A chromium-contaminated soil remediation agent based on plant-microbe rhizosphere interaction mechanism, its preparation method and application

Abstract

This invention relates to the field of soil remediation, and discloses a chromium-contaminated soil remediation agent based on plant-microbe rhizosphere interaction mechanisms, its preparation method, and its application. The chromium-contaminated soil remediation agent comprises biochar and Arthrobacter alginate supported on the biochar. Arthrobacter The invention relates to a plant root exudate mimicry solution, which includes low-molecular-weight organic acids, amino acids, and soluble sugars with a molecular weight less than 500 Da. The chromium-contaminated soil remediation agent of this invention uses biochar as a carrier and is loaded with Arthroblastus alginate. Arthrobacter The plant root exudate mimicry solution has advantages such as the remediation cycle not being limited by plant growth and strong soil adaptability. Furthermore, the plant root exudate mimicry solution and hexavalent chromium-reducing bacteria in this invention are highly coupled, and the combination of the two can produce a significant synergistic effect, which can significantly improve the remediation effect on hexavalent chromium-contaminated soil.

Description

Technical Field

[0001] This invention relates to the field of soil remediation, and in particular to a chromium-contaminated soil remediation agent based on the plant-microbe rhizosphere interaction mechanism, its preparation method, and its application. Background Technology

[0002] Chromium, a heavy metal, is an important raw material for industries such as alloy materials, leather, dyes, electroplating, printing and dyeing, pharmaceuticals, and catalysis. In my country, approximately 750,000 to 900,000 tons of chromium-containing waste are generated annually. Due to the long-term accumulation of chromium slag in some chemical plants without proper disposal, chromium pollution has migrated and expanded its scope. According to relevant reports, chromium emissions account for 95% of the total industrial heavy metal emissions in Zhejiang Province. The 2014 National Soil Pollution Survey Bulletin released by the Ministry of Environmental Protection showed that 1.1% of soil nationwide exceeded chromium standards. Chromium in soil exists mainly in two forms: hexavalent and trivalent. Trivalent chromium has low mobility and low bioavailability in soil, while hexavalent chromium has high mobility and high bioavailability. Furthermore, hexavalent chromium is approximately 100 times more toxic to humans than trivalent chromium. Promoting the conversion of hexavalent chromium to trivalent chromium in paddy field soil is an important way to reduce soil chromium toxicity and crop absorption. Therefore, developing environmentally friendly, sustainable, low-cost, and high-performance chromium pollution remediation technologies for areas or sites severely contaminated with hexavalent chromium is of great significance.

[0003] Bioremediation, including microbial and phytoremediation technologies, is an eco-friendly approach to addressing hexavalent chromium (CHP) pollution. Some microorganisms thrive in chromium-contaminated soils, tolerating high concentrations of CHP. Some of these microorganisms can reduce highly toxic CHP to less toxic trivalent CHP; these are known as chromium-reducing bacteria. Currently reported CHP species include *Pseudomonas*, *Microbacterium*, *Desulfovibrio*, *Enterobacter*, and *Bacillus*. *Leersia hexandra* Swartz is the first wetland chromium hyperaccumulator discovered in China. It can convert highly toxic Cr(VI) to less toxic Cr(III) and accumulate it in its stems and leaves, making it a high-quality plant material for remediating chromium-contaminated soils. However, the mechanism by which *Leersia hexandra* remediates CHP in soils is complex and not yet fully understood. It involves both phytophysiological mechanisms and the role of root exudates. The phytophysiological mechanism is mainly reflected in the hyperaccumulation of CHP, while the role of root exudates is mainly in promoting the reduction of CHP. Current phytoremediation methods primarily involve planting Rhizophora in the soil. However, this method has drawbacks such as being limited by the plant's growth cycle and having a limited range of rhizosphere effects.

[0004] Currently, the commonly used remediation techniques are the aforementioned single technologies, such as phytoremediation or microbial remediation alone. To address the shortcomings of these single remediation techniques, the applicant proposed a plant-microbe co-remediation technology. This technology utilizes the symbiotic relationship between plants, soil, and microorganisms, fully leveraging the respective advantages of microorganisms and plants to compensate for deficiencies, ultimately achieving the goal of remediating heavy metal pollution in soil. In our preliminary research, the study of plant-microbe co-remediation of hexavalent chromium contaminated soil mainly focused on the co-remediation of plants and hexavalent chromium-reducing bacteria. Co-remediation can accelerate the reduction of hexavalent chromium in soil, primarily through the enhancing effect of plant root exudates on chromium-reducing bacteria. Plant root exudates provide nutrients for chromium-reducing microorganisms, promoting their reduction of hexavalent chromium and achieving a rapid reduction in its bioavailability and toxicity.

