Simulation device for nitrogen migration and transformation

Abstract

The invention provides a simulation device for nitrogen migration and transformation, which comprises an input unit, a simulation unit, a biological unit, a regulation and control unit and a data processing unit, and is characterized in that the input unit is used for simulating migration of a nitrogen source input downstream river to a surrounding area; the simulation unit comprises a riverway simulation mechanism, an intersection triangular area simulation groove, a main stream first side bank simulation groove and a main stream second side bank simulation groove, and the biological unit controls soil structures / particles through carbon source regulation and control and oxygen content regulation and control so as to achieve the purpose of controlling the aerobic / anaerobic subarea and the nitrification / denitrification subarea; the regulation and control units are arranged in the intersection triangular area simulation tank, the main stream first side bank simulation tank and the main stream second side bank simulation tank respectively and used for regulating and controlling dissolved oxygen, PH and conductivity, and the data processing unit is used for giving a prediction result. The problem that a traditional water tank cannot simulate the interaction of two rivers is solved, and the accuracy of a simulation experiment is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nitrogen migration and transformation simulation devices, and particularly relates to a nitrogen migration and transformation simulation device. BACKGROUND

[0002] Water pollution has become an important limiting factor for the sustainable development of human society. Due to the rapid economic development and urban population activities, a large amount of industrial wastewater and urban domestic sewage is discharged into rivers, leading to further deterioration of river and coastal groundwater quality. Globally, the amount of nitrogen fertilizer applied to farmland is as high as 120 million tons per year, plus organic fertilizer and biological nitrogen fixation, the total input is about 200 million tons. However, the utilization rate of nitrogen fertilizer by crops is less than 50%, and the excess nitrogen enters the water body through runoff, becoming a major source of pollution. At the same time, nitrogen oxides discharged by industry and traffic exhaust are important sources of atmospheric nitrogen pollution, especially in rapidly urbanizing areas. Meanwhile, the interaction zone refers to the water-saturated sediment layer below the river bed and extending to the riparian zone and both sides. As the area of mutual exchange and mixing of river water and groundwater, the interaction zone has a certain natural purification capacity and good effect on the removal of pollution in river water and groundwater.

[0003] The confluence zone is the connection point of different river systems. Its specific hydrodynamic characteristics can greatly affect the migration and distribution of pollutants, and further affect the growth of microorganisms and biogeochemical processes. Due to the difference in density and flow rate between the tributaries and the main stream, a low-flow backflow zone or separation zone appears, and the water flow forms eddies or counterflows in this area, resulting in energy loss, sediment deposition and pollutant retention. At the same time, the velocity difference between the two water flows at the intersection forms a shear layer, leading to enhanced water flow turbulence and intense mixing. This phenomenon has an important influence on the diffusion of pollutants and the transport of sediment. The difference in dissolved oxygen and pH between the two rivers will directly affect the composition and structure of microorganisms in the confluence zone, thereby further affecting the migration and transformation of nutrients such as nitrogen and phosphorus. In the river confluence zone, especially in the backflow zone, the increase in water retention time and the decrease in flow rate promote the deposition and retention of pollutants. The increase in the content of pollutants or nutrients in the sediment makes these areas high-risk areas of eutrophication, and the accumulation of nutrients promotes the growth of phytoplankton, which may lead to water blooms and other ecological problems.

[0004] The interaction zone at the river intersection is significantly different from the normal river interaction zone, mainly in terms of hydrodynamic characteristics, chemical properties, ecological functions and spatial range. The hydrodynamic conditions at the intersection are complex, affected by the flow rate, flow and water level fluctuations of the two rivers, and the exchange process between surface water and groundwater is more frequent, and multidirectional flow may occur. Secondly, the chemical conditions are more diverse, and the two rivers may carry different nutrients, dissolved ions or pollutants, forming a mixed reaction zone at the intersection.

[0005] As one of the means of assisting scientific research, scientific research not only has higher requirements for flexibility in the simulation process and accuracy of the simulation results. A large amount of data simulated through a physical model (simulation device) often needs to be combined with a mathematical model to extract scientific elements in the data and solve the scientific problems under study. Further research requires fitting of past data and prediction of the future. Taking a traditional nitrogen conversion prediction method as an example, existing methods mainly include: traditional supervised learning methods (such as linear regression fitting method, decision tree, and random forest), which have the advantages of strong interpretability and fast and convenient processing of simple problems, but still have the disadvantages of easy overfitting and being easily affected by complex environments; deep learning methods (artificial neural network ANN, recurrent neural network RNN / long short-term memory network LSTM), which process any complex function through machine learning of a large sample.

