Efficient, nutrient-increasing and emission-reducing selenium-loaded composite biochar and application thereof in invasive biological compost

Abstract

The invention discloses selenium-loaded composite biochar (SeBC) with high efficiency, nutrient increasing and emission reduction and application of the selenium-loaded composite biochar (SeBC) in invasive biological compost. The preparation method comprises the following steps: by taking invasive animal ampullaria gigas shells as raw materials, preparing pyrolytic biochar (BC) by adopting a pyrolysis method, then carrying out iron modification on the BC to obtain MBC, then proportioning the ampullaria gigas shells BC and MBC to form composite biochar, and loading a selenium element to obtain the selenium-loaded composite biochar. When the SeBC is used for invasive biological composting, on one hand, the defects of long composting period, low maturing efficiency, high nutrient loss and the like in the traditional composting process are overcome; and on the other hand, the invading organisms are subjected to resource utilization, so that the composting process can be improved, the composting quality can be improved, the environmental pollution can be reduced, the pressure of the invading organisms on the ecological environment is relieved, and a new way is provided for resource utilization of the invading organisms and improvement of low-carbon compost.

Description

Technical Field

[0001] The present invention relates to the fields of composting technology and environmental materials, and more specifically, to a selenium-loaded composite biochar with high efficiency, nutrient enhancement, and emission reduction and its application in the composting of invasive organisms. Background Art

[0002] Biological invasion refers to the process in which organisms invade a new environment from their original habitats through natural or human means, causing economic losses or ecological disasters to the biodiversity, agricultural, forestry, animal husbandry, and fishery production, and human health in the invaded area. Alien invasive species will pose a threat to the survival of local species, disrupt the ecological balance, and may carry pathogenic microorganisms, posing a potential threat to human health. The key is that alien invasive species may lead to the extinction of local species, destroy biodiversity, and have a serious impact on the ecological security of a country. Therefore, it is urgent to solve ecological problems. In order to control alien invasive species to the greatest extent, it is necessary to select ecological and environmentally friendly control methods.

[0003] Pomacea canaliculata ( Pomacea canaliculata ), also known as the apple snail, belongs to the Mollusca phylum and the Ampullariidae family. Pomacea canaliculata has strong adaptability and reproductive ability. As an invasive species, its shell, flesh, and eggs have their own characteristics in terms of resource utilization, but the shell has significant advantages in the production of biochar. The shell of Pomacea canaliculata is rich in calcium carbonate (CaCO 3 ), with high thermal stability and mechanical strength. During the pyrolysis process, the shell can maintain good structural integrity and form porous biochar, which is beneficial to improving the adsorption performance of biochar. The flesh and eggs are more easily affected by chemical substances, such as heavy metal and pesticide pollution. During the pyrolysis process, the yield of eggs is about 30%, while the yield of the shell reaches more than 90%. Therefore, the shell of Pomacea canaliculata is more suitable for the production of biochar.

[0004] Bidens pilosa L. Bidens pilosa is a worldwide invasive herbaceous plant widely distributed in tropical and subtropical regions. The characteristics of the seeds of Bidens pilosa L. enable them to be widely spread by the wind and easily adhere to clothes and animal fur. It is listed as a harmful agricultural and environmental weed in more than 40 countries, causing serious negative impacts on natural ecosystems and crop production. Pomacea canaliculata ( Pomacea canaliculata ) is an invasive harmful mollusk. P. canaliculata It is listed as one of the world's 100 most serious alien invasive species by the International Union for Conservation of Nature and the Invasive Species Specialist Group. Its high reproductive capacity and rapid growth characteristics cause serious damage to the growth of rice and various aquatic crops, as well as wetland diversity and ecosystem functions.

[0005] Traditional solutions mainly include manual removal, chemical control, biological control, and alternative control, but they involve a large amount of human and financial resources and have limited sustainable value. Using invasive plants as raw materials for aerobic composting is an effective way to turn waste into treasure and utilize resources. However, the nutrient components of invasive plants are different from those of native plants. They may absorb a large amount of specific nutrients during growth, and the secondary metabolite components accumulated in their bodies are unique, which affects the compost properties.

[0006] Biochar has a large specific surface area and abundant functional groups. The application of biochar helps with the composting of *Bidens pilosa*, but it will increase the composting cost. Selenium (Se) is an essential trace element for the human body and is crucial for maintaining good health. Food is the main source of Se intake by the human body. The Se content in crops depends on the bioavailability of selenium by the crops. Selenium-rich compost can provide available selenium for crop growth. Using invasive organisms to prepare selenium-rich compost is beneficial to improving the economic value of fertilizers and reducing the additional cost of biochar application. However, directly applying Se in selenium-rich compost will cause Se loss, which will affect the absorption and utilization of selenium. Previous studies have shown that directly adding Se will increase the global warming potential value. At the same time, there are problems in traditional composting processes such as a short duration of the high-temperature period, low degradation efficiency of organic matter, and greenhouse gas emissions. Therefore, how to effectively utilize selenium in invasive plant selenium-rich compost and improve the short duration of the high-temperature period, low degradation efficiency of organic matter, and greenhouse gas emissions in traditional composting are problems that need to be solved urgently at present. Summary of the Invention

[0007] The purpose of the present invention is to overcome the above-mentioned defects and deficiencies existing in the prior art and provide a preparation method of selenium-loaded composite biochar.

[0008] Another purpose of the present invention is to provide the selenium-loaded composite biochar prepared by the above preparation method.

[0009] Another purpose of the present invention is to provide the application of the selenium-loaded composite biochar as a compost selenium source additive in invasive organism composting.

[0010] The above purposes of the present invention are achieved by the following technical solutions: A preparation method of selenium-loaded composite biochar includes the following steps: S1. Wash, dry, crush, and sieve the *Pomacea canaliculata* shells, and pyrolyze them to obtain *Pomacea canaliculata* shell biochar (BC); S2. Grind and sieve the BC, and use a mixed solution of Fe 3+ and Fe 2+ to prepare iron-modified biochar (MBC) by chemical co-precipitation in an alkaline medium; S3. Add the BC from step S1 and the MBC from step S2 to a Se(IV) solution with a concentration of 0.01 - 0.06 g / L in a mass ratio of 1 - 9:1, adjust the pH to neutral, and perform oscillatory adsorption to obtain selenium-loaded composite biochar (SeBC).

