In-situ remediation methods for riverbed sediment

Abstract

This invention belongs to the field of water environment management technology, specifically referring to a method for in-situ remediation of riverbed sediment. By adding remediation and solidifying agents to the sediment, sediment pollution is eliminated, establishing an ecological restoration zone for deteriorated and degraded sediment layers. Simultaneously, water pollution control measures are employed to construct a multi-level AO (anaerobic / aqueous) riverbed environment, enhancing the content and variety of functional microorganisms; forming a plant-based remediation zone and a shoreline buffer zone. This invention effectively solves the problems of recurring pollution and the inability to address river pollution at its source in existing technologies. It has advantages such as low investment, environmental friendliness, no secondary pollution, ecological sustainability, and addressing river pollution at its root.

Description

Technical Field

[0001] This invention belongs to the field of water environment management technology, and specifically refers to a method for in-situ treatment and remediation of riverbed sediment. Background Technology

[0002] In recent years, the state has gradually strengthened the management and control of river and lake basins, and has done a great deal of work in reducing land-based pollutant emissions. Pollutants in water bodies have decreased significantly, and the results are remarkable. However, eutrophication and other pollution phenomena still occur frequently in many water bodies. Bottom sediment is an important component of river ecosystems, but long-term pollution has turned it into a reservoir for pollutants such as nutrients, persistent organic matter, and heavy metals. Even if external pollution sources are effectively controlled, the release of pollutants from bottom sediment can still cause "secondary pollution" to water bodies.

[0003] Currently, the main approaches to treating contaminated sediment are ex-situ treatment and in-situ treatment. Ex-situ treatment primarily refers to sediment dredging, which is widely used in water environment management projects. This involves excavating the contaminated sediment, transporting it to a treatment site, treating it, and then landfilling it. However, in practice, it suffers from drawbacks such as high engineering costs, difficult construction, limited landfill space, and difficulty in controlling secondary pollution. In-situ treatment of sludge generally involves a single method of remediation using chemicals. While it provides rapid but not long-term treatment, pollution is prone to recurrence, and it only treats the sediment, failing to address the root cause of river pollution.

[0004] The applicant has not found any patent documents similar to this application in domestic patent databases. Summary of the Invention

[0005] The purpose of this invention is to eliminate sediment pollution by adding remediation and solidifying agents to the sediment, and to establish an ecological restoration zone for deteriorated and degraded sediment layers. At the same time, it is supplemented by water pollution control measures to construct a multi-level AO riverbed environment, enhance the content and types of functional microorganisms, and form a plant base restoration zone and shoreline buffer zone, so as to achieve the purpose of rebuilding sediment habitat and restoring sediment ecological function.

[0006] The overall technical concept of this invention is:

[0007] The in-situ remediation method for riverbed sediment includes the following steps: A. Collecting sediment samples from the riverbed to be treated and analyzing them to determine the pollution characteristics and depth; B. Diverting water from the riverbed to be treated and adding a sludge remediation agent to the sediment for remediation; wherein:

[0008] Step B involves adding sludge remediation agent to the deteriorated bottom sludge layer on the surface of the sediment, and then diverting the water into the river until the remediation is completed.

[0009] C. After the repair in step B is completed, the water in the river to be treated is diverted out, and the sludge solidification agent is mixed evenly with the sludge in the deteriorated bottom layer after the repair in step B.

[0010] D. Cover the surface of the deep degraded sediment layer with the repaired and solidified stabilized sediment to form a stabilized sediment layer; stack the surface degraded sediment layer sludge mixed with sludge solidifying agent in step C on the surface of the stabilized sediment layer to form spaced solidified base blocks and solidify them.

[0011] E. Micro-nano aeration tubes and immobilized microbial carriers are set on one side of the solidified substrate prepared in step D, and the river water to be restored is introduced into the river channel.

[0012] F. Construct a plant-based restoration zone and a shoreline buffer zone.

