Method for optimizing permeability of sludge solidified soil

Abstract

The invention provides a sludge solidified soil permeability optimization method, and belongs to the technical field of soil permeability, and the method comprises the following steps: collecting multiple layers of sludge samples, and carrying out detailed physical and chemical characterization on the multiple layers of sludge samples, including water content, granularity, specific surface area and other indexes; and determining sludge solidified soil samples with different proportions by adopting a curing agent dosage equation set according to a characterization result. The optimal water content, the maximum dry density and the permeability coefficient of each sample are obtained through a standard compaction test and a variable head permeability test. And establishing a relation model of the sludge solidified soil ratio and the permeability coefficient by utilizing multiple regression analysis, and identifying key factors influencing the permeability. Based on key factors, designing and optimizing an experimental scheme, adjusting the type and dosage of a curing agent, preparing an optimized sludge solidified soil sample, and verifying the improvement of the permeability coefficient. According to the method, the permeability of the sludge solidified soil can be effectively optimized, and the problems that a sludge solidification formula is difficult to optimize and the permeability of a solidified product is difficult to improve in the prior art are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of soil permeability, and in particular relates to a method for optimizing the permeability of sludge-solidified soil. Background Art

[0002] Sludge is an indispensable byproduct of sewage treatment, which contains a large amount of pollutants such as organic matter and heavy metals. In recent years, with the acceleration of urbanization and the development of industrialization, the amount of sewage discharged into rivers and lakes has continued to increase, and the amount of sludge produced has also shown a rapid upward trend. Traditional sludge treatment methods mainly include incineration, landfill and agricultural use, but these methods often have problems such as high energy consumption and high environmental risks. Therefore, how to achieve the stabilization and resource utilization of sludge has become a key area of ​​current environmental governance.

[0003] As a widely used sludge treatment technology, solidification / fixation is a method of physically and chemically modifying sludge by adding various solidifying agents to improve its strength, stability and durability. Commonly used solidifying agents include cement, lime, fly ash, etc. During the solidification process, these additives can undergo complex reactions with the inorganic and organic components in the sludge to form a stable solidified body. However, the existing sludge solidification technology generally has the problem of poor permeability of solidified products, which will lead to the inability to fully restrict and fix heavy metals and organic pollutants, resulting in the risk of secondary pollution. On the other hand, excessive use of solidifying agents will also increase the economic cost of solidification treatment. Therefore, how to optimize the sludge solidification formula and improve the permeability of solidified products is a technical problem that urgently needs to be solved. Summary of the invention

[0004] In view of this, the present invention provides a method for optimizing the permeability of sludge solidified soil, which can solve the problem that it is difficult to optimize the sludge solidification formula in the prior art and improve the permeability performance of the solidified product.

[0005] The present invention is achieved in that:

[0006] The present invention provides a method for optimizing the permeability of sludge-solidified soil, comprising the following steps:

[0007] S10, collecting sludge samples to be treated, and using a multifunctional sludge sampler for stratified sampling to obtain multi-layer sludge samples;

[0008] S20. Physical and chemical characterization of the collected multi-layer sludge samples, including moisture content detection, particle size analysis, specific surface area determination, mineral composition analysis, organic matter content determination and heavy metal content detection;

[0009] S30, according to the physical and chemical characterization results, according to the preset types of curing agents, the proportion of each curing agent is determined by using a curing agent dosage equation group, and multiple groups of sludge-cured soil samples with different proportions are prepared;

[0010] S40. Use standard compaction test method to determine the optimum moisture content and maximum dry density of each group of sludge solidified soil samples;

[0011] S50, using the variable head permeability test method to determine the permeability coefficient of each group of sludge solidified soil samples;

[0012] S60. Establish a relationship model between the ratio of sludge solidified soil and permeability coefficient, and use multiple regression analysis to determine the key factors affecting permeability;

[0013] S70, based on the key factors, design an optimized experimental plan, adjust the type and amount of the solidifying agent, and prepare a new sludge solidified soil sample; repeat steps S40 to S50 for the newly prepared sludge solidified soil sample to obtain optimized permeability coefficient data;

[0014] S80, comparing the permeability coefficients before and after optimization to verify the effectiveness of the optimization method, and performing step S70 multiple times to form a final sludge-solidified soil permeability optimization plan.

[0015] On the basis of the above technical solution, the method for optimizing the permeability of sludge-solidified soil of the present invention can also be improved as follows:

[0016] The step of detecting the moisture content specifically includes:

[0017] Step 2001, prepare a clean and dry aluminum box, weigh and record the mass of the aluminum box, denoted as m1;

[0018] Step 2002, taking an appropriate amount of fresh sludge sample and putting it into an aluminum box, weighing and recording the total mass of the humidified sludge in the aluminum box, recorded as m;

[0019] Step 2003, placing the aluminum box containing the wet sludge in an oven at 105±5°C and drying to constant weight;

[0020] Step 2004, take out the dried sample together with the aluminum box, put them into a dryer to cool to room temperature, weigh and record the total mass of the aluminum box and the dried sludge after drying, recorded as m3;

[0021] Step 2005: Calculate the moisture content of the sludge sample using the following formula:

[0022] Moisture content (%) = [(m2-m3) / (m3-m1)] × 100;

[0023] Among them: m1 is the mass of the aluminum box; m2 is the total mass of the aluminum box plus wet sludge; m3 is the total mass of the aluminum box plus dry sludge after drying.

[0024] Drying to constant weight usually takes 24 hours or more.

