Method for controlling release of phosphorus in bottom mud of water body

Abstract

The invention discloses a method for controlling the release of phosphorus in water body bottom mud, which comprises the following steps: determining the occurrence form of phosphorus in the water body bottom mud, calculating to obtain the content of potential removable dynamic phosphorus in the bottom mud per unit mass, and determining the total amount of potential removable dynamic phosphorus in the bottom mud of the water body to be repaired by combining the total dry bottom mud mass of the water body to be repaired; according to the unit saturation adsorption capacity of the covering material on phosphorus in water and the total amount of potential movable dynamic phosphorus, the total adding amount of the covering material needing to be added is determined, and then the covering material is equally divided into a plurality of parts; the method comprises the following steps: adding a covering material into a water body needing to be restored for multiple times, checking the formation condition of a phosphorus static layer in bottom mud of the water body by adopting an in-situ passive sampling technology, and judging whether the adding of the covering material is stopped or not; the total amount of the covering material added before the forming moment of the phosphorus static layer is calculated as the conventional adding amount, and the covering material is added according to the conventional adding amount at equal time intervals; or regularly analyzing the phosphorus concentration in the bottom mud of the water body so as to determine whether to continuously add according to the conventional adding amount.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental pollution control, and in particular relates to a method for controlling phosphorus release in water body sediment. Background Art

[0002] Eutrophication of water bodies is one of the serious water environment problems, and phosphorus is the key nutrient element that causes eutrophication of water bodies. The sources of phosphorus in surface water bodies such as lakes, rivers, reservoirs, and ponds are divided into exogenous and endogenous sources. When the input of exogenous phosphorus is effectively controlled, controlling the release of endogenous phosphorus in the sediment becomes an important measure for the treatment of eutrophication of water bodies.

[0003] Active covering is currently an important method for controlling the release of endogenous phosphorus in water bodies. Its working principle is: adding active covering materials above the sediment-water interface, and utilizing the active covering material's ability to adsorb phosphorus in water to achieve the purpose of controlling the release of sediment phosphorus. In addition, the covering material can also isolate the contaminated sediment, thereby achieving the purpose of controlling the release of sediment phosphorus. Therefore, screening sediment covering materials and determining the application method are the key to using active covering technology to control the release of sediment phosphorus.

[0004] At present, the methods for determining the amount of covering material added at home and abroad are mostly based on the total content of phosphorus in the sediment, which ignores the fact that the release potential of different forms of phosphorus in the sediment is different, resulting in an unreasonable amount of covering material added. In addition, the current application method of covering materials mostly adopts one-time addition, but the covering materials added to the water body at one time are prone to aging, resulting in a decrease in the ability of the covering materials to adsorb phosphorus in the water, thereby reducing the effect of the covering materials on controlling the release of phosphorus from the sediment. In addition, metal-based materials are the most common covering materials used to control the release of phosphorus from the sediment, and the impregnation method is a common method for preparing metal-based covering materials. However, the existing methods for preparing metal-based covering materials are prone to secondary pollution problems. Therefore, a method for controlling the release of endogenous phosphorus in the sediment of water bodies proposed to address the above-mentioned shortcomings is urgently needed. Summary of the invention

[0005] The invention provides a method for controlling phosphorus release in bottom mud of a water body, which solves the technical problems that the existing active covering methods mostly adopt one-time addition, resulting in a decrease in the ability of the covering material to adsorb phosphorus in water and unreasonable determination of the covering material addition amount.

