Matrix unit type lake sediment dredging effect estimation method

Abstract

The invention relates to the technical field of water pollution treatment, in particular to a matrix unit type lake sediment desilting effect estimation method, which comprises the following steps of: isolating a plurality of test units in a to-be-desilted area, desilting sediment of each test unit at different depths, arranging monitoring points inside and outside the test units, and evaluating the desilting effect according to monitoring data. The method has the advantages that the dredging depth is optimized, resource waste is reduced, the method is suitable for sediment dredging projects of various lakes, the dredging effect is pre-evaluated before the dredging projects are implemented, and support is provided for implementation necessity of the dredging projects.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution treatment, and in particular to a matrix unit type lake sediment desilting effect prediction method. Background Art

[0002] Lake sediments are both the source and sink of water pollution. During the lake restoration process, to improve water quality and reduce the release of endogenous sediments, environmentally friendly dredging techniques are often used to dredge the sediments. During the lake restoration process, to improve water quality and reduce the release of endogenous sediments, environmentally friendly dredging techniques are often used to dredge the sediments. Before the dredging project begins, it is necessary to conduct a preliminary survey of the lake sediments, define the specific dredging scope, and estimate the dredging effect, so as to achieve efficient dredging, avoid insufficient dredging depth to achieve the treatment effect, or avoid dredging too deep to damage the lake ecology, and avoid wasting resources.

[0003] Existing methods for estimating the effectiveness of lake sediment desilting include empirical analogy, laboratory simulation, short-term field monitoring, and model simulation. The empirical analogy method uses historical engineering data or engineering experience to predict the effectiveness of desilting in similar lakes. While simple and easy to use, the empirical analogy method suffers from significant differences in water environments and sediment properties across lakes, leading to large errors in estimation. The laboratory simulation method collects sediment samples and measures pollutant release after simulated desilting in the laboratory. However, laboratory simulations cannot simulate the impact of changing natural conditions (such as wind disturbance and temperature) on desilting effectiveness, leading to misjudgments and large errors in estimation. The short-term field monitoring method monitors water quality changes after desilting, using a single parameter (such as TP) to assess effectiveness. However, short-term field monitoring methods often rely on a single indicator (such as TP) and ignore the synergistic effects of dissolved oxygen concentration (DO) at the mud-water interface on water quality. Furthermore, water quality fluctuates significantly in the short term after desilting, making it difficult to assess desilting effectiveness. Model simulation methods use hydrodynamic models to predict pollutant diffusion trends after dredging. However, these methods require extensive parameters and monitoring data, are technically demanding, and come with high cost. Therefore, there is an urgent need to develop methods that can accurately and cost-effectively pre-evaluate the effectiveness of dredging projects. Summary of the Invention

[0004] The purpose of the present invention is to provide a matrix unit lake sediment dredging effect prediction method, optimize the dredging depth, reduce resource waste, and be applicable to sediment dredging projects of various lakes. The dredging effect can be pre-evaluated before the dredging project is implemented, providing support for the necessity of implementing the dredging project.

[0005] The present application provides the following technical solutions: a matrix unit lake sediment dredging effect estimation method, which isolates multiple test units in the area to be dredged, performs dredging operations on the sediments of each test unit at different depths, sets monitoring points inside and outside the test unit, and evaluates the dredging effect based on the monitoring data.

[0006] Beneficial Effects: Dividing the area to be desilted into multiple independent test units effectively eliminates interference from environmental variables. This facilitates simultaneous testing of multiple desilting depth schemes under the same environmental conditions. By comparing monitoring data from test units with different desilting depths, desilting effectiveness can be scientifically and accurately assessed, effectively conserving resources, avoiding unnecessary and ineffective desilting, and ensuring the reliability of desilting effect assessment results, effectively supporting decision-making for subsequent large-scale desilting projects.

[0007] Furthermore, isolation belts were used to isolate multiple test units in the area to be desilted. The multiple test units were arranged in a matrix, and the area of ​​each test unit was 100~150㎡.

[0008] Beneficial Effects: Isolation zones physically separate different test units, preventing cross-contamination and potential experimental errors during dredging. The matrix arrangement ensures that basic conditions, such as topography, water depth, and sediment, are as consistent as possible across all test units, reducing experimental errors due to regional variations. The test units are 100-150 square meters in size, ensuring ample operating space for dredging equipment, while also minimizing variations in results due to uneven sediment distribution within the region and reducing construction and dredging costs.

[0009] Furthermore, the isolation belt includes a frame and waterproof fabric.

[0010] Beneficial Effects: The framework provides effective support, while the waterproof fabric completely blocks the migration of liquid water and sediment between test units. During dredging experiments, this can completely block the diffusion of water, dissolved pollutants, and nutrients (such as nitrogen and phosphorus) between test units, preventing cross-contamination of monitoring data between thin- and thick-layer dredging units.

[0011] Furthermore, the test unit includes at least an undredged unit, a thin-layer dredging unit, a thick-layer dredging unit, and a transition-layer dredging unit. The undredged unit retains the original sediment, the thin-layer dredging unit removes the upper part of the sediment contamination layer, the thick-layer dredging unit removes all sediment contamination layers, and the transition-layer dredging unit removes all sediment contamination layers and the transition layer.

[0012] Beneficial Effects: No desilting was performed in the undesilted units, providing a reference for background pollution values ​​and natural evolution for the other test units. Desilting of thin layers, thick layers, and transition layers formed a gradient test group, ranging from "partial treatment" to "complete treatment." This facilitated analysis of the impact of different desilting depths on the treated water body and enabled a scientific and accurate assessment of desilting effectiveness.

[0013] Furthermore, the indicators monitored at the monitoring points inside and outside the experimental unit include diurnal variation data of total nitrogen concentration, total phosphorus concentration and dissolved oxygen concentration at the sediment-water interface.

[0014] Furthermore, the monitoring period of the test unit is at least 8 weeks, the monitoring frequency of total nitrogen concentration and total phosphorus concentration is once a week, and the dissolved oxygen concentration at the sediment-water interface is monitored in real time for at least 8 weeks at a frequency of once an hour.

[0015] Beneficial effects: By collecting data on water quality indicators such as total nitrogen concentration and total phosphorus concentration inside and outside the test unit, as well as diurnal variation data on dissolved oxygen concentration at the sediment-water interface, the effect of lake sediment dredging is estimated. This solves the limitations of traditional dredging project implementation, which is difficult to evaluate, relies on experience, and is greatly affected by the environment. It can scientifically predict the environmental benefits of different dredging depths and provide a basis for dredging project decision-making.

[0016] Furthermore, the monitoring probe for dissolved oxygen concentration at the sediment-water interface is located at the bottom of the water body, with a distance from the sediment surface of 1 to 20 cm.

[0017] Beneficial effects: The dissolved oxygen concentration probe should be set at the lake sediment-water interface, as close to the sediment as possible, so that it can accurately measure the changes in the dissolved oxygen concentration at the interface over the day and night time, thereby more accurately judging the oxygen consumption capacity of the sediment and whether pollution release will occur. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the test unit structure of the matrix unit lake sediment desilting effect prediction method of the present invention.

[0019] Figure 2 This is a cross-sectional view of each test unit of the matrix unit lake sediment desilting effect prediction method of the present invention.

[0020] Figure 3 This is a schematic diagram of the sediment status and dredging depth of each test unit in the matrix unit lake sediment dredging effect prediction method of the present invention.

[0021] Figure 4 This is a graph showing the changes in dissolved oxygen concentration (DO) at the sediment-water interface during the day and night in each test unit of the matrix unit lake sediment desilting effect estimation method of the present invention.

[0022] The marks in the drawings of the specification include: isolation zone 1, first monitoring point 2, second monitoring point 3, undredged unit 4, thin layer dredged unit 5, thick layer dredged unit 6, transition layer dredged unit 7, mud discharge field 8, upper part of the polluted layer 9, lower part of the polluted layer 10, transition layer 11, and natural layer 12. DETAILED DESCRIPTION

[0023] The following is further described in detail through specific implementation methods: Example 1 like Figures 1 to 3 As shown, a matrix unit lake sediment desilting effect estimation method includes the following steps: 1. Set up sampling points in the area to be desilted to conduct water and sediment surveys, and select representative polluted areas for setting up test units.

[0024] Sediment samples were collected at sampling points in the area to be desilted, and the sediment thickness and stratified distribution of pollutants in the sediment were determined based on the sediment samples. Representative polluted areas are those where, after preliminary water quality and sediment surveys, typical water quality indicators were assessed to be poor, unable to meet the functional requirements of the lake, and where endogenous pollution is present. The area used to set up the test unit was set within 2 km of the lakeshore mud discharge site to facilitate the transportation of desilting mud. In this example, the area to be desilted on the east side of the lake near the shore was selected as the representative polluted area for setting up the test unit. The area used to set up the test unit was approximately 1 km from the lakeshore, with an average water depth of 2 m. The sediment contamination layer thickness was 0.2 m, and the transition layer thickness was 0.15 m. The main pollutants were phosphorus (water concentration 0.1 mg / L, sediment content 790 mg / kg) and organic matter (sediment content 9%).

[0025] 2. In the area to be desilted, isolation belts are used to isolate multiple test units. The multiple test units are arranged in a matrix, and the area of ​​each test unit is 100~150㎡.

