Method for preparing bio-organic fertilizer by using biochar and biogas residue synergistic compost and application thereof

Abstract

This invention provides a method and application for preparing bio-organic fertilizer through synergistic composting of biochar-containing biogas residue, belonging to the field of organic fertilizer preparation technology. The method includes: preparing biogas residue through anaerobic fermentation of livestock and poultry manure and crop straw; adding biochar and a compound microbial agent; conducting high-temperature aerobic composting; and obtaining bio-organic fertilizer through maturation and aging. The amount of biochar added is 5%-10% of the dry basis weight of the composting raw materials; the aerobic composting time is 35-45 days; and the high-temperature composting temperature is 55-65℃. The compound microbial agent includes *Bacillus steatophilus*, *Bacillus amyloliquefaciens*, and *Bacillus mucilaginosus*. The bio-organic fertilizer obtained by this invention can be used for crop soil improvement. This invention, through the synergistic effect of biogas residue, biochar, and compound microbial agent, effectively shortens the composting cycle, improves compost maturity, reduces nitrogen loss, passivates heavy metals, and significantly improves the quality of organic fertilizer.

Description

Technical Field

[0001] This invention belongs to the field of organic fertilizer preparation technology, specifically a method and application for preparing bio-organic fertilizer by co-composting with biochar and biogas residue. Background Technology

[0002] Biogas residue, the anaerobic fermentation residue of livestock and poultry manure and agricultural waste such as straw, is rich in organic matter, humic acid, and nutrients such as nitrogen, phosphorus, and potassium, making it a high-quality raw material for organic fertilizer production. However, directly returning fresh biogas residue to the field presents several problems: it has a high water content, is easily putrefied and develops a foul odor, contains pathogens and anti-nutritional factors, and its nutrients are mainly in the form of fast-acting substances, easily lost after being applied to the soil, posing a risk of secondary pollution. Aerobic composting is an effective way to achieve the harmlessness and resource utilization of biogas residue, but biogas residue itself has a low carbon-to-nitrogen ratio and a high content of cellulose and other recalcitrant organic matter. When composted alone, it suffers from drawbacks such as slow heating, short high-temperature period, low degree of humification, severe nitrogen loss, and large greenhouse gas emissions. Therefore, there is an urgent need to develop additives and processes that can accelerate the composting process of biogas residue and improve product quality.

[0003] Biochar, due to its abundant pore structure, large specific surface area, and strong adsorption properties, has been widely used in aerobic composting in recent years. Studies have shown that adding an appropriate amount of biochar to sludge compost can significantly increase the peak temperature of the compost pile, prolong the duration of the high-temperature period, and reduce ammonia and greenhouse gas emissions through adsorption. Simultaneously, it promotes the conversion of heavy metals from exchangeable to residual states, reducing their bioavailability. However, existing technologies still have shortcomings: on the one hand, the composite microbial agents used are often of a single type or have unclear functions, lacking targeted synergistic design of microbial communities for the high-temperature and maturation periods; on the other hand, there is a lack of systematic optimization of key parameters such as the initial carbon-nitrogen ratio, moisture content, and duration of the high-temperature period, resulting in the failure to fully realize the synergistic effect between biochar and microorganisms. Furthermore, there is still room for improvement in the effectiveness of existing biochar-based sludge composting methods in shortening the fermentation cycle, increasing the number of viable bacteria in the product, and passivating heavy metals.