[0006] The present invention can be achieved through the following technical solutions:

[0007] A method for controlling phosphorus release in water sediment comprises the following steps:

[0008] Step 1: Determine the occurrence form of phosphorus in the sediment of the water body, calculate the potential mobile phosphorus content per unit mass in the sediment, and then determine the total amount of potential mobile phosphorus in the sediment of the water body that needs to be repaired based on the total dry sediment mass of the water body that needs to be repaired;

[0009] Step 2: Determine the total amount of covering material to be added according to the unit saturated adsorption amount of phosphorus in water and the total amount of potential mobile phosphorus of the covering material, and then divide the total amount of covering material into several equal parts;

[0010] Step 3: Add an equal amount of covering material to the water body that needs to be repaired, and use the in-situ passive sampling technology to check the formation of the "phosphorus static layer" in the bottom mud of the water body. If it is formed, stop adding covering materials; if it is not formed, continue to add an equal amount of covering material, and use the in-situ passive sampling technology to check the formation of the "phosphorus static layer" in the bottom mud, and so on, until the "phosphorus static layer" is formed, and then calculate the total amount of covering material added before the formation of the "phosphorus static layer" as the conventional dosage;

[0011] Step 4: Add covering material at regular dosage and time intervals;

[0012] Alternatively, the phosphorus concentration in the bottom sediment of the water body can be analyzed regularly using in-situ passive sampling technology. Once the phosphorus concentration is found to exceed the preset value, the covering material should continue to be added according to the normal dosage.

[0013] Further, in the step 2, the total amount of potential mobile phosphorus M in the bottom mud of the water body is calculated and determined according to the following formula;

[0014] M=m×q

[0015]

[0016] Where m is the total dry sediment mass in the water body kg; q is the potential mobile phosphorus content per unit mass of dry sediment mg / kg; A is the area of ​​the sediment-water interface m 2 , h is the thickness of the water body sediment m, ρ is the density of the water body sediment kg / m 3 , W is the moisture content of the bottom mud in the water body.

[0017] Further, the total amount of covering material required to be added, Q, is determined using the following formula:

[0018]

[0019] Where, M is the total mass of potentially mobile phosphorus in the water sediment, mg; Q m It is the unit saturated adsorption capacity of phosphate in water by the covering material, mg / kg.

[0020] Further, the total amount of covering material added is divided into 20-200 equal portions;

[0021] Or use the following formula to calculate the number of equal parts n;

[0022]

[0023] Where F is the phosphorus release flux of sediment mg / (m 2 ·d), t is the duration d that the covering material controls the release of phosphorus from the sediment, which needs to be determined based on actual conditions.

[0024] Furthermore, the calculation method of the sediment phosphorus release flux is set to be a sediment core culture method or a sediment available phosphorus and pore water dissolved concentration profile estimation method.

[0025] Furthermore, the method for determining the unit saturated adsorption amount of phosphorus in water by the covering material comprises the following steps:

[0026] Step I, preparing phosphorus solutions with different initial concentrations, and adjusting the pH value of the phosphorus solutions to a certain pH value, which is determined according to the pH value of the actual water body;

[0027] Step II, adding the covering material and phosphorus solutions of different concentrations to conduct an oscillating reaction, and after the reaction is completed, measuring the phosphorus concentration in the solution;

[0028] Step III: Use the following formula to calculate and determine the unit adsorption amount Q of phosphorus in water by the covering material: e ;

[0029]

[0030] Wherein, V represents the volume of phosphorus solution L; a represents the amount of covering material added in step II g; c0 and c e represent the phosphorus concentration in the phosphorus solution before the adsorption reaction and at the reaction equilibrium moment, respectively;

[0031] Unit saturated adsorption capacity of phosphorus in water by covering material Q m The unit adsorption amount Q corresponding to different concentrations of phosphorus solution e The maximum value of , or determined by fitting the experimental data through the following isothermal adsorption model;

[0032]

[0033] In the formula, c e Indicates the equilibrium concentration of phosphorus in the solution in mg / L; K L is the isothermal adsorption model constant L / mg; Q m Indicates the unit saturated adsorption of phosphorus in water by the covering material, mg / g; Q e It indicates the unit adsorption amount of phosphorus in water by the covering material at the equilibrium moment, mg / g.

[0034] Furthermore, the covering material is configured to be a metal-based covering material prepared by a multi-stage impregnation method.

