Method for inhibiting sand storm by adding microorganisms

Abstract

The invention discloses a method for inhibiting sand storm by adding microorganisms, and belongs to the technical field of weathered sand stability. The invention investigates the effectiveness of a microbial induced calcite precipitation (MICP) technology in the aspect of enhancing the stability of aeolian sand. The stability effectiveness of the weathered sand is improved. The microorganism induced calcite precipitation technology is applied to the karst desert sand sample in the Uygur autonomous region in Xinjiang, and the result shows that in a wind erosion test, the treated soil has obvious structural stability and erosion resistance. And wind erosion test. Particularly, after 14 days of treatment, the soil sample shows optimal wind erosion resistance and surface crusting strength.

Description

Technical Field

[0001] The invention relates to the technical field of weathered sand stability, in particular to a method for adding external microorganisms to inhibit sandstorms. Background Art

[0002] The Kashgar region of Xinjiang Uygur Autonomous Region is adjacent to the Taklimakan Desert, the world's second largest mobile desert, and is frequently hit by sandstorms in spring and summer. These complex weather phenomena, including blowing sand and dust storms, are caused by winds rolling up loose soil on the ground to form a layer of sand and dust aerosols that cover the surface, which has a negative impact on local residents. In the 21st century, global warming is expected to exceed 2°C, causing soil in arid and semi-arid areas to become increasingly loose and more vulnerable to extreme windy and sandy weather. Wind erosion not only causes soil loss, but also consumes soil fertility in semi-arid areas, destroys vegetation, and leads to ecosystem degradation, which directly affects agricultural productivity. Vegetation is an important component of the ecosystem and helps stabilize soil and reduce wind erosion. However, continuous erosion makes it difficult for vegetation to grow, exacerbating soil loss and ecological degradation, forming a vicious cycle. In order to eliminate the harmful effects of wind erosion, people have conducted extensive research on the formation and control methods of sandstorms. The formation of sandstorms is affected by many factors, including soil particle size distribution, soil moisture content, vegetation coverage, and wind speed. It is widely acknowledged that maintaining soil stability is key to controlling wind erosion. Soil stabilization is an important aspect of geotechnical engineering that addresses issues related to soil erosion, subsidence, and the overall structural integrity of the built environment. Traditional soil stabilization methods, such as chemical additives and mechanical compaction, often face environmental concerns, high costs, and limited long-term effectiveness. Moreover, these methods are difficult to implement in areas prone to frequent sandstorms.

[0003] Therefore, it is crucial to develop a new wind erosion control technology that is energy-efficient, durable, and suitable for field applications. In recent years, microbial induced calcite precipitation (MICP) has emerged as a promising biotechnological approach to stabilizing soils. This innovative technology uses the natural process of urea-decomposing bacteria to induce calcite precipitation, thereby improving soil consolidation and strength.

[0004] MICP technology uses bacteria such as Sporosarcina pasteurii to hydrolyze urea to produce carbonate ions. These ions then react with calcium ions in the environment to form calcium carbonate (CaCO3). The precipitated calcium carbonate can act as a binder to bind soil particles together and improve the mechanical properties of the soil. This bioconsolidation process is environmentally friendly and can be used on-site, making it a sustainable alternative to traditional methods. MICP has been applied in many fields. The basic mechanism of MICP includes the following reactions:

[0005] CH4N2O+2H2O=2NH4 ++CO3 2- (1);

[0006] Ca 2+ +CO3 2- =CaCO3 (2).

[0007] Microbial urease catalyzes the hydrolysis of urea to produce ammonium ions and carbonate ions. When the generated carbonate ions combine with the introduced calcium ions, calcium carbonate precipitation is formed, such as Figure 1 As shown, calcium carbonate precipitation uses bacteria as nucleation sites. This process fills the spaces between soil particles, acting as a binder and thus strengthening the soil.

[0008] Many studies have demonstrated the effectiveness of MICP in various soil types and environmental conditions. For example, DeJong et al. 9 reported that soils treated with MICP showed significant improvements in shear strength and bearing capacity. The study by Whiffin et al. 10 further highlighted the potential of MICP in reducing soil permeability and enhancing soil resistance to erosion. Similarly, Cheng and Cord-Ruwisch 14 also demonstrated that MICP can improve the stiffness and strength of sandy soils, indicating its potential for wide application in civil engineering.

