Plant-microorganism combined uranium pollution treatment method

Abstract

The invention discloses a plant-microorganism combined uranium pollution treatment method which comprises the following steps: planting seeds of disinfected uranium-tolerant plants into soil to be remediated, and applying a bacterial suspension of uranium-tolerant strains, namely rhodotorula M1, aspergillus M2 and bacillus M3, into the soil to be remediated, so that the uranium enrichment capacity of the uranium-tolerant plants is remarkably improved; and a relatively good effect of repairing the uranium-polluted soil in the medium-temperature climate region is achieved. Uranium-tolerant plants can be harvested manually or mechanically and transferred to a safe place in a centralized manner to be treated, so that uranium-contaminated soil in the medium-temperature climate zone is effectively repaired.

Description

Technical Field

[0001] The present invention belongs to the technical field of phytoremediation of uranium - contaminated soil, and particularly relates to a method for jointly treating uranium pollution by plants and microorganisms. Background Art

[0002] Nuclear energy is a low - carbon clean energy. With the development of industry, nuclear energy has become one of the important energy sources in China. However, the development of nuclear energy depends on the mining and smelting of uranium ore. The rapid development of the nuclear industry has increased the demand for nuclear fuel and accelerated the uranium ore mining and smelting work. However, during the process of uranium ore mining and smelting, a large amount of waste and tailings will be generated. The uranium content in these waste and tailings is much higher than that in natural soil. The uranium element in these wastes spreads into the soil, air or groundwater, which will have a significant impact on the ecological environment. Compared with uranium pollution in the atmosphere and water bodies, uranium pollution in the soil has the characteristics of concealment, accumulation, long repair cycle, strong toxicity, etc., and has attracted more and more attention from scholars and the public.

[0003] The remediation methods of uranium - contaminated soil can be mainly divided into physical remediation, chemical remediation, biological remediation and comprehensive remediation technologies, etc. In recent years, phytoremediation technology has attracted people's attention due to its in - situ, economic, green and other advantages, and has become an effective means to treat heavy metal - and radionuclide - contaminated soil. The microbial - plant combined remediation technology combines microbial remediation and phytoremediation, gives full play to the advantages of the two remediation materials, can improve the rhizosphere micro - environment of plants, has the functions of cooperating with plants and promoting plant growth, etc., and improves the remediation efficiency of plants for radionuclide - contaminated soil. However, at present, most of the uranium pollution in the soil uses single microbial remediation or phytoremediation alone in soil pollution, and such methods all have limitations. Therefore, using microorganisms to enhance phytoremediation is a mutually beneficial method and will not cause secondary pollution to the environment, which is the direction of future sustainable development. The current uranium - enriched plants and radiation - resistant microorganisms mainly target the radioactive - contaminated soil environment system in the south subtropical region (such as East China and South China regions). The hard - rock uranium mines in the northwest region of China (such as the Longshoushan in Gansu and the Helan Mountain mining area in Ningxia) generally show typical continental arid climate characteristics: low annual average precipitation, large temperature difference between day and night, and low organic matter content. Such extreme environments have led to multiple dilemmas for traditional bioremediation technologies. First, the adaptability of microorganisms and plants is poor: due to temperature differences, etc., the survival rate of radiation - resistant strains and plants screened in the East China region is low in the northwest soil; second, the occurrence form of uranium is complex: the uranyl carbonate complex (UO2(CO3)3 4⁻) has a high proportion, and conventional microorganisms have poor fixation efficiency for soluble uranium; finally, the ecological restoration ability is weak: the soil microbial diversity index in the northwest mining area is significantly lower than that in the southern uranium mining area, and the indigenous microbial community is difficult to support the niche competition of exogenous repair bacteria. Therefore, finding a combined phytoremediation method of radiation-resistant microorganisms and plants suitable for the mid-temperate climate zone is crucial for the treatment of soil radioactive pollution around uranium mines in the northwest of China. Summary of the Invention

[0004] In order to overcome the above deficiencies existing in the prior art, the purpose of the present invention is to provide a combined phytoremediation method for uranium pollution.

[0005] The purpose of the present invention is achieved by at least one of the following technical solutions.

[0006] A combined phytoremediation method for uranium pollution specifically includes the following steps: (1) Plant the seeds of uranium-tolerant plants after disinfection into the soil to be repaired; (2) Apply the bacterial suspension of uranium-tolerant strains to the soil to be repaired; the uranium-tolerant strains include one or more of Rhodotorula mucilaginosa M1, Aspergillus sp. M2, and Bacillus sp. M3; (3) Harvest the uranium-tolerant plants and conduct centralized treatment.