[0035] Furthermore, the graded continuous chemical extraction method was used to determine the occurrence forms of phosphorus in the sediment of the water body, and the easily desorbed phosphorus and redox-sensitive phosphorus in the sediment were set as potentially mobile phosphorus.

[0036] The beneficial technical effects of the present invention are:

[0037] (1) By adopting a multi-stage impregnation method to prepare metal-based covering materials, all metal ions in the liquid phase can be loaded onto the surface of low-cost natural mineral materials, which not only can obtain efficient and economical bottom sediment active covering materials, but also will not cause waste of metal salts, save resources, and be safe and environmentally friendly.

[0038] (2) Through the total dosage and single dosage calculation method of the active covering material for sediment proposed in the present invention, the dosage of active covering material required to control the release of phosphorus from sediment can be accurately determined, and then the covering material can be accurately added to the bottom of the sediment-water interface to form a covering layer. Compared with the traditional method, the sediment phosphorus release control method of the present invention can not only more effectively control the release of phosphorus from sediment, but also save the dosage of active covering material for sediment, thereby reducing the cost of sediment remediation. Therefore, this method has great application and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the overall process of the present invention;

[0040] Figure 2 The figures are actual pictures of the covering materials of the present invention, wherein (a) represents iron-modified dolomite; (b) represents iron-modified bentonite;

[0041] Figure 3 is an X-ray diffraction pattern of the iron-modified dolomite covering material of the present invention;

[0042] Figure 4 Schematic diagram of the chemical composition of the original dolomite and iron-modified dolomite of the covering material of the present invention;

[0043] Figure 5 The adsorption kinetic curve of phosphate in water by the iron-modified dolomite covering material of the present invention is shown;

[0044] Figure 6 It is a schematic diagram showing the effect of the initial phosphorus concentration on the adsorption of phosphate in water by the iron-modified dolomite covering material of the present invention;

[0045] Figure 7 It is a schematic diagram of the removal effect of the iron-modified dolomite covering material of the present invention on the DGT effective phosphorus on the vertical section of the overlying water-sediment. The zero scale of the vertical coordinate represents the sediment-overlying water interface, the overlying water is above the interface, and the sediment is below the interface. The higher the DGT effective phosphorus concentration is, the heavier the phosphorus pollution is.

[0046] Among them, (a) represents the change curve of DGT effective phosphorus concentration in different states, and (b) represents the change of DGT effective phosphorus removal rate of covering materials using the existing one-time covering method and the multiple covering method of the present invention. DETAILED DESCRIPTION

[0047] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings and preferred embodiments.

[0048] There are defects in the existing methods for controlling phosphorus release in water sediments, such as Figure 1 As shown, the present invention proposes a method for controlling phosphorus release in water sediments. Specifically, first, a sediment active covering material that can reduce secondary pollution, is simple to prepare, and has good phosphate adsorption performance in water is developed. Then, the total amount of active covering material to be used is determined according to the potential mobile phosphorus content in the sediment and the specific conditions of the water body, and then the amount of active covering material added in a single addition is determined. Finally, a method for gradually adding the covering material to the water body is provided. Compared with the existing sediment phosphorus release control method, the sediment covering layer formed by gradual addition can effectively control the release of phosphorus in the water sediment. The method proposed by the present invention is more environmentally friendly, has a better effect on controlling the release of sediment phosphorus, and can more accurately determine the amount of active covering material added, thereby reducing the cost of controlling the release of sediment phosphorus in the water body and environmental remediation.

[0049] The details are as follows:

[0050] Step 1: Prepare covering material

[0051] The metal-based covering material is prepared by a multi-stage impregnation method, and the preparation steps are as follows:

[0052] 1) Mixing a metal salt solution with a mass ratio of metal salt to natural mineral material of 0.5:1 or above with a natural mineral material, collecting the solid material after reacting for a period of time such as 30 to 1440 minutes, and obtaining the first metal-based covering material after washing; wherein the natural mineral material may refer to bentonite, montmorillonite, attapulgite, illite, kaolinite, rectorite, calcite, dolomite, etc.; the metal salt may refer to ferric chloride, ferric sulfate, ferric nitrate, polyferric sulfate, aluminum chloride, aluminum sulfate, polyaluminum chloride, lanthanum chloride, lanthanum nitrate, zirconium oxychloride octahydrate, etc.

[0053] The ratio of the mass of the natural mineral material to the volume of water is 1 g: (5-100) mL, that is, 1 g of the natural mineral material is mixed with 5-100 mL of water.

[0054] 2) mixing the reacted solution with the natural mineral material, and obtaining a second metal-based covering material according to the same step 1);

[0055] 3) Repeat step 2) until all the metal ions in the solution are loaded by the natural mineral material.

[0056] Step 2: Determine the occurrence form of phosphorus in the sediment of the water body, calculate the potential mobile phosphorus content per unit mass in the sediment, and then determine the total amount of potential mobile phosphorus in the sediment of the water body that needs to be repaired based on the total dry sediment mass of the water body that needs to be repaired.

[0057] S2.1. Analyzing the Phosphorus Forms in Sediment Using the Graded Continuous Chemical Extraction Method

[0058] This method divides the phosphorus in the sediment into five forms, namely, easily desorbed phosphorus, redox sensitive phosphorus, metal bound phosphorus, calcium bound phosphorus and residual phosphorus. These five forms of phosphorus are respectively measured using 1 mol / L ammonium chloride solution, a mixed solution of 0.11 mol / L sodium bicarbonate and 0.11 mol / L sodium dithionite, 1 mol / L sodium hydroxide solution (room temperature), 1 mol / L hydrochloric acid solution and 1 mol / L sodium hydroxide solution (85 degrees Celsius).

[0059] Among them, easily desorbed phosphorus and redox-sensitive phosphorus are potentially mobile phosphorus in the sediment. The content of this potentially mobile phosphorus is the sum of the contents of easily desorbed phosphorus and redox-sensitive phosphorus in the sediment.

[0060] S2.2. Determine the sediment-overlying water interface area and sediment thickness of the surface water bodies such as lakes, reservoirs, ponds, etc. that need to be repaired, and calculate the total dry sediment mass m according to the following formula;

[0061]

[0062] Where A is the area of ​​the sediment-water interface m 2 , h is the thickness of the water body sediment m, ρ is the density of the water body sediment kg / m 3 , W is the moisture content of the bottom mud in the water body.

[0063] S2.3. Determine the total amount of potentially mobile phosphorus M in the sediment of the water body that needs to be repaired according to the following formula:

[0064] M=m×q

[0065] Where q is the potential mobile phosphorus content per unit mass of dry sediment, mg / kg, which is equal to the sum of the easily desorbed phosphorus and redox-sensitive phosphorus contents in the sediment, and can be obtained by direct measurement.

[0066] Step 3: Determine the total amount of covering material to be added based on the unit saturated adsorption capacity of phosphorus in water by the covering material and the total amount of potential mobile phosphorus M, and then divide the total amount of covering material into several equal parts.

[0067] S3.1. Calculate the unit saturated adsorption capacity of phosphorus in water by the covering material, specifically including the following steps:

[0068] Step I, preparing phosphorus solutions of different initial concentrations, and adjusting the pH values ​​of these phosphorus solutions to a certain pH value, which is determined according to the pH value of the actual water body;

[0069] Step II, subjecting the covering material to an oscillating reaction with phosphorus solutions of different phosphorus concentrations, and measuring the phosphorus concentration in the solution after the reaction is completed;

[0070] Step III: Use the following formula to calculate and determine the unit adsorption amount Q of phosphorus in water by the covering material: e ;

[0071]

[0072] Wherein, V represents the volume of phosphorus solution L; a represents the amount of covering material added in step II g; c0 and c e represent the phosphorus concentration in the phosphorus solution before the adsorption reaction and at the reaction equilibrium moment, respectively;

[0073] Unit saturated adsorption capacity Q of the covering material for phosphorus in water m The unit adsorption amount Q in the adsorption equilibrium data can be obtained through the above steps. e It can be determined by fitting the experimental data with the following isothermal adsorption model;

[0074]

[0075] In the formula, c e Indicates the equilibrium concentration of phosphorus in the solution (mg / L); K L is the isothermal adsorption model constant (L / mg); Q m It indicates the unit saturated adsorption capacity (mg / g) of the covering material for phosphorus in water, that is, the saturated adsorption capacity of phosphate in water per unit mass of the covering material; Q e It indicates the unit adsorption amount of phosphorus in water by the covering material at the equilibrium moment (mg / g).

[0076] S3.2. Use the following formula to determine the total amount of covering material to be added: Q

[0077]

[0078] Where, M is the total mass of potentially mobile phosphorus in the water sediment, mg; Q m It is the unit saturated adsorption capacity of phosphate in water by the covering material, mg / kg.

[0079] S3.3. Divide the covering material to be added into several equal parts and determine the amount of covering material to be added for each equal part. You can choose the following two methods to determine the number of equal parts.

[0080] The first method is to divide the total amount of covering material into 20-200 equal portions;

[0081] The second method is to use the following formula to calculate the number of equal parts n;

[0082]

[0083] Where F is the phosphorus release flux of sediment mg / (m 2 ·d), t is the duration d of the covering material controlling the release of phosphorus from the sediment, which needs to be determined based on actual conditions and is generally 20 to 200 days.

[0084] Among them, the calculation methods of sediment phosphorus release flux F are in situ observation method, sediment core culture method, sediment available phosphorus and pore water dissolved concentration profile estimation method, mass balance method, isotope mass balance method and empirical formula method. Generally, the sediment core culture method and sediment available phosphorus and pore water dissolved concentration profile estimation method are used.

[0085] 1. The steps for determining the phosphorus release flux of sediment using the sediment core culture method are as follows:

[0086] 1) Collect the sediment core and then seal it with a rubber stopper;

[0087] 2) Analyze phosphorus concentration in overlying water;

[0088] 3) Calculate and determine the sediment phosphorus release flux according to the following formula.

[0089]

[0090] Where F is the phosphorus release flux of sediment [mg / (m 2 / d)]; V is the volume of water overlying the sediment column (L); V j-1 is the volume of the water sample taken for the j-1th time (L); C0, C n and C j-1 represents the phosphorus concentration (mg / L) of the water samples taken at the 1st, nth and j-1st times, respectively; C a represents the phosphorus concentration in the supplemented water (mg / L); A represents the surface area of ​​the sediment-water interface (m 2 );t is the sediment culture period (d).

[0091] 2. The steps for determining the sediment phosphorus release flux using the sediment available phosphorus and pore water dissolved concentration profile estimation method are as follows:

[0092] 1) Determine the concentration of dissolved or available phosphorus above and below the sediment-water interface;

[0093] 2) For dissolved phosphorus, the sediment phosphorus release flux was calculated according to the following formula;

[0094]

[0095] Where, φ represents the porosity of the sediment; D s The effective diffusion coefficient of phosphate in the sediment (cm 2 / s); It represents the concentration gradient at the sediment-overlying water interface [mg / (L·cm)].

[0096] 3) For available phosphorus, the sediment phosphorus release flux was calculated according to the following formula.

[0097]

[0098] In the formula, It represents the concentration gradient of available phosphorus in sediment [mg / (L·cm)]; represents the available phosphorus concentration gradient in the overlying water [mg / (L·cm)]; D s represents the effective diffusion coefficient of phosphate in sediment (cm 2 / s); D w represents the effective diffusion coefficient of phosphate in water (cm 2 / s).

[0099] Step 4. Add an equal amount of covering material to the water body that needs to be repaired, and use the in-situ passive sampling technology to check the formation of the "phosphorus static layer" in the bottom mud of the water body. If it is formed, stop adding covering material; if it is not formed, continue to add an equal amount of covering material, and use the in-situ passive sampling technology to check the formation of the "phosphorus static layer" in the bottom mud, and so on, until the "phosphorus static layer" is formed, and then calculate the total amount of covering material added before the formation of the "phosphorus static layer", which is the regular dosage.

[0100] S4.1. Determination of “Phosphorus Static Layer”

[0101] In-situ passive sampling technology can be used to analyze the concentration of available or dissolved phosphorus in surface sediments. The judgment method is: the concentration of available or dissolved phosphorus in 0~(10-40)mm sediments is 50% or more lower than the initial concentration.

[0102] The in-situ passive sampling technology refers to thin film gradient diffusion (DGT for short) technology or high-resolution dialysis sampling technology or sediment pore water in-situ collector.

[0103] S4.2. The total amount of covering material added before the formation of the "static phosphorus layer" in the sediment is the regular amount of addition, which is used to determine the mass of the covering material added each time thereafter.

[0104] Step 5: Add covering material at regular dosage and time intervals;

[0105] Alternatively, the phosphorus concentration in the bottom sediment of the water body can be analyzed regularly using in-situ passive sampling technology. Once the phosphorus concentration is found to exceed the preset value, the covering material should continue to be added according to the normal dosage.

[0106] In order to verify the feasibility of the method for controlling phosphorus release in sediment of the present invention, we take the use of iron-based covering materials to control phosphorus release in sediment of surface water as an example to illustrate the implementation process and effects of the present invention.

[0107] After measurement, the potential mobile phosphorus content in the sediment in the implementation case was 141 mg / kg, and iron-modified dolomite was used to control the release of phosphorus in the sediment.

[0108] 1. The preparation steps of iron-modified dolomite are as follows: 1) weigh a certain mass of dolomite and place it in a container, then add a certain volume of water so that the ratio of dolomite mass to water volume is 1g:2.5mL; 2) weigh a certain mass of ferric nitrate nonahydrate and place it in a container, add a certain volume of water to prepare an iron solution so that the ratio of ferric nitrate nonahydrate mass to water volume is 1g:5mL; 3) drop the iron solution into the dolomite suspension so that the ratio of ferric nitrate nonahydrate mass to dolomite mass is 0.5, and continue the reaction for 24h; 4) wash 3 times, dry at 105 degrees Celsius, crush, and pass 200 mesh. Its specific structure is shown in the attached Figure 2-4 .

[0109] The unit saturated adsorption capacity of the prepared iron-modified dolomite for phosphate in water was determined to be 2.64 mg / g by adsorption experiments. Figure 5-6 shown.

[0110] 2. Based on the surface area of ​​1 square meter of surface water, the thickness of the surface sediment is 4 cm, and the sediment phosphorus that needs to be controlled per unit water surface area is calculated to be 2543 mgP / m 2 , further calculation to determine 1m 2 Water surface area, a total mass of 963g of iron-modified dolomite needs to be added.

[0111] The DGT concentration in the surface sediment was determined by using the thin film diffusion gradient (DGT) technique, and the sediment phosphorus release flux F was determined to be 11.9 mg / (m 2 ·d).

[0112] 3. Divide the covering material into several equal parts.

[0113] The dosage of each equal portion of covering material is 11.9×21 / 2.64=95g / m 2 The number of covering materials is 963 / 95≈10. According to the determined number of equal portions, the amount of covering material added per equal portion is corrected to 96.3g / m 2 .

[0114] After testing, adding an equal amount of iron-modified dolomite, that is, covering the bottom mud-water interface, the addition amount is 96.3g / m 2 The iron-modified dolomite can form a "static phosphorus layer" in the surface mud. Therefore, the single addition amount of iron-modified dolomite is determined to be 96.3g / m 2 .

