Garden waste carbon sink storage method for improving planting soil

Abstract

The invention discloses a garden waste carbon sequestration and storage method for improving planting soil, which comprises the following steps: collecting, classifying and crushing garden wastes, classifying different collected objects, carrying out incomplete carbonization treatment, merging roots, stems and leaves of herbaceous plants and leaves of woody plants into a first type of garden wastes, and ensuring that the carbonization rate is 75-83%; roots, branches and stems of woody plants are combined into second-class garden waste, and the carbonization rate is 55-65%; and mixing carbonized products according to a weight ratio of 1: (2-3) to obtain the carbon sequestration plant material for improving the planting soil. The carbon sequestration planting material has a good carbon sequestration effect, so that the carbon sequestration planting material is not easily and completely degraded in nature, meanwhile, due to the fact that the carbon sequestration planting material is not completely carbonized, part of lignin can be retained and can be slowly decomposed, the self structure is not easily collapsed, high porosity is maintained, long-acting water retention and fertilizer retention can be achieved, meanwhile, attachment growth of microorganisms can be facilitated, and the vitality of planting soil is kept.

Description

Technical Field

[0001] The present invention relates to a method for treating garden waste, and in particular to a method for carbon sequestration of garden waste and application of the method in soil improvement. Background Art

[0002] The extensive use of oil and coal has led to a gradual increase in CO2 levels in nature. CO2 is a greenhouse gas, and changes in its atmospheric content can negatively impact the Earth's environment. Consequently, the concept of carbon sinks has been proposed in recent years. Carbon sinks generally refer to the processes, activities, and mechanisms that remove carbon dioxide from the air. Carbon sinks are natural carbon storage vehicles. They primarily utilize measures such as afforestation, forest management, and vegetation restoration to absorb atmospheric carbon dioxide through plant photosynthesis and store it in vegetation and soil, thereby reducing the concentration of greenhouse gases in the atmosphere.

[0003] Existing garden waste primarily consists of naturally fallen and artificially trimmed leaves and branches. These natural substances, primarily cellulose and lignin, are naturally decomposed by various bacteria in nature, converting them into CO2 and H2O, which enter the natural cycle, thus forming a dynamic balance. Reducing or delaying the return of biogenic carbon to the natural environment can theoretically keep atmospheric greenhouse gas concentrations relatively low. Carbonized plants can remain in nature for decades to thousands of years, depending on the degree of carbonization.

[0004] Existing soil, especially clay, has low porosity and is easily compacted, which is not conducive to plant rooting and bacterial growth and needs to be improved.

[0005] Prior art reports have reported using charcoal to improve soil. However, this charcoal, primarily formed from the incomplete combustion of tree trunks and branches, has large pores and a lower porosity than carbonized leaves. Its small total pore volume, smaller specific end point, and fewer surface functional groups weaken the material's adsorption capacity, impairing its ability to retain water, fertilizer, and oxygen to microorganisms, making it a poor soil improvement solution. Carbonized leaves alone have a higher porosity, but their carbon skeleton is weak. When mixed with soil for improvement, the effects of water, oxygen, and microorganisms can easily lead to structural breakdown and pore collapse, rendering the improved soil ineffective.

[0006] How to effectively fix carbon in garden waste and apply it to soil improvement so that the soil can remain suitable for plant and bacterial growth for a long time is a technical problem that needs to be solved. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for carbon sequestration of garden waste for improving planting soil, so that it can achieve long-term carbon fixation. At the same time, it can also improve the soil, make the planting soil breathable, water-retaining, and fertilizer-retaining, and provide a good living environment for the growth of plants and soil microorganisms.

