A method for nitrogen and phosphorus pollution source analysis based on pollution load integration

Abstract

The present invention relates to the field of electronic digital data processing, and in particular to a method for analyzing nitrogen and phosphorus pollution sources based on pollution load integration, including a point source nitrogen and phosphorus pollution load calculation step, a non-point source nitrogen and phosphorus pollution load calculation step, an integrated model parameter calibration step, and a nitrogen and phosphorus pollution load calculation step. Calculate the nitrogen and phosphorus pollution load of industrial wastewater, calculate the nitrogen and phosphorus pollution load of urban domestic wastewater, and then calculate the point source nitrogen and phosphorus pollution load. Calculate the dissolved nitrogen and phosphorus pollution load, then calculate the adsorbed nitrogen and phosphorus pollution load, and then calculate the non-point source nitrogen and phosphorus pollution load. Calculate the comprehensive nitrogen and phosphorus pollution load based on the total amount of point source nitrogen and phosphorus pollution load and non-point source nitrogen and phosphorus pollution load. The present invention integrates point source and non-point source nitrogen and phosphorus pollution load calculation modes, and combines the modified RUSLE soil erosion general equation to calculate multiple phase nitrogen and phosphorus pollution loads, which can significantly improve the accuracy and reliability of nitrogen and phosphorus pollution comprehensive source analysis.

Description

Technical Field

[0001] The invention relates to the field of electrical digital data processing, and in particular to a nitrogen and phosphorus pollution source analysis method based on pollution load integration. Background Art

[0002] Excessive nitrogen and phosphorus pollutants in water bodies will lead to eutrophication, pollute drinking water sources, destroy the living environment of aquatic organisms, and cause a decline in soil production potential and water quality. Nitrogen and phosphorus pollutants brought by various industrial and agricultural pollution sources have brought tremendous pressure to the river environment, and nitrogen and phosphorus pollutants have become one of the characteristic pollutants affecting river water quality.

[0003] To this end, the quantitative study of nitrogen and phosphorus pollution load is carried out according to the emission characteristics of different pollution sources. Accurately identifying the sources of nitrogen and phosphorus pollution in water pollutants and their contribution is an important basis for river environmental quality assessment, risk assessment, water source protection area division, and nitrogen and phosphorus pollutant reduction. It is also an important means to effectively control river pollution and ensure water safety. At present, the research on source analysis technology of toxic organic matter and heavy metals in the atmosphere, soil, and sediments at home and abroad is relatively in-depth, and the methods are relatively mature, forming a pollution source analysis technology system with diffusion model and receptor model as the main body. However, due to the extremely complex water environment, irregular pollution emissions, non-conservation of pollutant migration, non-linear source spectrum independence and other factors, it is difficult to use diffusion model or receptor model to achieve source analysis of nitrogen and phosphorus pollutants in water. Pollution source analysis refers to the process of identifying pollution sources that affect pollutant concentration or load through pollution source investigation and calculating their contribution rate. In view of the characteristics of nitrogen and phosphorus pollution in water bodies, the analysis of nitrogen and phosphorus pollution sources can be achieved by calculating the pollution load entering the water body.

[0004] The pollution load model method is the most commonly used method for calculating pollution load. This method helps us analyze the temporal and spatial distribution characteristics of pollution generation, identify its main sources and migration pathways, and estimate the pollution load generated by different pollution sources such as industrial and agricultural pollution, domestic sewage and livestock and poultry sewage through quantitative description of the entire environmental system and its internal pollution process. Pollution load models usually include empirical models (such as plot test method, correlation method, rainfall difference method, pollution partitioning method, etc.), output coefficient method models and mechanistic process models. Among them, the empirical model does not require high data, but due to the lack of a mechanism basis, the accuracy is often not high.

[0005] The output coefficient method model uses relatively easy-to-obtain data such as the type of watershed land use, and directly establishes the relationship between the type of watershed land use and the output of non-point source pollution through multivariate linear correlation analysis, which greatly reduces the dependence on experiments and data, and provides an application method with a certain degree of accuracy for the estimation of watershed non-point source pollution load. Therefore, it is widely used. The mechanistic process model integrates the mechanisms of hydrology, soil erosion and pollutant migration and transformation to form a relatively complete system model, which can quantitatively describe the continuous process of non-point source pollution. However, this type of model contains many variables, a large amount of basic data, and high precision requirements. It is often difficult to calibrate parameters due to limited data, which limits its application in large-scale non-point source pollution load estimation. Summary of the invention

[0006] In order to solve the problem of inaccurate quantitative accounting of nitrogen and phosphorus pollution loads in existing water bodies, the present invention provides a nitrogen and phosphorus pollution source analysis method based on pollution load integration.