[0115] The following experiment was conducted to test the effect of adding iron-modified dolomite in multiple times on the control of phosphorus release from sediment. The experimental steps are as follows:

[0116] 1) Take 9 cylindrical columns with a diameter of 11.5 cm and a height of 30 cm, and add the bottom mud into the columns until the bottom mud height reaches 10 cm;

[0117] 2) The columns were divided into three groups: control group, group with one-time high-dose iron-modified dolomite addition, and group with multiple small-dose iron-modified dolomite addition, with three columns in each group; for the control group (T0), 5 g of dry suspended particulate matter (SPM) was added every 2 days; for the one-time iron-modified dolomite addition group (T1), 5 g of dry SPM was added every 2 days, and before the start of sediment culture, 10 g of iron-modified dolomite was covered on the top of the sediment (equivalent to 963 g / m 2 ); for the iron-modified dolomite multiple addition group (T2), 5g of dry SPM was added every 2 days, and 10g of covering material was divided into 10 batches, with an initial addition of 1g of covering material (equivalent to 96.3g / m 2 ), and then add once every 4 days, and all the additions will be completed in 36 days;

[0118] 3) Determine the dissolved reactive phosphorus (SRP) and dissolved total phosphorus (DTP) in the overlying water.

[0119] The experimental results showed that on the 28th day, the SRP concentrations in the overlying water of the T0, T1 and T2 groups were 0.517, 0.242 and 0.022 mg / L, respectively, and the DTP concentrations were 0.590, 0.309 and 0.068 mg / L, respectively. The removal rates of SRP in the overlying water by T1 and T2 were 53.1% and 95.7%, and the removal rates of DTP were 40.2% and 86.7%, respectively. On the 48th day, the SRP concentrations in the overlying water of the T0, T1 and T2 groups were 0.891, 0.521 and 0.034 mg / L, and the DTP concentrations were 0.921, 0.528 and 0.061 mg / L, respectively. The removal rates of SRP in the overlying water by T1 and T2 were 41.5% and 96.1%, and the removal rates of DTP were 40.7% and 93.2%, respectively. This shows that multiple additions of iron-modified dolomite can effectively control the release of phosphorus in the sediment into the overlying water. This also shows that the effect of multiple additions of iron-modified dolomite in controlling the release of phosphorus from the sediment is significantly better than the one-time addition of iron-modified dolomite, which further proves the effectiveness of the method proposed in the present invention.

[0120] The DGT device was further used to measure the DGT effective phosphorus concentration in the vertical section of overlying water and sediment, such as Figure 7 As shown, the results show that: under the action of multiple additions of iron-modified dolomite, the concentration of DGT-available phosphorus in the overlying water is significantly lower than that in the control group, and under the action of the former, the concentration of DGT-available phosphorus in the 0-18 mm sediment is significantly lower than that in the control group. This further illustrates that the multiple additions of iron-modified dolomite can effectively control the release of phosphorus in the sediment into the overlying water. In addition, the removal efficiency of DGT-available phosphorus in the overlying water and surface sediment by the multiple additions of iron-modified dolomite is significantly higher than that of the one-time addition of iron-modified dolomite. This further confirms that the effect of the multiple additions of iron-modified dolomite in controlling the release of phosphorus from the sediment is significantly better than that of the one-time addition of iron-modified dolomite, which further proves the effectiveness of the method proposed in the present invention.

[0121] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to these embodiments without departing from the principles and essence of the present invention. Therefore, the scope of protection of the present invention is limited by the appended claims.

Claims

1. A method for controlling phosphorus release in water sediment, characterized in that The following steps are involved: Step 1: Determine the occurrence form of phosphorus in the sediment of the water body, calculate the potential mobile phosphorus content per unit mass in the sediment, and then determine the total amount of potential mobile phosphorus in the sediment of the water body that needs to be repaired based on the total dry sediment mass of the water body that needs to be repaired; Step 2: Determine the total amount of covering material to be added according to the unit saturated adsorption amount of phosphorus in water and the total amount of potential mobile phosphorus of the covering material, and then divide the total amount of covering material into several equal parts; Step 3: Add an equal amount of covering material to the water body that needs to be repaired, and use the in-situ passive sampling technology to check the formation of the "static phosphorus layer" in the bottom mud of the water body. If it is formed, stop adding covering materials; if it is not formed, continue to add an equal amount of covering material, and use the in-situ passive sampling technology to check the formation of the "static phosphorus layer" in the bottom mud, and so on, until the "static phosphorus layer" is formed, and then calculate the total amount of covering material added before the formation of the "static phosphorus layer" as the conventional dosage; Step 4: Add covering material at regular dosage and time intervals; Alternatively, the phosphorus concentration in the bottom sediment of the water body can be analyzed regularly using in-situ passive sampling technology. Once the phosphorus concentration is found to exceed the preset value, the covering material should continue to be added according to the normal dosage.

