Method for repairing heavy metal contaminated soil through composite material reinforced microbial mineralization

Abstract

The invention discloses a method for repairing heavy metal contaminated soil through composite material reinforced microbial mineralization. The invention belongs to the technical field of soil remediation, and particularly relates to a method for preparing biochar by utilizing waste biomass and loading a zeolite material, so that an efficient heavy metal adsorption material is obtained, and the problem that a large amount of agriculture and forestry solid waste is difficult to utilize is solved. According to the method, the biochar-zeolite composite material is utilized to reinforce microbial mineralization to repair the heavy metal contaminated soil, so that the removal effect on colored heavy metals in the soil is improved, and the soil improvement and repair time is shortened; and the composite material can enhance microbial mineralization and repair heavy metal contaminated soil, and has a promoting effect on improving the growth environment of crops.

Description

Technical Field

[0001] The invention belongs to the technical field of soil remediation, and in particular relates to a method for remediating heavy metal contaminated soil by strengthening microbial mineralization using composite materials. Background Art

[0002] Soil is the most important component of the earth's terrestrial natural ecosystem and the most basic material resource for human survival. Soil heavy metal pollution is a global ecosystem and human health problem. The 2014 "National Soil Pollution Status Survey Bulletin" shows that the total soil exceeding the standard rate in the country is 16.1%, and the lead content exceeding the standard rate in farmland is 19.4%. This is one of the most serious threats to human, animal and plant health. For example, lead can affect bone and intellectual development, and cadmium can cause bone pain and osteoporosis. Therefore, it is necessary to identify and implement green, environmentally friendly, efficient and low-cost remediation methods to treat soil in lead and cadmium contaminated sites.

[0003] The main remediation methods currently used to treat heavy metal contaminated soil are: soil washing, passivation solidification, and electric extraction. However, the above methods are energy-consuming, cause secondary pollution, and are destructive to soil properties. Biochar is very effective in improving the physical and chemical characteristics of agricultural soils and balancing heavy metal pollution in the soil. Zeolite has a strong adsorption capacity for heavy metal Pb. At the same time, the excellent chemical adsorption of zeolite can also have a certain effect on controlling the lack of nutrition in biochar.

[0004] At present, there are still many problems in the remediation methods for soil heavy metal complex pollutants. At the same time, a single type of remediation material also has corresponding technical defects, and it is difficult to adapt to the needs of soil heavy metal complex environmental pollution. Therefore, it is necessary to use biochar-zeolite composite remediation materials to solidify soil heavy metal cadmium and lead complex pollutants.

[0005] The plant extraction remediation method for high-concentration cadmium and zinc contaminated soil proposed by the Sichuan Institute of Eco-Environmental Sciences (publication number CN117900253A) belongs to the field of heavy metal contaminated soil remediation. This method plants agapanthus in cadmium and zinc contaminated soil, and harvests the stems and leaves of agapanthus every 6-12 months to achieve the remediation of cadmium and zinc contaminated soil. However, its remediation cycle is long and requires long-term application of chemical fertilizers, which can easily cause secondary environmental pollution. Summary of the invention

[0006] The present invention provides a soil remediation method which improves the physical and chemical properties of soil and has good adsorption for Pb and Cd, can strengthen the mineralization of microorganisms, and improve the removal rate of heavy metal ions in composite polluted soil, thus having good application prospects.

[0007] The technical solution adopted by the present invention is as follows: A method for composite material-enhanced microbial mineralization repair of heavy metal contaminated soil, comprising the following steps:

[0008] Step 1, preparation of biochar: putting the waste biomass into a crucible, compacting it and wrapping it with tin foil, putting it into a muffle furnace, pyrolyzing it at a certain temperature, and cooling it after the pyrolysis is completed to obtain biochar;

[0009] Step 2, preparation of biochar-zeolite composite material: placing biochar and zeolite material in a ball mill, setting the ball mill speed to 700 r / min, and ball milling at room temperature, and obtaining the biochar-zeolite composite material after the ball milling is completed and the wall of the ball mill is cooled;

[0010] Step 3, preparation of bacterial solution: select an existing strain preserved in the laboratory, which originates from the General Microbiological Center of China Microbiological Culture Collection Administration Committee CGMCC, and is Lysinibacillus sp., the strain preservation number is CGMCC NO.27819, and the preservation time is July 6, 2023. Take the preserved Lysinibacillus sp. bacterial solution and inoculate it in a liquid culture medium, place it in a shaker at 150-190 r / min for 24 hours to obtain a bacterial solution;

[0011] Step 4: Remediation of contaminated soil: Take the heavy metal contaminated soil, dry it naturally, and sieve it to remove rocks, vegetation residues and other debris. Add the biochar-zeolite composite material, bacterial solution and nutrient solution to the contaminated soil, mix them evenly and keep the soil moisture. After static cultivation for 4 weeks, measure the indicators of the repaired soil.