[0007] The present invention provides a method for analyzing nitrogen and phosphorus pollution sources based on pollution load integration, which adopts the following technical solutions:

[0008] A method for nitrogen and phosphorus pollution source analysis based on pollution load integration includes the following steps:

[0009] Calculate the nitrogen and phosphorus pollution loads of industrial wastewater and urban sewage, and calculate the point source nitrogen and phosphorus pollution loads based on the nitrogen and phosphorus pollution loads of industrial wastewater and urban sewage;

[0010] Calculate the dissolved nitrogen and phosphorus pollution loads carried by surface runoff generated on different land types;

[0011] Calculate nitrogen and phosphorus pollution loads output by different emission sources;

[0012] Calculate the adsorbed nitrogen and phosphorus pollution load;

[0013] Calculate the total non-point source nitrogen and phosphorus pollution load based on the nitrogen and phosphorus pollution load output by different emission sources and the adsorbed nitrogen and phosphorus pollution load;

[0014] The total pollution load is calculated based on the total amount of point source nitrogen and phosphorus pollution load and non-point source nitrogen and phosphorus pollution load.

[0015] In a specific implementation scheme, calculating the nitrogen and phosphorus pollution loads of industrial wastewater and the nitrogen and phosphorus pollution loads of urban sewage includes the following steps:

[0016] The flow concentration calculation method is used to calculate the nitrogen and phosphorus pollution load of industrial wastewater. The calculation formula is:

[0017]

[0018] In the above formula, is the load of nitrogen and phosphorus pollution in industrial wastewater;

[0019] is the number of industrial pollution source industry types, Indicates Types of industrial pollution sources, ;

[0020] is the number of industrial enterprises in the industry, Indicates Industrial enterprises in the same industry, ;

[0021] For the The first type of industrial pollution source industry The amount of wastewater discharged by each industrial enterprise;

[0022] For the The first type of industrial pollution source industry The average emission concentration of nitrogen and phosphorus pollutants of each industrial enterprise;

[0023] The unit load method is used to calculate the nitrogen and phosphorus pollution load of urban sewage. The calculation formula is:

[0024]

[0025] In the above formula, is the nitrogen and phosphorus pollution load of urban domestic sewage;

[0026] is the per capita pollution equivalent coefficient;

[0027] is the population of the catchment area;

[0028] is the sewage treatment rate.

[0029] In a specific implementation scheme, calculating the dissolved nitrogen and phosphorus pollution load carried by surface runoff generated on different land types includes the following steps:

[0030] The PLOAD model is used to calculate the dissolved nitrogen and phosphorus pollution load carried by surface runoff generated on different land types. The calculation formula is:

[0031]

[0032]

[0033] In the above formula, The dissolved nitrogen and phosphorus pollution loads carried by surface runoff generated on different land types;

[0034] is the number of land use types, Indicates land use type, ;

[0035] For the The average pollutant concentration of rainfall events under the land use type meets the following requirements:

[0036] , is the average annual vegetation coverage of the watershed;

[0037] For the land area of ​​the same land use type;

[0038] is the monthly rainfall;

[0039] is the runoff coefficient correction value, which is obtained by statistical analysis of annual rainfall runoff data;

[0040] For the The average runoff coefficient of the land use type is estimated by the imperviousness of the underlying surface of the land use type;

[0041] For the The imperviousness of the underlying surface of the watershed of this land use type was determined by using GIS tools through graphic overlay and calculation of corresponding attribute data.

[0042] In a specific embodiment, the calculation of the average pollution concentration includes the following steps:

[0043] For a single rainfall event, multiple samplings are carried out in different rainfall periods, and the flow in the corresponding period is weighted averaged;

[0044] For annual rainfall, the pollutant concentration of each rainfall is obtained by taking the weighted average of the flow rate generated by each rainfall in the year.

[0045] In a specific implementation scheme, calculating the nitrogen and phosphorus pollution loads output by different emission sources includes the following steps:

[0046] The nitrogen and phosphorus pollution loads output by different emission sources are calculated using the output coefficient model. The calculation formula is:

[0047]

[0048]

[0049]

[0050] In the above formula, is the pollution source type, , When , it indicates rural life pollution, When , it indicates livestock and poultry breeding pollution;

[0051] For the The output coefficient of this type of pollution source is estimated based on the output coefficient model or obtained through statistics or experiments;

[0052] For the The area or number of such pollution sources;

[0053] For the The amount of pollutant input from this type of pollution source;

[0054] Pollution load input for rainfall;

[0055] It represents the daily output of nitrogen and phosphorus per person;

[0056] is the population in the basin;

[0057] Mechanical removal of nitrogen and phosphorus coefficients in pollution treatment processes;

[0058] It is the coefficient of biological nutrient removal in the sewage treatment process;

[0059] is the nutrient retention coefficient;

[0060] is the phosphorus removal coefficient;

[0061] is the concentration of nitrogen and phosphorus pollutants in rainwater;

[0062] is the annual rainfall;

[0063] is the runoff coefficient.

