A method and device for producing selenium-rich liquid fertilizer using invasive organisms and agricultural waste

Abstract

This invention discloses a method and apparatus for producing selenium-enriched liquid fertilizer using invasive organisms and agricultural waste. The method involves mixing the invasive organism *Alternanthera philoxeroides* and agricultural waste rice straw in a specific ratio, then using the invasive animal *Pomacea canaliculata* to biotransform the mixture. Different forms of selenium source are added to the biotransformation residue, and selenium-enriched liquid fertilizer is prepared using an aerobic liquid composting fermentation method. The composting apparatus consists of a composting bin, an automatic oxygen supply mechanism, and an intelligent temperature control mechanism, enabling fully automated management, simple operation, and no cumbersome setup. It is suitable for the efficient production of selenium-enriched liquid compost. This invention not only provides a new approach for the green production of selenium-enriched liquid compost from invasive organisms and agricultural waste, but also provides a new technology of "high-temperature composting, nutrient enrichment, and low-carbon environmental protection," realizing the resource utilization of invasive organisms and agricultural waste by converting them into selenium-enriched liquid compost, turning harm into benefit and waste into treasure.

Description

Technical Field

[0001] This invention relates to the field of invasive species and agricultural waste resource utilization technology. Specifically, it relates to a method and apparatus for producing selenium-enriched liquid fertilizer using invasive species and agricultural waste. More specifically, it relates to a method and apparatus for producing low-carbon selenium-enriched liquid fertilizer by combining material pretreatment with selenium-enriched liquid aerobic composting. Background Technology

[0002] Biological invasion refers to the process by which organisms enter a new habitat from their original habitat through human or non-human means, causing ecological damage and socio-economic losses. Invasive species have extremely strong adaptability and reproductive capacity. They seize resources, change habitat conditions, reduce the biodiversity of native species, weaken the stability of ecosystems, and pose a continuous threat to agriculture, forestry, fisheries, and public health.

[0003] Hollow lotus ( Alternanthera philoxeroides (Mart.) Griseb), commonly known as water peanut, also called drought-loving lotus grass, hollow amaranth, or revolutionary grass, is a species of lotus in the genus Alternanthera of the family Amaranthaceae, native to South America. Alternanthera Alternanthera philoxeroides is a perennial herbaceous plant with rhizomes. It has now spread to many parts of the world and is considered one of the world's most notorious weeds. It thrives in warm, humid environments and is amphibious, spreading rapidly in lakes, ponds, swamps, ditches, paddy fields, vegetable gardens, dry fields, orchards, rivers, and roadsides. Its plants reproduce asexually through rhizome segments, exhibiting extremely strong regenerative capacity and an astonishingly fast spread rate; once established, it is difficult to eradicate completely. Currently, the large amount of fresh plant matter produced after controlling Alternanthera philoxeroides is often disposed of through dumping or landfill due to a lack of efficient utilization technology, which occupies land, causes secondary pollution, and results in a low resource utilization rate. Therefore, it is urgent to develop new high-value utilization pathways for Alternanthera philoxeroides, including energy, fertilizer, feed, and substrate applications, to achieve a synergistic promotion of "turning a pest into a treasure" and "green pest control."

[0004] Golden apple snail ( Pomacea canaliculata Native to the Amazon rainforest in South America, the golden apple snail (Pomacea canaliculata), also known as the apple snail or snow snail, is an amphibian freshwater mollusc and is listed as one of the world's 100 most dangerous invasive alien species. Lacking natural predators, the golden apple snail consumes large quantities of aquatic plants, disrupting the balance of aquatic ecosystems and causing significant negative impacts on native ecosystems and agricultural production in my country. Therefore, as a typical invasive alien animal, the golden apple snail urgently requires more effective integrated management measures and strengthened research on resource utilization to achieve effective ecosystem protection and sustainable agricultural development.

[0005] Traditional methods for controlling invasive species mainly include physical removal, chemical control, and biological control. However, these methods often suffer from drawbacks such as high cost, low efficiency, and secondary pollution. In recent years, resource utilization has gradually become a new direction for invasive species control. By transforming invasive species into valuable resources, not only can their environmental damage be reduced, but a win-win situation of ecological and economic benefits can also be achieved.

[0006] Selenium (Se) is an essential trace element for organisms. Currently, the production of selenium-enriched fertilizers mainly relies on chemical synthesis methods, which suffer from high costs and environmental unfriendliness. Chemical synthesis of selenium-enriched liquid fertilizers typically requires chemical reagents, resulting in high energy consumption and significant pollution during the production process. Furthermore, the form and content of selenium in the product are difficult to control precisely. Physical doping of selenium-enriched liquid fertilizers is also costly and poses potential risks to the environment and human health. The preparation of selenium-enriched liquid compost through bio-fermentation has attracted research attention; however, current research on bio-synthetic selenium-enriched liquid fertilizers, both domestically and internationally, is limited by raw material costs and availability, resulting in a relatively singular technological approach. Regarding the preparation of selenium-enriched fertilizers using invasive organisms, Chinese patent application CN119528622A discloses a formula and preparation method for invasive organism-enriched selenium compost, including compost materials and a selenium source. The compost materials are *Mikania micrantha* and *Pomacea canaliculata* meat, with *Pomacea canaliculata* meat serving as the nitrogen source and *Mikania micrantha* as the carbon source. However, this method suffers from a mismatch between carbon and nitrogen degradation rates, and *Mikania micrantha* has a high lignocellulose content, leading to slow natural degradation. Although the resource utilization of invasive organisms has been achieved to some extent, the slow degradation of their carbon sources leads to insufficient fermentation efficiency of selenium-enriched liquid fertilizer raw materials, long composting cycle, and low organic selenium conversion efficiency, making it difficult to achieve efficient and stable industrial production.

[0007] Agricultural waste refers to organic waste generated from agricultural production, animal husbandry, processing, and rural life. Agriculture produces a large amount of waste annually, but most of it is not fully utilized. In developing countries, the trend in agricultural development may make the use of agricultural waste as an energy source more attractive. In recent years, the energy utilization of agricultural waste has received increasing attention from scientists and the general public.

[0008] Currently, the synergistic resource utilization of selenium-enriched liquid fertilizer using invasive organisms and agricultural waste is still lacking, which is not conducive to reducing control costs and causes waste of biomass resources. At the same time, the production of selenium-enriched liquid fertilizer has problems such as high cost and high environmental risk, which restricts the sustainable development and ecological security of selenium-enriched agriculture. Summary of the Invention

[0009] The purpose of this invention is to overcome the above-mentioned defects and deficiencies in the prior art and to provide a method for producing selenium-enriched liquid fertilizer using invasive organisms and agricultural waste.

[0010] A second objective of this invention is to provide an apparatus for producing selenium-enriched liquid fertilizer using invasive organisms and agricultural waste.

[0011] The above-mentioned objective of this invention is achieved through the following technical solution: A method for producing selenium-enriched liquid compost using invasive species and agricultural waste includes the following steps: S1. The invasive plant Alternanthera philoxeroides and agricultural waste rice straw are washed, dried, and sieved, and then mixed in equal mass ratios to obtain compost material. S2. Feed the starved apple snails with the compost material from step S1 to carry out bioconversion; S3. Add selenium source to the mixed residue of compost material and golden apple snail after bioconversion in step S2 for aerobic composting fermentation. After completion, filter the supernatant, extract the compost residue, and combine the filtrates to obtain selenium-enriched liquid fertilizer.

