Phosphorus bacteria enhanced sludge hydrothermal carbonization soil heavy metal remediation matrix, preparation method and application

Abstract

The present application relates to a kind of phosphorus bacteria reinforced sludge hydrothermal carbonization soil heavy metal remediation matrix and preparation method and application, wherein soil heavy metal remediation matrix is treated by hydrothermal carbonization to phosphorus-rich municipal sludge, and calcium chloride is added to obtain sludge hydrothermal carbonization product, acid-tolerant and heavy metal-tolerant phosphorus bacteria are enriched and screened from pyrite mountain soil, and it is loaded on the surface of rice husk modified by NaOH to obtain phosphorus bacteria-rice husk composite material, sludge hydrothermal carbonization product and phosphorus bacteria-rice husk composite material are mixed according to certain proportion, and soil heavy metal remediation matrix is obtained after open stacking for a certain time.Compared with prior art, the matrix can release a large amount of phosphate into the soil, which can form stable minerals with soil heavy metals to immobilize heavy metals, and on the other hand, it can provide sufficient phosphorus source for overlying remediation plants, promote plant growth, and ultimately realize ecological greening of soil.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of heavy metal contaminated soil remediation, in particular to a phosphorus solubilizing bacteria reinforced sludge hydrothermal carbonization heavy metal remediation matrix for soil, and a preparation method and application thereof. BACKGROUND

[0002] Municipal sludge contains rich phosphorus resources. Generally, the sludge contains 1-5% (by dry weight) of phosphorus. In some sludge from biological phosphorus removal processes, the content of phosphorus can be as high as 8%. At the same time, the sludge also contains pathogens, antibiotics, microplastics and heavy metals and other pollutants. Once these pollutants are released into the environment during the resource utilization of sludge, they will pose a great ecological threat. Therefore, in order to effectively utilize the phosphorus resources in the sludge, the sludge must be pretreated.

[0003] Among the inorganic pollutants in soil, heavy metals are particularly prominent. This is mainly because heavy metals cannot be decomposed by soil microorganisms, but can be easily accumulated and converted into more toxic methyl compounds. Even some heavy metals can be accumulated in the human body in harmful concentrations through the food chain, seriously endangering human health. Soil heavy metal pollutants mainly include mercury, cadmium, lead, copper, chromium, arsenic, nickel, iron, manganese and zinc. Although arsenic is not a heavy metal, it is usually included in the discussion of heavy metals because of its behavior, source and harm. In terms of plant needs, metal elements can be divided into two categories: ① elements that are not needed for plant growth and development, but that pose a significant threat to human health, such as cadmium, mercury and lead. ② elements that are needed for normal plant growth and development and have certain physiological functions for the human body, such as copper and zinc, but too much of them can cause pollution and hinder plant growth and development.

[0004] For soil heavily contaminated with heavy metals, plants have difficulty growing, soil water retention capacity decreases, bare areas form, fertility disappears, and it is difficult to restore green through the process of natural evolution. SUMMARY

[0005] The present application relates to the field of heavy metal contaminated soil remediation, in particular to a phosphorus solubilizing bacteria reinforced sludge hydrothermal carbonization heavy metal remediation matrix for soil, and a preparation method and application thereof.

[0006] The object of the present application can be achieved by the following technical solutions:

[0007] The present application provides a preparation method of a phosphorus solubilizing bacteria reinforced sludge hydrothermal carbonization heavy metal remediation matrix for soil, comprising the following steps:

[0008] Sludge carbonization product preparation: phosphorus-rich municipal sludge is subjected to hydrothermal carbonization treatment, and calcium chloride is added to improve the conversion rate of inorganic phosphorus, thereby obtaining a sludge hydrothermal carbonization product;

[0009] Phosphorus solubilizing bacteria solution preparation: acid-tolerant and heavy metal-tolerant phosphorus solubilizing bacteria are enriched and screened from pyrite mine soil, and expanded culture is performed to obtain a phosphorus solubilizing bacteria solution;

[0010] Phosphorus solubilizing bacteria-rice husk composite material preparation: rice husk material is subjected to chemical pretreatment, and is compounded with the phosphorus solubilizing bacteria solution to obtain a phosphorus solubilizing bacteria-rice husk composite material;

[0011] Soil heavy metal remediation substrate preparation: the sludge hydrothermal carbonization product and the phosphorus solubilizing bacteria-rice husk composite material are mixed according to a preset ratio, and then are left to stack open for a preset time to obtain a soil heavy metal remediation substrate finished product.

[0012] Further, the sludge carbonization product preparation process specifically comprises:

[0013] Phosphorus-rich municipal sludge with a water content of less than 80% and calcium chloride are added to a hydrothermal reactor for high-temperature carbonization;

[0014] The phosphorus content of the municipal sludge is greater than 3%;

[0015] The hydrothermal reaction conditions are that the volume of the hydrothermal reactor is at least 1 L, the heating rate of the reactor is 5-10 ℃ / min to a temperature of 150-300 ℃, the temperature is maintained for 0.5-2 h after reaching the set temperature, and then the reactor is cooled to room temperature to separate the sludge carbonization product;

[0016] The mass of the calcium chloride is 1%-20% of the dry mass of the municipal sludge.

