Biochar-based soil conditioner and preparation method thereof

Abstract

The invention discloses a preparation method of a biochar-based soil conditioner, which comprises the following steps: crushing, pyrolyzing and carbonizing biomass to obtain a biochar matrix; the preparation method comprises the following steps: mixing a K3PO4 solution and a biochar matrix, stirring for 2-3 hours, adding an H2O2 solution, stirring for 2-3 hours, soaking for 24 hours, and filtering to obtain modified biochar; mixing the modified charcoal with the gelatin-chitosan composite emulsion, performing ultrasonic treatment for 1-2 hours, filtering, and performing vacuum drying to constant weight to obtain the charcoal-based soil conditioner. The gelatin is connected with the modified biochar through hydrogen bonds, so that the gelatin wrapped with chitosan is more stably connected to the modified biochar, the gelatin releases the chitosan, harmful germs such as newborn or existing pythium aphanidermatum in the soil can be killed, and the soil can be effectively protected; in addition, the multiplication of harmful germs such as pythium in the biochar microenvironment can be effectively inhibited, so that a very good root rot prevention and treatment effect is achieved.

Description

Technical Field

[0001] The present invention relates to the field of soil improvement and soil environment repair, and more specifically, to a biochar-based soil conditioner and a preparation method thereof. Background Art

[0002] Landfill is the most widely used method of waste disposal in my country, but domestic waste often contains a variety of heavy metal elements such as Cd, Cu, Pb, Zn, etc. These heavy metal ions enter the soil through leachate, causing soil pollution, destroying the original ecological structure, and posing a potential threat to the health of residents.

[0003] Biochar is a highly aromatic solid object produced by pyrolysis and carbonization of plant biomass in the complete or partial absence of oxygen. It has strong adsorption capacity, can maintain soil moisture and nutrients, and is a good soil conditioner. Common biochars include straw charcoal, bamboo charcoal, rice husk charcoal, etc., which can not only provide soil with elements such as Ca, P, Mg, Si, S and a small amount of amorphous carbon, but also provide a good microenvironment for soil microorganisms through the loose porous structure of biochar, and increase the number of microbial groups such as bacteria and actinomycetes in the soil. However, these microorganisms are not all beneficial to plant growth. For example, the pythium that can cause plant root rot, using this type of biochar to improve the soil is not conducive to plant disease prevention and control. At present, this problem is solved by simply mixing fungicides (including pesticides) in biochar, but these fungicides cannot play a stable role in the microenvironment of biochar, resulting in the continued growth of microorganisms that are not conducive to plant growth in the microenvironment of biochar.

[0004] Therefore, it is worth considering how to design biochar-based soil conditioners to solve the above technical problems. Summary of the invention

[0005] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0006] In order to achieve these purposes and other advantages according to the present invention, a method for preparing a biochar-based soil conditioner is provided, comprising the following steps: S1, the biomass is crushed, pyrolyzed and carbonized to obtain a biochar matrix; S2, K3PO4 solution and biochar matrix were mixed in a mass ratio of 5-10:1, stirred and reacted at room temperature for 2-3 h, H2O2 solution was added, stirred and reacted for another 2-3 h, and then soaked for 24 h, filtered, and the residue was washed until the filtrate was neutral to obtain modified biochar; S3, the modified biochar and gelatin-chitosan composite emulsion are mixed in a mass ratio of 1:1-2, subjected to ultrasonic reaction at room temperature for 1-2 h, filtered and washed the filter residue for multiple times, vacuum dried at 60-80°C to constant weight, and ground to obtain a biochar-based soil conditioner; Wherein, the preparation method of gelatin-chitosan composite emulsion comprises the following steps: Step 1, dissolving chitosan in acetic acid solution to obtain a 0.5-3 wt% chitosan solution, dissolving gelatin in water to obtain a 3-7 wt% gelatin solution, and then mixing the chitosan solution with the gelatin solution at a mass ratio of chitosan to gelatin of 1-4:1 to obtain a chitosan / gelatin mixed solution; Step 2, mixing the emulsifier and liquid paraffin at a volume ratio of 1:100-300 to obtain a paraffin mixed liquid, and then mixing the paraffin mixed liquid and the chitosan / gelatin mixed solution at a volume ratio of 4-8:1, and emulsifying at 25-35° C. for 10-25 minutes; Step 3: Add glutaraldehyde solution to the liquid emulsified in step 2, cross-link and cure at 40-60° C. for 2-5 h. After the reaction is completed, rinse repeatedly with isopropanol and anhydrous ether to remove the liquid paraffin to obtain a gelatin-chitosan composite emulsion.

