Method for preparing polyglutamic acid based on kitchen waste liquid

Abstract

The invention belongs to the technical field of preparation of polyglutamic acid, and particularly relates to a method for preparing polyglutamic acid based on kitchen waste liquid. According to the method, the kitchen waste liquid is used as a raw material, the content of total sugar and glutamic acid in the waste liquid is measured, for the kitchen waste liquid with low content of total sugar and glutamic acid, the glutamic acid concentrated solution is supplemented to improve nutrient components of the culture medium and reduce the cost of the polyglutamic acid culture medium, and resource utilization of the two waste liquids is realized; meanwhile, ammonium sulfate is added to produce a hypertonic environment, inhibit growth of infectious microbes, reduce sterilization energy consumption, stimulate the polyglutamic acid synthesis capability of strains, reduce the viscosity of the fermentation liquor and reduce ventilation stirring energy consumption, and the low-cost polyglutamic acid fermentation liquor is obtained. The fermentation liquor is concentrated to prepare a liquid polyglutamic acid product, the content of ammonium sulfate is further increased, the corrosion resistance of the product is enhanced, degradation of polyglutamic acid is effectively prevented, and zero discharge treatment of waste liquid of the kitchen waste is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of polyglutamic acid, and particularly relates to a method for preparing polyglutamic acid based on kitchen waste liquid. Background Art

[0002] Urban food waste refers to the waste from food waste generating units such as restaurants and canteens. This type of waste is mostly collected by municipal companies and transported directly to food waste treatment centers for terminal treatment. The treatment method is mostly heating and stirring. After centrifugal separation by a three-phase centrifuge, oil phase, water phase and solid phase are formed. The oil phase is used to prepare biodiesel, the solid phase is used as feed for insects such as black soldier flies, and the water phase is anaerobic fermented to prepare biogas. In this treatment mode, the sales of oil phase and solid phase products obtained from food waste separation can realize corporate profits; however, the cost of treating the biogas slurry formed after the water phase is used to prepare biogas is relatively high, far greater than the benefits of the biogas generated. This has gradually become a bottleneck problem restricting the treatment of urban food waste.

[0003] Polyglutamic acid is a new type of green biostimulant product with good hydrophilic and water-retaining capabilities. It can balance soil pH, precipitate toxic heavy metals, promote root growth and strengthen plants, increase plant resistance, and promote crop yields. Currently, this product has become an international mainstream green farmland input and is widely used in large-scale water-soluble fertilizers, liquid fertilizers, organic compound fertilizers and other fertilizers.

[0004] However, due to factors such as the high cost of fermentation medium, the large amount of sterilization steam used, and the high energy consumption of ventilation and stirring during the fermentation process (due to the high viscosity of the fermentation liquid), the production cost of polyglutamic acid is relatively high, which greatly limits the expansion of the product's application in the fertilizer field.

[0005] Since the amount of monosodium glutamate (sodium glutamate) used in Chinese cuisine is large, the waste liquid of restaurant kitchen waste contains monosodium glutamate residues and has a high content of polysaccharides. If polyglutamic acid can be produced from the waste liquid of restaurant kitchen waste as raw material, the economic value of the restaurant waste will be increased, and the production cost of polyglutamic acid will be significantly reduced, which is of great significance to the application and promotion of polyglutamic acid in agriculture. The patent with application number 201510295019.8 discloses a method for producing γ-polyglutamic acid by fermentation of restaurant waste. The patent is to filter and crush the restaurant waste, add nitric acid for acid hydrolysis to obtain a hydrolyzate, add 4% sodium glutamate to the hydrolyzate, and then sterilize at 121°C and ferment to produce polyglutamic acid. Although the patent uses restaurant waste to produce polyglutamic acid, the fermentation raw material of the above patent is the product of solid-phase acid hydrolysis of restaurant waste, the pre-treatment process is complex, the equipment working conditions are high, the production cost is high, and it is difficult to connect with the mainstream restaurant kitchen waste comprehensive treatment system, and it is impossible to achieve large-scale industrial production.