[0025] Furthermore, the step of particle size analysis specifically includes:

[0026] Step 2101, drying the sludge sample at 105°C for 24 hours;

[0027] Step 2102, grinding the dried sample and passing it through a 2 mm sieve;

[0028] Step 2103, take 50 g of the sample under the sieve, add 500 ml of deionized water and dispersant, and disperse by ultrasonic for 30 minutes;

[0029] Step 2104, pouring the dispersed sample into a laser particle size analyzer;

[0030] Step 2105, setting instrument parameters, including sample refractive index and dispersion medium refractive index;

[0031] Step 2106, start the instrument to measure and obtain a particle size distribution curve;

[0032] Step 2107: Analyze the particle size distribution curve and calculate the percentage of each particle size range.

[0033] Furthermore, the step of determining the specific surface area specifically comprises:

[0034] Step 2201, drying the sludge sample at 105° C. for 24 hours;

[0035] Step 2202, grinding the dried sample and passing it through a 100-mesh sieve;

[0036] Step 2203, weigh 1-2 g of sample and put it into a sample tube;

[0037] Step 2204, placing the sample tube into a specific surface area measuring instrument for degassing;

[0038] Step 2205, setting the adsorption gas and test temperature;

[0039] Step 2206: perform an isothermal adsorption-desorption experiment to obtain BET specific surface area data.

[0040] The adsorption gas is usually nitrogen; the test temperature is usually liquid nitrogen temperature.

[0041] Furthermore, the step of mineral composition analysis specifically includes:

[0042] Step 2301, drying the sludge sample at 60° C. for 48 hours;

[0043] Step 2302, grinding the dried sample to less than 200 mesh;

[0044] Step 2303, loading the ground sample into a sample slot of an X-ray diffractometer;

[0045] Step 2304, set the X-ray diffractometer parameters, perform scanning analysis, obtain the diffraction pattern and perform qualitative and semi-quantitative analysis of the mineral composition.

[0046] Furthermore, the step of determining the organic matter content specifically includes:

[0047] Step 2401, drying the sludge sample at 105°C for 24 hours;

[0048] Step 2402, weigh 1 g of the dried sample and put it into a crucible;

[0049] Step 2403, placing the crucible in a muffle furnace and calcining at 550° C. for 4 hours;

[0050] Step 2404, taking out the crucible, cooling it to room temperature, and placing it in a desiccator;

[0051] Step 2405, weigh the mass of the sample after ignition and calculate the loss on ignition, which is the organic matter content.

[0052] Furthermore, the step of heavy metal content detection specifically includes:

[0053] Step 2501, drying the sludge sample at 105°C for 24 hours;

[0054] Step 2502, weigh 0.5 g of dried sample and put it into a digestion tank;

[0055] Step 2503, adding a mixed acid of concentrated nitric acid and concentrated hydrochloric acid, and performing microwave digestion;

[0056] Step 2504, transfer the digested solution to a volumetric flask and adjust the volume to 50 ml;

[0057] Step 2505, filtering the sample solution using a 0.45 μm filter membrane;

[0058] Step 2506: Use an inductively coupled plasma mass spectrometer (ICP-MS) or an atomic absorption spectrometer (AAS) to determine the heavy metal content in the filtrate.

[0059] The mixed acid is aqua regia.

[0060] Furthermore, the preset types of curing agents include cement, lime, fly ash, phosphogypsum, and steel slag;

[0061] The cement is used to improve the strength and stability of sludge-solidified soil;

[0062] The lime is used to adjust the pH value and improve the physical properties of the sludge;

[0063] The fly ash is used to reduce the amount of cement and improve the durability of the solidified soil;

[0064] The phosphogypsum is used to improve the permeability of solidified soil and utilize industrial waste;

[0065] The steel slag is used to increase the strength of the solidified soil and improve the solidification effect of heavy metals.

[0066] Furthermore, the curing agent dosage equation group includes a cement dosage equation, a lime dosage equation, a fly ash dosage equation, a phosphogypsum dosage equation, and a steel slag dosage equation;

[0067] The cement dosage equation is used to calculate the optimal cement addition amount, the input is the sludge moisture content, particle size distribution, specific surface area and organic matter content, and the output is the cement dosage percentage;

[0068] The lime dosage equation is used to calculate the optimal lime addition amount, the input is the sludge moisture content, organic matter content, sludge pH value and heavy metal content, and the output is the lime dosage percentage;

[0069] The fly ash dosage equation is used to calculate the optimal fly ash addition amount, the input is the sludge particle size distribution and specific surface area, and the output is the fly ash dosage percentage;

[0070] The phosphogypsum dosage equation is used to calculate the optimal phosphogypsum addition amount, the input is the sludge mineral composition and the preset target permeability coefficient, and the output is the phosphogypsum dosage percentage;

[0071] The slag dosage equation is used to calculate the optimal slag addition amount, the input is the sludge heavy metal content and the preset target strength, and the output is the slag dosage percentage.

[0072] Among them, the formula of the curing agent dosage equation group is expressed as follows:

[0073] 1. Cement dosage equation:

[0074] C c =α1W+α2D 50 +α3S a +α4O m +β1+ε1;

[0075] In the formula, C c is the percentage of cement usage; W is the moisture content of sludge, %; D 50 is the median particle size of sludge, μm; Sa is the specific surface area, O m is the organic matter content, %; α1, α2, α3, α4 are regression coefficients; β1 is the constant term; ε1 is the error term.

[0076] Parameter acquisition method:

[0077] W was determined by the drying method, and the specific steps were as follows: (1) weighing the fresh sludge sample; (2) drying at 105°C to constant weight; and (3) calculating the weight loss percentage.

[0078] D 50 The particle size was determined by a laser particle size analyzer, and the specific steps are: (1) pretreatment of sludge samples; (2) instrument measurement; and (3) data analysis to obtain the median particle size.

[0079] S a The BET method was used for determination, and the specific steps were as follows: (1) sample degassing pretreatment; (2) nitrogen adsorption-desorption; and (3) data analysis to calculate the specific surface area.

[0080] O m The ignition method is used for determination. The specific steps are as follows: (1) drying the sample; (2) igniting at 550°C for 4 hours; and (3) calculating the ignition loss.

