A combined remediation system for as and vocs groundwater composite pollution

Abstract

The application provides a combined remediation system for As and VOCs groundwater composite pollution. The remediation system comprises a "concave" concrete retaining wall, an aeration system and a gas phase extraction system. The two sides of the concrete retaining wall are outwardly opened, a plurality of aeration wells are distributed in the horizontal retaining wall of the concrete retaining wall, and microbial nutrient liquid injection pipes are distributed on both sides of each aeration well. The aeration system comprises an air compressor arranged on the ground and a plurality of micro-nano aeration heads arranged in each aeration well. The gas phase extraction system comprises a first vacuum pump arranged on the ground and a gas phase extraction outer pipe arranged in each aeration well. The gas phase extraction outer pipe is sleeved outside the plurality of micro-nano aeration heads. The aeration well is provided with an aeration inner pipe and an extraction outer pipe. Aeration makes the dissolved toluene in the groundwater exchange with air, aeration strengthens the microbial activity, and promotes the degradation of As and toluene.

Description

Technical Field

[0001] This invention relates to the field of groundwater pollution remediation technology, specifically a combined biological PRB-photocatalytic aeration well remediation system for groundwater with combined As and VOCs pollution. Background Technology

[0002] In the processes of oil extraction, arsenic mining and smelting, and landfill treatment, arsenic (As) pollution, along with other pollutants (volatile organic compounds (VOCs), such as toluene), forms complex pollutants that leachate into soil. These pollutants, carried by rainwater and surface runoff, wash away, migrate, and infiltrate groundwater, posing a significant threat to the environment, ecology, and human health. Currently, groundwater pollution caused by As and VOCs complex pollutants suffers from limitations such as single remediation efficiency, lack of oxygen and light sources underground, and insufficient microbial activity. Therefore, a comprehensive treatment system capable of overcoming these technological shortcomings is urgently needed.

[0003] Permeable reactive barriers (PRBs) are permeable reactive packing materials placed along the flow path of contaminated groundwater. They remove pollutants through oxidation-reduction, chelation, adsorption, sedimentation, chemical degradation, or biodegradation. For complex pollutants or highly contaminated sites, activated carbon, due to its abundant pore structure and large specific surface area, possesses strong adsorption capacity and can effectively remove organic pollutants from groundwater. Furthermore, microbial agent-based PRBs, i.e., bio-reactive barriers (Bio-PRBs), utilize biodegradation. By adding microbial agents, electron donors / acceptors are provided, synergistically with the packing material to degrade and adsorb pollutants in groundwater. However, a single PRB may not achieve ideal remediation results and needs to be used in conjunction with other technologies.

[0004] Photocatalytic remediation technology utilizes electron-hole pairs generated by semiconductor materials (such as TiO2) under light to oxidize or reduce pollutants into harmless substances. Underground environments lack sunlight, necessitating the introduction of a light source; catalysts may become deactivated due to the adsorption of pollutants or byproducts, requiring periodic regeneration or replacement.

[0005] Aeration well technology involves installing aeration wells underground and using methods such as pressure difference or airlift to create a circulating flow of groundwater within the well, promoting the migration and degradation of pollutants. It can be combined with aeration extraction and microbial remediation; aeration allows dissolved VOCs in the groundwater to exchange with air within the well, which is then extracted for centralized treatment. Aeration also provides oxygen to anaerobic microorganisms underground, accelerating the degradation rate of pollutants.

[0006] Currently, for groundwater pollution caused by combined As and VOCs pollutants, the remediation efficiency for such combined pollution is limited, and there are problems such as lack of oxygen and light sources underground, and insufficient microbial activity. This paper proposes a PRB aeration well photocatalytic combined remediation system and method for groundwater pollution caused by combined As and VOCs. Summary of the Invention

[0007] This invention addresses the problems existing in the prior art by providing a combined remediation system for groundwater contaminated with As and VOCs. This system combines multiple remediation methods, including PRB, aeration wells, and photocatalysis. It can perform oxidation-reduction adsorption and degradation of As and VOCs in groundwater through a microbial permeable reactive barrier, while the aeration extraction system works in conjunction with photocatalysis to further degrade and remediate VOCs.

[0008] To achieve the above-mentioned technical objectives, the present invention provides a combined remediation system for groundwater pollution by As and VOCs. The remediation system includes a U-shaped concrete retaining wall, an aeration system, and a gas phase extraction system. The two sides of the concrete retaining wall open outward to form a concave structure with an opening width greater than the width of the horizontal retaining wall. The concave opening of the concrete retaining wall corresponds to the direction of groundwater inflow. Multiple aeration wells are distributed within the horizontal retaining wall of the concrete retaining wall. The walls of the multiple aeration wells are connected in sequence. Microbial nutrient solution injection pipes are distributed on both sides of each aeration well.

[0009] The aeration system includes an air compressor installed on the ground and multiple micro-nano aeration heads installed in each aeration well. The multiple micro-nano aeration heads are connected to the air compressor through aeration pipes.

[0010] The gas phase extraction system includes a first vacuum pump installed on the ground and a gas phase extraction outer pipe installed in each aeration well. The gas phase extraction outer pipe is sleeved on the outside of multiple micro-nano aeration heads, and its upper and lower ends are closed. A water inlet valve is provided at the position of each micro-nano aeration head on the gas phase extraction outer pipe. Each gas phase extraction outer pipe is connected to the first vacuum pump on the ground. The gas outlet of the first vacuum pump is connected to the activated carbon purification device through the gas outlet pipe, and the extracted gas is transported to the photocatalytic activated carbon purification device.

