Method for rapidly determining COD (Chemical Oxygen Demand) concentration of cyanobacterial bloom water body

Abstract

The invention relates to a method for rapidly determining the COD concentration of cyanobacterial bloom water body, which comprises the following steps: sequentially carrying out filtration treatment, digestion treatment and acidification treatment on the cyanobacterial bloom water body to obtain a treatment solution; measuring the absorbance of the treatment liquid; and obtaining the COD concentration of the cyanobacterial bloom water body based on the absorbance of the treating fluid and the mapping relation between the COD concentration of the COD series standard working fluid and the absorbance of the digested and acidified solution. The cyanobacterial bloom water body is filtered, then organic substances in the cyanobacterial bloom water body are digested, the influence of the organic substances on COD measurement is reduced, then acidification treatment is performed, the activity of biotoxin is reduced, the influence of the biotoxin on COD measurement is reduced, and the accuracy of COD measurement of the cyanobacterial bloom water body is improved.

Description

Technical Field

[0001] The present application relates to the technical field of chemical oxygen demand measurement, and particularly relates to a method for rapidly determining the COD concentration of cyanobacterial bloom water bodies. Background Art

[0002] With the intensification of climate change and water eutrophication, cyanobacterial bloom is an important environmental problem faced by many lakes and reservoirs at present, and has gradually evolved into a worldwide ecological environment problem. Cyanobacterial bloom is a water ecological environment problem. When the environment is suitable, the water body is rich in nutrients, and the CO2 concentration increases, the carbon fixation ability and metabolic level of cyanobacteria increase, and they reproduce and aggregate in large quantities and rapidly. When it reaches a certain level, cyanobacterial bloom is formed. Its outbreak will trigger a series of chain reactions, and the most obvious impact is the drinking water supply safety and water body biodiversity. Monitoring the dynamic changes of cyanobacterial bloom and analyzing the driving factors of the cyanobacterial bloom growth and decline process will contribute to the management of important water body water quality targets, prevention and control of the occurrence of harmful algal blooms.

[0003] Chemical oxygen demand (abbreviated as COD) is an important indicator for characterizing the pollution degree of environmental water bodies, and is also one of the key indicators for the control of lake environmental pollution treatment. For the pollution control of cyanobacterial bloom water bodies, the detection of COD in lake water bodies is particularly important. The outbreak speed of cyanobacterial bloom is relatively fast, and the appearance and duration of cyanobacterial bloom often only last for several hours, showing large temporal and spatial differences. Therefore, it is necessary to rapidly measure the COD of cyanobacterial water, and take targeted measures for cyanobacterial bloom according to the measured COD concentration.

[0004] At present, the traditional methods for measuring water body COD include the dichromate method, the permanganate method and the rapid digestion method.

[0005] The dichromate method has the disadvantages of cumbersome operation, time-consuming, water and electricity consumption, large reagent consumption, difficulty in rapid determination in large batches, and secondary pollution to the environment.

[0006] The permanganate method is time-consuming and has relatively low measurement accuracy, and is mainly aimed at surface water with relatively low pollutants.

[0007] The disadvantage of the rapid digestion method is that different types of digestion equipment have different powers and times for the test, and the measurement results are different.

[0008] These three traditional water quality monitoring methods have a long analysis cycle, large reagent consumption, and a large amount of waste liquid generated, and are not suitable for measuring the COD concentration of cyanobacterial bloom water bodies. The measurement accuracy is relatively poor, and it is necessary to improve the chemical oxygen demand determination method according to the particularity of cyanobacterial bloom water quality. Summary of the Invention

[0009] An embodiment of the present application provides a method for quickly measuring the COD concentration of cyanobacterial bloom water bodies, which is applicable to the measurement of the COD concentration of cyanobacterial bloom water bodies, eliminates the influence of organic substances and biotoxins in cyanobacterial bloom water bodies on the measurement of the COD concentration of cyanobacterial bloom water bodies, and improves the measurement accuracy.

[0010] An embodiment of the present application provides a method for quickly measuring the COD concentration of cyanobacterial bloom water bodies, which includes:

[0011] Filtering, digesting, and acidifying the cyanobacterial bloom water body in sequence to obtain a treatment solution;

[0012] Measuring the absorbance of the treatment solution;

[0013] Based on the absorbance of the treatment solution and the mapping relationship between the COD concentration of the COD series standard working solution and the absorbance of its digested and acidified solution, the COD concentration of the cyanobacterial bloom water body is obtained.

