Method for preparing roadbed filler by solidifying and modifying sludge of water supply plant

Abstract

The invention belongs to the field of sludge utilization, and relates to a method for preparing roadbed filler through solidification and modification of water supply plant sludge. Comprising the following main steps: mud detection: aiming at dewatered sludge of a water supply plant, carrying out mud index detection, analyzing mud characteristics of the sludge, and evaluating feasibility of preparing roadbed filler from the sludge and key of a curing modification technology; sludge conditioning: uniformly mixing dewatered sludge of a water supply plant with a hydration conditioner, carrying out material covering and stacking, and then digging, airing and crushing for later use; curing and modifying: sequentially adding a gel curing agent, high polymer fibers and a resin water-retaining agent into the conditioned sludge, and uniformly mixing to obtain roadbed filler; and filler detection: carrying out environmental index detection and indoor soil test on roadbed filler, and evaluating whether the mechanical properties of the sludge curing modified filler meet the design requirements or not. The method can realize water supply plant sludge solidification modification, improve the sludge bearing ratio and shear strength, reduce the environmental risk of using heavy metals and pathogenic bacteria in sludge building materials, and is beneficial to solving the double dilemma of sludge outlet shortage and road base material shortage in urban development.

Description

Technical Field

[0001] The invention belongs to the field of sludge utilization and relates to a method for preparing roadbed filler by solidifying and modifying sludge from a water supply plant. Background Art

[0002] As my country's urbanization process advances, the water supply coverage rate has increased significantly, with the total daily water supply exceeding 300 million cubic meters. The water purification process of water plants is accompanied by the generation of a large amount of sludge, which includes suspended solids, colloids, algae and coloring organic matter, heavy metals, and coagulant residues. Improper treatment and disposal can easily lead to secondary pollution. At present, the sludge from water plants in my country is mainly landfilled. Due to the small particle size, strong water holding capacity, low shear strength, and poor stability of the sludge, landfills often reject sludge.

[0003] At the same time, with the continuous tightening of environmental protection policies, the mining of building materials such as roadbed fillers is increasingly restricted. The content of inorganic aggregates such as silica, alumina, and calcium oxide in water supply plant sludge is as high as more than 70%. Research on building material utilization technology for water supply plant sludge is conducive to solving the two major difficulties of lack of sludge outlets and construction substrates in the process of urbanization, and is currently a hot research topic in the field of environmental resources.

[0004] However, there are the following bottleneck problems in the resource utilization of water plant sludge as roadbed filler: 1) The content of fine-grained soil such as silt or clay in the sludge is relatively high, and the bearing ratio and shear strength are low, which cannot meet the geotechnical performance requirements of building materials. When the sludge is directly used in concrete as an admixture, the high organic matter content in the sludge may delay the formation of hydration products and affect the cementitious properties, resulting in high porosity and low bonding strength; 2) The sludge is enriched with pollutants such as heavy metals and pathogens. Improper treatment and disposal can easily cause environmental pollution and human health risks. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing roadbed filler by solidifying and modifying sludge from a water supply plant, so as to improve the sludge bearing ratio and shear strength, reduce the environmental risks of heavy metals and pathogens in the use of sludge building materials, and solve the dual dilemma of lack of sludge outlets and shortage of road base materials in urban development.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing roadbed filler by solidifying and modifying sludge from a water supply plant comprises the following main steps:

[0008] Step (1): Mud quality testing. Carry out mud quality index testing on dewatered sludge from water supply plants, analyze the mud quality characteristics, and evaluate the feasibility of preparing sludge as roadbed filler and the key to solidification and modification technology.

[0009] Step (2): Sludge conditioning. The dewatered sludge from the water supply plant is mixed evenly with the hydration conditioning agent, piled up, and then dug, dried, and crushed for later use.

[0010] Step (3): Solidification and modification. Add gel curing agent, high polymer fiber and resin water retaining agent to the sludge conditioned in step (2) in sequence, and mix them evenly to obtain roadbed filler.