[0081] 2. Lime dosage equation:

[0082]

[0083] In the formula, C l is the percentage of lime usage; W is the sludge moisture content, %; m is the organic matter content, %; pH is the sludge pH value; M i is the content of the ith heavy metal, n is the number of heavy metal types; β1, β2, β3, β4 are regression coefficients; γ1 is the constant term; ε2 is the error term.

[0084] Parameter acquisition method:

[0085] The pH was measured using a pH meter. The specific steps were as follows: (1) mixing the sludge sample with deionized water in a ratio of 1:5; (2) shaking for 30 min; and (3) measuring the pH value of the supernatant after standing for 10 min.

[0086] M i The specific steps of ICP-MS determination are: (1) acid digestion of samples; (2) instrument measurement; and (3) data analysis and calculation of heavy metal content.

[0087] 3. Fly ash dosage equation:

[0088]

[0089] In the formula, C f is the percentage of fly ash used; D 50 is the median particle size of sludge, μm; S a is the specific surface area, D 90 and D 10 are the particle sizes corresponding to 90% and 10% on the particle size distribution curve, μm; δ1, δ2, δ3 are regression coefficients; θ1 is a constant term; ε3 is an error term.

[0090] Parameter acquisition method:

[0091] D 90 and D 10 The laser particle size analyzer was used to determine the specific steps. 50 same.

[0092] 4. Phosphogypsum dosage equation:

[0093]

[0094] In the formula, C p is the percentage of phosphogypsum usage; w j is the mass fraction of the jth mineral; M j is the influence coefficient of the jth mineral; m is the number of mineral species; K t is the target permeability coefficient, K0 is the initial permeability coefficient, λ1, λ2 are regression coefficients; μ1 is the constant term; ε4 is the error term.

[0095] Parameter acquisition method:

[0096] w j The results are obtained by X-ray diffraction (XRD) analysis, and the specific steps are as follows: (1) sample grinding; (2) XRD scanning; and (3) spectrum analysis to calculate the mineral content.

[0097] K0 is determined by a variable head permeability test, the specific steps of which are: (1) sample preparation; (2) saturation treatment; (3) permeability test; (4) data analysis and calculation of permeability coefficient.

[0098] 5. Slag dosage equation:

[0099]

[0100] In the formula, C s is the percentage of steel slag usage; M i is the content of the ith heavy metal, n is the number of heavy metal types; q uis the target unconfined compressive strength, kPa; q0 is the initial unconfined compressive strength, kPa; ρ1, ρ2 are regression coefficients; σ1 is the constant term; ε5 is the error term.

[0101] Parameter acquisition method:

[0102] q0 is determined by an unconfined compressive strength test, and the specific steps are: (1) sample preparation; (2) curing; (3) loading test; (4) data analysis and strength calculation.

[0103] Relationship model between sludge solidification soil ratio and permeability coefficient:

[0104] logK=a1C c +a2C l +a3C f +a4C p +a5C s +b1W+b2ρ d +c1+ε6;

[0105] Where K is the permeability coefficient, C s , C l , C f , C p , C s are the percentages of cement, lime, fly ash, phosphogypsum and steel slag respectively; W is the moisture content, %; ρ d is the dry density, a1, a2, a3, a4, a5, b1, b2 are regression coefficients; c1 is the constant term; ε6 is the error term.

[0106] Parameter acquisition method:

[0107] ρ d The density is measured by compaction test, the specific steps are: (1) sample preparation; (2) layered compaction; (3) measurement of mass and volume; (4) calculation of dry density.

[0108] K is determined by a variable head permeability test, and the specific steps are the same as K0.

[0109] Furthermore, the design optimization experimental scheme is specifically:

[0110] Step 7001, design an orthogonal test scheme and select a factor combination of 3-5 levels;

[0111] Step 7002: prepare new sludge-solidified soil samples, with at least 3 parallel samples for each group of samples;

[0112] Step 7003: Perform compaction test and penetration test to obtain optimized permeability coefficient data;

[0113] Step 7004: Analyze the experimental results using response surface methodology and establish an optimization model;

[0114] Step 7005: Determine the optimal ratio scheme through numerical simulation and experimental verification.

[0115] Compared with the prior art, the method for optimizing the permeability of sludge-solidified soil provided by the present invention has the following beneficial effects:

[0116] 1. A representative sludge sample was obtained by stratified sampling, and a series of physical and chemical characterization methods were used to fully understand the properties of the sludge, including key parameters such as moisture content, particle size distribution, specific surface area, mineral composition, organic matter content and heavy metal concentration. This provides reliable basic data for the subsequent optimization of the curing agent ratio.

[0117] 2. A prediction model for the dosage of various curing agents, including cement, lime, fly ash, phosphogypsum and steel slag, was established, which can determine the optimal addition ratio of various curing agents according to different sludge properties. This can not only improve the curing effect, but also reduce the economic cost caused by excessive addition of curing agents.

[0118] 3. The standard compaction test and variable head permeability test methods were used to determine the mechanical properties and permeability parameters of sludge-stabilized soil under different solidifying agent ratios, and a quantitative prediction model was established, revealing the influence of factors such as solidifying agent dosage, moisture content and dry density on the permeability coefficient.

[0119] 4. Based on the above analysis results, orthogonal experimental design and response surface optimization method were used to adjust the type and dosage of the solidifying agent in a targeted manner to prepare sludge solidified soil with excellent permeability. The experimental results show that this optimization method can effectively improve the permeability coefficient of the solidified product and significantly reduce the dissolution risk of heavy metals and organic pollutants.

[0120] 5. The method is relatively simple to operate, and the data analysis logic is clear, which can provide reliable technical support for engineering practice. Compared with the traditional empirical method, the present invention has stronger pertinence and operability, and can greatly improve the environmental benefits of sludge solidification treatment.

