River and lake bottom material particle size grading optimization method and integrated process

Abstract

The present application belongs to the technical field of river and lake water ecological management and restoration. More specifically, it relates to a river and lake bottom material particle size grading optimization method and integrated process. The specific optimization method of the present application comprises: S1: selectively screening fine particle sediment with a particle size not greater than 75 μm in the surface layer of river and lake bottom material, and retaining coarse particles with a particle size greater than 75 μm to form a cover layer in situ; S2: sequentially subjecting the fine particle sediment to flocculation co-precipitation, sludge concentration and mechanical dewatering to obtain dewatered sediment with a moisture content of 50-60%; S3: mixing the dewatered sediment and auxiliary materials, stirring uniformly, and then pressing into particles to obtain an ecological restoration substrate with a particle size distribution of 5 mm-5 cm; S4: covering the ecological restoration substrate to the riverbed surface in layers according to the particle size gradient to realize bottom material particle size grading optimization.

Description

Technical Field

[0001] This invention belongs to the technical field of river and lake water ecological governance and restoration. More specifically, it relates to a method and integrated process for optimizing the particle size distribution of river and lake sediment. Background Technology

[0002] The particle size distribution of sediment in urban rivers and lakes directly affects the oxygen permeability, pollutant adsorption and degradation characteristics, and the habitat quality of benthic organisms. Affected by runoff non-point source pollution and overflow pollution from drainage outlets, a large amount of ultra-fine particles (≤75μm) sediment accumulates in rivers and lakes, enriching nitrogen and phosphorus nutrients, organic matter, and heavy metals. The sediment tends to become a strongly reducing environment, leading to decreased water transparency and continuous deterioration of water quality.

[0003] Traditional dredging techniques have the following main problems: First, indiscriminate removal of bottom sediment disturbs the mud-water interface, easily leading to the release of large amounts of pollutants and resuspension of bottom sediment; second, extremely fine particles are difficult to settle naturally, resulting in long-term turbidity of the overlying water; third, the bottom habitat is severely damaged after dredging, and the recovery period for benthic organisms is long; fourth, the cost of transporting and disposing of dredged sediment is high, the resource utilization rate is low, and there is a lack of in-situ remediation technology pathways for on-site utilization.

[0004] Currently, there is no known process that organically integrates sediment washing, mud-water separation, preparation of sediment resource-based ecological restoration substrates, and sediment particle size distribution remediation. Therefore, developing a method for optimizing sediment particle size distribution and improving sediment habitats with low disturbance, volume reduction, and resource utilization is of significant practical importance. Summary of the Invention

[0005] The technical problem this invention aims to solve is the existence of problems in existing dredging technologies, such as long-term turbidity of the overlying water, low utilization rate of dredged sediment as an ecological resource, and lack of integrated processes for bottom sediment habitat restoration. Based on these challenges, this invention provides a method and integrated process for optimizing the particle size distribution of river and lake bottom sediments.

[0006] The purpose of this invention is to provide a complete set of treatment methods and equipment integration solutions for the precise separation of pollutants in river and lake sediments, in-situ utilization of sediment resources, optimization of particle size distribution of river and lake sediments, and in-situ restoration of habitats.

[0007] Another objective of this invention is to provide an integrated process for optimizing the particle size distribution of river and lake sediments.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution: A method for optimizing the particle size distribution of river and lake sediments includes the following steps: S1: Selective screening is used to obtain fine-grained sediment particles with a particle size of no more than 75 μm from the surface layer of river and lake bottoms, while coarse particles with a particle size of more than 75 μm are retained in situ to form a cover layer. S2: Fine-particle bottom sludge is subjected to flocculation co-precipitation, sludge thickening and mechanical dewatering in sequence to obtain dewatered bottom sludge with a moisture content of 50-60%. S3: After mixing the dehydrated sediment and auxiliary materials, stir evenly, and then press into granules to obtain an ecological restoration substrate with a particle size distribution of 5mm-5cm; S4: Apply the ecological restoration substrate to the riverbed surface in layers according to the particle size gradient to optimize the particle size distribution of the substrate.