[0009] Recent advances in the understanding of microbial behavior and the mechanisms of calcite precipitation have paved the way for optimizing the MICP process for large-scale application. A study by van Paassen et al.15 explored the field implementation of MICP and demonstrated its feasibility and effectiveness in the real world. Al-Thawadi16 also investigated the role of different bacterial species in MICP, suggesting that it may be possible to optimize the microbial consortium to improve performance.

[0010] MICP is more promising given the challenges of methods such as plant cultivation in terms of cost, complexity of implementation, and survival rates in arid and water-deficient environments. Despite these promising results, there are still some challenges in applying MICP in soil stabilization. These challenges include optimizing bacterial growth conditions, ensuring uniform distribution of the biosolidifier, and addressing potential impacts on the soil microbiome and local ecosystems. Addressing these challenges requires a multidisciplinary approach that integrates insights from microbiology, geotechnical engineering, and environmental science.

[0011] Currently, many studies have focused on soil instability caused by drought cracking of clay soils, but not much research has been done on desert soils, especially in the Kashgar region of the Xinjiang Uyghur Autonomous Region. Summary of the invention

[0012] The purpose of the present invention is to provide a method for suppressing sandstorms by adding external microorganisms to solve the problems existing in the above-mentioned prior art.

[0013] To achieve the above object, the present invention provides the following solutions:

[0014] One of the technical solutions of the present invention is the application of Bacillus pasteurianus in improving the stability of weathered sand.

[0015] The second technical solution of the present invention is the use of Bacillus pasteurianus in the preparation of products for improving the stability of weathered sand.

[0016] The third technical solution of the present invention is a product for improving the stability of weathered sand, comprising Bacillus pasteurianus.

[0017] The fourth technical solution of the present invention is a method for preparing the product, comprising the following steps:

[0018] (1) Bacillus pasteurianus was activated and cultured to prepare 7.838×10 7 / ml of Bacillus pasteurianus suspension;

[0019] (2) 1 mol / L urea and 1 mol / L calcium chloride solution were mixed to prepare a solidifying solution.

[0020] A fifth technical solution of the present invention is a method for improving the stability of weathered sand, which comprises spraying the product on the surface of the weathered sand.

[0021] The sixth technical solution of the present invention is the use of Bacillus pasteurianus in inducing calcite precipitation.

[0022] The seventh technical solution of the present invention is the use of Bacillus pasteurianus in the preparation of products that induce calcite precipitation.

[0023] Based on the above technical solution, the present invention has the following technical effects:

[0024] The present invention aims to simulate local conditions and evaluate the effect of Bacillus pasteurianus induced calcite precipitation (MICP). For this purpose, a series of wind tunnel experiments were conducted to simulate different wind speeds and erosion of the biologically treated soil. The study evaluated the resistance of the MICP-treated soil to wind erosion through a comprehensive analysis of factors such as the curing period, amount of bacterial solution, soil retention after wind erosion, and penetration strength. In addition, the formation of calcium carbonate was analyzed using infrared scanning and XRD (X-ray diffraction) techniques. The insights gained from this study provide valuable scientific evidence to support sand control measures in the region.

[0025] Bio-augmentation can effectively stabilize and suppress sand and dust in the Taklimakan Desert.

[0026] Within the scope of the study, when the application rate of the microbial solution and the combined solution were both set at 20 ml (about 0.67 L / m2), the mass retention rate, permeability and calcium carbonate production in the desert soil samples reached their maximum values, enhancing their ability to resist wind erosion.

[0027] X-ray diffraction (XRD) analysis showed that the calcium carbonate content in the samples treated with MICP was significantly increased compared with that in the untreated samples, thus confirming the efficacy of MICP in stabilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 This is the MICP mechanism diagram.

[0030] Figure 2 The particle size distribution of aeolian sand.

[0031] Figure 3 Schematic diagram of the wind tunnel.

[0032] Figure 4 is the retention rate of aeolian sand treated by MICP after wind erosion test.

[0033] Figure 5 (A) calcium carbonate content; (B) crustal strength.

[0034] Figure 6 XRD spectra; (a) loose aeolian sand; (b) MICP-modified aeolian sand; (c) FTIR spectrum.

[0035] Figure 7 SEM images: (a) loose aeolian sand; (b) calcium carbonate crystals; (c) bridge structure; (d) filling effect. DETAILED DESCRIPTION

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0038] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0039] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0040] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0041] The technical solutions described in the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0042] The embodiment of the present invention provides the use of Bacillus pasteurianus in improving the stability of weathered sand.

