Modified biochar as well as preparation method and application thereof

Abstract

The invention discloses modified biochar as well as a preparation method and application thereof, and belongs to the technical field of biochar materials. The preparation method of the modified biochar comprises the following steps: performing ultrasonic treatment on a mixed solution of biochar and a ferric iron solution, then adjusting the pH value of the mixed solution to 10.5-11, and enabling iron adsorbed by the biochar to form ferric hydroxide; washing the biochar adsorbed with the ferric hydroxide until the pH value of a washing solution is 6.5-7.5, and then drying the biochar adsorbed with the ferric hydroxide. The modified biochar prepared by the method can macroscopically improve the hydrolytic acidification rate and methane production efficiency, microscopically enrich hydrolytic flora and methane production flora, participate in electron transfer in biochemical reaction and accelerate material mass transfer, and can be popularized and applied as a kitchen waste anaerobic digestion technology for efficiently producing methane.

Description

Technical Field

[0001] The present invention relates to the technical field of biochar materials, and in particular to a modified biochar and a preparation method and application thereof. Background Art

[0002] Kitchen waste, mainly composed of organic solid waste such as starch, cellulose, protein and fat, is one of the important sources of municipal solid waste. It is rich in nutrients and easily biodegradable. Currently, the main treatment strategies for kitchen waste include landfill, incineration, composting and anaerobic digestion. Landfills have disadvantages such as large land area, unpleasant odor and high leachate concentration, which make it difficult to realize the resource utilization of kitchen waste. Although incineration has the advantages of relatively simple operation and low pathogen rate, kitchen waste has a high moisture content and low calorific value. Incineration is prone to produce toxic pollutants such as dioxins, and the cost is relatively high. Composting is relatively cheap, but due to the high moisture content of kitchen waste, it is not suitable for the growth and reproduction of microorganisms, and the resulting fertilizer is also likely to be of poor quality. Anaerobic digestion has attracted much attention due to its advantages such as good reduction effect and low operating costs.

[0003] Anaerobic digestion primarily relies on the synergistic action of hydrolytic acidifying microorganisms and methanogenic microorganisms to convert organic matter into biogas, biogas residue, and fermentation liquid rich in carbon sources. The main component of biogas is methane, a valuable energy carrier. Anaerobic digestion is currently mainly used to treat high-concentration organic matter and wastewater, and is expected to play a key role in future sustainable development. In addition to greatly improving environmental pollution problems, the use of anaerobic digestion technology to treat food waste can also convert the methane produced during the anaerobic digestion process into electricity or biogas, thereby realizing the resource utilization of food waste and contributing dual value to environmental protection and energy utilization.

[0004] Anaerobic digestion reactions can be divided into three stages: hydrolysis, acid and hydrogen production, and methanogenesis. Furthermore, food waste has high water content, high organic matter content, and a high CN ratio. This leads to the accumulation of ammonia nitrogen and volatile fatty acids during simple anaerobic digestion, which in turn affects the activity of methanogens and the efficiency of the methanogenesis stage. This ultimately leads to low methane yields, unsatisfactory results, and even reactor collapse.

[0005] Therefore, finding a good way to speed up the anaerobic digestion process and improve the efficiency of the methane production stage has become a technical difficulty in the current research on anaerobic digestion technology to treat kitchen waste.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of the present invention is to provide a modified biochar and a preparation method and application thereof, so as to solve or improve the above-mentioned technical problems.

[0008] The present invention can be implemented like this:

[0009] In a first aspect, the present invention provides a method for preparing modified biochar, comprising the following steps: ultrasonically treating a mixture of biochar and a trivalent iron solution, then adjusting the pH value of the mixture to 10.5-11 and allowing the iron adsorbed by the biochar to form ferric hydroxide; washing the biochar adsorbed with ferric hydroxide until the pH value of the washing liquid is 6.5-7.5, and then drying the biochar adsorbed with ferric hydroxide.

[0010] In an optional embodiment, the ferric iron source in the ferric iron solution includes at least one of FeCl3·6H2O, Fe2(SO4)3 and Fe(NO3)3.

[0011] In an optional embodiment, the ultrasonic treatment time is 1 h to 4 h.

[0012] In an optional embodiment, before washing, the mixed solution is further post-treated by adjusting the pH value to 10.5-11.

[0013] In an alternative embodiment, post-processing comprises shaker processing.

[0014] In an optional embodiment, the shaking treatment is performed at 170-180 rpm for 10-12 hours.