[0009] The beneficial effects of the above technical solution are as follows: The above-mentioned solution differs from traditional dredging in its treatment targets and technical principles. Traditional dredging does not clearly distinguish the particle size distribution of pollutants, removing coarse and fine particles of sediment along with pollutants simultaneously, resulting in a large amount of silt on land, increasing subsequent treatment costs and landfill volume. This solution uses an underwater washing robot to selectively remove fine particles of sediment ≤75μm, retaining coarse particles >75μm for in-situ coverage. The removed fine particles are then dewatered, solidified, and granulated to create an ecological restoration matrix. Finally, the matrix is ​​layered and re-covered according to particle size gradient, achieving optimized sediment particle size distribution and sediment habitat restoration.

[0010] Specifically, since fine particles smaller than 75μm are the main carriers for the enrichment of TOC, TN, and TP, selective removal can directly reduce the pollution load in the sediment and reduce the potential for pollutants to be released into the water. Meanwhile, retaining coarse particles larger than 75μm for in-situ coverage avoids the drastic disturbance to the mud-water interface caused by traditional dredging, reduces sediment resuspension, and keeps the water clear. The screened fine pollutants are transformed into ecological restoration substrates on-site, avoiding the costs of off-site disposal and secondary pollution, and achieving a synergistic effect of "reduction, harmlessness, and resource utilization". The backfilled substrate, covered in a gradient, can systematically improve the porosity, permeability, and aerobic environment of the sediment, creating a suitable habitat for benthic organisms and submerged plants.

[0011] Furthermore, in step S1, the surface layer of the river / lake bottom is a region with a depth of 0-30cm.

[0012] This depth is the layer where bottom sediment pollutants are most concentrated and the mud-water exchange is most active. It is also a key layer for the activity of benthic organisms and the root systems of submerged plants. Limiting the treatment depth ensures efficient removal of pollutants while avoiding excessive dredging that could damage the deep bottom structure and preserve the supporting role of the natural matrix.

[0013] Furthermore, in step S2, the flocculation sedimentation, sludge thickening, and mechanical dewatering include: adding polyaluminum chloride, polyacrylamide, and fly ash to fine-particle bottom sludge, stirring evenly, performing flocculation co-precipitation thickening, then performing multi-layer radial flow sludge thickening to reduce the moisture content to 70-80%, and finally mechanically dewatering to a moisture content of 50-60% under a pressure of 0.6-0.8 MPa to obtain dewatered mixture.

[0014] The above technical solution introduces polyaluminum chloride and polyacrylamide, which can neutralize the negative charge on the surface of fine particles and form large flocs through bridging. Fly ash acts as a weighting agent to increase the density of flocs, accelerate the settling of ultrafine particles, and significantly reduce the turbidity of the effluent. By utilizing the principle of shallow sedimentation, the sedimentation path is shortened, the solid-liquid separation efficiency is improved, and the floor space required is reduced.

[0015] Furthermore, the excipients comprise the following raw materials in parts by weight: 100-110 parts silicate curing agent, 80-90 parts loess binder, 6-8 parts microbial inoculant; The microbial agents include: photosynthetic bacteria, Bacillus, nitrifying bacteria, denitrifying bacteria, and sulfur-oxidizing bacteria; Furthermore, the mass ratio of the dehydrated mixture to the auxiliary material is 3.5-4.0:1.

[0016] The beneficial effects of the above technical solution are as follows: The aforementioned technical solution incorporates a silicate curing agent, which hydrates to form a CSH gel that encapsulates sediment particles, physically sealing pollutants and providing compressive strength to resist water erosion. The loess binder, with its high specific surface area and cation exchange capacity, adsorbs ammonium ions, heavy metals, and other ionic pollutants, while increasing the matrix's cohesion and formability. Finally, microbial agents are colonized in the matrix pores, forming a "microbial-algae symbiotic" system that continuously degrades organic matter, converts nitrogen, and oxidizes sulfides, achieving biological purification of the sediment and water. Controlling the mass ratio of the dewatering mixture and auxiliary materials ensures the matrix has sufficient strength while retaining sufficient porosity, facilitating oxygen infiltration and microbial activity.

