Liquid manure floating covering material and liquid manure storage method

Abstract

The invention discloses a liquid manure floating covering material and a liquid manure storage method, the liquid manure floating covering material comprises expanded vermiculite and hydrophobic silicon dioxide, and the hydrophobic silicon dioxide is distributed on the surface of the expanded vermiculite. The problems that a traditional covering material is poor in floating performance, easy to settle, limited in adsorption capacity and the like are solved in a targeted mode, and the liquid manure floating covering material can reduce the influence of gas emission in the manure storage process at the same time, has the advantages of being high in ecological and economic benefits and provides new technical support for efficient gas emission reduction in manure storage in animal husbandry.

Description

Technical Field

[0001] The present invention belongs to the technical field of manure treatment, and in particular relates to a floating covering material for liquid manure and a method for storing liquid manure. Background Art

[0002] Livestock manure storage is an important part of manure resource management, accounting for about 23% of the total livestock and poultry NH3 emissions. At the same time, anaerobic sulfate-reducing bacteria in the storage process will produce H2S, which has a low odor threshold (0.57μg.m -3 ), lower concentrations can cause physical discomfort to people, and high concentrations may even lead to the risk of acute poisoning and death.

[0003] Currently, covering and acidification technologies are the primary gas emission reduction measures during liquid manure storage. Acidification can effectively reduce NH3 emissions, with a potential reduction of approximately 75%. However, the safety and high cost of conventional acidifiers (sulfuric acid, hydrochloric acid, and lactic acid) have limited the widespread application of acidification technology. Covering reduces gas emissions by preventing gases from the manure surface from escaping into the air. Covering materials are primarily categorized as natural and synthetic.

[0004] Natural mulches include natural crusts, straw, peat, clay, and minerals. However, the formation of natural crusts requires time and sufficient dry matter, and is significantly affected by the nature of the manure and natural conditions. They are prone to cracking, have poor gas emission reduction effects, are unstable, and can even increase NH3 emissions by 11%. Biomaterials such as straw, corn stalks, and sugarcane waste can reduce NH3 emissions by 79%, but their limited buoyancy and easy sedimentation and degradation can alter the physical and chemical properties of manure and increase greenhouse gas emissions. While peat and light expanded clay have floating properties and can reduce NH3 and other gas emissions, peat is non-renewable, and light expanded clay carries the risk of gas exposure during operation. Perlite, as a mulch material, can reduce NH3 emissions by 80%, but its sedimentation after absorbing water can significantly increase greenhouse gas emissions. Synthetic mulches are divided into permeable synthetic materials, impermeable synthetic materials, and petroleum-based oils. Long-term use of permeable synthetic materials (such as geotextiles and polyurethane) can cause gases to escape at the edges, reducing emission reduction effectiveness. The use of geotextiles can increase NH3 emissions by 15%. Impermeable covering materials (such as PVC and aluminum foil) can inhibit gas flow, but they can generate H2S in anaerobic environments and pose a risk of gas exposure. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology. The present invention provides a liquid manure floating covering material and a liquid manure storage method, which specifically solves the problems of poor floating performance, easy sedimentation and limited adsorption capacity of traditional covering materials. The liquid manure floating covering material can also reduce the impact of gas emissions during the manure storage process, has high ecological and economic benefits, and provides new technical support for efficient gas emission reduction in livestock manure storage.

[0006] A floating covering material for liquid manure, comprising expanded vermiculite and hydrophobic silica; The mass ratio of the expanded vermiculite to the hydrophobic silica is (8-11):1; The expanded vermiculite is an expanded vermiculite with a particle size of 3 to 6 mm; The hydrophobic silica is nano-scale hydrophobic silica.

[0007] In the above technical solution, optionally, the hydrophobic silica is distributed on the surface of the expanded vermiculite.

[0008] In the above technical solution, optionally, the mass ratio of the expanded vermiculite to the hydrophobic silica is 8:1, 8.5:1, 9:1, 9.5:1, 10:1, 10.5:1 or 11:1; preferably, the mass ratio of the expanded vermiculite to the hydrophobic silica is 9:1 or 10:1.