[0007] Further, in step (1), the uranium-tolerant plants include one or more of corn, mustard, asparagus, Artemisia annua, rosemary, spruce, gentian, fescue, Caragana sinica, Phtheirospermum japonicum, Paris polyphylla, Cirsium setosum, Gueldenstaedtia verna, and Bothriochloa ischaemum.

[0008] Furthermore, in step (1), the uranium-tolerant plants include one or more of corn, mustard, and Cirsium setosum.

[0009] Further, in step (1), the planting spacing of the seeds of the uranium-tolerant plants is 20 - 50 cm.

[0010] Furthermore, in step (1), the planting spacing of the seeds of the uranium-tolerant plants is 30 cm.

[0011] Further, in step (1), the seed disinfection method of the uranium-tolerant plants is: first wash the seeds of the uranium-tolerant plants with 75% ethanol for 3 - 10 min, then wash them 3 times with sterile distilled water, then soak them in 10% H2O2 for 10 - 30 min, and finally wash them with 30 - 100 mL of Hoagland nutrient solution.

[0012] Furthermore, in step (1), the method for disinfecting the seeds of uranium-tolerant plants is as follows: The seeds of uranium-tolerant plants are first washed with 75% ethanol for 4 min, then washed three times with sterile distilled water, then soaked in 10% H2O2 for 20 min, and finally washed with 50 mL of Hoagland nutrient solution.

[0013] Further, in step (2), the method for applying the bacterial suspension of uranium-tolerant strains is to apply it to the soil above the seeds of uranium-tolerant plants or to the rhizosphere soil of uranium-tolerant plants.

[0014] Further, in step (2), the application amount of the bacterial suspension of uranium-tolerant strains is 30 - 100 mL per plant per application.

[0015] Furthermore, in step (2), the application amount of the bacterial suspension of uranium-tolerant strains is 50 mL per plant per application.

[0016] Further, in step (2), the uranium-tolerant strains in the bacterial suspension are in the logarithmic growth phase.

[0017] Furthermore, the cell concentration of Rhodotorula mucilaginosa M1 in the logarithmic growth phase is OD600 = 2.5 - 3.6; the suspended solid concentration of the mixed solution of Aspergillus sp. M2 in the logarithmic growth phase is 3.0 - 4.5 mg / L; the cell concentration of Bacillus sp. M3 in the logarithmic growth phase is OD600 = 0.6 - 1.2.

[0018] Further, in step (2), the bacterial suspension of uranium-tolerant strains is repeatedly applied to the soil to be repaired every 3 - 10 d.

[0019] Furthermore, in step (2), the bacterial suspension of uranium-tolerant strains is repeatedly applied to the soil to be repaired every 5 d.

[0020] Further, in step (3), the specific method for harvesting uranium-tolerant plants and conducting centralized treatment is as follows: The uranium-tolerant plants are harvested manually or mechanically, and then the harvested uranium-tolerant plants are transferred to a safe place for centralized drying, crushing, incineration, and finally landfilled or leached to recover uranium.

[0021] Further, in step (3), the uranium-tolerant plants are harvested once every 30 d or 60 d.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) After applying uranium-tolerant strains M1, M2 or M3 to the rhizosphere of uranium-tolerant plants, their uranium enrichment ability is significantly improved, and a good effect is achieved in the remediation of uranium-polluted soil in the mid-temperate climate region. The uranium-tolerant plants can be harvested manually or mechanically and centrally transferred to a safe place for treatment.

[0023] (2)The uranium-resistant strains M1, M2, and M3 can all enhance the uranium enrichment in the roots of uranium-resistant plants, while increasing the translocation of uranium to the above-ground parts of the plants, and promoting the uranium enrichment in the plants.

[0024] (3)Under the combined action of plants and microorganisms, the remediation effects of adding M1 and M3 bacterial agents are generally better than that of M2. The uranium loss in the soil of the corn field and mustard field with M1 addition is more obvious. After adding M1, the transfer coefficients of corn, mustard, and Cirsium setosum all exceed 1, and the translocation of uranium from the underground to the above-ground increases. Among them, the transfer coefficient of mustard is the highest, reaching 2.818. Description of the Drawings

[0025] Figure 1 This is the geological map of the research area of the present invention.

[0026] Figure 2 This is the content diagram of the typical nuclide U in each sampled plant in Example 1.

[0027] Figure 3 This is the change diagram of the soil uranium concentration in the pot experiment of the combined uranium pollution treatment of plants and microorganisms in Example 2.

[0028] Figure 4 This is the change diagram of the uranium concentration in the soil under the condition of a single plant before adding the bacterial agent in the field site experiment of Example 3. Detailed Embodiments

[0029] The following further illustrates the specific implementation of the present invention in conjunction with the drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that for the processes not specifically described in detail below, those skilled in the art can implement or understand them with reference to the prior art. The reagents or instruments not indicating the manufacturer are regarded as conventional products that can be obtained through commercial purchase.

