Co-pyrolysis biochar as well as preparation method and application thereof

Abstract

The invention provides co-pyrolysis biochar as well as a preparation method and application thereof, and relates to the technical field of solid waste recycling. The preparation method comprises the following steps: drying biogas residue and straw, and crushing to respectively obtain biogas residue powder and straw powder; the biogas residue powder and the straw powder are mixed for pyrolysis, and co-pyrolysis biochar is obtained. According to the invention, biogas residue and straw produced by anaerobic digestion of kitchen waste are used as raw materials, and co-pyrolysis biochar is prepared by a high-temperature pyrolysis method; the prepared co-pyrolysis biochar can increase the amount of methane produced through anaerobic digestion of the kitchen waste, and compared with biochar obtained through pyrolysis of a single biomass raw material, the co-pyrolysis biochar has a better strengthening effect on methane produced through anaerobic digestion of the kitchen waste; the biogas residues are waste products of kitchen waste anaerobic digestion, the biogas residues can be effectively used as biochar preparation raw materials, the biochar can be returned again to be used for strengthening anaerobic digestion to produce methane, a raw material closed loop is formed, and in-situ recycling of kitchen biogas residues is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization, and in particular to a co-pyrolysis biochar and a preparation method and application thereof. Background Art

[0002] Kitchen waste is an important component of organic solid waste in urban domestic waste. Due to its high water content and high organic matter content, it is very easy to spoil and deteriorate, and has potential environmental pollution risks. Kitchen waste rich in organic matter can be used as a substrate for anaerobic fermentation for resource utilization. However, the anaerobic fermentation process of kitchen waste not only has problems such as accumulation of intermediate metabolites, low biogas yield, long lag period, and poor system stability, but also produces a large amount of biogas residue. At present, the resource utilization of biogas residue has always been a difficult problem. It is generally believed that composting kitchen biogas residue is a resource-based treatment method with the least impact on the environment, but the transportation of biogas residue raw materials increases transportation costs, the composting cycle is long, and auxiliary materials need to be added and the amount of odor treatment is large, which makes the market acceptance of biogas residue composting technology and products low. The development of new biogas residue resource treatment methods has become a technical problem that needs to be solved urgently. Summary of the invention

[0003] In view of this, the object of the present invention is to provide a co-pyrolysis biochar and a preparation method and application thereof. The present invention co-pyrolyzes the methane-producing biogas residue from anaerobic digestion of food waste and straw to prepare biochar, which can enhance the methane production from anaerobic digestion of food waste and realize the in-situ resource recycling of food waste.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing co-pyrolysis biochar, comprising the following steps:

[0006] The biogas residue and the straw are dried and then crushed to obtain biogas residue powder and straw powder respectively; the biogas residue is a byproduct of anaerobic digestion of kitchen waste to produce methane;

[0007] The biogas residue powder and the straw powder are mixed and pyrolyzed to obtain the co-pyrolysis biochar; the mass ratio of the biogas residue powder to the straw powder is 4:1 to 1:4, and the pyrolysis temperature is 400 to 800°C.

[0008] Preferably, the straw is rice straw, corn straw, wheat straw or cotton straw.

[0009] Preferably, the mass ratio of the biogas residue powder to the straw powder is 1:1.

[0010] Preferably, the pyrolysis holding time is 1 to 4 hours.

[0011] Preferably, after the pyrolysis, the solid phase product obtained is sequentially washed with dilute hydrochloric acid, washed with water and dried to obtain the co-pyrolysis biochar.

[0012] The present invention provides co-pyrolysis biochar prepared by the preparation method described in the above technical scheme.

[0013] The present invention provides the use of the co-pyrolysis biochar described in the above technical solution in enhancing the anaerobic digestion of food waste to produce methane.

[0014] The present invention provides a method for producing methane through anaerobic digestion of food waste, comprising the following steps:

[0015] The kitchen waste, anaerobic digestion sludge and co-pyrolysis biochar are mixed and anaerobic digested to obtain methane; the co-pyrolysis biochar is the co-pyrolysis biochar described in the above technical solution.

[0016] Preferably, the mass ratio of the volatile solids in the food waste to the volatile solids in the anaerobic digestion sludge is (0.5-2):1; and the amount of co-pyrolysis biochar in the mixed system obtained by mixing is 0.5-6.0 g / L.