[0011] The preferred technical solution of this invention is as follows: the concrete retaining wall is made of ordinary silicate cement, the upper end of the concrete retaining wall is 1.0-2.0 m above the groundwater level, and the lower end penetrates the impermeable groundwater layer by 1.5-2.5 m; the length of the retaining walls on both sides of the concrete retaining wall is 1.2-1.6 times the actual length of the pollution plume, and the distribution length of the aeration wells 2 is 0.8-1.0 times the actual length of the pollution plume. The well wall of each aeration well is divided into an upper backfill section, a middle permeable section, and a bottom permeable section from top to bottom. The middle permeable section is filled with microbial permeable reactive wall filler. Each aeration well has a maintenance channel with an impermeable well cover; the upper end of the bottom permeable section of the aeration well is 0.5-1.0 m above the impermeable layer, and the lower end penetrates the impermeable layer by 1.5-2.5 m. The upper end of the middle permeable section is 1.5-2.5 m above the groundwater level.

[0012] A preferred technical solution of the present invention: The photocatalytic activated carbon purification device includes a first VOCs detector, a photocatalytic reaction chamber, a second VOCs detector, an activated carbon purification device, and a third VOCs detector. The outlet of the first vacuum pump is connected to the inlet of the photocatalytic reaction chamber via an outlet pipe. The first VOCs detector is arranged on the outlet pipe between the first vacuum pump and the photocatalytic reaction chamber. A first exhaust pipe is provided near the first VOCs detector on the outlet pipe, and a first valve is provided on the first exhaust pipe. A second valve is provided near the inlet of the photocatalytic reaction chamber on the outlet pipe. The first exhaust pipe is located between the first VOCs detector and the second valve. The outlet of the photocatalytic reaction chamber is connected to the inlet of the activated carbon purification device via a connecting pipe. A second exhaust pipe is provided on the connecting pipe, and a third valve is provided on the second exhaust pipe. A second VOCs detector, a fourth valve, and a second vacuum pump are sequentially arranged on the connecting pipe. The second exhaust pipe is located between the second VOCs detector and the fourth valve. The third VOCs detector is arranged on the exhaust pipe of the activated carbon purification device.

[0013] The preferred technical solution of the present invention is as follows: each microbial nutrient solution injection pipe is embedded in the packing material of the middle permeable section, and the upper end is connected to the microbial nutrient solution storage tank through a connecting pipe. A peristaltic pump and a fifth valve are provided near the outlet of the storage tank through the connecting pipe. The injection of microbial nutrient solution is controlled by the peristaltic pump and the fifth valve. The microbial nutrient solution is obtained by mixing LB medium, mineral salt medium and TSB medium in a volume ratio of 4:1:1 and then diluting it 2 to 4 times.

[0014] The preferred technical solution of this invention is as follows: the filler between the impermeable section, the permeable section, and the backfill section of the aeration well is fixed by a steel cage. The impermeable section is made of ordinary silicate cement, and the main body of the maintenance channel is made of ordinary silicate concrete. The impermeable well cover contains a sealing ring and an HDPE membrane inside. The microbial permeable reactive wall filler is composed of the following substances by mass percentage: 8%-20% functional microorganisms fixed by sodium alginate biochar gel, 15%-25% oxygen slow-release agent, 20%-30% magnetite, and 45%-60% zeolite.

[0015] The preferred technical solution of this invention: The combined remediation system for groundwater pollution by As and VOCs further includes a PLC system. The peristaltic pump, fifth valve, first vacuum pump, air compressor, inlet valve, first VOCs detector, first valve, second valve, second VOCs detector, third valve, fourth valve, second vacuum pump, third VOCs detector, and fifth valve are connected to the PLC system via signal lines. The PLC system controls the peristaltic pump and valves, thereby controlling the injection of microbial nutrient solution. The PLC system also controls the first vacuum pump, air compressor, and inlet valve. When the VOCs detector detects that the toluene concentration exceeds the standard, the PLC system controls the valve to close the inlet valve, isolating the groundwater in the gas phase extraction pipe for separate aeration and extraction treatment. The air compressor is turned on to drive the micro-nano aeration head to generate micro-nano bubbles, converting the toluene VOC pollutant from the liquid phase to the gas phase. The gas is then absorbed and collected by the vacuum pump and purified by the photocatalytic activated carbon purification device for subsequent purification and degradation. When the VOCs detector detects that the toluene concentration meets the emission standards, the PLC system controls the valve to directly discharge the treated gas. After the VOCs detector continuously detects that the toluene concentration meets the emission standards for 5-7 days, the PLC system controls the shutdown of the first vacuum pump, air compressor, and water inlet valve. After treatment in the photocatalytic reaction chamber, when the VOCs detector detects that the toluene concentration meets the emission standards, the PLC system controls the valve to open and close, directly discharging the photocatalyst-treated gas. Conversely, if the VOCs detector detects that the toluene concentration exceeds the standard after treatment in the photocatalytic reaction chamber, the PLC system controls the valve to open and close the second vacuum pump, drawing the photocatalyst-treated gas to an activated carbon purification device for adsorption and purification. After the toluene concentration is detected by the VOCs detector and meets the emission standards, the gas is then discharged.

[0016] A preferred technical solution of the present invention: the functional microorganisms immobilized by the sodium alginate biochar gel are obtained by diluting the concentration of the functional microbial community to 10. 7 CFU / mL-10 8 The solution is prepared by adding 1.5%–3% (w / v) sodium alginate and 3%–5% (w / v) biochar to a 0.15–0.25 mol / L calcium chloride solution. After the sodium alginate gel hardens for 1–2 hours, it is rinsed with water and allowed to air dry in a cool, ventilated place. The functional microbial community consists of a native resistant microbial community, *Pseudomonas*, *Bacillus*, and *Rhodococcus*. The native resistant microbial community is obtained by culturing soil or groundwater samples from contaminated sites using LB medium at 25–30°C and 150–180 rpm.

