Lightweight foamed sand based on low temperature tolerant microbial solidifier and method of making

Abstract

The application discloses a kind of light foam sandy soil based on low-temperature resistant microbial curing agent and its preparation method, the light foam sandy soil includes solid matter and liquid matter, the mass ratio of solid matter and liquid matter is 3.5-6:1, the proportion of each substance in solid matter is 78-84wt% of sandy soil, 12-18wt% of composite activator, 4-6wt% of bacterial foam adsorbent, and the liquid matter is cementing solution.The preparation method includes the following steps: preparing low-temperature resistant microbial curing agent;The prepared low-temperature resistant microbial curing agent is mixed uniformly with sandy soil to obtain solid matter;The obtained solid matter is mixed uniformly with cementing solution, i.e. to obtain light foam sandy soil based on low-temperature resistant microbial curing agent.The technical scheme of the application significantly improves the survival rate and mineralization efficiency of the strain in low-temperature environment, and the light foam sandy soil prepared using the technical scheme has a lower mass per unit volume, higher compressive strength and higher permeability resistance.

Description

Technical Field

[0001] This invention belongs to the field of sand and soil solidification technology, specifically relating to a lightweight foamed sand based on a low-temperature resistant microbial solidifying agent and its preparation method, which is particularly suitable for the solidification treatment of sandy soil in low-temperature areas. Background Technology

[0002] Sandy soils in low-temperature regions are prone to frost heave and exhibit unevenness, which can lead to engineering problems such as soil collapse and landslides. Microbial mineralization technology can effectively solve these problems. This technology induces calcium carbonate precipitation through microbial metabolism. The generated calcium carbonate crystals can effectively cement sand particles and fill sand voids. After microbial treatment, the sand structure becomes more stable, effectively mitigating sand collapse.

[0003] Microbial mineralization technology has advantages such as environmental friendliness and low energy consumption, and has achieved significant results in the field of sand and soil solidification. However, the application of microbial mineralization technology in special soils under complex environments still faces challenges, especially in sandy soils in low-temperature regions (specifically referring to the solidification of sandy soils). These challenges mainly manifest as low bacterial survival rate, poor permeability of bacterial solutions, and uneven distribution of mineralization products under low-temperature conditions. These problems severely limit the engineering applicability of microbial mineralization technology.

[0004] Temperature is a key factor affecting the application of microbial mineralization technology. *Pasteurella multocida* exhibits significantly reduced activity below 10°C, making it difficult to adapt to environments with large diurnal temperature variations and low temperatures. Currently, existing research on strain domestication lacks systematic cultivation methods for low-temperature-adaptable *Pasteurella multocida* strains. Although UV mutagenesis can increase the mutation rate of strains, strains that have not undergone systematic temperature gradient domestication still struggle to maintain stable mineralization capabilities at low temperatures. Furthermore, existing liquid culture media typically do not contain trehalose, and its application in low-temperature strain domestication is currently unexplored. Even when trehalose is used, current techniques primarily utilize it as a nutrient to maintain cell growth, rather than for low-temperature adaptation. In other words, current technology lacks a technical approach for early domestication based on trehalose. The role of trehalose should not be limited to nutrient supply but should focus on establishing a stable low-temperature tolerance through early domestication—that is, using trehalose-assisted domestication in the early stages of strain cultivation to enable the strain to develop adaptability to low-temperature environments from an early age.

[0005] Furthermore, existing technologies for reducing roadbed loads have the following problems: First, directly adding foaming agents can be problematic. These agents are toxic to microorganisms, and their coating on the surface can inhibit microbial growth. In low-temperature environments, the compatibility of foaming agents is poor, leading to uneven foaming, and their adhesion to microbial mineralization products is unstable. Second, directly adding lightweight foam without any pretreatment can result in structural instability and an inability to maximize the specific surface area. Maximizing the specific surface area is crucial for providing a space for microorganisms to survive and implant. Moreover, the specific surface area varies and is uneven between different manufacturers and batches of lightweight foam, leading to uncertainties in the treatment results.

[0006] Therefore, how to use microbial mineralization technology to solidify sandy soil in low-temperature regions in order to solve the problem of soil collapse caused by uneven frost heave has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a lightweight foamed sand based on a low-temperature resistant microbial curing agent. The lightweight foamed sand comprises solid and liquid substances, with a mass ratio of solid to liquid of 3.5-6:1. The solid substances comprise, by mass percentage, 78-84 wt% sand, 12-18 wt% composite activator, and 4-6 wt% bacterial foam adsorbent. The composite activator and the bacterial foam adsorbent together constitute the low-temperature resistant microbial curing agent, and the liquid substance is a cementing solution.

[0008] Preferably, the mass percentage of each substance in the composite activator is 34-50 wt% calcium oxide, 12-22 wt% sodium sulfate, 20-32 wt% gypsum dihydrate, and 10-20 wt% urea.

[0009] In any of the above embodiments, preferably, the bacterial foam adsorbent is composed of pretreated polystyrene foam and a low-temperature acclimated bacterial solution, wherein the mass ratio of the pretreated polystyrene foam to the low-temperature acclimated bacterial solution is 1:2-3; the particle size of the polystyrene foam is controlled within the range of 2-4 mm; and the bacterial solution is a Bacillus pasteurellus bacterial solution with a concentration of 1×10⁻⁶. 8 ~1×10 9 cfu / ml. In this invention, polystyrene foam is also referred to as EPS lightweight foam balls, EPS foam balls, etc.

[0010] In any of the above embodiments, it is preferred that the cementing solution is prepared by mixing calcium chloride and urea in a certain mass ratio and then fully dissolving them in water, wherein the mass ratio of calcium chloride to urea is 1.6-2:1, and the mass-volume ratio of the sum of calcium chloride and urea to water is 160-180:1000, wherein the mass unit is g and the volume unit is ml.

[0011] This invention also provides a method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent, the preparation method comprising the following steps in sequence:

[0012] Step 1: Prepare a low-temperature resistant microbial curing agent according to the preset process regime;

[0013] Step 2: Mix the prepared low-temperature resistant microbial solidifying agent with sand at room temperature to obtain a solid substance;

[0014] Step 3: Mix the obtained solid material with the cementing solution at room temperature to obtain lightweight foamed sand based on low-temperature resistant microbial curing agent.