[0011] In the present invention, the shell of the invasive animal Pomacea canaliculata is used as a raw material, and pyrolytic biochar BC of Pomacea canaliculata shell is prepared by pyrolysis. Then, the pyrolytic biochar is iron-modified to obtain MBC. Subsequently, the pyrolytic biochar of Pomacea canaliculata shell and MBC are proportioned to form composite biochar and selenium element is loaded to obtain SeBC. The present invention creatively uses BC and MBC to proportion and form composite biochar, and then selenium is loaded. Selenium-loaded biochar can fix selenium in the form of nanoparticles on the surface or pores of the biochar, realizing the slow release of selenium. This slow-release mechanism can avoid the rapid loss or fixation of selenium during the composting process due to direct application, thereby improving the biological availability of selenium. At the same time, selenium can promote the activity of microorganisms during the composting process, accelerate the decomposition and transformation of organic matter, and improve the formation efficiency of organic matter. Selenium has a regulatory effect on greenhouse gas emissions and nitrogen loss during the composting process, and can appropriately extend the thermophilic stage of composting and improve the degradation of organic matter. In addition, the specific surface area, pore size, and pore volume of the biochar after selenium loading are better than those before loading. The increase in pore size means stronger adsorption ability, which has a significant effect on greenhouse gas emissions during composting. At the same time, BC can provide a larger support structure for MBC, enabling MBC to be better dispersed in the composting system, increasing the contact area between selenium and compost raw materials, improving the adsorption and fixation ability of a large number of nutrients and trace elements, and reducing nutrient loss. On the other hand, the combination of the porous structure of BC and the stimulating effect of MBC on microorganisms can attract more types and quantities of microorganisms to participate in the composting process, accelerate the decomposition and transformation of organic matter, and improve the maturity and quality of compost. In summary, the present invention fully considers MBC, BC, and selenium element, gives play to the advantages of the three, and applying SeBC obtained by compounding and loading MBC and pyrolytic biochar with selenium to composting has significant economic and environmental benefits.

[0012] Further, the sieving in step S1 is sieving through a 50 - 70 mesh sieve.

[0013] Preferably, the sieving in step S1 is sieving through a 60 mesh sieve.

[0014] Further, the pyrolysis in step S1 is pyrolysis at 300 - 400 °C for 1.5 - 2.5 h.

[0015] Preferably, the pyrolysis in step S1 is pyrolysis at 342 °C for 2 h.

[0016] Further, the sieving in step S2 is sieving through a 90 - 110 mesh sieve.

[0017] Preferably, the sieving in step S2 is sieving through a 100-mesh sieve.

[0018] Further, the Fe in step S2 3+ and Fe 2+ in the mixed solution, the molar ratio of Fe 3+ to Fe 2+ is 2.5 - 3.

[0019] Preferably, the molar ratio of Fe 3+ to Fe 2+ in the mixed solution of Fe 3+ and Fe 2+ is 2.72.

[0020] Further, the solid-liquid ratio of BC and MBC to Se(IV) solution in step S3 is 0.4 - 0.6:1 (g / mL).

[0021] Preferably, the solid-liquid ratio of BC and MBC to Se(IV) solution in step S3 is 0.5:1 (g / mL).

[0022] Further, the oscillating adsorption in step S3 is carried out at 24 - 26 °C with an oscillation speed of 170 - 190 r / min for 22 - 26 h.

[0023] Preferably, the oscillating adsorption in step S3 is carried out at 25 °C with an oscillation speed of 180 r / min for 24 h.

[0024] The present invention also provides the SeBC prepared as above.

[0025] By coupling selenium element and biochar, the SeBC of the present invention can improve the composting process, including increasing the duration of the high-temperature period, enhancing the availability of nitrogen and phosphorus, and reducing greenhouse gas emissions, etc., which helps to construct an efficient and environmentally friendly composting system. Therefore, the present invention also provides the application of the above SeBC as a compost selenium source additive in the composting of invasive organisms.

[0026] The present invention also provides a formula for selenium-rich compost of invasive organisms, which includes invasive plant Bidens pilosa and chicken manure as compost raw materials, and the above-mentioned SeBC as a compost selenium source additive; the carbon-nitrogen ratio of the compost raw materials is 20 - 30:1, the moisture content of the compost materials is 60 - 70%; the mass addition ratio of the SeBC is 3% - 16%.

[0027] In the compost formula of the invasive biological selenium-enriched compost of the present invention, the compost raw material Bidens pilosa is a common invasive plant, which contains rich organic carbon with a content of 407.72 g / kg; chicken manure, as another raw material in the compost, has a relatively high nitrogen content with a content of 22.05 g / kg. Since Bidens pilosa and chicken manure contain relatively high carbon and nitrogen contents respectively, the compost of Bidens pilosa and chicken manure can provide rich carbon and nitrogen sources.

[0028] By adjusting three parameters: the BC / MBC ratio, selenium concentration, and the dosage of SeBC selenium-loaded biochar, the present invention can specifically obtain three different functional compost formulas: temperature-extending and rapid-ripening type, nutrient-increasing and retention type, and emission-reducing and air-control type.

[0029] Furthermore, when preparing SeBC, the mass ratio of BC to MBC is 1-3:1, and the Se(IV) concentration is 0.01-0.02 g / L; the added mass ratio of SeBC is 3%-8%. The obtained formula is of the temperature-extending and rapid-ripening type, which can extend the thermophilic time of the compost and effectively accelerate the compost ripening process.

[0030] Preferably, the mass ratio of BC to MBC is 2:1, the Se(IV) concentration is 0.015 g / L, and the mass ratio of SeBC in the compost is 6%.

[0031] Furthermore, when preparing SeBC, the mass ratio of BC to MBC is 4-6:1, and the Se(IV) concentration is 0.02-0.04 g / L; the added mass ratio of SeBC is 9%-12%. The obtained formula is of the temperature-extending and rapid-ripening type, which can make MBC better dispersed in the compost system, increase its contact area with the compost raw materials, thereby improving the adsorption and fixation ability of nutrients such as nitrogen, phosphorus, and potassium, and reducing nutrient loss.

[0032] Preferably, the mass ratio of BC to MBC is 5:1, the Se(IV) concentration is 0.03 g / L, and the mass ratio of SeBC in the compost is 10%.

[0033] Furthermore, when preparing SeBC, the mass ratio of BC to MBC is 7-9:1; the Se(IV) concentration is 0.04-0.06 g / L; the added mass ratio of SeBC is 13%-16%. The obtained formula is of the emission-reducing and air-control type, which can reduce the emissions of methane (CH 4 ), carbon dioxide (CO 2 ), and nitrous oxide (N 2 O) during the composting process.

[0034] Preferably, the mass ratio of BC to MBC is 8:1, the Se(IV) concentration is 0.05 g / L, and the mass ratio of SeBC in the compost is 15%.

[0035] Furthermore, the carbon-nitrogen ratio of the compost raw materials is 25:1, and the initial water content of the compost is 65%.

[0036] The present invention also provides the application of the above-mentioned invasive-biology selenium-enriched compost formula in the preparation of invasive-biology review compost.

[0037] The present invention also provides a preparation method of invasive-biology selenium-enriched compost based on the above-mentioned invasive-biology selenium-enriched compost formula. The above-mentioned invasive-biology selenium-enriched compost formula is subjected to aerobic composting at 26-35 °C for 30-40 days to obtain SeBC compost, that is, invasive-biology selenium-enriched compost.

[0038] Preferably, the compost reaction is carried out in a commercially available conventional aerobic composting container.