[0043] The embodiments of the present invention also provide the use of Bacillus pasteurianus in preparing a product for improving the stability of weathered sand.

[0044] An embodiment of the present invention further provides a product for improving the stability of weathered sand, comprising Bacillus pasteurianus.

[0045] In some specific embodiments, the Bacillus pasteurianus suspension and a consolidation liquid are included.

[0046] In some specific embodiments, the consolidation liquid is prepared from 1 mol / L urea and 1 mol / L calcium chloride solution.

[0047] The present invention also provides a method for preparing the product, comprising the following steps:

[0048] (1) Bacillus pasteurianus was activated and cultured to prepare 7.838×10 7 / ml of Bacillus pasteurianus suspension;

[0049] (2) 1 mol / L urea and 1 mol / L calcium chloride solution were mixed to prepare a solidifying solution.

[0050] The embodiment of the present invention also provides a method for improving the stability of weathered sand, which can be achieved by spraying the product on the surface of the weathered sand.

[0051] In some specific embodiments, the dosage of the Bacillus pasteurianus suspension and the consolidation liquid is 0.67 liters per square meter, respectively.

[0052] The embodiment of the present invention also provides the use of Bacillus pasteurianus in inducing calcite precipitation.

[0053] The embodiments of the present invention also provide the use of Bacillus pasteurianus in preparing a product that induces calcite precipitation.

[0054] Effectiveness of improving the stability of weathered sand. The microbial induced calcite precipitation technology was applied to desert sand samples from Kashgar, Xinjiang Uygur Autonomous Region, and the results showed that the treated soils had significant structural stability and erosion resistance in wind erosion tests. Wind erosion tests. In particular, soil samples showed the best wind erosion resistance and surface crust strength after 14 days of treatment.

[0055] In addition, the formation of calcite also significantly improved the soil's permeability and wind erosion resistance. Strength and wind resistance SEM analysis confirmed that the calcite "bridges" between soil particles enhanced the bonding between particles. Environmental impact assessment showed that MICP technology is not only environmentally friendly, but also effectively reduces soil loss. Not only environmentally friendly, but also effectively reduces the risk of soil environmental pollution. Risk of environmental pollution. These research results verify the application potential of MICP technology in improving the stability and environmental adaptability of weathered sand. Stability and environmental adaptability of weathered sand.

[0056] Example 1

[0057] 1 Materials and Methods

[0058] Sample collection Soil samples were collected from the desert not far from Markit County, Kashgar County. According to the "Standard Test Methods for Geotechnical Engineering" (GB / T 50123-2019), the test results are shown in Table 1. The soil is classified as fine sand, which is characterized by uniform particle size and poor gradation. The particle size distribution is as follows Figure 2 shown.

[0059] Table 1 Basic characteristics of desert sand

[0060]

[0061] Note: G S Represents the specific gravity of sand particles, C U represents the uniformity coefficient, C C Curvature coefficient, ρ dmax represents the maximum dry density, ρ dmin represents the minimum dry density, d 10 Represents the diameter of sand particles with a weight percentage less than 10%, d 30 Represents the diameter of sand particles with a weight percentage less than 30%, d 60 Represents the diameter of sand particles corresponding to a weight percentage less than 30%.

[0062] 2 Bacteria and solidification solution

[0063] In this study, MICP treatment used a urease-active strain of Bacillus pasteurii (Sporosarcina pasteurii, ATCC 11589) purchased from the Shanghai Biological Resources Collection Center. The bacteria were cultured on a special LB agar medium (Luria-Bertani) in the form of lyophilized powder. The formula of LB liquid medium (1 liter) is as follows: dissolve 10 g of tryptone, 5 g of yeast extract, 10 g of sodium chloride, and 15 g of agar in 950 ml of ddH2O. Adjust the pH value to 7.0 with 1M NaOH and add it to 1 liter. Then autoclave at 121°C for 20 min and store at 4°C. In addition, 20 g / L of filter-sterilized urea was added. After successful activation, the inoculated LB liquid medium was cultured in a constant temperature incubator at 25°C with a stirring speed of 180 rpm for 48 h. The OD of the bacterial solution (BS) after 5-fold dilution 600 The value is 0.287. According to the formula:

[0064] y=8.59×10 7 × 1.3627 (3)

[0065] Where z represents OD 600 The value of .

