A method and device for treating biogas residue

Abstract

The application discloses a biogas residue treatment method and a treatment device, wherein the biogas residue treatment method comprises the following steps: 1) performing ultrasonic treatment on a to-be-treated substance comprising biogas residue and porous substances at 40 kHz for not less than 3 times to obtain an ultrasonic system; the frequency of each ultrasonic treatment is 10 min / h; 2) performing ozone treatment on the ultrasonic system to obtain degraded biogas residue; the porous substances are selected from at least one of biochar, zeolite and ceramic granule, the particle size is 2-5 mm, and the mass of the porous substances is 5-10% of the mass of the biogas residue. The biogas residue treatment method provided by the application has the characteristics of deep utilization of organic matters in the biogas residue, low treatment cost and no waste generation.

Description

Technical Field

[0001] This invention relates to a method for treating biogas residue, and more particularly to a method and apparatus for treating biogas residue. Background Technology

[0002] Anaerobic digestion can extract energy from organic matter such as kitchen waste, livestock and poultry manure, and crop straw to produce biogas and obtain biogas residue. In actual production, anaerobic digestion can only degrade 50-60% of organic matter, and the resulting biogas residue still contains a large amount of organic matter.

[0003] Currently, biogas residue is typically subjected to aerobic fermentation or long-term composting and aging to further degrade the organic matter within it. However, these methods not only fail to effectively utilize the organic matter present in the biogas residue but also suffer from high processing costs.

[0004] Therefore, developing a biogas residue treatment method that can effectively utilize the organic matter in biogas residue and has a low treatment cost has become a research direction. Summary of the Invention

[0005] This invention provides a method for treating biogas residue, which features deep utilization of organic matter in biogas residue, low treatment cost, and no waste generation.

[0006] The present invention also provides a degraded biogas residue, which has the characteristic of being usable for preparing plant nutrients.

[0007] The present invention also provides a plant nutrient agent that has the characteristic of promoting plant growth.

[0008] This invention also provides a method for using a plant nutrient, which has the characteristics of promoting plant growth and high planting efficiency.

[0009] The present invention also provides a biogas residue treatment device, which is convenient to use and does not pollute the environment.

[0010] This invention provides a method for treating biogas residue, comprising the following steps:

[0011] 1) The material to be treated, including biogas residue and porous materials, is subjected to ultrasonic treatment at 40 kHz for no less than 3 times to obtain an ultrasonic system; the frequency of each ultrasonic treatment is 10 min / h.

[0012] 2) The ultrasonic system is subjected to ozone treatment to obtain degraded biogas residue;

[0013] The porous material is selected from at least one of biochar, zeolite, and ceramsite, with a particle size of 2-5 mm, and the mass of the porous material is 5-10% of the mass of the biogas residue.

[0014] In the treatment method described above, the ozone system in the ozone treatment includes ozone and air in a volume ratio of 1:5 to 1:8.

[0015] In the treatment method described above, the mass ratio of ozone to organic matter in the ultrasonic system during ozone treatment is (0.05-0.08):1.

[0016] In the treatment method described above, the ozone treatment time is 2-4 days, and the ozone release rate is 5-8 min / 30 min.

[0017] The present invention also provides a degraded biogas residue, which is obtained by any of the methods described above.

[0018] The present invention also provides a plant nutrient agent comprising the above-mentioned degraded biogas residue.

[0019] The present invention also provides a method for using a plant nutrient, wherein the plant nutrient is used to grow plants.

[0020] The method of using the plant nutrient as described above, wherein the plant is selected from at least one of comfrey, giant reed, alfalfa, licorice, king grass, and leafy grass;

[0021] The soil used for planting the plant includes a 10-15cm thick layer of plant nutrient solution, the upper surface of which is 5-10cm away from the ground surface.

[0022] The present invention also provides a biogas residue treatment device for performing any of the above-described biogas residue treatment methods. The biogas residue treatment device includes an ultrasonic treatment unit and an ozone treatment unit that are interconnected.

[0023] The ultrasonic processing unit is used to perform ultrasonic processing;

[0024] The ozone treatment unit is used to perform ozone treatment.

[0025] In the biogas residue treatment device described above, the ozone treatment unit includes a treatment container, and the surface of the treatment container is provided with at least one ozone system inlet.

[0026] The biogas residue treatment method provided by this invention has the characteristics of deep utilization of organic matter in biogas residue, low treatment cost, and no waste generation. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced one by one below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A schematic diagram of soil-plant nutrients-soil structure;

[0029] Figure 2 Flowcharts for biogas residue treatment methods and plant nutrient application methods;

[0030] Figure 3 This is a schematic diagram of an ozone reactor.

