Characterisation of bubble diameter and gas hold-up in simulated hydrocarbon-based bioprocesses in a bubble column reactor

Abstract

Hydrocarbon substrates can be upgraded to high-value products through biological oxidation processes, whereby an oxygen moiety is inserted into the hydrocarbon backbone by microbes in a suitable bioreactor system such as a bubble column reactor (BCR). However, there is a need to understand the behaviour of the Sauter bubble diameter (D32) and gas hold-up (ƐG) in a simulated four-phase (air, water, hydrocarbon and microbes) system in the BCR. This study has investigated the impact of operational conditions, such as hydrocarbon concentration (HC), superficial gas velocity (UG) and yeast loading (SL) (using deactivated S. cerevisiae as test microorganism) on D32 and ƐG. It was found that D32 and ƐG were mainly affected by UG and SL, whereas HC had an insignificant impact on both D32 and ƐG. Any increase in UG (1–3 cm/sec) resulted in a significant increase in D32 and ƐG, due to the increase in the number of bubbles in the system. On the other hand, an increase in SL was found to result in D32 linearly increasing, which thereafter caused a decrease of ƐG in the system. This influence can be attributed to the yeast cells in the system affecting the fluid properties and the system hydrodynamics. The outcome of this work provides fundamental understanding of the impact of operating conditions (HC, UG and SL) on D32 and ƐG, which underpins the system hydrodynamics in a simulated four-phase hydrocarbon-based bioprocess.