[0005] However, the main limitation of plant-microbe co-remediation technology is the failure to effectively couple and optimize chromium-reducing bacteria with plant root exudates. This is mainly reflected in two aspects: firstly, the growth of chromium-reducing bacteria is easily affected by soil environmental factors, and their survival time is uncontrollable, thus affecting the remediation effect; secondly, the amount of plant root exudates is still limited by the plant growth cycle and the scope of rhizosphere effects. Therefore, how to further innovate and optimize plant-microbe co-remediation technology for hexavalent chromium-contaminated soil and broaden its adaptability is of great significance for the remediation of hexavalent chromium-contaminated soil. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a chromium-contaminated soil remediation agent based on plant-microbe rhizosphere interaction mechanisms, its preparation method, and its applications. This chromium-contaminated soil remediation agent uses biochar as a carrier and is loaded with *Arthrobacter aegypti* and a plant root exudate mimicry solution. It has advantages such as the remediation cycle not being limited by plant growth and strong soil adaptability, showing broad application prospects. Furthermore, in this invention, the plant root exudate mimicry solution and hexavalent chromium-reducing bacteria are highly coupled; their combination produces a significant synergistic effect, significantly improving the remediation effect on hexavalent chromium-contaminated soil.

[0007] The specific technical solution of this invention is as follows:

[0008] In a first aspect, the present invention provides a chromium-contaminated soil remediation agent based on the plant-microbe rhizosphere interaction mechanism, comprising biochar as a carrier, and Arthrobacter abacterium loaded on the biochar and a plant root exudate mimicry solution. The plant root exudate mimicry solution comprises low-molecular-weight organic acids, amino acids, and soluble sugars with a molecular weight less than 500 Da.

[0009] This invention's chromium-contaminated soil remediation agent simultaneously contains *Arthrobacter axolotl* and a plant root exudate mimicry solution. Through preliminary screening and testing by the invention team, *Arthrobacter axolotl* was discovered for the first time to possess both extremely strong chromium tolerance and excellent hexavalent chromium reduction capacity. The plant root exudate mimicry solution contains low-molecular-weight organic acids, amino acids, and soluble sugars. These components are typical components screened from the root exudates of the chromium hyperaccumulating plant *Rhizophora leuciscus*, targeting *Arthrobacter axolotl*, and are capable of promoting the reduction of hexavalent chromium by *Arthrobacter axolotl*. Based on this, this invention loads *Arthrobacter axolotl* and the plant root exudate mimicry solution onto biochar, overcoming the problems of conventional plant-microbe co-remediation technologies, such as the susceptibility of microbial growth to soil environmental factors, the limitation of plant root exudate secretion by the plant growth cycle, and the limited range of rhizosphere effects. The remediation cycle of this chromium-contaminated soil remediation agent is not limited by plant growth, exhibits strong soil adaptability, and has broad application prospects. Furthermore, the plant root exudate simulation solution and hexavalent chromium reducing bacteria in this invention are highly coupled, and the combination of the two can produce a significant synergistic effect. At the same time, using biochar as a carrier can significantly improve the remediation effect on hexavalent chromium contaminated soil.

[0010] Preferably, in the simulated plant root exudate solution: the low molecular weight organic acid is a mixture of citric acid, oxalic acid, lactic acid, succinic acid and malic acid; the concentration ratio of citric acid, oxalic acid, lactic acid, succinic acid and malic acid is (2.5-3.5):(1.5-2.5):(1.5-2.5):(0.8-1.2):1; the amino acid is a mixture of glutamic acid, arginine and serine; the concentration ratio of glutamic acid, arginine and serine is 1:(0.8-1.2):(0.8-1.2); the soluble sugar is a mixture of glucose and fructose; the concentration ratio of glucose and fructose is 1:(0.8-1.2).

