Oxygen transfer in viscous xanthan gum fermentation broth:
A comparative study
 

Y.M. Lo and C.H. Hsu
Department of Animal and Food Sciences
Agriculture and Natural Resources 
University of Delaware
531 S. College Ave
Newark, DE 19717
ymlo@udel.edu
(302) 831-1045

Oxygen transfer into viscous xanthan fermentation broth in a
centrifugal, packed-bed bioreactor (CPBR) is compared to the conventional
stirred-tank reactor with disc turbine (STR-DT) or with marine propeller
(STR-MP), and the water-in-oil emulsion system (STR-WIO).  STR-WIO showed
the highest maximal volumetric transfer coefficient (k_La) values,
while STR-MP had the lowest.  However, practical difficulties existed in
recovering xanthan polymers from such an emulsion system.  In CPBR it was
found that, at xanthan concentrations at lower than 2%, maximum kLa values
were slightly lower than those of STR-DT.  On the other hand, when xanthan
concentration higher than 2%, maximum k_La values in CPBR were
higher than those of STR-DT and close to the values of STR-WIO system,
indicating improved oxygen transfer in CPBR at high xanthan concentrations.
In addition, the recirculation stream used to provide better mixing and
gas-liquid contact in CPBR had an important role in providing aeration for
the gas-continuous CPBR system.