[0017] The preferred technical solution of the present invention is as follows: During the aeration and extraction process, the PLC system controls the inlet valve to be closed for 20 min to 30 min, and then the inlet valve is opened for 3 min to 5 min. During the aeration and extraction process, the micro-nano aeration head aerates for 3 min to 5 min and then pauses for 5 min to 10 min.

[0018] A preferred technical solution of the present invention is as follows: Multiple partitions are arranged within the photocatalytic reaction chamber, spaced vertically to divide the chamber into multiple cavities. The lower or upper parts of adjacent cavities are connected, and the arrangement of the partitions creates an "S"-shaped gas flow channel within the chamber. A fan and a UV lamp are installed in each cavity of the photocatalytic reaction chamber. A ceramic honeycomb lampshade is fitted over the UV lamp. A bottom groove and a sliding base plate are located at the bottom of the photocatalytic reaction chamber. The fan and UV lamp are connected to a PLC system via signal lines. The sliding base plate has a bottom groove inside, allowing water and dust to fall into it by pulling the plate. The bottom groove can be disassembled for cleaning.

[0019] The preferred technical solution of this invention is as follows: The fans are vertically distributed within the photocatalytic reaction chamber. The ceramic honeycomb lampshade has a photocatalytic coating on its surface. The ceramic honeycomb lampshade is a cylindrical cover with inner and outer holes on its inner and outer walls, respectively, and a hook at the top. The inner and outer holes of the ceramic honeycomb lampshade are connected. The vertically distributed fans in the photocatalytic reaction chamber generate turbulence. The activated carbon purification device consists of multiple layers of activated carbon filters, which can be maintained and replaced via pre-reserved slots on the side.

[0020] The beneficial effects of this invention are:

[0021] (1) The aeration of the aeration well and the oxygen slow-release material in PRB of the present invention provide a high OPR environment for the detoxification of As and the degradation of VOCs, and enhance the activity of aerobic functional microbial community and improve the degradation rate of compound pollutants.

[0022] (2) The aeration system and gas phase extraction system of the present invention adopt a double pipe design to form a closed circulating airflow, which is conducive to the collection of VOC pollutant toluene, reduces the phenomenon of condensation and backflow of toluene on the well wall of the aeration well, and enhances the efficiency of the aeration system and gas phase extraction system for toluene conversion and collection.

[0023] (3) The present invention uses a replaceable ceramic honeycomb lampshade. The porous structure is conducive to the utilization of ultraviolet light source and heat dissipation, and improves the energy consumption efficiency of VOCs reaction degradation. The S-shaped air flow channel and fan generate turbulence, which can effectively make toluene molecules diffuse to the catalyst surface faster and more evenly, and improve the reaction rate.

[0024] (4) The present invention effectively controls the graded treatment of the entire remediation system through the PLC system, and only performs subsequent treatment on pollutants that do not meet the standards, thereby reducing energy consumption and material consumption and improving the overall pollutant degradation efficiency; at the same time, it enhances the degradation effect of complex pollutants through multi-stage treatment. Attached Figure Description

[0025] Figure 1 is a top view of the distribution of the concrete retaining wall and aeration well group in this invention;

[0026] Figure 2 yes Figure 1 Sectional view of AA in the middle;

[0027] Figure 3 This is a schematic diagram of the internal structure of a single aeration well in this invention;

[0028] Figure 4 This is a schematic diagram of the photocatalytic activated carbon purification device in this invention;

[0029] Figure 5 This is a schematic diagram of the activated carbon purification device in this invention;

[0030] Figure 6 This is a schematic diagram of the structure of the ceramic honeycomb lampshade in this invention.

[0031] In the diagram: 1—Concrete retaining wall, 2—Aeration well, 21—Backfill section, 22—Permeable section, 23—Impervious section, 24—Maintenance passage, 3—Microbial nutrient solution injection pipe, 4—Aeration system, 41—Microporous aeration head, 42—Air compressor, 43—Aeration pipe, 5—Gas phase extraction system, 51—Gas phase extraction external pipe, 52—Inlet valve, 53—First vacuum pump, 54—Outlet pipe, 6—PLC system, 7—Photocatalytic activated carbon purification device, 71—First VOCs detector, 72—First valve, 73—Second valve Door, 74—Second VOCs detector, 75—Third valve, 76—Fourth valve, 77—Second vacuum pump, 78—Activated carbon purification device, 79—Third VOCs detector, 711—Connecting gas pipe, 712—First exhaust pipe, 713—Second exhaust pipe, 710—Photocatalytic reaction chamber, 7101—Fan, 7102—UV lamp tube, 7103—Base plate, 7104—Partition plate, 7105—Sliding base plate, 7106—Ceramic honeycomb lamp cover, 8—Storage tank, 9—Peristaltic pump, 10—Fifth valve. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, wherein, the appendix Figures 1 to 6The drawings are for illustrative purposes only and are not intended to be representations of actual products. They should not be construed as limiting the invention. To better illustrate the specific embodiments of the invention, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings. All other specific embodiments obtained by those skilled in the art based on the specific embodiments of the invention without creative effort are within the scope of protection of the invention.

