Method for co-producing single-cell protein and microbial oil by using lignocellulose and cheap inorganic nitrogen source

Abstract

The invention provides a method for joint production of single-cell protein and microbial oil. The method comprises the following steps: (1) pretreatment and detoxification treatment of a lignocellulose raw material; (2) carrying out simultaneous saccharification and co-fermentation to produce single-cell protein and microbial oil; (3) carrying out solid-liquid separation on the fermentation liquor to obtain a product and nitrogen-containing fermentation wastewater; and (4) recovering or not recovering the wastewater, and providing a nitrogen source for a fermentation strain when the wastewater is recycled. According to the method, the characteristic of high ammonia nitrogen content in the fermentation wastewater is utilized, the emission of the ammonia nitrogen wastewater is reduced by recycling the fermentation wastewater, the use of a fresh nitrogen source is reduced, and the production cost is controlled. The fermentation strain has good tolerance to the composition of the fermentation wastewater, and meanwhile, by adopting a high-solid-content fermentation mode, the conversion efficiency is improved, and the use amount of enzyme is reduced. The fermentation indexes of the fermentation wastewater for joint production of single-cell protein and microbial oil are stable. The fermentation wastewater can be recycled for multiple times, so that the method has remarkable economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of microbial application, and in particular to a method for producing single-cell protein and microbial oil by recycling inorganic nitrogen source and lignocellulose raw material through synchronous saccharification and co-fermentation. Background Art

[0002] The rapid growth of population has led to a relative scarcity of natural resources, and the research on new sustainable food sources has become a pressing issue for the world. Proteins and oils are important and indispensable components of human and animal nutrition. Single-cell proteins and microbial oils produced by yeast, bacteria, fungi or algae provide an alternative source of animal / plant proteins and oils. Yeast strains producing single-cell proteins have the advantages of high protein content, fast growth rate, good flocculability, non-pathogenicity, and rich in vitamins and trace nutrients. Among them, oil yeast has become the preferred cell factory for the co-production of single-cell proteins and microbial oils due to its good polysaccharide metabolism and intracellular product accumulation ability.

[0003] In the production process of single-cell proteins and oils, the substrate cost accounts for a high proportion. The selection of cheap carbon and nitrogen sources is an important step in the production of single-cell proteins and oils for practical applications. Grain starch carbon sources and organic nitrogen sources are generally not considered reasonable choices due to their high costs, and the route of producing single-cell proteins from hydrocarbon compounds from petroleum and natural gas has been abandoned because they do not have the characteristics of carbon neutrality. Lignocellulosic biomass, which is widely available and low-cost, is the most potential carbon source raw material for the production of single-cell proteins and oils, and a reasonable nitrogen source should come from cheap inorganic ammonia nitrogen compounds.

[0004] Zheng Longyu et al. from Huazhong Agricultural University proposed a method for the joint production of lignocellulose-derived protein and oil using insects (CN106819662A), but this method has a long production cycle and is subject to environmental constraints. Single-cell protein and oil produced using microorganisms have many advantages, such as short production time, high content, rich content of nucleic acids, vitamins and minerals, and rich in certain essential amino acids, such as lysine and methionine. Wu Hong et al. from South China University of Technology proposed a method for the simultaneous production of single-cell protein and oil using oleaginous yeast (CN10675440), but this method must use expensive yeast extract and peptone as nitrogen sources, and cannot achieve the simultaneous saccharification and co-fermentation production of high-index lignocellulose raw materials. Shanghai Jitailai Biotechnology Co., Ltd. also proposed a method for producing single-cell protein and oil using microbial fermentation (CN107557309A), but still requires expensive yeast paste as a nitrogen source supplement. In addition, in the process of fermenting single-cell protein and oil using lignocellulose as substrate, the generation of a large amount of high-ammonia nitrogen wastewater is likely to greatly increase the nitrogen source cost and downstream wastewater treatment cost, but there is currently no report on its recycling. Summary of the invention

[0005] Based on the above shortcomings, the present invention provides a method for the combined production of single cell protein and microbial lipids. The method comprises the following steps:

[0006] (1) Pretreatment and detoxification of lignocellulosic raw materials;

[0007] (2) Synchronous saccharification and co-fermentation to produce single-cell protein and microbial lipids to obtain fermentation broth;

[0008] (3) after solid-liquid separation of the fermentation broth, a cell product containing single-cell protein and microbial lipids and nitrogen-containing fermentation wastewater are obtained;

[0009] (4) The nitrogen-containing fermentation wastewater is recycled or not recycled, and when recycled, it is used to provide a nitrogen source for the fermentation strain.