[0008] The object of the present invention is achieved as follows: a method for carbon sequestration of garden waste for improving planting soil, comprising the following steps:

[0009] S1, collecting garden waste, performing rough separation and drying, during rough separation, combining the roots, stems, and leaves of herbaceous plants with the leaves of woody plants into the first category, and combining the roots, branches, and stems of woody plants into the second category; drying to make the moisture content of the material less than 15%;

[0010] S2, chopping the first type of garden waste after the treatment in step S1 into pieces so that its average planar size is 6-10 mm, stirring evenly, then sampling and weighing it and performing pyrolysis in an anaerobic environment, first rapidly heating it to 200°C during pyrolysis, keeping it warm for 15-20 minutes to dehydrate it, then slowly heating it to 380-400°C at a heating rate of 10-15°C / min, keeping the pyrolysis device warm, while releasing the gas produced by the cracking, draining the liquid oil in the product, and continuously weighing the remaining solid matter. When the solid product after pyrolysis has a constant weight for 30 minutes, stop the pyrolysis and record the holding time corresponding to the weight loss of the solid product; compare the weight of the material before and after carbonization, divide the weight loss into 100 equal parts, and consider each part reduced as a 1% increase in the carbonization rate. The first target time is determined to be 75-83% carbonization rate;

[0011] S3. Pyrolyzing the remaining first type of garden waste from step S2 in an anaerobic environment, first rapidly heating to 200° C. and holding for 15-20 minutes to dehydrate the waste, then slowly heating to 380-400° C. at a heating rate of 10-15° C. / min, and then holding the pyrolysis device until the carbonization rate of the remaining solids reaches 75-83% after a first target time.

[0012] S4, after step S1, the second type of garden waste is first crushed into blocks with a maximum three-dimensional size of less than 3 cm; then a sample is weighed and pyrolyzed in an oxygen-free environment. During pyrolysis, the temperature is first rapidly raised to 200°C and kept at this temperature for 15-20 minutes to dehydrate it. Then, the temperature is slowly raised to 450-480°C at a heating rate of 10-15°C / min. The pyrolysis device is kept warm while releasing the gas produced by the cracking, draining the liquid oil in the product, and continuously weighing the remaining solid matter. When the solid product after pyrolysis maintains a constant weight for 30 minutes, the pyrolysis is stopped; the weight of the material before and after carbonization is compared, and the weight loss portion is divided into 100 equal parts. For each weight loss of 1 part, the carbonization rate is considered to increase by 1%. The second target time is determined to be 55-65% carbonization rate.

[0013] S5. Pyrolyzing the remaining second type of garden waste from step S4 in an oxygen-free environment, first rapidly heating to 200° C. and holding for 15-20 minutes to dehydrate the waste, then slowly heating to 450-480° C. at a heating rate of 10-15° C. / min, and holding the pyrolysis device for a second target time, so that the carbonization rate of the remaining solids reaches 55-65%.

[0014] S6. Take the solids obtained in steps S3 and S5, mix them in a weight ratio of 1:(2-3), and obtain a carbon sink planting material for improving planting soil.

[0015] Furthermore, in steps S2 and S4, if the weight loss within 30 minutes is less than 5% of the sample weight, it is determined to be constant weight.

[0016] Furthermore, when improving the planting soil, the volume mixing ratio of the carbon sink planting material and the planting soil is (3-8):1.

[0017] Pyrolysis of plant biomass is a thermochemical process. During pyrolysis, hemicellulose decomposes first at lower temperatures, cellulose decomposes at moderate temperatures, and lignin decomposes last at higher temperatures. Leaves and trunks differ significantly in their biological structure, chemical composition, and physical properties. Leaves have a lamina structure dominated by parenchyma, while trunks have a dense, woody structure dominated by xylem. This leads to significant differences in their carbonization processes, rates, and characteristic indicators. Pyrolysis of leaves at relatively low temperatures, while that of trunks at relatively high temperatures, is intended to achieve better carbon sequestration. Excessively high pyrolysis temperatures can reduce the yield of biochar, but increasing the pyrolysis temperature can increase the biochar's overall structure, thereby increasing its specific surface area. Lower pyrolysis temperatures impart hydrophilic properties to the biochar. The present invention utilizes different pyrolysis temperatures for the first and second types of garden waste to ensure efficient carbon sequestration, reduce the volatilization of oil and gas, and retain as much of the converted carbon as possible while maintaining a constant carbonization rate, thereby ensuring a carbon sequestration effect. Compared with the existing technology, the present invention has the following beneficial effects: the roots, stems, and leaves of herbaceous plants are combined with the leaves of woody plants to form the first type of garden waste, with a carbonization rate of 75-83%; the roots, branches, and stems of woody plants are combined to form the second type of garden waste, with a carbonization rate of 55-65%; the carbonized products are mixed in a weight ratio of 1:(2-3) to obtain a carbon sink planting material for improving planting soil. The carbon sink planting material has a good carbon sequestration effect, making it difficult to completely degrade in nature. At the same time, because it is not completely carbonized, some lignin is retained, which can be slowly decomposed, and its own structure is not easy to collapse, maintaining a high porosity, can effectively retain water and fertilizer for a long time, and at the same time facilitates the attachment and growth of microorganisms, thereby maintaining the vitality of the planting soil. DETAILED DESCRIPTION