[0039] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses the shell of the invasive animal Pomacea canaliculata as a raw material, prepares pyrolytic biochar of Pomacea canaliculata shell by pyrolysis method, then modifies the pyrolytic biochar BC with iron to obtain iron-modified biochar MBC, and then mixes the pyrolytic biochar of Pomacea canaliculata shell and the iron-modified biochar to form a composite biochar and load selenium element to obtain selenium-loaded composite biochar SeBC. SeBC can fix selenium in the form of nanoparticles on the surface or pores of the biochar, realizing the slow release of selenium. This slow-release mechanism can avoid the rapid loss or fixation of selenium during the composting process due to direct application, thereby improving the biological availability of selenium. At the same time, selenium can promote the activity of microorganisms during the composting process, accelerate the decomposition and transformation of organic matter, and improve the formation efficiency of organic matter. Selenium has a regulatory effect on greenhouse gas emissions and nitrogen loss during the composting process, and can appropriately extend the thermophilic stage of composting and improve the degradation of organic matter. In addition, the specific surface area, pore size and pore volume of SeBC are better than those before loading. The increase in pore size means stronger adsorption ability, which has a significant effect on greenhouse gas emissions in composting; at the same time, BC can provide a larger support structure for MBC, enabling MBC to be better dispersed in the composting system, increasing the contact area between selenium element and compost raw materials, improving the adsorption and fixation ability of a large amount of nutrients and trace elements, and reducing nutrient loss; on the other hand, the combination of the porous structure of BC and the stimulating effect of MBC on microorganisms can attract more types and quantities of microorganisms to participate in the composting process, accelerate the decomposition and transformation of organic matter, and improve the maturity and quality of compost. In short, the present invention fully considers MBC, BC and selenium element, gives play to the advantages of the three, and applying SeBC obtained by compounding and loading MBC and BC with selenium to composting has significant economic and environmental benefits. The SeBC composting technology of the present invention can extend the high-temperature period of composting, accelerate the ripening process; enhance the adsorption and fixation ability of nutrients such as nitrogen, phosphorus and potassium in composting, reduce the loss of selenium element, reduce the greenhouse gas emissions of composting, and applying SeBC to composting has significant economic and environmental benefits. Description of the Drawings

[0040] Figure 1 For the surface structure characteristics and energy-dispersive X-ray (EDS) spectrum of the SeBC material. Among them, Figure 1 in (I) is the morphology of MBC biochar, (II) is the morphology of SeBC biochar, (III) is the EDS spectrum and elemental content percentage of MBC, and (IV) is the EDS spectrum and elemental content percentage of SeBC.

[0041] Figure 2 For the influence of the temperature-extending and ripening-accelerating formula on the temperature of SeBC composting. Among them, Figure 2 in a is the result of the temperature change trend during composting; b is the result of the comparison of the number of high-temperature days.

[0042] Figure 3Effect of the temperature-retention and quick-ripening formula on the pH of SeBC compost.

[0043] Figure 4 Effect of the temperature-retention and quick-ripening formula on the electrical conductivity of SeBC compost.

[0044] Figure 5 Effect of the temperature-retention and quick-ripening formula on the germination index of SeBC compost.

[0045] Figure 6 Effect of the temperature-retention and quick-ripening formula on the ash content of SeBC compost.

[0046] Figure 7 Effect of the nutrient-enriching and retention formula on the organic matter of SeBC compost.

[0047] Figure 8 Effect of the nutrient-enriching and retention formula on the total nitrogen content of SeBC compost.

[0048] Figure 9 Effect of the nutrient-enriching and retention formula on the total phosphorus content of SeBC compost.

[0049] Figure 10 Effect of the nutrient-enriching and retention formula on the total potassium content of SeBC compost.

[0050] Figure 11 Effect of the nutrient-enriching and retention formula on the ammonium nitrogen content of SeBC compost.

[0051] Figure 12 Effect of the nutrient-enriching and retention formula on the nitrate nitrogen content of SeBC compost.

[0052] Figure 13 Effect of the emission-reduction and gas-control formula on the methane emission flux of SeBC compost.

[0053] Figure 14 Effect of the emission-reduction and gas-control formula on the cumulative methane emissions of SeBC compost.

[0054] Figure 15 Effect of the emission-reduction and gas-control formula on the nitrous oxide emission flux of SeBC compost.

[0055] Figure 16 Effect of the emission-reduction and gas-control formula on the cumulative nitrous oxide emissions of SeBC compost.

[0056] Figure 17 Effect of the emission-reduction and gas-control formula on the carbon dioxide emission flux of SeBC compost.

[0057] Figure 18 Effect of the emission-reduction and gas-control formula on the cumulative carbon dioxide emissions of SeBC compost.

[0058] Figure 19 Impact of the emission reduction and air control type formula on the global warming potential of SeBC compost Specific implementation mode

[0059] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0060] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0061] Example 1 Preparation and characterization of SeBC (1) Preparation of biochar (BC): Collect Bidens pilosa L. and air-dry it, then evenly cut it into lengths of about 2 - 3 cm by a cutting machine; remove impurities from chicken manure and crush it into uniform small pieces (diameter < 5 cm); collect the shells of the invasive animal Pomacea canaliculata, wash, dry, crush, and sieve through a 60-mesh sieve. Subsequently, the shell BC is obtained by pyrolyzing the shells in a muffle furnace at 342 °C for 2 h. (2) Preparation of modified biochar (MBC): Grind the BC and sieve it through a 100-mesh nylon screen. Use a mixed solution of Fe 3+ 、Fe 2+ (molar ratio 2.72) and BC to prepare MBC by chemical co-precipitation method in an alkaline medium (NaOH). (3) Preparation of selenium-loaded composite biochar (SeBC): Add a certain amount of BC and MBC to a 0.03 g / L Se(IV) solution according to a mass ratio of 7:1. The solid-liquid ratio of BC and MBC to the Se(IV) solution is 0.5:1 (g / mL), and the pH is adjusted to neutral (pH 7.0). Oscillate and adsorb at 180 r / min for 24 h at 25 °C to obtain SeBC.

[0062] Use a scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) (ZEISS Merlin compact, Carl Zeiss, Germany) to qualitatively analyze the surface morphology characteristics and element distribution of biochar before and after loading. The acceleration voltage is 20 V - 30 kV, and the elemental mass characteristics of the phosphorus crystallization products on the biochar surface are analyzed by an X-ray energy spectrometer (EDS).

[0063] The SEM-EDS of MBC and SeBC are as Figure 1 shown. The SEM results are as shown in (I) - (II) in Figure 1 . It can be seen from the figure that there are certain differences in the surface morphology of biochar before and after loading. The surface structure of MBC is compact, and the pore sizes are different ( Figure 1In (I)). During the carbonization process, energy may be released from the pores of the material, making the surface of biochar rougher. Some studies have shown that carbonization is of great significance for the changes in the pores of biochar. SeBC is rough, loose, and porous, with many small particles attached to its surface ( Figure 1 In (II)). The EDS results are as Figure 1 shown in (III) - (IV) below. After loading, the C content on the surface of biochar decreases, and the O content increases. The O / C can characterize the polarity strength of biochar. Among them, the mass percentage of Fe in MBC is 24.48%, the mass percentage of O is 43.13%, and the Fe - O ratio is 0.57 ( Figure 1 in (III)); the mass percentage of Se in SeBC is 0.21%, the mass percentage of Fe is 10.15%, and the mass percentage of O is 43.44% ( Figure 1 in (IV)). There is Fe on the surface of MBC ( Figure 1 in (III)), and there are Fe and Se on the surface of SeBC ( Figure 1 in (IV)). This indicates that Fe and Se have been successfully loaded onto the surface of biochar.