[0011] Although *Leymus chinensis* is a known chromium hyperaccumulator, its specific mechanism of action is complex, especially since current literature reports on the composition of its root exudates are incomplete, only showing organic acid components, with no reports on other components such as amino acids and soluble sugars and their functions. After preliminary analysis and screening of the root exudates of *Leymus chinensis*, the team selected the specific types and proportions of low-molecular-weight organic acids, amino acids, and soluble sugars mentioned above. This invention uses these three components—low-molecular-weight organic acids, amino acids, and soluble sugars—in the aforementioned proportions to construct a plant root exudate mimicry solution, which can synergistically interact with *Arthrobacter*, a bacterium capable of reducing hexavalent chromium. In this invention, the plant root exudate mimicry solution plays two main roles: firstly, it provides a carbon source for microbial growth, promoting the growth of chromium-reducing bacteria; secondly, and more importantly, it provides electron donors for the chromium-reducing bacteria to reduce hexavalent chromium, thereby significantly enhancing the chromium reduction effect.

[0012] Preferably, the concentration of low-molecular-weight organic acids in the simulated plant root exudate solution is 40–60 mg / L, the concentration of amino acids is 70–80 mg / L, and the concentration of soluble sugars is 30–50 mg / L.

[0013] The above concentrations were determined after measuring the components of root exudates from the chromium hyperaccumulator plant, Rhizophora oryzae.

[0014] Secondly, the present invention provides a method for preparing a chromium-contaminated soil remediation agent, comprising the following steps:

[0015] (1) Arthrobacter was fermented and cultured to obtain fermentation broth.

[0016] (2) Mix the fermentation liquid with the plant root secretion simulation liquid to obtain a mixed solution.

[0017] (3) Biochar was added to the mixed solution for mixed adsorption and fixation. After filtration, a chromium-contaminated soil remediation agent was obtained.

[0018] Preferably, in step (1), the fermentation culture step includes: inoculating Arthrobacter onto LB agar plates and activating and culturing at 28-32℃ for 2-4 days; then picking microbial colonies and inoculating them into LB liquid medium, and fermenting and culturing at 28-32℃ on a shaker at 150-200 rpm for 2-4 days to obtain a bacterial concentration of 10. 8 Fermentation broth with CFU / mL.

[0019] Preferably, in step (2), the volume ratio of the fermentation liquid to the plant root exudate simulation liquid is 1:(1.5-2.5).

[0020] Preferably, in step (3), the biochar is obtained by pyrolysis of rice straw at 450-550℃.

[0021] Preferably, in step (3), the mass-to-volume ratio of the mixed solution to biochar is 1 g: (8-12) mL.

[0022] Preferably, in step (3), the adsorption fixation is performed by oscillation adsorption at 25-35℃ and 100-200rpm for 15-25h.

[0023] Thirdly, the present invention provides the application of the above-mentioned chromium-contaminated soil remediation agent in the remediation of hexavalent chromium-contaminated soil, including the following steps: applying the chromium-contaminated soil remediation agent to the hexavalent chromium-contaminated soil, thoroughly tilling the soil to mix the chromium-contaminated soil remediation agent evenly with the soil, maintaining the soil moisture content at 30-50%, remediating for 50-70 days, detecting the hexavalent chromium content in the soil, stopping the remediation if the remediation target is reached, and adding a second round of soil remediation agent to continue the remediation until the remediation target is reached.

[0024] Preferably, for hexavalent chromium contaminated soil with a hexavalent chromium content of 0–50 mg / kg, a chromium-contaminated soil remediation agent is applied at 0.5% of the soil weight; for hexavalent chromium contaminated soil with a hexavalent chromium content of 50–100 mg / kg, a chromium-contaminated soil remediation agent is applied at 1.0% of the soil weight; for hexavalent chromium contaminated soil with a hexavalent chromium content of 100–200 mg / kg, a chromium-contaminated soil remediation agent is applied at 1.5% of the soil weight; and for hexavalent chromium contaminated soil with a hexavalent chromium content higher than 200 mg / kg, a chromium-contaminated soil remediation agent is applied at 2.0% of the soil weight.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] (1) The chromium-contaminated soil remediation agent of this invention uses biochar as a carrier and is loaded with Arthrobacter and plant root exudate mimicry solution. It has the advantages of the remediation cycle not being limited by plant growth and strong soil adaptability. Furthermore, in this invention, the plant root exudate mimicry solution and hexavalent chromium-reducing bacteria are highly coupled, and the combination of the two can produce a significant synergistic effect, which can significantly improve the remediation effect on hexavalent chromium-contaminated soil. Compared with the single microbial remediation method, the hexavalent chromium reduction rate can be increased by 50-80%.

