Nickel-iron hydrotalcite, its preparation method and application in methanogenesis from amino acid wastewater

Abstract

This invention provides a nickel-iron hydrotalcite, its preparation method, and its application in methanogenesis from amino acid wastewater, relating to the synthesis of composite materials and clean energy production. In preparing the nickel-iron hydrotalcite, dodecylamine, water, and n-butanol are first mixed into a microemulsion liquid. Then, nickel salt and ferrous salt are added, and the pH is adjusted to 9-12 with a mixture of ammonia and sodium carbonate. After hydrothermal crystallization, a flower-shaped nickel-iron hydrotalcite is obtained. The resulting nickel-iron hydrotalcite exhibits a densely clustered layered structure, resulting in a uniform and stable flower-shaped lamellae structure. The layers contain pores, resulting in a large specific surface area, which is conducive to the enrichment and growth of methanogenic bacteria and can significantly improve the anaerobic utilization rate of amino acid wastewater.

Description

Technical Field

[0001] This invention relates to the synthesis of composite materials and the field of clean energy production, specifically to nickel-iron hydrotalcite, its preparation method, and its application in the production of methane from amino acid wastewater. Background Technology

[0002] The COD concentration of fermentation wastewater in amino acid production is very high, generally exceeding tens of thousands of mg / L. Even the diluted mixed wastewater has a COD concentration of nearly ten thousand mg / L, and contains high concentrations of organic matter and various inorganic salts. Anaerobic fermentation technology can simultaneously treat organic wastewater and recover bioenergy (H2 and CH4), offering good environmental and economic benefits and promising development prospects. However, at high organic matter concentrations, the anaerobic digestion efficiency of sludge decreases significantly, and the low anaerobic utilization rate is a bottleneck in the fermentation of amino acid wastewater.

[0003] Anaerobic digestion refers to the process by which organic matter is degraded to a stable state, forming gases such as methane and carbon dioxide, through the metabolic activities of anaerobic bacteria under anaerobic conditions. Currently, the mainstream theory in academia divides anaerobic digestion into four stages: hydrolysis, acidification, acetogenesis, and methanogenesis. These four stages of anaerobic digestion form an interdependent and transformative system, with different microorganisms completing each stage. Furthermore, the differences in biodynamics and bioenergetics among these microbial populations lead to an inherent imbalance between substrate and product, which is the fundamental reason for the poor stability of the anaerobic digestion process. A typical example of this imbalance is the accumulation of VFAs, which are mainly produced by Firmicutes and Bacteroidetes. These are the most active microbial phyla in the anaerobic system, primarily responsible for promoting VFA production. On the other hand, bacteria that degrade VFAs (such as syntrophs) grow slowly and only thrive under hydrogen partial pressures below 10⁻⁶. -3 VFAs are decomposed only at time ATM. Therefore, symbiotic bacteria and methanogens need to coexist to efficiently convert VFAs into CH4 and CO2. Thus, to improve the methanogenic efficiency of anaerobic digestion, it is necessary not only to increase electron transfer but also to promote the growth of symbiotic bacteria and methanogens.

[0004] Chinese patent document CN114752632A (202210581442.4) proposes a method for applying modified biochar in the anaerobic digestion of food waste to produce methanogens. The method involves thoroughly mixing biochar particles loaded with the iron-nickel composite oxide NiFe2O4 with food waste and then conducting anaerobic digestion to produce methanogens at a mesophilic temperature. This method optimizes the conductivity of the biochar, supplements the trace metal elements required for anaerobic digestion, enriches anaerobic functional bacteria, strengthens the electron transfer process between acid-producing and methanogenic bacteria, alleviates system acidification problems, and significantly increases the methane yield from the anaerobic digestion of food waste. However, food waste differs from chemical wastewater; it does not contain high concentrations of organic matter and contains a large amount of nutrients suitable for bacterial growth, thus requiring relatively lower anaerobic digestion conditions. In contrast, amino acid wastewater has a high COD and contains high concentrations of organic matter and various inorganic salts, and the existing composite materials do not significantly promote methanogen production during its anaerobic digestion. Summary of the Invention

[0005] This invention aims to improve the yield and efficiency of methanogenesis from amino acid wastewater fermentation by providing a nickel-iron hydrotalcite and its preparation method, and applying it to the anaerobic digestion of amino acids for methanogenesis. This invention utilizes nickel-iron hydrotalcite to accelerate the degradation and conversion rate of amino acids. The layered structure of nickel-iron hydrotalcite accelerates microbial aggregation and provides trace metal elements required by microorganisms during anaerobic digestion, enhancing the activity of methanogenic bacteria in metabolizing amino acid wastewater and promoting amino acid degradation. This achieves the goal of increasing methane production and yield; simultaneously, this technical solution has the advantages of convenient operation and easy large-scale implementation.

