Metal-based biochar composite material and preparation method and application thereof

Abstract

The application discloses a metal-based biochar composite material and a preparation method and application thereof, and the preparation method comprises the following steps: preparing a primary metal-based biochar by high-temperature pyrolysis of waste biomass and a metal precursor under an oxygen-free condition; and further loading trace element promoters into the primary metal-based biochar by an ion immersion method, and then performing drying and high-temperature solidification treatment to obtain the metal-based biochar composite material. When kitchen waste is fermented to produce acid, calcium and magnesium oxides in the metal-based biochar composite material are used to adjust the acid-base microenvironment of the fermentation system, so that the accumulation of products is avoided to inhibit excessive acidification; a primary cell is formed by metal Fe and biochar to strengthen metal corrosion, regulate and control the release of metal trace elements, promote the growth metabolism of acid-producing bacteria and interspecific electron transfer, so that the acid production efficiency of fermentation is improved, and the metal-based biochar composite material has the advantages of efficient utilization and cyclic use.

Description

Technical Field

[0001] This invention belongs to the field of municipal solid waste resource utilization technology, specifically involving a metal-based biochar composite material, its preparation method, and its application. Background Technology

[0002] With the rapid improvement of living standards in my country in recent years, the amount of food waste has also been increasing year by year. Compared with traditional sanitary landfill and high-temperature incineration, anaerobic digestion has unique advantages and is one of the more suitable technical means for reducing, rendering harmless, and recycling food waste. Through anaerobic digestion, food waste can be converted into biogas energy, which is more easily utilized. The biogas slurry and biogas residue can be used as raw materials for organic fertilizer, which has positive significance for alleviating energy shortages and reducing environmental pressure.

[0003] Food waste mainly consists of rice, noodles, vegetables, meat, grease, bones, and miscellaneous items such as paper towels and disposable tableware. Because carbohydrates like rice, noodles, and vegetables are easily acidified, methanogenesis often fails, making methanogenesis a limiting factor in gas production. Based on the four-stage theory of anaerobic digestion—hydrolysis, acidification, hydrogen and acetic acid production, and methanogenesis—terminating anaerobic digestion at the acidification stage to obtain higher-value volatile organic acids (VFAs) has become a more promising technical approach. This not only shortens the food waste treatment cycle but also avoids the problem of methanogenesis inhibition. However, due to the poor solubility and slow hydrolysis of cellulose, protein, and lipids, the hydrolysis reaction is considered the rate-limiting stage of acid production during the free fermentation of food waste. Furthermore, the accumulation of acidification products (VFAs) leads to a sharp drop in system pH, affecting the normal metabolism of related microbial communities and the activity of extracellular hydrolytic enzymes. Therefore, accelerating the hydrolysis mass transfer of the complex components of food waste and regulating the system's acid-base environment are key to improving the efficiency of acid production during anaerobic fermentation of food waste.

[0004] Currently, researchers mostly employ physicochemical pretreatment techniques such as heat treatment, steam explosion, and acid-base treatment to disrupt the complex structure of macromolecular organic matter in the substrate. They also use methods such as adding alkaline chemical reagents and reducing the load to adjust the acid-base environment of the anaerobic fermentation system, thereby improving the acid production efficiency of anaerobic fermentation. However, all of the above methods have certain limitations, causing unnecessary obstacles to the practical application of food waste fermentation products and the post-treatment of fermentation liquid. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] One objective of this invention is to provide a method for preparing a metal-based biochar composite material.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a metal-based biochar composite material, comprising,

[0009] Primary metal-based biochar is prepared by high-temperature pyrolysis of waste biomass and metal precursors under anaerobic conditions.

[0010] The primary metal-based biochar was further loaded with trace element promoters by ion impregnation, and then dried and cured at high temperature to obtain a metal-based biochar composite material.

[0011] In a preferred embodiment of the preparation method of the metal-based biochar composite material of the present invention, the metal precursor is composed of precursor A and precursor B.

[0012] The precursor A includes one or more of CaCO3, CaO, MgCO3, and MgO, and the amount of precursor A added is 5 to 15% of the mass of waste biomass.

[0013] The precursor B includes one or more of zero-valent iron, scrap iron, iron oxide, and magnetite, and the mass ratio of precursor B to waste biomass is 1:4 to 10.