[0017] Further, the phosphorus solubilizing bacteria solution preparation specifically comprises the following steps:

[0018] 1) 5-10 g of pyrite mine soil is added to 200 mL of enrichment culture solution, and the solution is shaken and cultured at a temperature of 25-35 ℃ and a rotation speed of 120 rpm for 24 h to obtain a bacterial enrichment solution;

[0019] 2) 5-10 mL of the bacterial enrichment solution is added to 200 mL of new enrichment culture solution, and the solution is shaken and cultured at a temperature of 25-35 ℃ and a rotation speed of 120 rpm for 24 h, and the supernatant of the enrichment solution is obtained after standing for 0.5-1 h, which is the bacterial enrichment solution;

[0020] 3) The bacterial enrichment solution is diluted and spread on a selective culture medium, and selection culture is performed at a temperature of 25-35 ℃, and the largest transparent circle is inoculated on a subculture medium and subculture is performed at a temperature of 25-35 ℃ to obtain a phosphorus solubilizing bacteria solution.

[0021] Further, the enrichment culture solution is configured by protein peptone, beef extract, sodium chloride and ultrapure water and obtained by high-temperature and high-pressure sterilization.

[0022] The concentration of each substance in the enrichment culture solution is: protein peptone 8 g / L, beef extract 2.5 g / L, sodium chloride 4 g / L, and pH is 7.2-7.5.

[0023] Further, the selection medium is configured by glucose, ammonium sulfate, sodium chloride, magnesium sulfate, manganese sulfate, potassium sulfate, ferrous sulfate, calcium phosphate, agar and ultrapure water and obtained by high-temperature and high-pressure sterilization.

[0024] The concentration of each substance in the selection medium is: glucose 10 g / L, ammonium sulfate 0.5 g / L, yeast extract powder 0.5 g / L, sodium chloride 0.3 g / L, potassium chloride 0.3 g / L, magnesium sulfate 0.3 g / L, ferrous sulfate 0.03 g / L, tricalcium phosphate 5 g / L, agar 15 g / L, and pH is 7.0-7.5.

[0025] Further, the subculture medium is configured by glucose, ammonium sulfate, sodium chloride, magnesium sulfate, manganese sulfate, potassium sulfate, ferrous sulfate, calcium phosphate and ultrapure water and obtained by high-temperature and high-pressure sterilization.

[0026] The concentration of each substance in the subculture medium is: glucose 10 g / L, ammonium sulfate 0.5 g / L, yeast extract powder 0.5 g / L, sodium chloride 0.3 g / L, potassium chloride 0.3 g / L, magnesium sulfate 0.3 g / L, ferrous sulfate 0.03 g / L, manganese sulfate 0.03 g / L, tricalcium phosphate 5 g / L, and pH is 7.0-7.5.

[0027] Further, the preparation of the phospha bacteria-rice hull composite material comprises the following steps:

[0028] 1) The naturally air-dried rice hull is ground through a sieve with a pore size of 1 mm;

[0029] 2) The sieved rice hull is added to a 3-8 wt% sodium hydroxide solution at a ratio of 0.3-0.6 kg / L, soaked at room temperature for 1-2 h, then taken out and washed with deionized water until neutral, and naturally air-dried;

[0030] 3) The rice hull is added to the phospha bacteria solution with a concentration of 1×10 7 -10 9 CFU / mL at a ratio of 0.5-1 kg / L, and shaken in a shaker for 1-2 h to adsorb, then the rice hull is collected and the surface culture solution is washed clean with sterilized water to obtain the phospha bacteria-rice hull composite material.

[0031] Further, the preparation process of the soil heavy metal remediation substrate is specifically: uniformly mixing the dry basis mass of the phosphorus-rich municipal sludge hydrothermal carbonization product and the phosphorus-dissolving bacteria-rice husk composite material according to a mass ratio of 1:0.02-0.1 and open stacking for a preset time to obtain the soil heavy metal immobilization substrate.

[0032] The height of the stack body during open stacking is 0.1-1.5 m, and the stacking time is 1-28 days.

[0033] The second aspect of the present application provides a phosphorus-dissolving bacteria-enhanced sludge hydrothermal carbonization soil heavy metal remediation substrate prepared by the above method.

[0034] The third aspect of the present application provides an application of the above soil heavy metal remediation substrate in the remediation of heavy metal contaminated soil and plant planting. The soil remediation substrate can release phosphate into the soil, which can form stable minerals with soil heavy metals to immobilize the heavy metals, and on the other hand, can provide sufficient phosphorus source for the overlying remediation plants to promote the growth of the plants, and finally realize the ecological greening of the soil.

