Method for preparing microbial protein by utilizing soapstock wastewater

Abstract

The invention relates to the technical field of microorganisms, in particular to a method for preparing microbial protein from soapstock wastewater, and aims to solve the problems of soapstock wastewater pollution and high protein preparation cost. According to the method, soapstock wastewater containing glycerin and sodium acetate is taken as a raw material, and recycling is realized through multi-stage treatment: firstly, toxic impurities are removed through combined detoxification of ferric salt sedimentation filtration, diatomite adsorption and activated carbon adsorption, a nitrogen source, a phosphorus source and growth promoting factors are supplemented after pH is adjusted to construct a balanced nutrition system, and a microbial culture medium is prepared after sterilization; microbial strains are cultured and activated through a liquid seed solution and inoculated into a culture medium for aerated fermentation; and carrying out solid-liquid separation on the fermentation liquor and collecting thalli to obtain microbial mycoprotein, and recycling the separated fermentation waste liquor for nutrition blending. The method realizes unification of efficient purification of the nigre wastewater and preparation of the microbial protein, is environment-friendly in process, low in cost and high in product purity, and has remarkable economic and environmental benefits.

Description

Technical Field

[0001] This application relates to the field of microbial technology, specifically to a method for preparing microbial proteins using soap residue wastewater. Background Technology

[0002] Microbial protein, also known as single-cell protein, is a protein resource obtained through large-scale microbial cultivation using various industrial and agricultural wastes as raw materials. It mainly includes yeast protein, bacterial protein, and algal protein. Microorganisms grow and reproduce rapidly, with fermentation cycles much shorter than planting cycles, resulting in a significantly higher unit protein production efficiency than traditional agriculture. However, microbial protein production is entirely dependent on the fermentation industry. Conventional carbon sources from agriculture, such as glucose and molasses, are the main raw materials for microbial protein production, leading to high costs and severely limiting its development and widespread adoption. Therefore, current efforts focus on two aspects: firstly, improving carbon source conversion rates or increasing the added value of microbial proteins through strain modification and advanced processing technologies; and secondly, developing widely available, high-content, and low-cost low-value fermentation carbon sources to further reduce the production cost of microbial proteins.

[0003] Soap residue wastewater is formed during the process of saponification, salting out, and decolorization of oil residue from edible oil refining plants, which involves heating the residue with a large amount of NaOH to hydrolyze it into glycerol and sodium fatty acids. This wastewater has a pH greater than 12 and contains a large amount of impurities such as lower fatty acids, phospholipids, proteins, fat-soluble pigments, and salts such as NaOH and Na₂CO₃, making it a highly concentrated alkaline organic industrial wastewater that is extremely difficult to treat. In industry, soap residue wastewater is neutralized with acetic acid to adjust its pH to neutral or weakly acidic, and then used as a carbon source in the denitrification process of wastewater treatment. Although soap residue wastewater is a low-value wastewater resource, its main organic components are glycerol and sodium acetate, which are high-value components with potential for resource utilization. However, due to factors such as purity and content, the reuse of high-value components in soap residue wastewater is difficult. Therefore, developing new methods for the resource utilization of high-value components in soap residue wastewater is of great significance for achieving the resource-based treatment of soap residue wastewater. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a method for preparing microbial proteins from soap residue wastewater. The method involves a multi-stage detoxification process on soap residue wastewater containing glycerol and sodium acetate, including iron salt sedimentation filtration, diatomaceous earth adsorption, and activated carbon adsorption. After supplementing with nutrients, a microbial culture medium is prepared. Yeast strains such as Yersinia lipolytica are inoculated and fermented. The fermentation broth is then separated into solid and liquid phases to collect the microbial cells and obtain microbial protein. Furthermore, the fermentation wastewater is recycled for nutrient preparation, thus achieving the resource utilization of soap residue wastewater and the efficient preparation of high-value proteins.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] In a first aspect, this application provides a method for preparing microbial proteins using soap residue wastewater, comprising the following:

[0007] S1. After detoxifying the soap residue wastewater, adjust the pH to obtain solution A; the detoxification process involves first adding iron salts for sedimentation and filtration, and then sequentially treating the filtrate with diatomaceous earth and activated carbon adsorption.