[0007] Preferably, in step S1, the biomass is crushed to 2.5-10 mesh, and the biomass includes any one or more of straw, coconut shell, and chestnut shell.

[0008] Preferably, the specific operation of pyrolysis carbonization in step S1 includes the following steps: After the biomass is crushed, it is pyrolyzed and burned in an atmosphere furnace. During the pyrolysis process, the quartz tube of the atmosphere furnace is kept sealed, and N2 is introduced into the quartz tube at a flow rate of 400 mL / min. The heating program of the atmosphere furnace is: heating from room temperature to 450°C at a heating rate of 10°C / min, and pyrolysis is continued at this temperature condition for 2~3 h, and then naturally cooled to room temperature. During the cooling process, N2 is continuously introduced at the same flow rate to obtain a biochar matrix.

[0009] Preferably, the concentration of the K3PO4 solution is 0.1-0.3 mol / L.

[0010] Preferably, the mass ratio of glutaraldehyde to chitosan is 1:2-5, and the concentration of the glutaraldehyde solution in step three is 50-60 wt%.

[0011] Preferably, the deacetylation degree of the chitosan is 89-96%, and the volume fraction of the acetic acid solution is 2-6%.

[0012] Preferably, the emulsifier comprises Span 80 and Tween 80, wherein the volume ratio of Span 80 to Tween 80 is 1-6:1.

[0013] Preferably, the concentration of the H2O2 solution is 8-10 wt%.

[0014] Provided is a biochar-based soil conditioner prepared by the method described.

[0015] The present invention has at least the following beneficial effects: First, the present invention utilizes K3PO4 to modify the biochar matrix, and the obtained modified biochar has more surface active sites and loaded phosphorus-containing components and richer functional groups.

[0016] Second, the present invention emulsifies gelatin and chitosan using a microemulsion method to obtain a gelatin-chitosan composite emulsion, which is then reacted with modified biochar. This can not only increase the adsorption capacity through gelatin, but also enable the functional groups such as phenolic hydroxyl groups on the surface of the modified biochar to form stable hydrogen bonds with the large number of amino groups contained in the gelatin, thereby increasing the stability of the functional groups on the modified biochar and reducing the desorption phenomenon.

[0017] Third, the present invention connects gelatin and modified biochar through hydrogen bonds, so that the gelatin wrapped with chitosan is more stably connected to the modified biochar. The gelatin releases chitosan, which can not only kill new or existing harmful pathogens such as Pythium in the soil, but also effectively inhibit the proliferation of harmful pathogens such as Pythium in the biochar microenvironment, thereby having the effect of preventing and controlling root rot.

[0018] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0019] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0020] <Example 1> The method for preparing the biochar matrix comprises the following steps: Step 1: Collect 100 kg of straw, wash it with deionized water, and then dry it at 80°C for 24 h. The dried biomass is crushed into 10 meshes; Step 2: Place the crushed biomass into a tubular atmosphere furnace for pyrolysis and burning. During the pyrolysis process, the quartz tube of the atmosphere furnace is kept sealed, and N2 is introduced into the tube at a flow rate of 400 mL / min to maintain anaerobic conditions throughout the pyrolysis process. The heating program of the tubular furnace is set as follows: heating from room temperature to 450°C at a heating rate of 10°C / min, and pyrolysis is continued at this temperature for 2 h, and then a natural cooling process is started. During the cooling process, N2 is continuously introduced at the same flow rate to obtain a fired biochar matrix.

[0021] <Example 2> The method for preparing modified biochar comprises the following steps: Prepare 0.1-0.3 mol / L K3PO4 solution, mix 5 kg of K3PO4 solution and 1 kg of biochar matrix prepared in Example 1, stir at room temperature for 3 h, add 1 L of 8 wt% H2O2 solution, stir for 3 h, soak at room temperature for 24 h, filter, and wash the residue with water until the filtrate is neutral. This residue is modified biochar.

