Method and experimental equipment for reinforcing and repairing pb contaminated sludge by nano-sio2 and micp technology

Abstract

The application discloses experimental equipment and a method for reinforcing and repairing Pb-polluted sludge by using nano-SiO2 and MICP technology. 2+ And the concentration of Pb 2+ , the harm of metal cations to bacteria and the damage of urease activity are alleviated; secondly, the urease-producing bacteria decompose urea, so that the concentration of OH ‑ in the environment gradually increases, which provides the possibility for the occurrence of the pozzolanic effect of nano-SiO2, further improves the utilization rate of Ca 2+ in the MICP technology, and increases the strength of the sludge sample; in addition, the metal carbonate precipitate and co-precipitate induced by microorganisms effectively reduce the mobility of Pb 2+ existing in the environment. Therefore, the nano-SiO2 and MICP technology has a wide application prospect in the field of reinforcing and repairing heavy metal-polluted soil.

Description

Technical Field

[0001] This invention belongs to the field of foundation solidification / stabilization treatment technology, and particularly relates to an experimental device and method for the reinforcement and remediation of Pb-contaminated sludge using nano-SiO2 synergistic microbial induced carbonate precipitation (MICP) technology. Background Technology

[0002] Dredging of ports, lakes, and waterways generates large amounts of silt, which not only occupies land but also, due to its high water content, low cohesion, and low strength, cannot be directly used in engineering projects. Therefore, silt reinforcement has become an urgent problem to be solved in infrastructure construction to meet foundation engineering requirements. Common methods for silt foundation reinforcement include cement grout, chemical grout, and the injection of coarse sand or gravel. However, the high energy consumption of these materials, the demanding requirements of the grouting technology, and the secondary pollution to the environment are all issues that cannot be ignored.

[0003] Microbial induced carbonate precipitation (MICP) technology utilizes microbial mineralization mechanisms to induce the production of biogenic carbonate minerals with cementing capabilities, thereby reinforcing soil particles. Taking urease-producing bacteria as an example, the bacteria use their secreted urease to hydrolyze urea to generate carbonate ions, which combine with calcium ions in the cementing solution. The resulting CaCO3 adheres to the bacterial surface, filling soil pores or binding soil particles, ultimately increasing the soil's bearing capacity. Although MICP technology, as a novel, green, and efficient soil reinforcement technique, has been widely applied in foundation reinforcement, its implementation is limited by several factors. For example, high concentrations of Ca... 2+ The solution causes irreversible damage to bacterial growth and urease activity. In most microbial circulating grouting systems, uneven grouting of the bacterial solution and cementing solution leads to significant differences in the distribution of the target product, resulting in weak surfaces in soil column samples and even destroying the integrity of the samples. Therefore, a more comprehensive solution is needed to further reinforce the foundation using MICP technology. In addition, the environmental pollution caused by NH3 released from the decomposition of urea by urease-producing bacteria is also an urgent problem to be solved. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an experimental apparatus and method for the reinforcement and remediation of Pb-contaminated sludge using nano-SiO2 synergistic with nano-SiO2 synergistic with MICP technology. This method aims to solve the technical problems of insufficient soil strength reinforcement due to microbially induced cementitious materials and uneven distribution of biogenic calcium carbonate caused by cyclic grouting; and, specifically, for the application of MICP technology in reinforcing heavy metal-contaminated sludge with high concentrations of metal ions, including Pb... 2+ and Ca 2+This invention addresses the problem of damage caused by Bacillus pasteurellii and urease. It employs a process combining a one-time mixing of high-concentration cementitious solution and bacterial solution with omnidirectional grouting of the cementitious solution. By utilizing the unique properties of nano-SiO2 combined with MICP technology, it significantly reduces soil Pb levels. 2+ Effectiveness, increases soil strength.

[0005] The technical solution adopted in this invention is as follows:

[0006] In a first aspect, the present invention provides a method for reinforcing and remediating Pb-contaminated sludge using nano-SiO2 synergistic with MIP technology, comprising the following steps:

[0007] (1) Preparation of 1-(2-pyridineazo)-2-naphthol graft-modified nano-SiO2--PAN-nano-SiO2;

[0008] (2) Mix PAN-nano SiO2 with sieved dry sludge powder evenly, and then mix with nano SiO2 to obtain powder A;

[0009] (3) Add the cementing liquid to powder A, stir well and let stand, then add the bacterial suspension and mix well.

[0010] (4) It can be obtained after maintenance.

[0011] Furthermore, the preparation method of PAN-nano SiO2 in step (1) includes the following steps:

[0012] 1.1: Activated nano-SiO2 was added to an organic solvent, ultrasonically dispersed, and 3-aminopropyltriethoxysilane was added dropwise. The mixture was heated under reflux, vacuum filtered, washed, and dried to obtain APTES-modified nano-SiO2-APTES.

