Biochar-based soil conditioner and its preparation method

Abstract

The present invention discloses a preparation method of a biochar-based soil conditioner, which comprises the following steps: Biomass is crushed and pyrolytically carbonized to obtain a biochar matrix; The K3PO4 solution and the biochar matrix are mixed, stirred for 2-3 h, then the H2O2 solution is added, stirred for another 2-3 h, soaked for 24 h, and then filtered to obtain modified biochar; The modified biochar and the gelatin-chitosan composite emulsion are mixed, ultrasonicated for 1-2 h, filtered, and vacuum dried to constant weight to obtain the biochar-based soil conditioner. In the present invention, gelatin is connected to the modified biochar through hydrogen bonds, so that the gelatin wrapped with chitosan is more stably connected to the modified biochar. The release of chitosan by gelatin can not only kill harmful pathogens such as newly generated or existing Pythium in the soil, but also effectively inhibit the proliferation of harmful pathogens such as Pythium in the microenvironment of biochar, thus achieving a good effect of preventing root rot disease.

Description

Technical Field

[0001] The present invention relates to the fields of soil improvement and soil environmental restoration. More specifically, the present invention relates to a biochar-based soil conditioner and a preparation method thereof. Background Art

[0002] Landfill is the most widely used waste treatment method in China at present. However, domestic waste often contains various heavy metal elements such as Cd, Cu, Pb, and Zn. 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 class of highly aromatic solid objects produced by pyrolytic carbonization of plant biomass under completely or partially anoxic conditions. It has strong adsorption ability and can retain soil moisture and nutrients. It is a good soil conditioner. Common biochars include straw charcoal, bamboo charcoal, rice husk charcoal, etc. They can not only provide elements such as Ca, P, Mg, Si, S, etc. and a small amount of amorphous carbon for the soil, but also provide a good microenvironment for the habitation of soil microorganisms through the porous structure of biochar, increasing the number of microbial groups such as bacteria and actinomycetes in the soil. However, not all of these microorganisms are beneficial to plant growth. For example, Pythium, which can cause plant root rot. Using such biochar to improve the soil is not conducive to plant disease control. Currently, this problem is solved by simply mixing fungicides (including pesticides) in biochar. However, these fungicides cannot stably play their roles in the microenvironment of biochar, resulting in the continuous growth of microorganisms that are not conducive to plant growth in the microenvironment of biochar.

[0004] Therefore, how to design a biochar-based soil conditioner to solve the above technical problems is worthy of consideration. Summary of the Invention

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

[0006] To achieve these objects and other advantages according to the present invention, a preparation method of a biochar-based soil conditioner is provided, including the following steps:

[0007] S1. The biomass is crushed and pyrolytically carbonized to obtain a biochar matrix.

[0008] S2. The K3PO4 solution and the biochar matrix are mixed at a mass ratio of 5-10:1, stirred and reacted at room temperature for 2-3 h, then the H2O2 solution is added, and then stirred and reacted for 2-3 h. After soaking for 24 h, filtered, and the filter residue is washed until the filtrate is neutral to obtain modified biochar.

[0009] S3. Mix the modified biochar and the gelatin-chitosan composite emulsion at a mass ratio of 1:1 - 2, and perform ultrasonic reaction at room temperature for 1 - 2 h. After filtering and washing the filter residue multiple times, vacuum dry it at 60 - 80 °C until constant weight, and then grind it to obtain the biochar-based soil conditioner;

[0010] Among them, the preparation method of the gelatin-chitosan composite emulsion includes the following steps:

[0011] Step 1. Dissolve chitosan in an acetic acid solution to obtain a 0.5 - 3 wt% chitosan solution, dissolve gelatin in water to obtain a 3 - 7 wt% gelatin solution, and then mix the chitosan solution and the gelatin solution according to a mass ratio of chitosan:gelatin of 1 - 4:1 to obtain a chitosan / gelatin mixed solution;

[0012] Step 2. Mix an emulsifier and liquid paraffin according to a volume ratio of 1:100 - 300 to obtain a paraffin mixed liquid, and then mix the paraffin mixed liquid and the chitosan / gelatin mixed solution according to a volume ratio of 4 - 8:1, and emulsify at 25 - 35 °C for 10 - 25 min;

[0013] Step 3. Add a glutaraldehyde solution to the liquid emulsified in Step 2, and crosslink and cure at 40 - 60 °C for 2 - 5 h. After the reaction, repeatedly rinse with isopropanol and anhydrous ether to remove the liquid paraffin to obtain the gelatin-chitosan composite emulsion.

