阅读说明：本技术 一种利用污泥基质发酵制备γ-聚谷氨酸的调控方法 (Regulation and control method for preparing gamma-polyglutamic acid by sludge matrix fermentation ) 是由 董滨 李昕 于 2020-07-30 设计创作，主要内容包括：本发明公开了一种利用污泥基质发酵制备γ-聚谷氨酸的调控方法,属于固体废物处理与资源化技术领域。包括以下步骤：1)污泥蛋白-谷氨酸提取(高压水热处理、重力压滤处理)；2)次生代谢合成γ-聚谷氨酸(激活驯化菌种、次生代谢发酵)；3)γ-聚谷氨酸纯品的制备(酸化、离心、过滤、极性互斥析出沉淀、纯化除杂、干燥)。本发明可实现污泥的高值碳氮源回收利用并不造成二次污染,操作简单可行性好,制备成本低,合成的γ-聚谷氨酸具有较高经济价值,应用前景广阔。(The invention discloses a regulation and control method for preparing gamma-polyglutamic acid by utilizing sludge substrate fermentation, belonging to the technical field of solid waste treatment and recycling. The method comprises the following steps: 1) extracting sludge protein-glutamic acid (high-pressure hydrothermal treatment, gravity filter pressing treatment); 2) synthesizing gamma-polyglutamic acid by secondary metabolism (activating domesticated strain, secondary metabolic fermentation); 3) preparing the pure gamma-polyglutamic acid (acidifying, centrifuging, filtering, precipitating with polarity exclusion, purifying, removing impurities, and drying). The method can realize the recycling of the high-value carbon nitrogen source of the sludge without causing secondary pollution, has simple operation and good feasibility, low preparation cost, and the synthesized gamma-polyglutamic acid has higher economic value and wide application prospect.)

1. A regulation and control method for preparing gamma-polyglutamic acid by sludge substrate fermentation is characterized by comprising the following steps: the method comprises the following steps:

1) sludge protein-glutamic acid extraction:

A. pretreatment: putting sludge with the solid content of 10-15% into a high-pressure reaction kettle for pretreatment to obtain sludge slurry;

B. gravity filter pressing treatment: b, performing gravity filter pressing on the sludge slurry obtained in the step A through a filter press to obtain dried sludge and supernatant with the water content of 40-60%, reserving the supernatant, and performing harmless treatment on the dried sludge and recycling the dried sludge;

2) secondary metabolism for synthesis of gamma-polyglutamic acid:

C. activating and domesticating strains: activating and culturing a fermentation strain by using a bacillus seed culture medium with a bacillus number standard, and acclimatizing and culturing the fermentation strain by using a fermentation culture medium added with a fermentation raw material to amplify and propagate the strain to a maximum value to obtain activated and acclimated bacillus;

D. secondary metabolic fermentation: c, inoculating the activated and domesticated bacillus obtained in the step C into the supernatant obtained in the step B, properly ventilating to ensure sufficient oxygen supply, and adjusting fermentation conditions to obtain a fermentation product containing gamma-polyglutamic acid;

3) preparing a pure gamma-polyglutamic acid product:

E. acidifying, centrifuging and filtering: acidifying the fermentation product obtained in the step D, adjusting the pH value to precipitate thalli and polysaccharide, centrifuging, filtering and collecting supernatant;

F. and (3) polarity exclusion precipitation: c, regulating the pH value of the supernatant obtained in the step E, separating out the gamma-polyglutamic acid by using an organic solvent with mutually exclusive polarity, and centrifuging to collect precipitate;

G. purifying and removing impurities: dissolving the precipitate obtained in the step F with deionized water to obtain a gamma-polyglutamic acid solution, dialyzing at 4 ℃ for 6-24 h, and removing small molecular organic substances and inorganic salt impurities by using a dialysis bag with the molecular weight cutoff of 8-12kDa to obtain dialysate;

H. and (3) drying: and D, carrying out vacuum freeze drying on the dialysate obtained in the step H for 24-72H to obtain a pure gamma-polyglutamic acid product.

2. The method for regulating and controlling the fermentation of gamma-polyglutamic acid by using sludge substrate as claimed in claim 1, which is characterized in that: the pretreatment conditions in the step A are as follows: the temperature is 110-220 ℃, the pressure is 0.1-0.3 MPa, and the time is 15min-5 h.

3. The method for regulating and controlling the fermentation of gamma-polyglutamic acid by using sludge substrate as claimed in claim 1, which is characterized in that: in the step C, the C/N ratio of the thallus amplification and propagation is set to be 100:0.5-5, the temperature is controlled to be 25-32 ℃, the pH value is 6.8-7.2, and the culture time is 24-72 h.