[0017] Preferably, the temperature of the anaerobic digestion is 35-39° C., and the time is 20-30 days.

[0018] The present invention provides a method for preparing co-pyrolysis biochar, comprising the following steps: drying and crushing biogas residue and straw to obtain biogas residue powder and straw powder respectively; the biogas residue is a byproduct of anaerobic digestion of food waste to produce methane; the biogas residue powder and straw powder are mixed and pyrolyzed to obtain the co-pyrolysis biochar; the mass ratio of the biogas residue powder to the straw powder is 4:1 to 1:4, and the pyrolysis temperature is 400 to 800°C. Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention uses biogas residue and straw produced by anaerobic digestion of food waste to produce methane as raw materials, and adopts a high-temperature co-pyrolysis method to prepare co-pyrolysis biochar; the prepared co-pyrolysis biochar can be used as an additive to increase the methane production of anaerobic digestion of food waste, and has a better strengthening effect on the methane production of anaerobic digestion of food waste than biochar produced by pyrolysis of a single biomass raw material;

[0020] The present invention uses biogas residue as a raw material for preparing biochar. The biogas residue is a waste product of anaerobic digestion of food waste. The present invention can effectively use the biogas residue as a raw material for preparing biochar, and can return the biochar to be used again for enhanced anaerobic digestion to produce methane, forming a closed loop of raw materials, realizing the in-situ recycling of food waste resources, and providing a new solution for waste treatment and reducing environmental pollution.

[0021] The preparation method of the present invention is simple, low-cost, easy to standardize and mass-produce, and has good potential in future practical applications. The prepared biochar does not require modification and has stable properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The SEM images of three biochars prepared in Example 1, Comparative Example 1 and Comparative Example 2 at different scales are shown in FIG. Figure 1 JC(a) and JC(b) represent SEM images of straw biochar at different scales, ZC(a) and ZC(b) represent SEM images of biogas residue biochar at different scales, and ZJC(a) and ZJC(b) represent SEM images of biogas residue-straw co-pyrolysis biochar at different scales.

[0023] Figure 2 The cumulative methane production per unit biomass (a) and daily methane production (b) of the anaerobic digestion process of the control group (Control), ZC group, JC group and ZJC group in Example 3;

[0024] Figure 3 The changes in the volatile short-chain fatty acids (VFAs) content, total volatile fatty acids (TVFA) content and pH value during the anaerobic digestion process of each experimental group in Example 3 are shown in FIG. Figure 3 (a) to (e) show the changes in the content of volatile short-chain fatty acids (VFAs) and total volatile fatty acids (TVFA) in each experimental group during the entire experimental period, and (f) shows the changes in the pH value of each experimental group during the entire experimental period.

[0025] Figure 4 The changes in COD content (a) and ammonia nitrogen content (b) during the anaerobic digestion process of each experimental group in Example 3;

[0026] Figure 5 The bacterial community structures at the phylum level on the 5th day (a) and the 16th day (b) during the anaerobic digestion process of each experimental group in Example 3, as well as the bacterial community structures at the genus level on the 5th day and the 16th day (c). DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing co-pyrolysis biochar, comprising the following steps:

[0028] The biogas residue and the straw are dried and then crushed to obtain biogas residue powder and straw powder respectively; the biogas residue is a byproduct of anaerobic digestion of kitchen waste to produce methane;

[0029] The biogas residue powder and the straw powder are mixed and pyrolyzed to obtain the co-pyrolysis biochar; the mass ratio of the biogas residue powder to the straw powder is 4:1 to 1:4, and the pyrolysis temperature is 400 to 800°C.

[0030] In the present invention, unless otherwise specified, the raw materials involved are commercially available products well known to those skilled in the art.

[0031] The present invention dries and crushes biogas residue and straw to obtain biogas residue powder and straw powder respectively.

[0032] In the present invention, the biogas residue is a byproduct of methane production from anaerobic digestion of food waste (also referred to as food biogas residue in the present invention); the straw is preferably rice straw, corn straw, wheat straw or cotton straw. In the present invention, the drying temperature is preferably 10 to 30°C. In an embodiment of the present invention, the drying is carried out at room temperature; the present invention has no special requirements for the pulverization method, and a pulverization method familiar to those skilled in the art can be used. After the pulverization, it is also preferred to sieve the obtained pulverized material, take the sieve under the sieve, and obtain the biogas residue powder and straw powder respectively; the sieving is preferably through a sieve of 80 to 140 mesh, which can be 80, 100, 120 or 140 mesh.