[0014] Preferably, in step S1, the biomass is crushed to 2.5 - 10 meshes, and the biomass includes any one or more of straw, coconut shell, and chestnut shell.

[0015] Preferably, the specific operation of pyrolytic carbonization in step S1 includes the following steps:

[0016] After crushing the biomass, pyrolytically burn it in an atmosphere furnace. During the pyrolysis process, keep the quartz tube of the atmosphere furnace sealed, and at the same time, introduce N2 into the quartz tube at a flow rate of 400 mL / min. Among them, the heating program of the atmosphere furnace is: heat up from room temperature to 450 °C at a heating rate of 10 °C / min, and continuously pyrolyze at this temperature for 2 - 3 h, and then naturally cool down to room temperature. During the cooling process, keep N2 continuously introduced at the same flow rate to obtain the biochar matrix.

[0017] Preferably, the concentration of the K3PO4 solution is 0.1 - 0.3 mol / L.

[0018] Preferably, 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%.

[0019] Preferably, the deacetylation degree of the chitosan is 89 - 96%, and the volume fraction of the acetic acid solution is 2 - 6%.

[0020] Preferably, the emulsifier includes Span 80 and Tween 80, and the volume ratio of Span 80 to Tween 80 is 1-6:1.

[0021] Preferably, the concentration of the H2O2 solution is 8-10 wt%.

[0022] Provide a biochar-based soil conditioner prepared by the described method.

[0023] The present invention has at least the following beneficial effects:

[0024] First, the present invention uses K3PO4 to modify the biochar matrix, and the obtained modified biochar has more surface active sites and phosphorus-containing components loaded, and richer functional groups.

[0025] Second, the present invention emulsifies gelatin and chitosan by the microemulsion method to obtain a gelatin-chitosan composite emulsion, and then reacts with the modified biochar. It can not only increase the adsorption capacity through gelatin, but also form stable hydrogen bonds between the phenolic hydroxyl groups and other functional groups on the surface of the modified biochar and the large number of amino groups contained in gelatin, increasing the stability of the functional groups on the modified biochar and reducing the desorption phenomenon.

[0026] Third, the present invention connects gelatin and modified biochar through hydrogen bonds, making the gelatin wrapped with chitosan more stably connected to the modified biochar. The release of chitosan by gelatin can not only kill harmful pathogens such as newly born or existing Pythium in the soil, but also effectively inhibit the proliferation of harmful pathogens such as Pythium in the microenvironment of biochar, thus having the effect of preventing root rot.

[0027] Other advantages, objectives and features of the present invention will be partially reflected by the following description, and partially will be understood by those skilled in the art through the research and practice of the present invention. Detailed implementation manners

[0028] It should be noted that the experimental methods described in the following implementation schemes are all conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0029] <Example 1>

[0030] The preparation method of the biochar matrix includes the following steps:

[0031] Step 1: Collect 100 kg of straw, wash it with deionized water, then dry it at 80°C for 24 h, and crush the dried biomass to 10 mesh;

[0032] Step 2: Put the crushed biomass into a tubular atmosphere furnace for pyrolysis firing. During the pyrolysis process, keep the quartz tube of the atmosphere furnace sealed, and at the same time, introduce N2 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: heat up from room temperature to 450°C at a heating rate of 10°C / min, and continue pyrolysis at this temperature for 2 h, then start the natural cooling process. During the cooling process, keep N2 flowing continuously at the same flow rate, and then obtain the fired biochar matrix.

[0033] <Example 2>

[0034] The preparation method of the modified biochar includes the following steps:

[0035] Prepare a K3PO4 solution with a concentration of 0.1 - 0.3 mol / L, mix 5 kg of the K3PO4 solution with 1 kg of the biochar matrix prepared in Example 1, stir at room temperature for 3 h, then add 1 L of 8 wt% H2O2 solution, stir for 3 h, soak at room temperature for 24 h, filter, wash the filter residue with water until the filtrate is neutral, and this filter residue is the modified biochar.

