Modified biochar and preparation method and application thereof

Abstract

The application discloses modified biochar as well as a preparation method and application thereof, and belongs to the technical field of biochar. The modified biochar is obtained by mechanically and chemically modifying biochar raw materials by a modifier; and the modifier is selected from alkali or acid. The preparation method of the modified biochar is simple, easy to operate and short in time consumption. The obtained modified biochar can be applied to an anaerobic digestion system to produce acid or methane according to the different modifiers, the hydrolysis acidification capacity of the anaerobic digestion system can be improved when the modifier is acid, and the production of methane can be improved while preventing the acidification of the system when the modifier is alkali.

Description

TECHNICAL FIELD

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

[0002] As a complex biochemical reaction process, anaerobic digestion requires the cooperation of multiple groups of microorganisms in each stage. Therefore, by regulating key conditions, including basic parameters that directly affect the activity of anaerobic microorganisms, operation parameters of anaerobic digestion reactors, and main working modes of anaerobic digestion systems, and improving the properties of enzymes and microorganisms or screening domesticated bacterial flora under specific conditions, the stability of the anaerobic digestion process and the biogas production efficiency can be improved, and resources such as methane and VFAs can be recovered.

[0003] In recent years, green materials such as activated carbon, biochar, graphene, carbon nanotubes, carbon black, and carbon cloth have been used to enhance the efficiency of anaerobic digestion. A series of studies have reported that the above-mentioned materials can effectively enhance the hydrolysis and acidification of organic matter in excess sludge, and improve the efficiency of carbon dioxide conversion to produce methane in anaerobic digestion systems of multi-source perishable organic solid waste such as kitchen waste. In comparison, biochar has a wide range of raw material sources, low production cost, simple process addition, and green recycling, making it particularly popular in the environmental-friendly treatment and disposal of organic solid waste reduction, stabilization, harmlessness, and resource utilization.

[0004] However, the effect of biochar in the present technology in producing acid or methane in anaerobic digestion systems still needs to be further improved.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] One of the purposes of the present application is to provide a modified biochar to solve the above technical problems.

[0007] The second purpose of the present application is to provide a preparation method of the above-mentioned modified biochar.

[0008] The third purpose of the present application is to provide an application of the above-mentioned modified biochar.

[0009] The present application can be achieved as follows:

[0010] In a first aspect, the present application provides a modified biochar, which is obtained by mechanically and chemically modifying a biochar raw material with a modifier.

[0011] The modifier is selected from an alkali or an acid.

[0012] In an optional embodiment, the modified biochar has at least one of the following characteristics:

[0013] Characteristic one: the particle size of the modified biochar is 4-6 mm.

[0014] Feature two: when the modifier is a base, the surface of the modified biochar is smooth; when the modifier is an acid, the surface of the modified biochar is irregular pore structure;

[0015] Feature three: when the modifier is a base, the surface of the modified biochar has small pores of 8-12 μm; when the modifier is an acid, the surface of the modified biochar has large pores of ≥50 μm;

[0016] Feature four: the specific surface area of the modified biochar is less than that of the biochar raw material.

[0017] In an optional embodiment, the base includes at least one of NaOH and KOH.

[0018] In an optional embodiment, the acid includes sulfuric acid.

[0019] In a second aspect, the present application provides a method for preparing the modified biochar according to any one of the preceding embodiments, comprising the following steps: mechanically and chemically modifying the biochar raw material with a modifier.

[0020] In an optional embodiment, the mechanical and chemical modification is performed by ball milling the biochar raw material with the modifier.

[0021] In an optional embodiment, the ball milling includes at least one of the following features:

[0022] Feature one: the ratio of the biochar raw material to the modifier is (1.5 g:0.075) to (1.5 g:0.15 mol);

[0023] Feature two: the mass ratio of the ball milling beads used in the ball milling process to the biochar raw material is (35:1) to (45:1);

[0024] Feature three: the ball milling beads used in the ball milling process include large balls with a diameter of 14-16 mm, medium balls with a diameter of 4-6 mm, and small balls with a diameter of 2-4 mm, and the mass ratio of the large balls, the medium balls, and the small balls is (2.5-3.5):(4.5-5.5):(1.5-2.5);

[0025] Feature four: the rotation speed of the ball milling is 180-220 rpm, and the ball milling time is 12-18 min;

[0026] Feature five: when the modifier is a base, the surface of the modified biochar is rich in hydroxyl groups; when the modifier is an acid, the surface of the modified biochar is rich in carboxyl groups.

