Method for repairing heavy metal contaminated soil by using plants

Abstract

The invention provides a method for repairing heavy metal contaminated soil by using plants, which comprises the following steps: turning over the heavy metal contaminated soil to remove stones, and paving soil for cultivation on the heavy metal contaminated soil to obtain pretreated heavy metal contaminated soil; mixing the pretreated heavy metal contaminated soil with original soil of the plant planting land, and then performing ploughing and ridging; planting a plurality of plants with an enrichment effect on heavy metals in the plant planting field at intervals; the planted plants are maintained, and the heavy metal content of the soil of the plant planting land is detected till the heavy metal content in the soil meets the requirement. According to the method, the heavy metal contaminated soil is remediated through plants, the heavy metal contaminated soil can be immediately put into use without being remediated, operation is easy, and practicability is high.

Description

Technical Field

[0001] The invention belongs to the technical field of soil remediation and relates to a method for remediating heavy metal contaminated soil. Background Art

[0002] At present, the remediation methods for heavy metal contaminated soil include chemical remediation, physical remediation and biological remediation. Among them, chemical remediation technology is to add chemical modifiers such as phosphate fertilizer or lime to the soil to change the existence form of heavy metals to achieve solidification or stabilization. Physical remediation technology directly removes contaminated soil through excavation, soil turning and replacement. Biological remediation technology is to apply microorganisms with heavy metal tolerance and degradation ability to contaminated soil, and use organic acids, polysaccharides and other substances secreted by microbial metabolic activities to transform or degrade pollutants such as heavy metals, thereby changing the physical and chemical properties of the soil, thereby achieving purification and ecological restoration of heavy metal contaminated soil.

[0003] However, the current methods for remediating heavy metal contaminated soil are mainly aimed at reducing the heavy metal content or heavy metal leaching in the soil. Large-scale excavation, mixing or agent injection and other engineering activities are required at the remediation site. The site disturbance is large, the remediation time is long, the degree of external interference is large, and it is easy to cause secondary pollution and other problems. It is not suitable for soil remediation or soil environmental quality improvement in areas where the soil heavy metal content is slightly exceeded and the ecological environment requirements are high. It is not suitable for the remediation of heavy metal contaminated soil in mountain scenic areas. Summary of the invention

[0004] In order to solve the problems described in the background technology of the current heavy metal contaminated soil remediation method, such as large on-site disturbance, long remediation time, large degree of external interference and easy to cause secondary pollution, the present invention provides a method for remediating heavy metal contaminated soil using plants.

[0005] The method of the present invention comprises:

[0006] The heavy metal contaminated soil is tilled and stones are cleared, and then cultivation soil is laid on the heavy metal contaminated soil to obtain pre-treated heavy metal contaminated soil;

[0007] The pre-treated heavy metal contaminated soil is mixed with the original soil of the plant planting site and then plowed and ridged;

[0008] Plant various heavy metal-accumulating plants at intervals in the plant planting area;

[0009] Maintain the planted plants and test the heavy metal content in the soil where the plants are planted until the heavy metal content in the soil meets the requirements.

[0010] Furthermore, the heavy metal contaminated soil is soil containing at least one heavy metal element among Cd, As, Ni, Pb, Cu, Zn, Cr and Hg exceeding the soil pollution risk control standard.

[0011] Furthermore, the cultivation soil includes green sand and peat soil.

[0012] Furthermore, the laying thickness of the green sand is 5 cm, and the laying thickness of the peat soil is 5 cm.

[0013] Furthermore, the plants are planted in ridges.

[0014] Furthermore, the width of the ridge planting is 2.5-3.5m, the ditch width is 0.5-0.6m, the ridge length is 10-12m, and each plant is planted in one ridge.

[0015] Furthermore, the plants include purple calyx, lucky grass, ophiopogon, broad scale hair ferns, and large flower daylily. Through experiments, it can be known that these five plants can enrich 8 heavy metal elements including Cd, As, Ni, Pb, Cu, Zn, Cr, and Hg, effectively reduce the heavy metal content in the soil, and can adjust the soil pH value to weak alkalinity.

[0016] Furthermore, the planting density of the purple calyx is 25 plants / m 2 The planting density of the lucky grass is 49 plants / m 2 The planting density of Ophiopogon japonicus is 49 plants / m 2 The planting density of Dryopteris latifolia is 25 plants / m 2 The planting density of the large-flowered daylily is 36 plants / m 2 .

[0017] Furthermore, the plant plants to be planted are selected from pure seedling varieties, free of diseases and insect pests, with straight seedling trunks and intact root systems without mechanical damage.

[0018] Furthermore, after the plant is planted and survives, the maintenance and planting cycle is at least 6 months.