[0017] Furthermore, the silicate curing agent is ordinary silicate cement with a grade of not less than 42.5; The loess binder is selected from any one of kaolin, bentonite or attapulgite; and the particle size of the loess binder is ≤200 mesh.

[0018] Furthermore, in step S4, the particle size gradient is as follows: first, a first matrix with a particle size distribution of 5mm-1cm is applied to the surface of a cover layer formed in situ by coarse particles with a particle size greater than 75μm, and the thickness of the first matrix cover is 3cm-5cm; then, a second matrix with a particle size distribution of 1cm-3cm is applied to the surface of the first matrix, and the thickness of the second matrix cover is 5cm-10cm; finally, a third matrix with a particle size distribution of 3-5cm is applied to the surface of the second matrix, and the thickness of the third matrix cover is 5-10cm.

[0019] The beneficial effects of the above technical solution are as follows: Because the first matrix can form a particle size transition with the cover layer, it acts as an "active layer" for pollutant adsorption and microbial attachment, thereby reducing the particle size abrupt interface and preventing the "short-circuit" release of bottom pollutants; it provides a microenvironment for anaerobic / facultative anaerobic bacteria such as denitrifying bacteria; and it improves the degradation efficiency of bottom pollutants.

[0020] Medium-sized particles are used to construct a stable framework to resist water flow shear forces; large thickness forms a physical barrier to isolate bottom pollutants from spreading upwards to the overlying water; moderate porosity balances permeability and barrier properties; long-term stability of the mud-water interface is achieved, inhibiting bottom sediment resuspension; reducing the release flux of endogenous pollutants; and providing walking and habitat space for benthic animals (such as snails and clams). Finally, the large particle size creates an uneven surface structure, increasing water turbulence and oxygen exchange; the large blocks provide anchoring points to support the roots of submerged plants; it creates diverse microhabitats; it significantly improves water transparency (promoting photosynthesis in submerged plants); and it increases substrate heterogeneity, thereby enhancing benthic biodiversity.

[0021] Furthermore, the first matrix also includes 6-10% amorphous carbon by mass of the first matrix.

[0022] Furthermore, the specific surface area of ​​the amorphous carbon is 300-500 m² / g.

[0023] The beneficial effects of the above technical solution are as follows: Amorphous carbon, with its abundant porous structure, can efficiently capture TOC, ammonium ions, TP, and hydrophobic organic pollutants released from the bottom layer. When placed in the first matrix (closest to the pollution source), it can form an "in-situ adsorption barrier," intercepting pollutants on their upward migration path and reducing pollution exposure in the second and third matrices and overlying water. Moreover, the porous structure of amorphous carbon provides ideal attachment sites for microorganisms, protecting the microbial community from water erosion. The black surface of carbon absorbs solar radiation, which can slightly increase the bottom temperature in shallow water areas, promoting the activity of microorganisms and plant roots.

[0024] An integrated process for implementing the above-mentioned method for optimizing the particle size distribution of river and lake bottom sediments, with a supporting mobile equipment system, including an underwater washing and desorption equipment unit, an ultra-fine particle high-efficiency flocculation unit, a dehydration and solidification unit, an ecological restoration matrix processing and preparation unit, and a particle spreading and backfilling unit. Each unit is connected by a closed pipeline to achieve full-process on-site operation.

[0025] Furthermore, the underwater washing and desorption equipment unit includes: a spiral propulsion walking unit, a mud and water extraction pump and pipeline unit, a hydraulic screening chamber and keel frame unit, a return pump flushing unit, a stainless steel shell and curtain unit, and a remote control and camera unit.

[0026] The beneficial effects of this invention include: This invention achieves the synergistic goal of "pollution control, habitat construction, and landscape optimization" through a particle size stratification remediation strategy: small particle size components regulate gradation, medium particle size components stabilize the mud-water interface, and large particle size components create landscape structures. It also realizes a closed-loop process of "sediment washing-ecological resource utilization-substrate habitat restoration".

[0027] This optimized particle size distribution has a dual function: on the one hand, it facilitates oxygen infiltration into the substrate; on the other hand, it adsorbs and degrades bottom pollutants, thereby effectively reducing the release rate of pollutants to the overlying water. Based on this, an "algae-bacteria symbiosis" system can form on the surface of the ecological restoration substrate within 30 to 60 days. This system not only continuously purifies pollutants in the water and sediment but also meets the growth needs of submerged plants and benthic organisms, promoting the transformation of the water body from a turbid steady state to a clear steady state.