[0006] Existing seepage tank simulation boxes mainly simulate the migration of nutrient salts in the interaction zone under a main stream or a branch stream, and reflect limited geophysical and chemical processes. In view of the scientific problems of nitrogen migration and transformation in the confluence area of the two rivers, the present application provides a simulation device for nitrogen migration and transformation. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a simulation device for nitrogen migration and transformation to solve the problems raised in the background art in view of the deficiencies of the prior art.

[0008] To solve the above technical problems, the technical scheme adopted by the present application is: a simulation device for nitrogen migration and transformation, comprising; An input unit, which inputs the prepared nitrogen simulation liquid into the simulation unit through a water pump, so as to simulate the migration of the nitrogen source input into the downstream river to the surrounding area; A simulation unit, which comprises a river channel simulation mechanism, an intersection triangular area simulation tank, a main stream first side bank simulation tank, and a main stream second side bank simulation tank; The river channel simulation mechanism is used to simulate the main stream and the branch stream of the river channel, the intersection triangular area simulation tank is arranged at the intersection of the main stream and the branch stream, and the main stream first side bank simulation tank and the main stream second side bank simulation tank are arranged on the two sides of the main stream, respectively. A biological unit, which is used to control the aerobic / anaerobic partition and the nitrification / denitrification partition by controlling the carbon source, controlling the oxygen content, and controlling the soil structure / particle. The dissolved oxygen in the water body can be controlled by stirring the water body in the water tank or by flushing inert gas, and the migration of nitrogen in two different environments can be monitored by burying a sampler in the aerobic / anaerobic partition; secondly, the C / N ratio of the simulation liquid can be adjusted to 10:1~20:1 to promote / limit the denitrification behavior. When the non-homogeneous soil is filled, the uneven distribution of porosity will change the transmission of oxygen and nutrients and thus change the distribution of microorganisms; The carbon source regulation controls the soil structure / particle, so as to control the aerobic / anaerobic partition and nitrification / denitrification partition. The carbon source regulation promotes / limits the denitrification behavior by regulating the carbon-nitrogen element ratio in the simulation liquid, the simulation liquid with different concentration ratios is added to the input unit, the C / N ratio of the simulation liquid is adjusted to 10:1~20:1, the composition of the simulation tank is controlled, the homogeneous soil is filled in the geological unit in the simulation tank, the aerobic partition is formed at 0~-10cm from the surface layer of the geological unit, and the remaining part of the geological unit is the anaerobic partition; when the non-homogeneous soil is filled, the uneven distribution of porosity will change the oxygen and nutrient transmission simultaneously, so as to change the distribution of microorganisms; at the same time, the pore water samplers are embedded in the aerobic partition and the anaerobic partition, the pore water samplers are connected to the output module, the change of nitrogen compounds in the pore water is analyzed, and the migration of nitrogen in the two different environments is monitored; The regulation unit is arranged in the intersection triangular area simulation tank, the first side bank simulation tank of the main stream and the second side bank simulation tank of the main stream, and is used for regulating dissolved oxygen, PH and conductivity. The data processing unit includes a monitoring terminal and a computer, the monitoring terminal is arranged in the simulation unit, the monitored data is transmitted to the computer, the computer is provided with an LSTM neural network model, the data is learned by the LSTM neural network model, and a prediction result is given.

[0009] As a further description of the application, the riverway simulation mechanism includes a main stream water tank, and a main stream water tank is connected with a main stream water tank at the water inlet end; The branch water tank is connected with a branch water tank at the water inlet end; The branch water tank is connected with a main stream water tank at one side; The confluence water tank is movably connected with the tail end of the main stream water tank, and the tail end of the confluence water tank is connected with a wastewater tank.

[0010] As a further description of the application, the communication path of the main stream water tank and the main stream water tank and the communication path of the branch water tank and the branch water tank are provided with flow valves, and a plurality of river sampling ports are arranged on the branch water tank.

[0011] As a further description of the application, the intersection triangular area simulation tank includes a first movable water baffle, a first water baffle and a first glass bottom plate, the first water baffle is provided with two, the two first water baffles are rotatably connected on the torsional spring hinge to form a zigzag structure, the zigzag structure is installed on the first glass bottom plate, and the first movable water baffle is movably connected at the opening end of the zigzag structure to form a sand tank structure with an open top end, and a plurality of adjustable bases are installed at the bottom end of the first glass bottom plate.

