A simulation method coupling the complete geochemical reaction and migration processes of surface water pollutants

Abstract

The present invention discloses a simulation method for coupling the complete geochemical reaction and migration process of surface water pollutants, comprising the following steps: Step 1, collect the surface water hydrological data of the research area; Step 2, construct the surface water dynamic model of the research area; Step 3, construct the mass transport model of the research area; Step 4, collect the surface water quality data of the research area; Step 5, construct the multi-type pollutant model of the research area based on the thermodynamic equilibrium theory; Step 6, couple the surface water dynamic model in Step 2, the mass transport model in Step 3 and the multi-type pollutant model in Step 5 to obtain the multi-type pollutant migration model of surface water. The present invention uses PhreeqcRM as the reaction engine, can simulate various reaction processes such as dissolution and precipitation reactions, ion exchange reactions, surface complexation reactions, kinetic reactions, etc., has the characteristics of strong portability and scalability, and greatly improves the applicability of the surface water quality model.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental simulation, and in particular to a simulation method for coupling the complete geochemical reactions and transport processes of surface water pollutants. Background Art

[0002] Water is the source of life, and about 71% of the earth's surface is covered by water. Among them, surface water refers to the general term for dynamic water and static water on the land surface, including various liquid and solid water bodies, mainly rivers, lakes, swamps, glaciers, ice sheets, etc. It is one of the important sources of water for human life and production. However, with the continuous development and progress of society, natural water resources are constantly being damaged. The large-scale discharge of industrial wastewater and domestic sewage has made the pollution problems of rivers, lakes, reservoirs, etc. become more and more serious, causing a huge impact on human production and life and threatening human health at all times.

[0003] The surface water quality model is a mathematical equation that describes the mixing, transport with water flow, and migration and transformation of pollutants in surface water bodies, and is an important tool and effective means for decision-making analysis in the treatment and planning of surface water environmental pollution. Currently, there are many surface water quality models, such as WASP, EFDC, etc. However, most of the existing water quality models at present have strong pertinence and can only simulate specific types of elements, such as ammonia nitrogen and phosphate, and their use has certain limitations. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a simulation method for coupling the complete geochemical reactions and transport processes of surface water pollutants. By coupling surface water dynamics, mass transport and thermodynamic equilibrium mechanisms, a surface water quality model for the research area is established, realizing the efficient simulation of the surface water dynamic field and geochemical field and the simulation of multi-type pollutant processes.

[0005] To solve the above technical problem, the present invention provides a simulation method for coupling the complete geochemical reactions and transport processes of surface water pollutants, including the following steps:

[0006] Step 1: Collect the surface water hydrological data of the research area;

[0007] Step 2: Construct a surface water dynamic model for the research area;

[0008] Step 3: Construct a mass transport model for the research area;

[0009] Step 4: Collect the surface water quality data of the research area;

[0010] Step 5: Construct a multi-type pollutant model for the research area based on the thermodynamic equilibrium theory;

[0011] Step 6: Couple the surface water hydrodynamic model in Step 2, the mass transport model in Step 3, and the multi-type pollutant model in Step 5 to obtain a surface water multi-type pollutant transport model.

[0012] Preferably, in Step 1, collecting the surface hydrological data of the study area includes monitoring the topography, water level, salinity, flow velocity, flow rate, and rainfall of the area.

[0013] Preferably, in Step 2, the surface water study area includes rivers, lakes, and coastal waters.

[0014] Preferably, in Step 2, the control equations of the surface water hydrodynamic model are as follows:

[0015]

[0016] In the formula: V is the velocity, P is the free surface pressure, r is the unit weight of water, ρ m is the water density, z is the water depth, and υ is the kinematic viscosity.

[0017] Preferably, in Step 3, the mass transport control equations are as follows:

[0018]

[0019] In the formula: H is the water depth; C is the mass concentration at the same depth; t is the time; u and v are the velocities in the x and y directions respectively; K xx 、K xy 、K yx and K yy are the two-dimensional diffusion coefficient tensors, S is the source-sink term; Equation (2) is solved by finite volume method for difference, and using the operator splitting algorithm, the above equation is divided into two parts: the convection term and the diffusion term for step-by-step calculation, and the model is written in Fortran90 language.

