Ecological restoration method for heavy metal polluted farmland

Abstract

The invention discloses an ecological restoration method for a heavy metal polluted farmland. The ecological restoration method for the heavy metal polluted farmland comprises the following steps: S1, sampling polluted farmland soil to be restored, carrying out preliminary analysis, and determining the concentration and the variety of heavy metals in the soil and the soil pollution depth; s2, an impermeable layer is arranged below the polluted cultivated land soil to be repaired; s3, a biological control material is applied to the polluted cultivated land soil to be repaired; s4, planting a cinnamomum burmannii pure forest or a plant community combination. According to the ecological restoration method for the heavy metal polluted farmland, heavy metals in the polluted farmland soil are adsorbed and complexed by using the microbial compound inoculant, and the cinnamomum burmannii trees and the plant communities with the heavy metal absorption capacity are matched, so that ecological restoration can be effectively performed on the heavy metal polluted farmland, and high-quality wood can be produced; the method has various economic values, has strong ecological benefits, and brings strong economic values and landscape benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of polluted farmland treatment, and in particular to an ecological restoration method for farmland polluted by heavy metals. Background Art

[0002] As we all know, soil is the material basis for human survival and an indispensable and non-renewable natural resource. Not only does it have the function of producing green plants, but it is also a natural purification site for various pollutants. Due to insufficient attention paid to soil environmental protection, the development of heavy metal pollution control has lagged behind.

[0003] Due to the complexity, long-term accumulation and concealment of heavy metal pollution in farmland, there are many difficulties in the treatment of heavy metals in farmland. Current research on soil remediation technology mainly includes guest soil method, dilution method, stabilization / immobilization technology, glass method, in-situ passivation, thermal desorption (volatile heavy metals), electric remediation, chemical leaching, plant remediation and microbial remediation. Among these methods, in-situ passivation remediation technology is a relatively ideal technology that can be used to remediate large areas of contaminated soil. Guest soil method, dilution method, stabilization / immobilization technology, in-situ passivation and plant remediation are all in-situ soil remediation. However, in actual application, although guest soil method and dilution method are easy to operate in engineering, the remediation cost is high and it is difficult to promote and apply on a large scale; after the immobilization technology remediates the soil, the soil is solidified and crops are difficult to grow in unremediated soil; plant remediation technology generally takes a long time to remediate and is greatly affected by climate and soil conditions.

[0004] Phytoremediation (also known as extraction remediation or extraction remediation) is one of the most studied and most promising methods. It refers to using plant roots to absorb heavy metals from contaminated soil, enriching them in the aboveground parts, and harvesting the aboveground parts of plants to achieve the purpose of removing heavy metals from contaminated soil. This technology has low cost and simple operation, and generates multiple ecological service values.

[0005] Therefore, it is necessary to provide an ecological restoration method for heavy metal polluted farmland to solve the above technical problems. Summary of the invention

[0006] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides an ecological restoration method for heavy metal polluted farmland, which can perform ecological restoration on heavy metal polluted farmland.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] The ecological restoration method of heavy metal polluted farmland includes the following steps:

[0009] S1. Conduct preliminary analysis on the soil samples of the contaminated cultivated land to be repaired to determine the concentration, type and depth of heavy metals in the soil;

[0010] S2. Setting an impermeable layer under the contaminated cultivated land soil to be restored;

[0011] S3. Apply biological control materials to the contaminated cultivated soil to be remediated;

[0012] S4. Planting pure forests of Cinnamomum burmannii or plant community combinations;

[0013] S5. In the middle of plant growth, spray the mixture containing biological control materials;

[0014] S6. Collect dead branches and leaves, and incinerate them harmlessly. The residues after incineration are sealed and landfilled;

[0015] S7. Extract the infiltrated sewage above the anti-seepage layer and treat the sewage.

[0016] Preferably, the plant community combination includes at least two plants having the ability to absorb heavy metals.

[0017] Preferably, dead branches and leaves are collected at least once a month, and the collection time can be appropriately shortened during the leaf-falling period in autumn or winter, while the collection density can be increased.

[0018] Preferably, the impermeable layer is disposed at a depth of 0.5-1 meter below the contaminated soil.

[0019] Preferably, the temperature of harmless incineration treatment is controlled at 900-1350°C to promote oxidation and pyrolysis of harmful substances.

[0020] Preferably, the design and application of the anti-seepage layer should take into account the engineering characteristics, geological conditions and environmental factors, and select appropriate materials and technical means to ensure its long-term stability and effectiveness.

[0021] Preferably, a vertical shaft for sewage discharge is provided above the anti-seepage layer.

[0022] Preferably, the biological control material is a mixed microbial solution and a mixed microbial culture medium.

[0023] Preferably, sewage treatment should minimize the generation of secondary pollution.

[0024] Preferably, storage and landfilling comply with environmental protection laws and standards to ensure that no secondary pollution occurs.