[0009] In the above technical solution, the hydrophobic silica is spherical hydrophobic silica modified with a silane coupling agent.

[0010] In the above technical solution, the expanded vermiculite is alkali-modified expanded vermiculite.

[0011] In the above technical solution, the alkali-modified expanded vermiculite is prepared by the following method: Mixing 3-6 mm expanded vermiculite with an alkali solution at a volume ratio of 1:0.5-1.5, soaking, filtering, washing, and drying to obtain alkali-modified expanded vermiculite; The alkaline solution is KOH solution or NaOH solution; preferably KOH solution; The concentration of the alkaline solution is 0.50-1.55 mol / L, preferably 1.0-1.55 mol / L, and more preferably 1.0-1.1.

[0012] In the above technical solution, during the soaking process, stirring is performed at 150-200 r / min for 4-8 hours, and the soaking temperature is 40-80°C; preferably, stirring is performed at 180 r / min for 6 hours, and the soaking temperature is 60°C.

[0013] In the above technical solution, the cleaning process is to repeatedly rinse the filtered expanded vermiculite with deionized water to remove the floating alkali on the surface until the pH of the outlet water does not change.

[0014] In the above technical solution, the drying process is to dry the washed expanded vermiculite at 100-105°C until the quality no longer changes, preferably 105°C.

[0015] A method for preparing a floating covering material for liquid manure and sewage, comprising: thoroughly mixing expanded vermiculite and hydrophobic silica to obtain the floating covering material for liquid manure and sewage; The mass ratio of the expanded vermiculite to the hydrophobic silica is (8-11):1; The expanded vermiculite is an expanded vermiculite with a particle size of 3 to 6 mm; The hydrophobic silica is nano-scale hydrophobic silica.

[0016] In the above technical solution, the hydrophobic silica is spherical hydrophobic silica modified with a silane coupling agent.

[0017] In the above technical solution, the expanded vermiculite is alkali-modified expanded vermiculite.

[0018] In the above technical solution, the mixing process is carried out in a mortar; Alternatively, the mixing process is carried out in a mixer; preferably a drum mixer.

[0019] A liquid manure storage method comprises: during the liquid manure storage process, covering the surface of the liquid manure with the liquid manure floating covering material.

[0020] In the above technical solution, the surface of the liquid excrement is covered with the liquid excrement floating covering material with a thickness of 2 to 10 cm, preferably 3 to 5 cm.

[0021] The advantages and beneficial effects of the present invention are: Manure storage has always been a hotspot for gas emissions in manure management. NH3 and H2S emissions have significant impacts on air pollution and human health. This study evaluated the effects of traditional inorganic (expanded vermiculite), traditional organic (wood chips), and the liquid manure floating cover described in this invention on gas emissions. The results showed that traditional cover materials have significant limitations in reducing gas emissions and may even exacerbate them. The use of wood chips increases NH3 and H2S emissions, as well as total solids (TS), volatile solids (VS), chemical oxygen demand (COD), and dissolved organic carbon (DOC) in manure. Furthermore, wood chip settling alters the pH of the slurry, promoting H2S generation. In contrast, while expanded vermiculite has some adsorption capacity, its insufficient flotation properties make it ineffective in preventing gas escape. Furthermore, its limited adsorption capacity makes it difficult to control gas generation at the source. However, the surface modification of the liquid manure floating cover with nano-hydrophobic silica significantly enhances its flotation and adsorption capacity. The floating covering material for liquid manure and sewage can effectively isolate the escape of NH3, with an emission reduction effect exceeding 87%, and does not cause the production of H2S. This is because the adsorption capacity of the modified expanded vermiculite is increased to a certain extent, and the produced H2S is adsorbed. Moreover, when the expanded vermiculite is modified with alkali, the pH value of the manure water can be further changed during storage, causing the pH value to increase, thereby further reducing hydrogen sulfide emissions. At the same time, it can still ensure that no ammonia emissions overflow during storage, playing a good isolation role. The liquid manure floating covering material developed by this invention exhibits multiple advantages: First, the hydrophobic modification of the material's surface provides it with durable floating properties, continuously preventing gas-liquid interface contact. Second, the material consistently maintained a high NH3 emission reduction rate over a 30-day test period. This long-term, stable performance in controlling gaseous pollutants provides a more practical solution for livestock and poultry manure treatment. Comparing the emission reduction rates, environmental costs, and economic benefits of traditional and novel covering materials reveals that covering technology can help reduce the environmental costs of gas emissions. The floating liquid manure covering material offers significant advantages, particularly due to its high NH3 reduction potential, reduced resource consumption, and long service life. It also avoids the problem of traditional covering materials sinking and being difficult to recover. Therefore, the floating liquid manure covering material is expected to become an economical, safe, and feasible covering for manure storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1The following are scanning electron microscope (SEM) images of expanded vermiculite before and after storage and the floating covering material for liquid manure obtained in Example 1, wherein: (a) is the expanded vermiculite before storage, (b) is the floating covering material for liquid manure obtained in Example 1, (c) is the expanded vermiculite after storage, and (d) is the floating covering material for liquid manure obtained in Example 1 after storage.

