A Method for Optical Quantification of Local Oxygen Limitations in Multiphase Bioreactors

Area of Science:

• Biochemical Engineering
• Chemical Engineering
• Biotechnology

Background:

• Spatial oxygen limitation causes physiological stress and metabolic heterogeneity in aerobic bioprocesses.
• Oxygen availability in stirred tank reactors is non-uniform due to hydrodynamics and mass transfer.
• Current methods for measuring local oxygen supply are often point-wise or intrusive.

Purpose of the Study:

• To develop and validate a non-intrusive optical method for visualizing spatial oxygen limitation in gas-liquid stirred tank reactors.
• To provide a continuous, two-dimensional map of local oxygen supply.
• To identify oxygen-limiting regions and understand their relationship with hydrodynamics and mass transfer.

Main Methods:

• Utilized the reversible redox chemistry of methylene blue in alkaline glucose solutions as an optical indicator.
• Drove the system to a reduced, colorless state, then monitored spatial reoxidation during aeration.
• Analyzed pixel-wise colorization time to generate 2D fields indicating local oxygen supply.

Main Results:

• Established a robust reaction medium by assessing glucose and sodium hydroxide concentrations.
• Observed characteristic spatial structures of oxygen-limiting regions at different impeller speeds.
• Identified under-supplied zones at low agitation and transport limitations near walls at high agitation.

Conclusions:

• The optical method provides a simple, cost-effective tool for visualizing oxygen supply heterogeneities.
• The technique offers qualitative, physically meaningful insights into oxygen transport and mixing.
• It supports the identification of limiting operating points and complements CFD analyses in bioreactors.