Question

Batch sterilization and continuous sterilization

Answer 1

Continuous sterilization is the rapid transfer of heat to medium through steam condensate without the use of a heat exchanger. Once the media is in a holding loop, steam is injected to the system via a nozzle. The medium stays in this loop for a predetermined holding time until the entire medium is sterile.

Continuous sterilization is the rapid transfer of heat to medium through steam condensate without the use of a heat exchanger. Once the media is in a holding loop, steam is injected to the system via a nozzle. The medium stays in this loop for a predetermined holding time until the entire medium is sterile. This is more efficient than batch sterilization because instead of expending energy to heat, hold, and cool the entire system, small portions of the inlet streams are heated at a time. By looping sterile media tubes (which are at higher temperatures) past inlet tubes, the difference in temperature is used to help heat the unsterile medium. So instead of having a cold-water stream cool the sterile media, the lower temperature unsterile media stream absorbs heat from the warm stream, cooling the sterile media. Finally, the sterile media is flash cooled through an expansion valve to adjust the temperature to meet process parameters.



Advantages:
Uniform steam requirements throughout the duration of the sterilization
Simplified process control
Shorter sterilization time means less thermal degradation of medium
Disadvantages:
High demand for steam in a shorter period of time than batch
Concentration of media becomes dilute due to steam condensation
Since steam is actually dispersed in media, steam must be clean to avoid contamination



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.

Advantages:
Most widely used technique
Simple operation
No additional materials are added to the media itself
Disadvantages:
More expensive heat requirements than continuous sterilization
Best results occur in well-mixed closed vessels

Answer 2

Answer: batch and continuous sterilization

Explanation: