Multi-element compound microbial agent for solidifying and improving special soil and application thereof

Abstract

The invention is applicable to the technical field of geotechnical engineering and ecological restoration, and provides a multi-element compound microbial agent for special soil solidification and improvement and application thereof, and the multi-element compound microbial agent constructs a difunctional synergistic solidification system composed of functional bacteria A, regulation bacteria B and an organic binding agent. The functional bacteria A are responsible for inducing to generate inorganic mineral deposition so as to enhance a soil body skeleton; the regulating bacterium B regulates and strengthens the mineralization process by secreting extracellular polymeric substances and regulating the microenvironment to form biological cementation; and the two components cooperate to construct a continuous and stable mineralization-cementation composite network in a soil body. The multi-element compound microbial agent can significantly improve the engineering strength and volume stability of special soil such as expansive soil and saline soil, effectively maintain the pore connectivity, water-gas exchange capacity and ecological suitability of soil, and realize the synergism and unification of engineering performance improvement and ecological performance maintenance. The method is suitable for projects such as foundation treatment, slope protection and ecological restoration.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering and ecological restoration technology, and particularly relates to multi-component composite microbial agents for solidification and improvement of special soils and their applications. Background Technology

[0002] Expansive soils, saline soils, and other special soils commonly suffer from problems such as loose structure, low strength, and poor volume stability, which seriously affect engineering safety and ecological sustainability. Traditional chemical solidification methods (such as cement and lime solidification) can improve strength in the short term, but they have drawbacks such as high energy consumption, high alkalinity, damage to the soil's ecological environment, pore closure, and restricted vegetation growth.

[0003] In recent years, microbial induced mineral deposition (MICP) technology has been used for soil improvement. However, existing MIP technologies mostly rely on single-function microorganisms, primarily focusing on strength enhancement, and generally suffer from problems such as uneven mineral deposition distribution, insufficient pore structure stability, and difficulty in simultaneously addressing soil ecological performance (such as permeability, water retention, and biocompatibility). Current technologies have not yet provided a systematic and synergistic solution to achieve structural enhancement and ecological performance maintenance in specific soil types.

[0004] Therefore, developing a special soil solidification technology that can simultaneously meet engineering strength requirements and eco-friendliness is of great practical significance and application value. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-component microbial agent for special soil solidification and improvement and its application, aiming to solve the problems mentioned in the background art.

[0006] The present invention is implemented as follows: a multi-component composite microbial agent for the solidification and improvement of special soils is constructed as a dual-functional microbial synergistic solidification system for special soils, comprising: Functional bacteria A: These are microorganisms with mineral deposition capabilities, capable of inducing the generation of inorganic mineral deposition products in soil pores to construct a load-bearing inorganic framework structure within the soil. Regulatory Bacterium B: To distinguish it from the environmental regulation type microorganism of functional bacterium A, it can secrete extracellular polymers and dynamically regulate the pH and ion balance of the microenvironment during the mineral deposition process, thereby continuously regulating and enhancing the mineral deposition process of functional bacterium A. Organic binder: used to optimize the distribution of functional bacteria A and regulatory bacteria B in the soil and provide a continuous supply of nutrients; The inorganic mineral deposits induced by the functional bacteria A and the extracellular polymers secreted by the regulatory bacteria B together form a continuous and controllable biocementation network, constructing a stable mineralization-cementation composite structure in the soil.

[0007] In a further technical solution, the functional bacteria A is a composite functional bacterial community formed by two urease-producing microorganisms through co-culture, which induces the generation of inorganic mineral deposits mainly composed of calcium carbonate through a urease-mediated microbial mineralization pathway.

[0008] In a further technical solution, the functional bacteria A is formed by co-culturing Bacillus pasteurii and Bacillus megaterium.

[0009] In a further technical solution, the regulating bacteria B is Saccharomyces cerevisiae.

[0010] In a further technical solution, based on the volume ratio of bacterial liquid, the regulating bacteria B accounts for 10% to 30% of the total bacterial liquid volume of functional bacteria A and regulating bacteria B.

