Resource utilization method for treating straw and livestock and poultry manure solid waste and hydrothermal carbon-based fertilizer

Abstract

The invention relates to a resource utilization method for treating straw and livestock and poultry manure solid waste and a hydrothermal carbon-based fertilizer, and belongs to the technical field of comprehensive resource utilization of agricultural waste. The method comprises the following steps: in the presence of water, carrying out hydrothermal treatment on straws and livestock and poultry manure, and then sequentially carrying out solid-liquid separation and drying treatment to obtain the hydrothermal carbon-based fertilizer, the use amount mass ratio of the straw on the dry basis to the livestock and poultry manure on the dry basis is 1: (0.5-5); the temperature of the hydrothermal reaction is 100 to 180 DEG C. Compared with a hydrothermal method in the prior art, the method provided by the invention has the advantages that the cost is lower, secondary pollution is not generated while the soil environment is improved, the hydrothermal carbon-based fertilizer provided by the invention has improvement and promotion effects in both physical and chemical aspects of soil, and finally resource utilization of the straws and the livestock and poultry manure is realized; the environmental pollution in the fertilizer preparation process is reduced, and the quality efficiency of the prepared fertilizer is improved.

Description

Technical Field

[0001] The present invention relates to a method for resource utilization of solid waste disposal of straw and livestock manure and a hydrothermal carbon-based fertilizer, belonging to the technical field of comprehensive utilization of agricultural waste resources. Background Art

[0002] China is a large agricultural country with a huge annual demand for chemical fertilizers. At present, the utilization rate of chemical fertilizers in China is only between 38% and 42%. The rest are either left in the soil or leached into water bodies through rainwater or irrigation water, causing water pollution, eutrophication of water bodies, and a large number of plankton such as algae to multiply, destroying the ecological balance. At the same time, the extensive use of chemical fertilizers will also affect the soil structure, resulting in problems such as shallower plough layers, soil compaction, and reduced soil microbial activity. The negative impacts of soil degradation and soil pollution on agricultural production and food safety are hot issues that China has long been concerned about.

[0003] At the same time, with the development of large-scale industrialization of agriculture in China, the continuous transformation of livestock and poultry breeding models, and the increasing separation of planting and breeding industries, a large amount of agricultural waste has been generated in agricultural production practices, mainly including livestock and poultry manure and a large amount of crop straw, etc., which has affected the ecological environment of nearby areas and also caused a waste of a large amount of collectible biomass resources. Making organic fertilizers or hydrothermal carbon-based fertilizers is a good way to achieve the efficient resource utilization of livestock and poultry manure and crop straw. Applying the organic fertilizers or hydrothermal carbon-based fertilizers made from livestock and poultry manure and crop straw into the soil can improve soil pollution, soil compaction, and soil degradation problems.

[0004] Organic fertilizers or hydrothermal carbon-based fertilizers have many benefits for the soil. Organic fertilizers or hydrothermal carbon-based fertilizers contain a large amount of organic matter, which can increase the organic matter content in the soil and improve soil fertility. The porosity of hydrothermal carbon-based fertilizers can improve the physical structure of the soil, increase soil porosity, improve soil ventilation and water permeability, reduce soil compaction, increase soil microbial activity, reduce water evaporation, and improve water use efficiency; it can also adsorb and fix nutrients in the soil, reduce nutrient loss, improve nutrient utilization rate, reduce environmental pollution, and reduce the risk of water body eutrophication. It can not only improve soil fertility and crop yield, but also improve the soil environment, reduce environmental pollution, and promote the sustainable development of agriculture.

[0005] At present, there are problems such as low efficiency, long time, and easy secondary pollution in the large-scale preparation of hydrothermal carbon-based fertilizers by microbial composting.