[0010] In one embodiment, the lignocellulosic raw material in step (1) includes, but is not limited to, one or a combination of two or more of wheat straw, corn straw, cotton straw, rice stalks, straw, bagasse, reeds, and forest waste, and is further corn straw or wheat straw.

[0011] The method for pretreating the lignocellulose raw material in the present invention is not particularly limited and may be a conventional method in the art, including at least one of acid pretreatment, alkali pretreatment, steam explosion pretreatment and organic solvent pretreatment, further comprising acid pretreatment.

[0012] In one embodiment, the pretreatment in step (1) is an acid pretreatment. The pretreatment system is a high solid content system. Further, the solid-liquid ratio of the pretreatment system is (1-5): 1 g / mL, further (1-3): 1 g / mL, the pretreatment temperature is 100-220°C, further 150-200°C, and the pretreatment time is 3-20 min. Sulfuric acid is preferably used for acid pretreatment.

[0013] In one embodiment, H 2 SO 4 The content is 2-6kg.

[0014] In one embodiment, the pretreated lignocellulosic feedstock may or may not be pre-hydrolyzed before being detoxified.

[0015] In one embodiment, the pretreated lignocellulosic raw material is subjected to a prehydrolysis treatment before the detoxification treatment to obtain a hydrolyzate, and the hydrolyzate is used for the detoxification treatment to obtain a detoxified hydrolyzate. The detoxified hydrolyzate is used for simultaneous saccharification and co-fermentation.

[0016] In one embodiment, the method comprises the following steps:

[0017] (1) Pretreatment, prehydrolysis and detoxification of lignocellulosic raw materials;

[0018] (2) Synchronous saccharification and co-fermentation to produce single-cell protein and microbial lipids to obtain fermentation broth;

[0019] (3) after solid-liquid separation of the fermentation broth, a cell product containing single-cell protein and microbial lipids and nitrogen-containing fermentation wastewater are obtained;

[0020] (4) The nitrogen-containing fermentation wastewater is recycled or not recycled, and when recycled, it is used to provide a nitrogen source for the fermentation strain.

[0021] The amount of cellulase used in the pre-hydrolysis treatment is 1-10 mg protein / g substrate. The substrate is a pre-treated lignocellulose raw material. The solid content of the pre-hydrolysis treatment system is 10wt%-40wt%, the pre-hydrolysis treatment time is 5-48h, and the pH value of the pre-hydrolysis treatment is 4.7-5.6. The hydrolyzate is obtained by the pre-hydrolysis treatment, and the hydrolyzate is used for biological detoxification treatment.

[0022] In one embodiment, the detoxification treatment in step (1) is biological detoxification, and the detoxification strain used is a strain that has the ability to preferentially utilize acetic acid and then utilize glucose. Further, the detoxification strain includes resin cladosporium, filamentous white rot fungi, Pseudomonas acinetobacter or Paecilomyces variotii. Further, the detoxification strain is Paecilomyces variotii FN89 (deposit number is CGMCC No.17665, deposit date is May 8, 2019, deposit address is China National Committee for the Administration of Microbiological Culture Collection, General Microbiological Center, see patent CN201911039157.4). Paecilomyces variotii FN89 is a strain that has the ability to preferentially utilize acetic acid, an inhibitor produced during pretreatment that has an inhibitory effect on subsequent fermentation, and then reuse glucose.

[0023] The temperature of the detoxification treatment is 25-45°C, further 35-45°C, the ventilation volume is 0.2-4vvm, and the time is 5-48h. The inoculation amount of the detoxified strain seed solution is 5%-20% (w / w). The ratio of the seed dry weight (g) of the detoxified strain seed solution to the seed solution volume (L) is 2-5g / L.

[0024] The detoxification process can also be stirred, with a stirring speed of 400-1000rpm.

[0025] In one embodiment, in the simultaneous saccharification and co-fermentation in step (2), the nitrogen source is provided by any one or both of inorganic ammonia nitrogen compounds and nitrogen-containing wastewater.

[0026] Furthermore, inorganic ammonia nitrogen compounds include but are not limited to any one or a combination of two or more of ammonium sulfate, ammonium chloride, and ammonium nitrate. The nitrogen-containing wastewater is, for example, the nitrogen-containing fermentation wastewater of step (4).

