A phosphorus-rich sludge pyrolysis biochar combined with soil remediation agent of phosphorus-dissolving bacteria and preparation method and application thereof

Abstract

The application relates to the field of soil remediation, in particular to a phosphorus-rich sludge pyrolysis biochar combined with phosphorus-dissolving bacteria as a soil remediation agent, a preparation method and application thereof, which comprises the following steps: mixing dewatered phosphorus-rich sludge and a calcium-based additive according to a Ca / P molar ratio of 1-2, pyrolyzing under an inert atmosphere to obtain phosphorus-rich sludge pyrolysis biochar; mixing the phosphorus-rich sludge pyrolysis biochar with the phosphorus-dissolving bacteria after expansion culture, adding 1x10 9 -10x10 9 phosphorus-dissolving bacteria per gram of phosphorus-rich sludge pyrolysis biochar to obtain the soil remediation agent, so as to be used for the treatment of heavy metals in soil, and the method solves the problems of high cost, long cycle, low soil fertility after remediation and difficulty in remediation of high-concentration heavy metal contaminated soil in the prior art heavy metal contaminated soil remediation method, realizes efficient heavy metal fixation and phosphorus fertilizer supply to promote plant growth.

Description

TECHNICAL FIELD

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

[0002] Due to the influence of human activities such as industrial pollution, mineral development, and pollutant discharge of abandoned mines, soil heavy metal pollution has become a global environmental problem. Soil heavy metal pollution has the characteristics of universality, concealment, biological accumulation, irreversibility, and long-term, which can cause serious harm to the ecological environment and the living space of soil microorganisms, and can spread along the food chain, seriously affecting human health. It is urgent to find a simple and fast means to solve the problem of soil heavy metal pollution.

[0003] The remediation technology of heavy metal contaminated soil mainly includes two kinds. The first kind is to directly remove heavy metals in soil, and the common means mainly include engineering remediation and hyperaccumulating plant remediation. For example, Chinese patent CN108160688A provides a five-step leaching method, which can realize efficient removal of various heavy metal ions in soil. Chinese patent CN103357655A uses a leaching solution composed of ferric chloride and organic acid to leach heavy metal contaminated soil, and the removal rate of heavy metal cadmium reaches 80%, and the removal rate of heavy metal lead reaches 55%. Chinese patent CN109127720A uses the enrichment of big leaf Jingkou edge grass or Pteridium aquilinum to heavy metals, and cooperates with indole acetic acid and kinetin, and after two harvests, the contents of lead and cadmium in soil decrease by 18% and 27% respectively, which has a significant effect. However, engineering measures have high cost and are easy to cause damage to the natural properties of soil; hyperaccumulating plant remediation measures are greatly limited in practical application due to low target biomass and long remediation period.

[0004] The second kind is to change the occurrence form of heavy metals in soil, weaken its migration ability and reduce its bioavailability, for example, using soil remediation agents. At present, common soil remediation agents include biomass-based biochar, activated carbon, inorganic fertilizer and phosphate rock, etc., among which biomass-based biochar is most widely used, and its adsorption mechanism of heavy metals includes surface complexation, electrostatic attraction, ion exchange, mineral precipitation, etc. Chinese patent CN114797779A pyrolyzes reed straw at 400℃, and then adds ferric nitrate and potassium hydroxide to obtain a hydro ferrite modified biochar, which can be used for remediation of arsenic, lead and cadmium heavy metal contaminated soil. However, the nutrient element content of biomass source biochar is low, and direct application may even adsorb the nutrient elements in soil, resulting in low soil fertility, so it is usually necessary to jointly apply fertilizer to promote plant growth, which increases the process cost.

[0005] In addition to biochar, microorganisms are also applied in the remediation of contaminated soil due to their low cost and little environmental pollution. Chinese patent CN118256370A discloses a method for remediation of heavy metal contaminated soil by using a mixed bacterial solution of multiple strains. Chinese patent CN114644992A provides a Kosakonia sp. GRINML13 strain, which has good phosphorus solubilizing effect and can efficiently release phosphorus from calcium phosphate to form insoluble lead chlorophosphate with lead ions to achieve a stabilizing effect. However, the patent can only remediate soil with a heavy metal concentration of less than 50 mg / kg. This is because free microorganisms are easily affected by heavy metal toxicity and are subject to competition from the original soil microbial population during the remediation of heavy metals, resulting in a significant reduction in remediation effect and only low-polluted soil can be remediated.