[0006] Therefore, if the aqueous waste liquid generated in the mainstream comprehensive food waste treatment process can be used for polyglutamic acid fermentation, the cost of the culture medium can be reduced, and low-cost production of polyglutamic acid can be achieved, it will be of great significance for the production of polyglutamic acid and the comprehensive treatment of food waste. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for preparing polyglutamic acid based on restaurant kitchen waste liquid, which uses the sterilized waste liquid produced by heating and separation in the existing restaurant kitchen waste treatment process as a matrix, and creates a hypertonic environment by adding ammonium sulfate to achieve antibacterial effect, thereby eliminating the energy consumption of the sterilization link in the traditional biological fermentation process; then, polyglutamic acid is fermented and synthesized by hypertonic polyglutamic acid-producing bacteria, and the polyglutamic acid synthesis ability of the bacteria is activated by hypertonic conditions, and the viscosity of polyglutamic acid is effectively reduced, thereby increasing the yield of the polyglutamic acid product and reducing the energy consumption of ventilation and stirring; in addition, the obtained polyglutamic acid fermentation liquid is concentrated to obtain a low-cost polyglutamic acid liquid product, thereby realizing the zero-emission green comprehensive utilization of restaurant waste liquid.

[0008] The method for preparing polyglutamic acid based on kitchen waste liquid provided by the present invention comprises the following steps: S1 determines the contents of total sugar and glutamic acid in the waste liquid of restaurant kitchen waste. If the total sugar content in the waste liquid is ≥1.2% (w / v) and the glutamic acid content is ≥0.8% (w / v), then proceed to step S11, otherwise proceed to step S12; in the following steps, unless otherwise specified, "%" is w / v, w is g, and v is 100mL, for example: 1.2%, actually means 1.2g / 100mL; S11: maintaining the temperature of the kitchen waste liquid at above 70° C., adding ammonium sulfate to the kitchen waste liquid to a concentration of 6% (w / v), stirring evenly, and adjusting the pH value to 5.0-6.5, thereby obtaining a polyglutamic acid fermentation medium for standby use; S12: maintaining the temperature of the kitchen waste liquid at above 70° C., adding a regulating liquid until the total sugar content in the kitchen waste liquid is ≥1.2% (w / v), and the glutamic acid content is ≥0.8% (w / v); at the same time, adding ammonium sulfate to the kitchen waste liquid to a concentration of 6% (w / v), stirring evenly, and adjusting the pH value to 5.0-6.5, thereby obtaining a polyglutamic acid fermentation medium for standby use; S2 Add Bacillus licheniformis to the polyglutamic acid fermentation medium obtained in S11 or S12 Bacillus licheniformis A-A2-10 seed liquid, fermenting to obtain fermentation liquid; S3 concentrates the fermentation liquid in S2 to obtain a liquid polyglutamic acid product.

[0009] Preferably, in the above S12, the regulating liquid is a mixture of molasses and sodium glutamate, or a concentrated glutamate waste liquid; the concentrated glutamate waste liquid is the ammonium sulfate crystallization mother liquor remaining after the glutamate fermentation liquid is subjected to glutamate isoelectric crystallization, impurity removal, and ammonium sulfate concentration crystallization, and the total sugar content in the mother liquor is 6-8% (w / v), the glutamate content is 6-8% (w / v), and the ammonium sulfate content is 30-40% (w / v). If the ammonium sulfate concentration in the kitchen waste liquid is less than 6% (w / v) after the addition of the concentrated glutamate waste liquid, ammonium sulfate is added until its concentration reaches 6% (w / v).

[0010] Preferably, the Bacillus licheniformis described in S2 Bacillus licheniformis The A-A2-10 strain was deposited in the China Center for Type Culture Collection on March 6, 2020, with the deposit number CCTCC NO: M 2020051; Preferably, the seed culture medium is: 3% (w / v) glucose, 0.2% (w / v) yeast powder, 0.1% (w / v) corn syrup powder, 2% (w / v) ammonium sulfate, pH value is 6.5, and inoculation is performed after sterilization at 117°C; the culture conditions are shaking culture at 37°C for 18 hours to obtain seed liquid, which is then inoculated into polyglutamic acid fermentation medium, and the inoculation amount is 2~10% (v / v, volume percentage).

