CN110280582B - Method for restoring organochlorine contaminated soil by zero-valent iron reduction combined with indigenous microorganisms - Google Patents

Abstract

The invention discloses a method for restoring organic chlorine-contaminated soil by combining zero-valent iron reduction with indigenous microorganisms. The method firstly utilizes the strong reduction effect of micron zero-valent iron to remove the chlorinated groups of organochlorine pesticides in the soil, and then adds biological carbon sources, electron donors and nitrogen and phosphorus nutrients to promote the growth, reproduction and metabolic degradation of indigenous microorganisms in the soil Organochlorine pesticides, and then add sulfate reduction inhibitors and methanogenesis inhibitors to suppress the consumption of electrons. While the enzymatic action of Fe ²⁺ and Fe ³⁺ produced by the reduction of Fe ⁰ on indigenous microorganisms promotes their growth, the organic acids secreted by the metabolic activities of indigenous microorganisms affect the reductive dechlorination process of organochlorine pesticides at the soil colloid interface and adjust soil pH. , to accelerate the etching of zero-valent iron and promote the reductive dechlorination of zero-valent iron. Compared with the remediation methods that simply use zero-valent iron to reduce or use indigenous microorganisms to remediate organochlorine pesticide-contaminated soil, the method has the advantages of high remediation efficiency, short construction period, complete remediation, and no secondary pollution.

Description

A method of combining zero-valent iron reduction with indigenous microorganisms to remediate organochlorine-contaminated soil

technical field

The invention belongs to the technical field of soil pollution restoration, and in particular relates to a method for restoring organochlorine-contaminated soil by combining zero-valent iron reduction with indigenous microorganisms.

Background technique

Organochlorine pesticides are a typical class of environmental pollutants, and they usually have the characteristics of high chemical stability (long half-life), lipophilic hydrophobicity, bioconcentration, and biotoxicity. These pollutants mainly come from waste raw materials of pesticide production, running, running, dripping and leaking in the production process of chemical pesticides. my country's "Soil Environmental Quality Construction Land Soil Pollution Risk Management and Control Standards (Trial)" (GB36600-2018) published 85 kinds of pollution projects, organochlorine accounted for 46 kinds; )" (GB15618-2018) published in the other projects of agricultural land soil pollution risk screening pollutants, the risk screening values of the total amount of 666 and the total amount of DDT are clarified. Studies have shown that organochlorine pesticides have strong carcinogenic, teratogenic and mutagenic effects on organisms, and most organochlorine pesticides are endocrine disruptors or potential endocrine disruptors. Since organochlorine pesticides are difficult to degrade naturally, they can exist stably in the environment for a long time. If they cannot be effectively repaired, they will pose a serious threat to human health and even survival.

At present, the remediation methods for soil contaminated by organochlorine pesticides mainly include physical method, thermal desorption method, advanced oxidation, chemical reduction, biological method, etc. The physical method mainly transfers the organochlorine pesticide-contaminated soil to the ground by means of soil removal and landfilling, which cannot completely eliminate the pollutants, and its environmental risks still exist. Thermal desorption is a remediation method in which the contaminated soil is heated in situ or ex situ, and the organochlorine pesticides in the soil are desorbed and then collected and processed by heating up to above the boiling point of the pollutant. The thermal desorption equipment has large capital investment, high operating energy consumption, and high repair cost, which is difficult to implement in some small organochlorine pesticide-contaminated sites. Advanced oxidation is a remediation method for oxidative degradation of pollutants by adding oxidants to the soil; however, due to the strong electron-withdrawing ability of the chlorine-containing groups on organochlorine pesticides, the efficiency of the advanced oxidation method is directly used for the degradation of organochlorine pesticides. Not high. Chemical reduction is a remediation method that removes chlorine-containing groups in organochlorine pesticides through chemical reduction by adding reducing agents to the soil. Zero-valent iron is an active substance with strong reducing properties, which can reduce organochlorine pesticides, reduce the biological toxicity of organochlorine pesticide-contaminated soil, and generate intermediate products with higher biodegradability; and reduce pollutants in zero-valent iron. At the same time, it can be oxidized into iron oxides with larger specific surface area. These iron oxides also have a certain reduction activity under anaerobic conditions, and have a strong adsorption effect on organic pollutants. The organochlorine pesticides and their reduced intermediates can be further decomposed. Although chemical reduction has a good reductive dechlorination effect on organochlorine pesticides, which can remove the chlorine-containing groups in organochlorine pesticides and effectively reduce the biological toxicity of soil, the intermediates after dechlorination still remain in the soil. The repair is not complete. Biological method refers to a restoration method that uses microorganisms to degrade organochlorine pesticides; under aerobic conditions, microorganisms use organochlorine pesticides as electron donors, transfer electrons to electron acceptors such as oxygen, and decompose organochlorine pesticides into Carbon dioxide, water and chlorine; under anaerobic conditions, microorganisms use some food sources as electron donors and organochlorine pesticides as electron acceptors to start the reduction process of hydrogen substitution of chlorine, gradually reducing the chlorine-containing groups in organochlorine pesticides. Remove and generate olefins, alkanes and other substances that are harmless to the environment. However, there are certain problems in the biological remediation of organochlorine pesticide-contaminated soil. Under anaerobic conditions, as the chlorine-containing groups in the organochlorine pesticide are replaced by hydrogen one by one, the reaction rate will decrease, and the low-chlorinated intermediate products will be in the environment. Under aerobic conditions, only low-chlorinated organic pollutants can be directly metabolized and decomposed into water and carbon dioxide by microorganisms as electron donors, and polychlorinated organic pollutants can only be decomposed by microorganisms. Co-metabolism degrades gradually, but the co-metabolism of microorganisms consumes a large amount of electron donors, and the metabolic rate is extremely slow.