[0014] As a preferred embodiment of the preparation method of the metal-based biochar composite material of the present invention, wherein: the ion impregnation method involves impregnating primary metal-based biochar in a metal trace element ion solution, and after full contact impregnation, solid-liquid separation is performed to obtain the solid phase;

[0015] The total cation concentration of the metal trace element ion solution is 0.5–2 mol / L, and its solute includes one or more of CoCl2, Co(NO3)2, CoSO4, NiCl2, Ni(NO3)2, NiSO4, FeCl2, FeSO4, FeCl3, and Fe2(SO4)3.

[0016] As a preferred embodiment of the preparation method of the metal-based biochar composite material of the present invention, wherein: the waste biomass includes one or a mixture of multiple biomass such as sawdust, straw, and bio-fermentation residues;

[0017] The sawdust includes one or more of poplar sawdust, pine sawdust, and willow sawdust; the straw includes one or more of wheat straw, rice straw, and corn straw; and the bio-fermentation residue includes one or more of distiller's grains, biogas residue, and lactic acid fermentation residue.

[0018] As a preferred embodiment of the preparation method of the metal-based biochar composite material of the present invention, the method involves high-temperature pyrolysis under anaerobic conditions, or high-temperature pyrolysis under nitrogen gas conditions, with a nitrogen gas introduction rate of 10-80 mL / min, a pyrolysis temperature of 400-800℃, a heating rate of 5-15℃ / min, and holding at the set temperature for 30-60 min after reaching the set temperature.

[0019] As a preferred embodiment of the preparation method of the metal-based biochar composite material of the present invention, wherein: the drying involves drying the solid phase of the primary metal-based biochar after ion impregnation in an oven at 80-105°C for 12-24 hours.

[0020] The high-temperature curing process involves a temperature of 400–600°C, a heating rate of 10–50°C / min, and a holding time of 30–60 min after reaching the set temperature.

[0021] Another object of the present invention is to provide a metal-based biochar composite material obtained by the preparation method described in any of the above claims.

[0022] Another object of the present invention is to provide the application of the metal-based biochar composite material as described above in free fermentation acid production, wherein fermentation sludge is inoculated in a mesophilic anaerobic free fermentation system for kitchen waste, and the metal-based biochar composite material is added at the same time.

[0023] As a preferred embodiment of the present invention, the mesophilic anaerobic free fermentation is carried out under anaerobic conditions by inoculating biogas engineering anaerobic sludge that has been treated at 100°C for 10 minutes as fermentation sludge, with the fermentation temperature being 37±1°C, to produce acid through free fermentation.

[0024] In a preferred embodiment of the present invention, the inoculum amount of the fermented sludge is 20-40%, and the amount of the metal-based biochar composite material added is 0.5-5% of the total mass.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention utilizes methods such as high-temperature pyrolysis, metal precursor doping, and ion impregnation to load trace element promoters into the pore structure of biochar in atomic form, thereby enabling specific metal ions or metal compounds to be loaded or combined into the biochar pore structure. Alkali metal compounds can both regulate the pore structure during biochar formation and modify its surface chemical properties. Furthermore, besides forming a galvanic cell to promote metal corrosion, both Fe metal and biochar are conductive and can promote interspecies electron transfer among microorganisms, which is beneficial for accelerating the acid production process of hydrolysis products. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0028] Figure 1 The graph shows a comparison of the volatile acid concentrations at different fermentation times when the metal-based biochar composite materials prepared in Examples 1-2 and Comparative Examples 1-2 of this invention are applied to fermentation for acid production. Detailed Implementation

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0030] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0032] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0033] Example 1

[0034] (1) Poplar wood chips were dried in an oven at 105℃ for 12 hours and industrial waste iron chips were calcined in a muffle furnace at 400℃ for 30 minutes. After processing, they were ground thoroughly. After grinding, 50g of poplar wood chips and 10g of industrial waste iron chips were weighed and mixed evenly. Then, 9g of magnesite powder was added and mixed evenly. The mixture was then placed in a horizontal pyrolysis furnace for high-temperature pyrolysis. The pyrolysis temperature was 600℃, the heating rate was 10℃ / min, the holding time was 30min, and the nitrogen rate was 50mL / min. Primary metal-based biochar was prepared.