[0022] <Example 3> The preparation method of gelatin-chitosan composite emulsion comprises the following steps: Step 1, dissolving chitosan with a deacetylation degree of 89% in a 6% by volume acetic acid solution to obtain a 1 wt% chitosan solution; Dissolving gelatin in water to obtain a 7 wt % gelatin solution, wherein the temperature of the water is 45-60° C.; Mix 1.4 kg of chitosan solution and 0.5 kg of gelatin solution to obtain a chitosan / gelatin mixed solution; Step 2: Mix 10 mL of emulsifier and 1 L of liquid paraffin to obtain a paraffin mixed liquid, then add 252.5 mL of chitosan / gelatin mixed solution, and emulsify at 35° C. for 10 min, wherein the emulsifier includes Span 80 and Tween 80, and the volume ratio of Span 80 to Tween 80 is 6:1; Step 3: Add 50 wt% glutaraldehyde solution to the emulsified liquid in step 2, cross-link and cure at 60°C for 2h, then repeatedly rinse with isopropanol and anhydrous ether to remove liquid paraffin to obtain a gelatin-chitosan composite emulsion, wherein the mass ratio of glutaraldehyde to chitosan is 1:5.

[0023] <Example 4> The preparation method of the biochar-based soil conditioner comprises the following steps: 1 kg of the modified biochar prepared in Example 2 and 2 kg of the gelatin-chitosan composite emulsion prepared in Example 3 were mixed, subjected to ultrasonic reaction at a power of 350 W at room temperature for 2 h, filtered, and the filter residue was washed with water 5 times, vacuum dried at 60° C. to constant weight, and ground to obtain a biochar-based soil conditioner.

[0024] <Elemental Analysis> The qualitative and elemental analyses of the biochar matrix prepared in Example 1 and the modified biochar prepared in Example 2 are shown in Table 1 below: Table 1 Element contents of biochar matrix and modified biochar According to the data in Table 1, compared with the biochar matrix prepared in Example 1, the C element content in the modified biochar decreased, the H element and O element contents increased, and the H / C and O / C ratios increased significantly, indicating that the modified biochar had a lower degree of aromatization, increased surface polarity, and enhanced hydrophilicity than the biochar matrix. Among them, the H / C ratio increased significantly to 0.69, and the N element content also increased significantly, indicating that the modified biochar had more surface active sites and loaded phosphorus-containing components and richer functional groups.

[0025] <Comparative Example 1> The preparation method of the biochar-based soil conditioner comprises the following steps: 2 kg of the gelatin-chitosan composite emulsion prepared in Example 3 was vacuum dried at 60° C. to constant weight, ground, and evenly mixed with 1 kg of the modified biochar prepared in Example 2 to obtain a biochar-based soil conditioner.