[0066] It was calculated that there are about 7.838×10 7 The consolidation solution (CS) was prepared from 1 mol / L urea and 1 mol / L calcium chloride solution. Then BS and CS were placed in a graduated spray bottle for later use.

[0067] 3 Test procedures and treatment methods

[0068] The soil samples were divided into 19 groups and naturally deposited in circular plates with an average diameter of 19.5 cm and a depth of 1.9 cm. The internal volume of the plate was about 567 cm3 and the dry density of desert sand was 1.45 g / cm3. Therefore, the mass of each sample was about 822 g. The results reported are based on the average of three identical samples with similar experimental conditions. The liquid was sprayed evenly on the surface of the weathered sand from a height of 30 cm using a hand-held sprayer. The first group was untreated, while the next three groups were treated with 10, 15 and 20 ml of distilled water, respectively. The subsequent 15 groups were treated with MICP and were divided into groups A, B and C, with group A receiving 10 ml each of BS and CS, group B receiving 15 ml each of BS and CS, and group C receiving 20 ml each of BS and CS. The samples were sprayed in the following order: BS+CS+BS+CS.

[0069] When preparing samples containing 10 ml of solution each, 5 ml of BS was first sprayed on the sample, followed by 5 ml of CS, then 5 ml of BS, and finally 5 ml of CS. When preparing samples containing 15 ml of solution each, 5 ml of BS was first sprayed on the sample, followed by 5 ml of CS, and this was repeated 3 times. When preparing samples containing 20 ml of solution each, 5 ml of BS was first sprayed on the sample, followed by 5 ml of CS, and this was repeated 4 times. Each group was cured for 1, 3, 7, 14, and 21 days, respectively.

[0070] After the curing period, a simulated wind tunnel test was conducted. In this experiment, in order to ensure that the wind erosion effect of the soil samples was close to the actual situation, the direction angle of the wind was close to the wind erosion angle of natural wind. The wind erosion angle is crucial to obtaining accurate and applicable results. Generally, wind erosion processes in natural environments involve various angles, but studies have shown that angles close to parallel to the ground (low-angle wind erosion) can more accurately reflect the main characteristics of wind erosion in desert areas. Specifically, wind erosion angles in the range of 0° to 30° are most common, because at these angles, the wind force contacts the ground to the greatest extent, resulting in more obvious detachment and migration of soil particles. In this experiment, the erosion angle was set to 30° to simulate common wind erosion phenomena in desert areas, such as dune formation and surface soil erosion, while ensuring that the wind at this angle can most effectively erode soil samples, thereby more accurately evaluating the effect of MICP treatment on soil erosion resistance. Wind tunnel design as shown in the figure. Figure 3 The wind speed was 11 m / s, and after 8 minutes of continuous wind erosion, the mass retention ratio W before and after wind erosion was measured.

[0071] W=m2 / m1×100% (4)

[0072] Among them, m1 represents the mass before wind erosion, and m2 represents the mass after wind erosion.

[0073] The greater the mass retention, the stronger the wind erosion resistance of the treated weathered sand. Subsequently, the surface crust strength was measured using a micropenetrometer, and the calcium carbonate content in the crust was determined by EDTA titration. X-ray diffraction (XRD) was used to describe the mineralogical characteristics of the treated powdered samples. In addition, Fourier transform infrared spectroscopy attenuated total reflectance (FTIR-ATR) was used to characterize the mineralogy of the treated powdered samples in order to understand the changes in chemical bonds during the treatment. -1 Up to 4000cm -1 Infrared scanning was performed. Finally, the microstructure of the weathered sand was evaluated using scanning electron microscope (SEM) micrographs.

[0074] 4 Results and discussion

[0075] The effectiveness of this approach in stabilizing aeolian sand has been extensively verified through various engineering test programs. This section presents the test results and infers changes in the state of the aeolian sand matrix.