[0012] Complete and highly active cellulase was detected in the liver and digestive secretions of *Pomacea canaliculata*, and significant endo-β-1,4-xylanase activity was found in the gastric juice and hepatopancreas of *Pomacea canaliculata*, demonstrating a marked ability to degrade soluble xylan. These enzymes can rapidly soften plants and release soluble carbon sources, making them suitable for pretreatment in the bioconversion of selenium-enriched liquid compost, providing a favorable foundation for the degradation of cellulose and hemicellulose in compost materials. Furthermore, both *Alternanthera philoxeroides* and rice straw, raw materials for selenium-enriched liquid compost, are rich in basic nutrients such as nitrogen, phosphorus, and potassium, and have complementary carbon-nitrogen ratios, possessing the potential to become high-quality compost substrates. Based on this, this invention addresses the dual environmental problems of invasive allium tuberosum and pollution from burning agricultural waste, rice straw, by proposing a new approach of "treating waste with waste and recycling nutrients": Invasive allium tuberosum and agricultural waste, rice straw, are mixed at a carbon-to-nitrogen ratio of approximately 22:1 (1:1 by dry weight). The mixture is first pretreated with golden apple snails for bioconversion, disrupting the lignin-cellulose composite structure. Then, the pretreated compost and the golden apple snail residue are mixed with a selenium source for aerobic composting fermentation, yielding selenium-enriched liquid fertilizer. This achieves the simultaneous harmlessness, functionalization, and high-value utilization of invasive organisms and agricultural waste, providing a new pathway for the resource utilization and low-carbon environmental protection of invasive organisms and agricultural waste.

[0013] This invention utilizes invasive animals to pre-convert invasive plants and large quantities of rice straw waste into a "biological pre-conversion-selenium-enriched fermentation" integrated composite technology to prepare selenium-enriched liquid fertilizer raw materials. This technology directly breaks through the existing framework of conventional raw materials and traditional methods for preparing selenium-enriched liquid fertilizer. Its core lies in fully utilizing the digestive capacity of invasive animals. While pre-treating invasive plants and agricultural straw, it completes the nutrient ratio of selenium-enriched liquid compost, significantly improving the fermentation efficiency of selenium-enriched liquid fertilizer raw materials. Currently, there is no biological pre-treatment technology that utilizes invasive animals to convert invasive plants and rice straw, nor is there any technology that uses this pre-treated raw material for combined aerobic liquid composting. Selenium element forms highly bioactive components through biological conversion. This composite technology can produce highly active and highly stable selenium-enriched liquid fertilizer through the synergistic effect of animal conversion and selenium bio-enrichment.

[0014] Furthermore, the drying temperature in step S1 is 58–62°C, and the mesh size of the sieve is 1–3 mm.

[0015] Furthermore, in step S2, the biotransformation involves feeding the starved golden apple snails with compost material daily at a temperature of 25–28°C, a pH of 7–8, and an aeration time of 12–14 h / d for 15–20 days.

[0016] Preferably, the temperature is 25-26°C, the pH is 7-8, and the aeration time is 13-14 hours per day.

[0017] More preferably, the temperature is 25.6℃, the pH is 7.12, and the aeration time is 13.30 h per day. At this temperature, the degradation rate of lignocellulose by the golden apple snails on the compost material reaches its maximum.

[0018] Preferably, the feeding amount is 60-80 g of compost material per day for 12-20 golden apple snails.

[0019] Preferably, the golden apple snail weighs 20-30 g, has a width of 4-5 cm, and a height of 4.5-5.5 cm.

[0020] Preferably, in order to add starved golden apple snails to a composting container filled with clean water and feed them compost materials for bioconversion, the clean water containing the golden apple snails has a pH of 6.6 to 8.5 and dissolved oxygen ≥ 6.8 ± 0.35 mg / L.

[0021] Preferably, the starvation treatment involves placing the golden apple snails in dechlorinated water for 24 hours to starve them.

[0022] Furthermore, the selenium source is composed of sodium selenite, sodium selenate, and / or nano-selenium, and the addition amount is 996.93–1909.67 mg / kg of mixed residue; the aerobic composting fermentation time is 21–30 days.

[0023] Preferably, during the aerobic composting fermentation process, aeration and oxygen supply are stopped for 5-10 minutes every 2-3 days, and the mixture is stirred 1-2 times.

[0024] As a preferred embodiment, the method includes the following steps: S1. Remove sand, gravel, and weeds from the collected invasive plant Alternanthera philoxeroides and agricultural waste rice straw, dry them separately, crush them, and sieve them for later use; the drying temperature is 60℃, and the mesh screen has a 2 mm aperture. S2. Mix the invasive plant *Alternanthera philoxeroides* and rice straw treated in step S1 at a mass ratio (dry weight) of 1:1 to obtain compost material; place 12-20 invasive animals of uniform weight and size, *Pomacea canaliculata*, in a compost container filled with clean water and feed them the compost material for bioconversion; the bioconversion temperature is 26-28℃, pH=7-8, aeration time is 12-14h / d, and bioconversion is carried out for 15-20 days, with a total daily feeding of 60-80 g; each *Pomacea canaliculata* weighs 20-30g, has a snail width of 4-5 cm, and a snail height of 4.5-5.5 cm.

[0025] S3. The bioconverted material from step S2 (a mixture of compost and golden apple snail residue) is mixed with selenium source and subjected to aerobic composting fermentation for 21–30 days. Aeration and oxygen supply are stopped for 5–10 minutes every 2–3 days, and the mixture is stirred 1–2 times. After the fermentation is completed, the supernatant is centrifuged and filtered, and the compost residue is repeatedly extracted three times to obtain selenium-enriched liquid fertilizer. The amount of selenium source added to the compost material is 996.93–1909.67 mg / kg mixed residue / 10L water. The centrifugation temperature is 4–8℃, the relative centrifugal force is 8000–10000 g, and the centrifugation time is 5–10 minutes.

[0026] This invention employs a three-factor, three-level response surface methodology, using *Pomacea canaliculata* (golden apple snail) to pretreat the invasive plant *Alternanthera philoxeroides* and agricultural waste rice straw through biotransformation. It then utilizes aerobic liquid composting technology, adding different proportions of selenium source to create three formulations for producing selenium-enriched liquid fertilizer: High-temperature composting selenium-enriched liquid compost formulation I (SeLC-I), Nutrient-enriched selenium-enriched liquid compost formulation II (SeLC-II), and Low-carbon emission-reduction selenium-enriched liquid compost formulation III (SeLC-III). The specific steps include: 1. The method for producing high-temperature composting selenium-enriched liquid compost formulation I (SeLC-I) is as follows: Steps S1 to S2 are the same as the preferred implementation method described above; Step S3 is basically the same as the preferred implementation method described above, except that the amount of selenium source added to the compost material is 1432.25 to 1909.67 mg / kg mixed residue / 10L clean water.

[0027] Further, the selenium source mentioned in step S3 is a compound of sodium selenite and sodium selenate in a ratio of 1:1.09. Specifically, in the compost material, the amount of sodium selenite added is 684.44–912.59 mg / kg mixed residue / 10L water, and the amount of sodium selenate added is 747.81–997.08 mg / kg mixed residue / 10L water. The resulting formula is a high-temperature composting type, which can effectively extend the high-temperature composting period of liquid compost, accelerate the composting process, and promote a more comprehensive and thorough decomposition of organic matter, thereby improving composting efficiency and quality. The liquid fertilizer obtained by this method is a high-temperature composting type selenium-enriched liquid compost formula I (SeLC-I).

[0028] Preferably, the sodium selenite addition amount is 782.22 mg / kg mixed residue / 10L water, and the sodium selenate addition amount is 854.64 mg / kg mixed residue / 10L water.

[0029] 2. The method for producing nutrient-enriched selenium-enriched liquid compost formulation II (SeLC-II) is as follows: Steps S1 to S2 are the same as the preferred implementation method described above; Step S3 is basically the same as the preferred implementation method described above, except that the amount of selenium source added to the compost material is 996.93 to 1332.59 mg / kg mixed residue / 10L water or 1060.3 to 1417.08 mg / kg mixed residue / 10L water.

