Engineering waste shield slurry dewatering method

Abstract

This invention discloses a method for dewatering waste tunnel boring machine (TBM) slurry, comprising the following steps: First, pre-condition the waste slurry by adding 2.8-3.2 mg / g of plant waste residue (dry basis weight) based on the dry weight of the waste slurry; then, add 0.75-1.5 mg / g of sodium carboxymethyl cellulose (dry basis weight) to the treated slurry and stir evenly; finally, add 1.5-6.0 mg / g of anionic polyacrylamide (dry basis weight) to the slurry and stir evenly; after allowing the treated slurry to stand to remove the supernatant, dewater the treated waste slurry using a vacuum filtration device. This method uses plant waste residue as a physical conditioner, anionic polyacrylamide and sodium carboxymethyl cellulose as chemical conditioners, and a vacuum filtration device to achieve slurry-water separation. This not only effectively reduces the amount of traditional flocculant polyacrylamide used, achieving good flocculation results and mitigating environmental pollution caused by flocculants, but also promotes the recycling and reuse of solid waste.

Description

Technical Field

[0001] This invention belongs to the field of engineering waste shield tunneling mud treatment technology, and particularly relates to a method for dewatering engineering waste shield tunneling mud. Background Technology

[0002] Mud is an indispensable material in engineering construction. It mainly plays a role in wall protection, slag removal, cooling, and hole cleaning in construction such as drilling, diaphragm wall construction, and tunnel boring. A large amount of waste mud is generated during the construction of high-rise buildings, highways, large bridges, tunnels and other projects.

[0003] Waste mud has a high water content and high fluidity, making it inconvenient to transport. Therefore, the key to treating engineering waste mud lies in its dewatering. Currently, my country mainly uses the following methods for dewatering waste mud: flocculation dewatering, mechanical dewatering, evaporation dewatering, and solidifying agent methods. Flocculation dewatering is widely used due to its simple operation and high efficiency. It effectively agglomerates waste mud colloids into polymers through the charge neutralization and bridging flocculation effect of flocculants, which is beneficial for waste mud sedimentation and filtration.

[0004] The most commonly used flocculant in practical engineering is anionic polyacrylamide, which can be modified into many polyacrylamide derivatives and is widely used in industries such as papermaking, mineral processing, petroleum production, metallurgy, building materials, and wastewater treatment. Taking the treatment of waste sludge as an example, the optimal dosage of anionic polyacrylamide is around 15 mg / g. However, the flocculant is difficult to degrade after use, and the residual monomers are toxic, which can harm the aquatic environment and human health. Moreover, the polymers formed by flocculation make the sludge more compressible during subsequent filtration, causing the filter cake pores to close and hindering dewatering. As a result, longer filtration times or higher pressures are required to achieve good dewatering results, thus affecting the efficiency of the entire treatment process. Summary of the Invention

[0005] The main objective of this invention is to provide a method for dewatering engineering waste shield tunneling mud. This method uses plant waste as a physical conditioner, anionic polyacrylamide and sodium carboxymethyl cellulose as chemical conditioners, and then uses a vacuum filtration device to achieve mud-water separation. This method can not only effectively reduce the amount of traditional flocculant polyacrylamide used, achieve good flocculation effect, reduce environmental pollution caused by flocculants, but also promote the recycling and reuse of solid waste.

[0006] Therefore, the present invention provides a method for dewatering abandoned tunnel boring machine mud, comprising the following steps:

[0007] S1. Based on the dry weight of the waste mud to be treated, add 2.8-3.2 mg / g of plant waste residue to pre-condition the waste mud.

[0008] S2. Add sodium carboxymethyl cellulose at a dry basis weight of 0.75-1.5 mg / g to the slurry treated in step S1, and stir until homogeneous;

[0009] S3. Add 1.5 to 6.0 mg / g of anionic polyacrylamide (dry basis weight of waste mud) to the mud treated in step S2 and stir until homogeneous.