[0018] A method for carbon sequestration of garden waste for improving planting soil is carried out according to the following steps:

[0019] S1, collect garden waste, perform rough separation and drying, during rough separation, combine the roots, stems, leaves of herbaceous plants and the leaves of woody plants into the first category, and combine the roots, branches, and stems of woody plants into the second category; drying makes the moisture content in the material less than 15%; herbaceous plants can also be discarded, and only leaves are collected as the first category of garden waste, and trunks as the second category of garden waste; branches with a diameter of more than 0.8 cm are classified as the second category of garden waste; branches with a diameter of less than 0.8 cm are classified as the first category of garden waste.

[0020] S2, chopping the first type of garden waste after the treatment in step S1 into pieces so that its average planar size is 6-10 mm, stirring evenly, then sampling and weighing it and performing pyrolysis in an oxygen-free environment, the reactor used for pyrolysis is a fluidized bed, fixed bed or tubular furnace, and during pyrolysis, the temperature is first rapidly raised to 200°C, kept warm for 15-20 minutes to dehydrate it, and then slowly heated to 380-400°C at a heating rate of 10-15°C / min, and the pyrolysis device is kept warm, while releasing the gas produced by the cracking, draining out the liquid oil in the product, and continuously weighing the remaining solid matter. When the solid product after pyrolysis has a constant weight for 30 minutes, the pyrolysis is stopped, and the holding time corresponding to the weight loss of the solid product is recorded; the weight of the material before and after carbonization is compared, and the weight loss portion is divided into 100 equal parts. For each reduction of 1 part, the carbonization rate is considered to increase by 1%, and the first target time is determined to be 75-83%;

[0021] S3. Pyrolyzing the remaining first type of garden waste from step S2 in an anaerobic environment, first rapidly heating to 200° C. and holding for 15-20 minutes to dehydrate the waste, then slowly heating to 380-400° C. at a heating rate of 10-15° C. / min, and then holding the pyrolysis device until the carbonization rate of the remaining solids reaches 75-83% after a first target time.

[0022] S4, after step S1, the second type of garden waste is first crushed into blocks with a maximum three-dimensional size of less than 3 cm; then a sample is taken, weighed, and pyrolyzed in an oxygen-free environment. The reactor used for pyrolysis is a fluidized bed, fixed bed, or tubular furnace. During pyrolysis, the temperature is first rapidly raised to 200°C and kept warm for 15-20 minutes to dehydrate it. Then, the temperature is slowly raised to 450-480°C at a heating rate of 10-15°C / min. The pyrolysis device is kept warm while releasing the gas produced by cracking, draining the liquid oil in the product, and continuously weighing the remaining solid matter. When the solid product after pyrolysis maintains a constant weight for 30 minutes, the pyrolysis is stopped; the weight of the material before and after carbonization is compared, and the weight loss portion is divided into 100 equal parts. For each weight loss of 1 part, the carbonization rate is considered to increase by 1%. The second target time is determined to be 55-65% carbonization rate;

[0023] S5. Pyrolyzing the remaining second type of garden waste from step S4 in an oxygen-free environment, first rapidly heating to 200° C. and holding for 15-20 minutes to dehydrate the waste, then slowly heating to 450-480° C. at a heating rate of 10-15° C. / min, and holding the pyrolysis device for a second target time, so that the carbonization rate of the remaining solids reaches 55-65%.

