Preparation method and application of acidic magnetized charcoal base fertilizer

Abstract

The invention discloses a preparation method and application of an acidic magnetized biochar base fertilizer, and belongs to the technical field of industrial and agricultural waste resource utilization and soil improvement, the preparation method of acidic magnetized biochar comprises the following steps: carrying out anaerobic fermentation on a to-be-fermented material under nitrogen and stirring conditions to obtain an acidic fermentation product; the preparation method comprises the following steps: preparing acidic charcoal, filtering and drying to obtain an acidic charcoal precursor, carbonizing the acidic charcoal precursor and magnetized biomass, drying and sieving to obtain acidic magnetized charcoal, mixing the acidic magnetized charcoal with urea, monoammonium phosphate, potassium phosphate, bentonite and an organic fertilizer, and granulating to obtain the acidic magnetized charcoal base fertilizer. The acidic magnetized biochar and the acidic magnetized biochar base fertilizer can be used for saline-alkali soil improvement.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial and agricultural waste resource utilization and soil improvement, and in particular relates to a preparation method and application of an acidic magnetized biochar-based fertilizer. Background Art

[0002] my country is one of the countries with the most saline-alkali land in the world, and the salinization of coastal areas has been increasing year by year. + Salinization is a general term for alkaline soils with a high content of (mainly) salt. Salinization can cause soil compaction, poor permeability, inhibit soil fertility, reduce the activity of enzymes and soil microorganisms, corrode plant roots, and hinder plant nutrient intake. Once the soil has salinization problems, it is extremely difficult to deal with, so it is also called "cancer of the land." The key task in improving coastal saline-alkali land is to effectively reduce the salt content in the soil, optimize the soil structure, increase soil nutrients, and enable the soil microhabitat to meet the long-term and stable growth requirements of crop roots.

[0003] At present, the improvement methods of saline-alkali land mainly include physical and water conservancy engineering regulation, biological improvement, chemical conditioning and other measures. Among them, physical improvement and water conservancy engineering measures are costly and affected by many factors. Biological improvement has poor timeliness in improving soil quality and requires long-term observation of the stability and long-term effect of its impact on the ecosystem. Although chemical improvement is economical, quick-acting and easy to operate, it has the problems of low efficiency or secondary pollution. Therefore, there is an urgent need for a low-cost, green and reasonable conditioning and improvement material to improve soil salinity, increase plant productivity and restore the ecology of saline-alkali areas. Biochar has rich pore structure, huge specific surface area and strong adsorption and slow release properties, which can effectively increase soil pores, promote salt leaching and reduce salt activity, thereby providing methods and approaches for the improvement of coastal saline-alkali land. However, the nutrient content of biochar is low, and the nutrients that can be directly supplied to crops are limited. It does not have the potential to significantly improve soil fertility, which limits its wide promotion and application in agricultural production. Moreover, the biochar currently prepared directly by sintering is usually alkaline and is not suitable for treating water bodies and soils with high alkalinity. The existing method for preparing acidic biochar is mainly chemical acidification, which uses acidic reagents such as nitric acid, sulfuric acid or phosphoric acid to change the pH to increase the acidic functional groups on the surface of biochar. However, this method is costly and easily causes secondary pollution to the environment. Therefore, there is an urgent need for a green method that can directly prepare acidic biochar without adding additional acidic reagents. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a preparation method and application of acidic magnetized biochar-based fertilizer.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention:

[0007] A method for preparing acidic magnetized biochar comprises the following steps:

[0008] Anaerobic fermentation of the fermented material under nitrogen and stirring conditions to obtain an acidic fermentation product, filtering and drying to obtain an acidic biochar precursor, co-carbonizing the acidic biochar precursor with magnetized biomass, and drying and sieving to obtain the acidic magnetized biochar;

[0009] The anaerobic fermentation comprises two steps of hydrolysis and acidification. The temperature during the hydrolysis is 55-60°C and the pH is 5.5-6.5; the temperature during the acidification is 45-50°C and the pH is 4.5-6.

[0010] The invention provides a green method for directly preparing acidic magnetized biochar without adding additional acidic reagents.

[0011] Preferably, the hydrolysis is carried out in a hydrolysis reactor unit, and the acidification is carried out in an acidification reactor unit, and both the hydrolysis reactor unit and the acidification reactor unit are connected to a PLC automatic control unit.

[0012] Preferably, in the method for preparing the acidic magnetized biochar, nano zero-valent iron (nZVI), sodium carbonate and sodium 2-bromoethane sulfonate are added during the anaerobic fermentation process.

[0013] Preferably, in the method for preparing the acidic magnetized biochar, the anaerobic fermentation process is:

[0014] The fermented material is crushed and sieved, nano zero-valent iron is added, and hydrolyzed under nitrogen and stirring conditions to obtain a hydrolyzed slurry, wherein the temperature during the hydrolysis is 55-60° C., the pH is 5.5-6.5, and the hydrolysis time is 2-4 days;

[0015] Sodium carbonate and sodium 2-bromoethane sulfonate are added to the hydrolysis slurry for acidification. The temperature during the acidification is 45-50° C., the pH is 4.5-6, and the acidification time is 2-5 days.

[0016] More preferably, in the method for preparing the acidic magnetized biochar, the anaerobic fermentation process is:

[0017] S1: Put the material to be fermented into the crushing device;

[0018] S2: After crushing, the impurities that are not completely crushed are screened by the gravity sorting device and returned to S1; the materials that pass the 40-60 mesh screen after crushing flow into the pulping reactor, and are further screened by the sand and foam removal device. The waste slurry flows into the impurity collection device, and the rest flows into the hydrolysis reactor;

[0019] S3: After the fermentation slurry treated by the sand and foam removal device is passed into the hydrolysis reactor, nZVI is added into the hydrolysis reactor at a ratio of 50-100 mgnZVI / gTSS (total suspended solids), and uninterrupted stirring is performed to accelerate the reaction rate of the hydrolysis bacteria, and the hydrolysis reactor is regulated to be in the optimal hydrolysis condition (temperature is 55-60° C., pH is 5.5-6.5), to ensure that the fermentation product is in the optimal hydrolysis condition, maximize the hydrolysis efficiency, and obtain a fully hydrolyzed homogeneous slurry;

