WO2023226271A1 - Biochar-based three-dimensional composite material and method for remediating high-concentration chromium-contaminated soil - Google Patents

Abstract

The present invention provides a biochar-based three-dimensional composite material and a method for remediating high-concentration chromium-contaminated soil. The biochar-based three-dimensional composite material is obtained by loading, oxidizing, and polymerizing biochar and m-phenylenediamine. The biochar-based three-dimensional composite material and a domesticated dominant strain are used together for remediating chromium-contaminated soil. According to the method, the defects that the microbial remediation period is long, the environmental adaptability is poor, physical adsorption of common biochar cannot fundamentally eliminate contaminants, and the like can be overcome. The synergistic effect of the two can enhance the actual remediation effect on the contaminated soil and shorten the remediation operation period. The biochar-based three-dimensional composite material of the present invention is simple in the preparation process, low in cost, environmentally friendly, free of secondary contamination, and significant in effect, thereby greatly increasing the reduction rate of Cr(VI), reducing the migration capacity and biological effectiveness of chromium, improving the soil stability, enhancing the soil fertility, and improving the diversity of soil microbial species.

Description

Biochar-based three-dimensional composite materials and their methods for remediating high-concentration chromium contaminated soil Technical field

The present invention relates to the field of soil environment restoration, and in particular to a biochar-based three-dimensional composite material and a method for repairing high-concentration chromium contaminated soil.

Background technique

Chromium has its special application value in industry and is widely used in fields such as fur tanning, electroplating, dyes, pigments, organic synthesis and light industrial textiles. Cr(VI) exists in the form of CrO ₄ ^2- , HCrO ₄ ^2- , Cr ₂ O ₇ ^2- and H ₂ CrO _4. Since Cr(VI) is easily absorbed by organisms, it destroys cell structures and interferes with redox reactions in the body. It is highly bioaccumulative and concentrated, so it is more toxic than Cr(III). The migration and transformation of chromium in the environment are mainly determined by physical and chemical processes such as redox reactions, precipitation, dissolution, adsorption and desorption. Cr(VI) reacts in the presence of oxygen and reducing ions (such as S ^2- , Fe ²⁺ , etc.) Or in the presence of organic matter, it can be reduced to Cr(III).

my country's "Comprehensive Wastewater Discharge Standard" (GB8978-1996) stipulates that the maximum allowable discharge concentrations of Cr(VI) and total chromium are 0.5mg/L and 1.5mg/L respectively. my country's "Soil Environmental Quality Standards for Soil Pollution Risk Management and Control of Construction Land (Trial)" (GB 36600-2018) stipulates that the controlled value concentration of Cr(VI) in soil is 30mg/kg-78mg/kg. "Soil Environmental Quality Agricultural Land Soil" According to the "Pollution Risk Management and Control Standards (Trial)" (GB 15618-2018), the total chromium concentration in dryland soil is 150mg/kg-250mg/kg, and the total chromium concentration in paddy soil is 250mg/kg-350mg/kg. It can be seen from these national standards that the concentration of chromium emission standards is extremely low. Therefore, it is necessary to find a method that does not damage the soil structure, is low cost, is easy to operate, responds quickly, and can be put into large-scale production to remediate heavy metal contaminated soil. It seemed particularly urgent.

Biochar is currently a hot spot for remediating heavy metals. Its porous and loose structure, high ion exchange capacity, and rich functional groups, such as hydroxyl, phenolic hydroxyl, carboxyl, amino, etc., all illustrate its position in soil remediation; and due to The presence of carbonates in the soil and functional groups such as -COOH and -OH contained in biochar can improve the stability of metals by increasing the pH of soil and sediments.

Polym-phenylenediamine, a derivative of polyaniline, serves as an adsorbent. The large number of functional groups on its molecular chain and the redox ability of the polymer itself can reduce Cr(VI) to Cr(III) and integrate Cr(III) in the The polymer surface achieves the purpose of processing Cr(VI) in one step. The reaction formula is as follows:

The redox reaction between poly-m-phenylenediamine and Cr(VI) during the adsorption process:

The overall oxidation-reduction reaction equation:

At present, there are no reports on the chemical-microbial remediation method of using biochar as a carrier to load poly-m-phenylenediamine on biochar-based three-dimensional composite materials and working with Cr(VI)-reducing bacteria to quickly and efficiently reduce the heavy metal Cr(VI) in soil. .