[0033] In the description of this invention, it should be noted that the terms "front," "rear," "upper," "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0034] The embodiment provides a combined remediation system for groundwater contaminated with As and VOCs, such as Figure 1 As shown, the structure includes a U-shaped concrete retaining wall 1. The two side retaining walls of the concrete retaining wall 1 open outwards, forming a concave structure with an opening width greater than the width of the horizontal retaining wall. The concave opening of the concrete retaining wall 1 corresponds to the direction of groundwater inflow, and the length of the two side retaining walls of the concrete retaining wall 1 is 1.2 to 1.6 times the actual length of the pollution plume. Multiple aeration wells 2 are distributed within the horizontal retaining walls of the concrete retaining wall 1, and the distribution length of the aeration wells 2 is 0.8 to 1.0 times the actual length of the pollution plume. The contaminated groundwater can be guided to the PRB through the two side retaining walls of the concrete retaining wall 1, reducing groundwater bypass and ensuring its passage through the reaction medium layer, thereby enhancing the interception capacity of pollutants and improving the pollutant removal efficiency. The walls of multiple aeration wells 2 are connected as one, forming an aeration well group. The arrangement of the well group is perpendicular to the direction of groundwater flow. The joint between the concrete retaining wall 1 and the aeration well group is connected with ordinary silicate concrete. The concrete as a whole is connected with the same material, which can reduce uneven deformation caused by temperature stress or foundation settlement and improve the sealing of joints and corners.

[0035] refer to Figure 2As shown in the AA cross-sectional view, the well wall of the aeration well 2 is divided into three sections: an impermeable section 23 at the bottom, a permeable section 22 in the middle, and a backfill section 21 at the top. The filler material between the three sections is fixed by a steel cage and is filled sequentially from bottom to top. The impermeable section 23 of the aeration well is filled with ordinary silicate cement, the permeable section 22 is filled with microbial permeable reactive wall filler (Bio-PRB), and the backfill section 21 is filled with construction backfill soil. Each aeration well 2 has a maintenance passage 24. The main body of the maintenance passage 24 is poured with ordinary silicate concrete. The entrance of the passage is sealed with an impermeable well cover. The impermeable well cover contains a sealing ring and an HDPE membrane to prevent VOCs from escaping. The maintenance passage 24 facilitates the maintenance of the facilities and passage inside the aeration well 20. The top surface of the impermeable section 23 is 0.5 m-1.0 m higher than the underground impermeable layer, and the lower end of the impermeable section 23 extends 1.5 m-2.5 m into the underground impermeable layer to ensure that pollutants can be effectively intercepted and purified and repaired through the reaction zone of the permeable section 22 in the middle of the aeration well. The upper end of the permeable section 22 is 1.5 m-2.5 m higher than the groundwater level. Firstly, the filling area above the groundwater level is usually an unsaturated zone, which can exchange oxygen with the atmosphere to form an aerobic environment. Secondly, if the water level rises, the originally unsaturated filling area may become saturated, but it can still continue to play a reaction role and prevent pollutants from flowing around.

[0036] In the embodiments, such as Figure 2 As shown, microbial nutrient solution injection pipes 3 are distributed on both sides of each aeration well 2. The microbial nutrient solution injection pipes 3 are buried in the middle permeable packing material, and sieve holes are distributed only in the middle permeable section 22 to deliver microbial nutrient solution. The microbial nutrient solution is obtained by diluting a mixed culture medium (LB medium: mineral salt medium: TSB medium = 4:1:1) 2-4 times. A storage tank 7 is set on the ground to store the microbial nutrient solution. The microbial nutrient solution injection pipes 3 on both sides of each aeration well 2 are connected to the storage tank 8 through connecting pipes. A peristaltic pump 9 and a fifth valve 10 are set near the outlet of the storage tank 8 on the connecting pipes. The injection of microbial nutrient solution is controlled by the peristaltic pump 9 and the fifth valve 10.

[0037] In this embodiment, the microbial permeable reactive barrier (Bio-PRB) packing material of the aeration well 2 is composed of the following substances by mass percentage: 8%-20% functional microorganisms immobilized by sodium alginate biochar gel, 15%-25% oxygen slow-release agent, 20%-30% magnetite, and 45%-60% zeolite. The sodium alginate biochar gel immobilizes microorganisms, forming a three-dimensional network structure to prevent microbial loss and maintain their long-term activity. Simultaneously, the porous structure of the biochar can adsorb toluene and arsenic, reducing pollutant concentration and alleviating the pressure on microbial treatment. The oxygen slow-release agent can be calcium peroxide or MgO2, which can slowly release oxygen, maintaining the aerobic microorganisms' ability to degrade As(III) and toluene (toluene has higher aerobic metabolic efficiency). The continuous release of oxygen by the oxygen slow-release agent maintains biological activity, and the oxygen generation also provides an environment for the oxidative degradation of pollutants. The Fe³⁺ and Fe²⁺ in magnetite (Fe3O4) adsorb As(III) and As(V) through surface complexation and co-precipitation, forming Fe-As complexes (such as ferric arsenate). At the same time, as a conductive mineral, it accelerates electron transfer between microorganisms and pollutants (such as electron donor / acceptor in toluene degradation). The porous structure of zeolite adsorbs toluene (hydrophobic effect) and arsenic (through surface hydroxyl groups), while providing an attachment surface to promote microbial colonization and biofilm formation.

[0038] The functional microbial community consists of native resistant microbial communities, domesticated Pseudomonas, Bacillus, and Rhodococcus. Many studies have shown that Pseudomonas, Bacillus, and Rhodococcus microorganisms can tolerate As(III) and As(V) and can degrade aromatic compounds and petroleum hydrocarbons. Introducing functional microorganisms of Pseudomonas, Bacillus, and Rhodococcus and re-domesticating them with native resistant microbial communities can: 1) promote the division of labor in the degradation of complex pollutants by mixed microbial communities, forming a chain of metabolic pathways and accelerating the degradation rate of As(III) and VOCs; 2) provide an ecological buffer, buffering the decline in activity of exogenous functional microorganisms due to environmental fluctuations.

