Oxygen transfer to mixed cultures in tower systems

Abstract

Abstract A modified dynamic method is introduced to determine the oxygen transfer coefficient, K L a, in aerobic fermentation systems which are not mechanically agitated. The dissolved oxygen concentration is measured continuously following a step down or a step up in aeration rate. The response curve is analyzed to obtain the value of K L a Experiments were carried out at several different air flow rates using mixed culture in concurrent tower fermentors with motionless mixers. The effect of sieve trays and Koch motionless mixers on oxygen transfer was investigated using a 3 in. diameter column. The values of K L aobtained at the bottom of each column were found to be higher than those obtained at the top. Comparison of the results showed that the values of K L a were higher when the Koch mixers were used than when the sieve trays were employed. The oxygen uptake rate by the organisms rX , is also calculated by using the K L a values obtained. They compare favorably withthe experimentally measured values.