[0020] S4: The homogenized slurry after sufficient hydrolysis enters the acidification reactor again, and 2000-3000 mg / L of sodium carbonate is added to the acidification reactor as an alkalinity substance to prevent excessive acidification and improve the efficiency of anaerobic fermentation; 2-5 mM of sodium 2-bromoethane sulfonate is added to the acidification reactor to inhibit the activity of acetic acid fermentation bacteria and ensure that the anaerobic fermentation environment is in the acidification stage; the temperature during acidification is regulated to 45-50°C and the pH is 4.5-6 to ensure that the fermentation product is in the optimal acidification condition, and the acidified slurry is obtained;

[0021] S5: The acidified slurry flows into the slurry storage tank, and the slurry that meets the complete fermentation reaction conditions after sampling and measurement flows into the filter for filtration; the complete fermentation reaction condition is that the production of SCFAs in the fermentation system is greater than 1200 mg COD / L; the fermentation product that is not completely reacted can also be refluxed and conditioned, returned to the front end of the hydrolysis reactor, and the hydrolysis and acidification reaction stages are repeated;

[0022] S6: The remaining mixture after being filtered by the filter is dried by air at 80-105° C. to obtain an acidic biochar precursor; impurities filtered out by the filter flow into an impurity collection device.

[0023] Preferably, the impurities collected in steps S2 and S6 can be used as biomass fuel after being squeezed and dehydrated.

[0024] Preferably, the weight ratio of the acidic biochar precursor to the magnetized biomass is 4:1.

[0025] Preferably, the preparation method of the magnetized biomass is: mixing the roots of water hyacinth and cattail in a weight ratio of 1:1, placing them in a phosphoric acid solution for ultrasonic stirring modification, filtering the biomass after the modification, placing it in a hydrothermal kettle, adding water, and reacting at a temperature of 150-200° C. for 1-3 hours to obtain the magnetized biomass.

[0026] More preferably, the preparation method of the magnetized biomass is: mixing the roots of water hyacinth and cattail in a weight ratio of 1:1, placing them in a 0.5-2M phosphoric acid solution and ultrasonically stirring them for 4-12 hours, filtering the biomass and placing it in a hydrothermal kettle, adding 80-100 mL of deionized water, and reacting them for 1-3 hours at a heating rate of 5-10°C / min and a temperature of 150-200°C to obtain the magnetized biomass.

[0027] Preferably, in the method for preparing the acidic magnetized biochar, the carbonization is: uniformly mixing the acidic biochar precursor with the magnetized biomass, and pyrolyzing them under anaerobic conditions at 350 to 650° C. for 60 to 120 minutes.

[0028] Preferably, in the preparation method of the acidic magnetized biochar, the fermentation material is composed of the following raw materials in parts by weight: 20 to 40 parts of agricultural and forestry waste, 60 to 80 parts of livestock and poultry manure, 1 to 2 parts of composite bacterial agent and 3 to 6 parts of binder.

[0029] Preferably, in the method for preparing the acidic magnetized biochar, the agricultural and forestry waste includes at least one of rice straw, corn straw and wheat straw.

[0030] Preferably, in the method for preparing the acidic magnetized biochar, the livestock and poultry manure is at least one of pig manure, cow manure and sheep manure, and the pig manure, cow manure and sheep manure have not been composted and fermented.

[0031] Preferably, in the method for preparing the acidic magnetized biochar, the livestock and poultry manure is calculated by weight percentage, with pig manure accounting for 40% to 60%, cow manure accounting for 30% to 60%, and sheep manure accounting for 0% to 20%, wherein the pig manure, cow manure and sheep manure are not composted. It is impossible to control whether the livestock and poultry manure that has been composted is in the hydrolysis and acidification stage. If it has been composted, there may be a large number of methanogenic bacteria in the fermented product, which is not conducive to the acid production of the fermented product.

[0032] Preferably, in the preparation method of the acidic magnetized biochar, the composite bacterial agent is composed of 40-55% Bacillus subtilis fermentation broth, 20-30% Bacillus amyloliquefaciens fermentation broth, 15-20% Bacillus stearothermophilus fermentation broth and 10-20% yeast fermentation broth, and the total effective viable count in the composite bacterial agent is ≥2×10 8 CFU / g.

[0033] Preferably, in the preparation method of the acidic magnetized biochar, the preparation method of the Bacillus subtilis fermentation broth, the Bacillus amyloliquefaciens fermentation broth, the Bacillus stearothermophilus fermentation broth and the yeast fermentation broth is: the slant strains stored in an environment of 0 to 4°C are activated, and test tube-shake flask culture is performed respectively to obtain the primary seed liquid of each strain; the above-mentioned primary seed liquid is further expanded in a fermentation tank to obtain a fermentation liquid.

[0034] Preferably, in the method for preparing the acidic magnetized biochar, the binder is bentonite.

[0035] Preferably, in the method for preparing the acidic magnetized biochar, the screening is through a 100-mesh sieve.

[0036] The present invention uses agricultural and forestry waste and livestock and poultry manure for anaerobic fermentation, and adopts a method without the need to add additional acidic reagents to prepare acidic biochar. The present invention innovatively designs and adopts a PLC fermentation device comprising a hydrolysis reactor and an acidification reactor, which can automatically regulate the environmental state and the input and output sample amounts in anaerobic fermentation, and adds nZVI, sodium carbonate and sodium 2-bromoethane sulfonate respectively in the hydrolysis and acid production stages, which not only ensures that the reactor is in the best hydrolysis or acid production state, but also accelerates the anaerobic fermentation reaction rate. The method of the present invention provides effective means and basic materials for biochar improvement applied to saline-alkali land, and also provides new ideas and approaches for waste utilization. At the same time, organic waste (such as the roots of water hyacinth and cattail) is processed to form fertilizer, which can not only increase soil organic matter, prolong soil fertilizer efficiency, but also promote microbial reproduction, becoming an effective soil conditioner. The acidic biochar obtained by the present invention has high adsorption performance, cation exchange capacity and chemical reaction characteristics, can be used as a good slow-release carrier of fertilizer, slows down nutrient release and thus reduces loss, has good water and fertilizer retention performance, can increase soil organic matter content, improve soil structure, promote water-salt balance, increase the number and activity of soil microorganisms, and is beneficial to crop growth and development.

[0037] The acidic magnetized biochar of the present invention can achieve the purpose of "reducing weight and increasing efficiency" to improve saline-alkali land, forming an effective management model for resource utilization and recycling of waste straw, and providing an economical, environmentally friendly and practical application prospect new fertilizer preparation method for agricultural production.

[0038] The second technical solution of the present invention:

[0039] The present invention also provides a method for preparing an acidic magnetized biochar-based fertilizer. The acidic magnetized biochar, urea, monoammonium phosphate, potassium phosphate, bentonite and organic fertilizer prepared by the above method are mixed, and wood vinegar is added under stirring conditions, mixed evenly, and granulated together to obtain the acidic magnetized biochar-based fertilizer.

