DEVELOPMENT OF A NEW COMMERCIAL-SCALE AIRLIFT FERMENTER FOR RAPID GROWTH OF YEAST

To grow yeast rapidly, it is necessary to supply sufficient oxygen to the yeast and to effectively remove the heat of the fermentation. We succeeded in developing a commercial-scale fermentor for growing a food yeast (Candida utilis) to produce RNA rapidly. This fermentor is an internal-loop airlift type with vertical heat transfer tubes between inner and the outer columns. The volume of the fermentor is 145 m3 (working volume 75 m3). The oxygen transfer rate (OTR) was 9.9 kg-O2/m3/h using a superficial gas velocity of 30 cm/s based on the outer column. Much of the heat of fermentation and the energy resulting from aeration could be removed effectively by the heat transfer tubes. This unique airlift fermentor was driven at a dilution rate of 0.43 h-1 for about 70 d, with the yeast concentration being maintained at 22.8 kg-dry cell/m3. The yeast production rate was 9.79 kg-dry cell/m3/h. Compared with a traditional stirred-type fermentor, two Vogelbush-type fermentors and another airlift fermentor, our fermentor was far superior with respect to OTR and yeast productivity.