[0010] S4. After the mud treated in step S2 is allowed to stand to remove the supernatant, the treated waste slurry is dewatered in a filtration device.

[0011] Specifically, the plant waste is sugarcane bagasse and / or wheat residue.

[0012] Specifically, the dosage of sodium carboxymethyl cellulose is 1.5 mg / g of the dry weight of the waste mud, and the dosage of anionic polyacrylamide is 1.5 mg / g of the dry weight of the waste mud.

[0013] Specifically, the sodium carboxymethyl cellulose dosage is 0.75 mg / g of the dry weight of the waste mud, and the anionic polyacrylamide dosage is 6 mg / g of the dry weight of the waste mud.

[0014] Specifically, the amount of plant waste added is 3 mg / g of the dry basis of the waste mud.

[0015] Specifically, the anionic polyacrylamide has a molecular weight of 20 million.

[0016] Specifically, the waste mud to be treated has a water content of 70% ± 10% and a pH value of 11.62 ± 0.5.

[0017] Specifically, plant waste is added to waste mud and stirred evenly at 350 rpm for 45 minutes.

[0018] Principles and advantages

[0019] This application uses both physical and chemical conditioning agents to treat waste slurry. Plant waste is used as the physical conditioning agent, while anionic polyacrylamide and sodium carboxymethyl cellulose are used as the chemical conditioning agents. A vacuum filtration device is then used to separate the slurry from the water.

[0020] The added anionic polyacrylamide is a high-molecular-weight water treatment flocculant product. It effectively adsorbs suspended particles in water through charge neutralization, then acts as a bridging link between particles, causing fine particles to form larger flocs, which is beneficial for particle sedimentation, filtration, and permeation. The added sodium carboxymethyl cellulose is an organic compound with hygroscopic properties; its solution is a transparent colloid. In the sludge flocculation process, it mainly acts as a bridge. The added plant waste acts as a skeleton builder and filter aid. It can connect with the anionic polyacrylamide and sodium carboxymethyl cellulose to form a bridging structure, promoting flocculation. It can also form a more robust crystal structure, maintaining porosity during mechanical dewatering and improving dewatering efficiency. Furthermore, the sludge cake produced by pretreatment with plant waste has a higher calorific value and a higher filter cake solids content, making it more suitable for incineration. Therefore, plant waste, as a physical regulator, not only improves dewatering performance but also serves as a practical method for solid waste recycling and reuse.

[0021] In summary, this application pre-conditions the waste slurry using plant waste residue, then adds a small amount of sodium carboxymethyl cellulose to connect with the plant waste residue to form a bridging structure, followed by the addition of traditional flocculant polyacrylamide for flocculation, and finally uses a vacuum filtration device to achieve mud-water separation. This not only effectively reduces the amount of traditional flocculant polyacrylamide used, achieving good flocculation effect and mitigating environmental pollution caused by flocculants, but also promotes the recycling and reuse of solid waste. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a SEM image of sodium carboxymethyl cellulose involved in the embodiments of the present invention;

[0024] Figure 2 This is an SRF diagram of the waste slurry after co-treatment with different amounts of APAM and different amounts of CMC-Na, as described in the embodiments of the present invention.

[0025] Figure 3 This is a TTF diagram of the waste slurry after co-treatment with different amounts of APAM and different amounts of CMC-Na, as described in the embodiments of the present invention.

[0026] Figure 4 This is an SV30 diagram of the waste slurry after co-treatment with different amounts of APAM and different amounts of CMC-Na, as described in the embodiments of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] A method for dewatering abandoned tunnel boring machine mud includes the following steps:

[0029] S1. First, add plant waste residue to pre-condition the waste slurry;

[0030] S2. Add sodium carboxymethyl cellulose (CMC-Na) to the slurry treated in step S1 and stir until homogeneous;

[0031] S3. Add anionic polyacrylamide (APAM) to the slurry treated in step S2 and stir until homogeneous;

[0032] S4. After the mud treated in step S2 is allowed to stand to remove the supernatant, the treated waste slurry is dewatered in a filtration device.