[0039] The functional microbial community preparation steps in the embodiment are as follows: Step 1: Purification and amplification of functional microorganisms. Pseudomonas was cultured on LB medium, Rhodococcus on mineral salt medium (with 1% diesel added as a carbon source), and Bacillus on TSB medium. The culture conditions were 25℃-30℃ and 150rpm-180rpm. Step 2: Collection and pretreatment of native communities. Soil / groundwater samples were taken from the contaminated site and cultured on LB medium. The culture conditions were 25℃-30℃ and 150rpm-180rpm for 7 days. Step 3: Mixed culture and gradient acclimatization. The mixed culture medium was LB medium: mineral salt medium: TSB medium = 4:1:1. The functional microorganisms (Pseudomonas:Bacillus:Rhodococcus = 1:1:1) and the native community bacterial solution were mixed at a ratio of 1:3 and inoculated into the mixed culture medium at 8% by volume. The mixture was cultured at 25℃-30℃ and 150rpm-180rpm for 3-7 days to obtain the functional microbial community.

[0040] In this embodiment, the acclimatization steps for the functional microbial community are as follows: For the first week of acclimatization, As(III) and toluene are added to the mixed culture medium to concentrations of 20 ppm and 200 ppm, respectively. The mixture is then inoculated into the mixed culture medium at 20% volume and cultured at 25℃-30℃ and 150-180 rpm for 7 days. For the second week of acclimatization, the mixed culture medium is reduced by 30%, and the same volume of sterile water is added. As(III) and toluene are added to concentrations of 40 ppm and 400 ppm, respectively. The functional microbial community acclimatized in the first week is then inoculated into the mixed culture medium at 20% volume. The culture medium was incubated at 25℃-30℃ and 150rpm-180rpm for 7 days. In the third week of acclimatization, the mixed culture medium was reduced by 60%, and an equal volume of sterile water was added. As(III) and toluene were added to concentrations of 60ppm and 600ppm, respectively. The functional microbial community acclimatized in the second week was inoculated into the mixed culture medium at 20% volume and incubated at 25℃-30℃ and 150rpm-180rpm for 7 days. The functional microbial community obtained in the third week of acclimatization was then passaged under the same conditions until it could stably degrade As(III) and toluene. By gradually increasing the concentrations of As(III) and toluene in the culture medium, the functional microbial community was gradually promoted to adapt to high concentrations of pollutants, promoting the enrichment of microorganisms with high degradation capabilities, optimizing the community structure, and improving the stability of the functional microbial community.

[0041] The steps for immobilizing the functional microbial community with sodium alginate biochar gel are as follows: the concentration of the functional microbial community is diluted to 10. 7 CFU / mL-10 8CFU / mL, prepare a 1.5%-3% (w / v) sodium alginate solution and 3-5% (w / v) biochar using the diluted functional microbial community solution, add it dropwise to a 0.15-0.25 mol / L calcium chloride solution, and after the sodium alginate gel hardens for 1-2 hours, rinse with water and let it stand in a cool, ventilated place to air dry naturally to obtain the functional microbial community fixed by sodium alginate biochar gel.

[0042] The embodiment provides a combined remediation system for groundwater contaminated with As and VOCs, such as Figure 2 and Figure 3 As shown, the remediation system also includes an aeration system 4 and a gas phase extraction system 5. The aeration system includes an air compressor 42 installed on the ground and multiple micro-nano aeration heads 41 arranged in each aeration well 2. The multiple micro-nano aeration heads 41 are connected to the air compressor 42 through aeration pipes 43. In this embodiment, three micro-nano aeration heads 41 are located in the middle of the aeration well 2 and are arranged at equal intervals along the vertical direction of the aeration well 2. One micro-nano aeration head 41 is provided in each of the impermeable section 23, the permeable section 22, and the backfill section 21 of the aeration well 2. First, it promotes the degradation of compound pollutants. The complete degradation of toluene depends on the oxidation of aerobic microorganisms. The aeration system continuously supplies oxygen to the groundwater, maintains the dissolved oxygen (DO) concentration in the PRB, activates the metabolic activity of aerobic microorganisms, and accelerates the decomposition of toluene into CO2 and H2O. Dissolved oxygen can directly oxidize As(III) into As(V), which is less toxic and more easily adsorbed, reducing its mobility. Second, it maintains the activity of functional microbial communities. Oxygen, as a highly efficient electron acceptor, supports efficient microbial metabolism, preventing metabolic stagnation or accumulation of intermediate products (such as toxic intermediates produced by toluene degradation) caused by hypoxia; thirdly, it mitigates the risk of reactive barrier clogging. Appropriate aeration can inhibit the formation of excessively thick biofilms, prevent pore blockage of the PRB medium, and maintain permeability.

[0043] In the embodiments, such as Figure 2 and Figure 3 As shown, the gas phase extraction system 5 includes a first vacuum pump 53 installed on the ground and a gas phase extraction outer pipe 51 installed in each aeration well 2. The gas phase extraction outer pipe 51 is sleeved on the outside of multiple micro-nano aeration heads 41, and its upper and lower ports are closed. A water inlet valve 52 is provided on the gas phase extraction outer pipe 51 corresponding to each micro-nano aeration head 41. Water inlet valves 52 are arranged on both sides of each micro-nano aeration head 41. Each gas phase extraction outer pipe 51 is connected to the first vacuum pump 53 on the ground. The gas outlet of the first vacuum pump 53 is connected to the activated carbon purification device 7 through the gas outlet pipe 54, and the extracted gas is transported to the photocatalytic activated carbon purification device 7.