[0014] In some embodiments, a glass fiber filter membrane is used to filter the cyanobacterial bloom water body;

[0015] Among them, the pore size of the glass fiber filter membrane is 4.5 - 7 μm.

[0016] In some embodiments, before using the glass fiber filter membrane to filter the cyanobacterial bloom water body, the method further includes: pre-treating the glass fiber filter membrane;

[0017] Pre-treating the glass fiber filter membrane specifically includes:

[0018] Using deionized water or distilled water to wash the surface of the glass fiber filter membrane to remove surface impurities;

[0019] Soaking the glass fiber filter membrane in a (1 + 9) sulfuric acid solution for 20 - 30 hours;

[0020] Placing the soaked glass fiber filter membrane in a dry and ventilated environment to air dry naturally.

[0021] In some embodiments, the conditions of the filtering treatment include: the negative pressure is controlled at 0.1 - 0.3 MPa, and the flow rate is controlled at 1 - 5 m / s.

[0022] In some embodiments, the digestion treatment includes:

[0023] Adding the cyanobacterial bloom water body to a determination test tube containing a COD digestion solution, tightening the lid, and shaking well;

[0024] Putting the determination test tube into a digester preheated to 150 °C, heating and digesting for 2 h, and then cooling.

[0025] In some embodiments, the acidification treatment includes:

[0026] Adding a (1+9) sulfuric acid solution to the digested cyanobacterial bloom water body for acidification to acidify the cyanobacterial bloom water body to a pH value of 1.8 to 2.2.

[0027] In some embodiments, the method further includes: obtaining the mapping relationship between the COD concentration of the COD series standard working solution and the absorbance of its digested and acidified solution;

[0028] Among them, obtaining the mapping relationship between the COD concentration of the COD series standard working solution and the absorbance of its digested and acidified solution specifically includes:

[0029] Digesting and acidifying the COD series standard working solution to obtain the digested and acidified solution of the COD series standard working solution;

[0030] Measuring the absorbance of each digested and acidified solution, and making a standard curve with the absorbance as the abscissa and the COD concentration of the COD series standard working solution as the ordinate to obtain the mapping relationship between the COD concentration of the COD series standard working solution and the absorbance of its digested and acidified solution.

[0031] In some embodiments, prepare a (1+9) sulfuric acid solution: Mix concentrated sulfuric acid with a concentration of 18.4 mol / L and water in a volume ratio of 1:9, stir and shake well to obtain a (1+9) sulfuric acid solution;

[0032] Prepare a mercury sulfate solution: Dissolve mercury sulfate in the (1+9) sulfuric acid solution and mix well to obtain a mercury sulfate solution with a concentration of 100 g / L;

[0033] Prepare a sulfuric acid-silver sulfate solution: Add silver sulfate to sulfuric acid with a concentration of 18.4 mol / L, let it dissolve for 1 to 2 days and mix well to obtain a sulfuric acid-silver sulfate solution with a silver sulfate concentration of 10 g / L;

[0034] Prepare a potassium dichromate solution: Weigh 12.258 g of potassium dichromate dried to constant weight at 105±2 °C, dissolve it in 800 mL of distilled water, make up the volume to 1000 mL after dissolution, and dilute it 10 times to obtain a potassium dichromate solution with a concentration of 0.0250 mol / L;

[0035] Prepare a potassium hydrogen phthalate solution: Weigh 0.4251 g of potassium hydrogen phthalate dried at 105 °C for 2 h, dissolve it in distilled water, and dilute it to 1000 mL and mix well to obtain a potassium hydrogen phthalate solution with a concentration of 2.0824 mmol / L, and its COD Cr value is 500 mg / L;

[0036] Prepare the COD digestion solution: Add 0.5 mL of a mercuric sulfate solution with a concentration of 100 g / L, 1.5 mL of a potassium dichromate solution with a concentration of 0.0250 mol / L, and 4 mL of a sulfuric acid - silver sulfate solution with a silver sulfate concentration of 10 g / L to a test tube for determination. After mixing, prepare 6 mL of the COD digestion solution;

