1 Aseptic downstream process problems The downstream process of the fermented product usually requires that the equipment used meets specific needs, especially in the process of concentrating and washing pathogenic microorganisms or microorganisms sensitive to infection, requiring the process to be closed and absolute. safe.
On the one hand, the process must ensure that the product is not infected by external bacteria; on the other hand, the process must ensure that the pathogenic microorganisms are not released.
Large-scale production of bacteria, actinomycete cultures, and industrial extraction of toxoid or live virus vaccines required by the food industry are examples of closed steam sterilization separation systems. Such systems have been used more and more widely in recent years, which puts more stringent requirements on centrifuges. [1~3]
The advantage of the centrifuge for separating and concentrating microorganisms is that it has a compact structure that can be operated continuously and completely automatically, and can be adapted to handle changing products in a safe, reliable and rapid manner. Figure 1 lists fermentation products that can be centrifuged, including feed yeast, intracellular enzymes, extracellular enzymes, antibiotics, and the like. These large-scale industrial production of fermentation products, the requirements for centrifuges are only limited to the operation is simple and fast, such as the need to open the machine cleaning can be put into use (only need to "clean in place"), but for the production of those genetically modified The resulting product, the requirements are much more complicated, and the sterile centrifuge is put into use.
In extracting these cultures, the system is completely sealed and steam sterilized at 121 °C to ensure no external bacterial contamination. The newly designed centrifuge system meets these needs for the production of vaccines and other products. It consists of automatically controlled in-situ cleaning (CIP) to remove residual liquid, followed by automated steam sterilization.
2 Aseptic Separator System The design of the centrifuge for closed aseptic processing is based on the existing automated high performance disc drum centrifuge. Figure 2 is a cross-sectional view of the mechanism of the centrifuge.
There are two ways of feeding: Type A is non-hermetic, it has an outlet centripetal pump to discharge the supernatant with pressure; Type B is airtight or mechanically sealed. Type A does not have the wear phenomenon caused by mechanical seals, and can rely on the liquid pressure discharge to prevent or reduce the generation of foam; Type B machine can operate under high airtight pressure (0 588 ~ 0 686MPa), so it can isolate any The gas is discharged. Both feeding methods ensure that the material is isolated from the outside world when it is processed.
The centrifuge drum has a large number of tapered discs, each having a spacer of 0 3 to 0 5 mm thick. When the drum rotates at a certain rotation speed, the drum having a volume of 1 to 20 L can provide a clarified area equivalent to 1000 to 20000 m 2 . The ability to continuously separate microorganisms can reach 30-8000 L/h (using E. coli as a reference standard).
At the bottom of the drum is a water-operated sliding piston that can be periodically opened and closed to collect the separated sediment from the storage chamber. Such slagging can be continuously fed, only for partial slag discharge, that is, the solid-liquid separation interface is not destroyed, and the liquid is not discharged.
Since the solid content in the feed will inevitably fluctuate, the use of timing slagging may have limitations. Therefore, a photocell is installed at the outlet of the clear liquid for monitoring, and the device is used to control the opening and slag discharge of the drum to ensure Drainage is timely and reasonable.
In addition to the pressure design, the aseptically operated centrifuge is also equipped with a double-effect mechanical seal on the drive shaft, which provides safety assurance, the gear transmission chamber (ie the power zone) and the sediment collector on the periphery of the drum and others. It is completely separated from the material contact parts (ie the material area). The gap between the two slip rings acts both as a cooling and sealing chamber. Therefore, when the separator is in operation, about 200L of sterile water per hour is required to pass through the gap chamber, and the water flow has an automatic monitoring and alarm device to prevent leakage or malfunction.
The purpose of using sterile water is that once the upper sliding ring seal is damaged, no bacteria enter the system.
All parts of the centrifuge that are in contact with the material are made of high-alloy chrome-nickel stainless steel and polished to prevent material from sticking.
Since the separator is operated at a high speed, it is inevitable to rub against the air to increase the temperature of the treated material. Therefore, the casing and the sediment collector of the separator are designed as a double jacket, which can pass cooling water or thermal insulation, so that Cool the sediment or indirectly cool the drum to 5 ~ 10 ° C to ensure the performance of heat sensitive materials.
In order to ensure reliable operation and pipeline safety acceptance procedures, the aseptic separator has strict acceptance and testing during the normal design and production process, and the factory has a corresponding safety, hygiene and sterility certificate. The following is an example of a modular design splitter.
3 Aseptic separator system process characteristics
In order to ensure that the separator is operated under reliable aseptic conditions, in the process system there is an effective steam sterilization in the case of on-site cleaning after the end of production and without having to disassemble the system (SIP). Therefore, in addition to the separator, the system also needs to add a lot of auxiliary equipment, so that all the inlet and outlet pipes, valves and equipment can be reliably disinfected with saturated steam, including all the components of the mechanical seal. In order to eliminate dead ends, all pipes must be connected with an exhaust port so that condensate and steam can be freely discharged from the system, while ensuring that materials, control media, coolant and sealant can enter and exit under normal operation.
To accommodate different steam sterilization stages, the system is equipped with approximately 40 manual or automatic diaphragm valves, using approximately 0 196 MPa of saturated steam. Lines such as condensate and cooling medium are installed with safety mirrors before flowing through the steam valve into the sterilizing unit. When the centrifuge is running, the air entering and leaving the machine is passed through a sterile filter. The first stage of exhaust is about 15 minutes, after which the temperature is raised to sterilize the system at 127 ° C, 0 147 MPa pressure for 60 to 90 minutes, and then enter the cooling stage. At this point, a 0 049 MPa compressed sterile air introduction system was purged to avoid the formation of a vacuum to prevent the entry of external bacteria, at which point the separator had been aseptically processed.
The operating room of the separator must also pass through a sterile filter when it is exchanged with the outside air.
As with all plumbing connections in the separator system and the connections in the system, sterile joints must be used. Sterile joints avoid gaps and dead spots at the point of contact with the product, minimizing the chance of infection. All pipe fittings must be securely fastened.
4 Enlarging the design When designing a process around the centrifuges of different sizes used, the following indicators must be considered: the flow rate of the required process, the type and nature of the microorganisms, the corresponding culture medium together with the solids content and the associated turnover. Drum discharge frequency.
Generally speaking, it is difficult to understand the physical properties of the fermented material, and it is necessary to design a special device. First, a small test is required to accumulate experience.
The main parameter of the clarification capacity of a disc centrifuge is the so-called equivalent settlement area. The equivalent settlement surface is related to the separation factor of the drum and the number of discs. If the material parameters are known, it is easy to calculate the amplification parameters using the equivalent settlement area based on the results of the small-scale test. The equivalent settlement area parameter can also be used to compare centrifuges of different types and sizes. When choosing a scale-up centrifuge, you should also pay attention to the size of the drum sediment storage chamber. The size of this space determines the maximum solids content that can be handled by the separation function in the case of 30 to 60 partial slagging per hour.
If part of the slag is discharged too frequently, the slag in the drum cannot be fully compressed, and the frequent opening of the drum also affects the clarification effect and service life.
The fermenter emptying is usually limited to 3 to 4 hours, and the processing capacity of the aseptic centrifuge is generally 5 to 3000 L/h.
Based on the research and processing work done by laboratory-scale equipment, there is no problem with scaling up.
5 Aseptic operation example of the separator The aseptic operation example of the separator is mainly used in vaccine production. Table 1 exemplifies some examples of bacterial concentration and purification [4]. The specified separator size yields a treatment capacity of 200 to 300 L/h and a separator effect of 97% to 99%.
More mini centrifuge login:
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