[0015] Preferably, in step one, the preparation of the low-temperature resistant microbial curing agent includes the following steps in sequence:

[0016] Step 1.1: According to the preset material ratio, calcium oxide, sodium sulfate, gypsum dihydrate and urea are mixed evenly at room temperature, and then subjected to low-temperature drying treatment to obtain the composite activator;

[0017] Step 1.2: Pre-treat the polystyrene foam according to the preset process.

[0018] Step 1.3: According to the preset process, the bacterial solution is subjected to trehalose acclimatization and low-temperature acclimatization in sequence;

[0019] Step 1.4: According to the preset material ratio, add the pretreated polystyrene foam to the low-temperature acclimatized bacterial solution for stirring and adsorption, and then freeze-dry to obtain the bacterial foam adsorbent.

[0020] Step 1.5: Mix the composite activator and bacterial foam adsorbent evenly at room temperature according to the preset material ratio to obtain the low-temperature resistant microbial curing agent.

[0021] In any of the above schemes, it is preferred that in step 1.1, the low-temperature drying temperature is 60-80℃ and the low-temperature drying time is 4-8h; in step 1.4, the freeze-drying temperature is -40~-50℃ and the freeze-drying time is 12-24h.

[0022] In any of the above schemes, preferably, in step 1.2, the pretreatment process of the polystyrene foam is as follows: First, the polystyrene foam is completely immersed in a 4-6% sodium hydroxide solution for 25-35 minutes to remove the surface oil film, then rinsed with deionized water and air-dried; then, the polystyrene foam is completely immersed in a 6-8% hydrochloric acid solution for 50-60 minutes to corrode its surface, then rinsed with deionized water and air-dried; finally, the polystyrene foam is completely immersed in a 0.2-0.5 mol / L calcium chloride solution for 5-10 minutes to allow its surface to adsorb and accumulate calcium ions. After immersion, the pretreatment of the polystyrene foam is completed.

[0023] In this invention, the pretreatment of polystyrene foam increases its surface roughness, maximizing its specific surface area. Simultaneously, calcium ions are pre-enriched on its surface, significantly improving the subsequent curing efficiency and stability of bacteria on the foam surface. Furthermore, this pretreatment eliminates differences in specific surface area between foams from different manufacturers and batches, ensuring the certainty and repeatability of the treatment results.

[0024] In any of the above schemes, it is preferred that, in step 1.3, the trehalose-based domestication of the bacterial solution includes the following steps in sequence:

[0025] S1. Inoculate the bacterial culture into liquid culture medium I and incubate at 20°C for 24 hours. The volume ratio of bacterial culture to liquid culture medium I is 1:20. The concentration of trehalose in liquid culture medium I is 5 g / L. After incubation, centrifuge to obtain concentrated bacterial cells. Spread the bacterial cells on the surface of solid culture medium and incubate at 20°C for 24 hours.

[0026] S2. Select the three largest strains from S1, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 5g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 19℃ for 24h.

[0027] S3. Select the three largest strains from S2, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 10g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 18℃ for 24h.

[0028] S4. Select the three largest strains from S3, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 10g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 17℃ for 24h.

[0029] S5. Select the three largest strains from S4, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 15g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 16℃ for 24h.

[0030] S6. Select the three largest strains from S5, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 15g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 15℃ for 24h, thus completing the basic acclimatization of the bacterial solution to trehalose.

[0031] In this invention, before the basic domestication of trehalose, it is necessary to perform routine operations such as activation, purification, and scale-up of the microbial strains to bring the resulting bacterial solution into the logarithmic growth phase. These routine operations can be performed using existing technologies and there are no special requirements for process parameters.

[0032] This invention innovatively employs trehalose-based acclimatization of bacterial cultures, aiming to establish stable low-temperature tolerance in the strains through early acclimatization. Specifically, in the early stages of bacterial culture, the aid of trehalose-assisted acclimatization enables the strains to develop adaptability to low-temperature environments from an early stage.

[0033] During the basic acclimatization process of trehalose, gradually increasing the trehalose content in the liquid culture medium helps to form a protective film on the surface of bacteria under low temperature conditions, effectively protecting the molecular structure of microorganisms from being destroyed, thereby enhancing the survival rate of the strains under low temperature conditions.

[0034] In any of the above schemes, it is preferred that, in step 1.3, the low-temperature acclimatization of the bacterial solution includes the following steps in sequence:

[0035] A1. Turn on the 20W UV lamp and preheat for 20-30 minutes. Take the bacterial culture after trehalose basic domestication, inject it into the culture dish and place it 30-50cm away from the UV lamp. Irradiate for 60-90 seconds under continuous stirring with a magnetic stirrer to complete the UV mutagenesis treatment.

[0036] A2. The strain treated with UV mutagenesis was inoculated into 200 ml of liquid culture medium II and cultured at 20°C for 12 h. Then the culture temperature was lowered to the initial low-temperature acclimatization temperature of 15°C and cultured for another 24 h to obtain the initial bacterial suspension. 25 μl of the initial bacterial suspension was spread on the surface of a solid culture medium and cultured at 20°C for 24 h. If bacterial spots appeared on the surface of the solid culture medium, the first generation of low-temperature acclimatization at the initial low-temperature acclimatization temperature of 15°C was completed, and one strain was selected as the next generation of low-temperature acclimatization strain. Otherwise, the initial bacterial suspension was spread on the surface of the solid culture medium again and combined with UV mutagenesis treatment to continue acclimatization until bacterial spots appeared on the surface of the solid culture medium.

[0037] A3. At an initial low-temperature acclimatization temperature of 15℃, the strains selected in A2 are used as low-temperature acclimatization strains. The second generation of low-temperature acclimatization is completed according to the low-temperature acclimatization process in A2. One strain is selected from the second generation of low-temperature acclimatization strains. This process is repeated to complete the third, fourth, and fifth generation of low-temperature acclimatization. After completing at least five generations of low-temperature acclimatization, a stable acclimatized strain at an initial low-temperature acclimatization temperature of 15℃ is obtained.

