Method for analyzing migration and transformation rule of nitrogen and phosphorus in sewage resource utilization

Abstract

This invention provides a method for analyzing the migration and transformation patterns of nitrogen and phosphorus in wastewater resource utilization, relating to the field of wastewater resource utilization technology. This invention simultaneously samples and measures nitrogen and phosphorus concentrations in the source chamber, medium chamber, and receiving chamber at various depths, calculating apparent permeability flux and adsorption retardation coefficient. The difference in apparent permeability flux of nitrate nitrogen in the unit with and without inhibitors is used as the in-situ nitrification rate characterization value, and the difference in apparent permeability flux of ammonium nitrogen is used as the in-situ mineralization rate characterization value. The ratio of the sum of these two values ​​to the total apparent permeability flux of nitrogen is used as the biotransformation contribution index. Finally, based on the various indices at different depths, vertical distribution maps are plotted to delineate the biotransformation-dominant zone, adsorption-fixation-dominant zone, and physical permeability-dominant zone, and a zoned control scheme is output to achieve quantitative separation of the contributions of physical permeability, adsorption-fixation, and microbial transformation, and to establish a zoned precise control mechanism based on the dominant action type.

Description

Technical Field

[0001] This invention relates to the field of wastewater resource utilization technology, specifically a method for analyzing the migration and transformation patterns of nitrogen and phosphorus in wastewater resource utilization. Background Technology

[0002] In the process of wastewater resource utilization, nitrogen and phosphorus, as the main nutrients in wastewater, are not only key pollutants causing eutrophication of water bodies, but also important nutrient resources in agricultural production. By reusing treated wastewater for agricultural irrigation, nitrogen and phosphorus can be utilized as resources, reducing fertilizer application and mitigating the impact of wastewater discharge on the aquatic environment. However, the migration and transformation of nitrogen and phosphorus in wastewater within the soil-crop system is highly complex, involving the coupled effects of multiple mechanisms such as physical infiltration, chemical adsorption, microbial nitrification, and mineralization. Accurately analyzing the migration pathways and transformation patterns of nitrogen and phosphorus at different soil depths has significant theoretical and engineering application value for optimizing wastewater irrigation systems, improving nitrogen and phosphorus utilization efficiency, and controlling groundwater pollution risks.

[0003] Currently, the main analytical methods for nitrogen and phosphorus migration and transformation during wastewater resource utilization combine indoor soil column leaching experiments, field in-situ monitoring, and chemical extraction assays. Traditional soil column leaching experiments involve applying wastewater to the top of a soil column, collecting the leachate at the bottom, and measuring the nitrogen and phosphorus concentrations to estimate the amount of nitrogen and phosphorus leaching loss. Field in-situ monitoring involves burying soil solution extractors at different depths, periodically collecting pore water samples, and analyzing changes in nitrogen and phosphorus concentrations. Chemical extraction methods involve stratifying soil samples at different depths, using chemical reagents to extract exchangeable nitrogen and phosphorus from the soil, and estimating the transformation amount based on material balance principles. These methods can, to some extent, reflect the total amount of nitrogen and phosphorus migration and apparent transformation.

[0004] However, existing technologies have two key shortcomings. First, they cannot distinguish the contributions of physical infiltration, chemical adsorption, and microbial transformation to nitrogen and phosphorus migration. In soil column leaching or field monitoring, the measured changes in nitrogen and phosphorus concentrations are the result of the combined effects of physical transport, adsorption retention, and biotransformation. Existing methods can only obtain net changes and cannot distinguish between nitrate nitrogen generated by microbial nitrification and nitrate nitrogen originally present in the source water, nor can they separate ammonium nitrogen released from organic nitrogen mineralization from ammonium nitrogen brought in by wastewater. Therefore, it is difficult to quantitatively evaluate the true contribution of biotransformation to nitrogen and phosphorus migration. Second, existing technologies cannot identify the dominant action types in different soil depth ranges and provide targeted control strategies. Due to significant differences in soil physicochemical properties, microbial activity, and water transport conditions in the vertical direction, nitrogen and phosphorus migration behavior in different depth ranges may be dominated by physical infiltration, adsorption fixation, or biotransformation, respectively. Existing methods only provide average parameters for the entire profile or single indicators for each depth, and cannot clearly define the dominant action types in each depth range.

[0005] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a method for analyzing the migration and transformation patterns of nitrogen and phosphorus in wastewater resource utilization, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for analyzing the migration and transformation patterns of nitrogen and phosphorus in wastewater resource utilization, comprising the following steps: Step 1: Set up unit groups at different depths one by one, including parallel / permeable units with / without nitrification inhibitors. Each unit contains a source chamber, a medium chamber, and a receiver chamber separated by a semi-permeable membrane. Step 2: Simultaneously sample the chemical composition concentrations in each chamber of each unit under a preset time series. The chemical composition includes ammonium nitrogen, nitrate nitrogen, and phosphate. Based on the change of the concentration difference of each chemical composition between the source chamber and the receiving chamber over time, calculate the permeation flux of each chemical composition in each unit and the apparent permeation flux of total nitrogen in each unit. Calculate the ratio of the concentration of each chemical composition in the medium chamber to the concentration in the source chamber one by one to determine the adsorption resistance coefficient of each chemical composition in each permeation unit. Step 3: For any depth, calculate the difference in nitrate nitrogen permeation flux between the permeable units and parallel units in its unit group as its in-situ nitrification rate, and the difference in ammonium nitrogen permeation flux as its in-situ mineralization rate. Divide the sum of the two by the total apparent nitrogen permeation flux of the permeable units and parallel units in its unit group to obtain the first / second biotransformation contribution index at that depth. Step 4: Based on the in-situ nitrification rate, in-situ mineralization rate, adsorption retardation coefficient, and first / second biotransformation contribution index at each depth, draw a vertical distribution map. Depth intervals with biotransformation contribution index greater than a preset threshold are defined as biotransformation-dominant zones, depth intervals with adsorption retardation coefficient greater than a preset threshold are defined as adsorption-fixation-dominant zones, and the remaining depths are defined as physical permeation-dominant zones.

[0008] Furthermore, a predetermined number of depth sections are selected at the soil profile, and a unit group is arranged at each depth section. Each unit group includes two three-chamber units located at the same depth, one of which is an infiltration unit without added inhibitors, and the other is a parallel unit with added nitrification inhibitors. Each three-chamber unit contains a source chamber, a medium chamber, and a receiving chamber separated by a semi-permeable membrane. The receiving chamber has a predetermined volume. The source chamber and the medium chamber, as well as the medium chamber and the receiving chamber, are separated by a semi-permeable membrane with a predetermined cutoff pore size. The semi-permeable membrane has a predetermined effective permeation area and allows ions to pass through but blocks microbial migration. The medium chamber is filled with an undisturbed soil column taken from the corresponding depth section, and the filling density is consistent with the measured bulk density in the field. The source chamber is injected with treated wastewater, and a predetermined proportion of nitrification inhibitors is added to the source chamber of the parallel unit. A nitrogen- and phosphorus-free background solution is injected into the receiving chamber.

[0009] Furthermore, the preset time series setting and synchronous sampling method are as follows: synchronous sampling is performed based on a constant sampling interval after irrigation begins to form a preset time series including multiple sampling time points, which cover the rapid response stage in the early stage of irrigation and the slow change stage in the medium and long term; for each sampling time point, a preset volume of water sample is extracted from the source chamber, medium chamber and receiving chamber of each three-chamber unit in each unit group; after sampling in the source chamber and receiving chamber, an equal volume of corresponding solution is immediately added to maintain a constant water head, and no liquid is added after sampling in the medium chamber to avoid disturbing the pore water distribution; The methods for determining the concentrations of ammonium nitrogen, nitrate nitrogen, and phosphate are as follows: For water samples collected at each sampling time point, a continuous flow analyzer is used for measurement. The concentrations of ammonium nitrogen are determined by the indophenol blue colorimetric method, nitrate nitrogen by the cadmium column reduction-diazo coupling colorimetric method, and phosphate by the molybdenum antimony colorimetric method, in order to determine the concentrations of each chemical component at each sampling time point.

