Method for preparing humic acid by two-step hydrothermal method and application of humic acid

Abstract

The invention relates to the technical field of waste mushroom bran hydrothermal resource conversion, and particularly discloses a method for preparing humic acid by a two-step hydrothermal method and application thereof. The method comprises the following steps: S1, crushing and sieving collected waste mushroom residues after drying; s2, dispersing the mushroom residue powder in a hydrochloric acid solution according to a preset solid-to-liquid ratio, and then carrying out a first hydrothermal reaction on the mixed solution; after the reaction is finished, cooling the system to room temperature, and filtering to retain an upper reaction clear liquid; s3, adjusting the pH value of the upper reaction clear liquid with a sodium hydroxide solution, and carrying out a second hydrothermal reaction; s4, reactants are taken out, humic acid liquid and hydrothermal carbon are separated through first centrifugation, supernate is subjected to second centrifugation, obtained solids are freeze-dried, and the humic acid is obtained. The acid hydrolysis pretreatment is carried out, so that the content of alkali heat humification monomers is increased; the generation of high-yield humic acid is facilitated. The humic acid can significantly promote seed germination and can be completely used as a humic acid fertilizer for plant growth and development.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrothermal resource conversion of waste mushroom substrates, and particularly relates to a method for preparing humic acid by a two-step hydrothermal method and its application. Background Art

[0002] At present, the disposal methods of spent mushroom substrates (SMS) are discarding or random stacking, and the resource utilization rate is only 30%. The main treatment methods include energy utilization, base utilization, feed utilization and fertilizer utilization. Among them, the fertilizer utilization of SMS is the main treatment and disposal method, and the main ways are composting and direct returning to the field. The main reason is that SMS is not only rich in the same three elements (lignin, cellulose and hemicellulose) as ordinary agricultural solid wastes, but also contains proteins, fungi and various biological enzymes, etc. These components are important factors for improving SMS composting. However, due to the long composting time and the occupation of a large amount of space, the economic benefits and technical feasibility of SMS composting treatment are limited. In addition, the three-element substances in SMS have been utilized by fungi during mushroom growth, so the degradation ability of cellulase to them is limited during the secondary composting process, and the cellulase activity is not high, resulting in a significant increase in the cost of mushroom residue composting compared with straw. Therefore, it is crucial to develop high-value resource utilization technologies for SMS.

[0003] In recent years, hydrothermal humification technology, as a new thermochemical disposal technology, has become an important way for the efficient resource utilization of biomass waste. This technology can achieve the efficient preparation of biomass humic acid, and humic acid, as a fertilizer synergist and soil conditioner, can effectively improve soil quality. The synthesis path of hydrothermal humic acid can be summarized as follows: First, carbohydrates are hydrolyzed into monosaccharides such as glucose, fructose and xylose, and then these substances respectively undergo dehydration reactions to generate hydroxymethylfurfural and furan, and finally form artificial humic acid through condensation and polymerization with the carboxyl and phenolic hydroxyl groups of lignin. However, SMS is not only rich in the three elements, but also contains primary proteins and fats, so that SMS will involve the Maillard reaction between the hydrolysis product amino acid of monosaccharide and protein during the hydrothermal process to form sugar-amine condensation humic acid. Therefore, the structure of the humic acid generated by the hydrothermal conversion of SMS is different from that of the humic acid of traditional straw, and thus the biological fertilizer efficiency caused must also be different. However, there are few studies on the high-value hydrothermal conversion of mushroom sticks. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing humic acid by a two-step hydrothermal method and its application in view of the deficiencies in the prior art. An acid-base two-step method is used for the acid-base two-step hydrothermal reaction of waste mushroom residues (SMS) rich in protein and three elements. The pretreatment of acid hydrolysis of SMS increases the content of monomers for alkali-heat humification and is conducive to the formation of humic acid with high yield.

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

[0006] The first aspect of the present invention is to provide a method for preparing humic acid by a two-step hydrothermal method, including the following steps:

[0007] S1. Physical pretreatment,

[0008] The collected waste mushroom residues are dried at low temperature to constant weight; then they are pulverized and sieved to obtain a powder sample of mushroom residues.

[0009] S2. Acid hydrolysis,

[0010] The mushroom powder is dispersed in a hydrochloric acid solution according to a preset solid-liquid ratio, and then the above mixed solution is subjected to a first hydrothermal reaction; after the reaction is completed, when the system cools to room temperature, the upper-layer reaction supernatant is filtered and retained.