[0064] The Brunauer - Emmett - Teller (BET) adsorption - desorption method was used to evaluate the surface area, pore volume, and pore diameter of MBC and SeBC, and the results are shown in Table 1. According to the International Union of Pure and Applied Chemistry (IUPAC), pores are classified into micropores (size < 2 nm), mesopores (size = 2 - 50 nm), and macropores (size > 50 nm). The results show that the specific surface area and pore volume of SeBC are 26.37 m 2 ² / g and 0.09 cm 2 ³ / g, respectively. Compared with MBC, after loading, the specific surface area of SeBC increased by 10.58%, and the pore volume increased by 33.33%. The average pore diameter of MBC before loading was 10.39 nm, and the average pore diameter of SeBC after loading was 13.78 nm, with an increase of 24.68%. The results indicate that after the loading treatment, the specific surface area, pore volume, and pore diameter of biochar are all improved compared to the unloaded biochar. The increase in specific surface area and pore volume can, on the one hand, promote the degradation of organic matter in compost and shorten the composting time; on the other hand, it enables biochar to adsorb more nutrients such as nitrogen, phosphorus, potassium, etc., reducing the loss of these nutrients during the composting process and also contributing to the emission of greenhouse gases. 3 / g, while contributing to the emission of greenhouse gases.

[0065] Table 1 BET characterization results of biochar before and after loading

[0066] Example 2 Effect of the temperature - prolonging and rapid - ripening formula on the temperature of SeBC compost (1)Collect Bidens pilosa, air-dry it, and evenly cut it into lengths of about 2 - 3 cm using a cutting machine; remove impurities from chicken manure and crush it into uniform small pieces (diameter < 5 cm); collect the shells of the invasive animal Pomacea canaliculata, wash, dry, crush them, and pass them through a 60-mesh sieve. Subsequently, use a muffle furnace to pyrolyze the shells at 342 °C for 2 h to obtain shell biochar (BC); grind this biochar and pass it through a 100-mesh nylon sieve. Use Fe 3+ and Fe 2+ (molar ratio of 2.72) mixed solution and biochar material to prepare MBC (MBC) by chemical co-precipitation method in an alkaline medium (NaOH); add a certain amount of BC and MBC to the Se(IV) solution according to a mass ratio of 1 - 3:1, with a solid-liquid ratio of BC and MBC to the Se(IV) solution of 0.5:1 (g / mL), and adjust the pH to neutral (pH 7.0). Oscillate and adsorb at 25 °C at 180 r / min for 24 h to obtain SeBC.

[0067] (2)Mix the materials described in step (1) (Bidens pilosa, chicken manure) evenly according to a carbon-nitrogen ratio of 25:1, that is, Bidens pilosa:chicken manure = 3:1 (mass ratio), and adjust the moisture content of the materials to 65%.

[0068] (3)Set up a control (CK) (without adding biochar) and treatment SeBC in the experiment. The mass ratio of BC and MBC in SeBC is 2:1, the Se(IV) concentration is 0.015 g / L, and the added mass ratio of SeBC is 6%. Both the control and SeBC treatments are carried out using commercial compost containers, and air is provided by an air pump.

[0069] (4)Observe the temperature in the compost pile during the composting process using a high-precision digital display thermometer, check and record the temperature of the compost pile of each treatment at 9:00 in the morning, 14:00 at noon, and 19:00 in the evening every day. The composting lasts for 35 days.

[0070] (5)Determination of weed seed activity: Determine the activity of weed seeds in the samples collected on the 35th day of composting. Weigh a certain amount of compost sample (fresh sample) into a tray and culture it in a light incubator at 28 °C - 32 °C for 20 - 25 days. During the experiment, replenish water every 2 - 3 days. Just spray the surface of the compost sample wet with a sprayer. Record the seed germination situation while replenishing water, and finally count the total number of germinated seeds during the experiment. Calculate the weed seed activity using the following formula (1): (1) The determination of weed seed activity in composting shows that no seeds germinated during the experiment. Bidens pilosa has been completely decomposed during the composting process, confirming that the seeds are completely inactivated and will not cause harm to the ecological environment, agricultural production, and human health.

[0071] Temperature is an important indicator reflecting microbial activities and organic matter degradation during the composting process. The temperature change trend during the composting process is as shown in Figure 2 . As can be seen from Figure 2 a, the thermophilic peak of the SeBC treatment is 55.5 °C. Compared with the control, the temperature of the treatment with added SeBC rises faster and lasts longer. As can be seen from Figure 2 b, with the rapid temperature rise at the initial stage of composting, the SeBC treatment lasts for a total of 6 days in the thermophilic stage (>55 °C), which is 2 days longer than the control. The SeBC treatment maintains >5 d at 55 °C, meeting the requirements for compost sanitation and humification. A compost temperature exceeding 55 °C is beneficial to killing pathogens in the compost and making it easier to obtain a harmless compost product.

[0072] Example 3 Influence of the temperature-prolonging and ripening-accelerating formula on the pH and electrical conductivity of SeBC compost Steps (1) to (3) are the same as in Example 1.

[0073] (4) Turn the compost materials and take samples on the 0th, 3rd, 6th, 11th, 16th, 21st, 28th, and 35th days of composting. Samples are taken from the top, side, center, and bottom using the multi-point sampling method and collected after turning and thorough mixing. One part of the fresh samples is stored at 4 °C for measuring the pH value and electrical conductivity (EC), and the other part is naturally dried, crushed, and sieved (0.5 mm) for measuring other indicators.

[0074] (5) Dilute the fresh samples of the compost samples and deionized water at a solid-liquid ratio of 1:10 ( w / v ). First, shake and adsorb at 25 °C in a constant-temperature shaker for 1 h, and then centrifuge at 4000 r / min for 5 min in a centrifuge to obtain the compost extract.

[0075] (6) Collect the extract and measure the pH value and EC value of the compost sample extract using a pH meter and an electrical conductivity meter, where both pH and EC have been calibrated using standard solutions.

[0076] The pH value of the acidity and alkalinity is an important environmental factor for the survival of microorganisms. The most suitable pH value is conducive to the growth and function of compost microorganisms and has a significant impact on the maturation process of compost. The change trend of the pH value during the composting process is shown in Figure 3As shown in the figure, in the early stage of composting, there were significant differences in the initial pH values between the CK and SeBC treatments, which was related to the alkalinity of SeBC. As the composting entered the thermophilic stage, the pH value gradually increased and reached a peak (9.03 - 9.08) on the 6th day. At the end of composting, the final pH value of the SeBC treatment was 0.3 units higher than that of the CK group, which might be due to the promotion of the degradation of organic acids in the compost by the SeBC treatment. At the end of composting, the pH values of the CK and SeBC treatments were between 8.1 and 8.4, meeting the optimal pH value (7.0 - 8.5) for efficient composting.