[0030] It should be understood that the terms such as "having", "including", and "comprising" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0031] In the present invention, the terms "Rhodotorula rubra M1" and "M1" both refer to the strain with the preservation number of CGMCC No. 34591, and the taxonomic name is Rhodotorula toruloides. This strain was preserved in the China General Microbiological Culture Collection Center on May 19, 2025. The address of the preservation unit is: Institute of Microbiology, Chinese Academy of Sciences, No. 3, Beichen West Road, Chaoyang District, Beijing.

[0032] In the present invention, the terms "Aspergillus M2" and "M2" both refer to the strain with the preservation number CGMCC No. 41942, classified and named as Aspergillus welwitschiae. This strain was deposited at the General Microbiological Center of the China Committee for Culture Collection of Microorganisms on May 19, 2025. The address of the depository unit is Institute of Microbiology, Chinese Academy of Sciences, No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing.

[0033] In the present invention, the terms "Bacillus M3" and "M3" both refer to the strain with the preservation number CGMCC No. 34592, classified and named as Bacillus wiedmannii. This strain was deposited at the General Microbiological Center of the China Committee for Culture Collection of Microorganisms on May 19, 2025. The address of the depository unit is Institute of Microbiology, Chinese Academy of Sciences, No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing.

[0034] In the present invention, the mixed liquor suspended solids concentration (MLSS) refers to the mass of activated sludge suspended solids in a unit volume of the mixed liquor, with the unit of milligram per liter (mg / L).

[0035] In the present invention, Rhodotorula M1 and Aspergillus M2 are cultured in a potato dextrose liquid medium until the logarithmic growth phase.

[0036] In the present invention, Bacillus M3 is cultured in a beef extract peptone liquid medium until the logarithmic growth phase.

[0037] In the present invention, the preparation method of the potato dextrose liquid medium is as follows: Peel and wash the potatoes, cut them into small cubes of uniform size, weigh 200 g, add them to an appropriate amount of boiling water, and simmer over low heat for about 15 - 20 min (stop heating when a glass rod can just pierce through the potato cubes). Then filter and collect the filtrate with eight-layer gauze, add 20 g of glucose to the filtrate, and continuously stir with a glass rod to accelerate its dissolution. Finally, make up the volume to 1000 mL with distilled water. Aliquot, sterilize at 121 °C under high-pressure steam for 30 min, and store for later use after cooling.

[0038] In the present invention, the preparation method of the beef extract peptone liquid medium is as follows: Dissolve all solutes in deionized water according to the ratio of 3 g / L beef extract, 10 g / L peptone, and 5 g / L NaCl, and sterilize in a high-pressure steam sterilizer at 121 °C for 20 min.

[0039] In the present invention, the following method is used to determine the radionuclide content of soil samples: The soil samples were air-dried naturally, impurities were removed, and they were placed in an oven at 80 °C until constant weight was achieved. Then they were ground, passed through a 200-mesh sieve, and the collected samples were placed in a desiccator for later use. For the soil samples whose pH values were determined by the potentiometric method, after being dried to constant weight, they were directly passed through a 20-mesh sieve. The soil pH value was measured using a pH meter (the mass ratio of water to soil m(water):m(soil) = (2.5:1)). Weigh 0.1 g of soil sample into a beaker and digest it using aqua regia and perchloric acid (2:1, v / v). After digestion was completed, it was made up to the mark in a 100 mL volumetric flask, and the content of radionuclides in the sample was determined by inductively coupled plasma optical emission spectrometry.

[0040] In the present invention, the following method was adopted for determining the nuclide content of plant samples: The plants were divided into aboveground and underground parts. After being washed with tap water, they were rinsed 3 times with deionized water. The roots were soaked in 10 mmol·L -1 EDTA solution for 10 min to remove the metal ions adsorbed on the root surface, then washed with deionized water, drained of water, placed in an oven at 105 °C for 30 min for blanching, and then placed in an oven at 75 °C until constant weight was achieved. Then the aboveground and underground parts were separately placed into porcelain crucibles, and the temperature in the muffle furnace was gradually raised to 600 °C for ashing for 6 h. The collected samples were placed in a desiccator for later use.

[0041] Weigh 0.1 g of plant sample into a beaker and digest it using aqua regia and perchloric acid (2:1, v / v). After digestion was completed, it was made up to the mark in a 100 mL volumetric flask, and the content of radionuclides in the sample was determined by inductively coupled plasma optical emission spectrometry. The unit of uranium content in plants is mg·kg -1 (calculated based on ash).

