CN101391261A - A method for remediating heavy metal-contaminated soil by using the enrichment plant S. - Google Patents

Abstract

The present invention relates to the phytoremediation technology of heavy metal-contaminated soil, specifically a method for repairing heavy metal-contaminated soil by using the enriched plant S. chinensis, planting S. sylvestris on the soil containing pollutant cadmium, through the root system of S. ts. Absorb cadmium in the polluted soil and transfer it to the aboveground organs. When the plant grows to the maximum aboveground biomass, the aboveground organs of the plant are removed from the polluted soil, so as to achieve the purpose of removing the pollutant cadmium in the soil. The present invention utilizes the enrichment plant S. japonica to control cadmium-contaminated soil, and has the advantages of low cost, strong operability, no damage to the physical and chemical properties of the soil, no secondary pollution, and good effects on preventing wind erosion and water erosion of the polluted soil, etc. .

Description

A method for remediating heavy metal-contaminated soil by using the enrichment plant S.

technical field

The invention relates to a phytoremediation technology for heavy metal-contaminated soil, in particular to a method for remediating heavy-metal-contaminated soil by using the enriched plant Distilleria chinensis.

Background technique

There are usually two ways for heavy metals to pollute soil: one is the environmental pollution caused by metal mining activities. Serious soil; heavy metal polluted soil caused by leaching and other reasons during the mining waste rock stacking process; soil pollution caused by mine wastewater containing high concentrations of heavy metals, etc. The second is heavy metal-contaminated soil caused by industrial sewage irrigating farmland. The representative example is the earliest discovered, large-scale, and seriously polluted soil in Zhangshi Irrigation District, Shenyang. The main heavy metal pollutant is Cd (Document 1: Wu Yan Yu, Chen Tao, Zhang Xuexun. 1986. Research on the Pollution Ecology of Cadmium in Zhangshi Irrigation District, Shenyang. See: Edited by Gao Zhengmin, Ecological Research on Soil-Plant System Pollution. 295-301). Cd is a toxic substance in the environment and a non-essential element for organisms. Its compounds are highly toxic and highly accumulative. High concentrations of cadmium have teratogenic, mutagenic and carcinogenic effects on most animals. Therefore, cadmium polluted soil Governance is urgently needed.

Countries all over the world attach great importance to soil heavy metal pollution and have adopted various repair methods, such as solidification technology to eliminate the toxicity of heavy metals, vitrification technology, and electrodynamic repair technology to control volatile heavy metals. However, these technologies have great damage to polluted sites, expensive treatment costs, and new environmental problems such as transportation, storage, and backfilling. It is difficult to apply to the less polluted soil. Therefore, people place their hopes on phytoremediation technology, an innovative technology with low cost and good restoration effect (Document 2: Edited by Zhou Qixing, Wei Shuhe, Zhang Qianru, etc. Ecological Restoration. China Environmental Science Press. 2006).

Phytoremediation (Phytoremediation) is an environmental pollution control technology developed in the past 20 years. It widely uses the metabolic activities of green plants to fix, degrade, extract and volatilize pollutants in the environment, just like a "green clean factory" that will pollute Substances are processed into substances that can be directly removed or transformed into substances with low toxicity or even non-toxicity, so as to thoroughly control the polluted environment; it has the functions of not causing secondary pollution of groundwater, making sustainable use of polluted soil and water and beautifying the environment, etc. characteristics, so it is also a very ideal green restoration technology. The scope of application of phytoremediation is quite wide, involving almost all aspects of polluted environment treatment. It can not only purify air and water, but also remove pollutants in soil (Document 3: Zhou Qixing, Song Yufang et al. Principles and Methods of Contaminated Soil Restoration. Science Press, 2004).