[0024] S6. Take the solids obtained in steps S3 and S5, mix them in a weight ratio of 1:(2-3), and obtain a carbon sink planting material for improving planting soil.

[0025] The measurement of porosity and carbonization rate in the present invention is a key factor in realizing the present invention, and the measurement method is as follows:

[0026] Porosity measurement method: Porosity refers to the percentage of the internal pore volume of a material to the total volume. To measure porosity, it is necessary to determine the total volume of the material and the internal pore volume. Specifically, the air in the carbonized leaves and trunks is removed by vacuuming. Then, under vacuum, the carbonized leaves or trunks are immersed in water. The vacuum is then released. The material is soaked or boiled for about 1-3 hours to allow water to fully penetrate the pores of the material and become saturated with water. The weight change before and after water absorption is used to determine the amount of water absorbed by the material, and the pore volume can be calculated. The saturated material is immersed in water as a whole, and the change in water volume can be measured to determine the total volume of the material. This method can relatively accurately measure the porosity of carbonized leaves or trunks.

[0027] Method for measuring carbonization rate: First, carbonize the sample material until it reaches a constant weight. At this point, the carbonization rate of the material is considered 100%. Compare the weight of the material before and after carbonization, and divide the weight loss into 100 equal parts. Each weight loss is considered a 1% increase in the carbonization rate. For example, if a 100-gram tree trunk reaches a constant weight of 45 grams after carbonization (in the present invention, a weight loss of less than 5% of the sample weight within 30 minutes is defined as constant weight), then its weight loss is 55 grams. Divide 55 grams into 100 equal parts, each weighing 0.55 grams. When the weight of 100 grams of carbonized material is 78 grams, its carbonization rate = (78-45) / 0.55*100% = 60%. This method can avoid errors caused by different sample materials and achieve relatively accurate measurement results.

[0028] The following is a comparison of the complete pyrolysis data of leaves of common tree species under the conditions of step S2 above, as shown in Table 1:

[0029]

[0030] The comparison of complete pyrolysis data of common tree species trunks under the conditions of step S5 above is shown in Table 2 below:

[0031]

[0032] When carbonizing the first type of garden waste, due to its loose original structure, numerous thin-walled cells, and large interstitial spaces, it tends to retain these interstitial spaces and generate a large number of uniformly fine pores. In contrast, when carbonizing the second type of garden waste, its original structure is dense, with primarily thick-walled cells and few interstitial spaces. After carbonization, it primarily retains its original macropores, such as vessels, with few newly generated micropores. When the carbonization rates for the first type of garden waste are 75-83% and the second type of garden waste are 55-65%, the dominant pore type, pore distribution uniformity, and pore connectivity are essentially the same as those for fully carbonized waste, except for the porosity.

[0033] The comparative pore indexes of the first type of garden waste and the second type of garden waste after carbonization are shown in Table 3 below:

[0034]

[0035] The degradation of incompletely carbonized first-category garden waste (carbonization rate of 75-83%) and incompletely carbonized second-category garden waste (carbonization rate of 55-65%) was compared with that of completely carbonized first-category garden waste and completely carbonized second-category garden waste under composting conditions. The comparative data are shown in Table 4 below:

[0036]

[0037] Table 4 above shows that, compared with the completely carbonized first and second types of garden waste, the incompletely carbonized first and second types of garden waste have different effects on the growth of microorganisms. The roots of plants need to rely on the help of microorganisms to absorb nutrients. The above table shows that the incompletely carbonized first and second types of garden waste are more conducive to supporting the growth of soil microorganisms and have better effects in soil improvement.

[0038] In March 2022, fallen leaves and pruned tree trunks were collected from the campus. The primary tree species on campus were camphor, sycamore, and poplar. The sample weight ratio of the three species was 4:3:2, and the leaf:trunk weight ratio was 1:2.5. The mixed leaves were considered the first type of garden waste, and the mixed trunks were considered the second type of garden waste, for carbonization treatment.

