A microbial remediation method for uranium-contaminated groundwater

Abstract

The present invention discloses a microbial remediation method applicable to uranium-contaminated groundwater, and relates to the field of water pollution remediation. The method comprises the following steps: conducting a uranium pollution survey on groundwater in a contaminated area, determining the contamination plume according to the uranium concentration, calculating the permeability coefficient of the rock and soil layer and the influence radius of the remediation well; constructing a plurality of remediation well positions so that the remediation areas of the plurality of remediation wells overlap and cover the contamination plume; adding a remediation agent in each remediation well, the remediation agent comprising sodium bicarbonate, sodium acetate, ethanol, ferrous sulfide and water. The present invention is applicable to the microbial remediation technology of uranium-contaminated groundwater, and the remediation agent considers three aspects, namely, regulating the environment, providing nutrition and preventing rebound, improving the living environment of microorganisms, stimulating and improving the biological reduction efficiency of heavy metal uranium by indigenous microorganisms in groundwater, and will not cause secondary pollution to the environment. The uranium contamination of groundwater can be continuously remediated, and the remediation area can be wide, and a large amount of manpower and material resources are not required, so the method is simple and economical.

Description

Technical Field

[0001] The invention relates to the field of water pollution remediation, and in particular to a microbial remediation method suitable for uranium-contaminated groundwater. Background Art

[0002] Uranium is the most radioactive actinide element in the periodic table. It has extremely strong chemical toxicity and radioactivity. Irrational use will cause serious harm to the environment and human health. With the continuous development of industry, uranium will cause uranium contamination to groundwater during human activities such as production, processing, enrichment, use, nuclear research and weapons manufacturing. In the natural environment, uranium mainly exists in the form of hexavalent uranium (U(VI)) and tetravalent uranium (U(IV)). U(VI) has higher solubility and fluidity than U(IV), which means that U(VI) is more harmful to the environment. When uranium accumulates in the food chain, it will eventually cause damage to the reproductive system, digestive system, hematopoietic organs and nervous system in the human body. Therefore, uranium contamination must be remediated, especially to reduce the concentration of U(VI) to improve the environment and protect human health.

[0003] Researchers have adopted various physical, chemical and biological methods to repair uranium contamination in groundwater. Among them, bioremediation is considered the most promising method because it is cost-effective and has no secondary pollution. It is mainly achieved through internal accumulation, surface adsorption, reduction and mineralization. Some scholars have shown that Desulfovibrio, Geobacter and Shewanella are widely present in uranium-contaminated environments. These microorganisms can reduce U(VI) to U(IV) in oligotrophic environments. In addition, laboratory results show that Staphylococcus aureus can reduce 47% hexavalent uranium within 1 hour, and has a high potential for repairing uranium-contaminated groundwater. However, the underground environment in actual contaminated areas is complex and changeable. The content of organic matter, nitrates, sulfates in groundwater, as well as conditions such as temperature and pH, will affect microbial activity and reduce or increase the efficiency of microbial repair of uranium-contaminated groundwater.

[0004] Therefore, how to improve the adaptability of microorganisms in groundwater environments and increase the efficiency of microorganisms in reducing U(VI) in groundwater is a problem that needs to be solved. Summary of the invention

[0005] The present invention provides a microbial remediation method applicable to uranium-contaminated groundwater, which is applicable to the remediation of groundwater in uranium-contaminated areas, improves the living environment of microorganisms in groundwater, and increases the activity of microorganisms and the ability to reduce heavy metal uranium.

[0006] In order to solve the above technical problems, the present invention provides a microbial remediation method applicable to uranium-contaminated groundwater, comprising the following steps:

[0007] (1) Conduct uranium contamination surveys on groundwater in the contaminated area, determine the contamination plume based on uranium concentration, and conduct geological exploration to calculate the permeability coefficient of the rock and soil layers. Based on the permeability coefficient, calculate the impact radius of the remediation well;

[0008] (2) Taking the impact radius as the remediation area of ​​the remediation well, construct several remediation well locations so that the remediation areas of several remediation wells overlap and cover the pollution plume;

[0009] (3) Adding a repair agent to each repaired well at intervals, wherein the repair agent includes 3-6wt% sodium bicarbonate, 5-9wt% sodium acetate, 4-8wt% ethanol, 0-4wt% ferrous sulfide and the balance water.

