A method for simultaneous remediation of pesticide and arsenic contamination in acidic soils

Abstract

This invention discloses a method for the simultaneous remediation of pesticide and arsenic pollution in acidic soil, belonging to the field of soil remediation technology. *Pseudomonas arsenicoxydans* Y24-2 is used as the remediation microbial agent, and calcium peroxide is used as remediation agent A. Sodium acetate, urea, potassium dihydrogen phosphate, manganese salt, and ferrous salt are mixed to obtain remediation agent B. Remediation agents A and B must be stored separately and mixed immediately before remediation. Remediation agents A and B are dispersed in water, and the remediation microbial agent is added to obtain a remediation agent suspension. The remediation agent suspension is immediately applied to the acidic soil to be remediated for simultaneous remediation of pesticide and arsenic pollution. According to experiments, after remediation using the method provided by this invention, glyphosate in the soil is effectively degraded, arsenic is effectively oxidized and passivated, and the soil pH value is raised to neutral, achieving the goal of pollutant removal and soil restoration to health.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology, specifically relating to a method for the simultaneous remediation of pesticide and arsenic pollution in acidic soil. Background Technology

[0002] In my country, the production and use of pesticides are high, but their recovery and utilization rates are relatively low. This results in large amounts of pesticide residues accumulating in the soil, causing widespread pollution and seriously threatening human health and the balance of the ecosystem. Furthermore, soil arsenic pollution in my country is also a very serious problem. Reports indicate that nearly 2.0 × 10⁻⁶ acres of arable land are contaminated with heavy metals such as cadmium, arsenic, and lead. 7 hm 2 Pesticide and arsenic pollution in soil is mainly caused by human activities, including instances of co-contamination of soil by pesticides and arsenic. In areas where chemical plants discharge arsenic-containing waste and where agriculture uses large quantities of pesticides, the co-contamination of pesticides and arsenic is particularly prominent. This not only leads to reduced crop yields but may also pose a threat to human health.

[0003] Currently, various remediation methods have been developed for pesticide and arsenic pollution in soil, including physical remediation, chemical remediation, and bioremediation. (1) Physical remediation methods mainly include solidification and soil replacement, which can simultaneously remediate pesticide and arsenic pollution. However, these methods involve large-scale engineering construction, are costly, and may damage the original structure and fertility of the soil. Therefore, they are only suitable for soils with small areas and high pollution concentrations. For polluted soils with large areas and low concentrations, these methods are less economical. (2) Chemical remediation mainly involves adding arsenic passivating agents to the polluted soil to enhance the soil's adsorption and precipitation capacity for arsenic, thereby reducing the bioavailability of arsenic and reducing its migration. For organic pesticides, chemical remediation usually uses oxidants for oxidative degradation. Although chemical remediation can improve soil pollution to some extent, it may affect the physical and chemical properties of the soil, and the remediation effect is not durable. (3) Bioremediation is a low-cost and environmentally friendly method. For arsenic pollution, bioremediation involves bioseparation and genetic engineering to control plant uptake of arsenic. This involves plants extracting arsenic from the soil and accumulating it in their aboveground parts, which are then removed through harvesting. Pesticide-based bioremediation primarily relies on adding nutrient substrates and surfactants to enhance the degradation rate by soil microorganisms. Traditional bioremediation technologies mainly rely on the over-absorption of arsenic by plants to accumulate it in the soil solution. This process is time-consuming, and requires significant manual labor to harvest the aboveground parts of the plants after remediation.

[0004] In conclusion, there is an urgent need for an economical, efficient, and stable remediation method for acidic soils contaminated with large areas and medium to high concentrations of organic pesticides and arsenic. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for the simultaneous remediation of pesticide and arsenic pollution in acidic soils.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] This invention provides a method for the simultaneous remediation of pesticide and arsenic pollution in acidic soils, the specific steps of which are as follows:

[0008] The *Pseudomonas sarsenicoxydans* Y24-2, which has undergone activity and adaptability testing, was used as the remediation agent. Calcium peroxide was used as remediation agent A. Sodium acetate, urea, potassium dihydrogen phosphate, manganese salt, and ferrous salt were mixed to obtain remediation agent B. Remediation agents A and B should be stored separately and mixed and used immediately before remediation.

[0009] After mixing remediation agent A, remediation agent B and remediation microbial agent, the mixture is dispersed in water to obtain a remediation agent suspension. The remediation agent suspension is then immediately applied to the acidic soil to be remediated for simultaneous remediation of pesticide and arsenic pollution.