[0044] In the embodiments, such as Figure 4As shown, the photocatalytic activated carbon purification device 7 includes a first VOCs detector 71, a photocatalytic reaction chamber 710, a second VOCs detector 74, an activated carbon purification device 77, and a third VOCs detector 79. The outlet of the first vacuum pump 53 is connected to the inlet of the photocatalytic reaction chamber 710 through an outlet pipe 54. The first VOCs detector 71 is arranged on the outlet pipe 54 between the first vacuum pump 53 and the photocatalytic reaction chamber 710. A first exhaust pipe 712 is provided near the first VOCs detector 71 on the outlet pipe 54, and a first valve 72 is provided on the first exhaust pipe 712. The outlet pipe 54 is located near the inlet of the photocatalytic reaction chamber 710. The part is equipped with a second valve 73, and the first exhaust pipe 712 is located between the first VOCs detector 71 and the second valve 73; the outlet of the photocatalytic reaction chamber 710 and the inlet of the activated carbon purification device 77 are connected by a connecting pipe 711, a second exhaust pipe 713 is provided on the connecting pipe 711, a third valve 75 is provided on the second exhaust pipe 713, and a second VOCs detector 74, a fourth valve 76 and a second vacuum pump 77 are sequentially provided on the connecting pipe 711, the second exhaust pipe 713 is located between the second VOCs detector 74 and the fourth valve 76, and the third VOCs detector 79 is provided on the exhaust pipe of the activated carbon purification device 78.

[0045] In the embodiments, such as Figure 2 As shown, the combined remediation system for groundwater pollution by As and VOCs also includes a PLC system 6. The peristaltic pump 9, the fifth valve 10, the first vacuum pump 53, the air compressor 42, the water inlet valve 52, the first VOCs detector 71, the first valve 72, the second valve 73, the second VOCs detector 74, the third valve 75, the fourth valve 76, the second vacuum pump 77, the third VOCs detector 79, and the fifth valve 10 are connected to the PLC system 6 via signal lines. The PLC system 6 controls the peristaltic pump 9 and the fifth valve 10, thereby controlling the injection of microbial nutrient solution. The PLC system 6 also controls the first vacuum pump 53, the air compressor 42, and the water inlet valve 52.

[0046] When the first VOCs detector 71 detects that the toluene concentration exceeds the standard, the PLC system 6 controls the opening of the second valve 73, the closing of the first valve 72, and the closing of the inlet valve 52, isolating the groundwater in the gas phase extraction outer pipe 51. The air compressor 42 is turned on to drive the micro-nano aeration head 41 to generate micro-nano bubbles, converting the toluene VOC pollutant from the liquid phase to the gas phase. Then, the first vacuum pump 53 absorbs and collects the VOCs through the photocatalytic activated carbon purification device 7 for subsequent purification and degradation. The aeration system and the gas phase extraction system adopt a dual-pipe design. After the water in the gas phase extraction outer pipe 51 is aerated, the VOCs are collected into the air. Naturally, the VOCs concentration in the water phase of the gas phase extraction outer pipe 51 is lower than that in the aeration well. The inner pipe is used for aeration, and the outer pipe is connected to the vacuum pump to extract VOC pollutants, forming a circulating airflow. This is beneficial for the collection of the VOC pollutant toluene, reducing the phenomenon of condensation and backflow into the aeration well 2, and enhancing the efficiency of the aeration system and the gas phase extraction system in the conversion and collection of toluene.

[0047] In this embodiment, the inlet valve 52 is closed for 20-30 minutes for aeration and extraction treatment. Then, the inlet valve 52 is opened for 3-5 minutes, using the concentration difference to introduce the VOC pollutant toluene from the water in the aeration well between the inner aeration pipe 43 and the outer gas extraction pipe 51 for the next round of aeration and gas extraction. During the aeration and extraction treatment, the micro-nano aeration head 41 aerates for 3-5 minutes followed by a 5-8 minute interval.

[0048] After the first VOCs detector 71 detects that the toluene concentration meets the emission standards, the PLC system 6 controls the closure of the second valve 73 and the opening of the first valve 72, allowing the treated gas to be discharged directly through the first exhaust pipe 713. After the first VOCs detector 71 continuously detects that the toluene concentration meets the emission standards for 5-7 days, the PLC system 6 controls the closure of the first vacuum pump 53, the air compressor 42, and the water inlet valve 52.

[0049] When the first VOCs detector 71 detects that the toluene concentration exceeds the standard, the PLC system 6 controls the opening of the second valve 73 and the closing of the first valve 72, extracting the VOC pollutant toluene to the photocatalytic reaction chamber 710 for treatment. After treatment in the photocatalytic reaction chamber 710, the toluene concentration is detected by the second VOCs detector 74. When the toluene concentration detected by the second VOCs detector 74 meets the emission standards, the PLC system 6 controls the opening of the third valve 75 and the closing of the fourth valve 76, directly discharging the photocatalytically treated gas through the second exhaust pipe 713. Alternatively, after treatment in the photocatalytic reaction chamber 710, if the second VOCs detector 74 detects that the toluene concentration exceeds the standard, the PLC system 6 controls the closing of the third valve 75, the opening of the fourth valve 76, and the activation of the second vacuum pump 77, extracting the photocatalytically treated gas to an activated carbon purification device for adsorption and purification. After the toluene concentration is detected by the third VOCs detector 79 and meets the emission standards, the gas is discharged. Through multi-method graded treatment and real-time monitoring of pollutants, treatment efficiency and resource utilization are improved. Graded treatment reduces redundancy: only pollutants that do not meet the standards are subsequently treated, avoiding the need for all pollutants to pass through all devices, thus reducing energy and material consumption; Optimized process: the treatment path is dynamically adjusted based on real-time detection results, ensuring that each device operates only when necessary, improving overall efficiency; Multi-technology synergy and complementarity: multi-stage treatment ensures that pollutants ultimately meet the standards, especially for complex pollutants (such as compound pollution and persistent organic pollutants that are difficult to degrade).