[0013] The applicant should clarify that, based on the degree of pollution, the riverbed sediment to be treated and remediated is divided into two layers from the outside in: a surface deteriorated sediment layer and a deep degraded sediment layer. The surface deteriorated sediment layer is the most severely polluted layer, ranging in color from black to dark black. Its upper part is slurry-like, while the lower part is fluid and plastic, emitting a foul odor. It is the main reservoir for endogenous pollutants. The deep degraded sediment layer is a less polluted layer, representing a gradual transition from normal to polluted sediment. Generally, in areas polluted by organic matter and nutrients, this layer is often grayish-black.

[0014] The specific technical concept of this invention also includes:

[0015] Studies have shown that nitrates can act as electron acceptors to improve the microenvironment of sediments and regulate the structure of sediment microbial communities, thereby improving sediment quality and enhancing water quality. The preferred technical approach involves using calcium nitrate slow-release agents as sludge remediation agents. The main function is to activate the activity of denitrifying bacteria. Heterotrophic denitrifying bacteria utilize nitrates as electron acceptors to degrade organic matter in the sediment, while autotrophic denitrifying bacteria use nitrates as electron acceptors to oxidize sulfides in the sediment. Simultaneously, the redox potential of the sediment rapidly increases, enhancing the overall reoxygenation capacity of the water body. The calcium ions released after the addition of calcium nitrate quickly bind to phosphorus free in the overlying water, reducing the total phosphorus content in the aqueous phase and forming relatively stable calcium-bound phosphorus in the sediment. This achieves the effect of eliminating black and odorous sediment and organic pollutants in the deteriorated surface sediment layer, while simultaneously fixing the nutrient element phosphorus in a stable form, forming stable sediment.

[0016] The main purpose of using calcium nitrate slow-release agent as sludge remediation agent is to achieve long-term remediation effect. A more preferred technical approach is to use calcium nitrate slow-release agent produced by the Institute of Microbiology, Guangdong Academy of Sciences, and add it to the deteriorated sludge layer on the surface at a dosage of 100-1000 grams per square meter for remediation.

[0017] Because the calcium nitrate slow-release agent has the highest release rate on the 4th day, and then slowly decreases until it decreases linearly after the 8th day, in order to obtain a better repair effect, and considering factors such as the release amount of calcium nitrate slow-release agent and treatment cost, the preferred technical implementation method is that the repair time in step B is 4 to 8 days.

[0018] To facilitate the mixing of sludge remediation agent with sludge, the preferred technical implementation is as follows: In step B, after the water from the river to be treated is drawn out, a floating platform and a grid are laid on the bottom sediment. A seeder is used to bury the sludge remediation agent into the deteriorated bottom sediment layer of the grid. The main function of the floating platform is to facilitate manual walking and operation, as well as equipment loading and transportation. The main function of the grid is to divide the sludge into areas of equal size so that the sludge remediation agent can be mixed evenly with it to achieve a more consistent remediation effect.

[0019] To facilitate the use of sludge remediation agents and achieve better remediation results, the preferred technical implementation is that, in step B, the sludge remediation agent is buried to a depth of 1 / 2 of the surface deteriorated bottom sludge layer.

[0020] The main function of the solidifying agent is to fully react with the bottom sludge to disrupt its colloidal properties, rapidly establishing and increasing capillary channels. This allows the solidifying agent and the free water in the sludge, as well as the water released during the breakdown of the sludge, to undergo hydrolysis and hydration reactions, producing a large amount of cementitious and chain-like crystalline substances. The sludge then forms a dense, porous, honeycomb-like structure. This physically isolates the water body from the deep degraded bottom layer, stabilizing the contaminated bottom sludge and preventing its resuspension or migration. This avoids the deep degraded bottom layer sludge from affecting the water body again, preventing repeated sludge pollution, and allowing microorganisms to exert a long-term remediation effect. A preferred technical implementation is that, in step C, the solidifying agent is a quicklime-slag composite solidifying agent, and the amount added is 3% to 5% of the mass of the remediated degraded surface bottom sludge.

[0021] To ensure that the solidified sludge maintains effective sludge strength and porosity, the preferred technical means is to achieve a solidified sludge strength of 150–180 kPa.