Phytoremediation of heavy metal-contaminated soil refers to the use of plants and their rhizosphere microbial system to extract, volatilize and transform and fix heavy metals in contaminated soil, or to stabilize heavy metals at the polluted site to prevent them from causing greater pollution to groundwater and the surrounding environment . Phytoremediation mainly includes four modes of action: Phytoextrtion, Phytovoltiliztion, Rhizofiltrtion and Phytostiliztion. Among them, research on plant extraction has attracted increasing attention [Document 4: Chaney R.L., Malik M., Li Y.M., et al.1997, Phytomediation of soil metals. Current Opinions in Biotechnology.8: 279～284; Literature 5: Wong M.H., 2003, Ecological restoration of mine degraded soils, with emphasis on metal contaminated soils. Chemosphere. 50: 775-780]. Plant extraction, that is, using heavy metal enrichment plants (especially hyperaccumulator plants) to overabsorb one or several heavy metals from polluted soil, and transfer and store them to the aboveground organs such as stems and leaves, and then the whole plant ( including part of the roots) were harvested and treated intensively, and then planted continuously in order to reduce the concentration of heavy metals in the soil to an acceptable level.

The main characteristics (measures) of hyperaccumulator plants are:

1) The content of heavy metals in the aerial parts of plants (mainly stems and leaves) exceeds a certain critical content, such as Zn10000mg/kg, Cd100mg/kg, Au1mg/kg, Pb, Cu, Ni, Co are all 1000mg/kg, etc. ( Document 6: Baker AJM, Brooks RR. Terrestrial higher plants which hyperaccumulate metallic elements-a review of their distribution, ecology and phytochemistry. Biorecovery 1989, 1:81～126);

2) The heavy metal content in the aerial part of the plant is greater than that in the root;

3) The growth of the plant does not show obvious symptoms of toxicity;

4) The aboveground biomass of plants (the sum of dry weight of stems, leaves and inflorescences) did not decrease significantly compared with the control without metal addition;

5) The enrichment coefficient of the aboveground part of the plant (the average value of stems, leaves and inflorescences) for a certain heavy metal is greater than 1, at least when the heavy metal content in the soil is equivalent to the enrichment/accumulation level that hyperaccumulator/hyperaccumulation plants should achieve , the enrichment coefficient of the aboveground part (mainly stems or leaves) is greater than 1 (for example, the heavy metal content in the soil is Zn 10000mg/kg, Cd 100mg/kg, Au 1mg/kg, Pb, Cu, Ni, Co are all 1000mg/kg );

Enrichment coefficient AC = heavy metal content in aboveground parts of plants/heavy metal content in soil;

Enrichment plants are measured as follows:

1) The heavy metal content in the aerial part of the plant is greater than that in the root;

2) The aboveground biomass of plants (the sum of dry weight of stems, leaves and inflorescences) did not decrease significantly compared with the control without adding heavy metals;

3) The growth of the plant does not show obvious symptoms of toxicity;

4) The enrichment coefficient of certain heavy metals in the aerial parts of plants (the average value of stems, leaves and inflorescences) is greater than 1, but the standard of heavy metal content in the aerial parts of plants (stems and leaves) exceeds a certain critical content.

5) After the concentration gradient test, if the plant still does not reach the standard of hyperaccumulator plants, it is considered as an enrichment plant (Document 7: Ma LQ, Komar KM, Tu C, et al. A fern thhyperaccumulates arsenic. Nature 2001; 409: 579; Literature 8: Wei S, Zhou Q, Koval PV. Flowering stage characteristics of cadmium hyperaccumulator Solanum nigrum L. and their significance to phytomediation. Science of the Total Environment. 2006, 369 (2006) 441-446).

Contents of the invention

The object of the present invention is to provide a method for treating cadmium-contaminated soil with low cost, strong operability, no damage to soil physical and chemical properties, no secondary pollution, and good effect on preventing polluted soil from wind erosion and water erosion.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A method for repairing heavy metal-contaminated soil by using the enrichment plant S. chinensis, planting S. sylvestris on the soil containing pollutant cadmium, absorbing a large amount of cadmium in the polluted soil through the root system of S. sylvestris, and transferring it to the above-ground organs , when the plant grows to the maximum aboveground biomass, the aboveground organs of the plant are removed from the polluted soil, so as to achieve the purpose of removing the pollutant cadmium in the soil.