[0010] The hydrolysis of calcium peroxide produces hydrogen peroxide and calcium hydroxide. Hydrogen peroxide undergoes a Fenton reaction with ferrous ions, chemically oxidizing and degrading pesticides. Calcium hydroxide increases the pH of the acidic soil to be remediated, reduces the migration of heavy metals in the soil, and enhances the activity of soil microorganisms. The hydrogen peroxide further decomposes to produce oxygen, which stimulates arsenic-oxidizing Pseudomonas aeruginosa to carry out arsenic oxidation, passivating toxic trivalent arsenic compounds in the soil.

[0011] Preferably, the *Pseudomonas arsenicoxydans* Y24-2 is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 16655 on October 29, 2018.

[0012] Preferably, the manganese salt is manganese carbonate, manganese sulfate, or manganese chloride; and the ferrous salt is ferrous sulfate or ferrous chloride.

[0013] Preferably, the remedial agent suspension comprises: 0.2–1.5 g / L calcium peroxide, 0.01–0.05 g / L *Pseudomonas arsenicius* powder, 14–18 g / L sodium acetate, 0.8–2 g / L urea, 0.1–0.8 g / L manganese carbonate, 0.1–0.8 g / L ferrous sulfate, and 0.1–0.8 g / L potassium dihydrogen phosphate.

[0014] Preferably, the activity and fitness testing procedures for the *Pseudomonas arsenicoxydans* Y24-2 are as follows:

[0015] Arsenic-oxidizing Pseudomonas aeruginosa was dispersed in physiological saline to obtain an initial bacterial culture, with a mass concentration of 2 g / L. The initial bacterial culture was then inoculated into growth medium at an inoculum size of 1–2% for growth activity culture, and the OD value of the bacterial culture was measured. 600 Value, take OD 600 For bacterial suspensions with a value greater than 1.5, the activity test is completed;

[0016] The bacterial suspension that has completed the activity test is inoculated into the adaptation medium at an inoculum rate of 1-2% and incubated at a constant temperature; the OD of the bacterial suspension in the adaptation medium is then measured. 600 If the value is greater than 1.5, take the supernatant; determine the content of trivalent arsenic and pentavalent arsenic in the supernatant by atomic fluorescence spectrometry. If the content of pentavalent arsenic is greater than 80% of the total arsenic content, the suitability test is completed.

[0017] The growth medium comprises: sodium acetate 15 g / L, urea 1 g / L, manganese carbonate 0.4 g / L, ferrous sulfate 0.4 g / L and potassium dihydrogen phosphate 0.4 g / L;

[0018] The adaptive culture medium comprises: 15 g / L sodium acetate, 1 g / L urea, 0.4 g / L manganese carbonate, 0.4 g / L ferrous sulfate, 0.4 g / L potassium dihydrogen phosphate, and 20 mg / L sodium arsenite, with the pH adjusted to 5.5 using dilute sulfuric acid.

[0019] Preferably, when applying the repair agent suspension, the repair agent suspension is sprayed while tilling the soil with a tiller.

[0020] Preferably, for lightly contaminated soil, the application rate of the remediation agent suspension is 35–70 L / m³. 3 In lightly polluted soil, glyphosate ≤20mg / kg, arsenic ≤50mg / kg, and pH>5.0 are present.

[0021] Preferably, for moderately contaminated soil, the application rate of the remediation agent suspension is 105–140 L / m³. 3 In moderately polluted soil, the concentrations are: 20 mg / kg < glyphosate ≤ 100 mg / kg, 50 mg / kg < arsenic ≤ 200 mg / kg, and 4.0 mg / kg. <pH≤5.0。

[0022] As a preferred option, for heavily contaminated soil, the application rate of the remediation agent suspension is 175–260 L / m³. 3 Severely polluted soil contains glyphosate >100mg / kg, arsenic >200mg / kg, and pH <4.0.

[0023] As a preferred method, remediation should be carried out when the average daily temperature is between 15 and 30°C, the soil moisture content should be controlled at 20% to 30%, and the remediation period should be 5 to 30 days.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) This invention utilizes the slow hydrolysis of calcium peroxide to produce hydrogen peroxide, oxygen, and calcium hydroxide, thereby increasing the soil redox potential and stimulating arsenic-oxidizing Pseudomonas aeruginosa and soil microorganisms to carry out manganese oxidation, iron oxidation, arsenic oxidation, and pesticide biodegradation. The manganese oxides and iron oxides synthesized by microorganisms have very high oxidizing and adsorption properties, enabling them to chemically oxidize and adsorb and passivate highly toxic trivalent arsenic compounds, and also degrade pesticides. In addition, the generated calcium hydroxide can increase the pH value of acidic soils, reduce the migration of heavy metals in the soil, and restore the soil microecology. Compared with traditional remediation methods, the agents involved in this invention are simple, but the remediation pathways are diversified, including a series of reactions such as advanced oxidation, chemical oxidation, microbial oxidation, microbial mineralization, adsorption precipitation, and acid-base neutralization, which degrade pesticides and remediate arsenic pollution through multiple pathways, resulting in higher soil remediation efficiency, more stable effects, and wider adaptability. Furthermore, the hydrolysis rate of calcium peroxide in the soil is slow and the reaction is mild, which not only does not damage the soil structure but also restores the soil microecology.