[0022] The main function of the stabilized bottom sludge remaining on the surface of the deep degraded bottom sludge in the river channel is to isolate the water body from the deep degraded bottom sludge. The main function of the solidified substrate is to raise and solidify the substrate of the remediated surface deteriorated bottom sludge, forming a high-low-high-low wavy ecological substrate. At the same time, the solidified substrate blocks in step D are distributed in parallel at intervals, and the solidified substrate blocks are in the form of raised blocks and / or raised strips.

[0023] To reduce the impact of surface sludge and water on deep sludge, the preferred technical approach is that, in step D, a 5 cm thick layer of solidified and repaired stable bottom sludge is applied to the surface of the deep degraded bottom sludge layer to form a stable bottom sludge layer.

[0024] Immobilized microbial carriers are constructed by immobilizing over 80 strains of bacteria from 16 genera, including photosynthetic bacteria, yeast, lactic acid bacteria, actinomycetes, and fermentative filamentous fungi, onto a silicon-based ultraporous microbial carrier using high-density enzyme immobilization technology. The immobilized microbial carriers, combined with an aerobic environment, promote the reproduction and maintenance of dominant bacterial species, effectively improving the microbial community in the sediment. The solidified substrate, along with the immobilized microbial carriers and micro / nano aeration pipes, forms an alternating anaerobic-aerobic-anaerobic substrate environment, constructing a multi-stage AO (anaerobic-aerobic) treatment process for water bodies. This achieves dual purification of both water and sediment, ensuring a healthy ecological environment at the bottom of the river. To achieve the above objectives, a preferred technical means is that the immobilized microbial carriers in step E are produced by Fujian Bayer Biotechnology Co., Ltd. The immobilized microbial carriers are placed in a porous reactor and added at a mass ratio of 1:1000 to 5000 of the immobilized microbial carriers to the water in the area.

[0025] The main function of the solidified substrate side of the micro-nano aeration tube is to form an anaerobic-aerobic-anaerobic environment to meet the growth of microorganisms. The preferred technical means is that the solidified substrate side with the micro-nano aeration tube in step E is an aerobic zone, and the dissolved oxygen concentration in the aerobic zone is not less than 7 mg / L.

[0026] The main function of constructing plant substrate remediation zones and shoreline buffer zones is to form a stable microbial-plant ecological environment and improve the water body and bottom sediment's resistance to shock loads. The preferred technical means is that, in step F, constructing plant substrate remediation zones involves planting submerged plants in the deep degraded bottom sediment layer sludge under the stable bottom sediment layer sludge, and constructing shoreline buffer zones involves planting emergent plants on the riverbank.

[0027] Since the sludge remediation agent, solidifying agent and immobilized biological carrier in this application are all mature technologies and commercially available products, the applicant will not elaborate on their technical contents here.

[0028] The essential features and significant technical advancements of this invention are as follows:

[0029] 1. This invention uses a combination of chemical, physical, and biological methods to treat and remediate contaminated sediment in situ. Compared with commonly used ex-situ treatment methods such as dredging, it has lower investment costs, is more environmentally friendly, produces no secondary pollution, and is ecologically sustainable.

[0030] 2. This invention adds a remedial agent and a solidifying agent to the bottom sediment, which transforms the deteriorated surface sediment layer into a stable sediment and solidifies it into a solidified block. This physically isolates the water body from the deep degraded sediment layer, thereby stabilizing the polluted sediment and preventing it from re-suspension or migration. This avoids the deep degraded sediment layer from affecting the water body again and causing repeated sediment pollution.

[0031] 3. This invention, while treating bottom sediment, also incorporates aquatic ecological restoration technology. It solidifies the substrate to form a high-low-high-low wavy base on the river / lake bottom, using immobilized microbial carriers and a micro-nano aeration system to construct an alternating anaerobic-aerobic substrate environment and microbial community. This not only facilitates the dual restoration and purification of both bottom sediment and water, but also addresses the root causes of river pollution.

[0032] 4. Plant aquatic plants on the wavy base and riverbank to create a plant base restoration zone and shoreline buffer zone, so that the river channel as a whole forms a stable microbial-plant ecosystem and improves the river water and bottom sediment's resistance to shock loads.