[0028] Furthermore, the ecological restoration substrate possesses an aerobic / anoxic / anaerobic active stratified structure from the outside in, providing a suitable growth environment for functional microorganisms that co-convert carbon, nitrogen, and sulfur (such as nitrifying and denitrifying bacteria, anaerobic ammonia-oxidizing bacteria, sulfur-autotrophic denitrifying bacteria, and sulfur-reducing bacteria). The substrate exhibits a significant controlled-release effect on organic pollutants, nitrogen and phosphorus nutrients, and sulfur-containing compounds in the sediment, further inhibiting the rate at which these pollutants are released into the overlying water.

[0029] Furthermore, this integrated equipment differs from traditional dredging and transportation equipment. Traditional dredging utilizes excavators and dump trucks. This solution employs a spiral-propelled underwater washing robot, which can flexibly adapt to complex terrains such as soft soil and silt. The equipment is miniaturized, measuring 1.7m × 1.2m × 0.8m (length × width × height), weighing ≤400kg, and suitable for narrow rivers with a width <2m, with a daily processing capacity of 1000-5000m³. 2 Treatment efficiency requirements. Traditional coagulation sedimentation is not effective in separating mud and water for extremely fine particles with a particle size of less than 75μm. High-efficiency flocculation co-sedimentation increases the capture and sedimentation of fine particles through weighting, resulting in effluent turbidity of less than 5 NTU. Multi-layer radial flow sedimentation tanks reduce bottom sludge sedimentation time by more than 2 / 3. Attached image description: Figure 1 This is a schematic diagram of the process principle corresponding to Embodiment 1 of the present invention.

[0030] Figure 2 This is a flowchart of the equipment corresponding to Embodiment 1 of the present invention.

[0031] Figure 3 This is a schematic diagram of the spiral propulsion underwater sediment washing robot used in Embodiment 1 of the present invention; wherein, 1-spiral propulsion walking unit, 2-sludge extraction pump and pipeline unit, 3-hydraulic screening chamber and keel frame unit, 4-return pump flushing unit, 5-stainless steel shell and curtain unit.

[0032] Figure 4 This is a structural diagram of the integrated high-efficiency flocculation co-precipitation and dewatering equipment used in Embodiment 1 of the present invention; wherein, 1-high-efficiency flocculation co-precipitation chemical preparation and dosing unit, 2-multi-layer radial flow sludge thickening unit, 3-mechanical dewatering unit, and 4-electrical control unit.

[0033] Figure 5 This is a structural diagram of the ecological restoration substrate processing and backfilling equipment used in Embodiment 1 of the present invention; wherein, 1-material mixing unit, 2-ecological restoration substrate pressing unit, 3-substrate centrifugal spreading unit, 4-air and dust purification unit, and 5-electrical control unit. Detailed Implementation

[0034] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0035] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0036] Example 1 This embodiment provides a method for optimizing the particle size distribution of river and lake bottom sediments. It is applied to a city river (approximately 1.2 km long, approximately 15 m wide on average, and 0.8-1.5 m deep). The sediment deposition thickness is approximately 0.4 m. In the top 0-30 cm sediment layer, fine particles with a particle size ≤75 μm account for approximately 65%, and the organic matter content reaches 45.6 g / kg, exhibiting a distinctly black and foul-smelling condition.

[0037] S1: Selective screening of fine-particle sediment A spiral-propelled underwater sediment washing robot (1.6m × 1.1m × 0.7m, weighing 380kg) moves underwater and disturbs the top 0-30cm layer of sediment. Particle size is classified through a hydraulic screening chamber, selectively extracting fine sediment particles ≤75μm in diameter, while retaining coarse particles >75μm to settle in situ and form a capping layer. The washing treatment area is approximately 18,000m², with a treatment cycle of 30 days, yielding approximately 9,000m³ of fine sediment particles (approximately 99% moisture content) ashore.

