The effect of Alcanivorax borkumensis SK2, a hydrocarbon-metabolising organism, on gas holdup in a 4-phase bubble column bioprocess.

To design bioprocesses utilising hydrocarbon-metabolising organisms (HMO) as biocatalysts, the effect of the organism on the hydrodynamics of bubble column reactor (BCR), such as gas holdup, needs to be investigated. Therefore, this study investigates the first use of an HMO, Alcanivorax borkumensis SK2, as a solid phase in the operation and hydrodynamics of a BCR. The study investigated the gas holdup in 3-phase and 4-phase systems in a BCR under ranges of superficial gas velocities (UG) from 1 to 3 cm/s, hydrocarbon (chain length C13-21) concentrations (HC) of 0, 5, and 10% v/v and microbial concentrations (MC) of 0, 0.35, 0.6 g/l. The results indicated that UG was the most significant parameter, as gas holdup increases linearly with increasing UG from 1 to 3 cm/s. Furthermore, the addition of hydrocarbons into the air-deionized water -SK2 system showed the highest increase in the gas holdup, particularly at high UG (above 2 cm/s). The solids (yeast, cornflour, and SK2) phases had differing effects on gas holdup, potentially due to the difference in surface activity. In this work, SK2 addition caused a reduction in the fluid surface tension in the bioprocess which therefore resulted in an increase in the gas holdup in BCR. This work builds upon previous investigations in optimising the hydrodynamics for bubble column hydrocarbon bioprocesses for the application of alkane bioactivation.

Quantification of oxygen transfer coefficients in simulated hydrocarbon-based bioprocesses in a bubble column bioreactor.

This study investigates the overall volumetric oxygen transfer coefficient (KLa) in multiphase hydrocarbon-based bioprocess under a range of hydrocarbon concentrations (HC), solid loadings (deactivated yeast) (SL) and superficial gas velocities (UG) in a bubble column reactor (BCR). KLa increased with increasing UG in the air-water system; due to an increase in the number of small bubbles which enhanced gas holdup. In air-water-yeast systems, the initial addition of yeast increased KLa significantly. Further increases in SL reduced KLa, due to increases in the bubble size with increasing SL. KLa decreased when HC was added in air-water-hydrocarbon systems. However, UG, SL and HC affected KLa differently in air-water-yeast-hydrocarbon systems: an indication of the complex interactions between the yeast and hydrocarbon phases which changed the system's hydrodynamics and therefore affected KL. This work illustrates the effect of the operating conditions (SL, HC and UG) on oxygen transfer behaviour in multiphase systems.