Method for determining a comprehensive degradation coefficient of a pollutant

Abstract

The present application relates to a kind of determination methods of comprehensive degradation coefficient of pollutant, comprising: the comprehensive degradation coefficient of pollutant K is divided into the K0 obtained by laboratory simulation, and the influence coefficient K1 generated by neglecting part of point, surface pollution source;Calculate the preliminary K value;Get the value of K0;Calculate the preliminary K1 value;The value of coefficient a, b of preliminary K1 value is obtained using least square method;The value of coefficient a, b of rating completion is obtained;According to the value of coefficient a, b of rating completion, the value of K1 is obtained, and the final K value is obtained in combination with the value of K0.The present application considers the specific situation in actual river on the basis of laboratory simulation method, makes up the deficiency that laboratory simulation method does not fully consider actual;The present application uses the method that least square method and steepest descent method are combined in the process of parameter rating, improves the convergence speed of parameter rating and the precision of water quality simulation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water quality parameter determination, and particularly relates to a method for determining a comprehensive degradation coefficient of pollutants. BACKGROUND

[0002] During the river transport of pollutants, the concentration of the pollutants will be attenuated due to the comprehensive action of physics, chemistry and biology, and the rate constant of the attenuation is represented by the comprehensive degradation coefficient. However, the input of point and area pollution sources on both banks of the river may also cause the concentration to rise, and therefore the influence of the point and area pollution sources needs to be considered in the determination of the comprehensive degradation coefficient of the pollutants.

[0003] The comprehensive degradation coefficient is an important parameter for calculating the water environmental capacity and determining the reduction amount of pollutants, and plays an important role in the formulation of the regional total pollutant discharge control plan, the scientific allocation of the total load index and the management during the execution of the control plan. Therefore, the accuracy of the comprehensive degradation coefficient of the pollutants is of great significance in the pollution treatment of the river basin.

[0004] At present, the determination methods of the comprehensive degradation coefficient of the pollutants mainly include the laboratory simulation method, the empirical formula method and the measured data backstepping method. The laboratory simulation method does not consider the external influences such as the hydrology, water conservancy, temperature and river characteristics of the actual river; the empirical formula method is to refer to the values of other similar rivers, and the actual situation of the river is not considered; and the measured data backstepping method is to calibrate the comprehensive degradation coefficient according to the actual water quality parameters, which reflects the actual situation to a certain extent, but a large amount of manpower and material resources are consumed, and the convergence speed is slow during the parameter calibration. The above methods all have certain limitations. SUMMARY

[0005] In order to solve the defects that the conventional method for determining the comprehensive degradation coefficient of the pollutants of the river cannot fully consider the influence of the external pollution sources of the river, and a large amount of data is needed for parameter calibration, which may cause poor simulation precision of the water quality, the purpose of the present application is to provide a method for determining the comprehensive degradation coefficient of the pollutants, which is accurate, has a fast convergence speed during parameter calibration and improves the simulation precision of the water quality.

[0006] In order to achieve the above purpose, the present application adopts the following technical scheme: a method for determining the comprehensive degradation coefficient of pollutants, which comprises the following sequential steps:

[0007] (1) dividing the comprehensive degradation coefficient K of the pollutants into K0 obtained by laboratory simulation and an influence coefficient K1 generated by neglecting part of the point and area pollution sources;

[0008] (2) calculating the preliminary K value by using the measured water quality data of each section;

[0009] (3) According to the water quality parameters measured under indoor conditions, the value of K0 is obtained by fitting according to the fitting formula;

[0010] (4) According to the preliminary K value obtained in step (2) and the K0 value obtained in step (3), the preliminary K1 value is calculated;

[0011] (5) According to the preliminary K1 value obtained in step (4), the values of coefficients a and b of the preliminary K1 value are obtained by using the empirical formula and the least square method;

[0012] (6) The values of coefficients a and b are further calibrated by using the steepest descent method, and the calibrated values of coefficients a and b are obtained;

[0013] (7) According to the calibrated values of coefficients a and b, the value of K1 is obtained, and the final K value is obtained in combination with the K0 value obtained in step (3).