[0008] S2. Transfer the solution A to the nutrient preparation tank, add nitrogen source, phosphorus source and growth promoter to obtain solution B;

[0009] S3. After adjusting the pH value of the solution B, perform high-temperature sterilization to prepare a microbial culture medium;

[0010] S4. Take the microbial bacteria and inoculate them into the liquid seed culture medium for cultivation to obtain the microbial seed culture;

[0011] S5. Inoculate the microbial seed liquid into the microbial culture medium, and culture it by aeration to obtain fermentation broth;

[0012] S6. The fermentation broth is subjected to solid-liquid separation to collect microbial cells and obtain microbial cell protein; the fermentation waste liquid is transported to the nutrient mixing tank for recycling.

[0013] The S1 method described in this application involves adding iron salts, which hydrolyze to form positively charged ferric hydroxide colloids in soap residue wastewater. Glycerol and sodium acetate, as soluble small-molecule organic compounds in the soap residue wastewater, contribute to maintaining the stability of the wastewater system through their carbon chain structure and functional groups. The ferric hydroxide colloids effectively flocculate and settle negatively charged colloidal particles and some toxic anions in the soap residue wastewater through charge neutralization and adsorption. Subsequently, the porous structure of diatomaceous earth physically adsorbs and filters residual suspended solids and large-molecule organic matter, and activated carbon, with its large specific surface area and surface functional groups, removes small-molecule toxic substances and pigments through van der Waals forces and chemical adsorption, thereby achieving detoxification treatment of the soap residue wastewater and maximizing the retention of carbon source components in the wastewater, including glycerol and sodium acetate, that can be utilized by microorganisms.

[0014] The S2 process replenishes nitrogen, phosphorus, and growth factors in the detoxified soapberry wastewater, adjusting and optimizing the carbon-nitrogen-phosphorus ratio and other micronutrients in the culture medium. Nitrogen provides essential amino acids for microbial protein synthesis, phosphorus participates in energy metabolism and nucleic acid construction, and growth factors activate key metabolic enzymes, providing a nutrient environment for efficient microbial growth and protein synthesis.

[0015] S3 adjusts the pH of the culture medium to the optimal growth range for microorganisms and eliminates competition from other microorganisms through high-temperature sterilization, providing a pure growth environment for the microorganisms. During fermentation, controlling the appropriate inoculum size ensures the rapid establishment of the dominant microbial community, and introducing sterile air meets the aerobic respiration requirements of aerobic strains, while maintaining a suitable temperature to preserve the optimal activity of metabolic enzymes. Under these conditions, the microorganisms efficiently convert carbon sources in soap residue wastewater into microbial proteins through metabolic pathways such as glycolysis and the tricarboxylic acid cycle. S6, after fermentation, harvests the microbial cells through solid-liquid separation, ultimately obtaining the microbial protein product. By setting the fermentation endpoint at the stable period when the microbial protein synthesis rate reaches its maximum, the efficient conversion of carbon sources into microbial proteins is achieved, improving carbon source utilization efficiency and protein yield.

[0016] Preferably, in S1, the pH is 4-5; the iron salt includes at least one of ferrous sulfate, polyferric sulfate and ferric sulfate, and the mass-to-volume ratio of the iron salt to the soap residue wastewater is (0.5-1.0) g: 1 L.

[0017] By controlling the pH to 4-5, the hydrolysis of iron salt is promoted to generate highly positively charged hydroxyl polymers, which enhances the charge neutralization effect and destabilizes and flocculates colloidal particles. This dosage range can form dense flocs to effectively capture impurities, while avoiding excessive iron salt that would increase the load on subsequent treatments or inhibit microbial activity.

[0018] Preferably, in S1, the settling temperature is controlled at 20-35℃ and the settling time is 2-5h.

[0019] By controlling the settling temperature and time, the flocs are fully formed and completely settled, achieving effective solid-liquid separation and providing a clarified supernatant for subsequent adsorption processes.

[0020] Preferably, in S1, the mass-to-volume ratio of diatomaceous earth, activated carbon, and soapberry wastewater is (5-15)g:(3-10)g:1L, the adsorption time of the diatomaceous earth is 30-60min, and the adsorption time of the activated carbon is 60-120min.

