Bioreactor Operation Modes
Basic Modes of Operation
2.1. Batch culture
Batch fermentation refers to a partially closed system in which most of the materials required are loaded onto the fermentor, decontaminated before the process starts and then, removed at the end. The only material added and removed during the course of a batch fermentation is the gas exchange and pH control solutions. In this mode of operation, conditions are continuously changing with time, and the fermentor is an unsteady-state system, although in a well-mixed reactor, conditions are supposed to be uniform throughout the reactor at any instant time.
The principal disadvantage of batch processing is the high proportion of unproductive time (down-time) between batches, comprising the charge and discharge of the fermentor vessel, the cleaning, and sterilization and re-start process26.
2.2. Continuous culture
Continuous culture is a technique involving feeding the microorganism used for the fermentation with fresh nutrients and, at the same time, removing spent medium plus cells from the system1. An unique feature of the continuous culture is that a time-independent steady-state can be attained which enables one to determine the relations between microbial behavior (genetic and phenotypic expression) and the environmental conditions18.
2.3. Fed-batch processes
The fed-batch technique was originally devised by yeast producers in the early 1900s to regulate the growth in batch culture of Saccharomyces cerevisiae18. Yeast producers observed that in the presence of high concentrations of malt, a by-product - ethanol - was produced, while in low concentrations of malt, the yeast growth was restricted. The problem was then solved by a controlled feeding regime, so that yeast growth remained substrate limited13.
The concept was then extended to the production of other products, such as some enzymes, antibiotics, growth hormones, microbial cells, vitamins13, amino acids and other organic acids14. Basically, cells are
2.1. Batch culture
Batch fermentation refers to a partially closed system in which most of the materials required are loaded onto the fermentor, decontaminated before the process starts and then, removed at the end. The only material added and removed during the course of a batch fermentation is the gas exchange and pH control solutions. In this mode of operation, conditions are continuously changing with time, and the fermentor is an unsteady-state system, although in a well-mixed reactor, conditions are supposed to be uniform throughout the reactor at any instant time.
The principal disadvantage of batch processing is the high proportion of unproductive time (down-time) between batches, comprising the charge and discharge of the fermentor vessel, the cleaning, and sterilization and re-start process26.
2.2. Continuous culture
Continuous culture is a technique involving feeding the microorganism used for the fermentation with fresh nutrients and, at the same time, removing spent medium plus cells from the system1. An unique feature of the continuous culture is that a time-independent steady-state can be attained which enables one to determine the relations between microbial behavior (genetic and phenotypic expression) and the environmental conditions18.
2.3. Fed-batch processes
The fed-batch technique was originally devised by yeast producers in the early 1900s to regulate the growth in batch culture of Saccharomyces cerevisiae18. Yeast producers observed that in the presence of high concentrations of malt, a by-product - ethanol - was produced, while in low concentrations of malt, the yeast growth was restricted. The problem was then solved by a controlled feeding regime, so that yeast growth remained substrate limited13.
The concept was then extended to the production of other products, such as some enzymes, antibiotics, growth hormones, microbial cells, vitamins13, amino acids and other organic acids14. Basically, cells are