[0121] In summary, the sludge solidification soil permeability optimization method proposed in the present invention makes full use of tools such as mathematical modeling and statistical analysis to systematically solve the problem that the existing technology is difficult to optimize the sludge solidification formula and improve the permeability performance of the solidified product. BRIEF DESCRIPTION OF THE DRAWINGS

[0122] Figure 1 A flow chart of the method provided by the present invention;

[0123] Figure 2It is the particle size distribution curve of each group of samples in the embodiment. DETAILED DESCRIPTION

[0124] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0125] like Figure 1 FIG. 1 is a flow chart of a method for optimizing the permeability of sludge-solidified soil provided by the present invention. The method comprises the following steps:

[0126] S10, collecting sludge samples to be treated, and using a multifunctional sludge sampler for stratified sampling to obtain multi-layer sludge samples;

[0127] S20. Physical and chemical characterization of the collected multi-layer sludge samples, including moisture content detection, particle size analysis, specific surface area determination, mineral composition analysis, organic matter content determination and heavy metal content detection;

[0128] S30, according to the physical and chemical characterization results, according to the preset types of curing agents, the proportion of each curing agent is determined by using a curing agent dosage equation group, and multiple groups of sludge-cured soil samples with different proportions are prepared;

[0129] S40. Use standard compaction test method to determine the optimum moisture content and maximum dry density of each group of sludge solidified soil samples;

[0130] S50, using the variable head permeability test method to determine the permeability coefficient of each group of sludge solidified soil samples;

[0131] S60. Establish a relationship model between the ratio of sludge solidified soil and permeability coefficient, and use multiple regression analysis to determine the key factors affecting permeability;

[0132] S70, based on the key factors, design an optimized experimental plan, adjust the type and amount of the solidifying agent, and prepare a new sludge solidified soil sample; repeat steps S40 to S50 for the newly prepared sludge solidified soil sample to obtain optimized permeability coefficient data;

[0133] S80, comparing the permeability coefficients before and after optimization to verify the effectiveness of the optimization method, and performing step S70 multiple times to form a final sludge-solidified soil permeability optimization plan.

[0134] The specific implementation methods of the above steps are described in detail below:

[0135] The specific implementation method of step S10 is: first, use a multifunctional sludge sampler to perform stratified sampling to obtain multi-layer sludge samples. The multifunctional sludge sampler is a commonly used sampling tool that can obtain sludge samples from different depths, which is conducive to a comprehensive understanding of the vertical distribution of sludge properties. The purpose of this step is to obtain representative sludge samples to provide basic data for subsequent physical and chemical characterization.

[0136] The specific implementation of step S20 includes the following sub-steps:

[0137] 2001) Prepare a clean and dry aluminum box, weigh and record the mass of the aluminum box (m1).

[0138] 2002) Take an appropriate amount of fresh sludge sample and put it into an aluminum box, weigh and record the total mass (m2) of the humidified sludge in the aluminum box.

[0139] 2003) Place the aluminum box containing wet sludge in an oven at 105±5℃ and dry it to constant weight (usually takes 24 hours or longer).

[0140] 2004) Take out the dried sample together with the aluminum box, put it into a dryer to cool to room temperature, weigh and record the total mass (m3) of the aluminum box and dry sludge after drying.

[0141] 2005) using the formula Calculate the moisture content of the sludge sample.

[0142] The purpose of this step is to determine the moisture content of the sludge by a standard drying method, which is a key parameter for subsequent solidification treatment.

[0143] The particle size analysis sub-steps of step S20 are as follows:

[0144] 2101) The sludge sample was dried at 105°C for 24 hours.

[0145] 2102) Grind the dried sample and pass it through a 2 mm sieve.

[0146] 2103) Take 50 g of the sample under the sieve, add 500 ml of deionized water and dispersant, and disperse by ultrasonic for 30 minutes.

[0147] 2104) Pour the dispersed sample into a laser particle size analyzer.

[0148] 2105) Set the instrument parameters, including the sample refractive index, the dispersion medium refractive index, etc.

[0149] 2106) Start the instrument to measure and obtain the particle size distribution curve.

[0150] 2107) Analyze the particle size distribution curve and calculate the percentage of each particle size range.

[0151] The purpose of this step is to use laser particle size analysis to determine the particle size distribution of the sludge, providing a basis for subsequent optimization of the solidifying agent ratio.

[0152] The specific surface area determination sub-steps of step S20 are as follows:

[0153] 2201) The sludge sample was dried at 105°C for 24 hours.

[0154] 2202) Grind the dried sample and pass it through a 100 mesh sieve.

[0155] 2203) Weigh 1-2g of sample and put it into a sample tube.

[0156] 2204) Place the sample tube into a specific surface area measuring instrument for degassing.

[0157] 2205) Set the adsorption gas (usually nitrogen) and test temperature (usually liquid nitrogen temperature).

[0158] 2206) to conduct isothermal adsorption-desorption experiments and obtain BET specific surface area data.

[0159] The purpose of this step is to determine the specific surface area of ​​sludge using the BET method, which is an important factor affecting the amount of curing agent.

[0160] The mineral composition analysis sub-steps of step S20 are as follows:

[0161] 2301) The sludge sample was dried at 60°C for 48 hours.

[0162] 2302) Grind the dried sample to less than 200 mesh.

[0163] 2303) Load the ground sample into the sample slot of the X-ray diffractometer.

[0164] 2304) Set the X-ray diffractometer parameters, perform scanning analysis, obtain diffraction patterns and conduct qualitative and semi-quantitative analysis of mineral composition.

[0165] The purpose of this step is to analyze the mineral composition of the sludge by X-ray diffraction, so as to provide a basis for the subsequent optimization of the dosage of phosphogypsum.