[0021] Preferably, in S2, the nitrogen source includes any one of ammonium sulfate, ammonium chloride, and ammonium nitrate; the phosphorus source includes any one of potassium hydrogen phosphate, potassium dihydrogen phosphate, and ammonium dihydrogen phosphate; and the growth promoter includes at least one of yeast extract, peptone, and corn steep liquor.

[0022] By selecting water-soluble, inorganic nitrogen / phosphorus sources and natural organic growth factors, we provide microorganisms with directly usable nutrients. Nitrogen sources participate in protein synthesis, phosphorus sources construct nucleic acids and provide energy, while growth factors supplement vitamins, amino acids, and other trace active ingredients, working together to activate metabolic pathways and promote rapid bacterial growth and protein accumulation.

[0023] Preferably, in S2, the mass-to-volume ratio of nitrogen source, phosphorus source, growth promoter and solution A is (0.5-3.0) g : (0.1-0.8) g : (0.1-3) g : 1 L.

[0024] Preferably, in step S3, the pH value is 4-7; the high-temperature sterilization temperature is 121-132℃, and the sterilization time is 30-40 minutes.

[0025] Preferably, in S4, the inoculation amount of the microbial strain is 1%-5% (v / v) of the volume of the liquid seed culture medium; the microbial strain includes one or more of Yarrowia lipolytica, Fusarium venenatum, and Lipomyces starkeyi.

[0026] Preferably, the liquid seed culture medium is potato glucose medium, which includes potato filtrate, glucose, potassium dihydrogen phosphate, magnesium sulfate, vitamin B1 and chloramphenicol; the mass ratio of potato filtrate, glucose, potassium dihydrogen phosphate, magnesium sulfate, vitamin B1 and chloramphenicol is (150-250):(15-25):(2.0-4.0):(0.5-1.5):(0.05-0.15):(0.05-0.15) g / L.

[0027] Preferably, in S5, the ventilation is sterile air or oxygen-enriched air, and the ventilation rate is 0.8-2.0 VVM; the inoculation amount of the microbial seed liquid is 1%-10% (v / v) of the volume of the microbial culture medium; the fermentation temperature is 25-35℃ and the fermentation time is 36-96h.

[0028] Preferably, in S6, the solid-liquid separation is performed by sedimentation separation, and the sedimentation temperature is 25-35℃ and the time is 2-8h.

[0029] Compared with the prior art, the beneficial effects of this application are as follows:

[0030] This application provides a method for preparing microbial proteins from soap residue wastewater. The method involves the hydrolysis of ferric salt to generate positively charged ferric hydroxide colloid, which uses electrostatic attraction to adsorb negatively charged impurities and toxic anions from the soap residue wastewater, forming flocs that settle. After filtration, diatomaceous earth, with its porous structure, adsorbs residual particles and large organic molecules. Activated carbon, with its surface functional groups and large specific surface area, captures small-molecule toxic substances and pigments through van der Waals forces and chemisorption. This selectively retains soluble small-molecule carbon sources such as glycerol and sodium acetate contained in the soap residue wastewater. Glycerol can serve as a direct carbon source for microbial growth, while sodium acetate ions maintain cell osmotic pressure balance, and acetate ions can participate in metabolism as a rapid energy source. Simultaneously, nitrogen, phosphorus, and growth-promoting factors are supplemented into the soap residue wastewater while retaining carbon sources, providing… The microbial strain requires a necessary carbon, nitrogen, and phosphorus nutrient environment. Nitrogen provides the amino acids needed for protein synthesis, while phosphorus provides energy metabolism and nucleic acid construction. Growth factors activate the activity of key metabolic enzymes. By adjusting the pH of the culture medium, the optimal growth environment for the strain is provided, and high-temperature sterilization eliminates competition from other microorganisms. During the fermentation stage, sterile air is introduced to meet the aerobic respiration requirements of the aerobic strain, while the culture temperature is controlled within the optimal activity range of metabolic enzymes. This enables the strain to efficiently convert carbon sources into microbial proteins through metabolic pathways such as glycolysis and the tricarboxylic acid cycle. By controlling the fermentation cycle, the microbial cells are harvested during the stable period when protein accumulation reaches its peak, improving carbon source utilization and protein yield, thereby achieving the treatment and resource recovery of soap residue wastewater. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a method for preparing microbial proteins using soap residue wastewater.

[0032] Figure 2 High-performance liquid chromatography (HPLC) chromatogram of type I soap residue wastewater;

[0033] Figure 3 The image shows a high-performance liquid chromatogram of type II soap residue wastewater. Detailed Implementation

[0034] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the application will be further described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of this application to the following examples. All other embodiments obtained by those skilled in the art without creative effort without departing from the above-described methodological spirit of this application are within the scope of protection of this application.

[0035] In this application, the terminology used is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0036] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0037] The sources of the various microbial strains used in this application are as follows:

[0038] Yarrowia lipolytica: Ningbo Nais Biotechnology Co., Ltd.;

[0039] Fusarium venenatum: Ningbo Taisto Biotechnology Co., Ltd.;

[0040] Lipomyces starkeyi: Hangzhou Hongsai Biotechnology Co., Ltd.

[0041] The following will describe in detail, with reference to different embodiments, a method for preparing microbial proteins using soap residue wastewater provided by this application.

[0042] The soap residue wastewater used in the examples and comparative examples was directly from the factory's waste liquid concentrate, and was divided into two types: Type I and Type II soap residue wastewater. Their high-performance liquid chromatograms are shown in the attached figures. Figure 2 Appendix Figure 3 As shown.

[0043] Table 1. Main physicochemical properties of soap residue wastewater

[0044]

[0045] From the appendix Figure 2 It can be seen from the data that sodium acetate is the main carbon source component of Type I soap residue wastewater; from the attached data... Figure 3 As can be seen, type II soapstock wastewater primarily contains glycerol as its carbon source. Its physicochemical properties are shown in Table 1. Considering the different carbon source preferences of various microbial species, the following examples utilize suitable soapstock wastewater types to specifically describe the method for preparing microbial proteins using soapstock wastewater provided in this application.

[0046] Example 1

[0047] like Figure 1 As shown, this embodiment provides a method for preparing microbial protein using soap residue wastewater, including the following steps:

[0048] S1. Take type I soap residue wastewater containing glycerol and sodium acetate, first add ferrous sulfate, controlling the mass-to-volume ratio of ferrous sulfate to soap residue wastewater to be 0.5 g: 1 L, settle at 20 °C for 2 h and then filter; then add diatomaceous earth to the filtrate and adsorb for 30 min; then add activated carbon and adsorb for 60 min to complete the detoxification treatment, wherein the mass-to-volume ratio of diatomaceous earth, activated carbon and soap residue wastewater is 5 g: 3 g: 1 L; finally adjust the pH of the system to 4 to obtain solution A.

[0049] S2. Transfer solution A to the nutrient mixing tank, add ammonium sulfate, potassium hydrogen phosphate and yeast extract in sequence, stir evenly to obtain solution B. The mass-volume ratio of ammonium sulfate, potassium hydrogen phosphate, yeast extract and solution A is 0.5g:0.1g:0.1g:1L.

[0050] S3. Adjust the pH of solution B to 4, then sterilize it at 121°C for 30 minutes, and after cooling, prepare it as a microbial culture medium.

[0051] S4. Take 1% (v / v) of the seed culture medium volume of Yersinia lipolytica and inoculate it into the seed culture medium to obtain microbial seed culture.

[0052] S5. Inoculate the microbial seed liquid into the above microbial culture medium at an inoculation rate of 1% (v / v) of the microbial culture medium volume, introduce sterile air, control the aeration rate at 0.8 VVM, and culture the fermentation at 25℃ for 36 h to obtain the fermentation broth.

[0053] S6. The fermentation broth is subjected to solid-liquid separation by sedimentation at 25°C for 2 hours. The precipitated microbial cells are collected, which are the microbial protein products.

