Modified biogas residue-based hydrothermal carbon, preparation method thereof and dry digestion method of kitchen waste

Abstract

The invention discloses modified biogas residue-based hydrothermal carbon, a preparation method thereof and a dry digestion method for kitchen waste, and belongs to the technical field of waste organic matter recycling. The preparation method comprises the following steps: soaking biogas residues in a phosphoric acid solution to obtain pretreated biogas residues; mixing the pretreated biogas residues, transition metal salt, biochar loaded with vitamin B12 and water with the mass being 8-15 times that of the pretreated biogas residues, and performing hydrothermal reaction for 1-4 hours under the conditions that the temperature is 180-250 DEG C and the pressure is 1.5-4 MPa to obtain a hydrothermal product; and activating the hydrothermal product for 1-2 hours under the protective atmosphere of 300-400 DEG C to obtain the modified biogas residue-based hydrothermal carbon. The surface Fe-Cu composite oxide sequentially catalyzes and oxidizes H2S into elemental sulfur and sulfate ions, the vitamin B12-loaded biochar can promote MA directional proliferation, the sulfate ions can competitively inhibit SRB substrate uptake, the quantity ratio of MA to SRB is increased, and the methane production efficiency is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of waste organic matter resource utilization technology, specifically relating to a modified biogas residue-based hydrothermal char and its preparation method, and a dry digestion method for kitchen waste. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Food waste, a typical type of municipal solid waste with high organic matter and high moisture content, has always presented a significant challenge in the environmental field in terms of its harmless and resource-based treatment. Anaerobic digestion technology can convert food waste into clean energy biogas, and is one of the mainstream technologies for its resource utilization. Among them, dry anaerobic digestion technology (total solids content TS=20~30%) shows great application potential due to its advantages such as small reactor volume, low energy consumption, and no need for dehydration pretreatment.

[0004] However, food waste typically contains high levels of sulfates, which are reduced by sulfate-reducing bacteria (SRB) during anaerobic digestion, producing high concentrations of hydrogen sulfide (H2S). H2S is not only highly toxic and foul-smelling, but it also causes equipment corrosion, catalyst poisoning, and severely inhibits microbial activity. The problem of H2S inhibition is particularly prominent in dry digestion systems: high solids content leads to high system viscosity and extremely low mass transfer efficiency, making it difficult for the generated H2S to be effectively released from the solid-liquid phase to the gas phase and removed by subsequent end-of-pipe desulfurization units. This results in localized accumulation of H2S, which has a strong toxic effect on the microbial community (especially methanogenic archaea, MA).

[0005] Currently, conventional control technologies for H2S in anaerobic digestion mainly include end-of-pipe treatment (such as chemical absorption and biofilters) and process control (such as iron salt precipitation and oxide addition). However, end-of-pipe treatment cannot solve the problem of H2S inhibiting microorganisms inside the reactor. Although adding ferric chloride in process control can remove H2S by generating FeS precipitate, in a dry system with TS=25%, Fe³⁺ easily agglomerates to form local high-concentration areas, and the inhibition of MA still exists. Moreover, sulfur is fixed in the biogas residue in the form of FeS, and sulfur form conversion cannot be achieved, leading to sulfur accumulation in the system over a long period of time. If biochar adsorbent is used to adsorb H2S in a dry system, it will reach saturation within ten days, turning into hazardous waste and increasing the environmental burden.

[0006] Therefore, developing a low-cost, in-situ regulation technology and functional materials that are suitable for high solids concentration environments and can optimize microbial ecology and increase methane production through the synergistic effect of multiple mechanisms to efficiently reduce H2S emissions while increasing methane production has become a technical challenge that needs to be overcome in the dry anaerobic digestion technology of food waste. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a modified biogas residue-based hydrothermal char and its preparation method, as well as a method for dry digestion of food waste. The method utilizes biogas residue to prepare hydrothermal char, and through a modification process, enables it to selectively inhibit sulfate-reducing bacteria (SRB) and promote the metabolic activity of methanogenic archaea (MA), thereby optimizing the substrate competition balance and achieving multiple objectives in the dry digestion of food waste, including efficient H2S emission reduction, improved biogas yield and quality, and stable system operation.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, a method for preparing modified biogas residue-based hydrothermal carbon includes the following steps: S1. Soak the biogas residue in a phosphoric acid solution to obtain pretreated biogas residue; S2. Mix pretreated biogas residue, transition metal salts accounting for 2-5% of the dry weight of pretreated biogas residue, vitamin B12-loaded biochar accounting for 1-3% of the dry weight of pretreated biogas residue, and water at 8-15 times the mass of pretreated biogas residue. React hydrothermally at 180-250℃ and 1.5-4MPa pressure for 1-4 hours to obtain hydrothermal products. S3. Activate the hydrothermal products under a protective atmosphere at 300~400℃ for 1~2h to obtain modified biogas residue-based hydrothermal carbon.

[0009] Secondly, the modified biogas residue-based hydrothermal carbon obtained by the above-mentioned method for preparing modified biogas residue-based hydrothermal carbon.

[0010] Thirdly, a method for dry digestion of kitchen waste includes the following steps: S4. Mix the kitchen waste with the inoculum at a volatile solids ratio of (2~3):1; S5. Add the above-mentioned modified biogas residue-based hydrothermal carbon at a ratio of 5-15% of the dry weight of kitchen waste, and carry out anaerobic digestion at 35-55℃.