[0012] Furthermore, in the step 1, the waste biomass is 20-mesh corn stalk powder, the high-temperature pyrolysis temperature of the corn stalk powder is 300-700° C., and the pyrolysis time is 2 hours.

[0013] Furthermore, in the step 2, the mass ratio of biochar to zeolite is 1:1-1:2, and the ball milling time is 2h-12h.

[0014] Furthermore, in step three, the liquid culture medium comprises: 10 g / L tryptone, 10 g / L NaCl and 5 g / L yeast extract powder, and the pH value is adjusted to 7.0.

[0015] Furthermore, in step 4, the ingredients of the nutrient solution are: 27 g / L anhydrous calcium chloride and 20 g / L urea.

[0016] Furthermore, in the step 4, the amount of the biochar-zeolite composite material, bacterial solution and nutrient solution added is: 1% per 1 kg of soil.

[0017] Furthermore, in step 4, the soil contaminated by heavy metals comes from a polluted area in a village in Baotou City, and is contaminated by a combination of lead and cadmium heavy metals, wherein the content of lead and cadmium is 268 mg / kg and 0.61 mg / kg, respectively.

[0018] After adopting the above structure, the beneficial effects of the present invention are as follows: by using waste biomass to prepare biochar and load zeolite material, not only a highly efficient heavy metal adsorption material is obtained, but also the problem of difficulty in utilizing a large amount of agricultural and forestry solid waste is solved; by using the biochar-zeolite composite material of the present invention to strengthen microbial mineralization and repair heavy metal contaminated soil, the removal effect of non-ferrous heavy metals in the soil is improved, thereby reducing soil improvement and repair time; it also has a promoting effect on improving the crop growth environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0020] Figure 1 The effects of different restoration materials on the effectiveness of soil heavy metal elements Pb and Cd in the embodiments of the present invention;

[0021] Figure 2 The morphological changes of heavy metal Cd in soil in the embodiment of the present invention;

[0022] Figure 3 The form change of heavy metal Pb in soil in the embodiment of the present invention;

[0023] Figure 4 The effects of different treatment groups on heavy metal elements leached from soil toxicity in the embodiments of the present invention;

[0024] Figure 5 Graph 1 shows the change in particle size of soil aggregates in the embodiment of the present invention. DETAILED DESCRIPTION

[0025] The following is the process of microorganisms inducing calcium carbonate precipitation to capture heavy metals and fix heavy metals by carbonate co-precipitation:

[0026] (NH2)2CO+H2O→2NH3+CO2

[0027]

[0028] Embodiment 1:

[0029] (1) Preparation of biochar:

[0030] The 20-mesh corn straw powder was placed in a crucible, compacted and wrapped in tin foil, and placed in a muffle furnace for high-temperature pyrolysis. The temperature was set at 500°C for 2 hours. After the pyrolysis was completed, it was cooled and sealed for storage to obtain corn straw biochar.

[0031] (2) Preparation of biochar-zeolite composite materials:

[0032] Weigh 10 g of biochar and zeolite material in a ratio of 1:1 and place them in a ball mill. Set the ball mill speed to 700 r / min and perform ball milling at room temperature for 2 h. After the ball milling is completed and the wall of the ball mill is cooled, a biochar-zeolite composite material is obtained.

[0033] (3) Preparation of bacterial solution:

[0034] Select the existing strains in the laboratory, take the preserved lysine Bacillus liquid and inoculate it into the liquid culture medium, wherein the liquid culture medium comprises: 10 g / L tryptone, 10 g / L NaCl and 5 g / L yeast extract powder, adjust the pH value to 7.0, then place it in a shaker at 150-200 r / min and 30-35°C for culturing for 24-48 hours to obtain the bacterial liquid.