[0035] (2) The above-mentioned primary metal-based biochar was impregnated in a mixed solution of 0.6 mol / L CoCl2, 0.45 mol / L Ni(NO3)2, and 0.15 mol / L FeCl2 in 100 mL of room temperature for 24 h to load trace metal ions. After loading, the solid phase was dried in an oven at 80 °C for 12 h. After thorough drying, it was placed in a horizontal pyrolysis furnace for high-temperature curing. The curing temperature was 500 °C, the heating rate was 10 °C / min, the holding time was 30 min, and the nitrogen gas rate was 50 mL / min. The resulting metal-based biochar composite material was named Fe-Mg-Co-Ni@C 杨木 .

[0036] Example 2

[0037] (1) Poplar wood chips were dried in an oven at 105℃ for 12 hours and magnetite was calcined in a muffle furnace at 400℃ for 30 minutes. After processing, they were ground thoroughly. After grinding, 50g of poplar wood chips and 10g of industrial waste iron chips were weighed and mixed evenly. Then, 9g of calcite powder was added and mixed evenly. The mixture was then placed in a horizontal pyrolysis furnace for high-temperature pyrolysis. The pyrolysis temperature was 600℃, the heating rate was 10℃ / min, the holding time was 30min, and the nitrogen rate was 50mL / min. Primary metal-based biochar was prepared.

[0038] (2) The above-mentioned primary metal-based biochar was impregnated in a mixed solution of 0.6 mol / L CoCl2, 0.45 mol / L Ni(NO3)2, and 0.15 mol / L FeCl2 in 100 mL of room temperature for 24 h to load trace metal ions. After loading, the solid phase was dried in an oven at 80 °C for 12 h. After thorough drying, it was placed in a horizontal pyrolysis furnace for high-temperature curing. The curing temperature was 500 °C, the heating rate was 10 °C / min, the holding time was 30 min, and the nitrogen gas rate was 50 mL / min. The resulting metal-based biochar composite material was named Fe-Ca-Co-Ni@C 杨木 .

[0039] Comparative Example 1

[0040] (1) Poplar wood chips were dried in an oven at 105℃ for 12 hours and industrial waste iron chips were calcined in a muffle furnace at 400℃ for 30 minutes. After processing, they were ground thoroughly. After grinding, 50g of poplar wood chips and 10g of industrial waste iron chips were weighed and mixed evenly. Then, 9g of magnesite powder was added and mixed evenly. The mixture was then placed in a horizontal pyrolysis furnace for high-temperature pyrolysis. The pyrolysis temperature was 600℃, the heating rate was 10℃ / min, the holding time was 30min, and the nitrogen rate was 50mL / min to prepare primary metal-based biochar.

[0041] (2) Primary metal-based biochar was loaded with trace element promoters without ion impregnation, resulting in a metal-based biochar composite material named Fe-Mg@C. 杨木 .

[0042] Comparative Example 2

[0043] (1) Poplar wood chips were dried in an oven at 105℃ for 12 hours and industrial waste iron chips were calcined in a muffle furnace at 400℃ for 30 minutes. After processing, they were ground thoroughly. After grinding, 50g of poplar wood chips and 10g of industrial waste iron chips were weighed out, mixed evenly, and then placed in a horizontal pyrolysis furnace for high-temperature pyrolysis. The pyrolysis temperature was 600℃, the heating rate was 10℃ / min, the holding time was 30min, and the nitrogen rate was 50mL / min to prepare primary metal-based biochar.

[0044] (2) The primary metal-based biochar prepared above was impregnated in a mixed solution of 100 mL of 2 mol / L CoCl2, 0.5 mol / L Ni(NO3)2, and 0.5 mol / L FeCl2 at room temperature for 24 h to load metal ions. After loading, it was placed in an oven at 80 °C for 12 h to dry. After thorough drying, it was placed in a horizontal pyrolysis furnace for high-temperature curing. The curing temperature was 500 °C, the heating rate was 10 °C / min, the holding time was 30 min, and the nitrogen gas rate was 50 mL / min. The resulting metal-based biochar composite material was named Fe-Co-Ni@C. 杨 Wood.