[0027] In a third aspect, the present application provides an application of the modified biochar according to any one of the preceding embodiments, such as in an anaerobic digestion system.

[0028] In an alternative embodiment, the acid-modified modified biochar is used to promote acid production in an anaerobic digestion system.

[0029] In an alternative embodiment, the base-modified modified biochar is used to promote methane production in an anaerobic digestion system.

[0030] The beneficial effects of the present application include:

[0031] The modified biochar provided by the present application is obtained by mechanical-chemical modification of biochar raw materials with a modifier. The preparation method of the modified biochar is simple, easy to operate, and time-saving. The obtained modified biochar can be used to promote acid production or methane production in an anaerobic digestion system according to different modifiers, realizing multi-dimensional resource recovery. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be considered as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0033] Figure 1 The particle size and surface morphology of the biochar raw material before modification and the modified biochar after modification in Example 1 are shown in the following figures:

[0034] Figure 2 The particle size and surface morphology of the biochar raw material before modification and the modified biochar after modification in Example 2 are shown in the following figures:

[0035] Figure 3 The pH value and SCOD change in the anaerobic digestion process of the two systems in Test Example 1 are shown in the following figures:

[0036] Figure 4 The FTIR spectrum of the modified biochar in Test Example 1 is shown in the following figure:

[0037] Figure 5 The surface morphology of the biochar raw material and the modified biochar after modification after the anaerobic digestion in Test Example 1 is shown in the following figures:

[0038] Figure 6 The microbial sample analysis after anaerobic digestion of the two systems in Test Example 1 is shown in the following figure:

[0039] Figure 7 The methane production result figure after anaerobic digestion of the two systems in Test Example 1 is shown in the following figure:

[0040] Figure 8 The pH value and SCOD change in the anaerobic digestion process of the two systems in Test Example 2 are shown in the following figures:

[0041] Figure 9 Figure for the change of VFAs in the two systems in the anaerobic digestion process in Test Example 2;

[0042] Figure 10 FTIR spectrum of the modified biochar in Test Example 2;

[0043] Figure 11 Surface morphology of the biochar raw material and the modified biochar after modification after the anaerobic digestion in Test Example 2;

[0044] Figure 12 Microbial sample analysis after the anaerobic digestion of the two systems in Test Example 2. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be clearly and completely described below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions suggested by the manufacturer are adopted. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased in the market.

[0046] The modified biochar and the preparation method and application thereof provided in the present application will be specifically described below.

[0047] The present application provides a modified biochar, which is obtained by mechanically and chemically modifying a biochar raw material with a modifier; the modifier is selected from an alkali or an acid.

[0048] For reference, the alkali used may exemplarily include at least one of NaOH and KOH; the acid used may exemplarily include sulfuric acid.

[0049] Correspondingly, the present application also provides a preparation method of the above modified biochar, which comprises the following step: mechanically and chemically modifying the biochar raw material with a modifier.

[0050] Specifically, the mechanical and chemical modification method is ball milling of the biochar raw material with the modifier.

[0051] The ball milling can be performed in a planetary ball mill.

[0052] The usage ratio of the biochar raw material to the modifier can be (1.5 g:0.075) to (1.5 g:0.15 mol), such as 1.5 g:0.075 mol, 1.5 g:0.1 mol, 1.5 g:0.12 mol or 1.5 g:0.15 mol, etc., and can also be any other value within the range of (1.5 g:0.075) to (1.5 g:0.15 mol).

[0053] When the modifier is a base, the preferred ratio of the biochar raw material to the modifier is 1.5 g:0.15 mol; when the modifier is an acid, the preferred ratio of the biochar raw material to the modifier is 1.5 g:0.075 mol.

