A bioremediation method for heavy metal contaminated soil

Abstract

The present invention belongs to the technical field of heavy metal contaminated soil remediation, and specifically relates to a biological remediation method for heavy metal contaminated soil. The method adopts sunflower and mustard crop rotation, combined with microbial agents, and achieves efficient removal of lead, chromium and cadmium elements in heavy metal contaminated soil through two remediation methods, namely microbial bacteria and plants. At the same time, it will not damage the physical and chemical properties of the soil, and can also improve the soil flora structure. The remediated soil can be directly used for crop planting and other purposes.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy metal contaminated soil treatment, and in particular to a bioremediation method for heavy metal contaminated soil. Background Art

[0002] Heavy metal pollution in soil refers to the phenomenon that the content of heavy metals entering the soil through human activities is significantly higher than its natural background value, which in turn causes the deterioration of ecological environment quality. At present, with the development of social economy, heavy metal pollutants enter the soil environment through various channels, such as electroplating, steel manufacturing and chemical processing industries. Heavy metal pollution in soil is becoming more and more serious and gradually threatening human health and the ecosystem. Among them, the mixed pollution of lead, chromium and cadmium is more prominent, and it is difficult to be effectively treated because of its large amount and wide range, strong concealment, difficult to remove and irreversible accumulation over time.

[0003] As people's environmental awareness gradually increases, heavy metal pollution remediation work has also been carried out in large quantities. At present, the main way to deal with soil heavy metal pollution is passivation remediation technology. The heavy metals in the soil are passivated by passivation remediation technology, and certain passivators with ion adsorption characteristics are applied to the soil to achieve the passivation and detoxification of heavy metals. Among them, lime, clay minerals, biochar and other materials have become the main materials for heavy metal pollution remediation because of their characteristics of regulating soil pH and adsorbing and passivating heavy metals. However, their use is too large and the potential risk of secondary pollution is not optimistic. How to efficiently remove heavy metal elements in contaminated soil without destroying the physical and chemical properties of the soil and causing secondary pollution to the environment is a very difficult technical problem faced by the field of soil remediation. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a bioremediation method, which combines phytoremediation with microbial remediation to achieve efficient removal of lead, chromium and cadmium elements in heavy metal contaminated soil.

[0005] In order to achieve the above-mentioned purpose of the invention, the embodiment of the present invention adopts the following technical solutions:

[0006] A bioremediation method for heavy metal contaminated soil, using sunflower and mustard rotation to repair the contaminated soil, the specific steps are:

[0007] The soil contaminated by lead, chromium and cadmium is plowed, and sunflowers and mustard are planted from March to August and from August to October, respectively. Before planting each crop, the previous crop is uprooted, the soil is plowed and a microbial agent containing Bacillus phragmitetus, Bacillus licheniformis and Bacillus subtilis is applied. The preservation number of Pannonibacterphragmitetus BB is CGMCC No.3052, which has been disclosed in a patent with application number CN106834184B and name "A composite bacterial community and its application in the remediation of Cr(VI) contaminated soil".

[0008] Compared with the prior art, the bioremediation method for heavy metal contaminated soil provided by the present invention utilizes plant-microorganism combined treatment of lead, chromium and cadmium elements in the contaminated soil. The Lac. panlongensis CGMCC No. 3052 has a strong tolerance to chromium ions, and the special substances it secretes can also act as electron shuttles to transfer Cr in the soil. 6+ Reduction to Cr 3+ Bacillus subtilis and Bacillus licheniformis can decompose complex organic matter in the soil, provide nutrients for the growth and reproduction of Bacillus panloniae, and promote the dissociation of lead and cadmium ions complexed with organic matter, thereby acting as electron donors to reduce Cr for Bacillus panloniae CGMCC No.3052. 6+ Provide electrons to improve the reduction of Cr by Lac. panlonicum CGMCC No.3052 6+ rate; sunflowers are highly adaptable to the living environment, and have strong absorption and accumulation capabilities for lead and chromium. Mature sunflowers have well-developed stems, making them the best choice for absorbing lead and chromium in the soil. Mustard is also a soil heavy metal hyperaccumulator, and has strong scavenging capabilities for heavy metals such as chromium and cadmium. The two plants work together to extract and enrich heavy metal ions activated and dissociated by microorganisms, and treat them synergistically. At the same time, the life cycles of the two plants are completely staggered, so that the synergistic treatment process of microbial remediation and plant remediation covers the entire remediation process, further improving the treatment efficiency. The entire remediation method is simple and easy, with low remediation costs, environmental protection and no pollution, and has broad application prospects.