[0031] Explanation of reference numerals in the attached figures:

[0032] A-Processing container;

[0033] B-Aeration tube;

[0034] C-coating. Detailed Implementation

[0035] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The first aspect of this invention provides a method for treating biogas residue, comprising the following steps:

[0037] 1) The material to be treated, including biogas residue and porous materials, is subjected to ultrasonic treatment at 40 kHz for no less than 3 times to obtain an ultrasonic system; the frequency of each ultrasonic treatment is 10 min / h.

[0038] 2) Ozone treatment of the ultrasonic system yields degraded biogas residue.

[0039] The porous material is selected from at least one of biochar, zeolite, and ceramsite, with a particle size of 2-5 mm, and the mass of the porous material is 5-10% of the mass of the biogas residue.

[0040] Biogas residue is a solid substance obtained by solid-liquid separation after organic fertilizer has undergone anaerobic fermentation to produce biogas. This invention does not specifically limit the source of biogas residue; it can be obtained using methods commonly used in the art. In one embodiment, one or more organic materials from kitchen waste, livestock manure, and crop straw are anaerobically digested, and the solid portion is then subjected to centrifugal dehydration, belt filter press, or other methods to reduce the moisture content to no more than 80%, which can be used as biogas residue in this method.

[0041] Porous materials can overcome the inherent defects of biogas residue, such as its soft and porous nature and large spatial structure. In ozone treatment, they can provide air passageways for the biogas residue, facilitating ozone diffusion within the ultrasonic system and improving the efficiency of ultrasonic treatment. The particle size of the porous material should be controlled at 2-5 mm, and the addition mass should be 5-10% of the biogas residue mass. Selecting porous materials within this particle size range avoids both excessively fine particles that would fail to effectively provide air passageways and excessively large particles that would hinder the diffusion of adsorbed substances into the porous material. This addition amount is a relatively economical and appropriate amount while ensuring sufficient air passageways and adsorption capacity. This particle size range and addition amount balance effectiveness, efficiency, and cost.

[0042] Biogas residue is an aggregate of numerous small particles, containing a significant amount of ammonia, volatile fatty acids, and other substances. These substances are toxic to plant roots, and directly using biogas residue containing these substances for plant cultivation is detrimental to plant growth. Ultrasonic treatment can break down these small particle aggregates, dispersing the biogas residue into smaller particles that expose the interior, allowing the ammonia, volatile fatty acids, and other substances attached to the biogas residue aggregates to come into more thorough contact with the porous material. Furthermore, ultrasonic treatment can also cause the dispersed small particles to collide violently with the porous material through localized vibrations, accelerating the absorption of ammonia, volatile fatty acids, and other substances by the porous material. Simultaneously, ultrasound helps to activate the porous material, activating the microporous structure on the surface to create more cavities, thus allowing a unit mass of porous material to adsorb a greater mass of free ammonia, volatile fatty acids, and other substances.

[0043] In the processing method provided by this invention, ultrasonic treatment uses a frequency of 40 kHz. Ultrasonic waves at this frequency have strong penetrating power and can effectively break up larger aggregates internally, making them suitable for complex systems like biogas residue. Furthermore, during ultrasonic treatment, ultrasonic treatment is performed for 10 minutes every hour, repeated at least three times (i.e., the total treatment time is no less than 3 hours, with each hour consisting of 10 minutes of ultrasonic treatment). Since the instantaneous adsorption rate of porous materials is limited, multiple adsorption cycles can achieve a larger total adsorption amount from an adsorption kinetics perspective. In addition, because biogas residue is a semi-solid system, the diffusion rates of ammonia and volatile fatty acids are relatively slow. A certain time interval between ultrasonic treatments allows ammonia and volatile fatty acids to diffuse and accumulate better around the porous material, resulting in more thorough release and absorption.

[0044] Ozone treatment involves contacting an ozone-containing gas with an ultrasonic system to degrade biogas residue. The ultrasonic system contains biogas residue and porous materials, which adsorb substances such as ammonia and volatile fatty acids that have been released from the biogas residue during ultrasonic treatment. During ozone treatment, ozone oxidizes these substances in the biogas residue and porous materials, neutralizing their toxicity to plant roots. It also oxidizes large organic molecules in the ultrasonic system into smaller, more easily degradable organic molecules, stabilizing the biogas residue. Simultaneously, ozone decomposes into oxygen, providing oxygen for the biodegradation process in the ultrasonic system.