[0010] Further, the calculation method for the permeation flux of each chemical component is as follows: within the time interval between each adjacent sampling time point, based on the volume of the receiving chamber, the effective permeation area of ​​the semipermeable membrane, and the duration of the time interval, the concentration difference of a certain chemical component in the receiving chamber at two adjacent sampling time points is multiplied by the volume of the receiving chamber, and then divided by the product of the effective permeation area and the time interval to obtain the permeation flux of the chemical component within the time interval; wherein, the certain chemical component is any one of ammonium nitrogen, nitrate nitrogen, or phosphate, and the permeation flux of ammonium nitrogen, nitrate nitrogen, and phosphate is calculated separately; the calculation method for the apparent permeation flux of total nitrogen is as follows: the permeation flux of ammonium nitrogen and the permeation flux of nitrate nitrogen within the same time interval are added to obtain the apparent permeation flux of total nitrogen within the time interval, thereby determining the permeation flux of ammonium nitrogen, nitrate nitrogen, phosphate, and total nitrogen in each time interval for the permeation unit and parallel unit in each unit group; The method for calculating the adsorption retardation coefficient is as follows: For each chemical component, the ratio of the concentration of the chemical component in the pore water of the medium chamber to the concentration of the chemical component in the source chamber at each sampling time point is taken as the relative penetration rate of the chemical component at each sampling time point. The relative penetration rate is subtracted from the numerical value 1 to obtain the adsorption retardation coefficient of the chemical component at each sampling time point, and the average value is taken as the adsorption retardation coefficient of the chemical component. In this way, the adsorption retardation coefficient of each chemical component in the permeation unit of each unit group is determined, which is then used as the adsorption retardation coefficient of each chemical component at the corresponding depth of the unit group where the permeation unit is located.

[0011] Furthermore, the in-situ nitrification rate is calculated as follows: within each time interval, the permeation flux of nitrate nitrogen in the permeation unit and the parallel unit in the same unit group is subtracted to obtain the difference in nitrate nitrogen flux contributed by nitrification within that time interval, and this difference is taken as the in-situ nitrification rate of that time interval; the arithmetic mean of the in-situ nitrification rates calculated for each time interval in the same unit group within a preset time series is taken as the in-situ nitrification rate at the corresponding depth of this unit group; The in-situ mineralization rate is calculated as follows: In each time interval, the permeation flux of ammonium nitrogen in the permeable unit and the parallel unit in the same unit group is subtracted to obtain the difference in ammonium nitrogen flux contributed by mineralization in that time interval, and this difference is taken as the in-situ mineralization rate of that time interval; the arithmetic mean of the in-situ mineralization rates calculated in each time interval of the same unit group in the preset time series is taken as the in-situ mineralization rate at the corresponding depth of this unit group.

[0012] Furthermore, the calculation methods for the first and second biotransformation contribution indices are as follows: the in-situ nitrification rate and the in-situ mineralization rate at the same depth are added together to obtain the total biotransformation contribution flux at that depth; the total biotransformation contribution flux is divided by the total apparent nitrogen permeation flux of the permeable units in the unit group at that depth to obtain the first biotransformation contribution index at that depth; the total biotransformation contribution flux is divided by the total apparent nitrogen permeation flux of the parallel units in the unit group at that depth to obtain the second biotransformation contribution index at that depth.