[0015] In an optional embodiment, the drying is performed at 150° C. to 160° C. for 1 h to 3 h.

[0016] In a second aspect, the present invention provides a modified biochar prepared by the preparation method of any one of the aforementioned embodiments.

[0017] In an optional embodiment, the Fe contained in the modified biochar mainly exists in the form of Fe2O3, and the modified biochar has both carbon-carbon double bonds and carbon-oxygen single bonds.

[0018] In a third aspect, the present invention provides a use of the modified biochar according to the aforementioned embodiment in promoting methanogenesis by anaerobic digestion.

[0019] In an optional embodiment, the modified biochar is used in the anaerobic digestion of food waste to produce methanogen.

[0020] The beneficial effects of the present invention include:

[0021] The biochar modified with iron in this invention exhibits no significant changes in pore structure or surface roughness compared to the unmodified biochar. However, the surface of the modified biochar contains iron, primarily in the form of Fe₂O₃. Furthermore, the modified biochar has more carbon-carbon double bonds and carbon-oxygen single bonds than the unmodified biochar, and a higher carboxyl group content.

[0022] The modified biochar prepared by this method can improve the hydrolysis and acidification rate and methane production efficiency on a macro level. On a micro level, it can enrich the hydrolytic and methanogenic bacteria, participate in electron transfer in biochemical reactions, and accelerate material mass transfer. It can be promoted and applied as an anaerobic digestion technology for efficient methane production of kitchen waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 SEM images of biochar materials before and after modification;

[0025] Figure 2 is the EDS graph of biochar before and after modification;

[0026] Figure 3 FTIR spectra of biochar before and after iron modification;

[0027] Figure 4 To study the effect of adding different concentrations of modified biochar on pH during anaerobic digestion;

[0028] Figure 5 The effect of different concentrations of modified biochar on dissolved chemical oxygen demand in anaerobic digestion;

[0029] Figure 6 To simulate the kinetics of methanogenesis in anaerobic digestion under the influence of modified biochar at different concentrations;

[0030] Figure 7 The effects of modified biochar at different concentrations on volatile fatty acids;

[0031] Figure 8 The effects of modified biochar at different concentrations on EPS;

[0032] Figure 9 is the XRD pattern of modified biochar after anaerobic digestion reaction;

[0033] Figure 10 The X-ray photoelectron spectroscopy analysis results of modified biochar before and after the reaction;

[0034] Figure 11 The phylum-level community distribution of anaerobic digestion system of biochar before and after modification;

[0035] Figure 12Horizontal heat map of the anaerobic digestion system of biochar before and after modification. DETAILED DESCRIPTION

[0036] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0037] The modified biochar provided by the present invention and its preparation method and application are described in detail below.

[0038] The present invention provides a method for preparing modified biochar, comprising the following steps: subjecting a mixed solution of biochar and a ferric iron solution to ultrasonic treatment, subsequently adjusting the pH value of the mixed solution to 10.5-11 and allowing the iron adsorbed by the biochar to form ferric hydroxide; washing the biochar adsorbed with the ferric hydroxide until the pH value of the washing solution is 6.5-7.5, and subsequently drying the biochar adsorbed with the ferric hydroxide.

[0039] The above-mentioned trivalent carbon solution is used to modify biochar, and the trivalent iron source in the trivalent iron solution can illustratively include at least one of FeCl3·6H2O, Fe2(SO4)3 and Fe(NO3)3.

[0040] In some optional embodiments, the biochar can be first filtered through a sieve (e.g., 40 mesh), then rinsed with deionized water, and then fully dried. The drying temperature during the process can be illustratively 70° C. to 80° C. (preferably 75° C.).

[0041] Taking the ferric iron as FeCl3·6H2O as an example, the ferric iron solution is prepared by dissolving FeCl3·6H2O in deionized water. For example, 5.42 g of FeCl3·6H2O can be dissolved in 200 mL of deionized water and stirred thoroughly.

[0042] In some optional embodiments, the ultrasonic treatment time can be 1 hour to 4 hours, such as 1 hour, 2 hours, 3 hours or 4 hours, etc. In some more typical embodiments, the ultrasonic treatment time is 2 hours.

[0043] In some optional embodiments, an alkaline solution can be used to adjust the pH of the mixed solution. For example, the alkaline solution can include a NaOH solution and / or a KOH solution. Taking a NaOH solution as an example, a 2 mol / L NaOH solution can be used to adjust the pH of the mixed solution to 10.87.