[0050] Referring to Figure 5, the photocatalytic reaction chamber 710 in this embodiment is equipped with multiple partitions 7103. These partitions 7103 are spaced vertically within the photocatalytic reaction chamber 710, dividing it into multiple cavities. The lower or upper parts of adjacent cavities are connected. The arrangement of the partitions 7103 creates an "S"-shaped gas flow channel within the photocatalytic reaction chamber 710. This S-shaped channel significantly increases the gas flow path length within the reactor, prolonging the contact time between toluene gas and the photocatalyst coating. This allows the gas to be reacted with photogenerated electron-hole pairs and reactive oxygen species (such as ·OH, O2). -Oxidative degradation; each compartment of the photocatalytic reaction chamber 710 is equipped with a fan 7101 and a UV lamp 7102. The fans 7101 are distributed vertically within the photocatalytic reaction chamber 710. This arrangement generates turbulence, reduces local toluene accumulation, effectively breaks the gas boundary layer, and allows toluene molecules to diffuse to the catalyst surface more quickly, thereby increasing the reaction rate. A ceramic honeycomb lamp cover 7103 is fitted over the UV lamp 7102. The surface of the ceramic honeycomb lamp cover 7103 is coated with a photocatalytic coating, mainly composed of TiO2 and doped with WO3. At the bottom of the photocatalytic reaction chamber 710, there is a bottom groove 7104 and a sliding bottom plate 7105. The sliding bottom plate 7105 is located at the bottom end of the photocatalytic reaction chamber 710, and its lower side is connected to the bottom groove 7104. Water and dust can be drained into the bottom groove 7104 by pulling the sliding bottom plate 7105. The bottom groove 7104 can be disassembled for cleaning of water and dust. During the dredging and maintenance of the photocatalytic reaction chamber 710, the sliding base plate 7105 can be pulled out to effectively clean up accumulated water and dust.

[0051] In the embodiments, such as Figure 6 As shown, the ceramic honeycomb lampshade 7103 in this embodiment is a cylindrical cover with inner and outer holes on its inner and outer walls, respectively. A hook is provided at the top, and the ceramic honeycomb lampshade 7103 is suspended by the hook. The UV lamp tube 7102 is located inside the ceramic honeycomb lampshade 7103. The inner and outer holes of the ceramic honeycomb lampshade 7103 are connected, allowing ultraviolet light emitted by the UV lamp tube 7102 to pass through. The honeycomb structure of the ceramic honeycomb lampshade 7103 has a large surface area, suitable for loading photocatalysts. The honeycomb channels can prolong the gas residence time, promoting the contact between toluene molecules and the catalyst surface; simultaneously increasing the density of active sites. The porous structure of the ceramic honeycomb lampshade 7103 can increase the propagation path of light within the reactor by reflecting and scattering ultraviolet light, thereby improving photon utilization.

[0052] In this embodiment, both the fan 7101 and the UV lamp 7102 are controlled by the PLC system 6. Both the UV lamp 7102 and the ceramic honeycomb lampshade 7103 can be disassembled, maintained, and replaced. The activated carbon purification device 78, composed of multiple layers of activated carbon filters, can be maintained and replaced via pre-reserved slots on the side. Activated carbon efficiently captures residual toluene molecules through physical / chemical adsorption. The activated carbon unit can be independently disassembled for easy periodic maintenance or adjustment of the adsorption capacity according to the pollution load.

[0053] The above description is merely one embodiment of the present invention, and while it is detailed and specific, it should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A combined remediation system for groundwater contaminated with As and VOCs, characterized in that: The remediation system includes a U-shaped concrete retaining wall, an aeration system, and a gas extraction system. The two sides of the concrete retaining wall open outwards, forming a concave structure with an opening width greater than the width of the horizontal retaining wall. The concave opening of the concrete retaining wall corresponds to the direction of groundwater inflow. Multiple aeration wells are distributed within the horizontal retaining wall of the concrete retaining wall, and the well walls of the multiple aeration wells are connected in sequence. Microbial nutrient solution injection pipes are distributed on both sides of each aeration well. The well wall of each aeration well is divided into an upper backfill section, a middle permeable section, and a bottom impermeable section from top to bottom. The middle permeable section is filled with microbial permeable reactive wall filler. The aeration system includes an air compressor installed on the ground and multiple micro-nano aeration heads installed in each aeration well. The multiple micro-nano aeration heads are connected to the air compressor through aeration pipes. The gas phase extraction system includes a first vacuum pump installed on the ground and a gas phase extraction outer pipe installed in each aeration well. The gas phase extraction outer pipe is sleeved on the outside of multiple micro-nano aeration heads, and its upper and lower ports are closed. A water inlet valve is provided at the position of each micro-nano aeration head on the gas phase extraction outer pipe. Each gas phase extraction outer pipe is connected to the first vacuum pump on the ground. The gas outlet of the first vacuum pump is connected to the photocatalytic activated carbon purification device through the gas outlet pipe, and the extracted gas is transported to the photocatalytic activated carbon purification device. The combined remediation system for groundwater contaminated with As and VOCs also includes a PLC system. During aeration and extraction treatment, the PLC system controls the inlet valve to close for 20 to 30 minutes, followed by opening the inlet valve for 3 to 5 minutes. The concentration difference is used to introduce VOCs from the water in the aeration well into the space between the aeration pipe and the gas phase extraction outer pipe for the next round of aeration and gas phase extraction. During the aeration and extraction treatment, the micro-nano aeration heads aerate for 3 to 5 minutes and then pause for 5 to 10 minutes.

