Critical assessment of gassing-in methods to determine mass transfer coefficient in miniature and microbioreactors with gas-liquid flow

Abstract

Accurate measurements of mass transfer coefficients are critical for reliable characterization of bioreactors. While standardized methods to measure mass transfer coefficients have been established for simple stirred tank reactors, existing methods to characterize mass transfer coefficients have not yet been standardized for alternative reactor types such as miniaturized and biofiltration reactors, leading to inconsistencies in implementation and confusion about the validity of comparisons across different methodologies, volume scales, or reactor types. This study evaluated the accuracy of two commonly used lab-scale methods for the measurement of mass transfer coefficients in a miniature plug-flow reactor: the Dynamic Gassing-In and the Steady State Gassing-In Methods were evaluated. Results revealed that while both experimental methods can be equally accurate and applicable at small scales, there must be careful consideration of mass transfer and volumes peripheral to the reactor itself. To address these findings, a detailed mathematical model was developed and applied to each experimental method, which enabled accurate calculation of the mass transfer coefficients. This approach can be used to analyze experimental data and determine mass transfer coefficients for many reactor types and at any scale. We also propose best practices for mass transfer methods which will enable more consistency in testing and clarity in comparisons between studies.