[0044] The pH value of the mixed solution is adjusted by using an alkaline solution to convert the iron adsorbed on the biochar into iron hydroxide.

[0045] In some optional embodiments, before washing, the mixed solution is further subjected to post-treatment after adjusting the pH value to 10.5-11. The post-treatment may include shaking treatment, which may be performed at 170-180 rpm for 10-12 hours. The shaking treatment allows the iron ions to react more fully to form ferric hydroxide, that is, all the iron ions are converted into ferric hydroxide.

[0046] It should be noted that the shaking table treatment method can also be replaced by conventional slow stirring or small amplitude shaking.

[0047] The washing can be performed with deionized water. The number of washing times is not limited. The pH value of the washing solution is preferably 6.5 to 7.5 (preferably 7.0).

[0048] In some optional embodiments, drying can be performed at 150° C. to 160° C. for 1 hour to 3 hours, preferably at 155° C. for 1 hour.

[0049] As mentioned above, the above preparation method is simple to operate, the process is easy to control, and is suitable for batch preparation of modified biochar.

[0050] Correspondingly, the present invention also provides a modified biochar, which is prepared by the above preparation method.

[0051] This modified biochar, designated "BC-Fe" (abbreviated "BF"), exhibited no significant changes in pore structure or surface roughness compared to the unmodified biochar. However, the surface of this modified biochar contained iron, primarily in the form of Fe₂O₃. Furthermore, this modified biochar had more carbon-carbon double bonds and carbon-oxygen single bonds than the unmodified biochar, and a higher carboxyl group content.

[0052] In addition, the present invention also provides an application of the modified biochar in promoting anaerobic digestion and methane production.

[0053] In some optional embodiments, the modified biochar can be used in the anaerobic digestion of food waste to produce methane. Specifically, the modified biochar can macroscopically increase the hydrolysis and acidification rate and methane production efficiency. Microscopically, it can enrich hydrolytic and methanogenic bacteria, participate in electron transfer in biochemical reactions, and accelerate material mass transfer. Therefore, it can be promoted and applied as a highly efficient methane-producing anaerobic digestion technology for food waste.

[0054] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0055] Some of the materials and reagents used in the following examples and test examples are from the following sources:

[0056] Biochar: Wood biochar particles were purchased from Shanghai Vita Chemical Reagent Co., Ltd.

[0057] Ferric chloride: analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0058] Sodium hydroxide: analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0059] The kitchen waste substrate is the kitchen waste prepared by the laboratory. The core components are starch, vegetables, fruits and meat products, accounting for 40%, 30%, 20% and 10% respectively (wet weight basis). Specifically, pork, rice, cabbage and banana peels with a fat-to-lean ratio of 1:1 are combined according to the above ratio to form the digestion substrate required for the experiment. Then, the combined substrate is broken up with a blender to ensure that the particle size does not exceed 5 mm after breaking, so that it is convenient for use and addition in subsequent experiments. Inoculated anaerobic sludge: taken from the continuously running kitchen waste medium-temperature anaerobic digestion reaction device.

[0060] The properties of the above-mentioned kitchen waste and inoculated sludge are shown in Table 1.

[0061] Table 1 Properties of kitchen waste and inoculated sludge

[0062] index kitchen waste Inoculated sludge pH 4.44 7.39 TS(g / L) 42.145 32.685 VS (g / L) 40.445 23.0170 VS / TS 0.96 0.71 TCOD (mg / L) 27775 12210 SCOD (mg / L) 9200 580

[0063] Example 1

[0064] This embodiment provides a modified biochar, the preparation method of which is as follows:

[0065] The biochar was filtered through a 40-mesh sieve, rinsed with deionized water, and thoroughly dried at 75°C. 5.42 g of FeCl₃·6H₂O was dissolved in 200 mL of deionized water and stirred thoroughly. Then, 5 g of biochar was added to the solution to obtain a mixed solution. The mixed solution was then ultrasonically treated at room temperature for 2 h. After ultrasonic treatment, a 2 mol / L NaOH solution was added dropwise to adjust the pH to 10.87. The glass bottle was then placed in a shaker at 175 rpm for 12 h. After the reaction stabilized, the solution was filtered using filter paper. After filtration, the filtered biochar was repeatedly washed with deionized water until the pH of the washing solution reached 7.0. Finally, the biochar was dried in a 155°C oven for 1 h to obtain the modified biochar.

