Testing device and method for simulating migration and transformation of pollutants in underground water

Abstract

The invention discloses a test device for simulating migration and transformation of pollutants in underground water. The test device comprises a sand box, a water supply system and a drainage system, the sandbox is internally divided into a water inlet well, a water outlet well and a sand tank; the water inlet well adjusts water head height and is connected with the water supply system; the water supply system, the water inlet well and a passage therebetween are sealed; the sand tank simulates an aquifer soil body and is filled with a soil sample or quartz sand; the water outlet well is connected with a drainage system; the water inlet well and the water outlet well are separated from the sand tank through partition plates, a plurality of through holes are formed in the partition plates, and filter cloth is arranged on the surfaces of the partition plates facing the sand tank. A plurality of pore water sampling holes are formed in the front upper part of the sand tank; a plurality of underground water sampling holes are formed in the front lower part of the sand tank; a plurality of pressure measuring holes connected with a pressure measuring pipe or inserted into a soil moisture tensiometer are formed behind the sand tank; water of the water supply system enters the water inlet well and then permeates into the sand tank filler, water in the filler permeates into the water outlet well, and water of the water outlet well is discharged from the drainage system. Compared with a field test, the material and time cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of simulated soil-groundwater system, and in particular to a test device and method for simulating the migration and transformation of pollutants in groundwater. Background Art

[0002] At present, with the acceleration of industrialization, environmental pollution problems are becoming increasingly serious, especially soil and groundwater pollution, which poses a serious threat to the ecological environment and human health. The migration and transformation of pollutants in the soil-groundwater system is a complex process involving the cross-action of multiple fields such as physics, chemistry, and biology, such as the multi-field coupling effect of hydrodynamic field, chemical field, and biological field. In particular, groundwater level fluctuations caused by irrigation or rainfall are an important process in the hydrological cycle between unsaturated soil and saturated aquifers. It will accelerate the migration, transformation and redistribution of pollutants and further pose potential environmental risks to humans. In the prior art, the migration and transformation of pollutants in the soil-groundwater system are mostly studied by numerical simulation, field experiments, or small-scale laboratory simulations. However, these methods have limitations in simulating the migration and transformation process of pollutants under the coupling of complex multiple fields (such as hydrodynamic field, chemical field, biological field, etc.), and it is difficult to fully and accurately reflect the complex mechanisms in the actual environment. Although numerical simulation can predict trends over a wide range, its accuracy is greatly affected by model parameters and is difficult to verify; field experiments are costly, time-consuming, and complex to operate; and traditional small-scale laboratory experiments often simplify the multi-field conditions and are difficult to reproduce the complex interactive processes in the real environment. Therefore, there is an urgent need for an experimental device that can more realistically and comprehensively simulate the migration and transformation of pollutants under irrigation or rainfall conditions under the multi-field effects of the soil-groundwater system.

[0003] The migration and transformation of pollutants in the natural environment is affected by a variety of physical, chemical and biological processes, such as water flow, solute diffusion, adsorption and desorption, and biodegradation. These processes are interrelated and influence each other, forming a complex multi-field coupling system. Existing technologies often find it difficult to fully and accurately simulate the migration and transformation process of pollutants under such multi-field coupling, resulting in deviations in research results.

[0004] Conditions in the natural environment (such as groundwater level, groundwater flow rate, temperature, pH value, etc.) are often in dynamic change, and these changes have an important impact on the migration and transformation of pollutants. Existing technologies often find it difficult to simulate the behavior of pollutants in this dynamic process in real time and accurately, resulting in research results that are difficult to reflect the actual situation. Achieve high-precision simulation under irrigation and rainfall conditions, including controllable adjustment of water volume, intensity and distribution pattern, to more accurately reflect the hydrological conditions in the actual environment.

[0005] Although on-site monitoring or large-scale testing can obtain relatively accurate data, it is costly, time-consuming, and difficult to repeat. Although numerical simulation is low-cost and time-efficient, its accuracy and reliability are often questioned. Therefore, how to find a balance between comprehensive cost and time efficiency has become an urgent problem to be solved.

[0006] Natural groundwater usually has a low dissolved oxygen content, and its anaerobic conditions can affect the balance of certain chemical substances in the groundwater, such as iron reduction, sulfide formation, and microbial metabolism, all of which may affect the migration and transformation of pollutants. Therefore, simulating the migration and transformation of pollutants in the soil-groundwater system at a laboratory scale, especially under irrigation or rainfall conditions, and maintaining anaerobic conditions for the prepared solution is a key and complex technical issue. Summary of the invention

[0007] The present invention provides a test device and method for simulating the migration and transformation of pollutants in groundwater in order to solve the technical problems existing in the known technology.

[0008] The technical solution adopted by the present invention to solve the technical problems existing in the known technology is:

[0009] A test device for simulating the migration and transformation of pollutants in groundwater, comprising: a sand box, a water supply system for supplying water to the sand box, and a drainage system for discharging water in the sand box; the interior of the sand box is divided into three chambers from left to right, corresponding to a water inlet well, a sand trough, and a water outlet well, and except for the top opening of the sand trough, the four side walls and the upper and lower surfaces of the sand box are sealed; the water inlet well is used to adjust the water head height and is connected to the water supply system, and the water supply system, the water inlet well and the passages therebetween are sealed; the sand trough is used to simulate the soil of the aquifer, and is filled with site soil samples or quartz sand; the water outlet well is connected to the drainage system to allow water to enter the water well. Well; the water inlet well and the water outlet well are separated from the sand trough by a partition, and a plurality of through holes are opened on the partition. A filter cloth is arranged on the surface of the partition facing the sand trough, and the filter cloth is used to prevent the filling in the sand trough from entering the water inlet well and the water outlet well; a plurality of pore water sampling holes are arranged on the upper front part of the sand trough; a plurality of groundwater sampling holes are arranged on the lower front part of the sand trough; a plurality of pressure measuring holes are arranged behind the sand trough, and the pressure measuring holes are connected with pressure measuring tubes or inserted with soil moisture tensiometers; water from the water supply system enters the water inlet well, and infiltrates into the filling of the sand trough from the water inlet well, and the water in the filling infiltrates into the water outlet well, and the water in the water outlet well is discharged from the drainage system.

[0010] Furthermore, quartz sand and clay of different mesh sizes are filled into the sand trough in a certain proportion and order according to the actual soil sediment and aquifer structure of the field site; or soil samples of different depths obtained by sampling the contaminated site are directly used for filling.

[0011] Furthermore, the water supply system includes a circulating water tank, a water inlet regulating tank and a first circulating water pump which are interconnected; the water inlet regulating tank is provided with a first water inlet, a first water outlet and a second water outlet; the first water outlet is provided with a first stop valve; the second water outlet of the water inlet regulating tank is connected to the water inlet well; when the water level in the water inlet regulating tank is lower than the set low water level, the first stop valve is closed, and the water in the circulating water tank flows into the water inlet regulating tank through the circulating water pump; when the water level in the water inlet regulating tank is higher than the set high water level, the first stop valve is opened, and the water in the water in the water inlet regulating tank flows into the circulating water tank through the first water outlet.

[0012] Furthermore, it also includes a first lifting device for lifting the water inlet regulating tank, and the first lifting device includes a manual or electric jack.