[0045] The metal-based biochar composite materials prepared in Examples 1-2 and Comparative Examples 1-2 were applied to fermentation for acid production. The specific method is as follows:

[0046] Kitchen waste from a university student canteen was crushed into a paste using a high-speed blender. Anaerobic sludge from the biogas project was placed in a 100°C autoclave to inactivate methanogenic bacteria for 30 minutes. Then, 700g of kitchen waste and 300g of fermented sludge were weighed and mixed evenly, and added to an anaerobic fermentation tank with a working volume of 1L.

[0047] 10g of metal-based biochar composite material was weighed and added to an anaerobic fermenter. After purging the air from the reactor with nitrogen, it was placed in a constant temperature water bath at 37±1℃ for anaerobic free fermentation to produce acid. Samples were taken at 24h, 48h, 96h, 144h, and 192h of fermentation, and the concentration of volatile acids (VFAs) in the fermenter was determined by gas chromatography.

[0048] The anaerobic free fermentation of 700g of kitchen waste and 300g of fermented sludge without any added materials served as a blank control group. The test results are as follows: Figure 1 As shown.

[0049] Depend on Figure 1 It can be seen that the concentration of VFAs gradually increases with increasing fermentation time; compared with the control group, Fe-Mg@C 杨木 The composite material showed only a moderate effect in improving acid production; after 192 hours of fermentation, the VFA concentration was only 13842 mg / L. (Fe-Co-Ni@C) 杨木 The acid production rate of the composite material is significantly better than that of Fe-Mg@C. 杨木 The VFA concentration of the composite material can reach 20169 mg / L after 192 hours of fermentation.

[0050] Fe-Ca-Co-Ni@C 杨木 With Fe-Mg-Co-Ni@C 杨木 The acid-producing performance is significantly better; in addition, through Fe-Ca-Co-Ni@C 杨木 With Fe-Mg-Co-Ni@C 杨木 The comparison shows that during the early fermentation stage (0–144 h), Fe-Ca-Co-Ni@C 杨木 With Fe-Mg-Co-Ni@C 杨木 It exhibits a considerable acid production rate, but at the later stage of fermentation (192 hours), Fe-Mg-Co-Ni@C... 杨木 The concentration of volatile acids produced reached 23925 mg / L, Fe-Ca-Co-Ni@C 杨木 The concentration was 21798 mg / L, indicating that Fe-Mg-Co-Ni@C 杨木 It has a higher effect on promoting acid production in the later stages of fermentation.

[0051] Example 3

[0052] Based on Example 1, the biomass raw material poplar sawdust was replaced with biogas residue and distiller's grains, and the other steps were the same as in Example 1, respectively, to obtain Fe-Mg-Co-Ni@C. 沼渣 and Fe-Mg-Co-Ni@C 酒糟 .

[0053] Following the above method, the obtained metal-based biochar composite material was applied to fermentation for acid production. Samples were taken periodically, and the concentration of VFAs in the fermenter was determined by gas chromatography. The results of the VFAs concentration test after 192 hours of fermentation are shown in Table 1.

[0054] Table 1

[0055]

[0056]

[0057] As can be seen from the data in Table 1, biomass raw materials have a certain impact on the performance of composite materials, and poplar wood chips have the best performance.

[0058] Example 4

[0059] Based on Example 1, the amount of precursor A was adjusted, while other steps remained the same as in Example 1. The resulting metal-based biochar composite material was applied to fermentation for acid production according to the above method. Samples were taken periodically, and the concentration of VFAs in the fermenter was determined by gas chromatography. The test results of VFAs concentration after 192 hours of fermentation are shown in Table 2.

[0060] Table 2

[0061]

[0062] As shown in Table 2, the volatile acid concentration initially increases and then decreases with increasing precursor A content, reaching its highest level at a precursor A content of 9g. This may be because an increase in precursor A represents an increase in magnesium compounds in the composite material, leading to a relative decrease in the percentage of Fe and C in the metal-based biochar. When the amount of metal-based biochar material remains constant, the Fe-C effect is slightly weakened.

[0063] Example 5

[0064] Based on Example 1, the amount of precursor B was adjusted, while other steps remained the same as in Example 1. The resulting metal-based biochar composite material was applied to fermentation for acid production according to the above method. Samples were taken periodically, and the concentration of VFAs in the fermenter was determined by gas chromatography. The test results of VFAs concentration after 192 hours of fermentation are shown in Table 3.

