The specifications for the piping used in the air line will be affected by the sterility requirements of the process. If a high degree of sterility is required then the piping will need to be able to withstand either steam or chemical sterilization before each fermentation: For example, it may be necessary to use stainless steel. If sterility is not a crucial issue, then less resistant materials can be used.
Also, given that saturated air will typically be supplied to the bioreactor, it is possible that condensation will occur within the air line. It is advisable to have strategically placed drains (or "purges") in the air line in order to remove this water intermittently during the process. Rotation of the bioreactor can complicate the aeration system. If the bioreactor rotates while air is introduced into it, then a rotating seal will be necessary between the air line and the bioreactor body. If the inlet and outlet air lines are removed before rotation of the bioreactor, then it is necessary to have a connection that is fully airtight when connected, but simple to remove and re-attach. Also, manually operated butterfly valves may be necessary on the air inlet and air outlet of the bioreactor in order to prevent substrate from flowing out of the bioreactor as it is rotated.
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