[0014] In step (1), the calculation formula of the comprehensive degradation coefficient K of the pollutants is as follows:

[0015] K = K0 + K1 (1).

[0016] In step (2), the formula for calculating the preliminary K value by using the measured water quality data of each section is as follows:

[0017]

[0018] In the formula, u is the average flow rate of the river section; ΔX is the distance between the upper and lower sections; C A is the pollutant concentration of the upper section; and C B is the pollutant concentration of the lower section.

[0019] Step (3) specifically refers to: after collecting the water samples from the sampling points, the water samples are quickly taken back to the laboratory, and the water samples are placed at room temperature for 5 to 7 days, and the water quality is measured daily to obtain the measured water quality parameters: initial concentration C0 and pollutant concentration C t after a period of time.

[0020] The fitting formula is as follows:

[0021]

[0022] In the formula, t is time.

[0023] In step (4), the formula for calculating the preliminary K1 value is as follows:

[0024] K1 = K - K0 (4).

[0025] In step (5), the empirical formula is as follows:

[0026] K1 = s x u + b (5)

[0027] Wherein: u is the average flow velocity of the river section.

[0028] The step (6) specifically comprises the following steps:

[0029] (6a) collecting the measured water quality data of each section i represents the ith time, i = 1, 2, …, n;

[0030] (6b) calculating the water quality value of each section under the same condition by using the water quality model i represents the ith time;

[0031] (6c) using the measured water quality data and the difference between the water quality value of each section to form an objective function;

[0032] (6d) searching for the value of the coefficients a and b at which the objective function value is the smallest under the condition of constraint by using the first order gradient method, that is, the value of the coefficients a and b of the rate determination is completed.

[0033] The calculation formula of the final K value in the step (7) is as follows:

[0034] K = K0 + K1 = K0 + (a x u + b) (6)

[0035] Wherein: u is the average flow velocity of the river section.

[0036] The calculation formula of the water quality of each section in the step (6b) is as follows:

[0037]

[0038] Wherein: C x is the pollutant concentration after flowing through the distance x; C A is the pollutant concentration of the upper section; x is the longitudinal distance along the river section; and u is the average flow velocity of the river section.

[0039] The formula of the two norms in the step (6c) is as follows:

[0040]

[0041] It can be known from the above technical solution that the present application has the following beneficial effects: first, in the process of determining the comprehensive degradation coefficient of pollutants, the present application considers the specific conditions in the actual river on the basis of the laboratory simulation method, which makes up for the deficiency that the laboratory simulation method does not fully consider the actual conditions; second, in the process of parameter rate determination, the present application uses the method combining the least square method and the steepest descent method, which improves the convergence speed of parameter rate determination and the accuracy of water quality simulation. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a flow chart of the method of the present application;

[0043] Figure 2 is a comparison chart of measured and calculated COD values during flood season;

[0044] Figure 3 is a comparison chart of measured and calculated NH3-N values during flood season;

[0045] Figure 4 is a comparison chart of measured and calculated TP values during flood season;

[0046] Figure 5 is a comparison chart of measured and calculated COD values during non-flood season;

[0047] Figure 6 is a comparison chart of measured and calculated NH3-N values during non-flood season;

[0048] Figure 7 is a comparison chart of measured and calculated TP values during non-flood season. DETAILED DESCRIPTION

[0049] As shown in Figure 1 , a method for determining a comprehensive pollutant degradation coefficient, the method comprising the following sequential steps:

[0050] (1) dividing the comprehensive pollutant degradation coefficient K into K0 obtained from laboratory simulation, and an impact coefficient K1 generated by neglecting part of point, surface pollution sources;

