CN103592242B - A kind of method measuring seawater cod - Google Patents

Abstract

The invention discloses a method for measuring seawater chemical oxygen demand, which comprises the following steps: (1) preparing a standard solution with tyrosine, and measuring the COD of the standard solution with an alkaline potassium permanganate method; (2) using ultraviolet spectroscopic Photometrically measure the absorbance of each standard solution at the peak, trough and 400nm; (3) linearly fit the absorbance and COD to obtain a linear regression equation; (4) randomly sample in the sea area to be tested; (5) use alkaline permanganate Potassium method for measuring step (4) COD at the sampling point; measure the absorbance at the peak, trough and 400nm of 3 parallel samples; (6) check and correct the linear regression equation; (7) take three parallel samples of seawater to be tested For the sample, measure the same peak, trough and absorbance at 400nm as in step (5), and take the average of the absorbance of 3 parallel samples at each place; substitute it into step (6) to obtain the chemical oxygen demand of the seawater to be measured. The method of the invention is simple and convenient to operate.

Description

A method for measuring seawater chemical oxygen demand

technical field

The invention belongs to the technical field of environmental monitoring and relates to a method for measuring seawater chemical oxygen demand.

Background technique

Chemical Oxygen Demand (Chemical Oxygen Demand referred to as COD) refers to the amount of oxidant consumed by reducing substances in water that are easily oxidized by strong oxidants under certain conditions, expressed in mg/L of oxygen. It is a comprehensive index to characterize the reducing substances in water body. For the study of river and industrial wastewater and the effect evaluation of sewage treatment plants, it is an important and relatively easy-to-obtain parameter, and it is a must-test item in environmental monitoring.

The traditional COD measurement methods mainly include potassium dichromate method and permanganate index method. The permanganate index method includes alkaline potassium permanganate method and acid potassium permanganate method. The current national standard method for seawater COD measurement is Alkaline potassium permanganate method, the alkaline potassium permanganate method requires manual sampling for measurement in the laboratory, the operation is complicated, the capital investment is large, and the environment is polluted due to the use of more chemical reagents.

Spectrophotometry is a method based on Lambert-Beer's law, which uses the molecules or ions of the measured substance to quantitatively analyze the absorption degree of characteristic electromagnetic radiation. It is a purely physical optical detection method without chemical reagents. There is no secondary pollution, and the operation is simple and time-consuming. Experiments have proved that ultraviolet absorbance can reflect the degree of organic pollution in water, especially sensitive to a large class of aromatic organic substances and organic substances with double bonds in water. In recent years, many people have begun to study the use of ultraviolet spectrophotometry with low pollution and high speed to measure the chemical oxygen demand of freshwater. However, due to the complex influencing factors in seawater, there are few studies on seawater. There is no mature method reported.

Contents of the invention

The purpose of the present invention is to overcome the disadvantages of complex operation, long time-consuming, and easy to produce secondary pollution in the prior art, and provide a method for quickly measuring seawater chemical oxygen demand without pollution, fast, and capable of real-time monitoring.

Technical scheme of the present invention is summarized as follows:

A method for measuring seawater chemical oxygen demand is characterized in that it comprises the steps:

(1) Weigh 0.2462g of tyrosine and add artificial seawater to 1000mL, make a solution with a COD concentration of 100mg/L and dilute it with artificial seawater to prepare 6 standard solutions with a theoretical COD concentration within the range of 1-10mg/L. Alkaline potassium permanganate method was used to measure the COD of the 6 standard solutions; the formula of the artificial seawater was: weigh 26.8g of NaCl, 8.6g of MgSO ₄ 7H ₂ O, and dilute to 1L with distilled water;

(2) Measure the absorbance at the peak, trough and 400nm of each standard solution described in step (1) by ultraviolet spectrophotometry;

(3) Linearly fit the absorbance of the standard solution obtained in step (2) with the COD of the standard solution measured by the alkaline potassium permanganate method in step (1) to obtain a linear regression equation; COD(Mn)=21.4664X1- 0.0003X2-16.6895X3, wherein, X1 is the absorbance of each standard solution at the peak, X2 is the absorbance of each standard solution at the trough, X3 is the absorbance of each standard solution at 400nm, and COD (Mn) is each The COD of a standard solution measured by the alkaline potassium permanganate method;

(4) Randomly sample 6-8 seawater sampling points in the sea area to be tested, and take 3 parallel samples at each sampling point;

(5) Use the alkaline potassium permanganate method to measure the COD of the 3 parallel samples at each sampling point in step (4), and take the average value of the COD of the 3 parallel samples; and measure the 3 parallel samples by UV spectrophotometry Absorbance at the peak, trough and 400nm, and take the average of the absorbance of 3 parallel samples;

(6) Use step (5) to obtain the average value of COD and the average value of absorbance of each sampling point to test and correct the linear regression equation obtained in step (3), and obtain a revised linear regression equation. The form of the regression equation is COD(Mn)=aY1+bY2-cY3, where Y1, Y2, and Y3 are the average absorbance at the peak, trough and 400nm obtained in step (5) respectively, and COD(Mn) is obtained in step (5) The average value of COD; using MATLAB drawing software, input the existing Y1, Y2, Y3 and COD (Mn) data, and get the image and coefficients a, b, c;

(7) Take three parallel samples of the seawater to be tested, measure the absorbance at the same peak, trough and 400nm as in step (5), and take the average of the absorbance of the three parallel samples; Y1, Y2 respectively , Y3, into the regression equation obtained in step (6) in the form of COD(Mn)=aY1+bY2-cY3, since a, b, and c are known, the obtained COD(Mn) is the chemical oxygen demand of the seawater to be measured.

