Bioreactor Design and Operation - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 943

(3) Immerse in 1 mol/L NaOH or sodium hypochlorite (2% available chlorine) for 1 h;
remove and rinse in water, then transfer to an open pan and heat in a gravity-
displacement (121 C) or in a porous-load (134 C) autoclave for 1 h; clean; and then
perform routine sterilization processes.

18.8. ASEPTIC OPERATIONS AND PRACTICAL CONSIDERATIONS
FOR BIOREACTOR SYSTEM CONSTRUCTION

18.6 ensures the sterility of the entering process fluids
during operations. To maintain a sterile operation, one must also ensure the sterility of the
equipment at the start of operation and consider the potential of biocontaminants accumula-
tion and/or unintended entrapment especially. Aseptic operations are achieved by a combi-
nation of sterile system at the start and elimination of the potential of biocontaminants during
the operations. A good example of the failure caused by the negligence of aseptic operation
(around fermentors) was that of the former North East Biofuels, Fulton, New York. The
project was a $200 million retrofit from a closed brewery to 110 million gal/year capacity
ethanol facility. It operated for 6 months before going bankrupt and was sold to Sunoco
for $8.5 million.
Industrial bioreactors for sterile operation are usually designed as steel pressure vessels
capable of withstanding full vacuum up to about 3 atm positive pressure at 150 e 180 C. A
manhole is provided on large vessels to allow workers entry into the tank for cleaning and
maintenance; on smaller vessels the top is removable.
For pressure vessels, spherical (or round) structure is most stable, while cubic or flat
structures are weak. Cylindrical reactors are commonly constructed to save space and
material use. Flat head plates are commonly used with laboratory-scale fermentors; for
larger vessels, a domed construction is preferred for lower material cost. Large fermen-
tors are equipped with a lighted vertical sight glass for inspecting the contents of the
reactor.
Nozzles for medium, antifoam, acid and alkali addition, air-exhaust pipes, pressure
gauge, and a rupture disc for emergency pressure release are normally located on the
head plate. Side ports for pH, temperature, and DO sensors are required at minimum;
a steam-sterilizable sample outlet should also be provided. The vessel must be fully drainable
via a harvest nozzle located at the lowest point of the reactor. If the vessel is mechanically
agitated, either a top- or bottom-entering stirrer is installed.

Sterilization as described in section x

18.8.1. Equipment, Medium Transfer, and Flow Control
Bioprocess operations outside of the food and beverage industry are commonly carried
out utilizing pure (most cases single) cultures. Aseptic conditions must be maintained to
ensure the efficiency of these bioprocesses. Keeping the reactor free of foreign organisms is
especially important for slow-growing cultures which can be quickly overrun by contamina-
tion. Fermentors must be capable of operating aseptically for a number of days, sometimes
months.