When the aboveground biomass is the largest, it refers to the period from the flowering stage to the mature stage of the plant, and the mature stage refers to the period from the growth of the small white wine grass to the maturity of the seeds. When the plant grows to the maximum aboveground biomass, the whole plant can be removed from the polluted soil, so as to achieve the purpose of removing the pollutant cadmium in the soil.

To plant small white winegrass on the soil containing pollutant cadmium, open-air cultivation can be adopted, and water should be watered according to the soil water shortage to keep the soil water content at 40-95% of the field water holding capacity.

The planting of the chrysanthemum refers to directly sowing the seeds of the chrysanthemum on the soil or transplanting the chrysanthemum at the seedling stage on the soil containing the pollutant cadmium.

When planting white wine grass on the soil containing pollutant cadmium, the method of multiple cropping can be adopted, that is, when the first crop of small wine grass grows to the maximum biomass of the aboveground part, the aboveground organs of the plant are removed from the polluted soil, and then repeated The above process, until the final remediation of cadmium-contaminated soil; in this way, a large amount of cadmium can be taken away from the soil, so as to achieve the purpose of quickly and completely removing polluted heavy metals in the soil.

The cadmium content in the soil containing pollutant cadmium is 0.3-240mg/kg.

The present invention utilizes the enrichment plant S. japonica to control cadmium-contaminated soil, and has the advantages of low cost, strong operability, no damage to the physical and chemical properties of the soil, no secondary pollution, and good effects on preventing wind erosion and water erosion of the polluted soil, etc. . Experiments have proved that the plant chrysanthemum is a kind of enrichment plant, and the present invention utilizes the super-enrichment and extraction of cadmium metal by chrysanthemum, and by planting this enrichment plant on cadmium-contaminated soil, the polluted soil can be repaired, which is the same as Compared with the prior art, it does not destroy the soil structure and fertilize the soil at the polluted site, and greatly reduces the restoration cost.

Description of drawings

Figure 1 shows the biomass of aboveland grass in Xiaobaijiu under different Cd concentration treatment conditions.

Detailed ways

Embodiment 1 Pot concentration gradient test

The test site is located in the Shenyang Ecological Experiment Station of the Chinese Academy of Sciences. The geographical location is 123°41' east longitude, 41°31' north latitude, and an altitude of about 50m. There is no pollution source around the test station, and it is an uncontaminated area of heavy metals. The station is located in the center of the southern part of the Songliao Plain, about 35km away from the urban area of Shenyang. The amount is 520～544KJ/cm ² , the frost-free period is 127～164 days, and the annual precipitation is 650～700mm. The pot test was collected from the topsoil (0-20cm) of the station, and the soil type was meadow brown soil.

A total of 6 treatments were set up in the test, which were the control (CK, no Cd added) and 5 different Cd dosing concentration experiments, Cd dosing concentration: 10mg/kg (T1), 25mg/kg (T2), 50mg /kg(T3), 100mg/kg(T4), 200mg/kg(T5), the form of the added heavy metal is CdCl ₂ 2.5H ₂ O, which is an analytically pure reagent, and it is added to the soil in solid state and mixed well. Equilibrate for two weeks before use.

The experiment started in spring, and the seedlings of Liquor chinensis were transplanted from the Shenyang Ecological Station, with 4 plants per pot and repeated 3 times. Outdoor cultivation. According to the lack of water in the pot, water it irregularly (Cd was not detected in the water), so that the soil water content is often kept at about 80% of the field water capacity. Harvest when the plants are mature.

The test results are as follows:

Figure 1 shows the aboveground biomass of Liquor Grass under different Cd concentrations. Significant difference analysis showed that, compared with the control, the biomass of the aboveground parts did not decrease (p<0.05), showing a strong However, when the Cd pollution level is very high, that is, when the dosage concentration is 200mg/kg, the biomass of the aboveground part decreases (p<0.05), indicating that although the tolerance of the small winegrass to Cd is strong, it is still There is a certain limit, that is to say, when the soil Cd concentration is greater than 200mg/kg, the growth of plants will be inhibited.