[0064] In a specific embodiment, calculating the adsorbed nitrogen and phosphorus pollution load includes the following steps:

[0065] The soil erosion modified RUSLE equation was used to calculate the adsorbed nitrogen and phosphorus pollution load. The calculation formula is:

[0066]

[0067]

[0068] In the above formula, is the total amount of adsorbed pollution load;

[0069] is the sediment transport ratio, The average annual rainfall Satisfies the regression equation: ;

[0070] is the number of land use types, Indicates land use type, ;

[0071] For the land area of ​​the same land use type;

[0072] For the Annual soil erosion modulus for each land use type;

[0073] is the background mass fraction of pollutants in soil;

[0074] is the pollutant enrichment rate;

[0075] is the rainfall erosion dynamic factor, obtained based on empirical calculations;

[0076] is the soil erodibility factor, indicating the The soil erodibility factor of the land use type is calculated by the EPIC algorithm;

[0077] is the slope length factor, which is calculated according to the slope length index formula in the soil loss equation;

[0078] For the Soil and water conservation factors for type of land use;

[0079] For the Vegetation cover factor for type of land use.

[0080] In a specific embodiment, the slope length factor The calculation formula is:

[0081]

[0082] In the above formula, is the slope length;

[0083] is the slope;

[0084] is the slope length index, satisfying .

[0085] In a specific embodiment, the soil erodibility factor The calculation formula is:

[0086]

[0087] In the above formula, is the mass fraction of sand particles, is the mass fraction of powder particles, is the clay mass fraction, is the mass fraction of organic carbon.

[0088] In a specific implementation scheme, the calculation formula of the rainfall erosion dynamic factor is:

[0089]

[0090] In the above formula, It is Average rainfall per month;

[0091] is the average annual rainfall.

[0092] In a specific feasible implementation plan, before calculating the nitrogen and phosphorus pollution loads of industrial wastewater and urban sewage, basic data is collected, the watershed is divided into multiple sub-basins, and the corresponding land use conditions and soil types are extracted based on the delineated watershed boundaries and sub-basins.

[0093] In summary, the present invention has the following beneficial effects:

[0094] 1. Based on the integrated calculation of the nitrogen and phosphorus pollution loads in small watershed water bodies based on the coupled PLOAD model, output coefficient model and URSLE model, it can effectively calculate the different forms of nitrogen and phosphorus loads in the water body and calculate the proportion of pollution loads from different emission sources.

[0095] 2. Through the integration of multi-morphological models, the various forms of nitrogen and phosphorus pollution loads including farmland runoff, livestock and poultry breeding, urban sewage and rural domestic sewage can be calculated in detail, which can provide detailed data support for nitrogen and phosphorus pollution in river basins from multiple angles.

[0096] 3. The multi-morphological model parameter calibration method can provide the accuracy of water body single benefit pollution load calculation through multiple verifications and inversions on the basis of comprehensive estimation of nitrogen and phosphorus pollution load, effectively improving the traditional methods in estimating water body nitrogen and phosphorus pollution load, such as high uncertainty, unclear pollution source tracing and poor stability of calculation results.

[0097] 4. Compared with the existing technology that mostly adopts a single-thread calculation method to obtain the nitrogen and phosphorus pollution load of the basin water body, which leads to complex analysis results, the present invention adopts a multi-threaded model integrated accounting method to calculate the multi-phase single-benefit pollution load results of the water body, which covers all nitrogen and phosphorus emission patterns and storage forms in the small basin water body from a macro perspective, and calculates the source pathways, source methods and storage amounts of all possible nitrogen and phosphorus pollution sources within the controllable range. Therefore, it can maximize the reliability of the analysis results of nitrogen and phosphorus pollution sources in the small basin water environment and enhance the reference value of the result data.

[0098] 5. The parameter design and parameter calibration in each calculation thread model are verified through various methods. The existing data, experimental data and statistical analysis inversion data are used to determine the parameter values ​​in the multi-thread model, optimize the input parameter errors in the chemical transport model and the receptor model, and further correct the accuracy of the nitrogen and phosphorus pollution load calculation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0099] Figure 1 This is a flow chart of a method for analyzing nitrogen and phosphorus pollution sources based on pollution load integration proposed in the present invention.

[0100] Figure 2 This is a comparison chart of the simulated and measured monthly flux of nitrogen load in Creek A according to an exemplary embodiment of the present invention.

[0101] Figure 3 This is a comparison chart of the simulated and measured monthly flux of phosphorus load in Creek A according to an exemplary embodiment of the present invention.

[0102] Figure 4 This is a comparison chart of the simulated and measured monthly flux of nitrogen load in Creek B according to an exemplary embodiment of the present invention.

[0103] Figure 5 This is a comparison chart of the simulated and measured monthly flux of phosphorus load in Creek B according to an exemplary embodiment of the present invention.

[0104] Figure 6 This is a comparison chart of the simulated and measured monthly flux of nitrogen load in a watershed according to an exemplary embodiment of the present invention.

[0105] Figure 7 This is a comparison chart of the simulated and measured monthly flux of basin phosphorus load according to an exemplary embodiment of the present invention.

[0106] Figure 8 This is a graph of the contribution rate of nitrogen pollution load in a watershed according to an exemplary embodiment of the present invention.