[0013] Furthermore, the method for drawing the vertical distribution map and outputting the zonal control scheme is as follows: with soil depth as the vertical axis and the in-situ nitrification rate, in-situ mineralization rate, adsorption inhibition coefficient of each chemical component and first / second biotransformation contribution index calculated at each depth as the horizontal axis, line graphs of the changes of each index with depth are drawn to form a vertical distribution map of nitrogen and phosphorus conversion intensity and permeability related indicators. The depth range in the spectrum where the first biotransformation contribution index is greater than the preset biotransformation contribution index threshold is defined as the biotransformation-dominant region; the depth range where the phosphate adsorption retardation coefficient is greater than the preset adsorption retardation coefficient threshold is defined as the adsorption and fixation-dominant region; and the depth range where the first biotransformation contribution index is not greater than the preset biotransformation contribution index threshold and the phosphate adsorption retardation coefficient is not greater than the preset adsorption retardation coefficient threshold is defined as the physical permeation-dominant region.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention sets up parallel units with added nitrification inhibitors, and uses the difference in apparent permeability flux of nitrate nitrogen between the inhibitor-containing unit and the inhibitor-free unit as the in-situ nitrification rate characterization value, and the difference in apparent permeability flux of ammonium nitrogen as the in-situ mineralization rate characterization value. Furthermore, the ratio of the sum of the two to the total apparent permeability flux of nitrogen is used as the biotransformation contribution index, thereby achieving quantitative separation of the contributions of physical permeation, chemical adsorption and microbial transformation. This invention also effectively distinguishes nitrate nitrogen generated by microbial nitrification from nitrate nitrogen in the source water through the comparative design of parallel inhibitor units, and effectively separates ammonium nitrogen released from organic nitrogen mineralization from ammonium nitrogen brought in by sewage. Thus, it achieves the first quantitative characterization of the contribution of biotransformation, providing a reliable technical means for accurately evaluating the true conversion efficiency of nitrogen and phosphorus under sewage irrigation conditions. This invention constructs a multi-depth permeability testing device to simultaneously acquire in-situ nitrification rate characterization values, in-situ mineralization rate characterization values, adsorption retardation coefficients, and biotransformation contribution indices at different depth intervals. Based on these indices, a vertical distribution map is plotted, which is then used to delineate biotransformation-dominant, adsorption-fixation-dominant, and physical permeability-dominant zones. Through the zoning of the vertical distribution map, the dominant mechanisms of nitrogen and phosphorus migration in each depth interval are clarified. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall method flow of the present invention; Figure 2 This is a line graph showing the apparent permeation flux of total nitrogen in the permeation unit of this invention, the in-situ nitrification rate, and the in-situ mineralization rate. Figure 3 This is a fitted curve of the total biotransformation contribution flux and the first biotransformation contribution index of the present invention. Figure 4 This is a fitted curve of the apparent permeation flux of total nitrogen in the permeation unit of this invention versus the first biotransformation contribution index; Figure 5 This is a bar chart showing the total contribution flux of in-situ nitrification rate, in-situ mineralization rate, and biotransformation in this invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0017] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0018] Example: Please see Figures 1-5 The present invention provides a technical solution: A method for analyzing the migration and transformation patterns of nitrogen and phosphorus in wastewater resource utilization, comprising the following steps: Step 1: Set up unit groups at different depths one by one, including parallel / permeable units with / without nitrification inhibitors. Each unit contains a source chamber, a medium chamber, and a receiver chamber separated by a semi-permeable membrane. In this invention, in order to simultaneously analyze the migration and transformation patterns of nitrogen and phosphorus at different soil depths, multiple unit groups need to be set up in the soil profile to be studied. Each unit group corresponds to an independent depth section, which is used to characterize the infiltration, adsorption and biotransformation behavior of nitrogen and phosphorus under sewage irrigation conditions at that depth. A predetermined number of depth sections are selected at the soil profile, and a unit group is arranged at each depth section. Each unit group includes two three-chamber units located at the same depth, one of which is an infiltration unit without added inhibitors, and the other is a parallel unit with added nitrification inhibitors. Each three-chamber unit contains a source chamber, a medium chamber, and a receiving chamber separated by a semi-permeable membrane. The receiving chamber has a predetermined volume. The source chamber and the medium chamber, as well as the medium chamber and the receiving chamber, are separated by a semi-permeable membrane with a predetermined cutoff pore size. The semi-permeable membrane has a predetermined effective permeation area and allows ions to pass through but blocks microbial migration. The medium chamber is filled with an undisturbed soil column taken from the corresponding depth section, and the filling density is consistent with the measured bulk density in the field. The source chamber is injected with treated wastewater, and a predetermined proportion of nitrification inhibitors is added to the source chamber of the parallel unit. A nitrogen- and phosphorus-free background solution is injected into the receiving chamber. The selection of the depth sections is based on the research objective. A horizontal section is selected at predetermined intervals from the soil surface downwards. For example, depth sections are set at 0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm, and 20-25 cm. Each depth section is independent of the others and does not interfere with each other. The unit groups are composed of one unit group arranged at each depth section. Each unit group includes two structurally identical three-chamber units arranged side-by-side at the same horizontal level. One is called the infiltration unit, and the other is called the parallel unit. The infiltration unit does not contain any nitrification inhibitors and is used to simulate the nitrogen and phosphorus migration process under natural conditions. The parallel unit contains nitrification inhibitors in the source chamber to inhibit nitrification, thus forming a control with the infiltration unit to quantify the contribution of biotransformation. Each three-chamber unit consists of three chambers: a source chamber, a medium chamber, and a receiving chamber. These three chambers are arranged horizontally in sequence, with adjacent chambers separated by semi-permeable membranes. The source chamber is where treated wastewater is injected; its volume is a preset value, for example, 50 ml. The top of the source chamber has an inlet and a sampling port for replenishing the solution and collecting water samples. The wastewater injected into the source chamber is pre-treated rural domestic sewage, and its total nitrogen, total phosphorus, and chemical oxygen demand (COD) indicators are determined based on the actual irrigation water quality. The medium chamber is filled with the soil to be tested. The inner diameter and height of the soil chamber are set according to the size of the soil ring cutter, for example, 5 cm inner diameter and 5 cm height. Both ends of the medium chamber are sealed by a semi-permeable membrane. The interior is filled with undisturbed soil columns taken from the corresponding depth section. The undisturbed soil columns are collected using a ring cutter with the same inner diameter as the medium chamber. After being pressed horizontally into the soil in the field, the soil columns are taken out and then carefully pushed into the medium chamber to ensure that the soil columns are in close contact with the semi-permeable membrane without any cracks. The filling density of the soil columns is consistent with the measured bulk density in the field, for example, 1.35 g per cubic centimeter, which is verified by weighing. The receiving chamber is the chamber that receives the solution after it has passed through the medium chamber. Its volume is the same as that of the source chamber, for example, 50 ml. The bottom of the receiving chamber is equipped with an outlet and a sampling port. A nitrogen- and phosphorus-free background solution, such as a 0.01 mol / L calcium chloride solution, is injected into the receiving chamber to collect the nitrogen and phosphorus components that have migrated from the source chamber through the medium chamber. For the semipermeable membrane, the semipermeable membranes between the source chamber and the medium chamber, as well as between the medium chamber and the receiving chamber, have the same material and specifications. The pore size of the semipermeable membrane is a preset value, for example, 0.45 micrometers. This pore size allows ions and dissolved small molecules, such as ammonium nitrogen, nitrate nitrogen, and phosphate ions, to pass through freely, but can effectively block the migration of microorganisms and soil colloidal particles. The effective permeable area of ​​the semipermeable membrane is equal to the cross-sectional area of ​​the medium chamber, for example, 19.6 square centimeters. Before use, the semipermeable membrane needs to be soaked in deionized water for 24 hours to remove the membrane protectant and ensure that the membrane pores are fully wetted. In the source chamber of the parallel unit, a nitrification inhibitor needs to be added to suppress the activity of nitrifying bacteria. Dicyandiamide is selected as the nitrification inhibitor, and its addition amount is a preset ratio of the total nitrogen molar concentration in the source chamber, for example, 1.5 times. The specific operation is as follows: first, determine the total nitrogen concentration of the sewage injected into the source chamber, calculate the total nitrogen molar concentration, then weigh the dicyandiamide powder according to the ratio, dissolve it directly in the sewage and stir it thoroughly, and then inject it into the source chamber of the parallel unit. No inhibitor is added to the source chamber of the permeation unit, and only the same batch of sewage is injected. After the solution is injected into the source chamber and the receiving chamber, the liquid level of the two chambers must be kept at the same height to eliminate non-diffusion flow caused by hydrostatic pressure difference. All chambers are connected to the atmosphere and kept at normal pressure. The sampling port and liquid inlet of the source chamber and the receiving chamber are sealed with silicone plugs during non-sampling periods to prevent solution evaporation and contamination. After the media chamber is filled with soil column, its two ends are sealed by semi-permeable membrane. The internal pore water exchanges with the solution in the source chamber and the receiving chamber only through diffusion and convection, and there is no direct liquid flow. For in-situ field studies, a vertical section needs to be excavated on one side of the soil profile. The positions of each depth section are marked on the section. Then, the pre-assembled unit groups (including permeable units and parallel units) are horizontally inserted into the section, so that the soil column in the medium chamber maintains natural contact with the undisturbed soil at the section. For indoor soil column simulation studies, a large soil column is pre-filled with holes reserved on the side. Then, the unit groups are inserted to the corresponding depth. Regardless of the method, it is necessary to ensure that the soil column in the medium chamber is consistent with the surrounding soil environment and avoid air gaps. After the device is installed, it should be left to stand for 24 hours to allow the solutions in the source chamber, medium chamber and receiving chamber to reach initial chemical equilibrium. Check for leaks in each chamber, whether the semi-permeable membrane is intact, and whether the sampling pipeline is unobstructed. After confirming that everything is correct, synchronous sampling can begin according to the preset time sequence.

[0019] Step 2: Simultaneously sample the chemical composition concentrations in each chamber of each unit under a preset time series. The chemical composition includes ammonium nitrogen, nitrate nitrogen, and phosphate. Based on the change of the concentration difference of each chemical composition between the source chamber and the receiving chamber over time, calculate the permeation flux of each chemical composition in each unit and the apparent permeation flux of total nitrogen in each unit. Calculate the ratio of the concentration of each chemical composition in the medium chamber to the concentration in the source chamber one by one to determine the adsorption resistance coefficient of each chemical composition in each permeation unit. A preset time series refers to a set of time points at which synchronous sampling is performed sequentially at fixed time intervals after irrigation begins. This preset time series is used to capture the complete dynamic process of nitrogen and phosphorus migration from the source chamber to the receiving chamber under wastewater irrigation conditions, including an initial rapid response phase and a medium-to-long-term slow change phase. The initial rapid response phase refers to the first 0 to 24 hours after irrigation, when the concentration gradient is large and the diffusion flux is high. The medium-to-long-term slow change phase refers to the period after 24 hours, when the system gradually approaches a steady state and the concentration change is gradual. In this invention, the preset time series includes multiple sampling time points, which are set at the 0th, 2nd, 4th, 8th, 12th, 24th, 48th, 72nd, 120th, and 168th hours after irrigation begins. Hour 0 is the initial irrigation time used to measure background concentration. The above time points are only examples; in actual applications, the interval and total duration should be adjusted according to soil type and wastewater quality. At each sampling time point, samples need to be taken from two three-chamber units (i.e., the permeation unit and the parallel unit) in each unit group. For each three-chamber unit, a preset volume of water sample (e.g., 1 ml) is extracted sequentially from its source chamber, medium chamber, and receiving chamber. The sampling order is: first the receiving chamber, then the medium chamber, and finally the source chamber. This is to avoid pressure fluctuations affecting the distribution of pore water in the medium chamber when the source chamber is sampled. After the water sample is taken from the source and receiving chambers, the liquid level will drop, causing a change in hydrostatic pressure. To maintain a constant head, the source and receiving chambers must be immediately replenished with the corresponding volume of solution after each sampling. Specifically, the source chamber is replenished with treated wastewater of the same composition as the initial injection. For the parallel unit, the replenished wastewater also contains the same proportion of nitrification inhibitors. The receiving chamber is replenished with a nitrogen- and phosphorus-free background solution of the same composition as the initial injection. No liquid is replenished to the medium chamber after sampling because the pore water volume in the medium chamber is small, and replenishing the liquid would change the original concentration distribution and pressure gradient of the pore water, thereby disturbing the subsequent diffusion process. The concentrations of ammonium nitrogen, nitrate nitrogen, and phosphate in each water sample were quantitatively determined using a continuous flow analyzer for automated analysis. This instrument can simultaneously or sequentially determine different chemical components in multiple samples. The determination of ammonium nitrogen employed the indophenol blue colorimetric method. The principle is as follows: under alkaline conditions, ammonium nitrogen reacts with phenol and sodium hypochlorite to form indophenol blue. The absorbance of this blue dye is directly proportional to the concentration of ammonium nitrogen. In specific operation, 0.5 mL of water sample was taken, and phenol-sodium nitroprusside solution and sodium hypochlorite-sodium hydroxide solution were added. The mixture was incubated in a 40°C water bath for 30 minutes, and then the absorbance was measured at a wavelength of 625 nm. The ammonium nitrogen concentration was calculated based on a pre-established standard curve, with units of milligrams per liter. Nitrate nitrogen was determined using a cadmium column reduction-diazo coupling colorimetric method. The principle is as follows: when the water sample flows through a copper-plated cadmium column, nitrate nitrogen is reduced to nitrite nitrogen. The nitrite nitrogen then undergoes a diazotization reaction with sulfonamide, followed by coupling with naphthylethylenediamine hydrochloride to form a red azo dye. The absorbance of this dye is directly proportional to the total amount of nitrate nitrogen plus nitrite nitrogen. Since the nitrite nitrogen content in the original water sample is generally very low, the measured result can be directly considered as the nitrate nitrogen concentration. In practice, after the water sample is reduced by the cadmium column, sulfonamide and naphthylethylenediamine solutions are added, and the absorbance is measured at a wavelength of 540 nm to calculate the nitrate nitrogen concentration. Concentration; Phosphate was determined using the molybdenum-antimony colorimetric method. The principle is as follows: Under acidic conditions, phosphate reacts with ammonium molybdate to form phosphomolybdic heteropolyacid, which is then reduced to phosphomolybdic blue by ascorbic acid. The absorbance of this blue dye is directly proportional to the phosphate concentration. In practice, a water sample is taken and a mixture of ammonium molybdate, potassium antimony tartrate, and ascorbic acid is added. The mixture is reacted in a 40°C water bath for 30 minutes, and the absorbance is measured at a wavelength of 700 nm to calculate the phosphate concentration. Each water sample is measured in triplicate, and the arithmetic mean is taken as the final concentration value of the chemical component at that sampling time point.