[0038] S2: High-efficiency flocculation sedimentation and dehydration The fine-particle sediment from the shore is transported to the onshore treatment system. First, polyaluminum chloride (PAC, 0.8% of the dry weight of the sludge), polyacrylamide (PAM, 0.05% of the dry weight of the sludge), and fly ash (3% of the dry weight of the sludge) are added to the sludge. After thorough mixing, flocculation and co-precipitation are carried out for concentration. The sludge then enters a multi-layer radial flow sludge thickening tank to reduce the moisture content to 75%. Finally, a screw press is used for dewatering at 0.7 MPa pressure, yielding dewatered sediment with a moisture content of 55%. Calculations show that the volume of wet sediment after dewatering is approximately 250 m³, representing a volume reduction of approximately 97.2%.

[0039] S3: Preparation of Ecological Restoration Matrix The dehydrated mixture and auxiliary materials were mixed at a mass ratio of 3.8:1. The auxiliary material ratio was as follows: 105 parts silicate curing agent (PO 42.5 ordinary silicate cement), 85 parts loess binder (kaolin, particle size ≤200 mesh), and 7 parts microbial inoculant. The microbial inoculant was a compound of photosynthetic bacteria, Bacillus, nitrifying bacteria, denitrifying bacteria, and sulfur-oxidizing bacteria in equal mass ratios. The mixture was then cured, stirred, and granulated to prepare ecological restoration substrates with three different particle sizes. First matrix: Particle size distribution 5mm-1cm; Second matrix: Particle size distribution 1cm-3cm; The third matrix has a particle size distribution of 3cm-5cm.

[0040] S4: Grain size gradient stratification coverage Three types of matrix were layered and re-applied to the riverbed surface according to particle size gradient: First, cover the surface of the coarse-particle in-situ cover layer with the first matrix (5mm-1cm), with a thickness of 4cm; Then cover the first substrate with a second substrate (1cm-3cm), with a thickness of 10cm; Finally, the third substrate (3cm-5cm) is placed on the outermost layer, with a thickness of 10cm.

[0041] After the covering was completed, the river channel was restored to flow.

[0042] Monitoring of treatment effectiveness: Monitoring results 30 days after treatment showed: The water transparency increased from 15-25cm before treatment to 65-80cm; The proportion of particles with a diameter of 75μm-10mm in the 0-30cm layer of the substrate increased from approximately 25% to 68%; The substrate porosity reached 42%, and the redox potential (ORP) increased from -120mV to 45mV; The TOC content in the sediment decreased from 45.6 g / kg to 8.2 g / kg, the TP content decreased from 1.8 g / kg to 0.6 g / kg, and the TN content decreased from 1.2 g / kg to 0.3 g / kg. On the 42nd day, a distinct "bacterial-algae symbiosis" biofilm formed on the substrate surface, and submerged plants such as *Hydrilla verticillata* and *Ceratophyllum demersum* germinated naturally.

[0043] Example 2 This embodiment is basically the same as Embodiment 1, except that in step S4, amorphous carbon is added to the first matrix.

[0044] Specifically, during the preparation of the first matrix, 8% by weight of amorphous carbon (rice husk-based biochar, specific surface area 420 m² / g, particle size ≤ 0.5 mm) was added to the first matrix. The remaining layering and covering parameters were the same as in Example 1.

[0045] Monitoring of treatment effectiveness: Monitoring results 30 days after treatment showed: The water transparency increased to 80-95cm, an improvement of approximately 20% compared to Example 1; The TOC content in the sediment decreased to 5.6 g / kg, TP decreased to 0.4 g / kg, and TN decreased to 0.2 g / kg, with pollutant residue levels reduced by 30-35% compared to Example 1; The formation time of the algal-microbe symbiotic system was shortened from 42 days to 28 days; The amount of microorganisms attached to the substrate surface increased by approximately 45% compared to Example 1, and the denitrification rate increased by approximately 35%. The AVS (acid volatile sulfur oxide) content in the bottom sediment decreased from 2.1 mg / g to 0.3 mg / g, resulting in a more thorough elimination of black and odorous substances.

[0046] Example 3 This embodiment is basically the same as Embodiment 2, except that the amount of amorphous carbon added and the specific surface area are different.

