A method for detecting chemical oxygen demand of water quality based on laser spectroscopy

Abstract

This invention proposes a method for detecting chemical oxygen demand (COD) in water based on laser spectroscopy, comprising the following steps: Step 1, shining a laser beam into a water sample to be tested, causing the water sample to generate a light signal upon laser excitation; Step 2, receiving the light signal using a spectrometer, converting it into an electrical signal, and then into a digital signal; Step 3, receiving the digital signal through a data processing system to form a spectral curve; Step 4, calculating the relative integrated fluorescence intensity I based on the information in the spectral curve. T λ1 and λ2 are the starting and ending wavelengths of the fluorescence spectrum, respectively, and Iλ represents the fluorescence intensity at wavelength λ. r This represents the light intensity of the Raman peak after subtracting the fluorescence background; Step 5: Calculate the COD value of the water sample according to the chemical oxygen demand formula for water quality. The chemical oxygen demand formula for water quality is COD = KI T +C. The above detection method can greatly reduce the influence of various interference factors on COD detection results, and has the advantages of high sensitivity, fast measurement speed, convenient measurement, and high accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of water quality chemical oxygen demand detection, and in particular to a water quality chemical oxygen demand detection method based on laser spectroscopy technology. Background Art

[0002] Water quality analysis is an important task of environmental monitoring. The chemical oxygen demand (COD) value reflects the concentration of reducing substances in water. It is an important indicator for measuring organic pollution in water and one of the important measurement items in water quality monitoring and analysis. Traditional water quality COD detection mostly uses chemical analysis methods, including potassium dichromate method (COD Cr ) and potassium permanganate method (COD Mn ), but they all have problems such as long measurement cycle, many chemical reagents and secondary pollution, which make it difficult to meet the requirements of real-time water quality detection. Compared with chemical methods, optical analysis is based on the characteristic spectrum of substances, and has the advantages of fast analysis speed, simple operation, good selectivity, high sensitivity, and no damage to samples. It has achieved rapid development in the field of online water quality monitoring and is increasingly valued by people.

[0003] Among them, three-dimensional fluorescence spectroscopy has the characteristics of large spectral data volume and high sensitivity in water quality detection, but it has the disadvantages of slow detection speed and complex operation, and it is not easy to perform rapid online analysis of water quality. Compared with three-dimensional fluorescence spectroscopy, two-dimensional fluorescence spectroscopy uses a single wavelength laser or LED as the excitation light source, which simplifies the measurement device. Since only the two-dimensional spectral curve is analyzed, it has a faster analysis speed. In recent years, researchers at home and abroad have also begun to apply two-dimensional fluorescence spectroscopy to rapid water quality detection.

[0004] At present, although the two-dimensional fluorescence spectroscopy method can measure COD parameters by analyzing fluorescence intensity, due to the influence of factors such as ambient light changes, water flow fluctuations, instrument vibration and light source aging, there are often problems such as unstable measurement data and low accuracy in practical applications. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present application proposes a water quality chemical oxygen demand detection method based on laser spectroscopy technology, so as to greatly reduce the influence of various interference factors on the COD detection results. This method has the advantages of high sensitivity, fast measurement speed, convenient measurement and high accuracy.

[0006] In order to achieve the above objectives, the present application proposes a method for detecting chemical oxygen demand of water quality based on laser spectroscopy technology, comprising the following steps:

[0007] Step 1, making laser incident on the water sample to be tested, and the water sample to be tested is excited by the laser to generate a light signal;

[0008] Step 2: receiving the optical signal generated in step 1 through a spectrometer, converting the optical signal into an electrical signal, and then converting it into a digital signal;

[0009] Step 3: Receive the digital signal transmitted by the spectrometer through the data processing system to form a spectrum curve, wherein the spectrum curve includes the Raman scattering peak of water and the fluorescence peak of dissolved organic matter in water, wherein the light intensity of the Raman peak after deducting the fluorescence background is expressed as I r express;

[0010] Step 4: Calculate the relative integrated fluorescence intensity I according to the information in the spectral curve. T ,in, Where λ1 is the starting wavelength of the fluorescence spectrum, λ2 is the ending wavelength of the fluorescence spectrum, Iλ represents the fluorescence intensity at wavelength λ, and I r It represents the light intensity of the Raman peak after deducting the fluorescence background;

[0011] Step 5: Calculate the COD value of the water sample according to the chemical oxygen demand formula. The chemical oxygen demand formula is COD = KI T +C, where I T is the relative integrated fluorescence intensity calculated in step 4, K is the proportionality coefficient, C is the detection limit, K and C are constants, and the relative integrated fluorescence intensity I of the standard solution is used. T The correlation with the COD value detected by the national standard method can obtain the values ​​of K and C.

