Phosphorus-rich sludge pyrolytic charcoal and phosphate-solubilizing bacteria combined soil remediation agent as well as preparation method and application thereof

Abstract

The invention relates to the field of soil remediation, in particular to a soil remediation agent with phosphorus-rich sludge pyrolysis biochar combined with phosphorus-solubilizing bacteria and a preparation method and application thereof.The preparation method comprises the following steps that dehydrated phosphorus-rich sludge and a calcium-based additive are mixed according to the Ca / P molar ratio of 1-2, pyrolysis is conducted in the inert atmosphere, and the phosphorus-rich sludge pyrolysis biochar is obtained; the phosphorus-rich sludge pyrolytic charcoal is mixed with the phosphorus-solubilizing bacteria subjected to amplification culture, the phosphorus-solubilizing bacteria with the colony count being 1 * 10 < 9 >-10 * 10 < 9 > are added into per gram of the phosphorus-rich sludge pyrolytic charcoal for mixing, and the soil remediation agent is obtained and used for treating heavy metal in soil. The method solves the problems of high cost, long period, low fertility of the repaired soil and difficulty in repairing the high-concentration heavy metal polluted soil in a heavy metal polluted soil repairing method in the prior art, and realizes the double effects of efficiently fixing heavy metals and supplying phosphate fertilizer to promote plant growth.

Description

Technical Field

[0001] The present invention belongs to the field of soil remediation, and more specifically, relates to a soil remediation agent of phosphorus-rich sludge pyrolysis biochar combined with phosphorus-dissolving bacteria, and a preparation method and application thereof. Background Art

[0002] Due to the impact of human activities such as industrial pollution, mineral development, and the discharge of pollutants from abandoned mines, heavy metal pollution in soil has become a global environmental problem. Heavy metal pollution in soil is characterized by universality, concealment, bioaccumulation, irreversibility, and long-term nature. It will cause serious harm to the ecological environment and the living space of soil microorganisms, and will spread along the food chain, seriously affecting human health. It is urgent to find a simple and quick way to solve the problem of heavy metal pollution in soil.

[0003] There are two main technologies for remediation of heavy metal contaminated soil. The first is to directly remove heavy metals from the soil. Common methods include engineering remediation and hyperaccumulation phytoremediation. For example, Chinese patent CN108160688A provides a five-step elution method that can achieve efficient removal of various heavy metal ions in the soil. Chinese patent CN103357655A uses a leaching solution composed of ferric chloride and organic acid to elute heavy metal contaminated soil, with a removal rate of 80% for heavy metal cadmium and 55% for heavy metal lead. Chinese patent CN109127720A uses the enrichment of heavy metals by large-leaf wellhead grass or centipede grass, combined with indoleacetic acid and kinetin, and the lead and cadmium contents in the soil decreased by 18% and 27% respectively after two harvests, with significant effects. However, engineering measures are costly and easily lead to damage to the natural properties of the soil; hyperaccumulation phytoremediation measures are greatly limited in practical applications due to low target biomass and long remediation cycles.

[0004] The second is to change the occurrence form of heavy metals in the soil, weaken their migration ability and reduce their bioavailability, such as using soil remediation agents. At present, common soil remediation agents include biomass-based biochar, activated carbon, inorganic fertilizers and phosphate rock, among which biomass-based biochar is the most widely used. Its adsorption mechanism of heavy metals includes surface complexation, electrostatic attraction, ion exchange, mineral precipitation and other effects. Chinese patent CN114797779A pyrolyzes reed straw at 400°C, and then adds iron nitrate and potassium hydroxide to obtain ferrihydrate-modified biochar, which can be used to repair soil contaminated by arsenic, lead and cadmium heavy metals. However, the nutrient content of biomass-derived biochar is low, and direct application may even adsorb nutrients in the soil, resulting in low soil fertility. Therefore, it is usually necessary to apply fertilizers in combination to promote plant growth, which increases the process cost.

[0005] In addition to biochar, microbial remediation has been applied to pollution remediation technology due to its advantages such as low remediation cost and low environmental pollution. Chinese patent CN11 8256370A discloses a method for remediating heavy metal contaminated soil using a bacterial solution mixed with multiple strains. Chinese patent CN114644992A provides a Kosakonia sp.GRINML13 strain, which has a good phosphate solubilization effect and can efficiently release phosphorus from calcium phosphate to form insoluble lead chlorophosphate with heavy metal lead ions to achieve a stable effect, but the heavy metal concentration of the patented soil is less than 50 mg / kg. This is because free microorganisms are susceptible to heavy metal poisoning while repairing heavy metals, and will be subject to competition from the original soil microbial community, so the remediation effect is greatly reduced, and only low-polluted soil can be repaired.