[0030] Further, the selenium source mentioned in step S3 is a mixture of sodium selenite and nano-selenium in a ratio of 2.17:1 or a mixture of sodium selenate and nano-selenium in a ratio of 2.37:1. The sodium selenite content is 684.44–912.59 mg / kg mixed residue / 10L water, the sodium selenate content is 747.81–997.08 mg / kg mixed residue / 10L water, and the nano-selenium content is 312.50–420.00 mg / kg mixed residue / 10L water. The resulting formulation is nutrient-enriching, effectively improving the organic matter degradation rate and simultaneously increasing the total nitrogen, total phosphorus, and total potassium content of the compost. It also enhances the enrichment and retention of nitrogen, phosphorus, and potassium, effectively reducing nutrient loss. Furthermore, it can effectively regulate the nitrogen release rate, achieving a coordinated supply of ammonium and nitrate nitrogen, which helps reduce nitrogen volatilization and leaching, improve nitrogen utilization efficiency, and enhance the environmental friendliness and agricultural adaptability of fertilizers. The liquid fertilizer obtained by this method is nutrient-enriched selenium-enriched liquid compost formulation II (SeLC-II).

[0031] Preferably, the sodium selenite addition amount is 782.22 mg / kg mixed residue / 10L water, the sodium selenate addition amount is 854.64 mg / kg mixed residue / 10L water, and the nano selenium addition amount is 357.15 mg / kg mixed residue / 10L water.

[0032] 3. The application method of low-carbon emission reduction selenium-enriched liquid compost formulation III (SeLC-III) is as follows: Steps S1 to S2 are the same as the preferred implementation method described above; Step S3 is basically the same as the preferred implementation method described above, except that the amount of selenium source added to the compost material is 1163.15 to 1739.63 mg / kg mixed residue / 10L water.

[0033] Further, the selenium source mentioned in step S3 is a compound of sodium selenite, sodium selenate, and nano-selenium in an addition ratio of 2.19:2.39:1. Specifically, the addition amount of sodium selenite is 456.29–608.39 mg / kg mixed residue / 10L water, the addition amount of sodium selenate is 498.54–664.71 mg / kg mixed residue / 10L water, and the addition amount of nano-selenium is 208.32–466.67 mg / kg mixed residue / 10L water. The resulting formula is a low-carbon emission reduction type, which can effectively inhibit the emission of greenhouse gases such as methane (CH4) and nitrous oxide (N2O) during composting, providing a feasible path for emission reduction and efficiency improvement in green agriculture, achieving a win-win situation for environmental protection and economic benefits. The resulting liquid fertilizer is low-carbon emission reduction selenium-enriched liquid compost III (Se-LF III).

[0034] Preferably, the sodium selenite addition amount is 521.48 mg / kg mixed residue / 10L water, the sodium selenate addition amount is 569.76 mg / kg mixed residue / 10L water, and the nano selenium addition amount is 238.08 mg / kg mixed residue / 10L water.

[0035] This invention introduces a series of methods for synergistically regulating a composite selenium source by adding different forms of selenium sources during the aerobic composting fermentation stage. Employing an aerobic liquid composting fermentation method under suitable pH and intermittent aeration conditions, it ultimately produces a high-temperature matured, nutrient-rich, low-carbon, and environmentally friendly green selenium-enriched liquid compost. This achieves the simultaneous harmlessness, functionalization, and high-value utilization of invasive species and agricultural waste, providing a new pathway for the resource utilization and low-carbon environmental protection of invasive species and agricultural waste. Therefore, the integrated "biological pre-conversion-selenium-enriched fermentation" technology of this invention can produce an eco-friendly, highly efficient, nutrient-enriched, and low-carbon selenium-enriched liquid fertilizer, possessing significant scientific and application value.

[0036] The present invention also provides selenium-enriched liquid compost prepared by any of the methods described above.

[0037] Furthermore, to further reduce costs, the implementation of this composite technology requires integrated supporting equipment. Although conventional anaerobic fermentation reactors or liquid fertilizer fermentation tanks are disclosed in existing technologies, their functions are limited and they are not designed for the integrated composite technology of "biological preconversion-selenium enrichment fermentation". They cannot complete the preconversion of invasive plants and straw by invasive animals, nor can they control the fermentation process of selenium-enriched raw materials, which can easily lead to an increase in greenhouse gas emissions. They are only suitable for the degradation and composting of ordinary organic materials and lack the bioaccumulation of selenium and the enrichment of nutrients.

[0038] Therefore, the present invention also provides a selenium-enriched liquid composting device for implementing the above method, the device comprising a composting bin, an automatic oxygen supply mechanism for supplying oxygen to the material in the composting bin, and an intelligent temperature control mechanism for keeping the material in the composting bin warm. The composting bin includes a material container, a feeding bin, a material distributor, a sampling port, and a gas sampler. The feeding bin is funnel-shaped and fixed to the material container. The material distributor is inverted funnel-shaped and fixed below the feeding bin for allowing compost material to slide into the material container. The sampling port is located below the material container for collecting liquid compost. The gas sampler is installed on the outside of the material container for collecting greenhouse gases during the composting process. The automatic oxygen supply mechanism includes an automatic oxygenation pump and an air stone; the air stone is located at the bottom of the material container, and the automatic oxygenation pump is connected to the air stone to supply oxygen to it. The intelligent temperature control mechanism includes an insulation strip, an intelligent temperature monitor, and an intelligent temperature monitoring probe. The intelligent temperature monitoring probe is located at the bottom of the material container, and the intelligent temperature monitor is connected to the temperature monitoring probe to provide real-time temperature feedback. The insulation strip is located on the outer wall of the material container and adjusts the temperature in real time based on the feedback temperature information.

[0039] Furthermore, the material container is a PVC plastic drum.

[0040] Preferably, the material container is a PVC plastic bucket with a weight of 2.65 kg, a height of 64.5 cm, an outer diameter of 24 cm, an inner diameter of 22.5 cm, a bottom diameter of 31 cm, and a volume of 25 L.

[0041] Furthermore, the feeding bin is fixed to the material container by having symmetrical slots on both sides.

[0042] Preferably, the feeding hopper is funnel-shaped, with an upper diameter of 56cm, a lower diameter of 14cm, and a height of 18cm.

[0043] Preferably, the sampling port comprises two 1 / 4-inch ball core faucets and two small stainless steel filters, with the 1 / 4-inch ball core faucets having double sealing gaskets and a set of 1 / 4-inch internal thread bucket nuts.

[0044] Preferably, the gas sampler is composed of a 4mm*6mm corrosion-resistant silicone tubing of about 20cm and a YCG-S type three-way valve.

[0045] Preferably, there are two automatic oxygenation pumps, model ACO-002, with external dimensions of 145mm×85mm×95mm, voltage of 220V, power of 25W, pressure >0.025Mpa, exhaust volume of 40L / min, two 8-head diverters, 16 check valves, and one diverter pipe.

[0046] Preferably, the gas stone is a small cylindrical steel shot connected to a 4mm*6mm corrosion-resistant silicone hose.

[0047] Preferably, the insulation tape includes a heat tracing wire, a power cord, a leakage protection plug, and aluminum foil tape. The voltage is 220V, the width is 8mm, and the power consumption is 25W per meter when the intelligent temperature control structure is activated, and 6W per meter after the temperature is constant.

[0048] Preferably, the intelligent temperature monitor 4 has an ABS shell, a temperature range of -50℃ to 200℃, a length of 130mm, and a width of 96mm.

[0049] Preferably, the intelligent temperature monitoring probe 5 is a 304 stainless steel 1 / 2-inch threaded waterproof probe with a probe tube diameter of 6mm and an accuracy of ±0.1℃.

