A method for measuring salinity in wastewater based on conductivity measurement with multiple compensations

Abstract

The present invention provides a method for measuring the salinity of wastewater based on multiple compensations of conductivity measurement, and belongs to the technical field of wastewater treatment. The method includes the following steps: selecting wastewater to be measured, eliminating organic interference, and conducting a salt content test; measuring the pH of the treated wastewater, and conducting volatile substance compensation; collecting test data, conducting laboratory data analysis, conducting outlier screening for each pair of conductivity and salt content analysis data, and using data analysis methods to determine the relationship formula between conductivity and salt content; and calculating the salinity of wastewater based on the relationship formula between conductivity and salt content. Accurate measurement of high-salt wastewater is achieved through laboratory water quality analysis and analysis data calculation and management, as well as multiple compensation calculation methods such as wastewater temperature.

Description

Technical Field

[0001] The invention relates to a method for measuring salinity in wastewater based on conductivity measurement with multiple compensations, and belongs to the technical field of wastewater treatment. Background Art

[0002] Salt content is an indicator of wastewater monitoring. At present, the method for determining the salt content of wastewater is mainly based on the "Gravimetric Method for Determination of Total Salt Content of Water Quality" (HJ / T 51-1999). The "Standard Test Methods for Urban Wastewater Quality" (CJ / T51-2018) and "Water and Wastewater Monitoring Methods (Fourth Edition)" proposed analysis methods for soluble solids and filterable residues. In actual measurements, the dissolved solids or filterable residues in wastewater are also measured to indicate the value of salt content. The above methods have the same measurement process, and all require the steps of filtration, evaporation, constant weight, and weighing, but there are slight differences in operating conditions such as sampling volume and evaporation temperature. The above methods are cumbersome to measure, with a large workload and a long operation time (generally about 4 hours). Online measurement cannot be achieved in actual production or wastewater discharge.

[0003] With the continuous deepening of water pollution control, the pollution control of general high-salt wastewater (wastewater without hazardous wastes such as heavy metals) is basically achieved by two methods, thermal and membrane methods, to fix the salt content, thereby achieving wastewater reuse and zero discharge. Due to the influence of environmental protection regulations, construction costs, operating costs, etc., more and more wastewater treatment uses flue method to concentrate desulfurization wastewater (the device is usually called "low temperature concentration tower"), and then dry it to achieve zero wastewater discharge.

[0004] In actual operation, the concentration ratio of the cryogenic concentration tower is actually to control the salt content in the wastewater. Since the salt content measurement operation is cumbersome and time-consuming, it cannot guide the operation control. As a result, in actual operation, the concentration ratio of the cryogenic concentration tower cannot be controlled, and the salt content of the concentrated brine fluctuates greatly. If the concentration ratio is low, the amount of high-salt wastewater treated is small and the energy consumption is high; if the concentration ratio is high, problems such as crystallization and blockage of the pipeline after the disturbance pump occur. Real-time measurement of the salt content is urgently needed to achieve stable and reliable operation of the cryogenic concentration tower. Summary of the invention

[0005] The present invention aims to provide a method for measuring the salinity of wastewater based on conductivity measurement with multiple compensations, which is not only simple and convenient to operate but also has high measurement accuracy.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] Step 1: Select the wastewater to be measured, eliminate organic interference, and conduct a salt content test; evaporate the selected wastewater in a water bath, and slowly add a small amount of H2O2 solution before and during the water bath until the wastewater or residue turns white or the color is stable and no longer changes;

[0008] Conduct parallel sample tests on the wastewater, retain the test results with the absolute value of the relative standard deviation of the parallel samples less than 0.5%, and take the arithmetic mean of the parallel samples for the salt content;

[0009] Step 2: Measure the pH of the treated wastewater and perform volatile matter compensation;

[0010] pH≤2, determination of CL in wastewater - Content [CL - ], if [CL - ]≥400mg / L, the salt content is compensated by hydrogen chloride, the calculation formula is: pH≥-lg([CL - ] / 35500), salt content plus 10 -pH ×36500mg / L hydrogen chloride compensation; if pH < -lg[CL - ], salt content plus [CL - ]×1.028mg / L hydrogen chloride compensation;