[0037] Prepare a series of standard working solutions of COD: Dilute the potassium hydrogen phthalate solution with a COD value of 500 mg / L by 5 times to a COD value of 100 mg / L, and then successively dilute it to COD values of 0 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, 60 mg / L, and 80 mg / L to obtain a series of standard working solutions of COD; Cr value of 500 mg / L to a COD Cr value of 100 mg / L, and then successively dilute it to COD Cr values of 0 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, 60 mg / L, and 80 mg / L to obtain a series of standard working solutions of COD;

[0038] Sequentially add 3 mL of the series of standard working solutions of COD, in the order from the lowest concentration of 0 mg / L to the highest concentration of 80 mg / L, to seven test tubes for determination containing 6 mL of the COD digestion solution respectively. Tighten the caps and shake well. Then place the test tubes for determination in a digestion instrument preheated to 150 °C for heating and digestion for 2 h. After cooling, add 1 mL of (1 + 9) sulfuric acid solution and measure the absorbance;

[0039] Using the absorbance as the abscissa and the COD Cr value of the series of standard working solutions of COD as the ordinate, make a standard curve to obtain the mapping relationship between the COD concentration of the series of standard working solutions of COD and the absorbance of its digested and acidified solution.

[0040] In some embodiments, the standard curve is as follows:

[0041] y = -565.4x + 107.07, R 2 = 0.9996

[0042] where y is the absorbance, x is the COD Cr value, and R 2 is the correlation coefficient of the standard curve.

[0043] In some embodiments, the dosage of the cyanobacterial bloom water body is 3 mL, the dosage of the COD digestion solution during digestion treatment is 6 mL, and the dosage of the (1 + 9) sulfuric acid solution during acidification treatment is 1 mL.

[0044] The beneficial effects brought by the technical solution provided by this application include:

[0045] This application filters the cyanobacterial bloom water body, then decomposes the organic substances in the cyanobacterial bloom water body to reduce the impact of organic substances on the COD measurement. After that, through acidification treatment, the activity of biotoxins is reduced, the impact of biotoxins on the COD measurement is reduced, and the accuracy of COD measurement of the cyanobacterial bloom water body is improved.

[0046] This method is based on the rapid digestion spectrophotometry and the potassium dichromate method. The detection limit of the measured COD concentration is 0-80mg / L, and surface water of Class I-V can be measured. Moreover, the measurement takes a short time, the results are stable, the accuracy is high, and the environmental pollution is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0048] Figure 1 It is a flowchart of a method for rapidly measuring the COD concentration of a cyanobacterial bloom water body provided by an embodiment of the present application;

[0049] Figure 2 It is a standard curve graph provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments in the present application fall within the scope of protection of the present application.

[0051] See Figure 1 As shown, an embodiment of the present application provides a method for rapidly measuring the COD concentration of a cyanobacterial bloom water body, which includes the following steps:

[0052] 101: Sequentially perform filtration treatment, digestion treatment, and acidification treatment on the cyanobacterial bloom water body to obtain a treatment solution.

[0053] In the present application, a DRB 200 Hach digestion instrument and a Hach COD measurement test tube (with a capacity of 10 mL) can be used for digestion.

[0054] 102: Measure the absorbance of the treatment solution.

[0055] In this application, the absorbance is measured using a UV-8000 spectrophotometer at a wavelength of 420 nm.

[0056] 103: Based on the absorbance of the treatment liquid and the mapping relationship between the COD concentration of the COD series standard stock solution and the absorbance of its digested and acidified solution, the COD concentration of the cyanobacterial bloom water body is obtained.

[0057] In this application, the cyanobacterial bloom water body is filtered, and then the organic substances in the cyanobacterial bloom water body are digested to reduce the influence of organic substances on the COD measurement. After that, through acidification treatment, the activity of biotoxins is reduced, the influence of biotoxins on the COD measurement is reduced, and the accuracy of COD measurement of the cyanobacterial bloom water body is improved.