[0038] A4. Select one strain from the stable acclimatized strains in A3, inoculate the strain into 200ml of liquid medium II and culture at 20℃ for 12h. Then, lower the culture temperature to 14℃ and continue to culture for 24h to obtain a bacterial suspension. Take 25μl of the bacterial suspension and spread it on the surface of a solid medium and culture at 20℃ for 24h to complete one generation of low-temperature acclimatization at 14℃. After completing at least five generations of low-temperature acclimatization at 14℃, a stable acclimatized strain at 14℃ is obtained.

[0039] A5. Following this pattern, the low-temperature acclimatization temperature is lowered to 10℃, with each decrease being 1℃. At least five generations of low-temperature acclimatization are continuously completed at the same low-temperature acclimatization temperature until a stable acclimatized strain at 10℃ is obtained, thus completing the low-temperature acclimatization of the bacterial solution.

[0040] Temperature is a key factor affecting the application of microbial mineralization technology. This invention employs a synergistic effect of trehalose-based domestication and low-temperature domestication to gradually increase the cold resistance of microorganisms from 20℃ to 10℃. Specifically: First, through trehalose-based domestication, leveraging the protective effect of trehalose on cell membranes and proteins, strains gradually establish preliminary low-temperature tolerance within the range of 20℃ to 15℃; then, combining UV mutagenesis treatment and low-temperature domestication, cold-resistant strains are further screened within the range of 15℃ to 10℃. The synergistic effect of these two methods achieves a stepwise decrease in cold resistance temperature, ultimately obtaining strains that maintain stable mineralization ability below 10℃. After this domestication, the survival rate of the strains at extreme temperatures reaches over 90%, thus ensuring the sustainability of microbial mineralization in low-temperature regions.

[0041] In step A2 of the low-temperature acclimatization, the initial bacterial suspension is re-spread onto the surface of the solid culture medium and combined with ultraviolet mutagenesis treatment to continue acclimatization. The process is as follows: the solid culture medium with the initial bacterial suspension is placed 30-50 cm away from the ultraviolet lamp for irradiation. The optimal irradiation time for ultraviolet mutagenesis is 60-90 s. After mutagenesis, the solid culture medium with the initial bacterial suspension is transferred to a 250 ml Erlenmeyer flask for further enrichment culture. At this time, the light is normal and the shaking speed is 160 rpm.

[0042] Sandy soils in low-temperature regions are exposed to large diurnal temperature variations and low temperatures. Well-acclimated bacteria can survive better in low-temperature environments. After the calcium oxide in the composite activator reacts with the cementing solution, it not only provides a calcium source to enhance the precipitation efficiency of calcium carbonate, but also generates heat. EPS foam balls also play a role in heat preservation in low-temperature regions with large diurnal temperature variations and low temperatures, slowing down temperature fluctuations and making bacteria more stable in low-temperature environments. All these aspects provide a more suitable growth environment for bacteria in low-temperature environments.

[0043] In any of the above schemes, it is preferred that, during the trehalose-based acclimatization and low-temperature acclimatization stages, the raw materials for preparing the solid culture medium include, by weight, 12 parts casein peptone, 5 parts soybean peptone, 2 parts sodium chloride, 16 parts urea, and 20 parts agar; it also includes deionized water, wherein the mass-to-volume ratio of the sum of casein peptone, soybean peptone, sodium chloride, urea, and agar to deionized water is 55:1000, with mass units in g and volume units in ml.

[0044] In any of the above schemes, it is preferred that, during the trehalose basic acclimatization stage, the raw materials for preparing the liquid culture medium I include, by weight, 8 parts casein peptone, 2 parts sodium chloride, 8 parts urea, and 5-15 parts trehalose; it also includes deionized water, wherein the mass-to-volume ratio of the sum of casein peptone, sodium chloride, urea, and trehalose to deionized water is 23-33:1000, with mass units in g and volume units in ml.

[0045] In any of the above schemes, it is preferred that, during the low-temperature acclimatization stage, the raw materials for preparing the liquid culture medium II include, by weight, 8 parts casein peptone, 2 parts sodium chloride, 8 parts urea, and 5 parts trehalose; and also include deionized water, wherein the mass-to-volume ratio of the sum of casein peptone, sodium chloride, urea, and trehalose to deionized water is 23:1000, with mass units in g and volume units in ml.

[0046] This invention innovatively adds trehalose to a liquid culture medium. Its functions are as follows: First, trehalose can form a protective layer on the bacterial surface, reducing damage to bacteria caused by ice crystals forming when the liquid freezes at low temperatures. Simultaneously, trehalose forms a protective film on the bacterial surface during the air-drying of the bacterial complex, providing protection. Second, trehalose can serve as a carbon source, enhancing soil consolidation. Furthermore, trehalose can improve the hydrophilicity of polystyrene foam surfaces, helping to increase bacterial adsorption while reducing polystyrene foam adhesion, resulting in a more uniform distribution of the bacterial complex. Third, trehalose can improve the bacteria's adaptability to low-temperature environments, strengthening their own cold resistance mechanisms.

[0047] In this invention, solid culture media can be prepared using existing technology, and there are no special requirements for process parameters. For liquid culture media, casein peptone, sodium chloride, urea, and trehalose are added to deionized water according to the preset material ratio and stirred at room temperature until completely dissolved.

[0048] This invention relates to lightweight foamed sand based on a low-temperature resistant microbial solidifying agent and its preparation method, which has the following beneficial effects:

[0049] (1) This invention uses the synergistic effect of trehalose-based domestication and low-temperature domestication to gradually increase the cold resistance of microorganisms from 20℃ to 10℃. The two work together to achieve a step-by-step decrease in cold resistance temperature, and finally obtain strains that can maintain stable mineralization ability below 10℃.

[0050] (2) The present invention pre-treats EPS foam balls, effectively removes surface oil film, increases surface roughness and enriches calcium ions, maximizes the specific surface area of ​​foam, and provides sufficient survival and implantation space for microorganisms.