[0040] Preferably, the method for preparing the acidic magnetized biochar-based fertilizer comprises the following steps:

[0041] The following raw materials are mixed according to weight percentage: 20% to 30% of the acidic magnetized biochar prepared by the above method, 10% to 20% of urea, 10% to 20% of monoammonium phosphate, 10% to 15% of potassium phosphate, 5% to 10% of wood vinegar, 10% to 20% of organic fertilizer and 10% to 15% of bentonite;

[0042] Add wood vinegar under stirring conditions and mix well;

[0043] After granulation at a speed of 100 to 200 revolutions per minute for 0.5 to 1 hour, a round granular mixture is obtained. After drying, particles of 2 to 3 mm are sieved out to obtain the acidic magnetized biochar-based fertilizer, and the remaining particles are returned to the granulator for re-granulation.

[0044] Preferably, in the method for preparing the acidic magnetized biochar-based fertilizer, the acidic magnetized biochar, urea, monoammonium phosphate, potassium phosphate, bentonite and organic fertilizer are all sieved through 80-100 meshes before mixing.

[0045] Preferably, in the method for preparing the acidic magnetized biochar-based fertilizer, the organic fertilizer is livestock and poultry manure.

[0046] Preferably, in the preparation method of the acidic magnetized biochar-based fertilizer, there is no limitation on the drying method as long as the drying effect can be achieved. For example, the drying can be carried out in a dryer at a drying temperature of 70 to 80° C. and a drying time of 6 to 12 hours.

[0047] The third technical solution of the present invention:

[0048] The present invention also provides the use of the acidic magnetized biochar prepared by the above method, or the acidic magnetized biochar-based fertilizer prepared by the above method in improving saline-alkali soil.

[0049] The acidic magnetized biochar prepared by the method of the present invention is acidic after carbonization and can be used for improving saline-alkali soil without further acidification modification.

[0050] The acidic magnetized biochar-based fertilizer obtained by the invention has the advantages of retaining water and fertilizer and reducing salinity, and is beneficial to the development and utilization of saline-alkali land and the improvement of crop yield and soil quality.

[0051] Compared with the prior art, the present invention has the following advantages and technical effects:

[0052] (1) By using agricultural and forestry wastes for anaerobic fermentation to directly form acidic biochar precursors, acidic biochar is prepared in a greener and more economical way without the need to add additional acidic chemical modifiers, thus avoiding secondary pollution. It also effectively utilizes organic wastes from agriculture, forestry and animal husbandry, promoting the circular development of pollution reduction and carbon reduction.

[0053] (2) The present invention sets up a hydrolysis reactor unit and an acidification reactor unit separately and regulates their parameters separately, so that the two reactors can independently exert their maximum efficiency, and both the hydrolysis microorganisms and the acidification microorganisms are in the best activity state, which greatly improves the reaction rate and the stability of each reactor.

[0054] (3) The present invention further magnetizes the biochar on the basis of acidic biochar. The acidic magnetized biochar has the characteristics of high specific surface area, complex pore structure, rich surface active functional groups and strong conductivity. The prepared acidic magnetized carbon-based fertilizer provides a suitable carrier for microorganisms, which can effectively stimulate the enrichment of microorganisms and improve the physical and chemical properties of the soil.

[0055] (4) The PLC automatic control device provided in the present invention supports full-process automatic control and sample inlet and outlet, automatic operation, ensures the stable operation of each reactor and can effectively recycle the waste slurry, forming a green recyclable system. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0057] Figure 1 It is a schematic diagram of the structure of an anaerobic fermentation device, wherein 1-a hydrolysis reactor sample pump, 2-a hydrolysis reactor sample inlet, 3-a hydrolysis reactor temperature controller, 4-a hydrolysis reactor pH meter, 5-a hydrolysis reactor stirring pump, 6-a hydrolysis reactor sample port, 7-a hydrolysis reactor stirring head, 8-a hydrolysis reactor constant temperature heating electromagnetic induction coil, 9-a hydrolysis reactor sample pump, 10-acidification reactor sample inlet, 11-acidification reactor temperature controller, 12-acidification reactor pH meter, 13-acidification reactor stirring pump, 14-acidification reactor sample port, 15-acidification reactor stirring head, 16-acidification reactor constant temperature heating electromagnetic induction coil, 17-acidification reactor sample valve, 18-acidification reactor sample pump, 19-slurry storage tank, 20-circulation valve, 21-sample valve, 22-circulation pump, 23-PLC automatic control unit;

[0058] Figure 2 This is a scanning electron microscope image (10 μm) of the acidic magnetized biochar prepared in Example 1;

[0059] Figure 3 This is a scanning electron microscope image of ordinary biochar (10 μm);

[0060] Figure 4 Fourier transform infrared spectra FTIR graphs of ordinary biochar (BC) and acidic magnetized biochar (AMBC) prepared in Example 1. DETAILED DESCRIPTION

[0061] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0062] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0063] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0064] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0065] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0066] In the preparation process of the acidic magnetized biochar of the present invention, hydrolysis is carried out in the hydrolysis reactor unit, and acidification is carried out in the acidification reactor unit. Both the hydrolysis reactor unit and the acidification reactor unit are connected to the PLC automatic control unit. There is no limitation on the equipment of the hydrolysis reactor and the acidification reactor, as long as the hydrolysis and acidification can be carried out separately. As an example, the fermentation equipment for preparing acidic magnetized biochar in an embodiment of the present invention includes a hydrolysis reactor unit, an acidification reactor unit, a slurry storage tank unit and a PLC automatic control unit;

[0067] The hydrolysis reactor unit comprises a hydrolysis reactor, a hydrolysis reactor sampling valve, a hydrolysis reactor sampling pump, a hydrolysis reactor temperature controller, a hydrolysis reactor pH meter, a hydrolysis reactor stirring pump, a hydrolysis reactor stirring head, a hydrolysis reactor constant temperature heating electromagnetic induction coil and a hydrolysis reactor sampling pump;

[0068] The acidification reactor unit comprises an acidification reactor, an acidification reactor sampling valve, an acidification reactor sampling pump, an acidification reactor temperature controller, an acidification reactor pH meter, an acidification reactor stirring pump, an acidification reactor stirring head, an acidification reactor constant temperature heating electromagnetic induction coil, an acidification reactor sampling valve and an acidification reactor sampling pump;