[0011] In a further technical solution, the organic binder comprises urea and calcium chloride.

[0012] Another objective of this invention is the application of a multi-component composite microbial agent for the solidification and improvement of special soils, specifically in the solidification and ecological synergistic improvement of expansive soils and saline soils.

[0013] The beneficial effects of the multi-component composite microbial agent for special soil solidification and improvement provided in this invention are as follows: (1) Synergistic effect: Through the synergistic effect of functional bacteria A (mineralization) and regulatory bacteria B (regulation and cementation), a composite solidification mechanism of "mineral deposition to enhance the framework and biological cementation to stabilize the pores" is formed, which significantly improves the solidification efficiency, structural uniformity and stability.

[0014] (2) Eco-friendly: The solidification process does not introduce highly alkaline or polluting chemicals. The formed mineralized-cemented network has porous interconnected characteristics, which can effectively maintain the soil's air permeability, water retention and water-air exchange capacity, creating favorable conditions for plant growth and achieving synergistic improvement of engineering performance and ecological performance.

[0015] (3) Wide applicability: Designed for the characteristics of poor soils such as expansive soil and saline soil, it can effectively suppress their expansion and contraction deformation and improve their strength. It is applicable to multiple engineering fields such as foundation treatment, slope protection, and ecological restoration.

[0016] (4) Long-lasting effect: The organic binder provides continuous nutrients, and the bacterial agent maintains its metabolic activity in the soil for a long time, which is conducive to forming a continuous and stable solidification effect. Attached Figure Description

[0017] Figure 1 SEM images of the mineralized-cemented composite structure of expansive soil after treatment with multi-component microbial agents (where a is the SEM image after treatment with a conventional single microbial agent, and b is the SEM image after treatment with a composite microbial agent). Figure 2 A comparison of calcium carbonate yield and urease activity under different inoculation ratios of bacterial strains; Figure 3 A comparison chart of calcium carbonate production under different compound bacterial systems; Figure 4 Figure 1 shows the soil strength test results after solidification of saline soil using different methods. Figure 5 Figures showing the soil strength test results after solidifying expansive soil using different methods; Figure 6 Figure showing plant growth after improvement of saline soil with a multi-component microbial inoculant. Figure 7 Figure showing plant growth after expansive soil was improved with a multi-component microbial inoculant. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0020] Example 1: Preparation of multi-component compound microbial inoculant and synergistic mineralization test of compound bacteria (standard example) The aim is to illustrate the specific preparation method of multi-component microbial agents and to verify the synergistic mineralization effect of the composite microbial system composed of functional bacteria A and regulatory bacteria B in the mineral deposition process.

[0021] (1) Cultivation of functional bacteria A; A highly efficient urease-producing functional bacterium, A, constructed through co-culture, was selected as the mineral deposition microorganism. This functional bacterium A was formed by the synergistic co-culture of Bacillus pasteurii and Bacillus megaterium under specific culture conditions. The resulting co-cultured bacterial community maintained stable growth characteristics while exhibiting higher urease activity and mineralization efficiency than the single strain.

[0022] Specifically, *Bacillus pasteurellii* and *Bacillus megaterium* were activated separately and co-inoculated into liquid LB medium at a predetermined ratio (5:5). Co-culture was carried out under constant temperature and shaking conditions (30 °C and 120 r / min for 72 hours) to allow the two strains to undergo metabolic synergy in the same culture system, forming functional bacterium A with synergistic urease-producing ability. During the mineralization reaction, the co-cultured functional bacterium A can more efficiently decompose urea and continuously provide carbonate ions, thereby inducing the formation of inorganic mineral deposits in the soil pores to construct a stable inorganic framework structure.

[0023] The test results show (e.g.) Figure 2 As shown in the figure, compared with a single strain system using only Bacillus pasteurellii or Bacillus megaterium, functional strain A formed by co-culturing the two showed higher urease activity and mineral deposition efficiency under the same conditions, providing a more favorable microbial basis for the stable formation of subsequent mineralization-cementation complex structures.

