Sulfur-modified carbon-based sulfate reducing bacterial agent and application thereof in remediation of water and soil pollution

Abstract

The invention is applicable to the field of water and soil heavy metal pollution remediation, and provides a sulfur-modified carbon-based sulfate reducing microbial inoculum and application thereof in water and soil pollution remediation. In a preparation method, straw biochar is obtained by pretreating a straw raw material; and selecting one of a plurality of sulfur-modified straw carbon obtained based on sulfur modification treatment as a carrier, and loading sulfate reducing bacteria to obtain the sulfur-modified carbon-based sulfate reducing bacterial agent. The invention further provides application of the sulfur-modified carbon-based sulfate reducing bacterium agent in remediation of heavy metal pollution of water and soil. The sulfur-modified carbon-based sulfate reducing bacterium agent obtained by the invention has the capability of being stored at normal temperature, shows relatively high tolerance to heavy metals, and is an environment-friendly, low-cost and high-efficiency reducing bacterium product; the preparation method is simple in process, low in cost, suitable for remediation of polluted soil, capable of improving soil quality and maintaining microbial diversity and also suitable for treatment of polluted water.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal soil and water pollution remediation, and particularly relates to a sulfur-modified carbon-based sulfate-reducing bacterium agent and its application in soil and water pollution remediation. Background Art

[0002] At present, those skilled in the art mainly repair heavy metal-polluted soil and water through three approaches: chemical, physical, and biological. In the chemical remediation method, for example, a patent document with the publication number CN111940495A discloses a method for treating heavy metal-polluted soil, in which the heavy metal-polluted soil and a special plant extract are mixed and granulated and then leached; however, the preparation process of the plant extract used in this method is complex, the raw materials are specific, the cost is high, it is not conducive to large-scale application, and there is also a risk of secondary pollution if the leaching process is not properly handled.

[0003] At present, in the physical remediation methods of related technologies, such as the soil replacement method, in-situ soil replacement operations will damage the soil structure and ecosystem, affect the living environment of microbial communities and soil animals, and thus affect the soil ecological function and vegetation growth; in addition, in the biological remediation method such as the animal remediation method, it is difficult to select animal species and handle the animal carcasses enriched with heavy metals.

[0004] In related technologies, many pollution remediation technologies have been developed based on biochar. However, whether directly applying biochar or chemically modified biochar has the problem of unstable effects, and long-term application of biochar may inhibit the growth of microorganisms and plants. Therefore, it is necessary to load microorganisms onto biochar or chemically modified biochar to improve the remediation effect and stability of biochar and reduce the negative impact on soil quality caused by long-term or high-dose application of biochar.

[0005] There are few studies on the existing methods for loading microorganisms onto biochar, and there is a lack of reliable and mature technologies. The method of directly mixing microorganisms with biochar is simple, but the shelf life of microorganisms needs to be studied; loading microorganisms onto a carrier and then mixing with biochar requires cost optimization; directly inoculating microorganisms onto biochar requires exploring the microbial activity and shelf life. Summary of the Invention

[0006] The purpose of the embodiments of the present invention is to provide a sulfur-modified carbon-based sulfate-reducing bacterium agent and its application in soil and water pollution remediation. The sulfur-modified carbon-based sulfate-reducing bacterium agent provided by the present invention is suitable for the remediation of polluted soil and water, is environmentally friendly and low in cost. It can not only improve the effect of chemically modified biochar in remediating polluted water bodies and soil, achieve stabilization and persistence, but also improve the soil microbial diversity, opening up a new way to solve the decline in soil quality and biodiversity caused by long-term application of passivators such as biochar.

[0007] To achieve the above object, the present invention provides the following technical solutions.

[0008] An embodiment of the present invention provides a sulfur-modified carbon-based sulfate-reducing bacterium agent, and the preparation method of the sulfur-modified carbon-based sulfate-reducing bacterium agent includes the following steps: Pretreat the straw raw material to obtain straw biochar; Based on the modifier, perform sulfur modification treatment on the straw biochar to obtain sulfur-modified straw charcoal; the sulfur-modified straw charcoal includes elemental sulfur-modified straw charcoal, ferrous sulfide-modified straw charcoal, carbon disulfide-modified straw charcoal, and sulfur-based-iron-based composite-modified straw charcoal. Among them, sublimed sulfur is selected as the modifier to prepare elemental sulfur-modified straw charcoal; ferrous sulfide is selected as the modifier to prepare ferrous sulfide-modified straw charcoal; CS2 and NaOH are selected as the modifiers, and carbon disulfide-modified straw charcoal is prepared by the adsorption equilibrium method; CS2, NaOH, and ferrous sulfate are selected as the modifiers to prepare sulfur-based-iron-based composite-modified straw charcoal; Based on the sulfur-modified straw charcoal obtained by the sulfur modification treatment, select one as the carrier and load sulfate-reducing bacteria to prepare a sulfur-modified carbon-based sulfate-reducing bacterium agent; the loading scheme includes: sterilize the selected sulfur-modified straw charcoal, mix the bacterial suspension with an equal volume of sterilized sodium alginate solution, inject the mixture into a syringe, and let it naturally drip from the syringe mouth into the sterilized CaCl2 solution to form small balls. The formed small balls are cross-linked at a low temperature in an environment of 4°C, and after being washed three times with 0.9% sterile normal saline, they are freeze-dried.