[0035] In the conception process, the applicant believes that:

[0036] Sludge hydrothermal carbonization can achieve rapid inactivation or degradation of pathogens, drugs, microplastics and other pollutants in municipal sludge, passivation of heavy metals, while most of the organic phosphorus (OP) in the sludge is converted into inorganic phosphorus (IP). The hydrothermal carbonization reaction converts the non-apatite inorganic phosphorus in the sludge into apatite inorganic phosphorus, improves the biological availability of phosphorus, and promotes its resource utilization. The addition of calcium chloride can promote the conversion of phosphorus elements in the sludge into calcium phosphate and improve the conversion rate of apatite. Inorganic phosphorus in sludge and soil usually exists in the form of insoluble solid. Phosphorus-dissolving bacteria can dissolve calcium phosphate and other insoluble phosphates under acidic conditions by secreting small-molecule organic acids, and can also chelate metal ions such as iron, aluminum and calcium, thereby releasing the phosphate ions combined therewith and increasing the content of soluble phosphorus in the soil. The released phosphate ions can combine with heavy metal ions in the soil and sludge to form stable mineral precipitates, achieving the purpose of immobilizing soil heavy metals. At the same time, the free phosphate ions can also be absorbed by plants, promoting the growth of overlying vegetation on heavy metal contaminated soil, achieving two purposes at once. After municipal sludge carbonization treatment, organic matter will decompose, and the organic matter content of heavy metal contaminated soil is very low, so it is necessary to provide a stable carbon source for the growth and reproduction of phosphorus-dissolving bacteria. The porosity and specific surface area of modified rice husk increase, and the adsorption sites of phosphorus-dissolving bacteria increase, which can effectively serve as a carrier for phosphorus-dissolving bacteria. At the same time, rice husk as a natural slow-release material can provide a carbon source for the growth and reproduction of phosphorus-dissolving bacteria.

[0037] The application believes that by removing a large amount of pollutant through hydrothermal carbonization of municipal sludge, mixing and stacking the carbonization product with a phosphorus solubilizing bacteria composite material, the phosphorus element enriched in the sludge can be fully released, the heavy metals in the sludge and soil can be effectively fixed, the growth of the repair plants can be promoted, and the goal of ecological greening can be achieved.

[0038] Compared with the prior art, the application has the following technical advantages:

[0039] (1) The application disposes the phosphorus-rich municipal sludge by hydrothermal carbonization, calcium chloride is added in the hydrothermal process to promote the conversion of phosphorus element into inorganic phosphorus, improve the resource utilization efficiency, and the phosphorus solubilizing bacteria-rice husk composite material is matched to promote the dissolution and release of inorganic phosphorus, the rice husk can provide a slow-release carbon source for the phosphorus solubilizing bacteria, the generated phosphate under the action of the phosphorus solubilizing bacteria can combine with the heavy metals in the soil and sludge to generate stable phosphate precipitate, and the phosphate can also be absorbed and utilized by the repair vegetation to promote the growth of the vegetation and achieve the sustainable repair goal.

[0040] (2) The application can prepare a large amount of heavy metal fixing substrate for mine soil, promote the repair of the soil in the heavy metal pollution serious area such as the pyrite mine and the tailing pond, and realize the stable greening of the mine. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The process flow chart of the soil heavy metal fixing substrate preparation method using the phosphorus solubilizing bacteria-rice husk composite material and the hydrothermal carbonization product of the phosphorus-rich municipal sludge as the main substrate in the application. DETAILED DESCRIPTION

[0042] In the application, the soil heavy metal repair substrate is obtained by hydrothermal carbonization treatment of the phosphorus-rich municipal sludge, adding CaCl2 to improve the conversion rate of inorganic phosphorus, thereby obtaining the sludge hydrothermal carbonization product, enriching and screening the acid-tolerant and heavy metal-tolerant phosphorus solubilizing bacteria from the pyrite mine soil, loading the phosphorus solubilizing bacteria on the surface of the NaOH modified rice husk, and the rice husk can provide a large number of adsorption sites and stable carbon source for the phosphorus solubilizing bacteria, thereby obtaining the phosphorus solubilizing bacteria-rice husk composite material, mixing the sludge hydrothermal carbonization product and the phosphorus solubilizing bacteria-rice husk composite material according to a certain proportion, and obtaining the soil heavy metal repair substrate after open stacking for a certain time, the substrate can release a large amount of phosphate into the soil, on the one hand, the phosphate can form stable minerals with the heavy metals in the soil to fix the heavy metals, on the other hand, the phosphate can provide sufficient phosphorus source for the overlying repair plants to promote the growth of the plants, and finally realize the ecological greening of the soil.

