A fermentation reactor is charged with a sterile feed of growth media at $35C$ and inoculated with a batch of microorganisms. The batch is allowed to grow for $10$ days.

During the growth period the temperature is maintained at $37C$ by circulating cold water through a jacket on the vessel. Sterile air is sparged into the fermenter to maintain a desired dissolved oxygen concentration.

The $pH$ of the fermenter is controlled by periodic addition of a dilute solution of sodium hydroxide. At the end of the growth period the batch is discharged from the reactor to the harvesting section of the process.

What pressure would you choose for operation of the fermenter, and how would you control it$?$

a$.$ At atmospheric pressure, add a simple pressure control loop.

b$.$ At $10$ bar, add a pressure control loop.

c$.$ Slightly higher than atmospheric pressure, ratio pressure control loop.

d$.$ At $10$ bar, add a cascade control loop $($flow$-$pressure$).$

e$.$ A few psi greater than atmospheric pressure, control pressure on vent line $($air$).$