[0013] 1.2: The product from step 1.1 was added to formaldehyde, concentrated hydrochloric acid and 1-(2-pyridinium azo)-2-naphthol, then anhydrous ethanol was added, stirred, heated under reflux, and then vacuum filtered, washed, centrifuged and dried to obtain PAN-nano SiO2.

[0014] Furthermore, in step 1.1, the activation temperature is 110℃~115℃, the organic solvent is toluene, and the heating reflux temperature is 110℃~115℃.

[0015] Furthermore, in step 1.2, the heating reflux temperature is 80℃~90℃.

[0016] Furthermore, in step (2), the particle size range of PAN-nano SiO2 is 30 ~ 60 nm, the dry sludge powder is sludge particles that have passed through a 2 mm diameter sieve, and the particle size of nano silica is approximately 30 nm ~ 40 nm. Preferably, the particle size of nano silica is approximately 30 nm.

[0017] Further, in step (2), the mass ratio of PAN-nano SiO2, nano SiO2, and sieved dry sludge powder is 0.01:(0.01~1):100. Preferably, the mass ratio of PAN-nano SiO2, nano SiO2, and sieved dry sludge powder is 0.01:(0.01~0.1):100.

[0018] Furthermore, in step (3), the cementing solution is a mixture of urea, nutrient broth, NH4Cl, NaHCO3, and CaCl2, wherein Ca... 2+ The concentration of the active ingredient was 0.5 mol / L to 2 mol / L, and the concentration of urea was 0.5 mol / L to 2 mol / L; the bacterial suspension was a suspension of Bacillus pasteurellii, with an OD value of [missing information]. 600 The range is 1 to 1.5. Preferably, the fixed volume ratio of the gelling solution to the cell suspension is 4:1.

[0019] Furthermore, in step (4), the curing time is 3 to 14 days.

[0020] Relevant principles:

[0021] This invention utilizes PAN grafting to modify the surface functional groups of nano-SiO2, enabling the modified nano-SiO2 to enhance its affinity for Pb through complexation and chelation. 2+ Chemical adsorption reduces Pb in the environment. 2+ The bioavailable content of Pb hinders the absorption of Pb by Bacillus pasteurellii in the MIP technology. 2+ The absorption and accumulation of [something]; simultaneously, it alleviates the damage of metal ions to the intracellular and extracellular urease structures, promoting the stable progress of MICP; furthermore, the CO3 produced by MICP [something]... 2- With Pb 2+ The combination of these elements also promotes the fixation of heavy metal ions. The negative charge held by ordinary nano-SiO2 on Ca... 2+ Electrostatic adsorption (physical adsorption) can not only alleviate the high concentration of Ca in MIP technology, but also... 2+ It inhibits bacterial activity and provides new nucleation sites for carbonate precipitation or co-precipitation. More importantly, the active nano-SiO2 utilizes the OH- produced by urease-producing bacteria during the decomposition of urea. - In the MIP technology, a certain degree of pozzolanic effect occurs, which not only increases the Ca content in the cementitious solution... 2+This invention improves soil utilization and, moreover, forms silica gel that further reinforces the soil and fixes Pb. It combines modified PAN-nano SiO2 and ordinary nano SiO2 in different ratios, cleverly combining the strong adsorption of modified nano SiO2, the nucleation effect of nano SiO2, and the properties of volcanic ash with MIP technology to better advance joint research on the reinforcement and remediation of heavy metal contaminated soil foundations.

[0022] In a second aspect, the present invention provides an experimental apparatus for implementing the method of reinforcing silt and solidifying Pb by nano-SiO2 synergistic microbial-induced carbonate precipitation technology as described in the first aspect, including a soil column reinforcement module, a grouting module, a signal acquisition module, and a liquid collection cylinder;

[0023] The soil column reinforcement module includes a base, a mold shell, a mold chamber, fixing hoops, and a liquid collection funnel. The mold shell is placed on the base and is a cylindrical body formed by symmetrical semi-circular cylinders fixed and spliced ​​together by fixing hoops. The mold chamber is a cylindrical body formed by splicing symmetrical semi-circular cylinders, with through holes on its side walls. The mold chamber is placed inside the mold shell, and a bottom cover is provided at the lower part of the mold shell. The bottom cover seals the gap between the mold shell and the mold chamber, and seepage holes are provided in the vertical projection area of ​​the mold chamber. The liquid collection funnel is connected to the lower end of the mold shell. A grouting inlet is provided in the gap between the mold shell and the mold chamber.

[0024] The grouting module includes a cementing liquid storage tank and a peristaltic pump; the cementing liquid storage tank, the peristaltic pump, and the grouting inlet pipe are connected;

[0025] The signal acquisition module includes a sensor, a signal converter, and a PC terminal installed in the soil column sample, which are connected in sequence.