[0006] Chinese Patent (Publication No. CN 118894747A) discloses a preparation method and application of hydrothermal humic carbon with the function of improving soil. By mixing biomass raw materials with a catalyst and through hydrothermal catalytic reaction, nutrients and humic acid substances are enriched in the biomass during the reaction process, enhancing the soil improvement function of the product. Although this method overcomes the problem of low efficiency in microbial composting fermentation in the prior art, the use of catalysts such as sodium hydroxide, potassium hydroxide, and ferric chloride will increase the salt content in the soil. Although the soil environment is improved, the soil environment is secondarily polluted due to excessive salt content, and the addition of the catalyst also increases the production cost. Summary of the Invention

[0007] Aiming at the problems existing in the above-mentioned prior art, one of the purposes of the present invention is to provide a method for resource utilization of straw and livestock manure solid waste. The present invention uses the hydrothermal method to prepare hydrothermal carbon-based fertilizer from straw and livestock manure. During the hydrothermal reaction process, no other substances need to be added. Compared with the traditional microbial composting process, this method shortens the time for preparing fertilizer and avoids the problem of odor treatment and emission during the composting process. At the same time, compared with the hydrothermal method in the prior art, this method has lower cost, does not cause secondary pollution while improving the soil environment, and the hydrothermal carbon-based fertilizer provided by the present invention has both physical and chemical improvement effects on the soil, ultimately realizing the resource utilization of straw and livestock manure, reducing environmental pollution during the fertilizer preparation process, and improving the quality and efficiency of fertilizer preparation. This method can promote the sustainable development of agriculture, making the production of organic fertilizer more efficient, more environmentally friendly, safer, and more suitable for large-scale production of high-value products.

[0008] Another purpose of the present invention is to provide a hydrothermal carbon-based fertilizer. The content of nutrient elements such as P and N in this hydrothermal carbon-based fertilizer is more abundant, and the heavy metal content is lower. According to the industry standards "NY525-2021 Detection Methods for Organic Fertilizers" and "NY / T1978-2022 Detection Methods for Heavy Metals in Fertilizers", the nitrogen, phosphorus, potassium, and heavy metal contents in the sample are measured. After testing, the prepared hydrothermal carbon-based organic fertilizer meets the requirements of the organic fertilizer industry standard.

[0009] To achieve the above purpose, the first aspect of the present invention is to provide a method for resource utilization of straw and livestock manure solid waste, which includes: in the presence of water, subjecting straw and livestock manure to hydrothermal treatment, and then successively performing solid-liquid separation and drying treatment to obtain hydrothermal carbon-based fertilizer;

[0010] The mass ratio of the straw on a dry basis to the livestock manure on a dry basis is 1:0.5 - 5;

[0011] The temperature of the hydrothermal reaction is 100 - 180°C, and the pH value of the hydrothermal reaction is < 7.

[0012] The innovative point of the present invention is to hydrothermally react straw with livestock and poultry manure, and no additional substances need to be added during the hydrothermal process. The method of the present invention retains the nutrients such as nitrogen, phosphorus and potassium in straw and livestock and poultry manure to the maximum extent. Further, the inventors found that when the conditions of the hydrothermal reaction are controlled to be acidic, the dissolution of heavy metal elements in the liquid phase can be increased, the leaching of heavy metals in livestock and poultry manure can be accelerated during the hydrothermal reaction, and the migration of heavy metals in the liquid phase can be promoted. The hydrothermal temperature provided by the present invention is relatively low, which can reduce the mineral phase deposition of heavy metals, and due to the heating effect, arsenic and mercury in the raw materials will further volatilize. If the temperature is higher than 200°C, the heavy metals will generate a stable mineral phase and deposit in the hydrothermal carbon product. Too high a temperature will also lead to a decrease in the yield of hydrothermal carbon, the shedding of surface functional groups and other problems. If the temperature of the hydrothermal reaction is too low, the hydrothermal carbonization will not be thorough. The hydrothermal reaction temperature provided by the present invention is suitable, and the temperature is low, the energy consumption is lower, the production cost is low, the safety is high, and it is suitable for large-scale production.