[0019] Compared with the prior art, the present invention pre-treats the heavy metal contaminated soil, mixes it with the original soil of the plant planting site, and then plants a variety of plants that have an enrichment effect on heavy metals in the plant planting site at intervals, enriches the heavy metals in the soil through the plants, and uses a variety of plants to repair the composite heavy metal contaminated soil, so as to achieve the purpose of reducing the heavy metal content in the soil and adjusting the soil pH value to weak alkalinity; in addition, the plants can have a good landscape effect, and can be used with trees to create a landscape while repairing the heavy metals. The present invention uses plants to repair the heavy metal contaminated soil, and the repair site does not require large-scale excavation, stirring or agent injection and other engineering activities. The on-site disturbance is small, the repair time is short, it is not easily disturbed by the outside world, and it will not cause secondary pollution, so that the heavy metal contaminated soil can be put into use at the original site, the operation is simple, and the practicability is strong. The present invention is suitable for soil repair or soil environmental quality improvement in areas where the soil heavy metals slightly exceed the standard and have high requirements for the ecological environment, such as scenic spots, and is particularly suitable for the repair of heavy metal contaminated soil in mountain scenic spots. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a graph showing the pH changes between the original cultivation soil and the sixth sampling soil after plant cultivation.

[0021] Figure 2 Figure 2 shows the Cd content of the original cultivated soil and the sixth sampling soil after plant cultivation.

[0022] Figure 3 This is a graph showing the changes in Cd content in the original cultivation soil and the sixth sampling soil after plant cultivation.

[0023] Figure 4 As content in the original cultivated soil and the sixth sampling soil after plant cultivation

[0024] Figure 5 This is a graph showing the changes in As content in the original cultivation soil and the sixth sampling soil after plant cultivation.

[0025] Figure 6 Figure 2 shows the Ni content of the original cultivated soil and the sixth sampling soil after plant cultivation.

[0026] Figure 7 This is a graph showing the changes in Ni content between the original cultivation soil and the sixth sampling soil after plant cultivation.

[0027] Figure 8 Figure 2 shows the Pb content of the original cultivated soil and the sixth sampling soil after plant cultivation.

[0028] Fig. 9 This is a graph showing the changes in Pb content between the original cultivation soil and the sixth sampling soil after plant cultivation.

[0029] Fig.10 Cu content of the original cultivated soil and the sixth sampling soil after plant cultivation

[0030] Fig.11 This is a graph showing the changes in Cu content between the original cultivation soil and the sixth sampling soil after plant cultivation.

[0031] Fig.12 Figure 2 shows the Zn content of the original soil and the sixth sampling soil after plant cultivation.

[0032] Fig.13 This is a graph showing the changes in Zn content between the original cultivation soil and the sixth sampling soil after plant cultivation.

[0033] Fig.14 Figure 2 shows the Cr content of the original cultivated soil and the sixth sampling soil after plant cultivation.

[0034] Fig.15 This is a graph showing the changes in Cr content between the original cultivation soil and the sixth sampling soil after plant cultivation.

[0035] Fig.16 Hg content in the original soil and the sixth sampling soil after plant cultivation

[0036] Fig.17 This is a graph showing the changes in Hg content between the original cultivation soil and the sixth sampling soil after plant cultivation. DETAILED DESCRIPTION

[0037] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0038] A method for using plants to repair heavy metal contaminated soil, the specific steps are as follows:

[0039] Firstly, the heavy metal contaminated soil is tilled and stones are cleared, and then cultivation soil is spread on the heavy metal contaminated soil to obtain pre-treated heavy metal contaminated soil.

[0040] Specifically, heavy metal contaminated soil refers to soil that contains at least one heavy metal element among Cd, As, Ni, Pb, Cu, Zn, Cr, and Hg that exceeds the soil pollution risk control standard; for details, please refer to the relevant content of GB 15618-2018 "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standards (Trial)".

[0041] The soil for cultivation includes green sand and peat soil, among which the thickness of green sand is 5cm and the thickness of peat soil is 5cm.

[0042] Then, the pre-treated heavy metal contaminated soil is mixed with the original soil of the plant planting site and plowed and ridged.

[0043] Next, various plants that have the effect of accumulating heavy metals are planted at intervals in the plant planting area.

[0044] Specifically, the plants are planted in ridges, with a ridge width of 2.5-3.5m, a ditch width of 0.5-0.6m, a ridge length of 10-12m, and one ridge for each plant.

[0045] More specifically, the plants grown include purple calyx, lucky grass, ophiopogon japonicus, broad-leaved tricholoma, and large-flowered daylily.

[0046] More specifically, the planting density of purple calyx is 25 plants / m 2 The planting density of lucky grass is 49 plants / m 2 The planting density of Ophiopogon japonicus is 49 plants / m 2 The planting density of Dryopteris latifolia is 25 plants / m 2 The planting density of large-flowered daylilies is 36 plants / m 2 .

[0047] More specifically, the plant plants to be planted are selected from pure seedling varieties, free of diseases and insect pests, with straight seedling trunks and intact root systems without mechanical damage.

[0048] Finally, the planted plants are maintained and the heavy metal content of the soil where the plants are planted is tested until the heavy metal content in the soil meets the requirements.

[0049] Specifically, after the plant plants are planted and survive, the maintenance and planting cycle is at least 6 months.

[0050] Example

[0051] The experimental site is located in the eastern part of a lake area. 2 The pilot test site is an area with high heavy metal content during the soil detailed investigation stage, and the risk screening value in the "Agricultural Soil Pollution Risk Control Standard" (GB15618-2018) is used as the standard. The cadmium and arsenic concentrations are exceeded at some points.

[0052] Plants to be planted are: Purple Calyx, Lucky Grass, Ophiopogon japonicus, Dryopteris latifolia, and Hemerocallis dasyphylla. The seedlings selected are pure varieties, free of pests and diseases, with straight stems and intact root systems without mechanical damage.