[0011] The beneficial effects of this invention are as follows: 1. This invention provides a modified biogas residue-based hydrothermal char. Its mesoporous structure can rapidly capture free H2S within the system, reducing the local H2S concentration from 2000 ppm to below 500 ppm. This process "creates a high-concentration reactant environment" for subsequent catalytic reactions, solving the problems of slow H2S diffusion and insufficient contact with catalytic sites in dry systems. The Fe-Cu composite oxide on the surface catalytically oxidizes the adsorbed H2S sequentially into elemental sulfur and sulfate ions, preventing elemental sulfur from clogging the pores of the hydrothermal char and maintaining the adsorption capacity at over 90% of the initial value. The vitamin B12-loaded biochar can specifically activate methyl-CoM reductase (a key methanogen) of methanogens (MA), promoting its directional proliferation, while sulfate ions can competitively inhibit substrate uptake by sulfate-reducing bacteria (SRB), increasing the MA / SRB ratio and effectively improving methanogenesis efficiency. On the other hand, the modified biogas residue-based hydrothermal char can still maintain high desulfurization efficiency after calcination and regeneration, effectively reducing its usage cost. It also solves three technical problems: the inability of end-of-pipe treatment to address microbial inhibition, the risk of toxicity arising from process control, and the unsustainability of single adsorption materials.

[0012] 2. The dry digestion method for kitchen waste provided by this invention is suitable for high solids concentrations, effectively overcoming the mass transfer limitation problem under this system, and is also suitable for medium and high temperature conditions, further broadening its application scope. Attached Figure Description

[0013] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0014] Figure 1 This is a schematic flowchart of the preparation method in Embodiment 1 of the present invention.

[0015] Figure 2 This is a statistical chart of the H2S concentration results for Example 3 and Comparative Example 3 of the present invention.

[0016] Figure 3 This is a statistical chart of the cumulative methane accumulation in Example 3 and Comparative Example 3 of the present invention. Detailed Implementation

[0017] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods or product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0019] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0020] One or more embodiments of the present invention provide a method for preparing modified biogas residue-based hydrothermal carbon, comprising the following steps: S1. Soak the biogas residue in a phosphoric acid solution to obtain pretreated biogas residue; S2. Mix pretreated biogas residue, transition metal salts accounting for 2-5% of the dry weight of pretreated biogas residue, vitamin B12-loaded biochar accounting for 1-3% of the dry weight of pretreated biogas residue, and water at 8-15 times the mass of pretreated biogas residue. React hydrothermally at 180-250℃ and 1.5-4MPa pressure for 1-4 hours to obtain hydrothermal products. S3. Activate the hydrothermal products under a protective atmosphere at 300~400℃ for 1~2h to obtain modified biogas residue-based hydrothermal carbon.

[0021] In the above process, Fe-Cu phosphate ions provide anchoring sites. Based on the anchoring sites, the Fe-Cu composite metal oxide can catalytically oxidize H2S into elemental sulfur and sulfate in sequence, realizing the self-regeneration of hydrothermal biochar. The added vitamin B12-loaded biochar can provide microbial regulation function and realize directional proliferation, while activation can prevent the degradation of microbial components such as B12 and loss of regulatory function.

[0022] Optionally, in S1, the total carbon (TC) of the biogas residue is ≤55% and ≥30%, and the total sulfur (TS) is ≤1%. Selecting TC ≥30% is to ensure that the hydrothermal carbon has a sufficient carbon skeleton and pore structure basis. Controlling TC ≤55% is to avoid excessive organic matter leading to excessive adhesion and uneven pore development. Limiting TS ≤1% is to prevent the inherent sulfur in the raw material from being released or transformed in subsequent processes, interfering with the loading and function of Fe-Cu active sites, and avoiding becoming an additional source of hydrogen sulfide.

[0023] Optionally, in S1, the biogas residue is crushed to a particle size of 0.5~5mm and dried at 100~110℃ to constant weight to prepare for phosphoric acid solution treatment.

[0024] Optionally, in S1, the concentration of the phosphoric acid solution is 0.1~0.3 mol / L, and the soaking time is 2~4 h. This pretreatment aims to remove some impurities, initially introduce oxygen-containing functional groups, and regulate the path of subsequent hydrothermal reactions. After filtration, the residue is washed with deionized water until neutral, and then dried again to constant weight to obtain pretreated biogas residue. Phosphoric acid pretreatment not only removes 12~15% of the ash in the biogas residue, but also introduces -OH and -COOH functional groups on the surface through the esterification reaction of H3PO4 with hydroxyl groups in the biogas residue, providing anchoring sites for Fe-Cu ions and preventing the loss of metal ions during the hydrothermal reaction.

[0025] Optionally, in S2, the transition metal salt includes one or more of copper chloride and ferric chloride, wherein the mass ratio of ferric chloride to copper chloride is 1:(1~2); the transition metal salt can provide catalytic active centers; the formed Fe-Cu composite metal oxide sites will sequentially catalytically oxidize the adsorbed H2S: Fe³+ first oxidizes H2S to elemental sulfur (S²⁺). - →S 0 (Conversion rate exceeding 85%), Cu²⁺ further converts some S 0 Further oxidation to SO4² - This process avoids the blockage of hydrothermal carbon pores by elemental sulfur, maintaining the adsorption capacity at more than 90% of the initial value; and the hydrothermal carbon anchors metal ions (dissolution amount <65mg / L), reducing the accumulation of volatile fatty acids (VFA) produced during the dry digestion of food waste by 20-30%, significantly improving the system's shock resistance.