[0166] The organic matter content determination sub-steps of step S20 are as follows:

[0167] 2401) Dry the sludge sample at 105°C for 24 hours.

[0168] 2402) Weigh 1 g of dried sample and put it into a crucible.

[0169] 2403) Place the crucible in a muffle furnace and burn at 550°C for 4 hours.

[0170] 2404) Take out the crucible, cool it to room temperature, and put it in a desiccator.

[0171] 2405) Weigh the mass of the sample after ignition and calculate the loss on ignition, which is the organic matter content.

[0172] The purpose of this step is to determine the organic matter content of the sludge by the incineration method, which is an important factor affecting the amount of lime.

[0173] The heavy metal content detection sub-steps of step S20 are as follows:

[0174] 2501) The sludge sample was dried at 105°C for 24 hours.

[0175] 2502) Weigh 0.5 g of dried sample and put it into the digestion tank.

[0176] 2503) Add a mixed acid of concentrated nitric acid and concentrated hydrochloric acid (aqua regia) and perform microwave digestion.

[0177] 2504) Transfer the digested solution to a volumetric flask and make up to 50 ml.

[0178] 2505) Filter the sample solution using a 0.45 μm filter membrane.

[0179] 2506) using inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectrometry (AAS) to determine the heavy metal content in the filtrate.

[0180] The purpose of this step is to determine the content of heavy metals in the sludge by ICP-MS or AAS, so as to provide a basis for optimizing the amount of lime and slag.

[0181] The specific implementation of step S30 is: first, according to the physical and chemical characterization results obtained in step S20, combined with the preset curing agent types, the following curing agent dosage equation group is used to calculate the optimal ratio of various curing agents:

[0182] 1. Cement dosage equation:

[0183] C c =α1W+α2D 50 +α3S a +α4O m +β1+ε1;

[0184] Among them, C c is the percentage of cement usage; W is the moisture content of sludge, %; D 50 is the median particle size of sludge, μm; S a is the specific surface area, O mis the organic matter content, %; α1, α2, α3, α4 are regression coefficients; β1 is the constant term; ε1 is the error term.

[0185] 2. Lime dosage equation:

[0186]

[0187] Among them, C l is the percentage of lime usage; W is the sludge moisture content, %; m is the organic matter content, %; pH is the sludge pH value; M i is the content of the ith heavy metal, n is the number of heavy metal types; β1, β2, β3, β4 are regression coefficients; γ1 is the constant term; ε2 is the error term.

[0188] 3. Fly ash dosage equation:

[0189]

[0190] Among them, C f is the percentage of fly ash used; D 50 is the median particle size of sludge, μm; S a is the specific surface area, D 90 and D 10 are the particle sizes corresponding to 90% and 10% on the particle size distribution curve, μm; δ1, δ2, δ3 are regression coefficients; θ1 is a constant term; ε3 is an error term.

[0191] 4. Phosphogypsum dosage equation:

[0192]

[0193] Among them, C p is the percentage of phosphogypsum usage; w j is the mass fraction of the jth mineral; M j is the influence coefficient of the jth mineral; m is the number of mineral species; K t is the target permeability coefficient, K0 is the initial permeability coefficient, λ1, λ2 are regression coefficients; μ1 is the constant term; ε4 is the error term.

[0194] 5. Slag dosage equation:

[0195]

[0196] Among them, C s is the percentage of steel slag usage; M i is the content of the ith heavy metal, n is the number of heavy metal types; qu is the target unconfined compressive strength, kPa; q0 is the initial unconfined compressive strength, kPa; ρ1, ρ2 are regression coefficients; σ1 is the constant term; ε5 is the error term.

[0197] The purpose of these dosage equations is to predict the optimal usage ratio of various solidifying agents based on the physical and chemical properties of the sludge, so as to provide the mix ratio for subsequent sample preparation.

[0198] The specific implementation method of step S40 is: using a standard compaction test method to determine the optimal moisture content and maximum dry density of each group of sludge solidified soil samples. The standard compaction test is a commonly used experimental method. By performing layered static pressure compaction on the sample, the moisture content-dry density relationship curve is measured to obtain the maximum dry density and the optimal moisture content. The purpose of this step is to lay the foundation for the subsequent permeability test and ensure the molding quality of the sample.

[0199] The specific implementation of step S50 is: using the variable head permeability test method to determine the permeability coefficient of each group of sludge solidified soil samples. The variable head permeability test is a commonly used permeability performance test method. By controlling the change of the water inlet head, the volume of water flowing out of the sample is measured, and then the permeability coefficient is calculated. The purpose of this step is to obtain the permeability performance parameters of sludge solidified soil under various curing agent ratios to provide data support for optimizing the formula.

[0200] The specific implementation of step S60 is: firstly, a relationship model between the sludge solidification soil ratio and the permeability coefficient is established:

[0201] logK=a1C c +a2C l +a3C f +a4C p +a5C s +b1W+b2ρ d +c1+ε6;

[0202] Where K is the permeability coefficient, C c , C l , C f , C p , C s are the percentages of cement, lime, fly ash, phosphogypsum and steel slag respectively; W is the moisture content, %; ρ d is the dry density, a1, a2, a3, a4, a5, b1, b2 are regression coefficients; c1 is the constant term; ε6 is the error term.

[0203] Then, the multivariate regression analysis method was used to determine the key factors affecting permeability. The purpose of this step is to establish a quantitative model to describe the relationship between factors such as curing agent ratio, moisture content and dry density and permeability coefficient, providing a theoretical basis for subsequent optimization.

[0204] The specific implementation of step S70 includes the following sub-steps:

[0205] 7001) Design an orthogonal experimental scheme and select a factor combination with 3-5 levels.

[0206] 7002) Prepare new sludge-solidified soil samples, with at least 3 parallel samples for each group of samples.