[0011] Step (4): Filler testing. For roadbed fillers, environmental index testing and indoor geotechnical tests are conducted to evaluate whether the mechanical properties of sludge solidified modified fillers meet the design requirements, as well as the environmental risks of resource utilization.

[0012] In the present invention, in the step (1), the sludge quality detection indicators include moisture content, organic matter content, heavy metal content, liquid limit, plastic limit, optimum moisture content, maximum dry density, particle size distribution and other indicators.

[0013] Preferably, the dewatered sludge from the water supply plant in step (1) should have a moisture content below 80% and an organic matter content within 10%. The economic efficiency of using sludge outside this moisture content and organic matter content range to prepare roadbed filler is poor.

[0014] Preferably, the heavy metal content of the dewatered sludge from the water supply plant in step (1) should meet the second category screening value requirement of the soil pollution risk screening value for construction land, and sludge exceeding the screening value shall not be used for roadbed filling improvement.

[0015] In the present invention, in step (2), the hydration conditioning agent is an alkaline metal oxide such as calcium oxide, magnesium oxide, sodium oxide, etc., which has the characteristics of undergoing a strong hydration reaction when in contact with water, generating alkaline products and accompanied by high temperature. On the one hand, the conditioning agent undergoes a hydration reaction with water in the sludge, which can reduce the water content of the sludge, create a strong alkaline environment, and is conducive to stimulating the rapid dissociation of minerals in the sludge and strengthening the subsequent gelation reaction; on the other hand, the high temperature and strong alkaline environment generated by the hydration reaction are conducive to killing pathogens in the sludge and reducing human health risks.

[0016] Preferably, in step (2), the sludge and the hydration conditioner are mixed and then simmered for no less than 12 hours to completely kill pathogens in the sludge; the moisture content after airing should be 2% to 5% higher than the optimum moisture content; the particle size of the sludge particles after crushing should not be greater than 15 mm, and the mass of particles with a particle size greater than 10 mm should be less than 5% of the total sludge amount.

[0017] In the present invention, in the step (3), the gel curing agent is cement or slag powder, which has the characteristics of promoting the agglomeration of fine clay particles, improving the grading of sludge particles, and reducing the leaching content of heavy metals through ion exchange, hydration and crystallization. The strength grade of the cement is not less than 32.5, and the grade of the slag powder is not less than S75.

[0018] In the present invention, in step (3), the high polymer fiber is polypropylene fiber, polyethylene fiber, polyethylene terephthalate fiber, polyamide fiber, etc., and has a length of no less than 6 mm, which can effectively improve the tensile properties of the modified and cured fiber.

[0019] In the present invention, in the step (3), the resin water retaining agent is a polymer water-absorbing resin having a three-dimensional cross-linked grid structure, and has the functions of water retention and slow water release. It can fix free water inside the polymer grid by swelling. When the gel curing agent reacts with the sludge, it can stably provide water to ensure the continuous progress of the gel reaction, which is conducive to the generation of more gel products. At the same time, it can also fill the sludge pores, thereby increasing the density of the solidified sludge and improving the strength of the solidified modified filler.

[0020] Preferably, the hydration conditioner, gel curing agent, high polymer fiber and resin water retaining agent described in steps (2) to (3) are all added in an external doping method, and the addition ratios are as follows: hydration conditioner 1-6%, gel curing agent 5-15%, high polymer fiber 1-5‰, resin water retaining agent 0.5-3‰, where the percentages are the mass percentages of the materials to the dry solids of the sludge.

[0021] In the present invention, in step (4), the environmental detection indicators include water content, organic matter content, heavy metal leaching content, pathogenic bacteria, etc.

[0022] Preferably, the moisture content of the filler after curing and modification in step (4) should be the optimal moisture content ±2%, the organic matter content should be less than 5%, the heavy metal leaching content should meet the requirements of the groundwater quality classification index of the corresponding area, the fecal coliform value should not be greater than 0.01, and the ascaris egg mortality rate should be greater than 95%.

