A method for preparing microbial protein by using biomass gasification gas

Abstract

The application discloses a method for preparing microbial protein by using biomass gasification gas, and the method comprises the following steps: (1) preparing biomass pyrolysis gas; (2) mixing and activating strains: taking the strains of Tagetes erecta yellow bacillus, Pseudomonas aeruginosa and Rhodococcus, and mixing the strains according to the volume ratio of Tagetes erecta yellow bacillus:Pseudomonas aeruginosa:Rhodococcus=2:1:0.5 or Tagetes erecta yellow bacillus:Pseudomonas aeruginosa=2:1, to obtain mixed strains; (3) seed culture; (4) two-phase co-production fermentation culture; and (5) product separation, to obtain microbial protein. The method is characterized in that tar and impurities are removed according to the characteristics of the pyrolysis gas, Tagetes erecta yellow bacillus is mixed with 1-2 suitable strains to construct a high-tolerance composite strain, and biomass gasification gas and tar are simultaneously converted into microbial protein. The research has important significance for large-scale synthesis of microbial protein, efficient utilization of biomass and efficient degradation of tar.

Description

Technical Field

[0001] This invention relates to a method for preparing microbial protein using biomass gasification gas, belonging to the fields of biomass utilization technology and microbial fermentation technology. Background Technology

[0002] Biomass, as a renewable energy source, is abundant. Through gasification technology, it can be converted into gasified gas containing components such as hydrogen, carbon dioxide, and carbon monoxide, achieving efficient utilization of biomass. Currently, biomass gasified gas is mostly used directly for power generation or heating, resulting in low added value. Furthermore, the gasification process generates impurities such as tar, sulfur, phenols, and thiophenes. The treatment of these impurities is complex and can inhibit microbial growth, limiting the application of gasified gas in the synthesis of high-value-added products.

[0003] Meanwhile, the global shortage of protein resources is becoming increasingly severe, and traditional protein production methods face constraints from land and water resources as well as carbon emission pressures. Microbial protein, with its advantages of high production efficiency and environmental sustainability, has become an important alternative to traditional proteins. The core of microbial protein production lies in screening highly efficient strains suitable for substrates. Existing strains mostly rely on pure substrates and have poor compatibility with complex gas mixtures such as biomass gasification gas and tar, resulting in low substrate utilization and insufficient protein synthesis efficiency. Furthermore, trace organic pollutants in the gasification gas further inhibit strain growth, making it difficult to achieve the synergistic resource utilization of tar and gasification gas.

[0004] Xanthobacter tagetidis is a Gram-negative aerobic rod-shaped bacterium with unique metabolic characteristics. It can grow using hydrogen and carbon dioxide and degrade thiophene-based organic pollutants. However, single strains have low tolerance to impurities such as tar, sulfur, and phenols, making it impossible to directly and efficiently produce protein using tar as a substrate. Therefore, how to efficiently produce microbial protein and degrade substances such as tar using Xanthobacter tagetidis is an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned limitations of existing technologies, this invention provides a method for preparing microbial protein using biomass gasification gas. This method uses biomass gasification products as raw materials, enhances impurity tolerance through strain formulation, and utilizes the properties of pyrolysis gas to remove tar and impurities. During strain cultivation, tar serves as a co-substrate, achieving efficient conversion and production of microbial protein.