4. The method for regulating and controlling the fermentation of gamma-polyglutamic acid by using the sludge substrate as claimed in claim 3, which is characterized in that: the bacillus used in the step C is one of bacillus subtilis, bacillus natto, bacillus amyloliquefaciens, bacillus licheniformis and domesticated bacteria capable of producing gamma-polyglutamic acid.

5. The method for regulating and controlling the fermentation of gamma-polyglutamic acid by using the sludge substrate as claimed in claim 1, wherein the conditions for secondary metabolism in the step D are that C/N is 100:5-40, the temperature is 32-40 ℃, the pH is 5.5-8.5, the rotation speed is 80 r/min-220 r/min, and the fermentation time is 48-96 h.

6. The method for regulating and controlling the fermentation of gamma-polyglutamic acid by using the sludge substrate as claimed in claim 1, wherein in the step E, acid solution is used for regulating the pH value to 1.5-3.5, the centrifugal rotation speed is 3000 rpm-18000 rpm, the time is 5 min-40 min, and the supernatant is separated and collected.

7. The method for regulating and controlling the fermentation of gamma-polyglutamic acid by using the sludge substrate as claimed in claim 6, wherein the acid solution is phosphoric acid, oxalic acid or sulfuric acid.

8. The method for regulating and controlling the fermentation of gamma-polyglutamic acid by using the sludge substrate as claimed in claim 1, wherein the pH value of the step F is adjusted to 3.5-6.5 by using an alkaline solution, and then the gamma-polyglutamic acid is precipitated and separated by using an organic solvent with polarity repulsion and 2-6 times of the volume of the concentrated solution; centrifuging at 8000-15000 rpm for 5-40 min, separating and collecting precipitate.

9. The method for regulating and controlling the fermentation of gamma-polyglutamic acid by using the sludge substrate as claimed in claim 8, wherein the alkaline solution is ammonium bicarbonate, sodium hydroxide or calcium oxide, and the organic solvent with mutually exclusive polarity is one or a mixture of ethanol, acetone and ethylene glycol.

10. The method for regulating and controlling the fermentation of gamma-polyglutamic acid by using the sludge substrate as claimed in claim 9, wherein when the organic solvent with mutually exclusive polarity is mixed by two of ethanol, acetone and ethylene glycol, the mixing ratio is 1: 0.1 to 20; when ethanol, acetone and ethylene glycol are mixed, the mixing ratio is 1: 1-15: 6-30.

Technical Field

The invention relates to the technical field of organic solid waste treatment and recycling, in particular to a regulation and control method for preparing gamma-polyglutamic acid by utilizing sludge substrate fermentation.

Background

In a common secondary sewage treatment plant, the cost generated by sludge treatment is about 30-40% of the total investment, and the total sludge yield is up to 7000 million tons (calculated by 80% water content) in 2020 China is predicted. In the face of such high sludge yield, landfill or incineration after sludge digestion becomes a current common disposal method in China. The landfill method is economic and has been a main means before, but has large occupied area and potential risks of secondary pollution of underground water and the like. Therefore, the sludge resource utilization or high-efficiency treatment method becomes a very concerned research hotspot in China and even all over the world.

Gamma-polyglutamic acid (gamma-PGA) is an extracellular polymer which can be generated by fermentation of glutamic acid by microorganisms, is a novel water-soluble and biodegradable polymer material, and has wide application prospect in the fields of environmental protection, chemical industry and the like. The existing fermentation technology adopts fermentation culture media synthesized by substances such as natto, dipotassium hydrogen phosphate and the like, so that the cost of the fermentation culture media is overhigh. In addition, the traditional purification method has many problems, such as great difficulty in removing inorganic salts generated in the traditional purification process, high price of ultrafiltration permeation purification and the like. These result in a lack of market competitiveness in the price of gamma-polyglutamic acid.

The sludge is used as an organic waste with high protein content (the protein accounts for about 60-80% of the organic matter content), and the amino acid contained in the sludge is mainly alanine (Ala) and glutamic acid (Glu), and can reach 20-30% of the total amount of the amino acid; this provides the possibility of fermentation production of polyglutamic acid by using sludge as a cheap base material. However, the sludge components are complex, and the key points of the problems are how to ensure that microorganisms can utilize protein-glutamic acid in the sludge to carry out secondary metabolism to generate gamma-PGA, and how to change a large amount of inorganic salts brought by the traditional purification method for adjusting the pH value and ensure the feasibility and the economic benefit of the process.