[0006] Layered double hydroxides (LDHs) are a class of layered materials composed of positively charged layers and anions with balanced charges. They are produced by using trivalent cations (e.g., Al) to form the layers. 3+ Co 3+ Fe 3+ Cr 3+ Partially substituted divalent cations (e.g., Ni) 2+ Mg 2+ Ca 2+ Mn 2+ Co 2+ Cu 2+ Zn 2+ ) or monovalent cations (e.g., Li) + This is used to construct a positively charged layer. The inserted anion is usually carbonate (CO3-). 2- However, this can be easily replaced by other anions (such as NO3-). - SO4 2- Cl - ,Br -Therefore, the unique structure of LDH makes it widely used in electrochemical research. During the preparation of hydrotalcite, after the formation of a layered structure, the trivalent metal cations exhibit significant polarization, making directional alignment difficult and hindering the formation of crystalline precipitates. Therefore, the raw material used in this invention is divalent iron, resulting in a well-formed nickel-iron hydrotalcite crystal.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing nickel-iron hydrotalcite includes the following steps:

[0009] (1) Mix dodecylamine, water and n-butanol and stir to form a microemulsion liquid;

[0010] (2) Add nickel salt and ferrous salt, or a solution containing nickel salt and ferrous salt, to the microemulsion liquid obtained in step (1); adjust the pH to 9-12 to obtain the precursor solution;

[0011] (3) The precursor solution obtained in step (2) is subjected to a hydrothermal crystallization reaction to obtain nickel-iron hydrotalcite precursor;

[0012] (4) After drying, grinding and purifying the precursor, dry and grind it again to obtain nickel-iron hydrotalcite.

[0013] Preferably, in step (1), dodecylamine and n-butanol are 0.9-1.1% and 0.4-0.6% of the molar amount of water, respectively.

[0014] Preferably, the nickel salt and ferrous salt (i.e., Ni) in step (2) 2+ and Fe 2+ The molar ratio of nickel salt to ferrous salt is 0.5 to 3:1; more preferably, the molar ratio of nickel salt to ferrous salt is 1 to 2:1.

[0015] The total amount of nickel salt and ferrous salt added in step (2) is in a molar ratio of 1.5 to 2.5:1 to dodecylamine.

[0016] Preferably, in step (2), the pH is adjusted to 9.5–11.2, more preferably 10–11. The pH is adjusted using a mixed solution of ammonia and sodium carbonate; the mixed solution is slowly added dropwise at a rate of one drop every 3–5 seconds. The mass fractions of NH3 and sodium carbonate in the mixed solution are 24.8%, and the molar ratio of NH3 to sodium carbonate in the mixture is 1:1.

[0017] Preferably, the hydrothermal crystallization reaction temperature in step (3) is 110-130°C, the reaction time is 20-26 h, and the pressure is normal.

[0018] Preferably, the precursor drying conditions in step (4) are 100-120°C for 12-24 hours.

[0019] Preferably, the purification method in step (4) is to wash with deionized water and anhydrous ethanol alternately 2 to 5 times, that is, wash with deionized water and anhydrous ethanol 2 to 5 times each.

[0020] Preferably, the vacuum drying temperature in step (5) is 40-60°C, the time is 12-24 hours, and the vacuum degree is -0.1 MPa.

[0021] This invention provides nickel-iron hydrotalcite prepared by the above method.

[0022] The X-ray diffraction pattern of the nickel-iron layered double hydroxide (TLD) shows that 2θ = 11.4°, 22.9°, 34.4°, 38.9°, 59.9°, and 61.2° correspond to the characteristic peaks (003), (006), (012), (015), (110), and (113) of the nickel-iron layered double hydroxide with card number 40-0215 ​​in the JCPDS standard document, respectively. The XRD pattern shows almost no impurity peaks, indicating that the material has high crystallinity and purity.