[0006] This invention is achieved through the following technical solution: A method for preparing microbial protein using biomass gasification gas includes the following steps: (1) Preparation of biomass pyrolysis gas Biomass is pyrolyzed at 700–900℃ to obtain crude pyrolysis gas (gasification gas). The crude pyrolysis gas contains H2, CO2, CO, trace amounts of tar, as well as impurities such as sulfur, phenols, and thiophenes. The crude pyrolysis gas is cracked at 700–900℃, utilizing the high-temperature characteristics of the pyrolysis gas itself to decompose the tar into usable small-molecule organic compounds; then, dust removal, activated carbon adsorption desulfurization, and hydrogen supplementation are carried out sequentially to make the volume ratio of hydrogen to carbon dioxide (5.5–6.5):1, to obtain refined pyrolysis gas. The refined pyrolysis gas has a tar content ≤5 ppm and a thiophene content ≤5 ppm. (2) Strain compounding and activation Take strains of *Xanthomonas marigoldii*, *Pseudomonas aeruginosa*, and *Rhodococcus rubrum*, and mix them at a volume ratio of *Xanthomonas marigoldii*: *Pseudomonas aeruginosa*: *Rhodococcus rubrum* = 2:1:0.5 (tolerance to tar concentrations up to 20%, suitable for high impurity concentration scenarios) or *Xanthomonas marigoldii*: *Pseudomonas aeruginosa* = 2:1 (tolerance to tar concentrations up to 15%, suitable for low impurity concentration scenarios) to obtain a compound bacterial strain; inoculate the compound bacterial strain into an activation medium and culture it with shaking at 28–31℃ and 180–220 r / min for 18–24 h to obtain an activated compound bacterial strain; The activated culture medium consists of the following components: peptone 4.8–5.2 g / L, yeast extract 2.8–3.2 g / L, glucose 8–12 g / L, NaCl 4.8–5.2 g / L, with the balance being water, and a pH of 7.6–7.8. The complex organic nitrogen source can enhance the secretion of surfactants by Pseudomonas aeruginosa, promote the synthesis of degrading enzymes by Rhodococcus aureus, and improve the strain's ability to adapt to impurities. (3) Seed culture The activated compound bacterial strain was inoculated into the seed culture medium at an inoculation rate of 5%–10% (volume percentage), and cultured with shaking at 28–31℃ and 180–220 r / min for 24–36 h to obtain the seed liquid (OD). 600 The value is approximately 1.2 to 1.5). The seed culture medium comprises: NH4Cl 1.8–2.2 g / L, sodium acetate 7.5–8.5 g / L, KH2PO4 0.8–1.2 g / L, K2HPO4 0.8–1.2 g / L, MgSO4·7H2O 0.45–0.55 g / L, trace element solution 0.8–1.2 mL / L, with the remainder being water, and a pH of 7.6–7.8. The inorganic nitrogen source is adapted to the rapid proliferation requirements of the compound strains during the logarithmic growth phase, accumulating sufficient quantities of highly tolerant and active bacterial strains. (4) Two-phase co-production fermentation culture The seed culture was inoculated into the fermentation medium at an inoculation rate of 8% to 12% (volume percentage), and fermentation was carried out using a two-phase co-production fermentation process to obtain the fermentation broth. The fermentation medium consists of the following components: NH4NO3 2.8–3.2 g / L, KH2PO4 1.4–1.6 g / L, K2HPO4 1.4–1.6 g / L, MgSO4·7H2O 0.7–0.9 g / L, CaCl2 0.1 g / L, trace element solution 0.8–1.2 mL / L, with the remainder being water, and a pH of 7.6–7.8. The first stage is anaerobic fermentation, in which refined pyrolysis gas is introduced at a flow rate of 0.8–1.2 L / min, and cultured for 36–48 h at a temperature of 28–31℃, pH 7.6–7.8, pressure of 0.1–0.15 MPa, and stirring speed of 100–150 r / min. During this stage, *Xanthomonas marigoldii* in the compound strains grows autotrophically using hydrogen and carbon dioxide from the refined pyrolysis gas, while *Pseudomonas aeruginosa* and *Rhodococcus rubrum* initially degrade the tar. The second stage is aerobic fermentation, in which air is introduced at a rate of 1–2 L / min, and acetic acid is added at a final concentration of 5–8 g / L as a supplementary carbon source. The fermentation is continued for 24–36 h at a temperature of 28–31℃, a pH of 7.6–7.8, and a speed of 200–300 r / min. During this stage, Pseudomonas aeruginosa and Rhodococcus faecalis efficiently degrade tar and work synergistically with Chlorella vulgaris to rapidly synthesize microbial protein. (5) Product separation After fermentation, the fermentation broth was centrifuged (8000-10000 r / min, 10-15 min), and the bacterial precipitate was collected, washed, and dried to obtain microbial protein.

