Particle size division monitoring method for suspended sand particle phosphorus in rivers, lakes and reservoirs

Abstract

The invention discloses a particle size monitoring method for suspended sand particle phosphorus in rivers, lakes and reservoirs, and relates to the technical field of environmental monitoring analysis, and the method comprises the following steps: 1, carrying out suspended sand sampling in rivers, lakes and reservoirs; 2, screening and sampling the suspended sand sample; step 3, carrying out particle size meter grading analysis on the screened suspended sand sample; step 4, performing suction tube method grading analysis on the sample subjected to grading analysis by the particle size meter; and step 5, carrying out phosphorus measurement analysis on the sample after the suction tube grading analysis. The suspended sand is subjected to particle size grading and then phosphorus measurement, the mass of phosphorus in suspended sand particles with different particle sizes can be directly obtained, the method is more accurate, the relation between the particle size of the suspended sand and the phosphorus content is reflected, and compared with an existing monitoring method, the method has higher practical application value.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental monitoring and analysis, and particularly relates to a method for monitoring phosphorus in suspended sediment particles of rivers, lakes and reservoirs by particle size. Background Art

[0002] Phosphorus is both a biogenic element in rivers, lakes and reservoirs and the main element causing water eutrophication. Its forms in water are mainly divided into dissolved state and particulate state. Among them, the phosphorus adsorbed on suspended sediment particles is particulate phosphorus (PP). Due to the "particle adsorption property", particulate phosphorus accounts for more than 90% of the total phosphorus in natural water bodies. In particular, the phosphorus adsorbed on suspended sediment can migrate with the movement of suspended sediment, which is also called suspended sediment particulate phosphorus. When the phosphorus content in the aqueous phase decreases, part of the particulate phosphorus can be converted into dissolved reactive phosphorus and utilized by organisms. Therefore, particulate phosphorus is also an important reservoir of bioavailable phosphorus and is of great significance for water ecological safety. At present, dams are important factors affecting the transport of phosphorus in rivers. While intercepting suspended sediment, they also intercept particulate phosphorus and reduce the biogenic elements transported to the downstream, affecting the ratio of various nutrient elements in the downstream water body. However, the interception effect of dams on suspended sediment mainly depends on the particle size of suspended sediment. Particle size is not only the basic physical property of suspended sediment but also the key factor determining the phosphorus adsorption capacity of suspended sediment and the characteristics of phosphorus migration and transformation. Therefore, analyzing the particle size of particulate phosphorus is conducive to predicting the movement law of particulate phosphorus in water bodies and accurately calculating the interception effect of dams on particulate phosphorus of different particle sizes.

[0003] At present, traditional particulate phosphorus monitoring is calculated by the "subtraction method", that is, the monitoring value is based on the difference between the total phosphorus TP (total phosphorus, TP) and dissolved total phosphorus (dissolved phosphorus, DP) in the water sample (turbid sample) (CPP = CTP - CDP), which belongs to indirect determination and does not contain suspended sediment particle size information. In addition, although in some reports, filtration with filter paper or screening with a sieve is used before determination, which contains some sediment particle size information, the particle size values are quite different from the standards in the "Regulations for Analysis of River Sediment Particles" (SL42 - 2010), so the practicability is not strong.

[0004] Therefore, the technical personnel in this field are committed to developing a method for monitoring phosphorus in suspended sediment particles of rivers, lakes and reservoirs by particle size. First, the suspended sediment is classified by particle size and then phosphorus is measured, which can directly obtain the mass of phosphorus in suspended sediment particles of different particle sizes, is more accurate, and also reflects the relationship between suspended sediment particle size and phosphorus content. Summary of the Invention

[0005] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is how to monitor the phosphorus content in suspended sediment particles of different particle sizes in rivers, lakes and reservoirs.

[0006] To achieve the above object, the present invention provides a method for monitoring phosphorus in suspended sediment particles of rivers, lakes and reservoirs by particle size, characterized in that the method comprises the following steps:

[0007] Step 1. Conduct suspended sediment sampling in rivers, lakes and reservoirs;

[0008] Step 2. Conduct screening sampling on the suspended sediment sample;

[0009] Step 3. Conduct particle size grading analysis on the screened suspended sediment sample;

[0010] Step 4. Conduct pipette method grading analysis on the sample after particle size grading analysis;

[0011] Step 5. Conduct phosphorus measurement analysis on the sample after pipette method grading analysis.