Disclosure of Invention

The invention aims to solve the technical problem of the prior art and provides a regulation and control method for preparing gamma-polyglutamic acid by utilizing sludge substrate fermentation, which has low preparation cost, simple and convenient operation and stable product quality.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a regulation and control method for preparing gamma-polyglutamic acid by sludge substrate fermentation comprises the following steps:

1) sludge protein-glutamic acid extraction:

A. pretreatment: putting sludge with the solid content of 10-15% into a high-pressure reaction kettle for pretreatment to obtain sludge slurry;

B. gravity filter pressing treatment: b, performing gravity filter pressing on the sludge slurry obtained in the step A through a filter press to obtain dried sludge and supernatant with the water content of 40-60%, reserving the supernatant, and performing harmless treatment on the dried sludge and recycling the dried sludge;

2) secondary metabolism for synthesis of gamma-polyglutamic acid:

C. activating and domesticating strains: activating and culturing a fermentation strain by using a bacillus seed culture medium with a bacillus number standard, and acclimatizing and culturing the fermentation strain by using a fermentation culture medium added with a fermentation raw material to amplify and propagate the strain to a maximum value to obtain activated and acclimated bacillus;

D. secondary metabolic fermentation: c, inoculating the activated and domesticated bacillus obtained in the step C into the supernatant obtained in the step B, properly ventilating to ensure sufficient oxygen supply, and adjusting fermentation conditions to obtain a fermentation product containing gamma-polyglutamic acid;

3) preparing a pure gamma-polyglutamic acid product:

E. acidifying, centrifuging and filtering: acidifying the fermentation product obtained in the step D, adjusting the pH value to precipitate thalli and polysaccharide, centrifuging, filtering and collecting supernatant;

F. and (3) polarity exclusion precipitation: c, regulating the pH value of the supernatant obtained in the step E, separating out the gamma-polyglutamic acid by using an organic solvent with mutually exclusive polarity, and centrifuging to collect precipitate;

G. purifying and removing impurities: dissolving the precipitate obtained in the step F with deionized water to obtain a gamma-polyglutamic acid solution, dialyzing at 4 ℃ for 6-24 h, and removing small molecular organic substances and inorganic salt impurities by using a dialysis bag with the molecular weight cutoff of 8-12kDa to obtain dialysate;

H. and (3) drying: and D, carrying out vacuum freeze drying on the dialysate obtained in the step H for 24-72H to obtain a pure gamma-polyglutamic acid product.

In order to optimize the technical scheme, the adopted measures further comprise:

the pretreatment conditions in the step A are as follows: the temperature is 110-220 ℃, the pressure is 0.1-0.3 MPa, and the time is 15min-5 h.

C/N for the thallus amplification and propagation in the step C is set to be 100:0.5-5, the temperature is controlled to be 25-32 ℃, the pH is 6.8-7.2, and the culture time is 24-72 h.

The bacillus used in the step C is one of bacillus subtilis, bacillus natto, bacillus amyloliquefaciens, bacillus licheniformis and domesticated bacteria capable of producing gamma-polyglutamic acid.

Setting the conditions of the secondary metabolism in the step D to be 100:5-40, the temperature to be 32-40 ℃, the pH to be 5.5-8.5, the rotating speed to be 80-220 r/min and the fermentation time to be 48-96 h.

And E, adjusting the pH to 1.5-3.5 by using acid liquor, carrying out centrifugation at 3000-18000 rpm for 5-40 min, and separating and collecting supernate.

The acid solution is phosphoric acid, oxalic acid or sulfuric acid.

In the step F, the pH value is adjusted to 3.5-6.5 by using an alkaline solution, and then the gamma-polyglutamic acid is precipitated and separated out by using an organic solvent with polarity exclusion of 2-6 times of the volume of the concentrated solution; centrifuging at 8000-15000 rpm for 5-40 min, separating and collecting precipitate.

The alkaline solution is ammonium bicarbonate, sodium hydroxide or calcium oxide, and the organic solvent with mutually exclusive polarity is one or a mixture of ethanol, acetone and glycol.

When the organic solvent with mutually exclusive polarity is mixed by two of ethanol, acetone and glycol, the mixing ratio is 1: 0.1 to 20; when ethanol, acetone and ethylene glycol are mixed, the mixing ratio is 1: 1-15: 6-30.

Compared with the prior art, the regulation and control method for preparing the gamma-polyglutamic acid by utilizing the sludge substrate fermentation has the following advantages:

(1) the present invention can produce 1kg of highly pure (> 95%) gamma-polyglutamic acid with about 42-50kg of sludge (85% water basis). Meanwhile, the sludge is used as organic waste, the yield is huge, and the treatment and disposal of the sludge are always difficult at home and abroad; the invention provides a large amount of free fermentation base material, and can solve the problem of high price of the fermentation base material in the prior art.

(2) The invention changes the traditional acid-base regulating medicament, solves the problem of excessive introduction of inorganic salt impurities in the purification process in the prior art, reduces the dialysis times, and ensures simple and convenient operation and reduces the total cost.