[0013] Furthermore, the present invention can obtain an organic fertilizer with excellent performance by controlling the dosage relationship between straw and livestock and poultry manure and by the interaction of various technical features. The present invention also controls the organic matter content in the hydrothermal charcoal by adjusting the ratio of whole straw to livestock and poultry manure, reduces the proportion of the complex formed by heavy metals and organic matter (heavy metal-humic acid combination) in the hydrothermal charcoal, and further reduces the content of heavy metals. If the straw ratio is too high, the nutrient element content of the hydrothermal charcoal will be low, which is not suitable for making organic fertilizer and can only be prepared as a matrix; if the livestock and poultry manure ratio is too high, the morphological structure of the hydrothermal charcoal will change, and it will form a hard block during the drying process, which is not conducive to soil improvement and will cause problems such as soil compaction. The excessive livestock and poultry manure ratio will also significantly reduce the yield of the hydrothermal charcoal. At the same time, the organic matter content in the hydrothermal charcoal is low, which does not meet the relevant standards of organic fertilizer, and is not conducive to improving the soil environment and increasing the water retention performance of the soil.

[0014] The hydrothermal charcoal prepared under the conditions provided by the present invention has a high organic matter content and an appropriate carbonization degree, and is more suitable for soil improvement, replenishing organic matter and nutrient elements in the soil, and increasing the activity of microorganisms in the soil.

[0015] As a preferred solution, the pH value of the hydrothermal reaction is A, and 4≤A<7.

[0016] As a preferred solution, the hydrothermal treatment time is 2 to 12 hours.

[0017] As a preferred solution, the mass ratio of the straw on a dry basis to the livestock and poultry manure on a dry basis is 1:0.5-4.

[0018] As a preferred embodiment, the mass ratio of the total amount of straw on a dry basis and livestock manure on a dry basis to the amount of water is 1:4 to 10. More preferably, it is 1:5 to 9. If the amount of water added is too small, it will affect the autogenous pressure in the hydrothermal reaction process to be too small, resulting in incomplete hydrothermal carbonization. If the amount of water added is too large, it will lead to problems such as loss of nutrient elements and increased hydrothermal treatment costs.

[0019] As a preferred embodiment, the conditions of the drying treatment are controlled such that the water content of the hydrothermal carbon-based fertilizer is 20 to 40 wt%.

[0020] As a preferred embodiment, the straw is selected from at least one of rice straw, tobacco straw, cotton straw, and corn straw.

[0021] As a preferred embodiment, the livestock manure is selected from at least one of chicken manure, pig manure, cow manure, and sheep manure.

[0022] As a more preferred embodiment, the livestock manure is chicken manure and / or pig manure.

[0023] As a preferred embodiment, the method further includes: first drying, pulverizing, and sieving the straw and livestock manure at 70 to 90 °C in sequence, and then performing the hydrothermal reaction. Through drying, most of the volatile heavy metals such as mercury (Hg) and arsenic (As) in the raw materials can be removed.

[0024] As a preferred embodiment, the sieving treatment makes the particle size of the sieved material ≤ 500 μm.

[0025] As a preferred embodiment, the temperature of the hydrothermal reaction is 120 to 160 °C. The inventors found that in this preferred case, a hydrothermal carbon-based fertilizer with rich nutrients and low heavy metal content can be obtained, and under this condition, the energy consumption is lower.

[0026] The present invention also provides a hydrothermal carbon-based fertilizer. The hydrothermal carbon-based fertilizer provided by the present invention has both the improvement effects on the physical and chemical aspects of the soil, and finally realizes the resource utilization of straw and livestock manure. At the same time, the content of nutrient elements such as P and N in the hydrothermal carbon-based fertilizer is more abundant, and the heavy metal content is lower, meeting the national standard requirements for organic fertilizers.