[0009] Further, the loading scheme is replaced with: sterilize the selected sulfur-modified straw charcoal, inoculate the bacterial solution, place it in a shaker and shake it for cultivation to obtain a biochar-strain composite solution; after centrifuging the solution, discard the supernatant, collect the precipitate, and finally wash it three times with sterile normal saline and then perform freeze-drying; Among them, the dosage of the sulfur-modified straw charcoal is 0.5 g, the dosage of the culture medium is 25 mL, the inoculation amount of the bacterial solution is 25 mL, and the ratio of the bacterial solution to the sulfur-modified straw charcoal is 50:1; the shaking culture conditions are shaking at 37°C for 12 h; the centrifugation speed is 3500 rpm, and the centrifugation time is 5 min.

[0010] Further, the steps for pretreating the straw raw material include: Dry the straw raw material at 100°C until it reaches a constant weight, crush it and put it in a crucible, and then put it into a muffle furnace; The pyrolysis program of the muffle furnace is to continuously heat up to 600°C at a constant temperature and continue to dry for 4 h; After cutting off the power supply, wait until the temperature in the furnace drops to an appropriate temperature and then take it out to obtain straw biochar.

[0011] Furthermore, sublimated sulfur is selected as a modifier to prepare elemental sulfur modified straw charcoal, comprising: The straw biochar and sublimed sulfur were shaken thoroughly in a 1:1 ratio, and the mixture was evenly spread in a porcelain crucible with a lid, placed in a tube furnace and sealed; Nitrogen was introduced for pyrolysis at a rate of 100 mL min -1 After 10 minutes of ventilation, the ventilation rate was adjusted to 50 mL min -1 ; After the temperature of the tube furnace is raised to 550°C, keep it for 2 hours, and take it out after the temperature in the tube furnace drops to room temperature; The sulfur-modified biochar was washed with ethanol and ultrapure water until the pH of the eluent was constant, and then placed in a vacuum drying oven to obtain elemental sulfur-modified straw charcoal, wherein the environment in the vacuum drying oven was 40° C. and the pressure was less than 2000 Pa.

[0012] Furthermore, the step of selecting ferrous sulfide as a modifier to prepare ferrous sulfide modified straw charcoal comprises: Weigh 0.5 g of ferrous sulfide particles and dissolve them in 40 mL of ultrapure water. Ultrasonicate for 30 min to obtain a ferrous sulfide suspension. Weigh 10 g of straw biochar and add it to the suspension for magnetic stirring at a speed of 200 rpm for 2 h. After that, put it in an oven for drying at 80 °C for no less than 18 h. The obtained char was placed in a sealed tube furnace, and then nitrogen was introduced for pyrolysis at a nitrogen flow rate of 100 mL min. -1 After 10 minutes of ventilation, the ventilation rate was adjusted to 50 mL min -1 ; After the tube furnace is heated to 550℃, keep it for 2 hours. After the temperature in the furnace drops to room temperature, take it out and filter it with a sand core funnel; The biochar was washed with ethanol and ultrapure water until the pH of the eluate was constant, and then placed in a freeze dryer. After being taken out, it was sieved with a mesh size of 100 to obtain ferrous sulfide modified straw charcoal.

[0013] Further, CS2 and NaOH are selected as modifiers, and the steps of preparing carbon disulfide modified straw charcoal by adsorption equilibrium method include: Take 60mL of CS2 and 40mL of NaOH and mix them thoroughly. The concentration of NaOH is 0.4mol·L -1 ; The mixed solution was subjected to magnetic stirring and then ultrasonic oscillation. The magnetic stirring time of the mixed solution was 4 hours and the ultrasonic oscillation time was 1 hour; Weigh 10 g of straw biochar and add it to the mixed solution. Heat and stir it using a thermostatic magnetic stirrer. The temperature of the thermostatic magnetic stirrer is 45 °C, and the heating and stirring time is 8 h. After stirring is completed, filter it using a fritted funnel, and wash the biochar with ethanol and ultrapure water until the pH of the eluate is constant. Then place it in a freeze dryer; after taking it out, sieve it. The sieve mesh size is 100 meshes to obtain carbon disulfide-modified straw carbon.