[0024] (2) Regulating the culture of bacteria B; Microorganisms with environmental regulation capabilities and the ability to secrete extracellular polymers were selected as regulatory bacteria B, specifically *Saccharomyces cerevisiae* (ATCC 9763). It was inoculated into SRB medium and cultured under suitable temperature conditions until the stable growth phase (48 hours at 26℃ and 120 r / min).

[0025] (3) Preparation of multi-component compound microbial inoculants; The above-cultured functional bacteria A solution and regulatory bacteria B solution were mixed at a predetermined volume ratio to form a composite bacterial system; an organic binder (1:1 urea:calcium chloride, 0.7 mol·L⁻¹) was added to the system as needed. -1 To optimize the distribution of the microbial community in the system and maintain its metabolic activity, a multi-component microbial agent was prepared.

[0026] (4) Synergistic mineralization test of compound bacteria; A multi-component microbial inoculant was added to a mineralization reaction system containing urea and a calcium source, and the mineralization reaction was carried out under constant environmental conditions (10 mL of bacterial solution was mixed with 30 mL of cementing solution (containing urea and calcium source) and placed in a 50 mL centrifuge tube, and reacted in a constant temperature incubator at 30 ℃ for 48 h). As a control, a single mineralization system containing only functional bacteria A was set up. After the reaction, the inorganic mineral deposits generated in different systems were collected and characterized.

[0027] SEM images of the formed mineralized-cemented composite structure are shown below. Figure 1 a and Figure 1As shown in b. The results indicate (as shown in Figure 2). Figure 3 As shown in the figure, compared with the single-functional bacterial mineralization system, the mineral deposition process under the composite bacterial system is more stable, and the amount of mineral deposition and the uniformity of deposition distribution are improved, which verifies the synergistic effect of functional bacteria A and regulatory bacteria B in the mineralization process.

[0028] Subsequent examples use saline soil and expansive soil as representatives of special soils to illustrate how the optimal ratio (7:3) of bacteria A and bacteria B obtained through the standard examples is used to improve their engineering performance and ecological conditions.

[0029] Example 2: Strength test of solidified saline soil by multi-component composite microbial agent; This embodiment aims to illustrate the effect of the multi-component composite microbial agent prepared in Example 1 on improving the engineering strength of saline soil.

[0030] Typical saline soil samples were selected, air-dried, crushed, and sieved before use. The saline soil was divided into an experimental group and a control group. The experimental group was treated with the multi-component composite microbial agent prepared in Example 1 and mixed thoroughly to ensure uniform distribution of the agent in the soil. The control groups were respectively treated with no agent added and with a single mineralization system containing only functional bacteria A.

[0031] The treated soil samples were cured under controlled conditions, and after curing, engineering strength tests were conducted on each group of soil samples. The results showed (e.g.) Figure 4 As shown in the figure, the saline soil treated with multi-component microbial agents has a denser soil structure and significantly improved overall engineering strength, indicating that the agents can effectively improve the engineering performance of saline soil.

[0032] Example 3: Strength test of expansive soil solidified by multi-component composite microbial inoculant; This embodiment aims to illustrate the solidification effect of the multi-component composite microbial agent prepared in Example 1 on expansive soil.

[0033] Expansive soil samples with moderate expansion potential were selected and pretreated before being grouped. The experimental group was treated with a multi-component compound microbial agent and thoroughly mixed, while the control group consisted of a single mineralization system without the agent and with only functional bacteria A.

[0034] The treated expansive soil samples were cured under suitable conditions, and after curing, their strength and stability were tested. The results showed (e.g.) Figure 5 As shown in the figure, compared with the control group, the expansive soil treated with multi-component microbial agents showed significantly improved structural stability and effectively suppressed volume change trends.

[0035] Example 4: Plant growth experiment after improvement of saline soil with multi-component compound microbial inoculant; This embodiment is used to verify the effect of the multi-component composite microbial agent prepared in Example 1 on the ecological performance of saline soil while improving the engineering performance of the soil.