[0011] Preferably, the Bacillus licheniformis described in S2 Bacillus licheniformis The fermentation conditions of A-A2-10 are: ventilation ratio of 0.2~0.5vvm at 37℃, tank pressure of 0.06~0.1Mpa, maintaining dissolved oxygen at 10~15% by controlling the stirring speed of the fermenter, maintaining pH at 6.0~7.0 during the fermentation process, and the fermentation cycle is 20~28h.

[0012] Preferably, the polyglutamic acid fermentation broth in S3 is concentrated to 1 / 3 to 2 / 5 of the original volume by a multi-effect concentration treatment.

[0013] The beneficial effects of the present invention are: (1) The present invention uses the aqueous waste liquid generated in the mainstream restaurant kitchen waste treatment process as the raw material for producing polyglutamic acid. Since the waste liquid contains organic components such as sugar, glutamic acid, and protein, it can not only solve the problem of difficult disposal of restaurant kitchen waste, but also turn waste into treasure, reduce the production cost of polyglutamic acid, and provide a new idea for the production of polyglutamic acid; (2) The present invention utilizes the heating process in the existing mainstream restaurant kitchen waste treatment process to sterilize the waste liquid, and then adds ammonium sulfate to create a hypertonic environment to inhibit the growth of miscellaneous bacteria, and uses hypertonic-resistant polyglutamic acid-producing bacteria to ferment and synthesize polyglutamic acid, thereby overcoming the high energy consumption defect of high-temperature sterilization (sterilization at 115°C to 121°C for 20min to 30min) in the traditional polyglutamic acid biological fermentation process; (3) The present invention uses the high ammonium sulfate condition in the liquid to activate the polyglutamic acid synthesis ability of the strain, and the yield of polyglutamic acid reaches 10-12 g / L, and the conversion rate (product yield / total sugar consumption) is as high as 90%. At the same time, the high ammonium sulfate condition effectively reduces the viscosity of polyglutamic acid and reduces the energy consumption of ventilation and stirring; (4) The present invention concentrates the fermentation liquid to prepare a liquid polyglutamic acid product, thereby achieving zero-emission green comprehensive treatment of food waste liquid. At the same time, the ammonium sulfate content after concentration reaches about 20%, and the anti-corrosion ability of the product is significantly improved, effectively preventing polyglutamic acid from being degraded by microorganisms. In addition, the ammonium sulfate increases the total nitrogen content in the liquid polyglutamic acid product, which is conducive to the promotion and application of the product in agricultural production.

[0014] (5) The present invention uses concentrated glutamate waste liquid to supplement the total sugar and glutamate in food waste water, and then synthesizes polyglutamic acid, thereby realizing the high-value comprehensive utilization of the two wastes, which not only solves the environmental protection problem but also reduces the production cost, and has a good market prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a diagram of the fermentation broth after shake flask fermentation in Example 1; Figure 2 For the general Figure 1 In the picture of the fermented liquid being poured out, the stringing phenomenon can be clearly seen; Figure 3 To remove Figure 1 In the fermentation liquid, the wire drawing phenomenon can be clearly seen. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in conjunction with specific implementation methods.

[0017] In the following examples, Bacillus licheniformis Bacillus licheniformis The strain A-A2-10 was deposited in the China Center for Type Culture Collection on March 6, 2020, with the deposit number CCTCC NO: M 2020051, and the classification name: Bacillus licheniformis A-A2-10 ( Bacillus licheniformis A-A2-10), deposit address: Wuhan University, Wuhan, China; The seed culture medium of the seed liquid is: 3% (w / v) glucose, 0.2% (w / v) yeast powder, 0.1% (w / v) corn steep liquor, 2% (w / v) ammonium sulfate, pH value is 6.5, and it is inoculated after sterilization at 117°C; the culture conditions are shaking culture at 37°C for 18 hours to obtain the seed liquid, which is then inoculated into the polyglutamic acid fermentation medium with an inoculation amount of 2~10% (v / v).