[0026] <Determination of Physically Available Cd and Cu Content in Soil> The test soil was Cu and Cd composite contaminated soil, which was taken from the tillage layer of a farmland near a smelter (depth 0-20 cm), air-dried, foreign matter removed, and passed through a 5 mm sieve and potted. Each pot contained 5 kg of soil. 100 g of the products prepared in Examples 1 to 4 and Comparative Example 1 were mixed uniformly with the potted soil by mass, and no product was added as a blank group. The soil was cultured at 25°C and 65% of the field water holding capacity for 90 days. Soil samples were taken on the 30th and 90th days, respectively. After the soil samples were air-dried, they were ground through a 1 mm sieve to determine the contents of effective Cd and Cu in the soil. Among them, the effective heavy metals extracted by CaCl2 solution were significantly correlated with the contents of heavy metals in plants, which can better predict the biological effectiveness of heavy metals in soil. 0.01 mol / L CaCl2 was used as an extractant to extract the effective states of Cu and Cd in the soil. 3 g of air-dried soil sample was accurately weighed, 20 mL of CaCl2 solution with pH = 7 was added, and the soil was shaken and extracted for 2 h at 20°C, centrifuged at 4000 r / min for 15 min, and filtered through 0.45 μm filter membrane, measured by ICP-MS (Agilent-7900, USA), repeated 3 times, and the average value was taken. The results are shown in Table 2 below: Table 2 Available contents of Cu and Cd in soil of each treatment group on the 30th and 90th day According to the data in Table 2, compared with the blank group, the effective Cu content and the effective Cd content in the air-dried soil samples of Examples 1 to 4 and Comparative Example 1 were significantly reduced. Among them, the effective Cu content decreased most significantly during the treatment of the soil with the biochar-based soil conditioner prepared in Example 4, which was 17.56 mg / kg on the 30th day and 17.78 mg / kg on the 90th day, with no obvious desorption phenomenon. Compared with Example 4, the effective Cu content of the soil treated with Examples 1 and 2 on the 30th day increased, and on the 90th day it was 17.78 mg / kg. d The overall Cu effective content in the soil increased slightly, and there was a certain desorption phenomenon. The Cu effective content in Example 2 decreased compared with that in Example 1. The reason for this was that the modified biochar had more surface active sites after being modified with K3PO4, and was able to adsorb more Cu. The effective contents of Cu and Cd in the soil treated with Example 3 also decreased compared with those in the blank group, indicating that the gelatin-chitosan composite emulsion prepared in Example 3 could also adsorb heavy metals such as Cu and Cd, but there was also a certain desorption phenomenon. This was because gelatin was a hydrolyzate of collagen and had a large number of polar groups. The carboxyl and amino groups on the macromolecular chain segments could undergo coordination and complexation reactions and electrostatic adsorption with free heavy metal ions in the soil, but the electrostatic adsorption effect was poor and it was easy to fall off. Compared with Comparative Example 1, the effective contents of Cu and Cd in the soil treated with Example 4 were lower on the 30th and 90th days. There is no significant difference in d, and there is no obvious desorption phenomenon. The reason is that the functional groups on the surface of modified biochar, such as phenolic hydroxyl, form stable hydrogen bonds with the large number of amino groups contained in gelatin. The functional groups on the modified biochar are more stable, and the CEC (cation exchange capacity) content does not decrease significantly. Therefore, the modified biochar rarely desorbs heavy metals due to its structural changes.

[0027] <Comparative Example 2> The preparation method of the biochar-based soil conditioner comprises the following steps: 1 kg of the modified biochar prepared in Example 2 and 180 g (the same mass as the chitosan in Example 4) of chitosan were mixed evenly to obtain a biochar-based soil conditioner.

[0028] <Determination of the incidence of plant root rot> Example 2, Example 4 and Comparative Examples 1-2 were applied to the planting site to adjust and improve the soil of the planting site. 5 kg of the products prepared in Example 2, Example 4 and Comparative Examples 1-2 were added to every 100 kg of the planting soil. The blank group was not added with any conditioner. Cucumbers were continuously planted in the solar greenhouse of the planting site. The root rot of cucumbers was investigated in the winter of the first year and the winter of the second year (the peak period of root rot). The measured incidence of plant root rot is shown in Table 3 below: Table 3 Root rot incidence of plants in each treatment soil According to the data in Table 3, the incidence of root rot in each group in the first year was not much different, but the incidence of root rot in the second year was very different. The reason is that the loose porous structure of biochar can provide a good microenvironment, carbon source and various minerals for microorganisms in the soil, which is conducive to the growth and reproduction of harmful pathogens such as Pythium. Compared with the blank group, the incidence of the second root rot in comparative example 1 increased because there was a certain density difference between gelatin and modified biochar. They were simply mixed together and the two were in a separated state. The chitosan in the gelatin could not act on the microenvironment of the modified biochar and could not inhibit the growth of Pythium in the microenvironment of the biochar. Compared with the blank group, the incidence of the second root rot in comparative example 2 also increased because the modified biochar adsorbed chitosan through electrostatic adsorption. The application of chitosan is beneficial to killing harmful pathogens such as Pythium in the soil, but it is easy to fall off during the mixing process of the soil in the planting area, and it cannot effectively inhibit the growth of Pythium in the biochar microenvironment. The incidence of root rot in the second year of Example 4 was significantly lower than that of the blank group because more functional groups on the surface of the modified biochar formed stable hydrogen bonds with a large number of amino groups contained in gelatin, making the gelatin wrapped with chitosan more stably connected to the modified biochar. Gelatin releases chitosan, which can not only kill new or existing harmful pathogens such as Pythium in the soil, but also effectively inhibit the proliferation of harmful pathogens such as Pythium in the biochar microenvironment, thereby achieving a good effect in preventing and controlling root rot.