[0012] Further, Step 1 further includes:

[0013] Step 1.1. Let the suspended sediment stand for 7 days after collection.

[0014] Further, in Step 2, a 1 mm sieve and a 0.062 mm sieve are used to screen the suspended sediment sample, and the particle size of the screened suspended sediment sample is between 0.062 mm and 1 mm.

[0015] Further, Step 3 further includes:

[0016] Step 3.1. Before conducting grading analysis, fill a particle size meter with pure water as a temperature reference.

[0017] Further, in Step 3, the particle size grading analysis of the particle size meter includes the following steps:

[0018] Step 3.2. Put a nipple without eyes soaked in water on the sand receiving hole at the bottom of the particle size meter, and add pure water to the particle size meter to the scale line;

[0019] Step 3.3. Insert the sand injector into the top of the particle size meter. When the iron sheet below the sand injector touches the water surface, the sand sample starts to fall and be classified, and time is measured with a stopwatch;

[0020] Step 3.4. Collect sand samples of corresponding particle sizes at corresponding time periods according to the particle size meter analysis operation schedule;

[0021] Step 3.5. Transfer the water-sand mixture in each particle size meter to different beakers and let it stand for precipitation.

[0022] Further, Step 3.4 further includes: After collecting each sand sample, put on the nipple without eyes.

[0023] Further, in Step 4, the pipette method grading analysis includes the following steps:

[0024] Step 4.1: After removing the upper-layer water from the water-sand mixture sample analyzed by particle size grading, transfer it to a graduated cylinder, make up the volume to 600 ml, and let it stand for 5 minutes.

[0025] Step 4.2: Add a retarder, use a perforated sand ramming tool to ram the sand for 5 minutes, and then let it stand for 1.5 hours.

[0026] Step 4.3: Ram the sand sample after standing for 2 minutes. Measure the temperature of the water-sand mixture in the graduated cylinder with a thermometer, then ram the sand sample in the graduated cylinder again. Refer to the operation schedule of the pipette method analysis and extract the corresponding sediment suspension with a large-bellied pipette within 12 s - 15 s, and put it into a sediment suspension beaker.

[0027] Step 4.4: After each extraction of the sediment suspension, wash the large-bellied pipette once, and transfer the washing liquid to the sediment suspension beaker.

[0028] Step 4.5: Dry and weigh the sand sample after the pipette method grading analysis.

[0029] Further, in the said Step 5, the phosphorus measurement analysis includes the following steps:

[0030] Step 5.1: Weigh 0.25 g of the sand sample after the pipette method grading analysis at the bottom of a crucible. Moisten the sand sample with absolute ethanol, then add sodium hydroxide and spread it evenly on the surface of the sand sample, and cover the crucible lid.

[0031] Step 5.2: Put the crucible into a muffle furnace, raise the temperature to 400 °C, keep it for 15 min, then continue to raise the temperature to 640 °C, keep it for 15 min, and take it out to cool.

[0032] Step 5.3: Add 10 mL of water to the crucible and heat it to 80 °C. After the sand sample dissolves, transfer all the solution in the crucible to a centrifuge cup, centrifuge for 10 min, and after standing, transfer all the supernatant to a volumetric flask. Measure 10 mL of the supernatant and put it into a 50 mL colorimetric tube, and add water to the scale.

[0033] Step 5.4: Add 2,4-dinitrophenol to the colorimetric tube, then adjust the pH value to 4.4 with sulfuric acid solution and sodium hydroxide solution. Then add 1.0 mL of ascorbic acid solution and mix well. After 30 s, add 2 mL of molybdate solution and mix well, and let it stand at 20 - 30 °C for 15 min.

[0034] Step 5.5: Use a 30 mm cuvette, at a wavelength of 700 nm, with water as the reference, measure the absorbance of the sample obtained in Step 5.4.

[0035] Further, step 5.3 further includes: washing the crucible 3 times each with a sulfuric acid solution and water before centrifugal separation, and transferring the washing liquid into the centrifuge cup.

[0036] Further, in step 5, the content of total phosphorus is calculated by the following formula:

[0037]

[0038] In the formula, ω represents the content of total phosphorus in the suspended sediment, with the unit of mg / kg; A represents the absorbance value of the test sample; A0 represents the absorbance value of the blank test; a represents the intercept of the calibration curve; V1 represents the volume of sample constant volume, with the unit of mL; b represents the slope of the calibration curve; m represents the mass of the sample, with the unit of g; V2 represents the volume of the test sample, with the unit of mL; w dm represents the proportion of the dry matter content in the suspended sediment.