[0018] Example 1 The food waste liquid used in this embodiment was taken from the January 2024 batch samples of the Jinan Food Waste Comprehensive Treatment Center. The treatment process is that the food waste is collected and transported to the treatment center by the municipal company. After simply removing plastic bags, packaging boxes and other debris, it is heated to 80°C~90°C and heated for 1 hour. Then, a three-phase centrifuge is used to separate it to form an oil phase, an aqueous phase and a solid phase. The aqueous phase is collected in a sterile sampling bucket and used as a raw material in this embodiment 1.

[0019] (1) The above samples were tested, and the results showed that the total sugar content in the above kitchen waste liquid was 1.8% (w / v), the glutamic acid content was 1.0% (w / v), and the total number of miscellaneous bacteria in the sample was about 3 cfu / mL, and it can be directly used as a polyglutamic acid fermentation medium without treatment; (2) The food waste liquid in (1) was transferred into a 100 L sterile fermentation tank, ammonium sulfate was added to a concentration of 6% (w / v), stirred evenly, and the pH value was adjusted to 6.5 to obtain a polyglutamic acid fermentation medium; (3) Inoculate the culture medium prepared in (2) with the prepared Bacillus licheniformis Bacillus licheniformis A-A2-10 seed solution, inoculation amount of 3% (v / v), then adjusted the ventilation ratio to 0.5vvm, tank pressure to 0.08Mpa, by adjusting the fermentation tank stirring speed, maintaining the dissolved oxygen to 12%, observing the pH changes of the materials during the fermentation process. The results showed that the pH value of the whole fermentation process first decreased and then increased, but was within the range of 6.0-7.0, and there was no need to add acid or alkali to adjust the pH value; the fermentation cycle was 24h, and the polyglutamic acid content was 11.32g / L and the total sugar consumption was 12g / L determined by QB / T5189-2017 standard, and the conversion rate (polyglutamic acid yield / total sugar consumption ratio) reached 94.33%; as shown in the attached Figures 1-3 The fermentation liquid in the above steps is shown. Figures 2-3 It can be clearly seen that the fermentation broth has obvious stringing phenomenon, which indicates that the fermentation broth is rich in polyglutamic acid.

[0020] (4) The fermentation broth was concentrated 3 times to prepare a liquid polyglutamic acid product, wherein the polyglutamic acid content reached 33 g / L.

[0021] Example 2 The food waste liquid used in this embodiment was taken from the March 2024 batch samples of the Jinan Food Waste Comprehensive Treatment Center. The treatment process was that the food waste was collected and transported to the treatment center by the municipal company. After simple impurity removal, it was heated to 80°C~90°C and heated for 1 hour. Then, it was separated by a three-phase centrifuge to form an oil phase, an aqueous phase and a solid phase. The aqueous phase was collected in a sterile sampling bucket for use in this embodiment 2.

[0022] (1) After testing, the total sugar content in the kitchen waste liquid used in this embodiment was 0.97% (w / v), the glutamic acid content was 0.2% (w / v), and the total number of miscellaneous bacteria in the sample was about 1 cfu / mL. It was necessary to first supplement the waste liquid with nutrients in order to prepare the polyglutamic acid fermentation liquid.

[0023] The nutrient used in this embodiment is glutamate concentrated waste liquid from Inner Mongolia Fufeng Biotechnology Co., Ltd., which has a glutamate content of 6.6% (w / v), a total sugar content of 6.8% (w / v), and an ammonium sulfate content of 33% (w / v).

