A method for carbon sequestration and nitrogen conservation of biogas residue composting

Abstract

The application discloses a kind of methane residue carbon sequestration nitrogen conservation composting methods, belong to organic solid waste resource utilization technical field.The method includes: the calcium-based bentonite is mixed with dilute wood vinegar aging, and the phenolic acid pre-loaded calcium-based bentonite conditioner is prepared;Dehydrated methane residue, plant fiber conditioner and the conditioner are mixed, and after adjusting moisture content and C / N ratio, first-stage high-temperature aerobic fermentation is carried out;When the temperature of the pile drops to 45-55 DEG C from high-temperature period, add the second stage of humification nitrogen fixation fermentation of laccase-producing composite microbial inoculum is carried out, and it is obtained after maturity and stabilization.The application utilizes the interlayer structure of calcium-based bentonite to realize the slow release of wood vinegar organic acid and phenolic components and enriches ammonium nitrogen, cooperates with laccase system in temperature reduction period to promote phenolic substance oxidation condensation, so that ammonium nitrogen, amino acid and peptide are converted into humus combined nitrogen.The application reduces NH3 release amount by 79.7%, total nitrogen retention rate reaches 88.7%, humic acid content increases by 97.7%, and GI reaches 98%, and is suitable for methane residue high-value preparation of high humic acid organic fertilizer.

Description

Technical Field

[0001] This invention belongs to the field of organic solid waste resource utilization technology, specifically relating to a method for composting biogas residue to fix carbon and retain nitrogen. 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] Biogas residue is the main solid byproduct of anaerobic digestion of organic waste. It contains cellulose, protein, and nutrients such as nitrogen, phosphorus, and potassium, possessing the potential for resource utilization in the production of organic fertilizer. Aerobic composting is an effective way to achieve the harmlessness and resource utilization of biogas residue. However, direct composting of biogas residue faces several limitations. First, biogas residue has a high water content and viscosity, poor particle dispersion, and is prone to compaction and low porosity, hindering oxygen transfer, affecting the composting heating rate, and potentially forming localized anaerobic zones. Second, biogas residue is usually alkaline (pH 7.5–8.8) and has a high concentration of ammonium nitrogen, resulting in high NH4+ concentrations during the composting heating period. + It is easily converted into NH3 and volatilizes, resulting in a large loss of nitrogen. Thirdly, although biogas residue contains humic precursors, the humification rate is slow and the formation of humic acid is insufficient, which affects the stability and fertilizer efficiency of compost products.

[0004] Conventional improvement methods have significant limitations. Adding fibrous materials such as straw and sawdust can improve the pore structure of the pile, but it does not inhibit ammonia volatilization. Clay minerals such as bentonite can adsorb some NH4 through ion exchange. + However, its adsorption capacity is limited and its long-term nitrogen stability is poor. Wood vinegar contains organic acids and phenolic substances, which can lower the pH of the compost pile and participate in the humification reaction, but direct spraying can easily cause local acidification and excessively high phenolic concentrations, which in turn inhibits the activity of composting microorganisms. Laccase or laccase-producing microorganisms can promote the oxidation and polymerization of phenolic substances, but the humification effect is unstable when there is a lack of sufficient phenolic precursors and appropriate temperature and timing.

[0005] It is evident that the aforementioned methods in the existing technologies each address a single problem and have not yet formed a solution to the problems of easy clumping, poor air permeability, unstable temperature rise, strong ammonia volatilization, low degree of humification, and insufficient nitrogen stability in the current biogas residue composting process. Summary of the Invention

[0006] In view of this, the present invention provides a method for composting biogas residue to fix carbon and retain nitrogen.

[0007] In a first aspect, the present invention provides a method for composting biogas residue to fix carbon and retain nitrogen, comprising the following steps: S1. Mix calcium-based bentonite with diluted wood vinegar and age it to obtain phenolic acid preloaded calcium-based bentonite conditioner. S2. Mix the dehydrated biogas residue, plant fiber conditioner and the phenolic acid preloaded calcium-based bentonite conditioner, and adjust the moisture content and C / N ratio of the pile after mixing to obtain the pile to be fermented. S3. The first stage of high-temperature aerobic fermentation is carried out on the pile to be fermented. S4. After the process is completed, the temperature is lowered, and laccase-producing compound microbial inoculant is added to the pile to carry out the second stage of humification and nitrogen fixation fermentation. After the process is completed, the pile is further decomposed and stabilized to obtain the final product.

[0008] Preferably, in S1, the diluted wood vinegar is obtained by diluting the original wood vinegar solution with water by 5–20 times; The calcium-based bentonite has a particle size of 80–300 mesh and a cation exchange capacity of not less than 50 cmol(+) / kg.

[0009] Preferably, in S1, calcium-based bentonite and diluted wood vinegar are mixed at a mass-volume ratio of 1:0.6–1.5, stirred for 20–60 min, and allowed to stand for aging for 2–12 h; after aging, the moisture content of the material is adjusted to 25%–45%.

[0010] Preferably, in S2, dehydrated biogas residue, plant fiber conditioner and phenolic acid preloaded calcium-based bentonite conditioner are mixed in a mass ratio of 55–75:15–35:5–15. The dehydrated biogas residue has a moisture content of 60%–80% and a pH of 7.5–8.8; The plant fiber conditioner is one or more of the following: corn stalks, rice husks, sawdust, garden branch fragments, peanut shells, and mushroom residue, with a particle size of 2–20 mm.

[0011] Preferably, in S2, the moisture content of the mixture is adjusted to 55%–62% and the C / N ratio is 22:1–32:1.

[0012] Preferably, in S3, the pile temperature of the first stage of high-temperature aerobic fermentation is 55–70 ℃, the first stage of high-temperature aerobic fermentation time is 1–7 days, and the ventilation intensity is 0.05–0.30 L / (min•kg dry matter).

[0013] Preferably, in step S4, the temperature is lowered to 45–55 °C; the amount of the laccase-producing composite microbial agent added is 1%–5% of the wet weight of the stockpile; the laccase-producing composite microbial agent is Bacillus subtilis (…). Bacillus subtilis ), Proteobacterium chrysosporum ( Phanerochaete chrysosporium Trichoderma reesei ( Trichoderma reesei ) and thermophilic actinomycetes ( Thermobifida fuscaOne or more of the following: the second stage fermentation time is 8–20 days, the ventilation intensity is 0.03–0.20 L / (min•kg dry matter), and the pile is turned over every 2–4 days.

[0014] Preferably, in S4, the maturation and stabilization time is 5–15 days.

[0015] Secondly, the present invention provides an organic fertilizer prepared by the above method.

[0016] Thirdly, the present invention provides organic fertilizers prepared by the above method or applications of the above organic fertilizers for use on crops.

[0017] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) In this invention, wood vinegar is preloaded onto the interlayer and surface of calcium-based bentonite, and then compounded with dehydrated biogas residue and plant fiber conditioner to construct a continuous composting process of "phenolic acid preloading - pore conditioning - weak acid slow release - cooling period to promote humification". Compared with direct spraying of wood vinegar, adding bentonite alone or conventional biogas residue composting, this invention can simultaneously improve the aeration of biogas residue pile, reduce ammonia volatilization, increase total nitrogen retention rate, and promote the formation of humic acid and humic nitrogen bound to humic substances, thereby improving the maturity and nutrient stability of biogas residue compost products.

[0018] (2) This invention utilizes calcium-based bentonite to pre-load and age the organic acids and phenolic components in wood vinegar, transforming the rapid acidification process of direct spraying into a slow-release phenolic acid supply method. This method reduces the problems of localized acidification and excessively high phenolic concentrations caused by direct addition of wood vinegar, maintaining a relatively mild weakly acidic to neutral microenvironment in the initial stage of the pile. Simultaneously, the interlayer exchange sites and surface adsorption sites of calcium-based bentonite can enrich some NH4. + Reduce NH4 during high-temperature composting + There is a risk of conversion and release of NH3. Plant fiber conditioners provide skeletal support, and when used with bentonite, they improve the problems of high water content, easy clumping, and insufficient aeration in biogas residue, which is conducive to rapid heating and stable aerobic fermentation in composting.

[0019] (3) In this invention, the laccase-producing compound microbial agent is not directly added at the initial stage of composting. Instead, it is inoculated after the first stage of high-temperature aerobic fermentation has ended and the temperature of the compost pile has dropped to 45–55°C. This allows the exogenous laccase-producing agent to avoid the high-temperature stress stage and connect with the slow release of phenolic components from wood vinegar, the degradation of organic nitrogen in biogas residue, and the humification reaction stage. The laccase produced during the cooling period can promote the oxidative polymerization of phenolic substances and promote the conversion of amino acids, peptides, and ammonium nitrogen into humic nitrogen bound to humic substances. This reduces nitrogen volatilization loss while increasing humic acid content, HA / FA value, and compost maturity stability. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] Figure 1 This is a schematic diagram of the interlayer slow-release and ammonium nitrogen enrichment structure of the phenolic acid preloaded calcium-based bentonite conditioner of the present invention.

[0022] Figure 2 This diagram illustrates the mechanism of phenolic precursor formation in wood vinegar—laccase oxidation—humic nitrogen formation.

[0023] Figure 3 The graph shows a comparison of the cumulative NH3 release and total nitrogen retention rate for Example 1 and Comparative Examples 1-5, where (a) represents the cumulative NH3 release and (b) represents the total nitrogen retention rate.

[0024] Figure 4 The graph shows a comparison of the humic acid content, fulvic acid content, and humic nitrogen ratio of Example 1 and Comparative Examples 1-5, where (a) represents the humic acid content and fulvic acid content, and (b) represents the humic nitrogen ratio.

[0025] Figure 5 The graphs show the changes in laccase activity and humic acid content under different inoculation times for Examples 1, 5, and 6, where (a) represents laccase activity and (b) represents humic acid content. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. All reagents and materials used in this application are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods in the art or as per the product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this application. The preferred embodiments and materials described herein are for illustrative purposes only.

[0029] This invention provides a method for composting biogas residue to fix carbon and retain nitrogen, comprising the following steps: S1. Mix calcium-based bentonite with diluted wood vinegar and age it to obtain phenolic acid preloaded calcium-based bentonite conditioner. S2. Mix the dehydrated biogas residue, plant fiber conditioner and the phenolic acid preloaded calcium-based bentonite conditioner, and adjust the moisture content and C / N ratio of the pile after mixing to obtain the pile to be fermented. S3. The first stage of high-temperature aerobic fermentation is carried out on the pile to be fermented. S4. After the process is completed, the temperature is lowered, and laccase-producing compound microbial inoculant is added to the pile to carry out the second stage of humification and nitrogen fixation fermentation. After the process is completed, the pile is further decomposed and stabilized to obtain the final product.

[0030] Specifically, this invention utilizes the interlayer structure of calcium-based bentonite to achieve the slow release of organic acids and phenolic components from wood vinegar, while enriching ammonium nitrogen and soluble organic matter; it uses the weak acidity of wood vinegar to regulate and reduce ammonia volatilization; and it utilizes the laccase system during the cooling period to promote the oxidative condensation of phenolic substances, converting ammonium nitrogen, amino acids, and peptides into humic-bound nitrogen. This method can significantly improve the permeability of biogas residue, reduce NH3 release, increase total nitrogen retention, humic acid content, and degree of composting, without relying on heavy metal salts, strong oxidants, or synthetic flocculants, and is suitable for the high-value preparation of high-humic acid organic fertilizer from biogas residue.

[0031] This invention is not merely about proposing a simple combination of wood vinegar, calcium-based bentonite, and laccase-producing bacteria, but rather about constructing a continuous technological chain of "phenolic acid preloaded mineral microreactor—weak acid nitrogen retention in biogas residue—laccase-induced condensation during cooling period—formation of nitrogen bound to humus".

[0032] First, this invention changes the way wood vinegar is used. In existing composting processes, wood vinegar is usually sprayed directly, primarily to adjust pH, suppress odor, or promote decomposition. However, wood vinegar contains organic acids and phenolic substances, and direct spraying can easily lead to localized acidification and short-term microbial inhibition. This invention pre-loads wood vinegar into the interlayer and surface of calcium-based bentonite, transforming it from a transient acidifier into a slow-release phenolic acid precursor pool. This change not only prolongs the time of nitrogen retention by the weak acid but also provides a stable substrate source for subsequent laccase-induced humification.

[0033] Secondly, this invention changes the functional positioning of calcium-based bentonite. Conventional bentonite is mainly used as a water absorbent, swelling agent, or NH4+. + The use of adsorbents typically focuses on improving physical structure and ion exchange adsorption. This invention utilizes preloading of phenolic acids in wood vinegar to enable calcium-based bentonite to simultaneously act as an acid buffer, provide sustained phenolic release, and release NH4+. + It functions as an enrichment and humification interface reaction platform. In other words, calcium-based bentonite is no longer just a passive adsorbent material, but forms a mineral microreactor.

[0034] Furthermore, this invention optimizes the timing of laccase-producing bacteria activity. Adding laccase-producing fungi at the initial stage of composting may reduce their activity during the high-temperature period; adding them in the later stages of composting results in insufficient phenolic precursors and amino acid substrates. This invention selects to add the laccase-producing bacteria when the compost temperature drops from the high-temperature period to 45–55 °C, aligning the peak laccase activity with the slow release of phenols from wood vinegar, the degradation of biogas residue proteins producing amino acids, and the production of NH4+. + The enrichment process at the bentonite interface is matched, thereby significantly increasing the proportion of humic acid formation and humic bound nitrogen.

[0035] Finally, this invention achieves an upgrade in nitrogen retention mechanisms. Traditional nitrogen-retaining composting mainly relies on lowering the pH or adsorbing NH4. + While methods can reduce NH3 volatilization, this type of nitrogen can still be released again during environmental changes. This invention utilizes laccase-catalyzed phenolic oxidative condensation to reduce NH4+ volatilization. + Amino acids and peptides enter the structure of humic substances, forming humic-bound nitrogen, which transforms nitrogen from a volatile and weakly adsorbed state into a stable organic bound state.

[0036] In some other embodiments, in S1, the diluted wood vinegar is obtained by diluting the wood vinegar concentrate with water by 5–20 times. The dilution ratio parameter can precisely control the acidity and phenol concentration of the wood vinegar, adapting it to subsequent pre-loading processes and ensuring the stability of the conditioner's performance. Further, the diluted wood vinegar is obtained by mixing the wood vinegar concentrate and water at a volume ratio of 1:4–19, so that the total volume of the diluted wood vinegar is 5–20 times the volume of the original wood vinegar.

[0037] In some other embodiments, in S1, the wood vinegar stock solution has a pH of 2.5–4.0, a total acid content of 20–80 g / L, and a total phenol content of 0.5–8.0 g / L.

[0038] In some other embodiments, in S1, the calcium-based bentonite has a particle size of 80–300 mesh and a cation exchange capacity of not less than 50 cmol(+) / kg. This ensures that the bentonite has sufficient specific surface area and ion exchange sites to hold the organic acids and phenolic components in the wood vinegar and to provide NH4+. + Provides sufficient inter-layer switching capacity.

[0039] In some other embodiments, in S1, calcium-based bentonite and diluted wood vinegar are mixed at a mass-to-volume ratio of 1:0.6–1.5, stirred for 20–60 min, and allowed to stand for aging for 2–12 h; after aging, the moisture content of the material is adjusted to 25%–45%. This ensures that the organic acids and phenolic components in the wood vinegar fully penetrate the bentonite interlayer or are adsorbed on the surface.

[0040] In some other embodiments, in S2, dehydrated biogas residue, plant fiber conditioner, and phenolic acid preloaded calcium-based bentonite conditioner are mixed in a mass ratio of 55–75:15–35:5–15; after mixing, the moisture content of the compost pile is adjusted to 55%–62%, and the C / N ratio is 22:1–32:1. The dry weight ratio of dehydrated biogas residue, plant fiber conditioner, and phenolic acid preloaded calcium-based bentonite conditioner is defined as 55–75:15–35:5–15, and the compost pile moisture content is 55%–62%, with a C / N ratio of 22:1–32:1, constituting suitable material proportions and initial conditions for aerobic composting. If the fiber content is too low, the skeletal support will be insufficient; if it is too high, the nutrient concentration of the biogas residue will be diluted. If the bentonite conditioner content is too low, the slow release of phenolic acid and enrichment of ammonium nitrogen will be insufficient; if it is too high, the cost will increase and it may absorb too much water. The limits on moisture content and C / N ratio ensure the smooth start of microbial activity and composting process.

[0041] In some other embodiments, the dehydrated biogas residue has a moisture content of 60%–80% and a pH of 7.5–8.8; The plant fiber conditioner is one or more of the following: corn stalks, rice husks, sawdust, garden branch fragments, peanut shells, and mushroom residue, with a particle size of 2–20 mm.

[0042] In some other embodiments, in S3, the pile temperature of the first-stage high-temperature aerobic fermentation is 55–70 °C, the first-stage high-temperature aerobic fermentation time is 1–7 days, and the ventilation intensity is 0.05–0.30 L / (min•kg dry matter).

[0043] Specifically, in the first stage, phenolic acid preloaded calcium-based bentonite slowly releases organic acids, maintaining the microenvironment of the pile in a weakly acidic to neutral state and reducing the proportion of NH3 formation; at the same time, calcium-based bentonite enriches NH4 through interlayer exchange and surface adsorption. + Plant fibers and bentonite work together to improve the pore structure of biogas residue piles.

[0044] In some other embodiments, in S4, the temperature is lowered to 45–55 °C; the amount of the laccase-producing compound microbial agent added is 1%–5% of the wet weight of the pile; the laccase-producing compound microbial agent is one or more of Bacillus subtilis, Protozoa chrysospora, Trichoderma reesei, and thermophilic actinomycetes; the second-stage fermentation time is 8–20 days, the ventilation intensity is 0.03–0.20 L / (min•kg dry matter), and the pile is turned over every 2–4 days.

[0045] Specifically, in the second stage, the laccase-producing compound microbial agent oxidizes the phenolic substances slowly released from the wood vinegar into quinone or semiquinone free radical intermediates. These intermediates then undergo oxidative condensation reactions with amino acids, peptides, and ammonium nitrogen produced by the degradation of biogas residue, transforming nitrogen from a volatile and weakly adsorbed state to a humic-bound state.

[0046] In some other embodiments, Bacillus subtilis ( Bacillus subtilis The effective viable bacteria count is not less than 1.0 × 10⁻⁶. 8 CFU / g, *Phanerochaete chrysosporium* ( Phanerochaete chrysosporium The number of spores is not less than 1.0 × 10⁻⁶. 7 CFU / g, Trichoderma reesei ( Trichoderma reesei The number of effective spores is not less than 1.0 × 10⁻⁶. 7 CFU / g, thermophilic actinomycetes ( Thermobifida fusca The effective viable bacteria count is not less than 1.0 × 10⁻⁶. 8 CFU / g.

[0047] In some other embodiments, in S4, the stabilization time is 5–15 days. This ensures that the compost products are fully stabilized, allowing for further decomposition of residual biodegradable organic matter, and the compost temperature to naturally drop to near ambient temperature, ensuring that the product meets the stabilization standards.

[0048] This invention provides an organic fertilizer prepared by the above method.

[0049] This invention provides organic fertilizer prepared by the above method or its application in agricultural crops.

[0050] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Components used, unless otherwise specified, are all commercially available conventional products.

[0051] Unless otherwise stated, the dehydrated biogas residue used in the following examples and comparative examples is derived from the solid-liquid separation residue after co-anaerobic digestion of food waste and sludge, and its basic properties are: moisture content 70.2%, pH 8.15, total organic carbon 342 g / kg DM, total nitrogen 24.8 g / kg DM, NH4+ + N 4.85 g / kg DM. Corn stalks were crushed to 5–15 mm and used as a plant fiber conditioner. Calcium-based bentonite had a particle size of 200 mesh and a cation exchange capacity of 68 cmol(+) / kg. The wood vinegar stock solution had a pH of 3.25, a total acid content of 46.5 g / L, and a total phenol content of 2.85 g / L.

[0052] Bacillus subtilis ( Bacillus subtilis ), Proteobacterium chrysosporum ( Phanerochaete chrysosporium Trichoderma reesei ( Trichoderma reesei ) and thermophilic actinomycetes ( Thermobifida fusca All strains were commercially available or preserved strains obtained from microbial culture collection institutions, prepared through routine activation and scale-up culture. Specifically, *Bacillus subtilis* could be purchased from the China General Microbiological Culture Collection Center, the China Industrial Microbiological Culture Collection Center, or commercially available microbial agent manufacturers; *Phanerochaete chrysospora* and *Trichoderma reesei* could be purchased from the China General Microbiological Culture Collection Center, the China Industrial Microbiological Culture Collection Center, or agricultural microbial culture collection institutions; and thermophilic actinomycetes could be purchased from the China General Microbiological Culture Collection Center, the China Industrial Microbiological Culture Collection Center, or other publicly available microbial culture collection institutions. The above strains were activated by slant culture, liquid seed culture, or solid carrier adsorption culture to prepare laccase-producing compound microbial agents.

[0053] Example 1 Take 10 kg of 200-mesh calcium-based bentonite and add 10 L of diluted wood vinegar (diluted 10 times) (i.e., the mass-to-volume ratio of calcium-based bentonite to diluted wood vinegar is 1 kg:1 L). Stir the mixture in a mixer for 30 min to ensure the wood vinegar fully wets the calcium-based bentonite particles, then allow it to stand for aging for 6 h. After aging, adjust the moisture content of the material to 35% to obtain a phenolic acid preloaded calcium-based bentonite conditioner.

[0054] Weigh out dehydrated biogas residue, crushed corn stalks, and the above-mentioned phenolic acid preloaded calcium-based bentonite conditioner, and mix them at a dry weight ratio of 65:25:10. Adjust the initial moisture content to 58.0%, the C / N ratio to 26:1, and the initial pH after mixing is measured to be 6.50.

[0055] The mixture was loaded into a 60 L forced-ventilation composting reactor for the first stage of high-temperature aerobic fermentation. The ventilation rate was 0.12 L / (min·kg dry matter) from day 1 to day 7. When the pile temperature exceeded 70 °C, the pile was turned over to cool it down.

[0056] When the temperature of the stockpile drops to 50°C after the high-temperature period, a laccase-producing compound microbial agent is added at a rate of 3% of the stockpile's wet weight. The laccase-producing compound microbial agent consists of Bacillus subtilis, Phanerochaete chrysosporium, and thermophilic actinomycetes in a mass ratio of 2:1:1; wherein, based on the finished microbial powder, the effective viable count of Bacillus subtilis is 1.2 × 10⁻⁶. 8 CFU / g, the effective spore count of *Phanerochaete chrysosporium* is 1.5 × 10⁻⁶. 7 CFU / g, the effective viable count of thermophilic actinomycetes is 1.0 × 10⁻⁶. 7 CFU / g.

[0057] During the second stage of fermentation, the moisture content of the compost pile was controlled at 45%–55%, the ventilation intensity was 0.08 L / (min·kg dry matter), and the pile was turned over every 3 days. After 25 days, the compost entered the maturation and stabilization stage, and continued to mature for another 5 days to obtain a carbon-fixing and nitrogen-retaining biogas residue compost product.

[0058] Example 2 The difference between this embodiment and Embodiment 1 is that in step (1), 10 kg of 200-mesh calcium-based bentonite is taken and 8 L of diluted wood vinegar diluted 10 times is added, that is, the mass-volume ratio of calcium-based bentonite to diluted wood vinegar is 1 kg: 0.8 L. Other steps and parameters are the same as in Embodiment 1.

[0059] Example 3 The difference between this embodiment and Embodiment 1 is that in step (1), 10 kg of 200-mesh calcium-based bentonite is taken and 15 L of diluted wood vinegar diluted 10 times is added, that is, the mass-volume ratio of calcium-based bentonite to diluted wood vinegar is 1 kg: 1.5 L. Other steps and parameters are the same as in Embodiment 1.

[0060] Comparative Example 1 (Conventional biogas residue compost, without the addition of wood vinegar, bentonite, and laccase agent) Weigh out dehydrated biogas residue and crushed corn stalks, and mix them at a dry weight ratio of 65:35. Calculate the amount of water to add based on the moisture content of the biogas residue and the corn stalks, and adjust the initial moisture content of the mixture to 60.0% and the C / N ratio to 25:1. The initial pH after mixing was measured to be 8.10.

[0061] The mixture was loaded into a 60 L forced-ventilation composting reactor, with a loading amount of 40 kg of wet material. The ventilation rate was 0.10 L / (min·kg dry matter). The compost was turned every 2 days from day 1 to day 10, and every 4 days from day 11 to day 30.

[0062] Comparative Example 2 (direct spraying of wood vinegar treatment, without preloading) Weigh out dehydrated biogas residue and crushed corn stalks, and mix them at a dry weight ratio of 65:35. Dilute the diluted wood vinegar solution 10 times with water, and spray it evenly onto the biogas residue and straw mixture while stirring, so that the initial pH of the compost pile decreases from 8.10 to 6.50. Adjust the moisture content of the compost pile to 60.0%, and the C / N ratio to 25:1.

[0063] The material was loaded into the forced ventilation composting reactor, with the ventilation intensity and turning frequency the same as in Comparative Example 1.

[0064] Comparative Example 3 (Calcium-based bentonite added alone, without wood vinegar) Dehydrated biogas residue, crushed corn stalks, and calcium-based bentonite were weighed and mixed at a dry weight ratio of 65:25:10. During mixing, the calcium-based bentonite was first pre-mixed with a portion of the biogas residue to allow it to fully absorb the free water in the residue. The remaining biogas residue and corn stalks were then added and mixing continued. The initial moisture content of the mixture was adjusted to 59.0%, and the C / N ratio was set to 25:1. After mixing, the initial pH was measured to be 7.90.

[0065] The material was loaded into the forced ventilation composting reactor, with the ventilation intensity and turning frequency the same as in Comparative Example 1.

[0066] Comparative Example 4 (wood vinegar and calcium-based bentonite were directly mixed without pre-loading and aging). Weigh out dehydrated biogas residue, crushed corn stalks, and calcium-based bentonite, and mix them at a dry weight ratio of 65:25:10. Dilute the wood vinegar solution 10 times and spray it directly into the mixture, stirring thoroughly to adjust the initial pH of the compost pile to 6.50. Adjust the moisture content of the compost pile to 58.5% and the C / N ratio to 26:1.

[0067] The material was loaded into the forced ventilation composting reactor, with the ventilation intensity and turning frequency the same as in Comparative Example 1.

[0068] Comparative Example 5 (Phenolic acid preloaded with calcium-based bentonite, without the addition of laccase agent) A phenolic acid-preloaded calcium-based bentonite conditioner was prepared according to the method in Example 1 (calcium-based bentonite to diluted wood vinegar mass-volume ratio 1 kg:1 L, stirred for 30 min, and aged for 6 h). Dehydrated biogas residue, crushed corn stalks, and the conditioner were weighed and mixed at a dry weight ratio of 65:25:10. The moisture content of the compost pile was adjusted to 58.0%, the C / N ratio was 26:1, and the initial pH after mixing was measured to be 6.50.

[0069] The mixture was loaded into a forced-ventilation composting reactor, with the ventilation intensity and turning frequency the same as in Comparative Example 1. No laccase agent was added throughout the composting process.

[0070] Comparative Example 6 The difference between this comparative example and Example 1 is that the first stage of composting involves a single inoculation with 3% laccase-producing compound microbial agent. All other steps and parameters are the same as in Example 1.

[0071] Comparative Example 7 The difference between this comparative example and Example 1 is that in step (1), 10 kg of 200-mesh calcium-based bentonite was taken and 5 L of diluted wood vinegar diluted 10 times was added, that is, the mass-volume ratio of calcium-based bentonite to diluted wood vinegar was 1 kg: 0.5 L. Other steps and parameters were the same as in Example 1.

[0072] Comparative Example 9 The difference between this comparative example and Example 1 is that in step (1), 10 kg of 200-mesh calcium-based bentonite was taken and 20 L of diluted wood vinegar diluted 10 times was added, that is, the mass-volume ratio of calcium-based bentonite to diluted wood vinegar was 1 kg: 2.0 L. Other steps and parameters were the same as in Example 1.

[0073] Performance Test Results and Analysis The performance of the compost products obtained in Examples 1-3 and Comparative Examples 1-9 was tested. The composting experiments were conducted in 60 L forced-ventilation composting reactors, with each reactor loaded with 40 kg of wet material. The composting period was 30 days. During the composting process, the center temperature and pH of the compost pile were measured daily, and NH4+ was measured every 3 days. + -N, NO3 - -N and NH3 release, and the levels of humic acid, fulvic acid and GI were determined on days 0, 10, 20 and 30.

[0074] NH3 release was determined using the acid absorption method with boric acid as the absorption solution, and the cumulative NH3 release was calculated through periodic titration. Humic acid and fulvic acid were determined using the alkaline extraction and acid precipitation method. The seed germination index (GI) was determined using a germination test of Chinese cabbage seeds. Laccase activity was determined using the ABTS method. Humic bound nitrogen was determined by separating the humic components and calculating their nitrogen content. The total nitrogen retention rate was calculated as (total nitrogen at the end of composting / total nitrogen at the beginning of composting) × 100%.

[0075] The results are summarized in Tables 1 to 4.

[0076] Table 1. Composting temperature rise and decomposition effects of Example 1 and Comparative Examples 1-5

[0077] Table 2. NH3 release and nitrogen retention effects in Examples 1 and 1-5

[0078] Table 3. Humic effects of Example 1 and Comparative Examples 1-5

[0079] As shown in Tables 1-3, the temperature of the pile in Example 1 reached 55 °C on day 2, with a maximum temperature of 66.5 °C, and the high-temperature period lasted for 8 days. Laccase activity increased rapidly from day 10 to 18, reaching a peak of 57.6 U / g DM on day 15. The cumulative NH3 release was 1.75 g N / kg DM, a decrease of 79.7% compared to Comparative Example 1; the total nitrogen retention rate reached 88.7%; NO3... - The final N content was 1040 mg / kg DM. At the end of composting, the humic acid content was 103.6 g / kg DM, an increase of 97.7% compared to control example 1; the fulvic acid content was 55.8 g / kg DM, the HA / FA ratio was 1.86, the E4 / E6 ratio decreased to 3.74, the humification index was 61.2%, the proportion of humus-bound nitrogen was 25.9%, and the GI was 98%. The results indicate that phenolic acid preloaded calcium-based bentonite can slowly release phenolic precursors from wood vinegar and enrich NH4+. + Adding laccase-producing bacteria during the cooling period can promote the oxidative condensation of phenolic substances, further converting nitrogen into humic-bound nitrogen. This example demonstrates a significant synergistic effect of carbon fixation, nitrogen retention, and humification.

[0080] In Comparative Example 1, the temperature of this compost pile reached 55 °C on day 4, with a maximum temperature of 60.8 °C, and the high-temperature period lasted for 5 days. Due to the initial alkaline pH, a significant NH3 release peak was observed from day 2 to day 8 of composting, with a cumulative NH3 release of 8.60 g N / kg DM. At the end of composting, the total nitrogen retention rate was 61.2%, and the NH4+ retention rate was... + -N decreased by 38.5%, NO3 - -N endpoint content was 420 mg / kg DM.

