Bioprocess Intensification: Application of Centrifugal Field Packed Bed Bioreactor for Mass Transfer Enhancement in Fermentation Processes
Integration of life sciences & engineering
Biochemical Engineering (T5-1)
Keywords: fermentation, oxygen mass transfer, impellers, process intensification
Fermentation reactions produce many low volume, high value products for medical applications such as antibiotics and insulin. Aerobic fermentation systems often tend to become oxygen transfer limited especially in viscous liquid media and high cell density cultures, thus reducing the dissolved oxygen concentration available to the microbial culture. The slowest mass transfer step in the process occurs in the liquid film at the interface between the gas-liquid boundary layer when oxygen dissolves into the liquid from the gas bubble. If the oxygen mass transfer into the system is not as fast as the oxygen uptake rate to the microbial culture, this will lead to the microbes not receiving enough oxygen which will either decrease the productivity and/or lead to the death of the culture.
Our research is exploring the use of porous mesh impellers to enhance oxygen transfer in aerobic fermentation systems. Our preliminary studies have shown that volumetric mass transfer coefficients Kla may be doubled when a knitted wire mesh impeller is employed instead of a conventional Rushton turbine operating under identical conditions in a water-like medium. The present work reports on further mass transfer experiments conducted in air-water and air-water/glycerol systems using different types and sizes of porous mesh impellers. Application of the porous mesh impellers to an Escherichia coli K12 batch fermentation system has also been investigated and results indicate higher cell growth rate under certain conditions in comparison with the double Rushton turbine. We believe the improvements observed in the oxygen transfer rate with the porous mesh systems are attributable to smaller oxygen bubbles being formed and sustained in the reactor, thereby increasing the interfacial area available for mass transfer. This paper will also report on the experimental work currently underway to measure the size of the oxygen bubbles produced by the novel impeller systems using the Phase Doppler Anemometery technique.
Presented Wednesday 19, 11:00 to 11:20, in session Biochemical Engineering (T5-1).