[0011] pH ≥ 12, determine the ammonium ion content in water [NH 4 + ], if [NH 4 + ]≥180mg / L, NH 3 Compensation, the calculation formula is: [NH 4 + ]≤18×10 (pH-11) , salt content [NH 4 + ]×1.89mg / L NH 3 Compensation; if [NH 4 + ]≥18 × 10 (pH-11) , salt content plus 10 (pH-14) ×44000mg / L NH 3 compensate;

[0012] Step 3: Collect test data, conduct laboratory data analysis, screen outliers for each pair of conductivity and salinity analysis data, and use data analysis methods to determine the relationship formula between conductivity and salinity;

[0013] Step 4: Calculate the salinity of the wastewater based on the relationship between conductivity and salinity.

[0014] Preferably, the conductivity and salt content analysis data are subjected to outlier screening, and a relationship formula between conductivity and salt content is determined using a data analysis method, and the specific steps are as follows:

[0015] Step 1: Use the salt conductivity ratio parameter to perform an outlier test on the data. The salt conductivity ratio is equal to the ratio of salt content to conductivity. The data outliers are screened to select the analytical data involved in the data calculation;

[0016] Step 2: Use 20% of the analysis data as test data and 80% for sample training to establish the relationship between high salt conductivity and salt content:

[0017] Y=(ax b +Obj) / 2

[0018]

[0019] Where a is the power function coefficient, b is the power exponent, x is the conductivity, Y is the salinity, n is the number of training function samples, l is the loss of a single sample, y is i , y′ i are the true value and predicted value of the salt content of the i-th sample in the model, respectively, and f t is the base model, t is the cumulative variable, representing the number of trees, that is, the complexity of each tree is accumulated.

[0020] Preferably, the value of a is 465.6852, and the value of b is 1.3051.

[0021] Preferably, the outlier screening is performed by dividing the conductivity value interval into 1 as a unit, and performing deviation analysis by comparing the standard deviation in the normal distribution. When it exceeds 1.5 standard deviations, it is filtered out as an outlier.

[0022] The advantages of the present invention are: the present invention can utilize the conductivity generated by the ionization of dissolved salt in water to quickly measure the salt content in wastewater using conductivity, it has high sensitivity, simple operation, high measurement accuracy within the measurement range, and is economical and convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a schematic diagram of the conductivity-salinity power function fitting of the present invention. The correlation R2=0.91, the sample average absolute deviation mae=9201.41.

[0024] Figure 2 This is a schematic diagram of XGBoost fitting regression of the present invention. Correlation R2=0.89, sample mean absolute deviation mae=11946.34.

[0025] Figure 3This is a schematic diagram of the integration of the power function and the XGBoost model of the present invention. Correlation R2 = 0.94, sample mean absolute deviation mae = 8932.94. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] A method for measuring salinity in wastewater based on multiple compensations of conductivity measurement can utilize the conductivity brought by the ionization of salt in wastewater to accurately measure the salinity, and includes the following steps:

[0028] 1. Select high-salt wastewater with a salt content of 20g / L-400g / L. For wastewater from the same water source and the same production process, the various components in the wastewater are relatively stable, and this method is more suitable for total salt content determination.

[0029] 2. Accurately measure conductivity. Select the appropriate measurement range and temperature compensation to ensure sensitive and accurate conductivity. It should also be resistant to corrosion, pollution and polarization effects to ensure accurate and reliable measurement of conductivity.

[0030] 3. Test the salt content of water source according to HJ / T51.

[0031] (1) Eliminate organic interference. After evaporation in a water bath, remove the evaporating dish and wait for the evaporating dish to cool slightly. Depending on the water quality, add 30% H2O evenly and slowly in the water bath. 2 O 2 Add an appropriate amount of solution and slowly rotate the evaporating dish until the bubbles disappear, then evaporate to dryness. Repeat the process several times until there are no steam pockets in the evaporation residue and the residue turns white or the color is stable and no longer changes.