Based on this, the present invention combines chemical reduction and bioremediation, selects zero-valent iron with high reduction activity and is environmentally friendly for the reductive dechlorination of organochlorine pesticides, makes full use of the reduction characteristics of zero-valent iron and its oxides, and accelerates soil At the same time, Fe ²⁺ and Fe ³⁺ produced by the oxidation of organochlorine pesticides reduced by zero-valent iron have an enzymatic effect on the production of indigenous microorganisms, which can promote the growth of indigenous microorganisms. The method of activating indigenous microorganisms without the addition of exogenous organisms and without the risk of secondary pollution is selected for the complete degradation of low-chlorinated organic pollutants after dechlorination, and the indigenous microorganisms are used to decompose them into carbon dioxide and water; The organic acids secreted by the metabolic activities of microorganisms can directly or indirectly affect the reductive dechlorination process of organochlorine pesticides at the soil colloid interface. At the same time, organic acids can effectively adjust soil pH, accelerate the etching of zero-valent iron, and promote the reductive dechlorination of zero-valent iron. effect. Therefore, the present invention utilizes the outstanding reductive dechlorination of zero-valent iron and its oxides, combined with the metabolism of indigenous microorganisms and the activity of metabolizing to produce organic acids, and gives full play to the advantages of chemical reduction and the degradation of organochlorine pesticides by indigenous microorganisms. The advantages of this method are combined to establish an economical, efficient, clean and green remediation method for organochlorine pesticide-contaminated soil.

SUMMARY OF THE INVENTION

The purpose of the invention is to break through the technical bottleneck existing in the field of soil remediation, solve the problem that organochlorine pesticide-contaminated soil is difficult to remediate up to the standard by chemical methods, and provide a method for restoring organochlorine-contaminated soil by combining zero-valent iron reduction with indigenous microorganisms. On the basis of using the reduction effect of micron zero-valent iron to remove the chlorinated groups of organochlorine pesticides in the soil and reducing the biological toxicity of the soil, adding biological carbon sources, electron donors, nitrogen and phosphorus nutrients to promote the growth of indigenous microorganisms in the soil, Reproduction and metabolic degradation of organochlorine pesticides, addition of sulfate reduction inhibitors to inhibit the consumption of electrons by sulfate in soil, and addition of methanogenesis inhibitors to inhibit the consumption of electrons in the process of metabolizing hydrocarbons by methane bacteria to produce methane. The Fe ²⁺ and Fe ³⁺ produced by the oxidation of organochlorine pesticides reduced by zero-valent iron have an enzymatic effect on the production of indigenous microorganisms and can promote the growth of indigenous microorganisms. Indigenous microorganisms can completely degrade low-chlorinated organic pollutants after dechlorination into carbon dioxide and water; at the same time, the organic acids secreted by the metabolic activities of indigenous microorganisms can directly or indirectly affect the reductive dechlorination process of organochlorine pesticides at the soil colloid interface. Acid can also effectively adjust soil pH, accelerate the etching of zero-valent iron, and promote the reductive dechlorination of zero-valent iron. Compared with the remediation methods that simply use zero-valent iron to reduce or use indigenous microorganisms to remediate organochlorine pesticide-contaminated soil, this method has the advantages of high remediation efficiency, short construction period, less investment, complete restoration, and no secondary pollution.