[0004] Therefore, it is necessary to provide a method for preparing bio-organic fertilizer through co-composting of biochar and biogas residue, so as to achieve efficient stabilization, nutrient retention and functional enhancement of biogas residue, thereby obtaining high-quality bio-organic fertilizer to meet the application needs of crop soil improvement. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for preparing bio-organic fertilizer by co-composting biochar and sludge. This method can effectively shorten the composting cycle, improve the compost maturity, reduce nitrogen loss, passivate heavy metals, and significantly improve the quality of organic fertilizer.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing bio-organic fertilizer through co-composting of biochar and biogas residue, comprising the following steps: Biogas residue is prepared by anaerobic fermentation of livestock and poultry manure and crop straw. Biochar and compound microbial agents are added, and high-temperature aerobic composting is carried out. After decomposition and aging, bio-organic fertilizer is obtained. The amount of biochar added is 5%-10% of the dry basis mass of the composting raw materials; the aerobic composting time is 35-45 days, and the high-temperature composting temperature is 55-65℃. The compound microbial agent includes Bacillus stearothermophilus, Bacillus amyloliquefaciens, and Bacillus gelatinosa.

[0007] Preferably, the preparation method of the biogas residue is as follows: livestock and poultry manure and crop straw are mixed at a dry matter ratio of 4:1-6:1, the total solid content is adjusted to 15%-25%, and the mixture is anaerobic fermented at 33-37℃ for 28-35 days. The solid and liquid are then separated to obtain biogas residue.

[0008] Preferably, the biochar is obtained by pyrolyzing corn cobs at 500-650°C under anaerobic conditions for 1-3 hours.

[0009] Preferably, the specific surface area of ​​the biochar is ≥120 m². 2 / g, with a particle size of 0.1-0.5mm.

[0010] Preferably, the live bacteria ratio of the thermophilic Bacillus stearothermophilus, Bacillus amyloliquefaciens and Bacillus gelatinosa is 3-5:1-2:1-2.

[0011] Preferably, the effective viable count of the compound microbial agent is ≥2.0 × 10⁻⁶. 8 cfu / g.

[0012] Preferably, the composting process also includes adjusting the initial C / N ratio to 22-30:1 and the initial moisture content to 55%-65%.

[0013] Preferably, the duration of the high-temperature period in the high-temperature aerobic composting is ≥7 days.

[0014] The present invention also provides a bio-organic fertilizer prepared by the method.

[0015] The present invention also provides an application of the aforementioned bio-organic fertilizer in crop soil improvement.

[0016] Compared with the prior art, the present invention has the following advantages: (1) This invention significantly improves composting efficiency and product quality through the synergistic effect of biogas residue, biochar, and compound microbial agents. Experimental results show that the high-temperature period lasts for more than 9 days, the composting cycle is only 35-45 days, the seed germination index of the compost product reaches 92.5%, the total nutrient content is 8.2%, and the number of effective viable bacteria reaches 1.8 × 10⁻⁶. 8 CFU / g. The addition of biochar effectively reduces nitrogen loss and promotes the passivation of heavy metals, significantly improving the quality of organic fertilizer.

[0017] (2) Pot experiments with wheat further verified that, compared with conventional chemical fertilizers, the organic fertilizer of this invention increased soil pH by 0.36 units, increased organic matter content by 30.2%, and provided phosphorus and potassium reached 32.1 mg / kg and 138.4 mg / kg, respectively, showing good slow-release characteristics. Wheat plant height increased by 12.7%, aboveground dry weight increased by 23.2%, root-to-shoot ratio was balanced, and growth advantage was obvious.

[0018] (3) Regarding heavy metal passivation, the organic fertilizer of this invention significantly reduced the bioavailability of copper and cadmium in the soil. Compared with the control organic fertilizer, the copper and cadmium content in the aboveground parts of wheat decreased by 22.8% and 28.2%, respectively, and the enrichment coefficients decreased to 0.049 and 0.014. This invention realizes the efficient resource utilization of biogas residue, and the resulting bio-organic fertilizer has multiple functions, including soil enrichment, growth promotion and yield increase, and heavy metal passivation, and has broad prospects for agricultural application. Detailed Implementation

[0019] This invention provides a method for preparing bio-organic fertilizer through co-composting of biochar and biogas residue, comprising the following steps: Biogas residue is prepared by anaerobic fermentation of livestock and poultry manure and crop straw. Biochar and compound microbial agents are added, and high-temperature aerobic composting is carried out. After decomposition and aging, bio-organic fertilizer is obtained. The amount of biochar added is 5%-10% of the dry basis mass of the composting raw materials; the aerobic composting time is 35-45 days, and the high-temperature composting temperature is 55-65℃. The compound microbial agent includes Bacillus stearothermophilus, Bacillus amyloliquefaciens, and Bacillus gelatinosa.

[0020] In this invention, livestock and poultry manure and crop straw are mixed evenly at a dry matter mass ratio of 4:1 to 6:1. The livestock and poultry manure can be at least one of pig manure, cow manure, or chicken manure, and the crop straw can be corn straw, wheat straw, or rice straw. The crop straw needs to be pre-crushed to a length of less than 1 cm. The total solids content of the mixture is adjusted to 15%-25%, and then it is put into an anaerobic digester. Anaerobic fermentation is carried out under mesophilic conditions of 33-37℃ for 28-35 days. After fermentation, solid-liquid separation is performed using plate and frame filter press or centrifugation, and the solid portion is collected to obtain biogas residue. The resulting biogas residue typically has a moisture content of 70%-80%, an organic matter content of 50%-60%, a total nitrogen content of 1.2%-1.8%, and a carbon-to-nitrogen ratio of 15-22:1. To meet the carbon-to-nitrogen ratio requirements of aerobic composting, pulverized dry straw needs to be added to the biogas residue as a conditioner to adjust the carbon-to-nitrogen ratio to 22-30:1. Simultaneously, biochar is added at a ratio of 5%-10% of the dry weight of the composting raw materials. This biochar is preferably produced by pyrolyzing corn cobs at 500-650℃ under anaerobic conditions for 1-3 hours, and has a specific surface area ≥120 m². 2 / g, with a particle size of 0.1-0.5mm. In addition, a compound microbial agent is inoculated at a ratio of 0.5%-1% of the dry weight of the compost raw materials. This agent is composed of *Bacillus steatophilus*, *Bacillus amyloliquefaciens*, and *Bacillus mucilaginosus* at a viable count ratio of 3-5:1-2:1-2, with an effective viable count ≥2.0×10⁻⁶. 8 CFU / g. Thoroughly mix the above-mentioned biogas residue, straw, biochar, and microbial agent, and add an appropriate amount of water to adjust the initial moisture content to 55%-65%. Simultaneously, 1%-2% (by dry weight of the compost raw materials) of superphosphate can be added for chemical ammonium fixation. The uniformly mixed material is then fed into an aerobic composting reactor or windrow, and high-temperature aerobic composting is carried out using a combination of forced ventilation and regular turning. During composting, the pile temperature is controlled at 55-65℃, with the high-temperature period lasting no less than 7 days. The entire aerobic composting cycle is 35-45 days. After composting, the material is transferred to an aging workshop and aged for 7-15 days under natural ventilation conditions, turning the pile every 5-7 days to further mature and stabilize the material. Finally, the matured and aged material is dried at a low temperature below 60℃ until the moisture content is ≤20%. After crushing and screening (2-5mm), granular bio-organic fertilizer is obtained.