[0020] Preferably, in Step 4, collecting the surface water quality data of the study area includes the pH value, pe value, temperature of the water, and the concentration of the elements to be studied.

[0021] Preferably, in Step 5, the multi-type pollutant model constructed based on the thermodynamic equilibrium theory refers to the water quality model established based on the geochemical package PhreeqcRM.

[0022] Preferably, in Step 6, coupling the surface water hydrodynamic model, the mass transport model, and the multi-type pollutant model refers to full coupling at the code level. The surface water hydrodynamic and mass transport programs written in Fortran90 are unifiedly compiled with the Fortran version of PhreeqcRM, and the hydrodynamic model, the mass transport model, and the water quality model are synchronously solved within each time step.

[0023] Preferably, in step 6, the calculation process for each time step is as follows: First, solve the hydrodynamic field at the current moment, then perform mass transport calculations based on the currently calculated hydrodynamic field to obtain the concentration distribution field of each substance at the current moment. Finally, input the current concentration results of each substance into the water quality model to perform calculations of the geochemical reaction process, and obtain the initial concentration field of each substance for the next time step.

[0024] The beneficial effects of the present invention are as follows: The present invention uses PhreeqcRM as the reaction engine, which can simulate various reaction processes such as dissolution and precipitation reactions, ion exchange reactions, surface complexation reactions, and kinetic reactions. This model is based on the Fortran90 programming language and has the characteristics of strong portability and scalability, greatly improving the applicability of the surface water quality model. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic flow chart of the method of the present invention.

[0026] Figure 2 It is a schematic flow chart of a surface water multi-type pollutant transport model based on the thermodynamic equilibrium theory provided by an example of the present invention.

[0027] Figure 3 It is a verification diagram of the simulation results and analytical solutions of the first-order substances of the surface water migration model considering sequential first-order degradation reactions in an example of the present invention.

[0028] Figure 4 It is a verification diagram of the simulation results and analytical solutions of the second-order substances of the surface water migration model considering sequential first-order degradation reactions in an example of the present invention.

[0029] Figure 5 It is a verification diagram of the simulation results and analytical solutions of the third-order substances of the surface water migration model considering sequential first-order degradation reactions in an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] As Figure 1 shown, a simulation method for coupling the complete geochemical reaction and transport process of surface water pollutants includes the following steps:

[0031] Step 1: Collect the surface water hydrological data of the research area;

[0032] Collecting the surface hydrological data of the research area includes monitoring the topography, water level, salinity, flow velocity, flow rate, rainfall, etc. of the area.

[0033] Step 2: Construct a surface water hydrodynamic model for the research area;

[0034] The control equations of the surface water hydrodynamic model are as follows:

[0035]

[0036] In the formula: V is the velocity, P is the free surface pressure, r is the unit weight of water body, ρ m is the density of the water body, z is the water depth, and υ is the kinematic viscosity coefficient.

[0037] Discretize the control equation (1) of the surface water dynamic model, determine the boundary of the research area, use triangular mesh division to divide the research area, and at the same time perform interpolation of terrain data and definition of the regional boundary. The model is written in Fortran90 language.

[0038] Step 3: Construct a mass transport model for the research area;

[0039] The control equation of the mass transport model is as follows:

[0040]

[0041] In the formula: H is the water depth; C is the concentration of substances at the same depth; t is the time; u and v are the velocities in the x and y directions respectively; K xx , K xy , K yx and K yy are the two-dimensional diffusion coefficient tensors, and S is the source-sink term; the derivation of the diffusion coefficient is as follows;

[0042] K xx = K L cos 2 (θ) + K T sin 2 (θ) (3)

[0043] K xy = K yx = (K L - K T )cos(θ)sin(θ) (4)

[0044] K yy = K L sin 2 (θ) + K T cos 2 (θ) (5)

[0045] In the formula: θ is the angle between the flow velocity direction and the x-axis; K L , K T are the transverse and longitudinal diffusion coefficients respectively; for the diffusion coefficients in the downstream direction and the direction perpendicular to the flow, the following Elder formula can be used:

[0046]

[0047] Where: C is the Chezy coefficient; α and β are constants, and their theoretical values are taken as 5.93 and 0.23 respectively. When the water body turbulence is strong, they can be taken as 13 and 1.2. The differences in the mass diffusion characteristics in the transverse and longitudinal directions are very obvious.