[0045] During ultrasonic treatment, ammonia and volatile fatty acids in biogas residue dissociate from the aggregates of the particles, becoming free or adsorbed onto the surface of porous materials. These substances are thus more easily oxidized by ozone. Therefore, combining ultrasonic and ozone treatment significantly improves the removal efficiency of ammonia and volatile fatty acids compared to ultrasonic or ozone treatment alone, resulting in a synergistic effect. If porous materials are added and only ultrasonic treatment is performed, ammonia and volatile fatty acids are released in large quantities from within the aggregates, preventing them from being quickly and completely adsorbed, leading to greater short-term toxicity to plant roots. If only ozone treatment is performed, these substances, being within the aggregates, are difficult to oxidize completely and may continue to be released, negatively impacting plant growth in the long term.

[0046] The biogas residue treatment method provided by this invention combines ultrasonic treatment and ozone treatment to process biogas residue containing porous materials. This effectively removes substances such as ammonia and volatile fatty acids that are toxic to plants, and degrades some large organic molecules into smaller molecules that are easily utilized by plants, thus effectively utilizing the organic matter in the biogas residue. Furthermore, because the treatment process is relatively simple and does not require the addition of additional chemicals, the biogas residue treatment method provided by this invention also has the advantage of low treatment costs. The final products are only plants and nutrient soil, both of which have good resource utilization potential. The biogas residue treatment method provided by this invention also has the advantage of not generating waste.

[0047] In one embodiment, the treatment method provided by the present invention uses an ozone system comprising ozone and air for ozone treatment, with an ozone-to-air volume ratio of 1:5 to 1:8. The reasons for controlling the ozone-to-air volume ratio within this range are as follows: firstly, the ozone concentration should not be too high, as this would lead to the death of a large number of microorganisms in the biogas residue, which is detrimental to subsequent composting; secondly, the biogas residue is soft and prone to internal collapse, and incorporating a large proportion of air can generate a larger airflow and pressure, opening up the internal channels of the biogas residue and allowing ozone to enter. However, it is not advisable to incorporate an even larger proportion of air, as this would result in insufficient ozone concentration and poor oxidation effect, and would also lead to a faster airflow rate, compromising the contact time between ozone and ammonia and volatile fatty acids. The ozone dosage at the above-mentioned volume ratio plays a positive role in maintaining the air passages and ensuring oxidation capacity.

[0048] Furthermore, in one embodiment of ozone treatment, the mass ratio of ozone to organic matter in the ultrasonic system is (0.05-0.08):1. Controlling the mass ratio of ozone to organic matter within the above range can improve the efficiency of ozone treatment and reduce the amount of ozone used, thus helping to lower treatment costs.

[0049] Furthermore, the ozone treatment time can be 2-4 days, with an ozone release rate of 5-8 min / 30 min. During ozone treatment, the ozone system can be fully released within 2-4 days, with the ozone release time being 5-8 min per 30 min interval. Controlling the ozone release rate within the above range helps the ozone to react fully with the ultrasonic system, while reducing the large-scale inactivation of microorganisms in the ultrasonic system by high-concentration ozone accumulation, thus helping to preserve microorganisms for degradation reactions.

[0050] In one embodiment, during ozone treatment, the total mass of organic matter in the ultrasonic system is first determined using potassium dichromate titration. The required total mass of ozone is calculated based on an ozone-to-air mass ratio of (0.05-0.08):1. The total volume of the ozone system is determined according to an ozone-to-air volume ratio of 1:5-1:8. This volume of ozone system is then evenly distributed over 2-4 days, with the ozone release time being 5-8 minutes per 30-minute interval. Controlling the ozone treatment under these conditions can further improve the efficiency of ozone treatment.

[0051] A second aspect of this invention provides a degraded biogas residue, prepared using any of the above-described biogas residue treatment methods. This degraded biogas residue has a low content of components toxic to plants and a high content of substances easily absorbed and utilized by plants, therefore it can be used to prepare plant nutrients.

[0052] A third aspect of this invention provides a plant nutrient agent comprising degraded biogas residue. This invention does not specifically limit the other components and mass fractions of the plant nutrient agent; commonly used plant nutrients in the art can be selected, such as at least one of inorganic or organic substances containing nitrogen, phosphorus, and potassium. Because the plant nutrient agent provided by this invention comprises degraded biogas residue, which has a low content of components toxic to plants and a high content of substances easily absorbed and utilized by plants, the plant nutrient agent provided by this invention has the characteristic of promoting plant growth.

[0053] A fourth aspect of this invention provides a method for using a plant nutrient agent to grow plants. Since the plant nutrient agent provides nutrients for plant growth, the method of using the plant nutrient agent provided by this invention has the characteristics of promoting plant growth and achieving high planting efficiency.

[0054] The method provided by this invention does not specifically limit the types of plants to be planted; plant varieties that are water- and fertilizer-tolerant, grow rapidly, can be harvested multiple times a year, and can survive for many years can be selected.