[0077] The electrical conductivity (EC) represents the concentration of soluble salts in the compost, and it is an important chemical index for evaluating the maturity and stability of compost. The dynamic changes of electrical conductivity during composting are as Figure 4 shown. At the beginning of composting, the EC value of the SeBC treatment was higher than that of CK, which might be due to the increased release of ammonium ions and salts caused by the enhanced biodegradation of organic matter during the thermophilic stage. At the end of composting, the EC value of CK was 2444.25 us / cm, and the EC value of the SeBC treatment was 2919.75 us / cm, indicating that the addition of SeBC could increase the EC value of the compost. Finally, the EC values of both the CK and SeBC treatments were lower than 4000 us / cm, suggesting that the compost products met the standards of safe organic fertilizers and had no negative impact on plants when directly applied.

[0078] Example 4 Effects of the temperature - extending and rapid - ripening formula on the germination index and ash content of SeBC compost Steps (1) - (3) are the same as in Example 1.

[0079] (4) Determination of the germination index (GI): Put the fresh compost sample on the 35th day into a centrifuge tube, add ultrapure water according to the solid - liquid ratio of 1:10, place the centrifuge tube in a constant - temperature shaker, and shake it at a speed of 180 r / min for 1 h at 25 °C for extraction. After shaking, centrifuge it at 4000 r / min for 5 min, and the supernatant obtained after filtration is the compost extract. Then, place filter paper and 10 plump lettuce ( Lactuca sativa var. ramosa Hort.) seeds in a petri dish in sequence, add 10 mL of the compost extract, use distilled water as a blank control, and place the petri dish in a constant - temperature incubator at 25 °C for dark cultivation for 48 h. After 48 h, measure the number of germinated seeds and their root lengths. Calculate the seed germination index (GI) using formula (2).

[0080] (2) (5)Determination of ash content: Differential weight determination was used. The fresh compost sample was dried in an oven at 105 °C until a constant weight (M1, g) was achieved. After reaching a constant weight, the crucible containing the sample was placed in a muffle furnace and baked at 600 °C for 2 h. After cooling to room temperature, it was taken out and weighed (M2, g), and the ash content of the compost was calculated using formula (3): (3) The seed germination index (GI) is an indicator for determining the quality, maturity, and phytotoxicity of compost. Therefore, in order to evaluate the quality and toxicity of the compost mixture, the present invention conducted a seed germination experiment as a basis for examining its characteristics. The changes in the germination index of the compost are as Figure 5 shown. The GI values of the compost materials treated with CK and SeBC both reached over 85% after composting. The seed germination rates of CK and SeBC treatments were 86% and 100% respectively. Compared with the control, the GI value of the SeBC treatment was higher, and the addition of SeBC improved the degree of compost maturity. When GI > 80%, the final compost product can be considered suitable for agricultural production. According to the research of Wang et al. (Wang Z, Ding Y, Ren X, et al . Effect of micronutrient selenium on greenhouse gas emissions and related functional genes during goat manure composting[J]. Bioresource Technology, 2022, 349: 126805.), the seed germination index of directly applying selenite fertilizer was 84.95%, while in the SeBC compost of the present invention, the seed germination index reached 100%. Compared with directly adding selenite, it significantly stimulated seed germination and increased its root activity.

[0081] Ash is an indicator reflecting the organic matter content of compost and represents the biodegradability of organic matter. The changes in the ash of the compost are as Figure 6 shown. The initial volatile solid content was affected by the SeBC added to the compost mixture. Its initial ash content was 75%, while the initial ash of CK was 73%. After 35 days of the composting process, the ash contents of CK and SeBC treatments decreased to about 55% respectively. At the end of the thermophilic stage, the loss of organic matter decreased, and the ash reduction rate decreased, indicating that the compost had reached a relatively high stability.

[0082] Example 5 Effect of the nutrient retention-enhancing formula on the organic matter and nutrient contents of SeBC compost (1) Collect Bidens pilosa, air-dry it, and cut it into 2-3 cm long pieces by a cutting machine; remove impurities from chicken manure and crush it into uniform small pieces (diameter <5 cm); collect the shells of the invasive animal Pomacea canaliculata, clean, dry, crush and pass through a 60-mesh sieve, and then use a muffle furnace to pyrolyze the shells at 342°C for 2 hours to obtain shell biochar (BC); grind the biochar through a 100-mesh nylon sieve. 3+ , Fe 2+ MBC was prepared by chemical co-precipitation of a mixed solution of BC (molar ratio 2.72) and biochar material in an alkaline medium (NaOH). A certain amount of BC and MBC was added to Se(IV) solution in a mass ratio of 4-6:1, the solid-liquid ratio of BC and MBC to Se(IV) solution was 0.5:1 (g / mL), and the pH was adjusted to neutral (pH 7.0). SeBC was obtained by oscillating and adsorbing at 180 r / min for 24 h at 25°C.

[0083] (2) The materials described in step (1) (Bidens pilosa and chicken manure) are mixed evenly according to a carbon-nitrogen ratio of 25:1, that is, Bidens pilosa: chicken manure = 3:1 (mass ratio), and the moisture content of the materials is adjusted to 65%.

[0084] (3) Experimental setup: control (CK) (no biochar added) and SeBC treatment, the mixed mass ratio of BC and MBC in SeBC was 5:1, the Se(IV) concentration was 0.03 g / L, and the added mass ratio of SeBC was 10%. Both the control and SeBC treatments were piled in commercial composting containers, and air was provided by an air pump.

[0085] (4) Turn the composting materials and take samples on days 0, 3, 6, 11, 16, 21, 28 and 35 of composting. Samples are collected from the top, side, center and bottom using a multi-point sampling method after turning over and thoroughly mixing.

[0086] (5) Determination of weed seed activity: The determination method was the same as in Example 1. The determination of weed seed activity in compost showed that no seeds germinated during the test period. Bidens pilosa was completely decomposed during the composting process, confirming that the seeds were completely inactivated and would not cause harm to the ecological environment, agricultural production and human health.

[0087] (6) The organic matter content of compost is determined by potassium dichromate oxidation-external heating method; the total nitrogen content is determined by semi-micro Kjeldahl method; the total phosphorus content is determined by potassium hydroxide fusion-molybdenum antimony countercolorimetry method; the total potassium content is determined by potassium hydroxide fusion-flame photometry.

[0088] Organic matter (OM) is a necessary condition for the survival and reproduction of microorganisms. The degree of maturity of compost can be understood by the changes in organic matter during composting. Figure 7As shown, with the continuous progress of composting, the OM content in the CK and SeBC treatments showed a downward trend. When the compost was mature, the OM degradation rates in the CK and SeBC treatments were 13% and 16% respectively, indicating that the addition of SeBC might promote the degradation of OM. This shows that biochar provides a more suitable environment for microorganisms, enhances microbial activity, and thus promotes the degradation of organic matter.

[0089] The changes in total nitrogen during the composting process are as Figure 8 shown. At the initial stage of composting, the total nitrogen content in the CK and SeBC treatments decreased slightly. As composting progressed, the total nitrogen content gradually increased. This is attributed to the decomposition of organic nitrogen into ammonium nitrogen by microorganisms and then volatilization in the form of ammonia. After composting, the total nitrogen contents in the CK and SeBC treatments were 15 g / kg and 19 g / kg respectively. The increase in TN content might be due to the slower degradation rate of nitrogen compounds compared to carbonaceous compounds.