2. The method for controlling phosphorus release in water sediment according to claim 1, characterized in that: In the step 2, the total amount of potential mobile phosphorus M in the bottom mud of the water body is calculated and determined according to the following formula; M=m×q Where m is the total dry sediment mass in the water body kg; q is the potential mobile phosphorus content per unit mass of dry sediment mg / kg; A is the area of ​​the sediment-water interface m 2 , h is the thickness of the water body sediment m, ρ is the density of the water body sediment kg / m 3 , W is the moisture content of the bottom mud in the water body.

3. The method for controlling phosphorus release in water sediment according to claim 2, characterized in that: Use the following formula to determine the total amount of covering material required to be added Q Where, M is the total mass of potentially mobile phosphorus in the water sediment, mg; Q m It is the unit saturated adsorption capacity of phosphate in water by the covering material, mg / kg.

4. The method for controlling phosphorus release in water sediment according to claim 2, characterized in that: Divide the total amount of covering material into 20-200 equal portions; Or use the following formula to calculate the number of equal parts n; Where F is the phosphorus release flux of sediment mg / (m 2 ·d), t is the duration d that the covering material controls the release of phosphorus from the sediment, which needs to be determined based on actual conditions.

5. The method for controlling phosphorus release in water sediment according to claim 4, characterized in that: The calculation method of the sediment phosphorus release flux is set to be a sediment core culture method or a sediment available phosphorus and pore water dissolved concentration profile estimation method.

6. The method for controlling phosphorus release in water sediment according to claim 1, characterized in that The method for determining the unit saturated adsorption amount of phosphorus in water by the covering material comprises the following steps: Step I, preparing phosphorus solutions with different initial concentrations, and adjusting the pH value of the phosphorus solutions to a certain pH value, which is determined according to the pH value of the actual water body; Step II, adding the covering material and phosphorus solutions of different concentrations to conduct an oscillating reaction, and after the reaction is completed, measuring the phosphorus concentration in the solution; Step III: Use the following formula to calculate and determine the unit adsorption amount Q of phosphorus in water by the covering material: e ; Wherein, V represents the volume of phosphorus solution L; a represents the amount of covering material added in step II g; c0 and c e represent the phosphorus concentration in the phosphorus solution before the adsorption reaction and at the reaction equilibrium moment, respectively; Unit saturated adsorption capacity of phosphorus in water by covering material Q m The unit adsorption amount Q corresponding to different concentrations of phosphorus solution e The maximum value of , or determined by fitting the experimental data through the following isothermal adsorption model; In the formula, c e Indicates the equilibrium concentration of phosphorus in the solution in mg / L; K L is the isothermal adsorption model constant L / mg; Q m Indicates the unit saturated adsorption of phosphorus in water by the covering material, mg / g; Q e It indicates the unit adsorption amount of phosphorus in water by the covering material at the equilibrium moment, mg / g.

7. The method for controlling phosphorus release in water sediment according to claim 1, characterized in that: The covering material is configured to adopt a multi-stage impregnation method to prepare the metal-based covering material.

8. The method for controlling phosphorus release in water sediment according to claim 1, characterized in that: The graded continuous chemical extraction method was used to determine the occurrence forms of phosphorus in the sediment of water bodies, and the easily desorbed phosphorus and redox-sensitive phosphorus in the sediment were set as potentially mobile phosphorus.

Images