The concrete technical scheme adopted in the present invention is as follows:

A method for restoring organochlorine-contaminated soil by combining zero-valent iron reduction with indigenous microorganisms, the steps of which are as follows:

(1) The organochlorine pesticide-contaminated soil to be repaired is excavated to the surface, and transferred to a closed disposal greenhouse;

(2) The organochlorine pesticide-contaminated soil is sieved and crushed to form fine-grained soil with a particle size of less than 50 mm;

(3) Stack the fine-grained organochlorine pesticide-contaminated soil after screening and crushing into soil stacks, add micron zero-valent iron powder on the soil stacks, and use a turning machine to turn the soil stacks and mix them evenly; and during the turning process Spray biological carbon sources, electron donors, sulfate reduction inhibitors, methanogenesis inhibitors, nitrogen fertilizers and phosphate fertilizers on the mound in sequence to ensure that the sprayed reagents are fully mixed with the contaminated soil;

(4) Cover the surface of the soil stack evenly mixed with micron zero-valent iron, biological carbon source, electron donor, sulfate reduction inhibitor, methanogenesis inhibitor, nitrogen fertilizer and phosphate fertilizer to create anaerobic reducing conditions, static During the maintenance process, the soil moisture content is basically in a saturated state, and the micron zero-valent iron is used for reductive dechlorination and the degradation of indigenous microorganisms, and finally the complete degradation of organochlorine pesticides is achieved.

Preferably, the airtight disposal greenhouse described in step (1) is equipped with an air extraction device and a tail gas treatment device, and the ventilation frequency is 2-6h/time.

Preferably, the specifications of the mounds described in the step (3) are trapezoidal long stacks, the width of the lower bottom is 4-8m, the width of the upper bottom is 2-5m, the length is 30m-50m, the height is 1m-2m, and the spacing between the stacks is 1.5-2m .

Preferably, the particle size of the micron zero-valent iron used in the step (3) must be less than 74 microns (200 meshes), the mass ratio of the iron powder with reducibility is greater than or equal to 80%, and the added mass ratio of the micron zero-valent iron powder in the mound is 1.0～3.0%. The added mass ratio of micron zero-valent iron powder can be determined according to the content of organochlorine pesticides and other oxidizing substances in the soil.

Preferably, the biological carbon source and the electron donor described in the step (3) are sodium acetate solution, the sulfate reduction inhibitor is sodium molybdate solution, the methanogenesis inhibitor is BES solution, the sprayed sodium acetate solution, molybdic acid The concentration of the sodium solution and the BES solution is 20 to 40 mMol/L.

Further, the concentration of sodium acetate solution, sodium molybdate solution and BES solution sprayed in step (3) are all 20mMol/L, and the volume ratio of spraying is sodium acetate solution: sodium molybdate solution: BES solution=1:1 : 1, the total amount of spraying of sodium acetate solution, sodium molybdate solution and BES solution is 0.1% to 1.0% of soil mass. The total amount of spraying can be determined according to the type and concentration of organochlorine pesticides in the soil.

Preferably, the nitrogen fertilizer sprayed in step (3) is preferably sodium nitrate solution or potassium nitrate solution, and the solution concentration is 0.25g～0.5g/L; the phosphate fertilizer is preferably sodium phosphate solution or potassium phosphate solution, and the solution concentration is 0.1g～0.2 g/L; the volume ratio of the sprayed nitrogen fertilizer and the phosphate fertilizer is 1:1, and the total amount of the sprayed nitrogen fertilizer and the phosphate fertilizer is 0.1% to 1.0% of the soil mass. The total amount of spraying is specifically determined according to the original N and P content in the contaminated soil, and it is necessary to ensure that the indigenous microorganisms in the organochlorine pesticide-contaminated soil can grow and develop stably and rapidly to exert the effect of bioremediation.

Preferably, during the standing maintenance process in step (4), it is necessary to spray tap water or sodium acetate solution, sodium molybdate solution, and BES solution to keep the soil moisture content basically in a saturated state.