[0069] The slurry storage tank unit comprises a slurry storage tank, a slurry storage tank sample inlet pump, a slurry storage tank circulation valve, a slurry storage tank circulation pump and a slurry storage tank sample outlet valve;

[0070] The sample inlet of the hydrolysis reactor is connected to the sample outlets of the pulping reactor and the slurry storage tank, the sample outlet of the hydrolysis reactor is connected to the sample inlet of the acidification reactor, and the sample outlet of the acidification reactor is connected to the sample inlet of the slurry storage tank;

[0071] The PLC automatic control unit is connected to the following devices: a hydrolysis reactor stirring pump, a hydrolysis reactor pH meter, a hydrolysis reactor constant temperature heating electromagnetic induction coil, an acidification reactor stirring pump, an acidification reactor pH meter, an acidification reactor constant temperature heating electromagnetic induction coil, a hydrolysis reactor sampling pump, an acidification reactor sampling pump, a slurry storage tank sampling pump and a slurry storage tank circulation pump;

[0072] The hydrolysis reactor and the acidification reactor are both double-layer structures, with a constant temperature heating electromagnetic induction coil on the outer layer, a reaction space on the inner layer, and a cover on the top;

[0073] A sample inlet is arranged at the bottom of one side of the hydrolysis reactor, the sample inlet is connected to a sample injection valve of the hydrolysis reactor and a sample injection pump of the hydrolysis reactor, and a sample outlet is arranged at the bottom of the other side;

[0074] A sampling port is arranged at the bottom of one side of the acidification reactor, the sampling port is connected to the sampling valve of the acidification reactor and the sampling pump of the acidification reactor, and a sampling outlet valve is arranged at the other side and is connected to the slurry storage tank;

[0075] A sample inlet and a sample inlet pump are arranged on one side of the slurry storage tank, two sample outlets and a sample outlet valve are arranged at the bottom, and a slurry storage tank circulation pump is arranged at one of the sample outlets at the bottom and connected to the sample inlet of the hydrolysis reactor.

[0076] The embodiments of the present invention do not limit the specific equipment models of the crushing device, the sand and foam removal device, the impurity collection device and the filter, as long as the corresponding effects can be achieved.

[0077] The schematic diagram of the anaerobic fermentation device is shown in Figure 1 , wherein 1-a hydrolysis reactor sampling pump, 2-a hydrolysis reactor sampling port, 3-a hydrolysis reactor temperature controller, 4-a hydrolysis reactor pH meter, 5-a hydrolysis reactor stirring pump, 6-a hydrolysis reactor sample addition port, 7-a hydrolysis reactor stirring head, 8-a hydrolysis reactor constant temperature heating electromagnetic induction coil, 9-a hydrolysis reactor sample discharge pump, 10-acidification reactor sampling port, 11-acidification reactor temperature controller, 12-acidification reactor pH meter, 13-acidification reactor stirring pump, 14-acidification reactor sample addition port, 15-acidification reactor stirring head, 16-acidification reactor constant temperature heating electromagnetic induction coil, 17-acidification reactor sample discharge valve, 18-acidification reactor sample discharge pump, 19-a slurry storage tank, 20-circulation valve, 21-sample discharge valve, 22-circulation pump, 23-PLC automatic control unit.

[0078] In the embodiment of the present invention, the pig manure, cow manure and sheep manure are not composted.

[0079] In an embodiment of the present invention, the preparation method of Bacillus subtilis fermentation broth, Bacillus amyloliquefaciens fermentation broth, Bacillus stearothermophilus fermentation broth and yeast fermentation broth is as follows: each slant strain stored in an environment of 0 to 4°C is subjected to activation treatment, and test tube-shake flask culture is performed respectively to obtain a primary seed liquid of each strain; the primary seed liquid is further subjected to fermentation tank expansion culture to obtain a fermentation broth. For example, the preparation method of Bacillus subtilis fermentation broth is as follows: the Bacillus subtilis slant strain stored in a refrigerator is subjected to activation treatment, and test tube-shake flask culture is performed respectively to obtain a primary seed liquid of the Bacillus subtilis strain; the primary seed liquid is further subjected to fermentation tank expansion culture to obtain a Bacillus subtilis fermentation broth.

[0080] All raw materials used in the embodiments of the present invention are purchased from the market. As an example, nZVI is purchased from Shanghai McLean Biochemical Technology Co., Ltd., which is a nano iron powder with a particle size of less than 50 nm.

[0081] The “parts” used in the embodiments of the present invention refer to “parts by weight” unless otherwise specified; and the “%” refers to “percentage by weight” unless otherwise specified.

[0082] In the examples and comparative examples of the present invention, the organic fertilizer is livestock manure, specifically, cow manure and sheep manure mixed in a mass ratio of 1:1.

[0083] The technical solution of the present invention is further illustrated by the following embodiments.

[0084] Example 1

[0085] 1) Preparation of acidic biochar precursor: 20 parts of rice straw, 10 parts of corn straw, 33 parts of cow dung, 30 parts of pig dung, 4 parts of bentonite and 2 parts of composite bacterial agent (consisting of 50% (weight percentage, the same below) Bacillus subtilis fermentation broth, 20% Bacillus amyloliquefaciens fermentation broth, 18% Bacillus stearothermophilus fermentation broth and 12% yeast fermentation broth, the total effective viable bacteria count in the composite bacterial agent is 1×10 9 CFU / g) as the material to be fermented. The material to be fermented first passes through a crushing device, a gravity sorting device, and a sand and foam removal device, and then flows into the hydrolysis reactor of the anaerobic fermentation device. 80 mg n ZVI / g TSS is added to the hydrolysis reactor, and it is stirred continuously. The temperature of the hydrolysis reactor is regulated to be 58°C and the pH is 6.0. After hydrolysis for 3 days, a fully hydrolyzed homogeneous slurry is obtained. The fully hydrolyzed homogeneous slurry flows into an acidification reactor, and 2400 mg / L of sodium carbonate (dosage, that is, 2400 mg of sodium carbonate is added per liter of homogeneous slurry, the same below) and 3 mM of sodium 2-bromoethane sulfonate (dosage, that is, 3 mmol of sodium 2-bromoethane sulfonate is added per liter of homogeneous slurry, the same below) are added for acidification. The temperature during acidification is regulated to be 48°C and the pH is 5.0. The acidification is completed after 4 days. The slurry after acidification is filtered and dried at 90°C to obtain an acidic biochar precursor;

[0086] 2) Preparation of magnetized biomass: The roots of water hyacinth and cattail were placed in a 1M phosphoric acid solution in a mass ratio of 1:1 and ultrasonically stirred for 6 h. The biomass was filtered and placed in a hydrothermal kettle. 100 mL of deionized water was added and reacted at a heating rate of 10°C / min and a temperature of 180°C for 2 h to obtain magnetized biomass.