[0006] In summary, existing methods for remediating heavy metal contaminated soil have problems such as high cost, long cycle, low soil fertility after remediation, and difficulty in remediating soil contaminated with high concentrations of heavy metals. Summary of the invention

[0007] In view of the above defects or improvement needs of the prior art, the present invention aims to provide a phosphorus-rich sludge pyrolysis biochar combined with phosphate-dissolving bacteria as a soil remediation agent, and a preparation method and application thereof. The use of phosphorus-rich sludge pyrolysis biochar combined with phosphate-dissolving bacteria to remediate heavy metal contaminated soil can combine the advantages of biochar remediation and microbial remediation. Its purpose is to solve the problems of high cost, long cycle, low soil fertility after remediation, and difficulty in remediating high-concentration heavy metal contaminated soil in the prior art heavy metal contaminated soil remediation methods, and achieve the dual effects of efficient fixation of heavy metals and supply of phosphate fertilizers to promote plant growth.

[0008] In order to achieve the above object, according to one aspect of the present invention, a method for preparing a soil remediation agent of phosphorus-rich sludge pyrolysis biochar combined with phosphorus-dissolving bacteria is provided, characterized in that it comprises the following steps:

[0009] (1) mixing dehydrated phosphorus-rich sludge having a phosphorus mass percentage of 3-10% with a calcium-based additive at a Ca / P molar ratio of 1-2, and pyrolyzing the mixture under an inert atmosphere to obtain phosphorus-rich sludge pyrolysis biochar;

[0010] (2) The pyrolysis biochar of phosphorus-rich sludge was mixed with the expanded cultured phosphate-dissolving bacteria, and the colony count was added at 1×10 per gram of pyrolysis biochar of phosphorus-rich sludge. 9 -10×10 9 The phosphate-dissolving bacteria are mixed to obtain a soil remediation agent.

[0011] Preferably, the calcium-based additive is selected from one or more of calcium chloride, calcium oxide, calcium hydroxide, calcium phosphate and calcium carbonate.

[0012] Preferably, the phosphate-solubilizing bacteria are one or more of Pseudomonas aeruginosa, Bacillus, Escherichia coli, Burkholderia cepacia, Bacillus subtilis, and Enterobacter cloacae.

[0013] Preferably, the heavy metal is one or more of lead, cadmium, zinc and copper.

[0014] Preferably, the pyrolysis temperature in step (1) is 500-700°C, the heating rate is 5-20°C / min, and the pyrolysis time is 1-3h.

[0015] Preferably, the dewatered phosphorus-rich sludge is pre-treated before being mixed with the calcium-based additive, and the pre-treatment is sequentially drying, grinding and screening.

[0016] Preferably, the surface tar of the phosphorus-rich sludge pyrolysis biochar is cleaned with dichloromethane before being mixed with the phosphate-dissolving bacteria, and then rinsed with deionized water and dried, ground and sieved. The liquid-solid ratio of dichloromethane to phosphorus-rich sludge pyrolysis biochar is 5-50 g / L, and the cleaning time is 1-2 h.

[0017] According to another aspect of the present invention, a soil remediation agent prepared by a method for preparing a soil remediation agent of pyrolysis biochar of phosphorus-rich sludge combined with phosphorus-dissolving bacteria is provided.

[0018] According to another aspect of the present invention, a method for treating heavy metal contaminated soil using the soil remediation agent is provided, characterized in that heavy metal contaminated soil is prepared, the heavy metal concentration in the soil is controlled to be 100-1000 mg / kg, the soil is allowed to stand and age for 10-20 days, the soil remediation agent is added to the heavy metal contaminated soil, the soil is allowed to stand and age again for 10-20 days, and the mass of the added phosphorus-rich sludge pyrolysis biochar is 1-5% of the mass of the heavy metal contaminated soil.

[0019] Preferably, the heavy metal is one or more of lead, cadmium, zinc and copper.

[0020] According to another aspect of the present invention, there is provided an application of the soil remediation agent, which is used as a phosphate fertilizer.

