Method for resourcefully treating dredged sludge in rivers and lakes by combining flocculation-mesh electroosmosis with ardealite and construction waste

Abstract

The invention discloses a method for resourcefully treating dredged sludge in rivers and lakes by combining flocculation-mesh electroosmosis with ardealite and construction wastes, and belongs to the technical field of comprehensive treatment of solid wastes. The method comprises the following steps: carrying out electroosmosis treatment on dredged sludge, and curing the treated sludge by using construction waste and phosphogypsum as curing agents to obtain recyclable cured sludge which can be used as flood control road and embankment top road filler and other projects. The construction waste and the ardealite are used as curing agents to be applied to the technical field of river dredging sludge, only a small amount of construction waste and ardealite need to be added after electroosmosis, resource recycling is achieved through the two solid waste materials, resources are rich, and compared with a traditional cement lime curing agent, the curing agent is more economical and environmentally friendly. The method provided by the invention is an efficient and environment-friendly river and lake dredged sludge treatment technology, has remarkable environmental benefits and economic benefits, and provides a new thought and solution for comprehensive treatment of solid wastes.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive solid waste treatment technology, specifically relating to a method for the resource-based treatment of river and lake dredging sludge by combining flocculation-network electroosmosis with phosphogypsum and construction waste. Background Technology

[0002] With the acceleration of urbanization in China, river dredging projects have generated a large amount of silt. Dredged silt is a suspended system composed of water, bentonite particles, clay particles, and additives, existing in a liquid-solid state. Due to its high water content, high compressibility, high fluidity, and low strength, dredged silt treatment is time-consuming and costly, wasting resources and posing a threat to the environment. Therefore, there is an urgent need to develop an environmentally friendly river dredged silt treatment technology.

[0003] To address the challenges of treating dredged silt from rivers, numerous drainage consolidation engineering technologies have emerged, such as physical consolidation (surcharge preloading and vacuum preloading) and chemical consolidation (solidifying agents and electroosmosis). Physical consolidation requires applying loads to the site, but due to the low initial strength of the silt, it's difficult to install conventional equipment, leading to clogging and poor drainage. Furthermore, it only removes free water, making it difficult to remove bound water, resulting in poor overall treatment efficiency. Traditional chemical solidification materials, such as cement and lime, are effective for silt with low water content; however, they are ineffective with silt with high water content, and their large quantities and high costs can easily cause environmental pollution. Traditional single electroosmosis methods suffer from high energy consumption and poor later-stage consolidation. Traditional electroosmosis devices use a single electrode plate arrangement, but this is ineffective in large treatment tanks, and unreasonable arrangement leads to high energy consumption and poor drainage.

[0004] Construction waste refers to the excavated soil, materials, and other solid waste generated during the construction, renovation, expansion, and demolition of various buildings, structures, and pipelines, as well as during the decoration and renovation of homes. The indiscriminate dumping of construction waste occupies large amounts of land, hinders land reuse, and exacerbates land resource scarcity.

[0005] Phosphogypsum is a solid waste generated during the wet-process phosphoric acid production. It is a byproduct of the decomposition of phosphate rock by sulfuric acid in phosphoric acid production. Phosphogypsum is mainly composed of calcium phosphate, containing small amounts of other oxide impurities. Specifically, the main component of phosphogypsum is calcium sulfate dihydrate (CaSO4·2H2O), obtained during the dehydration reaction in the wet-process phosphate production process. Currently, most phosphogypsum is still stored in open-air stockpiles.

[0006] Currently, the utilization of construction waste and phosphogypsum is quite difficult and limited in scale. The main problems are that phosphogypsum has low chemical activity as a cementitious material, making it difficult to dissolve in cement systems and participate in pozzolanic reactions. Furthermore, phosphogypsum contains acidic impurities, which significantly negatively impact the early strength of cement-cured materials. Additionally, waste dredged sludge has a high liquid limit and high clay content, making it unsuitable for use as compacted roadbed fill, resulting in significant springy soil problems. As a fluid fill material, it often fails to meet the requirements for fluidity and self-compacting properties due to insufficient moisture content. Summary of the Invention

[0007] To address the problems of existing technologies that fail to effectively utilize industrial wastes such as phosphogypsum and construction waste, as well as abandoned dredged sludge, occupying large storage areas, incurring high processing costs, and causing environmental pollution, this invention provides a method for the resource-based treatment of river and lake dredged sludge by combining flocculation-network electroosmosis solidification with phosphogypsum and construction waste.