[0026] The liquid collecting cylinder is located at the bottom of the liquid collecting funnel.

[0027] Furthermore, during the experiment, the following materials were arranged in the mold chamber from bottom to top: geotextile, zeolite, geotextile, permeable stone, soil column sample, permeable stone, geotextile, zeolite, and geotextile.

[0028] The beneficial effects of this invention are:

[0029] (1) In the process of preparing soil samples by uniform mixing in one step, the present invention first realizes the adsorption of Pb in silt by PAN-nano SiO2 with strong adsorption capacity. 2+ The toxicity was alleviated, and the subsequent application of the cementing solution and bacterial suspension further promoted the formation of PbCO3 and other metal co-precipitates, reducing the mobility of heavy metal ions.

[0030] (2) This invention employs a high-concentration cementitious liquid and a sludge sample containing nano-SiO2, which are thoroughly mixed and then combined with an all-around grouting method to ensure the uniform generation and distribution of the target product, avoiding the formation of weak soil surfaces caused by common grouting methods. The zeolite layer designed during the preparation of the soil column sample effectively adsorbs NH3 released from the decomposition of urea by urease. This invention combines the MICP technology of nano-SiO2 with high-concentration cementitious liquid using a one-time mixing and molding technique and an all-around grouting method, effectively increasing soil strength and reducing environmental pollution.

[0031] (3) This invention is based on the microbial-induced production of carbonates to reinforce soil, and the nano-SiO2 surface has a high affinity for Ca. 2+ The adsorption effect reduces the high concentration of free Ca in the solution. 2+ The inhibition of bacterial and urease activity, while simultaneously becoming a new mineral nucleation site, alleviates the hindrance to biochemical reactions by MICP when bacteria serve as nucleation sites; furthermore, OH in the metabolism of urease-producing bacteria... - The release of Ca in the cementitious solution 2+ The application of nano-SiO2 enables the pozzolanic effect of nano-SiO2 in MIP-reinforced silt, further enhancing the soil's reinforcement strength. Therefore, the addition of nano-SiO2 to the silt not only provides new nucleation sites for CaCO3, but the resulting silica gel further cements soil particles on the basis of MIP-reinforced silt, increasing soil strength. Attached Figure Description

[0032] Figure 1 This is a diagram of the experimental apparatus for the present invention;

[0033] Figure 1 In the middle: 1-Mold shell; 2-First grouting inlet; 3-Second grouting inlet; 4-Left half of mold chamber; 5-Right half of mold chamber; 6-Small hole; 7-Peristaltic pump; 8-Gluing liquid storage tank; 9-Latex tube; 10-Fixing hoop; 11-Sensor; 12-Signal converter; 13-Base; 14-Collection funnel; 15-Collection tank; 16-Seepage hole; 17-PC terminal.

[0034] Figure 2 This is a flowchart of the construction process of the present invention.

[0035] Figure 3 This is a schematic diagram of silty sand with different amounts of nano-SiO2 content according to the present invention.

[0036] Figure 4 The diagram and SEM image show the PAN-nano SiO2+nano SiO2 (mass ratio 0.01:0.01) of this invention.

[0037] Figure 5 The present invention provides nano-SiO2 synergistic MICP in different Ca2+ Unconfined compressive strength of reinforced silt at different concentrations (a) and effective Pb concentration (b).

[0038] Figure 6 The present invention relates to the unconfined compressive strength (a) and effective Pb concentration (b) of silt reinforced by nano-SiO2 synergistic with MICP at different curing times.

[0039] Figure 7 The present invention relates to the unconfined compressive strength (a) and effective Pb concentration (b) of silt reinforced by nano-SiO2 synergistically with MICP under different nutrients.

[0040] Figure 8 This invention describes the fracture mode of a silt sample reinforced with nano-SiO2 and MICP.

[0041] Figure 9 SEM images of MICP-reinforced sludge under (A) conditions without nano-SiO2 and (B) conditions with nano-SiO2. Detailed Implementation

[0042] The present invention will now be described in conjunction with specific implementation methods and embodiments, so that the advantages and effects of the present invention can be more clearly demonstrated. The specific implementation methods and embodiments in this invention are for illustrative purposes only and are not intended to limit the invention.

[0043] To better apply MIP technology to the fields of foundation reinforcement and heavy metal remediation, the process flow of this invention is as follows: preparation of silt samples, incorporation of PAN-nano SiO2, incorporation of nano SiO2, addition of cementing solution, addition of bacterial suspension, curing at 30℃, circulation grouting of cementing solution, and sample completion.

