Possible Causes And Prevention Methods Of Bacterial Contamination In Fermentation Tanks

2023-09-12 09:03:24
Possible Causes And Prevention Methods Of Bacterial Contamination In Fermentation Tanks
In the fermentation tank and its ancillary equipment (air purification system, temperature, pressure flow and other control systems and corresponding pipeline valves), problems in any link may cause fermentation failure. Therefore, enterprises should first establish the concept of "prevention first" and start with equipment to eliminate various hidden dangers that may cause fermentation contamination.

Ensure fermentation tank sealing

The fermentation tank is the main equipment for fermentation production. Before use, the fermentation tank needs to be carefully inspected, such as whether there is any abnormality in the rotation of the mixing system, whether the mechanical seal is tight, whether the screws in the tank are loose, whether the pipes in the tank are blocked, whether the mezzanine or the coil in the tank is leaking , and whether the tank connection valve is tight, etc.

At present, mechanical seals are widely used in fermentation tanks, replacing the previous packing seal form of the mixing shaft. However, if the installation accuracy is not high or the mechanical seal system selected is inappropriate, shaft seal leakage will still occur, causing bacterial contamination. Therefore, pay attention to the alignment when installing the mixing shaft.

Remove sight glass and flush pipe

In order to facilitate the observation of the fermentation conditions in the fermentation tank, steam pipes for rinsing the sight glasses are generally installed in large fermentation tanks. However, once steam condenses in the pipe, the sterility of the condensed water cannot be guaranteed. Therefore, the steam pipe for flushing the sight glass should be removed to reduce the risk of bacterial contamination. If you can't see clearly due to heavy fog inside the tank, you can use a higher brightness sight glass light.

PVDF membrane purification effect is reliable

Traditional air purification systems use activated carbon, cotton, and ultra-fine glass fiber paper as filter elements, which have poor filtration effects and complicated operations. At present, domestic membrane filtration technology is relatively mature. For example, the pleated microporous membrane filter element made of vinylidene fluoride (PVDF) not only has high filtration accuracy, but also has a large flow rate. When using it, technicians only need to pay attention to dehumidification and deoiling of the compressed air in front of the filter, and sterilize the filter according to specifications to ensure that the air is sterile. In addition, because the PVDF membrane is not sensitive to moisture in compressed air and the membrane itself is highly hydrophobic, it can solve the problem that cotton filters cannot be used when the air humidity is too high.

Regular testing and monitoring system

The sterilization treatment of the fermentation medium uses high-temperature supersaturated steam to coagulate and kill various bacteria and fungal proteins. In the sterilization of the pharmaceutical industry, there are strict requirements for preheating time, steam valve opening, sterilization temperature, sterilization pressure and foam control. Problems in any of these links can easily lead to bacterial contamination. Generally, the sterilization temperature in industry is 110°C and the sterilization pressure is above 0.5 MPa. Ensuring the accuracy of sterilization temperature and pressure relies on various temperature probes, pressure sensors and other monitoring systems. Therefore, it is very important to test such probes, sensors, etc. regularly. In addition, as the volume of the fermentation tank increases, the tank temperature corresponding to the same tank pressure decreases. Therefore, when the correlation between temperature and pressure is found to change, the temperature should prevail.

Valves should use soft seals

Valves are ancillary equipment commonly used in fermentation equipment, among which stop valves are most commonly used. The sealing performance of valves to media can be divided into four levels, namely nominal level, low leakage level, steam level and atomic level. Nominal grade and low leakage grade seals are suitable for valves with loose closing requirements, such as valves used to control flow. Steam grade sealing is suitable for sealing the valve seat, valve stem and valve body connection of steam and most other industrial valves. Atomic level sealing is suitable for occasions where media sealing is required, such as spacecraft and atomic power equipment. Since high-temperature steam is used to sterilize fermentation equipment in the fermentation industry, the sealing performance of the valve to the medium is required to be steam-level sealing.