[0066] Example 2

[0067] This embodiment provides a modified biochar, the preparation method of which is as follows:

[0068] The biochar was filtered through a 40-mesh sieve, rinsed with deionized water, and thoroughly dried at 70°C. 5.42 g of FeCl3·6H2O was dissolved in 200 mL of deionized water and stirred thoroughly. Then, 5 g of biochar was added to the above solution to obtain a mixed solution. The mixed solution was then ultrasonically treated at room temperature for 1 h. After ultrasonic treatment, a 2 mol / L NaOH solution was added dropwise to adjust the pH to 10.5. The glass bottle was then shaken at 170 rpm for 12 h. After the reaction stabilized, the solution was filtered using filter paper. After filtration, the filtered biochar was repeatedly washed with deionized water until the pH of the washing solution was 6.5. Finally, the biochar was dried in a 150°C oven for 3 h to obtain modified biochar.

[0069] Example 3

[0070] This embodiment provides a modified biochar, the preparation method of which is as follows:

[0071] The biochar was filtered through a 40-mesh sieve, rinsed with deionized water, and thoroughly dried at 80°C. 5.42 g of FeCl₃·6H₂O was dissolved in 200 mL of deionized water and stirred thoroughly. Then, 5 g of biochar was added to the above solution to obtain a mixed solution. The mixed solution was then ultrasonically treated at room temperature for 4 h. After ultrasonic treatment, a 2 mol / L KOH solution was added dropwise to adjust the pH to 11. The glass bottle was then stirred at 180 rpm for 10 h. After the reaction stabilized, the solution was filtered using filter paper. After filtration, the filtered biochar was repeatedly washed with deionized water until the pH of the washing solution reached 7.5. Finally, the biochar was dried in a 160°C oven for 1 h to obtain the modified biochar.

[0072] Test example

[0073] The modified biochar prepared in Example 1 was subjected to structural detection and characterization.

[0074] (1) Analysis of basic properties of modified biochar materials

[0075] In order to deeply study the surface microstructure of modified biochar materials, scanning electron microscopy (SEM) technology was used, combined with energy dispersive X-ray spectroscopy (EDS) for comprehensive analysis. This method can accurately capture the microscopic features of the surface of modified biochar materials and reveal the distribution of their chemical elements. In addition, in order to explore the crystal structure of modified biochar materials, X-ray diffractometer (XRD) was used for measurement. In the test, Cu target K α The X-ray source was set at a 2θ angle range of 10° to 80° and a scan rate of 2° / min to ensure data accuracy and reliability. Furthermore, the X-ray tube voltage was set at 40 kV to ensure stability and consistency in experimental conditions. These tests were conducted to characterize the crystal structure of the modified biochar.

[0076] ①. Scanning by electron microscope, the surface characteristics of biochar before and after modification were analyzed. The results are as follows: Figure 1 As shown, (a) and (c) are SEM images of the biochar before modification at different magnifications, and (b) and (d) are SEM images of the biochar after modification at different magnifications.

[0077] Depend on Figure 1 It can be seen that the surface of biochar before and after modification is relatively rough and contains a relatively porous structure. Through image comparison, iron modification has almost no effect on surface roughness and porosity.

[0078] ②, Analyze the surface characteristic X-ray of biochar before and after modification by EDS, the results are as follows Figure 2 As shown, (a) is the EDS scanning image of the material before modification, (b) is the EDS scanning image of the material after modification, (c) is the SEM image of the material after modification; (d) is the position of the Fe element on the SEM image. Figure 2 It can be seen from (a), (c) and Table 2 that the presence of Fe element was not obviously found in the biochar before modification. Figure 2 It can be seen from (b), (d) and Table 2 that after iron modification, obvious Fe elements were found on the surface of biochar.

[0079] Table 2 Surface elements of biochar before and after modification

[0080]

[0081]

[0082] (2) Analysis of surface functional groups of modified biochar materials

[0083] To accurately analyze the surface functional group structure of BF materials, Fourier transform infrared absorption spectroscopy (FTIR) was used. This technique can provide qualitative analysis of surface functional groups and semi-quantitative analysis through changes in vibrational modes, thereby revealing the vibration of polar covalent bonds in the product and providing a deeper understanding of the structural characteristics of the functional groups.