[0053] In early June 2023, the pilot plot will be tilled, the site stones will be cleared, and then 5cm green sand and 5cm biochar peat soil will be spread, mixed with the original soil and tilled again, and ridges will be formed. It is planned to use the ridge planting method for the experiment, with a tentative ridge width of 3m, a ditch width of 0.6m, a ridge length of 10m, a single ridge area of ​​30m2, one ridge for each plant species, and a total of 5 ridges, totaling 150m 2 .

[0054] The plant planting plan is shown in Table 1 below.

[0055] Table 1 Plant planting plan

[0056]

[0057] The physical and chemical properties of the pilot experiment soil are as follows: the proportions of clay, silt and sand in the soil particles are 9.37±0.04%, 68.15±0.23% and 22.48±0.27%, respectively. According to the U.S. soil texture classification standard, the soil belongs to silty loam. The total nitrogen, total phosphorus and total potassium contents in the soil are 0.85±0.04, 0.42±0.05 and 0.73±0.06 g / kg, respectively. The total phosphorus content is higher than the quality standard of cultivated land soil in my country (the total phosphorus content needs to be higher than 0.01%), and the total nitrogen and total potassium contents are lower than the quality standard of cultivated land soil in my country (the total nitrogen content needs to be higher than 0.1%, and the total potassium content needs to be higher than 0.15%), indicating that the soil fertility is insufficient. The specific values ​​of the basic physical and chemical properties of the soil are shown in Table 2 below, and the initial concentrations of heavy metals in the soil are shown in Table 3 below.

[0058] Table 2 Basic physical and chemical properties of the tested soils

[0059]

[0060]

[0061] Table 3 Heavy metal content in each field ridge

[0062] index Lucky grass Dryopteris latifolia Purple Calyx Ophiopogon japonicus Hemerocallis pH 6.45 6.61 6.54 6.46 6.61 Cd(mg / kg) 0.22 0.16 0.25 0.21 0.23 As (mg / kg) 20.0 22.0 19.9 21.0 29.7 Ni(mg / kg) 17.5 18.5 17.5 17.5 25.9 Pb(mg / kg) 24.0 28.3 29.6 24.7 25.0 Cu(mg / kg) 27.5 24.9 26.0 26.0 32.9 Zn(mg / kg) 23.6 23.9 22.1 21.6 24.2 Cr(mg / kg) 69 71 68 68 83 Hg(mg / kg) 61 68 54 50 63

[0063] After the planted plants survived, sampling was carried out six times on July 11, July 27, August 18, September 11, October 10 and November 2, 2023.

[0064] When sampling, plant samples were selected from plants with good growth and similar growth. Three plant samples and three root soil samples were collected from each plant each time, totaling 15 plant samples and 15 soil samples. In addition, no less than 10% of parallel samples were taken, namely, 2 parallel plant samples and 2 parallel soil samples.

[0065] In summary, 17 plant samples and 17 soil samples were collected each time, for a total of 6 times, with a total of 102 plant samples and 102 soil samples. Biomass, Cd, Hg, As, Pb, Cr, Cu, Ni, Zn and pH were measured for plant samples, and Cd, Hg, As, Pb, Cr, Cu, Ni, Zn and pH were measured for soil samples.

[0066] After collecting plant samples, clean the surface impurities with tap water, rinse with deionized water several times and wipe dry. Then put them in a sample bag and fix them at 105℃ for 30 minutes, dry them at 70℃ to constant weight, weigh the biomass (dry weight) of each sample, and crush them with a grinder for testing. The plant index detection methods and instruments are shown in the following table.

[0067] Table 4 Plant index detection basis and main instruments and equipment list

[0068]

[0069] The soil index detection methods and instruments are shown in Table 5. After soil samples were collected, they were naturally air-dried, ground, passed through a 100-mesh sieve, and bagged for later use. The soil pH was measured using a pH meter, and the soil-water ratio was 1:2.5.

[0070] Table 5 Soil index testing basis and main instruments and equipment list

[0071]

[0072]

[0073] The experimental data were statistically analyzed using Excel and plotted using Origin 2018. The bioaccumulation coefficient was used as an evaluation index for the ability of plants to accumulate heavy metals in soil.

[0074] Bio-concentration factor (BCF): The bio-concentration factor is the ratio of the content of a certain heavy metal element in the plant to the content of the corresponding heavy metal element in the soil. The calculation formula is:

[0075] BCF=C 植物 / C 土壤

[0076] In the formula, C 植物 Indicates the concentration of heavy metal elements in the aboveground part or in the plant body, in mg / kg; C 土壤 Indicates the concentration of heavy metal elements in soil, in mg / kg.

[0077] In the following figures, the auspicious grass is abbreviated as JXC, the broad-scaled hair fern is abbreviated as MJ, the purple-calyx is abbreviated as ZE, the Ophiopogon japonicus is abbreviated as MD, and the large-flowered daylily is abbreviated as XC.