[0023] Preferably, the nickel-iron hydrotalcite is a flower-shaped aggregate obtained from densely clustered platy structures, with a flower-shaped aggregate diameter of 8–15 micrometers and a platy structure thickness of 20–50 nanometers. In this invention, the pH of the reaction solution is controlled to be 9–12, and crystallization is promoted by simultaneously adding ammonia and sodium carbonate, resulting in a flower-shaped aggregate with a larger specific surface area.

[0024] The nickel-iron hydrotalcite obtained by this invention has a uniform distribution of Fe, Ni, O and C elements, with atomic percentages of Fe, Ni, O and C of 23-30%, 28-50%, 10-20% and 15-21%, respectively, and the remainder being small amounts of H, Cl and other elements.

[0025] The nickel-iron hydrotalcite obtained by this invention has a specific surface area of ​​50-60 m². 2 / g. A larger specific surface area is more conducive to nickel-iron hydrotalcite promoting electron transfer and thus accelerating methanogenesis. The average adsorption pore size is 9–10 nm, and the average desorption pore size is 11–13 nm.

[0026] The nickel-iron hydrotalcite prepared by this invention has a layered structure. Its densely clustered layered structure forms a uniform and stable flower-shaped lamellae structure. The layers contain pores, resulting in a large specific surface area, which is beneficial for the enrichment and growth of methanogenic bacteria. Simultaneously, it can release trace elements Ni and Fe, supplementing the trace elements needed by microorganisms and enhancing the metabolism of amino acids by anaerobic fermentation bacteria. The nickel-iron hydrotalcite of this invention has a significant promoting effect on methanogenesis in amino acid wastewater, increasing methanogenesis by up to 41.62%, which is significantly superior to other nickel-iron composite materials (such as biochar materials loaded with the iron-nickel composite oxide NiFe2O4).

[0027] The nickel-iron hydrotalcite of this invention can significantly enhance the yield and rate of methane conversion from amino acid wastewater under mesophilic conditions. This suggests that nickel-iron hydrotalcite can selectively increase the activity of methanogenic microorganisms and optimize the sludge microbial community structure of the methanogenic anaerobic fermentation system. Furthermore, nickel-iron hydrotalcite can release trace amounts of Fe and Ni ions in weakly acidic fermentation broth.

[0028] This invention also provides the application of nickel-iron hydrotalcite in promoting anaerobic methanogenesis in amino acid wastewater, utilizing the aforementioned nickel-iron hydrotalcite to increase the yield and rate of methanogenic fermentation in amino acid wastewater. The mesophilic temperature is 35–40°C, preferably 37°C.

[0029] This invention also provides a method for promoting methane production from amino acid wastewater through anaerobic fermentation using nickel-iron hydrotalcite. The method is characterized by using an anaerobic fermentation system composed of amino acid wastewater, inoculated sludge enriched with methanogenic bacteria, nickel-iron hydrotalcite, and water to increase the methane yield and rate of mesophilic anaerobic fermentation of amino acid wastewater. The mesophilic temperature is 35–40°C, preferably 37°C.

[0030] The volume percentage of inoculated sludge in the anaerobic fermentation system is 30-40%; the amount of nickel-iron hydrotalcite added is 50-1000 mg / L.

[0031] This invention also provides a method for promoting the anaerobic fermentation of amino acid wastewater to produce methane using nickel-iron hydrotalcite, characterized by comprising the following steps:

[0032] (1) Acclimation of inoculated sludge: The wastewater sludge from the amino acid plant was cultured in an anaerobic environment at 35-40℃.

[0033] (2) Enriching sludge inoculated with methanogens: Add glucose to the sludge from step (1) and continue culturing under anaerobic conditions to achieve the large-scale reproduction of methanogens.

[0034] (3) Using amino acid waste liquid as substrate, inoculate the sludge obtained in step (2) with a volume fraction of 30-40% in the fermentation system, add 50-1000 mg / L of nickel-iron hydrotalcite, add a certain amount of water to form an anaerobic fermentation system, and carry out anaerobic fermentation.