[0026] Optionally, in S2, the vitamin B12-loaded biochar includes vitamin B12-loaded corn cob biochar with a loading of 1-3 wt%. The loaded vitamin B12 (containing cobalt) acts as a key coenzyme factor for methanogenic archaea, specifically promoting their growth and metabolism. The catalytic process effectively inhibits the activity of SRB substrates through consumption and transformation, thereby optimizing the MA to SRB ratio to over 100:1, reducing H2S generation at the source, and guiding more electrons towards the methanogenic pathway. On the other hand, the catalytic product SO4 from the Fe-Cu composite metal oxide... 2- It can competitively inhibit substrate uptake by sulfate-reducing bacteria (SRB), effectively reducing the number of SRBs and correspondingly increasing the relative proportion of MA.

[0027] Optionally, in S2, the hydrothermal reaction temperature is 200~230℃.

[0028] Optionally, in S2, after the hydrothermal reaction is completed, the product is cooled, washed, filtered, and dried.

[0029] One or more embodiments of the present invention provide modified biogas residue-based hydrothermal carbon obtained by the above-described method for preparing modified biogas residue-based hydrothermal carbon.

[0030] One or more embodiments of the present invention provide a method for dry digestion of kitchen waste, comprising the following steps: S4. Mix the kitchen waste with the inoculum at a volatile solids ratio of (2~3):1; S5. Add the above-mentioned modified biogas residue-based hydrothermal carbon at a ratio of 5-15% of the dry weight of kitchen waste, and carry out anaerobic digestion at 35-55℃.

[0031] The above process is applicable to the design of dry digestion systems for food waste with high solids concentration (20~30% TS), effectively overcoming the mass transfer limitation problem under this system, and is applicable to medium-temperature and high-temperature anaerobic digestion conditions.

[0032] Optionally, in S4, the total solids (TS) content of the mixture of food waste and inoculum is adjusted to 20-30%, the pH is 7.0-8.0, and the oxidation-reduction potential (ORP) is -300--400 mV; ORP ≤ -300 mV indicates that the system has established a strict anaerobic environment, which is conducive to the enrichment and function of anaerobic microbial communities (especially MA).

[0033] Optionally, in S5, the mixture is stirred 2-4 times a day during anaerobic digestion; moderate stirring is used to promote mass transfer, at 30-50 r / min, for 15-30 min each time.

[0034] Optionally, in S5, a micronutrient mixture is added every 3 to 5 days; including a micronutrient mixture of elements such as manganese, cobalt, nickel, and molybdenum, to maintain the nutritional balance of the microorganisms.

[0035] Optionally, the anaerobic digestion in S5 can be either mesophilic dry anaerobic digestion or thermophilic dry anaerobic digestion.

[0036] Optionally, the process may also include the following steps: S6, separating the modified biogas residue-based hydrothermal carbon, calcining it at 500-600℃ for 1-2 hours to regenerate it, and then reusing it in step S5; thus achieving a closed loop of "treating waste with waste" and solving the problem of the non-renewability of existing materials.

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 1 A modified biogas residue-based hydrothermal char, prepared by the following method: Figure 1 As shown, it includes the following steps: S11. Select raw materials: anaerobic digestion residue from kitchen waste taken from normal kitchen waste treatment plants is selected as residue A; anaerobic digestion residue from livestock and poultry farms is selected as residue B; and anaerobic digestion residue from municipal sludge taken from municipal sewage treatment plants is selected as residue C.

[0039] S12. Three fresh biogas residue samples were sent to a third-party testing institution or an elemental analyzer to determine their total carbon (TC), total nitrogen (TN), and total sulfur (TS) content. Results: Biogas residue A (TC: 42.3%, TN: 3.51%, total sulfur: 0.58%); Biogas residue B (TC: 35.1%, TN: 2.83%, total sulfur: 0.79%); Biogas residue C (TC: 28.4%, TN: 1.92%, total sulfur: 1.25%). According to the preset standard (TC≥30%, TS≤1%), biogas residues A and B were determined to be qualified raw materials, while biogas residue C was unqualified and was excluded. This is because biogas residue C (TC<30%, total sulfur>1%) had insufficient carbon source, resulting in poor hydrothermal carbon structure development, and excessive sulfur in the raw material would poison active sites and increase the sulfur load of the system. Using such raw materials would seriously weaken the core function of the material's "adsorption-catalysis" and interfere with the targeted regulation target of microorganisms.

[0040] S13. Take 2 kg each of qualified biogas residue A and biogas residue B, crush them separately using a crusher, and pass them through a 5 mm standard sieve. Spread the sieved material evenly on a tray and place it in a 105℃ forced-air drying oven to dry for 24 hours until constant weight is achieved. The standard is that the change in mass between two consecutive weighings is <0.5%.

[0041] S14. Take 13.6 mL of 85% H3PO4 and dilute it with deionized water to 1 L to obtain a phosphoric acid solution with a concentration of 0.2 mol / L. Weigh 500 g (dry weight) of dried biogas residue A, place it in a 2 L beaker, add 1 L of phosphoric acid solution, and place it in a 25℃ water bath shaker at 150 rpm for 3 h. Treat biogas residue B in the same way.