[0013] Furthermore, the discharge system includes a water outlet overflow box, a second circulating water pump and a water outlet regulating tank which are interconnected; the water inlet of the water outlet regulating tank is connected to the water outlet well, and the water outlet of the water outlet regulating tank is connected to the water outlet overflow box; the water outlet regulating tank is provided with a second water inlet and a third water outlet; when the water level in the water outlet regulating tank is lower than the set low water level, the water in the water outlet well enters the water outlet regulating tank through the second water inlet; when the water level in the water outlet regulating tank is higher than the set high water level, the water in the water outlet well flows into the water outlet overflow box through the second circulating water pump.

[0014] Furthermore, a rainfall simulation device is provided above the sand box, and the rainfall simulation device includes: a rainfall pump, a flow meter, and rainfall nozzles and a rainfall water distribution plate arranged in sequence from top to bottom; water from the water supply system enters the rainfall nozzles through the rainfall pump, and a flow meter for adjusting the flow rate is connected between the rainfall pump and the rainfall nozzles; the rainfall nozzles are evenly distributed directly above the sand trough; the rainfall water distribution plate is evenly distributed with multiple filter holes, so that the water sprayed by the rainfall nozzles can evenly reach the upper surface of the sand trough.

[0015] Furthermore, it also includes an anaerobic protection system, which includes a nitrogen delivery pipe, a nitrogen protection connecting pipe and a sealing tank; the residual top space of the circulating water tank and the water inlet regulating tank is purged with nitrogen through the nitrogen delivery pipe, and then the sealing cover is used to press the plug, and the circulating water tank and the water inlet regulating tank are connected by the nitrogen protection connecting pipe to ensure that the nitrogen is sealed in the circulating water tank and the water inlet regulating tank.

[0016] Furthermore, it also includes a data acquisition system and a data processing system. The data acquisition system is used to collect data reflecting the physical and chemical characteristics of the aquifer soil, and the data processing system is used to process and analyze the data collected by the data acquisition system; the data acquisition system includes a dissolved oxygen monitoring module, and the dissolved oxygen monitoring module includes a dissolved oxygen membrane and an optical fiber data collector; the dissolved oxygen membrane is pasted on the inner wall of the sand tank near the sampling hole, one end of the optical fiber data collector is connected to the data processing system, and the other end is vertically irradiated to the dissolved oxygen membrane, and the dissolved oxygen data processing system receives the received signal and automatically converts it into dissolved oxygen concentration information according to the temperature and pressure changes during the experiment, thereby realizing in-situ monitoring of the dissolved oxygen concentration.

[0017] The present invention also provides a test method for simulating the migration and transformation of pollutants in groundwater using the test device for simulating the migration and transformation of pollutants in groundwater, the method comprising the following steps:

[0018] Step 1: According to the soil sediment and aquifer structure of the actual field site, the actual field soil sample and water-containing medium are selected as the sand trough filling medium; according to the experimental needs, the natural bulk density of the soil sample and the aquifer medium is filled; or according to the aquifer structure profile of the actual field site, quartz sand and clay of different mesh sizes are filled into the sand trough in a certain proportion and order, and the quartz sand is first acid-washed and alkaline-washed to remove impurities before being filled into the sand trough body; during the sample filling process, the method of filling and compacting layer by layer is adopted;

[0019] Step 2: After the sand tank is filled, deionized water is input into the water inlet well through the water supply system to reach the set water inlet level. During this period, water passes through the baffle until it reaches the aquifer medium filled in the sand tank. When it is fully saturated, the water enters the water outlet well through the porous baffle. When it reaches the set water outlet level, the excess water will flow out through the water outlet well and the water outlet regulating tank to maintain the water level. During the process of the sand tank being saturated with water, the water head in the sand tank rises by 5 cm every time, and water is continued to be supplied after it stabilizes to completely exhaust the air in the sand tank. After the sand tank is saturated with water, water is continued to be supplied.

[0020] Step 3: prepare a water supply solution according to the groundwater chemical indicators measured in the field, inject a sufficient amount of the water supply solution into the circulating water tank, first purge the residual top space of the circulating water tank and the water inlet regulating tank with nitrogen, then use a sealing cover to perform a plug seal, and connect the circulating water tank and the water inlet regulating tank by installing a nitrogen protection connecting pipe to form a closed nitrogen protection environment;

[0021] Step 4: During the experiment, water supply solution is used instead of deionized water to inject into the sand tank, and the height of the water inlet regulating tank and the water outlet regulating tank is adjusted to control the groundwater level and seepage rate; the sampling frequency is set, the seepage rate is tested, and the dissolved oxygen membrane is used to monitor the oxygen concentration in the sand tank in real time. The change rules of other relevant physical and chemical indicators are synchronously monitored through the pore water sampling holes and the groundwater sampling holes; the water head height at each pressure measuring hole is obtained through the pressure measuring device, and the permeability coefficient and hydraulic gradient of each area are calculated;

[0022] Step 5. After the experiment, collect sediment medium samples at each layer and test the change patterns of relevant indicators. Use deionized water instead of tracer solution to continue to pass into the sand tank, control the liquid injection rate, and detect the conductivity of the seepage fluid in the pore water sampling holes and groundwater sampling holes until the conductivity data drops below the background value, indicating that the flushing process has been completed.

[0023] Furthermore, in step 4, the flow direction, flow velocity, and swept area of ​​the water supply solution are tracked by injecting tracers into the sand tank, injecting tracers from the water inlet well, sampling at the water outlet well according to the tracer sampling frequency, monitoring the output of the tracer, and obtaining the tracer output curve, which is then fitted to observe the migration of the tracer and determine the distribution range of the diffusion zone, transition zone, and convection zone, thereby reflecting the law of fluid movement between the water inlet well and the water outlet well;

[0024] Liquid is sampled through the pore water sampling holes and groundwater sampling holes. The liquid sampling time interval is inversely proportional to the seepage velocity. The seepage velocity is calculated by the amount of water discharged from the outlet well of the sand trough. After the samples are collected, the conductivity is measured until the conductivity in the pore water sampling holes and groundwater sampling holes reaches a peak value and remains stable. The acquired data is processed to obtain the concentration changes at different locations at the same time and at different times at the same location, and a concentration contour map is drawn.

[0025] In step five, irrigation or rainfall conditions are simulated, a rainfall sprinkler is set above the sand box to simulate rainfall, and a rainfall water distribution plate with multiple filter holes evenly distributed is set below the rainfall sprinkler, so that the water sprayed by the rainfall sprinkler can evenly reach the upper surface of the sand trough.

[0026] The advantages and positive effects of the present invention are:

[0027] The present invention provides an experimental device for simulating the migration and transformation of pollutants in groundwater, which can adjust experimental parameters according to specific research needs, such as soil type, groundwater flow conditions, type and concentration of pollutants, etc., thereby enhancing the flexibility and applicability of the experiment. Compared with field tests, the device greatly reduces research costs and time costs.

[0028] The present invention utilizes the constant water head device of the water inlet well and the water outlet well to adjust different water levels of the prepared solution, sets the water inlet regulating tank and the water outlet regulating tank as the water head control device, and controls the water level of the sand tank by raising and lowering the water levels of the water inlet regulating tank and the water outlet regulating tank 15, utilizes the peristaltic pump to adjust the flow rate of the prepared solution, and the rainfall device is connected with the flow meter and the speed-regulating peristaltic pump, and the rainfall intensity is accurately adjusted by adjusting the flow rate of the peristaltic pump.

[0029] The present invention can monitor key parameters such as soil structure changes, water flow paths, pollutant distribution and concentration changes in real time by setting detection devices such as dissolved oxygen patches and sensors in the sand trough, and automatically process data through data analysis software to provide an intuitive graphical display, which is convenient for researchers to quickly capture experimental phenomena and laws.