[0090] Appropriate phosphorus (P) can effectively promote the growth and cell proliferation of microorganisms. During the composting process, the TP content in the CK and SeBC treatments showed an increasing trend with the prolongation of composting time, as Figure 9 shown. At the beginning of composting, the TP contents in the CK and SeBC treatments were 5.1 g / kg and 4.9 g / kg respectively. After composting, the TP contents in both the CK and SeBC treatment groups increased to varying degrees. The results show that the TP content in the compost product increased, and the TP content under the Se BC treatment was lower than that under CK, which might be due to the "concentration effect" caused by the decomposition of organic matter and microbial metabolism during composting, while the addition of biochar reduced the loss of organic matter during composting.

[0091] The changes in total potassium (TK) during the composting process are as Figure 10 shown. The TK contents in both the CK and SeBC treatments showed an increasing trend. As the composting time prolonged, compared with CK, the TK content in the SeBC treatment increased by 3.3%. The increase in the TK content of CK was smaller compared to the SeBC treatment, indicating that the SeBC treatment could effectively retain TK.

[0092] Example 7 Effect of nutrient retention and fixation formula on the ammonium nitrogen and nitrate nitrogen contents in SeBC compost Steps (1) to (3) are the same as in Example 4.

[0093] (4) Turn the composting materials and take samples on the 0th, 3rd, 6th, 11th, 16th, 21st, 28th, and 35th days of composting. The samples are taken from the top, side, center, and bottom using the multi-point sampling method and collected after turning and thorough mixing.

[0094] (5) Ammonium nitrogen (NH 4 +The determination of the content of ammonium nitrogen (NH₄⁺-N) was carried out by the phenol-hypochlorite colorimetric method; the determination of the content of nitrate nitrogen (NO₃⁻-N) was carried out by ultraviolet spectrophotometry. 3 – According to the HKORC standard, the NH₄⁺-N content in mature compost must be less than 500 mg / kg for safe use. The change trend of ammonium nitrogen (NH₄⁺-N) during the composting process is as

[0095] shown. At the initial stage of composting, the NH₄⁺-N in CK and selenium-loaded biochar treatments increased rapidly and reached the peak on the 3rd day. Among them, the NH₄⁺-N content under the selenium-loaded biochar treatment was the highest, reaching 1756 mg / kg. As the composting proceeded, the NH₄⁺-N content in each treatment gradually decreased. The decrease in the NH₄⁺-N content of CK was less and slower. As the composting proceeded, the ammonium nitrogen content in the compost gradually stabilized, and at this time the compost basically reached the mature state. 4 + -N content must be less than 500 mg / kg for safe use. The change trend of ammonium nitrogen (NH₄⁺-N) during the composting process is as 4 + shown. At the initial stage of composting, the NH₄⁺-N in CK and selenium-loaded biochar treatments increased rapidly and reached the peak on the 3rd day. Among them, the NH₄⁺-N content under the selenium-loaded biochar treatment was the highest, reaching 1756 mg / kg. As the composting proceeded, the NH₄⁺-N content in each treatment gradually decreased. The decrease in the NH₄⁺-N content of CK was less and slower. As the composting proceeded, the ammonium nitrogen content in the compost gradually stabilized, and at this time the compost basically reached the mature state. Figure 11 shown. At the initial stage of composting, the NH₄⁺-N in CK and selenium-loaded biochar treatments increased rapidly and reached the peak on the 3rd day. Among them, the NH₄⁺-N content under the selenium-loaded biochar treatment was the highest, reaching 1756 mg / kg. As the composting proceeded, the NH₄⁺-N content in each treatment gradually decreased. The decrease in the NH₄⁺-N content of CK was less and slower. As the composting proceeded, the ammonium nitrogen content in the compost gradually stabilized, and at this time the compost basically reached the mature state. 4 + -N increased rapidly and reached the peak on the 3rd day. Among them, the NH₄⁺-N content under the selenium-loaded biochar treatment was the highest, reaching 1756 mg / kg. As the composting proceeded, the NH₄⁺-N content in each treatment gradually decreased. The decrease in the NH₄⁺-N content of CK was less and slower. As the composting proceeded, the ammonium nitrogen content in the compost gradually stabilized, and at this time the compost basically reached the mature state. 4 + -N content gradually decreased. The decrease in the NH₄⁺-N content of CK was less and slower. As the composting proceeded, the ammonium nitrogen content in the compost gradually stabilized, and at this time the compost basically reached the mature state. 4 + -N content gradually decreased. The decrease in the NH₄⁺-N content of CK was less and slower. As the composting proceeded, the ammonium nitrogen content in the compost gradually stabilized, and at this time the compost basically reached the mature state. 4 + -N content decreased less and slower. As the composting proceeded, the ammonium nitrogen content in the compost gradually stabilized, and at this time the compost basically reached the mature state.