[0042] S15. Vacuum filter the mixture after acid leaching; repeatedly wash the filter cake with deionized water until the pH of the filtrate stabilizes at 6.5~7.0; place the washed filter cake in a drying oven at 105℃ and dry it to constant weight, weigh it and record the mass loss to obtain pretreated A biogas residue; treat B biogas residue in the same way to obtain pretreated B biogas residue.

[0043] After pretreatment, the mass loss rate of biogas residue A was 12.5%, and that of biogas residue B was 15.1%. The main components of the loss were water-soluble salts and some ash. The biogas residue after pretreatment became lighter in color and looser, and a porous structure was initially formed, which is beneficial to the mass transfer and doping of subsequent hydrothermal reactions.

[0044] S21. Weigh 1.50g FeCl3•6H2O and 1.05g CuCl2•2H2O (metal mass ratio Fe:Cu = 1:1) into a small beaker, dissolve them in 20mL of deionized water to prepare a transition metal salt solution.

[0045] S22. Weigh 2.00g of corn cob biochar, immerse it in 40mL of an aqueous solution containing 0.03g of vitamin B12, stir for 2 hours, and then evaporate to dryness at 60℃ to obtain vitamin B12-loaded biochar.

[0046] S23. Transfer 100.00 g (dry weight) of pretreated biogas residue A, the transition metal salt solution prepared in S21, and the vitamin B12-loaded biochar prepared in S22 to a 2L high-pressure reactor. Add 1000 mL of deionized water (solid-liquid ratio 1:10). After sealing, the temperature is increased to 220℃ (corresponding pressure approximately 2.3 MPa) at a rate of 3℃ / min and kept at this temperature for 2.5 hours. After the reaction is complete, allow it to cool naturally to room temperature. Open the reactor and transfer all the product to a Buchner funnel for vacuum filtration. Wash the product multiple times with 2L of deionized water until the pH of the filtrate is 7.0. Wash it once with 500 mL of 0.5 mol / L hydrochloric acid solution to remove loose amorphous substances on the surface. Finally, wash the product with 1L of deionized water until the filtrate is neutral. Transfer the filter cake to a tray and dry it in a 105℃ drying oven for 12 hours until constant weight to obtain the hydrothermal product (i.e., the hydrothermal carbon precursor).

[0047] S3. Place the hydrothermal product in a quartz boat and place it in the center of a tube furnace; purge with high-purity nitrogen at a flow rate of 200 mL / min for 30 minutes to remove air; then, under a nitrogen atmosphere, program the temperature to 350℃ at a heating rate of 8℃ / min and activate at this temperature for 1.5 hours; after activation, allow it to cool naturally to room temperature under continuous nitrogen purging, and remove it to obtain the final product—modified biogas residue-based hydrothermal carbon (i.e., heterogeneous element-doped biogas residue-based hydrothermal carbon).

[0048] In this embodiment, the modified hydrothermal carbon product obtained from biogas residue A is a black, lightweight powder. Its specific surface area was determined to be 482 m² / g using a BET method, and the pore size distribution was concentrated between 2 and 15 nm using the BJH method. X-ray photoelectron spectroscopy (XPS) detected obvious characteristic peaks for Fe 2p, Cu 2p, and N 1s, confirming that Fe and Cu elements exist in oxide / chloride forms, and N element was successfully doped. The static adsorption capacity of this hydrothermal carbon for H₂S was determined to be 165 mg / g. Correspondingly, heteroelement-doped biogas residue-based hydrothermal carbon meeting the requirements could also be obtained using biogas residue B.

[0049] Example 2 Based on Example 1, the influence of hydrothermal temperature and transition metal ratio on the physical structure and chemical properties of hydrothermal carbon was investigated, and the optimal process window was determined.

[0050] The difference between Series 1 and Example 1 is that the hydrothermal temperatures are set to 180℃, 200℃, 230℃, and 250℃ respectively, while other conditions are the same as in Example 1.

[0051] The difference between Series II and Example 1 is that the mass ratio of Fe to Cu is selected as 1:0 (pure iron), 2:1, 1:1, 1:2, and 0:1 (pure copper), and the total addition amount of each of the five groups is maintained at 3% of the dry weight of the biogas residue.

[0052] The modified biogas residue-based hydrothermal carbon obtained in Series 1 and Series 2 were characterized as follows: Specific surface area and pore size distribution (BET): determined using a nitrogen adsorption-desorption apparatus.

[0053] H2S adsorption capacity: A fixed-bed adsorption evaluation device was used; 0.100 g of hydrothermal carbon sample was weighed and placed in a quartz tube. At 25 °C, a N2 mixture containing 1% H2S (total flow rate 100 mL / min) was introduced until the outlet H2S concentration reached 10% of the inlet concentration, which was the breakthrough point. The saturated adsorption capacity was then calculated.

[0054] The results showed that as the temperature increased from 180℃ to 230℃, the specific surface area of ​​the carbon material increased from 350 m² / g to 505 m² / g, and the H₂S adsorption capacity increased from 130 mg / g to 162 mg / g. When the temperature rose to 250℃, the specific surface area decreased slightly to 480 m² / g, and the adsorption capacity was 158 mg / g, possibly due to the collapse of some micropores caused by excessive carbonization; the optimal temperature window was 200~230℃.