[0012] As a further illustration of the present application, the angle of the fold angle of the fold line type structure can be adjusted within 20~60°, and the length of the first movable waterproof baffle 30 is 30~60cm.

[0013] As a further illustration of the present application, the first movable waterproof baffle is also provided with a plurality of first water outlets and first water level control water heads, the first water outlet is connected with a pore water sampler, the collection end of the pore water sampler is arranged in the sand box structure, and the output end of the pore water sampler is connected with the input end of the data processing unit.

[0014] As a further illustration of the present application, the first side bank simulation tank of the main stream is specifically a cavity structure composed of two first waterproof baffles, a second waterproof baffle, a first organic glass bottom plate, a second permeable baffle and a waterproof baffle with a reserved port, and a sampling thin tube is connected to the second water outlet of the second waterproof baffle, and the sampling thin tube is connected with the input end of the data processing unit. A plurality of second water level control water heads are connected to the waterproof baffle with a reserved port, which is used to simulate the spatial distribution of river bank groundwater level.

[0015] As a further illustration of the present application, the second side bank simulation tank of the main stream comprises a second permeable baffle, a movable baffle with holes, two second waterproof baffles, a second movable waterproof baffle and a second organic glass bottom plate. The second permeable baffle is arranged close to the confluence water tank, the second permeable baffle, the second waterproof baffle, the second movable waterproof baffle and the second organic glass bottom plate form a main cavity structure, pulleys are installed at the movable side bottom ends of the movable baffle with holes and the second movable waterproof baffle, the movable baffle with holes is arranged in the main cavity structure, and the second movable waterproof baffle is also provided with a second water outlet and a second water level control water head.

[0016] As a further illustration of the present application, the dissolved oxygen regulation in the regulation unit is completed by a stirrer, an inert gas bottle and a dissolved oxygen sensor prearranged in the river simulation mechanism, and the regulation of dissolved oxygen is achieved by opening the stirrer or injecting inert gas. The PH regulation in the regulation unit is completed by adding acid-base reagents or buffer agents to the confluence triangular area simulation tank, the first side bank simulation tank of the main stream and the second side bank simulation tank of the main stream, and the PH of the water bodies in the confluence triangular area simulation tank, the first side bank simulation tank of the main stream and the second side bank simulation tank of the main stream is controlled at 5~10. The conductivity regulation in the regulation unit is completed by mixing NaCl solution with raw water and then adding it into the river simulation mechanism.

[0017] As a further illustration of the present application, the monitoring terminal monitors hydrological information in the simulation unit, and classifies and arranges the monitored hydrological information according to a set index.

[0018] Compared with the prior art, the present application has the following advantages: The present application can truly simulate the migration and conversion of nitrogen salts in the actual confluence area by controllable hydraulic conditions, solves the problem that the traditional water tank cannot simulate the interaction of two rivers, changes the flow ratio of the branch and trunk streams and the groundwater level, the simulation conditions are flexible and controllable, the adaptability to the natural river confluence is enhanced, and therefore the accuracy of the simulation experiment is further improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a top view of the overall structure of the present application; Figure 2 is a side view of the confluence triangular area simulation tank of the present application; Figure 3 is a front view of the confluence triangular area simulation tank of the present application; Figure 4 is a front view of the first side bank simulation tank of the main trunk stream of the present application; Figure 5 is a perspective view of the first side bank simulation tank of the main trunk stream of the present application; Figure 6 is a perspective view of the second side bank simulation tank of the main trunk stream of the present application; Figure 7 is a comparison chart of the training model output 26-28 days data, the true value and the predicted value in the experimental example of the present application.