[0096] The change of nitrate nitrogen (NO₃⁻-N) during the composting process is as 3 – shown. As the composting proceeded, during ammonia oxidation (AOB; oxidizing NH₄⁺-N to form NO₃⁻-N) and nitrite oxidation (NOB; oxidizing NO₂⁻-N to form NO₃⁻-N), nitrifying bacteria proliferated rapidly, and a large amount of ammonia nitrogen was converted into nitrate nitrogen. Therefore, the nitrate nitrogen content increased rapidly at the initial stage of composting. At the end of composting, there were significant differences in the change of nitrate nitrogen content between CK and SeBC treatments, and the increase in nitrate nitrogen content in CK was less. This difference may be due to the addition of SeBC, which is beneficial to the accumulation of nitrate nitrogen in the compost. The high porosity of SeBC enables microorganisms to better adsorb on its surface, and it will also increase the looseness of the compost pile, increase the oxygen flux and promote nitrification, resulting in the accumulation of nitrate nitrogen during the composting process. Figure 12 shown. As the composting proceeded, during ammonia oxidation (AOB; oxidizing NH₄⁺-N to form NO₃⁻-N) and nitrite oxidation (NOB; oxidizing NO₂⁻-N to form NO₃⁻-N), nitrifying bacteria proliferated rapidly, and a large amount of ammonia nitrogen was converted into nitrate nitrogen. Therefore, the nitrate nitrogen content increased rapidly at the initial stage of composting. At the end of composting, there were significant differences in the change of nitrate nitrogen content between CK and SeBC treatments, and the increase in nitrate nitrogen content in CK was less. This difference may be due to the addition of SeBC, which is beneficial to the accumulation of nitrate nitrogen in the compost. The high porosity of SeBC enables microorganisms to better adsorb on its surface, and it will also increase the looseness of the compost pile, increase the oxygen flux and promote nitrification, resulting in the accumulation of nitrate nitrogen during the composting process. 4 + -N to form NO₃⁻-N) and nitrite oxidation (NOB; oxidizing NO₂⁻-N to form NO₃⁻-N), nitrifying bacteria proliferated rapidly, and a large amount of ammonia nitrogen was converted into nitrate nitrogen. Therefore, the nitrate nitrogen content increased rapidly at the initial stage of composting. At the end of composting, there were significant differences in the change of nitrate nitrogen content between CK and SeBC treatments, and the increase in nitrate nitrogen content in CK was less. This difference may be due to the addition of SeBC, which is beneficial to the accumulation of nitrate nitrogen in the compost. The high porosity of SeBC enables microorganisms to better adsorb on its surface, and it will also increase the looseness of the compost pile, increase the oxygen flux and promote nitrification, resulting in the accumulation of nitrate nitrogen during the composting process. 2 - -N) and nitrite oxidation (NOB; oxidizing NO₂⁻-N to form NO₃⁻-N), nitrifying bacteria proliferated rapidly, and a large amount of ammonia nitrogen was converted into nitrate nitrogen. Therefore, the nitrate nitrogen content increased rapidly at the initial stage of composting. At the end of composting, there were significant differences in the change of nitrate nitrogen content between CK and SeBC treatments, and the increase in nitrate nitrogen content in CK was less. This difference may be due to the addition of SeBC, which is beneficial to the accumulation of nitrate nitrogen in the compost. The high porosity of SeBC enables microorganisms to better adsorb on its surface, and it will also increase the looseness of the compost pile, increase the oxygen flux and promote nitrification, resulting in the accumulation of nitrate nitrogen during the composting process. 2 - -N to form NO₃⁻-N) and nitrite oxidation (NOB; oxidizing NO₂⁻-N to form NO₃⁻-N), nitrifying bacteria proliferated rapidly, and a large amount of ammonia nitrogen was converted into nitrate nitrogen. Therefore, the nitrate nitrogen content increased rapidly at the initial stage of composting. At the end of composting, there were significant differences in the change of nitrate nitrogen content between CK and SeBC treatments, and the increase in nitrate nitrogen content in CK was less. This difference may be due to the addition of SeBC, which is beneficial to the accumulation of nitrate nitrogen in the compost. The high porosity of SeBC enables microorganisms to better adsorb on its surface, and it will also increase the looseness of the compost pile, increase the oxygen flux and promote nitrification, resulting in the accumulation of nitrate nitrogen during the composting process. 3 - -N bacteria, nitrifying bacteria proliferated rapidly, and a large amount of ammonia nitrogen was converted into nitrate nitrogen. Therefore, the nitrate nitrogen content increased rapidly at the initial stage of composting. At the end of composting, there were significant differences in the change of nitrate nitrogen content between CK and SeBC treatments, and the increase in nitrate nitrogen content in CK was less. This difference may be due to the addition of SeBC, which is beneficial to the accumulation of nitrate nitrogen in the compost. The high porosity of SeBC enables microorganisms to better adsorb on its surface, and it will also increase the looseness of the compost pile, increase the oxygen flux and promote nitrification, resulting in the accumulation of nitrate nitrogen during the composting process.

[0097] Example 8 Effect of Emission Reduction and Gas Control Formula on Greenhouse Gas Emissions from SeBC Compost (1) Collect Bidens pilosa, air-dry it, and cut it into 2-3 cm long pieces by a cutting machine; remove impurities from chicken manure and crush it into uniform small pieces (diameter <5 cm); collect the shells of the invasive animal Pomacea canaliculata, clean, dry, crush and pass through a 60-mesh sieve, then use a muffle furnace to pyrolyze the shells at 342°C for 2 hours to obtain shell biochar (BC); grind the biochar through a 100-mesh nylon sieve. 3+ , Fe 2+ MBC was prepared by chemical co-precipitation of a mixed solution of BC (molar ratio 2.72) and biochar material in an alkaline medium (NaOH). A certain amount of BC and MBC was added to Se(IV) solution in a mass ratio of 7 to 9:1, the solid-liquid ratio of BC and MBC to Se(IV) solution was 0.5:1 (g / mL), and the pH was adjusted to neutral (pH 7.0). SeBC was obtained by oscillating and adsorbing at 180 r / min for 24 h at 25°C.

[0098] (2) The materials described in step (1) (Bidens pilosa and chicken manure) are mixed evenly according to a carbon-nitrogen ratio of 25:1, that is, Bidens pilosa: chicken manure = 3:1 (mass ratio), and the moisture content of the materials is adjusted to 65%.

[0099] (3) Experimental setting: control (CK) (no biochar added) and treatment (SeBC), the mass ratio of BC to MBC in SeBC was 8:1, the Se(IV) concentration was 0.05 g / L, and the mass ratio of SeBC was 15%. Both the control and SeBC treatments were piled in commercial composting containers, and air was provided by an air pump.

[0100] (4) Turn the composting materials and take samples on days 0, 3, 6, 11, 16, 21, 28 and 35 of composting. Samples are collected from the top, side, center and bottom using a multi-point sampling method after turning over and thoroughly mixing.

[0101] (5) Determination of weed seed activity: The determination method was the same as in Example 1. The determination of weed seed activity in compost showed that no seeds germinated during the test period. Bidens pilosa was completely decomposed during the composting process, confirming that the seeds were completely inactivated and would not cause harm to the ecological environment, agricultural production and human health.

[0102] (6) Greenhouse gas CH during composting 4 , CO 2 and N 2 O was collected from the composting device using a syringe with a three-head valve and measured using a gas chromatograph (A7890b, Agilent Technologies, USA). The gas chromatograph was equipped with an electron capture and flame ionization detector (FID) with a detection temperature of 250 °C, a column temperature of 60 °C, and a carrier gas of 99.99% high-purity N 2, the flow rate is 30 ml / min. Compost gas sampling is carried out every morning from 9:00 to 11:00. CH 4 , CO 2 and N 2 emission fluxes and cumulative emissions are calculated according to the following formula (4): (4) In the formula, V represents the greenhouse gas emission flux of each treatment (mg / d), Δc is the change in gas concentration (ppm) within the time interval, Δt (in days), M represents the molecular mass of the relevant gas (CH 4 , CO 2 and N 2 O are 16 g, 44 g and 44 g respectively), the ash is the volume occupied by 1 mol of gas at standard temperature and pressure (22.4 L), P is the atmospheric pressure (bar), P0 is the standard pressure (1.01×10 5 Pa), T is the temperature inside the compost bin (K), V is the headspace volume (L), in Kelvin; The trapezoidal integration rule is used to calculate the cumulative greenhouse gas emissions (mg), and the formula is as follows (5): (5) In the formula, F is the cumulative emissions between two consecutive measurements (mg), ta and tb are the time intervals between two measurements (d), and Fta and Ftb are the gas emission fluxes on the days of the two measurements (mg) respectively.

[0103] On a hundred-year scale, the global warming potential (GWP) of methane is 25 times that of CO 2 , and N 2 O is 298 times that of CO 2 , and the GWP calculation formula is as follows (6): (6) In the formula, F CH4 is the cumulative methane emissions during composting (mg), FN 2 O is the cumulative nitrous oxide emissions during composting (mg), and F CO2 is the cumulative carbon dioxide emissions during composting.