The measurement results of Cd content in plants showed that (Table 1), when the concentration of Cd in the soil was 10, 25 mg/kg, the enrichment lines in the upper part of the Xiaobaijiu grassland were all greater than 1, and the transfer coefficient was also greater than 1, showing the enrichment of plants. fundamental feature. When the concentration of Cd in the soil is 50mg/kg, the enrichment coefficient of the shoot is greater than 1. Although the Cd content in the leaves or stems of plants is greater than 100 mg/kg when the concentration of Cd is 100, 200 mg/kg, the content in the shoots is less than the content in the roots, and the enrichment coefficient of the shoots is also less than 1, and the Cd When the dosage concentration was 200mg/kg, the aboveground biomass of plants decreased significantly.

Therefore, considering the tolerance and enrichment characteristics of plants to Cd, Liquor chinensis does not meet the standard of hyperaccumulator plants, but is only a Cd-enrichment plant.

Table 1 The enrichment characteristics of cadmium in Xiaobaijiucao (mg/kg)

Handling Roots Stems Leaves Inflorescences Aboveground TF AC

T1 13.9 29.7 44.5 18.0 27.8 2.00 2.81

T2 46.6 50.2 59.7 21.1 47.5 1.02 1.92

T3 79.0 77.9 93.4 47.5 70.4 0.89 1.39

T4 166.1 86.6 114.7 48.5 80.0 0.48 0.79

T5 186.8 199.3 280.3 130.4 191.1 1.02 0.96

^* TF is the number of transfer coefficient; AC is the enrichment coefficient

Example 2 Enrichment characteristics of heavy metals in the mining polluted area of Xiaobaijiu

The Qingchengzi lead-zinc mine in Fengcheng, Liaoning is located at 123°37' east longitude and 40°41' north latitude. The annual average temperature of the mining area is 6.5-8.7°C, and the precipitation is 674.4 mm. The main host rocks in the mining area are marble and mica schist, and the soil is brown loam. The vegetation cover is mainly secondary forests, sparse shrubs and some artificial metasequoia and black locust forests. The elevation of each pit mouth of the ore body is about 270-405m, and the mining site is about 180-390m from the ground. mine. For plant sampling, the sampling method is to pick one tree at a time.

The chrysanthemum plants collected in the lead-zinc mining area with serious Cd pollution did not show symptoms of poisoning from the appearance characteristics. The results of physical and chemical properties and Cd content measurement of the corresponding root zone soil of these plants showed that the basic physical and chemical properties of the soil at the sampling point were pH 6.53-6.95, organic matter 14.31-15.04g/kg, total N 0.58-0.72g/kg, total N P 0.49～0.68g/kg, effective P 9.27～10.72mg/kg, available K 80.24～90.43mg/kg. The total amount of Cd in the soil of sampling points (1~8) is 0.9~11.8mg/kg, the effective state content is 0.3~6.2mg/kg, and the effective state accounts for 38.9%~64.7% of the total (Table 2).

Table 2 Cd content and dry weight of aboveground parts of Liquor chinensis and its root zone soil in the lead-zinc mining area

The Cd enrichment coefficients of the aboveground parts of the collected Xiaobaijiu were 1.10, 1.56, 1.08, 1.06, 2.27, 1.59, 1.59 and 2.06, all greater than 1, and the Cd content of the aboveground parts was greater than that of its roots (Table 2), which also showed The main characteristics of enriched plants were revealed. But the content of Cd in the stems and leaves of these plants did not reach 100mg/kg, which was consistent with the enrichment characteristics of Cd in the pot plant concentration gradient test.

Example 3. The enrichment characteristics of chrysanthemum in sewage irrigation area to Cd

Shenyang Zhangshi Sewage Irrigation District is located in the western suburbs of Shenyang, about 30km away from the Shenyang Ecological Station of the Chinese Academy of Sciences. Since 1962, due to the unreasonable use of Cd-containing industrial sewage from Shenyang Weigong open channel to irrigate rice fields, most of the farmland in the irrigation area has been polluted. According to the survey in 1975, the soil is mainly polluted by Cd and Cd is mainly distributed on the soil surface (about 0 ~ 35cm) , the area of land polluted by Cd is about 2800hm ² , and the concentration of Cd in the soil of the seriously polluted area is 5-7mg/kg. Random sampling method was adopted to collect soil samples of plants and their root zones in Zhangshi irrigation area of Shenyang when the plants were mature.