[0020] BRIEF DESCRIPTION OF DRAWINGS 1-first side bank simulation tank of the main trunk stream; 2-water tank of the main trunk stream; 3-water tank of the branch stream; 4-water pump; 5-waste water tank; 6-flow valve; 7-confluence triangular area simulation tank; 8-CMOS monitoring camera; 9-first water outlet; 10-adjustable base; 11-gauze screen; 12-pore water sampler; 13-first water level control water head; 14-water level control tank; 15-second water outlet; 16-second water level control water head; 17-second water-permeable baffle; 18-waterproof baffle with reserved opening; 19-movable baffle with hole; 20-second waterproof baffle; 21-main trunk stream water tank; 22-branch stream water tank; 23-confluence water tank; 24-second side bank simulation tank of the main trunk stream; 25-river sampling port; 26-sampling capillary tube; 27-dissolved oxygen sensor; 28-torsion spring hinge; 29-pulley; 30-first movable waterproof baffle; 31-first water-permeable baffle; 31-first glass bottom plate; 33-second waterproof baffle; 34-second water-permeable baffle; 35-first waterproof baffle; 36-first organic glass bottom plate; 37-second movable waterproof baffle; 38-second organic glass bottom plate. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0022] As shown in Figures 1-7 The present application provides a technical solution: a nitrogen migration and transformation simulation device, comprising: The nitrogen migration and transformation simulation device comprises an input unit, a simulation unit, a regulation and control unit and a data processing unit. The input unit inputs the configured nitrogen simulation liquid into the simulation unit through the water pump 4, so as to simulate the migration of the nitrogen source input from the downstream river to the surrounding area; the simulation unit comprises a river channel simulation mechanism, a confluence triangular area simulation tank 7, a main stream first side bank simulation tank 1 and a main stream second side bank simulation tank 24. The river channel simulation mechanism is used to simulate the main stream and the branch stream of the river channel, the confluence triangular area simulation tank 7 is arranged at the confluence of the main stream and the branch stream, and the main stream first side bank simulation tank 1 and the main stream second side bank simulation tank 24 are arranged on the two sides of the main stream, respectively. The biological unit is to control the aerobic / anaerobic partition and the nitrification / denitrification partition by regulating the carbon source, regulating the oxygen content and controlling the soil structure / particle.

[0023] The dissolved oxygen in the water body can be controlled by stirring the water body at the main stream water tank 2 or by flushing inert gas, and at the same time, the sampling device is buried in the aerobic / anaerobic partition to monitor the migration of nitrogen in two different environments; secondly, the C / N ratio of the simulation liquid can be adjusted to 10:1~20:1 to promote / limit the denitrification behavior. When the non-homogeneous soil is filled, the uneven distribution of porosity will change the transmission of oxygen and nutrients, thereby changing the distribution of microorganisms. The carbon source regulation, control of soil structure / particle, to achieve control of aerobic / anaerobic partition and nitrification / denitrification partition. The carbon source regulation adjusts the C / N ratio of the simulation liquid to 10:1~20:1 by adjusting the carbon-nitrogen element ratio in the simulation liquid, promotes / limits the denitrification behavior, controls the composition of nutrients in the simulation tank, fills the homogeneous soil in the geological unit in the simulation tank, forms an aerobic zone at 0~-10cm from the surface layer of the geological unit, and the remaining part of the geological unit is an anaerobic zone. When non-homogeneous soil is filled, the uneven distribution of porosity will change the oxygen and nutrient transfer simultaneously, thereby changing the distribution of microorganisms; at the same time, the pore water samplers 12 are embedded in the aerobic zone and the anaerobic zone, the pore water samplers 12 are connected to the output module, and the migration of nitrogen in the two different environments is monitored by analyzing the changes of nitrogen compounds in the pore water; The regulation unit is arranged in the intersection triangular area simulation tank 7, the first side bank simulation tank 1 of the main stream and the second side bank simulation tank 24 of the main stream, and is used for regulating dissolved oxygen, PH and conductivity. The data processing unit includes a monitoring terminal and a computer, the monitoring terminal is arranged in the simulation unit, the monitored data is transmitted to the computer, the computer is preinstalled with an LSTM neural network model, the data is learned by the LSTM neural network model and a prediction result is given.

[0024] In this embodiment, the river simulation mechanism includes a main stream water tank 21, a main stream water tank 21, a main stream water tank 2 is connected to the water inlet end, a flow valve 6 is arranged on the communication passage of the main stream water tank 21 and the main stream water tank 2, and the flow valve 6 can control the water flow of the main stream water tank 2 to the main stream water tank 21; A branch water tank 22, the water inlet end of the branch water tank 22 is connected with a branch water tank 3, and a flow valve 6 is also arranged on the communication passage of the branch water tank 22 and the branch water tank 3, which is used for controlling the water flow of the branch water tank 3 to the branch water tank 22, The branch water tank 22 is obliquely communicated with one side of the main stream water tank 21, which is used for simulating the flow mode of the main stream and the branch stream in the river.

[0025] A confluence water tank 23, the tail end of the main stream water tank 21 is movably connected with the confluence water tank 23, the confluence water tank 23 has a certain inclination angle, which can be freely adjusted through the adjustable base 10, and the tail end of the confluence water tank 23 is connected with a wastewater tank 5 The communication passages of the main stream water tank 21 and the main stream water tank 2 and the communication passages of the branch water tank 22 and the branch water tank 3 are all provided with flow valves 6, and a plurality of river sampling ports 25 are arranged on the branch water tank 22, which are used for monitoring the water quality in the simulated river.