[0033] The anionic polyacrylamide added in this application has a molecular weight of 20 million and is abbreviated as APAM. It is a commonly used polymeric flocculant for water treatment. It can effectively adsorb suspended particles in water through charge neutralization, and then act as a linker between particles, causing fine particles to form larger flocs, which is beneficial for particle sedimentation, filtration, and penetration. The added sodium carboxymethyl cellulose (CMC-Na) is an organic compound with hygroscopic properties. Its solution is a transparent colloid and is commonly used as a thickener in the food industry; as a drug carrier in the pharmaceutical industry; as a binder and anti-re-coagulation agent in the daily chemical industry; as a sizing agent and protective colloid for printing pastes in the printing and dyeing industry; and as a component of oil fracturing fluids in the petrochemical industry. The microstructure of CMC-Na is long-chain (e.g., ...). Figure 1 In the flocculation process, plant waste primarily acts as a bridging agent. As a skeleton builder and filter aid, the added plant waste can connect with APAM and CMC-Na to form voids, promoting flocculation. It can also form a more robust lattice structure that maintains porosity during mechanical dewatering. The sludge cake produced by pretreatment with plant waste has a higher calorific value and a higher filter cake solids content, making it more suitable for incineration. Therefore, plant waste, as a physical regulator, not only improves dewatering performance but also serves as a practical method for solid waste recycling. The plant waste can include materials such as sugarcane bagasse and wheat residue.

[0034] This application pre-conditions the waste slurry with plant waste residue, then adds a small amount of sodium carboxymethyl cellulose to connect with the plant waste residue to form a bridge, then adds the traditional flocculant polyacrylamide for flocculation, and finally uses a vacuum filtration device to achieve mud-water separation. This not only effectively reduces the amount of traditional flocculant polyacrylamide used, but also achieves good flocculation effect, reduces the environmental pollution caused by flocculants, and promotes the recycling and reuse of solid waste.

[0035] Further research by the inventors revealed that the optimal sludge treatment effect is achieved when the dosage of plant waste residue is 2.8-3.2 mg / g of the dry weight of the waste sludge, the dosage of sodium carboxymethyl cellulose is 0.75-1.5 mg / g of the dry weight of the waste sludge, and the dosage of anionic polyacrylamide is 1.5-6 mg / g of the dry weight of the waste sludge. This is because if the dosage of plant waste residue is below the above range, the treatment effect will not be achieved, while excessive dosage will lead to resource waste and increased costs. Both sodium carboxymethyl cellulose and anionic polyacrylamide are thickening agents, and when the dosage is below the above range, the effect of flocculants in agglomerating sludge particles cannot be realized; instead, the sludge system will become more stable. The flocculant solution has a slight viscosity, and when the dosage exceeds the above range, the viscosity of the sludge supernatant will be too high, making it difficult to filter in the subsequent vacuum filtration device.

[0036] During sludge treatment, the pH of the original sludge was maintained at 11.62±0.5. 3 mg / g of plant waste was added to the original sludge, and the mixture was stirred uniformly at 350 rpm for 45 min. After uniform stirring, samples were taken. A 50 g / L APAM solution and a 25 g / L CMC-Na solution were prepared. The solids content of the sludge to be treated was determined. First, 0.75–1.5 mg / g of sodium carboxymethyl cellulose (carboxymethyl cellulose) based on the dry weight of the sludge was added, and the mixture was stirred uniformly for 5 min. Then, 1.5–6.0 mg / g of anionic polyacrylamide was added, and the mixture was stirred uniformly. The stirred sludge was quickly poured into a 100 mL graduated cylinder and allowed to settle naturally for 30 min. Obvious mud-water separation was observed. After the remaining sludge had stood for a specified time, 100 mL of the sludge was poured into the Buchner funnel of a vacuum filtration device for vacuum filtration. Filtration was stopped after 20 min or when the vacuum was broken. The resulting sludge cake was placed in a 105℃ oven and dried for 4 h until constant weight. The dewatering performance parameters of the mud were determined to evaluate the dewatering effect, with mud specific resistance being the main parameter.