[0107] Fig. 9 This is a graph showing the contribution rate of phosphorus pollution load in a watershed according to an exemplary embodiment of the present invention.

[0108] Fig.10 A time distribution diagram of the contribution rate of nitrogen load sources in a watershed is provided for an exemplary embodiment of the present invention.

[0109] Fig.11 A time distribution diagram of the contribution rate of phosphorus load sources in a watershed is provided as an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0110] The following combination Figure 1-Figure 11 The present invention is described in further detail.

[0111] Reference Figure 1 The nitrogen and phosphorus pollution source analysis method based on pollution load integration includes the following steps:

[0112] S100, basic data collection.

[0113] The basic data sources include digital elevation models, land use data, meteorological data, industrial point source pollutant emission data, population distribution data, agricultural planting / breeding data, etc. The data used in an exemplary embodiment of the present invention and the method for obtaining them are shown in Table 1; based on the DEM database, according to the natural flow and confluence characteristics of the rivers in the basin, the basin range is determined, and 27 sub-basins are divided using the ArcSwat tool. The parameters of each sub-basin are shown in Table 2. At the same time, the corresponding land use and soil type are extracted based on the demarcated basin boundaries and sub-basins.

[0114] Table 1 List of pollution load model data

[0115]

[0116] Table 2 Sub-basin attributes of watershed delineation

[0117]

[0118] S200, calculation of dissolved non-point source load parameters and adsorbed non-point source load parameters.

[0119] S210, PLOAD model parameter calculation.

[0120] The key parameters required for the PLOAD model are determined based on the collected data, specifically the runoff coefficient and pollutant concentration for different land use types.

[0121] Confirmation and calculation of runoff coefficient:

[0122] In the PLOAD model, the runoff coefficient is defined as:

[0123] in, is the net runoff coefficient;

[0124] The runoff coefficient correction value is a factor used to correct rainfall that does not produce surface runoff, that is, the proportion of rainfall events that produce runoff to the total rainfall events. It can be obtained by statistical analysis of annual rainfall and runoff data and is usually considered to be 0.9;

[0125] For the The average runoff coefficient of a land use type is the ratio of runoff generated by rainfall to rainfall. It is related to factors such as rainfall intensity, soil properties, soil moisture content, and surface cover, and is estimated by the imperviousness of the underlying surface of the land use type.

[0126] For the The imperviousness of the underlying surface in the watershed of this land use type.

[0127] The underlying surface factors under different land use types are different, and their permeability is also different. The value of the underlying surface impermeability is determined by using GIS tools through graphic overlay and calculation of corresponding attribute data. The underlying surface permeability and corresponding runoff coefficient of 8 major land use types in the basin of an exemplary embodiment described in the present invention are shown in Table 3 below.

[0128] Confirmation and calculation of pollution concentration:

[0129] Pollutant concentrations in rainfall runoff are affected by many factors, such as rainfall, fertilization, topography, vegetation cover, soil properties, field management, etc., and the formation process is very complex. The corresponding rainfall pollutant concentration is generally obtained by taking multiple samples at different rainfall periods and using the weighted average of the flow in the corresponding period; for annual rainfall pollutant concentrations, the flow generated by each rainfall in the year is used to weight the average of the pollutant concentrations of each field. Compared with the agricultural planting level of the reference basin, the nitrogen and phosphorus runoff concentrations of various land use types in the basin are determined in Table 3.

[0130] Table 3 Impermeability of underlying surface and pollutant concentration of different land uses in the basin

[0131]

[0132] S220, output coefficient model parameter calculation.

[0133] An exemplary embodiment of the present invention uses an output coefficient model to estimate the nitrogen and phosphorus loads in rural life pollution and livestock and poultry breeding (including cattle, sheep, pigs and poultry). The application of this model is mainly to determine the output coefficient of pollutants. Among them, rural life pollution output is the pollution generated by people maintaining normal life, and its pollution discharge equivalent is often determined by statistical and experimental means to determine the pollution output per person in a certain area, that is, the life output coefficient; livestock and poultry breeding pollution output refers to the pollution generated by the growth of livestock in agricultural breeding, and its pollution discharge equivalent can be determined by statistical and experimental means to determine the pollution output per unit scale of livestock in a certain area, that is, the breeding output coefficient.

[0134] Referring to the basin’s 2019 pollution discharge declaration data, the values ​​of nitrogen and phosphorus pollution output coefficients for rural life and livestock and poultry breeding are shown in Table 4.

[0135] Table 4 Nitrogen and phosphorus pollution output coefficients of rural life and livestock and poultry breeding in the basin

[0136]

[0137] S230, calculating the river entry coefficient.