[0027] (2) The root exudate solution formulation that promotes the reduction of hexavalent chromium by target microorganisms obtained by the present invention is clearly defined and commercially available. The present invention uses rice straw as a precursor to prepare biochar carrier, which is easily obtained in large quantities and simultaneously realizes the resource utilization of agricultural waste. The soil remediation agent of the present invention is low in cost, has good remediation effect, and has significant economic and social benefits. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments.

[0029] General Implementation Examples

[0030] A chromium-contaminated soil remediation agent based on plant-microbe rhizosphere interaction mechanism includes biochar as a carrier, and Arthrobacter and plant root exudate mimicry solution loaded in the biochar.

[0031] The simulated plant root exudate solution includes low-molecular-weight organic acids with a molecular weight less than 500 Da at a concentration of 40–60 mg / L, amino acids at a concentration of 70–80 mg / L, and soluble sugars at a concentration of 30–50 mg / L. Further, the low-molecular-weight organic acids are a mixture of citric acid, oxalic acid, lactic acid, succinic acid, and malic acid; the concentration ratio of citric acid, oxalic acid, lactic acid, succinic acid, and malic acid is (2.5–3.5):(1.5–2.5):(1.5–2.5):(0.8–1.2):1; the amino acids are a mixture of glutamic acid, arginine, and serine; the concentration ratio of glutamic acid, arginine, and serine is 1:(0.8–1.2):(0.8–1.2); and the soluble sugars are a mixture of glucose and fructose; the concentration ratio of glucose and fructose is 1:(0.8–1.2).

[0032] A method for preparing a chromium-contaminated soil remediation agent includes the following steps:

[0033] (1) Arthrobacter was inoculated onto LB agar plates and activated at 28-32℃ for 2-4 days; then, microbial colonies were picked and inoculated into LB liquid medium and fermented on a shaker at 150-200 rpm at 28-32℃ for 2-4 days to obtain a bacterial concentration of 10. 8 Fermentation broth with CFU / mL.

[0034] (2) Mix the fermentation liquid with the simulated plant root exudate liquid at a volume ratio of 1:(1.5-2.5) to obtain a mixed solution.

[0035] (3) Add biochar (obtained by pyrolysis of rice straw at 450-550℃) to the mixed solution at a mass-volume ratio of 1g:(8-12)mL and mix. Shake and adsorb at 25-35℃ and 100-200rpm for 15-25h. After filtration, chromium-contaminated soil remediation agent is obtained.

[0036] A method for remediating hexavalent chromium-contaminated soil includes the following steps: applying a chromium-contaminated soil remediation agent to the hexavalent chromium-contaminated soil, thoroughly tilling the soil to ensure the chromium-contaminated soil remediation agent is evenly mixed with the soil, maintaining the soil moisture content at 30-50%, remediating for 50-70 days, testing the hexavalent chromium content in the soil, stopping the remediation if the remediation target is reached, and adding a second round of soil remediation agent to continue the remediation until the remediation target is reached.

[0037] Specifically, for hexavalent chromium-contaminated soil with a hexavalent chromium content of 0–50 mg / kg, a chromium-contaminated soil remediation agent is applied at 0.5% of the soil weight; for hexavalent chromium-contaminated soil with a hexavalent chromium content of 50–100 mg / kg, a chromium-contaminated soil remediation agent is applied at 1.0% of the soil weight; for hexavalent chromium-contaminated soil with a hexavalent chromium content of 100–200 mg / kg, a chromium-contaminated soil remediation agent is applied at 1.5% of the soil weight; and for hexavalent chromium-contaminated soil with a hexavalent chromium content higher than 200 mg / kg, a chromium-contaminated soil remediation agent is applied at 2.0% of the soil weight.

[0038] Example 1

[0039] (1) Isolation, screening and fermentation culture of chromium-reducing bacteria

[0040] Chromium-reducing bacteria were isolated using the dilution plate spread method. 20 g of hexavalent chromium-contaminated soil sample was accurately weighed and transferred to a conical flask containing 250 mL of sterile water. The sample was homogenized by shaking at 180 rpm for 30 min at room temperature. LB solid medium was prepared, consisting of: 10 g / L peptone, 5 g / L yeast extract, 10 g / L NaCl, 15 g / L agar, pH = 7, and 250 mg / L Cr(VI). The medium was autoclaved at 121 °C for 40 min. The homogenized soil sample was then serially diluted and spread onto LB agar plates. The LB solid medium was incubated at 30 °C for 3 days. After 3 days, five isolates of hexavalent chromium-resistant bacteria with different coloring and morphological parameters were selected and cultured in 100 mL of LB liquid medium. The LB liquid medium consisted of: 10 g / L peptone, 5 g / L yeast extract, 10 g / L NaCl, pH 7, and 250 mg / L Cr(VI). After 7 days, the hexavalent chromium content in the medium was measured to screen for strains with optimal hexavalent chromium reducing ability (JZ1, i.e., Arthrobacter).

