Successful fermentation processes require tight control of such parameters as aeration/dissolved oxygen (DO), carbon dioxide (CO2), pH, temperature, and foam. Accurate control of these conditions is imperative to maximize cell growth and productivity. Below is a brief description of the types and sizes of fermentation vessels, and system components (paragraph numbers correspond labels in photograph).
Vessel Size and Type
The first and most important step when designing a fermentation system is to determine what type of cell you wish to growmicrobial or mammalian (cell culture).
- Microbial cells have sturdy cell walls, and tend to clump together. They withstand rigorous treatment, require large amounts of air, and need shearing impellers to break apart the clumps.
- Mammalian cells have no cell walls and are fragile and sensitive. Vessels for these cells come equipped with impellers that gently mix the media and minimize shearing. Mammalian cell culture vessels are available in water jacketed and non-jacketed configurations depending on the desired method of temperature control.
Determine what size vessel your research requires. Vessels are available in three sizes: 3-, 7-, and 15-liters. A 3-liter system is ideal when you are conducting very basic or introductory research. Once optimal cell growth is achieved scale up to a larger vessel. For sizes larger than 15 liters, call for more information.
Controllers and Accessories
- Temperature Control
1A. RTD Probe: Because all organisms have an optimum temperature for growth and/or production, controlling temperature is critical. A fermentation process at an incorrect temperature will result in poor growth, low production, or cell death. There are three ways to control temperature in fermentation: 1) a water-jacketed vessel (1B), 2) a heat exchanger, or 3) a heating blanket. Water-jacketed vessels and heat exchangers require a circulating water bath (1C). Heating blankets wrap around nonjacketed vessels and supply uniform heat. However, they also require a temperature controller.
- pH Measurement and Control
2A. pH Probe: Any change in pH can adversely affect the viability, growth, and metabolism of cultured cells. Use a pH controller (2B) in conjunction with a peristaltic pump (2C) to add acids or bases to your culture.
- Aeration/Dissolved Oxygen (DO) Control
3A. DO Probe: DO and proper aeration are essential in the fermentation process. Dissolved oxygen controllers (3B) drive air pumps (9) that add oxygen, air, or nitrogen to the vessel according to the needs of your process.
- Carbon Dioxide (CO2) Measurement and Control: many mammalian cells need CO2 for survival and growth. CO2 is introduced into the system during aeration. Too much CO2 can cause the culture to become acidic; too little can cause it to become basic.
- Antifoam Control (not pictured): Microbial fermentation requires a high amount of agitation and aeration which often results in excessive foaming. There are two reasons to control foam: 1) If foam levels get too high, foam will be forced out of the ports in the headplate, opening the system to contamination; and 2) Excessive foam inhibits oxygen transfer. Control your foam levels with antifoam controllers and probes.
- Filters are used for the removal of particles and for maintaining sterility from incoming and outgoing process air, gas, or liquid. For syringe filters, in-line filters, and other filtration devices, see our "Filtration" section.
- Flowmeters can be used with your pumps to help control, monitor, and measure air, gas, and liquid flow. Here a flowmeter is shown with our vacuum pressure station for DO control. For flowmeters see our "Flowmeters" section.
- Tubing is required with both peristaltic and air pumps. Silicone is the most common type used because it is flexible, durable, nontoxic, autoclavable, and can be visually inspected for contamination or wear.
- Air Pumps are used to add air to the fermentation vessel. Choose a pump that is oil free and suitable for continuous duty.
- Peristaltic Pumps are used to remove liquid from the vessel or to add acids and bases (as in 2C), antifoam reagents, and nutrients for continuous or batch cultures.
- Reagent Bottles* are used to hold acids, bases, or fresh media.
Fittings and Clamps are sometimes required when using flexible tubing. Fittings let you connect tubing to equipment or to other pieces of tubing. Clamps keep tubing from slipping off fittings.