[0054] The mass ratio of the ball milling beads used in the ball milling process to the biochar raw material can be (35:1)-(45:1), such as 35:1, 38:1, 40:1, 42:1, or 45:1, etc.

[0055] The ball milling beads used in the ball milling process can include large balls with a diameter of 14-16 mm, medium balls with a diameter of 4-6 mm, and small balls with a diameter of 2-4 mm, and the mass ratio of the large balls, medium balls, and small balls is (2.5-3.5):(4.5-5.5):(1.5-2.5).

[0056] In some preferred embodiments, the ball milling beads used in the ball milling process can include large balls with a diameter of 15 mm, medium balls with a diameter of 5 mm, and small balls with a diameter of 3 mm, and the mass ratio of the large balls, medium balls, and small balls is 3:5:2.

[0057] In this application, the ball milling speed can be 180-220 rpm, such as 180 rpm, 190 rpm, 200 rpm, 210 rpm, or 220 rpm, etc. The ball milling time can be 12-18 min, such as 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, or 18 min, etc.

[0058] By modifying in the above-mentioned manner, it can be completed in about 15 min, which is significantly shorter than the time of 6 h at 80 °C in the hydrothermal method in the prior art, and the temperature is also lower, greatly shortening the preparation time of the material.

[0059] In some embodiments, before ball milling, the biochar raw material can be pretreated, such as filtering the biochar with a 20-mesh screen and then washing it with deionized water and fully drying it at 70 °C.

[0060] In some embodiments, after ball milling, the modified biochar can also be post-treated, for example, the modified biochar powder can be cooled to room temperature after modification, the solid phase powder in the suspension is centrifuged and separated, and then the modified biochar powder is repeatedly separated and recovered after continuous washing with deionized water until the pH of the supernatant after washing is close to neutral (pH = 7.0 ± 0.5). Finally, the separated modified biochar powder is dried in a vacuum drying oven (such as 60 °C for 24 h), and the dried modified biochar is sealed and stored in the dark at room temperature.

[0061] The modified biochar provided in the present application has a particle size of 4-6 mm, such as 4 mm, 5 mm or 6 mm, which is smaller than the particle size of the biochar raw material.

[0062] When the modifier is an alkali, the surface of the modified biochar becomes smoother, the surface has small pores of 8-12 μm, and the specific surface area of the modified biochar is smaller than that of the biochar raw material, but the proportion of micropores is significantly increased. In addition, the surface of the modified biochar is rich in hydroxyl groups.

[0063] When the modifier is an acid, the surface of the modified biochar has an irregular pore structure (such as a cave pore type), the surface has large pores of ≥50 μm, and the specific surface area of the modified biochar is smaller than that of the biochar raw material. In addition, the surface of the modified biochar is rich in carboxyl groups.

[0064] Further, the present application also provides the use of the above-mentioned modified biochar, for example, in an anaerobic digestion system.

[0065] In some embodiments, the acid-modified modified biochar can be used to promote acid production in an anaerobic digestion system. In other embodiments, the alkali-modified modified biochar can be used to promote methane production in an anaerobic digestion system. In other embodiments, the acid-modified modified biochar can be used to promote acid production in an anaerobic digestion system, and the alkali-modified modified biochar can be used to promote methane production in an anaerobic digestion system. For reference, the modified biochar can be added to the anaerobic digestion system at a concentration of 5 g / L, for example.

[0066] It should be noted that the principle of anaerobic digestion is generally considered to include four stages of hydrolysis, acidification, hydrogen and acetic acid production, and methane production.

[0067] The first stage of hydrolysis: complex solid organic matter composition including proteins, fats, carbohydrates and other substances that cannot be directly metabolized by microorganisms are converted into amino acids, long-chain fatty acids, monosaccharides and other soluble monomer or dimer substances that can be utilized by acidification bacteria under the action of hydrolytic enzymes. Microorganisms include protein-degrading bacteria, fat-degrading bacteria and carbohydrate-degrading bacteria, which mainly participate in the hydrolysis reaction in this stage.