[0009] Preferably, Bacillus subtilis is a commercial strain purchased from Beina Biological, numbered BNCC193111, Bacillus licheniformis is a commercial strain purchased from Beina Biological, numbered BNCC221464, and the microbial agent is compounded by Bacillus panlongensis agent, Bacillus licheniformis agent and Bacillus subtilis agent, wherein the mass ratio of Bacillus panlongensis agent: Bacillus licheniformis agent: Bacillus subtilis agent = 4-6:1-2:1-2.

[0010] Bacillus subtilis CGMCC No.0954 and Bacillus licheniformis CGMCC No.1.7461 not only have the ability of traditional Bacillus subtilis and Bacillus licheniformis to decompose organic matter, but the special substances they secrete can also improve the biological activity of Bacillus panlongensis CGMCC No.3052, thereby enhancing its ability to reduce chromium in the soil. The reasonable combination of the dosage of each species, symbiosis and coordination, non-antagonism and mutual promotion can effectively improve the treatment efficiency of microbial agents.

[0011] Preferably, the preparation method of the Panlonga alkaline lake bacillus agent in the microbial agent is:

[0012] The CGMCC No.3052 strain is inoculated into a culture medium adsorbed with a carbon source, a nitrogen source, an inorganic salt and water, and is cultured and activated at a speed of 200-300 r / min for 15-30 hours under an environment of a C / N ratio ≥5, an initial pH of 7-10, and 25-35°C. Then, attapulgite equivalent to 2-4 times the mass of the culture medium is added, and the mixture is evenly mixed and dried at a constant temperature of 40-60°C to obtain the Panlongia alkali lake bacillus agent.

[0013] The preparation methods of Bacillus subtilis inoculant and Bacillus licheniformis inoculant are the same, which are: the corresponding strains are inoculated into a culture medium adsorbed with a nitrogen source, a carbon source, an inorganic salt and water, respectively, and after culturing and activating for 36 to 48 hours at a speed of 100 to 150 r / min in an environment with a C / N ratio greater than or equal to ≥10, an initial pH of 6.0 to 7.5, and 25 to 35° C., attapulgite with a mass 2 to 4 times that of the culture medium is added, mixed evenly, and dried at a constant temperature of 30 to 50° C. to obtain the Bacillus subtilis inoculant and the Bacillus licheniformis inoculant.

[0014] Attapulgite has a strong adsorption capacity, which can adsorb and protect the activated and amplified microorganisms and nutrients, preventing the amplified strains from being inactivated in large quantities due to the influence of the soil environment, and providing a buffer time for the strains to adapt to the soil environment, so as to better play their role.

[0015] Preferably, the bacterial content of the Bacillus panlongensis, Bacillus subtilis and Bacillus licheniformis is ≥ 1×10 8 / g, particle size of bacterial agent ≤2mm.

[0016] Preferably, during the tillage process, the tillage depth is controlled to be 30-50 cm, and the diameter of the soil particles is ≤20 mm.

[0017] Preferably, the spacing between sunflowers is controlled to be 30 to 50 cm, and the spacing between mustard is controlled to be 20 to 30 cm.

[0018] Preferably, during the tillage process, the tillage depth is controlled to be 30-50 cm, and the diameter of the soil particles is ≤20 mm. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] Example

[0021] The test scheme provided in this embodiment was carried out in a farmland contaminated by heavy metals in Shijiazhuang City, Hebei Province, with a soil pH>7.5, wherein the average Pb content was 202.76 mg / kg; the average Cr content was 315.75 mg / kg; and the average Cd content was 0.75 mg / kg, all exceeding the national soil environmental quality standard (GB15618-2018);

[0022] A total of 6 treatment areas were set up: each area is 0.5 mu. Different treatment strategies were adopted in each area. The specific strategies are shown in Table 1;

[0023] Table 1

[0024]

[0025]

[0026] The specific operations of each step are as follows:

[0027] Planting sunflowers from March to August:

[0028] In March, the soil in each area was plowed to a depth of 40 cm. When the diameter of soil particles was ≤20 mm, 200 kg / mu of microbial agent was applied. Sunflowers were planted in holes with 3 to 5 sunflower seeds per hole. After application, irrigation was carried out to maintain soil moisture ≥50%. Sunflowers were cultivated in the conventional way.

[0029] The microbial agent is composed of the respective agents of Bacillus panloniae, Bacillus licheniformis and Bacillus subtilis, the deposit number of Bacillus panloniae is CGMCC No.3052, Bacillus subtilis is a commercial strain purchased from Beina Biological, numbered BNCC193111, and Bacillus licheniformis is a commercial strain purchased from Beina Biological, numbered BNCC221464;

[0030] The preparation method of the panlongia alkali lake bacillus agent is:

[0031] The CGMCC No.3052 strain was inoculated into a sterile culture medium containing 10 g of tryptone, 5 g of yeast extract, 10 g of sodium chloride and 1 L of deionized water. After culturing and activation for 24 h at a C / N ratio of ≥5, initial pH = 9 and 30 °C at a speed of 200-300 r / min, 100 g of attapulgite was added, mixed evenly and dried at a constant temperature of 40-60 °C. After sieving, the particles with a size of ≤2 mm and a viable bacterial content of ≥1×10 8 / gram of Panlongae alkali lake bacillus agent;