[0065] Table 3

[0066]

[0067] As can be seen from the data in Table 3, with the increase of the amount of precursor B, the percentage of Fe and C in the metal-based biochar increases, and the Fe-C effect gradually strengthens. However, when the amount of precursor B is further increased, the increase in volatile acid concentration is limited. For cost-effectiveness, the optimal amount of precursor B is selected as 10g.

[0068] Example 6

[0069] Based on Example 1, the total molar concentration of cations in the trace metal element ion solution was adjusted, while other steps remained the same as in Example 1. The resulting metal-based biochar composite material was applied to fermentation for acid production according to the above method. Samples were taken periodically, and the concentration of VFAs in the fermenter was determined by gas chromatography. The test results of VFAs concentration after 192 hours of fermentation are shown in Table 4.

[0070] Table 4

[0071]

[0072]

[0073] As can be seen from the data in Table 4, the concentration of volatile acids increases significantly when Co, Ni, and Fe ions are all present. In particular, the concentration of volatile acids is highest when the total concentration of Co, Ni, and Fe cations is 1.2 mol / L and the molar ratio of the three is 4:3:1.

[0074] Example 7

[0075] Based on Example 1, the pyrolysis temperature was adjusted, while other steps remained the same as in Example 1. The resulting metal-based biochar composite material was applied to fermentation for acid production according to the above method. Samples were taken periodically, and the concentration of VFAs in the fermenter was determined by gas chromatography. The test results of VFAs concentration after 192 hours of fermentation are shown in Table 5.

[0076] Table 5

[0077]

[0078] As shown in Table 5, the highest concentration of volatile acids was observed at a pyrolysis temperature of 600℃. This may be because at 400℃, pyrolysis was incomplete, potentially due to interference from other organic groups, resulting in a poor FC structure and low porosity, leading to a lower concentration of volatile acids. At 800℃, some pore structures may have collapsed, excessive loss of surface hydroxyl groups, and decreased affinity for microorganisms, ultimately resulting in a reduction in the concentration of volatile acids.

[0079] Example 8

[0080] Based on Example 1, the amount of metal-based biochar composite material added was adjusted, while other steps remained the same as in Example 1. The resulting metal-based biochar composite material was applied to fermentation for acid production according to the above method. Samples were taken periodically, and the concentration of VFAs in the fermenter was determined by gas chromatography. The test results of VFAs concentration after 192 hours of fermentation are shown in Table 6.

[0081] Table 6

[0082]

[0083]

[0084] As shown in Table 6, the volatile acid concentration gradually increases with the addition of metal-based biochar composite material from 5g to 25g, reaching its highest level at 25g. However, when the addition of metal-based biochar composite material is further increased to 50g, the volatile acid concentration decreases significantly.

[0085] Among them, when the amount of metal-based biochar composite material added is 10g, the volatile acid concentration reaches 23925mg / L; when the amount added is increased to 25g, the volatile acid concentration only increases to 24178mg / L. Therefore, the optimal amount of metal-based biochar composite material added is 10g.

[0086] This invention uses waste biomass (poplar sawdust, distiller's grains, etc.) and metal precursors (magnesite, calcite, industrial waste iron filings, etc.) as raw materials, which are widely available, inexpensive, and readily accessible. A trace element promoter is loaded using an ion solution impregnation method, resulting in high trace element utilization. The metal-based biochar composite material of this invention has a simple preparation process, low cost, and does not cause secondary pollution during application; it is also recyclable.

[0087] This invention utilizes methods such as high-temperature pyrolysis, metal precursor doping, and ion impregnation to load trace element promoters, thereby loading or combining specific metal ions or metal compounds into the pore structure of biochar in atomic form. Alkali metal compounds can both regulate the pore structure during biochar formation and modify its surface chemical properties.

[0088] In this invention, the metal-based biochar composite material, by doping with alkali metal compounds such as Ca and Mg, can regulate the pH value of the anaerobic fermentation system, alleviate the excessive acidification of the system due to product accumulation, and maintain a suitable acid-producing environment. In this invention, the metal-based biochar composite material, by loading Fe, Co, and Ni, can provide anaerobic microorganisms with trace metal elements, promote the growth and metabolism of microorganisms, and thus improve the acid-producing efficiency of anaerobic fermentation of kitchen waste.