Contents of the invention

In view of this, in order to solve the shortcomings of the existing remediation methods of Cr(VI)-contaminated soil, such as poor microbial effect and long remediation time when single microorganisms exist in the presence of high concentrations of Cr(VI), the present invention proposes a biochar-based three-dimensional composite material. Collaborating with Cr(VI)-reducing bacteria to quickly remediate Cr(VI)-contaminated soil. On the one hand, biochar-based three-dimensional composite materials can greatly shorten the remediation time of Cr(VI)-contaminated soil and reduce Cr(VI) in Cr(VI)-contaminated soil. ) concentration; on the other hand, the soil after collaborative microbial remediation can enhance the fertility of contaminated soil and enrich the species diversity in the soil, while meeting the second category of the "Soil Environmental Quality Standard for Soil Pollution Risk Management and Control of Construction Land (Trial)" (GB36600-2018) Land use control value provides a new, efficient, economical and environmentally friendly method for Cr(VI)-contaminated soil.

In order to achieve the above objects, the technical solutions of the present invention are as follows:

A biochar-based three-dimensional composite material is characterized in that: the material is prepared by a method including the following steps:

Mix biochar and m-phenylenediamine aqueous solution for 2-2.5 hours to allow m-phenylenediamine to adhere to the biochar, and add oxidants and alkali salt solutions for loading and oxidative polymerization, followed by filtration, washing, and drying to obtain biochar-based three-dimensional Composite material; among them, the mass ratio of biochar and m-phenylenediamine monomer is 1:30-1:50.

Further, the oxidizing agent is sodium persulfate, the molar ratio of the oxidizing agent and m-phenylenediamine is 0.5-2, and the alkali salt solution is a 2 mol/L Na ₂ CO ₃ solution.

Furthermore, the biochar is obtained by roasting biomass peanut shells, corn cobs, straw, rice straw or bark under oxygen-insulated conditions at 400-550°C for a roasting time of 2-4 hours and cooling.

The biomass, such as peanut shells, corn cobs, straw, rice straw or bark, etc., is washed with water to remove surface attachments, air-dried for 2-3 days, and then pulverized.

Further, the particle size of the biochar is 0.05-1.5mm, and the concentration of the m-phenylenediamine solution is 30-50g/L.

Further, the polymerization reaction time is 5-5.5 h, and the polymerization reaction conditions are ice bath at 0°C.

Furthermore, the pore diameter of the obtained biochar-based three-dimensional composite material was 7.72-10.29nm.

Further, the washing was performed with deionized water, 1:1 ammonia water, deionized water, and absolute ethanol in sequence.

Further, the drying temperature is -60°C, and vacuum freeze-drying is used.

The invention provides a method for repairing high-concentration chromium-contaminated soil using the above-mentioned biochar-based three-dimensional composite material. The method includes the following steps:

1) Strain domestication: Select dominant strains from the soil of chromium-contaminated sites that can perform metabolic activities using organic matter and glycerol as electron donors and Cr(VI) as electron acceptor, and domesticate and expand the dominant strains. nourish;

2) Mix the biochar-based three-dimensional composite material, the dominant bacterial species obtained in step 1) and the high-concentration chromium-contaminated soil to be repaired to evenly and fully react, add water to adjust the soil moisture content, and perform repair at normal temperature; wherein, the biochar The dosage of the base three-dimensional composite material is 0.6g/kg of soil, the dosage of the dominant bacterial species is 166-266mL/kg, and the soil moisture content is 20%-50%.

Further, the pH value of the high-concentration chromium-contaminated soil is 4-9, the particle size is 0.1-3mm, and the chromium pollution concentration is 10-500mg/kg.

Furthermore, in step 1), the culture medium for expanding the culture of the dominant bacterial species is LB medium, and the Cr(VI) concentration gradient method is used to domesticate the bacterial species, and the Cr(VI) concentration is 50-500 mg/L.

LB medium is obtained by dissolving 10g NaCl, 10g peptone, and 5g yeast extract powder in 1L deionized water, and adjust the pH to 7 with NaOH solution.