[0078] like Figure 1 As shown, the initial soil pH values ​​of Dryopteris japonica, Dryopteris latifolia, Purple Calyx, Ophiopogon japonicus, and Hemerocallis fulva were 6.45, 6.61, 6.54, 6.46, and 6.61, respectively. At the end of the pilot test, the pH values ​​of each field ridge sampled were 7.65, 7.99, 7.78, 7.62, and 7.66, respectively. The soil pH of each field ridge sampled for the sixth time increased compared with the original soil.

[0079] Table 6 shows the biomass (dry weight) data of the five plant species at each sampling time. The biomass reflects the growth status of the plants under heavy metal stress. Due to the influence of seasons and growth cycles, the biomass of the plants fluctuates in different sampling periods.

[0080] Table 6 Statistics of biomass (dry weight) of different plants sampled at each time

[0081]

[0082]

[0083] Figure 2 The trend of Cd content in the original soil and final sampling soil of different plants is shown. Compared with the original soil, the Cd content in the soil around the roots of the final sampling of Lucky Grass, Dryopteris latifolia, Purple Calyx, Ophiopogon japonicus, and Hemerocallis dasyphylla decreased by 19.28%, 14.12%, 29.49%, 19.15%, and 29.17%, respectively, and the Cd content in the soil was lower than the risk screening value in the "Agricultural Land Soil Pollution Risk Control Standard" (GB15618-2018) (0.3 mg / kg when pH ≤ 7.5, 0.6 mg / kg when pH > 7.5). The order of Cd remediation efficiency in soil is: Purple Calyx > Hemerocallis dasyphylla > Lucky Grass ≈ Ophiopogon japonicus > Dryopteris latifolia.

[0084] like Figure 3The Cd content of 5 plants was measured respectively. The Cd content of each plant in the sixth sampling was 0.65±0.54mg / kg for Lucky Grass, 0.75±0.12mg / kg for Dryopteris latifolia, 0.12±0.03mg / kg for Purple Calyx, 0.35±0.07mg / kg for Ophiopogon japonicus, and 0.50±0.30mg / kg for Hemerocallis dasyphylla. Compared with the first sampling, the Cd content of Lucky Grass in the sixth sampling increased by 43.7%, that of Dryopteris latifolia increased by 30.8%, that of Purple Calyx decreased by 36.4%, that of Ophiopogon japonicus increased by 25.0%, and that of Hemerocallis dasyphylla increased by 208.2%. According to the calculation formula of bioaccumulation coefficient, the enrichment coefficient of each plant to Cd can be obtained. The enrichment coefficient of the lucky grass is 4.98±3.57, the enrichment coefficient of the broad-scaled hair ferns is 7.31±0.53, the enrichment coefficient of the purple calyx is 1.57±0.52, the enrichment coefficient of the ophiopogon is 2.27±0.20, and the enrichment coefficient of the large-flowered daylily is 4.63±2.60. The bioaccumulation coefficient of different plants to Cd is ranked from high to low as follows: broad-scaled hair ferns> lucky grass> large-flowered daylily> ophiopogon> purple calyx.

[0085] Figure 4 The trend of As content in the original soil and final sampled soil of different plants is shown. Compared with the original soil, the As content in the soil around the roots of the final sampled auspicious grass, broad-scaled hair fern, purple calyx, ophiopogon japonicus, and large-flowered daylily decreased by 12.78%, 16.20%, 11.67%, 16.84%, and 12.99%, respectively, and the As content in the soil was lower than the risk screening value in the "Agricultural Land Soil Pollution Risk Control Standard" (GB15618-2018) (40 mg / kg when pH ≤ 6.5, 30 mg / kg when 6.5 < pH ≤ 7.5, and 25 mg / kg when pH > 7.5). The order of As remediation efficiency in soil is: ophiopogon japonicus ≈ broad-scaled hair fern > large-flowered daylily ≈ auspicious grass > purple calyx.

[0086] like Figure 5The As content of 5 kinds of plants was measured respectively. The As content of each plant in the sixth sampling was 0.29±0.05mg / kg for Lucky Grass, 0.21±0.07mg / kg for Dryopteris latifolia, 0.18±0.03mg / kg for Purple Calyx, 0.26±0.07mg / kg for Ophiopogon japonicus, and 0.18±0.09mg / kg for Hemerocallis dasyphylla. Compared with the first sampling, the As content of Lucky Grass decreased by 4.4%, that of Dryopteris latifolia decreased by 47.5%, that of Purple Calyx decreased by 34.9%, that of Ophiopogon japonicus increased by 48.1%, and that of Hemerocallis dasyphylla decreased by 40.2%. According to the calculation formula of bioaccumulation coefficient, the enrichment coefficient of each plant to As can be obtained. The enrichment coefficient of the lucky grass is 0.04±0.01, the enrichment coefficient of the broad-scaled hair fern is 0.03±0.01, the enrichment coefficient of the purple calyx is 0.02±0.01, the enrichment coefficient of the ophiopogon is 0.03±0.01, and the enrichment coefficient of the large-flowered daylily is 0.02±0.01. The order of the bioaccumulation coefficient of As of different plants from high to low is: lucky grass> broad-scaled hair fern=ophiopogon> large-flowered daylily=purple calyx.