[0014] Furthermore, the steps for preparing sulfur-based-iron-based composite modified straw carbon by using CS2, NaOH, and ferrous sulfate as modifiers include: Weigh 5.7 g of ferrous sulfate particles and add them to 25 mL of ultrapure water to prepare a ferrous sulfate solution with a concentration of 1.5 mol·L -1 Weigh 5 g of carbon disulfide-modified straw carbon and add it to the ferrous sulfate solution; Heat and stir it using a thermostatic magnetic stirrer. The temperature of the thermostatic magnetic stirrer is 40 °C, and the heating and stirring time is 16 h; after stirring is completed, perform ultrasonic dispersion, and then filter it using a fritted funnel; Wash the biochar with ethanol and ultrapure water until the pH of the eluate is constant. Then place it in a vacuum drying oven. The environment inside the vacuum drying oven is 40 °C, and the pressure is less than 2000 Pa; After taking it out, sieve it. The sieve mesh size is 100 meshes to obtain sulfur-based-iron-based composite modified straw carbon.

[0015] Furthermore, the preparation method of the bacterial suspension includes: Take 25 mL of the bacterial solution of sulfate-reducing bacteria, centrifuge it at 7000 rpm for 5 min using a high-speed centrifuge, pour off the supernatant, add 25 mL of sterilized fresh medium, take sulfur-modified straw carbon according to the ratio of the bacterial solution to sulfur-modified straw carbon of 50:1, and incubate it at a constant speed of 180 rpm at 37 °C for 24 h to prepare a bacterial suspension; The preparation method of the sodium alginate solution includes: Weigh 1 g of sodium alginate, add it to 25 mL of ultrapure water and stir until the sodium alginate is completely dissolved without residue sticking to the wall; the concentration of the CaCl2 solution is 2%, and its preparation method is to weigh 2 g of CaCl2 and add it to ultrapure water, and make the volume up to 100 mL.

[0016] Furthermore, after sterilization, mix the sodium alginate with the bacterial suspension in equal volume in a sterile operating table. Inject the mixed solution into a syringe, and let the mixed solution naturally drip from the syringe mouth into the sterilized CaCl2 solution to form small balls with a diameter of about 2.5 - 3.0 mm. Place the formed small balls in a 4 °C refrigerator for 24 h of low-temperature crosslinking; after crosslinking is completed, take them out, wash them three times with 0.9% physiological saline, and then perform freeze drying.

[0017] In another embodiment of the present invention, there is provided an application of a sulfur-modified carbon-based sulfate-reducing bacterium agent in the remediation of soil and water pollution.

[0018] Compared with the prior art, the technical advantages of the sulfur-modified carbon-based sulfate-reducing bacterium agent of the present invention are reflected in the following aspects: First, it can improve the activity and stability of microorganisms: By the loading method, sulfate-reducing bacteria are immobilized on biochar, providing a relatively stable microenvironment for the microorganisms, protecting them from interference by other factors in the soil, thereby significantly enhancing the activity and stability of the microorganisms; Biochar itself has excellent biocompatibility, can provide ideal attachment points for sulfate-reducing bacteria, promote their growth and reproduction, and ensure that they can continuously play a remediation function in the soil; Second, it enhances the cadmium remediation effect: Due to its rich pore structure and large specific surface area, biochar can, on the one hand, effectively capture cadmium ions in the soil through physical adsorption, and on the other hand, the functional groups on its surface can undergo chemical adsorption or complexation reactions with cadmium ions to fix the cadmium ions on the surface or inside of the biochar, reducing the migration ability and bioavailability of cadmium ions in the soil; At the same time, sulfate-reducing bacteria attached to the surface of biochar can use sulfate in the soil as an electron acceptor and reduce it to sulfide; These sulfides react with cadmium ions to form extremely insoluble cadmium sulfide precipitates, further reducing the bioavailability of cadmium, thereby improving the remediation efficiency of cadmium-contaminated soil; The sulfur-modified biochar has a significant improvement in cadmium adsorption efficiency; Third, it is environmentally friendly and low-cost: As a green and sustainable material, biochar has a wide range of sources and can be prepared using agricultural waste (such as straw, rice husks, etc.), with low cost; The present invention combines biochar with sulfate-reducing bacteria to achieve bioremediation of cadmium-contaminated soil, reducing the use of chemical reagents in the chemical remediation process, effectively reducing the risk of secondary pollution, and demonstrating good environmental benefits; Fourth, the preparation method of the present invention has a relatively simple process, does not require complex equipment and high-cost investment, and is conducive to large-scale popularization and application; Fifth, the present invention also provides an application of the sulfur-modified carbon-based sulfate-reducing bacterium agent, which is suitable for the remediation of heavy metal pollution in polluted water bodies and soils. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention.

