Chapter 18 - Bioreactor design and operation

Abstract

For a well-mixed reactor, there are three common operational modes: batch, steady continuous stirred tank reactor (CSTR), and fed-batch. Batch operation has the best flexibility, while CSTR has the highest productivity. There are three basic reactor types for aerobic cultivation of suspended cells: internal mixing, bubble columns, and loop reactors, each with different properties. Scale-up is difficult because conditions in a large vessel are more heterogeneous than in a small vessel. Scale-up problems are all related to transport processes. Scale-down techniques are useful in identifying the controlling regime at the smaller scale, where many parameters can be tested more quickly and less expensively than at the production scale. Bioreactor instrumentation and control are important for bioreactor operations. Improvements in sensor technology and the dynamical models of bioreactors are critical to improvements in control technology. Sterilization is the removal of biocontaminants or foreign organisms for a fermentation system and the surrounding equipment. Industrial fermenters and associated pipings are designed for in situ steam sterilization under pressure, or steam in place. The use of saturated steam is common and advantageous over other hot fluids. Stringent requirement leads to longer reduced sterilization time tS. Bacterial spores are known to be more thermal resistant than vegetative forms of yeast, bacteria and bacterophages. One particularly resistant undesired biocontaminant is prions, or infectious proteins. Sterilizing prions requires special attention. To maintain aceptic operations, special considerations are needed for sealing the opening where stirrer shaft entering the vessel, control valves and sampling ports. Microbes, especially shear sensitive bacteria and mammalian cells, tend to attach to surfaces. Surface adhesion delays washout in a chemostat. The washout is more gradual if cells adhere to the vessel surfaces, and a long tail could exist if the adhesion is strong.