Further, in step 2), the reaction time is 3-14d, the moisture content is 30%, and the temperature is 10-40°C.

Compared with the existing technology, the biochar-based three-dimensional composite material and its method for repairing high-concentration chromium contaminated soil according to the present invention have the following advantages:

1) The source of the repair material of the present invention is natural crop residues, which has a wide range of sources, is environmentally friendly, can reuse resources, is easy to be produced in batches, and has stable performance. By carbonizing straw and other biomass and returning it to the field, it can realize the carbonization of soil, especially farmland soil. Seal. In addition, biochar can provide a habitat surface for attached materials and microorganisms, and can also be used as a growth matrix to provide part of the growth metabolic energy for microorganisms, improve microbial activity, and enhance their rate of Cr(VI) reduction.

2) The present invention obtains a new type of biochar-poly-m-phenylenediamine composite material by polymerizing m-phenylenediamine so that it can evenly adhere to the surface of biochar, which can achieve low usage, efficient and rapid adsorption in reducing environments. Cr(VI) in (water, soil), in conjunction with Cr(VI) reducing bacteria to repair contaminated soil, can achieve a Cr(VI) reduction rate of more than 90%, significantly reduce weakly acidic chromium, and increase the content of residual chromium.

3) The repair method of the present invention is simple and easy to operate, has low repair cost and mild reaction conditions. After repair, it can increase soil fertility and microbial species richness, and can be applied to large-scale Cr(VI) contaminated soil. Compared with existing microorganisms that cannot directly remediate high-concentration Cr(VI)-contaminated soil, the synergy between biochar-based three-dimensional composite materials and economical, environmentally friendly, safe and harmless microbial remediation can accelerate the adsorption and reduction of Cr(VI) during the remediation process. process to improve the remediation effect of Cr(VI) contaminated soil and has broad application prospects.

Description of the drawings

The drawings forming a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached picture:

In Figure 1, (a) is a scanning electron microscope image (SEM) of biochar; (b) is a scanning electron microscope image (SEM) of biochar-based three-dimensional composite material; (c) is a scanning electron microscope image of YT-Cr(VI) reducing bacteria. Figure (SEM);

Figure 2 shows the Fourier transform infrared spectroscopic analysis (FIRT) of biochar (BC), biochar-based three-dimensional composite material (BC/PmPD), and biochar-based three-dimensional composite material after reaction with Cr(VI) (BC/PmPD+Cr);

Figure 3 is a growth curve diagram of the Cr(VI) reducing bacteria YT domesticated in Example 2;

Figure 4 is a growth curve diagram of the Cr(VI) reducing bacteria YH domesticated in Example 2;

Figure 5 is a diagram showing the removal effect of Cr(VI)-reducing bacteria in 100 mg/L aqueous solution by the domesticated Cr( ^VI) -reducing bacteria in Example 2;

Figure 6 is a diagram showing the removal effect of Cr(VI)-reducing bacteria in 150 mg/L aqueous solution by the domesticated Cr( ^VI) -reducing bacteria in Example 2;

Figure 7 is a comparison chart of the adsorption and reduction effects of Cr ⁶⁺ in aqueous solution using different mass ratios of biochar and m-phenylenediamine monomers for the composite materials prepared in Example 1 and Comparative Example 1;

Figure 8 is a comparison chart of the adsorption and reduction effects of Cr ⁶⁺ in aqueous solution using different biochar and m-phenylenediamine attachment times for the composite materials prepared in Example 1 and Comparative Example 2;

Figure 9 is a comparison chart of the adsorption and reduction effects of Cr ⁶⁺ in aqueous solution using different molar ratios of oxidants and m-phenylenediamine for the composite materials prepared in Example 1 and Comparative Example 3;

Figure 10 is a comparison chart of the adsorption and reduction effects of Cr ⁶⁺ in aqueous solution using different Na ₂ CO ₃ solution dosages for the composite materials prepared in Example 1 and Comparative Example 4;

Figure 11 is a comparison chart of the adsorption and reduction effects of the biochar-based three-dimensional composite materials prepared in Example 1 and Comparative Example 5 using different polymerization reaction system reaction temperatures on Cr ⁶⁺ in aqueous solution;

Figure 12 is a comparison chart of the adsorption and reduction effects of biochar-based three-dimensional composite materials on Cr ⁶⁺ in aqueous solution at different experimental temperatures in Experiment 1.