[0044] The principles and functions of some processes are as follows:

[0045] Incorporation of PAN-nano SiO2: Grafting organic active groups onto the surface of nano SiO2 to modify surface functional groups (-Si-O). - (e.g., Si-OH, -NH2), through coordination chelation of silicon-oxygen bonds, amino groups, or hydroxyl groups, increase their affinity for the heavy metal Pb. 2+ and Ca 2+ It has strong adsorption properties, and when combined with MIP technology, it produces metal carbonate (such as PbCO3) precipitates, which further reduces the mobility of metal ions in the environment and alleviates their toxicity.

[0046] Incorporation of nano-SiO2: The silicon-oxygen bonds on the surface of active nano-SiO2 affect Ca... 2+ The adsorption effect makes it possible to achieve high concentrations of Ca... 2+In its presence, the inhibitory effect of free metal ions on bacterial growth and urease activity is reduced, and the Ca adsorbed on the surface of nano-SiO2 particles is also reduced. 2+ In relation to CO3 2- During the precipitation process, nano-SiO2 particles become new mineral nucleation sites, which alleviates the problem in MIP technology where calcium carbonate precipitation encapsulates bacteria, hindering their material and energy exchange and inhibiting their growth and metabolism when bacteria are used as nucleation sites.

[0047] This invention combines nano-SiO2 and PAN-nano-SiO2 with MICP. On one hand, it utilizes adsorption capacity to reduce the environmental hazards of heavy metal ions and the toxicity of metal cations to bacterial cells and urease. On the other hand, it leverages the precipitation or co-precipitation produced by MICP and the alkaline environment induced by MICP to induce the pozzolanic effect of nano-SiO2, thereby enhancing soil strength and reducing Pb. 2+ Mobility.

[0048] The biochemical equation for using urease-producing bacteria as the strain in MIP technology, which utilizes urease to decompose urea and generate calcium carbonate to reinforce soil, is as follows:

[0049] (NH2)2CO + H2O → 2NH3 + CO2

[0050] 2NH3 + 2H2O → 2NH4 + + 2OH -

[0051] CO2 + 2OH - HCO3 - + OH - CO3 2- + H2O

[0052] Cell-Ca 2+ + CO3 2- → Cell-CaCO3(s) ↓

[0053] Based on this process, it was found that the byproducts, besides NH3 or NH4, include... + In addition, OH- is also present. - Furthermore, the pH level of this bacterium continuously increases during its growth in an alkaline environment, providing conditions for the pozzolanic effect of nano-SiO2. Therefore, in addition to the calcium carbonate precipitate produced by MICP technology filling soil pores and cementing soil particles, the CSH generated by nano-SiO2 in soil containing cementing solution further binds soil particles in an alkaline environment, increasing soil strength and improving the calcium content. 2 +This will improve utilization and reduce the cost of MIP technology.

[0054] Compared to the common single-cycle grouting method, the one-time uniform mixing of experimental materials (nano-SiO2, bacterial solution, and cementing solution) in the soil, combined with omnidirectional grouting, solves the problem of low-concentration reactant materials (Ca) in grouting. 2+ Insufficient urea content and high concentration of Ca in the cementing solution 2+ This addresses key issues that impair bacterial growth and urease activity, resulting in a more uniform target product of MICP. More importantly, the zeolite layer's absorption of NH3 reduces atmospheric pollution.

[0055] In addition, the physical micro-filling effect of nano-SiO2 in soil pores has a certain corresponding effect on soil strength.

[0056] In summary, using urease-producing bacteria as the strain in MIP technology can be cleverly combined with the special properties of nano-SiO2 to synergistically promote soil reinforcement and heavy metal fixation.

[0057] One specific implementation of the method described in this invention is as follows:

[0058] (1) Preparation of PAN-nano SiO2:

[0059] Includes the following steps:

[0060] Step 1.1: First, activate nano-SiO2 at 110℃ for 1 h. Weigh 500 mg of activated nano-SiO2 and place it in a 100 mL round-bottom flask. Add 30 mL of toluene and sonicate for 20 min. Add 2 mL of 3-aminopropyltriethoxysilane (APTES) dropwise over 10 min. Stir magnetically and reflux at 110℃ for 8 h. Filter under vacuum and wash with anhydrous ethanol and toluene sequentially. Dry under vacuum at 60℃ to obtain APTES-modified nano-SiO2-APTES (product I).

[0061] Step 1.2: Transfer product I to a round-bottom flask, add 15 mL of formaldehyde, 2 mL of concentrated hydrochloric acid and 400 mg of PAN, then add 80 mL of anhydrous ethanol, stir magnetically, reflux at 80 °C for 5 h, then vacuum filter, transfer to an Erlenmeyer flask, wash thoroughly with anhydrous ethanol, centrifuge and settle, and dry at 70 °C under vacuum for 4 h to finally obtain PAN-grafted nano-SiO2 adsorbent (PAN-nano-SiO2).