[0030] The present invention can also more accurately simulate the water flow dynamics and pollutant migration process under irrigation and rainfall conditions through a precise irrigation and rainfall simulation system and a sand box structure with good sealing performance.

[0031] The present invention can also adopt nitrogen headspace technology, which can effectively exclude oxygen and maintain anaerobic conditions in groundwater, thereby more accurately evaluating the migration and transformation process of pollutants in an anaerobic environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a front view of a test device for simulating the migration and transformation of pollutants in a prepared solution.

[0033] Figure 2 Connection diagram of the pressure measuring hole on the back of the sand box, the pressure measuring tube and the soil moisture tensiometer of the indoor sand box experimental device for simulating the migration and transformation of pollutants in groundwater.

[0034] Figure 3 Schematic diagram of the structure of the soil moisture tensiometer.

[0035] Figure 4 The invention discloses a dissolved oxygen monitoring module of a test device for simulating the migration and transformation of pollutants in a prepared solution.

[0036] In the figure: 1. circulating water tank; 2. sealing cover of circulating water tank; 3. water inlet of water inlet well; 4. anaerobic protection connecting pipe; 5. first circulating water pump; 6. water inlet well; 7. first water outlet; 8. first water inlet; 9. second water outlet; 10. water inlet regulating tank; 11. sealing cover of water inlet regulating tank; 12. nitrogen supply valve; 13. rainfall nozzle; 14. rainfall water distribution board; 15. water outlet regulating tank; 16. third water outlet; 17. second water inlet; 18. Pore ​​water sampling hole; 19, water outlet well; 20, solution preparation sampling hole; 21, sand trough; 22, second circulating water pump; 23, water outlet overflow box; 24, sand trough discharge port; 25, water outlet of water outlet well; 26, fiber optic data acquisition device; 27, data processing system; 28, dissolved oxygen diaphragm; 29, pressure measuring tube; 30, drain valve; 31, access port; 32, soil moisture tensiometer; 32-1, sealing cover; 32-2, vacuum gauge; 32-3, ceramic tube. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0038] In the description of the present invention, the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention rather than requiring the present invention to be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention. The terms "connected" and "connection" used in the present invention should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate component; it can also be an electrical connection or signal transmission; for those of ordinary skill in the art, the specific meanings of the above terms can be understood according to the specific circumstances.

[0039] See also Figures 1 to 4, a test device for simulating the migration and transformation of pollutants in a prepared solution, comprising: a sand box, a water supply system for supplying water to the sand box, and a drainage system for discharging water in the sand box; the interior of the sand box is divided into three chambers from left to right, corresponding to a water inlet well 6, a sand trough 21 and a water outlet well 19, and except for the top opening of the sand trough 21, the four side walls and the upper and lower surfaces of the sand box are sealed; the water inlet well 6 is used to adjust the water head height and is connected to the water supply system; the water supply system, the water inlet well 6 and the passage between the two are sealed; the sand trough 21 is used to simulate the soil of the aquifer, and is filled with site soil samples or quartz sand; the water outlet well 19 is connected to the drainage system; the water inlet well 6 and the water outlet well 19 are separated from the sand trough 21 by a partition, and a plurality of through holes are opened on the partition, The through hole has a small aperture, which may be 0.1 to 1 mm, and is used for water to infiltrate into or out of the sand trough 21. A filter cloth is provided on the surface of the partition facing the sand trough 21, and the filter cloth is used to prevent the filler in the sand trough 21 from entering the water inlet well 6 and the water outlet well 19; a plurality of pore water sampling holes 18 are provided on the upper front part of the sand trough 21; a plurality of prepared solution sampling holes 20 are provided on the lower front part of the sand trough 21; a plurality of pressure measuring holes are provided on the back of the sand trough 21, and the pressure measuring holes are connected to the pressure measuring tube 29 or inserted into the soil moisture tensiometer 32; a water pressure gauge may be provided on the pressure measuring tube 29; water from the water supply system enters the water inlet well 6, and infiltrates into the filler of the sand trough 21 from the water inlet well 6, and the water in the filler infiltrates into the water outlet well 19, and the water in the water outlet well 19 is discharged from the drainage system.

[0040] According to the experimental requirements, an appropriate number of pore water sampling holes 18 and prepared solution sampling holes 20 are set in front of the sand box to monitor the physical, chemical and biological characteristics of the aquifer soil. According to the experimental requirements, an appropriate number of pressure measuring holes are set behind the sand box to connect the pressure measuring tube 29 or the soil moisture tensiometer 32. The pressure measuring tube can be connected to a pressure gauge, and the pressure gauge is used to monitor the water pressure changes at different positions of the sand box. The soil moisture tensiometer 32 is used to monitor the pressure of the air-filled zone.

[0041] For example, 30 to 50 pore water sampling holes 18 and 30 to 50 solution sampling holes 20 are set on the front of the sand box. According to the experimental requirements, an appropriate number of sampling holes are selected to regularly monitor various physical, chemical and biological indicators. During the experiment, the pore water sampling holes and solution sampling holes are determined based on the relative thickness of the aeration zone and the saturated zone.

[0042] The pressure measuring tube 29 can observe the pressure changes at different positions of the saturated zone in real time based on the principle of the communicating vessel, while the soil moisture tensiometer 32 is mainly used to monitor the pressure changes in the air-filled zone. Figure 3 As shown, some pressure holes of the sand box are connected to the pressure tubes, and the sampling tube of the soil moisture tensiometer 32 is inserted into the pressure tubes.

[0043] The pressure hole is connected to the pressure measuring tube 29, and the pressure changes at different positions of the sand box can be observed in real time according to the communicating vessel principle. The pressure values ​​at different positions of the sand box can be directly determined according to the water level reading of the pressure measuring tube.

[0044] The soil moisture tensiometer 32 consists of a ceramic tube 32-3 with a porous ceramic tip at the bottom, a vacuum gauge 32-2 near the top, and a sealing cap 32-1. The ceramic tube 32-3 is provided with a water inlet hole, and when filled with deoxygenated water and inserted into the soil, water can enter and exit the soil moisture tensiometer 32 through the water inlet hole at the tip. When the soil is dry and water flows out of the soil moisture tensiometer 32, a vacuum (negative pressure) is generated inside the soil moisture tensiometer 32. When the vacuum generated corresponds to the "soil suction", the outflow of water from the soil moisture tensiometer 32 stops. The dial gauge then measures the force required to remove water from the soil, thereby deriving the water potential of the soil.

[0045] Preferably, the sand trough 21 can be filled with quartz sand and clay of different mesh sizes in a certain proportion and order according to the actual field soil sediment and aquifer structure; or the sand trough 21 can be directly filled with soil samples of different depths obtained by sampling the contaminated site.

[0046] Preferably, the water supply system may include a circulating water tank 1, a water inlet regulating tank 10 and a first circulating water pump 5 which are interconnected; the water inlet regulating tank 10 may be provided with a first water inlet 8, a first water outlet 7 and a second water outlet 9; the first water outlet 7 is provided with a first stop valve; the second water outlet 9 of the water inlet regulating tank 10 is connected to the water inlet well 6; when the water level in the water inlet regulating tank 10 is lower than the set low water level, the first stop valve is closed, and the water in the circulating water tank 1 flows into the water inlet regulating tank 10 through the circulating water pump; when the water level in the water inlet regulating tank 10 is higher than the set high water level, the first stop valve is opened, and the water in the water inlet regulating tank 10 flows into the circulating water tank 1 through the first water outlet 7. The water inlet 3 of the water inlet well may be arranged at the bottom of the water inlet well 6.

