Hydrodynamics and mass transfer in miniaturized bubble column bioreactors

Area of Science:

• Biochemical Engineering
• Chemical Engineering
• Fluid Dynamics

Background:

• Miniaturized bubble columns (MBCs) lack detailed hydrodynamic data compared to larger systems.
• Understanding MBC hydrodynamics is crucial for optimizing bioprocesses.
• Microorganisms can significantly influence gas-liquid mass transfer.

Purpose of the Study:

• Investigate gas hold-up, flow regimes, and bubble size distribution in MBCs.
• Determine the effect of sparger pore size and gas flow rate on oxygen mass transfer.
• Compare MBC hydrodynamics and performance with bench-scale columns and stirred tank bioreactors.

Main Methods:

• Experimental investigation of gas hold-up, flow regimes, and bubble size distribution.
• Measurement of volumetric oxygen mass transfer coefficient (K_La) in MBCs.
• Comparison of MBCs with different pore size spargers (16-40 µm and 40-100 µm) and gas flow rates.
• Evaluation of MBC performance with and without microorganisms.

Main Results:

• Flow regime transitions occurred at 1.18 cm/s (small pores) and 0.85 cm/s (large pores).
• MBCs with small pore spargers exhibited higher gas hold-up and K_La, enhanced by microorganisms.
• Wall effects in MBCs were more pronounced than in bench-scale columns.
• K_La increased up to tenfold with small pore spargers.
• Maximum cell concentrations (OD₆₀₀) were 41.5 in MBCs and 43.0 in stirred tank bioreactors.

Conclusions:

• Small pore size spargers significantly enhance K_La in MBCs, particularly in the presence of microorganisms.
• MBCs demonstrate greater wall effects, influencing flow regimes and gas hold-up.
• Optimal K_La and reduced turbulence are achievable in MBCs at the conclusion of the bubbly flow regime.