(3) The invention adopts the organic solvent with mutually exclusive polarity to separate out the gamma-polyglutamic acid, can be recycled by reduced pressure distillation, and only 1-2L of the organic solvent with mutually exclusive polarity needs to be lost for purifying 1-3kg of supernate each time.

(4) The cost for preparing each kilogram of pure gamma-polyglutamic acid is about 60-100 yuan, the production cost of the gamma-polyglutamic acid is greatly reduced, and the finished product can reach the standard of agricultural gamma-polyglutamic acid; the price of the polyglutamic acid on the market is generally more than 150 yuan/kg.

Drawings

FIG. 1 is a process flow diagram of the present invention.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and examples.

As shown in figure 1, the regulation and control method for preparing gamma-polyglutamic acid by utilizing sludge substrate fermentation comprises the following steps:

1) sludge protein-glutamic acid extraction:

A. pretreatment: putting sludge with the solid content of 10-15% into a high-pressure reaction kettle for pretreatment to obtain sludge slurry; the pretreatment conditions were: the temperature is 110-220 ℃, the pressure is 0.1-0.3 MPa, and the time is 15min-5 h.

B. Gravity filter pressing treatment: b, performing gravity filter pressing on the sludge slurry obtained in the step A through a filter press to obtain dried sludge and supernatant with the water content of 40-60%, reserving the supernatant, and performing harmless treatment (aerobic fermentation and the like) on the dried sludge to recycle resources; the dried sludge can be used as a soil conditioner after resource recovery.

2) Secondary metabolism for synthesis of gamma-polyglutamic acid:

C. activating and domesticating strains: activating and culturing a fermentation strain by using a bacillus seed culture medium with a bacillus number standard, and acclimatizing and culturing the fermentation strain by using a fermentation culture medium added with a fermentation raw material to amplify and propagate the strain to a maximum value to obtain activated and acclimated bacillus; setting the C/N ratio of thallus amplification propagation at 100:0.5-5, controlling the temperature at 25-32 ℃, the pH at 6.8-7.2, and culturing for 24-72 h; the bacillus is one of bacillus subtilis, bacillus natto, bacillus amyloliquefaciens, bacillus licheniformis and domesticated bacteria capable of producing gamma-polyglutamic acid.

D. Secondary metabolic fermentation: c, inoculating the activated and domesticated bacillus obtained in the step C into the supernatant obtained in the step B, properly ventilating to ensure sufficient oxygen supply, and adjusting fermentation conditions to obtain a fermentation product containing gamma-polyglutamic acid; setting the conditions of secondary metabolism as C/N of 100:5-40, temperature of 32-40 deg.C, pH of 5.5-8.5, rotation speed of 80-220 r/min, and fermentation time of 48-96 h.

3) Preparing a pure gamma-polyglutamic acid product:

E. acidifying, centrifuging and filtering: acidifying the fermentation product obtained in the step D, adjusting the pH value to precipitate thalli and polysaccharide, centrifuging, filtering and collecting supernatant; adjusting pH to 1.5-3.5 with acid solution, centrifuging at 3000-18000 rpm for 5-40 min, separating, and collecting supernatant; the acid solution is phosphoric acid, oxalic acid or sulfuric acid.

F. And (3) polarity exclusion precipitation: c, regulating the pH value of the supernatant obtained in the step E, separating out the gamma-polyglutamic acid by using an organic solvent with mutually exclusive polarity, and centrifuging to collect precipitate; adjusting pH to 3.5-6.5 with alkaline solution, and precipitating with polar mutual exclusion organic solvent 2-6 times the volume of the concentrated solution; centrifuging at 8000-15000 rpm for 5-40 min, separating and collecting precipitate; the alkaline solution is ammonium bicarbonate, sodium hydroxide or calcium oxide, the organic solvent with mutually exclusive polarity is one or a mixture of ethanol, acetone and glycol, and when the organic solvent with mutually exclusive polarity is mixed by two of the ethanol, the acetone and the glycol, the mixing ratio is 1: 0.1 to 20; when ethanol, acetone and ethylene glycol are mixed, the mixing ratio is 1: 1-15: 6-30.

G. Purifying and removing impurities: dissolving the precipitate obtained in the step F with deionized water to obtain a gamma-polyglutamic acid solution, dialyzing at 4 ℃ for 6-24 h, and removing small molecular organic substances and inorganic salt impurities by using a dialysis bag with the molecular weight cutoff of 8-12kDa to obtain dialysate;

H. and (3) drying: and D, carrying out vacuum freeze drying on the dialysate obtained in the step H for 24-72H to obtain a pure gamma-polyglutamic acid product.

The preparation of gamma-polyglutamic acid according to the invention is further illustrated by the following specific examples: