Regulation Method for Preparing Gamma-Polyglutamic Acid by Sludge Substrate Fermentation

A regulation method for preparing γ-polyglutamic acid by sludge substrate fermentation, comprising the following steps:

• 1) extraction of glutamic acid from a sludge protein
• A. pretreatment:
• putting a sludge with a solid content of 10%-15% into a high-pressure reactor for a pretreatment to obtain a sludge slurry;
• B. gravity pressure filtration treatment:
• performing a gravity pressure filtration on the sludge slurry obtained in step A through a filter press, to obtain a dried sludge with a moisture content of 40%-60% and a first supernatant, keeping the first supernatant, and recycling the dried sludge after performing a harmless treatment on the dried sludge;
• 2) synthesis of the γ-polyglutamic acid by a secondary metabolism
• C. activation of domesticated strains:
• using a standard Bacillus seed medium to activate and cultivate fermentation strains to obtain activated fermentation strains, and then using a fermentation medium added with fermentation raw materials to domesticate and cultivate the activated fermentation strains to obtain domesticated fermentation strains, and to amplify and propagate the domesticated fermentation strains to a maximum value, to obtain activated and domesticated Bacillus;
• D. secondary metabolic fermentation:
• inoculating the activated and domesticated Bacillus obtained from step C into the first supernatant of step B, performing a predetermined ventilation to ensure a sufficient oxygen supply, and adjusting fermentation conditions to obtain a fermentation product containing the γ-polyglutamic acid;
• 3) preparation of pure γ-polyglutamic acid
• E. acidification, centrifugation and filtration:
• acidifying the fermentation product containing the γ-polyglutamic acid obtained in step D to adjust a pH level of the fermentation product to precipitate the activated and domesticated Bacillus and polysaccharides, filtering after a first centrifugation, and collecting a second supernatant;
• F. precipitation based on polar repulsion:
• restoring a pH level of the second supernatant obtained in step E and using an organic solvent with repellent polar to precipitate the γ-polyglutamic acid, and collecting a precipitation after a second centrifugation;
• G. purification and impurity removal:
• dissolving the precipitation obtained in step F in deionized water to obtain a γ-polyglutamic acid solution, dialyzing the γ-polyglutamic acid solution at 4° C. for 6 hr-24 hr, removing small molecular organic substances and inorganic salt impurities by a dialysis bag with a molecular weight cut-off of 8-12 kDa to obtain a dialysate;
• H. drying:
• performing a vacuum freeze-drying on the dialysate obtained in step G for 24-72 hr to obtain the pure f-polyglutamic acid.