[0027] Compared with the prior art, the present invention has at least the following advantages:

[0028] (1) Agricultural wastes such as straw and livestock and poultry manure are converted into hydrothermal carbon by hydrothermal carbonization. The existing technology mainly converts them into biochar by pyrolysis. However, compared with pyrolysis, the hydrothermal carbonization provided by the present invention has the following advantages: (1) Hydrothermal treatment increases the pressure of the reaction system, accelerates the reaction rate, and makes the carbonization proceed at a lower temperature, with lower energy consumption. At the same time, when the hydrothermal reaction conditions are controlled to be acidic, the dissolution of heavy metal elements in the liquid phase can be increased, and the leaching of heavy metals in livestock and poultry manure can be accelerated during the hydrothermal reaction, promoting the migration of heavy metals in the liquid phase, and reducing the pollution of heavy metals in the soil. (2) When straw and livestock and poultry manure are hydrothermally treated, the organic matter therein will undergo a hydrolysis reaction to form a certain pore structure, thereby increasing the porosity of the hydrothermal carbon. At the same time, the synergistic effect of straw and livestock and poultry manure makes the hydrothermal carbon have more abundant functional groups (such as hydroxyl, carboxyl, aldehyde, etc.). These functional groups can chelate with the nutrients in livestock and poultry manure, reducing the loss of nutrients during the hydrothermal treatment process. (3) Hydrothermal charcoal also retains a large part of organic matter, which can improve soil fertility, improve soil physical structure, prevent soil compaction, and increase the activity of microorganisms in the soil. However, during the pyrolysis carbonization process, the organic matter in the straw and livestock and poultry manure undergoes a thorough decomposition reaction, and the organic matter in the straw is completely carbonized into carbon material, and a large amount of nutrient elements are gasified and lost, which is not conducive to direct use as charcoal-based fertilizer.

[0029] (2) The traditional method of preparing organic fertilizer is to use microbial composting to ferment straw and livestock and poultry manure to make them decompose into organic fertilizer. The method of microbial composting has a long history and has been improved through modernization to cultivate high-temperature fiber-decomposing bacteria. After use, it can promote the temperature of the compost and quickly decompose the cellulose components. The fermentation time can be reduced to 3 weeks for complete decomposition. However, for modern agricultural production, the fermentation time of microbial composting is still long, the area occupied is large, and the microbial composting process is prone to secondary pollution such as wastewater and odor. At the same time, these problems are inevitable for the microbial composting process. Therefore, in the manufacture of organic fertilizer, some new means are needed. The method can avoid the above problems. Compared with the traditional microbial composting, the preparation method provided by the present invention has the following advantages: (1) The time required is short. Compared with the one month required for the traditional microbial composting, the hydrothermal treatment only takes 2 to 12 hours, which greatly shortens the processing time; (2) There is no discharge of wastewater and odor. The hydrothermal treatment process will not produce leakage liquid and odor, etc., which reduces the pollution to the environment; (3) The organic fertilizer preparation process is more controllable. The hydrothermal treatment process can monitor the real-time temperature of the organic fertilizer and make timely adjustments. However, in the microbial composting process, it is impossible to accurately judge the microbial reproduction situation and deal with related problems in a timely manner.

[0030] (3) The hydrothermal carbon-based fertilizer provided by the present invention has both the improvement effects on the physical and chemical aspects of the soil, finally realizing the resource utilization of straw and livestock manure, reducing the environmental pollution in the fertilizer preparation process, and improving the quality and efficiency of the prepared fertilizer. This method can promote the sustainable development of agriculture, making the production of organic fertilizers more efficient, more environmentally friendly, safer, and more suitable for large-scale production of high-value products. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flow chart for preparing the hydrothermal carbon-based fertilizer in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0033] The following further illustrates the present invention in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments. All other embodiments obtained by those skilled in the art without creative efforts still fall within the protection scope of the present invention.

[0034] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0035] Raw Material Treatment

[0036] The straw and livestock manure are respectively dried at 80°C for 6 h to remove moisture, obtaining dried straw and dried livestock manure. Then, both are respectively ground into powders, passed through a 40-mesh sieve, and the undersize is taken to remove larger particles and other mechanical impurities, obtaining straw powder and livestock manure powder respectively.