[0007] Furthermore, the biomass is selected from straw, sawdust, rice husks, etc.; the straw is selected from corn straw, wheat straw, sorghum straw, etc.

[0008] Furthermore, during pyrolysis, the vaporizing agent used is a mixture of air and water vapor, with a volume ratio of air to water vapor of 3:1.

[0009] Furthermore, in step (4), tar can be added to the fermentation medium, and the amount of tar added is 5% to 15% of the volume of the fermentation medium.

[0010] Preferably, the activated culture medium comprises: 5 g / L peptone, 3 g / L yeast extract, 10 g / L glucose, 5 g / L NaCl, with the remainder being water, and a pH of 7.6–7.8.

[0011] Preferably, the seed culture medium comprises: 2 g / L NH4Cl, 8 g / L sodium acetate, 1 g / L KH2PO4, 1 g / L K2HPO4, 0.5 g / L MgSO4·7H2O, 1 mL / L trace element solution, with the remainder being water, and a pH of 7.6–7.8.

[0012] Preferably, the fermentation medium comprises: NH4NO3 3 g / L, KH2PO4 1.5 g / L, K2HPO4 1.5 g / L, MgSO4·7H2O 0.8 g / L, CaCl2 0.1 g / L, trace element solution 1 mL / L, with the remainder being water, and a pH of 7.6–7.8.

[0013] Preferably, in step (4), the aeration rate is 1 L / min, and the culture is carried out at a temperature of 30℃, pH 7.7, and pressure of 0.12MPa for 45 h; the second stage is aerobic fermentation, in which air is introduced at an aeration rate of 1.5 L / min, and acetic acid with a final concentration of 6 g / L is added as a supplementary carbon source, and the culture is carried out at a temperature of 30℃, pH 7.7, and 250 r / min for another 30 h.

[0014] Furthermore, the composition of the trace element solution is as follows: FeSO4·7H2O 0.1 g / L, MnSO4·H2O 0.05 g / L, ZnSO4·7H2O 0.02 g / L, CuSO4·5H2O 0.01 g / L, CoCl2·6H2O 0.01 g / L, NaMoO4·2H2O 0.01 g / L. This formulation can specifically promote the synthesis of Rhodotorula rubra degrading enzymes and Pseudomonas aeruginosa surfactants in the compound strains, thus meeting the needs of synergistic metabolism.

[0015] This invention utilizes a composite strain of *Pseudomonas aeruginosa*, *Rhodococcus sp.*, and *Xanthomonas marigoldii* to construct a unique strain. *Pseudomonas aeruginosa* secretes biosurfactants to emulsify tar, improving substrate accessibility and exhibiting tolerance to high concentrations of phenolic impurities. *Rhodococcus sp.* possesses the ability to efficiently degrade polycyclic aromatic hydrocarbons (the core component of tar) and can synergistically remove heterocyclic impurities. The combination of these three strains significantly enhances tolerance to impurities. Furthermore, this invention innovatively utilizes the high-temperature properties of pyrolysis gases to assist in impurity removal, achieving a synergistic effect of "impurity removal-tolerance-protein production," thus overcoming existing technological bottlenecks.