[0087] Figure 6 The changing trend of Ni content in the original soil and final sampling soil of different plants is shown. Compared with the original soil, the Ni content of the soil around the roots of the final sampling of Lucky Grass, Dryopteris latifolia, Purple Calyx, Ophiopogon japonicus, and Daylily of the Big Flower decreased by 13.69%, 20.05%, 18.16%, 12.60%, and 15.83%, respectively, and the Ni content in the soil was lower than the risk screening value in the "Standard for Risk Control of Soil Pollution in Agricultural Land" (GB15618-2018) (60 mg / kg when pH≤5.5, 70 mg / kg when 5.5<pH≤6.5, 100 mg / kg when 6.5<pH≤7.5, and 190 mg / kg when pH>7.5). The order of Ni remediation efficiency in the soil is: Dryopteris latifolia>Purple Calyx>Daylily of the Big Flower>Lucky Grass>Ophiopogon japonicus.

[0088] like Figure 7The Ni content of 5 plants was measured respectively. The Ni content of each plant in the sixth sampling was 5.33±0.58mg / kg for Lucky Grass, 20.00±7.00mg / kg for Dryopteris scaly, 8.00±3.00mg / kg for Purple Calyx, 4.67±2.08mg / kg for Ophiopogon japonicus, and 7.00±0.01mg / kg for Hemerocallis dasyphylla. According to the calculation formula of bioaccumulation coefficient, the enrichment coefficient of Ni of each plant can be obtained. The enrichment coefficient of Lucky Grass is 0.26±0.02, the enrichment coefficient of Dryopteris scaly is 0.89±0.32, the enrichment coefficient of Purple Calyx is 0.34±0.16, the enrichment coefficient of Ophiopogon japonicus is 0.24±0.17, and the enrichment coefficient of Hemerocallis dasyphylla is 0.29±0.01. The ranking of Ni bioaccumulation coefficients of different plants from high to low is: Dryopteris scaly>Purple Calyx>Hemerocallis dasyphylla>Lucky Grass>Ophiopogon japonicus.

[0089] Figure 8 The trend of Pb content in the original soil and final sampling soil of different plants is shown. Compared with the original soil, the Pb content in the soil around the roots of the final sampling of Lucky Grass, Dryopteris latifolia, Purple Calyx, Ophiopogon japonicus, and Hemerocallis dasyphylla decreased by 12.27%, 17.99%, 17.65%, 15.10%, and 19.61%, respectively, and the Pb content in the soil was lower than the risk screening value in the "Standard for Risk Control of Soil Pollution in Agricultural Land" (GB15618-2018) (70 mg / kg when pH ≤ 5.5, 90 mg / kg when 5.5 < pH ≤ 6.5, 120 mg / kg when 6.5 < pH ≤ 7.5, and 170 mg / kg when pH > 7.5). The order of Pb remediation efficiency in soil is: Hemerocallis dasyphylla > Dryopteris latifolia ≈ Purple Calyx > Ophiopogon japonicus > Lucky Grass.

[0090] like Fig. 9The Pb content of 5 kinds of plants was measured respectively. The Pb content of each plant in the sixth sampling was 1.27±0.59mg / kg for Lucky Grass, 1.33±0.45mg / kg for Dryopteris scalyx, 1.07±0.15mg / kg for Purple Calyx, 1.07±0.12mg / kg for Ophiopogon japonicus, and 0.57±0.15mg / kg for Hemerocallis dasyphylla. Compared with the first sampling, the Pb content of Lucky Grass in the sixth sampling increased by 54.0%, that of Dryopteris scalyx decreased by 42.0%, that of Purple Calyx decreased by 18.5%, that of Ophiopogon japonicus increased by 53.1%, and that of Hemerocallis dasyphylla decreased by 70.2%. According to the calculation formula of bioaccumulation coefficient, the enrichment coefficient of each plant for Pb can be obtained. The enrichment coefficient of lucky grass is 0.10±0.07, the enrichment coefficient of broad-scaled hair fern is 0.15±0.09, the enrichment coefficient of purple calyx is 0.09±0.02, the enrichment coefficient of ophiopogon is 0.09±0.02, and the enrichment coefficient of large-flowered daylily is 0.07±0.06. The bioaccumulation coefficient of different plants for Pb is ranked from high to low as follows: broad-scaled hair fern> ophiopogon=purple calyx>large-flowered daylily>lucky grass.

[0091] Fig.10 The change trend of Cu content in the original soil and final sampling soil of different plants is shown. Compared with the original soil, the Cu content of the soil around the roots of the final sampling of Lucky Grass, Dryopteris latifolia, Purple Calyx, Ophiopogon japonicus, and Hemerocallis grandiflora decreased by 19.68%, 15.05%, 12.98%, 13.77%, and 17.43%, respectively, and the Cu content in the soil was lower than the risk screening value in the "Agricultural Land Soil Pollution Risk Control Standard" (GB15618-2018) (50 mg / kg when pH ≤ 6.5, 100 mg / kg when pH > 6.5). The Cu remediation efficiency in the soil is ranked as follows: Lucky Grass > Hemerocallis grandiflora > Dryopteris latifolia > Ophiopogon japonicus > Purple Calyx.