[0058] In step 101, this application uses a glass fiber filter membrane to filter the cyanobacterial bloom water body; in order to reduce the influence of the filtration method on the accuracy of subsequent tests, the following correction process can be adopted:

[0059] ① Select a suitable filter membrane. Select a filter membrane with a moderate pore size and good retention effect to reduce the loss of the cyanobacterial bloom water body and filter membrane blockage. The diameter of cyanobacterial cells is usually in the range of 4.8 - 6 μm, but there may also be smaller cyanobacterial particles or fragments. Therefore, when selecting a filter membrane, it is necessary to ensure that the pore size of the filter membrane can effectively intercept these particles. The glass fiber filter membrane has high mechanical strength and chemical stability, and can withstand a certain pressure and the erosion of chemical substances. The pore size is the key parameter. For cyanobacteria filtration, a glass fiber filter membrane with a pore size between 4.5 - 7 μm can be selected. This pore size can effectively intercept cyanobacterial particles and maintain a certain filtration rate. Therefore, select a glass fiber filter membrane with a pore size between 4.5 - 7 μm and a filter membrane diameter of 47 mm.

[0060] ② Pretreat the filter membrane. Before using the glass fiber filter membrane to filter the cyanobacterial bloom water body, pre-treat the glass fiber filter membrane to reduce the adsorption of the components of the cyanobacterial bloom water body by the filter membrane.

[0061] The pre-treatment of the glass fiber filter membrane specifically includes:

[0062] 201: Gently wash the surface of the glass fiber filter membrane with deionized water or distilled water to remove impurities such as dust and oil stains on the surface;

[0063] 202: Immerse the glass fiber filter membrane in a (1 + 9) sulfuric acid solution for 20 - 30 hours;

[0064] 203: Place the soaked glass fiber filter membrane in a dry and ventilated environment to dry naturally. Avoid direct sunlight and high-temperature environments to prevent the filter membrane from deforming or aging.

[0065] In step 101, the conditions for the filtration treatment include: the negative pressure is controlled at 0.1 - 0.3 MPa, and the flow rate is controlled at 1 - 5 m / s.

[0066] Specifically, after retrieving the cyanobacterial bloom water body, the cyanobacterial bloom water body is pre-treated. A glass fiber filter membrane with a pore size of 4.5 - 7 μm is installed on the vacuum filtration device. A certain volume of the mixed cyanobacterial bloom water body is measured with a measuring cylinder and filtered. During the filtration process, the filtration conditions such as pressure and flow rate should be strictly controlled to ensure the filtration effect and test accuracy. The negative pressure during filtration is controlled at 0.1 - 0.3 MPa, and the flow rate is controlled at 1 - 5 m / s. The filter membrane is immediately replaced after each water sample is filtered, and 30 - 50 mL of the cyanobacterial bloom water body is filtered each time to ensure the filtration efficiency. The suction filtration is ended when the sample has just completely passed through the filter membrane, and the filter membrane is taken out with tweezers. The filtered cyanobacterial bloom water body is poured into a polyethylene bottle for storage and standby.

[0067] In step 101, the digestion treatment includes:

[0068] 301: Add the cyanobacterial bloom water body to the determination test tube containing the COD digestion solution, tighten the lid, and shake well. Specifically, add 3 mL of the cyanobacterial bloom water body to the determination test tube containing 6 mL of the COD digestion solution.

[0069] 302: Put the determination test tube into a digestion instrument pre-heated to 150 °C for heating and digestion for 2 h, and then cool it.

[0070] In step 101, the acidification treatment includes: adding 1 mL of (1 + 9) sulfuric acid solution to the digested cyanobacterial bloom water body for acidification, so that the cyanobacterial bloom water body is acidified to a pH value of 1.8 - 2.2 to completely eliminate the activity of biotoxins in the cyanobacterial bloom water body and prevent it from affecting the COD determination.

[0071] In step 103, obtaining the mapping relationship between the COD concentration of the COD series standard working solutions and the absorbance of their digested and acidified solutions specifically includes:

[0072] 401: Digest and acidify the COD series standard working solutions to obtain the digested and acidified solutions of the COD series standard working solutions.

[0073] 402: Measure the absorbance of each digested and acidified solution, and make a standard curve with the absorbance as the abscissa and the COD concentration of the COD series standard working solutions as the ordinate to obtain the mapping relationship between the COD concentration of the COD series standard working solutions and the absorbance of their digested and acidified solutions.

[0074] Specifically, prepare a (1 + 9) sulfuric acid solution: Mix concentrated sulfuric acid with a concentration of 18.4 mol / L and water in a volume ratio of 1:9, stir and shake well to obtain a (1 + 9) sulfuric acid solution.

[0075] Prepare a mercuric sulfate solution: Dissolve mercuric sulfate in the (1 + 9) sulfuric acid solution, mix well to obtain a mercuric sulfate solution with a concentration of 100 g / L.