[0087] 3) Preparation of acidic magnetized biochar: The acidic biochar precursor and the magnetized biomass were uniformly mixed at a weight ratio of 4:1, pyrolyzed under anaerobic conditions at 500°C for 80 minutes, and passed through a 100-mesh sieve to obtain acidic magnetized biochar.

[0088] Example 2

[0089] According to the weight percentage, 30% of the acidic magnetized biochar prepared in Example 1, 15% of urea, 15% of monoammonium phosphate, 10% of potassium phosphate, 5% of wood vinegar, 15% of organic fertilizer and 10% of bentonite are accurately weighed, and the acidic magnetized biochar, urea, monoammonium phosphate, potassium phosphate, bentonite and organic fertilizer are respectively passed through a 100-mesh sieve, and all the above raw materials are put into a granulator and granulated at a speed of 150 rpm for 1 hour to obtain a round granular mixture, which is then sent to a dryer for drying for 12 hours, and the drying temperature is controlled at 80°C. After drying, 2-3 mm particles are sieved out, which are acidic magnetized biochar-based fertilizers, and the remaining particles are returned to the granulator for re-granulation.

[0090] Example 3

[0091] 1) Preparation of acidic biochar precursor: 15 parts of rice straw, 15 parts of corn straw, 32 parts of cow dung, 28 parts of pig dung, 3 parts of bentonite and 2 parts of composite bacterial agent (the composite bacterial agent consists of 55% Bacillus subtilis fermentation broth, 20% Bacillus amyloliquefaciens fermentation broth, 15% Bacillus stearothermophilus fermentation broth and 10% yeast fermentation broth, and the total effective viable bacteria count in the composite bacterial agent is 8×10 8 CFU / g) as the material to be fermented. The material to be fermented first passes through a crushing device, a gravity sorting device, and a sand and foam removal device, and then flows into the hydrolysis reactor of the anaerobic fermentation device. 50 mg nZVI / g TSS is added to the hydrolysis reactor, and uninterrupted stirring is performed. The temperature of the hydrolysis reactor is regulated to 60°C and the pH is 5.5. The hydrolysis is performed for 3 days to obtain a fully hydrolyzed homogeneous slurry. The fully hydrolyzed homogeneous slurry flows into an acidification reactor, and 2000 mg / L of sodium carbonate and 5 mM of sodium 2-bromoethane sulfonate are added for acidification. The temperature during acidification is regulated to 45°C and the pH is 6. The acidification is completed after 2 days. After the acidification is completed, the slurry is filtered and then dried at 90°C to obtain an acidic biochar precursor;

[0092] 2) Preparation of magnetized biomass: The roots of water hyacinth and cattail were placed in a 2M phosphoric acid solution at a weight ratio of 1:1 and ultrasonically stirred for 4 h. The biomass was filtered and placed in a hydrothermal reactor. 100 mL of deionized water was added and the reaction was carried out at a heating rate of 5°C / min and a temperature of 150°C for 3 h to obtain magnetized biomass.

[0093] 3) Preparation of acidic magnetized biochar: The acidic biochar precursor and the magnetized biomass were uniformly mixed at a weight ratio of 4:1, pyrolyzed at 450°C under anaerobic conditions for 120 min, and passed through a 100-mesh sieve to obtain acidic magnetized biochar;

[0094] 4) Preparation of acidic magnetized biochar-based fertilizer: According to the weight percentage, accurately weigh 28% acidic magnetized biochar, 15% urea, 15% monoammonium phosphate, 10% potassium phosphate, 5% wood vinegar, 15% organic fertilizer and 12% bentonite, and pass the acidic magnetized biochar, urea, monoammonium phosphate, potassium phosphate, bentonite and organic fertilizer through a 100-mesh sieve respectively. Put all the above raw materials into a granulator and granulate at a speed of 200 rpm for 0.5h to obtain a round granular mixture, which is then sent to a dryer for drying for 6h. The drying temperature is controlled at 80°C. After drying, the particles of 2 to 3 mm are sieved out, which are the acidic biochar-based fertilizer, and the remaining particles are returned to the granulator for re-granulation.

[0095] Example 4

[0096] 1) Preparation of acidic biochar precursor: 18 parts of rice straw, 20 parts of corn straw, 15 parts of cow dung, 40 parts of pig dung, 5 parts of bentonite and 1 part of composite bacterial agent (the composite bacterial agent consists of 48% Bacillus subtilis fermentation broth, 25% Bacillus amyloliquefaciens fermentation broth, 15% Bacillus stearothermophilus fermentation broth and 12% yeast fermentation broth, and the total effective viable bacteria count in the composite bacterial agent is 5×10 8 CFU / g) as the material to be fermented. The material to be fermented is put into the fermentation device, and after passing through the crushing device, the gravity sorting device, and the sand and foam removal device, it flows into the hydrolysis reactor, 90 mg nZVI / g TSS is added to the hydrolysis reactor, and it is stirred continuously. The temperature of the hydrolysis reactor is regulated to 55°C and the pH is 6.5. The hydrolysis is carried out for 4 days to obtain a fully hydrolyzed homogeneous slurry. The fully hydrolyzed homogeneous slurry flows into the acidification reactor, and 3000 mg / L of sodium carbonate and 2 mM of sodium 2-bromoethane sulfonate are added for acidification. The temperature during acidification is regulated to 50°C and the pH is 4.5. The acidification is completed after 3 days. After the acidification is completed, the slurry is filtered and then dried at 90°C to obtain an acidic biochar precursor;

[0097] 2) Preparation of magnetized biomass: The roots of water hyacinth and cattail were placed in a 0.5 M phosphoric acid solution at a weight ratio of 1:1 and ultrasonically stirred for 8 h. The biomass was filtered and placed in a hydrothermal kettle. 80 mL of deionized water was added and the reaction was carried out at a heating rate of 10 °C / min and a temperature of 160 °C for 2 h to obtain magnetized biomass.