[0021] The principle of the method of the present invention is as follows: the phosphorus in the pyrolysis biochar of municipal sludge mainly exists in the form of iron phosphate, aluminum phosphate and the like with low bioavailability. The present invention uses municipal sludge and calcium-based additives for co-pyrolysis. During the pyrolysis process, the calcium-based additives react with the phosphorus-containing phase in the sludge to produce calcium-phosphorus binding phases such as hydroxyapatite, thereby improving the bioavailability of phosphorus therein to promote plant growth. In addition, a calcium carbonate phase will be generated on the biochar obtained by co-pyrolysis, which has a high adsorption performance for heavy metals. Phosphorus-dissolving bacteria can promote the dissolution of phosphorus in the pyrolysis biochar of phosphorus-rich sludge, and they themselves can fix heavy metals through biological adsorption. The porous structure of the pyrolysis biochar of phosphorus-rich sludge and the generated calcium carbonate can protect the phosphorus-dissolving bacteria and provide a phosphorus source for the phosphorus-dissolving bacteria. Therefore, the pyrolysis biochar of phosphorus-rich sludge combined with phosphorus-dissolving bacteria has the dual functions of repairing soil heavy metals and providing phosphorus fertilizer to promote plant growth.

[0022] Taking CaO as an example of calcium-based additives and AlPO4 as an example of phosphorus form in sludge, the possible reactions that may occur during the co-pyrolysis of municipal sludge and calcium-based additives are shown in the following equations (1)-(6).

[0023] Sludge → H2 + CO2 + H2O + CH4 + tar + biochar (1)

[0024] CaO+H2O=Ca(OH)2 (2)

[0025] Ca(OH)2+CO2=CaCO3+H2O (3)

[0026] 2ALPO4+4CaO=Ca3(PO4)2+CaAl2O4 (4)

[0027] 2AlPO4+CaO+3H2O=2H3PO4+CaAl2O4 (5)

[0028] 16ALPO4+40CaO+2H2O=4Ca 10 (PO4)4(OH)+8Al2O3+7O2 (6)

[0029] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0030] (1) The phosphorus-rich sludge pyrolysis biochar used in the present invention has a high specific surface area, and its porous structure makes it have a high adsorption performance relative to heavy metals. Using sludge as a raw material for preparing biochar can save the preparation cost of the repair agent. Using phosphorus-rich sludge, on the one hand, phosphorus-dissolving bacteria can release phosphorus in the phosphorus-rich sludge pyrolysis biochar, and phosphorus reacts with heavy metals to form a phosphorus mineral phase to achieve the effect of fixing heavy metal ions. On the other hand, phosphorus-dissolving bacteria can release phosphorus in the phosphorus-rich sludge pyrolysis biochar for plant utilization, thereby increasing soil fertility, so that the soil repair agent prepared by the present invention also has the potential of phosphorus fertilizer.

[0031] (2) The addition of calcium-based additives during the pyrolysis of phosphorus-rich sludge in the present invention generates hydroxyapatite, which improves the bioavailability of phosphorus. The addition of calcium-based additives will also generate calcium carbonate. Since calcium carbonate has a porous structure, it also has a high adsorption performance for heavy metals, so it also has excellent heavy metal fixation ability.

[0032] (3) The phosphate-dissolving bacteria used in the present invention have the ability to further fix heavy metals due to their own metabolite mineralization, cell wall adsorption and intracellular accumulation capabilities.

[0033] (4) The phosphorus-rich sludge pyrolysis biochar, calcium-based additives and phosphate-dissolving bacteria used in the present invention have a synergistic effect. The addition of calcium-based additives during the sludge pyrolysis process generates bioavailable hydroxyapatite that provides a phosphorus source for phosphate-dissolving bacteria, which helps the growth and reproduction of phosphate-dissolving bacteria. The growth and reproduction of phosphate-dissolving bacteria can further promote the dissolution of phosphorus. At the same time, the porous structure of biochar and the generated calcium carbonate can also protect microorganisms from damage by heavy metals and the original soil microbial community, thereby improving the remediation efficiency. Therefore, the three work together to improve the ability to control heavy metals in the soil.