[0026] In this embodiment, the intersection triangular area simulation tank 7 comprises a first movable waterproof baffle 30, a first water-permeable baffle 31, and a first glass bottom plate 32. The first water-permeable baffle 32 is provided with two, and the two first water-permeable baffles 32 are rotationally connected to the torsion spring hinge 28 to form a zigzag structure. The zigzag structure is installed on the first glass bottom plate 32, and the first movable waterproof baffle 30 is movably connected to the opening end of the zigzag structure to form a sand box structure with an open top end. The first glass bottom plate 32 is installed at the bottom end with a plurality of adjustable bases 10, and the height can be adjusted through the adjustable base 10.

[0027] As a possible implementation in this embodiment, the folding angle of the zigzag structure can be adjusted within 20-60°, and the length of the first movable waterproof baffle 30 is 30-60 cm.

[0028] The first movable waterproof baffle 30 is also provided with a plurality of first water outlets 9 and a first water level control head 13. The first water outlet 9 is connected to the pore water sampler 12, and the inside end of the pore water sampler 12 is provided with a gauze screen 11 to prevent silt from flowing into the pore water sampler 12. The collection end of the pore water sampler 12 is arranged in the sand box structure, and the output end of the pore water sampler 12 is connected to the input end of the data processing unit.

[0029] The first side bank simulation tank 1 of the main stream is a cavity structure with a water level control box 14 composed of two first waterproof baffles 35, a second waterproof baffle 33, a first organic glass bottom plate 36, a second water-permeable baffle 34, and a waterproof baffle 18 with a reserved port. The second water outlet 15 of the second waterproof baffle 33 is connected with a sampling thin tube 26, and the sampling thin tube 26 is connected to the input end of the data processing unit. The waterproof baffle 18 with a reserved port is connected with a plurality of second water level control heads 16 to simulate the spatial distribution of the groundwater level of the river bank.

[0030] The second side bank simulation tank 24 of the main stream comprises a second water-permeable baffle 17, a movable baffle with holes 19, two second waterproof baffles 20, a second movable waterproof baffle 37, and a second organic glass bottom plate 38. The second water-permeable baffle 17 is arranged near one side of the confluence water tank 23. The second water-permeable baffle 17, the second waterproof baffle 20, the second movable waterproof baffle 37, and the second organic glass bottom plate 38 form a main cavity structure with a water level control box 14. The movable side bottom end of the movable baffle with holes 19 and the second movable waterproof baffle 37 is installed with a pulley 29. The movable baffle with holes 19 is arranged in the main cavity structure, and the second movable waterproof baffle 37 is also provided with a second water outlet 15 and a second water level control head 16.

[0031] The dissolved oxygen regulation in the regulation unit is completed by the stirrer, inert gas bottle and dissolved oxygen sensor 27 preset in the river simulation mechanism. The dissolved oxygen regulation is achieved by opening the stirrer or injecting inert gas. The PH regulation in the regulation unit is achieved by adding acid-base reagent or buffer to the confluence triangular area simulation tank 7, the first side bank simulation tank 1 of the main stream and the second side bank simulation tank 24 of the main stream. The PH of the water in the confluence triangular area simulation tank 7, the first side bank simulation tank 1 of the main stream and the second side bank simulation tank 24 of the main stream is controlled at 5-10. The conductivity regulation in the regulation unit is achieved by mixing NaCl solution with raw water and then adding it into the river simulation mechanism.

[0032] The monitoring terminal monitors the hydrological information in the simulation unit and classifies and arranges the monitored hydrological information according to the set index. The hydrological information includes the content of ammonia nitrogen, nitrate nitrogen, COD, PH, dissolved oxygen, conductivity and DOC in water, as well as the flow rate and flow direction of water. The environmental information such as soil particle size and temperature is also recorded synchronously.

[0033] In the experiment, the nitrogen concentration of the branch stream is the measured value of the river. The nitrogen simulation liquid of the main stream is prepared as follows: 980mg / L carbon source CH3COONa, 400mg / L C, 220mg / L NaNO3, 48mg / L N, 6mg / L NH4Cl, 5mg / L N.

[0034] Before the experiment, the intersection angle of the main stream and the branch stream and the inclination angle of the main stream are determined. The nitrogen simulation liquid is constantly outputted through the flow valve.