[0033] After obtaining the biogas residue powder and the straw powder, the present invention mixes the biogas residue powder and the straw powder for pyrolysis to obtain the co-pyrolysis biochar.

[0034] In the present invention, the mass ratio of the biogas residue powder to the straw powder is preferably 4:1 to 1:4 (can be 4:1, 2:1, 1:1, 1:2, 1:4), more preferably 2:1 to 1:2, and further preferably 1:1. In the present invention, the mass ratio of the biogas residue powder to the straw powder will affect the specific surface area, element content, and physical structure of the biochar, thereby affecting the amount of methane increased when the biochar is used for anaerobic digestion to produce methane.

[0035] In the present invention, the temperature of the pyrolysis (also known as high-temperature calcination or carbonization) is 400-800°C, and can be 400, 500, 550, 600, 700 or 800°C. The holding time is preferably 1-4h, and can be 1, 2, 3 or 4h; the pyrolysis is preferably carried out in a nitrogen atmosphere. In the present invention, the temperature of the pyrolysis will affect the specific surface area and pore structure, pore size distribution, elemental composition, functional group changes, and physicochemical properties (pH value, conductivity) of the biochar. In an embodiment of the present invention, the pyrolysis is carried out in a muffle furnace. During the pyrolysis process, the rapid decomposition of organic components leads to CO, CO 2 Gases are continuously released from the solid phase to form larger pores. Compared with biochar produced by pyrolysis of a single biomass raw material, the co-pyrolysis biochar has a more regular and delicate surface, with obvious pores and lamellae, and less pore ash. In addition, pathogenic bacteria such as Escherichia coli, Salmonella, Listeria, etc. that may be contained in the sludge can be completely inactivated through the pyrolysis.

[0036] In the present invention, the food waste has a high nitrogen (N) content and contains a high proportion of easily degradable organic matter (such as oil, protein, carbohydrate, etc.); food waste contains more protein, fat, starch, etc., and the waste after anaerobic digestion usually contains a certain proportion of nitrogen, phosphorus, and potassium nutrients. Straw is rich in cellulose, hemicellulose and lignin, has a high carbon content, can be well converted into biochar during pyrolysis, and has a strong carbon fixation capacity. Food waste contains more nitrogen (N), phosphorus (P), potassium (K) and other mineral elements necessary for microorganisms, but the carbon content is low when pyrolyzed alone. After co-pyrolysis with straw, the minerals of food waste can adhere to the surface of straw biochar, which is conducive to the growth of microorganisms such as methanogens. The porosity of biochar is low, and the addition of straw to pyrolysis can promote the improvement of porosity. The inorganic matter in the waste can prevent the excessive collapse of the biochar pores, and improve the porosity and specific surface area of ​​the co-pyrolyzed biochar. Food digester residue is rich in alkaline substances such as carbonates and phosphates. The pH of biochar prepared from digester residue alone is relatively high. Co-pyrolysis with straw can reduce the pH of digester residue biochar, which is conducive to the growth of microorganisms such as methanogens in anaerobic digestion. Direct burning of straw pollutes the environment, and the stacking of digester residue is prone to secondary pollution. Digester residue that is composted alone or applied to the soil may release methane and ammonia. Co-pyrolysis treatment not only reduces pollution, but also achieves efficient use of resources, reduces volatile substances, and helps reduce greenhouse gas emissions.

[0037] After the pyrolysis, the present invention preferably cools to room temperature, takes out the solid phase product, and sequentially washes the obtained solid phase product with dilute hydrochloric acid, water and dries it to obtain the co-pyrolysis biochar. In the present invention, the concentration of the dilute hydrochloric acid is preferably 1 mol / L, and the function of the dilute hydrochloric acid washing is to wash away inorganic matter and ash in the product; the water washing is preferably washed with deionized water to neutrality; the drying temperature is preferably 100 to 110°C, which can be 100, 105 or 110°C, and the time is preferably 10 to 48 hours, which can be 10, 12, 24 or 48 hours, and the drying is specifically carried out in an oven.