[0042] In the specific embodiments of the present invention, the following method was adopted for disinfecting plant seeds: The plant seeds were first washed with 75% ethanol for 4 min, then washed 3 times with sterile distilled water, soaked in 10% H2O2 for 20 min, and finally washed with 50 mL of Hoagland nutrient solution.

[0043] In the present invention, the formula of Hoagland nutrient solution is as follows: Calcium nitrate 945 mg / L Potassium nitrate 607 mg / L Ammonium phosphate 115 mg / L Magnesium sulfate 493 mg / L Iron salt solution 2.5 mL / L Trace elements 5 mL / L pH = 6.0. The formula of the trace element solution is the trace element solution: Potassium iodide 0.83 mg / L Boric acid 6.2 mg / L Manganese sulfate 22.3 mg / L Zinc sulfate 8.6 mg / L Sodium molybdate 0.25 mg / L Copper sulfate 0.025 mg / L Cobalt chloride 0.025 mg / L.

[0044] In the present invention, the calculation formulas for the translocation factor and the enrichment factor of plants are as follows: (1) (2) BCF: Plant enrichment factor; C_plant: Concentration of pollutants in the plant, mg·kg⁻¹; C_soil: Concentration of pollutants in the rhizosphere soil of the plant, mg·kg⁻¹.

[0045] TF: Plant translocation factor; C_aboveground: Concentration of pollutants in the aboveground part of the plant, mg·kg⁻¹; C_underground: Concentration of pollutants in the underground part of the plant, mg·kg⁻¹.

[0046] The translocation factor can reflect the ability of a plant to transfer a specific substance from the roots to the stems and leaves. The higher the translocation factor, the higher the efficiency of the translocation and distribution of the specific substance. Plants with a high translocation factor can remove specific pollutants by harvesting the aboveground parts and are preferred plants for the application of phytoremediation technology.

[0047] The present invention provides a method for jointly treating uranium pollution by plants and microorganisms, which specifically includes the following steps: (1) Plant the seeds of uranium-tolerant plants after disinfection into the soil to be repaired; (2) Apply the bacterial suspension of uranium-tolerant strains to the soil to be repaired; the uranium-tolerant strains include one or more of Rhodotorula sp. M1, Aspergillus sp. M2, and Bacillus sp. M3; (3) Harvest the uranium-tolerant plants and conduct centralized treatment.

[0048] In some embodiments of the present invention, in step (1), the uranium-tolerant plants include one or more of corn, mustard, asparagus, Artemisia annua, rosemary, spruce, gentian, fescue, caragana, Phtheirospermum japonicum, Paris polyphylla, Cirsium setosum, Gueldenstaedtia verna, and Bothriochloa ischaemum. Preferably, in step (1) of the present invention, the uranium-tolerant plants include one or more of corn, mustard, and Cirsium setosum.

[0049] In some embodiments of the present invention, in step (1), the planting spacing of the seeds of the uranium-tolerant plants is 20 - 50 cm. Preferably, in step (1) of the present invention, the planting spacing of the seeds of the uranium-tolerant plants is 30 cm.

[0050] In some embodiments of the present invention, in step (1), the method for disinfecting the seeds of uranium-tolerant plants is as follows: The seeds of uranium-tolerant plants are first washed with 75% ethanol for 3 - 10 min, then washed three times with sterile distilled water, then soaked in 10% H2O2 for 10 - 30 min, and finally washed with 30 - 100 mL of Hoagland nutrient solution. Preferably, in step (1) of the present invention, the method for disinfecting the seeds of uranium-tolerant plants is: The seeds of uranium-tolerant plants are first washed with 75% ethanol for 4 min, then washed three times with sterile distilled water, then soaked in 10% H2O2 for 20 min, and finally washed with 50 mL of Hoagland nutrient solution.

[0051] In some embodiments of the present invention, in step (2), the method for applying the bacterial suspension of uranium-tolerant strains is to apply it to the soil above the seeds of uranium-tolerant plants or to the rhizosphere soil of uranium-tolerant plants.

[0052] In some embodiments of the present invention, in step (2), the application amount of the bacterial suspension of uranium-tolerant strains is 30 - 100 mL per plant per application. Preferably, in step (2) of the present invention, the application amount of the bacterial suspension of uranium-tolerant strains is 50 mL per plant per application.

[0053] In some embodiments of the present invention, in step (2), the uranium-tolerant strains in the bacterial suspension are in the logarithmic growth phase. Preferably, the cell concentration of Rhodotorula mucilaginosa M1 in the logarithmic growth phase is OD600 = 2.5 - 3.6; the suspended solid concentration of the mixed solution of Aspergillus M2 in the logarithmic growth phase is 3.0 - 4.5 mg / L; the cell concentration of Bacillus M3 in the logarithmic growth phase is OD600 = 0.6 - 1.2.