[0026] (2) This invention can simultaneously remediate pesticide and arsenic pollution in soil, and can also regulate the pH value of acidic soil. In addition, the urea and potassium dihydrogen phosphate in the soil remediation agent can also serve as nitrogen and phosphorus fertilizers, providing nutrients for plants and soil microorganisms, promoting the restoration of soil microecology and increasing crop yield.

[0027] (3) The soil remediation agent of the present invention is low in cost, simple to prepare, easy to store, and has a long shelf life. Calcium peroxide has oxidizing properties and needs to be stored separately from other components. Therefore, the soil remediation agent of the present invention includes remediation agent A (calcium peroxide), remediation agent B (sodium acetate, urea, potassium dihydrogen phosphate, manganese salt and ferrous salt), and remediation bacteria, which are packaged separately and stored in a cool and dry place.

[0028] (4) The construction and operation of this invention are simple. During soil tillage, the suspension of the soil remediation agent is sprayed into the soil at a predetermined dosage, and the soil remediation agent is mixed into the soil during tillage. No special machinery or professional personnel are required. Detailed Implementation

[0029] The present invention will be further described and illustrated below with reference to specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0030] The concept of this invention is as follows: A mixture of *Pseudomonas arsenicoxydans* Y24-2 (which has passed activity and adaptability tests), calcium peroxide, sodium acetate, urea, potassium dihydrogen phosphate, manganese salt, and ferrous salt is applied as a remediation agent to the soil to be remediated. Calcium peroxide slowly hydrolyzes in water to generate hydrogen peroxide, which undergoes a Fenton reaction with ferrous ions, chemically oxidizing and degrading pesticides. Hydrogen peroxide decomposes to generate oxygen, which stimulates *Pseudomonas arsenicoxydans* and soil microorganisms to oxidize manganese, oxidize iron, oxidize arsenic, and biodegrade pesticides. The biosynthesized manganese oxides and iron oxides have very high oxidizing and adsorption properties, which can efficiently oxidize and passivate highly toxic trivalent arsenic compounds in the soil, while also oxidizing and degrading pesticides. In addition, the calcium hydroxide generated from the hydrolysis of calcium peroxide can increase the pH value of acidic soils, reduce the migration of heavy metals in the soil, restore the soil microecology, and improve soil fertility. In summary, after the remediation agent is applied to the soil, a series of reactions occur, including advanced oxidation, chemical oxidation, microbial oxidation, microbial mineralization, adsorption and precipitation, and acid-base neutralization, which accelerate the degradation of pesticides in the soil and the oxidation and passivation of arsenic, thus restoring soil health. The following specific examples demonstrate the technical effects achievable by this invention.

[0031] The *Pseudomonas arsenicoxydans* Y24-2 used in the following embodiments of the present invention is deposited at the China General Microbiological Culture Collection Center (CGMCC), located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, with accession number CGMCC No. 16655, and deposited on October 29, 2018. This strain has been disclosed in Chinese Invention Patent CN109722394B, with an authorization announcement date of May 17, 2022.

[0032] Example 1

[0033] This embodiment verifies the effectiveness of the method provided by the present invention in remediating combined pesticide and arsenic pollution in acidic soil through a small-scale soil test, as detailed below:

[0034] (1) Contaminated soil to be remediated

[0035] Topsoil (0–20 cm) contaminated with both glyphosate and arsenic was collected, passed through a 20-mesh sieve to remove impurities such as plastic, gravel, and plant roots, and then dried in a cool, well-ventilated place. The total arsenic content of the collected soil was 14.9 mg / kg, the glyphosate content was 13.2 mg / kg, and the soil pH was 5.5. This soil is classified as slightly contaminated.