[0038] The present invention provides co-pyrolysis biochar prepared by the preparation method described in the above technical solution. In an embodiment of the present invention, the co-pyrolysis biochar is called biogas residue-straw co-pyrolysis biochar. The present invention uses biogas residue and straw produced by anaerobic digestion of food waste to produce methane as raw materials, and adopts a high-temperature pyrolysis method to prepare co-pyrolysis biochar, which can effectively combine the beneficial properties of the raw materials and enhance the properties of biochar. Compared with biochar produced by pyrolysis of a single biomass raw material, the surface of the co-pyrolysis biochar is more regular and delicate, with obvious pores and lamellae, and less ash in the pores, which is conducive to the attachment of microorganisms to the pores, promotes the interspecies electron transfer process, and ultimately has a positive effect on the amount of methane produced. Compared with biochar produced by pyrolysis of a single biomass raw material, the co-pyrolysis biochar provided by the present invention has a better strengthening effect on the anaerobic digestion of food waste to produce methane.

[0039] The present invention provides the application of the co-pyrolysis biochar described in the above technical solution in strengthening the production of methane by anaerobic digestion of food waste. The present invention prepares biochar by co-pyrolysis of biogas residue and straw produced in the process of producing methane by anaerobic digestion of food waste. Biochar is used as an additive to strengthen the production of methane by anaerobic digestion of food waste, promote the increase of methane production by anaerobic digestion, and is used to strengthen the production of methane by anaerobic digestion, so as to realize the in-situ recycling of food waste residue, and provide a new method for the in-situ recycling of food waste residue.

[0040] The present invention provides a method for producing methane through anaerobic digestion of food waste, comprising the following steps:

[0041] The kitchen waste, anaerobic digestion sludge and co-pyrolysis biochar are mixed and anaerobic digested to obtain methane; the co-pyrolysis biochar is the co-pyrolysis biochar described in the above technical solution.

[0042] In the present invention, the mass ratio of the volatile solids (VS, which refers to the part lost from the total solids (TS, Total Solids) after high-temperature burning at 550°C, mainly composed of organic matter) in the food waste to the volatile solids (VS) in the anaerobic digestion sludge is preferably (0.5-2):1, which can be 0.5:1, 1:1 or 2:1. The mass ratio of the volatile solids in the food waste to the volatile solids in the anaerobic digestion sludge has an impact on the methane production process and the final methane production. If the ratio is too high, a large amount of volatile short-chain fatty acids (VFAs) will be produced, which will inhibit the methane production. If the ratio is too low, the anaerobic digestion process will be slow and the methane production will be low. In the present invention, the amount of co-pyrolysis biochar in the mixed system obtained by mixing is preferably 0.5-6.0 g / L, which can be 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0 or 6.0 g / L.

[0043] In the present invention, the mixing method is preferably: mixing the food waste and anaerobic digestion sludge, adding the co-pyrolysis biochar thereto, to obtain a mixed system.

[0044] In the present invention, the temperature of the anaerobic digestion is preferably 35-39°C, which can be 35, 36, 37, 38 or 39°C, and the time is preferably 20-30 days, which can be 20, 25 or 30 days. In an embodiment of the present invention, the mixed system is preferably purged with high-purity nitrogen (purity 99.999%) for 5 minutes and placed in a constant temperature shaker for anaerobic digestion; the rotation speed of the constant temperature shaker is preferably 120-180 rpm, which can be 120, 130, 150 or 180 rpm.

[0045] In order to further illustrate the present invention, the co-pyrolysis biochar provided by the present invention and its preparation method and application are described in detail below in combination with examples, but they should not be construed as limiting the scope of protection of the present invention.

[0046] Example 1

[0047] The steps for preparing biochar from biogas residue and straw co-pyrolysis are as follows:

[0048] The biogas residue (biogas residue is a byproduct of anaerobic digestion of kitchen waste to produce methane) and rice straw are dried at room temperature and then crushed, and passed through a 100-mesh sieve to obtain biogas residue powder and straw powder respectively;

[0049] The biogas residue powder and the straw powder are mixed in a mass ratio of 1:1 to obtain a biogas residue straw mixture;

[0050] The sludge-straw mixture was placed in a muffle furnace and pyrolyzed at 600°C in a nitrogen atmosphere for 2 h, and then naturally cooled to room temperature; the obtained biochar was washed several times with dilute hydrochloric acid (1 mol / L), then washed with deionized water until neutral, and placed in an oven at 105°C to dry for 12 h to obtain sludge-straw co-pyrolysis biochar, recorded as ZJC.

