K L a measurement in two‐phase partitioning bioreactors: new insights on potential errors at low power input

BACKGROUND: Two‐phase partitioning bioreactors (TPPBs) are based on the addition of a non‐aqueous phase (NAP) to a biological process in order to overcome a limited delivery of gaseous substrates to the microorganisms in the case of compounds with low affinity for water. However, the high power input ( P g / V ) required to disperse the NAP is often the major limitation for TPPB applications at full scale. Therefore, the accurate determination of the overall mass transfer coefficient ( K L a ) at low P g / V values is a critical issue as these operational conditions are more attractive from a scale‐up point of view. RESULTS: NAP addition altered the typical shape of the dissolved oxygen curves used for K L a determination at the lowest P g / V values tested (70–80 W m −3 ). Below a threshold P g / V value of 600 W m −3 , the presence of the NAP increased the error in K L a measurements up to 115% relative to controls deprived of NAP. CONCLUSIONS: The error in K L a measurements at low P g / V values might be related to failures in the fundamental assumption regarding liquid phase homogeneity in the mass transfer model used. Copyright © 2010 Society of Chemical Industry