[0062] (2) Preparation of powder A:

[0063] Based on the mold volume, ensure the soil sample compaction degree is 1.48 g / cm³. 3Under the premise of [condition], 7 soil samples (total 700 g) of 100 g / sample of dried silty sand (moisture content 1.05%) that have passed through a 2 mm sieve were weighed and ultrasonically mixed with two types of nano-SiO2 and silty soil samples according to the mass ratio of PAN-nano-SiO2:nano-SiO2:soil sample of 0:0:100, 0.01:0:100, 0.01:0.01:100, 0.01:0.05:100, 0.01:0.1:100, 0.01:0.5:100 and 0.01:1:100. After the PAN-nano-SiO2 was added to the soil sample, it was ultrasonically mixed multiple times within one week. Then, ordinary nano-SiO2 was added to the soil sample to obtain powder A.

[0064] (3) Add cementing solution and bacterial suspension:

[0065] Preparation of bacterial suspension: The liquid culture medium (20 g / L yeast extract, 10 g / L NH4Cl, 10 mg / L MnSO4·H2O and 24 mg / L NiCl2·6H2O) was sterilized at 121℃ for 25-30 min. In a sterile operating table, 1% *Bacillus pasteurellii* was inoculated into the liquid culture medium and cultured in a shaker at 30℃ at 180 ± 2 rpm / min. After 24 h of culture, the bacterial suspension was centrifuged with sterile water at 8000 rpm / min for 20 min. The bacteria were washed three times using this method, and the bacterial concentration (OD) was adjusted using a spectrophotometer. 600 =1.0), that is, we get.

[0066] Preparation of cementing solution: Prepare a 2 mol / L cementing solution (nutrient broth 3 g / L, NH4Cl 10 g / L, NaHCO3 2.12 g / L, CaCl2 221.96 g / L, urea 120.012 g / L, pH=6.0).

[0067] A cementing solution was added to powder A containing different amounts of nano-SiO2. The mixture was stirred evenly for 5 minutes using a small electric stirrer, then allowed to stand for 2 hours. OD was then added again. 600 The bacterial suspension with a concentration of 1.0 was stirred again for 5 minutes. The fixed volume ratio of the cementing solution to the cell suspension was 4:1. The amount of cementing solution and bacterial suspension added was based on the optimal moisture content of the sludge, which was approximately 15.1%, i.e., 15 mL of the mixture of cementing solution and cell suspension was added to 100 g of powder A.

[0068] (4) Maintenance:

[0069] The sample from step (3) was divided into three equal portions and filled into the soil column mold (Φ40×80 mm). After being placed in an incubator at 30℃ for a certain period of time, a peristaltic pump was used to inject 0.5 mol / L cementing solution into the cavity of the soil column mold at a rate of 5 mL / min, so that the cementing solution seeped into the soil column sample from the inner small hole until the solution flowed out of the collection funnel evenly. Then the injection of cementing solution was stopped. The cycle was repeated once every 12 h.

[0070] To stop the ongoing biochemical reactions in the MIP technology, the cured samples were subjected to unconfined compressive strength tests and toxicity leaching tests at 105°C for 8 hours.

[0071] Example 1

[0072] Weigh 700 g of dried silty sand that has passed through a 2 mm sieve, and ultrasonically mix it thoroughly and evenly according to the mass ratios of PAN-nano SiO2:nano SiO2:soil sample:0:0:100, 0.01:0:100, 0.01:0.01:100, 0.01:0.05:100, 0.01:0.1:100, 0.01:0.5:100, and 0.01:1:100. Note that after mixing PAN-nano SiO2 for one week, then add nano SiO2 to obtain powder A. The examples without either or both types of nano SiO2 are comparative examples.

[0073] The prepared 0.5 mol / L, 1.0 mol / L, and 2 mol / L cementing solutions (nutrient broth 3 g / L, NH4Cl 10 g / L, NaHCO3 2.12 g / L, CaCl2 and urea, pH=6.0) and OD were compared. 600 A bacterial suspension with a concentration of 1.0 was added to powder A in a 4:1 volume ratio (12 mL of cementing solution and 3 mL of bacterial suspension) at 2-hour intervals, with each addition followed by 5-minute mixing. The concentration (e.g., 0.5 mol / L) represents the concentration of CaCl2 or urea, and the concentrations of CaCl2 and urea were consistent. The soil sample compaction was ensured to be 1.48 g / cm³. 3 Under the premise of ensuring proper mixing, the stirred sludge sample was evenly filled into a soil column mold (Φ40×80 mm) in three portions. After curing in an incubator at 30℃ for 7 days, a 0.5 mol / L cementing solution was injected into the cavity of the soil column mold at a rate of 5 mL / min using a peristaltic pump. This allowed the cementing solution to seep into the soil column sample through the internal small holes until the solution flowed out of the collection funnel. The injection of cementing solution was then stopped. This process was repeated every 12 h, and the seepage was collected. To stop the continuous biochemical reaction in the MIP technique, the cured sample was subjected to an unconfined compressive strength test at 105℃ for 8 h.