[0043] The preparation method of the municipal sludge hydrothermal carbonization product in the technical solution is as follows: 1) the phosphorus-rich municipal sludge with a water content of more than 80% and calcium chloride are added into a hydrothermal reactor for high-temperature carbonization; 2) the mass of calcium chloride is 0.5%-3% of the dry basis mass of the municipal sludge; 3) the hydrothermal reaction conditions are that the volume of the hydrothermal reactor is at least 1L, the heating rate of the reactor is 5-10℃ / min to heat the reactor to a temperature of 150-300℃, the temperature is kept for 0.5-2h after reaching the set temperature, and then the reactor is cooled to room temperature to separate the sludge carbonization product.

[0044] In the above preparation method, the raw material further includes calcium chloride, and the mass of the calcium chloride is 0.5%-3% of the dry basis mass of the municipal sludge, and specifically can be 0.5% or 3%.

[0045] In the above preparation method, the phosphorus content of the municipal sludge is greater than 3%, and the water content of the hydrothermal carbonization product of the municipal sludge is less than 60%, and specifically can be 54.3%±0.1%.

[0046] The preparation method of the phosphorus solubilizing bacteria solution is as follows: 1) 5-10g of pyrite mountain acid soil (pH<4) is added to 200mL of the enrichment culture, and the bacteria enrichment liquid is obtained by shaking culture at a temperature of 25-35℃ and a rotation speed of 120rpm for 24h; wherein the enrichment culture medium is prepared by configuring protein peptone, beef extract, sodium chloride and ultrapure water and is obtained by high-temperature and high-pressure sterilization; 2) 5-10mL of the bacteria enrichment liquid is added to 200mL of new enrichment culture, and the bacteria enrichment liquid is obtained by shaking culture at a temperature of 25-35℃ and a rotation speed of 120rpm for 24h, and the supernatant of the enrichment liquid is obtained after standing for 0.5-1h; 3) the bacteria enrichment liquid is diluted and coated on the selection medium, and the bacteria spot with the largest transparent circle diameter is inoculated on the subculture medium and subcultured at a temperature of 25-35℃ to obtain the phosphorus solubilizing bacteria solution; the selection medium is prepared by configuring glucose, ammonium sulfate, sodium chloride, magnesium sulfate, manganese sulfate, potassium sulfate, ferrous sulfate, calcium phosphate, agar and ultrapure water and is obtained by high-temperature and high-pressure sterilization; and the subculture medium is prepared by configuring glucose, ammonium sulfate, sodium chloride, magnesium sulfate, manganese sulfate, potassium sulfate, ferrous sulfate, calcium phosphate and ultrapure water and is obtained by high-temperature and high-pressure sterilization.

[0047] Preparation of the phosphorus solubilizing bacteria-rice husk composite material: 1) the naturally air-dried rice husk is ground through a screen with a pore size of 1mm and is used as needed; 2) the rice husk is added to a 3-8% sodium hydroxide solution, and the proportion is 0.3-0.6kg of rice husk per liter of solution; the rice husk is soaked in the solution at room temperature for 1-2h, taken out, washed with deionized water, and naturally air-dried; 3) the rice husk is added to the phosphorus solubilizing bacteria solution at a proportion of 0.5-1kg / L, and the concentration of the bacteria solution is 1×10 7 -10 9The phosphorus solubilizing bacteria solution is shaken in a shaker for 1-2 h, and the rice husks are collected and rinsed with sterile water to remove the surface culture solution, and then reserved.

[0048] The raw materials of the preparation method of the soil heavy metal fixing substrate provided by the application include phosphorus solubilizing bacteria, rice husks and phosphorus-rich municipal sludge; the dry basis mass ratio of the municipal sludge carbonization product to the phosphorus solubilizing bacteria-rice husk composite material is 1:0.02-0.1, specifically 1:0.02 or 1:0.1, and the raw materials are uniformly mixed and stacked in an open state for a certain time to obtain the soil heavy metal fixing substrate.

[0049] In the preparation method, the height of the stack is 0-1.5 m (such as 1 m), and the stacking time is 0-4 weeks (such as 2 weeks), but not 0.

[0050] The soil heavy metal fixing substrate prepared by the preparation method is also within the protection scope of the application.

[0051] The application further provides the application of the soil heavy metal fixing substrate in the vegetation planting and repair of heavy metal contaminated soil.

[0052] In the application, the soil is a soil with high heavy metal concentration and lacking of nutrients.

[0053] The soil heavy metal fixing substrate can be mixed and stirred with the heavy metal contaminated surface soil (0-20 cm in depth), and then laid on the surface of the land.

[0054] The application will be described in detail below with reference to the drawings and specific examples. In the technical solution, the preparation means, materials, structures or component ratios of features not explicitly described are regarded as common technical features disclosed in the prior art. In the following examples, the experimental methods are conventional methods unless otherwise specified. In the following examples, the materials and reagents are commercially available unless otherwise specified.

[0055] The mine soil is taken from the surface exposed soil of Xiaonanshan pyrite mine in Xiangshan Town, Ma'anshan, and has a water content of about 8.2%±0.3%, and the content of heavy metals is shown in Table 1.

