensor, a pollutant concentration sensor, a redox potential / pH sensor, and a water level sensor, which are used to collect water quality parameters and water level parameters of the aquifer. The intelligent control layer includes a multivariable fuzzy controller and its subordinate pumping balance adjustment module and oxygen release rate adjustment module. The multivariable fuzzy controller takes three variables as input: dissolved oxygen deviation, pollutant concentration change rate and water level difference between the upper and lower chambers. Based on a predefined fuzzy rule base and membership function, it outputs the pump operating frequency adjustment amount and the oxygen release rate adjustment amount. The execution layer includes a variable frequency water pump, a regulating valve group, an oxygen release device, and upper and lower packers. The variable frequency water pump passes through the upper and lower packers and pumps water from the lower chamber to the upper chamber or runs in the reverse direction. The oxygen release device is located in the upper chamber or the outflow section of the circulation well. The repair medium layer includes PVA-SA-BC immobilized microbial microspheres placed in the aquifer. These PVA-SA-BC immobilized microbial microspheres use polyvinyl alcohol and sodium alginate as a double-network gel skeleton and biochar as a functional porous filler, and are loaded with degrading bacteria inside. The real-time sensing layer, intelligent control layer, execution layer, and repair medium layer form a closed-loop data link of perception-decision-execution-feedback. The multivariate fuzzy controller drives the execution layer to adjust the pumping and oxygen release rates based on the data collected by the real-time sensing layer, so that the hydraulic parameters of the circulating well are coupled with the microbial degradation process in real time.

2. The immobilized microorganism coupled circulation well in-situ low-carbon remediation system according to claim 1, characterized in that, The formulation of the PVA-SA-BC immobilized microbial microspheres is as follows: 6-10% (w / v) polyvinyl alcohol, 1-3% (w / v) sodium alginate, 2-5% (w / v) biochar, and 5-15% (v / v) bacterial suspension. The biochar has a particle size of 50-200 μm, and the microspheres have a particle size of 2-5 mm. The microspheres form an interpenetrating network hydrogel structure through chemical cross-linking and ionic cross-linking.

3. The immobilized microorganism coupled circulation well in-situ low-carbon remediation system according to claim 1, characterized in that: The universe of discourse for the input variables of the multivariate fuzzy controller is [-5, 5] mg / L for dissolved oxygen deviation, [-20, 20]% / h for pollutant concentration change rate, and [-30, 30] cm for water level difference between upper and lower chambers; the universe of discourse for the output variables is [-20, 20] Hz for pump frequency adjustment and [-5, 5] mg / (L·min) for oxygen release rate adjustment; the fuzzy inference adopts the Mamdani type, and the centroid method is used for defuzzification.

4. The immobilized microorganism coupled circulation well in-situ low-carbon remediation system according to claim 1, characterized in that, The control logic of the multivariable fuzzy controller includes: When dissolved oxygen is below the minimum threshold required for microbial degradation and the rate of decrease in pollutant concentration is lower than expected, the oxygen release rate is increased and the pump speed is reduced to extend the hydraulic residence time. When the water level difference between the upper and lower chambers exceeds the limit, the pump speed should be reduced or the valve group should be adjusted to ensure pumping balance. When dissolved oxygen is sufficient but pollutant concentration decreases slowly, increase pump speed to expand the circulation radius while maintaining the current oxygen release rate.

5. The immobilized microorganism coupled circulation well in-situ low-carbon remediation system according to claim 1, characterized in that: The basic oxygen release rate of the oxygen release device is 0.5-2.0 mg / (L·min), and the emergency enhanced oxygen release rate is 3.0-5.0 mg / (L·min); the circulation flow rate of the circulation well is 10-200 L / min, the injection-extraction ratio is dynamically adjusted to 0.95-1.05 by a fuzzy controller, the hydraulic retention time is 2-24 h, and the radius of influence is 5-50 m.

6. An in-situ low-carbon remediation method for immobilized microorganisms coupled with circulating wells, employing the immobilized microorganisms coupled with circulating wells in any one of claims 1-5, characterized in that, Includes the following steps: S1. Based on the site hydrogeological survey results and the distribution of the pollution plume, determine the well location, well depth, screen section location and packer installation depth of the circulating well, prepare PVA-SA-BC immobilized microbial microspheres and place them into the target aquifer area, start the circulating well system to establish a three-dimensional circulating flow field of the aquifer; S2, the multi-parameter sensors of the real-time sensing layer collect dissolved oxygen, pollutant concentration trends, oxidation-reduction potential, pH and water level data of the upper and lower chambers at preset time intervals and transmit them to the multivariable fuzzy controller. S3, the multivariate fuzzy controller takes three variables as input: dissolved oxygen deviation, pollutant concentration change rate and water level difference between the upper and lower chambers. Based on the predefined fuzzy rule base and membership function, it simultaneously outputs the pump operating frequency adjustment and oxygen release rate adjustment, which are respectively sent to the frequency converter and oxygen release device for execution, realizing real-time feedback coupling between the hydraulic parameters of the circulating well and the microbial degradation process. S4, circulating water containing dissolved oxygen flows through the immobilized microsphere distribution area in the aquifer. Biochar in the microspheres adsorbs and enriches dissolved organic pollutants, and the degrading bacteria use dissolved oxygen for aerobic degradation. The changes in pollutant concentration caused by degradation are continuously monitored by the sensing layer and fed back to the control layer. S5, repeat S2 to S4 until the pollutant concentration drops below the remediation target value.

7. The method for in-situ low-carbon remediation of immobilized microorganisms coupled with circulating wells according to claim 6, characterized in that, The collaborative control strategy of the multivariate fuzzy controller in S3 includes: When the dissolved oxygen concentration is sufficient and the pollutant decrease rate is normal, a higher pump speed is output to expand the circulation radius. When the dissolved oxygen concentration is low, the pump speed is reduced while the oxygen release rate is increased, thereby prolonging the residence time of dissolved oxygen-containing water in the immobilized microsphere area. When the pollutant concentration enters a plateau period and the rate of concentration decline continues to be lower than the preset threshold, the circulation direction is switched to change the water flow path to contact new polluted areas.

8. The method for in-situ low-carbon remediation of immobilized microorganisms coupled with circulating wells according to claim 6, characterized in that: The preset time interval is 5-15 minutes, and the initial operating pump speed of the circulation well is 60-80% of the design flow rate.

9. The method for in-situ low-carbon remediation of immobilized microorganisms coupled with circulating wells according to claim 6, characterized in that, The method also includes a microsphere recovery step: after the pollutant concentration drops below the remediation target value, immobilized microspheres are captured by an in-well recovery device, and the recovered microspheres are reloaded with microbial communities and put back into use after activity testing.

10. The method for in-situ low-carbon remediation of immobilized microorganisms coupled with circulating wells according to claim 6, characterized in that, The preparation method of the PVA-SA-BC immobilized microbial microspheres includes: mixing polyvinyl alcohol, sodium alginate, biochar and bacterial suspension evenly, dropping the mixture into a crosslinking solution of saturated boric acid and calcium chloride, crosslinking at room temperature for 4 hours, and washing with deionized water; the concentration of calcium chloride in the crosslinking solution is 1-2% (w / v).

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