[0047] In this embodiment, the amount of amorphous carbon added is 6% of the total mass of the first matrix, and the specific surface area is 300 m² / g (corn cob-based biochar).

[0048] Monitoring of treatment effectiveness: Monitoring results 30 days after treatment showed: Water transparency increased to 75-88cm; The TOC content in the sediment decreased to 6.8 g / kg, TP decreased to 0.5 g / kg, and TN decreased to 0.25 g / kg. The formation time of the bacterial-algal symbiotic system is approximately 32 days; The matrix compressive strength test showed that the matrix with 6% amorphous carbon added had a compressive strength of about 0.62 MPa, which was slightly higher than that of Example 2 (0.55 MPa), indicating that the lower addition amount had less impact on strength.

[0049] Example 4 This embodiment is basically the same as Embodiment 2, except that the amount of amorphous carbon added is 10%, and the specific surface area is 500m² / g (coconut shell-based activated carbon).

[0050] Monitoring of treatment effectiveness: Monitoring results 30 days after treatment showed: The water transparency was improved to 82-98cm, which was the best among all the embodiments; The TOC content in the sediment decreased to 4.8 g / kg, TP decreased to 0.3 g / kg, and TN decreased to 0.15 g / kg, indicating the strongest adsorption effect on pollutants. The formation time of the bacterial-algal symbiotic system is approximately 26 days; However, the matrix compressive strength dropped to 0.48 MPa, slightly below the design threshold of 0.5 MPa, and the material cost increased compared to Example 2.

[0051] Comparative Example 1 A traditional cutter suction dredger was used to perform indiscriminate dredging of the same river section as in Example 1, with a dredging depth of 0.3-0.5m and a dredging area of ​​18,000m². The silt was then transported off-site for disposal.

[0052] Governance Results and Problems: During the dredging process, the mud-water interface was violently disturbed, and the turbidity of the overlying water reached a peak of 180 NTU, which remained turbid for about 15 days. A large amount of coarse particles with a diameter >75μm in the sediment were removed (accounting for about 40% of the total dredging volume), resulting in a waste of clean sand resources; The amount of silt brought ashore was approximately 15,000 m³ (with a water content of approximately 98%), an increase of approximately 67% compared to Example 1; The cost of off-site disposal is approximately RMB 180 / m³, with a total disposal cost of approximately RMB 2.7 million, which is 200% higher than that of Example 1 (approximately RMB 900,000). The bottom habitat was severely damaged after dredging, and the recovery period for benthic organisms exceeded 6 months. Three months later, the TOC in the bottom sediment was still 12.5 g / kg, the ORP was -85 mV, the water transparency was only 35-50 cm, and it was difficult for submerged plants to establish themselves.

[0053] Comparative Example 2 The process is basically the same as in Example 1, except that the S4 layered covering is not performed. Instead, the prepared ecological restoration matrix is ​​uniformly covered once, with a total covering thickness of about 38 cm.

[0054] Governance Results and Problems: Thirty days after covering, the water transparency was only 45-60cm, lower than that of Example 1 (65-80cm). The substrate porosity was only 28%, and the ORP was -15mV, so the improvement effect was limited. Pollutants released from the bottom layer are more likely to float to the surface through the gaps between large particles, resulting in a TOC removal rate that is about 25% lower than in Example 1. The substrate surface was flat and lacked habitat heterogeneity, with a benthic biodiversity index (Shannon-Wiener) of only 1.2, significantly lower than 2.1 in Example 1; Submerged plants germinate unevenly, growing only sporadically at the edges of large sections.

[0055] The above embodiments and comparative examples demonstrate that the method for optimizing the particle size distribution of river and lake sediments provided by the present invention, through an integrated process of "selective screening—mud-water separation—matrix preparation—particle size gradient coverage," particularly when a specific amount (6-10%) and a specific specific surface area (300-500 m² / g) of amorphous carbon are added to the first matrix, can significantly improve the removal efficiency of sediment pollutants, accelerate the establishment of a bacterial-algae symbiotic system, optimize the sediment habitat, and create favorable conditions for the restoration of submerged plants. This method is superior to traditional dredging processes and control schemes lacking key steps.