[0055] When plant nutrients are used in planting, the plants absorb the nutrients provided by the plant nutrients. Since these nutrients come from degraded biogas residue, more specifically, from biogas residue, the planting process completes the final energy transfer from the biogas residue, transferring the energy contained in the biogas residue to the plant. Furthermore, this invention does not limit the use of the plant obtained from planting. In one embodiment, the plant obtained from planting can be used for livestock farming, for the production of fuel ethanol, and for the preparation of plant fiberboard, papermaking, etc., realizing the resource utilization of new energy and new materials. It is understood that since freshly harvested plants are rich in organic matter, the plant obtained from planting can also be used as raw material for anaerobic fermentation. Specifically, the harvested plants are chopped into pieces of about 5cm using a cutter and placed in an anaerobic digester, where they are anaerobic digested together with kitchen waste, livestock and poultry manure, and crop straw, so that the biogas residue produced by anaerobic digestion enters the next cycle, providing a nutrient source for plant growth.

[0056] Furthermore, in one embodiment, the plant is selected from at least one of comfrey, giant reed, alfalfa, licorice, elephant grass, and leafy grass. These plants have the advantages of being easy to cultivate, highly adaptable, and growing very quickly. They can be harvested after just over a month of planting, and can be harvested approximately every 20 days, enabling rapid extraction of nutrients from biogas residue.

[0057] Furthermore, in one embodiment, the soil used for planting plants includes a plant nutrient layer with a thickness of 10-15 cm, and the upper surface of the plant nutrient layer is 5-10 cm away from the ground surface.

[0058] Specifically, low-quality dry soil, especially construction land soil or nutrient-poor soil, can be taken and spread evenly on the ground to a thickness of 15-20cm. The aforementioned plant nutrient solution is then spread evenly on top of the soil layer to a thickness of 5-10cm. On top of the plant nutrient solution, another layer of low-quality soil is laid to a thickness of 5-10cm. The completed soil structure is as follows: Figure 1 As shown in the diagram. When planting plants using the above soil structure, the nutrients in the plant nutrient solution can be slowly released into the upper and lower soil layers. This sandwich structure achieves three functions: first, it prevents the water in the plant nutrient solution from directly seeping into the ground; second, it slightly isolates oxygen, preventing the aerobic fermentation of the plant nutrient solution from generating excessive heat that could damage the plant roots; and third, it prevents the plant roots from directly contacting the plant nutrient solution, providing a buffer layer, and the sandwich structure also prevents the plants from lodging. After the sandwich structure is laid, let it sit for 3-5 days to allow some of the moisture and nutrients in the biogas residue to diffuse into the soil layer before sowing.

[0059] After sowing, the aforementioned plants will first take root and sprout in the upper soil layer. Due to their rapid growth and high nutrient requirements, their roots will continuously grow towards nutrient-rich areas. Because the plant nutrient solution is too potent, the plant roots will initially grow extensively horizontally at the boundary between the plant nutrient solution and the upper soil layer. Some roots will penetrate through this boundary to the surface of the plant nutrient solution layer to absorb nutrients. Once the nutrients in the surface layer of the plant nutrient solution layer are exhausted, or as the plant's tolerance increases, a large number of roots will penetrate deeper into the plant nutrient solution layer to absorb nutrients. In this way, the plant roots can obtain the nutrients they need while avoiding burning the seedlings due to excessive fertilizer.

[0060] Once the plants reach harvestable condition, they are harvested. The plant roots remaining in the soil continue to grow leaves, achieving a cycle of harvesting. After 5-10 harvests, the residue and soil layers contain a significant amount of water and organic matter, and the plant nutrients have largely stabilized, although they remain rich in organic matter, nitrogen, phosphorus, potassium, and other nutrients. Using a rotary tiller to mix the soil layers, including the plant nutrients, from the multiple harvests can create nutrient-rich soil.

[0061] There are two ways to dispose of potting soil:

[0062] Method 1: The nutrient soil can be mixed again with biogas residue and poor soil to form a substrate and nutrient interlayer, reducing the need for external soil. The specific method is as follows: Take low-quality dry soil and spread it evenly on the ground to a thickness of 15-20cm. Spread biogas residue evenly on top of the soil layer to a thickness of 5-10cm. Then, cover the biogas residue layer with the aforementioned nutrient soil to a thickness of 5-10cm. Because the nutrient soil layer contains a large amount of grass seeds and roots, plants can grow again without further sowing, thus achieving a cyclical production.