[0036] (2) The activity and fitness tests of Pseudomonas arsenicoxydans Y24-2 were performed as follows:

[0037] Weigh 0.1 g of *Pseudomonas arsenic-oxidizing* powder and disperse it in 50 mL of physiological saline to obtain the initial bacterial suspension. Transfer 1 mL of the initial bacterial suspension to 100 mL of growth medium for growth activity culture and detect the OD of the bacterial suspension. 600 Value, take OD 600 Bacterial solutions with a pH value greater than 1.5 were used for activity testing. The growth medium consisted of: sodium acetate 15 g / L, urea 1 g / L, manganese carbonate 0.4 g / L, ferrous sulfate 0.4 g / L, and potassium dihydrogen phosphate 0.4 g / L.

[0038] Take 1 mL of the bacterial suspension that has undergone activity testing and inoculate it into 100 mL of adaptation medium. Place the medium in a constant temperature shaker and incubate for 24 hours at 30°C and 170 rpm. The OD of the bacterial suspension in the adaptation medium is then measured. 600 If the value is greater than 1.5, take 5 mL of supernatant into a centrifuge tube and determine the content of As(III) and As(V) by atomic fluorescence spectrometry. If the content of As(V) is greater than 80% of the total arsenic content, the suitability test is passed.

[0039] The adaptive culture medium was prepared as follows: sodium acetate 15 g / L, urea 1 g / L, manganese carbonate 0.4 g / L, ferrous sulfate 0.4 g / L, potassium dihydrogen phosphate 0.4 g / L and sodium arsenite 20 mg / L, and the pH was adjusted to 5.5 with dilute sulfuric acid.

[0040] (3) Preparation of soil remediation agent suspension

[0041] Repair agent A is calcium peroxide. Repair agent B is sodium acetate, urea, manganese carbonate, ferrous sulfate, and potassium dihydrogen phosphate in a mass ratio of 50:5:1:1:1. The repair microbial agent is *Pseudomonas arsenicoxydans* Y24-2 powder, which has passed activity and adaptability tests. Repair agent A, repair agent B, and the repair microbial agent are mixed at a mass ratio of 20:300:1 to obtain a mixture. The mixture is then dispersed in water at a concentration of 20 g / L to prepare a repair agent suspension.

[0042] (4) Soil remediation test

[0043] Take 400g of the contaminated soil to be remediated obtained in step (1) and divide it into a remediation group of 200g and a control group of 200g.

[0044] In the remediation group, 30 mL of the above-mentioned remediation agent suspension was added. In the control group, 30 mL of water was added. After thorough mixing, the soil was allowed to stand in an open beaker, with the soil moisture content controlled at 20-30%, and remediated for 5 days at room temperature (25±5℃).

[0045] (5) Soil remediation effect

[0046] The initial glyphosate content in the soil was 13.2 mg / kg. After 5 days of remediation, the glyphosate residue in the experimental group was 3.4 mg / kg, with a removal rate of 74.2%; while the glyphosate residue in the control group was 10.5 mg / kg, with a removal rate of only 20.5%. The initial mobile arsenic content in the soil was 0.84 mg / kg. After 5 days of remediation, the residue in the experimental group was 0.41 mg / kg, with a removal rate of 51.2%; while the residue in the control group was 0.61 mg / kg, with a removal rate of only 27.4%. The initial exchangeable As(III) content in the soil was 0.095 mg / kg. After 5 days of remediation, the residue in the experimental group was 0.009 mg / kg, with a removal rate as high as 90.5%; while the residue in the control group was 0.031 mg / kg, with a removal rate of 67.4%. In addition, after 5 days of remediation, the soil pH increased to 7.67; while the pH of the control group was 5.79. The above results indicate that after remediation using the method of the present invention, glyphosate in the soil was effectively degraded, arsenic was effectively oxidized and passivated, and the soil pH was also raised to neutral, achieving the goal of pollutant removal and soil restoration to health.

[0047] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A method for the simultaneous remediation of pesticide and arsenic contamination in acidic soils, characterized in that, The specific steps are as follows: The *Pseudomonas arsenicoxydans* Y24-2, which has undergone activity and adaptability testing, was used as the remediation agent. Calcium peroxide was used as remediation agent A. Sodium acetate, urea, potassium dihydrogen phosphate, manganese salt, and ferrous salt were mixed to obtain remediation agent B. Remediation agents A and B should be stored separately and mixed and used immediately before remediation. After mixing remediation agent A, remediation agent B and remediation microbial agent, the mixture is dispersed in water to obtain a remediation agent suspension; the remediation agent suspension is immediately applied to the acidic soil to be remediated for simultaneous remediation of pesticide and arsenic pollution; The hydrolysis of calcium peroxide produces hydrogen peroxide and calcium hydroxide. Hydrogen peroxide undergoes a Fenton reaction with ferrous ions, chemically oxidizing and degrading pesticides. Calcium hydroxide increases the pH of the acidic soil to be remediated, reduces the migration of heavy metals in the soil, and enhances the activity of soil microorganisms. The hydrogen peroxide further decomposes to produce oxygen, which stimulates arsenic-oxidizing Pseudomonas aeruginosa to carry out arsenic oxidation, passivating toxic trivalent arsenic compounds in the soil.