[0081] Regarding humification, at the end of composting, the humic acid content was 52.4 g / kg DM, the fulvic acid content was 67.1 g / kg DM, the HA / FA ratio was 0.78, the E4 / E6 ratio was 5.82, the proportion of humic bound nitrogen in total nitrogen was 11.6%, and the GI was 76%. The results indicate that although conventional biogas residue composting can achieve a certain degree of temperature-induced maturation, it suffers from significant nitrogen loss, insufficient humification, and low product stability.

[0082] In Comparative Example 2, after direct spraying of wood vinegar, the initial pH of the compost pile dropped to 6.50, and the NH3 release during composting days 1–5 was significantly lower than in Comparative Example 1. This group reached 55 °C on day 3.5, with a maximum temperature of 59.6 °C, and the high-temperature period lasted for 5 days. The cumulative NH3 release was 5.75 g N / kg DM, a decrease of 33.1% compared to Comparative Example 1; the total nitrogen retention rate was 70.4%. However, after day 8 of composting, as organic acids were consumed and ammonium nitrogen was converted, the pH of the compost pile rose back to above 7.8, and NH3 release increased somewhat in the later stages. At the end of composting, the humic acid content was 63.8 g / kg DM, the fulvic acid content was 66.5 g / kg DM, the HA / FA ratio was 0.96, the proportion of humic bound nitrogen was 14.3%, and the GI was 84%. The results showed that direct spraying of wood vinegar could inhibit NH3 volatilization in the early stage, but its acidification and nitrogen retention effects were limited in duration, and the humification and nitrogen fixation effects were still insufficient.

[0083] In Comparative Example 3, the addition of calcium-based bentonite significantly reduced the adhesion of biogas residue and improved the looseness of the compost pile. This group reached 55 °C on day 3, with a maximum temperature of 63.2 °C, and the high-temperature period lasted for 6 days, superior to Comparative Example 1. The cumulative NH3 release was 6.10 gN / kg DM, a decrease of 29.1% compared to Comparative Example 1; the total nitrogen retention rate was 68.1%. At the end of composting, the humic acid content was 58.2 g / kg DM, the fulvic acid content was 64.9 g / kg DM, the HA / FA ratio was 0.90, the E4 / E6 ratio was 5.35, the proportion of humic bound nitrogen was 13.7%, and the GI was 82%. The results indicate that calcium-based bentonite can improve the biogas residue pile structure and adsorb some NH4+. + However, when added alone, it mainly manifests as physical adsorption and pore conditioning effects, with limited promotion of the formation of nitrogen bound to humic substances.

[0084] In Comparative Example 4, after direct mixing of wood vinegar and calcium-based bentonite, the compost reached 55 °C on day 3, with a maximum temperature of 64.5 °C, and the high-temperature period lasted for 7 days. The cumulative NH3 release was 3.45 g N / kg DM, a decrease of 59.9% compared to Comparative Example 1; the total nitrogen retention rate was 79.6%. However, due to the direct spraying of wood vinegar onto the compost pile, the distribution of its organic acid and phenolic components was not completely uniform in local areas. On day 2 of composting, the pH of some samples was below 6.0, and the dehydrogenase activity was lower than in Comparative Example 3, indicating that direct mixing still carries a short-term risk of microbial inhibition. At the end of composting, the humic acid content was 76.9 g / kg DM, the fulvic acid content was 61.2 g / kg DM, the HA / FA ratio was 1.26, the proportion of humic bound nitrogen was 17.8%, and the GI was 88%. The results indicate that direct mixing can improve nitrogen retention and humification, but it has not fully solved the problems of excessively rapid release of wood vinegar and excessively high local concentrations.

[0085] Compared to Comparative Example 4, the phenolic acid pre-loaded calcium-based bentonite treatment in Comparative Example 5 resulted in a more stable release of organic acids and phenols from the wood vinegar solution. During the first 10 days of composting, the pH of the compost pile remained between 6.5 and 7.3, with no localized areas of excessively low pH. This group reached 55 °C on day 2.5, with a maximum temperature of 65.7 °C, and the high-temperature period lasted for 7 days. The cumulative NH3 release was 2.85 g N / kg DM, a decrease of 66.9% compared to Comparative Example 1; the total nitrogen retention rate was 83.4%; and the NH4+ release was... + -N decreased by 61.3%, NO3 - The final N content was 860 mg / kg DM. At the end of composting, the humic acid content was 84.5 g / kg DM, the fulvic acid content was 59.3 g / kg DM, the HA / FA ratio was 1.43, the E4 / E6 ratio was 4.25, the proportion of humic bound nitrogen was 20.5%, and the GI was 91%. The results indicate that phenolic acid preloading of calcium-based bentonite not only improves the compost structure and reduces NH3 release, but also promotes the humification process through the slow release of phenolic precursors, with better effects than direct compounding of wood vinegar and calcium-based bentonite.

[0086] Table 4. Effects of inoculation sequence of different laccase-producing bacterial communities on humic nitrogen fixation.

[0087] As shown in Table 4, in Comparative Example 5, which was not inoculated with laccase-producing bacteria, the peak laccase activity was only 18.5 U / g DM, the humic acid content was 84.5 g / kg DM, and the proportion of humic bound nitrogen was 20.5%.