[0035] The flow rate of the main stream is 1m / s, the flow rate of the branch stream is 0.5m / s, the flow rate ratio of the main stream and the branch stream is 2, the flow ratio is 10:1, and the intersection angle is 30°. After the intersection angle is determined, the simulation tanks are installed as shown in Figure 1 The CMOS camera 8 is installed on the upper part of the main stream water tank 21, the branch stream water tank 22 and the confluence water tank 23, and the computer is used to control the regulation unit to adjust the dissolved oxygen, PH and conductivity in the confluence triangular area simulation tank 7, the first side bank simulation tank 1 of the main stream and the second side bank simulation tank 24 of the main stream.

[0036] The experimental setup is non-uniform soil, and the landfill soil is air-dried and deposited soil, and is sieved. In the intersection triangle area, in the simulation tank 7, the first side bank simulation tank 1 of the main stream, and the second side bank simulation tank 24 of the main stream, the soil samples of 0-300mm, 300-500mm, and 500-700mm layers are respectively placed according to the stratification of the riverbed undisturbed sediment of the interaction zone, and the soil samples are filled in the order of fine sand, clay, and coarse sand. At the same time, the pore water samplers 12 are filled in each stratification, and the samplers are placed in series. The pore water samplers 12 are connected to the simulation tank through a rubber tube, and a gauze 11 is installed inside to prevent the sand from being washed in. The water outlet is connected to a sampling tube 26, and the sampling tube 26 is connected to an automatic sampling device through a peristaltic pump. The peristaltic pump is set at an interval of 20 minutes, and the sampling amount is 100ml. Subsequently, the sampling is automatically entered into a water quality analyzer to analyze and measure each chemical index. In order to simulate the interaction process in the interaction zone, the water level control water head 16 in the simulation tank on the left and right banks of the main stream is opened, and the water head h0 is recorded. The water head is connected to the water pump through a rubber tube, so that the seepage water is sent to the waste water tank.

[0037] The experiment measures the content of NH 3+ , NO 3- , COD, DOC, and electrical conductivity in real time through the intelligent water quality analyzer of the output module.

[0038] Further, the flow velocity of the confluence area is observed and recorded by using the COMS camera 8, whether the backflow area and vortex appear is observed, the water levels h1, h2, and h3 of each river section are determined, and the water head difference h1-h0 is recorded. The simulation device is continuously operated for three months. Optionally, a filter membrane is added to the sampling port, and the community structure of each nitrification / denitrification bacteria is detected to analyze the migration and transformation rule of nitrogen nutrients under different soil and rock layer structures. Through data analysis, in the vertical heterogeneous structure of fine sand, clay, and coarse sand: The surface layer (0-10cm) has good aeration and is the main nitrification zone, NH 4+ is rapidly converted to NO 3- ; The middle layer (10-20cm) is rich in water and oxygen is gradually depleted, which is the NO 2- accumulation and denitrification start-up zone; The deep layer (>20cm) is in an anaerobic state and is the main denitrification zone, NO 3- is completely converted, and NH 4+ is easily accumulated due to strong adsorption. The content of nitrate nitrogen in the triangular confluence area is observed, and the specific data are shown in Table 1: Table 1 Content of nitrate nitrogen in the triangular confluence area

[0039] Further, real-time observation of each index data change. Optionally, after each data is stable, by changing the key variables, further simulate the change of nitrogen migration after the change of biological unit, such as the change of the interaction of the interactive zone of the confluence area under the non-constant environmental conditions. Optionally, by setting the dissolved oxygen gradient: 5~10mg / L, PH fluctuation: 5~10, organic matter load (C / N ratio) range: 10~20. Focus on observing the changes of the content of each form of nitrogen in the three simulation boxes. Take 1 mg / L of dissolved oxygen concentration and PH adjustment to 8 as an example, take nitrate nitrogen as the key observation object, and the specific data is shown in Tables 2-4: Table 2 Nitrate nitrogen change in the triangular confluence area

[0040] Table 3 Nitrate nitrogen change in the left bank simulation tank

[0041] Table 4 Nitrate nitrogen change in the right bank simulation tank

[0042] As can be seen from the above, the nitrate nitrogen in the triangular confluence area first increases and then decreases. The nitrate nitrogen content on the left bank of the river has no obvious change on the left side of the confluence area, and gradually increases on the right side after about 10 days of simulation. The right bank of the river is most affected, and the degree of influence decreases from top to bottom. After increasing the PH and dissolved oxygen content, the denitrification reaction is inhibited to a certain extent, the nitrate nitrogen generation increases, so the nitrate nitrogen content is improved.