[0024] (2) The above-mentioned food waste liquid was transferred into a 100L sterile fermentation tank, and glutamic acid concentrated waste liquid was added in a ratio of 6:1. After stirring and mixing, the glutamic acid content reached 1.1% (w / v), the total sugar content reached 1.83% (w / v), and the ammonium sulfate content reached 4.71% (w / v). Then, ammonium sulfate was added to a concentration of 6wt% and stirred evenly; the pH value was adjusted to 6.7; (3) Inoculate the prepared Bacillus licheniformis into the material whose pH value has been adjusted in (2) Bacillus licheniformis A-A2-10 seed solution, inoculation amount was 5% (v / v), ventilation ratio was adjusted to 0.4vvm, tank pressure was 0.07Mpa, dissolved oxygen was maintained at 15% by adjusting the stirring speed of the fermenter, and pH changes were observed. The results showed that the pH value first decreased and then increased during the entire fermentation process, but was within the range of 6.0-7.0, and there was no need to add acid or alkali to adjust the pH value; the fermentation cycle was 25h, and the polyglutamic acid content was 10.89 g / L and the total sugar consumption was 11.32 g / L determined by QB / T5189-2017 standard, and the conversion rate (polyglutamic acid yield / total sugar consumption ratio) reached 96.2%; (4) The fermentation broth was concentrated 3 times to prepare a liquid polyglutamic acid product, wherein the polyglutamic acid content reached 32.5 g / L.

[0025] Example 3 The difference from Example 2 is that molasses, sodium glutamate and ammonium sulfate are added to the kitchen waste liquid instead of glutamate concentrated waste liquid. After the addition, the total sugar, sodium glutamate and ammonium sulfate contents in the fermentation liquid are the same as those in Example 2, as follows: The kitchen waste liquid described in Example 2 was transferred into a 100L sterile fermentation tank, and molasses, sodium glutamate, and ammonium sulfate were added to the contents of 1.83% (w / v), 1.1% (w / v), and 6% (w / v), respectively. The mixture was stirred evenly, and the pH value was adjusted to 6.7, and the prepared Bacillus licheniformis was inoculated. Bacillus licheniformisA-A2-10 seed liquid, inoculation amount was 5% (v / v), ventilation ratio was adjusted to 0.4vvm, tank pressure was 0.07Mpa, dissolved oxygen was maintained at 15% by adjusting the stirring speed of the fermenter, and pH changes were observed. The results showed that the pH value first decreased and then increased during the whole fermentation process, but it was within the range of 6.0-7.0, and there was no need to add acid-base conditions. The fermentation cycle was 25h, and the polyglutamic acid content was 10.22 g / L and the total sugar consumption was 12.32 g / L determined by QB / T5189-2017 standard. The conversion rate (polyglutamic acid yield / total sugar consumption ratio) reached 82.95%.

[0026] The fermentation liquid was concentrated 3 times to prepare a liquid polyglutamic acid product, and the polyglutamic acid content reached 30.5 g / L.

[0027] The cost of Examples 1 to 3 is calculated, and the results are shown in Table 1. As can be seen from Table 1, the liquid polyglutamic acid products obtained in Examples 1 to 3 all have low costs, and the costs of Examples 1 and 2 are much lower than those of Example 3, indicating that the use of concentrated glutamic acid waste liquid to replace glutamic acid, molasses and ammonium sulfate can further reduce product costs. The polyglutamic acid content in the obtained liquid polyglutamic acid product is about 3% (w / v), and the price of the commercially available competitive product is about 3,000 yuan / t. The product has a high profit margin and broad market prospects.

[0028] Table 1. Comparison results of Examples 1 to 3

[0029] Calculation basis: (1) Cost of liquid food waste: In the existing mainstream food waste treatment process, the profit of preparing biogas from wastewater is lower than the cost of liquid food waste treatment. Therefore, the price of this raw material is set to 0.

[0030] (2) Cost of sodium glutamate: In Examples 1 and 2, there is no need to add sodium glutamate. In Example 3, the amount of sodium glutamate added is 0.9% (w / v). The current price of sodium glutamate products is about RMB 8,000 per ton, and the cost of adding sodium glutamate per ton of fermentation broth is about RMB 72.