[0026] Each test unit separated by barrier 1 is a closed rectangular structure, measuring 10 meters in length and width. The top of barrier 1 is at least 0.5 meters above the water surface, and its bottom is embedded in the mud at least 0.2 meters deeper than the desilting depth of the corresponding test unit. Barrier 1 consists of a frame and waterproof fabric. The frame is constructed of scaffolding steel pipe (Ø48 mm); the waterproof fabric is made of polyvinyl chloride (PVC) and features floats. Pinewood stakes (15 cm diameter, 2.5 m long) are used for anchoring at the corners. To construct the test unit, one side of the fabric is pressed under the frame, through the mud, and embedded into the lake bottom. The other side is then pulled up and enclosed around the frame, creating a double-layer waterproof fabric structure to form an independent test unit. The frame of each test unit is embedded in the lake bottom to a depth of 0.6 meters, ensuring ease of construction and structural stability.

[0027] 3. Dredging operations are carried out at different depths on the bottom mud of each test unit. According to the different dredging operation depths, the test units include at least four types, namely, undredged unit 4, thin layer dredged unit 5, thick layer dredged unit 6, and transition layer dredged unit 7.

[0028] Dredging operations utilize underwater environmentally friendly pump-suction dredging equipment with integrated environmentally friendly cutter heads to remove dredging to the appropriate depth. Mud is transported to an onshore discharge site 8 via DN300 pressure-resistant bellows. A relay pumping station is located 500 meters away. Undredged unit 4 retains the original sediment, and the dredging operation depth is zero. Thin-layer dredging unit 5 removes the upper contaminated layer 9 of the sediment, operating at a depth of 0.1 meters and removing a 0.1-meter-thick layer of sediment. Thick-layer dredging unit 6 removes the entire contaminated layer (including the upper contaminated layer 9 and the lower contaminated layer 10), operating at a depth of 0.2 meters and removing a 0.2-meter-thick layer of sediment. Transition layer dredging unit 7 removes the entire contaminated layer and transition layer 11, operating at a depth of 0.4 meters and removing a 0.35-meter-thick layer of sediment, exposing the natural layer 12. The operating depth is greater than the sediment thickness to ensure complete removal of the sediment.

[0029] 4. Set up monitoring points inside and outside the test unit for monitoring. The monitoring points include a first monitoring point 2 set in the middle of each test unit and a second monitoring point 3 set at the periphery of the matrix test unit.

[0030] Monitoring point 1, monitoring site 2, was used to monitor the water within the experimental unit. Monitoring indicators included diurnal variations in total nitrogen (TN), total phosphorus (TP), and dissolved oxygen (DO) at the sediment-water interface. The probe monitoring DO at the sediment-water interface was located at the bottom of the water, 10 cm from the sediment surface.

[0031] Four secondary monitoring points (3) were evenly distributed around the perimeter of the matrix test unit, each 50–100 m from the matrix unit's perimeter isolation zone. These points monitored the water surrounding the test unit, monitoring indicators including total nitrogen (TN) and total phosphorus (TP). These points eliminated environmental interference.

[0032] The monitoring period of the test unit is at least 8 weeks, the monitoring frequency of total nitrogen concentration and total phosphorus concentration is once a week, and the dissolved oxygen concentration at the sediment-water interface is monitored in real time for at least 8 weeks with a monitoring frequency of once an hour.

[0033] 5. Evaluate the dredging effect based on monitoring data.

[0034] According to the dynamic changes of the monitoring indicators of the test unit during the monitoring period, a comprehensive analysis is conducted on the dynamic changes of dissolved oxygen at the sediment-water interface to conduct a preliminary assessment of the subsequent large-scale dredging effects.

[0035] The difference in total nitrogen (TN) and total phosphorus (TP) concentrations after desilting was calculated for each test unit. Coupled with dynamic dissolved oxygen monitoring, the degree of improvement in water quality due to desilting was determined and the optimal desilting depth was selected. The degree to which desilting improved the redox state of the sediment was determined by comparing dissolved oxygen concentrations at the sediment-water interface. Dissolved oxygen concentrations at the lake sediment-water interface vary both diurnally and seasonally. When dissolved oxygen concentrations fall below 2 mg / L, the surface sediment is likely to enter a reducing state. Below 1 mg / L, this state is more likely to occur, leading to the release of large amounts of pollutants.

[0036] The indicator difference rate is calculated as follows: ; in, is an indicator of the undrained unit; It is an indicator of the test unit for dredging operation (such as thin layer dredging unit, thick layer dredging unit, or transition layer dredging unit).

[0037] The unsilted unit, thin-layer silted unit, thick-layer silted unit, and transition-layer silted unit were monitored for 8 weeks. The monitoring data of total phosphorus concentration (TP) of each test unit are shown in Table 1 below, the monitoring data of total nitrogen concentration (TN) of each test unit are shown in Table 2 below, and the day and night monitoring data of dissolved oxygen concentration (DO) at the sediment-water interface of each test unit are shown in Table 2 below. Figure 4 .