[0050] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for producing selenium-enriched liquid fertilizer using invasive species and agricultural waste. The method involves mixing the invasive species *Alternanthera philoxeroides* and agricultural waste rice straw in a specific ratio, then using the invasive animal *Pomacea canaliculata* to bioconvert the mixture. Different forms of selenium sources are added to the bioconversion residue, and the selenium-enriched liquid fertilizer is prepared using an aerobic liquid composting fermentation method. This invention utilizes the invasive animal *Pomacea canaliculata* to achieve the pre-conversion of the invasive plant *Alternanthera philoxeroides* and a large amount of rice straw waste, thus preparing raw materials for selenium-enriched liquid fertilizer. This integrated "biological pre-conversion-selenium-enrichment fermentation" technology directly breaks through the framework of existing conventional raw materials and traditional methods for preparing selenium-enriched liquid fertilizer. Its core lies in fully utilizing the digestive capacity of invasive animals, simultaneously pre-treating the invasive plants and agricultural straw while completing the nutrient ratio of the selenium-enriched liquid compost, significantly improving the fermentation efficiency of the selenium-enriched liquid fertilizer raw materials, shortening the composting maturity cycle, and increasing the conversion efficiency of organic selenium. Currently, there is no biological pretreatment technology that utilizes invasive animals to transform invasive plants and rice straw, nor is there any technology that uses this pretreated raw material for combined aerobic liquid composting. Selenium, through biotransformation, forms highly bioactive components. This composite technology, through the synergistic effect of animal transformation and selenium biofortification, can produce highly active and stable selenium-enriched liquid fertilizer. This invention not only streamlines the entire chain from "invasive species safety control—agricultural waste recycling—liquid selenium enrichment," but also significantly improves the bioavailability of selenium, achieving the triple goals of turning waste into treasure, increasing yield and quality, and protecting the environment. It provides a replicable and scalable new approach for green, high-value agriculture.

[0051] This invention opens up new pathways for the resource utilization of invasive species and agricultural waste, as well as the production of selenium-enriched liquid compost, achieving a highly efficient transformation from "high-temperature composting to nutrient enrichment to low-carbon and environmentally friendly processes." It not only transforms hazardous waste into selenium-enriched liquid compost but also significantly improves the nutrient content and environmental performance of the fertilizer, offering both economic and ecological benefits. Furthermore, the accompanying selenium-enriched liquid composting apparatus provided by this invention has a clear principle, is easy to operate, and features an automated structure. This apparatus is of great significance for promoting the resource utilization of agricultural waste, controlling invasive species, and enhancing the selenium content of liquid fertilizers, thus contributing to the sustainable development of agriculture. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the selenium-enriched liquid compost production device of the present invention. Figure 1 1 is the material container, 2 is the feeding bin, 3 is the material distributor, 4 is the sampling port, 5 is the gas sampler, 6 is the automatic oxygenation pump, 7 is the gas stone, 8 is the intelligent temperature monitor, 9 is the intelligent temperature monitoring probe, and 10 is the base.

[0053] Figure 2 The images show contour plots and 3D diagrams of the interaction factor between lignocellulose degradation rate and response values. Figure 2In the diagram, a represents the interaction between temperature (°C) and pH; b represents the interaction between temperature (°C) and aeration time (h); and c represents the interaction between pH and aeration time (h).

[0054] Figure 3 The effect of high-temperature composting formulation on the temperature of selenium-enriched liquid compost for invasive organisms. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0055] Figure 4 The effect of a high-temperature composting formulation on the pH of selenium-enriched liquid compost containing invasive species. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0056] Figure 5 The effect of a high-temperature composting formulation on the electrical conductivity of selenium-enriched liquid compost containing invasive organisms. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0057] Figure 6 The effect of high-temperature composting formulation on the germination index of selenium-enriched liquid compost for invasive organisms. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0058] Figure 7 The effect of nutrient-enriched formulations on the total organic carbon in selenium-enriched liquid compost for invasive species. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0059] Figure 8 The effect of nutrient-enriched formulations on the total nitrogen content of selenium-enriched liquid compost containing invasive species. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0060] Figure 9 The effect of nutrient-enriched formulations on the total phosphorus content of selenium-enriched liquid compost containing invasive species. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0061] Figure 10 The effect of nutrient-enriched formulations on the total potassium content of selenium-enriched liquid compost containing invasive species. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0062] Figure 11 The effect of nutrient-enriched formulations on the ammonium nitrogen content of selenium-enriched liquid compost for invasive species. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0063] Figure 12 The effect of nutrient-enriching formulations on nitrate nitrogen content in selenium-enriched liquid compost containing invasive species. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0064] Figure 13 The impact of low-carbon emission reduction formulations on the cumulative methane emissions from selenium-enriched liquid composting of invasive species. * indicates the impact of low-carbon emission reduction formulations on the cumulative methane emissions from invasive species. P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0065] Figure 14 The impact of low-carbon emission reduction formulations on methane emission flux in selenium-enriched liquid compost from invasive organisms. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0066] Figure 15The impact of low-carbon emission reduction formulations on nitrous oxide emission fluxes from selenium-enriched liquid compost containing invasive species. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant.

[0067] Figure 16 The impact of low-carbon emission reduction formulations on the cumulative nitrous oxide emissions from selenium-enriched liquid compost containing invasive species. * indicates that... P ≤0.05 indicates a significant difference; ** represents a statistically significant difference. P ≤0.01 indicates a significant difference; *** represents a statistically significant difference. P A difference of ≤0.01 is significant. Detailed Implementation

[0068] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0069] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0070] Example 1: An apparatus for producing selenium-enriched liquid compost using invasive species and agricultural waste. like Figure 1 As shown, this embodiment provides an apparatus for producing selenium-enriched liquid compost using invasive organisms and agricultural waste, including a compost bin, an automatic oxygen supply mechanism for supplying oxygen to the materials in the compost bin, an intelligent temperature control mechanism for keeping the materials in the compost bin warm, and a base 10.

[0071] The composting bin includes a material container 1, a feeding bin 2, a material distributor 3, a sampling port 4, and a gas sampler 5. The material container 1 is a PVC plastic bucket, weighing 2.65 kg, 4 cm high, with an outer diameter of 24 cm, an inner diameter of 22.5 cm, a bottom diameter of 31 cm, and a volume of 25 L. The feeding bin 2 is funnel-shaped, with an upper diameter of 56 cm, a lower diameter of 14 cm, and a height of 18 cm. It has symmetrical slots on both sides for fixing it to the material container 1. The material distributor 3 is an inverted funnel-shaped device fixed below the feeding bin 2. After aeration, it pushes the solid and liquid components together, allowing them to slide into the material container 1. The sampling port 4 consists of two 1 / 4-inch ball-core taps and two small stainless steel filters. The 1 / 4-inch ball-core taps have double sealing gaskets and a set of 1 / 4-inch internal thread water tank nuts; the small filters are for preventing clogging. The gas sampler 5 is composed of a 4mm*6mm corrosion-resistant silicone hose of about 20cm and a YCG-S type three-way valve. It is installed on one side of the material container 1 to collect greenhouse gases such as CH4 and N2O during the composting process.

[0072] The automatic oxygen supply mechanism includes an automatic oxygen pump 6 and an air stone 7. There are two automatic oxygen pumps, model ACO-002, with dimensions of 145mm × 85mm × 95mm, voltage of 220V, power of 25W, pressure > 0.025Mpa, and exhaust volume of 40L / min. There are two 8-head distributors, 16 check valves, and one distributor pipe. The air stone 7 is a small cylindrical steel shot connected to a 4mm*6mm corrosion-resistant silicone hose.

[0073] The intelligent temperature control mechanism includes an insulation strip, an intelligent temperature monitor 8, and an intelligent temperature monitoring probe 9. The insulation strip is located on the outer wall of the material container 1 and includes a heating wire, power cord, leakage protection plug, and aluminum foil tape. It operates at 220V and is 8mm wide. When the intelligent temperature control mechanism is activated, it consumes 25W per meter, and after reaching a constant temperature, it consumes 6W per meter. The intelligent temperature monitor 8 has an ABS shell, a temperature range of -50℃ to 200℃, a length of 130mm, and a width of 96mm. The intelligent temperature monitoring probe 9 is a 304 stainless steel 1 / 2-inch threaded waterproof probe with a 6mm probe diameter and an accuracy of ±0.1℃.