[0023] In the present invention, in the step (4), the indoor geotechnical test indicators include bearing ratio, 7d unconfined compressive strength, compaction test, quick shear test, etc.

[0024] Preferably, the load ratio of the filler after curing and modification in step (4) should be greater than 2%, the 7d unconfined compressive strength should be greater than 0.05MPa, and meet the design requirements of roadbed fillers of corresponding road grades.

[0025] Preferably, the cured and modified filler that meets the detection requirements of step (4) should be layered and rolled on the roadbed within 3 hours and rolled to survive before the cement begins to set.

[0026] Compared with the prior art, the invention has the following advantages and beneficial effects:

[0027] The present invention utilizes the coupling effect of hydration conditioning agent, gel curing agent, high polymer fiber and resin water retaining agent to realize the solidification and modification of water supply plant sludge:

[0028] (1) Using alkaline metal oxides as hydration conditioners, such as calcium oxide and magnesium oxide, can effectively adjust the water content of sludge. These substances will produce high temperature and strong alkaline environment when reacting with water, which is not only conducive to reducing the water content of sludge, but also can kill pathogens in sludge, significantly reducing the risk to human health;

[0029] (2) Using cement or slag powder as a gel curing agent can promote the agglomeration of fine particles in the sludge and improve the particle grading through ion exchange, hydration and crystallization. At the same time, these substances can effectively reduce the leaching content of heavy metals in the sludge, making the cured filler more environmentally friendly and safe;

[0030] (3) High polymer fibers, such as polypropylene fibers, have the characteristics of three-dimensional disordered distribution and will not participate in chemical reactions, but can effectively prevent cracks from appearing in the solidified filler during the drying process, thereby ensuring the overall strength and stability of the filler;

[0031] (4) As a polymer water-absorbing material, the resin water-retaining agent has a three-dimensional cross-linked grid structure that can absorb and slowly release water. This property helps to stably provide water during the reaction between the gel curing agent and the sludge, promoting the generation of more gel products. In addition, the resin water-retaining agent can also fill the pores of the sludge, increase the density of the solidified filler, and improve the overall strength of the filler;

[0032] The above materials are organically combined and complement each other, which improves the strength of the solidified modified filler as a whole, and solidifies heavy metals in the sludge lattice for a long time, reducing the leaching content and improving environmental safety. It is conducive to solving the two major problems of lack of sludge outlets and shortage of road substrates in urban development, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The comparison of the electron microscope scanning results of the original dewatered sludge and the solidified modified filler at 2KX magnification; (a) is the original dewatered sludge; (b) is the solidified modified filler;

[0034] Figure 2 The comparison of the electron microscope scanning results of the original dewatered sludge and the solidified modified filler at 5KX magnification; (c) is the original dewatered sludge; (d) is the solidified modified filler;

[0035] Figure 3 The comparison of the electron microscope scanning results of the original dewatered sludge and the solidified modified filler at 10KX magnification; (e) is the original dewatered sludge; (f) is the solidified modified filler; DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the embodiments. The advantages and features of the present invention will become more apparent from the following description and claims.

[0037] Example:

[0038] The preparation of roadbed filler by solidification and modification of dewatered sludge from a water supply plant includes the following main steps:

[0039] Step (1): Mud quality testing. Carry out mud quality index testing on dewatered sludge from water supply plants, analyze the mud quality characteristics, and evaluate the feasibility of preparing sludge as roadbed filler and the key to solidification and modification technology.

[0040] Step (2): Sludge conditioning. The dewatered sludge from the water supply plant is mixed evenly with the hydration conditioning agent, piled up, and then dug, dried, and crushed for later use.

[0041] Step (3): Solidification and modification. Add gel curing agent, high polymer fiber and resin water retaining agent to the sludge conditioned in step (2) in sequence, and mix them evenly to obtain roadbed filler.