[0051] (2) using measured water quality data of each section to calculate a preliminary K value;

[0052] (3) fitting according to a fitting formula based on measured water quality parameters under indoor conditions to obtain a K0 value;

[0053] (4) calculating a preliminary K1 value based on the preliminary K value obtained in step (2) and the K0 value obtained in step (3);

[0054] (5) using an empirical formula, and using the least square method to obtain values of coefficients a and b of the preliminary K1 value based on the preliminary K1 value obtained in step (4);

[0055] (6) using the steepest descent method to further calibrate the values of coefficients a and b to obtain calibrated values of coefficients a and b;

[0056] (7) obtaining a K1 value based on the calibrated values of coefficients a and b, and combining the K0 value obtained in step (3) to obtain a final K value.

[0057] In step (1), the formula for calculating the comprehensive degradation coefficient K of the pollutants is as follows:

[0058] K = K0 + K1 (1).

[0059] In step (2), the formula for calculating the preliminary K value using the measured water quality data of each section is as follows:

[0060]

[0061] In the formula, u is the average flow rate of the river section; ΔX is the distance between the upstream and downstream sections; C A is the pollutant concentration of the upstream section; and C B is the pollutant concentration of the downstream section.

[0062] Step (3) specifically refers to collecting water samples from sampling points and quickly bringing them back to the laboratory. The water samples are placed at room temperature for 5 to 7 days, and the water quality is measured daily to obtain the determined water quality parameters: initial concentration C0 and pollutant concentration C t after a period of time.

[0063] The fitting formula is as follows:

[0064]

[0065] In the formula, t is time.

[0066] In step (4), the formula for calculating the preliminary K1 value is as follows:

[0067] K1 = K - K0 (4).

[0068] In step (5), the empirical formula is as follows:

[0069] K1 = a × u + b (5)

[0070] In the formula, u is the average flow rate of the river section.

[0071] Step (6) specifically includes the following steps:

[0072] (6a) Collecting the measured water quality data of each section i represents the ith time, i = 1, 2, …, n;

[0073] (6b) Using the water quality model to calculate the water quality values of each section under the same conditions i represents the ith time;

[0074] (6c) Using the difference between the measured water quality data and the water quality values of each section to form an objective function;

[0075] (6d) In the constrained condition, the first order gradient method is used to search the value of the coefficients a and b at the minimum of the objective function value, that is, the calibrated value of the coefficients a and b.

[0076] The calculation formula of the final K value obtained in step (7) is as follows:

[0077] K = K0+ K1= K0+ (a x u + b) (6)

[0078] In the formula, u is the average flow velocity of the river section.

[0079] The calculation formula of the cross-section water quality in step (6b) is as follows:

[0080]

[0081] In the formula, C x is the pollutant concentration after flowing through x distance; C A is the pollutant concentration of the upper cross-section; x is the longitudinal distance along the river section; and u is the average flow velocity of the river section.

[0082] The formula of the two-norm in step (6c) is as follows:

[0083]

[0084] Example 1

[0085] The water quality data of Shierbu River in Hefei City in flood season, i.e., June, July and August 2022, were used for parameter calibration, and the water quality data in September 2022 were used for verification. The coefficient of determination (R 2 ) and Nash efficiency coefficient (NSE) were used to evaluate the performance of the model. The R 2 of the simulation of COD, NH3-N and TP was 0.950, 0.901 and 0.874 respectively, and the NSE was 0.941, 0.900 and 0.834 respectively, all greater than 0.6, indicating good reliability. The comparison between the measured and simulated values of water quality is shown in Figure 2 , 3 , 4.

[0086] Example 2

[0087] The water quality data of Shierbu River in Hefei City in non-flood season, i.e., October, November and December 2022, were used for parameter calibration, and the water quality data in January 2023 were used for verification. The coefficient of determination (R 2 ) and Nash efficiency coefficient (NSE) were used to evaluate the performance of the model. The R 20.886, 0.671 and 0.919, and NSE is 0.824, 0.671 and 0.682 respectively, which is greater than 0.6, indicating good reliability. Comparison between the measured value and the simulated value of water quality is shown in Table 2. Figure 5 、 6 、7.