[0063] Method 2: In addition to the nutrient soil that is reused, excess nutrient soil is used to cover the site where low-quality soil was previously taken, or landfills, wastelands, barren land, and rock surfaces, to a thickness of approximately 20-25 cm. This nutrient soil is fully stabilized, environmentally harmless, and rich in nutrients. It also contains a large number of grass seeds and plant roots, has good water retention, and can regrow without sowing, achieving ecological restoration and land improvement of wastelands at low cost.

[0064] A fifth aspect of the present invention provides a biogas residue treatment apparatus for performing any of the above-described biogas residue treatment methods. The biogas residue treatment apparatus includes an ultrasonic treatment unit and an ozone treatment unit connected to each other; the ultrasonic treatment unit performs ultrasonic treatment, and the ozone treatment unit performs ozone treatment.

[0065] Flowcharts of biogas residue treatment methods and plant nutrient application methods are shown below. Figure 2 As shown.

[0066] The biogas residue treatment device provided by this invention uses interconnected ultrasonic treatment units and ozone treatment units to sequentially treat biogas residue with ultrasonic treatment and ozone treatment, which has the characteristics of high treatment efficiency.

[0067] Furthermore, the ozone treatment unit includes a treatment container, the surface of which is provided with at least one ozone system inlet. During ozone treatment, the ozone system enters the treatment container through at least one ozone system inlet and comes into contact with the ultrasonic system.

[0068] Furthermore, in one embodiment, the ozone treatment unit uses, for example... Figure 3 The ozone processor shown. (By...) Figure 3 The ozone processor includes a treatment container A, at least one aeration pipe B, and a membrane C. The treatment container A houses the ultrasonic system. The aeration pipe B is located at the bottom of the treatment container and releases the ozone system into the treatment container A through aeration holes on the pipe. The point where the aeration pipe B meets the surface of the treatment container A is the ozone system inlet. The membrane C is detachably fixed to the surface of the treatment container to reduce gas exchange between the inside and outside of the container, preventing ozone gases from escaping into the surrounding air and causing pollution during ozone treatment.

[0069] The following describes in detail the biogas residue treatment method provided by the present invention with reference to embodiments:

[0070] Example 1

[0071] This embodiment provides a method for stabilizing and utilizing biogas residue as a resource, the specific steps of which include:

[0072] 1) After anaerobic digestion of kitchen waste and livestock manure (mass ratio 2:8) for 25 days, the waste is centrifuged and dehydrated to a moisture content of 80% to obtain biogas residue.

[0073] 2) Add straw biochar with a particle size of 3 mm to the biogas residue at a mass percentage of 10% of the biogas residue mass. After mixing evenly, the mixture is ultrasonically treated at a frequency of 40 kHz for a total of 3 times, with 10 minutes of ultrasonic treatment every 1 hour to obtain the ultrasonic system.

[0074] 3) The ultrasonic system is laid into the ozone reactor to a thickness of 40cm. An ozone system containing ozone and air is introduced into the reactor at a volume ratio of 1:5. Intermittent aeration is performed, with an aeration time of 5 minutes every 30 minutes, for a total of 3 days. The total ozone input is 75mg O3 / g organic matter, resulting in degraded biogas residue. This degraded biogas residue is then used as a plant nutrient.

[0075] 4) Spread the construction waste soil evenly on the ground to a thickness of 15cm. Spread the plant nutrient solution evenly on top of the soil layer to a thickness of 10cm. On top of the plant nutrient solution layer, spread another layer of construction waste soil to a thickness of 10cm. After the above layers are laid, leave them for 5 days to allow the moisture and nutrients in the plant nutrient solution to slowly diffuse into the soil layer.

[0076] 5) To plant leafy grass in the interlayer, first soak the leafy grass seeds in room temperature water. After the seeds absorb the water and swell, take them out and drain the water. Let the seed coat dry in the wind. Once the seeds are no longer sticking together, scatter them on the surface of the interlayer.

[0077] 6) Harvest 1-2 months after planting. After the first harvest, harvest again every 20 days or so. The roots of the leafy grass left in the soil will continue to grow leaves, and the harvesting cycle will continue.

[0078] 7) Chop freshly harvested leafy grass into pieces about 5cm using a cutter, and use them as raw materials for anaerobic fermentation, and carry out anaerobic digestion together with kitchen waste, livestock and poultry manure and crop straw.

[0079] 8) The biogas residue produced by anaerobic digestion enters the next cycle, along with low-quality soil, as a substrate and nutrient source for plant growth.

[0080] 9) After 5-10 harvests of leafy grasses, a large amount of water and organic matter have been extracted from the waste marsh, and the condition has basically stabilized. Use a rotary tiller to evenly mix the waste marsh with the soil layer to create nutrient-rich soil.