[0041] Table 1. Hexavalent chromium reduction rate of five different bacterial strains

[0042]

[0043] The strain with the best hexavalent chromium reducing ability was screened and inoculated onto LB agar plates and activated at 30°C for 3 days. Then, microbial colonies were picked from the LB agar plates and inoculated into LB liquid medium, and fermented on a shaker at 180 rpm at 30°C for 3 days to obtain a strain concentration of 10. 8 Fermentation broth of hexavalent chromium-reducing bacteria (CFU / mL).

[0044] (2) Determination of root exudate components in Rhes oryzae, a chromium hyperaccumulating plant

[0045] Root exudates from the chromium hyperaccumulator *Leymus chinensis* were collected through hydroponic experiments. After concentration, the components and contents of typical small-molecule organic acids, amino acids, and soluble sugars were determined. Ion chromatography was used to analyze the small-molecule organic acids in the *Leymus chinensis* root exudates. Citric acid, oxalic acid, lactic acid, succinic acid, and malic acid were detected. Among the five detected acids, citric acid had the highest concentration at 18.8 mg / L, while the contents of oxalic acid, lactic acid, succinic acid, and malic acid were 12.2 mg / L, 11.8 mg / L, 6.3 mg / L, and 6.1 mg / L, respectively.

[0046] The amino acid composition of root exudates from *Rhizophora stylosa* was analyzed using an aminophenol analyzer. Ten amino acids were detected: glutamic acid, arginine, serine, threonine, glycine, alanine, valine, tyrosine, lysine, and histidine. Glutamic acid, arginine, and serine had relatively high concentrations, at 25.6 mg / L, 22.5 mg / L, and 23.2 mg / L, respectively, accounting for 92% of the total amino acid composition.

[0047] Soluble sugars in the root exudates of Rhizophora leuciscus were analyzed using the anthrone method. The concentration of soluble sugars was 42 mg / L, mainly glucose and fructose.

[0048] (3) Preparation of plant root exudate simulation solution

[0049] Based on the results of root exudate analysis of the chromium hyperaccumulating plant *Rhizophora leuciscus*, three components—sugars, small-molecule acids, and amino acids—were selected to construct a simulated root exudate solution, aiming to obtain a simulated root exudate formulation that can synergistically interact with hexavalent chromium-reducing bacteria. The small-molecule organic acid components were citric acid, oxalic acid, lactic acid, succinic acid, and malic acid, with concentrations of 18.0 mg / L, 12.0 mg / L, 12.0 mg / L, 6.0 mg / L, and 6.0 mg / L, respectively; the amino acid components were glutamic acid, arginine, and serine, with concentrations of 25.0 mg / L, 25.0 mg / L, and 25.0 mg / L, respectively; and the sugar components were glucose and fructose, with concentrations of 20.0 mg / L and 20.0 mg / L, respectively.

[0050] (4) Biochar preparation

[0051] Rice straw was air-dried, crushed, and ground, then passed through a 2mm sieve to obtain straw powder. The straw powder was packed into a crucible, covered, and placed in a muffle furnace. The temperature was increased to 500℃ at a rate of 4℃ / min, maintained for 2 hours, and then allowed to cool naturally before being removed. The powder was then crushed and passed through a 60-mesh sieve to obtain biochar.

[0052] (5) Preparation of hexavalent chromium contaminated soil remediation agent

[0053] The fermentation broth of hexavalent chromium-reducing bacteria and the simulated root exudate solution were mixed at a volume ratio of 1:2 to obtain a mixed solution. Then, biochar was added to the mixed solution at a mass-volume ratio of 1:10 (g / mL). The mixture was shaken and adsorbed at a constant temperature of 30℃ and 150 rpm for 20 h. After filtration, a hexavalent chromium-contaminated soil remediation agent was obtained.