[0098] 3) Preparation of acidic magnetized biochar: The acidic biochar precursor and the magnetized biomass were uniformly mixed at a weight ratio of 4:1, pyrolyzed at 600°C under anaerobic conditions for 120 min, and passed through a 100-mesh sieve to obtain acidic magnetized biochar;

[0099] 4) Preparation of acidic magnetized biochar-based fertilizer: According to the weight percentage, accurately weigh 24% acidic magnetized biochar, 17% urea, 14% monoammonium phosphate, 14% potassium phosphate, 7% wood vinegar, 12% organic fertilizer and 12% bentonite, and pass the acidic magnetized biochar, urea, monoammonium phosphate, potassium phosphate, bentonite and organic fertilizer through a 100-mesh sieve, put all the above raw materials into a granulator and granulate at a speed of 180 rpm for 1 hour to obtain a round granular mixture, which is then sent to a dryer for drying for 12 hours, and the drying temperature is controlled at 80°C. After drying, the 2-3mm particles are screened out as acidic biochar-based fertilizer, and the remaining particles are returned to the granulator for re-granulation.

[0100] Example 5

[0101] 1) Preparation of acidic biochar precursor: 18 parts of wheat straw, 16 parts of corn straw, 22 parts of cow dung, 30 parts of pig dung, 8 parts of sheep dung, 4 parts of bentonite and 2 parts of composite bacterial agent (the composite bacterial agent consists of 40% Bacillus subtilis fermentation broth, 23% Bacillus amyloliquefaciens fermentation broth, 20% Bacillus stearothermophilus fermentation broth and 17% yeast fermentation broth, and the total effective viable bacteria count in the composite bacterial agent is 6×10 8 CFU / g) as the material to be fermented. The material to be fermented is put into the fermentation device, and after passing through the crushing device, the gravity sorting device, the sand and foam removal device, it flows into the hydrolysis reactor, 100 mg nZVI / gTSS is added to the hydrolysis reactor, and it is stirred continuously. The temperature of the hydrolysis reactor is regulated to 60°C and the pH is 6. The hydrolysis is carried out for 3 days to obtain a fully hydrolyzed homogeneous slurry. The fully hydrolyzed homogeneous slurry flows into the acidification reactor, and 2500 mg / L of sodium carbonate and 4 mM of sodium 2-bromoethane sulfonate are added for acidification. The temperature during acidification is regulated to 45°C and the pH is 5. The acidification is completed for 3 days. After the acidification is completed, the slurry is filtered and then dried at 90°C to obtain an acidic biochar precursor;

[0102] 2) Preparation of magnetized biomass: The roots of water hyacinth and cattail were placed in a 0.5 M phosphoric acid solution at a weight ratio of 1:1 and ultrasonically stirred for 10 h. The biomass was filtered and placed in a hydrothermal reactor. 90 mL of deionized water was added and the reaction was carried out at a heating rate of 10 °C / min and a temperature of 200 °C for 1 h to obtain magnetized biomass.

[0103] 3) Preparation of acidic magnetized biochar: The acidic biochar precursor and the magnetized biomass were uniformly mixed in a weight ratio of 4:1, pyrolyzed under anaerobic conditions at 650°C for 60 minutes, and passed through a 100-mesh sieve to obtain acidic magnetized biochar;

[0104] 4) Preparation of acidic magnetized biochar-based fertilizer: According to the weight percentage, accurately weigh 22% acidic magnetized biochar, 16% urea, 17% monoammonium phosphate, 12% potassium phosphate, 8% wood vinegar, 15% organic fertilizer and 10% bentonite, and pass the acidic magnetized biochar, urea, monoammonium phosphate, potassium phosphate, bentonite and organic fertilizer through an 80-mesh sieve respectively. Put all the above raw materials into a granulator and granulate at a speed of 180 rpm for 1 hour to obtain a round granular mixture, which is then sent to a dryer for drying for 12 hours. The drying temperature is controlled at 80°C. After drying, the particles of 2 to 3 mm are sieved out, which are the acidic biochar-based fertilizer, and the remaining particles are returned to the granulator for re-granulation.

[0105] Comparative Example 1 (without acidic biochar)

[0106] 1) Preparation of magnetized biochar: The roots of water hyacinth and cattail were placed in a 1M phosphoric acid solution in a mass ratio of 1:1 and ultrasonically stirred for 6 h. The biomass was filtered out and placed in a hydrothermal autoclave. 100 mL of deionized water was added and reacted at a heating rate of 10 °C / min and a temperature of 180 °C for 2 h. The biochar was then pyrolyzed at 500 °C under anaerobic conditions for 80 min and passed through a 100-mesh sieve to obtain magnetized biochar.

[0107] 2) Preparation of magnetized biochar-based fertilizer: According to the weight percentage, 30% magnetized biochar, 15% urea, 15% monoammonium phosphate, 10% potassium phosphate, 5% wood vinegar, 15% organic fertilizer and 10% bentonite are accurately weighed, and the magnetized biochar, urea, monoammonium phosphate, potassium phosphate, bentonite and organic fertilizer are respectively passed through a 100-mesh sieve, and all the above raw materials are placed in a granulator and granulated at a speed of 150 rpm for 1 hour to obtain a round granular mixture, which is then sent to a dryer for drying for 12 hours. The drying temperature is controlled at 80°C. After drying, the particles of 2 to 3 mm are sieved out, which are acidic magnetized biochar-based fertilizer, and the remaining particles are returned to the granulator for re-granulation.

[0108] Comparative Example 2 (without magnetized biochar)

[0109] 1) Take 20 parts of rice straw, 10 parts of corn straw, 33 parts of cow dung, 30 parts of pig dung, 4 parts of bentonite and 2 parts of composite bacterial agent (composed of 50% (weight percentage, the same below) Bacillus subtilis fermentation liquid, 20% Bacillus amyloliquefaciens fermentation liquid, 18% Bacillus stearothermophilus fermentation liquid and 12% yeast fermentation liquid, and the total effective viable bacteria count in the composite bacterial agent is 1×10 9CFU / g) as the material to be fermented. The material to be fermented is put into the fermentation device, and after passing through the crushing device, gravity sorting device, and sand and foam removal device, it flows into the hydrolysis reactor, 80 mg nZVI / g TSS is added to the hydrolysis reactor, and it is stirred continuously. The temperature of the hydrolysis reactor is regulated to 58°C and the pH is 6.0. After hydrolysis for 3 days, a fully hydrolyzed homogeneous slurry is obtained. The fully hydrolyzed homogeneous slurry flows into the acidification reactor, and 2400 mg / L of sodium carbonate and 3 mM of sodium 2-bromoethane sulfonate are added for acidification. The temperature during acidification is regulated to 48°C and the pH is 5.0. The acidification is completed after 4 days. The slurry after acidification is filtered and dried at 90°C to obtain an acidic biochar precursor;

[0110] 2) pyrolyzing the acidic biochar precursor under anaerobic conditions at 500°C for 80 min, and passing through a 100-mesh sieve to obtain acidic biochar;

[0111] 3) According to the weight percentage, 30% acidic biochar, 15% urea, 15% monoammonium phosphate, 10% potassium phosphate, 5% wood vinegar, 15% organic fertilizer and 10% bentonite are accurately weighed, and the magnetized biochar, urea, monoammonium phosphate, potassium phosphate, bentonite and organic fertilizer are respectively passed through a 100-mesh sieve, and all the above raw materials are put into a granulator and granulated at a speed of 150 rpm for 1 hour to obtain a round granular mixture, which is then sent to a dryer for drying for 12 hours, and the drying temperature is controlled at 80°C. After drying, 2-3 mm particles are sieved out, which are acidic biochar-based fertilizers, and the remaining particles are returned to the granulator for re-granulation.