[0051] Example 2

[0052] The mass ratios of biogas residue powder and straw powder were changed to 2:1, 4:1, 1:2, and 1:4, respectively. The rest were the same as in Example 1. The biogas residue-straw co-pyrolysis biochars prepared were recorded as ZJC-1, ZJC-2, ZJC-3, and ZJC-4, respectively.

[0053] Comparative Example 1

[0054] The difference between the preparation of biogas residue biochar and Example 1 is that only biogas residue is used as the raw material for preparing biochar, and the remaining steps are consistent with Example 1. The biogas residue biochar obtained in Comparative Example 1 is denoted as ZC.

[0055] Comparative Example 2

[0056] The preparation of straw biochar is different from that of Example 1 in that only rice straw is used as the raw material for preparing biochar, and the remaining steps are the same as those of Example 1. The straw biochar obtained in Comparative Example 2 is denoted as JC.

[0057] Figure 1 The SEM images of three biochars prepared in Example 1, Comparative Example 1 and Comparative Example 2 at different scales are shown in FIG. Figure 1JC(a) and JC(b) represent SEM images of straw biochar at different scales, ZC(a) and ZC(b) represent SEM images of biochar from digestate at different scales, and ZJC(a) and ZJC(b) represent SEM images of biochar from digestate-straw co-pyrolysis at different scales. The volatile matter of straw is high, and a large amount of gas products are released during the pyrolysis process, which has a significant effect on the pore structure and surface properties of the final char. Figure 1 It can be seen that the co-pyrolysis biochar (ZJC) has a smooth surface and low ash content. This morphology is conducive to the attachment of microorganisms to the pores, promotes the interspecies electron transfer process, and ultimately has a positive effect on methane production.

[0058] Table 1 shows the physical and chemical properties of food waste, anaerobic digestion sludge, rice straw, biogas residue, biogas residue biochar, straw biochar and biogas residue-straw co-pyrolysis biochar (ZJC).

[0059] Table 1 Physical and chemical properties of each material

[0060]

[0061]

[0062] Note: In Table 1, FW: food waste; AS: anaerobic digestion sludge; RS: rice straw; DG: digestate; ZC: digestate biochar; JC: straw biochar; ZJC: digestate-straw co-pyrolysis biochar; TS: total solids content; VS: volatile solids; SSA: specific surface area.

[0063] As can be seen from Table 1, the nitrogen content of co-pyrolysis biochar (ZJC) (1.19%) is higher than that of straw biochar (JC, 0.55%) and digestate biochar (ZC, 0.84%), indicating that it can provide an appropriate amount of nitrogen source while maintaining carbon stability, promote the growth of anaerobic microorganisms, and increase methane production. The Fe content in co-pyrolysis biochar (ZJC) (3.89 mg / g) is higher than that in JC (3.12 mg / g). Iron is an important medium for electron transfer in anaerobic digestion, which can promote direct electron transfer (DIET), accelerate organic matter degradation, and improve methanogenesis efficiency. The sulfur content in digestate (DG) is relatively high (0.51%), which may form H 2 S inhibits methane production, but the sulfur content of co-pyrolysis biochar (ZJC) (0.36%) is lower than that of DG, indicating that co-pyrolysis helps to reduce the release of sulfur, thereby reducing H 2S inhibits the growth of rice straw and improves methane production. Both rice straw (RS) and digestate (DG) are rich in organic matter (RS: VS 85.67%, DG: VS 90.26%), but using digestate alone can easily lead to incomplete degradation of organic matter. Co-pyrolysis biochar (ZJC) can promote substrate degradation and methane production by adjusting the C / N ratio, providing microbial attachment sites and improving electron transfer. The C / N ratio is a key indicator to measure the nutritional balance of anaerobic digestion microorganisms, which directly affects their growth, metabolism and system stability. Maintaining a C / N ratio of 20:1 to 30:1 is an important condition for optimizing anaerobic digestion efficiency. As can be seen from Table 1, the C / N of straw biochar (JC), digestate biochar (ZC) and digestate-straw co-pyrolysis biochar (ZJC) are 73.38, 16.51 and 21.69, respectively, and the C / N of ZJC is in the optimal range for anaerobic digestion and methane production.