[0035] (4) Remediation of contaminated soil:

[0036] The heavy metal contaminated soil was taken, naturally air-dried, and passed through a 2mm sieve to remove rocks, vegetation residues and other debris. 20g of biochar-zeolite remediation material and 20ml of MICP bacterial solution were added to 2kg of contaminated soil, mixed evenly and the soil moisture was maintained. After static cultivation for 4 weeks, the soil moisture content and pH value were tested during the remediation period, and the soil indicators were measured after the remediation was completed.

[0037] Embodiment 2:

[0038] (1) Preparation of biochar:

[0039] The 20-mesh corn straw powder was placed in a crucible, compacted and wrapped in tin foil, and placed in a muffle furnace for high-temperature pyrolysis. The temperature was set at 500°C for 2 hours. After the pyrolysis was completed, it was cooled and sealed for storage to obtain corn straw biochar.

[0040] (2) Preparation of biochar-zeolite composite materials:

[0041] Weigh 10 g of biochar and zeolite material in a ratio of 1:1 and place them in a ball mill. Set the ball mill speed to 700 r / min and perform ball milling at room temperature for 6 h. After the ball milling is completed and the wall of the ball mill is cooled, a biochar-zeolite composite material is obtained.

[0042] (3) Preparation of bacterial solution:

[0043] Select the existing strains in the laboratory, take the preserved lysine Bacillus liquid and inoculate it into the liquid culture medium, wherein the liquid culture medium comprises: 10 g / L tryptone, 10 g / L NaCl and 5 g / L yeast extract powder, adjust the pH value to 7.0, then place it in a shaker at 150-200 r / min and 30-35°C for culturing for 24-48 hours to obtain the bacterial liquid.

[0044] (4) Remediation of contaminated soil:

[0045] The heavy metal contaminated soil was taken, naturally air-dried, and passed through a 2mm sieve to remove rocks, vegetation residues and other debris. 20g of biochar-zeolite remediation material and 20ml of MICP bacterial solution were added to 2kg of contaminated soil, mixed evenly and the soil moisture was maintained. After static cultivation for 4 weeks, the soil moisture content and pH value were tested during the remediation period, and the soil indicators were measured after the remediation was completed.

[0046] Embodiment 3:

[0047] (1) Preparation of biochar:

[0048] The 20-mesh corn straw powder was placed in a crucible, compacted and wrapped in tin foil, and placed in a muffle furnace for high-temperature pyrolysis. The temperature was set at 500°C for 2 hours. After the pyrolysis was completed, it was cooled and sealed for storage to obtain corn straw biochar.

[0049] (2) Preparation of biochar-zeolite composite materials:

[0050] Weigh 10 g of biochar and zeolite material in a ratio of 1:1 and place them in a ball mill. Set the ball mill speed to 700 r / min and perform ball milling at room temperature for 12 h. After the ball milling is completed and the wall of the ball mill is cooled, a biochar-zeolite composite material is obtained.

[0051] (3) Preparation of bacterial solution:

[0052] Select the existing strains in the laboratory, take the preserved lysine Bacillus liquid and inoculate it into the liquid culture medium, wherein the liquid culture medium comprises: 10 g / L tryptone, 10 g / L NaCl and 5 g / L yeast extract powder, adjust the pH value to 7.0, then place it in a shaker at 150-200 r / min and 30-35°C for culturing for 24-48 hours to obtain the bacterial liquid.

[0053] (4) Remediation of contaminated soil:

[0054] The heavy metal contaminated soil was taken, naturally air-dried, and passed through a 2mm sieve to remove rocks, vegetation residues and other debris. 20g of biochar-zeolite remediation material and 20ml of MICP bacterial solution were added to 2kg of contaminated soil, mixed evenly and the soil moisture was maintained. After static cultivation for 4 weeks, the soil moisture content and pH value were tested during the remediation period, and the soil indicators were measured after the remediation was completed.

[0055] Embodiment 4:

[0056] (1) Preparation of biochar:

[0057] The 20-mesh corn straw powder was placed in a crucible, compacted and wrapped in tin foil, and placed in a muffle furnace for high-temperature pyrolysis. The temperature was set at 500°C for 2 hours. After the pyrolysis was completed, it was cooled and sealed for storage to obtain corn straw biochar.

[0058] (2) Preparation of biochar-zeolite composite materials:

[0059] Weigh 10 g of biochar and zeolite material in a ratio of 1:2 and place them in a ball mill. Set the ball mill speed to 700 r / min and perform ball milling at room temperature for 2 h. After the ball milling is completed and the wall of the ball mill is cooled, a biochar-zeolite composite material is obtained.