[0088] In summary, in the process of determining the comprehensive degradation coefficient of pollutants, the specific conditions in the actual river are considered on the basis of the laboratory simulation method, which makes up for the deficiency that the laboratory simulation method does not fully consider the actual situation; in the process of parameter calibration, the method combining the least square method and the steepest descent method is used, which improves the convergence speed of parameter calibration and the accuracy of water quality simulation.

Claims

1. A method for determining the comprehensive degradation coefficient of pollutants, characterized in that: The method includes the following steps in sequence: (1) The overall degradation coefficient of pollutants Divided into laboratory simulations And the impact coefficient caused by ignoring some point and area pollution sources. ; (2) Preliminary results were calculated using the measured water quality data from each cross-section. value; (3) Fit the measured water quality parameters under indoor conditions according to the fitting formula to obtain the results. The value; (4) Based on the preliminary results obtained in step (2) The value and the result obtained in step (3) The value was calculated to obtain the preliminary result. value; (5) The preliminary results obtained from step (4) The value was obtained using an empirical formula and the least squares method. coefficient of value , The value; (6) Use the steepest descent method to adjust the coefficients , The value is further calibrated to obtain the coefficients after calibration. , The value; (7) Based on the coefficients completed by calibration , The value is obtained The value, and combined with the value obtained in step (3). The value is used to obtain the final result. value; In step (2), preliminary water quality data from each cross-section are used to calculate the results. The formula for the value is as follows: ； In the formula: The average flow velocity of the river section; This refers to the distance between the upstream and downstream sections. This refers to the pollutant concentration at the upper cross section. The concentration of pollutants at the lower cross section; Step (3) specifically refers to: after collecting water samples from the sampling point, quickly bringing them back to the laboratory, placing the water samples at room temperature for 5 to 7 days, measuring the water quality daily, and obtaining the measured water quality parameters: and pollutant concentration after a period of time ; The fitting formula is as follows: ； In the formula: For time; In step (4), preliminary calculations are obtained. The formula for the value is as follows: In step (5), the empirical formula is as follows: ； In the formula: The average flow velocity of the river section.

2. The method for determining the comprehensive degradation coefficient of pollutants according to claim 1, characterized in that: In step (1), the overall degradation coefficient of the pollutants The calculation formula is as follows:

3. The method for determining the comprehensive degradation coefficient of pollutants according to claim 1, characterized in that: Step (6) specifically includes the following steps: (6a) Collect measured water quality data at each cross-section , Represented as the first Second-rate, =1, 2, ..., n; (6b) Using a water quality model, calculate the water quality values ​​for each cross-section under the same conditions. , Represented as the first Second-rate; (6c) Use measured water quality data and water quality values ​​at each cross-section The L2 norm of the difference constitutes the objective function; (6d) Under constrained conditions, use the first-order gradient method to search for the coefficients that minimize the objective function value. , The value is the coefficient for calibration completion. , The value of .

4. The method for determining the comprehensive degradation coefficient of pollutants according to claim 1, characterized in that: The final result is obtained in step (7). The formula for calculating the value is as follows: ； In the formula: The average flow velocity of the river section.

5. The method for determining the comprehensive degradation coefficient of pollutants according to claim 3, characterized in that: The calculation formula for the cross-sectional water quality in step (6b) is as follows: ； In the formula: For flowing through Pollutant concentration after distance; This refers to the pollutant concentration at the upper cross section. This represents the longitudinal distance along the river section; The average flow velocity of the river section.

6. The method for determining the comprehensive degradation coefficient of pollutants according to claim 3, characterized in that: The formula for the L2 norm in step (6c) is as follows: 。

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