[0039] The beneficial technical effects of the present invention are as follows:

[0040] 1. The traditional method for monitoring particulate phosphorus is mainly the "subtraction method". The monitored value is based on the difference between the total phosphorus and dissolved total phosphorus in the water sample, which belongs to an indirect monitoring method. Compared with the traditional monitoring method, the present invention first classifies the suspended sediment by particle size and then measures phosphorus, directly measuring the phosphorus content in the suspended sediment, which is more accurate. It also reflects the relationship between the particle size and phosphorus content of the suspended sediment, is easy to operate, can directly obtain the mass of phosphorus in suspended sediment particles of different particle sizes, and can directly obtain the phosphorus content in the suspended sediment compared with the traditional monitoring method.

[0041] 2. The traditional monitoring method does not contain information on the particle size of the suspended sediment or the obtained particle size information is inconsistent with the current standard, and its practicability is not strong. The present invention conducts monitoring in accordance with the "Regulations for Analysis of River Sediment Particles" (SL 42 - 2010). The particle size range of the suspended sediment used during monitoring is consistent with the current standard, meeting the standards of the "Regulations for Analysis of River Sediment Particles" (SL 42 - 2010). It is the particle size range used by the hydrological departments in China for sediment particle analysis, fully meeting the requirements of particle size classification monitoring in the current standard, and has more practical application value compared with existing monitoring methods.

[0042] The following will further illustrate the concept, specific structure, and technical effects generated by the present invention with reference to the accompanying drawings to fully understand the purpose, features, and effects of the present invention. Description of the Drawings

[0043] Figure 1 is a flow schematic diagram of a method for monitoring particulate phosphorus in suspended sediment in rivers, lakes, and reservoirs according to a preferred embodiment of the present invention;

[0044] Figure 2This is the particle size analyzer analysis operation schedule and pipette method analysis operation schedule for the particle size monitoring method of suspended sediment phosphorus in rivers, lakes and reservoirs in a preferred embodiment of the present invention. Detailed implementation manners

[0045] The following introduces multiple preferred embodiments of the present invention with reference to the accompanying drawings of the specification to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0046] As Figure 1 shown, the present invention first collects suspended sediment in accordance with the "River Suspended Sediment Measurement Specification" (GB / T 50159-2015) during suspended sediment sampling. After the suspended sediment is collected, it is left to stand in place for 7 days and concentrated into 500 mL and then transported back to the laboratory for sediment grading analysis and phosphorus measurement. For the concentrated sand sample, visually observe whether the mass of the sand sample deposited at the bottom of the sand sample bottle is within the range of particle size analyzer grading analysis (1.5 - 2 g). If the mass exceeds the grading analysis range, use a splitter to divide the sand sample equally and take the sand sample within the particle size grading analysis range for grading analysis. Before grading, first fill one particle size analyzer with pure water as a reference for temperature. The water sample passes through 1 mm and 0.062 mm sieves, and the obtained sand sample (0.062 mm < D < 1 mm) is first subjected to particle size analyzer grading analysis and then pipette method grading analysis, and the suspended sediment of different particle sizes obtained by grading is used for phosphorus measurement.

[0047] Particle size analyzer grading analysis process: Put a blind nipple soaked in water on the sand receiving hole at the bottom of the particle size analyzer, add pure water to the particle size analyzer to the scale line, and add an appropriate amount of pure water to the ceramic bowl to receive the sand sample. Slowly insert the sand injector into the top of the particle size analyzer. When the iron sheet below the sand injector touches the water surface, the sand sample starts to fall and be graded, and at the same time start the stopwatch. Refer to the particle size analyzer operation schedule (as Figure 2 shown in a) to receive the sand sample of the corresponding particle size period. When receiving the sand sample, dip the ceramic bowl filled with pure water at the sand hole, and after each sand sample is received, put on the nipple in time. When all the sand samples in the particle size tubes are received, transfer the water-sand mixture in each particle size tube to a beaker, let it stand and precipitate, and then perform pipette method grading.

