Modelling the inhibitory effect of 1,2-epoxyoctane on the growth kinetics of Pseudomonas oleovorans

During the production of 1,2-epoxyoctane from 1-octene by Pseudomonas oleovorans cells, both cell growth and epoxide production are inhibited by the product. To investigate this product inhibition the kinetics of cell growth were investigated as a function of epoxide concentration, in both a batch and a turbidostat culture system. The experiments were carried out in a simplified three-phase fermentation system, using gaseous n-octane as the organic substrate, instead of liquid 1-octene. In this reaction system, complicating factors such as cell damage and emulsifier production, both as a result of direct contact of the cells with the organic liquid phase, are prevented. The epoxide also was introduced into the fermenter via the oxygen and n-octane-containing gas phase. The cell growth rate constant (for cell growth on n-octane as the organic substrate) was measured at various partial pressures of 1,2-epoxyoctane. The experimentally observed product inhibition model parameters are different for the batch and the turbidostat culture system. By changing the product concentration the dynamic behaviour of the cells was investigated. From these experiments, time constants for the change in the cell growth rate constant with time were calculated, showing that the time constants for experiments with increasing epoxide concentration (decreasing rate constant) were smaller than for experiments with decreasing epoxide concentration (increasing rate constant). These time constants can probably be used to model oscillations in biomass and product concentrations, as encountered in the fermentation system, used to produce 1,2-epoxyoctane from 1-octene

Mixing in large-scale vessels stirred with multiple radial or radial and axial up-pumping impellers: modelling and measurements

Mixing phenomena are regarded as one of the major factors responsible for the failure to successfully scale up some bioprocesses. Such phenomena have been investigated within the framework of an EC project `Bioprocess Scale-up Strategy'. Mixing in bioreactors depends on energy input, impeller type, reactor configuration and impeller geometry. Here, two different reactors of volumes 12 and 30 m3 were used, and they were equipped with either multiple Rushton turbines or with a combination of a Scaba 6SRGT radial impeller with multiple 3SHP axial up-pumping hydrofoils above it. Mixing time, power consumption, gas hold-up and liquid velocities were measured at different stirrer speeds and aeration rates in water. At the same total specific power input, aeration did not influence the mixing time much unless it changed the bulk flow pattern. A considerable reduction of mixing time was achieved if the upper impellers were axial instead of radial Rushtons at the same power consumption. The improvement with the axial impellers could be related to the reduction of axial flow barriers due to different circulation flow patterns. The Compartment Model Approach (CMA) was used to develop a flow model based on the general knowledge of the hydrodynamics of both unaerated and aerated stirred vessels. The model was successfully verified for different impeller and reactor configurations and different scales with measured pulse response curves, using either a fluorescent or a hot water tracer. The model can be used for process design purposes

Mixing in large-scale vessels stirred with multiple radial or radial and axial up-pumping impellers: modelling and measurements

Mixing phenomena are regarded as one of the major factors responsible for the failure to successfully scale up some bioprocesses. Such phenomena have been investigated within the framework of an EC project `Bioprocess Scale-up Strategy'. Mixing in bioreactors depends on energy input, impeller type, reactor configuration and impeller geometry. Here, two different reactors of volumes 12 and 30 m3 were used, and they were equipped with either multiple Rushton turbines or with a combination of a Scaba 6SRGT radial impeller with multiple 3SHP axial up-pumping hydrofoils above it. Mixing time, power consumption, gas hold-up and liquid velocities were measured at different stirrer speeds and aeration rates in water. At the same total specific power input, aeration did not influence the mixing time much unless it changed the bulk flow pattern. A considerable reduction of mixing time was achieved if the upper impellers were axial instead of radial Rushtons at the same power consumption. The improvement with the axial impellers could be related to the reduction of axial flow barriers due to different circulation flow patterns. The Compartment Model Approach (CMA) was used to develop a flow model based on the general knowledge of the hydrodynamics of both unaerated and aerated stirred vessels. The model was successfully verified for different impeller and reactor configurations and different scales with measured pulse response curves, using either a fluorescent or a hot water tracer. The model can be used for process design purposes