Further, the saturated moisture content of the soil varies according to different soil properties, and is generally 30% to 60%.

Preferably, in step (4), the period of standing and curing is 14 to 28 days.

Compared with the prior art, the present invention has the following beneficial effects:

(1) Environmental friendliness: The present invention utilizes the high reducibility, environmental friendliness, enzymatic action of zerovalent iron and its oxides, and the metabolic effect of the dominant indigenous microorganisms in the soil on organochlorine pesticide pollution, and utilizes micron zerovalent iron. The high reducing property removes the chlorinated groups of organochlorine pesticides in the soil, greatly reduces the biological toxicity of the soil, and adds nutrients such as biological carbon sources, electron donors, nitrogen and phosphorus to promote the growth, reproduction and metabolism of the dominant indigenous microorganisms in the soil. Degradation of organochlorine pesticides and the chlorine-containing intermediates produced by their metabolism, the final products are carbon dioxide and water, and the complete degradation of organochlorine pesticides is finally achieved. No exogenous pollutants and microorganisms are introduced in the restoration process, and the whole restoration process is clean, safe, environmentally friendly, and free of secondary pollution.

(2) the cost is low: the micron zero-valent iron used in the present invention can be obtained by ball milling of industrial wastes such as cheap scrap iron filings, iron wire, iron powder, iron flakes as raw materials, and has a wide range of sources; the acetic acid that promotes the production of indigenous microorganisms Sodium and nitrogen and phosphorus nutrients are common chemical raw materials and agricultural fertilizers, and are also commonly used remediation materials in the field of soil remediation. The remediation investment of ex-situ restoration of organochlorine-contaminated soil through zero-valent iron reduction combined with indigenous microorganisms can be controlled within 1,000 yuan/ton of soil, compared with the currently commonly used thermal desorption remediation technology of 2,000 yuan/ton of soil. Fees are reduced by at least 50%.

(3) Wide range of restoration objects: Most of the organochlorine pesticides in the soil can be effectively degraded.

Description of drawings

1 is a schematic diagram of the operation flow of a method of the present invention for the reduction of zero-valent iron combined with indigenous microorganisms to remediate organochlorine-contaminated soil.

Figure 2 is a schematic diagram of the content and degradation rate of hexahexahexanol in soil.

Detailed ways

The present invention will be further elaborated and described below with reference to the accompanying drawings and specific embodiments.

The organochlorine pesticide-contaminated soil to be rehabilitated by the present invention contains suitable types of dominant indigenous anaerobic microorganisms capable of degrading organochlorine pesticides; the dominant indigenous microorganisms in the invention are usually bacteria, fungi, actinomycetes and some protozoa. After the dechlorination of valence iron reduces the biological toxicity of the soil, the dominant indigenous microorganisms can directly degrade part of the organochlorine pesticides and some intermediate products after dechlorination into carbon dioxide and water in an anaerobic environment, so as to achieve the purpose of completely degrading the organochlorine pesticides in the soil. . The flow chart of the repair method of the present invention is shown in FIG. 1 .

The invention utilizes the characteristics that indigenous microorganisms have strong vitality, adaptability and degradation ability in the environment polluted by organochlorine pesticides for a long time, makes full use of the anaerobic indigenous microorganisms in the soil polluted by organochlorine pesticides, creates a suitable anaerobic environment, and After the use of zero-valent iron reduction and dechlorination to reduce soil biological toxicity, the addition of biological carbon sources, electron donors, and nitrogen and phosphorus nutrients stimulates the growth and reproduction of indigenous microorganisms, and at the same time degrades organochlorine pesticides, which greatly shortens the remediation of organochlorine pesticide-contaminated soil. Time, the removal rate of the restored organochlorine pesticides is close to 80%, which greatly weakens the harm caused by the contaminated soil of the organochlorine pesticides.

Example 1

In this example, the polluted site to be rehabilitated that was polluted by organochlorine pesticides was selected, and the site survey results showed that the pollutants were mainly the total concentrations of hexahexahexanol, alpha-hexahexahexanol, beta-hexahexanol, and gamma-hexahexanol. It is 500～10000mg/kg, and the pollution depth is from 1m underground to 6m underground.