[0207] 7003) to conduct compaction test and penetration test to obtain optimized permeability coefficient data.

[0208] 7004) Response surface method was used to analyze the experimental results and establish an optimization model. Response surface method is a commonly used multi-factor optimization method. By establishing a mathematical model between the objective function and the design factors, the design space is explored and the optimal process parameters are finally determined. The specific formula is as follows:

[0209] y=f(x1,x2,…,x p )+ε;

[0210] Among them, y is the response value (such as permeability coefficient), x1, x2, ..., x p is the design factor (such as curing agent dosage, moisture content, etc.), and ε is the random error. Through experimental design and statistical analysis, the response surface model f(x1, x2, ..., x p ), and use numerical optimization methods to determine the optimal process parameters.

[0211] 7005) The optimal ratio scheme is determined through numerical simulation and experimental verification.

[0212] The purpose of this step is to further design optimization experiments based on the above analysis results, adjust the type and dosage of the solidifying agent, prepare new sludge solidified soil samples, test their permeability, and finally determine the optimal solidifying agent ratio. Response surface methodology is a commonly used multi-factor optimization method that can effectively explore the design space and obtain the optimal process parameters.

[0213] The specific implementation of step S80 is: compare and analyze the permeability coefficient data before and after optimization to verify the effectiveness of the optimization method. If the optimization effect meets expectations, the final sludge solidification soil permeability optimization plan is formed; if further optimization is required, step S70 is repeated until the optimal permeability performance is achieved. The purpose of this step is to ensure the reliability and practicality of the optimization method and provide a reliable basis for subsequent engineering applications.

[0214] Specifically, the principle of the present invention is: first, through stratified sampling and system characterization, the properties of the sludge to be treated are fully understood; then, a solidifying agent dosage prediction model suitable for different sludges is established to determine the optimal addition ratio of various solidifying agents; next, standard mechanical and permeability test methods are used to measure the performance parameters of sludge solidified soil with different ratios, and a quantitative prediction model is established; finally, based on optimization analysis, the type and dosage of the solidifying agent are adjusted in a targeted manner to prepare sludge solidified soil with excellent permeability.

[0215] The scientificity and feasibility of this series of methods are reflected in the following aspects:

[0216] 1. Characterization of sludge properties is the key foundation. Through stratified sampling and systematic testing, the physical and chemical properties of sludge can be fully understood, providing a reliable parameter basis for the subsequent solidification formula design. For example, moisture content, particle size distribution and specific surface area are important factors affecting the dosage of curing agent; mineral composition and heavy metal content are directly related to the amount of phosphogypsum and steel slag added. Only by fully understanding the properties of sludge can targeted optimization measures be taken.

[0217] 2. The establishment of a prediction model for the amount of curing agent is a key step. The present invention uses a multivariate regression analysis method to construct five prediction models for the amount of curing agent, including cement, lime, fly ash, phosphogypsum and steel slag. These models can organically link the physical and chemical properties of sludge with the optimal amount of curing agent added, providing a reliable mix ratio for sample preparation. Compared with the empirical curing agent selection method, this modeling method is more scientific and systematic.

[0218] 3. The establishment of a permeability prediction model is a key innovation. On the basis of the above, the present invention further establishes a quantitative relationship model between the sludge solidification soil ratio and the permeability coefficient. This can not only predict the permeability performance under different formulations, but also find the optimal solidifying agent ratio that can meet the target permeability coefficient through numerical optimization methods. This optimization method based on mathematical models can greatly improve the optimization efficiency and reliability compared to the traditional empirical trial and error process.

[0219] 4. Orthogonal experimental design and response surface optimization are key means. In the specific optimization process, the present invention adopts the method of orthogonal experimental design and response surface analysis. Orthogonal experiment can systematically explore the design space and find out the main influencing factors within a limited number of experiments; response surface analysis can further fit the mathematical relationship between the objective function and the design factors, providing a theoretical basis for determining the optimal parameters. This method of combining experimental design and numerical optimization gives full play to the advantages of engineering practice and computational analysis, and greatly improves the optimization effect.

[0220] In summary, the sludge solidification soil permeability optimization method proposed in the present invention makes full use of computer algorithms such as mathematical modeling and statistical analysis to systematically solve the problem of poor permeability in existing solidification technologies.

[0221] In order to better understand and implement the present invention, an example of a specific application scenario of the present invention is provided below: the sludge from a shrimp pond on a beach urgently needs to be stabilized. The physical and chemical properties of the sludge are as follows: the water content is 78.3%, the median particle size D 50 The specific surface area is 35.7 μm. a for The mineral composition is mainly quartz, kaolinite and chlorite, and the organic matter content is O m It is 12.6%, and the content of heavy metals is also high. The concentrations of copper, cadmium, lead and mercury are 120mg / kg, 15mg / kg, 68mg / kg and 2.3mg / kg respectively.

[0222] In order to improve the permeability of the sludge solidified soil, the optimization method proposed in the present invention was used for treatment. The specific steps are as follows:

[0223] 1. Sludge sampling and characterization

[0224] Firstly, three parallel sludge samples were obtained from different depths using a multifunctional sludge sampler. After indoor analysis and testing, the physical and chemical characteristic parameters of the sludge were obtained.

[0225] 2. Prediction of curing agent dosage

[0226] According to the above sludge property data, five solidifying agent dosage prediction models provided by the present invention were used to calculate and determine the optimal addition ratio of various solidifying agents:

[0227] Cement dosage c =12.5%;

[0228] Lime dosage C l =4.8%;

[0229] Fly ash dosage C f =10.2%;

[0230] Phosphogypsum dosage C p =6.4%;

[0231] Slag dosage C s =8.1%;

[0232] 3. Preparation of Sludge Solidified Soil Samples

[0233] According to the above curing agent ratio, three groups of parallel sludge solidified soil samples were prepared by using the standard mix ratio blending method. At the same time, in order to further optimize the formula, four groups of different curing agent ratio schemes were designed by using the orthogonal experimental design method, with three parallel samples in each group, for a total of 12 samples. After these samples were cured for 28 days under standard curing conditions, subsequent performance tests were carried out.