[0064] Example 3

[0065] Application of biogas residue-straw co-pyrolysis biochar prepared in Example 1 in enhancing methane production from anaerobic digestion of kitchen waste:

[0066] Add a mixture of food waste and inoculum (anaerobic digestion sludge) to a serum bottle with a working volume of 400 mL (capacity of 500 mL) and mix them at a mass ratio of 1:1 (VS). Add 600 mg of ZC, JC, and ZJC to 9 serum bottles (3 replicates in each experimental group), purge with high-purity nitrogen (purity 99.999%) for 5 minutes to remove excess gas in the serum bottle and headspace, keep the environment in the serum bottle anaerobic throughout the process, and seal the serum bottle with a butyl rubber stopper and an aluminum foil double-valve gas collection bag. Finally, place the serum bottle in a constant temperature shaker at 35°C and 130rpm for incubation. The anaerobic digestion reactor continued to operate for 30 days.

[0067] The above treatment is the experimental group. In order to verify the strengthening effect of biochar from biogas residue-straw co-pyrolysis on methane production from anaerobic digestion of food waste, a control group (Control) was also set up in this example. The difference between the control group and the experimental group is that no biochar was added, and other operations were the same as the experimental group.

[0068] During the whole process, the biogas is collected separately with gas bags, and the composition of the biogas is determined by gas chromatography, and the methane content is measured.

[0069] Summarizing the methane production of each group, the results are as follows Figure 2 The ZJC group had the highest cumulative methane production of 156 mL / gVS, followed by the ZC, JC and control groups, with cumulative methane production of 138, 123 and 114 mL / gVS, respectively. Figure 2(a)). Compared with the control group, the addition of ZJC increased the total methane production by 37%. The daily methane production of the ZJC experimental group was higher than that of the ZC and JC experimental groups and the control group ( Figure 2 (b)), indicating that ZJC has obvious advantages in promoting the increase of methane production.

[0070] Figure 3 The figure shows the changes in the volatile short-chain fatty acids (VFAs) content, total volatile fatty acids (TVFA) content and pH value of each experimental group during the entire experimental period of Example 3. Figure 3 (a) to (e) show the changes in the content of volatile short-chain fatty acids (VFAs) and total volatile fatty acids (TVFA) in each experimental group during the entire experimental period, and (f) shows the changes in the pH value of each experimental group during the entire experimental period.

[0071] VFAs are key intermediates in anaerobic digestion, including acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid and isovaleric acid. The imbalance between VFA production and consumption can undermine the stability of the anaerobic digestion process. At the beginning of anaerobic digestion, the total volatile fatty acid (TVFA) concentrations in all systems were less than 500 mg / L, with acetic acid as the main component. On the 5th day, the TVFA concentrations in each group reached a peak. The peak TVFA concentrations in the ZJC group were 4341 mg / L, the peak TVFA concentrations in the ZC group were 4494 mg / L, and the peak TVFA concentrations in the JC group were 4141 mg / L. These values ​​were 18.0%, 22.1% and 12.5% ​​higher than the peak values ​​of the control group (3680 mg / L), respectively, indicating that ZJC has the advantage of improving acid production capacity in the AD (anaerobic digestion) system. After reaching the peak, TVFA decreased rapidly, mainly due to the significant decrease in acetic acid concentration. During this stage, the acetic acid content of all treatments was significantly reduced compared with the control group, indicating that the addition of biochar significantly promoted the consumption of VFAs during anaerobic digestion.

[0072] During the first 5 days of anaerobic digestion, the pH values ​​of all groups dropped below 7.60 as VFAs accumulated rapidly. The addition of biochar initially caused a slight increase in pH. However, from the start of anaerobic digestion to day 5, the pH of all groups decreased significantly (p < 0.05), which was consistent with the accumulation of VFAs. By day 8, the pH levels of all groups gradually increased to approximately 8, and the biochar treatment showed a faster recovery level compared to the control group. After day 8, the pH values ​​of all groups tended to stabilize, which is consistent with the results of a previous study that determined the optimal pH range for methanogen activity to be 7.00-7.50.

[0073] Figure 4 What is shown is the change of COD content (a) and the change of ammonia nitrogen content (b) of each experimental group in the whole experimental period of Example 3. The ammonia nitrogen removal rate of the control group is 49.01%, while that of ZC, JC and ZJC groups is 74.21%, 88.66% and 91.32% respectively, which are much higher than that of the control group. The ZJC group shows a very obvious effect in the removal of ammonia nitrogen. The COD removal rates of the control group, ZC, JC and ZJC groups are 66.13%, 63.29%, 68.80% and 68.66% respectively, and the COD removal rates of JC and ZJC are all improved compared with the control group.