[0055] The adsorption capacities of pure iron and pure copper samples were 142 mg / g and 135 mg / g, respectively. When the Fe / Cu ratio was 2:1, 1:1, and 1:2, the adsorption capacities were 152 mg / g, 165 mg / g, and 155 mg / g, respectively. A peak value appeared at Fe / Cu = 1:1, indicating a significant synergistic catalytic oxidation effect between the Fe and Cu bimetallic samples. The optimal ratio was Fe:Cu = 1:1.

[0056] Example 3 Under strictly controlled laboratory conditions, the effects of functionalized hydrothermal char on H2S emission reduction, biogas quality improvement, and system stability enhancement in mesophilic dry anaerobic digestion were quantitatively evaluated. In this field, the temperature range for mesophilic dry anaerobic digestion is 33~37℃, and in this embodiment, 35±2℃ was selected. It is referred to as "hydrothermal char group of the present invention" in Tables 1 and 3.

[0057] S4. Food waste taken from the university canteen was manually sorted to remove large impurities and used as substrate. Its TS was measured to be 25.5% and VS / TS was 92.5%. The effluent from the anaerobic digester that was operating stably in the same food waste treatment plant was used as inoculum. Its TS was measured to be 5.1% and VS / TS was 45.2% and pH was 7.6. The food waste and inoculum were weighed according to the VS ratio (substrate VS : inoculum VS = 3:1).

[0058] S51. Add the modified biogas residue-based hydrothermal carbon prepared in Example 2 at a ratio of 10% of the dry weight of kitchen waste, place it in a glass fermentation bottle as a digestion reactor, adjust the initial TS to 25.0% with deionized water, and adjust the initial pH to 7.5±0.1 with 1 mol / L NaOH or HCl solution.

[0059] S52. The reactor was purged with high-purity N2 for 5 minutes to create an anaerobic environment, then sealed; placed in a 35℃ water bath; the stirring program was set to three times a day (8:00, 14:00, 20:00), stirring at 40 rpm for 20 minutes each time; the nutrient supplementation method was as follows: every 5 days, a trace element mixture (MnCl2•4H2O, CoCl2•6H2O, NiCl2•6H2O, (NH4)6Mo7O) was injected through the sampling port. 24 • 4H₂O (mass ratio 2:1:1:0.5, soluble in water), the amount added is 0.2% of the total mass of the system. The experimental period is 40 days.

[0060] Comparative Example 1 The difference from Example 3 is that the modified biogas residue-based hydrothermal carbon prepared in Example 2 is not added in step S51, while the other methods are the same as in Example 3.

[0061] The monitoring and data analysis items for Example 3 and Comparative Example 1 include: Biogas: Daily biogas production was recorded, and biogas samples were collected every two days using a gas bag. The H2S concentration and CH4 and CO2 contents were analyzed using an H2S detector and gas chromatography, respectively.

[0062] Liquid chromatography: 5 mL samples were taken every 5 days, centrifuged, and the supernatant was collected. The concentration of volatile fatty acids (VFA) was determined by gas chromatography.

[0063] Microorganisms: Samples were taken at the start of the experiment and on day 40. Real-time quantitative PCR (qPCR) was used to quantitatively analyze the absolute copy number of MA and SRB in the samples using specific primers for the MGB-MA and DSR genes.

[0064] The results include: Regarding H2S control: The H2S concentration in biogas of Comparative Example 1 was 1800~2200 ppm; in Example 3 it was stable at 85~120 ppm, with an average removal rate of >95%.

[0065] Regarding biogas production rate: The cumulative biogas production rate of Example 3 is expected to increase by 10-15% compared to Comparative Example 1.

[0066] Regarding the microbial community: at the end of the experiment, the number of MA in Example 3 was expected to be more than 1.5 times that of Comparative Example 1, the number of SRB was less than 50% of that of Comparative Example 1, and the MA / SRB ratio increased from ~15:1 in Comparative Example 1 to >100:1 in Example 3.

[0067] Regarding system stability: In Example 3, the peak accumulation of VFA (especially propionic acid) was 25-30% lower than that in Comparative Example 1, and the system pH was more stable.

[0068] Example 4 To evaluate the applicability, stability and synergistic effect of modified biogas residue-based hydrothermal carbon in the more challenging system of high-temperature dry anaerobic digestion, the temperature range of high-temperature dry anaerobic digestion in this field is 53~57℃, and 55±2℃ is selected in this embodiment.

[0069] The difference from Example 3 is as follows: Adjust the total toxicity (TS) of food waste to 28.0%; Adjust the water bath temperature to 55℃; Since microbial activity is higher at high temperatures, the amount added was slightly reduced, and the modified biogas residue-based hydrothermal carbon prepared in Example 2 was added at a ratio of 8% of the dry weight of kitchen waste to evaluate its efficiency. Because the reaction rate is fast at high temperatures, the stirring frequency is increased to ensure mass transfer. The stirring program is set to 4 times a day (6 hours apart), each time stirring at 45 rpm for 15 minutes. Because the digestion cycle is shortened at high temperatures, the experimental period is 35 days.

[0070] The other methods are the same as in Example 3.

[0071] Comparative Example 2 The difference from Example 4 is that no modified biogas residue-based hydrothermal carbon is added, but the other methods are the same as in Example 4.