[0016] This invention discloses a method for preparing microbial protein using biomass gasification gas. The method utilizes a composite strain of *Xanthomonas marigoldii*, *Pseudomonas aeruginosa*, and *Rhodococcus rubrum* as the fermentation substrate. The process involves pretreatment with biomass gasification gas (pyrolysis gas), strain blending and activation, seed culture, two-phase co-production fermentation, and product separation to complete microbial protein production. The composite strain exhibits extremely high tolerance and can adapt to complex systems containing tar and impurities. The gasification gas pretreatment leverages the high-temperature characteristics of the pyrolysis gas itself, supplemented by activated carbon adsorption, to simultaneously remove impurities such as tar, sulfur, and phenols, eliminating the need for additional purification reagents and achieving "self-purification + resource utilization" of the pyrolysis gas. Fermentation uses the purified gasification gas as the primary substrate and tar as a co-substrate, employing an anaerobic-aerobic two-phase process to fully utilize the metabolic advantages of the composite strain. This invention enables the synergistic high-value conversion of biomass gasification gas and tar, achieving a substrate comprehensive utilization rate of over 88% and a microbial protein content of over 72%. It simultaneously solves the problems of low added value in gasification gas utilization, tar pollution, and high substrate costs in microbial protein production, thus combining environmental and economic benefits.

[0017] The method for preparing microbial protein using biomass gasification gas of the present invention has the following significant beneficial effects: (1) Dual innovation synergy, significant technical barriers: The first-of-its-kind synergistic technology of "pyrolysis gas self-purification and impurity removal + compound strain high tolerance" simplifies the impurity removal process by utilizing the high temperature characteristics of pyrolysis gas itself, and the compound strain specifically solves the problem of impurity inhibition. At the same time, it realizes the synergistic conversion of gasification gas and tar as dual substrates, breaking through the limitation of single substrate in traditional processes. The technology is innovative and practical.

[0018] (2) Excellent strain tolerance and yield: The combination of 1 to 2 strains can be adapted to different impurity concentration scenarios as needed, with a maximum tolerance concentration of tar up to 20%, effectively eliminating the inhibitory effects of sulfur, phenols, and thiophene impurities; combined with a two-phase fermentation process, the microbial protein content exceeds 72%, per 3000 m 3 Refined pyrolysis gas + 15 kg of tar can produce 1 ton of microbial protein, with a substrate utilization rate of over 88% and a yield increase of over 40% compared to traditional processes.

[0019] (3) Substrate resource utilization and cost control: The pyrolysis gas is self-purified and impurities are removed without the need for additional impurity removal reagents and equipment, reducing the pretreatment cost by 30%; using industrial waste tar as a co-substrate, combined with biomass gasification gas, the "waste-high value protein" conversion is realized, and the overall process cost is reduced by more than 40%, which is suitable for large-scale industrial production.

[0020] (4) Dual benefits of environmental protection and economy: Simultaneously solves the two major industry pain points of low added value of biomass gasification and tar waste pollution, realizing the triple value of "solid waste disposal + gas resource utilization + protein production"; the fermentation process has no secondary pollution, and carbon emissions are reduced by more than 50% compared with traditional protein production, which is in line with environmental protection industry policies.

[0021] In summary, the method for preparing microbial protein using biomass gasification gas of this invention utilizes the characteristics of pyrolysis gas to remove tar and impurities. It constructs a highly tolerant composite strain by combining *Xanthomonas marigoldii* with 1-2 suitable bacterial strains, achieving the co-conversion of biomass gasification gas and tar into microbial protein. This method balances production efficiency, cost control, and environmental value, overcoming the shortcomings of existing technologies such as low added value from biomass gasification gas utilization, complex tar and impurity treatment, insufficient tolerance of microbial protein-producing strains to impurities, and inability to efficiently co-produce protein using tar as a substrate. The research of this invention is of great significance for the large-scale synthesis of microbial protein, the efficient utilization of biomass, and the efficient degradation of tar. Detailed Implementation

[0022] The present invention will be further described below with reference to embodiments. However, the scope of the present invention is not limited to the following embodiments. Those skilled in the art will understand that various changes and modifications can be made to the present invention without departing from the spirit and scope thereof.