[0035] Preferably, the sludge cultivation time in step (1) is 15–25 days; the sludge moisture content is 90%. The preferred cultivation temperature is 37 ± 0.2 °C.

[0036] Preferably, the amount of glucose added in step (2) is 0.1 to 0.2 g / L, and the culture is continued for 15 to 25 days under anaerobic conditions.

[0037] Preferably, the amount of nickel-iron hydrotalcite added to the anaerobic fermentation system in step (3) is 200–800 mg / L, more preferably 400–600 mg / L. The anaerobic fermentation temperature is 35–40℃.

[0038] The amino acid concentration in the amino acid waste liquid described in step (3) is 30-50%. The amino acid concentration in the anaerobic fermentation system is 6-10%.

[0039] Preferably, the anaerobic fermentation system may further include a nutrient solution, wherein the volume of the nutrient solution in the anaerobic fermentation system accounts for 0.1% to 0.2% of the total volume of the fermentation system.

[0040] The nutrient solution is a commonly used nutrient solution for anaerobic fermentation to produce methanogens. It includes one or more inorganic salts containing potassium, sodium, ammonium, calcium, iron, copper, zinc, manganese, aluminum, cobalt, nickel or molybdenum, as well as boric acid.

[0041] Preferably, the nutrient solution composition is as follows: 260–300 g / L NH4Cl, 950–1000 g / L NaHCO3, 200–300 g / L K2HPO4, 0.04–0.06 g / L H3BO3, 8–12 g / L CaCl2·2H2O, 1–3 g / L FeCl3·6H2O, 0.02–0.04 g / L CuCl2, 0.04–0.06 g / L ZnCl2, 0.4–0.6 g / L MnCl2·4H2O, 0.04–0.06 g / L AlCl3, 0.04–0.06 g / L CoCl2·6H2O, 0.04–0.06 g / L NiCl2, and 0.04–0.06 g / L (NH4)6Mo7O 24 The remainder is water. To ensure thorough mixing, the nutrient solution can be added to the fermentation system as a diluted solution.

[0042] The beneficial effects of this invention are:

[0043] The nickel-iron hydrotalcite prepared by this invention has a layered structure. Its densely clustered layered structure forms a uniform and stable flower-shaped lamellae structure. There are pores between the layers, resulting in a large specific surface area, which is conducive to the enrichment and growth of methanogenic bacteria and significantly improves the anaerobic utilization rate of amino acid waste liquid.

[0044] In the anaerobic fermentation process for methane production, nickel-iron hydrotalcite not only increases electron transport capacity and promotes interspecies electron transfer due to its high specific surface area, but also releases trace amounts of Fe and Ni elements into the fermentation broth, supplementing the methane-producing bacteria with trace inorganic nutrients. These positive factors significantly enhance the activity of methane-producing bacteria in utilizing amino acid wastewater, thereby increasing methane production.

[0045] The nickel-iron hydrotalcite of this invention has a significant promoting effect on methane production from amino acid wastewater, increasing the methane production by 41.62%, which is significantly better than other nickel-iron composite materials. Attached Figure Description

[0046] Figure 1 This is the X-ray diffraction pattern of nickel-iron hydrotalcite from Example 1.

[0047] Figure 2 This is the surface energy spectrum analysis diagram of nickel-iron hydrotalcite from Example 1.

[0048] Figure 3 This is a scanning electron microscope (SEM) image of nickel-iron hydrotalcite from Example 1.

[0049] Figure 4 This is the elemental distribution diagram of nickel-iron hydrotalcite in Example 1.

[0050] Figure 5 This is the effect of nickel-iron hydrotalcite in Example 1 on the cumulative methane production during anaerobic fermentation of amino acid waste liquid.

[0051] Figure 6 This describes the effect of nickel-iron hydrotalcite in Example 1 on the methane rate during the anaerobic fermentation of amino acid waste liquid. Detailed Implementation

[0052] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following embodiments.

[0053] Example 1

[0054] The preparation method of nickel-iron hydrotalcite includes the following steps:

[0055] (1) Mix 10 mmol dodecylamine with water (molar ratio of dodecylamine to water is 1:100), turn on the stirrer, and then add an appropriate amount of 5 mmol n-butanol (molar ratio of n-butanol to water is 1:200) and stir to form a microemulsion liquid.

[0056] (2) Add 10 mmol of nickel chloride and 10 mmol of ferrous chloride to deionized water and dissolve them completely. Add them to the microemulsion liquid obtained in step (1). Then slowly add a mixture of ammonia and sodium carbonate (the molar ratio of NH3 to sodium carbonate in the mixture is 1:1, and the mass fraction of NH3 is 24.8%), adjust the pH to 10, and obtain the precursor solution.

[0057] (3) The solution obtained in step (2) was subjected to hydrothermal crystallization reaction at 120°C for 24 hours;

[0058] (4) The sample obtained in step (3) is centrifuged to obtain the nickel-iron hydrotalcite precursor;

[0059] (5) The precursor obtained in step (4) was dried at 110°C for 16 hours, ground, and then washed three times alternately with deionized water and anhydrous ethanol.

[0060] (6) The purified product from step (5) was vacuum dried at 50°C and under a vacuum of -0.1 MPa for 24 hours and then ground to obtain nickel-iron hydrotalcite.

[0061] The prepared nickel-iron hydrotalcite was characterized as follows:

[0062] Figure 1 The X-ray diffraction pattern of nickel-iron hydrotalcite is shown. 2θ = 11.4°, 22.9°, 34.4°, 38.9°, 59.9°, and 61.2° correspond to the characteristic peaks (003), (006), (012), (015), (110), and (113) of nickel-iron hydrotalcite with card number 40-0215 ​​in the JCPDS standard document, respectively. Furthermore, in... Figure 1 The absence of impurity peaks in the sample indicates that the prepared material has a high purity.

[0063] Figure 2 The image shows the energy dispersive spectroscopy (EDS) analysis of the nickel-iron hydrotalcite surface. The results indicate that the atomic distribution of Ni and Fe is uniform.

[0064] Figure 3 The image shows nickel-iron hydrotalcite magnified by scanning electron microscopy (SEM) at 12,000x. It reveals that the nickel-iron hydrotalcite is a flower-shaped structure formed by dense clusters of platy structures, with a diameter of 8–15 micrometers and a thickness of 20–50 nanometers for the platy structure.

[0065] Figure 4 The elemental distribution map obtained by scanning electron microscopy shows that Fe, Ni, O, and C are evenly distributed in the nickel-iron hydrotalcite, indicating that the prepared material has very few impurities. The atomic percentages of Fe, Ni, O, and C are 29.8%, 28.6%, 17.2%, and 21.3%, respectively.

[0066] The BET specific surface area of ​​nickel-iron hydrotalcite is 56.0462 m². 2 / g, with an average adsorption pore size of 9.3074nm and an average desorption pore size of 12.0643nm.

[0067] Example 2

[0068] The preparation method of nickel-iron hydrotalcite includes the following steps:

[0069] Everything else is the same as in Example 1, except for the reaction conditions, which are shown in Table 1.

[0070] Table 1 Preparation conditions of nickel-iron hydrotalcite

[0071]

[0072] Products 1-6 obtained in Example 2 were subjected to X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy, and specific surface area analysis. The peak positions, atomic types and distributions, morphology, and specific surface areas of the obtained products were basically the same as those of the products in Example 1. The elemental analysis results of products 1-5 were basically the same as those of the products in Example 1. In the elemental analysis results of product 6, the percentage of nickel atoms was 48.3%, the percentage of iron atoms was 23.6%, the percentage of oxygen atoms was 11.3%, and the percentage of carbon atoms was 13.2%.

[0073] Product 7 exhibits a predominantly platy structure with only a few granular inclusions. The thickness of the platy structure is greater than 100 nanometers. The distribution of Fe, Ni, O, and C elements in the nickel-iron hydrotalcite is uneven, with Fe and Ni elements showing varying degrees of accumulation. The atomic percentages of Fe, Ni, O, and C are 46.4%, 22.6%, 16.4%, and 12.3%, respectively, with a specific surface area of ​​18.3270 m². 2 / g.