[0037] Parameters: ① Sludge Specific Resistance (SRF): A comprehensive indicator of sludge filtration characteristics. The smaller the SRF, the better the dewatering performance.

[0038] ②TTF: The time it takes for the filtrate volume to reach half the sludge volume. The lower the TTF, the faster the dewatering rate and the better the dewatering performance.

[0039] ③30-minute settling ratio (SV30): The volume ratio (%) of settled sludge to the mixed liquor after 30 minutes of settling. The smaller the SV30, the better the flocculation effect.

[0040] Experimental group 1:

[0041] In this experimental group, the water content of the waste slurry to be treated was 71%, and the solid content was 29%. The amounts of plant waste and anionic polyacrylamide added were kept constant at 3 mg / g and 1.5 mg / g, respectively. The effect of changing the content of sodium carboxymethyl cellulose was investigated on its dehydration performance. The sodium carboxymethyl cellulose contents in the experimental groups were 0 mg / g, 0.75 mg / g, 1.5 mg / g, and 2.25 mg / g, respectively. Sugarcane bagasse was used as the plant waste in this application. Of course, in practical applications, wheat residue can also be used as a substitute.

[0042] In the experiment, 3 mg / g of plant waste residue was added to the waste slurry for pre-conditioning. 50 g / L APAM solution and 25 g / L CMC-Na solution were prepared. The water content of the waste slurry to be treated was measured to be 71%, and the solid content was 29%. Sodium carboxymethyl cellulose was added at a predetermined content based on the dry weight of the waste slurry, stirred evenly, and allowed to stand for 5 minutes. Then, 1.5 mg / g of anionic polyacrylamide was added, stirred evenly, and allowed to stand for 2 hours. At this time, obvious mud-water separation was observed. The treated waste slurry was poured into a vacuum filter for dewatering, and SRF, TTF, and SV30 were measured.

[0043] Experimental group 2:

[0044] In this experimental group, the water content of the waste slurry to be treated was 71%, the solid content was 29%, and the amount of plant waste and anionic polyacrylamide added were kept constant at 3 mg / g and 6 mg / g, respectively. The effect of changing the content of sodium carboxymethyl cellulose on its dehydration performance was investigated. The contents of sodium carboxymethyl cellulose in the experimental group were 0 mg / g, 0.75 mg / g, 1.5 mg / g, and 2.25 mg / g, respectively.

[0045] In the experiment, 3 mg / g of plant waste residue was added to the waste slurry for pre-conditioning. 50 g / L APAM solution and 25 g / L CMC-Na solution were prepared. The water content of the waste slurry to be treated was 71%, and the solid content was 29%. Sodium carboxymethyl cellulose with a set dry basis weight was added first, stirred evenly, and allowed to stand for 5 minutes. Then, 6 mg / g of anionic polyacrylamide was added, stirred evenly, and allowed to stand for 2 hours. At this time, obvious mud-water separation was observed. The treated waste slurry was poured into a vacuum filter for dewatering, and SRF, TTF, and SV30 were measured.

[0046] Comparative Example 1

[0047] First, 3 mg / g of plant waste residue was added to the waste slurry for pre-conditioning. A 50 g / L APAM solution was prepared. The water content of the waste slurry to be treated was 71%, and the solid content was 29%. Anionic polyacrylamide with a dry basis of 1.5 mg / g of waste slurry was added, stirred evenly, and allowed to stand for 2 hours. The treated waste slurry was then poured into a vacuum filter for dewatering, and the SRF, TTF, and SV30 were measured.