[0234] 4. Mechanical properties test

[0235] For the above 16 sludge solidified soil samples, the standard compaction test method was used to determine the optimal moisture content W and maximum dry density ρ of each group of samples. The results are shown in Table 1:

[0236] Table 1 Mechanical properties of sludge solidified soil samples

[0237]

[0238]

[0239] It can be seen from Table 1 that different curing agent ratios have a great influence on the mechanical properties of sludge-stabilized soil. The maximum dry density of formula 8 is the highest, reaching 1.65 g / cm 3 , the corresponding optimal moisture content is 28.0%, which is beneficial to improving the strength and stability of the solidified soil.

[0240] 5. Penetration performance test

[0241] On the basis of the mechanical properties test, the 16 sludge solidified soil samples were subjected to variable head permeability test and their permeability coefficient K was determined. The results are shown in Table 2:

[0242] Table 2 Permeability coefficient of sludge solidified soil samples

[0243]

[0244]

[0245] It can be seen from Table 2 that the permeability coefficients of sludge-stabilized soil under different formulations vary greatly, with the lowest reaching 9.02×10 -8 cm / s, up to 1.74×10 -6 Based on these results, the response surface analysis method was further used to establish a quantitative relationship model between the permeability coefficient and the curing agent ratio, moisture content and dry density:

[0246] logK=-0.032C c -0.041C l -0.027C f -0.036C p-0.028C s +0.025W-0.039ρ d -5.12+ε6;

[0247] Through numerical optimization, the permeability coefficient K that can meet the target is determined. t =1×10 -7 The optimal curing agent ratio of cm / s:

[0248] Cement dosage c =10.3%;

[0249] Lime dosage C l =5.6%;

[0250] Fly ash dosage C f =8.7%;

[0251] Phosphogypsum dosage C p =7.2%;

[0252] Slag dosage C s =9.4%;

[0253] 6. Analysis and discussion of test results

[0254] According to the above optimization scheme, three groups of parallel sludge solidified soil samples were prepared and permeability tests were carried out after 28 days of curing. The results showed that the average permeability coefficient of the three samples was 8.26×10 -8 cm / s, in line with the preset target permeability coefficient K t .

[0255] In order to further verify the optimization effect, the particle size distribution curves of each group of samples were drawn, such as Figure 2 As shown, from Figure 2 It can be seen that the particle size distribution curve of the optimized sludge solidified soil sample obviously moves towards the fine particle direction. 10 , D 50 and D 90 This indicates that by optimizing the ratio of the solidifying agent, the pore structure of the sludge-solidified soil was successfully adjusted, thereby improving its overall permeability.

[0256] In addition, heavy metal leaching tests were carried out on the sludge solidified soil samples before and after optimization, and the results are shown in Table 3:

[0257] Table 3 Heavy metal leaching characteristics of sludge solidified soil

[0258] heavy metal Initial content (mg / kg) Leaching amount before optimization (mg / L) Optimized leaching amount (mg / L) copper 120 1.38 0.56 cadmium 15 0.21 0.09 lead 68 0.92 0.38 mercury 2.3 0.04 0.01

[0259] As can be seen from Table 3, after optimization treatment, the leaching amount of heavy metals in sludge-solidified soil was significantly reduced, for example, the leaching concentrations of copper, cadmium, lead and mercury were reduced by 59.4%, 57.1%, 58.7% and 75.0%, respectively. This shows that by optimizing the ratio of the solidifying agent, not only the overall permeability of the sludge-solidified soil is improved, but also the migration risk of heavy metals is greatly reduced, further enhancing the solidification effect.

[0260] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for optimizing the permeability of sludge-solidified soil, characterized in that: The following steps are involved: S10, collecting sludge samples to be treated, and using a multifunctional sludge sampler for stratified sampling to obtain multi-layer sludge samples; S20. Physical and chemical characterization of the collected multi-layer sludge samples, including moisture content detection, particle size analysis, specific surface area determination, mineral composition analysis, organic matter content determination and heavy metal content detection; S30, according to the physical and chemical characterization results, according to the preset types of curing agents, the proportion of each curing agent is determined by using a curing agent dosage equation group, and multiple groups of sludge-cured soil samples with different proportions are prepared; S40. Use standard compaction test method to determine the optimum moisture content and maximum dry density of each group of sludge solidified soil samples; S50, using the variable head permeability test method to determine the permeability coefficient of each group of sludge solidified soil samples; S60. Establish a relationship model between the ratio of sludge solidified soil and permeability coefficient, and use multiple regression analysis to determine the key factors affecting permeability; S70, based on the key factors, design an optimized experimental plan, adjust the type and amount of the solidifying agent, and prepare a new sludge solidified soil sample; repeat steps S40 to S50 for the newly prepared sludge solidified soil sample to obtain optimized permeability coefficient data; S80, comparing the permeability coefficients before and after optimization to verify the effectiveness of the optimization method, and performing step S70 multiple times to form a final sludge-solidified soil permeability optimization plan.

2. The method for optimizing the permeability of sludge-stabilized soil according to claim 1, characterized in that: The step of moisture content detection specifically includes: Step 2001, prepare a clean and dry aluminum box, weigh and record the mass of the aluminum box, denoted as m1; Step 2002, taking an appropriate amount of fresh sludge sample and putting it into an aluminum box, weighing and recording the total mass of the humidified sludge in the aluminum box, recorded as m; Step 2003, placing the aluminum box containing the wet sludge in an oven at 105±5°C and drying to constant weight; Step 2004, take out the dried sample together with the aluminum box, put them into a dryer to cool to room temperature, weigh and record the total mass of the aluminum box and the dried sludge after drying, recorded as m3; Step 2005: Calculate the moisture content of the sludge sample using the following formula: Moisture content (%) = [(m2-m3) / (m3-m1)] × 100; Among them: m1 is the mass of the aluminum box; m2 is the total mass of the aluminum box plus wet sludge; m3 is the total mass of the aluminum box plus dry sludge after drying.

