Possible causes and prevention methods of bacterial contamination in fermentation tanks

Possible causes and prevention methods of bacterial contamination in fermentation tanks

Any problem in the fermentation tank and its ancillary equipment (air purification system, temperature, pressure and flow control system, and corresponding pipeline valves) 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 and bacterial contamination.

Ensure the sealing of the fermentation tank

Fermentation tank is the main equipment for fermentation production. Before use, it is necessary to carefully inspect the fermentation tank, such as checking whether the mixing system rotates abnormally, whether the mechanical seal is tight, whether the screws inside the tank are loose, whether the pipes inside the tank are blocked, whether the interlayer or coil inside the tank leaks, and whether the tank body connecting valves are tight.

At present, mechanical seals are widely used in fermentation tanks, replacing the previous packing seal form of mixing shafts. However, if the installation accuracy is not high or the mechanical seal system selected is not suitable, shaft seal leakage can still occur, causing bacterial contamination. Therefore, attention should be paid to alignment when installing the mixing shaft. It is reported that a fermentation workshop in Xinjiang adopts a fixed and adjustable intermediate bearing with a pull rod. By adjusting the position of the intermediate bearing, the swing of the mixing shaft is reduced, and a multi spring balanced mechanical seal is used to offset the partial offset of the mixing shaft with the spring force in different directions, effectively achieving sealing.

■ Remove the mirror flushing pipeline

In order to facilitate observation of the fermentation situation inside the fermentation tank, steam pipes for flushing sight glasses are generally installed in large fermentation tanks. However, once steam condenses in the pipeline, the sterility of the condensed water cannot be completely guaranteed. Therefore, the steam pipeline for flushing the sight glass should be removed to reduce the risk of bacterial contamination. If the fog inside the tank is too thick to see clearly, a higher brightness mirror light can be used.

The purification effect of PVDF membrane is reliable

Traditional air purification systems use activated carbon, cotton, and ultra-fine glass fiber paper as filter cartridges, which have poor filtration efficiency and complex operation. At present, the membrane filtration technology in China is relatively mature. For example, the folded microporous membrane filter made of polyvinylidene fluoride (PVDF) not only has high filtration accuracy, but also has a large flow rate. When using, technicians only need to pay attention to dehumidification and degreasing of the compressed air before the filter, and sterilize the filter according to specifications to ensure that the air is sterile. In addition, due to the insensitivity of PVDF membrane to moisture in compressed air and its strong hydrophobicity, it can solve the problem of cotton filters being unusable when the air humidity is too high in the past. A fermentation workshop in Xinjiang investigated the purification effect of PVDF filters on 10 ton fermentation tanks. The technicians hung a sample bottle after the filter, using sterilized LB universal bacterial culture medium without inoculation. Compressed air was continuously introduced after filtration to monitor the effectiveness of the filter (as long as the LB universal bacterial culture medium remained clear, it indicated that the filter was operating normally). The results showed that the filter of the 10 ton fermentation tank in the workshop was used continuously for 3 months, and the microscopic inspection of the sample bottles showed that the LB bacterial culture medium was sterile. Therefore, the purification effect of the microporous membrane (PVDF) was reliable.