[0084] The data of FTIR spectrum analysis of biochar before and after modification are as follows Figure 3 As shown by Figure 3 It can be seen that the biochar before and after modification showed obvious peaks at specific wavelengths, which were 3450, 1585, and 1000-1200 cm -1 Within the range of 600cm -1 3450cm -1This is a broad peak caused by intermolecular hydrogen bonding. This peak is mainly attributed to the -OH group in alcohols and phenols, that is, the absorption peak of hydroxyl groups. 1585cm -1 The absorption peak near the wavelength is usually associated with a specific chemical bond vibration mode. It is generally believed that this peak is caused by the stretching vibration of -C=C (carbon-carbon double bond) and -C=O (carbon-oxygen double bond). 1000~1200cm -1 The absorption peaks in this region are related to specific chemical bonds. They are mainly attributed to -CO (carbon-oxygen single bond). If COC (ether bond) is involved, the absorption peaks usually show a double peak structure. 600~900cm -1 The absorption peaks in the region are generally believed to be caused by the vibration of CH (carbon-hydrogen bond). The chemical bond spectrum peaks of the corresponding functional groups can be found in both biochars before and after modification. Among them, the modified biochar has the peaks at 1580, 1040-1120 cm -1 The peak at 100 nm is more prominent than that of biochar, indicating that the iron-modified biochar has more carbon-carbon double bonds and carbon-oxygen single bonds, which can be inferred to be due to a higher BF carboxyl content. The number of oxygen-containing functional groups is positively correlated with methane yield, and increasing the BF carboxyl content can accelerate the rate of methane production during anaerobic digestion.

[0085] Application Examples

[0086] To understand the effects of iron-modified materials on the anaerobic digestion of food waste, this study designed five batch experiments. Under the same conditions, 10 g / L biochar, 1 g / L, 2 g / L, 5 g / L, and 10 g / L BF were added to the reactor for anaerobic digestion of food waste. The VS of the inoculated anaerobic sludge was 23.5 g / L, and the VS of the substrate (food waste) was 65.0 g / L. The anaerobic digestion reaction was carried out in 100 mL serum bottles. During the startup phase, 60 mL of inoculated sludge, 11 mm L of food waste, and 9 mL of water were added to each group. A set of parallel samples was set up for each group. The entire experiment was terminated after the gas production curve stabilized. Basic indicators such as methane production, pH value, dissolved chemical oxygen demand, and volatile fatty acids were measured during the experiment.

[0087] The following is the method for basic indicator analysis:

[0088] TS and VS were determined by gravimetric method, and the drying and calcination temperatures were 105°C and 550°C, respectively, to determine VS;

[0089] Water samples were filtered through a 0.45 μm pore size filter for the determination of dissolved substances, such as SCOD, ammonia nitrogen, and dissolved phosphate, and then filtered through a 0.22 μm pore size filter for the determination of VFAs. SCOD was determined by rapid digestion spectrophotometry. VFAs (acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, isovaleric acid, and n-hexanoic acid) were determined using a gas chromatograph equipped with a flame ionization detector and a DB-FFAP capillary column.

[0090] Extracellular polymeric substances (EPS) were classified into soluble EPS, loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS) based on their binding tightness. These three types of EPS were fractionated and extracted using a "heating-centrifugation-0.45 μm pore filter" method. Protein was determined using the bicinchoninic acid (BCA) method, with bovine serum albumin (BSA) as the standard. Total sugars were determined using the phenol-sulfuric acid method, with glucose as the standard.

[0091] The methane content of the gas produced in the experiment was measured by gas chromatograph.

[0092] (1) Effects of different concentrations of materials on the methane production process of anaerobic digestion of kitchen waste

[0093] ① Effect of modified biochar on pH

[0094] The pH value can show the macroscopic parameters of the biochemical reaction performance of anaerobic digestion at each stage, and its changing trend can indicate the stability of the anaerobic reaction system. Figure 4 shown.

[0095] The initial pH of the reaction was adjusted to 7.5. Figure 4 As can be seen, the five systems rapidly acidified during the initial reaction, with a significant drop in pH. The pH did not begin to recover until the ninth day. The pH quickly returned to neutral between days 10 and 15, then slowly increased to around 8.0. The pH in the group with 10 g / L BF addition rose significantly from days 5 to 9 compared to the other groups, returning to neutral levels more quickly. The pH in the blank group (biochar group) was lower than that of the other groups before day 22. Furthermore, considering that the optimal growth environment for methanogens is neutral, the pH monitoring results of the anaerobic digestion reaction system suggest that BF, compared to biochar, has a more favorable effect on mitigating acidification. Therefore, during the initial acidification process, there was a trend toward greater acidification mitigation with increasing BF concentration.