[0051] (3) In view of the problem of weak bonding between EPS foam balls and soil, the present invention uses bacterial liquid adsorption to form a three-dimensional network structure of calcium carbonate crystals on the surface of EPS foam balls; after pretreatment, the thickness of the transition zone between EPS foam balls and soil is reduced and the bonding strength of the interface is improved, thereby effectively solving the problem of slippage and damage of lightweight fill materials.

[0052] (4) The curing agent prepared by the present invention can significantly improve the compressive strength, impermeability and durability of soil, while reducing construction costs. When applied to roadbed construction, it can effectively reduce the roadbed load and significantly improve the survival rate and mineralization efficiency of bacteria under low temperature conditions.

[0053] (5) The raw materials used in this invention are green, environmentally friendly, pollution-free and low cost, realizing the resource utilization of sand in low-temperature areas and the waste reuse of EPS foam balls, forming a green and efficient low-temperature microbial lightweight foam sand with good ecological protection benefits. Attached Figure Description

[0054] Figure 1 Photograph of the sand used in a preferred embodiment of the lightweight foamed sand based on the low-temperature resistant microbial solidifying agent and the preparation method thereof according to the present invention;

[0055] Figure 2 for Figure 1 The sand particle size distribution diagram used in the illustrated embodiment;

[0056] Figure 3 for Figure 1 Photograph of the polystyrene foam used in the illustrated embodiment;

[0057] Figure 4 for Figure 1 Photograph of the bacterial foam adsorbent prepared in the example shown;

[0058] Figure 5 To adopt Figure 1 Photograph of a shear strength test specimen made from lightweight foamed sand prepared in the example shown;

[0059] Figure 6 To adopt Figure 1 Photograph of the compressive strength test specimen made from the lightweight foamed sand prepared in the example shown;

[0060] Figure 7 for Figure 6 The photograph shown shows the state of the specimen after being crushed following a compressive strength test.

[0061] Figure 8 This is a comparison chart of dry and wet cycle tests;

[0062] Figure 9 This is a comparison chart of immersion tests;

[0063] Figure 10 This is a comparison chart of compressive strength test results;

[0064] Figure 11 This is a comparison chart of the mineralization efficiency test results for bacterial strains. Detailed Implementation

[0065] To further understand the invention, the following detailed description of the invention will be provided in conjunction with specific embodiments.

[0066] Example 1:

[0067] According to a preferred embodiment of the lightweight foamed sand based on a low-temperature resistant microbial curing agent of the present invention, the lightweight foamed sand comprises solid and liquid substances, wherein the mass ratio of the solid substance to the liquid substance is 4.7:1, and the mass percentage of each substance in the solid substance is 80wt% sand, 15wt% composite activator, and 5wt% bacterial foam adsorbent. The composite activator and the bacterial foam adsorbent constitute a low-temperature resistant microbial curing agent, and the liquid substance is a cementing solution.

[0068] The mass percentages of each substance in the composite activator are: calcium oxide 42wt%, sodium sulfate 17wt%, gypsum dihydrate 26wt%, and urea 15wt%.

[0069] The bacterial foam adsorbent is composed of pretreated polystyrene foam and a low-temperature acclimated bacterial solution, with a mass ratio of 1:2.5 between the pretreated polystyrene foam and the low-temperature acclimated bacterial solution; the particle size of the polystyrene foam is controlled within the range of 2-4 mm; the bacterial solution is a Bacillus pasteurellis bacterial solution with a concentration of 1×10⁻⁶. 8 ~1×10 9 cfu / ml.

[0070] The cementing solution is prepared by mixing calcium chloride and urea in a certain mass ratio and then fully dissolving them in water. The mass ratio of calcium chloride to urea is 1.8:1, and the mass-to-volume ratio of the sum of calcium chloride and urea to water is 170:1000. The mass unit is g and the volume unit is ml.

[0071] This embodiment also provides a method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent, the preparation method comprising the following steps in sequence:

[0072] Step 1: Prepare a low-temperature resistant microbial curing agent according to the preset process regime;

[0073] Step 2: Mix the prepared low-temperature resistant microbial solidifying agent with sand at room temperature to obtain a solid substance;

[0074] Step 3: Mix the obtained solid material with the cementing solution at room temperature to obtain lightweight foamed sand based on low-temperature resistant microbial curing agent.

[0075] In step one, the preparation of the low-temperature resistant microbial curing agent includes the following steps in sequence:

[0076] Step 1.1: According to the preset material ratio, calcium oxide, sodium sulfate, gypsum dihydrate and urea are mixed evenly at room temperature, and then subjected to low-temperature drying treatment to obtain the composite activator;

[0077] Step 1.2: Pre-treat the polystyrene foam according to the preset process.

[0078] Step 1.3: According to the preset process, the bacterial solution is subjected to trehalose acclimatization and low-temperature acclimatization in sequence;

[0079] Step 1.4: According to the preset material ratio, add the pretreated polystyrene foam to the low-temperature acclimatized bacterial solution for stirring and adsorption, and then freeze-dry to obtain the bacterial foam adsorbent.

[0080] Step 1.5: Mix the composite activator and bacterial foam adsorbent evenly at room temperature according to the preset material ratio to obtain the low-temperature resistant microbial curing agent.

[0081] In step 1.1, the low-temperature drying temperature is 70℃ and the low-temperature drying time is 6h; in step 1.4, the freeze-drying temperature is -45℃ and the freeze-drying time is 18h.

[0082] In step 1.2, the pretreatment process of the polystyrene foam is as follows: First, the polystyrene foam is completely immersed in a 5% sodium hydroxide solution for 30 minutes to remove the surface oil film, then rinsed with deionized water and air-dried. Next, the polystyrene foam is completely immersed in a 7% hydrochloric acid solution for 55 minutes to corrode its surface, then rinsed with deionized water and air-dried. Finally, the polystyrene foam is completely immersed in a 0.35 mol / L calcium chloride solution for 7.5 minutes to allow its surface to adsorb and accumulate calcium ions. After immersion, the pretreatment of the polystyrene foam is completed.