[0042] Step (4): Filler testing. For roadbed fillers, environmental index testing and indoor geotechnical tests are conducted to evaluate whether the mechanical properties of sludge solidified modified fillers meet the design requirements, as well as the environmental risks of resource utilization.

[0043] In the step (1), the sludge quality detection indicators include moisture content, organic matter content, heavy metal content, liquid limit, plastic limit, optimum moisture content, maximum dry density, particle size distribution and other indicators. Example Sludge was taken from the dewatering room of a water supply plant in East China. The main properties of the dewatered sludge are shown in the following table:

[0044] Table 1 Example Water Plant Sludge Properties

[0045] index unit Detection value 1 Detection value 2 Detection value 3 Moisture content ％ 68.4 72.2 68.2 Organic matter ％ 7.73 8.11 8.24 Liquid limit ％ 68.2 67.5 68.1 Plastic Limit ％ 19.0 16.9 17.4 Optimum moisture content ％ 57.2 58.1 57.6 Maximum dry density <![CDATA[g / cm 3 ]]> 1.44 1.46 1.45

[0046] Furthermore, the control of the sludge moisture content directly affects the mechanical properties of the filler after solidification. Too high a moisture content will lead to low strength of the filler after solidification, which is not conducive to its application in roadbed engineering and increases maintenance and repair costs. Therefore, controlling the moisture content within an appropriate range is conducive to ensuring the quality and service life of the filler, thereby reducing the overall project cost. A high organic matter content in the sludge will increase the complexity of the treatment process, especially during the solidification process, which may cause environmental problems such as volatile organic matter emissions. By controlling the organic matter content within a certain range, the risk of environmental pollution can be reduced, meeting the requirements of sustainable development, and improving resource utilization efficiency. Preferably, the dehydrated sludge of the water supply plant described in step (1) has a moisture content of less than 80% and an organic matter content of less than 10%. The sludge within this moisture content and organic matter content range is more economical when used to prepare roadbed filler using the present invention.

[0047] Furthermore, the heavy metal content of the dewatered sludge from the water supply plant in step (1) meets the second category of the screening value for construction land soil pollution risk screening value.

[0048] In the step (2), the hydration conditioning agent is an alkaline metal oxide such as calcium oxide, magnesium oxide, sodium oxide, etc., which has the characteristics of undergoing a strong hydration reaction when in contact with water, generating alkaline products and accompanied by high temperature. On the one hand, the conditioning agent undergoes a hydration reaction with water in the sludge, which can reduce the water content of the sludge, create a strong alkaline environment, and is conducive to stimulating the rapid dissociation of minerals in the sludge and strengthening the subsequent gelation reaction; on the other hand, the high temperature and strong alkaline environment generated by the hydration reaction are conducive to killing pathogens in the sludge and reducing human health risks.

[0049] In the step (2), the sludge and the hydration conditioner are mixed and then simmered for no less than 12 hours to completely kill the pathogens in the sludge; the moisture content after airing should be 2% to 5% higher than the optimum moisture content; the particle size of the sludge particles after crushing should not be larger than 15 mm, and the mass of particles with a particle size larger than 10 mm should be less than 5% of the total sludge amount.

[0050] It is understandable that after the sludge is mixed with the hydration conditioner, the sludge is piled up for no less than 12 hours, which helps the hydration conditioner to fully mix and react with the sludge. During this period, the sludge will be affected by the hydration conditioner, chemical reactions will occur, and a certain amount of heat will be released. These reactions also help to improve the physical structure and chemical properties of the sludge, and enhance the effect of subsequent solidification and modification.

[0051] It is understandable that during the drying process, the water on the surface of the sludge evaporates, causing the moisture content of the surface layer to gradually decrease. The moisture content is 2% to 5% higher than the optimal moisture content in order to ensure that the overall moisture content of the sludge can be controlled within a suitable range during the subsequent crushing and processing process, which is conducive to the uniform mixing of the subsequent addition of curing agent and fiber.