[0074] Product 8 exhibits a flower-like morphology formed by densely packed, plate-like clusters, with a diameter of 5-10 micrometers and a plate-like structure thickness exceeding 100 nanometers. The distribution of Fe, Ni, O, and C elements in the nickel-iron hydrotalcite is uneven, with Ni showing accumulation. The atomic percentages of Fe, Ni, O, and C are 22.8%, 35.6%, 25.6%, and 12.2%, respectively, with a specific surface area of ​​32.1570 m². 2 / g.

[0075] Example 3

[0076] Inoculation sludge acclimatization:

[0077] The sludge used was sourced from Jilin Meihua Amino Acid Co., Ltd. Before inoculation, it was anaerobically cultured at a mesophilic temperature for 15–25 days to enrich methanogenic bacteria. Then, 0.1–0.2 g / L of glucose was added, and the mixture was cultured for another 15–25 days to obtain sludge inoculum for anaerobic fermentation and methanogenesis. Specific sludge acclimatization conditions are shown in Table 2.

[0078] Table 2 Conditions for Acclimation and Cultivation of Inoculated Sludge

[0079]

[0080] The properties of the inoculated sludge obtained from acclimatization in items 1 to 4 are basically the same. The basic properties of the obtained sludge are as follows: pH = 7.39 ± 0.17, TSS = 76.53 ± 0.48 g / L, and VSS = 43.76 ± 0.31 g / L.

[0081] Example 4

[0082] A method for producing methane from amino acid wastewater by anaerobic fermentation was proposed. Multiple reactors were used, with each reactor containing 100 mL of amino acid wastewater (the amino acid content in the wastewater was approximately 40%, and the COD value was 8342 mg / L; the wastewater was sourced from an amino acid production company in Jinan). The inoculum addition amount (the No. 1 inoculum sludge acclimated in Example 3) was 150 mL (the inoculum accounted for 30% of the fermentation system's volume). In addition, each reactor was replenished with 150 mL of nutrient solution dilution. The nutrient solution concentration in the dilution was 5 mL / L, and the nutrient solution composition was: 280 g / L NH4Cl, 1000 g / L NaHCO3, 250 g / L K2HPO4, 0.05 g / L H3BO3, 10 g / L CaCl2·2H2O, 2 g / L FeCl3·6H2O, 0.03 g / L CuCl2, 0.05 g / L ZnCl2, 0.5 g / L MnCl2·4H2O, 0.05 g / L AlCl3, 0.05 g / L CoCl2·6H2O, 0.05 g / L NiCl2, and 0.05 g / L (NH4)6Mo7O 24 The nickel-iron hydrotalcite obtained in Example 1 was added to the reactor described above, and its concentration in the anaerobic fermentation system was set to 0, 200, 400, 600, and 800 mg / L, with three parallel experiments for each concentration. The volume of the fermentation reaction system was 500 mL, with any portion less than 500 mL made up by deionized water, and 125 mL of headspace was left in the reactor headspace.

[0083] Before the experiment, the initial pH of the system was adjusted to 7.1 ± 0.1, and the reactor was flushed with nitrogen for about 3 minutes to ensure anaerobic conditions. The reactor was then incubated at 37°C for 10 days. Methane production was measured daily. The methane collection device used an alkali removal method, utilizing 10% NaOH to absorb acidic gases such as CO2 and H2S from the gas; the discharged NaOH solution flowed into a graduated cylinder for easy measurement of CH4 volume.

[0084] Results of anaerobic fermentation for methanogenesis: Figure 5 As shown, the data is presented in Table 3. From Table 3 and... Figure 5It was found that when the amount of nickel-iron hydrotalcite added was between 200 and 800 mg / L, the CH4 production was significantly increased. The maximum cumulative methane production was obtained at an addition of 600 mg / L, with a methane production of 305.6 mL after 12 days of fermentation, which was 41.62% higher than that of the control group, indicating a significant increase in methane production.

[0085] Table 3. Effect of Nickel-Iron Hydrotalcite Addition Amount on Methane Production (mL)

[0086]

[0087] Figure 6 Table 4 shows the effect of nickel-iron hydrotalcite (NiFe) addition on the methane production rate of amino acids. The results indicate that when the NiFe added NiFe ranged from 200 to 800 mg / L, the methane production rate was significantly higher than that of the control group. The fermentation group with NiFe NiFe added 600 mg / L achieved the highest methane production rate on day 5 of the experiment. However, when the NiFe NiFe added NiFe exceeded 800 mg / L, the methane production rate began to decrease. The highest methane production rate was observed at a NiFe NiFe added NiFe of 600 mg / L.