[0074] Unconfined compressive strength samples were collected, dried, ground, and passed through a 2 mm sieve. 1 g of soil sample was weighed into a 50 mL centrifuge tube. The required volume of extractant was calculated based on a soil-to-extractant ratio of 20:1 (L / kg). The tube was then capped and fixed on a tilting shaker at 30 ± 2 rpm / min for 18 h at 23 ± 2℃. During shaking, the generated gases were periodically released in a fume hood. The extracted sample was filtered through a 0.45 μm filter membrane, and the filtrate was analyzed using atomic absorption spectrometry. Simultaneously, the corresponding permeate was filtered through a 0.45 μm filter membrane, and the heavy metal ion content was determined. The sum of both results, compared with a control sample, can be used to evaluate the remediation effect of nano-SiO2 combined with MICP technology on heavy metals.

[0075] Example 2

[0076] In this embodiment, the Ca in the cementitious solution is controlled. 2+ The concentration was 2.0 mol / L, and the OD of the bacterial suspension was... 600 =1.0, and the curing time was adjusted to 3 days, 7 days and 14 days at 30℃. Other operating steps were the same as in Example 1.

[0077] Example 3

[0078] In this embodiment, the OD of the bacterial suspension is controlled. 600 =1.0, cured at 30℃ for 7 days, Ca in the cementitious solution 2+ The concentration was 2.0 mol / L, but the nutrient concentrations of the cementing solution were set to standard × 0.5, standard × 1, and standard × 2. Standard × 0.5 represents 3 × 0.5 g / L of nutrient broth, 10 × 0.5 g / L of NH4Cl, 2.12 × 0.5 g / L of NaHCO3, and pH = 6.0; Standard × 1 represents 3 g / L of nutrient broth, 10 g / L of NH4Cl, 2.12 g / L of NaHCO3, and pH = 6.0; Standard × 2 represents 3 × 2 g / L of nutrient broth, 10 × 2 g / L of NH4Cl, 2.12 × 2 g / L of NaHCO3, and pH = 6.0. Other operating steps were the same as in Example 1.

[0079] Example 4

[0080] like Figure 1 As shown, an experimental apparatus for a method of consolidating silt and solidifying Pb by nano-SiO2 synergistic microbial-induced carbonate precipitation technology includes a soil column reinforcement module, a grouting module, a signal acquisition module, and a liquid collection cylinder 15.

[0081] The soil column reinforcement module includes a base 13, a mold shell 1, a mold chamber, a fixing hoop 10, and a liquid collection funnel 14. The mold shell 1 is placed on the base 13 and is formed by symmetrical semi-circular cylindrical bodies fixedly spliced ​​together by the fixing hoop 10. The mold chamber is a cylindrical body formed by splicing symmetrical semi-circular cylindrical bodies, with through holes 6 on its side walls. The mold chamber is placed in the mold shell 1, and a bottom cover is provided at the lower part of the mold shell 1. The bottom cover seals the gap between the mold shell and the mold chamber, and seepage holes 16 are provided in the vertical projection area of ​​the mold chamber. The lower end of the mold shell 1 is connected to the liquid collection funnel 14. A grouting inlet is provided in the gap between the mold shell 1 and the mold chamber.

[0082] The grouting module includes a cementing liquid storage tank 8 and a peristaltic pump 7; the cementing liquid storage tank 8, the peristaltic pump 7, and the grouting inlet pipe are connected.

[0083] The signal acquisition module includes a sensor 11, a signal converter 12, and a PC terminal 17 installed in the soil column sample, which are connected in sequence.

[0084] The liquid collecting cylinder 15 is located at the lower part of the liquid collecting funnel 14.

[0085] During the experiment, the mold chamber was arranged from bottom to top as follows: geotextile, 2 cm zeolite, geotextile, permeable stone, soil column sample, permeable stone, geotextile, 2 cm zeolite, and geotextile, to achieve the desired effect on NH4+. + The adsorption of NH3 reduces the amount of NH3 released into the air.