[0033] 5. The applicant's experiments have confirmed that the method of this invention significantly reduces organic matter, total phosphorus, and total nitrogen compared to the original river treatment and restoration. Specifically, the organic matter content of the sludge in the deteriorated surface geological layer is reduced by 62%, and the total nitrogen and total phosphorus content is reduced by 90%. After 20 days of restoration and purification, the water quality indicators are close to the Class IV standard for surface water, which meets the environmental protection standards. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments, but it should not be construed as limiting the present invention. The scope of protection of the present invention shall be determined by the contents of the claims. Any equivalent technical means substitution made in accordance with the specification shall not depart from the scope of protection of the present invention.

[0035] The overall method of this embodiment is as follows: a method for in-situ treatment and remediation of riverbed sediment, including the following steps:

[0036] A. Collect sediment samples from the river channel to be treated and test them to determine the pollution characteristics and depth of the sediment;

[0037] B. Drain the water from the river to be treated to a bypass or temporary storage tank. Lay floating platforms and grids on the bottom sediment. Use a seeder to bury the sludge remediation agent into the deteriorated bottom sediment sludge inside the grids. Then, introduce the water from the river to be treated into the river until the remediation is completed. The sludge remediation agent used is calcium nitrate slow-release agent produced by the Institute of Microbiology, Guangdong Academy of Sciences. Add the calcium nitrate slow-release agent to the deteriorated bottom sediment sludge at a dosage of 100-1000 grams per square meter for remediation. The remediation time in step B is 4-8 days, and the depth of the sludge remediation agent added to the deteriorated bottom sediment sludge is 1 / 2.

[0038] C. After the repair in step B is completed, the water in the river to be treated is diverted out, and the sludge solidifying agent is mixed evenly with the sludge of the deteriorated surface bottom layer after repair in step B. The solidifying agent is a quicklime-slag composite solidifying agent. The amount of solidifying agent added is 3% to 5% of the mass of the sludge of the deteriorated surface bottom layer after repair. The strength of the solidified sludge is 150 to 180 kPa.

[0039] D. After covering the surface of the deep degraded bottom sludge layer with a 5 cm thick layer of solidified and repaired stable bottom sludge, a stable bottom sludge layer is formed. On the surface of the stable bottom sludge layer, the surface degraded bottom sludge layer mixed with sludge solidifying agent in step C is stacked to form spaced solidified base blocks and solidified. The solidified base blocks in step D are spaced parallel and have a raised truncated quadrangular shape.

[0040] E. Micro-nano aeration pipes and immobilized microbial carriers are set on one side of the solidified substrate prepared in step D, and the river water to be restored is introduced into the river channel; the immobilized microbial carriers are produced by Fujian Bayer Biotechnology Co., Ltd., and the immobilized microbial carriers are placed in a porous reactor and added at a mass ratio of 1:1000 to 5000 of the immobilized microbial carriers to the water in the area; the side of the solidified substrate with micro-nano aeration pipes in step E is the aerobic zone, and the dissolved oxygen concentration in the aerobic zone is not less than 7 mg / L;

[0041] F. Constructing a plant substrate restoration zone and a shoreline buffer zone. In step F, constructing a plant substrate restoration zone involves planting submerged plants, such as Vallisneria natans, Ceratophyllum demersum, and Elodea nuttallii, in the deep degraded sedimentary sludge layer beneath the stable sedimentary sludge layer at the bottom of the river. Constructing a shoreline buffer zone involves planting emergent plants, such as reeds, on the riverbank.

[0042] To verify the technical effects achieved in this embodiment, the applicant conducted the following simulation experiment:

[0043] I. Experiment Location: Laboratory of Hebei Tianda Environmental Research Institute Co., Ltd.

[0044] II. Experiment Time: May 2024

[0045] III. Experimental Personnel: Zhong Huan, Hou Yimiao

[0046] IV. Experimental Objective: To simulate the treatment and restoration process of riverbed sediment and water using the method of this invention, to verify its treatment and restoration effect, and to compare it with the original water and sediment of black and odorous rivers.