[0036] <Example 3>

[0037] The preparation method of the gelatin-chitosan composite emulsion includes the following steps:

[0038] Step 1: Dissolve chitosan with a deacetylation degree of 89% in an acetic acid solution with a volume fraction of 6% to obtain a 1 wt% chitosan solution;

[0039] Dissolve gelatin in water to obtain a 7 wt% gelatin solution, where the temperature of the water is 45 - 60°C;

[0040] Mix 1.4 kg of the chitosan solution and 0.5 kg of the gelatin solution to obtain a chitosan / gelatin mixed solution;

[0041] 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 the chitosan / gelatin mixed solution, and emulsify at 35°C for 10 min. Among them, the emulsifier includes Span 80 and Tween 80, and the volume ratio of Span 80 to Tween 80 is 6:1;

[0042] Step 3: Add a 50 wt% glutaraldehyde solution to the liquid emulsified in Step 2, crosslink and cure at 60°C for 2 h, then repeatedly rinse with isopropanol and anhydrous ether to remove liquid paraffin, and obtain the gelatin-chitosan composite emulsion. Among them, the mass ratio of glutaraldehyde to chitosan is 1:5.

[0043] <Example 4>

[0044] The preparation method of the biochar-based soil conditioner comprises the following steps:

[0045] Mix 1 kg of the modified biochar prepared in Example 2 and 2 kg of the gelatin-chitosan composite emulsion prepared in Example 3, carry out ultrasonic reaction at room temperature with a power of 350 W for 2 h, then filter, wash the filter residue 5 times with water, vacuum dry it at 60 °C until constant weight, and grind it to obtain the biochar-based soil conditioner.

[0046] <Elemental analysis>

[0047] Qualitative and quantitative elemental analyses were carried out on the biochar matrix prepared in Example 1 and the modified biochar prepared in Example 2, as shown in Table 1 below:

[0048] Table 1 Elemental contents of the biochar matrix and the modified biochar

[0049] According to the data in Table 1, compared with the biochar matrix prepared in Example 1, the content of C element in the modified biochar decreased, the contents of H element and O element increased, and the ratios of H / C and O / C increased significantly, indicating that compared with the biochar matrix, the degree of aromatization of the modified biochar decreased, the surface polarity increased, and the hydrophilicity enhanced. Among them, the increase in the H / C ratio was obvious, being 0.69, and the content of N element also increased significantly, indicating that the modified biochar had more surface active sites and loaded phosphorus-containing components and richer functional groups.

[0050] <Comparative Example 1>

[0051] The preparation method of the biochar-based soil conditioner comprises the following steps:

[0052] Vacuum dry 2 kg of the gelatin-chitosan composite emulsion prepared in Example 3 at 60 °C until constant weight, then grind it and mix it evenly with 1 kg of the modified biochar prepared in Example 2 to obtain the biochar-based soil conditioner.

[0053] <Determination of available Cd and Cu contents in soil conditioning>

[0054] The tested soil was Cu and Cd composite contaminated soil, taken from the plough layer soil (depth 0 - 20 cm) of farmland near a smelter, air-dried, foreign matters removed, passed through a 5 mm sieve and filled into pots, with 5 kg of soil filled in each pot;

[0055] 100 g of the products prepared in Examples 1 to 4 and Comparative Example 1 were respectively mixed evenly with the above-mentioned potted soil by mass. Taking no addition of any product as the blank group, they were cultured for 90 d under the conditions of 25 °C and 65% field water holding capacity. Soil samples were taken at the 30th d and the 90th d respectively. After the soil samples were air-dried, they were ground and passed through a 1 mm sieve, and the contents of available Cd and Cu in the soil were determined. Among them, the available heavy metals extracted by CaCl2 solution were extremely significantly correlated with the heavy metal contents in plants, and could better predict the bioavailability of soil heavy metals. 0.01 mol / L CaCl2 was used as the extractant to extract the available Cu and Cd in the soil. 3 g of the air-dried soil sample was accurately weighed, 20 mL of CaCl2 solution with pH = 7 was added, and it was extracted by shaking at 20 °C for 2 h, centrifuged at 4000 r / min for 15 min, and passed through a 0.45 μm filter membrane. It was measured by ICP-MS (Agilent-7900, Agilent Technologies, USA), repeated 3 times, and the average value was taken. The results are shown in Table 2 below:

