Batch sterilization is the reduction of contaminant organisms through the heating of a vessel. The entire volume of media is sterilized at once through the use of thermal or radiation techniques. When running a thermal batch sterilization, a system goes through 3 steps: heating, holding, and cooling. Heating requires the addition of energy throughout the entire medium volume. This can be done by adding heat through a jacket on the vessel. The temperature is increased until it reaches the sterilization temperature where it is held for a set period of time. During this phase, most of the unwanted microorganisms are destroyed. Finally, the system is cooled to bring the sterile media back to the desired temperature. For radiation sterilization, the process is similar to above, although it uses radiation intensity instead of heat.
t = time
No = initial spore concentration
Nf = final spore concentration
Vo = initial batch volume
Vf = final batch volume
k = death rate constant
By the Arrhenius equation, the death kinetics are k = Ae-E/RT.
In order to sterilize a batch, calculate the total area underneath the curve. Therefore, model death using first order kinetics and integrate as seen above. This will yield a temperature and the corresponding duration of time needed to sterilize the media.
- Most widely used technique
- Simple operation
- No additional materials are added to the media itself
- More expensive heat requirements than continuous sterilization
- Best results occur in well-mixed closed vessels