[0029] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing a biochar-based soil conditioner, characterized in that: The following steps are involved: S1, the biomass is crushed, pyrolyzed and carbonized to obtain a biochar matrix; S2, K3PO4 solution and biochar matrix were mixed in a mass ratio of 5-10:1, stirred and reacted at room temperature for 2-3 h, H2O2 solution was added, stirred and reacted for another 2-3 h, and then soaked for 24 h, filtered, and the residue was washed until the filtrate was neutral to obtain modified biochar; S3, the modified biochar and gelatin-chitosan composite emulsion are mixed in a mass ratio of 1:1-2, subjected to ultrasonic reaction at room temperature for 1-2 h, filtered and washed the filter residue for multiple times, vacuum dried at 60-80°C to constant weight, and ground to obtain a biochar-based soil conditioner; Wherein, the preparation method of gelatin-chitosan composite emulsion comprises the following steps: Step 1, dissolving chitosan in acetic acid solution to obtain a 0.5-3 wt% chitosan solution, dissolving gelatin in water to obtain a 3-7 wt% gelatin solution, and then mixing the chitosan solution with the gelatin solution at a mass ratio of chitosan to gelatin of 1-4:1 to obtain a chitosan / gelatin mixed solution; Step 2, mixing the emulsifier and liquid paraffin at a volume ratio of 1:100-300 to obtain a paraffin mixed liquid, and then mixing the paraffin mixed liquid and the chitosan / gelatin mixed solution at a volume ratio of 4-8:1, and emulsifying at 25-35° C. for 10-25 min; Step 3: Add glutaraldehyde solution to the liquid emulsified in step 2, cross-link and cure at 40-60° C. for 2-5 h. After the reaction is completed, rinse repeatedly with isopropanol and anhydrous ether to remove the liquid paraffin to obtain a gelatin-chitosan composite emulsion.

2. The method for preparing the biochar-based soil conditioner according to claim 1, characterized in that: In step S1, the biomass is crushed to 2.5-10 mesh, and the biomass includes any one or more of straw, coconut shell, and chestnut shell.

3. The method for preparing the biochar-based soil conditioner according to claim 1, characterized in that: The specific operation of pyrolysis carbonization in step S1 includes the following steps: After the biomass is crushed, it is pyrolyzed and burned in an atmosphere furnace. During the pyrolysis process, the quartz tube of the atmosphere furnace is kept sealed, and N2 is introduced into the quartz tube at a flow rate of 400 mL / min. The heating program of the atmosphere furnace is: heating from room temperature to 450°C at a heating rate of 10°C / min, and pyrolysis is continued at this temperature condition for 2~3h, and then naturally cooled to room temperature. During the cooling process, N2 is continuously introduced at the same flow rate to obtain a biochar matrix.

4. The method for preparing the biochar-based soil conditioner according to claim 1, characterized in that: The concentration of the K3PO4 solution is 0.1-0.3 mol / L.

5. The method for preparing the biochar-based soil conditioner according to claim 1, characterized in that: The mass ratio of glutaraldehyde to chitosan is 1:2-5, and the concentration of the glutaraldehyde solution in step 3 is 50-60 wt%.

6. The method for preparing the biochar-based soil conditioner according to claim 1, characterized in that: The deacetylation degree of the chitosan is 89-96%, and the volume fraction of the acetic acid solution is 2-6%.

7. The method for preparing the biochar-based soil conditioner according to claim 1, characterized in that: The emulsifier includes Span 80 and Tween 80, wherein the volume ratio of Span 80 to Tween 80 is 1-6:

1.

8. The method for preparing the biochar-based soil conditioner according to claim 1, characterized in that: The concentration of the H2O2 solution is 8-10 wt%.

9. A biochar-based soil conditioner, characterized in that: A biochar-based soil conditioner prepared by the method according to any one of claims 1 to 8.

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