Batch Cultivation
Closed system. Growth is allowed to proceed at a suitable temperature and gaseous environment for a suitable period. During the entire fermentation, nothing is added, except oxygen (in the case of aerobic microorganisms), an antifoam agent, acid, or base to control pH. The composition of the medium, the biomass concentration and the metabolite concentration generally change constantly because of the metabolism of the cells.
Applications
Products that must be produced with minimal risk of contamination or organism mutation
Operations in which only small amounts of product are produced
Processes using one reactor to make various products
Processes in which batch or semi-continuous product separation is adequate
Fed-batch Cultivation
The fed batch method is characterised by the addition of small concentrations at the beginning of the fermentation and these substances are added in small doses during the fermentation process. Despite the apparent similarity between the fed batch reactor model and the continuous culture model, they are very different. Whereas the continuous culture for biomass accumulation is composed of a growth and removal process, the fed batch procedure is composed of a growth and dilution process.
Applications
- Can be operated in a variety of ways, e.g., the reactor can be operated in the following sequence: Batch » Fed batch » Batch
- The feed can also be manipulated to maximise product formation
- Maintenance of low nutrient and substrate concentrations, thus well suited for producing product or cells when the substrate is inhibitory by allowing the maintenance of low levels of the substrate so that cells are not inhibited
- Useful when the product or biomass yield is highest at low substrate concentrations as in the case of mammalian cell systems for recombinant protein, baker’s yeast products and antibiotic production
- Another suitable application is when the product formation is dependent on specific nutrient composition, e.g., specific carbon to nitrogen ratio
Continuous cultivation
In continuous fermentation, an open system is set up. The sterile nutrient solution is added to the bioreactor continuously and an equivalent amount of converted nutrient solution with microorganisms is simultaneously taken out of the system.
Applications
- Continuous reactions offer increased opportunities for system investigation and analysis. As the variables remain unchanged, a benchmark can be determined for the process results, and then the effects of even minor changes to physical or chemical variables can be evaluated.
Airlift bioreactors can provide an attractive alternative to stirred tanks, particularly for bioprocesses with gaseous reactants or products.
Applications
- Can be used to culture highly shear-sensitive cells
- Cultivation of filamentous fungi in liquid media-pellet