Detailed ways

It should be noted that, as long as there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

Example 1 Preparation of biochar-based three-dimensional composite materials

1) Biomass such as peanut shells, corn cobs, straw, rice straw or bark, etc., are washed with water to remove surface adherents, air-dried for 2 days, and then crushed; then roasted under oxygen-isolated conditions at 550°C for 2 hours. , cooling, and finally obtained biochar particles with a particle size of 1.5 mm; (a) in Figure 1 is the scanning electron microscope image (SEM) of the prepared biochar, and BC in Figure 2 is the Fourier transform infrared spectroscopic analysis (FIRT) of the biochar. ;

2) Under 0°C ice bath conditions, weigh 3g of m-phenylenediamine monomer, place it in a 250mL beaker, add 100mL of deionized water, stir and dissolve; weigh 0.1g of biochar particles and add to the above solution, stir magnetically for 2 hours. Add 6.611g sodium persulfate; at the same time, prepare a Na ₂ CO ₃ solution with a concentration of 2 mol/L. Use a 50 mL injection needle to fill up the Na ₂ CO ₃ solution. Set the injector: inject 30 mL at a sampling rate of 2 mL. /min was added dropwise into the beaker, and the solution was kept magnetically stirred; after the dropwise addition was completed, the reaction was continued for 5 hours;

3) After the reaction, pour the beaker solution into the sand core funnel for vacuum filtration, and wash the sample solution with deionized water, 1:1 ammonia water, and deionized water in order until it is neutral, and wash away the remaining ions and monomers. Finally, Wash with absolute ethanol to remove oligomers; put the sample into a -60°C vacuum freeze-drying oven to dry for 12 hours to obtain a biochar-based three-dimensional composite material. The pore diameter of the biochar-based three-dimensional composite material is 10.29nm.

The picture (b) in Figure 1 shows the scanning electron microscope (SEM) image of the biochar-based three-dimensional composite material, and the BC/PmPD in Figure 2 shows the Fourier transform infrared spectroscopic analysis (FIRT) of the biochar-based three-dimensional composite material.

Example 2 Domestication and cultivation of Cr(VI) reducing bacteria

1. Weigh 10g of soil from a chromium-contaminated site into a 250mL Erlenmeyer flask, add 100mL of LB culture medium sterilized at 121°C for 20min, place it in a 30°C, 150r/min shaker for 24h, then centrifuge, and take the supernatant The solution was then diluted 10 times and spread on the solid LB medium, and the Cr(VI) concentration of the solid LB medium was gradually increased to isolate, screen and culture the strains.

Finally, two strains of Cr(VI)-reducing bacteria were screened out that could tolerate 150 mg/L Cr(VI) concentration: YH-fibrobacterium Fibrobacterium cellulosa and YT-Microbacterium microbacterium.

Microbial liquid: Inoculate Cr(VI)-reducing bacteria YH and YT into LB medium (pH 7) for enrichment, culture in a shaking table at 30°C and 180r/min, and grow to the late logarithmic growth phase. (OD600) is about 2.50-3.00, and the growth curves are shown in Figure 3 and Figure 4.

2. The domesticated Cr(VI)-reducing bacteria YH and YT can use glycerol as electron donor, and the Cr(VI) reduction rate in the culture solution can reach 100%.

Cr(VI)-reducing bacteria YH and YT were cultured in LB medium with Cr ⁶⁺ concentrations of 100 mg/L and 150 mg/L respectively, and reacted for 96 hours under horizontal shaking conditions of 30°C and 180 r/min. At the 24th hour, respectively , 48h, 72h, and 96h were taken to measure the Cr(VI) concentration in the solution. Cr(VI) was measured using diphenylcarbazide spectrophotometry. The Cr ⁶⁺ reduction rate in the obtained solution is shown in Figure 5 and Figure 6. As the concentration of Cr ⁶⁺ in the solution increases, the two strains of bacteria show different reducing activities. YT shows a high level of electron accepting ability in the presence of electron donors and expresses strong reducing activity. Complete reduction of Cr ⁶⁺ can be achieved in both 100mg/L and 150mg/L LB solutions.