[0023] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0024] The *Xanthomonas marigoldii* strain of this invention is a publicly disclosed type strain in the prior art and is routinely available for purchase. This strain has been deposited by others, and its accession number at the China General Microbiological Culture Collection Center is CGMCC 1.3797.

[0025] The *Pseudomonas aeruginosa* strain involved in this invention is a type strain already disclosed in the prior art and is routinely available for purchase. This strain has been deposited by others, and its accession number at the China General Microbiological Culture Collection Center is CGMCC 1.1785.

[0026] The Rhodococcus rubescens strain involved in this invention is a strain already disclosed in the prior art and can be routinely purchased. This strain has been deposited by others, and its accession number at the China General Microbiological Culture Collection Center is CGMCC 4.1037.

[0027] Example 1 Construction and tolerance test of compound strains Take the strains of *Xanthomonas amaranthii*, *Pseudomonas aeruginosa*, and *Rhodococcus rubrum*, and mix them in the following volume ratio: *Xanthomonas amaranthii*: *Pseudomonas aeruginosa*: *Rhodococcus rubrum* = 2:1:0.5 to obtain the mixed strain.

[0028] Tolerance test: A single *Xanthomonas marigoldii* group and a compound strain group were set up and cultured at 30℃ for 72 hours in a simulated gasification gas environment containing 15% tar and 30 ppm sulfur (inoculum size 5%, volume ratio). The growth of the strains and the tar degradation rate were then detected. Results showed that the OD of the single *Xanthomonas marigoldii* group was... 600 The value was 0.68, while the OD of the compound strain was... 600 The value reached 1.42, which was 108.8% higher than that of the single strain; the tar degradation rate of the single strain of *Xanthomonas marigoldii* was 38.5%, while the tar degradation rate of the compound strain reached 90%, which indicates that the compound strain has high tolerance to tar.

[0029] Example 2: Production of microbial protein through co-conversion of biomass gasification gas and tar. The steps are as follows: (1) Preparation of biomass pyrolysis gas Biomass corn stalks are placed in a fixed-bed gasifier and pyrolyzed at 800℃. The gasifying agent used is a mixture of air and water vapor with a volume ratio of 3:1, yielding crude pyrolysis gas (gasification gas). The main components of the crude pyrolysis gas (by volume percentage) are: 35% hydrogen, 15% carbon dioxide, 20% carbon monoxide, and 30% nitrogen. It also contains trace amounts of tar, as well as impurities such as sulfur, phenols, and thiophenes.

[0030] Then, the crude pyrolysis gas is cracked at 800℃, utilizing the high-temperature properties of the pyrolysis gas itself to break down the tar into usable small-molecule organic compounds. Next, it undergoes sequential dust removal (using a bag filter), activated carbon adsorption desulfurization (using an activated carbon adsorption tower), and hydrogen supplementation to achieve a hydrogen-to-carbon dioxide volume ratio of 6:1, yielding refined pyrolysis gas with a dust content of 5 mg / m³. 3 The following values ​​are present: sulfur content below 28 ppm, tar content below 4 ppm, and thiophene content below 4 ppm.

[0031] (2) Strain compounding and activation Strains of *Xanthomonas amaranthii*, *Pseudomonas aeruginosa*, and *Rhodococcus rubrum* were mixed at a volume ratio of *Xanthomonas amaranthii*: *Pseudomonas aeruginosa*: *Rhodococcus rubrum* = 2:1:0.5 to obtain a compound bacterial strain. The compound bacterial strain was inoculated into 50 ml of activation medium and cultured with shaking at 30℃ and 200 r / min for 20 h to obtain an activated compound bacterial strain. At this time, the surfactant secretion of *Pseudomonas aeruginosa* reached 0.8 g / L, and the degrading enzyme activity of *Rhodococcus rubrum* reached 120 U / mL.