[0037] In the following examples, the total usage amounts of the straw powder and the livestock manure powder are both 5 g.

[0038] Example 1

[0039] Mix the rice straw powder and dry chicken manure powder evenly at a mass ratio of 3:2, then add water (the mass ratio of the total amount of rice straw powder and dry chicken manure powder to the amount of water is 1:6), put it into a hydrothermal reaction kettle, the pH value of the hydrothermal reaction is 5.35, control the reaction temperature at 140 °C and maintain it for 8 h. After the reaction is completed, cool it to room temperature, then open the hydrothermal reaction kettle, and carry out solid-liquid separation by centrifugation without water washing. Finally, dry the hydrothermal carbon (temperature is 60 °C, time is 120 min), and control the water content in the hydrothermal carbon to be 25 wt%.

[0040] Example 2

[0041] This example is carried out by referring to a method similar to that of Example 1. The difference is that the mass ratio of the amount of rice straw powder to dry chicken manure powder is adjusted to 1:4, and the pH value of the hydrothermal reaction is 5.95.

[0042] Example 3

[0043] This example is carried out by referring to a method similar to that of Example 1. The difference is that the mass ratio of the amount of rice straw powder to dry chicken manure powder is adjusted to 2:3, and the temperature of the hydrothermal reaction is adjusted to 140 °C, the time is 12 h, and the pH value of the hydrothermal reaction is 5.47.

[0044] Example 4

[0045] This example is carried out by referring to a method similar to that of Example 1. The difference is that the mass ratio of the amount of rice straw powder to dry chicken manure powder is adjusted to 1:4, and the temperature of the hydrothermal reaction is adjusted to 140 °C, the time is 12 h, and the pH value of the hydrothermal reaction is 6.05.

[0046] Example 5

[0047] This example is carried out by referring to a method similar to that of Example 1. The difference is that the mass ratio of the amount of rice straw powder to dry chicken manure powder is adjusted to 2:3, and the temperature of the hydrothermal reaction is adjusted to 160 °C, the time is 8 h, and the pH value of the hydrothermal reaction is 5.26.

[0048] Example 6

[0049] This example is carried out by referring to a method similar to that of Example 1. The difference is that the mass ratio of the amount of rice straw powder to dry chicken manure powder is adjusted to 1:4, and the temperature of the hydrothermal reaction is adjusted to 160 °C, the time is 8 h, and the pH value of the hydrothermal reaction is 5.88.

[0050] Example 7

[0051] This example was carried out by referring to a method similar to that of Example 1. The difference is that the rice straw powder was replaced with an equal mass of corn straw powder, the dried chicken manure powder was replaced with an equal mass of pig manure powder, and the pH value of the hydrothermal reaction was 5.42.

[0052] Comparative Example 1

[0053] This comparative example was carried out by referring to a method similar to that of Example 1. The difference is that 5 g of rice straw powder was added in this comparative example, and no dried chicken manure powder was added.

[0054] Comparative Example 2

[0055] This comparative example was carried out by referring to a method similar to that of Example 1. The difference is that 5 g of dried chicken manure powder was added in this comparative example, and no rice straw powder was added.

[0056] Comparative Example 3

[0057] This comparative example was carried out by referring to a method similar to that of Example 5. The difference is that 5 g of rice straw powder was added in this comparative example, and no dried chicken manure powder was added.

[0058] Comparative Example 4

[0059] This comparative example was carried out by referring to a method similar to that of Example 5. The difference is that 5 g of dried chicken manure powder was added in this comparative example, and no rice straw powder was added.

[0060] Test Example

[0061] The hydrothermal carbon products prepared in the above examples were detected. The detection standards were the industry standards "NY525-2021 Detection Methods for Organic Fertilizers" and "NY / T1978-2022 Detection Methods for Heavy Metals in Fertilizers", and the detection results are shown in Tables 1 and 2.

[0062] At the same time, the present invention also detected the heavy metal contents in rice straw powder, dried chicken manure powder, corn straw, and dried pig manure respectively. The detection standard was "NY / T1978-2022 Detection Methods for Heavy Metals in Fertilizers", and the specific results are shown in Table 2.

