In batch cultivation, the bacteria are inoculated into the bioreactor (always stirred tank bioreactor). Then, under certain conditions (temperature, pH, aeration, etc.) the bacteria go through all the growth phases (lag, exponential, stationary). At last, the fermentation is stopped and  the product is collected. Then, after cleaning and sterilization of the fermenter,  the fermenter is ready for another batch.

In continuous cultivation, the fresh medium flows into the fermentor continuously, and part of the medium in the reactor is withdrawn from the fermenter at the same flow rate of the inlet flow. The table below shows the advantages and disadvantages of different modes of operation of the stirred tank rector. (Ref 1.)
 

Mode of operation	Advantages	Disadvantages
Batch	Versatile: can be used for different reactions every day. Safe: can be properly sterilized.          Little risk of infection or strain mutation Complete conversion of substrate is possible	High labor cost: skilled labor is required Much idle time: Sterilization, growth of inoculum, cleaning after the fermentation Safety problems: when filling, emptying, cleaning
Continuous	Works all the time: low labor cost, good utilization of reactor Often efficient: due to the autocatalytic nature of microbial   reactions, the productivity can be high. Automation may be very appealing Constant product quality	Often disappointing: promised continuous production for months fails due to a. infection. b. spontaneous mutation of microorganisms to non producing strain Inflexible: can rarely be used for other productions without substantial retrofitting

From the above comparison, although continuous culture has some disadvantage, it can outperform batch culture by eliminating the inherent down time for cleaning and sterilization and the long lags before the organisms enter a brief period of high productivity.

Continuous culture is superior to batch culture in several ways for research. Interpretation of results is difficult for batch culture because of changing concentrations of products and reactants, varying pH and redox potential, and a complicated mix of growing, dying, and dead cells. Data from continuous cultures have much less complexity because there are dynamic equilibria or small excursions from steady state. Cause and effect relationships tend to be obvious.

Reference:

1. "Bioreaction Engineering Principles", Jens Nielsen and John Villadsen
 

Last modify: 05/01/2000, by Xuezhen Kang