[0112] Comparative Example 3 (without acidic magnetized biochar)

[0113] The same as Example 2, except that the preparation method of the basal fertilizer is as follows: according to the weight percentage, 20% urea, 20% monoammonium phosphate, 15% potassium phosphate, 10% wood vinegar, 20% organic fertilizer and 15% bentonite are accurately weighed, and the urea, monoammonium phosphate, potassium phosphate, bentonite and organic fertilizer are respectively passed through a 100-mesh sieve, and all the above raw materials are put into a granulator and granulated at a speed of 150 rpm for 1h to obtain a round granular mixture, which is then sent to a dryer for drying for 12h, and the drying temperature is controlled at 80°C. After drying, 2-3mm particles are sieved out as the basal fertilizer, and the remaining particles are returned to the granulator for re-granulation.

[0114] The scanning electron microscope image of the acidic magnetized biochar prepared in Example 1 is shown in Figure 2The scanning electron microscope image of ordinary biochar (the preparation method is: clean the corn stalks of agricultural and forestry waste, cut them into small pieces of 3-4 cm, put them into an oven and dry them for 12 hours until constant weight, put the dried stalks into a tube furnace for pyrolysis, heat them to 500℃ at a rate of 10℃ / min under nitrogen protection, and pyrolyze them at 500℃ for 2 hours, and repeatedly rinse the pyrolysis products with anhydrous ethanol and pure water until neutral, and pass them through a 100-mesh sieve. The obtained biochar is ordinary biochar) is shown in Figure 3 It can be seen that ordinary biochar presents a better tubular structure, but no obvious macroporous structure; while the acidic magnetized biochar has a spherical structure with distinct pores, which has a larger specific surface area than ordinary biochar and can provide more active adsorption sites.

[0115] The specific surface area and pore data of the acidic magnetized biochar (AMBC) and ordinary biochar (BC) prepared in Example 1 are shown in Table 1.

[0116] Table 1 Specific surface area and pore data of AMBC and BC

[0117] sample <![CDATA[Specific surface area / (m 2 ·g -1 )]]> <![CDATA[Pore volume / (cm 3 ·g -1 )]]> Pore ​​diameter / (nm) BC 89.5782 0.071639 9.1264 AMBC 168.7469 0.318547 12.0423

[0118] As can be seen from Table 1, the acidic magnetized biochar of the present invention has the characteristics of high specific surface area, complex pore structure, rich surface active functional groups and strong electrical conductivity.

[0119] The Fourier transform infrared spectra FTIR of ordinary biochar (BC) and acidic magnetized biochar (AMBC) prepared in Example 1 are shown in Figure 4 It can be seen that both acidic magnetized biochar and ordinary biochar are rich in chemical bonds or functional groups such as -OH, C=O, C=C, -OCH3, CH, Si-O, etc., and compared with ordinary biochar, acidic magnetized biochar has a higher concentration of -OH at 2870cm -1 Symmetrical stretching vibration of -CH2 bond appears at the position of the carbonyl group, and a more obvious CC bond characteristic peak appears, indicating that acidic magnetized biochar has more active sites than ordinary biochar.

[0120] Effect verification: A field rice planting experiment was conducted, and the products prepared in Examples 1-5 and Comparative Examples 1-3 were applied to a saline-alkali land test field with a pH of 8.5, wherein the experimental group was Examples 1-5, the control group was Comparative Example 1-4, Comparative Example 4 was urea, and the blank group was not applied with anything. The fertilizer application rate of each group was 40 kg / mu, and it was applied once 7 days before rice planting.

[0121] The soil pH and soil salinity were tested 60 days after the product was applied. The salt reduction performance of each group is shown in Table 2.

[0122] Table 2 Salt reduction performance of each group

[0123]

[0124]

[0125] It can be seen that the acidic magnetized biochar prepared by the method of the present invention and the acidic magnetized biochar-based fertilizer prepared by the method of the present invention can reduce the soil pH value and soil salinity of saline-alkali land, and the acidic magnetized biochar of the present invention can be directly used to improve saline-alkali soil. Compared with the blank group soil, the application of the acidic magnetized biochar-based fertilizer prepared by the embodiment of the present invention effectively reduced the soil pH value and soil salinity, and the soil pH value was reduced by 15.5% to 22.6%, and the soil salinity was reduced by 31.8% to 47.9%. Compared with the blank group, the acidic magnetized biochar of Example 1 reduced the soil pH by 11.9% and the soil salt content by 24.3%; compared with the blank group, the acidic magnetized biochar-based fertilizer of Example 2 reduced the soil pH by 22.6% and the soil salt content by 47.9%; compared with the blank group, the acidic magnetized biochar-based fertilizer of Example 3 reduced the soil pH by 21.4% and the soil salt content by 45.1%; compared with the blank group, the acidic magnetized biochar-based fertilizer of Example 4 reduced the soil pH by 17. 86%, and the soil salt content decreased by 36.7%; the acidic magnetized biochar-based fertilizer of Example 5 decreased the soil pH value by 15.5% and the soil salt content by 31.8% compared with the blank group; the acidic magnetized biochar-based fertilizer prepared in Comparative Example 1 decreased the soil pH value by 7.1% and the soil salt content by 14.0% compared with the blank group. Comparative Example 1 did not add acidic biochar, but actually only applied magnetized biochar-based fertilizer. Although magnetized biochar can regulate soil flora, its ability is limited, and the overall soil pH The soil pH value of the acidic biochar-based fertilizer prepared in Comparative Example 2 was reduced by 13.1% and the soil salt content was reduced by 27.3% compared with the blank group. In Comparative Example 2, only the acidic biochar-based fertilizer was added. Although it can effectively reduce the pH of the saline-alkali soil and make the soil in a normal state, it lacks the component of magnetized biochar. Magnetized biochar can promote the enrichment of microbial flora in the soil and play a better role. The soil pH value of the base fertilizer prepared in Comparative Example 3 was reduced by 4.76% and the soil salt content was reduced by 9.1% compared with the blank group. Comparative Example 3 does not contain acidic magnetized biochar, but only contains base fertilizer. Because the base fertilizer contains wood vinegar, but the content is low, the improvement effect is not as strong as that of adding acidic magnetized biochar. The nitrogen fertilizer applied in Comparative Example 4 is compared with the blank group. The soil pH value is reduced by 1.2%, and the soil salt content is reduced by 2.8%. It can be seen from the above data that the acidic magnetized biochar and acidic magnetized biochar-based fertilizer prepared in the embodiment of the present invention can effectively reduce the salinity of saline-alkali soil and improve soil properties.

