Application of membrane separation technology in biological fermentation industry (reprinted)

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Membrane Separating is a method that uses natural or artificially prepared selectively permeable membranes to separate, classify, purify and concentrate two-component or multi-component solutes and solvents using external energy or chemical potential differences as the driving force. Membrane separation method can be used for liquid phase and gas phase. For liquid phase separation, it can be used for aqueous solution system, non-aqueous solution system and hydrosol system. According to its separation method, it can be divided into reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), electrodialysis (ED), gas separation (GS) and pervaporation (PV), as well as separation processes combined with other processes. Because membrane separation technology is energy-saving, efficient, simple, low-cost, and easy to operate, it can replace traditional separation technology. Therefore, it is a revolution in traditional separation methods and is recognized as one of the most promising high technologies from the end of the 20th century to the middle of the 21st century. The fermentation industry is an emerging industry that emerged rapidly in the second half of the 20th century. It is basically an industry that uses grain as the main raw material and manufactures products through microbial fermentation. The fermentation industry is a new growth point for the development of my country's light industry, and membrane separation is one of the key technologies for the technological transformation of the fermentation industry. Usually, the methods for separation and refining of fermentation products mainly include precipitation method, salting out method, solvent extraction method, adsorption method, etc. In addition to these main separation processes, they must also be supplemented by processes such as bacterial separation, concentration, decolorization, and crystallization. In order to improve product quality, reduce costs, increase yield and shorten processing time, existing post-processing processes and methods need further research and improvement. In addition, with the rapid development of biotechnology, new products are constantly emerging, and a variety of substances with complex structures that were not available in the past have been obtained. The purity requirements of new products have increased accordingly, which has put forward new requirements for the post-processing process. As a new type of separation technology, membrane technology does not involve phase changes during the separation process and does not cause secondary pollution. It also has the function of biofilm concentration and enrichment during separation. At the same time, it is easy to operate, has a compact structure, low maintenance costs, and is easy to automate. Therefore, it has been applied in the post-processing process of a variety of fermentation products. The use of membrane technology to treat fermentation broth can remove various impurities that are significantly different from the molecular weight of the target product according to the molecular weight of the substance, improve the quality of the fermentation broth, facilitate the subsequent process, increase product purity and yield, reduce solvent consumption, and reduce energy consumption. The most commonly used ones are microfiltration, ultrafiltration, nanofiltration and reverse osmosis. A large number of experimental studies have been conducted on the application of membrane technology in the post-treatment process of fermentation broth, and some have achieved industrialization. Its research and application work mainly focuses on antibiotics, vitamins, amino acids, enzyme preparations, etc. The production process of antibiotics is roughly divided into four processes: fermentation, filtration, concentration and drying. At present, membrane technology is mainly used for clarification of antibiotic fermentation broth, concentration and desalination of products, and concentration of antibiotics in waste liquid. The antibiotic stock solution produced by fermentation method contains 4% biological residues, variable salt, and about 0.1% to 0.2% antibiotics. The traditional method uses solvent extraction to separate the antibiotics from the fermentation broth, and then vacuum evaporates the extract to obtain the antibiotics. However, this method has the disadvantages of purifying and concentrating antibiotics, such as large amounts of organic solvents, high energy consumption for evaporation and concentration, and poor operating environment. Nanofiltration membranes can be used in two ways to recover and purify antibiotics: One is to first use solvent extraction and then use nanofiltration membrane to concentrate. This process can save 80% of the cost because the solvent can be recycled. ； The other is to use membrane concentration first and then solvent extraction. This method can * * Improve the production capacity of extraction equipment and reduce the amount of solvent. In the post-treatment process of antibiotics, in addition to nanofiltration membranes, ultrafiltration and reverse osmosis are also widely used. Microfiltration membrane is used to remove mycelium in penicillin G fermentation broth, and the recovery rate of penicillin G can reach 98%. The combined separation technology of ultrafiltration and nanofiltration is used to purify and concentrate the lincomycin fermentation broth. * * It saves solvent and energy, shortens and optimizes the traditional process route, and improves product yield and quality. The use of ultrafiltration membrane separation technology during the refining process of penicillin can remove proteins and other macromolecular impurities, eliminate emulsification during extraction, and improve the yield of the extraction process. The fermentation filtrates of kanamycin sulfate and cephalosporin C were treated using suitable ultrafiltration membranes with satisfactory results. Vitamin C (VC for short) is a typical product produced by fermentation method. VC is sorbitol fermented under the action of bacteria to form 2-homo-L-gulonic acid, an intermediate for the preparation of VC. Guronic acid is further converted and produced after purification. Due to the use of bacterial fermentation, impurities such as mycelium, proteins and suspended particles remain in the fermentation broth. The use of ultrafiltration membrane systems can eliminate the need for pretreatment, heating, centrifugation and other processes, which not only reduces energy consumption, but also increases the yield of gulonic acid. ； A lot of research has been done on using membrane technology to treat VC fermentation broth and has been successfully industrialized. Amino acids are widely used in the food and pharmaceutical industries and as animal feed additives. In addition, they are also used as synthetic intermediates for certain special compounds. At present, most amino acids can be produced by microbial fermentation. In the process of producing amino acids by fermentation, ultrafiltration membranes can be used to intercept and recycle the yeast in the production liquid. The permeate liquid is concentrated through a nanofiltration membrane or a reverse osmosis membrane, and then is crystallized to obtain high-purity amino acid products, while saving strain cultivation costs and separation energy consumption. In addition, nanofiltration membranes can be used to recycle and concentrate the residual liquid in amino acid production, which can not only increase production but also reduce pollution. Enzymes are special proteins with high catalytic activity. Liquid enzyme preparations produced industrially must be concentrated and purified. The traditional production process includes fermentation, flocculation and sedimentation, filtration, solvent extraction, vacuum evaporation, and drying. The production process has high energy consumption, high enzyme inactivation rate, and low yield. The molecular weight of commonly used enzyme preparations is between 10,000 and 100,000 Dal, which is exactly within the application range of ultrafiltration technology. The enzyme fermentation broth is concentrated and purified using membrane technology and operated at normal temperature, which reduces the impact of temperature on the quality of the enzyme preparation, eliminates phase changes during the evaporation process, has low energy consumption, is simple to operate, uses no or less solvents, and reduces solvent consumption and solvent recovery costs.