[0054] In some embodiments of the present invention, in step (2), the bacterial suspension of uranium-tolerant strains is repeatedly applied to the soil to be repaired every 3 - 10 d. Preferably, in step (2) of the present invention, the bacterial suspension of uranium-tolerant strains is repeatedly applied to the soil to be repaired every 5 d.

[0055] In some embodiments of the present invention, in step (3), the specific method for harvesting uranium-tolerant plants and conducting centralized treatment is as follows: The uranium-tolerant plants are harvested manually or mechanically, and then the harvested uranium-tolerant plants are transferred to a safe place for centralized drying, crushing, incineration, and finally landfilled or leached to recover uranium.

[0056] In some embodiments of the present invention, in step (3), the uranium-tolerant plants are harvested once every 30 d or 60 d.

[0057] In a specific embodiment of the present invention, the uranium-tolerant plant is mustard, and the uranium-tolerant strain is Rhodotorula mucilaginosa M1. The combination of the two can effectively promote the translocation of uranium to the above-ground parts of plants and enhance the uranium enrichment in plants, showing excellent performance in the remediation of uranium-contaminated soils in the mid-temperate climate zone.

[0058] Example 1 Screening of uranium-tolerant plants In this paper, the soil around a uranium mine in the northwest of the Liupanshan Basin was selected as the study area. The Liupanshan Basin extends in a northwestern direction as a whole, being wider in the north and narrower in the south, presenting an inverted triangle shape. The basin is located in a relatively special tectonic position. To its southwest is the North Qilian - Qinling orogenic belt, to its north is the Xiangshan fault uplift on the southern margin of the Alxa block, and to its east is the rift zone on the western margin of the Ordos block. The basin has developed three sets of sedimentary covers, namely the Upper Paleozoic Devonian - Carboniferous - Permian, the Mesozoic Triassic - Lower Cretaceous, and the Cenozoic Paleogene - Quaternary. The study area belongs to the arid hilly area of the Loess Plateau, with the terrain being lower in the south and higher in the north, and the altitude ranging from 1688 to 2633 m away from the Liupanshan Mountains. It is 140 Km to the east, 28 Km to the Xumishan Scenic Area, 63 Km to Guyuan City, and 391 Km to Yinchuan City in the north. The geological map of the study area is as Figure 1 shown.

[0059] Twelve native plants were collected around the contaminated soil in the study area, including annual, perennial, flowering, and non-flowering plants. Different types of plants have different abilities to enrich radionuclides, namely Asparagus cochinchinensis, Artemisia annua, Rosmarinus officinalis, Picea asperata, Gentiana scabra, Festuca ovina, Caragana sinica, Phtheirospermum japonicum, Paris polyphylla, Cirsium setosum, Gueldenstaedtia verna, and Bothriochloa ischaemum. When collecting plant samples, the sample size was controlled at about 30 cm × 40 cm. For small plants and long and slender plants, the whole plant was collected and folded into a V shape or an N shape for storage; for thick plants, representative parts were collected. The collected plant samples were placed in a collection cylinder lined with straw paper and stored together for delivery to the laboratory for processing and testing. To distinguish the enrichment characteristics of the above-ground and underground parts of plants, the collected plants were divided into above-ground and underground parts respectively for testing the nuclide content of plant samples. The content of the typical nuclide U in each sampled plant is as Figure 2 shown.

[0060] From Figure 2 it can be seen that there are certain differences in the uranium enrichment abilities of different plants. Among them, Cirsium setosum, Asparagus cochinchinensis, and Picea asperata have the best enrichment ability (above-ground + underground), Paris polyphylla, Gueldenstaedtia verna, Festuca ovina, Caragana sinica, and Gentiana scabra have average uranium enrichment abilities, while Artemisia annua and Rosmarinus officinalis have poor uranium enrichment effects.

[0061] Analysis in combination with the growth characteristics of plants found that the top 3 plants with the best enrichment ability were all perennial plants, while the plants with general enrichment ability were mainly annual plants. The uranium enrichment ability of the above-ground parts of plants was generally higher than that of the underground parts. Among the 12 plants, the uranium content in the above-ground parts ranged from 59.76 to 1267.07 mg·kg -1 , while that in the underground parts ranged from 53.66 to 370.73 mg·kg -1 . Among them, the above-ground part of Cirsium setosum had the highest uranium content, reaching 1267.07 mg·kg -1 , and the transfer coefficient was also the highest, being 3.79. Asparagus cochinchinensis was the opposite of Cirsium setosum. Although the overall uranium enrichment performance of Asparagus cochinchinensis was strong, its underground part had a relatively high uranium content of 370.73 mg·kg -1 , while the uranium content in its above-ground part was relatively low, being 59.76 mg·kg -1 . Therefore, its transfer coefficient was the lowest, only 0.16.