[0023] Figure 2 Characterization diagrams of expanded vermiculite before and after storage and the liquid manure floating covering material obtained in Example 1, (a) is an infrared spectrum, (b) and (c) are X-ray photoelectron spectra, (d) is the specific surface area, and (e) is the contact angle; Figure 2 The bar graph in e is a photograph of the contact angle of the material; Figure 2 * in d indicates that there is a significant difference between the two groups.

[0024] (V-BS) is expanded vermiculite before storage, (V-AS) is expanded vermiculite after storage, (MV-BS) is the floating covering material for liquid manure obtained in Example 1, and (MV-AS) is the floating covering material for liquid manure obtained in Example 1 after storage.

[0025] Figure 3 Figure 2 shows the gas emission diagram during the storage of manure water under different covering material treatments, where: (a) is the NH3 emission rate, (b) is the cumulative NH3 emission, (c) is the H2S emission concentration, and (d) is the cumulative H2S emission. Figure 3 Letters a, ab, b, c, and d in b are markers of significant differences, and different lowercase letters indicate significant differences between treatments (P < 0.05); Figure 3 The letters e, ef, and f in d are marks of significant differences, and different lowercase letters indicate significant differences among treatments (P < 0.05).

[0026] Figure 4 Characterization diagrams of expanded vermiculite and the floating covering material for liquid manure obtained in Example 2; wherein (a) is the contact angle of different materials, (b) is the average particle size, and (c) is the FTIR spectrum; Figure 4 The bar graph in a is a photograph of the contact angle of the material.

[0027] Figure 5 These are scanning electron microscope (SEM) images of expanded vermiculite and the floating covering material for liquid excrement obtained in Example 2, wherein: (a) is expanded vermiculite, and (b) is the floating covering material for liquid excrement obtained in Example 2.

[0028] Figure 6The diagram shows the effect of various covering materials on gas emissions during manure storage, where: (a) is the NH3 emission rate, (b) is the cumulative NH3 emissions, (c) is the H2S emission concentration, (d) is the cumulative H2S emissions, (e) is the CH4 emission rate, and (f) is the cumulative CH4 emissions; Figure 6 The letters h, g, and i in d are marks of significant differences, and different lowercase letters indicate significant differences among treatments (P < 0.05); Figure 6 Letters k and j in f are marks of significant differences, and different lowercase letters indicate significant differences among treatments (P<0.05).

[0029] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention are further described below with reference to specific embodiments.

[0031] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased through regular channels.

[0032] Example 1 A method for preparing a liquid manure floating covering material, comprising: thoroughly mixing expanded vermiculite and hydrophobic silica in a mortar to obtain the liquid manure floating covering material (MV); The mass ratio of the expanded vermiculite to the hydrophobic silica is 9:1; The expanded vermiculite is an expanded vermiculite with a particle size of 3 to 6 mm; The hydrophobic silica is spherical nano-scale hydrophobic silica modified with a silane coupling agent.