[0012] In some embodiments, in step 5, the process of obtaining the values ​​of K and C includes the following steps:

[0013] Step 501: using a mixture of glucose solution and sodium humate solution of equal volume as a standard solution, wherein the concentration ratio of the glucose solution to the sodium humate solution is in the range of 1:10 to 1:50;

[0014] Step 502, selecting a standard solution at any concentration ratio in step 501;

[0015] Step 503, allowing laser to be incident on the standard solution, and the standard solution is excited by the laser to generate a light signal;

[0016] Step 504: receiving the optical signal generated in step 503 through a spectrometer, converting the optical signal into an electrical signal, and then converting it into a digital signal;

[0017] Step 505: receiving the digital signal transmitted by the spectrometer through the data processing system to form a spectrum curve;

[0018] Step 506: Calculate the relative integrated fluorescence intensity I according to the information in the spectral curve.T ,in, Where λ1 is the starting wavelength of the fluorescence spectrum, λ2 is the ending wavelength of the fluorescence spectrum, Iλ represents the fluorescence intensity at wavelength λ, and I r It represents the light intensity of the Raman peak after deducting the fluorescence background;

[0019] Step 507: Detect the COD value of the standard solution using the national standard method and compare it with the I obtained in step 506. T The values ​​form a set of data;

[0020] Step 508: dilute the standard solution in step 502 at least once, repeat the operations of steps 503 to 507 for each diluted standard solution, and obtain several groups of relative integrated fluorescence intensities I T Value and COD value;

[0021] Step 509: Obtain several groups of relative integrated fluorescence intensities I T Substitute the value and COD value into the formula COD=KI T +C, calculate the values ​​of K and C by the least squares method.

[0022] The beneficial effect of the scheme of the present application is that the above-mentioned water quality chemical oxygen demand detection method based on laser spectroscopy technology adopts a mixed solution of sodium humate solution and glucose solution as a standard solution for spectroscopy detection of COD, and uses the relative integrated fluorescence intensity I of the standard solution to detect COD. T The relationship between the COD value detected by the national standard method can obtain the values ​​of K and C, and then use the water quality chemical oxygen demand formula COD = KI T +C calculates the COD value of the tested water sample, where The above detection method can greatly reduce the influence of various interference factors on the COD detection results. This method has the advantages of high sensitivity, fast measurement speed, convenient measurement and high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A flow chart of a method for detecting chemical oxygen demand of water quality based on laser spectroscopy technology in an embodiment is shown.

[0024] Figure 2 A schematic diagram showing a typical spectrum curve generated when laser is incident on a water sample to be tested in an embodiment.

[0025] Figure 3 The figure shows the relationship between the COD value of the standard solution and the relative integrated fluorescence intensity in the example. DETAILED DESCRIPTION

[0026] The specific implementation of the present application is further described below in conjunction with the accompanying drawings.

[0027] like Figure 1 As shown, the water quality chemical oxygen demand detection method based on laser spectroscopy technology involved in this application includes the following steps:

[0028] Step 1: Make laser incident on the water sample to be tested, and the water sample to be tested generates a light signal when excited by the laser.

[0029] Step 2: Receive the optical signal generated in step 1 through a spectrometer, convert the optical signal into an electrical signal, and then convert it into a digital signal.

[0030] Step 3: Receive the digital signal transmitted by the spectrometer through a data processing system (such as a computer) to form a spectrum curve, such as Figure 2 As shown, the spectral curve includes the Mie scattering peak of suspended particles in water (its intensity is expressed as I S ), water Raman scattering peak (its intensity is represented by I R The fluorescence peak of dissolved organic matter (DOM) in water (the intensity of which is expressed as I F The light intensity of the Raman peak after deducting the fluorescence background is represented by I r express.

[0031] Step 4: Calculate the relative integrated fluorescence intensity I according to the information in the spectral curve. T ,in, Where λ1 is the starting wavelength of the fluorescence spectrum, λ2 is the ending wavelength of the fluorescence spectrum, Iλ represents the fluorescence intensity at wavelength λ, and I r It represents the light intensity of the Raman peak after deducting the fluorescence background.

[0032] Since the fluorescence spectrum range produced by laser excitation of organic matter in the measured water sample is relatively wide, in order to fully reflect the fluorescence contribution of organic matter in water, the relative integrated fluorescence intensity is used in this patent application to calculate the COD parameters in water so as to improve the accuracy of detection.

[0033] Step 5: Calculate the COD value of the water sample according to the chemical oxygen demand formula. The chemical oxygen demand formula is COD = KI T +C, where I T is the relative integrated fluorescence intensity calculated in step 4, K is the proportionality coefficient, C is the detection limit, K and C are constants, and the relative integrated fluorescence intensity I of the standard solution is used. T The correlation with the COD value detected by the national standard method can obtain the values ​​of K and C.

[0034] Specifically, the process of obtaining the values ​​of K and C includes the following steps:

[0035] Step 501: Mix the same volume of glucose solution and sodium humate solution as a standard solution, and the concentration ratio of the glucose solution to the sodium humate solution is in the range of 1:10 to 1:50. In this embodiment, the same volume of glucose solution and sodium humate solution are mixed as the standard solution to make the laser induced fluorescence intensity of the standard solution consistent with the fluorescence intensity of the actual water sample.

[0036] Step 502: Select a standard solution at any concentration ratio in step 501.