[0052] It is understandable that controlling the particle size of sludge particles, especially those larger than 10 mm, can effectively reduce the content of large particles in the filler that are not conducive to engineering use. Doing so helps to ensure the uniformity and stability of the filler, while reducing the risk of engineering construction problems or unsatisfactory subsequent use results caused by overly large particles.

[0053] In the step (3), the gel curing agent is cement or slag powder, which has the characteristics of promoting the agglomeration of fine clay particles, improving the grading of sludge particles, and reducing the leaching content of heavy metals through ion exchange, hydration and crystallization. The strength grade of the cement is not less than 32.5, and the grade of the slag powder is not less than S75.

[0054] In the step (3), the high polymer fiber is polypropylene fiber, polyethylene fiber, polyethylene terephthalate fiber, polyamide fiber, etc., and has a length of no less than 6 mm, which can effectively improve the tensile properties of the modified and cured fiber.

[0055] In the step (3), the resin water retaining agent is a polymer water-absorbing resin having a three-dimensional cross-linked grid structure and has the functions of water retention and slow water release. It can fix free water inside the polymer grid through swelling. When the gel curing agent reacts with the sludge, it can stably provide water to ensure the continuous progress of the gel reaction, which is conducive to the generation of more gel products. At the same time, it can also fill the sludge pores, thereby increasing the density of the solidified sludge and improving the strength of the solidified modified filler.

[0056] Furthermore, the amounts of the hydration conditioning agent, gel curing agent, high polymer fiber and resin water retaining agent in steps (2) to (3) are all measured by external mixing method, and the mixing ratios are shown in the following table:

[0057] Figure 2 Different examples of drug mixing ratio

[0058]

[0059]

[0060] In the step (4), the environmental testing indicators include moisture content, organic matter content, heavy metal leaching content, pathogenic bacteria, etc.; the indoor geotechnical test indicators include bearing ratio, 7d unconfined compressive strength, compaction test, quick shear test, etc.

[0061] Furthermore, in step (4), the moisture content of the filler after curing and modification in each embodiment is the optimal moisture content of the mixture ±2%, the organic matter content is less than 5%, the heavy metal leaching content meets the requirements of the groundwater quality classification index in the corresponding area, the fecal coliform value of the filler is not greater than 0.01, and the ascaris egg mortality rate is greater than 95%.

[0062] Furthermore, the 7d unconfined compressive strength test was conducted on the cured and modified products of different embodiments, and the results are shown in the following table: The 7d unconfined compressive strength of the cured and modified fillers of each embodiment is greater than 0.05MPa, and meets the design requirements of the roadbed fillers of the corresponding road grade.

[0063] Table 3 Unconfined compressive strength of cured and modified products of different embodiments at 7d

[0064]

[0065]

[0066] Furthermore, compaction test, bearing ratio, 7d unconfined compressive strength test and quick shear test were carried out on the original dewatered sludge and the solidified modified filler of Example 5, and the results are shown in the following table. Compared with the original dewatered sludge, the maximum dry density of the solidified modified filler of Example 5 increased by 8%, the cohesion increased by 15%, the 7d unconfined compressive strength increased by 129%, the optimum moisture content, expansion amount and internal friction angle were all reduced, the sludge rainwater expansion effect was greatly improved, and the solidification and modification effect was significant.

[0067] Table 4 Comparison of sludge solidification and modification effects

[0068]

[0069] Furthermore, scanning electron microscopy (SEM) was performed on the original sludge and the filler after curing and modification in Example 5, and the results are shown in the attached figure. Figures 1 to 3 At different magnifications, the original sludge appears in stacked sheets, but after solidification and modification, the sludge fine clay particles agglomerate significantly, and the particle gradation is significantly improved, which can prove the beneficial effect of the solidification and modification of the present invention from a microscopic perspective.