[0006] In summary, the existing methods for remediation of heavy metal contaminated soil have the problems of high cost, long cycle, low soil fertility after remediation, and difficulty in remediation of high concentration heavy metal contaminated soil. SUMMARY

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

[0008] To achieve the above-mentioned purpose, according to one aspect of the present application, a preparation method of a soil remediation agent of phosphorus-rich sludge pyrolysis biochar combined with phosphorus-solubilizing bacteria is provided, characterized in that it comprises the following steps:

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

[0010] (2) mixing the phosphorus-rich sludge pyrolysis biochar with the phosphorus-solubilizing bacteria after expansion culture, and adding 1x10 9 -10x10 9 phosphorus-solubilizing bacteria per gram of phosphorus-rich sludge pyrolysis biochar to obtain the 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 phosphorus-dissolving bacteria are one or more of Pseudomonas aeruginosa, Bacillus, Escherichia coli, Burkholderia cenocepacia, 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 dehydrated phosphorus-rich sludge is further subjected to a pretreatment before being mixed with the calcium-based additive, and the pretreatment comprises sequentially performing drying, grinding, and sieving.

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

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

[0018] According to another aspect of the present application, there is provided a method for treating heavy metal-contaminated soil using the soil remediation agent, which comprises the following steps: configuring heavy metal-contaminated soil, controlling the concentration of heavy metals in the soil to be 100-1000mg / kg, and standing and aging for 10-20 days; adding the soil remediation agent to the heavy metal-contaminated soil, and standing and aging again for 10-20 days, wherein the added amount of the 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 application, there is provided an application of the soil remediation agent, which is used as a phosphorus fertilizer.

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

[0022] The calcium-based additive takes CaO as an example, and the phosphorus form in the sludge takes AlPO4 as an example, and the possible reaction formula of the co-pyrolysis of the municipal sludge and the calcium-based additive is shown in the following formula (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] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages:

[0030] (1) The phosphorus-rich sludge pyrolysis biochar adopted in the present application has a high specific surface area, and its porous structure makes it have a relatively high adsorption performance for heavy metals. The use of sludge as a raw material for preparing biochar can save the preparation cost of remediation agents. The use of phosphorus-rich sludge can release phosphorus in the phosphorus-rich sludge pyrolysis biochar through phosphorus-dissolving bacteria, and the phosphorus reacts with heavy metals to form phosphorus minerals to fix heavy metal ions. On the other hand, the phosphorus-dissolving bacteria can release phosphorus in the phosphorus-rich sludge pyrolysis biochar for plant use, increase soil fertility, and make the soil remediation agent prepared by the present application have phosphorus fertilizer potential.

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

[0032] (3) The phosphorus-dissolving bacteria adopted in the present application have the ability to mineralize metabolites, adsorb cell walls and accumulate in cells, so they further have the ability to fix heavy metals.

[0033] (4) The phosphorus-rich sludge pyrolysis biochar, calcium-based additives and phosphorus-dissolving bacteria adopted in the present application have a synergistic effect. The addition of calcium-based additives in the sludge pyrolysis process generates bioavailable hydroxyapatite, which provides a phosphorus source for phosphorus-dissolving bacteria, helps the growth and reproduction of phosphorus-dissolving bacteria, and the growth and reproduction of phosphorus-dissolving bacteria further promotes the dissolution of phosphorus. At the same time, the porous structure of biochar and generated calcium carbonate can also protect microorganisms from damage by heavy metals and original soil microorganisms, improve remediation efficiency, so the three have a synergistic effect, and improve the heavy metal treatment ability in soil.

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

[0035] Figure 1 Figure 1 is a preparation method flowchart of the soil remediation agent using phosphorus-rich sludge pyrolysis biochar combined with phosphorus-dissolving bacteria;

[0036] Figure 2 Figure 3 is an XRD graph of the biochar prepared in Comparative Example 1 and the biochar prepared in Example 2;

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

[0038] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0039] Example 1

[0040] (1) After the dewatered sludge (obtained from the dewatering workshop of Wuhan Tangxunhu Sewage Treatment Plant, 85% water content, dried at 105°C to obtain dewatered sludge, the same below) was dried in an oven at 105°C for 24h, it was ground through a 40-mesh sieve to obtain dry sludge, and the phosphorus content in the sludge was measured to be 30.36mg / g.

