Hydrodynamics and mass transfer coefficients of airlift reactors with net draft tubes of different sizes: Production of cyclodextrin glucanotransferase using <i>Bacillus</i> sp. DSM 2523

Abstract

The hydrodynamics of airlift reactors with net draft tubes (ALR–NDTs) constructed with certain geometric specifications were characterized according to dependencies of the overall gas holdup, mixing time, liquid velocity, and volumetric gas–liquid mass transfer coefficient on the air flow rate (Q g ). The mesh size and height‐to‐diameter ratio ( H / D ) of the net draft tube, and the downcomer‐to‐riser cross‐sectional area ratio ( A d / A r ) were among the geometric characteristics used to compare the performances of bubble column and airlift reactors with the ALR–NDTs. Several empirical correlations were developed to describe the relationship between the hydrodynamic characteristics and the geometric details under certain values of Q g . The specific cell growth rate (µ) was improved considerably in ALR–NDT‐12 ( H / D = 10.7, A d / A r = 1.3, and Q g = 1 vvm) compared to free cells suspended in a flask experiment (0.070 vs. 0.465 h −1 ). The cells were performed efficiently and the time to reach the maximum production of the enzyme was notably decreased over that of the free cells in the flask studies (44 vs. 34 h for ALR–NDT‐12).