The method for the restoration of organochlorine-contaminated soil by the combination of zero-valent iron reduction and indigenous microorganisms provided in this embodiment is implemented through the following steps:

(1) Use an excavator to excavate the contaminated soil of 666 from the ground to the surface. The test results of sampling and sending to a third-party testing laboratory show that the total concentration of 666 in the contaminated soil is 1296.495 mg/kg. The 666 polluted soil is transferred to a closed greenhouse for temporary storage by a loader. The greenhouse is a steel structure closed greenhouse. The greenhouse is equipped with an exhaust device and an exhaust gas treatment device. The ventilation frequency is once every 4h.

(2) Use screening and crushing equipment to screen out the stones in the organochlorine pesticide-contaminated soil, crush the large pieces of the consolidated organochlorine pesticide-contaminated soil into fine-grained soil with a particle size of less than 50 mm, and pile the soil into piles. It is a trapezoidal long stack with a bottom width of 4m, an upper bottom width of 2m, a length of 30m, a height of 1m, and the spacing between the stacks is 1.5m.

(3) Add micron zero-valent iron according to the mass ratio of 1.64% (that is, 1.64% of the soil mass in the mound), the particle size of micron zero-valent iron is 325 mesh, and the effective content is ≥90%. Turn the polluted soil and micron zero-valent iron 3 to 5 times with a turning machine to mix evenly. During turning, spray 20 mMol/L sodium acetate solution, 20 mMol/L sodium molybdate solution, and 20 mMol/L BES solution in turn. , the sodium nitrate solution of 0.25g/L, the sodium phosphate solution of 0.1g/L, the volume ratio of the sprayed sodium acetate solution, sodium molybdate solution and BES solution V _{sodium acetate solution} : V _{sodium molybdate solution} : V _BES solution =1:1:1, the total amount of sprayed sodium acetate solution, sodium molybdate solution and BES solution is 0.1% of soil mass; the volume ratio of sprayed sodium nitrate solution and sodium phosphate solution V _{sodium nitrate solution} : V _{sodium phosphate solution} = 1:1, and the total amount of spraying of sodium nitrate solution and sodium phosphate solution is 0.1% of the soil mass.

In this step, sodium acetate is used as biological carbon source and electron donor, sodium molybdate is used as sulfate reduction inhibitor, BES solution is used as methanogenesis inhibitor, sodium nitrate solution is used as nitrogen fertilizer (N nutrient solution), and sodium phosphate is used as phosphate fertilizer (P nutrient solution).

(4) Spray tap water on the surface of the mound and continue to turn it over to ensure that the moisture content of the contaminated soil is close to saturation. After turning and throwing to make the remediation agents, nutrients and polluted soil evenly mixed, cover the surface of the mound with a rain-proof cloth and compact and seal it to create an anaerobic reduction environment, let it stand for maintenance, and take samples after 8 days and 16 days to detect the six or six in the soil. Six content. The test results are shown in Figure 2.

The test results showed that the total amount of hexahexahexanol decreased from 1296.495mg/kg to 278.1424mg/kg in the samples maintained for 16 days, and the degradation efficiency reached 78.547%, which greatly reduced the biological toxicity of soil.

In the above remediation process, zero-valent iron and indigenous microorganisms play a role in coupling. Micron zero-valent iron first removes the chlorinated groups of organochlorine pesticides in the soil through reduction, and on the basis of reducing soil biological toxicity, biochar is added. Source, electron donor, nitrogen and phosphorus nutrients promote the growth, reproduction and metabolic degradation of organochlorine pesticides of indigenous microorganisms in the soil, adding sulfate reduction inhibitors to inhibit the consumption of electrons by sulfate in soil, adding methanogenic inhibitors to inhibit the metabolism of methanogens The consumption of electrons by the methanogenesis of hydrocarbons. The Fe ²⁺ and Fe ³⁺ produced by the oxidation of organochlorine pesticides reduced by zero-valent iron have an enzymatic effect on the production of indigenous microorganisms and can promote the growth of indigenous microorganisms. Indigenous microorganisms can completely degrade low-chlorinated organic pollutants after dechlorination into carbon dioxide and water; at the same time, the organic acids secreted by the metabolic activities of indigenous microorganisms can directly or indirectly affect the reductive dechlorination process of organochlorine pesticides at the soil colloid interface. Acid can also effectively adjust soil pH, accelerate the etching of zero-valent iron, and promote the reductive dechlorination of zero-valent iron. Compared with the remediation methods that simply use zero-valent iron to reduce or use indigenous microorganisms to remediate organochlorine pesticide-contaminated soil, the combined method of this method has significantly improved remediation efficiency.