[0083] In step 1.3, the trehalose-based domestication of the bacterial solution includes the following steps in sequence:

[0084] S1. Inoculate the bacterial culture into liquid culture medium I and incubate at 20°C for 24 hours. The volume ratio of bacterial culture to liquid culture medium I is 1:20. The concentration of trehalose in liquid culture medium I is 5 g / L. After incubation, centrifuge to obtain concentrated bacterial cells. Spread the bacterial cells on the surface of solid culture medium and incubate at 20°C for 24 hours.

[0085] S2. Select the three largest strains from S1, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 5g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 19℃ for 24h.

[0086] S3. Select the three largest strains from S2, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 10g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 18℃ for 24h.

[0087] S4. Select the three largest strains from S3, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 10g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 17℃ for 24h.

[0088] S5. Select the three largest strains from S4, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 15g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 16℃ for 24h.

[0089] S6. Select the three largest strains from S5, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 15g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 15℃ for 24h, thus completing the basic acclimatization of the bacterial solution to trehalose.

[0090] In step 1.3, the low-temperature acclimatization of the bacterial solution includes the following steps in sequence:

[0091] A1. Turn on the 20W UV lamp and preheat for 25 minutes. Take the bacterial culture after trehalose basic domestication, inject it into the culture dish and place it 40cm away from the UV lamp. Irradiate for 75s under continuous stirring with a magnetic stirrer to complete the UV mutagenesis treatment.

[0092] A2. The strain treated with UV mutagenesis was inoculated into 200 ml of liquid culture medium II and cultured at 20°C for 12 h. Then the culture temperature was lowered to the initial low-temperature acclimatization temperature of 15°C and cultured for another 24 h to obtain the initial bacterial suspension. 25 μl of the initial bacterial suspension was spread on the surface of a solid culture medium and cultured at 20°C for 24 h. If bacterial spots appeared on the surface of the solid culture medium, the first generation of low-temperature acclimatization at the initial low-temperature acclimatization temperature of 15°C was completed, and one strain was selected as the next generation of low-temperature acclimatization strain. Otherwise, the initial bacterial suspension was spread on the surface of the solid culture medium again and combined with UV mutagenesis treatment to continue acclimatization until bacterial spots appeared on the surface of the solid culture medium.

[0093] A3. At an initial low-temperature acclimatization temperature of 15℃, the strains selected in A2 are used as low-temperature acclimatization strains. The second generation of low-temperature acclimatization is completed according to the low-temperature acclimatization process in A2. One strain is selected from the second generation of low-temperature acclimatization strains. This process is repeated to complete the third, fourth, and fifth generation of low-temperature acclimatization. After completing at least five generations of low-temperature acclimatization, a stable acclimatized strain at an initial low-temperature acclimatization temperature of 15℃ is obtained.

[0094] A4. Select one strain from the stable acclimatized strains in A3, inoculate the strain into 200ml of liquid medium II and culture at 20℃ for 12h. Then, lower the culture temperature to 14℃ and continue to culture for 24h to obtain a bacterial suspension. Take 25μl of the bacterial suspension and spread it on the surface of a solid medium and culture at 20℃ for 24h to complete one generation of low-temperature acclimatization at 14℃. After completing at least five generations of low-temperature acclimatization at 14℃, a stable acclimatized strain at 14℃ is obtained.

[0095] A5. Following this pattern, the low-temperature acclimatization temperature is lowered to 10℃, with each decrease being 1℃. At least five generations of low-temperature acclimatization are continuously completed at the same low-temperature acclimatization temperature until a stable acclimatized strain at 10℃ is obtained, thus completing the low-temperature acclimatization of the bacterial solution.

[0096] During the basic acclimatization and low-temperature acclimatization stages of trehalose, the raw materials for preparing the solid culture medium include, by weight (1 part is denoted as 1g): 12 parts casein peptone, 5 parts soybean peptone, 2 parts sodium chloride, 16 parts urea, and 20 parts agar; it also includes deionized water, wherein the mass-to-volume ratio of the sum of casein peptone, soybean peptone, sodium chloride, urea, and agar to deionized water is 55:1000, with mass units in g and volume units in ml.

[0097] During the basic acclimatization stage of trehalose, the raw materials for preparing the liquid culture medium I include, by weight (1 part is denoted as 1g): 8 parts casein peptone, 2 parts sodium chloride, 8 parts urea, and 5-15 parts trehalose; it also includes deionized water, wherein the mass-to-volume ratio of the sum of casein peptone, sodium chloride, urea, and trehalose to deionized water is 23-33:1000, with mass units in g and volume units in ml.

[0098] During the low-temperature acclimatization stage, the raw materials for preparing the liquid culture medium II include, by weight (1 part is denoted as 1g): 8 parts casein peptone, 2 parts sodium chloride, 8 parts urea, and 5 parts trehalose; it also includes deionized water, wherein the mass-to-volume ratio of the sum of casein peptone, sodium chloride, urea, and trehalose to deionized water is 23:1000, with mass units in g and volume units in ml.

[0099] In this embodiment, the sand and polystyrene foam used are respectively as follows: Figure 1 and Figure 3 As shown in the figure, the particle size distribution diagram of sand is as follows: Figure 2 As shown, the prepared bacterial foam adsorbent is as follows: Figure 4 As shown, the shear strength test specimens and compressive strength test specimens made from the lightweight foamed sand prepared in this embodiment are respectively as follows: Figure 5 and Figure 6 As shown, the specimen was crushed after the compressive strength test. Figure 7 As shown.

[0100] This embodiment has the following beneficial effects: (1) By using the synergistic effect of trehalose-based domestication and low-temperature domestication, the cold resistance of microorganisms is gradually increased from 20℃ to 10℃. The two work together to achieve a step-by-step decrease in cold resistance temperature, and finally obtain strains that can maintain stable mineralization ability below 10℃. (2) Pretreatment of EPS foam balls effectively removes surface oil film, increases surface roughness and enriches calcium ions, maximizes the specific surface area of ​​foam, and provides sufficient survival and implantation space for microorganisms. (3) Through bacterial liquid adsorption, calcium carbonate crystals form a three-dimensional network structure on the surface of EPS foam balls. After pretreatment, the thickness of the transition zone between EPS foam balls and soil is reduced and the interfacial bonding strength is improved. (4) It can significantly improve the compressive strength, impermeability and durability of soil. When applied to roadbed construction, it can effectively reduce the roadbed load, and at the same time significantly improve the survival rate and mineralization efficiency of strains in low-temperature environments. (5) The raw materials used are green, environmentally friendly and pollution-free, realizing the resource utilization of sandy soil in low-temperature areas and the waste reuse of EPS foam balls.