[0031] (3) Molasses cost: In Examples 1 and 2, no molasses was needed. In Example 3, beet molasses was used to add total sugar to 1.83% (w / v). The total sugar content of the material was determined to be 46%, so the amount of beet molasses added was about 1.87% (w / v). The price of the material was RMB 1,200 per ton. Therefore, the cost of adding beet molasses per ton of fermentation liquid was about RMB 22.43.

[0032] (4) Cost of concentrated glutamic acid mother liquor: Concentrated glutamic acid mother liquor is currently difficult to process effectively. The existing processing method is mostly to pay relevant processing companies for processing. Therefore, the price of this raw material is set at 0.

[0033] (5) Ventilation energy consumption: In Example 1, the ventilation ratio is 0.5 vvm, the cycle is 24 h, and the ventilation volume per ton of fermentation liquid is 720 m³. Calculated based on the consumption of 1 kw of electricity for 16 m³ of air volume, the total power consumption is 45 kw, and the total cost is about 45 × 1.1 = 49.5 yuan; In Example 2, the ventilation ratio is 0.4 vvm, the cycle is 25 h, and the ventilation volume per ton of fermentation liquid is 600 m³. Calculated based on the consumption of 1 kw of electricity for 16 m³ of air volume, the total power consumption is 37.5 kw, and the total cost is about 37.5 × 1.1 = 41.25 yuan; The ventilation ratio and fermentation cycle of Example 3 are the same as those of Example 2, so the total cost is 41.25 yuan.

[0034] (6) The energy consumption for stirring is estimated to be about RMB 50 per ton of polyglutamic acid fermentation liquid based on the motor power.

[0035] (7) Cost of fermentation broth raw materials: 3 tons of polyglutamic acid fermentation broth are required to prepare 1 ton of liquid product, and the total cost is 3 times the cost of one ton of fermentation broth.

[0036] (8) Energy consumption for concentration: To prepare 1 ton of liquid product, 2 tons of water is produced by vacuum concentration. The steam consumption of four-effect concentration is about 0.8 tons. Based on the steam cost of RMB 250 per ton, the total cost is RMB 200.

[0037] Comparative Example 1 The difference from Example 1 is that ammonium sulfate is not added to the kitchen waste liquid, specifically as follows: The kitchen waste liquid described in Example 1 was transferred into a 100L sterile fermentation tank, and after adjusting the pH value to 6.5, the prepared Bacillus licheniformis was directly inoculated. Bacillus licheniformis A-A2-10 seed liquid, inoculation amount was 3%, ventilation ratio was adjusted to 0.5vvm, tank pressure was 0.08Mpa, dissolved oxygen was maintained at 12% by adjusting the fermentation tank speed, and pH changes were observed. The results showed that the pH value first decreased and then increased during the whole fermentation process, but it was within the range of 6.0-7.0, and there was no need to add acid or alkali to adjust the pH value; the fermentation cycle was 24h, and the polyglutamic acid content was only 3.2g / L determined by QB / T5189-2017 standard, the total sugar consumption was 15g / L, and the conversion rate (polyglutamic acid yield / total sugar consumption ratio) was only 21.33%.

[0038] Comparative Example 2 The difference from Example 1 is that the added bacteria is commercially available Bacillus licheniformis. After observation and determination, it was found that polyglutamic acid could not be produced by fermentation using this commercially available Bacillus licheniformis, which may be related to its lack of polyglutamic acid synthesis ability and inability to tolerate high ammonium sulfate conditions.

[0039] Comparative Example 3 The difference from Example 2 is that total sugar and glutamic acid concentrate are not added as nutrients, and fermentation is directly carried out after only ammonium sulfate is added, as follows: Transfer the kitchen waste liquid into a sterile fermentation tank, add 6wt% ammonium sulfate, stir evenly, adjust the pH value to 6.7, and inoculate the prepared Bacillus licheniformis Bacillus licheniformis A-A2-10 seed liquid, inoculation amount was 5% (v / v), ventilation ratio was adjusted to 0.4vvm, tank pressure was 0.07Mpa, dissolved oxygen was maintained at 15% by adjusting the fermentation tank speed, and pH changes were observed. The results showed that the pH value first decreased and then increased during the whole fermentation process, but it was within the range of 6.0-7.0, and there was no need to add acid or alkali to adjust the pH value; the fermentation cycle was 25h, and the polyglutamic acid content was 1.24g / L and the total sugar consumption was 8.1g / L determined by QB / T5189-2017 standard, and the conversion rate (polyglutamic acid / total sugar consumption ratio) was only 15.3%.