[0048] Furthermore, using the operator splitting algorithm, the above formula (2) is divided into the following convection term and diffusion term equations:

[0049] Convection term:

[0050] Diffusion term:

[0051] The finite volume method is used to perform the difference calculation on the above convection term and diffusion term, and its operator calculation form is as follows:

[0052] (HC) n+1 =L ADV L Diff (HC) n (10)

[0053] (HC) n+2 =L Diff L ADV (HC) n+1 (11)

[0054] Where: L ADV represents the convection operator, and L Diff represents the diffusion operator.

[0055] Step 4: Collect the surface water quality data of the study area;

[0056] The surface water quality data collected for the study area includes the pH value of the water, pe value, temperature, and the concentrations of the elements to be studied, etc.

[0057] Step 5: Construct a multi-type pollutant model for the study area based on the thermodynamic equilibrium theory; establish a multi-type pollutant model based on the geochemical package PhreeqcRM.

[0058] Specifically, the part of constructing the multi-type pollutant model includes two major parts, the initialization of PhreeqcRM part and the execution of the reaction part. The initialization of PhreeqcRM part includes creating PhreeqcRM, initializing PhreeqcRM, and setting the initial and boundary conditions of the model in PhreeqcRM. The execution of the reaction part mainly performs the transfer of data and realizes the reaction of the solution.

[0059] Specifically, the initialization of the PhreeqcRM part mainly involves the following functions: It is necessary to use the RM_Create function to create a PhreeqcRM thread, use the RM_SetComponentH2O function to set the component form of H 2 O in this instance, use the RM_SetFilePrefix function to set the output file name, use the RM_SetUnitsSolution function to set the solution unit, use the RM_RunFile function to load the initial reaction file, use the RM_SetTimeStep function to set the reaction time step, use the RM_SetTime function to set the current reaction time, use the RM_InitialPhreeqc2Module function to initialize the water quality model, and use the RM_RunCells function to perform an initial step run to obtain the initial concentration field.

[0060] Specifically, the execution of the reaction part mainly involves the following functions: It is necessary to use the RM_SetConcentrations function to transfer the substance transport concentration results to the water quality model, use the RM_RunCells function to simulate chemical reactions for the current time step, and use the RM_GetConcentrations function to transfer the reaction calculation results back to the substance transport model.

[0061] Step 6: Couple the surface water hydrodynamic model in Step 2, the substance transport model in Step 3, and the multi-type pollutant model in Step 5 to obtain a surface water multi-type pollutant transport model;

[0062] Specifically, for the full coupling at the code level of the surface water hydrodynamic model, the substance transport model, and the multi-type pollutant model, the surface water hydrodynamic and substance transport programs written in Fortran90 will be compiled together with the Fortran version of PhreeqcRM. The hydrodynamic model, the substance transport model, and the water quality model will be solved synchronously within each time step. The calculation process for each time step is as follows: First, solve the hydrodynamic field at the current moment, then perform substance transport calculations based on the currently calculated hydrodynamic field to obtain the concentration distribution field of each substance at the current moment. Finally, input the concentration results of each current substance into the water quality model to perform calculations for the geochemical reaction process to obtain the initial concentration field of each substance at the next time step.

[0063] As Figure 2 shown, it is a schematic flowchart of a surface water multi-type pollutant transport model provided by an embodiment of the present invention based on the thermodynamic equilibrium theory.

[0064] In addition, the present invention verified the reliability and practicality of the method through two cases. Figures 3 to 5It is a schematic diagram of the verification result of the surface water migration model considering the sequential first-order degradation reaction provided by an embodiment of the present technology. As can be seen from the figure, it further illustrates that the present invention has good reliability and practicability.