[0101] Example 2:

[0102] According to another preferred embodiment of the lightweight foamed sand based on a low-temperature resistant microbial solidifying agent and its preparation method, the raw material selection, preparation method, and beneficial effects are basically the same as those in Embodiment 1, except that:

[0103] The lightweight foamed sand comprises solid and liquid substances, with a mass ratio of solid to liquid of 3.5:1. The solid substances comprise 78 wt% sand, 18 wt% composite activator, and 4 wt% bacterial foam adsorbent. The composite activator and the bacterial foam adsorbent together form a low-temperature resistant microbial curing agent. The liquid substance is a cementing solution.

[0104] The mass percentages of each substance in the composite activator are: calcium oxide 36wt%, sodium sulfate 12wt%, gypsum dihydrate 32wt%, and urea 20wt%.

[0105] The bacterial foam adsorbent is composed of pretreated polystyrene foam and low-temperature acclimated bacterial solution, with a mass ratio of 1:2 between the pretreated polystyrene foam and the low-temperature acclimated bacterial solution.

[0106] The cementing solution is prepared by mixing calcium chloride and urea in a certain mass ratio and then fully dissolving them in water. The mass ratio of calcium chloride to urea is 1.6:1, and the mass-to-volume ratio of the sum of calcium chloride and urea to water is 160:1000. The mass unit is g and the volume unit is ml.

[0107] In step 1.1, the low-temperature drying treatment temperature is 60℃ and the low-temperature drying treatment time is 8h.

[0108] In step 1.2, the pretreatment process of the polystyrene foam is as follows: First, the polystyrene foam is completely immersed in a 4% sodium hydroxide solution for 25 minutes to remove the surface oil film, then rinsed with deionized water and air-dried. Next, the polystyrene foam is completely immersed in a 6% hydrochloric acid solution for 50 minutes to corrode its surface, then rinsed with deionized water and air-dried. Finally, the polystyrene foam is completely immersed in a 0.2 mol / L calcium chloride solution for 5 minutes to allow calcium ions to be adsorbed and enriched on its surface. After immersion, the pretreatment of the polystyrene foam is completed.

[0109] In step 1.3, during the low-temperature acclimatization process of the bacterial solution: A1, turn on the 20W ultraviolet lamp for 20 minutes to preheat, take the bacterial solution after acclimatization with trehalose and inject it into the culture dish and place it 30cm away from the ultraviolet lamp. Irradiate it for 60 seconds under continuous stirring with a magnetic stirrer to complete the ultraviolet mutagenesis treatment.

[0110] In step 1.4, the freeze-drying temperature is -40℃ and the freeze-drying time is 24h.

[0111] Example 3:

[0112] According to another preferred embodiment of the lightweight foamed sand based on a low-temperature resistant microbial solidifying agent and its preparation method, the raw material selection, preparation method, and beneficial effects are basically the same as those in Embodiment 1, except that:

[0113] The lightweight foamed sand comprises solid and liquid substances, with a mass ratio of solid to liquid of 6:1. The solid substances comprise 82 wt% sand, 12 wt% composite activator, and 6 wt% bacterial foam adsorbent. The composite activator and the bacterial foam adsorbent together form a low-temperature resistant microbial curing agent. The liquid substance is a cementing solution.

[0114] The mass percentages of each substance in the composite activator are: calcium oxide 48wt%, sodium sulfate 22wt%, gypsum dihydrate 20wt%, and urea 10wt%.

[0115] The bacterial foam adsorbent is composed of pretreated polystyrene foam and low-temperature acclimated bacterial solution, with a mass ratio of 1:3 between the pretreated polystyrene foam and the low-temperature acclimated bacterial solution.

[0116] The cementing solution is prepared by mixing calcium chloride and urea in a certain mass ratio and then fully dissolving them in water. The mass ratio of calcium chloride to urea is 2:1, and the mass-to-volume ratio of the sum of calcium chloride and urea to water is 180:1000. The mass unit is g and the volume unit is ml.

[0117] In step 1.1, the low-temperature drying temperature is 80℃ and the low-temperature drying time is 4h.

[0118] In step 1.2, the pretreatment process of the polystyrene foam is as follows: First, the polystyrene foam is completely immersed in a 6% sodium hydroxide solution for 35 minutes to remove the surface oil film, then rinsed with deionized water and air-dried. Next, the polystyrene foam is completely immersed in an 8% hydrochloric acid solution for 60 minutes to corrode its surface, then rinsed with deionized water and air-dried. Finally, the polystyrene foam is completely immersed in a 0.5 mol / L calcium chloride solution for 10 minutes to allow calcium ions to be adsorbed and enriched on its surface. After immersion, the pretreatment of the polystyrene foam is completed.

[0119] In step 1.3, during the low-temperature acclimatization process of the bacterial solution: A1, turn on the 20W ultraviolet lamp for 30 minutes to preheat, take the bacterial solution after acclimatization with trehalose and inject it into the culture dish and place it 50cm away from the ultraviolet lamp. Irradiate it for 90 seconds under continuous stirring with a magnetic stirrer to complete the ultraviolet mutagenesis treatment.

[0120] In step 1.4, the freeze-drying temperature is -50℃ and the freeze-drying time is 12h.

[0121] Performance tests were conducted on the three embodiments described above, with identical test environments, conditions, and equipment. The test procedures must comply with relevant industry requirements. Table 1 shows the shear strength test results under different normal stresses. Figures 8-11 The results are compared in the following tests: wet-dry cycle test, immersion test, compressive strength test, and microbial mineralization efficiency test.