[0036] Saline soil treated with a multi-component microbial agent was used as the test soil sample, while saline soil treated with a single mineralization system containing functional bacteria A was used as the control soil sample. Plants were sown and maintained under the same conditions.

[0037] By analyzing plant germination, growth status, and survival rate (e.g.) Figure 6 As shown in the figure, observations revealed that plants in saline soil improved by the multi-component microbial agent grew well, indicating that the agent can maintain good ecological suitability while improving the engineering performance of the soil.

[0038] Example 5: Plant growth experiment after improving expansive soil with multi-component microbial inoculant; This embodiment further verifies the effect of the multi-component composite microbial agent prepared in Example 1 on achieving synergistic improvement of engineering performance and ecological performance in expansive soil.

[0039] Expansive soil treated with multi-component microbial agents was used as the test soil sample, while expansive soil treated with a single mineralization system containing functional bacteria A was set up as the control. Plants were sown and maintained under the same environmental conditions.

[0040] The results show (e.g.) Figure 7 As shown in the figure, the plant roots in the expansive soil improved by the multi-component microbial agent were well developed and the overall growth status was stable, indicating that the agent did not have an adverse impact on the ecological function of the soil while inhibiting the unfavorable engineering characteristics of the expansive soil.

[0041] Example 6: Verification of Overall Effect; This embodiment verifies the comprehensive application effect of multi-component microbial agents in different special soils by comprehensively comparing the engineering strength test results in Embodiments 2 and 3 with the plant growth in Embodiments 4 and 5.

[0042] Comprehensive analysis results show that the multi-component composite microbial agent can simultaneously achieve structural enhancement and ecological performance maintenance in saline soil and expansive soil, verifying its comprehensive applicability in the field of special soil solidification and ecological restoration.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-component composite microbial agent for solidification and improvement of special soils, characterized in that, include: Functional bacteria A: These are microorganisms with mineral deposition capabilities, capable of inducing the generation of inorganic mineral deposition products in soil pores to construct a load-bearing inorganic framework structure within the soil. Regulatory Bacterium B: To distinguish it from the environmental regulation type microorganism of functional bacterium A, it can secrete extracellular polymers and dynamically regulate the pH and ion balance of the microenvironment during the mineral deposition process, thereby continuously regulating and enhancing the mineral deposition process of functional bacterium A. Organic binder: used to optimize the distribution of functional bacteria A and regulatory bacteria B in the soil and provide a continuous supply of nutrients; The inorganic mineral deposits induced by the functional bacteria A and the extracellular polymers secreted by the regulatory bacteria B together form a continuous and controllable biocementation network, constructing a stable mineralization-cementation composite structure in the soil.

2. The multi-component composite microbial agent for special soil solidification and improvement according to claim 1, characterized in that, The functional bacteria A is a complex functional bacterial community formed by two urease-producing microorganisms through co-culture. It induces the generation of inorganic mineral deposits, mainly calcium carbonate, through a urease-mediated microbial mineralization pathway.

3. The multi-component composite microbial agent for special soil solidification and improvement according to claim 2, characterized in that, The functional bacteria A is formed by co-culturing Bacillus pasteurellii and Bacillus megaterium.

4. The multi-component composite microbial agent for special soil solidification and improvement according to claim 1, characterized in that, The regulating bacteria B is Saccharomyces cerevisiae.

5. The multi-component composite microbial agent for special soil solidification and improvement according to claim 1, characterized in that, Based on the volume ratio of bacterial culture, the regulatory bacteria B accounts for 10% to 30% of the total bacterial culture volume of functional bacteria A and regulatory bacteria B.

6. The multi-component composite microbial agent for special soil solidification and improvement according to claim 1 and its application, characterized in that, The organic binder comprises urea and calcium chloride.

7. Application of a multi-component composite microbial agent for special soil solidification and improvement, based on the multi-component composite microbial agent for special soil solidification and improvement according to any one of claims 1-6, characterized in that, The aforementioned multi-component microbial agent was applied to the solidification and ecological synergistic improvement of expansive soil and saline soil.

Images