[0104] The methane (CH 4 ) emission rates of each treatment during the composting process are as Figure 13 shown. As composting progresses, the CH 4 emission rate tends to level off. After composting, the CH 4 emission rates of each treatment are CK (1.9 mg / d) > SeBC treatment (0.60 mg / d), where the CH 4The emission rates were all higher than those of other treatments, and the emission rate of the SeBC treatment was significantly lower than that of the CK. The cumulative methane (CH 4 ) emissions of each treatment during the composting process are as Figure 14 shown. The cumulative emissions of the CK and SeBC treatments showed that CK > SeBC treatment. Among them, the total emissions of the SeBC treatment were less, significantly lower than that of CK, indicating that SeBC can significantly reduce the cumulative emissions of CH 4 during composting.

[0105] Nitrous oxide (N 2 O) is produced by incomplete nitrification / denitrification and has a very high global warming potential (GWP). The N 2 O emission rates of the CK and SeBC treatments are as Figure 15 shown. As composting progresses, the nitrogen conversion efficiency slows down, the activity of denitrifying bacteria decreases, the formation rate of nitrous oxide slows down, and finally levels off until the end of composting. The nitrous oxide emission rates of each composting treatment were CK > SeBC treatment. The cumulative emissions of the CK and SeBC treatments are as Figure 16 shown. The nitrous oxide accumulation in the SeBC treatment was 34% less than that in the CK, significantly lower than that in the CK, confirming that the SeBC treatment has a significant effect on reducing the emissions of N 2 O released during composting.

[0106] Previous studies have shown that when sodium selenite solution is added to compost alone, compared with the control group, the emissions of methane (CH 4 ) and nitrous oxide (N 2 O) were reduced by 18.4% and 29.7% respectively. When biochar is added to compost alone, the emissions of methane (CH 4 ) and nitrous oxide (N 2 O) were reduced by 54.4% and 36.1% respectively. In summary, the research results of this invention have verified the feasibility of coupling selenium and biochar in composting. When SeBC is applied, the methane emissions from composting are reduced by 59%, and the nitrous oxide emissions are reduced by 43%.

[0107] Table 1 Effects of single application of selenium, biochar, and combined application of selenium and biochar in composting on greenhouse gases

[0108] References: Wang Z, Ding Y, Ren X, et al. Effect of micronutrientselenium on greenhouse gas emissions and related functional genes during goatmanure composting[J]. Bioresource Technology, 2022,349:126805. Mao H, Lv Z, Sun H, et al . Improvement of biochar and bacterial powderaddition on gaseous emission and bacterial community in pig manure compost[J]. Bioresource Technology, 2018,258:195-202. The dynamic distribution map of carbon dioxide (CO 2 ), as shown below, reveals the activity intensity of microorganisms during composting, such as Figure 17 shown. At the beginning of composting, the CO 2 emissions of the CK and SeBC treatments increased rapidly and then gradually decreased and stabilized on the 20th day. At the initial stage of composting, both the CK and SeBC treatments showed relatively high CO 2 gas emissions, and the emission peaks of both the CK and SeBC treatments occurred within the first 5 days of composting. The cumulative CO 2 emissions are as Figure 18 shown. According to the cumulative emissions, it was found that the cumulative emissions of CK were the largest, at 13958.62 mg, significantly higher than those of the SeBC treatment. The results indicate that the composting treatment with SeBC addition can reduce the total CO 2 emissions compared to CK.

[0109] The global warming potential (GWP) measures the warming impact of greenhouse gases based on 1 g of CO 2 . 1 g of CH 4 is equivalent to 25 g of CO 2 and 1 g of N 2 O is equivalent to 298 g of CO 2 . The GWP values in the compost after the CK and SeBC treatments are as Figure 19 shown. The results show that the GWP of N 2 O accounts for 86% of the total GWP, indicating that N 2O is a major contributor to GWP. Compared with CK, the GWP under SeBC treatment decreased by 46%, indicating that SeBC treatment significantly reduced the GWP value of compost. SeBC treatment can not only reduce the emissions of N 2 O, CH 4 and CO 2 during the co-composting of invasive plants and livestock manure, but also reduce air pollution and mitigate the risk of global warming.

Claims

1. A method for preparing selenium-loaded composite biochar, characterized in that: The steps include: S1. washing, drying, crushing, sieving, and pyrolyzing the shells of Pomacea canaliculata to obtain Pomacea canaliculata shell biochar; S2. Grind and sieve the biochar from the shell of Pomacea canaliculata, and use Fe 3+ with Fe 2+ The mixed solution was chemically co-precipitated in an alkaline medium to prepare iron-modified biochar; S3. Add the Pomacea canaliculata shell biochar of step S1 and the iron-modified biochar of step S2 to a Se(IV) solution with a concentration of 0.01 to 0.06 g / L in a mass ratio of 1 to 9:1, adjust the pH to neutral, and perform oscillation adsorption to obtain selenium-loaded composite biochar.

2. The preparation method according to claim 1, characterized in that: The pyrolysis in step S1 is pyrolysis at 300-400° C. for 1.5-2.5 hours.

3. The preparation method according to claim 1, characterized in that: Step S2: Fe 3+ with Fe 2+ Fe in mixed solution 3+ with Fe 2+ The molar ratio is 2.5~3.

4. Selenium-loaded composite biochar prepared by the preparation method according to any one of claims 1 to 3.

5. Use of the selenium-loaded composite biochar according to claim 4 as a compost selenium source additive in invasive organism composting.

6. A formula for selenium-rich compost of invasive organisms, characterized in that: The compost raw materials include the invasive plant Bidens pilosa and chicken manure, and the selenium-loaded composite biochar described in claim 4 is a compost selenium source additive; the carbon-nitrogen ratio of the compost raw material is 20-30:1, and the moisture content of the compost material is 60-70%; the added mass proportion of the selenium-loaded composite biochar is 3%-16%.

7. The invasive organism selenium-rich compost formula according to claim 6, characterized in that: When preparing the selenium-loaded composite biochar, the mass ratio of the Pomacea canaliculata shell biochar to the iron-modified biochar is 1-3:1, and the selenium Se(IV) concentration is 0.01-0.02 g / L; the added mass ratio of the selenium-loaded composite biochar is 3%-8%.

8. The invasive organism selenium-rich compost formula according to claim 6, characterized in that: When preparing the selenium-loaded composite biochar, the mass ratio of the Pomacea canaliculata shell biochar to the iron-modified biochar is 4-6:1, and the selenium Se(IV) concentration is 0.02-0.04 g / L; the added mass ratio of the selenium-loaded composite biochar is 9%-12%.

9. The invasive organism selenium-rich compost formula according to claim 6, characterized in that: When preparing the selenium-loaded composite biochar, the mass ratio of the Pomacea canaliculata shell biochar to the iron-modified biochar is 7-9:1; the selenium Se(IV) concentration is 0.04-0.06 g / L; and the added mass ratio of the selenium-loaded composite biochar is 13%-16%.

10. A method for preparing selenium-rich compost of invasive organisms based on the formula of selenium-rich compost of invasive organisms according to any one of claims 6 to 9, characterized in that: The invasive organism selenium-enriched compost formula according to any one of claims 6 to 9 is aerobically composted at 26 to 35° C. for 30 to 40 days to obtain selenium-loaded composite biochar compost, namely, invasive organism selenium-enriched compost.

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