[0032] The activated culture medium consists of: 5 g / L peptone, 3 g / L yeast extract, 10 g / L glucose, 5 g / L NaCl, with the remainder being water, and a pH of 7.7. The complex organic nitrogen source can enhance the secretion of surfactants by Pseudomonas aeruginosa, promote the synthesis of degrading enzymes by Rhodococcus aureus, and improve the strain's ability to adapt to impurities.

[0033] (3) Seed culture The activated compound bacterial strain was inoculated into the seed culture medium at an inoculation rate of 8% (volume percentage), and cultured with shaking at 30℃ and 200 r / min for 30 h to obtain the seed liquid. OD 600 The value is 1.35; The seed culture medium consists of the following components: NH4Cl 2 g / L, sodium acetate 8 g / L, KH2PO4 1 g / L, K2HPO4 1 g / L, MgSO4·7H2O 0.5 g / L, trace element solution 1 mL / L, with the remainder being water, and a pH of 7.6–7.7. The inorganic nitrogen source is adapted to the rapid proliferation requirements of the compound strains during the logarithmic growth phase, accumulating sufficient quantities of highly tolerant and active bacterial strains.

[0034] The trace element solution is composed of: FeSO4·7H2O 0.1 g / L, MnSO4·H2O 0.05 g / L, ZnSO4·7H2O 0.02 g / L, CuSO4·5H2O 0.01 g / L, CoCl2·6H2O 0.01 g / L, and NaMoO4·2H2O 0.01 g / L. This formulation can specifically promote the synthesis of Rhodococcus degrading enzymes and Pseudomonas aeruginosa surfactants in the compound strains, thus meeting the needs of synergistic metabolism.

[0035] (4) Two-phase co-production fermentation culture The seed culture was inoculated into a 50 L fermenter containing 30 L of fermentation medium at an inoculation rate of 10% (volume percentage), and tar was added. The fermentation culture was carried out using a two-phase co-production fermentation process to obtain the fermentation broth. The fermentation medium consists of the following components: NH4NO3 3 g / L, KH2PO4 1.5 g / L, K2HPO4 1.5 g / L, MgSO4·7H2O 0.8 g / L, CaCl2 0.1 g / L, trace element solution 1 mL / L, with the remainder being water, pH 7.7; the amount of tar added is 15% (4.5 kg) of the fermentation medium volume. The first stage is anaerobic fermentation, in which refined pyrolysis gas is introduced at a flow rate of 1.0 L / min, and cultured at a temperature of 30℃, pH 7.7, pressure of 0.12 MPa, and stirring speed of 120 r / min for 42 h. In this stage, the compound strain of *Xanthomonas marigoldii* utilizes hydrogen and carbon dioxide in the refined pyrolysis gas for autotrophic growth, while *Pseudomonas aeruginosa* and *Rhodococcus rubrum* initially degrade the tar. The second stage is aerobic fermentation, in which air is introduced at a rate of 1.5 L / min, and acetic acid with a final concentration of 6 g / L is added as a supplementary carbon source. The fermentation is continued for 30 h at a temperature of 30℃, pH 7.7, and 250 r / min. During this stage, Pseudomonas aeruginosa and Rhodococcus faecalis efficiently degrade tar and work synergistically with Chlorella vulgaris to rapidly synthesize microbial protein.

[0036] (5) Product separation After fermentation, the fermentation broth was centrifuged (9000 r / min, 12 min), and the bacterial precipitate was collected. It was washed three times with sterile physiological saline and then vacuum dried at 60℃ to constant weight to obtain microbial protein.

[0037] Meanwhile, a control group was set up: the bacterial strain was a single strain of *Brachys macrantha*, and crude pyrolysis gas was introduced during the culture.

[0038] (6) Product testing The Kjeldahl method was used to determine the protein content of microbial proteins, while gas chromatography was used to detect substrate consumption.