[0027] In one embodiment, the nitrogen content of the nitrogen-containing fermentation wastewater is 0.8-3 g / L.

[0028] In one embodiment, the nitrogen-containing fermentation wastewater has an ammonium sulfate content of 3-10 g / L.

[0029] In one embodiment, the nitrogen-containing fermentation wastewater of step (4) is recycled for use in any one or more of the pre-hydrolysis treatment step, the biological detoxification step, and the simultaneous saccharification and co-fermentation step.

[0030] Those skilled in the art will understand that since the lignocellulosic raw material is subjected to pretreatment, prehydrolysis and detoxification before simultaneous saccharification and co-fermentation, the nitrogen-containing fermentation wastewater of step (4) can be recycled for simultaneous saccharification and co-fermentation, or can be recycled for the prehydrolysis and detoxification steps before simultaneous saccharification and co-fermentation. The recycled fermentation wastewater will flow into the simultaneous saccharification and co-fermentation system to provide part of the nitrogen source for the fermentation strain.

[0031] In a preferred embodiment, the nitrogen-containing fermentation wastewater is recycled and used in the simultaneous saccharification and co-fermentation of step (2).

[0032] In one embodiment, the nitrogen-containing fermentation wastewater is mixed with the detoxified hydrolyzate obtained by detoxification treatment for simultaneous saccharification and co-fermentation.

[0033] In one embodiment, in the simultaneous saccharification and co-fermentation system, the carbon-nitrogen ratio of the simultaneous saccharification and co-fermentation system is adjusted before, simultaneously with, or after inoculation of the fermentation strain seed solution.

[0034] In one embodiment, the carbon-nitrogen ratio of the simultaneous saccharification and co-fermentation system in step (2) is (3-30):1, further (7.5-20):1, further 9.4:1 or 18.8:1.

[0035] In one embodiment, the simultaneous saccharification and co-fermentation system in step (2) includes (NH 4 ) 2 SO 4 .

[0036] In one embodiment, in the simultaneous saccharification and co-fermentation system in step (2), (NH 4 ) 2 SO 4 The content is 7-30g / L.

[0037] In one embodiment, the carbon-nitrogen ratio in the simultaneous saccharification and co-fermentation system is controlled by supplementing a nitrogen source to the simultaneous saccharification and co-fermentation system. The supplemented nitrogen source is, for example, the inorganic ammonia nitrogen compound defined above, or nitrogen-containing wastewater.

[0038] In one embodiment, the simultaneous saccharification and co-fermentation system in step (2) contains nutrient salts.

[0039] In one embodiment, the nutrient salt includes KH 2 PO 4 MgSO 4 7H 2 Any one or both of O.

[0040] In one embodiment, in the simultaneous saccharification and co-fermentation system, the nutrient salt content in the simultaneous saccharification and co-fermentation system is adjusted before, simultaneously with, or after inoculating the fermentation strain seed solution.

[0041] In one embodiment, the simultaneous saccharification and co-fermentation system in step (2) includes 0.1-10 g / L KH 2 PO 4 and 0.5-5g / L MgSO 4 7H 2 O, further comprising 0.1-5 g / L KH 2 PO 4 and 0.5-5g / L MgSO 4 7H 2 O.

[0042] In one embodiment, the nutrient salt content in the simultaneous saccharification and co-fermentation system is controlled by adding the nutrient salt to the simultaneous saccharification and co-fermentation system.

[0043] In one embodiment, the simultaneous saccharification and co-fermentation system is a high solid content system. Preferably, the solid content of the simultaneous saccharification and co-fermentation system is 10%-35% (w / w).

[0044] In one embodiment, in step (2), simultaneous saccharification and co-fermentation are performed, and the fermentation strain is Trichosporon dermatophyte. Suitable Trichosporon dermatophyte needs to satisfy an average cell volume of 10 -17 m 3 The fermentation strain has the ability to metabolize glucose, xylose, arabinose, mannose and galactose from lignocellulose at approximately the same metabolic rate. The "approximately the same metabolic rate" refers to the difference (v, in g / L / h) between the metabolic rates (v) of the fermentation strain for any two of the sugars glucose, xylose, arabinose, mannose and galactose. 1 -v 2 ) accounts for v 1 and v2 The percentage does not exceed 20%.