Example 2

In this embodiment, the selection of the contaminated site to be rehabilitated polluted by organochlorine pesticides is the same as that in Embodiment 1.

The method for the restoration of organochlorine-contaminated soil by the combination of zero-valent iron reduction and indigenous microorganisms provided in this embodiment is implemented through the following steps:

(1) Use an excavator to excavate the 666 contaminated soil from the ground to the surface, and use a loader to transfer the 666 contaminated soil to a closed greenhouse for temporary storage. The greenhouse is a steel structure closed greenhouse, and the greenhouse is equipped with an exhaust device and exhaust gas. Treatment device, the ventilation frequency is 1 ventilation every 6h.

(2) Use screening and crushing equipment to screen out the stones in the organochlorine pesticide-contaminated soil, crush the large pieces of the consolidated organochlorine pesticide-contaminated soil into fine-grained soil with a particle size of less than 50 mm, and pile the soil into piles. It is a trapezoidal long stack, with a bottom width of 8m, an upper bottom width of 5m, a length of 50m, a height of 2m, and the spacing between the stacks of 2m.

(3) Add micron zero-valent iron according to the mass ratio of 3% (that is, 3% of the soil mass in the mound), the particle size of micron zero-valent iron is 325 mesh, and the effective content is ≥80%. Turn the polluted soil and micron zero-valent iron by turning 3 to 5 times to mix evenly. During turning, spray 40 mMol/L sodium acetate solution, 40 mMol/L sodium molybdate solution, and 40 mMol/L BES solution in turn. , 0.5g/L potassium nitrate solution, 0.2g/L potassium phosphate solution, wherein the volume ratio of sprayed sodium acetate solution, sodium molybdate solution and BES solution V _{sodium acetate solution} : V _{sodium molybdate solution} : V _BES solution = 1:1:1, the total amount of sprayed sodium acetate solution, sodium molybdate solution and BES solution is 1% of the soil mass; the volume ratio of sprayed potassium nitrate solution and potassium phosphate solution V _{potassium nitrate solution} : V _{potassium phosphate solution} = 1:1, and the total amount of sprayed potassium nitrate solution and potassium phosphate solution is 1% of the soil mass.

In this step, sodium acetate is used as biological carbon source and electron donor, sodium molybdate is used as sulfate reduction inhibitor, BES solution is used as methanogenesis inhibitor, potassium nitrate solution is used as nitrogen fertilizer (N nutrient solution), and potassium phosphate is used as phosphate fertilizer (P nutrient solution).

(4) Spray tap water on the surface of the mound and continue to turn it over to ensure that the moisture content of the contaminated soil is close to saturation. After turning and throwing to make the remediation agents, nutrients and contaminated soil evenly mixed, cover the surface of the mound with a rain-proof cloth and compact and seal it to create an anaerobic reduction environment, and stand for maintenance. During the static maintenance process, continue to spray tap water or sodium acetate. solution, sodium molybdate solution and BES solution to keep the soil moisture basically in a saturated state. After curing for 14 days, sampling and testing the content of 666 in the soil showed that the degradation efficiency of 666 reached 71.235%, which greatly reduced the biological toxicity of the soil.

The above-mentioned embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. Various changes and modifications can also be made by those of ordinary skill in the relevant technical field without departing from the spirit and scope of the present invention. For example, the shape and size of the mound can be adjusted according to the site. Various process parameters in the soil treatment process can also be adjusted according to the degradation of pollutants in the soil. In addition, based on the remediation mechanism, it can be predicted that although the pollutants targeted in the examples are hexahexahexanol, this method is effective for most of the chlorine-containing organic pollutants in the soil. Therefore, all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims (10)

1. A method for restoring organochlorine contaminated soil by zero-valent iron reduction and indigenous microorganisms is characterized by comprising the following steps:

(1) the organochlorine pesticide polluted soil to be repaired is dug to the ground surface and is transported to a closed disposal greenhouse;

(2) screening and crushing the organochlorine pesticide contaminated soil to form fine-particle soil with the particle size of less than 50 mm;