[0068] The second stage of acidification: soluble monomer or dimer form organic matter is degraded and converted into end products, i.e. acidification products mainly including short-chain volatile fatty acids, lactic acid, ammonia, alcohol, etc., and hydrogen, carbon dioxide, by homoacetogenic bacteria and hydrogen-producing acetogenic bacteria under the regulatory action of acetyl-CoA. The reaction rate in the acidification stage is fast, and especially in the process of anaerobic digestion of kitchen waste and other high-organic-matter-containing waste, it is easy to cause the system load rate to be too high, resulting in imbalance between generation and consumption, and the reaction system is too acidified.

[0069] Third stage hydrogen production and acetic acid production: short-chain fatty acids or alcohol and other acidification stage products are further degraded by hydrogen production and acetic acid production bacteria to generate metabolic substrates such as acetic acid, H2 and CO2 which can be directly utilized by methanogens.

[0070] Fourth stage methane production: metabolic substrates such as acetic acid, CO and H2, CO2 are converted into methane by strict anaerobic methanogens through the catalysis of related reductases, and there are two main pathways, i.e., acetic acid decomposition and methylation of acetate methyl group, and synthesis of methane from carbon dioxide and hydrogen, which correspond to Methanosaeta and Methanobacterium, respectively.

[0071] In the present application, the raw material of biochar is modified by acid and / or alkali to endow the biochar with different surface properties (mainly the change of functional groups), so as to accelerate the reaction in different stages of anaerobic digestion and realize multi-dimensional resource recovery.

[0072] The features and performances of the present application are further described in detail in combination with the following examples.

[0073] Example 1

[0074] The present example provides a modified biochar, which is prepared by the following method:

[0075] After the biochar raw material is filtered with a 20-mesh screen and washed with deionized water, it is fully dried at 70°C.

[0076] 1.5 g of dried biochar raw material and 60 g of ball milling beads (large, medium and small balls with diameters of 15 mm, 5 mm and 3 mm, respectively, and a mass ratio of 3:5:2) are added to a 50 mL ball mill jar, and the mass ratio of biochar raw material to ball milling beads is kept at 1:40. 15 mL of 10 mol / L NaOH solution is added to each ball mill jar, which is sealed and placed in a planetary ball mill, and the mechanical chemical reaction is carried out at a speed of 200 rpm for 15 min, and the running direction is not changed during the reaction.

[0077] After the reaction is stable, the suspension is cooled to room temperature, and the NaOH ball-milled modified biochar (denoted as "BMB-NaOH") is separated by centrifugation, and then washed with deionized water and separated and recovered again, and this process is repeated several times until the supernatant after washing is close to neutral (pH=7.0±0.5). Finally, the separated modified biochar is placed in a vacuum drying oven at 60°C for 24 h, and the dried BMB-NaOH is sealed and stored in the dark at room temperature.

[0078] Figure 1The particle size and surface morphology of the raw biochar and the modified biochar after modification are shown in the figure, wherein (a) is a size comparison figure of the material before and after modification, (b) is an SEM figure of the raw biochar, and (c) is an SEM figure of the modified BMB-NaOH. It can be seen from the figure that the particle size of the raw biochar is about 9 mm, and the particle size of the BMB-NaOH after ball milling modification is about 5 mm. The surface of the raw biochar is rough, and there are a large number of pore structures; the surface of the modified BMB-NaOH becomes smoother, and small pores of about 10 μm can be seen on the surface. The specific surface area of the BMB-NaOH is smaller than that of the original biochar (as shown in Table 1), but the proportion of micropores is significantly increased. Figure 1 It can be seen from the figure that the particle size of the raw biochar is about 9 mm, and the particle size of the BMB-NaOH after ball milling modification is about 5 mm. The surface of the raw biochar is rough, and there are a large number of pore structures; the surface of the modified BMB-NaOH becomes smoother, and small pores of about 10 μm can be seen on the surface. The specific surface area of the BMB-NaOH is smaller than that of the original biochar (as shown in Table 1), but the proportion of micropores is significantly increased.

[0079] Table 1 Comparison of specific surface area, pore volume and average pore diameter before and after modification

[0080]

[0081] Example 2

[0082] The difference between this embodiment and Example 1 is that the modifier is 15 mL of 5 mol / L H2SO4. The modified biochar obtained by modification is denoted as “BMB-H2SO4”.