[0089] In this invention, the metal-based biochar composite material contains Fe and C forming a galvanic cell, which can regulate the release of trace metal elements in the composite material and extend its service life. The conductivity of Fe and biochar can promote electron transfer between microbial communities and accelerate the overall rate of acid production in anaerobic fermentation.

[0090] The addition of metal-based biochar composite material in this invention significantly increases the acid concentration produced by mesophilic anaerobic free fermentation of kitchen waste, eliminating the need for raw material pretreatment and process control.

[0091] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method of preparing a metal-based biochar composite material, characterized by: The application relates to a preparation method of a metal-based biochar composite material. The primary metal-based biochar is prepared by high-temperature pyrolysis of waste biomass and metal precursors under an oxygen-free condition; The metal precursors are composed of precursor A and precursor B; The precursor A comprises one or more of CaCO3, CaO, MgCO3 and MgO, and the adding amount of the precursor A is 5-15% of the mass of the waste biomass; The precursor B comprises one or more of zero-valent iron, scrap iron, iron oxide and magnetite, and the mass ratio of the precursor B to the waste biomass is 1:4-10; The primary metal-based biochar is further loaded with trace element promoters by an ion immersion method, and is dried and high-temperature solidified to obtain the metal-based biochar composite material; The ion immersion method is that the primary metal-based biochar is immersed in a metal trace element ion solution, and the solid phase is obtained after solid-liquid separation after sufficient contact and immersion; The total concentration of cations of the metal trace element ion solution is 0.5-2 mol / L, and the solutes include one or more of CoCl2, Co(NO3) 2、 CoSO4, NiCl2, Ni(NO3)2, NiSO4, FeCl2, FeSO4, FeCl3, Fe2(SO4)3. The metal-based biochar composite material is added into a mesophilic anaerobic free fermentation system of kitchen waste and inoculated with fermentation sludge to promote free fermentation to produce acid.

2. The method of claim 1, wherein the metal-matrix biochar composite is prepared by: The waste biomass comprises one kind of biomass or a mixture of multiple kinds of biomass selected from the group consisting of wood chips, straw and bio-fermentation residues; The wood chips comprise one or more of poplar wood chips, pine wood chips and willow wood chips; the straw comprises one or more of wheat straw, rice straw and corn straw; and the bio-fermentation residues comprise one or more of vinasse, biogas residue and lactic acid fermentation residue.

3. The method of claim 2, wherein the metal-based biochar composite is prepared by: The high-temperature pyrolysis under an oxygen-free condition is carried out under the condition that nitrogen is introduced at a rate of 10-80 mL / min, the pyrolysis temperature is 400-800 DEG C, the temperature rising rate is 5-15 DEG C / min, and the temperature is kept for 30-60 min after reaching the set temperature.

4. The method of claim 3, wherein the metal-based biochar composite is prepared by: The drying is that the solid phase after the ion immersion of the primary metal-based biochar is dried in an oven at 80-105 DEG C for 12-24 h; The high-temperature solidification is carried out at a temperature of 400-600 DEG C, a temperature rising rate of 10-50 DEG C / min, and a temperature keeping time of 30-60 min after reaching the set temperature.

5. The metal-based biochar composite material prepared by the preparation method in any one of claims 1-4.

6. Use of the metal-based biochar composite material according to claim 5 for free fermentation acid production, characterized by: Kitchen waste is inoculated with fermentation sludge in a mesophilic anaerobic free fermentation system, and the metal-based biochar composite material in claim 5 is added.

7. Use according to claim 6, wherein: The mesophilic anaerobic free fermentation is carried out under an oxygen-free condition, the fermentation sludge is the anaerobic sludge of a biogas engineering after being treated at 100 DEG C for 10 min, the fermentation temperature is 37 DEG C + / - 1 DEG C, and free fermentation is carried out to produce acid.

8. Use according to claim 7, wherein: The inoculation amount of the fermentation sludge is 20-40% of the total mass, and the adding amount of the metal-based biochar composite material is 0.5-5% of the total mass.

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