[0122] Table 1. Shear strength test results under different normal stresses

[0123]

[0124] As can be seen from the test results in Table 1, the shear strength of the lightweight foamed sand prepared in the three examples under different normal stresses is much higher than that of the original sand. After fitting the shear strength test data, the cohesion and internal friction angle were obtained. From the fitting results, the cohesion of the lightweight foamed sand prepared in the three examples is much higher than that of the original sand, and the internal friction angle is also greater than that of the original sand.

[0125] from Figure 8 It can be seen that the lightweight foamed sand prepared in the three embodiments can still maintain high unconfined compressive strength after undergoing multiple wet-dry cycle tests; while the original sand completely lost its unconfined compressive strength after only one wet-dry cycle test; from Figure 9 It can be seen that the lightweight foamed sand prepared in the three embodiments can still maintain a high unconfined compressive strength after 90 days of immersion test. Figure 8 and Figure 9 This indicates that lightweight foamed sand has excellent impermeability.

[0126] Figure 10 MICP clay consists of sand, un-trehalose-based and un-low-temperature-acclimated bacterial solution, and a cementing solution. MICP clay is suitable for a temperature environment of 30℃, meaning that microorganisms can reach their optimal growth state at 30℃. Figure 10 It can be seen that the lightweight foamed sand prepared in the three examples has a strength comparable to that of MICP clay at a low temperature of 10°C (the optimal growth temperature for microorganisms).

[0127] Figure 11In the reaction, the unacclimated bacterial culture at 30℃ (unacclimated with trehalose and not acclimated at low temperature) reacted with the cementing solution at 30℃ for 30 minutes; the unacclimated bacterial culture at 10℃ (unacclimated with trehalose and not acclimated at low temperature) reacted with the cementing solution at 10℃ for 30 minutes; and the acclimated bacterial culture at 10℃ (acclimated with trehalose and not acclimated at low temperature) reacted with the cementing solution at 10℃ for 30 minutes. After the reaction was completed, the bacteria were dried and the mass of calcium carbonate produced was measured. The greater the amount of calcium carbonate produced, the higher the bacterial survival rate and the higher the mineralization efficiency.

[0128] The microbial strains used in the above embodiments were purchased from the China National Microbial Culture Collection, and the raw materials for preparing solid and liquid culture media, as well as other chemical reagents, were purchased from Aladdin Reagent Co., Ltd.

[0129] Special Note: The technical solution of this invention involves numerous parameters, and the synergistic effects between these parameters must be comprehensively considered to achieve the beneficial effects and significant progress of this invention. Furthermore, the value ranges of each parameter in the technical solution were obtained through extensive experimentation. For each parameter and the combinations thereof, the inventors have recorded a large amount of experimental data; however, due to space limitations, the specific experimental data is not disclosed here.

[0130] It will be readily understood by those skilled in the art that this invention includes any combination of the inventive description and specific embodiments outlined in the foregoing specification, as well as the various parts shown in the accompanying drawings. Due to space limitations and for the sake of brevity, not all of these combinations have been described in detail. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent, characterized in that, The preparation method includes the following steps in sequence: Step 1: Prepare a low-temperature resistant microbial curing agent according to the preset process regime; Step 2: Mix the prepared low-temperature resistant microbial solidifying agent with sand at room temperature to obtain a solid substance; Step 3: Mix the obtained solid material with the cementing solution at room temperature to obtain lightweight foamed sand based on low-temperature resistant microbial solidification agent; In step one, the preparation of the low-temperature resistant microbial curing agent includes the following steps in sequence: Step 1.1: According to the preset material ratio, calcium oxide, sodium sulfate, gypsum dihydrate and urea are mixed evenly at room temperature, and then subjected to low-temperature drying treatment to obtain the composite activator; Step 1.2: Pre-treat the polystyrene foam according to the preset process. Step 1.3: According to the preset process, the bacterial solution is subjected to trehalose acclimatization and low-temperature acclimatization in sequence; Step 1.4: According to the preset material ratio, add the pretreated polystyrene foam to the low-temperature acclimatized bacterial solution for stirring and adsorption, and then freeze-dry to obtain the bacterial foam adsorbent. Step 1.5: According to the preset material ratio, mix the composite activator and the bacterial foam adsorbent evenly at room temperature to obtain the low-temperature resistant microbial curing agent; In step 1.2, the pretreatment process of the polystyrene foam is as follows: First, the polystyrene foam is completely immersed in a 4-6% sodium hydroxide solution for 25-35 minutes to remove the surface oil film, then rinsed with deionized water and air-dried. Next, the polystyrene foam is completely immersed in a 6-8% hydrochloric acid solution for 50-60 minutes to corrode its surface, then rinsed with deionized water and air-dried. Finally, the polystyrene foam is completely immersed in a 0.2-0.5 mol / L calcium chloride solution for 5-10 minutes to allow calcium ions to be adsorbed and enriched on its surface. After immersion, the pretreatment of the polystyrene foam is complete. In step 1.3, during the basic acclimatization process, the trehalose content in the liquid culture medium is gradually increased, which helps to form a protective film on the bacterial surface under low temperature conditions. Through basic acclimatization with trehalose, the strain gradually establishes preliminary low temperature tolerance in the range of 20℃ to 15℃. Then, combined with ultraviolet mutagenesis treatment and low temperature acclimatization, cold-resistant strains are further screened in the range of 15℃ to 10℃, and finally strains that can maintain stable mineralization ability below 10℃ are obtained. The lightweight foamed sand comprises solid and liquid substances, with a mass ratio of solid to liquid substances of 3.5-6:

1. The solid substances consist of 78-84 wt% sand, 12-18 wt% composite activator, and 4-6 wt% bacterial foam adsorbent. The liquid substance is a cementing solution. The composite activator comprises calcium oxide 34-50 wt%, sodium sulfate 12-22 wt%, gypsum dihydrate 20-32 wt%, and urea 10-20 wt%; the mass ratio of the pretreated polystyrene foam to the low-temperature acclimated bacterial solution is 1:2-3.