[0072] The monitoring and data analysis items for Example 4 and Comparative Example 2 also included three items: biogas, liquid phase, and microorganisms.

[0073] The results include: Regarding H2S control: In Comparative Example 2, due to the high activity of SRB at high temperatures, the H2S concentration could reach 2500~3000 ppm. In Example 4, thanks to the catalytic oxidation function of hydrothermal carbon, the H2S concentration could be stably controlled at 150~200 ppm, and the removal rate remained above 92%, proving its effectiveness at high temperatures.

[0074] In terms of digestion performance: The system in Example 4 starts up faster, and the peak gas production occurs about 3 to 5 days earlier. The cumulative biogas yield is 8 to 12% higher than that in Comparative Example 2. Since high temperature itself is conducive to methanogenesis, the methane content may be slightly higher than that of the mesophilic system, but because H2S inhibition is reduced, the methane content of Example 4 (65%) is still significantly higher than that of Comparative Example 2 (58%).

[0075] Regarding system stability: The VFA accumulation peak of Example 4 is expected to be 25-30% lower than that of Comparative Example 2, and the degradation rate is faster. The propionic acid / acetic acid ratio is always below the inhibition threshold of 1.5, while Comparative Example 2 may show propionic acid accumulation (ratio > 2.0).

[0076] Regarding the microbial community: qPCR results showed that Example 4 successfully maintained the absolute dominance of MA, with an MA / SRB ratio >90:1, while in Comparative Example 2 this ratio may be lower than 10:1.

[0077] Based on Examples 3, 4, Comparative Example 1, and Comparative Example 2, the following conclusion can be drawn: The functionalized hydrothermal char prepared by this invention also exhibits excellent in-situ H2S emission reduction and system regulation capabilities in high-temperature dry digestion systems, and has good adaptability over a wide temperature range.

[0078] Comparative Example 3 By setting up rigorous control experiments, the comprehensive performance of the present invention and existing mainstream desulfurization technologies in the dry digestion of kitchen waste was compared horizontally, highlighting the synergistic advantages and non-obviousness of the present invention.

[0079] Set up comparative examples 3-1, 3-2, and 3-3 respectively, with the following requirements for each comparative example.

[0080] Comparative Example 3-1, compared to Example 3, did not contain any desulfurizing agent and served as the control group (without desulfurizing agent).

[0081] Comparative Example 3-2: Compared with Example 3, 10% (by dry weight of kitchen waste) of commercial activated carbon was added. The selected commercial activated carbon was purchased from Sigma-Aldrich, coconut shell based, with a particle size of 4x8 mesh and a specific surface area of ​​~1000 m² / g, belonging to the commercial activated carbon group (CAC).

[0082] Comparative Example 3-3: Compared with Example 3, no modified biogas residue-based hydrothermal carbon was added. Instead, Fe and Cu ions in the same molar amounts as Fe and Cu contained in the modified biogas residue-based hydrothermal carbon in Example 3 were added: FeCl3•6H2O and CuCl2•2H2O were accurately calculated and weighed, dissolved in 50 mL of deionized water, and added to the reactor along with the substrate at startup. This was a direct addition of Fe-Cu salt group.

[0083] The monitoring indicators are the same as in Example 3, and the results are as follows: In terms of H2S control, such as Figure 2 As shown: Comparative Example 3-1 exhibited a persistently high H2S concentration (>1800 ppm). Comparative Example 3-2 showed good performance in the first 10-15 days, with H2S <500 ppm, but after adsorption saturation, the H2S concentration rapidly rebounded to over 1500 ppm, exhibiting a typical "breakthrough curve." Comparative Example 3-3 initially reduced H2S rapidly through precipitation, but the effect was not lasting and required multiple additions. With a single addition, the H2S concentration rebounded to 800-1200 ppm in the mid-to-late stages. This may also lead to a temporary increase in ORP, which is detrimental to strictly anaerobic bacteria. Example 3 maintained highly efficient and stable H2S removal (<150 ppm) throughout the process, thanks to the synergistic effect of "adsorption-catalytic oxidation," without any saturation rebound phenomenon.

[0084] In terms of system stability and output, such as Figure 3 As shown: Comparative Example 3-3 exhibited significant VFA accumulation (peak value reaching 3500 mg / L) and a decrease in pH, indicating that direct addition of metal salts inhibited or toxicized the microbial community. After adsorption saturation, the system performance of Comparative Example 3-2 was similar to that of Comparative Example 3-1. The Invent group of Example 3 showed the lowest VFA accumulation (<1500 mg / L), the fastest degradation, and a cumulative biogas yield 12% higher than the Ctrl group, 10% higher than Comparative Example 3-2, and 15% higher than Comparative Example 3-3.

[0085] Regarding microbial ecology: Only Example 3 significantly optimized the microbial community, increasing the MA / SRB ratio to over 100:1. In Comparative Example 3-3, the numbers of both MA and SRB were inhibited due to metal toxicity. Comparative Example 3-2 showed no significant targeted regulatory effect on microbial community structure. The data on microbial quantity and community structure regulation in each group at the end of digestion, detected by qPCR, are shown in Table 3.

[0086] The above results demonstrate that this invention is not a simple superposition of existing technologies. The hydrothermal carbon prepared by this invention achieves unexpected technical effects of "1+1>2" in terms of desulfurization efficiency, stability, system efficiency enhancement, and microbial regulation through the synergistic effect of multiple mechanisms.