[0054] Example 2

[0055] like Figure 1 As shown, this embodiment provides a method for preparing microbial protein using soap residue wastewater, including the following steps:

[0056] S1. Take type I soap residue wastewater containing glycerol and sodium acetate, add polyferric sulfate first, and control the mass-volume ratio of polyferric sulfate to soap residue wastewater to be 0.8 g: 1 L. After settling at 30℃ for 3 h, filter. Then add diatomaceous earth to the filtrate and adsorb for 45 min. Then add activated carbon and adsorb for 90 min to complete the detoxification treatment. The mass-volume ratio of diatomaceous earth, activated carbon and soap residue wastewater is 10 g: 7 g: 1 L. Finally, adjust the pH of the system to 4.5 to obtain solution A.

[0057] S2. Transfer solution A to the nutrient mixing tank, add ammonium chloride, potassium dihydrogen phosphate and peptone in sequence, stir evenly to obtain solution B. The mass-volume ratio of ammonium chloride, potassium dihydrogen phosphate, peptone and solution A is 2g:0.6g:2g:1L.

[0058] S3. Adjust the pH of solution B to 5, then sterilize it at 128°C for 40 minutes, and after cooling, prepare it as a microbial culture medium.

[0059] S4. Take 3% (v / v) of the seed culture medium volume of Fusarium filamentosa and inoculate it into the seed culture medium to obtain microbial seed culture.

[0060] S5. Inoculate the microbial seed liquid into the above microbial culture medium at an inoculation rate of 6% (v / v) of the microbial culture medium volume, introduce sterile air, control the aeration rate at 1.5 VVM, and culture the fermentation at 30℃ for 66 h to obtain the fermentation broth.

[0061] S6. The fermentation broth is subjected to solid-liquid separation by sedimentation at 30°C for 6 hours. The precipitated microbial cells are collected, which are the microbial protein products.

[0062] Example 3

[0063] like Figure 1 As shown, this embodiment provides a method for preparing microbial protein using soap residue wastewater, including the following steps:

[0064] S1. Take type II soap residue wastewater containing glycerol and sodium acetate, first add ferric sulfate, controlling the mass-to-volume ratio of ferric sulfate to soap residue wastewater to be 1.0 g: 1 L, settle at 35℃ for 5 h and then filter; then add diatomaceous earth to the filtrate and adsorb for 60 min; then add activated carbon and adsorb for 120 min to complete the detoxification treatment, wherein the mass-to-volume ratio of diatomaceous earth, activated carbon and soap residue wastewater is 15 g: 10 g: 1 L; finally adjust the pH of the system to 5 to obtain solution A.

[0065] S2. Transfer solution A to the nutrient mixing tank, add ammonium nitrate, ammonium dihydrogen phosphate and corn steep liquor in sequence, stir evenly to obtain solution B. The mass-volume ratio of ammonium nitrate, ammonium dihydrogen phosphate, corn steep liquor and solution A is 3.0g:0.1g:0.1g:1L.

[0066] S3. Adjust the pH of solution B to 7, then sterilize it at 132℃ for 40 minutes, and after cooling, prepare it as a microbial culture medium.

[0067] S4. Take 5% (v / v) of the seed culture medium volume of *Saccharomyces cerevisiae* and inoculate it into the seed culture medium to obtain microbial seed culture.

[0068] S5. Inoculate the microbial seed liquid into the above microbial culture medium at an inoculation rate of 10% (v / v) of the microbial culture medium volume, introduce sterile air, control the aeration rate at 2.0 VVM, and culture the fermentation at 35℃ for 96 h to obtain the fermentation broth.

[0069] S6. The fermentation broth was subjected to solid-liquid separation by sedimentation at 35°C for 8 hours. The precipitated microbial cells were collected, which are the microbial protein products.

[0070] Comparative Example 1

[0071] A method for preparing microbial protein using soap residue wastewater, which differs from Example 3 in that it does not involve detoxification treatment.

[0072] Comparative Example 2

[0073] A method for preparing microbial protein from soap residue wastewater, which differs from Example 3 in that the detoxification treatment uses only the flocculant polyacrylamide.

[0074] Comparative Example 3

[0075] A method for preparing microbial protein using soap residue wastewater, which differs from Example 3 in that the microbial strain used is a mixed microbial community of activated sludge.