[0032] In this step, the organic matter treatment process was optimized and H 2 O 2 Solution, to prevent the addition of H 2 O 2 The solution causes the evaporation residue to splash, or when the salt content is high, the organic matter in the residue is not completely removed, causing measurement errors. The limestone-gypsum wet desulfurization system adopts forced oxidation, and there is almost no reducing salt in the desulfurization wastewater. 2 O 2 The solution will foam during the process of removing organic matter, and even cause the sample to boil. In this step, add some H 2 O2 Solution, low temperature solution state, H 2 O 2 The reaction is mild, most of the organic matter is removed, and H is added in advance before evaporation in a water bath. 2 O 2 solution to ensure that the oxide is completely removed and to prevent the addition of H 2 O 2 The solution causes the evaporation residue to splash, causing measurement errors.

[0033] (2) Each water sample is tested in parallel. If the absolute value of the relative standard deviation of the parallel samples is less than 0.5%, the test results are retained and the salinity is the arithmetic mean value of the parallel samples x p .

[0034]

[0035] Where: cv is the relative deviation of parallel samples; S is the absolute deviation of parallel samples; x p is the average value of the parallel samples,

[0036] 4. Carry out volatile substance compensation to achieve accurate measurement of high brine salt content.

[0037] (1) Measure pH, pH ≤ 2, and determine CL in wastewater - Content (using [CL - ], the unit is mg / L), [CL - ]≥400mg / L, the salt content is compensated by hydrogen chloride, the calculation formula is: pH≥-lg([CL - ] / 35500), salt content plus 10 -pH × 36500mg / L hydrogen chloride compensation; if pH < -lg[CL - ], salt content plus [CL - ]×1.028mg / L.

[0038] (2) pH ≥ 12, determine the ammonium ion content in water (using [NH 4 + ], the unit is mg / L), [NH 4 + ]≥180mg / L, NH 3 Compensation, the calculation formula is: [NH 4 + ]≤18×10 (pH-11) , salt content plus [NH 4 + ]×1.89mg / L NH 3 Compensation; [NH4 + ]≥18×10 (pH-11) , salt content plus 10 (pH-14) ×44000mg / L NH 3 compensate.

[0039] 5. Collect test data, conduct laboratory data analysis, screen outliers for each pair of conductivity and salinity analysis data, and use data analysis methods to determine the relationship formula between conductivity and salinity.

[0040] (1) The salt conductivity ratio parameter was introduced to conduct an outlier test on the data. ≥50 groups of test data were collected. The salt conductivity ratio d parameter was introduced for each pair of conductivity and salinity. The salt conductivity ratio d was equal to the ratio of salinity to conductivity. The r value outlier data of d was screened, and it was determined that ≥45 groups of analytical data were involved in the final data calculation.

[0041] Outlier screening is divided into units of 1 per conductivity value interval. By comparing the standard deviation in the normal distribution, deviation analysis is performed. When it exceeds 1.5 standard deviations, it is filtered out as an outlier.

[0042] 20% of the analysis data is used as test data, and 80% is used for sample training to establish a model for calculating the salt content based on high salt conductivity:

[0043] Y=(465.6852x 1.3051 +Obj) / 2

[0044]

[0045] Where: a is the power function coefficient, b is the power exponent, x is the conductivity, Y is the salinity, n is the number of training function samples, l is the loss of a single sample, y is i , y′ i are the true value and predicted value of the salt content of the i-th sample in the model, respectively, and f t is the base model, and Ω is the regularization term.

[0046] The calculation process of the fitting regression high salt conductivity to salt content measurement model is as follows:

[0047] Fitting regression:

[0048] After removing the outliers, the conductivity-salinity sampling data still conforms to the characteristics of an increasing function and is consistent with the power function graph. b; When performing power function fitting regression, first perform a linear transformation to ln y = ln a + b ln x; Substitute the filtered data into the formula, establish a power function fitting regression equation, and solve the values ​​of a and b, a = 465.6852, b = 1.3051, then the power function regression equation is y = 465.6852x 1.3051 .