[0063] Table 1

[0064]

[0065] Table 2

[0066]

[0067]

[0068] Note: "--" indicates that the content is less than 0.02 mg / kg.

[0069] As can be seen from the above effect data, the contents of various heavy metal elements in the hydrothermal carbon-based fertilizer product prepared by the present invention are all less than the national standard requirements, and the nutrient content of the organic fertilizer provided by the present invention is very high. If only pure straw is added (Comparative Example 1 and Comparative Example 3), the nutrient element content of the hydrothermal carbon is relatively low and it is not suitable for manufacturing organic fertilizer, and it can only be prepared into a substrate; if only pure livestock and poultry manure is added (Comparative Example 2 and Comparative Example 4), although the nutrient element content of the hydrothermal carbon is very high, the morphological structure of the hydrothermal carbon has changed. It is found in the drying process that the moisture of the hydrothermal carbon in Comparative Example 2 and Comparative Example 4 is easy to evaporate, and due to the high mineral content, the pure manure hydrothermal carbon aggregates into hard lumps, which is not conducive to improving the soil environment and increasing the soil water retention performance, and will cause problems such as soil compaction. Adding only livestock and poultry manure will also significantly reduce the yield of hydrothermal carbon, and at the same time, the organic matter content in the hydrothermal carbon is relatively low. In contrast, co-hydrothermal treatment of straw and chicken manure can improve the morphology of the hydrothermal carbon, not only with a high organic matter content, but also can improve the water retention performance of the hydrothermal carbon.

[0070] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A resource utilization method for the disposal of solid waste from straw and livestock manure, characterized in that: The method includes: subjecting straw and livestock manure to hydrothermal treatment in the presence of water, followed by solid-liquid separation and drying treatment in sequence to obtain the hydrothermal carbon-based fertilizer; The mass ratio of the straw on a dry basis to the livestock manure on a dry basis is 1:0.5 - 5; The temperature of the hydrothermal reaction is 100 - 180 °C, and the pH value of the hydrothermal reaction is < 7.

2. The resource utilization method for the disposal of straw and livestock and poultry manure solid waste according to claim 1, characterized in that: The time of the hydrothermal treatment is 2 - 12 h.

3. A resource utilization method for the disposal of straw and livestock manure solid waste according to claim 1 or 2, characterized in that: The mass ratio of the total amount of the straw on a dry basis and the livestock manure on a dry basis to the amount of water is 1:4 - 10.

4. A resource utilization method for the disposal of straw and livestock and poultry manure solid waste according to claim 1 or 2, characterized in that: Control the conditions of the drying treatment so that the water content of the hydrothermal carbon-based fertilizer is 20 - 40 wt%.

5. A resource utilization method for the disposal of straw and livestock and poultry manure solid waste according to claim 1 or 2, characterized in that: The straw is selected from at least one of rice straw, tobacco straw, cotton straw, and corn straw.

6. A resource utilization method for the disposal of straw and livestock manure solid waste according to claim 1 or 2, characterized in that: The livestock manure is selected from at least one of chicken manure, pig manure, cow manure, and sheep manure.

7. A resource utilization method for the disposal of straw and livestock and poultry manure solid waste according to claim 6, characterized in that: The livestock manure is chicken manure and / or pig manure.

8. A resource utilization method for the disposal of straw and livestock and poultry manure solid waste according to claim 1 or 2, characterized in that: The method further includes: First, drying, pulverizing, and sieving the straw and livestock manure at 70 - 90 °C in sequence, and then performing the hydrothermal reaction.

9. The resource utilization method for the disposal of straw and livestock and poultry manure solid waste according to claim 8, wherein: The sieving treatment makes the particle size of the sieved material ≤ 500 μm.

10. The hydrothermal carbon-based fertilizer prepared by the resource utilization method for disposing of the solid waste of straw and livestock manure according to any one of claims 1 - 9.

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