[0039] The comparative data of the degradation of incompletely carbonized first-class garden waste (carbonization rate of 75-83%) and incompletely carbonized second-class garden waste (carbonization rate of 55-65%) under natural conditions are as follows:

[0040] Table 5: Initial stage (0-6 months)

[0041]

[0042]

[0043] Table 6: Mid-term stage (6-18 months)

[0044]

[0045] Table 7: Late stage (over 18 months)

[0046]

[0047] Tables 5-7 above show that during the degradation process, the porosity of incompletely carbonized Type 1 and Type 2 garden wastes changes differently. When mixed at a weight ratio of 1:2.5, the two maintain a sufficient number of pores for a long time, with a relatively stable number of mesopores and macropores. This ensures that the planting soil is breathable, water-retaining, and fertilizing, and provides a favorable living environment for the growth of plants and soil microorganisms. Under natural growth conditions, the weight ratio of leaf to trunk growth is approximately 1:(4-10). However, since the amount of branches pruned annually is relatively small, a carbonized leaf to trunk weight ratio of 1:(2-3) is more consistent with the actual ratio of fallen leaves to pruning volume.

[0048] When the first type of incompletely carbonized garden waste is degraded: in the initial rapid decomposition stage (0-6 months), it is mainly the decomposition of residual organic matter: the incompletely carbonized cellulose and hemicellulose are rapidly decomposed by microorganisms (such as fungi and bacteria), releasing CO2 and nutrients. The organic carbon loss rate of the first type of partially carbonized garden waste can reach 40%-60%. Pore structure changes: the micropores and mesopores formed by carbonization provide attachment sites for microorganisms, accelerating decomposition. In the later slow decomposition stage (more than 6 months), it is mainly lignin-dominated decomposition: the residual lignin and carbonized carbon skeleton decompose slowly, taking several years or even longer. The aromatic structures formed during the carbonization process (such as graphitized carbon) enhance the resistance to decomposition, resulting in long-term carbon storage.

[0049] Table 8 is a comparison of the degradation data of the first type of garden waste at different carbonization rates:

[0050]

[0051] In Table 8, the carbonization rate of the first type of garden waste is preferably 75-83%, so that it can still maintain a large porosity within 0-6 months. The main reason is that the newly formed pores continuously replenish the blockage of the pores, so that the porosity is maintained at a high level for a long time; the first type of garden waste with a low carbonization rate degrades too fast, and degrades rapidly after 6 months, and the porosity also decreases rapidly. The porosity of the first type of garden waste with an excessively high carbonization rate is basically in a state of continuous decrease. Within 6 months, the first type of garden waste with a carbonization rate of 75-83% is preferably used as a planting material for soil improvement.

[0052] Table 9 is a comparison of the degradation data of the second type of garden waste at different carbonization rates:

[0053]

[0054] Table 9 shows that the carbonization rate of the second type of garden waste is preferably 55-65%, so that its porosity remains basically stable within 18 months. When the carbonization rate is 40%, its porosity rises to a high level after 6 months and then drops rapidly, indicating that the degradation rate is too fast; when the carbonization rate is 85-100%, its porosity continues to decrease over time, mainly due to the attachment of biofilm filling its pores.

[0055] A combination of first-class garden waste with a carbonization rate of 75-83% and second-class garden waste with a carbonization rate of 55-65% is selected, which can maintain a high porosity within 0-18 months. Among them, from 0 to 6 months, the first-class garden waste is mainly reduced to provide new channels to maintain a high porosity. From 6 to 12 months, the first-class garden waste and the second-class garden waste are degraded together to maintain a high porosity. From 12 to 18 months, the second-class garden waste is degraded to maintain a high porosity.

[0056] When improving the planting soil, the volume mixing ratio of carbon sink planting material and planting soil is (3-8):1. This ratio can keep the soil breathable for a long time. Of course, other planting materials can also be added when improving the soil. The structure of the first and second types of garden waste is not easy to collapse and can maintain a high porosity. While ensuring carbon sequestration, it can also retain water and fertilizer for a long time, and at the same time facilitate the attachment and growth of microorganisms, thereby maintaining the vitality of the planting soil. It can be used to improve garden soil and can be obtained locally.