Claims

1. A method for preparing polyglutamic acid based on kitchen waste liquid, characterized in that: The following steps are involved: S1: determining the contents of total sugar and glutamic acid in the waste liquid of kitchen waste. If the total sugar content in the waste liquid is ≥1.2% and the glutamic acid content is ≥0.8%, then proceed to step S11, otherwise proceed to step S12; S11: maintaining the temperature of the kitchen waste liquid at above 70°C, adding ammonium sulfate to the kitchen waste liquid to a concentration of 6%, stirring evenly, and adjusting the pH value to 5.0-6.5, thereby obtaining a polyglutamic acid fermentation medium for standby use; S12: maintaining the temperature of the kitchen waste liquid at above 70° C., adding a regulating liquid until the total sugar content in the kitchen waste liquid is ≥1.2%, and the glutamic acid content is ≥0.8%. At the same time, adding ammonium sulfate to the kitchen waste liquid to a concentration of 6%, stirring evenly, and adjusting the pH value to 5.0-6.5, thereby obtaining a polyglutamic acid fermentation medium for standby use; S2 Add Bacillus licheniformis to the polyglutamic acid fermentation medium obtained in S11 or S12 Bacillus licheniformis A-A2-10 seed liquid, fermenting to obtain fermentation liquid; S3 concentrates the fermentation liquid in S2 to obtain a liquid polyglutamic acid product; "%" in S1, S11 and S12 are all w / v, w is g and v is 100 mL.

2. The method according to claim 1, characterized in that In S12, the regulating liquid is a mixture of molasses and sodium glutamate, or a concentrated solution of glutamate waste liquid; The glutamate waste liquid concentrate is the ammonium sulfate crystallization mother liquor remaining after the glutamate fermentation liquid is subjected to glutamate isoelectric crystallization, impurity removal, and ammonium sulfate concentration crystallization. The total sugar content of the mother liquor is 6-8%, the glutamate content is 6-8%, and the ammonium sulfate content is 30-40%; If the concentration of ammonium sulfate in the kitchen waste liquid is less than 6% after the addition of glutamic acid waste liquid concentrate, then add ammonium sulfate until the concentration reaches 6%; "%" is w / v, w is g, and v is 100mL.

3. The method according to claim 1, characterized in that Bacillus licheniformis Bacillus licheniformis The A-A2-10 strain was deposited in the China Center for Type Culture Collection on March 6, 2020, with the deposit number CCTCC NO: M 2020051; The seed culture medium comprises 3% glucose, 0.2% yeast powder, 0.1% corn steep liquor, 2% ammonium sulfate, and a pH value of 6.

5. The seed culture medium is sterilized at 117° C. and then inoculated. The culture condition is shaking culture at 37° C. for 18 hours to obtain seed liquid, which is then inoculated into a polyglutamic acid fermentation culture medium at an inoculation amount of 2-10%.

4. The method according to claim 1, characterized in that Bacillus licheniformis Bacillus licheniformis The fermentation conditions of A-A2-10 are: ventilation ratio of 0.2~0.5vvm at 37℃, tank pressure of 0.06~0.1Mpa, maintaining dissolved oxygen at 10~15% by controlling the stirring speed of the fermenter, maintaining pH at 6.0~7.0 during the fermentation process, and the fermentation cycle is 20~28h.

5. The method according to claim 1, characterized in that The polyglutamic acid fermentation broth in S3 is concentrated by vacuum concentration to 1 / 3 to 2 / 5 of the original volume.

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