[0096] ② Effect of modified biochar on dissolved chemical oxygen demand

[0097] The content of SCOD during anaerobic digestion can reflect the degradation performance of organic matter in the reaction system. The effects of different concentrations of modified materials on the SCOD content are as follows: Figure 5As shown in the figure, SCOD concentrations increased in all systems during the initial reaction, before gradually decreasing on day eight. The figure shows that the SCOD degradation rate in the system with a material concentration of 10 g / L was faster than in the other systems. Around day 20, it was clear that the unmodified material group had the highest SCOD content, indicating a slower degradation rate. These observations, combined with the pH effect, indicate that BF accelerates the degradation of organic matter.

[0098] ③ Effect of modified biochar on methane production and kinetic analysis

[0099] In order to more thoroughly evaluate the effects of different modified biochars on each stage of anaerobic digestion, the Gompertz model was used to accurately fit the cumulative methane production curve. The purpose of this method is to deeply analyze the hydrolysis rate, methanogenesis rate, and potential methanogenesis within the system from a quantitative perspective. The relevant kinetic parameters are shown in Table 3. The experimental data are highly consistent with the fitting results of the three-phase Gompertz model, which is reflected in the fact that all five anaerobic digestion systems showed R 2 The fitting results are consistent with the methane accumulation. Figure 6 shown.

[0100] Table 3 Kinetic parameters obtained using three-phase Gompertz simulation fitting

[0101] Biochar materials <![CDATA[M0(mL CH4 / g VS added )]]> <![CDATA[μ(mL CH4 / g VS added / d)]]> λ(d) <![CDATA[R 2 ]]> biochar 290.6±7.2 148.3±2.2 10.6 0.996 1g / L 310.4±3.1 143.8±2.3 9.2 0.999 2g / L 303.6±4.0 133.3±3.9 8.9 0.999 5g / L 306.0±6.4 127.5±4.0 9.3 0.997 10g / L 313.2±5.4 133.9±2.3 8.5 0.998

[0102] Through the methane accumulation and fitting results, it can be found that the methane production and methane production potential of the BF material concentration group of 10 / L are the highest, and the theoretical value of methane production potential is 313.2±5.4mL / gVS added , compared to biochar 290.6±7.2mL / gVS added The methane production potential increased by 7.78%. Furthermore, the methane production potential increased substantially with increasing concentration of the modified material. Based on the above, it can be concluded that BF has an effect on increasing methane production from anaerobic digestion of food waste, thereby enhancing biogas production efficiency.

[0103] ④ Effect of modified biochar on volatile fatty acids

[0104] In the anaerobic digestion reaction, VFAs is an important indicator that can reflect the acidification process and methanogenesis process of the anaerobic digestion system. The two processes correspond to the accumulation and degradation of VFAs respectively. Figure 7As shown, during the experimental reaction, VFAs existed primarily in the form of acetic acid, propionic acid, and butyric acid. VFA accumulation peaked on the fifth day of the reaction and decreased significantly on the seventh day, consistent with the pH values. This suggests that VFAs produced during the reaction are one of the primary causes of system acidification. VFA concentrations did not differ significantly between the groups. In the later stages of the reaction, the group with the highest concentration had lower VFA concentrations than the other groups, suggesting that BF has a positive effect on the decomposition and conversion of short-chain fatty acids.

[0105] ⑤. Effect of modified biochar on EPS after reaction

[0106] EPS is a high molecular weight polymer secreted by microorganisms under specific conditions, which can protect microorganisms from external harmful substances. EPS can be divided into soluble EPS (SEPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS). The main components of EPS are polysaccharides (PS), proteins (PN) and humus. In the experiment, the effects of different concentrations of BF on different types of EPS were as follows: Figure 8 shown.

[0107] Furthermore, the effects of modification on the crystal structure characteristics of biochar were studied and the crystal structure characteristics were analyzed by X-ray diffractometer. Figure 9 As shown by Figure 9 It can be seen that within the scanning range, the spectrum has sharp peaks at 77°, 64°, 44° and 38°. The peak morphology combination of these four regions is very similar to the carbon morphology. This result shows that although the biochar has undergone modification, the basic characteristics of its crystal structure remain stable.