[0033] Example 2 A method for preparing a floating covering material for liquid manure and sewage, comprising: thoroughly mixing alkali-modified expanded vermiculite and hydrophobic silica in a mortar to obtain the floating covering material for liquid manure and sewage (AMV); The mass ratio of the alkali-modified expanded vermiculite to the hydrophobic silica is 9:1; The alkali-modified expanded vermiculite is an alkali-modified expanded vermiculite with a particle size of 3 to 6 mm; The hydrophobic silica is a spherical nano-scale hydrophobic silica modified with a silane coupling agent; The alkali-modified expanded vermiculite is prepared by the following method: 3~6mm expanded vermiculite is mixed with 1.52mol / L KOH alkaline solution in a volume ratio of 1:1, stirred at 180r / min for 6h, maintained at 60℃, filtered, and the filtered expanded vermiculite is repeatedly rinsed with deionized water to remove the floating alkali on the surface until the pH of the effluent does not change. The washed expanded vermiculite is dried at 105℃ until the mass no longer changes, thereby obtaining alkali-modified expanded vermiculite.

[0034] Example 3 A 10L open storage tank was used to simulate the manure storage environment. The specific procedure was to first add 5L of pig manure to the tank, then evenly sprinkle the corresponding covering material on the surface of the manure. In this example, seven treatments were set up: no covering (CK), covering with 2cm thick sawdust (W2), covering with 5cm thick sawdust (W5), covering with 2cm thick expanded vermiculite (V2), covering with 5cm thick expanded vermiculite (V5), covering with 2cm thick liquid manure floating covering material obtained in Example 1 (MV2), and covering with 5cm thick liquid manure floating covering material (MV5). Three replicates were set up for each treatment. The storage period was set at 30 days, during which NH3 and H2S were measured daily. On days 0, 3, 7, 14, 21, and 30 of the storage experiment, 200 mL of manure liquid was extracted with a syringe without disturbing the surface cover for measurement of pH, chemical oxygen demand (COD), ammonium nitrogen, nitrate nitrogen, soluble organic carbon (DOC), total solids (TS), and volatile solids (VS). Before and after the experiment, 20 g of samples of expanded vermiculite and the floating manure cover were collected for measurement of material parameters such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), specific surface area, and contact angle.

[0035] The daily emission rate of NH3 was measured using the dynamic chamber-boric acid absorption method; the H2S concentration was measured using a Newforth portable hydrogen sulfide meter. The pH was measured using a pH meter. The soluble organic carbon concentration was measured using a total organic carbon (TOC) analyzer (TOC Lcph, Shimadzu, Japan). + 、NO3 - Concentration was measured using a flow analyzer (San++, AutoAnalyzer, Netherlands). COD was determined using a water quality analyzer. TS and VS were determined using the constant weight method. TS was oven-baked at 105°C for 24 hours and then measured after cooling. VS was measured by heating the weighed sample in a muffle furnace at 550°C for 2 hours and then cooling.

[0036] The surface structure and morphology of each material were observed using an emission scanning electron microscope (FESEM, Ultra Plus, Zeiss, Germany). A Nicolet Vetex70 FTIR spectrophotometer (Vetex70, Bruker Corporation, Germany) was used to monitor the wavelength of 400–4000 cm -1 Refractive index at 400 nm; X-ray photoelectron spectroscopy (XPS) was performed on an ESCALAB 250Xi (Thermo Scientific, UK) with a scan energy of 100 eV and an area scan of 20 eV. Samples were ground in an agate mortar and measured as pellets and powders. N₂ adsorption and desorption isotherms were measured at 77 K. The specific surface area was determined using the Brunauer, Emmett, and Teller (BET) method under N₂ adsorption. Contact angles were measured using a JY-82C contact angle meter.

[0037] Origin 2021 was used for data processing and charting, and SPSS 26.0 was used for one-way analysis of variance to test whether there were significant differences among treatments (P < 0.05). Avantage software was used for XPS data analysis.