[0034] (5) The use of pyrolysis biochar from phosphorus-rich sludge combined with phosphate-dissolving bacteria remediation agents in the present invention not only avoids the secondary pollution problem that may be caused by the chemical leaching remediation method, but also has both heavy metal pollution remediation capabilities and nutrient supply capabilities, providing an environmentally friendly and efficient soil remediation solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of the preparation method of using pyrolysis biochar from phosphorus-rich sludge combined with phosphorus-dissolving bacteria as a soil remediation agent;

[0036] Figure 2 XRD diagrams of the biochar prepared in Comparative Example 1 and the biochar prepared in Example 2;

[0037] Figure 3(a) is phosphate-dissolving bacteria, (b) is phosphate-dissolving bacteria + lead nitrate, (c) is sludge pyrolysis biochar + phosphate-dissolving bacteria + lead nitrate prepared in Comparative Example 3, and (d) is the SEM-EDS result of phosphorus-rich sludge pyrolysis biochar + phosphate-dissolving bacteria + lead nitrate prepared in Example 2. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Embodiment 1:

[0040] (1) Dehydrated sludge (taken from the dehydration workshop of Wuhan Tangxun Lake Wastewater Treatment Plant, with a moisture content of 85%, dried at 105°C to obtain dehydrated sludge, the same below) was dried in an oven at 105°C for 24 h, and then ground through a 40-mesh sieve to obtain dry sludge. The phosphorus content in the sludge was measured to be 30.36 mg / g.

[0041] (2) The dried sludge in (1) was loaded into a porcelain boat and placed in a horizontal tubular pyrolysis furnace. CaO was added according to a Ca / P molar ratio of 1, and the amount of CaO added was 55 mg / g. Inert atmosphere nitrogen (purity of 99.99%) was introduced for 45 minutes, and the carrier gas flow rate was 100 mL / min to ensure that the entire pyrolysis environment was oxygen-free. The temperature was raised to 500°C at a heating rate of 10°C / min and kept warm for 3 hours. After the pyrolysis was completed, the temperature in the furnace dropped to room temperature, and the biochar and dichloromethane were used in a ratio of 1:10 to clean the tar on the surface of the biochar for 1 hour. After suction filtration, it was rinsed with deionized water twice, and finally dried in a 105°C forced air drying oven, and passed through a 40-mesh sieve to obtain phosphorus-rich sludge pyrolysis biochar.

[0042] (3) Pseudomonas aeruginosa (accession number AB91095) was cultured in LB liquid medium until the absorbance at a wavelength of 600 was 0.8-1 (OD 600 =0.8-1).

[0043] (4) Add lead nitrate solution to the soil to prepare simulated lead-contaminated soil with a lead concentration of 500 mg / kg. Stir evenly and transfer to a space cup, with 200 g of soil per cup, and let it stand for 15 days.

[0044] (5) Add 2 g of phosphorus-rich sludge pyrolysis biochar and 2 × 10 9 CFU Pseudomonas aeruginosa was placed in simulated lead-contaminated soil and aged for 15 days.

[0045] (6) Soak corn seeds in ultrapure water for 24 hours, place them in a 30°C constant temperature incubator for germination for 48 hours, and then sow the germinated corn seeds in the aged soil, 4 seeds per cup. Water once in the morning and evening every day, adjust the soil moisture to 60% of the maximum water holding capacity, and set the light intensity to 15000 lx during cultivation. The light / dark cycle is set to 28°C, 16 hours, and the dark cycle is 20°C, 8 hours. Repeat for 20 days and then harvest.

[0046] According to Example 1, the root biomass and leaf biomass of the corn plants were measured to be 39 and 81 mg, respectively; the root phosphorus content and leaf phosphorus content of the corn plants were 1510 and 6000 mg / kg, respectively; the root lead content and leaf lead content of the corn plants were 247 and 158 mg / kg, respectively; and the proportions of free lead F1 (exchangeable state) and free lead F2 (carbonate-bound state) components in the soil were 3% and 12%, respectively.

[0047] Embodiment 2:

[0048] (1) The dehydrated sludge was dried in an oven at 105°C for 24 h and then ground through a 40-mesh sieve to obtain dry sludge. The phosphorus content in the sludge was measured to be 30.36 mg / g.