[0108] Furthermore, to fully explore the elemental composition, chemical bonds, and oxygen-containing functional groups on the surface of the modified biochar, a Thermo Scientific K-Alpha X-ray Photoelectron Spectrometer (XPS) was used for detailed examination. Peak searching and fitting were performed to conduct in-depth qualitative and detailed spectral analysis, revealing the microscopic chemical properties of the modified functional carbon surface.

[0109] By measuring the photoelectron spectrum, the chemical composition and chemical state information of the sample surface can be obtained. Figure 10As shown. (a) is the XPS of the material before the reaction. According to the peak fitting data, there are obvious peaks at 723.77eV and 710.97eV. These two peaks indicate that the Fe in the modified material before the reaction mainly exists in the form of Fe2O3. And (b) shows that the XPS peaks of the modified material after the reaction are mainly composed of peaks at 729.09eV, 712.12eV, 725.07eV, 710.51eV, and 722.81eV, 708.84eV. This shows that the Fe in the modified material after the experiment mainly exists in the form of Fe3O4, Fe2O3 and FeO. Compared with before the reaction, a considerable part of the Fe is reduced from trivalent to divalent after the reaction, that is, Fe is in the process of gaining electrons in the reaction. It may be that trivalent iron acts as an electron acceptor to promote interspecies electron transfer between microorganisms. BF has a positive promoting effect on the hydrolysis process and biogas production process of anaerobic digestion of kitchen waste.

[0110] (2) Analysis of microbial communities during anaerobic methanogenesis

[0111] After all the anaerobic digestion experiments of food waste are completed, the sludge samples in each anaerobic digestion reactor are extracted and all are centrifuged. The centrifugation conditions are set to ensure a centrifugal speed of 12,000 rpm (equivalent to a centrifugal force of 10,000 G) and a centrifugation time of 5 minutes to ensure that the samples can be properly extracted. After centrifugation, the supernatant is removed and only the treated precipitate is retained. These precipitates are first properly stored in a refrigerator at -20°C and then sent to an external institution at -40°C for metagenomic sequencing.

[0112] ①. Analysis of microbial species diversity

[0113] In microbiological research, Alpha diversity is used as a key indicator to evaluate the characteristics of microbial populations in a particular environment. It covers the richness, diversity and coverage of species. To quantify this diversity, researchers have used a series of statistical indices, the most common and widely used of which include the ACE index, Chao index and Shannon index. This study analyzed the microbial communities of anaerobic digestion samples before and after the addition of modified biochar. By sequencing samples on the 13th day (rapid biogas production period) and the 54th day (stable biogas production period), specific data on community abundance and diversity were obtained, which were presented in the form of Alpha diversity index, as shown in Table 4.

[0114] Among them, the ACE index and the Chao index are two particularly important indicators, which are mainly used to quantify the species richness of the community. It can be seen that the biological abundance of the BF group is greater than that of the biochar group in the rapid biogas production stage, which shows that BF can increase biodiversity. However, on the 54th day, the results were the opposite. This may be because the BF group preferentially degraded biodegradable substances compared to the blank group, resulting in an environment with insufficient nutrients, causing microbial self-digestion, and ultimately leading to a decrease in microbial abundance. There was no obvious difference in the Shannon index. The Coverage index is generally used as an index to measure sample coverage. It can be clearly seen that the Coverage index in the experimental samples is all >0.995, indicating that the effectively measured sludge in the experimental samples covers almost all microorganisms, and the constructed database has a very high authenticity.

[0115] Table 4 Microbial richness and diversity index

[0116] Ace Chao Shannon Coverage Day 13-B 779.940 768.392 3.870 0.998 Day 13-Fe 1332.607 1331.901 4.193 0.995 Day54-B 1007.707 992.803 3.189 0.996 Day54-Fe 729.663 718.000 3.976 0.998

[0117] ② Analysis of microbial community composition

[0118] In order to clarify the effect of BF on the microbial population structure in the anaerobic digestion process, the dominant bacterial communities of the microbial samples of the BF group with the best biochar and methanogenesis effects were analyzed at the phylum and genus levels.

[0119] The phylum-level community distribution of anaerobic digestion system of biochar before and after modification is as follows Figure 11As shown, the top five phyla in terms of abundance at 13 days were Euryarchaeota (35.63%), Chloroflexi (21.58%), Firmicutes (15.75%), Halobacterota (11.18%), and Bacteroidota (5.46%). At this time, the top five phyla in terms of abundance in BF were Firmicutes (51.83%), Eunyarchaeota (11.22%), Desulfobacterota (6.33%), Cyanobacteria (5.99%), and Proteobacteria (5.96%). At 54 days, the top five phyla in terms of abundance in biochar were Firmicutes (24.75%), Chloroflexi (17.98%), Euryarchaeota (17.77%), Bacteroidota (12.54%), and Halobacterota (7.70%). The top five BF phyla in terms of abundance were Euryarchaeota (31.12%), Chloroflexi (20.92%), Firmicutes (15.95%), Bacteroidota (7.83%), and Halobacterota (4.77%).

