Bioreactors contamination prevention

Some bioreactor systems must be completely protected from microbial contamination, meaning that not a single alien bacterium or virus particle can be allowed to penetrate the system. Reliable and economical systems need to be developed to achieve this level of contamination prevention. Along with the need for prevention is the need to be able to detect contamination at a level of a few microorganisms in a hundred kiloliters of medium. This degree of detection is not yet achievable. Research could vastly improve the crude detection methods that are used today. 

A process variable is a parameter of the current status of a process under operation, and, therefore, the measurement of process variables is a key to understanding what is happening in a bioreactor and to being able to control the process. Most of the sensors used for the measurements of process variables are inserted into the culture broth of a bioreactor. These must have qualities that will allow them to be repeatedly sterihzed (autoclavable) in order to prevent microbial contamination in bioreactors. Naturally, all the sensors must be calibrated before sterihzation. 

Two fundamentally different types of bioreactor setups can be distinguished. In the first type of reactors, MTBE-degradation occurs by bacteria in suspension in continuously stirred tank reactors (CSTR) (Table 6). An obvious advantage of this setup is the optimal mixing of MTBE-degrading biomass, contaminants and oxygen, reducing transport Hmitations to a minimum. However, specialized adaptations are required to prevent washout of biomass from the reactor. Three different methods exist. 

In general, landfills in the United States and Europe utilize a cap and seal strategy, wherein the bed of the landfill is lined with clay and then the top sealed to prevent contamination with ground water and to capture gases in the landfill. Landfill gases can be burned or collected to reduce dangers associated with overpressure. Methane can be captured in a bioreactor landfill for energy utilization. 

The chips were then incubated in an aerated static bed-bioreactor consisting of 21-L polypropylene containers. The lid on the containers vented to the atmosphere through an exit tube. At the bottom of the polypropylene container, a 1-cm side opening provided for controlled inlet airflow. Prior to inoculation, the clean, empty bioreactors were autoclaved for twenty minutes. After thp chips were added to the vessel, steam was injected for thirty minutes through latex tubing connection at the bottom of the reactor. The bioreactors lids were left slightly ajar to prevent over pressurization. After steaming, the bioreactor was drained to remove the excess water that had condensed inside the vessel. The vessel and its contents were then cooled for two hours before inoculation, with the inlet and outlet of the vessel covered with aluminum foil to avoid contamination. 

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