[0032] The preparation methods of Bacillus subtilis and Bacillus licheniformis are the same, which are:

[0033] The corresponding strains were inoculated into a culture medium containing 20 g of tryptone, 5 g of yeast extract, 10 g of sodium chloride and 1 L of deionized water. After activation at a C / N ratio of ≥10, an initial pH of 6.5, and 230 °C at a speed of 150 r / min for 18 h, 80 g of attapulgite was added, mixed evenly, and dried at a constant temperature of 30-50 °C. After sieving, the obtained culture medium had a particle size of ≤2 mm and a viable bacterial content of ≥1×10 8 / gram of Bacillus subtilis and Bacillus licheniformis;

[0034] The microbial agent is obtained by mixing the Bacillus panlongae agent, the Bacillus subtilis agent and the Bacillus licheniformis agent in proportion.

[0035] After the sunflowers mature in mid-August, pull out the sunflowers with their roots and plow the soil. The plowing standards are the same as in March. After plowing, apply microbial agents at a rate of 100 kg / mu. Then sow mustard seeds, with a hole 20 to 30 cm apart and 3 to 5 seeds per hole. Irrigate after application to keep the soil moisture ≥ 50%. Cultivate the mustard seedlings in the conventional way. Cultivate the mustard in the conventional way and pull out the roots when the mustard matures.

[0036] The content of heavy metal elements in the test soil was tested and the removal rate was calculated. The changes in the content of heavy metals in the soil before and after treatment are shown in Table 2:

[0037] Table 2

[0038]

[0039]

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A bioremediation method for heavy metal contaminated soil, characterized in that: The contaminated soil was repaired by rotating the crops of sunflower and mustard, which included the following steps: The soil contaminated by lead, chromium and cadmium was plowed, and sunflowers and mustard were planted from March to August and from August to October, respectively. Before planting each crop, the previous crop was uprooted, the soil was plowed, and a microbial agent containing Bacillus panloensis, Bacillus licheniformis and Bacillus subtilis was applied. The Bacillus panloensis ( Pannonibacter phragmitetus BB bacteria ) has a deposit number of CGMCC No.3052; the microbial agent is compounded by Bacillus panlureas, Bacillus licheniformis and Bacillus subtilis, and the mass ratio of Bacillus panlureas: Bacillus licheniformis: Bacillus subtilis is 3:2:

1.

2. The bioremediation method for heavy metal contaminated soil according to claim 1, characterized in that: The preparation method of the panlongia alkali lake bacillus agent is: The CGMCC No.3052 strain was inoculated into a sterile culture medium containing 10g of tryptone, 5g of yeast extract, 10g of sodium chloride and 1L of deionized water. Under the conditions of C / N ratio ≥5, initial pH=9 and 30°C, the culture was activated at a speed of 200-300r / min for 24h, and then 100g of attapulgite was added. After mixing evenly, the mixture was dried at a constant temperature of 40-60°C to obtain the Panlongia alkali lake bacillus agent.

3. The bioremediation method for heavy metal contaminated soil according to claim 1, characterized in that: The preparation methods of the Bacillus subtilis agent and the Bacillus licheniformis agent are the same, both of which are: The corresponding strains were inoculated into a culture medium of 20 g of tryptone, 5 g of yeast extract, 10 g of sodium chloride and 1 L of deionized water, respectively, and after activation at a C / N ratio of ≥10, an initial pH of 6.5, and a speed of 150 r / min for 18 hours in an environment of 230° C., 80 g of attapulgite was added, mixed evenly, and dried at a constant temperature of 30-50° C. to obtain the Bacillus subtilis inoculant and the Bacillus licheniformis inoculant.

4. The bioremediation method for heavy metal contaminated soil according to claim 1, characterized in that: The live bacterial contents of Bacillus panlonicus, Bacillus subtilis and Bacillus licheniformis are all ≥1×10 8 / gram.

5. The bioremediation method for heavy metal contaminated soil according to claim 1, characterized in that: The particle size of the microbial agent is ≤2mm.

6. The bioremediation method for heavy metal contaminated soil according to claim 1, characterized in that: The application amount of the microbial agent is 100-200 kg / mu.

7. The bioremediation method for heavy metal contaminated soil according to claim 1, characterized in that: The spacing between the sunflowers is 30-50 cm; The spacing between the columns of the mustard is 20-30 cm.

8. The bioremediation method for heavy metal contaminated soil according to claim 1, characterized in that: During the tillage process, the tillage depth is controlled at 30~50cm and the diameter of soil particles is ≤20mm.

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