[0076] 4.1 Wind erosion resistance

[0077] Experimental results: Untreated and distilled water treated soil samples were completely eroded by wind, leaving no residue in the pan. This indicates that untreated desert soil lacks sufficient resistance to wind erosion. In contrast, soil samples treated with microbial induced calcium carbonate precipitation (MICP) showed significant resistance to wind erosion after the erosion process. Figure 4 The mass retention rate W varied with the length of curing time. This phenomenon can be attributed to the fact that MICP effectively promoted the precipitation of calcium carbonate between soil particles within a certain curing time, making the weathered sand more stable and enhancing the overall structure and wind erosion resistance of the soil samples. Specifically, at 14 days, the cementation effect of calcium carbonate precipitation produced by MICP treatment reached the best state in all three groups, among which the treatment method of 10 ml BS + 10 ml CS + 10 ml BS + 10 ml CS (Group C) performed the best, with W = 99.979%. This treatment method greatly reduced the wind erosion of soil samples. The reason for the subsequent decrease in W value may be extracellular polymer substances (EPS), which are high molecular weight substances mainly composed of polysaccharides, proteins, lipids and nucleic acids secreted by microorganisms. During the MICP process, EPS can not only support microbial adhesion and provide a reaction site, but also enhance the precipitation of calcium carbonate and the cohesion of soil particles29-32, thereby improving the efficiency and effect of the whole process. However, in the later stages, the death of microorganisms and the dry environment will cause the previously hydrated EPS to lose water, become dry and brittle, and may lead to a decrease in the bonding strength and thus a decrease in the W value.

[0078] 4.2 Calcium carbonate content

[0079] The calcium carbonate content on the surface of soil samples at different time points was measured by ethylenediaminetetraacetic acid (EDTA) titration to evaluate the efficiency and stability of the MICP process. The experimental results showed that the calcium carbonate content reached a maximum after 14 days of treatment and remained stable for the next 21 days. Figure 5 As shown in (A), the amount of calcium carbonate generated increased significantly from the first day to the 14th day, indicating that the deposition rate of calcium carbonate was high in the initial stage of the MICP process. The specific data are as follows: During the solidification period, the calcium carbonate content of the distilled water treated group and the untreated group remained unchanged at 4.8%. For the biologically treated soil samples, the calcium carbonate content of groups A, B, and C increased by 1.59%, 1.87%, and 2.49% on the third day, respectively. The calcium carbonate increment was calculated as follows: the mass of calcium carbonate in the untreated sample was subtracted from the mass of calcium carbonate in the MICP treated sample, and then divided by the dry mass of the MICP treated sample. By the 14th day, the calcium carbonate content increased to 3.14%, 3.77%, and 5.09%, respectively, an increase of about 100% from the 3rd day. However, the amount of calcium carbonate generated remained relatively stable from the 14th day to the 21st day. This trend may be due to the exhaustion of nutrients in the bacterial solution, calcium ions in the coagulant, and urea, leading to bacterial death.

[0080] This trend of change indicates that during the MICP treatment of desert weathered sand, the experimental data obtained by EDTA titration showed that calcium carbonate accumulated rapidly in the first two weeks and then stabilized. These results provide an important reference for optimizing the MICP treatment time and indicate that the optimal time point for calcium carbonate deposition may be around 14 days. On this basis, extending the treatment time may not significantly increase the formation of calcium carbonate.

[0081] 4.3 Surface strength of the residual crust after wind erosion

[0082] The surface strength of the soil samples was measured using a microscopic permeability tester. In the wind erosion experiment on desert soil, the permeability strength of the untreated soil samples and the soil samples treated with distilled water was zero after one day of indoor curing, indicating that they could not resist external forces during wind erosion. In contrast, the permeability strength of soil samples treated with microbial induced calcium carbonate precipitation (MICP) increased significantly at different curing time periods. After one day of curing, the crust on the surface of the sample broke after wind erosion, and the surface strength was 0kP. But starting from the third day, as Figure 5As shown in (B), the permeability strength of the soil sample increases with the extension of the curing time. The strength of groups A and B continued to increase after 14 days, indicating that the bacteria were still actively growing and metabolizing during the 14-day curing period, resulting in the continuous deposition of calcium carbonate and the improvement of soil consolidation strength. The strength of group C reached a peak at 14 days and then decreased, indicating that under the condition of 20 ml of bacterial solution, the bacteria reached the optimal activity and metabolite peak within 14 days, at which time the soil strength was the greatest. Possible reasons for this phenomenon include nutrient exhaustion-the rapid growth and metabolism of bacteria in the early stage led to the exhaustion of nutrients (such as urea and calcium ions) and insufficient nutrient supply in the later stage. Gradual death or dormancy of bacteria-During the curing process, due to space limitations, waste accumulation and other reasons, excessive bacterial concentration may cause bacterial death or dormancy, thereby reducing the production of calcium carbonate. Dissolution or structural destruction of calcium carbonate-After the formation of high-concentration calcium carbonate, environmental changes (such as pH fluctuations, humidity changes) may cause partial dissolution or structural destruction of calcium carbonate, thereby reducing soil strength. The soil samples treated with MICP showed significant surface strength enhancement even after strong wind erosion, which may be due to the cumulative effect of calcium carbonate precipitation during the MICP process, which enhanced the cementation between particles and improved the surface structural stability and penetration strength. The peak strength was reached at 14 days with a fracture pressure of 63kPa, which is equivalent to withstanding a wind speed of about 320.75 m / s according to the wind pressure formula. According to the Beaufort wind scale, a level 12 wind speed is 32.7-36.9 m / s. The treated soil surface can withstand a wind speed of 320.75 m / s, far exceeding a level 12 wind speed.