[0008] This invention provides the following technical solutions: A method for the resource-based treatment of river and lake dredged sludge using a combination of flocculation-reticulated electroosmosis solidification and phosphogypsum with construction waste, the method comprising: (1) Collect dredged sludge on site, filter out floating impurities and large solids, let it stand or perform simple dehydration to reduce the initial moisture content to about 90% ± 5%, and obtain pretreated sludge; (2) The pretreated sludge is filled into the mesh electroosmosis device for electroosmosis treatment, and flocculant is added before electroosmosis begins. After stirring at low speed, the device is powered on. (3) The sludge treated by electroosmosis is mixed with solid waste solidifying agent to form a solidified mixture, and then molded and cured to obtain recyclable solidified sludge; The solid waste solidifying agent is a mixture of phosphogypsum, construction waste, and dry cement powder.

[0009] Furthermore, the flocculant is polyacrylamide.

[0010] Furthermore, the amount of flocculant added is 0.10%-0.20% of the dry weight of the silt.

[0011] Furthermore, the electroosmosis time is 8-24 hours. The specific electroosmosis time is determined based on the initial power and expected effect. This fully utilizes the advantages of the early stage of electroosmosis, saves energy, effectively reduces moisture content, facilitates the later solidification of solid waste materials, reduces the amount of solidifying agent used, and saves costs overall.

[0012] Furthermore, the solid waste solidifying agent comprises the following parts by weight: 20-30 parts phosphogypsum, 30-50 parts construction waste, and 10-20 parts dry cement powder. Using the above formula, the amount of solidifying agent can be further reduced on the basis of electroosmosis, saving costs and significantly increasing the strength of the solidified sludge.

[0013] Furthermore, the dosage of the solid waste solidifying agent is 5% to 12% of the total mass of the sludge after electroosmosis treatment.

[0014] Furthermore, the phosphogypsum is obtained by crushing and screening compacted phosphogypsum from the stockpile, with a particle size of 20–110 μm; the construction waste is obtained by crushing and screening compacted construction waste from the stockpile, with a particle size of 2–10 mm.

[0015] Furthermore, the mesh electroosmosis device includes a sludge tank, a drainage tank, an electrode plate, and a DC power supply. The electrode plate includes an anode plate and a cathode plate disposed on both sides of the soil sample tank. The anode plate and the cathode plate are respectively connected to the DC power supply through wires. The electroosmosis treatment refers to turning on the DC power supply to allow water in the solidified sludge to flow from the anode to the cathode and then be discharged.

[0016] Furthermore, adjacent anode plates and cathode plates are arranged alternately to form a grid-like electrode array with multiple rows and columns on the plane.

[0017] Furthermore, the anode plate and cathode plate are made of stainless steel. Due to the presence of electrochemical effects, the anode electrode will experience severe corrosion when current is applied to the electrode, while stainless steel electrode plates can effectively prevent electrode corrosion and reduce the cost of electroosmosis construction.

[0018] Furthermore, the cathode electrode plate is uniformly perforated with a hole diameter of 5mm to facilitate electroosmotic drainage.

[0019] More preferably, the outer layer of the cathode electrode plate is wrapped with short-fiber needle-punched nonwoven polyester fiber geotextile as a filter layer, which can prevent clay particles from clogging the drainage channel and facilitate the secondary use of electro-osmotic drainage.

[0020] In this invention, the mesh electroosmosis device includes an indoor electroosmosis device and an outdoor electroosmosis device. The indoor electroosmosis device is used for process verification and parameter optimization, while the outdoor electroosmosis device is used for pilot-scale and engineering treatment.