[0086] As a specific embodiment, the mold chamber has 30 through holes 6 evenly arranged on its sidewalls, allowing the cementing liquid to penetrate into the soil sample to be reinforced in a multi-directional, uniform, and comprehensive manner. During the testing phase, each hole 6 needs to be sealed with a geomembrane to prevent soil particles from flowing out. The upper end of the mold chamber has a first grouting inlet 2 and a second grouting inlet 3 with a diameter of 3 mm; the rest are closed. The mold shell 1 needs to be fixed with a fixing hoop 10. Vaseline needs to be evenly applied to the joints of the mold shell 1 and the connection between the mold shell and the base to ensure that the solution only flows out from the collection funnel 14 (without leakage), collecting the leachate. The outer diameter of the mold shell 1 matches the diameter of the circular groove on the base, thus fixing the mold shell 1. The collection funnel 14 is connected to the lower end of the mold shell 1 with silicone sealant. A collection cylinder 15 is installed below the collection funnel 14 to collect the liquid and predict Ca. 2+ Utilization rate.

[0087] The grout is injected into the gap between the mold shell 1 and the mold cavity through the grouting inlet, and then flows into the mold cavity through the small hole 6 and reacts with the soil. The vertical projection of the gap onto the area formed by the bottom cover is in a closed state to ensure that the grout can be injected into the soil through the small hole 6 without seeping out from the bottom cover. After the reaction is complete, the grout flows out from the seepage hole 16 of the bottom cover and flows into the collection tank 15 through the collection funnel 14.

[0088] In one specific embodiment, the mold cavity is formed by splicing together symmetrical semi-circular cylindrical bodies (left half 4 and right half 5) to create a bottomed cylinder, with through holes 6 on the side walls. The spliced ​​parts are connected using silicone sealant. Both the mold shell and the mold cavity are designed to be spliced ​​together to facilitate demolding after the experiment.

[0089] In one specific embodiment, the grouting module includes a binder liquid storage tank 8, a peristaltic pump 7, and a latex tube 9. One end of the latex tube 9 is inserted into the binder liquid storage tank 8, and the other end is connected to the first grouting inlet 2 and the second grouting inlet 3. The peristaltic pump 7 powers the binder liquid to enter the mold chamber at a rate of 5 mL / min, circulating it once every 12 hours. The binder liquid in the chamber enters the soil column sample through the small holes 6 in the inner wall at a certain rate.

[0090] In one specific embodiment, the sensor 11 is placed at three points—the top, middle, and bottom—of the soil column sample, with its other end connected to the signal converter 11. The sensor is a pH sensor, a temperature sensor, and a conductivity sensor, used to monitor the pH, temperature, and conductivity of the soil column's internal environment in real time at the terminal 12. Changes in conductivity reflect the level of urease activity, providing a reference for more suitable environmental conditions for the application of nano-SiO2 synergistic MICP solidification / stabilization technology in heavy metal-contaminated silt.

[0091] In the examples and comparative examples, the unconfined compressive strength was tested using a microcomputer-controlled electronic universal testing machine with a loading rate set to 0.1 mm / min. The unconfined compressive strength was calculated using the following formula:

[0092]

[0093] In the formula: q u This indicates the unconfined compressive strength (UCS, MPa) of the specimen.

[0094] P Indicates the pressure (N) at which the sample fails;

[0095] A a Indicates the cross-sectional area of ​​the sample after correction (mm²) 2 ).

[0096] Table 1

[0097]

[0098] Table 1 shows the basic parameters of the sludge sample used in this invention. According to the data, the sludge is Pb-contaminated soil. This invention uses seepage and leaching tests to determine the content of available heavy metal Pb in the treated sludge sample, thereby judging the remediation effect of this invention on heavy metals. The specific calculation formula is as follows:

[0099]

[0100] In the formula: C represents the concentration of available Pb in the sample (mg / kg);

[0101] c1 represents the concentration of Pb in the permeate (mg / L);

[0102] v1 represents the volume of seepage fluid (L);

[0103] c2 represents the concentration of Pb in the leachate (mg / L) during the leaching test;

[0104] v2 represents the volume of the leachate (L);

[0105] A represents the ratio between the tested soil sample and the total soil sample;

[0106] m represents the total mass (kg) of the soil column sample.

[0107] Results and conclusions:

[0108] Figure 4 The images show the physical sample and SEM image of nano-SiO2. It appears as a white powder, and under the scanning electron microscope, it shows spherical particles of about 30 nm. It tends to agglomerate, which is the main reason why ultrasonic mixing was used in the experiment.

[0109] In Ca 2+ The test results of the performance parameters of each sample are shown in Table 2 under the conditions of 2 mol / L, curing time of 14 days, and nutrient concentration of 1 in the cementitious solution.

[0110] Table 2

[0111]

[0112] As can be seen from Table 2, the combined use of the two nanomaterials effectively increased soil strength and reduced free Pb in the soil. 2+ concentration.

[0113] Figure 5 For different Ca 2+The unconfined compressive strength and available Pb content of sludge samples treated with nano-SiO2 and synergistic MIP at different concentrations were compared. Appropriate nano-SiO2 doping significantly improved the sample strength, and the Pb content increased with increasing Ca concentration. 2+ The effective Pb content increases with increasing concentration; however, it gradually decreases with increasing nano-SiO2 doping. The experimental results are best when the cementitious solution concentration is 2 mol / L.