[0049] (2) The dried sludge in (1) was loaded into a porcelain boat and placed in a horizontal tubular pyrolysis furnace. CaO was added according to a Ca / P molar ratio of 1.5, so the amount of CaO added was 82 mg / g. Inert atmosphere nitrogen (purity of 99.99%) was introduced for 45 minutes, and the carrier gas flow rate was 100 mL / min to ensure that the entire pyrolysis environment was oxygen-free. The temperature was raised to 600°C at a heating rate of 10°C / min and kept warm for 2 hours. After the pyrolysis was completed, the temperature in the furnace dropped to room temperature, and the biochar and dichloromethane were used in a ratio of 1:10 to clean the tar on the surface of the biochar for 1 hour. After filtration, it was rinsed with deionized water twice, and finally dried in a 105°C forced air drying oven, and passed through a 40-mesh sieve to obtain phosphorus-rich sludge pyrolysis biochar.

[0050] (3) The phosphate-soluble bacteria Pseudomonas aeruginosa (accession number AB91095, purchased from the China Type Culture Collection of Wuhan University) was cultured in LB liquid medium until OD 600 =0.8-1.

[0051] (4) Add lead nitrate solution to the soil to prepare simulated lead-contaminated soil with a lead concentration of 500 mg / kg. Stir evenly and transfer to a space cup, with 200 g of soil per cup, and let it stand for 15 days.

[0052] (5) Add 6 g of phosphorus-rich sludge pyrolysis biochar and 6 × 10 9 CFU Pseudomonas aeruginosa was placed in simulated lead-contaminated soil and aged for 15 days.

[0053] (6) Soak the corn seeds in ultrapure water for 24 hours, place them in a 30°C constant temperature incubator for germination for 48 hours, and then sow the germinated corn seeds in the aged soil, 4 seeds per cup. Water once in the morning and evening every day, adjust the soil moisture to 60% of the maximum water holding capacity, and set the light intensity to 15000lx during cultivation. The light / dark cycle is set to 28°C, 16h, and 20°C, 8h. Repeat for 20 days and harvest.

[0054] According to Example 2, the root biomass and leaf biomass of the corn plants were measured to be 42 and 90 mg respectively; the root phosphorus content and leaf phosphorus content of the corn plants were 1900 and 7200 mg / kg respectively; the root lead content and leaf lead content of the corn plants were 240 and 150 mg / kg respectively; the proportions of free lead F1 (exchangeable state) and free lead F2 (carbonate-bound state) components in the soil were 3% and 8% respectively.

[0055] Embodiment 3:

[0056] (1) The dehydrated sludge was dried in an oven at 105°C for 24 hours and then ground through a 40-mesh sieve to obtain dry sludge. The phosphorus content in the sludge was measured to be 30.36 mg / g.

[0057] (2) The dried sludge in (1) was loaded into a porcelain boat and placed in a horizontal tubular pyrolysis furnace. CaO was added according to a Ca / P molar ratio of 2, so the amount of CaO added was 110 mg / g. Inert atmosphere nitrogen (purity of 99.99%) was introduced for 45 minutes, and the carrier gas flow rate was 100 mL / min to ensure that the entire pyrolysis environment was oxygen-free. The temperature was raised to 700°C at a heating rate of 10°C / min and kept warm for 1 hour. After the pyrolysis was completed, the temperature in the furnace dropped to room temperature, and the biochar and dichloromethane were used in a ratio of 1:10 to clean the tar on the surface of the biochar for 1 hour. After filtration, it was rinsed with deionized water twice, and finally dried in a 105°C forced air drying oven, and passed through a 40-mesh sieve to obtain phosphorus-rich sludge pyrolysis biochar.

[0058] (3) Using LB liquid medium, the phosphate-soluble bacteria Bacillus subtilis (deposit number AB130001) was expanded to OD 600 =0.8-1.

[0059] (4) Add lead nitrate solution to the soil to prepare simulated lead-contaminated soil with a lead concentration of 500 mg / kg. Stir evenly and transfer to a space cup, with 200 g of soil per cup, and let it stand for 15 days.

[0060] (5) Add 10 g of phosphorus-rich sludge pyrolysis biochar and 1×10 10 CFU Pseudomonas aeruginosa was placed in simulated lead-contaminated soil and aged for 15 days.

[0061] (6) Soak corn seeds in ultrapure water for 24 hours, place them in a 30°C constant temperature incubator for germination for 48 hours, and then sow the germinated corn seeds in the aged soil, 4 seeds per cup. Water once in the morning and evening every day, adjust the soil moisture to 60% of the maximum water holding capacity, and set the light intensity to 15000 lx during cultivation. The light / dark cycle is set to 28°C, 16 hours, and the dark cycle is 20°C, 8 hours. Repeat for 20 days and then harvest.