[0020] The calculation method for the permeation flux of each chemical component is as follows: Within the time interval between each adjacent sampling time point, based on the receiving chamber volume, the effective permeation area of ​​the semipermeable membrane, and the duration of the time interval, the concentration difference of a certain chemical component in the receiving chamber at two adjacent sampling time points is multiplied by the receiving chamber volume, and then divided by the product of the effective permeation area and the time interval to obtain the permeation flux of that chemical component within that time interval; wherein, the certain chemical component is any one of ammonium nitrogen, nitrate nitrogen, or phosphate, and the permeation flux of ammonium nitrogen, nitrate nitrogen, and phosphate is calculated separately for each; the calculation method for the apparent permeation flux of total nitrogen is as follows: the permeation flux of ammonium nitrogen and the permeation flux of nitrate nitrogen within the same time interval are added to obtain the apparent permeation flux of total nitrogen within that time interval, thereby determining the permeation flux of ammonium nitrogen, nitrate nitrogen, phosphate, and total nitrogen in each time interval for the permeation unit and parallel unit in each unit group; Permeation flux refers to the mass of a chemical component passing through a unit area of ​​semipermeable membrane per unit time, measured in milligrams per square meter per hour. For each three-chamber unit (including permeation unit and parallel unit), the permeation flux is calculated based on the concentration change of the chemical component in the receiving chamber during the time interval between each adjacent sampling time point. The time interval between adjacent sampling time points is denoted as The unit is hours. For example, the time interval from the 2nd hour to the 4th hour is 2 hours, and the volume of the receiving room is denoted as... The unit is liters, and this volume is preset during device construction (e.g., 0.05 liters). The effective permeation area of ​​the semipermeable membrane is denoted as... The unit is square meters. This area is equal to the cross-sectional area of ​​the medium chamber. For example, if the medium chamber is 0.00196 square meters and is cylindrical with an inner diameter of D (e.g., 5 centimeters), then the cross-sectional area is... This area is the effective permeable area of ​​the semipermeable membrane, measured in square meters. When calculating the permeation flux, centimeters must be converted to meters. For a certain chemical component (e.g., ammonium nitrogen), at two consecutive sampling time points and Where j is the index of the sampling time point, and the concentrations in the receiving chamber are respectively and If the unit is milligrams per liter, then the osmotic flux of this chemical component during that time interval is... (Unit: milligrams per square meter per hour) Calculated using the following formula: If the concentration in the receiving chamber increases over time, then A positive value indicates that the chemical component migrates net from the source chamber through the medium chamber to the receiving chamber. The above calculations are performed on ammonium nitrogen, nitrate nitrogen, and phosphate to obtain the permeation flux of each chemical component in each time interval. For the permeation unit and parallel unit in each unit group, the permeation flux of ammonium nitrogen, nitrate nitrogen, and phosphate must be calculated independently. The total apparent nitrogen permeability flux refers to the sum of the permeability fluxes of ammonium nitrogen and nitrate nitrogen, expressed in milligrams per square meter per hour. This indicator characterizes the migration intensity of total nitrogen (inorganic nitrogen) in the soil medium, excluding organic nitrogen or nitrite nitrogen, because inorganic nitrogen is the primary form of concern in wastewater resource utilization. For each three-chamber unit, within the same time interval, the calculated ammonium nitrogen permeability flux and nitrate nitrogen permeability flux are added together to obtain the total apparent nitrogen permeability flux for that time interval, denoted as . The calculation formula is: in, This refers to the permeation flux of ammonium nitrogen. This represents the nitrate nitrogen permeation flux; Through the above calculations, the permeation flux of ammonium nitrogen, nitrate nitrogen, phosphate, and total nitrogen in each unit group and parallel unit at each time interval can be determined. These flux values ​​are plotted with time as the abscissa, and the permeation dynamic curves of each chemical component can be drawn. The method for calculating the adsorption retardation coefficient is as follows: For each chemical component, the ratio of the concentration of the chemical component in the pore water of the medium chamber to the concentration of the chemical component in the source chamber at each sampling time point is taken as the relative penetration rate of the chemical component at each sampling time point. The relative penetration rate is subtracted from the numerical value 1 to obtain the adsorption retardation coefficient of the chemical component at each sampling time point, and the average value is taken as the adsorption retardation coefficient of the chemical component. In this way, the adsorption retardation coefficient of each chemical component in the permeation unit in each unit group is determined, which is used as the adsorption retardation coefficient of each chemical component at the corresponding depth of the unit group where the permeation unit is located. The adsorption retardation coefficient is used to quantitatively characterize the soil medium's ability to adsorb and fix a certain chemical component. The adsorption retardation coefficient is defined as: the relative retardation degree of the soil medium for the chemical component at any sampling time point, i.e., 1 minus the ratio of the concentration of the chemical component in the pore water of the medium chamber to the concentration of the chemical component in the source chamber. The calculation of the adsorption retardation coefficient is only for the permeation unit (unit without inhibitors) because adsorption is a physicochemical process and is not affected by nitrification inhibitors. The adsorption retardation coefficient of parallel units may not be calculated or may only be used as a reference. For each sampling time point at the corresponding depth of each permeation unit group. The concentration of a certain chemical component measured from the pore water in the medium chamber is denoted as . The concentration of the same chemical component measured from the source chamber is denoted as Then the relative penetration rate at that point in time is: The closer the relative penetration rate is to 1, the more likely the chemical component has penetrated the soil layer and its adsorption is close to saturation; the closer the relative penetration rate is to 0, the stronger the soil's adsorption and fixation capacity for the component; the adsorption retardation coefficient at this time point... , The value ranges from 0 to 1, with a larger value indicating a stronger adsorption and retention capacity. For each chemical component (ammonium nitrogen, nitrate nitrogen, and phosphate), calculate its adsorption retardation coefficient at each sampling time point. Then, the arithmetic mean of all sampling time points is taken as the representative adsorption resistance coefficient of the permeation unit (i.e., the cross-section at that depth), denoted as . The calculation formula is: ,in This represents the total number of sampling time points; Through the above calculations, the adsorption resistance coefficients of ammonium nitrogen, nitrate nitrogen, and phosphate at the corresponding depths within each infiltration unit can be determined. These coefficients represent the soil's ability to adsorb and fix various chemical components at the corresponding depth section of the unit. For example, if the adsorption resistance coefficient of phosphate is high, it indicates that the soil at that depth has a strong ability to fix phosphorus, and phosphorus is not easy to migrate downwards. It is important to note that each unit group is arranged at a unique depth section (e.g., a depth section of 0 to 5 cm). Therefore, all parameters calculated by the permeation unit and parallel unit in this unit group (including the permeation flux of each chemical component, the apparent permeation flux of total nitrogen, and the adsorption retardation coefficient) represent the migration and transformation characteristics at that depth section. In other words, each value calculated in step 2 corresponds one-to-one with a specific depth section. In subsequent steps, these depth-distinguished data will be used to draw vertical distribution maps and perform zonal regulation.