[0062] In summary, the uranium enrichment abilities of 12 representative native plants around the study area varied greatly. Cirsium setosum had a significant uranium enrichment ability among the 12 plants, mainly because Cirsium setosum belongs to perennial plants, is cold-resistant, drought-resistant, and has strong adaptability. Its developed root system and high biomass are conducive to the absorption and transportation of uranium.

[0063] Example 2 Pot experiment on the combined uranium pollution treatment of plants and microorganisms The uranium-accumulating plants maize and mustard, which were verified in the early stage, were selected for the experiment. The seeds of the plants were first washed with 75% ethanol for 4 min, then washed 3 times with sterile distilled water, soaked in 10% H2O2 for 20 min, and finally washed with 50 mL of Hoagland nutrient solution.

[0064] Plant control group: The disinfected maize and mustard seeds were respectively planted in potting soil containing a certain uranium concentration (244.88 mg·kg -1 ). Three parallel samples were set for each plant. After regular watering and observation, the plants were removed after growing for 50 days.

[0065] Strain control group: The bacterial solutions of Rhodotorula rubra M1, Aspergillus sp. M2 or Bacillus sp. M3 in the logarithmic growth phase were added to the potting soil containing a certain uranium concentration (244.88 mg·kg -1 ) every 5 days (the single addition amount was 50 mL of bacterial solution per kilogram of soil). Three parallel samples were set for each strain, and the experimental period was 50 days. Among them, the concentration of the bacterial solution of Rhodotorula rubra M1 in the logarithmic growth phase was OD 600 = 2.5 - 3.6; the suspended solid concentration of the mixed solution of the bacterial solution of Aspergillus sp. M2 in the logarithmic growth phase was 3.0 - 4.5 mg / L; the concentration of the bacterial solution of Bacillus sp. M3 in the logarithmic growth phase was OD 600= 0.6 - 1.2.

[0066] Experimental group: The disinfected corn and mustard seeds were respectively planted in potting soil containing a certain uranium concentration (244.88 mg·kg -1 ). The bacterial solutions of Rhodotorula mucilaginosa M1, Aspergillus sp. M2 or Bacillus sp. M3 in the logarithmic growth phase were added every 5 days (the single addition amount was 50 mL of bacterial solution per kilogram of soil). Three parallel samples were set for each plant + strain combination. After growing for 50 days, the plants were removed. Among them, the concentration of the bacterial solution of Rhodotorula mucilaginosa M1 in the logarithmic growth phase was OD 600 = 2.5 - 3.6; the suspended solid concentration of the bacterial solution mixture of Aspergillus sp. M2 in the logarithmic growth phase was 3.0 - 4.5 mg / L; the concentration of the bacterial solution of Bacillus sp. M3 in the logarithmic growth phase was OD 600 = 0.6 - 1.2.

[0067] After the experiment, the potting soil and all plants were sampled and analyzed separately for aboveground and underground parts, and the nuclide content was measured.

[0068] Table 1 Sample numbers for the pot experiment on the combined uranium pollution treatment of plants and microorganisms The changes in the uranium concentration in the soil in the pot experiment on the combined uranium pollution treatment of plants and microorganisms are as Figure 3 shown. Whether it is a single plant or the combined remediation of plants and microorganisms, the uranium concentration in the soil has decreased to varying degrees. However, the uranium removal method in the combined remediation of plants and microorganisms is better than that of single plants or single strains. To further analyze the transfer characteristics of uranium into plants, the enrichment coefficient and transfer coefficient of uranium in the aboveground and underground parts of plants were calculated. The results are shown in Table 2.

[0069] Table 2 Enrichment coefficient and transfer coefficient of uranium in plants As can be seen from Table 2, for the corn system, the combination with microorganisms has significantly improved the ability of corn to enrich uranium. Among them, when the combined remediation of corn - M3 is carried out, the enrichment coefficient of uranium in plants is the highest both aboveground and underground, followed by corn - M1, corn - M2, and single corn. From Figure 3 this, it can be seen that the residual uranium concentration in the soil under the condition of corn - M3 is the lowest, further indicating that the combined remediation efficiency of corn - M3 is the best. However, from the change of the transfer coefficient, it can be found that the transfer coefficient of corn - M1 is the highest in the corn system, indicating that under the action of M1, the transfer of uranium from the underground to the aboveground part of corn in the body is promoted.

[0070] For the mustard system, it is consistent with the trend of microbial combination in the corn system, indicating that the combination of plant-microorganisms has a better remediation effect on uranium-contaminated soil. When mustard is combined with M1 for remediation, the uranium enrichment coefficient of mustard is the highest both above and below the ground, followed by mustard-M2, and then single mustard. From Figure 3 It can be seen that the residual concentration of uranium in the soil under the condition of mustard-M1 is the lowest, further indicating that the combined remediation effect of mustard-M1 is better.