[0021] like Figure 2As shown, the indoor mesh electroosmosis device includes an anode plate 1, a cathode plate 2, a model box 3, a drainage trough 4, an oscilloscope 5, a DC power supply 6, and a pump 7. The model box 3 is a rectangular box used to hold pretreated dredged sludge, with an outlet on one side of its bottom connected to the drainage trough. Both the anode plate 1 and cathode plate 2 are made of stainless steel flat electrodes, vertically inserted into the sludge, and spaced apart along the length of the model box 3. Adjacent anode and cathode plates are arranged alternately, forming a multi-row, multi-column mesh electrode array on a plane. The cathode plate 2 has evenly spaced circular holes with a diameter of approximately 5 mm. The outer side of the cathode plate 2 is covered with short-fiber needle-punched nonwoven polyester geotextile as a filter layer to prevent fine particles from clogging the drainage holes. The drainage trough 4 is connected to the model box 3 through an outlet at the bottom of the box and is used to collect water discharged from the cathode side during electroosmosis. The discharged water flows into a collection container for subsequent water quality testing and reuse. The positive terminal of DC power supply 6 is connected to the anode plate via a wire, and the negative terminal is connected to the cathode plate via a wire, forming a closed circuit. The indoor electroosmotic model uses a DC power supply with a limit of 25 V and 1 A, and the cross-sectional area of ​​the wire is approximately 2 mm² to meet the power requirements of the indoor model test.

[0022] The outdoor mesh electroosmosis system is located on open ground near the river channel and includes a treatment tank, anode plates, cathode plates, drainage ditches, a collection well, a DC power supply, and transmission lines. The treatment tank is enclosed by a dike or simple retaining structure, forming a rectangular tank to hold a large amount of dredged sludge. Several drainage ditches are arranged along the length of the tank at its bottom. The anode and cathode plates are made of stainless steel plates, inserted into the sludge in a staggered pattern. Adjacent anode and cathode plates are arranged in a grid pattern on the plane, forming multi-level electric field channels. The cathode plates have evenly spaced holes (approximately 5 mm in diameter) on the side closest to the drainage ditch, and are wrapped with short-fiber needle-punched polyester geotextile to prevent clogging. The bottom of the cathode plate is connected to the drainage ditch, allowing water to migrate to the cathode under the influence of the electric field, then enter the drainage ditch through the drainage holes, and finally flow into the collection well. The outdoor electroosmosis system uses a DC power supply limited to 220 V and approximately 1 A, with a matching conductor cross-sectional area of ​​approximately 5 mm² to meet the power requirements of the large-volume treatment tank. The collection well is connected to an external pipeline via a pumping device, which facilitates the testing of the drainage water quality and enables its reuse.

[0023] More preferably, when the electroosmotic treatment tank is an indoor model box, it uses a DC power supply with a limit of 25V and 1A and a cross-sectional area of ​​2mm². 2 The copper wires are used. Since the model box required for indoor electroosmosis is relatively small, the above-mentioned DC power supply and copper wires are sufficient to complete the electroosmosis treatment.

[0024] More preferably, when the electroosmosis treatment is performed on an open area near an outdoor river channel, a DC power supply with a limit of 220V and 1A and a 5mm diameter are used. 2Copper wires were used. Due to the large outdoor open space and the high power required for electroosmosis, a DC power supply with higher limits and larger diameter copper wires were used to complete the electroosmosis treatment more quickly.

[0025] In a further preferred embodiment, when the electroosmosis treatment is performed on an open area near an outdoor river, a grid-like staggered electrode arrangement method is adopted, with multiple electric field directions forming multiple migration paths, and water migrates from the anode to the cathode under the action of the electric field.

[0026] The indoor electroosmosis device is used for process verification and parameter optimization. The DC power supply is limited to 25 V and 1 A; the conductor cross-sectional area is approximately 2 mm²; stainless steel anode / cathode plates are used, with the cathode plate having 5 mm uniform perforations and an outer layer of short-fiber needle-punched polyester geotextile as a filter layer; typical electroosmosis time is 8–24 hours. The target moisture content is controlled at 55%–65%. The outdoor electroosmosis device is used for pilot-scale and engineering treatment. The electrodes are arranged in a grid pattern to create multi-path migration; the DC power supply is limited to 220 V and approximately 1 A; the conductor cross-sectional area is approximately 5 mm²; drainage channels are connected to water collection devices for easy pumping and water quality monitoring; typical electroosmosis time is 8–24 hours. The target moisture content is controlled at 60% ± 5% to meet the requirements of subsequent curing mixing and paving construction.