[0056] Table 2 Available Cu and Cd contents in the soil of each treatment group at the 30th d and the 90th d

[0057] According to the data in Table 2, compared with the blank group, the available Cu content and available Cd content in the air-dried soil samples of Examples 1-4 and Comparative Example 1 both decreased significantly. Among them, the decrease in the available Cu content was the most obvious during the treatment of 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, and there was no obvious desorption phenomenon. Compared with Example 4, the available Cu content in the soil treated with Examples 1 and 2 increased on the 30th day, and the overall available Cu content in the soil increased slightly on the 90th day, with a certain desorption phenomenon. Moreover, the available Cu content after the treatment with Example 2 was lower than that with Example 1. Analyzing the reasons, it is because the modified biochar has more surface active multi-sites after being modified with K3PO4 and can adsorb more Cu. The available Cu and Cd contents in the soil treated with Example 3 also decreased compared with the blank group, indicating that the gelatin-chitosan composite emulsion prepared in Example 3 can also adsorb heavy metals such as Cu and Cd, but there is also a certain desorption phenomenon. This is because gelatin is a hydrolysis product of collagen and has a large number of polar groups. The carboxyl and amino groups on the macromolecular chain segments can carry out coordination complexation reactions and electrostatic adsorption with free heavy metal ions in the soil, but the electrostatic adsorption effect is not good and it is easy to fall off. Compared with Comparative Example 1, there was no significant difference in the available Cu and Cd contents in the soil treated with Example 4 on the 30th day and the 90th day, and there was no obvious desorption phenomenon. Analyzing the reasons, it is because the functional groups on the surface of the modified biochar, such as phenolic hydroxyl groups, 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 has no obvious decrease. Therefore, the modified biochar rarely causes the desorption of heavy metals due to its structural changes.

[0058] <Comparative Example 2>

[0059] The preparation method of the biochar-based soil conditioner includes the following steps:

[0060] Mix 1 kg of the modified biochar prepared in Example 2 and 180 g (the same mass as chitosan in Example 4) of chitosan evenly to obtain the biochar-based soil conditioner.

[0061] <Determination of the incidence of plant root rot>

[0062] Apply Examples 2 and 4 and Comparative Examples 1-2 to the planting land respectively to adjust and improve the soil of the planting land. Add 5 kg of the products prepared in Examples 2 and 4 and Comparative Examples 1-2 to every 100 kg of planting soil respectively. Use the soil without adding any conditioner as the blank group. Plant cucumbers in the continuous cropping solar greenhouse of the planting land. Investigate the cucumber root rot situation in the first winter and the second winter (the high-incidence period of root rot) respectively. The measured incidence of plant root rot is shown in Table 3 below:

[0063] Table 3 Incidence of root rot disease in soil plants treated in each group

[0064] According to the data in Table 3, the incidence of root rot disease in the first year of each group is not very different, but the incidence of root rot disease in the second year is very different. Analyzing the reasons, it is because the loose and porous structure of biochar can provide a good microenvironment, carbon source and various minerals for the inhabitation of microorganisms in the soil, which is conducive to the growth and reproduction of harmful pathogens such as Pythium;

[0065] Compared with the blank group, the incidence of root rot disease in the second year of Comparative Example 1 increased because there is a certain density difference between gelatin and modified biochar. They are simply mixed together and in a separated state. Chitosan in the gelatin cannot act on the microenvironment of the modified biochar and cannot inhibit the growth of Pythium in the biochar microenvironment;

[0066] Compared with the blank group, the incidence of root rot disease in the second year of Comparative Example 2 also increased because the modified biochar adsorbed chitosan through electrostatic adsorption. Applying 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 planting soil and cannot effectively inhibit the growth of Pythium in the biochar microenvironment;

[0067] The incidence of root rot disease 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. The release of chitosan from gelatin 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, thus achieving a good effect of preventing and controlling root rot disease.

[0068] Although the embodiments of the present invention have been disclosed as above, it is not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, 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 and pyrolyzed to obtain a biochar matrix, wherein the specific operation of pyrolysis and carbonization includes the following steps: After the biomass is crushed, it is pyrolyzed and fired 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 temperature rise 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 for 2-3 hours, 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; 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 concentration of the K3PO4 solution is 0.1-0.3 mol / L.

4. 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%.

5. 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%.

6. 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.

7. 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%.

8. 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 7.

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