[0048] Comparative Example 2

[0049] First, 3 mg / g of plant waste residue was added to the waste slurry for pre-conditioning. A 50 g / L APAM solution was prepared. The water content of the waste slurry to be treated was 71%, and the solid content was 29%. Anionic polyacrylamide with a dry basis of 6.0 mg / g of waste slurry was added, stirred evenly, and allowed to stand for 2 hours. The treated waste slurry was then poured into a vacuum filter for dewatering, and the SRF, TTF, and SV30 were measured.

[0050] Comparative Example 3

[0051] First, 3 mg / g of plant waste residue was added to the waste slurry for pre-conditioning. A 50 g / L APAM solution was prepared. The water content of the waste slurry to be treated was 71%, and the solid content was 29%. Anionic polyacrylamide with a dry basis of 15.0 mg / g of waste slurry was added, stirred evenly, and allowed to stand for 2 hours. At this time, obvious mud-water separation was observed. The treated waste slurry was poured into a vacuum filter for dewatering, and SRF, TTF, and SV30 were measured.

[0052] Comparative Example 4

[0053] First, 3 mg / g of plant waste residue was added to the waste slurry for pre-conditioning. A 25 g / L CMC-Na solution was prepared. The water content of the waste slurry to be treated was 71%, and the solid content was 29%. 0.75 mg / g of sodium carboxymethyl cellulose was added to the waste slurry on a dry basis. The mixture was stirred evenly and allowed to stand for 2 hours. The treated waste slurry was then poured into a vacuum filter for dewatering, and the SRF, TTF, and SV30 were measured.

[0054] Comparative Example 5

[0055] First, 3 mg / g of plant waste residue was added to the waste slurry for pre-conditioning. A 25 g / L CMC-Na solution was prepared. The water content of the waste slurry to be treated was 71%, and the solid content was 29%. 1.5 mg / g of sodium carboxymethyl cellulose was added to the waste slurry on a dry basis. The mixture was stirred evenly and allowed to stand for 2 hours. The treated waste slurry was then poured into a vacuum filter for dewatering, and the SRF, TTF, and SV30 were measured.

[0056] Comparative Example 6

[0057] Unlike test group 1, no plant waste was added to the waste slurry to be treated. During the experiment, 1.5 mg / g sodium carboxymethyl cellulose was added on a dry basis of the waste slurry, stirred evenly, and allowed to stand for 5 minutes. Then, 1.5 mg / g anionic polyacrylamide was added, stirred evenly, and allowed to stand for 2 hours. At this time, obvious mud-water separation was observed. The treated waste slurry was poured into a vacuum filter for dewatering, and SRF, TTF, and SV30 were measured.

[0058] Comparative Example 7

[0059] Unlike test group 2, no plant waste was added to the waste slurry to be treated. During the experiment, 0.75 mg / g sodium carboxymethyl cellulose was added on a dry basis of the waste slurry, stirred evenly, and allowed to stand for 5 minutes. Then, 6 mg / g anionic polyacrylamide was added, stirred evenly, and allowed to stand for 2 hours. At this time, obvious mud-water separation was observed. The treated waste slurry was poured into a vacuum filter for dewatering, and SRF, TTF, and SV30 were measured.

[0060] Experimental results:

[0061]

[0062]

[0063] Results analysis:

[0064] Figure 2 , Figure 3 , Figure 4 The values ​​of SRF, TTF, and SV30 are respectively the values ​​of waste slurry after co-treatment with plant waste and different amounts of APAM and CMC-Na.

[0065] When plant waste and APAM are used together to treat waste slurry, the effect is best when the dosage is 15 mg / g. At this dosage, compared with the original slurry, SRF is reduced by 79.7%, TTF by 58.1%, and SV30 by 19.8%.