[0056] Table 1: Heavy metal content of surface exposed soil of Xiaonanshan pyrite mine (unit: mg / kg)

[0057]

[0058] The phosphorus-rich municipal sludge is taken from a sewage treatment plant in Ma'anshan, has a water content of 85%±0.3%, an organic matter content of 293.1 g / kg, and a phosphorus element content of 3.5%; and the water content of the hydrothermal carbonization product of the phosphorus-rich municipal sludge is 53.2%.

[0059] The phosphorus solubilizing bacteria were obtained by enrichment culture from the soil of Xiaonanshan pyrite mine in Ma'anshan City.

[0060] The rice hulls were purchased from a rural market in Ma'anshan City, with a moisture content of 8.4% ± 0.05% and a cellulose content of 38.6% ± 0.3.

[0061] Example 1

[0062] The phosphorus-rich municipal sludge was obtained from a sewage treatment plant in Ma'anshan City, with a moisture content of 85% ± 0.3%, an organic matter content of 293.1 g / kg, and a phosphorus element content of 3.5%. The water heat carbonization product of the phosphorus-rich municipal sludge had a moisture content of 53.2%.

[0063] The phosphorus solubilizing bacteria were obtained by enrichment culture from the soil of Xiaonanshan pyrite mine in Ma'anshan City.

[0064] The materials were prepared according to the following formulations, with a total amount of 1 t of phosphorus-rich municipal sludge dry substrate, i.e., 1.88 t of water heat carbonization product of phosphorus-rich municipal sludge, and a total amount of about 50 kg of phosphorus solubilizing bacteria-rice hull composite material, with a concentration of 1 × 10 8 CFU / mL of phosphorus solubilizing bacteria, 5 kg of calcium chloride, and 3% NaOH solution for rice hull modification.

[0065] The mine soil heavy metal fixation substrate was prepared according to the process flowchart shown in FIG. 1, and the specific steps are as follows: Figure 1

[0066] 1) The phosphorus-rich municipal sludge and calcium chloride were added to the hydrothermal reactor in proportion, heated to 150°C at a heating rate of 5°C / min and maintained for 2 h, and after cooling to room temperature, the sludge carbonization product was separated;

[0067] 2) 10 g of Xiaonanshan pyrite mine surface soil was taken, and the phosphorus solubilizing bacteria were enriched and cultured from the mine soil according to the established steps to obtain the phosphorus solubilizing bacteria solution;

[0068] 3) 50 kg of naturally air-dried rice hulls were added to 3% NaOH solution at a proportion of 0.3 kg / L, soaked at room temperature for 1 h, then washed with deionized water to neutralize, naturally air-dried, and then added to the phosphorus solubilizing bacteria solution with a concentration of 1 × 10 7 CFU / mL at a proportion of 0.5 kg / L, shaken in a shaker for 1 h for adsorption, and then the rice hulls were collected and washed with sterile water to remove the surface culture solution, and then stored for use.

[0069] 3) Mixing, the water heat carbonization product of municipal sludge and the phosphorus solubilizing bacteria-rice hull composite material were uniformly mixed at a mass ratio of 1:0.05, and were stacked to a height of 1 m, and were stacked for 1 week to obtain the soil heavy metal fixation substrate.

[0070] Example 2​

[0071] The phosphorus-rich municipal sludge was obtained from a sewage treatment plant in Maanshan City, with a water content of 85% ± 0.3%, an organic matter content of 293.1 g / kg, and a phosphorus element content of 3.5%; the water heat carbonization product of the phosphorus-rich municipal sludge had a water content of 53.2%.

[0072] The phosphorus solubilizing bacteria were obtained by enrichment culture from the soil of Xiaonanshan pyrite mine in Maanshan City.

[0073] The materials were prepared according to the following formulations, and the total amount of phosphorus-rich municipal sludge dry substrate was about 1 t for each formulation, i.e., the mass of the water heat carbonization product of the phosphorus-rich municipal sludge was 1.88 t, the total mass of the phosphorus solubilizing bacteria-rice husk composite material was about 100 kg, the concentration of the phosphorus solubilizing bacteria solution was 1 × 10 9 CFU / mL, the amount of added calcium chloride was 15 kg, and the rice husk modification solution was an 8% NaOH solution.

[0074] The mine soil heavy metal fixation substrate was prepared according to the process flow diagram shown in FIG. Figure 1 The specific steps are as follows:

[0075] 1) The phosphorus-rich municipal sludge and calcium chloride were added to the hydrothermal reactor in proportion, heated to 300°C at a heating rate of 10°C / min and maintained for 2 h, and the sludge carbonization product was separated after cooling to room temperature;

[0076] 2) 10 g of Xiaonanshan pyrite mine surface soil was taken, and the phosphorus solubilizing bacteria were enriched and cultured from the mine soil according to the established steps to obtain a phosphorus solubilizing bacteria solution;

[0077] 3) 100 kg of naturally air-dried rice husk was added to an 8% NaOH solution at a proportion of 0.6 kg / L, soaked at room temperature for 1 h, then taken out and washed with deionized water to neutral, naturally air-dried, and then the rice husk was added to the phosphorus solubilizing bacteria solution with a concentration of 1 × 10 9 CFU / mL at a proportion of 1 kg / L, and shaken in a shaker for 2 h for adsorption, and the rice husk was collected and washed with sterile water to prepare the surface culture solution for standby use.