[0047] Preferably, a first lifting device for lifting the water inlet regulating tank 10 may also be included, and the first lifting device may include a manual or electric jack.

[0048] Preferably, the drainage system may include an outlet overflow box 23, a second circulating water pump 22 and an outlet regulating tank 15 which are interconnected; the water inlet of the outlet regulating tank 15 is connected to the outlet well 19, and the water outlet of the outlet regulating tank 15 is connected to the outlet overflow box 23; the outlet regulating tank 15 is provided with a second water inlet 17 and a third water outlet 16; when the water level in the outlet regulating tank 15 is lower than the set low water level, the water in the outlet well 19 enters the outlet regulating tank 15 through the second water inlet 17; when the water level in the outlet regulating tank 15 is higher than the set high water level, the water in the outlet well 19 flows into the outlet overflow box 23 through the second circulating water pump 22. The outlet 25 of the outlet well may be set at the bottom of the outlet well 19.

[0049] A drain valve 30 is provided at the bottom of the circulating water tank 1 and the water outlet overflow tank 23 .

[0050] Preferably, a second lifting device for lifting the water outlet regulating tank 15 may also be included, and the first lifting device includes a manual jack.

[0051] Preferably, a rainfall simulation device may be provided above the sand box, and the rainfall simulation device may include: a rainfall pump, a flow meter, and a rainfall nozzle 13 and a rainfall water distribution plate 14 arranged in sequence from top to bottom; water from the water supply system enters the rainfall nozzle 13 through the rainfall pump, and a flow meter for adjusting the flow rate is connected between the rainfall pump and the rainfall nozzle 13; the rainfall nozzles 13 are evenly distributed directly above the sand trough 21; the rainfall water distribution plate 14 is evenly distributed with a plurality of filter holes, so that the water sprayed by the rainfall nozzle 13 can evenly reach the upper surface of the sand trough 21.

[0052] Preferably, an anaerobic protection system may also be included, which includes a nitrogen delivery pipe, a nitrogen protection connecting pipe and a sealing tank; the residual top space of the circulating water tank 1 and the water inlet regulating tank 10 is purged with nitrogen through the nitrogen delivery pipe, and then the sealing cover is used to press the plug, and the circulating water tank 1 is connected to the water inlet regulating tank 10 by the nitrogen protection connecting pipe to ensure that the nitrogen is sealed in the circulating water tank 1 and the water inlet regulating tank 10.

[0053] Preferably, a data acquisition system and a data processing system 27 may also be included. The data acquisition system is used to collect data reflecting the physical and chemical characteristics of the aquifer soil. The collected values ​​reflect the changes in the physical and chemical characteristics of the aquifer soil during the experiment. The data processing system 27 is used to process and analyze the data collected by the data acquisition system. The data acquisition system includes a dissolved oxygen monitoring module, and the dissolved oxygen monitoring module includes a dissolved oxygen membrane 28 and an optical fiber data collector 26. The dissolved oxygen membrane 28 is pasted on the inner wall of the sand tank 21 near the sampling hole. One end of the optical fiber data collector 26 is connected to the data processing system 27, and the other end is vertically irradiated to the dissolved oxygen membrane 28. The dissolved oxygen data processing system 27 receives the received signal and automatically converts it into dissolved oxygen concentration information according to the temperature and pressure changes during the experiment, thereby realizing in-situ monitoring of the dissolved oxygen concentration.

[0054] The present invention also provides a test method for simulating the migration and transformation of pollutants in a prepared solution using the test device for simulating the migration and transformation of pollutants in a prepared solution, the method comprising the following steps:

[0055] Step 1, according to the soil sediment and aquifer structure of the actual field site, select the actual field soil sample and water-containing medium as the filling medium of the sand trough 21; according to the experimental needs, fill according to the natural bulk density of the soil sample and the aquifer medium; or according to the aquifer structure profile of the actual field site, quartz sand and clay of different mesh sizes are filled into the sand trough 21 in a certain proportion and order, and the quartz sand is first acid-washed and alkaline-washed to remove impurities before filling into the sand trough 21; different sand filling methods are used according to different types of quartz sand or soil, and the filling height is determined according to different types of quartz sand or soil, and it can be compacted once every 3 to 7 cm filling height; during the sample filling process, a layer-by-layer filling and layer-by-layer compaction method is adopted.

[0056] Step 2. After the sand trough 21 is filled, deionized water is input into the water inlet well 6 through the water supply system to reach the set water inlet water level. During this period, water passes through the baffle until it reaches the aquifer medium filled in the sand trough 21. When it is fully saturated with water, the water enters the water outlet well 19 through the porous baffle. When it reaches the set water outlet level, excess water will flow out through the water outlet well 19 and the water outlet regulating trough 15 to maintain the water level. During the process of the sand trough 21 being saturated with water, the water head in the sand trough 21 rises by 5 cm every time, and water is continued to be supplied after it stabilizes to completely exhaust the air in the sand trough 21. After the sand trough 21 is saturated with water, water is continued to be supplied.

[0057] Step three, prepare the water supply solution according to the chemical indicators of the prepared solution measured in the field. After injecting a sufficient amount of the water supply solution into the circulating water tank 1, firstly purge the residual top space of the circulating water tank 1 and the water inlet regulating tank 10 with nitrogen, and then use the sealing cover to press the plug to seal, and connect the circulating water tank 1 and the water inlet regulating tank 10 by installing a nitrogen protection connecting pipe to form a closed nitrogen protection environment.

[0058] Step 4: During the experiment, water supply solution is used to replace deionized water and injected into the sand tank 21. The height of the water inlet regulating tank 10 and the water outlet regulating tank 15 is adjusted to control the water level and seepage rate of the prepared solution. The water supply system can provide a flow rate of about 0.3 to 1 mL / min, and the prepared solution is continuously injected for 8 to 12 hours to make the internal environment of the sand box uniform and stable. The flow rate, flushing time, etc. can be adjusted according to the type of medium filled.

[0059] Set the sampling frequency, test the seepage velocity, use the dissolved oxygen membrane 28 to monitor the oxygen concentration in the sand tank 21 in real time, and synchronously monitor the changes in other relevant physical and chemical indicators through the pore water sampling hole 18 and the prepared solution sampling hole 20; obtain the water head height at each pressure measuring hole through the pressure measuring device, and calculate the permeability coefficient and hydraulic slope of each area.

[0060] Step 5. After the experiment, collect sediment medium samples at different layers to test the changing patterns of related indicators. Use deionized water instead of tracer solution to continue to pass into the sand tank 21, control the liquid injection rate, and detect the conductivity of the seepage fluid in the pore water sampling hole 18 and the prepared solution sampling hole 20 until the conductivity data drops below the background value, indicating that the flushing process has been completed.

[0061] Preferably, in step 4, the flow direction, flow velocity and swept area of ​​the water supply solution are tracked by injecting a tracer into the sand tank 21, the tracer is injected from the water inlet well 6, and samples are collected at the water outlet well 19 according to the tracer sampling frequency, the output of the tracer is monitored, and the tracer output curve is obtained, and then fitting is performed to observe the migration of the tracer and determine the distribution range of the diffusion zone, transition zone and convection zone, thereby reflecting the fluid movement law between the water inlet well 6 and the water outlet well 19;

[0062] Liquid is sampled through the pore water sampling hole 18 and the groundwater sampling hole 20. The liquid sampling time interval is inversely proportional to the seepage velocity. The seepage velocity is calculated by the amount of water discharged from the outlet well 19 of the sand trough 21. After the samples are collected, the conductivity is measured until the conductivity in the pore water sampling hole 18 and the groundwater sampling hole 20 reaches a peak value and remains stable. The acquired data is processed to obtain the concentration changes at different positions at the same time and at different times at the same position, and a concentration contour map is drawn.