[0054] (6) Application and efficacy evaluation of hexavalent chromium contaminated soil remediation agents

[0055] Heavy metal-contaminated soil was collected from a contaminated site at an electroplating factory in Hangzhou for an indoor potted plant experiment. The total chromium content in the soil was 254.1 mg / kg, and the hexavalent chromium content was 72.6 mg / kg. One kg of chromium-contaminated soil was used for each pot, and deionized water was added to maintain the soil moisture at approximately 60% of its saturated water holding capacity. Seven experimental groups were set up: a blank control group (CK), a chromium-reducing bacteria group (JZ), a plant root exudate simulated solution group (RE), a chromium-reducing bacteria and plant root exudate simulated solution group (JZ+RE), a carbon-based soil remediation agent loaded with chromium-reducing bacteria (JZ+BC), a carbon-based soil remediation agent loaded with plant root exudate simulated solution (RE+BC), and a carbon-based soil remediation agent loaded with chromium-reducing bacteria and plant root exudate simulated solution (JZ+RE+BC). The CK group received no remediation agent. The other groups received 1% (by weight) of the following soil components: chromium-reducing bacteria fermentation broth (Arthrobacter), plant root exudate simulated solution, chromium-reducing bacteria and plant root exudate simulated solution, carbon-based soil remediation agent loaded with chromium-reducing bacteria, carbon-based soil remediation agent loaded with plant root exudate simulated solution, and carbon-based soil remediation agent loaded with chromium-reducing bacteria and plant root exudate simulated solution. The soil samples were placed under room temperature and natural light conditions for 60 days, and the changes in hexavalent chromium content were measured after 60 days.

[0056] Comparative analysis revealed that the hexavalent chromium content in the contaminated soil decreased in all experimental groups after the addition of the remediation agent. The group with the carbon-based soil remediation agent (JZ+RE+BC) loaded with chromium-reducing bacteria and simulated plant root exudates showed the largest decrease in hexavalent chromium content, reaching 91.5%. Therefore, the carbon-based soil remediation agent prepared by immobilizing hexavalent chromium-reducing bacteria and simulated plant root exudates on a biochar carrier exhibits significant remediation and transformation effects on soil contaminated with hexavalent chromium. Specific results from the embodiments are shown in Table 2.

[0057] Table 2. Changes in hexavalent chromium content and reduction rate in soil of different treatment groups in Example 1.

[0058]

[0059]

[0060] Example 2

[0061] The difference from Example 1 is that the total chromium content in the contaminated soil was 374.3 mg / kg and the hexavalent chromium content was 156.9 mg / kg. Each experimental group was supplemented with 1.5% of the soil weight of chromium-reducing bacteria fermentation broth, plant root exudate simulation broth, chromium-reducing bacteria and plant root exudate simulation broth, carbon-based soil remediation agent loaded with chromium-reducing bacteria, carbon-based soil remediation agent loaded with plant root exudate, and carbon-based soil remediation agent loaded with chromium-reducing bacteria and plant root exudate simulation broth.

[0062] Comparative analysis revealed that the hexavalent chromium content in the contaminated soil decreased in all experimental groups after the addition of the remediation agent. The group with the carbon-based soil remediation agent (JZ+RE+BC) loaded with chromium-reducing bacteria and simulated plant root exudates showed the largest decrease in hexavalent chromium content, reaching 90.3%. Therefore, the carbon-based soil remediation agent prepared by immobilizing hexavalent chromium-reducing bacteria and simulated plant root exudates on a biochar carrier exhibits significant remediation and transformation effects on soil contaminated with hexavalent chromium. Specific results from the embodiments are shown in Table 3.

[0063] Table 3. Changes in hexavalent chromium content and reduction rate in soil of different treatment groups in Example 2.

[0064] <![CDATA[Final concentration of hexavalent chromium (mg kg -1 )]]> Hexavalent chromium removal rate (%) CK 63.2 59.7 JZ 36.3 76.9 RE 43.2 72.5 JZ+RE 25.6 83.7 JZ+BC 32.5 79.3 RE+BC 38.6 75.4 JZ+RE+BC 15.2 90.3

[0065] Example 3

[0066] The differences from Examples 1 and 2 are as follows: the total chromium content in the contaminated soil is 456.2 mg / kg, and the hexavalent chromium content is 212.5 mg / kg; each experimental group was supplemented with 2.0% of the soil weight of chromium-reducing bacteria fermentation broth, plant root exudate simulation broth, chromium-reducing bacteria and plant root exudate simulation broth, carbon-based soil remediation agent loaded with chromium-reducing bacteria, carbon-based soil remediation agent loaded with plant root exudate simulation broth, and carbon-based soil remediation agent loaded with chromium-reducing bacteria and plant root exudate simulation broth.