[0045] Preferably, the fermentation strain is MP11 (deposit number is CGMCC No. 20481, deposit date is August 5, 2020, deposit address is General Microbiology Center of China Microbiological Culture Collection Administration). MP11 is an engineered bacterium of Trichosporon cutaneum, and the average cell volume of MP11 is 9.7×10 -17 m 3 , with significantly expanded intracellular space, which is conducive to product accumulation. At the same time, the strain also has the ability to metabolize glucose, xylose, arabinose, mannose and galactose from lignocellulose at approximately the same metabolic rate. The difference (v, in g / L / h) in the metabolic rate of MP11 for any two sugars among glucose, xylose, arabinose, mannose and galactose is 1 -v 2 ) accounts for v 1 and v 2 The percentage does not exceed 20%.

[0046] In one embodiment, in step (2) of simultaneous saccharification and co-fermentation, the inoculation amount of the fermentation strain seed solution is 5%-20% (w / w). The ratio of the seed dry weight (g) of the fermentation strain seed solution to the seed solution volume (L) is 2-5g / L.

[0047] In one embodiment, the simultaneous saccharification and co-fermentation in step (2) is carried out at a temperature of 28-35° C., an aeration rate of 0.5-3 vvm, a pH value of 4.0-6.5, and a fermentation time of 32-128 h.

[0048] During the simultaneous saccharification and co-fermentation process, stirring may also be performed at a rotation speed of 200-800 rpm, and further 300-700 rpm.

[0049] In one embodiment, in step (3), the fermentation broth is subjected to solid-liquid separation, such as centrifugal separation, to obtain a cell product containing single-cell protein and microbial lipids and nitrogen-containing fermentation wastewater.

[0050] In one embodiment, the liquid phase component obtained by solid-liquid separation of the fermentation liquid in step (3) is fermentation wastewater, which contains a large amount of residual inorganic ammonia nitrogen compounds and can be directly recycled or reused after decolorization, and / or oxidation treatment, and / or detoxification treatment.

[0051] By recovering and utilizing the nitrogen-containing fermentation wastewater in steps (3) and (4), a fermentation wastewater recycling process can be repeated at least five times.

[0052] The fermentation index of the fermentation wastewater used for simultaneous saccharification and co-fermentation is stable, and the nitrogen conversion rate from inorganic ammonia nitrogen compounds to single-cell protein is above 70%.

[0053] This application has the following beneficial technical effects:

[0054] The ammonia nitrogen content in fermentation wastewater is high. The recycling of fermentation wastewater reduces the discharge of ammonia nitrogen wastewater, reduces the use of fresh nitrogen sources, and controls production costs. The fermentation wastewater is recycled to provide part of the nitrogen source. The fermentation strain has good tolerance to the composition of the fermentation wastewater. At the same time, the high solid content fermentation method is used to improve the conversion efficiency and reduce the amount of cellulase. The fermentation indicators of fermentation wastewater used for the combined production of single-cell protein and microbial oil are stable. Fermentation wastewater can be recycled many times. The present application utilizes renewable lignocellulosic raw materials and cheap inorganic nitrogen sources, and uses engineered microorganisms to convert them into high-value-added single-cell proteins and microbial oils under the premise of strictly limiting the discharge of ammonia nitrogen wastewater, which has significant economic benefits. DETAILED DESCRIPTION

[0055] In order to enable those skilled in the art to more intuitively understand the technical solutions in the present application, the present invention is described below through specific implementation plans. What is described is only a part of the examples of the present invention, not all the examples and is not enough to limit the present invention.

[0056] Single cell protein yield: The protein content was determined by Kjeldahl method. Single cell protein yield (unit: g / L) = protein weight (g) / fermentation broth volume (L).

[0057] Oil yield: Extract the oil in the cells with methanol-chloroform solution, place the extract in a pre-weighed rotary evaporation bottle, remove the chloroform by rotary evaporation in a water bath at 80°C, and then dry at 65°C to remove the residual water, then weigh and subtract the weight of the rotary evaporation bottle to get the oil weight. Oil yield (unit g / L) = oil weight (g) / fermentation liquid volume (L).

[0058] Conversion rate of inorganic ammonia nitrogen fixed to single-cell protein: Conversion rate of inorganic ammonia nitrogen fixed to single-cell protein = mass of N in single-cell protein / mass of N in added inorganic ammonia nitrogen*100%.