[0076] Prepare a sulfuric acid - silver sulfate solution: Add silver sulfate to sulfuric acid with a concentration of 18.4 mol / L, let it stand for 1 - 2 days to dissolve, and mix well to obtain a sulfuric acid - silver sulfate solution with a silver sulfate concentration of 10 g / L.

[0077] Prepare a potassium dichromate solution: Weigh 12.258 g of potassium dichromate dried to constant weight at 105 ± 2 °C, dissolve it in 800 mL of distilled water, and make up the volume to 1000 mL after dissolution to obtain a potassium dichromate solution with a concentration C(1 / 6K 2 Cr 2 O 7 ) = 0.250 mol / L. Dilute it 10 times to obtain a potassium dichromate solution with a concentration C(1 / 6K 2 Cr 2 O 7 ) = 0.0250 mol / L.

[0078] Prepare a potassium hydrogen phthalate solution: Weigh 0.4251 g of potassium hydrogen phthalate dried at 105 °C for 2 h, dissolve it in distilled water, and dilute it to 1000 mL, mix well to obtain a potassium hydrogen phthalate solution with a concentration of 2.0824 mmol / L. Using potassium dichromate as the oxidant, the COD Cr value for complete oxidation of potassium hydrogen phthalate is 1.176 g of oxygen per gram (i.e., 1 g of potassium hydrogen phthalate consumes 1.176 g of oxygen), so the theoretical COD Cr value of this potassium hydrogen phthalate solution is 500 mg / L.

[0079] Prepare a COD digestion solution: Add 0.5 mL of a mercuric sulfate solution with a concentration of 100 g / L, 1.5 mL of a potassium dichromate solution with a concentration of 0.0250 mol / L, and 4 mL of a sulfuric acid - silver sulfate solution with a silver sulfate concentration of 10 g / L to a test tube for determination, mix them to prepare a 6 - mL COD digestion solution.

[0080] Prepare a series of COD standard working solutions: Dilute the potassium hydrogen phthalate solution with a COD Cr value of 500 mg / L by 5 times to a COD Cr value of 100 mg / L, and then serially dilute it to a COD CrThe values are 0 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, 60 mg / L, and 80 mg / L to obtain a series of standard COD working solutions.

[0081] Sequentially add 3 mL of the series of standard COD working solutions, in the order from the low concentration of 0 mg / L to the high concentration of 80 mg / L, into seven test tubes for determination containing 6 mL of COD digestion solution respectively. Tighten the lids and shake well. Then place the test tubes for determination into a digester preheated to 150 °C for heating and digestion for 2 h. After cooling, add 1 mL of (1+9) sulfuric acid solution, and measure the absorbance at a wavelength of 420 nm.

[0082] Using the absorbance as the abscissa and the COD Cr value of the series of standard COD working solutions as the ordinate to make a standard curve, and obtain the mapping relationship between the COD concentration of the series of standard COD working solutions and the absorbance of the solution after its digestion and acidification.

[0083] The principle of this application is as follows:

[0084] Filter a certain amount of cyanobacterial bloom water body with a filter membrane to intercept cyanobacteria. Then, under the action of sulfuric acid - silver sulfate, use a potassium dichromate solution with a known concentration to oxidize the reducing substances in the filtered cyanobacterial bloom water body in a closed test tube for determination. Part of Cr 2 O 7 2- is converted into Cr 3+ . Acidify the water sample with (1+9) sulfuric acid solution to reduce the activity of biotoxins in the water sample, and measure the absorbance value of potassium dichromate at a wavelength of 420 nm, then the concentration of COD in the cyanobacterial bloom water body can be calculated.

[0085] This method is based on the rapid digestion spectrophotometry and the potassium dichromate method. The detection limit for measuring the COD concentration is 0 - 80 mg / L. It can measure surface water bodies of Class I - V, and has the advantages of short measurement time, stable results, high accuracy, and less environmental pollution.

[0086] Example

[0087] (1) Prepare COD digestion solution

[0088] Prepare (1+9) sulfuric acid solution: Slowly add 50 mL of concentrated sulfuric acid with a concentration of 18.4 mol / L into about 400 - 450 mL of distilled water and continuously stir. Then transfer the mixed solution to a 500 mL volumetric flask for volume fixation and shaking to obtain 500 mL of (1+9) sulfuric acid solution.