Claims

1. A simulation method for coupling the complete geochemical reaction and migration processes of surface water pollutants, characterized in that, it includes the following steps: Step 1: Collect surface water hydrological data of the study area; Step 2: Construct a surface water hydrodynamic model of the study area; Step 3: Construct a mass transport model of the study area; Step 4: Collect surface water quality data of the study area; Step 5: Based on the thermodynamic equilibrium theory, construct multi-type pollutant models for the study area, including: initializing the PhreeqcRM part and executing the reaction part; initializing the PhreeqcRM part, including: the initialization of the PhreeqcRM part mainly involves the following functions: it is necessary to use the RM_Create function to create a PhreeqcRM thread, use the RM_SetComponentH2O function to set the component form of H2O in this instance, use the RM_SetFilePrefix function to set the output file name, use the RM_SetUnitsSolution function to set the solution unit, use the RM_RunFile function to load the initial reaction file, use the RM_SetTimeStep function to set the reaction time step, use the RM_SetTime function to set the current reaction time, use the RM_InitialPhreeqc2Module function to initialize the water quality model, and use the RM_RunCells function to perform the initial step operation to obtain the initial concentration field; executing the reaction part, including: it is necessary to use the RM_SetConcentrations function to transfer the mass transport concentration results to the water quality model, use the RM_RunCells function to simulate the chemical reaction for the current time step, and use the RM_GetConcentrations function to transfer the reaction calculation results back to the mass transport model; Step 6: Couple the surface water hydrodynamic model in Step 2, the mass transport model in Step 3, and the multi-type pollutant models in Step 5 to obtain a surface water multi-type pollutant migration model; In Step 3, the mass transport control equation is as follows: Where: H is the water depth; C is the substance concentration at the same depth; t is the time; u and v are the velocities in the x and y directions respectively; K xx , K xy , K yx and K yy are two-dimensional diffusion coefficient tensors, and S is the source-sink term; Equation (2) is solved by finite volume method for difference. Using the operator splitting algorithm, the above equation is divided into two parts, the convective term and the diffusion term, for step-by-step calculation. The model is written in Fortran90 language; Coupling the surface water hydrodynamic model, the mass transport model, and the multi-type pollutant models refers to full coupling at the code level. The surface water hydrodynamic and mass transport programs written in Fortran90 will be uniformly compiled with the Fortran version of PhreeqcRM, and the hydrodynamic model, the mass transport model, and the water quality model will be solved synchronously within each time step; The calculation process for each time step is as follows: First, solve the hydrodynamic field at the current moment, then perform mass transport calculations based on the hydrodynamic field obtained from the current calculation to obtain the concentration distribution field of each substance at the current moment. Finally, input the concentration results of each substance at the current moment into the water quality model to perform calculations of the geochemical reaction process to obtain the initial concentration field of each substance at the next time step.

2. The simulation method for coupling the complete geochemical reaction and migration processes of surface water pollutants according to claim 1, characterized in that, In Step 1, the surface hydrological data of the study area is collected, including the monitoring of the terrain, water level, salinity, flow velocity, flow rate, and rainfall in this area.

3. The simulation method for coupling the complete geochemical reaction and migration process of surface water pollutants as claimed in claim 1, characterized in that, in Step 2, the surface water study area includes rivers, lakes and the nearshore sea area.

4. The simulation method for coupling the complete geochemical reaction and migration process of surface water pollutants as claimed in claim 1, characterized in that, in Step 2, the control equations of the surface water dynamic model are as follows: Where: V is the velocity, P is the free surface pressure, r is the unit weight of water body, ρ m is the density of water body, z is the water depth, and υ is the kinematic viscosity coefficient.

5. The simulation method for coupling the complete geochemical reaction and migration process of surface water pollutants as claimed in claim 1, characterized in that, in Step 4, the surface water quality data of the study area is collected, including the pH value, pe value, temperature of the water and the concentrations of the elements to be studied.

6. The simulation method for coupling the complete geochemical reaction and migration process of surface water pollutants as claimed in claim 1, characterized in that, the multi-type pollutant model constructed based on the thermodynamic equilibrium theory refers to the water quality model established based on the geochemical package PhreeqcRM.

Images