[0138] In the process of pollutants being carried by runoff to the basin outlet, there will be interception by soil and vegetation, various biochemical reactions, emission into the atmosphere, infiltration into groundwater, adsorption and deposition by sediment, etc. It is impossible for all pollutants to reach the basin outlet control section, resulting in loss into the river. For this reason, the river entry coefficient is introduced to characterize the loss of pollutant transport. The non-point source river entry coefficient has a certain relationship with precipitation. There is a correlation between the ratio of pollution load at the basin outlet section to the amount of pollutants generated in the basin and the basin rainfall:

[0139]

[0140] In the above formula, is the monthly rainfall, is the average monthly rainfall, and All are parameters to be determined. Using nonlinear regression method to establish correlation analysis for the study area, we get , , therefore, the above formula can be further expressed as: .

[0141] S240, calculation of adsorption non-point source load parameters.

[0142] Calculate the rainfall erosion dynamic factor based on empirical calculation parameters:

[0143]

[0144] In the above formula, is the rainfall erosion dynamic factor;

[0145] It is Average monthly rainfall, in mm;

[0146] is the average annual rainfall in mm.

[0147] Calculation of soil erodibility factor using the EPIC algorithm :

[0148]

[0149] In the above formula, is the mass fraction of sand particles (%), is the mass fraction of powder particles (%), is the mass fraction of clay particles (%), is the mass fraction of organic carbon (%). , , and Collectively referred to as soil fraction, the basin soil type and corresponding soil fraction can be obtained by consulting literature, etc. The basin soil type, corresponding soil fraction, and soil erodibility factor See Table 5 below.

[0150] Table 5 Watershed soil texture attributes

[0151]

[0152] According to the slope length index formula in the soil loss equation, the slope length factor is calculated. :

[0153]

[0154] In the above formula, is the slope length, unit: m;

[0155] is the slope, unit: degree;

[0156] is the slope length index, satisfying .

[0157] The vegetation coverage factor is calculated based on the mathematical relationship between the slope sediment yield and vegetation coverage. :

[0158]

[0159] In the above formula, is the average annual vegetation coverage rate of the basin, expressed as a percentage.

[0160] Determine the soil and water conservation factors by consulting materials, etc. , The soil and water conservation factor of natural vegetation and sloping farmland, which usually do not take any soil and water conservation measures, is 1. The following Table 6 refers to the 2019 Environmental Statistics Yearbook to analyze and compare the soil and water conservation measures taken by different land use types in the basin, and the soil and water conservation factors by land use type. The value of .

[0161] Table 6 Soil and water conservation factors for different land use types in the basin

[0162]

[0163] The background concentration of pollutants was obtained based on experiments and literature review. Combined with the watershed reagent conditions, the background concentration values ​​of adsorbed nitrogen and phosphorus in different land use types are shown in Table 7.

[0164] Table 7 Background concentration of adsorbed nitrogen and phosphorus under different land use conditions in the basin (g / kg)

[0165]

[0166] The sediment transport ratio and annual average rainfall are expressed by the following regression equation: .

[0167] S300, calculate point source nitrogen and phosphorus pollution loads.

[0168] The flow concentration calculation method is used to calculate the nitrogen and phosphorus pollution load of industrial wastewater. The calculation formula is:

[0169]

[0170] In the above formula, is the load of nitrogen and phosphorus pollution in industrial wastewater, unit: t / a;

[0171] is the number of industrial pollution source industry types, Indicates Types of industrial pollution sources, ;

[0172] is the number of industrial enterprises in the industry, Indicates Industrial enterprises in the same industry, ;

[0173] For the The first type of industrial pollution source industry The amount of sewage discharged by an industrial enterprise, unit: m 3 ;

[0174] For the The first type of industrial pollution source industry The average emission concentration of nitrogen and phosphorus pollutants from each industrial enterprise, in mg / L.

[0175] The unit load method is used to calculate the nitrogen and phosphorus pollution load of urban sewage. The calculation formula is:

[0176]

[0177] In the above formula, is the nitrogen and phosphorus pollution load of urban domestic sewage, unit: t / a;

[0178] is the per capita pollution equivalent coefficient, unit: kg / person;

[0179] is the population of the catchment area;

[0180] is the sewage treatment rate.

[0181] Combined with the nitrogen and phosphorus pollution load of industrial wastewater and nitrogen and phosphorus pollution loads of urban domestic sewage , calculate point source nitrogen and phosphorus pollution loads , the calculation formula is:

[0182]

[0183] In the above formula, is the coefficient of point source pollution entering the river.

[0184] S400, calculate non-point source nitrogen and phosphorus pollution loads.

[0185] S410, calculate the dissolved nitrogen and phosphorus pollution load.

[0186] The PLOAD model is used to calculate the dissolved nitrogen and phosphorus pollution load carried by surface runoff generated on different land types. The calculation formula is:

[0187]

[0188]

[0189] In the above formula, is the number of land use types, Indicates land use type, ;

[0190] For the The average pollutant concentration of rainfall events under the land use type, in mg / L;

[0191] For the The land area of ​​this land use type, in ha.