3. A method for optimizing the permeability of sludge-stabilized soil according to claim 2, characterized in that: The step of particle size analysis specifically includes: Step 2101, drying the sludge sample at 105°C for 24 hours; Step 2102, grinding the dried sample and passing it through a 2 mm sieve; Step 2103, take 50 g of the sample under the sieve, add 500 ml of deionized water and dispersant, and disperse by ultrasonic for 30 minutes; Step 2104, pouring the dispersed sample into a laser particle size analyzer; Step 2105, setting instrument parameters, including sample refractive index and dispersion medium refractive index; Step 2106, start the instrument to measure and obtain a particle size distribution curve; Step 2107: Analyze the particle size distribution curve and calculate the percentage of each particle size range.

4. The method for optimizing the permeability of sludge-stabilized soil according to claim 3, characterized in that: The step of specific surface area specifically comprises: Step 2201, drying the sludge sample at 105° C. for 24 hours; Step 2202, grinding the dried sample and passing it through a 100-mesh sieve; Step 2203, weigh 1-2 g of sample and put it into a sample tube; Step 2204, placing the sample tube into a specific surface area measuring instrument for degassing; Step 2205, setting the adsorption gas and test temperature; Step 2206: perform an isothermal adsorption-desorption experiment to obtain BET specific surface area data.

5. The method for optimizing the permeability of sludge-stabilized soil according to claim 4, characterized in that: The steps of the mineral composition analysis specifically include: Step 2301, drying the sludge sample at 60° C. for 48 hours; Step 2302, grinding the dried sample to less than 200 mesh; Step 2303, loading the ground sample into a sample slot of an X-ray diffractometer; Step 2304, set the X-ray diffractometer parameters, perform scanning analysis, obtain the diffraction pattern and perform qualitative and semi-quantitative analysis of the mineral composition.

6. The method for optimizing the permeability of sludge-stabilized soil according to claim 5, characterized in that: The step of determining the organic matter content specifically includes: Step 2401, drying the sludge sample at 105°C for 24 hours; Step 2402, weigh 1 g of the dried sample and put it into a crucible; Step 2403, placing the crucible in a muffle furnace and calcining at 550° C. for 4 hours; Step 2404, taking out the crucible, cooling it to room temperature, and placing it in a desiccator; Step 2405, weigh the mass of the sample after ignition and calculate the loss on ignition, which is the organic matter content.

7. A method for optimizing the permeability of sludge-stabilized soil according to claim 6, characterized in that: The steps of heavy metal content detection specifically include: Step 2501, drying the sludge sample at 105°C for 24 hours; Step 2502, weigh 0.5 g of dried sample and put it into a digestion tank; Step 2503, adding a mixed acid of concentrated nitric acid and concentrated hydrochloric acid, and performing microwave digestion; Step 2504, transfer the digested solution to a volumetric flask and adjust the volume to 50 ml; Step 2505, filtering the sample solution using a 0.45 μm filter membrane; Step 2506: Use an inductively coupled plasma mass spectrometer (ICP-MS) or an atomic absorption spectrometer (AAS) to determine the heavy metal content in the filtrate.

8. The method for optimizing the permeability of sludge-stabilized soil according to claim 7, characterized in that: The preset curing agent types include cement, lime, fly ash, phosphogypsum, and steel slag; The cement is used to improve the strength and stability of sludge solidified soil; The lime is used to adjust the pH value and improve the physical properties of the sludge; The fly ash is used to reduce the amount of cement and improve the durability of the solidified soil; The phosphogypsum is used to improve the permeability of solidified soil and utilize industrial waste; The steel slag is used to increase the strength of the solidified soil and improve the solidification effect of heavy metals.

9. The method for optimizing the permeability of sludge-stabilized soil according to claim 8, characterized in that: The curing agent dosage equation group includes a cement dosage equation, a lime dosage equation, a fly ash dosage equation, a phosphogypsum dosage equation, and a steel slag dosage equation; The cement dosage equation is used to calculate the optimal cement addition amount, the input is the sludge moisture content, particle size distribution, specific surface area and organic matter content, and the output is the cement dosage percentage; The lime dosage equation is used to calculate the optimal lime addition amount, the input is the sludge moisture content, organic matter content, sludge pH value and heavy metal content, and the output is the lime dosage percentage; The fly ash dosage equation is used to calculate the optimal fly ash addition amount, the input is the sludge particle size distribution and specific surface area, and the output is the fly ash dosage percentage; The phosphogypsum dosage equation is used to calculate the optimal phosphogypsum addition amount, the input is the sludge mineral composition and the preset target permeability coefficient, and the output is the phosphogypsum dosage percentage; The slag dosage equation is used to calculate the optimal slag addition amount, the input is the sludge heavy metal content and the preset target strength, and the output is the slag dosage percentage.

10. The method for optimizing the permeability of sludge-stabilized soil according to claim 9, characterized in that: The design optimization experimental scheme is specifically: Step 7001, design an orthogonal test scheme and select a factor combination of 3-5 levels; Step 7002: prepare new sludge-solidified soil samples, with at least 3 parallel samples for each group of samples; Step 7003: Perform compaction test and penetration test to obtain optimized permeability coefficient data; Step 7004: Analyze the experimental results using response surface methodology and establish an optimization model; Step 7005: Determine the optimal ratio scheme through numerical simulation and experimental verification.

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