[0078] 3) Mixing, the municipal sludge hydrothermal carbonization product and the phosphorus solubilizing bacteria-rice husk composite material were uniformly mixed at a mass ratio of 1:0.1, and were stacked to a height of 1 m, and were stacked for 2 weeks to obtain the soil heavy metal fixation substrate.

[0079] Application Example 1

[0080] The strain identification analysis was performed on the phosphorus solubilizing bacteria prepared according to the method of Examples 1-2, DNA extraction was performed on the strain samples, amplification sequencing was performed using bacterial 16S universal primers, and the sequencing results were compared in the NCBI database to preliminarily identify the samples.

[0081] The sample DNA was amplified using 27F (5'-AGAGTTTGATCCTGGCTCAG-3) / 1492R (5'-GGTTACCTTGTTACGACTT-3) primers, and the strain with the largest transparent circle diameter was Pseudomonas aeruginosa. In the case of the phosphorus solubilizing bacteria in Example 1, the Pseudomonas aeruginosa is Pseudomonas aeruginosa strain DSM 50071, and the NCBI number is NR_117678.1.

[0082] Further, the applicant purchased Pseudomonas aeruginosa strain DSM 50071 at the following website: http: / / www.biofeng.com / junzhu / biaozhunjunzhu / DSM50071.html (Biofeng service platform), and applied the purchased Pseudomonas aeruginosa strain DSM 50071 directly to the experimental scenarios in Application Examples 2-4, and the results obtained were consistent with the effects of the phosphorus solubilizing bacteria enriched and cultured from the soil of the Ma'anshan Xiaonanshan pyrite mine in terms of copper ion fixation efficiency, effective phosphorus concentration in different substrates, heavy metal concentration in leachate, and heavy metal fixation rate. Therefore, the applicant believes that in the case of high cost and / or lack of sources of Pseudomonas aeruginosa strain DSM 50071 standard bacteria obtained through commercial purchase, the self-enrichment and culture method from the soil of the pyrite mine can be preferred for implementing the present solution.

[0083] It should be noted that the self-enrichment and culture method in the present technical solution uses the methods disclosed in the following literature:

[0084] 1) Nie Z. Screening of Phosphorus Solubilizing Bacteria and Its Effect on Rice Germination and Seedling Growth [D]. Hunan Agricultural University, 2021. DOI: 10.27136 / d.cnki.ghunu.2021.000858.

[0085] 2) Wan W, Qin Y, Wu H, et al. Isolation and Characterization of Phosphorus Solubilizing Bacteria With Multiple Phosphorus Sources Utilizing Capability and Their Potential for Lead Immobilization in Soil [J]. Frontiers in Microbiology, 2020, 11:752.

[0086] It should be noted that the core idea of the technical solution is the combination of the overall means, not the extraction and culture of the bacterial strain.

[0087] Application Example 2

[0088] Copper heavy metal solutions of 200 mg / L, 500 mg / L, 1000 mg / L and 1500 mg / L were respectively configured, and protein peptone, beef extract and sodium chloride were added to the copper heavy metal solution to make the concentration of the culture medium 10 g / L, 3 g / L and 5 g / L, respectively, then different mass of calcium phosphate was added to each concentration of heavy metal solution to make the concentration 15 g / L, and the phosphorus solubilizing bacteria in Example 1 was inoculated, after one week of culture, the concentration of copper ions in the solution was measured by ICP, as shown in Table 2.

[0089] Table 2 Copper ion fixation efficiency

[0090]

[0091] As can be seen from Table 2, the phosphorus solubilizing bacteria has a very good fixing effect on copper ions, and the fixation rate remains at about 90%, so the phosphorus solubilizing bacteria not only has good tolerance to high heavy metal concentration, but also can dissolve calcium phosphate to release phosphate ions and remove copper ions in the form of precipitation, which can be applied to soil with high heavy metal content, especially soil with high copper ion content.

[0092] Application Example 3

[0093] The municipal sludge carbonization product in Examples 1 and 2 and the soil heavy metal fixation substrate after one week of open stacking were taken and dried at 80°C for 24h, 5g of each substrate was taken and the content of available phosphorus in each substrate was determined by Olsen method (0.5mol / L NaHCO3 extraction at pH=8.5-molybdenum antimony anti-colorimetric method), as shown in Table 3.