[0192] The nitrogen and phosphorus pollution loads output by different emission sources are calculated using the output coefficient model. The calculation formula is:

[0193]

[0194]

[0195]

[0196] In the above formula, is the pollution source type, , When , it indicates rural life pollution, When , it indicates livestock and poultry breeding pollution;

[0197] For the Output coefficient of class pollution source;

[0198] For the The area or number of such pollution sources;

[0199] For the The amount of pollutant input from this type of pollution source;

[0200] Pollution load input for rainfall;

[0201] It indicates the daily output of nitrogen and phosphorus per person, in kg / d;

[0202] is the population in the basin;

[0203] Mechanical removal of nitrogen and phosphorus coefficients in pollution treatment processes;

[0204] It is the coefficient of biological nutrient removal in the sewage treatment process;

[0205] is the nutrient retention coefficient;

[0206] is the phosphorus removal coefficient;

[0207] is the concentration of nitrogen and phosphorus pollutants in rainwater, unit: g / m 3 ;

[0208] is the annual rainfall, unit: m 3 ;

[0209] is the runoff coefficient.

[0210] S420, calculate the adsorbed nitrogen and phosphorus pollution load.

[0211] The soil erosion modified RUSLE equation was used to calculate the adsorbed nitrogen and phosphorus pollution load. The calculation formula is:

[0212]

[0213]

[0214] In the above formula, is the total amount of adsorbed pollution load, unit: t / a;

[0215] is the sediment transport ratio;

[0216] For the Annual soil erosion modulus of land use type, unit: t / km 2 a;

[0217] is the background mass fraction of pollutants in the soil, unit: g / Kg;

[0218] is the pollutant enrichment rate, which is usually taken as 1;

[0219] is the soil erodibility factor, indicating the Soil erodibility factor for type of land use;

[0220] For the Soil and water conservation factors for type of land use;

[0221] For the Vegetation cover factor for type of land use.

[0222] The total non-point source nitrogen and phosphorus pollution load is the sum of dissolved and adsorbed nitrogen and phosphorus pollution loads, and the calculation formula is as follows:

[0223]

[0224] In the above formula, is the total amount of non-point source nitrogen and phosphorus pollution load;

[0225] It is the dissolved nitrogen and phosphorus pollution load.

[0226] S500, calculating the total amount of pollution load, and calibrating the integrated model parameters based on the comparison between the calculated value of the total amount of pollution load and the measured result.

[0227] The calculation formula for the pollution load calculation value is:

[0228]

[0229] In the above formula, It is the calculated value of pollution load, which is also the total amount of pollution load, and its unit is t / a.

[0230] Based on the calculated value of the total pollution load and the measured results, the relative errors of the nitrogen load and phosphorus load are calculated. If the relative error is less than 15%, it means that the error is within the allowable range, the model fitting effect is good, and the current model parameters can be used for calculation; otherwise, it means that the calculation error is too large, the model fitting effect is not good, and further model training is needed to adjust the model parameters.

[0231] The PLOAD model and output coefficient model were used to calculate the dissolved nitrogen and phosphorus loads in the land output runoff, rural pollution and point sources of different landscape types in the basin; the modified RUSLE general soil erosion equation was used to calculate the adsorbed nitrogen and phosphorus loads; finally, a comprehensive source analysis of nitrogen and phosphorus pollution was achieved.

[0232] For ease of understanding, the hydrological and water quality data of three hydrological stations in the mainstream of the river basin from 2005 to 2015 were selected. River A, River B and the river basin were used as the simulation calculation areas. According to the above model and corresponding parameters, the simulated values ​​of nitrogen and phosphorus loads were calculated and compared with the measured values ​​for verification (see Figure 2-Figure 7 ), the calculation results are shown in Table 8.

[0233] Table 8 Validation results of basin nitrogen and phosphorus load model

[0234]

[0235] From the comparison between the model simulation results and the measured results, it can be seen that the relative error of nitrogen load is between 3.64%-12.24%, and the relative error of phosphorus load is between 8.69%-14.69%, and the model fitting effect is good.

[0236] The following is further explanation based on actual data from a certain river basin.

[0237] Calculate point source pollution loads.

[0238] By consulting the pollution discharge declaration data and the Environmental Statistics Yearbook, supplemented by on-site investigations, a total of 146 large-scale industrial enterprises related to the designated watershed were selected. These enterprises came from 21 industries such as papermaking, chemicals, and metal products. The calculation shows that the nitrogen and phosphorus loads of wastewater discharged by these industrial enterprises are 611.41 tons / year and 33.06 tons / year respectively. Also through the formula: The calculated nitrogen and phosphorus loads from urban sewage are 1524.81 tons / year and 232.35 tons / year respectively.

[0239] Calculate non-point source pollution loads.

[0240] Through the PLOAD model, the dissolved nitrogen and phosphorus loads output by different land use types in the basin in 2019 were calculated, as shown in Table 9. The total nitrogen load output reached 2576.20 tons / year, of which paddy fields and woodlands contributed the most. The nitrogen load output from paddy fields reached 1384.05 tons / year, accounting for 53.72%, followed by woodlands, with a load of 492.16 tons / year. The total phosphorus load output was 124.08 tons / year, with paddy fields and woodlands accounting for 53.58 tons / year and 25.43 tons / year, respectively, and the contribution ratios reached 43.18% and 20.49%, respectively.