[0020] Figure 1 It is a schematic diagram of the preparation process of carbon disulfide-modified straw carbon of the present invention; Figure 2Schematic diagram of the operation of forming small balls by dropping solutions with a syringe in the preparation of sulfur-modified carbon-based sulfate-reducing bacteria agent of the present invention; Figure 3 Product physical diagram of the sulfur-modified carbon-based sulfate-reducing bacteria agent prepared by the present invention; Figures 4(a)-4(c) are schematic diagrams of the isothermal adsorption model of sulfur-modified straw carbon of the present invention; Figure 5 Schematic diagram of the isothermal adsorption model of the sulfate-reducing bacteria agent of sulfur-modified straw carbon of the present invention; Figures 6(a)-6(h) are schematic diagrams of the remediation effect of the sulfur-modified carbon-based sulfate-reducing bacteria agent of the present invention on cadmium-contaminated soil. Detailed implementation manners

[0021] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to 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 used to limit the present invention.

[0022] The present invention provides four sulfur modification schemes for straw biochar, and the four obtained sulfur-modified straw carbons are respectively used as carriers to load sulfate-reducing bacteria. For each sulfur-modified straw carbon, two loading schemes are provided. The prepared products have the ability to be stored at room temperature and show high tolerance to heavy metals; The preparation process of the sulfur-modified carbon-based sulfate-reducing bacteria agent of the present invention is simple and the cost is low. It is suitable for the remediation of contaminated soil, can improve soil quality and maintain microbial diversity, and is also suitable for the treatment of contaminated water bodies; the sulfur-modified carbon-based sulfate-reducing bacteria agent prepared by the present invention is an environmentally friendly, low-cost and high-efficiency reducing bacteria product.

[0023] The following describes in detail the specific preparation process of the sulfur-modified carbon-based sulfate-reducing bacteria agent of the present invention with reference to specific embodiments. In the embodiments of the present invention, a sulfur-modified carbon-based sulfate-reducing bacteria agent is provided, including the following steps: Pre-treat the straw raw material to obtain straw biochar; Based on the modifier, perform sulfur modification treatment on the straw biochar to obtain sulfur-modified straw carbon; the sulfur-modified straw carbon includes elemental sulfur-modified straw carbon, ferrous sulfide-modified straw carbon, carbon disulfide-modified straw carbon, and sulfur-based-iron-based composite-modified straw carbon. Among them, sublimed sulfur is selected as the modifier to prepare elemental sulfur-modified straw carbon; ferrous sulfide is selected as the modifier to prepare ferrous sulfide-modified straw carbon; CS2 and NaOH are selected as the modifiers, and carbon disulfide-modified straw carbon is prepared by the adsorption equilibrium method; CS2, NaOH, and ferrous sulfate are selected as the modifiers to prepare sulfur-based-iron-based composite-modified straw carbon; The sulfur-modified straw carbon obtained by sulfur modification treatment is selected as a carrier, and sulfate-reducing bacteria are loaded to prepare a sulfur-modified carbon-based sulfate-reducing bacteria agent; among them, in one implementation, the loading scheme provided by the present invention includes: sterilizing the selected sulfur-modified straw carbon, mixing the bacterial suspension with an equal volume of sterilized sodium alginate solution in an equal volume, injecting the mixture into a syringe, and allowing it to naturally drip from the syringe mouth into the sterilized CaCl2 solution to form small balls. The operation method is as Figure 2 shown. The formed small balls are subjected to low-temperature crosslinking in an environment of 4°C, washed three times with 0.9% sterile physiological saline, and then freeze-dried to obtain a sulfate-reducing bacteria product based on sulfur-modified straw carbon, as Figure 3 shown.

[0024] Furthermore, in another implementation, the loading scheme is replaced by: sterilizing the selected sulfur-modified straw carbon, inoculating the bacterial solution, and placing it in a shaker for shaking culture to obtain a biochar-strain composite solution; after centrifuging the solution, discard the supernatant, collect the precipitate, and finally wash it three times with sterile physiological saline and then perform freeze-drying. Preferably, 0.9% sterile physiological saline is used; In one implementation, in the operation of inoculating the bacterial solution, the bacterial solution with an OD600 adjusted to 1 is inoculated.

[0025] Among them, the dosage of sulfur-modified straw carbon is 0.5 g, the dosage of the culture medium is 25 mL, the inoculation amount of the bacterial solution is 25 mL, and the ratio of the bacterial solution to sulfur-modified straw carbon is 50:1; the shaking culture conditions are shaking at 37°C for 12 h; the centrifugation speed is 3500 rpm, and the centrifugation time is 5 min.

[0026] Furthermore, the steps for pre-treating the straw raw material provided by the embodiments of the present invention include: drying the straw raw material at 100°C until constant weight, crushing it and loading it into a crucible, and then putting it into a muffle furnace; the pyrolysis program of the muffle furnace is to continuously heat up to 600°C at a constant temperature and continue drying for 4 h; after cutting off the power supply, wait until the temperature in the furnace drops to an appropriate temperature and then take it out to obtain straw biochar.

