Novel method for treating foundation through microorganism mineralization

Abstract

The invention provides a novel method for treating a foundation through microorganism mineralization, belongs to the technical field of foundation reinforcement, and solves the problems that an existing technology for treating the foundation through microorganism mineralization is poor in uniformity, poor in economical efficiency and complex in construction process. The preparation method comprises the following steps: firstly, performing a series of treatment such as high-temperature carbonization on lotus roots, and uniformly spraying a mixed solution of starch and urease on the carbonized lotus root blocks; the starch can provide nucleation sites for calcium carbonate formed by urease induced deposition; the carbonized lotus root blocks can immobilize urease, protein molecules of the urease can be prevented from being mechanically damaged in the construction process, uniform distribution of the urease attached to the protein molecules in a foundation is facilitated, and the foundation reinforcement effect is improved.

Description

Technical Field

[0001] The invention relates to a new method for treating foundation by microbial mineralization, belonging to the technical field of foundation reinforcement. Background Art

[0002] Microbially induced calcium carbonate precipitation (MICP) for cementing loose granular materials has been gaining increasing attention and rapid development in recent years as a new, green, and environmentally friendly technology. However, MICP technology also presents some challenges. For example, the introduction of exogenous microorganisms may pose a risk of invasive species. Furthermore, because commonly used microorganisms have a limited size (1–3 μm), this method is generally only suitable for grouting reinforcement of soils with relatively high permeability. In light of this, some researchers have proposed using enzyme-induced calcium carbonate precipitation (EICP) as an alternative to MICP. This technique, which does not require the introduction of microorganisms but directly induces carbonate precipitation with urease, can be derived from bacteria such as Bacillus pasteurianus and Bacillus subtilis, or from common agricultural plants such as potatoes and soybeans. EICP offers the advantages of a wide range of applications and environmental friendliness.

[0003] Grouting and mixing are two common microbial foundation reinforcement technologies, but they each have some disadvantages. Grouting equipment, grouting materials and construction processes are complex, resulting in high costs and long construction periods. In addition, in large-scale construction, the uniformity of urease solution mixed with soil is difficult to control. When the mixing method is used to treat the foundation, microorganisms and Ca in the soil can be mixed in. 2+ The quantity is limited and the foundation reinforcement effect is poor. Therefore, it is necessary to provide a new method for microbial mineralization treatment of foundation to solve the above technical problems.

[0004] Lotus root is a naturally porous material with numerous pores and a large specific surface area. After carbonization and other treatments, it can increase its strength while also loading more urease molecules. Starch, as an admixture, provides the nucleation sites necessary for urease-induced calcium carbonate deposition and facilitates the adsorption of urease molecules onto the lotus root surface. The combination of carbonized lotus root, starch, and urease can effectively achieve uniform reinforcement of large-scale foundations on-site. Summary of the Invention

[0005] (1) Technical issues:

[0006] This invention provides a new method for microbial mineralization of soil foundations. This method uses carbonized lotus root as a carrier to construct an immobilized enzyme with starch and urease. The immobilized enzyme is then used to reinforce the soil foundation, addressing the current problems of poor uniformity, easy loss of enzyme protein molecules, and poor economic efficiency in microbial mineralization of soil foundations.

[0007] (2) Technical solution:

[0008] Given the current lack of cost-effective and effective microbial mineralization methods for treating soil foundations, the present invention provides a novel method for treating soil foundations with microbial mineralization. The present invention is characterized by methods for preparing a urease molecular carrier and adding and using a calcium carbonate nucleation site material. The technical solution is as follows:

[0009] Method 1: Add 1 g of biochar to 50 mL of immobilization medium (10 g of tryptone, 10 g of NaCl, 3 g of beef extract, 5 g of yeast extract, 15 g of agar, and 1000 mL of distilled water, pH = 6.8-7.4). Sterilize in an autoclave at 121°C for 20 min. After activation for 16 h, add a 5% inoculum of a urease and starch mixture. Incubate in a shaker at 130 r / min and 35°C for 18 h, remove the mixture, set the speed to 5000 r / min, centrifuge for 10 min, and discard the supernatant. Wash the lower gelatinous portion with 1% saline, centrifuge at 4000 r / min for 5 min, and repeat the wash three times. The solid obtained by centrifugation is the immobilized bacterial agent.

[0010] Method 2: Weigh 6% polyvinyl alcohol and 2% sodium alginate, and dissolve 2g of biochar in 100mL of deionized water to form an immobilization substrate. Stir evenly to prevent the biochar from sticking to the bottle walls and soak for 5-10 minutes. Weigh 0.5% (mass volume fraction) CaCl2 and dissolve it in a saturated H3BO3 solution to form an adhesive. Stir in an autoclave at 121°C for 20 minutes, remove from the autoclave, and cool to room temperature in a clean bench. Add a mixed solution of urease and starch to the immobilization substrate to a concentration of 10% (mass volume fraction) and stir evenly to form a mixed mucus. Slowly add the mixture to the crosslinker using a peristaltic pump set at 5-7mL / min, shaking the bottle as it drips, to form a spherical immobilized microbial carbon.

[0011] The method for using the immobilized enzyme is characterized in that the immobilized enzyme is evenly mixed into the foundation soil to be reinforced by a one-time mixing method to complete the foundation reinforcement.