[0241] Table 9 Dissolved nitrogen and phosphorus loads output by different land use types in the basin

[0242]

[0243] According to the established load estimation model, the output coefficient method was used to estimate the nitrogen and phosphorus pollution loads caused by rural domestic sewage and livestock and poultry breeding. The dissolved nitrogen and phosphorus loads caused by rural domestic sewage were 894.93 tons / year and 35.80 tons / year respectively; the nitrogen and phosphorus loads caused by livestock and poultry breeding were 1709.16 tons / year and 15.61 tons / year respectively.

[0244] Combining the above three types of non-point source dissolved nitrogen and phosphorus loads, the dissolved non-point source nitrogen and phosphorus loads are 5180.29 tons / year and 175.49 tons / year respectively. The largest contributor to nitrogen load is runoff load output from different land types, with a contribution ratio of 49.73%; followed by livestock and poultry breeding pollution, with a contribution ratio of 32.99%; rural domestic sewage is the least (17.28%). The contributors to phosphorus load are runoff output from different land uses (70.70%), rural domestic sewage (20.40%) and livestock and poultry breeding (8.90%), see Table 10 for details.

[0245] Table 10 Dissolved non-point source nitrogen and phosphorus loads in the basin

[0246]

[0247] Calculation of adsorption non-point source pollution load

[0248] Using the soil erosion model factor determination method, the rainfall erosion dynamic factor, soil erodibility factor, slope length factor, vegetation cover factor and soil and water conservation factor were calculated respectively. The K factor map based on soil type, the LS factor map based on sub-watershed, and the C factor map and P factor map based on land use type were generated using GIS tools. The soil erosion amount under different land use types was calculated using the MapAlgebra function. Finally, the adsorbed nitrogen and phosphorus pollution load was calculated using the solid pollutant load equation. The calculation results are shown in Table 11.

[0249] Table 11 Soil erosion and adsorbed nitrogen and phosphorus loads in the basin

[0250]

[0251] Source analysis of comprehensive nitrogen and phosphorus pollution load

[0252] Taking into account point source and non-point source pollution, the calculated nitrogen and phosphorus pollution loads and their proportions are shown in Table 12. The total phosphorus loads of the basin are 8039.04 tons / year and 729.54 tons / year respectively, and the contribution ratios of pollution sources are shown in Figure 8-Figure 9 . Draw a time series diagram of source contribution rate based on the contribution ratio of various pollution sources to nitrogen and phosphorus loads. Figure 10-11 .

[0253] Table 12 Nitrogen and phosphorus pollution loads and source analysis results in the basin

[0254]

[0255] The application results show that the nitrogen load in the basin mainly comes from farmland runoff, livestock and poultry breeding, urban sewage and rural domestic sewage, with contribution rates of 21.41%, 21.26%, 18.97% and 11.13% respectively; while the phosphorus load pollution mainly comes from soil erosion, urban sewage and farmland runoff, with corresponding source contribution rates of 39.57%, 31.85% and 10.75% respectively. Urban sewage, soil erosion, farmland runoff and livestock and poultry breeding are the core pollution sources affecting nitrogen and phosphorus pollutants in the basin, and are priority sources of nitrogen and phosphorus pollution.

[0256] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for nitrogen and phosphorus pollution source analysis based on pollution load integration, characterized in that: The steps include: Calculate the nitrogen and phosphorus pollution loads of industrial wastewater and urban sewage, and calculate the point source nitrogen and phosphorus pollution loads based on the nitrogen and phosphorus pollution loads of industrial wastewater and urban sewage; Calculate the dissolved nitrogen and phosphorus pollution loads carried by surface runoff generated on different land types; Calculate nitrogen and phosphorus pollution loads output by different emission sources; Calculate the adsorbed nitrogen and phosphorus pollution load; Calculate the total non-point source nitrogen and phosphorus pollution load based on the nitrogen and phosphorus pollution load output by different emission sources and the adsorbed nitrogen and phosphorus pollution load; Calculate the total pollution load based on the point source nitrogen and phosphorus pollution load and the total non-point source nitrogen and phosphorus pollution load; Calculation of dissolved nitrogen and phosphorus pollution loads carried by surface runoff from different land types includes the following steps: The PLOAD model is used to calculate the dissolved nitrogen and phosphorus pollution load carried by surface runoff generated on different land types. The calculation formula is: In the above formula, The dissolved nitrogen and phosphorus pollution loads carried by surface runoff generated on different land types; is the number of land use types, Indicates land use type, ; For the Average pollutant concentration of rainfall events under different land use types; For the land area of ​​the same land use type; is the monthly rainfall; is the runoff coefficient correction value, which is obtained by statistical analysis of annual rainfall runoff data; For the The average runoff coefficient of the land use type is estimated by the imperviousness of the underlying surface of the land use type; For the The imperviousness of the underlying surface of the watershed of this land use type was determined by using GIS tools through graphic overlay and calculation of corresponding attribute data.