In the present invention, tyrosine with high oxidation rate and ultraviolet absorption is used instead of potassium hydrogen phthalate or glucose to prepare a standard solution; the results of ultraviolet spectrophotometry are corresponding to the measurement results of the national standard method (alkaline potassium permanganate method) It can quickly measure the chemical oxygen demand of seawater; the method is simple, convenient to operate, short in time, and has good reproducibility, which solves the problem of complicated operation and secondary pollution caused by traditional methods; it is fast and convenient to evaluate seawater COD; measure The efficiency is high, which is conducive to further development as a real-time monitoring method for seawater COD.

Description of drawings

Fig. 1 is the ultraviolet spectrophotometric measurement result of the artificially prepared standard solution of 0-10mg/LCOD concentration.

Fig. 2 is the linear fitting of the standard solution alkaline potassium permanganate method and the ultraviolet spectrophotometry measurement result of the artificially prepared 0-10mg/LCOD concentration.

Fig. 3 is the ultraviolet spectrophotometric measurement result of the seawater to be tested.

Fig. 4 is the linear fitting of the measurement results of the alkaline potassium permanganate method and the ultraviolet spectrophotometry of the seawater to be tested.

detailed description

The present invention only uses the alkaline potassium permanganate method when fitting at the initial stage, but when the fitting result is confirmed, it can be operated by machine within a considerable period of time, with low cost and less pollution.

The present invention will be further described below in conjunction with specific examples. But the following examples are only for explaining the present invention, and do not limit the present invention in any way.

Example 1

A method for rapidly measuring seawater chemical oxygen demand, comprising the steps of:

(1) Weigh 0.2462g of tyrosine dried at 105°C for 2 hours and add artificial seawater to 1000mL to make a solution with a COD concentration of 100mg/L and dilute it with artificial seawater to prepare a theoretical COD concentration of 1.0, 2.0, 3.0, 4.0 , 5.0, 6.0, 8.0, 10.0mg/L8 standard solutions, the COD of the 6 standard solutions measured by the alkaline potassium permanganate method were 0.6565, 1.2274, 1.7226, 2.2966, 3.2870, 3.4452, 4.5938, 5.1844mg/L ; The formula of the artificial seawater is: weigh NaCl26.8g, _{MgSO4 ·} 7H2O8.6g, dilute to 1L with distilled water;

(2) Using a Kmac portable spectrophotometer, artificial seawater is used as a reference water sample, and the absorbance of each standard solution described in step (1) at the peak, trough and 400nm is measured by ultraviolet spectrophotometry to obtain the COD standard The ultraviolet spectrogram of the solution is shown in Figure 1; the absorbance is shown in Table 1;

(3) Linearly fit the absorbance of the standard solution obtained in step (2) with the COD of the standard solution measured by the alkaline potassium permanganate method in step (1) to obtain a linear regression equation; COD(Mn)=21.4664X1- 0.0003X2-16.6895X3 is shown in Figure 2, and its correlation coefficient can reach 0.9914, where X1 is the absorbance of each standard solution at the peak (220nm), X2 is the absorbance of each standard solution at the trough (236nm), and X3 is The absorbance of each standard solution at 400nm, COD (Mn) is the COD measured by the alkaline potassium permanganate method for each standard solution;

(4) Randomly sample 6 seawater sampling points in the sea area to be tested, and take 3 parallel samples at each sampling point;

(5) Use the alkaline potassium permanganate method to measure the COD of 3 parallel samples at each sampling point in step (4), and take the average value of the COD of the 3 parallel samples (see Table 2); Measure the absorbance at the peak, trough and 400nm of the 3 parallel samples, and take the average of the absorbance of the 3 parallel samples (see Figure 3, Table 3);

(6) Use step (5) to obtain the average value of COD and the average value of absorbance of each sampling point to test and correct the linear regression equation obtained in step (3), and obtain a revised linear regression equation. The form of the regression equation is COD(Mn)=aY1+bY2-cY3, where Y1, Y2, and Y3 are the average absorbance at the peak, trough and 400nm obtained in step (5) respectively, and COD(Mn) is obtained in step (5) The average value of COD; using MATLAB drawing software, input the existing Y1, Y2, Y3 and COD (Mn) data, and get the image (see Figure 4) and coefficient a=-42.4436, b=204.3414, c=248.9574;

(7) Take three parallel samples of the seawater to be tested, measure the absorbance at the same peak (223nm), trough (236nm) and 400nm as in step (5), and take the average of the absorbance of the three parallel samples at each place , respectively 0.1158, 0.0123, -0.0126; respectively Y1, Y2, Y3, substituting into the regression equation obtained in step (6) COD(Mn)=-42.4436Y1+204.3414Y2-248.9574Y3, in, due to a, b, c It is known that obtaining COD(Mn) means that the chemical oxygen demand of seawater to be tested is 0.7353 mg/L.