Therefore, the Cr(VI)-reducing bacterium YT was selected to conduct the following experiments. Figure 1(c) shows the scanning electron microscope image (SEM) of YT-Cr(VI)-reducing bacteria.

Comparative Example 1 Different mass ratios of biochar and m-phenylenediamine monomers

On the basis of the above Example 1, the usage amount of m-phenylenediamine monomer was changed to 0.1g, 0.5g, 1g, 1.5g, 3g (i.e. Example 1), 5g (biochar and m-phenylenediamine). The monomer mass ratio is 1:1, 1:5, 1:10, 1:15, 1:30, 1:50).

As shown in Figure 7, as the mass of the phenylenediamine monomer in the solution increases, the adsorption and reduction performance of the polymer for Cr ⁶⁺ in the aqueous solution is significantly enhanced, indicating that the biochar has enough sites to meet the requirements of poly-m-phenylenediamine. However, when the mass of m-phenylenediamine monomer exceeds 3g, the adsorption and reduction performance does not show a significant improvement trend. This is because poly-m-phenylenediamine is easy to agglomerate and cannot be fully dispersed to play its role. The figure shows that the best choice for adsorption and reduction performance is that the mass ratio of biochar and m-phenylenediamine monomer is 1:30. At this time, the adsorption and reduction performance is good and it is more economical.

Comparative Example 2 Different attachment times of biochar and m-phenylenediamine

On the basis of the above Example 1, the attachment time of biochar and m-phenylenediamine, that is, the mixing time of biochar and m-phenylenediamine, was changed to 1h, 2h, 3h, and 4h respectively.

As shown in Figure 8, as the attachment time of biochar and m-phenylenediamine increases, the adsorption and reduction performance of Cr ⁶⁺ in the aqueous solution of the polymer shows a trend of first promotion and then inhibition, indicating that increasing the attachment time of the two has a promoting effect on the reaction process itself. , but when all adsorption sites are attached, extending the time will not improve the adsorption and reduction performance of the polymer.

Comparative Example 3 Molar ratios of different oxidants and m-phenylenediamine

On the basis of the above Example 1, the amount of sodium persulfate as the oxidant was changed according to the molar ratio of the oxidant to m-phenylenediamine, respectively, according to the molar ratio of the oxidant to m-phenylenediamine: 1:2 (0.5), 1:1 (1 ), 2:1(2) add 3.305g, 6.611g, 13.222g.

As shown in Figure 9, appropriately increasing the amount of oxidant improves the polymer's adsorption and reduction performance of Cr6 ⁺ in aqueous solution. However, when the amount of oxidant is too much, more than the amount of m-phenylenediamine monomer, it not only fails to promote the synthesis of the polymer , but it hinders the adsorption and reduction performance of the polymer. When the amount of oxidant added is 6.611g, that is, when the molar ratio of oxidant and m-phenylenediamine is 1:1, the adsorption capacity of the polymer reaches 475mg/g.

Comparative Example 4 Different dosage of Na ₂ CO ₃ solution

On the basis of the above Example 1, the dosage of Na ₂ CO ₃ solution was changed to 5 mL, 10 mL, 30 mL, and 50 mL respectively.

As shown in Figure 10, the increase in the dosage of Na ₂ CO ₃ solution significantly improves the adsorption and reduction performance of the polymer for Cr6 ⁺ in aqueous solution. When 30 mL of Na ₂ CO ₃ solution is added, the pH of the reaction system is 9-10 , the adsorption capacity of the polymer reaches 552.99mg/g.

Comparative Example 5 Reaction temperatures of different polymerization reaction systems

On the basis of the above Example 1, the reaction temperatures of the polymerization reaction system were changed to 0°C in ice bath, 15°C in normal temperature, and 40°C in heating.