[0027] In some embodiments, the straw raw material of the present invention can be rapeseed straw, rice straw, rice husk, etc., and is not specifically limited.

[0028] Furthermore, the steps for preparing elemental sulfur-modified straw carbon by using sublimed sulfur as a modifier include: Fully shaking the straw biochar and sublimed sulfur evenly at a ratio of 1:1, spreading the mixture evenly in a covered porcelain crucible, putting it into a tube furnace and sealing it; passing nitrogen for pyrolysis, and the nitrogen ventilation rate is 100 mL·min -1 , after ventilating for 10 min, adjust the ventilation rate to 50 mL·min -1; After the temperature of the tubular furnace is raised to 550°C and maintained for 2 hours, it is taken out after the temperature inside the tubular furnace drops to room temperature; the sulfur-modified biochar is washed with ethanol and ultrapure water until the pH of the eluent is constant, and then placed in a vacuum drying oven to obtain elemental sulfur-modified straw charcoal, wherein the environment inside the vacuum drying oven is 40°C and the pressure is less than 2000Pa.

[0029] Furthermore, the step of selecting ferrous sulfide as a modifier to prepare ferrous sulfide modified straw charcoal comprises: weighing 0.5 g of ferrous sulfide particles and dissolving them in 40 mL of ultrapure water, ultrasonically shaking for 30 minutes to obtain a ferrous sulfide suspension; weighing 10 g of straw biochar and adding it to the suspension for magnetic stirring at a speed of 200 rpm for 2 hours, and then putting it in an oven for drying at a temperature of 80° C. for at least 18 hours; putting the obtained charcoal into a tubular furnace and sealing it, and then introducing nitrogen for pyrolysis at a nitrogen ventilation rate of 100 mL min -1 After 10 minutes of ventilation, the ventilation rate was adjusted to 50 mL min -1 ; After the tubular furnace is heated to 550°C and maintained for 2 hours, after the temperature in the furnace drops to room temperature, take it out and filter it using a sand core funnel; use ethanol and ultrapure water to wash the biochar until the pH of the eluent is constant, then put it into a freeze dryer, take it out and sieve it with a mesh size of 100 to obtain ferrous sulfide modified straw charcoal.

[0030] Please refer to Figure 1 In one implementation, the present invention uses CS2 and NaOH as modifiers, and the steps of preparing carbon disulfide modified straw charcoal by adsorption equilibrium method include: taking 60 mL of CS2 and 40 mL of NaOH and mixing them thoroughly, optionally, mixing them thoroughly in a beaker, and the NaOH concentration is 0.4 mol·L -1 ; The mixed solution is magnetically stirred and then ultrasonically shaken. The magnetic stirring time of the mixed solution is 4 hours and the ultrasonic shaking time is 1 hour. Weigh 10g of straw biochar and add it to the mixed solution. Use a constant temperature magnetic stirrer to heat and stir. The temperature of the constant temperature magnetic stirrer is 45°C and the heating and stirring time is 8 hours. After stirring, use a sand core funnel to filter, and use ethanol and ultrapure water to wash the biochar until the pH of the eluent is constant. Preferably, the constant pH can be neutral and remain stable; then put it into a freeze dryer; take it out and sieve it with a mesh size of 100 to obtain carbon disulfide modified straw charcoal.

[0031] Furthermore, in the embodiment of the present invention, CS2, NaOH and ferrous sulfate are selected as modifiers to prepare the sulfur-based-iron-based composite modified straw charcoal, comprising: weighing 5.7 g of ferrous sulfate particles and adding them into 25 mL of ultrapure water to prepare a concentration of 1.5 mol·L -1A ferrous sulfate solution; Weigh 5 g of carbon disulfide-modified straw charcoal and add it to the ferrous sulfate solution; Heat and stir using a thermostatic magnetic stirrer, with the temperature of the thermostatic magnetic stirrer being 40 °C and the heating and stirring time being 16 h; After stirring is completed, perform ultrasonic dispersion, and then filter using a sintered glass funnel; Wash the biochar with ethanol and ultrapure water until the pH of the eluate is constant, and then place it in a vacuum drying oven. The environment inside the vacuum drying oven is 40 °C and the pressure is less than 2000 Pa; After taking it out, sieve it with a sieve mesh of 100 meshes to obtain sulfur-based-iron-based composite modified straw charcoal.