[0062] According to Example 3, the root biomass and leaf biomass of the corn plants were measured to be 40 and 85 mg respectively; the root phosphorus content and leaf phosphorus content of the corn plants were 1555 and 6200 mg / kg respectively; the root lead content and leaf lead content of the corn plants were 250 and 160 mg / kg respectively; the proportions of free lead F1 (exchangeable state) and free lead F2 (carbonate-bound state) components in the soil were 4% and 10% respectively.

[0063] Comparative Example 1:

[0064] (1) The dehydrated sludge was dried in an oven at 105°C for 24 h and then ground through a 40-mesh sieve to obtain dry sludge. The phosphorus content in the sludge was measured to be 30.36 mg / g.

[0065] (2) The dried sludge in (1) was loaded into a porcelain boat and placed in a horizontal tubular pyrolysis furnace, and an inert atmosphere of nitrogen (purity of 99.99%) was introduced for 45 minutes, with a carrier gas flow rate of 100 mL / min to ensure that the entire pyrolysis environment is oxygen-free. The temperature was raised to 600°C at a heating rate of 10°C / min and kept warm for 2 hours. After the pyrolysis was completed, the temperature in the furnace dropped to room temperature, and the biochar and dichloromethane were used in a ratio of 1:10 to clean the tar on the surface of the biochar for 1 hour. After filtration, it was rinsed with deionized water twice, and finally dried in a 105°C forced air drying oven, and passed through a 40-mesh sieve to obtain sludge pyrolysis biochar.

[0066] (3) Add lead nitrate solution to soil to prepare simulated lead-contaminated soil with a lead concentration of 500 mg / kg. Stir evenly and transfer to a space cup, with 200 g of soil in each cup, and let it stand for 15 days.

[0067] (4) Add 2 g of sludge pyrolysis biochar to the simulated lead-contaminated soil and let it stand for 15 days.

[0068] (5) After soaking corn seeds in ultrapure water for 24 hours, they were placed in a 30°C constant temperature incubator for germination for 48 hours, and then the germinated corn seeds were sown in aged soil, 4 seeds per cup. Watering was performed once in the morning and evening every day, and the soil moisture was adjusted to 60% of the maximum water holding capacity. During the cultivation, the light intensity was 15000 lx, and the light / dark cycle was set to a light cycle of 28°C, 16 hours, and a dark cycle of 20°C, 8 hours. After repeating for 20 days, the harvest was performed. From Comparative Example 1, the root biomass and leaf biomass of the corn plants were measured to be 23 and 45 mg, respectively; the root phosphorus content and leaf phosphorus content of the corn plants were 380 and 1250 mg / kg, respectively; the root lead content and leaf lead content of the corn plants were 382 and 268 mg / kg, respectively; and the proportions of free lead F1 (exchangeable state) and free lead F2 (carbonate-bound state) in the soil were 5% and 39%, respectively.

[0069] Comparative Example 2:

[0070] (1) The phosphate-soluble bacteria Pseudomonas aeruginosa (accession number AB91095) was cultured in LB liquid medium until OD 600 =0.8-1.

[0071] (2) Add lead nitrate solution to the soil to prepare simulated lead-contaminated soil with a lead concentration of 500 mg / kg. Stir evenly and transfer to a space cup, with 200 g of soil in each cup, and let it stand for 15 days.

[0072] (3) Add 2×10 9 CFU Pseudomonas aeruginosa was placed in simulated lead-contaminated soil and aged for 15 days.

[0073] (4) Soak the corn seeds in ultrapure water for 24 hours, place them in a 30°C constant temperature incubator for germination for 48 hours, and then sow the germinated corn seeds in the aged soil, 4 seeds per cup. Water once in the morning and evening every day, adjust the soil moisture to 60% of the maximum water holding capacity, and set the light intensity to 15000lx during cultivation. The light / dark cycle is set to 28°C, 16h, and 20°C, 8h. Repeat for 20 days and harvest.

[0074] According to Comparative Example 2, the root biomass and leaf biomass of corn plants were measured to be 18 and 35 mg respectively; the root phosphorus content and leaf phosphorus content of corn plants were 200 and 680 mg / kg respectively; the root lead content and leaf lead content of corn plants were 450 and 300 mg / kg respectively; the proportions of free lead F1 (exchangeable state) and free lead F2 (carbonate-bound state) components in the soil were 30% and 49% respectively.