[0047] V. Detection Methods: Total nitrogen in sediment was determined using the alkaline potassium persulfate digestion ultraviolet spectrophotometric method; total phosphorus in sediment was determined using the "Alkali Fusion-Molybdenum Antimony Anti-Spectrophotometric Method" (HJ 632-2011); organic matter content was determined using standard NY / T85-1988; sludge moisture content was determined using the Lechter LXT-800 new generation sludge moisture meter; dissolved oxygen (DO) and oxidation-reduction potential (ORP) were determined using the YSIProPlus multi-parameter portable water quality analyzer; ammonium nitrogen (NH4) in the water was determined... + Total nitrogen (TN), total phosphorus (TP), total nitrogen (TN), and chemical oxygen demand (COD) were determined according to the methods described in the national environmental protection standards HJ 535-2009, HJ 671-2013, HJ 636-2012, and HJ 828-2017, respectively.

[0048] VI. Experimental Procedure:

[0049] 1. A column sampler was used to collect water samples from a black and odorous river, as well as sediment samples from the surface deteriorated sediment layer (0-25cm) and the deep degraded sediment layer (25-40cm). The samples were then placed in an 8L glass container in the original stratification order and left to stand for 24 hours to simulate the black and odorous river water and sediment environment in this experiment.

[0050] 2. Extract the raw water from the glass container and add calcium nitrate slow-release agent to the deteriorated bottom sediment layer at a dosage of 1000 grams per square meter. The calcium nitrate slow-release agent is a product produced by the Institute of Microbiology, Guangdong Academy of Sciences. Refill the extracted raw water into the glass container. The reaction time between the repair agent and the bottom sediment and water is 8 days.

[0051] 3. After the reaction in step 2 is completed, the water in the glass container will be extracted again. Add 3% sludge solidifying agent to the deteriorated bottom sediment layer and mix evenly. The solidifying agent is a quicklime-slag composite solidifying agent. After curing for 6 days under laboratory conditions, the reaction will continue until the solidified sludge strength is 150-180 kPa. Cover the surface of the deep degraded bottom sediment layer with a 5 cm thick layer of solidified and repaired stable bottom sediment to form a stable bottom sediment layer. Stack the solidified surface deteriorated bottom sediment layer sludge on the surface of the stable bottom sediment layer to form spaced solidified base blocks. The solidified base blocks are in the shape of a truncated pyramid.

[0052] 4. Micro-nano aeration pipes and immobilized microbial carriers are set on one side of the solidified substrate. At the same time, goldfish algae and withered grass are transplanted to the restored stable bottom sediment layer to form a plant substrate restoration zone. The pumped water is introduced and the changes in the bottom sediment in the glass container are observed and the water quality is tested after 20 days of plant-biological purification.

[0053] Relevant parameters of the deteriorated bottom sediment layer of the original river channel:

[0054] parameter numerical values ORP -410 millivolts Organic matter content 11.3％ Moisture content 90.5％ Total phosphorus 4760 mg / kg Total nitrogen 3450 mg / kg

[0055] The raw water from the black and smelly river:

[0056] parameter numerical values DO 0.45 mg / L ORP -256 millivolts C0D 71 mg / L Total phosphorus 0.79 mg / L Total nitrogen 13.8 mg / L

[0057] Experimental results:

[0058] After the calcium nitrate slow-release agent repaired the deteriorated surface sediment layer (i.e., after step 1), the sediment color changed from grayish-black to yellowish-brown. Relevant parameters of the deteriorated surface sediment layer are as follows:

[0059] parameter numerical values ORP +46 millivolts Organic matter content 4.3％ Moisture content 89.5％ Total phosphorus 410 mg / kg Total nitrogen 305 mg / kg

[0060] Water quality indicators after riverbed sediment and water body treatment and restoration:

[0061] parameter numerical values DO 4.89 mg / L ORP 116 millivolts C0D 30 mg / L Total phosphorus 0.37 mg / L Total nitrogen 2.3 mg / L

[0062] The experimental results show that the technical solution described in this invention has a good effect on the treatment and restoration of bottom sediment and water bodies. The organic matter content of the sludge in the deteriorated surface geological layer is reduced by 62%, and the total nitrogen and total phosphorus content is reduced by 90%. After 20 days of remediation and purification, the water quality indicators are close to the Class IV standard for surface water.