[0083] Figure 2 The particle size and surface morphology of the raw biochar and the modified biochar after modification are shown in the figure, wherein (a) is a size comparison figure of the material before and after modification, (b) is an SEM figure of the raw biochar, and (c) is an SEM figure of the modified BMB-H2SO4. It can be seen from the figure that the particle size of the raw biochar is about 9 mm, and the particle size of the BMB-H2SO4 after ball milling modification is about 5 mm. The surface of the raw biochar is rough, and there are a large number of pore structures; the surface of the modified BMB-H2SO4 presents irregular pore structures, all of which are hole type, and large holes of about ≥50 μm can be seen on the surface. The specific surface area of the BMB-H2SO4 is smaller than that of the original biochar (as shown in Table 2).

[0084] Table 2 Comparison of specific surface area, pore volume and average pore diameter before and after modification

[0085]

[0086] Based on the above, in combination with Example 1 and Example 2, the microstructure and surface characteristics of the modified functional carbon are detected and analyzed by using a scanning electron microscope. The surface structure of the raw biochar is relatively rough, and a large number of ash particles of different sizes are also attached, and there is almost no obvious pore structure. After ball milling, due to the use of a higher concentration of reagent, the surface corrosion effect is brought to the raw biochar, and the surface of the BMB-H2SO4 after ball milling is all irregular hole type, and the surface of the BMB-NaOH is especially smooth but has a large number of dispersed point-shaped micropores.

[0087] The specific surface area, pore volume, pore size distribution and nitrogen adsorption / desorption curves of the modified functional carbon materials were detected by a full-automatic specific surface and porosity analyzer. The test range was micropore (<2 nm), mesopore (2-50 nm) and macropore (>50 nm). The results showed that the BET of the modified biochar changed to different degrees compared with the biochar raw material. After acid and alkali modification, the specific surface area was significantly reduced by 21.9% and 16.1%, respectively. The micropore and mesopore of BMB-H2SO4 almost reduced at the same ratio, while the SBET of BMB-NaOH increased to 87%, and the Vt / V 微孔 of BMB-H2SO4 reached 84%. 微孔

[0088] Example 3

[0089] The difference between this example and Example 1 is that 1.5 g of dried biochar raw material and 52.5 g of ball milling beads (the diameters of large, medium and small balls are 15 mm, 5 mm and 3 mm, and the mass ratio is 2.5:5.5:2) are added into a 50 mL ball mill jar, and the mass ratio of biochar raw material to ball milling beads is kept at 1:35. 15 mL of 10 mol / L NaOH solution is added to each ball mill jar, which is sealed and placed in a planetary ball mill, and runs at a speed of 180 rpm for 18 min for mechanical chemical reaction, and the running direction is not changed during the operation.

[0090] Example 4

[0091] The difference between this example and Example 2 is that 1.5 g of dried biochar raw material and 67.5 g of ball milling beads (the diameters of large, medium and small balls are 15 mm, 5 mm and 3 mm, and the mass ratio is 3.5:4.5:2) are added into a 50 mL ball mill jar, and the mass ratio of biochar raw material to ball milling beads is kept at 1:45. 15 mL of 5 mol / L H2SO4 solution is added to each ball mill jar, which is sealed and placed in a planetary ball mill, and runs at a speed of 220 rpm for 12 min for mechanical chemical reaction, and the running direction is not changed during the operation.

[0092] Test Example 1

[0093] ​Taking the modified biochar prepared in Example 1 as an example, and using unmodified biochar as a comparison, two reactors were prepared and inoculated with equal amounts of anaerobic sludge from the anaerobic digestion reactor in the laboratory of the School of Environmental Science and Engineering, Huazhong University of Science and Technology. The total organic solids (TS) of the anaerobic sludge was 9.3 g / L, and the volatile organic compounds (VS) were 6.7 g / L. The substrate was prepared according to the typical proportion of kitchen waste, specifically: 40% rice, 30% cabbage, 20% banana peel, and 10% pork (proportion based on wet weight). The initial substrate TS was 127.7 g / L, and the VS was 125.2 g / L. The anaerobic digestion reaction was carried out in a biochemical methane potential (BMP) tester. During the start-up phase, 370 mL of anaerobic sludge and 30 mL of substrate were added. The initial pH of each reactor was similar and close to neutral, and no further artificial adjustment was made thereafter. Modified biochar was added to the anaerobic digestion system at a concentration of 5 g / L, and the anaerobic digestion process lasted for 17 days.