[0021] In this invention, as a preferred embodiment, the biochar is obtained from corn cobs through oxygen-limited pyrolysis. First, select corn cobs free of mold and impurities, place them in a forced-air drying oven and dry them at 105°C to constant weight. Then, coarsely pulverize them using a pulverizer, passing them through an 80-100 mesh sieve to obtain corn cob powder with uniform particle size. Place the corn cob powder in a tubular pyrolysis furnace, using high-purity nitrogen (purity ≥99.99%) as a protective gas, and heat it to a set temperature of 500-650°C at a heating rate of 10°C / min. Pyrolyze at this temperature for 1-3 hours, continuously introducing nitrogen to maintain an oxygen-deficient environment. After pyrolysis, stop heating and allow it to cool naturally to room temperature under nitrogen protection. The pyrolysis product is then removed to obtain crude biochar. To remove any ash and soluble impurities that may adhere to the surface of the biochar, repeatedly wash the obtained biochar with deionized water until the pH of the washing solution is close to neutral, and then dry it at 105°C to constant weight. The biochar prepared by the above method has a rich pore structure and a large specific surface area. Its specific surface area was determined using a specific surface area and pore size analyzer (BET method, with nitrogen as the adsorbate), and the results showed that the specific surface area of ​​this biochar can reach 120 m². 2 / g or more, preferably 120-150m 2 / g. The dried biochar is sieved through a 0.5mm sieve and then a 0.1mm sieve, collecting the sieved product with a particle size between 0.1mm and 0.5mm, thus obtaining a finished biochar product with a particle size of 0.1-0.5mm. Biochar within this particle size range maintains good dispersibility, allowing for thorough mixing with composting materials, without causing dust or clogging of the compost pile pores due to excessively fine particles. In practical applications, this biochar can be directly used for aerobic composting of biogas residue. Its large specific surface area is beneficial for adsorbing ammonia and heavy metal ions, and its rich pore structure provides a suitable habitat for microorganisms, thereby effectively promoting the composting process and improving the quality of organic fertilizer.

[0022] In this invention, as a preferred embodiment, the composite microbial agent is composed of *Bacillus stearothermophilus* (…). Geobacillus stearothermophilus ), Bacillus amyloliquefaciens ( Bacillus starch liquefier ) and gelatinous spores ( Mucilaginous BacillusThe above three strains are prepared by mixing live bacteria in a ratio of 3-5:1-2:1-2. All three strains can be legally obtained from domestically and internationally recognized microbial culture collection institutions. *Bacillus steatophilus*, a key functional bacterium in high-temperature aerobic composting, possesses excellent heat resistance and maintains high metabolic activity during the high-temperature composting period. The strain with accession number CICC 10267, deposited at the China Industrial Microbial Culture Collection Center (CICC), is preferred. *Bacillus amyloliquefaciens* mainly secretes extracellular enzymes such as amylase and protease to accelerate the decomposition of organic matter in compost raw materials. It can be purchased from the China General Microbial Culture Collection Center (CGMCC), with strain accession number CGMCC 1.7463 being preferred. The preferred strain of *Bacillus mucilaginosus* used is strain CICC 21700, preserved at the China Industrial Microbial Culture Collection Center (CICC). This strain, also known as silicate bacteria or potassium bacteria, possesses excellent potassium and phosphorus solubilizing, phosphorus solubilizing, and plant growth hormone secretion capabilities. During composting and after organic fertilizer application, it can effectively activate unavailable potassium and phosphorus in the soil, promoting crop growth. After activation and expansion culture of each strain, the viable cell concentration was determined using the plate count method. Then, a mixture was prepared with viable cells at a ratio of *Bacillus steatophilus*: *Bacillus amyloliquefaciens*: *Bacillus mucilaginosus* = 3-5: 1-2: 1-2, ensuring a total effective viable cell count ≥ 2.0 × 10⁻⁶. 8 CFU / g. The above three strains play a synergistic role in the composting process. Among them, Bacillus stearothermophilus dominates the rapid degradation of organic matter and the warming of the compost pile during the high-temperature period, Bacillus amyloliquefaciens provides a rich extracellular enzyme system to accelerate the decomposition of cellulose, hemicellulose and other recalcitrant substances, and Bacillus mucilaginosus plays a role in potassium solubilization and growth promotion during the maturation period and after application. When the three are used in combination according to the above live bacteria ratio, they can achieve functional relay and metabolic complementarity throughout the composting process, thereby significantly improving composting efficiency and product quality.

[0023] In this invention, as a preferred embodiment, the initial carbon-to-nitrogen ratio (C / N) of the compost is adjusted to 22-30:1, and the initial moisture content is adjusted to 55%-65%. After anaerobic fermentation, the carbon-to-nitrogen ratio of biogas residue is usually low. When composted alone, nitrogen is easily lost through volatilization in the form of ammonia, and the carbon source required for microbial metabolism is relatively insufficient. Therefore, it is necessary to add carbon-rich materials for adjustment. In this invention, crushed crop straw is preferably used as a carbon source regulator. Corn straw, wheat straw, or rice straw can be selected. Before use, it needs to be processed by a crusher to a length of less than 1 cm to increase its specific surface area, facilitating microbial attachment and decomposition.

[0024] The present invention also provides a bio-organic fertilizer prepared by the method.

[0025] This invention also provides an application of the aforementioned bio-organic fertilizer in crop soil improvement. The bio-organic fertilizer provided by this invention can be widely used for crop soil improvement, especially suitable for farmland contaminated with heavy metals or arable land degraded by long-term application of chemical fertilizers. The application method of the bio-organic fertilizer of this invention is basal application, that is, it is applied to the soil once before sowing or transplanting crops, combined with land preparation.

[0026] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0027] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available products.

[0028] Example 1 A method for preparing bio-organic fertilizer through co-composting of biochar and biogas residue, the specific steps of which are as follows: (1) Preparation of biogas residue: Livestock and poultry manure (pig manure) and corn stalks were mixed at a dry matter mass ratio of 5:1, and the total solid content was adjusted to 20%. The mixture was then put into an anaerobic fermentation tank and anaerobic fermented at 35°C for 30 days. After fermentation, biogas residue was obtained by solid-liquid separation. The residue had a moisture content of 72.5%, an organic matter content of 58.6%, a total nitrogen content of 1.52%, and a carbon-nitrogen ratio of 19.8:1.

[0029] (2) Biochar preparation: Corn cobs were crushed and passed through an 80-mesh sieve. After washing and drying, the cobs were placed in a tube furnace and heated to 600℃ at a rate of 10℃ / min under nitrogen protection. The pyrolysis was carried out at this constant temperature for 2 hours, followed by natural cooling to obtain biochar. The specific surface area of ​​the biochar was determined to be 125.6 m². 2 / g, particle size distribution is 0.1-0.5mm, pH value is 9.8.

[0030] (3) Preparation of compound microbial inoculant: Bacillus stearothermophilus, Bacillus amyloliquefaciens and Bacillus mucilaginosus were mixed at a viable count ratio of 4:1:1, and solid-state fermentation was carried out using wheat bran as a carrier. After drying, the compound inoculant was obtained with an effective viable count of 2.5 × 10⁻⁶. 8 cfu / g.

[0031] (4) Preparation of compost raw materials: Take 1000 kg of the above biogas residue (on a dry basis), add corn straw powder to adjust the carbon-nitrogen ratio to 25:1, add 80 kg of biochar (accounting for 8% of the dry basis mass of the compost raw materials), add 15 kg of superphosphate for nitrogen fixation, and inoculate with 6 kg of compound microbial agent. After mixing evenly, adjust the initial moisture content to 60% and the initial pH to 7.5.

[0032] (5) High-temperature aerobic composting: The mixture is placed in a composting reactor equipped with a forced ventilation system, and static composting is adopted, with the pile turned over every 2 days. The composting process lasts for 40 days, including a high-temperature period (55-65℃) lasting for 9 days, with the peak temperature of the pile reaching 64.2℃. A ventilation rate of 0.2 m³ / s is maintained during composting. 3 / (min·m 3 Ventilate for 30 minutes, then wait 1 hour.

[0033] (6) Composting and aging: After composting, the material is transferred to the aging workshop and left to stand naturally for 15 days, during which it is turned over twice to further mature and stabilize the material. The seed germination index (GI) of the compost product was measured to be 92.5%, and the carbon-nitrogen ratio was reduced to 16.8, which meets the standards for organic fertilizer composting.

[0034] (7) Drying and granulation: The decomposed material is dried at a low temperature below 60℃ until the moisture content is ≤20%, and then crushed and sieved (2-4mm) to obtain granular biological organic fertilizer.

[0035] Testing revealed that the bio-organic fertilizer prepared in this embodiment contained 8.2% total nutrients (N+P2O5+K2O), 56.4% organic matter, and 1.8×10⁻⁶ effective viable bacteria. 8 The cfu / g and heavy metal content were both lower than the national organic fertilizer standard limit (NY / T525-2021).

[0036] Example 2 The difference between this embodiment and Embodiment 1 is that: the amount of biochar added is 5% of the dry basis mass of the compost raw materials; the ratio of viable bacteria of Bacillus stearothermophilus, Bacillus amyloliquefaciens and Bacillus mucilaginosus in the compound microbial agent is 3:2:2; the initial carbon-nitrogen ratio of the compost is adjusted to 22:1; the moisture content is adjusted to 55%; and the composting time is 35 days.

[0037] Example 3 The difference between this embodiment and Embodiment 1 is that: the amount of biochar added is 10% of the dry basis mass of the compost raw materials; the ratio of viable bacteria of Bacillus stearothermophilus, Bacillus amyloliquefaciens and Bacillus mucilaginosus in the compound microbial agent is 5:1:1; the initial carbon-nitrogen ratio of the compost is adjusted to 30:1; the moisture content is adjusted to 65%; and the composting time is 45 days.

[0038] Comparative Example 1 The only difference between this comparative example and Example 1 is that biochar is not added, while the other raw material ratios, types and amounts of microbial agents, and composting process parameters are the same as in Example 1.

[0039] Example 4 1. Experimental Materials Test soil: Soil samples were taken from the top 0-20cm layer of a farmland, air-dried, and sieved through a 2mm sieve. The soil type was alluvial soil, with the following basic physicochemical properties: pH 7.2, organic matter 18.6 g / kg, available nitrogen 85.3 mg / kg, available phosphorus 22.4 mg / kg, and available potassium 110.5 mg / kg. To simulate heavy metal pollution, exogenous CuSO4·5H2O and CdCl2·2.5H2O were added to achieve a total Cu content of 150 mg / kg and a total Cd content of 2.0 mg / kg.

[0040] Test fertilizer: The bio-organic fertilizer prepared in Example 1, with total nutrients ≥8.2%, organic matter ≥56.4%, and effective viable bacteria count 1.8×10⁻⁶. 8 cfu / g.

[0041] Control fertilizer: The organic fertilizer prepared in Comparative Example 1 (the only difference from Example 1 is that no biochar was added), and other indicators are similar.

[0042] Test crop: wheat ( Summer wheat L.), the variety is Jimai 22.

[0043] 2. Experimental Design Four treatments were set up, with each treatment having three replicates, for a total of 12 pots, arranged in a randomized block design. The grouping is shown in Table 1.

[0044] Table 1 Experimental Groups

[0045] Fill each pot with 5 kg of soil, mixing fertilizer evenly before filling. Disinfect wheat seeds with 5% NaClO for 10 minutes, rinse with deionized water, and then germinate. Sow 15 seeds per pot, thinning to 10 seedlings per plant after emergence. Place the potted plants in an artificial climate chamber at a temperature of 20-25℃, with 12 hours of light per day, and maintaining soil moisture at 70% field capacity. Harvest after 60 days of growth.

[0046] 3. Measurement Indicators and Methods (1) Soil physicochemical properties: After harvest, rhizosphere soil was taken and pH (potential method), organic matter (potassium dichromate oxidation method), available nitrogen (alkaline diffusion method), available phosphorus (NaHCO3 extraction-molybdenum antimony colorimetric method), and available potassium (NH4OAc extraction-flame photometry method) were measured.

[0047] (2) Wheat growth indicators: plant height, aboveground dry weight, underground dry weight, root-to-shoot ratio.

[0048] (3) Heavy metal content of wheat: The aboveground and underground parts of the plant were digested by HNO3-H2O2, and the contents of Cu and Cd were determined by atomic absorption spectrophotometry. The enrichment coefficient (BCF = plant heavy metal content / total soil heavy metal content) was calculated.

[0049] 4. Results Analysis As shown in Table 2, the bio-organic fertilizer (BF) treatment of this invention significantly increased soil pH and organic matter, effectively improving soil nutrient retention capacity. Compared with conventional chemical fertilizer (CF), the BF treatment showed slightly lower available nitrogen and significantly lower available potassium, but no significant difference in available phosphorus, indicating that the organic fertilizer has a slow-release effect.

[0050] Table 2 Effects of different treatments on soil physicochemical properties

[0051] Note: Different lowercase letters in the same column indicate significant differences (P<0.05).

[0052] As shown in Table 3, the wheat treated with the bio-organic fertilizer (BF) of this invention exhibited the highest plant height, aboveground dry weight, and underground dry weight, with yield increases of 144.3% (aboveground dry weight) compared to the control (CK), 23.2% compared to conventional chemical fertilizer (CF), and 58.4% compared to the control organic fertilizer (OF). The root-to-shoot ratio showed no significant difference compared to CF, indicating that the bio-organic fertilizer promoted balanced growth of the aboveground and underground parts.

[0053] Table 3 Effects of different treatments on wheat growth

[0054] Note: Different lowercase letters in the same column indicate significant differences (P<0.05).

[0055] As shown in Table 4, the Cu and Cd contents in the aboveground parts of wheat treated with the organic fertilizer (BF) of this invention decreased by 40.7% and 46.2% respectively compared with the control (CK), by 31.8% and 39.1% respectively compared with the free radical (CF), and by 22.8% and 28.2% respectively compared with the free radical (OF). The significantly reduced enrichment coefficient indicates that the organic fertilizer of this invention effectively inhibits the absorption of heavy metals by wheat and their translocation to the aboveground parts.

[0056] Table 4. Effects of different treatments on heavy metal accumulation in wheat plants

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing bio-organic fertilizer through co-composting of biochar and biogas residue, characterized in that, Includes the following steps: Biogas residue is prepared by anaerobic fermentation of livestock and poultry manure and crop straw. Biochar and compound microbial agents are added, and high-temperature aerobic composting is carried out. After decomposition and aging, bio-organic fertilizer is obtained. The amount of biochar added is 5%-10% of the dry basis mass of the composting raw materials; the aerobic composting time is 35-45 days, and the high-temperature composting temperature is 55-65℃. The compound microbial agent includes Bacillus stearothermophilus, Bacillus amyloliquefaciens, and Bacillus gelatinosa.

2. The method of claim 1, wherein, The preparation method of the biogas residue is as follows: livestock and poultry manure and crop straw are mixed at a dry matter ratio of 4:1-6:1, the total solid content is adjusted to 15%-25%, and the mixture is anaerobic fermented at 33-37℃ for 28-35 days. The biogas residue is obtained by solid-liquid separation.

3. The method of claim 1, wherein, The biochar is obtained by pyrolyzing corn cobs at 500-650℃ under anaerobic conditions for 1-3 hours.

4. The method according to claim 1, characterized in that, The specific surface area of ​​the biochar is ≥120 m². 2 / g, with a particle size of 0.1-0.5mm.

5. The method according to claim 1, characterized in that, The viable cell ratio of the thermophilic Bacillus stearothermophilus, Bacillus amyloliquefaciens and Bacillus mucilaginosus is 3-5:1-2:1-2.

6. The method of claim 1, wherein, The effective viable count of the compound microbial agent is ≥2.0×10⁻⁶. 8 cfu / g.

7. The method of claim 1, wherein, It also includes adjusting the initial C / N ratio of the compost to 22-30:1 and the initial moisture content to 55%-65%.

8. The method according to claim 1, characterized in that, The duration of the high-temperature period in the high-temperature aerobic composting is ≥7 days.

9. The bio-organic fertilizer prepared by the method according to any one of claims 1 to 8.

10. The application of the bio-organic fertilizer according to claim 9 in the improvement of crop soil.

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