[0083] P = 1 / 2ρv^2 (5);

[0084] In the formula, P represents pressure (Pa), air density is assumed to be 1.225 kg / m3, and v represents wind speed (m / s). Therefore, theoretically, the soil surface treated with MICP can still resist wind forces far higher than level 12 after being eroded by level 6 wind for 8 minutes.

[0085] 4.4 Analysis of curing mechanism

[0086] In order to compare the mineral composition of weathered sand before and after solidification and to evaluate the effect of MICP solidification reaction on weathered sand, the crystal phase of the samples was determined by X-ray diffraction (XRD) test. Figure 6(a) and (b) show the X-ray diffraction spectra of loose weathered sand and MICP-cured weathered sand. As can be seen from the figure, the mineral composition of loose aeolian sand is mainly quartz, with fewer diffraction peaks, while the aeolian sand modified by MICP shows more characteristic diffraction peaks. By analyzing with Jade 6 software, these diffraction peaks were determined to be characteristic diffraction peaks of calcite, indicating that the precipitated crystals in the treated samples are mainly composed of calcite. In addition, the dolomite (NaSi3AlO8) in the untreated sample may be partially transformed into orthoclase (KSi3AlO8) only through ion exchange during the MICP process. The siderite (FeCO3) that appears after MICP treatment may be due to the combination of carbon ions produced by urea hydration and ferrous ions produced by the decomposition of part of the chlorite in the sample. Figure 6 (c) shows the Fourier transform infrared spectroscopy test results of loose weathered sand and MICP modified weathered sand. From the infrared spectrum of weathered sand, it can be seen that the composition of the two materials is basically the same. However, in the treated sample, the intensity of the functional group absorption peak is stronger, indicating that the number of functional groups is greater. 1404cm -1 The peak near is the stretching vibration absorption of carbonate ions, which is mainly caused by the carbonate mineral components in desert soil. Since the main component of desert soil is quartz, the characteristic infrared absorption peak of quartz appears. 1003cm -1 The absorption peak near 874 cm corresponds to the antisymmetric stretching vibration of Si-O-Si. -1 、745cm -1 and 455cm -1 The absorption peaks at and are attributed to the bending vibration and symmetric stretching vibration of Si-O, respectively. This is consistent with the XRD test results. It can be concluded that carbonate is generated during the MICP process.

[0087] 4.5 Microstructure

[0088] Figure 7 The microscopic changes of weathered sand before and after treatment are shown. Figure 7 (a) depicts a weathered sand sample before processing, which is characterized by being loose and porous. The processed sample usually has more densely arranged particles, and a layer of calcium carbonate deposits covers the surface of the particles and the original form. These deposits are crystalline or granular (under a scanning electron microscope, calcium carbonate crystals usually appear in regular geometric shapes, such as rhombuses or spheres). Figure 7 As shown in (b), the voids are partially filled with calcium carbonate, resulting in a decrease in overall porosity. The uniform distribution of calcium carbonate crystals indicates that the MICP process is relatively uniform and effective. Figure 7 In (c), calcium carbonate forms a "bridge" structure between particles, which can improve the overall strength of the soil. Due to the deposition of calcium carbonate, the contact points between particles become closer and more stable. Figure 7 In (c) to (d), crystals are deposited, aggregated, and grown between adjacent particles, bonding the adjacent particles into an integral structure and transforming the point contacts between the particles into surface contacts, thereby improving the overall stability of the sample.