[0094] During the anaerobic digestion process, no significant acidification was observed in either system (corresponding to the two reactors mentioned above). Figure 3 As shown in Figure a), the overall dissolved chemical oxygen demand (SCOD) of sludge showed a continuous downward trend. Figure 3 (As shown in b).

[0095] According to FTIR spectra (e.g.) Figure 4 Analysis showed that BMB-NaOH had a significantly higher hydroxyl peak (3450 cm⁻¹). -1 Electron microscopy of BMB-NaOH after anaerobic digestion revealed a clear biofilm encapsulation phenomenon (e.g., ...). Figure 5 (As shown). Figure 5 In the middle, (a) and (b) are taken at the same shooting size, (a) corresponds to the original biochar after anaerobic digestion, and (b) corresponds to the modified biochar after anaerobic digestion; (c) and (d) are taken at the same shooting size, (c) corresponds to the original biochar after anaerobic digestion, and (d) corresponds to the modified biochar after anaerobic digestion.

[0096] Analysis of microbial samples taken on day 17 (e.g.) Figure 6 As shown in the figure, in the anaerobic digestion system with added BMB-NaOH, the relative abundance of facultative anaerobic bacteria *Georgenia*, which has carbohydrate hydrolysis activity, decreased, while methanogenic bacteria *Methanobacterium* and *Methanosaeta* were enriched. BMB-NaOH enhanced the methanogenic capacity of the anaerobic digestion system while weakening its hydrolysis-acidification capacity, thus achieving a more balanced rate between the hydrolysis-acidification and methanogenesis processes. This prevented system acidification while increasing cumulative methane production by approximately 26% (e.g., ...). Figure 7 (As shown).

[0097] Experimental Example 2

[0098] Taking the modified biochar prepared in Example 2 as an example, and using unmodified biochar as a comparison, two reactors were prepared and inoculated with anaerobic sludge from the anaerobic digestion reactor in the laboratory of the School of Environmental Science and Engineering, Huazhong University of Science and Technology. The total organic solids (TS) of the anaerobic sludge was 9.3 g / L, and the volatile organic compounds (VS) were 6.7 g / L. The substrate was prepared according to the typical proportion of kitchen waste, specifically: 40% rice, 30% cabbage, 20% banana peel, and 10% pork (proportion based on wet weight). The initial substrate TS was 127.7 g / L, and the VS was 125.2 g / L. The anaerobic digestion reaction was carried out in a biochemical methane potential (BMP) tester. During the start-up phase, 370 mL of anaerobic sludge and 30 mL of substrate were added. The initial pH of each reactor was similar and close to neutral, and no further artificial adjustment was made thereafter. Biochar was added to the anaerobic digestion system at a concentration of 5 g / L, and the anaerobic digestion process lasted for 17 days.