2. The method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent according to claim 1, characterized in that, In step 1.1, the low-temperature drying temperature is 60-80℃ and the low-temperature drying time is 4-8h; in step 1.4, the freeze-drying temperature is -40~-50℃ and the freeze-drying time is 12-24h.

3. The method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent according to claim 2, characterized in that, In step 1.3, the trehalose-based domestication of the bacterial solution includes the following steps in sequence: S1. Inoculate the bacterial culture into liquid culture medium I and incubate at 20°C for 24 hours. The volume ratio of bacterial culture to liquid culture medium I is 1:

20. The concentration of trehalose in liquid culture medium I is 5 g / L. After incubation, centrifuge to obtain concentrated bacterial cells. Spread the bacterial cells on the surface of solid culture medium and incubate at 20°C for 24 hours. S2. Select the three largest strains from S1, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 5g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 19℃ for 24h. S3. Select the three largest strains from S2, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 10g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 18℃ for 24h. S4. Select the three largest strains from S3, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 10g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 17℃ for 24h. S5. Select the three largest strains from S4, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 15g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 16℃ for 24h. S6. Select the three largest strains from S5, inoculate the strains into 200ml of liquid culture medium I and culture at 20℃ for 24h. The concentration of trehalose in liquid culture medium I is 15g / l. After the culture is completed, centrifuge to obtain concentrated bacterial cells, spread the bacterial cells on the surface of solid culture medium and culture at 15℃ for 24h, thus completing the basic acclimatization of the bacterial solution to trehalose.

4. The method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent according to claim 3, characterized in that, In step 1.3, the low-temperature acclimatization of the bacterial solution includes the following steps in sequence: A1. Turn on the 20W UV lamp and preheat for 20-30 minutes. Take the bacterial culture after trehalose basic domestication, inject it into the culture dish and place it 30-50cm away from the UV lamp. Irradiate for 60-90 seconds under continuous stirring with a magnetic stirrer to complete the UV mutagenesis treatment. A2. The strain treated with UV mutagenesis was inoculated into 200 ml of liquid culture medium II and cultured at 20°C for 12 h. Then the culture temperature was lowered to the initial low-temperature acclimatization temperature of 15°C and cultured for another 24 h to obtain the initial bacterial suspension. 25 μl of the initial bacterial suspension was spread on the surface of a solid culture medium and cultured at 20°C for 24 h. If bacterial spots appeared on the surface of the solid culture medium, the first generation of low-temperature acclimatization at the initial low-temperature acclimatization temperature of 15°C was completed, and one strain was selected as the next generation of low-temperature acclimatization strain. Otherwise, the initial bacterial suspension was spread on the surface of the solid culture medium again and combined with UV mutagenesis treatment to continue acclimatization until bacterial spots appeared on the surface of the solid culture medium. A3. At an initial low-temperature acclimatization temperature of 15℃, the strains selected in A2 are used as low-temperature acclimatization strains. The second generation of low-temperature acclimatization is completed according to the low-temperature acclimatization process in A2. One strain is selected from the second generation of low-temperature acclimatization strains. This process is repeated to complete the third, fourth, and fifth generation of low-temperature acclimatization. After completing at least five generations of low-temperature acclimatization, a stable acclimatized strain at an initial low-temperature acclimatization temperature of 15℃ is obtained. A4. Select one strain from the stable acclimatized strains in A3, inoculate the strain into 200ml of liquid medium II and culture at 20℃ for 12h. Then, lower the culture temperature to 14℃ and continue to culture for 24h to obtain a bacterial suspension. Take 25μl of the bacterial suspension and spread it on the surface of a solid medium and culture at 20℃ for 24h to complete one generation of low-temperature acclimatization at 14℃. After completing at least five generations of low-temperature acclimatization at 14℃, a stable acclimatized strain at 14℃ is obtained. A5. Following this pattern, the low-temperature acclimatization temperature is lowered to 10℃, with each decrease being 1℃. At least five generations of low-temperature acclimatization are continuously completed at the same low-temperature acclimatization temperature until a stable acclimatized strain at 10℃ is obtained, thus completing the low-temperature acclimatization of the bacterial solution.

5. The method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent according to claim 4, characterized in that, During the basic acclimatization and low-temperature acclimatization stages of trehalose, the raw materials for preparing the solid culture medium include, by weight, 12 parts casein peptone, 5 parts soybean peptone, 2 parts sodium chloride, 16 parts urea, and 20 parts agar; it also includes deionized water, wherein the mass-to-volume ratio of the sum of casein peptone, soybean peptone, sodium chloride, urea, and agar to deionized water is 55:1000, with mass units in g and volume units in ml.

6. The method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent according to claim 5, characterized in that, During the basic acclimatization stage of trehalose, the raw materials for preparing the liquid culture medium I include, by weight, 8 parts casein peptone, 2 parts sodium chloride, 8 parts urea, and 5-15 parts trehalose; it also includes deionized water, wherein the mass-to-volume ratio of the sum of casein peptone, sodium chloride, urea, and trehalose to deionized water is 23-33:1000, with mass units in g and volume units in ml.

7. The method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent according to claim 6, characterized in that, During the low-temperature acclimatization stage, the raw materials for preparing the liquid culture medium II include, by weight, 8 parts casein peptone, 2 parts sodium chloride, 8 parts urea, and 5 parts trehalose; it also includes deionized water, wherein the mass-to-volume ratio of the sum of casein peptone, sodium chloride, urea, and trehalose to deionized water is 23:1000, with mass units in g and volume units in ml.

8. The method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent according to claim 7, characterized in that, The particle size of the polystyrene foam is controlled within the range of 2-4 mm; the bacterial solution is a Bacillus pasteurellus bacterial solution with a concentration of 1×10⁻⁶. 8 ~1×10 9 cfu / ml.

9. The method for preparing lightweight foamed sand based on a low-temperature resistant microbial solidifying agent according to claim 8, characterized in that, The cementing solution is prepared by mixing calcium chloride and urea in a certain mass ratio and then fully dissolving them in water. The mass ratio of calcium chloride to urea is 1.6-2:1, and the mass-volume ratio of the sum of calcium chloride and urea to water is 160-180:1000, where the mass unit is g and the volume unit is ml.

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