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

[0026] The present invention utilizes a microbial composite agent to adsorb and complex heavy metals in polluted farmland soil, and uses Cinnamomum burmanii and a plant community with heavy metal absorption capacity in combination, thereby being able to effectively carry out ecological restoration of farmland polluted by heavy metals, and being able to produce high-quality wood with multiple economic values, while having strong ecological benefits, bringing strong economic value and landscape benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of the ecological restoration method for heavy metal polluted farmland provided by the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The embodiments of the present invention include but are not limited to the following embodiments.

[0029] Example:

[0030] like Figure 1 As shown, the ecological restoration method for heavy metal polluted farmland provided by the present invention comprises the following steps:

[0031] S1. Conduct preliminary analysis on the soil samples of the contaminated cultivated land to be remediated to determine the concentration, type and depth of soil contamination of heavy metals in the soil. Soil sampling is carried out according to a grid system to ensure the representativeness of the samples. Heavy metal analysis uses analytical techniques such as atomic absorption spectroscopy (AAS) or inductively coupled plasma mass spectrometry (ICP-MS), and drilling is used to confirm the depth of soil contamination;

[0032] S2. An impermeable layer is set up under the contaminated cultivated land soil to be repaired. The contaminated soil can be transferred to a pre-built impermeable pool and an impermeable layer is built on the original site. The design and application of the impermeable layer shall comprehensively consider the engineering characteristics, geological conditions and environmental factors, and select appropriate materials and technical means to ensure its long-term stability and effectiveness. After the impermeable layer is built, the contaminated soil will be moved back to the landfill, and a vertical shaft will be installed above the impermeable layer. A water pump will be installed in the vertical shaft to pump out the infiltrated sewage;

[0033] S3. Apply biological control materials to the contaminated cultivated land soil to be repaired. The biological control materials are mixed microbial liquid and mixed microbial culture medium, including some live bacteria and fermentation waste. For details, please refer to the content disclosed in CN106734188B. The biological control materials can be reproduced in the soil environment and can continuously adsorb and complex heavy metals. Moreover, since the charcoal powder and microorganisms used are all biological materials, they can be completely degraded into organic matter and absorbed by plants without causing secondary pollution to the soil.

[0034] S4. Plant pure forests of Cinnamomum burmanii or plant community combinations, and select suitable pure forests of Cinnamomum burmanii or plant community combinations for artificial propagation or planting. Implementing closed management in the restoration of contaminated farmland can prevent the invasion of non-target species and human interference. The planting spacing of Cinnamomum burmanii is 2m×2m, and the planting spacing provides sufficient growth space for the plants. The plant community combination includes at least two plants with heavy metal absorption capabilities, such as vetiver, Indian mustard, centipede grass, etc. The plant community combination should consider the complementarity between plants, including growth cycle, root depth and ecological niche. The above plants are affected by the organic matter produced by the biological control materials in step S3 during their growth, which can promote plant growth, and thus help promote the absorption of heavy metals by plants;

[0035] S5. In the middle of plant growth, spray the mixed solution containing biological control materials as a nutritional supplement during the plant growth period. Apply it to the surface in the form of spraying, and then use small water irrigation to flush the culture solution into the soil layer. If it rains, no watering is required. This method further promotes the adsorption and complexation of heavy metals, and is beneficial to the growth of plants and the absorption and enrichment of heavy metals by plants;

[0036] S6. Collect dead branches and leaves and incinerate them harmlessly. The temperature of harmless incineration is controlled at 900-1350℃ to promote the oxidation and pyrolysis of harmful substances. The residues after incineration are sealed and landfilled. The sealing and landfilling shall comply with environmental protection laws and regulations to ensure that no secondary pollution will be caused.

[0037] S7. The accumulated infiltrated sewage above the anti-seepage layer shall be extracted through the vertical shaft and treated. The sewage treatment shall minimize the generation of secondary pollution.

[0038] A plot of land contaminated by heavy metals was selected nearby, with an area of ​​no less than one mu. The soil was treated according to the above steps for one year (short time due to experimental needs) (2-3 year-old Cinnamomum burmanii trees can be planted in this experiment). Before and after the soil treatment, 6 soil samples were collected at randomly arranged sampling points. At each sampling point, 0-20 cm surface and 100-150 cm deep soil samples were collected in an "S" shape within 5 m2. The soil pH and the effective contents of Cd, Zn, Pb and Cu were analyzed. In addition, a small amount of soil samples were ground and all passed through a 100-mesh sieve to determine the total amount of Cd, Zn, Pb and Cu before and after treatment.

[0039] Analytical method: The effective content of Cd, Zn, Pb and Cu in soil samples was determined after extraction with 0.1 mol.L-1 HCl, and the total amount of samples was digested in a polytetrafluoroethylene crucible using HF-HCIO4-HNO3 mixed acid and then determined. The content of Cd, Zn, Pb and Cu was determined using ICP-OES (Optima5300DV, Perkin-ElmerInstruments, USA). The experimental data are the average of 3 repetitions.

[0040] The following table shows the changes in the effective content of heavy metals in shallow soil before and after treatment

[0041]

[0042] Table 1

[0043] The following table shows the changes in the effective content of heavy metals in deep soil before and after treatment

[0044]

[0045] Table 2

[0046] It can be seen from Table 1 and Table 2 that the use of microbial agents in combination with plants with heavy metal absorption capacity can bioaccumulate and absorb heavy metals, and the adsorption rate is as high as over 75%. It has a strong adsorption effect on heavy metal ions and effectively reduces the heavy metal content in the soil.

