Bioreactor Scale-Up

Abstract

Scale-up is the process of expanding a fermentation process from a smaller-scale fermenter, where operational and production parameters have been studied, to a larger scale. Scale-up is perhaps one of the hardest and most complex steps of any fermentation process for engineers. Engineers must take into account all aspects that affect the integrity of the fermentation during the scale-up process. These aspects include physical (namely, heat and mass transfer phenomena such as oxygen transfer rates and mixing time), biochemical (such as medium compositions and rheology), and process (such as conditions of the pre-culture and inoculum) factors. Usually, engineers focus on the most effective factor and take in one of the common scale-up strategies. A constant height to diameter ratio for the bioreactors is perhaps the simplest and most common strategy. A constant oxygen transfer rate coefficient is usually the path for engineers, where oxygen is crucial for the fermentation and oxygen concentration limits product secretions. Also, a constant mixing time during the scale-up comes into play, where engineers usually face a viscous sophisticated fermentation broth. Yet, there are many other approaches that engineers can take. Often they blend these strategies and improvise a new strategy that serves the fermentation in the larger scale. However, engineers’ ultimate goal is to maximize production and efficiency in plant-scale production.