[0089] Prepare mercury sulfate solution: Dissolve 10 g of mercury sulfate in 100 mL of (1+9) sulfuric acid solution, mix well to obtain a mercury sulfate solution with a concentration of 100 g / L.

[0090] Preparation of sulfuric acid - silver sulfate solution: Add 10 g of silver sulfate to 1 L of sulfuric acid with a concentration of 18.4 mol / L, let it stand for 1 - 2 days to dissolve, and mix well to obtain a sulfuric acid - silver sulfate solution with a silver sulfate concentration of 10 g / L.

[0091] Preparation of potassium dichromate solution: Weigh 12.258 g of potassium dichromate dried to constant weight at 105 ± 2 °C, dissolve it in 800 mL of distilled water, and make up the volume to 1000 mL after dissolution to obtain a potassium dichromate solution with a concentration C(1 / 6K 2 Cr 2 O 7 ) = 0.250 mol / L. Dilute it 10 - fold to obtain a potassium dichromate solution with a concentration C(1 / 6K 2 Cr 2 O 7 ) = 0.0250 mol / L.

[0092] Preparation of COD digestion solution: Add 0.5 mL of mercury sulfate solution with a concentration of 100 g / L, 1.5 mL of potassium dichromate solution with a concentration of 0.0250 mol / L, and 4 mL of sulfuric acid - silver sulfate solution with a silver sulfate concentration of 10 g / L to the test tube for determination, and mix them to prepare 6 mL of COD digestion solution.

[0093] (2) Preparation of COD series standard working solutions

[0094] Preparation of potassium hydrogen phthalate solution: Weigh 0.4251 g of potassium hydrogen phthalate dried at 105 °C for 2 h, dissolve it in 800 mL of distilled water, and make up the volume to 1000 mL and mix well to obtain a potassium hydrogen phthalate solution with a concentration C(KHC 8 H 4 O 4 ) = 2.0824 mmol / L, and its COD Cr value is 500 mg / L.

[0095] Preparation of COD series standard working solutions: Put 50 mL of potassium hydrogen phthalate solution with a COD Cr value of 500 mg / L into a 250 - mL volumetric flask, make up the volume to the calibration line, dilute it 5 - fold to a COD Cr value of 100 mg / L, and then successively dilute it to COD Cr values of 0 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, 60 mg / L, and 80 mg / L to obtain COD series standard working solutions.

[0096] (3) Plotting the standard curve

[0097] Sequentially add 3 mL of COD series standard working solutions in the order from low concentration of 0 mg / L to high concentration of 80 mg / L into seven determination test tubes containing 6 mL of COD digestion solution respectively. Tighten the lids and shake well. Then place the determination test tubes into a digester preheated to 150 °C for heating digestion for 2 h. After digestion is completed, take out the determination test tubes from the digester and cool them at room temperature for 20 minutes. After cooling, add 1 mL of (1+9) sulfuric acid solution, and then place them into a UV-8000 spectrophotometer. Measure the absorbance with a colorimetric cuvette with a light path of 30 mm at a wavelength of 420 nm.

[0098] Use the absorbance as the abscissa and the COD Cr value of the COD series standard working solutions as the ordinate to make a standard curve.

[0099] As Figure 2 shown, the standard curve is as follows:

[0100] y = -565.4x + 107.07, R 2 = 0.9996

[0101] where y is the absorbance, x is the COD Cr value, the intercept of the standard curve is 107.07, and R 2 is the correlation coefficient of the standard curve.

[0102] (4) Pretreatment of glass fiber filter membrane

[0103] Select a glass fiber filter membrane with a filter membrane pore size of 5 μm and a filter membrane diameter of 47 mm. Conduct pretreatment on the filter membrane: ① Clean the filter membrane: Gently rinse the surface of the filter membrane with deionized water or distilled water to remove impurities such as dust and oil stains on the surface; ② Immersion treatment: Immerse the filter membrane in (1+9) sulfuric acid solution for 24 hours; ③ Natural drying: Place the immersed filter membrane in a dry and well-ventilated environment to dry naturally.

[0104] (5) Sampling

[0105] In summer, the temperature is relatively high, and cyanobacteria blooms occur in a certain lake. Take cyanobacteria bloom water bodies at 10 different points in the lake to obtain 10 water samples.

