Impact of Surface Aerationon Scale-Up with Aerobic Bioreactors

Birmingham, John
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University of Delaware
Gas-liquid mass transfer was examined on scale-up from a laboratory-scale fermentor (~1.3 L) to larger bioreactors (20-145 L). Correlations were developed to model the lumped mass transfer coefficient (kLa) as a function of gassed power input per unit volume and the superficial gas velocity. The kLa values were estimated using the Dynamic Gassing Method and the Dynamic Sulfite Method for the laboratory-scale and larger scale vessels, respectively. Air and deionized water were used as the system, and dissolved oxygen probe dynamics were incorporated. Data from the smaller bioreactor did not correlate well with the kLa values obtained at larger scales; however, the data from the two larger bioreactors were well described by a single correlation. Surface aeration enhancement was estimated for all three bioreactors and was determined to decrease with increasing bioreactor size and increasing superficial gas velocity. The maximum enhancement due to surface aeration corresponded to less than 9% of the total measured kLa. Results compared well with literature predictions of surface aeration under sparged conditions.