[0038] The microstructural changes of the expanded vermiculite and the floating covering material for liquid manure obtained in Example 1 before and after storage were observed using a scanning electron microscope (SEM). Figure 1 As shown, the pre-modified expanded vermiculite exhibited a smooth or slightly wrinkled appearance. The surface structure of the liquid manure floating cover material obtained in Example 1 underwent significant changes. After thorough grinding and mixing of the nano-hydrophobic silica and expanded vermiculite, fine particles adhered to the surface of the expanded vermiculite, indicating that the hydrophobic silica had successfully adhered to the surface of the expanded vermiculite, enhancing its buoyancy. During storage, the sawdust-treated material completely settled into the manure water by around the third day, while the unmodified expanded vermiculite completely sank by around the seventh day. Its surface was submerged in the manure water and adsorbed ions, forming massive crystals. This submersion phenomenon failed to reduce gas emissions and may even lead to increased emissions. In contrast, the liquid manure floating cover material obtained in Example 1 maintained excellent buoyancy throughout the storage process. Although fine particles on its surface also formed massive crystals due to gas adsorption, these fine particles remained firmly attached to the surface of the expanded vermiculite.

[0039] like Figure 2 As shown in (a), the infrared spectrum (FTIR) analysis found that the expanded vermiculite before and after modification was 3413 cm -1 and 1631cm-1 There are absorption peaks at 1023cm and 1060cm respectively, which are attributed to the stretching vibration of -OH. -1 The absorption peak at 1117 cm is derived from the vibration of Si-O; and after modification, the liquid manure floating covering material obtained in Example 1 has an absorption peak at 1117 cm -1 A strong Si-O-Si absorption peak appeared at 846 cm -1 Si-O-Si bending vibration was detected at 2965 cm, indicating that the surface hydroxyl groups and the modifier had a condensation reaction. In addition, the modified expanded vermiculite (i.e., the liquid manure floating covering material obtained in Example 1) -1 A sharp -CH3 asymmetric stretching vibration peak appears at the pores, indicating that hydrophobic groups are introduced into the material. XPS analysis further confirms this conclusion (e.g. Figure 2 As shown in (b)-(c)), the modified expanded vermiculite showed a CO vibration peak with a bond energy of 288.1 eV in the C1s spectrum, indicating that the modifier underwent a dehydration condensation reaction with the hydroxyl groups on the surface of the expanded vermiculite, confirming that the modifier has been successfully grafted onto the surface of the expanded vermiculite.

[0040] like Figure 2 As shown in (d), the specific surface area of ​​the liquid manure floating covering material obtained in Example 1 was significantly increased to 12.34 m 2 g -1 , much higher than the 5.64m of unmodified expanded vermiculite 2. g -1 This phenomenon is primarily due to the high specific surface area and surface activity of the nano-scale hydrophobic silica particles introduced during the modification process. These particles, loaded onto the expanded vermiculite skeleton, form a composite structure, significantly increasing the specific surface area of ​​the modified expanded vermiculite. The decrease in specific surface area after storage is due to the expanded vermiculite's strong water absorption, which causes it to sink into the slurry and adsorb ions, filling its interlayer pores and reducing its adsorption capacity. The increase in specific surface area of ​​the modified expanded vermiculite is due to changes in its interlayer structure after gas adsorption, further increasing its specific surface area.

[0041] The contact angle is a key indicator for evaluating the hydrophilicity and hydrophobicity of a material surface. When the contact angle is less than 90°, the solid surface is hydrophilic and the liquid wets the solid more easily. When the contact angle is greater than 90°, the solid surface is hydrophobic and the liquid does not wet the solid easily. Figure 2As shown in (e), the unmodified expanded vermiculite has a contact angle of 18.95°, indicating strong hydrophilicity. Therefore, it sinks in the manure after approximately 7 days of coverage. The modified expanded vermiculite, on the other hand, has a contact angle of 102.56°, indicating that its surface has been successfully transformed into a hydrophobic one, resulting in a good floating effect. After storage, the modified expanded vermiculite still maintains a contact angle close to 90°, indicating that it retains good floating properties after use. However, the duration of this performance requires further evaluation.