[0081] 10) Take more construction waste soil and spread it evenly on the ground to a thickness of 15cm. Then spread plant nutrients evenly on top of the soil layer to a thickness of 10cm, and finally cover the top layer with the aforementioned nutrient soil. Because this nutrient soil layer contains a large amount of grass seeds and roots, it can regrow without the need to sow leafy grass, thus achieving a cycle of production.

[0082] The remaining nutrient-rich soil can be used to cover the surface of barren land with sparse vegetation, with a layer of about 20-25cm. This nutrient-rich soil is not only rich in nutrients, but also contains a large number of grass seeds and plant roots. It has good water retention and can re-root and sprout without sowing, thus achieving ecological restoration and soil improvement of barren land.

[0083] Example 2

[0084] This embodiment provides a method for stabilizing and utilizing biogas residue as a resource, the specific steps of which include:

[0085] 1) After 20 days of anaerobic digestion of livestock and poultry manure, the biogas residue is centrifuged and dehydrated to a water content of 78% to obtain biogas residue.

[0086] 2) Add straw biochar with a particle size of 5 mm to the biogas residue at a mass percentage of 8% of the biogas residue mass. After mixing evenly, the mixture is ultrasonically treated at a frequency of 40 kHz for a total of 3 times, with 10 minutes of ultrasonic treatment every 1 hour to obtain the ultrasonic system.

[0087] 3) The ultrasonic system is laid into the ozone reactor to a thickness of 30cm. An ozone system containing ozone and air is introduced into the reactor. The volume ratio of ozone to air is 1:6. Intermittent aeration is performed, with an aeration time of 5 minutes every 30 minutes, for 3 consecutive days. The total ozone input is 60mg O3 / g organic matter, resulting in degraded biogas residue. This degraded biogas residue is then used as a plant nutrient.

[0088] 4) Take topsoil from nearby barren, sparsely vegetated wasteland and spread it evenly on the ground to a thickness of 20cm. Spread biogas residue evenly on top of the soil layer to a thickness of 10cm. On top of the biogas residue layer, spread another layer of construction waste to a thickness of 9cm. After the above layers are laid, leave it for 3 days to allow the moisture and nutrients in the plant nutrient solution to slowly diffuse into the soil layer.

[0089] 5) Plant giant reed grass in the interlayer, scatter the seeds on the surface of the interlayer, and then lay another layer of construction waste soil, 1cm thick. Sprinkle water on the surface of the interlayer to moisten the surface soil.

[0090] 6) Giant Napier grass can be harvested 60-80 days after planting, at which time the plant height can reach 1-2m and the leaf length is 0.6-1.3m. After the first harvest, it can be harvested again every 50 days or so. The roots of the giant Napier grass left in the soil layer continue to grow leaves, and the harvesting cycle continues. The harvested giant Napier grass can be used as animal feed. Giant Napier grass is rich in plant fiber, and it can also be dried and made into plant fiberboard, etc., for industrial use.

[0091] 7) After 2-3 harvests of giant reed grass, a large amount of water and organic matter have been extracted from the biogas residue, and the situation has basically stabilized. Use a rotary tiller to evenly mix the biogas residue with the soil layer to create nutrient soil.

[0092] 8) Take the topsoil from nearby barren wasteland with sparse vegetation, spread it evenly on the ground to a thickness of 20cm, spread fresh biogas residue evenly on the soil layer to a thickness of 10cm, and then cover the top layer with the above-mentioned nutrient soil. Since this nutrient soil layer contains a large number of grass seeds and roots, giant reeds can grow again without further sowing, thus creating a cycle of production.

[0093] 9) The remaining nutrient soil is directly applied to the surface of wasteland and exposed mines, with a thickness of about 20-25cm. This nutrient soil is not only rich in nutrients, but also contains a large number of grass seeds and plant roots. It has good water retention and can re-root and sprout without sowing, thus achieving ecological restoration and land improvement of abandoned land.

[0094] Comparative Example 1

[0095] This comparative example is basically the same as Example 1, except that the ultrasonic treatment in step 2) is not performed, but the biogas residue is added with straw biochar and then directly step 3 is performed.

[0096] Comparative Example 2

[0097] This comparative example is basically the same as Example 1, except that in step 2), an ultrasonic treatment is performed once, and the ultrasonic treatment time is 30 minutes.

[0098] Comparative Example 3

[0099] This comparative example is basically the same as Example 1, except that in step 2), the frequency of ultrasonic treatment is 28kHz.

[0100] Comparative Example 4

[0101] This comparative example is the same as some steps in Example 1. The difference is that in step 2), ultrasonic treatment is not performed. Instead, straw biochar with a particle size of 3 mm and a mass percentage of 10% of the biogas residue is mixed into the biogas residue and then treated with microwave at a frequency of 1800 MHz. The microwave treatment is performed 3 times, with 10 minutes of microwave treatment every 1 hour, to obtain the microwave treatment system.