[0094] Table 3 Concentration of available phosphorus in different substrates (mg / g)

[0095]

[0096] As can be seen from Table 3, the concentration of available phosphorus in the municipal sludge carbonization product after adding the phosphorus solubilizing bacteria-rice husk composite material and open stacking for one week is significantly increased, and it can be found that the content of available phosphorus in the municipal sludge carbonization product 1 added with CaCl2 is higher, indicating that CaCl2 promotes the conversion of phosphorus elements in the municipal sludge to inorganic phosphorus, thereby increasing the content of available phosphorus. Combined with Application Example 2, it can be seen that the phosphorus solubilizing bacteria can increase the concentration of available phosphorus, thereby enhancing the heavy metal fixation capacity of the soil heavy metal fixation substrate.

[0097] Application Example 4

[0098] The soil heavy metal fixing matrix obtained in Example 1 is applied to the surface soil of Xiaonanshan pyrite mine in Xiangshan town (mass ratio 1:3, No. 1), and municipal sludge (No. 2) and a blank control group (pure mine soil, No. 3) are applied as comparative application examples, and simulated sulfuric acid leaching of pyrite mine is carried out for 14 days using pH = 4 dilute sulfuric acid, and the concentration of heavy metals in the leaching solution is detected by ICP-OES, as shown in Table 4, and the heavy metal fixation rate of leaching is shown in Table 5.

[0099] Table 4 Heavy metal concentration in leaching solution (unit: mg / kg)

[0100]

[0101] Table 5 Heavy metal fixation rate of leaching (%)

[0102]

[0103] As can be seen from Table 5, the soil heavy metal fixing matrix of the present application has a strong fixing effect on the heavy metals in the mine soil, especially for copper ions and lead ions, with a fixation rate of more than 90%, and has obvious fixing effect on other heavy metal ions, which can well reduce the ecological risk of heavy metals in the soil and promote the ecological restoration of the mine.

[0104] As can be seen from the above, the mine soil heavy metal fixing matrix is prepared by using the hydrothermal carbonization product of phosphorus-rich municipal sludge and the phosphorus-dissolving bacteria-rice husk composite material, the rice husk can provide a stable carbon source for the phosphorus-dissolving bacteria, CaCl2 is added in the hydrothermal carbonization process to increase the conversion rate of phosphorus elements in the sludge to inorganic phosphorus, the phosphorus-dissolving bacteria can effectively dissolve the inorganic phosphorus salt in the sludge carbonization product and release a large amount of phosphate, and the phosphate can combine with the heavy metals in the mine soil to generate stable precipitates, thereby realizing the fixation of heavy metals, and the phosphate can also be absorbed by the restored plants to promote their growth, achieving the purpose of soil ecological restoration.

[0105] The above description of the embodiments is for the convenience of the ordinary skilled person in the art to understand and use the present application. Those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described herein to other embodiments without having to go through creative labor. Therefore, the present application is not limited to the above embodiments, and those skilled in the art can make improvements and modifications to the present application without departing from the scope of the present application.

Claims

1. A method for preparing a phosphorus solubilizing bacteria (PSB) enhanced sewage sludge hydrochar soil heavy metal remediation substrate, characterized in that, The method comprises the following steps: Sludge carbonization product preparation: hydrothermal carbonization treatment is performed on phosphorus-rich municipal sludge, and calcium chloride is added to improve the conversion rate of inorganic phosphorus, so as to obtain a sludge hydrothermal carbonization product; Phosphorus solubilizing bacteria liquid preparation: acid-tolerant and heavy metal-tolerant phosphorus solubilizing bacteria are enriched and screened from pyrite mine soil, and are expandedly cultured to obtain a phosphorus solubilizing bacteria liquid; Phosphorus solubilizing bacteria-rice husk composite material preparation: rice husk material is chemically pretreated, and is compounded with the phosphorus solubilizing bacteria liquid to obtain a phosphorus solubilizing bacteria-rice husk composite material; Soil heavy metal remediation substrate preparation: the sludge hydrothermal carbonization product and the phosphorus solubilizing bacteria-rice husk composite material are mixed according to a preset ratio, and are then open-stacked for a preset time to obtain a soil heavy metal remediation substrate product; The sludge carbonization product preparation process specifically comprises the following steps: Phosphorus-rich municipal sludge with a water content of less than 80% and calcium chloride are added into a hydrothermal reactor for high-temperature carbonization; The municipal sludge contains more than 3% of phosphorus elements; The hydrothermal reaction is performed under the following conditions: the volume of the hydrothermal reactor is at least 1 L, the heating rate of the reactor is 5-10 ℃ / min, the temperature is 150-300 ℃, the temperature is kept for 0.5-2 h after reaching the set temperature, and then the reactor is cooled to room temperature to separate the sludge carbonization product; The mass of the calcium chloride is 1%-20% of the dry mass of the municipal sludge; The phosphorus solubilizing bacteria-rice husk composite material preparation comprises the following steps: 1) The naturally air-dried rice husk is ground through a 1 mm sieve; 2) The sieved rice husk is added into a 3-8 wt% sodium hydroxide solution, the adding ratio is 0.3-0.6 kg / L, the rice husk is soaked in the solution at room temperature for 1-2 h, then the rice husk is taken out and washed with deionized water until neutral, and is naturally air-dried; 3) The rice husk is added to the phosphorus solubilizing bacteria solution at a ratio of 0.5-1 kg / L, and the concentration of the bacteria solution is 1 x 10 7 -10 9 CFU / mL, and the mixture is shaken for 1-2 h in a shaker. The rice husk is collected and the surface culture solution is washed clean with sterilized water to obtain a phosphorus solubilizing bacteria-rice husk composite material. The soil heavy metal remediation substrate preparation process specifically comprises the following steps: the dry mass of the sludge hydrothermal carbonization product and the phosphorus solubilizing bacteria-rice husk composite material are uniformly mixed according to a mass ratio of 1:0.02-0.1, and are then open-stacked for a preset time to obtain the soil heavy metal remediation substrate; The height of the stack is 0.1-1.5 m, and the stacking time is 1-28 days.