[0010] As a preferred solution, in step (1), the permeability coefficient is the average value of the results of a simple water head reduction water injection test and a simple water head constant water injection test;

[0011] The calculation formula of the simple precipitation head water injection test is: Where, K is the permeability coefficient of the rock and soil layer (cm / s); Q is the injection flow rate (L / min); l is the length of the test section (cm); H is the water head height (cm); r is the radius of the borehole in the test section (cm);

[0012] The calculation formula of the simple constant head water injection test is: Where, H1, H2 are the corresponding test water heads at time t1t2 (cm); t1, t2 are the test time at a certain moment of the water injection test (min).

[0013] As a preferred solution, in step (1), the calculation formula of the influence radius is: Where, R is the impact radius (m); S is the water level drop during pumping (m); h is the thickness of the aquifer (m); K is the permeability coefficient of the rock and soil layer (m / d).

[0014] As a preferred solution, in step (2), the repair well is constructed in the form of an isosceles triangle, the three vertices of the triangle are the repair wells, and the distance from the center of the triangle to the vertex is the impact radius.

[0015] As a preferred embodiment, in step (2), the diameter of the repair well is 100-300 mm, the depth of the repair well is the distance from the first groundwater aquifer to the ground, PVC pipes are inserted in the repair well from the bottom to the ground, and holes are drilled in the PVC pipes located in the aquifer for water to flow through.

[0016] As a preferred embodiment, in step (3), the repair agent further comprises 1-3 wt% of calcium sulfite and 1-3 wt% of manganese sulfite.

[0017] As a preferred solution, in step (3), the calculation formula for the amount of the repair agent added is: Where, V is the volume of the repair agent added (L), R is the impact radius (m), and h is the thickness of the aquifer (m).

[0018] As a preferred embodiment, in step (3), the repair agent is added every 48 hours, and the repair period is more than 10 days.

[0019] As a preferred embodiment, in step (3), the repair agent is added each time at 10 am.

[0020] As a preferred embodiment, in step (3), the ferrous sulfide in the repair agent is added once a month.

[0021] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0022] 1. The present invention is applicable to the microbial remediation technology of uranium-contaminated groundwater. The remediation agent improves the living environment of microorganisms and stimulates the indigenous microorganisms in the groundwater, thereby significantly improving their biological reduction efficiency of heavy metal uranium. Compared with other technologies, it is safe, will not cause secondary pollution to the environment, is sustainable, can continuously remediate uranium contamination in groundwater, can be used for a wide area of ​​remediation, does not require a large amount of manpower and material resources, and is simple and economical.

[0023] 2. In the case of uranium contamination in groundwater, the present invention uses a remediation agent that takes into account three aspects: regulating the environment, providing nutrition, and preventing rebound. It is simple and efficient to promote the indigenous microorganisms in the groundwater to reduce U(VI) to U(IV). The sodium bicarbonate in the remediation agent can accelerate the reduction of microorganisms, and can eliminate the effect of adding sodium acetate on the pH of groundwater, thereby maintaining the optimal pH of the microorganisms; sodium acetate and ethanol are electron donors for microorganisms, which can improve the efficiency of uranium reduction by microorganisms; ferrous sulfide plays a stabilizing role, preventing the U(IV) reduced by microorganisms from being subsequently oxidized to U(VI), thereby preventing the occurrence of rebound during the groundwater remediation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 : A schematic diagram of the construction of microbial remediation wells C1-C5 in Example 1 of the present invention;

[0025] Figure 2 : A statistical chart of hexavalent uranium concentration during the 30-day restoration process of the restoration well C3 in Example 1 of the present invention;

[0026] Figure 3: This is a diagram of the microbial structure of the repair wells C1-C5 before repair in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Embodiment 1

[0029] A microbial remediation method for uranium-contaminated groundwater comprises the following steps:

[0030] (1) Polluted area survey: Conduct uranium contamination survey on groundwater in a polluted area to determine the contamination plume; conduct geological exploration of the polluted area to determine the impact radius;

[0031] The strata in the contaminated area are composed of Quaternary sediments, rock fragments, sandstone and mud. The rock components are mostly flesh-red potassium feldspar granite with diameters ranging from 5 to 80 mm. The main components of sandstone are rock fragments and quartz. The downward bedrock aquiclude is a flesh-red medium-fine-grained granite structure with a blocky structure. The main components of the bedrock are potassium feldspar, quartz, plagioclase and biotite. Potassium feldspar is plate-shaped and distributed in a disorderly manner, slightly kaolinized and albitized. Quartz is granular and mixed in it. Biotite is leaf-shaped and scattered. In addition, there are sparse distributions of opaque magnetite and many cracks in the rock. The calculation method of the permeability coefficient of the aquifer adopts the average value obtained by the formula of the simple precipitation head water injection test formula 1) and the simple constant head water injection test formula 2). The water injection experiment shows that the permeability coefficient of the site is about 0.2m / d, and the influence radius is 5m calculated according to formula 3). Before the test, water quality analysis was carried out in the contaminated area, and the hexavalent uranium concentration in the groundwater was detected using the laser fluorescence method. The hexavalent uranium concentration in the groundwater exceeded the background value.