[0042] like Figure 3 As shown in (a) and (b), different covering materials significantly affect NH3 and H2S emissions during manure storage. Treatments with the 2 cm and 5 cm thick floating covering materials (MV2 and MV5) obtained in Example 1 reduced the NH3 volatilization rate. This is primarily due to the modified expanded vermiculite's ability to float on the surface of the manure for a long time, forming a stable covering layer that blocks the upward diffusion of the gas. Since NH3 is highly soluble in water, this covering layer effectively inhibits NH3 volatilization. In contrast, treatment with 2 cm thick sawdust (W2) increased NH3 emissions to some extent. This may be because the sawdust settles into the slurry during the initial storage period, preventing it from forming an effective covering layer. Furthermore, the sinking of the sawdust may release more nutrients, thereby promoting NH3 emissions. Cumulative NH3 emissions from the 2 cm thick sawdust (W2), 5 cm thick sawdust (W5), and 5 cm thick expanded vermiculite (V5) treatments did not differ significantly from those from the CK treatment. In contrast, MV2 and MV5 treatments significantly reduced NH3 emissions by 87%-95% (P<0.05), and MV2 and MV5 increased NH3 emission reduction efficiency by 53%-93% (P<0.05) compared with V2 and V5, indicating that the application of modified expanded vermiculite can effectively reduce NH3 emissions.

[0043] During the storage process, the emission concentration and cumulative emission of H2S are as follows: Figure 3 (c)-(d) The application of modified expanded vermiculite to form a floating layer can cause changes in the dissolved oxygen content of the slurry, thereby affecting H2S emissions. (Theoretically, the application of cover material creates an anaerobic environment, increasing hydrogen sulfide emissions.) However, the cumulative H2S emissions from the modified expanded vermiculite treatment were not significantly higher than those from the CK treatment throughout the storage period. This may be due to the inherent adsorption capacity of the modified expanded vermiculite, which was able to absorb some H2S. While both H2S concentrations and cumulative emissions increased in the W2 and W5 treatments, there was no significant difference. This may be due to the fact that the sinking of sawdust increased the carbon source in the slurry, resulting in more substrate available for microorganisms and promoting H2S emissions. It may also be due to the fact that sawdust, often used as a filler in biofilters, has a certain adsorption capacity, resulting in no significant difference in emissions.

[0044] After 30 days of storage, the physical and chemical properties of the manure water under each treatment are shown in Table 1. Under MV2 and MV5 treatments, NH4 + The content of modified expanded vermiculite was significantly higher than that of CK treatment (P<0.05). Compared with the initial ammonium nitrogen concentration in manure, CK treatment caused 68% loss of ammonium nitrogen, while V2 and V5 treatments caused 71% and 81% loss of ammonium nitrogen, respectively. However, MV2 and MV5 treatments caused 45% and 40% loss of ammonium nitrogen, respectively. It can be seen that the application of modified expanded vermiculite can reduce the loss of ammonium nitrogen by 23~28% compared with CK, and reduce the loss of ammonium nitrogen by 26~41% compared with ordinary expanded vermiculite. This shows that the modified expanded vermiculite reduces NH3 emissions, with NH4 + The form remains in the liquid phase, which significantly improves the agronomic utilization value of manure water.

[0045] The pH of manure is an important factor affecting gas emissions during its storage. The results showed that compared with CK, the pH of the W5 treatment was significantly reduced (P<0.05). This may be due to the hydrolysis of substances in the sawdust in the manure, producing organic acids that led to a decrease in the pH of the manure, and the acidic conditions of the manure promoted H2S emissions. In addition, COD (chemical oxygen demand) and DOC (soluble organic carbon) represent the content of organic matter and soluble organic carbon components in the manure that can be degraded by microorganisms, respectively. The COD and DOC contents of the W5 treatment were significantly higher than those of the CK (P<0.05), further confirming the effect of sawdust degradation on H2S emissions. Specifically, the degradation of sawdust increased the organic matter content in the manure, providing more substrates for microorganisms, thereby promoting the production and emission of H2S to a certain extent; Table 1 Physical and chemical properties of manure water after 30 days of storage under different covering materials ; CK: no mulch; W2: 2 cm thick sawdust mulch; W5: 5 cm thick sawdust mulch; V2: 2 cm thick expanded vermiculite mulch; V5: 5 cm thick expanded vermiculite mulch; MV2: 2 cm thick modified expanded vermiculite mulch; MV5: 5 cm thick modified expanded vermiculite mulch. Different lowercase letters in the same column indicate significant differences among treatments (P < 0.05). Table 2 Physical and chemical properties of pig manure water before storage in Example 3