[0114] Figure 6 The unconfined compressive strength and available Pb content of silt samples treated with nano-SiO2 and synergistic MIP were measured under different curing times. Overall, an appropriate amount of nano-SiO2 significantly improved the sample strength, which increased with increasing curing time; however, the available Pb content gradually decreased with increasing nano-SiO2 content. Within the curing time specified in the examples, the soil reinforcement and repair effects were best after 14 days of curing.

[0115] Figure 7 The unconfined compressive strength and available Pb content of silt samples treated with nano-SiO2 and synergistic MIP were measured under different nutrient concentrations. Overall, an appropriate amount of nano-SiO2 significantly improved the sample strength, with no significant change in strength at standard concentrations ×1 and ×2; however, the available Pb content gradually decreased with increasing nano-SiO2 content. Although the soil strength cured at a nutrient concentration of ×1 was lower than that at ×2, the reduction was not significant. Considering material costs, a nutrient concentration of ×1 is recommended.

[0116] Figure 8 After the samples were reinforced, all samples with different amounts of nano-SiO2 exhibited brittle fracture, indicating that the addition of nano-SiO2 and PAN-nano-SiO2 did not affect the fracture mode of the soil column reinforced by MICP technology.

[0117] Figure 9 Scanning electron microscopy images with and without nano-SiO2. Under MIP technology alone, the generated carbonate ions bind soil particles, increasing soil strength; after applying nano-SiO2, in addition to biogenic CaCO3, the micro-filling effect of the nanomaterials and the resulting gel further strengthen the soil particles.

[0118] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the invention.

Claims

1. A method for reinforcing and remediating Pb-contaminated sludge using nano-SiO2 synergistic with MIP technology, characterized in that, Includes the following steps: (1) Preparation of 1-(2-pyridineazo)-2-naphthol graft-modified nano-SiO2--PAN-nano-SiO2; The preparation method of the PAN-nano SiO2 includes the following steps: 1.1: Activated nano-SiO2 was added to an organic solvent, ultrasonically dispersed, and 3-aminopropyltriethoxysilane was added dropwise. The mixture was heated under reflux, vacuum filtered, washed, and dried to obtain APTES-modified nano-SiO2-APTES. 1.2: The product from step 1.1 was added to formaldehyde, concentrated hydrochloric acid and 1-(2-pyridinium azo)-2-naphthol, then anhydrous ethanol was added, stirred, heated to reflux, and then vacuum filtered, washed, centrifuged and dried to obtain PAN-nano SiO2. (2) Mix PAN-nano SiO2 with sieved dry sludge powder evenly, and then mix it with nano SiO2 to obtain powder A; (3) Add the cementing liquid to powder A, stir well and let stand, then add the bacterial suspension and mix well. (4) It can be obtained after maintenance.

2. The method for reinforcing and remediating Pb-contaminated sludge using nano-SiO2 synergistic MIP technology according to claim 1, characterized in that: In step 1.1, the activation temperature is 110℃~115℃, the organic solvent is toluene, and the heating reflux temperature is 110℃~115℃.

3. The method for reinforcing and remediating Pb-contaminated sludge using nano-SiO2 synergistic MIP technology according to claim 1, characterized in that: In step 1.2, the heating reflux temperature is 80℃~90℃.

4. The method for reinforcing and remediating Pb-contaminated sludge using nano-SiO2 synergistic MIP technology according to claim 1, characterized in that: In step (2), the particle size of PAN-nano SiO2 is 30-60 nm, the dry sludge powder is sludge particles that have passed through a sieve with a diameter of 2 mm, and the particle size of nano SiO2 is 30-40 nm.

5. The method for reinforcing and remediating Pb-contaminated sludge using nano-SiO2 synergistic MIP technology according to claim 1, characterized in that: In step (2), the mass ratio of PAN-nano SiO2, nano SiO2 and sieved dry sludge powder is 0.01:(0.01~1):

100.

6. The method for reinforcing and remediating Pb-contaminated sludge using nano-SiO2 synergistic MIP technology according to claim 1, characterized in that: In step (3), the cementing solution is a mixture of urea, nutrient broth, NH4Cl, NaHCO3, and CaCl2, wherein Ca... 2+ The concentration is 0.5–2 mol / L, and the urea concentration is 0.5–2 mol / L; the bacterial suspension is a suspension of Bacillus pasteurellii, OD 600 The range is 1 to 1.

5.

7. The method for reinforcing and remediating Pb-contaminated sludge using nano-SiO2 synergistic MIP technology according to claim 1, characterized in that: In step (4), the curing time is 3 to 14 days.

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