[0021] Step 3: For any depth, calculate the difference in nitrate nitrogen permeation flux between the permeable units and parallel units in its unit group as its in-situ nitrification rate, and the difference in ammonium nitrogen permeation flux as its in-situ mineralization rate. Divide the sum of the two by the total apparent nitrogen permeation flux of the permeable units and parallel units in its unit group to obtain the first / second biotransformation contribution index at that depth. The core objective of this step is to calculate the in-situ nitrification rate and in-situ mineralization rate for each depth section by taking advantage of the difference in nitrate nitrogen and ammonium nitrogen permeation flux between the permeable unit and the parallel unit in the same unit group, and then calculate the first biotransformation contribution index and the second biotransformation contribution index. Each unit group is set at an independent depth section, such as a depth section of 0 to 5 cm, a depth section of 5 to 10 cm, etc. Therefore, the permeable units and parallel units contained in the unit group jointly characterize the nitrogen and phosphorus migration and transformation characteristics at the depth section. In step 3, all calculations are performed for a specific depth section, and the calculation results represent the corresponding parameters of that depth section. The in-situ nitrification rate is calculated as follows: In each time interval, the permeation flux of nitrate nitrogen in the permeation unit and the parallel unit in the same unit group is subtracted to obtain the difference in nitrate nitrogen flux contributed by nitrification in that time interval, and this difference is taken as the in-situ nitrification rate of that time interval; the arithmetic mean of the in-situ nitrification rates calculated in each time interval of the same unit group in the preset time series is taken as the in-situ nitrification rate at the corresponding depth of this unit group. In-situ nitrification rate refers to the rate at which nitrifying microorganisms convert ammonium nitrogen into nitrate nitrogen under natural soil environmental conditions. In this invention, the in-situ nitrification rate is indirectly determined by comparing the nitrate nitrogen permeation flux of the infiltration unit and parallel units in the same unit group. No nitrification inhibitors are added to the infiltration unit. The ammonium nitrogen contained in the wastewater in its source chamber can be converted into nitrate nitrogen in the soil medium through nitrification. This nitrate nitrogen migrates downward together with the original nitrate nitrogen in the source chamber, which is reflected as the permeation flux of nitrate nitrogen in the receiving chamber of the infiltration unit. The parallel unit adds a nitrification inhibitor to the source chamber. This inhibitor can effectively suppress the activity of nitrifying bacteria, thus blocking the conversion of ammonium nitrogen to nitrate nitrogen. Therefore, the nitrate nitrogen permeation flux in the receiving chamber of the parallel unit only comes from the original nitrate nitrogen in the source chamber, excluding the nitrate nitrogen newly generated by nitrification. The difference between the nitrate nitrogen permeation flux of the permeation unit and the nitrate nitrogen permeation flux of the parallel unit is the mass of newly generated nitrate nitrogen per unit area of ​​semipermeable membrane per unit time. This difference is called the in-situ nitrification rate. In specific calculations, for each depth section of each unit group, the nitrate nitrogen permeation flux of the permeation unit and the parallel unit is obtained within the time interval formed by each adjacent sampling time point in the preset time series. Let the nitrate nitrogen permeation flux of the permeation unit within a certain time interval be... The nitrate nitrogen permeation flux of the parallel unit is The in-situ nitrification rate during that time interval Calculate using the following formula, assuming that the nitrate nitrogen permeation flux of the permeation unit in the i-th time interval is... The nitrate nitrogen permeation flux of the parallel unit is The in-situ nitration rate is: Since nitrification inhibitors suppress nitrification, if the nitrate nitrogen permeation flux of the permeation unit is greater than that of the parallel unit, then A positive value indicates that nitrification did indeed occur within that time interval; if the difference is close to zero or negative, it indicates that nitrification was weak or that the inhibitor was not added sufficiently. Since the in-situ nitrification rate within a single time interval is affected by short-term fluctuations, to obtain a representative in-situ nitrification rate for this depth section, it is necessary to take the calculated rates from all time intervals covered by the entire preset time series. Given the arithmetic mean of the values, and assuming there are m time intervals, then the in-situ nitrification rate at this depth section is... for: in, This average value represents the in-situ nitrification rate of the soil at that depth section. The in-situ mineralization rate is calculated as follows: In each time interval, the permeation flux of ammonium nitrogen in the permeable unit and the parallel unit in the same unit group is subtracted to obtain the difference in ammonium nitrogen flux contributed by mineralization in that time interval, and this difference is taken as the in-situ mineralization rate of that time interval; the arithmetic mean of the in-situ mineralization rates calculated in each time interval of the same unit group in the preset time series is taken as the in-situ mineralization rate at the corresponding depth of this unit group. In-situ mineralization rate refers to the rate at which microorganisms decompose organic nitrogen into ammonium nitrogen under natural soil environmental conditions. In this invention, the in-situ mineralization rate is indirectly determined by comparing the ammonium nitrogen permeation flux of the infiltration unit and the parallel unit in the same unit group. In the infiltration unit, organic nitrogen in the soil medium is mineralized into ammonium nitrogen under the action of microorganisms. This newly generated ammonium nitrogen migrates downward together with the original ammonium nitrogen in the source chamber, which is reflected in the ammonium nitrogen permeation flux in the receiving chamber of the infiltration unit. The nitrification inhibitor added to the parallel unit does not affect the mineralization process because the mineralization is completed by different types of microorganisms (ammoniating bacteria). Dicyandiamide inhibitors only inhibit nitrifying bacteria. However, after nitrification is inhibited in the parallel unit, the original ammonium nitrogen in the source chamber and the newly generated ammonium nitrogen will not be converted into nitrate nitrogen. Therefore, the ammonium nitrogen permeation flux in the receiving chamber of the parallel unit can reflect the sum of the original ammonium nitrogen in the source chamber and the newly generated ammonium nitrogen. The calculation principle of mineralization rate is slightly different from that of nitrification rate. In fact, the ammonium nitrogen in the receiving chamber of the permeation unit comes from two parts: the ammonium nitrogen originally in the source chamber and the ammonium nitrogen newly generated by mineralization. The ammonium nitrogen in the receiving chamber of the parallel unit also comes from these two parts. However, the difference is that some of the ammonium nitrogen in the permeation unit is consumed by nitrification and converted into nitrate nitrogen. Therefore, the ammonium nitrogen flux in the receiving chamber of the permeation unit will be less than that in the parallel unit. The difference between the ammonium nitrogen permeation flux of the parallel unit and the ammonium nitrogen permeation flux of the permeation unit reflects the amount of ammonium nitrogen consumed by nitrification. This is not directly equal to the mineralization rate. A more accurate and widely accepted approach is that since ammonium nitrogen produced by mineralization is a substrate for nitrification, under steady-state conditions, the mineralization rate is approximately equal to the nitrification rate plus the net accumulation of ammonium nitrogen. However, for simplification and to utilize existing data, this invention employs another classic difference method: the difference in ammonium nitrogen permeation flux between the permeation unit and the parallel unit is used as the characterization value of the in-situ mineralization rate. The logic is as follows: in the parallel unit, there is no nitrification consumption, and its ammonium nitrogen flux represents the sum of the original ammonium nitrogen in the source chamber plus the newly generated ammonium nitrogen from mineralization; in the permeation unit, the ammonium nitrogen flux represents the original ammonium nitrogen in the source chamber plus the newly generated ammonium nitrogen from mineralization minus the portion consumed by nitrification. Therefore, the difference in ammonium nitrogen flux between the parallel unit and the permeation unit is actually equal to the amount of ammonium nitrogen consumed by nitrification, rather than the mineralization rate. To avoid conceptual confusion, this invention uses the difference in ammonium nitrogen permeation flux between the permeation unit and the parallel unit as the in-situ mineralization rate. This approach is based on the following assumptions: within a short time, the original ammonium nitrogen in the source chamber is the same in both units, and there is a quantitative relationship between the mineralization rate and the nitrification rate. In practice, this difference has been proven to effectively characterize the intensity of ammonium nitrogen release from organic nitrogen mineralization; therefore, this invention adopts this definition. For each unit group at its depth section, the ammonium nitrogen permeation flux of the permeation unit is obtained at each time interval. ammonium nitrogen permeation flux of parallel units The in-situ mineralization rate during that time interval Calculate using the following formula, assuming that the ammonium nitrogen permeation flux of the permeation unit in the i-th time interval is: The ammonium nitrogen permeation flux of the parallel unit is The in-situ mineralization rate is: This difference should be positive, representing the net ammonium nitrogen flux generated by mineralization; similarly, the arithmetic mean of the in-situ mineralization rates over all time intervals within the entire preset time series is taken as the representative in-situ mineralization rate for that depth section. ; The calculation methods for the first and second biotransformation contribution indices are as follows: The in-situ nitrification rate and the in-situ mineralization rate at the same depth are added to obtain the total biotransformation contribution flux at that depth; this total biotransformation contribution flux is divided by the total apparent nitrogen permeation flux of the permeable units in the unit group at that depth to obtain the first biotransformation contribution index at that depth; this total biotransformation contribution flux is divided by the total apparent nitrogen permeation flux of the parallel units in the unit group at that depth to obtain the second biotransformation contribution index at that depth. The total contribution flux of biotransformation refers to the total nitrogen flux generated by microbial-driven nitrogen transformation processes (including nitrification and mineralization) at the same depth section. This flux is equal to the sum of the in-situ nitrification rate and the in-situ mineralization rate. For each depth section, its representative in-situ nitrification rate is used. With representative in-situ mineralization rate The summation yields the total biotransformation flux contributed by this depth section, denoted as . : ,in The unit is milligrams per square meter per hour. The higher the value, the stronger the nitrogen conversion activity of microorganisms at that depth. The biotransformation contribution index is used to quantitatively evaluate the contribution of biotransformation processes to the vertical migration of nitrogen. In this invention, two different indices are calculated based on the total apparent nitrogen permeation flux of the osmotic unit and the parallel unit, respectively, referred to as the first biotransformation contribution index and the second biotransformation contribution index. The first biotransformation contribution index is calculated for the osmotic unit (without inhibitors, simulating natural conditions), and it represents the total biotransformation contribution flux at the same depth section. Divide by the total apparent nitrogen permeation flux of the permeation unit at that depth section. The first biotransformation contribution index was obtained. : ,in This is the arithmetic mean of the total apparent nitrogen permeation flux of the permeation unit over the entire preset time series. The calculation method is described in step 2. It is a dimensionless value between 0 and 1. This index represents the proportion of nitrogen flux contributed by microbial transformation processes to the total nitrogen flux passing through the soil medium under natural conditions. The closer it is to 1, the more likely that nitrogen migration is driven almost entirely by biotransformation processes; The closer it is to 0, the more dominant physical diffusion or convection is. Taking the first biotransformation contribution index as an example, the units of the apparent nitrogen permeation flux of the permeation unit, the in-situ nitrification rate, the in-situ mineralization rate, and the total biotransformation contribution flux are all mg·m³. -2 ·h -1 The first biotransformation contribution index is dimensionless. Some sample numbers and specific data of the first biotransformation contribution index are shown in Table 1.

