Fermentation Requirements for Sterile Air

The fermentation process has very strict requirements for sterile air and needs to meet sterile, no dust, no impurities, no water, no oil, positive pressure such as core indicators, while the need to control. Temperature, humidity, cleanliness and flow pressure and other parameters, the specific requirements are as follows:

1. Core Sterility Index

1. microbial content
   • the total number of microorganisms in the air needs to be very low, usually requiring floating bacteria ≤ 5/m & sup3; settling bacteria ≤ 1/m & sup3; and there must be no pathogenic microorganisms or harmful fermentation bacteria (such as bacteriophage, yeast, mold, etc.).
   • In industrial practice, often only one contamination is allowed for 1000 fermentation cycles.(degree of sterility N = 10 * & sup3;) as a standard to ensure fermentation stability.
2. Particulate matter control
   • the concentration of particles with diameter ≥ 0.5μm in the air shall be ≤ 100pc/ft & sup3;(I .e. the number of particles per cubic foot shall not exceed 100), the number of particles with diameter ≥ 5μm and ≥ 10μm shall also be strictly limited to avoid blocking the filter medium or polluting the fermentation broth.
3. chemical pollutants
   • the air shall not contain organic solvents, heavy metals and other chemicals harmful to fermentation to prevent interference with microbial metabolism or damage to product purity.

2. physical parameter requirements

1. temperature and Humidity
   • temperature the air temperature in the tank is usually 10~30 ℃ higher than the fermentation culture temperature to prevent the production of condensed water (condensed water will breed bacteria).
   • Humidity: The relative humidity of the air entering the total filter should be controlled 60% to 70% to avoid the filter media (such as PTFE filter element) damp failure.
2. Flow and pressure
   • flow: According to the volume and ventilation ratio (VVM) of the fermenter, to ensure sufficient oxygen supply and maintain the metabolic demand of the cell.
   • Pressure: The outlet pressure of the air compressor is generally controlled 0.2~0.35MPa (gauge pressure) it can not only meet the production demand, but also save power consumption.
3. Positive pressure protection
   • the fermenter needs to maintain a slight positive pressure (usually ≥ 0.01MPa) to prevent the entry of untreated air from the outside and form a sterile barrier.

Key Technology of 3. Aseptic Air

1. high efficiency filtration system
   • adopt polytetrafluoroethylene (PTFE) filter element with 0.22 μm pore size it can filter most microorganisms and particles, and cooperate with the pre-filter device to extend the life of the main filter element.
2. Compressed air treatment
   • by cold dryer remove moisture and reduce humidity; some factories cancel the heating step and directly cool and dry the air to simplify the process.
3. Periodic sterilization and validation
   • air system steam sterilization to maintain the efficiency of the filter element; verify the indicators (such as floating bacteria, sedimentation bacteria detection) through the fermentation tank to ensure sterility.

The importance of 4. sterile air

• prevent contamination bacteria contamination can lead to fermentation failure, product purity decline, and even lead to biosafety issues.
• Guarantee efficiency clean air promotes the mixing of bacteria and culture medium, accelerates the growth and reproduction, and maintains the uniform diffusion of metabolites.
• Cost reduction strict aseptic control reduces raw material waste and equipment loss, and improves overall economic benefits.