[0063] In step 5, irrigation or rainfall conditions can be simulated, and a rainfall nozzle 13 is set above the sand box to simulate rainfall, and a rainfall water distribution plate 14 with multiple filter holes is evenly distributed below the rainfall nozzle 13, so that the water sprayed by the rainfall nozzle 13 can evenly reach the upper surface of the sand trough 21. The water level of the water inlet well 6 and the water outlet well 19 can be adjusted to adjust the water level of the prepared solution in the soil in the sand trough 21; adjust the flow rate of the prepared solution in the aquifer soil in the sand box; and evenly spray water to the upper surface of the aquifer soil in the sand trough 21 to simulate rainfall.

[0064] The sand box is made of low-permeability, corrosion-resistant materials, and all interfaces of the sand box are sealed with sealants or sealing rings; the sand box can be made of low-permeability, corrosion-resistant materials, and all interfaces of the sand box are sealed with sealants or sealing rings; the air permeability of the sand box is less than 5cm 3 / m 2 ·24h·0.1Mpa material enclosure. For example, organic plastic plate or stainless steel plate enclosure, and adopt sealing measures, except the top opening of the sand trough 21, the surrounding side walls and the upper and lower surfaces of the sand box are all sealed.

[0065] The structure and working principle of the present invention are further described below with reference to a preferred embodiment of the present invention:

[0066] The technical problem to be solved by the present invention is how to accurately simulate the migration and transformation process of pollutants under irrigation or rainfall conditions under the influence of multiple fields of the soil-groundwater system (including hydrodynamics, chemical reactions, microbial effects, etc.) on a laboratory scale, and maintain anaerobic conditions for the prepared solution, so as to better understand and evaluate the migration and transformation behavior of pollutants in the soil-groundwater system.

[0067] In order to solve the above technical problems, the technical solution adopted in this experiment is:

[0068] A test device for simulating the migration and transformation of pollutants in a prepared solution, comprising a sand box, a water supply system for supplying water to the sand box, and a drainage system for discharging water from the sand box; the interior of the sand box is divided into three chambers from left to right, corresponding to a water inlet well 6, a sand trough 21, and a water outlet well 19, and except for the top opening of the sand trough 21, the surrounding side walls and the upper and lower surfaces of the sand box are all sealed; the water inlet well 6 is used to adjust the water head height and is connected to the water supply system; the sand trough 21 is used to simulate aquifer soil, and is filled with site soil samples or quartz sand; the water outlet well 19 is connected to the drainage system; the water inlet well 6 and the water outlet well 19 are separated from the sand trough 21 by a partition, and the partition is opened There are several seepage holes with an aperture of 0.5 mm. A filter cloth is provided on the surface of the partition facing the sand trough 21. The filter cloth is used to prevent the filler in the sand trough 21 from entering the water inlet well 6 and the water outlet well 19; a plurality of pore water sampling holes 18 are provided on the upper front part of the sand trough 21; a plurality of prepared solution sampling holes 20 are provided on the lower front part of the sand trough 21; a plurality of pressure measuring holes are provided behind the sand trough 21, and the pressure measuring holes are connected to the pressure measuring tube 29, on which a water pressure gauge is provided; water from the water supply system enters the water inlet well 6, and seeps into the filler of the sand trough 21 from the water inlet well 6, and the water in the filler seeps out to the water outlet well 19, and the water in the water outlet well 19 is discharged from the drainage system.

[0069] A sand trough discharge port 24 may be provided at the bottom of the sand trough 21, and the sand trough discharge port 24 is equipped with a discharge stop valve.

[0070] The water inlet well 6, the water outlet well 19 and the sand trough 21 can be separated by a plexiglass plate covered with uniform filter holes, and a layer of gauze is attached to the plexiglass plate covered with uniform filter holes to ensure that the prepared solution in the prepared solution box can freely enter and exit the sand box while preventing the quartz sand in the sand box from flowing into the prepared solution box.

[0071] The water supply system includes a circulating water tank 1, a water inlet regulating tank 10 and a first circulating water pump 5 which are interconnected; the water inlet regulating tank 10 is provided with a first water inlet 8, a first water outlet 7 and a second water outlet 9; the first water outlet 7 is provided with a first stop valve; the second water outlet 9 of the water inlet regulating tank 10 is connected to the water inlet well 6; when the water level in the water inlet regulating tank 10 is lower than the set low water level, the first stop valve is closed, and the water in the circulating water tank 1 flows into the water inlet regulating tank 10 through the circulating water pump; when the water level in the water inlet regulating tank 10 is higher than the set high water level, the first stop valve is opened, and the water in the water in the water inlet regulating tank 10 flows into the circulating water tank 1 through the first water outlet 7.

[0072] The first circulating water pump 5 can be a peristaltic pump, and the circulating water tank 1 is used to store the solution required for the experiment. The solution in the water inlet regulating tank 10 enters the water inlet regulating tank 10 after being connected to the peristaltic pump through a catheter, and then is connected to the water inlet 3 of the water inlet well through the water inlet regulating tank 10. The water inlet 3 of the water inlet well is located at the bottom, and the peristaltic pump is used to control the infiltration rate.

[0073] The drainage system includes an outlet overflow box 23, a second circulating water pump 22 and an outlet regulating tank 15 which are interconnected; the outlet overflow box 23 is used to discharge the water in the sand tank 21. The water inlet of the outlet regulating tank 15 is connected to the outlet well 19, and the water outlet of the outlet regulating tank 15 is connected to the outlet overflow box 23; the outlet regulating tank 15 is provided with a second water inlet 17 and a third water outlet 16; when the water level in the outlet regulating tank 15 is lower than the set low water level, the water in the outlet well 19 enters the outlet regulating tank 15 through the second water inlet 17; when the water level in the outlet regulating tank 15 is higher than the set high water level, the water in the outlet well 19 flows into the outlet overflow box 23 through the second circulating water pump 22.

[0074] When the water is passed, the prepared solution for the experiment is input into the water inlet regulating tank 10 from the circulating water tank 1 through the first circulating water pump 5 to reach the set water inlet water level. During this period, the water passes through the porous partition to the quartz sand and soil filled in the sand tank 21. When it is fully saturated with water, the water passes through the porous partition to enter the water outlet regulating tank 15. When it reaches the set water outlet level, the excess water will flow out through the water outlet regulating tank 15 to maintain the water level.

[0075] The water inlet regulating groove 10 and the water outlet regulating groove 15 are used as water head control devices. The water inlet regulating groove 10 and the water outlet regulating groove 15 are installed on both sides of the sand box body, and the water level of the sand tank 21 is controlled by raising and lowering the water level of the water inlet regulating groove 10 and the water outlet regulating groove 15. The water inlet regulating groove 10 is used to inject water into the filler in the sand tank 21, and the water outlet regulating groove 15 is used to discharge the water in the sand tank 21; the water inlet regulating groove 10 and the water outlet regulating groove 15 are both installed with manual jacks, such as jacks composed of a threaded sleeve and a lifting shaft, the lifting shaft is installed with a lifting shaft in the threaded sleeve, the bottom end of the lifting shaft is rotatably installed on a stainless steel base, and a shaft handle is installed on the top side of the lifting shaft. Rotating the lifting shaft drives the water inlet regulating groove 10 or the water outlet regulating groove 15 to move vertically up and down through the threaded sleeve.