[0049] like Figure 3 As shown, real data will fluctuate, which will cause large errors in the values ​​predicted directly by the power function. Therefore, it is necessary to adjust the smoothness of the power function in combination with the XGBoost model.

[0050] XGBoost Data Modeling:

[0051] When using XGBoost to solve the extreme value of the loss function, a second-order Taylor expansion is performed to approximate the minimum value of the loss function. When using data to train the model, its objective function Obj is as follows:

[0052]

[0053] like Figure 2 As shown in the figure, there may be certain errors between the predicted value and the actual value in some cases.

[0054] Algorithm optimization and integration:

[0055] The power function formula and the average of the predicted values ​​of the XGBoost formula are integrated to obtain a new prediction model, as shown below:

[0056] Y=(465.6852x 1.3051 +Obj) / 2

[0057] Its correlation R2=0.94, sample mean absolute deviation mae=8932.94, compared with the single power function and XGBoost, there is a significant improvement.

[0058] 6. Carry out wastewater conductivity analysis and quickly obtain the salinity of the wastewater based on the relationship between conductivity and salinity.

Claims

1. A method for measuring salinity in wastewater based on conductivity measurement with multiple compensations, characterized in that: The following steps are involved: Step 1: Select the wastewater to be measured, eliminate organic interference, and conduct a salt content test; evaporate the selected wastewater in a water bath, and slowly add a small amount of H2O2 solution before and during the water bath until the wastewater or residue turns white or the color is stable and no longer changes; Conduct parallel sample tests on the wastewater, retain the test results with the absolute value of the relative standard deviation of the parallel samples less than 0.5%, and take the arithmetic mean of the parallel samples for the salt content; Step 2: Measure the pH of the treated wastewater and perform volatile matter compensation; pH≤2, measure the CL- content [CL-] in the wastewater. If [CL-]≥400mg / L, perform hydrogen chloride compensation on the salt content. The calculation formula is: pH≥-lg ([CL - ] / 35500), salt content plus 10 -pH ×36500mg / L of hydrogen chloride compensation; if pH <-lg[CL-], add [CL-]×1.028mg / L of hydrogen chloride compensation to the salt content; pH≥12, determine the ammonium ion content in water [NH4 + ], if [NH4 + ]≥180mg / L, NH3 compensation is performed on the salt content, and the calculation formula is: [NH4 + ]≤18×10 （pH-11） , salt content plus [NH4 + ]×1.89mg / L NH3 compensation; if [NH4 + ]≥18×10 （pH-11） , salt content plus 10 （pH-14） ×44000mg / L NH3 compensation; Step 3: Collect test data, conduct laboratory data analysis, screen outliers for each pair of conductivity and salinity analysis data, and use data analysis methods to determine the relationship formula between conductivity and salinity; Step 4: Calculate the salt content of the wastewater according to the relationship formula between conductivity and salt content; The conductivity and salt content analysis data are used to screen outliers, and a relationship formula between conductivity and salt content is determined using a data analysis method. The specific steps are as follows: Step 1: Use the salt conductivity ratio parameter to perform an outlier test on the data. The salt conductivity ratio is equal to the ratio of salt content to conductivity. The data outliers are screened to select the analytical data involved in the data calculation; Step 2: Use 20% of the analysis data as test data and 80% for sample training to establish the relationship between high salt conductivity and salt content: Where: is the power function coefficient, b is the power index, x is the conductivity, Y is the salt content, n is the number of training function samples, l is the loss for a single sample, are the true value and predicted value of the salt content of the i-th sample in the model, is the base model, t is the cumulative variable, representing the number of trees, that is, the complexity of each tree is accumulated.

2. The method for measuring salinity in wastewater based on conductivity measurement with multiple compensations according to claim 1, characterized in that: Said The value is 465.6852. b The value is 1.3051.

3. The method for measuring salinity in wastewater based on conductivity measurement with multiple compensations according to claim 1, characterized in that: The outlier screening is performed by dividing the conductivity value interval into 1 units, and performing deviation analysis by comparing the standard deviation in the normal distribution. When the standard deviation exceeds 1.5, it is filtered out as an outlier.

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