[0043] Taking three months of simulation data as an example, after data processing, each item of data is packaged into a data set, and is classified into a training set, a validation set, and a test set. Through the LSTM neural network, the long-term nitrogen migration trend is predicted, and according to the size of the data sample, the number of input layer and output layer neurons in the LSTM network is set.

[0044] The number of neurons in the input layer is 12, the number of neurons in the output layer is 1, and the time step is set to 6 to predict three days as the target to start training.

[0045] The main calculation formula and gate control in LSTM are as follows: The input gate decides how much memory state of the current unit is output as the hidden state of the current time step: ; Wherein: i t : Output of the input gate, controlling how much new information is written σ : Sigmoid function Wi : weight matrix of the forget gate b i : bias term of the forget gate C t : candidate memory state, new information W C : weight matrix of the candidate memory state b C : bias term of the candidate memory state forget gate, decides how much of the previous memory information to keep at the current time step: ; where: f t : output of the forget gate, controls how much old memory to keep σ : sigmoid function, output range is (0, 1) W f : weight matrix of the forget gate : hidden state of the previous time step x t : input vector of the current time step : vector concatenation operation b f : bias term of the forget gate update unit, "long-term memory" throughout the sequence, updated by the forget gate and the input gate: ; where: C t : memory cell state of the current time step : memory state of the previous time step f t : output of the forget gate i t : output of the input gate C t-1 : candidate memory state output gate, decides how much of the current cell's memory state to output as the hidden state of the current time step: ; where: o t : output of the output gate (controls how much current memory is output) σ : Sigmoid function W o : weight matrix of the output gate b o : bias term of the output gate : bias term of the output gate where the activation function is: ; ; where: σ(x) : output of the Sigmoid function, normalized for input x x : input value, scalar, vector, or matrix, weighted input from neurons For model validation, the mean absolute error (MAE), root mean square error (RMSE), and coefficient of determination (R2) are used as evaluation indicators: ; where: n : total number of samples, number of observations y i : true value of the i-th sample : predicted value of the i-th sample : absolute value of the prediction error of the i-th sample : sum of squared residuals After training, the training set and test set are predicted respectively, and the predicted values are de-normalized.

[0046] Taking the above triangular confluence area data as an example, the first 20 days of data are used as the training set, and the 20~25 days of data are used as the validation set. The output of the training model is 26~28 days of data, and the true value and the predicted value are compared as follows Figure 7 : The MAE of the LSTM model prediction result is 0.396, R2 is 0.956, and RMSE is 0.508. Compared with the true value, the predicted value is consistent with the true value in trend, the overall error is smaller than the true value error, R2 is 0.956, indicating that the fitting degree of this neural network training is good.

[0047] It should be noted that, in this paper, relational terms such as first and second are used merely to distinguish one entity or action from another, without necessarily requiring or implying that there is any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof are intended to cover non-exclusive inclusions, so that a process, method, article, or apparatus that includes a list of elements does not only include those elements, but also includes other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0048] Although embodiments of the present application have been shown and described, it will be understood by those having ordinary skill in the art that various changes, modifications, alternatives, and variations can be made thereto without departing from the principles and spirit of the application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A device for simulating nitrogen migration and transformation, characterized in that, include; The input unit uses a water pump (4) to input the prepared nitrogen simulation solution into the simulation unit to simulate the migration of nitrogen source input downstream river to the surrounding area; The simulation unit includes a river channel simulation mechanism, a confluence triangle area simulation tank (7), a main stream first side bank simulation tank (1), and a main stream second side bank simulation tank (24). The river simulation mechanism is used to simulate the main stream and tributaries of the river. The confluence triangle simulation tank (7) is set at the confluence of the main stream and tributaries. The first side bank simulation tank (1) and the second side bank simulation tank (24) of the main stream are respectively set on both sides of the main stream. Biological units, namely, controlling aerobic / anaerobic zones and nitrification / denitrification zones by regulating carbon sources, oxygen content, and soil structure / particles; The control units are respectively set in the confluence triangle region simulation tank (7), the main stream first side bank simulation tank (1) and the main stream second side bank simulation tank (24), and are used to control dissolved oxygen, pH and conductivity; The data processing unit includes a monitoring terminal and a computer. The monitoring terminal is set up in the simulation unit and transmits the monitored data to the computer. The computer has a preset LSTM neural network model. The data is processed by the LSTM neural network model for deep learning and prediction results are given.