[0087] Example 5 The regeneration and recycling performance of modified biogas residue-based hydrothermal carbon was evaluated. The regeneration steps included: S61. After the digestion in Example 3 is completed, the residue is diluted with deionized water, passed through a 100-mesh standard sieve, and the material on the sieve (mainly hydrothermal carbon and undegraded fibers) is collected. Then, gravity sedimentation is carried out in deionized water to initially separate the hydrothermal carbon and organic fibers by utilizing the density difference. Finally, the residue is dried at 105°C.

[0088] S62. Accurately weigh 50.00 g of the recovered, dried charcoal and place it in a quartz boat. Place the boat in a tube furnace and purge with high-purity N2 at a flow rate of 200 mL / min for 30 minutes. Under the N2 atmosphere, program the temperature to 550℃ at a rate of 10℃ / min and calcine at this temperature for 1.5 hours. After calcineation, allow it to cool naturally to room temperature (<50℃) under continuous N2 purging. Remove the charcoal, weigh it, and calculate the regeneration recovery rate (approximately 90-95%). The resulting product is the regenerated modified biogas residue-based hydrothermal charcoal.

[0089] The calcination process is also a regeneration process. The principle includes: ① oxidizing the elemental sulfur (S) deposited in the pores (through trace O2 impurities or self-crystallization) and removing it in the form of SO2; ② pyrolyzing the adsorbed VFA, protein and other organic matter into gaseous substances that escape and clear the pores.

[0090] The regenerated modified biogas residue-based hydrothermal carbon was characterized and its performance was evaluated. BET analysis showed that the specific surface area of ​​the regenerated carbon recovered to 420-450 m² / g (approximately 88-93% of that of fresh carbon). XPS results showed that the S 2p peak intensity was significantly reduced, and the peak positions and morphologies of Fe and Cu were similar to those of fresh carbon, proving that the active sites were effectively recovered.

[0091] Using the same raw materials and digestion method as in Example 3, the regenerated modified biogas residue-based hydrothermal char obtained in this example was subjected to mesophilic dry anaerobic digestion. The results showed that in the second usage cycle, the H2S removal efficiency of the regenerated char remained at 85-88%, compared to fresh char (95%+), with an efficiency retention rate of over 89%. The cumulative biogas yield of the regenerated char group was still about 10% higher than that of the blank control group, equivalent to 83% of the improvement effect of the fresh char group (12%). The MA / SRB ratio of the regenerated char group at the end of the cycle could be maintained above 80:1, indicating that its microbial competitive regulation ability was largely retained.

[0092] The performance statistics of Example 3, Comparative Example 3, and Example 5 are shown in Table 1. This demonstrates that the hydrothermal carbon possesses excellent thermal regeneration capabilities. After one complete "use-regeneration" cycle, most of its core physicochemical properties and functional performance are restored, proving the feasibility of recycling this material in practical engineering and greatly enhancing the economic and environmental benefits of this technical solution.

[0093] Table 1

[0094] Furthermore, following the method of Example 5, the modified biogas residue-based hydrothermal carbon obtained in Example 3 was regenerated multiple times. Each regeneration was carried out under the following conditions: calcination at 550℃ in a N2 atmosphere for 1.5 hours, followed by mesophilic dry anaerobic digestion according to the method of Example 3. The resulting technical effects are shown in Table 2. The modified biogas residue-based hydrothermal carbon exhibits good thermal regeneration performance and stable recycling. Although its desulfurization efficiency and biogas promotion effect show a gradual downward trend with increasing regeneration times, after four regenerations, the H2S removal rate remains above 84.8%, and the biogas production enhancement retention rate exceeds 76%, demonstrating that the material can maintain significant functionality in multiple cycles and has the potential for engineering recycling applications.

[0095] Table 2

[0096] Further analysis of the microbial community analysis steps described in Examples 3 and 5; specifically: Sampling time: at the end of the anaerobic digestion experiment (day 40 of Example 3, and at the end of the cycle of regenerated char in Example 5).

[0097] Analytical methods: Real-time quantitative PCR was used to quantify the absolute copy number of MA and SRB genes in the samples using specific primers for methanogenic archaea (MA) and sulfate-reducing bacteria (SRB).

[0098] The detection indicators included the number of macromolecular substances (MA), the number of biochar (SRB), the calculated MA / SRB ratio, and the vitamin B12 residue rate unique to the material of this invention. The results are shown in Table 3. The modified biogas residue-based hydrothermal char prepared by this invention exhibits significant microbial targeted regulation capabilities: its MA / SBR ratio reaches 110:1, far exceeding the control group and the commercial activated carbon group, successfully achieving the regulation target of "≥100:1," inhibiting H2S generation at the source and enhancing the methanogenesis pathway. Even after three regenerations (i.e., the hydrothermal char with "three regenerations" in Table 2, corresponding to the hydrothermal char group with three regenerations in Table 3), the MA / SBR ratio remained at 82:1, and the vitamin B12 residue rate was 75%, indicating that its regulatory function has good stability and recyclability. Compared to the MA inhibition caused by direct addition of Fe-Cu salt (MA / SBR=8:1), this invention, through the synergistic effect of carrier immobilization and biochar regulator, achieves efficient desulfurization while avoiding metal toxicity, demonstrating the significant advantages of multi-mechanism synergy.