[0071] To sum up, the combined remediation effect of plant-microorganisms is better than that of single plants or single strains. Adding indigenous uranium-resistant strains to contaminated soil can promote the transfer of uranium from soil to plants. Among the three uranium-resistant strains, M1 shows the most prominent performance and exhibits a significant enrichment-promoting function in different plants. The combined remediation of mustard-M1 has the best effect on removing uranium pollution in the soil.

[0072] Example 3 Field experiment on the combined treatment of uranium pollution by plants and microorganisms The experimental site is located in the research area, with a total area of 100 m2. The experimental plot is divided into three areas: corn, mustard, and Cirsium setosum, covering 45 m2, 33 m2, and 22 m2 respectively, and the initial uranium concentrations in the soil are 198.66 mg·kg -1 , 196.95 mg·kg -1 , 192.38 mg·kg -1 .

[0073] The disinfected corn and mustard seeds and the transplanted Cirsium setosum plants are planted in the soil of the field site in the research area (8 rows, 6 rows, 4 rows), with a plant spacing of 30 cm, thus forming a plant community. After the plant community grows for 60 days, the first plant harvest and soil sample collection are carried out. Every 5 days, the bacterial liquid of Rhodotorula mucilaginosa M1, Aspergillus sp. M2, or Bacillus sp. M3 in the logarithmic growth phase is added to the soil (the single addition amount is 50 mL of bacterial liquid per plant), making it a plant-microbial symbiotic system. Among them, the concentration of the bacterial liquid of Rhodotorula mucilaginosa M1 in the logarithmic growth phase is OD 600 = 2.5 - 3.6; the suspended solid concentration of the mixed liquid of the bacterial liquid of Aspergillus sp. M2 in the logarithmic growth phase is 3.0 - 4.5 mg / L; the concentration of the bacterial liquid of Bacillus sp. M3 in the logarithmic growth phase is OD 600 = 0.6 - 1.2. After growing for 30 days from then on, the second plant harvest and soil sample collection are carried out. The sample numbers after harvest are shown in Table 3. The field experiment lasts for 90 days in total, and the depth of the repaired soil is 20 cm.

[0074] The control group adds an equal volume of culture medium without bacteria.

[0075] Table 3 Sample numbers of uranium enrichment in the repaired site Under field conditions, the variation of uranium concentration in soil under single-plant conditions before adding bacterial agents is as shown in Figure 4 the figure. From Figure 4 the changing trend of soil uranium content, it can be seen that all three plants have a certain uranium removal effect on the soil. Compared with the changing pattern of the indoor pot experiment, there is more uranium concentration loss in the soil planted with corn, and less uranium concentration loss in the soil planted with mustard. This may be related to the meteorological and hydrological environments of the field. Corn adapts well to the local environment, while mustard likes humidity and is not tolerant of heat, and grows slowly when the temperature is higher than 25 °C. The study area is located in the northwest of China, and the climate of the field experiment site is dry and hot, which is not suitable for the growth of mustard compared with the southern regions, and this may also lead to a decrease in the uranium enrichment effect of mustard.

[0076] To further analyze the transfer characteristics of uranium entering the plant body under field conditions, the enrichment coefficients and transfer coefficients of uranium content in the aboveground and underground parts of the plants were calculated, and the results are shown in Table 4.

[0077] Table 4 Uranium enrichment effect of plants As can be seen from Table 4, there are still certain differences in the uranium enrichment abilities of the aboveground and underground parts of the plants. Generally, the underground part is higher than the aboveground part, which conforms to the typical distribution pattern of plants absorbing heavy metals and is consistent with the rule of the indoor pot experiment. Under single-plant conditions, among the aboveground parts, the best uranium enrichment ability is that of Cirsium setosum, and the uranium content reaches 84.15 mg·kg -1 , higher than that of corn (53.66 mg·kg -1 ) and mustard (59.76 mg·kg -1 ); in terms of the underground part, all three plants enrich uranium in the roots. Among them, the uranium content in the underground part of Cirsium setosum is the highest (108.54 mg·kg -1 ), followed by corn (71.95 mg·kg -1 ) and mustard (65.85 mg·kg -1 ).

[0078] Under single-plant conditions, compared with the indoor pot experiment, it can be seen that the changes in the uranium enrichment coefficients of the aboveground and underground parts of corn and mustard are not significant, and the enrichment coefficients of the aboveground and underground parts of corn increase slightly. This may be related to the fact that the uranium concentration in the field soil is lower than that in the indoor pot experiment soil, indicating that corn and mustard still have a certain uranium enrichment effect in the mid-temperate climate region.