[0039] Result: Consumption of refined pyrolysis gas 300 m 3 4.5 kg of tar yielded 12 kg of microbial protein with a protein content of 76.2%, a hydrogen and carbon dioxide conversion rate of 86.7%, and a tar degradation rate of 90% (polycyclic aromatic hydrocarbon degradation rate of 92%), meeting the standards for high-quality microbial protein. The control group (single *Xanthomonas marigoldii* + no pyrolysis gas for impurity removal) yielded only 4.2 kg of protein with a protein content of 64.5%. This indicates that the compound strains and synergistic process of the present invention have significant advantages.

[0040] Example 3: The impact of different compounding schemes on production results Three groups of experiments were set up: Group 1 (single *Xanthomonas marigoldii*), Group 2 (combined strain, *Xanthomonas marigoldii*: *Pseudomonas aeruginosa* = 2:1), and Group 3 (combined strain, *Xanthomonas marigoldii*: *Pseudomonas aeruginosa*: *Rhodococcus rubrum* = 2:1:0.5), with other conditions the same as in Example 2.

[0041] The results showed that the microbial protein yield in group 3 reached 0.33 kg / m³. 3The pyrolysis gas content was increased by 138.1% and 19.6% compared to Group 1 and Group 2, respectively, with a tar degradation rate of 90% and the best impurity tolerance stability. Group 2 showed an improvement of 107.0% compared to Group 1, indicating that both compounding schemes of the present invention have advantages, and the scheme of Group 2 is more suitable for high-impurity scenarios and has better results.

[0042] The above embodiments are provided to those skilled in the art to fully disclose and describe how the claimed implementations can be carried out and used, and are not intended to limit the scope of the disclosure herein. Modifications that will be obvious to those skilled in the art will be within the scope of the appended claims.

Claims

1. A method for preparing microbial protein using biomass gasification gas, characterized in that, Includes the following steps: (1) Preparation of biomass pyrolysis gas Biomass is pyrolyzed at 700–900℃ to obtain crude pyrolysis gas; the crude pyrolysis gas is then cracked at 700–900℃, and then subjected to dust removal, activated carbon adsorption desulfurization, and hydrogen replenishment to make the volume ratio of hydrogen to carbon dioxide (5.5–6.5):1, to obtain refined pyrolysis gas. (2) Strain compounding and activation Take strains of *Xanthomonas marigoldii*, *Pseudomonas aeruginosa*, and *Rhodococcus rubrum*, and mix them at a volume ratio of *Xanthomonas marigoldii*: *Pseudomonas aeruginosa*: *Rhodococcus rubrum* = 2:1:0.5 or *Xanthomonas marigoldii*: *Pseudomonas aeruginosa* = 2:1 to obtain a compound bacterial strain; inoculate the compound bacterial strain into an activation medium and culture it with shaking at 28–31℃ and 180–220 r / min for 18–24 h to obtain an activated compound bacterial strain; The activated culture medium consists of the following components: peptone 4.8–5.2 g / L, yeast extract 2.8–3.2 g / L, glucose 8–12 g / L, NaCl 4.8–5.2 g / L, with the remainder being water, and a pH of 7.6–7.

8. (3) Seed culture The activated compound bacterial strain was inoculated into the seed culture medium at an inoculation rate of 5% to 10%, and cultured with shaking at 28 to 31°C and 180 to 220 r / min for 24 to 36 h to obtain the seed liquid; The seed culture medium consists of the following components: NH4Cl 1.8–2.2 g / L, sodium acetate 7.5–8.5 g / L, KH2PO4 0.8–1.2 g / L, K2HPO4 0.8–1.2 g / L, MgSO4·7H2O 0.45–0.55 g / L, trace element solution 0.8–1.2 mL / L, with the remainder being water, and a pH of 7.6–7.