[0037] Step 503: allow laser light to enter the standard solution, and the standard solution is excited by the laser light to generate a light signal.

[0038] Step 504: Receive the optical signal generated in step 503 through a spectrometer, convert the optical signal into an electrical signal, and then convert it into a digital signal.

[0039] Step 505: Receive the digital signal transmitted by the spectrometer through the data processing system to form a spectrum curve.

[0040] Step 506: Calculate the relative integrated fluorescence intensity I according to the information in the spectral curve. T ,in, Where λ1 is the starting wavelength of the fluorescence spectrum, λ2 is the ending wavelength of the fluorescence spectrum, Iλ represents the fluorescence intensity at wavelength λ, and I r It represents the light intensity of the Raman peak after deducting the fluorescence background.

[0041] Step 507: Detect the COD value of the standard solution using the national standard method and compare it with the I obtained in step 506. T Values ​​form a set of data.

[0042] Step 508: dilute the standard solution in step 502 at least once, repeat the operations of steps 503 to 507 for each diluted standard solution, and obtain several groups of relative integrated fluorescence intensities I T Value and COD value.

[0043] Step 509: Obtain several groups of relative integrated fluorescence intensities I T Substitute the value and COD value into the formula COD=KI T +C, and the values ​​of K and C are calculated by the least squares method, such as Figure 3 shown.

[0044] The water quality chemical oxygen demand detection method based on laser spectroscopy technology involved in the present application adopts a mixed solution of sodium humate solution and glucose solution as a standard solution for spectral detection of COD, and uses the relative integrated fluorescence intensity I TThe relationship between the COD value detected by the national standard method can obtain the values ​​of K and C, and then use the water quality chemical oxygen demand formula COD = KI T +C calculates the COD value of the tested water sample, where The above detection method can greatly reduce the influence of various interference factors on the COD detection results. This method has the advantages of high sensitivity, fast measurement speed, convenient measurement and high accuracy.

[0045] The above is only a preferred specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can make equivalent substitutions or changes according to the technical solution and concept of the present application within the technical scope disclosed in the present application, which should be covered by the protection scope of the present application.

Claims

1. A method for detecting chemical oxygen demand of water quality based on laser spectroscopy technology, characterized in that: The following steps are involved: Step 1, making laser incident on the water sample to be tested, and the water sample to be tested is excited by the laser to generate a light signal; Step 2: receiving the optical signal generated in step 1 through a spectrometer, converting the optical signal into an electrical signal, and then converting it into a digital signal; Step 3: Receive the digital signal transmitted by the spectrometer through the data processing system to form a spectrum curve, wherein the spectrum curve includes the Raman scattering peak of water and the fluorescence peak of dissolved organic matter in water, wherein the light intensity of the Raman peak after deducting the fluorescence background is expressed as I r express; Step 4: Calculate the relative integrated fluorescence intensity I according to the information in the spectral curve. T ,in, , where λ 1 is the starting wavelength of the fluorescence spectrum, λ 2 is the end position wavelength of the fluorescence spectrum, I λ represents the fluorescence intensity at wavelength λ, I r It represents the light intensity of the Raman peak after deducting the fluorescence background; Step 5: Calculate the COD value of the water sample according to the chemical oxygen demand formula. The chemical oxygen demand formula is COD=K I T +C, where I T is the relative integrated fluorescence intensity calculated in step 4, K is the proportionality coefficient, C is the detection limit, K and C are constants, and the relative integrated fluorescence intensity I of the standard solution is used. T The correlation with the COD value detected by the national standard method can obtain the values ​​of K and C; In step 5, the process of obtaining the values ​​of K and C includes the following steps: Step 501: using the same volume of glucose solution and sodium humate solution mixed as a standard solution, the concentration ratio of the glucose solution to the sodium humate solution is in the range of 1:10 to 1:50; Step 502, selecting a standard solution at any concentration ratio in step 501; Step 503, allowing laser to be incident on the standard solution, and the standard solution is excited by the laser to generate a light signal; Step 504: receiving the optical signal generated in step 503 through a spectrometer, converting the optical signal into an electrical signal, and then converting it into a digital signal; Step 505: receiving the digital signal transmitted by the spectrometer through the data processing system to form a spectrum curve; Step 506: Calculate the relative integrated fluorescence intensity I according to the information in the spectral curve. T ,in, , where λ 1 is the starting wavelength of the fluorescence spectrum, λ 2 is the end position wavelength of the fluorescence spectrum, I λ represents the fluorescence intensity at wavelength λ, I r It represents the light intensity of the Raman peak after deducting the fluorescence background; Step 507: Detect the COD value of the standard solution using the national standard method and compare it with the I obtained in step 506. T The values ​​form a set of data; Step 508: dilute the standard solution in step 502 at least once, repeat the operations of steps 503 to 507 for each diluted standard solution, and obtain several groups of relative integrated fluorescence intensities I T Value and COD value; Step 509: Obtain several groups of relative integrated fluorescence intensities I T Substitute the value and COD value into the formula COD=K I T +C, calculate the values ​​of K and C by the least squares method.

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