[0079] After adding the microbial agents, all types of crops showed stronger uranium accumulation ability. Especially in the mustard fields with M1 added, the conversion ratio of the above-ground part to the underground part was as high as 2.818, significantly higher than that of other groups, indicating that M1 could effectively enhance the absorption and transport efficiency of plants for uranium, which was consistent with the rules of indoor pot experiments.

[0080] Under field conditions, the situation of combined microbial-plant remediation of uranium-contaminated soil is shown in Table 5.

[0081] Table 5 Changes in uranium concentration in field soil It can be found from Table 5 that after adding the microbial agents, the uranium concentration in the field soil decreased significantly. Among them, the uranium concentration in the field with M1 and M3 microbial agents added was significantly lower than that in the field with M2 added. Compared with the indoor pot experiments, the degree of reduction in soil uranium concentration was all expanded. This further shows that strains M1 and M3 have significant advantages in improving the uranium accumulation ability of plants and removing uranium from the soil, especially when applied in corn and mustard fields.

[0082] Through indoor pot experiments and field experiments, it is further shown that corn, mustard, thistle, and uranium-tolerant strains M1, M2, and M3 all have a certain ability to repair uranium-contaminated soil. And adding microbial agents helps plants to enrich uranium in the contaminated soil. Strain M1 has the best enrichment effect on uranium and the best effect in promoting plants to enrich uranium.

[0083] The above embodiments are only the preferred embodiments of the present invention, which are only used to explain the present invention, rather than limiting the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit and essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for jointly treating uranium pollution by plants and microorganisms, characterized in that, Specifically, it includes the following steps: (1) Plant the seeds of uranium-tolerant plants after disinfection into the soil to be repaired; (2) Apply the bacterial suspension of uranium-tolerant strains to the soil to be repaired; the uranium-tolerant strains include one or more of Rhodotorula mucilaginosa M1, Aspergillus sp. M2, and Bacillus sp. M3; (3) Harvest the uranium-tolerant plants and conduct centralized treatment.

2. The method for jointly treating uranium pollution by plants and microorganisms according to claim 1, characterized in that, In step (1), the uranium-tolerant plants include one or more of corn, mustard, asparagus, Artemisia annua, rosemary, spruce, gentian, fescue, Caragana sinica, Phtheirospermum japonicum, Paris polyphylla, Cirsium setosum, Gueldenstaedtia verna, and Bothriochloa ischaemum.

3. A plant-microorganism combined uranium pollution treatment method according to claim 2, characterized in that, In step (1), the uranium-tolerant plants include one or more of corn, mustard, and Cirsium setosum.

4. A plant-microorganism combined uranium pollution treatment method according to claim 1, characterized in that, In step (1), the planting distance between the seeds of the uranium-tolerant plants is 20 - 50 cm.

5. A plant-microorganism combined uranium pollution treatment method according to claim 1, characterized in that, In step (1), the seed disinfection method of the uranium-tolerant plants is as follows: the seeds of the uranium-tolerant plants are first washed with 75% ethanol for 3 - 10 min, then washed 3 times with sterile distilled water, then soaked in 10% H2O2 for 10 - 30 min, and finally washed with 30 - 100 mL of Hoagland nutrient solution.

6. The method for jointly treating uranium pollution by plants and microorganisms according to claim 1, characterized in that, In step (2), the application amount of the bacterial suspension of the uranium-tolerant strains is 30 - 100 mL per plant each time.

7. A plant-microbe combined uranium pollution treatment method according to claim 1, characterized in that, In step (2), the uranium-tolerant strains in the bacterial suspension are in the logarithmic growth phase.

8. A plant-microorganism combined uranium pollution treatment method according to claim 7, characterized in that, The cell density of Rhodotorula mucilaginosa M1 in the logarithmic growth phase is OD 600 = 2.5 - 3.6; the suspended solid concentration of the Aspergillus M2 bacterial liquid mixture in the logarithmic growth phase is 3.0 - 4.5 mg / L; the cell density of Bacillus M3 in the logarithmic growth phase is OD 600 = 0.6 - 1.

2.

9. A plant-microorganism combined uranium pollution treatment method according to claim 1, characterized in that, In step (2), the bacterial suspension of the uranium-tolerant strains is repeatedly applied to the soil to be repaired every 3 - 10 days.

10. A plant-microorganism combined uranium pollution treatment method according to claim 1, characterized in that, In step (3), the specific method for harvesting the uranium-tolerant plants and conducting centralized treatment is as follows: the uranium-tolerant plants are harvested manually or mechanically, and then the harvested uranium-tolerant plants are transferred to a safe place for centralized drying, crushing, incineration, and finally landfilled or leached to recover uranium.

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