[0089] In summary, the present invention uses a small-scale indoor wind tunnel test to study the feasibility of solidifying desert soil through bio-enhancement. The results show that the solidified desert surface soil has significantly improved in strength and wind erosion resistance. Changes in key indicators such as sample mass retention rate, sandy soil surface crust strength, and the quality of calcium carbonate produced, as well as microscopic analysis, all confirm this conclusion.

[0090] exist Figure 4 In the experiment, the spraying volume of the microbial solution and the binding solution was 20 ml, respectively, and the curing time was 21 days, and the sample mass retention rate was the highest, exceeding 95%. In contrast, when the spraying volume was 10 ml, the mass retention rate exceeded 90% after one day, but dropped sharply on the third day, and then gradually recovered, finally approaching the level observed in the high-dose group on the 14th day. This phenomenon can be attributed to the rapid initiation of the calcium carbonate precipitation reaction by microorganisms, even though the volume of the microbial solution and the binding solution was small at the beginning of the experiment. Most of the initial sediment accumulated on the surface of the sand, forming a thin and dense crust, which can effectively resist wind erosion in the short term, which is also the reason for the strong wind erosion resistance of the sand on the first day. However, the thin, uneven and unstable surface layer limits the long-term stability of the structure, making it vulnerable to external factors such as wind erosion and temperature fluctuations. Over time, the bacteria show stronger adaptability, their activities will resume, and the internal sediment will steadily consolidate. Over time, the strength will gradually increase after the seventh day.

[0091] exist Figure 5 In (b), the penetration resistance of groups A and B continued to increase over time, while that of group C continued to increase until the 14th day and then decreased. This difference may be due to the effect of extracellular polysaccharides. Initially, the exopolysaccharides secreted by bacteria can serve as nucleation sites for calcium carbonate crystals and wrap these crystals due to their high viscosity and gel-like properties, resulting in a rapid increase in strength. However, over time, the excess exopolysaccharides in group C may over-wrap the calcium carbonate particles, inhibiting crystal aggregation and tight bonding between crystals, resulting in a decrease in strength after 14 days. In contrast, the appropriate amount (not excessive) of microbial solution and binding solution in groups A and B did not have this problem and therefore continued to rise.

[0092] The Kashgar region is located on the western edge of the Taklimakan Desert, the largest desert in China. It is attacked by sandstorms for three to four months each year, and faces huge social and economic threats. The present invention proposes a new method for sustainably suppressing or completely eliminating sandstorms at a low cost.

[0093] Small-scale wind tunnel experiments using laboratory desert soil samples using the microbial inoculation method yielded the following conclusions:

[0094] Bio-augmentation can effectively stabilize and suppress sand and dust in the Taklimakan Desert.

[0095] Within the scope of the study, when the application rate of the microbial solution and the combined solution were both set at 20 ml (about 0.67 L / m2), the mass retention rate, permeability and calcium carbonate production in the desert soil samples reached their maximum values, enhancing their ability to resist wind erosion.

[0096] X-ray diffraction (XRD) analysis showed that the calcium carbonate content in the samples treated with MICP was significantly increased compared with that in the untreated samples, thus confirming the efficacy of MICP in stabilization.

[0097] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation methods of the present invention. For ordinary technical users in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. Application of Bacillus pasteurianus in improving the stability of weathered sand.

2. Application of Bacillus pasteurianus in the preparation of products for improving the stability of weathered sand.

3. A product for improving the stability of weathered sand, characterized in that: Including Bacillus pasteurianus.

4. The product according to claim 3, characterized in that The invention comprises the Bacillus pasteurianus suspension and a solidifying liquid.

5. The product according to claim 4, characterized in that The solidification liquid is prepared from 1 mol / L urea and 1 mol / L calcium chloride solution.

6. A method for preparing the product according to any one of claims 3 to 5, characterized in that: The following steps are involved: (1) Bacillus pasteurianus was activated and cultured to prepare 7.838×10 7 / ml of Bacillus pasteurianus suspension; (2) 1 mol / L urea and 1 mol / L calcium chloride solution were mixed to prepare a solidifying solution.

7. A method for improving the stability of weathered sand, characterized in that: The product according to any one of claims 3 to 5 is sprayed on the surface of weathered sand.

8. The method according to claim 7, characterized in that The dosage of the Bacillus pasteurianus suspension and the consolidation liquid is 0.67 liters per square meter respectively.

9. Application of Bacillus pasteurianus in inducing calcite precipitation.

10. Use of Bacillus pasteurianus in the preparation of products that induce calcite precipitation.

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