[0046] Example 4 The pig manure was collected from a pig farm in Nanxiaowu Village, Jinzhou City, Hebei Province. The experiment was conducted in the laboratory of the Luancheng Agricultural Ecological Experimental Station of the Chinese Academy of Sciences, using a 10L open storage tank to simulate the manure storage environment. Specifically, 5L of pig manure was added to the tank, and then the corresponding covering material was evenly sprinkled on the surface of the manure. In this example, three treatments were set up: a control group (CK), a 5cm-thick covering with expanded vermiculite (V), and a 5cm-thick covering with the liquid manure floating covering material (AMV) obtained in Example 2. Each treatment was replicated three times. The storage period was set to 30 days, during which ammonia and hydrogen sulfide were measured daily, and methane gas was sampled and measured every three days. On days 0, 3, 7, 14, 21, and 30 of the storage experiment, 200ml of manure was extracted using a syringe without disturbing the surface covering and stored in a -20°C refrigerator for subsequent physical, chemical, and microbiological analysis. Take 20 g of expanded vermiculite and the liquid manure floating covering material (AMV) obtained in Example 2, and perform SEM, FTIR, XPS, specific surface area, average particle size, contact angle and other material indexes. The characterization method is the same as that in Example 3.

[0047] like Figure 4 (a) shows the material indicators of each material. The contact angle of expanded vermiculite increased (111.73°) after alkali modification and then hydrophobic modification. This is because the alkali modification destroyed the surface structure of the expanded vermiculite and activated the surface groups, which facilitated the subsequent hydrophobic modification and increased the efficiency of the hydrophobic modification. Figure 4 (b) shows the change in the average particle size of each material. The average particle size of the material after alkali modification is significantly reduced, indicating that it is corroded by KOH into smaller particles. Figure 4 (c) shows the infrared spectra of each material. We found that the hydrophobic modified material was the same as that shown in Example 3, and both showed vibrations of the hydrophobic group -CH3 and Si-O-Si, which proved the success of the hydrophobic modification.

[0048] from Figure 5 Scanning electron microscopy (SEM) magnification of expanded vermiculite and alkali-modified hydrophobic expanded vermiculite (i.e., the liquid manure floating covering material obtained in Example 2) reveals significant surface changes in the alkali-modified expanded vermiculite. Compared to the hydrophobic expanded vermiculite, the alkali-modified hydrophobic expanded vermiculite undergoes alkali modification, leading to cracking and disruption of the interlayer structure. This indicates successful alkali modification. After reaction with the hydrophobic silica, fine particles adhere to the surface of the alkali-modified expanded vermiculite. The expanded vermiculite completely sank in the manure by around the seventh day of storage, while the alkali-modified hydrophobic expanded vermiculite maintained good floating properties throughout storage, without cracking or sinking.

[0049] like Figure 6As shown in (a) and (b), different covering materials have different effects on NH3 during storage. Similar to the results in Example 3, we found that V treatment can reduce ammonia emissions during manure storage to a certain extent, but it still does not form a fixed floating layer. AMV, on the other hand, maintains a good floating effect and effectively reduces ammonia emissions. Modification with hydrophobic silica ensures good floating performance, avoiding the theoretical increase in ammonia emissions that would be caused by alkaline modification, effectively reducing ammonia emissions.

[0050] During the storage process, the emission concentration and cumulative emission of H2S are as follows: Figure 6 As shown in (c)-(d), AMV significantly reduced hydrogen sulfide concentrations. This is due to a combination of factors: first, the alkali-modified vermiculite likely increases hydroxyl groups, which oxidize hydrogen sulfide and reduce its concentration. Second, the application of alkali-modified vermiculite alters the pH of the manure surface microenvironment, thereby altering the environment in which hydrogen sulfide is generated. Furthermore, AMV significantly reduced hydrogen sulfide emissions (P < 0.05), reducing them by 37%. Compared with V, the application of AMV increased the emission reduction rate by nearly 51% (P < 0.05).