2. The combined remediation system for groundwater contaminated with As and VOCs according to claim 1, characterized in that: The concrete retaining wall is made of ordinary silicate cement. The upper end of the concrete retaining wall is 1.0 to 2.0 m above the groundwater level, and the lower end penetrates the impermeable layer of groundwater by 1.5 to 2.5 m. The length of the retaining walls on both sides of the concrete retaining wall is 1.2 to 1.6 times the actual length of the pollution plume, and the distribution length of the aeration wells is 0.8 to 1.0 times the actual length of the pollution plume. Each aeration well has a maintenance passage with an impermeable cover. The upper end of the bottom impermeable section of the aeration well is 0.5 to 1.0 m above the impermeable layer, and the lower end penetrates the impermeable layer by 1.5 to 2.5 m. The upper end of the middle permeable section is 1.5 to 2.5 m above the groundwater level.

3. A combined remediation system for groundwater contaminated with As and VOCs according to claim 1 or 2, characterized in that: The photocatalytic activated carbon purification device includes a first VOCs detector, a photocatalytic reaction chamber, a second VOCs detector, an activated carbon purification device, and a third VOCs detector. The outlet of the first vacuum pump is connected to the inlet of the photocatalytic reaction chamber via an outlet pipe. The first VOCs detector is installed on the outlet pipe between the first vacuum pump and the photocatalytic reaction chamber. A first exhaust pipe is located near the first VOCs detector on the outlet pipe, and a first valve is installed on the first exhaust pipe. A second valve is located near the inlet of the photocatalytic reaction chamber on the outlet pipe, and the first exhaust pipe is located between the first VOCs detector and the second valve. The outlet of the photocatalytic reaction chamber is connected to the inlet of the activated carbon purification device via a connecting pipe. A second exhaust pipe is installed on the connecting pipe, and a third valve is installed on the second exhaust pipe. A second VOCs detector, a fourth valve, and a second vacuum pump are sequentially installed on the connecting pipe, and the second exhaust pipe is located between the second VOCs detector and the fourth valve. The third VOCs detector is installed on the exhaust pipe of the activated carbon purification device.

4. The combined remediation system for groundwater contaminated with As and VOCs according to claim 3, characterized in that: Each microbial nutrient solution injection pipe is embedded in the packing material of the middle permeable section. The upper end is connected to the microbial nutrient solution storage tank through a connecting pipe. A peristaltic pump and a fifth valve are installed near the outlet of the storage tank on the connecting pipe. The injection of microbial nutrient solution is controlled by the peristaltic pump and the fifth valve. The microbial nutrient solution is obtained by mixing LB medium, mineral salt medium and TSB medium in a volume ratio of 4:1:1 and then diluting it 2 to 4 times.

5. The combined remediation system for groundwater contaminated with As and VOCs according to claim 2, characterized in that: The filling material between the impermeable section, the permeable section, and the backfill section of the aeration well is fixed by a steel cage. The impermeable section is made of ordinary silicate cement, and the main body of the maintenance channel is made of ordinary silicate concrete. The impermeable well cover contains a sealing ring and an HDPE membrane inside. The microbial permeable reactive wall filling material is composed of the following substances by mass percentage: 8%-20% functional microorganisms fixed by sodium alginate biochar gel, 15%-25% oxygen slow-release agent, 20%-30% magnetite, and 45%-60% zeolite.

6. The combined remediation system for groundwater contaminated with As and VOCs according to claim 4, characterized in that: The peristaltic pump, fifth valve, first vacuum pump, air compressor, water inlet valve, first VOCs detector, first valve, second valve, second VOCs detector, third valve, fourth valve, second vacuum pump, third VOCs detector, and fifth valve are respectively connected to the PLC system via signal lines. The PLC system controls the peristaltic pump and fifth valve, thereby controlling the injection of microbial nutrient solution. The PLC system also controls the first vacuum pump, air compressor, and water inlet valve.

7. A combined remediation system for groundwater contaminated with As and VOCs according to claim 5, characterized in that: The functional microorganisms immobilized by the sodium alginate biochar gel are obtained by diluting the concentration of the functional microbial community to 10. 7 CFU / mL-10 8 CFU / mL, prepared by adding 1.5%–3% (w / v) sodium alginate solution and 3–5% (w / v) biochar to a diluted functional microbial community solution, then adding this solution dropwise to a 0.15–0.25 mol / L calcium chloride solution. After the sodium alginate gel hardens for 1–2 hours, it is rinsed with water and allowed to air dry naturally in a cool, ventilated place. The functional microbial community consists of a native resistant microbial community. Pseudomonas Pseudomonas spp. Bacillus Bacillus spp. Rhodococcus The domesticated composition of Rhodococcus is described as follows: the native resistant microbial community is obtained by taking soil or groundwater samples from contaminated sites and culturing them on LB medium at 25℃~30℃ and 150rpm~180rpm.

8. A combined remediation system for groundwater contaminated with As and VOCs according to claim 6, characterized in that: The photocatalytic reaction chamber is equipped with multiple partitions, which are spaced vertically within the chamber, dividing it into multiple cavities. Adjacent cavities are connected at their lower or upper parts, and the partitions create an "S"-shaped gas flow path within the chamber. Each cavity contains a fan and a UV lamp, with a ceramic honeycomb lampshade covering the UV lamp. The bottom of the chamber has a base groove and a sliding base plate. The fan and UV lamp are connected to a PLC system via signal lines.

9. A combined remediation system for groundwater contaminated with As and VOCs according to claim 8, characterized in that: The fans are distributed vertically within the photocatalytic reaction chamber. The ceramic honeycomb lampshade has a photocatalytic coating on its surface. The ceramic honeycomb lampshade is a cylindrical cover with an inner hole and an outer hole on its inner and outer walls, respectively. A hook is provided at the top. The inner hole and the outer hole of the ceramic honeycomb lampshade are connected.

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