[0059] MP11 is an engineered bacterium of Trichosporon cutaneum, with a deposit number of CGMCC20481, a deposit date of August 5, 2020, and a deposit address of the General Microbiology Center of China National Microbiological Culture Collection Administration.

[0060] Example 1 Co-production of single cell protein and microbial oil using corn stalks and ammonium sulfate as substrates

[0061] S1. Acid pretreatment: The corn stalks were acid pretreated with a solid-liquid ratio of 2:1, a temperature of 175°C, a time of 5 min, and H2O2 in the mixed system of 100 kg corn stalks and sulfuric acid solution. 2 SO 4 The content is 4kg.

[0062] S2. The pretreated corn stover was used as a substrate for prehydrolysis. The commercial cellulase used was Cellic CTec2.0. The enzyme dosage was 4 mg protein / g substrate. The solid content of the prehydrolysis treatment system was 30% (w / w). The time was 12 h. The pH value was 5.1 to obtain a hydrolyzate.

[0063] S3. The hydrolyzate was subjected to biological detoxification, and the seed solution of the detoxified strain Paecilomyces variotii FN89 was inoculated at a 10% (w / w) inoculation amount, and the ratio of the seed dry weight of the seed solution to the volume of the seed solution was 3.4 g / L. The detoxification conditions were 37° C., the stirring speed was 750 rpm, the ventilation volume was 1 vvm, and the time was 13 h to obtain a detoxified hydrolyzate.

[0064] S4. Simultaneous saccharification and co-fermentation: MP11 seed solution was inoculated into the detoxified hydrolyzate at a rate of 10% (w / w), with the ratio of seed dry weight to seed solution volume being 4 g / L. (NH 4 ) 2 SO 4 , KH 2 PO 4 MgSO 4 7H 2 0, the system contains 12g / L (NH 4 ) 2 SO 4 (equivalent to a carbon-nitrogen ratio of 18.8:1), 1g / LKH 2 PO 4 and 1g / LMgSO 4 7H 2 O. Subsequently, simultaneous saccharification and co-fermentation were performed to produce single-cell protein and microbial lipids under the following conditions: temperature of 30°C, solid content of 30% (w / w), stirring speed of 550 rpm, aeration of 1 vvm, pH of 5.2, and time of 48 h.

[0065] S5. The fermentation broth was centrifuged to obtain cell products containing single cell protein and microbial oil and fermentation wastewater. After testing, the single cell protein and microbial oil yields were 24.2±1.1 g / L and 11.5±0.7 g / L.

[0066] Example 2 Co-production of single cell protein and microbial oil using corn stalks and ammonium sulfate as substrates

[0067] The same as Example 1, except that the simultaneous saccharification and co-fermentation system in step S4 contains 36 g / L (NH 4 ) 2 SO 4 , which is equivalent to a carbon-nitrogen ratio of 6.27: 1. The final single-cell protein and microbial lipid yields were 20.2±1.3g / L and 10.1±1.3g / L.

[0068] Example 3 Co-production of single cell protein and microbial oil using corn stalks and ammonium sulfate as substrates

[0069] The same as Example 1, except that the simultaneous saccharification and co-fermentation system in step S4 contains 48 g / L (NH 4 ) 2 SO 4 , which is equivalent to a carbon-nitrogen ratio of 4.7: 1. The final single-cell protein and microbial lipid yields were 19.9±1.2g / L and 9.3±0.9g / L.

[0070] Example 4 Co-production of single cell protein and microbial oil using corn stalks and ammonium sulfate as substrates

[0071] The method is basically the same as Example 1, except that the pH value during the simultaneous saccharification and co-fermentation in step S4 is 4.0. The final single cell protein and microbial lipid yields are 21.8±0.4 g / L and 8.5±1.2 g / L.

[0072] Example 5 Co-production of single cell protein and microbial oil using corn stalks and ammonium sulfate as substrates

[0073] The method is basically the same as Example 1, except that the pH value during the simultaneous saccharification and co-fermentation in step S4 is 6.0. The final single cell protein and microbial oil yields are 20.3±1.5 g / L and 12.5±1.3 g / L.

[0074] Example 6: Co-production of single-cell protein and microbial oil using wheat straw and ammonium sulfate as substrates and recycling of nitrogen-containing fermentation wastewater

[0075] S1. Acid pretreatment: The wheat straw was acid pretreated. The acid pretreatment conditions were a solid-liquid ratio of 1:1, a temperature of 170°C, a time of 8 min, and H 2 SO 4 The content is 4.5kg.