[0051] The impact of various covering materials on methane emissions is as follows Figure 6 As shown in (e)-(f), the V treatment significantly increased methane emissions compared with CK (P<0.05), and the application of AMV had no significant effect on methane emissions compared with CK.

[0052] After 30 days of storage, the physical and chemical properties of the manure water from each treatment are shown in Table 3. The V treatment, after sinking into the manure water, absorbed ammonium and nitrate nitrogen due to the adsorption of the vermiculite itself, resulting in lower concentrations of ammonium and nitrate nitrogen in the manure water. In contrast, the AMV treatment showed higher ammonium and nitrate nitrogen contents than the CK treatment, indicating that the material blocked gas emissions and also served as a nitrogen conservation measure. Furthermore, nitrogen losses (combined ammonium and nitrate nitrogen) were 17%, 45%, and 10% in the CK, V, and AMV treatments, respectively. This suggests that the AMV treatment had an advantage, reducing losses by 7% compared to the CK treatment.

[0053] It can be seen from Tables 2 and 4 that the physical and chemical properties of the initial state of the manure in Example 3 and Example 4 are quite different, but the application of the materials can produce a good gas emission reduction effect. Therefore, the new liquid manure floating covering material disclosed in the present invention can have a good gas emission reduction and nitrogen fixation effect on manure of different properties.

[0054] The change in pH value is closely related to the generation of gas. After AMV treatment, the manure water is alkaline, which shows that the use of this material changes the pH of the manure water and thus reduces the emission of hydrogen sulfide. At the same time, it does not cause the emission of ammonia. This shows that the floating layer has a good barrier effect and does not cause the hidden danger of increasing ammonia emissions. Table 3 Physical and chemical properties of fecal water after storage for 30 days in Example 4 ; Table 4 Physical and chemical properties of pig manure before storage in Example 4

[0055] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A floating covering material for liquid manure, characterized in that: The liquid manure floating covering material comprises expanded vermiculite and hydrophobic silica; The mass ratio of the expanded vermiculite to the hydrophobic silica is 9:1; The expanded vermiculite is an expanded vermiculite with a particle size of 3 to 6 mm; The hydrophobic silica is nano-scale hydrophobic silica.

2. The floating covering material for liquid excrement according to claim 1, characterized in that: The hydrophobic silicon dioxide is distributed on the surface of the expanded vermiculite.

3. The floating covering material for liquid excrement according to claim 1, characterized in that: The hydrophobic silica is spherical hydrophobic silica modified with a silane coupling agent.

4. A method for preparing a floating covering material for liquid manure, characterized in that: The method comprises fully mixing expanded vermiculite and hydrophobic silica to obtain the liquid manure floating covering material; The mass ratio of the expanded vermiculite to the hydrophobic silica is 9:1; The expanded vermiculite is an expanded vermiculite with a particle size of 3 to 6 mm; The hydrophobic silica is nano-scale hydrophobic silica.

5. The method for preparing the floating covering material for liquid excrement according to claim 4, characterized in that: The hydrophobic silica is spherical hydrophobic silica modified with a silane coupling agent.

6. The method for preparing the floating covering material for liquid excrement according to claim 4, characterized in that: The mixing process is carried out in a mortar; Alternatively, the mixing process is carried out in a blender.

7. A method for storing liquid feces, characterized in that: The method comprises: during the storage of liquid feces, covering the surface of the liquid feces with the liquid feces floating covering material as claimed in any one of claims 1 to 3.

8. The liquid manure storage method according to claim 7, characterized in that: The liquid manure floating covering material is covered on the surface of the liquid manure with a thickness of 2 to 10 cm.

9. The liquid manure storage method according to claim 7, characterized in that: The liquid excrement floating covering material is covered on the surface of the liquid excrement with a thickness of 3 to 5 cm.

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