8. (4) Two-phase co-production fermentation culture The seed culture was inoculated into the fermentation medium at an inoculation rate of 8% to 12%, and tar was added. The fermentation culture was carried out using a two-phase co-production fermentation process to obtain the fermentation broth. The fermentation medium comprises the following components: NH4NO3 2.8–3.2 g / L, KH2PO4 1.4–1.6 g / L, K2HPO4 1.4–1.6 g / L, MgSO4·7H2O 0.7–0.9 g / L, CaCl2 0.1 g / L, trace element solution 0.8–1.2 mL / L, with the remainder being water; pH 7.6–7.8; and tar is added at 5%–15% of the fermentation medium volume. The first stage is anaerobic fermentation, in which refined pyrolysis gas is introduced at a flow rate of 0.8–1.2 L / min, and cultured for 36–48 h at a temperature of 28–31℃, pH of 7.6–7.8, pressure of 0.1–0.15 MPa, and stirring speed of 100–150 r / min. The second stage is aerobic fermentation, in which air is introduced at a rate of 1-2 L / min, and acetic acid at a final concentration of 5-8 g / L is added as a supplementary carbon source. The fermentation is continued for 24-36 h at a temperature of 28-31℃, pH 7.6-7.8, and a speed of 200-300 r / min. (5) Product separation After fermentation, the fermentation broth is centrifuged, the bacterial precipitate is collected, washed, and dried to obtain microbial protein.

2. The method for preparing microbial protein using biomass gasification gas according to claim 1, characterized in that: The biomass is selected from straw, sawdust, and / or rice husks.

3. The method for preparing microbial protein using biomass gasification gas according to claim 2, characterized in that: The straw is selected from corn straw, wheat straw, and / or sorghum straw.

4. The method for preparing microbial protein using biomass gasification gas according to claim 1, characterized in that: During pyrolysis, the vaporizing agent used is a mixture of air and water vapor, with a volume ratio of air to water vapor of 3:

1.

5. The method for preparing microbial protein using biomass gasification gas according to claim 1, characterized in that: In step (4), tar is added to the fermentation medium, and the amount of tar added is 5% to 15% of the volume of the fermentation medium.

6. The method for preparing microbial protein using biomass gasification gas according to claim 1, characterized in that, The activated culture medium consists of the following components: 5 g / L peptone, 3 g / L yeast extract, 10 g / L glucose, 5 g / L NaCl, with the remainder being water, and a pH of 7.6–7.

8.

7. The method for preparing microbial protein using biomass gasification gas according to claim 1, characterized in that, The seed culture medium consists of the following components: NH4Cl 2 g / L, sodium acetate 8 g / L, KH2PO4 1 g / L, K2HPO4 1 g / L, MgSO4·7H2O 0.5 g / L, trace element solution 1 mL / L, with the remainder being water, and a pH of 7.6–7.

8.

8. The method for preparing microbial protein using biomass gasification gas according to claim 1, characterized in that, The fermentation medium consists of the following components: NH4NO3 3 g / L, KH2PO4 1.5 g / L, K2HPO4 1.5 g / L, MgSO4·7H2O 0.8 g / L, CaCl2 0.1 g / L, trace element solution 1 mL / L, with the remainder being water, and a pH of 7.6–7.

8.

9. The method for preparing microbial protein using biomass gasification gas according to claim 1, characterized in that, In step (4), the aeration rate is 1 L / min, and the culture is carried out at a temperature of 30℃, pH 7.7, and pressure of 0.12MPa for 45 h. The second stage is aerobic fermentation, in which air is introduced at an aeration rate of 1.5 L / min, and acetic acid with a final concentration of 6 g / L is added as a supplementary carbon source. The culture is carried out at a temperature of 30℃, pH 7.7, and 250 r / min for another 30 h.

10. The method for preparing microbial protein using biomass gasification gas according to claim 1, characterized in that, The trace element solution has the following composition: FeSO4·7H2O 0.1 g / L, MnSO4·H2O 0.05 g / L, ZnSO4·7H2O 0.02 g / L, CuSO4·5H2O 0.01 g / L, CoCl2·6H2O 0.01 g / L, and NaMoO4·2H2O 0.01 g / L.