[0027] Dredged silt is removed from the riverbed, and most of the free water is filtered out, reducing its moisture content to 90%. This effectively reduces electroosmosis time, energy consumption, and the amount of solid waste solidifying agent required. Once the silt reaches the desired moisture content, it is fed into a mesh electroosmosis device for treatment. Under the influence of an electric field, cations move towards the cathode in the diffused double layer, carrying a certain amount of water, and are discharged through the pores of the cathode electroosmosis plate. This method overcomes the limitation of traditional drainage consolidation technology, which can only discharge free water, allowing some weakly bound water to escape the electrostatic field and be effectively discharged, significantly improving drainage efficiency.

[0028] This invention rapidly reduces the moisture content of dredged river silt using electroosmosis technology. After electroosmosis, fine aggregates of phosphogypsum and coarse aggregates of construction waste are used to fill the pores of the silt, resulting in uniform solidification. The advantages of this invention are that the reinforcement effect can be tested in laboratory settings, and it can be applied on a large scale to open areas near dredged river silt. Construction waste and phosphogypsum, as solid waste materials, are readily available and locally sourced. Furthermore, the amount of solidification material required after electroosmosis is small, making construction convenient. This verifies the effectiveness of this invention in treating dredged river and lake silt through electroosmosis solidification combined with phosphogypsum and construction waste, achieving both drainage reduction and stabilization.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention uses industrial waste as the main raw material for sludge solidification agent. Phosphogypsum and construction waste are sourced locally, which facilitates resource recycling. The SiO2 and Al2O3 in these materials undergo a hydration reaction with water in the sludge under alkaline conditions to generate hydrated calcium silicate gel and ettringite crystals, converting a large amount of free water into bound water, significantly reducing the water content of the sludge, and rapidly improving the strength of solidified river sludge.

[0030] 2) The overall approach employs a pre-electroosmosis followed by solidification technology. The electroosmosis time is 8-24 hours, and the wastewater after electroosmosis can be directly discharged or reused after passing water quality testing. The solidification curing time is 28 days, resulting in a short overall construction period. The solidification strength meets the standards for reuse, making it widely applicable to flood control roads and embankment roadbed filling projects. Furthermore, the significantly reduced moisture content after electroosmosis substantially decreases the amount of solid waste solidification agent required, saving costs and improving treatment efficiency.

[0031] 3) The electroosmosis tests were conducted in both an indoor model chamber and an outdoor treatment pond near the river, demonstrating strong engineering practicality. Different limits of DC power supplies were used to fully leverage the advantages of the initial stages of electroosmosis. This effectively reduced the water content of the sludge while significantly saving energy, creating favorable conditions for subsequent solidification treatment using solid waste materials.

[0032] 4) The electrodes in the outdoor electroosmosis treatment tank are arranged in a grid pattern to form multiple water migration paths. The drainage trough is connected to the water collection device through pipes, which facilitates the collection and reuse of the drained water, significantly improving drainage efficiency and reducing electroosmosis energy consumption. Attached Figure Description

[0033] Figure 1 This is a flowchart of a method for the resource-based treatment of river and lake dredged sludge using electroosmosis solidification combined with phosphogypsum and construction waste.

[0034] Figure 2 This is the front view of the indoor electroosmosis device.

[0035] Figure 3 This is a top view of an indoor electroosmosis device.

[0036] Figure 4 This is a top view of the outdoor electroosmosis unit.

[0037] Figure 5 This is a bottom view of the outdoor electroosmosis system. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the embodiments are only specific illustrations of the invention and should not be regarded as limitations on the invention. The purpose of the embodiments is to enable those skilled in the art to better understand and reproduce the technical solution of the present invention. The scope of protection of the present invention should still be determined by the scope defined in the claims. Example

[0039] This embodiment provides a method for the resource-based treatment of river and lake dredged sludge using a combination of flocculation-network electroosmosis and phosphogypsum with construction waste, such as... Figure 1 As shown. The method includes: S1. Collect dredged sludge on-site, filter to remove floating impurities and large solids, let it stand / dehydrate briefly to reduce the initial moisture content to about 90%, and obtain pretreated sludge.

[0040] S2, add the pretreated sludge into the mesh electroosmosis device and electroosmosis for 24 h; to accelerate floc formation and reduce resistivity, add anionic polyacrylamide flocculant (0.10% of dry soil mass) before electroosmosis and stir at low speed for 2–3 min to disperse it evenly before starting electroosmosis; control the electroosmosis process until the sludge moisture content is preferably 60%±5% and then stop electroosmosis.