[0099] Table 3

[0100] The above comparative examples and embodiments illustrate that, compared with the prior art, the present invention has the following significant advantages: 1. High-efficiency in-situ desulfurization and biogas upgrading: Addressing the issues of low mass transfer efficiency (<30%) and easy saturation of adsorption materials in existing end-of-pipe desulfurization methods, this invention achieves an H2S removal rate of over 90% through a synergistic process of "adsorption-catalytic oxidation," which is 4.5 times higher than that of commercial activated carbon (removal rate <20% after saturation). At the same time, the biogas yield is increased by 8%~15% compared to the control group, and the methane content is increased from 55% to 65%, solving the problem of H2S inhibiting methanogenic bacteria.

[0101] 2. Targeted regulation of microbial ecology: To address the problem that existing technologies cannot balance the competition between MA and SRB (MA / SRB < 15:1), this invention promotes MA proliferation (increasing its number by 1.5 times) through vitamin B12 and inhibits SRB through Fe-Cu catalysis (reducing its number to 50% of the control group), so that the MA / SRB ratio exceeds 100:1, thereby reducing H2S generation from the source. This represents a qualitative breakthrough compared to directly adding metal salts (MA / SRB = 8:1).

[0102] 3. Enhanced System Stability: Addressing the issues of metal ion leaching (>480mg / L) and system acidification caused by existing iron salt addition, this invention uses hydrothermal activated carbon to anchor metal ions (leaching amount <65mg / L), reducing the accumulation of volatile fatty acids (VFA) by 20%~30%, significantly improving the system's shock resistance. Furthermore, after regeneration by calcination at 550℃, the desulfurization efficiency remains above 85%, and after three cycles, the cost is reduced to 1 / 3 of that of commercial activated carbon, achieving a closed loop of "waste treatment with waste" and solving the problem of non-renewable existing materials.

[0103] 4. Strong technical adaptability: This invention is specifically designed for dry digestion systems of food waste with high solids concentration (20~30% TS), effectively overcoming the mass transfer limitation problem in this system and providing key technical support for the industrial promotion of dry digestion.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing modified biogas residue-based hydrothermal carbon, characterized in that, Includes the following steps: S1. Soak the biogas residue in a phosphoric acid solution to obtain pretreated biogas residue; S2. Mix pretreated biogas residue, transition metal salts accounting for 2-5% of the dry weight of pretreated biogas residue, vitamin B12-loaded biochar accounting for 1-3% of the dry weight of pretreated biogas residue, and water at 8-15 times the mass of pretreated biogas residue. React hydrothermally at 180-250℃ and 1.5-4MPa pressure for 1-4 hours to obtain hydrothermal products. S3. Activate the hydrothermal products under a protective atmosphere at 300~400℃ for 1~2h to obtain modified biogas residue-based hydrothermal carbon.

2. The method for preparing modified biogas residue-based hydrothermal carbon as described in claim 1, characterized in that, In S1, the total carbon content of the biogas residue is ≥30%, and the total sulfur content is ≤1%.

3. The method for preparing modified biogas residue-based hydrothermal carbon as described in claim 1, characterized in that, In S1, the concentration of the phosphoric acid solution is 0.1~0.3 mol / L, and the soaking time is 2~4 h.

4. The method for preparing modified biogas residue-based hydrothermal carbon as described in claim 1, characterized in that, In S2, the transition metal salt includes one or more of copper chloride and ferric chloride, and the mass ratio of ferric chloride to copper chloride is 1:(1~2).

5. The method for preparing modified biogas residue-based hydrothermal carbon as described in claim 1, characterized in that, In S2, the vitamin B12-loaded biochar includes vitamin B12-loaded corn cob biochar with a loading of 1-3 wt%.

6. The method for preparing modified biogas residue-based hydrothermal carbon as described in claim 1, characterized in that, in S2, the hydrothermal reaction temperature is 200~230℃; Alternatively, in S2, after the hydrothermal reaction is complete, the product is cooled, washed, filtered, and dried.

7. Modified biogas residue-based hydrothermal carbon prepared by a method according to any one of claims 1-6.

8. A method for dry digestion of kitchen waste, characterized in that, Includes the following steps: S4. Mix the kitchen waste with the inoculum at a volatile solids ratio of (2~3):1; S5. Add the modified biogas residue-based hydrothermal carbon as described in claim 7 at a ratio of 5-15% of the dry weight of the kitchen waste, and carry out anaerobic digestion at 35-55℃.

9. The method for dry digestion of kitchen waste as described in claim 8, characterized in that, In S4, the total solids content of the mixture of kitchen waste and inoculum is adjusted to 20-30%, the pH is 7.0-8.0, and the oxidation-reduction potential is -300 to -400 mV; Alternatively, in S5, the mixture is stirred 2-4 times daily during anaerobic digestion; Alternatively, in S5, supplement with a micronutrient mixture every 3-5 days; Alternatively, the anaerobic digestion in S5 may be mesophilic dry anaerobic digestion or thermophilic dry anaerobic digestion.

10. The method for dry digestion of kitchen waste as described in claim 8, characterized in that, The process also includes the following steps: S6, separating the modified biogas residue-based hydrothermal carbon, regenerating it by calcining at 500-600℃ for 1-2 hours, and reusing it in step S5.

Images