[0066] After conditioning with plant waste residue, when sludge was treated with 6.0 mg / g APAM combined with 0.75 mg / g CMC-Na, the SRF decreased by 72.9%, TTF decreased by 46.8%, and SV30 decreased by 26.9% compared to the original sludge. At low doses, the flocculant could not effectively interact with the dispersed sludge particles, resulting in poor dewatering performance. With excessive dosage, the charge reversal of the negatively charged sludge colloidal particles led to a restoring effect, increasing electrostatic repulsion and reducing dewatering capacity. The long-chain flocculant molecules may also adhere to each other, failing to stretch effectively, thus reducing the total amount of adsorbed sludge particles and lowering flocculation efficiency. When 6 mg / g APAM was used alone to treat the sludge, the dewatering performance deteriorated because the low dose of APAM solution exhibited a dispersing effect, making the sludge system more stable. At this point, SRF increased by 20.3%, TTF increased by 21.4%, and SV30 decreased by 2.5%. When CMC-Na at 0.75 mg / g was used alone to treat waste slurry, the SRF decreased by 25.4%, TTF decreased by 19.9%, and SV30 decreased by 2.5% compared with the original slurry. Therefore, the effect of using plant waste and CMC-Na flocculant together to treat waste slurry was not good.

[0067] The results showed that, compared with the plant waste-APAM treatment and the plant waste-CMC-Na treatment, the combined flocculant with appropriate dosage of plant waste significantly reduced the amount of APAM by adding only a small amount of CMC-Na, while still achieving good treatment results.

[0068] In addition, the test results also show that the key component of this application, plant waste residue, greatly helps to improve the dewatering performance of sludge. This is because the added plant waste residue can act as a skeleton builder and filter aid. It can form voids with APAM and CMC-Na connecting bridges to promote flocculation. It can also form a more robust lattice structure that can maintain a porous state during mechanical dewatering, thereby allowing wastewater to be smoothly discharged from the sludge cake, and the dewatering effect is greatly improved.

[0069] Furthermore, unless otherwise stated, the terms used to indicate positional relationships or shapes in any of the technical solutions disclosed in this invention include states or shapes that are similar to, analogous to, or close to those states or shapes. Any component provided by this invention can be assembled from multiple individual components or can be a single component manufactured using a one-piece molding process.

[0070] The above embodiments are merely illustrative examples to clearly illustrate the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all embodiments here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for dewatering abandoned tunnel boring machine mud, characterized in that, Includes the following steps: S1. Based on the dry weight of the waste mud to be treated, add 2.8-3.2 mg / g of plant waste residue to pre-condition the waste mud. S2. Add sodium carboxymethyl cellulose to the slurry treated in step S1 and stir until homogeneous; S3. Add anionic polyacrylamide to the slurry treated in step S2 and stir until homogeneous; S4. After the mud treated in step S3 is allowed to stand to remove the supernatant, the treated waste slurry is dewatered in a filtration device; the plant waste residue is sugarcane bagasse and / or wheat residue. The dosage of sodium carboxymethyl cellulose is 1.5 mg / g of the dry weight of the waste sludge, and the dosage of anionic polyacrylamide is 1.5 mg / g of the dry weight of the waste sludge. Or, The sodium carboxymethyl cellulose dosage is 0.75 mg / g of the dry weight of the waste mud, and the anionic polyacrylamide dosage is 6 mg / g of the dry weight of the waste mud.

2. The method for dewatering abandoned tunnel boring machine slurry according to claim 1, characterized in that: The amount of plant waste added is 3 mg / g of the dry basis of the waste mud.

3. The method for dewatering abandoned tunnel boring machine slurry according to claim 1, characterized in that: The anionic polyacrylamide has a molecular weight of 20 million.

4. The method for dewatering abandoned tunnel boring machine slurry according to claim 1, characterized in that: The waste mud to be treated has a water content of 70%±10% and a pH value of 11.62±0.

5.

5. The method for dewatering abandoned tunnel boring machine slurry according to claim 1, characterized in that: Add the plant waste residue to the waste mud and stir evenly at 350 rpm for 45 minutes.

Images