[0011] S3. Alkali hydrolysis,

[0012] The pH value of the above upper-layer reaction supernatant is adjusted with a sodium hydroxide solution for a second hydrothermal reaction.

[0013] S4. Humic acid extraction,

[0014] The reactant in step S3 is taken out, and the humic acid solution and hydrothermal carbon are separated by centrifugation for the first time. The supernatant is centrifuged for the second time, and the obtained solid is freeze-dried to obtain the humic acid.

[0015] Further, in step S1, the particle size of the powder sample is 140-150 mesh.

[0016] Further, in step S2, the preset solid-liquid ratio is 1:20-1:25.

[0017] Further, the pH value of the hydrochloric acid is 0.9-1.5.

[0018] Further, the conditions for the first hydrothermal reaction are 180°C-190°C, 3.5-4 h.

[0019] Further, in step S3, the pH value of the sodium hydroxide solution is 12-13.

[0020] Further, the conditions for the second hydrothermal reaction are 180°C-190°C, 3.5-4 h.

[0021] Further, in step S4, the rotation speeds of the first centrifugation and the second centrifugation are not less than 6,000 revolutions, and the centrifugation time is 8 - 10 min.

[0022] The second aspect of the present invention is to provide the application of the above method in the preparation of humic acid fertilizer.

[0023] The third aspect of the present invention is to provide a biological fertilizer, comprising the humic acid prepared by the above method.

[0024] Compared with the prior art, the beneficial effects brought by the technical solution provided by the present invention are as follows:

[0025] (1) The present invention provides a method for preparing humic acid by a two-step hydrothermal method. For the first time, an acid-base two-step method is used for the acid-base two-step hydrothermal reaction of waste mushroom residues rich in protein and three elements. The waste mushroom residues are pretreated by acid hydrolysis, increasing the content of monomers for alkali-heat humification; it is beneficial to the formation of high-yield humic acid, and the humic acid yield is as high as 45% (by mass fraction), which is 7 times that of conventional alkali heat treatment and about 2 times that of humic acid yield from similar straw sources.

[0026] (2) The hydrothermal humic acid of waste mushroom residues prepared by the present invention is used for indoor seed germination experiments. The practical process only needs to control the concentration of humic acid and the pH of the solution, which can ensure the promotion of plant germination and growth under the best conditions. For the indoor pakchoi seed germination experiment, the average root length during germination is 32 cm, and the seed germination rate is 112%. It can significantly promote seed germination and can be used as a humic acid fertilizer for plant growth and development.

[0027] (3) The method provided by the present invention is simple, low-cost, efficient, and has a wide application prospect. Description of the Drawings

[0028] Figure 1 It is the infrared spectrogram of humic acid in different hydrolysis products provided by the present invention;

[0029] Figure 2 It is the photo of seed germination cultivated with humic acid prepared by alkali hydrothermal treatment and acid-base hydrothermal treatment provided by the present invention;

[0030] Figure 3 It is the germination index diagram of pakchoi seeds cultivated with humic acid obtained by different hydrothermal methods provided by the present invention. Detailed Embodiments

[0031] To make the objectives, technical solutions and advantages of the present invention clearer, the following further describes in detail the specific embodiments of the present invention in conjunction with specific embodiments and the accompanying drawings. For those not specifying specific test methods, instrument equipment or conditions in the embodiments, they are all carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For those reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0032] Example 1

[0033] This example provides a method for efficiently preparing humic acid by two-step hydrothermal method.

[0034] The specific steps are as follows:

[0035] (1) Physical pretreatment: The collected waste mushroom residue is dried at low temperature in an oven until the mass of the solid powder is constant; then it is crushed using a solid crusher and passed through a 140-mesh stainless steel sieve to obtain a powder sample of the mushroom.

[0036] (2) Acid hydrolysis: The powdered mushroom is dispersed in a hydrochloric acid solution with a pH of 1 according to a solid-liquid ratio of 1:20. Then the above mixed solution is added to a high-temperature reaction kettle, sealed, and reacted at 180°C for 4 hours; after the reaction is completed, wait for the system to cool to room temperature, filter and retain the upper-layer reaction supernatant for further reaction.