[0048] Pipette method grading analysis process: Remove the upper layer of water from the water-sand mixture after standing and precipitating, transfer the remaining water-sand mixture to a graduated cylinder, make up the volume to 600 mL, let it stand for 5 minutes, and determine the volume of the coagulant retarder (20 g / L NaOH) added by the observation method. Use a perforated sand rammer to ram the sand for 5 minutes, and then let it stand for 1.5 hours. First ram the sediment after standing for 2 minutes. At this time, measure the temperature of the water-sand mixture in the graduated cylinder with a thermometer, and then start timing. Perform fast ramming on the sand sample in the graduated cylinder for 1 minute and slow ramming for 1 minute (≥ 30 times). Refer to the pipette method operation schedule (asFigure 2 As shown in Fig. 1(b), use a large-bore pipette to extract the corresponding sediment suspension (20 mL) within 12 s to 15 s, place it in a pre-prepared beaker, and record the order. To make the separated particle size more accurate, the pipette should be washed once after each extraction of the suspension, and the washing solution should also be transferred to the beaker. Dry the graded sand samples and subtract the net weight to obtain the weight of the graded sand samples.

[0049] Phosphorus measurement process: Weigh 0.2500 g of the suspended sediment obtained from grading at the bottom of a nickel crucible. Moisten the sample with a few drops of anhydrous ethanol, then add 2 g of NaOH (superior grade pure) and spread it evenly on the surface of the sample to cover the sample, and cover the crucible lid; place the crucible in a muffle furnace and heat it up. When the temperature rises to about 400 °C, maintain it for 15 min; then continue to heat up to 640 °C, maintain it for 15 min, and take it out and cool. Then add 10 mL of water to the crucible and heat it to 80 °C. After the fused mass dissolves, transfer all the solution in the crucible to a 50 mL centrifuge cup. Then wash the crucible 3 times each with 10 mL of sulfuric acid solution (3 mol / L) and water, and transfer all the washing solutions to the centrifuge cup. Centrifuge at 2500 - 3500 r / min for 10 min. After standing, transfer all the supernatant to a 100 mL volumetric flask and make up the volume with water. Pipette 10.0 mL into a 50 mL stoppered colorimetric tube and add water to the mark. Then add 2 - 3 drops of 2,4-dinitrophenol to the colorimetric tube, and then adjust the pH value to about 4.4 with sulfuric acid solution (0.5 mol / L) and sodium hydroxide solution (2 mol / L) until the solution just turns slightly yellow. Then add 1.0 mL of ascorbic acid solution (0.1 g / mL) and mix well. After 30 s, add 2.0 mL of molybdate solution (0.13 g / mL), mix well thoroughly, and let it stand at 20 - 30 °C for 15 min. Use a 30 mm colorimetric cell, measure the absorbance at a wavelength of 700 nm with water as the reference.

[0050] The total phosphorus content can be calculated according to formula (1).

[0051]

[0052] In the formula:

[0053] ω —— The total phosphorus content in the suspended sediment, unit: mg / kg;

[0054] A —— The absorbance value of the test sample;

[0055] A0 —— The absorbance value of the blank test;

[0056] a —— The intercept of the calibration curve;

[0057] V1 —— The volume of the sample after volume fixation, unit: mL;

[0058] b —— The slope of the calibration curve.

[0059] m——the mass of the test sample, unit: g;

[0060] V2——the volume of the test sample, unit: mL;

[0061] w dm ——the dry matter content (mass fraction) of the suspended sediment, %.

[0062] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field according to the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall fall within the protection scope determined by the claims.

Claims

1. A method for monitoring the particle size of suspended sediment phosphorus in rivers, lakes and reservoirs, characterized in that: The method comprises the following steps: Step 1: Sampling suspended sediment in rivers, lakes and reservoirs; Step 2, sieving and sampling the suspended sediment sample; Step 3, performing particle size meter gradation analysis on the suspended sediment sample after screening; Step 4, performing a straw method gradation analysis on the sample after the particle size meter gradation analysis; Step 5: Conduct phosphorus analysis on the samples after the straw method grading analysis.

2. A method for monitoring the particle size of suspended sediment phosphorus in rivers, lakes and reservoirs as claimed in claim 1, characterized in that: The step 1 also includes: Step 1.1: Collect the suspended sand and let it stand for 7 days.

3. The method for monitoring the particle size of suspended sediment phosphorus in rivers, lakes and reservoirs according to claim 1, characterized in that: In the step 2, the suspended sand sample is sieved using a 1 mm sieve and a 0.062 mm sieve, and the particle size of the suspended sand sample after sieving is between 0.062 mm and 1 mm.

4. The method for monitoring the particle size of suspended sediment phosphorus in rivers, lakes and reservoirs according to claim 1, characterized in that: The step 3 also includes: Step 3.1: Before conducting grading analysis, fill a particle size meter with pure water as a temperature reference.