[0092] like Fig.11The Cu content of 5 plants was measured respectively. The Cu content of each plant in the sixth sampling was 20.33±6.11mg / kg for Lucky Grass, 7.33±0.58mg / kg for Dryopteris scaly, 11.33±1.53mg / kg for Purple Calyx, 17.33±4.93mg / kg for Ophiopogon japonicus, and 4.67±2.08mg / kg for Hemerocallis dasyphylla. Compared with the first sampling, the Cu content of Lucky Grass increased by 10.9%, that of Dryopteris scaly, decreased by 51.1%, that of Purple Calyx, decreased by 15.0%, that of Ophiopogon japonicus, and that of Hemerocallis dasyphylla decreased by 23.8%, and that of Hemerocallis dasyphylla decreased by 75.0%. According to the calculation formula of bioaccumulation coefficient, the enrichment coefficient of each plant to Cu can be obtained. The enrichment coefficient of lucky grass is 1.47±0.34, the enrichment coefficient of broad-scaled hair fern is 0.73±0.41, the enrichment coefficient of purple calyx is 1.16±0.74, the enrichment coefficient of ophiopogon is 1.57±0.84, and the enrichment coefficient of large-flowered daylily is 0.35±0.23. The bioaccumulation coefficient of different plants to Cu is ranked from high to low as follows: ophiopogon> lucky grass> purple calyx> broad-scaled hair fern> large-flowered daylily.

[0093] Fig.12 The trend of Zn content in the original soil and final sampled soil of different plants is shown. Compared with the original soil, the Zn content in the soil around the roots of the final sampled auspicious grass, broad-scaled dry pteridophyte, purple calyx, ophiopogon japonicus, and large-flowered daylily decreased by 15.03%, 15.95%, 15.23%, 11.60%, and 18.15%, respectively. And the Zn content in the soil is lower than the risk screening value in the "Agricultural Land Soil Pollution Risk Control Standard" (GB15618-2018) (200 mg / kg when pH ≤ 6.5, 250 mg / kg when 6.5 < pH ≤ 7.5, and 300 mg / kg when pH > 7.5). The Zn remediation efficiency in the soil is ranked as follows: large-flowered daylily > broad-scaled dry pteridophyte > purple calyx ≈ auspicious grass > ophiopogon japonicus.

[0094] like Fig.13The Zn content of 5 kinds of plants was measured respectively. The Zn content of each plant in the sixth sampling was 30.33±3.06mg / kg for Lucky Grass, 31.33±4.62mg / kg for Dryopteris scaly, 29.33±1.53mg / kg for Purple Calyx, 40.00±3.60mg / kg for Ophiopogon japonicus, and 36.33±3.22mg / kg for Hemerocallis dasyphylla. Compared with the first sampling, the Zn content of Lucky Grass in the sixth sampling decreased by 43.1%, that of Dryopteris scaly decreased by 30.4%, that of Purple Calyx decreased by 3.3%, that of Ophiopogon japonicus increased by 0.8%, and that of Hemerocallis dasyphylla did not change significantly. According to the calculation formula of bioaccumulation coefficient, the enrichment coefficient of each plant to Zn can be obtained. The enrichment coefficient of lucky grass is 0.52±0.08, the enrichment coefficient of broad-scaled hair fern is 0.53±0.05, the enrichment coefficient of purple calyx is 0.51±0.06, the enrichment coefficient of ophiopogon is 0.67±0.10, and the enrichment coefficient of large-flowered daylily is 0.54±0.08. The bioaccumulation coefficient of Zn of different plants is ranked from high to low as follows: ophiopogon> large-flowered daylily> broad-scaled hair fern> lucky grass> purple calyx.

[0095] Fig.14 The changing trend of Cr content in the original soil and final sampled soil of different plants is shown. Compared with the original soil, the Cr content in the soil around the roots of the final sampled auspicious grass, broad-scaled hair fern, purple calyx, ophiopogon japonicus, and large-flowered daylily decreased by 17.52%, 13.81%, 15.37%, 17.10%, and 14.36%, respectively, and the Cr content in the soil was lower than the risk screening value in the "Agricultural Land Soil Pollution Risk Control Standard" (GB15618-2018) (150 mg / kg when pH ≤ 6.5, 200 mg / kg when 6.5 < pH ≤ 7.5, and 250 mg / kg when pH > 7.5). The order of Cr remediation efficiency in soil is: auspicious grass ≈ ophiopogon japonicus > purple calyx > large-flowered daylily > broad-scaled hair fern.

[0096] like Fig.15The Cr content of 5 kinds of plants was measured respectively. The Cr content of each plant in the sixth sampling was 13.33±3.22mg / kg for Lucky Grass, 49.00±7.81mg / kg for Dryopteris latifolia, 20.00±5.66mg / kg for Purple Calyx, 19.00±2.65mg / kg for Ophiopogon japonicus, and 20.00±0.01mg / kg for Daylily. Compared with the first sampling, Cr was not detected in the 5 kinds of plants. The plants in the sixth sampling had obvious absorption and enrichment of Cr. According to the calculation formula of bioaccumulation coefficient, the enrichment coefficient of Cr for each plant can be obtained. The enrichment coefficient of Lucky Grass is 0.27±0.07, the enrichment coefficient of Dryopteris latifolia is 0.84±0.10, the enrichment coefficient of Purple Calyx is 0.27±0.25, the enrichment coefficient of Ophiopogon japonicus is 0.48±0.14, and the enrichment coefficient of Daylily latifolia is 0.34±0.01. The bioaccumulation coefficient of Cr in different plants is ranked from high to low as follows: Dryopteris latifolia > Ophiopogon japonicus > Hemerocallis fulva > Lucky grass = Purple calyx.