[0076] Performance testing:

[0077] 1. COD Removal Rate: Water samples from Examples 1-3 and Comparative Examples 1-3 after S1 were filtered through a 0.22 μm filter membrane, and the contents of sodium acetate and glycerol in the water samples were detected by high performance liquid chromatography. The COD in the water samples is due to the presence of sodium acetate and glycerol. The COD removal rate of the original water samples was calculated by calculating the consumption of sodium acetate and glycerol.

[0078] 2. Dry weight of cells (g / L): Take a quantitative amount of fermentation broth from Examples 1-3 and Comparative Examples 1-3, collect the cells by centrifugation or filtration, wash several times with deionized water to remove culture medium residue, then dry the cells at 105°C to constant weight, weigh them after cooling, and divide the weight by the volume of the fermentation broth to obtain the dry weight of the cells.

[0079] 3. Protein yield (g / L): The protein yield per unit volume of fermentation broth can be calculated by multiplying the measured dry weight of the cells by the protein content of the cells determined by the Kjeldahl method (multiplying the measured nitrogen content by the protein conversion factor of 6.25).

[0080] 4. Protein purity (%): The Kjeldahl method is used. A known weight of dried bacterial sample is digested with concentrated sulfuric acid to convert nitrogenous substances into ammonium sulfate. Ammonia is released by distillation with alkali and absorbed by boric acid. Then, it is titrated with standard acid. The crude protein content is calculated by multiplying the nitrogen content by the conversion factor of 6.25. The percentage of this content to the dry weight of the bacterial cells is the protein purity.

[0081] 5. Final pH of fermentation broth: After fermentation, take an appropriate amount of fermentation broth supernatant cooled to room temperature, and directly immerse it in a pH meter electrode calibrated with a standard buffer solution to measure the pH value. Record the pH value after the reading stabilizes.

[0082] The performance test data analysis is as follows:

[0083] Table 2 Adsorption Function Test Data

[0084]

[0085] Table 2 shows that Examples 1-3, through the gradient-optimized multi-stage detoxification process of "iron salt flocculation-diatomaceous earth adsorption-activated carbon adsorption" and the synergistic regulation of dedicated protein-producing bacteria, exhibited a significant increasing trend in various performance aspects. Example 3 performed best, with a COD removal rate of 91.2%, a cell dry weight of 21.6 g / L, a protein yield of 11.58 g / L, a purity of 53.6%, and a final pH of 6.1 in the fermentation broth, which met the metabolic requirements of the bacteria. Comparative Example 1, compared to Example 3, lacked the multi-stage detoxification treatment, and the toxic substances in the soapstock wastewater were not removed, inhibiting the metabolism of the bacteria. The COD removal rate was only 38.5%, a decrease of 57.8% compared to Example 3; the cell dry weight was 3.0 g / L, a decrease of 86.1%; the protein yield was 1.06 g / L, only 9.1% of Example 3; the purity was 35.2%, a decrease of 34.3%; and the final pH of the fermentation broth was 3.8, indicating excessive acidity. In Comparative Example 2, the detoxification treatment using only polyacrylamide failed to adsorb small molecule toxic substances, thus inhibiting bacterial growth. The COD removal rate was 67.5%, a decrease of 26% compared to Example 3. The bacterial dry weight was 7.2 g / L, a decrease of 66.7%. The protein yield was 3.03 g / L, only 26.2% of Example 3, and the purity was 42.1%, a decrease of 21.5%. The final pH of the fermentation broth was 5.0, indicating poorer stability than Example 3. In Comparative Example 3, replacing the Starr oil yeast with a mixed activated sludge microbial community resulted in competition for nutrients and non-directional protein production. The COD removal rate was 75.0%, a decrease of 17.8% compared to Example 3. The bacterial dry weight was 9.1 g / L, a decrease of 57.9%. The protein yield was 4.17 g / L, only 36.0% of Example 3, and the purity was 45.8%, a decrease of 14.5%. The final pH of the fermentation broth was 5.5, deviating from the optimal metabolic range.

[0086] In summary, through the synergistic effect of the core steps described above, Examples 1-3 ultimately achieved efficient removal of COD from soap residue wastewater and high-yield, high-purity preparation of microbial proteins, thus balancing environmental benefits and resource utilization value.