[0041] After electroosmosis is completed, a water pump is used to remove the water discharged from the cathode of the electroosmosis device, and the water quality is tested. Once the water meets the standards, it can be discharged or reused.

[0042] S3, configured with solidified river silt mixture.

[0043] S3a, take the crusted phosphogypsum from the stockpile, crush and sieve it to obtain fine particles of 20–110 μm; S3b, take the compacted construction waste from the stockpile, crush and screen it to obtain coarse particles of 2–10 mm; S3c involves vibrating and mixing fine phosphogypsum particles, coarse construction waste particles, and dry cement powder to achieve a good particle size distribution and uniform mixing. By mixing fine phosphogypsum aggregate, coarse construction waste aggregate, and cement powder in different proportions and then vibrating to ensure uniform mixing, the cement is evenly distributed on the surface of the phosphogypsum aggregate and construction waste aggregate.

[0044] S4. The solidified mixture prepared in step S3 is mixed with the sludge after electroosmosis in a certain proportion. The mass of the solidified mixture is 10% of the total mass of the sludge after electroosmosis treatment. The proportion and dosage are shown in Table 1.

[0045] To maintain process continuity, the mixture can be directly mixed and molded in the same electroosmosis device or transferred to an independent mold box for molding and curing. Mixing and molding can be completed without removing the electrodes, resulting in recyclable solidified sludge that can be used as roadbed filler for flood control roads, embankment roads, and other roadbeds.

[0046] Table 1

[0047] The results of the unconfined compressive strength test of the solidified sludge are shown in Table 2.

[0048] Table 2

[0049] It should be noted that any technical features not described in detail in this invention can be implemented using any existing technology.

[0050] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

Claims

1. A method for the resource-based treatment of river and lake dredged silt using a combination of flocculation-reticulated electroosmosis solidification and phosphogypsum with construction waste, characterized in that... Includes the following steps: (1) Collect dredged sludge on site, filter out floating impurities and large solids, let it stand or perform simple dehydration to reduce the initial moisture content to about 90% ± 5%, and obtain pretreated sludge; (2) The pretreated sludge is filled into the mesh electroosmosis device for electroosmosis treatment, and flocculant is added before electroosmosis begins. After stirring at low speed, the device is powered on. (3) The sludge treated by electroosmosis is mixed with solid waste solidifying agent to form a solidified mixture, and then molded and cured to obtain recyclable solidified sludge; The solid waste solidifying agent is a mixture of phosphogypsum, construction waste, and dry cement powder.

2. The method according to claim 1, characterized in that, The flocculant is polyacrylamide.

3. The method according to claim 2, characterized in that, The amount of flocculant added is 0.10%-0.20% of the dry weight of the silt.

4. The method according to claim 1, characterized in that, The electroosmosis time is 8~24h.

5. The method according to claim 1, characterized in that, The dosage of the solid waste solidifying agent is 5% to 12% of the total mass of the sludge after electroosmosis treatment.

6. The method according to claim 5, characterized in that, The solid waste solidifying agent is composed of the following parts by weight: 20-30 parts phosphogypsum, 30-50 parts construction waste, and 10-20 parts dry cement powder.

7. The method according to claim 5, characterized in that, The phosphogypsum is obtained by crushing and screening compacted phosphogypsum from the stockpile, with a particle size of 20–110 μm; the construction waste is obtained by crushing and screening compacted construction waste from the stockpile, with a particle size of 2–10 mm.

8. The method according to claim 1, characterized in that, The mesh electroosmosis device includes a sludge tank, a drainage tank, electrode plates, and a DC power supply. The electrode plates include an anode plate and a cathode plate located on both sides of the soil sample tank. The anode plate and the cathode plate are connected to the DC power supply via wires. The electroosmosis treatment refers to turning on the DC power supply to allow water in the solidified sludge to flow from the anode to the cathode and then be discharged. Preferably, adjacent anode plates and cathode plates are arranged alternately to form a multi-row, multi-column mesh electrode array on a plane.

9. The method according to claim 8, characterized in that, The anode plate and cathode plate are made of stainless steel electrode plates.

10. The method according to claim 8, characterized in that, The cathode electrode plate is uniformly perforated. Preferably, the outer layer of the cathode electrode plate is wrapped with short-fiber needle-punched nonwoven polyester fiber geotextile as a filter layer.

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