[0088] Table 4. Effect of Nickel-Iron Hydrotalcite Addition Amount on Methane Generation Rate (mL / d)

[0089]

[0090]

[0091] Comparative Example 1

[0092] Products 7 and 8 were subjected to an anaerobic fermentation experiment to produce methane from amino acid wastewater according to the method described in Example 4. When the addition amount of products 7 and 8 was 600 mg / L, after 12 days of cumulative fermentation, compared with the blank control, their effects on the conversion of amino acid wastewater into methane were 5.26% and 13.53%, respectively.

[0093] Comparative Example 2

[0094] Nickel-iron hydrotalcite was prepared as follows: 30 mL of deionized water and 30 mL of ethylene glycol were measured into beakers and mixed thoroughly. Then, 1 mmol of nickel nitrate and 0.3 mmol of ferric nitrate were weighed and dissolved in the solution. 4 mmol of urea was added to form a homogeneous solution, which was then stirred in an ultrasonicator for 30 min. The homogeneous mixture was transferred to a 100 mL stainless steel-lined container and reacted at 160 °C for 24 h. After complete cooling, the mixture was filtered and dried.

[0095] The obtained nickel-iron hydrotalcite is exhibited as irregularly stacked flakes, with a thickness of less than 50 nanometers. The atomic percentages of Fe, Ni, O, and C are 12.2%, 35.5%, 22.4%, and 28.6%, respectively, with a specific surface area of ​​34.2312 m². 2 / g, with an adsorption average pore size of 8.1278nm and a desorption average pore size of 10.0238nm.

[0096] The above-mentioned nickel-iron hydrotalcite was used in an anaerobic fermentation experiment of amino acid wastewater to produce methane, according to the method described in Example 4, with an addition amount of 600 mg / L. After 12 days of cumulative fermentation, compared with the blank control, its effect on the fermentation and conversion of amino acid wastewater into methane was 15.32%.

[0097] Comparative Example 3

[0098] Iron-nickel was loaded onto biochar, following a method for preparing nickel-doped magnetic carbon disclosed in Example 1 of patent CN 111137891 A (202010028287.4). The prepared iron-nickel-loaded biochar material was subjected to an anaerobic fermentation experiment of amino acid wastewater to produce methane, according to the method described in Example 4, with an addition amount of 600 mg / L. After 12 days of cumulative fermentation, compared with the blank control, the improvement in the conversion of amino acid wastewater into methane was 21.34%.

[0099] Comparative Example 4

[0100] Nickel-iron hydrotalcite was prepared under the same conditions as in Example 1, except that only ammonia was used to adjust the pH. The resulting nickel-iron hydrotalcite exhibited a uniformly dispersed, flaky morphology with a flake thickness of less than 100 nanometers. The atomic percentages of Fe, Ni, and O were 36.2%, 35.8%, and 23.2%, respectively, and the specific surface area was 15.2312 m². 2 The adsorption average pore size was 6.2847 nm, and the desorption average pore size was 7.2822 nm. The above-mentioned nickel-iron hydrotalcite was used in an anaerobic fermentation experiment of amino acid wastewater to produce methane, according to the method described in Example 4, with an addition amount of 600 mg / L. After 12 days of cumulative fermentation, compared with the blank control, its effect on increasing the conversion of amino acid wastewater into methane by 11.26%.

[0101] The above content represents the preferred embodiments of the present invention. Without departing from the principles described in the present invention, improvements and adjustments can be made according to actual circumstances, and such improvements and adjustments should be within the protection scope of the present invention.