[0041] (2) The dry sludge in (1) was loaded into a porcelain boat and placed in a horizontal tube furnace, and CaO was added according to a Ca / P molar ratio of 1 to obtain an addition amount of CaO of 55mg / g. Nitrogen gas (purity of 99.99%) was introduced as an inert atmosphere for 45min, and the carrier gas flow rate was 100mL / 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 the temperature was maintained for 3h. After the pyrolysis was completed, when the temperature in the furnace dropped to room temperature, the biochar was washed with dichloromethane at a ratio of 1:10 for 1h, and then filtered and washed with deionized water twice. Finally, it was placed in a 105°C air-drying oven, ground through a 40-mesh sieve, and a phosphorus-rich sludge pyrolytic biochar was obtained.

[0042] (3) The Pseudomonas aeruginosa (preserved number AB91095) was expanded in LB liquid medium to an absorbance of 0.8-1 (OD 600 = 0.8-1) at a wavelength of 600nm.

[0043] (4) Lead nitrate solution was added to the soil to prepare simulated lead-contaminated soil with a lead concentration of 500mg / kg, and the soil was stirred uniformly and then transferred to a space cup. Each cup contained 200g of soil, and the soil was allowed to stand and age for 15 days.

[0044] (5) 2g of the phosphorus-rich sludge pyrolytic biochar and 2x10 9 CFU of Pseudomonas aeruginosa were added to the simulated lead-contaminated soil, and the soil was allowed to stand and age for another 15 days.

[0045] (6) The corn seeds were soaked in ultrapure water for 24 h, then placed in a constant temperature incubator at 30°C for 48 h to germinate, and then the germinated corn seeds were sown in the aged soil, 4 seeds per cup. Water was poured once in the morning and once in the evening every day, and the soil moisture was adjusted to 60% of the maximum water holding capacity. The light intensity was 15000 lx, and the light / dark cycle was set as 28°C, 16 h, and 20°C, 8 h. After 20 days of cultivation, the plants were harvested.

[0046] The root biomass and leaf biomass of the corn plants were measured to be 39 and 81 mg, respectively, according to Example 1. 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. The proportions of free lead F1 (exchangeable state) and free lead F2 (carbonate-bound state) in the soil were 3% and 12%, respectively.

[0047] Example 2:

[0048] (1) The dewatered sludge was dried in an oven at 105°C for 24 h, 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 dry sludge in (1) was loaded into a porcelain boat and placed in a horizontal tube furnace. CaO was added according to a Ca / P molar ratio of 1.5, so the amount of CaO added was 82 mg / g. Nitrogen gas (purity 99.99%) was introduced as an inert atmosphere for 45 min at a flow rate of 100 mL / min to ensure that the entire pyrolysis environment was oxygen-free. The temperature was raised to 600°C at a rate of 10°C / min and held for 2 h. After pyrolysis, when the temperature in the furnace dropped to room temperature, the biochar was washed with dichloromethane at a ratio of 1:10 for 1 h. After suction filtration, the biochar was washed with deionized water twice, then dried in a 105°C forced air drying oven, and sieved through a 40-mesh sieve to obtain phosphorus-rich sludge pyrolysis biochar.

[0050] (3) The phosphate-solubilizing bacterium Pseudomonas aeruginosa (preserved number AB91095, purchased from the China General Microbiological Culture Collection Center, Wuhan University) was cultured in LB liquid medium to an OD 600 = 0.8-1.

[0051] (4) Lead nitrate solution was added to the soil to prepare a simulated lead-contaminated soil with a lead concentration of 500 mg / kg. After stirring evenly, the soil was transferred to a space cup, 200 g of soil per cup, and allowed to stand and age for 15 days.

[0052] (5) 6 g of phosphorus-rich sludge pyrolysis biochar and 6 x 10 9 CFU of Pseudomonas aeruginosa were added to the simulated lead-contaminated soil, and the soil was allowed to stand and age for another 15 days.