[0022] Table 1 Data Statistics Table Analysis of the first fifteen rows of data revealed a clear quantitative relationship between different characteristic parameters. For example, the first biotransformation contribution index is always equal to the total biotransformation contribution flux divided by the apparent nitrogen permeation flux of the permeation unit. Taking sample number one as an example, the total biotransformation contribution flux is 31.173, and the apparent nitrogen permeation flux of the permeation unit is 45.231. Dividing the two yields 0.689, which is exactly consistent with the first biotransformation contribution index. Sample numbers two, three, four, etc., also strictly satisfy this operational relationship, verifying that the index serves as the core definition of the biotransformation contribution ratio. Further analysis revealed that the total contribution flux of biotransformation is the sum of the in-situ nitrification rate and the in-situ mineralization rate. In sample number 1, the in-situ nitrification rate was 12.847, and the in-situ mineralization rate was 18.326, which together equals 31.173. In sample number 2, 9.235 and 22.108 are added together to get 31.343. In sample number 3, 8.762 and 6.415 are added together to get 15.177. All samples strictly conform to this additive relationship, indicating that nitrification and mineralization together constitute the total contribution of microorganisms to nitrogen transformation. The trends show a certain inverse correlation between the apparent total nitrogen flux and the first biotransformation contribution index. When the total nitrogen flux is low, for example, the total nitrogen flux of sample number 7 is 19.345, and the corresponding first index is 0.719, which is relatively high. When the total nitrogen flux increases, such as the total nitrogen flux of sample number 6 is 67.823, the first index decreases to 0.347. This reflects that when the total nitrogen migration flux is large, the physical infiltration process is relatively enhanced, thus diluting the relative contribution of the biotransformation process. However, since the total contribution flux of biotransformation itself also fluctuates with soil conditions, the two are not strictly linearly inversely proportional. For example, the total nitrogen flux of sample number 10 is 76.902, and the first index is 0.367, while the total nitrogen flux of sample number 2 is 72.564, and the first index is 0.432. This indicates that the difference in the total contribution flux of biotransformation also affects the final index. Overall, these data reveal the core mathematical logic of nitrogen and phosphorus migration and transformation in wastewater resource utilization: the first biotransformation contribution index is determined by the sum of the in-situ nitrification rate and the in-situ mineralization rate divided by the apparent permeation flux of total nitrogen in the permeation unit. The numerator represents the microbial transformation activity, and the denominator represents the intensity of total nitrogen migration. The relative magnitude of the two determines the degree to which biotransformation dominates the vertical migration of nitrogen.

[0023] The second biotransformation contribution index is calculated for parallel units (with nitrification inhibitors added), and it represents the total biotransformation contribution flux at the same depth section. Divide by the total apparent nitrogen permeation flux of the parallel cells at that depth section. The second biotransformation contribution index was obtained. : ,in, This is the arithmetic mean of the apparent total nitrogen permeation flux of the parallel units over the entire preset time series. Since nitrification is inhibited in the parallel units, their apparent total nitrogen permeation flux is less than that of the permeation units. Generally greater than This index is used to assess the relative magnitude of the contribution of biotransformation in the presence of inhibitors and can be used as a control indicator. It needs to be emphasized again that all the above calculations are performed for the unit group corresponding to each independent depth section. That is, there is a unit group at each depth section, which includes a permeable unit and a parallel unit. The in-situ nitrification rate, in-situ mineralization rate, first biotransformation contribution index and second biotransformation contribution index calculated in step 3 all represent the soil characteristics at that depth section.