Since the valve is opened frequently during the fermentation process and is often damaged by medium corrosion, erosion and cavitation, the selection of the valve substructure, that is, the part where the valve seat and closing member contact each other for closing, is critical. The sealing of the valve auxiliary structure is divided into two types: soft seal and hard seal. The sealing pair structure of the hard seal relies on the valve seat and the closing member to squeeze each other and undergo slight elastic-plastic deformation to form a closed circular sealing contact line. Although this type of valve has a good sealing effect in the initial stage of application, the fermentation valve is opened more frequently, which easily wears the previously formed contact line, or causes indentation and damage to the sealing surface due to unclean pipes. The elastic deformation of the sealing structure of the hard seal is very small, and it is difficult to form a new sealing contact line. Therefore, long-term use may cause the valve to leak and cause fermentation to fail. Soft-sealed valve closing parts generally use soft gaskets, which use the larger elastic-plastic deformation of the gasket to form a wider annular sealing contact zone to fill up the unevenness on the sealing surface and eliminate gaps to form a seal. The processing accuracy is generally not high. If there are special requirements, the valve body material can be made of stainless steel, and the soft sealing closing part can be made of replaceable PTFE gaskets. In this way, the PTFE gaskets can be frequently replaced to ensure the valve's reliability. Tightness.

Emphasis on seal checks on valves

If the processing quality of the stem and the hole in the valve body of the stop valve is not good, or the matching gap between the packing and the valve stem is increased due to wear and tear due to long-term use, it will cause the medium to leak from the valve stem. This phenomenon is called valve "Leaking upper seal". However, in fermentation production, the upper seal inspection of the valve is often ignored. In 2003, a valve upper seal leakage caused a cordyceps fermentation workshop in Xinjiang to become contaminated with bacteria for a month, causing the company to suffer huge economic losses. Therefore, for fermentation valves, we must not only pay attention to the leakage of the sealing auxiliary structure, but also pay attention to the leakage of the upper seal.

In fermentation production, due to the requirements of the fermentation process, some valves are not installed according to the flow direction of the fluid. For example, in some fermentation tanks, the sampling valve is a valve close to the fermentation tank. In order to sterilize the valve before sampling, the valve The installation is opposite to the flow direction of the fermentation liquid, so that a small additional valve can be installed at the bottom of the sampling valve to allow steam to flow. The sealing requirements of the upper sealing structure of the sampling valve are very high, otherwise the fermentation liquid may penetrate into the upper sealing structure of the sampling valve or even leak from the upper sealing structure, thereby causing fermentation contamination.

At present, most domestic stop valves have a multi-layer packing structure, and a hard spacer ring is added to the packing structure, or the upper part of the sealing ring has a disc spring, which improves the ability to self-adjust the sealing force and improves the sealing performance. If upper seal leakage occurs, and it is difficult to change the upper seal structure of domestic valves, the leakage problem can be solved by changing the type of packing. For example, the current new expanded polytetrafluoroethylene sealing filler can replace conventional asbestos and expanded graphite fillers, which is wear-resistant, corrosion-resistant, and has a very good sealing effect. The main ones are the air system and the dead space in the tank, followed by the seed, operation and equipment systems. If it is spores, it is most likely a dead spot, and if it is a large area, it is mostly an air system. You can track the sterility test, see the time of infection and the relationship between bacteria types, and track sterility from seed preparation to fermentation tank.

Other points

1.Maintain aseptic operation throughout the process;

2.Ensure that the seeds are normal, free of contamination, miscellaneous bacteria and mutations;

3.The air filter must maintain its quality;

4.Be careful not to have too much foam;

5.Ensure the sterility of the air system;

6.The tightness of the tank, especially some dead corners, requires special attention;

7.When transplanting, ensure the sterility of pipelines and dead ends;

8.The feeding system must be sterile during mid-term feeding.