[0076] S2. The pretreated wheat straw was used as a substrate for prehydrolysis. The commercial cellulase used was CellicCTec2.0. The enzyme dosage was 6 mg protein / g substrate. The solid content of the prehydrolysis treatment system was 30% (w / w). The time was 18 h. The pH value was 5.1 to obtain a hydrolyzate.

[0077] S3. The hydrolyzate is subjected to biological detoxification. The seed solution of the detoxified strain Paecilomyces variotii FN89 is inoculated at a 10% (w / w) inoculation amount, and the ratio of the seed dry weight of the seed solution to the volume of the seed solution is 3.6 g / L. The detoxification conditions are 37° C., a stirring speed of 700 rpm, a ventilation volume of 1 vvm, and a time of 18 hours to obtain a detoxified hydrolyzate.

[0078] S4. Simultaneous saccharification and co-fermentation: Inoculate MP11 seed liquid in the detoxified hydrolyzate at an inoculation rate of 10%

[0079] (w / w), the ratio of seed dry weight to seed liquid volume is 4.2g / L. Add (NH 4 ) 2 SO 4 , KH 2 PO 4 MgSO 4 7H 2 0, the system contains 24g / L (NH 4 ) 2 SO 4 (equivalent to a carbon-nitrogen ratio of 9.4:1), 1g / LKH 2 PO 4 and 1g / LMgSO 4 7H 2 0. Subsequently, simultaneous saccharification and co-fermentation were performed to produce single-cell protein and oil under the following conditions: temperature of 30°C, solid content of 30% (w / w), stirring speed of 500 rpm, aeration of 1 vvm, pH of 6.1, and time of 48 h.

[0080] S5. The fermentation broth is centrifuged to obtain a cell product containing single cell protein and microbial lipids and fermentation wastewater. The fermentation wastewater is reused in step S4 for the simultaneous saccharification and co-fermentation process, and the fermentation wastewater is mixed with the detoxified hydrolyzate from S3 for simultaneous saccharification and co-fermentation. It has been determined that the fermentation wastewater contains about 7.5 g / L ammonium sulfate. Therefore, fresh ammonium sulfate is added to the simultaneous saccharification and co-fermentation system to a carbon-nitrogen ratio of 9.4:1. Fresh KH 2 PO 4 and MgSO 4 , so that the simultaneous saccharification and co-fermentation system contains 1g / L KH 2 PO 4 and 1g / LMgSO4 7H 2 0.

[0081] S6. Repeat steps S4-S5, and the fermentation wastewater is recycled and reused five times. The single-cell protein and microbial oil yields are measured in different recycling batches. The recycling fermentation time of the first batch of wastewater is 48 hours, and the recycling fermentation time of the subsequent batches of wastewater is extended to 72 hours. The results are shown in Table 1.

[0082] Table 1 Fermentation effect of single cell protein and microbial oil fermented by recycling fermentation wastewater

[0083]

[0084]

[0085] As shown in Table 1, the fermentation indicators such as single-cell protein yield, microbial oil yield, and inorganic ammonia nitrogen fixation conversion rate produced by recycling fermentation wastewater are stable.

[0086] In addition, the inventors found that no significant changes were observed in the contents of major elements such as Ca, Mg, P, K, Na and S during the five fermentation wastewater recycling processes, indicating that the recycling of fermentation wastewater will not lead to the accumulation of salt ions, saving fermentation production costs, reducing the difficulty of wastewater treatment, and making it easier to meet emission standards.

Claims

1. A method for the combined production of single cell protein and microbial lipids, the method comprising the following steps: (1) Pretreatment and detoxification of lignocellulosic raw materials; (2) Synchronous saccharification and co-fermentation to produce single-cell protein and microbial lipids to obtain fermentation broth; (3) after solid-liquid separation of the fermentation broth, a cell product containing single-cell protein and microbial lipids and nitrogen-containing fermentation wastewater are obtained; (4) The nitrogen-containing fermentation wastewater is recycled or not recycled, and when recycled, it is used to provide a nitrogen source for the fermentation strain.

2. The method according to claim 1, characterized in that The pretreatment in step (1) includes at least one of acid pretreatment, alkali pretreatment, steam explosion pretreatment, and organic solvent pretreatment, preferably acid pretreatment.