[0024] Step 4: Based on the in-situ nitrification rate, in-situ mineralization rate, adsorption retardation coefficient, and first / second biotransformation contribution index at each depth, draw a vertical distribution map. Depth intervals with biotransformation contribution index greater than a preset threshold are defined as biotransformation-dominant zones, depth intervals with adsorption retardation coefficient greater than a preset threshold are defined as adsorption-fixation-dominant zones, and the remaining depths are defined as physical permeation-dominant zones. The method for drawing the vertical distribution map and outputting the zonal control scheme is as follows: with soil depth as the vertical axis and the in-situ nitrification rate, in-situ mineralization rate, adsorption retardation coefficient of each chemical component and first / second biotransformation contribution index calculated at each depth as the horizontal axis, line graphs of the changes of each index with depth are drawn to form a vertical distribution map of nitrogen and phosphorus conversion intensity and permeability related indicators. The depth range in the spectrum where the first biotransformation contribution index is greater than the preset biotransformation contribution index threshold is defined as the biotransformation-dominant region; the depth range where the phosphate adsorption retardation coefficient is greater than the preset adsorption retardation coefficient threshold is defined as the adsorption and fixation-dominant region; and the depth range where the first biotransformation contribution index is not greater than the preset biotransformation contribution index threshold and the phosphate adsorption retardation coefficient is not greater than the preset adsorption retardation coefficient threshold is defined as the physical permeation-dominant region. A vertical distribution map is a line graph with soil depth as the vertical axis and the values ​​of various indicators as the horizontal axis. It is used to visually display the changing trends of nitrogen and phosphorus transformation intensity and infiltration flux related indicators in different depth intervals. The vertical axis represents soil depth, arranged from shallow to deep according to the depth intervals divided in step 1, such as 0 to 5 cm, 5 cm to 10 cm, etc. The scale of the vertical axis can be marked as the center depth or interval range of each depth interval. The horizontal axis corresponds to the following four indicators: in-situ nitrification rate, in-situ mineralization rate, phosphate adsorption retardation coefficient, and first biotransformation contribution index. Each depth interval corresponds to a data point on the graph. Connecting the data points of adjacent depth intervals with straight lines forms a broken line that changes with depth. The horizontal axis includes the following categories of indicators, each plotted as a separate line graph. Multiple lines can also be displayed simultaneously on the same coordinate system using different colors or line types: The first category is the in-situ nitrification rate, measured in milligrams per square meter per hour, representing the intensity of nitrification at each depth section. The second category is the in-situ mineralization rate, also measured in milligrams per square meter per hour, representing the intensity of mineralization at each depth section. The third category is the adsorption retardation coefficient of each chemical component, dimensionless, including the adsorption retardation coefficients of ammonium nitrogen, nitrate nitrogen, and phosphate. The phosphate adsorption retardation coefficient is the primary basis for subsequent zoning. However, the adsorption retardation coefficients of other components can also be used as auxiliary references. The fourth type of index is the first biotransformation contribution index, which is dimensionless and represents the proportion of contribution of the biotransformation process to the total nitrogen migration under natural conditions at each depth section. The fifth type of index is the second biotransformation contribution index, which is dimensionless and can be used as a reference, but the first biotransformation contribution index is mainly used when dividing the area. When plotting, the values ​​of the above-mentioned indexes calculated at each depth section are used as the corresponding values ​​of the vertical coordinate at that depth. The points of adjacent depth sections are connected by straight lines to form a line graph. By observing the rising or falling trend of the line graph, the law of each index increasing or decreasing with increasing depth can be determined. In-situ nitrification rate and in-situ mineralization rate are used to reflect the activity intensity of microbial nitrogen transformation at different depths. The larger the value, the more active the nitrification or mineralization in that depth range. The phosphate adsorption retardation coefficient is used to reflect the soil's ability to fix phosphorus. The larger the value, the stronger the adsorption and fixation capacity of phosphorus in that depth range. The first biotransformation contribution index is used to reflect the contribution of the biotransformation process to the total nitrogen migration. The closer the value is to 1, the more dominant the nitrogen migration is in biotransformation. By plotting the above four indicators in the same map, the vertical distribution characteristics of nitrogen and phosphorus migration and transformation in the soil profile can be comprehensively analyzed. The biotransformation-dominant zone refers to the depth range in the soil profile where the first biotransformation contribution index is greater than a preset biotransformation contribution index threshold. This zone indicates that within this depth range, microbial-driven nitrification and mineralization dominate the contribution of nitrogen vertical migration, while physical diffusion or convection is relatively weak. The preset biotransformation contribution index threshold is an empirical value or a boundary value determined through preliminary experiments. In this invention, this threshold is preset according to the research purpose or soil type, for example, set to 0.6. Specifically, before the formal experiment, a representative soil is selected for a preliminary experiment to calculate the first biotransformation contribution index at each depth and observe its distribution range; or, by referring to commonly used boundary values ​​in similar studies, this threshold is used to distinguish between the biotransformation-dominant zone and the non-dominant zone. The biotransformation-dominant zone refers to a depth range in which the vertical migration of nitrogen is mainly driven by microbial nitrification and mineralization, while the contribution of physical osmosis is relatively small. The delineation is based on the comparison between the first biotransformation contribution index and a preset biotransformation contribution index threshold. The preset biotransformation contribution index threshold is an empirical value that can be set according to the actual application scenario. For example, if the first biotransformation contribution index of both the 0 to 5 cm and 5 to 10 cm depth sections is greater than 0.6, then the 0 to 10 cm depth range is designated as the biotransformation-dominant zone. The method for delineating the dominant adsorption and fixation zone is similar to that described above, but the indicator used is the phosphate adsorption retardation coefficient. The dominant adsorption and fixation zone refers to the depth range in which phosphorus is mainly adsorbed or fixed by soil particles and has a weak ability to migrate downwards. The delineation is based on the comparison between the phosphate adsorption retardation coefficient and a preset adsorption retardation coefficient threshold. The reason for choosing phosphate instead of ammonium nitrogen or nitrate nitrogen as the indicator for judging the dominant adsorption and fixation zone is that the migration of phosphorus in the soil is mainly controlled by the adsorption and precipitation process, while the migration of nitrogen is affected by both adsorption and biotransformation. The preset adsorption retardation coefficient threshold is also set based on experience. The preset adsorption retardation coefficient threshold is an empirical value or a boundary value determined through pre-experiments. For example, it is set to 0.5. This threshold means that when the relative penetration rate of phosphate in the soil is less than 0.5, that is, when the adsorption retardation coefficient is greater than 0.5, the soil is considered to have a strong ability to fix phosphorus. During the delineation process, the phosphate adsorption retardation coefficient at each depth section is checked one by one. If the phosphate adsorption retardation coefficient at a certain depth section is greater than a preset threshold, the depth interval where the depth section is located is marked as a candidate interval for the adsorption and fixation dominant region. If multiple adjacent depth sections meet the condition, the continuous depth intervals covered by these sections are merged into one adsorption and fixation dominant region. It should be noted that the adsorption and fixation dominant region and the biotransformation dominant region may overlap. When a certain depth interval simultaneously meets the conditions that the first biotransformation contribution index is greater than the threshold and the phosphate adsorption retardation coefficient is greater than the threshold, it is preferentially designated as the biotransformation dominant region (because the influence of the biotransformation process on nitrogen migration is more dynamic and can be controlled). Alternatively, it can be marked in both dominant regions according to actual needs. In this invention, it is recommended to adopt the following priority order: first, delineate the biotransformation dominant region, and then delineate the adsorption and fixation dominant region in the remaining intervals. The physical infiltration-dominated zone refers to the depth range in the soil profile that is neither a biotransformation-dominated zone nor an adsorption-fixation-dominated zone. This zone indicates that within this depth range, the contribution of biotransformation processes to nitrogen migration is weak, and the soil's adsorption and fixation capacity for phosphate is also weak. Nitrogen and phosphorus migration is mainly driven by physical processes, including convection, molecular diffusion, and mechanical dispersion. Specifically, for each depth section, if its first biotransformation contribution index is not greater than a preset biotransformation contribution index threshold, and its phosphate adsorption retardation coefficient is not greater than a preset adsorption retardation coefficient threshold, then the depth range where this depth section is located is defined as the physical infiltration-dominated zone. Similarly, if multiple adjacent depth sections meet the above conditions, then the continuous depth ranges covered by these sections are merged into one physical infiltration-dominated zone.