[0074] The base 10 is located below the material container 1 and is used to support and fix the device.

[0075] Example 2: Optimization of Biotransformation Based on Box-Behnken Response Surface Model (1) Based on the Box-Behnken central experimental design principle, this invention uses the Box-Behnken response surface model to explore the optimal conditions for the degradation of cellulose, hemicellulose, and lignin (collectively referred to as lignocellulose) in the invasive species *Pomacea canaliculata* and agricultural waste rice straw. This invention selects three parameters related to the degradation rate—temperature (°C), pH, and aeration time—for optimization.

[0076] (2) This invention employs a three-factor, three-level experiment (as shown in Table 1), designing a total of 17 groups of experiments. The constructed model undergoes variance testing to determine its significance. The specific steps are as follows: ① Material Preparation: After collecting *Alternanthera philoxeroides*, rinse it thoroughly with deionized water to remove soil, gravel, and weeds. Agricultural waste, rice straw, was purchased from a farm in Shangtun Village, Yihe Town, Heyuan City, Guangdong Province. *Alternanthera philoxeroides* and rice straw were dried in a 60℃ hot air oven to constant weight. The dried samples were then pulverized using a high-speed pulverizer, passed through a 20-mesh standard sieve, and stored in a desiccator for later use. Healthy adult *Pomacea canaliculata* snails with a shell height of 4.5–5.5 cm, a snail width of 4–5 cm, and a single snail weight of 20–30 g were selected. Before the experiment, they were starved in dechlorinated water for 24 hours, and their surface soil and impurities were rinsed off with distilled water.

[0077] ② Bioconversion: For 15 consecutive days, 70g of sample was weighed daily into a transparent container (containing 14 starved golden apple snails). Materials were added according to 17 experimental treatments, with each treatment repeated 4 times. After thorough mixing, water was added to adjust the pH (5, 7, 9) according to the experimental conditions. The containers were placed in environments with set temperatures of 15℃, 25℃, and 35℃ for bioconversion. Aeration times between treatments were 0h / d, 12h / d, and 24h / d.

[0078] Table 1 Factors and experimental design levels in Box-Behnken design

[0079] (4) Use 3D graph interaction factor analysis to determine the degree of influence of each factor and the corresponding values ​​and combinations of factors for the optimal response value (e.g., Figure 2 (As shown). The surfaces for all three factors are quite steep, indicating that temperature (°C), pH, and aeration time (h) all have a significant impact on the degradation rate of lignocellulose. The interaction between any two factors is significant. The closer the contour lines are to a circle, the more significant the interaction between the two factors.

[0080] (5) 3D diagram of lignin-cellulose degradation rate interaction factor (e.g.) Figure 2 a, Figure 2 b, Figure 2c) explains the relationship between the dependent variable (response value) and the independent variables (A, B, C). With increasing temperature and pH... Figure 2 In (a), lignin-cellulose degradation increases first, and then decreases when both variables reach their maximum values. As temperature increases, the contour lines become denser, while the contour lines along the pH direction become sparser, indicating that temperature has a more significant effect on the response value than pH.

[0081] (6) With the increase of temperature and aeration time ( Figure 2 (b) In the figure, lignin-cellulose degradation initially increases and then decreases. The density of changes along the temperature contour line is greater than that along the aeration time contour line, indicating that temperature has a more significant impact on the response value than aeration time. Furthermore, the interaction between temperature and aeration time is strong and significantly affects the degradation rate of lignin-cellulose.

[0082] (7) With the increase of pH and aeration time ( Figure 2 In (c), lignin-cellulose degradation increases first, and then decreases when both variables reach their maximum values. The aeration time contour lines are denser than the pH contour lines, indicating that aeration time has a more significant impact on the peak response value than pH.

[0083] Therefore, temperature has the most significant impact on the response value, followed by aeration time and pH. The conditions corresponding to the maximum response value obtained using Design-Expert software analysis were 25.6℃, pH 7.12, and 13.30 h of aeration per day. Under these conditions, the degradation rate of lignocellulose by the golden apple snail reached its maximum.

[0084] (8) The present invention uses Design-Expert 13 software to optimize and predict the regression model, and determines the optimal process parameters for lignocellulose degradation as follows: temperature 25.6℃, pH 7.12, and aeration time 13.30 h. Under these conditions, the model predicts a degradation rate of 40.72%. To verify the reliability of the model, a verification experiment was conducted according to the above optimal parameters (see Table 2). The mean degradation rates of the control (without golden apple snails) and the treatment (with golden apple snails) were 19.55% and 40.14%, respectively. Compared with the control (CK), the treatment significantly improved by 51.25%. In addition, the relative deviation between the measured and predicted values ​​of the treatment was 1.44% (<5%), indicating that the model prediction accuracy was high and the experimental design method was scientific and reasonable. This shows that pretreatment with live golden apple snails is beneficial to improving the fermentation efficiency of subsequent selenium-enriched liquid fertilizer raw materials, shortening the composting cycle, and improving the conversion efficiency of organic selenium.

[0085] Table 2 Validation Results

[0086] Example 3: Temperature variation in selenium-enriched liquid compost for invasive organisms during the preparation of high-temperature composting formulation (1) Invasive organism Alternanthera philoxeroides and agricultural waste rice straw were collected, impurities were removed, and the mixture was dried at 60°C using an electric heating blower. The mixture was then pulverized using a high-speed pulverizer, passed through a 20-mesh sieve, and mixed at a set dry weight ratio of 1:1 to obtain a mixture, which was used as a substrate for bioconversion of golden apple snails. Invasive animal golden apple snails were collected, rinsed with clean water, and subjected to a 24-hour starvation treatment. Fourteen healthy, active, and uniformly sized golden apple snails were selected, with a snail weight of 20-30 g, a snail width of 4-5 cm, and a snail height of 4.5-5.5 cm. They were placed in the composting device of Example 1, and 10.5 L of dechlorinated water was added to adjust the pH to 7.12. The mixture was fed to each treatment at 25.6°C for 15 days.

[0087] (2) After the bioconversion in step (1), add 1432.25 to 1909.67 mg / kg / 10L of selenium source to the residue (the mixture of the converted substrate and golden apple snail) to start aerobic liquid composting. Stop aeration for 5 to 10 minutes every 2 to 3 days and stir 1 to 2 times. Take a sample after 21 days, centrifuge at 8000 g at 4℃ for 10 minutes, and discard the residue to obtain the high-temperature composting formula to prepare selenium-enriched liquid compost.

[0088] (3) Experimental setup: Control (CK) (no selenium source added) and high-temperature composting formulation treatment. The selenium source was a mixture of sodium selenite and sodium selenate in a ratio of 1:1.09. In the compost material, the amount of sodium selenite added was 684.44–912.59 mg / kg / 10L, and the amount of sodium selenate added was 747.81–997.08 mg / kg / 10L. Specifically, the amount of sodium selenite added was 782.22 mg / kg / 10L, and the amount of sodium selenate added was 854.64 mg / kg / 10L. Both the control (CK) and high-temperature composting formulation treatments were conducted using the liquid composting apparatus described in Example 1.

[0089] (4) During the composting process, the temperature in the liquid compost was monitored by the high-precision digital display thermometer in the device of Example 1. The compost temperature was recorded at 8:30 am, 2:30 pm and 6:30 pm every day. The indoor ambient temperature was also recorded. The average value of the three liquid compost temperature records each day was taken as the liquid compost temperature for that day. The liquid composting was carried out for a total of 21 days.