[0060] (3) Preparation of bacterial solution:

[0061] Select the existing strains in the laboratory, take the preserved lysine Bacillus liquid and inoculate it into the liquid culture medium, wherein the liquid culture medium comprises: 10 g / L tryptone, 10 g / L NaCl and 5 g / L yeast extract powder, adjust the pH value to 7.0, then place it in a shaker at 150-200 r / min and 30-35°C for culturing for 24-48 hours to obtain the bacterial liquid.

[0062] (4) Remediation of contaminated soil:

[0063] The heavy metal contaminated soil was taken, naturally air-dried, and passed through a 2mm sieve to remove rocks, vegetation residues and other debris. 20g of biochar-zeolite remediation material and 20ml of MICP bacterial solution were added to 2kg of contaminated soil, mixed evenly and the soil moisture was maintained. After static cultivation for 4 weeks, the soil moisture content and pH value were tested during the remediation period, and the soil indicators were measured after the remediation was completed.

[0064] Embodiment 5:

[0065] (1) Preparation of biochar:

[0066] The 20-mesh corn straw powder was placed in a crucible, compacted and wrapped in tin foil, and placed in a muffle furnace for high-temperature pyrolysis. The temperature was set at 500°C for 2 hours. After the pyrolysis was completed, it was cooled and sealed for storage to obtain corn straw biochar.

[0067] (2) Preparation of biochar-zeolite composite materials:

[0068] Weigh 10 g of biochar and zeolite material in a ratio of 1:2 and place them in a ball mill. Set the ball mill speed to 700 r / min and perform ball milling at room temperature for 6 h. After the ball milling is completed and the wall of the ball mill is cooled, a biochar-zeolite composite material is obtained.

[0069] (3) Preparation of bacterial solution:

[0070] Select the existing strains in the laboratory, take the preserved lysine Bacillus liquid and inoculate it into the liquid culture medium, wherein the liquid culture medium comprises: 10 g / L tryptone, 10 g / L NaCl and 5 g / L yeast extract powder, adjust the pH value to 7.0, then place it in a shaker at 150-200 r / min and 30-35°C for culturing for 24-48 hours to obtain the bacterial liquid.

[0071] (4) Remediation of contaminated soil:

[0072] The heavy metal contaminated soil was taken, naturally air-dried, and passed through a 2mm sieve to remove rocks, vegetation residues and other debris. 20g of biochar-zeolite remediation material and 20ml of MICP bacterial solution were added to 2kg of contaminated soil, mixed evenly and the soil moisture was maintained. After static cultivation for 4 weeks, the soil moisture content and pH value were tested during the remediation period, and the soil indicators were measured after the remediation was completed.

[0073] Embodiment 6:

[0074] (1) Preparation of biochar:

[0075] The 20-mesh corn straw powder was placed in a crucible, compacted and wrapped in tin foil, and placed in a muffle furnace for high-temperature pyrolysis. The temperature was set at 500°C for 2 hours. After the pyrolysis was completed, it was cooled and sealed for storage to obtain corn straw biochar.

[0076] (2) Preparation of biochar-zeolite composite materials:

[0077] Weigh 10 g of biochar and zeolite material in a ratio of 1:2 and place them in a ball mill. Set the ball mill speed to 700 r / min and perform ball milling at room temperature for 12 h. After the ball milling is completed and the wall of the ball mill is cooled, a biochar-zeolite composite material is obtained.

[0078] (3) Preparation of bacterial solution:

[0079] Select the existing strains in the laboratory, take the preserved lysine Bacillus liquid and inoculate it into the liquid culture medium, wherein the liquid culture medium comprises: 10 g / L tryptone, 10 g / L NaCl and 5 g / L yeast extract powder, adjust the pH value to 7.0, then place it in a shaker at 150-200 r / min and 30-35°C for culturing for 24-48 hours to obtain the bacterial liquid.

[0080] (4) Remediation of contaminated soil:

[0081] The heavy metal contaminated soil was taken, naturally air-dried, and passed through a 2mm sieve to remove rocks, vegetation residues and other debris. 20g of biochar-zeolite remediation material and 20ml of MICP bacterial solution were added to 2kg of contaminated soil, mixed evenly and the soil moisture was maintained. After static cultivation for 4 weeks, the soil moisture content and pH value were tested during the remediation period, and the soil indicators were measured after the remediation was completed.