[0053] (6) After the corn seeds were soaked in ultrapure water for 24 h, they were placed in a constant temperature incubator at 30°C for 48 h to germinate, and then the germinated corn seeds were sown in aged soil, 4 seeds per cup. Water was poured once in the morning and once in the evening every day, and the soil moisture was adjusted to 60% of the maximum water holding capacity. The light intensity during cultivation was 15000 lx, and the light / dark cycle was set to 28°C for 16 h and 20°C for 8 h. After 20 days of repeated cultivation, the plants were harvested.

[0054] The root biomass and leaf biomass of the corn plants were measured to be 42 and 90 mg, respectively, according to Example 2. 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) in the soil were 3% and 8%, respectively.

[0055] Example 3:

[0056] (1) After the dewatered sludge was dried in an oven at 105°C for 24 h, it was 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 dry sludge in (1) was loaded into a porcelain boat and placed in a horizontal tube furnace. CaO was added according to a Ca / P molar ratio of 2, so the amount of CaO added was 110 mg / g. Nitrogen gas (purity 99.99%) was introduced as an inert atmosphere for 45 min at a flow rate of 100 mL / min to ensure that the entire pyrolysis environment was oxygen-free. The temperature was raised to 700°C at a rate of 10°C / min and held for 1 h. After pyrolysis, when the temperature in the furnace dropped to room temperature, the biochar was washed with dichloromethane at a ratio of 1:10 for 1 h. After suction filtration, the biochar was washed twice with deionized water, and finally dried in a 105°C forced air drying oven, ground through a 40-mesh sieve, to obtain phosphorus-rich sludge pyrolysis biochar.

[0058] (3) The phosphorus-dissolving bacteria Bacillus subtilis (preserved number AB130001) were expanded in LB liquid medium to OD 600 = 0.8-1.

[0059] (4) Lead nitrate solution was added to the soil to prepare a simulated lead-contaminated soil with a lead concentration of 500 mg / kg. After stirring to ensure uniformity, the soil was transferred to a space cup, 200 g of soil per cup, and allowed to stand and age for 15 days.

[0060] (5) 10 g of phosphorus-rich sludge pyrolysis biochar and 1 x 10 10 CFU of Pseudomonas aeruginosa were added to the simulated lead-contaminated soil, and the soil was again allowed to stand and age for 15 days.

[0061] (6) The corn seeds were soaked in ultrapure water for 24 h, then placed in a constant temperature incubator at 30°C for 48 h to germinate, and then the germinated corn seeds were sown in the aged soil, 4 seeds per cup. Water was poured once in the morning and once in the evening every day, and the soil moisture was adjusted to 60% of the maximum water holding capacity. The light intensity was 15000 lx, and the light / dark cycle was set as 28°C, 16 h, and 20°C, 8 h. After 20 days of cultivation, the plants were harvested.

[0062] The root biomass and leaf biomass of the corn plants were measured to be 40 and 85 mg, respectively, according to Example 3. The root phosphorus content and leaf phosphorus content of the corn plants were measured to be 1555 and 6200 mg / kg, respectively. The root lead content and leaf lead content of the corn plants were measured to be 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 dewatered sludge was dried in an oven at 105°C for 24 h, 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 dry sludge in (1) was loaded into a porcelain boat and placed in a horizontal tube furnace, and an inert atmosphere of nitrogen gas (purity 99.99%) was introduced for 45 min at a flow rate of 100 mL / min to ensure that the entire pyrolysis environment was oxygen-free. The temperature was raised to 600°C at a rate of 10°C / min, and held for 2 h. After the pyrolysis was completed, when the temperature in the furnace dropped to room temperature, the biochar was washed with dichloromethane at a ratio of 1:10 for 1 h, then filtered and washed with deionized water twice, and finally dried in a 105°C air-drying oven, then ground through a 40-mesh sieve to obtain sludge pyrolysis biochar.

[0066] (3) Lead nitrate solution was added to the soil to configure a simulated lead-contaminated soil with a lead concentration of 500 mg / kg. After stirring evenly, the soil was transferred to a space cup, 200 g of soil per cup, and aged for 15 days.

[0067] (4) 2 g of sludge pyrolysis biochar was added to the simulated lead-contaminated soil, and the soil was aged again for 15 days.