[0076] A certain volume of tap water is introduced into the sand trough 21, and the water pressure is used to observe and record whether there is water seepage or leakage at each connection part and surface of the sand trough 21. In this process, special attention should be paid to observe whether the water flow is abnormally seeping along the edge or bottom of the sand trough 21, and whether there are any unusual wet marks. These are key indicators for judging whether the sealing of the sand trough 21 is good. By turning the shaft handle, the working state of the water level control overflow box can be adjusted, and the water level height of the inlet and outlet water can be accurately controlled, thereby simulating the water level fluctuation under different working conditions, and further testing the sealing stability and adaptability of the sand trough 21 under different water pressure conditions.

[0077] The anaerobic protection system consists of a nitrogen delivery pipe, a nitrogen protection connecting pipe and a sealing tank. After adding a sufficient amount of prepared solution to the circulating water tank 1, in order to maintain the anaerobic nature of the prepared solution, the residual top space of the circulating water tank 1 and the water inlet regulating tank 10 is purged with nitrogen, and then the sealing cover is used for plugging. At the same time, the nitrogen protection connecting pipe connects the circulating water tank 1 and the water inlet regulating tank 10 to ensure that the nitrogen is sealed in the circulating water tank 1 and the water inlet regulating tank 10.

[0078] The front end of the sand trough 21 is provided with 70 sampling holes, including 30 pore water sampling holes 18 and 40 prepared solution sampling holes 20. Each sampling hole is equipped with a sampling device, which is used to take out the water in the sand trough 21; the sampling device includes a soil moisture sampler and a syringe. The soil moisture sampler is made of a hydrophilic porous polyester material, including a composite tube with an inner diameter of 1 mm (the inner tube is made of PE and the outer tube is made of PVC), a connector and a protective cover, and can be reinforced with steel wire or nylon material according to sampling requirements. The soil moisture sampler can be directly connected to the syringe, and can automatically collect and filter the pore water solution and the prepared solution by vacuuming, so as to analyze soluble organic matter, heavy metals and other related chemical components, and reflect the migration and accumulation characteristics of pollutants in the sand trough 21 by monitoring the changes in the water chemical environment.

[0079] The rear side wall of the sand trough 21 is provided with 35 pressure measuring holes, which are evenly spaced vertically and horizontally. Each pressure measuring hole is connected to a pressure measuring tube 29, which is used to record the water head height at each pressure measuring hole; each pressure measuring hole is provided with a filter, and each pressure measuring hole is connected to a pressure measuring device, which is used to measure the water head height at each pressure measuring hole. The pressure measuring device includes a bracket frame and a pressure measuring tube 29 with a scale. Vertical pressure measuring tubes 29 corresponding to the pressure measuring holes are arranged at intervals in the bracket frame, and the lower ends of the pressure measuring tubes 29 are located in the same horizontal plane and are provided with access ports 31 at the same height at the lower ends, and each pressure measuring hole is connected to each access port 31 accordingly.

[0080] The rainfall simulation device is used to realize the rainfall process on the top of the sand trough 21. The rainfall simulation device includes a rainfall nozzle 13, a rainfall baffle, a rainfall water distribution plate 14, a rainfall pump and a flow meter. The rainfall nozzles 13 are evenly distributed just above the sand trough 21, and the rainfall pump pumps the water in the circulating water tank 1 into the rainfall nozzles 13 through the flow meter. The flow meter can adjust the rainfall intensity, and the rainfall water distribution plate 14 is covered with uniform filter holes, so that the rainfall reaches the sand trough 21 evenly. The rainfall baffle is used to prevent the water sprayed by the rainfall nozzle 13 from splashing out and ensure the sealing of the entire sand trough main system.

[0081] The dissolved oxygen monitoring module is composed of a dissolved oxygen diaphragm 28, an optical fiber data collector 26 and a dissolved oxygen data processing system 27, wherein the dissolved oxygen diaphragm 28 is pasted on the inner wall of the sand tank 21 near the sampling hole, one end of the optical fiber data collector 26 is connected to the dissolved oxygen data processing system 27, and one end of the optical fiber data collector 26 is vertically irradiated to the dissolved oxygen diaphragm 28. The optical fiber data collector 26 can automatically record the measurement information of the dissolved oxygen diaphragm 28 in real time and transmit the data to the dissolved oxygen data processing system 27. The dissolved oxygen data processing system 27 automatically converts the received signal into dissolved oxygen concentration information according to the temperature and pressure changes during the experiment, thereby realizing in-situ monitoring of the dissolved oxygen concentration.

[0082] A test method for simulating the migration and transformation of pollutants in groundwater using the test device for simulating the migration and transformation of pollutants in groundwater, the method comprising the following steps:

[0083] Pasting of dissolved oxygen diaphragm 28: When pasting the dissolved oxygen diaphragm 28, it is necessary to ensure that the detection surface of the diaphragm is in direct contact with the medium to be measured, and the pasting surface for pasting is firmly adhered to the inner wall of the sand tank 21. After the pasting work is completed, the entire system should be left to stand for 12 hours to ensure that the pasting glue used can be completely dried and achieve the best bonding effect. During this period, any external factors that may interfere with the curing process of the glue should be avoided to ensure the stability of the pasting. When the dissolved oxygen diaphragm 28 comes from the same production batch, only one of the sensors needs to be calibrated according to the attached instructions, and there is no need to calibrate each sensor separately.

[0084] Filling of sand trough 21: Paste gauze on the permeable baffles on both sides of sand trough 21 in advance to prevent medium particles from blocking the permeable holes. According to the soil sediments and aquifer structure of the actual field site, the actual field soil samples and water-containing media can be selected as the filling media of sand trough 21. According to the experimental needs, after certain pretreatment, fill according to the natural bulk density of soil samples and aquifer media; compact once every 5cm filling height to avoid the generation of voids and cracks, and at the same time prevent the generation of preferential flow, so that the medium in sand trough 21 is as close to the actual field soil and aquifer media as possible; according to the aquifer structure profile of the actual field site, quartz sand and clay of different mesh sizes can be filled into sand trough 21 in a certain proportion and order to ensure the authenticity and representativeness of the experimental conditions. Before filling the quartz sand into the sand trough 21, it is first acid-washed and alkaline-washed to remove impurities to reduce the possible interference with the experimental results. During the sample loading process, try to ensure consistent compaction density, and adopt a layer-by-layer filling and compaction method to ensure the compactness and uniformity of each layer of material to avoid differences in fluid migration characteristics caused by uneven compaction density.

[0085] The sand trough 21 is saturated with water: after the sand trough 21 is filled, deionized water is introduced into the water inlet regulating tank 10 through a peristaltic pump, and then input into the water inlet well 6 through the circulating water tank 1 to reach the set water inlet water level. During this period, water passes through the porous partition to the aquifer medium filled in the sand trough 21. When it is completely saturated with water, the water enters the water outlet well 19 through the porous partition. When it reaches the set water outlet level, the excess water will flow out through the water outlet well 19 and the water outlet regulating tank 15 to maintain the water level. During the process of the sand trough 21 being saturated with water, the water head in the sand trough 21 rises by 5 cm every time, and water is continued to be supplied after it stabilizes to completely exhaust the air in the sand trough 21. After the sand trough 21 is saturated with water, water is continued to be supplied.