As shown in Figure 11, the reaction temperature of the polymerization system is a key factor affecting the adsorption and reduction performance of the composite material. As the system temperature increases, the adsorption and reduction effect of the composite material on Cr ⁶⁺ in aqueous solution decreases significantly. When the entire reaction is at 0°C During the process, the prepared composite material was uniformly attached to the surface sites of biochar, in the shape of dispersed spheres, and had good adsorption performance. At this time, the performance of the composite material is the best, and the maximum adsorption capacity is 573.16mg/g.

Experiment 1 simulates the adsorption and reduction effects of different experimental temperatures on water with a Cr(VI) concentration of 800mg/L

Take an aqueous solution with a volume of 100mL and a Cr(VI) concentration of 800mg/L. Under the conditions of horizontal shaking at pH 2 and 180r/min, the dosage of the composite material is 0.1g. The experimental reaction temperatures are 5℃, 15℃, 25℃, 35℃, 45℃, 55℃, take samples at 0.1h, 0.5h, 1h, 2h, 4h, 6h, 8h, 12h, 24h to measure the Cr(VI) adsorption amount (Qe) in the solution under different temperature conditions. ), Cr(VI) was measured using diphenylcarbazide spectrophotometry. As shown in Figure 12, as the reaction temperature increases, the adsorption and reduction effect of the composite material on Cr ⁶⁺ in the aqueous solution is significantly enhanced. When the entire When the reaction conditions are carried out at 55°C, the adsorption and reduction performance of the composite material is the most outstanding at this time, and the maximum adsorption capacity is 773.01mg/g.

It can be seen that the higher the temperature, the more conducive to the adsorption of Cr ⁶⁺ . When performing soil remediation, the temperature is generally around 35°C, and the adsorption capacity is approximately 550mg/g. However, the existing soil remediation agent has a lower effect on Cr ⁶⁺ . The adsorption is approximately 400 mg/g, indicating that the material prepared by the present invention can achieve better adsorption effect.

In Figure 2, BC/PmPD+Cr is Fourier transform infrared spectroscopy (FIRT) analysis of biochar-based three-dimensional composite materials after reaction with Cr(VI).

Experiment 2 simulates the remediation of 200mg/kg Cr(VI) contaminated soil:

Take 30g of soil samples with a Cr(VI) contamination concentration of 200mg/kg in four 100mL beakers. The remediation experiment is designed into 4 groups:

Group A is the blank group (no biochar-based three-dimensional composite materials and no bacterial solution are added);

Group B composite material group (0.018g biochar-based three-dimensional composite material added alone);

Group C microbiome (add 5mL of YT bacterial liquid with an OD600 of 2.25 alone);

Group D composite material cooperates with the microbiome (add 0.018g biochar-based three-dimensional composite material, 5mL YT bacterial liquid with OD600 of 2.25, and stir evenly).

The dosage of biochar-based three-dimensional composite materials is strictly in accordance with the limit range of 663 mg/kg for the second type of land use control value of semi-volatile organic compounds aniline in the "Soil Environmental Quality" (GB36600-2018). Therefore, in this experiment to simulate the remediation of Cr(VI) contaminated soil and in subsequent experiments, the dosage of biochar-based three-dimensional composite materials was set to 600 mg/kg _soil , that is, 18 mg/30 g _soil .

Table 1 Analysis of physical and chemical properties of sample original soil and experimental group contaminated soil after remediation

After 5 days of restoration, the soil fertility index was determined according to the "Determination of Ammonium Nitrogen, Available Phosphorus, and Available Potassium in Neutral and Calcareous Soils Combined Extraction-Colorimetric Method". The experimental results were analyzed and shown in Table 1. It shows that biochar-based three-dimensional composite materials and YT bacterial liquid can greatly improve the soil fertility of Cr(VI)-contaminated soil. Available potassium, available phosphorus, and ammonium nitrogen increased by 34%, 17%, and 46% respectively. The soil pH before and after restoration was not the same. No significant changes.