[0032] Formula 1):

[0033]

[0034] In formula 1), K is the permeability coefficient of the rock and soil layer (cm / s); Q is the injection flow rate (L / min); l is the length of the test section (cm); H is the water head height (cm); r is the radius of the borehole in the test section (cm);

[0035] Formula 2):

[0036]

[0037] In formula 2), H1, H2 are the corresponding test water heads at time t1t2 (cm); t1, t2 are the test time at a certain moment of the water injection test (min).

[0038] Formula 3):

[0039]

[0040] In formula 3), R is the influence radius (m); S is the water level drop during pumping (m); h is the aquifer thickness (m); K is the permeability coefficient of the rock layer (m / d).

[0041] (2) Construction of restoration wells: The restoration wells are constructed in the form of an isosceles triangle. The three vertices of the triangle are the restoration wells, and the distance from the center of the triangle to the vertex is the impact radius.

[0042] The schematic diagram of the repair well layout is shown below Figure 1 , with the C3 well with the highest hexavalent uranium concentration of 1460μg / L as the center, the distance between C1 and C2 wells is 10m, C3 well is on the vertical line of the connecting line of C1 and C2 wells, 5m away from the connecting line of C1 and C2 wells, and the distance between C3 and C1 and C2 wells is 7.1m. According to the same design, the distance between C3 and C4 and C5 wells is also 7.1m, and the vertical line of the connecting line is 5m away from the connecting line of C3 and C4 wells. The vertical line of the connecting line is 5m away from the connecting line of C3 and C4 wells. The underground The uranium concentration in the water exceeded the background value, and the hexavalent uranium concentration was between 260-1460 μg / L. The restoration area of ​​the restoration well covered the entire contaminated area. The depth of the restoration well was the distance from the first groundwater aquifer to the ground. The wellhead diameter was 200 mm, and PVC pipes were buried from the lowest end to the ground to prevent collapse. The PVC pipes were perforated in the aquifer at a vertical distance of 7-10 m so that water could flow freely through the pipes. According to the previous calculation, the impact radius of the well was 5 m, and the total restoration area was about 400 m. 2 .

[0043] (3) Detection of the richness of the microbial communities in the repaired wells C1-C5 Figure 3 As shown, test and determine the repair agent solution:

[0044] Water samples from the repair wells C2, C3, and C4 were taken for testing, and different repair agent schemes were configured as shown in Table 1. The repair agent and groundwater from different repair wells were added at a volume ratio of 1:10, placed away from light, added between 10 a.m., and added once every 48 hours. The test period was 15 days, and the changes in uranium concentration in the groundwater samples of the repair wells were detected before and after the test. The test results are shown in Table 2. It can be found that in formula 3, due to the lack of sodium acetate and ethanol to provide electron donors for microorganisms, the ability of microorganisms to reduce U(VI) to U(IV) decreased, the reduction efficiency was low, and the repair cycle was long; the repair agent in formula 4 lacked the addition of sodium bicarbonate to balance the pH effect caused by sodium acetate, which caused the pH living environment of the microorganisms to change, affecting the growth of the microorganisms and resulting in low uranium reduction efficiency.

[0045] Table 1 - Repair agent test formula

[0046]

[0047] Table 2 - Results of 15-day changes in hexavalent uranium concentration in groundwater samples from different remediation wells

[0048]

[0049] Therefore, the repair agent components are determined to include 4.5wt% sodium bicarbonate, 7.5wt% sodium acetate, 6wt% ethanol, 3wt% ferrous sulfide, 1wt% calcium sulfite, 1wt% manganese sulfite and the remainder water. The amount of the repair agent added to each well is calculated according to the following formula 4) and added to the well before 10 am to ensure that the next addition time is more than 48 hours apart from the last addition time.

[0050] Formula 4):

[0051]

[0052] In formula 3), V is the amount of repair agent added (L); R is the impact radius (m); h is the thickness of the aquifer (m).