[0126] Table 3 Effects of each group on soil physical and chemical properties and productivity enhancement

[0127]

[0128]

[0129] The effects of each group on the physical and chemical properties of the soil and the results of the capacity enhancement are shown in Table 3. It can be seen that the acidic magnetized biochar prepared by the method of the present invention and the acidic magnetized biochar-based fertilizer prepared by the method of the present invention can effectively improve soil nutrients and crop yields, reduce soil bulk density, and increase yields; and the acidic magnetized biochar of the present invention can be directly used to improve saline-alkali soil. Compared with the blank group soil, the application of the acidic magnetized biochar-based fertilizer prepared by each embodiment of the present invention effectively improves soil nutrients and crop yields, soil bulk density is reduced by 14.7% to 19.6%, alkaline nitrogen increases by 15.3% to 28.2%, effective phosphorus increases by 33.1% to 92.1%, available potassium increases by 11.7% to 19.3%, organic matter increases by 34.0% to 72.9%, and the yield increase is 27.5% to 48.6%. Among them, the yield increase after the application of the acidic magnetized biochar-based fertilizer prepared in Example 2 is the highest. It can be seen that the acidic magnetized biochar-based and acidic magnetized biochar-based fertilizers prepared in various embodiments of the present invention can effectively reduce soil erosion, promote soil fertility, and increase crop yields, and have good economic value and promotion.

[0130] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing acidic magnetized biochar, characterized in that: The following steps are involved: Anaerobic fermentation of the fermented material under nitrogen and stirring conditions to obtain an acidic fermentation product, filtering and drying to obtain an acidic biochar precursor, co-carbonizing the acidic biochar precursor with magnetized biomass, and drying and sieving to obtain the acidic magnetized biochar; The anaerobic fermentation includes two steps of hydrolysis and acidification, wherein the hydrolysis temperature is 55-60°C and the pH is 5.5-6.5; The acidification temperature is 45-50°C, and the pH is 4.5-6.

2. The method for preparing acidic magnetized biochar according to claim 1, characterized in that: Nano-zero-valent iron, sodium carbonate and sodium 2-bromoethane sulfonate are added during the anaerobic fermentation process.

3. The method for preparing acidic magnetized biochar according to claim 1, characterized in that: The anaerobic fermentation process is: The fermented material is crushed and sieved, nano zero-valent iron is added, and hydrolyzed under nitrogen and stirring conditions to obtain a hydrolysis slurry, wherein the hydrolysis temperature is 55-60° C. and the pH is 5.5-6.5; Sodium carbonate and sodium 2-bromoethane sulfonate are added to the hydrolysis slurry for acidification. The acidification temperature is 45-50° C. and the pH is 4.5-6.

4. The method for preparing acidic magnetized biochar according to claim 1, characterized in that: The preparation method of the magnetized biomass comprises: mixing the roots of water hyacinth and cattail in a weight ratio of 1:1, placing them in a phosphoric acid solution for ultrasonic stirring and modification, filtering the biomass after the modification, placing it in a hydrothermal kettle, adding water, and reacting at a temperature of 150-200° C. for 1-3 hours to obtain the magnetized biomass.

5. The method for preparing acidic magnetized biochar according to claim 1, characterized in that: The carbonization comprises: uniformly mixing the acidic biochar precursor with the magnetized biomass, and pyrolyzing the mixture under anaerobic conditions at 350 to 650° C. for 60 to 120 minutes.

6. The method for preparing acidic magnetized biochar according to claim 1, characterized in that: In terms of weight, the material to be fermented consists of the following raw materials: 20 to 40 parts of agricultural and forestry waste, 60 to 80 parts of livestock and poultry manure, 1 to 2 parts of composite bacterial agent and 3 to 6 parts of binder.

7. The method for preparing acidic magnetized biochar according to claim 6, characterized in that: According to the weight percentage, the composite bacterial agent is composed of 40-55% of Bacillus subtilis fermentation liquid, 20-30% of Bacillus amyloliquefaciens fermentation liquid, 15-20% of Bacillus stearothermophilus fermentation liquid and 10-20% of yeast fermentation liquid, and the total effective viable bacteria count in the composite bacterial agent is ≥2×10 8 CFU / g.

8. A method for preparing an acidic magnetized biochar-based fertilizer, characterized in that: The acidic magnetized biochar prepared by the method according to any one of claims 1 to 7, urea, monoammonium phosphate, potassium phosphate, bentonite and organic fertilizer are mixed, wood vinegar is added under stirring conditions, mixed evenly, and granulated together to obtain the acidic magnetized biochar-based fertilizer.

9. The method for preparing the acidic magnetized biochar-based fertilizer according to claim 8, characterized in that: The following steps are involved: The following raw materials are mixed according to weight percentage: 20% to 30% of the acidic magnetized biochar prepared by the method according to any one of claims 1 to 7, 10% to 20% of urea, 10% to 20% of monoammonium phosphate, 10% to 15% of potassium phosphate, 5% to 10% of wood vinegar, 10% to 20% of organic fertilizer and 10% to 15% of bentonite; Add wood vinegar under stirring conditions and mix well; The mixture is granulated at a speed of 100 to 200 revolutions per minute for 0.5 to 1 hour to obtain a round granular mixture, which is dried and sieved to obtain particles of 2 to 3 mm, namely the acidic magnetized biochar-based fertilizer.

10. Use of the acidic magnetized biochar prepared by the method according to any one of claims 1 to 7 or the acidic magnetized biochar-based fertilizer prepared by the method according to claim 8 or 9 in improving saline-alkali soil.

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