3. The method according to claim 1 or 2, characterized in that: The pretreatment is acid pretreatment, and the solid-liquid ratio of the pretreatment system is (1-5): 1 g / mL, further (1-3): 1 g / mL; and / or, The pretreatment temperature is 100-220°C, further 150-200°C; and / or, The pretreatment time is 3-20min.

4. The method according to claim 1, characterized in that: The lignocellulosic raw material pretreated in step (1) may or may not be pre-hydrolyzed before being detoxified; Preferably, the pretreated lignocellulosic raw material is subjected to a prehydrolysis treatment before the detoxification treatment to obtain a hydrolyzate, the hydrolyzate is used for the detoxification treatment to obtain a detoxified hydrolyzate, and the detoxified hydrolyzate is used for the simultaneous saccharification and co-fermentation in step (2).

5. The method according to claim 1 or 4, characterized in that: The amount of cellulase used in the pre-hydrolysis treatment in step (1) is 1-10 mg protein / g substrate; and / or, The solid content of the pre-hydrolysis treatment system is 10wt%-40wt%; and / or, The pre-hydrolysis treatment time is 5-48h; and / or, The pH value of the pre-hydrolysis treatment is 4.7-5.

6.

6. The method according to claim 1 or 4, characterized in that: The detoxification treatment is biological detoxification, and the detoxification strain used is a strain that has the ability to preferentially utilize acetic acid and then utilize glucose. Further, the detoxification strain includes resin cladosporium, filamentous white rot fungi, pseudomonas acinetobacter or variotii. Preferably, the detoxified strain is Paecilomyces variotii FN89, with the deposit number being CGMCC No.17665.

7. The method according to claim 1 or 4, characterized in that: The temperature of the detoxification treatment is 25-45°C, further 35-45°C; and / or the ventilation volume is 0.2-4vvm; and / or the time is 5-48h; and / or the inoculation amount of the detoxified strain seed liquid is 5%-20%; and / or the stirring speed is 400-1000rpm.

8. The method according to claim 1, characterized in that The solid content of the simultaneous saccharification and co-fermentation system in step (2) is 10%-35%; and / or, The carbon-nitrogen ratio of the simultaneous saccharification and co-fermentation system in step (2) is (3-30):1, further (7.5-20):1; and / or, The simultaneous saccharification and co-fermentation system in step (2) contains nutrient salts. Preferably, the nutrient salts include any one or two of KH2PO4 and MgSO4·7H20.

9. The method according to claim 1 or 8, characterized in that: Simultaneous saccharification and co-fermentation, the nitrogen source is provided by any one or both of inorganic ammonia nitrogen compounds and nitrogen-containing wastewater; Preferably, the inorganic ammonia nitrogen compound includes but is not limited to any one or a combination of two or more of ammonium sulfate, ammonium chloride, and ammonium nitrate; Preferably, the nitrogen-containing wastewater is the nitrogen-containing fermentation wastewater of step (4).

10. The method according to claim 1, characterized in that The fermentation strain for simultaneous saccharification and co-fermentation in step (2) is Trichosporon fasciatus, preferably MP11, with a deposit number of CGMCC No. 20481; and / or, The inoculation amount of the fermentation strain seed liquid is 5%-20%; and / or, The temperature is 28-35°C; and / or, Ventilation volume is 0.5-3 vvm; and / or, pH value is 4-6.5; and / or, The time is 32-128 hours; and / or, The stirring speed is 200-800rpm.

11. The method according to claim 4, characterized in that The nitrogen-containing fermentation wastewater is recycled for use in any one or more of the pre-hydrolysis treatment step, the detoxification step, and the simultaneous saccharification and co-fermentation step.

12. The method according to claim 4 or 11, characterized in that: The nitrogen-containing fermentation wastewater is recycled for use in simultaneous saccharification and co-fermentation, and the nitrogen-containing fermentation wastewater is mixed with the detoxified hydrolyzate obtained by detoxification treatment for simultaneous saccharification and co-fermentation.

13. The method according to claim 11, characterized in that The nitrogen-containing fermentation wastewater is recycled, with or without decolorization, and / or oxidation treatment, and / or detoxification treatment before recycling.

14. The method according to claim 1, characterized in that The lignocellulosic raw material in step (1) includes, but is not limited to, one or a combination of two or more of wheat straw, corn straw, cotton straw, rice stalks, straw, bagasse, reeds, and forest waste, and is further corn straw or wheat straw.

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