[0120] On day 13, the abundance of Firmicutes in the BF group increased by 36.09% compared to biochar. Firmicutes are ubiquitous in anaerobic digestion reactions. As the dominant phylum in hydrolysis and acidification, they produce large amounts of extracellular hydrolases such as proteases, lipases, and cellulases. The hydrolysis stage is a severe deceleration stage in anaerobic digestion, and an increase in the hydrolysis rate can greatly improve methanogenesis. Desulfobacterota can oxidize fatty acids and reduce sulfate to sulfur. Chloroflexi are chemoheterotrophic microorganisms that promote carbohydrate metabolism, ultimately converting it into acetic acid. According to relevant literature, their abundance is negatively correlated with carbohydrate content.

[0121] On the 54th day of the reaction, the abundance of Euryarchaeota in the BF group increased by 13.35% compared with that in the biochar group. Euryarchaeota is an important phylum for methanogenesis in anaerobic digestion, and its content can reflect the efficiency of methanogenesis. It is not difficult to find that the addition of BF can promote the reproduction of methanogenic bacteria, which also explains why the methanogenesis efficiency of the BF group is higher than that of the biochar group.

[0122] according to Figure 12It can be seen that Methanobacterium is the main microorganism in Euryarchaeota at the genus level, and the methanogen type is hydrogenotrophic methanogen.

[0123] In summary, the pore structure of the modified biochar prepared by the present invention has no significant change compared with that before modification, and the surface of the modified biochar contains iron. The modified biochar has a promoting effect on the basic indicators of the anaerobic digestion process, such as pH recovery, SCOD degradation, and methane yield. After the anaerobic digestion reaction, the Fe in the modified biochar is partially composed of Fe 3+ Converted to Fe 2+ , which shows that Fe 3+ As an electron acceptor, it participates in interspecies electron transfer between microorganisms, thereby improving biogas production efficiency. In addition, modified biochar can increase the abundance of hydrolytic bacteria and methanogens, thereby promoting hydrolysis efficiency and methane production. Combining all experimental results, 10g / L modified biochar material can be added during the anaerobic digestion of kitchen waste, and the reactor VS addition ratio is set at 0.5gVS 底物 / gVS 接种物 When the substrate retention time is set to 28 days, the entire anaerobic digestion system can be better regulated.

[0124] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing modified biochar, characterized in that: The following steps are involved: Ultrasonic treatment is performed on a mixture of biochar and ferric iron solution, followed by adjusting the pH value of the mixture to 10.5 to 11 and allowing the iron adsorbed by the biochar to form ferric hydroxide; The biochar adsorbed with ferric hydroxide is washed until the pH value of the washing liquid is 6.5 to 7.5, and then the biochar adsorbed with ferric hydroxide is dried.

2. The preparation method according to claim 1, characterized in that The ferric iron source in the ferric iron solution includes at least one of FeCl3·6H2O, Fe2(SO4)3 and Fe(NO3)3.

3. The preparation method according to claim 1 or 2, characterized in that The ultrasonic treatment time is 1 h to 4 h.

4. The preparation method according to claim 1, characterized in that Before washing, the mixed solution is further post-treated by adjusting the pH value to 10.5 to 11; Preferably, the post-processing comprises shaking table treatment.

5. The preparation method according to claim 4, characterized in that The shaking treatment was carried out at 170-180 rpm for 10-12 hours.

6. The preparation method according to claim 1, characterized in that Drying is carried out at 150°C to 160°C for 1 hour to 3 hours.

7. A modified biochar, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 6.

8. The modified biochar according to claim 7, characterized in that The Fe contained in the modified biochar mainly exists in the form of Fe2O3, and the modified biochar has both carbon-carbon double bonds and carbon-oxygen single bonds.

9. Use of the modified biochar according to claim 7 or 8 in promoting methanogenesis through anaerobic digestion.

10. The use according to claim 9, characterized in that The modified biochar is used in the methane production process of anaerobic digestion of kitchen waste.

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