2. The method for simultaneous remediation of pesticide and arsenic pollution in acidic soil according to claim 1, characterized in that, The *Pseudomonas arsenicoxydans* Y24-2 strain is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 16655 on October 29, 2018.

3. The method for simultaneous remediation of pesticide and arsenic pollution in acidic soil according to claim 1, characterized in that, The manganese salt is manganese carbonate, manganese sulfate, or manganese chloride; the ferrous salt is ferrous sulfate or ferrous chloride.

4. The method for simultaneous remediation of pesticide and arsenic pollution in acidic soil according to claim 1, characterized in that, The remedial agent suspension comprises: 0.2–1.5 g / L calcium peroxide, 0.01–0.05 g / L Pseudomonas arsenicoxyformis powder, 14–18 g / L sodium acetate, 0.8–2 g / L urea, 0.1–0.8 g / L manganese carbonate, 0.1–0.8 g / L ferrous sulfate, and 0.1–0.8 g / L potassium dihydrogen phosphate.

5. The method for simultaneous remediation of pesticide and arsenic pollution in acidic soil according to claim 1, characterized in that, The activity and fitness testing procedures for the aforementioned Pseudomonas arsenicoxydans Y24-2 are as follows: Arsenic-oxidizing Pseudomonas aeruginosa was dispersed in physiological saline to obtain an initial bacterial culture, with a mass concentration of 2 g / L. The initial bacterial culture was then inoculated into growth medium at an inoculum size of 1–2% for growth activity culture, and the OD value of the bacterial culture was measured. 600 Value, take OD 600 For bacterial suspensions with a value greater than 1.5, the activity test is completed; The bacterial suspension that has completed the activity test is inoculated into the adaptation medium at an inoculation rate of 1-2% and then incubated at a constant temperature. OD of bacterial culture in acclimatization medium 600 If the value is greater than 1.5, take the supernatant; The contents of trivalent and pentavalent arsenic in the supernatant were determined by atomic fluorescence spectrometry. If the content of pentavalent arsenic was greater than 80% of the total arsenic content, the suitability test was completed. The growth medium comprises: sodium acetate 15 g / L, urea 1 g / L, manganese carbonate 0.4 g / L, ferrous sulfate 0.4 g / L and potassium dihydrogen phosphate 0.4 g / L; The adaptive culture medium comprises: 15 g / L sodium acetate, 1 g / L urea, 0.4 g / L manganese carbonate, 0.4 g / L ferrous sulfate, 0.4 g / L potassium dihydrogen phosphate, and 20 mg / L sodium arsenite, with the pH adjusted to 5.5 using dilute sulfuric acid.

6. The method for simultaneous remediation of pesticide and arsenic pollution in acidic soil according to claim 1, characterized in that, When applying the repair agent suspension, use a tiller to till the soil while simultaneously spraying the repair agent suspension.

7. The method for simultaneous remediation of pesticide and arsenic pollution in acidic soil according to claim 1, characterized in that, For lightly contaminated soil, the application rate of the remediation agent suspension is 35–70 L / m³. 3 In lightly polluted soil, glyphosate ≤20mg / kg, arsenic ≤50mg / kg, and pH>5.0 are present.

8. The method for simultaneous remediation of pesticide and arsenic pollution in acidic soil according to claim 1, characterized in that, For moderately contaminated soil, the application rate of the remediation agent suspension is 105–140 L / m³. 3 In moderately polluted soil, the concentrations are: 20 mg / kg < glyphosate ≤ 100 mg / kg, 50 mg / kg < arsenic ≤ 200 mg / kg, and 4.0 mg / kg. <pH≤5.0。 9. The method for simultaneous remediation of pesticide and arsenic pollution in acidic soil according to claim 1, characterized in that, For heavily contaminated soil, the application rate of the remediation agent suspension is 175–260 L / m³. 3 Severely polluted soil contains glyphosate >100 mg / kg, arsenic >200 mg / kg, and pH <4.

0.

10. The method for simultaneous remediation of pesticide and arsenic pollution in acidic soil according to claim 1, characterized in that, The remediation should be carried out when the average daily temperature is between 15 and 30°C, the soil moisture content should be controlled between 20 and 30%, and the remediation period should be between 5 and 30 days.