2. The method for preparing a phosphate-solubilizing bacteria-enhanced sludge hydrothermal carbonization soil heavy metal remediation matrix according to claim 1, characterized in that, The phosphorus solubilizing bacteria liquid preparation specifically comprises the following steps: 1) 5-10 g of pyrite mine soil is added into 200 mL of enrichment culture solution, and is cultured under the conditions of a temperature of 25-35 ℃ and a rotation speed of 120 rpm for 24 h to obtain a bacterial enrichment liquid; 2) 5-10 mL of the bacterial enrichment liquid is added into 200 mL of new enrichment culture solution, and is cultured under the conditions of a temperature of 25-35 ℃ and a rotation speed of 120 rpm for 24 h, and then the supernatant of the enrichment liquid is obtained after standing for 0.5-1 h, which is the bacterial enrichment liquid; 3) The bacterial enrichment liquid is diluted and inoculated on a selective culture medium, and is cultured at a temperature of 25-35 ℃, and then the largest transparent circle is selected and inoculated on a subculture medium and is subcultured at a temperature of 25-35 ℃ to obtain a phosphorus solubilizing bacteria liquid.

3. The method according to claim 2, wherein the sludge is a mixture of sewage sludge and manure, and the phosphorus solubilizing bacteria is Bacillus megaterium. The enrichment culture solution is prepared from peptone, beef extract, sodium chloride and ultrapure water, and is sterilized at high temperature and high pressure. The concentration of each substance in the enrichment culture solution is: 8 g / L of proteose peptone, 2.5 g / L of beef extract, 4 g / L of sodium chloride, and pH is 7.2-7.

5.

4. The method according to claim 2, wherein the sludge is a mixture of sewage sludge and manure, and the phosphorus solubilizing bacteria is Bacillus megaterium. The selection medium is configured by glucose, ammonium sulfate, sodium chloride, magnesium sulfate, manganese sulfate, potassium sulfate, ferrous sulfate, calcium phosphate, agar and ultrapure water, and is obtained by high-temperature and high-pressure sterilization; The concentration of each substance in the selection medium is: 10 g / L of glucose, 0.5 g / L of ammonium sulfate, 0.5 g / L of yeast extract powder, 0.3 g / L of sodium chloride, 0.3 g / L of potassium chloride, 0.3 g / L of magnesium sulfate, 0.03 g / L of ferrous sulfate, 5 g / L of calcium phosphate, 15 g / L of agar, and pH is 7.0-7.

5.

5. The method according to claim 2, wherein the method is characterized by, The subculture medium is configured by glucose, ammonium sulfate, sodium chloride, magnesium sulfate, manganese sulfate, potassium sulfate, ferrous sulfate, calcium phosphate and ultrapure water, and is obtained by high-temperature and high-pressure sterilization; The concentration of each substance in the subculture medium is: 10 g / L of glucose, 0.5 g / L of ammonium sulfate, 0.5 g / L of yeast extract powder, 0.3 g / L of sodium chloride, 0.3 g / L of potassium chloride, 0.3 g / L of magnesium sulfate, 0.03 g / L of ferrous sulfate, 0.03 g / L of manganese sulfate, 5 g / L of calcium phosphate, and pH is 7.0-7.

5.

6. A sludge hydrothermal carbonization soil heavy metal remediation substrate strengthened by phosphorus solubilizing bacteria, which is prepared by the method of any one of claims 1 to 5.

7. Use of a soil heavy metal remediation substrate as claimed in claim 6 in the remediation of heavy metal contaminated soil and plant growing, characterised in that, The soil remediation substrate can release phosphate into the soil, on the one hand, can form stable minerals with soil heavy metals to fix heavy metals, on the other hand, can provide sufficient phosphorus source for the overlying remediation plants, promote the growth of plants, and ultimately realize the ecological greening of the soil.

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