[0068] (5) The corn seeds are soaked in ultrapure water for 24 h, then placed in a constant temperature incubator at 30°C for 48 h to germinate, and then the germinated corn seeds are planted in the aged soil, 4 per cup. Water once in the morning and evening every day, adjust the soil moisture to 60% of the maximum water holding capacity, the light intensity is 15000 lx, the light / dark cycle is set, the light cycle is 28°C, 16 h, the dark cycle is 20°C, 8 h, repeat for 20 days, then harvest the corn plants; the root biomass and leaf biomass of the corn plants are 23 and 45 mg respectively; the root phosphorus content and leaf phosphorus content of the corn plants are 380 and 1250 mg / kg respectively; the root lead content and leaf lead content of the corn plants are 382 and 268 mg / kg respectively; the proportions of free lead F1 (exchangeable state) and free lead F2 (carbonate bound state) components in the soil are 5% and 39% respectively.

[0069] Comparative Example 2:

[0070] (1) The phosphorus-dissolving bacteria Pseudomonas aeruginosa (preserved number AB91095) is expanded in LB liquid medium to OD 600 = 0.8-1.

[0071] (2) Lead nitrate solution is added to the soil to configure a simulated lead-contaminated soil, the lead concentration is 500 mg / kg, after stirring evenly, it is transferred to a space cup, 200 g of soil per cup, and aged for 15 days.

[0072] (3) 2x10 9 CFU of Pseudomonas aeruginosa is added to the simulated lead-contaminated soil, and aged for 15 days again.

[0073] (4) The corn seeds are soaked in ultrapure water for 24 h, then placed in a constant temperature incubator at 30°C for 48 h to germinate, and then the germinated corn seeds are planted in the aged soil, 4 per cup. Water once in the morning and evening every day, adjust the soil moisture to 60% of the maximum water holding capacity, the light intensity is 15000 lx, the light / dark cycle is set, the light cycle is 28°C, 16 h, the dark cycle is 20°C, 8 h, repeat for 20 days, then harvest the corn plants; the root biomass and leaf biomass of the corn plants are 23 and 45 mg respectively; the root phosphorus content and leaf phosphorus content of the corn plants are 380 and 1250 mg / kg respectively; the root lead content and leaf lead content of the corn plants are 382 and 268 mg / kg respectively; the proportions of free lead F1 (exchangeable state) and free lead F2 (carbonate bound state) components in the soil are 5% and 39% respectively.

[0074] The root biomass and leaf biomass of the corn plants are 18 and 35 mg respectively; the root phosphorus content and leaf phosphorus content of the corn plants are 200 and 680 mg / kg respectively; the root lead content and leaf lead content of the corn plants are 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 are 30% and 49% respectively, measured by Comparative Example 2.

[0075] Comparative Example 3:

[0076] (1) The dried sludge was ground through a 40-mesh screen to obtain dry sludge, and 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 tube pyrolysis furnace, and an inert atmosphere of nitrogen gas (purity 99.99%) was introduced for 45 min at a flow rate of 100 mL / min to ensure that the entire pyrolysis environment was oxygen-free. Then the program was started, and the temperature was raised to 600°C at a rate of 10°C / min, and the temperature was maintained for 2 h. After the pyrolysis was completed, the temperature in the furnace was allowed to drop to room temperature, and the biochar was washed with dichloromethane at a ratio of 1:10 for 1 h, and then filtered and washed twice with deionized water. Finally, the biochar was dried in a 105°C forced air drying oven, ground through a 40-mesh screen, and obtained as sludge pyrolysis biochar.

[0078] (3) The phosphate-solubilizing bacterium Pseudomonas aeruginosa (preserved number AB91095) was expanded in LB liquid medium to OD 600 = 0.8-1.

[0079] (4) Lead nitrate solution was added to the soil to prepare a simulated lead-contaminated soil with a lead concentration of 500 mg / kg, and the soil was stirred uniformly and then transferred to a space cup. Each cup contained 200 g of soil, and the soil was allowed to stand and age for 15 days.

[0080] (5) 2 g of sludge pyrolysis biochar and 2 x 10 9 CFU of Pseudomonas aeruginosa were added to the simulated lead-contaminated soil, and the soil was again allowed to stand and age for 15 days.

[0081] (6) Corn seeds were soaked in ultrapure water for 24 h, then placed in a 30°C constant temperature incubator for 48 h to germinate, and then the germinated corn seeds were planted in the aged soil, with 4 seeds per cup. Water was applied once in the morning and once in the evening each day to adjust the soil moisture to 60% of the maximum water holding capacity. The light intensity during cultivation was 15000 lx, and the light / dark cycle was set to 28°C for 16 h and 20°C for 8 h. After 20 days of repeated cultivation, the corn plants were harvested.