[0087] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0088] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for preparing microbial protein using soap residue wastewater, characterized in that, Including the following: S1. After detoxifying the soap residue wastewater, adjust the pH to obtain solution A; the detoxification process involves first adding iron salts for sedimentation and filtration, and then sequentially treating the filtrate with diatomaceous earth and activated carbon adsorption. S2. Transfer the solution A to the nutrient preparation tank, add nitrogen source, phosphorus source and growth promoter to obtain solution B; S3. After adjusting the pH value of the solution B, perform high-temperature sterilization to prepare a microbial culture medium; S4. Take the microbial bacteria and inoculate them into the liquid seed culture medium for cultivation to obtain the microbial seed culture; S5. Inoculate the microbial seed liquid into the microbial culture medium, and culture it by aeration to obtain fermentation broth; S6. The fermentation broth is subjected to solid-liquid separation to collect microbial cells and obtain microbial cell protein; the fermentation waste liquid is transported to the nutrient mixing tank for recycling.

2. The method for preparing microbial protein from soap residue wastewater according to claim 1, characterized in that, In S1, the soap residue wastewater includes glycerol and sodium acetate; the pH is 4-5; the iron salt includes at least one of ferrous sulfate, polyferric sulfate and ferric sulfate, and the mass-to-volume ratio of the iron salt to the soap residue wastewater is (0.5-1.0) g: 1 L.

3. The method for preparing microbial protein from soap residue wastewater according to claim 1, characterized in that, In S1, the settling temperature is controlled at 20-35℃ and the settling time is 2-5h.

4. The method for preparing microbial protein from soap residue wastewater according to claim 1, characterized in that, In S1, the mass-to-volume ratio of diatomaceous earth, activated carbon, and soapberry wastewater is (5-15)g:(3-10)g:1L, the adsorption time of diatomaceous earth is 30-60min, and the adsorption time of activated carbon is 60-120min.

5. The method for preparing microbial protein from soap residue wastewater according to claim 1, characterized in that, In S2, the nitrogen source includes any one of ammonium sulfate, ammonium chloride, and ammonium nitrate; the phosphorus source includes any one of potassium hydrogen phosphate, potassium dihydrogen phosphate, and ammonium dihydrogen phosphate; the growth promoter includes at least one of yeast extract, peptone, and corn steep liquor; and the mass-volume ratio of the nitrogen source, phosphorus source, growth promoter, and solution A is (0.5-3.0) g : (0.1-0.8) g : (0.1-3) g : 1 L.

6. The method for preparing microbial protein from soap residue wastewater according to claim 1, characterized in that, In S3, the pH value is 4-7; the high-temperature sterilization temperature is 121-132℃, and the sterilization time is 30-40 minutes.

7. The method for preparing microbial protein from soap residue wastewater according to claim 1, characterized in that, In S4, the inoculation amount of the microbial strain is 1%-5% (v / v) of the volume of the liquid seed culture medium; the microbial strain includes one or more of Yersinia lipolytica, Fusarium filamentosa, and Saccharomyces davidii.

8. The method for preparing microbial protein from soap residue wastewater according to claim 1, characterized in that, In S4, the liquid seed culture medium is potato glucose medium, which includes potato filtrate, glucose, potassium dihydrogen phosphate, magnesium sulfate, vitamin B1 and chloramphenicol; the mass ratio of potato filtrate, glucose, potassium dihydrogen phosphate, magnesium sulfate, vitamin B1 and chloramphenicol is (150-250): (15-25): (2.0-4.0): (0.5-1.5): (0.05-0.15): (0.05-0.15).

9. The method for preparing microbial protein from soap residue wastewater according to claim 1, characterized in that, In S5, the ventilation is the introduction of sterile air or oxygen-enriched air, and the ventilation rate is 0.8-2.0 VVM; the inoculation amount of the microbial seed liquid is 1%-10% (v / v) of the volume of the microbial culture medium; the fermentation temperature is 25-35℃ and the fermentation time is 36-96h.

10. A method for preparing microbial protein from soap residue wastewater according to claim 1, characterized in that, In S6, the solid-liquid separation is carried out by sedimentation separation, and the sedimentation temperature is 25-35℃ and the time is 2-8h.

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