[0037] (3) Alkali hydrolysis: The pH of the above reaction solution is adjusted to pH = 13 with sodium hydroxide solution, and then it is loaded into the high-temperature reaction kettle again and reacted at 180°C for 4 hours under the same conditions.

[0038] (4) Extraction of humic acid: Take out the reactant, centrifuge at 6000 rpm for 8 minutes to separate the humic acid solution and hydrothermal carbon. Centrifuge the supernatant at 7500 rpm for 10 minutes again. The obtained solid is freeze-dried to obtain the humic acid.

[0039] Example 2

[0040] This example provides a method for efficiently preparing humic acid by two-step hydrothermal method.

[0041] The specific steps are as follows:

[0042] (1) Physical pretreatment: The collected waste mushroom residue is dried at low temperature in an oven until the mass of the solid powder is constant; then it is crushed using a solid crusher and passed through a 145-mesh stainless steel sieve to obtain a powder sample of the mushroom.

[0043] (2) Acid hydrolysis: The mushroom powder is dispersed in hydrochloric acid solution with a pH of 0.9 according to a solid-liquid ratio of 1:22. Subsequently, the above mixed solution is added into a high-temperature reaction kettle, sealed, and reacted at 185 °C for 4 hours. After the reaction, wait for the system to cool to room temperature, filter and retain the upper-layer reaction supernatant for further reaction;

[0044] (3) Alkaline hydrolysis: The pH of the above reaction solution is adjusted to pH = 12 with sodium hydroxide solution, and then loaded into the high-temperature reaction kettle again, and reacted at 180 °C for 4 hours under the same conditions;

[0045] (4) Extraction of humic acid: Take out the reactants, centrifuge at 6000 rpm for 10 minutes to separate the humic acid solution and hydrothermal carbon. Centrifuge the supernatant at 8000 rpm for 8 minutes again. The obtained solid is freeze-dried to obtain the humic acid.

[0046] Example 3

[0047] This example provides a method for efficiently preparing humic acid by two-step hydrothermal treatment.

[0048] The specific steps are as follows:

[0049] (1) Physical pretreatment: The collected waste mushroom residue is dried at low temperature in an oven until the mass of the solid powder is constant. Subsequently, it is crushed by a solid crusher and passed through a 150-mesh stainless steel sieve to obtain a powder sample of the mushroom;

[0050] (2) Acid hydrolysis: The mushroom powder is dispersed in hydrochloric acid solution with a pH of 1.5 according to a solid-liquid ratio of 1:25. Subsequently, the above mixed solution is added into a high-temperature reaction kettle, sealed, and reacted at 190 °C for 3.5 hours. After the reaction, wait for the system to cool to room temperature, filter and retain the upper-layer reaction supernatant for further reaction;

[0051] (3) Alkaline hydrolysis: The pH of the above reaction solution is adjusted to pH = 12.5 with sodium hydroxide solution, and then loaded into the high-temperature reaction kettle again, and reacted at 180 °C for 4 hours under the same conditions;

[0052] (4) Extraction of humic acid: Take out the reactants, centrifuge at 6500 rpm for 9 minutes to separate the humic acid solution and hydrothermal carbon. Centrifuge the supernatant at 8000 rpm for 9 minutes again. The obtained solid is freeze-dried to obtain the humic acid.

[0053] The humic acids prepared in Examples 1-3 were characterized and all had similar properties. Example 1 is taken as a representative for detailed description.

[0054] It was measured on a Fourier transform infrared spectrometer by the potassium bromide tablet method. Potassium bromide was used as a blank to deduct the background value, and the resolution was 2 cm -1 , and the wavenumber range was 400 - 4000 cm-1 with a scanning interval of 2 nm and a wavenumber accuracy of < 0.1 cm -1 Using the spectral purity of KBr as a reference sample. Mix the freeze-dried humic acid sample with the spectral potassium bromide sample (sample:KBr = 1:100, weigh 2 mg of the sample and 200 mg of KBr, grind and mix evenly), and press into tablets.

[0055] Reference Figure 1 As can be seen from the figure, a broad and strong absorption peak appears near 3400 cm -1 , which is due to the stretching vibration of the hydroxyl group in humic acid. The absorption peak around 1700 cm -1 is attributed to the stretching vibration of the carbonyl group (C=O) of the carboxyl group; the absorption peaks appearing near 1600 and 1500 cm -1 are usually related to the skeletal vibration of the aromatic ring, indicating the presence of an aromatic structure in humic acid. Therefore, its infrared spectroscopic analysis shows that the generated humic acid-like products have a typical humic acid structure.