Claims

1. In-situ remediation methods for riverbed sediment, including the following steps: A. Collect sediment samples from the river channel to be treated and test them to determine the pollution characteristics and depth of the sediment; B. The water from the river to be treated is diverted, and a sludge remediation agent is added to the bottom sediment for remediation; characterized in that: Step B involves adding sludge remediation agent to the deteriorated bottom sludge layer on the surface of the sediment, and then diverting the water into the river until the remediation is completed. C. After the repair in step B is completed, the water in the river to be treated is diverted out, and the sludge solidification agent is mixed evenly with the sludge in the deteriorated bottom layer after the repair in step B. D. After step C, the stabilized sediment is covered on the surface of the deep degraded sediment layer to form a stable sediment layer. The surface of the stable sediment layer is stacked to form spaced solidified blocks and then solidified. The solidified blocks are spaced parallel to each other and are in the form of raised blocks and / or raised strips. E. Micro-nano aeration tubes and immobilized microbial carriers are set on one side of the solidified substrate prepared in step D, and the river water to be restored is introduced into the river channel. F. Construct a plant-based restoration zone and a shoreline buffer zone.

2. The method for in-situ treatment and remediation of riverbed sediment according to claim 1, characterized in that... In step B, calcium nitrate slow-release agent is selected as the sludge remediation agent.

3. The method for in-situ treatment and remediation of riverbed sediment according to claim 2, characterized in that... The sludge remediation agent used is calcium nitrate slow-release agent produced by the Institute of Microbiology, Guangdong Academy of Sciences. The calcium nitrate slow-release agent is added to the deteriorated bottom sludge layer at a dosage of 100-1000 grams per square meter for remediation.

4. The method for in-situ treatment and remediation of riverbed sediment according to claim 3, characterized in that... The repair time in step B is 4 to 8 days.

5. The method for in-situ treatment and remediation of riverbed sediment according to any one of claims 1 to 4, characterized in that... In step B, after the water from the river to be treated is diverted out, floating platforms and bar screens are laid on the bottom sediment, and a seeder is used to bury the sludge remediation agent into the deteriorated bottom sediment layer inside the bar screen.

6. The method for in-situ treatment and remediation of riverbed sediment according to claim 5, characterized in that... In step B, the sludge remediation agent is buried to a depth of 1 / 2 of the surface deteriorated bottom sludge layer.

7. The method for in-situ treatment and remediation of riverbed sediment according to claim 1, characterized in that... In step C, the curing agent is a quicklime-slag composite curing agent, and the amount of curing agent added is 3% to 5% of the mass of the deteriorated sludge layer on the surface after repair.

8. The method for in-situ treatment and remediation of riverbed sediment according to claim 1 or 7, characterized in that... The strength of the solidified sludge in step C is 150–180 kPa.

9. The method for in-situ treatment and remediation of riverbed sediment according to claim 1, characterized in that... In step D, a 5-centimeter-thick layer of solidified and repaired stable sediment is applied to the surface of the deep degraded sediment layer to form a stable sediment layer.

10. The method for in-situ treatment and remediation of riverbed sediment according to claim 1, characterized in that... The immobilized microbial carrier in step E is produced by Fujian Bayer Biotechnology Co., Ltd. The immobilized microbial carrier is placed in a porous reactor and added at a mass ratio of 1:1000 to 5000 of the immobilized microbial carrier to the water in the area.

11. The method for in-situ remediation of riverbed sediment according to claim 1 or 10, characterized in that... In step E, the solidified substrate with micro-nano aeration tubes is located on one side as an aerobic zone, and the dissolved oxygen concentration in this aerobic zone is not less than 7 mg / L.

12. The method for in-situ remediation of riverbed sediment according to claim 1, characterized in that... In step F, the construction of the plant substrate remediation zone involves planting submerged plants in the deep degraded sediment layer beneath the stable sediment layer of the riverbed, while the construction of the shoreline buffer zone involves planting emergent plants on the riverbank.