[0067] Comparative analysis revealed that the hexavalent chromium content in the contaminated soil decreased in all experimental groups after the addition of the remediation agent. The group with the carbon-based soil remediation agent (JZ+RE+BC) loaded with chromium-reducing bacteria and simulated plant root exudates showed the largest decrease in hexavalent chromium content, reaching 88.9%. Therefore, the carbon-based soil remediation agent prepared by immobilizing hexavalent chromium-reducing bacteria and simulated plant root exudates on a biochar carrier exhibits significant remediation and transformation effects on soil contaminated with hexavalent chromium. Specific results from the embodiments are shown in Table 3.

[0068] Table 3. Changes in hexavalent chromium content and reduction rate in soil of different treatment groups in Example 2.

[0069] <![CDATA[Final concentration of hexavalent chromium (mg / kg -1 )]]> Hexavalent chromium removal rate (%) CK 88.6 58.3 JZ 67.8 68.1 RE 73.2 65.6 JZ+RE 48.7 77.1 JZ+BC 52.6 75.2 RE+BC 56.2 73.6 JZ+RE+BC 23.5 88.9

[0070] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for enhancing the chromium remediation effect of soil remediation agents by utilizing plant root exudate mimicry solution, characterized in that... include: 1) Arthroblastus aspirin Arthrobacter Fermentation culture yields fermentation broth; 2) Mix the fermentation broth with the plant root exudate simulated solution that provides electron donors for the reduction of hexavalent chromium in the fermentation broth at a volume ratio of 1:(1.5-2.5) to obtain a mixed solution; The plant root exudate simulation solution contains 40–60 mg / L of low molecular weight organic acids, 70–80 mg / L of amino acids, and 30–50 mg / L of soluble sugars; The low molecular weight organic acids are a mixture of citric acid, oxalic acid, lactic acid, succinic acid and malic acid in a concentration ratio of (2.5-3.5):(1.5-2.5):(1.5-2.5):(0.8-1.2):

1. The amino acids are a mixture of glutamic acid, arginine, and serine in a concentration ratio of 1:(0.8-1.2):(0.8-1.2); Soluble sugars are a mixture of glucose and fructose in a concentration ratio of 1:(0.8-1.2); 3) Add biochar to the mixed solution at (8-12) mL / g for mixing, adsorption and fixation, and then filter.

2. The method as described in claim 1, characterized in that: The soil remediation agent obtained by filtration in step 3) includes biochar as a carrier and Arthroblastus abacteria loaded on the biochar. Arthrobacter And plant root secretion simulation solution.

3. The method as described in claim 1, characterized in that: In step 3), the adsorption fixation is performed by oscillating adsorption at 25-35℃ and 100-200rpm for 15-25h.

4. The method as described in claim 1, characterized in that: In step 3), the biochar is obtained by pyrolyzing rice straw at 450-550℃.

5. The application of the soil remediation agent obtained by the method described in any one of claims 1-4 in the remediation of hexavalent chromium contaminated soil.

6. The application as described in claim 5, characterized in that: The process includes the following steps: applying the soil remediation agent to the hexavalent chromium-contaminated soil, thoroughly tilling the soil to ensure the agent is evenly mixed with the soil, maintaining the soil moisture content at 30-50%, remediating for 50-70 days, testing the hexavalent chromium content in the soil, stopping remediation if the target is reached, and adding a second round of soil remediation agent to continue remediation until the target is achieved.

7. The application as described in claim 6, characterized in that: For soil contaminated with hexavalent chromium at a content of 0–50 mg / kg, apply soil remediation agent at a rate of 0.5% of the soil weight.

8. The application as described in claim 6, characterized in that: For soil contaminated with hexavalent chromium at a content of 50–100 mg / kg, apply soil remediation agent at a rate of 1.0% of the soil weight.

9. The application as described in claim 6, characterized in that: For soil contaminated with hexavalent chromium containing 100–200 mg / kg, apply soil remediation agent at 1.5% of the soil weight.

10. The application as described in claim 6, characterized in that: For soil contaminated with hexavalent chromium containing more than 200 mg / kg, apply soil remediation agent at a rate of 2.0% of the soil weight.

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