[0082] According to Comparative Example 3, 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; and the proportions of free lead F1 (exchangeable state) and free lead F2 (carbonate-bound state) in the soil were 20% and 35%, respectively.

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

[0084] XRD analysis was performed on the pyrolytic biochar obtained in Example 2 and Comparative Example 3 as follows: Figure 2 As shown in the figure, the addition of CaO during the pyrolysis process results in the formation of 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 phosphate fertilizer to promote plant growth.

[0085] from Figure 3 As can be seen in (a), *Pseudomonas aeruginosa* is a slender rod-shaped bacterium, approximately 1-2 μm long and 0.5-1 μm wide. After the addition of Pb... Figure 3 In (b), most of the cells of Pseudomonas aeruginosa died, and their morphology changed significantly. Figure 3 Image (c) shows an electron micrograph of the remediation agent prepared in Comparative Example 3 used for lead remediation in soil. The image shows that phosphate-solubilizing bacteria can be well loaded onto sludge pyrolysis biochar, but the specific surface area, measured by a specific surface area and pore size analyzer, is only 25.61 m². 2 / g, with a relatively small specific surface area; Figure 3 Image (d) shows an electron micrograph of the remediation agent prepared in Example 2 used for lead remediation in soil. The image shows that phosphate-solubilizing bacteria can be well loaded onto the pyrolysis biochar of phosphorus-rich sludge, and the cell morphology of the phosphate-solubilizing bacteria does not change significantly, confirming the protective effect of the pyrolysis biochar of phosphorus-rich sludge on phosphate-solubilizing bacteria. Furthermore, the specific surface area was measured to be 40.64 m² using a specific surface area and pore size analyzer. 2 / g, with a relatively high specific surface area.

[0086] Table 1. Plant biomass, phosphorus content, lead content of plants and proportion of soil lead components in soil-plant systems in Examples 1 to 3 and Comparative Examples 1 to 3.

[0087]

[0088]

[0089] Those skilled in the art will readily understand that the above description is only preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a soil remediation agent combining phosphorus-rich sludge pyrolysis biochar and phosphate-solubilizing bacteria, characterized in that, Includes the following steps: (1) Dehydrated phosphorus-rich sludge with a phosphorus mass percentage of 3-10% is mixed with calcium-based additives at a Ca / P molar ratio of 1-2 and pyrolyzed under an inert atmosphere to obtain phosphorus-rich sludge pyrolysis biochar. (2) The phosphorus-rich sludge pyrolysis biochar is cleaned with dichloromethane to remove surface tar, then rinsed with deionized water, and subsequently dried, ground, and sieved. The liquid-to-solid ratio of dichloromethane to the phosphorus-rich sludge pyrolysis biochar is 5-50 g / L, and the cleaning time is 1-2 h. The cleaned phosphorus-rich sludge pyrolysis biochar is then mixed with phosphate-solubilizing bacteria, with an addition of 1×10⁶ colonies per gram of phosphorus-rich sludge pyrolysis biochar. 9 -10×10 9 The phosphate-solubilizing bacteria are mixed to obtain a soil remediation agent; the calcium-based additive is selected from one or more of calcium chloride, calcium oxide, calcium hydroxide, calcium phosphate, and calcium carbonate; The phosphate-solubilizing bacteria are selected from one or more of Pseudomonas aeruginosa, Bacillus subtilis, Escherichia coli, Burkholderia cepacia, and Enterobacter cloacae. The pyrolysis temperature in step (1) is 500-700 ℃, the heating rate is 5-20 ℃ / min, and the pyrolysis time is 1-3 h.

2. The method for preparing the soil remediation agent of phosphorus-rich sludge pyrolysis biochar combined with phosphate-solubilizing bacteria as described in claim 1, characterized in that, The dehydrated phosphorus-rich sludge underwent pretreatment before being mixed with calcium-based additives. The pretreatment consisted of drying, grinding, and sieving in sequence.

3. The soil remediation agent prepared by the preparation method according to any one of claims 1-2.

4. The application of the soil remediation agent as described in claim 3, using it as a phosphate fertilizer.

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