[0038] Table 1 Changes of total phosphorus concentration (TP) in each experimental unit over time

[0039] Table 2 Changes of total phosphorus concentration (TP) in each experimental unit over time

[0040] After eight weeks, the TP concentration in the undesilted unit increased to 0.14 mg / L, and the TN concentration increased to 2.23 mg / L. The TP concentration in the thin-desilted unit was 0.06 mg / L, with a 45.5% difference, and the TN concentration was 1.43 mg / L, with a 32% difference. The TP concentration in the thick-desilted unit was 0.04 mg / L, with a 60% difference, and the TN concentration was 0.95 mg / L, with a 59% difference. The TP concentration in the transition-desilted unit was 0.04 mg / L, with a 60% difference, and the TN concentration was 0.9 mg / L, with a 61% difference. The average TP and TN concentrations in the water outside the experimental unit were 0.09 mg / L and 1.73 mg / L, respectively. The average dissolved oxygen concentration at the sediment-water interface in the undesilted unit was 7.9 mg / L during the day, dropping to below 1 mg / L at night. Dissolved oxygen concentrations in the thin-desilted, thick-desilted, and transition-desilted units were similar to those in the undesilted unit during the day, but increased significantly at night, reaching a minimum of 4 mg / L. Monitoring data show that the dredging of thin and thick layers of sediment pollution has a significant effect on improving TP and TN concentrations. The TP and TN concentrations outside the test unit (the second monitoring point) are close to the initial water index data, indicating that the dredging operation has not affected the surrounding water body and the data is reliable. Figure 4 As can be seen in the figure, the dissolved oxygen concentration at the mud-water interface in the undredged units drops to below 1 at night, indicating that the surface sediment is in a reduced state at night, posing a high risk of nitrogen and phosphorus release. Combined with the increased TP and TN concentrations in the undredged units shown in Tables 1 and 2, this suggests endogenous releases from the sediment. After dredging, the dissolved oxygen concentration at the mud-water interface increases significantly, and the oxidized state of the surface sediment reduces release, ultimately leading to a decrease in TP and TN concentrations in the dredged units. Furthermore, transition layer dredging contributes very similarly to thick-layer dredging in reducing TP and TN concentrations in the water column. Thin-layer dredging can restore the surface sediment to an oxidized state. Therefore, depending on the actual dredging goals and budget, selecting a dredging depth of 0.1 m or 0.2 m can effectively reduce dredging and subsequent treatment costs.

[0041] The above are only embodiments of the present invention. The invention is not limited to the fields involved in this implementation case. Common knowledge such as the specific structure and characteristics of the scheme are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several modifications and improvements can be made, which should also be regarded as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A matrix unit lake sediment desilting effect estimation method, characterized in that: Multiple test units are isolated in the area to be dredged, and dredging operations are carried out on the bottom mud of each test unit at different depths. Monitoring points are set up inside and outside the test unit, and the dredging effect is evaluated based on the monitoring data.

2. The matrix unit lake sediment desilting effect estimation method according to claim 1, characterized in that: In the area to be desilted, isolation belts are used to isolate multiple test units, which are arranged in a matrix. The area of ​​each test unit is 100~150㎡.

3. The matrix unit lake sediment desilting effect estimation method according to claim 2, characterized in that: The isolation strip comprises a frame and waterproof fabric.

4. The matrix unit lake sediment desilting effect estimation method according to claim 1, characterized in that: The test unit includes at least an undredged unit, a thin-layer dredging unit, a thick-layer dredging unit, and a transition-layer dredging unit. The undredged unit retains the original bottom sediment, the thin-layer dredging unit removes the upper part of the bottom sediment contamination layer, the thick-layer dredging unit removes the entire bottom sediment contamination layer, and the transition-layer dredging unit removes the entire bottom sediment contamination layer and the transition layer.

5. The matrix unit type lake sediment desilting effect estimation method according to claim 1, characterized in that: The indicators monitored at the monitoring points inside and outside the experimental unit include diurnal variation data of total nitrogen concentration, total phosphorus concentration and dissolved oxygen concentration at the sediment-water interface.

6. The matrix unit lake sediment desilting effect estimation method according to claim 5, characterized in that: The monitoring period of the test unit is at least 8 weeks, the monitoring frequency of total nitrogen concentration and total phosphorus concentration is once a week, and the dissolved oxygen concentration at the sediment-water interface is monitored in real time for at least 8 weeks at a frequency of once an hour.

7. The matrix unit lake sediment desilting effect estimation method according to claim 5, characterized in that: The monitoring probe for dissolved oxygen concentration at the sediment-water interface is located at the bottom of the water body, with a distance from the sediment surface of 1 to 20 cm.

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