Technical solution for producing amino acid fertilizer from protein waste

The hydrolysis of protein waste to produce amino acid fertilizers mainly includes three steps: pretreatment of raw materials, protein hydrolysis and preparation of amino acid fertilizers.

(1) Raw materials and pretreatment

Source of raw materials: Amino acid-rich wastes produced by refined amino acids; protein-rich animal and plant wastes such as leather, hair, hoof, blood, cotton aphid, bean cake, etc. Some raw materials need to be cleaned and cleaned.

(2) Protein hydrolysis

There have been a lot of studies on the preparation of amino acids by protein hydrolysis. The main methods of protein hydrolysis are acid hydrolysis, alkaline hydrolysis and enzymatic hydrolysis.

Acid hydrolysis is currently the main method used in the production of amino acids. The commonly used acids are hydrochloric acid and sulfuric acid, and less hydrolysis with phosphoric acid and nitric acid. The auxiliary means used in the acid hydrolysis process are ultrasound, microwave, etc., which are common in the experimental research stage. Qin Weijia [2] optimized the silkworm pupa protein extraction and silkworm pupa protein complex amino acid preparation process, and hydrolyzed the remaining protein in sputum with hydrochloric acid (protein content 64.4%). The degree of proteolysis can be as high as 60.4% under the condition of ****. Li Baozhu et al [3] used soybean meal as raw material to hydrolyze by sulfuric acid, and the yield of ammonia nitrogen reached 59.9 mg/g.

Amino acid hydrolyzates prepared by acid hydrolysis often contain a large amount of acid, and there are two main methods for removing acid - neutralization and evaporation. The neutralization method removes the acid in the hydrolyzate by acid-base neutralization and simultaneously forms a certain salt. The substances commonly used to neutralize the acid are alkali metal salts such as sodium hydroxide, potassium hydroxide and calcium hydroxide. Ammonia, ammonia and ammonium salts, which substance is neutralized, depends on the intended product and economic cost. This method is applicable to all acid hydrolysis solutions for acid hydrolysis. Evaporation under reduced pressure: the acid is removed and recovered by evaporation under reduced pressure, and is recycled. The method is suitable for hydrolyzing protein to prepare amino acids, but correspondingly produces a certain energy consumption, and the effect of removing acid is not ideal. Only found in experimental research. The preparation of commercial amino acids is mostly carried out by ammonium neutralization and spray drying.

The base used for alkaline hydrolysis is mainly sodium hydroxide and potassium hydroxide. Most amino acids in the alkaline hydrolysis process are destroyed to varying degrees and produce racemization, and the hydrolysis rate is usually lower than that of acid hydrolysis. The amino acid hydrolysate prepared by alkaline hydrolysis usually contains a large amount of a base, which needs to be neutralized, and can be neutralized with an acid or protein acid hydrolyzate. Li Hao and others used sodium hydroxide to hydrolyze pig blood. Under the hydrolysis process conditions, 38.25 mg of complex amino acids per gram of pig blood powder was obtained.

Enzymatic hydrolysis does not produce racemization and does not destroy proteins. However, an enzyme often does not completely hydrolyze proteins, and it is often necessary to work synergistically with several enzymes to fully hydrolyze proteins. Enzymatic hydrolysis can be carried out directly by enzymes, or by means of microbial fermentation techniques, the proteins produced by microorganisms can be used to hydrolyze proteins into amino acids. The conditions for enzymatic hydrolysis are relatively harsh, and the current microbial fermentation technology is not mature enough to be used in the large-scale production of amino acids in proteolysis. Since the enzymatic hydrolysis does not require a neutralization procedure, it does not introduce neutralization into the fertilizer. The salt does not need to consider the adverse effects of salt accumulation caused by the use of continuous cultivation on the land. Based on the perspective of environmental protection, with the advancement of microbial fermentation technology, the preparation of amino acids by enzymatic hydrolysis, especially microbial fermentation. Quite an advantage. Li Tingxun et al [5] used Bacillus licheniformis and protease to degrade livestock blood to make liquid amino acids. Zhang Wenfeng [6] used the excess sludge as raw material to prepare sludge protein extract by enzymatic hydrolysis, and then enzymatically hydrolyzed the sludge protein extract obtained under the conditions of enzymatic hydrolysis to prepare complex amino acids at pH 10. 0. Under the hydrolysis condition of 9 mg/mL, 8 h, and 55 °C, 10.62 g of compound amino acid was obtained per 100 g of dry sludge.

(3) Preparation of amino acid fertilizer

The treated amino acid hydrolyzate can be directly prepared into a solid amino acid powder by concentration and drying treatment, and the powder can be directly sprayed into the crop in the form of nutrition, or can be added into the fertilizer in the form of a nutrient to prepare an amino acid ecological fertilizer and an amino acid compound fertilizer. Amino acid fertilizers such as amino acid water-soluble fertilizers and amino acid foliar fertilizers; by utilizing the complexing properties of amino acids, it is also possible to add medium and trace elements to amino acid hydrolyzate to prepare amino acid chelated micro-fertilizers. Xu Lijuan et al [7] prepared a complex amino acid trace element chelated fertilizer by using the composite amino acid hydrolyzed from animal protein waste and the trace elements manganese, zinc and copper as raw materials. Li Tingxun et al [5] of Qingdao Yujun Fertilizer Co., Ltd. [5] used amino acid liquid fertilizer prepared by degrading livestock blood with Bacillus licheniformis and soybean-derived protease to produce liquid amino acids.