Table 2 Effects of different experimental design groups on soil Cr(VI) remediation effects

​	Group A	Group B	Group C	Group D
Cr(VI) concentration (mg/kg)	198.67	127.33	137.00	47.00

"Determination of Cr(VI) in Soils and Sediments by Alkaline Solution Extraction—Flame Atomic Absorption Spectrophotometry" Extract and determine the mass concentration of Cr(VI) in the soil in accordance with "Solid Waste Leaching Toxicity Leaching Method—Sulfuric Acid Nitric Acid Method" and " Determination of Cr(VI) in water quality - Diphenylcarbazide spectrophotometry" was used to analyze the concentration of Cr(VI) in the soil. The experimental results are shown in Table 2. At the same time, both biochar-based three-dimensional composite materials and YT bacterial liquid played a significant role in the remediation of Cr(VI)-contaminated soil, but the combined use of the two had a high remediation effect on Cr(VI)-contaminated soil in just 5 days. The repair effect can reach 76.5%.

Table 3 Proportion of chromium forms in soil after remediation in different experimental design groups

After 15 days of restoration, according to the GB/T25282-2010 13 trace element form sequential extraction procedures for soil and sediment, weak acid-extractable Cr, reducible Cr, oxidizable Cr, and residual Cr in the soil were extracted and measured, as shown in Table 3 shown.

Characterizing the mobility and bioavailability of heavy metals in soil, weakly acidic Cr has the best mobility, is most easily absorbed by organisms, and has the greatest biological toxicity, while residual Cr is the most stable and has the least biological toxicity. The remediation effects of different experimental design groups are shown in Table 3. The experimental group using biochar-based three-dimensional composite materials and microbial collaborative remediation had a more significant remediation effect than using either of the two alone. After remediation, the stability of chromium in the soil was significantly enhanced, and the biological The toxicity is significantly reduced.

Experiment 3 Effect of bacterial solution dosage on soil remediation

Weigh 30g of chromium-contaminated soil with a concentration of 300mg/kg into a 100mL beaker. The original soil pH value is 8.2, and the soil moisture content is adjusted to 30% with water.

Blank group (no biochar-based three-dimensional composite material and no bacterial solution added),

Group A added 1 mL of biochar-based three-dimensional composite material with a concentration of 0.6 g/kg and a bacterial suspension with an OD600 of 2.25;

Group B added 3 mL of biochar-based three-dimensional composite material with a concentration of 0.6 g/kg and a bacterial suspension with an OD600 of 2.25;

Group C added 5 mL of biochar-based three-dimensional composite material with a concentration of 0.6 g/kg and a bacterial suspension with an OD600 of 2.25;

Group D added 8 mL of biochar-based three-dimensional composite material with a concentration of 0.6 g/kg and a bacterial suspension with an OD600 of 2.25;

After mixing evenly, cover with parafilm and incubate at room temperature 30°C for 14 days. After the reaction is completed, the Cr(VI) concentration in the soil is measured.

Table 4 Effect of different amounts of bacteria on the repair effect

​	Blank group	Group A	Group B	Group C	Group D
Cr(VI) concentration (mg/kg)	268.67	90.73	53.13	25.56	25.56

It can be seen from Table 4 that in soil with a Cr(VI) contamination concentration of 300mg/kg, when the dosage of bacterial solution increases from 1mL to 8mL, the reduction rate of soil Cr(VI) by the synergistic system after 14 days of reaction increases from 66.23% to 66.23%. 90.49%. However, when the microbial inoculation amount exceeds 5 mL, the synergistic system does not significantly improve the Cr(VI) reduction ability in chromium-contaminated soil, indicating that biochar-based three-dimensional composite materials are the main limiting factor for Cr(VI) reduction at this time.

Experiment 4 Effect of soil contaminated with different concentrations of chromium on the remediation effect

Weigh 30g of chromium-contaminated soil with different concentrations into a 100mL beaker. The original soil pH value is 8.2, and the soil moisture content is adjusted to 30% with water.

0.018g biochar-based three-dimensional composite material and 8mL bacterial liquid (OD600 is 2.25) were added respectively; group A is soil with chromium pollution concentration 200mg/kg, group B is soil with chromium pollution concentration 250mg/kg, and group C is chromium pollution concentration 300mg/kg. kg soil, group D is soil with chromium pollution concentration 350mg/kg, group E is soil with chromium pollution concentration 400mg/kg, group F is soil with chromium pollution concentration 450mg/kg, group G is soil with chromium pollution concentration 500mg/kg, mix them evenly. Cover with parafilm and incubate at room temperature 30°C for 14 days. After the reaction is completed, the Cr(VI) concentration in the soil is measured.