The test results are as follows:

The small white wine grass collected in the Zhangshi sewage irrigation area is also a normal growing plant and has matured from the appearance characteristics. The basic physical and chemical properties of the soil samples corresponding to these plants are pH 6.51-6.79, organic matter 16.07-17.53g/kg, total N0.69-0.82g/kg, total P0.62-0.71g/kg, effective P9.85-10.56 mg/kg, quick-acting K87.69～90.22mg/kg. The total Cd concentration in the soil is 1.6-2.9 mg/kg, the available Cd content is 0.6-2.1 mg/kg, and the available Cd accounts for 82.6-92.6% of the total. It can be seen that the available Cd content in the polluted soil of Zhangshi Irrigation Area is significantly higher than that in the soil of Qingchengzi lead-zinc mining area (Table 3).

Table 3 The Cd content and the dry weight of aboveground parts of Liquorgrass and its root zone soil in the sewage irrigation area

The Cd enrichment coefficients of the aboveground parts of all collected Liquorgrass were greater than 1, and the Cd content in the aboveground parts was greater than that in the roots (Table 3), which possessed the main characteristics of Cd-enriched plants. However, the Cd content in the stems and leaves of these plants did not reach 100 mg/kg, which is also consistent with the enrichment characteristics of Cd in the pot plant concentration gradient test.

The plant Xiaobaijiucao showed the basic characteristics of Cd-enriched plants no matter in the natural Cd-polluted area of lead-zinc mine or in the artificially polluted area of Cd under the condition of sewage irrigation. Under the pollution conditions, all the characteristics of Cd-enriched plants were achieved. Therefore, it can be considered that Liquor Grass is a Cd-enriching plant.

It can be seen from the above three examples that Liquor Grass has a strong ability to enrich heavy metal cadmium, is a cadmium-enriching plant, and has a strong ability to repair cadmium-contaminated soil.

Claims (8)

1. method of utilizing the abundant plants butter weed restoration of soil polluted by heavy metal, it is characterized in that: plant Conyza canadensis containing on the soil of cadmium contaminants, absorb cadmium in the contaminated soil in a large number by the Conyza canadensis root system, and it is transferred to the overground part organ, when plant length is maximum to the upperground part biomass, the plant shoot organ is removed from contaminated soil, thereby realized removing cadmium pollutant in soil.

2. according to the described method of claim 1, it is characterized in that: when described the upperground part biomass is maximum, be meant that plant is from this period of time in florescence to maturity period.

3. according to the described method of claim 2, it is characterized in that: the described maturity period is meant when Conyza canadensis grows into seed maturity.

4. according to the described method of claim 1, it is characterized in that: when plant length is maximum to the upperground part biomass, can is that plant integral body is removed from contaminated soil, thereby realizes removing cadmium pollutant in soil.

5. according to the described method of claim 1, it is characterized in that: plant Conyza canadensis containing on the soil of cadmium contaminants, can adopt open-air cultivation,, water, make soil moisture content remain on 40～95% of field capacity according to soil lack of water situation.

6. according to the described method of claim 1, it is characterized in that: described plantation Conyza canadensis is meant at direct sowing Conyza canadensis seed or the Conyza canadensis of seedling phase is implanted on the soil that contains cadmium contaminants on the soil.

7. according to the described method of claim 1, it is characterized in that: describedly plant Conyza canadensis containing on the soil of cadmium contaminants, can adopt the mode of multiple cropping, promptly when first batch of Conyza canadensis length is maximum to the upperground part biomass, the plant shoot organ is removed from contaminated soil, repeat said process again, until final cadmium pollution soil repair.

8. according to the described method of claim 1, it is characterized in that: cadmium content is 0.3-240mg/kg in the described soil that contains cadmium contaminants.