[0053] (3) Restoration effect monitoring:

[0054] The contaminated area was repaired for 30 days, and the water from the C1-C5 repair wells was collected once a day to monitor the hexavalent uranium concentration. The monitoring results are as follows: Figure 2 As shown in Table 3, Figure 2It can be seen that the initial hexavalent uranium concentration of Well C3 in the contaminated area was 1460μg / L, which was seriously contaminated by uranium. After adding the repair agent, the uranium concentration gradually decreased. After 30 days, the hexavalent uranium concentration of Well C3 dropped to 191μg / L, indicating that the repair agent has a good repair effect. The uranium removal rate can reach up to 86.9%, and there is no rebound and tailing phenomenon, indicating that the repair agent has good stability. At the same time, the uranium removal rate of C1-C5 reached more than 85.4%. After 30 days of repair, the uranium concentration dropped to below 191μg / L, which is suitable for repairing uranium-contaminated groundwater.

[0055] Table 3 - Changes in hexavalent uranium concentrations in repaired wells C1-C5 before and after 30 days of repair

[0056] Repair well Day 0 before repair Restoration Day 30 Uranium removal rate C1 610μg / L 89 μg / L 85.4％ C2 260μg / L 19 μg / L 92.7％ C3 1460μg / L 191μg / L 86.9％ C4 600μg / L 76 μg / L 87.3％ C5 1140μg / L 107 μg / L 90.6％

[0057] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A microbial remediation method for uranium-contaminated groundwater, characterized in that: The following steps are involved: (1) Conduct uranium contamination surveys on groundwater in the contaminated area, determine the contamination plume based on uranium concentration, and conduct geological exploration to calculate the permeability coefficient of the rock and soil layers. Based on the permeability coefficient, calculate the impact radius of the remediation well; (2) Taking the impact radius as the remediation area of ​​the remediation well, construct several remediation well locations so that the remediation areas of several remediation wells overlap and cover the pollution plume; (3) adding a repair agent to each repair well at intervals, wherein the repair agent comprises 3-6wt% sodium bicarbonate, 5-9wt% sodium acetate, 4-8wt% ethanol, 3-4wt% ferrous sulfide and the balance water; In step (1), the calculation formula of the influence radius is: Where, R is the influence radius (m); S is the water level drop during pumping (m); h is the thickness of the aquifer (m); K is the permeability coefficient of the rock and soil layer (m / d); In step (3), the repair agent further comprises 1-3wt% calcium sulfite and 1-3wt% manganese sulfite. The repair agent is added once every 48 hours. The calculation formula for the amount of the repair agent added is: Where, V is the volume of the repair agent added (L), R is the impact radius (m), and h is the thickness of the aquifer (m).

2. A microbial remediation method for uranium-contaminated groundwater according to claim 1, characterized in that: In step (1), the permeability coefficient is the average value of the results of the simple water injection test with reduced water head and the simple water injection test with constant water head; The calculation formula of the simple precipitation head water injection test is: Where, K is the permeability coefficient of the rock and soil layer (cm / s); Q is the injection flow rate (L / min); l is the length of the test section (cm); H is the water head height (cm); r is the radius of the borehole in the test section (cm); The calculation formula of the simple constant head water injection test is: Where, H1, H2 are the corresponding test water heads at time t1t2 (cm); t1, t2 are the test time at a certain moment of the water injection test (min).

3. A microbial remediation method for uranium-contaminated groundwater according to claim 1, characterized in that: In step (2), the repair well is constructed according to an isosceles triangle, the three vertices of the triangle are the repair wells, and the distance from the center of the triangle to the vertex is the impact radius.

4. A microbial remediation method for uranium-contaminated groundwater according to claim 1, characterized in that: In step (2), the diameter of the repair well is 100-300 mm, the depth of the repair well is the distance from the first groundwater aquifer to the ground, PVC pipes are inserted in the repair well from the bottom to the ground, and holes are drilled in the PVC pipes located in the aquifer for water to flow through.

5. A microbial remediation method for uranium-contaminated groundwater according to claim 1, characterized in that: In step (3), the repair period is more than 10 days.

6. A microbial remediation method for uranium-contaminated groundwater according to claim 1, characterized in that: In step (3), the repair agent is added each time at 10 am.

7. A microbial remediation method for uranium-contaminated groundwater according to claim 1, characterized in that: In step (3), the ferrous sulfide in the repair agent is added once a month.

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