[0088] In Comparative Example 6, after the initial single inoculation, some laccase-producing bacteria were affected by the high temperature period, with a peak laccase activity of 32.8 U / g DM, a humic acid content of 91.2 g / kg DM, and a humic bound nitrogen ratio of 22.1%.

[0089] In Example 1, when the pile temperature was reduced to 50 °C, the peak laccase activity reached 57.6 U / g DM, the humic acid content was 103.6 g / kg DM, the HA / FA ratio was 1.86, the proportion of humic bound nitrogen was 25.9%, and the GI was 98%.

[0090] The results showed that inoculating laccase-producing bacteria during the cooling period could match the release of laccase activity with the slow release of phenols, the accumulation of amino acids, and the humification condensation stage, which is a key process condition for improving humic acid formation and the proportion of nitrogen bound to humic substances.

[0091] Table 5. Effects of different wood vinegar preloading amounts on composting efficiency.

[0092] As shown in Table 5, Comparative Example 7 had a low preload of wood vinegar and an initial pH of 6.9, resulting in limited nitrogen retention and humification effects. The cumulative NH3 release was 3.25 g N / kg DM, the total nitrogen retention rate was 80.5%, and the humic acid content was 82.6 g / kg DM.

[0093] The reactors in Examples 2 and 1 heated up rapidly, reaching 55 °C on day 2, with the high-temperature period lasting 7–8 days. Example 1 showed the best results, with a cumulative NH3 release of 1.75 g N / kg DM, a total nitrogen retention rate of 88.7%, a humic acid content of 103.6 g / kg DM, and a GI of 98%. Example 3 had an initial pH of 6.1, a slightly delayed heating rate, a cumulative NH3 release of 2.60 g N / kg DM, and a total nitrogen retention rate of 84.2%.

[0094] The initial pH of the 8 control groups dropped to 5.6, and the temperature only reached 55 °C on day 5. The high temperature period lasted only 3 days, and the GI dropped to 84%, indicating that excessive preloading of wood vinegar would inhibit the early microbial activity of compost.

[0095] The results showed that the preferred mass-to-volume ratio of calcium-based bentonite to diluted wood vinegar was 1 kg:0.8–1.5 L, more preferably 1 kg:1.0 L.

[0096] 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 composting biogas residue to fix carbon and retain nitrogen, characterized in that, Includes the following steps: S1. Mix calcium-based bentonite with diluted wood vinegar and age it to obtain phenolic acid preloaded calcium-based bentonite conditioner. S2. Mix the dehydrated biogas residue, plant fiber conditioner and the phenolic acid preloaded calcium-based bentonite conditioner, and adjust the moisture content and C / N ratio of the pile after mixing to obtain the pile to be fermented. S3. The first stage of high-temperature aerobic fermentation is carried out on the pile to be fermented. S4. After the process is completed, the temperature is lowered, and laccase-producing compound microbial inoculant is added to the pile to carry out the second stage of humification and nitrogen fixation fermentation. After the process is completed, the pile is further decomposed and stabilized to obtain the final product.

2. The method according to claim 1, characterized in that, In S1, the diluted wood vinegar is obtained by diluting the original wood vinegar solution with water by 5–20 times; The calcium-based bentonite has a particle size of 80–300 mesh and a cation exchange capacity of not less than 50 cmol(+) / kg.

3. The method according to claim 1, characterized in that, In S1, calcium-based bentonite and diluted wood vinegar are mixed at a mass-to-volume ratio of 1:0.6–1.5, stirred for 20–60 min, and allowed to stand for aging for 2–12 h. After aging, the moisture content of the material is adjusted to 25%–45%.

4. The method according to claim 1, characterized in that, In S2, dehydrated biogas residue, plant fiber conditioner and phenolic acid preloaded calcium-based bentonite conditioner are mixed in a mass ratio of 55–75:15–35:5–15. The dehydrated biogas residue has a moisture content of 60%–80% and a pH of 7.5–8.8; The plant fiber conditioner is one or more of the following: corn stalks, rice husks, sawdust, garden branch fragments, peanut shells, and mushroom residue, with a particle size of 2–20 mm.

5. The method according to claim 1, characterized in that, In S2, the moisture content of the pile is adjusted to 55%–62% after mixing, and the C / N ratio is 22:1–32:

1.

6. The method according to claim 1, characterized in that, In S3, the pile temperature for the first stage of high-temperature aerobic fermentation is 55–70 ℃, the fermentation time is 1–7 days, and the ventilation intensity is 0.05–0.30 L / (min•kg dry matter).

7. The method according to claim 1, characterized in that, In S4, the temperature is lowered to 45–55 ℃; the amount of the laccase-producing compound microbial agent added is 1%–5% of the wet weight of the pile; the laccase-producing compound microbial agent is one or more of Bacillus subtilis, Protozoa chrysospora, Trichoderma reesei, and thermophilic actinomycetes; the second stage fermentation time is 8–20 days, the ventilation intensity is 0.03–0.20 L / (min•kg dry matter), and the pile is turned over every 2–4 days.

8. The method according to claim 1, characterized in that, In S4, the maturation and stabilization time is 5–15 days.

9. An organic fertilizer, characterized in that, The fertilizer is prepared according to any one of the methods described in claims 1-8.

10. The application of an organic fertilizer prepared by the method described in any one of claims 1-8 or the organic fertilizer described in claim 9, characterized in that, It is used in crops.

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