[0086] Nitrogen headspace: After a sufficient amount of experimental solution is injected into the circulating water tank 1, in order to ensure the maintenance of its anaerobic properties, the nitrogen supply valve 12 of the nitrogen source is first opened to purge the residual headspace of the circulating water tank 1 and the water inlet regulating tank 10 with nitrogen, and then the sealing cover is used for plugging and sealing. At the same time, by installing a nitrogen protection connecting pipe, the circulating water tank 1 and the water inlet regulating tank 10 are effectively connected to form a closed nitrogen protection environment, thereby ensuring the continuous sealing and circulation of nitrogen in the circulating water tank 1 and the water inlet regulating tank 10.

[0087] Tracer collection, testing and processing: Sampling and testing work can be started after the tracer is injected. The sampling time interval is selected according to the seepage velocity. The seepage velocity is calculated by the amount of water discharged from the outlet of the sand trough 21. The faster the seepage velocity, the smaller the sampling time interval is set. Conversely, the time interval can be increased. After the sample is collected, the conductivity is measured until the conductivity in the pore water sampling hole 18 and the prepared solution sampling hole 20 reaches a peak value and remains stable. The acquired data is processed to obtain the concentration changes at different positions at the same time and at different times at the same position, draw a concentration contour map, observe the migration of the tracer and determine the distribution range of the diffusion zone, transition zone and convection zone.

[0088] Flushing of sand trough 21: After the experiment, deionized water is used to replace the tracer solution and continue to be introduced into sand trough 21. The introduction speed is controlled by a water pump. The conductivity of the seepage fluid in the pore water sampling hole 18 and the prepared solution sampling hole 20 is tested until the conductivity data drops below the background value, indicating that the flushing process has been completed.

[0089] Experimental water injection and monitoring: During the experiment, the infiltration water source is prepared according to the water chemical indicators of the prepared solution measured in the field, and the artificially prepared solution is used instead of deionized water to pass into the sand trough 21, and the heights of the water inlet regulating trough 10 and the water outlet regulating trough 15 are adjusted to control the water level and seepage rate of the prepared solution; pollutants can be input into the sand trough 21 at the top of the sand trough 21 by using a peristaltic pump, or pollutants can be directly added to the circulating water tank 1 to reach a preset concentration and enter the sand trough 21 together with the artificially prepared solution.

[0090] Simulation of irrigation or rainfall conditions: A designed rainfall device is used to simulate the rainfall process. A rainfall simulation device is provided above the sand box, and the rainfall simulation device includes: a rainfall pump, a flow meter, and a rainfall nozzle 13 and a rainfall water distribution plate 14 arranged in sequence from top to bottom; water from the water supply system enters the rainfall nozzle 13 through the rainfall pump, and a flow meter for adjusting the flow rate is connected between the rainfall pump and the rainfall nozzle 13; the rainfall nozzles 13 are evenly distributed directly above the sand trough 21; the rainfall water distribution plate 14 is evenly distributed with multiple filter holes, so that the water sprayed by the rainfall nozzle 13 can evenly reach the upper surface of the sand trough 21.

[0091] The rainfall pump adopts a speed-regulating peristaltic pump. The rainfall device is connected to the flow meter and the speed-regulating peristaltic pump. The rainfall intensity is accurately adjusted by adjusting the flow rate of the peristaltic pump. In addition, by rotating the lifting shafts of the water inlet regulating trough 10 and the water outlet regulating trough 15, the water inlet regulating trough 10 and the water outlet regulating trough 15 are moved vertically up and down to change the water level of the prepared solution, simulating the actual field irrigation process.

[0092] Sample collection and testing: During the experiment, the dissolved oxygen membrane 28 is used to monitor the oxygen concentration in the sand trough 21 in real time, the sampling frequency is set, and the seepage rate is tested. During the experiment, sampling is carried out through the pore water sampling hole 18 and the groundwater sampling hole on the front side of the sand trough 21 to simultaneously monitor the changes in other relevant physical and chemical indicators; the water head height at each pressure measuring hole is obtained through the pressure measuring device, and the permeability coefficient and hydraulic gradient of each area are calculated; after the experiment, sediment medium samples are collected in layers to test the changes in relevant indicators.

[0093] The technical problem to be solved by the present invention is how to accurately simulate the migration and transformation process of pollutants under irrigation or rainfall conditions under the influence of multiple fields of the soil-groundwater system (including hydrodynamics, chemical reactions, microbial effects, etc.) on a laboratory scale, and maintain the anaerobic conditions of the prepared solution, so as to better track and evaluate the migration and transformation process of pollutants in the soil-groundwater system.

[0094] The above-mentioned circulating water tank 1, the sealing cover 2 of the circulating water tank, the water inlet 3 of the water inlet well, the anaerobic protection connecting pipe 4, the first circulating water pump 5, the water inlet well 6, the first water outlet 7, the first water inlet 8, the second water outlet 9, the water inlet regulating tank 10, the sealing cover 11 of the water inlet regulating tank, the nitrogen supply valve 12, the rainfall nozzle 13, the rainfall water distribution plate 14, the water outlet regulating tank 15, the third water outlet 16, the second water inlet 17, the pore water sampling hole 18, the water outlet well 19, the prepared solution sampling hole 20, the sand trough 21, the second circulating water pump 22, the water outlet overflow box 23, the sand trough discharge port 24, the dissolved oxygen diaphragm 28, the optical fiber data collector 26, the data processing system 27, the pressure measuring tube 29, the access port 31, the soil moisture tensiometer 32, etc. can all adopt applicable parts and structures in the prior art, or adopt parts and structures in the prior art and adopt conventional technical means to construct.

[0095] The embodiments described above are only used to illustrate the technical ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. The patent scope of the present invention cannot be limited only by this embodiment, that is, any equivalent changes or modifications made to the spirit disclosed by the present invention still fall within the patent scope of the present invention.

Claims

1. A test device for simulating the migration and transformation of pollutants in groundwater, characterized in that: include: A sandbox, a water supply system for supplying water to the sandbox, and a drainage system for draining water from the sandbox; The inside of the sandbox is divided into three chambers from left to right, corresponding to the water inlet well, sand trough and water outlet well. Except for the top opening of the sand trough, the four sides and the upper and lower surfaces of the sandbox are sealed; the water inlet well is used to adjust the water head height and is connected to the water supply system. The water supply system, the water inlet well and the passages between the two are sealed; the sand trough is used to simulate the aquifer soil, which is filled with site soil samples or quartz sand; the water outlet well is connected to the drainage system; the water inlet well and the water outlet well are separated from the sand trough by a partition, and a number of passages are opened on the partition. A filter cloth is arranged on the surface of the partition facing the sand trough, and the filter cloth is used to prevent the filling in the sand trough from entering the water inlet well and the water outlet well; a plurality of pore water sampling holes are arranged on the upper front part of the sand trough; a plurality of groundwater sampling holes are arranged on the lower front part of the sand trough; a plurality of pressure measuring holes are arranged behind the sand trough, and the pressure measuring holes are connected with pressure measuring tubes or inserted with soil moisture tensiometers; water from the water supply system enters the water inlet well, and infiltrates into the filling of the sand trough from the water inlet well, and the water in the filling infiltrates into the water outlet well, and the water in the water outlet well is discharged from the drainage system.

2. The experimental device for simulating the migration and transformation of pollutants in groundwater according to claim 1, characterized in that: The sand trough is filled with quartz sand and clay of different mesh sizes in a certain proportion and order according to the actual soil sediment and aquifer structure of the field site; or it can be filled directly with soil samples of different depths obtained from sampling at the contaminated site.

