OFF GAS FILTRATION

Generally in any aerobic fermentation process, we are faced with the situation of 'What comes in into the fermentor, must come out of the fermentor'. This is especially true in the case of the supply of air or oxygen into the fermentor. Usually large volumes of air are pumped into the fermentor usually at the rate pf 0.5 to 2 vvm. So in the overall fermentation run, the volumes of gas passing into the fermentor, through the fermentation broth and out through the exhaust gas outlet will be tremendous. At any instant a positive pressure will be maintained in the fermentor due to the air flow

The physical, chemical and microbiological characteristics of air entering and leaving the fermentor will be different and represent challenges in the fermentation industry.

The main problem faced in the introduction of air into the fermentor will be the prevention of microbial contaminants entering the fermentor that will create problems in the actual fermentation process. To this effect filters are often placed to prevent the entry of the microorganisms in the air flow into the fermentor. These inlet filters not only prevent the entrance of microorganisms but at the same time remove any other particulate solids or impurities in the air such as grease and water

At the other end of the air line will be the exhaust gas or called off gas leaving the fermentor through the condenser to the environment. In the past the nature of fermentations is such that putting a filter at the off gas outlet is not mandatory as the positive pressure sustained in the fermentor will prevent the entrance of microbial contaminants entering the fermentor from the outside environment. However in the redebt decades with the involvement of the fermentors in preparation of vaccines and cultivation of pathogenic microorganisms, there is now more danger of the actual microorganisms escaping from the fermentor to be hazardous to the environment.

In situation like this, sterilizations of the gas leaving the out gas outlet is mandatory. Sterilizations of the off gas could be achieved by sterilizations using heat or absolute filtration.
The filtration of the exhaust gas from the fermentor faced many problems created by the nature and characteristics of the off gas such as:

1 High moisture content of the off gas due through their passage through the fermentation broth
2 Large pressure drops as the gas leaves the off gas outlet
3 Higher amount of microbial particulate matters that got carried away in the off gas
4 Rapid drop in off gas temperature which leads to condensation of water and clogging of filters
This will lead to blockage of filters and increase in head pressure of the fermentor

Related links: AIR FILTERS IN FERMENTATION