[0090] (5) Temperature is a core indicator for measuring the activity of composting microorganisms and the maturation process. The dynamic changes in temperature during liquid composting are as follows: Figure 3As shown, the liquid composting process successively went through four stages: heating, high temperature, cooling, and maturation. The temperature curve showed a trend of "first rising, then falling—approaching room temperature." In the early stage of liquid composting (0-4 days), the temperature of both the control and high-temperature maturation formula treatments gradually increased. On the 5th day, the temperature of their liquid piles both exceeded 50℃. Figure 3 (a) Among them, the peak temperature of the high-temperature composting formula reached 57.7℃, which was significantly higher than that of the control (52.9℃). P <0.05). Subsequently, the high-temperature composting formula treatment was carried out at a high temperature range of ≥55℃ for 6 days, which was 2 days longer than the control. Figure 3 (b) After the high-temperature period ended, the temperature began to drop. By day 21, both the control and the high-temperature composting formula treatments had reached near ambient temperature (26±2℃). The initial temperature rise of liquid compost was due to the rapid mineralization and heat release of easily degradable organic matter. The high-temperature composting formula extended the thermophilic phase by promoting microbial activity and community expansion, which not only accelerated the composting process but also effectively inactivated pathogens, insect eggs, and weed seeds by utilizing sustained high temperatures (≥55℃), thus helping the liquid compost products to meet the harmlessness standards.

[0091] Example 4: Changes in pH and conductivity of selenium-enriched liquid compost containing invasive organisms during the preparation of a high-temperature composting formulation. Steps (1) to (3) are the same as in Example 3.

[0092] (4) On days 1, 3, 7, 9, 12, 15, 18 and 21 of liquid composting, the compost material was thoroughly stirred and mixed evenly. Fresh liquid compost samples were collected using the automatic filtration device of Example 1. The samples were divided into two parts: one part was stored in a 4°C refrigerator for pH and conductivity (EC) determination. The other part was stored in a -20°C refrigerator for gas parameters determination.

[0093] (5) Take a portion of fresh samples from different composting stages out of the 4℃ refrigerator and put them into centrifuge tubes. After shaking and mixing evenly, place the centrifuge tubes in a centrifuge and centrifuge at 4℃ and 8000×g for 5 min. The supernatant obtained after filtration is selenium-enriched liquid compost.

[0094] (6) The pH and conductivity of the liquid fertilizer were measured using a pH meter (PHSJ). In-situ measurements were performed using a 4F (Shanghai Instrument & Electronics Scientific Instruments Co., Ltd., Shanghai, China) and a conductivity meter (SW302, Zhejiang Shangyu Huafeng Hardware Co., Ltd., Zhejiang, China).

[0095] (7) pH value, as a key environmental factor for microbial growth, can not only effectively promote the reproduction and metabolic activities of composting microorganisms within its optimal range, but also significantly accelerate the composting process. The trend of pH value changes during liquid composting is shown in the figure below. Figure 4As shown, the entire process exhibits a pattern of rapid initial decrease followed by an increase and then a decrease again. In the initial composting stage (day 0), the pH values ​​of the control (CK) and the high-temperature composting formula treatments differed significantly because the selenium source, when dissolved in water, is weakly alkaline or near-neutral. In the early composting stage (days 1-3), the decomposition of easily degraded organic matter by microorganisms produces organic acids (such as acetic acid, propionic acid, and butyric acid), leading to a rapid decrease in the pH of the liquid compost. As the liquid compost enters the high-temperature phase, the temperature rises. On day 15 of composting, the pH values ​​of both the CK and high-temperature composting formula treatments reached their peak values ​​of 7.3 and 7.9, respectively. This is because organic acids are degraded or volatilized, and nitrogen-containing organic matter mineralizes, releasing NH4+. + When liquid compost enters the maturation period (>15 days), the pH value begins to drop. At the end of the composting process, the pH value stabilizes between 7.0 and 8.0, meeting the standard for compost maturation.

[0096] (8) Electrical conductivity (EC) is one of the important physicochemical indicators for evaluating the composting process and its maturity. Its changes can reflect key processes in the composting system, such as the concentration of soluble salt ions, the degree of organic matter mineralization, and microbial activity. The dynamic changes in electrical conductivity during liquid composting are shown in the following figures. Figure 5 As shown, the trend is one of initial increase followed by a decrease. In the initial stage of liquid composting, the rapid mineralization of easily degradable organic matter releases a large amount of soluble mineral salts. Simultaneously, the rapid increase in pile temperature and forced ventilation lead to moisture loss, resulting in a synchronous increase in the concentration of soluble solids. These two factors synergistically drive a rapid increase in the conductivity of the high-temperature composting formula treatment. It reaches its peak on day 9, with the conductivity of the high-temperature composting formula treatment (4454 μs / cm) significantly higher than that of the control (4024.25 μs / cm). P <0.05). Subsequently, the electrical conductivity of both treatments decreased synchronously and tended to stabilize at the end of composting. The high-temperature composting formulation maintained a higher EC level throughout the process, indicating that its organic matter degradation was more complete and its mineralization degree was significantly better than the control. At the end of liquid composting, the electrical conductivity of the high-temperature composting formulation was 3652.25 μs / cm, which was still significantly higher than the conductivity of the CK (3051 μs / cm) and met the safety threshold requirement for compost maturity (EC <4000 μs / cm).

[0097] Example 5: Effect of high-temperature composting formula on germination index of selenium-enriched liquid compost for invasive species Steps (1) to (3) are the same as in Example 3.

[0098] (4) The germination index (GI) was determined according to the method of Shan et al. A suitable size of filter paper was placed in a petri dish, and 20 plump, uniform lettuce seeds were selected. Lactuca sativa L. var. ramosa(Hort.) Seeds were placed in petri dishes, and 7 mL of compost extract diluted 250 times was added to each dish. A blank control of 7 mL of pure water was also provided. The petri dishes were placed in a constant temperature incubator at 25℃ and cultured in the dark for 48 h. After the culture was completed, the number of germinating seeds was recorded and the root length was measured with calipers. The seed germination index (GI) was calculated using formula (1).

[0099] (1) (5) Seed germination index is a core bioindicator parameter for quantifying compost maturity. Its numerical changes can systematically characterize the rise and fall of phytotoxic substances in compost products, and it is currently internationally recognized as the ultimate bioactivity indicator for evaluating the ecological safety of finished compost products. The changes in the germination index of liquid compost are as follows: Figure 6 As shown, at the end of liquid composting, the germination index of the high-temperature composting formula treatment reached 98.58%, which was significantly higher than the control (88.32%) by 11.62%. P <0.05), the high-temperature composting formula accelerated the composting process by promoting the decomposition of organic matter and simultaneously optimized the nutritional quality of the compost product. At the end of composting, both the control and Se treatments reached over 85%, meeting the requirements for harmlessness and conforming to the standards for farmland application.

[0100] Example 6: Changes in total organic carbon and nutrient content of selenium-enriched liquid compost from invasive organisms during the preparation of nutrient-enriched formulations. (1) Invasive organism Alternanthera philoxeroides and agricultural waste rice straw were collected, impurities were removed, and the mixture was dried at 60°C using an electric heating blower. The mixture was then pulverized using a high-speed pulverizer, passed through a 20-mesh sieve, and mixed at a set dry weight ratio of 1:1 to obtain a mixture, which was used as a substrate for bioconversion of golden apple snails. Invasive animal golden apple snails were collected, rinsed with clean water, and subjected to a 24-hour starvation treatment. Fourteen healthy, active, and uniformly sized golden apple snails were selected, with a snail weight of 20-30 g, a snail width of 4-5 cm, and a snail height of 4.5-5.5 cm. They were placed in the composting device of Example 1, and 10.5 L of dechlorinated water was added to adjust the pH to 7.12. The mixture was fed to each treatment at 25.6°C for 15 days.