When the seawater environment does not change much, technicians only need to perform steps (1)-(6) once a quarter to obtain the linear regression equation of seawater UV spectrophotometry and COD(Mn). Steps (1)-(6) need to be carried out to correct the linear regression equation, and the rest of the monitoring time only needs to be carried out in step (7) to obtain the chemical oxygen demand of seawater, which is convenient and quick without secondary pollution.

Considering that in different sea areas, the main organic substances may be different, resulting in different ultraviolet absorption, so for different sea areas, the fitting equation needs to be corrected by using the method of the present invention.

Table 1

Absorbance 1mg/L 2mg/L 3mg/L 4mg/L 5mg/L 6mg/L 8mg/L 10mg/L 220nm 0.0105 0.0262 0.0421 0.0718 0.0925 0.1077 0.1652 0.1992 236nm -0.0001 0.0031 -0.0002 0.0060 0.0073 0.0173 0.0268 0.0347 400nm -0.0129 -0.0109 -0.0130 -0.0110 -0.0102 -0.0111 -0.0123 -0.0108

Table 2

COD(Mn)/(mg·L ^-1 ) Sampling point 1 Sampling point 2 Sampling point 3 Sampling point 4 Sampling point 5 Sampling point 6 sample 1 1.5221 2.9853 1.0433 1.5922 1.5861 0.5168 sample 2 1.5219 2.9858 1.0428 1.5923 1.5866 0.5160 sample 3 1.5216 2.9858 1.0431 1.5926 1.5871 0.5166 average 1.5219 2.9856 1.0430 1.5924 1.5866 0.5164

table 3

Absorbance Sampling point 1 Sampling point 2 Sampling point 3 Sampling point 4 Sampling point 5 Sampling point 6 223nm 0.0970 0.0351 0.0752 0.0276 0.0477 0.0767 236nm 0.0159 0.0191 0.0072 -0.0028 0.0022 0.0053 400nm -0.0096 -0.0023 -0.0111 -0.0134 -0.0127 -0.0108

Claims (1)

1. measure a method for seawater cod, it is characterized in that comprising the steps:

(1) take 0.2462g tyrosine and add artificial seawater to 1000mL, being made into solution that COD concentration is 100mg/L and being mixed with theoretical COD concentration with artificial seawater dilution is 6 standard solution within the scope of 1-10mg/L, measures the COD of described 6 standard solution with basic potassium permanganate method; The formula of described artificial seawater is: take NaCl26.8g, MgSO ₄7H ₂o8.6g, with distilled water diluting to 1L;

(2) with determined by ultraviolet spectrophotometry step (1) described each standard solution at crest place, trough place and 400nm place absorbance;

(3) COD of the standard solution that the absorbance of standard solution step (2) obtained and step (1) basic potassium permanganate method measure carries out linear fit, obtains equation of linear regression; COD (Mn)=21.4664X1-0.0003X2-16.6895X3, wherein, X1 is the absorbance of each standard solution at crest place, X2 is the absorbance of each standard solution at trough place, X3 is the absorbance of each standard solution at 400nm place, the COD that COD (Mn) is measured by basic potassium permanganate method for each standard solution;

(4) random 6-8 the seawater sampling point sampling in marine site to be measured, each sampling spot gets 3 Duplicate Samples;

(5) utilize 3 Duplicate Samples COD of each sampling spot of basic potassium permanganate method determination step (4), and get the mean value of 3 Duplicate Samples COD; And measure the absorbance at the crest place of 3 Duplicate Samples, trough place and 400nm place respectively by ultraviolet spectrophotometry, and get the mean value of 3 Duplicate Samples absorbance throughout;

(6) mean value of the COD of each sampling spot is obtained by step (5) and the mean value of absorbance is tested and correction to the equation of linear regression that step (3) obtains, obtain the equation of linear regression revised, regression equation form is COD (Mn)=aY1+bY2-cY3, wherein Y1, Y2, Y3 are respectively the mean value of absorbance at crest place that step (5) obtains, trough place and 400nm place, the mean value of the COD that COD (Mn) obtains for step (5); Utilize MATLAB mapping software, existing Y1, Y2, Y3 and COD (Mn) data of input, obtain image and coefficient a, b, c;

(7) three Duplicate Samples are got to seawater to be measured, measure the absorbance at the crest place identical with step (5), trough place and 400nm place, and get the mean value of 3 Duplicate Samples absorbance throughout; Be respectively Y1, Y2, Y3, the regression equation form that substitution step (6) obtains is in COD (Mn)=aY1+bY2-cY3, because a, b, c are known, obtains COD (Mn) and is seawater cod to be measured.