[0102] Comparative Example 5

[0103] This comparative example is basically the same as Example 1, except that no porous material is added.

[0104] Test case

[0105] The biogas residue from an anaerobic digestion project was tested and recorded for the following characteristics of Examples 1, 2, and Comparative Examples 1 to 5:

[0106] 1) The concentrations of ammonia nitrogen and volatile fatty acids (VFA) in the pore water of the material to be treated before ultrasonic / microwave treatment;

[0107] 2) The concentrations of ammonia nitrogen and volatile fatty acids (VFA) in the pore water of the ultrasonic system after ultrasonic / microwave treatment;

[0108] 3) The concentrations of ammonia nitrogen and volatile fatty acids (VFA) in biogas residue after ozone treatment.

[0109] If the embodiments / comparative examples do not include ultrasonic treatment / microwave treatment / ozone treatment, then no corresponding tests will be performed.

[0110] Specifically, after adding porous materials to the biogas residue, samples were collected and measured at different stages, as follows:

[0111] Before ultrasonic / microwave treatment: Collect biogas residue samples and centrifuge at high speed (8000 rpm for 5 minutes). Measure the concentrations of ammonia nitrogen and total volatile fatty acids in the supernatant and record them as mg / L. Understand the amount of the two free substances in the pore water.

[0112] After ultrasonic / microwave treatment: Collect biogas residue samples and centrifuge at high speed (8000 rpm for 5 minutes). Measure the concentrations of ammonia nitrogen and total volatile fatty acids in the supernatant and record them as mg / L. Understand the amount of these two substances free in the pore water.

[0113] After ozone treatment: Samples of the degraded biogas residue were taken and extracted. The concentrations of ammonia nitrogen and total volatile fatty acids in the extract were measured and recorded as mg / kg. The residual ammonia nitrogen and volatile fatty acid content of the biogas residue were determined through the extract.

[0114] After all experimental groups were treated, grass seeds were sown. The experimental area was 1m×1m. The time when the seeds began to germinate, the seed germination index, the time from sowing to harvest, and the yield of the first harvest were recorded.

[0115] The data on ammonia nitrogen and VFA at each stage are shown in Table 1, and the data on germination time, germination rate, time from sowing to harvest and yield of the first harvest are shown in Table 2.

[0116] Table 1. Recording Table of Ammonia Nitrogen and VFA Data at Each Stage

[0117]

[0118] Table 2 Planting Data Record Sheet

[0119]

[0120]

[0121] From Tables 1 and 2, we can see that:

[0122] 1) By comparing the concentrations of ammonia nitrogen and VFA in pore water before and after ultrasonic treatment in Examples 1, 2, 2, 3, and 5, it can be seen that in the above embodiments, the concentrations of ammonia nitrogen and VFA in pore water after ultrasonic treatment are significantly increased compared with those before treatment. This indicates that ultrasonic treatment causes ammonia and volatile fatty acids to enter the liquid phase from the solid phase of the biogas residue in large quantities, thereby enhancing the desorption process of ammonia and volatile fatty acids.

[0123] 2) The concentrations of ammonia nitrogen and VFA extracted from the biogas residue after ozone treatment in Comparative Example 1 were significantly higher than those in Examples 1 and 2. This indicates that the ultrasonic treatment performed in Examples 1 and 2 can more effectively degrade ammonia nitrogen and VFA contained in the biogas residue. This may be because ultrasound treatment breaks down biogas residue agglomerates, making it easier for ammonia nitrogen and VFA to come into contact with porous materials and ozone, thus leading to their degradation.

[0124] 3) The seed germination rate of Example 1 was significantly higher than that of Comparative Example 1, and the germination time was shorter. The first harvest time was also shorter than that of Comparative Example 1, and the yield of leafy grass was higher than that of Comparative Example 1. This indicates that Example 1 has significant advantages over Comparative Example 1. The inventors speculate that the reason may be that ultrasonic treatment breaks down large particles, allowing the internal ammonia nitrogen and volatile fatty acids to come into more sufficient contact with the porous material and be more easily adsorbed. At the same time, because the contact surface with ozone is increased, it is easier to be oxidized by ozone, resulting in lower concentrations of ammonia nitrogen and volatile fatty acids, reduced plant toxicity, higher seed germination rate, and shorter emergence and harvest times.