[0106] (6) Filtration of water samples

[0107] After retrieving the water samples, filter the water samples. Install a glass fiber filter membrane (with a diameter of 47 mm and a pore size of 5 μm) on the vacuum filtration device. Measure 50 mL of the mixed water sample with a measuring cylinder and filter the 10 water samples in sequence. Control the negative pressure at 0.2 MPa during filtration, and immediately replace the filter membrane after each water sample is filtered. End the suction filtration when the water sample just completely passes through the filter membrane, and take out the filter membrane with forceps. Pour the filtered water sample into a polyethylene bottle for storage and standby.

[0108] (7) Addition and digestion of water samples

[0109] Add 3 mL of the filtered water sample to each of the test tubes for determination containing 6 mL of COD digestion solution, tighten the caps, and shake well. Then, place them successively into the DRB 200 Hach digestion instrument preheated to 150 °C and heat and digest for 2 h. After digestion is completed, take out the test tubes for determination from the Hach digestion instrument and cool them at room temperature for 20 minutes.

[0110] (8) Acidification of water samples

[0111] Add 1 mL of (1+9) sulfuric acid solution successively to the digested water samples to acidify the water samples.

[0112] (9) Measurement of water samples and calculation of concentration

[0113] After acidification, place the water samples successively into the UV-8000 spectrophotometer, use a colorimetric cell with a 30 mm optical path length to measure the absorbance successively at a wavelength of 420 nm to obtain the absorbance. Then, substitute the absorbance into the above standard curve to calculate the COD of the water sample Cr value.

[0114] The calculated concentrations of the water samples are shown in Table 1 below.

[0115] Table 1 COD Concentrations at Different Points in a Certain Lake

[0116] Water sample Added amount of water sample (mL) Dilution factor Absorbance at WL420 Concentration (mg / L) Sample 1 3 1 0.093 54.262 Sample 2 3 1 0.102 49.343 Sample 3 3 1 0.097 52.283 Sample 4 3 1 0.106 47.194 Sample 5 3 1 0.101 50.247 Sample 6 3 1 0.119 39.787 Sample 7 3 1 0.091 55.392 Sample 8 3 1 0.100 50.417 Sample 9 3 1 0.111 44.141 Sample 10 3 1 0.098 51.887

[0117] The above are only specific implementation manners of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will conform to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for rapidly determining the COD concentration of cyanobacteria bloom water, characterized in that: It includes: The cyanobacteria bloom water body is subjected to filtering treatment, digestion treatment and acidification treatment in sequence to obtain a treated liquid; measuring the absorbance of the treatment solution; Based on the absorbance of the treated solution and the mapping relationship between the COD concentration of the COD series standard working solution and the absorbance of the solution after digestion and acidification, the COD concentration of the cyanobacteria bloom water body is obtained.

2. The method for rapidly determining the COD concentration of cyanobacteria bloom water body according to claim 1, characterized in that: Use glass fiber filter membrane to filter the blue algae bloom water body; Wherein, the pore size of the glass fiber filter membrane is 4.5-7 μm.

3. The method for rapidly determining the COD concentration of cyanobacteria bloom water body according to claim 2, characterized in that: Before using the glass fiber filter membrane to filter the blue algae bloom water body, the method further includes: pre-treating the glass fiber filter membrane; The glass fiber filter membrane is pretreated, specifically comprising: Using deionized water or distilled water to clean the surface of the glass fiber filter membrane to remove impurities on the surface; The glass fiber filter membrane is immersed in a (1+9) sulfuric acid solution for 20 to 30 hours; The soaked glass fiber filter membrane is placed in a dry and ventilated environment to dry naturally.

4. The method for rapidly determining the COD concentration of cyanobacteria bloom water body according to claim 1, characterized in that: The conditions of the filtration treatment include: negative pressure is controlled at 0.1-0.3 MPa, and flow rate is controlled at 1-5 m / s.

5. The method for rapidly determining the COD concentration of cyanobacteria bloom water body according to claim 1, characterized in that: The digestion process comprises: Add the blue algae bloom water to the test tube containing COD digestion solution, tighten the lid, and shake well; The test tube was placed in a digestion apparatus preheated to 150° C. for 2 h and then cooled.