2. The nitrogen migration and transformation simulation device according to claim 1, characterized in that, The river simulation mechanism includes a main flow channel (21), and the inlet end of the main flow channel (21) is connected to a main flow tank (2). A branch water tank (22) is provided, with a branch water tank (3) connected to the water inlet end of the branch water tank (22); The tributary water channel (22) is obliquely connected to one side of the main water channel (21); The main water channel (21) is movably connected to the confluence water channel (23), and the confluence water channel (23) is connected to the wastewater tank (5) at its tail end.

3. The nitrogen migration and transformation simulation device according to claim 2, characterized in that, Flow valves (6) are provided on the connection passage between the main flow channel (21) and the main flow tank (2) and the connection passage between the tributary channel (22) and the tributary tank (3). Multiple river sampling ports (25) are also provided on the tributary channel (22).

4. The nitrogen migration and transformation simulation device according to claim 1, characterized in that, The intersection triangular area simulation tank (7) includes a first movable water-proof baffle (30), a first water-permeable baffle (31) and a first glass base plate (32). There are two first water-permeable baffles (32). The two first water-permeable baffles (32) are rotatably connected to a torsion spring hinge (28) to form a zigzag structure. The zigzag structure is installed on the first glass base plate (32), and the first movable water-proof baffle (30) is movably connected to the opening end of the zigzag structure to form a sandbox structure with an open top. Multiple adjustable bases (10) are installed at the bottom of the first glass base plate (32).

5. The nitrogen migration and transformation simulation device according to claim 4, characterized in that, The angle of the zigzag structure can be adjusted within 20~60°, and the length of the first movable water-proof baffle (30) is 30~60cm.

6. The nitrogen migration and transformation simulation device according to claim 4, characterized in that, The first movable baffle (30) is also provided with multiple first water outlets (9) and first water level control head (13). A pore water sampler (12) is connected to the first water outlet (9). The collection end of the pore water sampler (12) is set inside the sand box structure. The output end of the pore water sampler (12) is connected to the input end of the data processing unit.

7. The nitrogen migration and transformation simulation device according to claim 1, characterized in that, The main stream first side bank simulation channel (1) is specifically a cavity structure with a water level control box (14) consisting of two first water-proof baffles (35), one second water-proof baffle (33), a first plexiglass base plate (36), one second permeable baffle (34) and a water-proof baffle (18) with a reserved opening. A sampling tube (26) is connected to the second outlet (15) of the second water-proof baffle (33), and the sampling tube (26) is connected to the input end of the data processing unit. The water-blocking baffle (18) with a reserved opening is connected to multiple second water level control heads (16) to simulate the spatial distribution of groundwater level on the riverbank.

8. The nitrogen migration and transformation simulation device according to claim 1, characterized in that, The main stream second side bank simulation channel (24) includes a second permeable baffle (17), a movable perforated baffle (19), two second water-proof baffles (20), a second movable water-proof baffle (37), and a second plexiglass base plate (38). The second permeable baffle (17) is located on the side near the confluence water tank (23). The second permeable baffle (17), the second water-proof baffle (20), the second movable water-proof baffle (37), and the second plexiglass base plate (38) form a main cavity structure with a water level control box (14). The movable perforated baffle (19) and the movable water-proof baffle (37) are both equipped with pulleys (29) at the bottom of their movable sides. The movable perforated baffle (19) is located inside the main cavity structure. The second movable water-proof baffle (37) is also equipped with a second outlet (15) and a second water level control head (16).

9. The nitrogen migration and transformation simulation device according to claim 2, characterized in that, The dissolved oxygen regulation in the regulation unit is accomplished by a stirrer, an inert gas bottle and a dissolved oxygen sensor (27) pre-installed in the river simulation mechanism. The dissolved oxygen regulation is achieved by turning on the stirrer or injecting inert gas. The pH control in the control unit is accomplished by adding acid or alkali reagents or buffers to the confluence triangle area simulation tank (7), the main stream first side bank simulation tank (1), and the main stream second side bank simulation tank (24), so as to control the pH of the water in the confluence triangle area simulation tank (7), the main stream first side bank simulation tank (1), and the main stream second side bank simulation tank (24) to 5~10. The conductivity regulation in the control unit is achieved by mixing NaCl solution with raw water and then adding it into the river simulation mechanism.

10. The nitrogen migration and transformation simulation device according to claim 1, characterized in that, The monitoring terminal monitors the hydrological information within the simulation unit and categorizes and organizes the monitored hydrological information according to the set indicators.

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