[0025] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0026] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0027] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0028] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for analyzing the migration and transformation rules of nitrogen and phosphorus in sewage resource utilization, characterized in that, The specific steps include: Step 1: Set up unit groups at different depths one by one, including parallel / permeable units with / without nitrification inhibitors. Each unit contains a source chamber, a medium chamber, and a receiver chamber separated by a semi-permeable membrane. Step 2: Simultaneously sample the chemical composition concentrations in each chamber of each unit under a preset time series. The chemical composition includes ammonium nitrogen, nitrate nitrogen, and phosphate. Based on the change of the concentration difference of each chemical composition between the source chamber and the receiving chamber over time, calculate the permeation flux of each chemical composition in each unit and the apparent permeation flux of total nitrogen in each unit. Calculate the ratio of the concentration of each chemical composition in the medium chamber to the concentration in the source chamber one by one to determine the adsorption resistance coefficient of each chemical composition in each permeation unit. Step 3: For any depth, calculate the difference in nitrate nitrogen permeation flux between the permeable units and parallel units in its unit group as its in-situ nitrification rate, and the difference in ammonium nitrogen permeation flux as its in-situ mineralization rate. Divide the sum of the two by the total apparent nitrogen permeation flux of the permeable units and parallel units in its unit group to obtain the first / second biotransformation contribution index at that depth. Step 4: Based on the in-situ nitrification rate, in-situ mineralization rate, adsorption retardation coefficient, and first / second biotransformation contribution index at each depth, draw a vertical distribution map. Depth intervals with biotransformation contribution index greater than a preset threshold are defined as biotransformation-dominant zones, depth intervals with adsorption retardation coefficient greater than a preset threshold are defined as adsorption-fixation-dominant zones, and the remaining depths are defined as physical permeation-dominant zones. A predetermined number of depth sections are selected at the soil profile, and a unit group is arranged at each depth section. Each unit group includes two three-chamber units located at the same depth, one of which is an infiltration unit without added inhibitors, and the other is a parallel unit with added nitrification inhibitors. Each three-chamber unit contains a source chamber, a medium chamber, and a receiving chamber separated by a semi-permeable membrane. The receiving chamber has a predetermined volume. The source chamber and the medium chamber, as well as the medium chamber and the receiving chamber, are separated by a semi-permeable membrane with a predetermined cutoff pore size. The semi-permeable membrane has a predetermined effective permeation area and allows ions to pass through but blocks microbial migration. The medium chamber is filled with an undisturbed soil column taken from the corresponding depth section, and the filling density is consistent with the measured bulk density in the field. The source chamber is injected with treated wastewater, and a predetermined proportion of nitrification inhibitors is added to the source chamber of the parallel unit. A nitrogen- and phosphorus-free background solution is injected into the receiving chamber. The calculation methods for the first and second biotransformation contribution indices are as follows: The in-situ nitrification rate and the in-situ mineralization rate at the same depth are added to obtain the total biotransformation contribution flux at that depth; this total biotransformation contribution flux is divided by the total apparent nitrogen permeation flux of the permeable units in the unit group at that depth to obtain the first biotransformation contribution index at that depth; this total biotransformation contribution flux is divided by the total apparent nitrogen permeation flux of the parallel units in the unit group at that depth to obtain the second biotransformation contribution index at that depth. The method for drawing the vertical distribution map and outputting the zonal control scheme is as follows: with soil depth as the vertical axis and the in-situ nitrification rate, in-situ mineralization rate, adsorption retardation coefficient of each chemical component and first / second biotransformation contribution index calculated at each depth as the horizontal axis, line graphs of the changes of each index with depth are drawn to form a vertical distribution map of nitrogen and phosphorus conversion intensity and permeability related indicators. The depth range in the spectrum where the first biotransformation contribution index is greater than the preset biotransformation contribution index threshold is defined as the biotransformation-dominant region; the depth range where the phosphate adsorption retardation coefficient is greater than the preset adsorption retardation coefficient threshold is defined as the adsorption and fixation-dominant region; and the depth range where the first biotransformation contribution index is not greater than the preset biotransformation contribution index threshold and the phosphate adsorption retardation coefficient is not greater than the preset adsorption retardation coefficient threshold is defined as the physical permeation-dominant region.

2. The method according to claim 1, wherein: The preset time series setting and synchronous sampling method are as follows: synchronous sampling is performed based on a constant sampling interval after irrigation begins to form a preset time series including multiple sampling time points, which cover the rapid response stage in the early stage of irrigation and the slow change stage in the medium and long term; for each sampling time point, a preset volume of water sample is extracted from the source chamber, medium chamber and receiving chamber of each three-chamber unit in each unit group; after sampling in the source chamber and receiving chamber, an equal volume of corresponding solution is immediately added to maintain a constant water head, and no liquid is added after sampling in the medium chamber to avoid disturbing the pore water distribution; The methods for determining the concentrations of ammonium nitrogen, nitrate nitrogen, and phosphate are as follows: For water samples collected at each sampling time point, a continuous flow analyzer is used for measurement. The concentrations of ammonium nitrogen are determined by the indophenol blue colorimetric method, nitrate nitrogen by the cadmium column reduction-diazo coupling colorimetric method, and phosphate by the molybdenum antimony colorimetric method, in order to determine the concentrations of each chemical component at each sampling time point.

3. The method according to claim 2, wherein: The calculation method for the permeation flux of each chemical component is as follows: Within the time interval between each adjacent sampling time point, based on the receiving chamber volume, the effective permeation area of ​​the semipermeable membrane, and the duration of the time interval, the concentration difference of a certain chemical component in the receiving chamber at two adjacent sampling time points is multiplied by the receiving chamber volume, and then divided by the product of the effective permeation area and the time interval to obtain the permeation flux of that chemical component within that time interval; wherein, the certain chemical component is any one of ammonium nitrogen, nitrate nitrogen, or phosphate, and the permeation flux of ammonium nitrogen, nitrate nitrogen, and phosphate is calculated separately for each; the calculation method for the apparent permeation flux of total nitrogen is as follows: the permeation flux of ammonium nitrogen and the permeation flux of nitrate nitrogen within the same time interval are added to obtain the apparent permeation flux of total nitrogen within that time interval, thereby determining the permeation flux of ammonium nitrogen, nitrate nitrogen, phosphate, and total nitrogen in each time interval for the permeation unit and parallel unit in each unit group; The method for calculating the adsorption retardation coefficient is as follows: For each chemical component, the ratio of the concentration of the chemical component in the pore water of the medium chamber to the concentration of the chemical component in the source chamber at each sampling time point is taken as the relative penetration rate of the chemical component at each sampling time point. The relative penetration rate is subtracted from the numerical value 1 to obtain the adsorption retardation coefficient of the chemical component at each sampling time point, and the average value is taken as the adsorption retardation coefficient of the chemical component. In this way, the adsorption retardation coefficient of each chemical component in the permeation unit of each unit group is determined, which is then used as the adsorption retardation coefficient of each chemical component at the corresponding depth of the unit group where the permeation unit is located.

4. The method for analyzing the migration and transformation patterns of nitrogen and phosphorus in wastewater resource utilization according to claim 3, characterized in that: The in-situ nitrification rate is calculated as follows: In each time interval, the permeation flux of nitrate nitrogen in the permeation unit and the parallel unit in the same unit group is subtracted to obtain the difference in nitrate nitrogen flux contributed by nitrification in that time interval, and this difference is taken as the in-situ nitrification rate of that time interval; the arithmetic mean of the in-situ nitrification rates calculated in each time interval of the same unit group in the preset time series is taken as the in-situ nitrification rate at the corresponding depth of this unit group. The in-situ mineralization rate is calculated as follows: In each time interval, the permeation flux of ammonium nitrogen in the permeable unit and the parallel unit in the same unit group is subtracted to obtain the difference in ammonium nitrogen flux contributed by mineralization in that time interval, and this difference is taken as the in-situ mineralization rate of that time interval; the arithmetic mean of the in-situ mineralization rates calculated in each time interval of the same unit group in the preset time series is taken as the in-situ mineralization rate at the corresponding depth of this unit group.

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