[0101] (2) After the bioconversion in step (1), add 996.93-1332.59 mg / kg / 10L or 1060.31-1417.08 mg / kg / 10L of selenium source to the residue (the mixture of the converted substrate and golden apple snail) to start aerobic liquid composting. Stop aeration for 5-10 min every 2-3 days and stir 1-2 times. Take a sample after 21 days, centrifuge at 8000 g at 4℃ for 10 min, and discard the residue to obtain the selenium-enriched liquid compost prepared by the nutrient enrichment formula.

[0102] (3) Experimental setup: Control (CK) (no selenium source added) and Se treatment (selenium source added). The selenium source was prepared by mixing sodium selenite and nano-selenium in a ratio of 2.17:1 or sodium selenate and nano-selenium in a ratio of 2.37:1. The amount of sodium selenite added was 684.44–912.59 mg / kg / 10L, the amount of sodium selenate added was 747.81–997.08 mg / kg / 10L, and the amount of nano-selenium added was 312.50–420.00 mg / kg / 10L. Specifically, the amount of sodium selenite added was 782.22 mg / kg / 10L, the amount of sodium selenate added was 854.64 mg / kg / 10L, and the amount of nano-selenium added was 357.15 mg / kg / 10L. Both the control (CK) and Se treatment were carried out using the liquid composting apparatus of Example 1.

[0103] (4) The total organic carbon content of liquid compost was determined by the potassium dichromate-concentrated sulfuric acid external heating method; the total nitrogen content was determined by the alkaline potassium persulfate digestion method; the total phosphorus content was determined by the ammonium molybdate spectrophotometric method; and the total potassium content was determined by the H2SO4-H2O2 digestion flame photometer method.

[0104] (5) Changes in total organic carbon (TOC) directly reflect the degree of mineralization of organic matter, microbial activity, and the composting process. Changes in total organic carbon content during liquid composting are shown in the figure below. Figure 7 As shown, the nutrient-enriched formulation treatment and the control showed an overall decreasing trend during liquid composting. In the initial stage of liquid composting (0–7 days), the total organic carbon (TOC) in both the nutrient-enriched formulation treatment and the control decreased rapidly, possibly due to increased microbial activity and accelerated organic matter hydrolysis. Subsequently (≥7 days), the degradation rate of TOC in the liquid compost slowed down. At the end of liquid composting, the TOC content in the nutrient-enriched formulation treatment (2325.82 mg / L) was significantly lower than that in the control (3724.79 mg / L), a reduction of 37.55%. P <0.05), which indicates that nutrient enrichment formulation treatment can enhance microbial activity and functional gene expression, promote organic matter mineralization, and thus improve the maturity and stability of liquid compost.

[0105] (6) The changes in total nitrogen, total phosphorus and total potassium content during composting are as follows: Figure 8 , 9 As shown in Figures 1 and 10, at the end of liquid composting, the total nitrogen, total phosphorus, and total potassium contents of the nutrient-enriched formulation treatment were significantly higher than those of the control. P<0.05). The total nitrogen, total phosphorus and total potassium in the nutrient-enriched formula treatment increased by 24.63%, 18.70% and 9.61% respectively compared with the control, which indicates that the nutrient-enriched formula increased the nutrient content of total nitrogen, total phosphorus and total potassium in the compost.

[0106] Example 7: Effect of nutrient enrichment formulation on ammonium nitrogen and nitrate nitrogen content in selenium-enriched liquid compost for invasive species Steps (1) to (3) are the same as in Example 6.

[0107] (4) Ammonium nitrogen in liquid compost (NH4) + The content of nitrate nitrogen (NO3-N) was determined by the phenol-hypochlorite colorimetric method; - The content of -N was determined by ultraviolet spectrophotometry.

[0108] (5) The changes in ammonium nitrogen content during liquid aerobic composting are as follows: Figure 11 As shown, the overall trend is one of initial increase followed by a decrease. In the initial stage of liquid aerobic composting (0-7 days), as time increases, the compost enters a high-temperature period, organic matter decomposition accelerates, and a large amount of ammonium nitrogen is released. The ammonium nitrogen content in both the control (CK) and nutrient-enriched formulation treatments increases rapidly, reaching its peak on day 7. Specifically, the ammonium nitrogen content in the nutrient-enriched formulation treatment (4622.38 mg / L) significantly increased by 18.48% compared to the control (3768.04 mg / L). P <0.05). Subsequently, due to ammonia volatilization and nitration, the ammonium nitrogen content gradually decreased and eventually stabilized, dropping to below 200 mg / L.

[0109] (6) The changes in nitrate nitrogen content during liquid aerobic composting are as follows: Figure 12 As shown, in contrast to the change in ammonium nitrogen content, the overall trend was a gradual increase, especially in the middle and later stages of composting. Initially, the increase may have been slow due to high temperature and unsuitable pH, but in the middle and later stages, as the temperature decreased and the activity of nitrifying bacteria increased, the nitrate nitrogen content continued to rise. At the end of liquid composting, the nitrate nitrogen content in both the control and nutrient-enriched formulation treatments exceeded 2000 mg / L. Specifically, compared to the control (2081.53 mg / L), the nitrate nitrogen content in the nutrient-enriched formulation treatment (2729.35 mg / L) increased significantly by 23.73%, indicating that the nutrient-enriched formulation enhanced the activity of nitrifying bacteria and accelerated the nitrification process from ammonium nitrogen to nitrate nitrogen.

[0110] Example 8: Changes in greenhouse gases caused by invasive species-enriched selenium liquid compost during the preparation of a low-carbon emission reduction formulation. (1) Invasive organism Alternanthera philoxeroides and agricultural waste rice straw were collected, impurities were removed, and the mixture was dried at 60°C using an electric heating blower. The mixture was then pulverized using a high-speed pulverizer, passed through a 20-mesh sieve, and mixed at a set dry weight ratio of 1:1 to obtain a mixture, which was used as a substrate for bioconversion of golden apple snails. Invasive animal golden apple snails were collected, rinsed with clean water, and subjected to a 24-hour starvation treatment. Fourteen healthy, active, and uniformly sized golden apple snails were selected, with a snail weight of 20-30 g, a snail width of 4-5 cm, and a snail height of 4.5-5.5 cm. They were placed in the composting device of Example 1, and 10.5 L of dechlorinated water was added to adjust the pH to 7.12. The mixture was fed to each treatment at 25.6°C for 15 days.

[0111] (2) After the bioconversion in step (1), add 75-105 mg / L of selenium source to the residue (the mixture of the converted substrate and golden apple snail) to start aerobic liquid composting. Stop aeration for 5-10 min every 2-3 days and stir 1-2 times. Take a sample after 21 days, centrifuge at 8000 g for 10 min at 4℃, and discard the residue to obtain the selenium-enriched liquid compost prepared by the low-carbon emission reduction formula.

[0112] (3) The experiment set up a control (CK) (without selenium source) and a low-carbon emission reduction formulation treatment (with selenium source). The selenium source was composed of sodium selenite, sodium selenate, and nano-selenium in an addition ratio of 2.19:2.39:1, wherein the addition amount of sodium selenite was 456.29–608.39 mg / kg / 10L, the addition amount of sodium selenate was 498.54–664.71 mg / kg / 10L, and the addition amount of nano-selenium was 208.32–466.67 mg / kg / 10L. Specifically, the addition amount of sodium selenite was 521.48 mg / kg / 10L, the addition amount of sodium selenate was 569.76 mg / kg / 10L, and the addition amount of nano-selenium was 238.08 mg / kg / 10L. The resulting formula is a low-carbon emission reduction type, which can effectively suppress the emission of greenhouse gases such as methane (CH4) and nitrous oxide (N2O) during the composting process, providing a feasible path for green agriculture to reduce emissions and increase efficiency, and achieving a win-win situation for environmental protection and economic benefits.