5. The method for monitoring the particle size of suspended sediment phosphorus in rivers, lakes and reservoirs according to claim 1, characterized in that: In step 3, the particle size meter gradation analysis includes the following steps: Step 3.2, put the eyeless nipple soaked in water on the sand receiving hole at the bottom of the particle size meter, and add pure water to the particle size meter to the scale line; Step 3.3, embed the sand injector into the top of the particle size meter, and when the iron sheet below the sand injector touches the water surface, the sand sample starts to fall and be classified, and the time is measured with a stopwatch; Step 3.4, collect sand samples of corresponding particle sizes in the time period according to the particle size analyzer operation schedule; Step 3.5: Transfer the water-sand mixture in each particle size meter into different beakers and let it settle.

6. A method for monitoring the particle size of suspended sediment phosphorus in rivers, lakes and reservoirs as claimed in claim 5, characterized in that: The step 3.4 also includes: after each sand sample is taken, the eyeless nipple is put on.

7. A method for monitoring the particle size of suspended sediment phosphorus in rivers, lakes and reservoirs as claimed in claim 1, characterized in that: In step 4, the straw method gradation analysis includes the following steps: Step 4.1, remove the upper layer of water from the water-sand mixed sample after the particle size meter grading analysis, transfer it to a measuring cylinder, make up to 600 ml, and let it stand for 5 minutes; Step 4.2, add retarder, use a perforated sand tamping machine to tamp the sand for 5 minutes and then let it stand for 1.5 hours; Step 4.3, pound the sand sample after standing for 2 minutes, measure the temperature of the water-sand mixture in the measuring cylinder with a thermometer, and then pound the sand sample in the measuring cylinder, and extract the corresponding sediment suspension with a large-bellied straw within 12s to 15s according to the straw method analysis operation schedule, and put it into the sediment suspension beaker; Step 4.4, after each extraction of the sediment suspension, the big-bellied straw should be cleaned once, and the washing liquid is transferred to the sediment suspension beaker; Step 4.5: Dry and weigh the sand sample after the straw method grading analysis.

8. A method for monitoring the particle size of suspended sediment phosphorus in rivers, lakes and reservoirs as claimed in claim 1, characterized in that: In step 5, the phosphorus analysis comprises the following steps: Step 5.1, weigh 0.25 g of the sand sample after the pipette method gradation analysis and place it at the bottom of the crucible, wet the sand sample with anhydrous ethanol, add sodium hydroxide and spread it on the surface of the sand sample, and cover the crucible with a lid; Step 5.2, placing the crucible in a muffle furnace, raising the temperature to 400°C, maintaining for 15 minutes, then continuing to raise the temperature to 640°C, maintaining for 15 minutes, and taking out to cool; Step 5.3, add 10 mL of water to the crucible and heat it to 80°C. After the sand sample is dissolved, transfer all the solution in the crucible into a centrifuge cup, centrifuge for 10 minutes, let it stand, transfer all the supernatant into a volumetric flask, measure 10 mL of the supernatant into a 50 mL colorimetric tube, and add water to the scale; Step 5.4, add 2,4-dinitrophenol to the colorimetric tube, adjust the pH value to 4.4 with sulfuric acid solution and sodium hydroxide solution, add 1.0 mL of ascorbic acid solution and mix well, add 2 mL of molybdate solution after 30 seconds and mix well, and place at 20-30°C for 15 minutes; Step 5.5: Use a 30 mm cuvette to measure the absorbance of the sample obtained in step 5.4 at a wavelength of 700 nm with water as a reference.

9. A method for monitoring the particle size of suspended sediment phosphorus in rivers, lakes and reservoirs as claimed in claim 8, characterized in that: The step 5.3 further comprises: washing the crucible with sulfuric acid solution and water three times each before centrifugation, and transferring the washing solution into the centrifuge cup.

10. A method for monitoring the particle size of suspended sediment phosphorus in rivers, lakes and reservoirs as claimed in claim 1, characterized in that: In step 5, the total phosphorus content is calculated by the following formula: In the formula, ω represents the total phosphorus content in suspended sediment, in mg / kg; A represents the absorbance value of the sample; A0 represents the absorbance value of the blank test; a represents the intercept of the calibration curve; V1 represents the fixed volume of the sample, in mL; b represents the slope of the calibration curve; m represents the sample mass, in g; V2 represents the sample volume, in mL; w dm Represents the percentage of dry matter in suspended sediment.

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