[0012] (3) Beneficial effects of the present invention:

[0013] (1) The lotus root used in the present invention is a waste product from agricultural product processing, and the starch is obtained by grinding and separating natural crops. Compared with the carriers such as chitosan and ceramsite used in previous microbial foundation reinforcement methods, these materials are widely available, cheap and easy to obtain, which effectively reduces the construction cost and improves the economy of microbial soil consolidation technology.

[0014] (2) The present invention attaches a mixed solution of urease and starch to lotus root blocks. The lotus root blocks are green and environmentally friendly, do not produce toxic byproducts, and are suitable for use in ecologically sensitive areas. They have abundant pores, a large specific surface area, and a certain strength. They can fully attach the enzyme and starch mixed solution and provide a certain degree of protection for the enzyme molecules to prevent mechanical damage during the foundation treatment process. The urease attached to the lotus root blocks can be simply and efficiently evenly mixed into the foundation to be reinforced, achieving uniform distribution in the soil, with strong controllability, high efficiency, and wide applicability.

[0015] (3) The incorporation of starch not only helps to form a mixed solution with urease, facilitating adsorption on the surface of lotus root pieces, but also serves as a nucleation site in the precipitation process of calcium carbonate, thereby increasing the amount and rate of calcium carbonate deposition. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a cross-section of the carbonized lotus root block after being evenly sprayed with a mixed solution of urease and starch.

[0017] Figure 2 Microscopic mechanism diagram of the combined action of urease, starch and lotus root to produce calcium carbonate

[0018] Figure 3 The unconfined compressive strength diagram of the foundation under different starch dosages in Example 1 (carbonized lotus root dosage 10%) DETAILED DESCRIPTION

[0019] Example 1

[0020] In this example, a method for treating foundation soil by microbial mineralization includes the following steps:

[0021] a. Fresh lotus root was cut into strips of about 1.5cm × 0.5cm × 0.5cm, and the processed lotus root was dried at 700°C for 2h and then subjected to high-temperature carbonization treatment;

[0022] b. Mix a certain amount of starch (0%, 5%, 10%, 15%, 20%) into the treated urease solution;

[0023] c. Apply the mixed solution to the carbonized lotus root using method 1 and let it stand for later use;

[0024] d. Use a machine to plow the silty soil to be treated. During the plowing process, add the carbonized lotus root pieces coated with the mixed solution to the soil. Add 10g of carbonized lotus root pieces to every 100g of silty soil and spray with a 1mol / L calcium chloride solution. Stir thoroughly to mix and level the ground.

[0025] Application and effect: After 7 days, the unconfined compressive strength of the foundation is 1.2MPa.

Claims

1. Use carbonized lotus root as a porous carrier to carry the mixed solution of urease and starch. The carbonized lotus root has many pores, a large specific surface area, and a certain strength. It can carry a large amount of urease and starch mixed solution, which can not only protect the protein molecules of urease from mechanical damage during construction, but also help to evenly distribute the urease attached to it in the foundation, thereby improving the effect of foundation reinforcement. Compared with the grouting method, this method can more easily achieve uniform mixing of urease and foundation soil; compared with the mixing method, this method can continuously provide the urease molecules required for foundation soil solidification, and the reinforcement effect is better.

2. The pretreatment of lotus root is characterized by Fresh lotus root was cut into strips approximately 1.5 cm × 0.5 cm × 0.5 cm, washed, and dried at 80°C for 12 hours to remove moisture. The strips were then sieved and stored in sample bottles. Biochar was then produced by pyrolysis in a muffle furnace at 700°C for 2 hours.

3. Immobilization method of urease: Method 1: Add 1 g of biochar to 50 mL of immobilization medium (10 g of tryptone, 10 g of NaCl, 3 g of beef extract, 5 g of yeast extract powder, 15 g of agar, and 1000 mL of distilled water, pH = 6.8-7.4). Sterilize in an autoclave at 121°C for 20 min. After activation for 16 h, add a 5% inoculum of a mixed solution of urease and starch. Incubate in a shaker at 130 r / min and 35°C for 18 h, remove the mixture, set the speed to 5000 r / min, centrifuge for 10 min, and discard the supernatant. Wash the lower gelatinous portion with 1% saline, centrifuge at 4000 r / min for 5 min, and repeat the wash three times. The solid obtained by centrifugation is the immobilized bacterial agent. Method 2: Weigh 6% polyvinyl alcohol and 2% sodium alginate, and dissolve 2g of biochar in 100mL of deionized water to form an immobilization substrate. Stir evenly to prevent the biochar from sticking to the bottle walls and soak for 5-10 minutes. Weigh 0.5% (mass volume fraction) CaCl2 and dissolve it in a saturated H3BO3 solution to form an adhesive. Stir in an autoclave at 121°C for 20 minutes, remove from the autoclave, and cool to room temperature in a clean bench. Add a mixed solution of urease and starch to the immobilization substrate to a concentration of 10% (mass volume fraction) and stir evenly to form a mixed mucus. Slowly add the mixture to the crosslinker using a peristaltic pump set at 5-7mL / min, shaking the bottle as it drips, to form a spherical immobilized microbial carbon.

4. Starch is selected as a nucleation site for urease-induced calcium carbonate deposition. Starch contains numerous hydroxyl groups (-OH), which can generate electrostatic interactions with active groups in urease, such as carboxyl groups (-COOH). This electrostatic interaction binds the starch molecules to the urease. Starch provides nucleation sites for urease to attach to calcium carbonate precipitation.

5. The concentration of starch is 4-20 g / L, and the amount of lotus root added is 5-40% (mass volume fraction).

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