3. The experimental device for simulating the migration and transformation of pollutants in groundwater according to claim 1, characterized in that: The water supply system includes a circulating water tank, a water inlet regulating tank and a first circulating water pump which are interconnected; the water inlet regulating tank is provided with a first water inlet, a first water outlet and a second water outlet; the first water outlet is provided with a first stop valve; the second water outlet of the water inlet regulating tank is connected to the water inlet well; when the water level in the water inlet regulating tank is lower than a set low water level, the first stop valve is closed, and the water in the circulating water tank flows into the water inlet regulating tank through the circulating water pump; when the water level in the water inlet regulating tank is higher than a set high water level, the first stop valve is opened, and the water in the water in the water inlet regulating tank flows into the circulating water tank through the first water outlet.

4. The test device for simulating the migration and transformation of pollutants in groundwater according to claim 3, characterized in that: It also includes a first lifting device for lifting the water inlet regulating tank, and the first lifting device includes a manual or electric jack.

5. The test device for simulating the migration and transformation of pollutants in groundwater according to claim 1, characterized in that: The discharge system includes an outlet overflow box, a second circulating water pump and an outlet regulating tank which are interconnected; the water inlet of the outlet regulating tank is connected to the outlet well, and the water outlet of the outlet regulating tank is connected to the outlet overflow box; the outlet regulating tank is provided with a second water inlet and a third water outlet; when the water level in the outlet regulating tank is lower than the set low water level, the water in the outlet well enters the outlet regulating tank through the second water inlet; when the water level in the outlet regulating tank is higher than the set high water level, the water in the outlet well flows into the outlet overflow box through the second circulating water pump.

6. The experimental device for simulating the migration and transformation of pollutants in groundwater according to claim 1, characterized in that: A rainfall simulation device is provided above the sand box, and comprises: a rainfall pump, a flow meter, and rainfall nozzles and a rainfall water distribution plate arranged in sequence from top to bottom; water from the water supply system enters the rainfall nozzles through the rainfall pump, and a flow meter for regulating the flow is connected between the rainfall pump and the rainfall nozzles; the rainfall nozzles are evenly distributed directly above the sand trough; the rainfall water distribution plate is evenly distributed with a plurality of filter holes, so that the water sprayed by the rainfall nozzles can evenly reach the upper surface of the sand trough.

7. The experimental device for simulating the migration and transformation of pollutants in groundwater according to claim 1, characterized in that: It also includes an anaerobic protection system, which includes a nitrogen delivery pipe, a nitrogen protection connecting pipe and a sealing tank. The residual top space of the circulating water tank and the water inlet regulating tank is purged with nitrogen through the nitrogen delivery pipe, and then the sealing cover is used to press the plug. At the same time, the circulating water tank and the water inlet regulating tank are connected with the nitrogen protection connecting pipe to ensure that the nitrogen is sealed in the circulating water tank and the water inlet regulating tank.

8. The test device for simulating the migration and transformation of pollutants in groundwater according to claim 1, characterized in that: It also includes a data acquisition system and a data processing system. The data acquisition system is used to collect data reflecting the physical and chemical characteristics of the aquifer soil, and the data processing system is used to process and analyze the data collected by the data acquisition system; the data acquisition system includes a dissolved oxygen monitoring module, and the dissolved oxygen monitoring module includes a dissolved oxygen membrane and an optical fiber data collector; the dissolved oxygen membrane is pasted on the inner wall of the sand tank near the sampling hole, one end of the optical fiber data collector is connected to the data processing system, and the other end is vertically irradiated to the dissolved oxygen membrane, and the dissolved oxygen data processing system receives the received signal and automatically converts it into dissolved oxygen concentration information according to the temperature and pressure changes during the experiment, thereby realizing in-situ monitoring of the dissolved oxygen concentration.

9. A test method for simulating the migration and transformation of pollutants in groundwater using the test device for simulating the migration and transformation of pollutants in groundwater according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: Step 1: According to the soil sediment and aquifer structure of the actual field site, the actual field soil sample and water-containing medium are selected as the sand trough filling medium; according to the experimental needs, the natural bulk density of the soil sample and the aquifer medium is filled; or according to the aquifer structure profile of the actual field site, quartz sand and clay of different mesh sizes are filled into the sand trough in a certain proportion and order, and the quartz sand is first acid-washed and alkaline-washed to remove impurities before being filled into the sand trough body; during the sample filling process, the method of filling and compacting layer by layer is adopted; Step 2: After the sand tank is filled, deionized water is input into the water inlet well through the water supply system to reach the set water inlet level. During this period, water passes through the baffle until it reaches the aquifer medium filled in the sand tank. When it is fully saturated, the water enters the water outlet well through the porous baffle. When it reaches the set water outlet level, the excess water will flow out through the water outlet well and the water outlet regulating tank to maintain the water level. During the process of the sand tank being saturated with water, the water head in the sand tank rises by 5 cm every time, and water is continued to be supplied after it stabilizes to completely exhaust the air in the sand tank. After the sand tank is saturated with water, water is continued to be supplied. Step 3: prepare a water supply solution according to the groundwater chemical indicators measured in the field, inject a sufficient amount of the water supply solution into the circulating water tank, first purge the residual top space of the circulating water tank and the water inlet regulating tank with nitrogen, then use a sealing cover to perform a plug seal, and connect the circulating water tank and the water inlet regulating tank by installing a nitrogen protection connecting pipe to form a closed nitrogen protection environment; Step 4: During the experiment, water supply solution is used instead of deionized water to inject into the sand tank, and the height of the water inlet regulating tank and the water outlet regulating tank is adjusted to control the groundwater level and seepage rate; the sampling frequency is set, the seepage rate is tested, and the dissolved oxygen membrane is used to monitor the oxygen concentration in the sand tank in real time. The change rules of other relevant physical and chemical indicators are synchronously monitored through the pore water sampling holes and the groundwater sampling holes; the water head height at each pressure measuring hole is obtained through the pressure measuring device, and the permeability coefficient and hydraulic gradient of each area are calculated; Step 5. After the experiment, collect sediment medium samples at each layer and test the change patterns of relevant indicators. Use deionized water instead of tracer solution to continue to pass into the sand tank, control the liquid injection rate, and detect the conductivity of the seepage fluid in the pore water sampling holes and groundwater sampling holes until the conductivity data drops below the background value, indicating that the flushing process has been completed.

10. The test method for simulating the migration and transformation of pollutants in groundwater according to claim 9, characterized in that: In step 4, the flow direction, flow velocity and swept area of ​​the water supply solution are tracked by injecting tracers into the sand tank, injecting tracers from the water inlet well, sampling at the water outlet well according to the tracer sampling frequency, monitoring the output of tracers, and obtaining the tracer output curve, which is then fitted to observe the migration of tracers and determine the distribution range of the diffusion zone, transition zone and convection zone, thereby reflecting the fluid movement law between the water inlet well and the water outlet well; Liquid is sampled through the pore water sampling holes and groundwater sampling holes. The liquid sampling time interval is inversely proportional to the seepage velocity. The seepage velocity is calculated by the amount of water discharged from the outlet well of the sand trough. After the samples are collected, the conductivity is measured until the conductivity in the pore water sampling holes and groundwater sampling holes reaches a peak value and remains stable. The acquired data is processed to obtain the concentration changes at different locations at the same time and at different times at the same location, and a concentration contour map is drawn. In step five, irrigation or rainfall conditions are simulated, a rainfall sprinkler is set above the sand box to simulate rainfall, and a rainfall water distribution plate with multiple filter holes evenly distributed is set below the rainfall sprinkler, so that the water sprayed by the rainfall sprinkler can evenly reach the upper surface of the sand trough.

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