[0125] 4) Comparing Example 1 and Comparative Example 2, it was found that Example 1, which employed batch ultrasonic treatment, had higher concentrations of ammonia nitrogen and volatile fatty acids in the pore water after ultrasonic treatment. The inventors speculate that this may be because multiple ultrasonic treatments allow ammonia nitrogen and volatile fatty acids to dissociate from the surface of the biogas residue in multiple stages, leading to more efficient degradation during ozone treatment. Because ammonia nitrogen and VFA are removed more effectively, plant growth is better, the first harvest time is shorter, and the first harvest yield is greater.

[0126] 5) Comparing Example 1 and Comparative Example 3, it was found that the concentrations of ammonia nitrogen and volatile fatty acids in the pore water were higher after ultrasonic treatment using Example 1 at a frequency of 40 Hz. The inventors speculate that this may be because the 40 kHz ultrasonic waves used in Example 1 have stronger penetrating power and are less easily blocked, allowing them to effectively conduct into the digester residue and more effectively break down the agglomerates deep within the residue. This results in more efficient dissociation of the ammonia nitrogen and volatile fatty acids encapsulated in the agglomerates, which are then degraded during ozone treatment. Consequently, the germination rate of plant seeds is higher, the germination and maturity times are shorter, and the harvest yield is greater.

[0127] 6) Compared to Example 1, the ozone treatment of biogas residue in Comparative Example 4 resulted in higher levels of ammonia nitrogen and VFA extracted from the residue, a relatively lower seed germination index, longer germination and harvesting times, and lower yield. The inventors speculate that this may be due to several factors: First, microwaves cannot generate localized oscillations, resulting in poor particle breakage and hindering the desorption of ammonia and VFA for more effective adsorption by porous materials. Second, while microwaves can heat the biogas residue, it has already undergone anaerobic digestion at a certain temperature. The temperature increase from microwave heating is insufficient to significantly alter the residue's structure and properties and may even lead to the death or dormancy of many microorganisms, hindering the maturation process during ozone treatment. Finally, microwave activation consumes a significant amount of energy, requiring substantial amounts and incurring high costs. Therefore, ultrasonic treatment offers better treatment results and lower costs compared to microwave treatment.

[0128] 7) A comparison between Example 1 and Comparative Example 5 shows that the concentrations of ammonia nitrogen and VFA in the pore water after ultrasonic treatment in Example 1 are lower than those in Comparative Example 5. This indicates that porous materials can remove ammonia nitrogen and VFA through adsorption. The ammonia nitrogen and VFA content extracted from the biogas residue after ozone treatment in Example 1 is lower than that in Comparative Example 5, and the plant growth is better in Example 1. The inventors speculate that this may be because the porous material used in Example 1 provides ventilation channels for ozone penetration during ozone treatment, thus facilitating the degradation of ammonia nitrogen and VFA.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating biogas residue, characterized in that, Includes the following steps: 1) The material to be treated, including biogas residue and porous material, is subjected to ultrasonic treatment at 40 kHz for no less than 3 times to obtain an ultrasonic system; the frequency of each ultrasonic treatment is 10 min / h, wherein the ultrasonic treatment is used to break up small particle agglomerates, so that the biogas residue is dispersed and broken into small particles, and the interior is exposed. The ammonia and volatile fatty acids attached to the inside of the biogas residue agglomerates can come into more full contact with the porous material, thereby accelerating the absorption of ammonia and volatile fatty acids by the porous material, so that the porous material adsorbs more mass of free ammonia and volatile fatty acids; 2) The ultrasonic system is subjected to ozone treatment to obtain degraded biogas residue; wherein, the ozone is used to oxidize ammonia and volatile fatty acids in the biogas residue and porous materials, and also to oxidize macromolecular organic matter in the ultrasonic system into easily degradable small molecule organic matter. The porous material is selected from at least one of biochar, zeolite, and ceramsite, with a particle size of 2-5 mm, and the mass of the porous material is 5-10% of the mass of the biogas residue. In the ozone treatment, the ozone system includes ozone and air in a volume ratio of 1:5 to 1:8; the mass ratio of ozone to organic matter in the ultrasonic system is (0.05-0.08):

1.

2. The method according to claim 1, characterized in that, The ozone treatment time is 2-4 days, and the ozone release rate is 5-8 min / 30 min.

3. A method for degrading biogas residue, characterized in that, Prepared using the method described in claim 1 or 2.

4. A plant nutrient, characterized in that, Includes the biogas residue as described in claim 3.

5. A method for using a plant nutrient, characterized in that, Plants are grown using the plant nutrient solution described in claim 4.

6. The method according to claim 5, characterized in that, The plant is selected from at least one of comfrey, giant reed, alfalfa, licorice, king grass, and leafy grass; The soil used for planting the plant includes a 10-15cm thick layer of plant nutrient solution, the upper surface of which is 5-10cm away from the ground surface.

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