[0047] The microbial composite agent used in the present invention includes plant waste, bacteria, fungi and agricultural by-products and other biological materials that have the ability to separate metal ions in the soil. The principle is that heavy metal ions are adsorbed on the surface of biological molecules and accumulated in the body of the organism. Among them, biological adsorption is the combination of extracellular polymers, functional groups, etc. with heavy metal ions; heavy metal ions are combined with certain cell enzymes and transported into the cell and stored in the cell. For example, bacteria are rich in carboxyl anions and phosphate anions, so that the surface of the bacteria has the nature of anions, which is easy to react with metals, so that metals are easily bound to the surface of bacteria. In addition, many studies have also shown that bacteria and their metabolites have a strong complexing ability for dissolved metal ions, which is mainly attributed to the unique chemical composition of their surface, through the two dynamic equilibrium processes of surface adsorption and in vivo accumulation of biological substances. After the death of the bacteria, the bacteria will remain in the soil for a period of time, and after degradation, they can be reused as plants. Therefore, the method of the present invention has the advantages of simple production process, low operating cost, high adsorption rate, high selectivity, and can provide incremental dynamic adsorption of heavy metal ions, and no secondary pollution.

[0048] The dead branches and leaves of Cinnamomum burmannii (young forest) can reach 7-10 tons / year / hectare, especially under high-density planting conditions. The circulating biomass is much greater than that of the currently studied herbaceous plants such as centipede grass. Its dead branches and leaves have a high enrichment coefficient for heavy metals, and the enrichment coefficient for cadmium can reach 44.45 at low concentrations. It also has a certain enrichment effect on other heavy metals. In addition, Cinnamomum burmannii has high economic value and ornamental value.

[0049] The plants with heavy metal absorption ability used in the present invention generally absorb heavy metals in the soil through their root systems and transfer them to the aboveground parts, thereby achieving the removal of heavy metals in the soil. In addition, these plants can utilize the degradation products produced by the microbial composite agent during their growth process to promote the growth of these plants, thereby further improving their absorption and enrichment of heavy metals.

[0050] The present invention utilizes a microbial composite agent to adsorb and complex heavy metals in polluted farmland soil, and uses Cinnamomum burmanii and a plant community with heavy metal absorption capacity in combination, thereby being able to effectively carry out ecological restoration of farmland polluted by heavy metals, and being able to produce high-quality wood with multiple economic values, while having strong ecological benefits, bringing strong economic value and landscape benefits.

Claims

1. A method for ecological restoration of heavy metal-contaminated farmland, characterized in that: The following steps are involved: S1. Conduct preliminary analysis on the soil samples of the contaminated cultivated land to be repaired to determine the concentration, type and depth of heavy metals in the soil; S2. Setting an impermeable layer under the contaminated cultivated land soil to be restored; S3. Apply biological control materials to the contaminated cultivated soil to be remediated; S4. Planting pure forests of Cinnamomum burmannii or plant community combinations; S5. In the middle of plant growth, spray the mixture containing biological control materials; S6. Collect dead branches and leaves, and incinerate them harmlessly. The residues after incineration are sealed and landfilled; S7. Extract the infiltrated sewage above the anti-seepage layer and treat the sewage.

2. The ecological restoration method for heavy metal polluted farmland according to claim 1, characterized in that: The plant community combination includes at least two plants having the ability to absorb heavy metals.

3. The ecological restoration method for heavy metal polluted farmland according to claim 1, characterized in that: The dead branches and fallen leaves are collected at least once a month, and the collection time is appropriately shortened during the leaf-falling period in autumn or winter, while the collection density is increased.

4. The ecological restoration method for heavy metal polluted farmland according to claim 1, characterized in that: The anti-seepage layer is arranged at a depth of 0.5-1 meter below the contaminated soil.

5. The ecological restoration method for heavy metal polluted farmland according to claim 1, characterized in that: The temperature of the harmless incineration treatment is controlled at 900-1350° C. to promote oxidation and pyrolysis of harmful substances.

6. The ecological restoration method for heavy metal polluted farmland according to claim 1, characterized in that: The design and application of the anti-seepage layer must comprehensively consider the engineering characteristics, geological conditions and environmental factors, and select appropriate materials and technical means to ensure its long-term stability and effectiveness.

7. The ecological restoration method for heavy metal polluted farmland according to claim 1, characterized in that: A vertical shaft for sewage discharge is arranged above the anti-seepage layer.

8. The ecological restoration method for heavy metal polluted farmland according to claim 1, characterized in that: The biological control material is a mixed microbial bacterial liquid and a mixed microbial culture medium.

9. The ecological restoration method for heavy metal polluted farmland according to claim 1, characterized in that: The sewage treatment should minimize the generation of secondary pollution.

10. The ecological restoration method for heavy metal polluted farmland according to claim 1, characterized in that: The storage and landfilling shall comply with environmental protection laws and standards to ensure that no secondary pollution will be caused.

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