[0082] According to the above examples, the biochar-zeolite composite material with a pyrolysis temperature of 500°C and ball milling for 2h at a ratio of 1:2 has the best effect of strengthening microbial mineralization remediation. The results show that the effective content of soil heavy metals Pb and Cd after remediation decreased by 57.88% and 67.24%, respectively. In the remediated soil, the carbonate binding state of Pb increased, and the exchangeable state and organic binding state decreased. The carbonate binding state of Pb increased by 5.4% to 6.4% after remediation, and the exchangeable state content of Cd in the treated soil decreased by 5.7% to 6.5%. The biochar-zeolite composite material has the ability to reduce the biological effectiveness of Cd and Pb, and Pb and Cd were reduced by 73.61% and 83.33%, respectively. At the same time, the remediation material and MICP bacterial agent can promote the transformation of small aggregates in the soil into large aggregates, and fix the unstable heavy metals in the soil in large aggregates through reactions such as adsorption and coprecipitation.

[0083] Although the embodiments of the present invention have been shown and described, it is understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents. In short, if those skilled in the art are inspired by them and design structural modes and embodiments similar to the technical solution without creativity without departing from the purpose of the present invention, they shall all fall within the scope of protection of the present invention.

Claims

1. A method for composite material-enhanced microbial mineralization and restoration of heavy metal contaminated soil, characterized in that: The following steps are involved: Step 1, preparation of biochar: putting the waste biomass into a crucible, compacting it and wrapping it with tin foil, putting it into a muffle furnace, pyrolyzing it at a certain temperature, and cooling it after the pyrolysis is completed to obtain biochar; Step 2, preparation of biochar-zeolite composite material: placing biochar and zeolite material in a ball mill, setting the ball mill speed to 700 r / min, and ball milling at room temperature, and obtaining the biochar-zeolite composite material after the ball milling is completed and the wall of the ball mill is cooled; Step 3, preparation of bacterial solution: select an existing strain preserved in the laboratory, which originates from the General Microbiological Center of China Microbiological Culture Collection Administration Committee CGMCC, is Lysinibacillus sp., the strain preservation number is CGMCCNO.27819, and the preservation time is July 6, 2023. Take the preserved Lysinibacillus sp. bacterial solution and inoculate it in a liquid culture medium, place it in a shaker at 150-190r / min for 24h to obtain a bacterial solution; Step 4: Remediation of contaminated soil: Take the heavy metal contaminated soil, dry it naturally, and sieve it to remove rocks, vegetation residues and other debris. Add the biochar-zeolite composite material, bacterial solution and nutrient solution to the contaminated soil, mix them evenly and keep the soil moisture. After static cultivation for 4 weeks, measure the indicators of the repaired soil.

2. The method for composite material-enhanced microbial mineralization and remediation of heavy metal contaminated soil according to claim 1, characterized in that: In the step 1, the waste biomass is 20-mesh corn stalk powder, the high-temperature pyrolysis temperature of the corn stalk powder is 300-700° C., and the pyrolysis time is 2 hours.

3. The method for composite material-enhanced microbial mineralization and remediation of heavy metal contaminated soil according to claim 2, characterized in that: In the step 2, the mass ratio of biochar to zeolite is 1:1-1:2, and the ball milling time is 2h-12h.

4. The method of composite material enhanced microbial mineralization and remediation of heavy metal contaminated soil according to claim 3, characterized in that: In step 3, the liquid culture medium comprises: 10 g / L tryptone, 10 g / L NaCl and 5 g / L yeast extract powder, and the pH value is adjusted to 7.

0.

5. The method for composite material-enhanced microbial mineralization and remediation of heavy metal contaminated soil according to claim 4, characterized in that: In step 4, the ingredients of the nutrient solution are: 27 g / L anhydrous calcium chloride and 20 g / L urea.

6. The method of composite material-enhanced microbial mineralization and remediation of heavy metal contaminated soil according to claim 5, characterized in that: In the step 4, the amount of the biochar-zeolite composite material, bacterial solution and nutrient solution added is: 1% per 1 kg of soil.

7. The method for composite material-enhanced microbial mineralization and remediation of heavy metal contaminated soil according to claim 6, characterized in that: In the step 4, the soil contaminated by heavy metals is contaminated by a combination of lead and cadmium heavy metals, wherein the content of lead and cadmium is 268 mg / kg and 0.61 mg / kg respectively.

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