[0057] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some of the technical features therein according to the disclosed technical content without creative labor, and these substitutions and modifications are all within the protection scope of the present invention.

Claims

1. A method for carbon sequestration of garden waste for improving planting soil, characterized in that The steps include: S1, collecting garden waste, performing rough separation and drying, during which the roots, stems, and leaves of herbaceous plants and the leaves of woody plants are combined into the first category, and the roots, branches, and stems of woody plants are combined into the second category; drying is performed to reduce the moisture content of the materials to less than 15%; S2, chopping the first type of garden waste after the treatment in step S1 into pieces so that its average planar size is 6-10 mm, stirring evenly, then sampling and weighing, and pyrolyzing in an anaerobic environment, first rapidly heating to 200°C during pyrolysis, holding for 15-20 minutes to dehydrate it, then slowly heating to 380-400°C at a heating rate of 10-15°C / min, holding the pyrolysis device, while releasing the gas generated by the cracking, draining the liquid oil in the product, and continuously weighing the remaining solid matter. When the solid product after pyrolysis maintains a constant weight for 30 minutes, stop the pyrolysis, and record the holding time corresponding to the weight loss of the solid product; Compare the weight of the material before and after carbonization, divide the weight loss into 100 equal parts, and each weight loss is considered to be a 1% increase in the carbonization rate. The first target time is determined to be a carbonization rate of 75-83%; S3. Pyrolyzing the remaining first type of garden waste from step S2 in an anaerobic environment. During the pyrolysis, the temperature is first rapidly raised to 200° C., kept at this temperature for 15-20 minutes to dehydrate the waste, and then slowly raised to 380-400° C. at a heating rate of 10-15° C. / min. The pyrolysis device is then kept at this temperature until the carbonization rate of the remaining solids reaches 75-83% after a first target time. S4, after step S1, the second type of garden waste is first crushed into blocks with a maximum three-dimensional size of less than 3 cm; then a sample is weighed and pyrolyzed in an oxygen-free environment. During pyrolysis, the temperature is first rapidly raised to 200°C and kept at this temperature for 15-20 minutes to dehydrate it. Then, the temperature is slowly raised to 450-480°C at a heating rate of 10-15°C / min. The pyrolysis device is kept warm while releasing the gas produced by the cracking, draining the liquid oil in the product, and continuously weighing the remaining solid matter. When the solid product after pyrolysis maintains a constant weight for 30 minutes, the pyrolysis is stopped; the weight of the material before and after carbonization is compared, and the weight loss portion is divided into 100 equal parts. For each weight loss of 1 part, the carbonization rate is considered to increase by 1%. The second target time is determined to be 55-65% carbonization rate. S5. Pyrolyzing the remaining second type of garden waste from step S4 in an oxygen-free environment, first rapidly heating to 200° C. and holding for 15-20 minutes to dehydrate the waste, then slowly heating to 450-480° C. at a heating rate of 10-15° C. / min, and holding the pyrolysis device for a second target time, so that the carbonization rate of the remaining solids is 55-65%; S6. Take the solids obtained in steps S3 and S5, mix them in a weight ratio of 1:(2-3), and obtain a carbon sink planting material for improving planting soil.

2. The method for carbon sequestration of garden waste for improving planting soil according to claim 1, characterized in that: In steps S2 and S4, if the weight loss within 30 min is less than 5% of the sample weight, it is determined to be constant weight.

3. The method for carbon sequestration of garden waste for improving planting soil according to claim 1, characterized in that: The reactor used for pyrolysis is a fluidized bed, fixed bed or tubular furnace.

4. The method for carbon sequestration of garden waste for improving planting soil according to claim 1, characterized in that: When improving the planting soil, the volume mixing ratio of carbon sink planting material and planting soil is (3-8):

1.

5. The method for carbon sequestration of garden waste for improving planting soil according to claim 1, characterized in that: In step S1 , only leaves are collected as the first type of garden waste, and only tree trunks are collected as the first type of garden waste.

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