[0097] Fig.16 The changing trend of Hg content in the original soil and final sampled soil of different plants is shown. Compared with the original soil, the Hg content in the soil around the roots of the final sampled auspicious grass, broad-scaled hair fern, purple calyx, ophiopogon japonicus, and large-flowered daylily decreased by 17.35%, 18.69%, 15.16%, 14.31%, and 23.76%, respectively. The Hg content of each soil was low and had a large volatility. The Hg content in the soil was lower than the risk screening value in the "Agricultural Land Soil Pollution Risk Control Standard" (GB15618-2018) (1.3 mg / kg when pH ≤ 5.5, 1.8 mg / kg when 5.5 < pH ≤ 6.5, 2.4 mg / kg when 6.5 < pH ≤ 7.5, and 3.4 mg / kg when pH > 7.5). The Hg remediation efficiency in the soil is ranked as follows: auspicious grass > ophiopogon japonicus > broad-scaled hair fern > large-flowered daylily > purple calyx.

[0098] like Fig.17The Hg content of 5 kinds of plants was measured respectively. The Hg content of each plant in the sixth sampling was 0.02±0.008mg / kg for Lucky Grass, 0.02±0.008mg / kg for Dryopteris scaly, 0.01±0.007mg / kg for Purple Calyx, 0.01±0.006mg / kg for Ophiopogon japonicus, and 0.01±0.001mg / kg for Hemerocallis dasyphylla. Compared with the first sampling, the Hg content of Lucky Grass in the sixth sampling increased by 3.5%, the Hg content of Dryopteris scaly decreased by 33.7%, the Hg content of Purple Calyx decreased by 47.5%, the Hg content of Ophiopogon japonicus decreased by 12.1%, and the Hg content of Hemerocallis dasyphylla decreased by 65.5%. According to the calculation formula of bioaccumulation coefficient, the enrichment coefficient of each plant to Hg can be obtained. The enrichment coefficient of the lucky grass is 0.26±0.16, the enrichment coefficient of the broad-scaled hair fern is 0.20±0.02, the enrichment coefficient of the purple calyx is 0.05±0.03, the enrichment coefficient of the ophiopogon is 0.21±0.21, and the enrichment coefficient of the large-flowered daylily is 0.04±0.03. The bioaccumulation coefficient of different plants to Hg is ranked from high to low as follows: lucky grass> ophiopogon> broad-scaled hair fern> purple calyx> large-flowered daylily.

[0099] Through the above experiments, the heavy metal contaminated soil was repaired by planting five plants, namely, auspicious grass, broad-scaled hair fern, purple calyx, ophiopogon japonicus, and large-flowered daylily, and the conclusions were as follows:

[0100] 1. Plants’ ability to accumulate Cd in soil

[0101] The five plants all had good adsorption effects on Cd in the soil of the pilot site, with enrichment coefficients exceeding 1, and the soil Cd content decreased by 14.12%-29.49%. The order of reduction of Cd content in the soil was: purple calyx> big flower daylily> lucky grass ≈ ophiopogon> broad scale dryopsis, and the order of plant enrichment ability for Cd was: broad scale dryopsis> lucky grass> big flower daylily> ophiopogon> purple calyx. All of them are ideal soil Cd remediation plants.

[0102] 2. Plants’ ability to accumulate As in soil

[0103] The As content in the soil of the five plants generally decreased, and the order of the reduction of soil As content was Ophiopogon japonicus ≈ Dryopteris latifolia > Hemerocallis dasyphylla ≈ Aeschynophora chinensis > Purple Calyx. From the soil data, Ophiopogon japonicus and Dryopteris latifolia had better restoration effects. From the perspective of plant enrichment coefficient, the adsorption effect of the five plants on As was not strong. From the comparison of the sixth sampling and the first sampling data, Ophiopogon japonicus had better As enrichment.

[0104] 3. Plants’ ability to accumulate Ni in soil

[0105] The five plants all had good adsorption effects on Ni in the soil of the pilot site, among which Dryopteris latifolia and Purple Calyx had stronger Ni enrichment abilities. The Ni bioaccumulation coefficients of the five plants were ranked from high to low as follows: Dryopteris latifolia > Purple Calyx > Hemerocallis fulva > Herba Lycoris radiata > Ophiopogon japonicus.

[0106] 4. Plants’ ability to accumulate Pb in soil

[0107] The Pb content in the soil of each plant field ridge decreased by more than 5%, and the reduction ratio was as follows: Hemerocallis fulva > Dryopteris latifolia ≈ Purple-calyx > Ophiopogon japonicus > Herba Lycoris radiata. However, the five plants had average Pb enrichment ability, and the enrichment coefficients were all less than 0.2, among which Dryopteris latifolia had the highest enrichment coefficient of 0.15±0.09.

[0108] 5. Plants’ ability to accumulate Cu in soil

[0109] The Cu content in the soil of the five plants decreased to a certain extent, and the Cu remediation efficiency in the soil was ranked as follows: Lucky Grass > Hemerocallis dasyphylla > Dryopteris latifolia > Ophiopogon japonicus > Purple Calyx.