[0074] Figure 5 Shown are the bacterial community structures at the phylum level on the 5th day (a) and the 16th day (b) of anaerobic digestion in each experimental group, as well as the bacterial community structures at the genus level on the 5th day and the 16th day (c). Figure 5 ZJC-5 and ZJC-16 represent the ZJC group on day 5 and day 16, respectively, and the rest are similar. At the genus level, 28 bacterial sequences with a relative abundance of more than 1% were identified on day 5 ( Figure 5 (c)). The dominant genera were Fastidiosipila, W5053, Aminobacterium, DMER64, Fermentimonas, and Syntrophomonas. The relative abundances of the ZC, JC, and ZJC groups were 13.5%, 13.8%, and 17.6%, respectively. The high abundance of Fastidiosipila in the ZJC group can be attributed to its key role in the hydrolysis and acidification processes, in which it converts complex organic macromolecules into VFAs and CO 2. The genus W5053, belonging to the phylum Firmicutes, ranked second in number. It is an integral part of the acidogenesis process, with acetate being its major metabolite. In addition, DMER64 was more prevalent in the ZJC reactor, suggesting that it is a syntrophic butyrate-oxidizing bacterium capable of establishing direct interspecies electron transfer (DIET) via a pore-mediated mechanism. The data suggest that ZJC supplementation promotes electron transfer in DMER64 via a mechanism that replaces conductive hairs, thereby enhancing the DIET process.

[0075] In the anaerobic fermentation process of the present invention, the co-pyrolysis biochar is more suitable as an adsorbent and filler to stabilize the system operation and reduce the accumulation of volatile fatty acids (VFAs). The promotion effect on methanogens mainly comes from its specific surface area and pore adsorption function.

[0076] Example 4

[0077] The biogas residue-straw co-pyrolysis biochar prepared in Example 2 was applied to the enhanced anaerobic digestion of kitchen waste to produce methane, and the total methane production was tested according to the method of Example 3. Results: After 30 days of operation, the methane production of anaerobic digestion corresponding to the biogas residue-straw co-pyrolysis biochar ZJC-1, ZJC-2, ZJC-3, and ZJC-4 was 138.8 mL / gVS, 123.6 mL / gVS, 104.01 mL / gVS, and 52.44 mL / gVS, respectively.

[0078] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing co-pyrolysis biochar, characterized in that: The following steps are involved: The biogas residue and the straw are dried and then crushed to obtain biogas residue powder and straw powder respectively; the biogas residue is a byproduct of anaerobic digestion of kitchen waste to produce methane; The biogas residue powder and the straw powder are mixed and pyrolyzed to obtain the co-pyrolysis biochar; the mass ratio of the biogas residue powder to the straw powder is 4:1 to 1:4, and the pyrolysis temperature is 400 to 800°C.

2. The preparation method according to claim 1, characterized in that: The straw is rice straw, corn straw, wheat straw or cotton straw.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the biogas residue powder to the straw powder is 1:

1.

4. The preparation method according to claim 1, characterized in that: The heat preservation time of the pyrolysis is 1 to 4 hours.

5. The preparation method according to claim 1 or 4, characterized in that: After the pyrolysis, the solid phase product is sequentially washed with dilute hydrochloric acid, washed with water and dried to obtain the co-pyrolysis biochar.

6. Co-pyrolysis biochar prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the co-pyrolysis biochar described in claim 6 in enhancing the production of methane from anaerobic digestion of food waste.

8. A method for producing methane by anaerobic digestion of food waste, characterized in that: The following steps are involved: Mixing food waste, anaerobic digestion sludge and co-pyrolysis biochar for anaerobic digestion to obtain methane; The co-pyrolysis biochar is the co-pyrolysis biochar according to claim 6.

9. The method according to claim 8, characterized in that The mass ratio of the volatile solids in the food waste to the volatile solids in the anaerobic digestion sludge is (0.5-2):1; the amount of the co-pyrolysis biochar in the mixed system obtained by mixing is 0.5-6.0 g / L.

10. The method according to claim 8, characterized in that The temperature of the anaerobic digestion is 35-39° C. and the time is 20-30 days.

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