[0113] (4) During liquid composting, the collection of greenhouse gases methane (CH4) and nitrous oxide (N2O) must be completed between 8:30 and 11:00 every day. Before collecting gas samples, the oxygen pump must be turned off, and the gas supply must be stopped for 30 minutes. The gas is collected and stored using a 50 ml syringe. During gas collection, gas samples are collected with a syringe at 0, 10, 20, and 30 minutes respectively. The concentrations of CH4 and N2O produced in the gas samples are determined using a gas chromatograph with a hydrogen ion flame detector (GC-7890A, Agilent Technologies, Inc., Santa Clara, CA, USA). The formula (2) for calculating the greenhouse gas emission rate of composting is as follows: (2) In the formula, V The greenhouse gas emission rates for each treatment are (mg / d). Δ c / Δ t It is the change in gas concentration per unit time (day) (ppm); M These are the molecular masses of the relevant gases (methane and nitrous oxide are 16 and 44 g, respectively). Vs It is the volume occupied by 1 mol of gas under standard temperature and pressure (22.4 L). P It is atmospheric pressure (bar); P 0 is the standard pressure (1.01 × 10⁻⁶). 5 Pa); V It is the volume of the top space (L); T Temperature inside the compost bin (K), expressed in Kelvin; The cumulative greenhouse gas emissions (mg) are calculated using the trapezoidal integral rule, as shown in formula (3): (3) In the formula, F It is the cumulative amount of gas emitted during the composting process (mg or g). ta and tb are the time intervals (d) between the two measurements; F ta and F tb These are the emission fluxes (mg or g) on ​​the day of the two measurements.

[0114] (5) During liquid composting, the methane (CH4) emission rates ( / flux) of the control and low-carbon emission reduction formulation treatments are as follows: Figure 13 As shown, with the progress of liquid composting, the CH4 emission rates of the control and low-carbon emission reduction formulation treatments showed a trend of first increasing and then decreasing. On day 7 of composting, the emission rate reached its peak, with the CK (160.58 mg / d) > the low-carbon emission reduction formulation treatment (126.86 mg / d). Furthermore, throughout the entire liquid composting process, the emission rate of the low-carbon emission reduction formulation treatment was significantly lower than that of the CK (160.58 mg / d). P <0.05). During liquid composting, the cumulative CH4 emissions of the control and low-carbon emission reduction formulation treatments are as follows: Figure 14 As shown, the cumulative emissions of the control (CK) and the low-carbon emission reduction formulation treatments were CK > Se treatment, with the low-carbon emission reduction formulation treatment (106.16 mg) having significantly lower total emissions than the CK (141.66 mg). P <0.05), indicating that the low-carbon emission reduction formulation can significantly reduce the cumulative CH4 emissions during composting.

[0115] (6) Nitrous oxide (N2O) emission during composting is a complex microbially driven process, mainly involving two mechanisms: nitrification and denitrification. The N2O emission rates of the CK and Se treatments are as follows: Figure 15 As shown, the entire liquid composting process exhibited a trend of first increasing, then decreasing, and finally stabilizing. The peak was reached on the 3rd day of composting, with the low-carbon emission reduction formulation treatment at 63.65 mg / d, significantly lower than the control (86.46 mg / d). Compared to the control, the low-carbon emission reduction formulation treatment showed a significant reduction of 27.54% (mg / d). P <0.05). The cumulative nitrous oxide emissions from CK and Se treatments are as follows: Figure 16 As shown, at the end of liquid composting, the accumulation of nitrous oxide in the low-carbon emission reduction formulation treatment (236.95 mg) was reduced by 37.35% compared to the control (378.19 mg), significantly lower than the control (236.95 mg). P The value <0.05 indicates that the low-carbon emission reduction formula treatment has a significant emission reduction effect on N2O released from liquid compost.

Claims

1. A method for producing selenium-enriched liquid fertilizer using invasive species and agricultural waste, characterized in that, Includes the following steps: S1. The invasive plant Alternanthera philoxeroides and agricultural waste rice straw are washed, dried, and sieved, and then mixed in equal mass ratios to obtain compost material. S2. Feed the starved apple snails with the compost material from step S1 to carry out bioconversion; S3. Add selenium source to the mixed residue of compost material and golden apple snail after bioconversion in step S2 for aerobic composting fermentation. After completion, filter the supernatant, extract the compost residue, and combine the filtrates to obtain selenium-enriched liquid fertilizer.

2. The method according to claim 1, characterized in that, The biological transformation described in step S2 involves feeding the starved golden apple snails with compost material daily at a temperature of 25–28°C, pH of 7–8, and aeration for 12–14 hours per day for 15–20 days.

3. The method according to claim 1, characterized in that, The selenium source is composed of sodium selenite, sodium selenate, and / or nano-selenium, and the addition amount is 996.93–1909.67 mg / kg of mixed residue; the aerobic composting fermentation time is 21–30 days.

4. The method for producing selenium-enriched liquid compost according to claim 1, characterized in that, The selenium source mentioned in step S3 is a compound of sodium selenite and sodium selenate; the amount of sodium selenite added is 684.44 to 912.59 mg / kg / 10L, and the amount of sodium selenate added is 747.81 to 997.08 mg / kg of mixed residue.

5. The method for producing selenium-enriched liquid compost according to claim 1, characterized in that, The selenium source mentioned in step S3 is composed of sodium selenite and nano-selenium, or sodium selenate and nano-selenium in combination; the amount of sodium selenite added is 684.44 to 912.59 mg / kg of mixed residue, the amount of sodium selenate added is 747.81 to 997.08 mg / kg of mixed residue, and the amount of nano-selenium added is 312.50 to 420.00 mg / kg of mixed residue.

6. The method for producing selenium-enriched liquid compost according to claim 1, characterized in that, The selenium source mentioned in step S3 is a compound of sodium selenite, sodium selenate, and nano-selenium; the amount of sodium selenite added is 456.29 to 608.39 mg / kg of compost material, the amount of sodium selenate added is 498.54 to 664.71 mg / kg of mixed residue, and the amount of nano-selenium added is 208.32 to 466.67 mg / kg of mixed residue.

7. The selenium-enriched liquid fertilizer prepared by any one of the methods described in claims 1 to 6.

8. A selenium-enriched liquid composting apparatus for implementing the method according to any one of claims 1 to 6, characterized in that, Includes a composting bin, an automatic oxygen supply mechanism for supplying oxygen to the materials in the composting bin, and an intelligent temperature control mechanism for keeping the materials in the composting bin (1) warm. The composting bin includes a material container (1), a feeding bin (2), a material distributor (3), a sampling port (4), and a gas sampler (5); the feeding bin (2) is funnel-shaped and fixed on the material container (1); the material distributor (3) is inverted funnel-shaped and fixed below the feeding bin (2) for sliding compost material into the material container (1); the sampling port (4) is located below the material container (1) for collecting liquid compost; the gas sampler (5) is installed on the outside of the material container (1) for collecting greenhouse gases during the composting process. The automatic oxygen supply mechanism includes an automatic oxygenation pump (6) and an air stone (7); the air stone (7) is located at the bottom of the material container (1), and the automatic oxygenation pump (6) is connected to the air stone (7) to supply oxygen to it; The intelligent temperature control mechanism includes an insulation belt, an intelligent temperature monitor (8), and an intelligent temperature monitoring probe (9). The intelligent temperature monitoring probe (8) is located at the bottom of the material container (1), and the intelligent temperature monitor (8) is connected to the temperature monitoring probe (9) to provide real-time feedback of temperature information. The insulation belt is located on the outer wall of the material container (1) and adjusts the temperature in real time according to the feedback temperature information.

9. The apparatus according to claim 8, characterized in that, The material container (1) is a PVC plastic bucket.

10. The apparatus according to claim 8, characterized in that, The feeding bin (2) is fixed to the material container (1) by symmetrical slots on both sides.

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