The primary objective of fermentation air treatment
In the aerobic fermentation industry, microbial growth and metabolism require substantial oxygen consumption. However, ambient air contains dust, moisture, oil, and various contaminating microorganisms; if introduced directly into the fermenter, it can readily cause microbial contamination, leading to process failure or reduced product quality. Therefore, the air entering the fermentation system must undergo rigorous physical and chemical treatment to meet process specifications.
Disinfection and Filtration Requirements
Sterility is of paramount importance in fermentation air treatment. Air sterilization typically employs membrane filtration, which progressively removes microorganisms through a multi-stage filtration system.
- Pre-pretreatment filtrationIt is primarily used to capture large particulate matter, water droplets, and oil droplets in the air, protecting downstream precision filters and extending their service life.
- Terminal sterilizing filtration: Typically, micro-porous filter elements with extremely small pore sizes or sintered-metal filters are employed to ensure that the air entering the fermenter is absolutely sterile, with a retention efficiency meeting the highest standards.
In addition to water and temperature/humidity control
After air is compressed by an air compressor, its relative humidity increases significantly and, upon cooling, it readily condenses into liquid water. This moisture can cause the sterilizing filter element to become damp, not only increasing airflow resistance but also compromising the filter media’s structure and rendering the filtration ineffective.
- Cooling and dehydrationThe compressed high-temperature air must be cooled in a cooler and then passed through a gas–water separator to remove free‑phase liquid water.
- Heating and dehumidificationThe dehumidified saturated air must be reheated to reduce its relative humidity, ensuring that it remains dry when it enters the terminal filter.
Degreasing and Cleanliness Requirements
Oil in the air not only clogs the filter’s micropores and increases energy consumption, but may also exert toxic effects on certain sensitive microorganisms, disrupting their metabolic pathways.
- Source controlWhere conditions permit, the fermentation workshop should prioritize oil-free air compressors to eliminate oil contamination at its source.
- Deep degreasingIf a oil-injected screw air compressor is used, a high-efficiency oil removal filter and an activated carbon adsorption unit must be installed at the front end of the compressed air pipeline to ensure that the oil content in the air is reduced to an extremely low level.
Stability of Pressure and Flow Rate
The fermentation process has a high demand for dissolved oxygen, and the stability of the air supply directly affects the dissolved-oxygen level in the fermenter.
- Pressure matchingThe supply pressure must overcome the hydrostatic head of the fermenter’s liquid level, the frictional losses in the piping, and the pressure drop across the filter, ensuring that positive pressure is maintained within the vessel to prevent backflow of ambient air.
- Traffic is stable.Pipeline network design must be optimized to prevent severe pressure fluctuations. The system should be equipped with pressure stabilization devices and flow control valves to enable precise regulation of oxygen supply in accordance with the varying oxygen demand at different stages of fermentation.