[0032] Further, the preparation method of the bacterial suspension includes: Take 25 mL of the bacterial solution of sulfate-reducing bacteria, centrifuge it at a speed of 7000 rpm for 5 minutes using a high-speed centrifuge, pour off the supernatant, add 25 mL of sterilized fresh medium, take sulfur-modified straw charcoal according to the ratio of the bacterial solution to sulfur-modified straw charcoal being 50:1, and perform constant-temperature shaking culture at a speed of 180 rpm for 24 h in an environment of 37 °C to prepare the bacterial suspension; The preparation method of the sodium alginate solution includes: Weigh 1 g of sodium alginate, add it to 25 mL of ultrapure water and stir until the sodium alginate is completely dissolved without residue sticking to the wall; The concentration of the CaCl2 solution is 2%, and its preparation method is to weigh 2 g of CaCl2 and add it to ultrapure water and make the volume up to 100 mL.

[0033] Further, after sterilization, the sodium alginate is mixed with the bacterial suspension in equal volume on a sterile operating table, the mixed solution is injected into a syringe, and the mixed solution is allowed to naturally drip from the syringe opening into the sterilized CaCl2 solution to form small balls with a diameter of about 2.5 - 3.0 mm. The formed small balls are placed in a 4 °C refrigerator for 24 h of low-temperature crosslinking; After crosslinking is completed, take it out, wash it three times with 0.9% physiological saline, and then perform freeze-drying.

[0034] Further, the present invention verifies the adsorption performance of sulfur-modified straw charcoal and the sulfate-reducing bacteria agent of sulfur-modified straw charcoal on cadmium based on the following method. The steps are as follows: Step 1: Weigh straw biochar, sulfur-modified charcoal, and the sulfate-reducing bacteria agent of sulfur-modified straw charcoal and place them in a centrifuge tube. The addition amount of biochar is 2 g / L, and cadmium solutions with initial concentrations of 20 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, and 300 mg / L and the pH adjusted to 6.0 are respectively added; Step 2: Place the centrifuge tube in a constant-temperature shaking incubator and shake and adsorb at a speed of 200 rpm for 24 h in a 25 °C air bath environment; Step 3: After shaking is completed, use an atomic absorption spectrophotometer to measure the cadmium content in the supernatant; Step 4: Calculate the adsorption amount of biochar on cadmium according to the cadmium concentrations in the initial and final solutions.

[0035] Table 1 Isothermal adsorption model data of sulfur-modified rapeseed straw charcoal (RAB)

[0036] In Table 1, SS-RAB is sulfur-modified rape straw biochar, FeS-RAB is ferrous sulfide-modified rape straw biochar, S-RAB is carbon disulfide-modified rape straw biochar, and S-Fe-RAB is sulfur-based and iron-based composite-modified rape straw biochar; Table 2 Isothermal adsorption model data of sulfur-modified rice straw biochar (RIB)

[0037] Table 3 Isothermal adsorption model data of sulfur-modified rice husk biochar (RHB)

[0038] Table 4 Isothermal adsorption model data of sulfate-reducing bacteria agent of sulfur-modified straw biochar

[0039] In Table 4, B is rape straw biochar, S-B is carbon disulfide-modified rape straw biochar, B-SRB is sulfate-reducing bacteria agent of rape straw biochar, and S-B-SRB is sulfate-reducing bacteria agent of sulfur-modified straw biochar; Please refer to FIGS. 4(a)-4(c) and Tables 1-3. By comparing the parameters of the Langmuir model and the Freundlich model, the cadmium adsorption performance of sulfur-modified biochars of different types obtained by different modification methods was judged. It was found that the adsorption capacity and adsorption intensity coefficient of carbon disulfide-modified rape straw biochar were relatively high, and the adsorption behavior had a high degree of fitting with the model. Based on the above results, the cadmium adsorption performance of the sulfate-reducing bacteria agent of sulfur-modified straw biochar (S-B-SRB) was further compared, and the results also showed that the adsorption effect of the sulfate-reducing bacteria agent of sulfur-modified straw biochar was better ( Figure 5 、Table 4). This is because during the carbon disulfide modification process, abundant sulfur-containing groups were introduced onto the biochar surface, such as S 2- 、SO3 2- 、SO4 2- 、C-S, C=S, etc. These sulfur-containing groups can enhance the adsorption of cadmium through redox, ion exchange, and complexation.

[0040] Finally, in another embodiment of the present invention, the application of the carbon-based sulfate-reducing bacteria agent in the remediation of soil heavy metal pollution is provided.

[0041] The present invention uses a flooded soil culture experiment to explore the remediation effect of a carbon-based sulfate-reducing bacterium agent on cadmium-contaminated soil. The tested soil was collected from a cadmium-contaminated paddy field in Huangshan City, Anhui Province. After natural air drying, the soil was passed through a 2-mm sieve. A total of 3 treatments were set up in the experiment: blank control (CK), 1% addition of rapeseed straw biochar (B), and 1% addition of carbon-based sulfate-reducing bacterium agent (SRB-B), with 4 replicates for each treatment. Ultra-pure water was added to cover the soil interface, and the flooded layer was 2 cm. During the cultivation period, the constant weight was maintained by adding ultra-pure water. The sealed serum bottles were anaerobically cultured in the dark at a cultivation temperature of 25-35°C and an air relative humidity of 50%-80%.

[0042] Soil solutions were collected on the 15th and 30th days of soil cultivation, and soluble cadmium was not detected. Referring to FIGS. 6(a)-6(h), it can be seen from the research results that the carbon-based sulfate-reducing bacterium agent reduces the soil redox potential, promotes the reduction of sulfate ions to sulfide ions, forms stable cadmium sulfide precipitates with cadmium ions, thereby reducing the availability of cadmium.

[0043] Although the embodiments of the present invention have been disclosed as above, it is not limited to only the applications listed in the specification and the embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the illustrated and described examples here.

Claims

1. A sulfur-modified carbon-based sulfate-reducing bacterial agent, characterized in that: The following steps are involved: Pre-treating the straw raw material to obtain straw biochar; The straw biochar is subjected to sulfur modification treatment based on a modifier to obtain sulfur-modified straw charcoal; Sulfur-modified straw charcoal includes elemental sulfur-modified straw charcoal, ferrous sulfide-modified straw charcoal, carbon disulfide-modified straw charcoal and sulfur-based-iron-based composite modified straw charcoal, wherein sublimated sulfur is selected as a modifier to prepare elemental sulfur-modified straw charcoal; ferrous sulfide is selected as a modifier to prepare ferrous sulfide-modified straw charcoal; CS2 and NaOH are selected as modifiers to prepare carbon disulfide-modified straw charcoal through an adsorption equilibrium method; CS2, NaOH and ferrous sulfate are selected as modifiers to prepare sulfur-based-iron-based composite modified straw charcoal; Based on the sulfur-modified straw charcoal obtained by sulfur modification treatment, one is selected as a carrier to load sulfate-reducing bacteria to prepare a sulfur-modified carbon-based sulfate-reducing bacteria agent; wherein the loading scheme includes: sterilizing the selected sulfur-modified straw charcoal, mixing the bacterial suspension with an equal volume of sterilized sodium alginate solution, injecting the mixed solution into a syringe, allowing it to naturally drip from the syringe mouth into the sterilized CaCl2 solution to form small balls, the formed small balls are cross-linked in an environment of 4°C, washed three times with 0.9% sterile saline and then freeze-dried.

2. The sulfur-modified carbon-based sulfate-reducing bacterial agent according to claim 1, characterized in that: The loading scheme was replaced as follows: sterilize the selected sulfur-modified straw charcoal, inoculate the bacterial solution, place it in a shaker for shaking culture, and obtain a biochar-strain composite solution; centrifuge the solution and discard the supernatant, collect the precipitate, and finally wash it three times with sterile saline and freeze-dry it; wherein, the amount of sulfur-modified straw charcoal used was 0.5 g, the amount of culture medium used was 25 mL, the amount of bacterial solution inoculated was 25 mL, and the ratio of bacterial solution to sulfur-modified straw charcoal was 50:1; the shaking culture conditions were shaking at 37°C for 12 hours; the centrifugal speed was 3500 rpm, and the centrifugation time was 5 minutes.

3. The sulfur-modified carbon-based sulfate-reducing bacterial agent according to claim 2, characterized in that: The steps of pre-treating the straw raw material include: The straw raw material was dried at 100°C to constant weight, crushed and placed in a crucible, and then placed in a muffle furnace; The muffle furnace pyrolysis procedure was to continuously increase the temperature to 600°C and continue drying for 4 hours; After cutting off the power supply, wait until the furnace drops to a suitable temperature and then take it out to obtain straw biochar.

4. The sulfur-modified carbon-based sulfate-reducing bacterial agent according to claim 3, characterized in that: The steps of selecting sublimated sulfur as a modifier to prepare elemental sulfur modified straw charcoal include: The straw biochar and sublimed sulfur were shaken thoroughly in a 1:1 ratio, and the mixture was evenly spread in a porcelain crucible with a lid, placed in a tube furnace and sealed; Nitrogen was introduced for pyrolysis at a rate of 100 mL min -1 After 10 minutes of ventilation, adjust the ventilation rate to 50 mL min -1 ; After the temperature of the tube furnace is raised to 550°C, keep it for 2 hours, and take it out after the temperature in the tube furnace drops to room temperature; The sulfur-modified biochar was washed with ethanol and ultrapure water until the pH of the eluent was constant, and then placed in a vacuum drying oven to obtain elemental sulfur-modified straw charcoal, wherein the environment in the vacuum drying oven was 40° C. and the pressure was less than 2000 Pa.