(3) stacking the screened and crushed fine particle organochlorine pesticide contaminated soil into a soil pile, adding micron zero-valent iron powder into the soil pile, and turning over the soil pile by using a turner to uniformly mix; in the turning and throwing process, a biological carbon source, an electron donor, a sulfate reduction inhibitor, a methane production inhibitor, a nitrogen fertilizer and a phosphate fertilizer are sequentially sprayed on the soil stack, so that the sprayed reagent is fully mixed with the polluted soil;

(4) covering a waterproof cloth on the surface layer of a soil stack which is uniformly mixed with micron zero-valent iron powder, a biological carbon source, an electron donor, a sulfate reduction inhibitor, a methane production inhibitor, a nitrogen fertilizer and a phosphate fertilizer, creating an anaerobic reducing condition, standing and maintaining, keeping the water content of soil in a basically saturated state in the maintenance process, and finally realizing the complete degradation of the organochlorine pesticide by utilizing the reduction dechlorination and the degradation of indigenous microorganisms by the micron zero-valent iron powder.

2. The method for remediating organochlorine contaminated soil by zero-valent iron reduction in combination with indigenous microorganisms according to claim 1, wherein: and (2) the airtight treatment greenhouse in the step (1) is provided with an air draft device and a tail gas treatment device, and the air exchange frequency is that air exchange is carried out for 1 time every 2-6 hours.

3. The method for remediating organochlorine contaminated soil by zero-valent iron reduction in combination with indigenous microorganisms according to claim 1, wherein: in the step (3), the soil pile is in a trapezoidal strip pile, the width of the lower bottom is 4-8 m, the width of the upper bottom is 2-5 m, the length is 30-50 m, the height is 1-2 m, and the distance between every two adjacent piles is 1.5-2 m.

4. The method for remediating organochlorine contaminated soil by zero-valent iron reduction in combination with indigenous microorganisms according to claim 1, wherein: the particle size of the micron zero-valent iron powder adopted in the step (3) is less than 74 microns, the mass proportion of the iron powder with reducibility is more than or equal to 80%, and the addition mass ratio of the micron zero-valent iron powder in the soil pile is 1.0-3.0%.

5. The method for remediating organochlorine contaminated soil by zero-valent iron reduction in combination with indigenous microorganisms according to claim 1, wherein: the biological carbon source and the electron donor in the step (3) are sodium acetate solution, the sulfate reduction inhibitor is sodium molybdate solution, the methane production inhibitor is BES solution, and the concentration of the sprayed sodium acetate solution, sodium molybdate solution and BES solution is 20-40 mMol/L.

6. The method for remediating organochlorine contaminated soil by zero-valent iron reduction in combination with indigenous microorganisms according to claim 5, wherein: the concentrations of the sodium acetate solution, the sodium molybdate solution and the BES solution sprayed in the step (3) are all 20mMol/L, and the volume ratio of spraying is that of the sodium acetate solution: sodium molybdate solution: BES solution =1:1:1, and the total amount of the sodium acetate solution, the sodium molybdate solution and the BES solution sprayed is 0.1-1.0% of the soil mass.

7. The method for remediating organochlorine contaminated soil by zero-valent iron reduction in combination with indigenous microorganisms according to claim 1, wherein: the nitrogen fertilizer sprayed in the step (3) is a sodium nitrate solution or a potassium nitrate solution, and the concentration of the solution is 0.25-0.5 g/L; the phosphate fertilizer is a sodium phosphate solution or a potassium phosphate solution, and the concentration of the solution is 0.1-0.2 g/L; the volume ratio of the sprayed nitrogen fertilizer to the sprayed phosphorus fertilizer is 1:1, and the total amount of the sprayed nitrogen fertilizer and the sprayed phosphorus fertilizer is 0.1-1.0% of the soil mass.

8. The method for remediating organochlorine contaminated soil by zero-valent iron reduction in combination with indigenous microorganisms according to claim 1, wherein: in the standing and maintaining process in the step (4), tap water is sprayed, or sodium acetate solution is adopted according to the volume ratio: sodium molybdate solution: BES solution =1:1:1 sodium acetate solution, sodium molybdate solution and BES solution are sprayed to keep the water content of the soil in a saturated state.

9. The method for remediating organochlorine contaminated soil by zero-valent iron reduction in combination with indigenous microorganisms according to claim 8, wherein: the saturated water content of the soil is 30% -60%.

10. The method for remediating organochlorine contaminated soil by zero-valent iron reduction in combination with indigenous microorganisms according to claim 1, wherein: and (4) standing and maintaining for 14-28 days.

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