[0056] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for optimizing the particle size distribution of river and lake sediments, characterized in that, Includes the following steps: S1: Selective screening is used to obtain fine-grained sediment particles with a particle size of no more than 75 μm from the surface layer of river and lake bottoms, while coarse particles with a particle size of more than 75 μm are retained in situ to form a cover layer. S2: Fine-particle bottom sludge is subjected to flocculation co-precipitation, sludge thickening and mechanical dewatering in sequence to obtain dewatered bottom sludge with a moisture content of 50-60%. S3: After mixing the dehydrated sediment and auxiliary materials, stir evenly, and then press into granules to obtain an ecological restoration substrate with a particle size distribution of 5mm-5cm; S4: Apply the ecological restoration substrate to the riverbed surface in layers according to the particle size gradient to optimize the particle size distribution of the substrate.

2. The method for optimizing the particle size distribution of river and lake sediments according to claim 1, characterized in that, In step S1, the surface layer of the river or lake bottom is a region with a depth of 0-30cm.

3. The method for optimizing the particle size distribution of river and lake sediments according to claim 1, characterized in that, In step S2, the flocculation co-precipitation, sludge thickening, and mechanical dewatering include: adding polyaluminum chloride, polyacrylamide, and fly ash to fine-particle bottom sludge, stirring evenly, performing flocculation co-precipitation, then thickening the sludge through a multi-layer radial flow sludge thickening process to reduce the moisture content to 70-80%, and finally mechanically dewatering the sludge to a moisture content of 50-60% under a pressure of 0.6-0.8 MPa to obtain dewatered bottom sludge.

4. The method for optimizing the particle size distribution of river and lake sediments according to claim 1, characterized in that, The excipients comprise the following raw materials in parts by weight: 100-110 parts silicate curing agent, 80-90 parts loess binder, 6-8 parts microbial inoculant; The microbial agents include: photosynthetic bacteria, Bacillus, nitrifying bacteria, denitrifying bacteria, and sulfur-oxidizing bacteria; Furthermore, the mass ratio of the dewatered sediment to the auxiliary material is 3.5-4.0:

1.

5. The method for optimizing the particle size distribution of river and lake sediments according to claim 4, characterized in that, The silicate curing agent is ordinary silicate cement with a grade of not less than 42.5; The loess binder is selected from any one of kaolin, bentonite or attapulgite; and the particle size of the loess binder is ≤200 mesh.

6. The method for optimizing the particle size distribution of river and lake sediments according to claim 1, characterized in that, In step S4, the particle size gradient is as follows: first, a first matrix with a particle size distribution of 5mm-1cm is applied to the surface of a cover layer formed in situ by coarse particles with a particle size greater than 75μm, and the thickness of the first matrix is ​​3cm-5cm; then, a second matrix with a particle size distribution of 1cm-3cm is applied to the surface of the first matrix, and the thickness of the second matrix is ​​5cm-10cm; finally, a third matrix with a particle size distribution of 3-5cm is applied to the surface of the second matrix, and the thickness of the third matrix is ​​5-10cm.

7. The method for optimizing the particle size distribution of river and lake sediments according to claim 5, characterized in that, The first matrix also includes 6-10% amorphous carbon by mass of the first matrix.

8. The method for optimizing the particle size distribution of river and lake sediments according to claim 6, characterized in that, The specific surface area of ​​the amorphous carbon is 300-500 m² / g.

9. An integrated process for implementing the method for optimizing the particle size distribution of river and lake sediments as described in any one of claims 1-8, characterized in that, The system is equipped with a mobile integrated equipment system, including an underwater washing and dehydration unit, an ultra-fine particle high-efficiency flocculation and dewatering unit, an ecological restoration matrix processing and preparation unit, and a particle spreading and backfilling unit. Each unit is connected through a transmission system to achieve full-process on-site operation.

10. The integrated process for optimizing the particle size distribution of river and lake sediments according to claim 9, characterized in that, The underwater washing and desorption equipment unit includes: a spiral propulsion walking unit, a mud and water extraction pump and pipeline unit, a hydraulic screening chamber and keel frame unit, a return pump flushing unit, a stainless steel shell and curtain unit, and a remote control and camera unit.

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