Claims

1. A method for preparing roadbed filler by solidifying and modifying sludge from a water supply plant, characterized in that: The following steps are involved: Mud quality testing: Carry out mud quality index testing for dewatered sludge from water supply plants, analyze sludge characteristics, and evaluate the feasibility of using sludge to prepare roadbed filler; Sludge conditioning: Mix the dehydrated sludge from the water supply plant with the hydration conditioning agent evenly, pile it up, then dig it up, dry it in the sun, and crush it for use; the sludge should be dried for no less than 12 hours after mixing with the hydration conditioning agent, and the moisture content after drying should be 2% to 5% higher than the optimal moisture content. The particle size of the sludge particles after crushing should not be larger than 15mm, and the mass of particles larger than 10mm should be less than 5% of the total sludge; Solidification modification: add gel curing agent, high polymer fiber and resin water retaining agent to the conditioned sludge in sequence, mix well to obtain roadbed filler; the amount of hydration conditioner, gel curing agent, high polymer fiber and resin water retaining agent is measured according to the external mixing method, and the proportions are: hydration conditioner 1-6%, gel curing agent 5-15%, high polymer fiber 1-5‰, resin water retaining agent 0.5-3‰, the percentage is the mass percentage of the material to the dry solid of the sludge; Filler testing: For roadbed fillers, environmental index testing and indoor geotechnical tests are carried out to evaluate whether the mechanical properties of sludge solidified and modified fillers meet the design requirements, as well as the environmental risks of resource utilization.

2. The method for preparing roadbed filler by solidifying and modifying water supply plant sludge according to claim 1, characterized in that: The sludge quality testing indicators include moisture content, organic matter content, heavy metal content, liquid limit, plastic limit, optimum moisture content, maximum dry density, and particle size distribution.

3. The method for preparing roadbed filler by solidifying and modifying water supply plant sludge according to claim 1, characterized in that: The water content of the dewatered sludge from the water plant should be below 80%, and the organic matter content should be within 10%.

4. The method for preparing roadbed filler by solidifying and modifying water supply plant sludge according to claim 1, characterized in that: The hydration conditioner is a basic metal oxide, preferably calcium oxide, magnesium oxide or sodium oxide.

5. The method for preparing roadbed filler by solidifying and modifying water supply plant sludge according to claim 1, characterized in that: The gel curing agent is cement or slag powder, the strength grade of the cement is not less than grade 32.5, and the grade of the slag powder is not less than S75.

6. The method for preparing roadbed filler by solidifying and modifying water supply plant sludge according to claim 1, characterized in that: The high polymer fiber is polypropylene fiber, polyethylene fiber, polyethylene terephthalate fiber, polyamide fiber, and has a length of no less than 6 mm.

7. The method for preparing roadbed filler by solidifying and modifying water supply plant sludge as claimed in claim 1, characterized in that: The resin water retaining agent is a high molecular weight water absorbing resin having a three-dimensional cross-linked grid structure.

8. The method for preparing roadbed filler by solidifying and modifying water supply plant sludge as claimed in claim 1, characterized in that: Environmental monitoring indicators include moisture content, organic matter content, heavy metal leaching content, and pathogens.

9. The method for preparing roadbed filler by solidifying and modifying water supply plant sludge as claimed in claim 1, characterized in that: The moisture content of the filler after solidification and modification is the optimal moisture content ±2%, the organic matter content is less than 5%, the heavy metal leaching content should meet the requirements of the groundwater quality classification index in the corresponding area, the fecal coliform value is not more than 0.01, and the ascaris egg mortality rate is greater than 95%.

10. The method for preparing roadbed filler by solidifying and modifying sludge from a water supply plant according to claim 1, characterized in that: Indoor geotechnical test indicators include bearing ratio, 7d unconfined compressive strength, compaction test, and quick shear test; the bearing ratio of the cured and modified filler is greater than 2%, the 7d unconfined compressive strength should be greater than 0.05MPa, and meet the design requirements of the corresponding road grade subgrade filler.

11. The method for preparing roadbed filler by solidifying and modifying sludge from a water supply plant according to claim 1, characterized in that: The cured modified filler that meets the testing requirements shall be spread and rolled in layers on the road subgrade within 3 hours and rolled to become active before the cement begins to set.

Images