[0110] 6. Plants’ ability to accumulate Zn in soil

[0111] The Zn content in the soil of the five plants generally decreased, but judging from the enrichment coefficient and the sixth sampling data, only the Zn content of the sixth sampling of Ophiopogon japonicus was positive compared with the first sampling and only increased by 0.8%, and the enrichment coefficient reached 0.67±0.10, which had a certain enrichment effect on Zn.

[0112] 7. Plants’ ability to accumulate Cr in soil

[0113] The Cr content in the soil of the five plants generally decreased, and the Cr enrichment ability of plants from high to low was Dryopteris latifolia, Ophiopogon japonicus, Hemerocallis fulva, Glechoma longituba, and Purple Calyx.

[0114] 8. Plants’ ability to accumulate Hg in soil

[0115] The reduction ratio of Hg content in the soil of each plant field ridge is from high to low: acacia > Ophiopogon japonicus > Dryopteris latifolia > Hemerocallis fulva > Purple calyx. As the Hg content in the soil is relatively low, the measured data fluctuates greatly.

[0116] In addition, it is recommended that the five species of plants be planted according to the pilot test planting density, planting operation and maintenance methods during the project implementation phase, that is, the planting density is 49 plants / m 2 、Dryopteris latifolia 25 plants / m 2 、Purple calyx 25 plants / m 2 、Ophiopogon japonicus 49 plants / m 2 、Hemerocallis dasyphylla 36 plants / m 2The plant enrichment balance time is within 6 months. It is recommended that the follow-up monitoring period of the later project be controlled to half a year or more.

[0117] In the pilot experiment site, five plant species, including grass sedge, dryopteris latifolia, purple calyx, ophiopogon japonicus, and daylily, all showed good Cd adsorption and enrichment capabilities and can be selected as soil Cd remediation plants. Considering the landscape effect comprehensively, it is recommended that daylily and purple calyx be planted in key viewing areas.

[0118] Based on a comprehensive comparison of the changes in soil As content, As enrichment coefficient, and As changes in plants sampled multiple times, it is recommended that Ophiopogon japonicus or Dryopteris latifolia be used as soil As remediation plants.

[0119] Five plants, including lucky grass, broad-scaled fern, purple calyx, Ophiopogon japonicus, and large-flowered daylily, are shade-loving or shade-tolerant plants and can be used for subsequent project implementation.

[0120] In summary, Lucky Grass, Dryopteris latifolia, Purple Calyx, Ophiopogon japonicus, and Daylily lily can be used as preferred plants for heavy metal remediation. In terms of planting distribution, the restoration effect and landscape effect should be comprehensively considered, and they can be arranged in different areas according to the conditions of different locations.

[0121] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for remediating heavy metal contaminated soil using plants, characterized in that: include: The heavy metal contaminated soil is tilled and stones are cleared, and then cultivation soil is laid on the heavy metal contaminated soil to obtain pre-treated heavy metal contaminated soil; The pre-treated heavy metal contaminated soil is mixed with the original soil of the plant planting site and then plowed and ridged; Plant various heavy metal-accumulating plants at intervals in the plant planting area; The planted plants are maintained and the heavy metal content in the soil where the plants are planted is tested until the heavy metal content in the soil decreases.

2. The method for remediating heavy metal contaminated soil by using plants according to claim 1, characterized in that: The heavy metal contaminated soil is soil containing at least one heavy metal element among Cd, As, Ni, Pb, Cu, Zn, Cr, and Hg that exceeds the soil pollution risk control standard.

3. The method for remediating heavy metal contaminated soil by using plants according to claim 2, characterized in that: The cultivation soil includes green sand and peat soil.

4. The method for remediating heavy metal contaminated soil by using plants according to claim 1, characterized in that: The laying thickness of the green sand is 5 cm, and the laying thickness of the peat soil is 5 cm.

5. The method for remediating heavy metal contaminated soil by using plants according to claim 4, characterized in that: The plants are planted in ridges.

6. The method for remediating heavy metal contaminated soil by using plants according to claim 5, characterized in that: The width of the ridge planting is 2.5-3.5m, the furrow width is 0.5-0.6m, the ridge length is 10-12m, and each plant is planted in one ridge.

7. A method for remediating heavy metal contaminated soil by using plants according to claim 5 or 6, characterized in that: The plants include purple calyx, lucky grass, ophiopogon, broad-leaved tricholoma, and large-flowered daylily.

8. The method for remediating heavy metal contaminated soil by using plants according to claim 7, characterized in that: The planting density of the purple calyx is 25 plants / m 2 The planting density of the lucky grass is 49 plants / m 2 The planting density of Ophiopogon japonicus is 49 plants / m 2 The planting density of Dryopteris latifolia is 25 plants / m 2 The planting density of the large-flowered daylily is 36 plants / m 2 .

9. The method for remediating heavy metal contaminated soil by using plants according to claim 8, characterized in that: The plant plants to be planted are selected from pure seedling varieties, free of diseases and insect pests, with straight seedling trunks, and intact root systems without mechanical damage.

10. The method for remediating heavy metal contaminated soil by using plants according to claim 9, characterized in that: After the plant is planted and survives, the maintenance and planting cycle is at least 6 months.

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