5. The sulfur-modified carbon-based sulfate-reducing bacterial agent according to claim 4, characterized in that: The steps of selecting ferrous sulfide as a modifier and preparing ferrous sulfide modified straw charcoal include: Weigh 0.5 g of ferrous sulfide particles and dissolve them in 40 mL of ultrapure water. Ultrasonicate for 30 minutes to obtain a ferrous sulfide suspension. Weigh 10 g of straw biochar and add it to the suspension for magnetic stirring at a speed of 200 rpm for 2 hours. After that, put it in an oven for drying at 80°C for no less than 18 hours. The obtained char was placed in a sealed tube furnace, and then nitrogen was introduced for pyrolysis at a nitrogen flow rate of 100 mL min. -1 After 10 minutes of ventilation, adjust the ventilation rate to 50 mL min -1 ; After the tube furnace is heated to 550°C, keep it for 2 hours. After the temperature in the furnace drops to room temperature, take it out and filter it using a sand core funnel; The biochar was washed with ethanol and ultrapure water until the pH of the eluate was constant, and then placed in a freeze dryer. After being taken out, it was sieved with a mesh size of 100 to obtain ferrous sulfide modified straw charcoal.

6. The sulfur-modified carbon-based sulfate-reducing bacterial agent according to claim 5, characterized in that: The steps of selecting CS2 and NaOH as modifiers and preparing carbon disulfide modified straw charcoal by adsorption equilibrium method include: Take 60mL of CS2 and 40mL of NaOH and mix them thoroughly. The concentration of NaOH is 0.4mol·L -1 ; The mixed solution was subjected to magnetic stirring and then ultrasonic oscillation, the magnetic stirring time of the mixed solution was 4 hours, and the ultrasonic oscillation time was 1 hour; Weigh 10 g of straw biochar and add it to the mixed solution. Use a constant temperature magnetic stirrer to heat and stir. The temperature of the constant temperature magnetic stirrer is 45°C and the heating and stirring time is 8 hours. After stirring, filter with a sand core funnel, wash the biochar with ethanol and ultrapure water until the pH of the eluate is constant, and then put it into a freeze dryer; take it out and sieve it with a mesh size of 100 to obtain carbon disulfide modified straw charcoal.

7. The sulfur-modified carbon-based sulfate-reducing bacterial agent according to claim 6, characterized in that: The steps of selecting CS2, NaOH and ferrous sulfate as modifiers to prepare sulfur-based-iron-based composite modified straw charcoal include: Weigh 5.7 g of ferrous sulfate granules and add them into 25 mL of ultrapure water to prepare a concentration of 1.5 mol·L -1 ferrous sulfate solution; weigh 5g of carbon disulfide modified straw charcoal and add it to the ferrous sulfate solution; Use a constant temperature magnetic stirrer for heating and stirring, the temperature of the constant temperature magnetic stirrer is 40°C, and the heating and stirring time is 16 hours; after stirring, ultrasonic dispersion is performed, and then a sand core funnel is used for suction filtration; The biochar was washed with ethanol and ultrapure water until the pH of the eluent was constant, and then placed in a vacuum drying oven with an environment of 40°C and a pressure of less than 2000Pa; After being taken out, the product was sieved with a mesh size of 100 to obtain sulfur-based-iron-based composite modified straw charcoal.

8. The sulfur-modified carbon-based sulfate-reducing bacterial agent according to claim 7, characterized in that: The preparation method of the bacterial suspension includes: taking 25 mL of a bacterial solution of sulfate-reducing bacteria, centrifuging it at 7000 rpm for 5 minutes using a high-speed centrifuge, pouring out the supernatant, adding 25 mL of a sterilized fresh culture medium, taking sulfur-modified straw charcoal at a ratio of 50:1 of the bacterial solution to sulfur-modified straw charcoal, and culturing it at a constant temperature of 180 rpm for 24 hours at 37°C to prepare a bacterial suspension; The preparation method of the sodium alginate solution comprises: weighing 1 g of sodium alginate, adding it into 25 mL of ultrapure water and stirring it to completely dissolve the sodium alginate without any residue on the wall; the concentration of the CaCl2 solution is 2%, and its preparation method comprises: weighing 2 g of CaCl2, adding it into ultrapure water, and fixing the volume to 100 mL.

9. The sulfur-modified carbon-based sulfate-reducing bacterial agent according to claim 8, characterized in that: After sterilization, sodium alginate is mixed with the bacterial suspension in equal volumes on a sterile operating table, and the mixture is injected into a syringe, so that the mixture naturally drips from the syringe mouth into the sterilized CaCl2 solution to form small balls with a diameter of about 2.5-3.0 mm. The formed small balls are placed in a 4°C refrigerator for 24 hours of low-temperature cross-linking; After cross-linking, the samples were taken out, washed three times with 0.9% saline, and then freeze-dried.

10. Use of the sulfur-modified carbon-based sulfate-reducing bacteria agent according to any one of claims 1 to 9 in the remediation of water and soil pollution.

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