[0099] Compared to biochar feedstock, the BMB-H2SO4 system exhibits significant acidification during anaerobic digestion. Figure 8 As shown in Figure a), the pH value initially dropped significantly to below 6.5, and only gradually recovered after 5-7 days, indicating a long recovery period for pH. Meanwhile, SCOD remained at a high level. Figure 8 (As shown in b). Figure 9 As shown, both are propionic acid and acetic acid-dominant, but the concentration of VFAs in the BMB-H2SO4 group is significantly increased. Figure 9 As shown, (a) represents the change in VFAs in the biochar feedstock system, and (b) represents the change in VFAs in the modified biochar system, further indicating that sulfuric acid modification is beneficial for promoting hydrolysis and acidification. Based on FTIR spectra (e.g., ...), Figure 10 Analysis showed that BMB-H2SO4 had significantly higher peaks for functional groups such as carboxyl groups, esters, and ketones (1580, 1040-1120 cm⁻¹). -1 Electron microscopy of BMB-H2SO4 after anaerobic digestion revealed a clear biofilm encapsulation phenomenon (e.g., ...). Figure 11 (As shown). Figure 11 In the images (a) and (b), the same photographic size is used; (a) corresponds to the original biochar after anaerobic digestion, and (b) corresponds to the modified biochar after anaerobic digestion. Similarly, (c) and (d) are also photographed at the same size; (c) corresponds to the original biochar after anaerobic digestion, and (d) corresponds to the modified biochar after anaerobic digestion. Analysis of microbial samples taken on day 17 (e.g.) Figure 12As can be seen from the figure, in the anaerobic digestion system with the addition of BMB-H2SO4, the abundance of Georgenia, a facultative anaerobe with carbohydrate hydrolysis, increased from 35.23% to 38.82% compared with the original biochar. Therefore, the H2SO4 ball milling modification can provide electron acceptors for the organic hydrolysis process by increasing the surface carboxyl content of the biochar, enrich the hydrolysis and acidification functional flora, and enhance the hydrolysis and acidification capacity of the anaerobic digestion system.

[0100] In summary, the application modifies the raw material of biochar with acid and / or alkali to endow the biochar with different surface properties, which can accelerate the reactions in different stages of anaerobic digestion and realize multi-dimensional resource recovery.

[0101] The preferred embodiments of the application have been described above with the aid of drawings, and are not intended to limit the application, and for those skilled in the art, the application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A modified biochar, characterized in that, The preparation of the modified biochar comprises the following steps: ball-milling the biochar raw material with a modifier; the usage ratio of the biochar raw material to the modifier is (1.5g:0.075)-(1.5g:0.15mol); the mass ratio of the ball-milling beads used in the ball-milling process to the biochar raw material is (35:1)-(45:1); the ball-milling beads used in the ball-milling process comprise large balls with a diameter of 14-16mm, medium balls with a diameter of 4-6mm, and small balls with a diameter of 2-4mm, and the mass ratio of the large balls, the medium balls, and the small balls is (2.5-3.5):(4.5-5.5):(1.5-2.5); the ball-milling rotation speed is 180-220rpm, and the ball-milling time is 12-18min; the modifier is selected from NaOH or sulfuric acid; the specific surface area of the modified biochar is less than that of the biochar raw material.

2. The modified biochar of claim 1, wherein, The modified biochar has at least one of the following characteristics: Characteristic one: the particle size of the modified biochar is 4-6mm; Characteristic two: when the modifier is NaOH, the surface of the modified biochar is smooth; when the modifier is sulfuric acid, the surface of the modified biochar has irregular pore structures; Characteristic three: when the modifier is NaOH, the surface of the modified biochar has small pores with a diameter of 8-12μm; when the modifier is sulfuric acid, the surface of the modified biochar has large pores with a diameter of ≥50μm; Characteristic four: when the modifier is NaOH, the surface of the modified biochar is rich in hydroxyl groups; when the modifier is sulfuric acid, the surface of the modified biochar is rich in carboxyl groups.

3. A method of producing a modified biochar as claimed in claim 1 or 2, characterised in that, ball-milling the biochar raw material with a modifier; the usage ratio of the biochar raw material to the modifier is (1.5g:0.075)-(1.5g:0.15mol); the mass ratio of the ball-milling beads used in the ball-milling process to the biochar raw material is (35:1)-(45:1); the ball-milling beads used in the ball-milling process comprise large balls with a diameter of 14-16mm, medium balls with a diameter of 4-6mm, and small balls with a diameter of 2-4mm, and the mass ratio of the large balls, the medium balls, and the small balls is (2.5-3.5):(4.5-5.5):(1.5-2.5); the ball-milling rotation speed is 180-220rpm, and the ball-milling time is 12-18min.

4. Use of the modified biochar according to claim 1 or 2, characterized in that, The modified biochar is used in an anaerobic digestion system.

5. Use according to claim 4, characterized in that, The acid-modified modified biochar is used to promote acid production in an anaerobic digestion system.

6. Use according to claim 4, characterized in that, The alkali-modified modified biochar is used to promote methane production in an anaerobic digestion system.

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