Claims

1. A method for promoting anaerobic fermentation of amino acid wastewater to produce methane using nickel-iron hydrotalcite, characterized in that, Includes the following steps: (1) Acclimation of inoculated sludge: The wastewater sludge from the amino acid plant was cultured in an anaerobic environment at 35~40 ℃; (2) Enrichment of methanogenic bacteria inoculated sludge: Add glucose to the sludge in step (1) and continue to culture under anaerobic conditions to achieve the large-scale reproduction of methanogenic bacteria; (3) Using amino acid waste liquid as substrate, inoculate the sludge obtained in step (2) with a volume fraction of 30-40% in the fermentation system, add 400-600 mg / L of nickel-iron hydrotalcite, add a certain amount of water to form an anaerobic fermentation system, and carry out anaerobic fermentation. The preparation method of the nickel-iron hydrotalcite includes the following steps: (a) A microemulsion is formed by mixing dodecylamine, water, and n-butanol, wherein the molar amounts of dodecylamine and n-butanol in water are 0.9–1.1% and 0.4–0.6%, respectively; (b) Add nickel salt and ferrous salt, or a solution containing nickel salt and ferrous salt, to the microemulsion obtained in step (a), wherein the molar ratio of nickel salt to ferrous salt is 1 to 2:1; adjust the pH to 10 to 11 using a mixed solution of ammonia and sodium carbonate to obtain a precursor solution, wherein the molar ratio of the total amount of nickel salt and ferrous salt to dodecylamine is 1.5 to 2.5:1; (c) The precursor solution obtained in step (b) is subjected to a hydrothermal crystallization reaction to obtain nickel-iron hydrotalcite precursor. The hydrothermal crystallization reaction temperature is 110~130℃ and the reaction time is 20~26 h. (d) After drying, grinding and purifying the precursor, dry and grind it again to obtain nickel-iron hydrotalcite.

2. The method for promoting anaerobic fermentation of amino acid wastewater to produce methane using nickel-iron hydrotalcite according to claim 1, characterized in that, The anaerobic fermentation system contains a nutrient solution, the volume of which accounts for 0.1% to 0.2% of the total fermentation system volume. The nutrient solution comprises one or more inorganic salts containing potassium, sodium, ammonium, calcium, iron, copper, zinc, manganese, aluminum, cobalt, nickel or molybdenum, and boric acid.

3. The method for promoting anaerobic fermentation of amino acid wastewater to produce methane using nickel-iron hydrotalcite according to claim 2, characterized in that, The nutrient solution composition is as follows: 260~300 g / L NH4Cl, 950~1000 g / L NaHCO3, 200~300 g / L K2HPO4, 0.04~0.06 g / L H3BO3, 8~12 g / L CaCl2·2H2O, 1~3 g / L FeCl3·6H2O, 0.02~0.04 g / L CuCl2, 0.04~0.06 g / L ZnCl2, 0.4~0.6 g / L MnCl2·4H2O, 0.04~0.06 g / L AlCl3, 0.04~0.06 g / L CoCl2·6H2O, 0.04~0.06 g / L NiCl2, and 0.04~0.06 g / L (NH4)6Mo7O 24 The rest is water.

4. The method for promoting anaerobic fermentation of amino acid wastewater to produce methane using nickel-iron hydrotalcite according to claim 1, characterized in that, The precursor drying conditions in step (d) are 100~120℃ for 12~24h.

5. The method for promoting anaerobic fermentation of amino acid wastewater to produce methane using nickel-iron hydrotalcite according to claim 1, characterized in that, The purification method in step (d) is to wash the sample 2 to 5 times alternately with deionized water and anhydrous ethanol.

6. The method for promoting anaerobic fermentation of amino acid wastewater to produce methane using nickel-iron hydrotalcite according to claim 1, characterized in that, In step (d), the vacuum drying temperature for the second drying is 40~60 ℃, the time is 12~24 h, and the vacuum degree is -0.1MPa.

7. The method for promoting anaerobic fermentation of amino acid wastewater to produce methane using nickel-iron hydrotalcite according to claim 1, characterized in that, The atomic percentages of Fe, Ni, O and C in the nickel-iron hydrotalcite are 23-30%, 28-50%, 10-20% and 15-21%, respectively. The nickel-iron hydrotalcite has a flower-shaped structure obtained by densely clustering lamellar structures, with a flower-shaped diameter of 8-15 μm and a lamellar structure thickness of 20-50 nm.

8. The method for promoting anaerobic fermentation of amino acid wastewater to produce methane using nickel-iron hydrotalcite according to claim 1, characterized in that, Nickel-iron hydrotalcite has a specific surface area of ​​50~60 m². 2 / g, with an average adsorption pore size of 9~10 nm and an average desorption pore size of 11~13 nm.

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