Table 5 Effect of different chromium contaminated soil concentrations on remediation effect

It can be seen from Table 5 that when the concentration of contaminated soil continues to increase, the remediation effect of biochar-based three-dimensional composite materials in collaboration with Cr(VI) reducing bacteria solution shows a changing trend. When the pollution concentration increases from 200 to 500mg/kg, after 14 days of reaction, The synergistic system reduced the Cr(VI) concentration in soil from 92.33% to 69.83%. When the concentration of contaminated soil is 400mg/kg, the Cr(VI) concentration reduction rate can reach 87.29%. However, when the concentration of contaminated soil exceeds 450mg/kg, the synergistic system does not significantly improve the Cr(VI) reduction ability in the soil, indicating that this When the synergistic system meets the high-efficiency remediation and restoration effect, the optimal soil pollution concentration range for remediation is less than 400mg/kg. Remediation can also be carried out when it is greater than 400mg/kg, but the effect will be relatively poor.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the present invention. within the scope of protection.

Claims (10)

1. A biochar-based three-dimensional composite material is characterized in that: the material is prepared by a method including the following steps:

   Mix biochar and m-phenylenediamine aqueous solution for 2-2.5 hours to allow m-phenylenediamine to adhere to the biochar, and add oxidants and alkali salt solutions for loading and oxidative polymerization, followed by filtration, washing, and drying to obtain biochar-based three-dimensional Composite material; among them, the mass ratio of biochar and m-phenylenediamine monomer is 1:30-1:50.
2. The biochar-based three-dimensional composite material according to claim 1, characterized in that: the oxidant is sodium persulfate, the molar ratio of the oxidant and m-phenylenediamine is 0.5-2, and the alkali salt solution is 2 mol/L. Na ₂ CO ₃ solution.
3. The biochar-based three-dimensional composite material according to claim 1, characterized in that: the biochar is made of biomass peanut shells, corn cobs, straw, rice straw or bark roasted under oxygen isolation conditions of 400-550°C, The roasting time is 2-4h, and it is obtained after cooling.
4. The biochar-based three-dimensional composite material according to claim 1, characterized in that: the particle size of the biochar is 0.05-1.5 mm, and the concentration of the m-phenylenediamine solution is 30-50 g/L.
5. The biochar-based three-dimensional composite material according to claim 1, characterized in that: the polymerization reaction time is 5-5.5 h, and the polymerization reaction conditions are ice bath at 0°C.
6. The biochar-based three-dimensional composite material according to claim 1, characterized in that: the obtained biochar-based three-dimensional composite material has a pore diameter of 7.72-10.29 nm.
7. A method for repairing high-concentration chromium-contaminated soil using the biochar-based three-dimensional composite material according to any one of claims 1 to 6, characterized in that: the method includes the following steps:

   1) Strain domestication: Select dominant strains from the soil of chromium-contaminated sites that can perform metabolic activities using organic matter and glycerol as electron donors and Cr(VI) as electron acceptor, and domesticate and expand the dominant strains. nourish;

   2) Mix the biochar-based three-dimensional composite material, the dominant bacterial species obtained in step 1) and the high-concentration chromium-contaminated soil to be repaired to evenly and fully react, add water to adjust the soil moisture content, and perform repair at normal temperature; wherein, the biochar The dosage of the base three-dimensional composite material is 0.6g/kg of soil, the dosage of the dominant bacterial species is 166-266mL/kg, and the soil moisture content is 20%-50%.
8. The biochar-based three-dimensional composite material according to claim 7, characterized in that: the pH value of the high-concentration chromium-contaminated soil is 4-9, the particle size is 0.1-3mm, and the chromium pollution concentration is 10-500 mg/kg.
9. The biochar-based three-dimensional composite material according to claim 7, characterized in that: in step 1), the culture medium for expanding the culture of dominant bacterial species adopts LB culture medium, and the Cr(VI) concentration gradient method is used to culture the bacteria. species are domesticated, and the Cr(VI) concentration is 50-500mg/L.
10. The biochar-based three-dimensional composite material according to claim 7, characterized in that the reaction time in step 2) is 3-14d.

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