[0075] Comparative Example 3:

[0076] (1) The dehydrated sludge was dried in an oven at 105°C for 24 h and then ground through a 40-mesh sieve to obtain dry sludge. The phosphorus content in the sludge was measured to be 30.36 mg / g.

[0077] (2) The dried sludge in (1) was loaded into a porcelain boat and placed in a horizontal tubular pyrolysis furnace, and an inert atmosphere of nitrogen (purity of 99.99%) was introduced for 45 minutes, with a carrier gas flow rate of 100 mL / min to ensure that the entire pyrolysis environment was oxygen-free. The program was restarted, and the temperature was increased to 600°C at a heating rate of 10°C / min and kept warm for 2 hours. After the pyrolysis was completed, the temperature in the furnace dropped to room temperature, and the biochar and dichloromethane were used in a ratio of 1:10 to clean the tar on the surface of the biochar for 1 hour, and then filtered and rinsed with deionized water twice, and finally dried in a 105°C forced air drying oven, and passed through a 40-mesh sieve to obtain sludge pyrolysis biochar.

[0078] (3) Using LB liquid medium, the phosphate-soluble bacteria Pseudomonas aeruginosa (deposit number AB91095) was expanded to OD 600 =0.8-1.

[0079] (4) Add lead nitrate solution to soil to prepare simulated lead-contaminated soil with a lead concentration of 500 mg / kg. After stirring evenly, transfer the mixture into a space cup, with 200 g of soil per cup, and allow to age for 15 days.

[0080] (5) Add 2 g of sludge pyrolysis biochar and 2×10 9 CFU Pseudomonas aeruginosa was placed in simulated lead-contaminated soil and aged for 15 days.

[0081] (6) Soak corn seeds in ultrapure water for 24 hours, place them in a 30°C constant temperature incubator for germination for 48 hours, and then sow the germinated corn seeds in the aged soil, 4 seeds per cup. Water once in the morning and evening every day, adjust the soil moisture to 60% of the maximum water holding capacity, and set the light intensity to 15000 lx during cultivation. The light / dark cycle is set to 28°C, 16 hours, and the dark cycle is 20°C, 8 hours. Repeat for 20 days and then harvest.

[0082] Comparative Example 3 measured that the root biomass and leaf biomass of the corn plants were 25 and 48 mg respectively; the root phosphorus content and leaf phosphorus content of the corn plants were 420 and 1340 mg / kg respectively; the root lead content and leaf lead content of the corn plants were 368 and 256 mg / kg respectively; the proportions of free lead F1 (exchangeable state) and free lead F2 (carbonate-bound state) components in the soil were 20% and 35% respectively.

[0083] Table 1 shows the plant biomass, phosphorus content, lead content and soil lead component ratio of the soil-plant system in the above-mentioned embodiments and comparative examples. It can be seen that after the application of sludge pyrolysis biochar and / or phosphate-dissolving bacteria treatment, the total biomass of the corn plant is only 53-73 mg; the phosphorus content in the roots and leaves of the corn plant is only 200-420 mg / kg and 680-1340 mg / kg respectively; the lead content in the roots and leaves of the corn plant is as high as 368-450 mg / kg and 256-300 mg / kg respectively; the proportions of soil lead F1 and F2 components are both high, accounting for 20-30% and 35-49% respectively. The combined application of phosphorus-rich sludge pyrolysis biochar and phosphate-dissolving bacteria can significantly increase the total biomass of corn plants to 120-132 mg; significantly increase the phosphorus content in the roots and leaves of corn plants to 1510-1900 mg / kg and 6000-7200 mg / kg; significantly reduce the lead content in the roots and leaves of corn plants to 240-250 mg / kg and 150-160 mg / kg; and significantly reduce the proportion of soil lead F1 and F2 components to 3-4% and 8-12%.

[0084] The pyrolysis biochar obtained in Example 2 and Comparative Example 3 was subjected to XRD analysis. Figure 2 As shown in the figure, it can be seen that the addition of CaO during the pyrolysis process produces CaCO3 with strong Pb adsorption and Ca with high bioavailability in the biochar. 10 (PO4)4(OH) can not only achieve efficient fixation of heavy metals, but also provide phosphorus fertilizer to promote plant growth.