6. The method for rapidly determining the COD concentration of cyanobacteria bloom water body according to claim 1, characterized in that: The acidification treatment comprises: A (1+9) sulfuric acid solution is added to the digested cyanobacteria bloom water body for acidification, so that the cyanobacteria bloom water body is acidified to a pH value of 1.8 to 2.

2.

7. The method for rapidly determining the COD concentration of cyanobacteria bloom water body according to claim 1, characterized in that: The method further includes: obtaining a mapping relationship between the COD concentration of the COD series standard use solution and the absorbance of the solution after digestion and acidification; The mapping relationship between the COD concentration of the COD series standard solution and the absorbance of the solution after digestion and acidification is obtained, specifically including: Digest and acidify the COD series standard working solution to obtain a digested and acidified solution of the COD series standard working solution; The absorbance of each digested and acidified solution was measured, and a standard curve was prepared with the absorbance as the horizontal axis and the COD concentration of the COD series standard working solution as the vertical axis to obtain a mapping relationship between the COD concentration of the COD series standard working solution and the absorbance of the digested and acidified solution.

8. The method for rapidly determining the COD concentration of cyanobacteria bloom water body according to claim 7, characterized in that: Prepare (1+9) sulfuric acid solution: Mix concentrated sulfuric acid with a concentration of 18.4 mol / L and water in a volume ratio of 1:9, stir and shake well to obtain a (1+9) sulfuric acid solution; Prepare mercuric sulfate solution: dissolve mercuric sulfate in (1+9) sulfuric acid solution, mix well, and obtain a mercuric sulfate solution with a concentration of 100 g / L; Prepare sulfuric acid-silver sulfate solution: add silver sulfate to sulfuric acid with a concentration of 18.4 mol / L, leave it for 1 to 2 days to dissolve, and mix well to obtain a sulfuric acid-silver sulfate solution with a silver sulfate concentration of 10 g / L; Prepare potassium dichromate solution: weigh 12.258 g of potassium dichromate dried to constant weight at 105±2°C and dissolve it in 800 mL of distilled water. After dissolution, make up to 1000 mL and dilute 10 times to obtain a potassium dichromate solution with a concentration of 0.0250 mol / L. Preparation of potassium hydrogen phthalate solution: Weigh 0.4251 g of potassium hydrogen phthalate dried at 105°C for 2 hours, dissolve in distilled water, dilute to 1000 mL, and mix well to obtain a potassium hydrogen phthalate solution with a concentration of 2.0824 mmol / L. Its COD Cr The value is 500mg / L; Prepare COD digestion solution: add 0.5 mL of 100 g / L mercuric sulfate solution, 1.5 mL of 0.0250 mol / L potassium dichromate solution and 4 mL of 10 g / L sulfuric acid-silver sulfate solution into a test tube, mix and prepare 6 mL of COD digestion solution; Prepare COD series standard solution: Cr Dilute the potassium hydrogen phthalate solution with a value of 500 mg / L 5 times to COD Cr The value is 100mg / L, and then diluted step by step to COD Cr The values ​​are 0mg / L, 5mg / L, 10mg / L, 20mg / L, 40mg / L, 60mg / L and 80mg / L, and the COD series standard working solutions are obtained; 3 ml of COD series standard solution was added into seven test tubes containing 6 ml of COD digestion solution in the order from low concentration 0 mg / L to high concentration 80 mg / L, the lids were tightened, shaken well, and then the test tubes were placed in a digestion instrument preheated to 150°C for 2 h. After cooling, 1 ml of (1+9) sulfuric acid solution was added and the absorbance was measured. With absorbance as the horizontal axis, COD of COD series standard working solution Cr The standard curve is made with the value as the vertical axis to obtain the mapping relationship between the COD concentration of the COD series standard solution and the absorbance of the solution after digestion and acidification.

9. The method for rapidly determining the COD concentration of cyanobacteria bloom water body according to claim 8, characterized in that: The standard curve is as follows: y=-565.4x+107.07,R 2 =0.9996 Among them, y is absorbance and x is COD Cr Value, R 2 is the correlation coefficient of the standard curve.

10. The method for rapidly determining the COD concentration of cyanobacteria bloom water body according to claim 8, characterized in that: The amount of water used for cyanobacteria bloom is 3mL, the amount of COD digestion solution used during digestion treatment is 6mL, and the amount of (1+9) sulfuric acid solution used during acidification treatment is 1mL.

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