2. The method for nitrogen and phosphorus pollution source analysis based on pollution load integration according to claim 1 is characterized in that: Calculation of nitrogen and phosphorus pollution loads of industrial wastewater and urban sewage includes the following steps: The flow concentration calculation method is used to calculate the nitrogen and phosphorus pollution load of industrial wastewater. The calculation formula is: In the above formula, is the load of nitrogen and phosphorus pollution in industrial wastewater; is the number of industrial pollution source industry types, Indicates Types of industrial pollution sources, ; is the number of industrial enterprises in the industry, Indicates Industrial enterprises in the same industry, ; For the The first type of industrial pollution source industry The amount of wastewater discharged by each industrial enterprise; For the The first type of industrial pollution source industry The average emission concentration of nitrogen and phosphorus pollutants of each industrial enterprise; The unit load method is used to calculate the nitrogen and phosphorus pollution load of urban sewage. The calculation formula is: In the above formula, is the nitrogen and phosphorus pollution load of urban domestic sewage; is the per capita pollution equivalent coefficient; is the population of the catchment area; is the sewage treatment rate.

3. The method for nitrogen and phosphorus pollution source analysis based on pollution load integration according to claim 1 is characterized in that: The calculation of average pollutant concentration includes the following steps: For a single rainfall event, multiple samplings are carried out in different rainfall periods, and the flow in the corresponding period is weighted averaged; For annual rainfall, the pollutant concentration of each rainfall is obtained by taking the weighted average of the flow rate generated by each rainfall in the year.

4. The method for nitrogen and phosphorus pollution source analysis based on pollution load integration according to claim 1 is characterized in that: Calculating the nitrogen and phosphorus pollution loads output by different emission sources includes the following steps: The nitrogen and phosphorus pollution loads output by different emission sources are calculated using the output coefficient model. The calculation formula is: In the above formula, is the pollution source type, , When , it indicates rural life pollution, When , it indicates livestock and poultry breeding pollution; For the The output coefficient of this type of pollution source is estimated based on the output coefficient model or obtained through statistics or experiments; For the The area or number of such pollution sources; For the The amount of pollutant input from this type of pollution source; Pollution load input for rainfall; It represents the daily output of nitrogen and phosphorus per person; is the population in the basin; Mechanical removal of nitrogen and phosphorus coefficients in pollution treatment processes; It is the coefficient of biological nutrient removal in the sewage treatment process; is the nutrient retention coefficient; is the phosphorus removal coefficient; is the concentration of nitrogen and phosphorus pollutants in rainwater; is the annual rainfall; is the runoff coefficient.

5. The method for nitrogen and phosphorus pollution source analysis based on pollution load integration according to claim 1 is characterized in that: The calculation of adsorbed nitrogen and phosphorus pollution load includes the following steps: The soil erosion modified RUSLE equation was used to calculate the adsorbed nitrogen and phosphorus pollution load. The calculation formula is: In the above formula, is the total amount of adsorbed pollution load; is the sediment transport ratio, The average annual rainfall Satisfies the regression equation: ; is the number of land use types, Indicates land use type, ; For the land area of ​​the same land use type; For the Annual soil erosion modulus for each land use type; is the background mass fraction of pollutants in soil; is the pollutant enrichment rate; is the rainfall erosion dynamic factor, obtained based on empirical calculations; is the soil erodibility factor, indicating the The soil erodibility factor of the land use type is calculated by the EPIC algorithm; is the slope length factor, which is calculated according to the slope length index formula in the soil loss equation; For the Soil and water conservation factors for type of land use; For the Vegetation cover factor of land use type, satisfying: , is the average annual vegetation coverage rate of the basin.

6. The method for nitrogen and phosphorus pollution source analysis based on pollution load integration according to claim 5 is characterized in that: Slope length factor The calculation formula is: In the above formula, is the slope length; is the slope; is the slope length index, satisfying .

7. The method for nitrogen and phosphorus pollution source analysis based on pollution load integration according to claim 5 is characterized in that: Soil erodibility factor The calculation formula is: In the above formula, is the mass fraction of sand particles, is the mass fraction of powder particles, is the clay mass fraction, is the mass fraction of organic carbon.

8. The method for nitrogen and phosphorus pollution source analysis based on pollution load integration according to claim 5 is characterized in that: Rainfall erosion dynamics factor The calculation formula is: In the above formula, It is Average rainfall per month; is the average annual rainfall.

9. The method for nitrogen and phosphorus pollution source analysis based on pollution load integration according to claim 1, characterized in that: Before calculating the nitrogen and phosphorus pollution loads of industrial wastewater and urban sewage, basic data are collected, the watershed is divided into multiple sub-basins, and the corresponding land use conditions and soil types are extracted based on the delineated watershed boundaries and sub-basins.

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