[0085] from Figure 3 As can be seen in (a), Pseudomonas aeruginosa is in the shape of a slender rod, about 1-2 μm long and 0.5-1 μm wide. Figure 3 In (b), most of the P. aeruginosa cells died and their morphology changed significantly; Figure 3 (c) is an electron micrograph of the remediation agent prepared in comparative example 3 for the treatment of lead in soil. It can be seen from the figure that phosphate-dissolving bacteria can be well loaded on sludge pyrolysis biochar, but the specific surface area measured by the specific surface area and pore size analyzer is only 25.61 m 2 / g, small specific surface area; Figure 3 (d) is an electron micrograph of the repair agent prepared in Example 2 for the treatment of lead in soil. It can be seen from the figure that the phosphate-dissolving bacteria can be well loaded on the pyrolysis biochar of phosphorus-rich sludge, and the cell morphology of the phosphate-dissolving bacteria has not changed significantly, confirming the protective effect of the pyrolysis biochar of phosphorus-rich sludge on the phosphate-dissolving bacteria. The specific surface area and pore size analyzer measured that the specific surface area was 40.64 m 2 / g, with a higher specific surface area.

[0086] Table 1. Plant biomass, phosphorus content, lead content and soil lead component ratio of the soil-plant system in Examples 1 to 3 and Comparative Examples 1 to 3.

[0087]

[0088]

[0089] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a soil remediation agent of phosphorus-rich sludge pyrolysis biochar combined with phosphate-dissolving bacteria, characterized in that: The following steps are involved: (1) mixing dehydrated phosphorus-rich sludge having a phosphorus mass percentage of 3-10% with a calcium-based additive at a Ca / P molar ratio of 1-2, and pyrolyzing the mixture under an inert atmosphere to obtain phosphorus-rich sludge pyrolysis biochar; (2) The phosphorus-rich sludge pyrolysis biochar was mixed with phosphate-dissolving bacteria, and the colony count was 1×10 per gram of phosphorus-rich sludge pyrolysis biochar. 9 -10×10 9 The phosphate-dissolving bacteria are mixed to obtain a soil remediation agent.

2. The method for preparing a soil remediation agent of phosphorus-rich sludge pyrolysis biochar combined with phosphate-dissolving bacteria according to claim 1, characterized in that: The calcium-based additive is selected from one or more of calcium chloride, calcium oxide, calcium hydroxide, calcium phosphate, and calcium carbonate.

3. The method for preparing a soil remediation agent of phosphorus-rich sludge pyrolysis biochar combined with phosphate-dissolving bacteria according to claim 1, characterized in that: The phosphate-dissolving bacteria are selected from one or more of Pseudomonas aeruginosa, Bacillus subtilis, Escherichia coli, Burkholderia cepacia, and Enterobacter cloacae.

4. The method for preparing a soil remediation agent of phosphorus-rich sludge pyrolysis biochar combined with phosphate-dissolving bacteria according to claim 1, characterized in that: The pyrolysis temperature in step (1) is 500-700°C, the heating rate is 5-20°C / min, and the pyrolysis time is 1-3h.

5. The method for preparing a soil remediation agent of phosphorus-rich sludge pyrolysis biochar combined with phosphate-dissolving bacteria according to claim 1, characterized in that: The dewatered phosphorus-rich sludge is also pre-treated before being mixed with the calcium-based additive, and the pre-treatment is sequentially drying, grinding and screening.

6. The method for preparing a soil remediation agent of phosphorus-rich sludge pyrolysis biochar combined with phosphate-dissolving bacteria according to claim 1, characterized in that: The surface tar of the phosphorus-rich sludge pyrolysis biochar is cleaned with dichloromethane before being mixed with the phosphorus-dissolving bacteria, and then rinsed with deionized water and dried, ground and sieved.

7. The soil remediation agent prepared by the preparation method according to any one of claims 1 to 6.

8. A method for treating heavy metal contaminated soil using the soil remediation agent as claimed in claim 7, characterized in that: Prepare heavy metal contaminated soil, control the heavy metal concentration in the soil to 100-1000 mg / kg, let it stand for 10-20 days, add the soil remediation agent according to claim 7 to the heavy metal contaminated soil, let it stand for 10-20 days again, and the added mass of the phosphorus-rich sludge pyrolysis biochar is 1-5% of the mass of the heavy metal contaminated soil.

9. The method for treating heavy metal contaminated soil using the soil remediation agent according to claim 8, characterized in that: The heavy metal is one or more of lead, cadmium, zinc and copper.

10. Use of the soil remediation agent as claimed in claim 7, which is used as a phosphate fertilizer.

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