[0056] Example 4

[0057] Investigate the performance evaluation of the hydrothermal humic acid prepared in Example 1 as a fertilizer.

[0058] Select pakchoi as a representative vegetable crop for a seed germination experiment to evaluate the plant activity of the artificial humic acid. Select plump, round, and shiny pakchoi seeds from the purchased commercial seeds as the experimental receptors, soak them in a 1.0% H2O2 solution for 15 min for disinfection treatment, then wash them 5 times with ultrapure water, and place them on filter paper to drain. Measure 5.0 mL of the humic acid solution and put it into a petri dish lined with filter paper, and put 20 disinfected pakchoi seeds. Wrap the petri dish with tin foil and put it into an incubator, and culture it in the dark at a temperature of 25 ± 0.5 °C for 48 h, then count the seed germination rate, and measure the root length of the pakchoi with a vernier caliper. The experiment uses ultrapure water as the control group, and 5 parallel experimental groups are set for all samples. The calculation formulas for the pakchoi seed germination index (SGI) and the seedling root growth inhibition rate are as follows:

[0059] SGI (%) = 100 × (the germination rate of seeds cultured in the humic acid solution × the average root length of seeds cultured in the humic acid solution) / (the germination rate of seeds cultured in ultrapure water × the average root length of seeds cultured in ultrapure water).

[0060] Reference Figure 2 is a photo of the seeds germinated by the humic acid prepared by alkali hydrothermal treatment and acid-base hydrothermal treatment.

[0061] Reference Figure 3, as shown in the figure, humic acids from two sources can significantly increase the seed germination index (SGI) of pakchoi at appropriate concentrations. Generally, the higher the germination index, the more significant the promoting effect. There is no significant difference in the promoting effects of alkali-heating and two-step hydrothermal treatment on pakchoi. The possible reason is that humic acid is a supramolecular compound containing compounds rich in hydroxyl and carboxyl small molecules, showing an activity promoting effect similar to that of plant hormones. These components can regulate the hormone balance inside the seeds and promote seed germination.

[0062] In the case of no conflict, the above-mentioned embodiments and features in the embodiments in this article can be combined with each other.

[0063] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing humic acid by a two-step hydrothermal method, characterized in that, It includes the following steps: S1. Physical pretreatment The collected waste mushroom residue is dried at low temperature until constant weight; then it is pulverized and sieved to obtain a powder sample of the mushroom residue. S2. Acid hydrolysis The mushroom powder is dispersed in a hydrochloric acid solution according to a preset solid-liquid ratio, and then the above mixed solution is subjected to a first hydrothermal reaction; after the reaction is completed, when the system cools to room temperature, the upper-layer reaction supernatant is filtered and retained. S3. Alkaline hydrolysis The pH value of the above upper-layer reaction supernatant is adjusted with a sodium hydroxide solution for a second hydrothermal reaction. S4. Humic acid extraction Take out the reactant in step S3, centrifuge the humic acid solution and hydrothermal carbon for the first time, centrifuge the supernatant for the second time, and the obtained solid is freeze-dried to obtain the humic acid.

2. The method according to claim 1, characterized in that In step S1, the particle size of the powder sample is 140-150 mesh.

3. The method according to claim 2, wherein In step S2, the preset solid-liquid ratio is 1:20-1:

25.

4. The method according to claim 3, characterized in that, The pH value of the hydrochloric acid is 0.9-1.

5.

5. The method according to claim 4, wherein The conditions of the first hydrothermal reaction are 180°C-190°C, 3.5-4 h.

6. The method according to claim 5, wherein In step S3, the pH value of the sodium hydroxide solution is 12.5-13.

7. The method according to claim 6, characterized in that, The conditions of the second hydrothermal reaction are 180°C-190°C, 3.5-4 h.

8. The method according to claim 7, wherein In step S4, the rotation speeds of the first centrifugation and the second centrifugation are not less than 6000 revolutions, and the centrifugation time is 8-10 min.

9. An application of the method according to any one of claims 1-8 in the preparation of humic acid fertilizer.

10. A biological fertilizer, characterized in that, It contains humic acid prepared by the method according to claim 8.

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